JP2016131902A - Method for producing polyacrylic acid (salt)-based water-absorbing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyacrylic acid (salt)-based water-absorbing agent which exhibits excellent deodorant performance and antifungal performance both when an absorptive article such as a paper diaper is used and when the absorptive article is disposed after use.SOLUTION: In a method for producing a polyacrylic acid (salt)-based water-absorbing agent including a polymerization step of a monomer aqueous solution, a drying step and a surface crosslinking step. The method further includes a step of adding an aqueous solution containing a sterilization component to water-absorbing resin particles which has been surface crosslinked, while setting the total amount of acetic acid and propionic acid contained in the monomer or a polymer thereof at 200-2,500 ppm.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a polyacrylic acid (salt) water-absorbing agent. More specifically, the present invention relates to a method for producing a polyacrylic acid (salt) water-absorbing agent, which has an improved deodorizing function and fungicidal function by adding an aqueous liquid having a small amount of a sterilizing component to water-absorbing resin particles.

  Water-absorbent resin (SAP / Super Absorbent Polymer) refers to a water-swellable, water-insoluble polymer gelling agent, absorbent articles such as paper diapers and sanitary napkins, water retention agents for agriculture and horticulture, and industrial waterstops. It is widely used in various fields such as drugs.

  The water-absorbent resin uses many monomers and hydrophilic polymers as raw materials. Examples thereof include a polyacrylic acid partially neutralized cross-linked polymer, a starch-acrylic acid graft polymer hydrolyzate, and a vinyl acetate-acrylic acid ester copolymer saponified product. Among these, from the viewpoint of water absorption performance, polyacrylic acid (salt) water-absorbing resins using acrylic acid and / or a salt thereof as a monomer are industrially most produced.

  The water-absorbent resin is required to have various functions (higher physical properties) as the paper diaper, which is the main application, has improved performance. Specifically, in addition to the basic physical properties, water absorption capacity without pressure and water absorption capacity under pressure, gel strength, water-soluble content, water content, water absorption speed, liquid permeability, particle size distribution, urine resistance, antibacterial properties , Damage resistance, powder flowability, deodorization, coloration resistance, low dust, low residual monomer, and the like.

  Among the above physical properties, in recent years, it has been required to add functions such as “deodorant” and “antibacterial” to the water-absorbent resin. Addition to a functional resin has been studied.

  Specifically, a long-lasting antibacterial deodorant (Patent Document 1) comprising a wasabi extract, mustard extract, etc., and a long-lasting antibacterial deodorant action (water-absorbing gelling agent), water-absorbing resin, ammonia production A powdery deodorant / antibacterial water-absorbing agent (Patent Document 2) comprising a compound having an antibacterial function against bacteria and a drug having neutralizing ability or neutralizing ability and adsorption ability to ammonia Proposed.

  Further, as a water-absorbing resin composition (water-absorbing agent) imparted with deodorizing and antibacterial functions and a method for producing the same, a method for producing a water-absorbing resin composition for forming an antibacterial film on the surface of the water-absorbing resin (Patent Document 3) ), Water-absorbing resin composition containing antibacterial phosphate (Patent Documents 4 and 5), water-absorbing agent containing natural antibacterial components extracted from grapefruit seeds and / or herbs (Patent Document 6), or during surface treatment Later, a production method (Patent Document 7) or the like in which an antibacterial agent and a polyol are added is proposed.

  Furthermore, as a highly safe water-absorbing agent having an antibacterial (antibacterial) function and a deodorizing function, a water-absorbing resin composition (Patent Document 8) and the like in which a reflux extract of bamboo and green tea is blended with a water-absorbing resin has been proposed. ing.

  On the other hand, disposable diapers using a water-absorbing resin containing benzalkonium chloride and / or chlorhexacidin gluconate (Patent Document 9) have been proposed as an attempt to impart a deodorizing function and an antibacterial function to absorbent articles. Has been.

  In addition, when there are many impurities contained in the raw material of the water-absorbent resin, especially acetic acid and propionic acid in acrylic acid, the water-absorbent resin produced using such raw acid swelled by absorbing body fluid such as urine Odor may be generated. Therefore, a water-absorbing resin (Patent Document 10) in which the content of acetic acid or propionic acid in acrylic acid is set to a certain amount or less has been proposed.

JP 2000-51339 A JP 2000-79159 A JP-A-3-59075 Japanese Patent Laid-Open No. 5-179053 JP 7-165981 A JP-A-9-208787 Special table 2010-540004 gazette International Publication No. 2009/048145 Pamphlet JP-A-63-135501 International Publication No. 2003/095510 Pamphlet

  As described above, it is required to add functions such as “deodorant” and “antibacterial” to the water absorbent resin, and a compound such as a deodorant or an antibacterial agent is added to the water absorbent resin. In addition, the use of raw materials with reduced amounts of impurities has been studied.

  However, all of the above-mentioned patent documents are inventions made by paying attention to the odor generated when using a paper diaper, and the odor generated at the time of disposal after using the paper diaper has not been paid attention.

  Accordingly, an object of the present invention is to provide a polyacrylic acid (salt) -based water-absorbing agent that exhibits excellent deodorizing performance and fungicidal performance both at the time of use of absorbent articles such as paper diapers and at the time of disposal after use. It is in providing the manufacturing method of.

  As a result of intensive studies to solve the above-mentioned problems, the amount of impurities contained in the raw material is controlled within a certain range, and further, an aqueous liquid containing a trace amount of bactericidal components is added to the surface-crosslinked water-absorbing resin particles. The present invention was completed by discovering that not only odors generated during use of absorbent articles such as paper diapers but also odors generated during disposal after use can be suppressed.

  That is, in order to solve the above problems, the production method according to the present invention is a method for producing a polyacrylic acid (salt) water-absorbing agent, which includes a polymerization step of an aqueous monomer solution, a drying step, and a surface crosslinking step. A step of adding an aqueous liquid containing a bactericidal component to the surface-crosslinked water-absorbent resin particles, with the total amount of acetic acid and propionic acid contained in the monomer or polymer thereof being 200-2500 ppm, This is a method for producing a polyacrylic acid (salt) water-absorbing agent.

  By using the polyacrylic acid (salt) water-absorbing agent obtained by the production method according to the present invention for absorbent articles such as paper diapers, there is no odor generated after swelling when the absorbent article is actually used. In addition, the generation of odors and molds can be suppressed even when the absorbent article is discarded (final treatment, specifically, garbage collection).

  Furthermore, by employing the manufacturing method according to the present invention, troubles in the manufacturing apparatus are reduced, and stable operation can be performed.

  Hereinafter, 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 present invention can be modified and implemented as appropriate without departing from the scope of the present invention. Is possible. The present invention is not limited to the following embodiments, and various modifications can be made within the scope shown in the claims. Other embodiments obtained by appropriately combining technical means respectively described for a plurality of embodiments are also included in the technical scope of the present invention.

[1] Definition of terms (1-1) "Water absorbent resin""Waterabsorbent"
The “water-absorbent resin” in the present invention refers to a water-swellable, water-insoluble polymer gelling agent and satisfies the following physical properties. That is, CRC (centrifuge retention capacity) defined by ERT441.2-02 as water swellability is 5 g / g or more, and Ext (water-soluble) defined by ERT470.2-02 as water-insoluble The polymer gelling agent whose (min) is 50 weight% or less.

  The water-absorbent resin can be designed according to its use and purpose, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. Moreover, it is not limited to the form whose whole quantity is a crosslinked polymer, As long as each said physical property (CRC, Ext) satisfy | fills the said numerical range, the composition containing the additive etc. may be sufficient.

  The “water-absorbent resin” in the present invention is not limited to the final product before shipment, but an intermediate in the production process of the water-absorbent resin (for example, a hydrogel crosslinked polymer after polymerization, a dried polymer after drying, a surface crosslinked polymer). It may also refer to the previous water-absorbing resin powder or the like. All of these (including the above composition) are collectively referred to as “water absorbent resin”.

  Examples of the shape of the water absorbent resin include a sheet shape, a fiber shape, a film shape, a particle shape, and a gel shape. In the present invention, a particulate water absorbent resin is preferable.

  In the present invention, the “water-absorbing agent” refers to a composition obtained by adding an additive to the water-absorbing resin particles after surface crosslinking among the water-absorbing resins described above, or a water-absorbing resin after being subjected to a curing operation. I mean.

(1-2) "Polyacrylic acid (salt)"
The “polyacrylic acid (salt)” in the present invention refers to polyacrylic acid and / or a salt thereof, and acrylic acid and / or a salt thereof (hereinafter referred to as “acrylic acid (salt)”) as a main component is repeated. It means a crosslinked polymer containing as a unit and a graft component as an optional component.

  The “main component” is preferably 50 to 100 mol% based on the total amount of monomers (excluding the internal crosslinking agent) used for the polymerization (content) of acrylic acid (salt). It means preferably 70 to 100 mol%, more preferably 90 to 100 mol%, particularly preferably substantially 100 mol%.

  The “polyacrylic acid salt” as the crosslinked polymer includes a water-soluble salt of polyacrylic acid, preferably a monovalent salt, more preferably an alkali metal salt or an ammonium salt, still more preferably an alkali metal salt, particularly preferably. Contains sodium salt.

(1-3) “EDANA” and “ERT”
“EDANA” is an abbreviation for European Disposables and Nonwovens Associations, and “ERT” is an abbreviation for a method of measuring water-absorbent resin of the European standard (almost the world standard) (EDANA Recommended Test Methods). . In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured based on the original ERT (revised in 2002).

(A) "CRC" (ERT441.2-02)
“CRC” is an abbreviation for Centrifugation Retention Capacity (centrifuge retention capacity), and means the water absorption capacity of the water absorbent resin under no pressure (sometimes referred to as “water absorption capacity”). Specifically, 0.2 g of the water-absorbing resin was put in a non-woven bag, and then immersed in a large excess of 0.9 wt% sodium chloride aqueous solution for 30 minutes to freely swell, and then centrifuged (250 G ) Is the water absorption capacity (unit: g / g) after draining for 3 minutes.

(B) “AAP” (ERT442.2-02)
“AAP” is an abbreviation for Absorption Against Pressure, which means the water absorption capacity of a water absorbent resin under pressure. Specifically, the water absorption capacity after swelling 0.9 g of water-absorbing resin with a large excess of 0.9 wt% sodium chloride aqueous solution for 1 hour under a load of 21 g / cm ² (2.06 kPa). (Unit; g / g). In addition, ERT442.2-02 describes “Absorption Under Pressure”, which has substantially the same content.

(C) "Ext" (ERT470.2-02)
“Ext” is an abbreviation for Extractables, which means the water-soluble component (water-soluble component amount) of the water-absorbent resin. Specifically, 1.0 g of water-absorbing resin is added to 200 ml of 0.9 wt% sodium chloride aqueous solution, stirred for 16 hours at 500 rpm, and then the amount of substance dissolved in the aqueous solution (unit: wt%). . PH titration is used to measure the water-soluble content.

(D) “PSD” (ERT420.2-02)
“PSD” is an abbreviation for Particle Size Distribution, and means a particle size distribution of a water-absorbent resin measured by sieving. D50 (weight average particle diameter) and σζ (logarithmic standard deviation of particle size distribution) are described in US Pat. No. 7,638,570 “(3) Mass-Average Particle Diameter (D50) and Logical Standard Deviation (σζ) of”. It is measured by a method similar to “Particle Diameter Distribution”.

(E) "Moisture Content" (ERT430.2-02)
“Moisture Content” means the water content of the water-absorbent resin. Specifically, it refers to a value (unit:% by weight) calculated from loss on drying when 4.0 g of water-absorbent resin is dried at 105 ° C. for 3 hours. In some cases, the water-absorbing resin is changed to 1.0 g and the drying temperature is changed to 180 ° C., respectively.

(F) “Residual Monomers” (ERT410.2-02)
“Residual Monomers” means the amount of monomer (monomer) remaining in the water-absorbent resin. Hereinafter, the monomer remaining in the water absorbent resin is referred to as “residual monomer”. Specifically, it refers to the amount of monomer (unit: ppm) dissolved in an aqueous solution after adding 1.0 g of a water-absorbing resin to 200 ml of a 0.9 wt% aqueous sodium chloride solution and stirring at 500 rpm for 1 hour. High performance liquid chromatography (HPLC) is used for the measurement of the amount of residual monomers.

(1-4) Others In this specification, “X to Y” indicating a range means “X or more and Y or less”. Further, unless otherwise noted, “t (ton)” as a unit of weight means “Metric ton”, and “ppm” means “weight ppm” or “mass ppm”.

  Further, “˜acid (salt)” means “˜acid and / or salt thereof”, and “(meth) acryl” means “acryl and / or methacryl”.

[2] Method for Producing Polyacrylic Acid (Salt) -Based Water Absorbing Agent Hereinafter, production steps (2-1) to (2-9) of the polyacrylic acid (salt) -based water absorbing agent according to the present invention will be described.

(2-1) Preparation Step of Monomer Aqueous Solution This step is a step of preparing an aqueous solution containing acrylic acid (salt) as a main component (hereinafter referred to as “monomer aqueous solution”). The “main component” is preferably such that the amount (content) of acrylic acid (salt) used is the entire monomer (excluding the internal cross-linking agent) subjected to the polymerization reaction of the water absorbent resin. Means 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more (the upper limit is 100 mol%). In addition, a monomer slurry liquid can be used as long as the water absorption performance of the resulting water-absorbing agent does not deteriorate, but in this section, the monomer aqueous solution will be described for convenience.

(Acrylic acid (salt))
In the present invention, acrylic acid and / or a salt thereof (hereinafter referred to as “acrylic acid (salt)”) is used as a monomer from the viewpoint of physical properties and productivity of the resulting water-absorbing agent. As the “acrylic acid”, known acrylic acid containing a trace inhibitor such as a polymerization inhibitor and impurities can be used.

  The polymerization inhibitor is not particularly limited, but preferably includes phenols, more preferably methoxyphenols, and still more preferably p-methoxyphenols. The concentration of the polymerization inhibitor in acrylic acid is preferably 200 ppm or less, more preferably 10 to 160 ppm, and still more preferably 20 to 100 ppm from the viewpoint of the polymerizability of acrylic acid and the color tone of the water absorbent resin.

  Examples of the impurities include carboxylic acids such as acetic acid, propionic acid and maleic acid, and aldehydes such as acrolein and furfural. Among them, from the viewpoint of odor generated when using absorbent articles such as paper diapers, it is necessary to control the total amount of acetic acid and propionic acid within a certain range among the above impurities.

  The total amount of acetic acid and propionic acid is 200 to 2500 ppm, preferably 250 to 2000 ppm, more preferably 300 to 1500 ppm. The total amount is acrylic acid, that is, the amount contained in the monomer or the amount contained in the polymer obtained by polymerizing the monomer. That is, the total amount of acetic acid and propionic acid contained in the monomer or polymer thereof.

  Controlling the total amount within the above range is preferable because it can suppress odor during use of the absorbent article produced using the obtained water-absorbing agent.

  Further, the “acrylic acid salt” is obtained by neutralizing the above-mentioned acrylic acid with the following basic composition, but as the acrylic acid salt, a commercially available acrylic acid salt (for example, sodium acrylate) may be used. In addition, it may be obtained by neutralizing acrylic acid in a water absorbent resin production plant.

(Basic composition)
In the present invention, the “basic composition” refers to a composition containing a basic compound, such as a commercially available sodium hydroxide aqueous solution.

  Specific examples of the basic compound include alkali metal carbonates and hydrogen carbonates, alkali metal hydroxides, ammonia, and organic amines. Especially, it is preferable that it is strongly basic from a viewpoint of the physical property of the water absorbing agent obtained. That is, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are more preferable, and sodium hydroxide is more preferable.

(Neutralization)
In the present invention, acrylic acid can be neutralized with a basic composition in order to obtain an acrylate. The neutralization is neutralization with respect to acrylic acid (before polymerization) or neutralization with respect to a hydrogel crosslinked polymer obtained by crosslinking polymerization of acrylic acid (after polymerization) (hereinafter referred to as “post-neutralization”). Any one of these may be selected or used in combination.

  The neutralization may be a continuous type or a batch type, and any of them can be employed, but from the viewpoint of production efficiency and the like, the continuous type is preferable. In addition, about conditions, such as the apparatus which performs neutralization, neutralization temperature, residence time, the conditions described in international publication 2009/123197 and US Patent application publication 2008/0194863 are applied also to this invention. .

  The neutralization rate in the present invention is preferably from 10 to 90 mol%, more preferably from 40 to 85 mol%, still more preferably from 50 to 80 mol%, particularly preferably from 60 to 90 mol%, based on the acid group of the monomer. 75 mol%.

  When the neutralization rate is less than 10 mol%, the water absorption ratio may be remarkably lowered, which is not preferable. On the other hand, when the neutralization rate exceeds 90 mol%, a water absorbent resin having a high water absorption capacity under pressure may not be obtained, which is not preferable.

  In addition, the said neutralization rate is the same also in the case of post-neutralization. Moreover, said neutralization rate is applied also about the neutralization rate of the water absorbing agent as a final product.

(Other monomers)
In the present invention, a compound described in US Patent Application Publication No. 2005/0215734 as “other monomer” (excluding acrylic acid) is used in combination with the above acrylic acid (salt) to produce a water absorbing agent. May be. In addition, the water-absorbing agent obtained by the production method according to the present invention includes a water-absorbing agent having a hydrophilic or hydrophobic unsaturated monomer as a copolymerization component.

(Internal crosslinking agent)
As the internal crosslinking agent used in the present invention, the compounds described in US Pat. No. 6,241,928 are also applied to the present invention. From these, one or more compounds are selected in consideration of reactivity.

  Further, from the viewpoint of water absorption performance and the like of the obtained water-absorbing agent, preferably a compound having two or more polymerizable unsaturated groups, more preferably a compound having thermal decomposability at the following drying temperature, more preferably (poly) alkylene glycol. A compound having two or more polymerizable unsaturated groups having a structural unit is used as an internal crosslinking agent.

  The polymerizable unsaturated group is preferably an allyl group, a (meth) acrylate group, more preferably a (meth) acrylate group. Moreover, polyethylene glycol is preferable as the (poly) alkylene glycol structural unit, and the n number is preferably 1 to 100, more preferably 6 to 50.

  Therefore, in the present invention, (poly) alkylene glycol di (meth) acrylate or (poly) alkylene glycol tri (meth) acrylate is preferably used, and more preferably (poly) ethylene glycol di (meth) acrylate is used.

  The amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, based on the entire monomer. A desired water-absorbing agent can be obtained by setting the amount used within the above range. In addition, when there is too little this usage-amount, it exists in the tendency for gel strength to fall and a water soluble content to increase, and since there exists a tendency for a water absorption factor to fall when this usage-amount is too much, it is unpreferable.

  In the present invention, a method in which a predetermined amount of an internal cross-linking agent is previously added to a monomer aqueous solution and a cross-linking reaction is performed simultaneously with polymerization is preferably applied. On the other hand, in addition to this method, a method of adding an internal cross-linking agent during or after polymerization and post-crosslinking, a method of radical cross-linking using a radical polymerization initiator, radiation using active energy rays such as electron beams and ultraviolet rays A method of crosslinking and the like can also be employed. Moreover, these methods can also be used together.

(Other substances added to the monomer aqueous solution)
In the present invention, from the viewpoint of improving the physical properties of the resulting water-absorbing agent, the following substances may be added during preparation of the monomer aqueous solution.

  Specifically, hydrophilic polymer such as starch, starch derivative, cellulose, cellulose derivative, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked product, preferably 50% by weight or less, more preferably Is added in an amount of 20% by weight or less, more preferably 10% by weight or less, particularly preferably 5% by weight or less (the lower limit is 0% by weight), foaming agents such as carbonates, azo compounds and bubbles, surfactants, chelating agents. An agent, a chain transfer agent and the like are preferably added at 5% by weight or less, more preferably 1% by weight or less, still more preferably 0.5% by weight or less (the lower limit is 0% by weight).

  In addition to the form added to the monomer aqueous solution, the above substance may be added in the middle of the polymerization, or these forms may be used in combination.

  When a water-soluble resin or a water-absorbing resin is used as the hydrophilic polymer, a graft polymer or a water-absorbing resin composition (for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) is obtained. It is done. These polymers and water-absorbing resin compositions are also within the scope of the present invention.

(Concentration of monomer component)
In the present invention, each of the above substances is added when preparing the aqueous monomer solution. The concentration of the monomer component in the aqueous monomer solution (hereinafter sometimes referred to as “monomer concentration”) is not particularly limited, but is preferably 10 to 80 weight from the viewpoint of the physical properties and productivity of the water-absorbing agent. %, More preferably 20 to 75% by weight, still more preferably 30 to 70% by weight.

  Moreover, when employ | adopting aqueous solution polymerization or reverse phase suspension polymerization as a polymerization form, solvents other than water can also be used together as needed. In this case, the type of solvent used is not particularly limited.

  The “monomer component concentration” is a value obtained by the following (formula 1), and the weight of the monomer aqueous solution includes the hydrophobicity in the graft component, the water-absorbing resin, and the reverse phase suspension polymerization. Solvent weight is not included.

(2-2) Polymerization step In this step, the acrylic acid (salt) monomer aqueous solution obtained in the monomer aqueous solution preparation step is polymerized to form a hydrogel crosslinked polymer (hereinafter referred to as "hydrogel"). It is a process of obtaining.

(Polymerization initiator)
The polymerization initiator used in the present invention is not particularly limited because it is appropriately selected depending on the polymerization form and the like. For example, a thermal decomposable radical polymerization initiator, a photodegradable radical polymerization initiator, or a polymerization initiator thereof. And redox polymerization initiators in combination with a reducing agent that promotes the decomposition of. Specifically, one or two or more compounds are used among the polymerization initiators described in US Pat. No. 7,265,190. From the viewpoint of handling of the polymerization initiator and physical properties of the water-absorbing agent, a peroxide or an azo compound is preferably used, more preferably a peroxide, and still more preferably a persulfate.

  The amount of the polymerization initiator used is preferably 0.001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the monomer. The amount of the reducing agent used is preferably 0.0001 to 0.02 mol% with respect to the monomer. A desired water-absorbing agent can be obtained by setting the use amount of the polymerization initiator and the reducing agent within the above range.

  In addition, it may replace with the said polymerization initiator and may irradiate active energy rays, such as a radiation, an electron beam, and an ultraviolet-ray, and may implement a polymerization reaction, and these active energy rays and a polymerization initiator may be used together.

(Polymerization form)
The polymerization form applied to the present invention is not particularly limited, but is preferably spray polymerization, droplet polymerization, aqueous solution polymerization, reverse phase suspension polymerization, more preferably from the viewpoint of water absorption characteristics and ease of polymerization control. Examples include aqueous solution polymerization, reverse phase suspension polymerization, and more preferably aqueous solution polymerization. Among these, continuous aqueous solution polymerization is particularly preferable, and either continuous belt polymerization or continuous kneader polymerization is applied.

  As specific polymerization forms, continuous belt polymerization is disclosed in U.S. Pat. Nos. 4,893,999 and 6,241,928, U.S. Patent Application Publication No. 2005/0215734, and continuous kneader polymerization is disclosed in U.S. Pat. Nos. 6,987,151 and 6,710,141. , Respectively. By adopting these continuous aqueous solution polymerizations, the production efficiency of the water-absorbing agent is improved.

  Moreover, as a preferable form of the continuous aqueous solution polymerization, “high temperature initiation polymerization” and “high concentration polymerization” can be mentioned. “High temperature initiation polymerization” means that the temperature of the aqueous monomer solution is preferably 30 ° C. or higher, more preferably 35 ° C. or higher, still more preferably 40 ° C. or higher, particularly preferably 50 ° C. or higher (the upper limit is the boiling point). “High concentration polymerization” means that the monomer concentration is preferably 30% by weight or more, more preferably 35% by weight or more, still more preferably 40% by weight or more, and particularly preferably 45% by weight or more. The upper limit is a saturation concentration. These polymerization forms can also be used in combination.

  In the present invention, the polymerization can be carried out in an air atmosphere, but from the viewpoint of the color tone of the resulting water-absorbing agent, the polymerization is preferably carried out in an atmosphere of an inert gas such as nitrogen or argon. In this case, for example, the oxygen concentration is preferably controlled to 1% by volume or less. The dissolved oxygen in the monomer aqueous solution is also preferably replaced with an inert gas (for example, dissolved oxygen; less than 1 mg / l).

  Moreover, in this invention, it can also be set as foaming polymerization which superpose | polymerizes by disperse | distributing a bubble (especially said inert gas etc.) to monomer aqueous solution.

  In the present invention, the solid concentration may be increased during the polymerization. The solid content increase degree is defined by the following (Equation 2) as an index of such an increase in the solid content concentration. In addition, as a raise degree of this solid content concentration, Preferably it is 1 weight% or more, More preferably, it is 2 weight% or more.

  However, the solid content concentration of the monomer aqueous solution is a value obtained by the following (formula 3), and the components in the polymerization system are the monomer aqueous solution, the graft component, the water absorbent resin, and other solids (for example, water). Insoluble fine particles, etc.) and does not include a hydrophobic solvent in reverse phase suspension polymerization.

(2-3) Gel pulverization step In this step, the water-containing gel obtained in the polymerization step is subjected to gel pulverization with a screw extruder such as a kneader or meat chopper, or a gel pulverizer such as a cutter mill, to form a particulate water-containing gel ( Hereinafter, it is a step of obtaining “particulate hydrous gel”. In addition, when the said superposition | polymerization process is kneader polymerization, the superposition | polymerization process and the gel grinding | pulverization process are implemented simultaneously. Further, when the particulate hydrous gel is obtained directly in the polymerization process such as reverse phase suspension polymerization, the gel grinding process may not be performed.

  Regarding gel grinding conditions and forms other than those described above, the contents disclosed in International Publication No. 2011/126079 are preferably applied to the present invention.

(2-4) Drying step This step is a step of obtaining a “dried polymer” by drying the particulate hydrogel obtained in the polymerization step and / or the gel pulverization step to a predetermined solid content. The solid content after drying is a value obtained from loss on drying (weight change when 1 g of dried polymer is heated at 180 ° C. for 3 hours), preferably 80% by weight or more, more preferably 85 to 99% by weight. %, More preferably 90 to 98% by weight, particularly preferably 92 to 97% by weight.

  The drying method employed in this step is not particularly limited, but for example, heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, and a hydrophobic organic solvent. Examples include drying by boiling dehydration and high-humidity drying using high-temperature steam. Among these, hot air drying is preferable from the viewpoint of drying efficiency, and band drying in which hot air drying is performed on a ventilation belt is more preferable.

  The drying temperature in this step (specified by the temperature of hot air in the case of hot air drying) is preferably 100 to 300 ° C., more preferably 120 to 250 ° C., further preferably, from the viewpoint of the color tone and drying efficiency of the water-absorbing agent obtained. Is 150-200 ° C. The drying time is appropriately determined according to the desired properties of the water-absorbing agent, but is preferably 1 minute to 10 hours, more preferably 5 minutes to 3 hours, and even more preferably 10 minutes to 1 hour. Furthermore, in the case of hot air drying, the wind speed of the hot air is preferably 3.0 m / s or less, more preferably 0.5 to 2.0 m / s. Other drying conditions may be appropriately set according to the moisture content and total weight of the particulate hydrogel to be dried, the target solid content, and the like.

  By controlling the various drying conditions within the above range, the physical properties of the dried polymer are less likely to be uneven, the solid content can be controlled within a predetermined range, and the resulting water-absorbing agent is deteriorated in color tone and water absorption performance. Can be suppressed. When performing band drying, various conditions described in International Publication Nos. 2006/100300, 2011/025012, 2011/025013, 2011/111657, and the like are appropriately applied.

(2-5) Grinding step, classification step In this step, the dried polymer obtained in the drying step is pulverized (pulverization step), adjusted to a predetermined particle size (classification step), and water-absorbing resin powder ( This is a step of obtaining a powdery water-absorbing resin before surface cross-linking for the sake of convenience as “water-absorbing resin powder”.

  The equipment used in the pulverization process of the present invention is not particularly limited, and examples thereof include a high-speed rotary pulverizer such as a roll mill, a hammer mill, a screw mill, and a pin mill, a vibration mill, a knuckle type pulverizer, and a cylindrical mixer. Are used together if necessary.

  In addition, the particle size adjustment method in the classification step of the present invention is not particularly limited, and examples thereof include sieve classification using JIS standard sieve (JIS Z8801-1 (2000)), airflow classification, and the like. The particle size adjustment is not limited to the above pulverization step and classification step, but a polymerization step (especially reverse phase suspension polymerization, spray polymerization, droplet polymerization) or other steps (for example, granulation step, fine powder recovery step, etc.) ) Can be implemented as appropriate.

(Physical properties of water-absorbent resin powder)
(Solid content)
The solid content of the water absorbent resin powder obtained in this step is preferably 90% by weight or more, more preferably 93% by weight or more, and still more preferably 95% by weight or more. The upper limit of the solid content is preferably 98% by weight or less, more preferably 97% by weight or less from the viewpoint of grinding efficiency.

(Granularity)
The water-absorbent resin powder obtained in this step is preferably 200 to 600 μm, more preferably 200 to 550 μm, still more preferably 250 to 500 μm, and particularly preferably 250 to 450 μm as D50 (weight average particle diameter). The proportion of particles having a particle size of less than 150 μm is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1% by weight or less. The proportion of particles having a particle size of 850 μm or more is preferably Is 5% by weight or less, more preferably 3% by weight or less, and still more preferably 1% by weight or less. The lower limit of the proportion of these particles is preferably as small as possible in any case, and is preferably 0% by weight, but may be about 0.1% by weight. Furthermore, σζ (logarithmic standard deviation of particle size distribution) is preferably 0 to 0.50, more preferably 0.20 to 0.50, still more preferably 0.25 to 0.45, and particularly preferably 0.30. 0.40. In addition, these particle sizes are measured using a standard sieve according to the measurement methods described in US Pat. No. 7,638,570 and ERT420.2-02.

  The above particle size applies not only to the water-absorbing resin after surface crosslinking (hereinafter referred to as “water-absorbing resin particles” for convenience) but also to the water-absorbing agent as the final product. Therefore, it is preferable to carry out surface crosslinking so as to maintain the particle size in the above range, and it is more preferable to adjust the particle size by providing a sizing step after the surface crosslinking step.

(2-6) Surface cross-linking step This step is a step performed for the purpose of improving the liquid permeability and water absorption speed of the water-absorbent resin powder after drying and classification, and is obtained through the above-described steps. In this step, a portion having a higher crosslink density is provided on the surface layer of the water absorbent resin powder (a portion of several tens of micrometers from the surface of the water absorbent resin powder).

  This step includes a mixing step, a heat treatment step, and a cooling step (optional). In addition, when particle size control is performed at the time of polymerization, such as reverse phase suspension polymerization, gas phase polymerization, spray polymerization, and droplet polymerization, the pulverization step and the classification step before the surface cross-linking step are unnecessary, The following heat treatment step may be performed simultaneously with the drying step.

  In the surface cross-linking step, water-absorbing resin particles that are surface cross-linked by radical cross-linking or surface polymerization on the surface of the water-absorbent resin powder, a cross-linking reaction with a surface cross-linking agent, or the like are obtained.

(Surface cross-linking agent)
Although it does not specifically limit as a surface crosslinking agent used by this invention, An organic or inorganic surface crosslinking agent is mentioned. Among these, an organic surface cross-linking agent that reacts with a carboxyl group is preferable from the viewpoint of the physical properties of the resulting water-absorbing agent and the handleability of the surface cross-linking agent. Examples thereof include one or more surface cross-linking agents described in US Pat. No. 7,183,456. More specifically, polyhydric alcohol compounds, epoxy compounds, haloepoxy compounds, polyvalent amine compounds or their condensates with haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. Can be mentioned.

  The surface crosslinking agent is used in an amount of 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water-absorbent resin powder. It is. Moreover, it is preferable to add this surface crosslinking agent as aqueous solution, In this case, the usage-amount of water becomes like this. Preferably it is 0.1-20 weight part with respect to 100 weight part of water absorbent resin powder, More preferably, it is 0.00. 5 to 10 parts by weight. Furthermore, if necessary, when using a hydrophilic organic solvent, the amount used is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, with respect to 100 parts by weight of the water-absorbent resin powder.

  In addition, each additive added in the “rehumidification step” to be described later is added to the surface cross-linking agent (aqueous solution) within a range of 5 parts by weight or less, or added separately in the mixing step. You can also.

(Mixing process)
This step is a step of mixing the water absorbent resin powder and the surface cross-linking agent. The method for mixing the surface cross-linking agent is not particularly limited, but a surface cross-linking agent solution is prepared in advance, and the solution is preferably sprayed or dropped onto the water absorbent resin powder, and more preferably sprayed. And mixing them.

  The apparatus for performing the mixing is not particularly limited, but preferably a high-speed stirring type mixer, more preferably a high-speed stirring type continuous mixer.

(Heat treatment process)
In this step, heat is applied to the mixture discharged from the mixing step to cause a crosslinking reaction on the surface of the water absorbent resin powder.

  The apparatus for performing the crosslinking reaction is not particularly limited, but preferably includes a paddle dryer. The reaction temperature in the crosslinking reaction is appropriately set according to the type of the surface crosslinking agent to be used, but is preferably 50 to 300 ° C, more preferably 100 to 200 ° C.

(Cooling process)
This step is an optional step that is installed as necessary after the heat treatment step.

  The apparatus for performing the cooling is not particularly limited, but is preferably an apparatus having the same specifications as the apparatus used in the heat treatment step, and more preferably a paddle dryer. It is because it can be used as a cooling device by changing the heat medium to a refrigerant. In the cooling step, the water-absorbent resin particles obtained in the heat treatment step are forcibly cooled to 40 to 80 ° C., more preferably 50 to 70 ° C. as necessary.

(2-7) Rehumidification process (curing process)
This step is a step of adding an aqueous liquid containing a bactericidal component to the water-absorbent resin particles obtained in the surface cross-linking step. Further, in this step, at least selected from the group consisting of a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, an α-hydroxycarboxylic acid compound and a deodorant simultaneously with the addition of an aqueous liquid containing a bactericidal component. One kind of additive can also be added.

  In addition, in this process, since an aqueous liquid is added to the surface-crosslinked water-absorbing resin particles, the water-absorbing resin particles are again swollen with water. Therefore, this process is referred to as a “rehumidification process”. On the other hand, since the water present on the surface of the water-absorbent resin particles is also allowed to permeate into the interior, the operation is sometimes referred to as “curing”. In this case, it is called “curing step”.

  Moreover, the addition of the additive may be performed simultaneously with the cooling step, and any timing may be used as long as the surface-crosslinked water-absorbing resin particles can be re-humidified.

(Aqueous liquid containing bactericidal components)
From the viewpoint of sanitary aspects at the time of disposal and stable operation of the apparatus in the rehumidification process, the water-absorbent resin particles whose surfaces are cross-linked with respect to absorbent articles (especially paper diapers) prepared using the water-absorbing agent obtained in the present invention On the other hand, an aqueous liquid containing a sterilizing component is essential.

  The sterilizing component is not particularly limited, but is preferably at least one selected from the group consisting of sodium hypochlorite, chlorine dioxide, iodine tincture, and povidone iodine, and more preferably sodium hypochlorite.

  Moreover, as the concentration of the sterilizing component, the amount of free residual chlorine contained in the aqueous liquid containing the sterilizing component is preferably 0.1 to 5.0 mg / l, more preferably 0.2 to 3.0 mg / l, More preferably, it is 0.5-1.5 mg / l.

  By making the said amount of free residual chlorine into the said range, since the odor at the time of use of an absorbent article can be suppressed, it is preferable. Furthermore, from the viewpoint of stable operation of the manufacturing apparatus, it is preferable because it is possible to reduce apparatus troubles associated with product number switching. That is, in the product type that does not add the aqueous liquid, the rehumidification process (curing process) may not be performed. Therefore, conventionally, when the apparatus is stopped for a long time, the aqueous liquid stays in the piping, Although clogging may occur, it can be solved by adding an aqueous liquid containing a sterilizing component, which is preferable.

  Moreover, the addition amount of the aqueous liquid containing the sterilizing component is preferably 1 to 10% by weight, more preferably 2 to 8% by weight, and further preferably 3 to 7% by weight with respect to the water absorbent resin particles.

  The method for adding the aqueous liquid containing the sterilizing component is not particularly limited, but is preferably spray addition.

  Moreover, when adding the aqueous liquid containing the said bactericidal component, the temperature of the water-absorbent resin particles is preferably 30 to 70 ° C, more preferably 35 to 65 ° C, and further preferably 40 to 60 ° C. When the temperature of the water-absorbing resin particles is less than 30 ° C., the penetration rate of the aqueous liquid into the water-absorbing resin particles becomes slow. Conversely, when the temperature exceeds 70 ° C., the penetration rate becomes too fast. This is not preferable because appropriate penetrability and uniform dispersibility into the water-absorbent resin particles are deteriorated.

  It is preferable to operate the step of adding the aqueous liquid containing the sterilizing component again after stopping the step of adding the aqueous liquid containing the sterilizing component for one day or more.

  Hereinafter, a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, an α-hydroxycarboxylic acid compound, and a deodorant will be described as an example of the additive added in this step.

(Polyvalent metal salt and / or cationic polymer)
In the present invention, it is preferable to add a polyvalent metal salt and / or a cationic polymer from the viewpoint of the water absorption rate, liquid permeability, hygroscopic fluidity, and the like of the resulting water absorbing agent.

  As the polyvalent metal salt and / or cationic polymer, specifically, compounds described in “[7] Polyvalent metal salt and / or cationic polymer” of International Publication No. 2011/040530 and the amount of use thereof Applies to the present invention.

(Chelating agent)
In the present invention, it is preferable to add a chelating agent from the viewpoint of the color tone (coloring prevention) and deterioration prevention of the water-absorbing agent obtained.

  As the chelating agent, specifically, compounds described in “[2] chelating agent” of WO 2011/040530 and the amount of use thereof are applied to the present invention.

(Inorganic reducing agent)
In the present invention, it is preferable to add an inorganic reducing agent from the viewpoints of the color tone (anti-coloring), deterioration prevention, residual monomer reduction and the like of the obtained water-absorbing agent.

  Specifically, as the inorganic reducing agent, the compounds described in “[3] Inorganic reducing agent” of WO 2011/040530 and the amount used thereof are applied to the present invention.

(Α-hydroxycarboxylic acid compound)
In the present invention, it is preferable to add an α-hydroxycarboxylic acid compound from the viewpoint of the color tone (coloring prevention) of the water-absorbing agent to be obtained. The “α-hydroxycarboxylic acid compound” is a carboxylic acid having a hydroxyl group in the molecule or a salt thereof, and is a hydroxycarboxylic acid having a hydroxyl group at the α-position.

  As the α-hydroxycarboxylic acid compound, specifically, the compounds described in “[6] α-hydroxycarboxylic acid compound” of International Publication No. 2011/040530 and the amount used thereof are applied to the present invention. .

(Deodorants)
In the present invention, it is preferable to add a deodorant from the viewpoint of deodorization and the like when using the resulting absorbent article (especially paper diapers).

  As the deodorant, a natural product-derived deodorant is preferable, and specifically, compounds described in JP-A No. 2001-285021 and the amount of use thereof are applied to the present invention.

(2-8) Other additive addition process In this invention, in order to add various functions to water-absorbent resin, additives other than the additive mentioned above can also be added. Specific examples of the additive include a surfactant, a compound having a phosphorus atom, an oxidizing agent, an organic reducing agent, water-insoluble inorganic fine particles, organic powders such as metal soap, pulp, and thermoplastic fibers. The surfactant is a compound described in International Publication No. 2005/077500, and the water-insoluble inorganic fine particles are described in International Publication No. 2011/040530, “[5] Water-insoluble inorganic fine particles”. Each of these compounds is applied to the present invention.

  The amount of the additive used (addition amount) is appropriately determined according to the intended use of the water-absorbing agent, and is not particularly limited, but is preferably 3 parts by weight or less with respect to 100 parts by weight of the water-absorbing resin powder. More preferably, it is 1 part by weight or less. Moreover, this additive can be added in any manufacturing process of a polyacrylic acid (salt) type water absorbing agent.

(2-9) Other Steps In the present invention, in addition to the steps described above, a sizing step, a fine powder removal step, a fine powder reuse step, and the like can be provided as necessary. Moreover, you may further include 1 type, or 2 or more types of processes, such as a transport process, a storage process, a packing process, and a storage process. In addition, the “granulating step” includes a step of performing classification and pulverization when the fine powder removing step after the surface cross-linking step and the water absorbent resin are aggregated and exceed a desired size. In addition, the “fine powder recycling step” includes a step of adding the fine powder as it is as in the present invention to a large water-containing gel and adding it to any of the manufacturing steps of the water-absorbing agent.

[3] Physical properties of polyacrylic acid (salt) -based water-absorbing agent The polyacrylic acid (salt) -based water-absorbing agent obtained by the production method according to the present invention preferably satisfies the following physical properties. In addition, when using this water-absorbing agent for absorbent articles such as paper diapers, at least one of the physical properties listed in the following (3-1) to (3-6), preferably two including AAP More preferably, 3 or more including AAP, more preferably 4 or more including AAP, particularly preferably 5 or more including AAP, most preferably all 6 properties are controlled within a desired range. It is desirable to do. When these physical properties do not satisfy the following ranges, the effects of the present invention are not sufficiently obtained, and there is a possibility that sufficient performance is not exhibited in absorbent articles (particularly high-concentration paper diapers).

  The shape of the water-absorbing agent of the present invention is not particularly limited, but is preferably particulate. In this specification, the physical properties of the particulate water-absorbing agent which is a preferred embodiment will be described. In addition, the following physical property was measured based on EDANA method unless there is particular notice.

(3-1) CRC (centrifuge retention capacity)
The CRC (centrifuge retention capacity) of the water-absorbing agent of the present invention is usually 5 g / g or more, preferably 20 g / g or more, more preferably 25 g / g or more, and further preferably 30 g / g or more. The upper limit is not particularly limited and is preferably as high as possible, but from the viewpoint of balance with other physical properties, it is preferably 70 g / g or less, more preferably 50 g / g or less, and still more preferably 40 g / g or less.

  Therefore, a typical range of the CRC (centrifuge retention capacity) can be appropriately selected within the above-described upper limit value and lower limit value range. For example, arbitrary ranges, such as 5-70 g / g, 20-50 g / g, 25-40 g / g, can be selected.

  When the CRC is less than 5 g / g, the water absorption amount of the water absorbing agent is small, and it is not suitable as an absorbent body for absorbent articles such as paper diapers. In addition, when the CRC exceeds 70 g / g, the rate of absorbing body fluids such as urine and blood decreases, so that it is not suitable for use in a high water absorption rate type paper diaper. CRC can be controlled by an internal crosslinking agent, a surface crosslinking agent, or the like.

(3-2) AAP (absorption capacity under pressure)
The AAP (water absorption capacity under pressure) of the water-absorbing agent of the present invention is preferably 18 g / g or more, more preferably 20 g / g or more, still more preferably 23 g / g or more, particularly preferably 24 g / g or more, most preferably 25 g. / G or more. The upper limit is not particularly limited, but is preferably 30 g / g or less.

  Therefore, a typical range of the AAP (water absorption under pressure) can be appropriately selected within the above-described upper limit value and lower limit value range. For example, arbitrary ranges, such as 18-30 g / g, 22-30 g / g, 25-30 g / g, can be selected.

  When the above AAP is less than 20 g / g, when actually used in a paper diaper or the like, the amount of absorption in a state where pressure is applied to the absorbent body is reduced, so that it is suitable as an absorbent body for absorbent articles such as a paper diaper. Absent. AAP can be controlled by particle size, surface cross-linking agent, and the like.

(3-3) Particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (logarithmic standard deviation of particle size distribution))
The particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (logarithmic standard deviation of particle size distribution)) of the water-absorbing agent of the present invention is the same as the particle size of the water-absorbent resin powder before surface crosslinking. As controlled.

(3-4) Ext (water-soluble component)
The Ext (water-soluble content) of the water-absorbing agent of the present invention is usually 50% by weight or less, preferably 35% by weight or less, more preferably 25% by weight or less, and further preferably 15% by weight or less. Although it does not specifically limit about a lower limit, Preferably it is 0 weight%, More preferably, it is about 0.1 weight%.

  Therefore, a typical range of the Ext (water-soluble component) can be appropriately selected within the range of the above-described upper limit value and lower limit value. For example, arbitrary ranges, such as 0-50 weight%, 0.1-50 weight%, 0.1-35 weight%, can be selected.

  When the Ext exceeds 50% by weight, the gel strength is weak, and there is a possibility that the water absorbing agent is inferior in liquid permeability. Furthermore, since the amount of return increases, it is not suitable as an absorbent body for absorbent articles such as paper diapers. Ext can be controlled with an internal cross-linking agent or the like.

(3-5) Water content The water content of the water-absorbing agent of the present invention is preferably more than 1% by weight and 15% by weight or less, more preferably 2 to 15% by weight, still more preferably 2 to 12% by weight, particularly preferably. Is 2 to 10% by weight.

  By controlling the water content within the above range, a water-absorbing agent having excellent powder characteristics (for example, fluidity, transportability, damage resistance, etc.) can be obtained. The water content can be controlled by heat treatment in surface crosslinking.

(3-6) Residual monomer From the viewpoint of safety, the residual monomer contained in the water-absorbing agent of the present invention is preferably 500 ppm or less, more preferably 400 ppm or less, and even more preferably 300 ppm or less. Although it does not specifically limit about a lower limit, Preferably it is 0 ppm, More preferably, it is about 10 ppm.

  Therefore, a typical range of the residual monomer can be appropriately selected within the above-described upper limit value and lower limit value range. For example, arbitrary ranges, such as 0-500 ppm, 0-300 ppm, 10-400 ppm, can be selected.

  By controlling the residual monomer within the above range, a water-absorbing agent that can reduce irritation to human skin and the like can be obtained.

[4] Use of polyacrylic acid (salt) water-absorbing agent The use of the water-absorbing agent of the present invention is not particularly limited, but is preferably used as an absorbent for absorbent articles such as paper diapers, sanitary napkins and incontinence pads. It is done. In particular, it can be used as an absorber of high-concentration paper diapers (those with a large amount of water-absorbing agent used per paper diaper) that have been problematic in terms of odor, coloring, and the like derived from raw materials. Furthermore, a remarkable effect can be expected when used in the upper layer of the absorber.

  In addition to the water absorbent, an absorbent material such as pulp fiber can also be used as the absorber. In this case, the content (core concentration) of the water-absorbing agent in the absorber is preferably 30 to 100% by weight, more preferably 40 to 100% by weight, still more preferably 50 to 100% by weight, and even more preferably 60. -100% by weight, particularly preferably 70-100% by weight, most preferably 75-95% by weight.

  By making the said core density | concentration into the said range, when this absorber is used for the upper layer part of an absorbent article, an absorbent article can maintain the white state with a clean feeling. Furthermore, since the diffusibility of body fluids such as urine and blood is excellent, the amount of absorption can be improved by efficient liquid distribution.

  The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not construed as being limited thereto, and examples obtained by appropriately combining technical means disclosed in each example. Are also included in the scope of the present invention.

  In addition, as long as there is no comment, the electrical device (including the physical property measurement of a water absorbing resin) used by an Example and a comparative example used the power supply of 200V or 100V. Further, the physical properties of the water-absorbing agent of the present invention were measured under conditions of room temperature (20 to 25 ° C.) and relative humidity of 50% RH unless otherwise noted.

  In addition, “liter” may be expressed as “l” or “L” and “wt%” as “wt%” for convenience. Further, in the measurement of trace components, the value below the detection limit is expressed as “ND” (Non Detected).

[Measurement of physical properties of water-absorbing agent]
Hereinafter, the physical property measurement of the water-absorbing agent obtained by the production method according to the present invention will be described. When the measurement object is other than the water absorbent, for example, a water absorbent resin powder, “water absorbent agent” is replaced with “water absorbent resin powder” and applied.

(A) CRC (centrifuge retention capacity)
The CRC (centrifuge retention capacity) of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT441.2-02).

(B) AAP (water absorption magnification under pressure)
The AAP (water absorption capacity under pressure) of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT442.2-02).

(C) Particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (logarithmic standard deviation of particle size distribution))
The particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (logarithmic standard deviation of particle size distribution)) of the water-absorbing agent of the present invention is described in US Pat. No. 7,638,570 “(3) Mass-Average”. It was measured according to “Particle Diameter (D50) and Logical Standard Deviation (σζ) of Particle Diameter Distribution”.

(D) Ext (water soluble component)
The Ext (water-soluble content) of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT470.2-02).

(E) Water content, resin solid content The water content of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT430.2-02). In the present invention, the measurement was performed by changing the sample amount to 1.0 g and the drying temperature to 180 ° C.

  In addition, resin solid content (weight%) was prescribed | regulated by (100-water content) (weight%).

(F) Residual monomer The residual monomer of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT410.2-02).

(G) Odor test and mold generation test First, human urine for an odor test and a mold generation test was prepared. The human urine was collected from 10 adults within 2 hours after excretion to obtain a human urine mixture. Subsequently, 10 ml of the human urine mixture was collected and put into a polypropylene container with a capacity of 120 ml (trade name; Pac Ace, Terraoka Co., Ltd./size; caliber 58 mm × lower diameter 54 mm × height 74 mm). .

  Next, 1 g of the water-absorbing agent was added to a container containing 10 ml of the above human urine mixture to form a swollen gel that absorbed human urine, and the odor was confirmed after 1 minute (the odor when using paper diapers) ).

  Subsequently, the container was sealed and stored in a cool and dark place at room temperature (25 ° C.). After 10 days, the state of the swollen gel was confirmed (confirmation of mold generation when paper diapers were discarded).

  Confirmation of the said odor was performed by the monitor (20 adults) selected arbitrarily. It should be noted that the odor when the test was conducted only with the human urine mixture without adding the water-absorbing agent was “level 5”, and the odor when the water-absorbing agent was added was “level 3” as long as it was acceptable. "If it was odorless, it was evaluated as" Level 1 ".

  The above evaluation points of all the monitors were averaged (rounded off), and if the level was 3 or less, it was judged as “no odor”.

[Example 1]
As a continuous production device for water-absorbing agent, a production device is prepared to perform the steps of polymerization, gel pulverization, drying, pulverization, classification, surface cross-linking (mixing of surface cross-linking agent, heat treatment, cooling), addition of aqueous liquid and sizing. did. The manufacturing apparatus is configured in this order, and the apparatuses are connected by a transportation apparatus. A water absorbing agent was continuously produced at 1500 kg / hr using the continuous production apparatus. The continuous production apparatus for the water-absorbing agent includes a step of filling the shipping container with the water-absorbing agent obtained as a product.

  First, as the monomer aqueous solution (1), an aqueous solution of a partial sodium salt of acrylic acid having a neutralization rate of 75 mol% and a monomer concentration of 38% by weight was prepared. At that time, polyethylene glycol diacrylate (average n number; 9) was added as an internal crosslinking agent so as to be 0.03 mol% with respect to the number of moles of all monomers. The “average n number” means the average number of methylene chain polymerization in the polyethylene glycol chain.

  Next, the monomer aqueous solution (1) was continuously supplied (liquid fed) to the polymerization apparatus using a metering pump. At that time, nitrogen gas was continuously blown from the middle of the liquid feeding pipe, so that the concentration of dissolved oxygen in the aqueous monomer solution (1) was 0.5 mg / l or less.

  Subsequently, sodium persulfate and L-ascorbic acid as polymerization initiators were continuously mixed (line mixing) with the monomer aqueous solution (1) using separate supply pipes. The addition amounts of sodium persulfate and L-ascorbic acid were 0.12 g and 0.005 g, respectively, with respect to 1 mol of the monomer.

  The polymerization apparatus in the continuous production apparatus used in Example 1 is a flat steel belt polymerization apparatus having weirs at both ends, and static aqueous solution polymerization was continuously performed using the polymerization apparatus. The liquid supplied to the polymerization apparatus had a thickness of about 30 mm on a flat steel belt. The polymerization time was 30 minutes. By this operation, a band-like hydrogel crosslinked polymer (hydrogel) (1) was obtained.

  Next, after the band-like hydrogel (1) is cut at equal intervals perpendicular to the traveling direction of the flat steel belt, it is continuously supplied to a meat chopper having a pore diameter of 7 mm to obtain a particle shape of about 2 mm. The gel was crushed. By this operation, a particulate hydrous gel (1) was obtained.

  Subsequently, the particulate hydrogel (1) was continuously loaded on the perforated plate of the ventilation belt type drying device so as to have a thickness of 50 mm, and dried at 185 ° C. for 30 minutes. By this operation, a block-shaped dry polymer (1) was obtained. In addition, the time required until the hydrogel (1) discharged | emitted from the said polymerization apparatus was thrown into the said ventilation belt type drying apparatus was about 1 minute.

  Subsequently, the entire amount of the block-shaped dry polymer (1) was continuously supplied to a three-stage roll mill (roll gap; 1.0 mm / 0.55 mm / 0.32 mm in order from the top) and pulverized. By this operation, a ground polymer (1) was obtained. The temperature of the dry polymer (1) supplied to the three-stage roll mill was about 60 ° C. Moreover, the pressure reduction degree in a grinding | pulverization process was adjusted to 0.29 kPa.

  Subsequently, the whole amount of the pulverized polymer (1) was classified by continuously supplying it to a classification device (a sieving device composed of a total of two metal sieving nets; openings were 850 μm / 150 μm in order from the top). . By this operation, a water absorbent resin powder (1) was obtained. The temperature of the pulverized polymer (1) supplied to the classifier was about 60 ° C. Further, the gantry on which the classifier was installed was grounded (static elimination) with a ground resistance value of 5Ω.

  By the above series of operations, a water-absorbent resin powder (1) having a particle size of 98 μm or more and less than 850 μm in a proportion of 98% by weight and CRC (centrifuge retention capacity) of 43 g / g was obtained.

  Next, a surface cross-linking agent solution comprising 0.3 part by weight of 1,4-butanediol, 0.5 part by weight of propylene glycol and 3 parts by weight of ion-exchanged water with respect to 100 parts by weight of the heavy water resin powder (1). (1) was prepared. The electric conductivity of the ion exchange water was 0.5 μS / cm.

  The water absorbent resin powder (1) was continuously supplied to the high speed mixer (turbulator / 1000 rpm) at 1500 kg / hr using pneumatic transportation from the classifier. At that time, the surface cross-linking agent solution (1) was sprayed into the high-speed mixer by spraying to uniformly mix.

  Subsequently, the mixture (1) obtained by the above operation was continuously supplied to a horizontal stirrer (paddle dryer) and subjected to heat treatment. The temperature during the heat treatment was 198 ° C., and the average residence time was 45 minutes. The temperature at the time of the heat treatment is 2.5 MPa of pressurized steam as a heating source, and a thermometer installed in the vicinity of the discharge part of the horizontal stirrer is used for the mixture (1) in the device. The temperature was measured, and the flow rate of the pressurized steam was controlled so that the temperature was 198 ° C. Further, the position of the discharge weir was adjusted so that the average filling rate was 75% by volume.

  Subsequently, using a horizontal stirrer of the same type as the horizontal stirrer (paddle dryer) used in the heat treatment, the volume of the heat-treated mixture (1) is forcibly increased to 60 ° C. Cooling was performed. By this operation, water absorbent resin particles (1) were obtained. The total amount of acetic acid and propionic acid contained in the obtained water-absorbent resin particles (1) was 200 mg / kg.

  Next, 10 parts by weight of water (amount of free residual chlorine; 0.8 mg / l (in terms of chlorine)) in which sodium hypochlorite as a sterilizing component is added to 100 parts by weight of the water-absorbent resin particles (1). Were sprayed and mixed using a high speed mixer. In this mixing, water existing on the surface of the water-absorbent resin particles is also permeated to the inside, and this operation is sometimes referred to as “curing”.

  Subsequently, using a sieving apparatus having a JIS standard sieve screen having an opening of 850 μm, the water-absorbent resin particles (1) were pulverized until the entire amount passed through the sieve mesh. The “pulverization” means an operation of pulverizing the water-absorbent resin particles (1) aggregated at the time of curing until they pass through a sieve screen having an opening of 850 μm. Therefore, coarse particles (non-passed product / on product) that do not pass through the sieve mesh are pulverized again. By this operation, a water-absorbing agent (1) as a sized product was obtained. The obtained water-absorbing agent (1) had a CRC of 34.0 g / g and an AAP of 24.0 g / g. Further, the obtained water-absorbing agent (1) was subjected to an odor test and a mold generation test. The results are shown in Table 1.

  Next, after producing the water-absorbing agent (1) continuously for 5 days, the water-absorbing agent of the type that does not require the curing operation (with the water addition process suspended) is produced continuously for 10 days. Thereafter, production of the water-absorbing agent (1) was started. Table 2 shows operating conditions after the production of the water-absorbing agent (1) was resumed.

[Comparative Example 1]
In Example 1, instead of water added with sodium hypochlorite, which is a sterilizing component, ion-exchange water containing no sterilizing component was used, and the same operation as in Example 1 was carried out. 1) was obtained. Further, the obtained comparative water-absorbing agent (1) was subjected to an odor test and a mold generation test. The results are shown in Table 1.

  Next, as in Example 1, the comparative water-absorbing agent (1) was produced continuously for 5 days, and then the type of water-absorbing agent that does not require the curing operation was produced continuously for 10 days. Production of the water-absorbing agent (1) was started. The operational status at the start of production of the water-absorbing agent (1) is shown in Table 2.

[Comparative Example 2]
In Comparative Example 1, a comparative water-absorbing agent (2) was obtained by performing the same operation as in Comparative Example 1 except that 2800 mg / kg of acetic acid was added together when mixing ion-exchanged water containing no bactericidal component. . Further, the obtained comparative water-absorbing agent (2) was subjected to an odor test and a mold generation test. The results are shown in Table 1.

[Comparative Example 3]
In Comparative Example 1, the same operation as in Comparative Example 1 was performed except that 2800 mg / kg of propionic acid was added together with the ion-exchanged water not containing the bactericidal component to obtain a comparative water-absorbing agent (3). It was. Furthermore, an odor test and a mold generation test were performed on the comparative water-absorbing agent (3) obtained. The results are shown in Table 1.

[Comparative Example 4]
In Example 1, the same operation as in Example 1 was performed except that 2800 mg / kg of acetic acid was added together with the water added with sodium hypochlorite as a bactericidal component, and a comparative water absorbing agent (4 ) Furthermore, an odor test and a mold generation test were performed on the obtained comparative water-absorbing agent (4). The results are shown in Table 1.

(Summary)
As shown in Table 1, the water-absorbing agent (1) had no odor after absorption of human urine (when using a paper diaper), and no generation of mold was observed after 10 days (when the paper diaper was discarded). On the other hand, the comparative water-absorbing agent (1) cured with ion-exchanged water containing no bactericidal component has no odor after human urine absorption (when using paper diapers), but after 10 days (when disposable diapers are discarded). Mold generation was observed. From these facts, it can be seen that by including a sterilizing component in the water used at the time of curing, it is possible to suppress the occurrence of mold at the time of disposal of the paper diaper.

  In addition, from the results of the comparative water-absorbing agents (2) to (4), the total amount of acetic acid and propionic acid in the water-absorbing agent is 2500 mg / kg or more, so that odor is generated after absorption of human urine (when using paper diapers). Admitted. On the other hand, the water-absorbing agent (1) or the comparative water-absorbing agent (1) having a total amount of acetic acid and propionic acid of 200 mg / kg has no odor after human urine absorption (when using paper diapers). The odor of is estimated to be due to acetic acid and propionic acid in the water-absorbing agent.

  On the other hand, with regard to mold generation after 10 days (when disposable diapers are discarded), generation of mold is not observed even with comparative water-absorbing agents (2) and (3) cured with ion-exchanged water that does not contain bactericidal components. It was. From this, it is presumed that not only the sterilizing component but also acetic acid and propionic acid in the water-absorbing agent have an effect on the occurrence of mold after 10 days (when disposable diapers are discarded).

  From the above results, the total amount of acetic acid and propionic acid in the water-absorbing agent was used to suppress the generation of odors and molds both at the time of human urine absorption (when using paper diapers) and after 10 days (when paper diapers were discarded). It can be seen that it is necessary to keep the amount low and add an aqueous liquid containing a trace amount of bactericidal components.

  Moreover, as shown in Table 2, it can be understood that clogging of the water adding spray nozzle and piping can be prevented by including a sterilizing component in the water used at the time of curing.

  From the above results, in the step of adding an aqueous liquid to the water-absorbent resin particles after surface crosslinking, if ion-exchanged water containing a predetermined amount or more of sterilizing components is used, device troubles at the time of product type switching can be prevented. As a result, it became clear that stable operation with reduced production loss was possible.

  The method for producing a polyacrylic acid (salt) water-absorbing agent according to the present invention can be applied to production of a water-absorbing agent, particularly mass production. In addition, the polyacrylic acid (salt) water-absorbing agent obtained by the present invention is suitable for use as an absorbent material for sanitary goods such as paper diapers.

Claims (12)

A method for producing a polyacrylic acid (salt) water-absorbing agent, comprising a polymerization step of an aqueous monomer solution, a drying step, and a surface crosslinking step,
The total amount of acetic acid and propionic acid contained in the monomer or polymer thereof is 200-2500 ppm,
A method for producing a polyacrylic acid (salt) water-absorbing agent, further comprising a step of adding an aqueous liquid containing a bactericidal component to surface-crosslinked water-absorbing resin particles.   The manufacturing method according to claim 1, wherein the sterilizing component is at least one selected from the group consisting of sodium hypochlorite, chlorine dioxide, iodine tincture, and povidone iodine.   The manufacturing method of Claim 1 or 2 whose amount of free residual chlorine contained in the aqueous liquid containing the said disinfection component is 0.1-5.0 mg / l.   The manufacturing method of any one of Claims 1-3 whose addition amount of the aqueous liquid containing the said bactericidal component is 1 to 10 weight% with respect to the water absorbing resin particle.   The manufacturing method of any one of Claims 1-4 whose addition of the aqueous liquid containing the said bactericidal component is spray addition.   The manufacturing method of any one of Claims 1-5 which heat-process so that the moisture content of the said water absorbing agent may be 1 to 15 weight%.   The method according to any one of claims 1 to 6, wherein in the step of adding the aqueous liquid containing the sterilizing component, the temperature of the water-absorbent resin particles to which the aqueous liquid is added is 30 to 70 ° C. .   The manufacturing method according to any one of claims 1 to 7, wherein the step of adding the aqueous liquid containing the sterilizing component is operated again after stopping the step of adding the aqueous liquid containing the sterilizing component for one day or more. .   In the step of adding the aqueous liquid containing the sterilizing component, simultaneously with the addition of the aqueous liquid containing the sterilizing component, from the polyvalent metal salt, the cationic polymer, the chelating agent, the indefinite reducing agent, the α-hydroxycarboxylic acid compound, and the deodorant. The production method according to any one of claims 1 to 8, wherein at least one additive selected from the group consisting of:   The water-absorbing agent has a CRC (centrifuge retention capacity) of 30 g / g or more, an AAP (water absorption capacity under pressure) of 18 g / g or more, a D50 (weight average particle diameter) of 250 to 600 μm, and σζ (particle size distribution). The manufacturing method of any one of Claims 1-9 whose logarithmic standard deviation) is 0-0.50.   A polyacrylic acid (salt) -based water-absorbing agent obtained by the production method according to claim 1.   An absorbent article comprising the water-absorbing agent according to claim 11.