WO2002002849A2 - Methods for electrocoating a metallic substrate with a topcoat and articles produced thereby - Google Patents

Abstract

A method for coating an article having Class A and non-Class A surfaces, e.g., a metal, automotive substrate, includes selectively electrodepositing a first coating material, e.g., a durable color coat or topcoat, upon at least a portion of the Class A surface and electrodepositing an anticorrosion material upon at least a portion of the non-Class A surface. An optional clearcoat can be applied upon at least a portion of the Class A surface.

Description

METHODS FOR ELECTROCOATING A METALLIC SUBSTRATE WITH A TOPCOAT AND ARTICLES PRODUCED THEREBY

Field of the Invention

This invention relates -generally to methods for coating metallic substrates and, more particularly, to methods for applying electrodepositable coatings onto an automotive substrate using a reverse coating process.

Background of the Invention In the automotive industry, a conventional "reverse coating process" consists of applying a primer coat by powder coating or powder electrodeposition coating onto an article, baking the coated article to effect the hardening of the coating, subjecting the remaining uncoated portion to a second electrodeposition and then baking the article again to effect hardening of the second coating. A topcoat, e.g. a basecoat and a clearcoat, is applied to at least the electrocoated outer surface of the substrate to provide acceptable aesthetics .

U.S. Patent No. 4,333,807 discloses a different reverse coating process in which, after an initial resin powder primer coating is applied to the substrate, the resin powder is heated to a temperature sufficient to melt the coating but not to cure the coating, i.e., to cause a cross-linking reaction. The first coating is sanded and then an electrodeposition coating is applied, after which the coated substrate is heated to a temperature sufficient to cross-link both coatings.

U.S. Patent No. 4,259,163 discloses yet another method of reverse coating a substrate. A binder resin and synthetic resin in the form of fine powder in an aqueous bath is electrodeposited upon the substrate. Next, an ionic synthetic resin is electrodeposited upon the area of the substrate not covered by the first electrodeposited coating, and then the coated substrate is baked to simultaneously harden both coatings .

In known reverse coating processes, a topcoat, e.g., a basecoat and a clearcoat, is applied over the reverse coated substrate, typically over at least the outer facing portion of the substrate, to provide the substrate with an aesthetically acceptable finish. It would be advantageous to provide a reverse coating process that eliminates the need for a separate, additional topcoating step. It would also be desirable to provide a reverse coating process that permits selectively coating, particularly electrocoating, selected areas of the substrate.

Summary of the Invention An aspect of the present invention is a coated metallic article having a Class A surface and a non-Class A surface, the article comprising a topcoat electrodeposited upon at least a portion of the Class A surface, and a corrosion- inhibiting coating electrodeposited upon at least a portion of the non-Class A surface.

An additional aspect of the present invention is a method of coating a metallic substrate having a Class A surface and a non-Class A surface, the method comprising electrodepositing a topcoat upon at least a portion of the Class A surface of the substrate, and electrodepositing a corrosion-inhibiting coating upon at least a portion of the non-Class A surface.

Description of the Preferred Embodiments 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 and both homopolymers and copolymers. Additionally, any numeric reference to amounts, unless otherwise specified in the document are "by 5 weight", for instance, the phrase "solids of 34%" means "solids of 34% by weight".

The present invention is useful for coating metallic substrates, such as metallic automotive components designed for subsequent inclusion in an automotive vehicle, such as

10 doors, hoods, fenders, bumpers, etc. As will be appreciated by one of ordinary skill in the automotive art, automotive substrates are conventionally referred to as having Class A and non-Class A surfaces. "Class A" surfaces are those surfaces which will become part of the most visible portions

15 of the resulting vehicle, such as the outer portions of the door panels, hood, trunk, quarter panels, side panels, etc., which are exposed directly to the weather and are readily visible to the consumer. "Non-Class A" surfaces are those surfaces which are destined for non-highly visible areas or

20 even non-visible areas of the vehicle, such as the inside of the door panel, inside surface of the quarter and side panels, underneath the hood or trunk, etc. Although an aesthetic, durable finish is required for the Class A surfaces, applying such aesthetic finishes onto the non-Class A surfaces is not

25 desirable because such coatings are costly and time-consuming to apply. However, the non-Class A surfaces at least should be coated with an anticorrosion coating to prevent rust or corrosion. ₍

The metallic substrates used in the practice of the

30 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, galvanized (zinc coated) steel, electrogalvanized steel, stainless steel,

35. pickled steel, GALVANNEAL, GALVALUME, and GALVAN zinc-aluminum alloys coated upon 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. Before depositing coatings upon the surface of the metallic substrate, it is preferred to remove foreign matter from the metal surface by thoroughly cleaning and/or degreasing the substrate surface. As used herein, the terms "deposited upon" and "provided upon" a substrate mean deposited or provided above or over but not necessarily adjacent to the surface of the substrate. For example, a coating can be deposited directly upon the substrate or one or more other coatings can be applied therebetween.

The surface of the metallic 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 know to those skilled in the art, such as sodium metasilicate and sodium hydroxide. Non-limiting examples of preferred cleaning agents include CHEMKLEEN 163 and CHEMKLEEN 177 phosphate cleaners, both of which are commercially available from PPG Industries, Inc. of Pittsburgh, Pennsylvania.

Following the cleaning step, the surface of the metallic substrate may be 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 cleaners. 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 metallic 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 metallic 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. Patent Nos. 4,941,930; 5,238,506 and 5,653,790.

The substrate or portions thereof optionally can be coated with an anticorrosion pretreatment material, preferably an electroconductive zinc-rich epoxy-based pretreatment material, such as is disclosed in U.S. Application Serial No. 09/469,259, herein incorporated by reference. A preferred anticorrosion coating includes EPON® 1009 epoxy-functional resin commercially available from Shell Chemical Company of Houston, Texas, 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. Other preferred anticorrosion coatings include BONAZINC 3000 and 5000 zinc-rich, epoxy-resin containing weldable coatings, which are commercially available from PPG Industries, Inc.

In accordance with a preferred embodiment of the invention, the cleaned substrate is electrocoated with a first electrodepositable coating or "topcoat" of the invention as described below. As used with respect to the present invention, the term "topcoat" refers to either a monocoat, i.e., a chip-resistant final or finish coat without a subsequent clearcoat, or to a basecoat which may then be subsequently clearcoated. This topcoat may include pigments to provide the topcoat with a desired color. In this preferred embodiment, the topcoat is the outermost coating on the substrate. The topcoat provides good aesthetic appearance to the coated substrate, as indicated by one or more of the following: gloss, DOI (distinctness of image), and smoothness. Since the general process of electrodeposition will be readily understood by one of ordinary skill in the art, it will not be discussed in any great detail herein. In a typical electrodeposition process, a metal substrate being treated, serving as an electrode, and an electrically conductive counter electrode are placed in contact with an ionic, electrodepositable composition. Upon passage of an electric current between the electrode and counter electrode while they are in contact with the electrodepositable composition, ^" an adherent film of the electrodepositable composition will deposit in a substantially continuous manner on the metal substrate.

Electrodeposition is usually carried out at a constant voltage in the range of from about 1 volt to several thousand volts, typically between 50 and 500 volts. Current density is usually between about 1.0 ampere and 15 amperes per square foot (10.8 to 161.5 amperes per square meter) and tends to decrease quickly during the electrodeposition process, indicating formation of a continuous self-insulating film. Although electrodeposition processes can be cationic or anionic, in the preferred practice of the invention, the metal substrate being treated preferably serves as a cathode, with the electrodepositable composition preferably being cationic. In the practice of the invention, the substrate is positioned in the electrodeposition bath with the Class A surface facing the anode. The first coating material is deposited on the substrate at differing thickness depending on the distance of the substrate from the anode and the orientation of the substrate. Thus, during the first electrodeposition step, the Class A surface is coated by a thicker coating of the first coating material than the non- Class A surface. The non-Class A surface may be coated by a thinner layer of the first coating material or, more preferably, the substrate is positioned at sufficient distance from the anode such that at least portions of the non-Class A surface, preferably substantially the entire non-Class A surface are not coated with the first coating material due to the distance of the substrate from the anode.

Useful electrodepositable topcoating compositions for the first coating material can include anionic or cationic (preferred) electrodepositable compositions well known to those skilled in the art suitable for use as topcoats. Such compositions may comprise one or more film-forming materials and crosslinking materials. Suitable film-forming materials for' the formation of an electrodepositable color coat or topcoat of the invention comprise polyurethane film-forming materials, acrylic film-forming materials, and/or polyester film forming materials, one or more of which can be used alone or in combination with an epoxy film-forming material. Although not currently preferred, the film-forming material can comprise an epoxy-functional material . The amount of film-forming material in the electrodepositable composition generally ranges from about 50 to about 95 weight percent on a basis of total weight solids of the electrodepositable composition.

Suitable acrylic film-forming materials are disclosed in U.S. Application Serial No. 09/309,850; U.S. Patent No. 3,953,391, and British reference GB 1,159,390, which are each herein incorporated by reference. Suitable acrylic materials preferably include polymers derived from alkyl esters of acrylic acid and methacrylic acid such as are disclosed in U.S. Patent Nos . 3,455,806 and 3,928,157, which are incorporated herein by reference, along with crosslinking material as described below. An example of a suitable commercially available material is POWERCRON® 920 material commercially available from PPG Industries, Inc.

Suitable polyurethane film forming materials are disclosed in U.S. Application Serial No. 09/309,851, herein incorporated by reference. The term "polyurethane" as used herein is intended to include polyurethanes as well as polyureas, and poly (urethane-ureas) . The polyurethene preferably contains a polymeric segment derived from an active hydrogen-containing polymer having a glass transition temperature of 0°C or less and a number average molecular weight of 400-4000. The ionic polyurethane resin can be anionic or cationic, but preferably is cationic and the composition is cationically electrodepositable. The polyurethane should have a molecular weight (Mz) of less than 100,000, preferably less than 50,000 and most preferably from 10,000 to 40,000. However, for some applications, higher Tg and molecular weight material, or blends of low and high Tg and/or molecular weight materials may be used. The polyurethane also has active hydrogen functionality, i.e., hydroxyl, primary or secondary amine, and typically has an active hydrogen equivalent weight of 800 to 2500 grams per equivalent.

The polyurethane can be prepared from a polyisocyanate and an active hydrogen-containing material . Suitable polyisocyanates used for preparing the polyurethanes include those that have aliphatically, cycloaliphatically, araliphatically, and/or aromatically bound isocyanate groups. The amount of polyisocyanate used to make the polyurethanes is typically from 10 to 60, preferably 20 to 50 percent by weight based on total weight of the reactants used to make the polyurethane.

The active hydrogen-containing material for reaction with the polyisocyanate to form a cationic or anionic polyurethane comprises one or more active hydrogen-containing polymers. These materials preferably have an average active hydrogen functionality ranging from about 2 to 8, preferably from about 2 to 4, and a number average molecular weight ranging preferably from about 400 to 10,000, more preferably from 400 to 4,000, and a glass transition temperature (Tg) of 0°C or less. However, for some applications, higher Tg and molecular weight material, or blends of low and high Tg and/or molecular weight materials may be used.

Examples of suitable active hydrogen-containing materials include polyether polyols such as polyalkylene ether polyols. Also, other polyethers obtained from the oxyalkylation of various polyols can be used. One commonly utilized oxyalkylation method is by reacting a polyol with alkylene oxide such as ethylene or propylene oxide in the presence of an acidic or basic catalyst. Mixed polyoxyalkylenepolyamines can be used, that is, those in which the oxyalkylene group can be selected from more than one moiety. Derivatives of polyoxyalkylenepolyamines may also be usable. Examples of suitable derivatives would be aminoalkylene derivatives which are prepared by reacting polyoxyalkylenepolyamines with acrylonitrile followed by hydrogenation of the reaction product.

The above reference for the polyols is not inclusive, and many materials with multiple hydroxyl functionality may be used. These include, but are not limited to, materials which the main backbone is aliphatic, aromatic, organometallic, or combinations of the above . Functionality other than hydroxyl may be included along the backbone of the polyol as long as it does not interfere with the reaction of the isocyanate with the hydroxyl . For cationic polyurethanes, the ionizable moiety is typically a tertiary amine group that can be incorporated into the polyurethane by reaction with an active hydrogen- containing compound. The amine is neutralized with acid to form the amine salt groups. Suitable amine compounds include aminoalcohols, diethylaminopropylamine, hydroxyalkylmorpholine, and hydroxyalkylpiperazine, and the like and mixtures thereof. The amount of amine introduced into the polymer typically is that sufficient to give 0.1 to 1, preferably 0.2 to 0.5 milliequivalents (meqs) of amine per gram of resin solids as determined by titration. Suitable neutralizing agents include organic acids such as acetic acid, hydroxyacetic acid, propionic acid, lactic acid, formic acid, tartaric acid, sulfamic acid and dimethylolpropionic acid, as well as inorganic acids such as sulfuric acid, hydrochloric acid and phosphoric acid.

To achieve optimum chip resistance and- durability, the polyurethane preferably is curable or thermosetting. As such, it is used with a curing or crosslinking agent such as a capped or blocked isocyanate, which is preferred for cationic compositions, or an aminoplast, which is preferred for anionic compositions .

The polyisocyanate may be fully capped with essentially no free isocyanate groups and present as a separate component or it may be partially capped and reacted with hydroxyl or amine groups in the polyurethane backbone. Examples of suitable polyisocyanates and capping agents are described in U.S. Patent No. 3,947,339, herein incorporated by reference. When the crosslinking agent used with the polyurethane material contains free isocyanate groups, the film-forming composition is preferably a two-package composition (one package comprising the crosslinking agent and the other comprising the hydroxyl functional polymer) in order to maintain storage stability. Fully capped polyisocyanates are described in U.S. Patent No. 3,984,299. The polyisocyanate can be an aliphatic, cycloaliphatlc or an aromatic polyisocyanate or a mixture of the two.

Any suitable aliphatic, cycloaliphatic, or aromatic alkyl monoalcohol or phenolic compound may be used as a capping agent for the capped polyisocyanate crosslinking agent in the composition of the present invention e.g., oximes such as methyl ethyl ketoxime, acetone oxime and cyclohexanone oxime, lactams such as epsilon-caprolactam, and amines such as dibutyl amine .

For polyurethane materials, the crosslinking agent is typically present in an amount of at least 10 percent by weight, preferably at least 15 percent by weight, based on total resin solids weight of the composition. The crosslinking agent is also typically present in an amount of less than 60 percent by weight, preferably less than 50 percent by weight, and more preferably less than 40 percent by weight, based on total resin solids weight of the composition. The amount of crosslinking agent present may range between any combination of these values, inclusive of the recited values.

The equivalent ratio of hydroxyl groups in the polymer to reactive functional groups in the crosslinking agent is typically within the range of 0.5 to 2.0, preferably 1.0 to 1-.5.

Usually the polyurethane composition preferably contains catalysts to accelerate the cure of the crosslinking agent with reactive groups on the polymer (s) . The catalyst is usually present in an amount of about 0.05 to about 5.0 percent by weight, preferably about 0.08 to about 2.0 percent by weight, based on the total weight of resin solids in the thermosetting composition. Examples of suitable polyester film forming materials are disclosed in U.S. Patent Nos . 5,739,213 and 5,811,198, and in U.S. Application Serial No. 09/531,807, which patents and application are herein incorporated by reference. An exemplary polyester polymer suitable for the practice of the invention comprises the reaction product of an aromatic and/or cycloaliphatic carboxylic acid compound comprising at least two aromatic and/or secondary aliphatic carboxyl groups, or an anhydride thereof; a branched aliphatic, cycloaliphatic or araliphatic compound containing at least two aliphatic hydroxyl groups, the aliphatic hydroxyl groups being either secondary or tertiary hydroxyl groups or primary hydroxyl groups attached to a carbon adjacent to a tertiary or quaternary carbon; a compound comprising an ionic salt group or a group which is converted to an ionic salt group; and optionally, at least one hydroxyl substituted carboxylic compound comprising at least one tertiary aliphatic carboxyl group and at least two aliphatic hydroxyl groups. Preferably, the ionic salt group equivalent weight of the polyester polymer is between 1,000 and 10,000. The salt group can confer either an overall positive or negative charge to the ionic polyester polymer. However, as discussed above, the material is preferably cationic. A compound which is "a compound comprising an ionic salt group" is a compound which includes the ionic salt group prior to polymerization. A "compound comprising a group which is converted to an ionic salt group" is a compound which, when reacted with another compound, forms a salt group.

Cationic salt groups can be either present before polymerization or they can be later formed. For electrodeposition, the cationic salt group is typically a quaternary ammonium group, and amine salt group or a sulfonium group. A method for forming quaternary amine groups in a cationic resin is described in U.S. Patent No. 5,908,912. A method for forming amine salt groups is described in U.S. Patent No. 4,017,438.

Suitable polyesters for use as precursor compounds to the ionic polyester polymer of the present invention are described in U.S. Patent Nos. 5,739,213 and 5,811,198, herein incorporated by reference and described above . The ionic polyester polymer preferably contains at least one functional group that is reactive with a curing agent. Typically, the reactive functional group is an active hydrogen group, as described in U.S. Patent No. 5,908,912, which is most preferably a hydroxyl group. In the case of cationic embodiments of the resins, a hydroxyl group is present on the polyester polymer as a result of the opening of the epoxy ring during formation of the cationic groups .

Preferably, the ionic polyester includes active hydrogens which are generally reactive with curing agents for transesterification, transamidation, and/or transurethanization with isocyanate and/or polyisocyanate curing agents under coating drying conditions. Preferably, the ionic polyester polymer will have an active hydrogen content of 0.5 to 10 milliequivalents, more preferably 1.0 to 5 milliequivalents of active hydrogen per gram of resin solids. Curing agent (s) for the polyester material useful in the present invention can be a polyisocyanate curing agent (such as discussed above) which is preferred for use with cationic polyester polymers or an aminoplast curing agent which is preferred for use with anionic polymers.

The curing agent is typically present in amounts of 25 to 45, preferably 30 to 35 percent by weight based on weight of main vehicle resin solids.

The polyester resin described above preferably is present in the electrocoating composition in amounts of about 1 to about 60 percent by weight, preferably about 5 to about 25 based on total weight of the electrodeposition bath.

Aqueous polyester compositions of the present invention typically are in the form of an aqueous dispersion, i.e., a two-phase transparent, translucent or opaque resinous 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 and usually less than 0.5 micron, preferably less than 0.15 micron. The concentration of the resinous phase in the aqueous medium is at least 1 and usually from about 2 to about 60 percent by weight based on total weight of the aqueous medium. When the compositions of the present invention are in the form of resin concentrates, they generally have a resin solids content of about 20 to about 60 percent by weight based on weight of the aqueous medium.

Suitable epoxy-functional materials are disclosed in U.S. Application Serial No. 09/309,850, herein incorporated by reference. The epoxy-functional materials preferably contain at least one, and more preferably two or more, epoxy or oxirane groups in the molecule, such as di- or polyglycidyl ethers of polyhydric alcohols. Useful polyglycidyl ethers of polyhydric alcohols can be formed by reacting epihalohydrins with polyhydric alcohols in the presence of an alkali condensation and dehydrohalogenation catalyst. Suitable polyhydric alcohols can be aromatic, aliphatic, or cycloaliphatic. Suitable epoxy-functional materials preferably have an epoxy equivalent weight ranging from about 100 to about 2000, as measured by titration with perchloric acid using methyl violet as an indicator. Useful polyepoxides are disclosed in U.S. Patent No. 5,820,987 at column 4, line 52 through column 6, line 59, which is incorporated by reference herein. To form a cationic resin or composition, the epoxy-functional material can be reacted with an amine to form cationic salt groups, for example with primary or secondary amines which can be acidified after reaction with the epoxy groups to form amine salt groups or tertiary amines which can be acidified prior to reaction with the epoxy groups and which after reaction with the epoxy groups form quaternary ammonium salt groups. Other useful cationic salt group formers include sulfides. The material can be used in combination with a polyisocyanate curing agent that is at least partially capped with a capping agent.

The polyepoxide may be chain extended by reacting together a polyepoxide and a polyhydroxyl group-containing' material selected from alcoholic hydroxyl group-containing materials and phenolic hydroxyl group-containing materials to chain extend or build the molecular weight of the polyepoxide. Examples of phenolic hydroxyl group-containing materials are polyhydric phenols, such as Bisphenol A, Bisphenol F, resorcinol, Hexane Diol, 1,3 cyclohexanediol, polycaprolactone diol, polyether diols, propoxylated Bisphenol A, ethoxylated Bisphenol A, Butane diols, Hydroquinone, Catechol, Hydantoin, and other dialcohols. The resin contains cationic salt groups and active hydrogen groups selected from aliphatic hydroxyl and primary and secondary amino.

A chain extended polyepoxide is typically prepared by reacting together the polyepoxide and polyhydroxyl group- containing material neat or in the presence of an inert organic solvent such as a ketone, including methyl isobutyl ketone and methyl amyl ketone, aromatics such as toluene and xylene, and glycol ethers such as the dimethyl ether of diethylene glycol. The reaction is usually conducted at a temperature of about 80°C to 160°C for about 30 to 180 minutes until an epoxy group-containing resinous reaction product is obtained. The equivalent ratio of reactants; i. e., epoxy: polyhydroxyl group-containing material is typically from about 1.00:0.75 to 1.00:2.00. The polyepoxide can also contain cationic salt groups. The cationic salt groups are preferably incorporated into the resin by reacting the epoxy group-containing resinous reaction product prepared as described above with a cationic salt group former. By "cationic salt group former" is meant a material which is reactive with epoxy groups and which can be acidified before, during, or after reaction with the epoxy groups to form cationic salt groups. Examples of suitable materials include amines or sulfides which can be mixed with acid prior to reaction with the epoxy groups and form ternary sulfonium salt groups upon subsequent reaction with the epoxy groups. The extent of cationic salt group formation should be such that when the resin is mixed with an aqueous medium and the other ingredients, a stable dispersion of the electrodepositable composition will form. By "stable dispersion" is meant one that does not settle or is easily redispersible if some settling occurs. Moreover, the dispersion should be of sufficient cationic character that the dispersed particles will migrate toward and electrodeposit on a cathode when an electrical potential is set up between an anode and a cathode immersed in the aqueous dispersion. Generally, the cationic resin is non-gelled and contains from about 0.1 to 3.0, preferably from about 0.1 to 0.7 millequivalents of cationic salt group per gram of resin solids. The number average molecular weight of the cationic polyepoxide preferably ranges from about 2,000 to about

15,000, more preferably from about 5,000 to about 10,000. By "non-gelled" is meant that the resin is substantially free from crosslinking, and prior to cationic salt group formation, the resin has a measurable intrinsic viscosity when dissolved in a suitable solvent. In contrast, a gelled resin, having an essentially infinite molecular weight, would have an intrinsic viscosity too high to measure.

Active hydrogens associated with the cationic polyepoxide may include any active hydrogens which are reactive with isocyanates within the temperature range of about 93 to 204 °C, preferably about 121 to 177°C. Preferably, the polyepoxide will have an active hydrogen content of about 1.7 to 10 millequivalents, more preferably about 2.0 to 5 millequivalents of active hydrogen per gram of resin solids. The term "active hydrogen" means those groups which are reactive with isocyanates as determined by the Zerewitnoff test as is described in the JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol. 49, page 3181 (1927). Preferably, the active hydrogens are hydroxyl, primary amine and secondary amine. Beta-hydroxy ester groups may be incorporated into the polyepoxide by ring opening 1,2-epoxide groups of the polyepoxide with a material which contains at least one carboxylic acid group. Phenolic hydroxyl groups may be incorporated into the polyepoxide by using a stoichiometric excess of the polyhydric phenol during initial chain extension of the polyepoxide.

When the polyepoxide contains both phenolic hydroxyl groups and beta-hydroxy ester groups, the phenolic hydroxyl groups may be incorporated simultaneously with the beta- hydroxy ester groups, or sequentially before or after. The electrodepositable composition may further include additional ingredients having beta-hydroxy ester and/or phenolic hydroxyl groups, as well as customary auxiliaries typically used in electrodepositable compositions. Such electrodepositable compositions are described in WO 98/07770. Crosslinking materials for the first electrodepositable coating composition may comprise blocked or unblocked polyisocyanates such as are described above. The amount of the crosslinking material in the electrodepositable coating composition generally ranges from about 5 to about 50 weight percent on a basis of total resin solids weight of the electrodepositable coating composition.

The electrodepositable coating composition also can comprise one or more pigments which can be incorporated in the form of a paste, surfactants, wetting agents, catalysts, film build additives, flatting agents, defoamers, microgels, pH control additives and volatile materials such as water and organic solvents, as described in U.S. Patent No. 5,820,987 at column 9, line 13 through column 10, line 27. Suitable pigments include hiding pigments such as titanium dioxide, zinc oxide, antimony oxide, etc. and organic or inorganic UV opacifying pigments such as iron oxide, transparent red or yellow iron oxide, carbon black, phthalocyanine blue, and the like. Pigments can be present in amounts of up to 60 parts by weight or less based on 100 parts by weight of total solids of the electrodepositable composition. Useful solvents included in the composition, in addition to any provided by other coating components, include coalescing solvents such as hydrocarbons, alcohols, esters, ethers and ketones. Preferred coalescing solvents include alcohols, polyols, ethers and ketones. The amount of coalescing solvent is generally about 0.05 to about 5 weight percent on a basis of total weight of the electrodepositable coating composition.

Other optional ingredients are anti-oxidants, UV- absorbers and hindered amine light stabilizers. These ingredients are typically added in amounts up to about 6% based on the total weight of resin solids of the electrodepositable composition.

In addition to the specific electrodepositable coatings described above, examples of other useful commercially available electrodepositable coatings include POWERCRON® series coatings, such as but not limited to POWERCRON® 290, 390, 395, 756, 920, and 930 coating materials, commercially available from PPG Industries, Inc. Other useful electrodepositable coating compositions are disclosed in U.S. Patent Nos. 4,891,111; 5,760,107 and 4,933,056, which are incorporated herein by reference. The solids content of the liquid electrodepositable coating composition generally ranges from about 3 to about 75 weight percent, and preferably about 5 to about 50 weight percent.

In a preferred embodiment of the invention, the first coating material functions as a finish coat or monocoat and preferably comprises a durable, sulfonium polyester resin in liquid form, such as described above. The resin may optionally include coloring materials as discussed above to give the resin, and hence the resulting first coating, a selected color. The first electrodepositable material preferably is free or essentially free of powder material, e.g. preferably has less than about 5 weight percent powder > binder based on the total weight of the material.

The first coating material is applied to the substrate, e.g., at least a portion of the Class A surface of the substrate, to a preferred thickness of about 20 microns to about 40 microns, preferably about 30.5 microns, in similar manner as described above.

The substrate is removed from the bath and the coating set, dried or cured, as desired, e.g. using an infrared, electric, or gas (direct or indirect) oven. As used herein, the term "set" means that the coating is tack-free (resists adherence of dust and other airborne contaminants) and is not disturbed or marred (waved or rippled) by air currents which blow past the coated surface. For example, the coated substrate can be flashed at room temperature or baked in an oven. The heating or curing operation is usually carried out at a temperature in the range of from 90°C to 260°C for a period of time ranging from 10 to 60 minutes. The thickness of the resultant film is usually from about 10 to 50 microns.

Next, the coated substrate is positioned in the bath with the Class A surface again facing the anode. However, in this second electrodeposition process, uncoated or non-Class A surfaces of the substrate are electrocoated with a second, corrosion-inhibiting, electrodepositable coating composition preferably having a higher throwpower than the first electrodepositable coating composition. In the practice of the invention, the second, corrosion resistant coating composition is different from the first, aesthetic coating composition. By "different" is meant that the second coating composition is chemically different or has different components or amounts of components than the first coating composition to provide corrosion resistance rather than aesthetic appearance. Due to the higher throwpower of the second coating material, the portions of the non-Class A surface which were not covered by the first coating material will be covered by the corrosion resistant second coating material. In a preferred practice of the invention, the second material preferably comprises a clear, cationic resin liquid material and can be similar in composition to the coating materials described above for the first electrodepositable coating material. The second coating material can be a clear or pigmented material. Examples of useful commercially available electrodepositable coatings for the second coating include POWERCRON® series coatings, such as but not limited to POWERCRON® 290, 390, 395, 756, 920, and 930 coating materials, commercially available from PPG Industries, Inc. As discussed above, the second coating is different than the first coating. Therefore, if, for example, POWERCRON® 290 coating material is used in the first coating, a different POWERCRON® coating material will be used in the second coating. The substrate is electrocoated to provide a thickness of the second coating material on the non-Class A surface of about 12 microns to about 38 microns. The substrate may then be removed from the electrodeposition bath and cured to yield a final product, for example by heating to a temperature of about 170°C to about 180°C, preferably about 17β°C, for about 30 ins.

Alternatively, after application of the first and second coatings, a clearcoat can be applied over the coated Class-A surface. The clearcoat can be liquid, powder slurry (powder suspended in a liquid) or powder (solid), as desired. Preferably, the clearcoat composition is a crosslinkable coating comprising one or more thermosettable film-forming materials and one or more crosslinking materials. Useful film-forming materials include epoxy-functional film-forming materials, acrylics, polyesters and/or polyurethanes, as well as thermoplastic film-forming materials such as polyolefins can be used. The clearcoat composition can include additives, such as fillers, UV absorbers, rheology control agents, surfactants, flow control agents, thixotropic agents, anti- gassing agents, catalysts and other customary additives. Examples of such materials are described in U.S. Patent Nos. 4,220,679; 4,403,003; 4,147,769 and 5,071,904, herein incorporated by reference. Preferably the clearcoat does not contain pigments. If the clearcoat is a liquid or powder slurry, volatile material (s) such as water, organic solvents, or amines may be included.

Suitable waterborne clearcoats are disclosed in U.S. Patent No. 5,098,947 (incorporated by reference herein) and are based on water soluble acrylic resins. Useful solvent borne clearcoats are disclosed in U.S. Patent Nos. 5,196,485 and 5,814,410 and include epoxy-functional materials and polyacid curing agents. Suitable powder clearcoats are described in U.S. Patent No. 5,663,240 (incorporated by reference herein) and include epoxy functional acrylic copolymers and polycarboxylic acid crosslinking agents, such as dodecanedioic acid. The amount of the clearcoating composition applied to the substrate can vary based upon such factors as the type of substrate and intended use of the substrate, i.e., the environment in which the substrate is to be placed and the nature of the contacting materials. The transparent clearcoat composition is typically applied upon the coated substrate by spray application, however, the clearcoat can be applied by any convenient coating technique. Any of the known spraying techniques can be used such as compressed air spraying, electrostatic spraying and either manual or automatic methods .

During application of the clearcoat composition to the substrate, ambient relative humidity generally can range from about 30 to about 80 percent, preferably about 50 percent to 70 percent. In an alternative embodiment, after the second coating is applied (and cured or set, if desired), multiple layers of transparent ("clear") coatings can be applied upon the Class-A surface. This is generally referred to as a "clear-on-clear" application. Using a durable, optionally colored, electrodepositable topcoat material of the invention to coat the Class A surface eliminates the need for an underlying primer surfacer and a subsequent spray or powder conventional topcoat over the Class A surface. Additionally, since the corrosion resistant electrocoat is only or substantially only applied to the non- Class A surface, the cost of electrocoating the substrate in terms of time and materials is reduced. Further, the present invention results in additional cost savings since the operation of electrocoat lines is more economical than the operation of spray or powder lines because the transfer efficiency of electrodeposited coatings is near 100 %.

The following example shows how the methods of the present invention can be used to produce a coated substrate.

EXAMPLE This Example shows the preparation of a cationically electrodeposited topcoat according to the present invention applied to a substrate. A white color coat or topcoat of the invention was prepared and electrodeposited on panels, e.g., Class A surfaces, using a conventional Ford throwpower test apparatus. Three sets of coated panels were made for each substrate evaluated. For one set of panels, the white color coat was fully cured in an electric oven at 340°F for 30 minutes. The second set of coated panels was dehydrated and coalesced at 220°F for 30 minutes. The third set of coated panels was air flashed for 1 hr at room temperature. A corrosion resistant clear aromatic electrocoat primer with better throwpower than the white color coat of the invention was subsequently applied to the panels having the previously electrodeposited white color coat of the invention.

A white color coating composition of the invention, used to coat the test panels, was prepared as discussed below. Throughout the following discussion, the material referred to as Polyester 1 was produced by esterifying hydrogenated bisphenol-A with about two equivalents of 4- methyl hexahydrophthalic anhydride, and reacting the resulting polyester with about two equivalents of epichlorohydrin. Preferably, this polyester has the following general formula I:

where n ranges from about 1 to about 5.

Preparation of Sulfonium Polyester Resin

A sulfonium polyester resin used in the coating composition of the Example was prepared from the following ingredients :

TABLE 1

INGREDIENTS PARTS BY WEIGHT

Polyester 1 449.17

CHDA-HPA Adduct¹ 132.30

Ethyltriphenylphosphonium 1.10 Iodide

PROPASOL® B² 96.17

Thiodiethanol (50% solids) 113.87

Lactic Acid (88% in water) 47.74

Deionized Water 25.20

Crosslinker³ 567.47

Deionized Water 1727.01 ¹Cyclohexane dicarboxylic acid and hydroxy pivalic acid at a 1:2 ratio, respectively (100% solids) . ²2-butoxy propanol commercially available from Union Carbide Corp. ³DESN 3300® HDI Trimer commercially available from Bayer Corporation 100% blocked with dibutyl amine (75% solids in methyl isobutyl ketone) .

The Polyester 1 and CHDA-HPA Adduct from Table 1 were charged to a reaction vessel and heated under a nitrogen blanket to 105°C and held at temperature until the CHDA-HPA adduct completely dissolved. Ethyltriphenylphosphonium iodide was added as a catalyst and the reaction was allowed to exotherm, followed by a one-hour hold at 130°C to achieve a theoretical epoxy equivalent weight (EEW) of 1245. PROPASOL® B solvent was added to cool the reaction to 75°C followed by addition of thiodiethanol, lactic acid and the first portion of water listed in Table 1 above. The reaction mixture was then heated to 75°C and held for 2 hours until a minimum acid value of 5.1 was observed. The crosslinker was then added and the solution was mixed for 15 minutes. The final (second listed) portion of water was then added to the resin under agitation to produce a dispersion of organic resin in an aqueous phase. Volatiles were vacuum distilled from the resin at 60°C for 5 hours, resulting in a final resin solids of 41.35%.

Preparation of Grind Vehicle for DBTO Catalyst Paste

The dibutyl tin oxide (DBTO) catalyst paste used in. the white coating composition of the invention includes a polyester quaternary grind vehicle (Table 3) prepared using the reactants of Table 2 below.

\ TABLE 2

(Amine Salt Quaternizing Compound)

INGREDIENTS PARTS BY WEIGHT

MIBK 4. .68

Dimethylethanolamine 89

IPDI Adduct¹ 410. ,78

PROPASOL® B 41. .98

Lactic Acid (88% in water) 121. ,74

Deionized Water 99.7

^■"^■Isophorone diisocyanate with half of the isocyanate content reacted with 2-ethylhexanol, 80% solids in methyl isobutyl ketone .

The methyl isobutyl ketone (MIBK) and dimethylethanolamine were added to a 2 L flask equipped with an addition funnel , nitrogen purge , and stirrer . A blanket of nitrogen was placed over the solvent and the MIBK was heated to 30°C while stirring. The IPDI Adduct (Table 2 above) was added dropwise and the exotherm stabilized at approximately 60°C. The solution was held at 60°C until no isocyanate peak was observed for samples evaluated by IR spectroscopy. The solution was heated and held at 50°C while the Proposol B was added. Lactic acid was then added dropwise and the system was allowed to exotherm. The water was added slowly and the solution was allowed to cool to room temperature.

The polyester quaternary grind vehicle used in the dibutyl tin oxide (DBTO) catalyst paste was prepared from the following ingredients:

TABLE 3

(Quaternary Grind Vehicle)

INGREDIENTS PARTS BY WEIGHT

Polyester 1 (80% solids in methyl 21.1 isobutyl ketone)

CHDA-HPA Adduct 40.5

Ethyltriphenylphosphonium Iodide 1.1

PROPASOL® B 95.61

Reaction Product of table 2 360.59

Deionized Water , 2143.4

The Polyester 1 and CHDA-HPA Adduct were charged to a reaction vessel and heated under a nitrogen blanket to 105°C and. held at temperature until the CHDA-HPA adduct completely dissolved. Ethyltriphenylphosphonium iodide was added as a catalyst and the reaction allowed to exotherm followed by a one-hour hold at 130°C for a theoretical epoxy equivalent weight (EEW) of 1262. The PROPASOL® B solvent was added while allowing the reaction to cool to a temperature of 85°C followed by addition of the reaction product of Table 2 to cool the resin solution to 75°C. The reaction was then held at 75°C and titrated to obtain an acid value minimum, i.e., titrated until a constant acid value was obtained. The water (Table 3) was added under agitation to produce a dispersion of organic resin in an aqueous phase. Approximately 650 grams of volatiles were then vacuum distilled from the resin at 60°C, resulting in a final resin solids of 36.8%.

The DBTO Catalyst paste was prepared using the following mixture of ingredients:

TABLE 4

(DBTO Catalyst Past)

INGREDIENTS PARTS BY WEIGHT

Quaternary Grind Vehicle 402. ,6 (Table 3)

Dibutyl Tin Oxide 370. .3

Deionized Water 427. .1

The ingredients listed in Table 4 were sequentially added to a container under agitation and mixed until well blended. A RED HEAD laboratory dispersion mill, commercially available from Chicago Boiler Company, was filled with ceramic beads, and cold water was circulated through the unit' s cooling jacket. The components of Table 4 were added to the dispersion mill and ground for 3 hours. After grinding, the particle size was reduced to a Hegman value of 7, as measured using a Hegman fineness of grind gauge commercially available from Gardner Company.

Preparation of Tint Paste Grind Vehicle A polyester quaternary grind vehicle used in the white tint paste of this Example was prepared from the following ingredients : TABLE 5

(Tint Paste Grind Vehicle)

INGREDIENTS PARTS BY WEIGHT

Polyester 1 (80% solids in methyl 2808.40 isobutyl ketone)

CHDA-HPA Adduct 801.7

Ethyltriphenylphosphonium Iodide 3.6

PROPASOL® B 309.07

IPDI Adduct 446.30 n, n-Dimethylethanolamine 149.52

Lactic Acid (88% in Water) 171.86

Deionized Water 90.00

Deionized Water 4000

The Polyester 1 and CHDA-HPA Adduct were charged to a reaction vessel and heated under a nitrogen blanket to 105°C and held at temperature until the CHDA-HPA adduct completely dissolved. Ethyltriphenylphosphonium iodide was added as ^• a catalyst and the reaction allowed to exotherm followed by a one-hour hold at 130°C for a theoretical epoxy equivalent weight (EEW) of 1207. The solvent PROPASOL® B was added to cool the reaction to 75°C followed by slow addition of the IPDI adduct over 15 minutes. The reaction was then held until no isocyanate was observed by IR spectroscopy . The quaternary salt was then formed by adding a pre ix of n,n- dimethylethanolamine, lactic acid, and water followed by a hold for an acid value minimum. The final portion of water was added under agitation to produce a dispersion of organic resin in an aqueous phase. Approximately 1300 grams of volatiles were then vacuum distilled off of the resin at 60°C, resulting in a final resin solids of 37%.

Preparation of Tint Paste A white tint paste was prepared using the following mixture of ingredients: TABLE 6

White Tint Paste

INGREDIENTS PARTS BY WEIGHT

Tint Paste Grind Vehicle (Table 5) 2099.56

PROPASOL® B 25.64

Deionized Water 68.35

Titanium Dioxide Pigment 3107.35

Deionized Water 674.78

The ingredients of Table 6 were sequentially added to a container under agitation and mixed until well blended. A RED HEAD laboratory dispersion mill was filled with ceramic beads and cold water was circulated through the mill's cooling jacket. The ingredients of Table 6 were added to the dispersion mill and ground for 45 minutes. After grinding, the particle size was reduced to a Hegman value of greater than 7, as measured using a Hegman fineness of grind gauge.

White Color Coating Composition The white color coating composition was prepared as follows

TABLE 7

INGREDIENTS PARTS BY WEIGHT

Sulfonium Polyester Resin, 930 . . 65 as described above (Table 1), actual solids 37.77%

PROPASOL® B 19 . . 24

White Tint Paste, 278 . . 10 as described above (Table 6) , actual solids 67.08%

DBTO Catalyst Paste, 10.26 as described above (Table 4), actual solids 43.2%

Deionized Water 2561.75 The ingredients of Table 7 were added sequentially under agitation. The final paint was allowed to stir for at least 24 hours prior to use.

Corrosion Resistant Cationic Coating

The cationic high-throwpower corrosion resistant coating composition used to coat the non-Class A surface of the test panels was made from a cationic resin commercially available ' from PPG Industries, Inc. of Pittsburgh, Pennsylvania, a conventional cationic catalyst paste, and anticorrosive pigments, as described below.

TABLE 8 INGREDIENTS PARTS BY WEIGHT

POWERCRON® CR450¹ cationic resin 2081.13

Cationic Catalyst paste 36.12

(described in Table 11 below)

Clay Paste 120.77

(described in Table 12 below)

Yttrium Sulfamate 19.22

(45.09% solution in water)

Deionized Water 1542.76

¹POWERCRON® CR450 cationic epoxy-based electrocoat resin is commercially available from PPG Industries, Inc.

Each ingredient was added sequentially under agitation. The final paint was allowed to stir for at least 24 hours prior to use.

Preparation of Cationic Catalyst Paste

The cationic catalyst paste used in this Example includes a cationic grind vehicle (Table 10) prepared using the reactants of Table 9 below. TABLE 9

(Quaternizing agent for cationic grind vehicle)

INGREDIENTS PARTS BY WEIGHT

2-ethyl hexanol half-capped 320.0 toluene diisocyanate, 95% in MIBK

Dimethylethanolamine 87.2

Aqueous lactic acid solution, 117.6

88% in water

2-butoxyethanol 39.2

The 2-ethylhexanol half-capped toluene diisocyanate was added to the dimethyethanolamine in a reaction vessel at room temperature . The mixture exothermed and was stirred for one hour at 80°C. The aqueous lactic acid solution was then charged followed by the addition of 2-butoxyethanol. The reaction mixture was stirred for about one hour at 65 °C to form the quaternizing agent. The cationic grind vehicle used in the cationic catalyst past was prepared from the following ingredients.

TABLE 10

(Cationic grind vehicle)

INGREDIENTS PARTS BY WEIGHT

EPON 829¹ diglycidyl ether 710 . . 0

Bisphenol A 289 . . 6

2-ethylhexanol half-capped toluene 406 diisocyanate, 95% in MIBK

Reaction product of Table 9 496 . . 3

Deionized Water 71 . . 2

2-butoxyethanol 1205 . . 6

^PO 829 diglycidyl ether of Bisphenol A available from Shell Oil and Chemical Co.

The EPON 829 diglycidyl ether and Bisphenol A were charged under a nitrogen atmosphere to a reactor vessel and heated to 150°C - 160°C to initiate an exotherm. The reaction mixture was permitted to exotherm for one hour at 150°C - 160°C. The reaction mixture was then cooled to 120°C and the 2-ethylhexanol half-capped toluene diisocyanate was added. The temperature of the reaction mixture was held at 110°C - 120°C for one hour followed by the addition of the 2- butoxyethanol . The reaction mixture was then cooled to 85°C - 90°C, stirred until uniform, and charged with water followed by the quaternizing agent. The temperature of the reaction mixture was held at 80°C - 85°C until an acid value of about 1 was obtained. The final product had a solids content of about 55%. Preparation of the cationic dibutyltin oxide catalyst paste (stock material) used in the cationic high throwpower corrosion resistant coating composition used in the Example is shown in Table 11 below.

TABLE 11

₍ (Cationic catalyst paste)

INGREDIENTS PARTS BY WEIGHT

Cationic grind vehicle (Table 10) 212.4

Dibutyltin Oxide 300.0

Deionized water 400.0

The above ingredients were sequentially combined and sand milled to a Hegman number of 7.

Preparation of Clay Paste The clay paste used in the Example was made as follows:

TABLE 12

(Clay Paste)

INGREDIENTS PARTS BY WEIGHT

Cationic Grinding Vehicle 29.1

(Table 14 below)

PGV-5 MONTMORILLONITE¹ Pigment 2.04

Lactic Acid (88% in Water) 133

^■"^■Commercially available from Nanocor Company. The ingredients of Table 12 were sequentially added to a container under agitation and mixed until well blended. A horizontal Premier mill was used to mill the mix until an average particle size of 0.38 microns was achieved. The cationic grinding vehicle for the clay paste was made as shown in Table 13 below:

TABLE 13

(Prepolymer for Cationic grinding vehicle for clay paste)

INGREDIENTS PARTS BY WEIGHT

CHARGE 1

DER-732¹ diglycidyl ether 3523.94

Bisphenol A 853.62

Mazon 1651² butyl carbitol 43.78

CHARGE II

Benzyldimethylamine 8.25

Mazon 1651 17.16

CHARGE III

Mazon 1651 272.03

CHARGE IV

Jeffamine D-400³ 924.40 propylene glycol diamine

Mazon 1651 43.78

CHARGE V

Epon 880⁴ (85% in Mazon 1651) 112.36

Mazon 1651² diglycidyl ether 17.16

¹Diglycidyl ether of propylene glycol (600 molecular weight) commercially available from Dow Chemical Corp. ²Mazon 1651 butylcarbitol formal commercially available from BASF Corp. ³Propylene glycol diamine commercially available from Huntsman Chemical Corp. Diglycidyl ether of Bisphenol A commercially available from Shell Oil Co. Charge I was added to a vessel equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet and heated to 130°C under mild agitation. Charge II was then added and the reaction mixture was allowed to exotherm until reaching a temperature of 135°C. The temperature was held at 135 °C for approximately 2 hours until the reaction mixture had an epoxy equivalent weight of 1220 based on resin solids. Charge III and Charge IV were sequentially added to the reaction mixture, which was then cooled to 90°C and held at that temperature for a period of 4.5 hours. The reaction mixture had a viscosity of J/K (as determined by a Gardner Holt bubble viscosity tube with the sample reduced to 50% solids in l-methoxy-2- propanol) . Charge V was then added and the reaction mixture was held for 1.5 hours at 90°C. The epoxy resin thus prepared had a Gardner-Holt bubble viscosity of P.

TABLE 14 (Cationic grinding vehicle for clay paste)

INGREDIENTS PARTS BY WEIGHT

CHARGE 1

Lactic Acid Solution 232.33

(88% in water)

Deionized Water 5513.11

CHARGE II

Reaction Product of Table 13 5409.33

CHARGE III

Deionized Water 3771.21

Charge I was added to a vessel equipped with an agitator. Charge II was added under agitation and the mixture was then stirred for approximately 1.5 hours. Charge III was then added. The resulting dispersion had a theoretical resin solids of 35% and a Brookfield viscosity of 5800 centistokes per second (cps) (spindle #3 @ 12 RPM) . Physical Property Evaluation of Coated Test Panels A conventional Ford Throwpower apparatus was used in accordance with Ford Laboratory Test Method BI120-02 to evaluate the initial 'throwpower of the white color coat (Table 7) of the invention, final throwpower of the corrosion resistant coating (Table 8), and knitting at the overlap area of the two coatings. The structure and operation of a conventional Ford throwpower ^' box will be well understood by one of ordinary skill in the art and hence will not be described in detail herein. Each Ford Throwpower box is formed by placing a spacer between two rectangular panels and then using electrician' s tape to seal and hold the long edges of the two panels together to form a rectangular Ford throwpower box. The bottom and top of each "box" were left open.

Coated panels as described below (commercially available from ACT Laboratories, Inc. of Hillsdale, Michigan) were used to form the throwpower boxes tested in this Example:

C710DI: A commercially available (from PPG Industries, Inc.) spray phosphate pretreatment, C710, over cold rolled steel with a deionized water rinse. C700DI: A commercially available (from PPG Industries, Inc.) dip phosphate pretreatment, C700, over cold rolled steel with a deionized water rinse. C700HIA: A commercially available (PPG Industries, Inc.) dip phosphate, C700, over HIA60A60 (Hot Dip Galvanized Zinc / Iron Alloy) cold rolled steel with a deionized water rinse. C700EZG: A commercially available (PPG Industries, Inc.) dip phosphate, C700, over EZG E60 (Electro

Galvanized Zinc Only) cold rolled steel with a deionized water rinse. Bare CRS : Unpretreated cold rolled steel. A solvent wash of acetone followed by a lactolene was used to remove the protective oil layer from the steel. The white color coating composition (Table 7) described above was electrodeposited onto Ford throwpower boxes formed by pairs of the above panels . Each Ford throwpower box was . submersed in a stirring electrocoat paint bath with an anode placed within 3 inches of both exposed panel faces. Fifteen millimeters of the box, i.e. the panels, was left above the bath to allow good electrical contact with the cathodic leads allowing both panels to act as cathodes in the electrodeposition process. The white colorcoat was electrodeposited using bath and deposition conditions that gave a 1.2 +/- 0.16 mil (30.48 +/- 3.9 micron) film build on the outside face of each panel. The conditions used were a 90°F bath temperature with 165 volts applied as a DC potential between the anode and cathode, 15 second ramp time to full potential, and a 2 minute 30 second total application time. Three throwpower boxes were prepared for each of the above substrates. After the white color coat composition was applied, the Ford throwpower boxes were disassembled, i.e. the tape removed and the panels separated. The panels were rinsed with deionized water and each set of panels was cured in a different way. One set was allowed to flash at room temperature for 1 hour. The second had a coalescence bake at 220°F for 30 minutes in an electric oven. The final set of panels had a full cure cycle of 340°F for 30 minutes in an electric oven. The panels were then measured for film build on the back of the panel, i.e. the side of the panel on the inside of the throwpower box. This film build defines the limiting lengths of throw up the tube, i.e., the amount of coating that deposits on the inside of the throwpower box. The following two results for each panel set were recorded and are reported below:

(a) Test 1, the length in millimeters from the bottom of each panel to the region where the film build of the white coating was 0.1 mil (2.45 microns) thick (not done for the panels that were flashed for 1 hour at room temperature to avoid damage to the permascope probe) ; and

(b) Test 2, the length in millimeters from the bottom of the panel to the interface where no white coating was observable.

The Ford throwpower boxes were then reassembled, i.e. the same two panels were again taped together with the interposition of a spacer, and immersed in the corrosion resistant POWERCRON® P450-based anti-corrosive (AC) coating composition (Table 8) in a similar fashion as for the white coating. The anti-corrosive coating composition was electrodeposited cationically using a bath temperature of 90°F with an applied DC potential of 275 volts, a 15-second ramp to full potential and a total application time of 2 minutes 30 seconds. The Ford throwpower boxes were then disassembled and the panels rinsed with deionized water. All panels were then cured at 350°F for 30 minutes in an electric oven.

The following measurements for each panel were determined and are each reported below: Test 3: the length in millimeters from the bottom of the panel to where the film build of the anti-corrosive coating was 0.1 mil (2.45 microns); _v

Test : the length in millimeters from the bottom of the panel to the place where no paint was observed; Test 5: the film thickness at 1 cm above the interface between the white coating composition and the anticorrosive coating;

Test 6: the film thickness at 1 cm below the interface between the coating composition and the anti-corrosive coating; and

Test 7 : the total film thickness at the place where the film thickness of the white coating was initially measured as 0.1 mil (not done for the panels that were flashed for 1 hour at room temperature since initial film thickness were not recorded) . The last reading was taken to determine if there was sufficient conductivity through the thin portions of the white paint to allow the anti-corrosive coating to form on the top of the previously deposited white coating to ensure good knitting of the two electrodeposited coatings.

The results of these measurements are reported in Table 15 and Table 16 below.

Table 15

Substrate Bake of Test 3 Test 1 Test 7

White

Coating

Bare CRS 1 hr. 157 No data No data

Flash

Bare CRS 1 hr. 160 No data No data

Flash

C710 DI 1 hr. 175 No data No data

Flash

C710 DI 1 hr. 175 No data No data

Flash

C700 DI 1 hr. 175 No data No data

Flash

C700 DI 1 hr. 176 No data No data

Flash

HIA C700 1 hr. 176 No data No data

DI Flash

HIA C700 1 hr. 175 No data No data

DI Flash

EZG C700 1 hr. 167 No data No data

DI Flash

EZG C700 1 hr. 181 No data No data

DI Flash

Bare CRS 340F/30 183 67 0 .18 min.

Bare CRS 340F/30 186 68 0 .17 min.

C710 DI ₃40F/30 192 63 0 .18 min.

C710 DI 340F/30 195 55 0 .19 min.

C700 DI 340F/30 196 62 0 .19 min.

C700 DI 340F/30 196 57 0 .21 min.

HIA C700 340F/30 194 74 0 .39

DI min.

HIA C700 340F/30 196 78 0 .21

DI ^■ min.

EZG C700 340F/30 211 65 0 .26

DI min.

EZG C700 340F/30 210 62 0 .52

DI min.

Bare CRS ₂₂0F/30 165 64 0 .92 min.

Bare CRS ₂₂0F/30 164 68 0 .98 min.

C710 DI 220F/30 174 68 0 .89 min.

C710 DI ₂20F/30 177 70 0 .94 min.

C700 DI 220F/30 176 70 0 .88 min.

C700 DI 220F/30 180 68 0 .83 min.

HIA C700 220F/30 173 78 0 .88

DI min.

HIA C700 220F/30 175 81 1 .08

DI min.

EZG C700 220F/30 184 74 1 .31

DI min.

EZG C700 220F/30 186 72 0 .97

DI min. Table 16

Substrate Bake of Test 4 Test 2 Test 5 Test 6

Durable

White

Bare CRS 1 hr. 181 88 0.77 0.82 Flash

Bare CRS 1 hr. 181 88 0.84 0.84 Flash

C710 DI 1 hr. 190 109 0.62 0.83 Flash

C710 DI 1 hr. 188 108 0.71 0.77 Flash

C700 DI 1 hr. 189 108 0.76 0.79 Flash

C700 DI 1 hr. 191 107 0.69 0.8 Flash

HIA C700 DI 1 hr. 192 109 0.56 0.7 Flash

HIA C700 DI 1 hr. 190 110 0.47 0.77 Flash

EZG C700 DI 1 hr. 186 106 0.49 0.74 Flash

EZG C700 DI 1 hr. 190 109 0.48 0.73 Flash

Bare CRS 340F/30 210 89 0.86 0.03 min.

Bare CRS 340F/30 210 90 0.79 0.03 min.

C700 DI 340F/30 214 103 0.86 0.09 min.

C700 DI 340F/30 216 102 0.82 0.04 min.

C710 DI 340F/30 213 106 0.8 0.23 min.

C710 DI 340F/30 215 103 0.78 0.36 min.

HIA C700 DI 340F/30 215 110 0.54 0.4 min.

HIA C700 DI 340F/30 ₂15 110 0.63 0.45 min.

EZG C700 DI 340F/30 224 105 0.86 0.17 min.

EZG C700 DI 340F/30 225 107 0.7 0.17 min.

Bare CRS 220F/30 190 88 0.66 0.72 min.

Bare CRS 220F/30 189 89 0.69 0.78 min.

C710 DI 220F/30 191 107 0.59 0.71 min.

C710 DI 220F/30 194 106 0.63 0.74 min.

C700 DI 2₂0F/30 195 103 0.54 0.61 min.

C700 DI 220F/30 193 105 0.52 0.65 min.

HIA C700 DI 220F/30 198 109 0.45 0.67 min.

HIA C700 DI 220F/30 199 109 0.46 0.63 min.

EZG C700 DI 220F/30 197 106 0.4 0.61 min.

EZG C700 DI 220F/30 197 106 0.57 0.72 min.

The corrosion resistant POWERCRON® 450-based electrodeposited coating had higher throwpower than the white coating composition of the invention, as shown by the corrosion resistant paint being present significantly farther up the panels than was initially observed for the durable white colorcoat (see Table 16) .

The corrosion-resistant coating and white coating tested showed good knitting at the interface between the coatings as shown by the increase in total film thickness of the final panels over the place where the durable white color coat was only 0.1 mils thick (see Table 15), meaning that the corrosion resistant coating deposited over the color coating at this place. For most of the substrates and cure conditions evaluated, the final total combined thickness of the two coatings at this place was over 0.2 mils, and in some cases well over 0.5 mils.

Further evidence of the good knitting together of the tested coatings is shown by the total film thickness of the films at the -1 cm point on the panels. At 1 cm below the visually observable interface between the durable white coating and the .anticorrosive coating, very little film thickness of the white is expected. Since, for all panels, the white interface was more than 1 cm above the point where the durable white coating was observed to have a 0.1 mil film thickness, the film thickness at the -1 cm point is less than 0.1 mils. As shown in Table 16, except for the Bare CRS and the C700 DI panels where the white was initially fully cured, the film build at the -1 cm point was greater than 0.1 mils, and in some cases well over 0.5 mils. This is further evidence of good knitting between the two electrodeposited coatings, i.e. evidence that the corrosion-resistant coating deposits over the thin white coating at these areas. This knitting and improved throwpower show that application of the tested corrosion resistant coating applied to the non-Class A surface after applying the electrodeposited durable color coat of the invention to the Class A surface appears suitable for covering the non-Class A portions of a metal part and can improve coating coverage at locations where the durable white coating reaches its throwpower limit.

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.

Claims

What is claimed is:

1. A coated metallic article having a Class A surface and a non-Class A surface, comprising: a topcoat electrodeposited upon at least a portion of the Class A surface; and a corrosion-inhibiting coating electrodeposited upon at least a portion of the non-Class A surface.

2. The coated article according to claim 1, wherein the metallic article is formed from a metallic material selected from the group consisting of iron, steel, aluminum, zinc, magnesium, alloys and combinations thereof.

3. The coated article according to claim 1, wherein the topcoat is a monocoat.

4. The coated article according to claim 1, wherein the topcoat comprises a basecoat.

5. The coated article according to claim 1, wherein the topcoat comprises a clearcoat.

6. The coated article according to claim 1, wherein the corrosion-inhibiting coating is different from the topcoat.

7. The coated article according to claim 1, wherein the topcoat is formed from a topcoating composition comprising a crosslinkable film-forming material.

8. The coated article according to claim 1, wherein the topcoat has a thickness of about 10 microns to about 75 microns .

9. The coated article according to claim 1, wherein the corrosion-inhibiting coating is formed from an anticorrosion material comprising an electroconductive pigment and a binder.

10. The coated article according to claim 1, wherein the corrosion-inhibiting coating has a thickness of about 10 microns to about 50 microns.

11. The coated article according to claim 7, wherein the crosslinkable film-forming material is selected from the group consisting of polyesters, polyurethanes, acrylic polymers, polyepoxides, polyamides, polyethers, copolymers and mixtures thereof.

12. The coated article according to claim 7, wherein the topcoating composition further comprises a crosslinking material capable of reacting with the crosslinkable film- forming material to form a crosslinked topcoat.

13. The coated article according to claim 7, wherein the topcoating composition further comprises a pigment.

14. The coated article according to claim 7, wherein the topcoating composition further comprises a carrier material.

15. The coated article according to claim 9, wherein the anticorrosion material comprises a film-forming material selected from the group consisting of epoxy functional materials, polyurethane materials, acrylic materials, copolymers and mixtures thereof.

16. A method of coating a metallic substrate having a Class A surface and a non-Class A surface, comprising the steps of: electrodepositing a topcoat upon at least a portion of the Class A surface of the substrate; and electrodepositing a corrosion-inhibiting coating upon at least a portion of the non-Class A surface.

17. The method according to claim 16, wherein the topcoat is formed from a topcoating composition having less throwpower than an electrodepositable anticorrosion material used for depositing the corrosion-inhibiting coating.

18. The method according to claim 17, wherein the topcoat comprises a monocoat.

19. The method according to claim 17, including applying a clearcoat upon the topcoat.

20. The method according to claim 19, including setting the clearcoat.

21. The method according to claim 20, including curing any curable components of the anticorrosive coat, topcoat, or clearcoat.