JPS63275608A - Manufacture of water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain a water-absorptive resin excellent in absorbing power under pressure and diffusion rate, by polymerizing an aqueous solution or an aqueous dispersion of copolymerizable monomers comprising a (meth)acrylate, (meth) acrylic acid and a crosslinking agent in a specific method. CONSTITUTION:An aqueous solution or an aqueous dispersion of copolymerizable monomers comprising an acrylate and/or a methacrylate (A), acrylic acid and/or methacrylic acid (B) and a crosslinking agent (C) as essential components is polymerized. The polymerization is started at 90 deg.C or below, and the aqueous solution or the aqueous dispersion is strongly heated in a state of the degree of polymerization of 50% or less to complete the polymerization. It is necessary that the temperature of the heating to complete the polymerization is 100 deg.C or above.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing a water absorbent resin.

[Prior Art] Conventionally, a water-soluble salt of acrylic acid and/or a water-soluble salt of methacrylic acid, acrylic acid and/or methacrylic acid, and a crosslinking agent are copolymerized by heating at 100 to 250"C in an aqueous medium. There is a method of producing a highly water-absorbent hydrogel (for example, JP-A-56-147809).

[Problems to be Solved by the Invention] However, although this product has a certain degree of absorption capacity under normal pressure, it has a problem that its absorption capacity is low under pressure, and it tends to cause lumps when water is absorbed, and the diffusion rate is low. .

[Means for Solving the Problems] The present inventors have arrived at the present invention as a result of intensive studies on a method for producing a water-absorbing resin that has excellent absorption capacity under pressure and also has an excellent diffusion rate.

That is, the present invention provides an aqueous solution or aqueous dispersion of a copolymerizable monomer containing (A) an acrylate and/or a methacrylate; (B) an acrylic M and/or a methacrylic acid, and (C) a crosslinking agent. This is a method for producing a water-absorbing resin, which is characterized in that when polymerizing a liquid, the polymerization is initiated at 90° C. or lower, and then forcedly heated to complete the polymerization at a stage where the polymerization rate is 50% or lower.

In the present invention, (A) acrylate and/or methacrylate [abbreviated as (meth)acrylate]. The same description will be used below. ] Examples include alkali metal salts (sodium, potassium, lithium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), ammonium salts and amine salts (methylamine, trimethylamine, etc.) of (meth)acrylic acid. Salts of alkylamines;
salts of alkanolamines such as triethanolamine and jetanolamine) and two or more thereof. Preferred among these are alkali metal salts of (meth)acrylic acid, particularly preferred are sodium salts and potassium salts.

(C) The crosslinking agent is a compound (1) having at least two polymerizable double bonds and at least one functional group having at least one polymerizable double bond and reactive with the monomer. Compound (2) is rejected.

Examples of compound (1) include the following.

(2) Bis(meth)acrylamide: N,N''-alkylene (C1-Ce) bis(meth)acrylamide, such as N,N'-methylene-bisacrylamide.

■Di- or polyester of polyols and unsaturated mono- or polycarboxylic acids: Polyols (ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol,
(meth)acrylic acid esters of unsaturated polyesters (obtained by reaction of the above polyols with unsaturated acids such as maleic acid): and
meth)acrylic acid ester [polyepoxide and (meth)
etc. obtained by reaction with acrylic acid.

■Carbamyl ester: polyisocyanate [tolylene diisocyanate, hexamethylene diisocyanate, 4,4°-diphenylmethane diisocyanate, NCO group-containing prepolymer (obtained by reaction of the above polyisocyanate with an active hydrogen atom-containing compound), etc.] and hydroxyl Those obtained by reaction with group-containing monomers, for example carbamyl esters obtained by reaction of the polyisocyanates mentioned above with hydroxyethyl (meth)acrylate.

■Di- or polyvinyl compounds such as divinylbenzene, divinyltoluene, divinylxylene, divinyl ether, divinyl ketone, trivinylbenzene, etc.

■Di- or poly(meth)allyl ether of polyols: Polyols (alkylene glycol, glycerin, polyalkylene glycol, polyalkylene polyol,
di- or poly-(meth)allyl ethers of carbohydrates, etc.) such as polyethylene glycol diallyl ethers, allylated starches, allylated celluloses.

■ Di- or poly-allyl esters of polycarciboxylic acids: diallyl phthalate, diallyl adipate, etc.

■Ester of unsaturated mono- or poly-carboxylic acid and mono(meth)allyl ether of polyol: (meth)allyl ether of polyethylene glycol monoallyl ether
acrylic esters, etc.

■Allyloxyalkanes: Examples of compound (2) such as tetraallyloxyethane include (meth)acrylic acid and/or
or ethylenically unsaturated compounds containing groups reactive with other copolymerizable monomers, such as carboxyl groups and groups reactive with carboxylic anhydride groups (hydroxyl groups, epoxy groups, cationic groups, etc.). . Specifically, unsaturated compounds containing nonionic groups, such as hydroxyl group-containing unsaturated compounds [N-methylol (meth)acrylamide, etc.] and epoxy group-containing unsaturated compounds [glycidyl (
meth)acrylates; and unsaturated compounds containing cationic groups, such as quaternary ammonium base-containing unsaturated compounds [N,N,N-trimethyl-"N-(meth)
Acryloyloxyethylammonium chloride, N,
N,N-triethyl-N-(meth)acryloyloxyethylammonium chloride, etc.], and tertiary amino group-containing unsaturated compounds [dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, etc.]. It is required.

Among the crosslinking agents, preferred are bis(meth)acrylamide, polyesters or polyesters of polyols and unsaturated monocarboxylic acids, and allyloxyalkanes.
Particularly preferred are N,N-methylenebisacrylamide, ethylene glycol diacrylate, trimethylolpropane triacrylate and tetraallyloxyethane.

Other copolymerizable water-soluble monomers and water-insoluble monomers can be used together with the (meth)acrylate and (meth)acrylic acid, if necessary.

Examples of water-soluble monomers include monomers having other carboxyl groups or salt groups [maleic anhydride, itaconic acid, sodium maleate, methylamine maleate, etc.],
Monomers with sulfonic acid groups [styrene sulfonic acid sodium salt, styrene sulfonic acid methylamine salt, (meth)acrylic acid sulfopropyl sodium salt, (meth)acrylic acid sulfopropyl jetanolamine salt, vinyl sulfonate sodium salt salts], monomers having an amide group [(meth)acrylamide], phosphoric acid monoester monomers, and the like.

As a water-insoluble monomer, unsaturated carboxylic acid ((meth)
Alkyl (C1-10) esters of monocarboxylic acids such as acrylic acid; polycarboxylic acids such as maleic acid and fumaric acid, aromatic vinyl hydrocarbons (styrene, etc.), aliphatic vinyl hydrocarbons (ethylene, propylene, butene, etc.) ), unsaturated nitriles (acrylonitrile, etc.).

Among these, preferred are water-soluble monomers, and particularly preferred are monomers having a carboxyl group or a sulfonate type group.

The molar ratio of (meth)acrylic acid to (meth)acrylic acid is usually 95:5 to 20:80, preferably 90:10.
Must arrive at ~40:60. If the molar ratio of (meth)acrylate is less than 20, the water absorption capacity of the resin will be low, and if it exceeds 95, the pH of the resin will be too high, causing problems in terms of stability.

The amount of crosslinking agent is usually o.ooi to 1%, preferably o.o.o.i. to 15%, based on the weight of all copolymerizable monomers.
I'll go. When the amount of 1 in the crosslinking agent is less than 0.001%, the resulting resin has low gel strength upon water absorption and becomes sol-like.

On the other hand, if it exceeds 1%, the gel strength becomes too high and the water absorption capacity decreases.

The total amount of (meth)acrylate and (meth)acrylic acid is usually 70% or more, preferably 80 to 100%, based on the weight of all copolymerizable monomers.

If this total amount is less than 70%, the water absorption ability under pressure will decrease.

In the case of water-soluble monomers, the amount of other copolymerizable monomers is generally 30% or less, preferably 20% or less, based on the weight of all copolymerizable monomers. Usually 20 for water-insoluble monomers
% or less, preferably 10% or less.

In the present invention, when producing the water absorbent resin, the concentration of the copolymerizable monomer in the aqueous solution or aqueous dispersion is usually 10% or more, preferably 25% or more, and particularly preferably 30 to 90% by weight. It's %. If the concentration of the polymer is less than 10%, the resulting resin will have a low absorption capacity under pressure and a low diffusion rate.

The aqueous solution or dispersion is a copolymerizable monomer [(A).

CB), (C), etc.] in water or a mixed solvent of water and a water-soluble organic solvent (methanol, ethanol, acetone, N,N-dimethylformamide, dimethyl sulfoxide, etc.), preferably water. It will be done.

Polymerization is initiated using conventional radical polymerization initiators.

The polymerization initiator used is an azo compound [azobiscyanovaleric acid, azobisisobutyronitrile, 2,2゛-
azobis(2-amidinopropane) hydrochloride, etc.], inorganic peroxides (ammonium persulfate, potassium persulfate, lithium persulfate, etc.), and peroxides (hydrogen peroxide, benzoyl peroxide, di-t-butyl peroxide, etc.). oxide, cumene hydroperoxide, etc.), redox catalysts (alkali metal 5A salts or bisulfite, ammonium sulfite, ammonium bisulfite, reducing agents such as ascorbic acid, and alkali metal persulfates, ammonium peroxide) , peroxide, etc.). Two or more of the above polymerization initiators may be used in combination.

The amount of polymerization initiator is usually 0.001 to 5%, preferably 0.01 to 1%, based on the weight of all copolymerizable monomers.

It is necessary to initiate polymerization of an aqueous solution or aqueous dispersion at a temperature of 90°C or lower, preferably 10 to 50°C. 90
By starting polymerization at below °C,
The resulting resin has a lower absorption capacity under pressure and a slower diffusion rate than when polymerization is carried out at temperatures above ℃.

Although heating is not particularly required to initiate polymerization, depending on the type of polymerization initiator selected, polymerization may be initiated by heating to a temperature of 90° C. or lower. After the start of polymerization, the temperature rises due to the heat of polymerization, and the temperature rise at the stage where the polymerization rate is 50% or less varies depending on the monomer concentration, but is usually 5 to 30°C.

After the start of polymerization, the polymerization rate is 50% or less, preferably 5 to 40%.
It is necessary to complete the polymerization by forced heating at this stage.

If forced heating is not performed, the resin will have a low absorption capacity under pressure and a slow diffusion rate. Furthermore, if forced heating is performed when the polymerization rate exceeds 50%, the polymer has already become gel-like, making forced heating difficult. Moreover, the absorption capacity and diffusion rate of the produced resin under pressure are low. The polymerization rate can be determined by forcibly stopping the polymerization by a cooling operation and then checking the amount of unpolymerized monomer by liquid chromatography or the like. Heating is usually carried out at 100°C or higher, preferably 110 to 180°C. If the heating is less than 100°C, only a resin with low absorption capacity and low diffusion rate under pressure can be obtained. Also, after completion of polymerization,
A further drying step is required.

As a method of prepolymerizing to a stage where the polymerization rate is 50% or less and then completing the polymerization by forced heating, for example, the copolymerizable monomer and the polymerization initiator are passed through a static mixer, a spiral tube, etc., and the prepolymerization is carried out. After that, the polymer is spread on a drum dryer or rotating disk that is forcibly heated to complete polymerization and drying. Another method is to spread a mixed solution of a copolymerizable monomer and a polymerization initiator on a mobile belt, tray, vat, etc.

After starting the polymerization, when the polymerization rate is 50% or less, the polymer is forced to pass through an externally heated sheet to complete the polymerization and dry. Also,
There is also a method of prepolymerizing to a polymerization rate of 5σ% or less and then spraying it into a heating medium to complete the polymerization.

The time for these prepolymerizations is usually within several seconds from the start of polymerization, and the time for forced heating to complete polymerization is from several seconds to several minutes. No particular drying step is required.

The obtained water-absorbing resin has the ability to absorb 1% saline solution at least 10 times its own weight under a pressure of 20 g/ctA.

In addition, in the present invention, completion of polymerization does not necessarily mean a polymerization rate of 10.
This does not mean 0%, but a normally permissible amount of monomer (2% or less) may remain in the produced resin.

[Examples] The present invention will be further described below with reference to Examples, but the present invention is not limited thereto. The absorbency of the water-absorbing resin in the example for 1% saline under normal pressure is normal.

Measurements were made based on the conventional tea bag method. On the other hand, the absorption capacity under pressure is determined by spreading 0.2 g of resin evenly on a nylon mesh (250 mesh) with an area of 1 d, placing a weight from the top to apply a pressure of 20 g/crA, and applying pressure to the bottom nylon mesh. 1% saline is brought into continuous contact from the shell side.

After absorbing for 60 minutes, the weight of the water-absorbing gel was measured, and the absorption capacity under pressure was determined using the following formula.

Absorption capacity under pressure (g/g) (weight of water-absorbing gel i) x5-
1. Diffusion rate is the number of seconds it takes for 2 g of resin to be evenly spread in a Petri dish with a base area of 100 ctA, and 50 d of 1% saline solution being intravenously injected from the center of the top in 10 seconds until all of the saline solution is absorbed. was measured. The resin that is more likely to generate mamaco takes longer to complete absorption.

Note that the parts in the examples are important parts.

Example 1 115 parts of potassium acrylate, 25 parts of acrylic acid, N,
N'-methylenebisacrylamide 0.05 part and 2
．． 0.05 part of 2°-azobis(2-amidinopropane) hydrochloride was added to 93 parts of water to give a concentration of 60 parts.

A stock solution was prepared. This polymerization stock solution was prepolymerized to a polymerization rate of 31% by passing through a static mixer, and then spread on a heated drum dryer (rotation speed: 0.2 rl) (III) heated to a surface temperature of 130 °C, and forcedly heated. Polymerization was completed. The dried solid copolymer was continuously scraped off with a scraper to obtain a water absorbent resin with a water content of 3.2%. Grind this material to a particle size of 32 to 145 mesh,
Table 1 shows the results of measuring the absorption capacity and diffusion rate under normal pressure and under pressure.

Example 2-7 The procedure of Example 1 was repeated except that the polymerization rate of prepolymerization, the concentration of the copolymerizable monomer, and the forced heating temperature were changed as shown in Table 1. A water absorbent resin was obtained. The performance measurement results of these resins are also listed in Table 1.

Table 1 (1) Table 1 (2) Example 8 98 parts of sodium acrylate, 25 parts of acrylic acid, N,
A polymerization stock solution was prepared by dissolving 0.05 part of N'-methylenebisacrylamide, 0.01 part of hydrogen peroxide, and 0.005 part of ascorbic acid in 185 parts of water. After spreading this polymerization stock solution on a tray and prepolymerizing it to a polymerization rate of 36%,
Place in the oven at 150"C and force heat.

As a result, a water absorbent resin having a water content of 2.2% was obtained. This material was pulverized to a particle size of 32 to 145 mesh, and the performance was measured. The results are shown in Table 2.

Examples 9 to 10 A water-absorbing resin was obtained in the same manner as in Example 8, except that the amount of N,N'-methylenebisacrylamide was changed to 0.02 part or 0.1 part.

These performances are shown in Table 2. Example 11 Water absorption was carried out in the same manner as in Example 8 except that 85 parts of sodium acrylate and 28 parts of sodium styrene sulfonate were used instead of 98 parts of sodium acrylate in Example 8. A synthetic resin was obtained. The performance of this product is shown in Table 2.

Example 12 A water absorbent resin was obtained in the same manner as in Example 8 except that 0.1 part of trimethylolpropane triacrylate was used instead of 0.05 part of N,N''-methylenebisacrylamide. .The performance of this product is shown in Table 2.

Comparative Example 1 When the same polymerization stock solution as in Example 1 was prepolymerized to a polymerization rate of 60% by passing through a static mixer, the polymer was already in the form of a gel, and it was difficult to spread it on a drum dryer. Take this thing out to the tray,
A water absorbent resin was obtained by forced heating in an oven at 150°C.

The performance of this product is shown in Table 2.

Comparative Example 2 The same polymerization stock solution as in Example 1 was spread on a drum dryer that was forcibly heated under the same conditions as in Example 1 to obtain a water absorbent resin without prepolymerization. The performance of this product is shown in Table 2.

Comparative Example 3 The same polymerization stock solution as in Example 1 was heated to 60°C and polymerized. The polymerization temperature rose to 115° C. without external heating, most of the water vaporized, and the polymerization was completed. The polymerization rate upon completion of polymerization was 98.2%. The performance of this water-absorbing resin is
Shown in the table.

Table 2 [Effects of the Invention] According to the present invention, a water-absorbing resin having the following effects can be produced.

(1) A resin with high absorption capacity under pressure can be produced.

For sanitary materials such as disposable diapers, the baby's weight is placed on them, so the absorption capacity under pressure is more important than the absorption capacity under normal pressure.

A conventional method, for example, a water-soluble salt of acrylic acid and/or a water-soluble salt of methacrylic acid, an acrylic acid and/or methacrylic acid, and a crosslinking agent in an aqueous medium of 100 to 2
There is a method of copolymerizing by heating at 50°C, or a method of polymerizing a copolymerizable monomer whose main components are a water-soluble salt of acrylic acid, Acrylic M, and a crosslinking agent in water, and then drying the gel-like material formed. or a potassium acrylic acid salt and a water-miscible divinyl compound at a monomer concentration of 55 to 8.
When the polymer was produced as a 0% aqueous solution by setting the polymerization initiation temperature to 50 to 85° C. and vaporizing water by the heat of polymerization without external heating, a product with high absorption capacity under pressure could not be obtained.

However, according to the present invention, a product with excellent absorption capacity under pressure can be obtained.

(2) It does not generate mako even when it comes into contact with the absorbed liquid.

Therefore, a resin with excellent diffusion and absorption rates can be obtained.

(3) When applied to sanitary materials such as disposable diapers, it has effects such as improving dry touch properties and reducing leakage, and high quality products can be obtained.

(4) Polymerization and drying are completed in an extremely short time of a few minutes,
Manufacturing costs are low.

Because the resin obtained by the present invention exhibits the above effects, it can be used as absorbent materials, sanitary materials (disposable diapers for children and adults, sanitary napkins, sanitary cotton, bandages, incontinence pads, breast pads, paper towels, etc.) Applications that come into contact with the human body, such as water separation agents in oil, other dehydration or desiccant agents: water retention agents for plants, soil, etc.; sludge coagulants: useful for industrial applications such as dew condensation prevention agents used in interior building materials .

Claims (1)

[Claims] 1. An aqueous solution of a copolymerizable monomer containing (A) an acrylate and/or a methacrylate; (B) an acrylic acid and/or a methacrylic acid, and (C) a crosslinking agent as essential components. Alternatively, a method for producing a water-absorbing resin, which comprises polymerizing an aqueous dispersion, starting the polymerization at 90° C. or lower, and then forcibly heating the polymerization to complete the polymerization at a polymerization rate of 50% or lower. 2. The manufacturing method according to claim 1, wherein the temperature at which the polymerization is completed by forced heating is 100° C. or higher.