Dynamic water penetration behavior of top coating color and its effects on structure properties of double-coated layer

Abstract

The relationship between the dynamic water penetration behavior of top coating color and double-coated paper properties, including pore structure, surface roughness, gloss, and surface latex content, was investigated. Top coating was applied onto the precoated paper prepared using different pigment types, thereby having different pore structures. To investigate the effect of dwell time on pore structure and surface latex content, coating speed and the distance between two coating heads of a laboratory coater were adjusted. As the number of pores of the precoated layer increased, the amount of water that penetrated the precoated paper increased, regardless of low shear viscosity of the top coating color. The relative pore ratio and surface properties of the top coated layer were proportional to those of the precoated layer. A UV absorbance analysis was conducted to examine latex binder migration. The latex content on the surface of the coating layer was mainly affected by the dwell time to the dryer after coating.

Evaluation of print mottle of double coated paper by octave band filtering technique

“…Furthermore, dynamic water absorption of the top-coating color increased with the increase of the number of pores in the pre-coated layer. Accordingly, the surface latex concentration of the top-coated layer decreased with the increases in the water penetration rate of the topcoating color into the pre-coated layer (Im et al 2022). Thus, the increase in the mottle index of double-coated paper can be attributed to the uneven distribution of latex in the coated paper, depending on the type of pre-coating pigment used.…”

“…In a previous study (Im et al 2022), it was found that the number of pores per unit area at the surface of the coating layer was affected by the dwell time, which is the time between the rod and metering of the surplus coating color. Especially, the increase in dwell time during the pre-coating stage significantly increased the number of pores per unit area at the double-coated layer surface compared to the changes in dwell time during the topcoating.…”

“…As a follow-up study to previous papers (Im et al 2022;Youn and Lee 2022), preand top-coating processes were performed similarly. Briefly, pre-coating colors were prepared using the two types of GCC and No.…”

“…Thus, the higher water holding capacity of pre-coating color reduced binder migration into the base paper, while increasing latex content on the surface of double-coated paper. Additionally, Im et al (2022) investigated the relationship between the dynamic water penetration behavior of top-coating color and double-coated paper properties. Results showed that as the number of pores per unit area at the surface of the pre-coating layer increased, the amount of water that penetrated the pre-coated paper increased, regardless of the low shear viscosity of the top coating color.…”