JPS62133183A - Production of water absorbable 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] [Industrial application field] The present invention relates to a method for producing a water-absorbing composite.

More specifically, after mixing an aqueous solution of an acrylic acid monomer containing a small amount of crosslinking agent and an oxidizing radical polymerization initiator into a molded fibrous base at room temperature, the mixture is mixed with super absorbent polymer particles (' The superabsorbent polymer is impregnated with spray powder so that the particle diameter is 30 μm to 500 μm, and then a reducing agent is added in the form of a mist and polymerized for a short time at room temperature, so that the superabsorbent polymer is fixed to the molded fibrous substrate. The present invention relates to a continuous production method for water-absorbing composites.

The water-absorbing composite obtained by the production method of the present invention has excellent water absorption, has a high water absorption rate, and has a highly water-absorbing polymer stably fixed to a fibrous base, so it can be used to manufacture various water-absorbing materials. can be used advantageously.

[Prior art]

Conventionally, paper, paper, non-woven fabric, urethane resin sponge, etc. have been used as water-retaining agents in various sanitary materials such as sanitary napkins, paper diapers, etc., 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.
Not only does it become extremely bulky, but it also has drawbacks such as the fact that water is easily separated when the material that has absorbed water is pressurized.

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 (% Publication No. 30710, 1983, 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,
In order to use it in sanitary materials such as paper diapers, it is necessary to uniformly disperse it onto a base material such as tissue, nonwoven fabric, or cotton.

However, it is difficult to stably fix the solid polymer powder dispersed by this method on the substrate, and it often aggregates locally after dispersion, and the swelling kelp after water absorption also remains stable. It is not fixed on the material and easily moves from the substrate. For this reason, for example, when used in paper diapers, the absorbent material becomes stiff after urinating, making it extremely uncomfortable to wear.Furthermore, powdered polymers such as those described above are dispersed in the base material. In the method of obtaining absorbent material,
The cost is extremely high due to the complexity associated with handling the powder and process problems in achieving uniform dispersion efficiently.

[Problem that the invention seeks to solve]

Recently, one method to solve these problems has been 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 (t￥f Publication No. 57-500).
546). According to this method, the uniform dispersion and stable immobilization on the substrate when handling the above-mentioned powder are considerably improved, but when converting into a super absorbent polymer, electromagnetic radiation or fine particles Because ionizing radiation is used, the self-crosslinking reaction of the highly water-absorbing polymer is extremely easy to proceed, and as a result, its performance as an absorber, especially its water absorption capacity, is extremely low. It has the disadvantage that it is less than half the size. It is difficult to say that this is an inexpensive method in terms of safety and cost associated with handling the radiation generating device as described above in terms of the process as well.

Recently, Japanese Patent Application Laid-Open No. 60-149609 discloses that after pre-impregnating a water-absorbing organic material with an acrylate monomer water bath 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 material is proposed in which a reducing agent is added and polymerized.

However, in this method, a water-bath polymerization initiator is added after impregnating the water-absorbing organic material with the acrylic acid monomer, so even if it is atomized, "uneven polymerization" occurs and it is difficult to completely polymerize. This is extremely difficult, resulting in a large amount of residual monomer, which poses many safety problems, and also has disadvantages in terms of performance, particularly in terms of water absorption capacity.

Against this background, the present inventors have already filed a patent application in 1984-2384.
21, an aqueous acrylic acid monomer solution containing a small amount of a crosslinking agent and an oxidizing radical polymerization initiator are homogeneously mixed, applied to a fibrous substrate, and then amines or a reducing agent are applied to polymerize. A method for manufacturing a water-absorbing composite consisting of a super-absorbent polymer and a molded fibrous substrate was demonstrated. It was found that with this method, a product with almost no "uneven polymerization", easy polymerization, and high water absorption capacity was obtained.As a result of further detailed study, a certain controlled application method and It was found that the water absorption rate was significantly improved to 1% by adopting the polymerization conditions.

[Means for solving problems]

(Object of the Invention) The present invention is based on the aforementioned Japanese Patent Publication No. 57-500546, Japanese Patent Application Laid-Open No. 60-149609, and Japanese Patent Application No. 60-2384.
By improving the method for producing a water-absorbing composite described in Publication No. 21, we can easily and continuously produce a water-absorbing composite with no residual monomers, excellent water-absorbing performance, and particularly high water-absorbing speed under mild conditions. The aim is to provide a method for manufacturing the same.

(Structure of the Invention) As a result of various studies aimed at solving the above-mentioned problems, the present inventors have discovered that a cross-linking agent and oxidative radical polymerization are added to the water bath solution of the acrylic acid monomer containing the cross-linking agent in the evening view. The initiator is mixed and dissolved at room temperature, and the resulting mixture is molded onto a fibrous base material with a particle size of 30 μm to 500 μm.
By spraying and impregnating it so that it becomes m, and then adding the reducing agent in the form of a mist, the polymerization is completed in an extremely short time, there is almost no residual monomer, and it has excellent water absorption performance and water absorption speed. The present invention was achieved based on the discovery that a water-absorbing composite in which a highly water-absorbing polymer is stably fixed to a fibrous substrate can be easily and continuously obtained particularly quickly.

That is, the method for producing the water-absorbing composite of the present invention is based on Cal? An aqueous solution of a polymerizable monomer mainly composed of acrylic acid in which 20 or more xyl groups are neutralized with an alkali metal salt or ammonium salt (hereinafter referred to as an acrylic acid monomer) is applied to a molded fibrous substrate. Then, when the acrylic acid monomer is polymerized to continuously produce a water absorbent composite consisting of a super absorbent polymer and a molded fibrous substrate, a crosslinking agent and an oxidizing agent are added to the aqueous solution of the acrylic acid monomer. A radical polymerization initiator is mixed and dissolved at room temperature, and the resulting mixture is molded into a fibrous substrate with a superabsorbent polymer having a particle size of 30 μm.
Spray to impregnate the film to a thickness of 500 μm to 500 μm.

This is a continuous method for producing a water-absorbing composite consisting of a super-absorbent polymer and a molded fibrous substrate, characterized in that a reducing agent is then added in the form of a mist and polymerized in a short time at room temperature.

In the method for producing a water-absorbing composite of the present invention, by spraying an aqueous acrylic acid monomer solution to impregnate small dots, the surface area of the polymer becomes extremely large, facilitating the diffusion of the absorbed liquid and increasing the water absorption rate. By dissolving the oxidative radical polymerization initiator in advance in an aqueous acrylic acid monomer solution and spraying the reducing agent into the solution for polymerization, the amount of residual monomer in the polymer is extremely small and the polymerization operation is easy. In addition, the polymerization is completed in a very short time under mild conditions near room temperature, and the crosslinking agent used reacts efficiently with the acrylic acid monomer, resulting in a resin with an appropriate crosslink structure and crosslink distribution. Therefore, it has remarkable characteristics in that it has extremely excellent water absorption ability. For this reason, it is possible to easily obtain a water-absorbing composite material that is much superior to the method described in the above-mentioned publication and at a lower cost.

(Detailed Description of the Invention) FIG. 1 shows the manufacturing process of a water-absorbing composite according to the present invention.

The formed fibrous substrate 1 is first transferred to a monomer spraying zone 2.
The water bath solution of the acrylic acid monomer is then sprayed by the spraying device 3.

A small amount of a crosslinking agent and an oxidative radical polymerization initiator are dissolved in advance in the acrylic acid monomer aqueous solution, and the superabsorbent polymer is sprayed so that the particle size is 30 μm to 500 μm. In this case, when the polymer particle size is 30 μm or less, no particular improvement in performance is observed; on the contrary, when atomizing,
It is difficult to apply it efficiently to a fibrous substrate, and in practice, the loss rate of the raw monomer liquid increases, making it uneconomical. On the other hand, if the particle size is too large, i.e. 500μ
m or more, the ratio of polymer surface area to mass becomes extremely small, which poses a problem particularly in terms of water absorption rate.

The amount of the acrylic acid monomer aqueous solution sprayed onto 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, the amount of polymer is 0.000% per part by weight of the fibrous substrate.
1 to 100 parts by weight, usually 0.5 to 20 parts by weight, is employed.

The temperature of the spray zone of the acrylic acid monomer aqueous solution and the monomer aqueous solution is normal temperature to 60°C, usually room temperature to 4°C.
0°C is adopted.

The fibrous substrate onto which the aqueous acrylic acid monomer solution has been sprayed is then led to a reducing agent spraying zone 4, ie, a polymerization zone, where a reducing agent is sprayed by a spraying device 5 and polymerization occurs. The spraying method at this time is almost the same as in the case of the monomer aqueous solution. That is, the spray particles are 30 μm.
~500 μm is adopted.

The reducing agent is sprayed as it is when it is in liquid form at room temperature, or in a state dissolved in an aqueous solution or an aqueous acrylic acid monomer solution. In addition, if it is solid at room temperature, it is sprayed as an aqueous solution or dissolved in an aqueous acrylic acid monomer solution. The spray head at this time is not particularly limited, but generally 0.01 to 50 parts by weight per 100 parts by weight of the acrylic acid monomer aqueous solution,
Preferably it is 0.1 to 10 parts.

The temperature of the reducing agent spray zone and reducing agent ranges from room temperature to
60°C, usually room temperature to 40°C.

As soon as the reducing agent is sprayed, polymerization occurs and the reaction is completed. The polymerization time at this time is about 5 minutes or less, usually 1 minute or less. Examples of spray devices used in the acrylic acid monomer spray zone and the reducing agent spray zone include a method of atomizing through a spray nozzle;
Alternatively, there is a method using an ultrasonic device using an ultrasonic vibrator or a rotary atomizing centrifugal spray device.

From a practical point of view, the method of atomization through a spray nozzle is particularly preferred in the present invention.

Polymerization is completed in the reducing agent spray zone, the superabsorbent polymer is stably fixed, and the fibrous substrate is dried, if necessary, in a drying device such as the drying zone 6. When the monomer content in the acrylic acid monomer aqueous solution is particularly high, specifically, the monomer concentration in the aqueous solution is about 70! When it% or more, drying is performed at the same time due to the reaction heat during polymerization, so it is generally not necessary.

The dry fibrous substrate to which the superabsorbent polymer is stably fixed is first passed through a feed roll 8 and then wound up by a take-up roll 7 to form a product.

Next, the monomer, crosslinking agent, oxidizing radical polymerization initiator, reducing agent, and fibrous substrate used in the present invention will be explained in more detail.

(1) Monomer 1 The monomer used in the present invention has acrylic acid as its main component, and 20 or more, preferably 50 or more, of the monomer is neutralized with an alkali metal salt or an ammonium salt. If the degree of partial neutralization is too low, the water absorption performance of the polymer will drop significantly.

In addition, in the present invention, in addition to the above-mentioned acrylic acid and acrylic acid salts, monophonic substances copolymerizable with these, such as methacrylic acid,
itaconic acid, maleic acid.

Fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-
Acryloylgulononine sulfonic acid and its salts: itaconic acid, maleic acid.

Alkyl or alkoxy esters of dicarboxylic acids such as fumaric acid; acrylamide: pinylsulfonic acid; acrylic acid methyl ester, acrylic acid ethyl ester, etc.; (meth)acrylic acid hydroxyethyl ester, (meth)acrylic acid hydroxypropyl ester: 7f ? l
1 of J ethylene glycol mono(meth)acrylic V-) etc.
It is also possible to use one species or a combination of two or more species.

Alkali metal hydroxides, bicarbonates, etc. can be used to neutralize the above acid monomers, but alkali metal hydroxides are preferred, and specific examples include sodium hydroxide and potassium hydroxide. and lithium hydroxide. In terms of industrial availability, price, safety, etc.
Sodium hydroxide or potassium hydroxide is preferable.The concentration of these acrylic acid monomers in water is 20% by weight or more, preferably 30% by weight or more, and 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 is increased, and a composite with excellent water absorption performance can be obtained. [By increasing the L monomer concentration, conversely speaking, the water concentration can be decreased, which allows energy consumption during drying to be reduced, which is advantageous in terms of cost. Specifically, a solubility near saturation at the operating temperature is advantageously used; for example, in the case of sodium acrylate, it is about 45 fold f at room temperature.

(2) Crosslinking agent The crosslinking agent used in the production method of the present invention has two or more double bonds in the molecule and exhibits copolymerizability with the acrylic acid monomer, or has the acrylic acid monomer in the molecule. A monomer having two or more functional groups that can react with a functional group in an acidic monomer, such as a carboxyl group, during polymerization or during drying after polymerization, and which exhibits some degree of water bathability. Can be used.

Examples of the former crosslinking agents include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, f-ropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, Glycerin tri(meth)acrylate, N, 'N'
- methylenepis(meth)acrylamide, diallyl phthalate, diallyl maleate, diallyl terephthalate,
Examples include triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, and the like.

Examples of the latter crosslinking agents include ethylene glycol zoglycidyl ether, polyethylene glycol diglycidyl ether, and di- or polyglycidyl ether of aliphatic polyhydric alcohol.

Furthermore, as a device that has both the former and latter functions, for example, N-
Compounds such as methylol acrylamide, glycidyl methacrylate, etc. can also be used in the method of the invention. However, in the present invention, among these, those having two or more double bonds in the molecule and exhibiting copolymerizability with the acrylic acid monomer are particularly preferred.

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 parts by weight, preferably 0.01 to 2 parts by weight per acrylic acid monomer.
1I regret it. If it is less than 0.001% by weight, the water absorption capacity will be extremely large, but the glue strength of the super absorbent polymer during water absorption will be extremely weak.If it is less than 10% by weight, the water absorption strength will be particularly improved, but the water absorption capacity will be becomes quite small, which poses a practical problem.

(3) Oxidizing radical polymerization initiator The polymerization initiator used in the production method of the present invention forms a redox system with the reducing agent, exhibits a certain degree of water solubility, and is a radical generator that exhibits oxidizing properties. There must be. Examples of such oxidative radical polymerization initiators include hydrogen peroxide, persulfates such as ammonium persulfate and potassium persulfate, and hydroperoxides such as t-butyl hydroperoxide and cumene hydrono-oxide. Peroxides; other examples include ceric salts, permanganates, chlorites, hypochlorites, and the like.

Other water-bath radical polymerization initiators that do not exhibit oxidizing properties, such as azo compounds such as 2,2'-azobis(2-amidinozolonocune) dihydrochloride, do not form a redox system with the reducing agent and cannot be used in the present invention. Not used in manufacturing methods.

Particularly preferred among these oxidative radical polymerization initiators is hydrogen peroxide. The lid used is 0.01 to 10% by weight, preferably 0.01 to 10% by weight based on the acrylic acid monomer.
．． It is a 1-2 double f type.

(4) Reducing agent The reducing agent used in the production method of the present invention is capable of forming a redox system with the radical polymerization initiator and exhibits a certain degree of water solubility. Examples of such reducing agents include sulfites such as sodium sulfite and hydrogen sulfite, sodium thiosulfate, cobalt acetate, steel sulfate, ferrous sulfate, and L-ascorbic acid and sodium L-ascorbate. Can be mentioned. Among these, L-ascorbic acid and sodium L-ascorbate are particularly effective and are preferred in the present invention. The amount of these reducing agents used is 0.0 with respect to the acrylic acid monomer.
01 to 1ON violet, preferably 0.01 to 2% by weight.

(5) Fibrous substrate The fibrous substrate used in the present invention is a loosely formed fiber/4' cut, carded or air laid web, tissue paper, woven fabric such as cotton gauze, stockinette fabric. , or non-woven fabric. A "formed" fibrous substrate is one that does not require further web-forming operations, although cutting, bonding, shaping, etc. may be required to incorporate the fibrous substrate into an article. means.

It is generally preferred to use absorbent fibers for the fibrous substrate, such as wood bulb, rayon, cotton, other cellulosic fibers, or polyester fibers. But other types of fibers, e.g.

Polyethylene type, polyethylene group, polystyrene type, polyamide type, polyvinyl alcohol type, polyvinyl chloride type, polyvinylidene chloride type, tetraacrylonitrile type, polyurea type, polyurethane type, I-lyfluoroethylene type, polycyanide vinylidene type, etc. The molded fibrous substrate may contain fibers such as:

〔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. In a beaker with a physiological saline water absorption capacity of 300, we weighed the water-absorbing complex and saline 2009 with a concentration of 0.9 weight, and left it for about 4 hours to soak in the saline. 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.

B. Weigh out saline solution 2001 with a concentration of 0.9 weight in a beaker with a water absorption rate of 300 g. Next, the water-absorbing composite was added to about 0.
5.9 Weigh and place in the above saline solution.

After draining through a 5-minute diameter 100-mesh sieve, the amount of filtered saline is weighed, and the physiological saline water absorption capacity is determined based on the formula shown in A above, and this is taken as the water absorption rate.

Example 1 A water-absorbing composite in which a crosslinked product of partially neutralized sodium polyacrylate was stably fixed to a polyester nonwoven fabric was continuously produced according to the steps shown in FIG. That is, a 45% aqueous solution of partially neutralized sodium acrylate mixed with 0.12% N,N'-methylenebisacrylamide and 0.299% hydrogen peroxide was kept at 30°C. This was continuously sprayed from a spray nozzle onto a polyester nonwoven fabric that was continuously fed by an endless belt. The spray lid is about 6 liters for polyester non-woven fabric as a monomer.
It's double the weight. The polyester nonwoven fabric impregnated with the aqueous monomer solution in small droplets is then continuously fed to the next reducing agent spray zone. Here, a 1'1% L-ascorbic acid aqueous solution is continuously sprayed from a spray nozzle at 30°C. Polymerization was completed in a very short time of approximately 10 seconds, and the product was subsequently dried in a drum dryer.

In the obtained product, a crosslinked product of partially neutralized sodium polyacrylate is stably and finely dispersed in a polyester nonwoven fabric with a particle size of 100 to 300 μm, and its physiological saline water absorption capacity is 53.5 and the water absorption rate is 31. .5, and almost no residual monomer was observed.

When the water-absorbing composite obtained in this example was tested as a material for sanitary napkins and paper diapers, the water-absorbing performance and water-absorbing rate were good, and the texture was also very good.

Example 2 In Example 1, N,N'-methylenebisacrylamide 0.146% by weight, hydrogen peroxide 0.363% by weight
A water-absorbing composite was continuously produced using the same recipe as in Example 1, except that the acrylic acid monomer was a 75% partially neutralized potassium acrylate 65% aqueous solution. The obtained water-absorbent composite has a small crosslinked body of partially neutralized potassium polyacrylate with a size of 150 to 350 μm stably fixed to a polyester nonwoven fabric, and its physiological saline water absorption capacity is 45.5.
The water absorption rate was 29.8, and almost no residual monomer was observed.

Example 3 A water-absorbing composite was continuously produced using the same recipe as in Example 1, except that a rayon nonwoven fabric was used instead of the polyester nonwoven fabric in Example 1, and sodium L-ascorbate was used as the reducing agent. The obtained water-absorbent composite has a weight of 200
A small cross-linked product of partially neutralized sodium polyacrylate with a diameter of ~400 μm is stably fixed to a rayon nonwoven fabric, and its physiological saline water absorption capacity is 506. Water absorption rate is 36.5
, and almost no residual monomer was observed.

Example 4 In Example 1, potassium peroxide was used instead of hydrogen peroxide,
A water-absorbing composite was continuously produced using the same recipe as in Example 1, except that hydrogen sulfite was used instead of L-ascorbic acid. The obtained water absorbent composite has a molecular weight of 100 to 3
A cross-linked product of partially neutralized polyacrylic acid with a diameter of 00 μm is stably fixed to a polyester nonwoven fabric, and its physiological saline water absorption capacity is 48.2 and the water absorption rate is 2.
6.5, and almost no residual monomer was observed.

Example 5 Polyethylene glycol (PBG-600) was used instead of N,N'-methylenebisacrylamide in Example 1.
A water-absorbing composite was continuously produced using the same recipe as in Example 1 except that diacrylate was used. The obtained water-absorbent composite has a small crosslinked body of partially neutralized sodium polyacrylate with a size of 150 to 250 μm stably fixed to a polyester nonwoven fabric, and its physiological saline water absorption capacity is 58.2.
The water absorption rate was 33.5, and almost no residual monomer was observed.

Comparative Example 1 A partially neutralized aqueous sodium acrylate solution having a degree of neutralization of 75% and a 7-mer concentration of about 45 tL4 in the aqueous solution was prepared, and this was sprayed onto a polyester nonwoven fabric from a spray nozzle to impregnate it. The amount of monomer impregnated was 8 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 occurs immediately, with 71'0 in part
A water-absorbing composite in which a super-absorbent polymer made of a self-crosslinked product of polyacrylic acid (IJum) was stably fixed to a polyester nonwoven fabric was obtained.

Results of measuring the physiological saline water absorption capacity of this water-absorbing composite 25
．． 0, the water absorption rate was 18.0, and almost no residual smear was observed.

Comparative Example 2 A partially neutralized potassium acrylate aqueous solution was prepared with a degree of neutralization of 75 degrees and a concentration of about 64 percent by weight in the aqueous solution. This was sprayed onto a polyester nonwoven fabric from a spray nozzle to impregnate it. The amount of monomer impregnated was about 1031z times that of the nonwoven fabric. On the nonwoven fabric impregnated with this partially neutralized potassium acrylate monomer aqueous solution,
An electron beam device equipped with a dynamidron accelerator irradiates it with an electron beam at a dose of 10 megarads. Polymerization occurs immediately;
A water-absorbing composite was obtained in which a super-absorbent polymer consisting of a self-crosslinked product of partially neutralized potassium polyacrylate was stably fixed to a polyester nonwoven fabric.

Results of measuring the physiological saline water absorption capacity of the above water-absorbing composite 18
．． It was quite small at 5. Also, the water absorption rate is 1
0.5, and almost no residual monomer was observed.

Comparative Example 3 A 45% by weight aqueous solution of 75% partially neutralized sodium acrylate containing 0.12% by weight of N,N'-methylenebisacrylamide was sprayed onto a polyester nonwoven fabric using a spray nozzle and heated to 70°C.

The impregnated seven-layer lid was about 7 times heavier than the nonwoven fabric. A 6.3% by weight aqueous potassium persulfate solution, followed by a 5% F4 hydrogen sulfite solution, were each sprayed from a spray nozzle.

Polymerization was completed after about 7 minutes.

However, in the resulting absorbent composite, only the upper layer of the nonwoven fabric was polymerized and had a strong monomer odor. (The amount of remaining monomer was about 15% by weight.) Then, an additional 7
The initiator solution and reducing agent solution were sprayed from a spray nozzle at 0'C and held for about 30 minutes, but polymerization hardly progressed. 90 more of the super-absorbing complex obtained there.
When dried under reduced pressure at .degree. C., the physiological saline water absorption capacity was measured to be 16.5, and the water absorption rate was 2.9, which was extremely low.

Comparative Example 4 A 75% partially neutralized potassium acrylate aqueous solution containing 0.146% by weight of N,N'-methylenebisacrylamide in a 74% water bath solution was sprayed onto a rayon nonwoven fabric using a spray nozzle, and the temperature was set at 70°C.

The amount of impregnating monomer was 6 times the weight of the nonwoven fabric. When a 16.7 wt % 2.2-azobis(2-amidinopropane) dihydrochloride aqueous solution was sprayed onto this from a spray nozzle, polymerization started immediately.

However, as in Comparative Example 3, only the upper layer of the nonwoven fabric was polymerized in the obtained water absorbent composite, and it had a strong monomer odor. (It was approximately 12.1 weight f% as a residual nomer tray.) Therefore, it was held 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 complex is 1
4.2, and the water absorption rate is 2.9, which is extremely small.

〔Effect of the invention〕

As is clear from the above Examples and Comparative Examples, the water absorbent composite obtained by the production method of the present invention is
It has a particularly higher water absorption performance and water absorption rate than the other methods disclosed in Japanese Patent Application Laid-open No. 500546 and Japanese Patent Application Laid-open No. 149609/1984, and is highly safe with almost no residual monomer. Furthermore, because it is in the form of a sheet, it is easier to handle and cheaper than the powder-like superabsorbent resin that has been used in the past, making it a sanitary napkin.

It can be advantageously used in the production of various sanitary materials such as paper diapers.

Also. Utilizing its excellent water absorption performance and ease of handling, it can also be used in the production of various materials for horticultural and agricultural purposes, including soil conditioners, water retention agents, etc., which have recently attracted attention.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the manufacturing process of a water-absorbing composite according to the present invention.

Claims (6)

[Claims] (1) A fibrous material formed from an aqueous solution of a polymerizable monomer whose main component is acrylic acid (hereinafter referred to as acrylic acid monomer) in which 20% or more of the carboxyl groups are neutralized with an alkali metal salt or ammonium salt. A crosslinking agent and an oxidizing agent are added to the aqueous solution of the acrylic acid monomer in order to produce a water-absorbing composite consisting of a super absorbent polymer and a molded fibrous substrate by polymerizing the acrylic acid monomer. A radical polymerization initiator is mixed and dissolved at room temperature, and the resulting mixture is molded into a fibrous substrate with a superabsorbent polymer having a particle size of 30 μm to 5 μm.
A method for producing a water-absorbing composite consisting of a super-absorbent polymer and a molded fibrous substrate, characterized in that the polymer is impregnated by spraying to a thickness of 0.00 μm, then a reducing agent is added in the form of a mist, and polymerized. . (2) The crosslinking agent is ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate,
Polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, N,N'-methylene bis(meth)acrylamide, diallyl phthalate, diallyl maleate, diallyl 2. The manufacturing method according to claim 1, characterized in that it is one or more selected from the group consisting of terephthalate, triallyl cyanurate, triallyl isocyanurate, and triallyl phosphate. (3) The production method according to claim 1, wherein the oxidative radical polymerization initiator is hydrogen peroxide. (4) The manufacturing method according to claim 1, wherein the reducing agent is L-ascorbic acid or an alkali metal salt of L-ascorbic acid. (5) The manufacturing method according to claim 1, wherein the fibrous substrate is mainly composed of cellulose fibers or polyester fibers. (6) The method according to claim 5, 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.