Agglomerate-free, bubble-free, high barrier vinylidene chloride polymer films and process of preparation

An improved process for preparing extruded vinylidene chloride copolymer film containing an effective amount of one or more inorganic particulate additives, said film being generally free of bubbles, holes and white specks, said film being made by (a) preparing a blend of (1) a dry, powdered, generally plasticizer-free, normally crystalline vinylidene chloride copolymer having polymerized therein from about 70 to about 95 percent by weight, based on copolymer weight, vinylidene chloride and from about 30 to about 5 percent by weight, based on copolymer weight, of at least one monoethylenically unsaturated monomer copolymerized therewith, and (2) the inorganic particulate additives, each additive having an average particle size of greater than about 0.5 micron and less than about 40 microns, and (b) thermally fabricating said blend into film form by extrusion, the improvement which comprises dividing the inorganic additives into a first portion and a second portion, dividing the vinylidene chloride copolymer into a first portion and a second portion, forming a concentrate, the concentrate being formed by first admixing the first portion of the inorganic additives with from about 0.02 to about 0.5 weight percent, based upon total inorganic additive weight, of an alkali metal salt of an alkylaryl sulfonic acid using a high speed mixing means, then mixing in the second portion of the inorganic additives and the first portion of the vinylidene chloride copolymer, the concentrate then being blended with the second portion of the vinylidene chloride copolymer, whereby the blend and the film made therefrom are generally free of agglomerates without the necessity of an intermediate step to remove agglomerates.