JPH04218502A - Production of water-absorbable composite material - Google Patents

Abstract

PURPOSE:To produce the subject composite material containing a reduced amount of remaining monomers and having high water absorbability and whiteness by applying to a fibrous substrate an aqueous solution countering a polymerization initiator and monomers including acrylic acid, etc., whose carboxyl groups are partially neutralized, and subsequently applying an oxidative polymerization initiator and a reducing agent to the treated fibrous substrate. CONSTITUTION:An aqueous solution containing a water-soluble polymerization initiator [e.g. 2, 2'-azobis(2-amidinopropane) dihydrochloride] and polymerizable monomers consisting mainly of acrylic acid, >=20% of the polymerizable monomers being neutralized into the alkali metal salt groups or ammonium salt groups thereof, is applied to a molded fibrous substrate (e.g. polyester nonwoven fabric), and the polymerizable monomers applied to the fibrous substrate are subsequently treated with a mixture of an oxidative radical polymerization initiator (e.g. hydroperoxide) and a reducing agent (e.g. ascorbic acid) for forming the composite material of the fibrous substrate with a polymer originated from the polymerizable monomers to provide the objective water- absorbable composite material.

Description

[Detailed description of the invention]

[Background of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-absorbing composite. More specifically, the present invention involves applying an aqueous polymerizable monomer solution mixed with a water-soluble radical polymerization initiator to a molded fibrous substrate, and further adding a mixture of an oxidizing radical polymerization initiator and a reducing agent to this. The present invention relates to a method for producing a water-absorbing composite in which a water-absorbing polymer is fixed to a fibrous substrate, the method comprising polymerizing a polymerizable monomer by applying the same method.

[0002] The water-absorbing composite obtained by the production method of the present invention has high water-absorbing properties, has extremely low residual monomer content, has no coloring in the polymer, and has excellent whiteness, so it can be used in various water-absorbing materials. can be used advantageously.

0003

BACKGROUND OF THE INVENTION In recent years, superabsorbent polymers have been developed and used in various sanitary materials such as sanitary products and paper diapers, agricultural and horticultural materials, and civil engineering and construction materials.

Examples of this type of superabsorbent polymer include starch graft polymers (Japanese Patent Publication No. 53-46199, etc.), modified cellulose (Japanese Patent Publication No. 50-80376, etc.)
(Japanese Patent Publication No. 43-23), cross-linked water-soluble polymers (Japanese Patent Publication No. 43-23)
462, etc.), self-crosslinking type acrylic acid alkali metal salt polymer (Japanese Patent Publication No. 54-30710, etc.), and the like are known.

However, although these superabsorbent polymeric materials have a fairly high level of water absorption performance, most of them are obtained in powder form, so they cannot be used as sanitary materials such as sanitary napkins and paper diapers. To do this, it is necessary to uniformly disperse and fix onto a substrate such as tissue, nonwoven fabric, or cotton. However, it is difficult to stably fix such powdered superabsorbent polymer materials on the substrate, and they often aggregate partially after being dispersed, and the swollen gel after water absorption is also stable and stable on the substrate. They tended to be easily moved from the substrate without being fixed on top. For this,
For example, when used in paper diapers, the absorbent material becomes "stiff" after absorbing urine, making it extremely uncomfortable to wear. In addition, the method of dispersing the powdered superabsorbent polymer material into the base material as described above is complicated due to the complexity involved in handling the powder and process problems in achieving uniform dispersion efficiently. It is also extremely expensive in terms of cost.

As one method for solving these problems, various methods have recently been developed in which a composite material is produced by polymerizing an aqueous solution of an acrylic acid monomer onto a molded fibrous substrate.

However, although all of these composites have excellent polymer immobilization properties, it is difficult to say that they simultaneously satisfy required performances such as water absorption capacity, residual monomer, and polymer whiteness. For example, a method in which an aqueous solution of acrylic acid monomer is applied onto a substrate and irradiated with an electron beam (Japanese Patent Publication No. 57-500546 and Japanese Patent Application Laid-open No. 10504-1983)
No. 4 publications, etc.), there was a problem in that there was a large amount of residual monomer, and when an attempt was made to reduce the residual monomer, the crosslinking reaction of the polymer proceeded, resulting in a significant decrease in water absorption capacity.

Therefore, in order to improve these problems, a method has been proposed in which ultraviolet rays are further irradiated after electron beam irradiation (Japanese Patent Laid-Open Nos. 2-48944 and 2-11148).
5 publications). In these methods, although the water absorption capacity has been improved to some extent, there is still a problem in that a large amount of residual monomer remains.

[0009] Furthermore, a method has been proposed in which heat treatment is performed by irradiating electron beams in the presence of a water-soluble radical polymerization initiator (
JP-A-2-91129). However, this method
Although the amount of residual monomer can be kept low by heat treatment, there is a problem in that the water absorption capacity is lowered. A method has been proposed in which a water-soluble azo compound having an amidino group is used as a photosensitizer, irradiated with ultraviolet rays, polymerized, and then subjected to surface crosslinking treatment (Japanese Patent Application Laid-Open No. 63-63457). Although this method significantly improves water absorption capacity, it takes time to remove water after the polymerization reaction because the monomer concentration is lowered to suppress the polymerization reaction rate and prevent the resin from becoming porous. Therefore, there was a problem in productivity, and the cost of the photosensitizer was also high.

On the other hand, as a method that does not use electron beams, ultraviolet rays, etc., a method of thermally polymerizing a water-soluble radical polymerization initiator by incorporating it into an acrylic acid monomer (Japanese Patent Laid-Open No. 62-2
2811 and 63-275616) and a method of heating and drying in a steam atmosphere after thermal polymerization (Japanese Unexamined Patent Publication No. 1-271434). The latter has particularly low residual monomer content, but since both employ thermal polymerization, the productivity is usually very poor.

[0011] Also, there is a method in which the oxidizing agent component and the reducing agent component of a redox initiator are separately sprayed and polymerized (Japanese Patent Application Laid-open No. 149609/1983), or a method in which one of the redox components is included in the monomer, A method of spraying the other one (Japanese Unexamined Patent Publications Nos. 62-97978 and 62-97979) has also been proposed, but in the former method, "uneven polymerization" tends to occur because the redox components are sprayed separately, and residual monomers are There were many. Although the "polymerization unevenness" has been considerably improved in the latter case, there is still a large amount of residual monomer,
Also, depending on the conditions, the polymer became colored.

In order to improve these problems, a method has been proposed in which the residual monomer is reduced by electron beam treatment, heat treatment or ultraviolet treatment after redox polymerization (Japanese Patent Application Laid-open Nos. 10638-1988 and 1983-1983). -30505,
63-260906). However, although the residual monomer was reduced in the electron beam treatment, a crosslinking reaction occurred and the water absorption capacity was reduced, and in the ultraviolet ray treatment and heat treatment, although the decrease in the water absorption capacity was suppressed, the decrease in the residual monomer was also small.

[Summary of the invention]

[Problems to be Solved by the Invention] The present invention relates to a water-absorbing composite material proposed in the above-mentioned Japanese Patent Application Laid-Open No. 63-30505, Japanese Patent Application Laid-Open No. 63-10638, or Japanese Patent Application Laid-Open No. 63-260906, etc. The present invention aims to provide a method for producing a water-absorbing composite having excellent water-absorbing property, residual monomer, and polymer whiteness by further improving the method.

[0014]

[Means for Solving the Problems] As a result of various studies aimed at solving the above-mentioned problems, the present inventors have developed a fiber molded from an aqueous solution of polymerizable monomers mixed with a water-soluble radical polymerization initiator. By applying a mixture of an oxidizing radical polymerization initiator and a reducing agent to a solid substrate and polymerizing a polymerizable monomer, a water-absorbing composite with excellent whiteness, high water absorption, and extremely low residual monomer content can be obtained. The present invention was achieved by discovering that the following can be easily obtained.

That is, the method for producing a water-absorbing composite according to the present invention is to prepare a polymerizable material whose main component is acrylic acid, in which 20% or more of the total carboxyl groups in the specimen are neutralized with an alkali metal salt or an ammonium salt. An aqueous solution containing a monomer and a water-soluble radical polymerization initiator is applied to the formed fibrous substrate, and then an oxidizing radical polymerization initiator and an oxidizing radical polymerization initiator are applied to the polymerizable monomer applied to the fibrous substrate. It is characterized in that a mixture consisting of a reducing agent is applied to form a composite of a polymer derived from the polymerizable monomer and a fibrous substrate.

[Specific Description of the Invention] <Polymerizable Monomer> The polymerizable monomer used in the present invention is such that 20% or more, preferably 50% or more of the total carboxyl groups in the specimen are alkali metals. The main component is acrylic acid neutralized with salt or ammonium salt. Here, "containing acrylic acid as a main component" means that the above-mentioned specific acrylic acid is 50 mol% or more, preferably 8 mol% or more based on the total amount of polymerizable monomers.
This means that it is contained in an amount of 0 mol% or more. If the degree of partial neutralization of acrylic acid is too low, the water-absorbing capacity of the produced water-absorbing composite will be significantly reduced.

In addition to the above-mentioned acrylic acid and acrylate salts, the present invention also uses monomers copolymerizable with these, such as 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylethanesulfonic acid, and 2-acrylic acid. Acroylpropanesulfonic acid, methacrylic acid, and their alkali metal or ammonium salts, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-
Hydroxyethyl (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, 2-vinylpyridine, 4-vinylpyridine and their salts, itaconic acid, One member selected from the group consisting of maleic acid, fumaric acid, vinylsulfonic acid, their alkali metal salts or ammonium salts, and (meth)acrylic esters such as methyl (meth)acrylate and ethyl (meth)acrylate; or A combination of two or more types is also possible. Here "(meth)acrylic"
refers to both "acrylic" and "methacrylic".

[0018] The "polymerizable monomer" in the present invention is the above-mentioned specific acrylic acid (20% or more of which is in the form of a salt).
The amount of the copolymerizable monomer other than the above-mentioned specific acrylic acid is generally less than 50 mol%, preferably less than 20 mol%.

[0019]Although alkali metal hydroxides, bicarbonates, or ammonium hydroxide can be used to neutralize the above-mentioned acid monomers including acrylic acid, preferred in the present invention are is an alkali metal hydroxide. Specific examples include sodium hydroxide, potassium hydroxide and lithium hydroxide. Sodium hydroxide or potassium hydroxide is preferred from the viewpoint of industrial availability, cost, safety, and the like.

In the present invention, a polymerizable monomer mainly consisting of the above-mentioned specific acrylic acid (20% or more of which is a salt) is applied in the form of an aqueous solution to a fibrous base molded article. The concentration of the aqueous solution in this case can be any convenient value. Specifically, for example, 30% by weight or more is appropriate.

<Optional Components> When polymerizing this polymerizable monomer, a crosslinking agent may be present in the polymerizable monomer aqueous solution as necessary. Examples of crosslinking agents that can be used include those that have two or more double bonds in the molecule and exhibit copolymerizability with the above-mentioned specific polymerizable monomer, or those that contain the functionality of the above-mentioned specific polymerizable monomer in the molecule. It has two or more functional groups that can react with groups such as carboxyl groups during polymerization or during drying after polymerization. Any of these can be used as long as it exhibits some degree of water solubility.

Examples of the former crosslinking agent include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate. Examples include acrylate, glycerin tri(meth)acrylate, N,N'-methylenebis(meth)acrylamide, diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, and the like. Here, "(meth)acrylate" refers to both "acrylate" and "methacrylate."

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

Furthermore, compounds having both the former and latter functions, such as N-methylolacrylamide and glycidyl methacrylate, can also be used in the method of the present invention.

[0025] Such crosslinking agents can be used alone or as a mixture of two or more.

<Water-soluble radical polymerization initiator (first polymerization initiator)> The polymerization initiator (first polymerization initiator) to be present in the monomer aqueous solution in the present invention is water-soluble or water-miscible. It is a radical polymerization initiator that exhibits properties and is well known in the field of polymer chemistry. Specific examples include inorganic or organic peroxides (eg, persulfates, ammonium salts, sodium salts, potassium salts, etc.), hydrogen peroxide, di-tert-butyl peroxide, acetyl peroxide, and the like. In addition to these peroxides, if a given aqueous solution is obtained, azo compounds and other radical polymerization initiators, such as
2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride, 4,4'-azobis(4-cyanovaleric acid) etc. can also be used.

This water-soluble radical polymerization initiator is preferably a relatively low-temperature decomposition type initiator that is decomposed by the heat of polymerization caused by a redox system, which is the second polymerization initiator applied later. preferable. Examples of such preferred initiators include potassium persulfate, ammonium persulfate, sodium persulfate, 2,2'-azobis(2-
amidinopropane) dihydrochloride, 2,2'-azobis(N
, N'-dimethyleneisobutyramidine) dihydrochloride and the like are preferred.

The amount used is 0.00% relative to the polymerizable monomer.
0.01 to 2% by weight, preferably 0.05 to 1% by weight.

<Molded fibrous substrate> Specifically, the formed fibrous substrate to which the aqueous polymerizable monomer solution is applied is formed by loosely molding fibers, such as padding, carding, or air laying. woven web, tissue paper, cotton gauze-like fabric, knitted fabric, or non-woven fabric. Here, a "formed" fibrous substrate is one that does not require further web forming operations, although cutting, shaping, etc. may be necessary in order to incorporate the fibrous substrate into an article. means.

It is generally desirable to use absorbent fibers, such as wood pulp, rayon, cotton, other cellulosic fibers or polyester fibers, as the main component in the fibrous substrate. However, other types of fibers, such as polyethylene, polypropylene, polystyrene, polyamide, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile,
Fibers such as polyurea-based, polyurethane-based, polyfluoroethylene-based, polycyanide-based vinylidene, etc. can also be included in the molded fibrous substrate.

<Redox system (second polymerization initiator)> The second polymerization initiator used in the production method of the present invention is a mixture consisting of an oxidizing radical polymerization initiator and a reducing agent, and is a redox system. It forms the Both the oxidizing radical polymerization initiator and the reducing agent to form such a mixture must exhibit some degree of water solubility.

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 hydroperoxide. Other examples include peroxide, ceric salts, permanganates, chlorites, hypochlorites, and the like. All of these exhibit oxidizing properties. 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 used in the present invention. , therefore, is not used in the manufacturing method of the present invention.

Further, reducing agents used in the production method of the present invention include sulfites such as sodium sulfite and sodium bisulfite, sodium thiosulfate, cobalt acetate, copper sulfate, ferrous sulfate, L-ascorbic acid, and L-ascorbic acid. - Sodium ascorbate, aniline, monoethanolamine, hexamethylenediamine, diethanolamine, dimethylaniline, triethanolamine, tetramethylethylenediamine, and the like. Among these, a preferred combination is hydrogen peroxide as the oxidative radical polymerization initiator and L-ascorbic acid as the reducing agent.

The amount of these mixtures used is 0.00% of the oxidative radical polymerization initiator relative to the polymerizable monomer.
It is 1 to 10% by weight, preferably 0.01 to 5% by weight. Further, the amount of the reducing agent is 0.001 to 5% by weight, preferably 0.01 to 2% by weight.

The mixing ratio of these oxidizing radical polymerization initiators and reducing agents is one of the extremely important points in the production method of the present invention. The specific mixing ratio varies depending on the type of oxidizing radical polymerization initiator and reducing agent used, but generally the oxidizing radical polymerization initiator/reducing agent molar ratio is 0.5 to 25, preferably 2 to 25. 10. If the molar ratio is less than 0.5, there is a problem in that the resulting absorber tends to change color from yellow to brown in some places or all over. Further, if the usage amount exceeds 25, the effect will be small.

In the present invention, the method for obtaining the mixture of the oxidizing radical polymerization initiator and the reducing agent is not particularly limited, and a number of suitable methods may be used. Typical examples include a method in which an oxidizing radical polymerization initiator and a reducing agent are individually injected and mixed under stirring in a reaction vessel, and a method in which an oxidizing radical polymerization initiator and a reducing agent are continuously added using line mixing. Examples include a method of feeding.

<Method of applying an aqueous polymerizable monomer solution> The aqueous polymerizable monomer solution containing the above-mentioned water-soluble radical polymerization initiator is first applied to a molded fibrous substrate.

It is generally preferred that the ratio of polymer surface area to mass of the produced polymer be as large as possible from the viewpoint of water absorption amount and water absorption rate. Furthermore, from the viewpoint of the flexibility of the composite, it is preferable to apply the polymerizable monomer solution so that the polymer is produced in a discontinuous state in which the polymer is very finely dispersed.

Such application methods include spraying (
spraying), printing,
flowing through a nozzle, kiss coating, satura
ting), etc.

[0040] The amount of impregnation of the aqueous solution applied to 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 to be used. Generally, 0.1 to 1000 parts by weight per 1 part by weight of the fibrous base,
Usually 0.5 to 50 parts by weight is employed.

[0041] The temperature of the aqueous solution applied to the fibrous substrate is 10 to 100°C, usually around 20 to 60°C.

The polymerizable monomer may be applied to the fibrous substrate either on one side or on both sides.

<Polymerization> As described above, an aqueous solution of a polymerizable monomer containing a water-soluble radical polymerization initiator and, if necessary, a crosslinking agent, is first applied to the formed fibrous material at the predetermined temperature. It is applied to a substrate and adjusted to a predetermined temperature in a reaction tank. Next, a mixture consisting of an oxidizing radical polymerization initiator and a reducing agent is heated at room temperature or, if necessary, to a predetermined temperature, and then applied to the fibrous substrate coated with the aqueous solution of the polymerizable monomer. , carry out the polymerization. The method for applying the mixture at this time is the same as the method for applying the aqueous solution of the polymerizable monomer, but among these, the method by spraying is preferred.

[0044] Furthermore, there are no particular restrictions on the reaction vessel and reaction method, and any type can be employed. Typical methods include a method in which the reaction is carried out batchwise in an oven-type box-type reaction tank, or a method in which the reaction is carried out continuously on an endless belt. The temperature in the reaction tank, that is, the polymerization temperature, is not particularly limited and varies slightly depending on the type or amount of the oxidizing radical polymerization initiator and reducing agent used, but is generally 0 to 150°C, preferably The temperature is 20 to 100°C.

[0045]Also, the polymerization time varies depending on the polymerization temperature, etc., but is generally from several seconds to 2 hours, preferably from several seconds to 2 hours.
10 minutes, good quality.

The water-absorbing composite thus obtained is
Although it satisfies the conditions regarding water absorption capacity, residual monomer amount, and whiteness as it is, if it is particularly necessary to further reduce the residual monomer amount, ultraviolet rays, electron beams, or heat treatment can be performed.

<Ultraviolet irradiation treatment> For ultraviolet irradiation, an ordinary ultraviolet lamp may be used. The irradiation intensity, irradiation time, etc. of ultraviolet rays vary depending on the type of fibrous substrate used and the amount of polymerizable monomer impregnated, but generally the size of the ultraviolet lamp is 10 to 200 W/cm, preferably 30 to 120 W.
/cm, the irradiation time is 0.1 seconds to 30 minutes, and the distance between the lamp and the composite is 2 to 30 cm.

The irradiation temperature is not particularly limited, and the purpose can be sufficiently achieved at room temperature. There are no particular limitations on the ultraviolet irradiation device, and a method of irradiating the UV light in a stationary state for a certain period of time or a method of continuous irradiation using a belt conveyor can be used.

<Electron beam irradiation treatment> The dose of electron beam varies depending on the amount of residual monomer and water content in the composite, but
Generally 0.01 to 100 megarads, preferably 0.1
~50 megarads. If the dose exceeds 100 megarads, the amount of water absorbed will be extremely small, and if the dose is less than 0.01 megarads, the reduction of residual monomer will be insufficient. There are no particular restrictions on the irradiation temperature, and room temperature is sufficient to achieve the purpose.

<Heat treatment> The heat treatment was performed by heating the above composite to 100%
This can be carried out by heating to a temperature of -250°C, preferably 150-200°C. If the temperature exceeds 250°C, it is effective in reducing unpolymerized monomers, but the amount of water absorption decreases; on the other hand, if the temperature is less than 100°C, it takes an extremely long time to reduce the residual monomers, making it difficult for industrial use. It is inappropriate for this purpose. The time for heat treatment varies depending on the type of equipment used, heating method, etc., but generally it takes a few seconds to two seconds.
A suitable time is preferably several seconds to 30 minutes. Examples of the heating method or device include a method of batchwise heating using a box-type reactor whose interior is set to a predetermined temperature, a method of continuously bringing the target complex into contact with a roller whose surface temperature is set to a predetermined temperature using steam, etc. There are others.

[0051] The amount of water in the composite when subjected to post-treatments such as ultraviolet rays, electron beams or heat treatment is 0.05 to 1 part by weight, preferably 0.1 to 1 part by weight, per 1 part by weight of the polymer. 0
．． 5 parts by weight is adopted. If the amount is less than 0.05 part by weight and exceeds 1 part by weight, the residual monomer will be difficult to reduce and the polymer will also decompose, which is not preferable. This water content can be achieved by controlling the water content during polymerization, or
It can also be realized by adjusting the moisture content by drying or the like after polymerization.

[0052] As the atmosphere for the post-treatment in the present invention, any of vacuum, inert gas such as nitrogen, argon, helium, etc., or air can be used. The preferred atmosphere is air.

[0053] The water-absorbing composite thus obtained is
If necessary, it can be further surface crosslinked or dried to remove moisture, for example by passing it through a series of drying baths or using a forced draft oven.

[0054]

EXAMPLES [Experimental Examples] The following experimental examples illustrate the present invention in further detail.

<Example 1> In a conical flask with a capacity of 100 cc, sodium hydroxide (purity 95% by weight) 13.
1 g of the solution was taken, and 39 g of pure water was added thereto under ice cooling to dissolve the sodium hydroxide. Add 3 acrylic acid to this under ice-cooling.
The acrylic acid was gradually added to 0 g to neutralize the acrylic acid. The degree of neutralization of acrylic acid was about 75%, and the concentration of polymerizable monomer in the aqueous solution was about 45% by weight.

To this, 0.05 g of N,N'-methylenebisacrylamide was added as a crosslinking agent, and 2,2'-azobis(2-amidinopropane) was added as a water-soluble radical polymerization initiator.
A solution of 0.1 g of dihydrochloride dissolved in 2 g of water was added and mixed, and degassed with N2.

Separately, 0.9421 g of polyester nonwoven fabric was taken, and one side of the fabric was impregnated with the above polymerizable monomer aqueous solution using a spray nozzle. The amount of the aqueous polymerizable monomer solution impregnated was 10.9 times the weight of the nonwoven fabric. This is N
It was fixed in a 40° C. constant temperature reaction tank with double displacement.

Next, an aqueous solution (hydrogen peroxide/
L-ascorbic acid at a molar ratio of 3) was sprayed onto the nonwoven fabric using a hand sprayer. Polymerization occurred immediately, and a water-absorbing composite in which a crosslinked product of partially neutralized sodium polyacrylate was stably fixed to the nonwoven fabric was obtained.

<Example 2> 30 g of acrylic acid was placed in a 100 cc conical flask, and 14 g of pure water was added to it.
3g was added and mixed. Under ice cooling, 16.5 g of potassium hydroxide (85% by weight) was gradually added to neutralize the acrylic acid. The degree of neutralization of acrylic acid was about 60%, and the concentration of polymerizable monomer in the aqueous solution was about 65% by weight.

To this, add 0.1 g of ammonium persulfate to 2 ml of water.
The solution dissolved in g was added and mixed, and degassed with N2.

Separately, 1.0155 g of polyester nonwoven fabric was taken, and one side of the fabric was impregnated with the above polymerizable monomer aqueous solution using a spray nozzle. The amount of the aqueous polymerizable monomer solution impregnated was 8.0 times the weight of the nonwoven fabric.

[0062] This was fixed in a constant temperature reaction tank at 40°C which was purged with N2.

Next, an aqueous solution (hydrogen peroxide/
L-ascorbic acid at a molar ratio of 3) was sprayed onto the nonwoven fabric using a hand sprayer. Polymerization occurred immediately, and a water-absorbing composite in which a self-crosslinked partially neutralized potassium polyacrylate was stably fixed to the nonwoven fabric was obtained.

<Example 3> In a conical flask with a capacity of 100 cc, 10.
5 g was taken, and 24.0 g of pure water was added to it under ice-cooling to dissolve it. This was gradually added to 30 g of acrylic acid under ice cooling to neutralize the acrylic acid. The degree of neutralization of acrylic acid was 60%, and the concentration of polymerizable monomer in the aqueous solution was about 55% by weight.

A solution prepared by dissolving 0.1 g of potassium persulfate in 2 g of water was added and mixed, and the mixture was degassed with N2.

Separately, 0.9018 g of polyester nonwoven fabric was taken, and one side of the fabric was impregnated with the aqueous solution of the polymerizable monomer from a spray nozzle. The amount of the aqueous polymerizable monomer solution impregnated was 9.5 times the weight of the nonwoven fabric. This is N
It was fixed in a 40° C. constant temperature reaction tank with double displacement.

Next, an aqueous solution (hydrogen peroxide/
L-ascorbic acid at a molar ratio of 3) was sprayed onto the nonwoven fabric using a hand sprayer. Polymerization occurred immediately, and a water-absorbing composite in which a self-crosslinked product of partially neutralized sodium polyacrylate was stably fixed to the nonwoven fabric was obtained.

<Example 4> In Example 3, 0.05 g of N,N'-methylenebisacrylamide was added as a crosslinking agent and 2,2'-azobis( A water-absorbing composite was obtained by the same procedure except that 0.1 g of N,N'-dimethyleneisobutyramidine dihydrochloride was used.

<Example 5> In Example 3, as a mixture consisting of an oxidizing radical polymerization initiator and a reducing agent, 0.33% by weight of hydrogen peroxide and 1.7% by weight of L-ascorbic acid were used.
3% by weight (hydrogen peroxide/L-ascorbic acid molar ratio 1
A water-absorbing composite was obtained by the same procedure except that an aqueous solution containing ) was used.

<Example 6> In Example 3, 1.67% by weight of hydrogen peroxide and 1.7% by weight of L-ascorbic acid were used as a mixture consisting of an oxidative radical polymerization initiator and a reducing agent.
3% by weight (hydrogen peroxide/L-ascorbic acid molar ratio 5
A water-absorbing composite was obtained by the same procedure except that an aqueous solution containing ) was used.

<Example 7> The moisture content of the composite obtained in Example 1 was set to 25%, and ultraviolet rays were irradiated for 3 seconds from a distance of 8 cm from the composite using an 80 W/cm ultraviolet lamp.

<Example 8> The moisture content of the composite obtained in Example 2 was set to 30%, and as a post-treatment, it was irradiated with an electron beam at a dose of 5 megarads in an air atmosphere from an electron beam apparatus equipped with a dynamitron accelerator. A water-absorbing composite was obtained by the same procedure except for the following.

<Example 9> The same procedure was repeated except that the moisture content of the composite obtained in Example 3 was reduced to 40%, and as a post-treatment, it was heated by contacting it with a steam roller whose surface temperature was 160°C. A water-absorbing composite was obtained by the method.

<Comparative Example 1> In Example 2, 0.33% by weight of hydrogen peroxide and 3.4% by weight of L-ascorbic acid were used as a mixture consisting of an oxidative radical polymerization initiator and a reducing agent.
6% by weight (molar ratio of hydrogen peroxide/L-ascorbic acid 0)
．． A water-absorbing composite was obtained by the same procedure except that an aqueous solution containing 5) was used.

Comparative Example 2 A water-absorbing composite was produced according to Example 1 described in JP-A-63-260906.

That is, 13.1 g of sodium hydroxide (purity 95% by weight) was placed in a 100 cc conical flask, and 30 g of acrylic acid was gradually added thereto under ice cooling to neutralize it. The degree of neutralization was about 75%, and the monomer concentration in the aqueous solution was about 45% by weight.

To this, 0.05 g of potassium persulfate as a radical polymerization initiator was taken, dissolved in the above monomer aqueous solution, and degassed with N2.

Separately, 0.1569g of polyester nonwoven fabric
Then, the monomer aqueous solution was applied to the entire surface of the nonwoven fabric to impregnate it. The amount of monomer impregnated was 6.2 times the weight of the nonwoven fabric. This was placed in a constant temperature reaction tank that had been degassed with N2 and heated to 90°C. Polymerization occurred immediately, and a composite was obtained in which a highly water-absorbent polymer made of a self-crosslinked product of partially neutralized sodium polyacrylate was stably fixed to a polyester nonwoven fabric.

Next, the water content of this composite was made to be about 20% by weight based on the polymer, and a UV lamp of 80 W/cm was used to set the distance between the UV lamp and the composite to 8 cm, and the composite was heated for 2 seconds on each of the front and back surfaces. A water-absorbing composite material was obtained by irradiating each sample.

Comparative Example 3 A water-absorbing composite was obtained in the same manner as in Example 4, except that no water-soluble radical polymerization initiator was added to the aqueous polymerizable monomer solution.

<Comparative Example 4> A water-absorbing composite was produced according to Example 7 described in JP-A-63-30505.

That is, 30 g of acrylic acid was placed in a 100 cc conical flask, and 16.9 g of pure water was added thereto and mixed. 20.6 g of potassium hydroxide (85% by weight) was gradually added to this under ice cooling to neutralize it. The degree of neutralization was about 75%, and the monomer concentration in the aqueous solution was about 65% by weight.

To this, 0.1 g of N,N'-methylenebisacrylamide was taken as a crosslinking agent, added and dissolved in the above monomer solution, and heated to 40°C. In addition, 0.4 g of 31% hydrogen peroxide solution was added as a radical polymerization initiator and dissolved therein.

Separately, 0.1869g of polyester nonwoven fabric
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 5.8 times the weight of the nonwoven fabric.

Next, a 5% aqueous solution of L-ascorbic acid as a reducing agent was sprayed onto the entire surface of the nonwoven fabric using a spray nozzle. Polymerization occurred immediately, and a composite was obtained in which a highly water-absorbent polymer consisting of a partially neutralized potassium polyacrylate crosslinked with N,N'-methylenebisacrylamide was stably fixed to a polyester nonwoven fabric.

Next, this composite (water content is about 19% by weight)
) was heated by contacting it with a steam roller whose surface temperature was 160°C,
A water-absorbing composite material was obtained.

<Comparative Example 5> A water-absorbing composite was produced according to Example 8 described in JP-A-63-10638.

That is, 30 g of acrylic acid was placed in a 100 cc conical flask, and 16.9 g of pure water was added thereto and mixed. 20.6 g of potassium hydroxide (85% by weight) was gradually added to this under ice cooling to neutralize it. The degree of neutralization was about 75%, and the monomer concentration in the aqueous solution was about 65% by weight.

Add and dissolve 0.1 g of N,N'-methylenebisacrylamide as a crosslinking agent,
℃. In addition, 0.2 g of L-ascorbic acid was dissolved therein as a reducing agent.

Separately, 0.2582g of polyester nonwoven fabric
The raw material was applied to the entire surface of the nonwoven fabric to impregnate it, and the temperature was kept at 30°C in a constant temperature bath. The amount of monomer impregnated is
It was 6.2 times the weight of the nonwoven fabric.

Next, as an oxidative radical polymerization initiator, 1
A 0% by weight hydrogen peroxide solution was sprayed onto the entire surface of the nonwoven fabric from a spray nozzle. Polymerization occurred immediately, and a composite in which a superabsorbent polymer was stably fixed to a polyester nonwoven fabric was obtained from a partially neutralized potassium polyacrylate crosslinked with N,N'-methylenebisacrylamide.

Next, this composite (water content was 25% by weight) was irradiated with an electron beam at a dose of 20 megarads in an air atmosphere from an electron beam device equipped with a dynamitron accelerator to determine its water absorption. A composite material was obtained.

<Evaluation method> The water absorbent composites obtained in Examples 1 to 9 and Comparative Examples 1 to 5 above were heated at 40°C.
After drying under reduced pressure for 1 hour, the water absorption capacity of physiological saline, the amount of residual monomer, and the degree of coloring were measured. Furthermore, as an accelerated coloring test,
The degree of coloration of the water-absorbing composite after heat treatment at 180° C. for 1 hour was measured. Table 1 shows the results obtained. (A) Physiological saline water absorption capacity 1 g of the complex is placed in a 10 x 20 cm nylon mesh tea bag and immersed in 0.9% by weight saline in a 1 liter beaker. After leaving this for 1 hour,
Drain the excess salt water and measure the weight.

[0094] The weight of the tare bag is also measured by the same operation.

[0095] Physiological saline water absorption capacity is calculated according to the following formula. Physiological saline water absorption capacity = Absorbed tea bag weight (g) - Tare tea bag weight (g) / Prepared water absorbent polymer (g)
(B) Residual monomer concentration Accurately weigh 0.5 g of the composite or water-absorbing composite material, and add 2
Add to 1 liter of ion-exchanged water in a liter beaker and allow to swell sufficiently while stirring for about 10 hours. The swollen polymer gel is filtered through a 200 mesh sieve, and the filtrate is analyzed by high performance liquid chromatography.

Separately, a monomer standard solution having a known concentration was prepared, a calibration curve was prepared from this, and the absolute concentration was determined by taking into account the dilution ratio (2000 times). (C) Coloring degree The degree of coloring was evaluated using "SM Color Computer" (Model SM-5-IS-2B) manufactured by Suga Test Instruments Co., Ltd.

The results are shown in Table 1.

Table 1 *Those whose degree of coloration after heat treatment did not exceed 4 were considered acceptable and marked with a circle. Those with a degree of coloration exceeding 4 after heat treatment are rejected, and ×
It was shown in

0099

Effects of the Invention In the method for producing a water-absorbing composite of the present invention, (a) a water-soluble radical polymerization initiator (first polymerization initiator) is added to the aqueous polymerizable monomer solution applied to the fibrous substrate. However, when polymerization is initiated by the redox system, which is the second polymerization initiator, the first polymerization initiator in the polymerizable monomer decomposes due to the heat of polymerization, further promoting polymerization. Therefore, most of the polymerizable monomers are polymerized and become super absorbent polymers, so the water absorption performance increases.
and (b) it has remarkable characteristics in that the whiteness of the polymer is significantly improved depending on the conditions of the redox system (mixture of an oxidizing radical polymerization initiator and a reducing agent), which is the second polymerization initiator. be. Therefore, for these reasons, in the present invention, it is possible to easily obtain a water-absorbing composite material that is much superior to the above-mentioned prior inventions and the like at a low cost.

Claims (1)

[Claims] Claim 1: Contains a polymerizable monomer mainly composed of acrylic acid in which 20% or more of the total carboxyl groups in the standard are neutralized with an alkali metal salt or ammonium salt and a water-soluble radical polymerization initiator. A mixture of an oxidative radical polymerization initiator and a reducing agent is applied to the polymerizable monomer applied to the fibrous substrate to reduce the polymerizable A method for producing a water-absorbing composite, which comprises forming a composite of a monomer-derived polymer and a fibrous substrate.