JPH03195708A - Production of polymer having high water absorption property - Google Patents

Abstract

PURPOSE:To obtain the title polymer having narrow particle diameter distribution, high water absorption properties and strength of water absorbed gel by successively feeding part of (meth)acrylic acid, etc., and a dispersion medium to a dispersion medium containing a water-soluble polymerization initiator and a dispersant and subjecting to water-in-oil type reverse phase suspension polymerization. CONSTITUTION:In producing a polymer having high water absorption properties by subjecting an acrylic acid-based monomer comprising acrylic acid and (or) methacrylic acid, an alkaline metallic salt and ammonium salt thereof as main components to water-in-oil type reverse phase suspension polymerization in the presence of a water-soluble radical polymerization initiator and a dispersant in a dispersion medium, the acrylic acid-based monomer is successively fed to the dispersion medium corresponding to progress of the polymerization reaction and at least part of the dispersion medium containing the dispersant is successively added to the dispersion medium corresponding to the progress of the polymerization reaction to give the objective polymer having high water absorption properties.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] <Industrial Application Field> The present invention relates to a method for producing a superabsorbent polymer.

The polymer obtained by the production method of the present invention has a narrow particle size distribution and high water absorption capacity and water absorption gel strength, so it can be advantageously used for various materials such as sanitary materials, industrial materials, agriculture and horticulture. I can do it.

<Prior art> In recent years, superabsorbent polymers have been used not only for sanitary materials such as disposable diapers and sanitary products, but also for water-stopping agents, anti-condensation materials, freshness-preserving materials,
It has come to be used for industrial purposes such as solvent dehydration materials, greening, agricultural and horticultural purposes, and various products have been proposed so far.

Known examples of this type of superabsorbent polymer include hydrolysates of starch-acrylonitrile graft copolymers, carboxymethyl cellulose, polyacrylic acid (salts), acrylic acid (salts)-vinyl alcohol copolymers, and polyethylene oxide. ing.

Among these, polyacrylate-based superabsorbent polymers obtained by water-in-oil reverse phase suspension polymerization of alkali metal acrylates and the like are particularly important.

In this water-in-oil reverse phase suspension polymerization method of alkali metal acrylic acid salts, etc., the dispersant used is
Sorbitan fatty acid esters with HLB 3 to 6 described in JP-A No. 4-30710, nonionic surfactants with HLB 6 to 9 described in JP-A-57-167302, and JP-B 60-
HLB8-12 surfactant described in Publication No. 25045,
Special Publication No. 63-36321, Special Publication No. 63-3632
Lipophilic carboxyl group-containing polymers described in Publication No. 2, lipophilic basic nitrogen-containing polymers described in Japanese Patent Publication No. 63-36323, Komei No. 1-, 17482, JP-A-57-
Oil-soluble cellulose esters or cellulose ethers described in JP-A No. 158210 and JP-A-58-32607, copolymers of styrenes and dialkylaminoalkyl (meth)acrylates, etc. described in JP-A-61-40309, Sucrose fatty acid esters described in JP-A-61-43606, JP-A-61-87702, JP-A-62-53310, JP-A-62-628
Copolymer of α-olefin and α,β-unsaturated carboxylic acid anhydride or derivative thereof described in Publication No. 07, JP-A No. 6
Polyglycerin fatty acid esters with HLB of 2 to 16 and the like described in JP 2-172006 are known.

These reversed-phase suspension polymerization methods can be roughly divided into two methods: one is to mix the dispersion medium and monomer all at once and then start polymerization by increasing the temperature, and the other is to drop the monomer into the dispersion medium in parallel with the progress of the polymerization reaction. There is a way to do this. In particular, it is known that the latter method allows the concentration of unreacted monomers in the dispersion medium to be kept constant (for example, Komei No. 1-17482, JP-A-58-32607, JP-A-61-1999). 1
92703, JP-A-63-56512, JP-A-64-14205, etc.).

Among these, JP-A No. 61-192703 discloses that under specific monomer concentration conditions, the amount of hydrocarbon solvent is at least four times the weight of the monomer, and a seven-mer aqueous solution is prepared so as to prevent the polymerization temperature from rising above 20°C. The document describes a method of polymerizing by adding 100% by weight, and states that even if a surfactant with an HLB of 2 to 3 is used as a dispersant, the polymer does not aggregate during polymerization.

On the other hand, JP-A No. 64-22909 describes a method in which at least a portion of the dispersant is sequentially supplied to the system as the polymerization reaction progresses, along with at least a portion of the monomer, and the amount of the dispersant decreases over time. It is stated that the water absorption capacity and water absorption rate are improved because the effective dispersant concentration can be maintained within a certain range.

However, as far as the present inventors know, it is difficult to obtain a superabsorbent polymer with a narrow particle size distribution by any of the above methods, and therefore, the performance of the polymer depends on the difference in the particle size of the missing particles. It has not been easy to obtain a superabsorbent polymer with little variation in performance and well-balanced performance.

[Summary of the invention]

Summary> The present invention improves the above problems and achieves a narrow particle size distribution.
The present invention aims to provide a method for producing a superabsorbent polymer that simultaneously satisfies all required performances such as water absorption capacity, water absorption rate, gel strength, cohesiveness, and safety.

In order to improve the above-mentioned problems, the present inventors have conducted intensive research on a water-in-oil reversed-phase suspension polymerization method in which acrylic acid monomers are sequentially supplied into a dispersion medium as the polymerization reaction progresses. By keeping the ratio of the monomer aqueous solution, dispersant, and dispersion medium within a constant range as much as possible while the polymerization reaction is progressing, a polymer with a narrow particle size distribution can be obtained and variations in performance from particle to particle can be reduced. The present invention was achieved by discovering that all required performances can be satisfied simultaneously.

That is, in the method for producing a superabsorbent polymer of the present invention, an acrylic acid monomer containing acrylic acid and/or methacrylic acid and an alkali metal salt or ammonium salt thereof as a main component is combined with a water-soluble radical polymerization initiator and a water-soluble radical polymerization initiator. When producing a superabsorbent polymer by polymerizing in a dispersion medium in the presence of a dispersant by a water-in-oil reverse phase suspension polymerization method, the above acrylic acid monomer is added to the dispersion medium according to the progress of the polymerization reaction. The present invention is characterized in that at least a portion of the dispersion medium containing the dispersant is sequentially supplied into the dispersion medium as the polymerization reaction progresses.

Effect> According to the present invention, the particle size distribution is narrow, and the water absorption ability, water absorption rate,
It is possible to produce a superabsorbent polymer that simultaneously satisfies all required performances such as gel strength, cohesiveness, and safety.

[Detailed description of the invention]

Acrylic Acid Monomer> The acrylic acid monomer used in the polymerization reaction of the present invention contains acrylic acid and/or methacrylic acid and an alkali metal salt or ammonium salt thereof as main components. A preferred specific example of such an acrylic acid monomer is one in which 20% or more, preferably 50% or more of the total carboxyl groups in the specimen are neutralized with an alkali metal salt or ammonium salt. It is something. In this case, if the degree of neutralization is less than 20%, the water absorption capacity will be low and the strength of the obtained water absorption gel will be extremely low. The upper limit of the degree of neutralization is about 90%.

As the alkali agent for neutralizing the acid monomer to the alkali metal salt, alkali metal hydroxides, bicarbonates, and the like can be used, but alkali metal hydroxides are preferable. Specific examples of such alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide.

Sodium hydroxide is most preferred in terms of industrial availability, price, and safety.

Such an acrylic acid monomer is dissolved in an aqueous medium to form a solution. Water is often used as the aqueous medium, but one consisting of water and a small amount of a water-soluble organic solvent can also be used.

The larger the amount of the acrylic acid monomer in the solution, the better. Specifically, the acrylic acid monomer concentration is 20% by weight as the monomer concentration after neutralization in the aqueous medium.
Above, especially 30% by weight or more is preferable. The higher the monomer concentration, the better the yield per unit batch, and also the easier the dehydration operation after polymerization, which is economically advantageous.

In addition, in the present invention, monomers other than the above, such as (1) itaconic acid, maleic acid, fumaric acid, 2-acrylamide-
2-Methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acryloylpropanesulfonic acid and its salts, ■ Alkyl or alkoxyalkyl esters of dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid, ■ (meth)acrylamide , ■ Vinyl sulfonic acid, ■ Methyl acrylate, ethyl acrylate, etc., ■ Hydroxyethyl (meth)acrylate, Hydroxypropyl (meth)acrylate, ■ Polyethylene glycol 7-(meth)acrylate, N-methylol (meth)acrylamide , monomers having a copolymerizable double bond in the molecule such as glycidyl (meth)acrylate, etc., and low crosslinking agents thereof, such as ■ polyethylene glycol di(meth)acrylate,
Polybrobylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, N, N'
- Those that have two or more double bonds in the molecule and are copolymerizable with acrylic acid monomers, such as methylene bis(meth)acrylamide, or ■ ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and fats. Combination use of compounds having two or more functional groups such as di- or polyglycidyl ethers of group polyhydric alcohols that react with the carboxyl group during polymerization or during drying after polymerization. is also possible.

Here, "(meth)acrylic" means either acrylic or methacryl.

Similarly, "(meth)acrylate" means either acrylate or methacrylate.

Water-Soluble Radical Polymerization Initiator> As the water-soluble radical polymerization initiator used in the present invention, those well known in the field of polymer chemistry can be used. Specific examples of such water-soluble radical polymerization initiators include inorganic or organic peroxides, such as persulfates (ammonium salts, alkali metal salts (especially potassium salts), etc.), hydrogen peroxide, ditertiary butyl peroxide, etc. , acetyl peroxide, and the like. In addition to these peroxides, if a predetermined aqueous solution is obtained, an azo compound or other radical polymerization initiator, such as 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'- Azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride, 4,4'-azobis(4-cyanovaleric acid)
etc. can also be used.

Polymerization is initiated by the decomposition of these water-soluble radical polymerization initiators, and in the present invention, the decomposition of the water-soluble radical polymerization initiators is accomplished by not only heating, which is a conventional means, but also decomposition of the water-soluble radical polymerization initiators by chemical substances. It can also be carried out by well-known methods such as promoting the decomposition of . When the polymerization initiator is a peroxide, the decomposition promoting substance is a reducing compound (water-soluble in the present invention) such as an acidic sulfite, ascorbic acid, an amine, etc. for persulfates, and Polymerization initiators consisting of a combination of a peroxide and a reducing compound are well known in the field of polymer chemistry as "redox initiators." Therefore, in the present invention, the term "polymerization initiator" refers to combinations with such decomposition promoting substances, especially redox initiators,
This includes:

The amount of water-soluble radical polymerization initiator used as described above is 0.001 to 1 in the membrane, based on the acrylic acid monomer.
0% by weight, preferably 0.01-1% by weight.

Dispersant> As the dispersant in the present invention, various dispersants can be used as long as they can disperse the acrylic acid monomer aqueous solution in the dispersion medium, regardless of whether they are surfactant-based dispersants or polymer-based dispersants. Among these, HL, which is solid at room temperature, can be used.
Nonionic surfactants B2 to B12 are preferred, particularly sorbitan fatty acid ester, sucrose fatty acid ester, and polyglycerol fatty acid ester. When a dispersant having an HLB of less than 2 is used, there is a disadvantage that the resulting polymer tends to be sticky and easily aggregate. Furthermore, if the HLB exceeds 12, it is difficult to form a stable suspension state.

The amount of the dispersant to be used cannot be generally specified, but is usually 0.001 to 20% by weight, preferably 0.1 to 10% by weight, based on the acrylic acid monomer. 0.001% by weight
If it is less than 20% by weight, it will not be possible to maintain a stable suspended state, and if it exceeds 20% by weight, it will not only be economically disadvantageous, but may also lead to a decrease in water absorption capacity, etc.

Dispersion medium> In principle, almost any liquid can be used as the dispersion medium used in the present invention as long as it does not participate in the polymerization reaction and does not mix with water. For example, (a) aromatic hydrocarbons such as benzene, ethylbenzene, toluene, xylene, etc.
(b) Alicyclic hydrocarbons, such as cyclohexane, methylcyclohexane, cyclooctane, decalin, etc. (c)
Examples include aliphatic hydrocarbons, such as hexane, pentane, heptane, octane, etc., and (d) halogenated hydrocarbons, such as chlorobenzene, bromobenzene, dichlorobenzene, etc. Among these, preferred specific examples of such liquids include alicyclic hydrocarbons, especially cyclohexane, methylcyclohexane, etc., and aliphatic hydrocarbons, especially hexane, heptane, etc. Further, these dispersion media may be substantially composed of only one type, or may be a mixture of multiple types within each group or between each group.

The amount of these dispersion media used is 0.5 to 10% by weight relative to the aqueous solution containing the acrylic acid monomer, in order to make the polymerization reaction system water-in-oil type and to remove the heat of the polymerization reaction. , preferably at a weight ratio of 1 to 5.

<Sequential supply> In the method for producing a superabsorbent polymer according to the present invention, the acrylic acid monomer is sequentially supplied into the dispersion medium according to the progress of the polymerization reaction, and at least a part of the dispersion medium containing the dispersant is The polymerization reaction is carried out by sequentially feeding the polymer into the dispersion medium as the polymerization reaction progresses.

That is, the polymerization reaction is controlled by supplying the remainder of the dispersion medium containing the monomer and dispersant little by little into the dispersion medium without initially charging the monomer.

The dispersion medium containing the acrylic acid monomer and the dispersant is supplied under conditions such that the polymerization reaction temperature does not rise by 20°C or more, preferably 10°C or more, compared to the stage before the acrylic acid monomer is supplied. It takes place below. It is preferable to supply the dispersion medium containing the acrylic acid monomer and the dispersant continuously and with a small variation in the supply amount, but it is also possible to change the supply amount continuously or in stages. Alternatively, it can be supplied intermittently. The polymerization reaction temperature is usually 10 to 200°C, preferably 20 to 100°C.
, is appropriate.

Although it is not preferable to have a polymerizable monomer present in the initially charged dispersion medium before the monomers are sequentially supplied,
Even if a reactive inert substance, for example, a superabsorbent polymer in the present invention, is coexisting in advance, the same problem does not arise.

Sequential supply of dispersion medium containing a dispersant> The method for producing a superabsorbent polymer according to the present invention involves sequentially supplying at least a part of the dispersion medium containing a dispersant into the dispersion medium as the polymerization reaction progresses. This is done by supplying. The supply of the dispersion medium containing the dispersant is carried out in parallel with the sequential supply of the acrylic acid monomer. The amount of the dispersion medium that is sequentially supplied is preferably as large as the dispersion medium initially charged before the polymerization reaction, and is usually equal to or more, preferably 2.
More than double the amount is appropriate.

The most preferable form is for the dispersant to exhibit a constant value for both the dispersion medium and the aqueous acrylic acid monomer solution throughout the polymerization reaction by sequential feeding, and is usually fed sequentially with the dispersion medium charged before the polymerization reaction. The dispersion medium and the dispersion medium are supplied at the same concentration.

Further, in the present invention, the same problem does not occur even if the polymerization reaction liquid is sequentially withdrawn in parallel with the sequential supply.

Generally, the particle size of suspended particles is influenced by the stirring power, the interfacial tension of the two layers, and the viscosity of the dispersion medium, and the interfacial tension is thought to be largely dependent on the dispersion medium and the amount of dispersant in the monomer aqueous solution. . In the present invention, such a dispersant-containing dispersion medium and the acrylic acid monomer are sequentially supplied as the polymerization reaction progresses. This is thought to be due to the fact that the ratio of the dispersant, dispersion medium, and monomer aqueous solution is maintained within a certain range.

Specific manufacturing method> The method for manufacturing a superabsorbent polymer according to the present invention is to process a specific acrylic acid-based monomer in a water-in-oil reverse type in a dispersion medium in the presence of a water-soluble radical polymerization initiator and a dispersant. When producing superabsorbent polymers by polymerizing by phase suspension polymerization, the above acrylic acid monomers are sequentially supplied into a dispersion medium as the polymerization reaction progresses, and a dispersion medium containing a dispersant is added to the dispersion medium. At least a portion thereof is sequentially supplied to a dispersion medium as the polymerization reaction progresses.

An example of a specific embodiment of the method for producing a superabsorbent polymer according to the present invention is as follows.

Neutralize acrylic acid and (or) methacrylic acid in advance to obtain an aqueous alkali metal salt solution or an aqueous ammonium salt solution,
A water-soluble radical polymerization initiator and, if necessary, a crosslinking agent are added and dissolved therein, and an inert gas such as nitrogen is introduced to perform deaeration.

Separately, a dispersant is added to a dispersion medium, suspended by heating to a predetermined temperature, and degassed by introducing an inert gas such as nitrogen.

Next, less than half of the dispersion medium containing the dispersant is transferred to the reactor as an initial charge, and while maintaining the predetermined temperature, the aqueous solution containing the acrylic acid monomer is successively supplied. A dispersion medium containing a dispersant is sequentially supplied as the polymerization reaction progresses to polymerize the monomer.

The polymer after polymerization consists of wet bead-like particles, which can be separated into a dispersion medium and a container by performing a decantation or evaporation operation, either as is or after azeotropic dehydration. Then, the wet polymer is
For example, by drying at a temperature of 120'C or lower, a powdery polymer can be obtained. The polymer thus obtained usually has a particle size of 100 μm or more,
True spherical - granular particles containing a small amount of missing particles or secondary particles that are partially agglomerated.

These secondary particles can be easily broken down into primary particles by strong mechanical force.

In addition, in the present invention, other purposeful components and necessary treatments can be added or added at each stage of the production of the superabsorbent polymer, provided that they do not go against the spirit of the invention.

[Experiment example]

The following experimental examples are for more specifically explaining the present invention. The water absorption capacity and gel strength of the superabsorbent polymer were measured according to the following method.

Water Absorption Capacity ■Pure Water Water Absorption Capacity Approximately 0.2 g of super absorbent polymer is accurately weighed in 1000 cc of pure water, and the water is allowed to absorb water for 1 hour while stirring with a magnetic stirrer. After water absorption, the swollen gel was drained for 15 minutes using a 100-mesh sieve, and then the weight of the swollen gel was measured, and the pure water absorption capacity was calculated according to the following formula.

Wet gel weight (g) ■0.9% saline water absorption capacity Accurately weigh approximately 0.5 g of super absorbent polymer and place it in a 400 mesh nylon bag (10 cm x 10 cm size).
Soak in 500 cc of 0.9% physiological saline for 1 hour. After that, pull up the nylon bag, drain it for 15 minutes, and then
0.
9% physiological saline water absorption capacity was calculated.

Absorb 100 g of pure water in 0.5 g of gel strength super absorbent polymer (
The gel after water absorption was measured using a rheometer (Fudo Kogyo Model NMR-2002J), and the force at which the cell entered the gel was defined as the gel strength.

Example 1 Acrylic acid 30 in a conical flask with a capacity of 200 cc
．． While cooling the o, from the outside, water 44.
7g and 46.6g of 25% sodium hydroxide was added to remove 70% of the carboxyl groups.
neutralized. The monomer concentration relative to water in this case corresponds to 30% by weight as the monomer concentration after neutralization. Next, 0.042 g of N,N'-methylenebisacrylamide as a crosslinking agent and 0.104 g of potassium persulfate as a water-soluble radical polymerization initiator were added and dissolved, and then nitrogen gas was blown in to drive out dissolved oxygen. , maintained at room temperature.

Separately, in a 300cc three-day round bottom flask, sorbitan monostearate (I (LB4.7) 1.3
5 g of 182 g of cyclohexane was mixed and dissolved as a dispersion medium, and the internal temperature was maintained at 65° C. while nitrogen gas was introduced to drive out dissolved oxygen.

Stirrer, reflux condenser, thermometer, nitrogen gas introduction pipe and 2
First, while introducing nitrogen gas with stirring into a 500ee capacity 5-necked flat-bottomed flask equipped with a dropper tube,
Dispersant-containing dispersion medium in 00cc flask 60. was transferred.

Subsequently, while maintaining the polymerization reaction temperature at 64 to 66°C, 121 g of the monomer aqueous solution in the 200 cc flask was added dropwise over 60 minutes using a metering pump, and in parallel, the dispersant-containing dispersion was carried out in the 300 cc flask. Medium 1
23 g was added dropwise over 60 minutes using a metering pump, and after the addition was completed, polymerization was carried out at the same temperature for 30 minutes. Subsequently, azeotropic dehydration was performed for 4 and a half hours under cyclohexane reflux.

Incidentally, stirring was performed at 20 Orp.

When stirring was stopped, the wet beaded polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane layer by decantation. The separated polymer was transferred to a vacuum dryer and heated to 80 to 90°C to remove adhering cyclohexane and water, yielding a smooth powdery polymer.

Example 2 In Example 1, 36 g of the dispersant-containing dispersion medium in the 300 cc flask was first placed in a 500 cc five-necked flat bottom flask.
7. Transfer the liquid to the superabsorbent polymer obtained in advance in Example 1.
2g in a humidifier at 24. A powdered polymer was obtained by carrying out the same procedure except that the polymer swollen to 100% was added and the amount of the aqueous monomer solution added dropwise was changed to 97 g.

Example 3 900 g of acrylic acid and 1341 g of water were added to a reaction vessel with a volume of 15 liters, and the mixture was heated to 25 liters while being externally cooled.
% sodium hydroxide was added to neutralize 70% of the carboxyl groups. In this case, the concentration of 7mer in water corresponds to 30% of the monomer concentration after neutralization. Next, N, N'-
After adding and dissolving 1.26 g of methylenebisacrylamide and 3.12 g of potassium persulfate as a water-soluble radical polymerization initiator, the temperature was maintained at 20° C. while blowing nitrogen gas to drive out dissolved oxygen.

Separately, 40.5 g of sorbitan monostearate as a dispersant and 5460 g of cyclohexane as a dispersion medium were mixed and dissolved in a 10-liter reaction vessel B, and the internal temperature was maintained at 65° C. while nitrogen gas was introduced to drive out dissolved oxygen. .

First, 770 g (approximately 1 liter) of the dispersant-containing dispersion medium from reaction vessel B was transferred to an overflow type reaction vessel C with a capacity of 5 liters (overflow capacity: approximately 4 liters), the system was purged with nitrogen, and the internal temperature was lowered. The temperature was maintained at 65°C.

Subsequently, while maintaining the polymerization reaction temperature at 63 to 67°C, 3643 g (approximately 3.3 liters) of the monomer aqueous solution in reaction vessel A was continuously fed over 150 minutes, and in parallel, the dispersant in reaction vessel B was fed. 4730 g (approximately 6.1 liters) of the dispersion medium contained was continuously fed over 150 minutes. In addition, stirring is 1
It was carried out at 50 rpm. 48 minutes after the start of continuous supply, overflow started, and this fraction was preliminarily mixed with cyclohexane 2
liter into a reactor with a capacity of 10 liters.

After the continuous supply was completed, the temperature of the reaction kettle was raised and azeotropic dehydration was carried out for 8 hours, and the slurry solution was extracted from the bottom of the kettle and sieved to obtain a wet bead-shaped polymer.

Example 4 A powdered polymer was obtained in the same manner as in Example 1, except that the amount of sorbitan monostearate used as a dispersant was changed to 0.3 g.

Example 5 Acrylic acid 45 in a conical flask with a capacity of 200 cc
．． While cooling 0g from the outside, add 6.40g of water in advance.
An alkaline aqueous solution prepared from g and 69.9 g of 25% sodium hydroxide was added to neutralize 70% of the carboxyl groups. In this case, the monomer concentration with respect to water is 45 f! as the monomer concentration after neutralization! Corresponds to ij1%.

Next, 0.0158 g of N,N'-methylenebisacrylamide as a crosslinking agent and 0.104 g of potassium persulfate as a water-soluble radical polymerization initiator were added and dissolved, and then nitrogen gas was blown in to drive out dissolved oxygen. , maintained at room temperature.

Separately, 1.35 g of sorbitan monostearate as a dispersant and 182 g of cyclohexane as a dispersion medium were mixed and dissolved in a 300 cc three-day round bottom flask, and the internal temperature was raised to 65°C while nitrogen gas was introduced to drive out dissolved oxygen. I kept it.

Stirrer, reflux condenser, thermometer, nitrogen gas introduction pipe and 2
First, while introducing nitrogen gas with stirring into a 500ee capacity 5-necked flat-bottomed flask equipped with a dropper tube,
Dispersant-containing dispersion medium in 00cc flask 60. was transferred.

Subsequently, while maintaining the polymerization reaction temperature at 64 to 66°C, 121 g of the monomer aqueous solution in the 200 cc flask was added dropwise over 60 minutes using a metering pump, and in parallel, the dispersant-containing dispersion was carried out in the 300 cc flask. Medium 1
23 g was added dropwise over 60 minutes using a metering pump, and after the addition was completed, polymerization was carried out at the same temperature for 30 minutes. Subsequently, azeotropic dehydration was performed for 3 and a half hours under cyclohexane reflux.

Note that stirring was performed at 200 rpm.

When stirring was stopped, the wet beaded polymer particles settled to the bottom of the flask and could be separated into the cyclohexane layer and the container by decantation. The separated polymer was transferred to a vacuum dryer and heated to 80 to 90° C. to remove stoned cyclohexane and water, and a smooth powdery polymer was obtained.

Example 6 A powdered polymer was obtained in the same manner as in Example 1 except that n-hexane was used as the dispersion medium.

Example 7 A powdered polymer was obtained in the same manner as in Example 1 except that sorbitan monostearate (HLB 8.6) was used as a dispersant.

Example 8 In Example 1, sucrose fatty acid ester (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., part name: rDK Ester F-50) was used as a dispersant.
A powdered polymer was obtained in the same manner except that J (HLB6) was used.

Example 9 A powdered polymer was obtained in the same manner as in Example 1 except that decaglyceryl hebutastearate (HLB 2.0) was used as a dispersant.

Example 10 A powdered polymer was obtained in the same manner as in Example 1 except that hexaglyceryl monobenylate (HLB13.1) was used as a dispersant.

Comparative Example 1 Acrylic acid 30% in a conical flask with a volume R200cc
．． While cooling 0 g from the outside, add 44.7 g of water to it in advance.
．． An alkaline aqueous solution prepared from 46.6 g of 25% sodium hydroxide was added to neutralize 70% of the carboxyl groups. In this case, the monomer concentration with respect to water corresponds to 30% by weight as monomer a degree after neutralization. Next, 0.042 g of N,N'-methylenebisacrylamide as a crosslinking agent and 0.104 g of potassium persulfate as a water-soluble radical polymerization initiator were added and dissolved, and then nitrogen gas was blown in to drive out dissolved oxygen. .

Separately, 1 g 2 g s of cyclohexane as a dispersion medium and 1.35 g of sorbitan monostearate as a dispersant were added to a 1500 cc four-neck flat bottom flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube. The mixture was dissolved, nitrogen gas was introduced to drive out dissolved oxygen, and the internal temperature was maintained at 20°C.

Add the above 200 cc to the contents of this four-necked flat bottom flask.
The contents of the conical flask were added at room temperature, dispersed under stirring, and heated at a rate of 2°C/min.
After reaching ℃, the internal temperature rose rapidly and reached 75℃ several minutes later. While maintaining the internal temperature at 65-70℃,
Polymerization was carried out for 1 minute, followed by azeotropic dehydration for 4 and a half hours under cyclohexane reflux. Note that stirring was performed at 20 rpm.

When stirring was stopped, the wet beaded polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane layer by decantation. The separated polymer was transferred to a vacuum dryer and heated to 80 to 90°C to remove attached cyclohexane and water, yielding a smooth, finely powdered polymer.

Comparative Example 2 A powdered polymer was obtained in the same manner as in Example], except that the entire amount of 183 g of the dispersion medium containing the dispersant was added in advance to a 500 cc flat-bottomed flask.

Comparative Example 3 Acrylic acid 3 in a conical flask with a capacity of 200 cc
While cooling 0.0 g from the outside, add 44.4 g of water in advance.
7g and 46.6g of 25% sodium hydroxide was added to remove 70% of the carboxyl groups.
neutralized. In this case, the concentration of heptamer in water corresponds to 30% by weight as the monomer concentration after neutralization. Next, 0.042 g of N,N'-methylenebisacrylamide as a crosslinking agent and 0.104 g of potassium persulfate as a water-soluble radical polymerization initiator were added and dissolved, and then nitrogen gas was blown in to drive out dissolved oxygen. , maintained at room temperature.

Separately, 1.22 g of sorbitan monostearate as a dispersant and 18.2 g of cyclohexane as a dispersion medium were mixed and dissolved in a 50 cc three-necked flask, and the internal temperature was maintained at 65° C. while nitrogen gas was introduced to drive out dissolved oxygen.

Stirrer, reflux condenser, thermometer, nitrogen gas introduction pipe and 2
164 g of cyclohexane and 0.135 g of sorbitan monostearate were added to a 500 cc flat-bottomed flask with a capacity of 500 cc and equipped with a drop tube, and dissolved while nitrogen gas was introduced while stirring and maintained at 65°C.

Subsequently, while maintaining the polymerization reaction temperature at 64 to 66°C, 121 g of the monomer aqueous solution in the 200 cc flask was added dropwise over 60 minutes using a metering pump, and
In parallel, 19 g of dispersant-containing dispersion medium in a 50 cc flask
was added dropwise using a metering pump over a period of 60 minutes, and after the addition was completed, polymerization was carried out at the same temperature for 30 minutes. Subsequently, azeotropic dehydration was performed for 4 and a half hours under cyclohexane reflux. Note that stirring was performed at 200 rpm.

When stirring was stopped, the wet beaded polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane layer by decantation. The separated polymer was transferred to a vacuum dryer and heated to 80 to 90°C to remove attached cyclohexane and water, yielding a smooth powdery polymer.

Table 1 shows the average particle size and fine particle size (particle size of 74 μm or less) of superabsorbent polymers obtained in Examples and Comparative Examples.
fi, water absorption capacity, and gel strength.

As is clear from Table 1, the superabsorbent polymer produced according to the present invention has a narrow particle size distribution and is excellent in both water absorption capacity and gel strength.

Claims (1)

[Claims] Acrylic acid monomers containing acrylic acid and/or methacrylic acid and their alkali metal salts or ammonium salts as main components are dispersed into water droplets in oil in a dispersion medium in the presence of a water-soluble radical polymerization initiator and a dispersant. When a superabsorbent polymer is produced by polymerization by a reverse-phase suspension polymerization method, the above acrylic acid monomer is sequentially supplied to a dispersion medium as the polymerization reaction progresses, and a dispersion medium containing a dispersant is added. A method for producing a superabsorbent polymer, which comprises sequentially supplying at least a portion of the polymer into a dispersion medium as the polymerization reaction progresses.