Abstract: A sheet of thermoplastic material has a planar surface treated to enhance adhesion of paper thereto by means of an adhesive of the class consisting of animal glue and water base adhesives as used in book binding. The sheet is passed beneath a heated diamond knurling roll at a temperature and pressure, and at a rate to produce a dwell time, which are controlled to form in said planar surface a continuous pattern of small, shallow recesses separated by inter-recess planar areas of said surface, and a raised rim of the thermoplastic material bordering each of said recesses and projecting above the planar areas, a large percentage of said rims having at least a part of their outer periphery overhanging a portion of the adjacent inter-recess planar area.