JPS61194300A - Water absorbable fiber composite - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water absorbent fiber composite containing a super absorbent resin impregnated into pulp. Here, pulp is an aggregate mainly composed of cellulose fiber fragments obtained from pulp material, and fibrous material refers to a material consisting of fiber fragments such as natural fibers such as cellulose fibers and synthetic fibers. Also includes pulp.

BACKGROUND ART Water-absorbing materials for sanitary napkins and disposable diapers have been known in which water-absorbing properties are imparted by sprinkling super-absorbent resin powder onto pulp cotton or tissue paper.

In these products, the superabsorbent resin powder has properties such as specific gravity and shape that are different from the base material, so it does not blend with the base material as it is, and may fall off the base material due to excessive storage or transportation. There is a drawback that it is unevenly distributed and the desired effect is not fully exerted. For this reason, for example, measures have been taken such as adding moisture to tissue paper on which superabsorbent resin powder has been sprinkled, allowing the moistened resin to adhere to the substrate, and then drying.

In addition, when resin powder is sprinkled on pulp cotton, the resin concentrates on the surface of the substrate, preventing the resin from swelling when water is absorbed, and the water absorption capacity decreases by 60 to 70% compared to when it is uniformly dispersed over the entire substrate.
It is known that there is a gradual decline in In order to eliminate these drawbacks, it is desired to uniformly disperse the resin powder on the substrate and prevent it from falling off, but no effective means has yet been found.

Super absorbent resins made with acrylic acid as the main component are known. A problem in the production of polyacrylic acid-based superabsorbent resins lies in the control of the polymerization reaction of acrylic acid. When a radical initiator is added to an aqueous solution of acrylic acid neutralized to a neutral range with caustic soda at a concentration of over 40% by weight and heated, rapid polymerization occurs, producing a self-crosslinked superabsorbent resin. Once polymerization is initiated, the viscosity of the system increases and gelation occurs due to crosslinking. While the polymerization reaction is accelerated by the temperature rise caused by the reaction heat, the generated water vapor is prevented from dissipating out of the system due to increased viscosity and gel formation, making it difficult to remove the reaction heat.
As a result, the reaction explodes out of control.

As a means to avoid these difficulties, the following polymerization methods have been proposed, some of which have been implemented industrially. (1) A reverse-phase suspension polymerization method in which the aqueous stock solution is dispersed in the oil phase as fine water droplets; (2) the concentration of the aqueous stock solution is lowered to 3υ or less to suppress the formation of self-crosslinking, and it can be controlled as an industrial glucose (3) The aqueous stock solution is polymerized in a thin layer state from which the heat of reaction can be removed.

The basic structure of polyacrylic acid-based superabsorbent resin is a neutral alkali metal salt of polyacrylic acid into which appropriate crosslinking has been introduced, and minor changes such as the addition of water-soluble polymers such as starch or crosslinking agents However, the basics of the polymerization reaction are common69, and all three of the above three polymerization methods of Type 1 involve a significant cost increase factor. The above relationship is supported by the fact that the product price is abnormally high compared to the raw material cost, even though it is a mass-produced super absorbent resin/Ii product. Therefore, if a simple and inexpensive manufacturing method is found, it will be very effective.

The present invention provides a novel water-absorbing fiber composite that solves the two problems pointed out above regarding current super-absorbent resins and products using the same.

In the method of the present invention, pulp is impregnated with an aqueous stock solution containing a partial alkali metal salt of acrylic acid as a main component, and the impregnated product is polymerized by heating. Although the aqueous stock solution may selectively contain minor components of other water-soluble monomers, crosslinkable monomers, and water-soluble polymers, the concentration of the partial alkali metal salt of acrylic acid is sufficient for moderate crosslinking to impart high water absorption. This can be achieved simply by adjusting the polymerization conditions. A suitable concentration range is usually 40-60% by weight. Aqueous stock solutions are usually in the neutral range depending on the intended use of the product. The amount of the aqueous stock solution impregnated into the pulp is not particularly limited, but is limited to an amount that does not significantly hinder the release of water vapor from the impregnated material during polymerization.

When the aqueous stock solution impregnated into the pulp is polymerized, the water vapor generated by the reaction heat is easily dissipated and the reaction heat is removed, so that the polymerization reaction proceeds smoothly without runaway. The reaction is completed within several minutes at a temperature of 90 to 100°C, and a reaction product is obtained in which pulp fibers are coated with a water-use gel made of a super absorbent resin.

The reactants are then uniformly mixed and dispersed with the fibrous material. Fibrous substances are raw materials for paper and nonwoven fabrics, and the manufacturing processes for these products are generally known and do not differ greatly depending on the material, so pulp will be chosen as a representative for explanation.

The shape of the reactant changes from a pulp-like shape to a resin hydrated glue-like shape depending on the amount of the aqueous stock solution impregnated, and various methods are used to mix and grind the reactant with the pulp and disperse it uniformly. When the dried reactant is mixed with dry pulp and pulverized, a dry powder-like pulp containing a superabsorbent resin is obtained. This material is processed into a pulp-cotton-like sheet by known means and suitably used as a water-absorbing material for disposable diapers. Alternatively, by mixing and pulverizing the reactant in a wet state with wet pulp, a wet super absorbent resin-containing pulp can be obtained. When this material is subjected to wet paper making by known means, highly water-absorbent paper is obtained. At that time,
Since the superabsorbent resin in a swollen state functions as a binder, favorable effects are exhibited.

In the pulp flocculent sheet and superabsorbent paper obtained by the method exemplified above, the superabsorbent resin and 20 parts of the pulp come into close contact and are uniformly dispersed, eliminating the drawbacks seen in the current products. Not only that, but also superior water absorption speed and ability can be exhibited.

Many materials other than pulp can be applied as sll-like materials. For example, dispersing the reactant in short rayon fibers,
Paper or nonwoven fabric with high strength can be obtained by wet or dry methods. Furthermore, if polyolefin staple fibers such as polypropylene are used, water-absorbing paper or nonwoven fabric can be produced.

As for the method of heating and dispersing the reactant and the fibrous material material, an appropriate method is used depending on the material.

The mixing ratio of the reactant and the fibrous material is determined depending on each application. The water absorption capacity of the water absorbent fiber composite is controlled by the superabsorbent resin content.

Further, the fibrous material is not limited to one type, and a mixture of two or more types may be used, allowing a wide range of designs depending on the intended product.

Next, embodiments of the present invention will be described.

An aqueous stock solution is made by adding acrylic acid to an aqueous solution of caustic soda. Water-soluble valve monomers that are selectively added as minor components include methacrylic acid, acrylamide, maleic anhydride, and the like. As a crosslinkable monomer, N, N'
- polyfunctional monomers such as methylene bisacrylamide, N
- Monomers that react with functional groups of polymers to form crosslinks, such as methylol acrylamide. Further, water-soluble polymers include starch, cellulose derivatives, polyvinyl alcohol, and the like. In the case of using acrylic acid alone, moderate self-crosslinking is introduced when the concentration of the stock solution ranges from 40 to 60, producing a superabsorbent resin. A water-soluble peroxide is used as a radical polymerization initiator, such as potassium persulfate. It is desirable for the aqueous stock solution to be neutral for its intended use; in the case of acrylic acid, the neutral point is the point where about 70% of the carboxyl groups have been neutralized with caustic soda, and it is usually in the range of 60 to 80% neutralization. Vcl! I can finish 4 verses. The pulp is impregnated by means such as an aqueous concentrate if II mist. Polymerization is carried out by heating the impregnated material to a temperature of 80 DEG to 100 DEG C. in an inert atmosphere such as nitrogen, and is completed within a few minutes with smooth dissipation of water vapor.

Mixing and dispersion of the reactant and the fibrous material such as pulp is performed in the manner described above.

Example 1 Acrylic acid was added to an aqueous solution of caustic soda to form a solution at a concentration of 45 parts, with 70 parts of the carboxyl group neutralized, and 0.2 parts of potassium persulfate was added to this solution to prepare a stock solution.

15 parts of the stock solution was sprayed onto 10 parts of papermaking pulp to uniformly impregnate it, and the mixture was polymerized by heating at 90°C for KIO minutes in 2 atmospheres.

During this time, smooth generation of water vapor was allowed, and the temperature rose to 95°C. The reaction product was dried and weighed 16.7 g. 5 parts of the dry product were milled and mixed with 15 parts of the dry pulp in a mixer to obtain a uniform floc. 29 with pure water 0
．． In addition to 5e, after 1 hour, filter the water gel body with a wire mesh,
The weight was 1409. Separately, pulp 29 was treated in the same manner and had a weight of 249. It can be seen that approximately 6,009 ml of water was absorbed per 1 g of resin contained in the flocculent material.

Two parts of the dry product were mixed with 20 parts of pulp in water and milled to make paper. This paper exhibits a high degree of water absorption and also has good water retention capacity.

Example 2 To an aqueous solution with a concentration of 35% in which 701 of the carboxyl group of acrylic acid has been neutralized to a sodium salt, 0.02 weight of N,N'-methylenebisacrylamide of a partially neutralized salt of acrylic acid is added. A stock solution was prepared by adding 0.2 part of potassium persulfate to the solution.

Example 1: 10 parts of pulp for backing paper was impregnated with 10 parts of stock solution.
Polymerization was carried out in the same manner as above, and the reaction product was dried to obtain product 13.5.
I got the department. Five parts of the product and 30 parts of short rayon fibers were mixed uniformly in water, and a nonwoven fabric was exploded from the mixture. This nonwoven fabric 29 was added to pure water and filtered through a wire mesh, and the weight of the water absorbent body was determined to be 26 g.

Approximately 3,509 yen per gram of resin contained in the nonwoven fabric
It can be seen that the water has been absorbed.

Applicant for appetizer Kazuo Saotome

Claims (4)

[Claims] (1) Impregnating pulp with an aqueous stock solution containing acrylic acid as a main component and producing a superabsorbent resin through a radical polymerization reaction, and heating the impregnated material to polymerize the monomer components contained in the aqueous stock solution. A water-absorbing fiber composite made by mixing and dispersing the reactant obtained by mixing and dispersing a fibrous substance. (2) Carboxylic acid contained in a component whose aqueous stock solution is mainly composed of acrylic acid and one or more selected from water-soluble copolymerized monomers, crosslinkable monomers, and water-soluble polymers are added thereto. 60 to 80% of the groups are neutralized as alkali metal salts, and the water-soluble radical initiator is added to an aqueous solution having a concentration of 30 to 70% by weight. Water absorbent fiber composite. (3) The aqueous stock solution is made by adding a water-soluble radical initiator to an acrylic acid aqueous solution having a concentration of 35 to 70% by weight in which 60 to 80% of the carboxyl groups are neutralized as alkali metal salts. A water-absorbing fiber composite according to claim 1. (4) The water-absorbing fiber composite according to claim 1, wherein the fibrous material is composed of cellulose fibers.