WO2001083850A1

WO2001083850A1 - Process and composition for conversion coating with improved heat stability

Info

Publication number: WO2001083850A1
Application number: PCT/US2001/014135
Authority: WO
Inventors: Thomas H. Fick; Christopher D. Mckenzie; Gary L. Rochfort
Original assignee: Henkel Corporation
Priority date: 2000-05-02
Filing date: 2001-05-02
Publication date: 2001-11-08
Also published as: AU2001257492A1; TW538135B

Abstract

Substantially transparent conversion coatings may be formed on surfaces of metals such as aluminum by contacting such surfaces with aqueous compositions containing zirconium compounds, inorganically bonded fluorine, organic polymer molecules, and peroxy compounds such as hydrogen peroxide. The conversion coatings thus formed have improved heat stability as compared to conversion coatings obtained using aqueous compositions which do not contain zirconium compounds and/or peroxy compounds.

Description

PROCESS AND COMPOSITION FOR CONVERSION COATING WITH

IMPROVED HEAT STABILITY

BACKGROUND OF THE INVENTION

This invention relates to compositions and processes for forming on metals, particularly aluminum and its alloys, a conversion coating that is substantially trans- parent, so that aesthetically appealing characteristics of the metal surface that is conversion coated are not overly impaired by the conversion coating. (No quantitative test is in common use to measure the degree of preservation of the aesthetic qualities of the metal, but for the principal application area of this invention, aluminum beverage cans, any ordinary consumer can readily judge whether the bright reflectance of the can is as good as usual.)

The following discussion and the description of the invention will be set forth primarily for aluminum cans. However, it is to be understood that, with any obviously necessary modifications, both the discussion and the description of the invention apply also to tin plated steel cans and to other types of metal surfaces over which a transparent conversion coating is practically interesting.

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 partially decorated with lacquer and/or printing ink and the interior surfaces, including the inner dome, normally are protected with sanitary lacquer, but the outer domes of the cans usually do not have lacquer or any similar coating, except possibly for a "rim coat" on its 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 metal surfaces. Therefore, for this particular field of use, the conversion coated surface must have adequate adhesion to printing inks and/or lacquer.

In the most widely used current commercial practice, at least for large scale operations, aluminum cans are typically subjected to a succession of six cleaning and rinsing operations as described in Table A below. It is preferable to include another stage, usually called "Prerinse", before any of the stages shown in Table A; when used, this stage is usually at ambient temperature (i.e., 20 - 25 °C) and is most preferably supplied with overflow from Stage 3 as shown in Table A and is next most preferably supplied with overflow from Stage 1 as shown in Table A. The prerinse may also be tap water. Any of the rinsing operations shown as numbered stages in Table A preferably includes two, or more preferably three, sub-stages, which in consecutive order of their use are usually named "drag-out", "recirculating", and "exit" or "fresh water" sub-stages; if only two sub-stages are used, the name "drag-out" is omitted. Most preferably, when such sub-stages are used, a blow-off follows each sub-stage, but in practice such blow-offs are often omitted. Also, any of the stages numbered 1 and 4 - 6 in Table A may be omitted in certain operations.

A conversion coating over the metallic surfaces of beverage cans, prior to any lacquer coating or printing, is generally considered desirable, in order to increase the adhesion of the inner sanitary lacquer and exterior decorative and protective coatings, especially when the cans in process are to be subjected to stressful metal working operations such as necking (i.e., reducing the can diameter in its neck region) and flanging (to provide an anchoring point for a separate cap for the filled container). However, prior art conversion coatings that were sufficiently transparent to preserve the metallic luster of the surfaces coated with them were susceptible to at least one of the following disadvantageous characteristics when subjected to subsequent heating: development of exterior dome staining during pasteurization; loss of luster of the exterior dome surface upon its exposure to steam; and substantially weakened adhesion of lacquers and printing inks, compared with surfaces of otherwise identical aluminum having the same conversion coating not exposed to heat and sometimes even compared to otherwise identical aluminum that never had any conversion coating. A major object of the present invention is to provide a transparent conversion coating that will avoid or reduce at least one, or preferably all, of these disadvantageous characteristics of the prior art. Other objects will be apparent from the further description below. Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, "parts of", and ratio values are by weight or mass; the term "polymer" includes "oligomer", "copolymer", "terpolymer" and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; 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; the terms "solution", "soluble", "homogeneous", and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18 - 25 °C; and the first definition of an acronym or other abbreviation applies to all subsequent uses of the same acronym or other abbreviation. BRIEF SUMMARY OF THE INVENTION

In accordance with this invention, it has been found that the major object as stated above is achievable with an aqueous conversion coating composition that comprises, preferably consists essentially of, or more preferably consists of, water and the following components:

(A) a component of one or more dissolved transition metal compounds that contains zirconium, hafnium, or both (hereinafter, for brevity, only zirconium will be mentioned, but it is to be understood that zirconium may be partially or totally replaced by hafnium) and may also include titanium, provided that zirconium constitutes at least 30 % of the moles of the total moles of zirconium and titanium; (B) a component of at least one dissolved compound that contains inorganically bonded fluorine and is not part of component (A);

(C) a component of dissolved organic polymer molecules; and

(D) a component of dissolved molecules, other than O₂, that contain oxygen-to- oxygen atom chemical bonds: In certain embodiments of the invention, one or more of the following components may also be present:

(E) a component of dissolved chelating agent molecules that are not part of any of immediately previously recited components (A) through (D);

(F) for pH adjustment, a component of dissolved acid or base molecules that are not part of any of immediately previously recited components (A) through (E);

(G) a component of preservative molecules that are not part of any of immediately previously recited components (A) through (F);

(H) a component of dissolved cations of at least one metallic element comprised in a metal surface being or to be conversion coated; and (J) a component of organic solvent.

Various embodiments of the invention include a liquid working composition that will form a conversion coating upon contact with a suitable metal substrate for a sufficient period of time; a concentrate composition that when mixed with water, and optionally with other materials, will form a liquid working composition, a process including forming a substantially transparent conversion coating on a metal surface by contacting the metal surface with such a working composition, and a metal article having a conversion coating formed according to the invention on at least part of its surface.

DETAILED DESCRIPTION OF THE INVENTION

The zirconium that is required for component (A) and the titanium that is permitted as part of component (A) may be supplied by any water soluble compound of these two metals, which may be dissolved in either cationic or anionic form. At least for economy, because it reduces the amount of component (B) that is needed, hexa- fluorozirconic acid and its salts are the preferred sources of zirconium and hexfluorotitanic acid and its salts are the preferred source of titanium, with the acids independently most preferred in both instances. In a working composition according to the invention, the total concentration of dissolved zirconium and titanium atoms preferably is at least, with increasing preference in the order given, 0 25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, or 1.05 millimoles per liter of working composition, a unit of concentration that may be freely applied hereinafter to other constituents as well as to zirconium and titanium and is hereinafter usually abbreviated as "mM/l". Of this total, more than 30 mole % must be zirconium, and preferably, with increasing preference in the order given, at least 35, 40, 45, or 50 mole percent is zirconium. There is no technical disadvantage if the only transition metal atoms in component (A) are zirconium.

Considerably larger concentrations of zirconium and, optionally, titanium may be used without significant technical disadvantage. For example, more than 4 mM/l of hexafluorozirconic acid may be used without substantial deterioration in performance of the conversion treated containers in any of the tests described in the examples. However, there is somewhat increased danger of separation of the working composition into two phases and there is no improvement in performance. Therefore, at least for economy, the total concentration of zirconium and titanium in a working composition according to the invention preferably is not more than, with increasing preference in the order given, 4.0, 3.5, 3.0, 2.5, 2.1 , 1.9, 1.7, 1.5, 1.3, or 1.1 mM/l. Irrespective of the source(s) of zirconium and, optionally, titanium, a working composition according to the invention preferably contains more than enough dissolved fluorine atoms in anionic form to form ZrF₆ ² anions with all of the zirconium dissolved in the working composition and TiF₆ ² anions with any titanium present. For this reason, as already noted, supplying these metals in the form of salts or acids that contain these anions is normally preferred However, solutions that contain hexa- fluorozirconate with no additional fluoride are susceptible to precipitation of the zirconium as basic salts Therefore, the molar ratio of fluorine to the total of zirconium and titanium in a working composition according to the invention preferably is at least, with increasing preference in the order given, 6.05:1.00, 6.10.1.00, 6.15:1 00, 6.20:1.00, or 6.25 1 00. Component (B) preferably therefore contains at least a sufficient amount of soluble anionic fluoride to achieve at least one of these ratios in the working composition, when considered together with any fluorine present in component (A). Sufficient hydrofluoric acid to achieve one of these ratios is often added by commercial suppliers of hexafluorozirconic and hexafluorotitanic acids. If these materials are used as the sources for component (A), it may not be necessary to include any additional source for component (B). If such an additional source is needed, hydrofluoric and/or tetrafluoroboric acids are preferred, as considered further below.

Soluble anionic fluorine has at least two other important effects in a working composition according to the invention: It promotes the dissolution of aluminum atoms, which at least at the instant of dissolution are believed to be trivalent cations, from the surface to be conversion coated, and, to the extent stoichiometrically and thermodynamically possible, it forms coordinate complexes with the aluminum so dissolved or any other aluminum cations introduced into the solution. Only fluoride ions that are not already bound into complex ions and/or exist in equilibrium from dissociation of complex ions are effective in promoting dissolution of aluminum cations and complexing them. The effective concentration of this kind of fluoride, called "free fluoride" herein and "available fluoride" in U. S. Patent 4,273,592, is defined and can conveniently be measured by means of a fluoride sensitive electrode as described in U. S. Patent 3,431 ,182 and commercially available from Orion Instruments. "Free fluoride" as this term is used herein was measured relative to

"Standard Solution 120E" commercially available from the Henkel Surface Technologies ("HST") Division of Henkel Corporation, Madison Heights, Michigan by a procedure described in detail in HST Technical Process Bulletin No. 1580. The Orion Fluoride Ion Electrode and the reference electrode provided with the Orion instrument are both immersed in the noted Standard Solution and the millivolt meter reading is adjusted to 0 with a digital keypad on the instrument, after waiting if necessary for any initial drift in readings to dissipate. The electrodes are then rinsed with deionized or distilled water, dried, and immersed in the sample to be measured, which should be brought to the same temperature as the noted Standard Solution had when it was used to set the meter reading to 0. The reading of the electrodes immersed in the sample is taken directly from a millivolt (hereinafter usually abbreviated as "mv") meter on the instrument.

Free fluoride is preferably supplied to a working composition according to the invention as HF or soluble neutral or acid salts thereof, and the amount of it preferably is such as to give an electrical potential of a fluoride sensitive electrode in contact with the working composition that is at least, with increasing preference in the order given, -200, -170, -150, -140, -130, -120, -110, -105, -100, -95, or -91 mv, compared with the potential of the same fluoride sensitive electrode in contact with the Standard Solution noted above, and independently preferably is not more than, with increasing preference in the order given, 100, 70, 40, 10, 0, -10, -20, -30, -40, -50, -60, -70, -75, -80, -85, or -89 mv. If the working composition has a potential of less than

-200 mv, the aluminum surface being conversion coated will usually be etched too rapidly to retain a lustrous appearance as desired and may even fail to form any of the desired conversion coating, while if the working composition has a potential of more than 100 mv, the rate of formation of the conversion coating usually will be impractically slow, and the working composition is likely to form precipitates on standing. Free fluoride thus constitutes at least part of component (B) of a composition according to the invention.

Although the amount of free fluoride must be limited for the reasons given above, a "reservoir" of fluoride is advantageously present in a working composition according to the invention, so that the concentration of dissolved aluminum cations in the bulk of the working composition, as contrasted to the immediate vicinity of the surface being conversion coated, can not become so large as to cause difficulties in the conversion coating process. Such a reservoir of fluoride is conveniently and preferably provided by including in a working composition according to the invention, as part of its component (B), complex anions including fluorine that have a higher dissociation equilibrium constant than hexafluorozirconate but not so high as to contribute an excessive amount of free fluoride. Tetrafluoroboric acid and its salts are preferred for this purpose, the acid being more preferable at least for economy. Irrespective of the source, a working composition according to the invention preferably includes dissolved tetrafluoroborate in a concentration that is stoichiometrically equivalent to a concentration of tetrafluoroboric acid that is at least, with increasing preference in the order given, 0.005, 0.010, 0.020, 0.030, 0.035, 0.040, 0.045, 0.047, 0.049, or 0.051 parts by weight per thousand parts of total composition, this concentration unit being hereinafter usually abbreviated as "ppt", and independently preferably is not more than, with increasing preference in the order given, 0.5, 0.30, 0.20, 0.15, 0.10, 0.080,

0.075, 0.070, 0.065, 0.060, or 0.055 ppt. Fully satisfactory results can be obtained from freshly made working compositions that do not include any such free fluoride reservoir, but the presence of such a reservoir promotes performance stability after substantial amounts of aluminum have been dissolved into the working composition by prolonged use.

In addition to providing a reservoir of fluoride that can become free as free fluoride originally in the composition is consumed, tetrafluoroborate is believed to have a preservative effect because of its boron content. This can be advantageous to the storage stability of compositions according to the invention, because some of the organic ingredients in these compositions are capable of nourishing 5 microorganisms that may enter the compositions from various ambient environments.

Tetrafluoroborate may also contribute in some manner unknown in detail to retort stain resistance, and tetrafluoroboric acid is a more strongly ionized acid than HF, making it helpful in controlling the pH within an optimum range, without being so strongly ionized as to attack the polymer in the composition, as a still stronger acid0 such as nitric or sulfuric would be expected to do.

Component (C) as described above is preferably selected from the group of water soluble polymers that contain, in each molecule, at least one of two types of polar moieties: (1 ) acidic moieties such as carboxylate, phosphonate, sulfate, and the like, which are independently preferably neutralized with a strong alkali, in order tos maximize the degree of localization of electrically negative charges in the vicinity of these acidic moieties within the polymers that contain them, when these polymers are dissolved in the at least mildly acidic preferred compositions according to the invention; and (2) nucleophilic moieties such as amino nitrogen, phosphino phosphorus, and the like that form localized positive charge centers, when dissolved in preferredo compositions according to the invention, by attracting protons to themselves to form cationic moieties. More particularly, component (C) as described above preferably contains at least one of: a sufficient number of acidic moieties that the number ratio of acid moieties to total carbon atoms within component (C) is at least, with increasing5 preference in the order given, 1.0:9.0, 1.0:8.0, 1.0:7.0, 1.0:6.0, 1.0:5.0,

1.0:4.0, 1.0:3.0, or 1.0:2.0; and a sufficient number of nucleophilic moieties that the number ratio of nucleophilic moieties to total carbon atoms within component (C) is at least, with increasing preference in the order given, 1.0:50, 1.0:40, 1.0:30, 1.0:27,o 1.0:24, 1.0:22, 1.0:20, 1.0:18, or 1.0:16.

In a first particularly preferred embodiment of the invention, component (C) comprises polymers that contain, as at least 10 % of their total mass, one or more aminomethylphenyl moieties, each of which conforms to the following general formula: 5

R ₁ R ₂ wherein: each of R¹ through R³ is selected, independently of each other and independently from one aminomethylphenyl moiety of the component to another, from the group consisting of a hydrogen moiety, an alkyl moiety with from 1 to 5 carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms; each of Y¹ through Y³ is selected, independently of each other and independently from one aminomethylphenyl moiety to another, from the group consisting of: a hydrogen moiety; a -CH₂CI moiety; an alkyl moiety with from 1 to 18 carbon atoms; an aryl moiety with from 6 to 18 carbon atoms; a moiety conforming to the general formula - CR¹²R¹³OR¹⁴, where each of R¹² through R ⁴ is selected from the group consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety, a hy- droxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, and a phosphoalkyl moiety; and a moiety Z that conforms to one of the two immediately following general formulas:

/

N o r N — R

\ \

R

wherein: each of R⁵ through R⁷ is selected, independently of each other and independently from one aminomethylphenyl moiety to another, from the group consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, and a phosphoalkyl moiety; R⁸ is a polyhydroxy alkyl moiety and R⁹ is selected from the group consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety, a hydroxy or polyhydroxy alkyl moiety, an amino or polyamino alkyl moiety, a mercapto or polymercapto alkyl moiety, a phosphino or polyphosphino alkyl moiety, an -O^" moiety, and an -OH moiety; Y⁴ is a moiety Z as above defined; and W¹ is selected, independently from one molecule of the component to another and from one to another aminomethylphenyl moiety, from the group consisting of a hydrogen moiety, an acyl moiety, an acetyl moiety, a benzoyl moiety; a 3-allyloxy-2- hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety; a 3-butoxy-2-hydroxypropyl moiety; a 3-alkyloxy-2-hydroxypropyl moiety; a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a 2- hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkylphenylethyl moiety; a benzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstituted allyl, or unsubstituted alkylbenzyl moiety; a halo or polyhalo alkyl, or halo or polyhalo alkenyl, moiety; a moiety derived from a condensation polymerization product of ethylene oxide, propylene oxide or a mixture thereof by deleting one hydrogen atom therefrom; and a sodium, potassium, lithium, ammonium or substituted ammonium, or phosphonium or substituted phosphonium cation moiety. When component (C) is selected so as to correspond to this first particularly preferred embodiment: its molecules preferably have a weight average molecular weight that is at least, with increasing preference in the order given, 360, 700, 1500, 3000, 6000, or 10,000 daltons and independently preferably is not more than, with increasing preference in the order given, 2,000,000, 1 ,000,000, 500,000, 250,000, 125,000, 70,000, or 30,000 daltons; independently, the concentration of component (C) in a working composition according to the invention preferably is at least, with increasing preference in the order given, 0.009, 0.018, 0.030, 0.045, 0.050, or 0.053 grams per liter (hereinafter usually abbreviated as "g/l") and independently preferably is not more than, with increasing preference in the order given, 0.36, 0.30, 0.24, 0.21 , 0.18, 0.15, or 0.12 g/l; and, independently, the ratio of the concentration in g/l of component (C) to the concentration in mM/l of component (A) preferably is at least, with increasing preference in the order given, 0.010:1.00, 0.020:1.00, 0.030:1.00, 0.035:1.00, 0.040:1.00, 0.043:1.00, 0.046:1.00, 0.049:1.00, or 0.051 :1.00 and independently preferably is not more than, with increasing preference in the order given,

0.30:1.00, 0.20:1.00, 0.15:1.00, 0.010:1.00, 0.080:1.00, 0.075:1.00, 0.070:1.00, 0.065:1.00, 0.060:1.00, or 0.055:1.00.

Still more preferably within this first particularly preferred embodiment, component (C) is selected from molecules that include, as at least, with increasing preference in the order given, 10, 20, 30, 40, 50, 60, 70, 80, or 90 % of their total mass, aminomethylphenyl moieties that conform to the general formulas for such moieties given above when, independently for each part of the general formulas stated: each of R¹ through R³, R⁵, R⁶, Y¹ through Y³, and W¹ is a hydrogen moiety; R⁷ is an alkyl moiety or a hydrogen moiety, preferably an alkyl moiety having not more than, with increasing preference in the order given, 5, 4, 3, 2, or 1 carbon atoms; R⁸ is a moiety conforming to the general formula -CH₂(CHOH)_p-H, where p is an integer that is at least, with increasing preference in the order given, 2, 3, 4, or 5 and independently preferably is not more than, with increasing preference in the order given, 12, 10, 8, 7, or 6; and R⁹ is not present (or, in other words, Z conforms to the left rather than to the right one of its two alternative general formulas as above shown).

In a second particularly preferred embodiment, component (C) is selected from polymers of at least one of maleic, acrylic, and methacrylic acids. For this second particularly preferred embodiment: - the concentration of component (C) in a working composition according to the invention preferably is at least, with increasing preference in the order given, 0.009, 0.015, 0.030, 0.035, 0.040, 0.045, 0.050, 0.055, 0.060, or 0.064 g/l and independently preferably is not more than 1.0, 0.8, 0.6, 0.40, 0.30, 0.20, 0.15, or 0.10 g/l, these maximum preferences being primarily for economy; and, independently, the molecular weight of the polymer preferably is at least, with increasing preference in the order given, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 and independently preferably is not more than, with increasing preference in the order given, 10⁷, 10⁶, 10⁵, 8x10⁴, 6x10⁴, 4x10⁴, 2x10⁴, or 1.0x10⁴.

Necessary component (D) of dissolved molecules, other than the O₂ molecules of oxygen present in measurable concentration in any aqueous liquid in contact with the naturally ambient atmosphere at a temperature below the boiling point of the liquid, that contain oxygen-atom-to-oxygen-atom chemical bonds, is usually and preferably, at least for economy, supplied to a liquid conversion coating composition according to the invention by hydrogen peroxide. However, it may also be supplied by any of a variety of inorganic peroxy acids, their salts, ozone, and even organic peroxides, all of which are believed to hydrolyze at more or less rapid rates to produce hydrogen peroxide in aqueous solution. The following quantitative preferences, each independently of the others, apply for this component, which is measured as its stoichiometric equivalent as hydrogen peroxide: - the concentration in a working composition preferably is at least, with increasing preference in the order given, 0.030, 0.060, 0.090, 0.120, 0.150,

0.17, 0.19, 0.21 , or 0.23 g/l and independently, primarily for economy, preferably is not more than, 10, 7.0, 5.0, 3.0, 2.0, 1.5, 1.0, 0.80, 0.60, 0.40,

0.35, 0.30, or 0.25 g/l; - the concentration in g/l has a ratio to the concentration in g/l of component (C) that is at least, with increasing preference in the order given, 1.00:1 .00,

2.0:1.00, 2.5:1.00, 3.0:1.00, 3.3:1.00, 3.6:1.00, 3.9:1.00, 4.1 :1.00, or 4.3:1.00 and independently preferably is not more than, with increasing preference in the order given, 35:1.00, 30:1.00, 25:1.00, 20:1 .00, 15:1 .00, 10:1.00, 8.0:1.00, 7.0:1.00, 6.5:1 .00, 6.0:1.00, 5.5:1.00, 5.0:1.00, 4.7:1.00, or 4.5:1.00; and the concentration in g/l has a ratio to the concentration of component (A) in mM/l that is at least, with increasing preference in the order given, 0.03:1.00, 0.06:1.00, 0.09:1.00, 0.110:1.00, 0.130:1.00, 0.150:1.00, 0.170:1.00, 0.190:1.00, 0.21 :1.00, or 0.23:1 :00 and independently preferably is not more than, with increasing preference in the order given, 5:1.00, 3.0:1.00, 2.5:1.00,

2.0:1.00, 1.5:1.00, 1.0:1.00, 0.50:1.00, 0.40:1.00, 0.35:1.00, 0.30:1.00, or 0.25:1.00.

Although not necessary, the presence of optional component (E) of chelating agents in a composition according to the invention is usually preferred, at least when the composition contains amounts of dissolved calcium and/or magnesium ions that are characteristic of hard domestic and industrial water supplies. Any chelating agent present is preferably selected from the group consisting of molecules each of which contains at least two nucleophilic moieties selected from the group consisting of car- boxyl, carboxylate, non-carboxyl hydroxyl, amino, thio, phosphonic acid, phosphonate, phosphinic acid, and phosphinate moieties, with these at least two moieties being bonded into the molecule in positions such that a five- or six-membered ring of atoms can be formed by atoms in the molecule and a multivalent metal atom that is coordinatively covalently bonded to a nucleophilic atom (oxygen, nitrogen, sulfur, or phosphinic phosphorus) in each of said nucleophilic moieties in the molecule. More preferably, any chelating agent is selected from the group consisting of gluconic, citric, tartaric, and malic acids, and water soluble salts of all of these acids, or still more preferably from gluconic acid and its salts. Independently of its specific chemical nature, the concentration of chelating agents in a working composition according to the invention preferably is at least, with increasing preference in the order given, 0.020, 0.040, 0.060, 0.080, 0.10, 0.13, 0.16, 0.19, 0.22, 0.24, 0.26, 0.28, or 0.30 mM/l, and independently at least for economy, preferably is not more than, with increasing preference in the order given, 4.0, 3.0, 2.0, 1.0, 0.8, 0.60, 0.50, 0.40, 0.35, 0.30, or 0.32 mM/l.

A working composition according to the invention preferably has a pH value that is at least, with increasing preference in the order given, 0.8, 1.1 , 1.4, 1.7, 2.0, 2.2, 2.4, or 2.6 and independently preferably is not more than, with increasing preference in the order given, 5.0, 4.5, 4.0, 3.7, 3.4, 3.2, 3.0, or 2.8. When other ingredients of a composition according to the invention are near their most preferred values, achieving this pH value may require an acid that does not contain fluorine, and in such instances, nitric acid is preferred, although other acids such as sulfuric that do not contain phosphorus may alternatively be used as optional component (F).

If an initial concentration of aluminum is desired as considered further below, aluminum salts of one of these acids may conveniently be used to provide both constituents. On the other hand, a base may be required instead to achieve the desired pH, and in such an instance, ammoia is preferred because of its volatility. A preservative agent, optional component (G), may be needed in some environments to protect against growth of microorganisms in a stored composition according to the invention. Numerous suitable preservatives are known to those skilled in the art and may be utilized in such instances.

As already noted, a working composition according to the invention will dissolve some aluminum from a surface that it is conversion coating. If the working composition contains essentially no dissolved aluminum at the beginning of its use, some of the dissolved aluminum will not be incorporated into the conversion coating, but instead will accumulate in the solution to constitute optional component (H). Because of this, it is often preferred to add optional component (H) at the beginning, in order to reduce the possibility of excessive etching of the aluminum surface being conversion coated with a freshly made, aluminum-free working composition. If this is desired, water soluble aluminum salt(s) of strong, phosphorus-free acids are most preferably used for the purpose. Unless fresh working composition is supplied at a high rate that is usually not economically justifiable, component (H) will eventually accumulate to a steady state value that is usually at least 0.1 g/l, and may be as high as 1.0 g/l, of dissolved aluminum. Provided that the concentration of free fluoride is kept within the preferred range given above, this amount of component (H) has no harmful effect on the conversion coating process.

Optional component (J) of organic solvent is more tolerable than desirable. Normally, the only reason for inclusion of this component is that it is needed to prepare and/or dissolve all or part of water-soluble organic polymer component (C), and that the expense of removing this solvent is not justified by any adverse effect of the solvent on the performance of a conversion coating forming composition according to the invention that includes this solvent along with component (C).

Phosphate is one of the most common ingredients of conversion coatings in general. However, a working composition according to this invention preferably does not contain more than, with increasing preference in the order given, 1.0, 0.5, 0.3, 0.10, 0.050, 0.020, 0.0100, 0.0050, 0.0020, 0.0010, 0.00095, 0.00090, 0.00085, or 0.0081 percent of phosphorus atoms contained within any dissolved oxyacids of phosphorus, or any partially or completely neutralized salts of such acids, that are dis- solved in the composition, because it has been found that, if the concentration of phosphorus containing inorganic anions in a working composition according to the invention is too high, a hazy white stain usually develops on a beverage container treated with the working composition and later exposed to steam. Smaller concentrations of phosphorus containing inorganic cations, on the other hand, have been found to be advantageous, at least where the tap water used is high in at least one of alkali metal ions, carbonate ions, and acid carbonate ions. In such instances, the concentration of phosphorus atoms in dissolved anions or oxyacids in a composition according to the invention preferably is at least, with increasing preference in the order given, 0.00010, 0.00020, 0.00030, 0.00040, 0.00050, 0.00060, 0.00070, 0.00075, or 0.00080 percent

In a make-up concentrate composition according to the invention, the concentrations of the various components identified above preferably are considerably higher than those preferred for working compositions. More specifically, in a make-up concentrate according to the invention, independently for each component stated, the concentration of each of those of components (A) through (H) that are present in the make-up concentrate preferably corresponds to at least, with increasing preference in the order given, 10, 30, 50, 70, 90, 100, 150, 200, 300, 400, or 500 times the preferred values specified above for the same component in a working composition. Greater concentrations in the make-up concentrate are more economical, because of the reduced cost of shipping water that can readily be added at the point of use, but lower concentrations are less susceptible to phase separations during storage.

Although sometimes such phase separations are harmless if the entire concentrate is thoroughly mixed before being used, separations certainly increase the risk of not obtaining the intended concentrations of every ingredient when preparing a working composition from the concentrate. The pH and free fluoride values do not scale linearly with concentration as do the concentrations of ingredients such as zirconium and polymer, so that the preferred values for concentrates for these characteristics are those that will give the preferred pH and free fluoride values when diluted so as to provide the concentrations preferred for zirconium and polymer.

In a process according to the invention, the temperature of a working compo- sition as described above preferably is maintained during its contact with the metal surface to be conversion coated at a temperature that is at least, with increasing preference in the order given, 30, 32, 34, 36, 38, 40, 42, 44, 46, or 48 °C and independently, primarily for economy, preferably is not more than, with increasing preference in the order given, 75, 65, 60, 58, 56, 54, 52, or 50 °C. At least one tempera- ture within this range will normally achieve formation of an effective conversion coating within a contact time of from 2 to 50 seconds, as required by most existing commercial container manufacturing and decorating plants at their current and/or projected line speeds.

The invention may be further appreciated by consideration of the following examples and comparison examples.

TEST METHODS

Retort Test: The cans were exposed to steam at 1 atmosphere pressure for 30 minutes. Their appearance was then rated on the following scale: 5 = Best, with no haziness or patterning. 4 = Slight haze, may or may not be uniform over surface.

3 = Light cloudiness, may or may not be uniform over surface.

2 = Light cloudiness with an obvious veined pattern. 1 = Worst, very cloudy and obviously non-uniform over surface.

Dome Staining: The domes were removed from the cans to be tested. They were immersed in a solution which consisted of 0.3 gram per liter of sodium tetraborate decahydrate and 0.1 gram per liter of potassium chloride in deionized water. This solution was heated to 85 °C. The can domes were immersed in the hot solution for 30 minutes. (The solution was reused until the concentration of dissolved aluminum in it reached 50 parts of aluminum per million parts of total solution.) The can domes were then removed, rinsed with deionized water and dried. The following scale was used to report the dome staining performance of the domes: 4 = Best, silvery with no discoloration to 1 = complete dark discoloration, equivalent to the performance of a can without a conversion coating. SPECIFIC EXAMPLES EXAMPLE GROUP 1 In this group, a concentrate was first prepared. Its ingredients are shown as

Composition 1 in Table 1. A solution of 0.6 % by volume of this concentrate, with the pH value of the diluted concentrate adjusted if needed with nitric acid or ammonia to 2.6 - 2.8 and the free fluoride reading adjusted if needed with additional HF to a value from -70 to -110 mv was found to provide good dome stain resistance on aluminum beverage cans processed with it as a working conversion coating composition when used as Stage 4 in a process sequence as described in Table A. The tap water used was from the municipal supply of Jakarta, Indonesia, and other details were as follows: Stage 1 : An aqueous solution, in tap water, of sufficient sulfuric acid to result in a pH value of 2.0 was used as the treatment composition at 54 °C.

Stage 2: RIDOLINE® 123CO cleaning solution concentrate, a commercial product available from HST, was used according to the manufacturer's directions to prepare a treatment solution in tap water that also contained 24 grams per liter (hereinafter usually abbreviated as "g/l") of aluminum sulfate heptahydrate and had variable values for Free Acid (hereinafter usually abbreviated as "FA") points and free fluoride content. These values are shown in a table below. The treatment composition for this stage was maintained at 60 °C and was sprayed at 1.4 bars spray pressure. Stage 3: Rinse with tap water at ambient temperature of 20±10 °C. Stage 4: This was the conversion coating step. The compositions were sprayed onto the cans for 20 sec at 48 °C at 0.3 bar spray pressure.

Stage 5: Rinse with tap water at ambient temperature. Stage 6: Rinse with deionized water. Dry at 230 °C for about one minute. EXAMPLE GROUP 2

In this group, only working compositions are prepared. Details are given in Table 1 as Compositions 2.1 through 2.6. These are used as working compositions in Stage 4 of a process sequence otherwise as in Group 1 , and satisfactory dome

Table 1 INGREDIENTS IN SOME WORKING COMPOSITIONS AND A CONCENTRATE ACCORDING TO THE

INVENTION

Numbered Notes and Other Notes for Table 1

1. In these working compositions, the amount of HF was adjusted along with HBF₄ and nitric acid or aqueous ammonia to produce a fluoride activity reading in a range from -70 to -110 mv and a pH value between 2.6 and 2.8.

2. In these working compositions, the amount of HBF₄ was adjusted along with Hf and nitric acid or aqueous ammonia to produce a fluoride activity reading in a range from -70 to -110 mv and a pH value between 2.6 and 2.8.

For Concentrate Compositions 1 and 3, the values given in the table are in ppt rather than g/l.

The symbol "-" in a cell indicates that none of the ingredient on the row of the cell was added to the composition number in the column of the cell.

The polymer solution was obtained by practicing the teaching of column 11 lines 39 - 52 of U. S. Patent 4,963,596, except that (i) the amount of formaldehyde specified there was increased by about 10 % and (ii) less water was used in dilution, so that the solution contained 30 % of dissolved polymer rather than 9.6 %.

The balance not specified above for any composition was tap water except for Compositions 1 and 3 for which the balance was deionized water. The dilution of Compositions 1 and 3 to produce a working compositions were made with tap water, however. staining resistance and other properties are obtained on the thus treated cans. EXAMPLE GROUP 3

In this group, a concentrate that contained phosphorus was prepared. Its ingredients are shown as Composition 3 in Table 1 , and it was used in the same manner as the concentrate in Example Group 1.

Claims

What is claimed is:

1. An aqueous liquid composition of matter suitable for forming on a metal surface with which said aqueous liquid composition is contacted a transparent conversion coating, said aqueous liquid composition comprising:

(A) a component of one or more dissolved transition metal compounds that contains zirconium, hafnium, or both and may also include titanium, provided that zirconium constitutes at least 30 % of the moles of the total moles of zirconium and titanium; (B) a component of at least one dissolved compound that contains inorganically bonded fluorine and is not part of component (A);

(C) a component of dissolved organic polymer molecules; and

(D) a component of dissolved molecules, other than O₂, that contain oxygen- atom-to-oxygen-atom chemical bonds.

2. The aqueous liquid composition of matter of claim 1 wherein component (A) comprises one or more transition metal compounds selected from the group consisting of hexafluorozirconic acid, salts of hexafluorozirconic acid, hexafluorotitanic acid, and salts of hexaflurozirconic acid.

3. The aqueous liquid composition of matter of claim 1 wherein component (B) comprises at least one of HF, a soluble neutral or acid salt of HF, tetrafluoroboric acid, or a salt of tetrafluoroboric acid.

4. The aqueous liquid composition of matter of claim 1 wherein component (C) comprises at least one water soluble polymer containing at least one polar moiety selected from the group consisting of carboxylate, phosphonate, sulfate, amino nitrogen, and phosphino phosphorus.

5. The aqueous liquid composition of matter of claim 1 wherein component (D) comprises hydrogen peroxide.

6. The aqueous liquid composition of matter of claim 1 wherein the concentration of component (D) in g/l, measured as its stoichiometric equivalent as hydrogen peroxide, has a ratio to the concentration of component (C) in g/l that is at least

1.00:1.00 and is not more than 35:1.00.

7. The aqueous liquid composition of matter of claim 1 wherein the concentration of component (D) in g/l, measured as its stoichiometric equivalent as hydrogen peroxide, has a ratio to the concentration of component (A) in mM/l that is at least 0.03:1.00 and is not more than 5:1 .00

8. The aqueous liquid composition of matter of claim 1 additionally comprising one or more of the following components:

(E) a component of dissolved chelating agent molecules that are not part of any of the components (A) through (D); 5 (F) a component of dissolved acid or base molecules that are not part of any of the components (A) through (E); (G) a component of preservative molecules that are not part of any of the components (A) through (F); (H) a component of dissolved cations of at least one metallic element0 comprised in a metal surface being or to be conversion coated; and

(I) a component of organic solvent.

9. The aqueous liquid composition of matter of claim 1 having a pH value that is at least 0.8 and is not more than 5.0.

10. A process for forming a substantially transparent conversion coating on as metal surface, said process comprising a step of contacting the metal surface with an aqueous liquid composition of matter in accordance with any of claims 1 to 9.

11. The process of claim 10 wherein the metal surface is comprised of aluminum.

12. The process of claim 10 wherein said aqueous liquid composition of matter is maintained during said contacting at a temperature that is at least 30°C and is not0 more than 75°C.

13. A metal article having a surface, wherein a conversion coating formed in accordance with the process of claim 9 is present on at least part of said surface.

14. A method of making an aqueous liquid composition of matter suitable for forming on a metal surface with which said aqueous liquid composition is contacted a5 transparent conversion coating, said method comprising dissolving in water at least the following components:

(A) a component of one or more transition metal compounds that contains zirconium, hafnium, or both and may also include titanium, provided that zirconium constitutes at least 30% of the moles of zirconium ando titanium;

(B) a component of at least one compound that contains inorganically bonded fluorine and is not part of a component (A);

(C) a component of organic polymer molecules; and

(D) a component of molecules, other than O₂, that contain oxygen-atom-5 to-oxygen-atom chemical bonds.