KR100330127B1 - Method for producing absorbent resin - Google Patents

Abstract

PURPOSE: Provided is a method for producing an absorbent resin which has excellent productivity, and high absorption, and comprises a small amount of water-soluble ingredients and unreacted monomers. CONSTITUTION: The method comprises polymerizing a water-soluble, ethylenically unsaturated monomer comprising crosslinking agent by radiating ultraviolet in the presence of radical photoinitiator having benzoyl group and peroxide. The amounts of photoinitiator and peroxide are 0.001-0.01 wt% and 0.005-0.1 wt% with respect to the water-soluble, ethylenically unsaturated monomer, respectively. The method can produce an absorbent resin continuously with high productivity, in short time, wherein the absorbent resin shows no sticky feeling when absorbing, and has excellent quality.

Description

Manufacturing method of absorbent resin

The present invention relates to a method for producing an absorbent resin having a high absorption ratio and low water-soluble content and unreacted monomer.

In recent years, absorbent resins have been applied to a wide range of applications such as sanitary materials for hygiene products, paper diapers, drip absorbers, soil repair agents, and prevention of dry dew condensation.They are crosslinked polyacrylates, acrylates of acrylic acid ester-vinyl acetate copolymers, and crosslinked poly Polymers of ethylenically unsaturated monomers such as vinyl alcohol modified products, crosslinked isobutylene-maleic anhydride copolymers and starch-acrylic acid graft polymers have been used as absorbent resins.

There are several methods for producing a polymer used as such an absorbent resin. For example, Japanese Patent Laid-Open Publication Nos. 56-161408, 57-158209, and 57-198714 can be obtained by reverse phase suspension polymerization. The method described is known, and the method described by Unexamined-Japanese-Patent No. 2-170808 and 55-108407 is known as a method by aqueous solution polymerization.

Also, a special method of aqueous solution polymerization is a method of breaking and cooling a polymerized gel by stirring in a twin kneader, for example, in JP-A 57-34101 and JP-A 5-112654. Furthermore, the method of superposing | polymerizing a high concentration aqueous solution on a belt and carrying out superposition | polymerization and drying simultaneously, for example, Unexamined-Japanese-Patent No. 58-71507, the method of adding a photosensitizer to aqueous monomer solution, and irradiating an ultraviolet-ray to superpose | polymerize, For example, it is known from Japanese Patent Application Laid-Open No. 63-43912.

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

In other words, the reverse phase suspension polymerization method is poor in workability due to the use of organic solvents, and there is a risk of flammable explosion, so that the countermeasures must be taken. Furthermore, the cost is increased by adding the removal cost to the cost of the organic solvent itself. There is a problem. Attempting to remove the organic solvent completely from the product also costs more. Moreover, problems such as environmental hygiene to workers also exist.

On the other hand, the method by aqueous solution polymerization does not have the above-mentioned problems, and since the method described in JP-A-2-170808 is to perform aqueous solution polymerization under pressure, polymerization at a high concentration where boiling of the aqueous solution is suppressed is possible, Although there is an advantage that the absorbent resin having a high absorption ratio can be produced with excellent productivity, the temperature of the aqueous monomer solution or the resulting aqueous gel in the polymerization vessel becomes very high, and as a result, the water-soluble content is increased.

The method disclosed in Japanese Patent Application Laid-Open No. 57-34101 and Japanese Patent Laid-Open No. 5-112654 is a method of performing aqueous solution polymerization while subdividing the gel generated during the polymerization process by the shear force of the stirring blade. Although it is a method for producing a granular hydrogel polymer, there is a problem in that it requires a special polymerization apparatus and is difficult to produce a water absorbent resin having a high absorption ratio.

Since the method described in Japanese Patent Application Laid-Open No. 58-71507 is to warm up a high concentration of aqueous monomer solution in advance, and to polymerize it continuously on a rotary belt or the like without evaporating externally by adding a polymerization initiator, it evaporates moisture. The productivity is good because it does not require a process, but there is a drawback that the resin obtained due to excessive evaporation conditions becomes porous due to moisture evaporation by heat of polymerization, and lacks water-retaining ability or high water content.

The method described in Japanese Patent Laid-Open Nos. 63-43912, 63-317519 and 1-156310 is a method of initiating polymerization by ultraviolet irradiation by adding an azobis-based photosensitizer to an aqueous monomer solution. It is a method that can be polymerized continuously and has a good productivity. However, in order to reduce unreacted monomers, it is necessary to use a relatively large amount of a photosensitizer, and as a result, a low molecular weight polymer is generated, thereby increasing the amount of water soluble. Have

The water-soluble component is often leached from the absorbent resin when the absorbent resin forms a hydrogel structure in contact with the absorbent liquid such as water, urine or body fluid. It is desirable to reduce as much as possible because it causes deterioration and causes unpleasantness due to its stickiness and causes undesirable effects such as contaminating the liquid to be absorbed.

In addition, the unreacted monomer may likewise be leached therefrom when the hydrogel structure is formed, which may cause skin diseases, and thus cause an undesirable situation as in the water-soluble component.

Therefore, there has always been an urgent need for an absorbent resin having a high absorption ratio and low water content and unreacted monomer.

An object of the present invention is to provide a method for producing an absorbent resin which is excellent in productivity, high in absorption ratio, and low in water content and unreacted monomers.

MEANS TO SOLVE THE PROBLEM This inventor completed the present invention as a result of repeating the detailed research and examination about the manufacturing method of the absorbent resin which solved the said problem and was excellent in productivity, workability, and excellent quality.

That is, the present invention relates to a method for producing an absorbent resin, characterized in that the water-soluble ethylenically unsaturated monomer containing a crosslinking agent is polymerized by irradiating ultraviolet rays in the presence of a radical-based photopolymerization initiator having a benzoyl group and a peroxide. The present invention relates to a method for producing an absorbent resin, wherein the amount of the photopolymerization initiator is 0.001 to 0.01% by weight based on the water-soluble ethylenically unsaturated monomer, and the amount of the peroxide is 0.005-0.1% by weight relative to the water-soluble ethylenically unsaturated monomer.

Hereinafter, the present invention will be described in detail.

Specific examples of the water-soluble ethylenically unsaturated monomer used in the present invention include (meth) acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloyl ethanesulfonic acid, and 2- (meth) acrylic acid. Anionic monomers such as monopropanesulfonic acid and 2- (meth) acrylamide-2-methylpropanesulfonic acid and salts thereof: (meth) acrylamide, N-substituted (meth) acrylate and 2-hydroxyethyl (meth) acrylic Nonionic hydrophilic group-containing monomers such as acrylate, 2-hydroxypropyl (meth) acrylate, methoxy polyethylene glycol (meth) acrylate and polyethylene glycol (meth) acrylate: NN-dimethylaminoethyl (meth) acrylate, Amino group containing unsaturated monomers, such as N, N- dimethylaminopropyl (meth) acrylamide, its quaternized substance, etc. can be mentioned.

A water-soluble ethylenically unsaturated monomer can be used by selecting 1 type or 2 types or more from these groups, 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-methylpropanesulfonic 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, and it is especially preferable to use what contains a (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. Furthermore, partially neutralized (meth) acrylic acid is used in the present invention in combination with those having an arbitrary degree of neutralization by partially neutralizing (meth) acrylic acid with an alkali metal salt.

The crosslinking agent used in combination with the water-soluble ethylenically unsaturated monomer is a compound which makes a polymer obtained from such monomers a crosslinked structure, and this includes a compound having two or more polymerizable unsaturated groups or reactive functional groups in the molecule or at the terminal thereof.

Specific examples of the crosslinking agent include N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol (meth) acrylate, glycerin tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, trialkylamine , Triallyl cyanurate, glycidyl (meth) acrylate, (poly) ethylene glycol, diethylene glycol, (poly) glycerin, propylene glycol, diethanolamine, trimethylolpropane, pentaerythritol, (poly) ethylene Glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, epichlorohydrin, ethylenediamine, polyethyleneimine, (poly) aluminum chloride, aluminum sulfate, calcium chloride, magnesium sulfate and the like.

In consideration of the reactivity with the water-soluble ethylenically unsaturated monomer in the compound, one or two or more thereof may be used.

In the present invention, as a polymerization initiator for polymerizing the water-soluble ethylenically unsaturated monomer and the crosslinking agent, it is essential to use a radical type photopolymerization initiator having a benzoyl group and a peroxide together.

The radical type photoinitiator which has a benzoyl group satisfy | fills the polymerization rate and the solubility of the monomer aqueous solution at the time of aqueous solution polymerization of the said water-soluble ethylenically unsaturated monomer by ultraviolet-ray.

Specific examples of the radical photopolymerization initiator having a benzoyl group include benzoin, benzyl, acetophenone, benzophenone and derivatives thereof which are generally used for ultraviolet polymerization. Examples of such derivatives include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether, and the acetophenone compounds are diethoxyacetophenone and 2,2-. Dimethoxy-1, 2-diphenylethan-1-one, 1-hydroxy-cyclohexyl-phenylketone, 2-methyl-1- (4- (methylthio) phenyl) -2-morpholinopropane-1 , 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- (4- (2-hydroxyethoxy) -pentyl) -2-hydroxydi-2-methyl-1-propane-1-one, and as the benzophenone-based one, methyl 0-benzoylbenzoate and 4-phenylbenzophenone , 4-benzoyl-4'-methyldiphenylsulfate, 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 2,4,6-trimethylbenzophenone, 4-benzoyl- N, N-dimethyl-N- [2- (1-oxy-2-propenyloxy) ethyl] benzenemethananium bromide, (4-benzoylbenzyl) trimethylarm Can be exemplified such as nium chloride, 4,4'-dimethylamino-benzophenone, 4,4'-diethylamino benzophenone.

In the present invention, one kind or two or more kinds of such photopolymerization initiators are used in parallel, and furthermore, such photopolymerization initiators can initiate polymerization with a very small amount of addition.

As the peroxide, those generally used for radical polymerization may also be used in the present invention. Examples of peroxides more suitable for the present invention include sodium persulfate, ammonium persulfate, potassium persulfate, hydrogen peroxide, t-butylhydroperoxide, Peroxides, such as a succinic peroxide and t-butylperoxy maleic acid, are mentioned, These 1 type, or 2 or more types are used. Particularly suitable for the present invention are persulfates.

In the present invention, the polymerization of the electrically water-soluble ethylenically unsaturated monomer is generally carried out by aqueous polymerization, and the monomer concentration of the water-soluble ethylenically unsaturated monomer aqueous solution is usually about 25 to 50% by weight, preferably 30 to 45% by weight. Is done.

If the monomer concentration is less than 25% by weight, the hydrous gel polymer obtained is too soft to be difficult to cut finely to dry the gel, and also contains a large amount of water, resulting in poor drying efficiency and lower productivity. When the concentration of the monomer exceeds 50% by weight, it is difficult to control the polymer temperature of the reaction system during the reaction, so that the temperature may be excessively elevated, and the obtained hydrogel polymer foams to become porous, and the water-retaining ability is lowered and water-soluble. Minutes tend to increase.

The amount of crosslinking agent used in combination with the water-soluble ethylenically unsaturated monomer is determined in view of the degree of crosslinking of the obtained absorbent resin and the absorbent properties based thereon, but is generally 0.0001 to 5% by weight, preferably 0.005 to the water-soluble ethylenically unsaturated monomer. It is-3 weight%.

To the aqueous solution of the water-soluble ethylenically unsaturated monomer, starch, cellulose, and the like, which have conventionally been used for the production of absorbent resins, may be added to impart various properties.

Moreover, acrylic acid esters, such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate, vinyl acetate in the quantity of the grade which does not impair the hydrophilicity of the obtained polymer extremely, Hydrophobic monomers, such as vinyl propionate, can be added and used together.

It is essential to use the above-mentioned specific photoinitiator together with a peroxide in order to obtain the water absorbing resin which has the outstanding characteristic made into the objective of this invention.

When the polymerization is initiated by irradiating the aqueous solution of the aqueous monomer with ultraviolet rays using only the photopolymerization initiator, a considerable amount of unreacted water-soluble monomers remain because the polymerization is not sufficiently completed. On the other hand, polymerization is not initiated even when irradiated with ultraviolet light using only a peroxide alone, so that both of them can be used together to obtain an initially intended absorbent resin.

It is preferable that the addition amount of a photoinitiator is 0.001 to 0.01 weight% with respect to a water-soluble ethylenically unsaturated monomer component, More preferably, it is 0.003 to 0.008 weight%. By initiating the polymerization in such a very small amount as described above, high polymerization degree of the polymer is achieved, so that the water-absorbent resin having low water content can be obtained with very good efficiency.

When the amount of the photopolymerization initiator added is less than 0.001% by weight relative to the water-soluble ethylenically unsaturated monomer component, the polymerizability is extremely deteriorated. On the other hand, when the amount of the photopolymerization initiator is exceeded 0.01% by weight, a low degree of polymerization of the polymer is caused to increase the water-soluble content. There is this.

It is preferable that the addition amount with respect to the aqueous solution of the water-soluble ethylenically unsaturated monomer of a peroxide is 0.005 to 0.1 weight% with respect to a water-soluble ethylenically unsaturated monomer component, More preferably, it is 0.01-0.08 weight%.

If the added amount of peroxide is less than 0.005% by weight, the unreacted monomer cannot be sufficiently reduced, and if it is added more than 0.1% by weight, the water-soluble content may be increased and the resulting absorbent resin may be colored, which may be an unsuitable absorbent resin for sanitary products. There is.

In the present invention, the polymerization is initiated by ultraviolet irradiation, but it is desirable to sufficiently infiltrate the ultraviolet light into the aqueous ethylenically unsaturated monomer aqueous solution, so that the reaction vessel is preferably in a shape that satisfies these requirements. It is preferable to use a rotating belt and an open container having a large surface area as the reaction vessel in consideration of the efficiency of workability in the cutting, drying and grinding of the hydrous gel polymer obtained. In addition, the thickness of the aqueous monomer solution is preferably 50 mm or less, more preferably 20 mm or less, in order to sufficiently control the reaction temperature (the highest reaching temperature of the polymer) and to secure ultraviolet transmission. When the thickness of the aqueous monomer solution exceeds 50 mm, ultraviolet irradiation may not be uniformly performed, resulting in uneven polymerization.

The lower limit of the thickness of the aqueous monomer solution is not particularly limited, but is preferably 3 mm or more in consideration of productivity.

Although the light quantity of ultraviolet-ray is not specifically limited, Usually, what is necessary is just to be 100-400mJoule / cm <2>. If it is more than this range, the case where the crosslinking point of the polymer obtained by over irradiation is cut | disconnected and water solubility arises is unfavorable.

In addition, as a light source used for ultraviolet irradiation, a conventionally known light source can be used. For example, a mercury lamp, a metal halide lamp, etc. may be used in consideration of reaction conditions. Irradiation wavelength is not particularly limited either, and wavelength light of 200-450 nm is usually used.

The ultraviolet irradiation time is appropriately determined to reach the above light amount, and polymerization is initiated immediately after the irradiation is started under the above conditions, and the polymerization is sufficiently completed by a short time irradiation of usually 10-120 seconds.

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

If the aqueous solution temperature exceeds 30 ° C, since the temperature of the reaction system is excessively high, the hydrous gel polymer foams to become porous, the water-retaining capacity is lowered, and the water-soluble content may be increased. There is no restriction | limiting in particular about the lower limit of the said aqueous solution temperature, The temperature which is not freezing of the said aqueous solution is enough, but if it is 0 degreeC or more normally, there is no problem.

When the water-soluble ethylenically unsaturated monomer is initiated polymerization, the temperature in the system rises. In order to obtain a high quality absorbent resin, it is preferable to suppress the maximum reaching temperature in the system to 100 ° C or less, and more preferably to 90 ° C or less. It is good.

When the highest reaching degree in a system exceeds 100 degreeC, the hydrous gel polymer obtained by superposing | polymerizing a monomer aqueous solution may foam and a polymer may become porous, and a water holding capacity worsens. It is also thought to be due to its excessive heat of polymerization, solubility increases gradually.

There are several ways to suppress the maximum temperature at the time of polymerization, for example, cooling the polymer contacting part from the outside, and placing cold air on the polymer, which increases the size and costs of the equipment. There is this. Therefore, electrical conditions, i.e., the aqueous monomer concentration is 25-50% by weight, the aqueous solution temperature is 30 ° C. or less, and the aqueous solution thickness is 50 mm or less, preferably 3-20 mm. It is preferable to suppress temperature below 100 degreeC, and it is a method which can suppress the highest achieved temperature at the time of superposition | polymerization easily.

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

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 may not be completed, thereby increasing the unreacted monomer.

A method for reducing dissolved oxygen is sufficient by known methods, and dissolved oxygen can be easily reduced by inhaling an inert gas (for example, nitrogen gas) or a corresponding gas into the aqueous monomer solution before ultraviolet irradiation.

As a method of cutting the hydrogel polymer obtained in this way, a method using a device for cutting and extruding a rubbery elastomer may be used. For example, a known method using a cutter type cutter, a chopper type cutter, a kneader type cutter, or the like It can be easily cut by.

As a drying method of the cut hydrogel polymer, a dryer and a heating furnace can be generally used. Examples thereof include a hot air dryer, a fluidized bed dryer, an airflow dryer, an infrared dryer, and a dielectric heating dryer. Although drying temperature is not specifically limited, Usually, it is performed at 100-200 degreeC. If it is lower than this range, the drying efficiency is extremely deteriorated, and if it exceeds this range, thermal deterioration of the absorbent resin may be caused.

Conventionally known grinding methods can be employed to grind the dried gel. For example, the gel can be ground to a desired particle size by a vibratory 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 can be appropriately selected depending on the intended use. For example, when used as a sanitary material, it is preferable to have a particle size of about 10-200 mesh.

The absorbent resin powder may be surface treated as necessary. As a method of surface treatment, a conventionally well-known method can be used. For example, surface modification of the absorbent resin may be performed by reacting a carboxylate group contained in the absorbent resin with a known crosslinking agent such as an epoxy compound, a polyvalent metal salt, an aldehyde compound, or a polyhydric alcohol, which are represented by a water-soluble diglycidyl ether compound. Can be.

The absorbent resin obtained by the present invention can be used for the various purposes described above, and is particularly suitable for sanitary articles such as sanitary articles and paper diapers.

In general, when a large amount of polymerization initiator is added to the monomer to initiate polymerization, unreacted monomers are reduced, but it is known that low polymerization degree of the obtained polymer is caused and water solubility is increased. In the present invention, however, an excellent quality absorbent resin is obtained because a very small amount of a specific photopolymerization initiator is used and a peroxide is used in parallel.

It is thought that a very small amount of photopolymerization initiator generates radicals by ultraviolet rays to initiate polymerization of monomers, and the peroxide decomposes to some extent by its heat of polymerization to produce radicals, thereby completing the polymerization. Furthermore, the peroxide remaining in the hydrous gel phase polymer reacts with the unreacted monomer even in the drying step, and the resulting absorbent resin is estimated to have excellent performance with low water content and low amount of unreacted monomer.

The present invention will be described in detail with reference to the following Examples, but the scope of the present invention is not limited to these Examples.

The absorption ratio, water-soluble content, and unreacted monomer (residual monomer) concentration of the water-absorbent resin of the hydrogel polymer-based dry crushed powder described in this Example were measured by the following test methods.

A. Absorption Magnification:

0.5 g of absorbent resin powder was added to a 300 ml beaker, 200 ml of 0.9% aqueous sodium chloride solution was added thereto, stirred for 60 minutes, and then transferred to a glass filter connected to a suction filter adjusted to 200 mm Hg. The absorption rate (g / g) was calculated by the following Equation 1.

Equation 1: Absorption magnification = hydrogel weight after suction (g) / 0.5 (g)

B. Water Soluble:

0.5 g of the absorbent resin powder was dispersed in 1000 ml of physiological saline (0.9% saline), stirred for 12 hours, passed through a filter paper, the liquid was concentrated, and dried at 130 ° C. The water-soluble content (weight%) was calculated | required according to following formula (2).

Equation 2: water-soluble content = (dry matter (g) × 1000 / 0.5 × liquid (g)) × 100

C. Unreacted Monomer Concentration (Residual Monomer):

A 300 ml beaker contained 0.4 g of an absorbent resin powder, 200 ml of 0.9% aqueous sodium chloride solution was added thereto, stirred for 3 hours, passed through a filtration membrane, and then fractionated by high performance liquid chromatography. On the other hand, the monomer-standard solution having a known concentration was divided in the same manner to determine the amount of monomer remaining in the absorbent resin in consideration of the dilution ratio.

Example 1

Aqueous solution of monomer component composed of 75 mol% sodium acrylate and 25 mol% acrylic acid (40 wt% monomer component), 0.03 wt% trimethylolpropanetriacrylate (large monomer component) as crosslinking agent and 2,2-dimethoxy as photopolymerization initiator 0.005% by weight of -1.2-diphenylethan-1-one (large monomer component) and 0.02% by weight of sodium persulfate (large monomer component) were mixed and the aqueous solution was cooled to 10 ° C. Subsequently, nitrogen gas was sucked in and the dissolved oxygen amount was 1 ppm or less. 300 g of this aqueous solution was added to a glass share having an internal diameter of 146 mm and a height of 25 mm so that the thickness of the aqueous solution was 18 mm. To obtain a hydrous gel polymer. In this case, the highest reaching temperature of the polymer is a value obtained by measuring the surface temperature of the polymerized gel using a surface thermometer.

The obtained hydrous gel polymer was cut into 3 mm squares, dried for 60 minutes with hot air at 135 ° C. using a hot air dryer, and then pulverized with a rool mill grinder to select an absorbent resin having a particle size ranging from 300 μm to 500 μm.

Example 2

In Example 1, an absorbent resin was obtained in the same manner as in Example 1 except that the amount of the prepared aqueous solution was 100 g and the aqueous solution thickness was 6 mm. In this case, the highest achieved temperature of the polymer was about 84 ° C.

Example 3

In Example 1, the water absorbing resin was obtained in the same manner as in Example 1 except that the amount of the monomer component was 35% by weight, the aqueous solution temperature was 20 ° C, and the amount of the crosslinking agent was added at 400 ppm. In this case, the highest reaching temperature of the polymer was about 90 ° C.

Example 4

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

Example 5

In Example 1, an absorbent resin was obtained in the same manner as in Example 1 except that the amount of sodium persulfate was changed to 0.05% by weight (large monomer component).

Example 6

In Example 1, an absorbent resin was obtained in the same manner as in Example 1 except that sodium persulfate was added in an amount of 0.07% by weight (large monomer component) with t-butylhydroperoxide.

Example 7

In Example 1, an absorbent resin was obtained in the same manner as in Example 1 except that the crosslinking agent was added with N, N'-methylenebisacrylamide in an amount of 0.02% by weight (large monomer component).

Example 8

In Example 1, the photoinitiator is 2-methyl-1- (4- (methylthio) phenyl) -2-morpholinopropane-1, the addition amount thereof is 0.03% by weight (large monomer component), and sodium persulfate is used. A water absorbent resin was obtained in the same manner as in Example 1 except that the addition amount of ammonium persulfate was 0.03% by weight (large monomer component).

Example 9

In Example 1, the photopolymerization initiator was replaced with 1-hydroxy-cyclohexyl-phenyl ketone, and the amount thereof was changed to 0.008% by weight (large monomer component), and the amount of sodium persulfate added was 0.01% by weight. It was prepared by the method to obtain an absorbent resin.

Example 10

In Example 1, an absorbent resin was obtained in the same manner as in Example 1 except that acrylic acid was used as 2-acryloylpropanesulfonic acid.

Example 11

In Example 1, an absorbent resin was obtained in the same manner as in Example 1 except that the ultraviolet irradiation time was 90 seconds (light quantity 2250 m Joule / cm 2).

Comparative Example 1

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

Comparative Example 2

Example 1, except that the photopolymerization initiator was added with 2,2'-azobis (N, N'-dimethyleneisobutylamidine) dihydrochloride in an amount of 0.15% by weight (large monomer component). It was prepared in the same manner as to obtain an absorbent resin.

Comparative Example 3

Example 1, except that the photopolymerization initiator was added with 2,2'-azobis (N, N'-dimethyleneisobutylamidine) dihydrochloride in an amount of 0.003% by weight (large monomer component). It was prepared in the same manner as, but because of the large number of unpolymerized, it was not possible to obtain a hydrous gel phase polymer, the subsequent cutting, drying process and performance evaluation was abandoned.

The results of evaluating the performance of the absorbent polymers obtained in Examples and Comparative Examples are shown in Table 1 below.

Table 1

According to the method of the present invention, the absorbent resin can be manufactured continuously in a short time with high productivity, and the absorbent resin of high quality can be provided with a remarkably excellent quality without the sticky feeling when absorbed due to the high absorption ratio and the small amount of water-soluble and unreacted monomer. That has an excellent effect.

Claims (2)

A method for producing an absorbent resin, characterized in that a water-soluble ethylenically unsaturated monomer containing a crosslinking agent is polymerized by irradiation with ultraviolet rays in the presence of a radical photopolymerization initiator having a benzoyl group and a peroxide. The method of claim 1, The amount of the photopolymerization initiator is 0.001 to 0.01% by weight relative to the water-soluble ethylenically unsaturated monomer, the amount of peroxide is 0.005 to 0.1% by weight relative to the water-soluble ethylenically unsaturated monomer.