JPS6295308A - Production of highly water-absorbing polymer bead - 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 containing a small amount of crosslinking agent in the presence of hydroxyethyl cellulose using a specific crosslinking agent. CONSTITUTION:(Meth)acrylic acid containing a small amount (preferably 0.01-2wt%) of a crosslinking agent (e.g. N,N'-methylenebisacrylamide) and an alkali metal salt or ammonium salt of (meth)acrylic acid are polymerized by W/O-type reverse-phase suspension polymerization in the presence of a water- soluble radical polymerization initiator (e.g. hydrogen peroxide, ammonium persulfate, etc.), a dispersion medium (e.g. cyclohexane), a surfactant and water. 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.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has excellent water absorbency and high water absorption resistance.
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 absorbency and swells when it absorbs a large amount of water, but it is insoluble in water, has a high water absorbing strength, and has a large particle size, making it difficult for the polymer itself to absorb water. 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 rethane 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 polymer (%Koshō 53-46199
Publications, etc.), cellulose modified materials (JP-A-50-8037)
6, etc.), crosslinked products of water-soluble polymers (Japanese Patent Publication No. 43-2)
3462, etc.), self-crosslinking type acrylic acid acrylic metal salt polymer (Japanese Patent Publication No. 30710/1983, etc.), and the like have been 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, the above-mentioned publication has many problems in production on a practical or industrial scale, such as the polymer obtained by drying is extremely hard, making it difficult to crush easily and requiring a large mechanical crushing force. 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 (Japanese Patent Application No. 59-27
Publication No. 5308. Patent Application No. 60-202907゜hereinafter referred to as Publication. ) However, the water-absorbing material produced by the method disclosed in the above-mentioned publication also has various drawbacks. That is, the patent application No. 59-275
In Publication No. 308, a nonionic surfactant with an HLB of 3 to 6 is used as a surfactant in the water-in-oil type reversed-phase suspension polymerization method, so the polymerization reaction is stable when it is mixed, but the resulting polymer is The particle size is 100 μm or less, resulting in an extremely fine powder bed. For this reason, when handling powder, dust countermeasures are necessary. Furthermore, the glue strength upon water absorption is still insufficient, and there has been a desire for a polymer with better shape retention.

By polymerizing a copolymer of yne and an We have demonstrated a method for producing bead-shaped superabsorbent polymers that have a large aggregate particle size and can be easily crushed.

However, as a result of various detailed studies, it was found that in the above method, suspended particles tend to adhere to each other during the polymerization reaction, resulting in a lumpy state and causing abnormal polymerization. It was found that it was difficult to obtain bead-like water-absorbing polymers. 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 at most 5 μm.
00 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 safely produces a superabsorbent 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 seeding research in order to solve the above-mentioned problems, the inventor of the present invention has discovered the method of adding and dissolving hydroxyethyl cellulose into the aqueous phase of the polymerization reaction system described in the above-mentioned Japanese Patent Application No. 60-202907 and polymerizing it. Due to the dead weight of 5
We have discovered that it is possible to safely produce an extremely large flat water-absorbing polymer that has a water absorption capacity of 00 times or more, has a high glue strength, and has a maximum polymer particle size of about 3000 μm, and has completed the present invention. be.

That is, the present invention combines acrylic acid and an alkali metal salt or ammonium salt of acrylic acid, or methacrylic acid and an alkali metal salt or ammonium salt of methacrylic acid, containing a small amount of a crosslinking agent, with water, a water-soluble radical polymerization initiator, a dispersion medium,
and a method of polymerizing by a water-in-oil reverse phase suspension polymerization method in the presence of a surfactant, (,) an α-olefin and α,β- as a surfactant.
The bead-shaped super absorbent water-in-oil droplet of the present invention is characterized by using a copolymer with an unsaturated polycargenic acid anhydride or a derivative thereof, and (b) having hydroxyethyl cellulose present in the aqueous phase and polymerizing it. In this type of reverse phase suspension polymerization method, a copolymer of α-olefin and α,β-unsaturated polycargonic acid anhydride or a derivative thereof, which is used as a surfactant, is first prepared at a concentration of 1@57%. -743Q9 discloses a method for producing bead-like water-soluble Telimer, but as mentioned above, the present inventors have already developed a novel bead-like high We proposed a method for producing 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 studies on methods for preventing abnormal polymerization in the above production method, the present inventors have found that by further dissolving hydroxyethyl cellulose t-m in the aqueous phase and polymerizing it, the water absorption performance and water absorption glue strength can be improved. We have found a solution that completely prevents scales while retaining them. In addition, it was found that the particle size of the resulting polymer could be controlled arbitrarily by changing the amount and type of hydroxyethyl cellulose added, and that a giant bead-like polymer with a particle size of about 3000 μm could be obtained. The amount and the water absorption strength show contradictory tendencies. That is, in order to increase the amount of water absorbed, it is necessary to reduce the crosslinking ratio for insolubilization of the polymer as much as possible, but on the other hand, the strength of the water absorption glue 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 or more. 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 metal compound capable of reacting with a difunctional divinyl compound or cargexyl group, do not contain these crosslinking agents. Even if the amount is reduced as much as possible, the amount of water absorbed is at most 1000 times its own weight, and the water absorption strength of this product itself is extremely small.
It becomes a paste-like product, and when the amount of crosslinking agent is increased to obtain a sufficiently satisfactory water absorption glue strength, the amount of water absorbed is 3 of its own weight.
00 times or less.

The polymer produced by the present invention has a significantly large particle size, specifically from 100 μm or more to a maximum of about 3000 μm.
It has the characteristics of having high water absorption, specifically, 500 times or more of its own weight, and high dull 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 a β-unsaturated polycarboxylic acid anhydride or a derivative thereof and adding and dissolving hydroxyethyl cellulose in the aqueous phase.

JP-A No. 5F discloses a method for obtaining a super absorbent polymer by containing hydroxyethylcellulose in the aqueous phase and polymerizing an alkali metal acrylic acid monomer by a water-in-oil reverse phase suspension polymerization method without using a crosslinking agent. It is shown in '1-76419 publication. The water absorption amount of the polymer obtained by this method is 500 to 700 times its own weight, which is a relatively high value.
Since Nlupitan fatty acid ester of Hl and B 3 to 6 is used as a surfactant, the water absorption strength is extremely weak.
Poor durability. In addition, the polymer obtained by this method is
Although quite large particles with a particle size of several hundred μm can be obtained, it is difficult to obtain them with good uniformity, and they usually show a wide distribution, ranging from small particles of about 10 Am to fairly large particles of about 500 μm.

Furthermore, when polymerized by this method, the water-containing polymer after polymerization is somewhat sticky, so it tends to stick to the stirrer and reactor walls, and it is difficult to remove water during post-treatments such as the dehydration step 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 crushed.

The present invention solves the above-mentioned problems and has a high water absorption glue strength without reducing the amount of water absorption. Specifically, it has a water absorption capacity of 500 times or more than its own weight, and its average particle diameter is 100 μm or more. The present invention provides a method for safely and easily producing a superabsorbent polymer having a large size and a narrow distribution, and this is the most distinctive feature of the present invention.

(1) Monomer The monomer used in the polymerization reaction of the present invention is acrylic acid or methacrylic acid, and its total cal? It is an acrylic acid monomer in which at least 50 moles of xyl groups, preferably at least 65 moles, are neutralized with an alkali metal salt or anthonium salt.

It becomes small.

For neutralization of acid monomers to alkali metal salts, alkali metal hydroxides, bicarbonates, etc. can be used, but alkali metal hydroxides are preferable, and specific examples include hydroxides. Mention may be made of sodium, potassium hydroxide and lithium hydroxide. Sodium hydroxide is most preferred in terms of industrial availability, price, and safety.

The amount of the acrylic acid monomer used in the present invention is:
The more the better. Specifically, the concentration of 7mer after neutralization in water is 20% by weight or more, preferably 30% by weight.
It is more than 1. The higher the concentration of the polymer, the better the yield per unit patch, and the easier the dehydration operation after polymerization, which is also economically advantageous.

(2) Crosslinking agent The crosslinking agent used in the production method of the present invention has two or more double bonds in the molecule, exhibits a certain degree of water solubility, and has good copolymerizability with the acrylic acid monomer, It must be able to efficiently form a crosslinked structure and give a uniform crosslinking distribution.

Such crosslinking 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, N,N'-methylenebis(meth)acrylamide, diallyl maleate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate Among these, polyethylene glycol di(meth)acrylate, N, N'
- Methylenebisacrylamide is preferred.

The amount of these crosslinking agents used is 0.001 to 10% by weight, preferably 0.01 to 2% by weight, based on the acrylic acid monomer. If it is less than 0.001% by weight, the water absorption capacity will be extremely high, but the ripple strength of the superabsorbent polymer during water absorption will be extremely weak, and if it is more than 10% by weight, the water absorption strength will be significantly improved, but The water absorption capacity becomes considerably small, which poses a practical problem.

(3) Water-soluble radical polymerization initiator The polymerization initiators used in the production method of the present invention include hydrogen peroxide, persulfates such as ammonium persulfate and potassium persulfate, and t-butylhydrono-J? Hydroperoxides such as -oxide and cumene hydroperoxide, azo initiators such as azoisobutyronitrile and 2,2'-azobis(2-amidinopropane) dihydrochloride are used.

These water-soluble radical polymerization initiators may also be used in combination with a reducing substance such as sodium hydrogen sulfite, amines, etc. to form a redox type initiator.

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

(4) Surfactant The surfactant used in the production method of the present invention is α-
It is a copolymer of an olefin and an α,β-unsaturated polyhydric caldic acid anhydride or a derivative thereof. The α-olefin has 10 to 100 carbon atoms, preferably 16 to 60 carbon atoms. Further, examples of the α,β-unsaturated polycarboxylic 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. Examples of the partially esterified product include copolymer monomethyl ester, monoethyl ester, moptyl ester, and the like.

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

The molecular weight of the above copolymer or its derivative is 2000 to 10
0,000, preferably 10,000 to 50,000.

Furthermore, in the present invention, when the α-olefin/α,β-unsaturated polycarboxylic acid anhydride copolymer is used, it may be in the acid anhydride state or in the partially or completely ring-opened state. good.

The amount of these surfactants used is 0.0
1 to 10% by weight, preferably 0.405 to 5% by weight.

(5) Dispersion medium As the dispersion medium used in the present invention, in principle, any liquid can be used 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 decalin, aliphatic hydrocarbons such as hexane, pentane, peptane, and octane, chlorobenzene, Examples include halogenated hydrocarbons such as bromobenzene and dichlorobenzene.

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 preferably 0.5 to 10 times the amount of the monomer aqueous solution in terms of volume, in order to make the polymerization reaction system water-in-oil type, and from the standpoint of removing the heat of polymerization reaction. It is desirable to use 1 to 5 times the amount.

(6) Hydroxyethylcellulose The hydroxyethylcellulose used in the present invention may be any type of hydroxyethylcellulose that can be dissolved in an aqueous acrylic acid solution. Specific examples include the degree of etherification (a value indicating whether the core of the three OH groups in the glucose unit constituting cellulose is etherified), 0.4 to 2, the number of moles of ethylene oxide added (glue-- The number of moles of ethylene oxide added per unit is preferably 1 to 5.

When the degree of etherification and the number of moles added are smaller than the above values, hydroxyethylcellulose becomes insoluble in the aqueous acrylic acid monomer solution and cannot be used in the present invention.

The amount of hydroxyethyl cellulose added is 0.1 to 20% by weight, preferably 0.1 to 20% by weight, based on the acrylic acid monomer.
It is 5 to 10% by weight.

(7) Polymerization conditions Typical embodiments of the polymerization reaction of the present invention are as follows. That is, acrylic acid that has been neutralized in advance is dissolved, and an inert gas such as nitrogen is introduced for deaeration.

On the other hand, a surfactant is placed in a dispersion medium, heated slightly if necessary to dissolve it, and degassed by introducing an inert gas such as nitrogen. The above monomer aqueous 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. If the reaction temperature is too low, the resulting polymer will have a large soluble portion and its water absorption performance will be reduced; if it is too high, the water absorption performance will vary greatly and it will be difficult to produce a homogeneous polymer.

The polymerization reaction of the present invention is carried out in a water-in-oil type suspension polymerization system, and for this purpose, as described above, an α-olefin, an α,β-unsaturated polyhydric caldic acid anhydride, and a copolymer or copolymer thereof are required. The purpose can be achieved by combining the use of derivatives, adding and dissolving hydroxyethyl cellulose in the aqueous phase, adjusting the ratio of dispersion medium and water as appropriate, and further stirring appropriately. .

In addition, the stirring of the polymerization reaction system in the present invention is not only important for maintaining the desired stable water-in-oil type suspension system in the polymerization reaction system, but also for improving the properties of the produced polymer. But it's important.

In other words, if the stirring is too strong, the fine primary hydrodal 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, resulting in variations in polymer performance. growing. On the other hand, 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 polymer will also be significantly reduced. Therefore, it is necessary to carry out appropriate stirring, but when using a polymerization reactor equipped with a normal stirrer for carrying out suspension polymerization of this food, the stirring speed is 100 to 600 rpm, preferably 200 to 600 rpm.
By stirring at 400 rpm, water absorption, water absorption strength,
Bead-shaped polymers with excellent properties and 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, the separated wet polymer is, for example, 1
If dried at a temperature below 20°C, powdered polymer,
Alternatively, a powdered polymer containing easily pulverizable lumps is obtained. The polymer thus obtained usually has a diameter of 10
They are granules that have a diameter of 0 μm or more and have a narrow distribution, and that contain a small amount of true spherical primary particles whose surfaces are covered with a surfactant or secondary particles that are partially agglomerated. These secondary particles can also be easily pulverized by a small amount of mechanical force. This has great advantages in terms of polymer production and use.

[Effects of the invention, etc.] As mentioned above, the polymer obtained by the production method of the present invention has a high water absorption performance of 500 times or more of its own weight, a high water absorption dull strength, and whether the polymer itself is a powder from the beginning or not. Alternatively, it can be easily made into 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.

In addition, by taking advantage of its excellent water absorption performance and strength, it is also used in the production of various materials for horticultural and agricultural purposes, including soil conditioners and water retention agents, which have recently been attracting attention. be able to.

Hereinafter, the present invention will be further explained in detail by giving Examples and Comparative Examples.

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

A. Pure Water Absorption Capacity: About 0.5F polymer and about 11% pure water were weighed and mixed into a beaker with a water absorption capacity of 11. After mixing, the polymer was left to stand for about 2 hours to sufficiently swell the polymer with water.

After draining with a 100-mesh sieve, the amount of permeate was weighed, and the pure water absorption capacity was calculated according to the following formula.

B. Water-absorbing glue strength 200 times its own weight of pure water was added to the polymer to absorb water, and the strength of the resulting water-absorbing glue was examined by pressing the elasticity of the obtained water-absorbing glue with a finger, and evaluated according to the following criteria.

×: Weak Δ: Slightly weak ○: Jintong preparation) ■: Slightly strong 02 Strong Example 1 A 500-capacity four-day round bottom flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube. , cyclohexane 185y was added, and α-olefin and maleic anhydride copolymer (Mitsubishi Kasei@) cleaved product name “Diakarna 30” was added to this.
1.8 N (molecular weight: about 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 m, add acrylic acid 3
12.9. Water 63.11i was dissolved in 0F while cooling it from the outside. Add F's caustic powder, Cal? 77.4% of the xyl groups were neutralized.

The monomer concentration relative to water in this case corresponds to 35% by weight as the monomer concentration after neutralization.

This is then added with N,N'-methylenebisacrylamide)'
t-0,015, SJ, hydroxyethyl cellulose (
Degree of etherification = 1, number of moles of EO added = 2) 0.9I, and potassium persulfate 0. II was added and dissolved.

Add this 200ml to the contents of the four-day round bottom flask.
The contents of the flask were added, and polymerization was carried out at 65 to 70° C. for about 1 hour while stirring. Note that stirring was performed at 40 Orpm.

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 transferred to a vacuum dryer and heated at 80 to 90°C to remove attached 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 the Diacarna 30 used in Example 1 was treated with a large excess of methanol under reflux for about 8 hours, the excess methanol was removed under reduced pressure, and the product was used as a surfactant. Polymerization and post-treatment were carried out at.

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

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 free-flowing, easily grindable clumps.

Example 4 In place of acrylic acid in Example 1, methacrylic acid 3
011, and otherwise reacted in the same manner as in Example 1,
Post-processed.

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

Example 5 The amount of hydroxyethyl cellulose in Example 1 was reduced to 1
．． 8I! 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 m of hexane was placed in a 500 cc four-loaf flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas inlet tube.
After taking 1.8 I of sorbitan monostearate and blowing nitrogen gas to drive out dissolved oxygen, it was heated to 60 to 65°C. Separately, 98% of 13.4J of acrylic acid 3011 dissolved in water 49.9% while cooling with ice from the outside in a beaker.
78 carboxylic groups were neutralized with caustic soda.

The monomer concentration in the aqueous phase was 40% by weight.

Next, hydroxyethyl cellulose (degree of etherification 0.
8. Number of moles added: 1.9) After adding and dissolving 1.8.9, nitrogen gas was blown in to remove dissolved oxygen. 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, some of the swollen remer stuck to the flask wall and the stirrer, and the remaining swollen d? A portion of Lima 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 dull strength, and particle size of the dry polymers obtained in Examples 1 to 5 and Comparative Example 1.

As is clear from the results, the polymer obtained by the method of the present invention has a large water absorption capacity, a large water absorption strength, a large particle size, and a relatively narrow particle size distribution.

Furthermore, the swollen polymer after polymerization does not stick to the reactor, stirrer, etc., and the recovery rate and process operability are extremely excellent.

Claims (1)

[Scope of Claims] 1) Acrylic acid and an alkali metal salt or ammonium salt of acrylic acid, or methacrylic acid and an alkali metal salt or ammonium salt of methacrylic acid (hereinafter referred to as an acrylic acid monomer) containing a small amount of a crosslinking agent, When polymerizing by a water-in-oil reverse phase suspension polymerization method in the presence of a water-soluble radical polymerization initiator, a dispersion medium, a surfactant, and water, α-olefin and α,β-unsaturated 1. A method for producing a bead-like superabsorbent polymer, which comprises polymerizing a copolymer with a polyhydric carboxylic acid anhydride or a derivative thereof in the presence of hydroxyethyl cellulose. 2) The manufacturing method according to claim 1, wherein 50% or more of the total carboxyl groups of the acrylic acid monomer are neutralized with an alkali metal salt or an ammonium salt.