1. Field of the Invention
The present invention relates generally to a method for creating a clear barrier film, typically a polymer film, by means of coating the product with a clear barrier coating containing polyvinyl alcohol and starch. The clear barrier coating is also disclosed.
2. Description of Related Art
Barrier coatings are desirable for many applications, such as food packaging. These barrier coatings limit transmission of oxygen and/or water vapor through the coated substrate. For many end uses, it is desirable for the coating to be clear. When the substrate is also clear, as in a transparent polymer film, view through the substrate is not obstructed. However, known barrier coatings have suffered from numerous limitations, including high cost, inadequate transparency and limited barrier properties. There is a need for barrier coatings that address one or more of these problems. A need also exists for barrier coatings that are adapted for application to polymer film substrates. Coatings adapted for in-line application during film manufacture are also desirable.
Known barrier coatings include polyvinylidene chloride-based coatings. These coatings are solvent based, which may render their coating processes environmentally hazardous. In addition, because of possible solvent residue in the coating, they may pose some risk when used to package food items. These coatings also are not reclaimable, and decompose to give off HCl vapors if recycled. Furthermore, such coatings are coated off-line after film orientation is complete. This requires thick coatings that are not economically optimal, and additional processing steps that render the coated film more expensive. Other known barrier films are polyvinyl alcohol based. However, these coatings do not perform well at high humidity levels. Off-line coatings using polyvinyl alcohol are also known.
USPTO Backgrounds
USPTO Backgrounds