JPH11302306A - Production of water absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject resin having an excellent water absorption performance and a small amount of deteriorated soluble component by carrying out a polymerization by stirring polymerization in an early stage and by standing polymerization on and after that, in a method for supplying an aqueous solution containing a hydrophilic monomer to a polymerizer and polymerizing the monomer. SOLUTION: In this method for producing a water absorbing resin by supplying an aqueous solution containing a hydrophilic monomer (e.g. acrylic acid, its sodium salt or the like) to a polymerizer and polymerizing the hydrophilic monomer, the polymerization is carried out by stirring polymerization in an early stage and by standing polymerization on and after that. Preferably the polymerization is started at 0-50 deg.C starting temperature, stirring is performed for the stirring polymerization until the polymerization temperature is raised to 5-15 deg.C and the stirring is carried out until the polymerization ratio reaches 5-30%. The polymerizer is preferably a belt conveyor continuous polymerizer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a water-absorbent resin.

[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 a water-absorbing resin, generally, a method of performing aqueous solution polymerization while stirring an aqueous solution containing a hydrophilic monomer mainly containing acrylic acid or a salt thereof has been adopted. This is because stirring polymerization has an excellent advantage in that the polymerization temperature can be easily controlled and a hydrogel polymer finely divided by shearing during the polymerization can be obtained.
However, stirring polymerization has a problem that the performance of the water-absorbent resin is deteriorated due to shearing during the polymerization.
JP-A-56102, JP-A-1-126310, JP-A-3-174414, JP-A-4-175319
Japanese Patent Application Laid-Open No. Hei 4-236203 and the like, static polymerization without stirring is proposed. According to the method in which the monomer aqueous solution is allowed to stand for polymerization without stirring, a water-absorbing resin can be obtained without lowering the water absorption performance such as absorption capacity and water-soluble components.

[0004] Specifically, JP-A-4-175319 discloses an aqueous solution containing a relatively high concentration of a hydrophilic monomer.
A method of performing constant temperature polymerization without stirring (standing still) and controlling the polymerization temperature to 20 to 70 ° C. is disclosed. Further, Japanese Patent Application Laid-Open No. 1-126310 discloses a method of performing static polymerization using a thermal initiator and a redox initiator. However, even with these conventional water-absorbent resins obtained by polymerization without stirring (still standing), there is still a large amount of degradable soluble components, and in actual use, for example, when a water-absorbent resin is put into a paper diaper to produce a product. Was found to be problematic in that the performance was insufficient.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a water-absorbing resin which has excellent water-absorbing performance and has a small amount of degradable soluble components.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted detailed experiments and studies on a conventional static polymerization method. Then, when stirring was dared in the early stage of the polymerization, it was found that the amount of degradable soluble components could be reduced without causing a decrease in water absorption performance as in the conventional stirred polymerization, and the present invention was completed.

Therefore, a method for producing a water-absorbent resin according to the present invention is directed to a method for obtaining a water-absorbent resin by supplying an aqueous solution containing a hydrophilic monomer to a polymerization apparatus and polymerizing the hydrophilic monomer. The polymerization is characterized by being carried out by stirring polymerization at the initial stage, and thereafter by standing polymerization. The polymerization is started at a starting temperature of 0 to 50 ° C., and the polymerization temperature is 5 to 50 ° C.
Stirring for stirring polymerization can be performed until the temperature rises by 15 ° C. The stirring for the stirring polymerization has a polymerization rate of 5 to 5.
It can be performed until it reaches 30%. The polymerization device can be a belt type continuous polymerization device.

[0008]

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 these, 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 rate of the anionic unsaturated monomer is 50 to 9 of the acid group.
Preferably, 9 mol% is neutralized. Neutralization rate 9
If it exceeds 9%, 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.

The concentration of the aqueous solution of the hydrophilic monomer must 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, starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt),
A hydrophilic polymer such as a crosslinked polyacrylic acid (salt) or a chain transfer agent such as 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 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.
In performing the polymerization, a radical polymerization initiator such as sodium persulfate, potassium persulfate, ammonium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, Active energy rays such as ultraviolet rays and electron beams can be used. When using an oxidizing radical polymerization initiator,
Redox polymerization may be carried out using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination. The amount of the polymerization initiator to be used is generally 0.001 to 2 mol%, preferably 0.01 to 0.5 mol%, based on the hydrophilic monomer.

In the present invention, the polymerization is carried out by stirring polymerization only at the beginning of the polymerization, and thereafter the polymerization is carried out by static polymerization. The static polymerization is performed without substantially stirring the polymerization system until the polymerization starts and the polymerization system reaches the highest temperature due to the heat of polymerization. The apparatus used in the polymerization of the present invention 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. Examples of such a polymerization apparatus include, for example, a belt conveyor type continuous polymerization apparatus capable of heating and / or cooling from one lower surface of a belt conveyor; a heat exchange plate polymerization apparatus capable of heating and / or cooling from one surface from a plate surface; A centrifugal thin-film type device or a cylindrical type device capable of heating and / or cooling from the surrounding wall can be used. In order to enhance productivity, a belt conveyor type continuous polymerization apparatus is preferable.

An embodiment of the present invention using a belt conveyor type continuous polymerization apparatus will be described with reference to FIG. First, the material supply portion will be described. A monomer aqueous solution containing a hydrophilic monomer is prepared in a monomer preparation tank 1, and the monomer aqueous solution is supplied to a monomer degassing tank 2 through a tube 4 equipped with a valve.
The monomer degassing tank 2 is provided with a degassing tube 3 through which the monomer aqueous solution is degassed with an inert gas such as nitrogen. The deaerated monomer aqueous solution is supplied to a monomer supply pipe 7 equipped with a pump. The polymerization initiator tanks 5a and 5b are connected to the monomer supply pipe 7 via a pump, so that two kinds of polymerization initiators can be preliminarily mixed with the monomer aqueous solution in the pipe. ing. Thus, even when the polymerization initiator is mixed in advance (pre-mixing method), the type is not limited to two, but may be one or three or more. The front end 8 of the monomer supply pipe faces the start end of the continuous polymerization apparatus 12, and the front end of the initiator supply pipe 9 extending from another polymerization initiator tank 6 via a pump is concentric therewith. To form a double tube 10. As described above, the polymerization initiator can be supplied to the polymerization machine through a supply pipe different from the monomer aqueous solution. Such an initiator supply method (separation supply method) is such that polymerization occurs immediately when the monomer aqueous solution comes into contact with the polymerization initiator in the polymerization initiator tank 6 and clogging occurs in the monomer aqueous solution supply pipe. It is necessary to prevent it.
In such a case, the tip of the polymerization initiator supply pipe (inner pipe) is made to protrude beyond the tip of the monomer supply pipe (outer pipe), so that the hydrophilic monomer aqueous solution and the polymerization initiator can be mixed. Contact can be prevented until just before feeding to the continuous polymerization apparatus 12. As a method of supplying the polymerization initiator, there is also a method of using the above-mentioned premixing method and the separation supply method together.

The continuous polymerization apparatus 12 has a hood 15 for covering the entire upper part of the apparatus, a belt 16 whose upper half is covered by the hood 15, and a drive shaft 1 for rotating the belt 16 in one direction.
7. In addition to the temperature control unit 18 for cooling or heating the polymer gel (or monomer aqueous solution) 20 on the belt from below and the temperature control unit 19 for heating or cooling from below, nitrogen is also added to the atmosphere. Also provided is a nitrogen introduction tube 13 for introduction. The monomer aqueous solution is supplied onto the start end of the belt 16 from the double pipe 10 at the tip of the monomer supply pipe. The aqueous monomer solution 20 supplied on the belt 16 is stirred only at the beginning of the polymerization reaction by the stirring means 14 provided on the downstream side from the supply point 11, but thereafter the polymerization proceeds without stirring. As the stirring means 14, there are various forms such as stirring by a stirring blade, stirring by blowing gas, stirring by ultrasonic waves or low-frequency vibration. It is preferable that nitrogen is introduced from the nitrogen introduction pipe 13 to reduce the oxygen concentration in the atmosphere above the polymerization system to 5% by volume or less. It is more preferably at most 1% by volume. When the oxygen concentration exceeds 5% by volume, the dissolved oxygen concentration of the aqueous hydrophilic monomer solution increases before the polymerization starts, and the induction period of the polymerization may be prolonged. By controlling the amount of nitrogen introduced here, it is possible to perform cooling using the latent heat of evaporation, which will be described later.

The polymerization initiation temperature can be appropriately selected.
The temperature range is preferably 0 ° C, more preferably 5 to 40 ° C. If the polymerization initiation temperature is lower than 0 ° C., the induction time and the polymerization time become long, and stable physical properties cannot be obtained, resulting in a low-performance water-absorbent resin. On the other hand, if the temperature exceeds 50 ° C., it is difficult to control the maximum temperature of the polymerization system, and stable physical properties cannot be obtained, resulting in a low-performance water-absorbent resin. The maximum temperature of the polymerization system is preferably 70 ° C. or higher, more preferably 70 ° C. or higher but lower than 100 ° C., and further preferably 75 to 95 ° C. Most preferably 75
９０90 ° 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, it is preferable to carry out the polymerization while cooling, since polymerization heat is generated with the polymerization. If cooling is not performed, the temperature of the polymerization system may rise to 100 ° C. or higher. Performing polymerization while cooling means that the temperature is substantially lower than that of the polymerization system from the start of polymerization to the time when the polymerization system reaches the maximum temperature due to the heat of polymerization, for example, polymerization at a contact surface or a nitrogen stream. Cooling the system,
For example, it is within the scope of the present invention to perform heating or the like after reaching the highest temperature. When cooling is performed on the contact surface, the temperature of the contact surface is preferably set to 0 to 40 ° C. When the temperature is lower than 0 ° C., it is not practical because special means for achieving the temperature is required. The temperature is 40
If it is higher than ℃, the heat of polymerization cannot be sufficiently removed.

The cooling of the polymerization system can be carried out by a combination of cooling by conduction heat transfer and cooling by latent heat of evaporation. Cooling by latent heat of evaporation refers to removing heat from the polymerization system by mainly evaporating water from the aqueous hydrophilic monomer solution. This is, for example, at least 30 cm / min, preferably 3 cm / min.
0 to 6000 cm / min, more preferably 50 to 3000
The reaction can be performed by introducing an inert gas at a rate of cm / min above the polymerization system. The thickness of the polymerization system (the liquid height of the aqueous hydrophilic monomer solution) is not particularly limited, but is not less than 15 mm.
It is preferably 50 mm or less. A range of 15 to 35 mm is more preferable, and a range of 20 to 30 mm is still more preferable. 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 50 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.

Next, the stirring polymerization in the present invention will be described. In the present invention, the stirring polymerization is performed only at a time when the polymerization of the hydrophilic monomer has not sufficiently proceeded. As the timing, for example, the polymerization is started at a starting temperature of 0 to 50 ° C., and the stirring for the stirring polymerization is performed until the polymerization temperature rises by 5 to 15 ° C.
It is preferable to carry out stirring for the stirring polymerization until the amount reaches 0%.

The stirring may be continued throughout the above-mentioned period from the start of the polymerization, or may be performed only for a certain period of time within the above-mentioned period. The stirring method is not particularly limited, and a conventionally known method can be employed. For example, a method of mechanically applying a shearing force to an aqueous monomer solution, a method of applying vibration by shock waves, ultrasonic waves, or low frequencies, a method of creating a turbulent field, and a method of forming another fluid (bubbles or liquid) in an aqueous monomer solution. Drop), a method of applying an electric or magnetic field, and the like. These means may be used alone or two or more methods may be used in combination.

When the stirring means is introduced into the aqueous monomer solution, the polymer may adhere to the stirring means and grow, making stirring impossible. The stirring means, for example, polyethylene, polypropylene, polyester, polyamide,
Coating with a synthetic resin such as fluororesin, polyvinyl chloride, epoxy resin, and silicone resin can reduce adhesion. Among them, polyethylene tetrafluoride, polyethylene trifluorofluoride, polyethylene trifluorochloride, ethylene tetrafluoride-ethylene copolymer, ethylene trifluorochloride-
Ethylene copolymer, propylene pentafluoride
Particularly preferred are fluoroplastics such as ethylene tetrafluoride copolymers, perfluoroalkyl vinyl ether-ethylene tetrafluoride copolymers, and polyvinyl fluoride. Therefore, a method that can stir the aqueous monomer solution without directly introducing the stirring means into the aqueous monomer solution may be preferable.

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 preferable to carry out the polymerization in a relatively short time without lowering. Specifically, 1 to 60 minutes is preferable, and 3 to 30 minutes is more preferable. In the present invention, if necessary, an aging step of keeping the temperature of the obtained polymer and / or heating it after the polymerization system exhibits the highest temperature may be provided. The aging step is to keep the polymer in the range of 40 to 95 ° C for 1 minute to 5 minutes.
It can be provided for a time, preferably in the range of 50 to 90 ° C. for 5 to 240 minutes.

When the polymer obtained by the above polymerization is in the form of a hydrogel, the hydrogel polymer is pulverized and classified to an appropriate size for drying, and has an average particle size of 1 to 10 mm.
It can be a hydrogel polymer of a certain degree. The method of grinding 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 is pulverized and used as a particle.

In the present invention, the surface vicinity of the particulate water-absorbent resin may be further 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,
Polyhydric alcohol compounds such as 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene Polyhydric epoxy compounds such as glycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylene Pentamine, pentaethylenehexamine, polyethylene And polyvalent amine compounds such as amine,
Polyhydric isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan- 2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-
1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxane-2
-One, 4,6-dimethyl-1,3-dioxane-2-
Alkylene carbonate compounds such as on, 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and polyamine adducts thereof (eg, Hercules) And polyvalent metal compounds such as hydroxides and chlorides such as zinc, calcium, magnesium, aluminum, iron and zirconium. 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.

[0027]

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 following, “parts” means “parts by weight” unless otherwise specified. The methods for measuring the physical properties of the water-absorbent resin in Examples and Comparative Examples are as follows.

[Absorbency] Water-absorbent resin A (g) (about 0.
2 g) is uniformly placed in a nonwoven bag (60 mm × 60 mm), and artificial urine (I) (0.2% by weight of sodium sulfate, 0.2% by weight of potassium chloride, 0.05% by weight of magnesium chloride hexahydrate) , Calcium chloride dihydrate 0.025% by weight, ammonium dihydrogen phosphate 0.035% by weight, diammonium hydrogen phosphate 0.015% by weight, and deionized water 99.475% by weight). After 60 minutes, the bag was lifted up, drained at 250 G for 3 minutes using a centrifuge, and then the weight W (g) of the bag was measured. The same operation was performed without using the water absorbent resin, and the weight B of the bag at that time was
(G) 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)

[Water-soluble component] Water-absorbent resin C (g) (about 0.
5 g) was dispersed in 1000 g of deionized water.
After stirring for an hour, the mixture was filtered with filter paper. Next, 50 g of the obtained filtrate was placed in a 100 ml beaker, and 0.1N was added to the filtrate.
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 water-soluble component (% by weight) was calculated according to the following equation. Water soluble matter (% by weight) = (E (ml) -D (ml)) ×
0.005 / C (g) × F

[Degradable solubles] The product was classified and 425 μm
Of artificial urine (II) (composition: artificial urine (I), 0.005% by weight of L-alcorbic acid was added to 1 g of the sample, and deionized water was 99.4%).
After absorbing 25 g, the mixture was allowed to stand in a swollen state at 37 ° C. for 16 hours. After observing the state of the gel and the presence or absence of stringing, the swelled gel was removed for 975 times.
g of pure water and stirred for 1 hour. The obtained gel dispersion was filtered, and the soluble component was measured by the same colloid titration as described above, and this was defined as the deteriorated soluble component. The following equation was used as a urine resistance index. It can be said that the smaller this number is, the higher the urine resistance is. Urinary resistance index (%) = degradable soluble matter (%)-water soluble matter (%)

Example 1 In a reaction vessel consisting of a thermometer, a lid equipped with 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, 204 g of acrylic acid and 1339 g of a 37% aqueous sodium acrylate solution were placed. , 1.58 g of polyethylene glycol diacrylate (average molecular weight 478) and 442 g of deionized water were 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. At this time, this mixture was mixed with a stirrer chip having a length of 5 cm for 400 r.
This was done by rotating at pm and stirring. The monomer concentration was 35% by weight, and the thickness of the aqueous solution was 23 mm. When stirring was continued, polymerization started after 1 minute, and the temperature of the reaction system was 17 ° C. Continue to stir the polymerization system after the start of polymerization,
The temperature of the water bath was set at 10 ° C. for cooling, but when the temperature of the polymerization system reached 25 ° C. shortly, the stirring was stopped. Twelve minutes after the start of the reaction, the polymerization system showed a maximum temperature of 80 ° C. Thereafter, the temperature of the water bath was raised to 60 ° C. and the reaction was started 2
After 4 minutes, a plate-like hydrogel polymer was obtained. The thickness of the hydrogel polymer was 23 mm. This hydrogel polymer was pulverized with a meat chopper and dried with a hot air drier at 160 ° C. for 65 minutes. The obtained dried product was pulverized with a roll mill to obtain a water absorbent resin (1). This water-absorbent resin (1) had an absorption capacity of 66 g / g, a water-soluble content of 12%, and a deteriorated soluble content of 20%. That is, the urine resistance index was 8%.

Comparative Example 1 A comparative water-absorbent resin (1) was obtained in the same manner as in Example 1 except that stirring with a stirrer chip was not performed. This comparative water-absorbent resin (1) has an absorption capacity of 66 g / g and a water-soluble
%, And the degradable soluble content was 30%. That is, the urine resistance index was 18%.

Example 2 Using the apparatus shown in FIG. 1, a water-absorbing resin was produced. In the monomer preparation tank 1, 134 parts of 37% by weight of sodium acrylate, 20 parts of acrylic acid, 0.16 part of polyethylene glycol diacrylate (average number of ethylene oxide units: 8) and 44 parts of water were mixed, and an aqueous monomer solution was prepared. Prepared. In the monomer deaeration tank 2, the monomer aqueous solution 1
Nitrogen was blown into L at a rate of 0.8 L / min for 30 minutes to remove dissolved oxygen in the aqueous solution. Each of the polymerization initiator tanks 5a and 5b was added to the monomer aqueous solution degassed with nitrogen for 5 minutes.
% By weight 2,2'-azobis (2-amidinopropane) 2
2.0 g / min of a hydrochloride aqueous solution and 1.8 g / min of a 0.5 wt% L-ascorbic acid aqueous solution were supplied and mixed by line mixing. The amount of dissolved oxygen in the aqueous monomer solution mixed with the polymerization initiator was 0.25 ppm. The temperature of the aqueous monomer solution was 18 ° C. Further, while supplying 2.0 g / min of a 0.35 wt% aqueous hydrogen peroxide solution from the polymerization initiator tank 6 through the pipe 9, the monomer aqueous solution was driven at a rate of 14 kg / min at 1.2 kg / min. And the polymerization was continuously performed. The total length of the belt is 3.5 m, and the temperature control section 18 from the monomer aqueous solution supply point 11 to 1 m downstream (in the driving direction) is a cooling section for cooling the belt surface, and the temperature of the remaining portion is controlled. The adjusting section 19 is a heating section for heating the belt surface. Oxygen concentration on the belt is 0.2
% By volume. Then, a screw-type rotating blade was provided as stirring means 14 at a position 14 cm downstream from the monomer aqueous solution supply point 11, and stirring was performed at the beginning of the polymerization. The monomer aqueous solution supplied on the belt forms a viscous gel after about 1 minute,
The maximum temperature was reached after 7 minutes. Its temperature was 80 ° C.
Subsequently, the polymer gel was aged in a heating zone at 60 ° C. to obtain a transparent hydrogel polymer. This gel 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). It had an absorption capacity of 66 g / g, a water-soluble content of 13%, and a deteriorated soluble content of 20%. That is, the urine resistance index was 7%.

Comparative Example 2 A comparative water-absorbent resin (2) was produced using the same polymerization apparatus as in Example 2, except that the stirring means 14 was stopped, and under the same conditions as in Example 2. . Its absorption capacity is 66
g / g, water-soluble content 13%, and degradation-soluble content 32%.
The urine resistance index was 19%.

[0035]

According to the present invention, it is possible to obtain a water-absorbing resin having a high absorption capacity and a small amount of water-soluble components and deterioration-soluble components. If manufactured by a belt conveyor type continuous polymerization device,
Such a high-performance water-absorbing resin can be mass-produced. 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 materials for water in oil; Other dehydrating or drying agents; Water retention materials for plants and soil; Coagulants such as sludge;
Waterproof material for electric wire or optical fiber; useful for various industrial applications requiring water absorption, water retention, wetting, swelling, and gelling, such as a waterproof material for civil engineering and construction.

[Brief description of the drawings]

FIG. 1 schematically shows an apparatus for producing a water absorbent resin used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Monomer preparation tank 5, 6 Polymerization initiator tank 11 Monomer aqueous solution supply point 12 Belt conveyor type continuous polymerization apparatus 14 Stirrer 16 Belt 18 Temperature control section 19 Temperature control section 20 Polymer gel (or monomer aqueous solution)

Claims (4)

[Claims] 1. A method in which an aqueous solution containing a hydrophilic monomer is supplied to a polymerization apparatus to polymerize the hydrophilic monomer to obtain a water-absorbent resin, wherein the polymerization is initially carried out by stirring polymerization, and thereafter, Is a method for producing a water-absorbent resin, which is carried out by static polymerization. 2. The process for producing a water-absorbent resin according to claim 1, wherein the polymerization is started at a starting temperature of 0 to 50 ° C., and the stirring for the stirring polymerization is performed until the polymerization temperature rises by 5 to 15 ° C. . 3. The stirring for the stirring polymerization is carried out at a polymerization rate of 5 to 5.
The method for producing a water-absorbent resin according to claim 1, wherein the method is performed until the amount reaches 30%. 4. The method for producing a water-absorbent resin according to claim 1, wherein said polymerization apparatus is a belt conveyor type continuous polymerization apparatus.