US3898145A

US3898145A - Process for applying contrasting coatings to a workpiece

Info

Publication number: US3898145A
Application number: US116071A
Authority: US
Inventors: Gerald G Davis; William Trevor Lewis
Original assignee: SCM Corp
Current assignee: SCM Corp
Priority date: 1971-02-17
Filing date: 1971-02-17
Publication date: 1975-08-05
Anticipated expiration: 1992-08-05
Also published as: CA940869A

Abstract

A process for coating a workpiece with contrasting, nonsuperposed coatings, the first of which is a paint coating and the second selected from either paint or metal comprising: placing a nondeposit area of the workpiece in bath-shielding contact with a workpiece director surface, then immersing the resulting assembly in an electrocoating bath containing electrodepositable paint and depositing a paint film of sufficient thickness which, on cure, has a breakdown voltage of at least 1,000 volts. The partially coated workpiece then is withdrawn from the bath and disengaged from the director surface. The paint film is cured and the second coating is then applied to the workpiece by electrodeposition or electroplating.

Description

Davis et a1.

Aug. s, 1975 1 1 PROCESS FOR APPLYING CONTRASTING COATINGS TO A WORKPIECE [75] Inventors: Gerald G. Davis, Cooksville;

William Trevor Lewis, Burlington, both of Canada [731 Assignee: SCM Corporation, New York, NY.

[22] Filed: Feb. 17, 1971 121] App1.No.: 116,071

[52] U.S. Cl. 204/181 [51] Int. Cl.'- C25D 13/06 [58] Field of Search 204/18]. 185. 38

1561 References Cited UNITED STATES PATENTS 741.274 10/1903 Pritchard 204/ 1 81 3.361.658 1/1968 Tanner 204/181 3.403.089 9/1968 Joyce 204/181 3.481.842 12/1969 Grassby 204/38 3.488273 1/1970 Johnson 204/181 3,575,832 4/1971 Johnson 204/181 OTHER PUBLICATIONS Ycates, Electropainting (Oct. 70), p. 169.

Primary Exuminer1-l0wurd S. Williams Attorney, Agent, or FirmThomas M. Schmitz 57] ABSTRACT A process for coating a workpiece with contrasting, non-superposed coatings, the first of which is a paint coating and the second selected from either paint or metal comprising: placing a nondeposit area of the workpiece in bath-shielding contact with a workpiece director surface, then immersing the resulting assembly in an electrocoating bath containing electrodepositable paint and depositing a paint film of sufficient thickness which, on cure, has a breakdown voltage of at least 1,000 volts. The partially coated workpiece then is withdrawn from the bath and disengaged from the director surface. The paint film is cured and the second coating is then applied to the workpiece by electrodeposition or electroplating.

6 Claims, 3 Drawing Figures PROCESS FOR APPLYING CONTRASTING COATINGS TO A WORKPIECE This invention is an improvement in selectively electrocoating electrically conductive workpieces. The workpiece is first coated on selected areas with paint leaving nondeposit areas uncoated. The nondeposit areas of the workpiece are coated in a subsequent electrocoating or electroplating bath.

Advantages of selectively electrocoating a workpiece include: capability for producing multicolored electrocoated workpieces; capability for producing an electrocoated-electroplated workpiece where a combination of paint and metal film is desired in certain areas of a workpiece; and the capability of producing multiresinous coated substrates where properties, e.g., solvent resistance, impact strength, are desired.

Further advantages of this invention include an efficient, relatively simple method for masking nondeposit areas of a workpiece for electrocoating, dispensing with masking compounds, e.g., tape, sealants, etc., or devices used in electrocoating operations.

It has been found that a workpiece having a predetermined area and a nondeposit area can be coated with contrasting coatings, the first coating being a paint coating and applied to the predetermined area and the second coating different from the first and selected from the group consisting of paint or metal and applied to the nondeposit area. The process for accomplishing such coating comprises the steps of:

a. placing said nondeposit area of said workpiece in bath-shielding contact assembly with a workpiece director surface;

b. placing the resulting assembly in an electrocoating bath zone containing a dispersion of electrocoating paint in said electrocoating bath zone;

0. electrodepositing said electrocoating paint on the selected area of said workpiece until the electrocoated paint film is of such thickness that on cure it has a breakdown voltage of at least 1,000 volts;

(:1. withdrawing from said bath zone said partially painted workpiece, then disengaging said workpiece from said director surface;

c. curing said electrocoated paint on said workpiece to an ostensibly, tack-free surface; and

f. electrodepositing a coating on the remaining nondeposit area of said workpiece previously partially coated with cured electrocoated paint.

Referring to the drawings,

FIG. 1 is a block flow diagram of the process for selectively electrocoating the workpiece followed by electroplating, a specific embodiment of which is set forth in Example 2. Electrical current supply apparatus and control means, conveyors, piping, agitators, curing apparatus and process instrumentation are not shown as these are conventional. They are supplied where necessary or desirable. A flat workpiece strip 2 which has been conventionally cleansed and having a predetermined area and a nondeposit area is placed in zone 3 in contact with a workpiece director surface so that the nondeposit area is in bath-shielding contact with the director surface. Then the resulting assembly 4 is placed in electrocoating bath zone 5 containing electrodepositable paint, the nondeposit area of said workpiece being in bath-shielding relationship in the electrocoating bath zone while the predetermined area of the workpiece is exposed to the electrodepositable paint. In the electrocoating zone the electrodepositable paint is deposited on the predetermined area of the workpiece until a film thickness that on cure has a breakdown voltage of at least 1,000 volts is obtained. The resulting partially coated workpiece then is withdrawn from the electrocoating bath zone and disengaged from the director surface. The partially coated workpiece 6 then is conveyed to rinsing zone 7 wherein the workpiece is rinsed, usually with water, for removing bubbles, pinholes and any paint that is dragged out of the electrocoating bath zone. The rinsed workpiece 8 then is conveyed to curing zone 9, the curing zone generally being an oven for heating the film to cure temperature. The wet paint film is cured to an ostensibly tack-free surface with the cured film having a breakdown voltage of at least 1 ,000 volts. The partially coated workpiece 11, optionally, then is passed to a post-forming zone 12 for treatment, e.g., machining, bending, etc. The post-formed workpiece 13 then is conveyed to a chrome electroplating zone 14 wherein a chromium film is electroplated on the nondeposit areas from the first operation. The chromium paint coated workpiece then is withdrawn from the chrome electroplating bath as a finished product.

FIG. 2 is a side view of the apparatus for continuously electrocoating metal strip. Workpiece 108 which is a continuous flat strip of mild steel, passes over drive rollers 111 and 112 and is contacted with workpiece director surface 103. The workpiece director surface is a metal drum rotatably mounted on shaft 104. A flat side of workpiece 108 contacts the director surface 103 prior to passing into tank 101 containing electrodepositable paint 102 forming the electrocoating bath zone. A film is electrodeposited on the outer exposed flat surface and edges of workpiece 108 which is then withdrawn from the bath zone for rinsing and curing by means not shown. Drawing rolls after curing draw workpiece through the apparatus.

FIG. 3 is a side view of a continuous electrocoating operation where the workpiece to be coated is in the form of discrete strips of material rather than continuous form. Tank 201 contains electrodepositable paint 202 for forming the electrocoating bath zone. Drive

drums

203 and 208 have a caterpillar-like track mounted as a belt around the circumference of the drum, the caterpillar-like track having flat strips of metal 204 forming the continuous belt and constituting the workpiece director surface. Workpiece strips 207 being no larger than the strips 204 are placed directly over the metal strips 204 so that one side of the workpiece is in a bath-shielding relationship with the metal strips 204. The workpiece typically is held to the metal strip 204 by electromagnetic means. The

drive drums

203 and 208 cause the belt to move and the workpiece to be subsequently immersed in the electrocoating bath zone and contacted with the electrodepositable paint. The predetermined area of the workpiece which is the top side and edges of the workpiece is exposed to the paint and when the workpiece is charged to the desired polarity a film is deposited thereon. On withdrawal of the workpiece from the electrocoating bath, the workpiece is disengaged from the metal strip 204 and removed by means not shown, typically a conveyor belt. The disengaged workpiece being coated on one side only is passed to the rinsing and curing zone.

Electrocoating, sometimes referred to as electrodeposition of paint, of electrically conductive workpieces is widely described in the literature. Typically, an electrocoating operation involves immersion of the work piece in a liquid coating bath (paint) usually containing ionized, film-forming resinous binder particles dispersed in water, optionally with pigment, inorganic and/or organic filler and extender resin, but it also can be carried out in a shower bath by spraying the paint or a continuous stream onto the workpiece. Net undirectional electrical current is passed at voltage generally of 50-350 volts through the bath between the workpiece and an electrode of opposite polarity, thereby setting up an electrical circuit between the workpiece and the electrode. Often the workpiece itself is charged or can be charged by the workpiece director surface if it is made of a conductive material. The ionized resin particles in the liquid bath and other coating components, including pigment and filler, if present, travel to the workpiece and are deposited thereon in the form of a film. Most electrocoating operations are with anionic binders, the ionized resin particles being derived from polycarboxylic acid resin ionized with base such as an amine or potassium hydroxide. Cationic resinous binders can also be employed in the electrocoating operation and are often derived from amino alkyl esters of acrylic and methacrylic acid, amides N-alkylamide, N-hydroxyalkylamide, etc., ionized with acids such as acetic acid or mineral acids such as hydrochloric. A general discussion of anodic electrocoating with paint can be found in the Journalof Paint Technology, Vol. 41, No. 535, journal of 1969, pp. 461-471, and is heraby incorporated by reference.

The workpiece to be coated in the process can be any electrically conductive object, usually a metal such as steel stock, e.g., low and high carbon, stainless, mild and the like, as well as iron, aluminum, copper, metallized paper, zinc, tin, and the like, having substantial electrical conductivity on the surfaces to be electrocoated. In addition, the workpieces can be laminate, having one or more conductive layers. It makes no difference whether the inner laminate layers are electrically conductive or not so long as the surface to be coated can be charged sufficiently to carry a current adequate for attracting the ionized particles in the tank.

The surface of the workpiece prior to electrocoating generally is cleaned and prepared in conventional ways to maximize adhesion of the electrodeposited paint film. Surface preparation and cleaning can be accomplished by brushing, sanding, washing, chemical etching, buffing, and the like for removing surface grime, dirt, oil, rust, oxides, etc., from the surface. Other cleansing techniques include washing with surface active agents such as soap, detergents, or alkali metal hydroxide, etc.

Selective coating of electrically conductive workpieces is accomplished by placing the nondeposit surfaces of the workpiece against the workpiece director surface in substantially bath-shielding relationship. The nondeposit surface areas are those surfaces which are shielded from contact with the electrodepositable paint in the electrocoating bath zone. Bath-shielding of the workpiece surface is achieved by placing the nondeposit area in extremely close proximity to or in contact with the director surface and when the workpiece is withdrawn from the electrocoating bath zone this nondeposit area is substantially free of any electrocoated paint. The predetermined surface area, on the other hand, is distinguished from the nondeposit area in that this area is coated with paint in the electrocoating bath zone. The opportunity for selected predetermined surface areas is ilmited to those surfaces which can be exposed to effective electrocoating contact with the electrodepositable paint, or in other words, limited to the extent that the nondeposit areas can be effectively shielded. Flat surfaces are exemplary of those surfaces that can be effectively shielded by placing the flat side of the workpiece in contact with the flat side of the director surface. Thus, the predetermined areas are then exposed flat surfaces and edges of the workpiece. The nondeposit area is the other flat side.

By the term workpiece director surface is meant the surface which contacts the workpiece and directs it into the electrocoating bath zone and then out of the zone. Typically, the director is a cylinder having a flat side which intercepts the workpiece and directs it to the coating bath.

In order to maintain the nondeposit area of the workpiece in bath-shielding relationship with the director surface, the workpiece must be held tightly against the director surface. Otherwise, the electrodepositable paint can flow into the joint or gaps between the nondeposit area and the workpiece director surface. Any holding means, such as clamps, hooks (e.g., widgets), rollers or magnetic force can be used to accomplish this result, Often, where hooks, rollers or clamps are used a slight marring of coating may occur at the point of contact. However, the effects of marring can be minimized by allowing sufficient time to pass between the last point of contact with the clamp, hook, etc., and withdrawal from the tank.

Although it is preferred that the nondeposit areas of each workpiece be in contact all along the surface or periphery, this is not absolutely essential. Slight cracks and crevices (usually fractions of a millimeter) in the surfaces can be tolerated and yet the nondeposit areas can be effectively substantially shielded from the bath so that little or no electrocoating takes place through such cracks and crevices. By employing a paint having relatively low throwing power (throwing power being defined as the ability of the paint to coat surfaces at the interstices, cracks, crevices, and the like, the higher the throwing power the more ability it has for penetrating cracks and areas on the coated electrode that are remote from the opposite electrode), small cracks and crevices can be tolerated.

Often where the cracks and crevices are too large, a filler material can be placed between the workpieces to act as a sealant. Filler materials generally are nonconductive, plastic or semi-solid which perform as a sealant and include paraffin, wax, grease, petrolatum jelly, fat and putty. It is preferred that no filler material be employed usually because the tiller must be removed after the electrocoating operation, especially where the nondeposit areas are to be coated in a subsequent electrocoating or electroplating operation.

Broadly, the resins in the paint are film-forming at the electrodeposition bath temperature (usually 80F. These resins are curable to a tack-free film and are substantially non-conductive. Virtually any type of resin employed in electrodeposition work can be employed.

As mentioned before, the resins can be of both types, i.e., either cathodic or anodic. Typical anodic resins are the polycarboxylic acid resin type such as coupled siccative oils prepared by reaction of a drying or semidrying oil with a polycarboxylic acid or ahnydride optionally extended with vinyl monomer. Also suitable are the lower alkyl esters of acrylic and methacrylic acid such as methylmethacrylate, methylacrylate, ethylacrylate, Z-ethyl hexyl acrylate, etc. Other anodic resins include the alkyd resins prepared by the reaction of a polyol and a polybasic acid normally extended with a drying oil and epoxide resins usually prepared by condensing a chlorohydrin of a polyhydric alcohol with a polyol, e.g., glycerol dichlorohydrin with ethylene glycol.

Amines can be reacted with the carboxyl groups on the polymers formed to impart water solubility to the polycarboxylic acid resins. Typically, these amines include monoethanolamine and diisopropanol amine. Also, other bases such as ammonia and alkali metal hydroxides can be used.

Cathodic resins as mentioned before can be employed where desired and are generally derived from N-hydroxyalkyl esters of acrylic and methacrylic acid, the N-alkyl esters of acrylic and methacrylic acid, amides, and so forth. These polymers often are reacted with acid for forming an amine salt or quaternary ammonium compound thereby increasing water solubility for ionization of the resin.

Many anodic and cathodic electrocoating resins currently are available for use and those skilled in the art will be able to select those for achieving desired properties.

Optionally, conventional pigments and fillers can be used where desirable for making the paint compositions. Typical pigments and fillers are titanium dioxide, zinc oxide and iron oxides, barytes. barium sulfate, etc.

Under proper conditions in the electrocoating bath, the paint migrates to the workpiece and deposits as a film which on cure is uniform and substantially free of bubbles, pinholes. ripples, etc. Normally the film should be at least about V2 mil in thickness after cure and preferably between l-2 mils in thickness to provide protection to the substrate. Where such resin is a conventional polycarboxylic acid resin in present use, thicknesses of l /2 to 2 mils are generally useful here.

The breakdown voltage of the paint film is more critical than the thickness of the film when the nondeposit area in the first electrocoating operation is to be electrocoated with paint or electroplated with metal in the second coating operation. The term breakdown volt age" although normally used in conjunction with testing of electrical insulation for wires, refers to the voltage level at the point where the paint film on an electrically conductive surface fails. At this voltage, the electrical circuit is complete and a current begins to fiow. Usually a current of not more than milliamperes is sufficient to complete the circuit. To illustrate the concept of breakdown voltage, assume the paint film applied was perfect and had a breakdown voltage of 100; then any voltage less than 100 could be employed in the second electrocoating operation without risk of spotting. There would be no current flow because the voltage applied would not exceed the breakdown voltage of the film. Experience has shown that a paint film applied by electrocoating technique is not perfect and may contract small bubbles, pinholes, etc. To prevent spotting of such a paint film applied by electrocoating techniques in a subsequent electrocoating or electropainting operation, the breakdown voltage of the cured paint film applied in the first electrocoating operation should be at least about 1,000 volts. This voltage insures that substantially no spotting will result when the workpiece is subjected to a second electrocoating operation. Typically, the breakdown voltage for paint film having thicknesses of from l-2 mils and particularly lVz-Z mils is from about 1,000 to 2,000 volts which is the preferred breakdown voltage range for the cured paint film.

A test for determining the breakdown voltage of a paint film is as follows: A workpiece of flat metallic stock, e.g., mild steel, measuring 4 X 4 inches is electrocoated with paint on one side only, the other side being uncoated. A first aluminum foil electrode having a thickness of 0.002 inches and dimension of 3 X 3 inches is mounted on a 4 X 4 inches pressure-sensitive tape which in turn is mounted over the coated surface of the workpiece. The electrode is held in intimate contact with the painted surface by the pressure-sensitive tape. A second electrode is attached in like manner as the first to the exposed uncoated surface of the metal workpiece.

Voltage is applied to the workpiece by a transformer having a rating of 500 volts per ampere or greater and providing an essentially undistorted sinusoidal wave form under test conditions. The frequency of the alternating current applied is cycles per second plus or minus 6 cycles per second. In testing the paint film, the voltage initially is applied at zero voltage and then is increased uniformly to the breakdown voltage at a rate such that the minimum breakdown voltage specified or desired will be reached in approximately 5 seconds. The voltage is measured in rrns (root mean square) volts.

The test is repeated with three additional workpieces and the four breakdown voltages obtained are averaged. The average voltage is recorded as the breakdown voltage of the coating.

Another and a slightly different method for determining breakdown voltage is found in ASTM 1970 No. D495-6l, and such procedure is incorporated by reference.

After the electrodeposition of paint on the workpiece, the film usually is rinsed with water to remove any bubbles or paing dragged out (but not necessarily eleetrocoated) etc. Rinsing also can tend to reduce the number of pinholes and bubbles, thereby helping to perfect the film. Rinsing, however, is not required in all electrodeposition of paint operations and may be eliminated in some instances. Preferably, rinsing is done prior to disassembling the workpiece to prevent washover of paint onto the nondeposit areas.

Curing of the paint after electrodeposition and rinsing is necessary for imparting desired properties to the film. Most of the resins listed above are of a thermoset ting type and crosslink when heated at a temperature of about 300400F. for about 15 minutes to one hour to form a substantially tack-free surface. The common method of curing paints is by heating to effect crosslinking, However, in some instances, depending on the paint, curing can be accomplished by ultraviolet wave radiation, visible light, or electron beams.

After the first coating operation the nondeposit area can be coated with a contrasting paint for producing a multicolored or multi-resinous coated object. The second electrocoating operation can be conducted essentially as in the first operation where paint is to be applied. The mechanics are the same except that the predetermined area need not be blocked off from the bath during electrodeposition of paint or electroplating with metal. The cured paint film causes the predetermined area to remain in bath-shielding relationship.

Metal plating techniques by electrical methods are also particularly adapted to the second phase of the invention. Virtually any type of electrical metal plating operation for depositing a metalliferous material can be employed. Particular metals which may be deposited by conventional electrolytic means are copper, aluminum, nickel, chromium, zinc, tin, palladium. silver, iron, lead, and the like. Plating operations for the deposition of metal are widely described in the literature.

This invention is particularly adapted for making ornamental parts for motor vehicles. Examples of such parts include chrome plated objects such as bumpers, molding, trim, and the like. The invention is advantageous in that these parts normally are exposed to environmental conditions which causes rusting of the metal; thus the surfaces not coated with a layer of chrome are coated with a layer of protective paint.

Chromium can be deposited on a cathode by electrodeposition from a bath containing chromic acid, catalyst. fluoride and sulfate. Typically, the bath comprises an aqueous solution containing from about 150-350 grams per liter of chromic acid CrO and catalysts, e.g., S1F u provided by potassium silicon fluoride and 80 provided by sulfuric acid. Chromium can be applied to the nondeposit areas of the workpieces by passing direct (e.g., rectified a.c.) electric current between the cathode workpiece and anode when they are immersed in the chrome plating bath. An electrical circuit is established resulting in deposition of chromium depositing out in the uncoated cathode areas. Current densities are maintained at about 50-1000 amperes per square decimeter, but other conditions can be used depending on the type of plating desired. With the predetermined areas electrocoated with a paint having after cure a breakdown voltage of at least 1,000, practically no spotting through of chromium results on the coated predetermined areas. Often, the metal workpiece prior to chrome plating is nickel plated by immersing the workpiece into a nickel plating solution at a temperature of 100 F. to 200F. for about 30 seconds. The workpiece then is removed from the nickel plating bath, rinsed, and passed to an acid dip station usually containing sulfuric acid for activation of the nickel surface prior to chrome plating. Then the workpiece is introduced into a chrome plating bath as described above. Often when electrocoating with paint on the side of the workpiece, substantial savings in nickel and power is obtained as opposed to overall chromium plating of the workpiece.

The following specific examples are provided to illustrate preferred embodiments of this invention but are not intended to limit the scope thereof. All parts are parts by weight, all percentages are weight percentages, and all degrees are degrees Fahrenheit, unless otherwise specified.

EXAMPLE 1 An extended coupled glyceride drying oil paint binder is made by reacting in an agitator tank 8,467 parts of alkali-refined linseed oil and 2025 parts of maleic anhydride (heated together at 230C. for about 3 hours until an acid value of 80-90 results). then cooling this intermediate to 155C., adding 1,789 parts of vinyl toluene containing 48 parts of ditertiary butyl peroxide and reacting at 215C. for about 1 hour; the resulting vinyl tolucnated material is then cooled to 157C. and 5.294 parts of non-heat reactive, thermoplastic, oilsoluble phenolic resin are added, the temperature raised to 230C. and the mixture held 1 hour. The phenolic resin is a solid lump resin having softening point of 150C., specific gravity of 1.031.05 at 20C. and has been stripped to get out excess phenol and low molecular weight materials. It is a condensation product of about equimolar quantities of paratertiary butyl phenol and formaldehyde.

The material then is cooled to about 93C., and 1,140 parts are taken for forming a paint dispersion. To these l ,140 parts, 100 parts of distilled water are added, then 13.6 parts of triethylamine, the mixture agitated for a few minutes, then 74 more parts of water and 92.5 parts diisopropanol amine added. This mixture is further reduced with 1,825 parts water and 32.5 parts di ethylene triamine while agitation is continued.

To this paint dispersion there is added 50 parts of a treating mixture of mineral spirits, a light hydrocarbon liquid having A.P.l. gravity of 45-495, specific gravity at 15C. of 0.780.80, flash point (Cleveland Open Cup) between 37.846C., a negative doctor test and no acidity, 12 parts of a wetting agent (the oleic ester of sarcosine, having a maximum of 2% free fatty acid, a specific gravity of 0.948, color on the Gardner scale of 6, and a molecular weight of 340-350). This material is compatible with the paint dispersion; no distict hydrocarbon phase results either at this time, even though a substantial amount of hydrocarbon (predominantly aliphatic) has been used, nor after further addition of the pigment grind and addition of extra water to make the initial painting bath.

A pigment grind is made from 123 parts of vinyl toluenated, maleic-coupled linseed oil made in the same manner as the resin hereinahove shown in this example (except that the resulting polycarboxylic acid resin is not extended with the phenolic resin), 8.4 parts of diisopropanol amine, 0.7 part of an antifoam agent (a ditertiary acetylenic glycol with methyl and isopropyl substitution on the tertiary carbon atom), 233 parts of fine kaolin clay, parts of pigmentary titanium dioxide, 7.8 parts of fine lead chromate, 15.5 parts of fine red iron oxide, 16.9 parts of carbon black, and 201 parts of water. The resulting pigment grind is then blended with the foregoing paint dispersion and treating mixture to make a concentrated paint. The resulting paint is reduced further with water to make an initial painting bath for electroplating operations. The re sulting bath has resin solids (non-volatile matter) concentration of 7.24%. Specific resistance of the initial bath is about 900 ohm-centimeters.

EXAMPLE 2 Referring to FIG. 1, workpiece 2 of 16 gage (0.0598 inches) in thickness, 18.75 inches in width and approximately 2,000 feet in length of conventionally cleaned, mild, cold-rolled steel stock is conveyed to the placing Zone 3 wherein the flat side of the workpiece is brought into contact with the flat side ofa cylindrical workpiece director having its longitudinal axis perpendicular to the direction of movement of the workpiece. The workpiece director surface is approximately 3 feet wide in order to insure that the director surface adequately covers the flat side of the workpiece. The assembly of the workpiece and workpiece director surface then is immersed in the electrocoating bath zone 5. This elecv ocoating bath zone contains the electrodepositable paint formed in Example 1 which is an anodic type. When the front section of the workpiece is first immersed in the electrocoating bath zone it is maintained at neutral or ground potential and the bath and other electrode maintained at a potential positive to such workpiece to repel the paint macromolecules from depositing on the workpiece. On withdrawing the front section of the workpiece strip from the electrocoating bath and guiding it over the exiting conveyor belt the workpiece is then anodically charged with respect to the bath and other electrode to cause the paint macromolecules, pigment. etc., to deposit on the workpiece surface. Only the from section of approximately 20 feet is not painted. In the electrocoating bath zone the tank is normally cathodically charged, the workpiece being anodically charged. Direct electrical current is passed therebetween thereby establishing an electrical circuit. The workpiece strip is maintained in the electrocoating tank in its assembled position; i.e., the flat surface in contact with the flat surface of the cylindrical drum (workpiece director surface) and held there by the frontal and exit conveyor drive means. The voltage applied is 240 volts and the residence bath time for agiven section of the strip from immersion to withdrawal film of paint is deposited on the predetermined exposed flat surface and the edges of the workpiece. After the second residence in the bath zone for a section of the workpiece, it is withdrawn from the electrocoating bath zone and disengaged from the cylindrical workpiece director surface. The partially coated workpiece 6 then is conveyed to rinsing zone 7 wherein the wet paint film on the workpiece is rinsed for seconds with a cold water spray (60F).

The rinsed workpiece 8 then is passed to curing zone 9, a tunnel oven wherein the film is first dried at 100F. then cured by heating to a temperature of 350F. for a period of 30 minutes. At the tail-end of the oven the workpiece and paint film is cooled by a cooler to a temperature of about 70F. A cured film having a substantially uniform thickness of about 1 /2 mils is obtained on coating being a second coating nonsuperposed over the first paint coating. The electroplating tank contains a chrome plating solution of 245 grame per liter chromic acid CrO l .1 grams per liter sulfate 80 and 2.0 grams per liter silicofluoride SiF at F. The tank is anodically charged and the workpiece strip cathodically charged. A sufficient current is permitted to pass through the bath for producing an electroplate of chromium metal, 0.07 microns in thickness, on the nondeposit area from the first of the workpiece. Substantially no spotting through of chromium on the previously coated area (predetermined area) results, and the resulting part 15 chromed on one side and painted on the other side is dried and polished as a finished item.

Having thus described the invention, what is claimed l. A process for coating an electrode workpiece with at least two non-superposed coatings, the first coating being a paint coating and applied to a selected area of said workpiece in an electrocoating immersion bath, the second coating being applied to the non-selected area of said workpiece, the process comprising:

bath shielding the non-selected area of said workpiece with a surface contact assembly adapted to submerge said selected area of the workpiece within an electrocoating bath;

electrodepositing said first coating onto said selected area of the workpiece while being submerged in an electrocoating bath until the electrocoated paint film is at least about 0.5 mil thickness and has a breakdown voltage upon curing of at least 1000 volts;

withdrawing the selectively coated workpiece from said electrocoating bath to expose the non-selected areas of said workpiece by disassociating said surface contact assembly from said workpiece; curing said first coating to form a substantially tackfree surface thereof on the workpiece; and electrodepositing said second coating on said nonselected area of the workpiece.

2. The process of claim 1, wherein said second coating is an electroplated metal coating.

3. The process of claim 2, wherein said workpiece is electroplated with chromium by said second coating.

4. The process of claim 1, wherein said second coating is a paint coating.

'5. The process of claim 1 wherein the step of rinsing said selectively coated workpiece prior to the step of curing said first coating.

6. The process of claim 5, wherein said workpiece is post-formed after the paint film is cured and prior to the second coating.

Claims

2. The process of claim 1, wherein said second coating is an electroplated metal coating.
3. The process of claim 2, wherein said workpiece is electroplated with chromium by said second coating.
4. The process of claim 1, wherein said second coating is a paint coating.
5. The process of claim 1 wherein the step of rinsing said selectively coated workpiece prior to the step of curing said first coating.
6. The process of claim 5, wherein said workpiece is post-formed after the paint film is cured and prior to the second coating.