US20140131353A1

US20140131353A1 - Coated containers

Info

Publication number: US20140131353A1
Application number: US13/677,342
Authority: US
Inventors: Claudia Knotts; Yossef Moussa; Michael Revis
Original assignee: PPG Industries Ohio Inc
Current assignee: PPG Industries Ohio Inc
Priority date: 2012-11-15
Filing date: 2012-11-15
Publication date: 2014-05-15
Also published as: WO2014078618A1

Abstract

A coated container and a method for coating a container are disclosed. The coating on the container is derived from a composition comprising:

- a hydroxyl functional polyester comprising a reaction product prepared from a reaction mixture comprising:
- (i) an organic polycarboxylic acid, and
- (ii) a polyol component comprising tetramethyl-1,3-cyclobutane diol
  are disclosed.

Description

FIELD OF THE INVENTION

The present invention relates to coated containers and to methods of coating containers. The coating compositions used in coating the containers comprises hydroxyl functional polyesters comprising a reaction product comprising an organic polycarboxylic acid and 2,2,4,4-tetramethyl-1,3-cyclobutane diol.

BACKGROUND OF THE INVENTION

A wide variety of coatings have been used to coat the surfaces of food and beverage containers. For example, metal cans are sometimes coated using coil coating or sheet coating operations, that is, a plane or coil or sheet of a suitable substrate, for example, steel or aluminum, is coated with a suitable composition and cured. The coated substrate is then formed into the can body or can end. Alternatively, the coating composition may be applied, for example, by spraying and dipping, to the formed can and then cured. Coatings for food and beverage containers are typically capable of high speed application to the substrate while providing the necessary properties when cured to perform in a demanding end use. For example, the coating should be safe for food contact and have excellent adhesion to the substrate.
Many of the coating compositions for food and beverage containers are based on epoxy resins that are the polyglycidyl ethers of bisphenol A. Bisphenol A in packaging coatings either as bisphenol A itself (BPA), derivatives thereof, such as diglycidyl ethers of bisphenol A (BADGE), epoxy novolak resins and polyols prepared with bisphenol A and bisphenol F are problematic. Although the balance of scientific evidence available to date indicates that small trace amounts of BPA or BADGE that might be released from existing coatings does not pose health risks to humans, these compounds are nevertheless perceived by some as being harmful to human health. Consequently, there is a strong desire to eliminate these compounds from coatings for food and beverage containers. Accordingly, container coating compositions for food or beverage containers that do not contain extractable quantities of BPA, BADGE or other derivatives of BPA and yet have suitable properties for use in this application are therefore desired.

SUMMARY OF THE INVENTION

The present invention provides a container comprising a coating applied to at least a portion of the container, the coating is derived from a composition comprising:

- a hydroxyl functional polyester comprising a reaction product prepared from a reaction mixture comprising:
- (i) an organic polycarboxylic acid and/or ester and/or anhydride thereof, and
- (ii) a polyol component comprising tetramethyl-1,3-cyclobutane diol.

The invention also provides a method of coating a container comprising:

- (a) applying to a surface of the container the composition as described above
- (b) heating the composition applied in step (a) to a temperature sufficient to cure the composition.

DETAILED DESCRIPTION

The present invention is directed to a coated container in which the coating composition used in coating the container comprises a hydroxyl functional polyester comprising a reaction product prepared from a reaction mixture comprising: (i) an organic polycarboxylic acid and/or ester and/or anhydride thereof, and (ii) a polyol component comprising tetramethyl-1,3-cyclobutane diol, such as 2,2,4,4-tetramethyl-1,3-cyclobutane diol. In certain embodiments, the coating composition further comprises a curing agent reactive with the hydroxyl groups of the polyester.
As noted above, the polyester resin contains hydroxyl functionality and may optionally contain carboxylic acid functionality. The polyester resin may have a hydroxyl number of 5 to 40 mg KOH per gram of polyester resin, such as 5 to 10, and an acid value of 0 to 5 mg KOH per gram of polyester resin, each measured on a non-volatile solids basis. The polyester resin may have a number average molecular weight (Mn) of 2,000 to 15,000 g/mole (Daltons), such as 10,000 to 15,000. Other hydroxyl numbers, acid values and Mn values are also within the scope of the present invention.
Suitable polyester resins are typically prepared by condensation (esterification) according to known processes [see, for example, Zeno Wicks, Jr., Frank N. Jones and S. Peter Pappas, Organic Coatings: Science and Technology, Vol. 1, pp. 122-132 (John Wiley & Sons: New York, 1992)]. The polyester resin comprises the reaction product prepared from a reaction mixture comprising a polyol component comprising tetramethyl-1,3-cyclobutane diol and an organic polycarboxylic acid and/or ester and/or anhydride thereof. The term “reaction product prepared from a reaction mixture comprising” is used herein to indicate that the reaction products of the present invention may comprise additional components. In certain embodiments, however, the reaction products may consist of or consist essentially of the particular components listed.
The polyol component and the polycarboxylic acid are combined in desired proportions and chemically reacted using standard esterification (condensation) procedures to provide a polyester having hydroxyl, and optionally carboxylic acid, groups in the polyester resin.
Examples of suitable polycarboxylic acids include, but are not limited to, naphthalene dicarboxylic acid, such as 1,4- and 1,6-naphthalene dicarboxylic acid, maleic acid, fumaric acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexane dicarboxylic acid, trimellitic anhydride, adipic acid, azelaic acid, succinic acid, sebacic acid and various mixtures thereof.
Esters and/or anhydrides of any of these acids can also be used. In certain embodiments, the naphthalene dicarboxylic acid can be used, for example, in amounts of 100 percent by weight, such as 10 to 100 or 20 to 70 percent by weight, based on total weight of the polycarboxylic acid/ester/anhydride component.
As noted above, the polyol component comprises tetramethyl-1,3-cyclobutane diol, such as 2,2,4,4-tetramethyl-1,3-cyclobutane diol, alone or in combination with one or more additional polyols. Examples of suitable polyols that can be used include, but are not limited to, ethylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propane diolglycerol, diethylene glycol, dipropylene glycol, triethylene glycol, neopentyl glycol trimethylolpropane, trimethylolethane, tripropylene glycol, neopentyl glycol, pentaerythritol, 1,4-butanediol, trimethylol propane, hexylene glycol, cyclohexane dimethanol, and polyethylene or polypropylene glycol. The tetramethyl-1,3-cyclobutane is typically present in amounts of at least 5 percent by weight based on total weight of the polyol component, and can be 10 to 100, such as 20 to 70, weight percent of the polyol component or 100 weight percent of the polyol component.
The equivalent ratio of polyol component to polycarboxylic acid can be from 10 to 1.5:1.0.
The polyester typically is present in the coating composition in amounts of 10 to 95 percent by weight based on weight of resin solids.
In addition to the polyester polyol, the coating composition can optionally contain an adjuvant polymer. Examples of such adjuvant polymers are acrylic polymers and aliphatic polyether polyols.
The acrylic polymer, if used, can be a polymer derived from one or more acrylic monomers. Furthermore, blends of acrylic polymers derived from the monomers of acrylic acid can be used. Suitable monomers are acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, penta acrylate, hexyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, penta methacrylate and hexyl methacrylate. The acrylic polymer may also contain hydroxyl groups that typically are derived from hydroxy-substituted acrylic or methacrylic acid esters. Examples include hydroxyethyl acrylate and hydroxypropyl methacrylate. The weight average molecular weight (“Mw”) of the acrylic polymer component can be at least 5,000 g/mole, such as 15,000 to 100,000 g/mole. The acrylic polymer typically has an acid value of 30 to 70, such as 40 to 60 mg KOH/g, a hydroxyl value of 0 to 100, such as 0 to 70 mg of KOH/g, and a glass transition temperature (Tg) of −20 to +100° C., such as +20 to +70° C.
The aliphatic polyether polyol can be the reaction product of an alkylene oxide and a polyhydroxyl compound, such as sucrose polyol. The reaction is conducted in the presence of a suitable catalyst such as an amine or alkali metal hydroxide and optionally a non-reactive solvent such as an aromatic solvent, for example, toluene or xylene. The ratio of polyhydroxyl compound to alkylene oxide is adjusted to give a hydroxyl number of from 150 to 600. Such reaction products are commercially available from Dow Chemical Company under the trademark VORONOL and from Bayer Material Science under the trademark MULTRANOL. Typically, the adjuvant polymers, when used, are present in the coating composition in amounts of 2 to 50 percent by weight based on weight of resin solids in the coating composition.
The coating compositions may further comprise a curing agent that is reactive with the hydroxyl group of the polyester so as to provide a thermoset coating on the surface of the container. Among the curing agents that may be used are phenolplasts or phenol-formaldehyde resins and aminoplast or triazine-formaldehyde resins. The phenol-formaldehyde resins can be the resol type. Examples of suitable phenols are phenol itself, butyl phenol, xylenol and cresol. Cresol-formaldehyde resins, the types typically etherified with butanol, are often used. For the chemistry in preparation of phenolic resins, reference is made to “The Chemistry and Application of Phenolic Resins or Phenolplasts”, Vol. V, Part I, edited by Dr. Oldring; John Wiley & Sons/Cita Technology Limited, London, 1997. Examples of commercially available phenolic resins are PHENODUR PR285 and BR612 and those resins sold under the trademark BAKELITE, typically BAKELITE 6581 LB.
Examples of aminoplast resins are those that are formed by reacting a triazine such as melamine or benzoguanamine with formaldehyde. These condensates can be etherified typically with methanol, ethanol, butanol or mixtures thereof. For the chemistry preparation and use of aminoplast resins, see “The Chemistry and Applications of Amino Crosslinking Agents or Aminoplast”, Vol. V, Part II, page 21 ff., edited by Dr. Oldring; John Whey & Sons/Cita Technology Limited, London, 1998. These resins are commercially available under the trademark MAPRENAL such as MAPRENAL MF980 and under the trademark CYMEL such as CYMEL 303 and CYMEL 1128, available from Cytec Industries. Typically, the crosslinking agent, if used, is present in amounts of 5 to 30, such as 10 to 20 percent by weight, the percentages by weight being based on the weight of resin solids in the coating composition. One or more curing agents can be used. In certain embodiments when an adjuvant polymer is used, a curing agent reactive with that polymer is used. The selection of an appropriate curing agent depends on the chemistry of the polymer and is within the skill of one practicing in the art. The curing agent for the adjuvant polymer may be the same or different as that used for the hydroxyl functional polyester.
Optional ingredients can be included in the coating composition. Typically, the coating composition will contain a diluent, such as water, or an organic solvent or a mixture of water and organic solvent to dissolve or disperse the resinous binder. The diluent may be reactive or unreactive or mixtures thereof. In certain embodiments, the organic solvent is selected to have sufficient volatility to evaporate essentially entirely from the coating composition during the curing process such as during heating from 175-205° C. for about 6 to 15 minutes. Examples of suitable organic solvents are aliphatic; hydrocarbons such as mineral spirits and high flash point VM&P naphtha; aromatic hydrocarbons such as benzene, toluene, xylene and solvent naphtha 100, 150, 200 and the like; alcohols, for example, ethanol, n-propanol, isopropanol, n-butanol and the like; ketones such as acetone, cyclohexanone, methylisobutyl ketone and the like; esters such as ethyl acetate, butyl acetate, and the like; glycols such as butyl glycol, glycol ethers such as methoxypropanol and ethylene glycol monomethyl ether and ethylene glycol monobutyl ether and the like. Mixtures of various organic solvents can also be used. For aqueous compositions, the polyester and/or the acrylic polymer, if present, may contain acid functionality that is at least partially neutralized with an amine to assist in the dispersion or dissolution of the resinous binder in the aqueous medium. When present, the dilue nt is used in the coating compositions in amounts of about 20 to 80, such as 30 to 70, percent by weight based on total weight of the coating composition.
Another optional ingredient that can be used in the coating composition is a catalyst to increase the rate of cure or crosslinking of the coating compositions. Generally acid catalyst may be used and is typically present in amounts of about 0.05 to 5 percent by weight based on weight of resin solids. Examples of suitable catalyst are dodecyl benzene sulfonic acid, methane sulfonic acid, paratoluene sulfonic acid, dinonyl naphthalene disulfonic acid and phenyl phosphonic acid.
Another useful optional ingredient is a lubricant, for example, a wax, which facilitates manufacture of metal closures by imparting lubricity to the sheets of the coated metal substrate. Suitable lubricants include, for example, carnauba wax and polyethylene-type lubricants. If used, the lubricant can be used in the coating compositions of at least 0.1 percent by weight based on weight of resin solids in the coating composition.
Surfactants can optionally be added to the coating composition to aid in flow and wetting of the substrate. Examples of suitable surfactants include, but are not limited to, non ionic surfactants such as the reaction products of alkylene oxides and alkyl substituted phenols, for example, ethoxalated nonyl phenol polyether. If used, the surfactant is typically present in amounts of at least 0.01 percent and no greater than 10 percent based on weight of resin solids in the coating composition.
The coating compositions can also comprise any additives standard in the art of coating manufacture including colorants, plasticizers, abrasion-resistant particles, film strengthening particles, flow control agents, thixotropic agents, rheology modifiers, catalysts, antioxidants, biocides, defoamers, surfactants, wetting agents, dispersing aids, adhesion promoters, clays, hindered amine light stabilizers, UV light absorbers and stabilizers, a stabilizing agent, fillers, grind vehicles, and other customary auxiliaries, or combinations thereof. As used herein, the terms “colorant” and “abrasion-resistant particle” are as described in United States Patent Publication Number 2010/0055467A1, paragraphs 24-34, incorporated by reference herein.
in certain embodiments, the compositions and/or the resultant coatings on the container may be substantially free, may be essentially free and/or may be completely free of bisphenol A and derivatives or residues thereof, including bisphenol A (“BPA”) and bisphenol A diglycidyl ether (“BADGE”). Such compositions and/or coatings are sometimes referred to as “BPA non intent” because BPA, including derivatives or residues thereof, are not intentionally added but may be present in trace amounts because of impurities or unavoidable contamination from the environment. The compositions and/or coatings can also be substantially free and may be essentially free and/or may be completely free of bisphenol F and derivatives or residues thereof, including bisphenol F and bisphenol F diglycidyl ether (“BFDGE”). The term “substantially free” as used in this context means the compositions and/or coatings contain less than 1000 parts per million (ppm), “essentially free” means less than 100 ppm and “completely free” means less than 20 parts per billion (ppb) of any of the above mentioned compounds, derivatives or residues thereof.
The coating compositions can be applied to containers of all sorts and are particularly well adapted for use on food and beverage cans (e.g., two-piece cans, three-piece cans, etc.). Besides food and beverage containers, the coating compositions can be applied to containers for aerosol applications such deodorant and hair spray. After application as described below, the applied compositions are heated to a temperature sufficient to cure the coating. Typical curing temperatures are 150 to 300° C. for 2 to 60 minutes.
The containers can be, for example, metallic or non-metallic. Metallic substrates include tin, steel, tin-plated steel, tin free steel, black plate, chromium passivated steel, galvanized steel, aluminum, aluminum foil. Non-metallic substrates include polymeric, plastic, polyester, polyolefin, polyamide, cellulosic, polystyrene, polyacrylic, polyethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other “green” polymeric substrates, poly(ethylene terephthalate) (“PET”), polycarbonate and polycarbonate acrylobutadiene styrene (“PC/ABS”).
The coating compositions can be applied to the containers by any means standard in the art, such as electrocoating, spraying, electrostatic spraying, dipping, rolling, brushing, and the like.
The coatings can be applied in certain embodiments to a dry film thickness of 0.04 mils to 4 mils, such as 0.3 to 2 or 0.7 to 1.3 mils. In other embodiments the coatings can be applied to a dry film thickness of 0.1 mils or greater, 0.5 mils or greater 1.0 mils or greater, 2.0 mils or greater, 5.0 mils or greater, 10.0 mils or greater or even thicker. The coatings can be used alone, or in combination with one or more other coatings. For example, the coatings can comprise a colorant or not and can be used as a primer, basecoat, and/or top coat. For containers coated with multiple coatings, one or more of those coatings can be coatings as described herein. The present coatings can also be used as a packaging “size” coating, wash coat, spray coat, end coat, and the like.
It will be appreciated that the coating compositions described herein can be either one component (“1K”), or multi-component compositions such as two component (“2K”) or more. A 1K composition will be understood as referring to a composition wherein all the coating components are maintained in the same container after manufacture, during storage, etc. A 1K coating can be applied to a substrate and cured by any conventional means, such as by heating, forced air, and the like. The present coating compositions can also be multi-component coatings, which will be understood as coating compositions in which various components are maintained separately until just prior to application. The present coatings can be thermoplastic or thermosetting.
The coating compositions are particularly useful in the coating of metal cans. where the resultant coating is used to retard or inhibit corrosion, provide a decorative coating, provide ease of handling during the manufacturing process, and the like. The coating compositions can be applied to the interior of such cans to prevent the contents from contacting the metal of the container. Contact between the metal and a food or beverage, for example, can lead to corrosion of a metal container, which can then contaminate the food or beverage. This is particularly true when the contents of the can are acidic in nature. The coatings applied to the interior of metal cans also help prevent corrosion in the headspace of the cans, which is the area between the fill line of the product and the can lid; corrosion in the headspace is particularly problematic with food products having a high salt content. Coatings can also be applied to the exterior of metal cans. Certain coatings of the present invention are particularly applicable for use with coiled metal stock, such as the coiled metal stock from which the ends of cans are made (can end stock), and end caps and closures are made (“cap/closure stock”). Since coatings designed for use on can end stock and cap/closure stock are typically applied prior to the piece being cut and stamped out of the coiled metal stock, they are typically flexible and extensible. For example, such stock is typically coated on both sides. Thereafter, the coated metal stock is punched. For can ends, the metal is then scored for the “pop-top” opening and the pop-top ring is then attached with a pin that is separately fabricated. The end is then attached to the can body by an edge rolling process. A similar procedure is done for “easy open” can ends. For easy open can ends, a score substantially around the perimeter of the lid allows for easy opening or removing of the lid from the can, typically by means of a pull tab. For caps and closures, the cap/closure stock is typically coated, such as by roll coating, and the cap or closure stamped out of the stock; it is possible, however, to coat the cap/closure after formation. Coatings for cans subjected to relatively stringent temperature and/or pressure requirements should also be resistant to popping, corrosion, blushing and/or blistering.
The term “metal can” includes any type of metal can, container or any type of receptacle or portion thereof used to hold something. One example of a metal can is a food can; the term “food can(s)” is used herein to refer to cans, containers or any type of receptacle or portion thereof used to hold any type of food and/or beverage. Thus a “food can” includes a “beverage can”. The term “metal can(s)” specifically includes food cans and also specifically includes “can ends”, which are typically stamped from can end stock and used in conjunction with the packaging of foods and beverages. The term “metal cans” also specifically includes metal caps and/or closures such as bottle caps, screw top caps and lids of any size, lug caps, and the like. Metal cans can be used to hold other items as well as food and/or beverage, including but not limited to personal care products, bug spray, spray paint, and any other compound suitable for packaging in an aerosol can. The cans can include “two piece cans” and “three-piece cans” as well as drawn and ironed one-piece cans, such one piece cans often find application with aerosol products. Coated containers according to the present invention can also include plastic bottles, plastic tubes, laminates and flexible packaging, such as those made from PE, PP, PET and the like. Such packaging could hold, for example, food toothpaste, personal care products and the like.
The coating composition can be applied to the interior and/or the exterior of the container. For example, the coating can be rollcoated onto metal used to make three-piece can bodies, two- or three-piece can end stock and/or cap/closure stock in some embodiments, the coating is applied to a coil or sheet by roll coating; the coating is then cured and can ends are stamped out and fabricated into the finished product, i.e. can ends. In other embodiments, the coating is applied as a rim coat to the bottom of the can; such application can be by roll coating. The rim coat functions to reduce friction for improved handling during the continued fabrication and/or processing of the can. In certain embodiments, the coating is applied to caps and/or closures; such application can include, for example, a protective varnish that is applied before and/or after formation of the cap/closure and/or a pigmented enamel post applied to the cap, particularly those having a scored seam at the bottom of the cap. Decorated can stock can also be partially coated externally with the coating described herein, and the decorated, coated can stock used to form various metal cans.
As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear, Any numerical range recited herein is intended to include all sub-ranges subsumed therein. Plural encompasses singular and vice versa. For example, while the invention has been described in terms of “a” hydroxyl functional polyester, “an” organic polycarboxylic acid, “a” polyol, and the like, mixtures of these and other components can be used. Also, as used herein, the term “polymer” is meant to refer to prepolymers, oligomers and both homopolymers and copolymers; the prefix “poly” refers to two or more. When ranges are given, any endpoints of those ranges and/or numbers within those ranges can be combined with the scope of the present invention. “Including”, “such as”, “for example” and like terms means “including/such as/for example but not limited to”. The terms “acrylic” and “acrylate” are used interchangeably (unless to do so would alter the intended meaning) and include acrylic acids, anhydrides, and derivatives thereof, lower alkyl-substituted acrylic acids, e.g., C1-C2 substituted acrylic acids, such as methacrylic acid, ethacrylic acid, etc., and their C1-C6 alkyl esters and hydroxyalkyl esters, unless clearly indicated otherwise. The terms “(meth)acrylic” or “(meth)acrylate” are intended to cover both the acrylic/eon/late and methacrylic/methacrylate forms of the indicated material, e.g., a (meth)acrylate monomer. The term “(meth)acrylic polymer” refers to polymers prepared from one or more (meth)acrylic monomers. As used herein, the molecular weights are determined by gel permeation chromatography using a polystyrene standard.

EXAMPLES

The following examples are offered to aid in understanding of the present invention and are not to be construed as limiting the scope thereof. Unless otherwise indicated, all parts and percentages are by weight.

Example A

Synthesis of Polyester Prepared from 2,2,4,4-Tetramethyl-1,3-Cyclobutane Diol

300 grams of 2,2,4,4-tetramethyl-1,3-cyclobutane diol, 315 grams of adipic acid and 62 grams of aromatic solvent were added to a flask. Azeotropic distillation set up was added over the pack column filling the Dean Stark with aromatic solvent. The mixture was heated to 100° C. and 0.7 grams of stanuous octoate was added to flask. The temperature was raised again to 170° C. and a nitrogen sparge was used throughout the synthesis. Once the temperature reached 170° C., distillation began. To maintain a good distillation, the temperature was increased up to 230° C. and the mixture was synthesized until it reached an add value of 17.00 mg KOH/g. The flask temperature was reduced to 90° C. At 90° C., 470 grams of 2-methyl-1,3-propane diol, 7 grams of trimethylol propane, 830 grams of terephthalic acid and 0.8 grams of stanuous octoate were added. The temperature was raised to 200° C. Once the distillation began, the distillation was maintained by increasing the temperature up to 240° C. Glycol loss was monitored during the synthesis. The resin was synthesized until clear. Acid value was checked until it reached 5-6 mg KOH/g. Once the acid value was within range, the temperature of the flask was reduced to 180° C. At 180° C., aromatic solvent was added slowly and the resulting reaction product had a resin solids content of 59.74 percent by weight.

Example B

Comparative

Synthesis of Polyester Prepared from 1,4-Cyclohexane Dicarboxylic Acid

300 grams of 1,4-cyclohexane dimethanol and 315 grams of adipic acid were added to a flask. Pack column with head temperature reading set up was added to the flask. The mixture was heated to 100° C. and 0.7 grams of stanuous octoate was added to the mixture. The temperature was raised again to 170° C. and a nitrogen sparge was used throughout the synthesis. Once the temperature reached 170° C., distillation began. To maintain a good distillation, the temperature was increased up to 230° C. and the mixture was synthesized until it reached an acid value of 17.00 mg KOH/g. The flask temperature was reduced to 90° C. At 90° C., 470 grams of 2-methyl-1,3-propane diol, 7 grams of trimethylol propane, 830 grams of terephthalic acid and 0.8 grams of stanuous octoate were added. The temperature was raised to 200° C. Once the distillation began, the distillation was maintained by increasing the temperature up to 240° C. Glycol loss was monitored during the synthesis. The resin was synthesized until clear. Acid value was checked until it reached 5-6 mg KOH/g. Once the acid value was within range, the temperature of flask was reduced to 180° C. At 180° C., aromatic solvent was added slowly and the resulting reaction product had a resin solids content of 59.74 percent by weight. The resin was not clear at room temperature.

Example 1

Can Coating Formulation Prepared with Polyester of Example A

Coatings were prepared from the resin prepared as described above in Example A. All listed materials in the following table were added in order from top to bottom under agitation in 8 ounce glass jars. Coatings were formulated with PHENODUR PR 516, phenolic resin from Cytec Surface Specialties, Inc., at 25% by weight on coating non-volatiles and BYK-310 polyester modified silicone surface additive from Byk Chemie, Inc. and catalyzed with dodecylbenzylsulfonic acid, from Cytec Industries, diluted to 70% by weight with isopropanol.


Ingredient	A	B	C	D

DYNAPOL 912¹	63.8	63.7	—	—
Polyester resin-example A	—	—	42.70	42.60
Aromatic Solvent	21.9	21.9	19.90	19.90
Aromatic Solvent	—	—	20.00	20.00
BYK-310	0.10	0.10	0.10	0.10
Catalyst	—	0.10	—	0.10
Phenolic Resin	14.2	14.2	17.30	17.30
Total	100.00	100.00	100.00	100.00

¹Polyester commercially available from Evonik.

All coatings were applied to the substrate at 34% weight solids. Coatings were applied by drawing the coatings over either tin free steel (“IFS”) or electrolytic tin plate (“FTP”) using a #12 wire wound rod and baking them at 400° F. for 10 minutes. All coatings had a resultant dry coating weight of approximately 4 milligrams/square inch. Coatings were evaluated for their resistance to methyl ethyl ketone solvent by dousing a Fisher brand non-sterile cotton gauze sponge (4″×4″) with the solvent and 2 pound hammer rubbing it across the coating surface until the gauze broke through the coating to the metal surface. The gauze was re-doused with methyl ethyl ketone every twenty five double rubs across the coating surface. The number of double rubs to break through the coating was recorded for a maximum of 100 double rubs. Coating flexibility was evaluated in triplicate with a wedge bend test. A 4.6 inch long by 2 inch wide coated coupon was cut from the coated panel to intentionally have the metal grain run perpendicular to the length of the coated wedge bend test coupon. The length of the coupon was then bent over ¼ inch metal dowel with the coated side out, and then placed in a piece of metal where a wedge had been removed to result in, after being impacted with approximately a 2000 gram weight dropped from twelve inches above the bent coupons, one end of the coupon to touch or impinge upon itself and the other end to stay open to the ¼ inch dowel bend. After being impacted, all bent coupons were immersed in an aqueous solution of 20% copper sulphate and 10% hydrochloric acid, by weight, for two minutes to etch the exposed metal substrate to facilitate rating them. Using a 1.0× microscope, coating flex was evaluated by measuring along the length of the bent coupon to the last area that had any open cracks or spotty failure from the impinged end. Reported % flex failed=(length of last crack or open spot/length of the entire coupon)×100. Coatings were also evaluated for their sterilization resistance to common food aqueous simulants like salt (2% by weight) and acid/salt (2% acetic acid/3% salt by weight). The synthetic tests were run by making 307 inch diameter ends which were seemed on to DRD can. The retort conditions were 122° C. for 90 minutes, which are considered to be very harsh conditions. All coatings were rated for one or more of: adhesion 0 (nothing stuck) to 100% (nothing removed) using 3M's Scotch 610 tape; blush 0 (clear) to 10 (opaque); and corrosion 0 (none) to 10 (severe). The coatings of the present invention were compared to a standard commercial control, PPG2004877, commercially available form PPG Industries, Inc.

Example 2

Comparative

Preparation of can Coating Formulation with Polyester of Example B

No coating was formulated with polyester of Example B due to its incompatibility to solvent package.

TABLE 1

Comparison of Coating Formulations

2 lb.

Fabricated Ends

Hammer

2% NaCl

Wedge Bends

MEK

TFS

ETP

(mm of failure)

Rubs

Adhesion

Corrosion

Blush

Adhesion

Corrosion

Blush

Coating	TFS	ETP	TFS	ETP	ASTM	ASTM	ASTM	ASTM	ASTM	ASTM

PPG2004877²	12 mm	22 mm	73	55	9	9	9	9	9	9
A	5 mm	16 mm	30	18	5.5	9	9	3	9	9
B	13 mm	24 mm	40	32	3	9	9	1	9	9
C	14 mm	25 mm	10	8	6.5	9	9	4	9	9
D	14 mm	24 mm	10	10	8	9	9	7	9	9

Fabricated Ends

3% NaCl + 2% Acetic Acid

TFS

ETP

		Adhesion	Corrosion	Blush	Adhesion	Corrosion	Blush
	Coating	ASTM	ASTM	ASTM	ASTM	ASTM	ASTM

	PPG2004877²	9	6	9	9	9	9
	A	8	8	8	8	8	8
	B	8	8	8	8	8	8
	C	9	1	1	9	3	3
	D	5	1	1	9	2	2

²Epoxy coating, commercially available from PPG.

As can be seen in the above table, the coating of the present invention (coatings C and D) had good performance results overall, some of which were comparable to a commercially available epoxy coating (PPG 2004877) and a coating based on a commercially available polyester (coatings A and B).

Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims

1. A container comprising a thermoset coating applied to at least a portion thereof, the coating derived from a composition comprising:

a hydroxyl functional polyester comprising a reaction product prepared from a reaction mixture comprising:

(i) an organic polycarboxylic acid and/or ester and/or anhydride thereof, and

(ii) a polyol component comprising tetramethyl-1,3-cyclobutane diol.

2. The container of claim 1 wherein the polyester has a number average molecular weight of 2000 to 15,000 Daltons.

3. The container of claim 1 wherein the polyester has a hydroxyl number of 5 to 40.

4. The container of claim 1 wherein the organic polycarboxylic acid comprises naphthalene dicarboxylic acid, phthalic acid, isophthalic acid, terphthalic acid maleic acid, cyclohexane dicarboxylic acid and/or adipic acid.

5. The container of claim 1 wherein the polyol component further comprises 2-methyl-1,3-propane diol.

6. The container of claim 1 wherein the tetramethyl-1,3-cyclobutane diol is present in amounts of 10 to 100 percent by weight based on total weight of the polyol component.

7. The container of claim 1 in which the equivalent ratio of polyol to polycarboxylic acid is from 1.0 to 1.5:1.

8. The container of claim 1 in which the composition further comprises a curing agent.

9. The container of claim 8 in which the curing agent comprises phenolplast and/or aminoplast.

10. The container of claim 1 in which the composition is substantially free of bisphenol A and derivatives thereof.

11. The container of claim 1 in which the composition is essentially free of bisphenol A and derivatives thereof.

12. The container of claim 1 in which the composition is completely free of bisphenol A and derivatives thereof.

13. A container comprising a thermoset coating applied to at least a portion thereof, the coating derived from a composition comprising:

(a) from 10 to 95 percent by weight based on weight of resin solids of a hydroxyl functional polyester comprising a reaction product prepared from a reaction mixture comprising:

(i) an organic polycarboxylic acid comprising naphthalene dicarboxylic acid,

(ii) a polyol component comprising from 10 to 100 percent by weight based on total weight of polyol of tetramethyl-1,3-cyclobutane;

(b) from 5 to 30 percent by weight based on weight of resin solids of a phenolplast and/or an aminoplast curing agent.

14. The container of claim 12 wherein the container comprises a food can.

15. The container of claim 13 wherein the container comprises a food can.

16. A method of coating a container comprising:

(a) applying to a surface of the container the composition of claim 1

(b) heating the composition applied in step (a) to a temperature sufficient to cure the composition.

17. The method of claim 16 in which step (a) is by spraying or roll coating.

18. The method of claim 16 in which step (b) is conducted at a temperature of 150 to 300° C.