JP2011092930A - Water absorbent and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water absorbent which is high in the water absorbency under load (AAP) and in water absorption speed (Vortex) under a pressure and has antiblock properties when it absorbs moisture; and to provide a water absorbent which is high in the water absorbency under load (AAP) and in water absorption speed (Vortex) under a pressure and contains a prescribed amount of water (preferably 0.01-20 wt.%). <P>SOLUTION: In a method for producing the water absorbent, water-absorbable resin particles are mixed with a water dispersing material which contains a metallic soap and a dispersion stabilizer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a water-absorbing agent suitably used for sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, and a method for producing the same.

  For sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads, absorbents comprising hydrophilic fibers such as pulp and water-absorbing resin are widely used for the purpose of absorbing body fluids.

  In recent years, these sanitary materials have become highly functional and thin, and the amount of water-absorbing resin used per sanitary material and the ratio of water-absorbing resin to the entire absorbent body composed of water-absorbing resin and hydrophilic fibers have increased. Tend to. In other words, by reducing the number of hydrophilic fibers with a small bulk specific gravity, and using many water absorbent resins with excellent water absorption and a large bulk specific gravity, the ratio of the water absorbent resin in the absorbent body can be increased and the amount of water absorbed can be reduced. The sanitary material is made thinner.

  Therefore, when manufacturing various water-absorbing articles such as disposable diapers using a water-absorbing resin, it is necessary to incorporate a large amount of water-absorbing resin with high hygroscopicity into the fiber base material, its working environment, Depending on the climatic conditions, the problem that the resin particles cannot be stably manufactured due to blocking between the poppers and the line or adhering to the apparatus has been increasing.

  As a means for obtaining a water-absorbing agent having excellent fluidity at the time of moisture absorption, techniques for adding an inorganic substance such as amorphous silicon dioxide or kaolin to a water-absorbing resin are known (Patent Documents 1 to 4). However, the techniques described in Patent Documents 1 to 4 have a problem that the water absorption capacity of the water-absorbing agent is reduced.

  In addition, techniques for coating the surface of the water-absorbent resin with polysiloxane, specific surfactants, and the like have also been proposed (Patent Documents 5 to 8), but these also make the water-absorbent resin excessively hydrophobic or have a surface tension. And the amount of return (Re-Wet) in the diaper is increased.

  As a means for obtaining a water-absorbing agent having excellent fluidity at the time of moisture absorption (blocking resistance) without reducing the water absorption capacity under pressure, a technique of adding a water-absorbing resin and a metal soap by dry blending is known ( Patent Documents 9 and 10).

  However, the technique described in Patent Document 9 has a problem that the water absorption rate of the water-absorbing agent decreases because the metal soap is hydrophobic. For this reason, the absorbent article using the water-absorbing agent described in Patent Document 9 cannot exhibit sufficient water-absorbing performance. Furthermore, since the metal soap is handled in the form of powder, there are problems in health and safety, such as a high work environment deterioration due to the dust and a high possibility of dust explosion.

  In addition, Patent Documents 11 and 12 propose surface cross-linking agents with excellent fluidity during moisture absorption, but there are aspects that are insufficient for obtaining recent high physical properties (for example, high water absorption capacity under pressure). It was.

  Furthermore, a technique using a surfactant or a lubricant (Patent Document 13) is also known in addition to controlling the particle size of the water-absorbent resin narrowly, but the yield and productivity are reduced by controlling the particle size. There was a problem.

  In addition to the fluidity at the time of moisture absorption (blocking resistance) described in Patent Documents 1 to 13, the water-absorbent resin after surface crosslinking generally has a low water content and has problems such as impact stability as particles. It was. Therefore, a technique for adding about several percent of water to the water-absorbent resin after surface crosslinking (Patent Documents 14 to 16) has been proposed for impact resistance stability and dust prevention. The addition of (for example, an inorganic salt) has a problem that the properties of the water-absorbent resin (for example, water absorption capacity under pressure) are reduced.

JP 59-80459 A JP 2000-093792 A JP 2001-137704 A International Publication No. 2000/010619 Pamphlet International Publication No. 95/033558 Pamphlet JP2003-082250A International Publication No. 2002/034384 Pamphlet WO97 / 37695 pamphlet Japanese Patent Application Laid-Open No. 2004-261796 JP 61-51658 A JP-A-6-220227 JP-A-8-027278 International Publication No. 2005/077500 Pamphlet Special table hei 2003-511489 Special table hei 2001-523287 JP-A-9-124879

  The problem to be solved by the present invention is to provide a water-absorbing agent excellent in water absorption rate, fluidity at the time of moisture absorption, and water absorption magnification under pressure, and a method for producing the same, with respect to Patent Documents 1 to 13. . Another object of the present invention is to provide a water-absorbing agent containing a certain amount of water with respect to Patent Documents 14 to 16 and having improved physical properties and a method for producing the same. Furthermore, it is providing the method of manufacturing a water absorbing agent easily and efficiently, without accompanying the deterioration of the working environment by dust and generation | occurrence | production of dust explosion.

  The present inventor has intensively studied to solve the above problems. As a result, the present inventors have found that the above-mentioned problems can be solved by adding an aqueous dispersion containing metal soap and a dispersion stabilizer to the water-absorbent resin particles, and completed the present invention.

  The method for producing a particulate water-absorbing agent according to the present invention is characterized in that an aqueous dispersion containing metal soap and a dispersion stabilizer is mixed with water-absorbing resin particles.

  The particulate water-absorbing agent according to the present invention includes water-absorbing resin particles, metal soap, water, and a dispersion stabilizer.

  ADVANTAGE OF THE INVENTION According to this invention, the water absorbing agent which is excellent in the water absorption speed | rate, is excellent in the fluidity | liquidity at the time of moisture absorption, and the water absorption magnification under pressure, and its manufacturing method can be provided. In addition, a water-absorbing agent having high physical properties containing a certain amount of water can be provided.

  In addition, the method of the present invention handles the metal soap in the form of an aqueous dispersion, so there is no concern about dust generation and the like, which is extremely suitable in terms of safety and hygiene.

  Hereinafter, the present invention will be described in detail. However, the scope of the present invention is not restricted by these descriptions, and modifications other than the following examples can be made as appropriate without departing from the spirit of the present invention.

  In the present specification, unless otherwise specified, “mass” and “weight” are synonymous, and “X to Y” indicating a range means “X or more and Y or less”. “Acid (salt)” means “acid and / or salt thereof”, and “(meth) acryl” means “acryl and / or methacryl”.

(1) Water-absorbing resin The water-absorbing resin according to the present invention is a crosslinkable polymer having water swellability and water insolubility that can form a hydrogel. Here, the water swellability means that an aqueous solution having a weight of 5 times or more, preferably 50 to 1000 times the weight of the water absorbent resin particle itself is absorbed by immersing the water absorbent resin particles in ion-exchanged water. Refers to things. Water-insoluble means that the substantially uncrosslinked water-soluble component (water-soluble polymer) in the water-absorbent resin particles is usually 0 to 50% by mass, preferably 0 to 30% by mass, more The content is preferably 0 to 25% by mass, and particularly preferably 0 to 15% by mass, and most preferably 0 to 10% by mass. The measuring method of content of the said water-soluble component is prescribed | regulated by the below-mentioned Example.

  The crosslinkable polymer is a polymer having a cross-linked structure (hereinafter referred to as internal cross-linked structure) inside a polymer obtained by polymerizing an unsaturated monomer in order to obtain good absorption characteristics. Say. Furthermore, the water-absorbent resin particles may be subjected to a surface cross-linking treatment that forms a cross-linked structure on the surface of the water-absorbent resin particles, or may not be subjected to the surface cross-linking treatment. Among these, in order to obtain excellent absorption characteristics, it is preferable that a surface crosslinking treatment is performed. In the following, water absorbent resin particles that have not been subjected to surface cross-linking treatment may be referred to as a water absorbent resin precursor.

  Examples of the water-absorbent resin particles composed of the above-mentioned cross-linkable polymer include polyacrylic acid (salt) cross-linked polymer, starch-acrylonitrile graft polymer hydrolyzate, starch-acrylic acid graft polymer, vinyl acetate-acrylic. Among acid ester copolymer saponified products, acrylonitrile copolymer or acrylamide copolymer hydrolyzate or cross-linked products thereof, carboxyl group-containing cross-linked polyvinyl alcohol modified product, cross-linked isobutylene-maleic anhydride copolymer, etc. 1 type or 2 or more types can be mentioned. Among these, it is preferable to use the polyacrylic acid (salt) crosslinked polymer from the viewpoint of physical properties.

  The water-absorbent resin particles composed of the above-mentioned crosslinkable polymer are obtained by polymerizing and crosslinking an unsaturated monomer, and are subjected to surface crosslinking treatment as necessary. Hereinafter, an unsaturated monomer, a crosslinkable monomer, a polymerization initiator, and a method for producing the unsaturated monomer (polymerization method, drying treatment, surface crosslinking treatment) used for producing the water-absorbent resin particles will be described.

(2) Water-absorbing agent The water-absorbing agent means an aqueous liquid gelling agent mainly composed of a water-absorbing resin. The aqueous liquid is not limited to water, but may be urine, blood, feces, waste liquid, moisture or steam, ice, a mixture of water and an organic solvent and / or an inorganic solvent, rainwater, groundwater, etc. If water is included, there is no particular limitation. Among them, as the aqueous liquid, urine, particularly human urine can be mentioned more preferably.

  The content of the water absorbent resin according to the present invention is preferably 70 to 99.9% by weight, more preferably 80 to 99.7% by weight, and still more preferably 90%, based on the entire weight of the water absorbent. ˜99.5% by weight. As other components other than the water-absorbent resin, a metal soap described later, a dispersion stabilizer, and water are included.

(3) Particles The water-absorbing agent and the water-absorbing resin are particulate. The particle refers to a powder having fluidity, and is preferably a powder in which a flow rate (ERT450.2-02) can be measured or a powder that can be classified by (ERT420.2-02). The preferred water content and particle size are in the ranges described below, but are not particularly limited.

(4) Unsaturated monomer As the unsaturated monomer used to obtain the water-absorbing resin particles contained in the water-absorbing agent of the present invention, a monomer capable of obtaining a desired crosslinkable polymer is used. That's fine.

  For example, when the crosslinkable polymer is a polyacrylic acid (salt) cross-linked polymer, or a partially neutralized cross-linked polymer, acrylic acid and / or a salt thereof (neutralized product) is used as the unsaturated monomer. ) May be used as a main component, and together with the acrylic acid and / or salt thereof, other unsaturated monomers other than acrylic acid and / or salt thereof may be used as a copolymerization component. As a result, in addition to the water absorption property, other properties such as antibacterial and deodorizing can be imparted to the finally obtained water absorbent resin particles, and the water absorbent resin particles can be obtained at a lower cost. .

  Examples of the other unsaturated monomers include methacrylic acid, (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, vinyl sulfonic acid, 2- (meth) acrylamido-2-methylpropane sulfonic acid, ( (Meth) acryloxyalkanesulfonic acid and its alkali metal salts, ammonium salts, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) Water-soluble or hydrophobic unsaturated monomers such as acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, isobutylene, lauryl (meth) acrylate, etc. be able to.

  When an unsaturated monomer containing an acid group is used as the unsaturated monomer and the other unsaturated monomer, the salt of the unsaturated monomer may be an alkali metal salt, an alkaline earth salt. Similar metal salts and ammonium salts may be used. Among these, it is preferable to use a sodium salt or a potassium salt from the viewpoint of the performance of the water-absorbing resin particles obtained, industrial availability of unsaturated monomer salts, safety, and the like.

  When the other unsaturated monomer is used in combination, it is preferably 0 to 30 mol%, more preferably based on the total number of moles of all unsaturated monomers used to obtain water-absorbing resin particles. It is good to use in the ratio of 0-10 mol%, most preferably 0-5 mol%. In other words, with respect to the total number of moles of all unsaturated monomers used to obtain the water-absorbent resin particles, the total number of moles of acrylic acid and its salt as the main component is 70 to 100 mol%, Preferably it is 90-100 mol%, More preferably, it may be 95-100 mol%.

  Moreover, when the said crosslinkable polymer is a polyacrylic acid (salt) crosslinked polymer, the structural unit of this polyacrylic acid partial neutralized material polymer is 0-50 mol% of acrylic acid, and acrylates 100-50. It is preferably in the range of mol% (however, the sum of both is 100 mol% or less), more preferably in the range of 10 to 40 mol% acrylic acid and 90 to 60 mol% acrylate. In other words, the neutralization rate, which is the molar ratio of acrylate to the total amount of acrylic acid and acrylate, is preferably 50 to 100 mol%, and more preferably 60 to 90 mol%.

  In order to form the above-mentioned salt of acrylic acid, neutralize acrylic acid in the monomer state before polymerization of the monomer, neutralize in the polymer state during polymerization or after polymerization, or these It is sufficient to perform the above operations together. Moreover, you may form the salt of acrylic acid by mixing acrylic acid and acrylate.

(5) Crosslinkable monomer (internal crosslinking agent)
The water-absorbent resin particles according to the present invention are crosslinkable polymers having an internal cross-linked structure, and if the water-absorbent resin particles have water insolubility and water swellability, they are considered to have an internal cross-linked structure. be able to. Therefore, the internal cross-linking structure of the water-absorbent resin particles may be obtained by self-crosslinking of an unsaturated monomer without using a cross-linking monomer that is an internal cross-linking agent. Those obtained by copolymerizing or reacting an unsaturated monomer and a crosslinking monomer are preferred. Here, the cross-linking monomer as an internal cross-linking agent has two or more polymerizable unsaturated groups or two or more reactive groups in one molecule.

  Examples of the internal cross-linking agent include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylolpropane tri (meth) acrylate. , Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol 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 Le, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylenimine, and glycidyl (meth) acrylate.

  The said internal crosslinking agent may be used independently, and may mix and use 2 or more types suitably. Moreover, the said internal crosslinking agent may be added to a reaction system all at once, and may be divided and added. When using one or two or more types of internal cross-linking agents, a cross-linking monomer having two or more polymerizable unsaturated groups is used in consideration of the absorption characteristics of the water-absorbing agent finally obtained. It is preferable to always use at the time of polymerization.

  From the viewpoint of obtaining good physical properties of the water-absorbent resin particles, the amount of the internal cross-linking agent used is preferably relative to the total number of moles of all unsaturated monomers used to obtain the water-absorbent resin particles as described above. Is 0.001 to 2 mol%, more preferably 0.005 to 0.5 mol%, still more preferably 0.01 to 0.2 mol%, and particularly preferably 0.03 to 0.3 mol%. It is in the range of 15 mol%. When the amount of the internal crosslinking agent used is less than 0.001 mol% or exceeds 2 mol%, it is not preferable because sufficient absorption characteristics of the water-absorbent resin particles may not be obtained. .

  When the internal cross-linking structure is introduced into the water-absorbent resin particles using the internal cross-linking agent, the internal cross-linking agent is used before or during the polymerization of the unsaturated monomer, after the polymerization, or after neutralization. It may be added to the reaction system later.

(6) Polymerization initiator When the unsaturated monomer is polymerized in order to obtain the water-absorbing resin particles according to the present invention, a polymerization initiator may be used. Examples of the polymerization initiator include potassium persulfate, ammonium persulfate, sodium persulfate, potassium peracetate, sodium peracetate, potassium percarbonate, sodium percarbonate, t-butyl hydroperoxide, hydrogen peroxide, 2, 2 A radical polymerization initiator such as' -azobis (2-amidinopropane) dihydrochloride or a photopolymerization initiator such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one can be used.

  The amount of the polymerization initiator used is usually 0.001 to 2 mol%, preferably 0.01 to 0.00%, based on the total number of moles of all unsaturated monomers used to obtain water-absorbing resin particles. It is preferably 1 mol%. If the polymerization initiator is less than 0.001 mol%, the amount of unreacted residual monomer increases, and if it exceeds 2 mol%, it is difficult to control the polymerization.

(7) Production method of water-absorbent resin particles (polymerization method)
In the polymerization of each of the above-mentioned monomers (unsaturated monomer, other unsaturated monomer, crosslinkable polymer, etc.) to obtain the water-absorbent resin particles in the present invention, bulk polymerization or precipitation polymerization is performed. However, from the viewpoint of the performance of the water-absorbent resin particles, the ease of control of the polymerization, and the absorption characteristics of the swollen gel, aqueous solution polymerization or reverse phase suspension by using the above monomer as an aqueous solution. Polymerization is preferably performed.

  When each of the above monomers is an aqueous solution, the concentration of the monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) depends on the temperature of the aqueous solution and the type of monomer, and is particularly limited However, it is preferably in the range of 10 to 70% by mass, and more preferably in the range of 20 to 60% by mass.

  When the polymerization of the above monomer is started, it is started using the aforementioned polymerization initiator. In addition to the above polymerization initiator, it may be carried out by irradiation with active energy rays such as ultraviolet rays, electron beams, and γ rays, and the irradiation of active energy rays and the use of a polymerization initiator may be used in combination. .

  In addition, what is necessary is just to select suitably the reaction temperature in the said polymerization reaction according to the kind of polymerization initiator to be used, The inside of the range of 15-130 degreeC is preferable, and the inside of the range of 20-120 degreeC is more preferable. If the temperature at the start of polymerization is out of the above range, there is a risk that the water-absorbing performance of the water-absorbent resin particles may decrease due to an increase in the residual monomer of the obtained water-absorbent resin particles or an excessive self-crosslinking reaction. Therefore, it is not preferable.

  The reverse phase suspension polymerization is a polymerization method in which the aqueous monomer solution is suspended in a hydrophobic organic solvent. The reverse phase suspension polymerization is described in, for example, documents such as US Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735.

  The aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. Examples of the aqueous solution polymerization include U.S. Pat. Nos. 462501, 4883299, 4286082, 497632, 4985518, 5124416, 5250640, 5264495, 5145906, and 5380808. It is described in literatures and documents such as European Patent Nos. 081636, 0955506, and 0922717. In addition, when performing the said aqueous solution polymerization, you may use together solvents other than water as needed, and the kind of solvent used together is not specifically limited.

  Therefore, the water-absorbent resin particles according to the present invention can be obtained by using the above-exemplified monomers and polymerization initiators in the polymerization methods described in the above-mentioned documents.

(Drying process)
Since the polymer obtained by polymerizing the monomer by the above polymerization method is usually a hydrogel crosslinkable polymer, the hydrogel crosslinkable polymer is dried as necessary. In particular, when aqueous solution polymerization is performed, a pulverization treatment is usually performed before and / or after drying the water-containing gel-like crosslinkable polymer.

  When hot air drying is performed in the above drying treatment, drying is usually performed with hot air in a temperature range of 60 ° C to 250 ° C, preferably 100 ° C to 220 ° C, more preferably 120 ° C to 200 ° C. In addition, the drying time depends on the surface area and moisture content of the water-containing gel-like crosslinkable polymer and the type of the dryer, so that, for example, within a range of 1 minute to 5 hours, etc. What is necessary is just to select suitably.

  Water content of water-absorbent resin particles obtained by performing the drying treatment as described above (specified by the amount of water contained in the water-absorbent resin particles / weight loss when 1 g of water-absorbent resin particles is dried at 180 ° C. for 3 hours) In order to obtain good physical properties of the water-absorbing agent of the present invention containing the water-absorbent resin particles as a main component, the weight loss is expressed in a ratio to the mass of the water-absorbent resin particles before drying). For this, it is preferable to control the water content so that the powder exhibits fluidity even at room temperature. That is, the moisture content of the water-absorbing agent (specified by the amount of water contained in the water-absorbing agent / the weight loss when 1 g of the water-absorbing agent is dried at 180 ° C. for 3 hours is measured, (Expressed as a ratio) is usually 0 to 30% by mass, more preferably 0 to 20% by mass, further preferably 0 to 15% by mass, more preferably 0.3 to 15% by mass, particularly preferably 0.5. -10 mass%. Therefore, the water-containing gel-like crosslinkable polymer may be dried to obtain water-absorbing resin particles so that a water-absorbing agent having a water content within the above range can be obtained.

  In addition, when the polymerization method based on the above-described reverse phase suspension polymerization is used, the water-containing gel-like crosslinkable polymer obtained after the completion of the polymerization reaction may be dried by the following procedure without being particularly pulverized. That is, for example, a hydrated gel-like crosslinkable polymer is dispersed in a hydrocarbon-based organic solvent such as hexane and azeotropically dehydrated, and the water content of the hydrated gel-like crosslinkable polymer is 40% by mass or less, preferably 30% by mass or less. Thereafter, the organic solvent and the water-containing gel-like crosslinkable polymer are separated by decantation or evaporation to obtain the water-absorbent resin particles according to the present invention. In addition, you may further dry-process the water absorbing resin particle isolate | separated from the organic solvent as needed.

  The said drying process will not be specifically limited if it is a method which can be made into the target moisture content, A various method is employable. Specifically, heat drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, dehydration by azeotropy with a hydrophobic organic solvent, high-humidity drying using high-temperature steam may be used.

(Surface cross-linking treatment)
As described above, the cross-linking polymerization and the drying treatment are performed and pulverized as necessary to obtain the water-absorbent resin particles according to the present invention. Further, it is preferable to improve various properties of the water-absorbent resin particles by increasing the cross-linking density in the vicinity of the surface by subjecting the surface of the water-absorbent resin particles to a crosslinking (secondary crosslinking) treatment.

  Hereinafter, the water-absorbing resin particles before surface crosslinking are referred to as a water-absorbing resin precursor and are distinguished from surface-crosslinked water-absorbing resin particles. The water absorbent resin particles according to the present invention refer to water absorbent resin precursors and / or surface crosslinked water absorbent resin particles.

  As the surface cross-linking agent used in the surface cross-linking treatment, various materials can be exemplified. In order to improve the properties of the water-absorbent resin particles obtained, polyhydric alcohol compounds, epoxy compounds, One or more of polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, oxazoline compounds, monooxazolidinone compounds, dioxazolidinone compounds, polyoxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds may be used. preferable.

  More specifically, a surface cross-linking agent exemplified in US Pat. Nos. 6,228,930, 6,071,976 and 6,254,990 may be used. That is, monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene Glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexane Polyhydric alcohol compounds such as dimethanol; Epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; Ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pen Polyvalent amine compounds such as ethylenehexamine, polyethyleneimine, polyamide polyamine; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin; condensates of the polyvalent amine compounds and the haloepoxy compounds An oxazolidinone compound such as 2-oxazolidinone; an alkylene carbonate compound such as ethylene carbonate;

  Further, in addition to the above-described covalent bond surface cross-linking agent, an ion bond surface cross-linking agent, a polyvalent metal salt or a polyamine polymer may be used. Moreover, you may improve liquid permeability etc. using an inorganic surface crosslinking agent other than the said organic surface crosslinking agent.

  Examples of the inorganic surface crosslinking agent used include divalent or higher, preferably trivalent or tetravalent polyvalent metal salts (organic salts or inorganic salts) or hydroxides. Examples of the polyvalent metal that can be used include aluminum and zirconium, and examples thereof include aluminum lactate and aluminum sulfate. These inorganic surface crosslinks are used simultaneously or separately with the organic surface crosslinker.

  Surface cross-linking with a polyvalent metal is disclosed in International Publication No. 2007/121037, International Publication No. 2008/09843, International Publication No. 2008/09842, US Pat. Nos. 7,157,141, 6,605,673, and 6,620,889. 2005-0288182, 2005-0070671, 2007-0106013, and 2006-0073969.

  In addition to the organic surface crosslinking agent, polyamine polymers, particularly those having a weight average molecular weight of about 5,000 to 1,000,000 may be used simultaneously or separately to improve liquid permeability. Examples of the polyamine polymer used include US Pat. No. 7098284, WO 2006/082188, WO 2006/082189, WO 2006/082197, WO 2006/111402, Illustrated in International Publication No. 2006/111403 pamphlet, International Publication No. 2006/111404 pamphlet and the like.

  Among these surface cross-linking agents, in order to make the various characteristics of the water-absorbent resin particles as good as possible, they are selected from the group consisting of a covalent surface cross-linking agent, and further an oxazolidinone compound, an alkylene carbonate and a polyhydric alcohol. It is preferable to use a dehydration-reactive surface crosslinking agent, and it is more preferable to use at least a polyhydric alcohol. As the polyhydric alcohol, it is preferable to use a polyhydric alcohol having 2 to 10 carbon atoms, preferably 3 to 8 carbon atoms.

  The amount of the surface cross-linking agent used depends on the type of surface cross-linking agent used, the combination of the water-absorbing resin precursor and the surface cross-linking agent, etc. Is preferably in the range of 0.001 to 10 parts by mass, and more preferably in the range of 0.01 to 5 parts by mass.

  In the surface crosslinking treatment, it is preferable to use water together with the surface crosslinking agent. The amount of water used at this time depends on the water content of the water-absorbing resin precursor to be used, but is usually 0.5 to 20 parts by mass, preferably 0 to 100 parts by mass of the water-absorbing resin precursor. It is preferable to use water in the range of 5 to 10 parts by mass.

  When mixing the surface cross-linking agent or its aqueous solution, a hydrophilic organic solvent or a third substance may be used as a mixing aid.

  When a hydrophilic organic solvent is used, for example, lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and t-butyl alcohol; ketones such as acetone; Ethers such as dioxane, tetrahydrofuran and methoxy (poly) ethylene glycol; Amides such as ε-caprolactam and N, N-dimethylformamide; Sulphoxides such as dimethyl sulfoxide; Ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetra Ethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene Glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexane Examples include dimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymers, polyhydric alcohols such as pentaerythritol and sorbitol. Polyhydric alcohols are classified as surface cross-linking agents when they react with the water-absorbing resin, and are classified as hydrophilic organic solvents when they do not react. The presence or absence of the reaction can be easily discriminated by increasing the remaining amount of polyhydric alcohol or ester (IR analysis or the like).

  The amount of the hydrophilic organic solvent used is preferably 10 parts by mass or less with respect to 100 parts by mass of the solid content of the water-absorbent resin particles, although it depends on the type, particle size, water content and the like of the water-absorbent resin particles. A range of 1 part by mass to 5 parts by mass is more preferable. In addition, inorganic acids, organic acids, polyamino acids and the like shown in European Patent No. 0668080 may be present as the third substance. These mixing aids may act as a surface cross-linking agent, but those that do not deteriorate the water absorption performance of the water-absorbent resin particles after the surface cross-linking are preferable. In particular, volatile alcohols having a boiling point of less than 150 ° C. are volatilized during the surface cross-linking treatment, and therefore it is desirable that no residue remains.

  In order to mix the water absorbent resin precursor and the surface cross-linking agent more uniformly, non-crosslinkable water-soluble inorganic bases (preferably alkali metal salts, ammonium salts, alkali metal hydroxides, and ammonia or water thereof) Oxide) and non-reducing alkali metal salt pH buffer (preferably bicarbonate, dihydrogen phosphate, hydrogen phosphate, etc.), when mixing the water-absorbent resin precursor and the surface cross-linking agent. You may coexist. The amount of these used depends on the type and particle size of the water absorbent resin precursor, but is preferably in the range of 0.005 to 10 parts by mass with respect to 100 parts by mass of the solid content of the water absorbent resin precursor. More preferably within the range of 0.05 to 5 parts by mass.

  The surface cross-linking agent can be added by various methods, and the surface cross-linking agent is mixed with water and / or a hydrophilic organic solvent in advance as necessary and added dropwise to the water absorbent resin precursor. A method is preferred, and a spraying method is more preferred. The droplets to be sprayed have an average droplet diameter of preferably 0.1 to 300 μm, and more preferably 1 to 200 μm.

  The mixing device used when mixing the water-absorbing resin precursor, the surface cross-linking agent, water and the hydrophilic organic solvent has a large mixing force in order to mix these compounds uniformly and reliably. It is preferable. Examples of such a mixing apparatus include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a double-arm kneader, Pulverization type kneaders, rotary mixers, airflow type mixers, turbulizers, batch-type Redige mixers, continuous-type Redige mixers, and the like are preferably used.

  After the surface cross-linking agent and the water absorbent resin precursor are mixed, heat treatment is preferably performed. As conditions for performing the above heat treatment, the temperature of the water absorbent resin precursor or the temperature of the heat medium used for the heat treatment is preferably 100 to 250 ° C, more preferably 150 to 250 ° C, still more preferably 170. It is good that it is -210 degreeC. Moreover, the heating time of the heat treatment is preferably in the range of 1 minute to 2 hours. Preferable examples of the combination of the heating temperature and the heating time include 0.1 to 1.5 hours at 180 ° C. and 0.1 to 1 hour at 200 ° C.

  In these surface crosslinks, especially dehydration reactive surface crosslinkers and high temperature surface crosslinks (for example, 150 to 250 ° C.), the water-absorbing resin obtained has high physical properties, but its water content is 0 to 5%, 0 to 3%. 0 to 1%. Such a water-absorbing resin having a low water content has a problem of impact resistance stability, and a technique (Patent Documents 13 to 16) of adding about several percent of water to the water-absorbing resin after surface crosslinking has been proposed. In addition, there has been a problem that the physical properties (for example, water absorption capacity under pressure) of the water-absorbent resin are reduced by the addition of the auxiliary agent (for example, inorganic salt). In the present invention, water can be suitably used to add water to a surface-crosslinked water-absorbent resin having a low water content (0 to 5% by weight, 0 to 3% by weight, 0 to 1% by weight).

  When the water-absorbing resin precursor is obtained by reverse phase suspension polymerization, for example, during the azeotropic dehydration after the completion of polymerization and / or after the completion of the azeotropic dehydration, for example, the water content of the hydrogel crosslinked polymer When the surface cross-linking agent is dispersed in the hydrophobic organic solvent used in the reverse phase suspension polymerization, the surface is reduced to 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less. Crosslinked water-absorbing resin particles can be obtained.

(8) The particle size of the water-absorbent resin before and after surface crosslinking and the particle size of the water-absorbing agent As described above, the water-absorbent resin particles according to the present invention, which are subjected to surface crosslinking treatment as necessary, In order to secure fluidity at the time of moisture absorption and suppress deterioration of water absorption performance by mechanical impact force and fluidity at the time of moisture absorption, it is adjusted to a specific particle size. Specifically, the water-absorbing resin particles according to the present invention are 90 to 100 water-absorbing resin particles having a particle diameter of less than 850 μm and 106 μm or less with respect to 100% by mass of all the water-absorbing resin particles contained in the water-absorbing agent. The water-absorbent resin particles having a particle diameter of 300 μm or more are 60% by mass or more. Among these, Preferably, the water-absorbent resin particles having a particle diameter of less than 850 μm and 106 μm or more are 95 to 100% by mass, particularly 98 to It is preferable that it is 100 mass%. Further, the water-absorbing resin particles having a particle diameter of 300 μm or more are preferably 65 to 100% by mass, and 70 to 100% by mass with respect to 100% by mass of all the water-absorbing resin particles contained in the water-absorbing agent. Is more preferable, and 75 to 100% by mass is particularly preferable.

  The mass (weight) average particle diameter of the water-absorbent resin particles is preferably 200 to 700 μm, more preferably 300 to 600 μm, and particularly preferably 400 to 500 μm. Further, regarding the particle size distribution of the water-absorbent resin particles, the logarithmic standard deviation (σζ value) serving as an index of uniformity is preferably 0 to 0.40, more preferably 0 to 0.35, and most preferably. Is 0 to 0.30.

  When the water-absorbing resin particles having a particle diameter of 850 μm or more exceed 10% by mass with respect to 100% by mass of all the water-absorbing resin particles contained in the water-absorbing agent, a foreign material sensation occurs when a sanitary material such as a diaper is produced. The user feels uncomfortable and the user feels uncomfortable. Further, when the water-absorbing resin particles having a particle diameter of less than 106 μm exceed 10% by mass with respect to 100% by mass of all the water-absorbing resin particles contained in the water-absorbing agent, or when the logarithmic standard deviation σζ exceeds 0.40 Includes a significant reduction in water absorption capacity under pressure, a decrease in fluidity during moisture absorption, a deterioration in the working environment due to the generation of dust during the production of hygienic materials such as water absorbent resin particles and diapers, and a wide particle size distribution. Many problems such as an increase in segregation due to the presence of this are undesirable.

(9) CRC of water-absorbent resin particles after surface crosslinking and CRC of water-absorbing agent
The water-absorbing resin particles used in the present invention have a centrifuge retention capacity (CRC) of preferably 10 (g / g) or more, more preferably 15 g / g or more, and further preferably 25 g / g or more. Yes, and particularly preferably 28 g / g or more. Although an upper limit is not specifically limited, Preferably it is 50 g / g or less, More preferably, it is 45 g / g or less, More preferably, it is 40 g / g or less. When the centrifuge retention capacity (CRC) is less than 10 g / g, the amount of absorption is too small and it is not suitable for the use of sanitary materials such as diapers. Moreover, when the centrifuge retention capacity (CRC) is larger than 50 g / g, there is a possibility that a water absorbing agent having an excellent liquid uptake rate into the absorber cannot be obtained when used in the absorber.

(10) AAP of water-absorbent resin particles after surface crosslinking and AAP of water-absorbing agent
The water-absorbent resin particles used in the present invention have a water absorption capacity under a pressure of 4.83 kPa (under load) of 15 g / g or more, preferably 18 g / g or more, more preferably 20 g / g or more, and still more preferably. It is 23 g / g or more, most preferably 25 g / g or more. Although an upper limit is not specifically limited, Preferably it is 30 g / g or less. When the absorption power (AAP) with respect to the pressure of 4.83 kPa is less than 15 g / g, when used in the absorber, the liquid returns when the pressure is applied to the absorber (commonly called Re-Wet, rewetting). There is a risk that a small amount of water-absorbing agent cannot be obtained.

  Such AAP can be obtained, for example, by surface-crosslinking water-absorbent resin particles having the above-mentioned particle size at a high temperature so as to control to a predetermined CRC value, but is not particularly limited.

(11) Metal Soap The metal soap used in the present invention is an organic acid polyvalent metal salt, having 7 or more carbon atoms in the molecule, and an alkali metal such as a fatty acid, petroleum acid, or polymer acid. Consists of metal salts other than salts.

  The organic acid constituting the organic acid polyvalent metal salt may be an organic substance that forms a salt with the polyvalent metal, and is preferably an organic carboxylic acid, an organic sulfonic acid, or an organic sulfinic acid. Particularly preferred is an organic carboxylic acid having a carboxyl group. The organic acid polyvalent metal salt has 7 or more carbon atoms, more preferably 7 to 20 carbon atoms, and still more preferably 12 to 20 carbon atoms.

  When an organic acid having less than 7 carbon atoms in the molecule is used as the organic acid, the solubility of the organic acid polyvalent metal salt in water increases, and when using a paper diaper or absorbent, the organic acid polyvalent This is not preferable because the metal salt may elute into an absorbing solution such as urine or blood. In addition, when an acid such as oxalic acid or citric acid having less than 7 carbon atoms in the molecule was used, it received a mechanical impact force because the polyvalent metal salt of these organic acids had high hardness. In such a case, there is also a problem that water absorption characteristics may be deteriorated. Furthermore, when oxalic acid is used, it is not preferable from the viewpoint of safety.

  The organic carboxylic acid is a saturated or unsaturated organic carboxylic acid or aromatic carboxylic acid, and may have a substituent other than the carboxylic acid, such as a hydroxyl group or a halogen. The organic carboxylic acid may be a polyvalent carboxylic acid having a plurality of carboxyl groups in one molecule, but is preferably a monocarboxylic acid.

  Specifically, examples of the organic carboxylic acid include long-chain or branched fatty acids such as caproic acid, octylic acid, octic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid; Examples include petroleum acids such as benzoic acid, myristic acid, naphthenic acid, naphthoic acid, and naphthoxyacetic acid; and polymer acids such as poly (meth) acrylic acid and polysulfonic acid. Of these, fatty acids such as caproic acid, octylic acid, octoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, stearic acid, bovine fatty acid and castor hardened fatty acid are preferred, caproic acid, octylic acid, decanoic acid , Fatty acids having no unsaturated bond in the molecule (long-chain saturated fatty acids) such as lauric acid, myristic acid, palmitic acid, stearic acid are more preferable, and the number of carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid Is most preferably a long-chain fatty acid (long-chain saturated fatty acid) having no unsaturated bond in the molecule of 12-20. The reason for this is that when a fatty acid having an unsaturated bond in the molecule is used, the water-absorbing agent may generate color or odor when subjected to heat or oxidation during storage.

  On the other hand, the metal salt constituting the organic acid polyvalent metal salt is not particularly limited as long as it is a metal salt other than an alkali metal salt such as an alkaline earth metal salt or a transition metal salt. Therefore, barium salts, calcium salts, magnesium salts, aluminum salts, and zinc salts are preferable, and among these, calcium salts, magnesium salts, zinc salts, and aluminum salts are more preferable.

  Therefore, specific examples of the organic acid polyvalent metal salt include, for example, calcium laurate, magnesium laurate, zinc laurate, aluminum laurate, calcium myristate, magnesium myristate, aluminum myristate, myristine. Examples include zinc acid salts, calcium palmitate, magnesium palmitate, aluminum palmitate, zinc palmitate, calcium stearate, magnesium stearate, zinc stearate, and aluminum stearate.

In addition, the organic acid polyvalent metal salt may partially be a hydroxide or the like, and more specifically represented by (organic acid) _x M ^{n +} (OH) _nx or the like. It may have a salt structure. Here, M ^{n +} represents an n-valent metal ion species, x represents an integer from 1 to n, and n represents an integer of 2 or more.

  Furthermore, the combination of the organic acid and the metal salt constituting the organic acid polyvalent metal salt is not particularly limited. Moreover, you may use the said organic acid polyvalent metal salt 1 type or in mixture of 2 or more types.

  The organic acid polyvalent metal salt is not limited to those in which all acid groups are converted to a salt, but the organic acid polyvalent metal salt contains a small amount of organic acid, or contains excess polyvalent metal. It may be what is. Among these, Preferably, the salt by which 90 mol% or more was neutralized among the total mole number of an acid group (carboxyl group), More preferably, the salt by which 95-105 mol% was neutralized, More preferably, 98- A salt neutralized by 102 mol%, particularly preferably a neutralized salt neutralized by 99 to 101 mol%, is preferably used.

  In the case where a polymer acid such as polyacrylic acid is used as the organic acid, 95 mol% or more of the total number of acid groups (carboxyl groups) of the polymer acid is a polyvalent metal. It is preferable that the acid salt is neutralized, more preferably 98 mol% or more, and even more preferably 99 mol% or more of acid groups. The molecular weight of the polymer acid used is usually 10,000 to 5,000,000, preferably 50,000 to 1,000,000 in terms of weight average molecular weight.

  The organic acid polyvalent metal salt is in the form of a powder, and the particle diameter is not particularly limited, but is usually preferably smaller than the mass average particle diameter of the water absorbent resin particles. Specifically, the particle diameter of the organic acid polyvalent metal salt contained in the water-absorbing agent of the present invention is more than 0 in median diameter and is 100 μm, preferably 0.01 to 50 μm, more preferably 0.01 to It is good that it is 10 μm. The median diameter is the particle diameter (cumulative average diameter) at which the cumulative curve becomes 50% when the cumulative curve is obtained with the total volume of one group of particles as 100%, and the organic acid polyvalent The metal salt can be dispersed in a solvent such as methanol and measured using a particle size distribution analyzer LS-920 (Horiba, Ltd.).

  Furthermore, the melting point of the organic acid polyvalent metal salt is preferably 20 ° C. or higher and 250 ° C. or lower, more preferably 40 ° C. or higher and 250 ° C. or lower, and further preferably 50 ° C. or higher and 250 ° C. or lower. Among these, it is particularly preferably 60 ° C or higher and 250 ° C or lower, more preferably 70 ° C or higher and 250 ° C or lower, and most preferably 80 ° C or higher and 250 ° C or lower. When the melting point of the organic acid polyvalent metal salt is 250 ° C. or higher, the adhesion of the organic acid polyvalent metal salt to the surface of the water-absorbent resin particles is reduced, and the organic acid that drops off from the water-absorbent resin particles There is a risk that the polyvalent metal salt increases. Moreover, when melting | fusing point is 20 degrees C or less, since the fluidity | liquidity of the water absorbing agent obtained falls and handleability falls, it is unpreferable.

  That is, when industrially handling a water-absorbing agent, generally, a hopper, a transportation line, a quantitative feeder, etc. for storing the water-absorbing agent and water-absorbing resin particles are heated and kept warm in order to prevent the water-absorbing agent from absorbing moisture. Techniques are used, and these are usually maintained (heated or kept warm) at 30-80 ° C.

  Conventionally, additives such as polyethylene glycol and surfactants used for improving powder characteristics when moisture is absorbed or having a moisture content of 0 to less than 20% by mass, particularly improving fluidity, generally have a low melting point or glass transition temperature. There are many things. For this reason, even when the water-absorbing agent has excellent fluidity at room temperature, the additive is melted by heating by a manufacturing apparatus, a transportation line, etc. during the production of a water-absorbing agent or a diaper. There was a problem that the fluidity as a powder was lowered, and the handleability was lowered. However, in the present invention, since the organic acid polyvalent metal salt having the above-mentioned melting point is used, the industrial handleability of the water-absorbing agent at the time of heating is not lowered.

  In addition, about melting | fusing point of the said organic acid polyvalent metal salt, you may actually measure, for example, using the value described in the Chemical Dictionary (edited by the Chemical Dictionary, the Kyoritsu Publishing Co., Ltd.) etc. Also good. For example, zinc stearate is 128-130 ° C, aluminum stearate is 103 ° C, calcium stearate is 180 ° C, and magnesium stearate is 200 ° C. Therefore, these organic acid polyvalent metal salts are preferably used since they have an optimum melting point when used as the water-absorbing agent of the present invention. Moreover, if the organic acid polyvalent metal salt to be used is appropriately selected, the melting point can be adjusted over a wide range. However, in actual use, it is preferable to select and use an organic acid polyvalent metal salt having a melting point equal to or higher than the temperature at which the water-absorbing agent of the present invention is used.

  Further, the organic acid polyvalent metal salt preferably has a solubility in deionized water at 25 ° C. that is hardly soluble or insoluble, for example, 0 g / L or more and 10 g / L or less with respect to 1000 mL of deionized water. More preferably, it is 0 g / L or more and 5 g / L or less, and more preferably 0 g / L or more and 2 g / L or less. If the solubility of the organic acid polyvalent metal salt exceeds 10 g / L, as described above, the organic acid polyvalent metal salt may be eluted in an absorbing solution such as urine or blood, such being undesirable.

(12) Dispersion stabilizer In the present invention, a dispersion stabilizer is used in order to stably disperse the metal soap in water without agglomeration. The dispersion stabilizer used in the present invention is not particularly limited as long as it is conventionally used for stably dispersing water-insoluble fine particles in water. Examples of the dispersion stabilizer used in the present invention include water-soluble polymers, hydrophilic organic solvents, and surfactants.

(13) Water-soluble polymer Examples of the water-soluble polymer used as a metal soap dispersion stabilizer in the present invention include polyvinyl alcohol, starch, (carboxy) methyl cellulose, hydroxyethyl cellulose, and polyacrylic acid (salt). It is done. Here, the water-soluble polymer used is one that dissolves in water (25 ° C.) at 1% by weight or more, more preferably 5% by weight or more, particularly 10% by weight or more, and the molecular weight is usually 500 to 50 million, preferably Is in the range of 1,000,000 to 5,000,000, more preferably 1 to 1,000,000.

(14) Hydrophilic Organic Solvent As the hydrophilic organic solvent used as a metal soap dispersion stabilizer in the present invention, a hydrophilic organic solvent that may be used in combination with the above-described surface cross-linking treatment may be mentioned. In particular, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, Glycerin, polyglycerol, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol, etc. Polyhydric alcohols, in particular, polyhydric alcohols having 2 to 10 carbon atoms, more preferably 3 to 8 carbon atoms, are preferred. In these polyhydric alcohols, some of the hydroxyl groups are alkoxylated (for example, methoxypolyethylene glycol). It's okay. Among these polyhydric alcohols, ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, hexanediol, glycerin, and trimethylolpropane are preferable. These may use only 1 type and may use 2 or more types together.

(15) Surfactant In the present invention, examples of the surfactant used as a metal soap dispersion stabilizer include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether. Such as polyoxyalkylene alkyl ether, polyoxyethylene octyl phenyl ether, polyoxyalkylene alkyl phenyl ether such as polyoxyethylene nonyl phenyl ether, polyoxyalkylene alkylamino such as polyoxyethylene lauryl amino ether, polyoxyethylene stearyl amino ether Sorbitan such as ether, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate Fatty acid ester, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyalkylene sorbitan monooleate, polyoxyalkylene sorbitan monooleate, polyethylene glycol monolaurate, polyethylene Nonionics typified by glycerin fatty acid esters such as glycol monooleate, polyethylene glycol monostearate, polyethylene glycol dilaurate, polyethylene glycol distearate, polyalkylene glycol fatty acid esters, lauric acid monoglyceride, stearic acid monoglyceride, oleic acid monoglyceride Surfactant, polyoxyethylene lauryl ether sodium sulfate Sulfate, sodium polyoxyethylene octylphenyl ether sulfate, sodium polyoxyethylene nonylphenyl ether sulfate, triethanolamine lauryl sulfate, sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, alkylnaphthalene Sulfonates such as sodium sulfonate, sodium dialkylsulfosuccinate, anionic surfactants represented by phosphate esters such as potassium alkylphosphate, lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, Cationic field represented by quaternary ammonium salts such as stearyltrimethylammonium chloride Active agent, and the like, singly or 2 species selected from these can be used.

  Among these surfactants, it is preferable to use a nonionic surfactant or an anionic surfactant.

(16) Metal soap water dispersion In carrying out the present invention, metal soap is used as a water dispersion. As used herein, the aqueous dispersion is one in which metal soap is uniformly dispersed in water using the above dispersion stabilizer and has fluidity. As a preferred embodiment, an aqueous dispersion having an upper limit of viscosity of 10,000 cps (25 ° C.) and having a low viscosity is not a problem for the present invention, but can be used up to substantially the same viscosity as water. For example, a slurry, suspension, emulsified liquid, etc. are also included in the aqueous dispersion in the present invention. Further, when the metal soap is produced in the form of an aqueous dispersion, it can be used as it is without being dried, or it can be used after being concentrated or diluted to some extent.

  The concentration of the metal soap contained in the metal soap aqueous dispersion used in the present invention is preferably 1 to 90% by weight, more preferably 1 to 60% by weight, still more preferably 1 to 40% by weight, and The concentration of the dispersion stabilizer contained in the metal soap water dispersion is preferably more than 0 and not more than 10% by weight, more preferably more than 0 and not more than 5% by weight, still more preferably more than 0 and not more than 3% by weight.

  In the present invention, the preferred addition amount of the water-absorbent resin particles and metal soap, water, and dispersion stabilizer is 0.001 to 5 parts by weight of metal soap, more preferably 100 parts by weight of the water-absorbent resin particles. 0.005 to 4 parts by weight, water is 0.01 to 20 parts by weight, more preferably 0.05 to 15 parts by weight, and the dispersion stabilizer is 0.0001 to 1 part by weight, more preferably 0.0005 to 1 part by weight. Part. By adding the metal soap, water, and dispersion stabilizer to the water-absorbent resin particles, the problem of the present application is further solved.

  A surfactant is preferably used as the metal soap dispersion stabilizer. The method for producing an aqueous dispersion of metal soap using a surfactant as a dispersion stabilizer may be, for example, the methods described in JP-A-59-219400 and JP-B-4-7260. A commercially available dispersion such as zinc stearate N (manufactured by NOF Corporation) may be used as it is.

(17) Water absorbing agent (Method for producing water absorbing agent)
The water dispersion containing the water-absorbent resin particles, the metal soap and the dispersion stabilizer used when producing the water-absorbing agent of the present invention is as described above.

  In the method for producing a water absorbent according to the present invention, an aqueous dispersion containing a metal soap and a dispersion stabilizer is added to and mixed with the water absorbent resin particles.

  The water-absorbing resin particles contained in the water-absorbing agent of the present invention may be either a water-absorbing resin precursor that has not been subjected to surface crosslinking or a water-absorbing resin particle that has been subjected to surface crosslinking. Among these, when a surface-crosslinked water-absorbing resin is used in the production of the water-absorbing agent, after obtaining the water-absorbing resin precursor, the surface-crosslinking agent and the metal soap water dispersion are added to the water-absorbing resin precursor. May be mixed and added to obtain a surface-crosslinked water-absorbent resin, or after obtaining a surface-crosslinked water-absorbent resin, the surface-crosslinked water-absorbent resin and the metal soap water dispersion And may be mixed.

  The metal soap water dispersion to be added preferably contains the following amounts of water, a surfactant, and a dispersant (preferably a surfactant), and is a water-absorbing agent containing this range. The water-absorbent resin particles after the addition of the metal soap water dispersion or before the addition may be dried with water or a dispersant as needed, or may be separately added with water or a dispersant. The water and the dispersant (surfactant) added at the same time as the metal soap are contained and used in the water-absorbing agent within the following range.

  In addition, the aqueous dispersion containing metal soap and dispersion stabilizer used in the present invention contains, as other components, additives described below (for example, chelating agents, deodorants, anti-coloring agents, etc.) described below. The water absorbing agent may be further modified by dissolving or dispersing in the range. In addition, granulation and fine powder reduction (for example, less than 150 μm) may be performed by adding a metal soap water dispersion.

  In the case of granulation, it may be heated and crushed as necessary to classify it as necessary. In the case of granulation, the weight average particle diameter of the water-absorbing agent is preferably 1.01 to 10 times, more preferably 1.02 to 2 times, and particularly preferably 1 as compared with that before the addition of the metal soap water dispersion. 0.05 to 1.5 times. In addition, granulation refers to a state in which a plurality of water absorbent resin particles are bound on the surface.

  As the water absorbent resin particles used in the present invention, it is preferable to use surface-crosslinked water absorbent resin particles.

  The water-absorbing agent obtained by the present invention is a metal soap, preferably 0.001 to 5 parts by mass, more preferably 0.001 to 3 parts by mass, and still more preferably 0.01 to 100 parts by mass of the water-absorbing resin particles. -3 parts by mass and / or added. By including and / or adding metal soap, the moisture absorption fluidity is dramatically improved.

  The water-absorbing agent obtained by the present invention preferably contains and / or adds a dispersion stabilizer to the water-absorbing resin particles in an amount of 0.0001 to 1 part by mass, and more preferably 0.001 to 1 part by mass. Part. By including and / or adding a predetermined amount of the dispersion stabilizer, the water absorption speed is dramatically improved.

  The water-absorbing agent obtained by the present invention contains and / or adds water, preferably 0.01 to 20 parts by mass, more preferably 1 to 10 parts by mass, with respect to 100 parts by mass of the water-absorbing resin particles. By including and / or adding a predetermined amount of metal soap and water, impact resistance (for example, Patent Documents 14 to 16) is dramatically improved.

  In the present invention, an apparatus for adding an aqueous dispersion containing a metal soap and a dispersion stabilizer to the water-absorbent resin particles, and then mixing them is, for example, a cylindrical mixer, a screw-type mixer, a screw-type Extruder, Turbulizer, Nauta type mixer, V type mixer, Ribbon type mixer, Double arm kneader, Fluid type mixer, Airflow type mixer, Rotary disk type mixer, Roll mixer, Rolling type mixer Machine, Redige mixer and the like. As a mixing method, any of a batch type, a continuous type and a combination thereof can be adopted. Continuous mixing is more preferable from the viewpoint of industrial production. The number of rotations during mixing is not particularly limited, but a number of rotations that does not damage the water-absorbent resin particles is preferable. Specifically, the range of 1 to 3000 rpm is preferable, more preferably 2 to 500 rpm, and still more preferably 5 to 300 rpm. If it exceeds 3000 rpm, the water-absorbent resin particles are pulverized, which is not preferable in that the water absorption characteristics are deteriorated. On the other hand, if it is less than 1 rpm, the mixing property is not sufficient, and the intended effect of improving the hygroscopic fluidity cannot be obtained.

  Moreover, there is no restriction | limiting in particular as the powder temperature of the water absorbent resin particle before mixing the said solution, However, Room temperature-200 degreeC is preferable, More preferably, it is 50-200 degreeC, More preferably, it is 50-100 degreeC.

  In the present invention, the mixing time for mixing the water-absorbent resin particles and the metal soap water dispersion is not particularly limited, but is preferably 1 second to 20 minutes, more preferably 10 seconds to 10 minutes, still more preferably. Is 20 seconds to 5 minutes. Even if the mixing time exceeds 20 minutes, an effect commensurate with that cannot be obtained, and conversely, there is a possibility of causing powdering of the water-absorbent resin particles.

  Therefore, as mixing conditions for obtaining the water-absorbing agent of the present invention, it is most preferable that the powder temperature of the water-absorbent resin particles is 50 to 100 ° C., the rotation speed is 5 to 300 rpm, and the mixing time is 20 seconds to 5 minutes. . The mixed water-absorbing agent obtained under these conditions is excellent in handleability and does not cause problems such as adhesion and aggregation. Therefore, the drying process for improving the handleability of a subsequent water absorbing agent is not required.

  The water absorbent resin after mixing the metal soap dispersion may be heated or dried as necessary. By heating, the penetration of water into the water-absorbent resin is promoted, and the surface can be dried and rapidly formed into particles. Drying may be performed, or a predetermined amount (for example, the above-mentioned amount of water) of water may be left in the water absorbing agent as it is. By leaving a predetermined amount of water, it is possible to obtain a water-absorbing agent that suppresses electrification and has excellent impact resistance (abrasion resistance).

  The heating temperature is 30 to 250 ° C., further 50 to 150 ° C., particularly 60 to 100 ° C., and the time is also appropriately determined from 1 second to 3 hours, further 1 minute to 1 hour. If necessary, the water-absorbing agent that has been particulated by heating may be used as it is, and further, if necessary, pulverized, classified, or granulated.

(Other components contained in the water-absorbing agent)
In addition to the above-described components (water absorbent resin particles, organic acid polyvalent metal salt, internal cross-linking agent, polymerization initiator, surface cross-linking agent, etc.), the water-absorbing agent of the present invention is further provided with various performances. Alternatively, insoluble fine particles such as inorganic powder and a hydrophilic solvent such as water may be added to granulate the water-absorbing resin particles and the like.

  For example, specific examples of the inorganic powder include metal oxides such as silicon dioxide and titanium oxide, silicic acid (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay, bentonite and the like. Among these, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter measured by a Coulter counter method of 200 μm or less are preferable.

  The amount of the inorganic powder added depends on the combination of various components contained in the water-absorbing agent and the inorganic powder, but may be 0 to 6 parts by mass with respect to 100 parts by mass of the water-absorbent resin particles. More preferably, it is -5 mass parts, and it is especially preferable that it is 0.01-3 mass parts. If the amount of the inorganic powder exceeds the above range, the impact absorption capacity of the organic acid polyvalent metal salt may be exceeded, and it may be difficult to prevent deterioration of water absorption characteristics when subjected to impact force. is there.

  The mixing method of the water-absorbent resin particles and the inorganic powder is not particularly limited, and may be simultaneous with the metal soap water dispersion or separately. For example, a dry blend method, a wet mix method, or the like that mixes powders can be employed, but the dry blend method is more preferable.

  Further, the water-absorbing agent of the present invention may further include a deodorant, an antibacterial agent, a fragrance, a foaming agent, a pigment, a dye, a plasticizer, an adhesive, a surfactant, a fertilizer, an oxidizing agent, and a reducing agent, if necessary. , Water, salts, chelating agents, bactericides, hydrophilic polymers such as polyethylene glycol and polyethyleneimine, hydrophobic polymers such as paraffin, thermoplastic resins such as polyethylene and polypropylene, thermosetting resins such as polyester resins and urea resins A step of adding various additives to impart various functions, such as adding a resin or the like simultaneously or separately with the metal soap water dispersion, may be included. The addition amount of these additives should just be 0-30 mass parts with respect to 100 mass parts of water-absorbing resin particles, Preferably it is 0-10 mass parts, More preferably, it is 0-1 mass part. Good.

(18) Water absorption capacity under pressure of water-absorbing agent In the above production method, there is no significant change in physical properties due to the addition of metal soap. The water-absorbing agent of the present invention has a water absorption capacity under a pressure of 2.06 kPa and / or 4.83 kPa (under load) of 15 g / g or more, preferably 18 g / g or more, more preferably 20 g / g or more. More preferably, it is 23 g / g or more, and most preferably 25 g / g or more. Moreover, the upper limit of the water absorption capacity under pressure is not particularly limited and is preferably higher. However, the upper limit is 50 g / g or less, preferably 45 g / g or less, in view of balance with economics such as production costs.

  In addition, the water absorption under pressure under the load of 2.06 kPa and 4.83 kPa was used when the water-absorbing agent of the present invention was used as a sanitary material such as a disposable diaper and the infant was sleeping and sat This is because the load applied to the water absorbing agent is assumed in the state.

(19) Hygroscopic fluidity of the water-absorbing agent The water-absorbing fluidity of the water-absorbing agent of the present invention, which is the fluidity at the time of moisture absorption, refers to the flow as blocking, caking, or powder left at 25 ° C. and 90% RH. This is an evaluation of sex.

  In the water-absorbing agent of the present invention, the moisture absorption blocking rate used for evaluating the moisture absorption fluidity is 0% by mass to 10% by mass, preferably 0% by mass to 5% by mass, and more preferably 0%. The mass is 2% by mass or more.

  When the moisture absorption blocking ratio exceeds 10% by mass, the handling property of the water absorbing agent is poor under high humidity, and the water absorbing agent and / or the water absorbing resin is used in the production plant when producing a thin absorbent body for sanitary materials. There may be a problem that the particles are aggregated and clogged in the transport pipe, and that the particles cannot be uniformly mixed with the hydrophilic fiber.

(20) Particle size and CRC of water-absorbing agent
The particle size and centrifugal retention capacity (CRC) of the water-absorbing agent are preferably in the range of the water-absorbing resin particles described above. By setting the particle size or CRC, a suitable absorbent article can be provided. In the above production method, the addition of metal soap does not cause a large change in particle size or CRC, so that the water-absorbing agent having the above particle size can be obtained. In that case, classification or granulation may be performed as necessary.

(21) Absorber / Absorbent Article The water-absorbing agent of the present invention is used for water-absorbing purposes and is widely used as an absorber or absorbent article, particularly for the absorption of body fluids such as urine and blood. It is suitably used as a sanitary material. The absorbent body and absorbent article of the present invention comprise the water-absorbing agent of the present invention.

  Here, the absorber refers to an absorbent material molded mainly with water-absorbing resin particles and hydrophilic fibers. In the absorbent body, the content (core concentration) of the water-absorbing agent with respect to the total mass of the water-absorbing agent and the hydrophilic fiber is preferably 20 to 100% by mass, more preferably 30 to 100% by mass, and in particular. Preferably it is the range of 40-100 mass%. In the water-absorbing agent of the present invention, as the core concentration is higher, the effect of lowering the absorption characteristics of the water-absorbing agent at the time of producing an absorbent body, an absorbent article or the like becomes more prominent.

Moreover, the said absorbent article is equipped with the said absorber, the surface sheet which has liquid permeability, and the back sheet | seat which has liquid impermeability. For example, the absorbent article is prepared by first blending or sandwiching a fiber base material such as hydrophilic fiber and a water-absorbing agent to produce an absorbent body (absorbent core), and the absorbent core is a surface sheet having liquid permeability. And a back sheet having liquid impermeability. Then, if necessary, an absorbent article such as an adult paper diaper or a sanitary napkin can be obtained by installing an elastic member, a diffusion layer, an adhesive tape, and the like. In addition, at this time, the said absorption core is compression-molded in the range of density 0.06-0.50g / cm < ³ > and basic weight 0.01-0.20g / cm < ² >. Examples of the fiber substrate used include hydrophilic fibers such as pulverized wood pulp, cotton linters and cross-linked cellulose fibers, rayon, cotton, wool, acetate, and vinylon. These fiber substrates are preferably air-laid.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these. Moreover, all the electric equipments used in Examples and Comparative Examples were used under the conditions of 100 V and 60 Hz. Further, unless otherwise specified, it was used under the conditions of 25 ° C. ± 2 ° C. and relative humidity 50% RH.

  Various physical properties described in the claims and examples of the present invention were determined according to the following measuring methods. For convenience, “part by mass” may be simply referred to as “part”, “liter” may be simply referred to as “L”, and “mass%” may be referred to as “wt%”.

<Centrifuge retention capacity (CRC)>
The centrifuge retention capacity (CRC) indicates a water absorption capacity of 30 minutes under no pressure with respect to 0.90 mass% saline. Note that CRC is sometimes referred to as water absorption capacity without pressure.

  Water-absorbent resin particles or water-absorbing agent 0.200 g was uniformly put into a bag (85 mm × 60 mm) made of nonwoven fabric (Nangoku Pulp Industries Co., Ltd., trade name: Heatron paper, model: GSP-22), and heat-sealed. Then, it was immersed in 0.90 mass% salt solution (sodium chloride aqueous solution) of large excess (usually about 500 ml) at room temperature. After 30 minutes, the bag was pulled up and drained for 3 minutes with a centrifugal force (250 G) described in edana ABSORBENCY II 441.1-99 using a centrifuge (manufactured by Kokusan Co., Ltd., centrifuge: model H-122). After that, the mass W1 (g) of the bag was measured. Moreover, the same operation was performed without using a water absorbing agent, and the mass W0 (g) at that time was measured. The centrifuge retention capacity (CRC) (g / g) was calculated from these W1 and W0 according to the following formula.

Centrifuge retention capacity (CRC) (g / g)
= (W1 (g) -W0 (g)) / (mass of water-absorbing agent (g))-1
<Water absorption capacity under pressure (AAP 4.83 kPa)>
With reference to WO 2006/109844 pamphlet, 0.9 g of water-absorbing resin particles or water-absorbing agent is put into the measuring device, and the weight W3 (g) of the measuring device set is measured, and 0.9% sodium chloride aqueous solution The water absorption ratio under pressure (under load) of 4.83 kPa in 1 hour was measured. W4 (g) after 1 hour was measured, and the water absorption capacity under pressure (g / g) with respect to pressure was calculated from W3 and W4 according to the following formula.

AAP = (W4-W3) /0.9
<Amount of water-soluble component (water-soluble component)>
Weigh out 184.3 g of 0.90 mass% saline in a plastic container with a capacity of 250 ml, add 1.00 g of water-absorbing agent to the aqueous solution, and rotate and stir the stirrer for 16 hours to dissolve the soluble content in the resin. Extracted. Filtration of this extract using one sheet of filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) gave 50. 0 g was measured and used as a measurement solution.

  Next, only 0.90% by mass saline solution was titrated to pH 10 with a 0.1N aqueous NaOH solution, and then titrated to a pH 2.7 with a 0.1N aqueous HCl solution ([bNaOH ], [BHCl] ml).

  The titration ([NaOH] ml, [HCl] ml) was determined by performing the same titration operation on the measurement solution.

  For example, in the case of a water-absorbing resin or water-absorbing agent whose main component is a known amount of acrylic acid and its sodium salt, in the water-absorbing resin or water-absorbing agent based on the average molecular weight of the monomer and the titration amount obtained by the above operation. The soluble content of can be calculated by the following formula. In the case of an unknown amount, the average molecular weight of the monomer is calculated using the neutralization rate obtained by titration.

Soluble content (mass%) = 0.1 × (average molecular weight) × 184.3 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 50.0
Neutralization rate (mol%) = (1 − ([NaOH] − [bNaOH]) / ([HCl] − [bHCl])) × 100
<Granularity>
In accordance with the pamphlet of International Publication No. 2004/066944, a water-absorbing resin (or water-absorbing agent) is 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 45 μm JIS standard sieve (JIS Z8801-1 ( 2000)) or equivalent sieve and the residual percentage R was plotted on log probability paper. Thereby, the particle size corresponding to R = 50% by weight was read as the mass average particle size (D50). In addition, the logarithmic standard deviation (σζ) is expressed by the following equation, and the smaller the value of σζ, the narrower the particle size distribution.

σζ = 0.5 × ln (X2 / X1)
(X1 is R = 84.1%, X2 is a particle size corresponding to 15.9%)
<Solid content of water-absorbing agent>
In the water-absorbing agent, it represents the ratio of components that do not volatilize at 180 ° C. The relationship with the moisture content is as follows.

Solid content (mass%) = 100-water content (mass%)
The measurement method of solid content was performed as follows.

  About 1 g of water-absorbing resin is weighed (mass W1) into an aluminum cup (mass W0) having a bottom diameter of about 5 cm, and left to stand in a windless dryer at 180 ° C. for 3 hours to be dried. The mass (W2) of the dried aluminum cup + water-absorbent resin was measured, and the solid content was determined from the following formula.

Solid content (mass%) = ((W2−W0) / W1) × 100
<Paint shaker test>
The paint shaker test (PS) is a paint shaker (Toyo Seisakusho Co., Ltd. Product No. 488) in which a glass container having a diameter of 6 cm and a height of 11 cm is filled with 10 g of glass beads having a diameter of 6 mm and a water-absorbing resin or a water-absorbing agent. And is shaken at 800 cycle / min (CPM), and details of the apparatus are disclosed in Japanese Patent Laid-Open No. 9-235378.

  Paint shaker test 1 is the shake time of 30 minutes and paint shake test 2 is the test shake time of 10 minutes. After infiltration, the glass beads are removed with a JIS standard sieve having an opening of 2 mm, and a damaged water absorbent resin or water absorbent is obtained.

<Vortex (water absorption speed)>
According to JIS K7224-1996, the temperature of the test solution (0.9 wt% sodium chloride aqueous solution) was 30 ° C. ± 1 ° C., and the length of the stirrer chip was measured using a 40 mm one.

<Hygroscopic blocking rate>
About 2g of water absorbent or water absorbent resin is uniformly sprayed on an aluminum cup with a diameter of 52mm, and then a thermo-hygrostat (PLATINOUS LUCIFERPL-2G Tabie ESPEC) at a temperature of 25 ° C and a relative humidity of 90 ± 5% RH For 1 hour. After 1 hour, the water-absorbing agent or water-absorbing resin contained in the aluminum cup was gently transferred onto a JIS 8.6 mesh (aperture 2000 μm) JIS standard sieve (The IIDA TESTINGSIVE: inner diameter 80 mm), and a low-tap sieve shaker. Using a machine (ES-65 type sieve shaker manufactured by Iida Manufacturing Co., Ltd .; rotation speed: 230 rpm, impact number: 130 rpm), classification was performed for 5 seconds under conditions of room temperature (20 to 25 ° C.) and relative humidity of 50% RH. The weight of the water-absorbing agent or water-absorbing resin remaining on the mesh (i (g)) and the weight of the water-absorbing agent or water-absorbing resin that passed through the mesh (j (g)) were measured. And according to the following formula, the moisture absorption blocking rate which is a fluidity index at the time of moisture absorption was computed. In addition, the moisture absorption blocking rate used by this invention points out what is defined by a following formula.

Moisture absorption blocking rate (% by weight) = ((j (g)) / (i (g) + j (g))) × 100
The lower the moisture absorption blocking rate, the better the moisture absorption fluidity.

[Reference Example 1]
In a polypropylene container with an inner diameter of 80 mm and a capacity of 1 liter, covered with a polystyrene foam as a heat insulating material, acrylic acid 257.6 g, polyethylene glycol diacrylate (molecular weight 523) 0.84 g (0.045 mol%: acrylic acid) And a solution (A) in which 1.58 g of 1.0 mass% diethylenetriaminepentaacetic acid-5 sodium solution is mixed, 215.2 g of 48.5 mass% sodium hydroxide aqueous solution, and ion-exchanged water 210 adjusted to 50 ° C. The solution (B) mixed with 0.4 g was quickly added to the solution (A) in an open system while stirring with a magnetic stirrer and mixed. A monomer aqueous solution having a liquid temperature increased to about 102 ° C. by heat of neutralization and heat of dissolution was obtained.

  Wait until the resulting aqueous monomer solution reaches 95 ° C., add 14.30 g of a 3% by weight aqueous sodium persulfate solution, stir for a few seconds, and then hot plate (NEO HOPLLATE H1-1000, Seiei Inai Co., Ltd.). The obtained mixture was poured into an open system in a 250 × 250 mm bottom stainless steel vat type container whose surface temperature was heated to 100 ° C. by Teflon (registered trademark) on the inner surface. The stainless bat-shaped container had a bottom surface of 250 × 250 mm, a top surface of 640 × 640 mm, a height of 50 mm, a central cross section of a trapezoid, and an open top surface.

  Polymerization started soon after the aqueous monomer solution was poured into the vat. Polymerization proceeded while generating water vapor and expanding and foaming up and down, left and right, and then contracted to a size slightly larger than the bottom surface. This expansion and contraction was completed within about 1 minute, and after holding in the polymerization vessel for 4 minutes, the water-containing polymer was taken out.

  The obtained water-containing polymer was pulverized with a meat chopper (ROYAL MEAT CHOPPER VR400K, manufactured by Iizuka Kogyo Co., Ltd.) having a die diameter of 9.5 mm to obtain a finely divided water-containing polymer. At this time, the amount of gel charged was about 340 g / min, and pulverization was performed while deionized water was added at 48 g / min in parallel with gel charging.

  The non-volatile content of the gel after pulverization was 50 to 55 mass%.

  This finely divided hydrogel cross-linked polymer is spread on a 50-mesh wire mesh, dried with hot air at 180 ° C. for 35 minutes, and the dried product is pulverized using a roll mill, and further JIS with an opening of 850 μm and an opening of 150 μm. By classifying with a standard sieve, amorphous crushed water-absorbent resin particles (1) having a mass average particle diameter of 360 μm were obtained. The centrifuge retention capacity (CRC) of the water absorbent resin (1) was 36.0 g / g, and the water-soluble content was 12.0% by mass.

  A surface treatment agent comprising a mixed liquid of 100 parts by mass of the obtained water absorbent resin (1), 0.4 parts by mass of 1,4-butanediol, 0.6 parts by mass of propylene glycol, and 3.0 parts by mass of pure water. Were uniformly mixed, and the mixture was heat-treated at 200 ° C. for 30 minutes. Further, the particles were pulverized until they passed through a JIS standard sieve having an opening of 850 μm. Next, the paint shaker test 1 was performed on the particles. Thus, water-absorbing resin particles (A) having a crosslinked surface were obtained.

[Example 1]
Stirring 2 parts by mass of zinc stearate N (trade name, manufactured by NOF Corporation, zinc stearate aqueous dispersion, solid content 30% by mass, containing surfactant) to 100 parts by mass of water-absorbent resin particles (A) The resulting mixture was uniformly mixed and dried at 60 ° C. for 1 hour. The obtained dried product was crushed until it passed through a JIS standard sieve having an opening of 850 μm. In this way, a water absorbing agent (1) was obtained.

[Example 2]
To 100 parts by mass of the water absorbent resin (A), 3.33 parts by mass of an aqueous zinc stearate dispersion (trade name: Zinc stearate N; manufactured by NOF Corporation; solid content 30% by mass, including a surfactant) The mixture was mixed uniformly with stirring and dried at 60 ° C. for 1 hour. The obtained dried product was crushed until it passed through a JIS standard sieve having an opening of 850 μm. Thus, a water absorbing agent (2) was obtained.

[Example 3]
20 parts by mass of zinc stearate (manufactured by Kanto Chemical Co., Inc.), 8 parts by mass of sodium polyoxyethylene lauryl ether sulfate (product name: EMAL 20C, Kao Corporation, solid content 25% by mass), 72 parts by mass Were mixed with water to obtain a zinc stearate aqueous dispersion.

  To 100 parts by mass of the water-absorbent resin particles (A), 5.0 parts by mass of the aqueous zinc stearate dispersion were uniformly mixed with stirring and dried at 60 ° C. for 1 hour. The obtained dried product was crushed until it passed through a JIS standard sieve having an opening of 850 μm. Thus, a water absorbing agent (3) was obtained.

[Example 4]
20 parts by mass of zinc stearate (manufactured by Kanto Chemical Co., Inc.), 2 parts by mass of sodium dodecyl sulfate (manufactured by Kanto Chemical Co., Ltd.) and 78 parts by mass of water are mixed to obtain a zinc stearate aqueous dispersion. It was.

  To 100 parts by mass of the water-absorbent resin particles (A), 5.0 parts by mass of the aqueous zinc stearate dispersion were uniformly mixed with stirring and dried at 60 ° C. for 1 hour. The obtained dried product was crushed until it passed through a JIS standard sieve having an opening of 850 μm. In this way, a water absorbing agent (4) was obtained.

[Comparative Example 1]
In accordance with Patent Document 9, 100 parts by mass of water-absorbent resin particles (A) and 0.6 parts by mass of zinc stearate (manufactured by Kanto Chemical Co., Ltd.) are respectively used as a Redige mixer (manufactured by Redige, type: M5R). And stirred at 330 rpm for 15 seconds. In this way, a comparative water absorbing agent (1) was obtained.

[Comparative Example 2]
In accordance with Patent Document 9, 100 parts by mass of water-absorbent resin particles (A) and 1.0 part by mass of zinc stearate (manufactured by Kanto Chemical Co., Ltd.) were each prepared as a Redige mixer (manufactured by Redige, type: M5R). And stirred at 330 rpm for 15 seconds. In this way, a comparative water absorbing agent (2) was obtained.

[Comparative Example 3]
To 100 parts by mass of the water-absorbent resin particles (A), 1.4 parts by mass of water was uniformly mixed with stirring and dried at 60 ° C. for 1 hour. The obtained dried product was crushed until it passed through a JIS standard sieve having an opening of 850 μm. Next, the obtained pulverized product and 0.6 parts by mass of zinc stearate (manufactured by Kanto Chemical Co., Inc.) were respectively added to a Redige mixer (Redige Co., Ltd., type: M5R) and stirred at 330 rpm for 15 seconds. In this way, a comparative water absorbing agent (3) was obtained.

[Comparative Example 4]
In accordance with Patent Literatures 1 to 4, instead of using zinc stearate, Comparative Example 1 is used except that 0.5 parts by mass of hydrophilic silicon dioxide (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) is used. The same operation was performed to obtain a comparative water-absorbing agent (4).

[Comparative Example 5]
In accordance with Patent Documents 1 to 4, instead of using zinc stearate, Comparative Example 1 is used except that 1.0 part by mass of hydrophilic silicon dioxide (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) is used. The same operation was performed to obtain a comparative water-absorbing agent (5).

  Various physical properties of the water-absorbent resin particles (A), the water-absorbing agents (1) to (4), and the comparative water-absorbing agents (1) to (5) are shown in Table 1.

(Summary)
As shown in Table 1, the water-absorbing agents (1) to (4) in which the water-absorbing resin particles (A) are mixed with an aqueous dispersion containing a metal soap and a dispersion stabilizer are water absorption capacity under pressure (AAP), moisture absorption It can be seen that the fluidity (blocking rate) at the time is excellent and the water absorption rate (Vortex) is excellent.

  In accordance with Patent Document 9, the comparative water-absorbing agents (1) to (3) in which the water-absorbent resin particles (A) are mixed with metal soap have a large water absorption rate (Vortex) and are reduced (about 10 seconds). In addition, the comparative water absorbing agent (3) in which metal soap and water are mixed separately also has a large water absorption speed (Vortex) (approximately 10 seconds). According to Patent Documents 1 to 4, the comparative water-absorbing agents (4) and (5) in which hydrophilic silicon dioxide is mixed with the water-absorbing resin particles (A) have a large water absorption capacity under pressure (AAP) (about 4 to 4). 5 g / g).

  Unlike Patent Documents 14 to 16, the present invention provides a water-absorbing agent having a predetermined amount of water (preferably 0.01 to 20% by weight) at a high water absorption capacity under pressure (AAP) and a water absorption speed (Vortex). .

  The method for producing a water-absorbing agent of the present invention can be suitably used for producing a water-absorbing agent mainly composed of a water-absorbing resin having high physical properties.

Claims (16)

  A method for producing a particulate water-absorbing agent, comprising mixing water-absorbing resin particles with an aqueous dispersion containing a metal soap and a dispersion stabilizer.   The metal soap 0.001 to 5 parts by weight, water 0.01 to 20 parts by weight, and dispersion stabilizer 0.0001 to 1 part by weight are added to 100 parts by weight of the water absorbent resin particles. The manufacturing method as described.   The concentration of the metal soap in the aqueous dispersion containing the metal soap and the dispersion stabilizer is 1 to 90% by weight, and the concentration of the dispersion stabilizer is more than 0 and 10% by weight or less. The manufacturing method as described in.   The manufacturing method of any one of Claims 1-3 whose said dispersion stabilizer is surfactant.   The manufacturing method according to any one of claims 1 to 4, wherein the water-absorbent resin particles are subjected to surface crosslinking treatment.   The manufacturing method according to any one of claims 1 to 5, wherein the water-absorbent resin particles are a polyacrylic acid (salt) crosslinked polymer.   The manufacturing method of any one of Claims 1-6 whose water absorption capacity | capacitance (AAP4.83kPa) under pressure of the said water absorbing resin particle is 15 g / g or more.   The manufacturing method according to any one of claims 1 to 7, wherein the aqueous dispersion is mixed with the water-absorbent resin particles, and then the mixture is heated, crushed, and classified.   A particulate water-absorbing agent comprising water-absorbing resin particles, metal soap, water, and a dispersion stabilizer.   The metal soap according to claim 9, comprising 0.001 to 5 parts by weight of metal soap, 0.01 to 20 parts by weight of water, and 0.0001 to 1 part by weight of a dispersion stabilizer with respect to 100 parts by weight of the water absorbent resin particles. Particulate water-absorbing agent.   The particulate water-absorbing agent according to claim 9 or 10, wherein the dispersion stabilizer is a surfactant.   The particulate water-absorbing agent according to any one of claims 9 to 11, wherein the water-absorbent resin particles are subjected to surface crosslinking treatment.   The particulate water-absorbing agent according to any one of claims 9 to 12, wherein the water-absorbing resin particles are a polyacrylic acid (salt) crosslinked polymer.   The particulate water-absorbing agent according to any one of claims 9 to 13, wherein the water-absorbing resin particles have a water absorption capacity under pressure (AAP of 4.83 kPa) of 15 g / g or more.   The particulate water-absorbing agent according to any one of claims 9 to 14, wherein the water-absorbing resin particles are granulated.   An absorbent article comprising the particulate water-absorbing agent according to any one of claims 9 to 14.