Preparing heat resistant heat shrinkable films
AssigneeAmerican Can Company
InventorsJoseph C. Hsu, Donald W. Vought, George H. Walbrun
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Abstract
A three layer heat shrinkable film is disclosed, along with preferred process for making it. The film comprises a first heat sealable layer of an ionomer, a second layer of a vinylidene chloride copolymer, and a third layer of a blend of an ionomer and an EVA copolymer. The EVA content is no greater than 20% of the blend by weight, and the vinyl acetate content is at least 4.5% of the blend by weight. In the preferred process, a three layer tape is coextruded and cooled, and reheated to 197.degree.-203.degree. F., and oriented in a conventional double bubble process.
Claims1
A process for making a three layer heat shrinkable film, said process comprising the steps of:
- (a) coextruding a three layer tubular tape having a first inner layer of ionomer having two surfaces, a second layer of a vinylidene chloride copolymer having two surfaces, and having one of said surfaces on said second layer on one said surface of said first layer, and a third outer layer on the other said surface of said second layer, the composition of said third layer being a blend of an ionomer and an EVA copolymer, wherein the EVA content of said blend is no greater than 20% by weight, the vinyl acetate content of said EVA is at least 22 percent, and the vinyl acetate content of said blend is at least 4.5% by weight;
- (b) cooling said tape below the crystalline melting temperature of each of said three layers;
- (c) reheating said tape to a temperature of about 195.degree.-205.degree. F.;
- and
- (d) orienting said tape to form a film by blowing a bubble in the heated tape, providing an appropriate draw to said film to provide an oriented film having normally balanced shrink properties, and cooling said blown and drawn film
- whereby free shrink of said film at 160.degree. F. is about 20%-26% and at 180.degree. F. is about 42%-45%, and shrink force at 160.degree. F. is 160-219 grams per inch and at 180.degree. F. is 160-188 grams per inch.
Dependencies are inferred from the claim text.