# US 9,873,104 B2 · Method for producing polyacrylic acid (salt)-based water-absorbing resin > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,873,104 B2 - Document ID: US9873104B2 - Status: Granted - Kind: B2 - Application number: 15/123,040 - Filed: 2015-03-03 - Published: 2017-08-03 - Granted: 2018-01-23 - Earliest claimed: 2014-03-03 - Assignees: Nippon Shokubai Co., Ltd. - Applicants: Nippon Shokubai Co., Ltd. - Inventors: Satoshi Matsumoto; Shinichi Fujino; Kunihiko Ishizaki - Web page: https://patentgrep.com/patent/US9873104B2 ## CPC - B01J 20/267: {Cross-linked polymers} - A61L 15/24: Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof {(A61L15/225 takes precedence)} - A61L 15/60: Liquid-swellable gel-forming materials, e.g. super-absorbents - B01J 20/3021: {Milling, crushing or grinding} - C08F 220/06: Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof - C08J 3/075: Macromolecular gels - C08J 2333/02: Homopolymers or copolymers of acids; Metal or ammonium salts thereof - C08L 33/02: Homopolymers or copolymers of acids; Metal or ammonium salts thereof - B01J: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS - A61L: METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES (preservation of bodies or disinfecting characterised by the agents employed A01N; preserving, e.g. sterilising, food or foodstuffs A23; preparations for medical, dental or toiletry purposes A61K) - C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS - C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29) - C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06) ## 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. ## Claims ### Claim 1 A method for producing a polyacrylic acid (salt)-based water-absorbing resin, the method comprising: an aqueous monomer solution preparation step for preparing an aqueous solution containing a monomer having 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 comprises an adding step for adding a particulate additive to the aqueous monomer solution and/or the hydrogel-forming crosslinked polymer, and wherein, in the adding step, an oxygen concentration in an ambient atmosphere of the particulate additive is set to 5% by volume or less. ### Claim 2 (depends on 1) The method according to claim 1, further comprising a gel-crushing step for gel-crushing the hydrogel-forming crosslinked polymer concurrently with or after the polymerization step, wherein the adding step is performed along with the gel-crushing step. ### Claim 3 (depends on 2) The method according to claim 2, wherein the polymerization step, the gel-crushing step and the adding step are performed in a same kneader polymerization apparatus. ### Claim 4 (depends on 1) The method according to claim 1, wherein the polymerization step is performed by continuous kneader polymerization. ### Claim 5 (depends on 1) The method according to claim 1, further comprising a transportation step for transporting the particulate additive before the adding step, wherein at the transportation step pneumatic conveying is performed. ### Claim 6 (depends on 1) The method according to claim 1, further comprising a storing step for storing the particulate additive before the adding step, wherein at the storing step an oxygen concentration in an ambient atmosphere of the particulate additive is set to 5% by volume or less. ### Claim 7 (depends on 1) The method according to claim 1, further comprising an inert gas treatment step for lowering, using an inert gas, an oxygen concentration in an ambient atmosphere of the particulate additive. ### Claim 8 (depends on 7) The method according to claim 7, wherein a temperature of the particulate additive is heated to 30 to 150 C before the adding step and/or before the inert gas treatment step. ### Claim 9 (depends on 1) The method according to claim 1, wherein the particulate additive contains 0.01 to 5 parts by weight of inorganic particles per 100 parts by weight of the monomer in the aqueous monomer solution. ### Claim 10 (depends on 1) The method according to claim 1, wherein the particulate additive contains 1 to 30 parts by weight of a water-absorbing resin fine powder per 100 parts by weight of the monomer in the aqueous monomer solution. ### Claim 11 (depends on 10) The method according to claim 10, wherein the water-absorbing resin fine powder is a water-absorbing resin containing 70% by weight or more of fine particles having a particle diameter of less than 150 mm. ### Claim 12 (depends on 10) The method according to claim 10, wherein the aqueous monomer solution and the water-absorbing resin fine powder contain p-methoxyphenol, and wherein a concentration of p-methoxyphenol contained in the aqueous monomer solution is higher than a concentration of p-methoxyphenol contained in the water-absorbing resin fine powder. ### Claim 13 (depends on 10) The method according to claim 10, wherein at least one selected from the group consisting of polyol, alkanolamine, polyamine, and metal ions of three or higher valence is contained in the water-absorbing resin fine powder. ### Claim 14 (depends on 1) The method according to claim 1, wherein a FSR of the polyacrylic acid (salt)-based water-absorbing resin is 0.25 g/g/s or more, and a residual monomer of the polyacrylic acid (salt)-based water-absorbing resin is 350 ppm or less.