CN1348486A - Badge-free can coating - Google Patents

Abstract

An example coating of the present invention, suitable for use as an interior coating for metal cans, comprises (a) a polyester resin; (b) a fusible phenolic resin; and (c) a solvent, the coating being substantially free of bisphenol A-diglycidyl ether and bisphenol F-diglycidyl ether (e.g., “BADGE” or “BADGE-type” components), and preferably also substantially free of polyvinyl chloride.

Description

Bisphenol A diglycidyl ether free can coatings

Background of the invention

Metal containers containing food and beverages often have one or more coatings to prevent contact between the product being filled and the metal. This is to prevent or reduce product corrosion of metals and adverse effects on product quality. For the manufacture of containers of this type, such as steel or tin cans, the metal sheets used are coated with a suitable coating composition before they are formed (such as a three-piece can product) or deformed (such as a deep drawing process). When manufacturing food and beverage cans, the coatings used should have very good flexibility and low toxicity.

Epoxy novolac type coatings have been used as lacquers applied to metal can stock (for example, for three-piece cans) and baked to impart good resistance to aggressive filling products, mechanical properties and metal adhesion to the coating. Compatibility. However, many of these coatings contain 2,2'-bis(4-hydroxyphenyl)propane-bis(2,3-epoxypropyl)-ether (or its homologues), otherwise known as bisphenol A Glyceryl ether or "BADGE" (Bisphenol-A-DiGlycidyl-Ether).

It is an object of the present invention to provide a new can coating which is substantially free of BADGE (and BADGE-type components). Formulations containing BADGE are not approved for use in the food canning industry in some countries. Currently available polyester-based coatings, such as those cross-linked with amino- or isocyanate-type resins, are used as exterior coatings for three-piece cans, but are not resistant to processing when in contact with food, or do not comply with food laws, Therefore, it cannot be used as a formula for replacing paint. In view of the aforementioned shortcomings of the prior art, there is a need for a new type of can coating that does not contain BADGE (and also does not contain PVC).

Summary of the invention

To overcome the disadvantages of the prior art, the present invention provides a coating for sheet metal substrates such as metal cans or metal can stock which is substantially free of BADGE.

Another object of the present invention is to provide a coating that is substantially free of polyvinyl chloride (PVC).

It is a further object of the present invention to provide coatings for metal cans which have suitable flexibility and are safe for processing in contact with food. The coating should also be suitable for use on three-piece cans as well as deep-drawn metal cans.

An exemplary coating of the present invention comprises (a) polyester resin (20-50% by weight); (b) resole resin (1-15% by weight); and (c) solvent component (35-79% by weight ), all percentages by weight are based on the total weight of a coating that is substantially free of bisphenol-A-diglycidyl ether and bisphenol-F-diglycidyl ether (for example, "BADGE" or "BADGE-type "component), and preferably also substantially free of polyvinyl chloride. In a further preferred embodiment, the coating comprises a lubricant (0.1-2% by weight) and an acid catalyst (0-2% by weight).

Other advantages and features of the invention are discussed below. Detailed description of the invention

All weight percentages herein are based on the total weight of the coating composition including solvent.

As can be seen from the above overview, the exemplary coating composition of the present invention comprises (a) polyester resin in an amount of 20-50% by weight; (b) resole resin in an amount of 1-15% by weight, which comprises polycondensation products of homologues and formaldehyde; and (c) solvent in an amount of 35-79% by weight, all percentages by weight are based on the total weight of the coating, the coating composition is substantially free of bisphenol-A-bisphenol Glycidyl ether ("BADGE") and bisphenol-F-diglycidyl ether ("BADGE-type" components).

The term "substantially free" as used in the context of this application means that the coating composition of the present invention does not contain any BADGE, BADGE-type components or PVC, or at least does not exceed a minimum content of these components, for example, Less than 0.001% of the total weight.

An exemplary polyester resin component of the present invention comprises (a) trimethylolpropane in an amount of 0.1-10% by weight, more preferably 1-7% by weight; and in an amount of 15-30% by weight, more preferably 20-25% by weight Neopentyl glycol; at least one other polyhydric alcohol (such as ethylene glycol, propylene glycol) in an amount of 5-20% by weight, more preferably 10-15% by weight; an amount of 20-60% by weight, more preferably 20- 25% by weight of phthalic acid (including m- and p-); 10-35% by weight, more preferably 15-20% by weight of adipic acid. A polyester resin commercially available from DSM Resins in Zwolle under the tradename URALAC XP 8481 SN in The Netherlands is believed to be suitable as polyester resin component (a) of the present invention.

The resole resins (b) can be characterized as polycondensation resins prepared from phenol or phenol homologues (phenol, butylphenol, cresol, xylenol, bisphenol A) and formaldehyde. Preferably, the resole resin comprises bisphenol A, butylphenol, xylenol, or mixtures thereof, and formaldehyde. Commercially available resole resins believed to be suitable for use in the present invention are resins available under the tradename PHENODUR PR 401 from Vianova Resins AG (Germany) and PHENODUR PR 401 available from Deutsche Shell Chemie (Germany). Named EPICUREDX 200 resin.

The resin may be solvated in a solvent or solvent mixture such as n-butanol and/or butyl cellosolve or other conventional solvents for can coatings. The resin can be etherified with an alcohol (eg, butanol) and solvated in a solvent or solvent mixture. Other known solvents that can solvate polyesters and resoles include aromatic hydrocarbons (e.g., Aromatic 100 or Aromatic 150), glycol ethers/glycol ether acetates (e.g., methoxypropanol butyl cellosolve acetate, methoxypropyl acetate), alcohols (e.g., isobutanol, diacetone alcohol), ketones (e.g., methyl isobutyl ketone, isophorone) or esters (e.g., acetic acid Butyl esters, dibasic acid esters). In another exemplary coating composition of the present invention, at least two different solvents are used, preferably with different boiling ranges.

Preferably, the coating composition further comprises a lubricant, which is dispersed in the solvent in solid form. The lubricant is used in the coating composition in an amount of 0.1-2% by weight, more preferably 0.1-1% by weight. Exemplary lubricants may include polyethylene (PE), polypropylene (PP), PTFE, lanolin, carnauba wax, and petrolatum. Preferably, the lubricant comprises PE, PP or PTFE or mixtures thereof.

Preferred coating compositions also contain at least one catalyst, preferably an acidic catalyst, such as sulfonic acids (e.g. p-toluenesulfonic acid and dodecylbenzenesulfonic acid), phosphoric acid and phosphoric acid esters (e.g. monobutyl phosphate) , the amount used is 0.05-2.0% by weight, more preferably 0.05-1.0% by weight.

Accordingly, preferred coating compositions of the present invention comprise polyester resin (solids) (20-50% by weight); resol resin (solids) (1-15% by weight); lubricant (solids) (0.1-2% by weight) ; acidic catalyst (0-2% by weight); and solvent (35-79% by weight), all percentages are based on the total weight of the coating composition.

The coating can be applied to the metal substrate or panel from which the can is made, or applied to the formed can by methods such as roller coating or spraying. The preferred method of application is by roller coating on a flat metal surface prior to can formation. Preferred coating layer weights are 2-15 gsm (grams per square meter), more preferably 3-8 gsm. After application, the coating should be cured at 180°C-210°C, more preferably at 190°C-205°C, for 6-20 minutes, more preferably 8-13 minutes.

Example 1

Exemplary can coating compositions of the present invention can be prepared and used as follows. Coating batches may be formulated as follows using a mixer capable of mixing the components described below into a sufficiently uniform composition. The polyester resin comprising trimethylolpropane, neopentyl glycol and other polyols, as previously described, is preferably used in an amount of 40-85% by weight, more preferably 69-80% by weight (based on the total amount of the coating composition weight) was first added to the mixer. The polyester resin was URALAC XP 8481 SN (available from DSM Resins) solvated in a solvent mixture comprising SOLVESSO 150 and butyl cellosolve (they were used in a 4:1 weight ratio). SOLVESSO 150 aromatic hydrocarbon solvent is available from Exxon Chemical Company and is believed to have a boiling range of 186-210°C. Butyl cellosolve is also known as butyl glycol (eg, ethylene glycol monobutyl ether).

The polyester resin is added to the mixer first, and then the following other components are added during the mixing process: Preferred range% (total weight) More preferred range% (total weight) components Component description 40-85 60-80 polyester resin URALAC XP 8481 (it is about 50% resin component dissolved in Solvesso150/butyl cellosolve 4:1) 4-25% 6-15% Resole phenolic resin PHENODUR PR 401, 70% solution in butanol 0-25% 3-8% Methoxypropyl acetate optional other solvent 0-25% 3-8% Butyl Cellosolve Acetate optional other solvent 0-25% 3-10% Aromatic solvent Optionally other solvents (eg SOLVESSO 100 from Exxon) 0-5% 0.5-2.0% Mixture of methoxypropanol and phosphoric acid Optionally other solvents, where these components are preferably used in a 4:1 ratio 0.5-5.0% 0.8-3.0% lubricant in solvent Lubricants such as PTFE (solid) can be used if solvated in solvents such as SOLVESSO 100 and butyl cellosolve in a ratio of 1:1:1

An exemplary lubricant suitable for the present invention is micronized (e.g., extra fine) PFTE (polytetrafluoroethylene) modified with polyethylene wax, commercially available under the designation "TF 1780 EF" from the company Lanco Wax . A polyethylene/polypropylene lubricant supplied by Lanco Wax under the designation "PP 1350 FF" may also be used in the present invention. Lubricants in solid form should be mixed with a suitable solvent or solvent mixture, such as SOLVESSO 100 (a hydrocarbon-based solvent available from Exxon) and butyl cellosolve, in an amount sufficient to prevent aggregation of the lubricant in the mixture.

Once a homogeneous mixture of the coating composition is obtained, it can be rolled onto, for example, steel or aluminum can stock and baked preferably at about 200°C for 12-15 minutes. A BADGE-free can coating was thus produced.

The foregoing discussion is for illustration only and is not meant to limit the scope of the invention as set forth in the claims.

Claims (16)

1. A coating composition for metal capable of being formed into a container, said coating composition comprising: a) a polyester resin in an amount of 20-50% by weight; b) a phenolic resole resin in an amount of 1-15% by weight, comprising a polycondensation product of phenol or its homologues and formaldehyde; and c) a solvent component in an amount of 35-79%, all of the foregoing weight percentages being based on the total weight of the coating composition; and The coating composition is substantially free of bisphenol-A-diglycidyl ether, bisphenol-F-diglycidyl ether and homologues thereof, and polyvinyl chloride. 2. The coating composition of claim 1, further comprising at least one lubricant. 3. The coating composition of claim 2, wherein the lubricant comprises polyethylene, polypropylene, tetrafluoroethylene or mixtures thereof. 4. The coating composition of any one of claims 1-3, wherein the polyester resin comprises trimethylolpropane in an amount of 0.1-10% by weight, neopentyl glycol in an amount of 15-30% by weight, an amount of 5-20% by weight of at least one other polyol, phthalic acid in an amount of 20-60% by weight, and adipic acid in an amount of 10-35% by weight. 5. The coating composition of any one of claims 1-4, wherein the resole resin is a polycondensation product obtained from phenol, butylphenol, cresol, xylenol, bisphenol A or mixtures thereof. 6. The coating composition of claim 5, wherein the resol resin comprises bisphenol A, butylphenol, and xylenol, or mixtures thereof. 7. The coating composition of any one of claims 1-6, wherein the solvent comprises aromatic hydrocarbon, glycol ether/glycol ether acetate, n-butanol, aromatic hydrocarbon, glycol ether/glycol ether acetic acid Esters, alcohols, esters or mixtures thereof. 8. The coating composition of any one of claims 1-7, comprising polyester resin (20-50% by weight) dispersed in a solvent; resole resin (1-15% by weight) dissolved in solvent; lubricant (0.1-2% by weight) dispersed in at least one solvent in solid form; acidic catalyst (0-2% by weight); and said solvent or mixed solvent can solvate said resin and lubricant, all All component contents are based on the total weight of the coating composition. 9. The coating composition of claim 8, wherein said polyester and said resole resin are mixed together using at least two different solvents. 10. The coating composition of any one of claims 1-9, wherein the coating is applied to a metal substrate. 11. The coating composition of claim 1, wherein said polyester resin comprises trimethylolpropane and neopentyl glycol; said resole resin comprises a polycondensation resin made from phenol or phenolic homologues and formaldehyde; at least a lubricant comprising polyethylene, polypropylene, PTFE, lanolin, carnauba wax, petrolatum, or mixtures thereof; and at least two different solvents. 12. The coating composition of claim 11, wherein at least one of said two different solvents comprises an aromatic hydrocarbon solvent. 13. The coating composition of any one of claims 1-12, wherein the composition comprises at least two solvents having different boiling ranges. 14. A coated metal substrate comprising a metal sheet coated with the coating composition of any one of claims 1-13. 15. A coated can body having the coating composition of any one of claims 1-13. 16. The coating composition of claim 1, further comprising at least one catalyst.