JP3363000B2 - Method for producing water absorbent resin - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a water absorbent resin. More specifically, the present invention provides a water-containing polymer gel obtained by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer, in the presence of an inorganic powder, by additionally adding the monomer to polymerize the particle size. The present invention relates to a method for producing a large beaded water absorbent resin. According to the method of the present invention, a product granulated product having an average particle diameter of 200 to 3000 μ is arbitrarily obtained, and the obtained granulated product has few fine particles and has a narrow particle size distribution and a binding force of primary particles. Because of its large size, it can be used not only in sanitary materials such as disposable diapers and sanitary napkins, but also in the field of agriculture as a soil water retention agent, and also as a waterproofing material, a sliding material, a dew condensation prevention material, etc. as a civil engineering and construction material.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been used not only for sanitary materials such as diapers and sanitary products but also for industrial applications such as waterproofing materials, dew-prevention materials, freshness-retaining materials, solvent dehydration materials, greening, agricultural and horticultural applications, etc. It has come to be used also in the above, and various things have been proposed so far. As this type of water absorbent resin,
Hydrolyzates of starch-acrylonitrile graft copolymers, crosslinked carboxymethyl cellulose, crosslinked polyacrylic acid (salt), acrylic acid (salt) -vinyl alcohol copolymer, crosslinked polyethylene oxide and the like are known.

However, it has been difficult to say that all of these water-absorbent resins are satisfactory in particle size. In particular, polymers obtained by reverse phase suspension polymerization have various problems. For example, in water-in-oil type (hereinafter referred to as W / O type) reverse phase suspension polymerization of an alkali metal acrylate, HLB described in JP-B-54-30710 is used as a dispersant.
Sorbitan fatty acid ester of 3 to 6, JP-A-57-16
Nonionic surfactants of HLB 6 to 9 described in JP-A-7302 or HLB described in JP-B-60-25045.
When the surfactants of 8 to 12 were used, only the water absorbent resin having a fine particle size of about 10 to 100 μm was obtained. On the other hand, Japanese Examined Patent Publication No. 63-36321 and Japanese Examined Patent Publication No. 6
When a lipophilic carboxyl group-containing polymer is used as the dispersant described in JP-A No. 3-36322, a polymer having a particle size of about several hundred μm can be obtained, but the affinity between the dispersant and the acrylic acid-based monomer is high. Since it is high, there is a problem that it tends to agglomerate during the polymerization reaction.

As a method for increasing the particle size of the water-absorbent resin, Japanese Patent Publication No. 17482/1989 and Japanese Patent Laid-Open No. 57-158 (1982) are known.
No. 210 discloses a method of using an oil-soluble cellulose ester or a cellulose ether as a dispersant, but in such a method, the dispersant remaining at the time of drying is melted and the polymer is agglomerated or There was a problem that it easily adhered to the wall. Further, when the polyglycerin fatty acid ester of HLB 2 to 16 is used as the dispersant described in JP-A-62-172006, even if a polymer having a large particle size is obtained, the manufacturing conditions for obtaining it stably are acceptable. Since the range is very narrow, if it deviates from this condition, bulk polymerization is likely to occur, and it is difficult to say that it is advantageous in view of industrial stable production.

On the other hand, as an alternative method to the above, there has been proposed a method in which primary particles of a water-absorbent resin are granulated using a binder such as water or polyvinyl alcohol. However, the method using water as a binder in this method has a problem that the binding property between particles is extremely weak and the binding particles are easily broken during general transportation and handling. Further, the one using polyvinyl alcohol is not always a superior method because the binding property is improved but a large amount of polyvinyl alcohol is required and a special device is required, resulting in high cost. .

Further, in JP-A-62-230813, a dispersion of water-absorbent resin seed particles formed from a first monomer in a non-aqueous liquid is formed, and the water-soluble ethylenically unsaturated secondary particles are formed on the particles. A seed polymerization process has been shown which consists of absorbing a monomer and then polymerizing a second monomer. Then, according to this method, it is described that a water absorbent resin having a size larger than the seed particles or having a large particle size in which the seed particles are aggregated can be obtained. However, in this method, when the second monomer is polymerized, since the same dispersant (W / O type dispersant) or stabilizer as that of the first monomer is used, they are dissolved in the solvent. When the second monomer aqueous solution is added to the system under the state, the second monomer aqueous solution becomes a suspension state before being absorbed by the hydrogel particles obtained in the first-stage polymerization, There is a problem in that the liquid absorption of the second monomer is extremely slow and it is difficult to obtain an aggregate having excellent binding strength.

On the other hand, in Japanese Unexamined Patent Publication (Kokai) No. 3-227301, in a similar seed polymerization method, the slurry liquid after the completion of the first-step reverse phase suspension polymerization is cooled to obtain a surfactant and / or a polymeric protective colloid. There has been proposed a method for producing a water-absorbent resin, in which a second-stage monomer aqueous solution is added so as to be a precipitated state in a solvent, and after the liquid-absorption, the second-stage and subsequent polymerization is carried out. In this method, a surfactant and / or a polymeric protective colloid is deposited by cooling the first-stage polymerization liquid, so that the surfactant function, that is, the second-stage monomer aqueous solution is suspended, that is, W. / O-type emulsion is not formed, liquid is sufficiently absorbed, and when polymerized, there is little fine powder,
Moreover, it is stated that a water absorbent resin having a sharp particle size distribution can be obtained.

However, this method is aimed at precipitating the surfactant by cooling to stop the surfactant function, but in fact, the surfactant and / or the polymer protective colloid are from several kinds to several tens. It is composed of many kinds of components, and the precipitation temperatures of the components also differ considerably. Therefore, in order to completely precipitate such a multi-component substance, it may be necessary to select extremely severe conditions such as zero degrees or less in some cases, which is practically impossible. Therefore, in reality, it is the fact that the important component remains in the place where it is precipitated, and as a result, the W / O type surfactant and / or polymer protective colloid still dissolved in the suspension is present, and the second stage Remarkably inhibits absorption of the aqueous monomer solution in the eye. As a result, the water-absorbent resin obtained by the method contains a considerable amount of fine powder, and even if a granulated product in which primary particles are aggregated is formed, the binding strength is wide and it is not satisfactory.

Further, the liquid absorption rate is also markedly hindered by cooling, and it takes several tens of minutes to several hours for sufficient absorption. Therefore, for example, when handling an acrylic acid-based monomer having an extremely high polymerizability, not only is the risk of abnormal polymerization during liquid absorption extremely high, but also the process requires a long process time, and its operation is extremely complicated. Yes, and inferior in productivity.

Further, in Japanese Unexamined Patent Publication No. 6-184211, the first stage polymerization is carried out by using a specific radical polymerization reactive surfactant, and the radical polymerization reactivity used in the first stage in the seed polymer. A method of incorporating a surfactant and removing the surfactant from the medium for liquid absorption and polymerization after the second step is disclosed.

[0011]

This method emphasizes the advantage of being able to absorb the second monomer at a relatively high temperature without cooling the excess surfactant in the medium. This method is theoretically very interesting, but even if a specific radical-polymerization reactive surfactant is used, the substance remains a considerable amount of unpolymerized substance, and it is described in the specification. However, protective colloids with an emulsifier as a subordinate to physically stabilize the reactants taken up in the suspension, eg modified cellulose, polyethylene oxidized or modified with maleic anhydride or copolymers thereof. As stated in the availability of
Emulsion stability as a surfactant is poor, and seed particles cannot be stably obtained by itself. Therefore, as a result, this remains in the medium and the W / O also remains in the second and subsequent polymerization reaction systems.
There is a problem that an emulsified system of a mold is formed, the number of fine particles is large, and a satisfactory granulated product cannot be obtained.

An object of the present invention is a method for producing a bead-shaped water-absorbent resin obtained by the above-mentioned reverse phase suspension polymerization method, which can be easily carried out without depositing a surfactant and / or a polymer protective colloid. It is an object of the present invention to provide a method for producing a granulated product having good granulation efficiency, a small number of fine particles, and a large binding property.

[0013]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a reaction mixture containing hydrous polymer gel particles obtained by reverse phase suspension polymerization is used in the presence of an inorganic powder. By adding and absorbing the aqueous monomer solution and performing additional polymerization, the absorption of the aqueous monomer solution is very quickly and efficiently absorbed by the seed particles, and an average of 200-3 is obtained.
It was found that a product granulated product of 000μ can be arbitrarily obtained, and that the obtained granulated product has few fine particles, a narrow particle size distribution, and a large binding strength of the granulated particles, and completes the present invention. Came to.

That is, according to the present invention, when a water-absorbent resin is produced by subjecting a water-soluble ethylenically unsaturated monomer to reverse phase suspension polymerization, a water-soluble resin optionally containing a crosslinking agent in a hydrophobic organic solvent in the presence of an emulsifier. An ethylenically unsaturated monomer aqueous solution,
Subjected to a first-stage water-in-oil type reverse phase suspension polymerization reaction using a water-soluble radical polymerization initiator, then in the reaction mixture containing the resulting water-containing polymer gel particles, in the presence of inorganic powder,
Water-soluble water-soluble ethylenically unsaturated monomer optionally containing a crosslinking agent is additionally added, and after the monomer aqueous solution is absorbed by the polymer gel particles, an operation of additional polymerization is repeated at least once or more. It is a method for producing a resin.

In the present invention, the water-soluble ethylenically unsaturated monomer aqueous solution is added to the reaction mixture containing the hydrous polymer gel particles obtained in the first step to allow the above-mentioned specific inorganic powder to be present. The liquid can be absorbed very quickly and efficiently. Therefore, even an acrylic acid-based monomer having a high polymerizability can be added and absorbed in the first-stage slurry system at a relatively high temperature.

Secondly, no matter how the stirring is increased in the second and subsequent polymerizations, it is difficult to produce a single-powder fine powder polymer.
Meanwhile, the as JP-A 3-227301 discloses, in a method of depositing a surfactant remaining component is not precipitated just because the surfactant is a multi-component system, which is fine to generate forms an emulsion system. Thirdly, the liquid can be absorbed at any temperature, and, for example, cooling operation for depositing the surfactant is not required at all, as in JP-A-3-227301. Fourthly, the average particle size, binding strength and the like can be arbitrarily changed by appropriately selecting the type of the inorganic powder.

Fifth, it is possible to take a very wide range of the ratio of the liquid absorption amount of the second and subsequent monomer aqueous solutions with respect to the first stage aqueous monomer solution. That is, the target granulation is possible with an extremely small amount of the aqueous solution of the absorbing monomer. JP-A-3-227301, which is a prior art of the above-mentioned seed polymerization method
In the publication, the lower limit amount of the aqueous solution of the monomer in the second and subsequent stages is 50% in the first stage, and as described in this publication, various desired effects cannot be obtained by granulation. It has a wide variety of features such as extremely poor efficiency of chemical conversion. Hereinafter, the method of the present invention will be described in detail.

[0018]

DETAILED DESCRIPTION OF THE INVENTION

(Water-soluble ethylenically unsaturated monomer) As the water-soluble ethylenically unsaturated monomer used in the present invention, any water-soluble ethylenically unsaturated monomer can be basically used as long as it is soluble in water. For example, (meth) acrylic acid and / or its alkali metal salt, ammonium salt, 2- (meth) -acrylamido-2-methylsulfonic acid and / or its alkali metal salt, (meth) acrylamide, N, Amino group-containing unsaturated monomers such as N-dimethylacrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, diethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylate, and their quaternized products And one or more of these can be used. The term “(meth) acrylic” means both “acrylic” and “methacrylic”.

Of these, (meth) acrylic acid and / or its alkali metal salts, ammonium salts,
(Meth) acrylamide may be mentioned. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt, rubidium salt and the like, and the performance of the obtained polymer,
From the viewpoint of industrial availability, safety, etc., sodium salt or potassium salt is preferable.

The monomer concentration in the aqueous solution of these water-soluble ethylenically unsaturated monomers is generally 20% by weight.
As described above, the concentration is preferably 25% by weight to the saturated concentration. Also,
(Meth) acrylic acid, 2-methyl-acrylamide-2
-Sulfonic acid or the like is used in a form neutralized in part or in whole with an alkali metal compound or an ammonium compound, and the neutralization ratio (referred to as the degree of neutralization) at this time is 20 to 10
It is 0 mol%, preferably 30 to 100 mol%.

In the present invention, as the water-soluble ethylenically unsaturated monomer species as described above, the monomer components used in the second and subsequent stages may be the same or different from the monomer components used in the first stage. Good. Furthermore, when the monomer components used in the second and subsequent stages are of the same type as the monomer components used in the first stage, the monomer concentration in the aqueous solution, the degree of neutralization, etc. may change, and not only any type, but various It is possible to adopt various conditions.

(Emulsifier) The emulsifier used in the present invention is used in the reverse phase suspension polymerization system of the first stage, and these are soluble or compatible with a hydrophobic solvent and are W / O type emulsions. Any material can be used as long as it makes a system. Specific examples of the present emulsifier include, for example, sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkylphenyl ether, ethyl cellulose, ethyl hydroxyethyl cellulose, polyethylene oxide,
Maleic anhydride polyethylene, maleic anhydride polybutadiene, maleic anhydride ethylene propylene diene terpolymer, copolymer of α-olefin and maleic anhydride or its derivative, fatty acid salt, alkylbenzene sulfonate, polyoxyethylene alkyl ether Examples thereof include phosphate. The amount of these emulsifiers used is 0.05 to 10% by weight, preferably 0.
It is 1 to 1% by weight.

(Hydrophobic Solvent) The hydrophobic solvent used in the present invention is basically insoluble in water, and any solvent can be used as long as it is inert to the polymerization. As an example thereof, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, aromatic carbons such as benzene, toluene and xylene. Examples thereof include hydrogen. N-hexane, n-heptane, and cyclohexane can be mentioned as a preferable solvent in view of the stability and quality of industrial availability. The amount of these hydrophobic solvents used is 0. 0, based on the water-soluble ethylenically unsaturated monomer aqueous solution used in the first step.
5 to 10 times by weight, preferably 0.6 to 5 times by weight is adopted.

(Crosslinking Agent) In the present invention, a crosslinking agent can be used in the first step and the second step and thereafter, if necessary.
In the present invention, if necessary, for example, self-crosslinking by the so-called monomer itself occurs even in the absence of a crosslinking agent depending on the monomer conditions (type of monomer, concentration of monomer in aqueous solution, degree of neutralization, etc.), This is because a water absorbent resin can be formed thereby. However, a cross-linking agent may be necessary depending on the required performance such as water absorption capacity and water absorption speed. Examples of the cross-linking agent used in the present invention include cross-linking agents having two or more polymerizable unsaturated groups and / or reactive functional groups.

As the cross-linking agent having two or more polymerizable unsaturated groups, ethylene glycol, propylene glycol,
Di- or tri (meth) acrylic acid esters of polyols such as trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin, reacting the above polyols with unsaturated acids such as maleic acid and fumaric acid Unsaturated polyesters obtained by the reaction, bisacrylamides such as N, N'-methylenebisacrylamide, di- or tri (meth) acrylic acid esters obtained by reacting a polyepoxide with (meth) acrylic acid, and tolylenediene Di (meth) acrylic acid carbamyl esters obtained by reacting polyisocyanates such as isocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylate, allylated starch, allylated cellulose, diallyl phthalate, Other tetraallyloxyethane of pentaerythritol triallyl ether, trimethylolpropane triallyl ether, diethylene glycol diallyl ether, polyvalent allyl system, such as triallyl trimellitate and the like. Among these, in the present invention, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N′-methylenebis (meth) acrylamide, etc. Is usually used.

Examples of the cross-linking agent having two or more reactive functional groups include diglycidyl ether compounds, haloepoxy compounds and isocyanate compounds. Of these, diglycidyl ether compounds are particularly preferable.
Specific examples of the diglycidyl ether compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, polyglycerin diglycidyl ether, and the like. Among these, ethylene glycol diglycidyl ether is preferable. In addition, epichlorohydrin, epibromhydrin, β-methylepichlorohydrin and the like are used as the haloepoxy compound, and 2,4 of the isocyanate compound are used.
-Tolylene diisocyanate, hexamethylene diisocyanate and the like can be used in the present invention. The amount of the cross-linking agent used is usually 0 to 10% by weight, preferably 0.001 to 5% by weight, based on the ethylenically unsaturated monomer.
Is.

(Water-Soluble Radical Polymerization Initiator) The polymerization initiator used in the present invention is a water-soluble radical polymerization initiator. Examples thereof include hydrogen peroxide, potassium persulfate, sodium persulfate, persulfates such as ammonium persulfate,
2,2'-azobis- (2-amidinopropane) dihydrochloride, 2,2'-azobis- (N, N'-dimethyleneisobutylamidine) dihydrochloride, 2,2'-azobis {2methyl-N -[1,1-bis (hydroxymethyl) -2-
Azo initiators such as hydroxyethyl] propionamide}. These water-soluble radical initiators may be used as a mixture. Further, hydrogen peroxide and persulfate can be used also as a redox type initiator by combining reducing substances such as sulfite and L-ascorbic acid, amines and the like. The amount of these polymerization initiators used is 0.001 to 5% by weight, preferably 0.0 to 5% by weight, based on the ethylenically unsaturated monomer.
It is suitable to use in the range of 1 to 1% by weight.

(Inorganic powder) In the present invention, the monomer aqueous solution of the second stage was added to the reaction mixture containing the hydrous polymer gel particles after the reverse phase suspension polymerization of the first stage to form the first stage. The water-containing polymer gel particles are allowed to absorb the liquid, and at this time, a specific inorganic powder is present. The inorganic powder that can be used in the present invention is a metal oxide such as silica, alumina, titania, zirconia, silica-alumina, magnesia, iron oxide, copper oxide, nickel oxide, and synthetic zeolite, and one or more selected from these. May be a mixture of. Of these, one or a mixture of two or more selected from silica, alumina, titania, and zirconia is particularly preferable in the present invention. These inorganic powders usually have primary particles of several nm to several tens of μ.
Most of them are m, and they are usually present in an aggregated state, but any of them can be used in the present invention. The amount of the above-mentioned inorganic powder used varies depending on the monomer species and other operating conditions, but is generally 0.05 to 10% by weight, preferably 0. 0% by weight, based on the water-absorbent resin (dried product) after the additional polymerization. It is 1 to 5% by weight.

(Reaction Method) In the present invention, first, a water-soluble ethylenically unsaturated monomer aqueous solution is added in the presence of a W / O type emulsifier in a hydrophobic solvent to a crosslinking agent in an amount of 0 to 5% by weight based on the unsaturated monomer. In the presence, the first-stage reverse phase suspension polymerization is carried out using a water-soluble radical initiator. After the first-stage polymerization, the average is usually about 10 although it depends on the polymerization conditions such as the emulsifier used.
It exists in the form of a slurry consisting of ˜300 μ of hydrous gel, excess emulsifier and hydrophobic solvent. As the polymerization method at this time, either a batch polymerization method in which the aqueous monomer solution is charged all at once from the beginning or a dropping method in which the aqueous monomer solution is dropped into a hydrophobic solvent can be used. This slurry is maintained at the same temperature as the first-stage polymerization or a temperature lower than the polymerization temperature. Next, the water-soluble ethylenically unsaturated monomer aqueous solution is added to this slurry and allowed to absorb into the hydrogel, at which time the above-mentioned specific inorganic powder is allowed to exist.

The water-soluble ethylenically unsaturated monomer aqueous solution of the second and subsequent stages may be the same or different from the first water-soluble ethylenically unsaturated monomer aqueous solution. For example, when the monomer species themselves are completely different, for example, an aqueous solution of sodium acrylate is used in the first step, an aqueous solution of acrylamide is used in the second step, and so on. Further, even if the monomer species are the same, the compounding conditions, for example, the case where the first stage and the second stage and thereafter are carried out with different degrees of neutralization or monomer concentration in the aqueous solution, can be mentioned. The amount of the aqueous monomer solution used in the second and subsequent stages is 5 to 300% by weight, preferably 10% by weight, based on the aqueous monomer solution used in the first stage.
Is about 150% by weight. Further, the crosslinking agent and the water-soluble radical polymerization initiator are not necessarily essential in the second-stage monomer aqueous solution, and may be appropriately determined according to the product quality required. In particular, the water-soluble radical initiator is absorbed in the slurry of the first stage without being newly added to the monomers of the second stage and thereafter, and is easily polymerized at a predetermined temperature.

The inorganic powder may be added to the slurry before adding the second monomer aqueous solution, or may be added at the same time as adding the second monomer aqueous solution or after adding it to the second monomer aqueous solution. The inorganic powder can be added as it is, as an aqueous slurry solution, or by mixing it with the second monomer. In the present invention, the method for adding the inorganic powder is preferably a method in which the inorganic powder is mixed with the second monomer aqueous solution and added. The temperature at this time may be any temperature, but it is desirable that the temperature after the liquid absorption is below the polymerization initiation temperature. The slurry temperature is preferably a temperature at which the first stage W / O type emulsifier remaining in the slurry dissolves in a substantially hydrophobic solvent. On the other hand, the temperature of the second monomer aqueous solution varies depending on the presence or type of the radical polymerization initiator in the aqueous solution and the like, but is generally around room temperature, that is, 15-40 ° C.

As described above, the absorption of the second monomer aqueous solution occurs at an extremely large rate in the presence of the inorganic powder, and the whole system becomes a viscous slurry state due to the absorption gel. It is important to do it as uniformly as possible. A gel in which the second monomer is absorbed generally has a property of being slightly tacky and easy to aggregate. Therefore, if the liquid absorption is non-uniform or if there is uneven liquid absorption, the liquid absorption gel partially agglomerates and locally adheres or accumulates as a large lump, resulting in an average particle size or particle size of the produced granulated product. Not only the distribution but also the continuous production stability is greatly affected. There are various factors that influence the liquid absorption uniformity, and the type and concentration of the inorganic powder to be used are, of course, important, as well as the temperature, the rotation speed, and the supply rate of the second monomer. The higher the rotation speed and the lower the supply speed, the more uniform the liquid absorption. A preferable example of performing uniform liquid absorption of the monomer is a method of gradually lowering the rotational speed beyond the rotational speed limit at which the liquid can be absorbed initially. The method is such that the first stage suspension system is of W / O type even when the second-stage monomer aqueous solution is added, that is, the second monomer aqueous solution, by sufficiently increasing the rotation speed at the beginning. In this state, the liquid is not absorbed and the system is brought into a completely homogeneous mixed state, and thereafter, the number of rotations is gradually decreased to accelerate the liquid absorption and uniformly absorb the second monomer aqueous solution.

By the above operation, a gel in which the second monomer aqueous solution is uniformly absorbed can be formed, but the gel has a property of easily aggregating as described above. Therefore, the number of rotations after absorbing the liquid is one important factor that determines the average particle size of the product granulation. At this time, the higher the rotation speed, the smaller the average particle size of the granulation. When the gel slurry that has uniformly absorbed the liquid is polymerized by raising the temperature with stirring or the like, a grape-like gel in which water-containing substantially spherical gel particles adhere to each other is obtained. The rotation speed at this time is one important factor that determines the average particle size of the product granulated particles. That is, the larger the rotation number, the smaller the average particle diameter. When further absorbing the monomer aqueous solution after the second monomer aqueous solution,
Basically, the same method and operation as the method of absorbing the second monomer aqueous solution are performed.

[0034]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. The water absorption capacity, particle size distribution / average particle size, and binding strength of the water absorbent resins described in these examples are measured by the following methods.

(1) Water absorption capacity About 0.5 g of water-absorbent resin is precisely weighed and put in a 250-mesh nylon bag (size of 20 cm × 10 cm), and 500
Immerse in cc of artificial urine for 1 hour. After that, the nylon bag was pulled up and drained for 15 minutes, then the weight was measured, the blank was corrected, and the water absorption capacity was calculated according to the following formula.

[0036]

[Equation 1]

The composition of artificial urine is as follows. Artificial urine composition Urea 1.94% Sodium chloride 0.80% Calcium chloride 0.06% Magnesium sulfate 0.11% Pure water 97.09%

(2) Average particle size / particle size distribution The ASTM type standard sieve is 8 mesh, 12 mesh,
20mesh, 40mesh, 60mesh, 80mesh, 100mesh, 150mesh, 200mesh, 325mesh, saucer are combined in this order, about 50g of water-absorbent resin is put on the uppermost sieve, and low tap type automatic sieve shaker is used. Shake for 1 minute. The weight of the water-absorbent resin remaining on each sieve is weighed, and the ratio of 100% of the total amount is calculated on a mass basis.

(3) 8 cm center portion of a SUS plate having a binding strength of 10 cm × 10 cm
0.5 g of the water-absorbent resin of 20 mesh pass to 80 mesh-on fraction was evenly dispersed in 8 cm × 8 cm, and the SUS plate as described above was placed on the water-absorbent resin, and the water-absorbent resin was sandwiched.
A pressure of Kgf / cm ² is applied for 10 minutes. The water-absorbent resin after decompression is recovered and
Shake for minutes. The amount passed through an 80-mesh sieve is measured, and this ratio is calculated as weight% (a smaller value indicates less crushing of granulated particles, that is, higher binding strength).

Example 1 317 g of cyclohexane was placed in a 4-neck round-bottomed flask having a capacity of 1 liter equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube, and 317 g of cyclohexane was added thereto. 0.587 g was added and dissolved, and the internal temperature was set to 20 ° C. under a nitrogen gas atmosphere. Separately, 115.7 g of acrylic acid was added to a conical flask having a capacity of 500 cc while cooling it from the outside, and 55.7 g of water was added thereto.
0.6 g was added to neutralize 70% of the carboxyl groups.
The monomer concentration with respect to water in this case corresponds to 40% by weight as the monomer concentration after neutralization. Then add N,
0.0935 g of N-methylenebisacrylamide, 0.1208 g of potassium persulfate, and 0.1104 g of sodium hypophosphite hydrate as a water-soluble chain transfer agent were added and dissolved to 20 ° C.

About one half of the contents of this 500 cc flask was added to the contents of the 1 liter four-neck round bottom flask described above.
6.3 g was added and suspended with stirring. The stirring was performed at 150 rpm using a full zone blade. Next, when the temperature was raised at about the same rotation speed to about 55 ° C., the polymerization started, and the peak reached at about 77 ° C. Thereafter, it was kept at 70 ° C. for 15 minutes. After the reaction for 15 minutes, the temperature of the polymerization contents was cooled to 50 ° C.

Next, about 176.3 g of the remaining monomer aqueous solution in the 500 cc flask was taken and silica (Aerosil # 200, Nippon Aerosil Co., Ltd.) was used as an inorganic powder.
Manufactured) was added to form a slurry state and 2
The temperature was set to 0 ° C., and the polymerization content was added at a rotation speed of 200 rpm. The temperature of the content after addition was about 40 ° C., the system was in a slightly viscous slurry state, and after the addition was completed, it was almost completely absorbed in the hydrogel polymer particles of the first stage. Then, when the temperature was raised with stirring at 500 rpm, the polymerization started at about 55 ° C. and reached a peak at about 69 ° C. After that, the mixture was kept at 70 ° C. for 15 minutes, further heated at the same rotation number, and azeotropically distilled with cyclohexane to dehydrate the produced polymer to 7%.

When the stirring was stopped after the completion of the dehydration, the polymer particles settled at the bottom of the flask and could be easily separated by decantation. Separated polymer at 90 ° C
The mixture was heated to remove cyclohexane and some water attached. The resulting dry polymer was a powdery granulated product in which the free-flowing primary particles were bound in a grape shape.

Example 2 In Example 1, the inorganic powder was replaced with titania (Kronos KA1).
No. 0, manufactured by Titanium Industry Co., Ltd.) was used to obtain a powdery granulated product by the same operation and method.

Example 3 A powdery granulated product was obtained by the same procedure and method except that the inorganic powder was changed to zirconia (Wako Pure Chemical Industries, Ltd. reagent product) in Example 1.

Example 4 In Example 1, the inorganic powder was changed to alumina (Wako Pure Chemical Industries, Ltd.).
(Reagent product) except that the same procedure and method were used to obtain a powdery granulated product.

Example 5 In Example 1, 0.4760 g of Aerosil # 200 was used as the inorganic powder, and the amount of the liquid absorbing monomer was 61.71.
g, and a powdery granulated product was obtained by the same operation and the same method except that the number of revolutions during liquid absorption was 400 rpm.

Example 6 In Example 1, 0.5289 g of Aerosil # 200 was used as the inorganic powder, and the amount of the liquid absorbing monomer was 88.1.
A powdery granulated product was obtained by the same operation and the same method except that the amount was 5 g and the rotation speed at the time of liquid absorption was 400 rpm.

Comparative Example 1 An inorganic powder was not added to the liquid absorbent monomer solution in Example 1, but the monomer aqueous solution was added to the first polymerization content, and the same operation and the same method were used for polymerization and dehydration. The obtained dry polymer was a powdery polymer containing a considerable amount of fine powder.

Comparative Example 2 An additional test was carried out based on the method described in JP-A-3-227301. That is, 317 g of cyclohexane was placed in a four-neck round bottom flask with a capacity of 1 liter equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas introduction tube, and HLB = 4.
1.587 g of sorbitan monostearate of Example 7 was added and dissolved, and the internal temperature was set to 20 ° C. under a nitrogen gas atmosphere. Separately, add acrylic acid 116.2 to a conical flask with a capacity of 500 cc.
55.7 g of water is added while cooling g from the outside, and further 25
% Of caustic soda 180.6 g
0% was neutralized. The monomer concentration with respect to water in this case corresponds to 40% by weight as the monomer concentration after neutralization. Next, 0.0935 g of N, N-methylenebisacrylamide, 0.1208 g of potassium persulfate, and 0.11 of sodium hypophosphite hydrate as a water-soluble chain transfer agent.
04g was added and melt | dissolved and it was set as 20 degreeC.

About one half of the contents of this 500 cc flask was added to the contents of the 1 liter four-neck round bottom flask described above.
6.3 g was added and suspended with stirring. The stirring was performed at 150 rpm using a full zone blade. Next, when the temperature was raised at about the same rotation speed to about 55 ° C., the polymerization started, and the peak reached at about 77 ° C. Thereafter, it was kept at 70 ° C. for 15 minutes. After the reaction for 15 minutes, the temperature of the polymerization content was cooled to 20 ° C. to precipitate sorbitan monostearate as an emulsifier.

Next, about 176.3 g of the remaining monomer aqueous solution in the 500 cc flask was taken, added at 20 ° C. to the above polymerization contents at a rotation speed of 50 rpm, and the temperature was adjusted to 1 at the same temperature.
Held for hours. The added monomer aqueous solution was almost absorbed, and the system became a slightly viscous slurry state. Then, when the temperature was raised with stirring at 150 rpm, it was about 55 ° C.
Polymerization started at and peaked at around 69 ° C. After that, after holding at 70 ° C for 15 minutes, further heat at the same rotation speed,
The resulting polymer was dehydrated to 7% by azeotropic distillation with cyclohexane.

When the stirring was stopped after the completion of the dehydration, the polymer particles settled on the bottom of the flask and could be easily separated by decantation. Separated polymer at 90 ° C
The mixture was heated to remove cyclohexane and some water attached. A powdery polymer was obtained.

Comparative Example 3 In Comparative Example 2, the number of rotations in the first polymerization was 170 rp.
m, and a powdery polymer was obtained by the same procedure and the same procedure except that the temperature of the polymerization contents after the polymerization reaction and the temperature of the liquid absorbent monomer solution were both 13 ° C.

Comparative Example 4 An additional test was conducted based on the method described in JP-A-3-227301. That is, 376.2 g of n-heptane was placed in a four-neck round bottom flask having a capacity of 1 liter equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas introduction tube, and HLB = 3.
1.38 g of sucrose fatty acid ester (manufactured by Mitsubishi Kasei Foods Co., Ltd., Lyot Sugar Ester S-370) was added and the temperature was raised to 50 ° C. and dissolved to bring the internal temperature to 30 ° C. under a nitrogen gas atmosphere. Separately, in a conical flask with a capacity of 500 cc, while cooling 80.6 g of acrylic acid from the outside with water 2
1.3 g was added, and then 179.1 g of 25% caustic soda was added to neutralize 70% of the carboxyl groups. In this case, the monomer concentration for water is 4 as the monomer concentration after neutralization.
This corresponds to 0% by weight. Next, 0.059 g of N, N-methylenebisacrylamide and potassium persulfate of 0.
0765 g Further, 0.069 g of sodium hypophosphite hydrate as a water-soluble chain transfer agent was added and dissolved to 20 ° C.

The contents of the 500 cc flask were added to the contents of the 1-liter four-necked round bottom flask described above, and the mixture was stirred and suspended. In addition, a full zone blade is used for stirring at 225r.
It was done at pm. Then raise the temperature at the same number of revolutions at 68 ° C.
When the temperature was brought to the vicinity, polymerization started and reached a peak at around 84 ° C. Thereafter, the temperature was maintained at 70 ° C. for 1 hour to complete the polymerization.

Next, the temperature of the polymerization contents is cooled to 20 ° C.,
The emulsifier was precipitated. Next, 281.2 g of the same aqueous monomer solution as used in the first step was prepared, added to the polymerization contents at 20 ° C. at a rotation speed of 150 rpm, and kept at the same temperature for 30 minutes. The added monomer aqueous solution was almost absorbed. Next, when the temperature was raised by stirring at 500 rpm, about 67
Polymerization started at 0 ° C and peaked at around 75 ° C. After that, after holding at 70 ° C for 1 hour, further heating at the same rotation speed,
The resulting polymer was dehydrated to 7% by azeotropic distillation with n-heptane.

When the stirring was stopped after the completion of the dehydration, the polymer particles settled to the bottom of the flask and could be easily separated by decantation. Separated polymer at 90 ° C
The mixture was heated at 30 ° C. to remove the attached n-heptane and some water. A powdery polymer was obtained. The polymers obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated for water absorption capacity, average particle size, particle size distribution, and binding strength. The results are shown in Table 1.

As shown in Examples 1 to 6 and Comparative Examples 1 to 4 (Table), in the present invention, the absorption of the second monomer aqueous solution is performed very efficiently by using the specific inorganic powder, The obtained granulated product has high strength, a narrow particle size distribution, and a small amount of fine particle components (# 80 pass product).

[0060]

[Table 1]

[0061]

According to the present invention, the above-mentioned specific inorganic powder is allowed to exist in the reaction mixture containing the hydrogel polymer particles obtained by the reverse phase suspension polymerization, and the second monomer aqueous solution is absorbed into the reaction mixture. The granulated product having the above characteristics can be manufactured at a low cost by an extremely simple operation. And such a thing is suitable for a paper diaper, a sanitary napkin, and a water retention agent for soil, for example.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08F 2/00-2/60

Claims (5)

(57) [Claims] 1. A water-soluble ethylenically unsaturated monomer, which optionally contains a cross-linking agent, in a hydrophobic organic solvent in the presence of an emulsifier, when a water-absorbent resin is produced by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer. The aqueous monomer solution was subjected to a water-in-oil type reverse phase suspension polymerization reaction of the first stage using a water-soluble radical polymerization initiator, and then the reaction mixture containing the obtained water-containing polymer gel particles was treated with an inorganic powder. In the presence, optionally, a water-soluble ethylenically unsaturated monomer aqueous solution containing a cross-linking agent is additionally added, and after the monomer aqueous solution is absorbed by the polymer gel particles, an operation of additional polymerization is repeated at least once or more. Of producing water absorbent resin. 2. The temperature of the mixture after the absorption treatment of the aqueous monomer solution into the polymer gel particles is not more than the decomposition temperature of the polymerization initiator in the additional addition of the aqueous water-soluble ethylenically unsaturated monomer solution optionally containing a crosslinking agent. The method according to claim 1, wherein the additional addition is performed so that 3. The water-soluble ethylenically unsaturated monomer aqueous solution to be added in the second and subsequent polymerizations is added in an amount of 5-300 wt% of the water-soluble ethylenically unsaturated monomer aqueous solution in the first step.
The method according to claim 1, wherein the amount is added to the polymerization reaction system in the preceding stage. 4. The method according to claim 1, wherein the water-soluble ethylenically unsaturated monomer comprises one or a mixture of two or more selected from acrylic acid or a salt thereof, methacrylic acid or a salt thereof, acrylamide and methacrylamide. 5. The method according to claim 1, wherein the inorganic powder is one kind or a mixture of two or more kinds selected from metal oxide powders such as silica, alumina, titania and zirconia.