Patent ID: 8309667

Claim:
A water-soluble copolymer having alkyl-modified carboxyl groups obtained by polymerizing 100 parts by weight of (meth)acrylic acid, 0.5-5 parts by weight of alkyl (meth)acrylate comprising an alkyl group having a carbon number of 18-24, and 0.001-0.044 parts by weight of a compound having two or more of ethylenic unsaturated groups, wherein a 1 weight %-neutralized viscous liquid has a viscosity of 1500 mPa·s or lower and a transmittance of 90% or higher, and when 0.25-5 parts by weight of sodium chloride is added to 100 parts by weight of the neutralized viscous liquid, the liquid shows a viscosity of 15000-40000 mPa·s and a transmittance of 90% or higher, wherein the 1 weight %-neutralized viscous liquid is a liquid containing 1 weight % of said water-soluble copolymer having alkyl-modified carboxyl groups which has been neutralized with an alkali.