JPH06345819A - Production of highly water absorbing resin - Google Patents

Abstract

PURPOSE:To provide a method for producing a highly water absorbing resin by which particles having a moderately large primary particle diameter can stably be obtained by the polymerization. CONSTITUTION:The highly water absorbing resin having 280-450mum primary particle diameter is produced by carrying out the reserved phase suspension polymerization of a water-soluble unsaturated monomer consisting essentially of (meth)acrylic acid and a water-soluble (meth)acrylate in the presence or absence of a cross-linking agent in a hydrocarbon solvent using a radical polymerization initiator. The versed phase suspension polymerization is performed in the coexistence of a water-soluble polymer, sorbitan ester of a fatty acid and sucrose ester of the fatty acid. In the process, the blending ratios of the respective components are set at 0.05-1wt.%, 0.05-5wt.% and 0.05-5wt.% based on the water-soluble unsaturated monomer. The weight ratio of the sorbitan ester of the fatty acid to the sucrose ester of the fatty acid is set at (9:1) to (1:9).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superabsorbent resin which can stably obtain a superabsorbent resin having an appropriately large primary particle diameter.

[0002]

2. Description of the Related Art Starch is a resin that absorbs a large amount of water.
Acrylonitrile graft polymer partial hydrolyzate, polyacrylic acid partially neutralized salt, polyethylene oxide type,
Super water-absorbent resins such as polyacrylonitrile-based, polyvinyl alcohol-based, and cross-linked systems thereof are known. Among these, a partially neutralized polyacrylic acid salt obtained by reverse-phase suspension polymerization of (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid in a hydrocarbon solvent is particularly useful.

These highly water-absorbent resins are useful as a body fluid absorbent for absorbing body fluids and preventing leakage in sanitary and hygiene products, and also as a water retention agent for soil, a seed coating agent, a water blocking agent, and a thickener. Agent, anti-condensation agent, sludge coagulant,
It is used in applications such as desiccant and humidity control agent.

JP-A-2-153907 discloses that an acrylic acid-based monomer selected from the group consisting of (meth) acrylic acid and alkali metal salts thereof is used in the presence of a cross-linking agent and a radical polymerization initiator. In the method of performing reverse phase suspension polymerization in a hydrocarbon solvent, the surfactant used for reverse phase suspension polymerization has (a) a solid state appearance at least at room temperature and an HLB value in the range of 1 to 8. A method for producing a super absorbent polymer which is a mixed surfactant of sorbitan fatty acid ester and (b) sucrose fatty acid ester having an HLB value in the range of 1 to 6 is shown. Here, the amount of the surfactant added is usually 0.1 to 10 parts by weight with respect to the monomer in a state where both are mixed. Comparative Example 6 of this publication
Shows an example in which 2.3 parts by weight of hydroxyethyl cellulose was added to 70 parts by weight of the monomer in addition to the above mixed surfactant, and particles having an average particle size of 490 μm were obtained. However, these particles have a tendency to aggregate and have a small water absorption capacity, water absorption speed, and water retention capacity.

In Japanese Patent Laid-Open No. 2-196802, the average particle size is 100 to 600 μm, and the particle size distribution is logarithmic standard deviation value σ.
There is a disclosure regarding a water-absorbent resin having a particle size of ζ of 0.35 or less and having a particle surface cross-linked. Also, the average particle size is 100 to 6
A method for producing a water-absorbent resin, in which the surface of a polymer powder having a particle size distribution of 00 μm and a logarithmic standard deviation value σζ of 0.35 or less is subjected to a crosslinking treatment, is disclosed. An aqueous monomer solution is dispersed / suspended in a polymerization-inert hydrophobic organic solvent using sucrose fatty acid ester and / or polyglycerin fatty acid ester as a dispersant,
It has been shown to be obtained by polymerizing with a radical polymerization initiator. The examples also describe the presence of a small amount of hydroxyethyl cellulose or sodium polyacrylate in the aqueous monomer solution. Further, Comparative Example 2 shows an example in which sorbitan monostearate was used instead of sucrose fatty acid ester to obtain water-absorbent resin particles having an average particle diameter of 80 μm.

JP-A-3-195713 discloses an acrylic acid-based monomer containing (meth) acrylic acid and an alkali metal salt or ammonium salt thereof as main components.
In the presence of a water-soluble radical polymerization initiator and hydroxyethyl cellulose, a sorbitan fatty acid ester of HLB3 to 6 as a dispersant is used to polymerize an acrylic acid-based monomer when polymerized by a water-in-oil type reverse phase suspension polymerization method. A method for producing a superabsorbent polymer is described in which the reaction is carried out in a cyclohexane solvent in the presence of a crosslinking agent.

[0007]

The larger the particle size of the super absorbent polymer, the more the particle size of the super absorbent polymer is prevented from coming into contact with water or body fluid. If the particle size is large, the particles will not leak out of the eyes of the material even when used in combination with a material having coarse mesh such as nonwoven fabric. Therefore, it is strongly desired to obtain particles having an appropriately large particle size by polymerization. In this case, even if the apparent particle size is large,
If the particles are aggregates of primary particles, for example, when applied to a paper diaper, they may return to fine primary particles when absorbing urine and leak out from the eyes of a material such as a nonwoven fabric. is there.

The method disclosed in Japanese Patent Application Laid-Open No. 2-153907 is
Although it has succeeded in increasing the particle diameter to some extent, the particle diameter is 200 to
It is about 270 μm, and it is desired to further increase the particle size. The particles obtained in Comparative Example 6 of this publication, on the contrary, have an excessively large average particle size, tend to agglomerate as described above, and have various drawbacks that the water absorption capacity, the water absorption speed, and the water retention capacity are small. There is.

The water-absorbent resin of Japanese Patent Laid-Open No. 2-196802 can obtain particles having a large particle diameter, but the production conditions have a narrow allowable range, and the shapes of the stirring blade and the reaction container, stirring conditions, the amount of dropping, etc. are small. There is a problem that it tends to be agglomerated due to the difference in conditions, and it is difficult to industrially adopt. It is considered that this is because the sucrose fatty acid ester as the dispersant originally has a high affinity with the monomer, and is likely to be agglomerated during the polymerization reaction.

The method disclosed in Japanese Patent Laid-Open No. 3-195713 is
It seems that particles with a large particle size can be obtained, but since the particle size distribution is wide, a considerable proportion of fine particles are also generated, and the particles that are obtained are actually aggregates of small particles, and the primary particle size is small. There is a point.

Under such circumstances, the present invention provides a method for producing a highly water-absorbent resin capable of stably obtaining appropriately large particles having a primary particle size of 280 to 450 μm by polymerization. The purpose is.

[0012]

The method for producing a highly water-absorbent resin of the present invention comprises the step of using a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components as a crosslinking agent. In producing a highly water-absorbent resin having a primary particle size of 280 to 450 μm by carrying out reverse phase suspension polymerization in a hydrocarbon solvent using a radical polymerization initiator in the presence or absence of the above reverse phase suspension. Polymerization is carried out in the presence of a water-soluble polymer, sorbitan fatty acid ester and sucrose fatty acid ester, and the mixing ratio of each component at that time, the water-soluble polymer is 0.05 ~
1% by weight, sorbitan fatty acid ester 0.05 to 5% by weight, sucrose fatty acid ester 0.05 to 5% by weight,
In addition, the weight ratio of the sorbitan fatty acid ester to the sucrose fatty acid ester is set to 9: 1 to 1: 9.

The present invention will be described in detail below.

In the present invention, a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components is used as the monomer. This monomer can be obtained by partially neutralizing (meth) acrylic acid with an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, ammonium hydroxide or amines.

The mixing ratio of (meth) acrylic acid and water-soluble salt of (meth) acrylic acid is 30:70 to 10: 9 by weight.
It is preferably 0. That is, the degree of partial neutralization of (meth) acrylic acid is 70 to 90 of the total (meth) acrylic acid.
It is preferably mol%. If the degree of partial neutralization is too small, the water absorption capacity and water absorption rate will decrease, and the product will be difficult to exhibit acidity.If the degree of partial neutralization is too large, the water absorption capacity and water absorption rate will also decrease. In addition, the product is difficult to be alkaline.

The crosslinker may or may not be present. When the crosslinking agent is used, examples of the crosslinking agent include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane tri (meth). Acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, N, N'-methylenebis (meth) acrylamide, triallyl isocyanurate, (poly) ethylene glycol diglycidyl ether, glycerin polyglycidyl ether, sorbitol poly Glycidyl ether,
Examples thereof include pentaerythritol polyglycidyl ether. The amount of cross-linking agent used is 0.00 based on the monomer components.
It is often about 01 to 0.5% by weight.

Examples of the radical polymerization initiator include azobisisobutyronitrile, t-butyl peroxide, cumene hydroperoxide, di-t-butyl peroxide, acetyl peroxide, lauroyl peroxide, stearoyl peroxide and benzoyl peroxide. Examples include oxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, methyl ethyl ketone peroxide, cyclohexanone peroxide, hydrogen peroxide, ammonium persulfate, potassium persulfate, and cerium salt. Those that are water-soluble are particularly preferable. The amount of the radical polymerization initiator used is often about 0.01 to 1% by weight with respect to the monomer component.

As the hydrocarbon solvent, cyclohexane,
Alicyclic hydrocarbons such as cyclopentane and methylcyclohexane, n-pentane, n-hexane, n-heptane, n
-Oritan, aliphatic hydrocarbons such as ligroin, aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene, halogenated hydrocarbons such as chlorobenzene and carbon tetrachloride are exemplified, and boiling point of solvent, melting point, cost, industrial Considering the comprehensive availability, n-hexane and cyclohexane are particularly important.

A water-soluble unsaturated monomer mainly composed of (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid is used in a hydrocarbon solvent in the presence or absence of a crosslinking agent by using a radical polymerization initiator. Reverse phase suspension polymerization is performed. Polymerization temperature is 5
It is suitable that the temperature is 0 to 90 ° C. and the polymerization time is about 0.5 to 5 hours.

In the present invention, the above-mentioned reverse phase suspension polymerization is carried out in the presence of a water-soluble polymer, sorbitan fatty acid ester and sucrose fatty acid ester.

Examples of the water-soluble polymer include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, dextrin, sodium alginate, polyvinyl alcohol, polyacrylamide, polyethylene glycol and polyethyleneimine.

Examples of the sorbitan fatty acid ester include sorbitan monopalmitate, sorbitan monostearate, sorbitan sesquistearate and sorbitan tristearate.

Examples of the sucrose fatty acid ester include mono-, di- or triesters of sucrose and fatty acids such as stearic acid, palmitic acid, lauric acid and oleic acid.

The mixing ratio of the water-soluble polymer, sorbitan fatty acid ester and sucrose fatty acid ester is 0.05 to 1% by weight (preferably 0.1 to 1% by weight) and 0.05 to 5% by weight with respect to the water-soluble unsaturated monomer. (Preferably 0.1
.About.1% by weight) and 0.05 to 5% by weight (preferably 0.1 to 2% by weight). If it deviates from this range, the particle size of the resulting superabsorbent resin may become small or may become lumpy. The weight ratio of sorbitan fatty acid ester to sucrose fatty acid ester is 9: 1 to 1: 9 (preferably 5: 1 to 1: 1).
5) is desirable, and when the balance between the two is out of this range, particles having the target particle size cannot be stably obtained.

After the completion of the polymerization, the produced particles are separated by filtration, washed and dried according to a conventional method to obtain a desired particle diameter, that is, 1
A super absorbent resin having a secondary particle diameter of 280 to 450 μm can be obtained. The particle size referred to here is the average particle size determined based on the mesh size when 50% by weight passes when sieving is performed using a standard sieve.

The highly water-absorbent resin obtained by the method of the present invention is particularly useful as a body fluid absorbent that absorbs body fluids and excretions and prevents leakage in sanitary products and sanitary products. In addition, soil water retention agent, seed coating agent, water blocking agent, thickening agent, dew condensation preventive agent, dehydrating agent, desiccant, humidity control agent, coagulant for sludge and liquid waste, heavy metal adsorbent, drug, aromatic agent It can also be used for applications such as sustained-release preparations and poultices.

[0027]

In the present invention, the reverse phase suspension polymerization is devised so as to be carried out in the coexistence of a specific ratio of the water-soluble polymer, the sorbitan fatty acid ester and the sucrose fatty acid ester.
It is possible to stably produce particles having a primary particle size of 280 to 450 μm.

[0028]

EXAMPLES The present invention will be further described with reference to examples. Hereinafter, "%" means% by weight.

Example 1 A polyacrylic acid partially neutralized salt-based highly water-absorbent resin was produced by the reverse phase suspension polymerization method described in detail below.

In a 2 liter separable flask A equipped with a stirrer, a reflux condenser and a nitrogen gas inlet tube, 800 ml of cyclohexane and 1.56 g of sorbitan monostearate.
Then, 1.56 g of sucrose fatty acid ester (“DK Ester F-50” manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was charged and nitrogen bubbling was carried out for 30 minutes to expel the dissolved air and the air in the flask.

After 260 g of 80% acrylic acid was charged into another separable flask B, 310 g of 28% sodium hydroxide aqueous solution was gradually added dropwise under cooling to neutralize. Then, 8 g of a 0.5% N, N'-methylenebisacrylamide aqueous solution and 1.04 g of hydroxyethyl cellulose ("AX-15" manufactured by Fuji Chemical Co., Ltd.) were added and dissolved. After the dissolution, 4 g of a 10% ammonium persulfate aqueous solution was added, and nitrogen bubbling was performed while stirring to expel the dissolved air.

After the temperature of Flask A was raised to 73 ° C., the solution in Flask B was added dropwise over 1.5 hours. The rotation speed during polymerization was set to 350 rpm. Then, the warm water in the jacket was kept at 95 ° C., azeotrope with cyclohexane and 230 ml of water was expelled (the dehydration rate of water was 70%). Then, decantation was performed and the generated particles were dried at a temperature of 105 ° C. for 3 hours to obtain target particles. The average particle size of the particles was 300 μm.

Examples 2 to 3 sorbitan monostearate, sucrose fatty acid ester,
Example 1 was repeated except that the addition amount of hydroxyethyl cellulose was variously changed. The conditions and results are shown in Table 1. The conditions and results of Example 1 are also shown in Table 1.

Comparative Examples 1-5 Sorbitan monostearate, sucrose fatty acid ester,
Example 1 was repeated except that the addition amount of hydroxyethyl cellulose was variously changed. The conditions and results are also shown in Table 1.

Comparative Example 6 Sorbitan monostearate, sucrose fatty acid ester,
Example 1 was repeated except that the weight% of the hydroxyethyl cellulose to the monomers was 0.75%, 0.75% and 2%, respectively. However, dissolution of an amount of hydroxyethyl cellulose exceeding 1% is not practical because it takes a long time, and the amount that can be dissolved remains around 2%, and the viscosity after neutralization becomes high, which makes handling difficult. .

[0036]

[Table 1] Blending amount (% by weight of monomer) Sorbitan monosucrose fatty acid hydroxyethyl average particle size stearate ester cellulose Example 1 0.75% 0.75% 0.5% 300 μm Example 2 0.75% 0.75% 1.0% 330 μm Example 3 0.375% 1.125% 0.25 % 320 μm Comparative Example 1 0.01% 0.75% 0.5% Blocked Comparative Example 2 8.0% 0.75% 0.5% 70 μm Comparative Example 3 0.75% 0.01% 0.5% Granules ^# Comparative Example 4 0.75% 8.0% 0.5% 240 μm Comparative Example 5 0.75% 0.75% 0.01% 250 μm ^# Granules consisting of agglomerates of primary particles, particle diameter about 10 mm.

[0037]

INDUSTRIAL APPLICABILITY As described in the section of the action, in the present invention, the reverse phase suspension polymerization is devised so as to be carried out in the coexistence of the water-soluble polymer, the sorbitan fatty acid ester and the sucrose fatty acid ester in a specific ratio. Therefore, the primary particle size is 280
Particles of ˜450 μm can be stably produced.

The particles thus obtained do not cause a mamako phenomenon when they come into contact with water or body fluid, and do not cause troubles such as leakage even if they are used in combination with a material having a rough mesh such as a non-woven fabric.

Claims (1)

[Claims] 1. A hydrocarbon using a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components in the presence or absence of a crosslinking agent and a radical polymerization initiator. In producing a highly water-absorbent resin having a primary particle size of 280 to 450 μm by performing reverse phase suspension polymerization in a solvent, the reverse phase suspension polymerization is performed by using a water-soluble polymer, a sorbitan fatty acid ester and a sucrose fatty acid ester. In the coexistence of, and the mixing ratio of each component at that time,
With respect to the water-soluble unsaturated monomer, the water-soluble polymer is 0.05
~ 1% by weight, sorbitan fatty acid ester is set to 0.05 to 5% by weight, sucrose fatty acid ester is set to 0.05 to 5% by weight,
And the manufacturing method of the super absorbent polymer characterized by setting the ratio of sorbitan fatty acid ester and sucrose fatty acid ester in 9: 1 to 1: 9 by weight ratio.