Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-03-02
2002-03-19
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C523S407000, C523S408000, C528S103000
Reexamination Certificate
active
06359062
ABSTRACT:
BACKGROUND OF THE INVENTION
Coatings are applied to the interior of metal food and beverage cans to prevent the contents from coming into contact with the metal surfaces of the containers. Contact of the can contents with the metal surface, especially where acidic products such as soft drinks, tomato juice or beer are involved, can lead to corrosion of the metal container and result in contamination and deterioration of the contents. Coatings are applied to the interior of food and beverage cans also to prevent corrosion in the headspace of the cans between the fill line of the food product and the can lid, which is problematic particularly with food products with high salt content.
Can interiors are typically coated with a thin thermoset film to protect the interior metal surface from its contents. Synthetic resin compositions which include vinyls, polybutadiene, epoxy resins, alkyd/aminoplast and oleoresinous materials have typically been utilized as interior can coatings. These heat-curable resin compositions are usually applied as solutions or dispersions in volatile organic solvents.
Coatings used for food and beverage cans are generally applied and cured into films at high speed, on high speed coating lines (e.g., coil coating lines). Modern high speed coating lines require coatings that will dry and cure within a few seconds as it is heated very rapidly to peak metal temperatures of 450° F. to 550° F. (about 230° C. to about 300° C.).
High molecular weight polyesters have been used increasingly in recent years as metal can coatings. However, these polymers can suffer from a lack of solvent and headspace corrosion resistance because only their end groups are reactive with crosslinking agents. Moreover, the very short curing conditions further decrease the level of crosslinking in the baked film and the resistance to corrosion. Accordingly, there is a need for coatings which can provide superior solvent and headspace corrosion resistance upon faster rates of cure.
SUMMARY OF THE INVENTION
The present invention provides coating compositions including a film-forming component and an optional solvent component. The film-forming component includes (a) resin derived from a mixture including polymer containing alcohol and/or carboxylic acid functional groups, reacted with epoxy resin, and (b) phenolic resin that includes a polyvinyl alcoholic component. The coating composition generally also includes a solvent component, which may include organic solvent, water, or a mixture thereof.
The present invention also provides a method of coating a metal substrate to provide a cured film on at least one surface of the substrate. The method includes applying the coating composition onto the surface of the metal substrate to form a coating layer. The coated metal substrate is then heated so that the coating layer cures to form a cured film adhered to the substrate surface. The coated metal substrate is typically cured, for example, by heating for about 2 to about 20 seconds in an oven at a temperature of about 230° C. to about 300° C.
The present invention also provides a composite material which includes a metal substrate having at least one surface covered with a cured film, which is the result of coating the substrate surface with the above-described coating composition and heating the coated metal substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to protective coatings for metal surfaces and provides coating compositions which are particularly useful for protecting the interior of food and beverage cans. The inventive coating compositions include a film-forming component, including (a) a first resin component which can be produced by reacting carboxy functional polymer and/or hydroxy functional polymer with epoxy resin in the presence of a tertiary amine catalyst, and (b) polyvinyl alcoholic-containing resol phenolic resin. The first resin component can also be produced by reacting a resin which includes both epoxy and carboxy functional groups, optionally in the presence of additional epoxy resin(s) and/or alcohol and/or carboxy functional resin(s). In one embodiment, the film-forming component includes (a) the reaction product of an acid functional graft epoxy resin, and (b) phenolic resin that includes a polyvinyl alcoholic component. The coating compositions of the present invention typically have a faster rate of cure, greater solvent resistance and/or greater resistance to corrosion than conventional coating compositions. The coating compositions can also exhibit greater resistance to headspace corrosion than conventional coatings. The coating solids include all materials that remain on the coated article after the oven baking used to form the dry, thermoset coating. The amount of coating solids in the inventive coatings is typically at least about 35 wt. %, and preferably about 40 to about 50 wt. %.
The film-forming component of the coating compositions of the present invention contains one or more thermoplastic polymers capable of reacting with phenolic resins. The thermoplastic polymeric material is not critical, as long as it contains chemical groups that are reactive with phenolic resins, such as carboxylic acid and/or alcohol groups. A variety of polymeric materials may be used either singularly or in combination. The polymeric material typically used in the present invention includes carboxy functional and/or hydroxy functional polymers. It should be appreciated that polymers which are not carboxy functional or hydroxy functional, but which can be so functionalized, such as polyesters, polyvinyl chloride, polyvinyl acetate and polycarbonate, are also suitable for use in the present invention.
In one preferred embodiment of the invention, the thermoplastic polymer composition includes an epoxy-based resin, which is formed from epoxy resin and polymer capable of reacting with phenolic resins, such as carboxy functional and/or hydroxy functional polymer. The epoxy based-resin may be used singularly or may be combined with acrylic-based polymer and/or other polymers or resins, including polyesters, polyvinyl chloride, polyvinyl acetate and polycarbonate. Epoxy resin-based compositions commonly used in coating compositions are well-known in the art. Suitable epoxy resin-based polymer s for use in the present composition are disclosed, for example, in U.S. Pat. No. 5,567,781 to Martino et al., 5,635,049 to Mysliwczyk et al., U.S. Pat. No. 5,527,840 to Chutko et al., U.S. Pat. No. 5,296,525 to Spencer, U.S. Pat. No. 4,480,058 to Ting et al., U.S. Pat. No. 4,476,262 to Chu et al., U.S. Pat. No. 4,446,258 to Chu et al., U.S. Pat. No. 4,302,373 to Steinmetz, U.S. Pat. No. 4,247,439 to Matthews et al., and EP Patent No. 0 006 334 B1 to Brown et al., disclosures of which are hereby incorporated by reference.
In one embodiment of the invention, the epoxy-based resin is formed from a mixture which includes epoxy resin and a carboxy functional polymer. The epoxy resin-based polymer may be made by reacting a mixture including carboxy functional polymer and epoxy resin in the presence of a tertiary amine catalyst. The carboxy functional polymer is typically produced by reacting a mixture including one or more ethylenically unsaturated carboxylic acid monomers and one or more copolymerizable nonionic monomers. Preferred ethylenically unsaturated carboxylic acid monomers for use in forming the carboxy functional polymer invention include alpha, beta-unsaturated carboxylic acids, such as acrylic and methacrylic acid. Suitable nonionic monomers include lower alkyl acrylates (e.g., ethyl acrylate), lower alkyl methacrylates, hydroxy alkyl acrylates, hydroxy alkyl methacrylates, styrene, alkyl-substituted styrenes, vinyl acetate and acrylonitrile. The carboxy functional polymer may be reacted with any organic solvent-soluble resin containing epoxy groups in the presence of a tertiary amine catalyst.
The properties of the carboxy functional polymer vary depending upon the particular carboxy functional polymer selected. Typically, the carboxy functional p
Lovering Richard D.
Schwegman Lundberg Woessner & Kluth P.A.
The Valspar Corporation
LandOfFree
Coating compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coating compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coating compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2842038