JP2016060764A - Method for producing polyacrylic acid (salt)-based water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of efficiently and persistently producing a water-absorbing resin.SOLUTION: A method for producing a polyacrylic acid (salt)-based water-absorbing resin includes a production step which needs a temperature adjustment of a water-absorbing resin or a raw material thereof, separately from a drying step after polymerization and a heating treatment step after drying. As a heat exchange fluid of equipment for adjusting the temperature, water having a fouling factor at a temperature lower than 50°C of 0.0004 mK/W or less and a fouling factor at 50°C or higher of 0.0006 mK/W or less or water having a content of polyvalent metal ions of 200 ppm or less are used.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a polyacrylic acid (salt) water-absorbing resin. Specifically, the present invention relates to a method for producing a polyacrylic acid (salt) water-absorbing resin including a production process that requires temperature adjustment.

  Water-absorbent resin (SAP / Super Absorbent Polymer) is a water-swellable, water-insoluble polymer gelling agent, sanitary products such as paper diapers and sanitary napkins, water retention agents for agriculture and horticulture, and industrial water-stopping agents. As such, it is frequently used mainly in disposable applications.

  Such a water-absorbing resin uses many monomers and hydrophilic polymer compounds as raw materials. Among them, polyacrylic acid (salt) water-absorbing resins using acrylic acid and / or a salt thereof are most frequently used industrially because of their high water absorption performance.

  The water-absorbing resin described above is manufactured as a particulate product through manufacturing processes such as polymerization, drying, pulverization, classification, and surface cross-linking (Non-Patent Document 1), but the manufacturing process is usually a continuous operation. Have been mass produced. In addition, since the water-absorbent resin is controlled by many physical properties such as water absorption capacity, soluble content, water absorption capacity under pressure, liquid permeability, water absorption speed, etc., the above manufacturing process is stable and stable for a long time. Is required. In addition, stabilization of physical properties is also required.

  In view of this, various methods have been proposed so far for achieving stable operation over a long period of time and stabilization of physical properties. For example, a method of heating the raw material of the water-absorbent resin to a predetermined temperature (Patent Documents 1 and 2), a method of making a process consisting of a single device after a process consisting of a plurality of parallel devices, or a single device (Patent Documents 3 and 4), a method of vibrating when filling a container with a water absorbent resin as a product (Patent Document 5), a water absorbent resin A method of measuring the physical properties of the sample, separating and re-mixing those that are out of specification (Patent Document 6), and a method of using a mother liquor when preparing a solution such as a polymerization initiator or a surface cross-linking agent (Patent Document 7) ) And the like.

  In addition to the drying of the hydrogel crosslinked polymer obtained after polymerization and the heat treatment after drying (for example, surface crosslinking), the water-absorbing resin itself and the raw material of the water-absorbing resin (for example, acrylic acid, sodium hydroxide) It is known to control the temperature of a polymerization initiator, a surface cross-linking agent, etc. (Patent Documents 1, 2, etc.). Therefore, temperature adjusting devices are also used in the manufacturing process of the water absorbent resin other than the drying and heat treatment described above. For example, a heat exchanger, a polymerization reaction apparatus with a jacket, a mixing apparatus with a jacket, and the like can be given.

  Examples of a method for producing a water-absorbent resin using the temperature adjusting device include, for example, a technique using a heat exchanger to remove heat of neutralization of a monomer aqueous solution (Patent Documents 8 and 9), In order to gel the unreacted monomer remaining in the hydrogel crosslinked polymer immediately after the polymerization (Patent Documents 10 to 12), a technology comprising a heat exchanger in a part of the apparatus for continuous neutralization, A technique for transferring and heating the hydrogel crosslinked polymer to a heat exchanger (Patent Document 13), and using a heat exchanger for drying, heating, cooling and the like of a brittle and fragile water-absorbent resin after surface treatment. Techniques (Patent Documents 14) and techniques (Patent Documents 15 and 16) using a jacketed polymerization machine (for example, a kneader type polymerization machine) are disclosed. The temperature adjusting device described above uses steam, water (hot water), oil, or the like as a heat medium depending on the purpose.

US Patent Application Publication No. 2014/0031473 US Patent Application Publication No. 2014/0042364 US Patent Application Publication No. 2011/0006140 US Patent Application Publication No. 2008/0227932. US Patent Application Publication No. 2011/0011491 US Patent Application Publication No. 2004/0110006 US Patent Application Publication No. 2011/0039961 US Patent Application Publication No. 2010/0010184 International Publication No. 2013/104480 US Patent Application Publication No. 2008/0242816 US Patent Application Publication No. 2009/0221746 US Patent Application Publication No. 2008/0194863 JP 2004-352899 A US Patent Application Publication No. 2010/0018671 US Patent No. 8070351 US Pat. No. 6,987,151

Modern Supersorbent Polymer Technology (1998), p69-103.

  In the production of the water-absorbing resin described above, there have conventionally been problems that stable operation cannot be continued, productivity is deteriorated, and physical properties of the obtained water-absorbing resin greatly fluctuate. In order to solve such a problem, methods of the above Patent Documents 1 to 7 and the like have been proposed so far, but in either case, it is not sufficient.

  In addition, in the prior art (for example, Patent Documents 8 to 16 and the like) handling the temperature control device, no consideration is given to the fact that the heat transfer performance of the device affects the physical properties of the water absorbent resin. No consideration was given to the prevention of contamination from being adhered to the heat transfer surface of the temperature control device that affects the thermal performance, and the selection of the optimum heat exchange fluid.

  The object of the present invention is made in view of the above-mentioned problems, and is to provide a method capable of efficiently and continuously producing a water absorbent resin.

  In order to solve the above-mentioned problems, the present inventors paid attention to the heat transfer performance of the temperature adjusting device for the first time. In a manufacturing apparatus (for example, a polymerization apparatus) used in a process other than the drying process and the heat treatment process, the temperature adjustment is performed. It has been found that a decrease in the heat transfer performance of the equipment is a cause of a decrease in the physical properties of the water absorbent resin.

  Therefore, the present inventors have completed the present invention as a technique for preventing contamination from adhering to the heat transfer surface of the temperature adjusting device.

That is, in order to solve the above problems, the production method (first method) of the present invention requires temperature adjustment of the water-absorbent resin or its raw material separately from the drying step after polymerization and the heat treatment step after drying. A manufacturing method of a polyacrylic acid (salt) -based water-absorbent resin including a manufacturing process as described above, wherein a soil coefficient at less than 50 ° C. is 0.0004 m ² · K / Provided is a method for producing a polyacrylic acid (salt) -based water-absorbent resin, in which water having a soil coefficient at 50 ° C. or higher and a soil coefficient of 0.0006 m ² · K / W or lower is used.

  In addition, in order to solve the above problems, the production method (second method) of the present invention requires temperature adjustment of the water-absorbent resin or its raw material separately from the drying step after polymerization and the heat treatment step after drying. A method for producing a polyacrylic acid (salt) -based water-absorbing resin including a production process in which water having a polyvalent metal ion content of 200 ppm or less is used as a heat exchange fluid for a device for adjusting the temperature. A method for producing a polyacrylic acid (salt) -based water-absorbing resin is provided.

  By adopting the method for producing a polyacrylic acid (salt) water-absorbing resin according to the present invention, it is possible to reduce the adhesion of dirt to the surface of the heat transfer surface of the temperature adjusting device, and to perform constant heating and / or cooling. It becomes possible to maintain the ability stably over a long period of time. As a result, stable operation can be performed for a long period of time.

  Further, since excessive heating and / or cooling due to dirt adhesion is not necessary, energy cost can be reduced. In addition, maintenance such as cleaning for removing attached dirt can be reduced, and running costs can be reduced without stopping production of the water absorbent resin.

  Furthermore, since the temperature of the aqueous monomer solution at the start of polymerization and the cooling temperature of the water-absorbing resin after surface crosslinking are stabilized, the physical properties of the finally obtained water-absorbing resin can be further stabilized.

  Hereinafter, the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and modifications other than the following examples can be appropriately modified and implemented within a range not impairing the gist of the present invention. Specifically, the present invention is not limited to the following embodiments, and various modifications can be made within the scope shown in the claims, and technical means disclosed in different embodiments are appropriately combined. The obtained embodiment is also included in the technical scope of the present invention.

[1] Definition of terms (1-1) "Water absorbent resin"
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, as “water swellability”, CRC specified by ERT441.2-02 is 5 g / g or more, and as “water-insoluble”, Ext specified by ERT470.2-02 is 50% by weight or less. It refers to a polymer gelling agent that satisfies the above.

  The water-absorbent resin can be appropriately designed according to its use, 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, the whole amount (100 weight%) is not limited to the form which is a polymer, The water absorbing resin composition containing the additive etc. may be sufficient in the range which satisfies the said physical property (CRC, Ext).

  Furthermore, the water-absorbent resin in the present invention is not limited to the final product, but is an intermediate in the manufacturing process of the water-absorbent resin (for example, a water-containing gel-like crosslinked polymer after polymerization, a dried polymer after drying, a water absorption before surface crosslinking). In combination with the water-absorbent resin composition described above, all of which 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.

(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. A polymer containing a repeating component and a graft component as an optional component.

  The above-mentioned “main component” means that the amount (content) of acrylic acid (salt) used is usually 50 to 100 mol% with respect to the entire monomer (excluding the internal crosslinking agent) used for polymerization, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, still more preferably substantially 100 mol%. The polyacrylic acid salt essentially contains a water-soluble salt, preferably a monovalent salt, more preferably an alkali metal salt or an ammonium 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 according to the original ERT (revised in 2002 / known literature).

(1-3-1) “CRC” (ERT441.2-02)
“CRC” is an abbreviation for centrifugal 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 a water-absorbing resin was put in a nonwoven fabric, and then freely swollen by immersion in a large excess of 0.9 wt% sodium chloride aqueous solution for 30 minutes, and then drained with a centrifuge (250 G). It means the water absorption ratio (unit; g / g) after

(1-3-2) “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, for 1.0 g of water-absorbing resin, a value obtained by measuring the amount of dissolved polymer after stirring for 16 hours at 500 rpm with respect to 200 ml of 0.9 wt% aqueous sodium chloride solution (unit: wt%) ).

(1-3-3) “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, 0.9 g of the water-absorbing resin was swollen under a load of 0.3 psi (2.06 kPa, 21 g / cm ² ) for 1 hour against a large excess of 0.9 wt% sodium chloride aqueous solution. It refers to the subsequent water absorption ratio (unit: g / g). In the present invention, the load condition is changed to 0.7 psi (4.83 kPa, 49 g / cm ² ) for measurement.

(1-4) “Liquid permeability”
“Liquid permeability” of the water-absorbent resin refers to the fluidity of the liquid passing between the particles of the swollen gel under load or no load. As a typical measurement method, SFC (Saline Flow Conductivity / Saline flow conductivity) and GBP (Gel Bed Permeability / gel bed permeability).

  “SFC (Saline Flow Inducibility)” refers to the liquid permeability of a 0.69 wt% sodium chloride aqueous solution to a water absorbent resin under a load of 2.07 kPa, and the SFC test disclosed in US Pat. No. 5,669,894. Measured according to the method.

  “GBP (gel bed permeability)” refers to the liquid permeability of a 0.9 wt% sodium chloride aqueous solution to a water absorbent resin under load or free swelling, and is disclosed in International Publication No. 2005/016393. Measured according to the test method.

(1-5) “Water absorption rate”
The “water absorption rate” of the water absorbent resin refers to the speed at which a certain amount of aqueous liquid is absorbed, and “FSR” and “Vortex” (unit: seconds) are typical measurement methods. is there. In addition, the water absorption speed in this invention was evaluated by FSR. “FSR” is an abbreviation for Free Swell Rate. Specific measurement methods will be described in the examples described later.

(1-6) 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, “weight” and “mass”, “parts by weight” and “parts by mass”, “% by weight” and “% by mass” are treated as synonyms. Further, “˜acid (salt)” means “˜acid and / or salt thereof”, and “(meth) acryl” means “acryl and / or methacryl”.

[2] Manufacturing method of polyacrylic acid (salt) water-absorbing resin The present invention is a manufacturing that requires temperature adjustment of the water-absorbing resin or its raw material separately from the drying step after polymerization and the heat treatment step after drying. A method for producing a polyacrylic acid (salt) water-absorbing resin including a step, wherein a soil coefficient at less than 50 ° C. is 0.0004 m ² · K / W or less as a heat exchange fluid for a device for adjusting the temperature. There is also provided a method for producing a polyacrylic acid (salt) water-absorbing resin, in which water having a soil coefficient at 50 ° C. or higher and 0.0006 m ² · K / W or lower is used.

  Furthermore, the present invention provides a polyacrylic acid (salt) -based water-absorbing resin including a manufacturing step that requires temperature adjustment of the water-absorbing resin or its raw material, separately from the drying step after polymerization and the heat treatment step after drying. A method for producing a polyacrylic acid (salt) water-absorbing resin, wherein water having a polyvalent metal ion content of 200 ppm or less is used as a heat exchange fluid for a device for adjusting the temperature. Also provide.

  Hereinafter, the production steps (2-1) to (2-11) of the polyacrylic acid (salt) -based water absorbent resin according to the present invention will be described. The “manufacturing process requiring temperature adjustment” will be described in [3].

(2-1) Preparation Step of Monomer Aqueous Solution This step is a step of preparing and preparing an aqueous solution containing acrylic acid (salt) as a main component (hereinafter referred to as “monomer aqueous solution”). A monomer slurry liquid can be used as long as the water absorption performance does not deteriorate, but in this specification, the monomer aqueous solution will be described for convenience.

(Acrylic acid)
In the present invention, acrylic acid is used as a monomer from the viewpoint of the effects of the invention. The acrylic acid may be a known one, and the polymerization inhibitor preferably contains phenols, more preferably methoxyphenols. Further, the concentration of the polymerization inhibitor is preferably 1 to 200 ppm, more preferably 10 to 160 ppm from the viewpoint of the polymerizability of acrylic acid and the color tone of the water absorbent resin.

  As for impurities in acrylic acid, the contents disclosed in US Patent Application Publication No. 2008/0161512 also apply to the present invention.

(Monomer used together)
In the present invention, a water-absorbing resin can also be produced by using a monomer other than acrylic acid (salt) (hereinafter referred to as “other monomer”) in combination with acrylic acid (salt). Although it does not specifically limit as said other monomer, Water-soluble or hydrophobic unsaturated monomer is mentioned. Specific examples include monomers (excluding acrylic acid) disclosed in paragraph [0035] of US Patent Application Publication No. 2005/215734.

  The water-absorbent resin obtained by the production method according to the present invention includes those having the water-soluble or hydrophobic unsaturated monomer as a copolymerization component.

(Basic composition)
In the present invention, the “basic composition” means 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. Among these, from the viewpoint of producing a water-absorbing resin having high physical properties, a strongly basic compound is desired. That is, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are preferable, and sodium hydroxide is particularly preferable.

  The water-absorbent resin of the present invention is polyacrylic acid (salt) obtained by crosslinking and polymerizing acrylic acid (salt). Therefore, in order to obtain the polyacrylic acid (salt), it is preferable to have a step of neutralizing acrylic acid with the basic composition (neutralization step).

(Neutralization process)
In the present invention as the neutralization step, in addition to neutralization of the monomer acrylic acid, neutralization of the hydrogel crosslinked polymer obtained by crosslinking polymerization of acrylic acid (hereinafter referred to as “post-neutralization”). ) Is also included. These neutralizations may be continuous or batch, but continuous is preferred from the viewpoint of production efficiency. Moreover, these neutralization can also be used together.

  About the neutralization conditions, such as the apparatus applied in the said neutralization process, a basic composition, temperature conditions, and residence time, the content disclosed by international publication 2009/123197 or US Patent application publication 2008/0194863 Applies to the present invention.

  The acrylate obtained in the neutralization step is a substantially monovalent salt. For example, a very small amount of 5 mol% or less may be used as the polyvalent metal salt.

  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 said neutralization rate is less than 10 mol%, a water absorption factor may fall remarkably. On the other hand, when the said neutralization rate exceeds 90 mol%, the water absorbing resin with a high water absorption ratio under pressure may not be obtained. The neutralization rate is the same even in the case of post-neutralization. Moreover, the said neutralization rate is applied also about the neutralization rate of the water absorbing resin as a final product.

(Internal crosslinking agent)
Examples of the internal crosslinking agent used in the present invention include compounds having two or more substituents capable of reacting with acrylic acid. Specific examples include compounds described in column 14 of US Pat. No. 6,241,928. Of these, one or more compounds are used.

  Among these, from the viewpoint of the water absorption performance of the resulting water-absorbent resin, a compound having two or more polymerizable unsaturated groups is preferable, more preferably a compound having thermal decomposability at about the drying temperature described below, and more preferably ( And compounds having two or more polymerizable unsaturated groups having a poly) alkylene glycol structural unit.

  The polymerizable unsaturated group is preferably an allyl group or a (meth) acrylate group, more preferably a (meth) acrylate group. Moreover, as an alkylene glycol structural unit, polyethyleneglycol is preferable and as n number, 1-100 are preferable and 6-50 are more preferable.

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

  The amount of the internal cross-linking agent used is preferably 0.005 to 2 mol%, more preferably 0.01 to 1 mol%, still more preferably 0.05 to 0.5 mol%, based on the monomer. is there. By setting the amount to be used within the above range, a desired water absorbent resin can be obtained.

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

(Other substances added to the monomer aqueous solution)
In the present invention, for the purpose of improving various physical properties such as water absorption performance of the water absorbent resin, the following substances can be added when preparing the monomer aqueous solution.

  Specifically, the water-soluble resin or water-absorbing resin is preferably 50% by weight or less, more preferably 20% by weight or less, still more preferably 10% by weight or less, and particularly preferably 5% by weight or less (the lower limit is 0% by weight). Or a foaming agent such as carbonates, azo compounds and bubbles, surfactants, chelating agents, chain transfer agents and the like are preferably 5% by weight or less, more preferably 1% by weight or less, still more preferably 0.8%. Or 5% by weight or less (the lower limit is 0% by weight).

  These substances may be added not only in the form added to the monomer aqueous solution, but also in the form added during the polymerization, or these forms may be used in combination.

  When the above water-soluble resin or water-absorbent resin is used, a graft polymer or a water-absorbent resin composition (for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) is obtained. Combined and water-absorbing resin compositions are also within the category of the polyacrylic acid (salt) -based water-absorbing resin of the present invention.

(Concentration of monomer component)
In the present invention, the concentration of the monomer component in the aqueous monomer solution is not particularly limited, but is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, from the viewpoint of physical properties of the water absorbent resin. More preferably, it is 30 to 70% by weight. In addition, when employ | adopting high concentration polymerization mentioned later, the below-mentioned range is applied preferably.

  In addition, when employ | adopting aqueous solution polymerization or reverse phase suspension polymerization as a polymerization form, arbitrary solvents other than water can also be used together as needed. In that case, the kind of solvent used is not specifically limited.

  The “concentration of the monomer component” is a value calculated from the following formula (1). In the formula (1), the monomer aqueous solution includes a graft component, a water absorbent resin, and a reverse phase suspension polymerization. Hydrophobic solvents are not included.

（２−２）重合工程

(2-2) Polymerization process

  In this step, the monomer aqueous solution obtained in the monomer aqueous solution preparation step is polymerized to obtain a water-containing gel.

This is a step of obtaining a crosslinked polymer (hereinafter referred to as “water-containing gel”).

(Polymerization initiator)
Examples of the polymerization initiator used in the present invention include a thermally decomposable polymerization initiator, a photodegradable polymerization initiator, or a redox polymerization initiator used in combination with a reducing agent that promotes the decomposition of these polymerization initiators. Specific examples include compounds disclosed in column 5 of US Pat. No. 7,265,190. Of these, one or more compounds are used.

  Among these, from the viewpoint of water absorption performance and handleability of the obtained water absorbent resin, 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. By setting the amount to be used within the above range, a desired water absorbent resin can be obtained.

  In addition to the above polymerization initiator, an active energy ray such as an electron beam or ultraviolet ray may be irradiated to cause a polymerization reaction. Moreover, these can also 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 from the viewpoint of water absorption performance of the water absorbent resin and ease of polymerization control. More preferably, aqueous solution polymerization, reverse phase suspension polymerization, still more preferably aqueous solution polymerization, and particularly preferably continuous aqueous solution polymerization.

  Specific examples of the continuous aqueous solution polymerization include continuous belt polymerization and continuous kneader polymerization. In addition, as continuous belt polymerization, U.S. Pat. Nos. 4,893,999 and 6,241,928, U.S. Patent Application Publication No. 2005/215734, etc., and as continuous kneader polymerization, disclosed in U.S. Pat. Nos. 6,987,151 and 6,710,141, respectively. The contents applied are applied to the present invention. By adopting such continuous aqueous solution polymerization, the production efficiency of the water-absorbent resin is improved.

  Moreover, high temperature initiation polymerization and high concentration polymerization are mentioned as preferable embodiment of the said continuous aqueous solution polymerization. The “high temperature initiation polymerization” means that the temperature of the monomer aqueous 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 that of the monomer aqueous solution). Refers to a method in which the polymerization is started after the boiling point is raised, and “high concentration polymerization” means that the concentration of the monomer component is preferably 30% by weight or more, more preferably 35% by weight or more, and still more preferably 40% by weight. % Or more, particularly preferably 45% by weight or more (upper limit is 80% by weight), and then the polymerization is started. These polymerization methods can be used in combination.

  Moreover, in this invention, solid content concentration can also be raised during superposition | polymerization. The increase in the solid content concentration is defined by the following formula (2) as “solid content increase degree”. The degree of increase in the solid content is preferably 1% by weight or more, more preferably 2% by weight or more.

上式（２）中、「単量体水溶液の固形分濃度」とは、下記式（３）で定義される値であ

In the above formula (2), the “solid content concentration of the monomer aqueous solution” is a value defined by the following formula (3).

The

上式（３）中、「重合系内の成分重量」とは、単量体水溶液、グラフト成分、吸水性樹

In the above formula (3), “component weight in polymerization system” means monomer aqueous solution, graft component, water-absorbing resin

Refers to the total weight of fat and other solids (for example, water-insoluble fine particles). Reverse phase suspension polymerization, etc.

The hydrophobic solvent used in is not included. That is, the “solid content concentration of the monomer aqueous solution” refers to the concentration of the component that is solidified by polymerization.

  In the present invention, from the viewpoint of the color tone of the resulting water-absorbent resin, the polymerization is preferably performed in an inert gas atmosphere such as nitrogen or argon, and the oxygen concentration is controlled in an atmosphere of 1% by volume or less. Is more preferable. Further, in this case, it is also desired that the dissolved oxygen in the monomer or the monomer aqueous solution is sufficiently substituted with an inert gas (for example, the dissolved oxygen concentration is less than 1 mg / L). In addition, it can also be set as foaming polymerization which superpose | polymerizes by disperse | distributing bubbles, such as the said inert gas, in monomer aqueous solution.

  In the present invention, the polymerization rate of the hydrogel obtained after polymerization is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 98 mol% or more, and particularly preferably 99 mol% or more. The upper limit is preferably 99.99 mol% or less, more preferably 99.9 mol% or less, still more preferably 99.8 mol% or less. When the polymerization rate is less than 90 mol%, there are many residual monomers in the water-absorbent resin, while when the polymerization rate exceeds 99.99 mol%, it takes more polymerization time than necessary, and the productivity decreases. It is not preferable. Furthermore, depending on the case, the physical properties (relationship between water absorption and soluble content) of the water-absorbent resin after drying are lowered.

  In the present invention, it is not necessary to advance the polymerization excessively, and it is possible to reduce the residual monomer in the drying step described later, particularly in the hot air drying step, and as a result, productivity can be improved.

(2-3) Gel pulverization step In this step, the water-containing gel obtained in the polymerization step is subjected to gel pulverization with a gel pulverizer such as a kneader, meat chopper, or cutter mill, and then a particulate water-containing gel (hereinafter referred to as "particulate water-containing water"). This is a step of obtaining a “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.

  Although it does not specifically limit as a gel grinding | pulverization form applied to this invention, The method disclosed by international publication 2011/126079 is mentioned.

  The weight average particle diameter (D50) of the particulate hydrogel obtained by such gel pulverization is preferably 4000 μm or less, more preferably 2000 μm or less. By setting the weight average particle diameter (D50) of the particulate hydrogel within the above range, the surface area is increased, so that the residual monomer (particularly acrylic acid) is likely to volatilize, and the residual monomer can be reduced.

(2-4) Drying step This step is a step of obtaining a dry polymer by drying the particulate hydrogel obtained in the polymerization step and / or the gel grinding step to a desired solid content concentration.

  The drying form applied to the present invention is not particularly limited, but is heat drying, hot air drying, vacuum drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with a hydrophobic organic solvent. Various drying methods such as drying and high-humidity drying using high-temperature steam can be applied.

  Among these, hot air drying is preferable as a drying form suitable for the present invention, and band drying in which hot air drying is performed on a ventilation belt is particularly preferable. In addition, from a viewpoint of the color tone and drying efficiency of the water-absorbing resin obtained, the temperature of the hot air (drying temperature) is preferably 100 to 300 ° C, more preferably 120 to 220 ° C, and still more preferably 160 to 200 ° C. Also, the wind speed of the hot air is preferably 3.0 m / s or less, more preferably 0.5 to 2.0 m / s or less. Although drying time is suitably determined, Preferably it is 1 minute-10 hours, More preferably, it is 5 minutes-3 hours, More preferably, it is 10 minutes-1 hour. By setting it in such a range, it is difficult to cause unevenness in the physical properties of the dry polymer, the water content can be controlled to a desired range, and further, the deterioration of the color tone and water absorption performance of the obtained water absorbent resin can be suppressed. Can do.

  Further, the solid content concentration of the dry polymer obtained in this step is preferably 80% by weight or more, more preferably 85 to 99% by weight, still more preferably 90 to 98% by weight, and particularly preferably 92 to 97% by weight. . In addition, the said solid content density | concentration is calculated | required from drying loss (weight change amount when a sample 1g is heated at 180 degreeC for 3 hours).

  When performing the band drying, conditions disclosed in International Publication Nos. 2006/100300, 2011/025012, 2011/025013, 2011/111657, etc. are applied as conditions other than those described above. The

(2-5) Crushing 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 (surface) This is a step of obtaining a particulate water-absorbing resin before crosslinking, for convenience, as “water-absorbing resin powder”.

  The equipment used in the pulverization step 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. . These are used in combination as necessary.

  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 of the water-absorbing resin is not limited to the pulverization step and the classification step, but is also adjusted appropriately in the polymerization step (especially reverse phase suspension polymerization, spray polymerization, droplet polymerization) and other steps (for example, granulation step). can do.

  As the particle size of the water-absorbent resin powder, the weight average particle size (D50) is preferably 200 to 600 μm, more preferably 200 to 550 μm, still more preferably 250 to 500 μm, and particularly preferably 350 to 450 μm. 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, still more preferably 1% by weight or less (the lower limit is 0% by weight), and the particle size is 850 μm or more. The proportion of the particles is preferably 5% by weight or less, more preferably 3% by weight or less, still more preferably 1% by weight or less (the lower limit is 0% by weight). Furthermore, the logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and still more preferably 0.27 to 0.35.

  These particle sizes are measured using a standard sieve according to the measurement methods disclosed in US Pat. No. 7,638,570 and ERT420.2-02.

  The above particle size is applied 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 resin as a final product. Therefore, it is desired that the surface is crosslinked so as to maintain the particle size in the above range.

(2-6) Surface cross-linking step This step is a step of providing a portion having a high cross-linking density in the surface layer of the water-absorbent resin powder obtained through the above-described steps (portion of several tens of micrometers from the surface of the water-absorbent resin powder). , A mixing step, a heat treatment step and, if necessary, a cooling step. In the surface crosslinking step, surface-crosslinked water-absorbing resin (water-absorbing resin particles) is obtained by radical polymerization or surface polymerization on the surface of the water-absorbent resin powder, a crosslinking reaction with a surface crosslinking agent, or the like.

(Surface cross-linking agent)
The surface cross-linking agent used in the present invention is preferably various organic or inorganic surface cross-linking agents, and more preferably reacted with a carboxyl group from the viewpoint of water absorption performance of the water-absorbent resin and handling properties of the surface cross-linking agent. Organic surface cross-linking agents that form covalent bonds. Specifically, surface cross-linking agents described in columns 9 to 10 of US Pat. No. 7,183,456 can be mentioned. Of these, one or more surface cross-linking agents are used. Moreover, a hydrophilic organic solvent can also be used as needed.

  The amount of the surface cross-linking agent used is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin powder. Part. The surface cross-linking agent is preferably added as an aqueous solution. In this case, the amount of water used is preferably 0.1 to 20 parts by weight, more preferably 0 to 100 parts by weight of the water-absorbent resin powder. .5 to 10 parts by weight. Furthermore, the amount used when using a hydrophilic organic solvent as required 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.

(Mixing process)
This mixing step is a step of obtaining a mixture by mixing the water absorbent resin powder and the surface cross-linking agent. The method for adding and mixing the surface cross-linking agent is not particularly limited, but after preparing the surface cross-linking agent and water as a solvent, a hydrophilic organic solvent or a mixture thereof in advance, spraying or It is preferable to add and mix dropwise, and more preferably to add and mix by spraying.

  Further, the equipment used for the mixing is not particularly limited, but a high-speed stirring type mixer is preferable, and a high-speed stirring type continuous mixer is more preferable.

(Heat treatment process)
This heat treatment step is a step of obtaining water absorbent resin particles by heat-treating the mixture of the water absorbent resin powder and the surface cross-linking agent.

  Although it does not specifically limit as an apparatus used for the said heat processing, Preferably a paddle dryer is mentioned. Preferably it is 80-250 degreeC as temperature at the time of heat processing, More preferably, it is 100-220 degreeC.

(Cooling process)
This cooling process is an arbitrary process installed as necessary after the heat treatment process.

  Although it does not specifically limit as an apparatus used for the said cooling process, The apparatus of the same specification as the apparatus used at a heat processing process is preferable, and a paddle dryer is more preferable. It is because it can be used as a cooler by using a refrigerant instead of the heat medium.

(2-7) Re-humidification step This step comprises adding, as an additive to the water-absorbent resin particles obtained in the surface cross-linking step, a polyvalent metal salt compound, a polycationic polymer, a chelating agent, an inorganic reducing agent, and α- It is a step of adding at least one compound selected from the group consisting of hydroxycarboxylic acid compounds.

  The additive is preferably added as an aqueous solution or a slurry, and the water-absorbing resin is again swollen with water, so this step is referred to as a “rehumidification step”. In addition, in the said rehumidification process, it heats or dries as needed, Preferably the water content of the water-absorbing resin obtained is controlled to 1 to 10 weight%, More preferably, it is 2 to 9 weight%.

  The above additives may be added and mixed simultaneously with the surface cross-linking agent described above, or may be added separately from the surface cross-linking agent in the surface cross-linking step.

(Polyvalent metal salt compound and / or cationic polymer)
In the present invention, it is preferable to add a polyvalent metal salt compound and / or a cationic polymer from the viewpoint of the water absorption performance of the resulting water absorbent resin. By adding these compounds, the water absorption rate (for example, FSR) and liquid permeability (for example, SFC) of the water absorbent resin can be improved, and the fluidity at the time of moisture absorption can also be improved.

  Specifically, the compounds described in “[7] polyvalent metal salts and / or cationic polymers” of WO 2011/040530 and the amounts used thereof are applied to the present invention.

(Chelating agent)
In this invention, it is preferable to add a chelating agent from a viewpoint of the physical property of the water-absorbing resin obtained. By adding the compound, deterioration or deterioration of the color tone of the water-absorbent resin can be suppressed or prevented.

  Specifically, the compounds described in “[2] chelating agents” of WO 2011/040530 and the amounts used thereof are applied to the present invention.

(Inorganic reducing agent)
In this invention, it is preferable to add an inorganic reducing agent from a viewpoint of the physical property of the water absorbent resin obtained. By adding the compound, it is possible to suppress or prevent the color tone deterioration and deterioration of the water-absorbent resin, and further reduce the residual monomer.

  Specifically, the compounds described in “[3] Inorganic reducing agent” of International Publication No. 2011/040530 and the amounts 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 physical properties of the resulting water-absorbent resin. By adding the compound, deterioration of the color tone of the water-absorbent resin can be suppressed or prevented.

  Specifically, the compounds described in “[6] α-hydroxycarboxylic acid compound” of WO 2011/040530 and the amount of use thereof are applied to the present invention.

  The “α-hydroxycarboxylic acid compound” refers to a carboxylic acid having a hydroxyl group in the molecule or a salt thereof, and is a compound having a hydroxyl group at the α-position.

(2-8) Addition process of other additives This process is a process of adding additives other than the above-described additives, and is an arbitrary process installed to impart various functions to the water absorbent resin. It is a process. Such additives include surfactants, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders such as metal soaps, deodorants, antibacterial agents, compounds having phosphorus atoms, pulp and thermoplastic fibers. Can be mentioned.

  As the surfactant, specifically, a surfactant described in International Publication No. 2005/077500 is preferably applied.

  Further, the surfactant may be added to the aqueous monomer solution as described in (2-1) above, or may be added to the water-absorbing resin after surface crosslinking.

  The amount of the additive used is not particularly limited as long as it is appropriately set depending on the application, but is preferably 5% by weight or less, more preferably 3% by weight or less, and further preferably 1% by weight or less (the lower limit is 0% by weight). %).

(2-9) Other steps In addition to the steps described above, a granulation step, a sizing step, a fine powder removal step, a fine powder reuse step, and the like can be provided as necessary.

  The above sizing process includes a fine powder removing process after the surface cross-linking process and a pulverizing process and a classifying process performed when the water-absorbing resin aggregates and exceeds a desired size. The fine powder reuse step includes a step of adding the fine powder as it is or making it into a large hydrogel in the granulation step and adding it to any of the production steps of the water absorbent resin.

(2-10) Transportation process Between each process mentioned above, it is connected with various feeders, such as a screw feeder, a bucket conveyor, a flight conveyor, a belt conveyor, and pneumatic transportation, and intermediate storage is carried out between each process as needed. Is done. As a whole manufacturing process of the water-absorbent resin, each process is basically connected, and the manufacturing and filling are preferably performed in a closed system.

(2-11) Filling step This step is a step in which a water-absorbing resin as a final product manufactured through at least a part of the above-described steps is filled into a filling container such as a container bag or a paper bag. The water-absorbent resin filled in the filling container is shipped after undergoing a predetermined inspection.

  In addition, before filling the water-absorbent resin of the final product into the filling container, it is stored in a storage tank for a predetermined time, and then is filled according to the shipment form (for example, bag, box, bottle, silo, etc.) The physical properties of the water-absorbent resin after filling can be improved and stabilized. What is necessary is just to set suitably as a filling unit according to a shipment form, Preferably it is 100g-100t, More preferably, it is 10kg-10t.

[3] Manufacturing process requiring temperature adjustment The manufacturing process requiring temperature adjustment in the present invention is at least one selected from a monomer aqueous solution preparation step, a polymerization step, and a cooling step after surface crosslinking. It is preferable. Moreover, a rehumidification process etc. are mentioned other than the above. The monomer aqueous solution adjustment step includes cooling of the monomer aqueous solution after the neutralization reaction.

(Temperature adjustment equipment)
The temperature adjusting device used in each of the manufacturing processes is not particularly limited as long as it can stably control the temperature for a long period of time, and an appropriate device is selected according to the application. Specifically, a double-tube heat exchanger or a multi-tube heat exchanger is used for cooling the aqueous monomer solution after the neutralization reaction. In addition, a polymerization reactor with a jacket (kneader, etc.) is used in the polymerization process, and a mixing apparatus with a jacket, such as a screw mixer, a disk mixer, a vertical mixer, a paddle mixer, etc., is used in the surface crosslinking process or rehumidification process. Is done.

  In the present invention, the temperature of the water absorbent resin or its raw material is preferably adjusted to 0 to 100 ° C, more preferably 30 to 95 ° C, and still more preferably 40 to 90 ° C. By controlling the temperature within the temperature range, the physical properties become more stable.

The temperature control device, as the ratio cooling output, preferably more than 0 10 W / cm ² or less, more preferably 0.01~5W / cm ^2, more preferably you have a 0.1~2W / cm ² That's fine. When the specific cooling output exceeds 10 W / cm ² , not only is it disadvantageous in terms of energy, but also when used for cooling a monomer aqueous solution by supercooling, a monomer salt may be precipitated. Yes, not preferred.

(Dirts adhering to the heat transfer surface of the temperature control device)
Dirt adhering to the heat transfer surface of the temperature control device is classified into scaling, fine particle dirt, chemical reaction dirt, corrosive dirt, biological dirt, and frozen dirt.

  The “scaling” refers to, for example, in the case of water, a crystal in which calcium carbonate, calcium sulfate, calcium hydroxide, magnesium hydroxide, and sodium sulfate are attached.

  “Particulate contamination” refers to a deposit of fine particles floating in a fluid deposited on a heat transfer surface.

  “Chemical reaction soil” refers to a precipitate formed by a chemical reaction of a substance.

  “Corrosion dirt” refers to the heat transfer surface itself becoming dirty due to a corrosion reaction with the fluid.

  “Biological stains” refers to those to which solid organisms such as shellfish have adhered, and those to which mud substances called slime composed of bacteria, organic matter and inorganic matter have adhered.

  “Frozen soil” refers to a fluid that freezes and adheres to a cold heat transfer surface.

(Heat exchange fluid)
In the present invention, water having a specific fouling coefficient is used as the heat exchange fluid of the temperature control device. The “fouling coefficient” represents the magnitude of thermal resistance derived from dirt adhered to the heat transfer surface of the temperature control device in the overall heat transfer coefficient. The value varies depending on the type and temperature of the fluid, and is representative. The fluid value is empirically determined. Therefore, even if the fluid having a smaller contamination coefficient adheres as contamination to the heat transfer surface of the temperature adjustment device, it is possible to suppress a decrease in the heat transfer performance of the temperature adjustment device.

When the fluid temperature is less than 50 ° C., the soil coefficient is 0.0004 m ² · K / W or less, preferably 0.0002 m ² · K / W or less, more preferably 0.0001 m ² · K / W. It is as follows. Further, when the fluid temperature is 50 ° C. or higher, it is 0.0006 m ² · K / W or lower, preferably 0.0004 m ² · K / W or lower, more preferably 0.0002 m ² · K / W or lower, Preferably it is 0.0001 m ² · K / W or less. If the contamination coefficient exceeds the upper limit value for each of the fluid temperatures described above, it is not preferable because when the contamination is attached to the heat transfer surface of the temperature adjusting device, the heat transfer performance is greatly deteriorated.

  In particular, from the viewpoint of preventing scaling, in the present invention, water having a polyvalent metal ion content of 200 ppm or less is used as the heat exchange fluid of the temperature adjusting device. The content of the polyvalent metal ions is preferably 150 ppm or less, and in order, 100 ppm or less, 50 ppm or less, 20 ppm or less, 10 ppm or less, 5 ppm or less, 1 ppm or less, 0.5 ppm or less, and most preferably 0.1 ppm or less. It is. The lower limit is 0 ppm, but may be 0.01 ppm.

  When the content of the polyvalent metal ion exceeds 200 ppm, polyvalent metal salt crystals adhere to the surface of the heat transfer surface of the temperature control device, causing a decrease in heat transfer performance or blocking the flow of the heat exchange fluid. It is not preferable because a problem such as stopping can occur.

  The water with a low content of the polyvalent metal ions (for example, 100 ppm or less) is not particularly limited. For example, ion exchange water, distilled water, natural water (however, low hardness water), river water , Groundwater, rainwater, etc. Furthermore, industrially generated condensed water, such as a water-absorbing resin manufacturing process, also falls under this category.

  In the present invention, the polyvalent metal ion is not particularly limited, but from the viewpoint of the effect of the present invention, it is preferably a metal ion of Group 2 element of the periodic table, more preferably magnesium ion or calcium ion, and still more preferably calcium. Ion.

  In the present invention, a scale inhibitor can also be used. Although it does not specifically limit as the said scale inhibitor, For example, water-soluble polyacrylic acid (salt), phosphonic acid ester, benzotriazole, etc. are mentioned.

  The amount of the scale inhibitor used may be appropriately set according to the content of the polyvalent metal ion, the water temperature, the circulation amount, etc., and is not particularly limited, but is preferably 0 to 100 mg / L, more preferably 1 to 80 mg / L, more preferably 5-50 mg / L.

  In particular, from the viewpoint of preventing biological contamination, in the present invention, it is preferable to use disinfected water as the heat exchange fluid of the temperature adjusting device. The “disinfected water” is treated with a substance having a bactericidal action such as liquefied chlorine, sodium hypochlorite, calcium hypochlorite, chloramine, chlorine dioxide, ozone, ultraviolet rays, so-called anti-slime agent. It means water.

  In the present invention, water having a free residual chlorine content of preferably 0.1 mg / L or more, more preferably 0.3 to 5 mg / L, still more preferably 0.5 to 1 mg / L is used. Is preferred. When the content of the free residual chlorine is less than 0.1 mg / L, the effect of preventing biofouling is insufficient. On the other hand, when it exceeds 5 mg / L, the odor becomes stronger and the effect commensurate with the cost is obtained. Since it is not, it is not preferable.

  In order to obtain water having a free residual chlorine content of 0.1 mg / L or more, from the viewpoint of handleability and effects, the substance having a bactericidal action is preferably liquefied chlorine, sodium hypochlorite, hypochlorous acid. Calcium chlorate and chlorine dioxide, more preferably liquefied chlorine and sodium hypochlorite may be used.

(Production volume)
The method for producing a polyacrylic acid (salt) water-absorbing resin according to the present invention is suitable for long-term continuous operation on a large scale, and the production amount is preferably 1 t / hr or more, more preferably 2 t / hr per line. hr is preferable, and the continuous operation is preferably 10 days or more, more preferably 1 month or more as the number of working days. In the present invention, “continuous operation” refers to substantial continuous operation including switching of product numbers (change of physical properties), and even when temporarily stopped, it is within the category of continuous operation.

[4] Physical properties of polyacrylic acid (salt) water-absorbing resin and use thereof The polyacrylic acid (salt) water-absorbing resin obtained by the production method according to the present invention preferably satisfies the following physical properties.

  That is, the CRC (centrifuge retention capacity) is preferably 10 to 100 g / g, more preferably 20 to 50 g / g, still more preferably 25 to 40 g / g, and particularly preferably 27 to 36 g / g. (Water absorption capacity under pressure) is preferably 15 to 40 g / g, more preferably 20 to 35 g / g, and still more preferably 25 to 35 g / g.

Moreover, as SFC (saline flow-inductivity), Preferably it is 1 * 10 < ^-7 > * cm < ³ > * s * g- ¹ or more, More preferably, it is 10 * 10 < ^-7 > * cm < ³ > * s * g- ¹ or more. Yes, the FSR (water absorption rate) is preferably 0.1 to 2.0 g / g / s, more preferably 0.2 to 1.0 g / g / s.

  When the water-absorbent resin is used in sanitary goods, particularly paper diapers, at least one or more of the physical properties described above, preferably two or more including AAP (water absorption under pressure), more preferably AAP (water absorption under pressure). 3) or more, more preferably all four physical properties, including

  The polyacrylic acid (salt) -based water-absorbing resin obtained by the production method according to the present invention can be used as an absorbent article for absorbent articles, particularly sanitary articles such as paper diapers, sanitary napkins, and incontinence pads. preferable. At that time, it is combined with hydrophilic fibers and formed into a sheet or the like. In addition, when hydrophilic fiber is not used, an absorptive article is obtained by immobilizing the water-absorbent resin on paper, nonwoven fabric, or the like.

  The present invention will be described in more detail with reference to the following examples, but 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. It is intended to be included within the scope of the present invention.

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

  For convenience, “liter” may be described as “l” or “L”, and “wt%” may be described as “wt%”. Further, in the case of measuring a trace component, N.sub. Described as D (Non Detected).

[Measurement of physical properties of water-absorbing resin]
(A) CRC (centrifuge retention capacity)
The CRC (centrifuge retention capacity) of the water-absorbent resin 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-absorbent resin of the present invention was measured according to the EDANA method (ERT442.2-02). The load condition was changed to 4.83 kPa (0.7 psi).

(C) SFC (saline flow conductivity)
The SFC (saline flow conductivity) of the water-absorbent resin of the present invention was measured according to the measurement method disclosed in US Pat. No. 5,669,894.

(D) Weight average particle diameter (D50)
The weight average particle diameter (D50) of the water-absorbent resin of the present invention was measured in accordance with the measurement method disclosed in US Patent Application Publication No. 2006/204755.

(E) FSR (Water absorption rate)
The FSR (water absorption rate) of the water-absorbent resin of the present invention was measured according to the measurement method disclosed in International Publication No. 2009/016055.

[Production Example 1]
As a continuous production equipment for polyacrylic acid (salt) water-absorbing resin, preparation process of monomer aqueous solution, polymerization process, gel grinding process, drying process, grinding process, classification process, surface cross-linking process (mixing process, heat treatment process) , A cooling step), and a production apparatus including a sizing step.

  In the continuous manufacturing apparatus, the steps are configured in this order, and the steps are connected by a transport step. A water absorbent resin was continuously produced at 2000 kg / hr using the continuous production apparatus.

  First, 35.2 parts by weight of acrylic acid as an aqueous monomer solution (1), 11.7 parts by weight of a 48% by weight aqueous sodium hydroxide solution, polyethylene glycol diacrylate as an internal crosslinking agent (average number of ethylene oxide units: n = 9) 0.23 parts by weight, 0.22 parts by weight of a 1% by weight diethylenetriaminepentaacetic acid trisodium (abbreviation: DTPA · 3Na) aqueous solution as a chelating agent, and 33.6 parts by weight of deionized water were mixed. In addition, the temperature of monomer aqueous solution (1) rose to 50 degreeC.

  Next, the monomer aqueous solution (1) was passed through a heat exchanger to adjust the temperature to 40 ° C., and then continuously supplied (delivered) 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 ppm or less. Thereafter, 17.7 parts by weight of a 48% by weight sodium hydroxide aqueous solution was continuously mixed (line mixing), and then 1.38 parts by weight of a 4% by weight sodium persulfate aqueous solution was continuously added as a polymerization initiator. Mixed (line mixing). In addition, monomer aqueous solution (1) after mixing the said sodium hydroxide aqueous solution rose to 86 degreeC with the heat of neutralization.

  The polymerization apparatus is a flat steel belt polymerization apparatus having weirs at both ends, and aqueous solution polymerization was continuously performed using the polymerization apparatus. The liquid supplied to the polymerization apparatus had a thickness of about 7.5 mm on a flat steel belt, and the polymerization time for the polymerization was 3 minutes. By this operation, a band-shaped hydrogel crosslinked polymer (hydrogel) (1) was obtained.

  Next, the band-like hydrogel (1) is cut at equal intervals in the direction perpendicular to the traveling direction of the flat steel belt, and then continuously supplied to a meat chopper having a hole diameter of 22 mm. The gel was pulverized into 5 mm particles. By the operation, a particulate hydrous gel (1) was obtained.

  Subsequently, the particulate hydrogel (1) was loaded on the perforated plate of the ventilation band type continuous dryer so as to have a thickness of 50 mm, dried by aeration with hot air at a temperature of 185 ° C. for 30 minutes. A polymer (1) was obtained.

  The obtained dried polymer (1) is pulverized with a roll mill, and then sieved with a sieving device having a metal sieve mesh having openings of 710 μm and 175 μm, whereby a water absorbent resin powder having a particle diameter of 175 μm or more and less than 710 μm ( 1) was obtained.

  Next, surface cross-linking comprising 0.3 parts by weight of 1,4-butanediol, 0.6 parts by weight of propylene glycol, and 3.0 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin powder (1). Agent solution (1) was prepared.

  Thereafter, the water absorbent resin powder (1) was continuously supplied to a high-speed mixer (turbulator / 1000 rpm) at 2000 (kg / hr). In that case, the said surface crosslinking agent solution (1) was sprayed using the spray, and was mixed uniformly. Thereafter, the mixture was transferred to a paddle dryer and heat-treated at 208 ° C. for 40 minutes.

  After the above heat treatment, the paddle dryer of the same type as the paddle dryer used in the heat treatment step was used to forcibly cool the surface-crosslinked water absorbent resin powder (1) until the temperature reached 60 ° C. .

  During the cooling, 1.66 parts by weight of a 30% by weight aqueous sodium hydrogen sulfite solution is sprayed with 100 parts by weight of the surface-crosslinked water-absorbing resin powder (1) using a spray, and mixed uniformly. did.

  Then, the water-absorbent resin (A) was obtained by passing through a JIS standard sieve having an aperture of 710 μm.

The physical properties of the water absorbent resin (A) obtained by the above series of operations were as follows. That is, weight average particle diameter (D50); 375 μm, CRC; 27.0 g / g, AAP (4.83 kPa); 24.5 g / g, SFC; 76 × 10 ⁻⁷ · cm ³ · s · g ⁻¹ , FSR: 0.23 g / g / s.

[Example 1]
As a heat exchanger for adjusting the temperature of the monomer aqueous solution (1) before supplying (liquid feeding) to the polymerization apparatus in the preparation step of the monomer aqueous solution of Production Example 1, an effective heat transfer area is 80 m ² , And the vertical multi-tube heat exchanger whose cooling output is 480 kW (specific cooling output; equivalent to 0.6 W / cm < ² >) was used. Further, as a heat exchange fluid of the heat exchanger, water having a calcium ion content of 0.1 ppm (dirt coefficient: 0.0001 m ² · K / W, free residual chlorine content: 0.6 mg / L, temperature: 35 ° C) was used. Using the heat exchanger and the heat exchange fluid, the temperature of the monomer aqueous solution (1) was controlled to be 40 ° C.

  Although the above operation was continuously performed for 6 months, the temperature of the monomer aqueous solution (1) could be kept at 40 ° C. without any particular trouble.

[Comparative Example 1]
In Example 1, water having a calcium ion content of 300 ppm as a heat exchange fluid of a heat exchanger (stain coefficient: 0.00053 m ² · K / W, free residual chlorine content: 0 mg / L, temperature: 35 ° C.) The same operation as Example 1 was performed except having changed into.

  After 4 months from the start of continuous operation, the temperature of the comparative monomer aqueous solution (1) became unstable, and began to point to 40 to 50 ° C. Further, at the fifth month, the temperature of the comparative monomer aqueous solution (1) decreased only to 45 ° C., and became more unstable.

  Therefore, in order to adjust to the original set temperature, the temperature of the heat exchange fluid was further lowered to 30 ° C. When the operation was stopped and the equipment was washed, water-insoluble salts and algae were detected from the collected wastewater.

[Production Example 2]
A jacketed kneader reactor equipped with two sigma blades, a mixed solution consisting of acrylic acid, sodium acrylate and water (monomer concentration 38 wt%, neutralization rate 75 mol%), and internal cross-linking agent Polyethylene glycol diacrylate (average n number: 9) was added as 0.045 mol% (mole number of all monomers) to prepare an aqueous monomer solution (2).

  Next, nitrogen gas was blown into the monomer aqueous solution (2) to reduce dissolved oxygen in the monomer aqueous solution (2), and the entire reactor was purged with nitrogen.

  Subsequently, while adjusting the temperature of the aqueous monomer solution (2) to 22 ° C. while rotating two sigma blades, 0.12 g / mol of sodium persulfate (as a monomer) as a polymerization initiator, L-ascorbic acid was added so that it might become 0.005 g / mol (vs. monomer).

  The polymerization started immediately and the aqueous monomer solution became cloudy, so the rotation of the blade was stopped. After the polymerization temperature reached 50 ° C., the blade was rotated again, and the polymerization was continued with stirring in the kneader. After 50 minutes, a hydrogel crosslinked polymer (hydrogel) (2) having a weight average particle diameter of 2 mm was obtained. It was.

  The water-containing resin powder (2) was obtained by continuously processing the obtained hydrogel (2) in the same drying, pulverization and classification steps as in Production Example 1.

  Next, 0.025 part by weight of ethylene glycol diglycidyl ether, 0.3 part by weight of 1,4-butanediol, 0.5 part by weight of propylene glycol, 100 parts by weight of the water absorbent resin powder (2) A surface crosslinking agent solution (2) comprising 3.0 parts by weight of ionic water was prepared.

  Thereafter, the water-absorbent resin powder (2) was continuously supplied to a high-speed mixer (turbulator / 1000 rpm) at 2000 kg / hr. In that case, the said surface crosslinking agent solution (2) was sprayed using the spray, and was mixed uniformly. Thereafter, the mixture was transferred to a paddle dryer and heat-treated at 208 ° C. for 40 minutes.

  After the above heat treatment, the paddle dryer of the same type as the paddle dryer used in the heat treatment step was used to forcibly cool the surface-crosslinked water absorbent resin powder (2) until the temperature reached 60 ° C. .

  During the cooling, 0.44 parts by weight of a 45% by weight aqueous solution of diethylenetriaminepentaacetic acid 5 sodium salt is sprayed on 100 parts by weight of the surface-crosslinked water-absorbent resin powder (2) using a spray, and uniformly Mixed.

  Then, using a sieving device having a JIS standard sieve having a mesh size of 710 μm, the surface-treated water-absorbent resin powder (2) is crushed until it passes through, and 100 parts by weight of the water-absorbent resin powder (2) The water-absorbent resin (B) was obtained by adding and mixing 0.3 parts by weight of silica (trade name: Aerosil 200CF-5, manufactured by Nippon Aerosil Co., Ltd.).

  The physical properties of the water absorbent resin (B) obtained by the series of operations were as follows. That is, the weight average particle diameter (D50): 370 μm, CRC: 34.0 g / g, AAP (4.83 kPa): 18.0 g / g.

[Example 2]
In the polymerization step of Production Example 2 described above, in order to adjust the temperature of the aqueous monomer solution (2) before adding the polymerization initiator to 22 ° C., as a heat exchange fluid flowing through the jacket of the kneader reactor, Water having a content of 0.1 ppm (stain coefficient: 0.0001 m ² · K / W, free residual chlorine content: 0.6 mg / L, temperature: 20 ° C.) was used.

  Although the above operation was continuously performed for 6 months, the temperature of the monomer aqueous solution (2) could be maintained at 22 ° C. without any particular trouble. Furthermore, the physical properties of the water absorbent resin (2) obtained were also stable. Details are shown in Table 1.

[Comparative Example 2]
In Example 2, water having a calcium ion content of 300 ppm (stain coefficient: 0.00053 m ² · K / W, free residual chlorine content: 0 mg / L, temperature) as a heat exchange fluid that flows through the jacket of the kneader reactor The same operation as in Example 2 was performed except that the temperature was changed to 20 ° C.

  When 4 months passed from the start of continuous operation, the temperature of the comparative monomer aqueous solution (2) became unstable and came to indicate 20 to 30 ° C. Furthermore, at the 5th month, the temperature of the comparative monomer aqueous solution (2) decreased only to 27 ° C., and became more unstable. Therefore, the physical properties of the comparative water-absorbing resin (2) obtained were not stable and the variation was large. Details are shown in Table 1.

  Therefore, in order to adjust to the original set temperature, the temperature of the heat exchange fluid was further lowered to 15 ° C. When the operation was stopped and the equipment was washed, water-insoluble salts and algae were detected from the collected wastewater.

[Example 3]
In the cooling step after surface cross-linking in Production Example 2, the water-absorbent resin powder (2) after the heat treatment is cooled to 60 ° C., so that the content of calcium ions is 0 as the heat exchange fluid that flows through the jacket of the paddle dryer. 0.1 ppm of water (stain coefficient: 0.0001 m ² · K / W, free residual chlorine content: 0.6 mg / L, temperature: 50 ° C.) was used.

  Although the said operation was continuously operated for 6 months, there was no trouble in particular and the temperature of the water-absorbent resin powder (2) after the above heat treatment could be kept at 60 ° C. Furthermore, the physical properties of the water absorbent resin (3) obtained were also stable. Details are shown in Table 1.

[Comparative Example 3]
In Example 3, water having a calcium ion content of 300 ppm (stain coefficient: 0.00053 m ² · K / W, free residual chlorine content: 0 mg / L, temperature 50 ° C.) as a heat exchange fluid that flows through the jacket of the paddle dryer ) The same operation as in Example 3 was performed except that the change was made.

  When 4 months passed from the start of the continuous operation, the temperature of the comparative water absorbent resin powder (2) after the heat treatment became unstable and became 60 to 80 ° C. Further, at the fifth month, the temperature of the comparative water absorbent resin powder (2) decreased only to 70 ° C., and became more unstable. For this reason, the properties of the comparative water-absorbing resin (3) obtained were not stable, and the variation was large. Details are shown in Table 1.

  Therefore, in order to adjust to the original set temperature, the temperature of the heat exchange fluid was further lowered to 40 ° C. When the operation was stopped and the equipment was washed, water-insoluble salts and algae were detected from the collected wastewater.

(Summary)
As shown in Table 1, by using water with a calcium ion content of 0.1 ppm (fouling coefficient; 0.0001 m ² · K / W) as the heat exchange fluid of the temperature control device, It was confirmed that the physical properties of the water-absorbent resin (CRC, AAP 4.83 kPa) were stable.

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

Claims (9)

Separately from the drying step after polymerization and the heat treatment step after drying, there is provided a method for producing a polyacrylic acid (salt) water-absorbing resin including a production step that requires temperature adjustment of the water-absorbing resin or its raw material. ,
As a heat exchange fluid for the device for adjusting the temperature, the contamination coefficient at less than 50 ° C. is 0.0004 m ² · K / W or less, and the contamination coefficient at 50 ° C. or more is 0.0006 m ² · K / W. The manufacturing method of the polyacrylic acid (salt) type water absorbing resin in which the following water is used. Separately from the drying step after polymerization and the heat treatment step after drying, there is provided a method for producing a polyacrylic acid (salt) water-absorbing resin including a production step that requires temperature adjustment of the water-absorbing resin or its raw material. ,
A method for producing a polyacrylic acid (salt) water-absorbing resin, wherein water having a polyvalent metal ion content of 200 ppm or less is used as a heat exchange fluid for a device for adjusting the temperature.   The manufacturing method of Claim 1 or 2 whose content of the polyvalent metal ion contained in the water used as the said heat exchange fluid is 100 ppm or less.   The manufacturing method of any one of Claims 1-3 with which the temperature of the said water absorbing resin or its raw material is adjusted to 0-100 degreeC.   The manufacturing process that requires the temperature adjustment is at least one or more selected from a monomer aqueous solution adjustment process, a polymerization process, and a cooling process after surface crosslinking. Manufacturing method.   The manufacturing method according to any one of claims 2 to 5, wherein the polyvalent metal ion is a metal ion of a Group 2 element in the periodic table.   The production method according to any one of claims 1 to 6, wherein water used as the heat exchanger has been sterilized.   The manufacturing method of any one of Claims 1-7 whose content of the free residual chlorine contained in the water used as the said heat exchanger is 0.1 mg / L or more. The manufacturing method of any one of Claims 1-8 whose specific cooling output of the apparatus which performs the said temperature adjustment exceeds 0 and is 10 W / cm < ² > or less.