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: Provided is a method for producing a polyacrylic acid (salt)-based water absorbent resin, which is a convenient production method for a water absorbent resin for an absorbent suitable for practical use, the water absorbent resin having a reduced amount of residual monomers.

Abstract: Provided is a method for producing a particulate water absorbing agent, the method including the steps of: a polymerization step of polymerizing an acrylic acid (salt)-based aqueous monomer solution so as to obtain a crosslinked hydrogel polymer; a drying step of drying the crosslinked hydrogel polymer so as to obtain a dried polymer; a classification step of classifying a polymer subjected to classification so as to obtain a water-absorbing resin powder having a specific particle size; and a surface-crosslinking step of surface-crosslinking the water-absorbing resin powder that is not surface crosslinked, wherein the classification step is carried out at least either or both of before and/or after the surface-crosslinking step but after said drying step, and wherein a hole shape of a classification sieve used in the classification step is an irregular polygonal or non-circular.

Abstract: The present invention provides a method for producing, by adding an additive and/or gas bubbles to a monomer with high efficiency, a polyacrylic acid (salt)-based water-absorbing resin having high physical properties while high productivity is maintained. The step of preparing an aqueous monomer solution includes the steps of: preparing an aqueous solution; and adding a water-insoluble additive and/or gas bubbles. A retention time from when the water-insoluble additive and/or the gas bubbles is/are added to when polymerization starts is 1 second to 60 seconds.

Abstract: To provide a method for producing a water-absorbing resin by which problems caused by addition of a particulate additive or water-absorbing resin fine powder can be prevented and a water-absorbing resin having high physical properties can be stably and efficiently obtained. A method for producing a polyacrylic acid (salt)-based water-absorbing resin, the method including: an aqueous monomer solution preparation step for preparing an aqueous solution containing a monomer having an acrylic acid (salt) as a main component; a polymerization step for polymerizing the monomer to obtain a hydrogel-forming crosslinked polymer; and a drying step for drying the hydrogel-forming crosslinked polymer to obtain a dry polymer, wherein the method further includes an adding step for adding a particulate additive to the aqueous monomer solution and/or the hydrogel-forming crosslinked polymer, and in the adding step, an oxygen concentration in an ambient atmosphere of the particulate additive is set to 5% by volume or less.

Abstract: A method for producing polyacrylic acid (salt)-based water-absorbing resin includes a step of polymerizing an acrylic acid (salt)-based aqueous monomer solution, the polymerization step involving use of a polymerization reaction apparatus including a polymerization reaction unit covered with a casing, the polymerization step involving a polymerization reaction under internal pressure of the polymerization reaction unit, the internal pressure being slightly reduced and having a pressure reduction level of more than 0 kPa and not more than 10 kPa relative to the ambient pressure at the periphery of the polymerization reaction unit.

Abstract: To provide a method for producing a water-absorbing resin by which problems caused by addition of a particulate additive or water-absorbing resin fine powder can be prevented and a water-absorbing resin having high physical properties can be stably and efficiently obtained. A method for producing a polyacrylic acid (salt)-based water-absorbing resin, the method including: an aqueous monomer solution preparation step for preparing an aqueous solution containing a monomer having an acrylic acid (salt) as a main component; a polymerization step for polymerizing the monomer to obtain a hydrogel-forming crosslinked polymer; and a drying step for drying the hydrogel-forming crosslinked polymer to obtain a dry polymer, wherein the method further includes an adding step for adding a particulate additive to the aqueous monomer solution and/or the hydrogel-forming crosslinked polymer, and in the adding step, an oxygen concentration in an ambient atmosphere of the particulate additive is set to 5% by volume or less.

Abstract: The purpose of the present invention is to provide a process for stably and continuously producing a water-absorbing resin, specifically, a process for stably and continuously producing a water-absorbing resin, the process including a gas absorbing step in which a gas discharged from a step of producing a water-absorbing resin is efficiently and persistently absorbed. A main point of this process for producing a water-absorbing polyacrylic acid (salt) resin further including a step of absorbing a gas discharged from a production step of the water-absorbing polyacrylic acid (salt) resin in water having a pH of 7 to 11 and a polyvalent metal ion content of 100 ppm or less or a step of absorbing the gas in water having a pH of 7 to 11, the pH of the water having been adjusted by mixing a water having an electric conductivity of 500 (?S/cm) or less at 25° C. with an alkali compound.

Abstract: A polyacrylic acid (salt), or a polyacrylic acid (salt)-based water-absorbing resin, contains a tracer for detecting various troubles in the water-absorbing resin during the period from the production of the water-absorbing resin to the use and discard thereof by a consumer. The polyacrylic acid (salt)-based water-absorbing resin has a stable carbon isotope ratio, as determined by accelerator mass spectrometry, of less than ?20‰ and a radioactive carbon content of 1.0×10?14 or more. The polyacrylic acid (salt)-based water-absorbing resin has: a CRC of 10 [g/g] or more; an AAP of 20 [g/g] or more; an Ext of 35 wt. % or less; a content of residual monomers of 1,000 ppm or less; a PSD in which the proportion of particles having a particle diameter of 150 ?m or larger but less than 850 ?m is 90 wt. % or more; and an FSR of 0.15 [g/g/s] or more.

Abstract: Disclosed are a polyacrylate (salt) and a polyacrylate (salt) water-absorbent resin containing a tracer which can be verified back to the manufacturing process of the water-absorbent resin when dealing with various problems with the water-absorbent resin which can occur from the manufacturing process of the water-resistant resin, during the use thereof by a consumer, up until the disposal thereof. The disclosed polyacrylate (salt) and the polyacrylate (salt) water-absorbent resin have a carbon stable isotope ratio (?13C) of at least ?20‰ when measured by accelerator mass spectrometry.

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: The present invention provides a method for producing a water absorbent resin particle, in high productivity, not only in a controlled manner of particle size but also enhancing fundamental property (absorption capacity or absorption capacity against pressure) of a water absorbent resin.

Abstract: The present invention provides a method for producing, by adding an additive and/or gas bubbles to a monomer with high efficiency, a polyacrylic acid (salt)-based water-absorbing resin having high physical properties while high productivity is maintained. The step of preparing an aqueous monomer solution includes the steps of: preparing an aqueous solution; and adding a water-insoluble additive and/or gas bubbles. A retention time from when the water-insoluble additive and/or the gas bubbles is/are added to when polymerization starts is 1 second to 60 seconds.

Abstract: The purpose of the present invention is to provide a method for producing a water absorbent resin in which a water absorbent resin having excellent properties can be obtained effectively.

Abstract: A method for producing polyacrylic acid (salt)-based water-absorbing resin includes a step of polymerizing an acrylic acid (salt)-based aqueous monomer solution, the polymerization step involving use of a polymerization reaction apparatus including a polymerization reaction unit covered with a casing, the polymerization step involving a polymerization reaction under internal pressure of the polymerization reaction unit, the internal pressure being slightly reduced and having a pressure reduction level of more than 0 kPa and not more than 10 kPa relative to the ambient pressure at the periphery of the polymerization reaction unit.

Abstract: From a view point of reduction in an out of spec product after surface crosslinking, particularly, when an alkylene carbonate compound is used as a surface crosslinking agent, influence by an air temperature is great, and it is necessary to reduce ethylene glycol which is produced as a byproduct, and there is provided a process for producing a polyacrylic acid (salt)-based water absorbent resin powder, comprising a step of polymerizing an aqueous acrylic acid (salt)-based monomer solution, a step of drying the resulting polymer, an optional grinding•classifying step, and a surface crosslinking step, wherein in the surface crosslinking step, (1) a surface crosslinking agent containing an alkylene carbonate compound and a polyhydric alcohol compound is mixed into a water absorbent resin powder, the mixture is heat-reacted and, further, simultaneously with, or separately from the mixing, an ion reactive surface crosslinking agent is mixed, and/or (2) mixing treatment of mixing a surface crosslinking agent sol

Abstract: The physical properties of a water-absorbing resin with low residual monomer content are improved or stabilized, without sacrifices in productivity, production cost, stability, etc. Provided is a water-absorbing resin with low residual monomer content and excellent whiteness, wherein a water-absorbing resin consumed in large quantities in disposable diapers, etc., is preferably a sustainable and renewable water-absorbing resin that does not require excessive purification of the acrylic acid, particularly acrylic acids derived from non-fossil sources, that is the starting material of the water-absorbing resin. Disclosed is a method of manufacturing a hydrophilic polyacrylic acid (salt) resin, which is a method of manufacturing a water-absorbing polyacrylic acid resin that comprises a step in which a monomer is prepared from acrylic acid, a step in which said monomer is polymerized, and a step in which the resulting hydrous gel is dried.

Abstract: The purpose of the present invention is to provide a process for stably and continuously producing a water-absorbing resin, specifically, a process for stably and continuously producing a water-absorbing resin, the process including a gas absorbing step in which a gas discharged from a step of producing a water-absorbing resin is efficiently and persistently absorbed. A main point of this process for producing a water-absorbing polyacrylic acid (salt) resin further including a step of absorbing a gas discharged from a production step of the water-absorbing polyacrylic acid (salt) resin in water having a pH of 7 to 11 and a polyvalent metal ion content of 100 ppm or less or a step of absorbing the gas in water having a pH of 7 to 11, the pH of the water having been adjusted by mixing a water having an electric conductivity of 500 (?S/cm) or less at 25° C. with an alkali compound.

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: There is disclosed a process for continuous production of a water-absorbent resin product by which the water-absorbent resin product having high properties can continuously be produced easily and inexpensively with stable constant quality. In addition, there is disclosed a water-absorbent resin product having high properties and being stable in quality.