BARRIER RESIN COATED LAMINATES

Abstract: The invention is directed to metallized materials that have a metallic coating on one or more surfaces that show improved barrier layer coating adhesion and heat seal properties. These materials include a coating of vinylidene copolymer of at least 80 % vinylidene chloride, at least 4 % of an ethylenically unsaturated acrylic monomer, as well as coating additives for modifying film properties.

Description: TITLE BARRIER RESIN COATED LAMINATES FIELD OF THE INVENTION The invention relates to materials that have improved heat seal properties. In particular, the invention relates to metallized polymer films that have improved heat seal properties for use in packaging. BACKGROUND OF THE INVENTION Materials such as polymer film and metal foil have been employed to protect products such as food stuffs against the effects of oxidation and water vapor permeation. The polymer films typically are coated with polymeric, barrier layer compositions. These barrier layer compositions typically include coating additives such as aluminum silicates, talc, waxes and the like to impart desired film properties such as jaw release, printability, film slip and the like. Unfortunately, these additives tend to reduce the coating adhesion and heat seal properties of the coated polymer film. Metal foils such as aluminum foil also have been used as packaging materials for products such as food stuffs. Metal foils are useful for packaging due to their low permeability to oxygen and water vapor. Metal foils, however, are subject to significant cost variability, have poor heat seal properties, and poor flex-crack resistance. The art has made efforts to improve the heat seal properties of polymer films. In U.S. patents 3,896,066 and 3,985,065, the patentees apply a barrier coating of a copolymer of vinylidene chloride to the polymer substrate. Japanese 6223174, published October 12, 1987, shows production of metallized sheets of paper and plastic. The process comprises applying a polyvinylidene chloride copolymer of methacrylic ester, acrylonitrile, vinyl chloride, and methacrylic acid onto the metallized surface of a sheet of paper or plastic. The polyvinylidene chloride copolymer then is oxidized. Although the art has employed vinylidene chloride copolymer barrier layers with polymeric films, the ' metallized polymer films which employ these barrier compositions tend to be deficient as packaging materials because of the effects of coating additives. A need therefore exists for improved metallized packaging materials that employ barrier layer compositions that include coating additives and which overcome the deficiencies of the prior art materials. SUMMARY OF THE INVENTION The invention is directed to metallized materials that have a a metallic coating on one or more surfaces that show improved barrier layer coating adhesion and heat seal properties. These metallized materials include a coating of vinylidene copolymer on the metallic coating. The polyvinylidene chloride copolymer has at least 80% vinylidene chloride, at least 4% of an ethylenically unsaturated acrylic monomer, as well as. coating additives for modifying film properties. In accordance with the invention, the metallized materials that show improved barrier layer coating adhesion and heat seal properties are made by treating a substrate material that has at least one metallic surface thereon with a formulated solution of coating additives and vinylidene chloride copolymer. The polyvinylidene chloride copolymer comprises at least 80% by weight polyvinylidene chloride, at least 4% by weight of an ethylenically unsaturated acrylic ester. The solution of copolymer of vinylidene chloride and coating additives forms a barrier layer that imparts surprisingly improved adhesion and heat seal properties to materials such as polyesters that bear metal layers thereon. Application of the aforedescribed solution in accordance with the invention provides surprisingly improved adhesion and heat seal properties. Such substrate materials include, but are not limited to plastics, regenerated cellulose, paper, metallized plastics, metallized regenerated cellulose, metallized paper and the like. Suitable plastics for use in the invention include, but are not limited to polyesters, polyolefins, polyamides, vinyl chlorides, copolymers thereof, as well as blends thereof. Additional examples of materials whose adhesive and heat seal properties may be improved by the vinylidene chloride copolymer of the invention include but are not limited to metal foils such as aluminum foil. The formulated solution of vinylidene chloride copolymer and coating additives may be applied to the substrate materials by any conventional method known in the art. Such methods include solvent solution coating, emulsion coating, melt coating, and the like. Preferably, the vinylidene chloride copolymer is applied in a conventional coating tower by passing the substrate material through a solvent solution of formulated vinylidene chloride copolymer and coating additives, and thereafter evaporating the solvent to yield a layer of formulated vinylidene chloride polymer and coating additives on the substrate. The substrate materials, preferably metallized polymeric films, that are coated with the formulated solution of vinylidene chloride copolymer and coating additives have particular utility in packaging for materials such as foodstuffs. These coated substrate materials can be employed as produced. Alternatively, but without limitation, the coated metallized substrate materials may be used in the form of a laminated film structure. The coated substrate materials produced by the invention also may be used in applications such as, but not limited to, insulation materials for the construction industry. Having briefly summarized the invention, the invention will now be described in detail by reference to the following specification and non-limiting examples. Unless otherwise specified, all percentages are by weight and all temperatures are in degrees Celsius. DETAILED DESCRIPTION OF THE INVENTION In accordance with the invention, a formulated solution of vinylidene chloride (VDC) copolymer and up to 10% by weight of copolymer of coating additives is applied to a metal bearing substrate, preferably metallized polymer film, most preferably metallized polyethylene terephthalate. The VDC copolymer has at least 80%, but not more than 95% vinylidene chloride. The balance of the vinylidene chloride copolymer comprises an ethylenically unsaturated acrylate, preferably methyl methacrylate (MMA) . The ethylenically unsaturated acrylate comprises at least 4% of the VDC copolymer. Other ethylenically unsaturated polyacrylates may be employed in place of MMA or in combination with MMA. Examples of suitable ethylenically unsaturated acrylates include, but are not limited to, aliphatic C_-C 6 acrylates, aliphatic C 2 -C 8 methacrylates, and the like. Examples of ethylenically unsaturated acrylates include, but are not limited to butyl acrylate, methyl acrylate, ethyl acrylate and the like. Examples of aliphatic methacrylates include methyl methaσrylate, ethyl methacrylate, and the like. Optionally, acrylonitrile (AN) may be included in the vinylidene chloride copolymer provided that the copolymer has at least 4% of ethylenically unsaturated polyacrylate. Preferably, the copolymer has 80 to 95% vinylidene chloride and 4 to 20% ethylenically unsaturated acrylate, most preferably 88 to 92% vinylidene chloride and 6 to 12% ethylenically unsaturated acrylate. The metal bearing materials that can be coated with the formulated solution of vinylidene chloride copolymer and coating additives preferably are metallized polymers. Examples of suitable polymers include polyesters, polyolefins, polyamides, polyvinylchloride, copolymers thereof, and blends thereof. Any oxidizable metal such as Fe, Cu, Al, Ti, alloys thereof, and the like, most preferably aluminum, may form the metal component of the metallized polymer films. Most preferably, the metallized polymeric film is alu inized polyethylene terephthalate. Such metallized polymers are made by processes known in the art, as described for example in ''Encyclopedia of Chemical Technology", Kirk-Othmer, 3rd Edition, Volume 15, pp. 264-265, the disclosure of which is incorporated by reference. The metal bearing materials that may be coated, however, may be other than metallized polymers. Examples of additional metal bearing materials that may be employed in the invention include metallized regenerated cellulose and polyolefins such as metallized paper, metallized oriented polypropylene, and the like. The improved products of the invention are preferably prepared by applying a coating solution of more than 90% by weight of a vinylidene chloride copolymer that has at least four percent of ethylenically unsaturated acrylate and up to 10% by weight of coating additives to at least the metal bearing surface of a metal bearing substrate. Examples of coating additives include talc, waxes, aluminum silicates, and the like. Alternatively, the formulated solution of vinylidene chloride copolymer may be applied to both the metal bearing surface and the non-metal bearing surface of the substrate material. The formulated solution of vinylidene chloride copolymer and coating additives preferably is applied to the metallized substrate. Thereafter the solvent of the vinylidene chloride copolymer solution is evaporated to provide a coating of vinylidene chloride copolymer and coating additives on at least the metallized surface of the substrate. Application of the solution of formulated polyvinylidene chloride copolymer conveniently can be performed in a conventional coating tower, as is known in the art. Alternatively, but without limitation, the formulated solution of vinylidene chloride copolymer and coating additives may be applied by emulsion coating of a solution of formulated vinylidene chloride copolymer onto the substrate. In accordance with the preferred method for applying the formulated solution of vinylidene chloride copolymer, the copolymer of vinylidene chloride and ethylenically unsaturated monomer, preferably MMA, is dissolved in a solvent such as tetrahydrofuran (THF) , toluene, methyl ethyl ketone, nonpolar solvents such as 1,3-dibromopropane, bromobenzene, alpha-chloronaphthalene, 2-methylnaphthalene, o-dichlorobenzene, polar aproctic solvents such as tetramethylene sulfoxide, N-methyl pyrrolidone, trimethylene sulfide, isopropyl sulfoxide, N-acetyl pyrrolidine, N,N-dimethyl acetamide, or mixtures thereof. Preferably, the solvent is a mixture of at least 15% THF, the balance being toluene, most preferably 60-75% THF and 25-40% toluene. The formulated solution of vinylidene chloride copolymer then is applied to at least the metal bearing surface of a polymer substrate, preferably polyester, most preferably polyethylene terephthalate, in an air drying, laboratory-scale coating tower. The inlet temperature and the outlet temperature of the coating tower may be in the range of 70''C to 130"C. Preferably, the inlet temperature is 120"C and the outlet temperature is 80"C. The coated polyethylene terephthalate is passed through the coating tower at the rate of 30 to 90 feet per minute, preferably 90 feet per minute. The coated materials achieved by the invention have properties which make them particularly suited for use as packaging materials for foodstuffs where deterioration due to oxidation and change of moisture content is a concern. In the examples that follow, properties are determined by the tests described below. Heat seal strength is measured by cutting three samples of the coated metallized substrates that measure 1 x 10 inches. These samples are cut with the grain or machine direction of the film running in the long dimension of the sample. The samples are taken from the east, west and center edges of the coated, metallized substrate. Each sample is folded in half in the machine direction. The halves of the sample are sealed together at each end at right angles to the grain by applying a 0.75 inch wide sealing bar under carefully controlled conditions of temperature, pressure and contact time. The resulting three sets of strips are tested by opening each set at the free end, placing them in a Suter testing machine, and 5 pulling them apart while maintaining the folded end perpendicular to the pull direction. The highest force in grams required to pull the strips apart is taken as a measure of the heat seal bond strength. Heat seals are measured on the coated material as is. Q The laminate bond strength is measured by laminating a film sample to a 2-mil thick polyethylene film by using an adhesive such as a two-component curing type adhesive system. The adhesive coating weight applied is typically 1-1.5 lb dry solids per 5 ream. A heated pressure-nip roll is set at a lamination temperature of 170-2207, typically 215"F. While preparing the laminate of sample film to polyetherylene film, 15 or more sheets of release paper are inserted between the film sample and the polyethylene film at approximately 5 ft intervals to provide non-bonded areas in the laminate in order to assist initiation of delamination during bond strength tests. Typically, the laminates are cured at 25 β C for at least 7 days before being tested for bond strength. After the laminates are cured, both sides are reinforced from outside with a polyimide adhesive tape to prevent the test films from tearing. Five 1 x 8 inch specimens per test are cut with the long dimension parallel to the web direction. Samples are obtained from various locations across the web width. The laminate sample is tested "as is" for bond strength, or tested after being moisture conditioned. The moisture conditioning can be done in two ways. Samples with the non-bonded starting area exposed are conditioned in an enclosed dessicator at 40 β C for 1, 3, or 7 days, respectively. The bottom of each dessicator is filled with water. The laminate bond strength is recorded as "grams per inch width" by pulling apart the two films of the laminate (as separated by the release paper) in a tensile machine while holding the tail of the specimen at right angles to the direction of pull so that a constant shear peel is established. The bond strength reported for one sample is typically an average value of five film specimens tested under duplicating conditions. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. In the following examples, all temperatures are set forth in degrees Celsius; unless otherwise indicated, all parts and percentages are by weight. EXAMPLE 1 A. Preparation of the Formulated Solution - The vinylidene chloride copolymer employed has the following weight percentage composition: vinylidene chloride 91.3, acrylonitrile 1.8, methyl methacrylate 6.9; A formulated solution of 90.64% of the copolymer, 1.01% talc, 8.12% waxes, and a 0.23% aromatic polyester resin is prepared in a solvent of 65% THF and 35% toluene. The mixture is heated to 40"C to 45°C until the polymer is dissolved. The solid content of the bath solution is 18%. The aromatic polyester resin used in the formulated solution is prepared by trans-esterifying the bis-(ethylene glycol) esters of terephthalic acid. isophthalic acid, adipic acid, and azelaic acid using a tetraisopropyl titanate catalyst and following the procedures of U.S. patent 2,892,747. B. Coating of the Metallized Substrate - A conventional solvent coating tower is used to apply the formulated solution to both the metallized and non-metallized surfaces of a 1/2 mil aluminized polyethylene terephthalate film moving at 90 feet per minute. The formulated solution is placed in a dip tank maintained at 40"C and transferred to the metallized polyethylene terephthalate by a doctor roll. The doctor roll setting is 0.003 inches. Inlet and outlet tower temperatures of the coating tower are 120 β C and 80°C respectively. Inlet and outlet tower air supply is 250 and 300 cubic feet per minute respectively. The coating weight is determined by the weight difference between the coated and uncoated samples. The coated samples are tested for heat seal and laminate bond strength properties both as is, and after conditioning. Conditioning entails leaving the samples in a dessicator for periods of either 24 hours, 72 hours, or 1 week. The bottom of the dessicator is filled with water. The results are shown in Table 1. EXAMPLE 2 The procedure of Example 1 is followed except that the vinylidene chloride copolymer has the following weight percentage composition: vinylidene chloride 90.5, methyl ethacrylate 9.5. The heat seal and laminate bond strength properties are shown in Table 1. EXAMPLE 3 The procedure of Example 1 is followed except that the vinylidene chloride copolymer has the following weight percentage composition: vinylidene chloride 90.9, methyl methacrylate 9.1. The heat seal and laminate bond strength properties are shown in Table 1. EXAMPLE 4 The procedure of Example 1 is followed except that the vinylidene chloride copolymer has the following weight percentage composition: vinylidene chloride 91.6, acrylonitrile 4.0, methyl methacrylate 4.4. The heat seal and laminate bond strength properties are shown in Table 1. COMPARISON EXAMPLE 1 The procedure of Example 1 is followed except that the vinylidene chloride copolymer has the following weight percentage co positon: vinylidene chloride 92.1, acrylonitrile 5.5, methyl methacrylate 2.5. The heat seal and laminate bond strength properties are shown in Table 1. COMPARISON EXAMPLE 2 The procedure of Comparison Example 1 is followed except that no coating additives are included in the formulated solution. The vinylidene chloride copolymer employed has the following weight percentage composition: vinylidene chloride 92.1, acrylonitrile 5.5, methyl methacrylate 2.5. The heat seal and laminate bond strength properties are show in in Table 1. COMPARISON EXAMPLE 3 The procedure of Comparison Example 2 is followed except that the vinylidene chloride copolymer has the following weight percentage composition: vinylidene chloride 90.5, methyl methacrylate 9.5. The heat seal and laminate bond strength properties are shown in Table 1. TABLE 1 Cured laminate samples condicloned In a dessicator at 40"C for 24 hours. Bottom of dessicator filled with water. 2 Cured laminate samples conditioned in a dessicator at 40'C for 72 hours. Bottom of dessicator filled with water. 3 Cured laminate samples conditioned in a dessicator at 40'C for 1 week. Bottom of dessicator filled with water. • . Table 1 shows that the heat seal and laminate bond strength properties of the coated metallized side improve significantly as the quantity of methyl methacrylate in the vinylidene chloride copolymer contains at least 4% MMA or more. This improvement occurs despite the presence of coating additives. From the foregoing description, one skilled in the . art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Claims: CLAIMS 1. A method of manufacturing a product that has improved barrier coating adhesion and heat seal strength comprising, providing a substrate material that has at least one surface with metal thereon, and coating at least said surface with a formulated solution of vinylidene chloride copolymer and coating additives, said polyvinylidene chloride copolymer having at least 4% by weight of an ethylenically unsaturated acrylic ester to provide a product that has improved barrier coating adhesion and heat seal strength. 2. The method of Claim 1 wherein said substrate material is selected from the group of plastics, regenerated cellulose, and paper. 3. The method of Claim 2 wherein said plastic is selected from the group of polyesters, polyolefins, polyamides, polyvinylchloride, copoly ers thereof, and blends thereof. 4. The method of Claim 3 wherein said plastic is a polyester. 5. The method of Claim 4 wherein said polyester is polyethylene terephthalate. 6. The method of Claim 1 wherein said metal is selected from the group of Fe, Cu, Al, Ti, an alloys thereof. 7. The method of Claim 6 wherein said metal is aluminum. 8. The method of Claim 7 wherein sai vinylidene chloride copolymer is at least 80 vinylidene chloride. 9. The method of Claim 8 wherein sai vinylidene chloride copolymer is at least 88 vinylidene chloride. 10. The method of Claim 9 wherein said ethylenically unsaturated monomer is methyl methacrylate. 11. The method of Claim 9 wherein said coating solution includes coating additives selected from the group of talc, aluminum silicates, wax, aromatic polyester resins, or mixtures thereof. 12. The method of Claim 1 wherein said coating additives are present in up to 10% by v/eight of said polyvinylidene chloride copolymer. 13. A metal bearing material that has improved coating adhesion and heat seal properties comprising, a substrate material that has at least one surface with metal thereon, and a coating of a formulated solution of vinylidene chloride copolymer and coating additives on at least said surface, said polyvinylidene chloride copolymer having at least 4% by weight of an ethylenically unsaturated acrylic ester. 14. The material of Claim 13 wherein said substrate material is selected from the group of plastics, regenerated cellulose, and paper. 15. The material of Claim 13 wherein said plastic is selected from the group of polyesters, polyolefins, polyamides, polyvinylchloride, copolymers thereof, and blends thereof. 16. The material of Claim 15 wherein said plastic is a polyester. 17. The material of Claim 16 wherein said polyester is polyethylene terephthalate. 18. The material of Claim 13 wherein said metal is selected from the group of Fe, Cu, Al, Ti and alloys thereof. 19. The material of Claim 18 wherein said metal is aluminum. 20. The material of Claim 19 wherein said vinylidene chloride copolymer is at least 80% vinylidene chloride. 21. The material of Claim 20 wherein said vinylidene chloride copolymer is at least 88% vinylidene chloride. 22. The material of Claim 21 wherein said ethylenically unsaturated monomer is methyl methacrylate. 23. The material of Claim 13 wherein said coating solution includes coating additives selected from the group of talc, wax, aromatic polyester resin, or mixtures thereof. 24. The material of Claim 13 wherein said coating additives are present in up to 10% by weight of said polyvinylidene chloride copolymer.

Inventors: CHANG CLIFFORD CHENG-SHIOU, CHANG, CLIFFORD, CHENG-SHIOU
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: B65D65
IPC codes: B05D7, B32B15, B65D65