JP2008038128A - Surface crosslinking method for water-absorbing resin and method for producing water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a water-absorbing resin by using a stirring apparatus having a specific structure and a surface-crosslinking method for a water-absorbing resin with shortened treating time in heat-treatment. <P>SOLUTION: The surface-crosslinking method for a water-absorbing resin contains (1) a step to obtain a wet mixture, (2) a step to obtain a dried particulate composition and (3) a step to perform surface-crosslinking reaction. The treating time in each step can be shortened by the method and, accordingly, a water-absorbing resin having good physical properties can be produced in a mass. The method for producing the water-absorbing resin contains a modifying step and a cooling step, the modifying step and/or the cooling step are carried out by using a stirring means having a rotary shaft provided with a plurality of stirring boards, and the stirring means is provided with stirring boards having a specific thickness and/or scraping blades having a specific shape. Generation of fine powder in the modifying step and/or cooling step can be suppressed by the method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface cross-linking method for a water-absorbing resin, and more particularly to a surface cross-linking method for a water-absorbing resin suitable for producing a water-absorbing resin having good physical properties on an industrial scale. The present invention also relates to a method for producing a water-absorbent resin, and more specifically, by performing a reforming step and / or a cooling step using a stirrer having a specific structure, a high quality product with a small amount of fine powder. The present invention relates to a method for producing a water absorbent resin.

  The water-absorbent resin has the property of absorbing a large amount of water, and is a material that constitutes sanitary goods such as disposable diapers, sanitary napkins, incontinence pads, soil water retention agents, water stopping agents, anti-condensation agents, freshness retention agents, solvents Used for dehydrating agents and drip sheets for foods. As described above, since the water-absorbing resin has a wide range of industrial uses, the demand is increasing.

  In particular, sanitary products such as disposable diapers tend to reduce the amount of pulp and increase the amount of water-absorbent resin used to reduce the thickness of the product. Is increasing more and more.

  Conventionally, the water-absorbent resin is given a function of water-insoluble water swellability by slightly cross-linking a hydrophilic polymer (usually cross-linking during polymerization), and is usually produced in a powdery particle form. Examples of the water-absorbing resin include a crosslinked polyacrylic acid partial neutralized product, a hydrolyzate of starch-acrylonitrile copolymer, a neutralized product of starch-acrylic acid graft polymer, and a vinyl acetate-acrylic ester copolymer. Saponified product, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or cross-linked product thereof, carboxymethylcellulose cross-linked product, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) copolymer cross-linked product, polyethylene oxide cross-linked product , Cross-linked polyallylamine, cross-linked polyethyleneimine, and the like are known. However, in recent years, with the improvement in performance of diapers, high functionality of the water-absorbent resin has been demanded, and therefore various improvements have been made to the method for producing the water-absorbent resin. For example, in addition to crosslinking inside the powder, the polymerized resin is further surface-crosslinked (secondary crosslinking) to give a crosslink density gradient between the inside and the surface, so that the water-absorbing resin has a water absorption speed and liquid flow rate. In addition, the absorption capacity under pressure has been improved.

  And in sanitary goods uses, such as the said paper diaper, the water absorbing resin with a high absorption capacity under pressure is desired for thickness reduction of a product. In general, the water-absorbent resin is more preferable as the content of fine powder having a particle size of 150 μm or less is smaller. This is because the fine powder becomes a factor that the liquid permeability decreases due to clogging in a water-absorbing article such as a diaper. Such fine powder is easy to absorb moisture and not only causes clogging in the manufacturing process of the diaper, but is also unfavorable for the user in terms of safety and hygiene.

  As a method for producing a water-absorbent resin with a small amount of fine powder and excellent absorption capacity under pressure, etc., a cross-linking agent is added to the dried water-absorbent resin powder, and when the vicinity of the surface is cross-linked while grinding, a weight average There is a method of using coarse particles of a water-absorbent resin having a particle diameter of 200 to 1000 μm (Patent Document 1). When the water-absorbing resin is formed into a small particle diameter, the water-absorbing resin forms mamako due to contact with the aqueous liquid and the absorption rate decreases, so the particles of the water-absorbing resin powder before surface crosslinking By controlling the diameter to coarse grains and further cross-linking the vicinity of the surface while pulverizing at least a part of the particles, a water absorbing agent with a small amount of fine powder and a high absorption capacity under pressure and liquid permeability under pressure is obtained. is there.

  In addition, when performing surface cross-linking of the water-absorbent resin, a horizontal agitation dryer, rotary dryer, disk dryer, kneading dryer, fluidized bed dryer, aeration dryer, infrared dryer, or the like is used. A method for producing a water-absorbent resin characterized by completing a crosslinking reaction at ˜250 ° C. (Patent Document 2), or adding a surface crosslinking agent to an internally crosslinked polymer prepared to 150 to 850 μm by sieving and using a paddle mixer There is also a method for producing a water-absorbent resin (Patent Document 3) characterized in that surface crosslinking is performed by heating.

  However, the techniques described in Patent Documents 1 to 3 have a problem that many coarse particles (aggregates of the water absorbent resin) remain in the water absorbent resin. If the coarse particles are contained in the water-absorbent resin, the feeling of use of a product such as a diaper is impaired. Therefore, it is necessary to remove the diaper, but it takes time and effort to perform classification. Moreover, it is economically disadvantageous to discard the classified coarse particles. On the other hand, when the coarse particles are crushed, fine powder is generated.

  Therefore, in the step of heating the mixture of the water-absorbent resin and the aqueous solution containing the surface cross-linking agent to complete the surface cross-linking, a solution is provided between the stirrer and the stirrer having the stirrer equipped with the scraper blades. A method of performing surface cross-linking while suppressing the generation of coarse particles by heating using a stirring and drying apparatus provided with a crushing means is disclosed (Patent Document 4).

  In addition, as a method of performing the surface cross-linking treatment of the water-absorbent resin using a stirrer equipped with a stirrer, the stirrer equipped with a stirrer for the purpose of sufficiently exerting the physical property improvement effect by surface cross-linking on an industrial scale There is also disclosed a method for producing a water absorbent resin, characterized in that a water absorbent resin after heat treatment is stirred and cooled under an air stream using a cooling device (Patent Document 5).

  Further, in Patent Document 6, an aqueous liquid containing a surface cross-linking agent is further added to the water-absorbent resin powder obtained through the steps of monomer polymerization, heat drying, cooling, pulverization, etc., and the surface is obtained by heating and drying. A method of crosslinking is disclosed.

Patent Document 7 discloses a method in which heat is further applied to the water-absorbent resin that has been subjected to surface treatment in order to delay free water absorption. Patent Document 8 discloses that the expansion strength under pressure can be increased by repeating the step of mixing and heating the surface treatment agent-containing liquid with the water-absorbent resin twice.
Japanese Patent Laid-Open No. 11-302391 (published on November 2, 1999)) JP-A-4-214734 (published on August 5, 1992)) Japanese translation of PCT publication No. 2002-515079 (published on May 21, 2002) Japanese Patent Laying-Open No. 2004-352941 (Released on December 16, 2004)) Japanese Patent Laying-Open No. 2004-300425 (released on October 28, 2004)) JP 2002-121291 A (published April 23, 2002)) Special table 2003-503554 gazette (published January 28, 2003) Japanese Patent No. 2847113 (Registered on November 6, 1998, Publication Number: National Publication No. 9-502221 (announced on March 4, 1997))

  As described in Patent Documents 4 and 5, conventionally, when the functionality of the water-absorbent resin is improved by surface treatment, from the viewpoint of improving the mixing property, a stirring / drying apparatus equipped with a stirring plate, It has been considered effective to use a stirring device such as a cooling device. On the other hand, when using a stirrer like the technique described in the said patent documents 4 and 5, the problem that much fine powder generate | occur | produces still during a surface crosslinking process is confirmed. When a large amount of fine powder is generated, the surface cross-linked layer tends to be destroyed, which also adversely affects the physical properties of the water-absorbent resin.

  It is considered that the above problem is caused by the shape of the stirring plate not being an appropriate shape for stirring the hydrophilic cross-linked polymer. That is, in the prior art, the stirrer is used for improving the mixing property, and the shape is determined from the viewpoint of improving the mixing property, and the idea of using the stirrer for suppressing the generation of fine powder has not been made conventionally. . That is, the shape of the stirring board is not determined based on the viewpoint of suppressing the generation of fine powder.

  For example, the stirrer used in the prior art has a large difference between the maximum thickness and the minimum thickness of the stirrer, so that excessive pressure is applied to the powder when biting into the powder of the hydrophilic crosslinked polymer. As a result of the powder being compressed, there is a problem that the density of the powder is increased, and the water-absorbent resin is mechanically damaged during the surface cross-linking treatment, resulting in an increase in the amount of fine powder.

  In addition, while increasing the functionality of water-absorbent resins, there has also been a problem of how to efficiently mass-produce water-absorbent resins without compromising performance in order to meet the increasing demand for water-absorbent resins in recent years. It was. However, as in Patent Documents 7 and 8, a method for improving functionality by surface treatment has been proposed, but water absorption by a heat treatment apparatus equipped with a stirring blade is a concern at the time of scale-up of water absorbent resin production. The deterioration of physical properties due to damage to the functional resin has not been studied so far from the viewpoint of surface treatment.

  Here, as a method of increasing the production amount of the water-absorbent resin, it is conceivable to use a heat treatment device obtained by simply increasing the size of the current heat treatment device. The area becomes smaller. Therefore, in order to maintain the temperature of the water absorbent resin within a certain range and cause a desired surface crosslinking reaction, it is necessary to lengthen the residence time of the water absorbent resin in the apparatus. If the time during which the water-absorbing resin is stirred by the stirrer becomes longer during the surface cross-linking treatment, the water-absorbing resin is mechanically damaged accordingly. As a result, the amount of fine powder increases, causing a problem that the physical properties of the water-absorbent resin are lowered.

  That is, there is no knowledge regarding what kind of stirring device can be used to suppress the generation of fine powder and to produce a high-performance water-absorbent resin.

  In order to avoid the generation of fine powder due to the increase in the size of the apparatus and the problem that the physical properties deteriorate due to the generation, it is simply necessary to arrange a plurality of small heat treatment apparatuses in parallel. However, when a plurality of heat treatment apparatuses are arranged, the number of auxiliary devices before and after and the number of pipes increase, resulting in a large cost increase. In addition, it takes time and effort to control a plurality of heat treatment apparatuses, resulting in poor efficiency.

  Therefore, development of a method for surface cross-linking of a water-absorbent resin that efficiently performs mass production of water-absorbent resin on an industrial scale and maintains performance is required.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to stir the reforming step and / or the cooling step with a specific structure in order to produce a water-absorbing resin having good physical properties with a small amount of fine powder. In order to provide a method for producing a water-absorbent resin using an apparatus and to produce a water-absorbent resin having good physical properties with a small amount of fine powder, when the scale-up of the water-absorbent resin production is performed, heat treatment is performed. It is an object of the present invention to provide a surface cross-linking method for a water-absorbent resin in which the treatment time is shortened.

  As a result of intensive studies focusing on the structure of the stirring device used for the surface cross-linking treatment of the water-absorbent resin, the inventors have conducted the reforming step and / or the cooling step using a stirring device having a specific structure. When performing surface cross-linking of the water-absorbent resin, it is possible to optimize the stirring conditions and temperature conditions in each step by performing the stirring and drying step and the surface cross-linking step included in the modification step as different steps. Therefore, the treatment time of heat treatment can be shortened, and as a result, damage to the water absorbent resin can be reduced, and a water absorbent resin with a small amount of fine powder can be produced without reducing the production amount. The headline and the present invention were completed.

  That is, the method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is performed using a stirring means having a rotating shaft provided with a plurality of stirring plates, the direction parallel to the major axis length direction of the rotating shaft is the y direction, the direction orthogonal to the y direction, When the direction parallel to the axial diameter direction of the rotation axis is the x direction and the direction perpendicular to the x direction and the y direction is the z direction, the stirring plate is a cross section obtained by cutting the stirring means along the yz plane. Maximum thickness It is characterized in that the ratio of the minimum thickness is less than 5%.

  According to the above configuration, since a plurality of stirrers having a relatively uniform thickness with a ratio of the maximum thickness to the minimum thickness of 5 or less are used, the pressure per cross-sectional area of the stirrer applied to the hydrophilic crosslinked polymer Since the friction generated between the stirring plate and the hydrophilic cross-linked polymer can be reduced, the mechanical damage given to the hydrophilic cross-linked polymer is reduced and uniform. Can be stirred. Accordingly, it is possible to produce a water absorbent resin with a small amount of fine powder.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is carried out using a stirring means having a rotating shaft provided with a plurality of stirring plates equipped with scraping blades, and the direction parallel to the longitudinal direction of the rotating shaft is the y direction, and the direction perpendicular to the y direction. In the cross section obtained by cutting the stirring means along the yz plane when the direction parallel to the axial diameter direction of the rotating shaft is the x direction and the direction perpendicular to the x direction and the y direction is the z direction. the above The cross-sectional area of the lifting blade is not less than 10% and less than 50% of the area between the stirring plate of one stirring plate protruding the lifting blade and the other stirring plate disposed relative to the stirring plate. And the length in the y direction of the lifting blade in the section cut along the yz plane is 50% or more of the distance between the stirring plates of the one stirring plate and the other stirring plate. It is a feature.

  When using a stirring / drying device or a stirring / cooling device used in the prior art, the hydrophilic crosslinked polymer is excessively compressed as the stirring of the hydrophilic crosslinked polymer is continued. There is a problem that the coalescence is mechanically damaged and fine powder is generated, but according to the above configuration, the cross-sectional area and length of the lifting blade provided on the stirring board are adjusted to the above range. The hydrophilic crosslinked polymer can be stirred in a floating state without being excessively compressed, and aggregation and compression of the hydrophilic crosslinked polymer can be prevented, so that the mixture of the hydrophilic crosslinked polymer and the aqueous solution can be uniformly formed. The generation of fine powder can be suppressed.

  Therefore, a water-absorbing resin with a small amount of fine powder can be produced. Further, since it is difficult to apply pressure to the hydrophilic crosslinked polymer and the compressibility of the hydrophilic crosslinked polymer can be reduced, the hydrophilic crosslinked polymer can be stirred with less stirring power, and produced. Efficiency can be improved.

  Moreover, the surface cross-linking method of the water-absorbent resin according to the present invention comprises a step (1) of mixing a solution containing a surface cross-linking agent and a water-absorbent resin precursor to obtain a wet mixture, and stirring and drying the wet mixture. And (2) including a step (2) of obtaining a dry particulate composition containing a surface cross-linking agent, and a step (3) of subjecting the dry particulate composition to a surface cross-linking reaction by heat treatment. 80% by weight or more of the dry particulate composition is particles that pass through a sieve having an opening of 10 mm, and each of the steps (2) and (3) is performed using at least one processing apparatus. The processing apparatus used for the step (2) and the processing apparatus used for the step (3) are connected in series.

  According to the said structure, in order to suppress the aggregation of the particle | grains which occur when processing the said wet mixture, the dry particulate composition obtained becomes powder with good fluidity | liquidity by stirring and drying. Therefore, in the surface cross-linking reaction step, the surface cross-linking can be performed to a desired level even with an apparatus without weak stirring or stirring blades. Therefore, there is an effect that a water-absorbing resin having good physical properties can be produced stably.

  Moreover, in the surface cross-linking method of the water-absorbent resin according to the present invention, the processing device used in the step (2) and the processing device used in the step (3) are processing devices having different types and / or effective volumes. Preferably there is.

  According to the above configuration, it is possible to select a processing apparatus that is optimal for the properties of the water-absorbing resin to be manufactured and / or a processing apparatus that is optimal for each of the steps (2) and (3). it can.

  That is, for example, in the above step (2), a processing apparatus having a large heat transfer area / effective volume and having multiple axes and a plurality of stirring plates on the axis is used in order to increase the stirring force. it can. Further, for example, in the step (3), a processing apparatus having a small heat transfer area / effective volume and having a gentle stirring force because it does not include a stirring board can be used.

  As a result, in the step (2), the stirring efficiency is improved and the average heating rate is increased, and the wet mixture can be rapidly stirred and dried. Moreover, in the said process (3), the damage which a water-absorbent resin receives by gentle stirring also decreases, and it prevents the pulverization of a water-absorbent resin by controlling an average temperature increase rate, and controls a surface crosslinking density. be able to. Therefore, it is possible to stably produce a water absorbent resin having good physical properties.

  In the surface cross-linking method for the water-absorbent resin, the processing apparatus used in the step (2) and the processing apparatus used in the step (3) may be operated under different heating conditions and / or different stirring conditions. preferable.

  According to the above configuration, the heating conditions and / or the stirring conditions are values corresponding to the properties of the water-absorbing resin to be produced and / or values corresponding to each of the steps (2) and (3). Can be adjusted optimally.

  That is, for example, in the above step (2), the specifications of the heat source and the set temperature of the processing apparatus to be used are adjusted so as to increase the average rate of temperature rise, and the stirring plate is adjusted to a strong stirring force. . Further, for example, in the step (3), the processing apparatus used is adjusted such that the specifications and set temperature of the heat source are reduced so that the average rate of temperature increase is slow, or the stirring plate is adjusted to a thing with a small stirring force. .

  As a result, in the step (2), the stirring efficiency is improved and the average heating rate is increased, and the wet mixture can be rapidly stirred and dried. Moreover, in the said process (3), the damage which a water-absorbent resin receives by gentle stirring also decreases, and it prevents the pulverization of a water-absorbent resin by controlling an average temperature increase rate, and controls a surface crosslinking density. be able to. Therefore, it is possible to stably produce a water absorbent resin having good physical properties.

  Moreover, in order to solve the above-mentioned problem, the surface cross-linking method of the water-absorbent resin according to the present invention includes a step (1) of mixing a solution containing a surface cross-linking agent and a water-absorbent resin precursor to obtain a wet mixture, The wet mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent (2), and the dry particulate composition is subjected to a surface crosslinking reaction by heat treatment (3), 80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm, and the steps (2) and (3) are performed in one processing apparatus. And the step (2) and the step (3) are performed under different heating conditions and / or different stirring conditions.

  According to the said structure, it becomes possible to set the stirring conditions and temperature suitable for the property of powder for the said process (2) and the said process (3). As a result, the heat treatment time can be shortened. Therefore, damage to the water absorbent resin is reduced, and an effect is obtained that a water absorbent resin having good physical properties can be obtained without reducing the production amount.

  Further, by performing the step (2) and the step (3) in one processing apparatus, it is possible to avoid problems such as cost increase and space expansion due to an increase in the number of apparatuses.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, wherein the mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent; and the dried particulate form A modification step including a step (3) of subjecting the composition to a heat treatment to cause a surface cross-linking reaction, and a cooling step of cooling the hydrophilic cross-linked polymer subjected to the surface cross-linking. ) And at least one of the cooling steps is performed using a processing apparatus including a stirring unit having a rotating shaft provided with a plurality of stirring plates, and a direction parallel to the major axis length direction of the rotating shaft is set. y direction, above When the direction perpendicular to the direction and parallel to the axial diameter direction of the rotating shaft is the x direction, and the direction perpendicular to the x direction and the y direction is the z direction, the stirring plate is the stirring means. In the cross section taken along the yz plane, the ratio of the maximum thickness to the minimum thickness is 5 or less, and the above mixture contains a hydrophilic cross-linked polymer having a carboxyl group and a functional group capable of reacting with the carboxyl group. It is a wet mixture produced by the step (1) of mixing with an aqueous solution containing two or more surface cross-linking agents, and 80% by weight or more of the dry particulate composition obtained in the above step (2) A particle that passes through a sieve having an opening of 10 mm, and each of the steps (2) and (3) is performed using at least one processing device, and the processing device used in the step (2); For step (3) That the processing unit and has been characterized by being connected in series.

  According to the said structure, the stirring means which has a rotating shaft provided with the stirring board of the said shape can be used for at least 1 process or more in said process (2), process (3), and cooling process.

  Therefore, in the process of the said modification | reformation process and / or cooling process, it can stir uniformly, making the mechanical damage given to the said hydrophilic crosslinked polymer small. Furthermore, in the step (2), the dried particulate composition obtained becomes a powder with good fluidity by stirring and drying in order to suppress aggregation of particles that occurs when the wet mixture is processed. And in the said process (3), surface bridge | crosslinking can be performed to a desired grade with the apparatus without weak stirring or a stirring blade.

  As a result, it is possible to reduce mechanical damage and shorten the heat treatment time.

  Accordingly, it is possible to efficiently produce a water absorbent resin having good properties with a small amount of fine powder.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, wherein the mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent; and the dried particulate form A modification step including a step (3) of subjecting the composition to a heat treatment to cause a surface cross-linking reaction, and a cooling step of cooling the hydrophilic cross-linked polymer subjected to the surface cross-linking. ) And at least one of the cooling steps is performed using a processing apparatus having a stirring means having a rotating shaft provided with a plurality of stirring plates provided with scraping blades, and the major axis length direction of the rotating shaft And flat When the right direction is the y direction, the direction perpendicular to the y direction, the direction parallel to the axial direction of the rotation axis is the x direction, and the direction perpendicular to the x direction and the y direction is the z direction, A cross-sectional area of the lifting blade in a cross section obtained by cutting the stirring means along the yz plane, one stirring plate in which the lifting blade protrudes, and another stirring plate disposed relative to the stirring plate; Occupying 10% or more and less than 50% of the area in the yz plane between and the length in the y direction of the scraping blade in the cross section cut by the yz plane is 50% or more of the distance in the yz plane between the other stirring plates, and the mixture includes a hydrophilic cross-linked polymer having a carboxyl group and two or more functional groups capable of reacting with the carboxyl group. Contains surface cross-linking agent 80% by weight or more of the dry particulate composition obtained in the above step (2) is particles that pass through a sieve having an opening of 10 mm. Each of the steps (2) and (3) is performed using at least one processing apparatus, the processing apparatus used for the step (2), and the processing apparatus used for the step (3). Are connected in series.

  According to the said structure, the stirring means which has a rotating shaft provided with the several stirring board which comprises the said shape raising blade in at least 1 process or more in said process (2), process (3), and cooling process. Can be used. Therefore, in the process of the modification step and / or the cooling step, the hydrophilic cross-linked polymer and / or the water-absorbing resin can be stirred uniformly in a floating state. Furthermore, in the step (2), the dried particulate composition obtained becomes a powder with good fluidity by stirring and drying in order to suppress aggregation of particles that occurs when the wet mixture is processed. And in the said process (3), surface bridge | crosslinking can be performed to a desired grade with the apparatus without weak stirring or a stirring blade.

  As a result, reduction of mechanical damage, energy saving of stirring power, and shortening of heat treatment time can be realized. Accordingly, it is possible to efficiently produce a water absorbent resin having good properties with a small amount of fine powder.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is performed using a processing apparatus having a stirring means having a rotating shaft provided with a plurality of stirring plates, and a direction parallel to the major axis length direction of the rotating shaft is the y direction, and a direction orthogonal to the y direction. When the direction parallel to the axial diameter direction of the rotating shaft is the x direction and the direction perpendicular to the x direction and the y direction is the z direction, the stirrer moves the stirring means to the yz plane. In the cross section cut by The ratio of the maximum thickness to the minimum thickness is 5 or less, and the mixture comprises a hydrophilic cross-linked polymer having a carboxyl group and a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A wet mixture produced by the step (1) of mixing with the aqueous solution containing the step, wherein the modifying step comprises stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent (2 ) And a step (3) of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment, and 80% by weight or more of the dry particulate composition obtained in the step (2) has an opening of 10 mm. The particles pass through a sieve, and the steps (2) and (3) are performed in one processing apparatus, and the steps (2) and (3) are performed under different heating conditions and / or different stirring conditions. As a feature to do That.

  According to the said structure, the said modification | reformation process and / or a cooling process are performed using the stirring means which has a rotating shaft provided with the stirring board of the said shape, The said process (2) included in the said modification | reformation process, The above step (3) can be performed by one processing apparatus. Moreover, the stirring conditions and / or temperature conditions relating to the step (2) and the step (3) can be set so as to be optimal for each step.

  Therefore, in the process of the said modification | reformation process and / or cooling process, it can stir uniformly, making the mechanical damage given to the said hydrophilic crosslinked polymer small. Furthermore, it becomes possible to set the stirring conditions and temperature suitable for the properties of the powder in the step (2) and the step (3).

  As a result, it is possible to reduce mechanical damage and shorten the heat treatment time. Therefore, there is an effect that a water-absorbing resin having good physical properties can be obtained.

  Further, by performing the processing within one processing apparatus, it is possible to avoid problems such as an increase in cost and an increase in space due to an increase in the number of apparatuses.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is performed using a processing apparatus having a stirring means having a rotating shaft provided with a plurality of stirring plates each having a scraping blade, wherein the direction parallel to the longitudinal direction of the rotating shaft is the y direction, and the y When the x direction is a direction perpendicular to the axial direction of the rotation axis and the z direction is a direction perpendicular to the x direction and the y direction, the agitating means is a yz plane. Cut with The cross-sectional area of the lifting blade in the cross section is the area in the yz plane between one stirring plate from which the lifting blade protrudes and the other stirring plate disposed relative to the stirring plate. 10% or more and less than 50%, and the length in the y direction of the scraping blade in the cross section cut along the yz plane is the y− between the one stirring plate and the other stirring plate. The mixture is 50% or more of the distance in the z plane, and the mixture includes a hydrophilic cross-linked polymer having a carboxyl group, and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A wet mixture produced by the step (1) of mixing the step, wherein the modifying step comprises stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent, and the drying Particulate composition 80% by weight or more of the dry particulate composition obtained in the step (2) is a particle that passes through a sieve having an aperture of 10 mm, The step (2) and the step (3) are performed in one processing apparatus, and the step (2) and the step (3) are performed under different heating conditions and / or different stirring conditions.

  According to the above configuration, the reforming step and / or the cooling step is performed using a processing apparatus including a stirring unit having a rotating shaft including a plurality of stirring plates each including a scraping blade having the shape described above. The step (2) and the step (3) included in the reforming step can be performed with one processing apparatus. Moreover, the stirring conditions and / or temperature conditions relating to the step (2) and the step (3) can be set so as to be optimal for each step.

  Therefore, in the process of the modification step and / or the cooling step, the hydrophilic cross-linked polymer and / or the water-absorbing resin can be stirred uniformly in a floating state. Furthermore, it becomes possible to set the stirring conditions and temperature suitable for the normal style of the step (2) and the step (3).

  As a result, reduction of mechanical damage, energy saving of stirring power, and shortening of heat treatment time can be realized. Accordingly, it is possible to efficiently produce a water absorbent resin having good properties with a small amount of fine powder.

  Further, by performing the processing within one processing apparatus, it is possible to avoid problems such as an increase in cost and an increase in space due to an increase in the number of apparatuses.

  Moreover, the manufacturing method of the water absorbing resin which concerns on this invention is a processing apparatus from which the processing apparatus used for the said process (2) and the processing apparatus used for the said process (3) differ in kind and / or effective volume. Is preferred.

  According to the said structure, the processing apparatus with which the value of the stirring force of this stirring means and / or the temperature to add, and a heat-transfer area / effective volume is suitable for each process can be selected.

  Therefore, the stirring and drying efficiency in the step (2) and / or the surface crosslinking efficiency in the step (3) can be improved. As a result, it is possible to reduce the damage to the hydrophilic cross-linked polymer and / or the water-absorbent resin in each step and to shorten the time required for each step, and to produce a high-quality water-absorbent resin. Can do.

  Moreover, the manufacturing method of the water absorbing resin which concerns on this invention operates the processing apparatus used for the said process (2), and the processing apparatus used for the said process (3) on different heating conditions and / or different stirring conditions. Is preferred.

  According to the said structure, the value of the stirring force of this stirring means and / or the temperature to add, and a heat-transfer area / effective volume can be set according to each process.

  Therefore, the stirring and drying efficiency in the step (2) and / or the surface crosslinking efficiency in the step (3) can be improved. As a result, it is possible to reduce the damage to the hydrophilic cross-linked polymer and / or the water-absorbent resin in each step and to shorten the time required for each step, and to produce a high-quality water-absorbing back resin. Can do.

  In the method for producing a water-absorbent resin according to the present invention, a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is carried out by using a stirring means having a rotating shaft provided with a stirring plate equipped with scraping blades, and the direction parallel to the longitudinal direction of the rotating shaft is the y direction, and the direction perpendicular to the y direction. Then, when the direction parallel to the axial diameter direction of the rotating shaft is the x direction, and the direction orthogonal to the x direction and the y direction is the z direction, the stirrer is cut in the section taken along the yz plane. 10% or more of the area in the yz plane between the one stirring plate from which the lifting blade protrudes and the other stirring plate disposed relative to the stirring plate. The length in the y direction of the lifting blade in the cross section occupying less than 50% and cut in the yz plane is in the yz plane between the one stirring plate and the other stirring plate. It is preferable that the ratio of the maximum thickness to the minimum thickness is 5 or less in a cross section obtained by cutting the stirring means along the yz plane.

  According to the above configuration, since the cross-sectional area and the length of the lifting blade provided on the stirring board are adjusted to the above range, the hydrophilic crosslinked polymer is stirred in a floating state without being excessively compressed. It is possible to prevent aggregation and compression of the hydrophilic cross-linked polymer. Therefore, generation of fine powder can be suppressed. Further, since a stirrer having a relatively uniform thickness with a ratio of maximum thickness to minimum thickness of 5 or less is used, the compression and release applied to the hydrophilic cross-linked polymer per cross-sectional area of the stirrer is very small. The mechanical damage given to the hydrophilic crosslinked polymer can be reduced. Therefore, it is possible to produce a water-absorbent resin with a smaller amount of fine powder.

  Further, in the method for producing a water-absorbent resin according to the present invention, the scraping blades straddle a plurality of stirring boards, and among the scraping blades, the scraping blades that are present at adjacent positions make the stirring means y- In a cross section cut along the z plane, it is preferable that the rotating shafts are alternately arranged or connected in parallel.

  According to the above-described configuration, the cross-sectional area of the lifting blade is determined by the y-between one stirring plate projecting or connecting the lifting blade and the other stirring plate disposed relative to the stirring plate. It is possible to increase the area in the z plane (hereinafter referred to as “the area between the stirring plates”) and to increase the length of the scraping blade.

  Further, since the scraping blade is firmly fixed to the stirring board, the durability of the scraping blade can be increased. Therefore, stirring efficiency and powder transportability can be improved, and uniform surface crosslinking can be performed. Therefore, it is possible to produce a water-absorbent resin with a smaller amount of fine powder.

  Moreover, in the manufacturing method of the water absorbing resin which concerns on this invention, it is preferable that the said stirring disk is a disk shape or the disk shape from which one part was missing.

  According to the above configuration, for example, the pressure applied to the hydrophilic crosslinked polymer when stirring the hydrophilic crosslinked polymer can be reduced as compared with the case where the stirring plate is wedge-shaped. The powder density can be reduced. Therefore, a water-absorbing resin with a small amount of fine powder can be produced more efficiently.

  In the method for producing a water absorbent resin according to the present invention, it is preferable that the agitation means also acts as a heat transfer means.

  In order to crosslink the surface of the hydrophilic crosslinked polymer, a mixture of a hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. Need to be heated.

  According to the above configuration, the stirring unit is configured to be able to stir without causing mechanical damage to the hydrophilic crosslinked polymer, or to be stirred uniformly, and further acts as a heat transfer unit. Therefore, heat required for the crosslinking reaction can be uniformly conducted to the mixture while suppressing generation of fine powder. Accordingly, the crosslinking reaction can be efficiently performed and the modification time can be shortened, so that a water-absorbing resin with a small amount of fine powder can be efficiently produced.

  In addition, when the stirrer is disk-shaped or partly missing, the heat transfer area can be increased compared to, for example, a case where the stirrer is wedge-shaped, so that the efficiency of the crosslinking reaction is improved. be able to.

  Furthermore, since it is not necessary to provide a heat transfer means separately, it can contribute to size reduction of a water absorbing resin manufacturing apparatus.

  In the method for producing a water-absorbent resin according to the present invention, it is preferable that the agitation means also acts as a cooling means.

  According to the above configuration, the stirring means can be cooled while stirring uniformly without causing mechanical damage to the surface-crosslinked hydrophilic cross-linked polymer, thereby suppressing the generation of fine powder in the cooling step. And the entire hydrophilic crosslinked polymer can be uniformly cooled. Therefore, a water-absorbing resin with a small amount of fine powder can be produced without excessive surface crosslinking. Moreover, since it is not necessary to provide a cooling means separately, it can contribute to size reduction of a water absorbing resin manufacturing apparatus.

  As described above, the method for producing a water-absorbent resin according to the present invention includes a hydrophilic cross-linked polymer having a carboxyl group, and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A step of cross-linking the surface of the hydrophilic cross-linked polymer by heating the mixture, and a step of cooling the cross-linked hydrophilic cross-linked polymer. Alternatively, the cooling step is performed by using a stirring means having a rotating shaft provided with a plurality of stirring plates, and the direction parallel to the major axis length direction of the rotating shaft is a direction perpendicular to the y direction. When the direction parallel to the axial diameter direction of the rotating shaft is the x direction and the direction orthogonal to the x direction and the y direction is the z direction, the stirring plate cuts the stirring means along the yz plane. In the cross section The ratio to the minimum thickness of the thickness is 5 or less, a configuration called.

  Therefore, the compression and release applied to the hydrophilic cross-linked polymer per cross-sectional area of the stirring plate can be greatly reduced, and the mechanical damage given to the hydrophilic cross-linked polymer is reduced while being uniform. Since it can stir, there exists an effect that water-absorbing resin with little amount of fine powder can be manufactured.

  In addition, as described above, the method for producing a water-absorbent resin according to the present invention includes a hydrophilic cross-linked polymer having a carboxyl group and a surface cross-linking agent having two or more functional groups capable of reacting with a carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating the mixture with the solution, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step And / or the cooling step is performed using a stirring means having a rotating shaft provided with a plurality of stirring plates equipped with scraping blades, and the direction parallel to the longitudinal direction of the rotating shaft is the y direction, and the y When the x direction is a direction perpendicular to the axial direction of the rotation axis and the z direction is a direction perpendicular to the x direction and the y direction, the agitating means is a yz plane. Disconnected with The cross-sectional area of the lifting blade is 10 of the area in the yz plane between one stirring plate from which the lifting blade protrudes and the other stirring plate disposed relative to the stirring plate. % In the cross-section cut by the yz plane, the length in the y direction of the lifting blade is the yz between the one stirring plate and the other stirring plate. The configuration is that it is 50% or more of the distance in the plane.

  Therefore, the hydrophilic cross-linked polymer can be uniformly stirred without being excessively compressed, and the water-absorbent resin having a small amount of fine powder can be efficiently prevented from being generated in the reforming step and can be efficiently prevented. There is an effect that can be manufactured.

  Further, the surface cross-linking method of the water-absorbent resin according to the present invention includes a step (1) of mixing a solution containing a surface cross-linking agent and a water-absorbent resin precursor to obtain a wet mixture, and stirring and drying the wet mixture. And (2) including a step (2) of obtaining a dry particulate composition containing a surface cross-linking agent, and a step (3) of subjecting the dry particulate composition to a surface cross-linking reaction by heat treatment. 80% by weight or more of the dry particulate composition is particles that pass through a sieve having an opening of 10 mm, and each of the steps (2) and (3) is performed using at least one processing apparatus. The processing apparatus used in the step (2) and the processing apparatus used in the step (3) are connected in series.

  In order to suppress the aggregation of particles that occurs when the wet mixture is treated, the resulting dried particulate composition becomes a powder having good fluidity by stirring and drying. Therefore, in the surface cross-linking reaction step, the surface cross-linking can be performed to a desired level even with an apparatus without weak stirring or stirring blades. Therefore, the surface cross-linking method for a water-absorbent resin according to the present invention has an effect that a water-absorbent resin having good physical properties can be produced stably.

  Moreover, since the surface crosslinking method of the water absorbent resin according to the present invention can select efficient heating conditions and / or stirring conditions in each step, the residence time in the heat treatment apparatus is shortened. Therefore, there is an effect of improving the productivity of the water absorbent resin.

  Further, the surface cross-linking method of the water-absorbent resin according to the present invention includes a step (1) of mixing a solution containing a surface cross-linking agent and a water-absorbent resin precursor to obtain a wet mixture, and stirring and drying the wet mixture. And (2) including a step (2) of obtaining a dry particulate composition containing a surface cross-linking agent, and a step (3) of subjecting the dry particulate composition to a surface cross-linking reaction by heat treatment. 80% by weight or more of the dry particulate composition is particles that pass through a sieve having an opening of 10 mm, and the above steps (2) and (3) are performed in one processing apparatus, and the above steps (2) and (2) are performed. It is the structure of performing a process (3) on different heating conditions and / or different stirring conditions.

  In order to suppress the aggregation of particles that occurs when the wet mixture is treated, the resulting dried particulate composition becomes a powder having good fluidity by stirring and drying. Therefore, in the surface cross-linking reaction step, the surface cross-linking can be performed to a desired level even with an apparatus without weak stirring or stirring blades. Therefore, the surface cross-linking method for a water-absorbent resin according to the present invention has an effect that a water-absorbent resin having good physical properties can be produced stably.

  Moreover, it becomes possible to set the stirring conditions and temperature suitable for the properties of the powder in the step (2) and the step (3). As a result, the heat treatment time can be shortened. Therefore, damage to the water absorbent resin is reduced, and an effect is obtained that a water absorbent resin having good physical properties can be obtained without reducing the production amount.

  Further, by performing the step (2) and the step (3) in one processing apparatus, it is possible to avoid problems such as cost increase and space expansion due to an increase in the number of apparatuses.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, wherein the mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent; and the dried particulate form A modification step including a step (3) of subjecting the composition to a heat treatment to cause a surface cross-linking reaction, and a cooling step of cooling the hydrophilic cross-linked polymer subjected to the surface cross-linking. ) And at least one of the cooling steps is performed using a processing apparatus including a stirring unit having a rotating shaft provided with a plurality of stirring plates, and a direction parallel to the major axis length direction of the rotating shaft is set. y direction, above When the direction perpendicular to the direction and parallel to the axial diameter direction of the rotating shaft is the x direction, and the direction perpendicular to the x direction and the y direction is the z direction, the stirring plate is the stirring means. In the cross section taken along the yz plane, the ratio of the maximum thickness to the minimum thickness is 5 or less, and the above mixture contains a hydrophilic cross-linked polymer having a carboxyl group and a functional group capable of reacting with the carboxyl group. It is a wet mixture produced by the step (1) of mixing with an aqueous solution containing two or more surface cross-linking agents, and 80% by weight or more of the dry particulate composition obtained in the above step (2) A particle that passes through a sieve having an opening of 10 mm, and each of the steps (2) and (3) is performed using at least one processing device, and the processing device used in the step (2); For step (3) That the processing unit and is coupled in series, a configuration called.

  According to the said structure, the stirring means which has a rotating shaft provided with the stirring board of the said shape can be used for at least 1 process or more in said process (2), process (3), and cooling process.

  Therefore, in the process of the said modification | reformation process and / or cooling process, it can stir uniformly, making the mechanical damage given to the said hydrophilic crosslinked polymer small. Furthermore, in the step (2), the dried particulate composition obtained becomes a powder with good fluidity by stirring and drying in order to suppress aggregation of particles that occurs when the wet mixture is processed. And in the said process (3), surface bridge | crosslinking can be performed to a desired grade with the apparatus without weak stirring or a stirring blade.

  As a result, it is possible to reduce mechanical damage and shorten the heat treatment time.

  Therefore, there is an effect that it is possible to efficiently produce a water absorbent resin having good properties with a small amount of fine powder.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, wherein the mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent; and the dried particulate form A modification step including a step (3) of subjecting the composition to a heat treatment to cause a surface cross-linking reaction, and a cooling step of cooling the hydrophilic cross-linked polymer subjected to the surface cross-linking. ) And at least one of the cooling steps is performed using a processing apparatus having a stirring means having a rotating shaft provided with a plurality of stirring plates provided with scraping blades, and the major axis length direction of the rotating shaft And flat When the right direction is the y direction, the direction perpendicular to the y direction, the direction parallel to the axial direction of the rotation axis is the x direction, and the direction perpendicular to the x direction and the y direction is the z direction, A cross-sectional area of the lifting blade in a cross section obtained by cutting the stirring means along the yz plane, one stirring plate in which the lifting blade protrudes, and another stirring plate disposed relative to the stirring plate; Occupying 10% or more and less than 50% of the area in the yz plane between and the length in the y direction of the scraping blade in the cross section cut by the yz plane is 50% or more of the distance in the yz plane between the other stirring plates, and the mixture includes a hydrophilic cross-linked polymer having a carboxyl group and two or more functional groups capable of reacting with the carboxyl group. Contains surface cross-linking agent 80% by weight or more of the dry particulate composition obtained in the above step (2) is particles that pass through a sieve having an opening of 10 mm. Each of the steps (2) and (3) is performed using at least one processing apparatus, the processing apparatus used for the step (2), and the processing apparatus used for the step (3). Are connected in series.

  According to the said structure, the stirring means which has a rotating shaft provided with the several stirring board which comprises the said shape raising blade in at least 1 process or more in said process (2), process (3), and cooling process. Can be used. Therefore, in the process of the modification step and / or the cooling step, the hydrophilic cross-linked polymer and / or the water-absorbing resin can be stirred uniformly in a floating state. Furthermore, in the step (2), the dried particulate composition obtained becomes a powder with good fluidity by stirring and drying in order to suppress aggregation of particles that occurs when the wet mixture is processed. And in the said process (3), surface bridge | crosslinking can be performed to a desired grade with the apparatus without weak stirring or a stirring blade.

  As a result, reduction of mechanical damage, energy saving of stirring power, and shortening of heat treatment time can be realized. Therefore, there is an effect that it is possible to efficiently produce a water absorbent resin having good properties with a small amount of fine powder.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is performed using a processing apparatus having a stirring means having a rotating shaft provided with a plurality of stirring plates, and a direction parallel to the major axis length direction of the rotating shaft is the y direction, and a direction orthogonal to the y direction. When the direction parallel to the axial diameter direction of the rotating shaft is the x direction and the direction perpendicular to the x direction and the y direction is the z direction, the stirrer moves the stirring means to the yz plane. In the cross section cut by The ratio of the maximum thickness to the minimum thickness is 5 or less, and the mixture comprises a hydrophilic cross-linked polymer having a carboxyl group and a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A wet mixture produced by the step (1) of mixing with the aqueous solution containing the step, wherein the modifying step comprises stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent (2 ) And a step (3) of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment, and 80% by weight or more of the dry particulate composition obtained in the step (2) has an opening of 10 mm. The particles pass through a sieve, and the steps (2) and (3) are performed in one processing apparatus, and the steps (2) and (3) are performed under different heating conditions and / or different stirring conditions. To do .

  According to the said structure, the said modification | reformation process and / or a cooling process are performed using the stirring means which has a rotating shaft provided with the stirring board of the said shape, The said process (2) included in the said modification | reformation process, The above step (3) can be performed by one processing apparatus. Moreover, the stirring conditions and / or temperature conditions relating to the step (2) and the step (3) can be set so as to be optimal for each step.

  Therefore, in the process of the said modification | reformation process and / or cooling process, it can stir uniformly, making the mechanical damage given to the said hydrophilic crosslinked polymer small. Furthermore, it becomes possible to set the stirring conditions and temperature suitable for the properties of the powder in the step (2) and the step (3).

  As a result, it is possible to reduce mechanical damage and shorten the heat treatment time. Therefore, there is an effect that a water-absorbing resin having good physical properties can be obtained.

  In addition, by performing the processing within one processing apparatus, there is an effect that problems such as an increase in cost and an increase in space due to an increase in the number of apparatuses can be avoided.

  The method for producing a water-absorbent resin according to the present invention comprises a mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A modification step that is a step of crosslinking the surface of the hydrophilic crosslinked polymer by heating, and a cooling step of cooling the hydrophilic crosslinked polymer that has been surface-crosslinked, and the modification step and / or the cooling step Is performed using a processing apparatus having a stirring means having a rotating shaft provided with a plurality of stirring plates each having a scraping blade, wherein the direction parallel to the longitudinal direction of the rotating shaft is the y direction, and the y When the x direction is a direction perpendicular to the axial direction of the rotation axis and the z direction is a direction perpendicular to the x direction and the y direction, the agitating means is a yz plane. Cut with The cross-sectional area of the lifting blade in the cross section is the area in the yz plane between one stirring plate from which the lifting blade protrudes and the other stirring plate disposed relative to the stirring plate. 10% or more and less than 50%, and the length in the y direction of the scraping blade in the cross section cut along the yz plane is the y− between the one stirring plate and the other stirring plate. The mixture is 50% or more of the distance in the z plane, and the mixture includes a hydrophilic cross-linked polymer having a carboxyl group, and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A wet mixture produced by the step (1) of mixing the step, wherein the modifying step comprises stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent, and the drying Particulate composition 80% by weight or more of the dry particulate composition obtained in the step (2) is a particle that passes through a sieve having an aperture of 10 mm, Step (2) and step (3) are performed in one processing apparatus, and step (2) and step (3) are performed under different heating conditions and / or different stirring conditions.

  According to the above configuration, the reforming step and / or the cooling step is performed using a processing apparatus including a stirring unit having a rotating shaft including a plurality of stirring plates each including a scraping blade having the shape described above. The step (2) and the step (3) included in the reforming step can be performed with one processing apparatus. Moreover, the stirring conditions and / or temperature conditions relating to the step (2) and the step (3) can be set so as to be optimal for each step.

  Therefore, in the process of the modification step and / or the cooling step, the hydrophilic cross-linked polymer and / or the water-absorbing resin can be stirred uniformly in a floating state. Furthermore, it becomes possible to set the stirring conditions and temperature suitable for the normal style of the step (2) and the step (3).

  As a result, reduction of mechanical damage, energy saving of stirring power, and shortening of heat treatment time can be realized. Therefore, there is an effect that it is possible to efficiently produce a water absorbent resin having good properties with a small amount of fine powder.

  In addition, by performing the processing within one processing apparatus, there is an effect that problems such as an increase in cost and an increase in space due to an increase in the number of apparatuses can be avoided.

An embodiment of the present invention will be described as follows, but the present invention is not limited to this.

[Aspect of Stirring Device (Agitating Means) Used in Reforming Step and / or Cooling Step in Manufacturing Method of Water Absorbent Resin According to the Present Invention]
<Thickness of stirring plate>
In one embodiment, a method for producing a water-absorbent resin according to the present invention includes a hydrophilic crosslinked polymer having a carboxyl group, and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with a carboxyl group. A step of cross-linking the surface of the hydrophilic cross-linked polymer by heating the mixture, and a step of cooling the cross-linked hydrophilic cross-linked polymer. Alternatively, the cooling step is performed by using a stirring means having a rotating shaft provided with a plurality of stirring plates, and the direction parallel to the major axis length direction of the rotating shaft is a direction perpendicular to the y direction. When the direction parallel to the axial diameter direction of the rotating shaft is the x direction and the direction orthogonal to the x direction and the y direction is the z direction, the stirring plate cuts the stirring means along the yz plane. Scented cross section , The ratio of the minimum thickness of the maximum thickness is 5 or less.

  In the present embodiment, the reforming step and / or the cooling step are performed using a stirring unit having a thickness of the stirring plate in a predetermined range.

  FIG. 1 is a cross-sectional view showing an example of the configuration of a stirring device (stirring means) 100 used in the present embodiment. Moreover, in this specification, a stirring board and a stirring blade are synonymous.

  As shown in FIG. 1, the stirring device 100 includes a driving device 10, a horizontal drum 20, a raw material supply port 30, a heat medium and refrigerant inlet 40, 40 ′, a heat medium and refrigerant outlet 45, 45 ′, and a water absorbent resin discharge port. 50, a carrier gas introduction port 81, and an exhaust port 85. Inside the horizontal drum 20, a stirring plate 80 is disposed on a rotating shaft 70 that is rotated by a driving device 10, and a stirring blade 90 is disposed on the stirring plate 80. Established.

  In FIG. 1, the scraping blade 90 is disposed on the stirring plate 80. However, in the present embodiment, the stirring plate 80 may or may not have the scraping blade 90. Details of the scraping blade will be described later.

  The shape of the stirring board 80 is not particularly limited as long as the mixture supplied to the horizontal drum 20 from the raw material supply port 30 can be stirred. For example, a disk shape may be sufficient, and the disk shape from which one part was missing may be sufficient. Moreover, the fan shape which lacks a part of disk shaped stirring board may be sufficient. However, from the viewpoint of reducing the powder density of the hydrophilic cross-linked polymer, a disc shape, particularly a flat disc shape is preferable. The “disc shape” means that the cross-sectional shape when the stirrer is cut in the xz plane is a circle, but it is not necessarily a complete circle. “Planar disk shape” means a state in which the surface of the disk-shaped stirring disk is a flat surface. The “disc shape with a part missing” refers to a state in which the cross-sectional shape when the stirrer is cut in the xz plane is circular and a part thereof is missing. The missing part is not particularly limited, and may be, for example, a disk-shaped outer periphery or a disk-shaped inside. In the case where the disk-shaped interior is missing, for example, this includes a state in which the lack penetrates the stirring board and the stirring board is perforated.

  When using a fan-shaped stirring board, it is preferable that the internal angle of a fan is 15-75 degrees, More preferably, it is 30-60 degrees. When the angle is less than 15 ° and exceeds 75 °, the effect of suppressing the generation of fine powder is reduced.

  FIG. 2A is a cross-sectional view of a stirring device (stirring means) 100 cut along a yz plane when a stirring plate 80a having a wedge-shaped stirring plate is used, and FIG. A cross-sectional view of a stirring device (stirring means) 100 cut along an xz plane when a wedge-shaped stirring board 80a is used is shown.

  FIG. 3A is a cross-sectional view of the stirring device (stirring means) 100 cut along the yz plane when the stirring plate 80b having a flat disk shape (fan shape) is used as the stirring plate. B) represents a cross-sectional view of the stirring device (stirring means) 100 cut along the xz plane when the stirring plate 80b having a flat disk shape (fan shape) is used as the stirring plate. 2 and 3, only the stirring plates 80a and 80b, the rotary shaft 70, and the scraping blades 90a and 90b are shown, and other members are omitted.

The stirrer 80 needs to have a ratio of the maximum thickness to the minimum thickness of 5 or less in a cross section obtained by cutting the stirrer (stirring means) 100 along the yz plane. The ratio of the maximum thickness to the minimum thickness means the ratio between the maximum value and the minimum value of the thickness of the stirring plate in a cross section obtained by cutting the stirring means along the yz plane. For example, in FIG. 2A, the ratio can be expressed as T ₁ / T ₂ , and in FIG. 3A, the ratio can be expressed as T ₁ ′ / T ₂ ′.

  By setting the ratio of the maximum thickness to the minimum thickness to 5 or less, the thickness of the stirring plate 80 becomes relatively uniform. Therefore, the pressure per cross-sectional area of the stirring plate 80 applied to the hydrophilic cross-linked polymer is set. The friction between the stirring plate 80 and the hydrophilic crosslinked polymer can be reduced. Therefore, it can stir uniformly, making the mechanical damage given to the said hydrophilic crosslinked polymer small, and can suppress generation | occurrence | production of a fine powder. The ratio of the maximum thickness to the minimum thickness is not particularly limited as long as it is 5 or less, but is preferably 4 or less, more preferably 3 or less, and further preferably 2 or less. 1 is most preferable. Further, in order to improve the cutting into the powder layer, the stirring plate 80 may have R at the tip.

  So far, for example, as disclosed in Patent Document 4, stirring means using a stirring plate has been disclosed, but no investigation has been made regarding the thickness of the stirring plate, and generation of fine powder is sufficiently suppressed. It wasn't possible. The present invention has been completed as a result of intensive studies on the thickness of the stirrer optimal for suppressing the amount of fine powder.

  The closer the ratio of the maximum thickness to the minimum thickness of the stirring plate 80 approaches 1, the smaller the difference between the maximum thickness and the minimum thickness. That is, since the inclination of the stirring board 80 in the cross section obtained by cutting the stirring device (stirring means) 100 along the yz plane is reduced, the pressure and frictional force applied to the hydrophilic crosslinked polymer during stirring are further reduced, resulting in fine powder. Can be prevented from occurring. On the contrary, if the ratio of the maximum thickness of the stirring plate 80 to the minimum thickness exceeds 5, the inclination of the stirring plate 80 increases, and the pressure and friction force applied to the hydrophilic crosslinked polymer during stirring increase. As a result, the hydrophilic cross-linked polymer is compressed to increase the powder density and easily break down, so that it is difficult to suppress pulverization.

  A plurality of the stirring boards 80 are provided in order to sufficiently stir the hydrophilic crosslinked polymer and efficiently perform the surface crosslinking. However, the number of stirring plates 80 is not particularly limited as long as it is plural, and may be appropriately set according to the size of the stirring device (stirring means) 100 and the manufacturing scale. The ratio of the maximum thickness to the minimum thickness needs to be 5 or less in all the stirring boards, but if it is 5 or less, the thickness of each stirring board may be the same or different. It may be.

  Further, the size of the stirring board 80 is not particularly limited as long as the ratio of the maximum thickness to the minimum thickness is 5 or less, and is appropriately set according to the size of the stirring device (stirring means) 100. That's fine. Further, the diameter of the stirring plate is preferably 9.0 cm or more, more preferably 40 cm or more, and particularly preferably 60 cm or more.

<Kakiage feather>
In one embodiment, a method for producing a water-absorbent resin according to the present invention includes a hydrophilic crosslinked polymer having a carboxyl group, and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with a carboxyl group. A step of cross-linking the surface of the hydrophilic cross-linked polymer by heating the mixture, and a step of cooling the cross-linked hydrophilic cross-linked polymer. Alternatively, the cooling step is performed using stirring means having a rotating shaft provided with a plurality of stirring plates equipped with scraping blades, and the direction parallel to the major axis length direction of the rotating shaft is defined as the y direction and the y direction. The stirring means is cut along the yz plane when the direction perpendicular to the axis direction of the axis of rotation is the x direction and the direction perpendicular to the x and y directions is the z direction. Cut off The cross-sectional area of the lifting blade is 10 of the area in the yz plane between one stirring plate from which the lifting blade protrudes and the other stirring plate disposed relative to the stirring plate. % In the cross-section cut by the yz plane, the length in the y direction of the lifting blade is the yz between the one stirring plate and the other stirring plate. It is 50% or more of the distance in the plane.

  The scraping blade is a disk-like body fixed to the stirring board. The material is not particularly limited. So far, for example, as in Patent Document 4, a stirring means using a scraping blade has been disclosed, but a detailed study has not been made on the shape of the scraping blade for suppressing the generation of fine powder. For example, also in patent document 4, only the protrusion width | variety from the stirring board of a raising blade is described.

  The present inventor can adjust the area and length of the scraping blades to an optimal range so that the hydrophilic crosslinked polymer can be stirred in a floating state without being excessively compressed. Since aggregation and compression can be prevented, it has been found that the hydrophilic crosslinked polymer can be uniformly stirred and generation of fine powder can be suppressed, and the present invention has been completed.

  The scraping blade is disposed on the stirring plate so as to protrude from the stirring plate in the yz plane. In other words, “projecting from the stirring plate” means being arranged so as to cross the stirring plate in the yz plane. For example, in FIG. 2A, in the yz plane, the lifting blade 90a is disposed so as to protrude from the stirring plate so as to intersect the stirring plate 80a at a right angle. In FIG. 3A, for example, in the yz plane, the scraping blade 90b is disposed so as to protrude from the stirring plate so as to intersect the stirring plate 80b at a right angle. However, FIGS. 2A and 3A are merely examples, and the angle is not limited to a right angle.

  The scraping blade may be attached as a separate member from the stirring plate as long as it protrudes from the stirring plate in the yz plane. That is, the lifting blade may be formed of a member separate from the stirring board and connected to the stirring board. Moreover, as long as the function is not impaired, it may be integrally formed with the stirring board.

  The shape of the scraping blade is not particularly limited as long as the cross-sectional area and the length are within the above ranges. Further, the number of scraping blades is not particularly limited as long as it is one or more.

“Another stirring plate disposed relative to the stirring plate” refers to another stirring plate adjacent to the one stirring plate in which the scraping blades protrude in the y direction. In addition, “the area in the yz plane between one stirring plate protruding the lifting blade and another stirring plate disposed relative to the stirring plate” (area between the stirring plates); Is the area of the region sandwiched between these stirring plates in the yz plane. For example, the area is obtained as T ₃ × T ₄ in FIG. 2A, and the area is obtained as T ₃ ′ × T ₄ ′ in FIG.

  The cross-sectional area of the scraping blade occupies 10% or more and less than 50% of the area between the stirring plates. Preferably they are 10% or more and less than 40%, More preferably, they are 15% or more and less than 40%, Most preferably, they are 20% or more and less than 40%. If the cross-sectional area of the scraping blade is less than 10% of the area between the stirring plates, the stirring efficiency and powder transportability deteriorate, and the aggregation of the hydrophilic cross-linked polymer cannot be improved, thereby suppressing pulverization. It is difficult. If the cross-sectional area of the scraping blade is 50% or more of the area between the stirring plates, the scraping blade is too large and a load is applied to the power. This is not preferable because it causes non-uniformity in the cross-linked polymer layer.

In addition, the above-mentioned scraping blade only has to protrude from one stirring board, and does not necessarily have to straddle another stirring board. However, for example, as shown in FIG. Among the above-described scraping blades, the scraping blades present at adjacent positions may be alternately arranged or connected in parallel across the rotation axis in a cross section obtained by cutting the stirring means along the yz plane. preferable. The cross-sectional area of the scraping blade is, for example, the area of the scraping blade in the area between the stirring boards, and the area represented by (T ₆ × T ₅ ) / 2 × 4 in FIG. In (A), an area represented by T ₆ ′ × T ₅ ′ can be given as an example.

  Thereby, the cross-sectional area of the lifting blade can be increased with respect to the area between the stirring plates, and the length of the lifting blade can be increased. Further, the scraping blade is firmly fixed to the stirring board. Furthermore, it is possible to set an arbitrary angle in order to improve the progress of the powder layer. Therefore, stirring efficiency and powder transportability can be improved, and uniform surface crosslinking can be performed.

  The term “straddling a plurality of stirrers” does not necessarily include the case of straddling two stirrers as shown in FIG. 3A, but also includes the case of straddling three or more stirrers. The above-mentioned “scraping blades existing at adjacent positions” means one scraping blade and another scraping blade that are adjacent in the y direction in the cross section obtained by cutting the stirring means along the yz plane.

  In addition, the above-mentioned “in the cross section obtained by cutting the stirring means along the yz plane, the stirrer blades are alternately arranged across the rotation axis” means that the lifting blades sandwich the rotation axis in the yz plane. When it sees to az direction, it says that it is located on the opposite side, respectively.

  Furthermore, “the stirrer is connected in parallel in the cross-section cut along the yz plane” means that the above-mentioned scraping blades are arranged on the yz plane with the rotation axis in between, and the scraping blades are Having an inclination angle.

  Further, the above-mentioned scraping blade is inclined at an arbitrary angle within the range where the scraping blade is connected to the stirring board, within the xy plane and / or within the xz plane and / or within the yz plane. It can be attached in the state. The above-mentioned inclination angle is the above-mentioned arbitrary angle, but is preferably 0 ° or more and less than 45 °, more preferably 0.5 ° or more and less than 10 °, further preferably 1 ° or more and less than 7 °, most preferably 3. More than 7 degrees.

  The length in the y direction of the lifting blade in the cross section cut along the yz plane occupies 50% or more of the distance in the yz plane between the one stirring plate and the other stirring plate, Preferably it occupies 80% or more, and most preferably 100%. If the length of the scraping blade is less than 50% of the distance between the stirring plates, sufficient stirring force for stirring the mixture of the hydrophilic cross-linked polymer and the aqueous solution cannot be obtained, so that the resin surface is uneven. It will be cross-linked and is not suitable for a water-absorbing resin stirring device.

  On the other hand, the upper limit of the length in the y direction of the lifting blade is not particularly limited, and the length of the lifting blade is 100% of the distance between the stirring plates as long as the stirring efficiency and the powder transportability are not lowered. You may exceed.

“The length in the y direction of the scraping blade” is, for example, a length represented by T ₅ (T ₅ ÷ 2 × 2) in FIG. 2 (A). In FIG. 3 (A), T ₅ It is the length represented by '. The “distance in the yz plane between the one stirring plate and the other stirring plate” is, for example, the length represented by T ₄ in FIG. In (A), it is the length represented by T ₄ ′.

  The “distance in the yz plane between the one stirring plate and the other stirring plate” is preferably 5 cm or more and 40 cm or less on an industrial scale, and is 10 cm or more and 40 cm or less. Is more preferably 10 cm or more and 30 cm or less, and particularly preferably 15 cm or more and 25 cm or less.

  In this embodiment, the hydrophilic cross-linked polymer is stirred in a floating state without being excessively compressed by setting the cross-sectional area of the scraping blade and the length of the scraping blade in the y direction within the above range. Since it is possible to prevent aggregation and compression of the hydrophilic cross-linked polymer and to reduce the powder density, the mixture of the hydrophilic cross-linked polymer and the aqueous solution can be uniformly stirred, Occurrence can be suppressed.

  In one embodiment, the method for producing a water-absorbent resin according to the present invention sets the cross-sectional area of the scraping blade and the length in the y direction of the scraping blade within the above range, and the stirring plate includes: In the cross section obtained by cutting the stirring means along the yz plane, the ratio of the maximum thickness to the minimum thickness is preferably set to 5 or less. As a result, the shape of the scraping blade and the thickness of the stirring board are set in an optimum range, so that a high fine powder generation suppressing effect can be obtained.

<Mode of stirring plate>
It is preferable that the agitation board also acts as a heat transfer means. As described above, the surface cross-linking of the hydrophilic cross-linked polymer is carried out between the hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. This is done by heating the mixture. In this case, the heating means is not particularly limited as long as it can uniformly heat the mixture. For example, as long as the above mixture can be heated uniformly, steam, heat transfer oil, electric energy, hot air, or the like may be used as the heating means.

  However, as described above, in the present invention, since the thickness of the stirring plate is controlled and uniform stirring is possible, it is preferable that the stirring plate also serves as a heat transfer means. Thereby, the said mixture can be heated uniformly and surface cross-linking reaction can be advanced uniformly.

  In the case where the stirring plate also serves as a heat transfer means, for example, a flow path through which a heat medium can be circulated is provided inside or on the surface of the stirring board, and the heating medium is introduced into the flow path so that the surface of the stirring plate is For example, the heat transfer surface may be used to set the surface temperature to a temperature necessary for surface cross-linking. What is necessary is just to adjust the temperature of a heat medium suitably to temperature required for surface bridge | crosslinking using a conventionally well-known temperature control apparatus. For efficient use of the heat medium, the above-described flow path can also be provided on the rotating shaft so that the heat medium circulates in each stirring plate. Similarly, the above-described flow path may be provided in the scraping blade so that the heat medium can be introduced.

  Moreover, it is preferable that the said stirring board acts also as a cooling means. After the desired surface crosslinking is completed, it is preferable to cool the mixture immediately and uniformly in order to quickly terminate the surface crosslinking. In this case, the cooling means is not particularly limited as long as it can uniformly cool the mixture. For example, a conventionally known cooler can be used. The refrigerant is not particularly limited as long as the mixture can be uniformly cooled, and water, cold water, wind, ventilation, airflow, or the like may be used.

  However, as described above, in the present invention, since the thickness of the stirring plate is controlled and uniform stirring is possible, it is preferable that the stirring plate also serves as a cooling means. Thereby, the said mixture can be cooled uniformly and a surface crosslinking reaction can be stopped uniformly.

  In the case where the stirring plate also serves as a cooling means, for example, a flow path through which a coolant such as water can be circulated is provided inside or on the surface of the stirring plate, the coolant is introduced into the flow path, and the surface of the stirring plate Can be used as the cooling surface, and the temperature of the surface can be set to a temperature necessary for terminating the surface crosslinking. What is necessary is just to adjust the temperature of a refrigerant | coolant suitably to temperature required in order to complete | finish surface bridge | crosslinking using a conventionally well-known temperature control apparatus. For efficient use of the refrigerant, the flow path may be provided on the rotating shaft so that the refrigerant circulates in each stirring board. Similarly, the above-described flow path may be provided in the scraping blade so that the refrigerant can be introduced.

[Production of water-absorbing resin]
The method for producing a water-absorbing resin according to the present invention is a process for producing a hydrophilic cross-linked polymer having a carboxyl group (hereinafter, also referred to as “water-absorbing resin precursor”) (hereinafter referred to as “water-absorbing resin”). A precursor mixture manufacturing step) and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with a carboxyl group (hereinafter referred to as “aqueous solution”), and a wet mixture Step (1) (hereinafter also referred to as “wet mixture preparation step”), and step (2) (hereinafter referred to as “stirring”), wherein the wet mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent. Also referred to as a “drying step”), a step (3) in which the dried particulate composition is subjected to a heat treatment to cause a surface cross-linking reaction (hereinafter also referred to as a “surface cross-linking step”), and the hydrophilic cross-linked polymer having undergone surface cross-linking. "Cooling process" to cool .

  Here, the “surface crosslinking method” used in the present specification is a method including the step (1), the step (2) and the step (3). In addition, the modification step refers to heating the mixture of a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. A step of crosslinking the surface of the conductive cross-linked polymer, which includes the step (2) and the step (3).

  Next, referring to FIG. 1 and FIG. 5, first, the reforming step and the cooling step in the method for producing a water absorbent resin according to the present invention will be described, and then the method for producing the water absorbent resin according to the present invention will be described. The whole will be described.

(1. Modification process)
One embodiment of the reforming step will be described with reference to FIG. That is, the stirrer (stirring means) 100 contains a surface cross-linking agent having two or more functional groups capable of reacting with a hydrophilic cross-linked polymer supplied from the raw material supply port 30 through a wet mixture preparation step and a carboxyl group. The mixture with the aqueous solution is suspended by the rotation of the stirring plate 80 rotating in response to the rotation of the driving device 10 and the lifting blade 90 provided on the stirring plate, and comes into contact with the stirring plate 80 containing the heat medium. And then dried (stir drying step).

  The mixture is initially wet, but is stirred and heated by the stirring plate 80, and the hydrophilic crosslinked polymer is surface-crosslinked (surface crosslinking step). The mixture moves from the raw material supply port 30 to the discharge port 50 while moving in the drum 20. Water vapor generated during heating flows through the upper surface of the heated stirring layer by a slight amount of carrier gas such as air or inert gas introduced from the carrier gas inlet 81 and is discharged from the outlet 85. The continuously supplied mixture is mixed and heated by the rotation of the stirring plate 80. And it moves to the discharge port 50 and is discharged.

  In FIG. 1, the number of rotating shafts 70 attached to the stirring device (stirring means) is one, but the number of rotating shafts 70 is not particularly limited. A plurality of shafts 70 are preferable. For example, when a plurality of rotating shafts 70 are attached to a plurality of stirring devices (stirring means), they are preferably attached in parallel to each other in the xy plane. When there are a plurality of rotating shafts 70, the plurality of stirring boards 80 disposed on the different rotating shafts 70 may be configured to overlap and engage with each other, or may be independent of each other and not engaged with each other. May be.

  As shown in FIG. 1, the heat medium and refrigerant inlet 40 and the heat medium and refrigerant outlet 45 are provided at both ends of the hollow rotary shaft 70, and the heat medium is supplied from the heat medium and refrigerant inlet 40 to the heat medium. The surface of the stirring plate 80 is also heated by the heat medium because it flows into the stirring plate 80 while moving through the hollow of the rotating shaft to the refrigerant outlet 45. The flow of the heat medium and the refrigerant may be set to either a countercurrent or a parallel flow with respect to the material flow in the apparatus. In FIG. 1, the stirrer 80 has a heat transfer surface introduced into the heat medium, but the surface may not necessarily have a structure in which the heat medium flows into the stirrer 80 as described above. . In FIG. 1, the bladed arrow indicates the rotation direction of the stirring board 80. As the stirring device (stirring means) 100 shown in FIG. 1, for example, a multi-fin processor (Nara Machinery Co., Ltd .; NFP-1.6W) can be used.

The water-absorbing resin is a general-purpose resin that has a wide range of uses and requires mass production. Therefore, it is necessary to complete the surface cross-linking by heating uniformly in a short time and to achieve continuous operation. There is no particular limitation on the filling amount of the above mixture with respect to the internal volume of the stirring device (stirring means) 100, but it is preferably suitable for large-scale production of a certain amount or more and particularly continuous production. For example, the filling amount per internal volume is 150 to 700 kg / m ³ , particularly 200 to 200, based on the mass of the mixture of the water absorbent resin and the surface cross-linking agent-containing aqueous solution at the time of charging into the stirring device (stirring means) 100 It is preferably 600 kg / m ³ .

The water-absorbent resin can be obtained by stirring and heating the mixture to surface-crosslink the hydrophilic crosslinked polymer. In the present specification, a hydrophilic cross-linked polymer that has been subjected to surface cross-linking by the modifying step is referred to as a water-absorbing resin. Since the water-absorbent resin shrinks by drying, the filling rate in the stirring device changes with time. If it is less than 150 kg / m ³ , pulverization may occur. On the other hand, when it exceeds 700 kg / m ³ , surface crosslinking may be insufficient.

  In the present embodiment, the mixing time of the mixture, that is, the residence time in the apparatus, is the number of rotating shafts 70, whether the stirring plate 80 has the scraping blade 90, whether the stirring plate 80 has a defective portion, The agitation means) can be freely selected depending on the internal volume of 100 and the like, but is generally 10 to 120 minutes, preferably 20 to 90 minutes. This residence time can be controlled by adjusting the raw material supply amount.

  Further, the number of rotations of the stirring plate 80 is not particularly limited, but is preferably 2 to 40 rpm, more preferably 5 to 30 rpm, and is appropriately selected depending on the residence time and the presence or absence of aggregates. be able to.

  Another embodiment of the reforming step will be described with reference to FIG. That is, in the case of this embodiment, the water-absorbing resin manufacturing apparatus includes a first processing apparatus 2 and a second processing apparatus 3 as shown in FIG. The first processing apparatus 2 and the second processing apparatus 3 include a driving device 10, a horizontal drum 20, a raw material supply port 30, heat medium inlets 40 and 40 ′, heat medium outlets 45 and 45 ′, and a water absorbent resin discharge port 50, respectively. And a carrier gas introduction port 81 and an exhaust port 85 (see FIG. 5).

  In addition, the said 1st processing apparatus 2 and the 2nd processing apparatus 3 are connected by the water absorbing resin discharge port of the 1st processing apparatus 2, and the raw material supply port of the 2nd processing apparatus 3. FIG.

  The specific operation of the water absorbent resin shown in FIG. 5 is as follows. The wet mixture (raw material) composed of the water-absorbing resin precursor supplied from the raw material supply port 30 provided in the first processing device 2 and the solution containing the surface cross-linking agent rotates corresponding to the rotation of the driving device 10. It is floated by the rotation of the stirring plate 80 and heated and dried by coming into contact with the stirring plate 80 containing the heat medium. The wet mixture charged from the raw material supply port 30 is initially wet, but moves to the second processing apparatus 3 while passing through the deficient portion (not shown) of the stirring plate 80 through the drum 20. Water vapor generated during heating flows through the upper surface of the heated stirring layer by a slight amount of carrier gas such as air or inert gas introduced from the carrier gas inlet 81 and is discharged from the outlet 85. Even if the wet mixture is combined and agglomerates are generated by stirring and heating, such agglomerates are loosened by the rotation of the stirring plate 80. Similarly, the continuously supplied mixture moves to the second processing apparatus 3 while being mixed and heated by the rotation of the stirring plate 80.

  The dried particulate composition (powder) moved to the second processing device 3 moves in the same manner as the wet mixture moves in the first processing device 2. Finally, a water absorbent resin having good physical properties is discharged from the water absorbent resin discharge port 50.

  In the embodiment shown in FIG. 5, the first processing device 2 and the second processing device 3 are both biaxial groove type stirring and drying devices. However, as another embodiment, the first processing device 2 and the second processing device 3 are the same. The processing apparatus 3 can also use other conventionally known processing apparatuses and heat processing apparatuses. For example, as the processing apparatus and the heat processing apparatus, a mixer that is generally used for powder mixing can be used. When these apparatuses require heating, a heat source can be applied to the processing apparatus. For example, there is a heating mode by circulating pressurized steam, heat transfer oil or the like in a heat transfer device, heating by heating wire, microwave, electromagnetic induction, or the like. The heat medium circulation device and the heating device can be attached to any place such as a jacket that can be attached to the processing device or the inside of the stirring blade. The type of heat source, the specifications of the heat source device, the set temperature of the heat source, and the supply amount per unit time of the heat source can be appropriately set depending on the type of surface crosslinking agent used and the type of heat treatment apparatus.

  Generally speaking, mixing machines used for powders are classified according to the type of mechanical action that gives them to the powder. The container itself, which is called a container rotation type or a stirring blade built-in type container rotation type, rotates, vibrates or swings. Fixed and mixed with a stirring blade, etc. The rotating shaft is called a horizontal mechanical stirring type, the rotating shaft is called a mechanical stirring type such as a vertical mechanical stirring type, the so-called flow stirring type stirring with air or gas, gravity It is divided roughly into what divides a flow path by the flow and a branch plate and a pipe. Other examples include high-speed shearing type and impact type. Mixer types in each category include horizontal cylindrical type, inclined cylindrical type, V type, double conical type, continuous V type, etc. for the container rotation type. There are inclined cylindrical type, V type, double cone type, etc., and the rotation axis is horizontal type mechanical agitation type, there are ribbon type, screw type, lot or pin type, paddle type, etc., rotation axis is vertical type mechanical agitation There are ribbon type, screw type, conical screw type, high-speed flow type, rotating disk type, muller type, etc., and fluid agitation type includes fluidized bed type, swirling flow type, jet pump type, etc. .

  The processing forms of these devices are classified into batch type and continuous processing type, but are not particularly limited in the present invention. What is necessary is just to use what was suitable for the objective by the commercially available mixer, The mixer which can be used for the objective of this invention can be used besides what was illustrated above.

  In another embodiment, the first processing apparatus 2 and the second processing apparatus 3 may be different types of heat processing apparatuses or the same type of heat processing apparatuses. In another embodiment, when three or more heat treatment apparatuses are connected to a water absorbent resin manufacturing apparatus, the heat treatment apparatuses are partly the same heat treatment apparatus, and the others are different. Any combination is possible, such as a type of heat treatment apparatus.

  Since the said 1st processing apparatus 2 is used for a stirring drying process, it is preferable that it is an apparatus which performs strong stirring. In the type of the processing apparatus, for example, among the above-described examples, it is preferable that the processing apparatus includes a stirring blade. Examples thereof include a paddle dryer manufactured by Nara Machinery Co., Ltd. and a single paddle dryer manufactured by Nara Machinery Co., Ltd. On the other hand, since the 2nd processing apparatus 3 is used in a surface bridge | crosslinking process, it is preferable that stirring is weaker than the 1st processing apparatus 2. FIG. In the type of processing apparatus, for example, among the above-exemplified examples, it is preferable that the shape of the stirring blade is such that it does not take a share by stirring if it is a heat processing apparatus provided with a stirring blade. It may be. In the processing apparatus provided with a stirring blade with little damage caused by stirring, for example, a multi-fin processor manufactured by Nara Machinery Co., Ltd., and in a processing apparatus without a stirring blade, for example, a tally dryer manufactured by Nara Machinery Co., Ltd. may be used.

  Furthermore, in the apparatus shown in FIG. 5 for the water-absorbent resin according to the present embodiment, the second processing apparatus 3 is a biaxial groove type stirring and drying apparatus in which a stirring board 80 is disposed. The second processing device 3 may be a drying device that does not include the stirring plate 80.

  The shape of the stirring blade of the water absorbent resin shown in FIG. 5 is not particularly limited, and any conventionally known one can be arbitrarily used. For example, it may have a shape as described in the section <Thickness of stirring plate>. In addition, the stirring blade 80 may or may not be provided on the stirring board 80 in order to efficiently perform stirring as described in the section of <Skiing blade>.

  As for the shape of the stirring blade, in the first processing device 2, for example, a multi-axial one is preferable so that the powder can be stirred more efficiently. A thing with a large contact area to a body is preferable. In the 2nd processing apparatus 3, it is preferable that it is a plate-shaped stirring blade perpendicular | vertical with respect to an axis | shaft so that a share may not be given to powder, for example. The number of stirring blades per unit length of the stirring shaft depends on the shape of the stirring blade, but the larger the number, the higher the efficiency of stirring.

  In this specification, the agitation shaft is synonymous with the rotation axis.

  Further, the diameter of the stirring blade is not particularly limited, but the first processing device 2 needs to stir more strongly than the second processing device 3, and therefore the stirring blade and the first processing device 2 If the rotational speed of the two processing apparatus 3 is the same as that of the stirring blade, the diameter of the stirring blade of the first processing apparatus 2 is preferably larger than the diameter of the stirring blade of the second processing apparatus 3.

  If the diameters of the stirring blades of the first processing device 2 and the stirring blades of the second processing device 3 are the same, the rotation speed of the stirring blades of the first processing device 2 is the same as that of the second processing device 3. It is preferable to set larger than the rotation speed of a wing | blade. In addition, although the stirring conditions of the 1st processing apparatus 2 and the 2nd processing apparatus 3 satisfy | fill the above-mentioned conditions, a specific numerical value is not specifically limited.

  Generally, in the 1st processing apparatus 2, it is preferable that the rotation speed of a stirring blade is in the range of 5-300 rpm, it is more preferable in the range of 10-300 rpm, and it is in the range of 20-300 rpm. More preferably. Moreover, it is preferable that the peripheral speed of a stirring blade is 0.15-10 m / s, It is more preferable that it is 0.3-10 m / s, It is further more preferable that it is 0.5-10 m / s.

  In the 2nd processing apparatus 3, it is preferable that the rotation speed of a stirring blade is 0-30 rpm, It is more preferable that it is 0-20 rpm, It is further more preferable that it is 0-10 rpm. Further, the peripheral speed of the stirring blade is preferably 2 m / s or less, more preferably 1 m / s or less, and further preferably 0.3 m / s or less.

  In the apparatus shown in FIG. 5 for the water-absorbing resin, the discharge port preferably has a downward slope. In the said structure, since the forced stirring at the time of discharge | emission is not required, the damage to the manufactured water absorbing resin can be reduced. The downward tilt may be provided inside the apparatus, but can also be realized by tilting the apparatus when the apparatus is installed. Since the downward inclination is usually a slight inclination, there is no particular problem with respect to the operation of the apparatus and the installation of the apparatus even if the apparatus is inclined during the installation of the apparatus. Note that the downward slope is not necessarily formed. In particular, a heat treatment apparatus having a feeding blade may not require the downward inclination.

  Moreover, the apparatus shown in FIG. 5 of the water absorbent resin according to the present embodiment is provided with the water absorbent resin outlet 50 downward as shown in FIG. According to the above configuration, when transporting the water-absorbent resin powder, it can be discharged downward only by gravity, so that damage to the manufactured water-absorbent resin can be reduced.

  Furthermore, the apparatus shown in FIG. 5 of the water-absorbent resin connects the first processing apparatus 2 and the second processing apparatus 3 in a hierarchical manner. Therefore, no special power is required for transporting the resin powder from the first processing apparatus 2 to the second processing apparatus 3.

  The carrier gas introduction port 81 and the exhaust port 85 are for ventilating with carrier gas. The carrier gas is not particularly limited, and examples thereof include steam, air, and nitrogen. Further, the supply amount of the carrier gas is not particularly limited, and may be determined as appropriate. Furthermore, the carrier gas is preferably heated so as not to lower the temperature in the heat treatment apparatus.

  According to the said structure, since the water vapor | steam produced | generated during reaction is removed efficiently, a water absorbing resin can be dried in a short time.

Moreover, the 1st processing apparatus 2 and / or the 2nd processing apparatus 3 may be provided with the means for decompressing or pressurizing the said carrier gas. Furthermore, a means for heating or cooling the carrier gas may be provided. Specifically, the first processing apparatus 2 and / or the second processing apparatus 3 uses a carrier gas (for example, air) near room temperature (for example, 0 to 50 ° C.) at a substantially normal pressure (1.013 × 10 ^5). It is preferable that it can be supplied at Pa (1 atm) ± 10%, preferably ± 5%, more preferably ± 1%.

  In the present embodiment, the carrier gas introduction port 81 and the exhaust port 85 are provided. However, as another embodiment, the carrier gas introduction port 81 and the exhaust port 85 may be omitted. Good.

  Moreover, it is preferable that the heating capability of the 2nd processing apparatus 3 can be heated so that the temperature of the water absorbent resin powder discharged | emitted from the water absorbent resin discharge port 50 may be 180 to 250 degreeC, and is 180 to 230 degreeC. It is more preferable that it can be heated, and it is even more preferable that heating can be performed so that the temperature becomes 190 ° C to 210 ° C. Thereby, the surface cross-linking step in the surface cross-linking method of the water-absorbent resin can be efficiently performed.

(2. Cooling process)
The hydrophilic cross-linked polymer (hereinafter also referred to as “water-absorbing resin”) that has been subjected to surface cross-linking is subjected to a cooling step. The means for performing the cooling is not particularly limited as long as it can uniformly cool the mixture. For example, a conventionally known cooler that can be connected to the stirring device (stirring means) 100 can be used. In the cooling step, the water-absorbent resin may or may not be stirred, but is preferably stirred from the viewpoint of improving the cooling efficiency. Since the refrigerant is not particularly limited as described above, water, cold water, wind, or the like may be used, and the refrigerant may be configured to circulate in each stirring plate 80 such as the stirring device 100. An apparatus that can be used is preferred. Further, the surface-crosslinked water-absorbing resin is preferably cooled to room temperature to about 100 ° C. The cooler used in the cooling step is used by being connected to a stirrer (stirring means) 100 in order to cool the surface-crosslinked water-absorbing resin, for example, after performing the surface cross-linking.

  As the timing for starting the cooling step, the water-absorbent resin taken out from the stirring device (stirring means) 100 after surface crosslinking is preferably cooled within 1 minute, more preferably within 30 seconds. From the viewpoint of physical properties and productivity, the temperature of the water absorbent resin at the start of cooling is preferably 150 to 250 ° C., and the temperature of the water absorbent resin after cooling is preferably 40 ° C. to 100 ° C., 90 More preferably, it is below 70 degreeC, and it is especially preferable that it is below 70 degreeC.

  In the cooler, the water absorbent resin has a temperature gradient. In the vicinity of the inlet of the cooler, the surface treatment temperature or a temperature close thereto is shown, and in the vicinity of the outlet, the temperature is close to the planned cooling temperature. The factors governing the outlet temperature are the refrigerant temperature, the cooler heat transfer area, and the residence time in the cooler, and may be set as appropriate so as to obtain the desired outlet temperature.

  In addition, the cooler described above is preferably arranged so that the water-absorbing resin is continuously fed into the apparatus. The arrangement may be vertical (water-absorbing resin is fed from top to bottom) or horizontally. (The water-absorbing resin is fed in the lateral direction) may be used, but the cooler is not installed horizontally, particularly in the horizontal orientation, and is preferably installed so as to have a downward slope. When there is no inclination, since the stable feed is difficult as a powder characteristic of the heated water-absorbent resin, the physical properties of the water-absorbent resin may be lowered or unstable. The downward inclination is appropriately determined, 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, it is preferable to use a stirrer (stirring means) 100 having a downward slope in the reforming step. That is, the same inclination is preferably applied not only to the cooler having the above-described inclination but also to the reforming process before cooling, and the physical property process of the water absorbent resin of the present invention can be achieved. Since the stirring device (stirring means) 100 has a downward slope, the piston flow property of continuous powder operation can be improved, and the product can be easily switched when the product is changed.

  The piston flow (extruded flow, also referred to as PLUG FLOW) ideally has a uniform velocity distribution in the direction perpendicular to the flow of the substance flowing through the apparatus from the apparatus inlet to the outlet. Defined as a flow that moves without mixing or diffusion in the flow direction.

  By improving the piston flow property of the water-absorbent resin powder, the residence time of the water-absorbent resin powder in the stirrer (stirring means) 100 or the cooler is stabilized, and a stable reforming process / cooling process is performed. Thus, the water-absorbing resin powder having high physical properties can be stably produced, and the partial residence for a long time is eliminated, so that the water-absorbing resin is hardly pulverized and the generation of fine powder can be suppressed.

  Moreover, in the aqueous liquid addition mentioned later, by improving piston flow property, formation of the field (zone) of the essential specific temperature range in the powder layer in the cooler becomes clearer and the addition of the aqueous liquid becomes easier. Is.

  When the piston flow property is low, the dispersion time of the water-absorbent resin powder in the stirrer (stirring means) 100 or the cooler increases, resulting in unstable physical properties, low physical properties, and a large amount of fine powder. Or In addition, the formation of a field in a specific temperature region, which is essential for the addition of the aqueous liquid described below, becomes unclear, making it difficult to add the aqueous liquid.

  In the cooling step, it is also preferable to add an aqueous liquid as described in Patent Document 5. By adding water or an aqueous liquid containing water as a main component (hereinafter collectively referred to as an aqueous liquid) at a temperature of 40 to 100 ° C. during cooling after the reforming step, fine powder and Dust generation can be reduced, and a form corresponding to the granulation of the water-absorbent resin powder can be obtained without requiring a normal granulation step.

  That is, the water-absorbent resin powder can be granulated by adding the aqueous liquid. That is, granulation can be easily performed without using a high-cost equipment dedicated for granulation. In this case, the condition of the cooling step is that the temperature of the water-absorbent resin powder usually exceeds 100 ° C. at the start of the cooling step, and is preferably cooled to 70 ° C. or less after the cooling step.

  Addition of water to the water-absorbent resin is usually not endothermic but accompanied by heat generation. By adding an aqueous liquid to the water absorbent resin powder, an exothermic reaction occurs due to the heat of hydration, and the water absorbent resin generates heat, but at the same time it is forcibly cooled in a cooler, so the surface properties of the water absorbent resin change. Further, it is considered that a material having further excellent physical properties is obtained, generation of fine powder is suppressed, and the form of the resin powder is also improved.

  Moreover, the moisture absorption fluidity of the water absorbent resin is further improved by the addition of the aqueous liquid, the amount of fine powder of the water absorbent resin is reduced, and surface destruction of the water absorbent resin in the subsequent process can be prevented. Thus, by adding an aqueous liquid in the place where the temperature of the water absorbent resin powder is 40 to 100 ° C., the mass average particle diameter is 200 to 600 μm, preferably 300 to 500 μm, and the fine powder of 150 μm or less is 5% by mass. In addition, it is possible to obtain a water-absorbent resin powder that is preferably controlled to 3% by mass, and more preferably 1% by mass or less.

  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, more preferably 60 to 80 ° C. The field here refers to a region (zone) having a specific temperature, for example, when the temperature continuously changes (decreases) in the water-absorbing resin in a continuous flow. When an aqueous liquid is added at a temperature of 40 ° C. or lower, the water-absorbent resin becomes a lumpy (a lump) 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 lowered and the cooling efficiency is substantially lowered or the dama is destroyed, the water-absorbent resin itself constituting the dama itself may be damaged and the physical properties may be lowered.

  In addition, when an aqueous liquid is added at a temperature of 100 ° C. or higher, low-boiling components in the added aqueous liquid, such as water, are diffused, and the aqueous liquid is not effectively added to the water-absorbent resin. Condensation inside the cooler due to water, dew is generated by the condensed water, the cooler outlet is blocked by the dama, and stable operation cannot be performed, water absorbent resin adheres to the heat transfer surface of the cooler, The heat transfer efficiency is lowered, the cooling efficiency is substantially lowered, and the physical properties of the water absorbent resin are lowered. When the aqueous liquid is added in the cooling step, it is essential to add the aqueous liquid in the temperature field described above. These preferred temperature ranges can be found in the cooler by, for example, actually performing measurement under the set operating conditions, or by cooling the inlet, outlet water absorbent resin temperature, water absorbent resin specific heat, supply speed, refrigerant inlet, From the outlet temperature, etc., a countercurrent or cocurrent 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 is found by numerical analysis. The temperature of the aqueous liquid to be added is usually 0 ° C. or higher and lower 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, and 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 apparatus for adding the aqueous liquid is not particularly limited as long as it is a spraying apparatus that meets the purpose, but an apparatus that can spray the aqueous liquid uniformly over a narrow area is desirable. Preferably, a one-fluid type or two-fluid type spray having a flat spray, hollow cone, or full cone spray pattern is used, and more preferably, a narrow angle spray is used for spraying in a narrow area.

  Although the droplet size to spray is not specifically limited, It is preferable that it is 10-1000 micrometers on average. If the droplet size is too large, the water content of the water-absorbent resin becomes non-uniform, and a large amount of water-absorbed particles may be fooled and the device may be blocked. On the other hand, when the thickness is less than 10 μm, the sprayed water does not effectively adhere to the water-absorbent resin, and it is exhausted from the inside of the apparatus as droplets or becomes condensed water, causing problems. The optimum droplet size is 50 to 500 μm. As a general trend, if the airflow in the device is gentle, the droplet size may be small, and if the airflow is fast, it is important to carry out with large droplets to prevent escape as droplets. is there. It is preferable to add the aqueous liquid so that the aqueous liquid does not come in contact with anything other than the water absorbent resin. However, when there is a possibility that the added aqueous liquid may come into contact with the part inside the apparatus other than the water absorbent resin powder, for example, polyethylene glycol ( It is preferable to contain an anti-adhesive agent such as PEG) or polypropylene glycol (PPG).

  Various additives for developing an additional function may be dissolved or dispersed in the added aqueous liquid. Examples of such additives include metal salts, acids, alkalis, deodorants, colorants, inorganic or organic antibacterial agents, and surfactants. More specifically, for example, sulfites such as sodium bisulfite (SBS) for reducing residual monomers, organic or inorganic bases for adjusting the water absorption rate, organic acids or inorganic acids, monovalent metal salts or polyvalents A metal salt (for example, aluminum sulfate), a deodorant for imparting a deodorizing function, a colorant 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 stirrer used for the said modification | reformation process and cooling process is not specifically limited, The stirrer illustrated in this specification can be used.

  For example, for the reason that generation of fine powder can be suppressed, in the reforming step and the cooling step, only one of the reforming step and the cooling step is performed using the stirring device (stirring means) 100 described above. Also good. In this case, the other step can be performed using a conventionally known heating and stirring device or stirring and cooling device. As the conventionally known apparatus, for example, a biaxial groove type stirring apparatus described in Patent Document 4 can be used.

  In addition, since the surface cross-linking reaction and cooling can be performed uniformly, the generation of fine powder can be further suppressed. Therefore, the stirrer (stirring means) 100 described above is used for both the reforming step and the cooling step. More preferably.

(3. Details of production of water-absorbing resin)
Below, the manufacturing method of the water absorbing resin which concerns on this invention is demonstrated in detail.

(A-water absorbent resin)
The water-absorbing resin according to the present invention is not particularly limited, and has two or more functional groups capable of reacting with the carboxyl group on the surface of the hydrophilic cross-linked polymer having a carboxyl group (water-absorbing resin precursor). Any material that has been crosslinked with a surface crosslinking agent may be used.

  In the present specification, the water-absorbent resin refers to a surface-crosslinked product of the water-absorbent resin precursor. Conversely, in the present specification, the water absorbent resin precursor refers to a water absorbent resin that has not been subjected to surface crosslinking.

  That is, in the present specification, the hydrophilic crosslinked polymer and the water-absorbing resin precursor are synonymous.

  In the present specification, the “water absorbent resin” is a particle or a powder. “Powder” refers to an aggregate of particles, and is expressed as a powder when expressing bulk properties such as fluidity. That is, in this specification, the water-absorbent resin particles and the water-absorbent resin powder are synonymous.

  The shape of the water absorbent resin according to the present invention is not particularly limited, and may be various shapes such as a spherical shape, a scale shape, an irregular crushed shape, a fiber shape, a granular shape, a rod shape, a substantially spherical shape, a flat shape, and the like. Also good.

  The water absorbent resin according to the present invention may be a pulverized and classified particle-shaped water absorbent resin having a predetermined size. In that case, the particle size is preferably 2 mm or less, and more preferably 10 μm to 1 mm. Although a weight average particle diameter changes also with the uses to be used, it is preferable normally that they are 100 micrometers-1000 micrometers, it is more preferable that they are 150 micrometers-800 micrometers, and it is further more preferable that they are 300 micrometers-600 micrometers. Further, the ratio of particles passing through a sieve having an aperture of 150 μm is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less.

  The water-absorbent resin according to the present invention preferably has an absorption ratio (hereinafter also referred to as “CRC”) of 10 to 60 g / g, preferably 20 to 55 g / g. More preferably, it is more preferable that it is 25-50 g / g. Furthermore, the absorption capacity under pressure (hereinafter also referred to as “AAP”) by the measurement method employed in the examples described later is preferably 10 g / g or more, more preferably 15 g / g or more, and 20 g. / G or more is more preferable.

The step of producing the water absorbent resin precursor (hereinafter also referred to as “water absorbent resin precursor production step”) is not particularly limited, and for example, the following steps can be used (I. Production of water absorbent resin precursor). Process)
In the water absorbent resin precursor production process, a water absorbent resin precursor before surface cross-linking having a carboxyl group that can be used in the present invention is produced. As the water-absorbing resin precursor, for example, it is obtained by polymerizing a hydrophilic unsaturated monomer mainly composed of acrylic acid and / or a salt thereof, and a large amount of 50 to 1000 times in ion-exchanged water. Conventionally known resins that absorb water and form a water-swellable and water-insoluble hydrophilic crosslinked polymer can be mentioned.

  Moreover, it is preferable that a crosslinked structure is introduced into the water-absorbent resin precursor by using an internal crosslinking agent during the production thereof.

  Below, although the said hydrophilic unsaturated monomer, a hydrophilic crosslinked polymer, an internal crosslinking agent, and the polymerization method of a hydrophilic unsaturated monomer are demonstrated, this invention is not limited to this.

<Hydrophilic unsaturated monomer>
As said hydrophilic unsaturated monomer, the hydrophilic unsaturated monomer which has acrylic acid and / or its salt as a main component can be illustrated. Moreover, the hydrophilic unsaturated monomer may contain unsaturated monomers other than acrylic acid or its salt as needed. Examples of other unsaturated monomers include methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamido-2-methylpropane sulfonic acid, 2- (meth) acryloylethane sulfonic acid, And anionic unsaturated monomers such as 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl ( (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinyl Nonionic hydrophilic group-containing unsaturated monomers such as lysine, N-vinylpyrrolidone, N-acryloylpiperidine, and N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl ( Examples thereof include cationic unsaturated monomers such as (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, and N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof. It is not particularly limited. The amount used when these other unsaturated monomers are used in combination is preferably 30 mol% or less, more preferably 10 mol% or less of the entire hydrophilic unsaturated monomer.

<Hydrophilic cross-linked polymer>
In the present specification, the hydrophilic cross-linked polymer is synonymous with the water-absorbing resin precursor, absorbs a large amount of water, is water-swellable and water-insoluble, and is not particularly limited. In the hydrophilic crosslinked polymer, the acid group in the crosslinked polymer is more preferably neutralized with, for example, an alkali metal salt, an ammonium salt, an amine salt, or the like. Further, the proportion of the acid groups in the crosslinked polymer neutralized is preferably 30 mol% to 100 mol%, more preferably 50 mol% to 90 mol%, more preferably 60 mol% to It is especially preferable that it is 80 mol%. Therefore, in this specification, "the water-absorbing resin precursor having a carboxyl group" also includes "a water-absorbing resin precursor having a carboxyl group and / or a salt thereof". The neutralization of the acid groups includes (a) a step of preparing a hydrophilic unsaturated monomer before obtaining the crosslinked polymer, (b) during the polymerization of the hydrophilic unsaturated monomer, and (c) hydrophilicity. The polymerization reaction of the polymerizable unsaturated monomer may be completed and the crosslinking polymer may be obtained at any stage. Moreover, you may carry out in the several step of said (a)-(c).

<Internal cross-linking agent>
The internal cross-linking agent is not particularly limited as long as it is a compound having a plurality of reactive groups capable of reacting with a polymerizable unsaturated group and / or a carboxyl group in one molecule. That is, the internal cross-linking agent may be a compound that has a plurality of substituents in one molecule that copolymerize with the hydrophilic unsaturated monomer and / or react with the carboxyl group. The hydrophilic unsaturated monomer may be composed of a self-crosslinking type compound in which a crosslinked structure is formed without using an internal crosslinking agent.

  Examples of the internal crosslinking agent include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triary Lucyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol jig Ethers, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate and the like, but is not particularly limited. These internal crosslinking agents may be used alone or in combination of two or more. And the absorption characteristic etc. of the water-absorbent resin obtained can be further improved by using the internal crosslinking agent which has two or more polymerizable unsaturated groups in 1 molecule among the internal crosslinking agents of the said illustration.

  The amount of the internal crosslinking agent used is preferably within a range of 0.005 to 3 mol% with respect to the hydrophilic unsaturated monomer, and the hydrophilic unsaturated monomer is polymerized to form a water-absorbing resin precursor. When obtaining a body (hydrophilic unsaturated polymer), the reaction system includes starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), crosslinked polyacrylic acid (salt), etc. Hydrophilic polymers; chain transfer agents such as hypophosphorous acid (salts); water-soluble or water-dispersible surfactants and the like may be added.

<Polymerization method of hydrophilic unsaturated monomer>
The polymerization method of the hydrophilic unsaturated monomer is not particularly limited, and for example, a known method such as aqueous solution polymerization, reverse phase suspension polymerization, bulk polymerization, precipitation polymerization or the like can be employed. Moreover, reaction conditions, such as reaction temperature and reaction time, should just be set suitably according to the composition etc. of the hydrophilic unsaturated monomer component to be used, and are not specifically limited.

  When polymerizing a hydrophilic unsaturated monomer, for example, potassium persulfate, sodium persulfate, ammonium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) Radical polymerization initiators such as dihydrochloride; radical photopolymerization initiators such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one; use of active energy rays such as ultraviolet rays and electron beams, etc. it can. Moreover, when using an oxidizing radical polymerization initiator, you may perform redox polymerization, for example using together reducing agents, such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-ascorbic acid. The amount of these polymerization initiators used is preferably in the range of 0.001 mol% to 2 mol%, and more preferably in the range of 0.01 mol% to 0.5 mol%.

  The water-absorbent resin according to the present invention can be obtained by surface-crosslinking the water-absorbent resin precursor (hydrophilic crosslinked polymer) obtained by the above-described process using the following surface-absorbing method of the water-absorbent resin. .

(B-surface crosslinking method of water-absorbing resin)
The surface cross-linking method for a water-absorbent resin according to the present invention is suitable for mass production on an industrial scale. In the conventional heat treatment method using a single treatment device, there is a problem that the residence time becomes longer as the treatment device becomes larger, the water absorbent resin is damaged, and the physical properties are lowered.

  Conventionally, it has been difficult to achieve both improvement in physical properties of the resulting water-absorbent resin and improvement in productivity. Therefore, in order to achieve both improvement in the physical properties of the resulting water-absorbent resin and improvement in productivity, the inventors have made a solution containing the surface cross-linking agent and the water-absorbent resin in the surface cross-linking process of the water-absorbent resin. It is effective to obtain a dry particulate composition by stirring and drying a wet mixture comprising a precursor and heating the dry particulate composition to obtain a desired crosslinking density as separate steps. The present invention has been found uniquely and the present invention has been completed.

  Specifically, the surface cross-linking method of the water-absorbent resin according to the present invention is a step (1) (hereinafter referred to as “wet mixture preparation”) in which a solution containing a surface cross-linking agent and a water-absorbent resin precursor are mixed to obtain a wet mixture. Step (2) (hereinafter also referred to as “stir-drying step”), and the dry particulate composition obtained by stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent. (3) (hereinafter also referred to as “surface crosslinking step”). Further, 80% by weight or more of the dry particulate composition obtained in the stirring / drying step is particles passing through a sieve having an opening of 10 mm, and at least one of each step of the stirring / drying step and the surface cross-linking step is performed. The processing apparatus used in the above-described processing apparatus and used in the stirring and drying process and the processing apparatus used in the surface cross-linking process are connected in series.

  That is, in the surface cross-linking method of the water-absorbent resin, the solution containing the surface cross-linking agent and the water-absorbent resin precursor are mixed in the wet mixture preparation step to obtain a wet mixture. The wet mixture is put into a processing apparatus. The wet mixture tends to form aggregates when water evaporates, but in the stirring and drying step, the stirring is performed, and as the drying proceeds, the aggregation is loosened, the wet mixture is dispersed, It becomes a dry particulate composition with high fluidity of the powder in which particles passing through a sieve having an opening of 10 mm account for 80% by weight or more. As described above, inside the heat treatment apparatus, although the properties of the wet mixture differ depending on the elapsed time, in the conventional surface cross-linking method of the water absorbent resin, a single stirring and heating are performed with a single treatment apparatus. . That is, the treatment was performed under the same conditions without distinguishing between the stirring and drying step and the surface crosslinking step.

  On the other hand, in this invention, each process of the said stirring drying process and surface cross-linking process is performed using at least one processing apparatus, a processing apparatus used for the stirring and drying process, and a processing apparatus used for the surface cross-linking process. Are connected in series, it becomes possible to set the stirring conditions and temperature suitable for the properties of the powder in both steps. As a result, the heat treatment time can be shortened, damage to the water absorbent resin can be reduced, and a water absorbent resin having good physical properties can be obtained without reducing the production amount.

  That is, in the surface cross-linking method of the water absorbent resin according to the present invention, the solution containing the surface cross-linking agent and the water absorbent resin precursor are mixed and introduced into the heat treatment apparatus, and a large amount of aggregates are generated when water evaporates. For a wet mixture with low fluidity, the water content of the water-absorbent resin particles is reduced more quickly by increasing the agitation by increasing the agitation and further increasing the average heating rate of the wet mixture. Thus, the aggregation state can be loosened in a short time. Furthermore, once the agglomeration is loosened, the particles are dispersed, and the fluidity of the dried particulate composition, a relatively weak stirring, or a heat treatment apparatus without a stirring blade can be used. Can slow down the average temperature rise rate of the dry particulate composition and make it easier to control the surface cross-linking density of the water-absorbent resin that is the product.

  It is possible to heat-treat in a short time just by increasing the agitation and increasing the average heating rate, but as the production rate increases, the higher the average heating rate, the more difficult it is to control the crosslinking density. . Therefore, a process with a relatively slow average temperature rise rate is required to make it easier to control the surface crosslink density of the product.

  In the surface cross-linking method for a water-absorbent resin according to the present invention, the stirring and drying step and the surface cross-linking step are preferably performed continuously. Thereby, a water-absorbing resin having good physical properties can be produced in a short time.

  Furthermore, it is preferable that the processing apparatus used for the stirring and drying process and the processing apparatus used for the surface crosslinking process are processing apparatuses having different types and / or effective volumes. Moreover, it is preferable that the processing apparatus used for the stirring and drying process and the processing apparatus used for the surface crosslinking process are operated under different heating conditions and / or different stirring conditions. Thereby, the optimal heating conditions and / or stirring conditions for each step can be selected, and a water-absorbing resin exhibiting good physical properties can be efficiently produced.

  In addition, the above-mentioned “processing devices of different types” mean processing devices having different processing device shapes. Further, the above-mentioned “processing devices having different effective volumes” mean processing devices having different effective volume values of the processing devices. “Different heating conditions” means the type of heat source that can be attached to the processing apparatus, the specifications of the heat source apparatus that can be attached to the processing apparatus, the set temperature of the heat source that can be attached to the processing apparatus, It means heating conditions in which at least one or more of the supply amount per unit time of the heat source that can be produced is different. Further, the above “different stirring conditions” means that the stirring blade is different in at least one of the shape of the stirring blade, the size of the stirring blade diameter, the number of stirring blades per unit length of the stirring shaft, and the number of rotations of the stirring blade. Means a condition.

  As another form of the surface cross-linking method for the water-absorbent resin according to the present invention, the agitation drying step and the surface cross-linking step are performed in one processing apparatus, and the agitation drying step and the surface cross-linking step are performed under different processing conditions. It can be carried out.

  According to the said structure, it becomes possible to set the stirring conditions and temperature corresponding to the property of powder for the said stirring-drying process and surface cross-linking process. As a result, the heat treatment time can be shortened. Therefore, damage to the water absorbent resin is reduced, and an effect is obtained that a water absorbent resin having good physical properties can be obtained without reducing the production amount.

  In the surface cross-linking method for the water-absorbent resin, the stirring and drying step and the surface cross-linking step can be divided into a plurality of steps, respectively. That is, in the stirring and drying step, the step can be further divided according to the properties of the particles. Similarly, in the surface crosslinking step, the step can be further divided according to the properties of the particles.

  Hereafter, each said process is described in detail.

(I. Wet mixture preparation step)
In the wet mixture preparation step, it is only necessary to obtain a wet mixture by mixing the solution containing the surface cross-linking agent and the above water-absorbent resin precursor, and the specific configuration thereof is not particularly limited. In addition to the solution containing the surface crosslinking agent and the water-absorbent resin precursor, the wet mixture may contain an additive suitable for the present invention. Hereinafter, the surface cross-linking agent, usable additives, and a method of mixing the solution containing the surface cross-linking agent with the above water-absorbent resin precursor and a mixing apparatus used therefor will be described, but the present invention is limited to this. It is not something.

<Surface cross-linking agent>
The surface cross-linking agent used in the present invention may be a compound having a plurality of functional groups capable of reacting with two or more carboxyl groups in the water-absorbent resin precursor in one molecule, and forming a covalent bond by a cross-linking reaction. For example, there is no particular limitation. Preferable examples of the surface cross-linking agent include oxazoline compounds (US Pat. No. 6,297,319), vinyl ether compounds (US Pat. No. 6,372,852), epoxy compounds (US Pat. No. 625488), oxetane compounds (US Pat. No. 6,809,158), polyvalent compounds. Alcohol compounds (US Pat. No. 4,734,478), polyamide polyamine-epihalo adducts (US Pat. Nos. 4,755,562 and 4,824,901), hydroxyacrylamide compounds (US Pat. No. 6,239,230), oxazolidinone compounds (US Pat. No. 6,559,239), bis or polyoxazolidinone compounds (US Pat. No. 6,472,478), 2-oxotetrahydro-1,3-oxazolidine compounds (US Pat. No. 6,657,015), and alkylene carbonate compounds (US Pat. No. 5,672,633). These may be used alone or in combination of two or more.

  In addition, a water-soluble cation such as an aluminum salt (US Pat. Nos. 6,605,673 and 6,620,899) may be added to such a surface cross-linking agent, an alkali (US Pat. No. 2004-106745), an organic acid or an inorganic acid (US patent). 5610208) may be used in combination.

  Specific surface cross-linking agents include ethylene glycol, propylene glycol, glycerin, pentaerythritol, sorbitol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 1,4 -Butanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2,5-hexanediol, trimethylolpropane, etc. Polyhydric alcohols; ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate (4-methyl-1,3-dioxolan-2-one), 4,5-dimethyl-1,3-dioxolane-2 -ON Bonate compounds; polyamine compounds such as diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, triethylenetetramine; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl Polyvalent glycidyl compounds such as ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether; 2,4-tolylene diisocyanate, ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate (4-methyl-1) , 3-dioxolan-2-one), 4,5-dimethyl-1,3-dioxolan-2-one, ( Poly, aziridines such as 2-, di- or mono) 2-oxazolidinone, epichlorohydrin, epibromohydrin, diglycol silicate, 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate] A compound or the like can be used. These surface cross-linking agents may be used alone or in combination of two or more. Among these, at least one kind is preferably a surface cross-linking agent selected from polyhydric alcohols, carbonate compounds, polyvalent amine compounds, polyvalent glycidyl compounds, poly-2-oxazolidinones, bis-2-oxazolidinones, and mono-2-oxazolidinones. More preferably, at least one kind is a surface cross-linking agent containing a polyhydric alcohol, a carbonate compound, or a polyvalent amine compound.

  What is necessary is just to set the usage-amount of the said surface crosslinking agent suitably by the surface crosslinking agent to be used, those combinations, etc. In general, the amount of the surface cross-linking agent used is preferably in the range of 0.001 to 5 parts by mass with respect to 100 parts by mass of the solid content of the water-absorbent resin precursor. More preferably within the range of parts by mass. When the amount of the surface cross-linking agent exceeds the above range, it is not preferable because not only becomes uneconomical but also the amount of the surface cross-linking agent becomes excessive in forming an optimal cross-linking structure in the water absorbent resin. . Moreover, when the usage-amount of a surface crosslinking agent is less than the said range, there exists a tendency for obtaining the surface-crosslinked water-absorbing resin with a high absorption capacity | capacitance under pressure.

  In order to dissolve the surface cross-linking agent, it is preferable to use water as a solvent. Moreover, the usage-amount of the said solvent can be suitably changed with the kind, particle size, etc. of a water absorbing resin precursor. Generally, it is preferably greater than 0 and less than or equal to 20 parts by weight, more preferably within the range of 0.5 to 10 parts by weight, relative to 100 parts by weight of the solid content of the water absorbent resin precursor. .

  As a composition of the solution containing the surface cross-linking agent used in the present invention, an aqueous solution containing a surface cross-linking agent that reacts with the carboxyl group of the water-absorbent resin precursor by an esterification reaction such as polyhydric alcohol or alkylene carbonate is preferable.

  In the present specification, a solution obtained by dissolving the surface cross-linking agent in a solvent is referred to as a “solution containing a surface cross-linking agent”.

  In the present invention, the monomer may be polymerized on the surface of the water-absorbent resin precursor to form surface cross-linking (US Pat. No. 2005-48221).

<Other additives>
In addition to the surface cross-linking agent, the solution containing the surface cross-linking agent according to the present invention further includes a surfactant as a dispersant and particles for enhancing the mixing effect, a metal complex as a modifier, an antibacterial agent as an additive, An odorant, a fragrance, a food additive, an oxidizing agent, a reducing agent, a chelating agent, an antioxidant, a radical inhibitor, a pigment, and the like can be added. These additives can be added as necessary by dissolving in a solvent or dispersing to form an aqueous solution. Moreover, you may add with a separate nozzle.

  Examples of the surfactant that can be used as the dispersant include nonionic, anionic, cationic or amphoteric surfactants having an HLB value of 3 or more described in JP-T-2002-527547. Moreover, it is preferable that the usage-amount is in the range of 0-5 mass% with respect to a water absorbing resin precursor.

  Examples of the particles for enhancing the mixing effect include inorganic particles such as carbon black described in JP-A-4-214734. Moreover, it is preferable that the usage-amount is in the range of 0-10 mass parts with respect to 100 mass parts of water absorbent resin precursors.

  Examples of the metal complex used as the modifier include divalent or polyvalent metal salt solutions described in JP-T-2002-527547.

  The antibacterial agent is not particularly limited, and a conventionally known antibacterial agent having antibacterial properties can be used. Examples thereof include antibacterial agents described in JP-A-11-267500.

  The deodorant is not particularly limited, and a conventionally known deodorant that deodorizes unpleasant odor components of human urine such as mercaptan, hydrogen sulfide, and ammonia can be used. For example, a vine plant extract containing flavanols or flavonols as a deodorizing component can be used.

  The addition amount of the additive that imparts an additional function to the water-absorbent resin can be appropriately changed according to the purpose of addition and the type of additive. Generally, it is preferably 0.001 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and 0.05 to 1 part by mass with respect to 100 parts by mass of the water absorbent resin precursor. More preferably, it is a part.

<Mixing method and mixing apparatus>
In order to satisfy the above conditions, the water-absorbing resin precursor and the solution containing the surface cross-linking agent are put into a mixing apparatus and mixed. More specifically, in the present invention, the water-absorbing resin precursor and the solution containing the surface cross-linking agent are mixed by adding a solution containing the surface cross-linking agent from the nozzle to the water-absorbing resin precursor. can do. The mixing time is appropriately adjusted depending on the shape and size of the mixing apparatus and the amount of the solution containing the surface cross-linking agent. On a normal industrial scale, it is between 5 seconds and 10 minutes.

  Moreover, when mixing the water-absorbing resin precursor and the solution containing the surface cross-linking agent, a hydrophilic organic solvent can be used as a solvent, if necessary. Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and t-butyl alcohol; ketones such as acetone; And ethers such as tetrahydrofuran and alkoxy polyethylene glycol; amides such as N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide. The amount of the hydrophilic organic solvent used depends on the type and particle size of the water absorbent resin precursor, but is preferably 20 parts by mass or less with respect to 100 parts by mass of the solid content of the water absorbent resin precursor. 0 to 10 parts by mass is more preferable, 0 to 5 parts by mass is further preferable, and 0 to 1 part by mass is particularly preferable.

  The temperature of the water absorbent resin precursor before adding the solution containing the surface cross-linking agent is preferably 35 to 80 ° C, more preferably 35 to 70 ° C, and further preferably 35 to 50 ° C. preferable. After the temperature of the water absorbent resin precursor is adjusted to the above range, it is preferably mixed with a solution containing a surface crosslinking agent. When the temperature of the water-absorbent resin precursor before the addition of the solution containing the surface crosslinking agent is higher than the above range, the miscibility with the solution containing the surface crosslinking agent tends to deteriorate. In order to adjust the temperature to a temperature lower than the above range, not only takes time to forcibly cool and cool the water-absorbent resin precursor, but also agglomeration of the cooled water-absorbent resin precursor powder is observed. Energy loss during heating may increase.

  Moreover, it is preferable that the liquid temperature of the solution containing a surface crosslinking agent is lower than the temperature of a water absorbing resin precursor. Specifically, it is preferably 10 ° C. or more lower than the temperature of the water absorbent resin precursor, more preferably 20 ° C. or more, and particularly preferably 30 ° C. or more. In addition, as above-mentioned, the solution containing a surface crosslinking agent can be sprayed from a nozzle, In that case, the liquid temperature should be more than a freezing point. Moreover, when the liquid temperature of the solution containing the surface cross-linking agent is too high, the liquid absorption speed to the water-absorbent resin precursor is increased, which may inhibit uniform mixing.

  The droplets of the solution containing the surface crosslinking agent when sprayed from the nozzle preferably have an average particle size smaller than the average particle size of the water absorbent resin precursor. Specifically, it is preferably 300 μm or less, and more preferably 250 μm or less.

  Moreover, it is preferable that the maximum spray angle is 50 degrees or more as the spray angle from a nozzle. As a result, as described in JP-A-2002-201290, the solution containing the surface cross-linking agent is sprayed from the nozzle in an empty conical shape in which the spray pattern has an annular shape, or the spray pattern has a biconvex lens shape. It is possible to spray from the nozzle in the shape of an elliptic cone. On the other hand, when the spray angle is smaller than 50 °, the diffusion state of the solution containing the surface cross-linking agent sprayed in the mixing apparatus is diffused at a low density and the portion where the solution containing the surface cross-linking agent is excessively diffused. In some cases, the mixed state of the water-absorbing resin precursor and the solution containing the surface cross-linking agent may be biased. The maximum spray angle is 180 ° or less due to the structure of the nozzle.

  Further, when the solution containing the surface cross-linking agent is sprayed from the nozzle so as to have the above-mentioned predetermined spray angle, the aqueous solution is sprayed on the cross-sectional area perpendicular to the axial direction of the mixing apparatus and including the injection point of the nozzle. The projected area of the diffusion state is preferably 70% or more and 100% or less, more preferably 80% or more and 100% or less, and more preferably 90% or more and 100% or less of the cross-sectional area perpendicular to the axial direction of the mixing device. More preferably. When the cross-sectional area is less than 70%, the mixed state of the water-absorbing resin precursor and the solution containing the surface cross-linking agent may be biased.

  There may be only one nozzle or two or more nozzles provided in the mixing device, but the spray diffusion state is applied to the cross-sectional area of the mixing device including the injection point of the nozzle. In order to increase the projected area, two or more are preferable. The mixing device used when mixing the water-absorbing resin precursor and the solution containing the surface cross-linking agent preferably has a large mixing force in order to mix the two uniformly and reliably. The body is preferably flowing with stirring or airflow.

  The above mixing devices include vertical mixers, cylindrical mixers, double wall conical mixers, V-shaped mixers, ribbon mixers, screw mixers, fluidized-type furnace rotary disk mixers, airflow Examples thereof include a type mixer, a double-type kneader, an internal mixer, a pulverizing type kneader, a rotary mixer, a screw type extruder, a Ladige stirrer, and a turbulizer stirrer. Moreover, a high-speed stirring mixer having a stirring shaft provided with a plurality of stirring boards, a vertical mixing device, a saw-tooth mixing device, or the like can also be suitably used. The “high-speed stirring mixer” here refers to a mixer that generates a mixing force by rotating a stirring shaft provided with a plurality of stirring boards. Moreover, although the rotation speed of the said stirring shaft is 100 rpm-5000 rpm normally, it is preferable that it is 200 rpm-4000 rpm, and it is more preferable that it is 500 rpm-3000 rpm.

  Further, the inner wall of the mixing device has a contact angle with water of 60 ° or more in order to prevent a wet mixture composed of a water-absorbing resin precursor and a solution containing a surface crosslinking agent from adhering to form an aggregate. It is preferable to have an inner wall formed of a base material having a heat distortion temperature of 70 ° C. or higher. As such a base material, for example, any base material described in JP-A-4-214734 can be used.

  The inner wall temperature of the mixing apparatus preferably has a temperature exceeding room temperature. Specifically, the inner wall temperature of the mixing device is preferably maintained at 40 ° C. or higher, more preferably 50 ° C. to 100 ° C. or higher. The inner wall temperature of the mixing device is preferably higher than the temperature of the water absorbent resin precursor. Specifically, the temperature difference is preferably 40 ° C. or less, and more preferably 20 ° C. or less. When the inner wall temperature of the mixing apparatus is room temperature or lower, when the solution containing the surface cross-linking agent and the water-absorbing resin precursor are mixed, the wet mixture comprising the water-absorbing resin precursor and the solution containing the surface cross-linking agent becomes the inner wall. May adhere to and form aggregates.

(II. Stir drying step)
In the stirring and drying step, it is sufficient that the wet mixture is dried by stirring so that a dry particulate composition containing a surface cross-linking agent and occupying 80% by weight or more of particles passing through an opening of 10 mm can be obtained. Other specific configurations such as drying conditions and the like are not particularly limited. In other words, in the stirring and drying step, the wet mixture composed of the solution containing the surface crosslinking agent and the water-absorbing resin precursor is in an agglomerated state and the fluidity is low. It is a step of loosening and forming a dry particulate composition that is in a dispersed state with high fluidity. In the present specification, “drying” means reducing the water content of the aggregated water-absorbent resin particles.

  In the stirring and drying step, uniform drying is not efficiently performed in a state where the wet mixture is agglomerated, so it is preferable to eliminate such agglomerated state as quickly as possible. Thereby, a water absorbing resin can be manufactured more efficiently.

  In the stirring and drying step, it is preferable that the wet mixture composed of the solution containing the surface cross-linking agent and the water-absorbent resin precursor is made into particles having a particle diameter that can pass through a sieve having an opening of 10 mm. More specifically, the particle diameter is preferably 10 mm or less, more preferably 5 mm or less, further preferably 2 mm or less, and particularly preferably 1 mm or less. Such particles are sufficiently dispersed, the powder has high fluidity, and has the effect of improving the heating efficiency in the surface cross-linking step described later.

  Moreover, it is preferable that the particle | grains which have said particle diameter occupy 80 weight% or more of the particle | grains obtained in the said stirring drying process. If the particle having the above particle diameter is within the above range, the water-absorbent resin particles can be uniformly heat-treated in the surface cross-linking step described later.

  In addition, the method of measuring the particle | grains which pass a sieve with an opening of 10 mm can be performed according to the particle size measuring method which measures a water-absorbent resin particle with a JIS standard sieve. Specifically, the water-absorbent resin particles are charged into a JIS standard sieve (The IIDA TESTING SIEVE: 80 mm inner diameter) with an opening of 10 mm, and a low-tap type sieve shaker (manufactured by Iida Manufacturing Co., Ltd., ES-65 type sieve shaker). This is done by classifying for 1 minute and measuring the weight of the passed particles. The method for measuring particles passing through sieves having openings of 5 mm, 2 mm, and 1 mm is also the same as described above.

  In the stirring and drying step, the moisture content of the wet mixture in which the particles are aggregated, which is composed of the solution containing the surface cross-linking agent and the water-absorbing resin precursor, is reduced by drying. In the stirring and drying step, as the moisture content of the wet mixture decreases, the aggregation of the particles decreases and a powder having high fluidity can be obtained.

  The water content of the water-absorbent resin powder after the stirring and drying step is not particularly limited, but may be appropriately changed depending on the intended crosslinking reaction and / or the type of the surface crosslinking agent to be used. Moreover, although the decreasing rate of the moisture content of the said wet mixture in a stirring drying process is not specifically limited, Usually, it is preferable 20-90%, and it is more preferable that it is 30-90%, 40 It is more preferable that it is -90%, and it is especially preferable that it is 50-80%.

  In addition, the measuring method of the said moisture content in this specification is as follows.

  About 1.0 g of water-absorbent resin powder as a measurement sample is placed in an aluminum cup weighing 0.8 g, dried in an oven heated to 180 ° C. for 3 hours, then immediately placed in a desiccator and cooled to near room temperature. Weigh. The moisture content can be calculated using the following equation.

Moisture content (%) = (measurement sample weight before drying−measurement sample weight after drying) ÷ (measurement sample weight before drying) × 100
Moreover, the decreasing rate of the moisture content of the wet mixture by drying in the stirring and drying step can be calculated using the following equation.

Decreasing rate of moisture content of wet mixture (%) = (moisture content of wet mixture (%) − moisture content of water absorbent resin powder after stirring and drying step (%)) ÷ (moisture content of wet mixture ( %)) X 100
In the stirring / drying step, it is preferable to use a processing apparatus equipped with a stirring blade. When using a processing apparatus having a stirring blade of the same shape and the same size as the surface cross-linking process described later, the rotation speed of the stirring blade in the stirring and drying process may be larger than the rotation speed of the stirring blade in the surface cross-linking process. preferable. In the stirring and drying step, on a normal production scale, the number of rotations is preferably within a range of 5 to 300 rpm, more preferably 10 to 300 rpm, and further preferably 20 to 300 rpm.

  When stirring blades of different sizes are used in the stirring and drying step and the surface cross-linking step, in order to compare the stirring blades in both steps, the peripheral speed is a parameter expressed by the diameter of the stirring blade and the rotation speed of the stirring blade. Can be used. The peripheral speed is a parameter represented by the following formula.

V = 2πrn / 60
(In the formula, V represents the peripheral speed (m / s), r represents the diameter (m) of the stirring blade, and n represents the rotational speed (rpm) of the stirring blade.
The peripheral speed of the stirring blade in the stirring and drying step is preferably larger than the peripheral speed of the stirring blade in the surface cross-linking step. A preferable peripheral speed range in the stirring and drying step is preferably 0.15 to 10 (m / s), preferably 0.3 to 10 (m / s), although it depends on the size of the apparatus. More preferably, it is 0.5-10 (m / s).

  As described above, if the rotation speed of the stirring blade and the peripheral speed of the stirring blade are large, the time required for the stirring and drying step can be shortened.

  There are various types of the shape of the stirring blade, but it is not particularly limited in the present invention. Although the number of stirring blades per unit length of the stirring shaft depends on the shape of the stirring blade, the larger the number, the stronger the stirring can be performed.

  In general, the reaction rate of the surface cross-linking agent increases as the average temperature rise rate of the water-absorbent resin powder increases, so from the viewpoint of improving the productivity of the water-absorbent resin, the water-absorbent resin powder in the stirring and drying step. The average heating rate of the body is preferably fast. Further, in the present invention, increasing the average temperature rising rate of the water-absorbing resin powder in the stirring and drying step not only increases the reaction rate of the surface cross-linking agent but also the solution containing the surface cross-linking agent and the water-absorbing resin. Moisture contained in the wet mixture composed of the precursor is quickly evaporated. As a result, the agglomerated state is eliminated and a highly fluid powder can be obtained in a short time. If such a powder having good fluidity is obtained in the stirring and drying step, it is necessary to use a heat treatment apparatus having no stirring blades or a weaker stirring than the stirring and drying step in the surface crosslinking step described later. The reaction can be performed up to the surface crosslink density. As a result, damage to the finally obtained water-absorbing resin can be reduced, and a water-absorbing resin having good physical properties can be obtained.

  In the stirring and drying step, the average temperature rising rate is not particularly limited, and may be appropriately changed depending on the intended crosslinking reaction and / or the type of the surface crosslinking agent to be used. The “average rate of temperature increase” refers to the average value of the temperature of the water absorbent resin powder that has risen over a certain period of time in the temperature profile of the water absorbent resin from the inlet to the outlet inside the heat treatment apparatus. In a normal production scale, the average rate of temperature rise for 5 minutes from the start of the stirring and drying step is preferably 10 ° C./min or more, more preferably 15 ° C./min or more, and 20 ° C./min or more. More preferably. The average rate of temperature rise from 5 minutes to 15 minutes after the start of the stirring and drying step is preferably 3 ° C / min or more, more preferably 5 ° C / min or more, and 7 ° C / min or more. More preferably. Furthermore, it is preferable that the average rate of temperature increase after 15 minutes from the start of the stirring and drying step be 3 ° C./min or more. According to this, the wet mixture is exposed to a high temperature in a short time, and as a result, the water contained in the wet mixture composed of the solution containing the surface cross-linking agent and the water absorbent resin precursor is evaporated in a short time. In addition, particles with high fluidity can be obtained in a short time.

  However, if the average heating rate in the stirring and drying step is too fast, the surface crosslinking reaction proceeds too much, and CRC (saline solution), which is one of the important physical properties required for the finally obtained water-absorbing resin, is used. The centrifuge retention capacity tends to be too small. In particular, this tendency is remarkable when a highly reactive material is used as the surface cross-linking agent. Therefore, it is preferable that the average temperature increase rate in the stirring and drying step be within a range in which a desired CRC is obtained.

A factor that determines the rate of temperature rise in the heat treatment apparatus is the ratio of the heat transfer area to the volume. If a heat treatment apparatus having a relatively large heat transfer area with respect to the volume is used, it is possible to achieve a higher rate of temperature increase than described as preferable in the present invention. The stirring and drying step can be performed using a conventionally known heat treatment apparatus. The heat treatment apparatus to be used depends on the ratio between the heat transfer area and the effective volume (heat transfer area) depending on the production scale of the water absorbent resin. It is preferable to select a device having an appropriate (effective volume). Specifically, the heat transfer area / effective volume is preferably 10 m ⁻¹ or more, and more preferably 15 m ⁻¹ or more. In the same type of processing apparatus, the smaller the effective volume, the larger the (heat transfer area / effective volume) value.

  Moreover, in order to make it in the range of the preferable average temperature increase rate mentioned above, it can also achieve by making a heat source act on a heat processing apparatus and raising heating temperature. There are no particular limitations on the type of heat source, but there are, for example, heating by circulating pressurized steam, heat transfer oil, etc. in a heat transfer device, heating by heating wire, microwave, electromagnetic induction, etc. . The heat medium circulation device and the heating device can be attached to any place such as a jacket that can be attached to the processing device or the inside of the stirring blade. The type of heat source, the specifications of the heat source device, the set temperature of the heat source, and the supply amount per unit time of the heat source can be appropriately set depending on the type of surface crosslinking agent used and the type of heat treatment apparatus.

  Moreover, although the processing time of the said stirring drying process changes with processing apparatuses, it is preferable that the said processing time is 10 to 60 minutes, It is more preferable that it is 10 to 40 minutes, It is 10 to 30 minutes Is more preferable. If the treatment time is shortened, the productivity of the water absorbent resin can be improved.

  The processing apparatus used for the said stirring drying process is not specifically limited, A conventionally well-known processing apparatus and a heat processing apparatus can be used. For example, a wet mixture composed of a solution containing a surface cross-linking agent and a water-absorbing resin precursor is put into a biaxial groove type stirring and drying apparatus and heated to wet the surface cross-linking agent and the water-absorbing resin precursor. The mixture can be stirred and dried. In the stirring and drying step, the step can be further divided according to the properties of the particles.

  Moreover, it is preferable to perform the said stirring drying process, supplying the carrier gas for adjusting temperature and a dew point. Drying does not necessarily require heating. Moreover, it can also dry to a predetermined state by introduction | transduction of carrier gas. Examples of the carrier gas include steam, air, and nitrogen. Further, the supply amount of the carrier gas is not particularly limited, and may be determined as appropriate. By supplying the carrier gas, water vapor generated during the reaction is efficiently removed in the stirring and drying step. Thereby, the said wet mixture can be dried in a short time.

Further, the carrier gas may be appropriately depressurized or pressurized. Moreover, it may be appropriately heated or cooled. In general, air at around room temperature (for example, 0 to 50 ° C.) is subjected to substantial normal pressure (1.013 × 10 ⁵ Pa (1 atm) ± 10%, preferably ± 5%, more preferably ± 1%. ) Is preferably supplied.

  Further, in the stirring and drying step, when there is an upper space of a wet mixture composed of a solution containing a surface cross-linking agent not in contact with the heat transfer surface and a water absorbent resin precursor, the temperature may be controlled to a specific temperature and a specific dew point.

  In addition, the wet mixture composed of the solution containing the surface cross-linking agent and the water-absorbing resin precursor used in the stirring and drying step may be preheated to room temperature or to an extent that the powder is easy to handle. However, since the surface cross-linking agent reacts when heated too much, it is preferable to heat it so that the temperature is preferably in the range of room temperature to 100 ° C, more preferably room temperature to 80 ° C, and even more preferably room temperature to 40 ° C. .

  Further, even when both the stirring and drying step and the surface cross-linking step are performed in one processing apparatus, the heating and / or stirring conditions satisfying the above conditions are set in one processing apparatus in the stirring and drying step. It can provide in the front | former stage part.

(III. Surface cross-linking step)
In the surface cross-linking step, it is only necessary to heat-treat the dry particulate composition to cause a desired surface cross-linking reaction, and other configurations such as a device used and reaction conditions are not particularly limited. More specifically, the surface cross-linking step is obtained by stirring and drying a wet mixture comprising a solution containing the above-mentioned surface cross-linking agent and a water absorbent resin precursor in order to obtain a desired cross-linking density. This is a step of heating a high dry particulate composition to cause a desired crosslinking reaction to proceed.

  In the above-mentioned dry particulate composition, the aggregation is loosened, the particles are dispersed, and the fluidity is high. Therefore, in the surface cross-linking step, stirring may be weak, or a heat treatment apparatus without a stirring blade may be used. Good. Furthermore, the average temperature increase rate of the water-absorbent resin powder can be slowed down, and the surface cross-linking density of the product can be more easily controlled.

  The above-mentioned “desired crosslink density” specifically means that CRC and AAP by the measurement method employed in the examples described later are within the following ranges. That is, the CRC is preferably 10 to 60 g / g, more preferably 20 to 55 g / g, and still more preferably 25 to 50 g / g. Moreover, AAP is preferably 10 g / g or more, more preferably 15 g / g or more, and further preferably 20 g / g or more.

  The average temperature increase rate in the surface cross-linking step is not particularly limited, and may be appropriately changed depending on the average temperature increase rate in the above-described stirring and drying step, the target cross-linking reaction, and / or the type of the surface cross-linking agent. it can. Even in the agitation and drying process described above, the processing time can be shortened by increasing the agitation and increasing the average heating rate, and further, the processing time is shortened, thereby suppressing damage to the powder. be able to. However, if the heat treatment is performed only in the above-described stirring and drying step, the surface crosslinking density is more difficult to control because the average temperature rise rate is high. Therefore, in the present invention, in the surface cross-linking step, the surface cross-linking density of the product can be more easily controlled by relatively slowing the average temperature rising rate. Specifically, it is preferably 10 ° C./min or less, more preferably 5 ° C./min or less, further preferably 3 ° C./min or less, and particularly preferably 1 ° C./min or less. preferable. Thus, since the surface cross-linking step does not require a temperature increase as compared with the stirring and drying step, (heat transfer area / effective volume) may be smaller than the stirring and drying step. For these reasons, when using the same type of equipment in the stirring and drying step and the surface cross-linking step, regarding the temperature rise, the processing device used in the stirring and drying step may have a smaller effective volume than the processing device used in the surface cross-linking step. preferable.

  Furthermore, in the surface cross-linking step, setting the average temperature rising rate within the range can also be achieved by raising the heating temperature by applying a heat source to the heat treatment apparatus. The type of the heat source is not particularly limited. For example, heating by circulating pressurized steam, heat transfer oil, etc. in the heat transfer device, heating wire, microwave, heating by electromagnetic induction, etc. is there. The heat medium circulation device and the heating device can be attached to any place such as a jacket that can be attached to the processing device or the inside of the stirring blade. The type of heat source, the specifications of the heat source device, the set temperature of the heat source, and the supply amount per unit time of the heat source can be appropriately set depending on the type of surface crosslinking agent used and the type of heat treatment apparatus.

  When polyhydric alcohol, carbonate compound or the like is used as the surface cross-linking agent and surface cross-linking is performed by an esterification reaction, for example, esterification described in US Pat. No. 4,734,478 in an esterification cross-linking reaction with a polyhydric alcohol is performed. It is preferable to have a temperature profile that passes through 190 ° C. or more, which is the temperature of the water-absorbent resin powder that is sufficiently performed.

  In the surface cross-linking step, the dry particulate composition may or may not be stirred. In the case of stirring the dried particulate composition, the aggregation may be loosened in the stirring and drying step, and thus stirring may be weaker than in the stirring and drying step. Specifically, in the surface cross-linking step, the rotation speed of the stirring blade and the peripheral speed of the stirring blade are preferably smaller than those in the stirring and drying step. The rotation speed of the stirring blade is preferably in the range of 0 to 30 rpm, more preferably in the range of 0 to 20 rpm, and further preferably in the range of 0 to 10 rpm. Furthermore, the peripheral speed of the stirring blade is preferably 2 m / s or less, more preferably 1 m / s or less, and further preferably 0.3 m / s or less. Although the number of stirring blades per unit length of the stirring shaft depends on the shape of the stirring blade, the smaller the number, the weaker stirring is preferable.

  The apparatus used for the surface cross-linking step is not particularly limited, and apparatuses that can be used in the stirring and drying step can be similarly used. In the surface cross-linking step, it is not necessary to stir the mixture, and therefore an apparatus that does not include a stirring blade can be used. In the surface crosslinking step, the step can be further divided according to the properties of the particles.

  Further, even when both the stirring and drying step and the surface cross-linking step are performed in one processing apparatus, in the surface cross-linking step, the heating conditions and / or the stirring conditions satisfying the above conditions are set in one processing apparatus. It can be provided in the latter part of the inside.

  In the method for producing a water absorbent resin according to the present invention, it is preferable to cool the water absorbent resin after the surface cross-linking step is completed.

  When the surface crosslinking method of the present invention described above is used, in the step (2) and / or the step (3) and / or the cooling step, [in the method for producing a water absorbent resin according to the present invention, It can be suitably used as a treatment apparatus equipped with the stirring means described in the section of “Aspect of Stirring Device (Agitating Means) Used in Reforming Step and / or Cooling Step”.

  In this case, at least one of the step (2), the step (3), and the cooling step can be performed using a processing apparatus equipped with the stirring means described above. Since it can carry out uniformly, it is preferable to perform all the processes of the said process (2), the said process (3), and the said cooling process using the processing apparatus provided with the above-mentioned stirring means.

  In addition, also when performing at least 1 process of the said process (2), the said process (3), and the said cooling process using the processing apparatus provided with the above-mentioned stirring means, the above-mentioned stirring means was provided. It is possible to obtain the fine powder generation suppressing effect by the processing device. In this case, the processing apparatus and heat treatment apparatus described in (1. Modification process) can be used for the other process.

  Moreover, it is preferable that the above-mentioned processing apparatus used by the said process (2), the said process (3), and the said cooling process is a processing apparatus from which a kind and / or an effective volume differ, respectively. Moreover, it is preferable that the above-mentioned processing apparatuses used in the step (2), the step (3), and the cooling step are operated under different heating conditions and / or different stirring conditions. Thereby, the optimal heating conditions and / or stirring conditions for each step can be selected, and a water-absorbing resin exhibiting good physical properties can be efficiently produced.

  In addition, the above-mentioned “processing devices of different types” mean processing devices having different processing device shapes. Further, the above-mentioned “processing devices having different effective volumes” mean processing devices having different effective volume values of the processing devices.

  “Different heating conditions” means the type of heat source that can be attached to the processing apparatus, the specifications of the heat source apparatus that can be attached to the processing apparatus, the set temperature of the heat source that can be attached to the processing apparatus, It means heating conditions in which at least one of the heat supply units provided per unit time of the heat source that can be produced and the above-mentioned heat transfer means provided in the stirrer or rotating shaft and scraping blades are different.

  Furthermore, the “different stirring conditions” include the ratio of the maximum thickness of the stirring plate to the minimum thickness, the shape of the stirring plate, the size of the stirring plate diameter, the number of stirring plates per unit length of the rotating shaft, At least one of the number of rotations of the board, the cross-sectional area of the lifting blade, the length in the y direction of the lifting blade, and the number of the lifting blades attached to the stirring board means different stirring conditions.

  The present invention is not limited to the configurations described above, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments are appropriately combined. The obtained embodiment is also included in the technical scope of the present invention.

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

  In addition, since the water absorbent resin used as the final product such as sanitary materials absorbs moisture, the water absorbent resin is appropriately separated from the final product and dried under reduced pressure and low temperature (for example, at a pressure of 1 mmHg or less). And drying at 60 ° C. for 12 hours). In addition, the water content of the water-absorbent resin used in the examples and comparative examples of the present invention was 6% by mass or less.

  Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. In the following Examples and Comparative Examples, CRC (Centrification Retention Capacity), AAP (Absorbance Against Pressure; Absorbency against pressure of 4.83 kPa), SFC (Saline Flow Conductivity); ) And particle size measurement were evaluated as follows.

<CRC measurement>
CRC was evaluated with an absorption capacity of 30 minutes under no pressure against 0.90% by mass physiological saline. Specifically, under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%, 0.20 g of the water-absorbent resin is uniformly put in a non-woven bag (60 mm × 60 mm) and sealed, and then 0.9% at room temperature. It was immersed in the mass% physiological saline. After 30 minutes, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge (Centrifuge manufactured by Kokusan Co., Ltd .: Model H-122), and the mass W1 (g) of the bag was measured. Further, the same operation was performed without using the water absorbent resin, and the mass W0 (g) at that time was measured. And from these W1 and W0, the absorption capacity | capacitance (g / g) was computed according to following formula (1).

Absorption capacity (g / g)
= (W1 (g) -W0 (g)) / mass of water absorbent resin (g) (1)
<AAP measurement>
AAP was evaluated by the absorption capacity under pressure of 60 minutes at 4.83 kPa against 0.90% by mass physiological saline. Specifically, a stainless steel 400 mesh wire mesh (mesh size: 38 μm) is fused to the bottom of a plastic support cylinder having an inner diameter of 60 mm, and under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%, The outer diameter was adjusted so that 0.90 g of the water-absorbing resin was uniformly spread on the net, and a load of 4.83 kPa (0.7 psi) was uniformly applied to the water-absorbing resin thereon. Was slightly smaller than 60 mm, a gap with the support cylinder was not generated, and a piston and a load that could not be prevented from moving up and down were placed in this order, and the mass Wa (g) of this measuring device set was measured.

  A 90 mm diameter glass filter (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100 to 120 μm) is placed inside a 150 mm diameter Petri dish, and 0.90% by mass physiological saline (20 to 25 ° C.) is made of glass. It added so that it might become the same level as the upper surface of a filter. On top of that, a sheet of filter paper having a diameter of 90 mm (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retention particle diameter 5 μm) was placed so that the entire surface was wetted, and Excess liquid was removed.

  The set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. After 1 hour, the measuring device set was lifted and its mass Wb (g) was measured. And the absorption capacity | capacitance (g / g) under pressure was computed from Wa and Wb according to following formula (2).

Absorption capacity under pressure (g / g)
= (Wa (g) -Wb (g)) / mass of water-absorbent resin (0.9 g) (2)
<SFC measurement>
The saline flow conductivity (SFC) is a value indicating the liquid permeability during swelling of the water absorbent resin particles or the water absorbent resin composition. It shows that it has high liquid permeability, so that the value of SFC is large.

  This was performed according to the saline flow conductivity (SFC) test described in JP-T-9-509591.

  Using the apparatus shown in FIG. 4, a water-absorbent resin (water-absorbent resin composition) (0.900 g) uniformly placed in a container 400 was placed under pressure of 0.3 psi (2.07 kPa) in artificial urine (1). Swell for 60 minutes, record the gel layer height of gel 440, then swell 0.69 wt% saline 330 from tank 310 under constant hydrostatic pressure under pressure of 0.3 psi (2.07 kPa) The gel layer was passed through. The SFC test was performed at room temperature (20-25 ° C.).

  Using a computer and a balance, the amount of liquid passing through the gel layer at 20 second intervals as a function of time was recorded for 10 minutes. The flow rate Fs (T) through the swollen gel 440 (mainly between the particles) was determined in units of g / s by dividing the increased mass (g) by the increased time (s).

  Let Ts be the time at which a constant hydrostatic pressure and a stable flow rate were obtained, use only the data obtained between Ts and 10 minutes for the flow rate calculation, and use the flow rate obtained between Ts and 10 minutes. The value of Fs (T = 0), ie the initial flow rate through the gel layer, was calculated. Fs (T = 0) was calculated by extrapolating the result of the least squares method of Fs (T) versus time to T = 0.

Saline flow conductivity (SFC)
= (Fs (t = 0) × L0) / (ρ × A × ΔP)
= (Fs (t = 0) × L0) / 139506
here,
Fs (t = 0): flow rate expressed in g / s L0: height of gel layer expressed in cm ρ: density of NaCl solution (1.003 g / cm ³ )
A: Area above the gel layer in the cell 410 (28.27 cm ² )
ΔP: hydrostatic pressure applied to the gel layer (4920 dyne / cm ² )
The unit of the SFC value is (10 ⁻⁷ · cm ³ · s · g ⁻¹ ).

  In the apparatus shown in FIG. 4, a glass tube 320 is inserted into the tank 310, and the lower end of the glass tube 320 is 5 cm from the bottom of the swollen gel 440 in the cell 410 with 0.69 mass% saline solution 330. It was arranged so that it could be maintained at the upper height. The 0.69 mass% saline solution 330 in the tank 310 was supplied to the cell 410 through the L-shaped tube 340 with a cock. A container 480 that collects the liquid that has passed therethrough is disposed under the cell 410, and the collection container 480 is installed on the upper pan balance 490. The inner diameter of the cell 410 is 6 cm. A 400 stainless steel wire mesh (aperture 38 μm) 420 was installed.

  The bottom of the piston 460 has a hole 470 sufficient for the liquid to pass through, and the bottom has a glass filter 450 with good permeability so that water-absorbent resin particles or its swelling gel do not enter the hole 470. It was. The cell 410 was placed on a table on which the cell was placed, and the surface of the table in contact with the cell was placed on a stainless steel wire mesh 430 that did not prevent liquid permeation.

  Artificial urine (1) is calcium chloride dihydrate 0.25 g, potassium chloride 2.0 g, magnesium chloride hexahydrate 0.50 g, sodium sulfate 2.0 g, ammonium dihydrogen phosphate 0.85 g, What added 0.15 g of hydrogen ammonium hydrogenphosphate and 994.25 g of pure waters was used.

<Particle size measurement>
The water-absorbent resin particles are classified and screened with JIS standard sieves having openings of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, and 45 μm, respectively, and the weight percentage of the particle diameter of less than 150 μm is measured. At the same time, the residual percentage R of each particle size was plotted on a logarithmic probability paper. Thereby, the particle size corresponding to R = 50% by weight was read as the weight average particle size (D50).

  In addition, classifying sieving is performed by charging 10.00 g of a water-absorbing resin into the above-mentioned JIS standard sieve (The IIDA TESTING SIEVE: ID 80 mm) and a low-tap type sieve shaker (Iida Seisakusho, ES-65 type sieve shaker). Machine) for 5 minutes. The mass average particle diameter (D50) is a standard sieve particle diameter corresponding to 50% by mass of the whole particle with a standard sieve having a constant mesh as described in US Pat. No. 5,051,259.

<Production example: Production of water-absorbent resin precursor>
In a kneader equipped with two sigma blades, a monomer aqueous solution consisting of sodium acrylate, acrylic acid and water with a monomer concentration of 38% by mass and a neutralization rate of 70 mol% was prepared, and polyethylene glycol diacrylate (average) was used as an internal crosslinking agent. Ethylene glycol unit number: 9) It was dissolved so as to be 0.03 mol% (based on monomer).

  Subsequently, nitrogen gas was blown into the aqueous monomer solution to reduce dissolved oxygen in the aqueous monomer solution and to replace the entire reaction vessel with nitrogen. Subsequently, while rotating two sigma blades, sodium persulfate 0.12 g / mol (monomer) and L-ascorbic acid 0.005 g / mol (monomer) were added as polymerization initiators. Then, polymerization was performed with stirring in the kneader, and a hydrophilic crosslinked polymer having an average particle diameter of about 2 mm was obtained after about 40 minutes.

  When the obtained hydrophilic crosslinked polymer is used in the following Examples 1 to 4 and Comparative Examples 1 to 4, the following Examples 5 to 6 and Comparative Examples 5 to 6 are used at 170 ° C. for 55 minutes. When used, it was dried with a hot air dryer at 170 ° C. for 60 minutes. The dried product is pulverized with a roll mill pulverizer, classified with a sieve having openings of 850 μm and 105 μm, and a water absorbent resin precursor having a water content of 5%, a weight average particle size of 478 μm, and a weight percentage of less than 150 μm and a weight percentage of 0.8%. (A) was obtained.

<Example 1>
0.34 parts by mass of 1,4-butanediol (hereinafter, also referred to as “1,4-BD”) and propylene glycol (hereinafter “ (Also referred to as “PG”) 3.9 parts by mass of a surface cross-linking agent-containing aqueous solution consisting of 0.56 parts by mass and 3 parts by mass of pure water was spray mixed with a continuous high-speed stirring mixer (Hosokawa Micron Turbulizer). A humidified product was used. The humidified product is a conductive heat transfer type grooved stirrer with a paddle (stirring board) diameter of 170 mmφ, a heat transfer area of 1.5 m ² , and an effective volume of 0.089 m ³ (manufactured by Nara Machinery Co., Ltd., multi-fin processor; NFP- 1.6W type).

The conductive heat transfer type grooved stirring dryer is a flat disk-shaped (fan-shaped) stirring plate having scraping blades (ratio of the maximum thickness of the stirring plate to the minimum thickness in a section cut along the yz plane = 4 mm). / 4 mm = 1, the cross-sectional area of the scraping blade in the cross section cut along the yz plane: 120 mm × 30 mm = 3600 mm ² , the area between the stirrers 16366 mm ² ) is provided for each 15 rotation axes (total of 30 sheets). This is a biaxial groove type agitation dryer with shafts arranged parallel to each other. The stirring plates attached to the two rotating shafts are non-overlapping and arranged in parallel. “Overlap” means that when a conduction heat transfer type grooved stirring dryer has a plurality of rotating shafts, a plurality of stirring plates disposed on different rotating shafts are configured to engage with each other. To do.

Heated water vapor was injected into the inner wall, the stirring plate, and the rotating shaft of the agitating dryer, and the surface temperature of the inner wall, the stirring plate, and the rotating shaft was 210 ° C. The throughput was 45 kg / h and the average residence time was 60 minutes. After the heat treatment, the surface-crosslinked water-absorbing resin was supplied to a cooler (Okawara Seisakusho, horizontal continuous fluidized bed dryer with heating tube; FCA-2 type) connected in series to the agitation dryer. As cooler cooling, normal temperature tap water was circulated in the heat pipe, and the water-absorbent resin was cooled with a room temperature of 0.5 m / s with respect to a floor surface of 0.3 m ² . The water absorbent resin was sieved with a sieve having an aperture of 850 μm to obtain a modified water absorbent resin (water absorbent resin 1). The material passing through the 150 μm sieve was 1.0% of the total weight of the surface-crosslinked water absorbent resin. The modified water-absorbent resin had a CRC of 29 (g / g), an AAP of 26 (g / g), and an average particle size of 480 μm. The results are shown in Table 1.

<Example 2>
A surface cross-linking agent comprising 0.34 parts by mass of 1,4-butanediol, 0.56 parts by mass of propylene glycol and 3 parts by mass of pure water with respect to 100 parts by mass of the water absorbent resin precursor (A) obtained in the production example. 3.9 parts by mass of the aqueous solution was spray-mixed with a continuous high-speed stirring mixer (Turbulizer manufactured by Hosokawa Micron Corporation) to obtain a humidified product.

  The humidified product was continuously processed at a treatment rate of 40 kg / h using a conductive heat transfer type grooved stirring dryer (Nara Machinery Co., Ltd., paddle dryer; NPD-1.6W type). The agitation dryer was connected in series to a cooler (manufactured by Nara Machinery Co., Ltd., multi-fin processor; NFP-1.6W type). The rotation speed of the paddle (stirring board) of each apparatus was set to 30 rpm for the stirring dryer and 30 rpm for the cooling machine. As the heat medium, Matsumura Oil Barrel Therm 400 was used and circulated inside the paddle of the agitation dryer, and normal temperature tap water was circulated through the jacket and paddle in the cooler. The conduction heat transfer type grooved agitation dryer has two rotating shafts, and the attached agitators overlap and are arranged so as to engage with each other alternately.

  The powder temperature of the water absorbent resin at the raw material supply port of the agitation dryer was 40 ° C., and the powder temperature of the water absorbent resin at the water absorbent resin discharge port was 210 ° C. Stainless steel pipes are connected between the agitator and the cooler connected in series. The water-absorbent resin whose surface was cross-linked by the reforming process was immediately conveyed to a cooler and used for the cooling process. The surface-crosslinked water-absorbing resin thus obtained was sieved using a JIS standard sieve having an opening of 850 μm to obtain a modified water-absorbing resin (water-absorbing resin 2).

  The residence time was 60 minutes for the reforming process and 64.5 minutes for the cooling process. The material passing through the 150 μm sieve was 2.1% of the total weight of the surface-crosslinked water-absorbent resin. The modified water-absorbing resin had a CRC of 28 (g / g), an AAP of 25 (g / g), and an average particle size of 455 μm.

<Example 3>
The modified water-absorbent resin (water-absorbent resin 1) obtained in Example 1 was classified using a JIS standard sieve having an opening of 850 μm to 150 μm to obtain a water-absorbent resin whose particle size was adjusted. The average particle size of the water-absorbent resin whose particle size was adjusted was 480 μm, and 150 μm passed through a sieve (150 Pass amount) was 1.0%.

  Using the water-absorbent resin having the particle size adjusted, mixing was performed with a batch type cooler (manufactured by Nara Machinery Co., Ltd., multi-fin processor; NFP-1.6W type) with the water-absorbent resin outlet closed. The paddle (stirring board) of the batch-type cooler has a rotation speed of 30 rpm, normal temperature tap water is injected into the inner wall, stirrer board, and rotating shaft of the batch-type cooler, and the water-absorbent resin whose particle size is adjusted in the cooling container Was 50 kg.

  Sampling was carried out at a rotational speed of 30 rpm every predetermined time (30, 60, 120 minutes from the start of mixing) to obtain a water absorbent resin (3-1 to 3-3). The 150 Pass amount was 1.0% for the water absorbent resin 3-1, 1.1% for the water absorbent resin 3-2, and 1.3% for the water absorbent resin 3-3.

<Comparative Example 1>
A surface cross-linking agent comprising 0.34 parts by mass of 1,4-butanediol, 0.56 parts by mass of propylene glycol and 3 parts by mass of pure water with respect to 100 parts by mass of the water absorbent resin precursor (A) obtained in the production example. 3.9 parts by mass of the aqueous solution was spray-mixed with a continuous high-speed agitating mixer (Hosokawa Micron Turbulizer) to obtain a humidified product. The humidified product is heated using a conductive heat transfer type grooved stirrer (Nara Machinery Co., Ltd., NPD-1.6W type) having a paddle diameter of 160 mmφ, a heat transfer area of 2.5 m ² , and an effective volume of 0.065 m ^3. Processed.

The conduction heat transfer type grooved stirrer / dryer is provided with 17 scraping blades and 16 stirrer plates having a defect portion, and the maximum thickness of the stirrer plate in the cross section cut along the yz plane. minimum ratio thickness = 26 mm / 3 mm, the cross-sectional area of Kakiage blade in a cross section taken along the y-z plane: 39mm × 25mm × 2 sheets = 1950 mm ^2, a stirring machine between areas 15190mm ^2. Moreover, it is a biaxial groove type agitation dryer in which the agitators overlap each other. The stirring plates attached to the two rotating shafts overlap and are arranged so as to engage with each other alternately.

  Heated water vapor was injected into the inner wall, the stirring plate, and the rotating shaft of the agitating dryer, and the surface temperature of the inner wall, the stirring plate, and the rotating shaft was 210 ° C. The average residence time was 60 minutes and the throughput was 40 kg / h. The surface-crosslinked water-absorbent resin was taken out into a SUS container and cooled. The water-absorbent resin was sieved with a sieve having an opening of 850 μm to obtain a comparative water-absorbent resin 1. The 150 μm sieve passing material was 2.0% of the total weight of the surface-crosslinked water absorbent resin. The comparative water absorbent resin 1 had a CRC of 29 (g / g), an AAP of 25 (g / g), and an average particle size of 460 μm.

<Comparative example 2>
A surface cross-linking agent comprising 0.34 parts by mass of 1,4-butanediol, 0.56 parts by mass of propylene glycol and 3 parts by mass of pure water with respect to 100 parts by mass of the water absorbent resin precursor (A) obtained in the production example. 3.9 parts by mass of the aqueous solution was spray-mixed with a continuous high-speed agitating mixer (Hosokawa Micron Turbulizer) to obtain a humidified product.

  The humidified product was continuously processed at a treatment rate of 40 kg / h using a conduction heat transfer type grooved stirring dryer (Nara Machinery Co., Ltd., paddle dryer; NPD-1.6W type). The agitation dryer was connected in series to a cooler (Nara Machinery Co., Ltd., paddle dryer; NPD-1.6W type). The rotation speed of the paddle (stirring board) of each apparatus was set to 30 rpm for the stirring dryer and 30 rpm for the cooling machine. As the heat medium, Matsumura Oil Barrel Therm 400 was used and circulated inside the paddle of the agitation dryer, and normal temperature tap water was circulated through the jacket and paddle in the cooler. The conduction heat transfer type grooved agitation dryer has two rotating shafts, and the attached agitators overlap and are arranged so as to engage with each other alternately.

  The powder temperature of the water absorbent resin at the raw material supply port of the agitation dryer was 40 ° C., and the powder temperature of the water absorbent resin at the water absorbent resin discharge port was 210 ° C. Stainless steel pipes are connected between the agitator and the cooler connected in series. The water-absorbent resin whose surface was cross-linked by the reforming process was immediately conveyed to a cooler and used for the cooling process. The surface-crosslinked water-absorbing resin thus obtained was passed through a JIS standard sieve having an opening of 850 μm to obtain a comparative water-absorbing resin 2.

  The residence time was 64 minutes for the reforming process and 74 minutes for the cooling process. The product passing through the 150 μm sieve was 4.0% of the total weight of the surface-crosslinked water absorbent resin. The comparative water absorbent resin 2 had a CRC of 28.5 (g / g), an AAP of 25 (g / g), and an average particle size of 412 μm.

<Comparative Example 3>
The modified water-absorbent resin (water-absorbent resin 1) obtained in Example 1 was classified using a 850-150 μm JIS standard sieve to obtain a water-absorbent resin whose particle size was adjusted. In addition, the average particle diameter of the water-absorbent resin whose particle size was adjusted was 480 μm, and the 150 Pass amount was 1.0%.

  Using the water-absorbent resin having the particle size adjusted, mixing was performed with a batch type cooler (Nara Machinery Co., Ltd., NPD-1.6W type) in which the water-absorbent resin outlet was closed. The paddle (stirring board) of the batch-type cooler has a rotation speed of 30 rpm, normal temperature tap water is injected into the inner wall, stirrer board, and rotating shaft of the batch-type cooler, and the water-absorbent resin whose particle size is adjusted in the cooling container Was 40 kg.

  Sampling was carried out at a rotation speed of 30 rpm every predetermined time (30, 60, 120 minutes from the start of mixing) to obtain comparative water absorbent resins (3-1 to 3-3). The 150 Pass amount was 1.30% for the comparative water absorbent resin 3-1, 1.7% for the comparative water absorbent resin 3-2, and 2.2% for the comparative water absorbent resin 3-3.

<Example 4>
A surface cross-linking agent comprising 0.34 parts by mass of 1,4-butanediol, 0.56 parts by mass of propylene glycol and 3 parts by mass of pure water with respect to 100 parts by mass of the water absorbent resin precursor (A) obtained in the production example. 3.9 parts by mass of the aqueous solution was spray-mixed with a continuous high-speed stirring mixer (Turbulizer manufactured by Hosokawa Micron Corporation) to obtain a humidified product.

  The humidified product was continuously processed at a treatment rate of 40 kg / h using a conduction heat transfer type grooved stirring dryer (manufactured by Nara Machinery Co., Ltd., multi-fin processor; NFP-1.6W type). The agitation dryer was connected in series to a cooler (manufactured by Nara Machinery Co., Ltd., multi-fin processor; NFP-1.6W type). The rotation speed of the paddle (stirring board) of each apparatus was set to 30 rpm for the stirring dryer and 30 rpm for the cooling machine. As the heat medium, Matsumura Oil Barrel Therm 400 was used and circulated inside the paddle of the agitation dryer, and normal temperature tap water was circulated through the jacket and paddle in the cooler. The stirring plates attached to the two rotating shafts of the conductive heat transfer type grooved stirring dryer are non-overlapping and arranged in parallel.

  The powder temperature of the water absorbent resin at the raw material supply port of the agitation dryer was 40 ° C., and the powder temperature of the water absorbent resin at the water absorbent resin discharge port was 210 ° C. Stainless steel pipes are connected between the agitator and the cooler connected in series. The water-absorbent resin whose surface was cross-linked by the reforming process was immediately conveyed to a cooler and used for the cooling process. The surface-crosslinked water-absorbing resin thus obtained was sieved using a JIS standard sieve having an opening of 850 μm to obtain a modified water-absorbing resin (water-absorbing resin 4).

  The residence time was 60 minutes for the reforming process and 64.5 minutes for the cooling process. The material passing through the 150 μm sieve was 2.1% of the total weight of the surface-crosslinked water-absorbent resin. The modified water-absorbing resin had a CRC of 29 (g / g), an AAP of 26 (g / g), and an average particle size of 478 μm.

<Comparative Example 4>
Surface crosslinking agent containing 0.34 parts by mass of 1,4-butanediol, 0.56 parts by mass of propylene glycol and 3 parts by mass of pure water with respect to 100 parts by mass of the water-absorbent resin precursor (A) obtained in the production example. 3.9 parts by mass of the aqueous solution was spray mixed with a continuous high-speed stirring mixer (Turbulizer manufactured by Hosokawa Micron Corporation).

Conductive heat transfer groove type stirring and drying machine (made by Kurimoto Iron Works, model number CD-80, stirring plate) with paddle (stirring plate) diameter 80mmφ, heat transfer area 0.35m ² , effective volume 0.046m ³ (Conversion type).

The above-mentioned agitation dryer is provided with 14 scraping blades and 14 agitation plates having a defective portion, and the ratio of the maximum thickness of the agitation plate to the minimum thickness in a section cut along the yz plane = 15 mm. /2.5 mm, the cross-sectional area of the scraping blade in the cross section cut along the yz plane: 20 mm × 10 mm = 200 mm ² , and the area between the stirring plates is 2400 mm ² ). Moreover, the stirring board attached to the biaxial rotating shaft is a 2 axis | shaft groove type stirring dryer arranged so that it may overlap and it may mesh | engage alternately.

  Heated water vapor was injected into the inner wall, the stirring plate, and the rotating shaft of the agitation dryer, and the surface temperature of the inner wall, the stirring plate, and the rotating shaft was 220 ° C. The average residence time was 35 minutes and the throughput was 7 kg / h. The surface-crosslinked water-absorbent resin was taken out into a SUS container and cooled. The water absorbent resin was sieved with a sieve having an opening of 850 μm to obtain a modified water absorbent resin (Comparative water absorbent resin 4). The 150 μm sieve sieve was 1.5%. The comparative water absorbent resin 4 had a CRC of 27 (g / g), an AAP of 24 (g / g), and an average particle size of 475 μm.

Tables 1 and 2 show experimental conditions in the above Examples and Comparative Examples and various physical properties of the modified water absorbent resin. The “blade pitch” in the table means the distance in the y direction between adjacent stirring plates in the yz plane. For example, T ₄ in FIG. 2A and T ₄ ′ in FIG. Further, “blade length” in the table means the length in the y direction of the scraped blade in the yz plane. For example, T ₅ in FIG. 2A and T ₅ ′ in FIG. Furthermore, “raising blade (mm)” in the table means the dimensions (T ₅ × T ₆ ) in the z direction and y direction of the raking blade on the yz plane. On the other hand, the “cross-sectional area (%) of the lifting blade” in the table is, for example, the area of the lifting blade with respect to the area between the stirring boards, for example, (T ₆ × T ₅ × 2) in FIG. ) ÷ (T ₃ × T ₄ ) × 100. Further, “the distance (%) of the lifting blade” is the length of the lifting blade with respect to the area between the stirring plates, and for example, (T ₅ ) ÷ (T ₃ × T ₄ ) × 100 in FIG. .

<Example 5>
0.34 parts by mass of 1,4-butanediol (hereinafter, also referred to as “1,4-BD”) and propylene glycol (hereinafter, “100 parts by mass” of the water absorbent resin precursor (A) obtained in the production example. , Also referred to as “PG”) and 0.5 parts by mass of pure water, 3 parts by mass of pure water, and 500 parts by mass of a humidified product mixed at room temperature using white squeezed oil in an oil bath. Was added to a 5 L mortar heat treatment device (processor) manufactured by West Japan Testing Machine Co., Ltd., heated to 230 ° C., stirred at high speed stirring (autorotation motion 280 rpm, revolving motion 125 rpm), and immediately after heat treatment for 15 minutes, the same Is added to a 5 L mortar heat treatment device (processor) manufactured by West Japan Testing Machine Co., Ltd., heated to a set temperature of 210 ° C. for white squeezed oil bath, and stirred at low speed stirring (spinning motion 140 rpm, revolving motion 62 rpm). Between heat treatment was carried out (see Table 3). The mixture thus obtained was passed through a JIS standard sieve having an opening of 850 μm to obtain a water absorbent resin (1).

  The physical properties of the water absorbent resin composition (1) obtained by the above method were evaluated. The results are shown in Table 4.

  As shown in Tables 3 and 4, the treatment time for heat treatment to approximately the same surface crosslink density (in other words, equivalent CRC value) as Comparative Example 5 below was shortened from 30 minutes to 20 minutes.

<Example 6>
To 100 parts by mass of the water-absorbent resin precursor (A) obtained in the production example, 0.34 parts by mass of 1,4-BD, 0.56 parts by mass of PG, and 3 parts by mass of pure water were added and mixed. connecting the humidified substance, paddle diameter 160Mmfai, heat transfer area 2.5 m ^2, an effective volume 0.065 m ³ conductive heat transfer-type groove-type stirring dryer (Nara machinery Co., Ltd., NPD1.6W type) in three series Were continuously processed at a throughput of 50 kg / h (see Table 5). The first processing apparatus was used for the above-described stirring and drying process, the second processing apparatus was used for the above-described surface cross-linking process, and the third processing apparatus was used for the cooling process. The rotation speed of the paddle of each processing apparatus was set to 30 rpm in the stirring and drying process, 5 rpm in the surface crosslinking process, and 5 rpm in the cooling process. The height of the discharge weirs inside the first and second units was set to 60% (when the upper surface of the stirring blade was 100%). The heat carrier uses a barrel therm 400 made by Matsumura Oil Co., Ltd. The first and second units circulate the heat medium inside the paddle of the conduction heat transfer type grooved stirrer and the third unit is room temperature tap water. Was circulated between the jacket and the paddle. The water-absorbent resin powder temperature at the treatment apparatus inlet of the first heat transfer type grooved stir dryer is 40 ° C., and the water-absorbent resin powder temperature at the treatment apparatus outlet is 190 ° C. The temperature of the water-absorbent resin powder at the treatment apparatus inlet of the heat transfer type grooved agitation dryer was 190 ° C., and the temperature of the water-absorbent resin powder at the treatment apparatus outlet was 200 ° C. (see Table 5). The first and second devices connected in series are connected by a heat-insulated stainless steel pipe, and the second and third devices are connected by an unheated stainless steel pipe. The water-absorbent resin composition after the stirring and drying step was immediately treated in the surface cross-linking step (see Table 5), and then immediately cooled to room temperature in the cooling step. The mixture thus obtained was passed through a JIS standard sieve having an opening of 850 μm to obtain a water absorbent resin (2).

  The physical properties of the water absorbent resin composition (2) obtained by the above method were evaluated. The results are shown in Table 6.

  As shown in Tables 5 and 6, since the power required for stirring per unit weight of the dry particulate composition in the surface crosslinking step is smaller than in the case of Comparative Example 6 below, the amount of fine powder of 150 pass or less is suppressed, As a result, the values of AAP and SFC were improved.

<Comparative Example 5>
To 100 parts by mass of the water-absorbent resin precursor (A) obtained in the production example, 0.34 parts by mass of 1,4-BD, 0.56 parts by mass of PG and 3 parts by mass of pure water were added, 500 parts by weight of the humidified material mixed in the above was put into a 5 L mortar heat treatment device (processor) manufactured by West Japan Testing Machine Co., Ltd., which was heated using white squeezed oil in an oil bath and a set temperature of the oil bath at 230 ° C. The mixture was stirred with low-speed stirring (rotational motion: 140 rpm, revolving motion: 62 rpm) and heat-treated for 30 minutes (see Table 3). The mixture thus obtained was passed through a JIS standard sieve having an opening of 850 μm to obtain a water absorbent resin (3).

  The physical properties of the water absorbent resin composition (2) obtained by the above method were evaluated. The results are shown in Table 4.

<Comparative Example 6>
With respect to 100 parts by mass of the water absorbent resin precursor (A) obtained in Production Example 1, 0.34 parts by mass of 1,4-BD, 0.56 parts by mass of PG, and 3 parts by mass of pure water were added and mixed. Using two units of the conductive heat transfer type grooved stirrer (made by Nara Machinery Co., Ltd., NPD1.6W type) having a paddle diameter of 160 mmφ, a heat transfer area of 2.5 m ² and an effective volume of 0.065 m ³ , Continuous treatment was performed at a treatment amount of 25 kg / h (see Table 5). Regarding the rotation speed of the paddle of each processing apparatus, the rotation speed of the paddle of the first conduction heat transfer type grooved stirring dryer is set to 30 rpm, and The rotation speed of the paddle was set to 5 rpm. The first unit uses Matsumura Oil's Parrel Therm 400 as the heat medium, the heat medium is circulated inside the paddle of the conduction heat transfer type grooved stirrer, and the second generation room temperature tap water is circulated inside the jacket and paddle. It was. The temperature of the water absorbent resin powder at the inlet of the first processing apparatus was 40 ° C., and the temperature of the water absorbent resin powder at the outlet of the processing apparatus was 200 ° C. (see Table 5). The first and second units are connected by a stainless steel pipe that is not insulated. The mixture thus obtained was passed through a JIS standard sieve having an opening of 850 μm to obtain a water absorbent resin (4).

  The physical properties of the water absorbent resin composition (4) thus obtained were evaluated. The results are shown in Table 6.

  The present invention is not limited to the configurations described above, and various modifications are possible within the scope of the claims, and technical means disclosed in different embodiments and examples, respectively. Embodiments and examples obtained by appropriately combining the above are also included in the technical scope of the present invention. Moreover, all the patent documents described in this specification are used as reference in this specification.

As described above, in the present invention, the treatment is performed in two stages of the stirring and drying step and the surface cross-linking step, so that a water-absorbing resin having good physical properties can be mass-produced efficiently.
In addition, in the surface cross-linking treatment of the water-absorbent resin, fine powder can be efficiently generated by using a stirring plate having a predetermined thickness and / or a stirring means having a scraping blade having a predetermined cross-sectional area and length. Can be prevented.

  Therefore, the production method according to the present invention can greatly contribute to the efficient production of a water-absorbent resin having good physical properties, such as disposable diapers, disposable adult incontinence clothing, disposable sanitary napkins and disposable bandages. It can be widely used in the field relating to the production of various water-absorbing resins.

  It can also be used to produce packaging-related products such as drip sheets for foods.

  Furthermore, such as sealing composites between concrete blocks that make up the walls of underwater tunnels, tapes for water blocks of optical fiber cables and transmission cables, soil water retention agents, and transporters of insecticides, pesticides and / or herbicides Thus, it can be widely used in fields where water absorption and water retention are required for the resin used.

FIG. 1 is a cross-sectional view showing an example of the configuration of a stirring device (stirring means) used in the present embodiment. 2A is a cross-sectional view of a stirring device (stirring means) cut along a yz plane when a stirring plate having a wedge shape is used, and FIG. 2B is a wedge shape of the stirring plate. It is sectional drawing of the stirring apparatus (stirring means) cut | disconnected by the xz plane in the case of using a certain stirring board. FIG. 3A is a cross-sectional view of a stirring device (stirring means) cut along the yz plane when a stirring plate having a flat disk shape (fan shape) is used, and FIG. It is sectional drawing of the stirring apparatus (stirring means) cut | disconnected by the xz plane in the case of using the stirring disk whose stirring disk is planar disk shape (fan shape). FIG. 4 is a schematic diagram of the SFC measurement apparatus. FIG. 5 is a schematic diagram of a longitudinal section of the water absorbent resin manufacturing apparatus according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus of water absorbing resin 2 1st processing apparatus (1st processing means)
3 Second processing device (second processing means)
DESCRIPTION OF SYMBOLS 10 Drive apparatus 20 Horizontal drum 30 Raw material supply port 40 Heat medium inlet 40 'Heat medium inlet 45' Heat medium outlet 50 Water-absorbing-resin outlet 70 Rotating shaft 80 Stirrer panel 80a Stirrer panel 80b Stirrer panel 81 Carrier gas introduction port 85 Exhaust port 90 Scrape blade 90a Scrape blade 90b Scrape blade 100 Stirrer (stirring means)

Claims (17)

The surface of the hydrophilic crosslinked polymer is crosslinked by heating a mixture of the hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And a cooling step for cooling the hydrophilic cross-linked polymer whose surface has been cross-linked, wherein the reforming step and / or the cooling step includes stirring with a rotating shaft provided with a plurality of stirring plates. Done by means,
The direction parallel to the long axis length direction of the rotating shaft is the y direction, the direction orthogonal to the y direction, and the direction parallel to the shaft radial direction of the rotating shaft is the x direction, the x direction and the y direction. When the orthogonal direction is the z direction,
The method for producing a water-absorbent resin, wherein the stirring plate has a ratio of the maximum thickness to the minimum thickness of 5 or less in a cross section obtained by cutting the stirring means along a yz plane. The surface of the hydrophilic crosslinked polymer is crosslinked by heating a mixture of the hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And a cooling step for cooling the hydrophilic cross-linked polymer whose surface has been cross-linked, and the reforming step and / or the cooling step includes a plurality of stirrers equipped with scraping blades. Performed using a stirring means having a rotating shaft,
The direction parallel to the long axis length direction of the rotating shaft is the y direction, the direction orthogonal to the y direction, and the direction parallel to the shaft radial direction of the rotating shaft is the x direction, the x direction and the y direction. When the orthogonal direction is the z direction,
A cross-sectional area of the lifting blade in a cross section obtained by cutting the stirring means along the yz plane, one stirring plate in which the lifting blade protrudes, and another stirring plate disposed relative to the stirring plate; Occupying 10% or more and less than 50% of the area in the yz plane between and the length in the y direction of the scraping blade in the cross section cut by the yz plane is It is 50% or more of the distance in the said yz plane between other stirring boards, The manufacturing method of the water absorbing resin characterized by the above-mentioned. A step (1) of mixing a solution containing a surface crosslinking agent and a water-absorbent resin precursor to obtain a wet mixture;
Step (2) of stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent;
Including a step (3) of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment,
80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm.
Each of the steps (2) and (3) is performed using at least one processing apparatus, and a processing apparatus used for the step (2) and a processing apparatus used for the step (3) are provided. A method for surface cross-linking of a water-absorbent resin characterized by being connected in series.   The treatment apparatus used in the step (2) and the treatment apparatus used in the step (3) are treatment apparatuses having different types and / or effective volumes. Surface cross-linking method.   The water absorbing property according to claim 3 or 4, wherein the treatment device used in the step (2) and the treatment device used in the step (3) are operated under different heating conditions and / or different stirring conditions. Resin surface cross-linking method. A step (1) of mixing a solution containing a surface crosslinking agent and a water-absorbent resin precursor to obtain a wet mixture;
Step (2) of stirring and drying the wet mixture to obtain a dry particulate composition containing a surface cross-linking agent;
Including a step (3) of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment,
80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm.
The above step (2) and step (3) are performed in one processing apparatus,
A method for surface cross-linking a water-absorbent resin, wherein the step (2) and the step (3) are performed under different heating conditions and / or different stirring conditions. The surface of the hydrophilic crosslinked polymer is crosslinked by heating a mixture of the hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. A step (2) of stirring and drying the mixture to obtain a dry particulate composition containing a surface crosslinking agent; and a step of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment (3) And a cooling step for cooling the hydrophilic crosslinked polymer whose surface has been cross-linked, and at least one or more of the steps (2), (3) and the cooling step include a plurality of steps. It is carried out using a processing apparatus comprising a stirring means having a rotating shaft equipped with a stirring plate,
The direction parallel to the long axis length direction of the rotating shaft is the y direction, the direction orthogonal to the y direction, and the direction parallel to the shaft radial direction of the rotating shaft is the x direction, the x direction and the y direction. When the orthogonal direction is the z direction,
In the cross section obtained by cutting the stirring means along the yz plane, the stirring plate has a ratio of the maximum thickness to the minimum thickness of 5 or less,
The mixture is a wet mixture produced by the step (1) of mixing a hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And
80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm.
Each of the steps (2) and (3) is performed using at least one processing apparatus, and the processing apparatus used for the step (2) and the processing apparatus used for the step (3) A method for producing a water-absorbent resin, which is connected in series. The surface of the hydrophilic crosslinked polymer is crosslinked by heating a mixture of the hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. A step (2) of stirring and drying the mixture to obtain a dry particulate composition containing a surface crosslinking agent; and a step of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment (3) And a cooling step for cooling the hydrophilic crosslinked polymer whose surface has been cross-linked, and at least one of the step (2), the step (3) and the cooling step is a scraping blade. Is carried out using a processing apparatus comprising a stirring means having a rotating shaft equipped with a plurality of stirring plates.
The direction parallel to the long axis length direction of the rotating shaft is the y direction, the direction orthogonal to the y direction, and the direction parallel to the shaft radial direction of the rotating shaft is the x direction, the x direction and the y direction. When the orthogonal direction is the z direction,
A cross-sectional area of the lifting blade in a cross section obtained by cutting the stirring means along the yz plane, one stirring plate in which the lifting blade protrudes, and another stirring plate disposed relative to the stirring plate; Occupying 10% or more and less than 50% of the area in the yz plane between and the length in the y direction of the scraping blade in the cross section cut by the yz plane is 50% or more of the distance in the yz plane between other stirring plates,
The mixture is a wet mixture produced by the step (1) of mixing a hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And
80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm.
Each of the steps (2) and (3) is performed using at least one processing apparatus, and the processing apparatus used for the step (2) and the processing apparatus used for the step (3) are provided. A method for producing a water-absorbent resin, which is connected in series. The surface of the hydrophilic crosslinked polymer is crosslinked by heating a mixture of the hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And a cooling step for cooling the hydrophilic cross-linked polymer whose surface has been cross-linked, wherein the reforming step and / or the cooling step includes stirring with a rotating shaft provided with a plurality of stirring plates. Performed using a processing apparatus equipped with means,
The direction parallel to the long axis length direction of the rotating shaft is the y direction, the direction orthogonal to the y direction, and the direction parallel to the shaft radial direction of the rotating shaft is the x direction, the x direction and the y direction. When the orthogonal direction is the z direction,
In the cross section obtained by cutting the stirring means along the yz plane, the stirring plate has a ratio of the maximum thickness to the minimum thickness of 5 or less,
The mixture is a wet mixture produced by the step (1) of mixing a hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And
In the modification step, the wet mixture is stirred and dried to obtain a dry particulate composition containing a surface cross-linking agent (2);
Including a step (3) of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment,
80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm.
The above step (2) and step (3) are performed in one processing apparatus,
A method for producing a water-absorbent resin, wherein the step (2) and the step (3) are performed under different heating conditions and / or different stirring conditions. The surface of the hydrophilic crosslinked polymer is crosslinked by heating a mixture of the hydrophilic crosslinked polymer having a carboxyl group and an aqueous solution containing a surface crosslinking agent having two or more functional groups capable of reacting with the carboxyl group. And a cooling step for cooling the hydrophilic cross-linked polymer whose surface has been cross-linked. The reforming step and / or the cooling step includes a plurality of stirrers equipped with scraping blades. Carried out using a processing device equipped with a stirring means having a rotating shaft,
A direction parallel to the major axis length direction of the rotating shaft is the y direction, a direction orthogonal to the y direction, and a direction parallel to the axial diameter direction of the rotating shaft is the x direction, the x direction, and the y direction. When the orthogonal direction is the z direction,
A cross-sectional area of the lifting blade in a cross section obtained by cutting the stirring means along the yz plane, one stirring plate from which the lifting blade protrudes, and another stirring plate disposed relative to the stirring plate; Occupying 10% or more and less than 50% of the area in the yz plane between, and the length in the y direction of the lifting blade in the cross section cut by the yz plane 50% or more of the distance in the yz plane between other stirring plates;
The mixture is a wet mixture produced by the step (1) of mixing a hydrophilic cross-linked polymer having a carboxyl group and an aqueous solution containing a surface cross-linking agent having two or more functional groups capable of reacting with the carboxyl group. And
In the modifying step, the wet mixture is stirred and dried to obtain a dry particulate composition containing a surface crosslinking agent (2);
Including a step (3) of subjecting the dry particulate composition to a surface crosslinking reaction by heat treatment,
80% by weight or more of the dry particulate composition obtained in the step (2) is particles that pass through a sieve having an opening of 10 mm,
The above step (2) and step (3) are performed in one processing apparatus,
A method for producing a water-absorbent resin, wherein the step (2) and the step (3) are performed under different heating conditions and / or different stirring conditions.   The water absorption according to claim 7 or 8, wherein the treatment device used in the step (2) and the treatment device used in the step (3) are treatment devices having different types and / or effective volumes. Manufacturing method of resin.   The processing device used in the step (2) and the processing device used in the step (3) are operated under different heating conditions and / or different stirring conditions. 2. A method for producing a water-absorbent resin according to item 1.   13. The stirring plate according to claim 2, wherein the ratio of the maximum thickness to the minimum thickness is 5 or less in a cross section obtained by cutting the stirring means along the yz plane. The manufacturing method of the water absorbing resin of any one of Claims 1.   The scraping blades straddle a plurality of stirring boards, and among the scraping blades, the scraping blades present at adjacent positions sandwich the rotating shaft in a cross section obtained by cutting the stirring means along the yz plane. The method for producing a water-absorbent resin according to claim 1, wherein the water-absorbent resin is alternately arranged or connected in parallel.   The method for producing a water-absorbent resin according to any one of claims 1, 2, and 7 to 14, wherein the stirrer is disk-shaped or disk-shaped with a part missing.   The method for producing a water-absorbent resin according to any one of claims 1, 2, and 7 to 15, wherein the stirring plate also acts as a heat transfer means.   The method for producing a water-absorbing resin according to any one of claims 1, 2, and 7 to 16, wherein the stirring plate also acts as a cooling means.

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