JPH07121976B2 - Method for producing water-absorbent composite - Google Patents

Description

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for producing a water-absorbent composite comprising a water-absorbent polymer and a molded fibrous substrate. More specifically, in the present invention, an aqueous solution containing an acrylic acid-based monomer, a polyfunctional acrylate-based cross-linking agent and an oxidizing radical polymerization initiator is applied to a molded fibrous substrate, and then a reducing agent is added thereto. The present invention relates to a method for producing a water-absorbent composite, which is fixed to a fibrous substrate formed by molding a super-water-absorbent polymer, which comprises polymerizing the acrylic acid-based monomer.

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

2. Description of the Related Art Conventionally, paper, pulp, non-woven fabric, sponge-like urethane resin, etc. have been used as various water-retaining agents such as sanitary napkins, various kinds of sanitary materials such as paper naps, and various agricultural materials. However, since the water absorption amount of these materials is only about 10 to 50 times their own weight, a large amount of material is required to absorb or retain a large amount of water, and not only becomes extremely sublime, In addition, there is a drawback in that moisture is easily released when the water-absorbed material is pressurized.

In order to improve the above-mentioned drawbacks of this type of water absorbing material, various high water absorbing polymer materials have been proposed in recent years. For example, a starch graft polymer (Japanese Patent Publication No. 53-46199, etc.), a modified cellulose (Japanese Patent Publication No. 50-80376, etc.), a crosslinked product of a water-soluble polymer (Japanese Patent Publication No. 43-23462, etc.) A self-crosslinking alkali metal acrylate polymer (Japanese Patent Publication No. 54-30710, etc.) and the like have been proposed.

However, although these water-absorbent polymer materials have a considerably high level of water-absorbing performance, most of them are obtained in the form of powder, and therefore, for example, sanitary napkins,
To use it as a sanitary material such as paper cleats, tissue,
It is necessary to disperse it uniformly on a substrate such as non-woven fabric or cotton. However, the polymer powder dispersed by such a method is difficult to be stably fixed on the base material, and it is often aggregated locally after the dispersion, and the swollen gel after absorbing water is also stable. It is not fixed on the substrate well and easily moves from the substrate. For this reason, when this is used, for example, in a paper squeeze, the water absorbent body after urination becomes a "stiff" state, which makes it extremely uncomfortable to wear. In addition, the method of obtaining the absorbent body by dispersing the powdery polymer as described above in the substrate is costly because of the complexity involved in handling the powder and the process problems in efficiently performing uniform dispersion. It is also extremely expensive.

As one of the methods for solving these problems, an acrylic acid-based monomer aqueous solution is applied to a molded fibrous substrate in a predetermined pattern to produce a composite, which is irradiated with electromagnetic radiation or particulate ionizing radiation. , A method for producing a water-absorbing complex by converting an acrylic acid-based monomer into a super-water-absorbing polymer has been reported (Japanese Patent Publication No. 57-500546). According to this method, although there is a considerable improvement in terms of uniform dispersion in handling the above powder and stable immobilization on the substrate, in converting to a super absorbent polymer, Due to the use of electromagnetic radiation or particulate ionizing radiation, the superabsorbent polymer inherent in this particular monomer is too susceptible to cross-linking reactions, resulting in
The obtained composite has a remarkably small performance as an absorber, especially a water absorption capacity, and it seems that there is a drawback that it is usually less than half that in the case where the powdery superabsorbent polymer is used. Further, in terms of process, it is hard to say that it is an inexpensive method in terms of safety and cost associated with handling the radiation generator as described above.

Further, recently, JP-A-60-149609 discloses that a water-soluble radical polymerization initiator or a water-soluble radical polymerization initiator and a water-soluble reduction agent are prepared by previously impregnating a water-absorbing organic material with an aqueous solution of an acrylate monomer. A method for producing a water-absorbing complex in which the agent is atomized and added to perform polymerization is proposed. However, in this method, since the water-soluble polymerization initiator is added after the water-absorbing organic material is impregnated with the acrylic acid-based monomer, “polymerization unevenness” occurs even if the polymerization initiator is atomized, It is extremely difficult to completely polymerize the monomer, and as a result, the amount of residual monomer is large, and there are many safety problems, and it seems that there are drawbacks in terms of performance, especially in water absorption.

Possible Solution Against this background, the present inventors have already filed Japanese Patent Application No. 60-238421.
In the specification, after uniformly mixing an acrylic acid-based monomer aqueous solution containing a small amount of a cross-linking agent and an oxidizing radical polymerization initiator,
A method for producing a water-absorbing composite comprising a superabsorbent polymer and a molded fibrous substrate, characterized by being applied to a fibrous substrate, followed by applying an amine or a reducing agent and polymerizing, has been proposed. In this method, there is almost no "polymerization unevenness",
It was found that the polymerization proceeded easily and the water absorption capacity was large, but as a result of further detailed investigation, the presence of a specific cross-linking agent in the acrylic acid-based monomer and further control under certain controlled polymerization conditions. It has been found that the water absorption rate is particularly improved by the adoption.

[Outline of Invention]

OBJECT OF THE INVENTION The present invention provides the above-mentioned Japanese Patent Application No. 60-238421, Japanese Patent Publication No. 57-
By further improving the method for producing a water-absorbent composite described in JP-A-500546 and JP-A-60-149609, water-absorbing composite materials having excellent water-absorbing performance, especially a particularly high water-absorbing speed, are prepared under mild conditions. The present invention is intended to provide a method of manufacturing extremely easily.

The present inventors have conducted various studies for the purpose of solving the above problems, and as a result, an aqueous solution containing the acrylic acid-based monomer, a specific polyfunctional acrylate-based crosslinking agent, and an oxidizable radical polymerization initiator. Is applied to a molded fibrous substrate, and then the reducing agent is atomized to effect polymerization in a very short time, and there is almost no residual monomer, and the water absorption rate is particularly high, and a highly water-absorbing polymer. The present invention has been accomplished by finding that a water-absorbent composite material fixed to a fibrous substrate with good stability can be obtained very easily and at low cost.

That is, the method for producing a water-absorbent composite having an improved water absorption rate according to the present invention is characterized by comprising the following steps (A) to (B).

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

(A) A polymerizable monomer containing acrylic acid as a main component, in which 20% or more of carboxyl groups are neutralized with an alkali metal salt or ammonium salt, (b) 3 or more polymerizable vinyl groups in one molecule. A cross-linking agent comprising a (meth) acrylate compound, (c) an oxidative radical polymerization initiator, (B) a polymerizable monomer applied to the fibrous substrate, and a reducing agent applied to the polymerizable monomer. To form a composite of the polymer derived from the polymerizable monomer and the 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 cross-linking agent used efficiently reacts with an acrylic acid-based monomer, and the polymer obtained is a resin having an appropriate cross-linking structure and cross-linking distribution, and therefore has excellent water absorption, and particularly has a high water absorption rate (b) The oxidizing radical polymerization initiator is previously dissolved in the polyfunctional (meth) acrylate-based crosslinking agent and the acrylic acid-based monomer aqueous solution described above, and a reducing agent is added to the solution to polymerize, thereby remaining monomers in the polymer. The amount is extremely small, the polymerization operation is easy, and the polymerization is completed in an extremely short time under mild conditions near room temperature.

Therefore, the water-absorbent composite obtained by the production method of the present invention is the above-mentioned Japanese Patent Application No. 60-238421, Japanese Patent Publication No. 57-500546 as will be apparent from Examples and Comparative Examples of the present application described later.
It can be seen that the water absorption performance is higher than that of the method disclosed in Japanese Patent Laid-Open No. 60-149609 and the water absorption rate is particularly high. Furthermore, since its form is a sheet, it is easier to handle and cheaper than powdered superabsorbent resins that have been used conventionally, so it can be used for the production of various sanitary materials such as sanitary napkins and paper staples. Can be used to advantage. Further, by utilizing its excellent water absorption performance and handleability, it can also be used for the production of various materials for horticultural yang or agriculture such as a soil improving agent and a water retention agent, which have recently been receiving attention.

[Specific Description of the Invention]

Acrylic acid-based monomer The acrylic acid-based monomer used in the present invention, that is, the component (a) contains acrylic acid as a main component, but 20% or more, preferably 50% or more thereof is converted into an alkali metal salt or an ammonium salt. It has been neutralized. If the degree of partial neutralization is less than 20%, the water absorption performance of the produced polymer is significantly deteriorated, which is not preferable.

Further, in the present invention, in addition to the acrylic acid-based monomer, a monomer copolymerizable therewith, for example (a) methacrylic acid,
Itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acuroylpropanesulfonic 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,
(F) Polyethylene glycol mono (meth) acrylate, (to) acrylamide, methacrylamide, N, N '
One or two or more kinds of monomers such as -dimethylacrylamide, N, N'-dimethylmethacrylamide, (thi) 2-vinylpyridine, 4-vinylpyridine can be used in combination as long as the water absorption performance is not impaired.

Since the "polymerizable monomer" in the present invention is mainly composed of acrylic acid (of which 20% or more is in the form of a salt), the amount of the above-mentioned copolymerizable monomer added is generally In
It is less than 50 mol%, preferably 20% or less.

It should be noted that alkali metal hydroxides, bicarbonates, ammonium hydroxides and the like can be used for neutralizing the above-mentioned acid monomers including acrylic acid, but alkali metal hydroxides are preferable. And specific examples thereof include sodium hydroxide, potassium hydroxide and lithium hydroxide. Sodium hydroxide or potassium hydroxide is preferred from the viewpoints of industrial availability, price, and safety. The concentration of these monomers is more than 20% by weight in water,
It is 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 filling amount of the super absorbent polymer per unit surface area of the molded fibrous substrate increases, and a composite having excellent water absorbing performance can be obtained.
Further, by increasing the monomer concentration, conversely, by reducing the water concentration, it is possible to reduce energy during drying, which is advantageous in terms of cost.

Crosslinking Agent Consisting 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,
It exhibits copolymerizability with the acrylic acid-based monomer and has some solubility in an aqueous solution of the acrylic acid-based monomer. Specific examples of such a crosslinking agent include tetramethylolmethane tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, and dipentaerythritol hexaacrylate.

Among these, tetramethylolmethane tetraacrylate is particularly preferable in the present invention.

Such a cross-linking agent may be used alone or as a mixture of two or more kinds.

The amount of these cross-linking agents used is based on the acrylic acid monomer.
It is 0.001 to 10% by weight, preferably 0.01 to 2% by weight.
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 at the time of water absorption will be extremely weak. On the other hand, if the content exceeds 10% by weight, the water absorption speed and the water absorption gel strength are remarkably improved, but the water absorption capacity becomes considerably small, which is a practical problem.

Oxidizable radical polymerization initiator The polymerization initiator used in the production method of the present invention forms a redox system with a reducing agent described below, and has a certain degree of water solubility, and must be a radical generator exhibiting an oxidizing property. I have to. As such an oxidant, (a)
Hydrogen peroxide, persulfates such as ammonium persulfate and potassium persulfate, peroxides such as t-butyl hydroperoxide and cumene hydroperoxide, and the like; (b) Other secondary cerium salts, peroxides, etc. Examples thereof include manganate, chlorite, hypochlorite, and the like, of which hydrogen peroxide is particularly preferable.

Other water-soluble radical polymerization initiators that do not exhibit oxidative properties, for example, polymerization initiators such as azo compounds such as 2,2'-azobis (2-amidinopropane) dihydrochloride do not form a redox system with a 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 monomers.

Reducing Agent The reducing agent used in the production method of the present invention is capable of forming a redox system with the above-mentioned oxidizing radical polymerization initiator, and exhibits a certain degree of water solubility. Such reducing agent may be any, but specifically, sulfites such as sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, cobalt acetate, copper sulfate, ferrous sulfate, and L-ascorbic acid or L-ascorbic acid alkali metal salt etc. can be mentioned. Among them, L-ascorbic acid or L-alcorbic acid alkali metal salt is particularly preferable.

The amount of these reducing agents used is 0.001 to 10 with respect to the monomer.
% By weight, preferably 0.01 to 2% by weight.

Molded fibrous substrate A molded fibrous substrate to which an aqueous solution containing an acrylic acid-based monomer, a polyfunctional acrylate-based crosslinking agent and an oxidizing radical polymerization initiator as described above should be applied is a loosely-formed pad or carding. Alternatively, it may be an air-laid web, tissue paper, woven fabric such as cotton gauze, knitted fabric, or non-woven fabric. "Molded" fibrous substrate means that the fibrous substrate may need to be cut, bonded, shaped, etc. to be incorporated into an article, but no further web-forming work is required. To do.

It is generally preferred to use fibrous substrates based on absorbent fibers such as wood pulp, rayon, cotton and other cellulosic or polyester fibers. However, other types of fibers such as polyethylene, polypropylene, polystyrene, polyamide, polyvinyl alcohol, polyvinyl chloride, polyvinyldene chloride, polyacrylonitrile, polyurea, polyurethane, polyfluoroethylene It is also possible to include fibers, such as those of the type, vinylidene cyanide and the like, in a molded fibrous substrate.

Application Method An aqueous solution of an acrylic acid-based monomer containing a small amount of a polyfunctional acrylate-based crosslinking agent as described above is uniformly mixed with an oxidizable radical polymerization initiator in advance and then applied to a molded fibrous substrate. At this time, it is preferable to apply a small dot-like or linear periodic pattern. This pattern can be used to create so-called "wicking passages" in the water-absorbent composites produced by the method of the present invention, such as from water-absorbing polymers cross-linked around the edges of the water-absorbing pad portion of a diaper. The continuous linear shape has the advantage that this diaper has very little leakage around the edges. In general, it is preferred to employ a pattern consisting of very finely divided discontinuities in order to maximize the ratio of polymer surface area to mass. The method for applying to the fibrous substrate may be any purposeful means or modes. For example, printing, sprayin
g), flowing through a nozzle, kiss coating, saturating and the like. Further, if necessary, the mixed solution may be applied to the fibrous substrate in an overall pattern, and then the mixed solution may be applied in an amount sufficient to simply coat one surface of the fibrous substrate, or It can also be used in an amount sufficient to penetrate the thickness of the fibrous substrate.

The impregnated amount of the mixed liquid applied to the fibrous substrate is not particularly limited, and can be widely varied depending on the intended use of the water-absorbing composite. Generally, 0.1 to 1000 parts by weight, usually 0.5 to 50 parts by weight, is used for 1 part by weight of the fibrous substrate.

As described above, a mixed solution prepared by previously uniformly mixing an aqueous solution of an acrylic acid-based monomer containing a small amount of a polyfunctional acrylate-based crosslinking agent and an oxidizable radical polymerization initiator is first applied to a molded fibrous substrate. The reducing agent as described above is applied to the fibrous substrate to which this mixed liquid has been applied to cause a polymerization reaction. As a method for applying the reducing agent at this time, there is a method in which the reducing agent is atomized with a spray nozzle or the like, and by adopting such an application method, excellent results can be obtained in both polymerization reaction efficiency and operability. .

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

Polymerization conditions As described above, an acrylic acid-based monomer aqueous solution containing a small amount of a polyfunctional acrylate-based crosslinking agent and an oxidizing radical polymerization initiator are uniformly mixed in advance, and the mixed solution is applied to a fibrous substrate and then reduced. In producing a water-absorbent composite in which the agent is atomized and polymerized to stably fix the superabsorbent polymer on the formed fibrous substrate, the mixed solution is heated to around room temperature, specifically 20 The temperature is adjusted to -60 ° C, applied to the fibrous substrate, and adjusted to a predetermined temperature in the reaction tank. Next, the reducing agent is atomized and polymerized at room temperature or, if necessary, at a predetermined temperature, on the fibrous substrate on which the mixed solution is applied.

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

Further, the reaction tank and the reaction system are not particularly limited, and any type may be used. An example thereof is a method of performing batchwise in an oven-type box-type reaction tank, or a method of continuously performing on an endless belt.

Also, the polymerization time varies depending on the polymerization temperature and the like,
Generally, it is about several seconds to 2 hours, preferably several seconds to 10 minutes.

After the completion of the polymerization, if necessary, the composite may be dried by, for example, passing through a series of drying tanks or using a forced draft oven to remove water.

[Experimental example]

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, the physiological salt water absorption capacity and water absorption rate described in these examples refer to numerical values measured by the following test methods.

A. About 1.0g of water-absorbing complex and about 200g of saline solution with 0.9wt% concentration were weighed and put into a beaker with a capacity of 300ml of physiological saline solution. Allowed to swell. Then, after draining with a 100-mesh sieve, the amount of persaline solution is weighed, and the physiological saline water absorption capacity is calculated according to the following formula.

B. Weigh about 200 g of 0.9 wt% saline in a beaker with a water absorption rate of 300 ml. Next, about 1.0 g of the water-absorbent complex is weighed and placed in the saline solution. After 5 minutes, water was drained through a 100-mesh sieve, the amount of the oversalt water was weighed, the physiological salt water absorption capacity was determined based on the formula shown in A above, and these were taken as water absorption rates.

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

0.114 g of tetramethylolmethane tetraacrylate was taken as a cross-linking agent, added and dissolved therein, and further, 1.6 g of 31% hydrogen peroxide solution was taken as a radical polymerization initiator and dissolved.

Separately, 1.286 g of polyester non-woven fabric is applied and impregnated on the whole surface of the non-woven fabric, and the temperature is kept at 40 ° C in a constant temperature reaction tank.
Kept at. The amount of impregnated monomer is 6.
It was twice the weight.

Next, a 10 wt% L-ascorbic acid aqueous solution as a reducing agent was sprayed onto the entire surface of the non-woven fabric through a spray nozzle.

Polymerization immediately occurred, and a superabsorbent polymer was stably fixed to the polyester nonwoven fabric to obtain a superabsorbent composite.

The water-absorbent composite was dried at 80 ° C. under N ₂ atmosphere for 2 hours, and then the physiological salt water absorption capacity and the water absorption rate were measured, and the results were 52.0 and 36.5, respectively.

Example 2 Sodium hydroxide (purity of about 9
(5% by weight) 13.1 g was taken, and 39 g of pure water was added to and dissolved in this under ice cooling. To this, 30 g of acrylic acid was gradually added under ice cooling to neutralize. The degree of neutralization was about 75%.

0.114 g of tetramethylolmethane tetraacrylate as a cross-linking agent, and 31% as a radical polymerization initiator
1.6 g of hydrogen peroxide solution was taken and dissolved.

Separately, 1.321 g of polyester non-woven fabric was taken, and the above raw materials were applied and impregnated on the whole surface of the non-woven fabric and kept at 40 ° C. in a constant temperature reaction tank. The amount of the impregnated monomer was 5.8 times the weight of the nonwoven fabric.

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

Polymerization immediately occurred, and a superabsorbent polymer was stably fixed to the polyester nonwoven fabric to obtain a superabsorbent composite.

The water-absorbent composite was dried at 80 ° C. under N ₂ atmosphere for 2 hours, and then the physiological salt water absorption capacity and the water absorption rate were measured, and the results were 55.2 and 39.8, respectively.

Example 3 26.9 g of 25 wt% ammonia water was placed in a 100 cc conical flask, and 30 g of acrylic acid was added dropwise while cooling with ice to neutralize. The degree of neutralization of acrylic acid was approximately 95%.

To this, 0.114 g of tetramethylolmethane tetraacrylate as a crosslinking agent and 1.6 g of 31% hydrogen peroxide solution as a polymerization initiator were added and dissolved.

Separately, 1.631 g of polyester non-woven fabric was taken, and the above raw materials were applied and impregnated on the whole surface of the non-woven fabric, and kept at 40 ° C. in a constant temperature reaction tank. The amount of the impregnated monomer was 7.0 times the weight of the nonwoven fabric.

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

Polymerization immediately occurred, and a superabsorbent polymer was stably fixed to the polyester nonwoven fabric to obtain a superabsorbent composite.

The water-absorbent composite was dried at 80 ° C. for 2 hours in a N ₂ atmosphere, and then the physiological salt water absorption capacity and the water absorption rate were measured, and the results were 56.2 and 41.2, respectively.

Example 4 A water-absorbent composite was obtained by the same procedure as in Example 1 except that the non-woven fabric was a rayon non-woven fabric and the impregnation amount of raw material monomers was 6.5 times the weight of the non-woven fabric.

The water-absorbent complex had a physiological salt water-absorption capacity of 48.9 and a water absorption rate of 32.5.

Example 5 Pure water to be added to acrylic acid in Example 1 was 18.7
A water-absorbent complex was obtained by the same operation except that g and potassium hydroxide were changed to 14.7 g (the degree of neutralization was about 60%).

The water-absorbent complex had a physiological salt water-absorption capacity of 53.0 and a water absorption rate of 39.8.

Example 6 A water-absorbing complex was obtained by the same procedure as in Example 2 except that 0.2 g of potassium persulfate was used as the radical polymerization initiator and 5% sodium hydrogen sulfite aqueous solution was used as the reducing agent.

The water-absorbent complex had a physiological salt water-absorption capacity of 42.0 and a water absorption rate of 30.5.

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

The water absorbing complex had a physiological salt water absorption capacity of 48.2 and a water absorption rate of 32.5.

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

The water absorbing complex had a physiological salt water absorption capacity of 51.2 and a water absorption rate of 33.5.

Example 9 A water absorbent composite was obtained by the same procedure as in Example 1 except that 0.1 g of trimethylolpropane triacrylate was used instead of tetramethylolmethane tetraacrylate.

The water absorbing complex had a physiological salt water absorption capacity of 49.2 and a water absorption rate of 32.0.

Example 10 Partially neutralized potassium acrylate aqueous solution in Example 1,
When applying the mixture of the cross-linking agent and the polymerization initiator to the polyester non-woven fabric, by spraying from a spray nozzle, coating and impregnating, except that the impregnated amount was 5.3 times the weight of the non-woven fabric, a water-absorbent composite was obtained by the same operation. Obtained.

The water-absorbent composite had a physiological salt water-absorption capacity of 54.2 and a water absorption rate of 30.5.

In addition, the water-absorbent composite has a highly finely-divided highly water-absorbent polymer stably fixed on the fiber and has a very soft texture, which is a good sanitary material such as sanitary napkins and paper diapers. It was

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 non-woven fabric, the mixture is applied and impregnated with a roll coater so as to form a continuous striped pattern along the fiber, and the impregnation amount is 5.6 times the weight of the non-woven fabric. A water-absorbent complex was obtained by the same operation except for the above.

The water absorbing complex had a physiological salt water absorption capacity of 55.2 and a water absorption rate of 38.6.

Further, the above water-absorbent composite, superabsorbent polymer is continuously fixed along the fibers in the form of fine stripes with good stability,
The water absorption rate was high, and it was good not only as a sanitary material such as sanitary napkins and paper diapers, but also as a water retention agent for agriculture.

Comparative Example 1 In Example 1, N, N′-methylenebisacrylamide was used instead of tetramethylolmethane tetraacrylate.
A water absorbing complex was obtained by the same operation except that the amount was 0.1 g.

The water-absorbent complex had a physiological salt water-absorption capacity of 50.2 and a water absorption rate of 10.1.

Comparative Example 2 In Example 2, N, N'-methylenebisacrylamide was used instead of tetramethylolmethane tetraacrylate.
A water absorbing complex was obtained by the same operation except that the amount was 0.1 g.

The water absorbing complex had a physiological salt water absorption capacity of 48.5 and a water absorption rate of 8.5.

Comparative Example 3 In Example 3, N, N'-methylenebisacrylamide was used instead of tetramethylolmethane tetraacrylate.
A water absorbing complex was obtained by the same operation except that the amount was 0.1 g.

The water-absorbent complex had a physiological salt water-absorption capacity of 49.2 and a water absorption rate of 12.5.

Comparative Example 4 A water absorbent composite was obtained by the same operation as in Example 5, except that the cross-linking agent was polyethylene glycol (MW = 600) diacrylate.

The water-absorbent complex had a physiological salt water-absorption capacity of 55.0 and a water absorption rate of 10.5.

Comparative Example 5 The degree of neutralization is 75%, and the monomer concentration in the aqueous solution is about 65% by weight.
A partially neutralized potassium acrylate aqueous solution was prepared. This was applied and impregnated on the entire surface of the polyester nonwoven fabric.
The amount of the impregnated monomer was about 10 times the weight of the nonwoven fabric. The non-woven fabric impregnated with the 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 dynamitron accelerator.
Polymerization immediately occurred, and a superabsorbent polymer consisting of a self-crosslinked body of partially neutralized potassium polyacrylate was stably fixed to a polyester nonwoven fabric to obtain a superabsorbent composite.

Results of measuring the physiological saline water absorption capacity of the water-absorbent complex 20.5
And the water absorption rate was 13.5.

Comparative Example 6 The degree of neutralization is 75%, and the monomer concentration in the aqueous solution is about 45% by weight.
A partially neutralized sodium acrylate aqueous solution was prepared. This was applied and impregnated on the entire surface of the polyester nonwoven fabric.
The amount of the impregnated monomer was 7.6 times that of the nonwoven fabric.
The non-woven fabric impregnated with this partially neutralized sodium acrylate aqueous solution was irradiated with an electron beam at a dose of 10 megarads from an electron beam apparatus equipped with a dynamitron accelerator. Polymerization immediately occurred, and a superabsorbent polymer consisting of a self-crosslinked body of partially neutralized sodium polyacrylate was stably fixed to a polyester nonwoven fabric to obtain a superabsorbent composite.

The water absorbing complex had a physiological salt water absorption capacity of 21.0 and a water absorption rate of 15.1.

Comparative Example 7 Neutralization degree 75%, monomer concentration in the aqueous solution is about 45% by weight
A partially neutralized sodium acrylate aqueous solution was prepared. This was taken as a cross-linking agent and dissolved in an amount of 0.01% by weight of N, N'-methylenebisacrylamide. A polyester nonwoven fabric was coated and impregnated with this aqueous monomer solution to 70 ° C. The amount of the impregnated monomer was 11 times the weight of the nonwoven fabric. When a 16.7 wt% 2,2-azobis (2-amidinopropane) dihydrochloride aqueous solution was sprayed from a spray nozzle onto this, polymerization was initiated immediately.

However, the obtained water-absorbent composite had a strong monomer odor because only the upper layer of the nonwoven fabric was polymerized. (The amount of residual monomer was about 15% by weight.) Then 70 ℃
Then, the above initiator solution was sprayed from the spray nozzle and held for about 30 minutes, but the polymerization hardly proceeded. The water-absorbent composite thus obtained was further dried at 90 ° C. under reduced pressure to measure physiological saline absorption capacity, which was 16.5, and the water absorption rate was 2.
Was 5.

Comparative Example 8 The degree of neutralization is 75%, and the monomer concentration in the aqueous solution is about 65% by weight.
A partially neutralized potassium acrylate aqueous solution was prepared. As a cross-linking agent, 0.016 g% by weight of N, N'-methylenebisacrylamide was taken and dissolved therein. Polyester non-woven fabric is coated with this monomer aqueous solution and impregnated at 70 ℃
Held in. The amount of the impregnated monomer was 10 times the weight of the nonwoven fabric. 16.7% by weight of 2,2-azobis (2-
Polymerization was started immediately when an amidinopropane) dihydrochloride aqueous solution was sprayed from a spray nozzle.

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

Therefore, it was kept at 90 ° C. for another 30 minutes and dried under reduced pressure at the same temperature. The water absorbing complex had a physiological salt water absorption capacity of 14.2 and a water absorption rate of 2.9.

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Claims (5)

[Claims] 1. A process for producing a water-absorbing composite having an improved water absorption rate, which comprises the following steps (A) to (B). (A) A step of applying an aqueous solution containing the following components (a) to (c) to the molded fibrous substrate. (A) A polymerizable monomer containing acrylic acid as a main component, in which 20% or more of carboxyl groups are neutralized with an alkali metal salt or ammonium salt, (b) Three or more polymerizable vinyl groups in one molecule. A cross-linking agent comprising a (meth) acrylate compound, (c) an oxidative radical polymerization initiator, (B) a polymerizable monomer applied to the fibrous substrate, and a reducing agent applied to the polymerizable monomer. To form a composite of the polymer derived from the polymerizable monomer and the fibrous substrate. 2. The method according to claim 1, wherein the cross-linking agent is tetramethylolmethane tetraacrylate. 3. The method according to claim 1, wherein the oxidizing radical polymerization initiator is hydrogen peroxide and the reducing agent is L-ascorbic acid and / or L-ascorbic acid alkali metal salt. The method described in crab. 4. The method according to any one of claims 1 to 3, wherein the fibrous substrate is mainly composed of cellulosic fibers or polyester fibers. 5. The fibrous substrate is a loose fiber pad, a carded web, an airlaid web, paper, a non-woven fabric, a woven fabric or a knitted fabric.
~ The method according to any one of items 4 to 4.