KR20000002673A - Process for preparing porous absorbable resin - Google Patents

Abstract

PURPOSE: Manufacturing process for ethylene monomer in presence of carbonate is provided to give good hygroscopicity. CONSTITUTION: The resin is prepared by polymerization of cross-link agent containing water soluble ethylene unsaturated monomer using radical photopolymerization initiator and peroxide in presence of carbonate. For example, monomer solution(40 weight % of monomer component) of 75 mol % of sodium acrylate and 25 mol % of acrylic acid is mixed with 0.03 weight % of trimethylolpropanetriacrylate(per monomer component) as cross-link agent, 0.005 weight % of 2,2-dimethoxy-1.2-diphenylethane-1-one(per monomer component) and 0.1 weight % of hypersodiumsulfate(per monomer component) as photopolymerization initiator, cooled to 10°C, blown with N gas. 300g of Monomer solution is mixed with 1 weight % of sodium bicarbonate(per monomer component) pored into glass container, irradiated by ultraviolet for 30 sec with ultraviolet hardening apparatus to give porous gel polymer, which shows 70 of coefficient of absorption expansion, 20 sec of absorption rate, 428ppm of residue monomer. The resin is used as sanitary napkin, paper diaper, disposal towel, and soil conditioner.

Description

Manufacturing method of porous absorbent resin

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an efficient method for producing an absorbent resin having excellent physical properties through porous porous hydrogel polymer and having high absorption ratio, fast absorption rate, and low water content due to its properties. Belong.

Conventionally, absorbent resins include sanitary products such as sanitary products, paper diapers, disposable towels, and agricultural horticultural products such as repair agents and soil modifiers, and solidification of dirty soil, prevention of condensation of building materials, and dehydration during maintenance. Has been used in the field.

As such an absorbent resin, an acrylate polymer crosslinked product, a starch-acrylic acid kraft copolymer, a hydrolyzate of a starch-acrylonitrile kraft copolymer, a polyoxyethylene crosslinked product, a carboxymethylcellulose crosslinked product and the like are known.

As a method for producing a polymer used in such an absorbent resin, a method by reverse phase suspension polymerization, for example, those described in Japanese Patent Laid-Open Nos. 56-161408, 57-158209 and 57-198714 are known. By aqueous solution polymerization, the method as described in Unexamined-Japanese-Patent No. 2-170808, Unexamined-Japanese-Patent No. 55-108407, etc. is known, for example.

In addition, a method of polymerizing while crushing and cooling a polymer gel by stirring in a two-wing kneader by a special method belonging to aqueous solution polymerization, for example, the method described in Japanese Patent Application Laid-Open No. 57-34101 is known, and furthermore, Is a method of polymerizing a high concentration aqueous solution on a belt to perform polymerization and drying at the same time, for example, Japanese Patent Application Laid-Open No. 58-71507, a method of adding an azo polymerization initiator to an aqueous monomer solution to irradiate ultraviolet rays, for example, Japanese Patent It is known, for example, from Japanese Patent Application Laid-Open No. 8-253615.

However, there is a problem that any of these manufacturing methods must be solved.

In other words, the reverse phase suspension polymerization method has a high workability due to poor workability due to the use of an organic solvent, a risk of flammable explosion, and a cost and removal cost of the organic solvent.

Also, if the organic solvent is completely removed from the product, the price becomes higher.

In addition, there are problems such as environmental hygiene for employees.

On the other hand, aqueous solution polymerization does not have the same problem as described above, and the method described in JP-A-2-170808 performs the aqueous solution polymerization under pressure, so that boiling of the aqueous solution is suppressed and polymerization at a high concentration is possible, and high absorption magnification is achieved. Although there is an advantage that the water-absorbent resin can be produced with good productivity, the temperature of the aqueous monomer solution or the produced aqueous gel in the polymerization vessel, that is, the reaction is very high, and as a result, there is a problem that the water-soluble content is high.

The method disclosed in Japanese Patent Application Laid-Open No. 57-34101 is a method of performing aqueous solution polymerization while subdividing the gel produced by the progress of polymerization by the shear force of the stirring blade, and has a granular hydrogel having a crosslinking structure in the molecule. Although it is a method which can manufacture a polymer, it has a problem that a special polymerization apparatus is needed and production of the absorbent resin of high absorption ratio is difficult.

The method described in Japanese Patent Application Laid-Open No. 58-710507 discloses that a high concentration of aqueous monomer solution is pre-warmed and a polymerization initiator is added to carry out continuous polymerization on a circulating belt and evaporate moisture at the same time without external heating. Although a porous resin is obtained in a good productivity method that does not require a drying step, there is a disadvantage that low molecular weight of the water absorbent resin occurs due to severe polymerization conditions, resulting in a large amount of water-soluble water and a decrease in water retention rate.

The methods described in Japanese Patent Laid-Open Nos. 63-43912, 63-317519, 1-156310 and 8-253615 are prepared by adding an azobis-based photosensitizer to an aqueous monomer solution and subjecting the polymerization to UV irradiation. Although it is possible to polymerize continuously by the method of starting and a productive method, it is necessary to use a comparatively large quantity of photosensitizers in order to obtain a porous hydrogel polymer. Therefore, there is a problem in that a large amount of water soluble due to the generation of low molecular weight polymer.

The water-soluble components such as unreacted monomers and low molecular weight polymers in the absorbent resin are often leached therein when the absorbent resin contacts the absorbed liquid such as water, urine and body fluid to form a hydrogel structure. The water-soluble component thus spilled is required to accelerate the deterioration of the absorbent resin and to cause an unpleasant situation such as unpleasantness due to stickiness or to contaminate the liquid to be absorbed.

Therefore, there is a strong demand for a method for producing an absorbent resin having a high absorption ratio, a fast absorption rate, and low water content. On the other hand, the hydrous gel polymer obtained by polymerization is generally pulverized through a drying step and then commercially available as a powder product. In order to efficiently dry such a conventional hydrous gel polymer, many methods have been proposed to cut the hydrogel polymer as thin as possible and make the surface area as large as possible. For example, a method is known in which a hydrous gel polymer is pushed out of a porous plate to be broken. However, in the conventionally known method, it is difficult to obtain a particulate hydrogel polymer by reattaching the hydrogel gel even if it is fine and becoming a string. In order to increase the drying efficiency of the hydrogel polymer, it is necessary to reduce the pore size of the porous plate. When such a porous plate is used, the discharge rate of the hydrogel polymer is decreased and productivity is lowered. There is a problem.

As a method of solving the problem and producing a particulate water-containing gel polymer having a high absorption ratio and low water-soluble content with good productivity, one proposal is disclosed in Japanese Patent Application Laid-Open No. 5-70597 and 5-112654. This is polymerized while shearing the hydrogel polymer with a two-wing kneader, and the granulated gel polymer is obtained by repeatedly cutting the hydrogel gel polymer from the porous plate having a specific pore size.

However, the above method is ineffective if the hydrogel polymer is pushed out of the porous plate without being cut to some extent, and has a problem of using a special polymerization reactor.

When a hydrogel polymer is pushed out of a porous plate and crushed, a method of adding a release agent or the like to prevent reattachment is also known, but such additives often adversely affect the physical properties of the absorbent resin as a product.

In addition, the method described in Japanese Patent Laid-Open No. 7-185331, Japanese Patent Laid-Open No. 8-509521, and WO 96/17884 discloses a method of producing a microporous hydrogel by polymerization using a carbon dioxide-based blowing agent or the like. Since it is difficult to match the polymerization start time to the foaming start time, it is virtually impossible to adjust the foaming degree and pore size. In addition, even if the addition of a large amount of the catalyst for starting the polymerization can be performed at the same time as the foaming start and the polymerization start, at the same time, there is a problem in that the water-soluble component is accompanied with a decrease in the degree of polymerization and the generation of a low molecular weight polymer.

Therefore, there is a strong demand for a method for producing an absorbent resin that has high productivity, good drying efficiency, high absorption ratio, high absorption rate, and low water content.

An object of the present invention is to provide a manufacturing method which can solve the above problems and obtain an absorbent resin having good productivity, high absorption ratio, and high absorption rate by a simple process that does not use additives such as a release agent.

MEANS TO SOLVE THE PROBLEM The present inventors came to complete this invention, as a result of earnestly examining the manufacturing method of the water absorbing resin which solved the said problem, and was excellent in productivity, workability, and excellent quality.

That is, the present invention provides a method for producing a porous absorbent resin, wherein the water-soluble ethylenically unsaturated monomer containing a crosslinking agent is polymerized by ultraviolet irradiation using a radical photopolymerization initiator and a peroxide in the presence of a carbonate. A method for producing a porous absorbent resin, characterized in that the carbonate is an alkali metal salt or an ammonium salt, and a method for producing a porous absorbent resin, characterized in that the monomer is polymerized into a layered body of an aqueous solution having a thickness of 50 mm or less. will be.

Hereinafter, the present invention will be described in detail.

In the present invention, as the water-soluble ethylene-based unsaturated monomer used, specifically, (meth) acrylic acid, (maleic anhydride), fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloylethane sulfonic acid, 2- Anionic monomers and salts thereof such as (meth) acryloylpropane sulfonic acid and 2- (meth) acrylamide-2-methylpropane sulfonic acid; (Meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxy polyethylene glycol (meth) acrylate, polyethylene glycol ( Nonionic hydrophilic group-containing monomers such as meth) acrylate; And amino group-containing unsaturated monomers such as N, N-dimethylaminoethyl (meth) acrylate and N, N-dimethylaminopropyl (meth) acrylamide, and quaternized compounds thereof.

As a water-soluble ethylenically unsaturated monomer, 1 type, or 2 or more types can be selected and used out of these, but considering the absorbent property of the water absorbing resin finally obtained, (meth) acrylic acid (salt) and 2- (meth) acryloyl Ethane sulfonic acid (salt), 2- (meth) acrylamide-2-methylpropane sulfonic acid (salt), (meth) acrylamide, methoxy polyethylene glycol (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylic It is preferable to use 1 or more types chosen from the group which consists of a rate or its quaternized substance, etc., and it is especially preferable to use what contains (meth) acrylic acid (salt) as an essential component.

When making (meth) acrylic acid (salt) an essential component, it is most preferable to use (meth) acrylic acid which partially neutralized 20-100 mol% of (meth) acrylic acid with a basic substance. In addition, partial neutralization (meth) acrylic acid can be combined very easily by arbitrary neutralization degree by partially neutralizing (meth) acrylic acid with an alkali metal salt. The water-soluble ethylenically unsaturated monomer is mainly polymerized in an aqueous solution, but the aqueous solution may be added with starch, cellulose, and the like, which have been conventionally used in the manufacture of absorbent resins, to impart its characteristics.

In addition, acrylate esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, vinyl acetate, propionic acid, and the like, in an amount that does not extremely inhibit the hydrophilicity of the obtained polymer. Hydrophobic monomers, such as vinyl, can also be added and used together.

The crosslinking agent used together with a water-soluble ethylenically unsaturated monomer is a component which makes the polymer obtained from these monomers a crosslinked structure, and the compound which has two or more polymerizable unsaturated groups or reactive functional groups in the middle of a molecule, or a powder terminal is applied.

Specific examples of the crosslinking agent include N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol (meth) acrylate, glycerin tri (meth) acrylate, trimetholpropane tri (meth) acrylate, Triarylamine, triarylcyanurate, glycidyl (meth) acrylate, (poly) ethylene glycol, diethylene glycol, (poly) glycerine, propylene glycol, diethanolamine, trimetholpropane, pentaacethritol, (Poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, epichlorohydrin, ethylenediamine, polyethyleneimine, (poly) aluminum chloride, aluminum lactate, calcium chloride, magnesium lactate, and the like It is mentioned, In view of the reactivity of the whole water-soluble ethylenically unsaturated monomer in such a compound, 1 type, or 2 or more types are used.

In the present invention, in order to polymerize the water-soluble ethylenically unsaturated monomer and the crosslinking agent, a radical photopolymerization initiator as a polymerization initiator is used in combination with a peroxide.

The radical photoinitiator satisfies the polymerization rate and solubility in the aqueous monomer solution when the water-soluble ethylenically unsaturated monomer is polymerized by an ultraviolet solution.

As a specific example of a radical type photoinitiator, benzoin, benzyl, acetphenone, benzophenone, and derivatives thereof which are generally used for ultraviolet polymerization are mentioned. Examples of the derivatives include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and acetophenone, as the benzoin substance, diethoxyacetophenone and 2,2-dimethoxy. -1, 2-diphenylethan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1- (4- (methylthio) phenyl) -2-morpholin propane-1, 2-benzyl- 2-dimethylamino-1- (4-morpholinophenyl) butanone-1,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4- (2-hydroxyethoxy) -Phenyl) -2-hydroxy-2-methyl-1-propane-1-one and benzophenone-based substances include methyl 0-benzoylbenzoate, 4-phenylbenzophenone and 4-benzoyl-4'-methyldi Phenylsulfide, 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 2,4,6, -trimethylbenzophenone, 4-benzoyl-N, N-dimethyl-N- [ 2- (1-oxy-2-propenyloxy) ethyl] benzenemetasodium bromide, (4-benzoylbenzyl) trimethylammonium chloride, 4,4'-dimethylaminobenzophenone, 4,4'- diethylamino benzophenone etc. are mentioned.

As another radical type photoinitiator, an azo compound can also be used and an azonitrile compound, an azo amidine compound, an alkyl azo compound, etc. can also be used. However, for the reason that high polymerization degree is difficult when it is necessary to add a relatively large amount, the method of using the radical type photoinitiator which has a benzoyl group is preferable.

In this invention, 1 type, or 2 or more types of these photoinitiators are used together, and these photoinitiators can start superposition | polymerization with the addition amount of a very small amount.

In the present invention, the peroxide is used to reduce unreacted monomers. Examples of the most preferred peroxides of the present invention include peroxides such as sodium peroxide, ammonium peroxide, potassium peroxide, hydrogen peroxide, t-butylperoxide, succinic peroxide, t-butylperoxymaleic acid, and the like. Or it can use in combination of 2 or more type.

In the present invention, in order to obtain a porous hydrous gel polymer, the use of carbonate is indispensable. As the carbonate, all carbonates and hydrogen carbonates containing salts or mixed salts are also used in the present invention, but examples of the most preferred carbonates in the present invention include sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, ammonium carbonate and hydrogen carbonate Ammonium, magnesium carbonate, calcium carbonate, barium carbonate, and the like, and hydrates thereof; and one or two or more thereof are used. In particular, the most preferred carbonates in the present invention are monovalent cations such as carbonates or hydrogen carbonates of sodium, potassium, ammonium. When carbonates composed of polyvalent cationic species are used, the polymer having a carboxyl group is metal crosslinked by the polyvalent cationic species, which adversely affects the absorption performance, making it difficult to produce a good absorbent resin.

In the present invention, an antifoaming agent can also be used for the purpose of adjusting the bubble diameter and the foaming time. As the antifoaming agent, those generally known as defoamers, suppressors, foam stabilizers, and the like can be arbitrarily selected. It can also be used in combination.

Specific examples of the antifoaming agent include fats and oils, fatty acids, lower alcohols, higher alcohols, metal soaps, silicones, hydrophobic silica compounds, fatty acid esters, polyglycols, polyglycol esters, polyethers, and modified silicones. And oil-soluble polymers, organophosphorus compounds, lactic acid fatty acids, polyether derivatives, silica-modified silicone compounds, and the like.

In the present invention, the polymerization of the water-soluble ethylenically unsaturated monomer as described above is generally carried out by aqueous solution polymerization, and the monomer concentration in the aqueous solution of the water-soluble ethylenically unsaturated monomer is usually about 25 to 80% by weight, preferably The polymerization is carried out at 30 to 50% by weight.

When the monomer concentration is 25% by weight or less, the hydrous gel polymer obtained is very soft, it is difficult to cut small to dry the gel, and also contains a large amount of water, resulting in poor drying efficiency and poor productivity. When it exceeds 80% by weight, it is difficult to control the polymer temperature of the reaction system during the reaction, the temperature becomes high, and due to the severe polymerization conditions, low molecular weight of the absorbent resin occurs, the water-soluble content increases and the water retention rate decreases. Tend to be.

The amount of the crosslinking agent used in combination with the water-soluble ethylenically unsaturated monomer is determined in consideration of the crosslinking density of the obtained water absorbent resin, and the resulting water absorbing properties, but is generally 0.0001 to 5% by weight relative to the water-soluble ethylenically unsaturated monomer. Is 0.005 to 3% by weight.

In order to obtain the water absorbent resin having the excellent properties aimed at by the present invention, it is necessary to polymerize a water-soluble ethylenically unsaturated monomer containing a crosslinking agent by irradiating ultraviolet rays using a radical photopolymerization initiator and a peroxide in the presence of a carbonate.

In order to start the polymerization by irradiating the monomer aqueous solution with ultraviolet light alone with a photopolymerization initiator to obtain the desired porous hydrous gel polymer, it is necessary to adjust the temperature from the start of the polymerization to the end of the synthesis to be 100 ° C or higher. When the polymer chain deteriorates due to heat, the water content increases. Moreover, polymerization is not completed completely and a considerable amount of unreacted water-soluble ethylenically unsaturated monomers remain. The problem is solved by using a combination of carbonate and peroxide and then obtaining an absorbent resin. In this case, a porous gel having a relatively small pore size can be produced efficiently by adding the antifoaming agent as a third component.

It is preferable that the addition amount of a photoinitiator shall be 0.0001 to 0.1 weight% with respect to a water-soluble ethylenically unsaturated monomer component, More preferably, it is 0.001 to 0.01 weight%. By initiating the polymerization in such an extremely small amount of addition, the polymer is highly polymerized, so that the water-absorbent resin having low water content is particularly efficiently obtained.

If the amount of the photopolymerization initiator added is less than 0.0001% by weight relative to the water-soluble ethylenically unsaturated monomer component, the polymerizability is extremely poor, and if it is more than 0.1% by weight, low polymerization of the polymer occurs and the water-soluble content tends to increase.

The amount of carbonate added is preferably 0.01 to 10% by weight, more preferably 0.1 to 5% by weight based on the water-soluble ethylenically unsaturated monomer component.

If the amount of carbonate added is less than 0.01% by weight, the hydrous gel product obtained by polymerization does not exhibit the characteristics as a porous body. In addition, the addition of 10% by weight or more increases the water-soluble content, and also impedes the water holding capacity of the resin.

Moreover, it is preferable to add a carbonate before ultraviolet irradiation, and as an addition method, you may add a carbonate in that state, or may melt | dissolve in arbitrary solvent and add a carbonate solution.

It is preferable that the addition amount of a peroxide is 0.001-10 weight% with respect to a water-soluble ethylenically unsaturated monomer component, More preferably, it is 0.01-1 weight%.

If the addition amount of the peroxide is less than 0.001% by weight, it is difficult to sufficiently reduce the unreacted monomers. If the addition of 10% by weight or more, the water-soluble content increases, and the obtained absorbent resin may be colored. There is a risk of getting bad.

In the present invention, since the polymerization is initiated by irradiation of ultraviolet rays and the ultraviolet ray is sufficiently transmitted through the aqueous aqueous ethylenically unsaturated monomer solution, the reaction vessel is preferably in a shape that satisfies the requirements, and is obtained by polymerizing the aqueous monomer solution. In consideration of the working efficiency of the hydrogel polymer in the cutting, drying, and pulverizing process, it is preferable to use a circulating belt and a release container having a large surface area as a reaction vessel.

In addition, the thickness of the aqueous monomer solution is preferably 50 mm or less, more preferably 20 mm or less, so as to sufficiently maintain the transmission of ultraviolet rays under the control of the reaction temperature (the highest reaching temperature of the polymer). When the thickness of the monomer aqueous solution exceeds 50 mm, ultraviolet irradiation will not be uniform, and a polymer may become nonuniform.

Although there is no restriction | limiting in particular in the lower limit of the thickness of the said monomer aqueous solution, When productivity is considered, 1 mm or more is preferable.

Although the light quantity of an ultraviolet-ray is not specifically limited, It is good to set it as 100-4000 m Joule / cm <2> normally. When it is less than this range, superposition | polymerization may be inadequate, and when it is more than this range, since the crosslinking point of the polymer obtained by excessive irradiation is cut | disconnected and a water-soluble content may increase, it is unpreferable.

As a light source used for ultraviolet irradiation, a conventionally known light source is used. For example, a mercury lamp, a metal halide lamp, or the like may be used in consideration of reaction conditions. Irradiation wavelength is not specifically limited, either, Usually, the wavelength of 200-450 mm is used. Although ultraviolet irradiation time is suitably determined in order to become the said light quantity, superposition | polymerization starts immediately after starting irradiation on the said conditions, and superposition | polymerization is fully completed by the short time irradiation of 10 to 20 second normally.

It is preferable that the said liquid temperature is maintained at 30 degrees C or less, More preferably, the water-soluble ethylenically unsaturated monomer aqueous solution before ultraviolet irradiation is maintained at 0 to 20 degreeC.

When the said aqueous solution temperature exceeds 30 degreeC, since the temperature of a reaction system becomes too high, there exists a possibility that the water holding capacity may fall and the water-soluble content may increase at the same time by low molecular weight. There is no restriction | limiting in particular about the minimum of the said aqueous solution temperature, What is necessary is just to be the temperature at which the aqueous solution does not freeze, and if there is normally 0 degreeC or more, there is no problem.

When the water-soluble ethylenically unsaturated monomer starts polymerization, the temperature in the system rises, but in order to obtain an excellent water absorbent resin, it is preferable to suppress the maximum reaching temperature in the system to 120 ° C or less, and more preferably to 100 ° C or less. will be. When the maximum reaching temperature in a system exceeds 120 degreeC, the polymer obtained by superposing | polymerizing a monomer aqueous solution will increase water solubility and will be bad in water repair ability by severe heat of polymerization.

There are various ways to suppress the maximum temperature at the time of polymerization. For example, a method of cooling the polymer contacting part from the outside, a method of blowing cold air into the polymer, etc. can be considered. Since the price becomes high, the above conditions, that is, the monomer aqueous solution concentration is 25 to 50% by weight, the temperature of the aqueous solution is 30 ° C. or less, and the thickness of the aqueous solution is 50 mm or less, preferably 1 to 20 mm. It is preferable to suppress the highest reaching temperature in the system at 120 ° C or lower by employing the conditions described above, and it can be easily achieved.

Moreover, in order to advance superposition | polymerization more efficiently, it is good to reduce the dissolved oxygen in the monomer aqueous solution. That is, the dissolved oxygen amount in the monomer aqueous solution which inhibits the polymerization is preferably 4 ppm or less in the present invention, and more preferably 1 ppm or less.

When the dissolved oxygen of the monomer aqueous solution exceeds 4 ppm, the reactivity of the monomer deteriorates, the polymerization start time is delayed, and the reaction is not completed, so that unreacted monomer may increase.

A well-known method is good for the method of reducing dissolved oxygen, and it is easily solved by blowing inert gas (for example, nitrogen gas) or the gas equivalent to it in aqueous monomer solution before irradiating with ultraviolet-ray.

As a method of cutting the hydrogel polymer obtained in this way, a device for cutting and pushing out a rubbery elastomer can be used, for example, easily achieved by using a known technique such as a cutter cutter, a cutter cutter, a kneader cutter, or the like. do. In the case of using a cutter type cutter, polymer deterioration due to shear force during gel cutting is small, which is preferable.

As a drying method of the cut hydrogel polymer, a conventional dryer and a heating furnace can be used, and examples thereof include hot air dryers, fluidized bed dryers, airflow dryers, infrared dryers, and dielectric heating dryers. Although drying temperature is not specifically limited, Usually, it carries out at 60-200 degreeC. If it is lower than the range, the drying efficiency is extremely poor, and if it exceeds the range, thermal deterioration of the absorbent resin may occur.

Conventionally known grinding methods may be employed for grinding the dried gel.

For example, it may be pulverized to a desired particle size using a vibration mill, impact mill, friction mill, or the like.

The size of the water absorbent resin powder obtained by the method of the present invention is not particularly limited and may be appropriately selected depending on the intended use. For example, when using it as a sanitary material, it is preferable to have a particle diameter of about 10-200 mesh normally.

The absorbent resin powder may be subjected to surface treatment as necessary.

As the method of the surface treatment, a conventionally known method can be used. For example, it is possible to modify the surface of the absorbent resin reacted with a known crosslinking agent such as an epoxy compound, a polyvalent metal, an aldehyde compound, or a polyhydric alcohol represented by a water-soluble diglycidyl ether compound to the carboxylate group contained in the absorbent resin. Do.

The water absorbent resin obtained by the present invention can be used for the above various uses, and is particularly suitable for hygiene products such as sanitary products and paper diapers.

In general, when aqueous solution polymerization of water-soluble ethylenically unsaturated monomers is carried out at a high temperature, water evaporates to obtain a porous hydrous gel polymer, but the resulting polymer has low molecular weight due to thermal deterioration, resulting in increased water content and water-retaining ability. It is thought that this is lowered.

In addition, nitrogen gas is generated during the polymerization from the use of an azo polymerization initiator to obtain a porous hydrogel polymer, but a large amount of azo polymerization initiator is required for a satisfactory porous body. Wake up, solubility is increased.

According to the method of this invention, a very small amount of photoinitiators generate | occur | produce radicals by ultraviolet-ray, and start superposition | polymerization of a monomer, carbonate decompose | dissolves by the heat of polymerization, and carbon dioxide gas is generated. As a result, a large number of bubbles are present, and a hydrous gel polymer having bubbles of a certain size is obtained, which is efficiently dried and also improves the performance of the resulting absorbent resin.

EXAMPLE

Hereinafter, although an Example demonstrates this invention in detail, the scope of the present invention is not limited to these Examples.

The absorption ratio, water-soluble content, water absorption rate, and solid content as the water absorbent resin of the dry pulverized product of the hydrous gel polymers described in these examples represent numerical values measured by the following test methods.

A. Absorption Ratio

0.5 g of absorbent resin powder was accurately added to a 300 ml beaker, 200 ml of 0.9% aqueous sodium chloride solution was added thereto, stirred for 60 minutes, and then the contents were poured onto a glass filter connected to a filtration device set at a vacuum of 200 mm Hg, and 10 minutes. After filtration, the weight is measured, and the absorption ratio (g / g) is calculated by the following Equation 1.

[Equation 1]

Absorption ratio = hydrogel weight after suction (g) / 0.5 (g)

B. Water Soluble

0.5 g of absorbent resin powder was weighed accurately, which was dispersed in 1000 ml of physiological saline (0.9% saline), stirred for 12 hours, filtered through a filtrate, the filtrate was concentrated, and dried at 130 ° C.

Aqueous content (weight%) is calculated | required according to following formula (2).

[Formula 2]

Water Soluble (wt%) = (Dry (g) x 1000 / 0.5 g x filtrate (g)) x 100

C. Unreacted Monomer Concentration (Residual Monomer)

Accurately weigh 0.4 g of the absorbent resin powder into a 300 ml beaker, add 200 ml of 0.9% aqueous sodium chloride solution, stir for 3 hours, filter through a membrane filter, and analyze the filtrate by high performance liquid chromatography.

On the other hand, the calibration curve obtained by analyzing the monomer standard solution of known concentration in the same manner is taken as an external standard, and the amount of remaining monomer in the absorbent resin is determined in consideration of the dilution ratio of the filtrate.

D. Absorption Rate

Accurately weigh 2 g of the absorbent resin powder, add it to 50 ml of 0.9% saline, which is stirred with a magnetic stirrer, and measure the time when the liquid level becomes flat.

E. Solids

Accurately weigh 1 g of the water-absorbent resin powder, dry it in an oven heated to 120 ° C. for 3 hours, and then measure the weight, and calculate the solid content (wt%) by the following Equation 3.

[Equation 3]

Solid content (% by weight) = resin powder weight after drying (g) / 1 (g)) × 100

Example 1

An aqueous solution of a monomer component (40 wt% of a monomer component) of 75 mol% sodium acrylate and 25 mol% of acrylic acid and 0.03 wt% of trimetholpropane triacrylate (large monomer component) as a crosslinking agent, and 2,2-dimethoxy as a photopolymerization initiator 0.005% by weight of -1,2-diphenylethan-1-one (large monomer component) and 0.1% by weight of sodium peroxide (large monomer component) are mixed, the aqueous monomer solution is cooled to 10 ° C, followed by nitrogen gas. Blow in to make the dissolved oxygen less than 1 ppm. 1 weight% of sodium hydrogencarbonate (large monomer component) is mixed with 300 g of this monomer aqueous solution, poured into a glass shale with an internal diameter of 146 mm and a height of 25 mm (18 mm thick monomer solution), and an ultraviolet curing device (high pressure mercury lamp 4 kW). , 80 W / cm, a light emitting field of 500 mm) was irradiated with ultraviolet light for 30 seconds (light quantity 750 m Joule / cm 2) to obtain a porous hydrous gel polymer.

In this case, the highest reaching temperature of the polymer is about 88 ° C.

That is, the maximum reaching temperature is a value obtained by measuring the surface temperature of the polymerized gel using a visible light laser surface thermometer.

The obtained porous hydrogel polymer was cut into a 3 mm lattice shape, dried in a hot air dryer for 120 minutes with hot air at 135 ° C., and then pulverized with a roll mill grinder to select an absorbent resin in a particle size of 300 μm to 500 μm.

Example 2

In Example 1, the absorbent resin is obtained by performing the same operation as in Example 1 except that the amount of the prepared aqueous monomer solution is changed to 100 g and the thickness of the aqueous monomer solution is 6 mm. In this case, the highest reaching temperature of the polymer is about 84 ° C.

Example 3

In Example 1, the same procedure as in Example 1 was carried out except that the monomer component was changed to 35% by weight and the monomer aqueous solution temperature was 20 ° C, and the amount of the crosslinking agent added was 400 ppm. In this case, the highest reaching temperature of the polymer is about 90 ° C.

Example 4

In Example 1, the same procedure as in Example 1 was carried out except that the monomer component 35% by weight, the aqueous solution temperature was 20 ° C, the amount of the aqueous monomer solution was changed to 200 g, and the monomer aqueous solution thickness was 12 mm. Get In this case, the highest reaching temperature of the polymer is about 86 ° C.

Example 5

In Example 1, the same operation as in Example 1 was carried out except that the amount of the prepared aqueous monomer solution was changed to 100 g, and the thickness of the aqueous monomer solution was 6 mm to obtain an absorbent resin. In this case, the highest reaching temperature of the polymer is about 84 ° C.

Example 6

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that the amount of sodium hydrogencarbonate added is 0.5% by weight (large monomer component).

Example 7

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that the amount of sodium hydrogencarbonate added is 2.0% by weight (large monomer component).

Example 8

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that sodium hydrogen carbonate is used as sodium carbonate.

Example 9

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that sodium hydrogen carbonate is used as potassium hydrogen carbonate.

Example 10

In Example 1, the photoinitiator is 2-methyl-1- (4- (methylthio) phenyl) -2-monolinopropanone-1, and the addition amount thereof is 0.003% by weight (large monomer component). Except for the same operation as in Example 1, an absorbent resin was obtained.

Example 11

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that the ultraviolet irradiation time is 90 seconds (light quantity 2250 m Joule / cm 2). In this case, the highest reaching temperature of the polymer is about 91 ° C.

Comparative Example 1

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that no sodium hydrogen carbonate is added.

Comparative Example 2

In Example 1, operation similar to Example 1 was performed except having made superposition | polymerization initiator into 0.05 weight% of ammonium peroxide (large monomer component), and 0.005 weight% of L-ascorbic acid (large monomer component), and not performing ultraviolet irradiation. Although the reaction was stopped during the polymerization, there were many unpolymerized products and a hydrogel polymer could not be obtained.

Comparative Example 3

In Example 1, operation similar to Example 1 was performed except having made superposition | polymerization initiator into 0.5 weight% of ammonium peroxide (large monomer component), and 0.05 weight% of L-ascorbic acid (large monomer component), and not irradiating an ultraviolet-ray. And absorbent resin is obtained.

[Comparative Example 4]

In Example 1, an absorbent resin is obtained in the same manner as in Example 1 except that sodium peroxide is not added.

Table 1 shows the results of evaluating the performance of the water absorbent resin obtained in Examples and Comparative Examples.

TABLE 1

Absorption Magnification (g / g) Water Soluble (%) Residual Monomer (ppm) Absorption Rate (sec) Solid content (%) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 706960645868717072627469-7569 554435555455-1516 428447443434445442452439423435441523-8991438 202220201824182119192049-4024 949494949594959494949590-9193

As shown in Table 1, in the production method of the present invention, a porous absorbent resin having a relatively small pore size is uniformly produced very efficiently, and the absorption rate is not accompanied by a decrease in water absorption rate and an increase in water content. It has been found that an excellent water absorbent resin can be obtained.

Due to the present invention, in addition to providing a method for producing a porous hydrogel polymer having high drying efficiency and high productivity, the water absorbent resin obtained after drying and pulverizing has a high absorption ratio, a fast absorption rate, and low water solubility. The effect that resin is supplied is mentioned.

In addition, the absorbent resin obtained by the present invention, by using the good absorption rate, sanitary products such as physiological products, paper diapers, disposable towels, and agricultural horticultural products such as repairing agents and soil modifying agents, and solidification of dirty soil, It is used in various fields such as prevention of condensation of building materials and dehydration during maintenance.

Claims (3)

A water-soluble ethylenically unsaturated monomer containing a crosslinking agent is polymerized by ultraviolet irradiation using a radical photopolymerization initiator and a peroxide in the presence of a carbonate. The method for producing a porous absorbent resin according to claim 1, wherein the carbonate is an alkali metal salt or an ammonium salt. The method for producing a porous absorbent resin according to claim 1 or 2, wherein the monomer is polymerized into an aqueous solution layer having a thickness of 50 mm or less.