Pigment coating of porous foam formed structures

Coating of bulky foam formed products having more surface voids is challenging with traditional application methods. Our aim was to improve the coating hold-out of foam formed webs. This was done either by precalendering or by surface foam coating with starch before pigment coating. The effects of these pretreatments were studied with a metered size press (MSP) and curtain coating. Foam formed samples had lower coating hold-out than water formed ones. Precalendering reduced the proportion of large pores of the structures and therefore improved coating hold-out. Applying starch with the foam coating reduced large pores at the surface. Precalendering improved coating hold-out and smoothness better than starch but simultaneously it reduced bulk. Starch applied by foam coating closed the surface effectively and maintained the high bulk. Non-contact curtain coating led to higher coating hold-out than the MSP application with a high pressure pulse. Curtain coating is a suitable method for porous foam formed structures but coating formulations should be further developed for different printing methods.