JPS63275607A - Manufacture of water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain a water-absorptive resin excellent in absorbing power under pressure, by polymerizing an aqueous solution or an aqueous dispersion of copolymerizable monomers comprising a (meth)acrylate, (meth)acrylic acid and a crosslinking agent in a specific concentration by strongly heating at above a specified temperature. CONSTITUTION:An aqueous solution or an aqueous dispersion of copolymerizable monomers comprising an acrylate and/or a methacrylate (A), acrylic acid and/or methacrylic acid (B) and a crosslinking agent (C) as essential components is polymerized by heating, if desired, in the presence of a polymerization initiator to obtain a water-absorptive resin. The polymerization is carried by adjusting the concentration of the copolymerizable monomer to 65wt.% or more and strongly heating the aqueous solution or the aqueous dispersion to 90 deg.C or above. It is particularly preferred that the acrylate and/or the methacrylate is a potassium salt.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing a water absorbent resin.

[Prior Art] Conventionally, a water-soluble salt of acrylic acid and/or a water-soluble salt of methacrylic acid, acrylic acid and/or methacrylic acid, and a crosslinking agent are copolymerized in an aqueous medium at a concentration of 10 to 60% by weight. , there is a method to produce drogel with super water absorption. (
For example, Japanese Patent Application Laid-Open No. 147809/1983).

[Problems to be Solved by the Invention] However, although this material has a certain degree of absorption capacity under normal pressure, it has a problem in that its absorption capacity under pressure is low.

[Means for Solving the Problems] The present inventors have arrived at the present invention as a result of intensive studies on a method for producing a water-absorbing resin with excellent absorption capacity under pressure.

That is, the present invention provides an aqueous solution or aqueous dispersion of a copolymerizable monomer containing (A) an acrylate and/or a methacrylate, (B) an acrylic acid and/or a methacrylic acid, and (C) a crosslinking agent. is heated and polymerized, if necessary, in the presence of a polymerization initiator to produce a water-absorbing resin.The concentration of the copolymerizable monomer is set to 65% by weight or more, and the mixture is forcibly heated to 90°C or higher. This is a method for producing a water absorbent resin, which is characterized by carrying out polymerization.

In the present invention, (A) acrylate and/or methacrylate [abbreviated as (meth)acrylate]. The same description will be used below. ] as (Me.

a) Alkali metal salts (salts of sodium, potassium, lithium, etc.), alkaline earth metal salts (salts of calcium, magnesium, etc.), ammonium salts and amine salts (salts of alkylamines such as methylamine, trimethylamine, etc.) of acrylic acid; salts of alkanolamines such as triethanolamine and jetanolamine) and two or more thereof.

Preferred among these are alkali metal salts of (meth)acrylic acid, particularly potassium salts, from the viewpoint of easy preparation of highly concentrated aqueous solutions or dispersions; It becomes possible to create

(C) The crosslinking agent is a compound (1) having at least two polymerizable double bonds and at least one functional group having at least one polymerizable double bond and reactive with the monomer. Compound (2) is mentioned.

Examples of compound (1) include the following.

(2) Bis(meth)acrylamide: N,N'-alkylene (C1-CG>Bis(meth)acrylamide, for example, N,N'-methylenebisacrylamide.

■ G- or poly-esters of polyols and unsaturated mono- or poly-carboxylic acids: Polyols (ethylene glycol, trimethylolpropane, glycerin,
polyoxyethylene glycol, polyoxypropylene glycol, etc.); (meth)acrylic acid ester; unsaturated polyester (obtained by reaction of the above polyols with an unsaturated acid such as maleic acid); and (Meth)acrylic acid ester [Contains obtained by the reaction of polyepoxide and (meth)acrylic acid.

■Carbamyl ester: Polyisocyanate [tolylene diisocyanate, hexamethylene diisocyanate, 4,4''-diphenylmethane diisocyanate, NCO group-containing prepolymer (obtained by reaction of the above polyisocyanate with an active hydrogen atom-containing compound), etc. Those obtained by reaction with hydroxyl group-containing monomers, such as carbamyl esters obtained by reaction of the above-mentioned polyisocyanates with hydroxyethyl (meth)acrylate; Di- or polyvinyl compounds divinylbenzene, divinyltoluene, divinylxylene, Divinyl ether, divinyl ketone, trivinylbenzene, etc.

■Di- or poly(meth)allyl ether of polyols: Polyols (alkylene glycol, glycerin, polyalkylene glycol, polyalkylene polyol,
di- or poly(meth)allyl ethers of carbohydrates, etc.) such as polyethylene glycol diallyl ether, allylated starch, allylated cellulose.

■ Di- or poly-allyl nitrate of polycarciboxylic acid: diallyl phthalate, diallyl adipate, etc.

■Ester of unsaturated mono- or poly-carboxylic acid with mono(meth)furyl ether of polyol: (meth)furyl ether of polyethylene glycol monoallyl ether
acrylic esters, etc.

■Allyloxyalkanes: Tetraallyloxyethane etc.

Examples of compound (2) include (meth)acrylic acid and/or
or ethylenically unsaturated compounds containing groups reactive with other copolymerizable monomers, such as carboxyl groups, carboxylic acid anhydride groups, etc. (hydroxyl groups, epoxy groups, cationic groups, etc.) .

Specifically, nonionic group-containing unsaturated compounds such as hydroxyl group-containing unsaturated compounds [N-methylol (meth)
acrylamide, etc.] and epoxy group-containing unsaturated compounds [glycidyl (meth)acrylate, etc.]: as well as cationic group-containing unsaturated compounds, such as quaternary ammonium base-containing unsaturated compounds [N,N,N-trimethyl-N- (meth)acryloyloxyethylammonium chloride, N,N,N-triethyl-N-(meth)acryloyloxyethylammonium chloride, etc.],
and tertiary amine group-containing unsaturated compounds [such as dimethylaminoethyl (meth)acrylate (diedylaminoethyl (meth)acrylate)].

Among the crosslinking agents, preferred are bis(meth)acrylamide, di- or polyesters of polyols and unsaturated monocarboxylic acids, and allyloxyalkanes, and particularly preferred are N,N-methylenebisacrylamide and ethylene glycol diacrylate. , trimethylolpropane triacrylate and tetraallyloxyethane.

Other copolymerizable water-soluble monomers and non-aqueous monomers can be used together with the (meth)acrylate and (meth)acrylic acid, if necessary.

Other carboxyl groups or other water-soluble monomers.

Monomers with salt-form groups [maleic anhydride, itaconic acid,
Sodium maleate salt, methylamine maleate salt], monomers with sulfonic acid groups [styrene sulfone sodium salt, styrene sulfonate methylamine salt, (meth)acrylic acid sulfopropyl sodium salt, (
meth)acrylic acid sulfopropyl jetanolamine salt, vinyl sulfonic acid sodium salt, etc.], monomers having an amide group [(meth)acrylamide, etc.], phosphoric acid monoester monomers, etc. are required.

As water-insoluble monomers, unsaturated carboxylic acids [(meth)
Alkyl (C1-20) esters of monocarboxylic acids such as acrylic acid; polycarboxylic acids such as maleic acid and fumaric acid, aromatic vinyl hydrocarbons (styrene, etc.), aliphatic vinyl hydrocarbons (ethylene, propylene, butene, etc.) ), unsaturated nitriles (acrylonitrile, etc.).

Among these, preferred are water-soluble monomers, and particularly preferred are monomers having a carboxyl group or a sulfonic acid group.

The molar ratio of (meth)acrylate to (meth)acrylic acid is usually 95:5 to 20:80, preferably 90:10 to
40:60. If the molar ratio of (meth)acrylate is less than 20, the water absorption capacity of the resin will be low, and if it exceeds 95,
The l)H of the resin is too high, causing problems in terms of stability.

The amount of the crosslinking agent is usually 0.001 to 1%, preferably 0.01 to 0.5%, based on the weight of all copolymerizable monomers. If the amount of the crosslinking agent is less than 0.001%, the resulting resin will have a low gel strength upon water absorption and will be in the form of a sol.

On the other hand, if it exceeds 1%, the gel strength becomes too high and the water absorption capacity decreases.

The total amount of (meth)acrylate and (meth)acrylic acid is usually 70% or more, preferably 80 to 100%, based on the weight of all copolymerizable monomers.

If this total amount is less than 70%, the water absorption capacity under pressure will decrease.

In the case of water-soluble monomers, the amount of other copolymerizable monomers is generally 30% or less, preferably 20% or less, based on the weight of all copolymerizable monomers. Usually 20 for water-insoluble monomers
% or less, preferably 10% or less.

In the present invention, when producing a water absorbent resin, the concentration of the copolymerizable monomer in the aqueous solution or aqueous dispersion needs to be 65% or more, preferably 65% to 90%, on a weight basis. . If the monomer concentration is less than 65%, the resulting resin will have a low absorption capacity under pressure.

The aqueous solution or dispersion is a copolymerizable monomer [(A).

CB), (C) other monomers as necessary] in water or a mixed solvent of water and a water-soluble organic solvent (methanol, ethanol, acetone, N,N-dimethylformamide, dimethyl sulfoxide, etc.), preferably water. Obtained by dissolving or dispersing in.

An azo compound [
Azobiscyanovaleric acid, azobisisobutyronitrile,
2,2°-azobis(2-amidinopropane) hydrochloride, etc.], inorganic peroxides (ammonium persulfate, potassium persulfate, lithium persulfate, etc.), organic peroxides (hydrogen peroxide, benzoyl peroxide, -t-butyl peroxide, cumene hydroperoxide, etc.), redox catalysts (alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite with reducing agents such as ascorbic acid and alkali metal persulfates, ammonium persulfate) , peroxide, etc.). Two or more of the above polymerization initiators may be used in combination.

The amount of polymerization initiator is usually from o.ooi to 5%, preferably from o.ooi to 1%, based on the weight of all copolymerizable monomers.

It is necessary to carry out the polymerization by forcibly heating the aqueous solution or aqueous dispersion to 90°C or higher, preferably 110 to 180°C. If forced heating to 90°C or above is not performed, for example, if the polymerization initiation temperature is less than 90'C and the reaction temperature is raised to about 100 to 130'C by the heat of polymerization, only a resin with low absorption capacity under pressure will be obtained. do not have. In addition, the resin tends to form lumps when absorbing water and has a low diffusion rate.

Examples of the polymerization method include a thin film polymerization method using a drum dryer or the like. Specifically, an aqueous solution or aqueous dispersion of a copolymerizable monomer is deposited on the rotating surface of a drum dryer heated to a temperature of usually 90 to 200°C so that the polymerization initiation temperature is 90°C or higher to form a thin film. Spray or spread in a suitable state, polymerize and dry.

In addition to drum dryers, there are devices that spread an aqueous solution or aqueous dispersion as a thin film and polymerize it by heating, such as devices that are equipped with a heated moving belt or rotating disk, or devices that are equipped with heated moving belts or rotating disks, or devices that are spread on a tray or vat in advance and then heated externally. Any device that can pass through a polymerization/drying zone can be used.

In addition, the aqueous solution or aqueous dispersion of the copolymerizable monomer can be
An inert gas such as carbon dioxide or helium is sprayed into a heating medium heated to a temperature of usually 100 to 200'C such that the polymerization initiation temperature is 90C or higher, and is polymerized and dried.

The time for these polymerizations is usually several seconds to several minutes.

Further, no particular drying step is required.

The obtained water-absorbent resin has the ability to absorb 1% saline solution at least 10 times its own weight under a pressure of 209/cti.

[Examples] Hereinafter, the present invention will be briefly explained with reference to Examples, but the present invention is not limited thereto.

The absorption capacity of the water-absorbing resin in the examples for 1% saline at normal pressure was measured based on the usual tea bag method.

On the other hand, the absorption capacity under pressure was determined by uniformly spreading 0.2 g of resin on a nylon mesh (250 mesh) with an area of 1 cIi, placing a weight from the top to apply a pressure of 20 g/ci, and applying a pressure of 20 g/ci to the bottom. 1% saline solution is continuously brought into contact with the nylon mesh. After absorbing for 60 minutes, the weight of the water-absorbing gel was measured, and the absorption capacity under pressure was determined using the following formula.

Absorption capacity under pressure (g/g) = (weight fi of water-absorbing gel)
5-1 Diffusion rate is calculated by spreading the resin 29 uniformly in a petri dish with a base area of 100 cm, and intravenously injecting 1% saline solution for 10 seconds from the center of the top for 50 m until the saline solution is completely absorbed. The number of seconds was measured. The resin that is more likely to generate mamako,
It takes time to complete absorption.

Note that parts in the examples are parts by weight.

Example 1 115 parts of potassium acrylate, 25 parts of acrylic acid, 2N,
N'-methylenebisacrylamide 0.05 part and 2
．． 0.05 part of 2'-azobis(2-amidinopropane) hydrochloride was added to 60 parts of water to prepare an aqueous solution having a concentration of 70 parts. This aqueous solution was heated to a surface temperature of 130°C using a drum dryer (rotation speed: 0.2 r).
pHl) or higher, and thin film copolymerization was carried out in an air atmosphere.

The dried solid copolymer was continuously scraped off with a scraper to obtain a water absorbent resin with a water content of 3.2%.

This material was pulverized to a particle size of 32 to 145 mesh, and the absorption capacity and diffusion rate under normal pressure and pressure were measured.
Shown in the table.

Examples 2 to 6 At least one of the concentration of the copolymerizable monomer adjusted in Example 1, the amount of crosslinking agent (N,N'-methylenebisacrylamide) used, and the surface temperature of the drum dryer was A water absorbent resin was obtained in the same manner as shown in Table 1. These performance measurement results are also listed in Table 1.

Example 7 A water absorbent resin was obtained in the same manner as in Example 1 except that 100 parts of potassium acrylate and 28 parts of sodium styrene sulfonate were used instead of 115 parts of potassium acrylate in Example 1. The performance measurement results of this product are shown in Table 2.

Example 8 In Example 1, 0.1 part of trimethylolpropane triacrylate was used in place of the N,N'-methylenebisacrylamide O,OS part, and 2,2゛azobis(2-
A water-absorbing resin was obtained in the same manner as in Example 1, except that 0.05 part of potassium persulfate was used instead of 0.05 part of (amidinopropane) hydrochloride. The performance measurement results of this product are shown in Table 2.

Example 9 An aqueous solution with a concentration of 70 parts prepared in the same manner as in Example 1 was
A water-absorbing resin was obtained by spraying nitrogen gas heated to 150'C into a spray dryer in which convection was occurring. The performance measurement results of this product are shown in Table 2.

Comparative Example 1 In Example 1, 210 parts of water was used to prepare an aqueous solution having a concentration of 40 parts. This aqueous solution was copolymerized into a thin film using the same equipment as in Example 1 to obtain a water absorbent resin.

The performance measurement results of this product are also listed in Table 2.

Comparative Example 2 In Example 1, the surface temperature of the drum dryer was set to 80°C.
A polymer was obtained in exactly the same manner except for the following. The moisture content of this product was 15.2%, and further heat drying was required. The performance measurement results of the resin obtained by heating and drying are also listed in Table 2. .

Table 2 [Effects of the Invention] According to the present invention, a water-absorbing resin having the following effects can be produced.

(1) A resin with high absorption capacity under pressure can be produced.

For sanitary materials such as disposable diapers, the baby's weight is placed on them, so the absorption capacity under pressure is more important than the absorption capacity under normal pressure. Traditional ones, such as (meth)acrylates and (
meth)acrylic acid and a crosslinking agent at a monomer concentration of 10 to 60
% aqueous solution prepared by heating to 100°C or higher, or an aqueous solution of a potassium acrylate salt and a water-miscible divinyl compound with a monomer concentration of 55 to 80% and external heating at a polymerization initiation temperature of 50 to 85°C. In the case of products produced by vaporizing water by heat of polymerization without using the same method, a product with high absorption capacity under pressure could not be obtained.

However, according to the present invention, a product with excellent absorption capacity under pressure can be obtained.

(2) Even if it comes into contact with the liquid to be absorbed, it does not generate mako.

Therefore, a resin with good diffusion rate and absorption rate can be obtained.

(3) When applied to sanitary materials such as disposable diapers, it has effects such as improving dry touch and reducing leakage, resulting in high quality products.

(4) Polymerization and drying can be completed in an extremely short time of several minutes, and the manufacturing cost is low.

Because the resin obtained by the present invention exhibits the above effects, it can be used as absorbent materials, sanitary materials (disposable diapers for children and adults, sanitary napkins, sanitary cotton, bandages, incontinence pads, breast pads, paper towels, etc.) Applications that come into contact with the human body, such as: Separating agents for water in oil: Other dehydrating or drying agents: Water retention agents for plants, soil, etc.: Sludge coagulants: Useful for industrial applications such as anti-condensation agents used in interior building materials. .

Claims (1)

[Claims] 1. An aqueous solution of a copolymerizable monomer containing (A) an acrylate and/or a methacrylate, (B) an acrylic acid and/or a methacrylic acid, and (C) a crosslinking agent as essential components. Or, when producing a water absorbent resin by heating and polymerizing the aqueous dispersion in the presence of a polymerization initiator if necessary,
A method for producing a water-absorbing resin, characterized in that the concentration of a copolymerizable monomer is 65% by weight or more, and polymerization is carried out by forced heating to 90° C. or higher. 2. The manufacturing method according to claim 1, wherein the acrylate and/or methacrylate is a potassium salt.