JP2004300425A - Process for surface crosslinking treatment of water-absorbing resin powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for surface crosslinking treatment of a water-absorbing resin powder having excellent material properties which process solves various manufacturing problems in manufacturing a surface crosslinked water-absorbing resin powder in an industrial scale and does not cause degradation on properties of the resin. <P>SOLUTION: (1) In this process for surface crosslinking treatment of a water-absorbing resin powder, in which process the surface crosslinking treatment is carried out by adding a surface crosslinking agent to the water-absorbing resin powder and heat-treating it, the heat-treated water-absorbing resin powder is subjected to stirring and cooling treatment under gas flow. (2) While the heat-treated water-absorbing resin powder is subjected to cooling treatment under gas flow, at least a part of the fine powder of the water-absorbing resin powder and at least a part of the residual surface crosslinking agent are removed by the gas flow. (3) While the heat-crosslink-treated water-absorbing resin powder is subjected to cooling treatment, granulation is simultaneously carried out. Preferably, an aqueous liquid is further added to the water-absorbing resin powder at 40-100 °C after the heat-crosslink-treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for surface-crosslinking a water-absorbent resin powder.

  In recent years, for the purpose of absorbing a large amount of water, a water-absorbing resin has been widely used as one of materials constituting sanitary materials such as disposable diapers, sanitary napkins, incontinence pads, and the like. In addition to hygienic materials, water-absorbing resins are widely used for the purpose of absorbing and retaining water, such as soil water retention agents and drip sheets for foods and the like. Examples of the water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile copolymer, a neutralized product of a starch-acrylic acid graft polymer, and a vinyl acetate-acrylic ester. Saponified polymer, hydrolyzed acrylonitrile copolymer or acrylamide copolymer or crosslinked product thereof, crosslinked carboxymethylcellulose, copolymerized crosslinked product of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), polyethylene Crosslinked oxides, crosslinked polyallylamine, crosslinked polyethyleneimine, and the like are known, and many of them are used in powder form.

  As a method for producing these water-absorbent resin powders, a method mainly obtained by drying a hydrogel cross-linked polymer obtained by polymerizing an aqueous solution of a monomer containing a cross-linking agent and, if necessary, further pulverizing the polymer is mainstream. However, the hydrogel crosslinked polymer of the water-absorbent resin is extremely difficult to dry or pulverize in a high-temperature state immediately after drying due to its high water-absorbing ability, tackiness and adhesion, and low heat resistance. Since the properties and energy efficiency of the obtained water-absorbent resin are very low, the methods for producing the water-absorbent resin powder have been studied from various points as in Patent Documents 1 and 2. .

The water-absorbent resin is given a function of water-insoluble water swelling by slightly cross-linking the hydrophilic polymer (usually cross-linking during polymerization), and is usually produced as a powder. However, in recent years, higher functionality has been demanded. In addition to cross-linking inside the powder, cross-linking density gradient is given to the inside and the surface by performing surface cross-linking (secondary cross-linking) on the powder after further polymerization, so that Thus, the water absorption rate, liquid permeability, and absorption capacity under pressure have been improved.
For example, in Patent Literatures 1 and 2, polymerization of a monomer, drying by heating, cooling, and addition to a water-absorbent resin powder obtained through a process such as pulverization, an aqueous liquid containing a surface crosslinking agent and the like are further added, and heating is performed. It is described that the surface is crosslinked by drying.

  Patent Documents 1 and 2 describe a method for producing a water-absorbent resin powder and mention surface cross-linking of the water-absorbent resin powder, but do not pay attention to cooling treatment after heat treatment for surface cross-linking. .

  In some cases, cooling may be performed after the heat treatment for surface cross-linking, if necessary. As cooling means in that case, general methods include fluidized beds and low-temperature screws as described in Patent Documents 3 to 6. It was cooling by a conveyor.

On the other hand, with respect to the addition of the aqueous solution after the heat treatment, Patent Documents 7 and 8 disclose that an aqueous solution of the additive is added to the aqueous fluid-absorbing polymer after the heat treatment and then re-humidified, thereby accumulating static electricity and generating dust. To prevent aggregation of polymer particles. Patent Documents 9 and 10 also describe the addition of water after heat treatment in the production of a hydrogel-forming polymer.
Further, Patent Documents 11 to 13 describe that fine powder is granulated by adding an aqueous liquid. The addition of the aqueous liquid to the water-absorbent resin generally involved not heat absorption but heat generation (self-heating) due to heat of hydration of the water-absorbent resin and water.

  In addition, the techniques disclosed therein include surface crosslinking at a laboratory level and surface crosslinking in a batch system, and in a small-scale production of at most several tens of kg / hour, a water-absorbent resin having high physical properties due to surface crosslinking is used. Even if it was obtained, it was found that when it was manufactured on an industrial scale, the improvement of the physical properties by surface cross-linking was not sufficiently exhibited.

The present inventors, in such a conventional surface cross-linking process, as a result of exploring the cause of physical property deterioration on an industrial scale, as a cause, the condensation of water generated along with the progress of the surface cross-linking reaction, the resulting resin particles The inventors found a problem of production trouble and deterioration of resin physical properties due to agglomeration, and studied to solve such problems as mixing of resin fine powder and dust generation in this process.
In addition, in order to make the water-absorbent resin powder obtained after the surface cross-linking step finally usable, a granulation step may be required, and this step was also studied.

JP-A-2002-121291 US Pat. No. 6,576,713 Japanese Patent Publication No. Hei 8-508517 U.S. Pat. No. 5,610,220 Japanese Patent Publication No. 9-502221 U.S. Pat. No. 5,672,633 JP 2001-523287 A U.S. Pat. No. 6,323,252 International Publication No. 01/25290 pamphlet U.S. Pat. No. 6,414,214 U.S. Pat. No. 4,734,478 Japanese Patent Publication No. 7-62073 U.S. Pat. No. 5,369,148

The present invention solves various manufacturing problems, such as the inability to reproduce the physical properties of a small scale, in the production of a surface-crosslinked water-absorbent resin powder on an industrial scale, and does not cause deterioration of the resin physical properties. It is intended to provide a method for surface crosslinking treatment of a water-absorbent resin powder having the same.
More specifically, the method of performing surface cross-linking treatment of a water-absorbent resin powder in the production of a water-absorbent resin powder, which can be applied to an industrial scale, controls the reaction of a surface cross-linking agent, and has found the present inventors. The problem is that a method of surface cross-linking of a water-absorbent resin powder that prevents condensation of moisture generated by a surface cross-linking reaction and the like, thereby preventing aggregation of resin particles, stabilizing production, and preventing deterioration of resin properties. provide.
Furthermore, in the method of performing surface cross-linking treatment of the water-absorbent resin powder in the production of the water-absorbent resin powder which can be applied even on an industrial scale, the surface cross-linking treatment of the water-absorbent resin powder in which the fine resin powder is reduced and dust generation is prevented. Provide a way.

The above object is achieved by performing a specific cooling treatment in the surface crosslinking treatment. That is, in a method in which a surface cross-linking agent is added to a water-absorbent resin powder and heat-treated to perform a surface cross-linking treatment, the water-absorbent resin powder after the heat treatment is agitated and cooled in an air stream to obtain a first water-absorbing property. Surface cross-linking treatment method for resin powder,
A second water-absorbent resin powder characterized in that the water-absorbent resin powder after the heat treatment is cooled under an airflow, and at the same time, at least a part of the fine particles of the water-absorbent resin powder and the remaining surface crosslinking agent are removed by the airflow. Surface cross-linking treatment method, and
In a method in which a surface cross-linking agent is added to a water-absorbent resin powder and subjected to a heat treatment to perform a surface cross-linking treatment, the water-absorbent resin powder after the heat cross-linking treatment is granulated simultaneously with the cooling treatment, Achieved by a third method for surface crosslinking of a water-absorbent resin powder, wherein an aqueous liquid is added to the water-absorbent resin powder having a temperature of 40 to 100 ° C. Was done.

  In the surface cross-linking treatment of the water-absorbent resin powder in the production of the water-absorbent resin powder, a specific cooling treatment is indispensable to control the reaction of the surface cross-linking agent, resulting from the surface cross-linking reaction, etc. It is possible to prevent condensation of water resulting from water evaporation and thereby agglomeration of resin particles, to stabilize production, and to obtain a good surface-crosslinked water-absorbent resin powder without deterioration in physical properties of the resin. Can reduce the amount of resin fine powder and prevent dust generation, and obtain a surface-crosslinked water-absorbent resin powder in a good form.

Hereinafter, the present invention will be described in detail.
Laboratory-level surface crosslinking and batch-type surface crosslinking as shown in the prior art, and production on a small scale of at most several tens of kilograms / hour can provide high-performance water-absorbent resins by surface crosslinking. In the case of manufacturing on an industrial scale, the inventors of the present invention intensively pursued the cause that the physical property improvement by surface cross-linking is not sufficiently exhibited, and as a result, the cause is the uniformity of addition of the surface cross-linking agent and the reaction (heat treatment). Focusing on the cooling step which was optional in the past, rather than the surface cross-linking itself, and found that the presence or absence of the cooling step after the surface cross-linking and the method greatly contributed to the deterioration of the physical properties. The present invention has been completed with the above-described configuration, which has been improved by making an arbitrary cooling process which has not been conventionally performed indispensable.

  The surface cross-linking treatment of the water-absorbent resin powder of the present invention is such that the water-absorbent resin powder and the surface cross-linking agent are mixed at a predetermined ratio by a stirrer and mixed, and subjected to heat treatment by a heat treatment machine and cooling treatment by a cooler. Thus, a surface-crosslinked water-absorbent resin powder is obtained. That is, in the present invention, a specific cooling treatment is carried out with respect to a cooling treatment which may be performed as necessary in the conventional surface cross-linking treatment to obtain an excellent water-absorbent resin powder.

(Water absorbent resin powder)
The water-absorbent resin powder to be subjected to the surface crosslinking treatment in the present invention is not particularly limited, and is a known water-absorbent resin powder. For example, in ion-exchanged water, under no pressure, at least 5 times its own weight, Preferably, a crosslinked polymer that absorbs a large amount of water 50 to 1000 times and forms an anionic, nonionic or cationic water-insoluble hydrogel can be mentioned.
The water-absorbent resin powder generally contains, as a main component, a water-absorbent resin having a crosslinked structure obtained by polymerizing a water-soluble unsaturated monomer component (preferably an acid group, particularly an unsaturated monomer containing a carboxyl group). Resin powder, which is polymerized in the state of a monomer solution, dried if necessary, and usually pulverized before and / or after drying.
The water-absorbent resin is required to be water-swellable and water-insoluble, and therefore, the content of the water-soluble component (for example, an uncrosslinked water-soluble polymer) in the water-absorbent resin is preferably 50. It is at most 25 mass%, more preferably at most 25 mass%, still more preferably at most 20 mass%, still more preferably at most 15 mass%, particularly preferably at most 10 mass%. In addition, the measuring method of an absorption capacity and a water-soluble component is demonstrated in an Example.

Examples of the composition of the water-absorbent resin include, for example, polyacrylic acid partially neutralized polymer, starch-acrylonitrile graft polymer hydrolyzate, starch-acrylic acid graft polymer, and vinyl acetate-acrylate copolymer copolymer. One or two or more of a hydrolyzate, a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer, or a cross-linked product thereof, a carboxyl group-containing cross-linked polyvinyl alcohol modified product, a cross-linked isobutylene-maleic anhydride copolymer, or the like. be able to.
These water-absorbing resins may be used alone or as a mixture. Among them, an acid group-containing water-absorbing resin, and further, one or a mixture of a carboxylic acid or a carboxyl group-containing water-absorbing resin that is a salt thereof is preferable. , Typically a polymer obtained by polymerizing and cross-linking a monomer mainly containing acrylic acid and / or a salt thereof (neutralized product), that is, cross-linking a polyacrylic acid salt optionally containing a graft component It is mainly composed of a polymer.

In the polyacrylate crosslinked polymer, the total mol% of acrylic acid and / or a salt thereof essentially indicates 30 mol% or more and 100 mol% or less in all monomers, and is preferably 50 mol% in the present invention. Preferably at least 70 mol%, more preferably at least 90 mol%, particularly preferably substantially 100 mol% is used. The acrylate used is preferably a monovalent salt of acrylic acid comprising an alkali metal salt, an ammonium salt, or an amine salt, more preferably an alkali metal acrylate salt, more preferably a sodium salt, lithium An acrylate selected from salts and potassium salts is used. As the water absorbing resin, 20 to 99 mol%, preferably 50 to 95 mol%, more preferably 60 to 90 mol% of the acid groups of the polymer is neutralized. This neutralization may be performed on the monomer before polymerization or on the polymer during or after polymerization.
As described above, acrylic acid and / or its salt are used as the main component as described above, but other monomers may be used in combination. Monomers used in combination include methacrylic acid, (anhydride) maleic acid, fumaric acid, crotonic acid, itaconic acid, vinylsulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, (meth) acryloxy Alkanesulfonic acid and its alkali metal salt, ammonium salt, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2- Some copolymers include water-soluble or hydrophobic unsaturated monomers such as hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, isobutylene, and lauryl (meth) acrylate. included.

The crosslinking method used in the present invention is not particularly limited, but it is preferable to add a predetermined amount of an internal crosslinking agent to the unsaturated monomer in advance to carry out polymerization, and to carry out a crosslinking reaction simultaneously with or after the polymerization. Examples of the internal crosslinking agent used in such a method include N, N'-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and (polyoxyethylene) triacrylate. Methylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, polyethylene glycol di (β-acryloyloxypropionate), trimethylolpropane tri (β-acryloyloxypropionate), poly (meth) allyloxy One or more internal crosslinking agents such as alkanes, polyethylene glycol diglycidyl ether, ethylene glycol, polyethylene glycol, and glycerin are used. When one or more internal cross-linking agents are used, a compound having two or more polymerizable unsaturated groups must be used at the time of polymerization in consideration of the absorption characteristics of the resulting water-absorbent resin. preferable. The amount of the internal crosslinking agent to be used is preferably 0.005 to 2 mol%, more preferably 0.01 to 1 mol%, and still more preferably 0.05 to 0 mol% based on the monomer component. .2 mol%.

  The above-mentioned monomer is radically polymerized as an aqueous liquid, preferably as an aqueous solution, and its concentration is 15 to 80% by mass, more preferably 20 to 70% by mass, and further preferably 30 to 60% by mass. When polymerizing the above monomer aqueous solution, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride One or more polymerization initiators such as salts, 2-hydroxy-1-phenyl-propan-1-one and benzoin methyl ether can be used. Further, a reducing agent for promoting the decomposition of these polymerization initiators, ultraviolet light, or the like may be used in combination. Examples of the reducing agent include (bis) sulfite (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metals (salt) such as ferrous salt, and amines. Although not particularly limited, redox polymerization with persulfate and / or hydrogen peroxide is preferably applied. The amount of the polymerization initiator or the reducing agent to be used is generally 0.001 to 2 mol%, preferably 0.01 to 0.5 mol%, based on the monomer.

  As the polymerization method used in the present invention, aqueous solution polymerization or reversed phase suspension polymerization is applied. Aqueous solution polymerization is a polymerization method in which an aqueous monomer solution is polymerized as it is without suspending it. For example, US Pat. Nos. 4,985,514, 5,124,416, 5,250,640, Japanese Patent No. 2965639, WO 01/38402, U.S. Pat. Nos. 5,149,750, 4,769,427 and 4,873,299. Reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent in the form of particles having an average particle size of about 2 to 0.01 mm. For example, it is described in U.S. Pat. Nos. 4,093,776, 4,367,323, 4,446,261, 4,683,274 and 5,244,735.

  The gel-like crosslinked polymer obtained in the polymerization step (particularly, aqueous solution polymerization) is subdivided as necessary using a meat chopper or a gel pulverizer exemplified in Japanese Patent Application No. 2001-232734. More preferably, it is dried, and if necessary, crushed or classified. The drying temperature and method are not particularly limited, but may be, for example, in the range of 100 to 300C, more preferably in the range of 150 to 250C.

  When the water-absorbent resin is a powder, its mass average particle diameter is preferably from 100 to 1000 μm, more preferably from 200 to 600 μm, particularly from 300 to 500 μm from the viewpoint of physical properties, and further 850 μm or more of coarse particles and 150 μm or less. As the content of the fine powder is smaller, specifically, it is preferably 0 to 10% by mass or less, more preferably 5% by mass or less, and further preferably 1% by mass or less of all the particles. The resin solid content obtained from the loss on drying (1 g of powder is heated at 180 ° C. for 3 hours) is 80% by mass or more, preferably 85 to 99% by mass, more preferably 90 to 98% by mass, and particularly preferably 92 to 97% by mass. Adjusted to the% range. Further, the bulk specific gravity (as defined in US Pat. No. 6,562,879) is 0.5 to 0.9 g / ml, further 0.6 to 0.8 g / ml, and more preferably 0.65 to 0.75 g / ml. .

In the present invention, the production of the water-absorbent resin powder before the surface cross-linking treatment is performed is not particularly limited, and can be performed by a known method. For example, a method described in JP-A-2002-121291 (US Pat. No. 6,576,713) can be mentioned in addition to the aqueous solution polymerization and the reverse phase suspension polymerization. The following surface cross-linking treatment is not limited to once, and may be performed two or more times.

(Heat treatment step)
In the surface cross-linking method of the water-absorbent resin powder of the present invention, first, a heat treatment is performed on the water-absorbent resin powder by adding a surface cross-linking agent. The following surface cross-linking treatment is not limited to once, but may be performed twice or more.

The mixing of the water-absorbent resin powder and the surface cross-linking agent is generally performed by using a mixer in an amount of 0.001 to 10 parts by mass, preferably 0.01 to 5 parts by mass, based on 100 parts by mass of the water-absorbent resin powder. It is carried out at a ratio of parts by mass, more preferably 0.05 to 3 parts by mass.
The mixing may be carried out by dispersing the water-absorbent resin powder in an inert solvent, but preferably, the surface cross-linking agent or a solution or dispersion thereof is dropped or spray-mixed directly to the water-absorbent resin powder, preferably by spray-mixing. . A water spray device described later can be used for the spraying, and the size of the droplet when spraying is also described later.
The surface cross-linking agent is preferably added to a solvent to form a solution, particularly an aqueous solution, and then mixed with the water-absorbent resin powder.
The amount of the solvent at that time is usually in the range of 0.001 to 10 parts by mass, preferably 0.01 to 5 parts by mass, and more preferably 0.05 to 3 parts by mass with respect to 100 parts by mass of the water-absorbent resin powder. It is determined as appropriate.
Examples of the mixer include a high-speed paddle mixer, an air-flow mixer, a rotary disk mixer, a roll mixer, a cylindrical mixer, a screw mixer, a turbulizer, a Loedige mixer, a Nauta mixer, and a V mixer. , A ribbon-type mixer, a double-arm type kneader, a universal mixer, a flow-type mixer, or the like is used continuously or batchwise, preferably continuously. Preferably, the stirring blade is 50 rpm or more, and more preferably 100 to 10,000 rpm. A high-speed stirring mixer is applied.

  The heating temperature for the surface cross-linking depends on the type of the surface cross-linking agent, but is preferably a material temperature or a heating medium temperature, preferably the material temperature is 100 ° C. or higher, more preferably 110 to 230 ° C., and further preferably 160 ° C. To 220 ° C., and the heating time is appropriately determined, but is preferably in the range of 1 to 120 minutes, more preferably 5 to 60 minutes. The heater used for heating is preferably of a continuous type, and includes a groove type mixing dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, a gas stream dryer, an infrared dryer, a paddle dryer, and a vibrating fluidizer. A dryer and the like can be mentioned.

  In the present invention, after the heat treatment step, the crosslinking reaction is stopped by a cooling step described below.

In the present invention, a dehydration-reactive cross-linking agent is preferably used as a surface cross-linking agent that reacts with a functional group (for example, an acid group) of the water-absorbent resin powder. Here, the dehydration-reactive cross-linking agent is a dehydration reaction between a functional group (particularly, a functional group near the surface) of the water-absorbent resin and the cross-linking agent, preferably a dehydration esterification reaction and / or a dehydration amidation reaction, and more preferably. Is a crosslinking agent that causes a dehydration esterification reaction to crosslink.
Specifically, when the water-absorbent resin contains a carboxyl group, a hydroxyl group-containing cross-linking agent such as a polyhydric alcohol, an amino group-containing cross-linking agent such as a polyvalent amine, and further, an alkylene carbonate or mono, di, or Poly oxazolidinone compounds; cyclic cross-linking agents such as oxetane compounds such as 3-methyl-3-oxetane methanol, which form hydroxyl groups or amino groups with a ring-opening reaction of the cyclic cross-linking agent; A cyclic crosslinking agent in which a group undergoes a crosslinking reaction, and the like are exemplified as a crosslinking agent exhibiting dehydration reactivity. One or more dehydration-reactive cross-linking agents are used, and a non-dehydration-reactive cross-linking agent such as a polyvalent metal may be used in combination.

  The dehydration-reactive cross-linking agent that can be used in the present invention can be used without limitation as long as it is a cross-linking agent that performs a dehydration reaction with the functional group of the water-absorbing resin. Examples thereof include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, and tetraethylene glycol. Ethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, glycerin, diglycerin, polyglycerin, 2-butene-1,4 -Diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamido , Polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol, polyhydric alcohol compounds such as sorbitol; ethylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamidepolyamine, polyallylamine, polyethyleneimine, etc. Polyamine compounds, and condensates of these polyamines and haloepoxy compounds; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1 , 3-Dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan- 2-one, 1,3-dioxane-2-o And alkylene carbonate compounds such as 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one, and ethylene glycol Polyvalent alkylene carbonate compounds such as bis (4-methylene-1,3-dioxolan-2-one) ether; mono-, di- or polyoxazolidinone compounds; oxetane compounds such as 3-methyl-3-oxetanemethanol; and polyvalent oxetanes One or more selected from compounds; and the like.

Among these dehydration-reactive cross-linking agents, an ester-reactive cross-linking agent that cross-links with a carboxyl group in a water-absorbent resin by an ester reaction, as the one that maximizes the effect of the cooling treatment of the present invention, specifically, One or more selected from a polyhydric alcohol, an alkylene carbonate, an oxazolidinone compound, and a (poly) oxetane compound are preferable, and it is particularly preferable to use at least a polyhydric alcohol.
Examples of the surface cross-linking agent include, in addition to these dehydration-reactive cross-linking agents, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and polyethylene diglycidyl. Epoxy compounds such as ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol, and γ-glycidoxypropyltrimethoxysilane; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; Polyvalent oxazoline compounds such as 2-ethylenebisoxazoline; γ-glycidoxypropyltrimethoxysilane, γ-aminopro Silane coupling agents such as rutrimethoxysilane; polyvalent aziridine compounds such as 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate]; beryllium, magnesium, calcium, strontium, zinc, aluminum and iron , Chromium, manganese, titanium, zirconium, and other polyvalent metal salts or hydroxides.

The surface crosslinking treatment method of the present invention is particularly effective in surface crosslinking using an ester-reactive crosslinking agent. The ester-reactive cross-linking agent requires a high temperature for the dehydration esterification reaction, and since the ester reaction is hardly completed to 100%, it is necessary to use an excessive cross-linking agent. Certain cooling steps of the present invention are required to stop the high temperature dehydration esterification. In the absence of the cooling step of the present invention, the water-absorbent resin powder taken out from the reactor (heating device) for the surface cross-linking step keeps the high temperature and the dehydration esterification reaction is in progress. (E.g., 300 kg / hr or more), dehydration esterification proceeds halfway in the subsequent steps (transportation step, storage step, granulation step and additive step if necessary) as a cause of physical property deterioration, resulting in water absorption. It has been found that the physical properties of the conductive resin are deteriorated or fluctuated. Such a phenomenon is not seen in the cooling effect of the present invention in laboratory-level production or production in pilots and small-scale plants, but as a result of intensive studies to solve physical property deterioration in the process of scale-up, large-scale It was found to be found in production.

The surface cross-linking treatment method of the present invention is preferably applied when the cross-linking reaction is a dehydration esterification reaction, and is more preferably applied when the dehydration esterification reaction is not completed. That is, in the dehydration esterification, heat crosslinking is carried out when the crosslinking agent or a decomposition product thereof (a crosslinking agent such as polyhydric alcohol, alkylene carbonate, or oxazolidinone, or a polyhydric alcohol derived from alkylene carbonate decomposition or an alkanolamine derived from oxazolidinone decomposition) remains. It is preferable to terminate the process, perform cooling in the cooling process, and stop the crosslinking reaction.
When the dehydration esterification reaction is completed to 100%, it is not preferable because the reaction time is long, the productivity is reduced, and the water-absorbent resin is deteriorated or colored due to the heat treatment at a high temperature. In the present invention, 100% of the dehydration esterification reaction is not completed, and the reaction is intentionally stopped by rapid cooling. Therefore, the reaction time is short and the water absorbent resin is not deteriorated. Further, in the case of continuous heating, the physical properties are deteriorated due to the variation in the conventional flow, but the present invention does not have such a problem and has high physical properties. The residual amount of the surface cross-linking agent and its decomposition product is controlled in the range of 5 to 95 mol%, more preferably 10 to 90 mol%, and further preferably 20 to 70 mol% of the added cross-linking agent. If the residual amount is too large, not only is it uneconomical, but also there is a risk of deteriorating physical properties. If the residual amount is too small, there is a risk of deterioration or coloring due to a long-time reaction. The residual amount can be easily determined by extracting from the final water-absorbing resin (concentrating and dissolving the extract if necessary) and performing liquid chromatography analysis.

(Cooling process)
The first method of surface cross-linking of the water-absorbent resin powder of the present invention is that the surface cross-linked water-absorbent resin powder after the heat treatment step is subjected to a stirring and cooling treatment under a stream of air as a cooling treatment step. Controls the reaction of the agent to prevent condensation of water (water vapor generated by heating) generated by surface cross-linking reaction and the like, thereby preventing aggregation of resin particles, stabilizing production, and preventing deterioration of resin physical properties. I found that I can do it.

  The cooling machine used in the cooling treatment step in the present invention is connected to an apparatus for performing the above-mentioned surface treatment in order to cool the surface-crosslinked water-absorbent resin to room temperature to about 60 ° C. after performing the above-mentioned surface treatment. Device. Apparatuses to be used include a groove type mixing cooler, a rotary cooler, a disk cooler, a fluidized bed cooler, an air flow cooler, a paddle type cooler, an oscillating flow cooler, and a paddle combined with air flow having an air flow ventilation mechanism. A cooler can be used.

After the surface treatment is completed, the surface-crosslinked water-absorbent resin is supplied to a continuously connected cooler. The temperature at the time of supply is in the range of (surface treatment temperature) to (surface treatment temperature −30 ° C.), and varies depending on the ambient temperature, connection distance, and the like.
In the cooler, the water absorbent resin has a temperature gradient. The temperature near the inlet of the cooler is at or near the surface treatment temperature, and the temperature near the outlet is close to the expected cooling temperature. Factors governing the outlet temperature are the refrigerant temperature, the heat transfer area of the cooler, and the staying time in the cooler, and may be appropriately set so that the desired outlet temperature is obtained.

In the present invention, in order to achieve the object, the water-absorbing resin taken out of the heat treatment machine after surface crosslinking is preferably cooled within 1 minute, more preferably within 30 seconds, and the heat treatment machine and the cooling machine Are substantially connected. From the viewpoint of physical properties and productivity, the temperature of the water-absorbent resin at the start of cooling is 150 to 250 ° C, and the temperature after cooling is 40 to 100 ° C, preferably 50 to 90 ° C, more preferably 50 to 80 ° C. It is.

(Stirring / cooling treatment)
The stirring and cooling treatment in the first method for cross-linking the surface of the water-absorbent resin powder of the present invention is a treatment by mechanical stirring (may be combined with stirring by airflow) or a combination of stirring by vibration and stirring by airflow. It is a process to agitate the water-absorbent resin powder, and at that time, refers to cooling the water-absorbent resin continuously or batchwise in a mixer (cooler) having a forced cooling function, as an essential condition under air flow A stirring and cooling process is performed.
(Mechanical stirring)
As a stirrer having a rotating shaft used for stirring and cooling, a mixer having a function of passing an air flow and having a cooling function is widely used as a cooler, and the direction of the air flow is not particularly limited as long as the purpose is achieved, such as up and down, left and right. Specifically, as a cooler, a type in which the rotation axis is horizontal and the container itself also rotates (horizontal cylindrical type, inclined cylindrical type, V type, double cone type, cubic shape, S-shaped, continuous V type) Various types of mixers), horizontal axis of rotation and fixed type of container itself (ribbon type, screw type, conical screw type, groove type stirring type, high speed flow type, rotating disk type, muller type, paddle type, rotary type, disk) Various types of mixers) and the like, a cooler in which an airflow is passed through, and the like, preferably a container-fixed type cooler that includes a rotary stirring blade that stirs the water-absorbent resin powder, and in which the airflow is passed, These are used in a continuous or batch mode, preferably in a continuous mode. It is indispensable that these devices have a sufficient upper space through which the air flow can pass in addition to the fixed container portion for stirring, and preferably, the filling rate of the water-absorbing resin is 10 to 100 times the internal volume of the fixed container. It is operated in the range of%.

[Agitation by vibration]
The stirring by vibration is a stirring operation performed by applying mechanical vibration to the water-absorbent resin particles and causing the particles to move three-dimensionally by the vibration.
Agitation by this vibration can be achieved by using an eccentric motor (vibration motor), an electromagnet, or the like. In addition, an eccentric motor is preferable because the vibration angle, the frequency, and the stroke can be easily controlled.
Depending on the direction of the applied vibration (excitation angle), it is possible to move the particles up and down or to change the translational movement in the lateral direction. Regarding the vibration direction, conditions suitable for the device may be set as appropriate.
In addition, in stirring by vibration, it is preferable to set the vibration angle to be larger than 0 and smaller than 90 ° in order to promote discharge from the inside of the apparatus. If the amount is outside this range, stirring may occur due to vibration of the water-absorbent resin, but the resin may not be discharged, or the discharge may be so strong that a required stay time may not be obtained. A more preferable excitation angle is more than 30 ° and less than 70 °.
For example, in the case of a vibrating fluidized cooler, the vibration angle is about 60 °, the frequency is about 1000 cps, and the stroke is about 3 mm.

[Agitation by air flow]
The agitation by the airflow is a stirring operation performed by applying an airflow to the water-absorbent resin particles and causing the particles to move three-dimensionally by the airflow. The direction in which the airflow is applied is not particularly limited, but it is preferable to apply the airflow from below.
When applying an airflow from below, the wind speed must be higher than the terminal speed of the particles to be agitated in the airflow (the airflow here is generally air, nitrogen or the like). The terminal velocity increases as the particle diameter increases, and when stirring is performed at a constant wind speed, particles having a small particle diameter move vigorously, and large particles move gently. A wind speed higher than the terminal speed of the particles may be selected as necessary.
The wind speed referred to here is a wind speed which is generally called a superficial tower wind speed, and refers to a wind speed in a cross section perpendicular to the direction in which an airflow flows. The terminal speed refers to a speed at which the acceleration term becomes zero, that is, a speed at which a constant speed is reached, in an equation of motion relating to free fall in a fluid (including the fluid resistance).
In the stirring by the airflow in the present invention, the wind speed is usually the upper limit of the terminal speed of the water-absorbent resin particles having the maximum particle size in the water-absorbent resin, preferably, about the terminal speed of the particles having a mass average particle size or less, It is more preferably about 50% or less of the terminal velocity of particles having a mass average particle diameter.
More specifically, the maximum wind speed is usually about 5 m / s, and when the mass average particle diameter is about 400 μm, it is preferably 2.5 m / s or less, more preferably 1.3 m / s or less. If the wind speed is too high, the water-absorbent resin will jump out of the device, and if the wind speed is extremely low, there will be problems such as that stirring will not be performed.
Determination of the terminal velocity may be determined by numerical analysis using the particle diameter, density, airflow temperature, viscosity of the particle based on the equation of motion of the particle in consideration of the fluid resistance, or by actually conducting an experiment. It may be determined appropriately.

The vibrating fluid cooler is a cooler that enables stirring by vibration and stirring by air flow, and is a device that cools the water-absorbent resin powder while flowing using both vibration and air flow. For example, a continuous vibration drying / cooling machine manufactured by Tamagawa Machinery Co., Ltd., a vibration drying machine / cooling machine manufactured by Dalton Co., Ltd., and a vibrating fluidized bed drying / cooling machine manufactured by Tsukishima Kikai Co., Ltd. are exemplified. Further, a heat transfer tube such as a cooling tube may be provided in these devices in order to promote cooling.
The vibrating fluid cooler causes the water-absorbent resin powder layer to flow by mechanical vibration and airflow, and at that time, the water-absorbent resin is cooled by the airflow introduced into the cooler. The frequency is usually 1000 cps (count per sec), and the stroke is about 3 mm.

In addition, examples of an apparatus that uses mechanical stirring and flow stirring by air flow in combination include Frisgo Mix manufactured by Nissei Engineering Co., Ltd. and a rotating disk type dryer / cooler with a fluidized bed manufactured by Tsukishima Kikai Co., Ltd., but are not limited thereto. It is not done.
In addition, a cooler using both mechanical agitation and air flow stirs the water-absorbent resin powder by mechanical agitation and air flow, and at this time, conducts heat transfer between the inner surface of the cooler and / or the rotary agitating shaft and the introduced air flow. Thereby, the water-absorbing resin is cooled. The rotational stirring speed is usually 1 to 1000 rpm, more preferably 3 to 500 rpm, and still more preferably 5 to 100 rpm. The air flow velocity in this case is usually 0.01 m / sec or more, preferably 0.1 to 10 m / sec, more preferably 0.2 to 5 m / sec as a linear velocity (aeration amount per sectional area of the container).

  Further, in the present application, the water-absorbent resin powder is mechanically stirred and cooled under an air stream. At this time, as described later, the water-absorbent resin is cooled under an air stream and simultaneously the fine particles or residual particles of the water-absorbent resin particles are removed. It is preferable to remove at least a part of the surface crosslinking agent. In addition, airflow is preferably used to remove at least part of the fine particles of the water-absorbent resin particles or the remaining surface cross-linking agent by airflow.However, the water-absorbent resin is caused to flow by airflow stirring, and the water-absorbent resin is simply removed. It is also preferable to remove the fine powder of the water-absorbent resin or the residual surface cross-linking agent by supplying an excess air flow that is more than the flowing air, and a continuous moving fluidized bed into which the excess air flow is inserted from the bottom can also be used as the cooler of the present application.

  That is, in the first invention, a cooler for stirring and mixing by mechanical stirring (or stirring by air flow) or a combination of stirring by vibration and stirring by air flow is used in the first invention. In the present invention, at least a part of the fine powder of the water-absorbent resin particles or the remaining surface cross-linking agent is removed by an air stream. However, such a cooler is not particularly limited as long as it has a structure through which a sufficient air stream can be passed and cooled. In addition, in addition to the cooler for agitating and mixing the gas stream used in the first invention, a continuously moving fluidized bed can also be used as the cooler.

The stirring / cooling machine used for performing the stirring / cooling treatment in the present invention preferably has a rotating stirring shaft, and the rotating stirring shaft has one or more axes (two axes, three axes, etc.), and these are usually rotated. The water-absorbent resin powder is rotated and stirred in a cooler having stirring blades (paddles). The inside of the cooler is rotated and agitated while the water-absorbent resin powder is substantially filled or deposited in the lower portion. At this time, the water-absorbent resin powder is cooled (rapidly cooled) by the inner surface of the cooler and / or the rotating stirrer shaft conduction electric heat. You.
For example, the cooling is performed by a low-speed stirring-type cooler having one or a plurality of paddles. In this cooler, the water-absorbent resin powder flows in a piston flow. As such a low-speed stirring-type cooler, for example, a CD dryer manufactured by Kurimoto Ironworks Co., Ltd. and an incline disk type dryer manufactured by Tsukishima Kikai Co., Ltd. can be used.
As a feature of these low-speed stirring type coolers, the rotation speed is usually 100 rpm (Revolutions per minute) or less, preferably 50 rpm or less, and more preferably 5 to 30 rpm. Although still depending on the paddle diameter, it is preferable that the above rotational speed is satisfied, and the peripheral speed of the outermost paddle is 5 m / s or less.
If the rotation speed is low, a sufficient cooling effect cannot be achieved, and the effect of the present invention cannot be obtained. If the rotation speed is too high, the water-absorbent resin is damaged by friction or mechanical destruction, and the physical properties deteriorate.

As such a stirring cooler, for example, a cooler having rotary stirring blades shown in FIGS.
FIG. 1 is a top view of a cooler having a rotary stirring blade 1 except for an upper lid. The shaft 2 is driven by power of a motor or the like to rotate the rotary stirring blade 1.
FIG. 2 is a side view of the cooler of FIG. 1, in which the resin powder is charged from the charging port 3 and collected from the collecting port 6. Using the inlet 3, the recovery port 6, and the exhaust ports 4 and 5, the inside of the jacket can be depressurized and an air current can be introduced.
FIG. 3 is a sectional view taken along line AA of FIG. In the bottom jacket 7 and the top jacket 8, the rotary stirring blade 1 is rotated by driving the shaft 2.

  Such coolers may be placed vertically (water-absorbent resin is fed from top to bottom) or horizontally (water-absorbent resin is fed in the horizontal direction) if they are continuously fed and under airflow. The state of filling inside these coolers is appropriately determined, but usually the water-absorbent resin powder is laminated under its own weight (usually 1 to 100 cm, preferably 5 to 80 cm, more preferably 10 to 50 cm thick). Once filled, they are preferably rotationally stirred under a stream of air.

(Under airflow)
In the air flow, it is essential that there is an air flow (gas flow) in the space of the cooler, and if there is no forced external or external ventilation, the water-absorbent resin after cooling has a moisture absorbing fluidity ( Not only is the powder fluidity and anti-blocking property after moisture absorption inferior, but also the physical properties such as absorption capacity under pressure are not stable.
As the air flow, air, an inert gas (such as nitrogen gas) or a mixture thereof is used, and may be any one of reduced pressure, increased pressure, and normal pressure.
It is sufficient that a blower or a decompression mechanism is provided outside the cooler so that an airflow of usually -50 ° C to 100 ° C, preferably 0 ° C to 50 ° C, more preferably 10 ° C to 40 ° C is passed through the cooler. Some coolers have a rotating stirring shaft (stirring blade), but these rotations do not cause an airflow. In the present invention, the airflow is essentially ventilated by decompression or blowing.
The structure of the cooler is preferably cooling by conduction electric heat having a jacket in which a coolant flows on the wall surface, and other methods may be used in combination. The refrigerant temperature is usually -50C to 90C, preferably 0 to 70C, more preferably 10 to 60C. If the temperature of the refrigerant is too low, the water-absorbent resin may aggregate, and if the temperature of the refrigerant is too high, a sufficient cooling effect cannot be obtained.

  As a method of ventilating the air flow, in the case of stirring and cooling, a method of opening one inlet of a cooler and suctioning (depressurizing) from another outlet is further used. A method of blowing (pressurizing) from the mouth may be mentioned, but these are not limited. Further, the intake port and the exhaust port may serve not only as an airflow but also as a discharge port and an inlet for the water-absorbing resin, but are preferably provided separately.

Airflow is preferably made at reduced pressure conditions (suction conditions), the degree of vacuum, preferably 0.5~300mmH ₂ O, more preferably 1~100mmH ₂ O (water column pressure), more preferably 5~50mmH ₂ O It is. Insufficient or excessive pressure reduction is not preferable because a sufficient cooling effect cannot be obtained.

(Partial removal of fine particles or residual surface crosslinking agent of water-absorbent resin powder by air flow)
The second method for surface cross-linking of the water-absorbent resin powder of the present invention is characterized in that the water-absorbent resin powder is obtained by removing at least a part of the fine particles of the water-absorbent resin powder or the remaining surface cross-linking agent by an air current in the cooling step. It has been found that the physical properties of the resin powder are improved. In this case, the cooling treatment step may be any cooling treatment under an air flow, but the above-described stirring cooling treatment under an air flow is preferable.

Removal of at least a part of the fine particles or the residual surface cross-linking agent of the water-absorbent resin powder by air current is performed by continuously charging, preferably lowering, the water-absorbent resin to a device having an upper space, and removing the water-absorbent resin dust. May be generated inside the cooler, and the dust may be removed by an air current. Further, the remaining surface cross-linking agent may be generated in the upper space at the time of cooling the water-absorbing resin, and the generated remaining surface cross-linking agent may be removed by an air current. In addition, when using a cooler that mechanically stirs and mixes the airflow used in the first invention, the water-absorbent resin is mechanically stirred, preferably mechanically stirred by a rotary stirring blade. At this time, it is sufficient to vent the air flow in an amount sufficient to remove at least a part of the fine particles or the residual surface cross-linking agent of the water-absorbing resin powder, and the amount is appropriately determined, but preferably the pressure is reduced to the above-described range. Ventilated. Further, when the continuously moving fluidized bed is also used as the cooler of the present invention, the air flow rate of the air flow is increased by supplying an excess air flow more than the water absorbent resin simply flows, and the fine powder of the water absorbent resin or the residual surface crosslinking agent is supplied. May be removed.
The captured fine powder of the water-absorbent resin can be reused as it is or, if necessary, granulated.

As the fine powder of the water-absorbing resin to be removed, fine particles having a particle diameter of 150 μm or less, or even 106 μm or less, are removed. % By mass, in the range of 0.1 to 3% by mass. If the removal amount is small, various physical properties such as moisture absorption fluidity and absorption capacity under pressure are reduced, and if the removal amount is large, the yield is reduced. The water-absorbent resin powder removed by the air current may be recycled or used separately as fine powder of the water-absorbent resin.
It is also preferred that the residual surface cross-linking agent, preferably the ester-reactive cross-linking agent, is removed using an air stream. The removal amount is preferably 0.01 to 50% by mass, more preferably 0.05 to 40% by mass, and particularly preferably 0.1 to 30% by mass of the used surface crosslinking agent. By removing the residual cross-linking agent, various physical properties of the water-absorbent resin, such as moisture-absorbing fluidity, are improved.

〔Throughput〕
The effect of removing the part of the water-absorbing fine particles or the remaining surface treatment agent by the above-described stirring and cooling process under the air stream and the air stream is suitable for large-scale production of a fixed amount or more per line, and particularly continuous production. is there. In a large-scale production, for example, a production having a cooling step in which the production amount per line is 300 kg / hour or more, further 500 kg / hour or more, particularly 700 kg / hour or more, the improvement of the physical properties of the water-absorbent resin powder is improved. The effect becomes remarkable. This is thought to be because in large-scale production, there are various causes of deterioration in physical properties such as a decrease in fluidity and clogging due to the form of the resin powder, but the cooling treatment of the present invention can avoid them. .
There is no particular upper limit on the throughput, but if the scale is too large, control may be difficult or the physical properties may be reduced. Usually, up to about 10,000 kg / hour per apparatus, such a problem does not occur, so that it is preferable. .

The above-mentioned coolers are preferably arranged to be fed continuously, but they may be arranged vertically (water-absorbent resin is fed from top to bottom) or horizontally (water-absorbent resin is fed in a horizontal direction). However, in view of the physical properties of the obtained resin powder, the resin powder is preferably set horizontally. These coolers are not installed vertically or horizontally, but preferably have a downward slope, particularly a horizontal installation, and preferably have a downward slope. When the resin does not have an inclination, it is difficult to feed it stably as powder characteristics of the heated water-absorbent resin, and the physical properties may be reduced or unstable. The downward inclination is determined as appropriate, but preferably has a downward inclination of about 0.1 to 30 °, more preferably 1 to 20 °, and more preferably about 3 to 15 °.
Furthermore, in the present invention, in the method of adding a surface crosslinking agent to the water-absorbent resin powder and performing a heat treatment to perform surface crosslinking, it is preferable to use a reactor having a downward inclination.
That is, the same inclination is preferably applied not only to the cooler having the above-described inclination but also to the heat treatment before cooling, and the physical property step of the water-absorbent resin of the present invention can be achieved. The downward inclination improves the flow of the piston during continuous operation of the powder, and makes it easy to switch between products when changing products.

Ideally, a piston flow (Push Flow) is a substance in which the material flowing in the device has a uniform velocity distribution in the direction perpendicular to the flow from the inlet to the outlet of the device, and at the same time, flows. It is defined as a flow that moves without mixing and diffusion in the direction.
By improving the piston flow property of the water-absorbent resin powder, the residence time of the water-absorbent resin powder in the heat treatment machine or the cooler of the water-absorbent resin powder is stabilized, and the stable thermal crosslinking / cooling treatment is performed. As a result, the water-absorbent resin powder having high physical properties can be manufactured stably, and partial long-term stagnation is eliminated, so that the water-absorbent resin is less likely to be powdered, and the generation of fine powder can be suppressed.
In addition, in the aqueous liquid addition described later, by improving the piston flow property, the formation of a field (zone) in an essential specific temperature range in the powder layer in the cooler becomes clearer, and the addition of the aqueous liquid becomes easier. Things.
When the piston flow property is low, the variation in the residence time of the water-absorbent resin powder in the heat treatment machine / cooler becomes large, and the physical properties become unstable, or the product has low physical properties and a large amount of fine powder. In addition, the formation of a field in a specific temperature region essential for the addition of the aqueous liquid described later becomes unclear, which makes it difficult to add the aqueous liquid.

  Moreover, in the above-mentioned method of cross-linking the surface of the water-absorbent resin powder, it is preferable to add an aqueous liquid as described later in the cooling step.

(Aqueous liquid addition)
Further, as a preferred embodiment of the third method for surface cross-linking of the water-absorbent resin powder of the present invention, at the time of cooling after the surface cross-linking treatment, water or an aqueous liquid containing water as a main component (hereinafter collectively referred to as an aqueous liquid) Is added in a place where the temperature of the water-absorbent resin powder is 40 to 100 ° C., thereby enabling reduction of fine powder and dust generation, and does not require a normal granulation step, and is equivalent to granulation of the water-absorbent resin powder. Has been found, that is, granulation can be performed by adding the above-mentioned aqueous liquid. That is, granulation can be easily performed without using a high-cost dedicated granulation equipment.
In this case, the condition of the cooling treatment is such that, at the start of the cooling treatment, the temperature of the water-absorbent resin powder usually exceeds 100 ° C., and is preferably cooled to 70 ° C. or less after the cooling treatment. . The cooling treatment is preferably the above-described cooling treatment under an air flow, and more preferably the stirring cooling treatment under an air flow.

As described above, the addition of water to the adsorptive resin is usually not endothermic, but involves exotherm. Due to the addition of the aqueous liquid to the water-absorbent resin powder of the present invention, an exothermic reaction occurs due to heat of hydration, and the water-absorbent resin generates heat. It is considered that the composition of the resin powder is changed to obtain more excellent properties, the generation of fine powder is suppressed, and the form of the resin powder is improved.
Further, the addition of the aqueous liquid further improves the moisture absorption fluidity, reduces the fine powder of the water absorbent resin, and prevents the surface destruction of the water absorbent resin in the subsequent process.
By the specific addition method of the aqueous liquid, the fine powder having a mass average particle diameter of 200 to 600 μm, preferably 300 to 500 μm, and 150 μm or less is controlled to 5% by mass, preferably 3% by mass, and more preferably 1% by mass or less. Water-absorbent resin powder can be obtained.

The addition of the aqueous liquid to the cooler is performed when the temperature of the water-absorbent resin powder is 40 to 100 ° C, preferably 50 to 90 ° C, and more preferably 60 to 80 ° C. The field here means, for example, a region (zone) having a specific temperature when the temperature continuously changes (decreases) with a continuous flow of the water-absorbing resin. When the aqueous liquid is added at a temperature of 40 ° C. or lower, the water-absorbent resin becomes lumps (lumps) and closes the cooler outlet, or the water-absorbent resin adheres to the heat transfer surface of the cooler, When the heat transfer efficiency is reduced, the cooling efficiency is substantially reduced, or when the lumps are broken, the water-absorbent resin constituting the lumps themselves may be damaged and the physical properties may be reduced. In addition, when the aqueous liquid is added at a temperature of 100 ° C. or higher, low boiling components in the added aqueous liquid, for example, water, are diffused, and the aqueous liquid is not effectively added to the water-absorbing resin, but, for example, is diffused. Condensation in the cooler due to water, lumps are generated by the condensed water, the cooler outlet is blocked by the lumps, and stable operation can not be performed, or the water absorbent resin adheres to the heat transfer surface of the cooler, By lowering the heat transfer efficiency, the cooling efficiency is substantially reduced, or the physical properties of the water-absorbing resin are reduced.
In the present invention, it is essential that the aqueous liquid is added in the temperature field described above.
Techniques for finding these preferable temperature regions in the cooler are, for example, actually measuring under set operating conditions, or the inlet of the cooler, the water absorbent resin temperature at the outlet, the specific heat of the water absorbent resin, the supply speed, the inlet of the refrigerant, From the outlet temperature or the like, a counter-current or parallel-flow contact heat exchanger is assumed, the overall heat transfer coefficient is calculated, the heat transfer area is made a function of the distance in the flow direction, and the temperature may be found by numerical analysis.

The temperature of the aqueous liquid to be added is generally 0 to less than the boiling point, preferably 10 to 50 ° C.
The addition amount of the aqueous liquid is usually 0.01 to 50 parts by mass, preferably 0.01 to 30 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the water-absorbent resin powder.

  The water spraying device for adding the aqueous liquid is not particularly limited as long as it is a spraying device suitable for the purpose, but a device capable of uniformly spraying the aqueous liquid onto a small area is desirable. Preferably, a one-fluid type or two-fluid type spray having a flat spray, hollow cone, full cone spray pattern is used, and more preferably, a narrow angle spray is used for spraying in a narrow area.

The size of the droplet to be sprayed is not particularly limited, but is preferably 10 to 1000 μm on average. If the droplet size is too large, the water content of the water-absorbent resin becomes non-uniform, and the particles that have absorbed a large amount of water may be clogged and block the device. If the thickness is less than 10 μm, the sprayed water does not effectively adhere to the water-absorbing resin, and is discharged from the inside of the apparatus as splashes or becomes dewed water, causing a problem. The optimal droplet size is between 50 and 500 μm.
As a general tendency, if the air flow in the device is gentle, the droplet size may be small, and if the air flow is fast, it is important to use large droplets in order to prevent escape as droplets. is there.

  It is preferable to add the aqueous liquid so that the aqueous liquid does not come into contact with anything other than the water-absorbent resin. However, when the added aqueous liquid may come into contact with parts inside the device other than the water-absorbent resin powder, for example, polyethylene glycol ( It is preferable to include an adhesion inhibitor such as PEG) and polypropylene glycol (PPG).

Various additives for developing additional functions may be dissolved or dispersed in the added aqueous liquid. Examples of such additives include metal salts, acids, alkalis, deodorants, coloring agents, inorganic or organic antibacterial agents, and surfactants . More specifically, for example, sulfites such as sodium bisulfite (SBS) to reduce residual monomers, organic or inorganic bases to adjust water absorption rate, organic or inorganic acids, monovalent metal salts or polyvalents A metal salt (for example, aluminum sulfate), a deodorant for imparting a deodorizing function, a coloring agent for imparting visual value, various chelating agents for improving urine resistance, and the like can be contained.
The concentration of various additives in the aqueous liquid is generally 0.01 to 50% by mass, preferably 0.1 to 40% by mass, and more preferably 1 to 30% by mass as a total amount.

The water-absorbent resin obtained by the first, second and third methods of the present invention has a water absorbency against physiological saline under pressure (4.9 kPa) of preferably 20 g / g or more, more preferably 23 g / g or more, More preferably, it is 25 g / g or more. The absorbency against pressure (1.9 kPa) with respect to physiological saline is usually 20 g / g or more, preferably 25 g / g or more, more preferably 28 g / g or more, and particularly preferably 32 g / g or more. A water-absorbing resin having high physical properties of 25 g / g or more, more preferably 28 g / g or more, particularly preferably 32 g / g or more can be easily and stably produced by the method of the present invention. . The flow rate under pressure (SFC) is 10 × 10 ⁻⁷ or more, preferably 20 × 10 ⁻⁷ or more, and more preferably 50 × 10 ⁻⁷ [cm ³ · s · g ⁻¹ ] or more. Further, the amount of the water-soluble component and the particle size are in the above ranges.

That is, the water-absorbent resin obtained in the present invention is a water-absorbent resin powder surface-crosslinked with 0.001 to 10 parts by mass of an ester-reactive crosslinker, preferably 0.001 to 10 parts by mass of a polyhydric alcohol, The features are as follows.
(1) A polyacrylate crosslinked polymer having a mass average particle diameter of 200 to 600 μm, preferably 300 to 500 μm, and particles of 850 μm or more and 150 μm or less, each of which is 1% by mass or less.
(2) The absorption capacity under pressure (4.9 kPa) is 20 g / g or more, preferably 28 g / g or more, and more preferably 32 g / g or more.
(3) The absorption capacity under no load is 25 g / g or more, preferably 28 g / g or more, more preferably 32 g / g or more.
(4) The flow rate under pressure (SFC) is 10 × 10 ⁻⁷ or more, preferably 20 × 10 ⁻⁷ or more, more preferably 50 × 10 ⁻⁷ or more.
(5) The amount of the water-soluble component is 25% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and particularly preferably 10% by mass or less.
(6) The residual amount of the ester-reactive crosslinking agent is 5 to 95 mol%, preferably 10 to 90, and more preferably 20 to 70 mol%.
The novel water-absorbent resin of the present invention has a small amount of fine powder and high physical properties, and furthermore, a specific amount of the ester-reactive crosslinking agent remains.
In addition, the cooler or heat treatment machine for a water-absorbent resin used in the present invention is a stirring type equipped with an airflow ventilation mechanism and a plurality of paddles, and has a downward slope. Machine or heat treatment machine.

  ADVANTAGE OF THE INVENTION According to the method of this invention, the absorption capacity under no pressure, the absorption capacity under pressure, and the water-absorbent resin with good absorption characteristics excellent in the balance of soluble components can be easily produced, Water retention agents, industrial water retention agents, hygroscopic agents, dehumidifiers, widely used in building materials, etc., but the water absorbent resin of the present application is particularly suitably used for sanitary materials such as disposable diapers, incontinence pads, breast milk pads, sanitary napkins and the like. Can be Furthermore, the water-absorbent resin of the present invention is excellent in the above three physical properties in a well-balanced manner. ) Can be used at a high concentration, specifically in the range of 30 to 100% by mass, preferably in the range of 40 to 100% by mass, and more preferably in the range of 50 to 95% by mass.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Various properties of the water-absorbing resin or the water-absorbing agent were measured by the following methods.

  In the case of a water-absorbing agent used as a final product such as a sanitary material, since the water-absorbing agent has absorbed moisture, the water-absorbing agent is appropriately separated from the final product and dried under reduced pressure and low temperature (for example, 1 mmHg or less, 60 ° C. 12 hours). Further, the water content of the water-absorbing resins used in Examples and Comparative Examples of the present invention were all 6% by mass or less.

(1) Absorption capacity under no pressure (absorption capacity for 30 minutes under no pressure against 0.90% by mass saline / CRC)
Under a condition of room temperature (20 to 25 ° C.) and humidity of 50 RH%, 0.20 g of the water-absorbent resin powder is uniformly placed in a nonwoven bag (60 mm × 85 mm, heatron paper GSP22 manufactured by Nankoku Pulp Industry Co., Ltd.). After putting and sealing, it was immersed in a large excess (for example, 100 g or more) of 0.9% by mass physiological saline at room temperature. Thirty minutes later, the bag was lifted up, and after draining at 250 G for 3 minutes using a centrifuge (centrifuge manufactured by Kokusan Co., Ltd .: Model H-122), the mass W1 (g) of the bag was measured. The same operation was performed without using a water-absorbing resin or a water-absorbing agent, and the mass W0 (g) at that time was measured. From these W1 and W0, the absorption capacity under no pressure (g / g) was calculated according to the following equation.
Absorption capacity under no pressure (g / g)
= (W1 (g) -W0 (g) -mass of water-absorbing resin or water-absorbing agent) / mass (g) of water-absorbing resin or water-absorbing agent

(2) Absorption capacity under pressure (absorption capacity under pressure at 4.83 kPa for 0.90 mass% physiological saline for 60 minutes / AAP)
A 400 mesh stainless steel wire mesh (mesh size: 38 μm) was fused to the bottom of a plastic support cylinder having an inner diameter of 60 mm, and water was absorbed on the mesh at room temperature (20 to 25 ° C.) and humidity of 50 RH%. 0.90 g of a water-soluble resin was evenly sprayed thereon, and the outer diameter was slightly smaller than 60 mm, adjusted so that a load of 4.83 kPa (0.7 psi) was uniformly applied to the water-absorbing agent. A piston and a load in which no gap was formed between the support cylinder and the vertical movement were not hindered were placed in this order, and the mass Wa (g) of the complete measuring apparatus was measured.
A glass filter with a diameter of 90 mm (manufactured by Mutual Science and Chemical Glass Co., Ltd., pore diameter: 100 to 120 μm) is placed inside a petri dish with a diameter of 150 mm, and 0.90% by mass physiological saline (20 to 25 ° C.) is placed in a glass. It was added so that it was at the same level as the top of the filter. A piece of filter paper having a diameter of 90 mm (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness of 0.26 mm, diameter of retained particles of 5 μm) is placed thereon, so that the entire surface is wetted, and Excess liquid was removed.
The above set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. One hour later, the set of measuring devices was lifted, and its mass Wb (g) was measured. Then, the absorption capacity under pressure (g / g) was calculated from Wa and Wb according to the following equation.
Absorption capacity under pressure (g / g) = (Wa (g) -Wb (g)) / mass of water absorbing agent (0.9 g)

(3) Mass Average Particle Size The water-absorbent resin powder is sieved with a JIS standard sieve having openings of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, etc., and the residual percentage R is log probability paper. Is plotted. Thereby, the mass average particle diameter (D50) was read.
The classification method is as follows: 10.0 g of the water-absorbent resin powder is JIS standard sieve having openings of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH% (THE IIDA TESTING SIEVE: (Diameter: 8 cm), and classified by a vibration classifier (IIDA SIEVE SHAKER TYPE: ES-65 type, SER. No. 0501) for 10 minutes.

(4) Moisture Absorbing Fluidity 1.0 g of hygroscopic resin powder was thinly spread on an aluminum plate having a diameter of about 50 mm, and allowed to stand at 37 ° C. and 60% RH for 30 minutes. It was inclined and evaluated visually.
：: Good fluidity of powder △: Partially aggregated ×: Completely aggregated

(5) Water-soluble content 500 mg of a water-absorbent resin was dispersed in 1,000 ml of room temperature deionized water, stirred for 16 hours with a 40 mm magnetic stirrer, and the swollen gel was separated with a filter paper (TOYO, No. 6). Filtered. Next, the water-soluble polyacrylate in the filtrate eluted from the water-absorbent resin is subjected to colloid titration using methyl glycol chitosan and polyvinyl potassium sulfate, whereby the mass% of the water-soluble component in the water-absorbent resin (vs. water absorption) Resin).
(6) Residual monomer In the above (5), the amount of the residual monomer of the water-absorbent resin (mass ppm / vs. Water-absorbent resin) was also determined by separately analyzing the filtrate after stirring for 2 hours by UV analysis using liquid chromatography. analyzed.

(7) Liquid permeability under pressure (SFC)
As a method for measuring liquid permeability under pressure, 0.9 g of a water-absorbent resin is swollen under a load of 20 g / cm ² (about 1.9 kPa) for 1 hour in accordance with WO95 / 22356, and then a 0.0018 M NaCl solution The saline flow conductivity (abbreviated as SFC) of the swollen gel at 20 g / cm ² (about 1.9 kPa) at (20-25 ° C.) was determined. The unit is [cm ³ · s · g ^-1 ], and the larger the value, the higher the liquid permeability.

(Production Example 1A)
An aqueous solution of partially neutralized sodium salt of 38% by weight of acrylic acid, neutralized at 71% by mole, containing 0.05% by mole (relative to monomer) of polyethylene glycol diacrylate (n = 9) as a cross-linking agent It is continuously supplied to a belt polymerization machine, and continuously subjected to standing aqueous solution polymerization (belt residence time: about 30 minutes, thickness: about 25 mm), and the obtained water-containing gel-like crosslinked polymer of a water-absorbent resin is subjected to a meat chopper. It was coarsely crushed into particles, and this was spread thinly on a perforated plate of a band dryer and placed thereon, followed by continuous hot-air drying at 160 to 180 ° C. for 30 minutes. A block-shaped dried polymer was obtained at the outlet of the dryer. The dried polymer was taken out and crushed at the same time, and the obtained particulate dried product was pulverized by continuously supplying a three-stage roll granulator at 1100 kg / h. The obtained powder of the particulate water-absorbent resin at about 60 ° C. is classified by a sieving apparatus having a sieve net having a mesh size of 850 μm, and 90% by mass or more of the water-absorbent resin powder having a size of less than 850 μm and less than 150 μm (mass) (Average particle diameter: 400 μm). The obtained amorphous water-absorbent resin powder (1) had an average absorption capacity (CRC) under no pressure of 40 g / g and a water-soluble content of 11% by mass.
Further, the water-absorbent resin powder (1) was continuously supplied at 1000 kg / h to a high-speed continuous mixer (Turbulizer manufactured by Hosokawa Micron Corporation / 1000 rpm), and 1,4-butane was further added to the water-absorbent resin powder (H). An aqueous solution of a surface cross-linking agent composed of diol / propylene glycol / water = 0.38 / 0.63 / 3.5 (mass% / vs. Powder) was sprayed and mixed with a spray that formed droplets having an average particle size of about 200 μm. Subsequently, the obtained mixture is continuously heated at 195 ° C. for 50 minutes by a paddle-type low-speed stirring type indirect heating dryer (paddle dryer) to thereby obtain a water-absorbing agent powder containing several thousand ppm of residual polyhydric alcohol (surface crosslinking). Water-absorbent resin powder).

(Example 1A)
Following the heat treatment by the paddle dryer (manufactured by Nara Machinery Co., Ltd.) of Production Example 1A, a slight suction was made into the upper space of the cooler in which a refrigerant (cold water) at 40 ° C. was flowed through a similar paddle dryer connected in series. The water-absorbent resin powder was cooled by a cooling device (jacket: 40 ° C.) in which the pressure was reduced to 100 mmH ₂ O through an air flow. Was excellent in fluidity, physical properties were stable with time, there was substantially no fine powder (100 μm or less), and no coagulation was observed during production. Table 1 shows the results. At the time of cooling, a part of the water-absorbent resin fine powder was removed by an air current.

(Example 2A)
In Example 1A, following the heat treatment of the paddle dryer of Example 1A, cooling was performed using a fluidized bed under airflow conditions with a yield of 100%. Note that a part of the fine powder was removed by a cyclone during cooling.

(Comparative Example 1A)
In Example 1A, without using a cooling device, the mixture was classified with an 850 μm sieve and stored directly in a product hopper. As a result, the properties were fluctuated or deteriorated, the fluidity at the time of moisture absorption was poor, and fine powder (100 μm or less) was contained in a slight amount of 0.2%. In the case of long-term production, aggregation during production was also observed.

(Comparative Example 2A)
In Example 1A, when no air flow due to reduced pressure was introduced into the cooling device, adhesion and agglomeration of the water-absorbing resin were gradually observed during continuous operation for 24 hours. Furthermore, the fluidity at the time of moisture absorption was poor, and fine powder (100 μm or less) was contained in 0.1%.

(Comparative Example 3A)
In Example 1A, subsequent to the heat treatment of the paddle dryer of Example 1A, cooling was performed using a fluidized bed (Okawara Seisakusho, Production Flow Co., Ltd.) under airflow conditions with a yield of 100%. Note that the yield of 100% refers to a condition in which an airflow necessary and sufficient for the water-absorbent resin to flow, and finally all the water-absorbent resin is discharged from the outlet.

It can be seen that Example 1A in which the agitation cooling treatment was performed under an air stream was superior to both Comparative Examples 1A and 2A in both water absorption performance and moisture absorption fluidity.
In Example 1A, when the airflow from the cooler was collected, the water-absorbent resin fine powder and the remaining surface cross-linking agent were removed.
It can be seen that Example 2A, in which cooling treatment under air current and partial removal of fine powder were performed, was excellent in water absorption performance as compared with Comparative Example 3A in which partial removal of fine powder was not performed.

(Production Example 1: Production of amorphous crushed water absorbent resin 1)
634.9 g of acrylic acid, 5564.2 g of a 37% by mass aqueous solution of sodium acrylate, and two internal aqueous crosslinking agents consisting of 9.0 g of polyethylene glycol diacrylate having 8 ethylene glycol repeating units and 322 g of water. Was supplied to a reactor equipped with a 10-L jacketed stainless steel kneader having a sigma-type blade and covered with nitrogen, and while keeping the temperature of the reaction system at 25 ° C., nitrogen gas was supplied for 30 minutes to perform degassing. .
Next, 24.6 g of a 15% by weight aqueous solution of sodium persulfate and 15.4 g of a 0.2% by weight aqueous solution of L-ascorbic acid were added while stirring the reaction solution. Later the reaction reached peak temperature. Thirty minutes after the start of the polymerization, the hydrogel polymer was taken out. The obtained hydrogel polymer was finely divided to a diameter of 5 mm or less. The obtained hydrogel polymer was spread on a wire mesh having a mesh size of 300 μm, and dried with hot air at 170 ° C. for 60 minutes. The dried product was pulverized with a roll mill, and further classified with a sieve consisting of two JIS 850 μm and 150 μm sieves to obtain a 150 μm sieve top distillate. The water absorption capacity (CRC) of the obtained irregularly crushed water-absorbent resin powder with respect to physiological saline was 36 g / g.

(Production Example 2: Production of amorphous crushed water-absorbent resin 2)
An aqueous solution consisting of 507.9 g of acrylic acid, 5344.9 g of a 37% by mass aqueous solution of sodium acrylate, 4.1 g of polyethylene glycol diacrylate having 8 ethylene glycol repeating units as an internal crosslinking agent, and 647 g of water was mixed with an aqueous solution of sodium persulfate. 22.6 g of a 15% aqueous solution and 14.1 g of a 0.2% by mass aqueous solution of L-ascorbic acid were added, and polymerization, drying and pulverization were carried out in the same manner as in Production Example 1. The mixture was further classified with a sieve consisting of JIS 850 μm and 197 μm sieves to obtain a 197 μm sieve top fraction. The water absorption capacity (CRC) of the obtained amorphous crushed water-absorbent resin powder with respect to physiological saline was 48 g / g.

(Reference Example 1)
The irregularly crushed water-absorbent resin 1 obtained in Production Example 1 was continuously supplied to a high-speed mixer at a rate of 60 g / min, and 1,4-butanediol / propylene glycol was added to 100 parts by mass of the water-absorbent resin. An aqueous liquid (referred to as a surface treatment agent) consisting of 0.32 / 0.5 / 2.73 parts by mass of water / water was spray-added in a high-speed mixer. Furthermore, the paddle type low-speed stirring indirect heating dryer having a total internal volume of 4.6 L was prepared by adjusting the height of the outlet weir to the water-absorbent resin to which the surface treatment agent was added by spraying so that the average residence time was about 40 minutes ( (Kurimoto Iron Works, Ltd. CD dryer CD-80 type, hereinafter referred to as heat treatment machine). The heating medium temperature was 210 ° C.
The height of the outlet weir was adjusted so that the average stay time of the surface-crosslinked water-absorbent resin was further increased to about 30 minutes, and the water-absorbent resin was continuously supplied to the apparatus installed in series and cooled with stirring. The temperature of the water absorbent resin at the time of supply was 205 ° C, and the temperature of the water absorbent resin at the time of discharge was 60 ° C. The temperature of the refrigerant used was 40 ° C. (In the above, when a refrigerant flows instead of a heat medium, it is called a cooler.)
The internal was between 100 mm H ₂ O of vacuum through a slightly suction airflow in the upper space of the cooler.
The water-absorbing capacity (CRC) of the resulting surface-crosslinked water-absorbing resin under no load was 28 g / g, and the water-absorbing capacity under pressure (AAP) was 24 g / g.
The amount of fine powder having a particle size of 150 μm or less at the start of the test of the water-absorbent resin 1 was 1.9% by mass, but increased to 2.4% by mass after the test. This was a water-absorbing resin with poor handling properties, in which the destruction of the particles occurred, the fine powder increased, and dust was easily generated.

(Example 1)
As in Reference Example 1, a paddle-type low-speed stirring indirect heating dryer having a total internal volume of 4.6 L, connected in series while continuously spraying and adding the surface treatment aqueous solution at a rate of 60 g / min. (CD Drier CD-80, manufactured by Kurimoto Tekkosho Co., Ltd.). The heat medium temperature of the heat treatment machine was 212 ° C, and the refrigerant temperature of the cooler was 40 ° C. When the temperature at a position (field) that was 1/3 of the length of the cooler as viewed from the outlet side was measured, it was found to be 65 ° C., so that two fluids manufactured by Spraying Systems Japan Co., Ltd. Using a nozzle (air atomizing nozzle SUF1 flat pattern), water was spray-added under the conditions of a water supply amount of 0.6 g / min and an air pressure of 0.02 Mpa. The water-absorbing resin to which water was added by spraying did not generate lumps (lumps) or the like in the apparatus, and was discharged from the outlet in a dry state. The temperature of the discharged water absorbent resin was 60 ° C. No adhesion of the water-absorbing resin into the device was observed. The fine powder having a particle size of 150 μm or less in the obtained water-absorbent resin was 1.6% by mass, the destruction was suppressed as compared with Reference Example 1, and the result of Reference Example 1 (2.4% by mass) was used as a reference. As a result, the fine powder having a size of 150 μm or less was reduced by 33%. Also, generation of dust was small. The performance of the obtained water-absorbent resin was almost the same, but the absorbency against pressure (AAP) was improved to 25 g / g.

(Example 2)
The operation was performed in the same manner as in Example 1, except that the water supply amount was 1.8 g / min. The water-absorbing resin to which water was added by spraying did not generate lumps (lumps) or the like in the apparatus, and was discharged from the outlet in a dry state. The temperature of the discharged water-absorbent resin was 58 ° C. No adhesion of the water-absorbing resin into the device was observed. The fine powder having a particle size of 150 μm or less in the obtained water-absorbent resin was 1.2% by mass, the destruction was suppressed as compared with Reference Example 1, and the result of Reference Example 1 (2.4% by mass) was used as a reference. As a result, fine powder having a size of 150 μm or less was reduced by 50%. Also, generation of dust was small.

(Example 3)
The operation was performed in the same manner as in Example 1, except that the amount of water supplied was 3 g / min. The water-absorbing resin to which water was added by spraying did not generate lumps (lumps) or the like in the apparatus, and was discharged from the outlet in a dry state. The temperature of the discharged water absorbent resin was 55 ° C. Adhesion of the water-absorbing resin into the device was observed. The fine powder having a particle size of 150 μm or less in the obtained water-absorbent resin was 1.0% by mass, the destruction was suppressed as compared with Reference Example 1 (2.4% by mass), and the result of Reference Example 1 was used as a reference. As a result, the fine powder of 150 μm or less was reduced by 58%. Also, generation of dust was small.

(Example 4)
In Example 3, since the adhesion of the water-absorbing resin to the inside of the apparatus was observed, the water added by spraying was changed to an aqueous solution containing polyethylene glycol having an average molecular weight of about 400 and containing 1% by mass of polyethylene glycol. The addition of the polyethylene glycol reduced the adhesion of the water-absorbing resin to the inside of the device, and the attached water-absorbing resin was easily detached from the inner surface of the device.
The obtained water-absorbent resin did not generate lumps (lumps) and the like in the apparatus, and was discharged from the outlet in a dry state.
The fine powder of 150 μm or less in the obtained water absorbent resin was 1.2% by mass, and the fine powder of 150 μm or less was reduced by 50% based on Reference Example 1 (2.4% by mass).

(Example 5)
Example 4 was changed to an aqueous solution containing 3% of polyethylene glycol. Similarly, the adhesion of the water-absorbing resin in the apparatus was reduced. The amount of the fine powder of 150 μm or less in the obtained water-absorbent resin was 1% by mass, and the fine powder of 150 μm or less was reduced by 58% based on Reference Example 1 (2.4% by mass).

(Reference Example 2)
In Reference Example 1, the water-absorbing resin 2 was used, and the surface-treating agent was ethylene glycol diglycidyl ether / 1,4-butanediol / propylene glycol / water = 0.024 / 0 with respect to 100 parts by mass of the water-absorbing resin. The aqueous liquid consisting of .32 / 0.5 / 2.73 parts by mass, the temperature of the heating medium was 210 ° C., the temperature of the refrigerant was changed to 38 ° C., and the other steps were the same. The temperature of the discharged water absorbent resin was 60 ° C. The water-absorbing capacity of the obtained surface-crosslinked water-absorbing resin under no load was 35 g / g, and the water-absorbing capacity under pressure was 24 g / g (4.9 kPa).
The amount of fine powder having a size of 150 μm or less at the start of the test of the water-absorbent resin 2 was 2.0% by mass, but increased to 4.2% by mass after the test. This was a water-absorbing resin with poor handling properties, in which the destruction of the particles occurred, the fine powder increased, and dust was easily generated.

(Example 6)
In Reference Example 2, water was supplied in the same manner as in Example 1 except that the water supply amount was 1.8 g / min.
No lump or the like was generated in the apparatus, and the substance was discharged from the outlet in a dry state. There was almost no adhesion of the water-absorbing resin into the apparatus. The amount of fine powder of 150 μm or less in the obtained water-absorbent resin was 3.2% by mass, and the amount of fine powder of 150 μm or less was reduced by 24% based on Reference Example 2 (4.2% by mass). The performance of the obtained water-absorbent resin was almost the same, but the water absorption capacity under pressure (AAP) was improved to 24.5 g / g.

(Example 7)
In the same manner as in Example 6, the water supply rate was changed to 3 g / min. No lump or the like was generated in the apparatus, and it was discharged from the outlet in a dry state. Adhesion of the water-absorbing resin into the device was observed. The fine powder of 150 μm or less in the obtained water-absorbent resin was 3.1% by mass, and the fine powder of 150 μm or less was reduced by 26% based on Reference Example 2 (4.2% by mass). Also, generation of dust was small.

(Example 8)
In Example 7, since adhesion of the water-absorbing resin to the inside of the apparatus was observed, the water to be added by spraying was changed to an aqueous solution containing polyethylene glycol having an average molecular weight of about 400 and containing 1% by mass of polyethylene glycol. The addition of the polyethylene glycol reduced the adhesion of the water-absorbing resin to the inside of the device, and the attached water-absorbing resin was easily detached from the inner surface of the device. The obtained water-absorbent resin did not generate lumps (lumps) and the like in the apparatus, and was discharged from the outlet in a dry state.
The fine powder of 150 μm or less in the obtained water-absorbent resin was 2.7% by mass, and the fine powder of 150 μm or less was reduced by 36% based on Reference Example 2 (4.2% by mass).

(Example 9: Inherence of chelating agent)
In Example 6, it carried out similarly, changing to the aqueous solution containing 0.53 mass% of 45 mass% aqueous solution of sodium diethylenetriamine pentaacetate, and supplying 1.5 g / min of aqueous solutions. No lump or the like was generated in the apparatus, and the substance was discharged from the outlet in a dry state. There was almost no adhesion of the water-absorbing resin into the apparatus. The urine resistance of the obtained water absorbent resin was determined by the following method.
1.0 g of a water-absorbent resin was added to 50 g of physiological saline containing 0.05% by mass of L-ascorbic acid, and the mixture was allowed to swell uniformly. Was visually observed, the water-absorbent resin to which diethylenetriamine pentaacetate was added maintained the state of a swollen gel, whereas the water-absorbent resin to which diethylenetriaminesodium pentaacetate was not added (in Examples, (Not shown), the shape of the swollen gel collapsed, and it was in a muddy state. The effect of adding sodium diethylenetriaminepentaacetate to the sprayed aqueous solution was clearly apparent.

(Example 10: Inherence of deodorant)
In Example 6, an aqueous solution containing 0.5% by mass of a 15% aqueous solution of a leaf extract of a camellia plant (NI-Fresca 800MO, manufactured by Shirai Matsushinyaku Co., Ltd.) was changed, and the amount of the aqueous solution supplied was 1.5 g. / Min. The temperature of the water-absorbent resin at the time of supply to the cooler was 205 ° C. No lump or the like was generated in the apparatus, and the substance was discharged from the outlet in a dry state. There was almost no adhesion of the water-absorbing resin into the apparatus. The deodorizing performance of the obtained water absorbent resin was determined by the following method.
After adding 2 g of water-absorbent resin to 50 g of human urine and swelling uniformly, it was allowed to stand in a constant-temperature bath at 40 ° C. for 8 hours, and after removing the odor, the water-absorbing water added with leaf extract of Camellia plant was added. The odor of the swelling of the water-soluble resin due to human urine was significantly reduced as compared with the swelling of the water-absorbing resin to which human swelling was not added.

(Reference example 3: water addition position 30 ° C)
In Example 7, the coolant temperature was changed to 10 ° C, and water was similarly added at a position where the temperature inside the device was 30 ° C.
The temperature of the discharged water absorbent resin was 25 ° C.
As the addition of water was continued, the water-absorbent resin to which the water had been added became a lump (dama), the bulk increased, and the outlet of the cooler was eventually closed. Since the outlet was blocked, the water-absorbent resin to which water had been added was not discharged, making it impossible to continue the operation.

(Reference example 4: water addition position 110 ° C)
In Example 7, water was similarly added at a position where the in-machine temperature was 110 ° C. The water-absorbed resin to which water was added by spraying did not generate lumps (lumps) in the apparatus and was discharged from the outlet in a dry state, but the added water was not absorbed by the water-absorbent resin effectively and volatilized. The inside of the aircraft was significantly condensed. The dust of the water-absorbing resin flying inside the machine adhered to the dewed water, grew with time, dropped off occasionally and was discharged as a large lump, and the outlet was blocked.
The amount of fine powder having a size of 150 μm or less in the obtained water-absorbent resin was 2.0% by mass, and reduction of fine powder was not performed.

FIG. 1 is a cross-sectional view as viewed from the top of a cooler having rotary stirring blades. FIG. 2 is a side view of the cooler of FIG. FIG. 3 is a sectional view taken along line AA of FIG.

Claims (11)

In a method of adding a surface cross-linking agent to a water-absorbent resin powder and performing a heat treatment to perform a surface cross-linking treatment, the water-absorbent resin powder after the heat treatment is stirred and cooled in an air stream. Processing method. In a method of performing a surface crosslinking treatment by adding a surface crosslinking agent to a water-absorbent resin powder and performing a heat treatment, the water-absorbent resin powder after the heat treatment is cooled under an air current, and the fine particles of the water-absorbent resin powder and / or Alternatively, a method for surface crosslinking a water-absorbent resin powder, comprising removing at least a part of a residual surface crosslinking agent. The method according to claim 1 or 2, wherein the treatment amount is 300 kg / hour or more. The method for surface cross-linking a water-absorbent resin powder according to any one of claims 1 to 3, wherein the air-flow is generated by reducing the air flow. A method of performing a surface cross-linking treatment by adding a surface cross-linking agent to the water-absorbent resin powder and performing a heat treatment, comprising a step of cooling the water-absorbent resin powder after the heat cross-linking treatment, wherein the water absorbing property after the heat treatment is included in the step. A method of surface cross-linking a water-absorbent resin powder, comprising granulating the resin powder. The method for cross-linking the surface of a water-absorbent resin powder according to any one of claims 1 to 5, wherein at least one of a heat treatment machine for performing a heat treatment and a cooler for performing a cooling treatment has a downward slope. The method according to any one of claims 1 to 6, wherein an aqueous liquid is added to the water-absorbent resin powder in the cooling treatment. The method for cross-linking the surface of a water-absorbent resin powder according to claim 7, wherein an aqueous liquid is added to the water-absorbent resin powder flowing through a piston at a temperature of 40 to 100C during the cooling process. 9. The method according to claim 7, wherein the addition of the aqueous liquid is performed using one or two or more nozzles selected from nozzles having a one-fluid or two-fluid flat spray, hollow cone, full cone spray pattern. The surface cross-linking treatment method for the water-absorbent resin powder according to the above. The water absorption according to any one of claims 7 to 9, wherein the aqueous liquid contains one or more selected from deodorants, antibacterial agents, coloring agents, chelating agents, inorganic salts, acids, alkalis, and surfactants. Method for surface cross-linking treatment of resin powder. The water absorption according to any one of claims 1 to 10, wherein the cooling process is performed by a low-speed stirring-type cooler provided with a plurality of paddles, and the water-absorbent resin powder flows in a piston flow in the cooler. Method for surface crosslinking treatment of conductive resin powder.