JP2001031704A - Manufacture of highly water absorptive resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the average particle size and improve resin fixation by supplying little by little a monomer aq. soln. contg. a phosphate ester dispersant to a hydrophobic org. solvent contg. a nonionic dispersant, and kept under a polymn. condition. SOLUTION: As a monomer, usually a monovinyl monomer selected from the group consisting of (meth)acrylic acid, its salt, or (meth)acryl amide, or one consisting mainly thereof. This monomer soln. contains a phosphoric acid dispersant represented by the formula I, wherein R1 is a 8-30C alkyl group may be replaced with a phenyl group, or an aryl group may be replaced with an alkyl group, R2 is a hydroxyl group or a group represented by the formula II, and n is an integer of 1-30. During the suspension polymn., wherein the monomer aq. soln. is continuously supplied to a hydrophobic org. soln. kept under a refluxing condition, and it is pref. that the monomer soln. is supplied in not less than 20% of the time required for the total polymn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a superabsorbent resin, and more particularly to an improvement in a method for producing a superabsorbent resin by suspension polymerization. The superabsorbent resin obtained by the method of the present invention has a large average particle size, a low bulk density, and a high water absorption rate, and thus is suitable for use in paper diapers and the like.

[0002]

2. Description of the Related Art Recently, the demand for superabsorbent resins has been rapidly increasing. Its main use is in sanitary materials such as disposable diapers and sanitary products, but it is also being considered for applications in various fields such as soil water retention agents, water stoppage agents, anti-condensation agents, freshness retention agents, and solvent dehydrating agents. I have. Various types of superabsorbent resins have been proposed, but currently the mainstream is obtained by polymerizing a water-soluble monomer. As the polymerization method, a water-soluble monomer aqueous solution is subjected to bulk polymerization as it is to form a gel polymer hydrated, then crushed, dehydrated and dried, or a water-soluble monomer aqueous solution is suspended in a hydrophobic organic solvent. Polymerization is mainly used. Among them, the former bulk polymerization method is considered to be preferable because the pulverization, dehydration and drying after the polymerization are difficult, and thus the latter suspension polymerization method which does not require a pulverization step and is easily dehydrated and dried. In this method, the water contained in the produced polymer particles is easily removed by azeotropic distillation with a hydrophobic organic solvent by using a hydrophobic organic solvent that forms an azeotrope with water. be able to.

[0003]

The production of superabsorbent resins by the suspension polymerization method still has some problems to be solved. One of the reasons is that, in the suspension polymerization method, a particulate superabsorbent resin which is difficult to handle is easily generated. To improve this point, Japanese Patent Application Laid-Open No. 57-158210 has been proposed.
And JP-B-1-17482 describe using an oil-soluble cellulose ester or cellulose ether as a dispersant. JP-A-61-2092
No. 01 describes that a monoalkyl phosphate having a straight-chain alkyl group having 12 to 24 carbon atoms is used as a dispersant. JP-A-6-93008 discloses that
It describes that polyoxyethylene alkyl ether sulfate is used as a dispersant. However, these methods can produce resin particles having a large average particle size. However, there are problems such as that the generated resin particles are easily attached to the walls of the apparatus and the range of conditions under which stable polymerization can be performed is narrow.

[0004] Also, in children's disposable diapers, which are main uses of superabsorbent resins, there is a tendency to increase the amount of superabsorbent resin used and decrease the amount of diaper base materials such as pulp.
Along with this, a resin fixing property has been required in which the superabsorbent resin is fixed to a diaper base material such as pulp before and after water absorption and is difficult to move. For this resin fixability, it is considered advantageous that the resin particles have large irregularities on the surface and are easily engaged with each other or with pulp or the like. However, resin particles obtained by suspension polymerization are generally spherical and have a smooth surface, which is considered to be disadvantageous for this requirement for resin fixability. Therefore, the present invention provides a high average water-absorbent resin having a large average particle size and a high resin fixability,
It is an object of the present invention to provide a method for producing by a suspension polymerization method.

[0005]

According to the present invention, there is provided a method for producing a superabsorbent resin by supplying an aqueous solution of a monomer containing a water-soluble monovinyl monomer and a polymerization initiator to a hydrophobic organic solvent and performing suspension polymerization. A nonionic dispersant is contained in a hydrophobic organic solvent, a phosphate dispersant represented by the general formula (1) is contained in an aqueous monomer solution, and the hydrophobic organic solvent is added under polymerization conditions. By maintaining and keeping supplying the monomer aqueous solution successively, it is possible to produce a superabsorbent resin having a large average particle size and a high resin fixability.

[0006]

Embedded image

(Wherein, R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group, and R ² represents a hydroxyl group or

[0008]

Embedded image

Represents a group. n shows the integer of 1-30. )

[0010]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, any water-soluble monovinyl monomer known to give a superabsorbent resin can be used as a raw material. Some examples are (a) ionic monomers such as (meth) acrylic acid and its alkali metal salts and ammonium salts, and (b) nonionic monomers such as acrylamide-2-ethylsulfonic acid and its alkali metal salts. For example, (meth) acrylamide, N, N-dimethylacrylamide, 2-hydroxyethyl (meth) acrylate, N
(C) amino group-containing monomers such as methylol (meth) acrylamide and quaternary compounds thereof, for example, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, and the like. They can be used together.

Of these, preferred are (meth) acrylic acid and its alkali metal salts and ammonium salts,
(Meth) acrylamide and the like. As the alkali metal salt, sodium salt, potassium salt, lithium salt, rubidium salt and the like are used, the performance of the resulting super absorbent resin,
Sodium salts or potassium salts are preferred from the viewpoint of industrial availability and safety. Usually these (meta)
A monovinyl monomer selected from the group consisting of acrylic acid, a salt thereof, and (meth) acrylamide, or a monomer mainly containing the same is used.

These water-soluble monovinyl monomers are used so that the monomer concentration in the aqueous solution is usually 20% by weight or more, preferably 25% by weight to a saturated concentration. The ionic monomers such as (meth) acrylic acid and acrylamido-2-ethylsulfonic acid are in a form in which at least a part thereof is neutralized with an alkali metal hydroxide, ammonium hydroxide, or the like, that is, a salt. It is preferred to use it in form. The degree of neutralization is usually 20 to 100 mol%, preferably 30 to 100 mol%.

Although these water-soluble monovinyl monomers, particularly acrylic acid monomers, give rise to a certain degree of self-crosslinking during polymerization even without the use of a crosslinking agent to give a highly water-absorbing resin. In order to obtain a functional resin, it is preferable to use a crosslinking agent in combination with the above monomer. As the cross-linking agent, a polyvinyl monomer or a compound having two or more functional groups that react with the functional groups of the above monomers is used. That is, the formation of the crosslinked structure is roughly divided into a method of copolymerizing a polyvinyl monomer having two or more ethylenically unsaturated bonds, and a method of forming a functional group of the water-soluble monovinyl monomer, such as a glycidyl group. And reacting a compound having two or more functional groups capable of reacting with a compound. In the latter method, if the reaction between the functional groups occurs before the polymerization, the resulting monomer compound having two or more ethylenically unsaturated bonds is copolymerized, which is essentially the same as the former method. Does not change.

Examples of the crosslinking agent having two or more ethylenically unsaturated bonds include (a) di- or tri (meth) acrylates of polyol, for example, when the polyol is ethylene glycol, propylene glycol, trimethylolpropane, glycerin, (B) In (b) above, the unsaturated acid is other than (meth) acrylic acid, for example, maleic acid, fumaric acid, etc. C) bisacrylamides,
For example, N, N'-methylenebisacrylamide, etc.
(D) Di or tri (meth) acrylates obtained by reacting polyepoxide with (meth) acrylic acid, di (meth) acrylate obtained by reacting (e) polyisocyanate with hydroxy (meth) acrylate Carbamyl acrylates, for example, those in which the polyisocyanate is tolylene diisocyanate, hexamethylene diisocyanate, etc .; Examples include stall triallyl ether, trimethylolpropane triallyl ether, diethylene glycol diallyl ether, triallyl trimellitate and the like. Among them, in the present invention, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N'-methylenebis (meth) acrylamide and the like are preferable.

Examples of the crosslinking agent having two or more functional groups which react with the functional group of the monovinyl monomer include diglycidyl ether compounds, haloepoxy compounds and isocyanate compounds. Among these, a diglycidyl ether compound is particularly preferred. Specific examples of the diglycidyl ether compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether,
Examples thereof include polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, and polyglycerin diglycidyl ether. Among them, ethylene glycol diglycidyl ether is preferable. Examples of the haloepoxy compound include epichlorohydrin and β-methylepichlorohydrin.
4-tolylene diisocyanate, hexamethylene diisocyanate and the like. The amount of the crosslinking agent used is usually 0 to 10% by weight based on the monovinyl monomer.
It is preferably from 5 to 5% by weight, particularly preferably from 0.01 to 1% by weight.

As the polymerization initiator, a conventional water-soluble radical polymerization initiator may be used. Some examples thereof include (a) hydrogen peroxide, (b) persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, and (c) azo-based initiators such as 2,2'-azobis-
(2-amidinopropane) dihydrochloride, 2,2'-azobis- (N, N'-dimethyleneisobutylamidine) dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1
-Bis (hydroxymethyl) -2-hydroxyethyl]
And propionamide. These water-soluble radical initiators can be used alone or in combination. In addition, hydrogen peroxide and persulfate can be used as a redox initiator by combining a reducing substance such as sulfite and L-ascorbic acid, an amine salt, and the like. These polymerization initiators are used in an amount of 0.001 to 5% by weight based on the monovinyl monomer. 0.
It is preferably used in an amount of from 01 to 1% by weight, particularly from 0.02 to 0.75% by weight.

As a hydrophobic organic solvent which is a reaction medium for suspension polymerization, any one can be used as long as it is basically insoluble in water and inert to polymerization. Some examples are (a) aliphatic hydrocarbons such as n-pentane, n
(B) alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and (c) aromatic hydrocarbons such as benzene, toluene and xylene. Preferably, the hydrophobic organic solvent has a lower boiling point than water and forms an azeotrope with water. Usually, n-hexane, n-heptane, cyclohexane or the like is used. The hydrophobic organic solvent is used usually in an amount of 0.5 to 10 times the weight of the aqueous monomer solution. It is preferably used in an amount of 0.5 to 3 times by weight, particularly 0.75 to 2.0 times by weight. If the ratio of the hydrophobic organic solvent is too small, it is easy to aggregate even if a dispersant is present, and it becomes difficult to obtain a highly water-absorbent resin having a desired particle size. Conversely, if this ratio is too large, productivity will decrease.

In the present invention, a nonionic dispersant is contained in a hydrophobic organic solvent. As the nonionic dispersant, any one can be used as long as it has solubility or affinity in a hydrophobic organic solvent and basically forms a W / O type emulsification system. Usually, those having an HLB of 1 to 9, preferably 2 to 7 are used. Some examples thereof include sorbitan fatty acid esters, sucrose fatty acid esters, polyglycerin fatty acid esters, polyoxyethylene alkylphenyl ether, sorbitol fatty acid esters, and the like. Of these, sorbitan fatty acid esters are preferably used. On the other hand, a phosphate dispersant represented by the general formula (1) is contained in the monomer aqueous solution.

[0019]

Embedded image

(Wherein, R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group, and R ² represents a hydroxyl group or

[0021]

Embedded image

Represents a group. n shows the integer of 1-30. )

This phosphate ester-based dispersant is a highly safe dispersant with low irritation and toxicity. In the general formula (1), R ¹ is preferably an alkyl group having 8 to 23 carbon atoms or a monoalkylphenyl group. n is 2
It is preferably 15. R ²

[0024]

Embedded image

The groups are preferably identical. Representative and preferred examples of R ¹ include a nonylphenyl group, an octylphenyl group, a tridecyl group, a lauryl group, a 2-ethylhexyl group, an octadecyl group, and a dodecylphenyl group. This commercially available phosphate ester-based dispersant is usually a mixture of a phosphate monoester and a phosphate diester.

The concentration X (% by weight) of the nonionic dispersant in the hydrophobic organic solvent and the concentration Y (% by weight) of the phosphate ester dispersant in the aqueous monomer solution are usually represented by the following formula (2).
And (3).

[0027]

1 ≦ Y / X ≦ 10 (2) 0.01 ≦ X + Y ≦ 2.0 (3)

Outside the range of the formula (2), it is difficult to obtain a porous superabsorbent resin. If the sum of the two concentrations is less than 0.01% by weight, the amount of the dispersant is too small, and it is difficult to disperse the monomer aqueous solution as stable droplets. Conversely, when the sum of the concentrations exceeds 2.0% by weight, the resin particles tend to aggregate when the superabsorbent resin particles obtained by suspension polymerization are dried.

In the present invention, the hydrophobic organic solvent is maintained under polymerization conditions, and an aqueous monomer solution is sequentially supplied thereto to carry out suspension polymerization. Usually, a hydrophobic organic solvent is maintained under reflux conditions, and an aqueous monomer solution is continuously supplied thereto at a constant rate for suspension polymerization.If desired, the supply rate of the aqueous monomer solution may be changed. May be temporarily interrupted on the way. Usually, the supply of the monomer aqueous solution is performed over a period of at least 20%, preferably at least 40% of the total polymerization time. The term “total polymerization time” means that the degree of polymerization of the monomer of the resin particles generated from the start of the polymerization is 98%, preferably 98.
Means the shorter of the time to reach 5% or the time to complete the polymerization operation. Also, as described above, the monomer aqueous solution is usually supplied to a hydrophobic organic solvent with stirring to disperse it in droplets. It may be supplied in an organic solvent.

According to the method of the present invention, a granular resin having an appearance such that fine resin particles having a size of 5 to 100 μm are fused and integrated can be obtained. The generation mechanism is considered as follows. First, the aqueous monomer solution supplied to the hydrophobic organic solvent in the initial stage of polymerization is dispersed and polymerized into fine droplets by the action of the nonionic dispersant in the solvent to form fine resin particles. However, when the monomer aqueous solution is subsequently supplied, the action of dispersing the monomer aqueous solution of the nonionic dispersant decreases due to the action of the phosphate ester dispersant in the monomer aqueous solution, and the monomer aqueous solution stabilizes to fine water droplets. As a result, the monomer aqueous solution supplied later is absorbed by the fine resin particles already existing in the system. As a result, it is considered that fine resin particles having a sticky surface by absorbing the aqueous monomer solution and resin particles newly generated from the aqueous monomer solution aggregate with each other to form granular resin particles. Since the polymerization system is vigorously stirred, if fine resin particles aggregate and grow to a size of several hundred μm, it is considered that further growth does not substantially occur due to the dispersing action due to the stirring. Can be

The polymerization reaction is usually carried out at 40 to 150 ° C., although it depends on the polymerization initiator. If the temperature is too high, self-crosslinking becomes active, and the water absorption capacity of the resin particles produced is reduced.
On the other hand, when the temperature is too low, not only long time is required for polymerization, but also sudden polymerization may be caused to form lumps. A suitable polymerization temperature is 60 to 90 ° C, and it is particularly preferable to carry out the polymerization under the reflux condition of a hydrophobic organic solvent.

After completion of the polymerization, resin particles produced by filtration or centrifugation are collected and dried by a conventional method to obtain a product.
When a hydrophobic organic solvent that forms an azeotropic mixture with water is used, it is preferable to dehydrate the resin particles by azeotropic distillation before collecting the resin particles by filtration or the like. In the suspension polymerization according to the method of the present invention, the polymerization conditions for producing the desired resin particles are wide and the adhesion of the resin to the walls of the polymerization vessel is small, so that the polymerization operation is easy. The resin particles obtained by the method of the present invention have a structure in which fine particles are fused and integrated, unlike true spherical particles obtained by a usual suspension polymerization method. The average particle size is usually as large as 300 to 1000 μm, and almost no fine powder having a size of less than 100 μm which is problematic in handling is not contained. Therefore, the resin particles obtained by the method of the present invention have a high water absorption rate and a high resin fixability before and after water absorption.

[0033]

The present invention will be described more specifically with reference to the following examples. The absorption capacity, water absorption speed, average particle size, bulk density, and fixability of the water-absorbing resin were measured as follows. (1) Absorption capacity A 250-mesh nylon bag (20 cm x 10 cm size) is immersed in 500 cc of artificial urine for 30 minutes. The nylon bag is pulled up, suspended in the air and drained for 15 minutes, and the weight (w ₁ (g)) is measured. About 0.5 g of resin particles are collected, and the weight (w ₂ (g)) is precisely weighed and placed in the above nylon bag. This was immersed in 500 cc of artificial urine for 30 minutes, then the nylon bag was pulled up, suspended in air and drained for 15 minutes, and then weighed (w ₃
(G)) is measured.

[0034]

## EQU3 ## Absorption capacity = (w ₃ −w ₁ ) / w ₂ (g / g)

The artificial urine used had the following composition by weight. Urea 1.94% Sodium chloride 0.80% Calcium chloride 0.06% Magnesium sulfate 0.11% Pure water 97.09%

(2) Water absorption rate The water absorption rate was measured using the apparatus shown in FIG. 1 according to JIS K-7224. 1.0 g of resin particles were placed on a nonwoven fabric spread on a support plate having small holes so as to have a uniform thickness. The lower surface of the resin particle layer was brought into contact with 0.9% by weight of a saline solution, and the amount of the resin particles absorbing the saline solution was measured. The water absorption rate was defined as the amount of 0.9% by weight saline solution absorbed for 20 minutes after the start.

(3) Average particle size The ASTM type standard sieve is 8 mesh, 12 mesh,
20 mesh, 32 mesh, 40 mesh, 60 mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh, and in the order of the tray, put about 50 g of the resin particles in the uppermost sieve and shake for 1 minute with a low tapping type automatic shaker. I let it. The weight of the resin particles remaining on each sieve was weighed, and the total weight was taken as 100%, the particle size distribution was determined from the weight fraction, and the 50% particle size on a weight basis was taken as the average particle size.

(4) Bulk density The bulk density was measured in accordance with JIS K-6721. The measurement was performed three times, and the average value was obtained. (5) Fixation of Resin Particles Absorbed by Water 2.5 g of resin particles were added to fluff pulp (basis weight: 150 g /
m ² , size 19 × 7.5 cm).
A fluff pulp of the same size was overlaid on the resin particle / fluff pulp composite to prepare a simple water-absorbing pad. This water-absorbing pad is put on a hydraulic press at room temperature for 100
After applying a load of kg for 20 minutes, 0.9% physiological saline 1
25 g of water was absorbed by the water absorbing pad. A 3.5 kg iron weight is placed on the water-absorbing pad, and a universal shaker (manufactured by Inuchi Seiseido Co., Ltd., model number MS-1) is used for 3 minutes in the horizontal direction with respect to the water-absorbing pad (number of shakes: 100) Times /
Min) Shake. The load was removed, and the resin particles existing in the pulp and the resin particles that had come out of the pulp by vibrating were respectively recovered, and their weights were measured. Resin particle fixability was calculated by the following equation.

[0039]

## EQU4 ## Fixability (%) of water-absorbed resin particles = {resin particles in pulp (g)} resin particles outside pulp (g) + resin particles in pulp (g)} × 100

Example 1 12.2 g of water was added to 186.9 g of acrylic acid, and 311.6 g of a 25% by weight aqueous sodium hydroxide solution was further added while cooling to neutralize. To the resulting solution, 0.0940 g of ethylene glycol diglycidyl ether (manufactured by Nagase Chemicals, Denacol EX810), 0.0190 g of sodium hypophosphite monohydrate, 0.940 g of potassium persulfate, and a dispersant 1.405 g of polyoxyethylene octyl phenyl ether phosphate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Plysurf A210G, average degree of polymerization of oxyethylene groups: about 7) was added and dissolved to prepare an aqueous monomer solution.

624 g of cyclohexane was placed in a three-liter four-necked round-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen gas inlet tube, and sorbitan monostearate having an HLB of 4.7 as a dispersant was added thereto. Set the rate to 0.
3120 g was added, and the mixture was stirred at 500 rpm. After replacing the flask with nitrogen gas, the temperature was raised to 75 ° C. to reflux cyclohexane. The aqueous monomer solution prepared above was added dropwise thereto at a dropping rate of 7.3 g / min over 70 minutes. After completion of the dropwise addition, the mixture was further kept at 75 ° C. for 30 minutes, and then dehydrated by azeotropic distillation with cyclohexane until the water content of the resin particles became 7%. When the stirring was stopped, the resin particles settled at the bottom of the flask. The resin particles were separated by decantation and dried at 90 ° C. to remove the attached cyclohexane and water. The obtained resin particles are 1 to
The granules had a structure in which 50 μm primary particles were fused to each other. Table 1 shows the physical properties of the resin particles, and FIG. 2 shows an electron micrograph.

Example 2 In Example 1, the dispersant was added to the aqueous monomer solution in an amount of 0.6%.
Suspension polymerization was carried out in exactly the same manner as in Example 1 except that 38 g and 0.650 g of cyclohexane were added. The results are shown in Table 1.

Example 3 In Example 1, 2.5 parts of the dispersant in the aqueous monomer solution was used.
The suspension polymerization was carried out in exactly the same manner as in Example 1 except that the amount was changed to 00 g. The results are shown in Table 1.

Example 4 The procedure of Example 1 was repeated except that the dispersant was added to the aqueous monomer solution in an amount of 1.5%.
Suspension polymerization was carried out in exactly the same manner as in Example 1, except that 60 g and 1.560 g were added to cyclohexane. The results are shown in Table 1.

Example 5 The procedure of Example 1 was repeated except that the dispersant was added to the aqueous monomer solution in 5.1.
Suspension polymerization was carried out in exactly the same manner as in Example 1 except that 10 g and 3.500 g of cyclohexane were added. The results are shown in Table 1.

Example 6 The procedure of Example 1 was repeated except that the dispersant in the aqueous monomer solution was changed to 1.5.
Exactly the same as Example 1 except that the sucrose fatty acid ester (a product of Daiichi Kogyo Seiyaku Co., Ltd., DK Ester F-50) was added in place of sorbitan monostearate as a dispersant in cyclohexane to 60 g. To perform suspension polymerization. The results are shown in Table 1.

Example 7 In Example 1, polyoxyethylene tridecyl ether phosphate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Plysurf) was used in place of polyoxyethylene octyl phenyl ether phosphate as a dispersant in the aqueous monomer solution. A
Suspension polymerization was carried out in exactly the same manner as in Example 1 except that 1.560 g of 212C) was added. The results are shown in Table 1.

Example 8 9.4 g of water was added to 145.4 g of acrylic acid, and 2
242.3 g of a 5% by weight aqueous sodium hydroxide solution was added while cooling to neutralize. Ethylene glycol diglycidyl ether (Denacol EX810) is added to the resulting solution.
0.0727 g and sodium hypophosphite monohydrate in 0.1 g.
0146 g, 0.727 g of potassium persulfate, and 1.00 of polyoxyethylene octyl phenyl ether phosphate (Plysurf A210G) as a dispersant.
0 g was added and dissolved to prepare an aqueous monomer solution.

624 g of cyclohexane was placed in a three-liter four-necked round-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen gas inlet tube, and sorbitan monostearate having an HLB of 4.7 as a dispersant was added thereto. Set the rate to 0.
312 g was added, and the mixture was stirred at 500 rpm. After replacing the flask with nitrogen gas, the temperature was raised to 75 ° C. to reflux cyclohexane. The monomer aqueous solution prepared above was added dropwise thereto at a dropping rate of 5.7 g / min over 70 minutes. After completion of the dropwise addition, the mixture was further kept at 75 ° C. for 30 minutes, and then subjected to post-treatment exactly in the same manner as in Example 1 to obtain a granular resin having a structure in which primary particles of 1 to 50 μm were fused together. The results are shown in Table 1.

Comparative Example 1 A suspension polymerization was carried out in the same manner as in Example 1 except that the dispersant was not added to the aqueous monomer solution and the amount of the dispersant in cyclohexane was changed to 1.56 g. . The results are shown in Table 1. A micrograph of this resin is shown in FIG.

Comparative Example 2 In Example 1, the dispersant in the aqueous monomer solution was changed to 1.4.
The suspension polymerization was carried out in exactly the same manner as in Example 1, except that the dispersant was not added to cyclohexane. The results are shown in Table 1. FIG. 4 shows a micrograph of the obtained resin particles.

[0052]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a water absorption rate measuring device.

FIG. 2 is a micrograph of the resin particles obtained in Example 1.

FIG. 3 is a micrograph of the resin particles obtained in Comparative Example 1.

FIG. 4 is a micrograph of the resin particles obtained in Comparative Example 2.

[Description of Signs] 1 Bullet 2 Rubber stopper 3 Support plate with small holes 4 Non-woven fabric 5 Resin particles

Claims (7)

[Claims] 1. A method for producing a super water-absorbent resin, which comprises the steps of: supplying a monomer aqueous solution containing a water-soluble monovinyl monomer and a polymerization initiator to a hydrophobic organic solvent to carry out suspension polymerization;
A nonionic dispersant is contained in a hydrophobic organic solvent, and a phosphate dispersant represented by the general formula (1) is contained in an aqueous monomer solution, and the hydrophobic organic solvent is maintained under polymerization conditions. And successively supplying an aqueous monomer solution thereto. Embedded image (In the formula, R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group, and R ² represents a hydroxyl group or And n represents an integer of 1 to 30) 2. An aqueous monomer solution is used for 20% of the total polymerization time.
2. The method according to claim 1, wherein the solution is supplied into the hydrophobic organic solvent over the above time. 3. The method according to claim 1, wherein in the formula (1), R ¹ is an octylphenyl group. 4. The method according to claim 1, wherein in the formula (1), n is 2 to 15. 5. The method according to claim 1, wherein the water-soluble monovinyl monomer is a monovinyl monomer selected from the group consisting of acrylic acid, acrylate, methacrylic acid, methacrylate, acrylamide and methacrylamide, or is mainly composed of the same. The method according to any one of claims 1 to 4, wherein 6. The aqueous monomer solution contains a crosslinking agent selected from the group consisting of a small proportion of a water-soluble monovinyl monomer and a polyfunctional compound having a plurality of functional groups that react with the functional groups of the monovinyl monomer. The method according to any one of claims 1 to 5, wherein the method is performed. 7. The concentration X (% by weight) of a nonionic dispersant in a hydrophobic organic solvent and the general formula (1) in an aqueous monomer solution
Concentration of phosphoric acid ester dispersant represented by Y (% by weight)
Satisfies the following formulas (2) and (3). 1 ≦ Y / X ≦ 10 (2) 0.01 ≦ X + Y ≦ 2.0 (3)