Paper coating methods
AssigneeWiggins Teape Limited
InventorsBronislaw Radvan, David J. Dobson
Life of this patent
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Abstract
A method of coating sheet material with a coating composition comprising particulate solid material suspended in a liquid carrier, wherein the coating composition is applied to the sheet material as a foam and subsequently dried, the air content of the foam being such that the viscosity of the coating composition is greater in its unfoamed state than in the foamed state in which the composition is applied.
Claims19
In the process of producing coated sheet material products which comprises using a sheet material coating composition of particulate solid material suspended in a liquid carrier, controlling the solids content of the coating composition to achieve a viscosity which provides satisfactory fluidity for coating, and drying the coating composition to deposit a particulate solid material coating on said sheet material, the improvement which comprises:
- (a) incorporating a minor amount of foaming agent in the sheet material coating composition, foaming the composition, and carefully controlling the air content of the foam such that the viscosity of the coating composition is greater in its unfoamed state than in the foamed state in which the foam is applied, thus (i) permitting greater control and reproducibility of the coating process than is achievable with a similar composition which is unfoamed, and (ii) minimizing the drying load at step (c), infra;
- (b) applying the foamed composition of step (a) to a surface of the sheet material;
- (c) drying the sheet material to obtain a resulting coated sheet having a coating of predetermined solids content.
In the method of coating paper material with particulate solids deposited from a coating composition comprising particulate solid material suspended in an aqueous system containing binder, which comprises the steps of
- (a) forming the coating composition so that it exhibits a desired viscosity which allows a substantially uniform, smooth coatweight of said particulate solids to be obtained on a surface of the paper material;
- (b) applying said coating composition in excess to a surface of the paper material;
- (c) removing the excess of such coating composition from said surface of the paper material to provide said desired coatweight;
- and then
- (d) drying the coated paper material to provide the coated paper product;
- the improvement which comprises:
- incorporating a minor amount of foaming agent in the coating composition, foaming the composition, and carefully controlling the air content of the foam such that the viscosity of the coating composition is greater in its unfoamed state than in the foamed state as applied in step (b), thus (i) permitting greater control and reproducibility of the coating process than is achievable with a similar composition which is unfoamed, and (ii) minimizing the drying load of step (d) by reducing the water content of the coating composition of step (a) relative to that which would otherwise provide said desired viscosity.
Dependencies are inferred from the claim text.