Patent ID: 8859679

Claim:
A coating composition containing an aqueous optical brightener solution consisting essentially of (a) at least one optical brightener of formula (1) wherein M is hydrogen, an alkali metal atom, ammonium or a cation derived from an amine, n is 1 or 2, and X is aspartic acid or iminodiacetic acid from which a hydrogen atom of the amino group has been removed; (b) a polyvinyl alcohol having a degree of hydrolysis greater than 75% and a Brookfield viscosity of 2-40 mPas; (c) water, wherein the weight ratio of the polyvinyl alcohol to the optical brightener is from 0.03:1 to 0.48:1 and wherein the concentration of the optical brightener is from 10 to 50% by weight, wherein the coating composition further comprises from 10 to 70% by weight of one or more white pigments, wherein the coating composition further contains a primary binder based on synthetic latex, wherein the primary binder is selected from the group consisting of: styrene-butadiene, vinyl acetate, styrene acrylic, vinyl acrylic and ethylene vinyl acetate polymer and a secondary binder selected from the group consisting of starch, carboxymethylcellulose, casein, soy polymers, and polyvinyl alcohol, wherein the primary binder is used in an amount from 5 to 25% by weight of the one or more white pigments, wherein the secondary binder is used in an amount from 0.1 to 10% by weight of the one or more white pigments and wherein the optical brightener of formula (1) is used in the coating composition in an amount from 0.01 to 1% by weight of the one or more white pigments.