Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/08—Anti-corrosive paints
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
  • C08F283/02—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polycarbonates or saturated polyesters
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L51/00—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
  • C08L51/08—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers grafted on to macromolecular compounds obtained otherwise than by reactions only involving unsaturated carbon-to-carbon bonds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
  • C08L67/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
  • C08L67/06—Unsaturated polyesters
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
  • C09D133/04—Homopolymers or copolymers of esters
  • C09D133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
  • C09D133/04—Homopolymers or copolymers of esters
  • C09D133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
  • C09D133/08—Homopolymers or copolymers of acrylic acid esters
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D151/00—Coating compositions based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Coating compositions based on derivatives of such polymers
  • C09D151/08—Coating compositions based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Coating compositions based on derivatives of such polymers grafted on to macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
  • C09D167/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
  • C09D167/04—Polyesters derived from hydroxycarboxylic acids, e.g. lactones
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
  • C09D167/06—Unsaturated polyesters having carbon-to-carbon unsaturation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
  • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/34—Heterocyclic compounds having nitrogen in the ring
  • C08K5/3467—Heterocyclic compounds having nitrogen in the ring having more than two nitrogen atoms in the ring
  • C08K5/3477—Six-membered rings
  • C08K5/3492—Triazines
  • C08K5/34922—Melamine; Derivatives thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L61/00—Compositions of condensation polymers of aldehydes or ketones; Compositions of derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L61/00—Compositions of condensation polymers of aldehydes or ketones; Compositions of derivatives of such polymers
  • C08L61/04—Condensation polymers of aldehydes or ketones with phenols only
  • C08L61/06—Condensation polymers of aldehydes or ketones with phenols only of aldehydes with phenols
  • C08L61/12—Condensation polymers of aldehydes or ketones with phenols only of aldehydes with phenols with polyhydric phenols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L87/00—Compositions of unspecified macromolecular compounds, obtained otherwise than by polymerisation reactions only involving unsaturated carbon-to-carbon bonds
  • C08L87/005—Block or graft polymers not provided for in groups C08L1/00 - C08L85/04
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
  • Y10T428/1352—Polymer or resin containing [i.e., natural or synthetic]

Definitions

• the present invention relates to compositions and methods for coating metal. More specifically, the present invention relates to compositions and methods for coating food cans, wherein the coating compositions comprise polyester and acrylic polymers.
• the present invention is directed to compositions and methods for coating the inside of food cans.
• the term “food cans” is used herein to refer to cans, containers or any type of metal receptacle used to hold any type of food or beverage.
• the methods generally involve coating the cans with a composition comprising a polyester and an acrylic polyol.
• a graft copolymer is formed from the polyester and the acrylic, and the composition further comprises a polyester resin.
• polyester coatings are good for flexibility, but are subject to hydrolysis in acid environments.
• acrylics are good for providing resistance, but are inflexible.
• the present invention is directed to compositions for coating food cans comprising an acrylic copolymer, a polyester, and a crosslinker.
• the polyester and acrylic copolymer should be made compatible to form the present compositions. This can be accomplished by any of various methods known in the art or described herein, including but not limited to employing blending techniques known in the art, preparing interpenetrating networks, or forming a graft copolymer.
• compositions for coating food cans comprising a polyester/acrylic graft copolymer, a polyester resin, and a crosslinker. It will be appreciated that the graft copolymer and/or polyester resin may contain solvent, and that additional solvents may also be used.
• any of the compositions of the present invention can be “epoxy-free”.
• “Epoxy-free” means that the polyester, acrylic, and every other portion of the composition are free from oxirane rings or residues of oxirane rings; bisphenol A; BADGE or adducts of BADGE; and/or polyvinylchloride or related halide-containing vinyl polymers.
• the polyester component(s) used in the present methods can be prepared by conventional means such as polyesterification of a polycarboxylic acid or anhydride with a polyol using techniques known to those skilled in the art.
• the polycarboxylic acids and polyols are aliphatic or aromatic dibasic acids and diols, although the invention is not so limited. Transesterification of polycarboxylic acid esters using conventional techniques is also possible.
• the weight average molecular weight (“Mw”) of the polyester used in the polyester/acrylic blends, networks or copolymers will range from 4,000 to 20,000, such as 5,000 to 13,000, or 7,000 to 11,000; the Mw of the polyester resin used in some embodiments of the present invention will range from 4,000 to 25,000, such as 6,000 to 22,000, or 8,000 to 22,000.
• the polyester used in the polyester/acrylic blends, networks, or copolymers will typically have a hydroxy value of from 0 to 200 mg KOH/g resin, such as from 30 to 70, or about 40, and an acid value of less than about 10, such as less than 5.
• the polyester resin used in some embodiments of the present invention will typically have a hydroxy value of from 10 to 50 mg KOH/g resin, such as about 25, +/ ⁇ 5, and an acid value of less than about 10, such as less than 5.
• any polyols known to be suitable for making the polyesters can be used to form the polyester component(s) of the present compositions.
• examples include but are not limited to alkylene glycols, such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol and neopentyl glycol; hydrogenated Bisphenol A; cyclohexanediol; 1,3-propane diol; glycol; 1,4-butane diol; 1,3-butane diol; butyl ethyl propane diol; trimethyl pentane diol; cyclohexanedimethanol; caprolactonediol, for example, the reaction product of epsilon-caprolactone and ethylene glycol; hydroxy-alkylated bisphenols; polyether glycols, for example, poly
• Polyols of higher functionality may also be used in limited quantity, provided they have no adverse effects on flexibility. Examples include trimethylolpropane, trimethylolethane, pentaerythritol, tris-hydroxyethylisocyanurate and the like.
• any acid known for use in the preparation of polyesters can be used to prepare the polyester polymer component(s) of the present invention, such as carboxylic acids or anhydrides having 2 to 18 carbon atoms per molecule.
• Examples include phthalic acid, isophthalic acid, 5-tert-butyl isophthalic acid, endomethylene tetrahydrophthalic acid, tetrachlorophthalic anhydride, chlorendic acid, naphthalene dicarboxylic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, decanoic diacid, dodecanoic
• the polyester component(s) may include minor amounts of monobasic acids such as benzoic acid, stearic acid, acetic acid and oleic acid. Also, there may be employed higher carboxylic acids, such as trimellitic acid and tricarballylic acid. Where acids are referred to above, it is understood that anhydrides thereof that exist may be used in place of the acid. Also, lower alkyl esters of diacids such as dimethyl glutarate and dimethyl terephthalate can be used.
• one or both of the polyester components are unsaturated. While any unsaturated polyester can be used according to the present invention, a particularly suitable polyester is formed from butanediol, ethylene glycol, cyclohexane dicarboxylic acid, isophthalic acid and maleic anhydride. This embodiment is particularly suitable when a graft copolymer is made between the polyester and acrylic copolymer; maleic anhydride promotes grafting with the acrylic copolymer. Maleic acid, fumaric acid and/or itaconic acid and/or the anhydrides of these acids can also be used instead of or in addition to maleic anhydride to produce polyesters that also have components particularly suitable for graft promotion. In certain instances, the polyester of this embodiment is also particularly desirable, as all of the components of the polyester are approved by the United States Food and Drug Administration (“FDA”) for direct food contact; these components are also listed on the European Inventory of Existing Commercial Substances (“EINECS”).
• FDA United States Food and Drug Administration
• EINECS European
• one or both of the polyester components is made with excess polyol as compared with acid so as to produce a polyester that has hydroxy functionality.
• One or both of the polyester components can also be prepared so as to either lack or have acid functionality.
• polyester component(s) is used herein to refer to one or both of these components as would be understood from the context.
• the two polyester components can have the same composition, that is they can be formed from the same starting materials; alternatively, they can be formed from different starting materials.
• each of the polyester components can have the same Mw or one can have a higher Mw than the other.
• the polyester resin can have an Mw that is higher than that of the polyester used in the graft copolymer, such as 3,000 to 15,000 daltons higher or 4,000 to 8,000 daltons higher.
• acrylic monomers can be combined to prepare the acrylic copolymer used in the present invention.
• examples include methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, (meth)acrylic acid, vinyl aromatic compounds such as styrene and vinyl toluene, nitrites such as (meth)acrylonitrile, and vinyl esters such as vinyl acetate. Any other acrylic monomers known to those skilled in the art could also be used.
• the term “(meth)acrylate” and like terms are used conventionally and herein to refer to both methacrylate and acrylate.
• a particularly suitable acrylic copolymer is formed with styrene, butyl acrylate, ethylhexyl acrylate and methacrylic acid, either alone or in further combination with hydroxyethyl methacrylate and methylmethacrylate.
• this acrylic copolymer comprises components approved by the FDA for use with food cans, and listed on EINECS.
• the Mw of the acrylic copolymer will range from about 10,000 to 250,000, such as 20,000 to 150,000, or 25,000 to 100,000.
• the acrylic copolymer and polyester used in the present composition can be treated in any manner so as to render the two compatible.
• compatible is meant that the polyester and the acrylic copolymer may be combined together in a coating without phase separation, thus forming a homogeneous product.
• Compatibilized copolymers can simply be blended together. In this blended embodiment, the acrylate copolymer used according to the present invention does not have pendant glycidyl groups when the polyester is acid terminated, and the acrylate copolymer does not have pendant hydroxy groups when the polyester is hydroxy terminated.
• Compatibilization can be achieved, for example, by using an acrylic copolymer having an Mw similar to the Mw of the polyester (i.e. within about 1,000).
• the acrylic copolymer can have N-(N-butoxymethyl)acrylamide (“NBMA”) functionality.
• NBMA N-(N-butoxymethyl)acrylamide
• Other compatibilizing functional groups include acid functional groups, hydroxy groups, amide groups and the like.
• Appropriate solvents referred to in the art as “coupling solvents” can also aid in compatibilization.
• An example is ethylene glycol monobutyl ether, commercially available as Butyl Cellosolve from Dow Chemical.
• the acrylate copolymer and polyester can also be compatibilized, for example, by forming interpenetrating polymer networks.
• the preparation of such networks is described, for example, in U.S. Pat. No. 6,228,919, incorporated by reference herein.
• polyester and acrylate copolymer can be compatibilized through the formation of a graft copolymer.
• a graft copolymer can be formed using techniques standard in the art.
• the terms “polyester/acrylic graft copolymer” or simply “graft copolymer” are used herein to refer both to graft copolymers wherein polyester is grafted to acrylic and wherein acrylic is grafted to polyester.
• a polyester is prepared according to conventional methods using the materials described above. The acrylic monomers are then added to the polyester. The acrylic can then be polymerized using a standard free radical initiator. In this manner, the acrylate copolymer is grafted to the already-made polyester.
• the polyester can be grafted to an already-made acrylic copolymer.
• a maleic anhydride group can be polymerized in the acrylic copolymer and, subsequently, hydroxyl groups from the polyester can be allowed to react with the acrylic to create a graft copolymer; the result will be an acrylic copolymer having polyester moieties grafted thereto.
• a particularly suitable example uses maleic anhydride in the formation of a polyester and styrene as one of the acrylic monomers.
• the styrene will react with the maleic anhydride; the acrylic copolymer will grow off of the styrene through the formation of free radicals.
• the result will be a polyester having acrylic copolymers grafted thereto.
• maleic anhydride and styrene are offered as examples of two components that will promote grafting between the normally incompatible polymers, but that the invention is not so limited.
• Other compounds such as fumaric acid/anhydride or itaconic acid/anhydride may be incorporated into a polyester for grafting with a styrene containing acrylic.
• Other moieties that will promote grafting between the polyester and acrylic can also be used. Any group of compounds can be used for this purpose. All of these compounds are referred to herein as “graft promoting components”. The amount of graft promoting component used in each of the polyester and/or acrylate portions can affect the final product.
• the product can gel or be otherwise unusable.
• the graft-promoting components should therefore be used in an amount effective to promote grafting but not to cause gelling. Enough grafting should be effected to allow the polyester and acrylate polymers to be compatible.
• usually 2 to 6 weight percent maleic with 8 to 30 weight percent styrene can be used, with weight percent being based on the weight of the polyester and the weight of the acrylic, respectively.
• the Mw of the graft copolymer will typically be from about 3,000 to 250,000, such as from about 5,000 to 125,000, or from about 60,000 to 120,000.
• the weight ratio of polyester to acrylic in the graft copolymer, blend or network can vary widely.
• the polyester to acrylic ratio in the graft copolymer, blend or network can range from 95:5 to 20:80. It has been determined that varying the amount of polyester in the composition will affect the amount of flexibility.
• a particularly suitable ratio of polyester to acrylic in the graft copolymer, blend or network, for embodiments used in coating food cans is 70:30, which gives a relatively flexible product that still has suitable acid resistance.
• the weight ratio of polyester in the graft copolymer will be as described above.
• the weight of polyester resin to graft copolymer will typically be 5:35 to 95:65, such as 25 to 75.
• the present compositions further comprise a suitable crosslinker.
• a suitable crosslinker can be determined based upon the needs and desires of the user, and can include, for example, melamine crosslinkers, and phenolic crosslinkers. Melamine crosslinkers are widely commercially available, such as from Cytec Industries, Inc. as CYMEL 303, 1130, 325, 327 and 370. Phenolic crosslinkers include, for example, novolacs, resoles, and bisphenol A. Phenolic resoles that are not derived from bisphenol A are particularly suitable for use on food cans.
• One embodiment of the present invention specifically excludes NCO group free crosslinkable urethane resins from the composition.
• compositions of the present invention may also comprise a solvent either introduced through the acrylic and/or polyester components.
• suitable solvents include esters, glycol ethers, glycols, ketones, aromatic and aliphatic hydrocarbons, alcohols and the like. Particularly suitable are xylenes, propyleneglycol monomethyl acetates, and dibasic esters such as dimethyl esters of adipic, glutaric and succinic acids.
• compositions of the present invention can also contain any other conventional additives such as pigments, colorants, waxes, lubricants, defoamers, wetting agents, plasticizers, fortifiers and catalysts.
• Any mineral or sulfonic acid catalyst can be used. Particularly preferred for food can applications are phosphoric acid and dodecyl benzene sulfonic acid.
• the compositions are prepared so as to be between about 30 and 50 weight percent solids. “Solids” will be understood by those skilled in the art as including such things as the polyester resin, the graft copolymer, crosslinkers, catalysts, other additives and the like. In the embodiments containing polyester resin in addition to the graft copolymer, higher amounts of crosslinker can be used as compared to embodiments lacking the polyester resin. This was found to result in films having higher solvent resistance and higher Tg without compromised flexibility.
• the present invention is further directed to a method for coating food cans comprising applying any of the compositions described above to the food can. More specifically, these compositions comprise a polyester, an acrylic copolymer, optionally a polyester resin, a crosslinker, one or more solvents and optionally one or more conventional additives.
• the polyester and acrylic copolymer can be made compatible by any means described above such as using blending techniques known in the art, interpenetrating networks, or the novel graft copolymerizations described herein.
• the coating composition can be applied to the food can by any means known in the art such as roll coating, spraying, and electrocoating. It will be appreciated that for two-piece food cans, the coating will typically be sprayed after the can is made. For three-piece food cans, on the other hand, a coil or sheet will typically be roll coated with one or more of the present compositions first and then the can will be formed.
• the coating is then cured.
• Cure is effected by methods standard in the art. For coil coating, this is typically a short dwell time (i.e. 9 seconds to 2 minutes) at high heat (i.e. 485° F. peak metal temperature); for coated metal sheets cure is typically longer (i.e. 10 minutes) but at lower temperatures (i.e. 400° F. peak metal temperature).
• Any material used for the formation of food cans can be treated according to the present methods.
• Particularly suitable substrates include tin-plated steel, tin-free steel, and black-plated steel.
• the coatings of the present invention can be applied directly to the steel, without any pretreatment or adhesive aid being added to the metal first. In addition, no coatings need to be applied over top of the coatings used in the present methods.
• compositions of the present invention perform as desired both in the areas of flexibility and acid resistance. Significantly, these results can be achieved with an epoxy-free composition, that is, one that excludes epoxy, glycidal groups BADGE, oxirane rings, halide-containing vinyls or derivatives or residues of any of these compounds.
• an epoxy-free composition that is, one that excludes epoxy, glycidal groups BADGE, oxirane rings, halide-containing vinyls or derivatives or residues of any of these compounds.
• the present invention provides particularly desirable compositions and methods for coating food cans, which avoid performance and health issues raised by other coatings and methods reported in the art.
• the present invention provides methods for compatibilizing a polyester and an acrylic. These methods are discussed above and include, for example, the use of an acrylamide in the formation of the acrylic copolymer, and the graft copolymerization of an acrylic onto a polyester or a polyester onto an acrylic.
• Polyester Polymer “A” was made as follows: TABLE 1 Ingredients Parts by Weight Charge #1 2-Methyl-1,3-Propanediol 2.4 Ethylene Glycol 1.0 1,6-Hexane Diol 3.6 Terephthalic Acid 7.1 Dibutyltin Oxide 0.035 Charge #2 Isophthalic Acid 3.0 Maleic Anhydride 0.54 Ionol 0.018 Charge #3 Xylene 0.81 Charge #4 Xylene 5.8
• Polyester Polymer “B” was made as follows: TABLE 2 Ingredients Parts by Weight Charge #1 1,3-Butylene Glycol 10.0 Ethylene Glycol 1.9 Charge #2 1,4-Cyclohexanedicarboxylic 14.5 Acid Isophthalic Acid 6.0 Maleic Anhydride 1.0 Dibutyltin Oxide 0.067 Methyl Hydroquinone 0.0029 Charge #3 Xylene 1.5 Charge #4 Xylene 10.8
• Acrylic Polyester Copolymer “A” was made as follows: TABLE 3 Ingredients Parts by Weight Charge #1 Toluene 12.9 SOLVESSO 150 1 11.0 Charge #2 Xylene 6.0 VAZO 67 2 2.0 Charge #3 Butyl Acrylate 12.0 2-Hydroxyethyl Methacrylate 11.2 Methacrylic Acid 1.0 Styrene 6.0 2-Ethylhexyl Acrylate 4.0 Methyl Methacrylate 5.8 Polyester A from Example 1 135.3 Charge #4 VAZO 67 0.1 Xylene 0.4 Charge #5 SOLVESSO 150 17.9
• Charge #1 was added to a 3 liter, 4 necked flask equipped with a motor driven stainless steel stir blade, water-cooled condenser and a heating mantle with a thermometer connected through a temperature feedback control device. The contents of the flask were heated to reflux (128° C.). Addition of Charge #2 (over 190 minutes) began followed by the addition of Charge #3 (over 180 minutes) five minutes later. During the feeds, the reflux temperature gradually rose to 138° C. After the additions were complete, the reaction was held at 138° C. for one hour. Charge #4 was added over 10 minutes and the mixture was held at 138° C. for an additional hour. The resin was thinned with Charge #5.
• Acrylic Polyester Copolymer “B” was made as follows: TABLE 4 Ingredients Parts by Weight Charge #1 SOLVESSO 150 8.0 Charge #2 SOLVESSO 150 6.3 Di-t-Butylperoxide 1.0 Charge #3 Butyl Acrylate 12.0 Methacrylic Acid 1.0 Styrene 2.0 2-Ethylhexyl Acrylate 5.0 Polyester B 67.3 (46.8 solid) Charge #4 SOLVESSO 150 0.45 Di-t-Butylperoxide 0.026 Charge #5 SOLVESSO 150 0.45 Di-t-Butylperoxide 0.026 Charge #6 SOLVESSO 150 0.45 Di-t-Butylperoxide 0.026 Charge #7 SOLVESSO 150 0.45 Di-t-Butylperoxide 0.026 Charge #8 Xylene 8.7
• Acrylic Polyester Copolymer “C” was made as follows: TABLE 5 Ingredients Parts by Weight Charge #1 SOLVESSO 150 10.1 Toluene 10.1 Charge #2 Xylene 3.1 VAZO 67 2.0 Charge #3 Butyl Acrylate 12.0 Methacrylic Acid 1.0 Styrene 6.0 2-Ethylhexyl Acrylate 4.0 2-Hydroxyethyl Acrylate 11.2 Methyl Methacrylate 5.8 Polyester B 14.4 (10.0 solid) Charge #4 Xylene 0.31 VAZO 67 0.10 Charge #5 Xylene 6.7
• Charge #1 was added to a 2 liter, 4 necked flask equipped with motor driven stainless steel stir blade, water cooled condenser and a heating mantle with a thermometer connected through a temperature feedback control device. The contents of the flask were heated to 128° C. Addition of Charge #2 (over 190 minutes) followed by Charge #3 (over 180 minutes) five minutes later. After the additions were complete, the reaction was held at 150° C. for 30 minutes. During the additions, the temperature was gradually increased reflux at 138° C. After the additions were complete, the reaction was held at 138° C. for 90 minutes. Charge #4 was then added over 10 minutes followed by a one hour hold at 138° C. The resin was then thinned with Charge #5 and then cooled.
• Coatings were prepared by drawing Samples 1-3 and a commercially available epoxy liner for food cans (Eurogold XF 12040, from PPG Industries, Inc.) over tin plated steel (E.T.P.) sheets with a #12 wire-wound rod. The coatings were baked for 10.5 minutes at 400° F. The drying coating weights were 4.0 mgs/sq.in.
• the coated sheets were evaluated for flexibility by bending and stamping wedges (2.0 inch by 4.5 inches), stamping 300 food can ends, and by drawing cups to 18 mm and 26 mm depths with one and two stages of drawing, respectively.
• the percent of coating that remained crack-free along the bend radius (for wedge bends) and along the drawn lengths (for cups) was determined.
• the measured current (in mA) was determined using a WACO enamel rater (obtained from Wilkens-Anderson Company) in 4 sec mode using an electrolyte solution of 7.0 grams of potassium ferrocyanurate, 5.4 grams of sodium chloride, 0.5 grams of sodium sulfosuccinate, and 1000 grams of water.
• the resistance properties of the coated stamped ends and drawn cups were evaluated by processing (retorting) them in three food simulants and measuring their ability to resist current (stamped ends) and cracking (drawn cups) after one hour in a sterilizer under 266° F./30 psi conditions.
• the three simulants were tap water, a 1% by weight solution of sodium chloride in tap water, and a 1% by weight solution of lactic acid in tap water. All of the results are presented in Table 7.
• TABLE 7 Commercial Sample Sample Sample Epoxy 1 2 3 Flexibility Tests. 1. Wedge Bend (% crack- 86% 93% 92% 73% free) 2. Enamel Rater of 300 2 mA 2 mA 7 mA 20 mA ends (mA) 3.
• Sample 1 had better results than did a current, epoxy-containing food can liner.
• Sample 2 also had very good results, especially acid resistance.
• Both Samples 1 and 2 had polyester to acrylic ratios of about 70:30.
• Sample 3, which had a polyester to acrylic ratio of 20:80 demonstrates that some flexibility can be lost with lower levels of polyester.
• Polyester Polymer “C” was made as follows: TABLE 8 Ingredients Parts by Weight Charge #1 1,3-Butylene Glycol 177.1 Ethylene Glycol 34.4 Charge #2 1,4-Cyclohexanedicarboxylic 259.6 Acid Isophthalic Acid 107.2 Maleic Anhydride 18 Dibutyltin Oxide 1.19 Methyl Hydroquinone 0.054 Charge #3 Xylene 27.2 Charge #4 Xylene 188.7
• the determined acid value was 2.1 mg KOH/gram, and hydroxy value was 20.9 mg KOH/gram.
• the determined non-volatile content of the resin was 69.9% as measured by weight loss of a sample heated to 110° C. for 1 hour.
• Analysis of the polymer by GPC (using linear polystyrene standards) showed the polymer to have an M w value of 10, 115, M n value of 2,798, and an M w /M n value of 3.6.
• a polyester-graft-acrylic copolymer “C” was prepared as follows: TABLE 9 Ingredients Parts by Weight Charge #1 SOLVESSO 150 44.3 Charge #2 SOLVESSO 150 19.6 LUPEROX 7M50 9 5.7 Charge #3 Butyl Acrylate 24.3 2-Hydroxyethyl Methacrylate 22.6 Methacrylic Acid 2.0 Styrene 12.1 2-Ethylhexyl Acrylate 8.1 Methyl Methacrylate 11.7 Polyester C 270.0 Charge #4 LUPEROX 7M50 1.6 Xylene 1.6 Charge #5 LUPEROX 7M50 1.6 Xylene 1.6 Charge #6 SOLVESSO 150 29.9
• the reaction product was then cooled, discharged and analyzed.
• the determined acid value was 4.2 mg KOH/gram, and hydroxy value was 35.8 mg KOH/gram.
• the determined non-volatile content of the resin was 59.3% as measured by weight loss of a sample heated to 110° C. for 1 hour.
• Analysis of the polymer by GPC (using linear polystyrene standards) showed the polymer to have an M w value of 113, 159, M n value of 3522, and an M w /M n value of 32.1.
• Polyester “D” was prepared as follows: TABLE 10 Ingredients Parts by Weight Charge #1 1,3-Butylene Glycol 217.3 Ethylene Glycol 42.3 Charge #2 1,4-Cyclohexanedicarboxylic 327.9 Acid Isophthalic Acid 135.7 Maleic Anhydride 22.4 Dibutyltin Oxide 1.49 Methyl Hydroquinone 0.067 Charge #3 Xylene 33.9 Charge #4 Xylene 241.2
• the determined acid value was 3.8 mg KOH/gram, and hydroxy value was 22.9 mg KOH/gram.
• the determined non-volatile content of the resin was 70.0% as measured by weight loss of a sample heated to 110° C. for 1 hour.
• Analysis of the polymer by GPC (using linear polystyrene standards) showed the polymer to have an M w value of 16,672, M n value of 3,972, and an M w /M n value of 3.7.
• Formulations were prepared using the compositions listed in below in Table 11. The ingredients were added to a paint can, while being agitated with a Cowles blade. The formulated paints were then further mixed to insure homogeneity. TABLE 11 Parts by Weight Ingredient Sample 4 Sample 5 Copolymer “C” 68.8 51.6 Polyester “D” 15.8 Phenolic resin 10 8.3 12.5 Catalyst 11 3.2 3.2 Siloxane 12 0.1 0.1 Wax dispersion 13 4.0 4.0 Solvent 14 6.6 6.6 Solvent 15 1.7 1.7 Solvent 16 4.5 Xylene 2.1 2.1
• Coatings were applied to tin-plated steel coupons using a wire-bound bar. The coatings were applied at a dry film weight of 6 grams per m2. After application the coated coupons were baked at a 200° C. peak metal temperature for 10 minutes. The cured coated coupons were then stamped into 300 size food can ends or drawn into various depth cups. The results of the testing of the can ends and cups are shown below in Table 12.
• compositions of the present invention have comparable performance to a commercially available epoxy-containing coating.

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