The formation of a microporous layer using a bubble coating method was described. A mixture of air and a coating is stirred in a closed system utilizing a bubbling apparatus. A large number of fine bubbles are observed in the coating mixture. A microporous layer was formed by the coating of the bubbled coating mixture and then drying in an oven.
It was found that the formation of air bubbles in the coating mixture and the stabilization of the foam in the coating layer were important. There was a clear correlation between the bubble size in the bubbled coating mixture and the pore size in the microporous surface layer. A large number of fine bubbles with an average diameter of 4 to 12μm was prepared using this bubble coating method.
A microporous paper sheet having the microporous layer on the top was also found to improve the printing quality in a thermal wax transfer printing. The microporous layer had good heat-insulating and elastic properties in addition to an excellent ink-receiving ability due to the large number of fine pores on the surface.
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