JPH0774277B2 - Method for producing water-absorbent composite - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a water-absorbing composite.
More specifically, a molded fibrous substrate is preliminarily homogeneously mixed with a polymerizable monomer mainly containing acrylic acid and an acrylate containing a small amount of a cross-linking agent and a water-soluble radical polymerization initiator, and then the mixture is sprayed. The present invention relates to a method for producing a water-absorbent composite which is fixed in a fibrous substrate formed of a super-water-absorbent polymer, which has been formed into a shape and then polymerized.

The water-absorbent composite obtained by the production method of the present invention is excellent in water absorption, has a high water absorption rate, has a high strength of the polymer gel swollen by water absorption, and has a high water-absorption polymer stable on a fibrous substrate. Since it is well fixed, it can be advantageously used for the production of various water-absorbing materials.

[Prior art]

Conventionally, paper, pulp, non-woven fabric, sponge-like urethane resin and the like have been used as various water-retaining agents such as sanitary napkins, paper shavings and various other sanitary materials and various agricultural materials. However, since the water absorption of these materials is only about 10 to 50 times their own weight, in order to absorb or retain a large amount of water, a large amount of material is required and not only becomes extremely sublime, There is a defect that water is easily separated when pressure is applied to the absorbed material.

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 superabsorbent polymers have a considerably high level of water absorption performance, most of them are obtained in the form of powder, and therefore, for example, sanitary napkins,
To use it with sanitary materials such as paper staples, it is necessary to uniformly disperse it on a substrate such as tissue, non-woven fabric or cotton.
However, it is difficult to stably fix the polymer powder dispersed by this method on the substrate, and it is often gathered locally in part after dispersion, and the swollen gel after absorbing water is also stable on the substrate. It is not fixed and easily moves from the substrate. For this reason, the absorbent body after urination becomes a "stiff" state when used for example in a paper sheet, which makes it extremely uncomfortable to wear. In addition, in the method of obtaining an absorbent body by dispersing the powdery polymer as described above into the base material, the cost is complicated due to the handling of the powder and the process problem in efficiently performing the uniform dispersion. It is also extremely expensive.

[Problems to be solved by the invention]

As one of the methods for solving these problems, recently, 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 fine particle ionizing radiation. Then, a method for producing a water-absorbing composite by converting an acrylic acid-based monomer into a superabsorbent polymer has been reported (Japanese Patent Publication No. 57-500546). According to this method, although the uniform dispersion in handling the powder and the stable immobilization on the substrate are considerably improved, in converting to the superabsorbent polymer, electromagnetic radiation or fine particles are required. Because of the use of ionic ionizing radiation, the self-crosslinking reaction of the extremely superabsorbent polymer is likely to proceed, and as a result, the performance as an absorber, especially the water absorption capacity is extremely small, and usually when the powdered superabsorbent polymer is used. However, there is a drawback that it is less than half. Further, in terms of process, it cannot be said that the method 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 composite material in which the agent is atomized and added and polymerized is proposed. However, in this method, since a water-soluble polymerization initiator is added after impregnating a water-absorbing organic material with an acrylic acid-based monomer, even if it is atomized, “polymerization unevenness” occurs and complete polymerization is not possible. It is extremely difficult, resulting in a large amount of residual monomer, which causes many safety problems, and also has a drawback in that the water absorption capacity is particularly small.

[Means for solving problems]

(Object of the Invention) The present invention is disclosed in the above-mentioned Japanese Patent Publication No. 57-500546 and JP-A-60-14.
It is an object of the present invention to provide a method for producing a water-absorbent composite which is free from residual monomers and is further excellent in water-absorbing performance and water-absorption rate by improving the method for producing a water-absorbing composite described in Japanese Patent No. 9609.

(Structure of the Invention) The present inventors have conducted various studies for the purpose of solving the above-mentioned problems, and as a result, the acrylic acid-based monomer containing a small amount of a crosslinking agent was preliminarily uniformly mixed with a water-soluble radical polymerization initiator. , The particle size of the superabsorbent polymer obtained after that is 30
It was found that by spraying the mixed solution onto a molded fibrous substrate so that the particle size becomes ~ 500 μm and polymerizing it, there is almost no residual monomer, and a water-absorbent composite having a particularly improved water absorption performance and water absorption rate can be obtained. The present invention has been reached.

That is, the method for producing the water-absorbent composite of the present invention is a polymerizable monomer containing acrylic acid and an acrylic acid salt as a main component, in which 20% or more of carboxyl groups are neutralized with an alkali metal salt or an ammonium salt ( Hereinafter, an aqueous solution of acrylic acid-based monomer) is applied to a molded fibrous substrate, and then the acrylic acid-based monomer is polymerized to produce a water-absorbent composite comprising a superabsorbent polymer and a molded fibrous substrate. Therefore, a fibrous material obtained by uniformly mixing an aqueous solution of an acrylic acid-based monomer containing a small amount of a cross-linking agent and a water-soluble radical polymerization initiator or a water-soluble radical polymerization initiator and a water-soluble reducing agent and then atomizing the mixture. A method for producing a water-absorbing composite comprising a superabsorbent polymer and a molded fibrous substrate, characterized in that the substrate is applied and then polymerized.

In the method for producing a water-absorbing complex of the present invention, an aqueous solution of an acrylic acid-based monomer and a water-soluble radical polymerization initiator or a water-soluble polymerization initiator and a water-soluble reducing agent are preliminarily and uniformly mixed, and then the mixed solution is obtained. That the superabsorbent polymer to be polymerized by spraying it onto a fibrous substrate molded so that the particle size of the superabsorbent polymer is 30 to 500 μm, and that the superabsorbent polymer obtained is a resin having an appropriate crosslinked structure and crosslinked distribution The two features have the greatest characteristics.
And for this reason, in the production method of the present invention, the residual monomer amount is much smaller than in the method described in the above publication, the water absorption performance and the water absorption rate are remarkably excellent, and an inexpensive and high-performance water-absorbing composite is obtained. is there.

(Detailed Description of the Invention) (1) Monomer The monomer used in the present invention contains acrylic acid as a main component, but 20% or more, preferably 50% or more thereof is neutralized with an alkali metal salt or an ammonium salt. It will be. If the degree of partial neutralization is too low, the water absorption performance of the polymer will be significantly reduced.

Further, in the present invention, a polymer further excellent in water absorption performance can be obtained by coexisting with the above acrylic acid and acrylic acid salt and a monomer copolymerizable therewith. Examples of these monomers include 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-
One selected from the group consisting of acryloylpropane sulfonic acid, methacrylic acid and their alkali metal salts or ammonium salts, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate Or two or more. Good results are obtained when the amount of these monomers is 20 mol% or less, preferably 10 mol% or less, based on the acrylic acid-based monomer. If the amount of this monomer is too large, the effect of addition will be smaller than that before addition, and the water absorption performance of the polymer may be significantly reduced.

For neutralization of the acid monomer, alkali metal hydroxides and bicarbonates can be used, but alkali metal hydroxides are preferred, and specific examples thereof include sodium hydroxide and potassium hydroxide. And lithium hydroxide. Sodium hydroxide or potassium hydroxide is preferable from the viewpoints of industrial availability, price, and safety.

The concentration of these acrylic acid-based monomers is 20% by weight or more, preferably 30% by weight or more in water, and the higher 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. Specifically, about saturation solubility at the use temperature is advantageously used, and for example, in the case of sodium acrylate, it is about 45 at room temperature.
% By weight.

(2) Water-soluble radical polymerization initiator The polymerization initiator used in the production method of the present invention includes hydrogen peroxide, persulfates such as ammonium persulfate and potassium persulfate, t-butyl hydroperoxide and cumene hydroperoxide. And other azo initiators such as hydroperoxides, azoisobutyronitrile, and 2,2'-azobis (2-amidinopropane) dihydrochloride. These water-soluble radical initiators may be used as a redox type initiator by combining a reducing substance such as sodium bisulfite and amines.

The amount of these water-soluble radical initiators used is 0.01-10% by weight, preferably 0.1-2, relative to the acrylic acid-based monomer.
% By weight.

(3) Crosslinking Agent The crosslinking agent used in the production method of the present invention has two or more double bonds in the molecule, exhibits water solubility to some extent, and has good copolymerizability with the acrylic acid-based monomer, It must have an efficient cross-linking structure and give a uniform cross-linking distribution. Such cross-linking agents include 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. ) Acrylate, N,
N'-methylene bis (meth) acrylamide, diallyl phthalate, diallyl malate, diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate and the like can be mentioned, among which polyethylene glycol di (meth) acrylate, N , N'-methylenebisacrylamide is preferred.

The amount of these cross-linking agents used is based on the acrylic acid-based 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 gel strength of the superabsorbent polymer at the time of water absorption will be extremely weak.If it is less than 10% by weight, the water absorption gel strength will be remarkably improved, but the water absorption capacity will be considerably small. It becomes a thing and becomes a problem in practical use.

(4) Application method This application method is a very important point in the present invention. That is, an aqueous solution of an acrylic acid-based monomer containing a small amount of the crosslinking agent is uniformly mixed with the water-soluble radical initiator in advance, and then the mixed solution is atomized to be applied to the molded fibrous substrate. In this case, it is preferable to apply a small dot-like periodic pattern. And it is important to spray the above mixed solution so that the particle diameter of the superabsorbent polymer fixed to the molded fibrous substrate is 30 μm to 500 μm. By applying a fine superabsorbent polymer in such a range to a fibrous substrate formed into a small dot-like periodic pattern, the ratio of the polymer surface area to the mass can be maximized and water absorption can be improved. A water absorbing composite having a high speed is obtained. This small dot-like periodic pattern can also be used to create so-called "wicking passages" in the absorbent composite produced by the method of the present invention, which is, for example, the part of the absorbent pad of a diaper. The presence of continuous dots of superabsorbent polymer around the rim has the advantage that this diaper has very little leakage around the rim.

If the particle size of the superabsorbent polymer fixed on the fibrous substrate in a small dot-like periodic pattern is too small, that is, 30
If it is less than μm, no particular effect on the performance is observed, and conversely, it is difficult to efficiently apply it to the fibrous substrate during atomization.
In addition, the loss rate of the raw material monomer liquid is actually large, which is not economical. On the other hand, if the particle size is too large, i.e., 500
When the particle size is more than μm, the ratio of the polymer surface area to the mass becomes extremely small, which causes a problem particularly in the water absorption rate.

In the present invention, a method of atomizing a uniform mixed solution of an acrylic acid-based monomer aqueous solution containing a small amount of a cross-linking agent and a water-soluble radical polymerization initiator is, for example, a method of atomizing through a spray nozzle, or an ultrasonic vibrator. There is a method using an ultrasonic type device and a rotary atomizing centrifugal atomizing device. From the practical point of view, the method of atomizing through a spray nozzle is particularly preferable in the present invention.

The impregnated amount of the mixed liquid applied to the fibrous substrate is not particularly limited and can be widely varied depending on the product use of the water-absorbent composite. Generally, the amount of polymer is 0.1 to 1000 parts by weight, usually 0.5 to 1 part by weight per 1 part by weight of the fibrous substrate.
50 parts by weight are adopted.

(4) Fibrous Substrate The fibrous substrate used in the present invention is a loosely shaped pad, a woven or air laid web, tissue paper, woven fabric such as cotton gauze,
It may be a knitted fabric or a non-woven fabric. "Molded" fibrous substrate refers to the incorporation of the fibrous substrate into the article.
It means that cutting, joining, shaping, etc. may be required, but the web forming work need not be further performed.

It is generally preferred to use absorbent fibers such as wood pulp, rayon, cotton or other cellulosic or polyester fibers for the fibrous substrate. However, other types of fibers may be included in the molded fibrous substrate.

(5) Polymerization conditions As described above, a mixed solution of an acrylic acid-based monomer containing a small amount of a cross-linking agent and a water-soluble radical polymerization initiator is atomized on a molded fibrous substrate and then polymerized to give a superabsorbent polymer. In producing the water-absorbent composite fixed in a small dot pattern on the molded fibrous substrate, the raw material mixture is kept at room temperature or preheated to a predetermined temperature. Then, it is polymerized by atomization in a reaction tank adjusted to a predetermined polymerization temperature. The reaction tank and reaction system are not particularly limited, and any type may be used. As an example thereof, there may be mentioned a batch method in an oven-type box-type reaction tank or a continuous method on an endless belt. The temperature in the reaction tank, that is, the polymerization temperature, is not particularly limited, and it varies slightly depending on the type and amount of the radical polymerization initiator used, but generally 20 to 150
C., preferably 40 to 100.degree. C., is adopted.

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

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

〔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 0.5g of water-absorbent complex and about 200g of saline solution with 0.9wt% concentration were weighed and put into a beaker of 300ml physiological saline water absorption capacity, and left for about 4 hours to swell the polymer sufficiently with saline solution. Let Then, after draining with a 100-mesh sieve, the amount of super saline solution is weighed, and the physiological salt 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 0.5 g of the water-absorbent complex is weighed and placed in the saline solution. After 5 minutes, water was drained through a 100-mesh screen, and the amount of supersaline solution was weighed to determine the physiological salt water absorption capacity based on the formula shown in A. above, and this was taken as the water absorption rate.

Example 1.A 100cc conical flask was charged with sodium hydroxide (purity 9
(5% by weight) 13.1 g was taken, and 39 g of pure water was added to this under ice cooling and dissolved. To this, 30 g of acrylic acid was gradually added under ice cooling to neutralize. The degree of neutralization was about 45% by weight as the monomer concentration in the about 75% aqueous solution.

0.0085 g of N, N'-methylenebisacrylamide as a cross-linking agent and 0.2 g of 2,2'azobis (2-amidinopropane) dihydrochloride as a radical polymerization initiator were dissolved in the above monomer aqueous solution. Degassed at ₂ .

Separately, 0.1051 g of a polyester non-woven fabric (2 denier) was taken, and an aqueous monomer solution in which a radical polymerization initiator containing the above-mentioned crosslinking agent was dissolved was sprayed from the spray nozzle. The amount of the applied monomer was 8.0 times the weight of the nonwoven fabric.

Put this in a constant temperature reactor at 50 ° C for 90 minutes in about 10 minutes.
The temperature was raised to ℃. Polymerization immediately occurred, and a superabsorbent polymer consisting of partially neutralized sodium polyacrylate was stably fixed to the polyester nonwoven fabric to obtain a superabsorbent composite.

The particle size of the water-absorbent polymer in the water-absorbent composite is 100 ~ 3
00μm, physiological saline water absorption capacity is 51.5, water absorption rate is 26.2
And almost no residual monomer was observed.

Example 2 A monomer aqueous solution obtained by the same formulation as in Example 1 was used as a crosslinking agent.
0.01 g of N, N'-methylenebisacrylamide was melted and the temperature was adjusted to 80 ° C. On the other hand, 2,2 as a radical polymerization initiator
0.2 g of -azobis- (2-amidinopropane) dihydrochloride was dissolved in 1 g of pure water. Separately polyester non-woven 0.43
5 g was taken, and this was kept at about 70 ° C. in a constant temperature bath. An aqueous solution in which a radical polymerization initiator was dissolved was mixed with the aqueous monomer solution and immediately sprayed onto the non-woven fabric from a spray nozzle. Polymerization immediately occurred in the nonwoven fabric, and a superabsorbent polymer composed of partially neutralized sodium polyacrylate was stably fixed to the polyester nonwoven fabric to obtain a water-absorbent composite. The amount of the applied monomer was 12.7 times that of the nonwoven fabric, and the particle size of the superabsorbent polymer was 80 to 300 μm. The water-absorbent complex had a physiological saline water supply capacity of 48.5 and a water absorption rate of 25.6, and no residual monomer was observed.

Example 3 The same formulation as in Example 2 except that the rayon nonwoven fabric was 0.6651 g and the amount of the monomer sprayed was 5.3 times the weight of the nonwoven fabric.
A water absorbent composite was obtained by the same operation. The particle diameter of the super absorbent polymer in the water absorbent composite was 100 to 250 μm, and almost no residual monomer was observed. The water-absorbent complex had a physiological salt water-absorption capacity of 51.5 and a water-absorption rate of 25.1.

Example 4 Instead of acrylic acid in Example 2, 30 g of acrylic acid
And 2-acrylamido-2-methylpropanesulfonic acid
Using the mixture with 5.2 g, otherwise using the same formulation as in Example 2,
A water absorbent composite was obtained by the same operation. The particle size of the super absorbent polymer in this water absorbent composite was 1000 to 200 μm, and almost no residual monomer was observed.

The water-absorbent composite has a physiological salt water absorption capacity of 78.5 and a water absorption rate of
It was 30.5.

Example 5 Instead of acrylic acid in Example 2, 30 g of acrylic acid
And a mixture of 2-hydroxyethyl methacrylate (3.5 g) were used. Other than that, the same formulation and operation as in Example 2 were carried out to obtain a water-absorbent composite.

The particle size of the super absorbent polymer in this water absorbent composite is 150.
˜300 μm, no residual monomer was observed.

The water-absorbent composite had a physiological salt water absorption capacity of 65.5 and a water absorption rate of 28.5.

Example 6 30 g of acrylic acid was placed in a 100 cc conical flask, and 9.3 g of pure water was added thereto and mixed. Under ice-cooling, 20.6 g of potassium hydroxide (85% by weight) was gradually added to neutralize and the temperature was maintained at 70 ° C. The degree of neutralization is about 75%, and the monomer concentration in the aqueous solution is about 74.
It became weight%. 0.015 g of polyethylene glycol diacrylate was dissolved in this solution.

Separately, as a radical polymerization initiator, 2,2-azobis- (2-
0.2 g of amidinopropane) dihydrochloride was dissolved in 1.0 g of water.

Separately, 0.5321 g of polyester non-woven fabric was sampled and kept at about 70 ° C. in a constant temperature bath. Immediately after the radical polymerization initiator aqueous solution was mixed with the monomer aqueous solution, the non-woven fabric was sprayed from a spray nozzle. Polymerization immediately occurred in the nonwoven fabric, and a superabsorbent polymer consisting of partially neutralized potassium polyacrylate was stably fixed to the polyester nonwoven fabric to obtain a water-absorbent composite.

The amount of the applied monomer was 10 times the weight of the nonwoven fabric, and the particle size of the super absorbent polymer was 100 to 300 μm. The water-absorbent composite had a physiological saline water absorption capacity of 65.3 and a water absorption rate of 32, and no residual monomer was observed.

Example 7 26.9 g of 25% aqueous ammonia was placed in a 100 cc conical flask,
Gradually add 30 g of acrylic acid while cooling to neutralize 70
The temperature was raised to ° C. The degree of neutralization was 95%, and the monomer concentration in the aqueous solution was about 55% by weight. 0.0085 g of N, N'-methylenebisacrylamide was taken as a cross-linking agent and dissolved.

Separately, as a radical polymerization initiator, 2,2-azobis- (2-
0.2 g of amidinopropane) dihydrochloride was dissolved in 1.0 g of water.

Separately, 0.4126 g of polyester non-woven fabric was taken and kept at about 70 ° C. in a constant temperature bath. Immediately after the radical polymerization initiator aqueous solution was mixed with the monomer aqueous solution, the non-woven fabric was immediately sprayed from the spray nozzle. Polymerization immediately occurred in the nonwoven fabric, and a superabsorbent polymer consisting of partially neutralized ammonium polyacrylate was stably fixed to the polyester nonwoven fabric to obtain a water absorbent composite.

The amount of the applied monomer was 11 times the weight of the nonwoven fabric, and the particle diameter of the super absorbent polymer was 80 to 200 μm. The water-absorbent complex had a physiological salt water-absorption capacity of 58.6 and a water-absorption rate of 24.6, and almost no residual monomer was observed.

Comparative Example 1 By the same procedure as in Example 1, a partially neutralized sodium acrylate aqueous solution containing a neutralization degree of 75% and a monomer concentration in the aqueous solution of about 45% by weight was prepared. This was sprayed onto a polyester non-woven fabric from a spray nozzle to apply and impregnate it. The amount of the impregnated monomer was 13 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 result of measuring the physiological salt water absorption capacity of this water-absorbing complex was 25.0.
The water absorption rate is 18.0, and the residual monomer is
It was hardly recognized.

Comparative Example 2 By the same procedure as in Example 6, a partially neutralized potassium acrylate aqueous solution containing a neutralization degree of 75% and a monomer concentration in the aqueous solution of about 74% by weight was prepared. This was sprayed onto a polyester non-woven fabric from a spray nozzle to apply and impregnate it. The amount of the impregnated monomer was about 10 weight based on the nonwoven fabric. The nonwoven fabric impregnated with the partially neutralized potassium acrylate monomer 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 potassium polyacrylate was stably fixed to a polyester nonwoven fabric to obtain a superabsorbent composite.

Results of measuring the physiological saline absorption capacity of the water-absorbent complex 1
It was quite small at 8.5. The water absorption rate is 10.
It was 5 and almost no residual monomer was observed.

Comparative Example 3 By the same procedure as in Example 1, a partially neutralized sodium acrylate aqueous solution containing a neutralization degree of 75% and a monomer concentration of about 45% by weight in the aqueous solution was prepared. 0.0085 g of N, N'-methylenebisacrylamide was taken and dissolved in this as a crosslinking agent. A polyester non-woven fabric was impregnated with this aqueous monomer solution at 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, and the physiological salt water-absorption capacity was measured to be 16.5 and the water absorption rate was 2.
It was as small as 9.

Comparative Example 4 By the same procedure as in Example 6, a partially neutralized potassium acrylate aqueous solution containing a neutralization degree of 75% and a monomer concentration in the aqueous solution of about 74% by weight was prepared. 0.010 g of N, N'-methylenebisacrylamide was taken as a cross-linking agent and dissolved. A polyester nonwoven fabric was impregnated with this aqueous monomer solution by spraying and kept at 70 ° C. The amount of the impregnated monomer was 10 times the weight of the nonwoven fabric. To this 16.7% by weight 2,2
-Azobis (2-amidinopropane) dihydrochloride aqueous solution was sprayed from the spray nozzle to immediately initiate polymerization.

However, the obtained water-absorbent composite had a strong monomer odor because only the upper layer of the nonwoven fabric was polymerized as in Comparative Example 3. (The residual monomer amount was about 12.1% by weight.) Then, the mixture was kept at 90 ° C. for another 30 minutes and dried under reduced pressure at the same temperature. The water absorption capacity of this water absorbent composite was 14.2 and the water absorption rate was 2.9, which was extremely small.

〔The invention's effect〕

The water-absorbent composite obtained by the production method of the present invention has the above-mentioned special disclosure 57- as apparent from the above-mentioned Examples and Comparative Examples.
Compared with the methods disclosed in JP-A-500546 and JP-A-60-149609, the water absorption performance and water absorption speed are particularly large, and there is almost no residual monomer, and the safety is high. Furthermore, since its form is sheet-like, it is easier to handle and cheaper than powdered superabsorbent resins that have been used conventionally, and therefore it can be used for various sanitary materials such as sanitary napkins, paper, and diaper. It can be used advantageously in manufacturing. Further, by utilizing its excellent water absorption performance and handleability, it can also be used for the production of various materials for gardening or agriculture such as a soil improving agent and a water retention agent, which have recently received attention.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // A61F 13/15 13/46

Claims (5)

[Claims] 1. Aqueous solution of acrylic acid obtained by neutralizing 20% or more of carboxyl groups with an alkali metal salt or an ammonium salt and a polymerizable monomer containing acrylic acid as a main component (hereinafter referred to as acrylic acid-based monomer). Is applied to a molded fibrous substrate, and then the acrylic acid-based monomer is polymerized to produce a water-absorbing composite composed of a superabsorbent polymer and a molded fibrous substrate. After premixing the aqueous solution of the acid monomer and the water-soluble radical polymerization initiator or the water-soluble polymerization initiator and the water-soluble reducing agent uniformly, the superabsorbent polymer particle size in the fibrous substrate is 30 to 500.
A method for producing a water-absorbing composite comprising a superabsorbent polymer and a molded fibrous substrate, which comprises applying the mixture to a fibrous substrate formed into a mist so as to have a particle size of μm, and then polymerizing the mixture. 2. An acrylic acid-based monomer containing 20 mol% or less of 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acryloylpropanesulfonic acid, methacrylic acid and alkali metal salts thereof. Or one or more copolymerizable monomers selected from the group consisting of ammonium salts, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and polyethylene glycol mono (meth) acrylate. The manufacturing method according to claim 1. 3. A cross-linking 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 ( One or two selected from the group consisting of (meth) acrylate, N, N'-methylenebis (meth) acrylamide, diallyl phthalate, diallyl malate, diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate The manufacturing method according to claim 3, which is as described above. 4. The method according to claim 1, wherein the fibrous substrate contains cellulosic fibers or polyester fibers. 5. The method according to claim 5, wherein 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.