HK1141841B - Pretreatment compositions and methods for coating a metal substrate - Google Patents

Description

Pretreatment composition and method for coating metal substrate

Technical Field

The present invention relates to pretreatment compositions and methods of coating metal substrates, including ferrous substrates such as cold rolled steel and electrogalvanized steel. The invention also relates to a coated metal substrate.

Background information

It is common to use protective coatings on metal substrates for improved corrosion resistance and paint adhesion. Conventional techniques for coating such substrates include techniques involving pretreatment of the metal substrate with phosphate conversion coating (phosphate conversion coating) and chrome-containing lotions. However, the use of such phosphate and/or chromate containing compositions can present environmental and health concerns.

Thus, chromate-free and/or phosphate-free pretreatment compositions have been developed. Such compositions are typically based on chemical mixtures that react in some way with the substrate surface and bond thereto to form a protective layer. For example, pretreatment compositions based on group IIIB or IVB metal compounds have recently become more prevalent. Such compositions often contain a source of free fluorine, i.e., fluorine that is isolated in the pretreatment composition as opposed to fluorine attached to another element, such as a group IIIB or IVB metal. The free fluorine can etch the surface of the metal substrate, thereby facilitating the deposition of the group IIIB or IVB metal coating. However, in general, the corrosion resistance of these pretreatment compositions is significantly lower than conventional phosphate and/or chromium containing pretreatments.

Accordingly, it would be desirable to provide a method of treating a metal substrate that overcomes at least some of the aforementioned deficiencies of the prior art, including the environmental drawbacks associated with the use of chromates and/or phosphates. Furthermore, it would be desirable to provide a method of treating a metal substrate that imparts corrosion resistance properties comparable to or even superior to those imparted by the use of phosphate conversion coatings in at least some instances. It is also desirable to provide related coated metal substrates.

Summary of The Invention

In certain aspects, the present invention relates to compositions for treating metal substrates. These compositions comprise: (a) a group IIIB and/or IVB metal; (b) an electropositive metal; (c) 0.1-300 parts per million ("ppm") free fluorine; (d) by forming a pK having a value of at least 11_spMetal fluoride salts of the fluoride salts of (a); and (e) water. In certain embodiments, the composition is substantially free of heavy metal phosphates such as zinc phosphate and chromate.

In other aspects, the invention relates to methods of treating a metal substrate comprising contacting the substrate with a pretreatment comprisingContacting the composition: (a) a group IIIB and/or IVB metal; (b) an electropositive metal; (c) free fluorine; (d) by forming a pK having a value of at least 11_spMetal fluoride salts of the fluoride salts of (a); and (e) water, wherein the amount sufficient to maintain the level of free fluorine in the composition to be no less than 0.1ppm and no more than 300ppm is provided to form a pK having a pK of at least 11_spThe metal of the metal fluoride salt of (1).

In other aspects, the present invention relates to a composition for treating a metal substrate comprising: (a) a group IIIB and/or IVB metal; (b)0.1-300ppm free fluorine; (c) by forming a pK having a value of at least 11_spMetal fluoride salts of the fluoride salts of (a); and (d) water. These compositions of the invention are substantially free of phosphate ions and chromate.

The invention also relates to substrates treated thereby.

Detailed Description

For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

In addition, it should be understood that all numerical ranges set forth herein are intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, i.e., all sub-ranges having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. Also in this application, the use of "or" means "and/or" unless specifically stated otherwise, although "and/or" may be explicitly used in certain instances.

As previously mentioned, certain embodiments of the present invention are directed to methods of coating a metal substrate. Suitable metal substrates for use in the present invention include those commonly used in components of automotive bodies, automotive parts, and other articles (e.g., small metal parts, including fasteners, i.e., nuts, bolts, screws, pins, nails, clamps, buttons, etc.). Specific examples of suitable metal substrates include, but are not limited to, cold rolled steel, hot rolled steel, galvanized metal, zinc compound or zinc alloy steel such as electrogalvanized steel, hot dip galvanized steel, galvanealed steel, and steel galvanized with zinc alloy. Aluminum alloy, aluminum plated steel, and aluminum alloy plated steel substrates may also be used. Other suitable non-ferrous metals include copper and magnesium, and alloys of these materials. In addition, the metal substrate coated by the method of the present invention may be a cut edge of the substrate that is additionally treated and/or coated over the remainder of its surface. The metal substrate coated according to the method of the invention may be in the form of, for example, a metal sheet or a preform (fabricated part).

The substrate to be coated according to the method of the invention may first be cleaned to remove grease, dirt or other foreign substances. This is typically done by using mild or strong alkaline cleaners such as those commercially available and conventionally used in metal pretreatment processes. Examples of alkaline cleaners suitable for use in the present invention include Chemkleen 163, Chemkleen 177 and Chemkleen 490MX, each commercially available from PPG Industries, inc. The detergent is typically applied before and/or after the water wash.

As previously mentioned, certain embodiments of the present invention are directed to methods of treating a metal substrate comprising contacting the metal substrate with a pretreatment composition comprising a group IIIB and/or IVB metal. The term "pretreatment composition" as used herein refers to a composition that, when contacted with a substrate, reacts with and chemically alters the surface of the substrate and bonds thereto to form a protective layer.

Typically, the pretreatment composition comprises a support, typically an aqueous medium, such that the composition is in the form of a solution or dispersion of the group IIIB or IVB metal compound in the support. In these embodiments, the solution or dispersion may be contacted with the substrate by any of a variety of known techniques, such as dipping or dipping, spraying, intermittent spraying, spraying after dipping, dipping after spraying, brushing, or rolling. In certain embodiments, the solution or dispersion is at a temperature of 60 to 150 ° F (15 to 65 ℃) when applied to a metal substrate. The contact time is typically from 10 seconds to 5 minutes, for example from 30 seconds to 2 minutes.

The term "group IIIB and/or IVB metal" as used herein refers to an element in group IIIB or group IVB of the CAS periodic table of elements, as shown, for example, in handbook of Chemistry and Physics, 63 rd edition (1983). Where applicable, the metal itself may be used. In certain embodiments, a group IIIB and/or IVB metal compound is used. The term "group IIIB and/or IVB metal compound" as used herein refers to a compound comprising at least one element from group IIIB or group IVB of the CAS periodic table of elements.

In certain embodiments, the group IIIB and/or group IVB metal compound used in the pretreatment composition is a compound of zirconium, titanium, hafnium, yttrium, cerium, or mixtures thereof. Suitable zirconium compounds include, but are not limited to, hexafluorozirconic acid, alkali metal and ammonium salts thereof, ammonium zirconium carbonate, zirconyl nitrate, zirconium carboxylates, and zirconium hydroxycarboxylic acid salts such as hydrofluorozirconic acid (hydro zirconic acid), zirconium acetate, zirconium oxalate, ammonium zirconium glycolate, ammonium zirconium lactate, ammonium zirconium citrate, and mixtures thereof. Suitable titanium compounds include, but are not limited to, fluorotitanic acid and salts thereof. Suitable hafnium compounds include, but are not limited to, hafnium nitrate. Suitable yttrium compounds include, but are not limited to, yttrium nitrate. Suitable cerium compounds include, but are not limited to, cerium nitrate.

In certain embodiments, the group IIIB and/or IVB metal compound is present in the pretreatment composition in an amount of at least 10ppm metal, such as at least 100ppm metal, or in some cases at least 150ppm metal (measured as elemental metal). In certain embodiments, the group IIIB and/or IVB metal compound is present in the pretreatment composition in an amount of no greater than 5000ppm metal, such as no greater than 300ppm metal, or in some cases no greater than 250ppm metal (measured as elemental metal). The amount of group IIIB and/or IVB metal in the pretreatment composition can range between any combination of the recited values, inclusive of the recited values.

In certain embodiments, the pretreatment composition further comprises an electropositive metal. The term "electropositive metal" as used herein refers to a metal that is more electropositive than the metal substrate. This means that for the purposes of the present invention, the term "electropositive metal" includes metals that are less susceptible to oxidation than the metal of the metal substrate being treated. As will be understood by those skilled in the art, the tendency of a metal to oxidize is referred to as the oxidation potential, expressed in volts, and measured relative to a standard hydrogen electrode arbitrarily designated as the 0 oxidation potential. The oxidation potentials of several elements are described in the table below. If it has a larger voltage value E + than the element being compared in the table below, the element is less easily oxidized than another element.

Element(s)	Half cell reaction	Voltage, E*
			Potassium salt	K++e→K	-2.93
Calcium carbonate	Ca2++2e→Ca	-2.87
			Sodium salt	Na++e→Na	-2.71
Magnesium alloy	Mg2++2e→Mg	-2.37
			Aluminium	Al3++3e→Al	-1.66
Zinc	Zn2++2e→Zn	-0.76
			Iron	Fe2++2e→Fe	-0.44
Nickel (II)	Ni2++2e→Ni	-0.25
			Tin (Sn)	Sn2++2e→Sn	-0.14
Lead (II)	Pb2++2e→Pb	-0.13
			Hydrogen	2H++2e→H2	-0.00
Copper (Cu)	Cu2++2e→Cu	0.34
			Mercury	Hg2 2++2e→2Hg	0.79
Aluminium	Ag++e→Ag	0.80
			Gold (Au)	Au3++3e→Au	1.50

Thus, it is apparent that when the metal substrate comprises one of the materials previously listed such as cold rolled steel, hot rolled steel, galvanized metal, zinc compound or zinc alloy steel, hot dip galvanized steel, galvanealed steel, and galvanized with zinc alloy steel, aluminum alloy, aluminum plated steel, aluminum plated alloy steel, magnesium and magnesium alloy, suitable electropositive metals for inclusion in the pretreatment composition include, for example, nickel, copper, silver and gold, as well as mixtures thereof.

In certain embodiments, the source of the electropositive metal in the pretreatment composition is a water soluble metal salt. In certain embodiments of the invention, the water-soluble metal salt is a water-soluble copper compound. Specific examples of water-soluble copper compounds suitable for use in the present invention include, but are not limited to, copper cyanide, copper potassium cyanide, copper sulfate, copper nitrate, copper pyrophosphate, copper thiocyanate, disodium copper ethylenediaminetetraacetate tetrahydrate, copper bromide, copper oxide, copper hydroxide, copper chloride, copper fluoride, copper gluconate, copper citrate, copper lauroyl sarcosinate, copper formate, copper acetate, copper propionate, copper butyrate, copper lactate, copper oxalate, copper phytate, copper tartrate, copper malate, copper succinate, copper malonate, copper maleate, copper benzoate, copper salicylate, copper aspartate, copper glutamate, copper fumarate, copper glycerophosphate, sodium copper chlorophyllin, copper fluorosilicate, copper fluoroborate and copper iodate, as well as copper salts of carboxylic acids in the family of homologs of formic acid to capric acid, copper salts of polybasic acids in the family of oxalic acid to suberic acid, and hydroxycarboxylic acids (including glycolic acid, copper sulfate, Lactic acid, tartaric acid, malic acid, and citric acid).

When the copper ions provided by the water-soluble copper compound precipitate as impurities in the form of copper sulfate, copper oxide, or the like, a complexing agent that inhibits the precipitation of copper ions may preferably be added, thereby stabilizing them in solution as a copper complex.

In certain embodiments, the copper compound is as a copper complex salt such as K₃Cu(CN)₄Or Cu-EDTA, may be present separately and stably in the composition, but a copper complex may also be formed by combining a complexing agent with a compound that is difficult to dissolve separately, which may be present stably in the composition. Examples thereof include copper cyanide complexes formed from a combination of CuCN and KCN or a combination of CuSCN and KSCN or KCN, and copper cyanide complexes formed from CuSO₄And EDTA-2 Na.

As the complexing agent, a compound capable of forming a complex with copper ions; examples thereof include inorganic compounds such as cyanide compounds and thiocyanate compounds, and polycarboxylic acids, and specific examples thereof include ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salts such as disodium dihydrogen ethylenediaminetetraacetate dihydrate, aminocarboxylic acids such as nitrilotriacetic acid and iminodiacetic acid, hydroxycarboxylic acids (oxocarboxylic acids) such as citric acid and tartaric acid, succinic acid, oxalic acid, ethylenediaminetetramethylenephosphonic acid, and glycerin.

In certain embodiments, the electropositive metal, e.g., copper, is included in the pretreatment composition in an amount of at least 1ppm, e.g., at least 5ppm, or in some cases at least 10ppm total metal (measured as elemental metal). In certain embodiments, the electropositive metal is included in the pretreatment composition in an amount of no greater than 500ppm, such as no greater than 100ppm, or in some cases no greater than 50ppm total metal (measured as elemental metal). The amount of electropositive metal in the pretreatment composition can range between any combination of the recited values inclusive of the recited values.

The pretreatment compositions of the present invention also comprise free fluorine. As will be appreciated, the source of free fluorine in the pretreatment compositions of the present invention may vary. For example, in some cases, the free fluorine can originate from a group IIIB and/or IVB metal compound used in the pretreatment composition, such as in the case of hexafluorozirconic acid. When the group IIIB and/or IVB metal is deposited on the metal substrate during the pretreatment process, the fluorine in the hexafluorozirconic acid will become free fluorine and as will be appreciated, when the metal is pretreated with the pretreatment composition of the present invention, the free fluorine content of the pretreatment composition, if unchecked, will increase over time.

In addition, the source of free fluorine in the pretreatment compositions of the present invention can include compounds other than group IIIB and/or IVB metal compounds. Non-limiting examples of such sources include HF, NH₄F、NH₄HF₂NaF and NaHF₂。

The term "free fluorine" as used herein refers to isolated fluoride ions, and its concentration in the pretreatment composition of the present invention can be determined by measuring the pretreatment composition with a meter having a fluoride ion electrode. The examples herein illustrate suitable methods for measuring the concentration of free fluorine in compositions for the purposes of the present invention.

The pretreatment compositions of the present invention also comprise a composition that results in a composition having a pK of at least 11, in some cases at least 15, or in other cases at least 20_spMetal fluoride salt of (a). As will be appreciated, pK_spRefers to the inverse logarithm of the solubility product constant of a compound. In the present invention, there is provided a method wherein the metal is selected such that it forms a pK with at least 11_spA metal-containing compound of the fluoride salt of (a). For the purposes of the present invention, the pK of the metal fluoride salt_spValues refer to the pK reported in Lange's Handbook of Chemistry, 15 th edition, McGraw-Hill, 1999, Table 8.6_spThe value is obtained. In certain embodiments of the invention, a pK having a pK of at least 11 is formed_spThe metal of the fluoride salt of (a) is selected from cerium (CeF)₃pK of (2)_sp15.1) lanthanum (LaF)₃pK of (2)_sp16.2) and scandium (ScF)₃pK of (2)_sp23.24), Yttrium (YF)₃pK of (2)_sp20.06), or mixtures thereof.

Furthermore, in the composition of the invention, such a selection is provided to form a pK having a pK of at least 11_spAmount of metal-containing compound of fluoride salt of (a): such that the free fluorine content of the composition is not less than 0.1ppm, and in some cases not less than 20ppm, and no greater than 300ppm, and in some cases no greater than 100 ppm. As will be appreciated and as previously described, the free fluorine content of the pretreatment composition of the present invention will increase over time when the metal is pretreated therewith. In the present invention, the metal-containing compound as described above is provided to the pretreatment composition as needed to keep the free fluorine content of the pretreatment composition at not less than 0.1ppm and not more than 300 ppm.

According to the invention, the formation of a pK having a value of at least 11 can be removed from the composition of the invention relatively immediately upon its formation_spOr if selected, the fluoride salt may be allowed to remain in the composition for a period of time. For the purposes of the present invention, it is important that the fluoride salt be formed and present in the composition, although only transiently.

Thus, in certain embodiments of the invention, the yttrium-containing compound is provided to the pretreatment composition. In particular, the source of yttrium added to the pretreatment composition of the present invention results in the formation of yttrium fluoride, such as YF, by reaction with free fluorine in the composition₃. In certain embodiments, the yttrium source in the pretreatment composition is a water-soluble yttrium salt such as yttrium acetate, yttrium chloride, yttrium formate, yttrium carbonate, yttrium sulfamate, yttrium lactate, and yttrium nitrate. Yttrium nitrate, a readily available yttrium compound, is a suitable source of yttrium when yttrium is to be added as an aqueous solution to the pretreatment composition. Other yttrium compounds suitable for use in the pretreatment compositions of the present invention are organic and inorganic yttrium compounds, such as yttrium oxide, yttrium bromide, yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate, and yttrium oxalate. Organic yttrium complexes and yttrium metal may also be used. Suitable cerium compounds include, but are not limited to, cerium nitrate hexahydrate. Suitable lanthanum compounds include, but are not limited to, lanthanum nitrate hydrate.

It has been found that by selecting a composition comprising a pK having a pK of at least 11_spMetal-containing compounds of the metal fluoride salt of (a) which are useful in removing free fluorine from a compositionAspect ratio wherein using comprises forming a pK having a pK of less than 11_spThe metal-containing compound of the metal fluoride salt of (a) is more effective, thereby making it easier to control the content of free fluorine in the composition. In addition, for example, the embodiment of the present invention in which the yttrium-containing compound is used, the resulting metal-containing fluoride salt YF₃The sludge of (a) is considered to be environmentally friendly, since yttrium is not considered to be a heavy metal. Thus, the composition of the present invention avoids the environmental drawbacks found in some prior art metal pretreatment compositions.

In certain embodiments, the pH of the pretreatment composition is from 2.0 to 7.0, e.g., from 3.5 to 5.5. The pH of the pretreatment composition can be adjusted, for example, using any acid or base, as desired. In certain embodiments, the pH of the solution is maintained by the inclusion of a basic material, including water-soluble and/or water-dispersible bases, such as sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium hydroxide, ammonia, and/or amines such as triethylamine, methylethylamine, or mixtures thereof.

In certain embodiments, the pretreatment composition further comprises a resinous binder. Suitable resins include the reaction product of one or more alkanolamines and an epoxy-functional material containing at least two epoxy groups, such as those disclosed in U.S. Pat. No.5,653,823. In some cases, such resins contain beta hydroxy ester, imide, or sulfide functionality introduced by using dimethylolpropionic acid, phthalimide, or thioglycerol (transcutosine) as an additional reactant in the preparation of the resin. Alternatively, the reaction product is the reaction product of diglycidyl ether of bisphenol A (commercially available as EPON 880 from Shell Chemical Company), dimethylolpropionic acid, and diethanolamine at a molar ratio of 0.6-5.0: 0.05-5.5: 1. Other suitable resin substrates include the water-soluble and water-dispersible polyacrylics disclosed in U.S. Pat. Nos.3,912,548 and 5,328,525; phenolic resins described in U.S. patent No.5,662,746; water-soluble polyamides such as those described in WO 95/33869; copolymers of maleic or acrylic acid with allyl ethers as described in canadian patent application 2,087,352; and water soluble and water dispersible resins including epoxy resins, aminoplasts, phenolic resins, tannins, and polyvinylphenols, as discussed in U.S. patent No.5,449,415.

In these embodiments of the invention, the resinous binder is present in the pretreatment composition in an amount of from 0.005 to 30 weight percent, for example from 0.5 to 3 weight percent, based on the total weight of the components in the composition.

In other embodiments, however, the pretreatment composition is substantially free, or in some cases completely free, of any resinous binder. As used herein, the term "substantially free," when used with respect to the absence of resinous binder in the pretreatment composition, means that any resinous binder is present in the pretreatment composition in an amount of less than 0.005 weight percent. The term "completely free" as used herein means that there is no resin binder at all in the pretreatment composition.

The pretreatment composition may optionally contain other materials conventionally used in the pretreatment art such as nonionic surfactants and adjuvants. In the aqueous medium, there may be present a water-dispersible organic solvent such as an alcohol having up to about 8 carbon atoms, e.g., methanol, isopropanol, and the like; or glycol ethers such as monoalkyl ethers of ethylene glycol, diethylene glycol or propylene glycol, and the like. When present, the water-dispersible organic solvent is typically used in an amount up to about 10 volume percent, based on the total volume of the aqueous medium.

Other optional materials include surfactants that act as defoamers or substrate wetting agents.

In certain embodiments, the pretreatment composition further comprises a reaction promoter, such as nitrite ions, nitrate ions, nitro-containing compounds, hydroxylamine sulfate, persulfate ions, sulfite ions, thiosulfate ions, peroxides, iron (III) ions, ferric citrate compounds, bromate ions, perchloride ions (perchlorinate ions), chlorate ions, chlorite ions, as well as ascorbic acid, citric acid, tartaric acid, malonic acid, succinic acid, and salts thereof. Specific examples of suitable materials and their amounts are described in U.S. patent application publication No.2004/0163736A1 [0032] - [0041], the cited portion of which is incorporated herein by reference.

In certain embodiments, the pretreatment composition further comprises a filler, such as a siliceous filler. Non-limiting examples of suitable fillers include silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gel, and glass particles. In addition to siliceous fillers, other finely divided, substantially water-insoluble fillers may also be used. Examples of such optional fillers include carbon black, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, antimony oxide, zirconium oxide, magnesium oxide, aluminum oxide, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate.

In certain embodiments, the pretreatment composition comprises phosphate ions. In certain embodiments, the phosphate ion is present in an amount of 10 to 500ppm phosphate ion, such as 25 to 200ppm phosphate ion. Exemplary sources of phosphate ions include H₃PO₄、NaH₂PO₄And/or (NH)₄)₂H₂PO₄. In certain embodiments, however, the pretreatment compositions of the present invention are substantially free or, in some cases, completely free of phosphate ions. As used herein, the term "substantially free," when used in reference to the absence of phosphate ions in the pretreatment composition, means that phosphate ions are present in the composition in an amount less than 10 ppm. As used herein, the term "completely free", when used in reference to the absence of phosphate ions, means that there are no phosphate ions at all in the composition.

In certain embodiments, the pretreatment composition is substantially free, or in some cases completely free, of chromate and/or heavy metal phosphate, such as zinc phosphate. The term "substantially free" as used herein when used in reference to the absence of chromate and/or heavy metal phosphate in the pretreatment composition means that these materials are not present in the composition to such an extent that they pose an environmental burden. That is, they are not substantially used and the formation of sludge such as zinc phosphate formed in the case of using a treating agent based on zinc phosphate is eliminated. As used herein, the term "completely free", when used in relation to the absence of heavy metal phosphates and/or chromates, means that there are no heavy metal phosphates and/or chromates at all in the composition.

Further, in certain embodiments, the pretreatment composition is substantially free, or in some cases completely free, of any organic material. The term "substantially free", when used in reference to the absence of organic material in the composition, as used herein, means that any organic material, if any, is present in the composition as an incidental impurity. In other words, the presence of any organic material does not affect the properties of the composition. The term "completely free", as used herein when used in reference to the absence of organic matter, means that there is no organic matter at all in the composition.

In certain embodiments, the film coverage of the residue of the pretreatment coating composition is generally from 1 to 1000 milligrams per square meter (mg/m)²) E.g. 10-400mg/m². The thickness of the pretreatment coating can vary, but it is typically very thin, often having a thickness of less than 1 micron, in some cases from 1 to 500 nanometers, and in other cases from 10 to 300 nanometers.

After contact with the pretreatment solution, the substrate may be rinsed with water and dried.

In certain embodiments of the method of the present invention, after the substrate is contacted with the pretreatment composition, it is then contacted with a coating composition comprising a film-forming resin. Any suitable technique can be used to contact the substrate with the coating composition, including, for example, brushing, dipping, flow coating, spraying, and the like. However, in certain embodiments described in more detail below, the contacting comprises an electrocoating step in which an electrodepositable composition is deposited on the metal substrate by electrodeposition.

The term "film-forming resin" as used herein refers to a resin that can form a self-supporting continuous film on at least the horizontal surface of a substrate when any diluent or carrier present in the composition is removed or when cured at ambient or elevated temperature. Conventional film-forming resins that may be used include, but are not limited to, those typically used in automotive OEM coating compositions, automotive refinish coating compositions, industrial coating compositions, agricultural coating compositions, coil coating compositions, and aerospace coating compositions.

In certain embodiments, the coating composition comprises a thermosetting film-forming resin. The term "thermoset" as used herein refers to a resin that is irreversibly "fixed" when cured or crosslinked, wherein the polymer chains of the polymeric components are linked together by covalent bonds. This property is often associated with crosslinking reactions of the composition components, which are often induced, for example, by heat or radiation. The curing or crosslinking reaction may also be carried out under ambient conditions. Once cured or crosslinked, the thermoset resin will not melt and be insoluble in solvents upon application of heat. In other embodiments, the coating composition comprises a thermoplastic film-forming resin. The term "thermoplastic" as used herein refers to a resin that comprises polymer components that are not linked by covalent bonds and therefore may undergo liquid flow when heated and is soluble in a solvent.

As previously mentioned, in certain embodiments, the substrate is contacted with a coating composition comprising a film-forming resin by an electrocoating step in which an electrodepositable composition is deposited on the metal substrate by electrodeposition. In the electrodeposition process, the treated metal substrate, which serves as an electrode, and a conductive counter electrode are contacted with an ionic electrodepositable composition. When an electric current is passed between the electrode and the counter electrode while they are in contact with the electrodepositable composition, an adherent film of the electrodepositable composition will be deposited on the metal substrate in a substantially continuous manner.

Electrodeposition is generally carried out at a constant voltage of 1 volt to several thousand volts, typically 50-500 volts. The current density is typically 1.0-15 amps/sq ft (10.8-161.5 amps/sq meter) and tends to decrease rapidly during the electrodeposition process, indicating the formation of a continuous self-insulating film.

The electrodepositable composition useful in certain embodiments of the present invention generally comprises a resinous phase dispersed in an aqueous medium, wherein the resinous phase comprises: (a) an active hydrogen group-containing ionic electrodepositable resin, and (b) a curing agent having functional groups reactive with the active hydrogen groups of (a).

In certain embodiments, the electrodepositable compositions useful in certain embodiments of the present invention comprise as the primary film-forming polymer an active hydrogen-containing, ionic, often cationic, electrodepositable resin. A wide variety of electrodepositable film-forming resins are known and can be used in the present invention, so long as the polymer is "water dispersible," i.e., suitable for dissolution, dispersion, or emulsification in water. The water dispersible polymer is ionic in nature, i.e., the polymer will contain anionic functional groups to impart a negative charge or, generally, preferably, cationic functional groups to impart a positive charge.

Examples of film-forming resins suitable for use in the anionic electrodepositable composition are alkali-soluble carboxylic acid-containing polymers, such as the reaction products or adducts of drying oils or semi-drying fatty acid esters with dicarboxylic acids or anhydrides; and the reaction product of a fatty acid ester, an unsaturated acid or anhydride and any additional unsaturated modifying material that is further reacted with a polyol. Also suitable are at least partially neutralized interpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acids and at least one other ethylenically unsaturated monomer. Another suitable electrodepositable film-forming resin includes an alkyd-aminoplast vehicle, i.e., a vehicle comprising an alkyd resin and an amine-aldehyde resin. Another anionic electrodepositable resin composition comprises a mixed ester of a resin polyol, such as described in U.S. Pat. No.3,749,657, columns 9, lines 1-75 and columns 10, lines 1-13, the cited portion being incorporated herein by reference. Other acid functional polymers may also be used, such as phosphated polyepoxides (phosphated polyepoxides) or phosphated acrylic polymers, as are well known to those skilled in the art.

As previously mentioned, it is generally desirable that the active hydrogen-containing ionic electrodepositable resin (a) be cationic and capable of being deposited on the cathode. Examples of such cationic film-forming resins include amine salt group-containing resins, such as acid-soluble reaction products of polyepoxides and primary or secondary amines, such as described in U.S. Pat. nos.3,663,389; 3,984,299; 3,947,338 and 3,947,339. Typically, these amine salt group-containing resins are used in combination with a blocked isocyanate curing agent. The isocyanate may be fully blocked, as described in U.S. Pat. No.3,984,299, or the isocyanate may be partially blocked and reacted with the resin backbone, as described, for example, in U.S. Pat. No.3,947,338. As film-forming resins, it is additionally possible to use one-component compositions as described in U.S. Pat. No.4,134,866 and DE-OS No.2,707,405. In addition to the epoxy-amine reaction product, the film-forming resin may also be selected from cationic acrylic resins, such as those described in U.S. Pat. Nos.3,455,806 and 3,928,157.

In addition to amine salt group-containing resins, quaternary ammonium salt group-containing resins, such as those formed from the reaction of an organic polyepoxide with a tertiary amine salt, as described in U.S. patent nos.3,962,165; 3,975,346, respectively; and 4,001,101. Examples of other cationic resins are tertiary sulfonium salt group-containing resins and quaternary phosphonium salt group-containing resins, such as those described in U.S. Pat. Nos.3,793,278 and 3,984,922, respectively. Film-forming resins which cure by transesterification, such as described in European application No.12463, may also be used. Additionally, cationic compositions prepared from mannich bases, such as described in U.S. Pat. No.4,134,932, can be used.

In certain embodiments, the resin present in the electrodepositable composition is a positively charged resin containing primary and/or secondary amine groups, such as described in U.S. patent nos.3,663,389; 3,947,339, respectively; and 4,116,900. In U.S. Pat. No.3,947,339, a polyketimine derivative of a polyamine, such as diethylenetriamine or triethylenetetramine, is reacted with a polyepoxide. When the reaction product is neutralized with an acid and dispersed in water, free primary amine groups are generated. Additionally, equivalent products are formed when polyepoxides are reacted with excess polyamines such as diethylenetriamine and triethylenetetramine and the excess polyamine is vacuum stripped from the reaction mixture, as described in U.S. Pat. nos.3,663,389 and 4,116,900.

In certain embodiments, the active hydrogen-containing ionic electrodepositable resin is present in the electrodepositable composition in an amount of from 1 to 60 percent by weight, such as from 5 to 25 percent by weight, based on the total weight of the electrodeposition bath.

As noted, the resin phase of the electrodepositable composition typically further comprises a curing agent suitable for reacting with the active hydrogen groups of the ionic electrodepositable resin. For example, both blocked organic polyisocyanates and aminoplast curing agents are suitable for use in the present invention, although blocked isocyanates are generally preferred for cathodic electrodeposition herein.

Aminoplast resins, which are generally the preferred curing agents for anionic electrodeposition (ionic electrodeposition), are condensation products of amines or amides with aldehydes. Examples of suitable amines or amides are melamine, benzoguanamine, urea and similar compounds. Generally, the aldehyde used is formaldehyde, although the product can be made from other aldehydes such as acetaldehyde and furfural. Depending on the particular aldehyde used, the condensation product comprises a hydroxymethyl group or a similar hydroxyalkyl group. Typically, these methylol groups are etherified by reaction with an alcohol, such as a monohydric alcohol containing from 1 to 4 carbon atoms, e.g., methanol, ethanol, isopropanol, and n-butanol. Aminoplast resins are commercially available under the trademark CYMEL from American Cyanamid co. and under the trademark RESIMENE from Monsanto Chemical co.

The aminoplast curing agent is typically used in combination with the active hydrogen-containing anionic electrodepositable resin in an amount of from 5 to 60 weight percent, such as from 20 to 40 weight percent, based on the total weight of resin solids in the electrodepositable composition.

As noted, blocked organic polyisocyanates are commonly used as curing agents in cathodic electrodeposition compositions. The polyisocyanate may be fully blocked as described in U.S. Pat. No.3,984,299, columns 1-68, lines 2 and columns 3, lines 1-15, or the polyisocyanate may be partially blocked and reacted with the polymer backbone as described in U.S. Pat. No.3,947,338, columns 2, lines 65-68, columns 3 and columns 4, lines 1-30, the references of which are incorporated herein by reference. By "blocked" is meant that the isocyanate groups have been reacted with a compound such that the resulting blocked isocyanate groups are stable to active hydrogen at ambient temperatures but are reactive with active hydrogen in the film-forming polymer at elevated temperatures, typically 90 ℃ to 200 ℃.

Suitable polyisocyanates include aromatic and aliphatic polyisocyanates, including cycloaliphatic polyisocyanates, and representative examples include diphenylmethane 4, 4 ' -diisocyanate (MDI), 2, 4-or 2, 6-Toluene Diisocyanate (TDI), including mixtures thereof, p-phenylene diisocyanate, tetramethylene diisocyanate and hexamethylene diisocyanate, dicyclohexylmethane 4, 4 ' -diisocyanate, isophorone diisocyanate, phenylmethane 4, 4 ' -diisocyanate and polymethylene polyphenylisocyanate. Higher polyisocyanates such as triisocyanates can be used. One example would include triphenylmethane-4, 4', 4 "-triisocyanate. Isocyanate prepolymers with polyols such as neopentyl glycol and trimethylolpropane, and with polymeric polyols such as polycaprolactone diols and triols (NCO/OH equivalent ratio greater than 1) may also be used.

The polyisocyanate curing agent is typically used in combination with the active hydrogen-containing cationic electrodepositable resin in an amount of from 5 to 60 weight percent, such as from 20 to 50 weight percent, based on the total weight of resin solids in the electrodepositable composition.

In certain embodiments, the coating composition comprising the film-forming resin further comprises yttrium. In certain embodiments, yttrium is present in the composition in an amount of from 10 to 10,000ppm, such as no greater than 5,000ppm, and in some cases no greater than 1,000ppm, of total amount yttrium (measured as elemental yttrium).

Both soluble and insoluble yttrium compounds can serve as sources of yttrium. Examples of sources of yttrium suitable for use in lead-free electrodepositable coating compositions are soluble organic and inorganic yttrium salts such as yttrium acetate, yttrium chloride, yttrium formate, yttrium carbonate, yttrium sulfamate, yttrium lactate, and yttrium nitrate. Yttrium nitrate, a readily available yttrium compound, is a preferred source of yttrium when yttrium is to be added to the electrocoat bath as an aqueous solution. Other yttrium compounds suitable for use in electrodepositable compositions are organic and inorganic yttrium compounds, such as yttrium oxide, yttrium bromide, yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate, and yttrium oxalate. Organic yttrium complexes and yttrium metal may also be used. Yttrium oxide is often a preferred source of yttrium when yttrium is to be incorporated into the electrocoat bath as a component in the pigment paste.

The electrodepositable compositions described herein are in the form of an aqueous dispersion. The term "dispersion" is considered to be a two-phase transparent, translucent or opaque resin system in which the resin is in the dispersed phase and the water is in the continuous phase. The average particle size of the resinous phase is generally less than 1.0 micron, typically less than 0.5 micron, and often less than 0.15 micron.

The concentration of the resinous phase in the aqueous medium is often at least 1% by weight, for example 2 to 60% by weight, based on the total weight of the aqueous dispersion. When the compositions are in the form of resin concentrates, they generally have a resin solids content of from 20 to 60 percent by weight, based on the weight of the aqueous dispersion.

The electrodepositable compositions described herein are often provided as two components: (1) a transparent resin feed generally comprising the active hydrogen-containing ionic electrodepositable resin, i.e., the primary film-forming polymer, a curing agent, and any additional water-dispersible non-tinting components; and (2) pigment pastes, which typically include one or more colorants (described below), a water-dispersible grinding resin that may be the same as or different from the primary film-forming polymer, and optionally, additives such as wetting or dispersing aids. Electrodeposition bath components (1) and (2) are dispersed in an aqueous medium comprising water and, typically, a coalescing solvent.

As previously mentioned, the aqueous medium may contain a coalescing solvent in addition to water. Coalescing solvents which may be used are often hydrocarbons, alcohols, esters, ethers and ketones. Preferred coalescing solvents are often alcohols, polyols and ketones. Specific coalescing solvents include isopropanol, butanol, 2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene glycol, and propylene glycol, as well as the monoethyl ether, monobutyl ether, and monohexyl ether of ethylene glycol. The amount of coalescing solvent is generally from 0.01 to 25 wt%, for example from 0.05 to 5 wt%, based on the total weight of the aqueous medium.

In addition, a colorant and, if desired, various additives such as surfactants, wetting agents or catalysts may be included in the coating composition containing the film-forming resin. The term "colorant" as used herein refers to any substance that imparts color and/or other opacity and/or other visual effect to the composition. The colorant can be added to the composition in any suitable form, such as discrete particles, dispersions, solutions, and/or flakes. A single colorant or a mixture of two or more colorants may be used.

Examples of colorants include pigments, dyes, and tints, such as those used in the coatings industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. The colorant may comprise, for example, a finely divided solid powder that is insoluble but wettable under the conditions of use. The colorant may be organic or inorganic and may be aggregated or non-aggregated. The colorant can be incorporated by utilizing a grind vehicle, such as an acrylic grind vehicle, the use of which is well known to those skilled in the art.

Examples of pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, disazo, naphthol AS, salt type (lakes), benzimidazolone, condensate, metal complex, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolopyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketopyrrolopyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures thereof. The terms "pigment" and "colored filler" are used interchangeably.

Examples of dyes include, but are not limited to, those that are solvent and/or aqueous based such as phthalocyangreen or phthalocyanblue, iron oxide, bismuth vanadate, anthraquinone, perylene, aluminum, and quinacridone.

Examples of tints include, but are not limited to, pigments dispersed in an aqueous-based or water-miscible vehicle such as AQUA-CHEM 896 commercially available from Degussa, inc., CHARISMA COLORANTS and maxi @ neutral COLORANTS commercially available from Accurate Dispersions of eastman chemical, inc.

As noted above, the colorant can be in the form of a dispersion, including but not limited to in the form of a nanoparticle dispersion. Nanoparticle dispersions can include one or more highly dispersed nanoparticle colorants and/or colorant particles that produce a desired visible color and/or opacity and/or visual effect. The nanoparticle dispersion may include a colorant such as a pigment or dye having a particle size of less than 150nm, such as less than 70nm or less than 30 nm. Nanoparticles can be produced by milling raw organic or inorganic pigments with grinding media having a particle size of less than 0.5 mm. Examples of nanoparticle dispersions and their methods of manufacture are described in U.S. Pat. No.6,875,800B 2, incorporated herein by reference. Nanoparticle dispersions can also be produced by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). To minimize re-aggregation of the nanoparticles in the coating, a dispersion of resin-coated nanoparticles may be used. As used herein, a "dispersion of resin-coated nanoparticles" refers to a continuous phase in which are dispersed discrete "composite particles" comprising nanoparticles and a resin coating on the nanoparticles. Examples of dispersions of resin-coated nanoparticles and methods for their manufacture are described in U.S. patent application publication 2005-0287348a1, filed 24.6.2004, and U.S. provisional application No. 60/482,167, filed 24.6.2003, and U.S. patent application No. 11/337,062, filed 20.1.2006, which are incorporated herein by reference.

Examples of special effect compositions that may be used include pigments and/or compositions that produce one or more appearance effects such as reflectance, pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism, photosensitivity, thermochromism, goniochromism (goniochromism), and/or color change. Additional special effect compositions may provide other perceptible properties such as opacity or texture. In certain embodiments, the special effect composition may produce a color shift such that the color of the coating changes when the coating is viewed at different angles. Examples of color effect compositions are described in U.S. Pat. No.6,894,086, which is incorporated herein by reference. Additional color effect compositions can include transparent coated mica and/or synthetic mica, coated silica, coated alumina, transparent liquid crystal pigments, liquid crystal coatings, and/or any composition in which interference is caused by refractive index differences within the material and not due to refractive index differences between the surface of the material and the air.

In certain embodiments, photosensitive compositions and/or photochromic compositions that reversibly change their color when exposed to one or more light sources may be used. Photochromic and/or photosensitive compositions can be activated by exposure to radiation of a particular wavelength. When the composition is excited, the molecular structure is altered and the altered structure exhibits a new color that is different from the original color of the composition. When the exposure to radiation is removed, the photochromic and/or photosensitive composition can return to a static state, wherein the original color of the composition is restored. In certain embodiments, the photochromic and/or photosensitive compositions can be colorless in a non-excited state and exhibit color in an excited state. Complete discoloration can occur in milliseconds to several minutes, for example 20 seconds to 60 seconds. Examples of photochromic and/or photosensitive compositions include photochromic dyes.

In certain embodiments, the photosensitive composition and/or photochromic composition can be associated and/or at least partially associated, such as by covalent bonding, with the polymeric material of the polymer and/or polymerizable component. In contrast to some coatings in which the photosensitive composition may migrate out of the coating and crystallize into the substrate, photosensitive compositions and/or photochromic compositions associated with and/or at least partially bound to polymers and/or polymerizable components according to certain embodiments of the present invention have minimal migration out of the coating. Examples of photosensitive and/or photochromic compositions and methods for their preparation are described in U.S. application No.10/892,919, filed on 7, 16, 2004, which is incorporated herein by reference.

In general, the colorant can be present in the coating composition in any amount sufficient to impart the desired visual and/or color effect. The colorant may comprise 1 to 65 weight percent, such as 3 to 40 weight percent or 5 to 35 weight percent, with weight percent based on the total weight of the composition.

After deposition, the coating is typically heated to cure the deposited composition. The heating or curing operation is typically carried out at a temperature of 120-250 deg.C, such as 190 deg.C for a time period of 10-60 minutes. In certain embodiments, the resulting film has a thickness of 10 to 50 microns.

As will be appreciated from the foregoing description, the present invention relates to a composition for treating a metal substrate. These compositions comprise: (a) a group IIIB and/or IVB metal; (b) an electropositive metal; (c) 0.1-300 parts per million ("ppm") of free fluorine; (d) by forming a pK having a value of at least 11_spMetal fluoride salts of the fluoride salts of (a); and (e) water. In certain embodiments, the composition is substantially free of heavy metal phosphates, such as zinc phosphate, and chromates.

In other aspects, the present invention relates to a composition for treating a metal substrate comprising: (a) a group IIIB and/or IVB metal; (b)0.1-300ppm free fluorine; (c) by formingHaving a pK of at least 11_spMetal fluoride salts of the fluoride salts of (a); and (d) water. These compositions of the invention are substantially free of phosphate ions and chromate.

As described throughout the foregoing specification, the methods and coated substrates of the present invention in certain embodiments include the deposition of crystalline phosphates, such as zinc phosphate or chromate. Thus, the environmental drawbacks associated with these substances can be avoided. However, the methods of the present invention have been shown to provide coated substrates that are, in at least some cases, corrosion resistant at levels comparable to, or in some cases even superior to, the methods in which these materials are used. This is a surprising and unexpected discovery of the present invention and meets the long-felt need in the art.

The following examples illustrate the invention and should not be construed as limiting the invention to their details. All parts and percentages in the examples, as well as throughout the specification, are by weight unless otherwise indicated.

Examples

Fluoride ion concentrations, both free and total fluoride, can be measured using various methods well known to those skilled in the art. Typically, ion selective electrodes ("ISEs"), such as those provided by VWR International, are usedA fluoride ion selective combination electrode or similar electrode measures fluoride ion concentration. By immersing the electrode in a solution having a known fluoride ion concentration and recording the reading in millivolts; these millivolt readings are then plotted against a log curve to normalize the fluoride ion ISE. The millivolt reading of the unknown sample can then be compared to the calibration curve and the fluoride ion concentration determined. Alternatively, the fluoride ion ISE may be used with a meter that will perform calibration calculations internally, and thus the concentration of the unknown sample may be read directly after calibration.

Fluoride ions are small negative ions with a high charge density and therefore in aqueous solution they are usually complexed with metal ions with a high positive charge density, such as zirconium or titanium, or with hydrogen ions. The fluoride ions thus complexed cannot be measured with fluoride ion ISE unless the solution in which they are present is mixed with an ionic strength adjusting buffer which releases fluoride ions from these complexes. At this point, the fluoride ion can be measured by the fluoride ion ISE, and this measurement is referred to as "total fluoride ion". Fluoride measurements made without this reagent are referred to as "free fluoride" because only fluoride is not bound to hydrogen ions or is in a metal complex.

For purposes of the following examples, fluoride ions were measured as follows: calibration standards were prepared by adding 2mL of standard solutions each containing 100ppm, 300ppm, and 1000ppm chloride ion, respectively, to 50mL of ionic strength adjustment buffer consisting of 10 wt% sodium citrate dihydrate (available from Aldrich Chemical, Milwaukee, Wis.) in deionized water. The millivolt readings of each of these standards were then measured with the fluoride ion ISE and used to construct the calibration curve as described above. For total fluoride values, 2mL of the unknown solution was mixed with 50mL of sodium citrate buffer and the millivolt reading of the fluoride ion ISE of the solution was compared to the generated calibration curve to determine total fluoride. The free fluoride ion was determined by directly reading the millivolts of the sample solution and comparing to the calibration curve, and then dividing this value by 26 (this division is necessary because the standard was diluted 26 times due to the ionic strength adjusting buffer, and the free fluoride ion sample was not diluted).

Example 1

A 12L zirconium pretreatment bath was prepared as follows: 10.5g of 45% hexafluorozirconic acid (commercially available from Honeywell specialty Chemicals, Morristown, NJ) and 17.57g of a 5% w/w copper nitrate 2/5 hydrate solution (commercially available from Fisher Scientific, Fair Lawn, NJ) were added to about 12 liters of tap water. The solution was neutralized to pH 4.5 with Chemfil buffer (a mild alkaline buffer commercially available from PPGIndustries, Euclid, OH). Free fluoride was measured with ISE as described above and a value of 22ppm free fluoride was obtained.

Clean Cold Rolled Steel (CRS) panels were treated in this solution at 80 ° F for 2 minutes with moderate mixing. The panel had a bronze appearance with some blue iridescence and the coating thickness was measured at about 43nm using a portable X-ray fluorescence instrument (XRF).

16.8g Chemfos AFL (liquid free fluoride ion additive available from PPGIndsuities, Euclid, OH) was then added to the zirconium pretreatment solution. This addition caused the pH to drop slightly to 3.8. The pH of the solution was adjusted back to 4.5 with Chemfil buffer. Free fluoride was measured as before and found to be 170 ppm. Clean CRS panels were then treated through the bath as before. The plaque had a light bronze appearance and the estimated coating thickness was 20nm as measured by XRF. The presence of higher levels of free fluoride ions therefore results in a reduction in coating thickness of greater than 50%.

At this point, 3.02g of yttrium nitrate hexahydrate (available from Acros Organics-Fisher scientific, a subsidiary) was added to the zirconium pretreatment solution. This caused the pH to drop slightly to pH 4.3. It was adjusted back to 4.5 with Chemfil buffer. Free fluoride was measured as above and determined to be 115 ppm. The cleaned CRS plaques treated as above had a medium bronze color with some blue iridescence and a coating thickness of about 31nm as measured by XRF. The pretreatment bath was slightly cloudy, presumably indicating precipitation of the yttrium fluoride compound.

An additional 3.06g of yttrium nitrate hexahydrate was added to the zirconium pretreatment bath, which caused the pH to drop slightly to 4.2. Chemfil buffer was added to return the pH to 4.5. The free fluoride ion measured as above was 61ppm and the pretreatment bath had additional precipitate. The cleaned CRS panels treated as above by the pretreatment bath had a similar appearance to the previous panels. The coating thickness was about 45nm as measured by XRF.

An additional 2.98g of yttrium nitrate hexahydrate was added to the zirconium pretreatment bath. The pH of the bath was slightly lowered to 4.2; sufficient Chemfil buffer was added to bring the pH back to 4.5. Free fluoride was measured as above and found to be 24ppm, which is close to the starting value. Clean CRS panels were treated as above. The panel had a blue appearance with some iridescence. The thickness of the coating was about 61nm as measured by XRF.

Example 2

A 4 liter zirconium pretreatment bath was prepared as follows: 3.5g of 45% hexafluorozirconic acid and 5.84g of a 5% w/w copper nitrate 2/5 hydrate solution were added to about 4 liters of tap water to obtain a solution having 175ppm Zr and 20ppm Cu. The solution was neutralized to pH 4.5 with Chemfil buffer. The free fluoride ion of this solution was measured to be 22 ppm. The solution temperature was 82 ° F. 2 liters of this solution was removed and used to pre-treat clean CRS plates for 2 minutes. The plate had a medium bronze appearance and the coating thickness was found to be about 28nm using a portable XRF instrument.

To the 2 liter bath was added 6g Chemfos AFL. The pH dropped slightly to 3.8. The solution was returned to pH 4.5 by the addition of Chemfil buffer. The free fluoride ion is now measured at 320 ppm. Clean CRS plaques treated for 2 minutes through the bath had virtually invisible pretreatment; thickness was measured to be 4nm using XRF.

To this solution was added lanthanum nitrate hydrate (commercially available from Aldrich Chemical, Milwaukee, Wis.; 32% La). At this point the slightly turbid solution immediately became hazy. The pH, which dropped to 3.3 when lanthanum nitrate was added, was adjusted back to 4.5 with Chemfil buffer. The free fluoride ion was measured to be 31 ppm. The cleaned CRS plaque treated for 2 minutes by this bath was bronze coloured with blue iridescence and had a coating thickness of 25nm as measured by XRF.

Example 3

The remaining 2 liter portion of the initial 4L bath was used to treat the cleaned CRS panel for 2 minutes. The plaque had a medium bronze color and the zirconium pretreatment coating was measured to be about 27nm thick. To this bath was added 6g Chemfos AFL. The pH was slightly lowered to 3.7 and adjusted back to 4.5 by adding Chemfil buffer dropwise. The free fluoride ion of the bath is now measured at 316 ppm. Clean CRS plaques treated for 2 minutes by this bath had little visible pretreatment; thickness was measured to be 5nm using XRF.

To this solution was added cerium nitrate hexahydrate (commercially available from Alfa Aesar, Ward Hill, MA). At this point the slightly turbid solution immediately became hazy. The pH, which dropped to 3.3 when cerium nitrate was added, was adjusted back to 4.5 with Chemfil buffer. The free fluoride ion was measured to be 28 ppm. The cleaned CRS plaque treated for 2 minutes by this bath was bronze coloured with blue iridescence and had a coating thickness of 29nm as measured by XRF.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims (20)

1. A method of treating a metal substrate comprising:

contacting the substrate with a pretreatment composition comprising:

a group IIIB and/or IVB metal;

an electropositive metal;

free fluorine; and

the amount of water is controlled by the amount of water,

providing a soluble metal salt to the pretreatment composition, the salt forming a pK having a pK of at least 11_spInsoluble metal fluoride of (a);

wherein the formation of a pK having a pK of at least 11 is provided in an amount sufficient to maintain a free fluorine content in the composition of not less than 0.1ppm and not more than 300ppm_spThe metal of the metal fluoride salt of (1).

2. The method of claim 1, wherein the metal substrate comprises cold rolled steel, hot dip galvanized steel, galvanealed steel, and/or a galvanized alloy steel.

3. The process of claim 1, wherein the group IIIB and/or IVB metal comprises zirconium.

4. The method of claim 1, wherein the group IIIB and/or IVB metal is present in the pretreatment composition in an amount of at least 100ppm metal.

5. The method of claim 1, wherein the electropositive metal comprises nickel, copper, silver, and/or gold.

6. The method of claim 1, wherein the electropositive metal is included in the pretreatment composition in an amount of at least 10ppm total metal measured as elemental metal.

7. The process of claim 1 wherein the free fluorine is derived from hexafluorozirconic acid.

8. The method of claim 1, wherein the pK is formed to have a pK of at least 11_spThe metal of fluoride salt of (a) forming a metal fluoride salt comprises yttrium.

9. The method of claim 1, wherein providing a pK to form a composition having a pK of at least 11 is in an amount sufficient to maintain a level of free fluorine in the composition of not less than 0.1ppm and not greater than 100ppm_spThe metal of the metal fluoride salt of (1).

10. The method of claim 1, wherein the pretreatment composition is substantially free of phosphate ions.

11. The method of claim 1, wherein the pretreatment composition is substantially free of chromate and/or zinc phosphate.

12. The method of claim 1, further comprising contacting the substrate with a coating composition comprising a film-forming resin, wherein contacting comprises an electrocoating step in which an electrodepositable composition is deposited on the metal substrate by electrodeposition.

13. A pretreatment composition for treating a metal substrate comprising:

a group IIIB and/or IVB metal;

an electropositive metal;

0.1-300ppm free fluorine;

by forming a pK having a value of at least 11_spA metal comprising yttrium, lanthanum, scandium, and combinations thereof; and

water;

wherein the formation of a pK having a pK of at least 11 is provided in an amount sufficient to maintain a free fluorine content in the composition of not less than 0.1ppm and not more than 300ppm_spInsoluble metal fluoride of (a).

14. The pretreatment composition of claim 13, wherein free fluorine is present in the composition in an amount not less than 0.1ppm and not greater than 100 ppm.

15. The pretreatment composition of claim 13, wherein the group IIIB and/or IVB metal comprises zirconium.

16. The pretreatment composition of claim 13, wherein the group IIIB and/or IVB metal is present in the pretreatment composition in an amount of at least 100ppm metal.

17. The pretreatment composition of claim 13, wherein the electropositive metal comprises nickel, copper, silver, and/or gold.

18. The pretreatment composition of claim 13, wherein the electropositive metal is included in the pretreatment composition in an amount of at least 10ppm total metal measured as elemental metal.

19. The pretreatment composition of claim 13, wherein the pretreatment composition is substantially free of phosphate ions.

20. A pretreatment composition for treating a metal substrate comprising:

(a) a group IIIB and/or IVB metal;

(b)0.1-300ppm free fluorine;

(c) by forming a pK having a value of at least 11_spMetal fluoride salts of the fluoride salts of (a); and

(d) the amount of water is controlled by the amount of water,

wherein the composition is substantially free of phosphate ions and chromate.