JP2000034307A - Production of water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a water-absorbing resin having high absorption ratio and excellent quality characterized by decreased amounts of water-soluble component and residual monomer compared with conventional water-absorbing resin by an aqueous solution polymerization method in high productivity by producing a water-containing gel polymer produced by a static aqueous solution polymerization and keeping and aging the gel polymer under specific condition. SOLUTION: A monomer component giving a water-absorbing resin by polymerization (preferably acrylic acid or its sodium salt) is subjected to static aqueous solution polymerization and the obtained water-containing gel polymer is kept for >=30 min at a temperature lower than the maximum temperature (peak temperature) of the polymerization system by >=10 deg.C. The objective resin preferably has a crosslinked structure. The polymerization is preferably a continuous static polymerization performing the polymerization on a belt without stirring from the viewpoint of productivity and the uniformity of the physical properties of the obtained water-absorbing resin. Preferably, the polymerization starting temperature is 15-25 deg.C and the peak temperature is 85-95 deg.C. The water- containing gel polymer is maintained preferably at 50-70 deg.C for 90-180 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-absorbent resin by subjecting a monomer component which is polymerized to a water-absorbent resin to a standing aqueous solution polymerization. More specifically, the present invention relates to a method for producing a water-absorbing resin suitably used for sanitary materials such as disposable diapers and sanitary napkins.

[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. -Saponified acrylate copolymers, hydrolyzed acrylonitrile copolymers or acrylamide copolymers, crosslinked products thereof, crosslinked products of cationic monomers, and the like are known.

[0004] As a method for producing these water-absorbing resins,
A method of performing aqueous solution polymerization while stirring an aqueous solution containing a hydrophilic monomer having acrylic acid or a salt thereof as a main component is generally adopted.

[0005] In the stirring polymerization, polymerization can be performed while cutting the hydrogel polymer produced as the polymerization proceeds into small chunks, so that the polymerization heat can be removed with a relatively compact apparatus to control the polymerization peak temperature to some extent. Although it is excellent in that it can be formed, it has problems that the molecular chain is hardly increased and the network of the crosslinked structure is easily disturbed because the molecular chain is cut by the shearing force due to stirring. On the other hand, Japanese Patent Application Laid-Open Nos.
According to the method proposed in, for example, Japanese Patent No. 75319, in which a monomer aqueous solution is subjected to static polymerization without stirring, a water-absorbing resin can be obtained without the above-mentioned problems.

[0006] Specifically, JP-A-3-174414 discloses an aqueous solution containing a relatively low concentration of a hydrophilic monomer.
A method is disclosed in which adiabatic polymerization is performed using a specific polymerization initiator, the obtained hydrogel polymer is shredded, and neutralized with an aqueous base solution. In order to perform such adiabatic polymerization,
As shown in the Example, the concentration of the aqueous monomer solution was set to about 20% by weight, and it was necessary to carry out polymerization for 1 to 5 hours, and further required a post-neutralization step, which was also considerable. It takes time and productivity is low. In addition, when a product is to be obtained using powder, a drying step is required, and since the concentration of the aqueous monomer solution is low, a large amount of energy is inevitably required for drying, so that not only productivity is low but also economical. From an economic point of view, it is difficult to adopt it on an industrial scale. Further, also in terms of physical properties, there is a problem that a large amount of residual monomer remains because the concentration of the aqueous monomer solution is low.

Japanese Patent Application Laid-Open No. 4-175319 discloses a constant temperature polymerization of an aqueous solution containing a relatively high concentration of a hydrophilic monomer without stirring (in a stationary state) and controlling the polymerization temperature to 20 to 70 ° C. A method for doing so is disclosed. 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.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and to achieve high productivity, high absorption capacity, and a water-soluble component amount and a residual monomer amount in aqueous solution polymerization. Another object of the present invention is to provide a production method capable of obtaining a water-absorbent resin of excellent quality, which is also reduced.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, they have obtained a monomer component which is polymerized to become a water-absorbing resin by standing aqueous polymerization. The hydrogel polymer at least 10 ° C. above the peak temperature
It has been found that by maintaining the temperature at a low temperature for at least 30 minutes, it is possible to stably obtain a water-absorbing resin having a high absorption capacity and a reduced water-soluble component amount and residual monomer amount as compared with the conventional case.

In the above method, a method is employed in which the hydrogel polymer is held at a temperature at least 10 ° C. lower than the peak temperature for at least 30 minutes and then pulverized.

In the above, a method is employed in which the polymerization is carried out using a polymerization initiator containing a persulfate.

Further, in the above, a method is employed in which a persulfate, an azo-based reaction initiator, an oxidizing agent and a reducing agent are used as the polymerization initiator.

In the above method, a method of exhibiting a peak temperature of at least 80 ° C. is adopted.

In the above method, the method is characterized in that the temperature for holding for at least 30 minutes is 50 to 70 ° C.

Further, in the above method, a method is adopted in which the relative humidity during holding for at least 30 minutes is 50% RH or more.

In the above, the specific surface area of the hydrogel polymer after holding for at least 30 minutes is 10 cm 2 / g
A method characterized by the following is adopted.

Further, in the above method, a method characterized in that the neutralization ratio of the monomer component is 40 to 100 mol%.

In the above method, a method characterized by adding a polymerization initiator to the hydrogel polymer is employed.

According to the above configuration, it is possible to provide a method for producing a water-absorbent resin having a high absorption capacity and a reduced amount of water-soluble components and residual monomers as compared with the conventional method.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail.

The monomer component used in the present invention to be a water-absorbing resin by polymerization is not particularly limited as long as it can literally be a water-absorbing resin by polymerization. Examples thereof include acrylic acid, methacrylic acid, and maleic acid. , Vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 2- (meth)
Anionic unsaturated monomers such as acryloylethanesulfonic acid and 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-
Nonionic properties such as hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-vinylacetamide, N-acryloylpiperidine, and N-acryloylpyrrolidine A hydrophilic group-containing unsaturated monomer;
N, N-dimethylaminoethyl (meth) acrylate,
N, N-dimethylaminoethyl (meth) acrylate,
Cationic unsaturated monomers such as N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and quaternary salts thereof can be mentioned. One or more of these can be used.

Of these, acrylic acid or a salt thereof (for example, salts of sodium, lithium, potassium, ammonium, amines, etc.) is preferably used as a main component, and acrylic acid or a sodium salt thereof is more preferable. The amount of other monomers other than acrylic acid or a salt thereof is usually 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 40 to 100 mol% of the acid groups are neutralized. If the neutralization ratio exceeds 100 mol%, the alkalinity is strong and may harm the human body. If it is less than 40 mol%, the absorption capacity of the resulting water-absorbent resin will decrease.

The concentration of the monomer component which becomes a water-absorbent resin by polymerization is preferably 15 to 45% by weight, more preferably 25 to 45% by weight, and even more preferably 30 to 40% by weight. If the amount is less than 15% by weight, the productivity may decrease. If the amount exceeds 45% by weight, the ratio of the self-crosslinking component of the polymer chain increases, and the absorption capacity of the obtained water-absorbent resin decreases. There is.

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 is a self-cross-linking type which does not use a cross-linking agent, or has an internal structure having two or more polymerizable unsaturated groups or two or more reactive groups. A type obtained by copolymerizing or reacting a crosslinking agent 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 triacrylate, 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, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, polyethylene Examples include imine and glycidyl (meth) acrylate. Alternatively, two or more of these internal crosslinking agents may be used.

The use amount of the internal crosslinking agent is preferably from 0.005 to 3 mol%, more preferably from 0.01 to 1.5 mol%, based on the monomer components. If the amount of the internal crosslinking agent is too small, the water-soluble component tends to increase, while if the amount of the internal crosslinking agent is too large, the absorption capacity tends to decrease.

The polymerization method of the monomer component is not particularly limited as long as it is a stationary aqueous solution polymerization, and continuous static polymerization may be performed without stirring on a belt,
Although static polymerization may be performed in a batch, continuous static polymerization performed without stirring on a belt is preferable in terms of productivity and uniformity of physical properties of the obtained water-absorbent resin.

In the present invention, it is preferable to use a persulfate as the polymerization initiator. When the polymerization is carried out only with a polymerization initiator other than the persulfate, the residual monomer may be high.

The persulfate may be used alone, but a polymerization initiator such as an azo compound or a peroxide other than the persulfate may be used in combination. Moreover, you may carry out in a redox system with a reducing agent.

Examples of the persulfate include sodium persulfate, potassium persulfate, and ammonium persulfate. Examples of the azo compound include 2,2′-azobis (N, N′-dimethyleneisobutylamide) dihydrochloride and 2,
2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutylamide), 4,4'-azobis-4-cyanopentanoic acid, azobisisobuty Ronitrile and the like are exemplified. As the peroxide, hydrogen peroxide, alkyl hydroperoxides, peresters, and diacryl peroxide are exemplified. As the reducing agent, an alkali metal sulfite and an alkali metal heavy metal are used. Examples include sulfites, ammonium sulfite, ammonium bisulfite, ascorbic acid, erythorbic acid, iron metal salts such as iron sulfate, saccharides, aldehydes and the like.

The use amount of these polymerization initiators is preferably in the range of 0.001 to 2 mol%, and more preferably in the range of 0.01 to 0.5 mol%, based on the monomer components. More preferred. The polymerization initiator may be dissolved or dispersed in a solvent such as water.

The polymerization initiation temperature can be appropriately selected.
The temperature range is preferably 0 ° C, more preferably 15 to 25 ° C. When the polymerization initiation temperature is lower than 0 ° C., the induction period and the polymerization time are lengthened, and the productivity may be reduced. On the other hand, when the starting temperature exceeds 30 ° C., depending on the monomer concentration, it is difficult to control the maximum temperature of the polymerization system, and the maximum temperature may exceed 100 ° C. As a result, the resulting water-absorbent resin Of water-soluble components may increase.

Maximum temperature of polymerization system (hereinafter peak temperature)
Is preferably 80 ° C. or higher, more preferably 8 ° C.
0 ° C. or higher and lower than 100 ° C., still more preferably 85 to 9
5 ° C. When the peak temperature is lower than 80 ° C., the absorption capacity of the obtained water-absorbent resin may be small, and the residual monomer may increase. On the other hand, when the peak polymerization temperature is 10
When the temperature exceeds 0 ° C., the water-soluble component of the obtained water-absorbent resin may increase.

In the present invention, polymerization is carried out 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 of the polymerization system is substantially lower than that of the polymerization system from the start of the polymerization until the polymerization system reaches the peak temperature due to the heat of polymerization, for example, the polymerization system at the contact surface or a nitrogen stream. Is to cool down. When cooling at the contact surface, the temperature of the contact surface is preferably set to 0 to 30 ° 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 30 ° C., the heat of polymerization cannot be sufficiently removed.

Thickness of polymerization system (liquid height of aqueous monomer component solution)
Is not particularly limited, but is preferably in the range of 15 to 50 mm, more preferably in the range of 20 to 30 mm. When the thickness of the polymerization system is less than 15 mm, the productivity may be low. On the other hand, when the thickness of the polymerization system exceeds 50 mm, it becomes difficult to control the temperature of the polymerization system, the peak temperature becomes high, and the resulting water absorption is obtained. The water-soluble component of the resin may increase.

According to the present invention, after showing the peak temperature, the obtained hydrogel polymer is at least 10 ° C. lower than the peak temperature.
Hold at low temperature for at least 30 minutes.

After showing the peak temperature, the temperature of the hydrogel polymer when the obtained hydrogel polymer is retained (hereinafter referred to as “aging” in the present invention) (hereinafter referred to as “ripened gel temperature” in the present invention) ") Is equal to or higher than the peak temperature, the water-soluble component increases. The aging gel temperature is preferably from 50 to 80 ° C, more preferably from 50 to 80 ° C.
70 ° C.

The temperature at this time is the central temperature of the hydrogel polymer.

The aging method is not particularly limited, but the hydrated gel polymer may be heated or cooled, or may be insulated and kept warm so that the obtained hydrogel polymer falls within the above temperature range. The relative humidity in the aging process at that time is 50% RH
Or more, more preferably 70% RH or more.

If the relative humidity at the time of aging is less than 50% RH, the water-soluble resin obtained may have an increased amount of degradable soluble components.

Here, the degradation soluble component in the present invention is:
This is the amount of water-soluble matter after a predetermined amount of artificial urine is absorbed by a water-absorbent resin and swollen to a predetermined magnification under a predetermined condition and left for a predetermined time. The water-absorbent resin after artificial urine absorption is
Deterioration with time, and at the same time the soluble content increases, but if the amount of the increased soluble content is large, the absorption capacity of the water-absorbent resin under normal pressure and under load is reduced, and the water absorbing resin becomes extremely uncomfortable due to its nullness. For example, it is not preferable as a water absorbing agent for sanitary materials. Therefore, as the amount of this degradable soluble component is smaller, the gel stability against urine is higher, and excellent performance is maintained for a long time,
It is most suitable as a water-absorbing resin used for disposable diapers and the like. The artificial urine is an aqueous solution in which urea, sodium chloride, magnesium sulfate, calcium chloride, and L-ascorbic acid are dissolved so that the contents are substantially equal to those of actual urine. The method for measuring the amount of the degradable soluble component will be described in detail in the examples below.

The aging time is preferably 30 to 300 minutes,
More preferably, it is 90 to 180 minutes. Aging time is 30
If the amount is less than minutes, the resulting water-absorbent resin has a low absorption capacity and a large amount of residual monomers. The aging time exceeding 300 minutes is not practical in terms of productivity.

The specific surface area of the hydrogel polymer upon aging is preferably 10 cm2 / g or less, more preferably 5 cm2 / g or less, even more preferably 1 cm2 / g or less. When the specific surface area of the hydrogel polymer at the time of aging is larger than 10 cm2 / g, the resulting water-absorbent resin may have a low water absorption capacity and may have a large amount of residual monomers.

As the polymerization apparatus used in the present invention, since it is preferable to increase the gel size during aging, a belt conveyor type polymerization apparatus capable of heating and / or cooling from one lower surface of the belt conveyor; A heat-exchange plate polymerization apparatus capable of heating and / or cooling from one side; a stationary polymerization apparatus such as a centrifugal thin film apparatus or a cylindrical apparatus capable of heating and / or cooling from a surrounding wall is preferable.

As the ripening device used in the present invention, the above polymerization device may be used as it is, or a new ripening device may be provided. Examples of the ripening device include a belt conveyor type ripening device in which the inside of the device is sealed; a belt type ripening device capable of controlling the temperature in the device; a heat exchange plate type ripening device capable of controlling the temperature from the plate surface; Or, a centrifugal thin film ripening device capable of cooling; an ultraviolet irradiation ripening device capable of irradiating ultraviolet rays; an infrared irradiation ripening device capable of irradiating infrared rays.

The hydrogel polymer obtained by the above polymerization and aging is first crushed, further crushed and dried. The crushing machine at this time is not particularly limited as long as it can crush the plate-shaped hydrogel polymer into a size of about 10 to 100 mm. For example, a vertical cutting machine having a rotary blade and a fixed blade ( A pulverizer and the like, which are sandwiched by a pair of spiral rotary blades provided opposite to each other and having different feed speeds and sheared. The secondary pulverizer is not particularly limited as long as it can be pulverized to an average particle diameter of about 1 to 10 mm for drying. For example, a vertical slitter having a cutter blade, a horizontal slitter having a cutter blade, and the like. Examples include a slitter, a cutter-type breaking machine equipped with a rotary blade, a meat chopper equipped with a perforated plate having a predetermined diameter and a rotary blade, a screw-type pre-extrusion-type granulator, a screw-type horizontal extrusion-type granulator, and the like.

In the present invention, a polymerization initiator may be added to the obtained hydrogel polymer.

When a polymerization initiator is added to the obtained hydrogel polymer, the hydrogel polymer may be a plate gel hydrogel polymer after polymerization and before ripening, or may be a plate gel gel after ripening. Hydrated gel polymer of 10 to 100
The hydrogel polymer having a size of about mm or a hydrogel polymer further pulverized to about 1 to 10 mm after secondary pulverization may be used. Considering the physical properties of
It is preferable to add a polymerization initiator to the hydrogel polymer having a size of about 100 mm or the hydrogel polymer which has been pulverized to about 1 to 10 mm after secondary pulverization. It is more preferable to add a polymerization initiator to the hydrogel polymer having a size of about 100 mm, and to mix the polymerization initiator simultaneously with the secondary pulverization.

The specific surface area of the hydrogel polymer when the polymerization initiator is added to the hydrogel polymer is not particularly limited, but is preferably 10 cm2 / g or less, more preferably 5 cm2 / g or less, and 1 cm2 / g or less. Is even more preferred.

The polymerization initiator when the polymerization initiator is added to the hydrogel polymer is not particularly limited, but it is preferable to use a persulfate. When only the polymerization initiator other than the persulfate is used, the effect of reducing the residual monomer in the residual monomer may decrease.

The persulfate may be used alone, or a polymerization initiator other than the persulfate, such as an azo compound or a peroxide, may be used in combination. Moreover, you may carry out in a redox system with a reducing agent.

Examples of the persulfate include sodium persulfate, potassium persulfate, and ammonium persulfate. Examples of the azo compound include 2,2′-azobis (N, N′-dimethyleneisobutylamide) dihydrochloride and 2,
2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutylamide), 4,4'-azobis-4-cyanopentanoic acid, azobisisobuty Ronitrile and the like are exemplified. As the peroxide, hydrogen peroxide, alkyl hydroperoxides, peresters, and diacryl peroxide are exemplified. As the reducing agent, an alkali metal sulfite and an alkali metal heavy metal are used. Examples include sulfites, ammonium sulfite, ammonium bisulfite, ascorbic acid, erythorbic acid, iron metal salts such as iron sulfate, saccharides, aldehydes and the like.

The use amount of these polymerization initiators is preferably in the range of 0.001 to 2 mol%, and more preferably in the range of 0.01 to 0.5 mol%, based on the monomer components. More preferred. The polymerization initiator may be dissolved or dispersed in a solvent such as water.

The mixer for adding the polymerization initiator to the hydrogel polymer is not particularly limited as long as the polymerization initiator can be uniformly mixed with the hydrogel polymer. The use of a secondary pulverizer is preferable because the pulverization of the hydrogel polymer and the addition and mixing of the polymerization initiator can be performed simultaneously.

As the crusher, for example, a vertical cutter having a rotary blade and a fixed blade (also called a rotoplex or a cutting mill); a pair of spiral rotary blades provided opposite to each other and having different feed speeds A pulverizer or the like that sandwiches and shears with each other can be exemplified. Examples of the secondary pulverizer include, for example, a vertical slitter with a cutter blade, a horizontal slitter with a cutter blade, a cutter-type breaking machine with a rotary blade, a perforated plate with a predetermined diameter and a rotary blade. , A screw-type pre-extrusion granulator, a screw-type horizontal extrusion granulator, and the like.

For drying the hydrogel polymer through the above-mentioned crusher and secondary crusher, a usual dryer or heating furnace can be used. For example, a thin stirring drier, a rotary drier, a disk drier, a fluidized bed drier, a flash drier, an infrared drier and the like can be exemplified.

The water-absorbing resin obtained by the above drying is used as it is as a coarse particle or as a powder after being pulverized.

In the present invention, the vicinity of the surface of the particulate water-absorbent resin may be subjected to 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 usually used for the purpose is exemplified.

As the surface crosslinking agent, for example, 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 glycidyl ether, glycidol; ethylenediamine Diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylene hexamine, polyvalent amine compounds and their inorganic salts or organic salts such as polyethyleneimine (e.g.,
Polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolane-2-
On, 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-
Alkylene carbonate compounds such as dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one; epichlorohydrin, epibromohydrin, α-methyl Haloepoxy compounds such as epichlorohydrin, and polyamine adducts thereof (for example, Caimen manufactured by Hercules: registered trademark); hydroxides such as zinc, calcium, magnesium, aluminum, iron, and zirconium; Metal compounds and the like. 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.

As the amount of the surface crosslinking agent, the
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.

For the heat treatment, a usual dryer or heating furnace can be used. For example, there are a thin stirring dryer, a rotary dryer, a disk dryer, a fluidized-bed dryer, a flash dryer, and an infrared dryer. In that case, the heat treatment temperature is preferably 4
The temperature is 0 to 250C, more preferably 90 to 230C, and still more preferably 120 to 220C. 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 silbitan monostearate and the like may be added during or after the production process.

[0066]

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” and “%” mean “parts by weight” and “% by weight” unless otherwise specified.

[Absorbency] Water-absorbent resin A (g) (about 0.2 g)
g) is uniformly placed in a nonwoven bag (60 mm × 60 mm), and artificial urine (sodium sulfate 0.200%, potassium chloride 0.200%, magnesium chloride hexahydrate 0.050)
%, Calcium chloride dihydrate 0.025%, ammonium dihydrogen phosphate 0.085%, diammonium hydrogen phosphate 0.015%, and deionized water 99.425%). After 60 minutes, pull up the bag and centrifuge for 2 minutes.
After draining at 50 G for 3 minutes, the weight W (g) of the bag was measured. The same operation was performed without using the water absorbent 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) [Water-soluble component] 1 g of water-absorbent resin C (g) (about 0.5 g)
After dispersing in 000 g of deionized water and stirring for 16 hours, the mixture was filtered with filter paper. Next, 50 g of the obtained filtrate was added to 1
In a 00 ml beaker, 1 ml of a 0.1 N aqueous solution of sodium hydroxide, 10 ml of an aqueous solution of N / 200-methylglycol chitosan, and 4 drops of a 0.1% aqueous solution of toluidine blue were added to the filtrate. 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.

Further, 50 g of deionized water was used instead of 50 g of the filtrate.
g, and the same procedure as above was performed.
(Ml) 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 component (% by weight) = (E (ml) -D
(Ml)) × 0.005 / C (g) × F [deteriorated soluble matter] artificial urine (artificial urine composition: 95 g of urea, 40 g of sodium chloride, 5 g of magnesium sulfate, 5 g of calcium chloride, 0.25 g of L-ascorbic acid) , 4855 g of deionized water), 1 g of the water-absorbent resin was swelled 25 times in a 100 ml plastic container with a lid,
It was left at 7 ° C. for 16 hours. After 16 hours, the swollen gel was dispersed in 975 g of deionized water and stirred for 1 hour.
Filtered through filter paper for 1 minute. Next, 50 g of the obtained filtrate was added to 1
In a 00 ml beaker, 1 ml of a 0.1 N aqueous solution of sodium hydroxide, 10 ml of an aqueous solution of N / 200-methylglycol chitosan, and 4 drops of a 0.1% aqueous solution of toluidine blue were added to the filtrate.

Next, the solution of the above beaker was added to N / 40
Colloidal titration was performed using an aqueous solution of 0-polyvinyl potassium sulfate, and a titration G (ml) was determined with the end point at which the color of the solution changed from blue to reddish purple. The same operation was performed without using the water-absorbing resin, and the titration
(Ml) was determined. Then, from these titration amounts G and H and the average molecular weight I of the constituent monomers of the water-absorbent resin, the degradable soluble matter (% by weight) was calculated according to the following equation.

Deteriorated soluble matter (% by weight) = (H−G) × 0.005 × I [Residual monomer] 0.5 g of a water-absorbent resin was added to 1000 g of deionized water, and extracted for 2 hours with stirring. The swelled gelled water-absorbent resin was separated by filtration using a filter paper, 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.

[Specific surface area of gel] Representative gels were selected, their triaxial diameters were measured, the surface area was determined therefrom, and the specific surface area of the gel was calculated from the weight of the gel according to the following equation. When the gel sizes varied, 15 to 20 gels were measured and averaged.

Specific surface area of gel (cm 2 / g) = surface area of gel (cm 2) / weight of gel (g) Example 1 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, polyethylene glycol An aqueous solution composed of 0.08 part of diacrylate (average molecular weight 478) and 19.15 parts of deionized water was prepared, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, Wako Pure Chemical Industries) aqueous solution degassed by introducing 1156 g / min of the above aqueous solution and nitrogen gas, 10 g / min of 0.982%
Aqueous sodium persulfate solution 10 g / min, and 0.088
% L-ascorbic acid aqueous solution 10 g / min was line-mixed, and then nitrogen gas was further introduced to deaerate 0.070 g / min.
7% hydrogen peroxide solution was line-mixed at 10 g / min.
The mixture was supplied to a movable belt polymerization machine under a nitrogen stream 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 after supply to the belt, polymerization starts, and the reaction system temperature is 21 ° C.
Met. The polymerization system was cooled at a temperature of 10 ° C. without stirring. After 9 minutes, the polymerization system showed a maximum temperature of 85 ° C. Thereafter, after 3 minutes, the temperature of the belt surface was raised to 70 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 300 m.
m, the thickness was 23 mm, and the temperature was 73 ° C. This hydrogel polymer was cut at 400 mm (gel weight 2744).
g, specific surface area 0.99 cm 2 / g), and the plate-shaped hydrogel polymer was placed in a plastic bag and kept in a heating device adjusted to 75 ° C. for 60 minutes. The gel temperature after holding was 74 ° C. (The total aging time after the peak is 75 minutes, and the aging time is 60 minutes or more after the temperature is lowered by 10 ° C. from the peak temperature.) The hydrogel polymer is pulverized by a meat chopper and
It dried at 65 degreeC and the hot air dryer for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (1).

The water-absorbent resin (1) has an absorption capacity of 63 g /
g, soluble component 10%, degraded soluble content 19%, and residual monomer 230 ppm.

COMPARATIVE EXAMPLE 1 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, 0.08 part of polyethylene glycol diacrylate (average molecular weight: 478), and 19.15 parts of deionized water Was adjusted, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, manufactured by Wako Pure Chemical Industries) aqueous solution deaerated by introducing 660 g / min of the above aqueous solution and nitrogen gas, 5.7 g / min of an aqueous solution, 0.982%
5.7 g / min sodium persulfate aqueous solution, and 0.08
After line-mixing 5.7 g / min of an 8% L-ascorbic acid aqueous solution, nitrogen gas was further introduced and degassed.
707% aqueous hydrogen peroxide was line-mixed at 5.7 g / min and supplied to a movable belt polymerization machine under a nitrogen stream atmosphere. Monomer concentration 35% by weight, thickness of aqueous solution 25mm
Met. The movable belt was driven at 80 mm / min.
One minute after the supply to the belt, the polymerization started, and the temperature of the reaction system was 2 minutes.
1 ° C. The polymerization system was cooled at a temperature of 10 ° C. without stirring. After 9 minutes, the polymerization system showed a maximum temperature of 85 ° C. Thereafter, after 3 minutes, the temperature of the belt surface was raised to 70 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 30.
The thickness was 23 mm and the temperature was 72 ° C. (Total ripening time after the peak is 15 minutes, 10
This hydrated gel polymer was pulverized with a meat chopper at 160 ° C and 65 ° C.
It was dried with a hot air drier for minutes. Crush the dried product obtained,
A comparative water absorbent resin (1) was obtained.

The comparative water absorbent resin (1) has an absorption capacity of 60
g / g, soluble component 11%, degradable soluble content 22%, and residual monomer 950 ppm.

Example 2 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, 0.08 part of polyethylene glycol diacrylate (average molecular weight 478), and 19.15 parts of deionized water Was adjusted, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, Wako Pure Chemical Industries) aqueous solution degassed by introducing 1156 g / min of the above aqueous solution and nitrogen gas, 10 g / min of 0.982%
Aqueous sodium persulfate solution 10 g / min, and 0.088
% L-ascorbic acid aqueous solution 10 g / min was line-mixed, and then nitrogen gas was further introduced to deaerate 0.070 g / min.
7% hydrogen peroxide solution was line-mixed at 10 g / min.
The mixture was supplied to a movable belt polymerization machine under a nitrogen stream 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 after supply to the belt, polymerization starts, and the reaction system temperature is 20 ° C.
Met. The polymerization system was cooled with the temperature of the belt surface at 7 ° C. without stirring. After 10 minutes, the polymerization system showed a maximum temperature of 80 ° C. After 2 minutes, the temperature of the belt surface was raised to 60 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 300 m.
m, the thickness was 23 mm, and the temperature was 62 ° C. This hydrogel polymer was cut at 400 mm (gel weight 2745).
g, specific surface area 0.99 cm 2 / g), and the plate-shaped hydrogel polymer was placed in a plastic bag and kept in a heating device adjusted to 60 ° C for 90 minutes. The gel temperature after holding was 61 ° C. (Total ripening time after the peak is 104 minutes, ripening time is 90 minutes or more after lowering by 10 ° C. from the peak temperature.) This hydrogel polymer is pulverized with a meat chopper,
It was dried with a hot air dryer at 0 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (2).

The water-absorbent resin (2) has an absorption capacity of 60 g /
g, soluble component 8%, degraded soluble content 18%, and residual monomer 340 ppm.

Comparative Example 2 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, 0.08 part of polyethylene glycol diacrylate (average molecular weight 478), and 19.15 parts of deionized water Was adjusted, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, Wako Pure Chemical Industries) aqueous solution degassed by introducing 1156 g / min of the above aqueous solution and nitrogen gas, 10 g / min of 0.982%
Aqueous sodium persulfate solution 10 g / min, and 0.088
% L-ascorbic acid aqueous solution 10 g / min was line-mixed, and then nitrogen gas was further introduced to deaerate 0.070 g / min.
7% hydrogen peroxide solution was line-mixed at 10 g / min.
The mixture was supplied to a movable belt polymerization machine under a nitrogen stream 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 after supply to the belt, polymerization starts, and the reaction system temperature is 21 ° C.
Met. The polymerization system was cooled at a temperature of 10 ° C. without stirring. After 9 minutes, the polymerization system showed a maximum temperature of 85 ° C. Thereafter, after 3 minutes, the temperature of the belt surface was raised to 95 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 300 m.
m, the thickness was 23 mm, and the temperature was 93 ° C. This hydrogel polymer was cut at 400 mm (gel weight 2743).
g, specific surface area 0.99 cm 2 / g), and the plate-shaped hydrogel polymer was put into a plastic bag and kept in a heating device adjusted to 95 ° C for 60 minutes. The gel temperature after holding was 93 ° C. (Total ripening time after the peak is 75 minutes, ripening time is 60 minutes after the peak temperature is 8 ° C. or more, and therefore ripening time is 15 minutes or less after the temperature is 10 ° C. lower than the peak temperature, practically almost none) 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 to obtain a comparative water absorbent resin (2).

The comparative water-absorbent resin (2) has an absorption capacity of 60
g / g, soluble component 16%, degradable soluble content 37%, and residual monomer 240 ppm.

Example 3 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, 0.10 part of polyethylene glycol diacrylate (average molecular weight 478), and 19.13 parts of deionized water Was adjusted, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, Wako Pure Chemical Industries) aqueous solution degassed by introducing 1156 g / min of the above aqueous solution and nitrogen gas, 10 g / min of 0.982%
Aqueous sodium persulfate solution 10 g / min, and 0.088
% L-ascorbic acid aqueous solution 10 g / min was line-mixed, and then nitrogen gas was further introduced to deaerate 0.070 g / min.
7% hydrogen peroxide solution was line-mixed at 10 g / min.
The mixture was supplied to a movable belt polymerization machine under a nitrogen stream 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 after supply to the belt, polymerization starts, and the reaction system temperature is 22 ° C.
Met. The polymerization system was cooled without stirring, with the belt surface temperature at 15 ° C. After 6 minutes, the polymerization system showed a maximum temperature of 93 ° C. After 6 minutes, the temperature of the belt surface was raised to 50 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 300 m.
m, the thickness was 23 mm, and the temperature was 65 ° C. This hydrogel polymer was cut at 400 mm (gel weight 2744).
g, specific surface area 0.99 cm 2 / g), and the plate-shaped hydrogel polymer was placed in a plastic bag and kept in a heating device adjusted to 65 ° C for 120 minutes. The gel temperature after holding was 65 ° C. (The total ripening time after the peak is 138 minutes, the time after the temperature was lowered by 10 ° C. from the peak temperature is 120 minutes or more.) This hydrogel polymer was pulverized with a meat chopper,
It was dried with a hot air dryer at 0 ° C. for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (3).

The water-absorbent resin (3) has an absorption capacity of 68 g /
g, soluble component 14%, deteriorated soluble content 20%, and residual monomer 220 ppm.

Comparative Example 3 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, 0.10 part of polyethylene glycol diacrylate (average molecular weight 478), and 19.13 parts of deionized water Was adjusted, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, Wako Pure Chemical Industries) aqueous solution degassed by introducing 1156 g / min of the above aqueous solution and nitrogen gas, 10 g / min of 0.982%
Aqueous sodium persulfate solution 10 g / min, and 0.088
% L-ascorbic acid aqueous solution 10 g / min was line-mixed, and then nitrogen gas was further introduced to deaerate 0.070 g / min.
7% hydrogen peroxide solution was line-mixed at 10 g / min.
The mixture was supplied to a movable belt polymerization machine under a nitrogen stream 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 after supply to the belt, polymerization starts, and the reaction system temperature is 22 ° C.
Met. The polymerization system was cooled without stirring, with the belt surface temperature at 15 ° C. After 6 minutes, the polymerization system showed a maximum temperature of 93 ° C. After 6 minutes, the temperature of the belt surface was raised to 85 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 300 m.
m, thickness 23 mm, temperature 90 ° C. This hydrogel polymer was cut at 400 mm (gel weight 2743).
g, specific surface area 0.99 cm 2 / g), and the plate-shaped hydrogel polymer was placed in a plastic bag and kept in a heating device controlled at 90 ° C. for 60 minutes. The gel temperature after holding was 90 ° C. (The total ripening time after the peak is 78 minutes, more than 60 minutes after 3 ° C lower than the peak temperature, and therefore less than 18 minutes after 10 ° C lower than the peak temperature, practically almost none) The gel 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 to obtain a comparative water absorbent resin (3).

The comparative water-absorbent resin (3) had an absorption capacity of 63
g / g, soluble component: 17%, degradable soluble component: 40%, and residual monomer: 220 ppm.

Example 4 In Example 1, when the hydrogel polymer was pulverized with a meat chopper, a 0.6% aqueous solution of sodium persulfate was used at 0.02 g / mol (based on 1 mol of the solid content of the hydrogel polymer). 0.02 g of sodium persulfate was added as a 0.6% aqueous solution.) A water-absorbent resin (4) was obtained in the same manner as in Example 1, except that the mixture was added and mixed uniformly.

The water-absorbent resin (4) had an absorption capacity of 64 g /
g, soluble component 10%, degraded soluble content 19%, and residual monomer 140 ppm.

Comparative Example 4 In Comparative Example 1, when the hydrogel polymer was pulverized with a meat chopper, a 0.6% aqueous solution of sodium persulfate was used at 0.02 g / mol (based on 1 mol of the solid content of the hydrogel polymer). 0.02 g of sodium persulfate was added as an aqueous solution having a concentration of 0.6%.) A comparative water-absorbent resin (4) was obtained in the same manner as in Comparative Example 1, except that the mixture was uniformly added and mixed.

The comparative water-absorbent resin (4) has an absorption capacity of 61.
g / g, soluble component 12%, degradable soluble content 23%, and residual monomer 740 ppm.

Example 5 An aqueous solution comprising 10.70 parts of acrylic acid, 70.07 parts of a 37% by weight aqueous solution of sodium acrylate, 0.08 part of polyethylene glycol diacrylate (average molecular weight 478), and 19.15 parts of deionized water Was adjusted, and nitrogen gas was introduced to degas. 0.982% V-50 (azo initiator, Wako Pure Chemical Industries) aqueous solution degassed by introducing 1156 g / min of the above aqueous solution and nitrogen gas, 10 g / min of 0.982%
Aqueous sodium persulfate solution 10 g / min, and 0.088
After 10 g / min of an aqueous solution of 10% L-ascorbic acid was subjected to line mixing, nitrogen gas was further introduced and degassed.
7% hydrogen peroxide solution was line-mixed at 10 g / min.
The mixture was supplied to a movable belt polymerization machine under a nitrogen stream 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 after supply to the belt, polymerization starts, and the reaction system temperature is 22 ° C.
Met. The polymerization system was cooled at a temperature of the belt surface of 10 ° C. without stirring. After 9 minutes, the polymerization system showed a maximum temperature of 86 ° C. After 3 minutes, the temperature of the belt surface was raised to 70 ° C., and the hydrogel polymer was held on the belt for 12 minutes. The width of the hydrogel polymer is 300 m.
m, the thickness was 23 mm, and the temperature was 73 ° C. This hydrogel polymer was cut into 100 mm x 100 mm x 23 mm (gel weight: 229 g, specific surface area: 1.28 cm2 / g).
The hydrogel polymer was placed in a plastic bag and kept in a heating device adjusted to 75 ° C. for 60 minutes. The gel temperature after holding was 74 ° C. (Total ripening time after peak is 75
(Aging time is 60 minutes or more after the temperature falls by 10 ° C. below the peak temperature.) When the hydrogel polymer is pulverized with a meat chopper, a 0.6% aqueous solution of sodium persulfate is 0.02 g / mol (hydrogel weight). 0.02 g of sodium persulfate was added as a 0.6% concentration aqueous solution to 1 mol of the solid content of the coalescence.)
Pulverize with meat chopper while adding and mixing uniformly.
It dried at 60 degreeC and the hot air dryer for 65 minutes. The obtained dried product was pulverized to obtain a water absorbent resin (5).

The water-absorbent resin (5) had an absorption capacity of 63 g /
g, soluble component 10%, degraded soluble content 19%, and residual monomer 170 ppm.

[0093]

According to the present invention, it is possible to obtain a water-absorbent resin having a high absorption capacity and a small amount of water-soluble components and residual monomers with high productivity.

Because of the above-mentioned effects, the water-absorbing resin obtained by the present invention can be used in contact with the human body such as sanitary materials (diapers for children and adults, sanitary napkins, incontinence pads, etc.); Water separating materials; other dehydrating or drying agents; water retaining materials for plants and soil; solidifying agents such as sludge; water stopping materials for electric wires or optical fibers; water absorbing materials for civil engineering and construction; It is useful for various industrial applications that require

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takumi Hatsuda 992, Okihama-shi, Nishioki, Aboshi-ku, Himeji-shi, Hyogo Prefecture 1 Nippon Shokubai Co., Ltd.

Claims (4)

[Claims] 1. When a stationary aqueous solution polymerization of a monomer component to be polymerized to become a water-absorbent resin is carried out, the obtained hydrogel polymer is kept at least 10 ° C. lower than the peak temperature for at least 30 minutes. A method for producing a water-absorbent resin, comprising: 2. The method according to claim 1, further comprising adding a polymerization initiator to the hydrogel polymer. 3. The water-absorbent material according to claim 1, wherein the obtained hydrogel polymer is held at a temperature at least 10 ° C. lower than the peak temperature for at least 30 minutes, and then pulverized. Method of manufacturing resin. 4. The water-absorbing composition according to claim 1, wherein a peak temperature of at least 80 ° C. is exhibited when the monomer component to be polymerized to become a water-absorbing resin is subjected to standing aqueous solution polymerization. Production method of conductive resin.