Process for producing dry finished paperboard

Claim 1

A process for producing a dry finished, coated paperboard web to attain a smoothness and printability equivalent to that of a wet finished product without any significant loss of caliper comprising: (a) applying a surface sizing composition with a surface sizing applicator to at least one side of the paperboard web before calendering and coating, said surface sizing composition comprising a binder, pigment in the ratio of from about 1:1 to 1:1.5 based on the weight of the binder and from about 5-20% based on the weight of the binder of a low molecular weight polyhydroxy alcohol plasticizing agent having a boiling point greater than about 100 degrees C. selected from the group consisting of glycerine, glycerol, glycol, propylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol and glycide, the solids content of said surface sizing composition being from about 4-32%, wherein the total pickup at the sizepress ranges from about 0.75 to 3.5 lb/ream/side in such a manner that the plasticizing agent remains substantially on the surface of the paperboard; (b) machine calendering the surface sized paperboard in the absence of a water treatment so that only the plasticizing agent containing surface layer of the paperboard becomes compacted and smoothed; (c) coating the calendered and surface size treated paperboard surface; and, (d) drying the thus treated paperboard to produce a dry finished web.