JPH0621131B2 - Water absorbent resin manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a water absorbent resin.

"Prior Art" Conventional water-absorbent resins derived from alkali metal acrylates contain 0 to 50 mol% of acrylic acid and 50 to 100 mol of acrylic acid alkali metal salt in the presence of a water-soluble and / or water-dispersible surfactant.
A method of copolymerizing a mixture of a mol% acrylate monomer and a crosslinkable monomer in an aqueous solution (see, for example, JP-B-58-2).
5500) and a method of polymerizing a potassium acrylate salt and a water-miscible divinyl compound as an aqueous solution having a monomer concentration of 55 to 80% (for example, JP-A-58-71907).

[Problems to be solved by the invention] However, the absorbency of the obtained water-absorbent resin for 1% saline is 40 to 55 g / g under normal pressure and 3 to 10 g / g under pressure,
It is insufficient for use in disposable diapers and sanitary products.

[Means for Solving Problems] The present inventors diligently studied a method for producing a water-absorbent resin having a high absorption capacity under both normal pressure and pressure and having a small amount of water-eluting components and a small amount of residual monomer. As a result, the present invention has been achieved.

That is, the present invention is obtained by polymerizing a polymerizable monomer and a copolymerizable cross-linking agent containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group and a phosphoric acid group as an essential component. A method for producing a water-absorbent resin, characterized in that an alkali metal compound is added to the obtained polymer to neutralize 50 to 90 mol% of acid groups in the polymer to partially form an alkali metal base ( One invention) and a polymerizable monomer containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group and a phosphoric acid group and a copolymerizable crosslinking agent as an essential component Add an alkali metal compound to the polymer and add 50-90 mol% of the acid groups in the polymer.
A water-absorbent resin, characterized in that a neutralized polymer partially neutralized with an alkali metal base is further crosslinked with a compound having at least two groups capable of reacting with an acid group and / or an alkali metal base. Is a manufacturing method (second invention).

In the present invention, as the polymerizable monomer containing a carboxylic acid group, unsaturated mono- or polycarboxylic acid [(meth)]
Acrylic acid (refers to acrylic acid and / or methacrylic acid. The same shall apply hereinafter), (eth) acrylic acid, crotonic acid, sorbic acid, maleic acid, itaconic acid, cinnamic acid, etc.] and their anhydrides. Examples include [maleic anhydride].

Examples of the polymerizable monomer containing a sulfonic acid group include aliphatic or aromatic vinyl sulfonic acids (vinyl sulfonic acid, allyl sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, etc.), (meth) acrylic sulfonic acid [( Sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, etc.], (meth) acrylamidesulfonic acid [2-acrylamido-2-methylpropanesulfonic acid, etc.] and the like.

Examples of the polymerizable monomer having a phosphoric acid group include (meth) acrylic acid hydroxyalkyl phosphoric acid monoester [2-hydroxyethyl acryloyl phosphate, 2-hydroxyethyl methacryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate. Oh, etc.]

Of these, preferred are polymerizable monomers containing a carboxylic acid group or sulfonic acid group, and particularly preferred are polymerizable monomers containing a carboxylic acid group. Monomers containing these acid groups may be used alone,
Moreover, you may use together 2 or more types.

If desired, other polymerizable monomers can be used together with the acid group-containing monomer. For example, unsaturated carboxylic acids [monocarboxylic acids such as (meth) acrylic acid; polycarboxylic acids such as maleic acid and fumaric acid. ] Alkyl (C ₁ -C ₁₀ )
Ester, aromatic vinyl hydrocarbons [styrene etc.], aliphatic vinyl hydrocarbons [ethylene, propylene, butene etc.], unsaturated nitriles [acrylonitrile etc.],
Examples include (meth) acrylamide.

In the present invention, the copolymerizable cross-linking agent is a compound (1) having at least two polymerizable double bonds, and at least a functional group having at least one polymerizable double bond and reactive with a monomer. Compound (2) which has one is mentioned.

The following are mentioned as an example of a compound (1).

Bis (meth) acrylamide: N, N-alkylene (C1-C6) bis (meth) acrylamide such as N, N-methylene-bisacrylamide.

Di- or polyesters of polyols and unsaturated mono- or polycarboxylic acids: Polyols [ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol,
Polyoxypropylene glycol, etc.] di- or tri- (meth) acrylic acid ester: unsaturated polyester [obtained by reaction of the above polyols with an unsaturated acid such as maleic acid] and di- or tri- (meth)
Acrylic ester [obtained by reaction of polyepoxide with (meth) acrylic acid] and the like.

Carbamyl ester: polyisocyanate [tolylene diisocyanate, hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate and NCO group-containing prepolymer (obtained by reaction of the above polyisocyanate with active hydrogen atom-containing compound)] Carbemyl ester obtained by reaction with hydroxyethyl (meth) acrylate.

Di- or polyvinyl compounds: divinylbenzene, divinyltoluene, divinylxylene, divinylether, divinylketone, trivinylbenzene and the like.

Di- or poly- (meth) allyl ether of polyols: polyols [alkylene glycol, glycerin, polyalkylene glycol, polyalkylene polyol,
Carbohydrates and the like] di- or poly- (meth) allyl ethers such as polyethylene glycol diallyl ether, allylated starch, allylated cellulose.

Di- or poly-allyl esters of polycarboxylic acids: diallyl phthalate, diallyl adipate and the like.

Esters of unsaturated mono- or poly-carboxylic acids with mono (meth) allyl ethers of polyols: (meth) polyethylene glycol monoallyl ethers
Acrylic ester etc.

Examples of compound (2) include (meth) acrylic acid and /
Or an ethylenically unsaturated compound containing a group reactive with another copolymerizable monomer, such as a carboxyl group or a group reactive with a carboxylic acid anhydride group (hydroxyl group, epoxy group, cationic group, etc.). . Specifically, a nonionic group-containing unsaturated compound such as a hydroxyl group-containing unsaturated compound [N-methylol (meth) acrylamide] and an epoxy group-containing unsaturated compound [glycidyl (meth) acrylate] and a cationic group-containing unsaturated compound. Saturated compounds, such as quaternary ammonium salt group-containing unsaturated compounds [N, N, N-trimethyl-N- (meth) acryloyloxyethyltrimethylammonium chloride,
N, N, N-triethyl-N- (meth) acryloyloxyethylammonium chloride, etc.] and tertiary amino group-containing unsaturated compounds [dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, etc.] And so on.

Among the copolymerizable crosslinking agents, preferred is bis (meth)
Di- or poly-esters of acrylamide, polyols and unsaturated monocarboxylic acids, particularly preferred are N, N-methylenebisacrylamide, ethylene glycol diacrylate and trimethylolpropane triacrylate.

In the present invention, the amount of the copolymerizable crosslinking agent is usually 0.001 to 1 based on the total weight of all the polymerizable monomers and the copolymerizable crosslinking agent.
It is 0%, preferably 0.01 to 5%. When the amount of the copolymerizable cross-linking agent is less than 0.001%, the obtained resin has a low gel strength when absorbing water and becomes a sol. On the other hand, if it exceeds 10%, on the contrary, the gel strength becomes excessive and the absorption capacity decreases.

The amount of the other polymerizable monomer used as necessary is usually based on the total weight of all the polymerizable monomers and the copolymerizable crosslinking agent.
It is 30% or less, preferably 10 or less.

The method for polymerizing the acid group-containing polymerizable monomer, the copolymerizable cross-linking agent, and the other polymerizable monomer used as necessary,
A conventionally known method may be used, for example, a method of polymerizing using a radical polymerization catalyst and radiation, electron beam,
The usual method of irradiating with ultraviolet rays and the like can be mentioned.

In the method using a radical polymerization catalyst, this catalyst includes azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid, 2,2′-azobis (2-amidinopropane) hydrochloride, etc.], inorganic peroxides [ammonium persulfate] , Potassium persulfate, sodium persulfate, etc.], organic peroxides [hydrogen peroxide, benzoyl peroxide,
Di-t-butyl peroxide, cumene hydroperoxide, etc.] and redox catalysts [alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, ascorbic acid and other reducing agents and alkali metal persulfates, peroxides] A combination of ammonium sulfate, peroxide, etc.] and two or more of these.

The method of polymerizing using this catalyst is not particularly limited, and for example, the temperature can be variously changed depending on the kind of the catalyst used, but is usually 0 to 150 ° C, preferably 10 to 100 ° C.

The amount of the catalyst may be the same as usual, and is usually 0.0005-based on the total weight of all the polymerizable monomers and the copolymerizable crosslinking agent.
It is 5%, preferably 0.0001 to 1%.

The polymerization may be carried out in the presence of a solvent, if necessary. Examples of this solvent include water, methanol, ethanol,
Acetone, N, N-dimethylformamide, dimethylsulfoxide, methyl ethyl ketone and mixtures of two or more of these can be mentioned. The concentration of the copolymerizable monomer when a solvent is used is not particularly limited, but is usually 10% or more, preferably 15 to 80% by weight. Concentration is 10
If it is less than%, the resulting resin has a low absorptivity.

In the present invention, an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, as an alkali metal compound used for partially neutralizing an acid group in the obtained polymer to form an alkali metal base) Examples thereof include lithium hydroxide) and alkali metal carbonates (sodium carbonate, sodium bicarbonate, etc.).

In the present invention, 50 to 90 mol%, preferably 60 to 80 mol% of the acid groups in the polymer are converted into alkali metal salts by a neutralization reaction with an alkali metal compound. When the conversion rate, that is, the degree of neutralization is less than 50 mol%, the obtained gel-like hydropolymer has a high tackiness, which makes it difficult to produce a water-absorbent resin with good workability. When it exceeds 90 mol%, the pH of the obtained resin becomes high, which poses a problem in terms of safety to human skin.

As a method of neutralizing the polymer with an alkali metal compound, when the polymerization is performed using a solvent, the obtained gel polymer is
There is a method in which an aqueous solution of an alkali metal compound is added while chopping into small pieces of 1 cm ³ or less and further kneading. In the case of polymerizing without using a solvent, there is a method in which the polymer is once swelled by adding a solvent such as water and then an alkali metal compound is added, or an aqueous solution of an alkali metal compound is added to the polymer. .

Then, the polymer neutralized product which is the reaction product can be dried and pulverized by the method described below to obtain the water absorbent resin of the present invention.

In the present invention, the polymer neutralized product contains at least a group that reacts with an acid group and / or an alkali metal base in the neutralized product.
By further crosslinking with a compound having two, a resin having higher gel strength can be produced.

The compound having at least two groups capable of reacting with an acid group and / or an alkali metal base in the polymer neutralized product includes a functional group capable of reacting with an acid group and / or an alkali metal base (epoxy group, hydroxyl group, amino group). Group, an isocyanate group, etc.) and a polyvalent metal compound capable of forming an ionic bridge.

Examples of the compound having a functional group capable of reacting with an acid group and / or an alkali metal base include polyepoxy or poiglycidyl ether compounds (ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether). , Polyethylene glycol diglycidyl ether, bisphenol A-epichlorohydrin type epoxy resin, etc.), polyols (glycerin, ethylene glycol, propylene glycol, etc.), and (poly) alkylene polyamines (ethylene diamine, etc.).

Examples of the polyvalent metal compound include compounds capable of forming an ionic bridge, for example, alkaline earth metals (calcium, magnesium, etc.), hydroxides, halides, salts (sulfates, carbonates, acetates) of zinc, aluminum, titanium and the like. Etc.), specifically calcium hydroxide, zinc diacetate, aluminum chloride and the like. Of these, preferred are polyglycidyl ether compounds and polyvalent metal compounds.

The addition amount of these compounds can be variously changed depending on the degree of crosslinking of the polymer by the copolymerizable crosslinking agent, but is usually 10% or less, preferably 0.001 to 5% with respect to the total weight of the acid group and the alkali metal base.

A compound having at least two functional groups is added to a polymer neutralized product, kneaded, dried and pulverized.

Addition and kneading are performed as an aqueous solution, if necessary, and usually performed by a kneader such as a kneader or a universal mixer.

The drying method is usually a method of drying by heating with hot air having a temperature of 100 to 230 ° C., a thin film drying method using a drum dryer or the like usually heated to 100 to 230 ° C., a reduced pressure drying method, a freeze drying method, etc. The method is good.

The crushing method is also not particularly limited, and ordinary devices such as a hammer crusher, an impact crusher, a roll crusher, and a jet stream crusher can be used.

The water-absorbent resin obtained by the present invention has a weight of 50 g under normal pressure.
It has the ability to absorb 10 g / g or more of its own weight of 1% saline under a pressure of 20 g / cm ² or more / g.

[Examples] Hereinafter, the present invention will be further described with reference to Examples, but the present invention is not limited thereto. Parts in the examples are parts by weight. The absorbency under normal pressure, the absorbency under pressure, the amount of water-eluted components and the amount of residual monomer in the examples were measured by the following methods.

(i) Absorbency under normal pressure 1 g of the sample was placed in a 250-mesh nylon bag tea bag, immersed in 1% saline for 60 minutes, and then drained for 15 minutes to measure the increased weight of the sample. did.

(ii) Absorbency under pressure A weight is placed on 0.2 g of the sample so that the load is 20 g / cm ² , and 1% saline solution is continuously contacted from the lower side. After absorbing for 120 minutes, the increased weight of the sample was measured, and this value was multiplied by 5 to obtain the absorbency under pressure.

(iii) Amount of water-eluting component 2 g of sample was added to 300 g of 1% saline to swell sufficiently, and 5
Continue stirring for hours. Then, it is filtered through a 0.2-micron membrane filter, and the filtrate (ag) is evaporated to dryness to measure the residual weight (bg).

(iv) Amount of residual monomer 10 μl of the filtrate was sampled and the amount of residual monomer was determined by high performance liquid chromatography.

Example 1 100 parts of acrylic acid, N, N-methylenebisacrylamide 0.
After charging 5 parts and 350 parts of water in a closed container that can be opened and closed and adjusting the liquid temperature to 10 ° C under a nitrogen atmosphere, 1 part of 0.5% ammonium persulfate aqueous solution and 1 part of 0.5% sodium bisulfite aqueous solution were added. When polymerized, it turned into a gel with heat generation. Eight hours after the initiation of polymerization, the closed reaction vessel was opened, and the produced gel-like water-containing crosslinked polymer was taken out. After 400 parts of this gel has been shredded, 73.5 parts of 50% aqueous sodium hydroxide solution is added to neutralize, and the mixture is kneaded evenly to convert about 75 mol% of polyacrylic acid in the polymer into sodium polyacrylate. did.

The neutralized gel was dried with a drum dryer heated to 150 ° C., and then pulverized to have a particle size of 32 to 145 mesh to obtain a water absorbent resin.

The performance measurement results of this product are shown in Table 1.

Example 2 To a neutralized gel prepared in the same manner as in Example 1, 6 parts of a 5% aqueous solution of ethylene glycol diglycidyl ether was further added and kneaded uniformly, and then heated at 150 ° C. in a drum dryer. And then pulverized to a particle size of 32 to 145 mesh to obtain a water absorbent resin.

The performance measurement results of this product are shown in Table 1.

Examples 3 to 4 Water absorbent resins were obtained in the same manner as in Examples 1 and 2 except that 60 parts of acrylic acid and 115 parts of 2-acrylamido-2-methylpropanesulfonic acid were used instead of 100 parts of acrylic acid. It was

The results of these performance measurements are shown in Table 1.

Examples 5 to 6 Water absorbent resins were obtained in the same manner as in Examples 1 and 2 except that 60 parts of acrylic acid and 115 parts of 2-hydroxyethylacryloyl phosphate were used instead of 100 parts of acrylic acid.

The results of these performance measurements are shown in Table 1.

Example 7 A water absorbent resin was obtained in the same manner as in Example 1 except that the amount of N, N'-methylenebisacrylamide was 1.2 parts.

The results of these performance measurements are shown in Table 1.

Comparative Example 1 Sodium acrylate 98 parts (75 mol%), acrylic acid 25
Part (25 mol%), N, N'-methylenebisacrylamide 0.5
Parts and 350 parts of water into a closed reaction container that can be opened and closed,
After the liquid temperature was adjusted to 10 ° C. in a nitrogen atmosphere, a gel-like hydrous cross-linked polymer was obtained by adding 1 part of 0.5% ammonium persulfate aqueous solution and 1 part of 0.5% sodium bisulfite aqueous solution and polymerizing for 8 hours. .

After the gel was shredded, it was dried with a drum dryer heated to 150 ° C. and pulverized to a particle size of 32 to 145 mesh to obtain a water absorbent resin.

The performance measurement results of this product are also shown in Table 1.

Comparative Example 2 6 parts of a 5% aqueous solution of ethylene glycol diglycidyl ether was added to a polymer gel prepared in the same manner as in Comparative Example 1 and kneaded uniformly, followed by drying with a drum dryer heated to 150 ° C., It was pulverized to a particle size of 32 to 145 mesh to obtain a water absorbent resin.

The performance measurement results of this product are also shown in Table 1.

Comparative Example 3 A water absorbent resin was obtained in the same manner as in Comparative Example 1, except that 46 parts of sodium acrylate and 128 parts of sodium 2-acrylamido-2-methylpropanesulfonate were used instead of 98 parts of sodium acrylate. .

The performance measurement results of this product are also shown in Table 1.

Comparative Example 4 A water absorbent resin was obtained in the same manner as in Comparative Example 1, except that 46 parts of sodium acrylate and 128 parts of sodium salt of 2-hydroxyethylacryloyl phosphate were used instead of 98 parts of sodium acrylate.

The performance measurement results of this product are also shown in Table 1.

[Effects of the Invention] The present invention has the following effects.

It is possible to produce a water absorbent resin having high absorbency under pressure and under normal pressure.

A water absorbent resin having a small amount of water-eluted components and a small amount of residual monomer can be produced. Therefore, it is safe for the skin and excellent in hygiene.

It is possible to produce a resin having a high molecular weight.

The effect of the second invention is to crosslink with a copolymerizable crosslinker, then neutralize, and react with a compound having a carboxylic acid group and / or a group reactive with a carboxylic acid group. A resin having further improved performance can be obtained.

In a resin produced by polymerizing a conventional alkali metal acrylate and acrylic acid in the presence of a copolymerizable crosslinking agent, the molecular weight of the main chain of the crosslinked polymer was difficult to increase. However, according to the present invention, after cross-linking polymerization in the state of an acid group, it is produced by partially converting into an alkali salt with an alkali metal compound, the molecular weight of the cross-linked polymer main chain is larger than the conventional one, A water-absorbent resin having a high water-absorbing ability and a small amount of water-eluting component and a small amount of residual monomer can be obtained.

Since the resin obtained by the present invention exerts the above-mentioned effects, it is a human body such as absorbent material, sanitary materials (paper diapers for children and adults, sanitary napkins, sanitary cotton, bandages, incontinence pads, paper towels, etc.). It is useful for industrial applications such as water-in-oil separating agents, other dehydrating or desiccating agents, water retention agents for plants and soil, sludge coagulating agents, anti-condensation agents used for interior building materials, etc.

Claims (2)

[Claims] 1. A polymerizable monomer containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group and a phosphoric acid group and a copolymerizable cross-linking agent are obtained by polymerization as essential components. A method for producing a water-absorbent resin, comprising adding an alkali metal compound to the obtained polymer to neutralize 50 to 90 mol% of acid groups in the polymer to partially form an alkali metal base. 2. A polymerizable monomer containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group and a phosphoric acid group, and a copolymerizable cross-linking agent are obtained by polymerization as essential components. The polymer neutralized product obtained by adding an alkali metal compound to the obtained polymer to neutralize 50 to 90 mol% of the acid groups in the polymer to partially form an alkali metal base is used as an acid group and / or an alkali metal. A method for producing a water-absorbent resin, which comprises further crosslinking with a compound having at least two groups capable of reacting with a base.