JPH11302391A - Surface crosslinking of water absorptive resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water absorbing agent having a high absorbing rate and excellent in magnification in absorption under a pressurized condition, liquid permeability under a pressurized condition and impact resistance, by adding a crosslinking agent to water absorptive resinous powder and then by crosslinking the resultant composition. SOLUTION: This water absorbing agent is obtained by adding a crosslinking agent to water absorptive resinous powder having a weight average particle diameter of 200-1000 μm while grinding tire powder, followed by surface crosslinking of the water absorptive resin. It is preferable that the weight average particle diameter is reduced by a factor of 1-50% through grinding the resinous powder, the content of arisen particulate having a particle diameter of <=150 μm becomes 10 wt.% or below and the BET specific surface area of the water absorptive resin is increased by 1.05-10 times. It is preferable that the grinding of the resinous powder is conducted by a reduction index of >=1,000 under a load of 20 g/cm<3> or in the presence of a ball mill. The surface crosslinking agent contains a polyhydric alcohol, and the resinous powder pref. has a low absorption power of 35 g/g or below in terms of an absorption magnification in an isotonic sodium chloride solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cross-linking a surface of a water-absorbent resin. More specifically, the present invention relates to a method of cross-linking the surface of a water-absorbing resin to obtain a water-absorbing agent (a water-absorbing resin having a specific property value or more) having a high absorption rate and an excellent absorption capacity under pressure. The present invention also relates to a water-absorbing agent containing a small amount of fine powder and having excellent absorption capacity under pressure, liquid permeability under pressure, and impact resistance, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been developed which absorb water tens to hundreds of times as much as their own weight. Various water-absorbing resins have been used for applications requiring water absorption and water retention, such as in the field, industrial fields such as dew condensation prevention and cooling materials.

[0003] As such a water-absorbing resin, for example,
Hydrolyzate of starch-acrylonitrile graft polymer (JP-B-49-043395) and neutralized product of starch-acrylic acid graft polymer (JP-A-51-125)
468), a saponified product of a vinyl acetate-acrylate copolymer (JP-A-52-014689),
Hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (Japanese Patent Publication No. 53-015959), or a crosslinked product thereof, or a self-crosslinked sodium polyacrylate obtained by reversed phase suspension polymerization (Japanese Unexamined Patent Publication No.
No. 3,046,389) and crosslinked polyacrylic acid partially neutralized products (Japanese Patent Application Laid-Open No. 55-084304).

[0004] The required properties of the water-absorbent resin differ depending on the application in which the water-absorbent resin is used. Fast absorption rate, large liquid permeability, etc. are mentioned. However, the relationship between these properties does not always show a positive correlation, and it has been difficult to improve these properties at the same time.

Among these properties, two properties, that is, the water absorption rate and the absorption capacity under load are desired for the water-absorbent resin as basic physical properties. Material with high concentration of 60% by weight or more of the core (US Pat. No. 5,149,335), 60 g
Water-absorbent resin having a high absorption capacity under pressure of 12 g / g under a load of 1 / cm ² and a high water absorption rate (US Pat. No. 57123).
No. 16, European Patent Publication No. 707603).

Therefore, as an attempt to increase the absorption rate of the water-absorbing resin, for example, in order to increase the surface area, an attempt has been made to reduce the particle size, to form a granulated material, or to make a scale. However, in general, when the water-absorbing resin is formed to have a small particle size, the water-absorbing resin forms a so-called "mamako" upon contact with the aqueous liquid, and the absorption rate is rather reduced. Further, when the water-absorbing resin is formed in the granulated material, a phenomenon occurs in which the granulated material itself changes into a “mamako” state by contact with the aqueous liquid, and the absorption rate is rather reduced. In addition, when the water-absorbent resin is formed in a flake shape, its absorption rate is improved, but to induce gel blocking, the absorption rate is not sufficient, and further the water-absorbent resin is formed in a flake shape. This is uneconomical because the water-absorbent resin produced is necessarily bulky and requires larger transportation and storage equipment.

Therefore, as a means other than the above-mentioned improvement of the surface area of the water-absorbent resin, the molecular chains near the surface of the water-absorbent resin are crosslinked to increase the crosslink density of the surface layer. Techniques for improving the absorption rate have also been proposed. Such surface cross-linking is particularly important for improving the absorbency against pressure of the water-absorbent resin. Such techniques are disclosed in, for example, JP-A-57-44627, JP-A-58-42602, JP-B-60-18690, JP-A-58-180233, JP-A-59-62665,
JP-A-61-16903, U.S. Pat.
No. 5,597,873, US Pat. No. 5,540,977
No. 1, European Patent 450923, European Patent 450924
And EP 668080. Furthermore, in order to achieve surface cross-linking with an improved water absorption rate, a method of performing granulation simultaneously with surface cross-linking of a water-absorbing resin (WO 91 /
17200, JP-T-6-216042, U.S. Pat.
No. 02986, U.S. Pat. No. 5,122,544, U.S. Pat.
86569, EP 695763) are also known. Further, a technique for keeping the particle size constant at the time of surface cross-linking (all Examples in JP-A-58-42602) is also known. Furthermore, a technique of adding a crosslinking agent to the hydrogel, drying the hydrogel, and then subdividing and further crosslinking (US Pat.
No. 06, US Pat. No. 5,385,983, US Pat.
727, U.S. Pat. No. 5,563,316) are also known.

Certainly, the above-mentioned surface crosslinking certainly improves the water absorption rate of the water-absorbing resin to some extent. However, the water absorption rate of the water-absorbent resin basically depends greatly on the contact area with the liquid to be absorbed. It is necessary to increase the specific surface area of the resin.
Thus, a technique of surface-crosslinking the foamed water-absorbent resin (Japanese Patent Application Laid-Open No. Hei 8-509521, Japanese Patent Laid-Open No. Hei 5-237378).
No., JP-A-63-88410, WO96 / 17884
No. 5,314,420, U.S. Pat.
No. 1, US Pat. No. 5,451,613, US Pat.
No. 72, EP 574435, EP 70760
No. 3, European Patent 744,435) have also been proposed. Also, a technique for finely controlling the average particle size is known.

However, when the specific surface area of the surface-crosslinked water-absorbent resin is increased by foaming / reducing the average particle diameter to increase the water absorption rate, the surface-crosslinked water-absorbent resin is not crosslinked. Since the added crosslinking agent is absorbed instantaneously, it becomes difficult to uniformly coat the surface of the water-absorbing resin with the surface crosslinking agent. Therefore, in general, a water-absorbent resin having a large specific surface area has a problem that it is difficult to uniformly crosslink the surface due to its too fast absorption rate, and the absorption capacity under pressure is low.

Further, the control of the average particle diameter also causes a problem of fine powder. That is, from the viewpoints of liquid permeability, dust generation, workability, and physical properties of the absorbent article, the content of the fine powder having a particle diameter of generally less than 150 μm is preferably smaller in the water-absorbent resin. However, if the average particle diameter is finely controlled to increase the surface area, as a result, many fine powders are by-produced, resulting in a decrease in the physical properties of the water-absorbent resin and an increase in the cost of collecting the fine powders due to the increase in the fine powders. Further, it is difficult to finely control the particle size industrially due to the stability of the particle size, and as a result, there has been a problem that the physical properties of the water-absorbent resin, such as the absorption capacity under pressure and the water absorption rate, vary.

In other words, two of the most basic characteristics of the water-absorbent resin, namely, the water absorption rate and the absorption capacity under pressure, are that uniform surface crosslinking becomes more difficult as the specific surface area of the water-absorbent resin increases. And contradictory characteristics.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water absorbing resin having a large specific surface area despite a strong demand for a water absorbing resin having a high water absorption rate and a high absorption capacity under pressure. It is an object of the present invention to solve such a problem in the reality that it is difficult to uniformly coat a surface cross-linking agent, so that the surface cross-linking is difficult, that is, the water absorption rate and the absorption capacity under pressure are contradictory. Accordingly, an object of the present invention is to obtain a water absorbing agent under high pressure at a high water absorption rate.

Another object of the present invention is to stably obtain a water-absorbing agent which has a small amount of fine powder, has excellent dry strength, and has a high absorption capacity under pressure and liquid permeability under pressure. In other words, the affinity for aqueous liquids is remarkably excellent, the water absorption capacity under no pressure and under pressure is improved as compared with conventional ones, and a stable water absorbing agent having improved liquid permeability and swelling gel strength is provided. is there.

[0014]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, a technique for granulating at the time of surface cross-linking (WO 91/17200, Japanese Patent Application Laid-Open No.
No. 216042) and a technique for keeping the particle size constant before and after surface crosslinking (all Examples in JP-A-58-42602) are known, but surprisingly, a crosslinking agent is added to the water-absorbing resin particles. In the method of cross-linking the vicinity of the surface, it was found that both the water absorption rate and the absorption capacity under pressure were satisfied at the same time by performing surface cross-linking while pulverizing at least a part of the particles, and completed the present invention. Was.

Further, by controlling the particle size of the water-absorbent resin powder before surface cross-linking to a large coarse particle and further cross-linking the vicinity of the surface while pulverizing at least a part of the particles, the amount of fine powder is small and the absorption capacity under pressure is increased. And found that a water-absorbing agent having excellent dry strength was obtained, and completed the present invention. That is, the method of cross-linking the surface of the water-absorbent resin of the present invention is such that a cross-linking agent is added to the dried water-absorbent resin powder to cross-link the vicinity of the surface, and the weight-average particle diameter is 200 to 1000 μm.
m, while simultaneously pulverizing and surface-cross-linking the powder.

The method for cross-linking the surface of a water-absorbent resin according to the second aspect of the present invention is the method for cross-linking a surface of a water-absorbent resin according to the first aspect, wherein the water-absorbent resin powder is pulverized at the time of surface cross-linking. Weight average particle size of the resin is 1 to 50
%. The method for cross-linking the surface of a water-absorbent resin according to the invention according to claim 3 is a method for cross-linking the surface of a water-absorbent resin according to any one of claims 1 and 2,
The method is characterized in that generation of fine particles having a size of 150 μm or less in the water-absorbent resin due to pulverization of the water-absorbent resin powder at the time of surface crosslinking is 10% by weight or less.

According to a fourth aspect of the present invention, there is provided a method for cross-linking a surface of a water-absorbent resin according to any one of the first to third aspects. Of water-absorbent resin by grinding
It is characterized in that the T specific surface area increases by 1.05 to 10 times. The method for cross-linking the surface of a water-absorbent resin according to the invention according to claim 5 is the method for cross-linking a surface of a water-absorbent resin according to any one of claims 1 to 4, wherein the pulverization of the water-absorbent resin powder at the time of surface cross-linking is performed. , Under a load of 20 g / cm ² or in the presence of a ball mill.

According to a sixth aspect of the present invention, in the method for cross-linking the surface of a water-absorbent resin according to the fifth aspect, the pulverization is performed at a pulverization index of 1000 or more. I do. The method for cross-linking the surface of a water-absorbent resin according to the invention according to claim 7 is the method for cross-linking a surface of a water-absorbent resin according to any one of claims 1 to 6, wherein the surface cross-linking agent contains a polyhydric alcohol. Features.

The method of cross-linking the surface of a water-absorbent resin according to the invention according to claim 8 is a method of adding a cross-linking agent to a dried water-absorbent resin powder and cross-linking the vicinity of the surface while pulverizing as necessary. The powder has a weight average particle size of 300 to 60.
0 μm, and the absorbency against physiological saline is 35 (g
/ G), and 25% by weight or more of the powder is coarse particles of 600 to 1000 µm.

The dry water-absorbent resin powder according to the ninth aspect of the invention is characterized in that the surface vicinity is crosslinked with a plurality of polyhydric alcohols having 3 to 8 carbon atoms. According to the above configuration, the water-absorbing resin before mixing the surface cross-linking agent has a large particle size and a small amount of fine powder, so that it is easy to uniformly mix the surface cross-linking agent. I do. That is, in the present invention, since the water-absorbing resin powder after the surface cross-linking agent is uniformly mixed is further pulverized, the water-absorbing resin having a high water absorption rate / high absorption capacity under pressure can be stably provided.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. The water-absorbing resin in the present invention,
Refers to a hydrophilic cross-linked polymer that swells by absorbing physiological saline 5 times or more its own weight under no load, and its water absorption capacity (water absorption)
Is preferably 10 times or more, more preferably 20 to 2 times.
The range is 00 times.

The water-absorbing resin used in the present invention may be a water-absorbing resin obtained by post-crosslinking an aqueous solution of an uncrosslinked water-soluble polymer. This is a water-absorbing resin obtained by the above method. The monomers used for such cross-linking polymerization include ring-opening polymerizable monomers, acid group-containing unsaturated monomers, nonionic unsaturated monomers, and cationic unsaturated monomers. Preferably, an acid group-containing unsaturated monomer (salt), more preferably, acrylic acid (salt) is used as a monomer.

In the polymerization in the present invention, only monomers other than acrylic acid (salt) may be used.
By superposing and polymerizing together, a water-absorbing resin may be obtained.
The monomer other than acrylic acid (salt) used in the present invention is not particularly limited, and specifically, for example, methacrylic acid, maleic acid, crotonic acid, sorbic acid, itaconic acid, silica Cinnamic acid, maleic anhydride, vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (Meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth)
Acid group-containing unsaturated monomers such as acryloyl phosphate and salts thereof; acrylamide, methacrylamide, N
-Ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth)
Acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone,
Nonionic hydrophilic group-containing unsaturated monomers such as N-acryloylpiperidine and N-acryloylpyrrolidine;
One or more unsaturated monomers are included. The water-absorbent resin may be formed by polymerizing only an unsaturated monomer other than the acrylic acid (salt). Preferably, it is used in an amount of at most mol%.

In the present invention, the acid group-containing unsaturated monomer (salt) /
When obtaining a water-absorbent resin using an acid group-containing polymer,
The neutralization rate of the acid groups of the water-absorbing resin is preferably 30 from the viewpoints of water absorption properties such as water absorption ratio and water absorption rate and safety.
To 100 mol%, more preferably 60 mol% to 90 mol%, even more preferably 65 mol% to 75 mol%. The neutralization of the acid group may be performed as an acid group-containing monomer in an aqueous solution before polymerization, or may be performed by neutralization after the aqueous solution of the polymer, that is, the polymer gel, or both may be used in combination. You may. When a cationic monomer is used, the monomer or the polymer may be neutralized.

In the present invention, the neutralizing agent used for neutralizing the monomer or polymer is not particularly limited, and a conventionally known inorganic or organic base or acid can be used. As the base of the neutralizing agent for the acid group,
Specifically, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate, sodium phosphate , Potassium phosphate, ammonium phosphate, sodium borate, potassium borate, ammonium borate, sodium acetate, potassium acetate, ammonium acetate, sodium lactate, potassium lactate, ammonium lactate, sodium propionate, potassium propionate, ammonium propionate And the like. Examples of the acid of the neutralizing agent for the basic group include acids such as acetic acid, propionic acid, hydrochloric acid, sulfuric acid, and phosphoric acid.

In obtaining a water-absorbing resin in the present invention, an uncrosslinked water-soluble polymer may be obtained and then cross-linked in an aqueous solution to form a water-absorbing resin. Crosslinking takes place simultaneously with the polymerization of the monomers. As a method of crosslinking at the time of polymerization, self-crosslinking may be performed at the time of polymerization without using an internal crosslinking agent. However, in the present invention, a water-absorbing resin polymerized in the presence of an internal crosslinking agent is preferably used.

The internal crosslinking agent used in the present invention is a compound capable of forming a crosslinked structure by having a plurality of substituents in one molecule which copolymerize and / or react with the unsaturated monomer and used without particular limitation. Can be Specifically, N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane Di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate , Triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether , Glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate, acetal such as tetraallyloxyethane, pentaerythritol tetraallyl ether, pentaerythritol triallylate The hydroxyl group of ether, pentaerythritol diallyl ether, trimethylolpropane diallyl ether, trimethylolpropane diallyl ether, ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, monosaccharide, disaccharide, polysaccharide, cellulose, etc. Polyants derived from compounds having two or more in the molecule Ethers such as ether, triallyl isocyanurate, the like triallyl null rate and the like, but is not particularly limited. Among these internal cross-linking agents, in the present invention, the use of an internal cross-linking agent having a plurality of polymerizable unsaturated groups in one molecule is preferable because the absorption characteristics and the like of the obtained water-absorbing resin can be further improved. .

These internal crosslinking agents may be used alone or in combination at the time of polymerization, and may be added all at once or in portions. The amount used depends on the type of the crosslinking agent and the desired crosslinking density, but is 0.0
The range is preferably from 0.05 mol% to 3 mol%, more preferably from 0.01 mol% to 1.5 mol%, and more preferably from 0.05 mol% to 1.5 mol%.
１1 mol%, more preferably 0.06 to 0.5 mol%. If it is out of this range, there is a possibility that a water-absorbing resin having desired absorption characteristics cannot be obtained.

The method for polymerizing the above monomer is not particularly limited, and for example, known methods such as aqueous solution polymerization, reverse phase suspension polymerization, bulk polymerization, and precipitation polymerization can be employed. Among them, from the viewpoint of easy control of the polymerization reaction and the performance of the obtained water-absorbent resin, a method of polymerizing the monomer component into an aqueous solution, that is, aqueous solution polymerization and reverse phase suspension polymerization are preferable. Such aqueous solution polymerization and reversed phase suspension polymerization are described in, for example, U.S. Pat.
No. 93776, No. 436, 7323, No. 4446
No. 261, No. 4683274, No. 4690996
No. 4,721,647, No. 4,738,867, and No. 4,748,076.

When the monomer is polymerized as an aqueous solution in the present invention, the monomer concentration is preferably 5 to 70% by weight, more preferably 10 to 50% by weight, and most preferably 15 to 40% by weight. Range. If the concentration is too high,
If it is too low, the effects of the present invention may not be easily exhibited. The reaction conditions such as the reaction temperature and the reaction time may be appropriately set depending on the composition of the monomer to be used and the like, and are not particularly limited, but are usually 10 ° C to 110 ° C, preferably 15 ° C. The polymerization is carried out within a temperature range of ~ 90 ° C. During the polymerization, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), crosslinked polyacrylic acid (salt), hypophosphorous acid (salt), etc. May be added, and a blowing agent such as an inert gas or a carbonate described below may be added. For the initiation of the polymerization, for example, radical polymerization of potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. Initiators or active energy rays such as ultraviolet rays and electron beams can be used. When an oxidizing radical polymerization initiator is used, redox polymerization may be performed using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination. The amount of the polymerization initiator used is 0.001 to the monomer.
Mol% to 2 mol%, preferably 0.01 mol%
The content is more preferably in the range of 0.5 mol% to 0.5 mol%, and the polymerization initiator is preferably added by being dissolved or dispersed in a solvent such as water.

In the present invention, the hydrogel polymer obtained as described above is essentially dried before adding the surface crosslinking agent,
Further, the powder is pulverized / classified as necessary to obtain a water-absorbent resin powder. When the addition of the surface cross-linking agent is not a powder, for example, in the case of a hydrogel (hydrogel), even if the cross-linking agent of the present invention is added or pulverized during the reaction of the cross-linking agent, it is excellent in absorption capacity under pressure and water absorption rate under pressure. The water absorbing agent intended for the invention cannot be obtained.

Thus, the drying temperature which is required before the addition of the surface cross-linking agent is not particularly limited. Should be inside. The drying time is not particularly limited, but may be 10
About 2 to 5 hours are preferable. Before drying,
The hydrogel polymer may be neutralized, or may be further crushed and fragmented.

The drying method used is heat drying,
Various methods such as hot air drying, vacuum drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with a hydrophobic organic solvent, and high-humidity drying using high-temperature steam can be used. It is not limited. In the present invention, near the surface of the water-absorbent resin powder obtained as described above is crosslinked.

In the present invention, the water-absorbing resin powder used for surface crosslinking has a substantially upper limit of 1000 μm or less, and has an average particle size of 200 to 1000 μm, preferably 300 to 600 μm, more preferably 400 to 5 μm.
Water-absorbent resin powder containing particles having a particle size of 00 μm, and particularly having a fine particle size of 150 μm or less, for example, a fine powder amount of 10% by weight or less,
Further, it is preferably at most 5% by weight, more preferably at most 1% by weight, particularly preferably substantially zero. If the amount of fine powder is large, granulation is likely to occur, and the pulverization does not occur in the present invention, and physical properties are hardly improved. Fine powder, that is, the present invention is characterized in that uniform surface cross-linking is achieved by reducing the amount of fine powder before surface cross-linking, and that the water absorption rate is improved by pulverizing during surface cross-linking.

The solid content of the water-absorbent resin powder is preferably more than 85% by weight, more preferably more than 90% by weight, and even more preferably 95% by weight, in order to achieve uniform pulverization during surface crosslinking. Larger particles are used. When the water content is high, uniform / efficient pulverization may not be performed, and the mixing property of the surface cross-linking agent may be reduced. In particular, instead of powders, EP 509708 / US 56333
No. 16 or U.S. Pat. No. 5,145,906, the water-containing gel polymer is specifically used as a water-containing gel polymer having a water content of 15% by weight or more, 15 to 90% by weight, particularly 30 to 45% by weight. On the other hand, even when the method of the present invention is applied, the effects of the present invention are not sufficiently achieved. Further, the shape is preferably an irregular crushed shape adjusted to a predetermined particle size in a crushing step after drying. Further, unless the particle size is controlled in advance as in US Pat. No. 5,385,983, the object of the present invention cannot be achieved.

Further, as a feature of the present invention, in order to stably perform surface cross-linking, and particularly to improve liquid absorbency under pressure, the absorption capacity of the water-absorbent resin powder under no load is preferably as low as possible. It is preferable that the low absorption capacity is 50 (g / g) or less, more preferably 35 (g / g) or less. Conventionally, it is naturally preferable that the water absorption capacity of the water-absorbent resin is high, but surprisingly, it has been found that the lower the absorption capacity, the more preferable it is 35 g / g or less. When the absorption capacity is high in the present invention, it is difficult to obtain a water-absorbing agent having the desired physical properties stably, the surface cross-linking becomes uneven, or the absorption capacity under pressure or liquid permeability under pressure is reduced. Thus, in the present invention, a low absorption capacity of 35 g / g or less, more preferably 33 to 27 g / g is particularly preferably used.

The water content and the particle size of the water-absorbent resin powder are as described above, and the powder is (a) porous or (b) coarse powder having a certain particle size, (c) granulated particles, Is preferably used. That is, the present invention provides a method of adding a crosslinking agent to a water-absorbent resin powder and crosslinking the vicinity of the surface thereof, wherein the powder having a weight average particle diameter of 200 to 1000 μm is simultaneously surface-crosslinked while being pulverized. This is a method of cross-linking the surface of the resin. For efficient pulverization at the time of surface cross-linking, it is preferable that (a) the water-absorbing resin used is porous. Such a porous water-absorbent resin, mechanical force or more at the time of surface crosslinking described below,
It is preferable because the specific device having the pulverizing function can stably and efficiently pulverize the porous water-absorbent resin powder starting from the pores and folds.

The porous water-absorbing resin preferably used in the present invention can be obtained by foaming the water-absorbing resin in at least one of the above-mentioned polymerization and crosslinking of the water-absorbing resin or a drying step described below. The porous water-absorbing resin is preferably obtained by foam polymerization during polymerization. Hereinafter, the method for producing (a) the porous water-absorbent resin preferably used in the present invention will be further described.

As a foaming method for obtaining the preferred porous water-absorbent resin of the present invention, the aqueous solution polymerization according to the present invention comprises:
Preferably, the reaction is carried out in a state in which bubbles are dispersed in the aqueous monomer solution disclosed in European Patent Application No. 97306427.2. The volume of the aqueous monomer solution in which the bubbles are dispersed at that time is 1.02 times or more, preferably 1.08 times or more, more preferably 1.11 times or more, and most preferably 1 time or more of the volume of the non-dispersed state. .2 times or more.

In the conventional polymerization reaction operation under stirring, some bubbles may be mixed in. However, according to the confirmation of the present inventors, even if bubbles are mixed in the normal operation, it is not The volume change is less than 1.01 times.
The change in volume of 1.02 times or more is the result of performing an operation of intentionally mixing bubbles, and an improvement in the performance of the resin obtained by this operation is recognized, and a porous water-absorbent resin suitable for the present invention is obtained. Can be Since the change in the volume of the aqueous monomer solution in the reaction vessel appears as a change only in the height of the waterline, the rate of the volume change can be easily confirmed. Further, as a result of the intentional operation of mixing bubbles, the transparency of the aqueous solution is reduced and the solution becomes white, so that the dispersion state of the bubbles in the aqueous solution can be visually confirmed.

In a preferred foaming method for obtaining a porous water-absorbent resin in the present invention, in order to disperse air bubbles in an aqueous monomer solution, a monomer aqueous solution and a gas are mixed by fluid mixing. After obtaining a monomer aqueous solution in which bubbles are dispersed,
This is a production method in which the monomer is polymerized in a state where the bubbles are dispersed. In the present invention, as one method for obtaining a porous water-absorbent resin, the monomer aqueous solution and a gas are fluid-mixed. The monomer aqueous solution or gas becomes a fluid state by, for example, being ejected or sucked from a nozzle. By mixing both in a fluid state, the gas can be uniformly and stably dispersed in the aqueous monomer solution. Then, by polymerizing the monomer in a state where the gas is dispersed in the aqueous monomer solution in advance, the pore size can be easily controlled, and a porous water-absorbent resin having a high absorption rate can be obtained.

As a method of mixing fluids, there is a method in which either one of a monomer aqueous solution and a gas is injected into a flow of one of the fluids from a nozzle to mix the two. Specifically, for example, a method of causing a gas to flow in parallel from another nozzle with respect to the fluid of the monomer aqueous solution ejected from the nozzle and mixing the two, or a method of simply mixing the gas fluid ejected from the nozzle from another nozzle A method in which an aqueous monomer solution is caused to flow in parallel to mix the two. Further, a gas can be directly blown into the fluid of the monomer aqueous solution. In the case of fluid mixing, both can be injected co-currently, counter-currently or vertically. It is preferable to inject in parallel. Bubbles can be uniformly dispersed by injecting in parallel. When sprayed in the countercurrent, the splash adheres to walls etc.
There is a risk of polymerization. Examples of the fluid mixing device include an aspirator and an ejector.

In the present invention, in order to obtain a porous water-absorbing resin, the polymerization reaction is preferably carried out in the presence of a surfactant. By using a surfactant, bubbles can be stably dispersed. Further, by appropriately controlling the type and amount of the surfactant, the pore size and the water absorption rate of the obtained water-absorbent resin can be controlled. Examples of such a surfactant include an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant.

Examples of the anionic surfactant used include fatty acid salts such as mixed fatty acid sodium soap, semi-hardened tallow fatty acid sodium soap, sodium stearate soap, potassium oleate soap and castor oil potassium soap; sodium lauryl sulfate, higher alcohol Alkyl sulfates such as sodium sulfate and triethanolamine lauryl sulfate; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; alkylnaphthalenesulfonates such as sodium alkylnaphthalenesulfonate; alkylsulfosuccinates such as sodium dialkylsulfosuccinate Alkyl diphenyl ether disulfonates such as sodium alkyl diphenyl ether disulfonate; alkyl phosphates such as potassium alkyl phosphate; Polyoxyethylene alkyl (or alkylallyl) sulfates such as sodium ethylene lauryl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, triethanolamine polyoxyethylene alkyl ether sulfate and sodium polyoxyethylene alkyl phenyl ether sulfate; special reaction type Anionic surfactant; Special carboxylic acid type surfactant; Naphthalenesulfonic acid formalin condensate such as sodium salt of β-naphthalenesulfonic acid formalin condensate, sodium salt of special aromatic sulfonic acid formalin condensate; Special polycarboxylic acid type Polymeric surfactants such as polyoxyethylene alkyl phosphates.

Examples of the nonionic surfactant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether and polyoxyethylene alkyl ether such as polyoxyethylene higher alcohol ether. , Polyoxyethylene alkylaryl ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene derivatives; sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, Sorbitan fatty acid esters such as sorbitan sesquioleate and sorbitan distearate; polyoxyethylene sorbitan mono Polyoxyethylene sorbitan fatty acid esters such as ureate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate; tetra Polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbite oleate; glycerin fatty acid esters such as glycerol monostearate, glycerol monooleate, and self-emulsifying glycerol monostearate; polyethylene glycol monolaurate, polyethylene glycol monostearate; Polio such as polyethylene glycol distearate and polyethylene glycol monooleate Shiechiren fatty acid ester, polyoxyethylene alkylamine;
Polyoxyethylene hydrogenated castor oil; alkyl alkanolamides and the like.

The cationic surfactant and the double-sided surfactant used include coconut amine acetate,
Alkylamine salts such as stearylamine acetate; quaternary ammonium salts such as lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, distearyldimethylammonium chloride, alkylbenzyldimethylammonium chloride; laurylbetaine, stearylbetaine, There are alkyl betaines such as lauryl carboxymethyl hydroxyethyl imidazolinium betaine; and amine oxides such as lauryl dimethyl amine oxide. Further, by using such a cationic surfactant, antibacterial properties can be imparted to the obtained water-absorbent resin.

Further, as the surfactant to be used,
There are fluorinated surfactants. By using the fluorine-based surfactant, bubbles of the inert gas can be stably dispersed in the aqueous monomer solution for a long time. It is also easy to control the amount of bubbles and the pore size. The resulting water-absorbent resin becomes a porous foam and has a high absorption rate. In addition, antibacterial properties can be imparted. As the fluorine-based surfactant used in the present invention, there are various ones. For example, a perfluoroalkyl group in which hydrogen of a lipophilic group of a general surfactant is replaced with fluorine to obtain a surfactant is used. Is much stronger.

The surfactant used in the present invention is not limited to the above surfactant. These surfactants are used in an amount of 0.0001 to 10 parts by weight, preferably 0.00 to 100 parts by weight per 100 parts by weight of the water-soluble ethylenically unsaturated monomer used.
003 to 5 parts by weight. That is, if the amount is less than 0.0001 part by weight, the dispersion of the gas may be insufficient. On the other hand, if the amount exceeds 10 parts by weight, the effect corresponding to the added amount may not be obtained, which is uneconomical.

Conventionally, it is known to use a surfactant in aqueous solution polymerization, but such a known technique does not improve the water absorption rate at all. In the present invention, it is preferable that the monomer is polymerized in a state where bubbles are dispersed. Nitrogen, argon,
Inert gases such as helium and carbon dioxide are included. When a gas containing oxygen is mixed, when a sulfite such as sodium hydrogen sulfite is used as a polymerization initiator, a water-absorbent resin having various molecular weights can be obtained by appropriately controlling the ratio of oxygen to sulfite. When an oxidizing agent is used as the polymerization initiator, the polymerization can be started by mixing sulfur dioxide.

The viscosity of the aqueous monomer solution is not particularly limited, but by adjusting the viscosity to 10 cP or more, bubbles can be more stably dispersed. Preferably 100 to 100,000 c
P, more preferably 20 to 3000 cP. By setting the viscosity of the aqueous monomer solution to 10 cP or more, bubbles can be stably dispersed in the aqueous monomer solution for a long time. still,
When the viscosity is higher than 100,000 cP, bubbles in the monomer aqueous solution become large, and it may be difficult to obtain a water absorbing resin having a high water absorbing rate.

In the present invention, if necessary, a thickener may be added to the aqueous monomer solution. The thickener may be a hydrophilic polymer, for example, polyacrylic acid (salt), polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyethylene oxide, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose and the like. As the thickener, a water-absorbing resin such as colloidal silica or crosslinked polyacrylic acid (salt) can be used. These hydrophilic polymers used as thickeners have an average molecular weight of 10,000 or more, preferably 100,000 or more. If the average molecular weight is less than 10,000, the amount of the thickener to be added becomes large, and the water absorption performance may decrease, which is not preferable. The viscosity of the monomer aqueous solution is 10 cP.
The amount is not particularly limited as long as it is as described above, but is generally in the range of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the monomer. If the amount of the thickener is less than 0.01% by weight, the viscosity may not reach 10 cP or more, and if it exceeds 10% by weight, the water absorption performance may decrease.

Next, the obtained hydrogel containing the air bubbles is shredded as necessary, dried and pulverized to obtain a water-absorbent resin having a high water absorption rate and a high dissolution rate in powder form. . Although the porous water-absorbing resin is obtained by the above method, it may be obtained by other foam polymerization. Examples of the foaming agent used include sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, calcium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate, magnesium hydrogen carbonate, calcium hydrogen carbonate, zinc carbonate, barium carbonate, and the like. And water-soluble azo polymerization initiators such as azobisamidinopropane dihydrochloride, dicarboxylic acids such as malonic acid, and volatile organic solvents such as trichloroethane and trifluoroethane.
When a foaming agent is added, the amount used is in the range of 0 to 5 parts by weight, more preferably 0 to 1 part by weight, per 100 parts by weight of the total amount of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer. Is appropriate.

The hydrogel polymer obtained by the above foam polymerization is broken into fragments of about 0.1 mm to about 50 mm by a predetermined method during or after the reaction, if necessary. Next, the foamed hydrogel polymer is dried in order to foam the foam more efficiently. In addition,
Foaming with a foaming agent can be performed not at the time of reaction but at the time of drying.

In the present invention, the hydrogel polymer obtained as described above is essentially dried before adding the surface crosslinking agent,
Further, it is pulverized as necessary to obtain a water-absorbent resin powder. The drying method used is as described above and is not particularly limited. Of the drying methods exemplified above, hot air drying and microwave drying are more preferred.
When microwaves are applied to the bubble-containing water-containing gel, the bubbles expand several times to several tens times, so that a water-absorbing resin with a further improved water absorption rate can be obtained.

When the foamed hydrogel polymer is microwave-dried, the thickness of the crushed hydrogel is 3 m.
m, preferably 5 mm or more, more preferably 10 mm or more. When the hydrogel is subjected to microwave drying, it is particularly preferable to form the hydrogel into a sheet having the above thickness.

By the above-mentioned polymerization, that is, by the above-mentioned production method, the porous water-absorbing resin according to the present invention can be easily obtained at low cost. The above water-absorbent resin has an average pore size in the range of 10 to 500 µm, more preferably 20 to 40 µm.
It is within the range of 0 μm, more preferably within the range of 30 to 300 μm, and most preferably within the range of 40 to 200 μm. The average pore diameter is determined by performing image analysis of a cross section of the dried water-absorbent resin using an electron microscope. That is, a histogram representing the pore size distribution of the water-absorbent resin is created by performing image analysis, and the number average of the pore sizes is calculated from the histogram, whereby the average pore size is obtained. The water-absorbing resin obtained as described above, preferably a porous water-absorbing resin, has a bulk specific gravity smaller than that of the conventional one, specifically 0.6 to 0.1 g / cc, more preferably 0.5 to 0. It is in the range of 2 g / cc. Also, that B
The ET specific surface area is larger than before, that is, 0.02
It is at least 5 m ² / g, more preferably at least 0.03 m ² / g, even more preferably at least 0.04 m ² / g. If the powder is pulverized simultaneously with surface crosslinking using such a water-absorbent resin, the object of the present invention can be further achieved.

In the present invention, in addition to the above (a) porous water-absorbent resin powder, it is also preferable that (b) a water-absorbent resin powder having a certain particle size can be used for pulverization simultaneously with crosslinking near the surface. . When the porous water-absorbing resin is not used, for example, in the case of a water-absorbing resin powder having a bulk specific gravity of 0.6, the particle size of the water-absorbing resin powder used is 150
90% by weight, more preferably 95% by weight or more, even more preferably 98% by weight or more, and still more preferably 20% by weight or more of particles of 600 μm or more.
It is preferable to contain 5% by weight or more, more preferably 25 to 50% by weight. The preferred particle size has an upper limit of substantially 100.
It is preferable that 0 μm is 5% by weight or less, and particles of 300 μm or more are 70-99% by weight. This 150μ
m, 300μm, 600μm or more particles by performing the cross-linking near the surface of the coarse particles of a specific particle size, less fine powder, water absorption rate, absorption capacity under pressure and liquid permeability under pressure,
Further, a water absorbing agent having excellent impact resistance can be stably obtained.
When the particle size is outside the above range, the pulverization according to the present invention hardly occurs.

In the present invention, in addition to (a) a porous powder and (b) a coarse powder having a certain particle size,
(C) Granulated particles may be used. (B) or (c)
Preferably, in (b) and (c), the fine powder in the crosslinked water-absorbent resin powder in the vicinity of the surface is reduced in advance, and the powder is pulverized at the same time as the surface cross-linking. Surface cross-linking, a high water absorption rate by pulverization at the time of surface cross-linking, and the dry impact resistance of the resulting water-absorbing agent after surface cross-linking. The present invention reduces the fine powder before surface cross-linking by pre-granulation and destroys a part of the granulated particles, thereby reducing the fine powder, having excellent liquid permeability under pressure, and high absorption capacity under high pressure. And achieve high absorption rate.

When granulated particles are used in the present invention, it is preferable to granulate the water-absorbent resin fine powder to a certain particle size using water. The granulation may be performed at the time of polymerization of the water-absorbent resin, may be performed at the time of drying, or may be performed on a powder after drying, preferably a fine powder (for example, particles having a size of 150 μm or less). From the viewpoint of physical properties, preferably, only the fine powder may be removed by classification or the like, and then granulated separately.

The method for obtaining granulated particles using an aqueous liquid in the present invention is not particularly limited. Examples of the method include rolling granulation, compression granulation, stirring granulation, and extrusion granulation. Granulation method, crushing type granulation method, fluidized bed granulation method, spray drying granulation method and the like. From the viewpoint of the granulation strength, granules further dried using water or an aqueous liquid are preferable. Like (a) and (b), (c) the granulated particles are preferable because at least part of the granulated particles is destroyed at the time of efficient surface crosslinking. The amount of water that can be used for the granulation of the fine powder is 2 to 300 parts by weight of water, 100 to 300 parts by weight of the water absorbent resin, further 30 to 250 parts by weight, 70 to 200 parts by weight, 100 to 200 parts by weight. In addition, it is preferable to use a granulated powder obtained by drying and pulverizing as necessary. When the amount of water is out of the above range, the absorption capacity under pressure and the liquid permeability under pressure tend to be poor.

In the present invention, after mixing the aqueous liquid, the aqueous liquid is heated before granulation, preferably at 50 ° C., in order to further improve the granulation strength and the water absorption capacity under pressure.
To the boiling point, and more preferably, the powder before granulation is mixed after being heated to 40 ° C. or higher, and more preferably 50 to 100 ° C. In the granulation, the heated aqueous liquid and the fine powder are more preferably mixed at a high speed, preferably 3 minutes or less, more preferably 1 minute or less, and most preferably 1 second to 60 seconds. If the mixing time is long,
Uniform mixing is difficult, resulting in huge aggregates, and an increase in water-soluble components and a decrease in water absorption under pressure. Further, the obtained granules, particularly the hydrogel granules, are essentially dried, and if necessary, pulverized and classified to obtain a water-absorbent resin powder. The drying temperature and method after mixing the aqueous liquid, and the particle size and moisture content of the dried powder are the same as described above.

When the granulated product is used in the present invention, only the above-mentioned granulated product may be used. In this case, the weight ratio between the primary particles and the granulated particles is preferably 50/50 to 99/1, more preferably 60/40 to 9/9.
8/2, and more preferably 70/30 to 95/5. In this range, the fine powder is reduced by granulation in advance, and then the surface is crosslinked while being pulverized, whereby a water absorbing agent having excellent absorption capacity under pressure and impact resistance can be obtained.

As described above, in the present invention, the above-described (a) porous powder, (b) coarse powder having a certain particle size, and (c) granulated powder are preferably used as the water-absorbing resin powder. Can also be used as appropriate. Hereinafter, in the method of adding a cross-linking agent to the water-absorbent resin powder of the present invention to cross-link the vicinity of the surface, the weight average particle diameter is 200 to 10
The surface cross-linking method of the water-absorbent resin, which is characterized in that the surface cross-linking is performed simultaneously while pulverizing the powder of 00 μm, will be further described.

Conventionally, a technique of binding a plurality of water-absorbent resins at the time of surface cross-linking and granulating particles simultaneously with surface cross-linking (W
O91 / 17200, JP-T-Hei 6-216042) is also known. Further, a technique for keeping the particle size constant at the time of surface cross-linking (all Examples in JP-A-58-42602) is also known. Furthermore, a technique of surface-crosslinking a foamed water-absorbent resin (Japanese Patent Application Laid-Open No. Hei 8-509521, Japanese Patent Laid-Open No.
-237378, JP-A-63-88410, WO9
No. 6/17884) is also known. It is also known that surface breakage due to mechanical stress on the water-absorbent resin after surface cross-linking is another problem (European Patent No. 812873).

However, in the present invention, contrary to the conventional wisdom that applying a mechanical stress to the water-absorbing resin adversely affects the resin, the present invention dares to apply a certain level of mechanical stress until the powder is pulverized. It was found that a water-absorbent resin satisfying both the water absorption rate and the absorption capacity under pressure can be obtained by performing surface cross-linking simultaneously with pulverization of the water-absorbent resin powder. Further, from the viewpoint of grinding efficiency and physical properties, the water-absorbent resin powder to be ground at this time before surface crosslinking is used as (a) porous powder, (b) coarse particles having a certain particle size, or (c) granulation. Particles are preferred. (A) Surface cross-linking by pulverization of a porous foam gives a water-absorbing agent satisfying the water absorption rate and absorption capacity under pressure, and (b) surface cross-linking by pulverization of coarse particles, absorption capacity under pressure and pressure reduction under pressure. A water-absorbing agent excellent in liquid permeability and impact resistance can be obtained.

The surface crosslinking agent used in the present invention includes:
Specifically, for example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentane Diol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-
Butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-
Polyhydric alcohol compounds such as cyclohexanedimethanol, 1,2-cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl Epoxy compounds such as ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine , Tetraethylenepentamine, Polyamine compounds such as ethylenehexamine, polyethyleneimine and polyamidepolyamine; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin; condensation of the above polyamine compounds with the above haloepoxy compounds Products; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one,
-Methyl-1,3-dioxolan-2-one, 4,5-
Dimethyl-1,3-dioxolan-2-one, 4,4-
Dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one , 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxane-
Alkylene carbonate compounds such as 2-one and 1,3-dioxoban-2-one; and the like, but are not particularly limited.

Of the above surface crosslinking agents, polyhydric alcohol compounds, epoxy compounds, polyamine compounds, condensates of polyamine compounds and haloepoxy compounds, and alkylene carbonate compounds are more preferable. Furthermore, in the case of using a polyhydric alcohol conventionally known to be easily granulated, the surface cross-linking while pulverizing of the present invention is
The method of the present invention is the most preferable in terms of suppressing physical property deterioration and dust generation due to breakage during granulation after surface crosslinking, and therefore, in the present invention, a polyhydric alcohol is most preferably used as a surface crosslinking agent or an organic solvent, More preferably, a plurality of polyhydric alcohols are used.

When one or more polyhydric alcohols are used, it is determined whether the polyhydric alcohol added near the surface of the water-absorbent resin powder works as a crosslinking agent or an organic solvent. Rate, reaction temperature, reaction time and the like. When a plurality of polyhydric alcohols are used, the reactivity or permeation of the polyhydric alcohol with respect to the water-absorbent resin is different, so one of them probably acts more as a solvent and the other acts more as a crosslinking agent. Thus, surface crosslinking of higher physical properties is achieved. When a plurality of polyhydric alcohols are used in the present invention, the number of carbon atoms is C2-15, more preferably C3-10, especially C3-
8, more preferably the range of C3-5.

These surface cross-linking agents may be used alone or in combination of two or more. When two or more surface crosslinking agents are used in combination, US Pat.
By combining the first surface cross-linking agent and the second surface cross-linking agent having different solubility parameters (SP values) exemplified in No. 5, etc., a water-absorbing resin having even more excellent water-absorbing properties can be obtained. The above-mentioned solubility parameter is a value generally used as a factor indicating the breadth of a compound.

The first surface cross-linking agent is a compound capable of reacting with the carboxyl group of the water-absorbing resin and having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more.
For example, glycerin, propylene glycol, etc. correspond. The second surface cross-linking agent is capable of reacting with a carboxyl group of the water-absorbent resin and has a solubility parameter of 12.5.
(Cal / cm ³ ) less than ^1/2 , such as ethylene glycol diglycidyl ether and butanediol.

The amount of the surface cross-linking agent used for the water-absorbing resin depends on the combination of the water-absorbing resin and the surface cross-linking agent.
Within the range of 01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight.
It may be within the range of parts by weight. By using the surface cross-linking agent within the above range, the water absorbing properties for body fluids (aqueous liquids) such as urine, sweat, menstrual blood, etc. can be further improved. If the amount of the surface crosslinking agent is less than 0.01 parts by weight,
The crosslink density near the surface of the water-absorbent resin can hardly be increased. If the amount of the surface cross-linking agent is more than 5 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and may make it difficult to control the cross-linking density to an appropriate value.

Specific examples of the organic solvent used include, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, t-butyl alcohol and the like. Lower alcohols; ketones such as acetone; dioxane, ethylene oxide (EO) adducts of monohydric alcohols, ethers such as tetrahydrofuran; amides such as N, N-dimethylformamide, ε-caprolactam; sulfoxides such as dimethyl sulfoxide And the like. These organic solvents may be used alone or in combination of two or more.
Further, the above-mentioned polyhydric alcohol may be used as an organic solvent.

The amount of the hydrophilic solvent used for the water-absorbing resin and the surface cross-linking agent depends on the combination of the water-absorbing resin, the surface cross-linking agent and the hydrophilic solvent.
200 parts by weight or less, more preferably 0.1 part by weight based on parts by weight.
001 to 50 parts by weight, more preferably 0.1 to 50 parts by weight.
The amount may be in the range of from 50 to 50 parts by weight, particularly preferably in the range of from 0.5 to 20 parts by weight.

In the present invention, the water absorbent resin powder 10
0 parts by weight, 0.01 to 5 parts by weight of a surface crosslinking agent, more preferably 0.05 to 3 parts by weight / organic solvent 2
00 parts by weight or less, more preferably 0.001 to 50 parts by weight, still more preferably 0.1 to 50 parts by weight, particularly preferably 0.5 to 20 parts by weight / water 0.1%. The water-absorbent resin mixture mixed in the range of 1 to 30 parts by weight, preferably 0.5 to 10 parts by weight may be subjected to surface crosslinking simultaneously with the above-mentioned pulverization.

The method for adding the cross-linking agent is not particularly limited, and the water-absorbing resin may be dispersed in an inert solvent and the cross-linking agent may be added. Is dissolved or dispersed, and then the solution or dispersion is sprayed or dropped onto the particle mixture and mixed. The pulverization performed simultaneously with surface cross-linking in the present invention is not provided with a separate pulverization step, but at the time of mixing a cross-linking agent or at the time of heat cross-linking reaction, a sufficient mixing force higher than the conventional pulverization to the water-absorbent resin powder. Or it may be under pressure. Note that, after mixing the crosslinking agent, pulverization and classification before heating are not intended because physical properties are hardly improved.

The pulverization of the present invention can be most simply and preferably defined by a reduction in the weight-average particle size of the water-absorbing resin powder before surface cross-linking and the water-absorbing agent obtained by surface cross-linking. It is also defined by the increase of generation and the increase of surface area. In the conventional surface cross-linking, granulation occurs preferentially due to the effect of the surface cross-linking agent, and these phenomena are not found. However, the present invention is characterized by performing pulverization exceeding granulation. In other words, when pulverized, the weight average particle diameter decreases, which is a phenomenon not seen in the conventional surface treatment (usually granulated to increase the particle diameter). In addition, the amount of fine powder increases and the specific surface area increases. An increase can also define the grinding according to the invention.

The mixing device used for mixing the water-absorbing resin and the surface cross-linking agent preferably has a large mixing force in order to uniformly and surely mix the two. Examples of the mixing device include a cylindrical mixer, a double-walled conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidized furnace rotary desk type. Mixers, air-flow mixers, double-arm kneaders, internal mixers, pulverizing kneaders, rotary mixers, screw-type extruders and the like are preferred.

Next, in the present invention, the powder is ground and simultaneously surface-crosslinked. The device used for pulverization at the same time as surface crosslinking in the present invention includes various types of pulverizers and pulverizers, depending on the structure of the device, the mechanical strength of the water-absorbing resin used, the operating conditions of the device, and the composition of the crosslinking agent. A mixer having a function can be given. Examples of the apparatus used include a cylindrical mixer, a double-walled conical mixer, a V-shaped mixer, a ribbon-type mixer, a meat chopper, a screw-type mixer, a fluid-type furnace rotary desk-type mixer, and an airflow. There are mold mixers, double-arm kneaders, internal mixers, pulverizing kneaders, rotary mixers, screw type extruders, etc.
What is necessary is just to operate under conditions until the shape of the stirring blade and the inner wall and the clearance thereof have a crushing function, and further, the crushing of the water-absorbing resin is observed.

That is, in the present invention, the water-absorbent resin powders are sufficiently agitated by using the above-mentioned mixer so that pulverization exceeding granulation can be observed before and after surface crosslinking. Further, the pulverization at the time of the surface cross-linking may be difficult at room temperature or lower, and therefore, is preferably performed while externally heating. The above device uses a jacket,
It is preferable that heating can be performed from outside using hot air, infrared rays, microwaves, or the like. The treatment temperature and treatment time at the time of pulverizing the water-absorbent resin at the time of surface cross-linking may be appropriately selected depending on the combination of the water-absorbent resin and the surface cross-linking agent, the desired cross-linking density, and the like, and are not particularly limited. However, for example, the processing temperature is 50-250 ° C., and even 10 ° C.
The range of 0 to 200 ° C. is preferable.

In order to achieve high physical properties by suitably performing pulverization in the present invention, pulverization of the powder at the time of surface crosslinking must be carried out by 2
It is preferably carried out under a load of 0 g / cm ² or in the presence of a ball mill. That is, as a ball mill for performing pulverization in the present invention, heat resistance is 100 ° C. or more, particularly 20 ° C.
A material having a temperature of 0 ° C. or higher, more preferably 300 ° C. or higher, is used. Specifically, the water-absorbing resin may be stirred in the presence of an iron ball. The shape of the ball mill is not particularly limited as long as it can be pulverized, and its size is 1 to 100 m.
m, more preferably 5 to 50 mm, 1 to 1000% by weight, more preferably 10 to 100% by weight based on the water-absorbent resin
Is used.

The pressure for pulverization in the present invention is preferably 20 g / cm ² or more at the lower part, and a load may be applied by covering the upper part of the water absorbent resin.
Alternatively, the lower portion may be pressurized by its own weight by stacking the water-absorbent resin vertically high. When pressurized by its own weight, if it is piled up 50 cm or more, preferably 100 cm or more in the vertical direction, the bulk specific gravity of the water-absorbent resin powder (for example, 0.6 g / c
According to c), the surface pressure can be adjusted.

Further, at the time of pulverization, it is preferable that the water-absorbing resin is rotated at a high speed after appropriately applying a weight in the above-mentioned mixer or heat treatment machine. Further, the pulverization index of the water-absorbent resin defined by the following formula is 1000 or more,
It is preferable to rotate at preferably 2000 to 100,000, more preferably 3000 to 50000. (Pulverization index) = (Area pressure on water-absorbent resin powder) × (Rotation speed B) × (Stirring time C) A: Pressure (g /
cm ² ), preferably 5 or more, more preferably 20 to 500.

B: Number of revolutions per second of the mixer (rpm)
, Preferably 2 or more, more preferably 8 to 20
00. C: residence time of the water-absorbent resin powder in the mixer (minut
es), preferably 10 or more, more preferably 15 to 100. In the present invention, at least a part of the particles is pulverized by pulverizing the water-absorbent resin powder at the time of surface cross-linking. Is preferred.

Conventionally, it has been known that fine particles having a size of 150 μm or less are not preferable for the surface crosslinking of the water-absorbing resin. However, there is also a problem that reducing the amount of the fine powder lowers the water absorption rate. On the other hand, in the present invention, 1 is required before surface crosslinking.
The problem of the water absorption rate was solved by reducing the amount of fine powder of 50 μm or less, specifically, to 10% by weight or less to perform uniform surface cross-linking and increasing the generation of fine powder during surface cross-linking. The amount of generated fine powder is preferably 0.5 to
6% by weight, more preferably 1-5% by weight. Further, the amount of fine powder of the water-absorbing agent obtained after the pulverization is preferably 10% by weight or less.

When the amount of generated fine powder is too large, the absorption capacity under pressure decreases, and when it is too small, the water absorption rate decreases. In order to reduce fine powder before surface crosslinking,
As a preferable method, it is preferable to use the above-mentioned (b) coarse particles having a certain particle size and (c) a granulated powder as the water-absorbing resin powder to be surface-crosslinked. In the case of (b), the generation amount of the fine powder due to the pulverization is small, and in the case of (c), the fine powder can be granulated.

In the present invention, the generation of fine particles having a particle size of 150 μm or less is suppressed to 10% by weight or less by pulverization of the powder at the time of surface crosslinking as described above. To increase. By pulverizing the powder by surface crosslinking, the BET specific surface area becomes 1.05 to 10
Fold, and further, 1.05 to 2 times. If the rate of increase of the surface area is too small, it is disadvantageous for improving the water absorption rate, and if it is too large, it is disadvantageous for the absorption capacity under pressure. Such an increase in surface area requires applying a certain level of mechanical stress before grinding.
The water-absorbent resin powder before surface crosslinking has a bulk specific gravity of 0.6 to 0.1
(G / cc) resin, and is easier to achieve because the water-absorbent resin powder before surface crosslinking is porous. The specific surface area can be determined by comparing the BET specific surface area of the water-absorbent resin powder coated with the surface crosslinking agent before and after the reaction.

Further, the simplest method of defining pulverization of the present invention is to reduce the weight average particle diameter. The weight average particle diameter can be compared by performing sieve classification on the water-absorbing resin powder before surface crosslinking and the water-absorbing resin powder after surface crosslinking. Conventionally, it has been known that the average particle diameter increases in the surface cross-linking of the water-absorbent resin. However, in the present invention, the weight average particle diameter is reduced by the surface cross-linking. The reduction of the weight average particle diameter in the present invention is preferably 1 to 50.
%, More preferably from 2 to 20%, even more preferably from 3 to 15%, most preferably from 4 to 10%.
If the decrease in the weight average particle size is too large, the absorption capacity under pressure will not be improved, and if it is too small, the water absorption rate and impact resistance will not be improved. Furthermore, the weight average particle diameter of the water absorbing agent obtained by pulverization at the time of surface crosslinking is 100 to 600 μm,
More preferably, it may be appropriately adjusted so as to be in the range of 300 to 600 μm, particularly preferably 400 to 600 μm.

In the present invention, pulverization is performed at the same time as surface crosslinking, but classification is not particularly performed because the particle size is controlled in advance. In the surface cross-linking method of the present invention, it is preferable that granulation is performed simultaneously with pulverization of the water-absorbent resin powder. In order to perform granulation, the surface cross-linking agent composition is appropriately adjusted, for example, while using a predetermined amount or more of water, so that all agglomerated particles are not destroyed, by appropriately adjusting the pulverizing conditions and the pulverizing device at the time of surface cross-linking. Good. Granulation after pulverization at the time of surface cross-linking can further improve the water absorption rate and optimize the particle size distribution.

The amount of water used in the present invention may be 0.1 to 100 parts by weight of the water-absorbent resin powder in terms of the absorption capacity under pressure and the efficiency of pulverization and granulation of the water-absorbent resin powder. The range is from 30 to 30 parts by weight, preferably from 0.5 to 10 parts by weight. If the amount of water is too large, pulverization is difficult, and if it is too small, granulation is difficult. In addition, for efficient granulation, in the present invention, it is preferable to use a polyhydric alcohol as a surface crosslinking agent.

The present invention is characterized in that the water-absorbent resin powder is simultaneously surface-crosslinked while being pulverized, more preferably simultaneously with the granulation.
Changes in particle size distribution before and after surface crosslinking, changes in specific surface area,
It can be confirmed from an electron micrograph (magnification of about 30 to 50 times) of the water absorbent resin. In addition to granulation, other than electron micrographs, a water-absorbent resin powder as a blank is pulverized with a mixer without using a surface cross-linking agent as a granulation binder and a solution thereof, and the particle size is compared. The grain ratio is required. The granulation rate determined from the particle size distribution is preferably 1% or more,
-10% by weight.

The water-absorbent resin of the present invention obtained as described above includes
Furthermore, if necessary, deodorants, fragrances, various inorganic powders, foaming agents, pigments, dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, water, Various functions may be imparted to the water-absorbent resin by adding salts or the like.

[0092]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to these Examples. In addition, the various physical properties of the water-absorbent resin were measured by the following methods. (1) Water absorption of water-absorbing resin under no load 0.2 g of water-absorbing resin is added to a tea bag type bag (6 cm × 6 c
m), heat-sealing the opening,
It was immersed in a 9% by weight aqueous solution of sodium chloride (physiological saline). After 60 minutes, the tea bag bag was pulled out and drained at 250 G for 3 minutes using a centrifuge, and then the weight W1 (g) of the bag was measured. The same operation was performed without using a water-absorbing resin, and the weight W0 (g) at that time was measured. Then, from these weights W1 and W0, the water absorption under no load (g / g) was calculated according to the following equation a.

Formula a; Water absorption (g / g) = (W1-W)
0) / Weight of water-absorbent resin (g) (2) Water-absorbing speed of water-absorbent resin 1.0 g of the water-absorbent resin was put into a bottomed cylindrical polypropylene cup having an inner diameter of 50 mm and a height of 70 mm. Next, 28 g of physiological saline was poured into the cup. Then, the time from when the physiological saline was poured to when the physiological saline was completely absorbed by the water-absorbent resin and disappeared was measured. The measurement is repeated three times, and the average value is determined by the water absorption rate (second).
And

(3) Solid Content (Water Content) of Water Absorbent Resin 1.000 g of the water absorbent resin was put into an aluminum cup (inner diameter 53 mm * height 23 mm), and dried in a windless oven at 180 ° C. for 3 hours. The water content / solid content (% by weight) of the water-absorbent resin was actually measured and calculated from the loss on drying. (4) Average particle size and particle size distribution of the water absorbent resin The average particle size is JIS standard sieve (850 μm, 600 μm,
(300 μm, 150 μm, 106 μm), the water absorbent resin was sieved and classified, and the residual percentage R was plotted on logarithmic probability paper, and the particle size corresponding to R = 50% by weight was defined as the average particle size. In addition, when calculating | requiring a weight average particle diameter, it is preferable to use four or more sieves, and as needed, 710 micrometers,
500 μm, 425 μm, 355 μm, 200 μm, 7
A sieve of 5 μm or the like may be used.

(5) Specific surface area of water-absorbent resin The specific surface area of the water-absorbent resin is determined by the BET one-point method (Brun
auer-Emmett-Teller adsorption method "). As the measuring device, "specimen fully automatic specific surface area measuring device 4-sorb UC" (manufactured by Yuasa Ionics Co., Ltd.) was used. First, a water-absorbent resin (previously sampled with a JIS standard sieve and used as a sample) was placed in a microcell (TYP
E: QS-400), and the sample-containing microcell was heated to 150 ° C. under a nitrogen gas stream to sufficiently deaerate and dehydrate the sample. Then, helium gas and 0.1%
The sample-containing microcell was cooled to −200 ° C. in a mixed gas stream composed of krypton gas, and the mixed gas was adsorbed to the sample until equilibrium was reached. Thereafter, the temperature of the microcell containing the sample was returned to room temperature, the mixed gas was desorbed from the sample, and the specific surface area of the water-absorbent resin was determined from the amount of desorbed krypton mixed gas. In addition. The adsorption / desorption step of the microcell containing the sample was performed three times, and the specific surface area (m ² / g) of the water-absorbent resin was determined from the average amount.

(6) Absorption Capacity Under Pressure of Water Absorbent Resin First, a measuring apparatus used for measuring the absorption capacity under pressure will be briefly described with reference to FIG. FIG.
As shown in (1), the measuring device comprises a balance 1, a container 2 having a predetermined capacity placed on the balance 1, an outside air suction pipe 3,
The conduit 4, the glass filter 6, and the glass filter 6
And a measuring unit 5 mounted thereon. The container 2 has an opening 2a at its top and an opening 2a at its side.
b, the outside air suction pipe 3 is fitted into the opening 2a, and the conduit 4 is attached to the opening 2b. The container 2 contains a predetermined amount of physiological saline 11.
Contains. The lower end of the outside air suction pipe 3 is immersed in a 0.9% by weight saline solution 11. The above glass filter 6 is formed to have a diameter of 70 mm. The container 2 and the glass filter 6 are in communication with each other by the conduit 4. The upper part of the glass filter 6 is fixed at a position slightly higher than the lower end of the outside air suction pipe 3.

The measuring section 5 includes a filter paper 7 and a support cylinder 8.
And a wire mesh 9 attached to the bottom of the support cylinder 8, and a weight 10. Then, the measuring unit 5 places the filter paper 7 and the support cylinder 8 (that is, the wire mesh 9) on the glass filter 6 in this order, and places the weight 10 inside the support cylinder 8, that is, on the wire mesh 9. It has been. Support cylinder 8
Has an inner diameter of 60 mm. The wire mesh 9 is made of stainless steel and has a JIS400 mesh (mesh size 38 μm).
m). Then, a predetermined amount of the water-absorbing resin is evenly spread on the wire mesh 9. Weight 1
0 is 50 g / cm with respect to the wire net 9, that is, the water-absorbent resin.
The weight is adjusted so that the load of No. ² can be applied uniformly.

The water absorption capacity under pressure was measured using the measuring apparatus having the above-mentioned structure. The measuring method will be described below. First, a predetermined amount of physiological saline 11 is put in the container 2.
A predetermined preparation operation, such as fitting the outside air suction pipe 3 into the pipe, was performed. Next, the filter paper 7 was placed on the glass filter 6. On the other hand, in parallel with these placing operations,
That is, 0.9 g of the water-absorbent resin was uniformly spread on the wire netting 9, and the weight 10 was placed on the water-absorbent resin. Then, filter paper 7
The support cylinder 8 on which the wire netting 9, that is, the water-absorbent resin and the weight 10 was placed, was placed on top. The weight W2 (g) of the physiological saline 11 absorbed by the water-absorbing resin for 60 minutes after the support cylinder 8 is placed on the filter paper 7.
Was measured using the balance 1. And the above weight W2
According to the following formula b, the water absorption capacity (g / g) under pressure 60 minutes after the start of absorption is calculated, and the water absorption capacity under pressure (50 g / cm) is calculated.
² ) The water absorption capacity (g / g) of the water absorption capacity (g / g).

Formula b; water absorption capacity under pressure (g / g) = weight W2 (g) / weight of water-absorbent resin (g) (7) Water-soluble content of water-absorbent resin After being dispersed in deionized water and stirred for 16 hours, the swollen gel was filtered with filter paper. Then, the water-soluble polymer in the obtained filtrate, that is, the water-soluble component (% by weight, relative to the water-absorbent resin) eluted from the water-absorbent resin was determined by titration by colloid titration.

(8) Bulk specific gravity of water-absorbent resin An apparent density measuring device (according to JIS K3362 6.2) was placed horizontally on a stable table, and 100.0 g of water-absorbent resin was placed.
Into an upper funnel of an apparent density measuring instrument, and a 100 cc acrylic resin cup (JIS) having a known weight (g).
Free fall according to K3362 6.2). The portion of the water-absorbent resin that has fallen and rises from the cup is gently ground with a glass rod, and then the weight of the cup (g)
Was measured in 0.01 g units to determine the weight (g) of the water-absorbent resin per 100 cc, and this was divided by the capacity of the cup (100 cc) to obtain the bulk specific gravity (g / cc). (Production Example 1) 305 g of acrylic acid, 3229.5 g of a 37% by weight aqueous solution of sodium acrylate, polyethylene glycol (n = 8) diacrylate 1 as an internal crosslinking agent
2.4 g, 0.15 g of interfacial polyoxyethylene sorbitan monostearate (trade name: Reodol TW-S120, manufactured by Kao Corporation), 1331.1 g of pure water, and 20.3 g of a 10% by weight aqueous sodium persulfate solution were mixed and mixed. An aqueous monomer solution was prepared. This monomer aqueous solution and nitrogen are fluid-mixed using Whip Auto Z manufactured by Aikosha Co., Ltd., and bubbles of nitrogen gas are dispersed in the monomer aqueous solution. Was done. In particular,
Using an aspirator 12 'shown in FIG. 2, the monomer aqueous solution 10 is supplied at a rate of 1 kg / min from the nozzle side using an aspirator 12' as shown in FIG. And the two were fluid-mixed, and further passed through a mixing zone 8 'having irregularities (projections) 9' and led to a polymerization tank 16 '. In the monomer aqueous solution 10 'passed through the mixing zone 8', nitrogen bubbles were dispersed and the volume increased 1.5 times. 101.6 g of a 2% by weight aqueous sulfurous acid solution was added to the bubble-containing monomer aqueous solution 13, and polymerization was immediately started. Subsequently, the temperature is 25 to 95 ° C. with the air bubbles dispersed.
For 1 hour. After the polymerization, the sponge-like hydrogel polymer containing a large amount of air bubbles was cut into squares of 10 to 30 mm, and then dried in a hot air drier at 160 ° C for 2 hours. The dried product was pulverized with a pulverizer, and the material passed through a sieve having an opening of 850 μm was fractionated to obtain a porous water-absorbent resin powder (1) having an average particle diameter of 310 μm. The water-absorbing resin powder (1) obtained by foaming polymerization has a water absorption of 41.8 (g / g), a water-soluble amount of 8% by weight, a solid content of 95.4% by weight, and a bulk specific gravity of 0.
It was 4 g / cc.

(Production Example 2) A partially neutralized sodium acrylate aqueous solution 60 having a concentration of 33% by weight in which 75 mol% was neutralized
In 0.0 g, 0.03 mol% of polyethylene glycol (n = 8) diacrylate as an internal crosslinking agent (based on monomer)
After preparing a monomer aqueous solution in which was dissolved, nitrogen was blown into the monomer aqueous solution to remove dissolved oxygen in the solution. Next, the aqueous monomer solution was poured into a double-arm kneader having an internal volume of 10 liters, and while stirring under a nitrogen stream, 0.14 g / mol of sodium persulfate (based on the monomer) and 0.005 g of L-ascorbic acid were added. / Mol (relative to the monomer) as an aqueous solution, and stirred polymerization was carried out while pulverizing the produced polymer gel. After 1 hour, an unfoamed hydrogel polymer of about 1 mm was taken out by a kneader and then dried in a hot air drier at 160 ° C. for 1 hour. The dried product is pulverized by a pulverizer, and the material having passed through a sieve having an opening of 850 μm is fractionated to have an average particle diameter of 400 μm.
A μm water-absorbent resin powder (2) was obtained. The water-absorbent resin powder (2) is unfoamed and non-porous, and has a water absorption of 50.
0 (g / g), water solubility 20.0% by weight, solid content 9
4% by weight and bulk specific gravity was 0.66 g / cc.

Example 1 After classifying the water-absorbent resin powder (1) obtained in Production Example 1 with a JIS standard sieve of 850 to 600 μm, ethylene glycol diglycidyl ether was added to 100 parts by weight of the classified material. 18.09 parts by weight of a crosslinking agent solution consisting of 09 parts by weight / 3 parts by weight of propylene glycol / 9 parts by weight of water / 6 parts by weight of isopropyl alcohol were mixed. The BET specific surface area of the mixture thus obtained was 0.0275 m ² / g. Next, the mixture is added to a mortar type mixer having a pulverizing function according to the shape (square type) and clearance (about 0.1 to 10 mm) of the stirring blade, and pulverized together with a pachinko ball (ball mill) as a pulverizing aid. A heat treatment was performed at 210 ° C. for 35 minutes with effective high-speed stirring (rotational motion: 285 rpm / planetary motion: 125 rpm).

The water absorbing agent (1) thus obtained has a specific surface area of 0.0302 m ² / g by pulverization at the time of surface crosslinking.
(1.10 times before surface cross-linking) and 150 μm
1% by weight of the following fine powder is generated and increased, and the water absorbing agent (1)
In the electron micrograph, granulation and pulverization of the powder were confirmed. The water absorption capacity of the water absorbing agent (1) was 34.0 (g / g), the absorption capacity under pressure was 16.3 (g / g), and the water absorption rate was 44 seconds. Further, the weight average particle diameter is 700 μm and 660.
μm.

(Example 2) In Example 1, the time of high-speed stirring in a mortar type mixer having a pulverizing function was extended to 50 minutes. The water absorbing agent (2) thus obtained has a specific surface area of 0.0334 m ² / g by pulverization at the time of surface crosslinking.
(1.21 times before surface cross-linking) and 15
Fine powder having a particle size of 0 μm or less was generated and increased by 2% by weight, and the electron micrograph of the water absorbing agent (2) confirmed that the powder was granulated and pulverized. The water absorption capacity of the water absorbing agent (2) is 32.1 (g /
g), the absorption capacity under pressure was 19.3 (g / g), and the water absorption rate was 42 seconds, which was even better than the water absorbing agent (1). Further, the weight average particle diameter was reduced to 640 μm.

Example 3 After classifying the water-absorbent resin powder (1) obtained in Production Example 1 with a JIS standard sieve of 600 to 300 μm, ethylene glycol diglycidyl ether was added to 100 parts by weight of the classified product. 18.09 parts by weight of a crosslinking agent solution consisting of 09 parts by weight / 3 parts by weight of propylene glycol / 9 parts by weight of water / 6 parts by weight of isopropyl alcohol were mixed. The BET specific surface area of the mixture thus obtained was 0.0372 m ² / g. Next, the mixture is added to a mortar type mixer having a pulverizing function according to the shape (square type) and clearance (about 0.1 to 10 mm) of the stirring blade, and pulverized together with a pachinko ball (ball mill) as a pulverizing aid. The heat treatment was performed at 210 ° C. for 45 minutes with effective high-speed stirring (rotational motion: 285 rpm / planetary motion: 125 rpm). The water-absorbing agent (3) thus obtained increased to 0.0391 m ² / g (1.05 times that before surface cross-linking) by pulverization at the time of surface cross-linking, and 1% by weight of fine powder of 150 μm or less was generated. In addition, granulation and pulverization of the powder were confirmed in the electron micrograph of the water absorbing agent (3).
The water absorption capacity of the water absorbing agent (3) was 28.5 (g / g), the absorption capacity under pressure was 22.9 (g / g), and the water absorption rate was 35 seconds. In addition, the weight average particle diameter is 450 μm and 410 μm.
m.

(Comparative Example 1) In Example 3, the mixture obtained by mixing 18.09 parts by weight of the aqueous solution of the crosslinking agent was replaced with a mortar-type mixer having a pulverizing function by heat treatment at 210 ° C. in a standing oven. Heat treatment was performed for 50 minutes. The specific surface area of the comparative water-absorbing agent (1) thus obtained was 0.0359 m ² because it was not pulverized during surface crosslinking and was granulated.
/ G (0.97 times before surface crosslinking), and no fine powder of 150 μm or less was observed. The weight average particle diameter increased to 500 μm, the water absorption capacity of the comparative water-absorbing agent (1) was 28.9 (g / g), and the absorption capacity under pressure was 20.7 (g).
/ G), the water absorption rate was 41 seconds, which was significantly inferior to the water absorbing agent (3).

Comparative Example 2 After classifying the water-absorbent resin powder (2) obtained in Production Example 2 with a JIS standard sieve of 500 to 300 μm, ethylene glycol diglycidyl ether was added to 100 parts by weight of the classified material. 6.03 parts by weight of a crosslinking agent aqueous solution consisting of 03 parts by weight / propylene glycol 1 part by weight / water 3 parts by weight / isopropyl alcohol 2 parts by weight was mixed. The BET specific surface area of the mixture thus obtained was 0.0174 m ² / g. Next, the mixture was added to a normal mortar type mixer, and stirred at a low speed for 2 hours.
Heat treatment was performed at 10 ° C. for 45 minutes. Since the comparative water-absorbing agent (2) thus obtained is not pulverized at the time of surface cross-linking and is granulated, the weight average particle diameter increases to 450 μm, and 0.0155 m ² / g (0.155 m ² / g before surface cross-linking). 89 times)
And no fine powder of 150 μm or less was observed. The water absorption capacity of the comparative water absorbing agent (2) was 39.3 (g / g).
g), the absorption capacity under pressure was 19.3 (g / g), and the water absorption rate was 165 seconds.

Production Example 3 0.085 mol% of polyethylene glycol diacrylate as an internal crosslinking agent was added to 5500 g (monomer concentration: 39% by weight) of an aqueous solution of sodium acrylate having a neutralization ratio of 71.3 mol%. After dissolving and degassing with nitrogen gas for 30 minutes, the aqueous solution is supplied to a reactor having a content of 10 L and a lid attached to a stainless steel double-armed kneader having two sigma-type blades and keeping the temperature at 20 ° C. The reaction system was continuously purged with nitrogen. Then, while rotating the blade, 3.5 g of sodium persulfate and 0.008 g of L-ascorbic acid were added as 10% by weight aqueous solutions, respectively. When 1 minute, the polymerization started, and after 20 minutes, the reaction system reached the peak temperature. did. The hydrogel polymer produced at that time was subdivided into a size of about 5 mm. Thereafter, stirring was further continued to start the polymerization, and after 60 minutes, the hydrogel polymer was taken out.

The obtained finely divided hydrogel polymer was spread on a metal mesh having a mesh size of 300 μm (50 mesh), and
It dried with hot air at 70 degreeC for 70 minutes. The dried product is pulverized with a desktop dual-purpose pulverizer FDS type (manufactured by Miyako Bussan Co., Ltd.), and further 85
The particles were classified with a 0 μm mesh to obtain irregularly crushed crosslinked polyacrylate particles (B) having a solid content of 96% by weight. Next, the crushed crosslinked polyacrylate particles (B) were classified using sieves having openings of 850 μm and 150 μm, and powders (B1) and 15
A fine powder (B2) of less than 0 μm was obtained.

(Production Example 4) Particle size 1 obtained in Production Example 3
Crosslinked polyacrylate fine particles (B2) 2 of less than 50 μm
00 g was placed in a 5 L mortar mixer manufactured by West Japan Testing Machine Co., Ltd. (5 L containers were kept warm in a 70 ° C. bath). 300 g of warm water heated to ° C. was poured at once from the funnel. The crosslinked polyacrylate fine particles (B2) and water were mixed within 10 seconds and stirred at high speed in a mortar mixer for 3 minutes.

The obtained hydrated gel-like granulated product (having a particle size of about 1-
3 mm) was taken out, placed on a metal mesh having a mesh size of 300 μm, and dried in a hot air drier until the water content became less than 5% by weight. Then, the dried granulated product was pulverized by the tabletop dual-purpose pulverizer of Reference Example 1, and substantially less than 850 μm, 150
By classifying the particles to not less than μm, granulated particles (E) of crosslinked polyacrylate fine particles having a water absorption capacity of 30 g / g were obtained.

Next, 8% by weight of the granulated particles (E) of the crosslinked polyacrylic acid fine particles were added to substantially 85% obtained in Reference Example 6.
The primary particles (B1) of 0 to 150 μm were mixed at a ratio of 92% by weight until uniform, to obtain a particle mixture (F) having a solid content of 96% by weight. The particle size distribution of the obtained particle mixture (F) was such that 850 to 600 μm was 32.1% by weight,
300 μm was 50.4% by weight, 300 to 150% by weight was 15.3% by weight, 150 μm passed through was 2.2% by weight, and the weight average particle size was 485 μm.

(Example 4) With respect to 500 g of the particle mixture (F) of the primary particles and the granulated particles obtained in Production Example 4,
1.4-butanediol / propylene glycol / water /
Isopropanol = 0.32 / 0.50 / 2.73 /
An oil temperature of 210 ° C. was mixed with a pachinko ball (28 pieces / 153 g in total) as a grinding aid in a mixer having a grinding function by mixing a crosslinking agent consisting of 0.45 (% by weight / water-absorbent resin powder). The mixture was heated and stirred in the bath for 30 minutes to obtain a water absorbing agent (4). The water absorption capacity of the water absorbing agent (4) is 28 g
/ G, the water absorption capacity under pressure was 25 g / g.

The particle size distribution of the obtained water absorbing agent (4) is 85
26.7% by weight of 0 to 600 μm, 600 to 300 μm
Is 53.9% by weight, 300 to 150% by weight is 16.5% by weight, and 150 μm pass-through is 2.9% by weight (0.7% by weight).
Increase), and the weight average particle diameter was 450 μm. (Example 5) In Example 4, the crosslinking agent was changed to only 1,4-butanediol 0.82, and a similar crosslinking agent aqueous solution was added to carry out a crosslinking reaction in the same manner. ) Got. Physical properties and particle size of the obtained water absorbing agent (5)
It was almost the same as in Example 4 (water absorption capacity: 28 g / g, water absorption capacity under pressure: 25 g / g, average particle diameter: 450 μm), but liquid permeability under pressure (for example, , 24.5 g to 50 g / cm ² ) of about 20
% Had dropped. An example of a method for measuring liquid permeability under pressure is also exemplified in European Patent 744,435.

(Example 6) In Example 4, the water absorbent resin mixed with the crosslinking agent was laminated to a height of about 50 cm to apply a load of about 30 g / cm ² to the lower water absorbent resin.
Next, while heating at 180 ° C., the whole was rotated at 15 rpm.
, And the surface was cross-linked simultaneously with the pulverization at a pulverization index of 18000. The physical properties and particle size of the obtained water absorbing agent (6) were almost the same as those of Example 4 (water absorption capacity was 28 g).
/ G, water absorption under pressure 25 g / g, average particle diameter 450
μm). The liquid permeability under pressure was the same as in Example 4.

(Example 7) The water-absorbent resin powder (1) obtained in Production Example 1 was further classified and blended, whereby 850-600 μm was 29.6% by weight, 600-3
51.7% by weight of 00 μm, 1% by weight of 300 to 150%
8.7% by weight of a water-absorbent resin powder (1 ′) having a weight average particle size of 470 μm was obtained. The obtained water absorbent resin powder (1 ')
1.4-butanediol / propylene glycol / water / isopropanol = 0.96 / 100 parts by weight
A crosslinker consisting of 1.50 / 8.19 / 1.35 (% by weight / based on water-absorbent resin powder) was mixed and, in a mixer having a grinding function, pachinko balls (28 pieces / total) as grinding aids 1
53g) in a bath at an oil temperature of 210 ° C.
The resulting mixture was heated and stirred for 2 minutes to obtain a water absorbing agent (7). The water absorption capacity of the water absorbing agent (7) is 30 g / g, and the water absorption capacity under pressure is 23.
g / g, and the water absorption rate was 25 seconds.

The particle size distribution is 850-600 μm.
m is 18.6% by weight, 600 to 300 μm is 50.4% by weight, 300 to 150% by weight is 23.6% by weight, 150
7.4% by weight of a μm-penetrating substance, and a weight average particle diameter of 4%.
It was 00 μm.

[0118]

According to the present invention, the water-absorbing resin before mixing the surface cross-linking agent has a large particle size and a small amount of fine powder, so that it is easy to mix the surface cross-linking agent uniformly. The water absorption speed is also improved. That is, in the present invention, since the water-absorbing resin powder after the surface crosslinking agent is uniformly mixed is further pulverized, the water-absorbing resin under high pressure at a high water absorption rate can be provided.

[Brief description of the drawings]

FIG. 1 is an apparatus for measuring absorption capacity under pressure used in the present invention.

FIG. 2 is a cross-sectional view of an aspirator used in Production Example 1.

FIG. 3 is a cross-sectional view of a mixed region having irregularities in a gap used in Production Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance 2 Container 3 External air suction pipe 4 Pipe 5 Measurement part 6 Glass filter 7 Filter paper 8 Support cylinder 9 Wire mesh 10 Weight 11 Physiological saline 2a Opening 2b Opening 1 'Inlet of fluid ejected from nozzle 2' Another fluid 3 'Nozzle 8' Mixing area 9 'Unevenness 10' Monomer aqueous solution 11 'Gas 12' Aspirator 13 'Bubble-containing monomer aqueous solution 14' Monomer preparation tank 15 'Pump 16' Polymerization tank

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Nobuyuki Harada 992, Nishioki, Okahama-ku, Abashi-ku, Himeji-shi, Hyogo Pref. Nippon Shokubai Co., Ltd.

Claims (9)

[Claims] 1. A method of adding a crosslinking agent to a dried water-absorbent resin powder to crosslink the vicinity of the surface thereof, wherein the powder having a weight average particle diameter of 200 to 1000 μm is simultaneously surface-crosslinked while being pulverized. A method for cross-linking the surface of a water-absorbent resin 2. The method for cross-linking a water-absorbent resin according to claim 1, wherein the weight-average particle size of the water-absorbent resin is reduced by 1 to 50% by crushing the water-absorbent resin powder at the time of surface cross-linking. 3. The water-absorbent resin according to claim 1, wherein the generation of fine particles having a size of 150 μm or less in the water-absorbent resin is 10% by weight or less by pulverization of the water-absorbent resin powder at the time of surface crosslinking. Surface cross-linking method. 4. A water absorbing resin having a BET specific surface area of 1.05 to 1 by pulverizing the water absorbing resin powder at the time of surface crosslinking.
The method for cross-linking the surface of a water-absorbent resin according to any one of claims 1 to 3, wherein the method increases the number by 0 times. 5. The surface cross-linking of the water-absorbent resin according to claim 1, wherein the pulverization of the water-absorbent resin powder at the time of the surface cross-linking is performed under a load of 20 g / cm ² or in the presence of a ball mill. Method. 6. The method according to claim 5, wherein the pulverization is performed at a pulverization index of 1000 or more. 7. The method according to claim 1, wherein the surface cross-linking agent contains a polyhydric alcohol. 8. A method of adding a crosslinking agent to a dried water-absorbent resin powder and, if necessary, pulverizing the powder in the vicinity of its surface, wherein the powder has a weight average particle diameter of 300 to 600 μm.
m, and the absorbency against physiological saline is 35 (g / g).
g) exhibits the following low absorption capacity and 25% by weight of the powder
A method for cross-linking the surface of a water-absorbent resin, characterized in that the above are coarse particles of 600 to 1000 μm. 9. A dry water-absorbent resin powder, the surface of which has been crosslinked with a plurality of polyhydric alcohols having 3 to 8 carbon atoms.