JP2012077157A - Water-absorbing resin and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing resin with high productivity, which is a water-absorbing resin obtained by using a raw material derived from biomass, and exhibits a high water absorption rate capable of sufficiently responding to required performance in practical use and in particular, a high water absorption rate under no pressure and a high water absorption rate under pressure.SOLUTION: A method for producing the water-absorbing resin includes: a polymerizing step of an aqueous monomer solution containing, as an essential component, an acid group-containing unsaturated monomer; a drying step of the obtained water-containing gel; and a surface crosslinking step of crosslinking the surface of water-absorbing resin particles after drying. In the polymerization step, polysaccharides are mixed at such a stage that the polymerization rate is higher than 0 mol% and not higher than 90 mol%, and further, polymerization is advanced.

Description

  The present invention relates to a water absorbent resin and a method for producing the same. More specifically, the present invention relates to a surface-crosslinked water-absorbing resin containing a polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component and a polysaccharide, and a method for producing the same.

  Water-absorbing resin (SAP / Super Absorbent Polymer) is a water-swellable, water-insoluble polymer gelling agent, and is a constituent material for absorbent articles such as paper diapers and sanitary napkins, as well as agricultural and horticultural water retention agents, industrial use. As a water stop material, etc., it is frequently used mainly for disposable applications. As such a water-absorbing resin, many monomers and hydrophilic polymers have been proposed as raw materials.

  As an example of an absorbent article, in the case of a paper diaper, as the paper diaper is thinned in recent years, the proportion of the water absorbent resin in the absorber (mixture of water absorbent resin and pulp) is high ( High concentration). For this reason, the water absorption performance required for water-absorbing resins has been advanced and diversified. In particular, with the increase in the concentration of the water-absorbing resin in the absorbent body, in addition to CRC (water absorption capacity under no pressure), high performance of AAP (water absorption capacity under pressure) is required (Patent Documents 1 to 3). .

  Also, in recent years, from the viewpoint of reducing environmental impact, resource protection, carbon neutral, etc., instead of depleting energy resources such as petroleum (hereinafter referred to as “fossil resources”), renewable organisms that are constituents of living organisms The movement to use the organic resources derived from animals and plants excluding the fossil resources (hereinafter referred to as “biomass”) is becoming active. In the field of water-absorbent resins, research using monomers obtained from biomass as raw materials has been promoted, and biomass-derived water-absorbent resins have been gradually demanded.

  Conventionally, polyacrylic acid (salt) -based water-absorbing resins that are most produced and used as water-absorbing resins have used acrylic acid obtained from fossil resource-derived propylene as the main raw material. In addition to the above reasons, it is necessary to reduce the amount used from the viewpoint of depletion of fossil resources.

  So far, proposals have been made for water-absorbing resins using biomass-derived raw materials. Specifically, a crosslinked carboxymethyl cellulose, a crosslinked galactomannan, a crosslinked polyamino acid (Patent Documents 4 to 6) and the like are known, but these water absorbent resins have low water absorption performance and high price. Therefore, it is hardly put into practical use.

  Furthermore, conventionally, composite water-absorbing resins have been developed by techniques such as graft polymerization of biomass-derived raw materials and acrylic water-absorbing resins (polyacrylic acid or polyacrylamide) (Patent Documents 7 to 9). ). Specifically, polymerization is performed in the presence of starch and / or cellulose (Patent Document 7), polymerization is performed in the presence of amylose (Patent Document 8), and starch is dissolved using neutralization heat. And a method for polymerizing the same (Patent Document 9) is disclosed. However, in these methods disclosed in Patent Documents 7 to 9, a method of drying at 100 ° C. or lower, such as reduced pressure drying or low temperature drying, is employed in order to avoid deterioration of polysaccharides due to heating and the accompanying decrease in water absorption performance. However, the productivity was extremely poor.

  In view of the above problems, methods for improving production efficiency, water absorption performance, and whiteness have also been proposed (Patent Documents 10 to 11). Specifically, a method of drying at a high temperature in a short time using a drum dryer (Patent Document 10), polymerizing an acid group-containing monomer having a neutralization rate of 0 to 85 mol% in the presence of starch glycolic acid In addition, a method for obtaining a water-absorbing agent having high whiteness (Patent Document 11), a method for introducing a starch compound in each production step of the water-absorbing agent (Patent Documents 12 and 13), and a soil water retaining agent having a neutralization rate of 96 mol% or more ( Patent Document 14) is disclosed. However, none of these methods is sufficient to meet the requirement to achieve high AAP (water absorption capacity under pressure) in addition to high CRC (water absorption capacity without pressure) while ensuring high productivity. It was.

US Pat. No. 6,646,179 US Pat. No. 5,797,893 US Pat. No. 7,473,470 US Pat. No. 4,650,716 Japanese Patent No. 3450914 Japanese Patent Laid-Open No. 2005-247891 U.S. Pat. No. 4,076,663 JP 54-37188 A US Patent Application Publication No. 2007/149701 International Publication No. 2007/098932 Pamphlet Japanese Patent Publication No.55-21041 Japanese Patent No. 2901480 Special table 2009-528412 Japanese Patent No. 2706727

  Many water-absorbing resins using biomass-derived raw materials have been studied in addition to the above patent documents. Examples of such a water-absorbing resin include a water-absorbing resin containing a polymer obtained by polymerizing a monomer solution containing an acid group-containing unsaturated monomer as an essential component and a polysaccharide. Such a water-absorbent resin has a problem in that the water absorption capacity is lowered by a condensation esterification reaction between the hydroxyl group in the polysaccharide and the acid group derived from the monomer in the polymer during drying. Furthermore, in order to eliminate this decrease in water absorption ratio, a technique for lowering the drying temperature has been adopted, but in this case, a new problem has arisen that productivity is lowered. Furthermore, the water-absorbing resin obtained in this case is not sufficient for actual use such as paper diapers because the water-absorbing capacity under no pressure is maintained at a certain level, but the water-absorbing capacity under pressure is low. Met.

  Therefore, the present invention has been made in view of the above-mentioned problems, and the purpose thereof is not accompanied by a decrease in productivity or an increase in manufacturing cost, and in a water-absorbing resin using a conventional biomass-derived raw material. It is an object of the present invention to provide a production method capable of obtaining a highly water-absorbent resin that exhibits high AAP (water absorption capacity under pressure) and high CRC (water absorption capacity without pressure) that could never be achieved.

  Furthermore, an object of the present invention is a water-absorbing resin using a biomass-derived raw material, and also exhibits a high water-absorbing capacity that can sufficiently satisfy the required performance during actual use, particularly a high water-absorbing resin under high pressure. Is to provide.

  In order to solve the above problems, the method for producing the water absorbent resin of the present invention and the water absorbent resin of the present invention are as follows.

  That is, in order to solve the above problems, the method for producing a water-absorbent resin of the present invention includes a polymerization step of an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component, and a drying step of the obtained hydrogel. , A method for producing a water-absorbent resin comprising a surface cross-linking step of surface cross-linking the dried water-absorbent resin particles, wherein the polysaccharide is mixed at a stage where the polymerization rate is 90% or less during the polymerization step to further proceed the polymerization A method for producing a water-absorbent resin is provided.

  In order to solve the above problems, the water-absorbent resin of the present invention includes a polyacrylic acid-based water-absorbent resin and a polysaccharide non-uniformly in the particles, and has a water absorption capacity under pressure (AAP) of 22 [g / g. ] The above water-absorbent resin is provided.

  According to the production method of the present invention, high production of a water-absorbing resin that expresses a high AAP (water absorption capacity under pressure) at a high CRC (water absorption capacity without pressure) without lowering productivity or increasing manufacturing cost. Can be obtained by sex.

  In addition, since the water-absorbing resin of the present invention includes the polyacrylic acid-based water-absorbing resin and the polysaccharide non-uniformly in the particles, the polyacrylic acid-based water-absorbing resin and the polysaccharide are uniformly included in the particles; In comparison, high AAP (water absorption under pressure) is shown. In general, an absorbent body using a water-absorbent resin is mainly placed under pressure during actual use. Therefore, an absorbent body using the water-absorbent resin of the present invention has high absorption performance during actual use. Demonstrate.

  Hereinafter, the water-absorbent resin and the production method thereof according to the present invention will be described in detail.

[1] Definition of terms (1-1) "Water absorbent resin"
The “water-absorbing resin” in the present invention is a water-swellable water-insoluble polymer gel containing a polymer obtained by polymerizing a monomer solution containing an unsaturated monomer having an acid group as an essential component and a polysaccharide. Means an agent. “Water swellability” means that the CRC (water absorption capacity under no pressure) specified by ERT441.2-02 is usually 5 [[g / g]] or more, and “water insoluble”. Means that Ext (water-soluble content) specified by ERT470.2-02 is usually 0 to 50% by weight.

  The water-absorbing resin can be appropriately designed according to its use and is not particularly limited. May contain additives and the like.

(1-2) “EDANA” and “ERT”
“EDANA” is an abbreviation for European Disposables and Nonwovens Associations, and “ERT” is an abbreviation for a method for measuring water-absorbent resin (EDANA Recommended Test Method), which is a European standard (almost world standard). is there.

  In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the ERT original (known document: revised in 2002).

(A) "CRC" (ERT441.2-02)
“CRC” is an abbreviation for Centrifugation Retention Capacity (centrifugal retention capacity) and means water absorption capacity without pressure (hereinafter also referred to as “water absorption capacity”). Specifically, it is the water absorption capacity (unit: [[g / g]]) after 30 minutes of free swelling with respect to 0.9% by mass sodium chloride aqueous solution and further drained with a centrifuge.

(B) “AAP” (ERT442.2-02)
“AAP” is an abbreviation for Absorption Against Pressure, which means water absorption capacity under pressure. Specifically, the water absorption capacity (unit: [[g / g]]) after swelling under a load of 2.06 kPa (0.3 psi) for 1 hour with respect to a 0.9 mass% sodium chloride aqueous solution.

(C) "Ext" (ERT470.2-02)
“Ext” is an abbreviation for Extractables and means a water-soluble component (water-soluble component amount). Specifically, it is a value (unit:% by mass) measured by pH titration of 1 g of water-absorbing resin with respect to 200 g of 0.9 wt% sodium chloride aqueous solution after stirring for 16 hours and then eluting the water-soluble component. .

(D) “PSD” (ERT420.2-02)
“PSD” is an abbreviation for Particle Size Distribution, and means a particle size distribution measured by sieve classification. The mass average particle size (D50) and the logarithmic standard deviation (σζ) of the particle size distribution are described in European publication 0349240, page 7, lines 25 to 43 “(1) Average Particle Diameter and Dielectric Particle Diameter”. ”And measure in the same way.

(1-3) Others In this specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise noted, “ppm” means “mass ppm”.

[2] Method for producing water-absorbing resin (2-1) Polymerization step This step comprises a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component. This is a step of mixing polysaccharides. Each item is listed below in order.

(A) Monomer In the present invention, a radically polymerizable compound containing an acid group (hereinafter abbreviated as “acid group-containing unsaturated monomer”) is used as a monomer. A polymer obtained by polymerizing an aqueous monomer solution containing an unsaturated monomer containing an acid group as an essential component exhibits a great osmotic pressure due to the dissociation of the acid group, and is therefore excellent in terms of water absorption characteristics. Because. Although it does not specifically limit as an acid group prescribed | regulated by this invention, A carboxyl group, a sulfone group, a phosphoric acid group etc. are mentioned.

  The acid group-containing unsaturated monomer referred to in the present invention is preferably a monomer containing an acid group among monomers having an unsaturated double bond (ethylenically unsaturated monomer). Specifically, (meth) acrylic acid, (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloylethane sulfonic acid, 2- (meth) acryloylpropane sulfonic acid, 2- (meth) ) Acrylamide-2-methylpropane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid and / or their salts. Of these, (meth) acrylic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid and / or a salt thereof are more preferable, and acrylic acid and / or a salt thereof are particularly preferable in terms of water absorption characteristics. That is, the water-absorbing resin obtained in the present invention is particularly preferably a polyacrylic acid-based water-absorbing resin obtained by polymerizing a monomer containing acrylic acid and / or a salt thereof as an essential component.

  The monomer used in the present invention essentially includes an acid group-containing unsaturated monomer, and the proportion thereof is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, particularly preferably all monomers. Preferably it is 90-100 mol%. The acid group-containing unsaturated monomer may be used alone or in a mixture of two or more.

  Although there is no restriction | limiting in particular in the neutralization rate of an acid group containing monomer, 50 mol% or more is preferable in the use which may touch a human body, such as sanitary goods. More preferably, they are 50 mol% or more and less than 80 mol%, More preferably, they are 55 mol% or more and 78 mol% or less, Most preferably, they are 60 mol% or more and 75 mol% or less.

  Preferred monovalent salts include alkali metal salts, ammonium salts and amine salts. More preferred are sodium salt, potassium salt, lithium salt and ammonium salt. Particularly preferred is a sodium salt.

  The basic substance used for neutralization is not particularly limited, but includes alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, sodium carbonate (hydrogen), potassium carbonate (hydrogen) and the like. Monovalent basic substances such as carbonic acid (hydrogen) salt and ammonia are preferred, and sodium hydroxide is particularly preferred.

  The neutralization may be performed by adding a basic substance to the polymer after polymerization (water-containing gel-like crosslinked polymer). When preparing an aqueous monomer solution before polymerization, a salt as a monomer is prepared. Polymerization may be performed using the acid group-containing unsaturated monomer in the form, or may be performed in the middle of the polymerization of the monomer aqueous solution. However, such as improvement in productivity and AAP (water absorption under pressure) From the viewpoint, it is preferable to use a neutralized monomer, that is, to polymerize using a partially neutralized salt of an acid group-containing unsaturated monomer as a monomer. It is particularly preferred to polymerize using as a monomer. In addition, the neutralization rate of the acid group of the obtained water-absorbent resin is Ext. It can also be measured at the time of measuring (soluble amount).

  Furthermore, for the purpose of improving various properties of the resulting water-absorbent resin, as an optional component other than the polysaccharide, an aqueous monomer solution or a hydrogel crosslinked polymer after polymerization, a dried product or a powder, Salt), water-soluble or hydrophilic resins (other than polysaccharides) such as polyvinyl alcohol and polyethyleneimine, thermoplastic resins such as polyethylene and polypropylene, various foaming agents (carbonates, azo compounds, bubbles, etc.), surfactants In addition, deodorants, antibacterial agents, fragrances, inorganic powders such as silicon dioxide and titanium oxide, pigments, dyes, hydrophilic short fibers, plasticizers, and other additives described below may be added. As the addition amount of these optional components, the water-soluble or hydrophilic resin is preferably 0 to 50% by mass, more preferably 0 to 20% by mass, and particularly preferably 0 to 10% by mass with respect to the monomer. 0-3 mass% is the most preferable. Moreover, 0-5 mass% is preferable with respect to a monomer, and the said foaming agent or surfactant has more preferable 0-1 mass%.

  When a chelating agent, hydroxycarboxylic acid or reducing inorganic salt is used as an additive, the amount used is preferably 10 to 5000 ppm, more preferably 10 to 1000 ppm, more preferably 50 to 1000 ppm is more preferable, and 100 to 1000 ppm is particularly preferable. Among these, the use of a chelating agent is preferable. By using a chelating agent, the color stability of the water-absorbent resin (color stability when stored for a long time under high temperature and high humidity conditions) and urine resistance (preventing gel degradation) can be achieved. Examples of the chelating agent include those exemplified in US Pat. No. 6,599,989 and International Publication No. 2008/090961, and among them, aminocarboxylic acid metal chelating agents and polyvalent phosphorus Acid compounds are preferred.

  In the present invention, a hydrophilic or hydrophobic unsaturated monomer other than the acid group-containing unsaturated monomer (hereinafter also referred to as “other monomer”) is included as another monomer. Also good. Examples of such other monomers include, but are not limited to, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl ( Examples include meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, and stearyl acrylate. When such other monomers are used, the amount used is not particularly limited as long as it does not impair the desired properties, but is preferably 50 mol% or less, based on the total monomers. Preferably it is 0-30 mol%, especially 0-10 mol%.

(B) Internal cross-linking agent In the present invention, when the aqueous monomer solution is polymerized, it is preferable to carry out the polymerization in the presence of the internal cross-linking agent in the aqueous monomer solution. Examples of the internal crosslinking agent that can be used include N, N′-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, (polyoxyethylene) trimethylolpropane tri ( Molecules such as (meth) acrylate, trimethylolpropane di (meth) acrylate, polyethylene glycol di (β-acryloyloxypropionate), trimethylolpropane tri (β-acryloyloxypropionate), poly (meth) allyloxyalkane Compounds having at least two polymerizable double bonds in them; such as polyglycidyl ether (ethylene glycol diglycidyl ether, etc.), polyol (ethylene glycol, polyethylene glycol, glycerin, sorbitol, etc.), etc. A compound capable of forming a covalent bond by reacting with carboxyl groups, can be exemplified a.

  These internal cross-linking agents may be used alone or in combination of two or more. However, when using the internal cross-linking agent, the absorption characteristics of the resulting water-absorbent resin are taken into consideration. It is preferable to use a compound having at least two polymerizable double bonds in the molecule. The amount of the internal cross-linking agent is 0 to 5.000 mol%, preferably 0. 0% with respect to the above monomer, for the purpose of making CRC (water absorption capacity under no pressure) and AAP (water absorption capacity under pressure) desired properties. 001 to 2.000 mol%, more preferably 0.003 to 0.10 mol%, particularly preferably 0.005 to 0.05 mol%, most preferably 0.01 to 0.04 mol%. . Moreover, when performing the polymerization by adding the above crosslinking agent to the monomer aqueous solution, a known crosslinking method such as radical self-crosslinking or radiation crosslinking during polymerization may be used in combination.

(C) Polysaccharide The polysaccharide used in the present invention is a polymer having a skeleton containing a monosaccharide repeating unit, such as starch, amylopectin, amylose, cellulose, galactomannan, glucomannan, xanthan gum, carrageenan, chitin, and chitosan. And modified products thereof. Specifically, examples of the starch include corn starch, potato starch, wheat starch, tapioca starch, waxy corn starch, rice starch, and sweet potato starch. Examples of cellulose include cotton, wood-derived pulp, bacterial cellulose, lignocellulose, regenerated cellulose (such as cellophane and regenerated fiber), and microcrystalline cellulose. Examples of the galactomannan include guar gum, locust bean gum, tara gum, and cassia gum.

  Moreover, the polysaccharide used by this invention may be the thing which is not modified | denatured as the said illustration, and the modified material which introduce | transduced the substituent etc. may be sufficient as it. Examples of the modified polysaccharide include modified starch, modified amylopectin, modified amylose, modified cellulose, modified galactomannan, modified glucomannan, modified xanthan gum, and modified carrageenan. Modification methods for obtaining these modified products include esterification such as acetylation treatment of each polysaccharide, etherification such as carboxyalkylation, phosphorylation, oxidation, sulfation, phosphate crosslinking, adipic acid crosslinking, enzyme It is obtained by processing and combinations thereof.

  One type of substituent may be introduced by modification, or two or more types may be used. The degree of substitution of the polysaccharide is 0 in the case of an unmodified product, and when a modified product is used, it is preferably 2 or less, more preferably 1 or less, particularly preferably 0.5, from the viewpoint of absorption performance and cost. Hereinafter, it is most preferably 0.25 or less.

  Among the polysaccharides, starch, cellulose, and modified products thereof are more preferable from the viewpoint of availability and cost, and unmodified starch and unmodified cellulose are most preferable.

  These polysaccharides may be cross-linked. Polysaccharides can be cross-linked by any known method, and may be cross-linked using a cross-linking agent, and may be cross-linked by radiation (for example, gamma ray, X-ray or electron beam radiation) and / or heat. Also good. When a crosslinking agent is used, the crosslinking agent is not particularly limited, but N-methylol compounds having a cyclic portion in the molecule (such as dimethylolethyleneurea and dimethyloldihydroxyethyleneurea), polycarboxylic acids (tricarbaryl citrate) And butanetetracarboxylic acid), polyfunctional epoxy compounds (ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerol diglycidyl ether, etc.), polyvalent metal ions (such as aluminum ions and chromium ions), polyfunctional amines And polyfunctional aldehydes (glutaraldehyde, glyoxal, etc.) such as amino acids, polyamines, triamines and diamines. These crosslinking agents may be used alone or in combination of two or more.

The mass average molecular weight of the polysaccharide used is preferably 500 or more, more preferably 1000 or more, further preferably 2000 or more, particularly preferably 5000 or more, and most preferably 10,000 or more. The upper limit is not particularly limited, but is preferably 10 million or less, more preferably 8 million or less, and particularly preferably 5 million or less. When the molecular weight is lower than the lower limit, polysaccharide elution increases from the water-absorbent resin, which is not preferable because the absorption capacity is reduced. When the molecular weight exceeds the above upper limit, it is not preferable because handling of the polysaccharide becomes difficult.
In the present invention, in the polymerization step, it is preferable to mix a hydrated gel-like cross-linked polymer (hereinafter also referred to as a hydrated gel) produced with the progress of polymerization and a polysaccharide. The polysaccharide used in this case may be a dry powdered polysaccharide as it is, or may be used in a state where the polysaccharide is dispersed or swollen in water and / or an organic solvent. From the viewpoint of improving the properties, it is preferable to use a polysaccharide in a dry powder form.

  The amount of the polysaccharide used is preferably 5 to 50% by mass with respect to the solid content of a polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component. 45 mass% is further more preferable, and 10-40 mass% is the most preferable. When the amount of the polysaccharide used exceeds this range, the absorption performance decreases, which is not preferable. When the amount used is less than this range, the biomass utilization rate is too low, which is not preferable from the viewpoint of the global environment.

(D) Polymerization initiator The polymerization initiator used in the present invention is appropriately selected depending on the form of polymerization. Examples of such polymerization initiators include photodegradable polymerization initiators, thermal decomposition polymerization initiators, and redox polymerization initiators. The amount of the polymerization initiator used is preferably 0.0001 to 1 mol%, more preferably 0.0005 to 0.5 mol%, based on the monomer.

  Examples of the photodegradable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, and the like. Examples of the thermal decomposition type polymerization initiator include persulfates (sodium persulfate, potassium persulfate, ammonium persulfate), peroxides (hydrogen peroxide, t-butyl peroxide, methyl ethyl ketone peroxide), and azo compounds. (2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, etc.) and the like.

  Examples of the redox polymerization initiator include a system in which a reducing compound such as L-ascorbic acid or sodium hydrogen sulfite is used in combination with the persulfate or peroxide and the both are combined. Moreover, it can also be mentioned as a preferable aspect to use the said photodegradable initiator and a thermal decomposable polymerization initiator together. Although the combined ratio (molar ratio) when these are used in combination is appropriately determined, it is 1/100 to 100/1, more preferably 1/10 to 10/1. Of these polymerization initiators, it is preferable to use a persulfate from the viewpoints of cost and ability to reduce residual monomers.

(E) Polymerization method The polymerization in the present invention is not particularly limited, and may be a conventionally known reverse phase suspension polymerization or aqueous solution polymerization. The reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, and 4,683,274. , U.S. Pat. No. 5,244,735. Aqueous polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, U.S. Pat. Nos. 4,462,001, 4,873,299, 4,286,082, 4,973,632, 4,985,518, No. 5124416, US Pat. No. 5,250,640, US Pat. No. 5,264,495, US Pat. No. 5,145,906, US Pat. No. 5,380,808, and other European patents such as European Patent Nos. 081636, 09555086, and 09221717. Are listed. The monomers, crosslinking agents, polymerization initiators, additives, and polymerization methods described therein can be applied as long as they do not depart from the spirit of the present invention.

  However, aqueous solution polymerization is preferred from the viewpoints of productivity, ease of polymerization control, and physical properties of the resulting water-absorbent resin. If it is aqueous solution polymerization, this invention can be implemented by the stationary polymerization method which superposes | polymerizes monomer aqueous solution in a stationary state, the stirring polymerization method which superposes | polymerizes within a stirring apparatus, etc.

  In the static polymerization method, continuous static polymerization using an endless belt (US Pat. Nos. 4,893,999 and 6,241,928 and US Patent Application Publication No. 2005/215734) is preferable. The material of the endless belt is preferably a resin or rubber belt that does not allow the heat of polymerization to escape from the contact surface. Furthermore, it is preferable that an open space exists above the polymerization vessel.

  In the present invention, the charged thickness of the aqueous monomer solution (or gel) when the aqueous monomer solution containing the monomer, the polymerization initiator, and the crosslinking agent is supplied to the belt is usually preferably 1 to 100 mm. Preferably it is 3-50 mm, Most preferably, it is 5-30 mm. When the thickness of the aqueous monomer solution is 1 mm or less, it is difficult to adjust the temperature of the aqueous monomer solution. On the other hand, when the thickness is 100 mm or more, it is difficult to remove the heat of polymerization, which causes the physical properties of the water-absorbent resin to deteriorate. Therefore, it is not preferable.

  In the stirring polymerization method, a single-shaft stirrer or a stirrer having a plurality of stirring shafts is preferably used. For example, batch kneader polymerization or continuous kneader polymerization (described in US Pat. Nos. 6,987,151 and 6,710,141) is preferable.

  In the present invention, the solid content concentration in the monomer solution (preferably in an aqueous solution) (the ratio of the total amount of the acid group-containing unsaturated monomer component and the optional component to the entire solution) is not particularly limited. However, it is preferably 30 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 30 to 65% by mass. When the resin concentration is less than 30% by mass, the productivity is low. On the other hand, when it exceeds 70% by mass, the absorption capacity is low, which is not preferable.

  In order to achieve both high productivity and high absorption capacity, which are the problems of the present invention, it is necessary to suppress the esterification reaction by polysaccharides and acid groups, and in the present invention, by polymerization of an aqueous monomer solution. The conversion rate (polymerization rate) of the monomer when mixing the resulting hydrogel crosslinked polymer and polysaccharide needs to be more than 0 and 90 mol% or less, preferably 20 to 85 mol%. More preferably, it is 30-80 mol%, Most preferably, it is 40-70 mol%. When the polymerization rate is 0 mol%, the absorption capacity under no pressure decreases, and when it exceeds 90 mol%, the absorption capacity under pressure decreases, which is not preferable. Here, the polymerization rate at the time of mixing the polysaccharide is defined by the polymerization rate at the start of mixing, and the polymerization rate during the polymerization is within the above range, 60 mass% or more of the polysaccharide to be mixed, 80 mass% or more, Furthermore, it is preferable that addition of 90% by mass or more, particularly 100% is completed.

  In order to solve the problems of the present invention, in the present invention, the polysaccharide is mixed during the polymerization, but preferably 50% or less, more preferably 40% or less, particularly 30% or less of the total time of the polymerization process. It is added at an early stage. The lower limit may be after the start of polymerization (can be confirmed by visual observation of the polymerization rate or the polymer), but is suitably determined within a range of, for example, 1% or more, further 5% or more, particularly 10% or more of the total polymerization time.

  In the present invention, in order to solve the problems of the present invention, it is characterized in that the polymerization reaction is further continued after mixing the polysaccharide in the polymerization step. % Or more, further 10 mol% or more, particularly 20 mol% or more. Furthermore, in order to solve the problem, the polymerization rate is preferably 93 mol% or more, more preferably 95 to 99.99%%, and even more preferably 98 to 99.9 mol% in the polymerization step. It is preferable to dry the resulting hydrogel polymer. In addition, the introduction of the polysaccharide may be performed by batch addition at the above polymerization rate, by divided addition divided into a plurality of times at different polymerization rates, or by continuous addition within the range of the polymerization rate.

  The pressure in the polymerization machine at the time of polymerization may be reduced pressure, increased pressure, or normal pressure, and the atmosphere at the time of polymerization may be air, inert gas or steam, and may be a mixed atmosphere thereof. From the aspect, it is preferably carried out under an inert gas, and in that case, preferably 90% or more, further 99% or more, particularly 99.9% or more is carried out in an inert gas atmosphere.

  Various feeders (table feeders, screw feeders, belt conveyors, bucket conveyors, pneumatic transportation, etc.) are used to add polysaccharides. From the viewpoint of physical properties, polysaccharides and inert gases are preferably added simultaneously. In particular, when the polysaccharide is a dry powder, it is preferable to add the dry powder at an inert gas pressure from the viewpoint of stable mixing and prevention of clogging such as piping. In addition, nitrogen, helium, argon, carbon dioxide, or the like can be used as the atmosphere and the inert gas at the time of addition, but nitrogen is particularly preferable from the viewpoint of ease of industrial use. When a polysaccharide, particularly a polysaccharide dry powder is introduced at a gas pressure, particularly an inert gas gas pressure, the apparatus, pressure, dew point, etc. are appropriately determined. For example, a gas pressure of 0.01 to 1 mPa Saccharides are introduced into the polymerization machine and aging machine.

  One polymerization machine may be used in the polymerization process, a plurality of polymerization machines may be used in combination, and an aging machine (polymer gel storage process or heat retention process) may be installed after the polymerization machine. Therefore, the polysaccharide may be added at least one of in the middle of one polymerization machine, in the middle of a plurality of polymerization machines, and in the middle of the polymerization machine and the aging machine after polymerization.

  In the present invention, it is preferable to mix the polysaccharide simultaneously with the crushing of the hydrogel crosslinked polymer during the polymerization. That is, by simultaneously crushing the water-containing gel-like cross-linked polymer produced as the polymerization proceeds, the water-containing gel-like cross-linked polymer and the polysaccharide are mixed at the same time, so that the water-containing gel-like cross-linked polymer is polymerized by a crusher after the polymerization. Since the step of further crushing the coalescence and the step of mixing the hydrogel crosslinked polymer and the polysaccharide are not required, the production efficiency of the water-absorbent resin can be increased.

  In the present invention, “pulverization” means that the water-containing gel-like crosslinked polymer produced as the polymerization proceeds when polymerizing the acid group-containing unsaturated monomer is finely divided so that it can be easily dried in the subsequent drying step. Anything to do. In addition, the crushing may be performed at any time between the start of polymerization and the end of polymerization, but it is not always necessary to perform crushing throughout the polymerization process. The crushed water-containing gel-like cross-linked polymer is more preferable as the number of large gel lumps that are undried under general drying conditions decreases. The average particle size of the crushed hydrogel crosslinked polymer particles is preferably in the range of 0.1 mm to 5 mm, and more preferably in the range of 0.5 mm to 3 mm. Moreover, it is preferable that it is 10 mass% or less with respect to all the water-containing gel-like crosslinked polymers, and, as for the particle | grains whose particle diameter is 5 mm or more, it is more preferable that it is 5 mass% or less. If the particle diameter or average particle diameter of the hydrogel crosslinked polymer particles is within the above range, it is preferable because drying can be performed efficiently and undried products can be reduced. Here, the particle size of the water-containing gel-like crosslinked polymer particles is classified by a sieve with a specific opening, similarly to the particle size of the water-absorbent resin after pulverization (measured by the method described later). Desired. Further, the average particle diameter is also obtained in the same manner as D50 described later. However, since the classification operation of the hydrated gel-like crosslinked polymer is difficult in the dry method, it is measured using the wet classification method described in paragraph [0091] of JP-A No. 2000-63527.

  In the present invention, “pulverization” is distinguished from “pulverization” in which a dried product obtained by drying a crushed hydrogel crosslinked polymer is further finely pulverized to obtain a final product.

  The method is not particularly limited as long as it is a method of crushing while polymerizing the acid group-containing unsaturated monomer. For example, in a reaction vessel (polymerizer) having a crushing means And crushing while performing polymerization. As such a reaction vessel, for example, it is possible to give a shearing force to the water-containing gel-like cross-linked polymer produced as the polymerization proceeds by polymerizing an acid group-containing unsaturated monomer by the rotation of a rotary stirring blade. For that purpose, it is more preferable that there are a plurality of rotary stirring blades.

  Examples of the reaction vessel include a uniaxial kneader, a uniaxial extruder, a double-arm kneader, and a triaxial kneader. Among them, the reaction vessel is preferably a continuous kneader or a batch kneader, and the water-absorbent resin of the present invention can be obtained by mixing polysaccharides during polymerization and further stirring and subdividing the polymer gel. The kneader is more preferably a double-arm kneader or a triaxial kneader, and even more preferably a double-arm kneader.

  When using a double-arm kneader, it is preferable to use two rotating stirring blades rotated in the opposite directions at a constant speed or an unequal speed. In the case of constant speed, the rotational radii of the two rotary stirring blades are used in a state where they overlap each other, and in the case of non-uniform speed, the rotational radii of the two rotary stirring blades are used in a state where they do not overlap each other.

  The form of the rotary stirring blade is not particularly limited, but for example, a rotary stirring blade such as a sigma type, S type, Banbury type, or fishtail type can be suitably used.

  Further, as the above reaction vessel, a continuous kneader capable of continuously supplying an acid group-containing unsaturated monomer (preferably an aqueous solution thereof) and / or continuously discharging the resulting hydrogel crosslinked polymer is also suitable. Can be used. Thereby, it becomes possible to perform superposition | polymerization continuously. Moreover, it is more preferable that such a continuous kneader has a plurality of rotary stirring shafts.

  Examples of the continuous kneader having a plurality of rotating stirring shafts include a triaxial kneader (kneader ruder) having two stirring blades and one discharging screw; a twin screw extruder kneader; a twin screw mixer, etc. Can be mentioned. Among them, the continuous kneader having the plurality of rotating stirring shafts is a continuous supply of an acid group-containing unsaturated monomer (preferably an aqueous solution thereof) from the viewpoint of producing a high-performance water-absorbing resin with high productivity. More preferably, it is a continuous kneader having two rotating stirring shafts capable of continuously discharging the resulting hydrogel crosslinked polymer and having piston flowability.

  The temperature during polymerization depends on the type of solvent used, but is preferably 0 ° C. or higher and 120 ° C. or lower, more preferably 10 ° C. or higher and 100 ° C. or lower, and 20 ° C. or higher and 90 ° C. or lower. Is more preferable.

  The temperature of the hydrogel crosslinked polymer when mixing with the polysaccharide is preferably 60 ° C. or higher. If the temperature at which the polysaccharide is mixed is not 60 ° C or higher, the fusion to the hydrogel crosslinked polymer due to the gelatinization of starch does not proceed. If it is less than 60 ° C, the fusion is insufficient and the polysaccharide is peeled off. This is not preferable.

  The polymerization time is not particularly limited, but is preferably 30 seconds or longer and 60 minutes or shorter, more preferably 2 minutes or longer and 40 minutes or shorter. It is preferable for the polymerization time to be 60 minutes or less because a decrease in physical properties of the resulting water-absorbent resin can be avoided. Here, the polymerization time refers to the time from when the polymerization initiator is added to the acid group-containing unsaturated monomer to when the hydrogel crosslinked polymer is removed from the reaction vessel. Here, when the hydrogel crosslinked polymer is taken out from the reaction vessel, that is, at the end of the polymerization time, the monomer conversion rate (polymerization rate) is preferably 90 mol% or more.

  When mixing the hydrogel crosslinked polymer and the polysaccharide, a dry powdered polysaccharide may be used, or the polysaccharide is used in a state dispersed or swollen in water and / or an organic solvent. However, from the viewpoint of improving productivity, it is preferable to use a dry powdered polysaccharide. The particle diameter of the dry powdered polysaccharide is preferably 2 mm or less, more preferably 1 to 0.001 mm in terms of mass average particle diameter (D50).

  Further, in order to reduce the residual monomer in the obtained water-absorbent resin, in the polymerization step, an oxidizing agent, a reducing agent such as sulfurous acid or sulfurous acid (hydrogen) salt, the polymerization initiator such as persulfate, A step of adding to the hydrogel crosslinked polymer to be contained may be included, and preferably, sulfurous acid, sulfurous acid (hydrogen) salt, or persulfate is added. The step of adding these additives may be performed simultaneously with the addition of the polysaccharide or after the addition of the polysaccharide, and may be performed once or plural times. The addition amount of these additives is appropriately determined depending on the polymerization rate and the like, but is 0 with respect to the solid content of the polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component. -3 mass% is preferable, 0-1 mass% is further more preferable, and 0-0.5 mass% is the most preferable. The amount of residual monomer in the resulting water-absorbent resin is preferably 500 ppm or less, more preferably 450 ppm or less, and even more preferably 400 ppm or less.

(2-2) Drying step In the production method of the present invention, the hydrogel crosslinked polymer obtained in the polymerization step is dried in the drying step to obtain a polymer dried product. There are various drying methods such as heat drying, hot air drying, vacuum drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with hydrophobic organic solvents, and high humidity drying using high temperature steam. Although it can employ | adopt, Preferably it is hot-air drying by a gas with a dew point of 40-100 degreeC, More preferably, a dew point is 50-90 degreeC.

  The drying temperature is not particularly limited, but is preferably in the range of 100 to 200 ° C, more preferably 120 to 180 ° C, and still more preferably in the range of 140 to 160 ° C. In particular, in the case of hot air drying, the hot air temperature is preferably in the range of 100 to 200 ° C, more preferably 120 to 180 ° C, still more preferably in the range of 140 ° C to 160 ° C.

  The drying time is appropriately determined and is not particularly limited, but is preferably 10 seconds to 2 hours, more preferably 1 minute to 1.5 hours, and particularly preferably 10 minutes to 1 hour.

  The surface temperature of the hydrogel immediately before entering the dryer is preferably 40 to 110 ° C, more preferably 60 to 100 ° C. When the temperature is lower than 40 ° C., a balloon-like dried product is formed at the time of drying, and a lot of fine powder is generated at the time of pulverization, which may cause deterioration of physical properties.

  After the polymerization step, it is preferable that the time from when the gel is crushed until the water-containing gel enters the dryer is shorter from the viewpoint of coloring in the water-absorbent resin. It is preferably within 2 hours, more preferably within 1 hour, further preferably within 30 minutes, particularly preferably within 10 minutes, and most preferably within 2 minutes.

  In the drying step, the moisture content of the dried product after drying is controlled in the range of 3 to 15% by mass, more preferably 4 to 14% by mass, further preferably 5 to 13% by mass, and particularly preferably 6 to 12% by mass. Then, it is preferable to dry, and it is possible to control and adjust by appropriately setting conditions such as drying temperature, dew point, and drying time. If the water content is excessively dried so as to be less than 3% by mass, an esterification reaction between an acid group and starch occurs, which is not preferable because the absorption capacity of the water-absorbent resin is greatly reduced. Further, when the moisture content exceeds 15% by mass and the dried product contains moisture, it cannot be pulverized in the pulverization step, which causes a trouble such as clogging of the pulverizer, which is not preferable.

(2-3) Grinding step In the production method of the present invention, the polymer dried product in a substantially dry state obtained after the drying step is preferably pulverized in order to obtain particles having a size within a predetermined range (pulverization step). ). The pulverization method at this time is also not limited, and for example, a vibration mill, a roll granulator (Japanese Patent Laid-Open No. 9-235378, paragraph “0174”), a knuckle type pulverizer, a roll mill (Japanese Patent Publication No. 2002-527547). Gazette, paragraph "0069"), high-speed rotary crusher (pin mill, hammer mill, screw mill, roll mill) (JP-A-6-41319, paragraph "0036"), cylindrical mixer (JP-A-5-202199, Paragraph “0008”) or the like.

(2-4) Classification step In the production method of the present invention, the pulverized product obtained in the pulverization step is preferably classified. Accordingly, only particles having a size within a predetermined range are selected, and the resulting water-absorbent resin is preferable because it can express desired high physical properties more efficiently. The classification method at this time is also not particularly limited. For example, sieving using a sieve is preferably used. Specifically, for example, when the size range of the pulverized product is set to 150 μm to 850 μm, the pulverized product is first screened with a sieve having a sieve opening of 850 μm and then passed through the sieve. The object is sieved with a sieve having a 150 μm sieve opening. The pulverized product remaining on the 150 μm sieve becomes a water-absorbing resin within a desired range.

  The obtained water-absorbent resin is subjected to surface cross-linking treatment in the surface cross-linking step described later, and the mass average particle diameter (D50) of the water-absorbent resin before being subjected to the surface cross-linking step is preferably 250 to 450 μm. More preferably, it is adjusted to 275 to 425 μm, and more preferably 300 to 400 μm. Moreover, it is so good that there are few particles below 150 micrometers, Usually, it is preferable to adjust to 0-5 mass%, More preferably, it is 0-3 mass%, Most preferably, it is adjusted to 0-1 mass%. In the present invention, the ratio of 850 to 150 μm is preferably 95% by mass or more, more preferably 96% by mass or more, and most preferably 98% by mass or more (upper limit 100% by mass). The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.2 to 0.5, more preferably 0.25 to 0.45, and still more preferably 0.30 to 0.40. About these measuring methods, it describes in WO2004 / 69915 and EDANA-ERT420.2-02 using a standard sieve, for example. The particle size before surface cross-linking is preferably applied to the final product after surface cross-linking, and is preferably subjected to surface cross-linking treatment so as to maintain the particle size characteristics before surface cross-linking after surface cross-linking. Surface crosslinking treatment is preferably performed so that the previous mass average particle diameter (D50) and the amount of particles less than 150 μm are maintained in the above range even after surface crosslinking.

  Such a classification step is preferably performed before the surface cross-linking after the drying step (first classification step), and further, after the surface cross-linking, a classification step (second classification step, and further, if necessary, a first step). 3 classification step) is preferably provided.

(2-5) Recovery / Regeneration of Water-absorbent Resin Fine Particles In the production method of the present invention, it is preferable to control the particle diameter within a fine range as described above. This causes a problem that a large amount of fine particles are generated. As a technique for reducing the contradictory amount of fine particles (particles less than 150 μm), for example, it is preferable to collect and regenerate fine particles.

  The water-absorbent resin fine particles (for example, particles of less than 150 μm) taken out by the classification step are returned to the monomer solution used for polymerization again or mixed with a large amount of hot water (especially a temperature of 50 ° C. to boiling point). Then, it is returned again to the water-containing gel-like substance, and then dried, pulverized, etc. to regenerate the intended water-absorbent resin particles. In addition, it is preferable that the mass ratio of the water-absorbent resin fine particles and hot water at this time is in the range of 5: 4 to 3: 7. Examples of such techniques include U.S. Pat. Nos. 228930, 5264495, 4950692, 5478879, and EP 844270. When the fine particles are collected and regenerated in this way, the amount of waste can be reduced.

(2-6) Surface cross-linking step The water-absorbent resin obtained by the production method of the present invention can be made into a water-absorbent resin more suitable for sanitary materials through a conventionally known surface cross-linking treatment step. Surface cross-linking means that a portion having a higher cross-linking density is provided in the surface layer of the water-absorbent resin (near the surface: usually around several tens of μm from the surface of the water-absorbent resin). It can be formed by a polymerization reaction of monomers on the particle surface or a crosslinking reaction with a surface crosslinking agent.

  Suitable surface crosslinking agents include oxazoline compounds (US Pat. No. 6,297,319), vinyl ether compounds (US Pat. No. 6,372,852), epoxy compounds (US Pat. No. 6,25,488), oxetane compounds (US Pat. No. 6,809,158). ), Polyhydric alcohol compounds (US Pat. No. 4,734,478), polyamide polyamine-epihalo adducts (US Pat. Nos. 4,755,562 and 4,824,901), hydroxyacrylamide compounds (US Pat. No. 6,239,230). Oxazolidinone compound (US Pat. No. 6,559,239), bis or poly-oxazolidinone compound (US Pat. No. 6,472,478), 2-oxotetrahydro-1,3-oxazolidine compound (US) No. 6657015), alkylene carbonate compounds (US Pat. No. 5,672,633), polyvalent metal ions such as aluminum (US Pat. Nos. 6,605,673 and 6,620,899), etc. More than seeds are used. Further, an organic acid or an inorganic acid (US Pat. No. 5,610,208) may be used in combination. Furthermore, it is good also as surface bridge | crosslinking (US Patent application publication 2005/48221 specification) by superposing | polymerizing a monomer on the surface of a water absorbing resin.

  Specific surface crosslinking agents include (di, tri, tetra, poly) ethylene glycol, (di, poly) propylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, (Poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, di- or tri Polyhydric alcohol compounds such as ethanolamine, pentaerythritol, sorbitol; epoxy compounds such as (poly) ethylene glycol diglycidyl ether, (di, poly) glycerol polyglycidyl ether, (di, poly) propylene glycol diglycidyl ether, glycidol; 1,2-ethylenebisoxazoline, etc. Oxazoline compounds; 1,3-dioxolan-2-alkylene carbonate compounds such as one; polyvalent metal compounds such as aluminum sulfate, polyamide polyamine - epihalohydrin adducts.

  Among these, in order to obtain a water-absorbent resin having a high absorption capacity and a high absorption capacity under pressure, a method that allows the crosslinking reaction to proceed while maintaining the moisture content at a low temperature is preferable. Polyamide polyamine-epihalo adducts and polyvalent metal ions such as aluminum are preferable. In addition, combined use of organic acids and / or inorganic acids, and methods of surface crosslinking by polymerizing monomers on the surface of the water-absorbent resin are preferable. .

  In particular, polyamide polyamine-epihalohydrin adduct is suitably Kymene 557LX, Kymene 557H, Kymene plus sold by Hercules, WS4002, WS4020, WS4010, WS4046, etc. sold by Seiko PMC.

  As a usage-amount of a surface crosslinking agent, it is preferable to use 0.005-10 mass parts with respect to 100 mass parts of water absorbing resin, It is more preferable to use 0.005-5 mass parts, 0.01-3 mass More preferably, parts are used. When the amount of the surface cross-linking agent is less than 0.005 parts by mass, the absorption capacity under pressure may decrease. If the amount exceeds 10 parts by mass, the absorption capacity may be extremely reduced.

  Water is preferably used as a solvent for mixing the water-absorbent resin and the surface cross-linking agent. When the total amount of water is 1 to 10 parts by mass with respect to 100 parts by mass of the water-absorbent resin, the surface of the water-absorbent resin is sufficiently penetrated by the aqueous solution of the surface cross-linking agent and has a multilayer surface having an appropriate thickness and density A crosslinked layer is formed.

  Moreover, when mixing a water absorbing resin and a surface crosslinking agent, you may use a hydrophilic organic solvent as a solvent as needed. Examples of the hydrophilic organic solvent include 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; Examples include ethers such as tetrahydrofuran and alkoxy polyethylene glycol; amides such as N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide. The amount of the hydrophilic organic solvent used is preferably 20 parts by mass or less with respect to 100 parts by mass of the solid content of the water-absorbent resin, although it depends on the type and particle size of the water-absorbent resin. Within the range is more preferable.

  The method for mixing the water-absorbing resin and the surface cross-linking agent is not particularly limited, but the surface cross-linking agent dissolved in water and / or a hydrophilic organic solvent is directly sprayed or dripped onto the water-absorbing resin. And mixing them is preferable.

  It is desirable that the mixing device used when mixing the water-absorbent resin and the surface cross-linking agent has a large mixing force in order to mix both uniformly and reliably. Examples of the mixing apparatus include a cylindrical mixer, a double wall conical mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a fluidized-type furnace rotary disk mixer, and an airflow mixer. A double-arm kneader, an internal mixer, a pulverizing kneader, a rotary mixer, a screw extruder, a turbulizer, and the like are suitable.

  The mixture of the water absorbent resin and the surface crosslinking agent may be heated as necessary for the crosslinking reaction. The heating temperature is preferably 20 to 250 ° C, more preferably 30 to 200 ° C, and further preferably 50 to 170 ° C. The heating time is preferably 1 minute to 2 hours, more preferably 5 minutes to 1 hour, and even more preferably 10 to 30 minutes. As a suitable example of a combination of heating temperature and heating time, there is an example of 3 minutes to 1 hour at 70 to 120 ° C and 1 to 30 minutes at 130 to 170 ° C.

  In the production method of the present invention, in order to obtain a water-absorbing agent capable of expressing a high absorption capacity and a high absorption capacity under pressure, the surface crosslinking is controlled by controlling the water content of the water-absorbing resin at 3 to 15% by mass. It is preferable to carry out, more preferably 4 to 14% by mass, more preferably 5 to 13% by mass, and most preferably 6 to 12% by mass. When the water content is less than the above range, a reaction such as an esterification reaction occurs between the polysaccharide and the acid group, which is not preferable because the absorption capacity of the water absorbent resin is greatly reduced. When the water content exceeds the above range, the handling property of the water-absorbent resin is lowered, and the fluidity of the powder is lowered, which is not preferable.

  In the present invention, after surface cross-linking, it may be further dried as necessary, or water and other additives may be added to adjust the water content and other physical properties. Moreover, the 2nd thru | or 3rd classification process may be provided for a particle size control, and you may granulate. As other additives, water-insoluble fine particles such as hydrophilic amorphous silica, reducing agents, antibacterial agents, deodorants, chelating agents, polyvalent metal compounds, and the like may be added. Is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 10 parts by mass, and particularly preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the water absorbent resin.

[3] Water-absorbent resin of the present invention In the production method of the present invention, when acrylic acid and / or a salt thereof is used as a monomer and starch is added as a polysaccharide during polymerization, particles of the obtained water-absorbent resin It is possible to contain polyacrylic acid-based water-absorbing resin and polysaccharide non-uniformly in the particles one by one. That is, in this case, the water-absorbent resin according to the present invention is a water-absorbent resin that includes a polyacrylic acid-based water-absorbent resin and a polysaccharide non-uniformly in the particles. In such a heterogeneous state, a “purple part (starch part)” and a “colorless or yellow part (polyacrylic acid water-absorbing resin part)” are mixed in one particle by an iodine starch reaction test. Can be confirmed. The proportion of such particles preferably comprises 10% or more, further 50% or more, in particular 90%, of the total number of particles (eg 100 grains).
That is, the present invention provides a water-absorbing resin that includes a polyacrylic acid-based water-absorbing resin and a polysaccharide non-uniformly in the particles and has a water absorption capacity under pressure (AAP) of 22 [g / g] or more. More preferably, the water-absorbent resin has a water content of 3 to 15% by mass. Moreover, Preferably, the ratio of the particle | grains whose mass mean particle diameter (D50) is 250-450 micrometers and less than 150 micrometers is 0-5 mass%. Further preferable ranges are as follows.

  Conventionally, a starch acrylic acid graft polymer obtained by adding starch or the like to a monomer is known. However, in such a graft polymer, starch is uniformly dissolved in the monomer. One of them contains starch uniformly, and as a result, in the iodine starch reaction, one whole particle becomes a “purple portion (starch portion)”. In the conventional starch graft product, the hydroxyl absorption of polysaccharides such as starch reacts with polyacrylic acid or the water absorption capacity (CRC) is low, whereas in the present invention, the polyacrylic acid water-absorbing resin and polysaccharide are used. Since it is contained in the particles non-uniformly, there is no such problem, and the water-absorbing resin has a high CRC, which solves the conventional problem (decrease in CRC due to the use of polysaccharides). Further, by controlling the polymerization rate at the time of polysaccharide mixing to 90 mol% or less, a water-absorbing resin having a water absorption capacity under pressure (AAP) of 22 [g / g] or more can be obtained. Improved). Even when the water content is 3 to 15% by mass, the mass average particle diameter (D50) is 250 to 450 μm, and the proportion of particles less than 150 μm is 0 to 5% by mass, the problem of the present invention is further solved. To do.

  The water-absorbent resin of the present invention has a mass average particle diameter (D50) of preferably 250 to 450 μm, more preferably 275 to 425 μm, and further preferably 300 to 400 μm. Outside these ranges, the absorption rate becomes slow and the absorption capacity under pressure decreases, which is not preferable.

  In the water-absorbent resin of the present invention, the mass percentage of particles having a particle diameter of less than 150 μm is preferably 0 to 5% by mass, more preferably 0 to 3% by mass, and further preferably 0 to 1% by mass. Outside these ranges, the water absorption magnification under pressure is reduced, and dust generation is increased in handling, which is not preferable in the work environment.

  The water-absorbent resin of the present invention has a water content of preferably 3 to 15% by mass, more preferably 4 to 14% by mass, still more preferably 5 to 13% by mass, and particularly preferably 6 to 12% by mass. The When the water content is smaller than the above range, a reaction such as an esterification reaction occurs between the polysaccharide and the acid group, which causes a significant reduction in the water absorption ratio, which is not preferable. Furthermore, since the impact resistance stability as particles is low, when subjected to mechanical impact during the production process, the water absorption capacity under pressure of the water absorbent resin tends to decrease, such being undesirable. When the water content exceeds the above range, the handling property of the water-absorbent resin is lowered, and the fluidity of the powder is lowered, which is not preferable.

  The water absorbent resin of the present invention preferably has a CRC (water absorption capacity under no pressure) of 25 to 60 [g / g], more preferably 31 to 50 [[g / g]], and more preferably 32 to 50 [[ g / g]], more preferably 33 to 50 [[g / g]], particularly preferably 34 to 50 [[g / g]], and most preferably 35 to 50 [[g / g]. g]]. When CRC is less than 25 [g / g], when used for absorbent articles such as diapers, problems such as insufficient absorption capacity occur, or it is necessary to increase the amount of water-absorbing agent, which is not preferable. . Moreover, when CRC is too high, a soluble part may increase or durability after liquid permeability and water absorption may fall. CRC can be appropriately controlled by, for example, the amount of crosslinking agent and polymerization concentration during the polymerization.

The water absorbent resin of the present invention has an AAP (water absorption capacity under pressure) of 22 to 50 [[g / g]], more preferably 23 to 50 [[g / g]], still more preferably 24 to. 50 [[g / g]]. When AAP is less than these ranges, urine leakage may occur under pressure when used for absorbent articles such as paper diapers. AAP can be appropriately controlled, for example, without the surface crosslinking.
The water-absorbent resin of the present invention has an extr (water-soluble content) of preferably 50% by mass or less, more preferably 40% by mass or less, and 30% by mass or less depending on the durability of the gel, etc. Can be controlled. The lower the lower limit of the water-soluble content, the better. However, 1% by mass, and even 5% by mass is sufficient because there is a risk of excessive decrease in CRC.

  In the present invention, including the examples described later, the water-soluble component refers to a water-soluble polymer derived from the polymerization of an acid group-containing monomer, such as a water-soluble polymer in a polyacrylic acid-based water absorbent resin. The amount of water-soluble polyacrylic acid is defined by pH titration described later according to ERT470.2-02. That is, in the present invention, the polysaccharide is not regarded as a water-soluble component.

  In the water absorbent resin of the present invention, the logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.2 to 0.50, more preferably 0.25 to 0.45, and further preferably 0.30. 0.40. Outside these ranges, segregation occurs and performance may vary, which is not preferable.

[4] Use of the water-absorbent resin of the present invention The use of the water-absorbent resin of the present invention is not particularly limited, but preferably for absorbent articles and absorbent articles such as paper diapers, pet sheets, incontinence pads, and sanitary napkins. used.

  Here, the absorber refers to an absorbent material formed mainly of a water absorbent resin and hydrophilic fibers, and absorbs water with respect to the mass of the absorber (total mass of the water absorbent resin and hydrophilic fibers, etc.). The content (core concentration) of the conductive resin is preferably 20 to 100% by mass, more preferably 30 to 90% by mass, and particularly preferably 40 to 80% by mass.

  The absorbent article is prepared by including the absorbent body, a top sheet having liquid permeability, and a back sheet having liquid impermeability.

  Since the absorbent article using the water absorbent resin of the present invention has a high absorption capacity of the water absorbent resin, it can quickly absorb a large amount of absorption liquid such as urine added at one time, and the return amount of the absorption liquid can be reduced. It is characteristic that it decreases. Furthermore, since the water-absorbent resin of the present invention has a high absorption capacity under pressure, even when a baby is sitting, the absorbent article such as urine can be surely absorbed even when pressure is applied to the absorbent article. I can do it.

〔Example〕
EXAMPLES Hereinafter, although this invention is demonstrated according to an Example and a comparative example, this invention is limited to these and is not interpreted. Further, the physical properties described in the claims and examples of the present invention are the EDANA method and the following measuring methods under conditions of room temperature (20 to 25 ° C.) and humidity of 50 ± 5 RH% unless otherwise specified. Sought according to. Furthermore, the electric devices presented in the examples and comparative examples were used under the conditions of 200 V or 100 V and 60 Hz. For convenience, “liter” may be referred to as “L” and “mass%” may be referred to as “wt%”.

[Measurement method 1] CRC (absorption capacity under no pressure)
The measurement of CRC (absorption capacity under no pressure) was performed according to ERT441.2-02.

  0.2 g of water-absorbent resin was weighed, uniformly put into a bag made of unemployed cloth (60 x 60 mm), heat-sealed, and then 500 mL of 0.9 wt% sodium chloride aqueous solution (saline) adjusted to 25 ± 3 ° C. Soaked in. After the elapse of 60 minutes, the bag was pulled up and drained using a centrifuge (centrifuge manufactured by Kokusan Co., Ltd., type: H-122) at 250 G for 3 minutes. Thereafter, the weight W1 [g] of the bag was measured.

  The same operation was performed without adding the water-absorbent resin, and the weight W2 [g] of the bag at that time was measured. CRC (absorption capacity under no pressure) was calculated according to the following formula.

[Measuring method 2] AAP (Water absorption capacity under pressure)
The measurement of AAP (water absorption capacity under pressure) was performed according to ERT442.2-02. Hereinafter, the measurement method will be described with reference to FIG.

  A plastic support cylinder 100 (inner diameter 60 mm) to which a stainless steel wire mesh 101 (aperture 38 μm; 400 mesh) was fused was prepared. Under an atmosphere of 20 to 25 ° C. (room temperature) and a relative humidity of 50 ± 5 RH%, 0.900 g of the water-absorbing resin 102 was uniformly sprayed on the wire mesh.

  Next, a piston 103 and a load (weight) 104 capable of uniformly applying a load of 2.06 kPa (0.3 psi) to the water absorbing agent are placed on the water absorbing agent in this order, and the weight of the measuring device set. W3 [g] was measured. The piston and the load (weight) had no gap between the support cylinder and the outer diameter was slightly smaller than 60 mm so that the vertical movement was not hindered.

  Next, a glass filter 106 (diameter 90 mm) (manufactured by Mutual Riken Glass Co., Ltd .; pore diameter 100 to 120 μm) was placed in a Petri dish 105 (diameter 150 mm), and the temperature was adjusted to 20 to 25 ° C. 0.9 wt% The sodium chloride aqueous solution 108 was poured until it became the same height as the upper surface of the glass filter. Next, one filter paper 107 (diameter 90 mm) (manufactured by ADVANTEC Toyo Co., Ltd., product name: JIS P 3801, No. 2, thickness 0.26 mm, reserved particle diameter 5 μm) is placed on a glass filter so that the entire filter paper gets wet. And an excess of 0.9 wt% sodium chloride aqueous solution was removed. Thereafter, the set of measuring devices was placed on the filter paper, and a 0.9 wt% sodium chloride aqueous solution was absorbed into the water absorbent resin.

  After 1 hour, the set of measuring apparatus was lifted and its weight W4 [g] was measured. From the obtained W3 [g] and W4 [g], AAP (water absorption capacity under pressure) was calculated according to the following formula.

[Measurement Method 3] Extract. (Water-soluble content)
Extr. The (water-soluble content) was measured according to ERT470.2-02.

  A plastic container with a lid with a capacity of 250 mL was charged with 1.00 g of a water absorbent resin and 200.0 g of a 0.90 wt% sodium chloride aqueous solution, and stirred for 16 hours to extract the water-soluble component in the water absorbent. This extract was filtered using one filter paper (ADVANTEC Toyo Corporation, product name: JIS P 3801, No. 2, thickness 0.26 mm, retention particle diameter 5 μm), and 50.0 g of the obtained filtrate was used for measurement. Liquid.

  Next, the above measurement solution was titrated with a 0.1 N NaOH aqueous solution until pH 10 and then titrated with a 0.1 N HCl aqueous solution until pH 2.7. At this time, titration ([NaOH] mL, [HCl] mL) was determined. Moreover, the same operation was performed only with respect to 0.90 wt% sodium chloride aqueous solution, and empty-quantity ([bNaOH] mL, [bHCl] mL) was calculated | required.

  In the case of the water-absorbent resin of the present invention, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, according to the following formula, Extr. (Water-soluble content) was calculated.

  In addition, when the average molecular weight of a monomer is unknown, the average molecular weight of a monomer is calculated using the neutralization rate calculated | required by the said titration operation. In addition, the neutralization rate was calculated | required according to following Formula.

[Measuring method 4] Water content 1.00 g of water absorbent resin was weighed into an aluminum cup having a bottom surface of about 50 mm in diameter, and the total weight W5 [g] of the sample (water absorbent resin and aluminum cup) was measured.

  Next, the sample was allowed to stand in an oven having an atmospheric temperature of 180 ° C., and the water absorbent resin was dried. After 3 hours, the sample was removed from the oven and cooled to room temperature in a desiccator. Thereafter, the total weight W6 [g] of the dried sample (water absorbent resin and aluminum cup) was measured, and the water content (unit: [% by mass]) was calculated according to the following formula.

[Measuring Method 5] Mass standard particle diameter (D50), logarithmic standard deviation of particle size distribution (σζ) and weight percentage of particle diameter less than 150 μm JIS standard sieve having a mesh size of 850 μm, 600 μm, 300 μm, 150 μm (The IIDA TESTING SIEVE: An inner diameter of 80 mm; JIS Z8801-1 (2000)) or a sieve corresponding to a JIS standard sieve was used to classify 10.00 g of the water absorbent resin. After classification, the weight of each sieve was measured, and the mass percentage (unit: mass%) of particles having a particle diameter of less than 150 μm was calculated. The “mass percentage of particles having a particle diameter of less than 150 μm” is the ratio of particles passing through a JIS standard sieve having an opening of 150 μm to the entire water-absorbent resin.

  The mass average particle diameter (D50) was measured according to the method disclosed in International Publication No. 2004/066944. That is, the residual percentage R of each particle size was plotted on logarithmic probability paper, and the particle diameter corresponding to R = 50 mass% was read from this graph as the mass average particle diameter (D50). In addition, a mass average particle diameter (D50) means the particle diameter of the standard sieve corresponding to 50 mass% of the whole water-absorbing agent.

  The logarithmic standard deviation (σζ) of the particle size distribution was calculated according to the following formula. The logarithmic standard deviation (σζ) of the particle size distribution means that the smaller the value, the narrower the particle size distribution.

  Here, X1 is a particle diameter corresponding to R = 84.1% by mass, and X2 is a particle diameter corresponding to R = 15.9% by mass.

[Measuring Method 6] Polymerization Rate After adding 0.5 g of polymer gel to 1000 g of deionized water and extracting the monomer for 2 hours with stirring, the polymer gel is filtered off using filter paper, and the amount of monomer in the filtrate is liquid. Analyzed by chromatography. On the other hand, a calibration curve obtained by analyzing a monomer standard solution having a known concentration in the same manner is used as an external standard, and the amount of monomer contained in the polymer gel is obtained in consideration of the dilution rate of the filtrate, and the polymerization rate (mol%) is calculated. did.

[Measuring Method 7] Iodine Starch Reaction Test 0.1 g of potassium iodide was dissolved in 50 g of deionized water to obtain an iodine solution. 2 g of iodine solution was added dropwise to 0.2 g of the water-absorbent resin, and coloring due to the iodine starch reaction was visually observed and, if necessary, observed with a microscope, thereby evaluating the non-uniformity of the starch present in the water-absorbent resin.

[Example 1]
In a reactor formed by attaching a lid to a stainless steel double-armed kneader with two sigma-shaped blades and having an inner volume of 10 liters, 437.2 g of acrylic acid, 4169.7 g of 37 mass% sodium acrylate aqueous solution, pure 636.0 g of water and 1.18 g (0.01 mol%) of polyethylene glycol diacrylate (molecular weight 523) were dissolved to prepare a reaction solution. Next, this reaction solution was degassed for 20 minutes in a nitrogen gas atmosphere. Subsequently, 13.48 g of a 20% by mass sodium persulfate aqueous solution and 22.47 g of a 0.1% by mass L-ascorbic acid aqueous solution were added to the reaction solution with stirring. Polymerization started after about 1 minute. Then, polymerization is performed at 25 ° C. or more and 92 ° C. or less while crushing the generated gel, and 10 minutes after the start of polymerization, powdered corn starch (Kanto) is added to the gel in the middle of polymerization at a polymerization rate of 56 mol% and a temperature of 70 ° C. Chemical Co., Ltd., Catalog No. 37325-02) 220.0 g (addition ratio; 11.1 mass% with respect to acrylic acid (sodium salt) component) as an inert gas while being pressurized with nitrogen gas in the reactor Added and continued stirring. 20 minutes after adding corn starch, the hydrogel crosslinked polymer was taken out. The obtained hydrogel crosslinked polymer had a polymerization rate of 98.1 mol% and the particle size of the substantial gel was subdivided to about 5 mm or less.

  The finely divided hydrogel crosslinked polymer obtained in the above-mentioned gel granulation step was spread on a wire mesh having an opening of 850 μm and dried with hot air at 150 ° C. for 30 minutes to obtain a dried product. The obtained dried product is pulverized using a roll mill (WML type roll pulverizer; manufactured by Inoguchi Giken Co., Ltd.), and further classified with JIS standard sieves having openings of 850 μm, 600 μm, 300 μm, and 150 μm, and the particle diameter is 600 μm. The ratio of particles having a particle diameter of 850 μm or less is 14% by mass, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by mass, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by mass. By blending, a water absorbent resin (E1-b) having an average particle diameter (D50) of 379 μm and a logarithmic standard deviation (σζ) of 0.330 was obtained. The other physical properties of the water absorbent resin (E1-b) obtained are shown in Table 1. FIG. 2 shows an optical micrograph of the particles obtained by the iodine starch reaction test of the water absorbent resin (E1-b).

  As a surface crosslinking treatment, 100 parts by mass of the water-absorbent resin (E1-b) obtained in the above step is 0.1 part by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of propylene glycol, and 3.0% pure water. After uniformly mixing a surface cross-linking agent comprising parts by mass and 1.0 part by mass of isopropyl alcohol, the mixture was heat-treated at 100 ° C. for 60 minutes. Thereafter, as a crushing treatment, the obtained particles were crushed until they passed through a JIS standard sieve having an opening of 850 μm. Thus, a surface-crosslinked water-absorbing resin (E1-st) was obtained. The particle size distribution of the surface-crosslinked water-absorbent resin (E1-st) obtained was such that the proportion of particles having a particle size of 600 μm or more and less than 850 μm was 16% by mass, and the proportion of particles having a particle size of 300 μm or more and less than 600 μm was 59. The proportion of particles having a mass% of 150 μm or more and less than 300 μm was 25% by mass, the average particle diameter (D50) was 397 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Example 2]
In Example 1, 15 minutes after the start of polymerization, 220.0 g of powdered corn starch (manufactured by Kanto Chemical Co., Ltd., catalog No. 37325-02) 220.0 g (addition) on the gel during polymerization at a polymerization rate of 84 mol% and a temperature of 90 ° C. The ratio: 11.1% by weight with respect to the acrylic acid (sodium salt) component) was added to the reactor while being pressurized with nitrogen gas as an inert gas, and stirring was continued. 20 minutes after adding corn starch, the hydrogel crosslinked polymer was taken out. The obtained hydrogel crosslinked polymer had a polymerization rate of 98.3 mol% and the particle size of the substantial gel was subdivided to about 5 mm or less.

  The finely divided hydrogel crosslinked polymer obtained in the above-mentioned gel atomization step was dried, ground and classified in the same manner as in Example 1, and the ratio of particles having a particle diameter of 600 μm or more and less than 850 μm was 14. The average particle diameter (D50) is adjusted by blending so that the ratio of particles having a mass% of 300 to less than 600 μm is 57 mass% and the ratio of particles having a particle diameter of 150 to 300 μm is 29 mass%. ) And a water-absorbent resin (E2-b) having a logarithmic standard deviation (σζ) of 0.330. It shows in Table 1 about the other physical property of the obtained water absorbing resin (E2-b).

  For 100 parts by mass of the water-absorbent resin (E2-b) obtained in the above step, the same surface cross-linking treatment and crushing treatment as in Example 1 were performed, and the surface-crosslinked water-absorbent resin (E2-st) was obtained. Obtained. The particle size distribution of the surface-crosslinked water-absorbent resin (E2-st) obtained was 15% by mass of particles having a particle size of 600 μm or more and less than 850 μm, and 58% of particles having a particle size of 300 μm or more and less than 600 μm. The proportion of particles having a mass% of 150 μm or more and less than 300 μm was 27 mass%, the average particle diameter (D50) was 388 μm, and the logarithmic standard deviation (σζ) was 0.339. Other physical properties are shown in Table 2.

[Example 3]
In a reactor formed by covering a stainless steel double-armed kneader with two sigma-shaped blades and having an internal volume of 10 liters, 416.4 g of acrylic acid, 3971.2 g of 37 mass% sodium acrylate aqueous solution, pure 605.7 g of water and 1.12 g (0.01 mol%) of polyethylene glycol diacrylate (molecular weight 523) were dissolved to obtain a reaction solution. Next, this reaction solution was degassed for 20 minutes in a nitrogen gas atmosphere. Subsequently, 12.84 g of a 20% by mass sodium persulfate aqueous solution and 21.40 g of a 0.1% by mass L-ascorbic acid aqueous solution were added to the reaction solution with stirring. Polymerization started after about 1 minute. Then, polymerization is performed at 25 ° C. or more and 92 ° C. or less while crushing the generated gel, and 10 minutes after the start of polymerization, powdered corn starch (Kanto) is added to the gel in the middle of polymerization at a polymerization rate of 56 mol% and a temperature of 70 ° C. Chemical Co., Ltd., Catalog No. 37325-02) 471.4 g (addition ratio; 25.0% by weight with respect to acrylic acid (sodium salt) component) as an inert gas while being pressurized with nitrogen gas in the reactor Added and continued stirring. 20 minutes after adding corn starch, the hydrogel crosslinked polymer was taken out. The obtained hydrogel crosslinked polymer had a polymerization rate of 98.1 mol% and the particle size of the substantial gel was subdivided to about 5 mm or less.

  The finely divided hydrogel crosslinked polymer obtained in the above-mentioned gel granulation step was spread on a wire mesh having an opening of 850 μm and dried with hot air at 150 ° C. for 30 minutes to obtain a dried product. The obtained dried product is pulverized using a roll mill (WML type roll pulverizer; manufactured by Inoguchi Giken Co., Ltd.), and further classified with JIS standard sieves having openings of 850 μm, 600 μm, 300 μm, and 150 μm, and the particle diameter is 600 μm. The ratio of particles having a particle diameter of 850 μm or less is 14% by mass, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by mass, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by mass. By blending, a water absorbent resin (E3-b) having an average particle diameter (D50) of 379 μm and a logarithmic standard deviation (σζ) of 0.330 was obtained. It shows in Table 1 about the other physical property of the obtained water absorbing resin (E3-b).

  For 100 parts by mass of the water absorbent resin (E3-b) obtained in the above step, the same surface cross-linking treatment and crushing treatment as in Example 1 were performed, and the surface cross-linked water absorbent resin (E3-st) was obtained. Obtained. The particle size distribution of the surface-crosslinked water-absorbent resin (E3-st) obtained was 17% by mass of particles having a particle size of 600 μm or more and less than 850 μm, and 59% of particles having a particle size of 300 μm or more and less than 600 μm. The ratio of particles having a mass% and a particle diameter of 150 μm or more and less than 300 μm was 24 mass%, the average particle diameter (D50) was 403 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Example 4]
In a reactor formed by attaching a lid to a stainless steel double-armed kneader with a jacket of 10 liters with two sigma-shaped blades, 392.4 g of acrylic acid, 3742.1 g of 37 mass% sodium acrylate aqueous solution, pure 570.7 g of water and 1.05 g (0.01 mol%) of polyethylene glycol diacrylate (molecular weight 523) were dissolved to prepare a reaction solution. Next, this reaction solution was degassed for 20 minutes in a nitrogen gas atmosphere. Subsequently, 12.10 g of a 20% by mass aqueous sodium persulfate solution and 20.17 g of a 0.1% by mass L-ascorbic acid aqueous solution were added to the reaction solution with stirring, and polymerization started about 1 minute later. Then, polymerization is performed at 25 ° C. or more and 92 ° C. or less while crushing the generated gel, and 10 minutes after the start of polymerization, powdered corn starch (Kanto) is added to the gel in the middle of polymerization at a polymerization rate of 56 mol% and a temperature of 70 ° C. Chemical Co., Ltd., Catalog No. 37325-02) 761.5 g (addition ratio; 42.8 wt% with respect to acrylic acid (sodium salt) component) as an inert gas while being pressurized with nitrogen gas in the reactor Added and continued stirring. 20 minutes after adding corn starch, the hydrogel crosslinked polymer was taken out. The obtained hydrogel crosslinked polymer had a polymerization rate of 98.1 mol% and the particle size of the substantial gel was subdivided to about 5 mm or less.

  The finely divided hydrogel crosslinked polymer obtained in the above-mentioned gel granulation step was spread on a wire mesh having an opening of 850 μm and dried with hot air at 150 ° C. for 30 minutes to obtain a dried product. The obtained dried product is pulverized using a roll mill (WML type roll pulverizer; manufactured by Inoguchi Giken Co., Ltd.), and further classified with JIS standard sieves having openings of 850 μm, 600 μm, 300 μm, and 150 μm, and the particle diameter is 600 μm. The ratio of particles having a particle diameter of 850 μm or less is 14% by mass, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by mass, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by mass. By blending, a water absorbent resin (E4-b) having an average particle diameter (D50) of 379 μm and a logarithmic standard deviation (σζ) of 0.330 was obtained. It shows in Table 1 about the other physical property of the obtained water absorbing resin (E4-b).

  For 100 parts by mass of the water absorbent resin (E4-b) obtained in the above step, the same surface cross-linking treatment and crushing treatment as in Example 1 were performed, and the surface cross-linked water absorbent resin (E4-st) was obtained. Obtained. The particle size distribution of the surface-crosslinked water-absorbent resin (E4-st) obtained was 16% by mass of particles having a particle size of 600 μm or more and less than 850 μm, and 60% of particles having a particle size of 300 μm or more and less than 600 μm. The ratio of particles having a mass% of 150 μm or more and less than 300 μm was 24% by mass, the average particle diameter (D50) was 400 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Example 5]
In Example 1, the obtained dried product was pulverized using a roll mill (WML type roll pulverizer; manufactured by Inoguchi Giken Co., Ltd.), and further classified with JIS standard sieves having openings of 850 μm, 600 μm, 300 μm, and 150 μm. The ratio of particles having a particle diameter of 600 μm or more and less than 850 μm is 13% by mass, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 54% by mass, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 28% by mass. %, The proportion of particles having a particle diameter of less than 150 μm is adjusted to 5% by mass so that the average particle diameter (D50) is 364 μm and the logarithmic standard deviation (σζ) is 0.480. E5-b) was obtained. The other physical properties of the water absorbent resin (E5-b) obtained are shown in Table 1.

  For 100 parts by mass of the water absorbent resin (E5-b) obtained in the above step, the same surface cross-linking treatment and crushing treatment as in Example 1 were performed, and the surface cross-linked water absorbent resin (E5-st) was obtained. Obtained. The particle size distribution of the surface-crosslinked water-absorbent resin (E5-st) obtained was such that the proportion of particles having a particle size of 600 μm or more and less than 850 μm was 14% by mass, and the proportion of particles having a particle size of 300 μm or more and less than 600 μm was 56. The percentage of particles having a mass% of 150 μm or more and less than 300 μm is 27% by mass, the particles having a particle diameter of less than 150 μm is 3% by mass, the average particle diameter (D50) is 376 μm, and the logarithmic standard deviation (σζ) is 0.451. Other physical properties are shown in Table 2.

[Comparative Example 1]
In Example 1, starch was dissolved in an aqueous monomer solution (polymerization rate: 0%) before polymerization. That is, 392.4 g of acrylic acid and 3742.1 g of 37 mass% sodium acrylate aqueous solution in a reactor formed by attaching a cover to a stainless steel double-arm kneader with a jacket of 10 liters and having two sigma blades. 570.7 g of pure water and 1.05 g (0.01 mol%) of polyethylene glycol diacrylate (molecular weight 523) were dissolved. Thereto, 220.0 g of corn starch (manufactured by Kanto Chemical Co., Ltd., catalog No. 37325-02) (addition ratio; 11.1% by weight with respect to the acrylic acid (sodium salt) component) was added to obtain a reaction solution. . Next, this reaction solution was degassed for 20 minutes in a nitrogen gas atmosphere. Subsequently, 12.10 g of a 20% by mass aqueous sodium persulfate solution and 20.17 g of a 0.1% by mass L-ascorbic acid aqueous solution were added to the reaction solution with stirring, and polymerization started about 1 minute later. Then, polymerization was performed at 25 ° C. or more and 92 ° C. or less while pulverizing the generated gel, and a hydrous gel-like crosslinked polymer was taken out 30 minutes after the polymerization started. The obtained hydrogel crosslinked polymer had a polymerization rate of 98.0 mol%, and the particle size of the substantial gel was subdivided to about 5 mm or less.

  The finely divided hydrogel crosslinked polymer obtained in the above-mentioned gel atomization step was dried, ground and classified in the same manner as in Example 1, and the ratio of particles having a particle diameter of 600 μm or more and less than 850 μm was 14. The average particle diameter (D50) is adjusted by blending so that the ratio of particles having a mass% of 300 to less than 600 μm is 57 mass% and the ratio of particles having a particle diameter of 150 to 300 μm is 29 mass%. ) And a logarithmic standard deviation (σζ) of 0.330 were obtained as comparative water absorbent resins (C1-b). The other physical properties of the comparative water absorbent resin (C1-b) obtained are shown in Table 1. FIG. 3 shows an optical micrograph of the particles obtained by the iodine starch reaction test of the comparative water absorbent resin (C1-b).

  For 100 parts by mass of the comparative water-absorbing resin (C1-b) obtained in the above process, the same surface cross-linking treatment and pulverization treatment as in Example 1 were performed, and the surface water-crosslinked comparative water-absorbing resin (C1) -St). The particle size distribution of the obtained surface-crosslinked comparative water-absorbing resin (C1-st) is 17% by mass of particles having a particle size of 600 μm or more and less than 850 μm, and the proportion of particles having a particle size of 300 μm or more and less than 600 μm. Was 58% by mass, the proportion of particles having a particle size of 150 μm or more and less than 300 μm was 25% by mass, the average particle size (D50) was 400 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Comparative Example 2]
In Example 1, starch was added at a polymerization rate of 98%. That is, 437.2 g of acrylic acid and 4169.7 g of 37 mass% sodium acrylate aqueous solution were formed in a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having two sigma-shaped blades and having an internal volume of 10 liters. Then, 636.0 g of pure water and 1.18 g (0.01 mol%) of polyethylene glycol diacrylate (molecular weight 523) were dissolved to obtain a reaction solution. Next, this reaction solution was degassed for 20 minutes in a nitrogen gas atmosphere. Subsequently, 13.48 g of a 20% by mass sodium persulfate aqueous solution and 22.47 g of a 0.1% by mass L-ascorbic acid aqueous solution were added to the reaction solution with stirring. Polymerization started after about 1 minute. Then, polymerization is performed at 25 ° C. or more and 92 ° C. or less while pulverizing the generated gel, and after 40 minutes from the start of polymerization, powdered corn starch (Kanto) is added to the gel in the middle of polymerization at a polymerization rate of 98 mol% and a temperature of 60 ° C. Chemical Co., Ltd., Catalog No. 37325-02) 220.0 g (addition ratio; 11.1 wt% with respect to acrylic acid (sodium salt) component) as an inert gas while being pressurized with nitrogen gas in the reactor Added and continued stirring. 20 minutes after adding corn starch, the hydrogel crosslinked polymer was taken out. The obtained hydrogel crosslinked polymer had a polymerization rate of 98.5 mol%, and the particle size of the substantial gel was subdivided to about 5 mm or less.

  The finely divided hydrogel crosslinked polymer obtained in the above-mentioned gel atomization step was dried, ground and classified in the same manner as in Example 1, and the ratio of particles having a particle diameter of 600 μm or more and less than 850 μm was 14. The average particle diameter (D50) is adjusted by blending so that the ratio of particles having a mass% of 300 to less than 600 μm is 57 mass% and the ratio of particles having a particle diameter of 150 to 300 μm is 29 mass%. ) And a logarithmic standard deviation (σζ) of 0.330 were obtained as comparative water-absorbing resins (C2-b). The other physical properties of the comparative water absorbent resin (C2-b) obtained are shown in Table 1.

  For 100 parts by mass of the comparative water-absorbing resin (C2-b) obtained in the above step, the same surface cross-linking treatment and crushing treatment as in Example 1 were performed, and the surface water-cross-linked comparative water-absorbing resin (C2) -St). The particle size distribution of the obtained surface-crosslinked comparative water-absorbing resin (C2-st) is such that the proportion of particles having a particle size of 600 μm or more and less than 850 μm is 14% by mass, and the proportion of particles having a particle size of 300 μm or more and less than 600 μm. Was 58 mass%, the proportion of particles having a particle diameter of 150 μm or more and less than 300 μm was 28 mass%, the average particle diameter (D50) was 382 μm, and the logarithmic standard deviation (σζ) was 0.330. Other physical properties are shown in Table 2.

[Comparative Example 3]
The pulverized product of the dried product obtained in Example 1 was treated by simply passing it through a JIS 850 μm standard sieve. The proportion of particles having a particle size of 600 μm or more and less than 850 μm was 13% by mass, and the particle size was 300 μm or more and less than 600 μm. The proportion of particles is 51% by mass, the proportion of particles having a particle size of 150 μm or more and less than 300 μm is 26% by mass, the proportion of particles having a particle size of less than 150 μm is 10% by mass, and the average particle size (D50) is 355 μm. A comparative water absorbent resin (C3-b) having a logarithmic standard deviation (σζ) of 0.558 was obtained. Other physical properties are shown in Table 1.

  For 100 parts by mass of the comparative water-absorbing resin (C3-b) obtained in the above step, the same surface cross-linking treatment and pulverization treatment as in Example 1 were performed, and the surface water-crosslinked comparative water-absorbing resin (C3) -St). The particle size distribution of the obtained surface-crosslinked comparative water-absorbing resin (C3-st) is 14% by mass of particles having a particle size of 600 μm or more and less than 850 μm, and the proportion of particles having a particle size of 300 μm or more and less than 600 μm. Is 52% by mass, the proportion of particles having a particle size of 150 μm or more and less than 300 μm is 27% by mass, the proportion of particles having a particle size of less than 150 μm is 7% by mass, the average particle size (D50) is 363 μm, logarithmic standard The deviation (σζ) was 0.519. Other physical properties are shown in Table 2.

[Comparative Example 4]
The same treatment was carried out except that the surface crosslinking conditions of Comparative Example 1 were changed to 195 ° C. for 30 minutes, to obtain a surface-crosslinked comparative water absorbent resin (C4-st). In the obtained particle size distribution of (C4-st), the proportion of particles having a particle size of 600 μm or more and less than 850 μm is 16% by weight, the proportion of particles having a particle size of 300 μm or more and less than 600 μm is 59% by weight, and the particle size is 150 μm. The proportion of particles having a particle size of less than 300 μm was 25% by weight, the average particle size (D50) was 397 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

なお、前述の特許文献１３（特表２００９−５２８４１２号公報）において、その実施例１では澱粉化合物を添加した単量体水溶液を重合する方法を開示し、また実施例１ｅ−１〜１ｅ−２４では単量体水溶液を重合した後のヒドロゲルに澱粉化合物を添加する方法を開示している。しかしながら、前者の方法は本願比較例１の方法に相当し、また後者の方法は本願比較例２の方法に相当する。したがって、本願発明の方法で得られる吸水性樹脂は、従来公知の方法で得られるものに比べて、優位に高いＣＲＣ（無加圧下吸水倍率）および高いＡＡＰ（加圧下吸水倍率）を発現できることが分かる。

In addition, in the above-mentioned patent document 13 (Japanese translations of PCT publication No. 2009-528412), the Example 1 discloses the method of superposing | polymerizing the monomer aqueous solution which added the starch compound, and Example 1e-1 to 1e-24. Discloses a method of adding a starch compound to a hydrogel after polymerization of an aqueous monomer solution. However, the former method corresponds to the method of Comparative Example 1 of the present application, and the latter method corresponds to the method of Comparative Example 2 of the present application. Therefore, the water-absorbing resin obtained by the method of the present invention can express a significantly higher CRC (absorption capacity under no pressure) and higher AAP (absorption capacity under pressure) than those obtained by a conventionally known method. I understand.

  As shown in FIGS. 2 and 3, since the water-absorbent resin of Example 1 is colored unevenly, it can be seen that starch is unevenly present in the particles. On the other hand, since the water-absorbent resin of Comparative Example 1 is uniformly colored, it can be seen that starch is uniformly present in the particles.

  According to the production method of the present invention, water absorption that exhibits high AAP (water absorption capacity under pressure) with high CRC (water absorption capacity under no pressure), which could never be achieved with a water absorbent resin using conventional biomass-derived raw materials. Resin can be obtained with high productivity. The water-absorbent resin obtained by the production method according to the present invention is suitable for sanitary materials such as paper diapers, sanitary napkins, and incontinence pads.

It is a conceptual diagram of the measuring device of AAP (water absorption magnification under pressure) used in an example. 2 is an optical micrograph of particles obtained by an iodine starch reaction test of the water-absorbent resin of the present invention obtained in Example 1. FIG. 2 is an optical micrograph of particles obtained by an iodine starch reaction test of the water-absorbent resin obtained in Comparative Example 1.

DESCRIPTION OF SYMBOLS 100 Plastic support cylinder 101 Stainless steel 400 mesh wire mesh 102 Water absorbing resin (swelling gel)
103 piston 104 load (weight)
105 Petri dish 106 Glass filter 107 Filter paper 108 0.90 wt% Sodium chloride aqueous solution

Claims (20)

  A water-absorbent resin comprising a polymerization step of an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component, a drying step of the obtained hydrogel, and a surface cross-linking step of surface-crosslinking the water-absorbent resin particles after drying A method for producing a water-absorbing resin, which is a production method, wherein a polysaccharide is mixed at a stage where the polymerization rate exceeds 0 in the course of the polymerization step and exceeds 90 mol%, and the polymerization further proceeds.   The production method according to claim 1, wherein the polymerization rate is further advanced by 5 mol% or more after mixing the polysaccharide in the polymerization step.   The production method according to claim 1 or 2, wherein after the polymerization rate is polymerized to 95 to 99.99 mol% in the polymerization step, the obtained hydrogel is dried.   The manufacturing method of the water absorbing resin of any one of Claims 1-3 which mix a polysaccharide simultaneously with crushing of a hydrogel crosslinked polymer at the time of superposition | polymerization in a superposition | polymerization process.   The manufacturing method of the water absorbing resin of any one of Claims 1-4 with which a superposition | polymerization process is performed with a continuous type or a batch type kneader.   The method for producing a water-absorbent resin according to any one of claims 1 to 5, wherein the polysaccharide is mixed at 50% or less of the total time of the polymerization step and at a stage after the start of polymerization.   The manufacturing method of any one of Claims 1-6 which adds a polysaccharide and an inert gas simultaneously in a superposition | polymerization process.   The manufacturing method of the water absorbing resin of any one of Claims 1-7 whose said polysaccharide is a dry powder.   The manufacturing method of any one of Claims 1-8 which adds the said polysaccharide by the pressure of an inert gas.   The polysaccharide is added at least one of (a) in the middle of one polymerization machine, (b) in the middle of a plurality of polymerization machines, and (c) in the middle of the polymerization machine and the aging machine after polymerization. The manufacturing method of any one of these.   The method for producing a water absorbent resin according to any one of claims 1 to 10, wherein in the step of mixing the hydrogel crosslinked polymer and the polysaccharide, the temperature of the hydrogel is 60 ° C or higher.   The method for producing a water absorbent resin according to any one of claims 1 to 11, wherein the water content of the water absorbent resin is controlled to 3 to 15% by mass in the surface crosslinking step.   The manufacturing method of the water absorbing resin of any one of Claims 1-12 which controls the moisture content of a water absorbing resin to 3-15 mass% at a drying process.   The method for producing a water-absorbent resin according to any one of claims 1 to 13, wherein the drying step is hot-air drying at 100 to 200 ° C.   The mass average particle diameter (D50) of the water-absorbent resin after the drying step and before the surface cross-linking step is 250 to 450 µm, and the proportion of particles less than 150 µm is 0 to 5% by mass. 2. A method for producing a water-absorbent resin according to item 1.   The method for producing a water-absorbent resin according to any one of claims 1 to 15, wherein a polymerization initiator, a reducing agent or an oxidizing agent is further added during or after the polymerization.   A water-absorbing resin containing a polyacrylic acid-based water-absorbing resin and a polysaccharide non-uniformly in particles and having a water absorption capacity under pressure (AAP) of 22 [g / g] or more.   The water-absorbent resin according to claim 17, wherein the water content is 3 to 15% by mass.   The water-absorbent resin according to claim 17 or 18, wherein a mass average particle diameter (D50) is 250 to 450 µm, and a ratio of particles less than 150 µm is 0 to 5 mass%.   The water-absorbent resin according to any one of claims 17 to 19, wherein the residual monomer is 500 ppm or less.

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