Coated metal substrates and methods for preparing and inhibiting corrosion of the same

The present invention provides a metal substrate coated with a first pretreatment composition including a transition element-containing material having one or more Group IIIB elements, Group IVB elements, lanthanide series elements or mixtures thereof; and a second pretreatment composition including a reaction product of at least one epoxy-functional material or derivative thereof and at least phosphorus-containing material, amine-containing material and/or sulfur-containing material deposited upon the first pretreatment composition. If desired, the first and second pretreatment compositions can be combined into a single pretreatment.

FIELD OF THE INVENTION
 This invention relates generally to corrosion-resistant coated metal
 substrates and, more particularly, to ferrous and non-ferrous metal
 substrates having environmentally friendly chrome-free and nickel-free
 coatings thereon which inhibit corrosion of the metal substrate.
 BACKGROUND OF THE INVENTION
 Pretreating metal substrates with a phosphate conversion coating and
 rinsing with a chrome-containing sealer is well known for promoting
 corrosion resistance and improving the adhesion of subsequently applied
 decorative and protective coatings. Cationic electrodeposition
 compositions are typically applied over phosphated steel substrates to
 further improve corrosion resistance. While the combination of phosphate
 conversion coating and electrodeposited coating provides superior
 corrosion resistance, heavy metals typically used in such coatings can
 provide environmental disposal concerns. For example, phosphate conversion
 coating compositions typically contain heavy metals such as nickel and
 post-rinses contain chrome, while cationic electrodeposition compositions
 typically are formulated with lead as a pigment or soluble lead salt.
 Also, conventional phosphating processes can require eleven to twenty-five
 stages that occupy a large amount of physical space in a plant and require
 significant capital investment. Another drawback of conventional
 phosphating processes is difficulty in coating mixed-metal objects
 including aluminum.
 Nickel-free phosphate coating compositions and chrome-free rinsing
 compositions having comparable corrosion resistance to nickel- and
 chrome-containing compositions are highly desirable. Rinsing compositions
 utilizing metal ions other than chromium are disclosed, for example, in
 U.S. Pat. Nos. 3,966,502 and 4,132,572. U.S. Pat. No. 3,966,502 discloses
 treatment of phosphated metals with zirconium-containing rinse solutions.
 U.S. Pat. Nos. 3,912,548, 5,209,788, and 5,653,823 disclose other rinse
 compositions containing combinations of Group IVB metal ions with
 polymeric materials that have been used over phosphated substrates.
 However, many post-rinse compositions are suitable for use over a limited
 number of substrates or over substrates that must be phosphated first.
 It would be desirable to provide a simplified pretreatment process free of
 heavy metals for coating metal substrates, including mixed metal
 substrates such as are commonly found on today's automobile bodies. Such a
 pretreatment process, when combined with a lead-free electrodeposition
 process, would provide an environmentally friendly alternative for
 providing corrosion resistance to metal substrates.
 SUMMARY OF THE INVENTION
 The present invention provides a coated metal substrate comprising: (a) a
 metal substrate; (b) a first pretreatment composition deposited upon at
 least a portion of the substrate, the first pretreatment composition
 comprising a transition element-containing material which comprises a
 transition element selected from the group consisting of Group IIIB
 elements, Group IVB elements, lanthanide series elements and mixtures
 thereof; and (c) a second pretreatment composition comprising a reaction
 product of at least one epoxy-functional material or derivative thereof
 and at least one material selected from the group consisting of
 phosphorus-containing materials, amine-containing materials,
 sulfur-containing materials and mixtures thereof deposited upon at least a
 portion of the first pretreatment composition.
 In another aspect of the present invention, a weldable, coated metal
 substrate is provided which comprises (a) a metal substrate; (b) a first
 pretreatment composition comprising a transition element-containing
 material which comprises a transition element selected from the group
 consisting of Group IIIB elements, Group IVB elements, lanthanide series
 elements and mixtures thereof deposited upon at least a portion of the
 substrate; (c) a second pretreatment composition comprising a reaction
 product of at least one epoxy functional material or derivative thereof
 and at least one material selected from the group consisting of
 phosphorus-containing materials, amine-containing materials,
 sulfur-containing materials and mixtures thereof deposited upon at least a
 portion of the first pretreatment composition; and (d) a weldable
 composition comprising an electroconductive pigment and a binder deposited
 upon at least a portion of the second pretreatment composition.
 In another aspect of the present invention, a coated metal substrate is
 provided which comprises: (a) a metal substrate; (b) a first pretreatment
 composition comprising a transition element-containing material which
 comprises a transition element selected from the group consisting of Group
 IIIB elements, Group IVB elements, lanthanide series elements and mixtures
 thereof deposited upon at least a portion of the substrate; and (c) a
 second pretreatment composition comprising an ester of a
 phosphorus-containing material deposited upon at least a portion of the
 first pretreatment composition.
 In another aspect of the present invention, a method for preparing a coated
 metal substrate is provided which comprises the steps of: (a) treating a
 surface of a metal substrate with a first pretreatment composition
 comprising a transition element-containing material which comprises a
 transition element selected from the group consisting of Group IIIB
 elements, Group IVB elements, lanthanide series elements and mixtures
 thereof; and (b) applying a second pretreatment composition comprising a
 reaction product of at least one epoxy functional material or derivative
 thereof and at least one material selected from the group consisting of
 phosphorus-containing materials, amine-containing materials,
 sulfur-containing materials and mixtures thereof over at least a portion
 of the first pretreatment composition to form a substrate having a
 pretreated surface.
 In another aspect of the present invention, a method for inhibiting
 corrosion of a metal substrate is provided which comprises: (a) treating a
 surface of a metal substrate with a first pretreatment composition
 comprising a transition element-containing material which comprises a
 transition element selected from the group consisting of Group IIIB
 elements, Group IVB elements, lanthanide series elements and mixtures
 thereof; (b) applying a second pretreatment composition comprising a
 reaction product of at least one epoxy functional material or derivative
 thereof and at least one material selected from the group consisting of
 phosphorus-containing materials, amine-containing materials,
 sulfur-containing materials and mixtures thereof over at least a portion
 of the first pretreatment composition to form a substrate having a
 pretreated surface; and (c) applying a weldable coating to the pretreated
 surface to form a corrosion-resistant coated metal substrate, the weldable
 coating comprising an electroconductive pigment and a binder.
 In another aspect of the present invention, a coated metal substrate is
 provide which comprises: (a) a metal substrate; and (b) a pretreatment
 composition deposited upon at least a portion of the substrate, the
 pretreatment composition comprising (1) a transition element-containing
 material which comprises a transition element selected from the group
 consisting of Group IIIB elements, Group IVB elements, lanthanide series
 elements and mixtures thereof; and (2) a reaction product of at least one
 epoxy-functional material or derivative thereof and at least one material
 selected from the group consisting of phosphorus-containing materials,
 amine-containing materials, sulfur-containing materials and mixtures
 thereof deposited upon at least a portion of the first pretreatment
 composition.
 In another aspect of the present invention, a method for preparing a coated
 metal substrate is provided which comprises the step of treating a surface
 of a metal substrate with a pretreatment composition comprising (1) a
 transition element-containing material which comprises a transition
 element selected from the group consisting of Group IIIB elements, Group
 IVB elements, lanthanide series elements and mixtures thereof; and (2) a
 reaction product of at least one epoxy functional material or derivative
 thereof and at least one material selected from the group consisting of
 phosphorus-containing materials, amine-containing materials,
 sulfur-containing materials and mixtures thereof over at least a portion
 of the first pretreatment composition to form a substrate having a
 pretreated surface.
 Other than in the operating examples, or where otherwise indicated, all
 numbers expressing quantities of ingredients, reaction conditions, and so
 forth used in the specification and claims are to be understood as being
 modified in all instances by the term "about". Also, as used herein, the
 term "polymer" is meant to refer to oligomers, homopolymers and
 copolymers.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The metal substrates used in the practice of the present invention include
 ferrous metals, non-ferrous metals and combinations thereof. Suitable
 ferrous metals include iron, steel, and alloys thereof. Non-limiting
 examples of useful steel materials include cold rolled steel, hot
 galvanized (zinc coated) steel, electrogalvanized steel, stainless steel,
 pickled steel, zinc-iron alloy such as GALVANNEAL, GALVALUME and GALFAN
 zinc-aluminum alloys coated over steel, and combinations thereof. Useful
 non-ferrous metals include aluminum, zinc, magnesium and alloys thereof.
 Combinations or composites of ferrous and non-ferrous metals can also be
 used. The shape of the metal substrate can be in the form of a sheet,
 plate, bar, rod or any shape desired.
 Before depositing the coating compositions of the present invention upon
 the surface of the metal substrate, it is preferred to remove dirt or
 foreign matter from the metal surface by thoroughly cleaning and
 degreasing the surface. The surface of the metal substrate can be cleaned
 by physical or chemical means, such as mechanically abrading the surface
 or cleaning/degreasing with commercially available alkaline or acidic
 cleaning agents which are well known to those skilled in the art, such as
 sodium metasilicate and sodium hydroxide. Non-limiting examples of
 suitable alkaline cleaning agents include CHEMKLEEN 163 and CHEMKLEEN 177
 phosphate cleaners that are commercially available from PPG Industries,
 Inc. of Pittsburgh, Pa.
 Following the cleaning step, the surface of the metal substrate is usually
 rinsed with water, preferably deionized water, in order to remove any
 residue. Optionally, the metal surface can be rinsed with an aqueous
 acidic solution after cleaning with the alkaline cleaner and before
 contact with the passivating compositions. Examples of rinse solutions
 include mild or strong acidic cleaners such as the dilute nitric acid
 solutions commercially available and conventionally used in metal
 pretreatment processes. The metal substrate can be air dried using an air
 knife, by flashing off the water by brief exposure of the substrate to a
 high temperature or by passing the substrate between squeegee rolls.
 Optionally, a phosphate-based conversion coating can be applied to the
 metal substrate. Suitable phosphate conversion coating compositions
 include those known in the art, such as zinc phosphate, optionally
 modified with nickel, iron, manganese, calcium, magnesium or cobalt.
 Useful phosphating compositions are described in U.S. Pat. Nos. 4,941,930,
 5,238,506, and 5,653,790.
 Following the optional acid rinsing and phosphating steps, the metal
 substrate is contacted with a first pretreatment or passivating
 composition that improves the corrosion resistance of the metal substrate
 compared to its corrosion resistance without such a treatment. The first
 pretreatment composition comprises one or more transition
 element-containing materials which comprise one or more transition
 elements selected from the group consisting of Group IIIB elements, Group
 IVB elements, lanthanide series elements and mixtures thereof. The Group
 IIIB elements, Group IVB elements and lanthanide series elements referred
 to herein are those elements included in such groups in the CAS Periodic
 Table of the Elements as shown, for example, in the Handbook of Chemistry
 and Physics, (56th Ed. 1975) inside cover, which are hereby incorporated
 by reference.
 Preferred Group IIIB elements include yttrium, lanthanum and mixtures
 thereof. Preferred lanthanide series elements include cerium,
 praseodymium, neodymium, samarium, europium, dysprosium and mixtures
 thereof. Preferred Group IVB elements include zirconium, titanium, hafnium
 and mixtures thereof. Mixtures of Group IIIB, Group IVB and/or lanthanide
 series elements can be used. Zirconium- and titanium-containing materials
 are preferred.
 Non-limiting examples of suitable Group IIIB transition element-containing
 materials include nitrates, acetates, sulfamates, lactates, glycolates,
 formates and dimethylol propionates of yttrium and/or lanthanum, where
 such compounds exist. Non-limiting examples of suitable lanthanide series
 transition element-containing materials include nitrates, acetates,
 sulfamates, lactates, glycolates, formates and dimethylol propionates of
 cerium, praseodymium, neodymium, samarium, europium and/or dysprosium,
 where such compounds exist.
 Non-limiting examples of suitable zirconium-containing materials include
 fluorozirconic acids, such as hexafluorozirconic acid, alkali metal and
 ammonium salts thereof such as potassium hexafluorozirconate, alkali or
 amine salts of zirconium hexafluoride; ammonium zirconium carbonate;
 zirconyl nitrate; zirconium carboxylates such as zirconium acetate,
 zirconium oxalate, ammonium zirconium glycolate, ammonium zirconium
 lactate, ammonium zirconium citrate, and mixtures thereof.
 Hexafluorozirconic acid is preferred. Non-limiting examples of suitable
 titanium-containing materials include fluorotitanic acid, alkali salts of
 hexafluorotitanate, amine salts of hexafluorotitanate and mixtures
 thereof.
 The first pretreatment composition typically is dispersed or dissolved in a
 carrier medium, such as an aqueous medium. Preferably, the transition
 element-containing materials are in the form of metal salts or acids that
 are water soluble. The transition element-containing materials can be
 present in the carrier medium in an amount of up to about 10,000 ppm,
 preferably about 10 to about 2000 ppm metal, and more preferably about 100
 to about 1000 ppm metal based on total weight of the composition. The pH
 of the medium is usually about 2.0 to about 7.0, preferably about 3 to
 about 5. The pH of the medium may be adjusted using mineral acids such as
 hydrofluoric acid, fluoroboric acid, phosphoric acid, and the like,
 including mixtures thereof; organic acids such as lactic acid, acetic
 acid, citric acid, sulfamic acid, or mixtures thereof; and water soluble
 or water dispersible bases such as sodium hydroxide, ammonium hydroxide,
 ammonia, or amines such as triethylamine, methylethanol amine, or mixtures
 thereof.
 Additionally, the first pretreatment composition can comprise one or more
 film-forming materials or resins. Suitable resins include reaction
 products 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. Preferably, such resins contain beta hydroxy ester, imide,
 or sulfide functionality, incorporated by using dimethylolpropionic acid,
 phthalimide, or mercaptoglycerine as an additional reactant in the
 preparation of the resin. Alternatively, the reaction product is that of
 the diglycidyl ether of Bisphenol A (commercially available from Shell
 Chemical Company as EPON 880 or EPON 828 LC), dimethylol propionic acid,
 and diethanolamine in a 0.6 to 5.0:0.05 to 5.5:1 mole ratio. Other
 suitable resins include water soluble and water dispersible polyacrylic
 acids as disclosed in U.S. Pat. Nos. 3,912,548 and 5,328,525;
 phenol-formaldehyde resins as described in U.S. Pat. No. 5,662,746,
 incorporated herein by reference; water soluble polyamides such as those
 disclosed in WO 95/33869; copolymers of maleic or acrylic acid with allyl
 ether as described in Canadian patent application 2,087,352; and water
 soluble and dispersible resins including epoxy resins, aminoplasts,
 phenol-formaldehyde resins, tannins, and polyvinyl phenols as discussed in
 U.S. Pat. No. 5,449,415.
 In this embodiment of the invention, the film forming resin is present in
 the first pretreatment coating composition in an amount of 0.005% to 30%
 based on the total weight of the first pretreatment composition, and the
 transition element-containing material is present in an amount of 10 to
 10,000, preferably 100 to 2000 ppm metal based on total weight of the
 first pretreatment composition. The weight ratio of the resin to
 transition element-containing materials is from 2.0 to 10.0, preferably
 3.0 to 5.0, based on metal.
 The pretreatment coating composition can further comprise one or more
 crosslinking materials for crosslinking crosslinkable components of the
 composition, such as the film-forming resin. Useful crosslinking materials
 include blocked or unblocked polyisocyanates, aminoplasts, polyacids,
 polyanhydrides and mixtures thereof such as are well known to those
 skilled in the art. The amount of the crosslinking material in the
 pretreatment coating composition can range from about 0.05 to about 60
 weight percent on a basis of total resin solids weight of the pretreatment
 coating composition.
 The pretreatment coating composition can further comprise surfactants that
 function as aids to improve wetting of the substrate. Generally, the
 surfactant materials are present in an amount of less than about 2 weight
 percent on a basis of total weight of the pretreatment coating
 composition. Other optional materials in the carrier medium include
 surfactants that function as defoamers or substrate wetting agents.
 Preferably, the pretreatment coating composition is essentially free of
 chromium-containing materials, i.e., contains less than about 2 weight
 percent of chromium-containing materials (expressed as CrO.sub.3), and
 more preferably less than about 0.05 weight percent of chromium-containing
 materials. Examples of such chromium-containing materials include chromic
 acid, chromium trioxide, chromic acid anhydride, and chromate and
 dichromate salts of ammonium, sodium, potassium, calcium, barium, zinc and
 strontium. Most preferably, the pretreatment coating composition is free
 of chromium-containing materials.
 The first pretreatment composition is deposited upon at least a portion of
 an exposed surface of the metal substrate. Preferably, the entire exposed
 surface of the metal substrate is coated with the first pretreatment
 composition.
 The first pretreatment composition can be applied to the metal substrate by
 known application techniques, such as dipping or immersion, which is
 preferred, spraying, intermittent spraying, dipping followed by spraying,
 spraying followed by dipping, brushing, or by roll-coating. Typically, the
 solution or dispersion when applied to the metal substrate is at a
 temperature ranging from 60 to 150.degree. F. (15 to 65.degree. C.). The
 contact time is generally between less than one second and five minutes,
 preferably 30 seconds to 2 minutes.
 Continuous coating processes are typically used in the coil coating
 industry and also for mill application. The first pretreatment coating
 composition can be applied by any of these conventional processes. For
 example, in the coil industry, the substrate is cleaned and rinsed and
 then usually contacted with the pretreatment coating composition by roll
 coating with a chemical coater. The treated strip is then dried by heating
 and painted and baked by conventional coil coating processes.
 Optionally, the pretreatment composition can be applied in a mill by
 immersion, spray or roll coating the freshly manufactured metal strip.
 Excess pretreatment composition is typically removed by wringer rolls.
 After the first pretreatment composition has been applied to the metal
 surface, the metal can be rinsed with deionized water and dried at room
 temperature or at elevated temperatures to remove excess moisture from the
 treated substrate surface and cure any curable coating components to form
 the first pretreatment coating. Alternately, the treated substrate can be
 heated at about 65.degree. C. to about 250.degree. C. for about 2 seconds
 to about 1 minute to produce a coated substrate having a dried or cured
 residue of the first pretreatment coating composition thereon. If the
 substrate is already heated from the hot melt production process, no post
 application heating of the treated substrate is required to facilitate
 drying. The temperature and time for drying the coating will depend upon
 such variables as the percentage of solids in the coating, components of
 the coating composition and type of substrate.
 The film coverage of the residue of the first pretreatment composition
 generally ranges from about 0.1 to about 500 milligrams per square meter
 (mg/m.sup.2), and is preferably about 0.1 to about 1 mg/m.sup.2. The
 thickness of the first pretreatment composition can vary, but is generally
 less than about 1 micrometer, preferably ranges from about 1 to about 500
 nanometers, and more preferably is about 10 to about 300 nanometers.
 In the present invention, a second pretreatment composition is deposited
 upon at least a portion of the first pretreatment composition. The second
 pretreatment composition comprises a reaction product of one or more
 epoxy-functional materials or derivatives thereof and one or more
 materials selected from phosphorus-containing materials, amine-containing
 materials, sulfur-containing materials and mixtures thereof.
 Useful epoxy-functional materials contain at least one epoxy or oxirane
 group in the molecule, such as monoglycidyl ethers of a monohydric phenol
 or alcohol or di- or polyglycidyl ethers of polyhydric alcohols.
 Preferably, the epoxy-functional material contains at least two epoxy
 groups per molecule and has aromatic or cycloaliphatic functionality to
 improve adhesion to the metal substrate. Further, it is preferred that the
 epoxy-functional materials be relatively more hydrophobic than hydrophilic
 in nature.
 Examples of suitable monoglycidyl ethers of a monohydric phenol or alcohol
 include phenyl glycidyl ether and butyl glycidyl ether. Useful
 polyglycidyl ethers of polyhydric alcohols can be formed by reacting
 epihalohydrins with polyhydric alcohols, such as dihydric alcohols, in the
 presence of an alkali condensation and dehydrohalogenation catalyst such
 as sodium hydroxide or potassium hydroxide. Useful epihalohydrins include
 epibromohydrin, dichlorohydrin and epichlorohydrin (preferred). Suitable
 polyhydric alcohols can be aromatic, aliphatic or cycloaliphatic.
 Non-limiting examples of suitable aromatic polyhydric alcohols include
 phenols that are preferably at least dihydric phenols. Non-limiting
 examples of aromatic polyhydric alcohols useful in the present invention
 include dihydroxybenzenes, for example resorcinol, pyrocatechol and
 hydroquinone; bis(4-hydroxyphenyl)-1,1-isobutane;
 4,4-dihydroxybenzophenone; bis(4-hydroxyphenyl)-1,1-ethane;
 bis(2-hydroxyphenyl)methane; 1,5-hydroxynaphthalene; 4-isopropylidene
 bis(2,6-dibromophenol); 1,1,2,2-tetra(p-hydroxy phenyl)-ethane;
 1,1,3-tris(p-hydroxy phenyl)-propane; novolac resins; bisphenol F;
 long-chain bisphenols; and 2,2-bis(4-hydroxyphenyl)propane, i.e.,
 bisphenol A (preferred).
 Non-limiting examples of aliphatic polyhydric alcohols include glycols such
 as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene
 glycol, 1,4-butylene glycol, 2,3-butylene glycol, pentamethylene glycol,
 polyoxyalkylene glycol; polyols such as sorbitol, glycerol,
 1,2,6-hexanetriol, erythritol and trimethylolpropane; and mixtures
 thereof. An example of a suitable cycloaliphatic alcohol is
 cyclohexanedimethanol.
 Suitable epoxy-functional materials have an epoxy equivalent weight ranging
 from about 100 to about 4000, and preferably about 100 to about 500, as
 measured by titration with perchloric acid using methyl violet as an
 indicator. Useful epoxy-functional materials are disclosed in U.S. Pat.
 Nos. 5,294,265; 5,306,526 and 5,653,823, which are hereby incorporated by
 reference.
 Examples of suitable commercially available epoxy-functional materials are
 EPON.RTM. 828 LC (880), 1001, 1002, 1004, 1007, 1009, 826 and 828 epoxy
 resins, which are epoxy functional polyglycidyl ethers of bisphenol A
 prepared from bisphenol-A and epichlorohydrin and are commercially
 available from Shell Chemical Company. EPON.RTM. 828 epoxy resin has a
 number average molecular weight of about 400 and an epoxy equivalent
 weight of about 185-192. EPON.RTM. 826 epoxy resin has an epoxy equivalent
 weight of about 178-186.
 Other useful epoxy-functional materials include epoxy-functional acrylic
 polymers, glycidyl esters of carboxylic acids and mixtures thereof.
 Useful derivatives of epoxy-functional materials include the reaction
 products of one or more epoxy-functional materials such as are discussed
 above with one or more substituted aldehydes or ketones or mixtures
 thereof. Suitable hydroxy-substituted aldehydes and ketones include
 4-hydroxybenzaldehyde, 3-hydroxybenzaldehyde, 2-hydroxybenzaldehyde
 (salicylaldehyde), vanillin, syringaldehyde, 2'-hydroxyacetophenone,
 3'-hydroxyacetophenone, 4'-hydroxyacetophenone,
 4'-hydroxy-2'-methylacetophenone, 4'-hydroxy-4'-methylacetophenone and
 2,4-dihydroxybenzophenone. Useful amino substituted aldehydes and ketones
 include 2'-aminoacetophenone, 3'-aminoactophenone and
 4'-aminoacetophenone. Suitable carboxy substituted aldehydes and ketones
 include 2-carboxybenzaldehyde, 3-carboxybenzaldehyde,
 4-carboxybenzaldehyde and succinic semialdehyde.
 An example of a useful derivative of an epoxy-functional material is the
 reaction product of a polyglycidyl ether of bisphenol A and
 4-hydroxybenzaldehyde.
 As discussed above, the epoxy-containing material or derivative thereof can
 be reacted with one or more phosphorus-containing materials to form an
 ester thereof, such as an organophosphate or organophosphonate. Suitable
 phosphorus-containing materials include phosphinic acids, phosphonic
 acids, phosphoric acids, phosphites, phosphonites and mixtures thereof.
 Examples of suitable phosphinic acids include those having at least one
 group of the structure:
 ##STR1##
 where R can be H, --C--, --(CH.sub.2).sub.n -- where n is an integer from 1
 to about 18, --O--CO--(CH.sub.2).sub.2 --, and preferably is an aryl group
 such as a phenyl group. A preferred phosphinic acid is phenyl phosphinic
 acid (benzene phosphinic acid). Other useful phosphinic acids include
 glyphosate-3 and hypophosphorous acid.
 Examples of suitable phosphonic acids include those having at least one
 group of the structure:
 ##STR2##
 where R can be H, --C--, --(CH.sub.2).sub.n -- where n is an integer from 1
 to about 18, --O--CO--(CH.sub.2).sub.2 --, and preferably is an aryl group
 such as a phenyl group. A preferred phosphonic acid is phenyl phosphonic
 acid.
 Non-limiting examples of other suitable phosphonic acids include
 phosphorous acid, 1-hydroxyethylidene-1,1-diphosphonic acid, methylene
 phosphonic acids, and alpha-aminomethylene phosphonic acids containing at
 least one group of the structure:
 ##STR3##
 such as (2-hydroxyethyl)aminobis(methylene phosphonic) acid,
 isopropylaminobis(methylenephosphonic) acid and other aminomethylene
 phosphonic acids disclosed in U.S. Pat. No. 5,034,556 at column 2, line 52
 to column 3, line 43, which is hereby incorporated by reference.
 Other useful phosphonic acids include alpha-carboxymethylene phosphonic
 acids containing at least one group of the structure:
 ##STR4##
 such as phosphonoacetic acid.
 Other examples of useful phosphonic acids include benzylaminobis(methylene
 phosphonic) acid, cocoaminobis(methylene phosphonic) acid,
 triethylsilylpropylamino(methylene phosphonic) acid and carboxyethyl
 phosphonic acid.
 Suitable esters of phosphorus-containing materials include esters of any of
 the phosphinic acids, phosphonic acids or phosphoric acid discussed above,
 for example phosphoric acid esters of bisphenol A diglycidyl ether,
 benzylaminobis(methylenephosphonic) ester of bisphenol A diglycidyl ether,
 carboxyethyl phosphonic acid ester of bisphenol A diglycidyl ether,
 phenylglycidyl ether and butyl glycidyl ether; carboxyethyl phosphonic
 acid mixed ester of bisphenol A diglycidyl ether and butylglycidyl ether;
 triethoxyl silyl propylaminobis(methylenephosphonic) acid ester of
 bisphenol A diglycidyl ether and cocoaminobis(methylenephosphonic) acid
 ester of bisphenol A diglycidyl ether.
 The epoxy-containing material or derivative thereof and
 phosphorus-containing material are typically reacted in an equivalent
 ratio of about 1:0.5 to about 1:10, and preferably about 1:1 to about 1:4.
 The epoxy-functional material or derivative and phosphorus-containing
 material can be reacted together by any method well known to those skilled
 in the art, such as a reverse phosphatization reaction in which the
 epoxy-containing material is added to the phosphorus-containing material.
 Typically, the reaction product of the epoxy-functional material or
 derivative and phosphorus-containing material has a number average
 molecular weight of up to about 10,000, and preferably about 500 to about
 1000, as measured by gel permeation chromatography using polystyrene as a
 standard.
 In an alternative embodiment, the pretreatment coating comprises one or
 more esters of a phosphorus-containing material, for example such as are
 discussed above. Other suitable esters include the reaction product of
 phosphorus pentoxide as P.sub.4 O.sub.10 and an alcohol in a 1:6 molar
 ratio of oxide to alcohol to produce a mixture of mono- and diphosphate
 esters, such as is disclosed in the 18 Encyclopedia of Chemical
 Technology, (4.sup.th Ed. 1996) at page 772, which is hereby incorporated
 by reference. Examples of suitable alcohols include aliphatic alcohols
 such as ethylene glycol, phenols such as bisphenol A, and cycloaliphatic
 alcohols.
 In an alternative preferred embodiment, the reaction product can be formed
 from one or more epoxy-containing materials or derivatives, such as are
 discussed above, and one or more amine-containing materials selected from
 primary amines, secondary amines, tertiary amines and mixtures thereof.
 Non-limiting examples of suitable primary amines include n-butyl amine and
 fatty amines such as ARMEEN 18D which is commercially available from Akzo
 Nobel. Suitable secondary amines include diisopropanolamine,
 diethanolamine and di-butyl amine. An example of a useful tertiary amine
 is ARMEEN DM18D dimethyl C18 tertiary amine.
 Preferably, the amine-containing material comprises at least one
 alkanolamine or a mixture of different alkanolamines. Primary or secondary
 alkanolamines are preferred, however tertiary alkanolamines can be used.
 Preferred alkanolamines include alkanol groups containing less than about
 20 carbon atoms, and more preferably less than about 10 carbon atoms.
 Non-limiting examples of suitable alkanolamines include
 methylethanolamine, ethylethanolamine, diethanolamine (preferred),
 methylisopropanolamine, monoethanolamine and diisopropanolamine. Preferred
 tertiary alkanolamines contain two methyl groups, such as
 dimethylethanolamine.
 The epoxy-functional material or derivative and amine-containing material
 are preferably reacted in an equivalent ratio ranging from about 5:1 to
 about 0.25:1, and more preferably about 2:1 to about 0.5:1. The
 epoxy-functional material or derivative and amine-containing material can
 be reacted together by any method well known to those skilled in the art
 of polymer synthesis, such as solution or bulk polymerization techniques.
 For example, an alkanolamine can be added to an epoxy-functional material
 and diluent, mixed at a controlled rate and the mixture heated at a
 controlled temperature under a nitrogen blanket or other procedure well
 known to those skilled in the art for reducing the presence of oxygen
 during the reaction. Suitable diluents for reducing the viscosity of the
 mixture during the reaction include alcohols containing up to about 8
 carbon atoms, such as ethanol or isopropanol; and glycol ethers such as
 the monoalkyl ethers of ethylene glycol, diethylene glycol or propylene
 glycol.
 If a tertiary alkanolamine is used, a quaternary ammonium compound is
 formed. Typically, this reaction is carried out by adding all of the raw
 materials to the reaction vessel at the same time and heating the mixture,
 usually with a diluent, at a controlled temperature. Usually, an acid such
 as a carboxylic acid is present to ensure that the quaternary ammonium
 salt is formed rather than a quaternary ammonium hydroxide. Suitable
 carboxylic acids include lactic acid, citric acid, adipic acid and acetic
 acid (preferred). Quaternary ammonium salts are useful because they are
 more easily dispersed in water and can be used to form an aqueous
 dispersion having a pH near the desired application range.
 Generally, the reaction product of the epoxy-functional material or
 derivative and amine-containing material has a number average molecular
 weight of up to about 10,000, and preferably about 500 to about 750, as
 measured by gel permeation chromatography using polystyrene as a standard.
 The second pretreatment composition can include one or more film-forming
 materials and/or crosslinking materials such as are discussed in detail
 above for the first pretreatment composition in similar amounts.
 In another alternative embodiment, the reaction product can be formed from
 one or more epoxy-containing materials or derivatives, such as are
 discussed above, and one or more sulfur-containing materials such as
 aliphatic or aromatic mercaptans, sulfonates, sulfones, sulfoniums,
 sulfides, sulfoxides and mixtures thereof.
 A treating solution of one or more of any of the reaction products
 discussed above can be prepared by mixing the reaction product(s) with a
 diluent, such as water, preferably at a temperature of about 10.degree. C.
 to about 70.degree. C., and more preferably about 15.degree. C. to about
 25.degree. C. Preferably, the reaction product is soluble or dispersible
 in water diluent to the extent of at least about 0.03 grams per 100 grams
 of water at a temperature of about 25.degree. C. The reaction product
 generally comprises about 0.05 to about 10 weight percent of the treating
 solution on a total weight basis.
 Useful diluents include water or mixtures of water and cosolvents. Suitable
 cosolvents include alcohols having up to about 8 carbon atoms, such as
 ethanol and isopropanol; and alkyl ethers of glycols, such as
 1-methoxy-2-propanol, monoalkyl ethers of ethylene glycol, diethylene
 glycol and propylene glycol and dialkyl ethers of ethylene glycol or
 ethylene glycol formal. Preferably, the diluent includes a propylene
 glycol monomethyl ether such as DOWANOL PM, dipropylene glycol monomethyl
 ether DOWANOL DPM, which are commercially available from Dow Chemical
 Company or MAZON 1651 butyl carbitol formal which is commercially
 available from BASF Corp. Other useful diluents include bases such as
 amines which can partially or completely neutralize the organophosphate or
 organophosphonate to enhance the solubility of the compound. Non-limiting
 examples of suitable amines include secondary amines, such as
 diisopropanolamine (preferred), and tertiary amines such as triethylamine,
 dimethylethanolamine and 2-amino-2-methyl-1-propanol. Non-aqueous diluents
 are typically present in amount ranging from about 0.1 to about 5 weight
 percent on a basis of total weight of the treating solution. Water can be
 present in amount ranging from about 50 to about 99 weight percent on a
 basis of total weight of the treating solution.
 Typically, water-soluble or water-dispersible acids and/or bases are used
 to adjust the pH of the treating solution to about 2 to about 9, and
 preferably about 3 to about 5. Suitable acids include mineral acids, such
 as hydrofluoric acid, fluoroboric acid, phosphoric acid, sulfamic acid and
 nitric acid; organic acids, such as lactic acid, acetic acid,
 hydroxyacetic acid, citric acid; and mixtures thereof. Suitable bases
 include inorganic bases, such as sodium hydroxide and potassium hydroxide;
 nitrogen-containing compounds such as ammonia, triethylamine,
 methanolamine, diisopropanolamine; and mixtures thereof.
 Optionally, the second pretreatment composition further comprises a
 fluorine-containing material as a source of fluoride ions. Suitable
 fluorine-containing materials include hydrofluoric acid, fluorosilicic
 acid, fluoroboric acid, sodium hydrogen fluoride, potassium hydrogen
 fluoride, ammonium hydrogen fluoride and mixtures thereof. Preferably, the
 concentration of fluorine-containing material in the pretreatment coating
 ranges from about 100 to about 5200 parts per million (ppm) and more
 preferably about 300 to about 3500 ppm. Generally, the weight ratio of
 reaction product to fluoride ions ranges from about 10:1 to about 55:1.
 The fluorine-containing material can be applied to the metal substrate
 prior to application of the second pretreatment composition or included in
 the second pretreatment composition itself. If applied prior to
 application of the treating solution, the pH of an aqueous solution
 including the fluorine-containing material generally ranges from about 2.4
 to about 4.0 and can be adjusted by adding sodium hydroxide.
 Optionally, the second pretreatment composition can further comprise one or
 more transition element-containing materials such as are discussed above.
 Generally, the transition element-containing material is included in the
 treating solution in an amount to provide a concentration of up to about
 10,000 ppm, and preferably about 500 to about 2000 ppm, based upon total
 weight of the treating solution.
 The treating solution can further comprise surfactants that function as
 aids to improve wetting of the substrate. Generally, the surfactant
 materials are present in an amount of less than about 2 weight percent on
 a basis of total weight of the treating solution.
 Preferably, the second pretreatment composition is essentially free of
 chromium-containing materials, i.e., contains less than about 2 weight
 percent of chromium-containing materials (expressed as CrO.sub.3), and
 more preferably less than about 0.05 weight percent of chromium-containing
 materials. Examples of such chromium-containing materials include chromic
 acid, chromium trioxide, chromic acid anhydride, and chromate and
 dichromate salts of ammonium, sodium, potassium, calcium, barium, zinc and
 strontium. Most preferably, the treating solution is free of
 chromium-containing materials.
 In a preferred embodiment, the reaction product of an epoxy-functional
 material and a phosphorus-containing material is formed from EPON.RTM. 880
 (828 LC) epoxy-functional resin and phenylphosphonic acid in an equivalent
 ratio of about 1:1 to about 1:2. The reaction product is present in the
 treating solution in an amount of about 0.1 weight percent on a basis of
 total weight of the treating solution. The preferred treating solution
 also includes diisopropanolamine, solvent and deionized water.
 In an alternative preferred embodiment, the reaction product of an epoxy
 functional material and phosphorus-containing material is formed from the
 reaction product of (a) EPON.RTM. 880 (828 LC) epoxy-functional resin and
 4-hydroxybenzaldehyde in an equivalent ratio of about 1:1 and (b)
 phenylphosphinic acid in an equivalent ratio of about 1:1. The reaction
 product is present in the treating solution in an amount of about 0.1
 weight percent on a basis of total weight of the treating solution. The
 preferred treating solution also includes diisopropanolamine, solvent and
 deionized water.
 In an alternative embodiment, the components of the first and second
 pretreatment compositions can be present in a single pretreatment
 composition.
 The treating solution is applied to the surface of the metal substrate by
 any conventional application technique, such as spraying, immersion or
 roll coating in a batch or continuous process. The temperature of the
 treating solution at application is typically about 10.degree. C. to about
 85.degree. C., and preferably about 15.degree. C. to about 40.degree. C.
 The pH of the preferred treating solution at application generally ranges
 from about 2.0 to about 9.0, and is preferably about 3 to about 5.
 The film coverage of the residue of the pretreatment coating generally
 ranges from about 0.1 to about 1000 milligrams per square meter
 (mg/m.sup.2), and is preferably about 1 to about 400 mg/m.sup.2.
 Optionally, a weldable coating can be deposited upon at least a portion of
 the pretreatment coating formed from the first and second pretreatment
 compositions. The weldable coating is formed from a weldable composition
 comprising one or more electroconductive pigments which provide
 electroconductivity to the weldable coating and one or more binders which
 adhere the electroconductive pigment to the pretreatment coating. The
 overall thickness of the pretreatment coating over which the weldable
 coating is applied can vary, but is generally less than about 1
 micrometer, preferably ranges from about 1 to about 500 nanometers, and
 more preferably is about 10 to about 300 nanometers.
 Non-limiting examples of suitable electroconductive pigments include zinc
 (preferred), aluminum, iron, graphite, iron phosphide, nickel, tungsten
 and mixtures thereof. Preferred zinc particles are commercially available
 from ZINCOLI GmbH as ZINCOLI S 620 or 520. The average particle size
 (equivalent spherical diameter) of the electroconductive pigment particles
 generally is less than about 10 micrometers, preferably ranges from about
 1 to about 5 micrometers, and more preferably about 3 micrometers.
 Since the metal substrates are to be subsequently welded, the weldable
 coating must comprise a substantial amount of electroconductive pigment,
 generally greater than about 10 volume percent and preferably about 30 to
 about 60 volume percent on a basis of total volume of electroconductive
 pigment and binder.
 The binder is present to secure the electroconductive pigment to the
 pretreatment coating. Preferably, the binder forms a generally continuous
 film when applied to the surface of the pretreatment coating. Generally,
 the amount of binder can range from about 5 to about 50 weight percent of
 the weldable coating on a total solids basis, preferably about 10 to about
 30 weight percent and more preferably about 10 to about 20 weight percent.
 The binder can comprise oligomeric binders, polymeric binders and mixtures
 thereof. The binder is preferably a resinous polymeric binder material
 selected from thermosetting binders, thermoplastic binders or mixtures
 thereof. Non-limiting examples of suitable thermosetting materials include
 polyesters, epoxy-containing materials such as are discussed above,
 phenolics, polyurethanes, and mixtures thereof, in combination with
 crosslinkers such as aminoplasts or isocyanates which are discussed below.
 Non-limiting examples of suitable thermoplastic binders include high
 molecular weight epoxy resins, defunctionalized epoxy resins, vinyl
 polymers, polyesters, polyolefins, polyamides, polyurethanes, acrylic
 polymers and mixtures thereof. Another useful binder material is a phenoxy
 polyether polyol.
 Particularly preferred binder materials are polyglycidyl ethers of
 polyhydric phenols, such as those discussed above, having a weight average
 molecular weight of at least about 2000 and preferably ranging from about
 5000 to about 100,000. These materials can be epoxy functional or
 defunctionalized by reacting the epoxy groups with phenolic materials.
 Such binders can have epoxy equivalent weights of about 2000 to about one
 million. Non-limiting examples of useful epoxy resins are commercially
 available from Shell Chemical Company as EPON.RTM. epoxy resins. Preferred
 EPON.RTM. epoxy resins include EPON.RTM. 1009, which has an epoxy
 equivalent weight of about 2300-3800. Useful epoxy defunctionalized resins
 include EPONOL resin 55-BK-30 which is commercially available from Shell.
 Suitable crosslinkers or curing agents are described in U.S. Pat. No.
 4,346,143 at column 5, lines 45-62 and include blocked or unblocked di- or
 polyisocyanates such as DESMODUR.RTM. BL 1265 toluene diisocyanate blocked
 with caprolactam, which is commercially available from Bayer, and
 aminoplasts such as etherified derivatives of urea-melamine- and
 benzoguanamine-formaldehyde condensates which are commercially available
 from Cytec Industries under the trademark CYMEL.RTM. and from Solutia
 under the trademark RESIMENE.RTM..
 Preferably, the weldable coating composition comprises one or more diluents
 for adjusting the viscosity of the composition so that it can be applied
 to the metal substrate by conventional coating techniques. The diluent
 should be selected so as not to detrimentally affect the adhesion of the
 weldable coating to the pretreatment coating upon the metal substrate.
 Suitable diluents include ketones such as cyclohexanone (preferred),
 acetone, methyl ethyl ketone, methyl isobutyl ketone and isophorone;
 esters and ethers such as 2-ethoxyethyl acetate, propylene glycol
 monomethyl ethers such as DOWANOL PM, dipropylene glycol monomethyl ethers
 such as DOWANOL DPM or propylene glycol methyl ether acetates such as PM
 ACETATE which is commercially available from Dow Chemical; and aromatic
 solvents such as toluene, xylene, aromatic solvent blends derived from
 petroleum such as SOLVESSO.RTM. 100. The amount of diluent can vary
 depending upon the method of coating, the binder components and the
 pigment-to-binder ratio, but generally ranges from about 10 to about 50
 weight percent on a basis of total weight of the weldable coating.
 The weldable coating can further comprise optional ingredients such as
 phosphorus-containing materials, including metal phosphates or the
 organophosphates discussed in detail above; inorganic lubricants such as
 GLEITMO 1000S molybdenum disulfide particles which are commercially
 available from Fuchs of Germany; coloring pigments such as iron oxides;
 flow control agents; thixotropic agents such as silica, montmorillonite
 clay and hydrogenated castor oil; anti-settling agents such as aluminum
 stearate and polyethylene powder; dehydrating agents which inhibit gas
 formation such as silica, lime or sodium aluminum silicate; and wefting
 agents including salts of sulfonated castor oil derivatives such as
 DEHYSOL R.
 Other pigments such as carbon black, magnesium silicate (talc), zinc oxide
 and corrosion inhibiting pigments including calcium modified silica, zinc
 phosphate and molybdates such as calcium molybdate, zinc molybdate, barium
 molybdate and strontium molybdate and mixtures thereof can be included in
 the weldable coating. Generally, these optional ingredients comprise less
 than about 20 weight percent of the weldable coating on a total solids
 basis, and usually about 5 to about 15 weight percent. Preferably, the
 weldable coating is essentially free of chromium-containing materials,
 i.e., comprises less than about 2 weight percent of chromium-containing
 materials and more preferably is free of chromium-containing materials.
 The preferred weldable coating includes EPON.RTM. 1009 epoxy-functional
 resin, zinc dust, salt of a sulfated castor oil derivative, silica,
 molybdenum disulfide, red iron oxide, toluene diisocyanate blocked with
 caprolactam, melamine resin, dipropylene glycol methyl ether, propylene
 glycol methyl ether acetate and cyclohexanone.
 The weldable coating can be applied to the surface of the pretreatment
 coating by any conventional method well known to those skilled in the art,
 such as dip coating, direct roll coating, reverse roll coating, curtain
 coating, air and airless spraying, electrostatic spraying, pressure
 spraying, brushing such as rotary brush coating or a combination of any of
 the techniques discussed above.
 The thickness of the weldable coating can vary depending upon the use to
 which the coated metal substrate will be subjected. Generally, to achieve
 sufficient corrosion resistance for coil metal for automotive use, the
 applied weldable coating should have a film thickness of at least about 1
 micrometer (about 0.04 mils), preferably about 1 to about 20 micrometers
 and more preferably about 2 to about 5 micrometers. For other substrates
 and other applications, thinner or thicker coatings can be used.
 After application, the weldable coating is preferably dried and/or any
 curable components thereof are cured to form a dried residue of the
 weldable coating upon the substrate. The dried residue can be formed at an
 elevated temperature ranging up to about 300.degree. C. peak metal
 temperature. Many of the binders such as those prepared from
 epoxy-containing materials require curing at an elevated temperature for a
 period of time sufficient to vaporize any diluents in the coating and to
 cure or set the binder. In general, baking temperatures will be dependent
 upon film thickness and the components of the binder. For preferred
 binders prepared from epoxy-containing materials, peak metal temperatures
 of about 150.degree. C. to about 300.degree. C. are preferred.
 After the weldable coating has been dried and/or cured, the metal substrate
 can be stored or forwarded to other operations, such as forming, shaping,
 cutting and/or welding operations to form the substrate into parts such as
 fenders or doors and/or to a subsequent electrocoat or topcoating
 operations. While the metal is being stored, transported or subjected to
 subsequent operations, the coatings protect the metal surface from
 corrosion, such as white and red rust, due to exposure to atmospheric
 conditions.
 Since the coated metal substrate prepared according to the present
 invention is electroconductive, topcoating of the coated substrate by
 electrodeposition is of particular interest. Compositions and methods for
 electrodepositing coatings are well known to those skilled in the art and
 a detailed discussion thereof is not believed to be necessary. Useful
 compositions and methods are discussed in U.S. Pat. No. 5,530,043
 (relating to anionic electrodeposition) and U.S. Pat. Nos. 5,760,107,
 5,820,987 and 4,933,056 (relating to cationic electrodeposition) which are
 hereby incorporated by reference.
 The weldable coated metal substrate optionally can be coated with a metal
 phosphate coating, such as zinc phosphate, which is deposited upon at
 least a portion of the weldable coating. Methods of application and
 compositions for such metal phosphate coatings are disclosed in U.S. Pat.
 Nos. 4,941,930 and 5,238,506, which are hereby incorporated by reference.
 The pretreatment coating and weldable coating provide the metal substrate
 of the present invention with improved adhesion and flexibility and
 resistance to humidity, salt spray corrosion and components of
 subsequently applied coatings. In addition, the disposal and use problems
 associated with chromium can be reduced or eliminated.

The present invention will now be illustrated by the following specific,
 non-limiting examples. All parts and percentages are by weight unless
 otherwise indicated.
 EXAMPLE
 In accordance with the present invention, the following example shows the
 preparation of first and second pretreatment compositions, their
 application to ferrous and galvanized substrates and comparative corrosion
 testing results of the coated substrates.
 Preparation of Panels for Corrosion Testing
 Bare, or untreated cold rolled steel (CRS), two-sided electrogalvanized
 (EZG-60G) steel, two-sided hot-dipped galvanized (HDG-G70 70U) steel and
 two-sided hot-dipped GALVANNEAL (HDA-Zn/Fe A45) test panels were purchased
 from ACT Laboratories, Inc. of Hillsdale, Mich. Each panel was about 10.16
 centimeters (cm) (4 inches) wide, about 15.24 cm (6 inches) long and about
 0.76 to 0.79 mm (0.030 to 0.031 inches) thick.
 The test panels were treated according to the process described in Table 1
 below.
 TABLE 1
 STAGE PROCESS DESCRIPTION
 1 CLEAN Chemkleen 163.sup.1 (2% by volume) sprayed at 140.degree.
 F.
 for 1 minute
 2 RINSE Tap water, 15-30 second immersion, ambient
 temperature
 3 TREAT Fluorozirconic acid.sup.2 (175 ppm Zr; pH 4.5) 60
 second immersion at ambient temperature
 4 RINSE Deionized water, 15-30 second immersion, ambient
 temperature
 5 TREAT Apply Pretreatment Solution A or B described
 below
 6 RINSE Deionized water, 15-30 second immersion, ambient
 temperature
 .sup.1 Alkaline based cleaner commercially available from PPG Industries,
 Inc., Pittsburgh, PA
 .sup.2 Available as a 45% solution from Alfa Aesar, Ward Hill, MA
 As used herein, "ambient temperature" means an air temperature of about
 20-26.degree. C. Each pretreatment composition was adjusted to the pH
 indicated below with 10% sodium hydroxide or 1% sulfamic acid, measured at
 ambient temperatures using a Digital lonalyzer Model SA720, commercially
 available from Orion Research.
 Preparation and Application of Pretreatment Solutions A and B
 In a preferred embodiment of the present invention, an epoxy ester of
 phenyl phosphonic acid was prepared in the following manner. To a 4-neck 1
 liter round-bottom flask fitted with a reflux condenser, a mechanical
 stirrer and a nitrogen inlet, was charged at ambient temperature 79 grams
 (0.5 mole) of phenylphosphonic acid (available from Aldrich Chemical Co.)
 and 184.3 grams of propylene glycol monomethylether (available from Dow
 Chemical Co. as Dowanol PM). The mixture was heated with stirring to 51
 degrees C. while maintaining a nitrogen blanket.
 A solution comprising 94 grams of EPON 880 epoxy-based resin (available
 from Shell Chemical Co.) (0.25 mole) in 219.3 grams of Dowanol PM was
 added to the flask at 51 degrees C. over 44 minutes. The reaction mixture
 was then held at 50-51 degrees C. for 196 minutes at which time the epoxy
 equivalent weight was determined to be &gt;30,000 as measured by
 potentiometric titration with perchloric acid. To the reaction mixture was
 then added over 7 minutes, a solution of 33.3 grams of diisopropanol amine
 (0.25 mole) in 77.7 grams of Dowanol PM while the temperature increased to
 53 degrees C. The mixture was mixed thoroughly and poured into a plastic
 container for storage. The product mixture had a solids content of 33.2%
 (measured @ 110 degrees C. for 1 hour) and an acid number of 59.8
 (measured by potentiometric titration with methanolic KOH).
 To form Pretreatment Solution A, 3.01 g of the epoxy based reaction product
 described above was added to a portion of deionized water with stirring.
 Enough deionized water was then added to bulk the solution to form one
 liter of solution. The pH of Pretreatment Solution A was then adjusted to
 a value of 4.5 by dropwise addition of 10% sodium hydroxide.
 In an alternative embodiment of the present invention, an epoxy aldehyde
 modified with phenyl phosphinic acid was prepared as follows. 75.20 g of
 EPON 880 epoxy-based resin (0.4 equiv.), 48.85 g of 4-Hydroxybenzaldehyde
 (0.4 equiv.), 0.11 g of Ethyltriphenylphosphonium iodide were charged at
 room temperature into a 4-neck 1 liter round-bottom flask fitted with a
 reflux condenser, a mechanical stirrer and a nitrogen inlet. The reaction
 mixture was heated to 130.degree. C. and 2.07 g of methyl isobutyl ketone
 was the charged into the flask. The sample was then held for 21/2 hours
 and then 0.37 g of benzyl dimethylamine and 11.64 g of MIBK were charged
 to the reaction. After 3 hours, the epoxy equivalent weight was 44,000.
 Phenylphosphinic acid (56.84 g (0.4 equiv.)) was added to the flask and
 the reaction was held for an additional three hours. The reaction was
 cooled to 90.degree. C. and 53.38 g of diisopropanolamine and 484.11 g of
 DI H.sub.2 O were charged to the flask. The final product had a pH of 8.5
 and a number average molecular weight of 666 by GPC in DMF. The product
 mixture had a solids content of 31.91% (110.degree. C.; 1 hr.), and an
 acid number of 28.6 (measured by potentiometric titration with methanolic
 KOH).
 To prepare Pretreatment Solution B, 3.13 g of the epoxy based reaction
 product described above was added to a portion of deionized water with
 stirring. Enough deionized water was then added to bulk the solution to
 one liter. The pH of the pretreatment solution was then adjusted to a
 value of 4.5 by dropwise addition of 10% sodium hydroxide to form
 Pretreatment Solution B.
 Performance in Corrosion Testing
 Metal panels were coated using the process described in Table 1 and
 evaluated for corrosion resistance. These include panels which were
 cleaned but not pretreated; those which were cleaned and treated with
 fluorozirconic acid (FZA) (Table 1, Stages 1-4 only); those in which a
 solution of phenyl phosphonic acid was used in Stage 5 instead of
 Pretreatment Solutions A or B; panels which were pretreated with FZA and
 either Pretreatment Solution A or B; and panels that were cleaned and
 phosphated with either CHEMFOS 850 or CHEMFOS 700 phosphating solutions
 and rinsed with CHEMSEAL 59 non-chrome containing post-rinse solution
 (which are commercially available from PPG Industries, Inc.).
 Each panel was electrocoated with ED 6650, an electrodepositable coating
 commercially available from PPG Industries, Inc. Electrocoated panels were
 cured to achieve a metal temperature of 340.degree. F. for 20 minutes. The
 overall coating thickness was about 23 microns (0.9 mils) on each panel.
 Three different corrosion resistance tests were performed on the panels,
 according to the Honda Salt Dip (warm salt water immersion--5% NaCl in
 deionized water solution at 55.degree. C.), GM 9540P (Cycle B) and VDA
 621-415 Test Procedures (Association of German Automobile Manufacturers).
 Before placing panels into test, they were scribed with either a large X
 for testing in warm salt water immersion testing, a straight vertical line
 for Cycle B testing, or 2 parallel lines for VDA-621-415 testing. Upon
 completion of corrosion testing, corrosion by-products and delaminated
 paint were removed by sand blasting according to warm salt water immersion
 and Cycle B test specifications or by pulling off with an adhesive tape
 according to VDA 621-415. Results obtained from these tests are summarized
 in Tables 2-4 below.
 TABLE 2
 CORROSION TEST PROTOCOL
 total paint loss from scribe (mm)
 SUBSTRATE TREATMENT WARM SALT GM 9540 P VDA
 TESTED APPLIED.sup.1 WATER.sup.2 CYCLE B.sup.3
 621-415.sup.4
 Cold Rolled Steel Clean only 12-16 13.0 4.66
 (Stages 1-2)
 Cold Rolled Steel FZA only 6-8 9.8 3.83
 (Stages 1-4)
 Cold Rolled Steel Phenyl 5-8 9.0 --
 phosphonic acid.sup.5
 (in Stage 5)
 Cold Rolled Steel FZA/Pretreatment 2-4 7.6 1.43
 Solution A
 Cold Rolled Steel FZA/Pretreatment 2-5 -- --
 Solution B
 Cold Rolled Steel CHEMFOS 850/ 0-1 5.0 0.90
 CHEMSEAL 59
 Cold Rolled Steel CHEMFOS 700/ 0-1 4.0 --
 CHEMSEAL 59
 Electrogalvanized Clean only 6-11 4.33 2.53
 Steel EZG 60 G (Stages 1-2)
 Electrogalvanized FZA only 4-10 2.33 2.36
 Steel EZG 60 G (Stages 1-4)
 Electrogalvanized Phenyl 4-8 3.66 --
 Steel EZG 60 G phosphonic acid.sup.5
 (in Stage 5)
 Electrogalvanized FZA/Pretreatment 2-7 3.33 2.33
 Steel EZG 60 G Solution A
 Electrogalvanized FZA/Pretreatment 2-8 -- --
 Steel EZG 60 G Solution B
 Electrogalvanized CHEMFOS 850/ 1-6 3.0 1.60
 Steel EZG 60 G CHEMSEAL 59
 Electrogalvanized CHEMFOS 700/ 0-4 3.33 --
 Steel EZG 60 G CHEMSEAL 59
 .sup.1 via process in Table 1 except for phosphated panels.
 .sup.2 10 day immersion; average range (in mm) of paint loss from scribe
 for 3 panels.
 .sup.3 40 cycles completed; value is average maximum paint loss from scribe
 of 3 panels.
 .sup.4 German cyclic automotive test run for 10 weeks. Scribe loss,
 U.sub.d, calculated by measuring the total scribe creep along one of 2
 parallel scribes in seven locations and using the following equation:
 U.sub.d = [U.sub.1 + U.sub.2 + . . . + U.sub.7)/7]/2.
 .sup.5 Commercially available from Acros Organics (a division of Fisher
 Scientific, USA); used at 0.3 g/L and pH 4.5.
 TABLE 3
 CORROSION TEST PROTOCOL
 total paint loss from scribe (mm)
 WARM
 SUBSTRATE TREATMENT SALT GM 9540 P VDA
 TESTED APPLIED WATER CYCLE B 621-415
 Hot dipped Clean only 2-6 2.66 1.83
 galvanized
 steel
 (HDG G70)
 Hot dipped FZA only 1-5 1.66 1.23
 galvanized
 steel
 (HDG G70)
 Hot dipped Phenyl 1-4 3.0 --
 galvanized phosphonic acid
 steel
 (HDG G70)
 Hot dipped FZA/Pretreatment 0-2 1.33 1.96
 galvanized Solution A
 steel
 (HDG G70)
 Hot dipped CHEMFOS 850/ 1-3 2.33 1.03
 galvanized CHEMSEAL 59
 steel
 (HDG G70)
 Hot dipped CHEMFOS 700/ 0-2 1.33 --
 galvanized CHEMSEAL 59
 steel
 (HDG G70)
 TABLE 4
 CORROSION
 TEST PROTOCOL
 total paint loss from scribe (mm)
 SUBSTRATE TREATMENT WARM SALT GM 9540 P
 TESTED APPLIED WATER CYCLE B
 GALVANNEAL Clean only 2-5 4.66
 (HDA-Zn/Fe A45)
 GALVANNEAL FZA only 0-4 4.00
 (HDA-Zn/Fe A45)
 GALVANNEAL FZA/Pretreatment 0-2 3.33
 (HDA-Zn/Fe A45) Solution A
 GALVANNEAL CHEMFOS 850/ 1-4 3.33
 (HDA-Zn/Fe A45) CHEMSEAL 59
 GALVANNEAL CHEMFOS 700/ 0-3 2.33
 (HDA-Zn/Fe A45) CHEMSEAL 59
 The data in Tables 2-4 above demonstrate that the process described in
 Table 1 using a pretreatment of fluorozirconic acid and Pretreatment
 Solution A or B according to the present invention offers a useful
 alternative pretreatment method to standard phosphate conversion coatings.
 The effectiveness of this pretreatment on a variety of substrates,
 particularly on cold rolled steel, an inherently difficult substrate on
 which to inhibit corrosion, is highly desirable.
 The coating compositions of the present invention provide a heavy
 metal-free alternative to conventional phosphating compositions; (2) a
 simpler operating procedure which is effective at ambient temperatures;
 (3) permits coating of objects comprised of mixed metallic substrates; and
 (4) significantly reduces the amount of heavy metal sludge typically
 produced with conventional phosphating treatments, thus eliminating
 disposal concerns.
 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 which are within the spirit and scope
 of the invention, as defined by the appended claims.