1. Field of the Invention
This invention relates to an improved process for preparing vinylidene chloride interpolymers. Specifically, it relates to the preparation of vinylidene chloride interpolymers having enhanced barrier to atmospheric gases and water vapor.
2. Description of the Prior Art
Vinylidene chloride interpolymers are well-known in the prior art. U.S. Pat. No. 3,642,743 teaches a method for preparing an interpolymer of vinylidene chloride and vinyl chloride. The polymerization is carried out in an aqueous suspension in a completely closed reaction vessel. Other methods of polymerization are well-known in the art.
Polymers and copolymers of vinylidene chloride with such well-known copolymers as acrylonitrile, vinyl chloride and lower alkyl acrylates are widely used as films for packaging foodstuffs and other articles. Such films possess many useful properties, such as inertness, ability to be heat sealed, transparency, shrinkability and low permeability to atmospheric gas and water vapor.
The present invention concerns a method of producing vinylidene chloride interpolymer articles possessing enhanced barrier to water vapor and atmospheric gases. The enhanced barrier is achieved by allowing a substantial degree of crystallization of the vinylidene chloride interpolymer article to occur after fabrication but before the article is substantially cooled.
It is known in the art that the use of nucleating agents will speed the crystallization of interpolymer films. Exemplary of such patents are U.S. Pat. Nos. 3,240,742; 3,793,265; 3,819,595.
It is desirable to produce a vinylidene chloride homopolymer or copolymer possessing enhanced barrier to atmospheric gases and water vapor without severely degrading the polymer's other physical properties. It is to this goal that the present invention is directed.