JPH0441522A - Production of water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain the title resin which retains its stable performances even when left standing for a long time in a state containing absorbed water and excels in durability by crosslinking a product obtained by neutralizing a specified copolymer with an alkali metal with a polyepoxy compound. CONSTITUTION:A product obtained by neutralizing a copolymer comprising structural units derived from an alpha-olefin or styrene and structural units of the formula (wherein R is 1-10C alkyl), e.g. monomethyl ester of isobutylene/ maleic anhydride copolymer, with an alkali metal (e.g. NaOH) is crosslinked with a polyepoxy compound (e.g. glycerol diglycidyl ether).

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing a water-absorbing resin with excellent durability.

(Conventional technology) In recent years, super absorbent resins that can absorb distilled water tens to hundreds of times their own weight have been developed. It is used in the sanitary field such as sanitary products and diapers, in the field of water-stopping materials that utilize water-swelling properties, and in applications such as soil conditioners and anti-condensation materials.

One such polymeric material is a copolymer of α-olefin or styrene and maleic anhydride. A water-absorbing resin cross-linked with an epoxy compound has been disclosed, but this material has poor gel durability and
In particular, the durability of the gel is poor when it contains water, making it unsuitable for applications such as water-stopping materials for covering communication cables and electric wires, water-stopping materials for civil engineering and construction, and anti-condensation agents that require long-term durability. there were.

(Problems to be Solved by the Invention) In view of the above circumstances, an object of the present invention is to provide a method for producing a water absorbent resin having excellent durability.

(Means for Solving the Problem) According to the present invention, the above object is achieved by a structural unit (1) based on α-olefin or styrene and a general (wherein R represents an alkyl group having 1 to 10 carbon atoms). This is achieved by crosslinking an alkali metal neutralized copolymer consisting of the structural unit (II) shown with a polyvalent epoxy compound.

In the present invention, the α-olefin constituting the copolymer means a linear or branched olefin having a double bond at the 1-position, such as ethylene, propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene, 1-hexene, 2-methyl-1-pentene, 3-
2 to 12 carbon atoms, preferably 2 to 12 carbon atoms, such as methyl-1-pentene, 2-ethyl-1-butene, diisobutylene, etc.
8 α-olefins are included. These α-olefins may be used alone or in combination of two or more.

The copolymer consisting of structural units (I) and (II) has α
- Obtained by copolymerizing an olefin or styrene and maleic anhydride using a radical catalyst, and reacting the resulting copolymer with an alcohol having 1 to 10 carbon atoms. Maleic anhydride groups in the copolymer are monoesterified by reaction with alcohol.

Radical polymerization catalysts used in such copolymerization include organic peroxides such as cumene hydroperoxide, t-butyl hydroperoxide, and benzoyl peroxide, α,α'-azobisisobutyronitrile,
α, α′-azo α diethyl methylonitrile tri α,
Examples include azo compounds such as α'-aso-α-methylvaleronitrile. Polymerization is carried out using solvents that do not inhibit radical polymerization, such as acetone, methyl ethyl ketone, benzene, toluene, ethyl acetate, isopropyl acetate, dioxane,
The polymerization is carried out by solution polymerization or precipitation polymerization using tetrahydrofuran, chloroform, etc., but in some cases it is also possible to carry out bulk polymerization without using a solvent. The polymerization temperature is not particularly limited, but is usually in the range of 0 to 200°C, and the polymerization time is usually in the range of 1 to 50 hours.

Separation of the produced copolymer from the polymerization-finished liquid is carried out in the case of precipitation polymerization by filtering and removing the liquid and drying the precipitated polymer, or in the case of solution polymerization by expelling the solvent and drying.

If the molecular weight of the copolymer of α-olefin or styrene and maleic anhydride is too small, a water-absorbing resin with a high water absorption capacity cannot be obtained. 10,000 to 1,0
Preferably, it is in the range of 00,000. The molecular weight of the copolymer can be adjusted to a desired value by adjusting the polymerization temperature, catalyst concentration, and monomer concentration, or by using a chain transfer agent.

Examples of alcohols having 1 to 10 carbon atoms used in the esterification reaction include methanol, ethanol, propatool, butanol, heptatool, nonanol, decanol, etc. However, from the viewpoint of ease of reaction, ease of handling, and cost, Methanol and ethanol are most preferred. The esterification method involves dispersing an α-olefin or a copolymer of styrene and maleic anhydride in an excess amount of alcohol, and then using an acid catalyst such as formic acid or p-toluenesulfonic acid or a tertiary amine, pyridine, A method of heating and stirring in the presence of a monobasic catalyst such as an imidazole compound is preferred. The appropriate amount of the esterification catalyst to be used is 0.61 to 3% by weight in the case of an acid catalyst, and 0.1 to 5% by weight in the case of a basic catalyst, based on the α-olefin or copolymer of styrene and maleic anhydride. be. The reaction temperature varies depending on the type of alcohol used, but is preferably 50 to 200°C for boat fishing. A suitable reaction time is 3 to 30 hours.

After the esterification reaction is completed, unreacted excess alcohol is distilled off, and the structural unit (1') and (It
), but in some cases it is also possible to use the alcohol solution as it is in the next neutralization reaction with an alkali.

The copolymer consisting of the above structural units CI) and [■] is further reacted with an alkali metal hydroxide to form an alkali metal neutralized product. This reaction is carried out, for example, by adding the copolymer to an aqueous solution of alkali metal hydroxide.

In the reaction, an organic solvent such as alcohol can be used as a reaction solvent, but care must be taken in its use due to problems such as flammability, pollution, and solvent recovery.

The alkali metal hydroxide used here refers to sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.
It reacts with carboxyl groups in the copolymer to make the copolymer water-soluble, or it imparts hydrophilic groups even if it is not completely soluble in water. Two or more types of alkali metal hydroxides may be used in combination, or a small amount of ammonia may be used in combination to promote solubility or increase crosslinking reaction.

The degree of neutralization (reaction ratio) of the alkali metal hydroxide to the copolymer is such that the degree of neutralization of the reaction product between the copolymer and the alkali metal hydroxide is 0.2 to 0.9, more preferably 0. 4-0.
8 is preferable.

The polyvalent epoxy compound used in the present invention is a compound that can partially crosslink the alkali metal neutralized product of the copolymer consisting of the structural units [■] and (II), and has an epoxy group in the molecule. It means a compound having two or more. Representative of these compounds are partially water-soluble, such as glycerin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin triglycidyl ether, propylene glycol diglycidyl ether, Examples include di- or triglycidyl ethers of polyhydric alcohols such as polypropylene glycol diglycidyl ether and trimethylolpropane triglycidyl ether. Also included are glycidyl esters of compounds containing carboxyl groups, and polyepoxy compounds containing alicyclic epoxy groups in the molecule, such as cyclohexene oxide, bicyclohebutene oxide, and cyclopentene oxide. Polyhydric epoxy compounds can be used even if they do not dissolve uniformly in the reaction system 6 but are uniformly dispersed; examples include diglycidyl ether of bisphenol A, dimer acid glycidyl ester type epoxy resin, metal-containing epoxy resin, etc. It will be done.

When the copolymer is neutralized by using caustic alkali, which is an alkali metal hydroxide, chlorohydrin ether compounds, which are precursors of epoxy compounds, such as glycerin dichlorohydrin ether, glycerin trichlorohydrin ether , ethylene glycol dichlorohydrin ether, propylene glycol dichlorohydrin ether, etc. can also be used.

Among these polyhydric epoxy compounds, diglycidyl ales of polyhydric alcohols such as glycerin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ale, or polypropylene glycol diglycidyl ether are preferably used. be done.

It is important to use a polyvalent epoxy compound having an epoxy equivalent of 100 to 500.

The amount of the polyvalent epoxy compound used is 0.1 to 5 parts by weight, preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the alkali metal neutralized copolymer. If the amount of the polyvalent epoxy compound used is too small than this range, the water absorption capacity of the resulting water-absorbent resin will increase, which is desirable, but the gel strength in the swollen state after absorbing water will be extremely poor, and the resin will There are problems such as mutual adhesion and part of the resin dissolving in water.

Moreover, if it is too large than this range, the crosslinking density of the obtained water absorbent resin becomes too high and the water absorption capacity decreases, making it impossible to obtain a resin with high water absorption performance, which is the desired objective of the present invention.

The crosslinking method for the alkali metal neutralized copolymer and the polyvalent epoxy compound is based on the reaction ratio (neutralization degree) of the copolymer consisting of the structural unit [■] and CI and the alkaline substance.
If the proportion of the polyvalent epoxy compound used in the reaction product and the epoxy equivalent of the epoxy compound are both within the above-mentioned specific ranges, a water-absorbing resin with the desired water absorption capacity can be obtained by various methods, but typical Examples of methods include: That is, a polyvalent epoxy compound is added to a solution or a partial suspension of the alkali metal neutralized copolymer in water or alcohol, thoroughly mixed and stirred until it is uniformly dispersed or dissolved, and then dried and pulverized. This makes it a water-absorbing resin. It is generally desirable to carry out the crosslinking reaction by heating, but if heat is applied during the drying process, removal of solvents such as water and alcohol and crosslinking will proceed at the same time, allowing drying and crosslinking to occur in the same process. can.

The form of the water-absorbing resin obtained by the present invention is not particularly limited, and may be one obtained by drying and pulverizing a crosslinked reaction product, or by dispersing it in water after drying and pulverizing it.
It can also be used as a water-retaining product. Furthermore, the solution before crosslinking reaction is applied to paper, nonwoven fabric, woven fabric, etc. and dried.
It may also be cross-linked. In this case, paper, non-woven fabric, or woven fabric can be used as the water-absorbing product.

The water-absorbing resin may contain fillers, pigments, dyes, ultraviolet absorbers, antioxidants, fungicides, fungicides, insecticides, herbicides, fertilizers, fragrances, deodorants, etc. .

Water-absorbent resins have a wide range of uses, such as disposable diapers, sanitary products, gauze, and paper towels that require liquid absorption ability.When mixed with soil, they can improve soil water retention, and they can also be used in agricultural chemicals and fertilizers. By impregnating a water-absorbing resin with water-absorbing resin, it is possible to prevent runoff due to rainwater, etc. Furthermore, these solutions can also be concentrated by adding a water-absorbing resin to aqueous solutions such as emulsions and latexes and filtering them.

The water-absorbing resin obtained by the present invention exhibits excellent absorption capacity for salt solutions, urine, blood, etc., and can be stored in the atmosphere because it has low hygroscopicity against moisture in the air when dry. In addition to this property, it maintains stable performance even when left in a water-absorbed state for a long period of time, and has excellent durability. It is particularly suitable for use in the fields of water-stopping materials for civil engineering and construction, anti-condensation agents, etc.

Hereinafter, the present invention will be specifically explained with reference to Examples.

(Example 1) 100 g of isobutylene-maleic anhydride copolymer (weight average molecular weight 160,000, molar ratio in the copolymer isobutylene:maleic anhydride = 1:1), methanol 300 g
0.5 g of methylimidazole 2 as a catalyst was placed in an autoclave 11, and an esterification reaction was carried out by heating and stirring at 70° C. for 8 hours to obtain a methanol solution of a monomethyl ester of isobutylene-maleic anhydride copolymer.

Next, 10 wt% methanol of sodium hydroxide? 8
After charging 155.8 g of liquid and continuing heating and stirring for another 1 hour, the autoclave was cooled to room temperature, the contents of the autoclave were taken out, and Na salt of isobutylene-maleic anhydride monomethyl ester copolymer (neutralization degree 0.6) was added. A methanol solution was obtained.

Methanol solution of copolymer Na salt obtained in this way 20
After adding 0.36 g of glycerin diglycidyl ether with an epoxy equivalent of 145 to 0 g and mixing thoroughly, a film was dried on a hot plate, and this was ground into a powder of 20 mesh passes in a constant temperature chamber at 110°C. The mixture was heat-treated for 2 hours and crosslinked to obtain a water-absorbing resin powder of the present invention.

(Example 2) 100 g of isobutylene-maleic anhydride copolymer (weight average molecular weight: 80,000, molar ratio in the copolymer: isobutylene:maleic anhydride - 1:1), 300 g of ethanol, and 0.5 g of pyridine were heated in an autoclave for 11 hours. The esterification reaction was carried out by heating and stirring at 80° C. for 8 hours to obtain an ethanol solution of monoethyl ester of isobutylene-maleic anhydride copolymer.

Then a 10% ethanol solution of sodium hydroxide 12
After adding 9.8 g and continuing heating and stirring for another hour,
After cooling to room temperature, the contents of the autoclave were taken out to obtain an ethanol solution of Na salt of isobutylene-maleic anhydride monoethyl ester copolymer (degree of neutralization: 0.5).

After adding 0.20 g of polyethylene glycol diglycidyl ether having an epoxy equivalent of 410 to 200 g of an ethanol solution of the Na salt of the above copolymer and mixing thoroughly,
A dry film was obtained on a hot plate, which was pulverized into a powder of 20 mesh baths, and heat-treated and crosslinked in a thermostat at 120° C. for 1 hour to obtain a water-absorbing resin powder of the present invention.

(Example 3) Ethylene-maleic anhydride copolymer weight average molecular weight 5
15,000, ethylene: maleic anhydride molar ratio in copolymer = 1: 1) 126 g, n-butanol 300 g, 2
-0.6 g of methylimidazole was placed in a No. 11 autoclave, and an esterification reaction was carried out by heating and stirring at 110° C. for 6 hours to obtain an n-butanol solution of monobutyl ester of ethylene-maleic anhydride copolymer. This ethanol solution was poured into a vat and vacuum dried at 80° C. in a vacuum dryer to obtain monobutyl ester of ethylene-maleic anhydride copolymer.

50 g of motuputyl ester of the ethylene-maleic anhydride copolymer thus obtained and 11.2 g of potassium hydroxide.
, and 200 g of water were mixed and heated and stirred at 90° C. for 6 hours to obtain an aqueous salt (neutralization degree 0.8) solution of the copolymer. After adding 0.20 g of glycerin diglycidyl ether with an epoxy equivalent of 145 to this aqueous solution and thoroughly mixing it, a dry film was obtained on a hot plate, and this was ground into a 20 mesh bath powder at 140°C for 30 minutes. A water absorbent resin powder of the present invention was obtained by heat treatment.

(Example 4) Styrene-maleic anhydride copolymer weight average molecular weight 1
20,000, molar ratio in copolymer styrene:maleic anhydride molar ratio -1: 1) 202g, methanol 400g, 2
- Prepare 1.50g of methylimidazole and heat at 65°C.
The esterification reaction was carried out by heating and stirring for a period of time to obtain a methanol solution of monomethyl ester of styrene-maleic anhydride copolymer. Next, 160 g of a 10% methanol solution of sodium hydroxide was charged, and heating and stirring were continued for another 2 hours. After cooling to room temperature, the contents of the autoclave were taken out, and methanol containing Na salt of the acid copolymer (neutralization degree 0.4) was added. A solution was obtained.

After adding 0.55 g of polypropylene glycol diglycidyl ether with an epoxy equivalent of 480 to 200 g of the methanol solution thus obtained and mixing thoroughly, a film was dried on a hot plate, and this was crushed to form a 20 mesh bath powder. The obtained product was heat-treated at 110° C. for 2 hours to obtain a water-absorbing resin powder of the present invention.

(Comparative Example 1) 154 g of isobutylene-maleic anhydride copolymer used in Example 1, 48 g of sodium hydroxide, and 400 g of water
were mixed and heated and stirred at 90°C for 4 hours to remove N of the copolymer.
An aqueous solution of a-salt (degree of neutralization 0.6) was obtained. Next, 1.50 g of the glycerin diglycidyl ether used in Example 1 was added to the above aqueous solution and thoroughly mixed, and then dried on a hot plate to obtain a film, which was further ground to make a 20 mesh bath powder.
A water absorbent resin for comparison was obtained by heat treatment at 110° C. for 2 hours.

The water absorbent resins obtained in Example L 2.3.4 and Comparative Example 1 were used to measure the water absorption capacity and durability in the water absorption state of distilled water, O, S% saline, and the results are shown. Shown in 1.

・Measurement method for water absorption capacity: Put 1 g of water-absorbent resin in a 500 mA' beaker, add 500 g of water or saline solution, let it absorb for 30 minutes, then transfer to 200 min. The weight was measured to determine the water absorption capacity.

Measurement of durability: Absorb 1 g of water-absorbing resin and 50 g of water, seal it in a sample tube, and measure the appearance and water absorption capacity of the water-containing resin after leaving it in a thermostat at 80°C for 24 hours.
Proposed Table 1 (Effects of the Invention) According to the present invention, a water-absorbing resin having excellent durability and high water absorption capacity can be obtained.

Claims (1)

[Claims] Structural units based on α-olefin or styrene [
I] and the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R represents an alkyl group having 1 to 10 carbon atoms) Alkali metal neutralization of a copolymer consisting of the structural unit [II] A method for producing a water-absorbing resin, which is characterized by crosslinking a material with a polyvalent epoxy compound.