JPH1045812A - Production of fiber-containing water absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a phenomenon such as bumping at the time of an exothermic reaction, facilitate the polymerization control and enable the efficient production of the subject resin by including prescribed staple fibers in an acrylic acid- based monomer before polymerization when carrying out the stationary polymerization. SOLUTION: (C) Staple fibers having 1-100μm average fiber diameter and 0.5-10mm length are contained in (A) an aqueous solution of an acrylic acid- based monomer to carry out the stationary polymerization when adding (B) a polymerization initiator to the component A and conducting the stationary polymerization without stirring the resultant reactional mixture. Furthermore, the component A is preferably contained in an amount of 0.1-5 pts.wt. based on 100 pts.wt. component A and, e.g. conjugated fibers such as a polyester/ polyethylene are preferably used as the component C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fiber-containing water-absorbent resin composition in which short fibers are contained before polymerization to prevent bumping by polymerization.

[0002]

BACKGROUND OF THE INVENTION In recent years, sanitary goods, soil improvers for agriculture and horticulture,
Water-absorbing resins have come into widespread use in various places such as adsorbents. In particular, the amount used for disposable diapers and sanitary napkins is increasing year by year. Ordinary water-absorbing resins are mainly those obtained by polymerizing acrylates, and known methods for producing such resins include reversed-phase suspension polymerization and static polymerization.

[0003] Among these, reversed-phase suspension polymerization has the advantage that heat of polymerization is easily removed, but has the disadvantage that it is costly because a solvent such as cyclohexane is used. On the other hand, static polymerization is a method in which a polymerization initiator is added to an aqueous solution of a monomer and polymerization is performed without stirring under heating, and a sheet-like water-absorbing resin can be produced at low cost. However, it is difficult to remove the heat of polymerization, so that excessive foaming, waving, and sheet deformation due to bumping are likely to occur. As a result, the transfer between the conveyors from the polymerization step to the drying step is hindered, and it becomes difficult to cut the sheet. Further, the quality is not uniform, which is not preferable.

[0004]

As a method for suppressing a rapid reaction of static polymerization, there is a polymerization method disclosed in Japanese Patent Application Laid-Open No. 4-175319. In this method, polymerization is carried out at a relatively low temperature without stirring an aqueous solution containing a vinyl monomer, and the polymerization temperature is raised as needed at a stage where the conversion is 70% or more to complete the polymerization.

However, this method has a low production efficiency because polymerization is performed at a relatively low temperature, requires complicated equipment for temperature control, and has a limitation in the thickness of a sheet that can be produced. Further, the obtained sheet-like water-absorbent resin has a disadvantage that the residual monomer is high in quality.
An object of the present invention is to provide a method for producing a fiber-containing water-absorbent resin capable of efficiently producing a water-absorbent resin without waving or deformation of a sheet by suppressing bumping in static polymerization.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, when static polymerization is carried out by containing short fibers in an aqueous solution of an acrylic acid monomer, an exothermic reaction occurs. Evaporation of water vapor from the inside of the gel phase during the reaction is facilitated, and the above-described phenomenon such as bumping can be suppressed. The present inventors have obtained a new finding that a fiber-containing water-absorbent resin can be efficiently produced, and have completed the present invention.

In the fiber-containing water-absorbent resin obtained by the method of the present invention, since short fibers are added from the beginning of polymerization,
There is also an effect that the fibers are hardly peeled off from the water absorbent resin.
In addition, since the fiber-containing water-absorbent resin has fibers protruding from the surface, it is possible to prevent the water-absorbent resin from moving and falling off in an absorbent body such as a diaper. That is, the method for producing a fiber-containing water-absorbent resin of the present invention is a method in which a polymerization initiator is added to an aqueous solution of an acrylic acid-based monomer, and the mixture is allowed to stand for polymerization without stirring. It is characterized in that short fibers having a length of 0.5 to 10 mm are contained in an aqueous solution of the acrylic acid-based monomer and subjected to static polymerization.

In this case, it is preferable that the short fibers are contained in a proportion of 0.1 to 5 parts by weight based on 100 parts by weight of the acrylic acid monomer. The fiber-containing water-absorbing resin is disclosed in JP-A-56-65630, Japanese Patent Publication No. 3-456.
No. 55, as disclosed in Japanese Patent Publication No. Hei 8-19609, conventionally known, the method described in these publications is to mix a polymerized water-absorbing resin and fiber, There is no known polymer obtained by adding a short fiber before polymerization and performing static polymerization.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The acrylic acid monomer in the present invention is, for example, one containing acrylic acid or methacrylic acid and its neutralized product as main components. Examples of the neutralized product include one or more selected from a sodium salt, a potassium salt, and an ammonium salt of (meth) acrylic acid, and an alkali metal salt such as a sodium salt and a potassium salt is preferable. Examples of the alkali agent for neutralizing the acrylic acid monomer into an alkali metal salt include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide.

A monomer other than (meth) acrylic acid may be used in combination with (meth) acrylic acid. As such other monomers, those which have been conventionally used in the production of water-absorbent resins can be used without any particular limitation. One or more water-soluble ethylenically unsaturated monomers selected from acids and neutralized products thereof are exemplified.

The degree of neutralization of the partially neutralized (meth) acrylic acid is usually 50 to 95 mol%, preferably 60 to 90 mol%. A crosslinking agent can be used in combination with the above monomers. Examples of such a crosslinking agent include those having two or more double bonds such as methylenebisacrylamide and polyethylene glycol diacrylate and exhibiting copolymerizability with an acrylic acid monomer, and acrylic acid such as ethylene glycol diglycidyl ether. Compounds having two or more functional groups that react with the carboxyl group in the monomer can be used.

In the present invention, the short fibers have an average fiber diameter of 1
It is a powder fiber having a length of 0.5 to 100 mm and a length of 0.5 to 10 mm. Average fiber diameter is less than 1μm or fiber length is 0.5mm
If it is less than 3, water vapor hardly escapes from the inside of the gel phase during the exothermic reaction, causing bumping. On the other hand, if the average fiber diameter is 100
If it exceeds μm or if the fiber length exceeds 10 mm, the quality is affected, such as a decrease in water absorption.

Examples of the short fibers include conjugate fibers such as polyester / polyethylene and polyester / vinyl acetate copolymer, hydrophobic fibers such as polypropylene, pulp, and the like.
And hydrophilic fibers such as rayon. The amount of the short fiber used in the present invention is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the acrylic acid monomer. If the amount of short fibers used is less than 0.1 parts by weight, bumping may occur. On the other hand, if the used amount exceeds 5 parts by weight, the viscosity of the acrylic acid monomer becomes too high, which makes the handling of the monomer difficult and undesirably prevents the fibers from being finely dispersed.

As the polymerization initiator in the present invention, a commonly used water-soluble radical polymerization initiator can be used. As such a radical polymerization initiator, for example, potassium persulfate, persulfates such as ammonium persulfate,
Hydroperoxides such as hydrogen peroxide and cumene hydroperoxide, and azo compounds such as 2.2-azobis-2-amidinopropane hydrochloride are exemplified.

One of these radical polymerization initiators may be used alone, or two or more of them may be used in combination. Further, a reducing agent such as sulfite or L-ascorbic acid may be used. Redox initiator systems in combination with are also possible. The polymerization temperature can be variously changed depending on the type of the radical polymerization initiator used,
It is usually 0 to 150 ° C, preferably 10 to 100 ° C.

By the polymerization, a hydrogel sheet of a water-absorbing resin is obtained. The product is obtained by drying, pulverizing and classifying the product. At that time, the method of the present invention has an advantage that a large amount of water vapor is generated at the time of polymerization, so that the water value of the gel sheet is low, and thus the time of the drying step is greatly reduced.

[0017]

【Example】

Example 1 75 mol% of sodium acrylate and 25 of acrylic acid
The amount of N.O.M. After adding and dissolving 0.2 g of N-methylenebisacrylamide, nitrogen gas was blown out to expel dissolved oxygen and the liquid temperature was set to 10 ° C.

Next, polypropylene short weave fiber (length 5 mm,
10 g of an average fiber diameter (25 μm) was charged into the monomer solution and stirred. Five minutes later, an aqueous solution (A) obtained by adding 1.3 g of potassium persulfate and 0.3 g of potassium thiosulfate to 130 g of ion-exchanged water was added to the monomer solution with stirring, and the mixture was heated to 70 ° C.
Teflon-coated stainless steel bat soaked in warm water (3
(70 mm × 470 mm × 50 mm).

The thickness of the obtained gel sheet was about 5 mm. After about 5 minutes, heat generation reached a peak, and although steam came out of the surface of the gel sheet, generation of large bubbles due to bumping and deformation of the gel sheet were not observed. The obtained hydrogel was dried, pulverized, and classified to obtain a fiber-containing water-absorbent resin product. Example 2 In Example 1, the added amount of the polypropylene short fiber was 20.
The same operation as in Example 1 was performed except for changing to g. As a result, as in Example 1, water vapor came out from the surface of the gel sheet 5 minutes after the start of polymerization, but generation of large bubbles due to bumping and deformation of the gel sheet were not observed. Example 3 Short polypropylene fiber (length 5 m) used in Example 1
The same operation as in Example 1 was performed except that polypropylene short fibers having a fiber length of 2 mm were used instead of m). As a result, as in Example 1, water vapor came out of the surface of the gel sheet 5 minutes after the polymerization was started, but generation of large bubbles due to bumping and deformation of the gel sheet were not observed. Example 4 The same operation as in Example 1 was performed, except that polypropylene / polyethylene composite fiber (length: 5 mm, average fiber diameter: 15 μm) was used instead of the polypropylene short fiber used in Example 1. As a result, as in Example 1, water vapor came out from the surface of the gel sheet 5 minutes after the start of polymerization, but generation of large bubbles due to bumping and deformation of the gel sheet were not observed. Example 5 The same operation as in Example 1 was performed except that polypropylene short fibers having an average fiber diameter of 5 μm were used instead of the polypropylene short fibers (average fiber diameter 25 μm) used in Example 1. As a result, as in Example 1, water vapor came out of the surface of the gel nut 5 minutes after the start of the polymerization, but no large bubbles were formed due to bumping and no deformation of the gel sheet was observed. Comparative Example 1 The same operation as in Example 1 was performed except that no fiber was added. As a result, bumping occurs 5 minutes after the start of polymerization,
The gel sheet has been partially torn. Comparative Example 2 The same operation as in Example 1 was performed except that polypropylene short fibers having a fiber length of 0.1 mm were used. As a result, bumping occurred 5 minutes after the start of the polymerization, and the gel sheet was partially torn. Comparative Example 3 The same operation as in Example 1 was carried out except that cellulose short fibers (average fiber diameter: 0.1 μm) were used instead of polypropylene short fibers. As a result, bumping occurred 5 minutes after the polymerization was started, and the gel sheet was partially torn. Comparative Example 4 The same operation as in Example 1 was performed except that polypropylene short fibers having an average fiber diameter of 300 μm were used. As a result, although water vapor came out from the gel sheet surface 5 minutes after the polymerization was started, generation of large bubbles due to bumping and deformation of the gel sheet were not observed. However, the obtained water-absorbent resin had only 2/3 times the amount of normal water-absorbent resin in water absorption.

[0020]

According to the present invention, a phenomenon such as bumping during an exothermic reaction can be suppressed by allowing a predetermined short fiber to be contained in an acrylic acid monomer before polymerization in static polymerization.
There is an effect that the polymerization can be easily controlled and the fiber-containing water-absorbent resin can be efficiently produced.

Claims (2)

[Claims] 1. A method for producing a water-absorbent resin, which comprises adding a polymerization initiator to an aqueous solution of an acrylic acid monomer and carrying out standing polymerization without stirring, comprising: an average fiber diameter of 1 to 100 μm and a length of 0.5 to 10 mm. A method for producing a fiber-containing water-absorbent resin, wherein a short fiber is contained in an aqueous solution of the acrylic acid-based monomer and subjected to static polymerization. 2. The process for producing a fiber-containing water-absorbent resin according to claim 1, wherein the short fibers are contained in the aqueous solution of the acrylic acid monomer in a ratio of 0.1 to 5 parts by weight based on 100 parts by weight of the monomer. .