JPH11181005A - Production of water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a water-absorbing resin, capable of giving the water-absorbing resin having an excellent quality in high productivity on a stationary aqueous solution polymerization. SOLUTION: This method for producing a water-absorbing resin comprises subjecting an aqueous solution containing a hydrophilic monomer to a stationary polymerization. Therein, the thickness of the aqueous solution is >=15 mm, and the concentration of the hydrophilic monomer in the aqueous solution is 15-45 wt.%. Four kinds of compounds comprising an azo compound, an inorganic peroxide, a reducing agent and hydrogen peroxide are together used as the polymerization initiator. The polymerization is carried out while cooling the polymerization solution. The maximum attainable temperature of the polymerization system is >=70 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a water-absorbent resin. More specifically, the present invention relates to a method for producing a water-absorbing resin by statically polymerizing an aqueous solution containing a hydrophilic monomer.

[0002]

2. Description of the Related Art In recent years, in the field of sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, water-absorbing resins have been widely used for the purpose of absorbing body fluids. Examples of the water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft copolymer, a neutralized product of a starch-acrylic acid graft copolymer, and vinyl acetate-acrylic acid. Saponified ester copolymers, hydrolysates of acrylonitrile copolymers or acrylamide copolymers, crosslinked products thereof, crosslinked products of cationic monomers, and the like are known.

[0003] As a method for producing these water absorbent resins,
There is known a method of performing aqueous solution polymerization while stirring an aqueous solution containing a hydrophilic monomer containing acrylic acid or a salt thereof as a main component. Stirring polymerization is excellent in that a hydrogel polymer is not fragmented due to shearing during polymerization and thus does not require a fragmentation step, but the performance of the water-absorbent resin obtained by shearing during polymerization is high. There are problems such as lowering.
In contrast, JP-A-62-156102, JP-A-1-126310, JP-A-3-174414, JP-A-4-175319, and JP-A-4-236.
According to the method of statically polymerizing a monomer aqueous solution without stirring, as proposed in JP-A-203, etc., a water-absorbent resin can be obtained without the above-mentioned problems.

[0004]

Specifically, Japanese Patent Laid-Open No.
Japanese Patent No. 175319 discloses a method in which an aqueous solution containing a relatively high concentration of a hydrophilic monomer is subjected to constant-temperature polymerization without stirring (in a stationary state) and controlling the polymerization temperature to 20 to 70 ° C. I have. In order to carry out the constant temperature polymerization at such a relatively low temperature, as shown in the Example, the thickness of the aqueous monomer solution is reduced to about 8 mm or less, and the temperature of the polymerization system is set to a polymerization time of 45 minutes or more. It needs to be controlled, the productivity is low and it is difficult to adopt it on an industrial scale.

[0005] Japanese Patent Application Laid-Open No. 1-126310 discloses a method in which static polymerization is carried out using a thermal initiator and a redox initiator. However, since the polymerization system is not cooled, the maximum temperature of the polymerization system is too high, and there is a problem that an undesired water-soluble component for the water-absorbent resin increases. An object of the present invention is to solve the above-mentioned problems and to provide a production method capable of obtaining a high-quality water-absorbent resin with high productivity in static aqueous solution polymerization.

[0006]

Means for Solving the Problems The present inventors considered that it is necessary to increase the thickness of the aqueous monomer solution to 15 mm or more in order to increase the productivity. Then, the present inventors carried out intensive studies on a formulation for cooling the polymerization system with this thickness and obtaining a water-absorbent resin of excellent quality, and completed the present invention.

That is, the present invention employs the following configuration. "A method for producing a water-absorbent resin by statically polymerizing an aqueous solution containing a hydrophilic monomer, wherein the aqueous solution has a thickness of 15
mm or more, and the concentration of the hydrophilic monomer in the aqueous solution is 1
5 to 45% by weight, using four kinds of azo compound, inorganic peroxide, reducing agent and hydrogen peroxide as a polymerization initiator in combination, performing polymerization while cooling, and setting the maximum temperature of the polymerization system to 70 ° C. A method for producing a water-absorbent resin as described above. Further, in the above, among the four types of polymerization initiators,
A method of finally adding hydrogen peroxide to an aqueous solution containing a hydrophilic monomer is employed.

Further, in the above, a method is employed in which an anionic unsaturated monomer in which 50 to 99 mol% of an acid group is neutralized is used as the hydrophilic monomer. In the above, a method in which the polymerization initiation temperature is 0 to 20 ° C is employed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrophilic monomer used in the present invention is not particularly limited as long as it can become a water-absorbing resin by polymerization. Examples thereof include acrylic acid, methacrylic acid, maleic acid, and vinyl sulfonic acid. Unsaturated monomers such as styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof Acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide,
N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) Nonionic hydrophilic group-containing unsaturated monomers such as acrylate, vinylpyridine, N-vinylpyrrolidone, N-vinylacetamide, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate; Cationic salts such as N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and their quaternary salts And the like can be mentioned sum monomer. One or more of these can be used.

Among them, acrylic acid or a salt thereof (eg, sodium, lithium, potassium, ammonia,
It is preferable to use a salt such as an amine) as a main component, more preferably acrylic acid or its sodium salt. Usually, the amount of other monomers other than acrylic acid or a salt thereof is preferably 0 to less than 50 mol%, more preferably 0 to 30 mol%, based on all monomers.

The neutralization ratio of the anionic unsaturated monomer is preferably such that 50 to 99 mol% of the acid groups are neutralized. If the neutralization ratio exceeds 99%, the alkalinity is strong and may harm the human body. If it is less than 50%, the absorption capacity of the resulting water-absorbent resin will be reduced. It is necessary that the concentration of the aqueous hydrophilic monomer solution be 15 to 45% by weight, preferably 25 to 45% by weight, and more preferably 30 to 40% by weight. If it is less than 15% by weight, the productivity is low. When the content exceeds 45% by weight, the ratio of the self-crosslinked portion of the polymer chain increases, and the absorption capacity of the obtained water-absorbent resin decreases.

In the polymerization, hydrophilic polymers such as starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), crosslinked polyacrylic acid (salt), and hypophosphorous acid (salt) May be added. In the present invention, the water-absorbing resin preferably has a cross-linking structure, and a self-cross-linking type which does not use a cross-linking agent, or an internal cross-linking agent having two or more polymerizable unsaturated groups or two or more reactive groups. Copolymerized or reacted types can be exemplified. Preferred is a water-absorbing resin having a crosslinked structure in which an internal crosslinking agent is copolymerized or reacted with a hydrophilic unsaturated monomer.

Specific examples of these internal crosslinking agents include, for example, N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, tri Methylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate,
Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, Triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether,
Examples include ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate. Further, two or more of these internal crosslinking agents may be used.

The amount of the internal crosslinking agent to be used is preferably 0.005 to 3 mol%, more preferably 0.01 to 1.5 mol%, based on the monomer component. If the amount of the internal crosslinking agent is too small, the absorption rate tends to decrease. Conversely, if the amount of the internal crosslinking agent is too large, the absorption capacity tends to decrease.
For the polymerization, it is necessary to use four kinds of azo compounds, inorganic peroxides, reducing agents and hydrogen peroxide in combination as polymerization initiators. In the present invention, hydrogen peroxide is not included in the inorganic peroxide. Since the azo compound is a thermal decomposition type polymerization initiator, it works after the temperature of the polymerization system rises above a certain temperature. Since inorganic peroxide and hydrogen peroxide are oxidizing polymerization initiators, they act as a redox-based initiator together with a reducing agent or independently as a thermal decomposition type initiator. Since redox-based initiators do not require heating, they work primarily at the lower temperature stages of the polymerization. The amount of residual monomer can be reduced by using an inorganic peroxide as the oxidative polymerization initiator.

Examples of the azo compound include 2,2'-azobis (N, N'-dimethyleneisobutylamide) dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, and 2,2'- Azobis (N,
N'-dimethyleneisobutylamide), 4,4'-azobis (4-cyanopentanoic acid, azobisisobutyronitrile, etc. are exemplified. Examples of inorganic peroxides include sodium persulfate, potassium persulfate, Examples of the reducing agent include an alkali metal sulfite, an alkali metal bisulfite, ammonium sulfite, ammonium bisulfite, ascorbic acid, erythorbic acid, etc. 2,2′-azobis ( A combination of (2-amidinopropane) dihydrochloride, sodium persulfate, L-ascorbic acid, and hydrogen peroxide is preferred.

These polymerization initiators are used in an amount of 0.001 to 0.1 mol% of an azo compound, 0.001 to 0.1 mol% of an inorganic peroxide, a reducing agent, 0.0001-0.01 mol%, hydrogen peroxide 0.001
The range of about to 0.01 mol% is preferable. In order to reduce the amount of the residual monomer, it is more preferable that the total amount of the inorganic peroxide and the hydrogen peroxide is larger than that of the reducing agent.

It is preferable that hydrogen peroxide is added last in the order of adding the above four polymerization initiators. If hydrogen peroxide is added prior to the other polymerization initiators, not only the polymerization becomes unstable, but also stable physical properties cannot be obtained, resulting in a low-performance water-absorbing resin. The polymerization initiation temperature can be appropriately selected, but is preferably in the range of 0 to 20 ° C, more preferably 5 to 18 ° C. If the polymerization initiation temperature is less than 0 ° C., the induction time and the polymerization time become longer and stable physical properties cannot be obtained.
The result is a low performance water absorbing resin. On the other hand, when the temperature exceeds 20 ° C., it is difficult to control the maximum temperature of the polymerization system, and stable physical properties cannot be obtained. As a result, a low-performance water-absorbent resin is obtained.

The maximum temperature of the polymerization system must be 70 ° C. or higher, preferably 70 ° C. or higher and lower than 100 ° C., more preferably 75 to 95 ° C. More preferably, it is 78 to 90 ° C. When the temperature is lower than 70 ° C., the absorption capacity of the obtained water-absorbent resin becomes small, and the amount of unreacted monomer increases. On the other hand, when the temperature is 100 ° C. or higher, the water-soluble content of the obtained water-absorbent resin is undesirably increased.

In the present invention, polymerization is carried out while cooling, since heat of polymerization is generated with the polymerization. If cooling is not performed, the temperature of the polymerization system may rise to 100 ° C. or higher. When performing polymerization while cooling, from the start of polymerization until the polymerization system reaches the highest temperature due to the heat of polymerization,
It is within the scope of the present invention to cool the polymerization system at a temperature substantially lower than that of the polymerization system, for example, a contact surface or a nitrogen stream, and to perform heating or the like after reaching the highest temperature, for example. When cooling at the contact surface, the temperature of the contact surface is preferably set to 0 to 20 ° C. When the temperature is lower than 0 ° C., it is not practical because special means for achieving the temperature is required. When the temperature is higher than 20 ° C., the heat of polymerization cannot be sufficiently removed.

The thickness of the polymerization system (the liquid height of the aqueous solution of the hydrophilic monomer) is 15 mm or more, preferably 15 to 35 mm, more preferably 20 to 30 mm.
When the thickness of the polymerization system is less than 15 mm, the productivity is low.
On the other hand, when the thickness of the polymerization system exceeds 35 mm, it is difficult to control the temperature of the polymerization system, the maximum temperature is increased, and the water-soluble content of the obtained water-absorbent resin is increased.

The polymerization time (the time from the start of polymerization to the time when the polymerization system reaches the maximum temperature) is not particularly limited, but may be shortened as long as the requirements of the present invention are satisfied. It is possible to carry out the polymerization in a relatively short time without lowering. Specifically, 1 to 30 minutes is preferable, and 3 to 20 minutes is more preferable. In the present invention, polymerization is performed by static polymerization. The standing polymerization means that the polymerization is carried out without substantially stirring from the start of the polymerization until the polymerization system reaches the highest temperature due to the heat of polymerization.

The polymerization apparatus used for the stationary polymerization is not particularly limited as long as it can heat and / or cool the surface in contact with the polymerization system and has a space in which the solvent can evaporate from the polymerization system. . As such a polymerization apparatus, for example, a belt conveyor type polymerization apparatus capable of heating and / or cooling from one lower surface of the belt conveyor;
A heat exchange plate type polymerization apparatus capable of heating and / or cooling from one side from the plate surface; a centrifugal thin film type apparatus or a cylindrical type apparatus capable of heating and / or cooling from a surrounding wall;

In the present invention, if necessary, an aging step for keeping the polymer warm and / or heated after the polymerization system has reached the highest temperature may be provided. The aging step is to reduce the polymer
1 minute to 5 hours in the range of 95 ° C, preferably 50 to 90 ° C
5 minutes to 120 minutes. When the polymer obtained by the above polymerization is a hydrogel, the hydrogel polymer is dried and pulverized to an appropriate size.
After classification, a hydrogel polymer having an average particle size of about 1 to 10 mm can be obtained.

The pulverization of the hydrogel polymer is not particularly limited. For example, a meat chopper or a cutting mill can be used. An ordinary dryer or heating furnace can be used for drying the hydrogel polymer. For example, a thin stirring dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, a flash dryer, an infrared dryer, and the like.

The water-absorbent resin obtained by the above drying is used as it is as a coarse particle or as a powder after being ground. In the present invention, the vicinity of the surface of the particulate water-absorbent resin may be subjected to a crosslinking treatment, whereby a water-absorbent resin having a large absorption capacity under load can be obtained. For the surface cross-linking treatment, a cross-linking agent capable of reacting with a functional group of the water-absorbent resin, for example, an acidic group may be used, and a known cross-linking agent used for the purpose is usually exemplified.

Examples of the surface crosslinking agent include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1. , 3-pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4
-Diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, poly Polyhydric alcohol compounds such as oxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl Polyepoxy compounds such as ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol; Polyamine compounds such as diamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine, and inorganic or organic salts thereof (e.g., aditinium salt); 2,4-tolylenediisocyanate; Polyvalent isocyanate compounds such as hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one; 4-methyl-1,3-dioxolan-2-one; 5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-
On, 4-hydroxymethyl-1,3-dioxolane-
2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-
Alkylene carbonate compounds such as 1,3-dioxan-2-one and 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and the like Polyvalent amine adducts (for example, Kaimen manufactured by Hercules: registered trademark); hydroxides such as zinc, calcium, magnesium, aluminum, iron, and zirconium; and polyvalent metal compounds such as chlorides. Among these, polyhydric alcohol compounds, polyepoxy compounds, polyamine compounds and salts thereof, and alkylene carbonate compounds are preferred. These surface cross-linking agents may be used alone or in combination of two or more.

The amount of the surface cross-linking agent may be selected from water-absorbent resin 10
It is preferably used in an amount of 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 0 parts by weight.
An ordinary dryer or heating furnace can be used for the heat treatment. For example, a thin stirring dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, a flash dryer, an infrared dryer, and the like. In that case, the heat treatment temperature is preferably 40 to 250.
° C, more preferably 90 to 230 ° C, still more preferably 120 to 220 ° C. The heat treatment time is usually preferably from 1 to 120 minutes, more preferably from 10 to 60 minutes.

The water-absorbing resin obtained by the production method of the present invention includes inorganic fine particles such as titanium oxide, silicon oxide and activated carbon; organic fine particles such as polymethyl methacrylate; hydrophilic fibers such as pulp; polyethylene fibers and polypropylene fibers. Synthetic fibers such as polyethylene glycol, polyoxyethylene sorbitan monostearate and the like may be added during or after the production process.

[0029]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In the examples, "parts" means "parts by weight" unless otherwise specified.
Shall be expressed. [Absorbency] A water-absorbent resin A (g) (about 0.2 g) was uniformly placed in a nonwoven bag (60 mm × 60 mm), and artificial urine (sodium sulfate 0.200%, potassium chloride 0.20%) was added.
0%, magnesium chloride hexahydrate 0.050%, calcium chloride dihydrate 0.025%, ammonium dihydrogen phosphate 0.035%, diammonium hydrogen phosphate 0.01
5%, 99.475% deionized water). 60
After a minute, the bag was lifted up, drained with a centrifuge at 250 G for 3 minutes, and then the weight W (g) of the bag was measured. The same operation was performed without using the water-absorbing resin, and the weight B (g) of the bag at that time was measured. Then, the absorption capacity of the water-absorbent resin was calculated from the obtained weight according to the following equation.

Absorption capacity (g / g) = (W (g) -B
(G) -A (g)) / A (g) [Soluble of water absorbent resin] Water absorbent resin C (g) (about 0.5
g) was dispersed in 1000 g of deionized water, stirred for 16 hours, and then filtered through filter paper. Next, the obtained filtrate 5
0 g was placed in a 100 ml beaker, and 0.1N-
1 ml of an aqueous sodium hydroxide solution, 10 ml of an aqueous N / 200-methylglycol chitosan solution, and 4 drops of an aqueous 0.1% toluidine blue solution were added. Next, the solution in the above beaker was subjected to colloidal titration using an N / 400 aqueous solution of polyvinyl potassium sulfate, and the titration end point was determined as the end point of the titration when the color of the solution changed from blue to magenta. The same operation was performed using 50 g of deionized water instead of 50 g of the filtrate, and the titration amount E (m
1) was determined. Then, from these titration amounts and the average molecular weight F of the monomers constituting the water-absorbing resin, the amount of soluble matter (% by weight) was calculated according to the following equation.

Soluble (% by weight) = (E (ml) -D (m
l)) × 0.005 / C (g) × F [Residual monomer] 0.5 g of a water-absorbent resin was added to 1000 g of deionized water, and the mixture was extracted for 2 hours with stirring. And the amount of residual monomer in the filtrate was analyzed by liquid chromatography. On the other hand, a calibration curve obtained by similarly analyzing a monomer standard solution having a known concentration was used as an external standard, and the amount of residual monomer in the water-absorbent resin was determined in consideration of the dilution ratio of the filtrate. Example 1 In a reaction vessel consisting of a lid provided with a thermometer, a nitrogen gas inlet pipe and an exhaust hole and a vat having a bottom surface of 300 mm × 220 mm and a depth of 60 mm, 204 g of acrylic acid, 1339 g of a 37% aqueous solution of sodium acrylate, and polyethylene glycol diacrylate (Average molecular weight 478) 1.58 g and deionized water 442 g were supplied and mixed, and immersed in a water bath at 17 ° C. to a height of 10 mm from the bottom. After degassing by introducing nitrogen gas into this aqueous solution, 5% V-50
(Azo-based polymerization initiator manufactured by Wako Pure Chemical Industries) Aqueous solution 3.24
g, 3.24 g of 5% sodium persulfate and 2.92 g of a 1% aqueous solution of L-ascorbic acid were added and mixed. next,
3.34 g of 35% hydrogen peroxide solution was added and mixed. The monomer concentration was 35% by weight, and the thickness of the aqueous solution was 23 mm.
One minute later, polymerization started, and the reaction system temperature was 17 ° C.
After the initiation of the polymerization, the temperature of the water bath was set at 10 ° C. without stirring the polymerization system.
And cooled. After 12 minutes, the polymerization system showed a maximum temperature of 80 ° C. Thereafter, the temperature of the water bath was raised to 60 ° C.
A minute later, a hydrogel polymer was obtained. The thickness of the hydrogel polymer was 23 mm. This hydrogel polymer was crushed with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (1).

The water absorbing resin (1) had an absorption capacity of 66 times, a soluble content of 12% and a residual monomer of 520 ppm. Example 2 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% aqueous sodium acrylate solution, 0.08 part of polyethylene glycol diacrylate (average molecular weight 478), and 19.15 parts of deionized water was prepared. Nitrogen gas was introduced and degassed. 19.6 g / min of the above aqueous solution and 10 g / min of a 9.6% V-50 (azo polymerization initiator manufactured by Wako Pure Chemical Industries) aqueous solution deaerated by introducing nitrogen gas, 10 g / min of a 14% aqueous sodium persulfate solution, and 0 g / min After line mixing 10 g / min of a 87% L-ascorbic acid aqueous solution,
Further, a 0.69% aqueous hydrogen peroxide solution degassed by introducing nitrogen gas was line-mixed at 10 g / min and supplied to a movable belt polymerization machine under a nitrogen gas atmosphere. The monomer concentration was 35% by weight, and the thickness of the aqueous solution was 25 mm. The movable belt was driven at 140 mm / min. One minute later, polymerization started, and the reaction system temperature was 18 ° C. The polymerization system was cooled at a temperature of 10 ° C. without stirring.
After 7 minutes, the polymerization system showed a maximum temperature of 87 ° C. Thereafter, the temperature of the belt surface was adjusted to 60 ° C. to obtain a hydrogel polymer. The thickness of the hydrogel polymer was 25 mm. This hydrogel polymer was crushed with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (2).

The water absorbing resin (2) had an absorption capacity of 64 times, a soluble content of 12% and a residual monomer of 500 ppm. Comparative Example 1 204 g of acrylic acid, 1339 g of a 37% aqueous sodium acrylate solution, 1339 g of polyethylene glycol diacrylate were placed in a reaction vessel consisting of a lid having a thermometer, a nitrogen gas inlet tube and an exhaust hole, and a vat having a bottom surface of 300 mm × 220 mm and a depth of 60 mm. 1.58 g of (average molecular weight 478) and 445 g of deionized water were supplied and mixed, and immersed in a water bath at 15 ° C. to a height of 10 mm from the bottom. After degassing by introducing nitrogen gas into this aqueous solution, 5% V-50
(Azo-based polymerization initiator manufactured by Wako Pure Chemical Industries) 3.24 g of aqueous solution
And 2.92 g of a 1% L-ascorbic acid aqueous solution were added and mixed. Next, 3.34 g of 35% aqueous hydrogen peroxide was added and mixed. The monomer concentration is 35% by weight and the thickness of the aqueous solution is 2
3 mm. One minute later, polymerization started, and the reaction system temperature was 15 ° C. After the initiation of the polymerization, the temperature of the water bath was set to 10 ° C. and the system was cooled without stirring the polymerization system. After 12 minutes, the polymerization system showed the highest temperature of 78 ° C. Thereafter, the temperature of the water bath was raised to 60 ° C., and after 20 minutes, a hydrogel polymer was obtained. The thickness of the hydrogel polymer was 23 mm. This hydrogel polymer was crushed with a meat chopper,
It was dried with a hot air drier for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (3).

The water absorbing resin (3) had an absorption capacity of 61 times, a soluble content of 12% and a residual monomer of 2300 ppm. Comparative Example 2 A reaction vessel in which a jacketed stainless steel double-armed kneader (manufactured by Koike Tekko Co., Ltd.) having two sigma-type blades having an internal volume of 10 L and a lid provided with a thermometer, a nitrogen gas inlet pipe, and an exhaust hole was attached. Then, 672 g of acrylic acid, 4400 g of a 37% aqueous sodium acrylate solution, 5.19 g of polyethylene glycol diacrylate (average molecular weight 478), and 1467 g of deionized water were supplied and mixed. While maintaining this aqueous solution at 25 ° C., nitrogen gas was introduced to degas. Then, while stirring the kneader blade under a nitrogen stream, 10
5.33 g of an aqueous solution of 5% V-50 (azo polymerization initiator manufactured by Wako Pure Chemical Industries) 5.33 g of an aqueous solution of 10% sodium persulfate
And 4.79 g of a 2% aqueous L-ascorbic acid solution were added and mixed. Next, 10.96 g of 0.35% hydrogen peroxide solution
Was added and mixed. The monomer concentration was 35% by weight. 1
After a minute, polymerization started, and the reaction system temperature was 25 ° C. After the start of the polymerization, the blade of the kneader was stirred, and the polymerization system was 13
After a minute, the highest temperature reached 75 ° C was shown. Thereafter, the temperature of the jacket was raised to 60 ° C., and after 20 minutes, a hydrogel polymer was obtained. The average particle diameter of the hydrogel polymer was about 3 mm. This hydrogel polymer was crushed with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (4).

The water absorbing resin (4) had an absorption capacity of 58 times, a soluble content of 13% and a residual monomer of 1100 ppm. Comparative Example 3 204 g of acrylic acid, 1339 g of a 37% aqueous sodium acrylate solution, 1339 g of polyethylene glycol diacrylate were placed in a reaction vessel consisting of a lid provided with a thermometer, a nitrogen gas inlet pipe and an exhaust hole and a vat having a bottom of 300 mm × 220 mm and a depth of 60 mm. (Average molecular weight 478) 1.58 g and deionized water 442 g were supplied and mixed, and immersed in a 30 ° C. water bath to a height of 10 mm from the bottom. After degassing by introducing nitrogen gas into this aqueous solution, 5% V-50
(Azo-based polymerization initiator manufactured by Wako Pure Chemical Industries) Aqueous solution 3.24
g, 3.24 g of 5% sodium persulfate and 2.92 g of a 1% aqueous solution of L-ascorbic acid were added and mixed. next,
3.34 g of 35% hydrogen peroxide solution was added and mixed. The monomer concentration was 35% by weight, and the thickness of the aqueous solution was 23 mm.
One minute later, polymerization started, and the reaction system temperature was 30 ° C.
After the initiation of the polymerization, the temperature of the water bath was set to 1 ° C. and the system was cooled without stirring the polymerization system. After 14 minutes, the polymerization system reaches the maximum temperature of 5
8 ° C was indicated. Thereafter, the temperature of the water bath was raised to 55 ° C., and after 20 minutes, a hydrogel polymer was obtained. The thickness of the hydrogel polymer was 23 mm. This hydrogel polymer was crushed with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (5).

The water absorbing resin (5) had an absorption capacity of 59 times, a soluble content of 12% and a residual monomer of 1600 ppm. Comparative Example 4 204 g of acrylic acid, 1339 g of a 37% aqueous sodium acrylate solution, 1339 g of polyethylene glycol diacrylate were placed in a reaction vessel consisting of a lid having a thermometer, a nitrogen gas inlet tube and an exhaust hole, and a vat having a bottom of 300 mm × 220 mm and a depth of 60 mm. (Average molecular weight 478) 1.58 g and deionized water 442 g were supplied and mixed, and immersed in a 30 ° C. water bath to a height of 10 mm from the bottom. After degassing by introducing nitrogen gas into this aqueous solution, 5% V-50
(Azo-based polymerization initiator manufactured by Wako Pure Chemical Industries) Aqueous solution 3.24
g, 3.24 g of 5% sodium persulfate and 2.92 g of a 1% aqueous solution of L-ascorbic acid were added and mixed. next,
3.34 g of 35% hydrogen peroxide solution was added and mixed. The monomer concentration was 35% by weight, and the thickness of the aqueous solution was 23 mm.
One minute later, polymerization started, and the reaction system temperature was 30 ° C.
After the initiation of the polymerization, the temperature of the water bath was set at 30 ° C. without stirring the polymerization system.
And cooled. After 12 minutes, the polymerization system showed the highest temperature of 105 ° C. Thereafter, the temperature of the water bath was raised to 60 ° C.
After 0 minute, a hydrogel polymer was obtained. The thickness of the hydrogel polymer was 23 mm. This hydrogel polymer was crushed with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (6).

The water absorbing resin (6) had an absorption capacity of 67 times, a soluble content of 20% and a residual monomer of 1300 ppm. Comparative Example 5 Lid with Thermometer, Nitrogen Gas Introducing Tube and Exhaust Hole and 2 L
Acrylic acid 25.2 in a reaction vessel consisting of
g, 502.3% aqueous solution of sodium acrylate 122.3 g,
Polyethylene glycol diacrylate (average molecular weight 4
78) 0.0487 g and 29.9 g of deionized water were fed and mixed, and immersed in a 30 ° C. water bath to a height of 20 mm from the bottom. After introducing nitrogen gas into this aqueous solution and degassing, 0.67 g of a 3% aqueous solution of V-50 (azo polymerization initiator manufactured by Wako Pure Chemical Industries), 0.67 g of 3% sodium persulfate and 0.1% in a nitrogen gas atmosphere. 0.72 g of 5% L-ascorbic acid aqueous solution was added and mixed. Next, 0.41 g of a 0.35% hydrogen peroxide solution was added and mixed. The monomer concentration was 48% by weight, and the thickness of the aqueous solution was 20 mm. One minute later, polymerization started, and the reaction system temperature was 30 ° C. After the polymerization was started, the temperature of the water bath was set at 5 ° C. without cooling the polymerization system, and the system was cooled. After 11 minutes, the polymerization system showed the highest temperature of 71 ° C. Thereafter, the temperature of the water bath was raised to 60 ° C., and after 20 minutes, a hydrogel polymer was obtained. The thickness of the hydrogel polymer is 20
mm. This hydrogel polymer was crushed with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (7).

The water absorbing resin (7) had an absorption capacity of 56 times, a soluble content of 12% and a residual monomer of 1000 ppm.

[0039]

According to the present invention, it is possible to obtain a water-absorbent resin having a high absorption capacity and a small amount of soluble components and residual monomers with high productivity. Due to the above effects, the water-absorbent resin obtained by the present invention can be used in contact with the human body such as sanitary materials (child and adult paper diapers, sanitary napkins, incontinence pads, etc.); separation of water in oil Materials; Other dehydrating or drying agents; Water retention materials for plants and soil; Coagulants such as sludge; Anti-condensation agents; Water blocking materials for electric wires or optical fibers; Water absorbing materials, water retention, wetting, swelling for civil engineering and construction It is useful for various industrial applications requiring gelation.

Claims (4)

[Claims] 1. A method for producing a water-absorbent resin by statically polymerizing an aqueous solution containing a hydrophilic monomer, wherein the aqueous solution has a thickness of 15 mm or more, and the aqueous monomer concentration of the aqueous solution is 15 mm or more. Up to 45% by weight, using four types of polymerization initiators, an azo compound, an inorganic peroxide, a reducing agent and hydrogen peroxide, and performing polymerization while cooling. The maximum temperature of the polymerization system is 70 ° C. or higher. A method for producing a water-absorbent resin. 2. The method for producing a water-absorbent resin according to claim 1, wherein, among the four polymerization initiators, hydrogen peroxide is finally added to an aqueous solution containing a hydrophilic monomer. 3. The method according to claim 1, wherein the hydrophilic monomer has an acid group of 50 to 50 or less.
The method for producing a water-absorbent resin according to claim 1 or 2, wherein an anionic unsaturated monomer having 99 mol% neutralized is used. 4. The method for producing a water-absorbing resin according to claim 1, wherein the polymerization initiation temperature is 0 to 20 ° C.