Method for production of inclusion water for hardening gypsum, method for production of shaped article of gypsum, and shaped article of gypsum

Claim 1

A method for the production of a shaped article of gypsum, comprising by producing an absorbent polymer by dissolving in an aliphatic hydrocarbon an acrylic copolymer using as components thereof (a) 40 to 95% by weight of an alkyl acrylate or an alkyl methacrylate, having an alkyl group of not less than 8 carbon atoms, (b) 5 to 40% by weight of a monomer, specifically at least one derivative selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, and methacrylamide and containing at least one group selected from the class consisting of carboxyl group, amino group, quaternary ammonium group, and hydroxyl group, and (c) to 40% by weight of an unsaturated monomer copolymerizable with the components (a) and (b) mentioned above, dispersing an aqueous solution of acrylic acid and an alkali metal salt thereof in the resultant solution, subjecting the resultant dispersion to reversed-phase suspension polymerization, cross-linking the resultant polymer with a cross-linking agent, and drying the cross-linked polymer, swelling said absorbent polymer thereby preparing an inclusion water for hardening gypsum, and mixing said inclusion water and hemihydrate gypsum or anhydrous gypsum each in the form of powder thereby causing the inclusion water to be released from the resultant mixture and allowed to harden the gypsum by hydration.

Claim 2

A method for the production of a shaped article of gypsum, comprising by producing an absorbent polymer by dissolving in an aliphatic hydrocarbon an acrylic copolymer using as components thereof (a) 40 to 95% by weight of an alkyl acrylate or an alkyl methacrylate, having an alkyl group of not less than 8 carbon atoms, (b) 5 to 40% by weight of a monomer, specifically at least one derivative selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, and methacrylamide and containing at least one group selected from the class consisting of carboxyl group, amino group, quaternary ammonium group, and hydroxyl group, and (c) to 40% by weight of an unsaturated monomer copolymerizable with the components (a) and (b) mentioned above, dispersing an aqueous solution of acrylic acid and an alkali metal salt thereof in the resultant solution, subjecting the resultant dispersion to reversed-phase suspension polymerization, cross-linking the resultant polymer with a cross-linking agent, and drying the cross-linked polymer, swelling said absorbent polymer thereby preparing an inclusion water for hardening gypsum, and mixing said inclusion water and hemihydrate gypsum or anhydrous gypsum each in the form of powder thereby causing the inclusion water to be released from the resultant mixture and allowed to harden the gypsum by hydration.