JPS63291908A - Production of water absorbing composite material - Google Patents

Abstract

PURPOSE:To readily obtain a composite material having excellent water absorption and especially high water absorption rate under a mild condition, by applying an aqueous solution containing an acrylic acid monomer, a specific crosslinking agent and a radical polymerization initiator to a fibrous substrate and treating the monomer on the substrate with a reducing agent. CONSTITUTION:A formed fibrous substrate is coated with an aqueous solution containing (A) a polymerizable monomer comprising acrylic acid containing >=20% carboxyl group neutralized with an alkali metallic salt or ammonium salt as a main component, (B) a crosslinking agent (e.g. tetramethylolmethane tetraacrylate) comprising a (meth)acrylate compound containing three or more polymerizable vinyl groups in one molecule and (C) an oxidizing radical polymerization initiator (e.g. hydrogen peroxide) and the polymerizable monomer applied to the substrate is treated with a reducing agent (e.g. L-ascorbic acid) and the polymerizable monomer is polymerized to form a composite material of the polymer derived from the monomer and the fibrous substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION Industrial Field of Application The present invention relates to a method for producing a water-absorbing composite comprising a water-absorbing polymer and a shaped fibrous substrate. More specifically, the present invention involves applying an aqueous solution containing an acrylic acid monomer, a polyfunctional acrylate crosslinking agent, and an oxidizing radical polymerization initiator to a molded fibrous substrate, and then adding a reducing agent thereto. , relates to a method for producing a water-absorbing composite in which a super-absorbent polymer is fixed to a molded fibrous substrate, which comprises polymerizing the acrylic acid monomer.

The water-absorbing composite obtained by the production method of the present invention has excellent water absorption properties, particularly a high water absorption rate, and since the super-absorbent polymer is stably fixed to the fibrous substrate, it can be used for various water-absorbing materials. It can be advantageously used in manufacturing.

BACKGROUND OF THE INVENTION Conventionally, paper, pulp, nonwoven fabrics, sponge-like urethane resins, and the like have been used as water-retaining agents in various sanitary materials such as sanitary napkins and paper diapers, and in various agricultural materials. However, these materials absorb only 10 to 50 times their own weight of water, so in order to absorb or retain a large amount of water, a large amount of material is required, which not only makes them extremely bulky. Another disadvantage is that when a material that has absorbed water is pressurized, the water is easily released.

In order to improve the above-mentioned drawbacks of this type of water-absorbing material, various highly water-absorbing polymeric materials have been proposed in recent years. For example, starch graft polymer (Japanese Patent Publication No. 53-46199
Publications, etc.), modified cellulose (Japanese Patent Application Laid-open No. 50-8037)
6, etc.), crosslinked products of water-soluble polymers (Japanese Patent Publication No. 43-2)
3462, etc.), self-crosslinking type acrylic acid alkali metal salt polymers (Japanese Patent Publication No. 54-30710, etc.), and the like have been proposed.

However, although these superabsorbent polymer materials have a fairly high level of water absorption performance, most of them are obtained in the form of powder, so they cannot be used for example in sanitary napkins,
Tissues to be used as sanitary materials such as paper diapers, etc.
It is necessary to disperse it evenly on a substrate such as nonwoven fabric or cotton. However, it is difficult to stably fix polymer powder dispersed by such a method on a substrate.
After dispersion, the gel often aggregates locally, and the swollen gel after water absorption is not stably fixed on the substrate and easily moves from the substrate. For this reason, when this material is used in paper diapers, for example, the water absorbent material after urinating becomes stiff and stiff, making it extremely uncomfortable to wear. The method of obtaining an absorbent body by dispersing powder into powder is extremely expensive in terms of cost due to the complexity involved in handling the powder and process problems in efficiently achieving uniform dispersion.

One method to solve these problems is to manufacture a composite by applying an aqueous solution of acrylic acid monomer to a molded fibrous substrate in a predetermined pattern, and then irradiating this with electromagnetic radiation or particulate ionizing radiation. , a method for producing a water-absorbing composite by converting an acrylic acid monomer into a superabsorbent polymer has been reported (Japanese Patent Publication No. 57-500546).
Publication No.). Although this method shows considerable improvement in terms of uniform dispersion and stable immobilization on the substrate when handling the above powder, it is difficult to convert it into a superabsorbent polymer. , due to the use of electromagnetic radiation or particulate ionizing radiation, the highly water-absorbing polymer inherent in this particular monomer is susceptible to excessive cross-linking reactions, so that the resulting composite has poor performance as an absorber. There seems to be a drawback in that the performance, particularly the water absorption capacity, is extremely low and is less than half that of the case where the above-mentioned powdered superabsorbent polymer is used. Furthermore, in terms of process, it cannot be said that this is an inexpensive method in terms of safety and cost associated with handling the radiation generating device as described above.

Recently, Japanese Patent Application Laid-Open No. 60-149609 discloses that after pre-impregnating a water-absorbing material with an acrylate-based aqueous solution, a water-soluble radical polymerization initiator or a water-soluble radical polymerization initiator is mixed with a water-soluble radical polymerization initiator. A method for producing a water-absorbing composite is proposed in which a water-absorbing composite is polymerized by adding a water-reducing agent in the form of a mist. However, in this method, the water-soluble polymerization initiator is added after the water-absorbing organic material is impregnated with the acrylic acid monomer, so even if the polymerization initiator is in the form of a mist, "polymerization unevenness" may occur.
occurs, making it extremely difficult to completely polymerize the monomer, resulting in a large amount of residual monomer.
It seems that there are many safety problems, and there are also drawbacks in terms of performance, particularly in terms of water absorption capacity.

Possible Solutions Against this background, the inventors have already filed a patent application in 1986-23.
No. 8421 describes that after uniformly mixing an acrylic acid monomer aqueous solution containing a small amount of crosslinking agent and an oxidizing radical polymerization initiator, the mixture is applied to a fibrous substrate, and then an amine or a reducing agent is applied to polymerize. We proposed a method for producing a water-absorbing composite consisting of a super-absorbent polymer and a molded fibrous substrate. It was found that with this method, there was almost no "uneven polymerization", the polymerization progressed easily, and a product with a high water absorption capacity was obtained. It has been found that the presence of a crosslinking agent and also the employment of certain controlled polymerization conditions particularly improve the water absorption rate.

[Summary of the invention]

Purpose of the Invention The present invention is based on the aforementioned Japanese Patent Application No. 60-238421, Japanese Patent Publication No. 57-500546, and Japanese Patent Application Laid-Open No. 60-14
The present invention further improves the method for producing a water-absorbing composite described in Publication No. 9609, and provides a method for extremely easily producing a water-absorbing composite material with excellent water-absorbing performance and especially a particularly high water-absorbing rate under mild conditions. This is what I am trying to do.

Structure of the Invention As a result of various studies aimed at solving the above problems, the present inventors have developed an aqueous solution containing the acrylic acid monomer, a specific polyfunctional acrylate crosslinking agent, and an oxidative radical polymerization initiator. is applied to a molded fibrous substrate, and then a reducing agent is applied in the form of a mist, so that the polymerization is completed in an extremely short period of time, there is almost no residual monomer, the water absorption rate is particularly high, and the polymer is highly water absorbent. The present invention was achieved by discovering that a water-absorbing composite material in which a water-absorbing composite material is stably fixed to a fibrous substrate can be obtained extremely easily and inexpensively.

That is, the method for producing a water-absorbing composite with improved water absorption rate according to the present invention is characterized by combining the following steps (A) and (B).

(A) A step of applying an aqueous solution containing the following components (a) to (c) to a molded fibrous substrate.

(a) A polymerizable monomer whose main component is acrylic acid in which 20% or more of the carboxyl groups are neutralized with an alkali metal salt or ammonium salt; (b) Three or more polymerizable vinyl groups in one molecule. have (
meth) a crosslinking agent consisting of an acrylate compound, (iii) an oxidizing radical polymerization initiator, and (B) applying a reducing agent to the polymerizable monomer applied to this fibrous substrate to polymerize the polymerizable monomer. A step of forming a composite of a polymer derived from the polymerizable monomer and a fibrous substrate.

Effects of the Invention The method for producing a water absorbent composite of the present invention has remarkable features in the following points.

(a) The crosslinking agent used reacts efficiently with the acrylic acid monomer, and the resulting polymer is a resin with an appropriate crosslinking structure and crosslinking distribution, so it has excellent water absorption and particularly high water absorption rate (b) The oxidative radical polymerization initiator is predissolved in the polyfunctional (meth)acrylate crosslinking agent and acrylic acid monomer aqueous solution shown above, and by adding a reducing agent to the aqueous solution and polymerizing it, the amount remaining in the polymer is reduced. The amount of polymer is extremely small, the polymerization operation is easy, and the polymerization can be completed in a very short time under mild conditions at around room temperature.

Therefore, the water-absorbing composite obtained by the production method of the present invention can be obtained from the above-mentioned Japanese Patent Application No. 60-238421 and Japanese Patent Publication No. 57, as is clear from the Examples and Comparative Examples of the present application described below. It can be seen that the water absorption performance is higher than the methods shown in Japanese Patent Application Laid-open No. 500546 and Japanese Patent Application Laid-Open No. 60-149609, and in particular, the water absorption rate is particularly high. Furthermore, since its form is sheet-like,
Since it is easier to handle and cheaper than conventionally used powdered superabsorbent resins, it can be advantageously used in the production of various sanitary materials such as sanitary napkins and paper diapers. In addition, by utilizing its excellent water absorption performance and ease of handling, it can be used to produce various materials for gardening and agriculture, including soil conditioners and water retention agents, which have recently attracted attention.

[Detailed description of the invention]

Acrylic acid monomer 1 The acrylic acid monomer used in the present invention, that is, component (a), has acrylic acid as its main component, and 20% of it is
Preferably 50% or more of the above is neutralized with an alkali metal salt or an ammonium salt. If the degree of partial neutralization is less than 20%, the water absorption performance of the resulting polymer will be significantly reduced, which is not preferable.

Furthermore, in the present invention, in addition to the above-mentioned acrylic acid monomers, monomers copolymerizable with these monomers, such as (a) methacrylic acid,
Itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acryloylethanesulfonic acid and its salts, (b) itaconic acid, maleic acid, fumaric acid, etc. Alkyl or alkoxy esters of dicarboxylic acids, (c) vinyl sulfonic acid, (d) acrylic acid methyl ester, acrylic acid ethyl ester, etc., (e)
(meth)acrylic acid hydroxyethyl ester, (meth)acrylic acid hydroxypropyl ester, (h)polyethylene glycol mono (meth)acrylate, (th)acrylamide, methacrylamide, N, N'-
One or more of dimethylacrylamide, N,N'-dimethylmethacrylamide, (th)2-vinylpyridine, and 4-vinylpyridine can also be used in combination as long as the water absorption performance is not impaired.

Since the "polymerizable monomer" used in the present invention is mainly composed of acrylic acid (20% or more of which is in the form of salt), the amount of the copolymerizable monomer added above is the same as the general amount. is less than 50 mol%, preferably 20% or less.

Note that alkali metal hydroxides, bicarbonates, or ammonium hydroxide can be used to neutralize the above-mentioned acid monomers including acrylic acid, but alkali metal hydroxides are preferable. Specific examples thereof include sodium hydroxide, potassium hydroxide, and lithium hydroxide.

Sodium hydroxide or potassium hydroxide is preferred from the viewpoint of industrial availability, price, safety, and the like. The concentration of these hexamers in water is 20% by weight or more, preferably 30% by weight or more. It can be said that the higher the concentration, the better.

That is, by increasing the monomer concentration, the amount of superabsorbent polymer filled per unit surface area of the molded fibrous substrate increases, making it possible to obtain a composite with excellent water absorption performance.

In addition, by increasing the monomer concentration, conversely speaking, the water concentration can be decreased, so that the energy required for drying can be reduced, which is advantageous in terms of cost.

Crosslinking agent composed of polyfunctional acrylate compound The crosslinking agent used in the production method of the present invention is a (meth)acrylate crosslinking agent having three or more double bonds in the molecule, and is copolymerizable with the acrylic acid monomer. and exhibits a certain degree of solubility in an aqueous solution of the acrylic acid monomer. Specific examples of such crosslinking agents include tetramethylolmethanetetra(meth)acrylate, trimethylolpropanetri(meth)acrylate, tetramethylolmethanetri(meth)acrylate, dipentaerythritol hexaacrylate, etc. .

Among these, tetramethylolmethanetetraacrylate is particularly preferred in the present invention.

Such crosslinking agents can be used alone or as a mixture of two or more.

The amount of these crosslinking agents used is 0.001 to 10% by weight, preferably 0.01 to 2% by weight, based on the acrylic acid monomer. If it is less than 0.001% by weight, the water absorption capacity will be extremely high, but the water absorption rate will be low, and the gel strength of the superabsorbent polymer upon water absorption will be extremely weak. Further, if the amount is more than 10% by weight, the water absorption rate and the water absorption gel strength are particularly improved, but the water absorption capacity becomes considerably small, which poses a practical problem.

Oxidizing radical polymerization initiator The polymerization initiator used in the production method of the present invention forms a redox system with the reducing agent described below, and must be a radical generator that exhibits some level of water solubility and oxidizing properties. Must be. Such oxidizing agents include (a)
Hydrogen peroxide, persulfates such as ammonium persulfate and potassium persulfate, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, (b) other ceric salts, peroxides, etc. Examples include manganate, chlorite, hypochlorite and the like, and among these, hydrogen peroxide is particularly preferred.

Other water-soluble radical polymerization initiators that do not exhibit oxidizing properties, such as azo compounds such as 2,2'-azobis(2-amidinopropane) dihydrochloride, do not form a redox system with the reducing agent. Therefore, it is not used in the present invention.

The amount of these radical polymerization initiators used is 0.01 to 10% by weight, preferably 0.1 to 2% by weight, based on the monomer.
It is.

Reducing Agent The reducing agent used in the production method of the present invention is capable of forming a redox system with the oxidative radical polymerization initiator, and exhibits a certain degree of water solubility. Such a reducing agent can be any one, but specifically includes sulfites such as sodium sulfite and sodium bisulfite, sodium thiosulfate, cobalt acetate, steel sulfate, ferrous sulfate, and L.
-Ascorbic acid or L-ascorbic acid alkali metal salts, etc. may be mentioned. Among these, mono-ascorbic acid or L-ascorbic acid alkali metal salts are particularly preferred.

The amount of these reducing agents used is 0.001 based on the monomer.
~10% by weight, preferably 0.01~2% by weight.

Molded fibrous substrate The molded fibrous substrate to which an aqueous solution containing an acrylic acid monomer, a polyfunctional acrylate crosslinking agent, and an oxidative radical polymerization initiator as described above is to be applied is a batt or carding made of loosely formed fibers. Alternatively, it may be an air-laid web, tissue vapor, woven fabric such as cotton gauze, stockinated fabric, or non-woven fabric. A "formed" fibrous substrate means that the fibrous substrate may require cutting, bonding, shaping, etc. in order to incorporate it into an article, but no further web-forming operations are required. do.

It is generally preferred to use a fibrous substrate based on absorbent fibers such as wood pulp, rayon, cotton, other cellulosic fibers, or polyester fibers. However, other types of fibers, such as polyethylene, polypropylene, polystyrene, polyamide, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyurea, polyurethane, polyfluoroethylene It is also possible to incorporate fibers such as polycyanide, vinylidene polycyanide, etc. into the molded fibrous substrate.

Application method The aqueous solution of acrylic acid monomer containing a small amount of polyfunctional acrylate crosslinking agent as described above is mixed uniformly with an oxidative radical polymerization initiator and then applied to a molded fibrous substrate. At this time, it is preferable to form a periodic pattern in the form of small dots or lines. This pattern can be used to create so-called "wicking channels" in the absorbent composite produced by the method of the invention, which can be used, for example, from absorbent polymers cross-linked around the edges of the absorbent pad portion of a diaper. The continuous linear shape of the diaper has the advantage that leakage around the edges is extremely reduced. In general, it is preferred to employ a pattern of very finely divided, discrete sections in order to maximize the ratio of polymer surface area to mass. The method for applying the coating to the fibrous substrate can be any suitable means or mode.

For example, printing, spraying (5t
playIng), pour through the nozzle (1'
loving), kiss coati
ng), impregnation (5a Lurat lng), etc. Further, if desired, the mixture may be applied to the fibrous substrate in an all-over pattern, whereupon the mixture may be applied in an amount sufficient to simply coat one side of the fibrous substrate; or It can also be used in an amount sufficient to penetrate the thickness of the fibrous substrate.

The amount of the liquid mixture to be impregnated into the fibrous substrate is not particularly limited, and can be varied over a wide range depending on the product use of the water-absorbing composite. Generally 0.1 to 1000 parts by weight, usually 0.5 to 5 parts by weight per 1 part by weight of the fibrous base.
0 parts by weight is adopted.

As mentioned above, a mixture of an aqueous solution of an acrylic acid monomer containing a small amount of a polyfunctional acrylate crosslinking agent and an oxidative radical polymerization initiator is first applied to a molded fibrous substrate. The above-described reducing agent is applied to the fibrous substrate coated with this mixed solution, and a polymerization reaction occurs. At this time, the reducing agent can be applied in the form of a mist using a spray nozzle, etc. By using such an application method, excellent results can be obtained in terms of polymerization reaction efficiency and operability. .

Furthermore, when the reducing agent is particularly solid at room temperature, it is preferable to apply it as an aqueous solution.

Polymerization conditions As mentioned above, an aqueous acrylic acid monomer solution containing a small amount of a polyfunctional acrylate crosslinking agent and an oxidizing radical polymerization initiator are homogeneously mixed in advance, and the mixed solution is applied to a fibrous substrate. In producing a water-absorbent composite in which a superabsorbent polymer is stably fixed to a molded fibrous substrate by applying a reducing agent in the form of a mist and polymerizing it, the mixed liquid is kept at around room temperature, specifically, at room temperature. It is applied to a fibrous substrate at a temperature of 20 to 60°C, and the temperature is adjusted to a predetermined temperature in a reaction tank. Next, a reducing agent is applied in the form of a mist to the fibrous substrate coated with the above mixture at room temperature or, if necessary, at a predetermined temperature, and polymerized.

The temperature in the reaction tank and the reducing agent is, for example, room temperature to 60°C.
°C, usually room temperature to 40 °C is employed.

Further, the reaction tank and reaction method are not particularly limited and may be of any type. Examples include a batch method in an oven-type box-type reaction tank, or a continuous method on an endless belt.

In addition, the polymerization time varies depending on the polymerization temperature, etc.
Generally, the duration is from several seconds to 2 hours, preferably from several seconds to 10 minutes.

After the polymerization is complete, if necessary, the composite may be dried to remove moisture, for example by passing it through a series of drying baths or using a forced draft oven.

[Experiment example]

Hereinafter, the present invention will be further explained in detail by giving Examples and Comparative Examples. Note that the physiological saline water absorption capacity and water absorption rate described in these examples refer to values measured by the following test method.

A. Physiological saline water absorption capacity: Weigh out about 1.0 g of the water-absorbing complex and about 200 g of saline solution with a concentration of 0.9 ffl volume % into a 300 ml beaker, and then leave it for about 4 hours to absorb the saline solution. The polymer was sufficiently swollen. Next, after draining through a 100-mesh sieve, the amount of filtered saline is weighed, and the physiological saline water absorption capacity is calculated according to the following formula.

Physiological saline water absorption capacity - Amount of physiological saline charged (g) - Filtrate ff1 (r) Prepared water-absorbing complex (g) B. A beaker with a water absorption rate of 300 ml at a concentration of 0. Weigh and add approximately 200 g of 9% by weight saline solution. Next, add about 1.
Weigh out 0g and add it to the above saline solution.

After 5 minutes, drain the water through a 100-mesh sieve, weigh the amount of hypersaline solution, determine the physiological saline water absorption capacity based on the formula shown in A above, and use this as the water absorption rate.

Example 1 30 g of acrylic acid was placed in a 100 cc conical flask, and 17.0 sr of pure water was added thereto. Next, 18.3 g of potassium hydroxide (approximately 95% by weight) was gradually added to the mixture under water cooling for neutralization. The degree of neutralization is approximately 75%.

0.114g of tetramethylolmethanetetraacrylate as a crosslinking agent was added and dissolved therein, and 1.6g of 31% hydrogen peroxide solution was added as a radical polymerization initiator.
g was taken and dissolved.

Separately, 1.286. The raw material was applied to the entire surface of the nonwoven fabric to impregnate it, and the temperature was kept at 40°C in a constant temperature reaction tank. The amount of monomer impregnated was 6.2 times the weight of the nonwoven fabric.

Next, a 10% by weight aqueous solution of L-ascorbic acid as a reducing agent was sprayed onto the entire surface of the nonwoven fabric from a spray nozzle.

Polymerization occurred immediately, and a water-absorbent composite in which the superabsorbent polymer was stably fixed to the polyester nonwoven fabric was obtained.

After drying the water-absorbing composite at 80° C. for 2 hours in an N2 atmosphere, the physiological saline water absorption capacity and water absorption rate were measured, and the results were 52.0 and 36.5, respectively.

Example 2 In a 100 cc conical flask, 13.1 sr of sodium hydroxide (purity approximately 95ii mass %) was taken, and 39 g of water-cooled water was added thereto to dissolve it. To this, 30 g of acrylic acid was gradually added while cooling with water to neutralize it.

The degree of neutralization was approximately 75%.

To this, 0.0% tetramethylolmethanetetraacrylate was added as a crosslinking agent. 114sr and 1.6 g of 31% hydrogen peroxide solution as a radical polymerization initiator were taken and dissolved in each.

Separately, 1.321 g of polyester nonwoven fabric was taken, and the above-mentioned raw material was coated on the entire surface of the nonwoven fabric to impregnate it, and the temperature was maintained at 40°C in a constant temperature reaction tank. The amount of monomer impregnated was 5.8 times the weight of the nonwoven fabric.

Next, 10% aqueous L-ascorbic acid as a reducing agent was sprayed over the entire surface of the nonwoven fabric from a spray nozzle.

Polymerization occurred immediately, and a water-absorbent composite in which the superabsorbent polymer was stably fixed to the polyester nonwoven fabric was obtained.

After drying the above-mentioned water-absorbing composite at 80°C under N2 atmosphere for 2 hours, the physiological saline water absorption capacity and water absorption rate were measured, and the results were 55.2 and 39.8, respectively.

Example 3 26.9 g of 25% by weight ammonia water was placed in a 100 cc conical flask, and 30 g of acrylic acid was added while cooling it on ice.
was added dropwise to neutralize it. The degree of neutralization of acrylic acid is approximately 95%
It became.

Add to this 0.114g of tetramethylolmethanetetraacrylate as a crosslinking agent, and 31% as a polymerization initiator.
1.6 g of hydrogen peroxide solution was added and dissolved in each.

Separately, 1.631 g of polyester nonwoven fabric was taken, and the above-mentioned raw material was coated on the entire surface of the nonwoven fabric to impregnate it, and the temperature was maintained at 40°C in a constant temperature reaction tank. The amount of impregnated monomer is 7.0 for the nonwoven fabric! It was twice as much as the i amount.

Next, a 10% by weight aqueous solution of L-ascorbic acid as a reducing agent was sprayed over the entire surface of the nonwoven fabric from a spray nozzle.

Polymerization occurred immediately, and a water-absorbent composite in which the superabsorbent polymer was stably fixed to the polyester nonwoven fabric was obtained.

After drying the above water-absorbing composite at 80°C under N2 atmosphere for 2 hours, the physiological saline water absorption capacity and water absorption rate were measured.
They were 56.2.41.2, respectively.

Example 4 A water-absorbing composite was obtained in the same manner as in Example 1 except that the nonwoven fabric was a rayon nonwoven fabric and the amount of Zimmer impregnated on the raw material was 6.5 times the weight of the nonwoven fabric.

The physiological saline water absorption capacity of the water-absorbing composite is 48.9,
The water absorption rate was 32.5.

Example 5 The amount of pure water to be added to acrylic acid in Example 1 was 18.
A water-absorbing composite was obtained in the same manner except that the amount of potassium hydroxide was 14.7 g (the degree of neutralization was approximately 60%).

The physiological saline water absorption capacity of the first-century water-absorbing composite was 53.0, and the water absorption rate was 39.8.

Example 6 A water-absorbing composite was obtained in the same manner as in Example 2, except that 0.2 t of potassium persulfate was used as the radical polymerization initiator and 5% aqueous sodium bisulfite solution was used as the reducing agent.

The physiological saline water absorption capacity of the water-absorbing composite is 42.0,
The water absorption rate was 30.5.

Example 7 A water-absorbing composite was obtained in the same manner as in Example 1, except that 0.1 g of dipentaerythritol hexaacrylate was used as the crosslinking agent.

The physiological saline water absorption capacity of this water-absorbing composite is 48.2,
The water absorption rate was 32.5.

Example 8 A water-absorbing composite was obtained in the same manner as in Example 2, except that 0.1 g of dipentaerythritol hexaacrylate was used as the crosslinking agent.

The physiological saline water absorption capacity of this water-absorbing composite is 51.2,
The water absorption rate was 33.5.

Example 9 A water-absorbing composite was obtained in the same manner as in Example 1, except that 0.1 g of trimethylolpropane triacrylate was used instead of tetramethylolmethanetetraacrylate.

The physiological saline water absorption capacity of this water-absorbing composite is 49.2,
The water absorption rate was 32.0.

Example 10 Partially neutralized potassium acrylate aqueous solution in Example 1,
When applying a mixture of a crosslinking agent and a polymerization initiator to a polyester nonwoven fabric, the water-absorbing composite was prepared using the same procedure except that the mixture was sprayed from a spray nozzle, applied and impregnated, and the amount of impregnation was 5.3 times the weight of the nonwoven fabric. I got a body.

The physiological saline water absorption capacity of this water-absorbing composite is 54.2,
The water absorption rate was 30.5.

In addition, the above-mentioned water-absorbent composite has extremely finely divided super-absorbent polymers fixed on the fibers with good stability, and is extremely soft to the touch, making it suitable for sanitary materials such as sanitary napkins and paper diapers. Ta.

Example 11 Partially neutralized potassium acrylate aqueous solution in Example 1,
When applying a mixture of a crosslinking agent and a polymerization initiator to a polyester nonwoven fabric, the mixture is coated and impregnated with a roll coater so as to form a continuous striped pattern along the fibers, and the amount of impregnation is adjusted to 5. A water absorbent composite was obtained in the same manner except that the weight was increased by 6 times.

The physiological saline water absorption capacity of this water-absorbing composite is 55.2,
The water absorption rate was 38.6.

In addition, in the above-mentioned water-absorbing composite, the super-absorbent polymer is continuously fixed in thin stripes along the fibers and fixed with good stability.
It also had a high water absorption rate, making it suitable not only for use as sanitary materials such as sanitary napkins and paper diapers, but also as a water retention agent for agricultural use.

Comparative Example 1 A water-absorbing composite was obtained in the same manner as in Example 1, except that 0.1 g of N,N'-methylenebisacrylamide was used instead of tetramethylolmethanetetraacrylate.

The physiological saline water absorption capacity of the water-absorbing composite is 50.2,
The water absorption rate was 10.1.

Comparative Example 2 A water-absorbing composite was obtained in the same manner as in Example 2, except that 0.1 g of N,N'-methylenebisacrylamide was used instead of tetramethylolmethanetetraacrylate.

The physiological saline water absorption capacity of the water-absorbing composite is 48.5,
The water absorption rate was 8.5.

Comparative Example 3 A water-absorbing composite was obtained in the same manner as in Example 3, except that 0.1 g of N,N'-methylenebisacrylamide was used instead of tetramethylolmethanetetraacrylate.

The physiological saline water absorption capacity of the water-absorbing composite is 49.2,
The water absorption rate was 12.5.

Comparative Example 4 In Example 5, the crosslinking agent was polyethylene glycol (
A water-absorbing composite was obtained in the same manner except that diacrylate (MW-600) was used.

The water-absorbing composite had a physiological saline water absorption capacity of 55.0 and a water absorption rate of 10.5.

Comparative Example 5 Neutralization degree 7596, 7mer concentration in aqueous solution approximately 65
A partially neutralized potassium acrylate aqueous solution containing % by weight was prepared. This was applied and impregnated onto the entire surface of the polyester nonwoven fabric. The amount of monomer impregnated was about 10 times the weight of the nonwoven fabric. The nonwoven fabric impregnated with this partially neutralized potassium acrylate monomer aqueous solution was irradiated with an electron surface at a dose of 10 megarads from an electron beam apparatus equipped with a dynamidron accelerator. Polymerization occurred immediately, and a water-absorbing composite in which a super-absorbent polymer made of a self-crosslinked partially neutralized potassium polyacrylate was stably fixed to a polyester nonwoven fabric was obtained.

Results of measuring the physiological saline water absorption capacity of the above water-absorbing composite 20
．． 5, and the water absorption rate was 13.5.

Comparative Example 6 A partially neutralized aqueous sodium acrylate solution was prepared with a degree of neutralization of 75% and a monomer concentration in the aqueous solution of about 45% by weight. This was applied and impregnated onto the entire surface of the polyester nonwoven fabric. The amount of monomer impregnated was 7.6 times that of the nonwoven fabric. The nonwoven fabric impregnated with this partially neutralized aqueous sodium acrylate solution was irradiated with an electron beam at a dose of 10 megarads from an electron beam device equipped with a dynamidron accelerator. Polymerization occurred immediately, and a water-absorbing composite in which a super-absorbent polymer made of a self-crosslinked partially neutralized sodium polyacrylate was stably fixed to a polyester nonwoven fabric was obtained.

The physiological saline water absorption capacity of this water-absorbing composite is 21.0,
The water absorption rate was 15.1.

Comparative Example 7 A partially neutralized sodium acrylate aqueous solution was prepared with a degree of neutralization of 75% and a monomer concentration in the aqueous solution of about 45% by weight. N was used as a crosslinking agent.

N'-methylenebisacrylamide 0.011JE amount%
It was taken and dissolved to give the following. A polyester nonwoven fabric was coated and impregnated with this 7-mer aqueous solution at 70°C. The amount of monomer impregnated was 11 times the weight of the nonwoven fabric. When a 16.7% by weight aqueous solution of 2,2-azobis(2-amidinopropane) dihydrochloride was sprayed onto this from a spray nozzle, polymerization started immediately.

However, in the obtained water absorbent composite, only the upper layer of the nonwoven fabric was polymerized and had a strong monomer odor. (The amount of the base monomer was about 15i1% by weight.) Then, the above initiator solution was further sprayed from a spray nozzle at 70°C.
Although the temperature was maintained for about 30 minutes, polymerization hardly progressed.

The water-absorbing composite thus obtained was further dried at 90° C. under reduced pressure, and its physiological saline water absorption capacity was measured to be 16.5, and the water absorption rate was 2.5.

Comparative Example 8 A partially neutralized potassium acrylate aqueous solution was prepared with a degree of neutralization of 75% and a monomer concentration in the aqueous solution of about 65% by weight. N was added to this as a crosslinking agent.

N'-methylenebisacrylamide was taken and dissolved in an amount of 0.016ffi. This aqueous monomer solution was applied and impregnated onto a polyester nonwoven fabric and maintained at 70°C. The amount of monomer impregnated was 10 times the weight of the nonwoven fabric. When a 16.7fff aqueous solution of 2°2-azobis(2-amidinopropane) dihydrochloride was sprayed onto the mixture from a spray nozzle, polymerization started immediately.

However, in the obtained water absorbent composite, only the upper layer of the nonwoven fabric was polymerized as in Comparative Example 7, and the monomer odor was strong (the base monomer amount was about 12.1% by weight).

Therefore, the temperature was maintained at 90° C. for an additional 30 minutes, and then dried at the same temperature under reduced pressure. The physiological saline water absorption capacity of this water-absorbing composite is 14
．． 2, and the water absorption rate was 2.9.

Claims (1)

[Scope of Claims] 1. A method for producing a water-absorbing composite with improved water absorption rate, which comprises combining the following steps (A) to (B). (A) An aqueous solution containing the following components (a) to (c),
A process applied to a formed fibrous base. (a) A polymerizable monomer whose main component is acrylic acid in which 20% or more of the carboxyl groups are neutralized with an alkali metal salt or ammonium salt; (b) Three or more polymerizable vinyl groups in one molecule. (iii) an oxidizing radical polymerization initiator; (B) a reducing agent is applied to the polymerizable monomer applied to this fibrous base material to form the polymerizable monomer; A step of polymerizing to form a composite of a polymer derived from the polymerizable monomer and a fibrous substrate. 2. The method according to claim 1, wherein the crosslinking agent is tetramethylolmethanetetraacrylate. 3. According to any one of claims 1 to 2, wherein the oxidative radical polymerization initiator is hydrogen peroxide, and the reducing agent is L-ascorbic acid and/or an alkali metal salt of L-ascorbic acid. the method of. 4. Claims 1 to 4, wherein the fibrous substrate is mainly composed of cellulose fibers or polyester fibers.
The method according to any one of Item 3. 5. The method according to any one of claims 1 to 4, wherein the fibrous substrate is a loose pad of fibers, a carded web, an air-laid web, paper, a nonwoven fabric, a woven fabric, or a knitted fabric. .