JPH09157313A - Production of highly water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly water-absorbing resin with a narrower particle size distribution. SOLUTION: A water soln. is subjected to a reversed-phase suspension polymn. while continuously supplying the soln. to a polymerizer 1 from a water soln. supply port. In the polymerizer 1, a stirrer shaft 5 rotatable from the outside of the polymerizer 1 is installed at the center of the upper part of the polymerizer 1; a bottom paddle 2 which is arranged at the lower part of the polymerizer 1 with its lower end kept near the bottom of the polymerizer 1 is attached to the shaft 5; a lattice blade comprising arm parts 3 and strips 4 extending vertically thereto is attached to the shaft 5 at above the bottom paddle 2; baffle plates 6 extending from the lower part to the upper part of the polymerizer 1 are installed with some distances in a parallel to the shaft 5 on the side wall of the polymerizer 1; and the supply port of a water soln. is installed on the side wall of the polymerizer 1.

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 super absorbent polymer, and more particularly to a method for producing a super absorbent resin having excellent particle size distribution.

[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.

The performance required of these superabsorbent resins is, of course, excellent in water absorption capacity.
It is also important that the resin has excellent particle size distribution (average particle size is relatively large and particle size distribution is narrow). If a large amount of so-called fine powder with a small average particle size is included, handling of the resin and use of the resin It is expected that the manufacturing efficiency of sanitary products and sanitary products will decrease, and the water absorption capacity will also be greatly affected. Therefore, the particle size distribution is also very important in superabsorbent resins.

For the purpose of improving the particle size distribution, a superabsorbent resin is produced by using a stirrer having a specific stirring blade and a baffle as described in JP-B-1-37173, that is, α, It has been proposed to suspension polymerize water-soluble monomers consisting of β-unsaturated carboxylic acids and their salts. (JP-A-7-25917)

[0006]

However, in the above-mentioned production method, although the particle size distribution of the superabsorbent resin obtained by using a specific stirrer has been considerably improved, the width of the particle size distribution is from 100 to 100. There is still a problem that it contains a large amount of particles of 500 μm, which is still as wide as 1000 (μm) and has a slow absorption rate, and a manufacturing method capable of obtaining a super absorbent polymer having a sharper particle size distribution is desired. It is rare.

[0007]

Means for Solving the Problems As a result of intensive studies in view of such circumstances, the present inventor has found that when the suspension polymerization is carried out using the above-mentioned stirrer to produce a highly water-absorbent resin, it is further water-soluble. It has been found that the above-mentioned problems can be solved by examining the monomer supply method. That is, (meta)
Reverse the stirring of an aqueous solution of acrylic acid and a water-soluble unsaturated monomer containing (meth) acrylic acid as a main component in a hydrocarbon solvent using a radical polymerization initiator in the presence or absence of a cross-linking agent. In producing superabsorbent resin by phase suspension polymerization, a stirring shaft rotatable from outside the polymerization reactor is provided in the upper center of the polymerization reactor, and the lower end is attached to the bottom wall of the polymerization reactor. The bottom paddle placed on the bottom of the polymerization reactor by sliding the parts into contact with each other is mounted, and the upper part of the stirring shaft above the bottom paddle is equipped with a lattice blade composed of an arm portion and a strip extending in a direction perpendicular to the arm portion. Along with the side wall surface of the polymerization reactor, a plurality of baffle plates along the axial direction from the lower part to the upper part are arranged at intervals, and the side wall surface is provided with the above-mentioned aqueous solution supply port. , Polymerize the aqueous solution from the supply port While continuously fed in a hydrocarbon solvent in 応器 it is characterized in carrying out the reversed phase suspension polymerization.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
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 a hydroxide of an alkali metal such as sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate, ammonium hydroxide, amines and the like.

The mixing ratio of (meth) acrylic acid and the 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.
Preferably it is 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. There are difficulties.

The crosslinker may or may not be present. When a 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, and trimethylolpropane tri (meth) acrylate. 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 the crosslinking agent used is 0.0 with respect to the monomer component.
It is often about 001 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-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, 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, ethylbenzene, halogenated hydrocarbons such as chlorobenzene and carbon tetrachloride are exemplified, and the boiling point of the solvent, melting point, cost, industrial Considering the comprehensive availability, n-heptane and cyclohexane are particularly important.

A water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble (meth) acrylic acid as a main component is used in a hydrocarbon solvent in the presence or absence of a cross-linking agent using a radical polymerization initiator. Reverse phase suspension polymerization is performed. Polymerization temperature is 5
It is suitable that the polymerization time 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 Japanese Patent Publication No. 37173/1989 and Japanese Patent Application Laid-Open No. 7-259.
As described in Japanese Patent Publication No. 17, a stirring shaft rotatable from the outside of the polymerization reactor is provided in the center of the upper part of the polymerization reactor, and the lower end of the stirring shaft is slidably contacted with the bottom wall surface of the polymerization reactor. A bottom paddle arranged at the bottom of the vessel is attached, and a lattice blade composed of an arm portion and a strip extending in a direction perpendicular to the arm portion is attached to a portion above the bottom paddle of the stirring shaft and a side wall surface of the polymerization reactor. 1 and 2 in which a plurality of baffles along the axial direction from the lower part to the upper part are arranged at intervals in the polymerization reactor, and a side wall of the polymerization reactor is provided with a supply port for the unsaturated monomer aqueous solution. It is the greatest feature to carry out while continuously supplying the aqueous monomer solution from the supply port to the hydrocarbon solvent in the polymerization reactor by using the polymerization reactor as shown in FIG. As for the shape of the machine, As described above, there is no particular limitation as long as a (bottom) paddle is provided at the lower part of the stirring shaft and a lattice blade made of the paddle is mounted, but preferably, the lattice portion has a plurality of strips and one or more strips. The length of the paddle part in the vertical direction is 15 ~
Those occupying 40% are used. Further, the baffle plate is provided on the side wall of the polymerization reactor, and the number of baffle plates is usually 4, and the clearance between the baffle plate and the grid-shaped paddle is usually 10 to 30% (particularly 10%) of the diameter of the polymerization reactor. ~ 20%)
It is.

As a method of supplying the water-soluble unsaturated monomer from the side surface of the polymerization reactor into the polymerization reactor, a supply (charging) port is provided on the side surface of the reactor and the water-soluble unsaturated monomer is introduced into the reactor from there. Unsaturated monomers can be fed. The installation position of the supply (charging) port is not particularly limited as long as it is on the side of the polymerization reactor, but in practice, the hydrocarbon solvent can be directly supplied to the hydrocarbon solvent liquid so that the hydrocarbon solvent can be directly supplied. It is preferable to install it at a position below the liquid level (including the highest liquid level at the time of stirring), and the shape and size of the supply (charge) port are arbitrarily selected depending on the amount of water-soluble unsaturated monomer supplied and the stirring conditions. can do. Further, it is also possible to provide two or more such supply (charge) ports and simultaneously supply the water-soluble unsaturated monomer from two or more places,
Further, it is also possible to supply the water-soluble unsaturated monomer from each supply (charge) port in order without continuous interruption. Feed rate of such water-soluble unsaturated monomer, can not be said categorically due stirring conditions, 0.1 to 100 m ³ / min / m ² (even 1 to 50 m ³ with respect to the cross-sectional area of the supply (feed) the mouth / Min / m ² ) is preferred.

After completion of the above-mentioned polymerization, the intended superabsorbent resin can be obtained by filtering the produced particles, washing and drying according to a conventional method.

The highly water-absorbent resin obtained by the method of the present invention is particularly useful as a body fluid absorbent for absorbing body fluids and excretions and preventing leakage in sanitary products and sanitary products. In addition, soil water retention agent, seed coating agent, water blocking agent, thickener, anti-condensation agent, dehydrating agent, drying agent, humidity control agent, coagulant for sludge and liquid waste, heavy metal adsorbent, chemicals and fragrances It can also be used for applications such as sustained release agents and poultices.

[0018]

The present invention will be further described with reference to the following examples. Hereinafter, "%" is% by weight. Example 1 As shown in FIG. 1, a stirring blade, a reflux condenser, a nitrogen gas inlet and a monomer supply port (shape; diameter 25.
In a 200 l polymerization reactor equipped with a 4 mm circle), 105 l of cyclohexane and 370 g of sorbitan monostearate as a polymerization dispersant were charged, and nitrogen bubbling was performed at 30
After a minute, the dissolved air was expelled and the temperature was raised to 70 ° C.
In another 150 l reactor, 80% aqueous acrylic acid solution 34.
1 kg was charged, and while cooling, 40.8 kg of 28% sodium hydroxide aqueous solution was added to neutralize. After adding 74 g of a 10% aqueous solution of ethylene glycol diglycidyl ether as a cross-linking agent and 583 g of ammonium persulfate as a polymerization initiator to this aqueous solution, nitrogen bubbling was carried out to expel the dissolved air to obtain an aqueous monomer solution.

The resulting aqueous monomer solution was continuously fed at a rate of 600 ml / min (approximately 1.18 m ³ / min / m ² with respect to the cross-sectional area of the feed port) from the monomer feed port on the side of the above-mentioned polymerization reactor. During stirring in the polymerization reactor (the stirring speed is 60 rp
m) was supplied into the cyclohexane solution for about 1.5 hours to carry out polymerization under reflux of cyclohexane. (The center of the monomer supply port is about 20c below the liquid surface of cyclohexane during stirring.
Next, 30.6 kg of water was extracted by azeotropic dehydration, the polymer was taken out, and further dried at 105 ° C. for 3 hours to obtain a highly water-absorbent resin. The obtained super absorbent polymer has an average particle size of 120 μm and a particle size distribution of 0
%, 350-74 μm was 83.9%, 74-45 μm was 11.4%, and less than 45 μm was 4.7%.

Example 2 In Example 1, the feed rate of the aqueous monomer solution was set to 900 m.
l / min (about 1.77 m ³ / min / min.
m ² ) and the polymerization time was 1 hour to obtain a super absorbent polymer. The average particle size of the resulting super absorbent polymer is 100 μm, and the particle size distribution is 0% for 350 μm or more, 74.3% for 350 to 74 μm, and 74 to 45.
μm was 20.6%, and less than 45 μm was 5.1%.

Example 3 A highly water-absorbent resin was obtained in the same manner as in Example 1 except that the stirring speed was 70 rpm. The average particle size of the obtained super absorbent polymer is 105 μm, and the particle size distribution is 350 μm.
0% above, 350-74 μm 72.3%, 74-4
5 μm was 19.9%, and less than 45 μm was 7.8%.

Comparative Example 1 A highly water-absorbent resin was obtained in the same manner as in Example 1 except that the monomer aqueous solution supply port was provided on the upper surface of the polymerization reactor and the monomer liquid was continuously added dropwise from above. The average particle size of the obtained super absorbent polymer is 100 μm, and the particle size distribution is 0% at 350 μm or more and 68.0 at 350 to 74 μm.
%, 74-45 μm is 10.5%, less than 45 μm is 2
It was 1.5%.

Comparative Example 2 A highly water-absorbent resin was obtained in the same manner as in Example 1 except that the aqueous monomer solution was supplied all at once. The superabsorbent resin thus obtained had an average particle size of 70 μm and a particle size distribution of 3
50% or more is 0%, 350 to 74 μm is 49.7%,
74-45 μm 35.0%, less than 45 μm 15.3
%Met.

Comparative Example 3 A highly water-absorbent resin was obtained in the same manner as in Example 1 except that a polymerization reactor having paddle-shaped stirring blades as shown in FIGS. 3 and 4 was used. The average particle size of the resulting superabsorbent resin is 100 μm, and the particle size distribution is 0 μm when 350 μm or more.
%, 350-74 μm was 66.8%, 74-45 μm was 20.5%, and less than 45 μm was 12.7%.

[0025]

INDUSTRIAL APPLICABILITY In the present invention, the polymerization reaction is carried out while continuously supplying the monomer from the supply port using a polymerization reactor having a specific stirring blade and having a side face provided with the monomer supply port. Therefore, a highly water-absorbent resin having a sharper particle size distribution can be obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a polymerization reactor having a lattice type stirring blade and a monomer supply port of the present invention.

FIG. 2 is a cross-sectional plan view of a polymerization reactor having a lattice-type stirring blade and a monomer supply port of the present invention.

FIG. 3 is a side sectional view of a polymerization reactor having a conventional paddle type stirring blade.

FIG. 4 is a plan sectional view of a polymerization reactor having a conventional paddle type stirring blade.

[Explanation of symbols] ・ ・ ・ Polymerization reactor ・ ・ ・ Bottom paddle ・ ・ ・ Arm part ・ ・ ・ Strip ・ ・ ・ Stirring shaft ・ ・ ・ Baffle plate ・ ・ ・ Monomer supply (preparation) port ・ ・ ・ Monomer supply ( (Preparation) Pipe ・ ・ ・ Liquid level of hydrocarbon solvent (10) ・ ・ ・ Stirrer consisting of bottom paddle, arm and strip (11) ・ ・ ・ Inclined paddle

Claims (1)

[Claims] 1. An aqueous solution of a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components is carbonized by using a radical polymerization initiator in the presence or absence of a crosslinking agent. In producing a highly water-absorbent resin by reverse-phase suspension polymerization in a hydrogen solvent with stirring, a stirring shaft rotatable from the outside of the polymerization reactor is disposed in the upper center of the polymerization reactor.
A bottom paddle, which is disposed at the bottom of the polymerization reactor by sliding its lower end to the bottom wall of the polymerization reactor, is attached to the shaft, and an arm portion and a right angle to the arm portion are provided above the bottom paddle of the stirring shaft. Is installed on the side wall surface of the polymerization reactor, and a plurality of baffle plates along the axial direction from the lower part to the upper part are arranged at intervals, and the aqueous solution is formed on the side wall surface. Using a polymerization reactor provided with a supply port for the above, a reversed phase suspension polymerization is carried out while continuously supplying the aqueous solution from the supply port into a hydrocarbon solvent in the polymerization reactor. Method for making flexible resin.