PACKAGING TRAY WITH CAPPING LAYER
The present invention is directed to rigid or semi-rigid trays having a bulk layer comprising a crystalline aromatic polyester and a capping layer which is in direct contact with the bulk layer. The capping layer comprises a copolymer having a first structural repeating unit of ethylene and a second structural repeating unit selected from the following: (i) an acrylate-based moiety: fit) at least 12% by weight relative to the total weight of the copolymer of vinyl acetate; and (iii) an anhydride or carboxylic acid. It has been discovered that the bulk layer and the capping layer of the present invention can be readily co-extruded together and have sufficient bond strength to each other despite their chemical dissimilarity. In some preferred embodiments, the capping layer acts as a heat seal layer and is formulated to heat seal to conventional polyolefin-based lidstock.
1 . A tray comprising:
a bulk layer comprising a crystalline aromatic polyester; and
a capping layer in direct contact with the bulk layer; wherein the capping layer comprises a copolymer comprising at least a first structural repeating unit of ethylene and a second structural repeating unit selected from the following:
i) an acrylate-based moiety;
ii) at least 12% by weight relative to the total weight of the copolymer of vinyl acetate; and
iii) an anhydride or carboxylic acid.
2 . The tray according to claim 1 , wherein the crystalline aromatic polyester is selected from the group consisting of polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate; polyethylene-2,6-naphthalate, polytrimethylene-2,6-naphthalate, polybutylene-2,6-naphthalate, polyhexamethylene-2,6-naphthalate, polyethylene isophthalate, polytrimethylene isophthalate, polybutylene isophthalate, polyhexamethylene isophthalate, poly-1,4-cyclohexane-dimethanol terephthalate, and polybutylene adipate terephthalate and derivatives thereof.
3 . The tray according to claim 1 , wherein the crystalline aromatic polyester is polyethylene terephthalate.
4 . The tray according to claim 1 , wherein the acrylate-based moiety is selected from the group consisting of butyl acrylate, ethyl acrylate, ethyl methacrylate, methyl acrylate, methyl methacrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, and blends thereof.
5 . The tray according to claim 4 , wherein the acrylate-based moiety is methyl acrylate.
6 . The tray according to claim 5 , wherein the methyl acrylate is at least 21% by weight relative to the total weight of the copolymer.
7 . The tray according to claim 1 , wherein the carboxylic acid is selected from the group consisting of acrylic acid, methacrylic acid, α-ethylacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, and endo-cis-bicyclo[2,2,1]-hepto-5-ene-2,3-dicarboxylic acid.
8 . The tray according to claim 1 , wherein the anhydride is maleic anhydride or a derivative thereof.
9 . The tray according to claim 1 , wherein the capping layer is a monolayer.
10 . The tray according to claim 1 , wherein the capping layer is a multilayer film.
11 . The tray according to claim 1 , wherein the capping layer comprises a copolymer comprising a third structural repeating unit.
12 . The tray according to claim 11 , wherein the third structural repeating unit is a different structural repeating unit than the second structural repeating unit.
13 . The tray according to claim 12 , wherein the second structural repeating unit is methyl acrylate and the third structural repeating unit is maleic anhydride.
14 . The tray according to claim 13 , wherein the methyl acrylate is about 24% by weight relative to the total weight of the copolymer and the maleic anhydride is about 0.1% by weight relative to the total weight of the copolymer.
15 . The tray according to claim 11 , wherein the second structural repeating unit is vinyl acetate and the third structural repeating unit is maleic anhydride.
16 . The tray according to claim 15 , wherein the vinyl acetate is at least about 9.5% by weight relative to the total weight of the copolymer and the maleic anhydride is at least about 0.1% by weight relative to the total weight of the copolymer.
17 . The tray according to claim 11 , wherein the second structural repeating unit is methyl acrylate and the third structural repeating unit is glycidyl methacrylate.
18 . The tray according to claim 17 , wherein the methyl acrylate is about 24% by weight relative to the total weight of the copolymer and the glycidyl methacrylate is about 8% by weight relative to the total weight of the copolymer.
19 . The tray according to claim 1 , wherein the bulk layer and the capping layer has a bond strength of at least about 450 grams/inch.
20 . The tray according to claim 1 , wherein the bulk layer and the capping layer has a bond strength of at least about 1,000 grams/inch.
21 . The tray according to claim 1 , wherein the bulk layer comprises a crystalline aromatic polyester having between 20% and 40% crystallinity.