JPS6295307A - Method for producing bead-shaped self-crosslinking water-absorbing polymer - Google Patents

Abstract

PURPOSE:To obtain an easily crushable polymer having large particle diameter keeping the water absorption and gel strength in water-absorbed state, by polymerizing an acrylic acid monomer in the presence of a specific surfactant and hydroxyethyl cellulose in the absence of a crosslinking agent. CONSTITUTION:Acrylic acid or an acrylic acid/methacrylic acid mixture and an alkali metal salt of acrylic acid or an acrylic acid/methacrylic acid mixture (hereinafter abbreviated as acrylic acid monomer) are polymerized by W/O-type reverse-phase suspension polymerization in the presence of water, a water-soluble radical polymerization initiator (e.g. hydrogen peroxide, persulfate, etc.), a dispersion medium (e.g. cyclohexane) and a surfactant. The surfactant is preferably a copolymer of 16-60C alpha-olefin and an alpha,beta-unsaturated polybasic carboxylic acid anhydride (e.g. maleic anhydride) or its derivative. The polymerization is carried out in the presence of hydroxyethyl cellulose in the aqueous phase in the absence of a crosslinking agent keeping the acrylic acid monomer concentration of 30wt% - saturated concentration based on water after neutralization.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has excellent water absorption properties, and has excellent water absorption strength.
The present invention relates to a method for safely producing a superabsorbent polymer having large particles that can be easily crushed.

[Industrial application field]

The polymer obtained by the production method of the present invention has excellent water absorption and swells when it absorbs a large amount of water, but it is insoluble in water, has a high water absorption strength, has a large particle size, and the polymer itself Since it can be easily pulverized, it can be advantageously used in the production of various absorbent materials or materials that are used in a swollen state after absorbing water.

[Prior art]

Conventionally, paper, pulp, nonwoven fabric, sponge-like urethane resin, etc. have been used as water-retaining agents in sanitary napkins, paper diapers, various sanitary materials, and various agricultural materials. However, these materials absorb only 10 to 50 times their own weight, so in order to absorb or retain a large amount of water, a large amount of material is required, which not only makes them extremely bulky, but also makes them extremely bulky. However, there were drawbacks such as the fact that when pressurizing a material that has absorbed water, the water easily separates.

In order to improve the above-mentioned drawbacks of this type of water-absorbing material, various highly water-absorbing polymeric materials have been proposed in recent years. For example, starch graft polymers (Japanese Patent Publication No. 53-46199, etc.), cellulose modified materials (I\J 1987-803, etc.)
Publication No. 76, etc.), crosslinked products of water-soluble polymers (Special Publication No. 1976, etc.)
23462, etc.), self-crosslinking acrylic acid alkali metal salt polymers (Japanese Patent Publication No. 54-30710, etc.),
etc. were proposed.

However, these superabsorbent polymer materials are still insufficient in terms of water absorption, and have low glue strength when water is absorbed.
In addition, in the above publication, the polymer obtained by drying is extremely hard, making it difficult to crush easily and requiring a large mechanical crushing force, which causes many problems in production on a practical or industrial scale. have.

The present inventors have already proposed a method for producing a water-absorbing material that improves the above-mentioned drawbacks of conventional water-absorbing materials, but the water-absorbing material produced by the method disclosed in the above-mentioned publication also has various drawbacks. . That is, in Japanese Patent Application No. 59-275308, a nonionic surfactant with T (LB of 3 to 6) is used as a surfactant in a water-in-oil reverse phase suspension polymerization method, so the polymerization reaction is extremely stable. However, the resulting polymer has a particle size of 100 μm or less, making it an extremely fine powder.For this reason, when handling powder, dust countermeasures are required.Furthermore, the glue strength upon water absorption is still insufficient. However, in order to achieve better shape retention, a copolymer of α-OVfin and α,β-unsaturated polyhydric caldic acid anhydride or a derivative thereof is used as a surfactant, and it is present in the polymerization reaction system. By setting the acrylic acid monomer concentration to the water to be 30% by weight or more and polymerizing in the absence of a crosslinking agent, the polymer has extremely high water absorption capacity, high glue strength, large particle size, and easy polymerization. We demonstrated a method for producing bead-shaped self-crosslinking water-absorbing polymers that can be crushed into powder.

However, in the above method, as a result of extensive detailed study, it was found that during the polymerization reaction, suspended particles tend to adhere to each other, resulting in a lumpy state and causing abnormal polymerization, which is not only extremely dangerous in terms of operation, but also However, it was found that it was difficult to obtain the desired bead-shaped water-absorbing polymer. In addition, the polymer obtained by the above method is characterized by having a particle size of 100 μm or more and a narrow distribution, but the polymer particle size is also up to 50 μm.
It is about 0 μm, and it is impossible to obtain giant particles of 500 μm or more.

[Problem that the invention seeks to solve]

The present invention improves the above-mentioned drawbacks, and produces in a safe and graceful manner a super absorbent polymer that maintains water absorbency and glue strength during water absorption, has a significantly larger polymer particle size, and can be easily crushed. The purpose is to provide a method.

[Means for solving problems]

As a result of repeated research in order to solve the above-mentioned problems, the inventor of the present invention discovered the solution of the above-mentioned Japanese Patent Application No. 193404/1983 by adding and dissolving hydroxyethylcellulose in the aqueous phase of the polymerization reaction system and polymerizing it. , dead weight 7
We have discovered that it is possible to safely produce a superabsorbent polymer that has a water absorbency of 00 times or more, has a high glue strength, and has an extremely large polymer particle size of about 3,000 μm at maximum, and has completed the present invention. It was.

That is, the present invention involves mixing acrylic acid or an acrylic V-methacrylic acid mixture and an alkali metal salt monomer of acrylic acid or an acrylic acid/methacrylic acid mixture with an oil in the presence of water, a water-soluble radical polymerization initiator, a dispersion medium, and a surfactant. In a method of polymerizing by a medium drop type reverse phase suspension polymerization method, (
a) Using a copolymer of α-olefin and α,β-unsaturated polycarboxylic acid anhydride or a derivative thereof as a surfactant, (b) Presence of hydroxyethylcellulose in the aqueous phase, (c) Water The acrylic acid monomer concentration for (d
) A method for producing a bead-like self-crosslinking water-absorbing polymer, which is characterized by polymerizing in the absence of a crosslinking agent.

[Background and characteristics of the invention]

In the water-in-oil type reverse-phase suspension polymerization method of the present invention, the copolymer of α-olefin and α,β-unsaturated polycarboxylic acid anhydride or its derivative used as a surfactant is:
Japanese Patent Application Laid-open No. 57-74309 previously disclosed a method for producing bead-shaped water-soluble polymers, but as mentioned above, the present inventors have already applied this technology in Japanese Patent Application No. 193404-1983. We proposed a new method for producing bead-like self-crosslinking water-absorbing polymers.

However, in this method, as mentioned above, during the polymerization reaction, the suspended polymer particles tend to adhere to each other, resulting in a lumpy state and abnormal polymerization, which is not only extremely dangerous for operation, but also It was found that it was difficult to obtain bead-shaped water-absorbing polymers.

As a result of intensive research into methods for preventing abnormal polymerization in the above production method, the present inventors further added and dissolved hydroxyethyl cellulose in the aqueous phase and polymerized it, while maintaining water absorption performance and water absorption glue strength. I have found a way to completely prevent scales. Furthermore, it has been found that the particle size of the obtained polymer can be arbitrarily controlled by changing the amount and type of hydroxyethyl cellulose added, and that a giant bead-shaped polymer with a particle size of about 3.000 μm can be obtained.

In general, water absorption amount and water absorption gluing strength show contradictory tendencies. That is, in order to increase the water absorption i', it is necessary to reduce the crosslinking ratio for insolubilization of the polymer as much as possible, but on the other hand, the water absorption glue strength decreases.

Therefore, in order to increase the water absorption glue strength, it is necessary to increase the crosslinking ratio, but in order to obtain a sufficiently satisfactory water absorption glue strength, the amount of water absorption is usually at a level that is difficult to put into practical use, that is, 300 times its own weight. The reality is that it becomes a process. That is, polymers obtained by a method other than the method of the present invention, such as aqueous solution polymerization or solution polymerization in the presence of a bifunctional divinylated metal or a bifunctional compound that can react with a carboxyl group, are free of these crosslinking agents. Even if the amount is reduced as much as possible, the amount of water absorbed is at most 100 times its own weight, and this product itself has extremely low water absorption strength and becomes paste-like, so the amount of crosslinking agent is increased to obtain a sufficiently satisfactory water absorption strength. If the weight is increased, the amount of water absorbed will be less than 300 times its own weight.

The polymer produced according to the present invention has a particle size of 70% of its own weight.
0 times or more, and has the characteristics of high glue strength.

Super absorbent polymers with such characteristics are produced by using conditions that cause a crosslinking reaction in reverse phase suspension polymerization as described above, and by using α-olefin and α-olefin as surfactants.
Production becomes possible only by using a copolymer with β-unsaturated polycarboxylic acid anhydride or a derivative thereof and by adding and dissolving hydroxyethyl cellulose in the aqueous phase.

Japanese Patent Laid-Open No. 56/1989 discloses a method for obtaining a super absorbent polymer by containing hydroxyethylcellulose in the aqueous phase and polymerizing an acrylic acid alkali metal salt monomer by a water-in-oil reverse phase suspension polymerization method without using a crosslinking agent. It is shown in the publication No.-76419. The water absorption amount of the polymer obtained by this method is relatively high, 600 to 700 times its own weight, but since norbitane fatty acid ester with HLB 3 to 6 is used as a surfactant, the water absorption strength is extremely weak. Poor durability. Although the polymer obtained by this method has a fairly large particle size of several hundred μm, it is difficult to obtain it with good uniformity, and it is usually as small as about 10 μm to about 500 μm. It has a wide distribution, including some quite large ones.

Furthermore, when polymerized by this method, the water-containing polymer after polymerization has some stickiness, so it tends to stick to the stirrer and reactor walls, and it is difficult to remove water during post-treatments such as dehydration following polymerization. Part polymer particles adhere to each other, and in extreme cases, they become lumpy, which poses a serious problem in process operation.

Furthermore, when the polymer is dried, it becomes extremely hard and cannot be easily pulverized.

The present invention solves the above-mentioned problems and has a high water absorption capacity without reducing the water absorption amount, specifically, has a water absorption capacity of 700 times or more than its own weight, and has an average particle size of 100 μm or more. The present invention provides a method for safely and easily producing a superabsorbent polymer having a high water absorption and a narrow distribution, and this is the most distinctive feature of the present invention.

(1) Monomer 1 The monomer used in the polymerization reaction of the present invention is acrylic acid or a mixture of acrylic acid and methacrylic acid containing 20 mol or less of methacrylic acid, and 50 mol % or more of the total rubixyl group, Preferably, the acrylic acid monomer has 60 moles or more partially neutralized with an alkali metal salt. In the case of a mixture of acrylic acid and methacrylic acid, it is possible to contain up to 20 mol% of methacrylic acid, but as the amount of methacrylic acid increases, the amount of water absorbed becomes significantly smaller, and the soluble The content of methacrylic acid is preferably 10 moles or less, since the content of methacrylic acid is preferably 10 moles or less. As mentioned above, the degree of neutralization is such that at least 50 moles, preferably at least 60 moles of the total rubixyl groups are converted to alkali metal salts. If the degree of partial neutralization becomes too low, the amount of water absorbed will drop significantly and the resulting water absorption delta strength will also be extremely weak.

Alkali metal hydroxides, bicarbonates, etc. can be used to neutralize the acid monomer, but alkali metal hydroxides and bicarbonates are preferably used.
It is a hydroxide, and specific examples thereof include sodium hydroxide, potassium hydroxide, and hydroxide. Sodium hydroxide is most preferred in terms of industrial availability, price, and safety.

(2) Water-soluble radical polymerization initiator The radical polymerization initiator used in the production method of the present invention is a persulfate such as potassium persulfate or ammonium persulfate, or hydrogen peroxide. These water-soluble radical initiators may be used in combination, or i! A combination of all injectable substances, amines, etc. may be used as a redox type initiator.

The amount of these persulfates and hydrogen peroxide used is 0.01 to 5% by weight, preferably 0.1 to 1% by weight, based on the neutralized acrylic acid monomer.

Note that if other water-soluble initiators are used as radical polymerization initiators, for example, azo compounds such as butylhydromonooxide, gun) dihydrochloride, the resulting polymer will not be water-soluble. It is not possible to achieve all goals.

(3) Surfactant The surfactant used in the production method of the present invention is α
- A copolymer of an olefin and an α,β-unsaturated polycarpinic acid anhydride or a derivative thereof. The α-olefin has 10 to 100 carbon atoms, preferably 16 to 60 carbon atoms.
It is.

Further, examples of the α,β-unsaturated polycarpinic acid anhydride include maleic anhydride, citraconic anhydride, itaconic anhydride, etc. Among these, maleic anhydride is preferred.

Derivatives of these copolymers include partially esterified or partially amidated copolymers. Partially esterified products include copolymer monomethyl ester, monoethyl ester, moptyl ester, and the like.

Further, examples of partially amidated copolymers include copolymers of monoethylamide, monopropylamide, moptilamide, and the like.

The molecular weight of the above copolymer or its derivative is 2000 to 10
0,000, preferred, 10.000-50.000
It is.

Furthermore, in the present invention, when the α-olefin/α,β-unsaturated polycarnoic acid anhydride copolymer is used, even if it is in an acid anhydride state or in a partially or completely ring-opened state. It's okay.

The amount of these surfactants used is 0.0
The amount is 1 to 10% by weight, preferably 0.05 to 5% by weight.

(4) Dispersion medium In principle, any liquid can be used as the dispersion medium used in the present invention as long as it does not participate in polymerization and does not mix with water. For example, aromatic hydrocarbons such as benzene, ethylbenzene, toluene, and xylene; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclooctane, and karin; aliphatic hydrocarbons such as hexane, pentane, hebutane, and octane; Hydrocarbons such as benzene, brobenzene, dichlorobenzene, etc. are produced in purple. Among these, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and aliphatic hydrocarbons such as hexane and heptane are particularly preferred.

Further, these dispersion media can be used alone or in combination of two or more.

The amount of these dispersion media to be used is 0.5 to 10 times the volume of monomer water @liquid volume, in order to make the polymerization reaction system water-in-oil type, and from the standpoint of removing heat of polymerization reaction. It is preferable to increase the amount by 1 to 5 times.

(5) Water In the polymerization reaction solution of the present invention, water and acrylic acid monomer are present in the proportions described above (this point will be explained in more detail later).

Further, water and dispersion medium are used in such a ratio that the dispersion medium is 0.5 to 10 times the volume of the aqueous phase, that is, the monomer aqueous solution, preferably 1 to 5 times the volume, as described above. is desirable. If the ratio of water to the dispersion medium becomes too large, it becomes extremely difficult to remove the heat of polymerization, making it impossible to obtain a stable water-in-oil type suspension system. However, if the ratio of water to dispersion medium washing is too small, the monomer concentration per unit patch will be low, productivity will be poor, and this will be economically disadvantageous.

As mentioned above, it is generally preferable to add water to the reaction system in the form of water that completely dissolves the neutralizing agent that neutralizes the acid monomer, but a portion of the water can be added separately using an appropriate method It is also possible to add In addition, some water is also generated by a neutralization reaction between an acid monomer and a neutralizing agent.

In the present invention, the acrylic acid monomer detailed above is used as a water-soluble radical polymerization initiator, a dispersion medium, a surfactant,
Polymerization is carried out by a water-in-oil reverse phase suspension polymerization method in the presence of water and water, but as described above, the water present in the polymerization reaction system at that time must be included in the polymerization reaction system. This constitutes two essential structural requirements. That is, if the monomer concentration after neutralization is 30% by weight or less, the obtained polymer will have a large water-soluble portion and the obtained water absorption strength will be low, making it impossible to achieve the object of the present invention.

(6) Hydroxyethylcellulose When used in the present invention, hydroxyethylcellulose is added and dissolved in an aqueous phase having an acrylic acid monomer concentration of 30% by weight or more, but as long as it can be dissolved in the aqueous solution. It may be something that is under your control. Specific examples include degree of etherification (value indicating whether or not the middle shell of the three OH groups in the glucose unit forming the cellulose unit is etherified) 0.4 to 2, mole of ethylene oxide added The number (number of moles of ethylene oxide added per one Glucose unit) is preferably 1 to 5.

When the degree of etherification and the number of added moles are smaller than the above values, hydroxyethyl cellulose becomes insoluble in an aqueous acrylic acid monomer solution with a concentration of 30 M (at% or more) and cannot be used in the present invention.

The addition W Id of hydroxyethylcellulose is 0.1 to 20% by weight, preferably 0.5 to 10M'; 4% based on the acrylic acid monomer.

(7) Polymerization conditions Typical embodiments of the polymerization reaction of the present invention are as follows. That is, hydroxyethyl cellulose and a water-soluble polymerization initiator are added and melted to a previously neutralized monomer aqueous solution, and an inert gas such as nitrogen is introduced to perform deaeration. On the other hand, put the surfactant in the dispersion medium, heat it slightly if necessary to dissolve it,
Introduce an inert gas such as nitrogen and perform deaeration. All of the above aqueous seven-mer solution is poured into this and heated to a predetermined temperature. During this time, the aqueous solution portion of the reaction system becomes minute droplets and is dispersed and suspended in the dispersion medium. After initiation of polymerization, cooling or heating is performed as appropriate depending on the state of heat generation.

The polymerization reaction temperature of the present invention is 60 to 100°C, preferably 60 to 80°C. Will it be formed if the reaction temperature is too low? Rimmer 〇 The soluble portion increases and the water absorption performance decreases, and the higher the height, the greater the variation in water absorption performance, making it difficult to form a homogeneous polymer.

The polymerization reaction of the present invention is carried out in a suspension polymerization system of the water-in-oil type, but as mentioned above, it is necessary to combine the α-olefin and α,β-unsaturated polyhydric cal. Using a copolymer with phosphoric acid anhydride or a derivative thereof, and not adding and dissolving hydroxyethyl cellulose in the aqueous phase, adjusting the ratio of dispersion medium and water appropriately, and performing appropriate stirring, etc. The goal can be achieved by clarifying the means.

However, the stirring of the polymerization reaction system in the present invention is carried out by
It is important not only to maintain the desired stable water-in-oil type suspension system in the yarn, but also to improve the properties of the resulting polymer.

In other words, if the stirring is too strong, the fine hydrogel primary particles of the produced polymer will aggregate and form a lump, or the crosslinked structure will be broken and a partially water-soluble polymer will be produced. The variation in performance increases.

Furthermore, if the stirring is too weak, a stable dispersion system will not be obtained and abnormal polymerization will occur, resulting in failure to form beads, and the water absorption performance of the obtained solid polymer will also be significantly reduced. Therefore,
Appropriate stirring is required, but when using a polymerization reactor equipped with a normal stirrer for carrying out this type of suspension polymerization, the stirring speed is 100 to 600 rpm, preferably 20 rpm.
0-4o.

By stirring at rpm, bead-shaped polymers that have excellent water absorption properties and water absorption dull strength and are easy to crush can be obtained with good reproducibility.

(8) Separation of polymer The polymer obtained by the production method of the present invention consists of wet, bead-like particles, and can be easily separated from the dispersion medium by decantation or evaporation. Then, by drying the separated wet polymer at a temperature of, for example, 120° C. or lower, a powdered polymer or a powdered polymer containing easily pulverized lumps can be obtained. The polymer thus obtained usually has a diameter of 100 μm or more and a narrow distribution, and the surface is covered with a surfactant and contains a small amount of spherical primary particles or secondary particles that are partially agglomerated. It is the body. These secondary particles can also be easily pulverized by a small amount of mechanical force. Is this t? There are significant advantages in the production and use of +1 mer.

[Effects of invention, etc.]

As mentioned above, the polymer obtained by the production method of the present invention has a high water absorption performance of over 700 times its own weight, and has a high water absorption glue strength. The remer itself is a powder from the beginning, or can be easily made into a powder by an extremely simple crushing operation.

Therefore, the polymer obtained by the production method of the present invention can be advantageously used in the production of sanitary napkins, paper diapers, etc., and other sanitary materials by utilizing its excellent water absorption performance.

It is also used in the production of various materials for horticulture and agriculture, including soil conditioners and water retention agents, which have recently been attracting attention due to their excellent water absorption performance and glue strength. be able to.

The present invention will be explained in more detail below with reference to Examples and Comparative Examples.

Note that the pure water absorption capacity and water absorption glue strength described in these examples are the results measured by the following test method.

A. Approximately 0.5 g of polymer and approximately 11' of water in a beaker with pure water absorption capacity of 1.
After each was weighed and mixed, it was left to stand for about 2 hours to sufficiently swell the polymer with water. Next, after draining with a 100 sieve filter, the filtrate fe is weighed, and the pure water absorption capacity is calculated according to the following formula.

B. Water Absorption Glue Strength 2 Add 200 times its own weight of pure water to the Rimmer to absorb water, check the strength of the water absorption glue by pressing the elasticity of the obtained water absorption glue with your fingers, and evaluate it according to the following criteria. Just in case.

×: Weak Δ: Slightly weak ○: Normal (standard) ■: Slightly strong 01 Strong Example 1 In a 500-capacity four-neck round bottom flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, Add 185g of cyclohexane, and add α-olefin and maleic anhydride copolymer (Mitsubishi Kasei's split product name "Diakarna 30")
, molecular weight approximately 10,000) was added and dissolved, and the internal temperature was set to 65° C. under a nitrogen gas atmosphere.

Separately, in a conical flask with a capacity of 200 g, add 3 acrylic acid.
While externally cooling 09, 12.9.9 of caustic soda in which 499 of water was dissolved was added to neutralize 77.4% of CalR xyl groups.

The monomer concentration with respect to water in this case corresponds to 401 Jt% as the monomer concentration after neutralization.

Next, 0.99 of hydroxyethyl cellulose (degree of etherification = 1, number of moles of -EO added = 2) and 0.19 of potassium persulfate were added and dissolved.

The contents of this 200 d flask were added to the contents of the four-neck round bottom flask, and polymerization was carried out at 65 to 70° C. for about 1 hour while stirring. Note that stirring was performed at 400 rpm.

When stirring was stopped after 1 hour of reaction, the wet polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane phase by decantation. The separated wet polymer was placed in a vacuum dryer and heated at 80 to 90°C to remove adhering cyclohexane and water.

The resulting dry polymer was a powder containing free-flowing, easily grindable clumps.

Example 2 The same recipe as in Example 1 except that Diacarte 30 used in Example 1 was treated with a large excess of methanol under reflux for about 8 hours, excess methanol was removed under reduced pressure, and the surfactant was used. Polymerization and post-treatment were carried out at.

The resulting polymer was a powder containing coarse, easily grindable clumps.

Example 3 The same procedure was carried out except that the Diacarna 30 used in Example 1 was treated with a large excess of butylamine under reflux at 70°C for about 8 hours, and the excess butylamine was removed under reduced pressure and the product was used as a surfactant. Polymerization and post-treatment were carried out using the same recipe as in Example 1.

The resulting polymer was a powder containing loose, easily grindable clumps.

Example 4 Instead of acrylic acid in Example 1, acrylic acid 28
A mixture of 9 and methacrylic acid 29 was used, and the reaction was otherwise carried out in the same manner as in Example 1, followed by post-treatment.

The resulting polymer was a powder containing free-flowing, easily grindable clumps.

Example 5 The amount of water used to dissolve caustic soda in Example 1 was reduced to 6
3.19, the polymerization reaction was carried out in the same manner as in Example 1, and the same post-treatments were carried out. In this case, the concentration of the monotumer relative to the water in the reaction system is 351 as the concentration after neutralization.

The resulting polymer was a powder containing free-flowing, easily grindable clumps.

Example 6 A polymerization reaction was carried out in the same manner as in Example 1, except that the amount of caustic soda in Example 1 was changed to 109 g, and the amount of water used to dissolve the caustic soda was changed to 48.8 g, and the same post-treatment was carried out. did. In this case, 60 moles of acrylic acid is neutralized, and the monomer concentration with respect to water in the reaction system is 40 moles of monomer after neutralization.

The resulting polymer was a powder containing shiny, easily grindable lumps.

Example 7 The amount of hydroxyethyl cellulose in Example 1 was reduced to 1
．． 89, the polymerization reaction was carried out in the same manner as in Example 1, and the same post-treatment was carried out.

The resulting polymer was a powder containing free-flowing, easily grindable clumps.

Comparative Example 1 Polymerization was carried out using the same recipe and procedure as in Example 1 of JP-A-56-76419 to obtain a dry polymer.

That is, 230 mL of hexane was placed in a 500 CC four-loaf flask equipped with a stirrer, reflux condenser, dropping pouch, and nitrogen gas inlet tube.
1. Take sorbitan monostearate 1.89, blow nitrogen gas to drive out dissolved oxygen, and then heat to 60-65℃.
It was heated to Separately, Acrylic 9309 was dissolved in water 499 while cooling with ice from the outside in a beaker, and 78% of the calgexyl group was neutralized with 13.4 g of 98% caustic soda.

The monomer concentration in the aqueous phase was 401%.

Next, hydroxyethyl cellulose (degree of etherification 0.
8. Number of moles added 1.9) After adding and dissolving 1.8E,
Dissolved oxygen was removed by blowing nitrogen gas. The contents in the beakers were added to the four flasks and dispersed, the internal temperature was maintained at 60 to 65° C., and stirring was continued for 3 hours. Although the hexane was distilled off under reduced pressure, a portion of the swollen polymer stuck to the flask wall and the stirrer, and the remaining swollen polymer was dried at about 80° C. under reduced pressure to obtain a powdery polymer.

Table 1 shows the results of measuring the pure water absorption capacity, water absorption glue strength, and particle size of the dry polymers obtained in Examples 1 to 7 and Comparative Example 1.

As is clear from these results, the polymer obtained by the method of the present invention has a high water absorption capacity, a large t*r ripple, a large particle size, and a relatively narrow particle size distribution.

In addition, the swollen polymer after polymerization does not stick to the reactor wall, stirrer, etc. at all, and the present method is excellent in terms of recovery rate and process operability.

Claims (1)

[Claims] 1) Acrylic acid or an acrylic acid/methacrylic acid mixture and an alkali metal salt of acrylic acid or an acrylic acid/methacrylic acid mixture (hereinafter referred to as an acrylic acid monomer) are combined in water to initiate water-soluble radical polymerization. In a method of polymerizing by a water-in-oil type inverse suspension polymerization method in the presence of an agent, a dispersion medium, and a surfactant, (a) an α-olefin and an α,β-unsaturated polycarboxylic acid anhydride as a surfactant; (b) hydroxyethyl cellulose is present in the aqueous phase; (c) the concentration of the acrylic acid monomer relative to water is 30% by weight or more as the concentration after neutralization or a saturated concentration. (d) A method for producing a bead-like self-crosslinking water-absorbing polymer, characterized in that the polymerization is carried out in the absence of a crosslinking agent. 2) The manufacturing method according to claim 1, wherein the methacrylic acid content of the acrylic acid/methacrylic acid mixture is 20 mol% or less. 3) The manufacturing method according to claim 1, wherein 50 mol% or more of the total carboxyl groups of the acrylic acid monomer are neutralized with an alkali metal salt. 4) The production method according to claim 1, wherein the water-soluble radical polymerization initiator is one or more selected from the group consisting of hydrogen peroxide and persulfates.