PAPER COATING COMPOSITIONS

1 . Coating composition for paper and cardboard comprising at least one white pigment, at least one polymeric binder and at least one natural or synthetic co-binder, and a mixture containing:

at least one optical brightener of formula (1)

wherein in formula (1) the number of the Z substituents, for each aromatic ring, equals 2 and at least one optical brightener of formula (2)

wherein in formula (2) the number of the Z substituents, for each aromatic ring, equals 1

and wherein:

Z=SO 3 M

M=H, Na, K, NH 4 or an organic ammonium radical

Y=N(CH 2 CH 2 OH) 2 , N[CH 2 CH(CH 3 )OH] 2

X=N(CHRCH 2 R 1 ) wherein R=H or C 1 -C 6 alkyl; R 1 =H or C 1 -C 6 alkyl.

2 . Composition according to claim 1 , wherein said mixture comprises said optical brightener of formula (1) in a weight percentage of 5% to 40% with respect to the mixture and said optical brightener of formula (2) in a weight percentage of 60% to 95% with respect to the mixture.

3 . Composition according to claim 2 , wherein the mixture comprises 15% to 25% by weight of the optical brightener of formula (1) and 75% to 85% by weight of the optical brightener of formula (2).

4 . Composition according to claim 1 wherein the optical brightener of formula (1) is

5 . Composition according to claim 1 wherein the optical brightener of formula (2) is

6 . Composition according to claim 1 , wherein said mixture of optical whiteners comprises at least one carrier compound.

7 . Method for coating paper or paperboard characterized in that a composition according to claim 1 is used.

8 . Method according to claim 7 , wherein the optical brighteners of formulas (1) and (2) are incorporated directly in the composition.

9 . Paper or cardboard coated with a composition according to claim 1 .