Patent ID: 7393886

Claim:
A cement dispersant comprising a water-soluble amphoteric copolymer, or a partly or a fully neutralized salt thereof, the copolymer being formed by copolymerizing a monomer mixture containing as a primary monomer component: at least one compound (compound A) obtained by addition of 0 to 8 moles of an alkylene oxide having 2 to 4 carbon atoms with respect to one equivalent of a residual amino group of a polyamide polyamine obtained by condensation of 1.0 mole of a polyalkylene polyamine, 0.5 to 0.95 moles of a dibasic acid or an ester the dibasic acid with a lower alcohol having 1 to 4 carbon atoms, and 0.05 to 0.70 moles of acrylic acid or methacrylic acid, or an ester of the acrylic acid or methacrylic acid with a lower alcohol having 1 to 4 carbon atoms; at least one compound (compound B) represented by general formula (1) wherein R 1 represents a hydrogen atom or a methyl group, and M represents a hydrogen atom, an alkali metal, an alkali earth metal, an ammonium group, or an alkanol ammonium group; at least one compound (compound C) represented by general formula (2) wherein R 2 represents an alkylene group having 2 to 4 carbon atoms, R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and m represents the number of addition molecules of a polyalkylene glycol and is an integer of 1 to 100; and at least one compound (compound D) represented by general formula (3) CH 2 ═CH—COO(R 4 O)nR 5 (3) wherein R 4 represents an alkylene group having 2 to 4 carbon atoms, R 5 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and n represents the number of molecules of a polyalkylene glycol for addition and is an integer of 1 to 100, wherein, when the cement dispersant is added to and is compounded with a concrete composition, dispersion performance increases with time.