JPH01304128A - Preparation of water-absorbing resin having improved particle diameter - Google Patents

Abstract

PURPOSE:To obtain easily a polymer having a large particle diameter by freezing a water-cotg. water-absorbing resin and then performing a freeze vacuum drying treatment thereof. CONSTITUTION:After a water-contg. water-absorbing resin is frozen at -10 deg.C or below, a freeze vacuum drying treatment thereof is performed under a pressure condition of 10Torr or below. As the applied water-absorbing resins, crosslinked polymers of salts of (meth)acrylic acid, saponified products of crosslinked (meth)acrylate-vinyl acetate copolymers, crosslinked starch-salt of acrylic graft copolymers, crosslinked maleic acid anhydride-grafted polyvinyl alcohol, etc., can be cited. When the temp. of the freezing operation is higher than -10 deg.C, too long a time is required for freezing and it is therefore not economical for an industrial operation. When the pressure condition is higher than 10Torr, too long a time is required for drying and it is therefore not economical for an industrial operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] Industrial Field of Application The present invention relates to a method for producing a water-absorbing resin with improved particle size. According to the present invention, it is possible to produce a water-absorbent resin in which the primary particle size of the water-absorbent resin is increased to an arbitrary size, so the present invention can also be considered as a method for improving the particle size of a water-absorbent resin.

In recent years, water-absorbing resins have been used in sanitary products such as sanitary products, diapers, and disposable rags, and in agriculture and horticulture as water retention agents and soil conditioners, as well as in coagulation of sludge, prevention of condensation on building materials, and dehydration of oils. It is used for various purposes such as.

Among these, water-absorbing resins have come to be particularly widely used in sanitary products such as sanitary products and diapers.

Prior Art This type of water-absorbing resin includes cross-linked acrylate polymers, saponified cross-linked acrylic ester-vinyl acetate copolymers, cross-linked starch-acrylate graft copolymers, and starch-acrylonitrile cross-linked products. Saponified products of graft copolymer crosslinked products, maleic anhydride grafted polyvinyl alcohol crosslinked products, polyethylene oxide crosslinked products, and the like are known.

These water-absorbing resins are generally produced by synthesizing a polymer by methods such as reverse-phase suspension polymerization, reverse-phase emulsion polymerization, aqueous solution polymerization, or reaction in an organic solvent, and then drying the polymer as it is, or It is manufactured through a pulverization process, optionally after drying.

However, when a water-absorbent resin is produced by such a method, it is common to obtain a product containing a considerable proportion of fine powder with a wide particle size distribution. For example, when these are used in the field of sanitary materials, the powdered water-absorbing resin is either uniformly sprinkled on the crushed valve layer or sandwiched between water-absorbing papers. There are many. When using water-absorbing resin that is in fine powder form or contains a large amount of fine powder, bridging is likely to occur during transportation and supply.
Not only is it difficult to handle, but it also generates dust that significantly deteriorates the environment, causing equipment contamination and failure. There is also a risk that fine powder may fall off from sanitary products.

Furthermore, when used as a water retention agent for agriculture and horticulture, there is a risk that it may adhere to machinery or become uneven when mixed with soil or sand.

As a method for solving such problems, methods described in, for example, Japanese Patent Application Laid-open Nos. 132936/1980, 97333/1982, and 101536/1980 have been proposed. However, these technologies require high manufacturing costs due to the use of auxiliary agents such as inorganic powders, surfactants, and mechanical binders, and the amount of ungranulated products increases depending on the amount of additives. It can be said that this technology is still not sufficient as it may have a negative impact on the quality of the product.

[Summary of the invention]

The present invention aims to eliminate the drawbacks of the above-mentioned conventional techniques and provide a method that can easily design, stably, and easily manufacture particles with a particle size suitable for the intended use.

As a result of intensive research into this problem, the present inventors discovered that a polymer with a large particle size can be obtained extremely easily by freeze-drying a water-containing water-absorbing resin under predetermined conditions. It was completed.

That is, the method for producing a water-absorbing resin with improved particle size according to the present invention involves freezing a water-containing water-absorbing resin at -10°C or lower, and then subjecting it to freeze-vacuum drying under a pressure condition of 10 Torr or lower. It is characterized by carrying out the following.

Effects of the Invention In the ordinary method for producing water-absorbing resins, especially for bead-like particles obtained by reverse-phase suspension polymerization, fine powder, especially fine powder with a particle diameter of 100 μm or less, is added to the final product as a -order particle size. It is common to obtain products containing a considerable proportion of carbon dioxide and having a wide particle size distribution.

However, by using the present invention, it is possible to easily carry out a design to obtain an appropriate particle size according to the intended use, and moreover, a water-absorbing resin that is very close to the designed value can be obtained. In particular, because it increases the secondary particle size, unlike fine powder aggregates obtained by conventional granulation technology during transportation and bagging operations, less dust is generated, resulting in deterioration of the working environment and equipment. contamination and failure of the product can be prevented.

In addition, when used as daily necessities or agricultural and horticultural supplies, fine powder does not fall off, and water-absorbing resin can be obtained with a particle size suitable for the purpose, so it has excellent dispersibility, mixability,
Water retention and other properties are significantly improved.

[Detailed description of the invention]

Water-absorbing resin Examples of water-absorbing resins used in the present invention, that is, water-absorbing resins (hereinafter referred to as raw water-absorbing resins) that are subjected to freeze-vacuum drying treatment after liquid absorption, include (meth)acrylates. Polymer crosslinked product, saponified product of (meth)acrylic acid ester-vinyl acetate copolymer crosslinked product, starch-acrylate graft copolymer crosslinked product, saponified product of starch-acrylic acid ester graft copolymer crosslinked product, Saponified product of starch-methyl methacrylate graft copolymer crosslinked product, saponified product of starch-acrylonitrile graft copolymer crosslinked product, saponified product of starch-acrylonitrile-vinylsulfonic acid graft copolymer crosslinked product, maleic anhydride graft Examples include polyvinyl alcohol crosslinked products, polyethylene oxide crosslinked products, and sodium carboxymethyl cellulose crosslinked products. In addition, the above-mentioned (meth)acrylic acid (salt) (co)polymer crosslinked product contains maleic acid (salt), itaconic acid (salt),
Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid,
A copolymer obtained by copolymerizing a comonomer such as 2-itacroylethanesulfonic acid or 2-hydroxyethyl methacrylate may also be used.

The crosslinked products of the various polymers described above used as the raw material superabsorbent resin in the present invention can be made into crosslinked products by various means. The crosslinking means includes, for example, entanglement of molecular chains by high polymerization of polymer molecules, self-crosslinking by pseudo-crosslinking, or divinyl compounds copolymerizable with the above monomers, such as N,N'-methylenebis(meth)acrylamide, Crosslinking with (poly)ethylene glycol (meth)acrylates, etc., and polyfunctional compounds that react with functional groups of polymers, such as carboxylate groups, such as (poly)glycidyl ethers, haloepoxy compounds, polyaldehydes, and polyols. Examples include methods of crosslinking by adding and reacting polyamines, polyamines, etc., and crosslinking based on reactions between functional groups present in the polymer, such as esterification with carboxyl groups and hydroxyl groups.

In addition, when the superabsorbent resin used as the raw material of the present invention is a carboxylate type, that is, a salt type, examples include those of an alkali metal salt type such as sodium and potassium, and an alkaline earth metal salt type such as magnesium and calcium. However, particularly preferred are alkali metal salt types.

Next, embodiments of the present invention will be described in detail.

The raw material water-absorbing resin is, for example, Japanese Patent Publication No. 60-25045, Japanese Patent Publication No. 57-158210, Japanese Patent Application Publication No. 57-2140.
No. 5, Special Publication No. 53-46199, Japanese Patent Publication No. 58-719
07, JP-A No. 55-84304, etc. can be used. Typical production examples of water-absorbent resins include the following.

Example-1 An aqueous solution of an α,β-unsaturated carboxylic acid and its alkali metal salt is suspended in a petroleum hydrocarbon solvent containing a sucrose fatty acid ester in the presence or absence of a crosslinking agent, and a radical polymerization initiator is A method of polymerizing in the presence of.

Example-2 Acrylic acid and acrylic acid alkali salt aqueous solution HL
A method in which B8-12 concentrated surfactants are suspended in a covalent alicyclic or aliphatic hydrocarbon solvent and polymerized in the presence of a water-soluble radical polymerization initiator.

Example-3 At least one of starch and cellulose (
A) and at least one monomer (
A method of polymerizing B) and a crosslinking agent (C) as essential components, and performing hydrolysis if necessary to obtain a polymer.

Example 4 Contains potassium acrylate and a water-miscible or water-soluble divinyl compound, and the concentration of these monomers is 55-
A method of obtaining a water-absorbing resin by adding a polymerization reaction initiator to a heated aqueous solution in a range of 80ffi mass %, causing a polymerization reaction to occur without external heating, and vaporizing water.

Example-5 1-20% α,β-unsaturated carboxylic acid or
The reaction product grafted with the anhydride or the product obtained by oxidizing the monoolefin polymer so that the final oxidation rate is 10-100 is used as a protective colloid, and the monomer aqueous solution is polymerized and inactivated. A method in which the polymer is suspended in a hydrophobic liquid and polymerized in the presence of a water-soluble radical polymerization initiator.

The water-absorbing resin targeted by the present invention is not limited to the above-mentioned method, and may be produced by any method.

Freeze-drying conditions and method In the present invention, a water-impregnated water-absorbing resin is used for freeze-drying these water-absorbing resins. 2) Resin that retains water during the process (example-1, example-2, example-
A hydrated resin can be obtained by, for example, using a method of obtaining a polymer using a method such as No. 3 (the resin after polymerization corresponds to this example), or the like.

In the case of (1), a predetermined amount of water is contained, but it is preferable that the water-absorbing resin used as a raw material absorbs water uniformly.For example, by stirring the water-absorbing resin in an inert solvent, etc. A method in which water is suspended and water is made into fine droplets by spraying or the like and water is absorbed; a method in which a third substance (for example, a powdered inorganic substance, etc.) that does not significantly affect the performance of the resulting water-absorbing resin is added and mixed and then water is absorbed; When the amount of water to be absorbed is relatively large, a method of directly absorbing water into the water-absorbing resin and then leaving it for a long time is carried out, but the method is not limited to these methods.

The amount of water required to obtain the desired particle size is obtained from the particle size and weight of the water-absorbing resin used as the raw material, the desired particle size, and the correction coefficient, and is calculated using the following formula 0 formula %...・Equation (1) (η is a correction coefficient of 0.9 to 1.5°. Also, the water absorption amount must be less than or equal to the saturated water absorption amount of the water-absorbing resin.) The correction coefficient η is the correction coefficient of the target water-absorbing resin. necessary to obtain the particle size,
This was set based on the data shown in the examples of the present invention, but since the absorbed water freezes, causing volumetric expansion, and the structure of the water-absorbing resin deforms slightly when drying. We estimate that this is a necessary coefficient. The correction coefficient η is 0. 9-1. 5, preferably 1.0-1.2.

In the freeze-vacuum drying process, the freezing operation is carried out at a temperature of -10°C or lower, preferably -30°C or lower. At temperatures higher than -10°C, freezing takes a long time and is therefore not economical to carry out as an industrial operation. The drying operation is performed under reduced pressure conditions of 10 Torr or less, preferably ITor.
Perform below r.

Pressure conditions higher than 10 Torr require a long time for drying and are therefore not economical to carry out as an industrial operation. The temperature conditions for the drying operation vary depending on the water retention amount of the material, the water retention form, etc., but it is preferably carried out at a temperature from the freezing operation temperature to 70°C.

[Experiment example]

EXAMPLES The present invention will be specifically explained using Examples and Comparative Examples.

Production Example-1 213 g of cyclohexane was charged into a 500 ml four-day round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas introduction tube, and 0.75 g of sucrose ditristearate of HLB3 was added and dispersed. . After blowing in nitrogen gas to drive out dissolved oxygen, the temperature was raised to 50°C, sucrose ditristearate was dissolved under stirring, and the mixture was cooled to 30°C.

Separately, in a 200 ml Erlenmeyer flask, 80% by weight acrylic acid aqueous solution 37.5. 2 while cooling from the outside.
After 49.3 g of a 5.4% by weight aqueous solution of caustic soda was added dropwise to neutralize 75% by mole, 0.04% of potassium persulfate was added.
5g was added and dissolved. This partially neutralized acrylic acid salt aqueous solution was added to a four-bottle flask and dispersed, and after the system was sufficiently replaced with nitrogen again, the temperature was raised to bring the bath temperature to 55-65°C.
The polymerization reaction was carried out while holding for 1 hour to obtain a polymerization liquid of a water-absorbing resin. After water and cyclohexane were removed by distillation, 41.0 g of bead-like polymer having a particle size of 50 to 200 μm was obtained by drying. The obtained water absorbent resin is classified with a sieve,
This was used as a water-absorbing resin for raw materials before treatment.

Examples-1 to 6 1 part by weight of cyclohexane was added to 1 part by weight of the classified water-absorbent resin of Production Example-1, and while stirring, a predetermined amount of water was sprayed into fine droplets to absorb the water, and the cyclohexane was removed by filtration.
A water-absorbing resin was obtained by freeze-vacuum drying. The freeze vacuum dryer used was a Freeze Cabin J 5F-02 model manufactured by Mari Okawara Seisakusho, and the results are shown in Table 1 below.

Table 1 Table 2 shows the results of changing the water absorption amount and freeze-vacuum drying conditions using the water absorbent resin obtained in Production Example-1.

Table 2 Production Example-2 Into a 500ml four-necked round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas inlet tube, 213g of cyclohexane was charged, and 0.5g of sorbitan monostearate with HLB3 was added. 75 g was added and dispersed. After blowing in nitrogen gas to drive out dissolved oxygen, the temperature was raised to 60°C, and while stirring, sorbitan monostearate was dissolved, and then heated to 30°C.
cooled down to. Separately, in a 200m1 Erlenmeyer flask, 37
．． Take 74.7 g of a 6% by weight aqueous acrylic acid solution, and while cooling from the outside, add 46% by weight of a 25% by weight aqueous caustic soda solution.
After neutralization of 70 mol% by dropping 7 g of N, N'
0.042 g of methylenebisacrylamide and 0.104 g of potassium persulfate were added and dissolved. This partially neutralized acrylic acid salt aqueous solution was added to a four-bottle flask and dispersed, and after the system was sufficiently purged with nitrogen again, the temperature was raised and the bath temperature was maintained at 55-65°C to carry out the polymerization reaction for 1 hour. A polymerization solution of water absorbent resin was obtained. After removing water and cyclohexane by distillation, the particle system is reduced to 550-200a by drying.
38.0 g of bead-like polymer was obtained. The obtained water absorbent resin was classified using a sieve to obtain a raw material water absorbent resin before treatment.

Examples 7 to 12 The experiments were carried out under the same conditions as in Examples 1-6, except that the classified water absorbent resin of Production Example 2 was used. The results are shown in Table 3 below.

Table 3 Production Example-3 After adding 44.5 g of water to 144.2 sr of acrylic acid and wiping with 49.5 g of potassium hydroxide with a purity of 85%,
N,N'-methylenebisacrylamide 0.02g
is added to prepare a potassium acrylate aqueous solution (degree of neutralization 75%) with a monomer concentration of 70%. This aqueous solution was kept at 70°C, and 5% of the 1896 aqueous solution of ammonium persulfate was added to it.
．． 8g and 30.6% aqueous solution of sodium bisulfite 3
．． 4 g of the mixture was mixed, and the mixed solution was spread on an endless moving belt in a two-flow layer with a thickness of about 10 mm. After about 30 seconds,
The polymerization reaction is started and completed in about 1 minute. Since the obtained water absorbent resin had a water content of 11%, it was further dried and then pulverized to obtain 175 g of a water absorbent resin with a diameter of 40 to 150 μm. Classified with a sieve in the same manner as Production Example-1 and Production Example-2,
This was used as a water-absorbing resin for raw materials before treatment.

Examples 13 to 16 It was carried out under the same conditions as in Example 1-5, except that the classified water absorbent resin of Production Example 3 was used. The results are shown in Table 4 below.

Table 4 Applicant's representative: Mr. Sato

Claims (1)

[Claims] A water-absorbent resin with improved particle size, characterized in that the water-containing water-absorbent resin is frozen at -10°C or lower, and then subjected to freeze-vacuum drying treatment under a pressure condition of 10 Torr or lower. Manufacturing method.