Dienophile additives to polyvinylidene chloride copolymers
View Patent ↗A flexible film for packaging articles such as food is provided. The film comprises a layer of polyvinylidene (“PVdC”) homopolymer, polyvinylidene and methyl acrylate (“PVdC-MA”) copolymer or other polyvinylidene chloride copolymer. A dienophile such as, for example, ethyl trans-cinnamate, methyl trans-cinnamate, dibutyl maleate, dimethyl maleate or maleic anhydride is blended with the PVdC polymer or PVdC-MA copolymer to reduce yellowing of the film caused by degradation of the PVdC or PVdC-MA through heat or electron beam irradiation. Preferably a range of about 0.05% and about 5% by weight of the dienophile is added to the PVdC or PVdC-MA.
1. A flexible film comprising:
a plurality of layers wherein a first layer comprises polyvinylidene chloride; and
a dienophile additive comprising a cinnamate in the first layer of polyvinylidene chloride wherein the cinnamate is selected from the group consisting of ethyl trans-cinnamate and methyl trans-cinnamate.
2. The flexible film of claim 1 wherein the polyvinylidene chloride comprises a copolymer with methyl acrylate.
3. The flexible film of claim 1 further comprising:
an outer layer disposed on a first surface of the first layer; and
a sealant layer disposed on a second surface of the first layer.
4. The flexible film of claim 3 further comprising:
an outer adhesive layer for bonding the first layer of polyvinylidene chloride and the dienophile to the outer layer; and
an inner adhesive layer for bonding the first layer of polyvinylidene chloride and the dienophile to the sealant layer.
5. The flexible film of claim 4 wherein the outer layer and the outer adhesive layer comprise polymer blends of linear low density polyethylene and ethylene-vinyl acetate copolymer.
6. The flexible film of claim 4 wherein the inner adhesive layer comprises linear low density polyethylene.
7. The flexible film of claim 4 wherein the sealant layer comprises a copolymer of ethylene-vinyl acetate.
8. A flexible film package for a food article comprising:
a flexible film having a plurality of layers contained therein wherein a first layer comprises polyvinylidene chloride and a dienophile additive comprising a cinnamate wherein the cinnamate is selected from the group consisting of ethyl trans-cinnamate and methyl trans-cinnamate.
9. The flexible film package of claim 8 wherein the outer layer comprises a copolymer of polyvinylidene chloride and methyl acrylate.
10. The flexible film package of claim 8 further comprising:
outer layers of the flexible film wherein the outer layers include an abuse layer and a sealant layer; and
adhesive layers between the outer layers and the first layer.
11. The flexible film of claim 10 wherein the abuse layer comprises a polymer blend of linear low density polyethylene and ethylene-vinyl acetate copolymer.
12. A method of making a flexible film, the method comprising the steps of:
providing polyvinylidene chloride;
blending a dienophile with the polyvinylidene chloride to produce a polyvinylidene chloride/dienophile blend wherein the dienophile is selected from the group consisting of ethyl trans-cinnamate and methyl trans-cinnamate; and
extruding the polyvinylidene chloride/dienophile blend through a die to make a film.
13. The method of claim 12 further comprising the steps of:
coextruding the polyvinylidene chloride/dienophile blend with a plurality of melt streams to produce a plurality of layers.
14. The method of claim 12 further comprising the steps of:
blending between about 0.05% and about 5% by weight of the dienophile to the polyvinylidene chloride polymer.