Abstract: A method according to the present invention for producing water absorbent resin powder is a method for producing water absorbent resin having a surface cross-linked structure, and includes: a polymerization step in which an unsaturated monomer aqueous solution is polymerized; a drying step in which a hydrogel cross-linked polymer obtained in the polymerization step is dried; a surface treatment step in which the hydrogel cross-linked polymer or a dried hydrogel cross-linked polymer is subjected to a surface treatment; and a sorting step, carried out after the drying step, in which a foreign matter included in a water absorbent resin is color-sorted from the water absorbent resin entirely or partially. As a result, it is possible to obtain a water absorbent resin which has high properties and is less likely to be colored. In this way, there is provided the water absorbent resin powder production method in which the color sorting technique is used to remove foreign matters from the water absorbent resin.

Abstract: A method according to the present invention for producing water absorbent resin powder is a method for producing water absorbent resin having a surface cross-linked structure, and includes: a polymerization step in which an unsaturated monomer aqueous solution is polymerized; a drying step in which a hydrogel cross-linked polymer obtained in the polymerization step is dried; a surface treatment step in which the hydrogel cross-linked polymer or a dried hydrogel cross-linked polymer is subjected to a surface treatment; and a sorting step, carried out after the drying step, in which a foreign matter included in a water absorbent resin is color-sorted from the water absorbent resin entirely or partially. As a result, it is possible to obtain a water absorbent resin which has high properties and is less likely to be colored. In this way, there is provided the water absorbent resin powder production method in which the color sorting technique is used to remove foreign matters from the water absorbent resin.

Abstract: The disclosed process for continuously producing a water-absorbing resin comprising a plurality of joined continuous steps; a polymerization step of polymerizing an aqueous unsaturated monomer solution, a drying step of drying a particulated water-containing gel-like crosslinked polymer obtained in a finely crushing step during the polymerization or after the polymerization, a pulverizing step after the drying, a classification step after the drying, and a surface treatment step for the water-absorbing resin powder after the classification step. In the process, with some of the above steps kept running, the other steps are interrupted, and subsequently all the steps are restarted.

Abstract: A method according to the present invention for producing water absorbent resin powder is a method for producing water absorbent resin having a surface cross-linked structure, and includes: a polymerization step in which an unsaturated monomer aqueous solution is polymerized; a drying step in which a hydrogel cross-linked polymer obtained in the polymerization step is dried; a surface treatment step in which the hydrogel cross-linked polymer or a dried hydrogel cross-linked polymer is subjected to a surface treatment; and a sorting step, carried out after the drying step, in which a foreign matter included in a water absorbent resin is color-sorted from the water absorbent resin entirely or partially. As a result, it is possible to obtain a water absorbent resin which has high properties and is less likely to be colored. In this way, there is provided the water absorbent resin powder production method in which the color sorting technique is used to remove foreign matters from the water absorbent resin.

Abstract: A water-absorbing resin composition including 100 parts by weight of water-absorbing resin particles and 0.01 to 1 part by weight of additive particles, wherein a percent by weight of the additive particles, (x [%]), based on 100% by weight of the water-absorbing resin particles in the composition, and weight ratio of free additive particles, (y), relative to the percent by weight, (x [%]), satisfy the following formula: 0.04(x)0.1?y?0.2(x)0.5.

Abstract: Provided is a process for producing a water-absorbing resin powder which contains a given amount of water added thereto, has a low dust content, and has high material properties. When a water-absorbing resin powder which has undergone surface crosslinking is produced on an industrial scale, various problems concerning production are eliminated and a long-term stable operation is possible without causing a deterioration in the material properties of the resin. Even when the process is continued over a long period, the material properties are stabilized (decrease in standard deviation) or improved (improvement in AAP). The process for producing a water-absorbing resin comprises, in the following order, a first classification step for classifying a water-absorbing resin, a surface crosslinking step after the classification, a water addition step for adding water to the water-absorbing resin powder after or during the surface crosslinking, a second classification step, and a conveying step.

Abstract: A method for producing a water absorbent resin, the method including a polymerization step, a drying step, a classification step, and a surface crosslinking step. The classification step carried out before or after the surface crosslinking step requires use of a tapping material and a metal sieve mesh, in which the tapping material being heated at 40° C. to 100° C. is installed below the metal sieve mesh, and the metal sieve mesh has an area of 1 to 10 m2/sheet. The classification step further requires introducing a classification aid particle, which has a specific gravity different from that of the water absorbent resin, to the metal sieve mesh; and monitoring the presence or absence of damage to the metal sieve mesh.

Abstract: A method for producing a water absorbent resin, the method including a polymerization step, a drying step, a classification step, and a surface crosslinking step. The classification step carried out before or after the surface crosslinking step requires use of a metal sieve mesh having stretch tension from 35 to 100 N/cm, in which an air jet cleaner or an air jet brush cleaner and plural tapping balls or tapping blocks are installed below the metal sieve mesh, a classification aid particle having specific gravity different from that of the water absorbent resin powder is added, and a fine powder of the water absorbent resin and the classification aid particle are removed.

Abstract: The disclosed process for producing a water-absorbing resin comprising: a polymerization step of polymerizing an aqueous unsaturated monomer; and a drying step of drying a particulated water-containing gel-liked crosslinked polymer, obtained in a finely crushing step during the polymerization or after the polymerization. In the process, the drying step is interrupted with a dryer kept in a heated state and thereafter the drying step is restarted.

Abstract: The disclosed process for producing a water-absorbing resin comprising: a polymerization step of polymerizing an aqueous unsaturated monomer; a drying step of drying a particulated water-containing gel-liked crosslinked polymer, obtained in a finely crushing step during the polymerization or after the polymerization; a pulverizing step after the drying, a classification step after the drying, and a surface treatment step after the classification. In the process is, the surface-treatment step is interrupted with a heating treatment apparatus kept in a heated state and thereafter the surface treatment step is restarted.

Abstract: Provided is a production method for the particulate water-absorbing agent, which can collecting the fine powders generated during the producing process efficiently without worsening working environment, and also the particulate water-absorbing agent produced by the production method thereof. This production method includes (1) a polymerization step for obtaining a polymer gel, (2) a drying step for drying said polymer gel to obtain a particulate water-absorbing resin, (3) a classification step for sieving said particulate water-absorbing resin, (4) a surface cross-linking step for cross-linking the neighborhood of the surface of said particulate water-absorbing resin (5) a packaging step for filling a packaging material container with said particulate water-absorbing agent for packaging and (6) a transportation step for transporting the products produced in each of the steps to the other steps.

Abstract: A method for being capable of sufficiently exerting property improvement effect by the addition of additive particles other than water-absorbing resin to water-absorbing resin particles. The problems can be solved by using additive particles having over cohesive particles in an amount equal to or less than a predetermined amount, or by using the additive particles by crushing or classifying in advance, before mixing with water-absorbing resin particles. Alternatively, the problem can be solved by subjecting a mixture of the water-absorbing resin particles and the additive particles to pneumatic transportation processing, in particular, in a heated state, after mixing or at the same time as mixing. Further, provided is a water-absorbing resin composition, which is capable of stably exerting high-level property. The problems can be solved by a water-absorbing resin composition, where the addition amount of additive particles and amount of free additive particles satisfies a predetermined relation.

Abstract: The present invention provides a method for being capable of sufficiently exerting property improvement effect by the addition of additive particles other than water-absorbing resin to water-absorbing resin particles. The problems can be solved by using additive particles having over cohesive particles in an amount equal to or less than a predetermined amount, or by using the additive particles by crushing or classifying in advance, before mixing with water-absorbing resin particles. Alternatively, the problem can be solved by subjecting a mixture of the water-absorbing resin particles and the additive particles to pneumatic transportation processing, in particular, in a heated state, after mixing or at the same time as mixing. Further, the present invention provides a water-absorbing resin composition, which is capable of stably exerting high-level property.

Abstract: A production method of a water-absorbent resin includes the steps of: obtaining a hydrogel by supplying monomer liquid to a reaction device so that the monomer liquid is polymerized; and detaching the hydrogel from the reaction device, wherein the reaction device's surface in contact with the monomer liquid at a position where polymerization occurs is made of a fluororesin having a melt viscosity of less than 1×108 poise at 380° C. On this account, it is possible to obtain a water-absorbent resin having less amounts of an extractable content with high productivity and it is possible to carry out continuous production for an extended period of time.

Abstract: Provided is a method which does not require alteration of the raw materials or high capital investment, and improves and stabilizes the physical property (for example, liquid permeability) of a water absorbent resin by means of a simple technique. A method for producing a water absorbent resin is disclosed, which method includes a polymerization step of polymerizing an aqueous solution of acrylic acid (salt) to obtain a water-containing gel-like crosslinked polymer; a drying step of drying the water-containing gel-like crosslinked polymer to obtain a water absorbent resin powder; a classification step of classifying the water absorbent resin powder; and a surface crosslinking step of surface crosslinking the water absorbent resin powder, wherein in the classification steps that are carried before the surface crosslinking step and/or after the surface crosslinking step, the stretch tension (tension) of the metal sieve mesh used in the classification step is from 35 [N/cm] to 100 [N/cm].

Abstract: A method of enhancing and stabilizing the physical property (for example, liquid permeability) of a water absorbent resin by means of a simple technique without requiring any alteration of the raw materials or high capital investment, is provided. Disclosed is a method for producing a water absorbent resin, which includes a polymerization step of polymerizing an aqueous solution of acrylic acid (salt) to obtain a water-containing gel-like crosslinked polymer; a drying step of drying the water-containing gel-like crosslinked polymer, to obtain a water absorbent resin powder; a classification step of classifying the water absorbent resin powder; and a surface crosslinking step of surface crosslinking the water absorbent resin powder, wherein in the classification step that is carried out before the surface crosslinking step and/or after the surface crosslinking step, a tapping material is installed below the metal sieve mesh used in the classification step, and thereby classification is carried out.

Abstract: The disclosed process for continuously producing a water-absorbing resin comprising a plurality of joined continuous steps; a polymerization step of polymerizing an aqueous unsaturated monomer solution, a drying step of drying a particulated water-containing gel-like crosslinked polymer obtained in a finely crushing step during the polymerization or after the polymerization, a pulverizing step after the drying, a classification step after the drying, and a surface treatment step for the water-absorbing resin powder after the classification step. In the process, with some of the above steps kept running, the other steps are interrupted, and subsequently all the steps are restarted.

Abstract: The disclosed process for producing a water-absorbing resin comprising: a polymerization step of polymerizing an aqueous unsaturated monomer; and a drying step of drying a particulated water-containing gel-liked crosslinked polymer, obtained in a finely crushing step during the polymerization or after the polymerization. In the process, the drying step is interrupted with a dryer kept in a heated state and thereafter the drying step is restarted.

Abstract: The disclosed process for producing a water-absorbing resin comprising: a polymerization step of polymerizing an aqueous unsaturated monomer; a drying step of drying a particulated water-containing gel-liked crosslinked polymer, obtained in a finely crushing step during the polymerization or after the polymerization; a pulverizing step after the drying, a classification step after the drying, and a surface treatment step after the classification. In the process is, the surface-treatment step is interrupted with a heating treatment apparatus kept in a heated state and thereafter the surface treatment step is restarted.

Abstract: Provided is a process for producing a water-absorbing resin powder which contains a given amount of water added thereto, has a low dust content, and has high material properties. When a water-absorbing resin powder which has undergone surface crosslinking is produced on an industrial scale, various problems concerning production are eliminated and a long-term stable operation is possible without causing a deterioration in the material properties of the resin. Even when the process is continued over a long period, the material properties are stabilized (decrease in standard deviation) or improved (improvement in AAP). The process for producing a water-absorbing resin comprises, in the following order, a first classification step for classifying a water-absorbing resin, a surface crosslinking step after the classification, a water addition step for adding water to the water-absorbing resin powder after or during the surface crosslinking, a second classification step, and a conveying step.