JP6993878B2 - Water-absorbent resin and water-absorbent - Google Patents

Description

The present invention relates to a water-absorbent resin and a water-absorbent agent. More specifically, the present invention relates to a water-absorbent resin and a water-absorbent agent having good water-absorbing properties and excellent productivity.

In recent years, water-absorbent resins and water-absorbents have been widely used in various fields such as sanitary products such as disposable diapers or sanitary products, agricultural and horticultural materials such as water-retaining agents or soil conditioners, and industrial materials such as water-stopping agents or anti-condensation agents. It has been used, and its usage is expanding. Further, for example, in the field of sanitary goods, the content of pulpwood tends to decrease, while the content of water-absorbing agent having excellent water-absorbing properties tends to increase, in response to a request for thinning of absorbent articles containing water-absorbing agents. There is. Therefore, not only the improvement of the water absorption characteristics but also the quantitative demand for the water absorption resin and the water absorption agent is increasing, and the improvement of the productivity thereof is also required.

Japanese Patent Application Laid-Open No. 2010-53296 (Patent Document 1) describes a step of polymerizing a monomer aqueous solution (1), a step of drying the hydrogel polymer obtained by the step (1) (2), and the step. The step (3) of crushing, or crushing and classifying the dried product obtained in (2) to control the particle size, and surface cross-linking are performed on the water-absorbent resin powder whose particle size is controlled by the step (3). A method for producing a water-absorbent resin, which sequentially comprises the step (5), wherein the water-absorbent resin powder whose particle size is controlled by the step (3) is secondly heated before the step (5) of performing the surface cross-linking. A method for producing a water-absorbent resin, which comprises the step (4) of performing drying is described. It is described that by this method, a particulate water-absorbent resin having excellent physical properties can be efficiently obtained at low cost while ensuring high productivity.

Further, in Japanese Patent Application Laid-Open No. 2015-14002 (Patent Document 2), the temperature of the particulate water-absorbent resin is set to 30 to 30 in advance in the step of adding the surface cross-linking agent and water to the particulate water-absorbent resin in the mixer. A method for producing a water-absorbent resin at 150 ° C. using the number of rotations of the stirring blade, the direction of the rotation axis of the stirring blade, and the continuous mixing device specified for the mixing tank is described. It is stated that by this method, a surface-crosslinked water-absorbent resin can be efficiently obtained at low cost while ensuring high productivity.

Japanese Unexamined Patent Publication No. 2010-53296 Japanese Patent Application Laid-Open No. 2015-14002

As described in the above patent document, various attempts have been made to improve the productivity of the water-absorbent resin and the water-absorbent agent, but there is still room for improvement. An object of the present invention is to provide a water-absorbent resin and a water-absorbent agent having good water-absorbing properties and improved productivity from various viewpoints.

The present inventors have been diligently researching to solve the above problems. As a result, it was found that the specific physical property value of the water-absorbent resin, which is the product of the step before cross-linking to the water-absorbent agent, greatly contributes to the productivity of the water-absorbent resin and the water-absorbent agent. It came to be completed.

That is, the present invention provides the following aspects.
[1]
A water-absorbent resin obtained by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of a water-soluble polymerization initiator, which satisfies all of the following (A) to (C).
(A) Pure water absorption capacity is 500 g / g or more (B) Pure water swelling gel fluidity is 25 g / 5 minutes or more (C) The amount of dissolved polymer in wastewater is less than 400 ppm [2]
A water-absorbent resin in which the water-soluble polymerization initiator contains an azo compound and a peroxide.
[3]
A water-absorbent resin in which the polymerization of the water-soluble ethylenically unsaturated monomer is reverse-phase suspension polymerization.
[4]
The above azo compounds are 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane. } A water-absorbent resin which is at least one selected from the group consisting of dihydrochloride and 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate.
[5]
A water-absorbent resin in which the peroxide is at least one selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, and hydrogen peroxide.
[6]
A water-absorbing agent obtained by post-crosslinking the water-absorbent resin with a post-crosslinking agent.
[7]
The water-soluble polymerization initiator contains an azo compound and a peroxide, and the total amount of the azo compound and the peroxide in each polymerization step is 0.015 to 0. For 100 mol of the water-soluble ethylenically unsaturated monomer. A method for producing a water-absorbent resin obtained by polymerizing 075 mol of a water-soluble ethylenically unsaturated monomer in the presence of a water-soluble polymerization initiator.
[8]
A method for producing a water-absorbent resin, wherein the polymerization of the water-soluble ethylenically unsaturated monomer is reverse-phase suspension polymerization.
[9]
The above azo compounds are 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane. } A method for producing a water-absorbent resin, which is at least one selected from the group consisting of dihydrochloride and 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate. ..
[10]
A method for producing a water-absorbent resin, wherein the peroxide is at least one selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, and hydrogen peroxide.
[11]
A method for producing a water-absorbent agent obtained by post-crosslinking the water-absorbent resin obtained by the above-mentioned production method with a post-crosslinking agent.

In the present specification, the "water-absorbent resin" means a resin obtained by polymerizing a water-soluble ethylenically unsaturated monomer, which is in the stage before so-called post-crosslinking. Further, the "water-absorbing agent" means a product which is a post-crosslinking reaction product obtained by post-crosslinking the above water-absorbent resin with a post-crosslinking agent.

The water-absorbent resin of the present invention is characterized in that it has a pure water absorption capacity, a pure water swelling gel fluidity, and an amount of a dissolved polymer in wastewater within a specific range. The water-absorbent resin of the present invention can ensure high productivity by satisfying such specific physical property values. By using the water-absorbent resin of the present invention, a water-absorbent agent having good water-absorbing properties can be produced with high productivity.

It is a schematic diagram which shows the schematic structure of the apparatus for measuring the pure water swelling gel fluidity of a water-absorbent resin.

First, the background to the present invention will be described. The present inventors have applied to the inner wall of a manufacturing apparatus such as a reactor and a dryer in each step for obtaining a water-absorbing resin before post-crosslinking when conducting a study for improving the productivity of the water-absorbing agent. We focused on adhesion. When the water-absorbent resin adheres to and accumulates on the inner wall of the manufacturing apparatus, the stirring efficiency and / or the heat transfer efficiency in each step is lowered, and the productivity is deteriorated from the viewpoint of energy loss. Further, the adhesion of the water-absorbent resin to the inner wall of the manufacturing apparatus may cause variations in the water-absorbing characteristics of the obtained water-absorbent resin and the water-absorbent agent.

In addition, in order to remove the water-absorbent resin adhering to the inner wall of the manufacturing apparatus accumulated by repeated manufacturing, it is necessary to periodically wash and remove it with a liquid substance such as water. Here, if it is difficult to remove the water-absorbent resin adhering to the inner wall, the required amount of the liquid material (cleaning liquid) used for cleaning and the cleaning time will increase, and the productivity will be reduced from the viewpoint of reducing the device operating time. Will be adversely affected. Therefore, if the water-absorbent resin adhering to the inner wall can be easily removed from the inner wall and the cleaning is easy, the amount of the cleaning liquid used is reduced, the cleaning time is shortened, and the productivity is improved as a result. Further, it has the effect of reducing the amount of wastewater generated by washing and reducing the environmental load.

On the other hand, the wastewater generated after cleaning the water-absorbent resin adhering to the inner wall is usually transferred to the wastewater treatment tank through a pipe. Here, the water-absorbent resin swells and becomes a gel due to its water absorption. The wastewater containing the swollen gel-like water-absorbent resin may have low fluidity. If the fluidity of the wastewater containing the gel is low, it will be necessary to dilute the wastewater to ensure fluidity for transfer, even if the adhesion to the inner wall is removed with a small amount of cleaning solution. Dilution of wastewater results in an increase in the amount of wastewater, increasing treatment costs and environmental burden. Therefore, the high fluidity of the wastewater containing the water-absorbent resin also affects the productivity from the viewpoint of treatment cost and the like.

Further, the wastewater used for cleaning the adhesion of the water-absorbent resin is usually treated by separating it into a solid substance and a liquid substance by aggregating a solid substance such as a swelling gel. Here, when the separated liquid material contains a large amount of dissolved polymers derived from the raw material or by-products of the water-absorbent resin, these dissolved polymers are subjected to biological treatment or chemical treatment as wastewater treatment. There is a need to do. When the wastewater contains a large amount of dissolved polymer, the load in the wastewater treatment increases, which adversely affects the productivity of the water-absorbent resin from the viewpoint of the treatment cost and the treatment time. Therefore, reducing the amount of the dissolved polymer in the wastewater of the water-absorbent resin also affects the productivity from the viewpoint of treatment cost and the like.

The present inventors conducted a study based on the above findings for the purpose of improving the productivity of the water-absorbent resin having good water-absorbing properties. Here, they have found that a water-absorbent resin satisfying a specific physical property value has all the means for solving the above-mentioned problems, and have completed the present invention. Hereinafter, the water-absorbent resin and the water-absorbent agent of the present invention will be described.

Water-absorbent resin The water-absorbent resin of the present invention is a water-absorbent resin obtained by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of a water-soluble polymerization initiator. The water-absorbent resin is characterized by satisfying all of the following (A) to (C).
(A) Pure water absorption capacity of 500 g / g or more (B) Pure water swelling gel fluidity of 25 g / 5 minutes or more (C) Amount of dissolved polymer in wastewater is less than 400 ppm

The water absorption capacity of the water-absorbent resin, the fluidity of the pure water swelling gel, and the amount of the dissolved polymer in the waste water are values measured by the measurement method described later.

In the water-absorbent resin of the present invention, the pure water absorption capacity is 500 g / g or more. From the viewpoint of improving the productivity of the water-absorbent resin, the pure water absorption capacity is preferably 500 to 1200 g / g, more preferably 550 to 1100 g / g, and 600 to 1100 g / g. Is even more preferable. If the water absorption capacity of pure water is less than 500 g / g, the water absorption characteristics of the obtained water-absorbent resin and water-absorbing agent may not be sufficiently satisfied.

In the water-absorbent resin of the present invention, the pure water swelling gel fluidity is 25 g / 5 minutes or more. The pure water swelling gel fluidity is preferably 28 g / 5 minutes or more, and more preferably 30 to 50 g / 5 minutes. When the fluidity of the pure water swelling gel is 25 g / 5 minutes or more, the fluidity of the wastewater containing the swollen gel-like water-absorbent resin becomes high, and the high productivity of the water-absorbent resin is ensured.

In the water-absorbent resin of the present invention, the amount of the dissolved polymer in the wastewater is less than 400 ppm. The amount of the dissolved polymer is preferably less than 380 ppm, more preferably less than 360 ppm, and even more preferably 1 to 340 ppm. When the amount of the dissolved polymer in the wastewater is less than 400 ppm, there is an advantage that the wastewater treatment generated in the production of the water-absorbent resin becomes easy, and as a result, the productivity is improved.

Further, in the water-absorbent resin of the present invention, the pure water absorption capacity is 500 g / g or more, and the pure water swelling gel fluidity is 25 g / 5 minutes or more, so that the water-absorbent resin is formed on the inner wall of the manufacturing apparatus. Even if it adheres, it can be easily removed by cleaning with a cleaning liquid.

When the water-absorbent resin of the present invention is prepared by polymerizing a water-soluble ethylenically unsaturated monomer, even if the water-absorbent resin adheres to the inner wall of the manufacturing apparatus, it can be easily removed by washing with a cleaning liquid. It has the feature that it can be used. This has the advantage that the cleaning liquid used for cleaning, the cleaning time required for cleaning, and the amount of wastewater generated by cleaning are reduced, and as a result, the productivity of the water-absorbent resin is improved.

As the cleaning liquid used for cleaning the inner wall of the manufacturing apparatus, it is preferable to use water from the viewpoint of ease of waste liquid treatment, and for example, industrial water, tap water, purified water and the like can be used. Here, it is preferable to wash the manufacturing apparatus every 1 to 1000 tons of the water-absorbent resin produced. By performing cleaning within such a range, there is an advantage that it is possible to prevent variations in the water absorption characteristics of the water-absorbent resin and the water-absorbent agent.

The water-absorbent resin can be produced, for example, by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of a water-soluble polymerization initiator. Here, the water-soluble polymerization initiator preferably contains an azo compound and a peroxide.

In each polymerization reaction, the amount of the water-soluble polymerization initiator used is preferably 0.015 mol or more with respect to 100 mol of the water-soluble ethylenically unsaturated monomer. Further, it is preferably 0.075 mol or less, more preferably 0.05 mol or less, based on 100 mol of the water-soluble ethylenically unsaturated monomer.

Regarding the embodiment in which the azo compound and the peroxide are used as the water-soluble polymerization initiator, which is a preferable embodiment in the above production method, the azo compound and the peroxide do not necessarily coexist at the start of the polymerization reaction. .. For example, the other compound may be present while the monomer conversion rate due to radical cleavage of one compound is less than 10%. As the water-soluble polymerization initiator, it is more preferable that both the azo compound and the peroxide coexist in the aqueous solution containing the monomer before the start of the polymerization reaction. These azo compounds and peroxides may be added to the polymerization reaction system in separate flow paths, or may be sequentially added to the polymerization reaction system in the same flow path. The form of the azo compound and the peroxide used may be a powder or an aqueous solution.

Examples of the azo compound include 1-{(1-cyano-1-methylethyl) azo} formamide, 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2. '-Azobis {2- [N- (4-chlorophenyl) amidino] propane} dihydrochloride, 2,2'-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} dihydrochloride, 2, 2'-azobis [2- (N-benzylamidino) propane] dihydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2'-azobis (2-amidino) Propane) dihydrochloride, 2,2'-azobis {2- [N- (2-hydroxyethyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (5-methyl-2-imidazolin-) 2-yl) Propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6) 7-Tetrahydro-1H-1,3-diazepine-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-yl) tetrahydropyrimidine-2-yl ) Propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis [2-( 2-imidazolin-2-yl) propane], 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis {2-Methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2' -Azobis (2-methylpropionamide) dihydrochloride, 4,4'-azobis-4-cyanovaleic acid, 2,2'-azobis [2- (hydroxymethyl) propionitrile], 2,2'-azobis [ 2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, 2, Examples thereof include compounds such as 2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide].
As azo compounds, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} Dihydrochloride, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate is more preferably used. By using these azo compounds, it is possible to satisfactorily adjust the polymerization reaction such as the polymerization temperature, which has the advantage that the pure water absorption capacity of the obtained water-absorbent resin can be designed in a high range. .. The azo compound may be used alone or in combination of two or more.

Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; hydrogen peroxide, and the like. Among these, potassium persulfate, ammonium persulfate, and sodium persulfate are preferable from the viewpoint of easy availability and handling.

The molar ratio of the azo compound and the peroxide used for the polymerization is preferably azo compound: peroxide = 0.95: 0.05 to 0.55: 0.45, preferably 0.93 :. It is more preferably 0.07 to 0.6: 0.4, and even more preferably 0.9: 0.1 to 0.6: 0.4. When the molar ratio of the azo compound and the peroxide is within the above range, the amount of the dissolved polymer in the waste water can be reduced, and further, high pure water absorption capacity can be realized.

The reaction temperature of the polymerization is preferably 20 to 120 ° C. from the viewpoint of increasing the productivity by rapidly advancing the polymerization and shortening the polymerization time, and more easily removing the heat of polymerization to carry out the reaction smoothly. 40 to 100 ° C. is more preferable. The reaction time is preferably 0.1 hour to 4 hours.

The polymerization of the water-soluble ethylenically unsaturated monomer is preferably carried out in the presence of an internal cross-linking agent. As a polymerization method, an aqueous solution of an ethylenically unsaturated monomer is polymerized to obtain a hydrogel-like substance, which is then pulverized and dried. An aqueous solution polymerization; an aqueous solution of an ethylenically unsaturated monomer is placed in a dispersion medium. There is a reverse phase suspension polymerization or the like in which a hydrogel is obtained by dispersion and suspension polymerization, and then dried, and the reverse phase suspension polymerization is more preferable. Further, it is preferable to use a dispersion stabilizer at the time of reverse phase suspension polymerization.

The reverse phase suspension polymerization preferably used in the present invention may be carried out in one stage or in two or more stages. The first-stage polymerization means a single-stage polymerization step and a first-stage polymerization step in two-stage or more multi-stage polymerization. In multi-stage polymerization of two or more stages, the particle size of the water-absorbent resin can be increased by aggregating the water-absorbent resin obtained in the first-stage reverse-phase suspension polymerization, so that, for example, absorption of paper diapers, etc. It becomes easier to obtain an appropriate particle size suitable for a sex article.

When performing two or more stages of reverse phase suspension polymerization, after performing the first stage reverse phase suspension polymerization, add a water-soluble ethylenically unsaturated monomer to the reaction mixture obtained by the first stage polymerization reaction. It may be added and mixed, and the reverse phase suspension polymerization of the second and subsequent stages may be carried out in the same manner as in the first stage. In the reverse phase suspension polymerization in each stage of the second and subsequent stages, in addition to the water-soluble ethylenically unsaturated monomer, azo compounds, peroxides and internal cross-linking agents are used in the reverse phase suspension in each stage of the second and subsequent stages. Based on the amount of water-soluble ethylenically unsaturated monomer added during turbid polymerization, it is added within the range of the mass ratio of each component to the above-mentioned water-soluble ethylenically unsaturated monomer, and the suspension is carried out under the same conditions. It is preferable to carry out turbid polymerization.

Examples of the water-soluble ethylenically unsaturated monomer used in the present invention include (meth) acrylic acid and a salt thereof; 2- (meth) acrylamide-2-methylpropanesulfonic acid and a salt thereof; (meth) acrylamide, N, N. Nonionic monomers such as -dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N-diethylaminoethyl (meth) acrylate, N , N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide and other amino group-containing unsaturated monomers and quaternized products thereof. These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

Among them, (meth) acrylic acid and its salt, (meth) acrylamide, N, N-dimethylacrylamide are preferable, and (meth) acrylic acid and its salt are more preferable, because they are easily available industrially.

Among these, acrylic acid and its salts are widely used as raw materials for water-absorbent resins, and these acrylic acids and their salts may be copolymerized with other water-soluble ethylenically unsaturated monomers described above. .. In this case, it is preferable that acrylic acid and a salt thereof are used as the main water-soluble ethylenically unsaturated monomer in an amount of 70 to 100 mol% with respect to the total water-soluble ethylenically unsaturated monomer.

Further, when polymerizing in two or more stages, the water-soluble ethylenically unsaturated monomer used in the second and subsequent stages is different even if it is the same as the water-soluble ethylenically unsaturated monomer used in the first stage. You may.

The above-mentioned water-soluble ethylenically unsaturated monomer may be used as an aqueous solution in order to increase the dispersion efficiency in the dispersion medium when performing reverse-phase suspension polymerization. By using an aqueous solution, the dispersion efficiency in the dispersion medium can be increased. The concentration of the water-soluble ethylenically unsaturated monomer in this aqueous solution is preferably in the range of 20% by mass to the saturation concentration or less. Further, since the polymerization rate tends to increase in the presence of the azo compound, the concentration of the monomer is set from the viewpoint that the performance of the water-absorbent resin according to the present invention can be easily obtained while avoiding excessive heat storage. Is more preferably 55% by mass or less, further preferably 50% by mass or less, and even more preferably 45% by mass or less. On the other hand, in order to maintain the productivity at a good level, the concentration of the monomer is more preferably 25% by mass or more, further preferably 28% by mass or more, still more preferably 30% by mass or more. ..

When the water-soluble ethylenically unsaturated monomer has an acid group such as (meth) acrylic acid and 2- (meth) acrylamide-2-methylpropanesulfonic acid, the acid group is previously an alkaline neutralizing agent if necessary. You may use the one neutralized by. Examples of such an alkaline neutralizer include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia and the like. In particular, these alkaline neutralizers may be used in the form of an aqueous solution in order to simplify the neutralization operation. The above-mentioned alkaline neutralizer may be used alone or in combination of two or more.

Regarding the degree of neutralization of the water-soluble ethylenically unsaturated monomer by the alkaline neutralizer, the water absorption performance is improved by increasing the osmotic pressure of the obtained water-absorbent resin, and the safety due to the presence of the excess alkaline neutralizer is present. From the viewpoint of preventing problems such as, the neutralization degree of the water-soluble ethylenically unsaturated monomer with respect to all acid groups is usually preferably 10 to 100 mol%, preferably 30 to 90 mol%. It is more preferably present, more preferably 40 to 85 mol%, still more preferably 50 to 80 mol%.

Further, a chain transfer agent may be added in order to control the water absorption characteristics of the water-absorbent resin. Examples of such chain transfer agents include hypophosphates, thiols, thiol acids, secondary alcohols, amines and the like.

As a dispersion medium preferably used in the reverse phase suspension polymerization of the water-soluble ethylenically unsaturated monomer, for example, a hydrocarbon dispersion medium can be mentioned. Examples of the hydrocarbon dispersion medium include n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, n-octane and the like having 6 to 8 carbon atoms. Alicyclic hydrocarbons; alicyclics such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane, etc. Group hydrocarbons; examples include aromatic hydrocarbons such as benzene, toluene and xylene. These hydrocarbon dispersion media may be used alone or in combination of two or more. Among these hydrocarbon dispersion media, n-hexane, n-heptane and cyclohexane are preferable in that they are industrially easily available, have stable quality, and are inexpensive. Further, as an example of the mixture of the above hydrocarbon dispersion medium, a commercially available exol heptane (manufactured by ExxonMobil Co., Ltd .: containing 75 to 85% by mass of hydrocarbon of heptane and its isomer) or the like is also suitable. Is obtained.

The amount of the dispersion medium used is preferably 100 to 1500 with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer used for the first-stage polymerization from the viewpoint of removing heat of polymerization and easily controlling the polymerization temperature. It is by mass, more preferably 200 to 1400 parts by mass.

A surfactant is mentioned as a dispersion stabilizer preferably used in the reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer. Examples of the surfactant include sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and polyoxyethylene alkyl. Ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, polyethylene Glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphoric acid esters of polyoxyethylene alkyl ethers, phosphoric acid esters of polyoxyethylene alkyl allyl ethers, etc. can be used. can. Of these, sorbitan fatty acid ester, polyglycerin fatty acid ester, and sucrose fatty acid ester are preferable from the viewpoint of dispersion stability of the water-soluble ethylenically unsaturated monomer. These surfactants may be used alone or in combination of two or more.

The amount of the surfactant used is the water-soluble ethylenically unsatisfied in the first stage from the viewpoint of maintaining a good dispersion state of the water-soluble ethylenically unsaturated monomer in the dispersion medium and obtaining a dispersion effect commensurate with the amount used. It is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass with respect to 100 parts by mass of the saturated monomer.

Further, as the dispersion stabilizer, a polymer-based dispersant may be used in combination with the surfactant. Examples of the polymer-based dispersant that can be used include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene / propylene / diene / tarpolymer), and anhydrous. Maleic acid-modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene Examples thereof include copolymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymers, ethylene / acrylic acid copolymers, ethyl cellulose, ethyl hydroxyethyl cellulose and the like. Among them, from the viewpoint of the dispersion stability of the monomer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride / ethylene copolymer, and maleic anhydride / propylene are both. Polymers, maleic anhydride / ethylene / propylene copolymers, polyethylene, polypropylene, ethylene / propylene copolymers, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymers are preferable. These polymer-based dispersants may be used alone or in combination of two or more.

The amount of the polymer-based dispersant used is the first-stage water-soluble ethylene from the viewpoint of maintaining a good dispersion state of the water-soluble ethylenically unsaturated monomer in the dispersion medium and obtaining a dispersion effect commensurate with the amount used. The amount is preferably 0.1 to 30 parts by mass, and more preferably 0.3 to 20 parts by mass with respect to 100 parts by mass of the unsaturated monomer.

As the internal cross-linking agent, for example, (poly) ethylene glycol [“(poly)” means with or without the prefix “poly”. The same shall apply hereinafter], (poly) propylene glycol, 1,4-butanediol, trimethylolpropane, diols such as (poly) glycerin, polyols such as triol, and (meth) acrylic acid (in the present specification, "acry" and "Methacyl" is collectively referred to as "(meth) acrylic"; the same applies hereinafter), unsaturated polyesters obtained by reacting with unsaturated acids such as maleic acid and fumaric acid; N, N'-methylenebis (meth). ) Bis (meth) acrylamides such as acrylamide; di or tri (meth) acrylic acid esters obtained by reacting polyepoxide with (meth) acrylic acid; polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate and (meth). ) Di (meth) acrylic acid carbamyl esters obtained by reacting with hydroxyethyl acrylate; allylated starch, allylated cellulose, diallyl phthalate, N, N', N''-triallyl isocyanurate, divinylbenzene Compounds having two or more polymerizable unsaturated groups such as; (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether and other diglycidyl compounds, triglycidyl compounds and the like poly Glyceryl compounds; Epihalohydrin compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; isocyanate compounds such as 2,4-trilenedi isocyanate and hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3- 2 reactive functional groups such as oxetane compounds such as oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetanethanol, 3-ethyl-3-oxetanethanol, 3-butyl-3-oxetanethanol Examples thereof include compounds having more than one. Among these, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether and N, N'-methylenebis from the viewpoint of excellent reactivity at low temperature. Acrylamide is preferred. These internal cross-linking agents may be used alone or in combination of two or more.

The amount of the internal cross-linking agent used with respect to 100 mol of the water-soluble ethylenically unsaturated monomer used for the polymerization is preferably 0.00001 to 1 mol, more preferably 0.0001 to 0.5 mol. More preferably, 0.001 to 0.013 mol.

The above-mentioned production method may include a drying treatment for removing water, a dispersion medium (hydrocarbon dispersion medium), etc. by distillation by applying energy such as heat from the outside after the completion of polymerization. The drying treatment may be carried out under normal pressure, under reduced pressure, or under an air flow such as nitrogen in order to improve the drying efficiency, and these methods may be used in combination. When the drying treatment is at normal pressure, the drying temperature is preferably 70 to 250 ° C, more preferably 80 to 180 ° C, and even more preferably 80 to 140 ° C. When the drying treatment is under reduced pressure, the drying temperature is preferably 40 to 160 ° C, more preferably 50 to 120 ° C.
Further, a pulverization step may be provided so that a water-absorbent resin having an appropriate particle size can be obtained, if necessary, during or after the drying step.

By producing the water-absorbent resin as described above, an appropriately finely divided water-containing gel can be obtained, and by extension, a fine-grained water-absorbent resin suitable for preparing an absorbent article can be easily obtained.

By adding a post-crosslinking agent to the water-absorbent resin obtained by polymerization and reacting it, post-crosslinking can be performed, whereby a water-absorbing agent can be obtained. The water absorbent is a post-crosslinking reactant. By adding a post-crosslinking agent to the water-absorbent resin and causing a post-crosslinking reaction, it has excellent water absorption characteristics such as water absorption capacity under load. In the post-crosslinking reaction, it is preferable that the water-absorbent resin obtained by the reverse phase suspension polymerization is post-crosslinked with a post-crosslinking agent in the form of a water-containing gel. After the hydrogel-like material is appropriately dried by a drying treatment, it may be post-crosslinked using a post-crosslinking agent.

Post-crosslinking is to crosslink a portion of the water-absorbent resin near the surface to increase the crosslink density of the portion near the surface as compared with the inside. Compared to those without post-crosslinking, the post-crosslinked resin particles have a harder gel during water absorption and are less likely to cause gel blocking (a phenomenon in which the water-absorbing resin particles are blocked after water absorption), so that they are liquid. Good diffusivity can be maintained. Therefore, when post-crosslinking is performed, it is possible to control the diffusion of the liquid in the initial stage of water absorption, and after a certain period of time from the start of water absorption, it is possible to secure a high water absorption amount due to the hardness of the gel. Therefore, the amount of reversion can be reduced.

Examples of the post-crossing agent used in the post-crossing reaction include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol and polyglycerin; (Poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether, trimethylolpropane triglycidyl ether, etc. Polyglycidyl compounds; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepicrolhydrin; isocyanate compounds such as 2,4-tolylene diisocyanate, hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3 -Oxetane compounds such as oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetan ethanol, 3-butyl-3-oxetane ethanol; 1,2-ethylenebis Examples thereof include oxazoline compounds such as oxazoline; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide. Among these post-crosslinking agents, (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether Etc., Polyglycidyl compounds such as are preferably used. These post-crosslinking agents may be used alone or in combination of two or more.

The amount of the post-crosslinking agent used is preferably 0.001 to 1 mol, more preferably 0.005 to 0.5 mol, based on 100 mol of the water-soluble ethylenically unsaturated monomer used for the polymerization.

The post-crosslinking agent may be added only after the polymerization reaction of the water-soluble ethylenically unsaturated monomer is almost completely completed, with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer used to obtain the water-absorbent resin. It is preferably added in the presence of water in the range of 1 to 400 parts by mass, more preferably in the presence of water in the range of 5 to 200 parts by mass, and in the presence of water in the range of 10 to 100 parts by mass. It is more preferable to add it, and it is even more preferable to add it in the presence of water in the range of 20 to 60 parts by mass.

Examples of the method for adding the post-crosslinking agent include a method of adding the post-crosslinking agent as it is, a method of adding it as an aqueous solution, and a method of adding it as a solution using a hydrophilic organic solvent as a solvent. Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane and tetrahydrofuran; N, N. -Amids such as dimethylformamide; sulfoxides such as dimethylsulfoxide and the like can be mentioned. These hydrophilic organic solvents may be used alone, in combination of two or more, or as a mixed solvent with water.

The reaction temperature in the post-crosslinking reaction is preferably 50 to 250 ° C, more preferably 60 to 180 ° C, still more preferably 70 to 150 ° C. The reaction time of the post-crosslinking reaction is preferably 1 to 300 minutes, more preferably 5 to 200 minutes.

The water-absorbent resin or water-absorbent agent thus produced can be made into a water-absorbent resin composition or a water-absorbent composition by blending additives according to various purposes in order to impart various performances. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain prohibiting agents, antioxidants, antibacterial agents, deodorants and the like. For example, the fluidity can be improved by adding 0.05 to 5 parts by mass of amorphous silica as an inorganic powder to 100 parts by mass of the water absorbing agent.

The water-absorbent resin or water-absorbent agent is used for absorbent articles. Typical examples of absorbent articles include sanitary materials such as paper diapers, sanitary napkins, panty liners, incontinence pads, and breast milk pads, urine absorbing materials for pets, civil engineering and construction materials such as packing materials, and drip absorption. Examples thereof include food freshness-preserving materials such as agents and cold insulators, and agricultural and horticultural articles such as soil water-retaining materials.

For example, absorbent articles used for sanitary materials include a liquid permeable sheet (top sheet) through which an aqueous liquid can pass through an absorber that absorbs and retains an aqueous liquid, and a liquid through which the aqueous liquid does not pass. It has a structure held between it and an impermeable sheet (back sheet). The liquid permeable sheet is arranged on the side that comes into contact with the body, and the liquid permeable sheet is arranged on the side that does not come into contact with the body.

Examples of the liquid permeable sheet include non-woven fabrics such as air-through type, spunbond type, chemical bond type and needle punch type, which are made of fibers such as polyethylene, polypropylene and polyester, and porous synthetic resin sheets.

Examples of the liquid impermeable sheet include a synthetic resin film made of a resin such as polyethylene, polypropylene, and polyvinyl chloride.

The absorber used in the absorbent article is composed of the water-absorbent resin obtained in the present invention and hydrophilic fibers. As the structure of the absorber, for example, the water-absorbent resin is sandwiched between the mixed dispersion obtained by mixing the water-absorbent resin and the hydrophilic fibers so as to have a uniform composition, and the layered hydrophilic fibers. Examples thereof include a sandwich structure, a structure in which a water-absorbent resin and hydrophilic fibers are wrapped with a tissue, a water-permeable non-woven fabric, or the like.

Other components, for example, an adhesive binder such as a heat-fusing synthetic fiber, a hot melt adhesive, or an adhesive emulsion for enhancing the shape retention of the absorber may be added to the absorber.

Examples of the hydrophilic fibers include cellulose fibers such as cotton-like pulp obtained from wood, mechanical pulp, chemical pulp, and semi-chemical pulp, artificial cellulose fibers such as rayon and acetate, hydrophilized polyamide, polyester, and polyolefin. Examples thereof include fibers made of the synthetic resin of.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

With respect to the water-absorbent resin and the water-absorbent agent obtained in each Example and Comparative Example, the pure water absorption capacity, the pure water swelling gel fluidity, and the amount of the dissolved polymer in the waste water were measured by the methods shown below.

The water-absorbent resin and the water-absorbent agent used for the evaluation shall have a water content of 10% or less. When the water content exceeded 10%, the water content was adjusted to 10% or less by using a known drying method or the like, and then the evaluation was performed. The water content is measured by the method shown below.

About 2 g of the water -absorbent resin was precisely weighed in a pre-weighed aluminum wheel case (No. 8) (Wa (g)). The above sample was dried for 2 hours in a hot air dryer (manufactured by ADVANTEC) whose internal temperature was set to 105 ° C., then allowed to cool in a desiccator, and the mass Wb (g) of the dried water-absorbent resin was measured. did. The water content of the water-absorbent resin was calculated from the following formula.
Moisture content (%) = [Wa-Wb] / Wa × 100

Weigh 1500 g of ion-exchanged water into a beaker with a pure water absorption capacity of 3 L, and add 0.5 g of water-absorbent resin while stirring at 600 r / min with a magnetic stirrer (stirrer: 10 mmφ x 40 mm without ring). It was dispersed so that mamaco did not occur. The water-absorbent resin was sufficiently swollen by leaving it to stand for 60 minutes in a stirred state. After that, the mass Wc (g) of a standard sieve with an opening of 75 μm is measured in advance, and the contents of the beaker are filtered using this so that the sieve has an inclination angle of about 30 degrees with respect to the horizontal. Excess water was filtered off by leaving it in an inclined state for 30 minutes. The mass Wd (g) of the sieve containing the water-absorbing gel was measured, and the pure water water-absorbing ability was determined by the following formula.
Pure water absorption capacity (g / g) = [Wd-Wc] (g) / Mass of water-absorbent resin (g)

Weigh 2000 g of ion-exchanged water into a beaker containing 3 L of dissolved polymer in the waste water, and stir at 1000 r / min with a two-stage paddle blade attached to a stirrer to generate 2.0 g of water-absorbent resin so that mamaco does not occur. And stirred for 3 hours. The contents of the beaker are filtered through a standard sieve with a mesh opening of 75 μm, and 50 g of the obtained filtrate is weighed in a 100 mL beaker that has been made constant in advance, and a hot air dryer at 140 ° C. (manufactured by ADVANTEC, model number: FV). After drying to a constant weight at −320), the mass We (g) of the solid content in the filtrate was measured.
On the other hand, the same operation as described above was carried out without using a water-absorbent resin, the mass Wf (g) of the solid content in the filtrate was measured, and the amount of the dissolved polymer in the wastewater was determined from the following formula.

Amount of dissolved polymer in wastewater (ppm) = (We-Wf) / 50 × 1000000

Pure water swelling gel fluidity The evaluation of pure water swelling gel fluidity was performed using the apparatus X shown in FIG. The device X is installed so that the tip is vertically downward, in order to fix the wax 1 (material: SUS304, input part: diameter 90 mm, height 70 mm, foot part: inner diameter 8 mm, length 100 mm). It is composed of a ring 2 and a clamp 3 of the above, a tray 4 for receiving the swelling gel 6 that has passed through the plumb bob 1, and a balance 5 for measuring the mass of the swelling gel that has passed. The tip of the slot 1 of the funnel 1 is fixed so as to have a height of 150 mm ± 5 mm above the bottom surface of the tray 4.
First, the water-absorbent resin was collected as a fraction having a particle size that passed through a sieve having an opening of 400 μm and was held on a sieve having an opening of 300 μm. Next, 1500 g of ion-exchanged water was weighed in a 3 L volume of poly-handled beaker, and the sample after the classification was described as 0. 5 g was dispersed so as not to generate mamaco. The water-absorbent resin was sufficiently swollen by leaving it to stand for 60 minutes in a stirred state. Then, the contents of the beaker are filtered using a standard sieve with a mesh opening of 75 μm, and the sieve is tilted so as to have an inclination angle of about 30 degrees with respect to the horizontal, and left for 30 minutes to obtain excess water. A swollen gel was prepared by filtration.
After filtering, 50 g of the swollen gel 6 was weighed and put into 1 in a funnel. The measurement starts when the swelling gel 6 that has flowed to the tip of the funnel 1 (point a in FIG. 1) arrives, and the mass of the swelling gel 6 on the tray 4 is measured 5 minutes after the start of the measurement to obtain the pure water swelling gel. The fluidity was set to (g / 5 minutes).

The pure water absorption capacity of the water absorbent, the fluidity of the pure water swelling gel, and the amount of the dissolved polymer in the waste water were also measured as described above in the same manner as the water absorbent resin.

[Example 1]
As a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer, a round-bottomed cylindrical separable flask having an inner diameter of 110 mm and a capacity of 2 L was prepared, which was equipped with a stirring blade having four inclined paddle blades having a blade diameter of 50 mm in two stages. .. To this flask, take 300 g of n-heptane as a hydrocarbon dispersion medium, add 0.74 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Co., Ltd., High Wax 1105A) as a polymer-based dispersant, and stir. After heating and dissolving, the mixture was cooled to 50 ° C.

On the other hand, 92 g (1.02 mol) of 80 mass% acrylic acid aqueous solution was taken in a 500 mL triangular flask, and 102.2 g of 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside to make 75 mol%. After neutralization, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener and 2,2'-azobis (2-amidinopropane) dihydrochloride as an azo compound 0. 055 g (0.204 mmol), potassium persulfate 0.009 g (0.034 mmol) as peroxide, ethylene glycol diglycidyl ether 0.006 g (0.037 mmol) as internal cross-linking agent, and ion-exchanged water 48.0 g. Was added and dissolved to prepare an aqueous monomer solution.

Then, the aqueous monomer solution prepared as described above was added to the separable flask, and after stirring for 10 minutes, 6.66 g of n-heptane was added with HLB3 sucrose stearate as a surfactant (Mitsubishi Chemical Foods Co., Ltd., After further adding 7.4 g of a surfactant solution obtained by heating and dissolving 0.74 g of Ryoto Sugar Ester S-370) and sufficiently replacing the inside of the system with nitrogen while stirring, the flask is immersed in a water bath at 70 ° C. The temperature was raised and the polymerization was carried out for 60 minutes to obtain a reaction mixture in the first stage.

On the other hand, 128.8 g (1.43 mol) of an 80 mass% acrylic acid aqueous solution was taken in another 500 mL triangular flask, and 143.1 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization of 75 mol%, 0.077 g (0.285 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride as an azo compound and 0.013 g of potassium persulfate as a peroxide. (0.048 mmol), 0.009 g (0.052 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent and 12.5 g of ion-exchanged water were added and dissolved to prepare a second-stage monomer aqueous solution.
After cooling the reaction mixture of the first stage to 25 ° C., the entire amount of the aqueous monomer solution of the second stage was added to the reaction mixture of the first stage, and the inside of the system was sufficiently replaced with nitrogen. Again, the flask was immersed in a water bath at 70 ° C. to raise the temperature, and the second-stage polymerization was carried out for 30 minutes.

After the second-stage polymerization, the temperature of the second-stage reaction mixture was raised in an oil bath at 125 ° C., and 245 g of water was added while refluxing n-heptane by azeotropic distillation of n-heptane and water. After extraction to the outside, n-heptane was evaporated and dried. The obtained polymer was passed through a sieve having an opening of 1000 μm to obtain 236.8 g of a water-absorbent resin in the form of aggregated spherical particles. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Example 2]
In Example 2, the amount of potassium persulfate used in the first-stage polymerization was 0.037 g (0.136 mmol). Further, the same procedure as in Example 1 was carried out except that the amount of potassium persulfate used in the second-stage polymerization was 0.052 g (0.191 mmol) to obtain 234.1 g of a water-absorbent resin. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Example 3]
In Example 3, the amount of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the first stage polymerization was 0.092 g (0.339 mmol), and the amount of potassium persulfate was 0.037 g (0. 136 mmol). Further, the amount of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the second stage polymerization was 0.129 g (0.475 mmol), and the amount of potassium persulfate was 0.052 g (0.191 mmol). The same procedure as in Example 1 was carried out to obtain 235.2 g of a water-absorbent resin. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Example 4]
In Example 4, 0.110 g (0.407 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the first stage polymerization and 2,2 used in the second stage polymerization The same procedure as in Example 1 was carried out except that the amount of azobis (2-amidinopropane) dihydrochloride was 0.155 g (0.570 mmol), and 233.2 g of a water-absorbent resin was obtained. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Example 5]
In Example 5, after the second-stage polymerization reaction was carried out by the method of Example 3, the mixture was heated using an oil bath at 120 ° C. and azeotropically distilled to reflux n-heptane into a flask to add 260 g of water. By removing it from the system, a dehydrated polymer dispersed in heptane was obtained. To the obtained heptane-dispersed dehydrated polymer, 8.2 g of a 2% ethylene glycol diglycidyl ether aqueous solution was added as a post-crosslinking agent, and a post-crosslinking reaction was carried out at 83 ° C. for 2 hours.
Then, it is heated using an oil bath at 120 ° C., n-heptane and water are removed from the system by distillation, dried under a nitrogen stream, and a water-absorbent resin having a shape in which spherical particles are aggregated is post-crosslinked. 234 g of the obtained water absorbent was obtained. This water absorbent was evaluated according to the various test methods described above.

[Comparative Example 1]
In Comparative Example 1, 234.6 g of a water-absorbent resin was obtained in the same manner as in Example 4 except that potassium persulfate was not used in both the first-stage polymerization and the second-stage polymerization. .. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Comparative Example 2]
In Comparative Example 2, 2,2'-azobis (2-amidinopropane) dihydrochloride is not used in both the first-stage polymerization and the second-stage polymerization, and the excess used in the first-stage polymerization. The procedure was the same as in Example 1 except that the amount of potassium persulfate was 0.110 g (0.408 mmol) and the amount of potassium persulfate used in the second stage polymerization was 0.155 g (0.572 mmol). 234.5 g of resin was obtained. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Comparative Example 3]
In Comparative Example 3, a water-absorbent resin was prepared by reducing the amount of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the polymerization with respect to Example 1. Specifically, 0.028 g (0.102 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the first stage polymerization and 0.009 g (0.034) of potassium persulfate are used. Millimole), 0.039 g (0.143 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the second stage polymerization, and 0.013 g (0.) of potassium persulfate. It was carried out in the same manner as in Example 1 except that it was set to 048 mmol) to obtain 234.1 g of a water-absorbent resin. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Comparative Example 4]
In Comparative Example 4, a water-absorbent resin having the same molar amount of the azo compound and the peroxide used at the time of polymerization was produced. Specifically, 0.110 g (0.407 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the first stage polymerization and 0.110 g (0.407) of potassium persulfate are used. Mmol). Further, the amount of 2,2'-azobis (2-amidinopropane) dihydrochloride used in the second stage polymerization was 0.155 g (0.570 mmol), and the amount of potassium persulfate was 0.154 g (0.570 mmol). Except for the above, the same procedure as in Example 1 was carried out to obtain 234.8 g of a water-absorbent resin. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Comparative Example 5]
As a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer, a round-bottomed cylindrical separable flask having an inner diameter of 110 mm and a capacity of 2 L was prepared, which was equipped with a stirring blade having four inclined paddle blades having a blade diameter of 50 mm in two stages. .. To this flask, take 300 g of n-heptane as a hydrocarbon dispersion medium, add 0.74 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Co., Ltd., High Wax 1105A) as a polymer-based dispersant, and stir. After heating and dissolving, the mixture was cooled to 50 ° C.

On the other hand, 92 g (1.02 mol) of an 80 mass% acrylic acid aqueous solution was placed in a 500 mL triangular flask, and 102.2 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside to make 75 mol%. After neutralization, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.110 g (0.408 mmol) of potassium persulfate as a peroxide, and an internal cross-linking agent. 0.006 g (0.037 mmol) of ethylene glycol diglycidyl ether and 48.0 g of ion-exchanged water were added and dissolved to prepare an aqueous monomer solution.

Then, the aqueous monomer solution prepared as described above was added to the separable flask, and after stirring for 10 minutes, 6.66 g of n-heptane was added with HLB3 sucrose stearate as a surfactant (Mitsubishi Chemical Foods Co., Ltd., After further adding 7.4 g of a surfactant solution obtained by heating and dissolving 0.74 g of Ryoto Sugar Ester S-370) and sufficiently replacing the inside of the system with nitrogen while stirring, the flask is immersed in a water bath at 70 ° C. The temperature was raised and the polymerization was carried out for 60 minutes to obtain a reaction mixture in the first stage.

On the other hand, 128.8 g (1.43 mol) of an 80 mass% acrylic acid aqueous solution was taken in another 500 mL triangular flask, and 143.1 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization of 75 mol%, 0.155 g (0.570 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride as an azo compound and ethylene glycol diglycidyl ether 0 as an internal cross-linking agent. .009 g (0.052 mmol) and 12.5 g of ion-exchanged water were added and dissolved to prepare a second-stage monomer aqueous solution.
After cooling the reaction mixture of the first stage to 25 ° C., the entire amount of the aqueous monomer solution of the second stage was added to the reaction mixture of the first stage, and the inside of the system was sufficiently replaced with nitrogen. Again, the flask was immersed in a water bath at 70 ° C. to raise the temperature, and the second-stage polymerization was carried out for 30 minutes.

After the second-stage polymerization, the temperature of the second-stage reaction mixture was raised in an oil bath at 125 ° C., and 245 g of water was added while refluxing n-heptane by azeotropic distillation of n-heptane and water. After extraction to the outside, n-heptane was evaporated and dried. The obtained polymer was passed through a sieve having an opening of 1000 μm to obtain 233.5 g of a water-absorbent resin in the form of aggregated spherical particles. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

[Comparative Example 6]
In Comparative Example 6, the same procedure as in Example 4 was carried out except that potassium persulfate and ethylene glycol diglycidyl ether were not used in both the first-stage polymerization and the second-stage polymerization, and the water-absorbent resin was used. 233.8 g was obtained. This water-absorbent resin was evaluated according to the above-mentioned various test methods.

The test results of the water-absorbent resins obtained in the above Examples and Comparative Examples are shown in Table 1 below.

The water-absorbent resins obtained in Examples 1 to 4 all had good water-absorbing properties, and the water-absorbing ability of pure water and the fluidity of pure water-swelling gel were within the scope of the present invention. Therefore, it was possible to easily clean the water-absorbent resin device. In addition, the amount of dissolved polymer in the wastewater was small, and the wastewater used for washing could be easily treated.
Example 5 is a water-absorbing agent obtained by post-crosslinking a water-absorbent resin prepared in the same manner as in Example 3. It was confirmed that this water-absorbing agent also has high water-absorbing properties and a small amount of dissolved polymer in wastewater.

The water-absorbent resin and the water-absorbent agent of the present invention have the features of having good water-absorbing properties and being excellent in productivity. INDUSTRIAL APPLICABILITY According to the present invention, the productivity of absorbent articles such as disposable diapers or sanitary napkins can be improved.

X Measuring device 1 Waist 2 Cut ring 3 Clamp 4 Tray 5 Balance 6 Swelling gel

Claims (14)

A water-absorbent resin having a structural unit derived from a water-soluble ethylenically unsaturated monomer.
Contains water-absorbent resin particles such that they pass through a sieve with a mesh size of 400 μm and are retained on a sieve with a mesh size of 300 μm.
A water-absorbent resin that satisfies all of the following (A) to (C) in a state where the water content is 7.5% to 8.2%.
(A) Pure water absorption capacity is 500 g / g to 960 g / g
(B) Pure water swelling gel fluidity is 25 g / 5 minutes or more (C) Dissolved polymer amount in waste water is 238 ppm or more and less than 400 ppm Here, pure water water absorption capacity, pure water swelling gel fluidity, and dissolved polymer in waste water The amount is measured by the following method:
[Pure water absorption capacity]
Weigh 1500 g of ion-exchanged water in a 3 L beaker and stir at 600 r / min with a magnetic stirrer (stirrer: 10 mmφ x 40 mm without ring) to generate 0.5 g of water-absorbent resin. Disperse as. Leave it for 60 minutes in a stirred state to sufficiently swell the water-absorbent resin. After that, the mass Wc (g) of a standard sieve with an opening of 75 μm is measured in advance, and the contents of the beaker are filtered using this so that the sieve has an inclination angle of about 30 degrees with respect to the horizontal. Excess water is filtered off by leaving it in a tilted state for 30 minutes. The mass Wd (g) of the sieve containing the water-absorbing gel is measured, and the pure water water-absorbing ability is determined by the following formula.
Pure water absorption capacity (g / g) = [Wd-Wc] (g) / Mass of water-absorbent resin (g)
[Pure water swelling gel fluidity]
A wax (material: SUS304, input part: diameter 90 mm, height 70 mm, foot part: inner diameter 8 mm, length 100 mm) installed so that the tip faces vertically downward, a ring and a clamp for fixing the wax, and a wax. Prepare a device consisting of a tray for receiving the swollen gel that has passed through and a balance for measuring the mass of the swollen gel that has passed through (the tip of the wax inlet is 150 mm ± 5 mm above the bottom of the tray. It is fixed as).
The water-absorbent resin is collected as a fraction having a particle size that passes through a sieve having a mesh size of 400 μm and is held on a sieve having a mesh size of 300 μm. Next, 1500 g of ion-exchanged water was weighed in a 3 L volume of poly-handled beaker, and the sample after the classification was described as 0. Disperse 5 g so that mamaco does not occur. Leave it for 60 minutes in a stirred state to sufficiently swell the water-absorbent resin. Then, the contents of the beaker are filtered using a standard sieve with a mesh opening of 75 μm, and the sieve is tilted so as to have an inclination angle of about 30 degrees with respect to the horizontal, and left for 30 minutes to obtain excess water. Make a swelling gel by filtration.
Weigh 50 g of the swollen gel after filtering and put it into a funnel. The measurement starts when the swelling gel that has flowed to the tip of the funnel reaches the measurement start, and the mass of the swelling gel on the tray is measured 5 minutes after the start of the measurement to obtain the pure water swelling gel fluidity (g / 5 minutes).
[Amount of dissolved polymer in wastewater]
2000 g of ion-exchanged water is weighed in a 3 L beaker, and while stirring at 1000 r / min with a two-stage paddle blade attached to a stirrer, 2.0 g of water-absorbent resin is dispersed so as not to generate mamaco for 3 hours. Stir. The contents of the beaker are filtered through a standard sieve having a mesh size of 75 μm, 50 g of the obtained filtrate is weighed in a pre-constantized 100 mL beaker, and dried in a hot air dryer at 140 ° C. until the constant volume is reached. The mass We (g) of the solid content in the filtrate is measured.
On the other hand, the same operation as described above is performed without using a water-absorbent resin, the mass Wf (g) of the solid content in the filtrate is measured, and the amount of the dissolved polymer in the wastewater is obtained from the following formula.
Amount of dissolved polymer in wastewater (ppm) = (We-Wf) / 50 × 1000000 The water-absorbent resin according to claim 1, which comprises at least one of a water-soluble polymerization initiator and a decomposition product thereof. The water-absorbent resin according to claim 1 or 2, wherein the crosslink density near the surface is higher than that inside. It comprises polymerizing a water-soluble ethylenically unsaturated monomer in the presence of a water-soluble polymerization initiator and a dispersion stabilizer, the water-soluble polymerization initiator contains an azo compound and a peroxide, and the azo compound in each polymerization step. The total amount of the peroxide is 0.015 to 0.075 mol with respect to 100 mol of the water-soluble ethylenically unsaturated monomer, and the molar ratio of the azo compound and the peroxide is the azo compound: peroxide. = 0.95: 0.05 to 0.55: 0.45,
A method for producing a water-absorbent resin, wherein the dispersion stabilizer contains a surfactant and a polymer-based dispersant. The method for producing a water-absorbent resin according to claim 4, wherein the polymerization of the water-soluble ethylenically unsaturated monomer is reverse-phase suspension polymerization. The azo compounds are 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane. } According to claim 4 or 5, at least one selected from the group consisting of dihydrochloride and 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate. The method for producing a water-absorbent resin according to the above method. The surfactant is sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether. , Polyoxyethylene alkylphenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, polyethylene glycol Selected from the group consisting of fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphoric acid esters of polyoxyethylene alkyl ethers, and phosphoric acid esters of polyoxyethylene alkyl allyl ethers. The method for producing a water-absorbent resin according to any one of claims 4 to 6, which is at least one of the above. The polymer-based dispersant includes maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene / propylene / diene / tarpolymer), and maleic anhydride. Modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer Claims 4 to 7 which are at least one selected from the group consisting of coalescing, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, and ethyl hydroxyethyl cellulose. The method for producing a water-absorbent resin according to any one. The surfactant is at least one selected from the group consisting of sorbitan fatty acid ester, polyglycerin fatty acid ester, and sucrose fatty acid ester.
The polymer-based dispersant includes maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, and anhydrous. Claimed to be at least one selected from the group consisting of maleic acid / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymer. Item 8. The method for producing a water-absorbent resin according to any one of Items 4 to 8. The amount of the surfactant used is 0.3 to 20 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage.
The production of the water-absorbent resin according to claim 9, wherein the amount of the polymer-based dispersant used is 0.3 to 20 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage. Method. The method for producing a water-absorbent resin according to any one of claims 4 to 10, wherein the peroxide is at least one selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, and hydrogen peroxide. A method for producing a water-absorbent agent, which comprises post-crosslinking the water-absorbent resin obtained by any of claims 4 to 11 by adding a post-crosslinking agent and reacting with the water-absorbent resin to obtain a post-crosslinking reactant. A water-absorbent resin having a structural unit derived from a water-soluble ethylenically unsaturated monomer.
Contains water-absorbent resin particles such that they pass through a sieve with a mesh size of 400 μm and are retained on a sieve with a mesh size of 300 μm.
A water-absorbent resin that satisfies all of the following (A) to (C) in a state where the water content is 7.5% to 8.2%.
(A) Pure water absorption capacity is 749 g / g to 960 g / g
(B) Pure water swelling gel fluidity is 25 g / 5 minutes or more
(C) The amount of dissolved polymer in wastewater is less than 400 ppm
Here, the water absorption capacity of pure water, the fluidity of pure water swelling gel, and the amount of dissolved polymer in wastewater are measured by the following methods:
[Pure water absorption capacity]
Weigh 1500 g of ion-exchanged water in a 3 L beaker and stir at 600 r / min with a magnetic stirrer (stirrer: 10 mmφ x 40 mm without ring) to generate 0.5 g of water-absorbent resin. Disperse as. Leave it for 60 minutes in a stirred state to sufficiently swell the water-absorbent resin. After that, the mass Wc (g) of a standard sieve with an opening of 75 μm is measured in advance, and the contents of the beaker are filtered using this so that the sieve has an inclination angle of about 30 degrees with respect to the horizontal. Excess water is filtered off by leaving it in a tilted state for 30 minutes. The mass Wd (g) of the sieve containing the water-absorbing gel is measured, and the pure water water-absorbing ability is determined by the following formula.
Pure water absorption capacity (g / g) = [Wd-Wc] (g) / Mass of water-absorbent resin (g)
[Pure water swelling gel fluidity]
A wax (material: SUS304, input part: diameter 90 mm, height 70 mm, foot part: inner diameter 8 mm, length 100 mm) installed so that the tip faces vertically downward, a ring and a clamp for fixing the wax, and a wax. Prepare a device consisting of a tray for receiving the swollen gel that has passed through and a balance for measuring the mass of the swollen gel that has passed through (the tip of the wax inlet is 150 mm ± 5 mm above the bottom of the tray. It is fixed as).
The water-absorbent resin is collected as a fraction having a particle size that passes through a sieve having a mesh size of 400 μm and is held on a sieve having a mesh size of 300 μm. Next, 1500 g of ion-exchanged water was weighed in a 3 L volume of poly-handled beaker, and the sample after the classification was described as 0. Disperse 5 g so that mamaco does not occur. Leave it for 60 minutes in a stirred state to sufficiently swell the water-absorbent resin. Then, the contents of the beaker are filtered using a standard sieve with a mesh opening of 75 μm, and the sieve is tilted so as to have an inclination angle of about 30 degrees with respect to the horizontal, and left for 30 minutes to obtain excess water. Make a swelling gel by filtration.
Weigh 50 g of the swollen gel after filtering and put it into a funnel. The measurement starts when the swelling gel that has flowed to the tip of the funnel reaches the measurement start, and the mass of the swelling gel on the tray is measured 5 minutes after the start of the measurement to obtain the pure water swelling gel fluidity (g / 5 minutes).
[Amount of dissolved polymer in wastewater]
2000 g of ion-exchanged water is weighed in a 3 L beaker, and while stirring at 1000 r / min with a two-stage paddle blade attached to a stirrer, 2.0 g of water-absorbent resin is dispersed so as not to generate mamaco for 3 hours. Stir. The contents of the beaker are filtered through a standard sieve having a mesh size of 75 μm, 50 g of the obtained filtrate is weighed in a pre-constantized 100 mL beaker, and dried in a hot air dryer at 140 ° C. until the constant volume is reached. The mass We (g) of the solid content in the filtrate is measured.
On the other hand, the same operation as described above is performed without using a water-absorbent resin, the mass Wf (g) of the solid content in the filtrate is measured, and the amount of the dissolved polymer in the wastewater is obtained from the following formula.
Amount of dissolved polymer in wastewater (ppm) = (We-Wf) / 50 × 1000000 The water-absorbent resin according to claim 13, which has a pure water absorption capacity of 857 g / g or more.

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