EP0809572A1 - Protective polymeric film for lamination to metal - Google Patents

Protective polymeric film for lamination to metal

Info

Publication number
EP0809572A1
EP0809572A1 EP96906379A EP96906379A EP0809572A1 EP 0809572 A1 EP0809572 A1 EP 0809572A1 EP 96906379 A EP96906379 A EP 96906379A EP 96906379 A EP96906379 A EP 96906379A EP 0809572 A1 EP0809572 A1 EP 0809572A1
Authority
EP
European Patent Office
Prior art keywords
scratch
layer
percent
ethylene
resistant layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96906379A
Other languages
German (de)
French (fr)
Inventor
Robert H. Kelch
Bradley Day Stevens
Terry H. Fiero
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Dow Chemical Co
Original Assignee
Dow Chemical Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Dow Chemical Co filed Critical Dow Chemical Co
Publication of EP0809572A1 publication Critical patent/EP0809572A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B32B15/085—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B32B15/088—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyamides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B32B15/09—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • B32B27/302—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising aromatic vinyl (co)polymers, e.g. styrenic (co)polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/40—Layered products comprising a layer of synthetic resin comprising polyurethanes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B2038/0052—Other operations not otherwise provided for
    • B32B2038/0076—Curing, vulcanising, cross-linking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/584—Scratch resistance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2311/00—Metals, their alloys or their compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2323/00—Polyalkenes
    • B32B2323/04—Polyethylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2323/00—Polyalkenes
    • B32B2323/10—Polypropylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2325/00—Polymers of vinyl-aromatic compounds, e.g. polystyrene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2375/00—Polyureas; Polyurethanes

Definitions

  • the present invention relates to a protective polymeric film which may be readily laminated to metal substrates to provide protection from scratches, solvents, and corrosion, and which exhibits good sealability and compressibility when the laminate is used to form metal containers.
  • Protective polymeric films or coatings are known in the art which can be laminated to metals such as tin-free steel, tin-plated steel, and aluminum, and then formed into parts such as aerosol valve mounting cups, aerosol can domes or bottoms, paint cans, food and beverage containers, and the like. Such films or coatings are used to protect the underlying metal surface from corrosion as well as to provide resistance to solvents and abrasions.
  • U.S. Patent No. 4,626,157 to Franek et al describes a method of making metal containers such as aerosol dispensing containers having top can end members and valve cup members formed from a metal laminate comprising a thin polymeric layer such as polyester or polypropylene overlaid on the metallic substrate.
  • the metal/film laminates using polypropylene do not exhibit good sealability and compressibility when used to fabricate metal containers such as aerosol cans. Specifically, such films do not form a good seal for compression formed joints or seals between two pieces of a metal laminate. Such a poor seal may result in leakage of pressurized propellant from a metal aerosol container formed from the metal laminate.
  • polypropylene has been found to be difficult to adhere to various metallic substrates.
  • Many commercial polypropylene film laminates currently in use are adhered tometal with solvent based-adhesives such as urethane adhesives.
  • solvent based-adhesives such as urethane adhesives.
  • such adhesives are undesirable as they are environmentally unfriendly and leave the potential for residual solvents from the adhesive to migrate gradually through the film laminate and contaminate the contents of the metal container.
  • inadequate curing of the adhesive can result in loss of adhesion of the film laminate, particularly following exposure to solvents that may be contained within the fabricated structure.
  • polymer films have more recently been laminated to metal using thermoplastic adhesive resins.
  • U.S. Patent No. 4,980,210 to Heyes et al describes a two-layer film bonded to the surface of a metal sheet comprising an inner adhesive layer of an acid-modified polyolefin resin and an outer layer of a polyolefin.
  • U.S. Patent No. 5,006,383 to Achille et al teach a blend of polypropylene and very low density polyethylene and an adhesive layer comprising a rubber and polar comonomer modified ⁇ -olefin polymer resin.
  • the films may not provide sufficient resistance to abrasions and scratches.
  • such film laminates can possibly be damaged by cutting, abrading or puncturing as the metal cups vibrate or move against each other. Damage can also occur during part die stamping or forming if the stamping dies or assembly mechanisms are not perfectly aligned. If the protective polymeric film becomes damaged, the corrosion resistance of the aerosol valve mounting cups is also weakened.
  • the present invention meets that need by providing a protective polymeric film which may be readily laminated to a metal substrate, which is resistant to scratches, solvents and corrosion, and which exhibits good sealability and compressibility when used to form metal containers.
  • the film may be produced by conventional coextrusion techniques.
  • a protective polymeric film comprising an adhesive layer comprising from 5 to 25 percent of the total film thickness, a scratch- resistant layer comprising from 5 to 40 percent of the total film thickness, and a compressible layer positioned between the adhesive and scratch-resistant layers comprising from 40-80 percent of the total film thickness.
  • the scratch-resistant layer preferably has an ASTM D2240 Shore D hardness of at least 60, and the adhesive and compressible layers have a Shore D hardness which is less than that of the scratch-resistant layer. Additionally, it is desired that the scratch-resistant layer have an ASTM D3363 pencil hardness of at least 3B, and preferably at least B.
  • the adhesive layer is selected from the group consisting of ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, or carbon monoxide; homopolymers of ethylene or propylene; copolymers of ethylene and propylene; ionomers of ethylene and methacrylic acid or acrylic acid; maleic anhydride modified polyethylene; polyamides; poly u ret anes; or compatible blends thereof.
  • the adhesive layer is preferably thermally activated for lamination to a metal substrate and is solvent free.
  • the scratch-resistant layer is preferably selected from the group consisting of polypropylene, polyethylene, polyester, polyamide, and blends thereof.
  • the hard scratch resistant layer functions to protect the underlying metal from scratches, and provides resistance to solvents and corrosion.
  • the scratch- resistant layer may be coated with curable hard coatings selected from the group consisting of urethane, epoxy, acrylic and silicone to provide enhanced scratch resistance properties.
  • the scratch-resistant layer may also contain an inorganic filler to further harden the layer and enhance scratch resistance. Chemical or radiation-induced crosslinking may also be used to further enhance the hardness and scratch resistance properties of the scratch-resistant layer.
  • the compressible layer preferably comprises homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ethylene-propylene rubbers, thermoplastic olefinic elastomer resins, styrene block copolymers, polyurethane, and blends thereof.
  • the compressible layer is a softer polymeric film layer which provides good sealability and compressibility properties when the protective film is laminated to a metal substrate and used to fabricate metal containers.
  • the compressible layer is foamed using a chemical blowing agent to provide improved compressibility.
  • the protective polymeric film of the present invention preferably has a thickness of from 0.5 to 20.0 mils (0.013 to 0.51 mm).
  • the protective polymeric 0 film is bonded to at least one major surface of a metal substrate to form a metal laminate where the film comprises scratch-resistant, adhesive, and compressible layers as described above.
  • Suitable metal substrates range from 5 to 100 mils (0.13 to 2.5 mm) in thickness and preferably from 5 to 15 mils (0.13 to 0.38) in thickness.
  • the protective polymeric film is preferably laminated to the metal laminate by thermally activating the adhesive layer and bonding the adhesive layer to the metal 5 laminate.
  • the film should exhibit at least 5.0 pounds per linear inch (.89 kg/cm) peel adhesion to the metal when subjected to a 180 degree peel test in accordance with ASTM D-903.
  • the scratch- resistant layer becomes the exposed outer protective layer of the metal laminate, and the softer, compressible layer remains between the adhesive and scratch-resistant layers.
  • the protective film protects the underlying metal substrate from scratches which could expose the metal to solvents and o corrosion.
  • a protective polymeric film which includes a scratch resistant layer and an adjacent layer which possesses both compressible and adhesive properties.
  • the compressible adhesive layer comprises from 10 to 90 percent of the total film thickness and the scratch-resistant layer comprises from 10 to 90 percent of the total film 5 thickness.
  • the scratch-resistant layer has a Shore D hardness of at least 60, and the compressible adhesive layer has a Shore 0 hardness which is less than that of the scratch-resistant layer. Additionally, it is desired that the scratch-resistant layer have an ASTM D3363 pencil hardness of at least 3B, and preferably at least B.
  • the compressible adhesive layer is preferably selected from the group consisting of o ethylenically unsaturatedcopolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, carbon monoxide, homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ionomers of ethylene and methyl acrylic acid or acrylic acid, grafted anhydride copolymers, polyamides, polyurethanes, and compatible blends thereof.
  • the compressible adhesive layer is foamed.
  • the scratch-resistant layer is preferably selected from the group consisting of polypropylene, polyethylene, polyester, polyamide, or blends thereof.
  • the scratch resistant layer may be coated with curable coatings, crosslinked, or may include organic fillers as described above to provide enhanced scratch resistance.
  • the protective polymeric film of the present invention can be laminated to metals such as tin- free steel, tin-plated steel, and aluminum. In one embodiment of the invention, the protective polymeric film is laminated to tin-plated steel to form an aerosol valve mounting cup.
  • the protective film of the present invention can also be fabricated into a number of other parts including aerosol can domes, can bottoms, paint cans, metal trays, pans and the like.
  • a protective polymeric film whic may be laminated to a metal substrate. It is a further feature of the invention to provide a protective polymeric film which provides resistance to scratches, solvents and corrosion, and which exhibits good sealability and compressibility when used in the fabrication of metal containers.
  • Fig. 1 is a cross-sectional view of the protective polymeric film of the present invention showing scratch-resistant, compressible, and adhesive layers;
  • Fig. 2 is a cross-sectional view of an alternative embodiment of the protective film comprising scratch-resistant and compressible adhesive layers;
  • Fig. 3 is a variation of the embodiment shown in Fig. 1 in which the film has been laminated t a metal substrate;
  • Fig. 4 is a perspective view of an aerosol valve mounting cup which has been formed from the protective film of the present invention.
  • the protective polymeric film and film/metal laminate of the present invention provides a combination of properties which has not been achieved by prior art protective films.
  • the present invention utilizes a soft film layer which exhibits good compressibility and sealing properties in combination with a hard film layer which resists nicks and abrasions which could expose the underlying metal surface and subject it to corrosion.
  • the film of the present invention may be readily laminated to a metal substrate by thermally activating a solvent-free adhesive film layer, and the resulting metal laminate may be formed into metal containers which are protected from scratches, solvents and corrosion. The bond formed between the adhesive film layer and metal substrate is strong and durable.
  • the laminate of the present invention can resist delamination or debonding of the film from the metal substrate after 30 days of immersion in methylene chloride.
  • the protective polymeric film of the present invention may comprise either a 3-layer film comprising adhesive, compressible, and scratch-resistant layers, or a two-layer film comprising a scratch-resistant layer and an adjacent layer having both compressible and adhesive properties.
  • the film includes a scratch-resistant layer 10, an adhesive layer 14, and a compressible layer 12 positioned between the scratch-resistant layer and the adhesive layer.
  • the scratch resistant layer exhibits a Shore D durometer hardness of at least 60 as tested according to ASTM D2240. A pencil scratch resistance of at least a "3B" rating according to ASTM D3363 is also preferable.
  • Films suitable for use as the scratch-resistant layer include polypropylene, polyethylene, polyester, polyamide, and blends thereof having the requisite hardness. Although olefin resins such as polypropylene and polyethylene are preferred, other suitable resins include polyester and polyamide or nylon resins. However, it is preferred that the scratch-resistant layer should be comprised of greater than 80 percent polypropylene to provide the desired scratch resistance properties.
  • the scratch-resistant layer 10 may be coated with hard curable coatings such as urethanes, epoxy, acrylic or silicones to provide enhanced surface scratch or abrasion resistance.
  • hard curable coatings such as urethanes, epoxy, acrylic or silicones to provide enhanced surface scratch or abrasion resistance.
  • Additives such as inorganic fillers or chemical or radiation induced crosslinking may also be used to further enhance the hardness and scratch resistance of the scratch-resistant layer.
  • the compressible layer 12 may be produced from homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ethylene-propylene or other olefinic rubbers.
  • Thermoplastic elastomers such as styrenic block copolymers, polyurethane, or blends of these resins are also suitable for use in the present invention.
  • the compressible layer is preferably foamed using chemical blowing agents such as sodium bicarbonate-citric acid blends or azodicarbonamide. The foamed compressible layer provides improved compressibility over a conventionally extruded solid layer.
  • Suitable adhesive polymers useful as the adhesive layer 14 include, but are not limited to, ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, and carbon monoxide.
  • Other examples include homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ionomers of ethylene and methyl acrylic acid or acrylic acid, grafted anhydride copolymers, polyamides, polyurethanes, and compatible blends thereof.
  • the adhesive layer should be readily adherable to the compressible layer as well as to a metal substrate.
  • the scratch-resistant layer comprises from 5-40 percent of the total film thickness
  • the compressible layer comprises from 40-80 percent of the total film thickness
  • the adhesive layer comprises 5-25 percent of the total film thickness.
  • a more preferred structure for the 3-layer film is a scratch-resistant layer comprising 20 percent of the total thickness, a compressible layer comprising 65 percent of the total thickness, and an adhesive layer comprising 15 percent of the total thickness.
  • FIG. 2 An alternative embodiment of the invention is illustrated in Fig. 2 in which the film comprises compressible adhesive layer 16 and a scratch resistant layer 10.
  • the compressible adhesive layer preferably comprises 75 percent of the total film thickness and the scratch-resistant layer comprises 25 percent of the total film thickness.
  • the scratch-resistant layer may comprise polypropylene, polyethylene, polyester, polyamide, and blends thereof, with polypropylene being the most preferred.
  • Suitable resins for use as the compressible adhesive layer include ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, carbon monoxide, homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ionomers of ethylene and methyl acryli acid or acrylic acid, grafted anhydride copolymers, polyamides, polyurethanes, and compatible blend thereof.
  • the protective polymeric film of the present invention is preferably produced by a coextrusio process on a conventional cast film line or tubular blown film line.
  • the layers may be coextruded together, and the resulting protective film may then be thermally laminated to a metal substrate using a hot roll laminator.
  • a metal laminate is shown in Fig. 3 in which adhesive layer 14 is adhered to a metal substrate 18 with the scratch-resistant layer 10 forming an outer protective layer for the metal.
  • the metal can be coated on one or both sides with the same or different protective films.
  • Fig. 4 illustrates an aerosol valve mounting cup 20 formed by stamping the metal laminate formed from the protective film of the present invention.
  • the compressible layer 12 allows the film to be readily compressed for fabricating such parts, and also provides a good seal, such as during crimping operations when the aerosol valve mounting cup is later crimped to a can body.
  • the protective film may be laminated to both sides of a metal substrate.
  • the film thickness may be from 5-10 mils (0.13 mm - 0.25 mm) on the inside of an aerosol valve mounting cup, forming a sealing gasket, and from 1 -2 mils (0.025 mm - 0.05 mm) on the outside of the cup, forming a scratch resistant, corrosion resistant coating.
  • a three-layer protective polymeric film was produced in accordance with the present invention on a conventional cast film line.
  • the scratch-resistant layer which comprised 25 percent of the total film thickness, was comprised of a polypropylene homopolymer (Himont ProFaxTM PD-064).
  • the compressible layer comprised 60 percent of the total film thickness and was comprised of a blend of 50 percent polypropylene (Himont ProFaxTM PD-064) and 50 percent ultra low density polyethylene (Dow Chemical ATTANE® 4201).
  • the adhesive layer comprised 15 percent of the total film thickness and was comprised of a blend of 60 percent Quantum Chemical PlexarTM 360 maleic anhydride modified linear low density polyethylene and 40 percent Quantum Chemical PlexarTM 206 maleic anhydride modified high density polyethylene.
  • Each layer was extruded at temperatures of 400-410°F (204-210°C) with a die temperature of 410°F (210°C).
  • the coextruded film was quenched on a 100°F (38°C) casting roll and then wound into a roll.
  • the resulting 8.0 mil (0.2 mm) thick film was then thermally laminated to a 10.5 mil (0.27 mm) tin-plated steel at 350°F (177°C) using a hot roll laminator.
  • the film exhibited peel adhesion greater than 10.0 pounds per linear inch (1.8 kg/cm) when subjected to 180 degree peel testing using an Instron tensile tester (ASTM D-903).
  • ASTM D-903 Instron tensile tester
  • a three-layer 8.0 mil (0.2 mm) thick coextruded film was produced on conventional cast film line.
  • the outermost scratch resistant layer which was 25 percent of the total film gauge, was comprised of a polypropylene random copolymer (Himont Profax 7531).
  • the compressible layer 60 percent of film gauge was comprised of a blend of 50 percent polypropylene random copolymer (Himont Profax 7531) and 50 percent ultra low density polyethylene (Dow Chemical ATTANE 4202).
  • the adhesive layer (15 percent of film gauge) was comprised of a blend of 60 percent Quantum
  • Example 2 Another 8.0 mil (0.2 mm) three-layer protective polymeric film was prepared as in Example 1.
  • the scratch-resistant layer comprised 25 percent of the total film thickness and was comprised of a polypropylene homopolymer (Himont ProFaxTM PD-064).
  • the compressible layer comprised 60 percent of the total film thickness and was comprised of a very low density metallocene catalyst ethylene copolymer (Dow AFFINITY® PL-1840).
  • the adhesive layer comprised 15 percent of the total film thickness and was comprised of 100 percent Quantum Chemical PlexarTM 360 maleic 5 anhydride modified linear low density polyethylene.
  • Eachlayer was coextruded as described in
  • Example 1 and the resulting film was quenched and thermally laminated to a 10.5 mil (0.27 mm) tin- plated steel.
  • a three-layer protective polymeric film was prepared as in Example 1.
  • the scratch-resistant l o layer (25 percent of total film thickness) was comprised of a polypropylene homopolymer (Himont ProFaxTM PD-064).
  • the compressible layer (60 percent of total film thickness) was comprised of a blend of 50 percent polypropylene (Himont ProFaxTM PD-191) and 50 percent ultra low density polyethylene (Dow Chemical ATTANE® 4201) with a 1.5 phr of a sodium bicarbonate-citric acid based foam concentrate (Henley HydrocerolTM CF-20).
  • the endothermic blowing agent was 15 activated during extrusion to produce a very fine closed cell foam compressible layer.
  • the adhesive layer (15 percent of total film thickness) was comprised of 100 percent Quantum Chemical PlexarTM 360 maleic anhydride modified linear low density polyethylene. Each layer was extruded as described in Example 1 , and the resulting film was quenched and thermally laminated to a 10.5 mil (0.27 mm) tin-plated steel.
  • a three-layer protective polymeric film was prepared as in Example 1 comprising a scratch- resistant layer (25 percent of total film thickness) of a polypropylene homopolymer (Himont ProFaxTM PD-064), a compressible layer (60 percent of total film thickness) comprising a blend of 65 percent polypropylene (Himont ProFaxTM PD-064) and 35 percent ethylene-propylene rubber (Exxon 25 Chemical VistalonTM 3708P).
  • the adhesive layer was comprised of 100 percent Quantum Chemical PlexarTM 360 maleic anhydride modified linear low density polyethylene. Each layer was extruded as in Example 1, and the resulting film was quenched and thermally laminated to tin-plated steel.
  • a two-layer 8.0 mil (0.2 mm) thick polymer film was produced on a conventional cast film line.
  • the scratch-resistant layer comprised 80 percent of the total film thickness and was comprised of a 50 percent polypropylene (ProFaxTM PD-064) and 50 percent ultra low density polyethylene blend (ATTANE® 4201).
  • the adhesive layer comprised 20 percent of the total film thickness and was comprised of a blend of 60 percent PlexarTM 360 linear low density polyethylene and 40 percent PlexarTM 206 high density polyethylene. The resulting film was thermally laminated to tin-plated steel
  • a pencil hardness test (ASTM D-3363) was used to determine scratch resistance of the plaques in Example 7.
  • the plaques containing polypropylene or blends of polypropylene and ultra low density polyethylene exhibit the highest scratch resistance.
  • aerosol valve mounting cups produced from the laminates described in Example 1 and Example 6, respectively were subjected to a vibratory shaker evaluation.
  • Five aerosol valve mounting cups of each sample were placed into empty glass 9 oz. bottles which were mounted on a Lab-Line Instruments Multi-Wrist Shaker.
  • the five identical metal laminate mounting cups in each of the bottles were subjected to vigorous shaking at an instrument setting of 10 (maximum) for five minutes.
  • Cups were then removed and inspected for damage in the form of nicks, scratches or abrasion on the film laminate side using a 10X optical magnifying lupe.
  • the cups of Example 6 50 percent polypropylene - 50 percent ultra low density polyethylene top layer
  • the cups of Example 1 100 percent polypropylene top layer

Landscapes

  • Laminated Bodies (AREA)
  • Containers And Packaging Bodies Having A Special Means To Remove Contents (AREA)

Abstract

The present invention provides a protective polymeric film which can be laminated to metal substrate (18) and which provides protection against scratches, solvents and corrosion. The film also exhibits good compressibility and sealability when used to form metal containers such as aerosol valve mounting cups, can domes, bodies, bottoms, and the like. The protective polymeric film includes a scratch-resistant layer (10) having a Shore D hardness of at least 60, an adhesive layer (14), and a compressible layer (12) positioned between the scratch-resistant and adhesive layers. In an alternative embodiment, the protective film includes a scratch-resistant layer and an adjacent compressible adhesive layer. The film may be laminated to a metal substrate by thermally activating the adhesive layer.

Description

PROTECTIVE POLYMERIC FILM FOR LAMINATION TO METAL
The present invention relates to a protective polymeric film which may be readily laminated to metal substrates to provide protection from scratches, solvents, and corrosion, and which exhibits good sealability and compressibility when the laminate is used to form metal containers.
Protective polymeric films or coatings are known in the art which can be laminated to metals such as tin-free steel, tin-plated steel, and aluminum, and then formed into parts such as aerosol valve mounting cups, aerosol can domes or bottoms, paint cans, food and beverage containers, and the like. Such films or coatings are used to protect the underlying metal surface from corrosion as well as to provide resistance to solvents and abrasions. For example, U.S. Patent No. 4,626,157 to Franek et al, describes a method of making metal containers such as aerosol dispensing containers having top can end members and valve cup members formed from a metal laminate comprising a thin polymeric layer such as polyester or polypropylene overlaid on the metallic substrate.
However, while such films provide resistance to corrosion, solvents and abrasions, due to the high modulus of the polypropylene film, the metal/film laminates using polypropylene do not exhibit good sealability and compressibility when used to fabricate metal containers such as aerosol cans. Specifically, such films do not form a good seal for compression formed joints or seals between two pieces of a metal laminate. Such a poor seal may result in leakage of pressurized propellant from a metal aerosol container formed from the metal laminate.
Further, polypropylene has been found to be difficult to adhere to various metallic substrates. Many commercial polypropylene film laminates currently in use are adhered tometal with solvent based-adhesives such as urethane adhesives. However, such adhesives are undesirable as they are environmentally unfriendly and leave the potential for residual solvents from the adhesive to migrate gradually through the film laminate and contaminate the contents of the metal container. Additionally, inadequate curing of the adhesive can result in loss of adhesion of the film laminate, particularly following exposure to solvents that may be contained within the fabricated structure. As a result, polymer films have more recently been laminated to metal using thermoplastic adhesive resins. For example, U.S. Patent No. 4,980,210 to Heyes et al describes a two-layer film bonded to the surface of a metal sheet comprising an inner adhesive layer of an acid-modified polyolefin resin and an outer layer of a polyolefin.
In an attempt to solve the sealability and compressibility problems associated with prior polypropylene adhesive films, U.S. Patent No. 5,006,383 to Achille et al teach a blend of polypropylene and very low density polyethylene and an adhesive layer comprising a rubber and polar comonomer modified α-olefin polymer resin. However, while such films exhibit good compressibility and formability, the films may not provide sufficient resistance to abrasions and scratches. For example, during handling, bulk packaging, and shipping of aerosol valve mounting cups, such film laminates can possibly be damaged by cutting, abrading or puncturing as the metal cups vibrate or move against each other. Damage can also occur during part die stamping or forming if the stamping dies or assembly mechanisms are not perfectly aligned. If the protective polymeric film becomes damaged, the corrosion resistance of the aerosol valve mounting cups is also weakened.
Accordingly, there is still a need in the art for a protective film which may be readily laminated to a metal substrate without the use of a solvent-based adhesive, which exhibits good sealability and compressibility, and which is scratch resistant as well as resistant to solvents and corrosion.
The present invention meets that need by providing a protective polymeric film which may be readily laminated to a metal substrate, which is resistant to scratches, solvents and corrosion, and which exhibits good sealability and compressibility when used to form metal containers. The film may be produced by conventional coextrusion techniques.
According to one aspect of the present invention, a protective polymeric film is provided comprising an adhesive layer comprising from 5 to 25 percent of the total film thickness, a scratch- resistant layer comprising from 5 to 40 percent of the total film thickness, and a compressible layer positioned between the adhesive and scratch-resistant layers comprising from 40-80 percent of the total film thickness. The scratch-resistant layer preferably has an ASTM D2240 Shore D hardness of at least 60, and the adhesive and compressible layers have a Shore D hardness which is less than that of the scratch-resistant layer. Additionally, it is desired that the scratch-resistant layer have an ASTM D3363 pencil hardness of at least 3B, and preferably at least B.
Preferably, the adhesive layer is selected from the group consisting of ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, or carbon monoxide; homopolymers of ethylene or propylene; copolymers of ethylene and propylene; ionomers of ethylene and methacrylic acid or acrylic acid; maleic anhydride modified polyethylene; polyamides; poly u ret anes; or compatible blends thereof. The adhesive layer is preferably thermally activated for lamination to a metal substrate and is solvent free.
The scratch-resistant layer is preferably selected from the group consisting of polypropylene, polyethylene, polyester, polyamide, and blends thereof. Once the protective film is laminated to a metal substrate, the hard scratch resistant layer functions to protect the underlying metal from scratches, and provides resistance to solvents and corrosion. Optionally, the scratch- resistant layer may be coated with curable hard coatings selected from the group consisting of urethane, epoxy, acrylic and silicone to provide enhanced scratch resistance properties.
The scratch-resistant layer may also contain an inorganic filler to further harden the layer and enhance scratch resistance. Chemical or radiation-induced crosslinking may also be used to further enhance the hardness and scratch resistance properties of the scratch-resistant layer. The compressible layer preferably comprises homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ethylene-propylene rubbers, thermoplastic olefinic elastomer resins, styrene block copolymers, polyurethane, and blends thereof. The compressible layer is a softer polymeric film layer which provides good sealability and compressibility properties when the protective film is laminated to a metal substrate and used to fabricate metal containers. In a preferred embodiment of the invention, the compressible layer is foamed using a chemical blowing agent to provide improved compressibility.
The protective polymeric film of the present invention preferably has a thickness of from 0.5 to 20.0 mils (0.013 to 0.51 mm). In a preferred embodiment of theinvention, the protective polymeric 0 film is bonded to at least one major surface of a metal substrate to form a metal laminate where the film comprises scratch-resistant, adhesive, and compressible layers as described above. Suitable metal substrates range from 5 to 100 mils (0.13 to 2.5 mm) in thickness and preferably from 5 to 15 mils (0.13 to 0.38) in thickness. The protective polymeric film is preferably laminated to the metal laminate by thermally activating the adhesive layer and bonding the adhesive layer to the metal 5 laminate. The film should exhibit at least 5.0 pounds per linear inch (.89 kg/cm) peel adhesion to the metal when subjected to a 180 degree peel test in accordance with ASTM D-903. Thus, the scratch- resistant layer becomes the exposed outer protective layer of the metal laminate, and the softer, compressible layer remains between the adhesive and scratch-resistant layers. The protective film protects the underlying metal substrate from scratches which could expose the metal to solvents and o corrosion.
In an alternative embodiment of the invention, a protective polymeric film is provided which includes a scratch resistant layer and an adjacent layer which possesses both compressible and adhesive properties. The compressible adhesive layer comprises from 10 to 90 percent of the total film thickness and the scratch-resistant layer comprises from 10 to 90 percent of the total film 5 thickness. The scratch-resistant layer has a Shore D hardness of at least 60, and the compressible adhesive layer has a Shore 0 hardness which is less than that of the scratch-resistant layer. Additionally, it is desired that the scratch-resistant layer have an ASTM D3363 pencil hardness of at least 3B, and preferably at least B.
The compressible adhesive layer is preferably selected from the group consisting of o ethylenically unsaturatedcopolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, carbon monoxide, homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ionomers of ethylene and methyl acrylic acid or acrylic acid, grafted anhydride copolymers, polyamides, polyurethanes, and compatible blends thereof. Preferably, the compressible adhesive layer is foamed.
5 The scratch-resistant layer is preferably selected from the group consisting of polypropylene, polyethylene, polyester, polyamide, or blends thereof. The scratch resistant layer may be coated with curable coatings, crosslinked, or may include organic fillers as described above to provide enhanced scratch resistance.
The protective polymeric film of the present invention can be laminated to metals such as tin- free steel, tin-plated steel, and aluminum. In one embodiment of the invention, the protective polymeric film is laminated to tin-plated steel to form an aerosol valve mounting cup. The protective film of the present invention can also be fabricated into a number of other parts including aerosol can domes, can bottoms, paint cans, metal trays, pans and the like.
Accordingly, it is a feature of the present invention to provide a protective polymeric film whic may be laminated to a metal substrate. It is a further feature of the invention to provide a protective polymeric film which provides resistance to scratches, solvents and corrosion, and which exhibits good sealability and compressibility when used in the fabrication of metal containers. These, and other features and advantages of the present invention, will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
Fig. 1 is a cross-sectional view of the protective polymeric film of the present invention showing scratch-resistant, compressible, and adhesive layers;
Fig. 2 is a cross-sectional view of an alternative embodiment of the protective film comprising scratch-resistant and compressible adhesive layers;
Fig. 3 is a variation of the embodiment shown in Fig. 1 in which the film has been laminated t a metal substrate; and
Fig. 4 is a perspective view of an aerosol valve mounting cup which has been formed from the protective film of the present invention.
The protective polymeric film and film/metal laminate of the present invention provides a combination of properties which has not been achieved by prior art protective films. The present invention utilizes a soft film layer which exhibits good compressibility and sealing properties in combination with a hard film layer which resists nicks and abrasions which could expose the underlying metal surface and subject it to corrosion. The film of the present invention may be readily laminated to a metal substrate by thermally activating a solvent-free adhesive film layer, and the resulting metal laminate may be formed into metal containers which are protected from scratches, solvents and corrosion. The bond formed between the adhesive film layer and metal substrate is strong and durable. Depending on the desired end use, the laminate of the present invention can resist delamination or debonding of the film from the metal substrate after 30 days of immersion in methylene chloride. The protective polymeric film of the present invention may comprise either a 3-layer film comprising adhesive, compressible, and scratch-resistant layers, or a two-layer film comprising a scratch-resistant layer and an adjacent layer having both compressible and adhesive properties.
Referring now to Fig. 1 , one embodiment of the protective polymeric film of the present invention is illustrated. The film includes a scratch-resistant layer 10, an adhesive layer 14, and a compressible layer 12 positioned between the scratch-resistant layer and the adhesive layer. The scratch resistant layer exhibits a Shore D durometer hardness of at least 60 as tested according to ASTM D2240. A pencil scratch resistance of at least a "3B" rating according to ASTM D3363 is also preferable. Films suitable for use as the scratch-resistant layer include polypropylene, polyethylene, polyester, polyamide, and blends thereof having the requisite hardness. Although olefin resins such as polypropylene and polyethylene are preferred, other suitable resins include polyester and polyamide or nylon resins. However, it is preferred that the scratch-resistant layer should be comprised of greater than 80 percent polypropylene to provide the desired scratch resistance properties.
The scratch-resistant layer 10 may be coated with hard curable coatings such as urethanes, epoxy, acrylic or silicones to provide enhanced surface scratch or abrasion resistance. Additives such as inorganic fillers or chemical or radiation induced crosslinking may also be used to further enhance the hardness and scratch resistance of the scratch-resistant layer.
The compressible layer 12 may be produced from homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ethylene-propylene or other olefinic rubbers. Thermoplastic elastomers such as styrenic block copolymers, polyurethane, or blends of these resins are also suitable for use in the present invention. The compressible layer ispreferably foamed using chemical blowing agents such as sodium bicarbonate-citric acid blends or azodicarbonamide. The foamed compressible layer provides improved compressibility over a conventionally extruded solid layer.
Suitable adhesive polymers useful as the adhesive layer 14 include, but are not limited to, ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, and carbon monoxide. Other examples include homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ionomers of ethylene and methyl acrylic acid or acrylic acid, grafted anhydride copolymers, polyamides, polyurethanes, and compatible blends thereof. The adhesive layer should be readily adherable to the compressible layer as well as to a metal substrate.
Generally, the scratch-resistant layer comprises from 5-40 percent of the total film thickness, the compressible layer comprises from 40-80 percent of the total film thickness, and the adhesive layer comprises 5-25 percent of the total film thickness. A more preferred structure for the 3-layer film is a scratch-resistant layer comprising 20 percent of the total thickness, a compressible layer comprising 65 percent of the total thickness, and an adhesive layer comprising 15 percent of the total thickness.
An alternative embodiment of the invention is illustrated in Fig. 2 in which the film comprises compressible adhesive layer 16 and a scratch resistant layer 10. In this embodiment, the compressible adhesive layer preferably comprises 75 percent of the total film thickness and the scratch-resistant layer comprises 25 percent of the total film thickness.
The scratch-resistant layer may comprise polypropylene, polyethylene, polyester, polyamide, and blends thereof, with polypropylene being the most preferred. Suitable resins for use as the compressible adhesive layer include ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, carbon monoxide, homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ionomers of ethylene and methyl acryli acid or acrylic acid, grafted anhydride copolymers, polyamides, polyurethanes, and compatible blend thereof.
The protective polymeric film of the present invention is preferably produced by a coextrusio process on a conventional cast film line or tubular blown film line. The layers may be coextruded together, and the resulting protective film may then be thermally laminated to a metal substrate using a hot roll laminator. A metal laminate is shown in Fig. 3 in which adhesive layer 14 is adhered to a metal substrate 18 with the scratch-resistant layer 10 forming an outer protective layer for the metal. The metal can be coated on one or both sides with the same or different protective films.
The resulting metal laminate may be used to fabricate a variety of parts such as aerosol valv mounting cups, aerosol can domes, aerosol can bottoms, paint cans, metal pans or trays, and the like. Fig. 4 illustrates an aerosol valve mounting cup 20 formed by stamping the metal laminate formed from the protective film of the present invention. The compressible layer 12 allows the film to be readily compressed for fabricating such parts, and also provides a good seal, such as during crimping operations when the aerosol valve mounting cup is later crimped to a can body.
It should also be appreciated that the protective film may be laminated to both sides of a metal substrate. For example, the film thickness may be from 5-10 mils (0.13 mm - 0.25 mm) on the inside of an aerosol valve mounting cup, forming a sealing gasket, and from 1 -2 mils (0.025 mm - 0.05 mm) on the outside of the cup, forming a scratch resistant, corrosion resistant coating.
In order that the invention may be more readily understood, reference is made to the followin examples, which are intended to be illustrative of the invention, but are not intended to be limiting in scope. Example 1
A three-layer protective polymeric film was produced in accordance with the present invention on a conventional cast film line. The scratch-resistant layer, which comprised 25 percent of the total film thickness, was comprised of a polypropylene homopolymer (Himont ProFaxTM PD-064). The compressible layer comprised 60 percent of the total film thickness and was comprised of a blend of 50 percent polypropylene (Himont ProFaxTM PD-064) and 50 percent ultra low density polyethylene (Dow Chemical ATTANE® 4201). The adhesive layer comprised 15 percent of the total film thickness and was comprised of a blend of 60 percent Quantum Chemical PlexarTM 360 maleic anhydride modified linear low density polyethylene and 40 percent Quantum Chemical PlexarTM 206 maleic anhydride modified high density polyethylene. Each layer was extruded at temperatures of 400-410°F (204-210°C) with a die temperature of 410°F (210°C). The coextruded film was quenched on a 100°F (38°C) casting roll and then wound into a roll. The resulting 8.0 mil (0.2 mm) thick film was then thermally laminated to a 10.5 mil (0.27 mm) tin-plated steel at 350°F (177°C) using a hot roll laminator. The film exhibited peel adhesion greater than 10.0 pounds per linear inch (1.8 kg/cm) when subjected to 180 degree peel testing using an Instron tensile tester (ASTM D-903). The resulting laminate was successfully stamped into aerosol valve mounting cups on a multistation progressive die. The film maintained excellent adhesion to the formed mounting cup.
Example 2
A three-layer 8.0 mil (0.2 mm) thick coextruded film was produced on conventional cast film line. The outermost scratch resistant layer, which was 25 percent of the total film gauge, was comprised of a polypropylene random copolymer (Himont Profax 7531). The compressible layer (60 percent of film gauge) was comprised of a blend of 50 percent polypropylene random copolymer (Himont Profax 7531) and 50 percent ultra low density polyethylene (Dow Chemical ATTANE 4202). The adhesive layer (15 percent of film gauge) was comprised of a blend of 60 percent Quantum
Chemical Plexar 360 maleic anhydride modified linear low density polyethylene and 40 percent Quantum Chemical Plexar 206 maleic anhydride modified high density polyethylene. Each layer was extruded at temperatures of 400-410°F (204-210°C) with a die temperature of 410°F (210°C). The film was quenched on a 100°F (38°C) casting roll and then wound into a roll. The 8.0 mil (0.2 mm) film was then thermally laminated to 10.5 mil (0.27 mm) tin plated steel at 350°F (177°C) using a hot roll laminator. The resulting laminate was successfully stamped into aerosol valve mounting cups on a multistation progressive die.
Example 3
Another 8.0 mil (0.2 mm) three-layer protective polymeric film was prepared as in Example 1. The scratch-resistant layer comprised 25 percent of the total film thickness and was comprised of a polypropylene homopolymer (Himont ProFaxTM PD-064). The compressible layer comprised 60 percent of the total film thickness and was comprised of a very low density metallocene catalyst ethylene copolymer (Dow AFFINITY® PL-1840). The adhesive layer comprised 15 percent of the total film thickness and was comprised of 100 percent Quantum Chemical PlexarTM 360 maleic 5 anhydride modified linear low density polyethylene. Eachlayer was coextruded as described in
Example 1 , and the resulting film was quenched and thermally laminated to a 10.5 mil (0.27 mm) tin- plated steel.
Example 4
A three-layer protective polymeric film was prepared as in Example 1. The scratch-resistant l o layer (25 percent of total film thickness) was comprised of a polypropylene homopolymer (Himont ProFaxTM PD-064). The compressible layer (60 percent of total film thickness) was comprised of a blend of 50 percent polypropylene (Himont ProFaxTM PD-191) and 50 percent ultra low density polyethylene (Dow Chemical ATTANE® 4201) with a 1.5 phr of a sodium bicarbonate-citric acid based foam concentrate (Henley HydrocerolTM CF-20). The endothermic blowing agent was 15 activated during extrusion to produce a very fine closed cell foam compressible layer. The adhesive layer (15 percent of total film thickness) was comprised of 100 percent Quantum Chemical PlexarTM 360 maleic anhydride modified linear low density polyethylene. Each layer was extruded as described in Example 1 , and the resulting film was quenched and thermally laminated to a 10.5 mil (0.27 mm) tin-plated steel.
20 Example 5
A three-layer protective polymeric film was prepared as in Example 1 comprising a scratch- resistant layer (25 percent of total film thickness) of a polypropylene homopolymer (Himont ProFaxTM PD-064), a compressible layer (60 percent of total film thickness) comprising a blend of 65 percent polypropylene (Himont ProFaxTM PD-064) and 35 percent ethylene-propylene rubber (Exxon 25 Chemical VistalonTM 3708P). The adhesive layer was comprised of 100 percent Quantum Chemical PlexarTM 360 maleic anhydride modified linear low density polyethylene. Each layer was extruded as in Example 1, and the resulting film was quenched and thermally laminated to tin-plated steel.
Example 6
A two-layer 8.0 mil (0.2 mm) thick polymer film was produced on a conventional cast film line.
3 o The scratch-resistant layer comprised 80 percent of the total film thickness and was comprised of a 50 percent polypropylene (ProFaxTM PD-064) and 50 percent ultra low density polyethylene blend (ATTANE® 4201). The adhesive layer comprised 20 percent of the total film thickness and was comprised of a blend of 60 percent PlexarTM 360 linear low density polyethylene and 40 percent PlexarTM 206 high density polyethylene. The resulting film was thermally laminated to tin-plated steel
35 and stamped into an aerosol valve mounting cup as described in Example 1. Example 7
Polypropylene, polyethylene, Plexar adhesives and blends, including those described in Examples 1-5, were hot pressed into 0.125 inch (0.32 cm) plaques using a heated platen press. The polymer plaques were then tested for durometer hardness using a Pacific Transducer Corp. Model 409 type D durometer tester according to ASTM D2240. The results are shown in Table I:
Example 8
A pencil hardness test (ASTM D-3363) was used to determine scratch resistance of the plaques in Example 7. A set of Eberhard Faber Design Drawing 3800 pencils with various lead hardnesses ranging from 6H (hard) to 6B (soft) were used to quantify hardness or scratch resistance of the various polymer blends given in Example 7. The results are shown below in Table II.
As can be seen, the plaques containing polypropylene or blends of polypropylene and ultra low density polyethylene exhibit the highest scratch resistance.
Example 9
In order to compare the relative abuse resistance of a film laminate with a 100 percent polypropylene protective layer with that of a film laminate with a protective layer comprised of 50 percent polypropylene and 50 percent ultra linear low density polyethylene, aerosol valve mounting cups produced from the laminates described in Example 1 and Example 6, respectively, were subjected to a vibratory shaker evaluation. Five aerosol valve mounting cups of each sample were placed into empty glass 9 oz. bottles which were mounted on a Lab-Line Instruments Multi-Wrist Shaker. The five identical metal laminate mounting cups in each of the bottles were subjected to vigorous shaking at an instrument setting of 10 (maximum) for five minutes. Cups were then removed and inspected for damage in the form of nicks, scratches or abrasion on the film laminate side using a 10X optical magnifying lupe. The cups of Example 6 (50 percent polypropylene - 50 percent ultra low density polyethylene top layer) exhibited an average of 22 surface damaging nicks on the laminate, while the cups of Example 1 (100 percent polypropylene top layer) exhibited an average of only 9 surface damaging nicks.
While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the methods and apparatus disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.

Claims

1. A protective film, comprising: a) a scratch-resistant layer, said scratch-resistant layer exhibiting a Shore D durometer hardness of at least 60 as tested according to ASTM D2240, said scratch-resistant layer comprising from 5 percent to 40 percent of the total protective film thickness; b) a compressible layer adjacent to said scratch-resistant layer, said compressible layer comprising homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ethylene-propylene rubbers, elastomeric olefinic resins, styrene block copolymers, polyurethane, or blends thereof, said compressible layer comprising from 40 percent to 80 percent of the total protective film thickness; and c) an adhesive layer adjacent to said compressible layer, said adhesive layer comprising ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl methacrylate, methyl acrylic acid, acrylic acid, or carbon monoxide; homopolymers of ethylene or propylene; copolymers of ethylene and propylene; ionomers of ethylene and methacrylic acid or acrylic acid; 5 maleic anhydride modified polyethylene; polyamides; polyurethanes; or compatible blends thereof, said adhesive layer comprising from 5 percent to 25 percent of the total protective film thickness, and said adhesive layer capable of exhibiting at least 5.0 pounds per linear inch (0.89 kg/cm) peel adhesion to metal substrates when subjected to a 180 degree peel test in accordance with ASTM D903, 0 wherein the total protective film thickness is from 0.5 to 20.0 mils ( 0.01 to 0.51 mm) thick.
2. A film according to Claim 1 , wherein the scratch-resistant layer comprises greater that 80 percent polypropylene.
3. A film according to Claim 1 , wherein the compressible layer consists essentially of a blend of polypropylene and polyethylene. 5 5. A film according to Claim 1 , wherein the adhesive layer consists essentially of a blen of maleic anhydride modified polyethylenes.
6. A metal laminate comprising a protective polymeric film bonded to at least one major surface of a metal substrate, said polymeric film comprising an adhesive layer comprising from 5 to 25 percent of the total film thickness, a compressible layer comprising from 40-80 percent of the total o film thickness, a scratch-resistant layer comprising from 5 to 40 percent of the total film thickness, said scratch-resistant layer having a Shore D hardness of at least 60, and said adhesive and compressible layers having a Shore D hardness of less than said scratch-resistant layer.
7. A metal laminate according to Claim 6, wherein said adhesive layer is selected from the group consisting of ethylenically unsaturated copolymers of vinyl acetate, ethyl acrylate, ethyl 5 methacrylate, methyl acrylic acid, acrylic acid, or carbon monoxide; homopolymers of ethylene or propylene; copolymers of ethylene and propylene; ionomers of ethylene and methacrylic acid or acrylic acid; maleic anhydride modified polyethylene; polyamides; polyurethanes; or compatible blends thereof."
8. A metal laminate according to Claim 6, wherein said scratch-resistant layer is selected from the group consisting of polypropylene, polyethylene, polyester, polyamide, and blends thereof.
9. A metal laminate according to Claim 6, wherein said compressible layer comprises homopolymers of ethylene or propylene, copolymers of ethylene and propylene, ethylene-propylene rubbers, olefinic resins, styrene block copolymers, polyurethane, and blends thereof.
10. A metal laminate according to Claim 6, wherein said compressible layer is foamed. 11. A metal laminate according to Claim 6, wherein said scratch-resistant layer includes a curable coating selected from the group consisting of urethane, epoxy, acrylic and silicone.
12. A metal laminate according to Claim 6, wherein said scratch-resistant layer contains an inorganic filler.
13. A metal laminate according to Claim 6, wherein said scratch-resistant layer has been crosslinked.
14. An aerosol valve mounting cup formed from a protective polymeric film laminated to metal, said protective film comprising an adhesive layer comprising from 5 to 25 percent of the total film thickness, a compressible layer comprising from 40-80 percent of the total film thickness, and a scratch-resistant layer comprising from 5 to 40 percent of the total film thickness, said scratch- resistant layer having a Shore D hardness of at least 60, and said adhesive and compressible layers having a Shore D hardness of less than said scratch-resistant layer.
EP96906379A 1995-02-17 1996-02-14 Protective polymeric film for lamination to metal Withdrawn EP0809572A1 (en)

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US6541568B1 (en) 2000-06-01 2003-04-01 Solvay Engineered Polymers Polyolefin materials having enhanced surface durability
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