Gloss of coated paper is affected by the surface shape and scattering intensity of pigment layer. The surface shape consists of various micro-plane slopes. Each degree of micro-plane slope is estimated by the differential value of curved surface. Scattering intensity of pigment layer is estimated by the pigment diameter. In this paper, we investigated surface structure of coated papers which had various degrees of surface smoothness in order to clarify the dominant factor of gloss of coated paper.
We found that there was a good correlation between degrees of print gloss and differential values of printed surface. This means that print gloss is dominated by the variety of micro-plane slopes forming the printed surface shape. We also found that there was a good correlation between degrees of differential values of printed surface and degrees of differential values of unprinted surface. This means that the printed surface shape mainly depends on the surface shape before printing.
Ink layer gives various affections to the surface shape of printed paper. In regard to gloss paper including LWC, the ink layer reduces the differential value of curved surface. The matte paper has no effect on that of curved surface. The cast-coated paper is affected increasing the differential value of curved surface. Therefore, as the paper surface becomes much smoother before printing, such as cast-coated paper, the printed surface shape has much stronger influence of ink layer.
We also found that sheet gloss was decided by differential values of the surface shape and the diameter of pigment constituting coated layer. Therefore, we assume that sheet gloss is dominated by the variety of micro-plane slopes on the paper surface and scattering intensity of pigment in the coated layer.