Abstract: Polypropylene films which have cavities distributed in the film and on the surfaces are suitable for writing or printing and have a low density. The films have surface qualities of each side of surface within .+-.2.times.10.sup.-6 inch of the average depth of the cavities, .+-.2% of the average of the gloss at 45.degree. angle and .+-.0.02 of the average of coefficient of friction. Such a film is obtained by passing the molded film from the calender through a set of heating rolls at temperatures revealed in this invention before entering the stretching system. The obtained polypropylene film has superior printability, low density and high stiffness, and thus is suitable for use as a paper substitute.

Abstract: A process which combines a calender with a stretching system and a set of heating rolls is provided in this invention to produce films of polypropylene resin of wide thickness range. The polypropylene films which have cavities distributed in the film and on the surfaces are suitable for writing or printing and have a low density. The films have surface qualities of each side of surface within .+-.2.times.10.sup.-6 inch of the average depth of the cavities, .+-.2% of the average of the gloss at 45.degree. angle and .+-.0.02 of the average of coefficient of friction. Such a film is obtained by passing the molded film from the calender through a set of heating rolls at temperatures revealed in this invention before entering the stretching system. The obtained polypropylene film has superior printability, low density and high stiffness, and thus is suitable for use as a paper substitute.

Abstract: The present invention is directed at polypropylene compositions containing a high level of filler, at a calendering process which uses the compositions to produce polypropylene films and sheets, and at the film or sheet produced from that process. The process of manufacturing polypropylene film involves formulating a polypropylene composition containing a resin, filler, matrix modifier, and processing aid. The resin comprises polypropylene resin ranging in concentration from about 100 to about 70 parts per hundred parts by weight of resin (PHR), and polyethylene resin ranging in concentration from about 0 to 30 PHR. The matrix modifier amounts to about 2 to 40 PHR. The filler ranges in concentration from about 0 to 450 PHR. The processing aid ranges in concentration for about 0 to 5.0 PHR. The composition is then mixed to obtain a homogeneous and plasticized mixture.