Paper coating composition
The present invention relates to a coating composition comprising an aqueous dispersion of a binder and first and second core-shell polymer particles having aqueous neutralized acid cores, wherein the dry bulk density of the first core-shell polymer particles is in the range of 0.25 to 0.5 g/mL; and the dry bulk density of the second core-shell polymer particles is in the range of 0.30 to 0.90 g/mL. The composition of the present invention is useful as an undercoat layer for a thermosensitive recording material.
1. A coating composition comprising an aqueous dispersion of a binder and first and second core-shell polymer particles having aqueous neutralized acid cores, wherein
a) the first core-shell polymer particles have a diameter in the range of from 1.0 μm to 1.8 μm;
b) the second core-shell polymer particles have a diameter in the range of from 0.25 μm to 1.0 μm;
c) the number ratio of the second to the first core-shell polymer particles is in the range of from 1:1 to 20:1;
d) the diameter of the second core-shell polymer particles is in the range of from 15 to 65% of the diameter of the first core-shell polymer particles;
e) the dry bulk density of the first core-shell polymer particles is in the range of 0.25 to 0.5 g/mL; and
f) the dry bulk density of the second core-shell polymer particles is in the range of 0.30 to 0.90 g/mL.
2. The coating composition of claim 1 wherein the first core-shell polymer particles have a diameter in the range of from 1.2 μm to 1.8 μm; and the second core-shell polymer particles have a diameter in the range of from 0.3 μm to 0.8 μm; wherein the number ratio of the second to the first core-shell polymer particles is in the range of from 2:1 to 15:1; wherein the diameter of the second core-shell polymer particles in the range of from 20 to 40% of the diameter of the first core-shell polymer particles.
3. The coating composition of claim 2 wherein the first core-shell polymer particles have a diameter in the range of from 1.3 μm to 1.7 μm; and the second core-shell polymer particles have a diameter in the range of from 0.35 μm to 0.6 μm; wherein the number ratio of the second to the first core-shell polymer particles is in the range of from 3:1 to 12:1; wherein the diameter of the second core-shell polymer particles in the range of from 25 to 33% of the diameter of the first core-shell polymer particles.
4. The coating composition of claim 3 the second core-shell polymer particles have a diameter in the range of from 0.4 μm to 0.5 μm; wherein the number ratio of the second to the first core-shell polymer particles is in the range of from 4:1 to 10:1; wherein the diameter of the second core-shell polymer particles is in the range of from 27 to 30% of the diameter of the first core-shell polymer particles; and wherein the first core-shell polymer particles have a diameter in the range of from 1.4 μm to 1.6 μm.
5. The coating composition of claim 2 wherein the dry bulk density of the first core-shell polymer particles is in the range of 0.30 to 0.45 g/mL; and the dry bulk density of the second core-shell polymer particles is in the range of 0.40 to 0.80 g/mL.
6. The coating composition of claim 3 wherein the dry bulk density of the first core-shell polymer particles is in the range of 0.35 to 0.40 g/mL; and the dry bulk density of the second core-shell polymer particles is in the range of 0.50 to 0.75 g/mL.
7. The coating composition of claim 4 wherein the dry bulk density of the first core-shell polymer particles is in the range of 0.35 to 0.40 g/mL; and the dry bulk density of the second core-shell polymer particles is in the range of 0.55 to 0.65 g/mL.
8. The coating composition of claim 1 wherein the first and second core-shell polymer particles have a total pigment volume concentration in the range of from 50 to 98%.