Conversion coating compositions

Abstract

Disclosed herein are optionally phosphorous-free conversion coating compositions that meet the requirements of BPANI adhesion, dome stain resistance, and corrosion resistance, while conferring surface texture and adhesion that are critical for compatibility with lacquer and printing inks.

Description

CONVERSION COATING COMPOSITIONSTECHNICAL FIELD

[0001] The present disclosure pertains to conversion coatings for the pretreatment of metal surfaces.BACKGROUND

[0002] Conversion coatings have been used for decades and are generally composed of aqueous metal fluorides, a phosphorus containing chemical, and sometimes a detergent for the pretreatment of aluminum beverage cans.

[0003] Aluminum cans are commonly used as containers for a wide variety of products, particularly beverages. The exterior cylindrical surfaces of such cans normally are at least particularly decorated with lacquer and / or printing ink. The interior surfaces, including the inner dome, normally are protected with a sanitary lacquer, whereas the outer domes of the cans do not have lacquer or any similar coating, except possibly for a “rim coat” on the outer margin. It is considered desirable in the market for all exterior parts of the can to have a lustrous surface, even in the parts that are printed or colored, with the reflective properties that are essentially unique to polished surfaces. Therefore, for this particular field of use, a conversion coated surface must have adequate adhesion to printing inks or lacquer.

[0004] There is presently a resurgence of interest for these products due to a change in lacquer technology. Bisphenol-A (BP A) or epoxy coatings have historically represented the industry standard for container coating performance. After cure, an epoxy coating creates an almost impermeable, and nearly defect-free liner. Despite its success in containing hard to hold or corrosive beverages, lacquer technology was forced to evolve because consumers have demanded products that do not contain Bisphenol-A (BP A). Bisphenol-A has become an emerging concern in relation to possible estrogen-like activity and potential endocrine effects. Efforts are ongoing to implement limits on discharge of BPA into the environment.

[0005] In response, manufacturers have moved to Bisphenol-A non-intent (BPANI) lacquers that are based on alternative chemistries, such as acrylic, polyester, vinyl, and others. A challenge in using these alternative chemistries is achieving adequate pre-cleaning of container surfaces. Due to BPANI lacquers being highly susceptible to surface quality comingout of the washer can cleanliness becomes critical. These lacquers are more sensitive than BPA to any residual soils remaining on the can. Remaining soils are likely not to be coated which can result in poor adhesion and subsequent loss of performance. Thus, cans that do not have impeccably cleaned surfaces are likely to exhibit pinholes and defects in the coatings. These lacquers are also susceptible to thinning from contact with beverages, particularly those that contain natural flavors that effectively act as paint thinners. Thus, there is a need to improve the container surfaces and pretreatments to support BPANI lacquer performance.

[0006] Conversion coatings have been used in the aluminum beverage container industry, also referred to as beverage can industry, to prevent staining of the can dome after retort or pasteurization. Existing products include pre-treatments or conversion coatings that are based on phosphorus, metal fluorides, and detergents. Some are designed specifically with water quality in mind, but still contain phosphorus. There exist market needs for the elimination of phosphorus from the aluminum beverage container production line such as environmental regulation of wastewater treatment. Phosphorus-free conversion coatings have yet to be developed that meet the needs of the aluminum container market, e.g. food contact safety, speed of application, lacquer compatibility and the like.SUMMARY

[0007] Embodiment 1. An aqueous conversion coating composition for pretreatment of a metal surface comprising: dissolved and / or dispersed zirconium, measured as elemental Zr, in a concentration of about 50 to 250 ppm; dissolved and / or dispersed titanium, measured as elemental Ti, in a concentration of about 20 to 100 ppm; a tridentate or quadridentate chelator in a concentration of about 0.5 to 20 ppm; and, free fluoride in a concentration of about 150 to 2,000 ppm, wherein the composition has a pH of about 2.3 to 3.3.

[0008] Embodiment 2. The conversion coating composition according toEmbodiment 1, wherein the zirconium is present in a concentration of about 60 to 190 ppm.

[0009] Embodiment 3. The conversion coating composition according to Embodiment 1 or Embodiment 2, wherein the titanium is present in a concentration of about 20 to 70 ppm.

[0010] Embodiment 4. The conversion coating composition according to any preceding Embodiment, wherein the tridentate or quadridentate chelator is present in a concentration of about 1 to 10 ppm.

[0011] Embodiment 5. The conversion coating composition according to any preceding Embodiment, comprising a tridentate chelator, preferably the tridentate chelator comprises methylglycinediacetic acid or a salt thereof.

[0012] Embodiment 6. The conversion coating composition according to any preceding Embodiment, wherein the zirconium and titanium are present in a ratio of about 2-4 : 1, about 2.5-3.5 : 1, or about 3 : 1.

[0013] Embodiment 7. The conversion coating composition according to any preceding Embodiment, wherein the free fluoride is present at -110 to -60 relative millivolts (RMV).

[0014] Embodiment 8. The conversion coating composition according to any preceding Embodiment, further comprising colloidal silica, polyacrylic acid, a detergent, phosphoric acid, or any combination thereof.

[0015] Embodiment 9. The conversion coating composition according to any preceding Embodiment, wherein the conversion coating composition does not include a source of phosphorus.

[0016] Embodiment 10. A method for pretreating a metal surface comprising contacting the metal surface with a conversion coating composition according to any one of Embodiments 1-9 for a time sufficient to form a conversion coating on the metal surface.

[0017] Embodiment 11. The method according to Embodiment 11, wherein the conversion coating composition contacts the metal surface by spraying.

[0018] Embodiment 12. The method according to Embodiment 10 or Embodiment 11, wherein conversion coating composition is contacted with the metal surface while the conversion coating is at a temperature of about 30-50°C.

[0019] Embodiment 13. The method according to any one of Embodiments 10-12, further comprising cleaning the metal surface with an aqueous acid or alkali agent, and optionally rinsing, prior to contacting the metal surface with the conversion coating composition.

[0020] Embodiment 14. A conversion coating that is produced by contacting a metal surface with a conversion coating composition according to any one of Embodiments 1-9.

[0021] Embodiment 15. A conversion coating on a metal surface that is produced by a method according to any one of Embodiments 10-13.

[0022] Embodiment 16. An article having a metal surface comprising a conversion coating that is produced by contacting the metal surface with a conversion coating composition according to any one of Embodiments 1-9.

[0023] Embodiment 17. An article having a metal surface comprising a conversion coating that is produced by a method according to any one of Embodiments 10-13.

[0024] Embodiment 18. A container comprising a metal surface bearing a conversion coating that was produced by contacting the surface with a conversion coating composition according to any one of Embodiments 1-9.

[0025] Embodiment 19. A container comprising a metal surface bearing a conversion coating that was produced by a method according to any one of Embodiments 10- 13.

[0026] Embodiment 20. A metal container for food and beverage contact having a layer of conversion coating comprising oxides of Zr, oxides of Ti, and acrylic polymer.

[0027] Embodiment 21. The metal container of Embodiment 20 having a surface roughness that is characterized by a surface energy of at least 50 mN / m.

[0028] Embodiment 22. The metal container of Embodiment 20 further comprising a lacquer layer on at least a portion of the conversion coating layer, the lacquer layer exhibiting an adhesion that is in accordance with ASTM D3359 method B.

[0029] Embodiment 23. A metal pretreatment process comprising steps of cleaning a metal surface of an article with an acidic or alkaline cleaner composition; conversion coating the cleaned metal surface with conversion coating composition according to any one of Embodiments 1-9; applying a mobility enhancer and optionally drying in place; and, optionally applying lacquer, labeling, or both.

[0030] The present disclosure provides aqueous conversion coating bath compositions for pretreatment of a metal surface, preferably aluminum or its alloys, the working composition comprising: dissolved and / or dispersed zirconium in a concentration of about 50 to 250 ppm; dissolved and / or dispersed titanium in a concentration of about 20 to100 ppm; a poly dentate chelator, preferably a tridentate or quadridentate chelator, in a concentration of about 0.5 to 20 ppm; and, free fluoride in a concentration of about 150 to 2,000 ppm, wherein the composition has a pH of about 2.3 to 3.3.

[0031] Also disclosed herein are methods for pretreating a metal surface comprising contacting the metal surface with a conversion coating composition according to the present disclosure for a time sufficient to form a conversion coating on the metal surface.

[0032] The present disclosure further provides conversion coatings that are produced by contacting a metal surface with a conversion coating composition according to any disclosed embodiment, as well as conversion coatings that are produced according to any embodiment of the present methods for pretreating a metal surface.

[0033] Also provided are articles and containers respectively having a metal surface comprising a conversion coating according to any disclosed embodiment, or that is produced according to a present method for pretreating a metal surface.

[0034] The present disclosure also provides metal containers for food or beverage contact having a layer of conversion coating comprising oxides of Zr, oxides of Ti, and acrylic polymer as described herein.

[0035] Further provided are metal pretreatment processes, in particular for containers, such as food or beverage cans, comprising steps of cleaning a metal surface of an article with an acidic or alkaline cleaner composition; conversion coating the cleaned metal surface with a conversion coating composition according to any embodiment disclosed herein; applying a mobility enhancer and optionally drying in place; and, optionally applying lacquer, decoration, or both. In preferred processing of cans, steps of cleaning, conversion coating, and mobility enhancer application steps , with rinsing between steps, if desirable as is known in the art; followed by decoration, lacquer, and over varnish may take place in a continuous or semi -continuous process.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIGS. 1 A-1F provide SEM images of an uncoated Al substrate, conversion coatings on Al substrates produced using comparative compositions and compositions according to the present disclosure, respectively, as further described herein.

[0037] FIG. 2 provides a TEM image of a conversion coating that was produced using an inventive composition.

[0038] FIG. 3 A depicts phase angle and FIG. 3B depicts impedance measurements of a bare Al substrate, comparative conversion coatings and a conversion coating according to the present disclosure using impedance spectroscopy.

[0039] FIGS. 4A-4F provide additional SEM images of an uncoated aluminum substrate (4A) and conversion coatings produced using compositions according to the present disclosure and modifications thereof, as further described herein.

[0040] FIG. 5 is a graph of results of an assessment of the effect of pH and RMV on dome stain using conversion coatings compositions according to the present disclosure that do not contain phosphoric acid.

[0041] FIG. 6 illustrates the results of an assessment of the effect of pH and RMV on dome stain using conversion coatings compositions according to the present disclosure that contain phosphoric acid.DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0042] The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying examples, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific products, methods, conditions or parameters described and / or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention.

[0043] The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in their entirety.

[0044] As employed above and throughout the disclosure, the following terms and abbreviations, unless otherwise indicated, shall be understood to have the following meanings.

[0045] In the present disclosure the singular forms “a”, “an”, and “the” include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to “a compound” is a reference to one or more of such compounds and equivalents thereof known to those skilled in the art, and so forth. Furthermore, when indicating that a certain chemical functional group “may be” X, Y, or Z, it is not necessarily intended by such usage to exclude other choices for the functional group; for example, a statement to the effect that a functionalgroup “may be alkyl, aryl, or amino” does not necessarily exclude other choices for the functional group, such as halo, aralkyl, and the like.

[0046] When values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. As used herein, “about X” (where X is a numerical value) preferably refers to ±10% of the recited value, inclusive. For example, the phrase “about 8” may refer to a value of 7.2 to 8.8, inclusive; as another example, the phrase “about 8%” may refer to a value of 7.2% to 8.8%, inclusive. Also, when the term “about” precedes a range, it is understood that the term modifies both recited endpoints and all points embraced within the range. For example, the phrase “about 1-10” is understood to mean “about 1 to about 10”, as well as “about x”, wherein x refers to any value between 1 and 10. Where present, all ranges are inclusive and combinable. For example, when a range of “1 to 5” is recited, the recited range should be construed as including ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 & 4-5”, “1-3 & 5”, and the like. In addition, when a list of alternatives is positively provided, such listing can be interpreted to mean that any of the alternatives may be excluded, e.g., by a negative limitation in the claims. For example, when a range of “1 to 5” is recited, the recited range may be construed as including situations whereby any of 1, 2, 3, 4, or 5 are negatively excluded; thus, a recitation of “1 to 5” may be construed as “1 and 3-5, but not 2”, or simply “wherein 2 is not included.” In another example, when a listing of possible choices for a functional group including “hydrogen, alkyl, and aryl” is provided, the recited listing may be construed as including situations whereby any of “hydrogen, alkyl, and aryl” is negatively excluded; thus, a recitation of “hydrogen, alkyl, and aryl” may be construed as “hydrogen and aryl, but not alkyl”, or simply “wherein the functional group is not alkyl”.

[0047] As used herein, a “conversion coating composition” represents the wet chemistry that reacts with a metal surface to form a conversion coating.

[0048] A “conversion coating” is a layer or film bonded to a metal surface, deposited by reaction of the conversion coating composition with the metal surface. The conversion coating generally comprises chemical elements from the metal surface, the conversion coating composition, and reaction products thereof.

[0049] In this disclosure, the terms “container” and “can” are used interchangeably, generally referring to a hollow receptacle for holding goods, typically formed partially or entirely from metal (e.g., sheet metal), and having a removable closure sealed against leakage of contents. More specifically, containers / cans for food and / or beverages are commonlyknown having been sold at grocers’ for more than 100 years, and there is still potential for improvement in processing containers in high speed processing lines.

[0050] Throughout the description, unless expressly stated to the contrary: percent, "parts of, and ratio values are by weight or mass; molecular weight (MW) is weight average molecular weight unless otherwise specified; the word "mole" means "gram mole", and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical or in fact a stable neutral substance with well-defined molecules.

[0051] As described above, alternatives to epoxy-based materials for the conversion coating of metal surfaces, including those of beverage and food containers, have been sought. The present inventors have developed conversion coating compositions and methods for using such compositions to provide conversion coating that not only fulfill this objective by meeting the requirements of BisPhenol-A Non-Intent (BPANI) coating adhesion, dome stain resistance, and corrosion resistance, but also, in certain embodiments, represent a more environmentally friendly alternative by satisfying the market need for eliminating phosphorus from the process line.

[0052] In one embodiment, the present disclosure provides aqueous conversion coating bath compositions, for pretreatment of a metal surface, comprising: dissolved and / or dispersed zirconium, measured as elemental Zr, in a concentration of about 50 to 250 ppm; dissolved and / or dispersed titanium, measured as elemental Ti, in a concentration of about 20 to 100 ppm; a tridentate or quadridentate chelator in a concentration of about 0.5 to 20 ppm; and, free fluoride in a concentration of about 150 to 2,000 ppm, wherein the composition has a pH of about 2.3 to 3.3.

[0053] In certain embodiments, the zirconium is present in the conversion coating bath composition in an amount of about 60-190 ppm, 70-150 ppm, 75-110 ppm, or 80-100 ppm, for example, in an amount of about, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200 ppm, measured as elemental Zr.

[0054] The zirconium may be provided in the composition from any suitable source, preferably water soluble source of zirconium, such as fluorozirconic acid (for example, as a 20% or 45% solution). Other sources of zirconium may include, for example, zirconiumnitrate, zirconium (IV) acetate, salts of fluorozirconic acid, and the like. Combinations of zirconium sources may be used.

[0055] In certain embodiments, the titanium is present in the conversion coating bath composition in an amount of about 20-90 ppm, 22-80 ppm, 25-75 ppm, 27-70 ppm, 27-60 ppm, 29-50 ppm, or 30-40 ppm, for example, in an amount of about 15, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 68, 70, 80, 90 or 95 ppm, measured as elemental Ti.

[0056] The titanium may be provided in the composition from any suitable source, preferably water soluble source of titanium, such as fluorotitanic acid (for example, as a 60% solution). Other sources of titanium may include, for example, titanium nitrate, titanium (IV) acetate, salts of hexafluor otitanic acid and the like.

[0057] In certain embodiments, the zirconium and titanium may be present in the conversion coating composition, bath and / or concentrate, in a ratio ranging from about 0.5 : 1 to 5.0 : 1, 1 : 1 to 4.0 : 1, 2 : 1 to about 3.75 : 1, about 2.5-3.5 : 1, 2.75 to 3.25 : 1 or about 3 : 1. For example, the zirconium and titanium may be present in the conversion coating composition in a ratio ranging from in increasing order of preference, at least about 0.5, 1.0, 1.5, 2.0, 2.1, 2.25, 2.3, 2.4, 2.5, 2.6, or 2.75 Zr to 1 Ti and up to, in increasing order of preference, no more than about 6.0, 5.0, 4.0„ 3.8, 3.75, 3.6, 3.5, 3.4, 3.3, 3.25, 3.1, or 3.0 Zr to 1 Ti.

[0058] It has been surprisingly found that the inclusion of a polydentate chelator, preferably a molecule having at least three or four chelating functional groups, also referred to herein as a tridentate or quadridentate chelator, in the conversion coating bath and / or concentrate compositions according to the present disclosure confers beneficial characteristics. Chelating functional groups will be understood by those of skill in the art to mean functional groups capable of interacting with metal ions to form stable, often water-soluble complexes (sometimes referred to as sequestering). Desirable chelating functional groups useful herein include acidic groups and coordinating groups particularly useful in chelating positively charged metal ions. Acidic groups may bond with a metal ion by loss of a hydrogen ion, while coordinating groups have electrons useful in stabilizing the metal ion in the chelate complex.

[0059] The chelator inhibits, preferably prevents, contamination of surfaces to be coated by hard water contaminants, such as Ca ions and Mg ions found in the conversion coating bath. Further, presence of the chelator improves surface characteristics of theconversion coating deposited on metal surfaces, including desirable texture to the conversion coated surface and improved adhesion of lacquer & printing inks to conversion coated surfaces, both features being critical for compatibility with lacquer and printing inks. Without being bound by a single theory, it appears that undesirable cations, for example calcium and magnesium cations, are isolated from the conversion coating bath by complexing with the chelator thereby reducing undesirable interaction between these cations and the coating bath and / or metal surfaces. In some embodiments, the cation / chelator complex may form solids (sometimes referred to as metal chelate precipitates) that are readily removed by conventional methods.

[0060] Applicant tested six different chelators having varied molecular weight and / or different numbers of chelating functional groups and / or types of functional groups. Out of the six chelators which had different types of chelating functional groups, carboxylic acid and carboxylate (COOH and COO-) functional group-containing molecules are preferred. The number of functional groups present desirably may be in increasing order of preference of 2, 3, or 4 functional groups. Generally, chelators comprising three (tridentate) or four (quadri dentate) chelating functional groups showed superior performance in complexing Ca ions and Mg ions. Exemplary tridentate or quadridentate chelators include methylglycinediacetic acid (“MGDA”, tridentate) or a salt thereof; or, glutamate diacetate (“GLDA”, quadridentate) or a salt thereof. One example of an alternative embodiment comprises addition of bidentate chelators, such as dimethyl and / or diethyl succinates and the like, to the conversion coating composition, without or preferably with a tridentate or quadridentate chelator. Chelators comprising three or four chelating functional groups capable of complexing cations, e.g., calcium and magnesium, found in the working bath are preferred. Other chelators having different numbers or types of chelating functional groups may be used in the compositions, provided that they do not negatively impact the objects of the invention. Negative impacts may include being unsuitable for food / beverage contact, inhibiting deposition of a conversion coating layer and / or causing container dome staining (e.g., nitrotriotris(methylenephosphonic) acid or hydroxyethylethylenediaminetriacetic acid (HEDTA)) or a salt thereof; or having undesirable environmental impact (e.g., EDTA), solubility characteristics or interaction with other components of the conversion coating composition.

[0061] The tridentate or quadridentate chelator may be present in the coating bath composition in an amount of about 10-100 ppm, 10-40 ppm, 10-90 ppm, 20-80 ppm, 30-70ppm, or 40-60 ppm, for example, in an amount of about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 ppm. Higher amounts of chelator may be added provided they do not unduly interfere with deposition of the conversion coating or other objects of the invention, e.g., potentially chelate other metal ions desired in the coating such as Zr and Ti. It is preferred to maintain chelator amounts in the range of 1-20 ppm, if only for cost savings.

[0062] In the present conversion coating bath compositions, the free fluoride may be present in a concentration of about 150-2,000 ppm, such as 200-1,500 ppm, 250 to 1200 ppm, 300-1,000 ppm, 350-800 ppm, 350-600 ppm, or 400-500 ppm, or in an amount of about 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500 ppm. When expressed in terms of relative millivolts (RMV), measured using a fluoride ion selective electrode (e.g., Thermo Scientific™ Orion™ Fluoride Electrode commercially available from Fisher Scientific), as known by those skilled in the art, the amount of free fluoride in the present compositions may be in a range of about -140 to -30, -110 to -60, -100 to -70, or -90 to -80 RMV, such as -110, -105, -100, -95, - 90, -85, -80, -75, -70, -65, or -60.

[0063] The conversion coating bath compositions may have a pH of about 2.0 to 3.5, or 2.2 to 3.4, provided that the objects of the invention are still achievable. Composition pH of 2.3 to 3.3 is desirable. For example, the pH of the conversion coating compositions may be about 2.3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3.0, 3.05, 3.1, 3.15, 3.2, 3.25, or 3.3.

[0064] The present conversion coating bath compositions may optionally include one or more further components. For example, the compositions may include colloidal silica. When included, colloidal silica may be present in the bath compositions in an amount of about 1-30 ppm, desirably 10-27 ppm, or 17.5-25 ppm, for example at least about 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 ppm and preferably no greater than 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or 35 ppm.

[0065] The concentrate compositions useful in preparing the conversion coating bath according to this disclosure may alternatively or additionally include a component of polyacrylic acid polymer and / or a salt thereof , desirably a homopolymer, in an amount of about 0.15 to 6 wt.%, such as at least about 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.3, 1.5, 1.8, 2, 2.3, or 2.5 wt.%, and preferably not more than about 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 5, 5.5, or 6 wt.%. Examples of polyacrylic acid polymer which may be used for the inventioninclude those with a weight average molecular weight of preferably at least about 45,000 to about 80,000 g / mol. Sources of commercially available polyacrylic acid polymers suitable for use in the invention include those sold under the tradenames Acusol™, Carbomer™, and Acumer™ by The Dow Chemical Company, Wilmington Del., USA; AQUATREAT® commercially available from AkzoNobel Strawinskylaan 2555 1077 ZZ Amsterdam Postbus 75730 1070 AS Amsterdam, as well as other sources of such materials, e.g. Polysciences Inc.

[0066] The compositions may alternatively or additionally include a detersive dispersing agent, different from the polyacrylic acid polymer component. Suitable detersive dispersing agents may include water soluble materials having water softening, sequestering and optionally soil and / or oil dissolution properties, which are compatible with the acidic aqueous conversion coating bath composition. The dispersing agent component in compositions according to the invention disperses materials in the conversion coating composition by one or more of, for example, increasing solubility and sequestration of soils and undesirable cations, such as those found in hard water, reducing or preventing formation of hard water soap scum. The dispersing agent component may also contribute to reduced redeposition of suspended materials onto the to-be-coated substrate surfaces in contact with the coating composition. In one embodiment, the dispersing agent may comprise polyacrylic acid, different from the polyacrylic acid polymer, and / or phosphorus. The dispersing agent may assist in dispersing solids (and possibly liquid in micelles) in the liquid coating composition. Exemplary materials to be dispersed may include hydrophobic material, drag in contaminants such as soils, or non-intentionally included material having low hydrophile to lipophile balance & a low HLB value, for example less than 10, 9, 8, 7, 6. The polyacrylic acid dispersing agent may have a pH in a range of about 1 to 3.5, preferably 1.5 to 2.5.

[0067] In one embodiment, the dispersing agent component may comprise polyacrylic acid homopolymer or copolymer, preferably a homopolymer, having an average molecular weight in a range of about 50,000 to 450,000 g / mol or more, provided that the polymer is water soluble. In some embodiments the dispersing agent may comprise a polymer having weight average MW of at least about 45,000, 50,000, 75,000, 80,000, 85000, 90000, 95000 100,000 g / mol and preferably not more than about 150,000 175,000, 200,000 or 250,000 g / mol. The dispersing agent component may be provided in concentrate compositions of the invention in an amount of about 1-10 wt.%, such as about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10 wt.%.

[0068] The concentrate compositions may optionally include phosphoric acid. The phosphoric acid may be provided in the concentrate compositions in an amount of about 0.2-3 wt.%, such as about 0.2. 0.3, 0.4, 0.5 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6. 1.7, 1.8, 1.9. 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6. 2.7, 2.8, 2.9, or 3 wt.%. In some preferred embodiments, the conversion coating composition contains no added sources of phosphorus. Desirably, phosphorus is present in amounts of less than 1 wt.%, 1 gram / Liter, or Ippm and preferred compositions are free of phosphorus.

[0069] The present conversion coating concentrate compositions may optionally include one or more further components. For example, the compositions may include colloidal silica. When present, colloidal silica may be in the concentrate compositions in an amount of about 1 to 8 wt.%, such as about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8 wt.%. In some embodiments, the compositions include only one of colloidal silica, polyacrylic acid, dispersing agent, or phosphoric acid. In other embodiments, the compositions include any two of colloidal silica, polyacrylic acid, dispersing agent, or phosphoric acid. In other embodiments, the compositions include any three of colloidal silica, polyacrylic acid, dispersing agent, or phosphoric acid. In certain embodiments, the compositions include each of colloidal silica, polyacrylic acid, dispersing agent, and phosphoric acid.

[0070] For a variety of reasons, it is preferred that inventions (e.g., compositions, concentrates, methods and articles of manufacture) disclosed herein may be made in the absence of certain ingredients, and, i.e., be free of certain materials whether added or generated in situ other than minor amounts of contaminants, or may be free or substantially free from many ingredients used in compositions for similar purposes in the prior art. Specifically, it is increasingly preferred in the order given, independently for each preferably minimized ingredient listed below, that at least some embodiments according to the invention contain less than 1.0, 0.5, 0.35, 0.10, 0.08, 0.04, 0.02, 0.01, 0.001, or 0.0002 percent, more preferably said numerical values in grams per liter, more preferably said numerical values in ppm, of each of the following constituents: silane and / or siloxane-based materials, epoxy resin, including bisphenol-based resins, chemicals with at least one aliphatic perfluorocarbon functional group (e.g., -CnF2n-) (PFAS); waxes, whether from plants, animals, or mineral origin, e.g. carnauba wax, beeswax, Montan wax, petrochemical-based waxes, synthetic waxes, or esters of long-chain fatty acids with long-chain monohydric alcohols; copper; oxidizing agents such as peroxyacids, permanganate, perchlorate, chlorate, chlorite,hypochlorite, perborate; hexavalent chromium, trivalent chromium, sulfuric acid and sulfate, nitric acid and nitrate ions; formaldehyde, formamide, hydroxylamines, cyanides, cyanates; rare earth metals; boron, e.g., borax, borate; strontium; chloride, bromide or iodide; or any combination thereof. In some embodiments, the inventions contain only non-intentionally added amounts the above-listed constituents, such as drag-in from another stage or trace amounts from an added component, and preferably the invention is free of one or more of these constituents.

[0071] In certain embodiments, the conversion coating composition does not include a source of phosphorus. Accordingly, the present compositions may be substantially phosphorus-free, meaning that the compositions do not include phosphorus in an amount exceeding trace quantities that are incidentally present deriving from one or more of the materials that are intentionally included in the composition. For example, at least some embodiments according to the invention contain no more than 1.0, 0.5, 0.35, 0.10, 0.08, 0.04, 0.02, 0.01, 0.001, or 0.0002 percent, more preferably said numerical values in grams per liter, more preferably said numerical values in ppm, of phosphorus.

[0072] The present disclosure also provides conversion coating concentrates that can be subjected to dilution in order to form the present conversion coating bath compositions described herein. Preferably, the dilution is performed using water, such as deionized (DI) water, but may be made with tap or city water provided that any materials in such water sources due not prevent or unduly interfere with objects of the invention. The concentrates generally comprise a source of zirconium, a source of titanium, a tridentate or quadridentate chelator, and a source of free fluoride.

[0073] In the present concentrates, the source of zirconium may be present in an amount of about 6-10 wt.%, such as about 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9 wt.% calculated as the source of zirconium being fluorozirconic acid 45% solution. Other sources of zirconium may include those described herein present in amounts necessary to achieve an equivalent amount of zirconium in the concentrate as may be readily calculated based on the mass percent of zirconium in the source selected.

[0074] The source of titanium may be present in the concentrates in an amount of about 3-6 wt.%, such as about 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5 wt.%, calculated as the source of titanium being fluorotitanic acid a 60% solution. Other sources of titanium may include those described herein present in amounts necessary to achieve an equivalentamount of titanium in the concentrate as may be readily calculated based on the mass percent of titanium in the source selected.

[0075] The tridentate or quadridentate chelator may be present in the concentrates in an amount of about 0.2 to 2.00 wt.%, such as about 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2 wt.%. Exemplary tridentate or quadridentate chelators are described above in connection with the inventive conversion coating compositions.

[0076] The source of free fluoride may be the same as or different from one of the other components of the present concentrates. For example, when the source of zirconium is fluorozirconic acid, this will also represent a source of free fluoride. In such instances, the weight percentage contribution of the source of free fluoride need not be accounted for separately. When the source of free fluoride is not also a source of one of the other components, z.e., the source of free fluoride represents an independent component, then the amount of such a source of free fluoride is such that upon dilution of the concentrate, the amount of free fluoride in the resulting conversion coating bath composition is about 150- 2,000 ppm, such as 200-1,500 ppm, 250 to 1200 ppm, 300-1,000 ppm, 350-800 ppm, 350-600 ppm, or 400-500 ppm, or in an amount of about 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500 ppm. When expressed in terms of relative millivolts (RMV), the amount of free fluoride in the compositions that result from dilution of the present concentrates may be about -110 to -60, -100 to -70, or -90 to -80 RMV, such as -110, -105, -100, -95, -90, -85, -80, -75, -70, -65, or -60.

[0077] Generally, the degree of dilution of the concentrate to form the conversion coating bath may be in a range of at least about, in increasing order of preference 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or 0.52 wt.% and up to an upper limit of about 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.1, 1.2, 1.3, 1.4, or 1.5 wt.%; in preferred embodiments the range is at least about 0.35 wt.% to up to about 1 wt.%. More preferably about 0.5wt.%, this dilution may be modified particularly in using a two-package concentrate where ratios of components must be accounted for as is known in the art.

[0078] When the conversion coating composition is to include one or more of the optional components described above, the present concentrates may also contain such components. For example, the concentrates according to the present disclosure can include colloidal silica, polyacrylic acid polymer, a dispersing agent, phosphoric acid, or anycombination thereof. In certain embodiments, the concentrates include polyacrylic acid polymer, for example, in an amount of about 0.75 to about 1.5 wt.%, such as in an amount of about 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5 wt.%. The polyacrylic acid polymer may be from any available source, may be a homopolymer, copolymer or terpolymer; and is desirably a homopolymer . For example, the polyacrylic acid polymer may be selected from any of the embodiments described above in connection with the inventive conversion coating compositions. The concentrate may also be provided in parts, for convenience, a two-pack, meaning the concentrate is separately packaged in two containers. For example, a two-pack may include Part (1) metal source, fluoride source (which may be the same compound, e.g., FfcZrFe or FFTiFe), chelator, phosphoric acid and water (preferably DI water); and Part (2) polyacrylic acids, silica, organic additives with or without chelator and optionally water (preferably DI water). A working bath may be prepared, as is known in the art, by adding sufficient amounts of each concentrate to achieve bath concentrations as detailed herein. Though not preferred various components may be omitted from the concentrate(s) and added directly to the bath to form a conversion coating bath composition within the scope of the invention.

[0079] Also disclosed herein are methods for pretreating a metal surface comprising contacting the metal surface with a conversion coating composition according to the present disclosure for a time sufficient to form a conversion coating on the metal surface. The metal surface may comprise steel, tin, aluminum, magnesium, nickel, zinc, titanium, or any combination or alloy thereof. In certain embodiments, the metal surface is aluminum, such as a portion of an aluminum container, e.g., a beverage can. Contacting the metal surface with the conversion coating composition may include immersing the metal surface in a bath containing the conversion coating bath composition, spraying the conversion coating bath composition onto the metal surface or similar application means know to those of skill in the art.

[0080] In some embodiments, the metal surface is contacted with the conversion coating composition by spraying. The duration of the period of spraying the metal surface with the conversion coating composition can be about 5-60 seconds, 10-45 seconds, 10-30 seconds, or 12-25 seconds, such as about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 seconds. The characteristics of the device that is used for spraying, the distance of the spray device from the metal surface, the pressure of the spray, and other relevant parameters may be in accordance with any suitable industrial spray process.

[0081] The temperature of the conversion coating composition when the metal surface is contacted with the conversion coating bath composition is preferably about 30- 50°C. In other words, the conversion coating composition is preferably at a temperature of about 30-50°C when the composition is in contact with the spray nozzle in the spraying process.

[0082] The present methods may further comprise cleaning the metal surface with an aqueous acid or alkali agent, and optionally rinsing, prior to contacting the metal surface with the conversion coating composition. Aqueous acid compositions that are suitable for this purpose include, for example, those sold under the trade name Bonderite C-IC, commercially available from Henkel Corp. Suitable alkali agents include, for example, KOH optionally with surfactant. When performed, rinsing of the metal surface following cleaning may employ water, such as deionized (DI) water.

[0083] The present disclosure further provides a conversion coating layer deposited on a metal surface, desirably a metal container surface, preferably an aluminum or aluminum alloy. The conversion coating layer desirably is produced by contacting a metal surface with a conversion coating composition according to any embodiment disclosed herein, as well as conversion coating layers that are produced according to any embodiment of the present methods for pretreating a metal surface. As described in the examples, infra, the inventive conversion coatings confer a unique surface texture generating a particular morphology, as shown in the Examples, providing excellent adhesion to lacquer or printing inks.

[0084] Also provided are articles and containers respectively having a metal surface comprising a conversion coating according to any disclosed embodiment, or that is produced according to a present method for pretreating a metal surface. As noted, the metal surface may comprise steel, aluminum, magnesium, nickel, zinc, titanium, or any combination or alloy thereof. In certain embodiments, the metal surface is aluminum. The container may be any type of metal -containing vessel, including those that are for housing a food or beverage material, examples of which include cans, cannisters, aerosol containers, tubes, boxes, metallic pouches, tins, or drums. The articles may be containers of the above-described types, but could also be, for example, containers or vessels that include a material in addition to the metal surface that is contacted with the conversion coating. For example, the article may be a container with a metal closure and a non-metallic body, or a non-metallic closure with a metal-containing body. Those of ordinary skill in the art can readily appreciate the types ofcontainers and articles that would benefit from the inclusion of conversion-coated metal surfaces, as described herein.

[0085] The present disclosure also provides metal containers for food or beverage contact having a layer of conversion coating comprising oxides of Zr, oxides of Ti, and acrylic polymer, optionally comprising phosphorus in the form of for example metal phosphates, and optionally trace amounts of substrate metal eluted from the substrate surface during coating, e.g., aluminum or iron. In a preferred embodiment, the quantity of substrate metal in the conversion coating is minimized, e.g., outside ordinary detection limits for equipment used in the art. In certain embodiments, the coating weight, measured as elemental Zr in the conversion coating layer, is about 3-20 mg / m2, 5-15 mg / m2, or 6-12 mg / m2. In certain embodiments, the coating weight measured as elemental Ti in the conversion coating layer is 3-20 mg / m2, 4-15 mg / m2, or 5-13 mg / m2. In some embodiments the molar ration of Ti : Zr, measured as elemental metal, ranges from about 2: 1 to 0.5: 1, e.g., in a range of about 1.75: 1, 1.5: 1, 1.25: 1, 1.0: 1.0, or 0.75: l

[0086] The metal surface of the container may be any of the types described above in connection with the inventive containers and articles. As noted, the present conversion coatings confer a particular morphology providing a beneficial degree of surface roughness to the as-coated metal surfaces. In some embodiments, the metal container having a layer of the inventive conversion coating may have a surface roughness that is characterized by a surface energy of at least 50 mN / m, such as about 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, or 72 mN / m, such as about 50-72 mN / m, or about 50 mN / m to complete wetting (greater than 72 mN / m). In some embodiments, the layer of conversion coating has a surface roughness that is characterized by a surface energy of about 65 mN / m to complete wetting (greater than 72 mN / m).

[0087] In comparison, cleaned-only bare metal surfaces typically have a roughness that is characterized by a surface energy of about 40.5-49 mN / m that is lower and thus less wettable than surfaces coated with compositions of this disclosure. Likewise, metal surfaces that bear a coating formed from commercially available conversion coating compositions, e.g., zinc phosphate, have a roughness that is characterized by a surface energy of about 44.9-46 mN / m, which is lower and thus less wettable than surfaces coated with compositions of this disclosure.

[0088] The metal containers according to the present disclosure may further comprise a lacquer layer on at least a portion of the conversion coating layer, wherein thelacquer layer exhibits excellent adhesion when tested according to ASTM D3359 method B Cross-Cut Tape Test. Measured on a scale of OB (worst) to 5B (best), the metal containers conversion coated according to the invention exhibited lacquer adhesion of at least Grade 4B (less than 5% loss) and mostly 5B (0% loss).

[0089] The present disclosure also provides metal pretreatment processes comprising the steps of cleaning a metal surface of an article with an acidic or alkaline cleaner composition; conversion coating the cleaned metal surface with a conversion coating composition according to any embodiment disclosed herein; contacting the conversion-coated metal surface with a mobility enhancer and optionally drying in place; and, optionally applying lacquer, labeling, or both.

[0090] The metal surface may comprise, for example, steel, aluminum, magnesium, nickel, zinc, titanium, or any combination or alloy thereof. In certain embodiments, the metal surface is aluminum. The article may be a container of any type described supra, but could also be, for example, containers or vessels that include a material in addition to the metal surface that is contacted with the conversion coating. For example, the article may be a container with a metal closure and a non-metallic body, or a non-metallic closure with a metal-containing body. Those of ordinary skill in the art can readily appreciate the types of containers and articles that would benefit from the inclusion of conversion-coated metal surfaces.

[0091] The cleaning of the metal surface with an acidic or alkaline cleaner may be conducted according to any acceptable parameters and followed by rinsing, with water, in accordance with conventional procedures. Acidic compositions that are suitable for this purpose include, for example, acidic cleaners containing sulfuric acid that run at about 110°F to 140°F (about 43 °C to 60°C) at a free acid of 8 and those sold under the trade name Bonderite C-IC, commercially available from Henkel Corp. Suitable alkaline cleaners include sodium and potassium containing cleaners, for example, KOH-based, optionally with surfactant, run at about 110°F to 140°F (about 43°C to 60°C) exposure time 30 to 90 seconds.

[0092] The conversion coating deposition using any embodiment of a conversion coating composition according to the present disclosure may be accomplished by contact with the metal surface according to any suitable process. Contacting the metal surface with the conversion coating composition may include immersing the metal surface in a bath containing the conversion coating composition, or spraying, painting, or rubbing the conversion coating composition onto the metal surface. In some embodiments, the metal surface is contactedwith the conversion coating composition by spraying. The duration of the period of spraying the metal surface with the conversion coating composition can be about 5-60 seconds, 10-45 seconds, 10-30 seconds, or 12-25 seconds, such as about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 seconds. The characteristics of the device that is used for spraying, the distance of the spray device from the metal surface, the pressure of the spray, and other relevant parameters may be in accordance with any suitable industrial spray process. Deposition of the inventive conversion coating layer on the metal surface is desirably followed by at least one water rinsing step, which may include a tap water rinse and / or a DI water (deionized water) rinse.

[0093] The conversion-coated metal surface may be contacted with the mobility enhancer by immersing the surface in the composition, or applying the composition to the surface, such as by spraying. In preferred embodiments, the composition is sprayed onto the metal surface.

[0094] Following the mobility enhancer contacting step, the mobility enhancer composition is dried in place on the metal surface. Drying may be accomplished by exposure to ambient conditions, or by heating to speed the process, such as at a temperature of about 40- 200°C.

[0095] Following the application of the mobility enhancer and optional drying in place, a step of applying lacquer, labeling, or both may be performed with respect to the metal surface. The application of lacquer and / or labeling may be performed according to any suitable procedure in accordance with industry convention, such as spraying, printing, shrink sleeve or label application.EXAMPLES

[0096] The present invention is further defined in the following Examples. It should be understood that these examples, while indicating preferred embodiments of the invention, are given by way of illustration only, and should not be construed as limiting the appended claims. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.Example 1 — Visual Assessment of Conversion Coatings

[0097] Aluminum samples were prepared by exposing the samples to sulfuric acid at a pH of 2 (measured by a pH probe) for 60 seconds at a temperature between 54°C and 60°C, followed by a cleaning step with a commercial acid cleaner for 90 seconds at a temperature between 54°C and 60°C, tap water rinse at ambient temperature for 60 seconds, then contacted with 0.5 wt. % conversion coating bath of an inventive formulation or comparative formulation for 20 seconds at 43 °C, followed by a tap water rinse at ambient temperature, and two DI water rinses for 60 seconds each. A mobility enhancer may or may not be applied in this or following examples and does not inhibit the imaging. Samples may be dried for 3 or 5 min depending on whether the surface is flat or curved.

[0098] All samples were cut into roughly 1” x 1” sizes from the center part of the sample. Once cut down and subsequently punched into a small circle and affixed to a sample stage using carbon tape prior to insertion into a FE-SEM for analysis. Samples were imaged at 100K for 500 nm resolution.

[0099] Test concentrate formulations, with concentrations in parts by weight (pbw), as provided in Table 1 were prepared and used to form respective conversion coating baths by diluting the respective concentrate in tap water to a concentration of 0.5 wt% and adjusting pH and fluoride ion concentration as is known in the art. The pH of each bath was adjusted to 2.8 & free fluoride was adjusted to 447 ppm. The separate conversion coating baths were used to prepare respective metal panels and / or cans which were coated and tested according to the description above, unless otherwise specified. Additionally, two commercial conversion coating baths were made up and metal panels and / or cans were coated according to manufacturer instructions.Table 1: Concentrates

[0100] A cleaned-only metal sample (z.e., without conversion coating or mobility enhancer), cleaned with an acidic cleaner was also evaluated using SEM for reference, and the SEM image of the cleaned only sample is shown in FIG. 1 A. FIG. IB depicts an incomplete coating formulation show a few large nodules resulting from a commercially available zirconium phosphate based-conversion coating for aluminum; this is labeled in FIG 3 A & FIG. 3B as “Com. Avail. Product”. The SEM revealed insufficient surface texture for BPANI organic coating adhesion. FIG. 1C depicts an incomplete coating showing a few nodules resulting from a commercially available zinc doped, zirconium phosphate based conversion coating for aluminum labeled; this is labeled “Sample A” in FIG 3A & FIG. 3B. The SEM revealed an insufficient coating layer and surface texture for BPANI organic coating adhesion. FIGS. ID, IE, and IF respectively depict SEMs showing conversion coatings deposited from working baths of Samples B, C, and D, respectively (see Table 1).

[0101] Without being bound by any particular theory, it is believed that the surface texture observed in FIG. IF, with respect to Sample D, according to an embodiment of the invention may result from the presence of the chelator complexing positively charged ions or moieties, such as Ca ions and Mg ions that are found in tap water. Additionally, or alternatively, the higher ME polyacrylic acid component tends to adopt a globular conformation, and it is believed that as pH increased, the polymer expanded to a move solvated and / or dispersed, open coil conformation that, especially given that the presence of contaminants was minimized (per the chelator), preferentially allowed for the reactivity of a hydrolyzed conversion coating at low pH.Example 2 — TEM evaluation of conversion coating

[0102] A further evaluation of Sample D was conducted in order to assess the conversion coating layer morphology on the metal surface. A conversion coating working bath was made from the composition of Sample D and deposited on the aluminum alloy surface forming a conversion coating. FIG. 2 provides a transmission electron microscopy (TEM) image of a cross-sectional view of the conversion coating of Sample D deposited on the aluminum alloy surface. Samples were prepared in the same method as they were inExample 1 with the addition of a subsequent commercially available lacquer which does not impact the analysis as indicated by the lack of interphase layer between the conversion coating and lacquer. The large bulk of the image represents the sizable grains of the aluminum 3014 Hl 9 substrate. The conversion coating which conforms quite readily to the surface of the can is amorphous as indicated by the lack of crystalline structure. Crystalline structure would be observed by the appearance of an ordered array of visible grain orientations. The highly textured amorphous nature of the coating is readily observed as indicated by the hair like appearance. The contrast at the various points within the hair like material is a higher or lower density of polymer. Another point is the material readily conforms to the surface of the aluminum substrate, providing more credence to the idea that the coating is in fact amorphous. The TEM shows a gradient of metal species where concentrations of Zr / Ti is highest near the aluminum substrate surface and decreasing but still present at the outer surface interface with the lacquer.Example 3 — Electrochemical Impedance Spectroscopy

[0103] Electrochemical Impedance Spectroscopy (EIS) was used to evaluate corrosion at an interface between a metal surface and a lacquer coating. For the present EIS measurement, aluminum substrate samples were contacted with an electrolyte solution of 0.5M Na2SC>4 for 30 minutes in a paint test cell supplied by Gamry (Gamry SKU 990-00197). Tests were run using a porthole of 10cm2(Gamry SKU 990-00256 10cmA2). A potentiostat was used to collect data from each of the substrates, including complex impedance and phase angle. Parameters for measurement were 0.01 Hz to 100,000 Hz with an applied AC current of 10 mV. Samples were measured before and after an aggressive beverage soak (defined as a malt beverage containing alcohol and natural flavors) which lasted for 72 hours at 80C. Modeling of the collected data was completed using Zview Version : 3.5i.

[0104] There are two aspects of the evaluation of electrochemical impedance spectroscopy: phase angle and complex impedance indicated by Z. Most informative data is the phase angle (results provided in FIG. 3A). In the figure, phase angles decrease at 1E+3, indicating the presence of corrosion at the interface. The impedance scan curve of Sample D (FIG. 3B) indicates no corrosion in the measured sample.Example 4 — Simplified Formulation on Drawn and Ironed Aluminum Cans

[0105] An investigation was conducted to assess whether the concentrate formulation could be simplified by omission of certain components of the conversion coating compositions while retaining beneficial functionality.

[0106] Several experiments were performed to assess the effect of removing individual components, thereby resulting in six further test concentrate formulations, with concentrations in parts by weight (pbw), as provided in Table 2. The concentrates of Table 2 were made according to the process of Example 1, and used to prepare respective conversion coating baths at 0.5wt.% dilution, also according to the process of Example 1, unless stated otherwise. Sample drawn and ironed aluminum 3104H19 substrates were coated and tested according to the procedure described in Example 1, unless specified otherwise.Table 2: Concentrate Samples E-I and Control (An Inventive Concentrate)SEM imaging was performed on samples of the conversion coated aluminum substrates ofSamples E to I and a bare Al substrate. The resulting images (FIGS. 4A-4F) depict the textureexhibited by the conversion coating layer when applied to the metal test surface (aluminum alloy AA3104H19). FIG. 4A is a micrograph of the bare Al substrate. Fig. 4B corresponds to Sample E, FIG. 4C corresponds to Sample F, FIG. 4D corresponds to Sample G, FIG. 4E corresponds to Sample H, and FIG. 4F corresponds to Sample I. In the images, brighter spots are indicative of a well-formed and highly textured surface. The images corresponding to Samples E, F, G, and I showed a puckered surface indicative of a less than optimal conversion coating and potentially requiring further adhesion promotion.

[0107] A second set of samples of the conversion coated aluminum substrates of Samples E to I and a bare Al substrate (“Cleaned only”, below), were tested according to the procedure of Example 2 by electrochemical impedance spectroscopy (EIS). In the modeling of the data collected, Rcoat or Rpore were of particular interest as describing the resistance of pores potentially present in the lacquer to the surface of the aluminum. In Table 3, the large difference in values, by several orders of magnitude is indicative of significant differences in performance, with H and I embodiments of the invention displaying high impedance.Table 3As shown in Table 3, the highest order of magnitude impedance achieved for Sample H and Sample I was in the range of more than 10,000 Ohms to more than 50,000 Ohms which shows a 10A2 order of magnitude improvement over the other tested substrates from base line (cleaned only) and the results indicated that adhesion of the lacquer was satisfactory.

[0108] To make wastewater more efficient, there is a need to reduce the number of raw materials and reduce or preferably omit added phosphorus from the container manufacturing product and processes. Sample H was selected for further development to satisfy at least some of these needs.Examples 5 and 6 — Influence of pH and Relative Milli Volts (RMV) on Dome Stain

[0109] Sample H was further modified to a more suitable formulation that would be more acceptable to the market. The first variation of modified H concentrate did not contain added phosphoric acid, and the second variation had phosphoric acid intentionally added in the concentration, similar to amounts added in Sample D. These formulations were explored further in order to evaluate sensitivity to pH and free fluoride by relative mV. These formulations were either phosphorous-free or phosphorous- containing in order to confirm whether the formulation required phosphorus for adequate conversion coating.

[0110] Borax Dome Stain Testing: This dome stain test was used to estimate the resistance that drawn and ironed aluminum cans have to staining under simulated pasteurizer conditions. This test is mainly used to evaluate the stain performance of cans used as containers for fermented beverages, such as beer or non-fermented beverages such as iced tea, which are packed, sealed, and pasteurized in the can.

[0111] The results shown in FIG. 5 and FIG. 6, show the outcomes of the dome stain. The figures provide a representation of adequate processing, with and without phosphoric acid. The squares (designating a rating of 4) indicate adequacy in dome stain resistance, meaning that the corresponding samples maintained their can appearance as though they had not been exposed to the dome stain solution. The circles (designating a rating of 3) indicate some browning of the can surface. The diamonds (designating a rating of 2) displayed progressively more browning or had a golden color. Triangles (those with a rating of 1) were fully brown or golden in color and are equivalent to a control sample in which there is no conversion coating intentionally deposited.

Claims

CLAIMSWhat is claimed:

1. An aqueous conversion coating composition for pretreatment of a metal surface comprising: dissolved and / or dispersed zirconium, measured as elemental Zr, in a concentration of about 50 to 250 ppm; dissolved and / or dispersed titanium, measured as elemental Ti, in a concentration of about 20 to 100 ppm; a tridentate or quadridentate chelator in a concentration of about 0.5 to 20 ppm; and, free fluoride in a concentration of about 150 to 2,000 ppm, wherein the composition has a pH of about 2.3 to 3.3.

2. The conversion coating composition according to claim 1, wherein the zirconium is present in a concentration of about 60 to 190 ppm.

3. The conversion coating composition according to claim 1, wherein the titanium is present in a concentration of about 20 to 70 ppm.

4. The conversion coating composition according to claim 1, wherein the tridentate or quadridentate chelator is present in a concentration of about 1 to 10 ppm.

5. The conversion coating composition according to claim 1, comprising a tridentate chelator, optionally the tridentate chelator comprises methylglycinediacetic acid or a salt thereof.

6. The conversion coating composition according to claim 1, wherein the zirconium and titanium are present in a ratio of about 2-4 : 1, about 2.5-3.5 : 1, or about 3 : 1.

7. The conversion coating composition according to claim 1, wherein the free fluoride is present at -110 to -60 relative millivolts (RMV).

8. The conversion coating composition according to claim 1, further comprising one or more of colloidal silica, polyacrylic acid, a detergent, phosphoric acid, or any combination thereof.

9. The conversion coating composition according to claim 1, wherein the conversion coating composition does not include a source of phosphorus.

10. A method for pretreating a metal surface comprising contacting the metal surface with a conversion coating composition according to claim 1 for a time sufficient to form a conversion coating on the metal surface.

11. The method according to claim 10, wherein the conversion coating composition contacts the metal surface by spraying.

12. The method according to claim 10, wherein conversion coating composition is contacted with the metal surface while the conversion coating is at a temperature of about SOSO^.

13. The method according to claim 10, further comprising cleaning the metal surface with an aqueous acid or alkali agent, and optionally rinsing, prior to contacting the metal surface with the conversion coating composition.

14. A conversion coating that is produced by contacting a metal surface with a conversion coating composition according to claim 1.

15. A conversion coating on a metal surface that is produced by a method according to claim 10.

16. An article having a metal surface comprising a conversion coating that is produced by contacting the metal surface with a conversion coating composition according to claim 1.

17. An article having a metal surface comprising a conversion coating that is produced by a method according to claim 10.

18. A container comprising a metal surface bearing a conversion coating that was produced by contacting the surface with a conversion coating composition according to claim 1.

19. A container comprising a metal surface bearing a conversion coating that was produced by a method according to claim 10.

20. A metal container for food and beverage contact having a layer of conversion coating deposited on at least a portion of the metal container, said conversion coating comprising oxides of Zr, oxides of Ti, and acrylic polymer.

21. The metal container of claim 20 having a surface roughness that is characterized by a surface energy of at least 50 mN / m.

22. The metal container of claim 20 further comprising a lacquer layer on at least a portion of the conversion coating layer, the lacquer layer exhibiting an adhesion of at least Grade 4B, optionally Grade 5B in ASTM D3359 method B testing.

23. A metal pretreatment process comprising steps of: cleaning a metal surface of an article with an acidic or alkaline cleaner composition; conversion coating the cleaned metal surface with conversion coating composition according to claim 1; applying a mobility enhancer and optionally drying in place; and, optionally applying lacquer, labeling, or both.

Images