Patent ID: 7838156

Claim:
A thickener for use in an alkaline battery, comprising: a cross-linked polymer (A) comprising a cross-linking agent composed of a cross-linking agent (a) unit alone that is hydrolytically decomposable; and a cross-linked polymer (B) comprising a cross-linking agent composed of a cross-linking agent (b) unit alone that is not hydrolytically decomposable, wherein a principal constituent monomer of the cross-linked polymer (A) and the cross-linked polymer (B) is a (meth)acrylic acid or salt thereof, the cross-linking agent (a) unit that is hydrolytically decomposable is a compound having at least one type of bond selected from the group consisting of an ester bond and an amide bond, or a compound that can form at least one type of bond selected from the group consisting of an ester bond and an amide bond, the cross-linking agent (b) unit that is not hydrolytically decomposable is a cross-linking agent having 2 to 10 allyl groups, a content (wt %) of the cross-linking agent (a) unit in the cross-linked polymer (A) is 0.05 to 3 wt % based on weight of the cross-linked polymer (A), a content (wt %) of the cross-linking agent (b) unit in the cross-linked polymer (B) is 0.05 to 3 wt % based on weight of the cross-linked polymer (B), the cross-linked polymers (A) and (B) are polymerized individually, in such a manner that each of the cross-linked polymers (A) and (B) excluding the cross-linking agent has a number-average polymerization degree of 5,000 to 1,000,000, and the thickener providing a gel viscosity ratio (N1h/N12h) of 0.7 to 1.3, the gel viscosity ratio (N1h/N12h) being a ratio of a viscosity (N1h) of a gel after being left to stand for one hour to a viscosity (N12h) of the gel after being left to stand for twelve hours, where the gel viscosity is a viscosity of a gel composed of 2.0 parts by weight of the thickener, 200 parts by weight of zinc powder, and 100 parts by weight of 37 wt % potassium hydroxide aqueous solution, measured at 40° C. according to JIS K7117-1: 1999.