HK1128301B - Food cans coated with a composition comprising an acrylic polymer - Google Patents

Description

Food cans coated with compositions comprising acrylic polymers

Technical Field

The present invention relates to coated food cans wherein the coating composition used to coat the cans comprises an acrylic polymer and a crosslinker.

Background

In order to retard or inhibit corrosion, it has long been known to apply various treatment and pretreatment solutions to metals. This approach is particularly true in the field of metal food and beverage cans. A coating is applied to the interior of such containers to prevent the contents from contacting the metal of the container. Contact between the metal and the food or beverage can cause corrosion of the metal container, which then contaminates the food or beverage. This is even more true when the contents of the can are acidic in nature, such as tomato-based products and soft drinks. Coatings applied to the interior of food and beverage cans can also help prevent corrosion of the headspace of the can, the space being the area between the fill tube of the food product and the can lid; corrosion in the headspace can be particularly problematic for food products with high salt content.

In addition to corrosion protection, the coating of food and beverage cans should be non-toxic and should not adversely affect the taste of the food or beverage in the can. It is also desirable to be resistant to "popping", "whitening" and/or "blistering".

Certain coatings are particularly suitable for application to coiled metal stock, such as the coiled metal stock "can end stock" from which can ends are made. They also typically have toughness and elongation properties due to the application of coatings designed for can end stock prior to cutting and stamping the end from the coiled metal stock. For example, can end stock is typically coated on both sides. The coated metal stock is then punched, scored for the "can" opening, and then the can ring is attached with a separately machined pin. The lid is then joined to the can body by a rolling process. Accordingly, in addition to the other desirable features discussed above, the coatings applied to can end stock typically have a minimized degree of rigidity and flexibility so that they can withstand a large scale manufacturing process.

Various epoxy-based coatings and polyvinyl chloride-based coatings have been used in the past to coat the interior of metal cans to prevent corrosion. However, the recycling of raw materials containing polyvinyl chloride or vinyl polymers containing related halides can produce toxic by-products; in addition, these polymers are typically formulated with epoxy functional plasticizers. In addition, epoxy-based coatings are prepared from monomers such as bisphenol a ("BPA") and bisphenol a diglycidyl ether ("BADGE"), which are reported to have negative health effects. Although attempts have been made to scavenge residual unreacted epoxide with, for example, acid-functionalized polymers, this has not adequately addressed the problem; some free BADGE or its by-products still remain. Governmental authorities, especially in europe, have limitations regarding the amount of free BPA, BADGE and/or by-products thereof that are acceptable. Accordingly, there is a need for food and beverage can liners that are substantially free of BPA, BADGE, epoxy and halogenated vinyl products.

Disclosure of Invention

The present invention relates to a food can coated at least partially on the inside with a composition comprising:

a) greater than 7 wt% based on total solids weight of an acrylic polymer having a weight average molecular weight of 41,000 or more and an acid value of <30mg KOH/g; and

b) a cross-linking agent which is a cross-linking agent,

wherein the composition is substantially free of epoxide and substantially free of polyester.

The invention further relates to a food can coated at least partially on the inside with a composition having a tensile strength of more than 11MPa, measured with an lnstron device.

Detailed Description

The present invention relates to food cans coated at least in part on the interior with a composition comprising an acrylic polymer and a crosslinking agent. The term "food can" as used herein refers to a can, container or any type of metal receptacle or portion thereof for holding any type of food or beverage. For example, the term "food can" specifically includes "can ends" which are typically stamped from can end stock and used in connection with beverage packaging.

The composition is substantially free of epoxide. By "substantially free of epoxide" is meant that the composition is substantially free of oxirane rings or residues of oxirane rings; bisphenol A; BADGE or an adduct of BADGE; a glycidyl group or a residue of a glycidyl group; polyvinyl chloride and/or vinyl polymers containing related halides. It is to be understood that trace or minor amounts of one or more of these components may be present, for example, 10 wt% or less, 5 wt% or less, 2 or even 1 wt% or less, based on total solids weight, and still be "substantially epoxide-free". The composition is also substantially free of polyester. By "substantially free of polyester" is meant that the composition is substantially free of polyester; that is, the composition contains less than an amount of polyester that would allow the polyester to aid in film formation and performance of the coating. It is to be understood that trace or minor amounts of polyester may be present, for example 10 wt% or less, 5 wt% or less, 2 or even 1 wt% or less, based on total solids weight, still "substantially polyester free".

The acrylic polymer used according to the invention may be, for example, an acrylic homopolymer or copolymer. Various acrylic monomers can be combined to prepare the acrylic polymer used in the present invention. Examples include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hydroxyalkyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, behenyl (meth) acrylate, lauryl (meth) acrylate, allyl (meth) acrylate, isobornyl (meth) acrylate, ethylene glycol di (meth) acrylate, (meth) acrylic acid, vinyl aromatic compounds such as styrene and vinyl toluene, nitriles such as (meth) acrylonitrile, and vinyl esters such as vinyl acetate. Any other acrylic monomer known to those skilled in the art may also be used. The term "(meth) acrylate" and similar terms as used conventionally and herein refer to both methacrylates and acrylates. In certain embodiments, the acrylic polymer includes components approved by the FDA for use with food cans and/or listed on EINECS and in certain embodiments, the acrylic polymer includes only components approved by the FDA for use with food cans and/or listed on EINECS.

Typically, the weight average molecular weight ("Mw") of the acrylic polymer is 41,000 or greater, for example 60,000 or greater. It has been found that acrylics having Mw of 41,000 or greater can form films having desirable tensile strength with minimal crosslink density. This feature is particularly suitable when can end stock is coated and can ends derived from the base are stamped.

In certain embodiments, the acrylic polymer is prepared without acrylamide-containing monomers.

In certain embodiments, the acrylic is copolymerized with a phosphate functional monomer. Thus, the acrylic polymer may be formed from acrylic monomers some of which have phosphate functional groups; in certain embodiments, the acrylic polymer is prepared with only some of the acrylic monomers having phosphate functional groups. Examples of phosphate functional acrylic monomers that can be used to form the phosphate functional acrylic polymer include: phosphoethyl (meth) acrylate, and phosphate-functional (meth) acrylates sold by Rhodia under the names SIPOMER PAM-100 and-200.

Certain embodiments of the present invention are directed to food cans at least partially coated on the interior with a composition consisting essentially of: an acrylic polymer formed from only some of the acrylic monomers, optionally having phosphate functional groups, and a crosslinking agent. In certain embodiments, the acrylic polymer is not a core-shell emulsion polymer, and in other embodiments, the acrylic polymer specifically excludes styrene and/or ethylene-containing components including, for example, ethylene-maleic acid copolymers and/or polyethylene resins.

The composition used according to the present invention further comprises a cross-linking agent, suitable cross-linking agents may be determined based on the needs and requirements of the user and may include, for example, aminoplast cross-linking agents, phenolic cross-linking agents and blocked isocyanates. The aminoplast crosslinker may be a melamine-based, urea-based, or benzoguanamine-based crosslinker. Melamine crosslinkers are widely commercially available, such as CYMEL303, 1130, 325, 327 and 370 available from Cytec Industries, inc. Phenolic cross-linking agents include, for example, novolacs, resoles, and bisphenol a. For food can applications, resole resins not derived from bisphenol a are particularly suitable.

The compositions used according to the present invention typically comprise greater than 7 wt% acrylic polymer, where the wt% is based on the total solids weight of the composition. Typically, the acrylic polymer is present in the range of from 8 to 99 wt%, for example 80 to 99 wt%. The crosslinker is typically present in an amount of 1 to 30 wt%, for example 2 to 5 wt%, wt% based on total solids weight. In certain embodiments, the wt% of crosslinker in the composition is 10 wt% or less, such as 5 wt% or less, based on total solids weight. It has been unexpectedly found that the use of acrylic polymers having a relatively high Mw (i.e., 41,000 or greater) can produce coatings having better film properties compared to coatings comprising acrylic polymers having a relatively low molecular weight. Furthermore, the high molecular weight allows for the use of reduced amounts of crosslinking agent compared to other can coatings. This is important because high amounts of cross-linking agent tend to make the coating more brittle; by "high amount" is meant greater than 15%, such as greater than 25%. This is surprising because acrylic coatings have not previously been thought to provide sufficient flexibility to food cans or portions thereof, such as can ends.

The compositions used according to the invention may also comprise a solvent. Suitable solvents include water, esters, glycol ethers, glycols, ketones, aromatic and aliphatic hydrocarbons, alcohols, and the like. Particularly suitable are xylene, propylene glycol monomethyl acetate, and dibasic esters such as the dimethyl esters of adipic, glutaric and succinic acids. It will be appreciated that the use of those solvents does not result in the composition containing polyester, since the solvent is substantially removed during the acquisition process. Typically, the compositions are prepared with a weight percent solids of between about 30 and 60. Alternatively, the composition may be aqueous. The term "aqueous" as used herein means that 50% or more of the non-solid components of the coating are water. Thus, it should be understood that the non-solid components of the composition may contain up to 50% solvent and still be "aqueous". The present compositions can be made aqueous by neutralizing the carboxylic acid functional acrylic polymer with an amine such as dimethylethanolamine and then dispersing it into water with stirring.

The compositions of the present invention may also contain any other conventional additives such as pigments, colorants, waxes, lubricants, defoamers, wetting agents, plasticizers, reinforcing agents, and catalysts. Any inorganic or sulfonic acid catalyst may be used. Particularly suitable for food cans are phosphoric acid and dodecylbenzene sulfonic acid.

The invention further relates to a food can coated at least partially on the inside with a composition having a tensile strength of more than 11MPa, determined as follows: using an lnstron Mini44 apparatus with a 50N force sensor, a crosshead speed of 10mm/min, a free film of approximately 25.4mm length, 12.7mm width, 0.3mm thickness and 1 inch gauge length was used. Compositions having such tensile strength may be formed, for example, in the manner described above. It has been found that can end stock coated with coatings having such tensile strengths can maintain their integrity when manufactured into a final product and that the coated can ends can maintain their resistance properties after forming, as compared to low tensile strength coatings.

The coating composition described above can be applied to food cans using any method known in the art, such as roll coating, spray coating, and/or electrocoating. It will be appreciated that for two-piece food cans, the coating is typically sprayed after the can is made. On the other hand, for three-piece food cans, a coil or sheet is typically first roll coated with one or more of the present compositions and then formed into a can. The coating is applied to at least a portion of the interior of the can, but may also be applied to at least a portion of the exterior of the can. For can end stock, a coil or sheet is typically roll coated with the present composition; the coating is then cured, the lid is stamped out, and the finished product, i.e. can end, is processed.

After application, the coating is then cured. Curing is effected by process standards in the art. For coil coatings, there is typically a short residence time (i.e., 9 seconds to 2 minutes) at high temperature (i.e., 485 ° f peak metal temperature); for coated metal sheets, curing is typically longer (i.e., 10 minutes), but at low temperature (i.e., 400 ° f peak metal temperature) conditions. Thus, it should be understood that the composition applied to the food can may produce a cured coating when reacted between the acrylic polymer and the crosslinker. The intention is to want to substantially retain the cured coating on the can to perform a protective function; thus, the present compositions are not pre-treatments or lubricants that are applied and then washed off or substantially removed during the coating step. In certain embodiments, transition metals in amounts that are conducive to corrosion control are also specifically excluded from the compositions used in the present invention.

Any materials used to form food cans may be processed according to the present method. Particularly suitable substrates include chromium treated aluminum, zirconium treated aluminum, tin plated steel, tin free steel and black plated steel.

In certain embodiments, the coating of the present invention may be applied directly to the metal without any pretreatment or first adding a co-adhesive to the metal. In certain other embodiments, such as when making can ends, pre-treated aluminum is desirable. Furthermore, there is no need to apply a coating on top of the coating used in the present method. In certain embodiments, the coating described herein is the last coating applied to the food can. In certain other embodiments, the food cans of the present invention do not have a polyester layer deposited thereon, e.g., above or below the layers described herein.

The composition used according to the invention can be used as desired in the area of flexibility and acid resistance. Notably, these results can be obtained with compositions that are substantially epoxy-free and substantially polyester-free. The present invention thus provides, among other things, desirable coated food cans that avoid the performance and health issues created by other can coatings.

Unless specifically stated otherwise, all numbers used herein, such as those expressing values, ranges, amounts or percentages, may be interpreted as if prefaced by the word "about", even if the term does not expressly appear. Also, any numerical range recited herein includes all sub-ranges subsumed therein. Singular encompasses plural and vice versa. For example, although reference is made herein to "an" acrylic polymer, "a" crosslinker, and "a" solvent, one or more of each of these and any other components may be used. The term "polymer" as used herein refers to oligomers and both homopolymers and copolymers, and the prefix "poly" refers to two or more.

Examples

The following examples are intended to illustrate the invention and should not be construed as limiting it in any way.

Example 1

Acrylic polymer "a" was prepared as follows:

TABLE 1

Components	#1 Charge	Parts by weightNumber of
			DOWANOL PM1		24.0
	#2 Charge
			DOWANOL PM		4.2
LUPEROX262		0.6
				#3 charging
Acrylic acid butyl ester		17.6
			2-hydroxypropyl methacrylate		16.5
Methacrylic acid		1.5
			2-ethylhexyl acrylate		5.9
Methacrylic acid methyl ester		17.4
				#4 Charge
DOWANOL PM (flushing #2)		1.0
				#5 Charge
DOWANOL PM (flushing #3)		7.7
				#6 Charge
DOWANOL PM		0.3
			LUPEROX26		0.3
	#7 Charge
			DOWANOL PM (flushing #6)		1.2
	#8 Charge
			DOWANOL PM		0.3
LUPEROX26		0.3
				#9 Charge
DOWANOL PM (flushing #9)		1.2

Propylene glycol monomethyl ether was used as a solvent, available from Dow Chemical. T-butyl peroxy-2-ethylhexanoate available from Arkema, Inc.

Charge #1 was added to a 2 liter 4-necked flask equipped with an electrically driven stainless steel stirring blade, a water condenser, and a heating mantle with a thermometer connected to the heating mantle via a temperature feedback control device. The contents of the flask were heated to reflux (119 ℃). Charge #2 and charge #3 (over 180 minutes) were started through two separate addition funnels. During the feed, the reflux temperature was gradually increased to 123 ℃. After all additions, both addition funnels were rinsed with charges #4 and #5, respectively, and then the reaction was held at 123 ℃ for thirty minutes. Charge #6 was added via addition funnel; the addition funnel was rinsed with charge #7 and the mixture was held at 123 ℃ for one hour. Charge #8 was added via addition funnel; the addition funnel was rinsed with charge #9 and the mixture was held at 123 ℃ for an additional hour. (Polymer M)_w＝24,744)

Example 2

Acrylic polymer "B" was prepared as follows:

TABLE 2

Components	#1 Charge	Parts by weight
			DOWANOL PM		6.2
	#2 Charge
			DOWANOL PM		3.6
LUPEROX26		0.6
				#3 charging
Acrylic acid butyl ester		17.6
			2-hydroxypropyl methacrylate		16.5
Methacrylic acid		1.5
			2-ethylhexyl acrylate		5.9
Methacrylic acid methyl ester		17.4
				#4 Charge
DOWANOL PM (flushing #3)		2.9
				#5 Charge
DOWANOL PM		0.3
			LUPEROX26		0.3
	#6 Charge
			DOWANOL PM (flushing #5)		3.5
	#7 Charge
			DOWANOL PM		0.3
LUPEROX26		0.3
				#8 Charge

DOWANOL PM (flushing #7)		0.9
				#9 Charge
DOWANOL PM		22.2

Charge #1 was added to a 3 liter 4-necked flask equipped with an electrically driven stainless steel stirring blade, a water condenser, and a heating mantle with a thermometer connected to the heating mantle via a temperature feedback control device. The contents of the flask were heated to reflux (120 ℃). Charge #2 and charge #3 (over 180 minutes) were started through two separate addition funnels. During the feed, the reflux temperature was gradually increased to 134 ℃. After the entire addition, the addition funnel used for charge #3 was rinsed with charge #4 and the reaction was held at 134 ℃ for 30 minutes. Charge #5 was added over 10 minutes via an addition funnel; the addition funnel was rinsed with charge #6 and the mixture was held at 130 ℃ for 60 minutes. Charge #7 was added via addition funnel; the addition funnel was rinsed with charge #8 and the mixture was held at 130 ℃ for an additional 60 minutes. The resin was cooled to 95 ℃ and diluted with charge # 9. (Polymer M)_w＝40,408)

Example 3

Acrylic polymer "C" was prepared as follows:

TABLE 3

Components	#1 Charge	Parts by weight
			Toluene		14.3
	#2 Charge
			Toluene		3.7
LUPEROX5753		0.4
				#3 charging
Acrylic acid butyl ester		15.6
			2-hydroxypropyl methacrylate		14.6
Methacrylic acid		1.3
			2-ethylhexyl acrylate		5.2
Methacrylic acid methyl ester		15.3
				#4 Charge
Toluene (flushing #3)		3.3
				#5 Charge
Toluene		1.2
				#6 Charge
Toluene (flushing #2)		0.8
				#7 Charge
Toluene		24.3

³T-amyl peroxy-2-ethylhexanoate, available from Arkema, Inc.

Charge #1 was added to a 3 liter 4-necked flask equipped with an electrically driven stainless steel stirring blade, a water condenser, and a heating mantle with a thermometer connected to the heating mantle via a temperature feedback control device. The contents of the flask were heated to reflux (111 ℃). Addition of 52% of charge #2 was started through the addition funnel over 120 minutes. 5 minutes after the start of the addition of charge #2, charge #3 was added over 115 minutes. During the feed, the reflux temperature was gradually increased to 118 ℃. After the charge #3 was completely added, the addition funnel used for the charge #3 was rinsed with charge # 4. The remainder of the #2 charge was added over 60 minutes. During the feed, charge #5 was added to reduce resin viscosity and foam. When the feed was complete, the addition funnel was flushed with charge #6 and the temperature was reduced to 104 ℃. After 60 minutes at this temperature, the resin was diluted with charge # 7. (Polymer M)_w＝75,255)

Example 4

Acrylic polymer "D" was prepared as follows:

TABLE 4

Components	#1 Charge	Parts by weight
			Toluene		12.6
	#2 Charge
			Toluene		4.4
LUPEROX575		0.4
				#3 charging
Acrylic acid butyl ester		14.9
			2-hydroxypropyl methacrylate		13.9
Methacrylic acid		1.2
			S IPOMER PAM-2004		1.0
2-ethylhexyl acrylate		5.0
			Methacrylic acid methyl ester		13.6
	#4 Charge
			DOWANOL PM		1.2
	#5 Charge
			DOWANOL PM (flushing #3)		4.7
	#6 Charge
			DOWANOL PM (flushing #2)		0.9
	#7 Charge
			DOWANOL PM		26.2

⁴A phosphate functional monomer derived from Rhodia.

Charge #1 was added to a 3 liter 4-necked flask equipped with an electrically driven stainless steel stirring blade, a water condenser, and a heating mantle with a thermometer connected to the heating mantle via a temperature feedback control device. The contents of the flask were heated to reflux (111 ℃). The addition of 50% of charge #2 was started through the addition funnel over 120 minutes. After the start of addition of #2 Charge 5Minute, charge #3 was added over 115 minutes. During the feed, charge #4 was added to reduce resin viscosity and foam; the reflux temperature was gradually increased to 117 ℃. After the charge #3 was completely added, the addition funnel used for the charge #3 was rinsed with the charge # 5. The remainder of the #2 charge was added over 60 minutes. When the feed was complete, the addition funnel was flushed with charge #6 and the temperature was reduced to 104 ℃. After 60 minutes at this temperature, the resin was diluted with charge # 7. (Polymer M)_w＝96,744)

Example 5

Acrylic polymer "E" was prepared as follows:

TABLE 5

Components	#1 Charge	Parts by weight
			Toluene		12.7
	#2 Charge
			Toluene		4.9
LUPEROX575		0.4
				#3 charging
Acrylic acid butyl ester		14.9
			2-hydroxypropyl methacrylate		13.9
Methacrylic acid		1.2
			SIPOMER PAM-200		1.0
Isobornyl methacrylate		7.4
			2-ethylhexyl acrylate		5.0
Methacrylic acid methyl ester		6.2
				#4 Charge
DOWANOL PM (flushing #3)		4.7
				#5 Charge
DOWANOL PM (flushing #2)		1.0
				#6 Charge
DOWANOL PM		26.7

Charge #1 was added to a 3 liter 4-necked flask equipped with an electrically driven stainless steel stirring blade, a water condenser, and a heating mantle with a thermometer connected to the heating mantle via a temperature feedback control device. The contents of the flask were heated to reflux (110 ℃). The addition of 50% of charge #2 was started through the addition funnel over 120 minutes. 5 minutes after the start of the addition of charge #2, charge #3 was added over 115 minutes. During the feed, the reflux temperature was gradually increased to 121 ℃. After the charge #3 was completely added, the addition funnel used for the charge #3 was rinsed with the charge # 4. The remainder of the #2 charge was added over 60 minutes. When the feed was complete, the addition funnel was flushed with charge #5 and the temperature was reduced to 104 ℃. After 60 minutes at this temperature, the resin was diluted with charge # 6. (Polymer M)_w＝85,244)

Example 6

Acrylic polymer "F" was prepared as follows:

TABLE 6

Components	#1 Charge	Parts by weight
			DOWANOL PM		13.3
	#2 Charge
			DOWANOL PM		4.7
LUPEROX575		0.4
				#3 charging
Acrylic acid butyl ester		15.6
			2-hydroxypropyl methacrylate		14.6
Methacrylic acid		1.6
			SIPOMER PAM-200		1.0
2-ethylhexyl acrylate		5.2
			Methacrylic acid methyl ester		14.1
	#4 Charge
			DOWANOL PM (flushing #3)		4.9
	#5 Charge
			DOWANOL PM (flushing #2)		1.0
	#6 Charge
			DOWANOL PM		23.6

Charge #1 was added to a 2 liter 4-necked flask equipped with an electrically driven stainless steel stirring blade, a water condenser, and a heating mantle with a thermometer connected to the heating mantle via a temperature feedback control device. The contents of the flask were heated to reflux (119 ℃). The addition of 50% of charge #2 was started through the addition funnel over 120 minutes. 5 minutes after the start of the addition of charge #2, charge #3 was added over 115 minutes. During the feed, the reflux temperature was gradually increased to 126 ℃. After the charge #3 was completely added, the addition funnel used for the charge #3 was rinsed with the charge # 4. The remainder of the #2 charge was added over 60 minutes. When the feed was complete, the addition funnel was flushed with charge #5 and the temperature was reduced to 104 ℃. After 60 minutes at this temperature, the resin was diluted with charge # 6. (Polymer M)_w＝63,526)

Acrylic polymer F was neutralized (80-120% neutralization) with dimethylethanolamine and dispersed in water.

Example 7

Five different samples were prepared as follows: polymers A, B, C, D and E, prepared as described in examples 1, 2, 3, 4 and 5, were added to separate containers and the following components shown in Table 7 were mixed in at ambient conditions until homogeneous.

TABLE 7

Components	Sample 1	Sample 2	Sample 3	Sample No. 4	Sample No. 5
						Polymer A	55.4 parts of	0	0	0	0
Polymer B	0	54.9 portions	0	0	0
						Polymer C	0	0	61.7 parts	0	0
Polymer D	0	0	0	65.1 parts	0
						Polymer E	0	0	0	0	64.1 parts
Aminoplast crosslinking agents5	1.2	0	0	0	0
						Phenolic crosslinking agents6	0	1.2	1.2	1.2	1.7
NACURE59257	0.7	0	0	0	0
						Phosphoric acid8	0	5.1	5.1	5.1	5.1
P-toluenesulfonic acid	0	0.9	0.9	0.9	0.9
						Solvent(s)9	42.7	37.9	31.1	27.7	38.2

⁵CYMEL 1123, benzoguanamine, available from Cytec.

⁶Methylon 75108 solution, available from Durez Corporation.

⁷Blocked dodecylbenzylsulfonic acid solution from King Industries.

⁸Diluted with isopropanol to a 10% by weight solution of orthophosphoric acid.

⁹1/1/1 Ethyl acetate/Dowanol PM/dibasic ester.

Samples 1-5 were pulled on Cr-treated aluminum sheet with a #18 wire-wound rod to prepare coatings. The coating was baked at 450 ° f for 10 seconds. The flexibility of the coated sheet was evaluated using bent and stamped wedges (2.0 inches by 4.5 inches). For wedge bending, the percentage of cracked or cracked coating along the direction of bending was determined (100 ═ cracked/uncured). The average flexibility was calculated from the results of the three wedges. To determine surface cure, the coating was rubbed with methyl ethyl ketone (MEK ═ double the rub number before the coating broke through to the substrate). The resistance of the coated sheets was determined by treating them (retorting) in two food simulants for 30 minutes at 127 ℃. Two simulants were a 2% by weight solution of citric acid in deionized water and a 3% by weight solution of acetic acid in deionized water. The coatings were evaluated for their ability to resist whitening immediately upon removal from the distilled solution using a visual scale of 0-4, with 0 being the best. For adhesion testing, the coating was engraved in a cross pattern and covered with tape; the tape was drawn off and the percentage of intact coating was recorded (100 ═ no coating removed). The tensile strength of samples 3 and 4 was measured on an lnstron apparatus using free films as described in the above specification. All results are provided in table 8.

TABLE 8

NT not tested

As can be seen from table 8, the coatings used according to the invention give overall better results for samples 3, 4 and 5 compared to samples 1 and 2.

Although specific embodiments of the invention have been described above for purposes of illustration, it will be understood by those skilled in the art that many changes in detail may be made without departing from the invention as defined in the appended claims.

Claims (17)

1. A food can having a composition at least partially coated on an interior, the composition comprising:

a) greater than 7 wt% based on total solids weight of an acrylic polymer having a weight average molecular weight greater than or equal to 60,000 and an acid number <30mg KOH/g; and

b) a cross-linking agent which is a cross-linking agent,

wherein the composition comprises 10 wt% or less of an epoxide and 5 wt% or less of a polyester.

2. The food can of claim 1 in which the acrylic polymer has a weight average molecular weight greater than or equal to 60,000.

3. The food can of claim 1 in which the wt% of acrylic polymer in the composition is 80 to 99 wt% based on total solids weight.

4. The food can of claim 1 in which the cross-linking agent is melamine.

5. The food can of claim 1 in which the cross-linking agent is a phenolic.

6. The food can of claim 5 in which the wt% of crosslinker in the composition is less than 10 wt% based on total solids weight.

7. The food can of claim 1 in which the composition, when cured, is the final coating applied to the can.

8. The food can of claim 1 in which the acrylic polymer comprises butyl acrylate, methyl methacrylate, 2-hydroxypropyl methacrylate, 2-ethylhexyl acrylate, methacrylic acid and/or a phosphate functional (meth) acrylate.

9. The food can of claim 1 in which the acrylic polymer has phosphate functional groups.

10. The food can of claim 9 in which the monomers used to form the acrylic polymer comprise a phosphate functional (meth) acrylate.

11. The food can of claim 1 in which the acrylic polymer is formed solely from acrylic functional monomers.

12. The food can of claim 1, wherein the composition further comprises a solvent.

13. The food can of claim 1 in which the acrylic polymer specifically excludes ethylene and components comprising ethylene.

14. The food can of claim 1 in which the composition specifically excludes transition metals in amounts that aid in corrosion control.

15. The food can of claim 1 in which the coated portion of the food can comprises a can end.

16. A food can having a composition at least partially coated on an interior thereof, the composition consisting essentially of:

a) an acrylic polymer having a weight average molecular weight greater than or equal to 60,000 and an acid number <30mg KOH/g; and

b) a cross-linking agent which is a cross-linking agent,

wherein the acrylic polymer optionally comprises phosphate functional groups.

17. A food can coated at least partially on the inside with a composition having a tensile strength greater than 11MPa as measured using an Instron apparatus, wherein the composition comprises

a) Greater than 7 wt% based on total solids weight of an acrylic polymer having a weight average molecular weight greater than or equal to 60,000 and an acid value of <30mg KOH/g; and

b) a crosslinking agent, wherein the composition comprises 10 wt% or less of an epoxide and comprises 5 wt% or less of a polyester.