JP2011213759A - Water-absorptive resin and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorptive resin with high performance, comprising: a polymer that is obtained by polymerizing an aqueous monomer solution containing an unsaturated monomer containing an acid group as an essential component; and polysaccharides, with high productivity.SOLUTION: The water-absorbing agent is a surface-crosslinked water-absorptive resin comprising: the polymer that is obtained by polymerizing the aqueous monomer solution containing the unsaturated monomer containing the acid group as the essential component; and the polysaccharides and meets the following (i)-(iv): (i) a neutralization index of the acid group of 80-100 mol%; (ii) a weight average particle size (D50) of 250-450 μm; (iii) a percent by weight of particles with less than a particle size of 150 μm of 0-5 wt.%; and (iv) a water content is 3-15 wt.%.

Description

  The present invention relates to a water absorbing agent 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 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, as the concentration of the water-absorbent resin is increased, 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 / cellulose (Patent Document 7), polymerization is performed in the presence of amylose (Patent Document 8), starch is dissolved using heat of neutralization, and the like. A polymerization method (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 / short time using a drum dryer (Patent Document 10), polymerization of an acid group-containing monomer having a neutralization rate of 0 to 85 mol% in the presence of starch glycolic acid A method of obtaining a water-absorbing agent with high whiteness (Patent Document 11), a method of introducing a starch compound in each step of the water-absorbing agent (Patent Document 12), and a soil water retention agent having a neutralization rate of 96 mol% or more (Patent Document 12) Although Patent Document 13) is disclosed, it is not sufficient to meet the demand 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 enough.

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 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 absorbent resin include a water absorbent resin containing a polymer obtained by polymerizing a monomer solution containing an acid group-containing monomer as an essential component and a polysaccharide. However, there has been a problem that the water absorption ratio decreases during drying due to the reaction between the polysaccharide and polyacrylic acid. Furthermore, a technique for lowering the drying temperature has been adopted in order to eliminate the decrease in the water absorption ratio, but a new problem has arisen that productivity is lowered.

  Accordingly, the present invention has been made in view of the above-described problems, and its purpose is to achieve high CRC (non-pressurized water absorption ratio) and high AAP (pressurized water absorption without sacrificing productivity and manufacturing cost. (Magnification) water-absorbent resin with high productivity.

  In order to solve the above problems, the water-absorbent resin of the present invention and the production method thereof (first and second inventions) are as follows.

  That is, the water-absorbent resin according to the present invention (the first invention) includes a polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component and a polysaccharide. A cross-linked water-absorbing resin that satisfies the following (i) to (iv).

(I) Neutralization rate of acid group is 80 to 100 mol%
(Ii) Weight average particle diameter (D50) is 250 to 450 μm
(Iii) 0 to 5% by weight by weight percentage with a particle size of less than 150 μm
(Iv) Moisture content of 3 to 15% by weight
Moreover, the manufacturing method (2nd invention) of another water-absorbent resin which concerns on this invention is a monomer component which uses the acid group containing unsaturated monomer whose neutralization rate is 80-100 mol% as an essential component. The step of polymerizing in the presence of polysaccharide, the step of drying after adjusting the moisture content after drying to 3 to 15% by weight, and the following (I) to (III) obtained through those steps are satisfied. It is a method for producing a water-absorbent resin, comprising a step of surface cross-linking polymer dry particles while maintaining the range of (I) to (III).

(I) Weight average particle diameter (D50) is 250 μm to 450 μm
(II) The weight percentage of particles having a particle diameter of less than 150 μm is 0 to 5% by weight.
(III) Water content is 3 to 15% by weight

  According to the present invention, a water-absorbing resin having a high CRC (absorption capacity under no pressure) and a high AAP (absorption capacity under pressure) can be obtained with high productivity without sacrificing productivity and manufacturing cost.

FIG. 1 is a schematic view showing an apparatus for measuring AAP (water absorption magnification under pressure) which is one of physical properties of a water absorbent resin.

  Hereinafter, the water-absorbent resin and the method for producing the same according to the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and other than the following examples, the scope of the present invention is not impaired. Can be changed and implemented as appropriate. Specifically, the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the claims, and technical means disclosed in different embodiments are appropriately combined. Embodiments obtained in this manner are also included in the technical scope of the present invention.

[1] Definition of terms (1-1) "Water absorbent resin"
The “water-absorbing resin” in the present invention means a water-swellable water-insoluble polymer gelling 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 insolubility” It 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, but is a polymer obtained by polymerizing a monomer solution containing an unsaturated monomer having an acid group as an essential component. And a hydrophilic polymer containing a polysaccharide. Further, the total amount (100% by weight) is not limited to a form of a polymer, and additives and the like may be included within a range in which the above performance is maintained.

(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 (centrifuge retention capacity) and means water absorption capacity without pressure (hereinafter also referred to as “water absorption capacity”). Specifically, the water absorption capacity (unit: [g / g]) after 30 minutes of free swelling with respect to a 0.9 wt% 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 wt% 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 weight) measured by pH titration after stirring 1 g of water absorbent resin for 16 hours with respect to 200 g of 0.9 wt% sodium chloride aqueous solution.

(D) “PSD” (ERT420.2-02)
“PSD” is an abbreviation for Particle Size Distribution, and means a particle size distribution measured by sieve classification. The weight average particle size (D50) and the particle size distribution range are the same as those described in “(1) Average Particle Diameter and Distillation of Particle Diameter” described in European Patent No. 0349240, page 7, lines 25-43. Measure with

(E) “pH” (ERT400.2-02)
“PH” means the pH of the water-absorbent resin. Specifically, it is the pH of the supernatant solution measured after dispersing 0.5 g of the water-absorbent resin in 100 g of 0.9 wt% sodium chloride aqueous solution and stirring for 10 minutes.

(1-4) Others In this specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise noted, “ppm” means “weight ppm” or “mass ppm”.

[2] Method for producing water-absorbing resin (2-1) Polymerization step In this step, a water-containing gel is prepared by polymerizing a monomer component having an acid group-containing unsaturated monomer as an essential component in the presence of a polysaccharide. This is a step of obtaining a crosslinked polymer. 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 essentially used. 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 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 salts thereof. Among these, (meth) acrylic acid and 2- (meth) acrylamido-2-methylpropanesulfonic acid are more preferable, and acrylic acid is particularly preferable in terms of water absorption characteristics. In the present invention, the acid group-containing unsaturated monomer is essentially included, and the proportion thereof is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, particularly preferably 90 to 100 mol% of all monomers. %. The acid group-containing unsaturated monomer may be used alone or in a mixture of two or more.

  In order to achieve both high productivity and high absorption capacity, which is the subject of the present invention, it is necessary to suppress the esterification reaction by polysaccharides and acid groups, and the acid group-containing unsaturated monomer as a repeating unit is It is preferably neutralized with a monovalent salt in the range of 80 to 100 mol%, more preferably neutralized in the range of 85 to 99 mol%, and neutralized in the range of 90 to 98 mol%. Most preferably.

  Preferred examples of the monovalent salt 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.

  Accordingly, the basic substance used for neutralization of the acid group-containing unsaturated monomer as a monomer or the polymer after polymerization (hydrogel) is not particularly limited, but sodium hydroxide, potassium hydroxide, Monovalent basic substances such as alkali metal hydroxides such as lithium hydroxide, carbonic acid (hydrogen) salts such as sodium carbonate (hydrogen) sodium and potassium carbonate (hydrogen), and ammonia are preferred, and sodium hydroxide is particularly preferred. .

  The neutralization may be performed on the polymer after polymerization (hydrous gel), or polymerization may be performed using an acid group-containing unsaturated monomer in the form of a salt as a monomer, From the viewpoint of improving productivity and AAP (water absorption capacity under pressure), etc., a neutralized monomer is used, that is, a partially neutralized salt of an acid group-containing unsaturated monomer is used as a monomer. It is preferable. 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 physical properties of the resulting water-absorbent resin, as an optional component, polyacrylic acid (salt), polyvinyl alcohol, polyethyleneimine can be added to an aqueous monomer solution, a hydrogel after polymerization, a dried product or a powder. Water-soluble resin or water-absorbing resin, thermoplastic resins such as polyethylene and polypropylene, various foaming agents (carbonates, azo compounds, bubbles, etc.), surfactants, deodorants, antibacterial agents, perfumes, silicon dioxide Inorganic powders such as titanium oxide, pigments, dyes, hydrophilic short fibers, plasticizers, and other additives described below may be added as optional components. As the addition amount of these optional components, the water-soluble resin or water-absorbent resin is preferably 0 to 50% by weight, more preferably 0 to 20% by weight, and particularly preferably 0 to 10% by weight with respect to the monomer. Preferably, 0 to 3% by weight is most preferable. Moreover, 0-5 weight% is preferable and, as for the said foaming agent, surfactant, and additive, 0-1 weight% is more preferable.

  Moreover, when using a chelating agent, hydroxycarboxylic acid, and a reducing inorganic salt, as the usage-amount, 10-5000 ppm is preferable with respect to a water absorbing resin, 10-1000 ppm is more preferable, 50-1000 ppm is further more preferable. 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.

  Further, 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”) may be included. 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 0-20 mol%.

(B) Internal crosslinking agent 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, and (polyoxyethylene). ) Trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, polyethylene glycol di (β-acryloyloxypropionate), trimethylolpropane tri (β-acryloyloxypropionate), poly (meth) Compounds having at least two polymerizable double bonds in the molecule such as allyloxyalkanes; polyglycidyl ethers (ethylene glycol diglycidyl ether, etc.), polyols (ethylene glycol, polyethylene glycol, glycerin, sol It can be exemplified one or more kinds of tall, etc.) compound capable of reacting with a carboxyl group capable of forming a covalent bond, such as.

  When using an internal cross-linking agent, it is preferable to essentially use a compound having at least two polymerizable double bonds in the molecule in consideration of the absorption characteristics of the resulting water-absorbent resin. From the viewpoint of physical properties, the internal crosslinking agent is from 0.000 to 5.000 mol%, preferably from 0.000 to 2.000 mol%, more preferably from 0.000 to 0.05 mol%, based on the above monomers. Particularly preferably, it is used in an amount of 0.000 to 0.01 mol%, most preferably 0.001 to 0.01 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.

  Further, as a modification method for obtaining modified starch, modified amylopectin, modified amylose, modified cellulose, modified galactomanna, modified glucomannan, modified xanthan gum, modified carrageenan, etc., esterification such as acetylation treatment, carboxyalkylation, etc. It is obtained by etherification, phosphorylation, oxidation, sulfation, phosphoric acid crosslinking, adipic acid crosslinking, enzyme treatment and combinations thereof.

  One type of substituent may be introduced by modification, or two or more types may be used. The degree of substitution is preferably 0.0 to 2, more preferably 0.0 to 1, particularly preferably 0.0 to 0.5, and most preferably 0.0 to 0.25 from the viewpoint of absorption performance and price. It is.

  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 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 range is less than the above range, polysaccharide elution is increased from the water-absorbent resin, which is not preferable because the absorption capacity decreases. When the molecular weight range exceeds the above range, it is not preferable because it is difficult to handle the polysaccharide.

  The amount of polysaccharide added is preferably 5 to 50% by weight, more preferably 7.5 to 45% by weight, based on a polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing monomer as an essential component. 10 to 40% by weight is most preferable. When the polysaccharide is added beyond this range, the absorption performance is lowered, which is not preferable. When the polysaccharide is added below this range, the utilization rate of biomass is too low, so From the viewpoint of

(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. The combination ratio (molar ratio) is appropriately determined, but is 1/100 to 100/1, more preferably 1/10 to 10/1. From the viewpoint of cost and ability to reduce residual monomer, it is preferable to use a persulfate.

(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 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, the crosslinking agent and the dispersed solid is supplied to the belt is usually preferably 1 to 100 mm. More 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, continuous kneader polymerization (US Pat. Nos. 6,987,151 and 6,710,141) is preferable.

  In the present invention, the resin content concentration in the solution (preferably in the aqueous solution) (the ratio of the total amount of the acid group-containing unsaturated monomer component, polysaccharide component, and optional component in the polymerization solution) is not particularly limited. However, it is preferably 30 to 80% by weight, more preferably 40 to 70% by weight, and still more preferably 45 to 65% by weight. When the resin concentration is less than 30% by weight, the productivity is low. On the other hand, when it exceeds 70% by weight, the absorption ratio is low, which is not preferable.

  The method of mixing the polysaccharide with the monomer aqueous solution containing the acid group-containing unsaturated monomer as an essential component is not particularly limited, but the following five methods are preferable.

  (1): Neutralization that occurs during neutralization by adding polysaccharide to a monovalent basic substance such as sodium hydroxide used as an acid group-containing unsaturated monomer or neutralizing agent unneutralized A method in which a polysaccharide is uniformly dispersed in an aqueous monomer solution using heat and then used for polymerization.

  (2): A polysaccharide is added to a monomer aqueous solution set at a predetermined neutralization rate / monomer concentration, and the polysaccharide is uniformly dispersed and dissolved in the polymer using heat generated by polymerization. How to make.

  (3): Polymerization of a monomer aqueous solution set to a predetermined neutralization rate / monomer concentration is started, and a polysaccharide is added during or after the polymerization, and the polymer is generated by heat generation after polymerization and after heating. A method of uniformly dispersing polysaccharides therein.

  (4): A method in which a polysaccharide is dispersed and dissolved in an aqueous acid group-containing monomer aqueous solution and then polymerized, and the polysaccharide is uniformly dispersed in the polymer using heat of polymerization and heat generation during post-neutralization.

  (5): A method in which a polysaccharide is added after polymerization of an acid group-containing monomer aqueous solution, and the polysaccharide is uniformly dispersed in the polymer using heat generated during post-neutralization.

  Among the above five methods, as in (1), the method in which the polysaccharide is allowed to coexist in the neutralization step of the acid group-containing unsaturated monomer is from the viewpoint of operability and uniform dispersion of the polysaccharide. preferable.

  When the polysaccharide is uniformly dispersed and dissolved in the monomer solution using the heat of neutralization and / or heat of hydration generated in the neutralization step, the temperature of the aqueous monomer solution is preferably 60 ° C. Above, more preferably 70 ° C. or higher, further preferably 80 ° C. or higher, particularly preferably 90 ° C. or higher. Moreover, since starch will not dissolve by pregelatinization unless it is 60 ° C. or higher, if it is less than 60 ° C., dissolution and dispersion may be insufficient, which is not preferable.

  The liquid temperature is measured using a general mercury thermometer, alcohol thermometer, platinum resistance thermometer, contact temperature sensor such as a thermocouple or thermistor, and a radiation thermometer. Thus, in order to effectively use the heat of neutralization and / or heat of hydration, it is preferable to perform neutralization in an adiabatic state, and it is more preferable to perform continuous neutralization and continuous polymerization. Therefore, for example, it is desirable to use a container that suppresses heat dissipation as much as possible, and as the material, a resin, rubber, stainless steel non-contact material part covered with a heat insulating material, or the like is preferably used.

  Furthermore, the generation of heat of neutralization and / or heat of hydration is effectively used for raising the temperature of the monomer aqueous solution, not only for dissolving the hydrophilic compound, but also for heat of neutralization and / or hydration. It is preferable to use heat for removing dissolved oxygen.

  Generally, in radical aqueous solution polymerization, before introducing a polymerization initiator, an inert gas is blown in or degassed under reduced pressure to remove dissolved oxygen that hinders polymerization, but this requires equipment and operating costs. It is the actual situation. More simply, it is preferable to perform the operation of removing dissolved oxygen by using neutralization heat and / or heat of hydration to elevate the aqueous monomer solution and volatilize the dissolved oxygen.

  In a more preferred embodiment, an acid group-containing unsaturated monomer such as acrylic acid, which is a raw material of the monomer aqueous solution, an aqueous alkaline solution, water, etc., is heated by neutralization without deoxygenation in advance, and dissolved oxygen The amount is preferably 4 [mg / L] or less, more preferably 2 [mg / L] or less, and most preferably 1 [mg / L] or less with respect to the monomer aqueous solution, and deoxidation work is performed as it is. Can be subjected to polymerization without. The amount of dissolved oxygen can be measured, for example, by using a measuring device (DO meter UD-1 type manufactured by Central Science Co., Ltd.). That is, the prepared monomer aqueous solution was ice-cooled in a nitrogen atmosphere while gently stirring so as not to engulf bubbles, and when the liquid temperature reached 50 ° C., the above-described measuring apparatus was used to dissolve dissolved oxygen. The amount can be measured.

  In addition, some or all of the acid group-containing unsaturated monomer such as acrylic acid, which is a raw material of the monomer aqueous solution, an aqueous alkaline solution, water, etc. is partially deoxygenated in advance, Deoxygenation is also preferred. In addition, when the acrylic acid and alkali are neutralized with line mixing and the polymerization initiator is further line mixed to start the polymerization at a high temperature of 80 ° C. or higher, the raw acrylic resin is used to prevent the polymerization from starting in the line. It is preferable to reduce the amount of acid, aqueous alkali solution, water, etc. previously deoxygenated or not deoxygenated. The polymerization is usually carried out under normal pressure, but it is also a preferred embodiment that water is distilled off under reduced pressure in order to lower the boiling temperature of the polymerization system. For ease of operation, etc., it is more preferably carried out under normal pressure.

  Although there is no restriction | limiting in particular in polymerization start temperature, 20-105 degreeC is preferable normally, 50-100 degreeC is more preferable, 60-100 degreeC is further more preferable, and 70-100 degreeC is the most preferable.

  In particular, when the polymerization start temperature is less than 20 ° C., not only the productivity is lowered due to the extension of the induction period and the polymerization time, but the physical properties of the water absorbent resin are also lowered. A higher polymerization start temperature is preferable because the induction period and the polymerization time become very short and productivity is improved. However, when the polymerization start temperature exceeds 105 ° C., the induction time becomes too short, and therefore, the initiator mixing operation, etc. This is not preferable because the polymerization control of the polymer becomes difficult.

  In order to set the polymerization initiation temperature to 50 ° C. or higher, the polymerization vessel itself may be heated, or it may be heated in the line when supplying the monomer aqueous solution to the polymerization vessel. The heat of neutralization of the monomer is used to raise the temperature. The generation of heat of neutralization and / or heat of hydration is preferable because it can be used not only for increasing the temperature of the aqueous monomer solution but also for removing dissolved oxygen.

  In order to effectively use heat of neutralization and / or heat of hydration, neutralization is preferably performed in an adiabatic state, and it is more preferable to perform continuous neutralization and continuous polymerization. Therefore, for example, it is desirable to use a container that suppresses heat dissipation as much as possible, and as the material, a resin, rubber, stainless steel non-contact material part covered with a heat insulating material, or the like is preferably used.

  The polymerization start temperature can be observed by the cloudiness of the aqueous monomer solution, the increase in viscosity, the increase in temperature, and the like. The polymerization initiation temperature and the maximum polymerization temperature can be measured using a general mercury thermometer, alcohol thermometer, platinum resistance thermometer, contact temperature sensor such as a thermocouple or thermistor, and a radiation thermometer. Active energy rays such as ultraviolet rays, redox polymerization using an oxidizing agent and a reducing agent, and thermal initiation polymerization using an azo initiator generally have a short induction period of about 1 second to 1 minute. You may prescribe | regulate by the temperature of the monomer aqueous solution before energy irradiation.

  The maximum temperature reached during polymerization in the present invention is not particularly limited, but is preferably 60 to 150 ° C, more preferably 70 to 140 ° C, further preferably 80 to 130 ° C, and particularly preferably 85 to 120 ° C. 115 ° C. is most preferred. When the maximum temperature reached during the polymerization exceeds 150 ° C., it is not preferable in that the physical properties of the obtained polymer (water-containing polymer, water-absorbing resin) are remarkably lowered. In addition, since starch and the like do not proceed with dissolution by pregelatinization unless the temperature is 60 ° C. or higher, if the maximum temperature during polymerization is less than 60 ° C., dissolution and dispersion may be insufficient.

  The polymerization temperature can be measured by using a PC card type data collection system NR-1000 manufactured by Keyence Corporation. Specifically, a thermocouple is placed at the center of the polymerization system, and measurement is performed at a sampling period of 0.1 seconds. From the obtained temperature-time chart, the polymerization start temperature and peak temperature (maximum temperature reached) can be read.

  In the present invention, the difference ΔT between the polymerization initiation temperature and the highest temperature reached during the polymerization is more than 0 ° C., preferably 70 ° C. or less, more preferably 60 ° C. or less, still more preferably 50 ° C. or less, Preferably it is 40 degrees C or less, More preferably, it is 30 degrees C or less, Most preferably, it is 25 degrees C or less. When ΔT is higher than 70 ° C., the physical properties of the resulting water-absorbent resin may be lowered, which is not preferable. In order to obtain the polymerization heat at which the temperature during the polymerization is as described above, the monomer concentration is more preferably 30% by weight or more.

  The polymerization time is not particularly limited, but is preferably 1 second to 60 minutes, more preferably 10 seconds to 40 minutes, particularly preferably 15 seconds to 10 minutes, and most preferably 30 seconds to 3 minutes. If it is longer than the above range, not only the productivity of the resulting polymer (water-containing polymer and water-absorbing resin) is lowered, but also the physical properties such as the absorption capacity and the soluble content are lowered in some cases, such being undesirable.

  Here, the polymerization time is calculated by the time when the aqueous monomer solution is placed in the polymerization vessel and the conditions for initiating the polymerization are complete (when using photodegradable initiator, use photodegradable initiator at the start of light irradiation). If not, it can be obtained by measuring the time from when the monomer aqueous solution and the polymerization initiator are put into the polymerization vessel) to the peak temperature. That is, the polymerization time can be calculated by measuring (induction period) + (time from the start of polymerization until reaching the peak temperature).

  In the polymerization method of the present invention, particularly preferred is a case where polymerization is carried out by initiation of polymerization at a high temperature, after the initiation of polymerization, the temperature of the system rapidly rises to lower the polymerization rate, for example, all monomers. When the polymerization rate is 10 to 20 mol%, the boiling point is reached at 10 to 20 mol%, water vapor is emitted, and the polymerization proceeds while increasing the solid content concentration. The polymerization heat is effectively used to increase the solid content concentration. Therefore, it is desirable to suppress the heat radiation from the contact portion of the polymerization vessel as much as possible, and the material is preferably a resin, rubber, stainless steel non-contact portion covered with a heat insulating material, or heated by a jacket. Used. The increase in solid content during polymerization is preferably 1% by weight or more, more preferably 2% by weight or more, and further preferably 3% by weight or more.

  The increase in solid content is defined by the difference between the solid content of the monomer aqueous solution and the solid content concentration of the obtained water-containing gel polymer, and a small amount of the water-containing polymer taken out from the polymerization vessel is measured as a measurement method. The amount of the water-containing polymer 5 g cut off quickly after being cut off and quickly subdivided with scissors was placed in a petri dish and dried for 24 hours in a 180 ° C. dryer to calculate. The solid content concentration of the particulate hydrous polymer can be calculated by weight loss after taking 5 g of a sample in a petri dish and drying it in a 180 ° C. dryer for 24 hours.

  As an example of a specific means for increasing the solid content in the polymerization of the present invention, for example, in the polymerization under normal pressure, when the polymerization rate is 40 mol%, the temperature is already 100 ° C. or higher, and the polymerization rate is 50 mol%. Polymerization at a temperature of 100 ° C. or higher is a preferred embodiment. Polymerization in which the temperature is already 100 ° C. or higher when the polymerization rate is 30 mol% and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol% is a more preferable embodiment. The most preferable embodiment is such that the temperature is already 100 ° C. or higher when the polymerization rate is 20 mol%, and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol%. In the case of low pressure polymerization, the boiling temperature is already reached when the polymerization rate is 40 mol%, and the boiling temperature is still preferable even when the polymerization rate is 50 mol%. The polymerization is such that the boiling point is already at the boiling point when the polymerization rate is 30 mol%, and the boiling point is still at the boiling point even when the polymerization rate is 50 mol%, and the boiling temperature is already reached when the polymerization rate is 20 mol%. Polymerization that is still at the boiling temperature even at a rate of 50 mol% is the most preferred embodiment.

  Thus, if it adjusts so that it may become high temperature with a low polymerization rate, the time for superposition | polymerization will also be short and it will usually finish in 10 minutes or less. Here, the polymerization time indicates the time from when the monomer aqueous solution to which the polymerization initiator is added to the polymerization vessel to when the water-containing polymer is taken out from the polymerization vessel.

(2-2) Gel pulverization step The hydrogel polymer obtained by polymerization may be dried as it is, but in the case of aqueous solution polymerization, it is dried after being shredded using a gel pulverizer or the like as necessary. . The shape of the water-absorbent resin particles of the present invention is not particularly limited, and can be any form such as granules, powders, flakes, and fibers.

  Accordingly, the shredding is performed by various methods, and examples thereof include a method of extruding from a screw type extruder having a porous structure of an arbitrary shape and pulverizing. The hydrogel crosslinked polymer obtained by aqueous solution polymerization during or after the completion of the polymerization reaction is about 0.1 mm to about 50 mm, further 0.2 to 10 mm, especially 0.5 to 5 mm particles by a predetermined method. It is preferable to grind to a diameter.

(2-3) Drying Step The hydrogel crosslinked polymer is dried 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 about 10 seconds to 2 hours, more preferably about 1 minute to 1.5 hours, and particularly preferably 10 minutes to 1 hour.

  The surface temperature of the particulate 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.

  From the viewpoint of coloring in the water-absorbent resin, it is preferable that the time from when the gel is pulverized until the hydrogel enters the dryer is shorter. 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 adjusted to 3 to 15% by weight, more preferably 4 to 14% by weight, still more preferably 5 to 13% by weight, and particularly preferably 6 to 12% by weight. And drying. Excessive drying so as to fall below this moisture content range is not preferable because an esterification reaction between an acid group and starch occurs and the absorption capacity of the water-absorbent resin is greatly reduced. Further, when the moisture content exceeds this moisture content range, the dried product cannot be pulverized in the pulverization step, which causes problems such as clogging of the pulverizer.

(2-4) Grinding step The polymer dried product in a substantially dry state obtained after the drying step is pulverized in order to obtain particles having a size within a predetermined range (pulverization step). The pulverization method at this time is 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 translations of PCT 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”).

(2-5) Classification process The pulverized product obtained in the pulverization process is classified. Thus, only particles having a size within a predetermined range are selected and used as a water absorbent resin. The classification method at this time is also not particularly limited. For example, sieving using a sieve is preferably used. For example, when the size range of the pulverized product is 150 μm to 850 μm, the pulverized product is first screened with a sieve having an opening of 850 μm, and then the pulverized product passing through the sieve is 150 μm. Sift with a sieve with a sieve opening. The pulverized product remaining on the 150 μm sieve becomes a water-absorbing resin within a desired range.

  The weight average particle diameter (D50) before surface crosslinking is adjusted to 250 to 450 μm, preferably 275 to 425 μm, more preferably 300 to 400 μm. Further, the smaller the particle size is less than 150 μm, the better, and usually 0 to 5% by weight, preferably 0 to 3% by weight, particularly preferably 0 to 1% by weight. In the present invention, the ratio of 850 to 150 μm is adjusted to 95% by weight or more, more preferably 96% by weight or more, and most preferably 98% by weight or more (upper limit 100% by weight). 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 weight average particle diameter (D50) and the amount of particles of less than 150 μm are maintained in the above range even after surface crosslinking.

(2-6) Recovery / regeneration of water-absorbent resin fine particles In the present invention, as a technique for finely controlling the particle diameter and reducing the amount of fine particles (particles less than 150 μm), for example, the recovery / regeneration of fine particles is performed. Made.

  The water-absorbing 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 50 ° C. to boiling point) ( The mass ratio of the water-absorbent resin fine particles to hot water is 5: 4 to 3: 7) It can be regenerated to the water-containing gel-like substance again, and then dried and pulverized to regenerate the desired water-absorbent resin particles. Examples of such techniques include U.S. Pat. Nos. 228930, 5264495, 4950692, 5478879, and EP 844270. The amount of waste can be reduced by collecting and regenerating particles that are not intended.

(2-7) Surface cross-linking step The water-absorbent resin obtained in the present invention can be made into a water-absorbent resin more suitable for hygiene 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 on the surface layer of the water-absorbent resin (near the surface: usually several tens of μm from the surface of the water-absorbent resin). It can be formed by a crosslinking reaction or the like.

  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), an alkylene carbonate compound (US Pat. No. 5,672,633), a polyvalent metal ion such as an aluminum salt (US Pat. Nos. 6,605,673 and 6,620,899) or the like, Two or more 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.

  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. Polyvalent metal ions such as polyamide polyamine-epihalo adducts and aluminum salts are preferred. In addition, a combination of organic acid / inorganic acid and a method of surface crosslinking by polymerizing monomers on the surface of the water-absorbent resin are preferred.

  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 sulfuric acid Aruminimu, polyamide polyamine - epihalohydrin adducts.

  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 weight part with respect to 100 weight part of water absorbing resin, It is more preferable to use 0.005-5 weight part, 0.01-3 weight More preferably, parts are used. When the amount of the surface cross-linking agent is less than 0.005 parts by weight, the absorption capacity under pressure may decrease. If it is used in excess of 10 parts by weight, 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 weight with respect to 100 parts by weight 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 weight or less with respect to 100 parts by weight 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 further 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 order to obtain a water-absorbing agent having a high absorption capacity and a high absorption capacity under pressure, it is preferable to carry out surface crosslinking in a state where the water content of the water-absorbent resin is maintained at 3 to 15% by weight, and maintained at 4 to 14% by weight. It is more preferable to carry out the surface crosslinking in a state where it is maintained, it is more preferable to carry out the surface crosslinking in a state where it is maintained at 5 to 13% by weight, and it is most preferable to carry out the surface crosslinking in a state where it is maintained at 6 to 12% by weight. 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.

  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 its physical properties. In addition, the hydrophilic amorphous of 0.001 to 20 parts by weight, more preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin as an additive Water-insoluble fine particles such as silica, reducing agents, antibacterial agents, deodorants, chelating agents, polyvalent metal compounds, and the like may be added.

[3] Water-absorbent resin of the present invention The water-absorbent resin produced by the above-described production method is a novel water-absorbent resin that has never existed. That is, the water-absorbing resin of the present invention is 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. The water absorbent resin is characterized by satisfying the following (i) to (iv).

(I) Neutralization rate of acid group is 80 to 100 mol%
(Ii) Weight average particle diameter (D50) is 250 to 450 μm
(Iii) The weight percentage of particles having a particle diameter of less than 150 μm is 0 to 5% by weight.
(Iv) Moisture content of 3 to 15% by weight
The water-absorbent resin of the present invention has (i) an acid group neutralization rate of 80 to 100 mol%, more preferably 85 to 99 mol%, and most preferably 90 to 98 mol%. When the neutralization rate of the acid groups is less than 80 mol%, the esterification reaction of polysaccharides and acid groups frequently occurs in the drying step and the like, so that the water absorption ratio is greatly reduced. On the other hand, when the drying temperature is lowered in order to avoid the reaction between the polysaccharide and the acid group, the productivity is greatly reduced, which is not preferable. In addition, the neutralization rate of the acid group in the water-absorbent resin is Ext. It can also be measured at the time of measuring (soluble amount).

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

  Further, in the water absorbent resin of the present invention, (iii) the weight percentage of particles having a particle diameter of less than 150 μm is 0 to 5% by weight, preferably 0 to 3% by weight, more preferably 0 to 1% by weight. The 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.

  Further, the water-absorbent resin of the present invention has (iv) a water content of 3 to 15% by weight, more preferably 4 to 14% by weight, still more preferably 5 to 13% by weight, particularly preferably 6 to 12% by weight. Adjusted to 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, it is not preferable because the water absorption capacity under pressure of the water-absorbent resin tends to decrease due to damage in the process. When the water content exceeds the above range, the handleability of the water-absorbing agent is lowered and the fluidity of the powder is lowered, which is not preferable.

[4] Other physical properties of the water-absorbent resin of the present invention (4-1) CRC
The water absorbent resin of the present invention has a CRC (water absorption capacity under no pressure) of 31 to 50 [g / g], more preferably 32 to 50 [g / g], and still more preferably 33 to 50 [g / g]. ], Particularly preferably 34 to 50 [g / g], most preferably 35 to 50 [g / g]. When the CRC is lower than these ranges, it is not preferable when used for an absorbent article such as a diaper because problems such as insufficient absorbent capacity occur or the amount of water-absorbing agent needs to be increased.

(4-2) AAP (absorption capacity under pressure)
The water absorbent resin of the present invention has an AAP (water absorption capacity under pressure) of 20 to 50 [g / g], more preferably 21 to 50 [g / g], and still more preferably 32 to 50 [g / g]. Especially preferably, it is 23-50 [g / g], Most preferably, it is 24-50 [g / g]. When AAP is below these ranges, urine leakage may occur under pressure when used for absorbent articles such as paper diapers.

(4-3) pH
The water-absorbent resin of the present invention has a pH of 6.5 to 7.5, more preferably 6.6 to 7.4, and still more preferably 6.7 to 7.3. If the pH is out of these ranges, it is not preferable because it may cause skin irritation when used in absorbent articles such as paper diapers.

(4-4) Logarithmic standard deviation of particle size distribution (σζ)
The water-absorbent resin of the present invention has a logarithmic standard deviation (σζ) of particle size distribution of 0.2 to 0.50, more preferably 0.25 to 0.45, and still more preferably 0.30 to 0.40. Outside these ranges, segregation occurs and performance varies, which is not preferable.

[5] 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, sanitary napkins and the like. 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. The physical properties described in the claims and examples of the present invention are determined according to the EDANA method and the following measurement examples under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH% unless otherwise specified. It was. 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 described as “L” and “wt%” may be described as “wt%”.

[Measurement Example 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-absorbing resin was weighed and uniformly put into a bag (60 × 60 mm) made of unwoven cloth and heat sealed, and then immersed in 500 mL of 0.9 wt% sodium chloride aqueous solution adjusted to 25 ± 3 ° C. 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.

[Measurement Example 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 RH%, 0.900 g of the water absorbent 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 Example 3] Ext. (Soluble content)
Ext (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, Ext (soluble amount) was calculated according to the following formula based on the average molecular weight of the monomer and the titration amount obtained by the above operation.

  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.

[Measurement Example 4] pH
The pH was measured according to ERT400.2-02.

  A beaker with a capacity of 250 mL was charged with 100 mL of a 0.9 wt% sodium chloride aqueous solution, and slowly stirred with a magnetic stirrer (length 30 mm, outer diameter 6 mm). In this state, 0.5 g of water-absorbing resin was added and stirred. After 10 minutes, the rotation of the magnetic stirrer was stopped and allowed to stand. After 1 minute, the pH electrode was immersed in the supernatant and the pH was measured. The pH electrode used was calibrated with standard solutions of pH 4.0 and 7.0.

[Measurement Example 5] 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: [wt%]) was calculated according to the following formula.

[Measurement Example 6] JIS standard sieve (The IIDA TESTING SIEVE) having a weight average particle size (D50), logarithmic standard deviation of particle size distribution (σζ), and weight percentage of particle size less than 150 μm, and openings 850 μm, 600 μm, 300 μm, 150 μm: 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 weight percentage (unit:% by weight) of particles having a particle diameter of less than 150 μm was calculated. The “weight 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 weight 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 wt% was read from this graph as the weight average particle diameter (D50). In addition, a weight average particle diameter (D50) means the particle diameter of the standard sieve corresponding to 50 weight% 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 weight, and X2 is a particle diameter corresponding to R = 15.9% by weight.

[Example 1]
(Polymerization process)
348.9 g (4.841 mol) of acrylic acid, 0.253 g of polyethylene glycol diacrylate (average number of added moles of ethylene oxide 9, average molecular weight 522) as an internal crosslinking agent, 1 wt% diethylenetriaminepentaacetic acid / 5 sodium aqueous solution as a chelating agent 2.25 g and 50.0 g of corn starch (manufactured by Kanto Chemical Co., Ltd., catalog No. 37325-02) (addition ratio; 11.1% by weight based on the acrylic acid (sodium salt) component) are added to a 1 L polypropylene resin. A solution (A) was prepared by mixing in a container made of glass, and the temperature was adjusted to 25 ° C. In another 1 L polypropylene resin container, 379.3 g of a 48.5 wt% sodium hydroxide aqueous solution (4.599 mol, neutralization rate equivalent to 95 mol%) and 250.0 g of ion-exchanged water were added. A solution (B) was prepared by mixing, and the temperature was adjusted to 25 ° C.

  Next, the monomer aqueous solution (C) is obtained by quickly adding and mixing the solution (B) into the solution (A) rotated at 500 rpm with a magnetic stirrer chip (length 50 mm, outer diameter 12.3 mm). It was. At this time, the temperature of the monomer aqueous solution (C) rose to 100 ° C. due to heat of neutralization and heat of dissolution.

  Next, when the temperature of the monomer aqueous solution (C) decreased to 95 ° C., 19.37 g of a 3 wt% aqueous sodium persulfate solution was added. After stirring for about 5 seconds, it was immediately poured into a stainless bat-type container in an open system. The stainless bat-shaped container is a container having a bottom surface of 250 × 250 mm, an upper surface of 640 × 640 mm, and a height of 50 mm and having a trapezoidal central cross section, and the upper surface is open. The inner surface of the bat-type container is processed with Teflon (registered trademark). Furthermore, the surface of the stainless steel bat-shaped container is heated by a hot plate (NEO HOTPLATE H1-1000; manufactured by Inoue Seieido Co., Ltd.) heated to 130 ° C. in advance.

  Polymerization of the solution poured into the stainless steel bat-shaped container was soon started, and stationary polymerization proceeded while generating water vapor. The peak temperature was shown within 1 minute after the start of polymerization, and the hydrogel crosslinked polymer (hydrogel) was taken out when 3 minutes had passed. The series of operations was performed in an open air system.

(Gel refinement process)
After the hydrogel crosslinked polymer obtained in the above polymerization step is cut into strips with a width of 30 mm, ion exchange water is added at 50 [mL / min], and about 6 [g / sec] is charged. It is charged into a meat chopper (MEAT-CHOPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 9.5 mm, hole number: 18, die thickness 8 mm) at a speed to obtain a finely divided hydrogel crosslinked polymer. It was.

(Drying process, grinding process and classification process)
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 weight, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by weight, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by weight. 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.

(Surface cross-linking process)
0.1 part by weight of ethylene glycol diglycidyl ether, 1.0 part by weight of propylene glycol, 3.0 parts by weight of pure water, isopropyl alcohol with respect to 100 parts by weight of the water absorbent resin (E1-b) obtained in the above step After uniformly mixing 1.0 part by weight of the surface crosslinking agent, the mixture was heat-treated at 150 ° C. for 30 minutes. Thereafter, the obtained particles were pulverized until passing 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 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 weight, the proportion of particles having a particle size of 300 μm or more and less than 600 μm was 59% by weight, The proportion of particles having a diameter of 150 μm or more and less than 300 μm was 25% by weight, 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]
(Polymerization process)
357.3 g (4.959 mol) of acrylic acid, 0.259 g of polyethylene glycol diacrylate (average number of moles of added ethylene oxide, average molecular weight 522) as an internal crosslinking agent, 1 wt% diethylenetriaminepentaacetic acid / 5 sodium aqueous solution as a chelating agent 2.25 g and 50.0 g of corn starch (manufactured by Kanto Chemical Co., Ltd., catalog No. 37325-02) (addition ratio; 11.1% by weight based on the acrylic acid (sodium salt) component) are added to a 1 L polypropylene resin. A solution (D) was prepared by mixing in a container made of glass, and the temperature was adjusted to 25 ° C. Further, in another 1L polypropylene resin container, 347.6 g of a 48.5 wt% sodium hydroxide aqueous solution (4.215 mol, neutralization rate equivalent to 85 mol%) and 272.7 g of ion-exchanged water were added. A solution (E) was prepared by mixing, and the temperature was adjusted to 35 ° C.

  Next, the aqueous solution of monomer (F) is obtained by quickly adding and mixing the solution (E) into the solution (D) rotated at 500 rpm with a magnetic stirrer chip (length 50 mm, outer diameter 12.3 mm). It was. At this time, the temperature of the aqueous monomer solution (F) rose to 100 ° C. due to heat of neutralization and heat of dissolution.

  Next, when the temperature of the monomer aqueous solution (F) decreased to 95 ° C., 19.83 g of a 3 wt% sodium persulfate aqueous solution was added. After stirring for about 5 seconds, it was immediately poured into a stainless bat-type container in an open system. The stainless bat-shaped container is a container having a bottom surface of 250 × 250 mm, an upper surface of 640 × 640 mm, and a height of 50 mm and having a trapezoidal central cross section, and the upper surface is open. The inner surface of the bat-type container is processed with Teflon (registered trademark). Furthermore, the surface of the stainless steel bat-shaped container is heated by a hot plate (NEO HOTPLATE H1-1000; manufactured by Inoue Seieido Co., Ltd.) heated to 130 ° C. in advance.

  Polymerization of the solution poured into the stainless steel bat-shaped container was soon started, and stationary polymerization proceeded while generating water vapor. The peak temperature was shown within 1 minute after the start of polymerization, and the hydrogel crosslinked polymer (hydrogel) was taken out when 3 minutes had passed. The series of operations was performed in an open air system.

(Gel refinement process)
After the hydrogel crosslinked polymer obtained in the above polymerization step is cut into strips with a width of 30 mm, ion exchange water is added at 50 [mL / min], and about 6 [g / sec] is charged. It is charged into a meat chopper (MEAT-CHOPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 9.5 mm, hole number: 18, die thickness 8 mm) at a speed to obtain a finely divided hydrogel crosslinked polymer. It was.

(Drying process, grinding process and classification process)
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 weight, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by weight, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by weight. By blending, a water absorbent resin (E2-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 (E2-b).

(Surface cross-linking process)
0.1 part by weight of ethylene glycol diglycidyl ether, 1.0 part by weight of propylene glycol, 3.0 parts by weight of pure water, isopropyl alcohol with respect to 100 parts by weight of the water absorbent resin (E2-b) obtained in the above step After uniformly mixing 1.0 part by weight of the surface crosslinking agent, the mixture was heat-treated at 100 ° C. for 60 minutes. Thereafter, the obtained particles were pulverized until passing through a JIS standard sieve having an opening of 850 μm. Thus, a surface-crosslinked water-absorbing resin (E2-st) was obtained. The particle size distribution of the surface-crosslinked water-absorbent resin (E2-st) obtained was 15% by weight 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 proportion of particles having a weight percentage of 150% to less than 300 μm was 25% by weight, the average particle diameter (D50) was 394 μm, and the logarithmic standard deviation (σζ) was 0.339. Other physical properties are shown in Table 2.

[Example 3]
Except that corn starch was changed to soluble starch (manufactured by Kanto Chemical Co., Ltd .; catalog No. 37328-01), the same operation as in Example 1 was performed, and the ratio of particles having a particle size of 600 μm or more and less than 850 μm was 14 wt%. The average particle size (D50) is 379 μm by blending so that the proportion of particles having a diameter of 300 μm or more and less than 600 μm is 57% by weight, and the proportion of particles having a particle size of 150 μm or more and less than 300 μm is 29% by weight. A water absorbent resin (E3-b) having a logarithmic standard deviation (σζ) of 0.330 was obtained. Other physical properties of the water absorbent resin (E3-b) obtained are shown in Table 1.
Moreover, surface-crosslinked water-absorbing resin (E3-st) was obtained by performing surface crosslinking in the same manner as in Example 1. The particle size distribution of the surface-crosslinked water-absorbent resin (E3-st) obtained was 18% by weight 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 weight percent of 150 μm or more and less than 300 μm was 22% by weight, the average particle size (D50) was 412 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Example 4]
Except for changing corn starch to soluble starch (manufactured by Kanto Chemical Co., Inc .; catalog No. 37328-01), the same operation as in Example 2 was performed, and the ratio of particles having a particle size of 600 μm or more and less than 850 μm was 14 wt%. The average particle size (D50) is 379 μm by blending so that the proportion of particles having a diameter of 300 μm or more and less than 600 μm is 57% by weight, and the proportion of particles having a particle size of 150 μm or more and less than 300 μm is 29% by weight. A water absorbent resin (E4-b) having a logarithmic standard deviation (σζ) of 0.330 was obtained. The physical properties of the water absorbent resin (E4-b) obtained are shown in Table 1.
Moreover, surface-crosslinked water-absorbing resin (E4-st) was obtained by performing surface crosslinking in the same manner as in Example 2. The particle size distribution of the surface-crosslinked water-absorbent resin (E4-st) obtained was 18% by weight 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 ratio of the particles having a weight percent of 150 μm or more and less than 300 μm was 24 wt%, the average particle size (D50) was 406 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Example 5]
(Polymerization process)
326.3 g (4.528 mol) of acrylic acid, 0.237 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide 9, average molecular weight 522) as an internal crosslinking agent, 1 wt% diethylenetriaminepentaacetic acid / 5 sodium aqueous solution as a chelating agent 2.10 g and soluble starch (manufactured by Kanto Chemical Co., Ltd .; catalog No. 37328-01) 105.2 g (addition ratio; 25.0 wt% based on acrylic acid (sodium salt) component) A solution (G) was prepared by mixing in a container made of glass, and the temperature was adjusted to 25 ° C. Further, in another 1 L polypropylene resin container, 354.8 g of a 48.5 wt% aqueous sodium hydroxide solution (4.302 mol, neutralization rate equivalent to 95 mol%) and 298.5 g of ion-exchanged water were added. A solution (H) was prepared by mixing, and the temperature was adjusted to 35 ° C.

  Next, a monomer aqueous solution (I) is obtained by quickly adding and mixing the solution (H) in the solution (G) rotated at 500 rpm with a magnetic stirrer chip (length 50 mm, outer diameter 12.3 mm). It was. At this time, the temperature of the monomer aqueous solution (I) rose to 100 ° C. due to heat of neutralization and heat of dissolution.

  Next, when the temperature of the monomer aqueous solution (I) decreased to 95 ° C., 18.11 g of a 3 wt% aqueous sodium persulfate solution was added. After stirring for about 5 seconds, it was immediately poured into a stainless bat-type container in an open system. The stainless bat-shaped container is a container having a bottom surface of 250 × 250 mm, an upper surface of 640 × 640 mm, and a height of 50 mm and having a trapezoidal central cross section, and the upper surface is open. The inner surface of the bat-type container is processed with Teflon (registered trademark). Furthermore, the surface of the stainless steel bat-shaped container is heated by a hot plate (NEO HOTPLATE H1-1000; manufactured by Inoue Seieido Co., Ltd.) heated to 130 ° C. in advance.

  Polymerization of the solution poured into the stainless steel bat-shaped container was soon started, and stationary polymerization proceeded while generating water vapor. The peak temperature was shown within 1 minute after the start of polymerization, and the hydrogel crosslinked polymer (hydrogel) was taken out when 3 minutes had passed. The series of operations was performed in an open air system.

(Gel refinement process)
After the hydrogel crosslinked polymer obtained in the above polymerization step is cut into strips with a width of 30 mm, ion exchange water is added at 50 [mL / min], and about 6 [g / sec] is charged. It is charged into a meat chopper (MEAT-CHOPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 9.5 mm, hole number: 18, die thickness 8 mm) at a speed to obtain a finely divided hydrogel crosslinked polymer. It was.

(Drying process, grinding process and classification process)
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 weight, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by weight, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by weight. By blending, a water absorbent resin (E5-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 (E5-b) obtained are shown in Table 1.

(Surface cross-linking process)
0.1 part by weight of ethylene glycol diglycidyl ether, 1.0 part by weight of propylene glycol, 3.0 parts by weight of pure water, isopropyl alcohol with respect to 100 parts by weight of the water absorbent resin (E5-b) obtained in the above step After uniformly mixing 1.0 part by weight of the surface crosslinking agent, the mixture was heat-treated at 160 ° C. for 30 minutes. Thereafter, the obtained particles were pulverized until passing through a JIS standard sieve having an opening of 850 μm. Thus, a surface-crosslinked water-absorbing resin (E5-st) was obtained. The particle size distribution is 17% by weight of particles having a particle size of 600 μm or more and less than 850 μm, 61% by weight of particles having a particle size of 300 μm or more and less than 600 μm, and 22% by weight of particles having a particle size of 150 μm or more and less than 300 μm. The average particle size (D50) was 409 μm, and the logarithmic standard deviation (σζ) was 0.347. Other physical properties are shown in Table 2.

[Comparative Example 1]
(Polymerization process)
368.0 g (5.107 mol) of acrylic acid, 0.267 g of polyethylene glycol diacrylate (average number of added moles of ethylene oxide 9, average molecular weight 522) as an internal crosslinking agent, 1 wt% diethylenetriaminepentaacetic acid / 5 sodium aqueous solution as a chelating agent 2.25 g and 50.0 g of corn starch (manufactured by Kanto Chemical Co., Ltd .; catalog No. 37325-02) (addition ratio; 11.1% by weight based on the acrylic acid (sodium salt) component) are added to a 1 L polypropylene resin. A solution (J) was prepared by mixing in a container made of glass, and the temperature was adjusted to 25 ° C. Further, in another 1 L polypropylene resin container, 307.5 g of a 48.5% by weight aqueous sodium hydroxide solution (3.728 mol, equivalent to a neutralization rate of 73 mol%) and 301.6 g of ion-exchanged water were added. The solution (K) was prepared by mixing, and the temperature was adjusted to 25 ° C.

  Next, the aqueous solution of monomer (L) is obtained by quickly adding and mixing the solution (K) in the solution (J) rotated at 500 rpm with a magnetic stirrer chip (length 50 mm, outer diameter 12.3 mm). It was. At this time, the temperature of the monomer aqueous solution (L) rose to 100 ° C. due to heat of neutralization and heat of dissolution.

  Next, when the temperature of the monomer aqueous solution (L) decreased to 95 ° C., 20.43 g of a 3 wt% aqueous sodium persulfate solution was added. After stirring for about 5 seconds, it was immediately poured into a stainless bat-type container in an open system. The stainless bat-shaped container is a container having a bottom surface of 250 × 250 mm, an upper surface of 640 × 640 mm, and a height of 50 mm and having a trapezoidal central cross section, and the upper surface is open. The inner surface of the bat-type container is processed with Teflon (registered trademark). Furthermore, the surface of the stainless steel bat-shaped container is heated by a hot plate (NEO HOTPLATE H1-1000; manufactured by Inoue Seieido Co., Ltd.) heated to 130 ° C. in advance.

  Polymerization of the solution poured into the stainless steel bat-shaped container was soon started, and stationary polymerization proceeded while generating water vapor. The peak temperature was shown within 1 minute after the start of polymerization, and the hydrogel crosslinked polymer (hydrogel) was taken out when 3 minutes had passed. The series of operations was performed in an open air system.

(Gel refinement process)
After the hydrogel crosslinked polymer obtained in the above polymerization step is cut into strips with a width of 30 mm, ion exchange water is added at 50 [mL / min], and about 6 [g / sec] is charged. It is charged into a meat chopper (MEAT-CHOPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 9.5 mm, hole number: 18, die thickness 8 mm) at a speed to obtain a finely divided hydrogel crosslinked polymer. It was.

(Drying process, grinding process and classification process)
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 weight, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by weight, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by weight. By blending, a comparative water absorbent resin (C1-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 comparative water absorbent resin (C1-b) obtained are shown in Table 1.

(Surface cross-linking process)
For 100 parts by weight of the comparative water-absorbing resin (C1-b) obtained in the above process, 0.1 part by weight of ethylene glycol diglycidyl ether, 1.0 part by weight of propylene glycol, 3.0 parts by weight of pure water, After uniformly mixing a surface cross-linking agent consisting of 1.0 part by weight of isopropyl alcohol, the mixture was heat-treated at 100 ° C. for 60 minutes. Thereafter, the obtained particles were pulverized until passing through a JIS standard sieve having an opening of 850 μm. In this manner, a comparative water-absorbing resin (C1-st) having a cross-linked surface was obtained. In the obtained particle size distribution of (C1-st), the proportion of particles having a particle size of 600 μm or more and less than 850 μm is 14% by weight, the proportion of particles having a particle size of 300 μm or more and less than 600 μm is 64% by weight, and the particle size is 150 μm. The proportion of particles having a particle size of less than 300 μm was 22% by weight, the average particle size (D50) was 400 μm, and the logarithmic standard deviation (σζ) was 0.332. Other physical properties are shown in Table 2.

[Comparative Example 2]
(Polymerization process)
368.0 g (5.107 mol) of acrylic acid, 0.267 g of polyethylene glycol diacrylate (average number of added moles of ethylene oxide 9, average molecular weight 522) as an internal crosslinking agent, 1 wt% diethylenetriaminepentaacetic acid / 5 sodium aqueous solution as a chelating agent 2.25 g and soluble starch (manufactured by Kanto Chemical Co., Ltd .; catalog No. 37328-01) 50.0 g (addition ratio; 11.1% by weight based on acrylic acid (sodium salt) component) and 1 L polypropylene resin A solution (M) was prepared by mixing in a container made of glass, and the temperature was adjusted to 25 ° C. Further, in another 1 L polypropylene resin container, 307.5 g of a 48.5% by weight aqueous sodium hydroxide solution (3.728 mol, equivalent to a neutralization rate of 73 mol%) and 301.6 g of ion-exchanged water were added. A solution (N) was prepared by mixing, and the temperature was adjusted to 25 ° C.

  Next, the aqueous solution of monomer (O) is obtained by quickly adding and mixing the solution (N) into the solution (M) rotated at 500 rpm with a magnetic stirrer chip (length 50 mm, outer diameter 12.3 mm). It was. At this time, the temperature of the aqueous monomer solution (O) rose to 100 ° C. due to heat of neutralization and heat of dissolution.

  Next, when the temperature of the monomer aqueous solution (O) decreased to 95 ° C., 20.43 g of a 3 wt% sodium persulfate aqueous solution was added. After stirring for about 5 seconds, it was immediately poured into a stainless bat-type container in an open system. The stainless bat-shaped container is a container having a bottom surface of 250 × 250 mm, an upper surface of 640 × 640 mm, and a height of 50 mm and having a trapezoidal central cross section, and the upper surface is open. The inner surface of the bat-type container is processed with Teflon (registered trademark). Furthermore, the surface of the stainless steel bat-shaped container is heated by a hot plate (NEO HOTPLATE H1-1000; manufactured by Inoue Seieido Co., Ltd.) heated to 130 ° C. in advance.

  Polymerization of the solution poured into the stainless steel bat-shaped container was soon started, and stationary polymerization proceeded while generating water vapor. The peak temperature was shown within 1 minute after the start of polymerization, and the hydrogel crosslinked polymer (hydrogel) was taken out when 3 minutes had passed. The series of operations was performed in an open air system.

(Gel refinement process)
After the hydrogel crosslinked polymer obtained in the above polymerization step is cut into strips with a width of 30 mm, ion exchange water is added at 50 [mL / min], and about 6 [g / sec] is charged. It is charged into a meat chopper (MEAT-CHOPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 9.5 mm, hole number: 18, die thickness 8 mm) at a speed to obtain a finely divided hydrogel crosslinked polymer. It was.

(Drying process, grinding process and classification process)
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 weight, the ratio of particles having a particle diameter of 300 μm or more and less than 600 μm is 57% by weight, and the ratio of particles having a particle diameter of 150 μm or more and less than 300 μm is 29% by weight. By blending, a comparative water absorbent resin (C2-b) having an average particle diameter (D50) of 379 μm and a logarithmic standard deviation (σζ) of 0.330 was obtained. Other physical properties are shown in Table 1.

(Surface cross-linking process)
For 100 parts by weight of the comparative water-absorbing resin (C2-b) obtained in the above step, 0.1 part by weight of ethylene glycol diglycidyl ether, 1.0 part by weight of propylene glycol, 3.0 parts by weight of pure water, After uniformly mixing a surface cross-linking agent consisting of 1.0 part by weight of isopropyl alcohol, the mixture was heat-treated at 100 ° C. for 60 minutes. Thereafter, the obtained particles were pulverized until passing through a JIS standard sieve having an opening of 850 μm. Thus, a comparative water-absorbing resin (C2-st) having a surface cross-linked was obtained. The particle size distribution of the obtained (C2-st) is 18% by weight of particles having a particle size of 600 μm or more and less than 850 μm, 62% by weight of particles having a particle size of 300 μm or more and less than 600 μm, and 150 μm or more but less than 300 μm. The proportion of the particles was 20% by weight, the average particle size (D50) was 418 μm, and the logarithmic standard deviation (σζ) was 0.347. 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 12 wt%, and the particle size was 300 μm or more and less than 600 μm. The proportion of particles is 51% by weight, the proportion of particles having a particle size of 150 μm or more and less than 300 μm is 26% by weight, the proportion of particles having a particle size of less than 150 μm is 11% by weight, and the average particle size (D50) is 349 μm. A comparative water absorbent resin (C3-b) having a logarithmic standard deviation (σζ) of 0.565 was obtained. Other physical properties are shown in Table 1.

  The obtained comparative water-absorbing resin (C3-b) was subjected to surface crosslinking in the same manner as in Example 1 to obtain a surface-crosslinked comparative water-absorbing resin (C3-st). The particle size distribution of the surface-crosslinked water-absorbing resin (C3-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 weight, and the proportion of particles having a particle size of 300 μm or more and less than 600 μm was 54. The proportion of particles having a weight percent of 150 μm or more and less than 300 μm is 24% by weight, and the proportion of particles having a particle size of less than 150 μm is 8% by weight, the average particle size (D50) is 370 μm, and the logarithmic standard deviation (σζ) is 0.525. Met. Table 2 shows other physical properties of the water-absorbing agent (C3-st) obtained.

[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.

  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.

DESCRIPTION OF SYMBOLS 100 Plastic support cylinder 101 Stainless steel 400 mesh wire mesh 102 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 (11)

A surface-crosslinked water-absorbent resin comprising a polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component and a polysaccharide, and comprising the following (i) to ( A water-absorbing agent characterized by satisfying iv).
(I) The neutralization rate of the acid group is 80 to 100 mol%,
(Ii) Weight average particle diameter (D50) is 250 to 450 μm
(Iii) The weight percentage of particles having a particle diameter of less than 150 μm is 0 to 5% by weight.
(Iv) Moisture content of 3 to 15% by weight   The water-absorbent resin according to claim 1, wherein the polysaccharide is at least one selected from starch, cellulose, and modified products thereof.   The water-absorbent resin according to claim 1 or 2, wherein the content of the polysaccharide is 5 to 50% by weight based on the acid group-containing unsaturated monomer component.   The water-absorbent resin according to any one of claims 1 to 3, wherein the acid group of the acid group-containing unsaturated monomer is a carboxyl group.   The CRC of the water-absorbing agent is 31 to 50 [g / g], and the AAP (water absorption under pressure) is 20 to 50 [g / g]. The water-absorbent resin according to any one of the above.   The water-absorbent resin according to any one of claims 1 to 5, wherein the pH of the water-absorbing agent is 6.5 to 7.5. A step of polymerizing a monomer component comprising an acid group-containing unsaturated monomer having a neutralization rate of 80 to 100 mol% as an essential component in the presence of a polysaccharide, and a moisture content after drying to 3 to 15% by weight The step of adjusting and drying, and the polymer dry particles satisfying the following (I) to (III) obtained through these steps are subjected to surface crosslinking while maintaining the range of (I) to (III) (I) Weight average particle diameter (D50) is 250 micrometers-450 micrometers characterized by including the process
(II) 0-5% by mass of particles less than 150 μm
(III) Water content is 3 to 15% by weight   The method for producing a water-absorbent resin according to claim 7, wherein the polymerization initiation temperature is 50 ° C or higher.   The method for producing a water-absorbent resin according to claim 7 or 8, wherein a polysaccharide is allowed to coexist in the neutralization step of the acid group-containing unsaturated monomer.   The resin content concentration in the polymerization (a proportion of the total amount of the monomer component, polysaccharide component, and optional component in the polymerization solution) is 40% by weight or more. A method for producing a water-absorbent resin as described in 1. The manufacturing method of the water absorbing resin of any one of Claims 7-10 whose said drying process is hot-air drying of the temperature of 100-200 degreeC.

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