JPS5962665A - Preparation of polymer having high water-absorption - Google Patents

Abstract

PURPOSE:To prepare a polymer having excellent water resistance and high rate of water-absorption, and suitable as a water-absorbing material, by compounding a crosslinking agent having a polyfunctional group reactive with carboxyl group, etc. with a hydrophilic polymer having carboxyl group and containing a specific amount of water. CONSTITUTION:The objective polymer is prepared by adding (A) 0.01-5.0wt% of a crosslinking agent (preferably polyglycidyl ether, etc.) having two or more functional groups reactive with carboxyl group (or carboxylate group) to (B) a water-containing hydrophilic polymer (generally polyacrylic acid or its salt) having carboxyl group (or carboxylate group) and adjusted to a water-content of 10-40wt% (based on the whole water-containing hydrophilic polymer) preferably prepared by the reverse-phase suspension polymerization, and the composition is crosslinked. The obtained composition is useful as a water-retaining agent for agricultural use, a water-absorbing agent for sanitary use, etc.

Description

[Detailed description of the invention] The present invention relates to a method for producing superabsorbent polymers.

More specifically, the present invention relates to a method for producing a water-absorbing material with excellent salt resistance and water absorption rate.

Conventionally, various water-absorbing materials such as paper and pulp have been used in the field of sanitary materials (napkins for fresh burial, disposable diapers) and in the agricultural field. When pressure is applied to water, a large portion of it is squeezed out.

In recent years, water-absorbing materials such as hydrolysates of starch-acrylonitrile graft polymers, modified cellulose ethers, and hydrolysates of methyl acrylate/vinyl acetate copolymers have been proposed as alternatives to these materials, and further improvements have been made. ing. However, these materials have poor water absorption ability and water absorption speed, so no satisfactory water absorption material has been obtained.

The present inventors have already proposed a water-absorbing material with unclear water-absorbing performance (Japanese Patent Publication No. 54-50710), and have also proposed a further improved water-absorbing material (Japanese Patent Application No. 56-45488,
(Patent application No. 56-43489).

However, since these water-absorbing materials are also made of polymeric materials, there is a problem that their performance in saline solutions is significantly reduced.
It was hoped that water-absorbing materials with low salt resistance would emerge as soon as possible.

We therefore proposed a polymer soaked in +1iit saltiness and water absorption rate that does not have this drawback. As a result, we have carefully determined how to obtain an effective solution by adding a cross-stripe agent to a hydrophilic polymer while controlling the water content in the hydrous material of the polymer within a specific range. Is it true that the resulting polymer has poor water absorption properties, especially salt resistance and water absorption rate? Heading: This invention is a big brother of the present invention.

In other words, ``Kine ψ'' refers to a hydrophilic polymer having a carboxyl group (or carboxylate group) whose water content h1 is adjusted to be 10 to 40%. The present invention provides a method for producing a superabsorbent polymer, which is characterized by crosslinking with a crosslinking agent having two or more functional groups capable of reacting with the polymer.

Conventionally, the main method for obtaining water-absorbing polymers is to cross-link a water-soluble polymer 2 slightly to make it 7 delta-like. 02) Cross-link the 4-height 7iIJ by adding gas 1 at two points either at the moment or after polymerization.

is being offered. Although some of the water-absorbing polymers obtained in this manner exhibit distinct properties, they do not satisfy all required performances. That is, the JPi-seeking properties of a water-absorbing polymer include 1) water absorption; 7. ,H:,2]
Water absorption and 6) gel strength can be cited, but it is generally accepted that there is a relationship between these properties, namely water absorption rate and water absorption rate, and conventional water-absorbing polymers are established on the balance of these factors. Because of this, each model was manufactured with 7Rs, whose performance was slightly sacrificed.

The present invention aims to improve these drawbacks and provide a method for producing an innovative water-absorbing polymer that satisfies the various performances required of super-absorbent polymers. This is what we provide.

The important points for achieving the purpose of the present invention are that the hydrophilic polymer has a carboxyl group (or carboxylate group) and that the water content of the hydrophilic polymer is
is the ratio of the time-determined range.

Hydrophilic polymers that can be used in the present invention include carboxylate (or carboxylate groups) in their constituent units.
er: 4jj The polymer size and polymerization method do not matter as long as it is suitable. Examples of materials that can be suitably used in the present invention include sodium polyacrylate produced by the reverse phase suspension polymerization method described in Japanese Patent Publication No. 54-30710, Japanese Patent Application Laid-open No. 56-26909, etc.
Also, aqueous solution polymerization (1) described in JP-A-55-153415
η1, which is exemplified by sodium polyacrylate obtained by thermal polymerization or thin film polymerization, and the starch-sodium acrylate graft Jπ combination described in Japanese Patent Publication No. 55-46199, etc., can be obtained. Further, when producing these polymers, the effects of the present invention are not hindered as long as a very small amount of crosslinking agent is added. Furthermore, it is desirable that these three ((') unions are self-assembling.

Since Kineri J uses heat to control the water content in the hydrous polymer, a dehydration step is normally required after the polymer is synthesized. For this reason, from the viewpoint of crop yield etc., the reverse phase suspension polymerization method is 71. ) is preferred. Polymers having carboxyl groups (or carboxylate groups) in their constituent units are generally polyacrylic 1
(and its salts), and polymethacrylic acid (and its salts), which can be preferably used in the method of the present invention.Also, acrylic acid or methacrylic acid, maleic acid, itaconic acid, acrylamide , 2-acrylamido-2-methylpropanesulfoneul, 2-(meth)
Copolymers prepared by copolymerizing comonomers such as acryloylethane sulfonate and 2-hydroxyethyl (meth)acrylate within a range that does not reduce the performance of the water-absorbing polymer may also be used in the method of Kiri J.

Is the crosslinking agent particularly important in the method of the present invention? Add,
This is a nail that collects moisture in a hydrophilic polymer hydrate when carrying out an elevating reaction. Conventionally, methods for producing water-absorbing polymers in which a crosslinking reaction is carried out after polymerization are known. Japanese Patent Publication No. 57-28505 describes a method of increasing the cross-A of polyacrylic acid (or its salt) in the presence of water.

However, the water content in these hydrous polymers is 5
The latter has a moisture content of 70% by weight or more, and the effect of 7) cannot be achieved with such a moisture content.

Usually, hydrophilic polymers have monomers of 45% or less,
That is, it is polymerized in an aqueous solution having a moisture content of 55% by weight or more. Therefore, one of the aspects of the present invention (in practice) is to reduce the water content in the hydrophilic polymer product obtained by conventional methods.
It is necessary to adjust jk.

According to the present invention, it is an essential condition that the moisture content is in the range of 10 to 40 weight percent (total weight loss of hydrophilic polymer water content).More preferably, it is 15 to 35 weight percent (total weight loss). ).If the water content in the hydrophilic polymer is outside the above range, the water absorption amount and/or water absorption rate will be poor, and the remarkable effects of the present invention will not be obtained.For example, in the present invention, the reverse Phase) The desired effect can be achieved by concentrating the polyacrylic acid polymer obtained by polymerization using the empiric suspension polymerization method and controlling the water content within the above range.

The crosslinking agent used in the present invention may be any compound having two or more functional groups capable of reacting with a carboxyl group (or carboxylate group). Such crosslinking agents include, for example, ethylene glycol diglycidyl ether,
Polyglycidyl ethers such as polyethylene glycol diglycidyl ether and glycidyl triglycidyl ether, helo-eboxy compounds such as epichlorohydrin and α-methylchlorohydrin, polyaldehydes such as glucuraldehyde and glyoxal, glycerin, pentaerythritol, ethylene glycol, etc. Examples include polyols and polyamines such as ethylenediamine.

Preferably, it is a polyglycidyl ether such as ethylene glycol diglycidyl ether.

The amount of crosslinking agent depends on the type of crosslinking agent and the type of polymer. Although it varies depending on the R class, it is usually 0.01 to 5 for the polymer.
．． An appropriate range is 0%. The amount of crosslinking agent added is 0.
If it is less than 0.01% by weight, the addition effect will be fully expressed; on the other hand, if it is more than 5.0% by weight, the crosslinking density will be
This results in a decrease in water absorption, which is not the intention of the present invention.

There are various methods for adding and reacting a crosslinking agent. That is, in the case of a polymer obtained by a reverse phase polymerization method (in the case of a polymer obtained by direct suspension polymerization method, a crosslinking agent is added in a state in which a hydrophilic polymer whose water content is adjusted to the range specified in the present invention is suspended in an organic solvent). In addition, a method of heat treatment is exemplified, and in the case of a thin film polymerization method, etc., the resulting polymer gel is crushed, the water content is adjusted by a drying process, and then this polymer is placed in a secondary tank and cross-linked there. An example of this method is to add a heat treatment agent and perform a crosslinking reaction.Heating is preferably performed at 41°C to 40'' to 150°C in order to carry out the crosslinking reaction smoothly.
It is preferable to react within this range.

By using the method of the present invention, it is possible to obtain a water-absorbing material with excellent salt resistance and water absorption rate, and it is very advantageous for use as a water-retaining agent for agriculture and a water-absorbing agent for sanitary materials. The superabsorbent polymer obtained by the method of the present invention can be particularly advantageously used in the field of disposable diapers, which do not need to quickly absorb large amounts of urine, and in the field of sanitary napkins, which must absorb blood. This can make it possible to eliminate leaks and discomfort.

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

In addition, the amount of water absorption in the following Examples and Comparative Examples is a value determined by the following operation. i.e. polymer approx. 1&'
a=One piece was placed in excess ion-exchanged water or physiological saline, allowed to swell sufficiently, and then filtered through 80 mesh gold Aj4. It is the value obtained by dividing by the initial polymer weight M(Wo).

In other words, water absorption amount (g/-9)-w/wo.

The water absorption rate was expressed as the value of physiological saline absorbed by Polymer 0.51 in 10 minutes.

Examples 1 to 3 A 500 ml four-necked 1M flask with a stirrer, a reflux condenser, a dropping tube, nitrogen gas, and an inlet tube was charged with 230 ml of cyclohexane. sorbitan monostear)
1.8 & was prepared and heated to 75°C.

Separately, in an Erlenmeyer flask, acrylic acid 30& was neutralized with caustic soda 13.4.9 dissolved in water 39I. The monomer concentration in the monomer aqueous solution was 45% (55% relative to water). Then, 0.1 g of potassium persulfate was added and dissolved.

This monomer aqueous solution was dropwise polymerized into the above-mentioned 4-hole flask in an indoor atmosphere for 1.5 hours, and then
The polymerization was completed by holding at °C for 0.5 hours. After this, water in the polymer is converted into cyclohexane by azeotropic dehydration (cyclohexane is refluxed). j (beggar 3
Controls were performed at 5%, 27%, and 20%, respectively.

After this, an aqueous solution of 0.05 g of ethylene glycol diglycidyl ether dissolved in 1 ml of water was added to each at 76°C.
After maintaining this temperature for 2 hours, the cyclohexane was removed, and the polymer was dried under reduced pressure at 80° to 100°C to obtain a water-absorbing polymer.

Example 4 Polymerization was carried out according to Example-1. Ethyl cellulose T-500 instead of sorbicun monostearate
, 5F was used. After the polymerization was completed, water molecules i and t in the polymer were controlled to 22% by azeotropic dehydration, and then 0.04 g of glycerin diglycidyl ether was added to 1 ml of water.
After adding the aqueous solution dissolved in
It was dried under reduced pressure at 0° to 100°C to obtain a water-absorbing polymer.

Example 5 Polymerization was carried out according to Example 4.1. It's c. However, the monomer concentration in the monomer aqueous solution is 65%, and further N, N'-
0.003 I of methylenebisacrylamide was added. After controlling the water content in the polymer to 27% by azeotropic dehydration after polymerization, an aqueous solution of 0.15 g of polyethylene glycol diglycidyl ether (n=9) dissolved in 1 rnl of water was added at 60°C. After holding for 3 hours, cyclohexane was removed and the polymer was heated to 80"~
It was dried at 110° C. under reduced pressure to obtain a water-absorbing polymer.

Example-6 Caustic soda 13 in which 30 g of acrylic acid was dissolved in 39 I of water
．． 4g, and the monomer concentration in the monomer aqueous solution is 4g.
It became 5%. Then, the persulfuric acid sorter o, 19y was added and dissolved. This aqueous monomer solution was poured into a thin film between two Teflon plates and held at 656 for 3 hours to polymerize. The resulting polymer gel was cut into 36 pieces and dried in a hot air dryer until the moisture content reached 60%.

This product was placed in a kneader, and an aqueous solution of 0.0311 ethylene glycol diglycidyl ether dissolved in 1 rnl of water was sprayed on it and held at 70°C for 1 hour.
The resulting polymer was dried under reduced pressure at 0° C. and pulverized to obtain a water-absorbing polymer having a center particle size of 100 to 250 μm.

Example 1 Polymerization was carried out according to Example 1. However, 0.033 g of ethylene glycol diglycidyl ether was added to the aqueous monomer solution, and cross-linking was carried out simultaneously with the polymerization. After the polymerization was completed, the cyclohexane was removed and the polymer was reduced to 80″′
It was dried under reduced pressure at ~100°C to obtain a water-absorbing polymer.

Comparative Example-2 Polymerization was carried out according to Example-1. However, after the completion of polymerization, an aqueous solution of 0.031 ethylene glycol diglycidyl ether dissolved in 1 ml of water (the water content of the water-containing polymer is 5
5%) and held at 73°C for 1 hour. After the completion of the reaction, the cyclohexane was removed and the polymer was
It was dried at 100° C. under reduced pressure to obtain a water-absorbing polymer.

Comparative Example-3 Polymerization was carried out according to Example-1. However, an aqueous solution of 0.03 I of ethylene glycol diglycidyl ether dissolved in 1 ml of water was subjected to azeotropic dehydration pressure to remove water a in the polymer.
It was added at a controlled time to 45% of the liquid and incubated at 60°C for 2 hours.
II: Note.

After the crosslinking reaction was completed, cyclohexane was removed and the polymer was
Dry under reduced pressure at 0' to 100°C to form a water-absorbing polymer 7! 'Obtained.

Comparative Example-4 After polymerization was carried out according to Example-1, cyclohegysan was removed and the product was dried under reduced pressure at 70° to 80°C. The water content, a, of this polymer was 7%. This polymer was again dispersed in cyclohexane (8M), and an aqueous solution prepared by dissolving 0.03.9'f of ethylene glycol diglycidyl ether in 1me of water was added thereto and held at 70°C for 1 hour. The cyclohexane was then removed and the polymer
It was dried under reduced pressure at 0' to 100°C to remove the water-absorbing polymer. Table 1 shows the water absorption amount and water absorption rate of each water absorbing polymer obtained in Examples 1 to 6 and Comparative Examples 1 to 4.

Clothing-1 From Table-1, it is clear that the polymer obtained through the inventive process exhibits excellent salt resistance and water absorption rate.

Applicant's agent: Kaoru Furuya Procedural amendment (spontaneous) August 4, 1981 Director of the Japan Patent Office Kazuo Wakasugi 1, Indication of the case Patent application No. 155097/1983 2, Name of the invention: Super absorbent polymer Manufacturing method 6, relationship with the case of the person making the amendment Patent applicant (091) Kao Soap Co., Ltd. 4, column 6 for claims and detailed description of the invention in the attorney's specification,
Contents of the amendment (1) Percentage The scope of the claim has been revised in the attached document as follows: ``When a reversed-phase suspension polymerization method is adopted as the polymerization method, persulfates, etc. are An aqueous solution of a hydrophilic monomer having a carboxyl group (or carboxylate group) containing a water-soluble initiator is subjected to reverse phase suspension polymerization using a retained colloid in a non-aqueous solvent.Sorbitan is used as a protective colloid at this time. Sorbitan fatty acid esters such as monostearate and sorbitan monolaurate, cellulose ethers such as ethyl cellulose and benzyl cellulose, cellulose esters such as cellulose acetate, cellulose butyrate, and cellulose acetate butyrate, maleated polybutadiene, maleated polyethylene, maleated α - Examples include polymeric dispersants such as olefins, and any one or more of these may be used. Also, non-aqueous solvents used at that time include aliphatic hydrocarbons such as hexane, heptane, and octane, and cyclohexane. , alicyclic hydrocarbons such as methylcyclohexane and decalin, aromatic hydrocarbons such as benzene, toluene and xylene, and chlorobenzene.

Examples include halogenated hydrocarbons such as bromobenzene and dichlorobenzene. 2. Claim 1 Adjusted so that the moisture content is 10 to 40% by weight.
It is characterized by crosslinking a hydrated hydrophilic polymer having fc carboxyl groups (or hacarboxylate groups) with a crosslinking agent having two or more functional groups capable of reacting with carboxyl groups (or carboxylate groups). A method for producing superabsorbent polymers.

Claim 1: The hydrophilic polymer having a carboxyl group (or carboxylate group) is a polymer or copolymer of acrylic acid (or an alkali salt of acrylic acid).
A method for producing a superabsorbent polymer according to item 1 or 2.

j A method for producing a superabsorbent polymer in which the crosslinking agent is polyglycidyl ether.

2. Claim 1 A hydrophilic polymer having a carboxyl group (or carboxylate group) whose water content is adjusted to have a moisture content of 10 to 40% by weight is reacted with a carboxyl group (or carboxylate group). 1. A method for producing a superabsorbent polymer, which comprises crosslinking with a crosslinking agent having two or more functional groups.

2. The hydrophilic polymer according to claim 1, wherein the hydrophilic polymer is a hydrophilic polymer obtained by reverse-phase suspension polymerization of an aqueous solution of a hydrophilic monomer having a carboxyl group (or carboxylate group) containing a water-soluble initiator. A method for producing superabsorbent polymers.

6 Claim 1 in which the hydrophilic polymer having a carboxyl group (or carboxylate group) is a polymer or copolymer of acrylic acid (or an alkali salt of acrylic acid)
A method for producing a superabsorbent polymer according to item 1 or 2.

4. The superabsorbent polymer according to claim 1, 2, or 3, wherein the crosslinking agent is a polyglycidyl ether.
manufacturing method.

Claims (1)

[Scope of Claims] 1. Water content of a hydrophilic polymer having a carboxyl group (or carboxylate group) adjusted to have a water content of 10 to 40% by weight is Two or more functional groups that can react with Noj()?
1. A method for producing a superabsorbent polymer, characterized in that cross-linking is carried out using a cross-linking agent. 2. A method for producing a claimed polymer, wherein the hydrophilic polymer having a carboxyl group (or carboxylate group) is a polymer or co-polymer of acrylic acid (or an alkali salt of acrylic acid). 6. Patent 6l in which the crosslinking agent is polyglycidyl ether
A method for producing a superabsorbent polymer according to Item 1 of V.