US3882009A

US3882009A - Electrodeposition of isothiouronium stabilized lyophobic colloids

Info

Publication number: US3882009A
Application number: US392700A
Authority: US
Inventors: Earl H Wagener; Ritchie A Wessling; Dale S Gibbs
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1973-08-29
Filing date: 1973-08-29
Publication date: 1975-05-06
Anticipated expiration: 1992-05-06

Abstract

A method for electrodeposition of an organic material on an electroconductive surface comprising placing the electroconductive surface to be coated in contact with an aqueous dispersion containing a water-insoluble, essentially electrically non-conductive, film-forming, organic polymer as cation-active particles wherein a substantial portion of the cation-activity is provided by isothiouronium cations and passing an electric current from an electrode through the latex to the electroconductive surface in such a direction that the electroconductive surface is negatively charged, i.e., becomes a cathode in an electrophoretic cell. By use of alternating current both electrodes become coated with the polymer.

Description

United States Patent Wagener et al.

May 6, 1975 ELECTRODEPOSITION OF ISOTHIOURONIUM STABILIZED LYOPHOBIC COLLOIDS Inventors: Earl H. Wagener, Concord Calif;

Ritchie A. Wessling; Dale S. Gibbs, both of Midland, Mich.

Assignee: The Dow Chemical Company,

Midland, Mich.

Filed: Aug. 29, 1973 Appl. No.: 392,700

[52] U.S. Cl. 204/181 [51] Int. Cl B01]: 5/02 [58] Field of Search 204/181 [56] References Cited UNITED STATES PATENTS 3,497,440 2/1970 Weigel 204/181 3,567,613 3/1971 Kraus et a] 204/181 Primary Examiner-Howard S. Williams Attorney, Agent, or Firm-l. A. Murphy [57] ABSTRACT A method for electrodeposition of an organic material on an electroconductive surface comprising placing the electroconductive surface to be coated in contact with an aqueous dispersion containing a waterinsoluble, essentially electrically non-conductive, filmforming, organic polymer as cation-active particles wherein a substantial portion of the cation-activity is provided by isothiouronium cations and passing an electric current from an electrode through the latex to the electroconductive surface in such a direction that the electroconductive surface is negatively charged, i.e., becomes a cathode in an electrophoretic cell. By use of alternating current both electrodes become coated with the polymer.

10 Claims, No Drawings ELECTRODEPOSITION OF ISOTHIOURONIUM STABILIZED LYOPHOBIC COLLOIDS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is concerned with electrodeposition of polymers in aqueous dispersion onto conductive surfaces wherein the article which comprises such surfaces is the cathode in an electric current carrying loop.

2. Description of the Prior Art The usual procedure for coating of polymers, which are dispersed in aqueous media, onto articles has been carried out by making the article to be coated the anode. Most such anodic depositions employ the carboxyl as the functional group which assists in the transport of the polymer to the electrode. There previously has been some recognition that a cathodic electrodepoa sition system would be desirable. However, there are also problems with the known cationic systems. In general, especially with amine and ammonium type surfactants, the known cationic methods are carried out at low pH. Corrosion of metals becomes a problem at low pH. Such a method, for example, is shown in [1.8. Pat. No. 3,159,558 in which the process is carried out at a pH of from about 2 to about 6. The cations, which provide the means of transport in most of the known cationic electrophoretic systems, remain with the polymer after deposition and continue to be points of moisture sensitivity. Furthermore, in the weak base systems the pH and the conductivity are interdependent and cannot be easily varied independently.

An improved process for cationic electrodeposition, in which cation-activity is provided by a sulfonium cation, is described in Applicants copending application, Ser. No. 128,533, filed Mar. 26, l97l, Cationic Electrodeposition of Polymers Onto a Conductive Surface". Other new cationic electrodeposition processes are described in Applicants two applications filed concurrently herewith: Cathodic Electrodeposition of Polymers Onto a Conductive Surface", Ser. No. 392,699, wherein cation activity is provided by reducible, nitrogen-containing cations and Electrodeposition of Sulfoxonium Stabilized Colloids, Ser. No. 392,701, wherein cation-activity is provided by sulfoxonium cations.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method of electrodeposition from aqueous dispersions of cation-active particles in an electrophoretic cell which comprises a coating bath and electrodes which constitute a cathode and at least one anode whereby a coating of polymer is applied to an object having an electroconductive surface by the steps of immersing the object to be coated into the coating bath comprising the aqueous dispersion of cationic particles, connecting a source of electric potential to the object to be coated as one electrode and to at least one other electrode in electrical contact with the coating bath, passing an electric current through the aqueous dispersion comprising the coating bath in such a direction that the electroconductive surface of the object to be coated becomes negatively charged and the other electrodes become positively charged. The aqueous dispersion comprising the cation-active polymer particles during the process has a conductance of from about 300 micromhos to about 3500 micromhos, preferably from about 600 to about 1800 micromhos, per centimeter and the polymer comprising the dispersed particles is a water-insoluble, essentially electrically non-conductive, film-forming organic polymer wherein a substantial portion, especially one-half or more, of the cation-activity is provided by isothiouronium cations.

Director alternating current may be used in the electrodeposition. Some of the hydrophilic character of the polymer due to the cationic groups is destroyed electrolytically during the deposition and at least most of the then remaining cationic groups may be destroyed by subsequent heating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The practice of the present invention requires an electroconductive surface to be coated, a source of electric current, an electrode to function as an anode and an aqueous dispersion of a water-insoluble, essentially electrically non-conductive, film-forming, organic polymer as cation-active particles in which a substantial portion, especially one-half or greater, of the cation activity is provided by the action of isothiouronium cations.

A wide variety of aqueous dispersions of water insoluble, essentially electrically non-conductive polymers are suitable for the practice of this invention.

Typically, such aqueous dispersions of the polymers are obtained by emulsion polymerization of one or more monomers. Ethylenically unsaturated monomers which are thus polymerized are represented by, but not restricted to, non-ionic monomers such as the alkenyl aromatic compounds, i.e., the styrene compounds; the derivatives of a-methylene monocarboxylic acids such as the acrylic esters, acrylic nitriles and methacrylic esters; derivatives of a,,8-ethylenically unsaturated dicarboxylic acids such as maleic esters; unsaturated alcohol esters; conjugated dienes; unsaturated ketones', unsaturated ethers; and other polymerizable vinylidene compounds such as vinyl chloride and vinylidene fluoride. Specific examples of such ethylenically unsaturated compounds are styrene, a-methylstyrene, armethylstyrene, ar-ethylstyrene, a-ar-dimethylstyrene, ar,ar-dimethylstyrene, ar,ar-diethylstyrene, tbutylstyrene, vinylnaphthalene, hydroxystyrene, methoxystyrene, cyanostyrene, acetylstyrene, monochlorostyrene, dichlorostyrene, and other halostyrenes, methyl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate, phenyl acrylate, 2-hydroxybutyl acrylate, 2- hydroxybutyl methacrylate, 4hydroxybutyl acrylate, and 4-hydroxybutyl methacrylate; acrylonitrile, methacrylonitrile, acryloanilide, ethyl a-chloroacrylate, ethyl maleate, vinyl acetate, vinyl propionate, vinyl chloride, vinyl bromide, vinylidene chloride, vinylidene fluoride, vinyl methyl ketone, methyl isopropenyl ketone, vinyl ethyl ether, 1,3-butadiene, and isoprene.

Such non-ionic monomers form water-insoluble homopolymers or water-insoluble copolymers when more than one of the group is used. However, there may be used as copolymerized constituents with the above kinds of monomers other monomers which as homopolymers would be water-soluble. The hydrophilic, water-soluble monomers are represented by hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide and other modified acrylamides such as diacetone acrylamide, and diacetone methacrylamide.

Such monomers are not used in sufficiently large proportions as to make the copolymer water-soluble or significantly electrically conductive. The proportion of such somewhat hydrophilic, water-soluble, monomers which may be copolymerized constituents of the polymers operable in the practice of this invention ordinarily ranges from to about 30 percent or more based on the total weight of the copolymer.

The hydrophilic monomers are used in sufficiently small proportions that they do not interfere substantially with the cationic deposition process.

The method also advantageously is used with polymers which are not prepared readily from monomers by emulsion polymerization, either because no substantial polymerization at a commercially acceptable rate is obtained under usual emulsion polymerization condi tions, such as with isobutene, or because a particular form of the polymerized monomer is desired, for example stereo-specific polyisoprene, stereospecific polybutadiene and the like Representative pre-formed polymers are polymers and copolymers of the mono-olefins having from 2 to carbon atoms such as ethylene, propylene, l-butene, 2-butene, isobutene, pentene, hexene, octene, dodecene, hexadecene, octadecene, and especially those mono-olefins having up to 8 carbon atoms. Especially common types are the various ethylene/propylene copolymers.

illustrative of still other polymers which are electrodeposited by the present invention are alkyd resins, block and graft copolymers; e.g., styrene/butadiene graft and block copolymers', epoxy resins such as the reaction products of epichlorohydrin and bisphenol-A; and thermosettable vinyl ester resins; e.g., the reaction products of approximately equimolar amounts of a polyepoxide and an unsaturated monocarboxylic acid such as acrylic acid and methacrylic acid or unsaturated fatty acids such as oleic acid.

Methods for preparing the above described polymers are well known and are not a part of this invention.

It is required in the practice of the present invention that the polymers must be in the form of an aqueous dispersion of cation-active particles in which a substantial portion, especially one-half or greater, of the cation activity is provided by isothiouronium cations. Such cations may be attached to the polymer particles in various ways. For illustration, a surfactant comprising an isothiouronium cation may be used in the preparation of the polymers by emulsion polymerization whereby the surfactant is adsorbed on the polymer particle. Alternatively, a latex can be prepared by emulsion polymerization using other emulsifiers then replacing at least a major proportion of the polymerization emulsifier in such latexes by removal of that emulsifier such as by dialysis or ion exchange methods and then substituting therefore an isothiouronium surfactant. in still another procedure, preformed polymers, obtained for example by mass polymerization, are converted to aqueous dispersions with the aid of the same kind of surfactant such as by dissolving the polymer in a solvent. then thoroughly mixing the solution with water and the surfactant and subsequently removing the solvent to obtain a latex composition. Yet another procedure is to prepare a water-in-oil dispersion by adding a surfactant comprising an isothiouronium cation to a preformed polymer, then slowly adding water to the water-in-oil dispersion with thorough mixing until inversion occurs to form an oil-in-water dispersion. The isothiouronium cation also may become a part of the polymer by the copolymerization, with the other monomeric constituents of the polymer, of a monomer containing an isothiouronium cation such as S-vinylbenzyl- N ,N ,N ,N tetramethylisothiouronium chloride.

isothiouronium surfactants, in common with other surfactants or emulsifiers, have a hydrophobic component and a hydrophilic component. The hydrophilic portion of an isothiouronium surfactant is provided by the isothiouronium group, i.e.,

wherein R' is a long chain, monovalent hydrophobic radical having from 8 to 25 carbon atoms, R and R individually are alkyl or hydroxyalkyl having from 1 to 4 carbon atoms, R and R individually are alkyl or bydroxyalkyl having from 1 to 4 carbon atoms or are combined in one divalent radical having 2 carbon atoms, and Z" is a water-soluble counteranion. R may be a hydrocarbon radical or a primarily hydrocarbon chain whose chain-length may be interrupted by oxygen, sulfur, nitrogen, phosphorous, or a keto, ester or amide linkage or a terminal group such as hydroxy, keto, ester or amidemay be present. The hydrophobic radicals are not restricted to linear chains and may include aromatic components such as aralkyl.

ln materials for use in the practice of the present invention, the counterion Z is an electrolytically acceptable anion and is not necessarily water-soluble over the entire pH range, but should be water-soluble over the pH range which is being used in a particular electrodeposition. The counteranion, Z, is an anion which does not coagulate the dispersion and typically is the anion of an inorganic acid such as chloride, bromide, fluoride, nitrate, sulfate, bicarbonate, and phosphate; an anion of an organic acid such as acetate, maleate, citrate, propionate, fumarate, acrylate, and benzoate, or hydroxide.

The isothiouronium surfactants may be obtained by the general method disclosed in US. Pat. No. 3,721,581 by reacting a compound R'X with a N- tetrasubstituted thiourea of the formula in which formulas R', R R R and R are as described supra and X is a halogen.

Representative compounds of the formula R'X are alkyl chlorides having from 8 to 25 carbon atoms such as n-octyl chloride, Z-ethylhexyl chloride, n-dodecyl chloride, tetradecyl chloride, cetyl chloride, eicosyl chloride, docosyl chloride and tetracosyl chloride; alltylbenzyl chlorides in which the alkyl has from 4 to 18 carbon atoms such as n-butylbenzyl chloride, namylbenzyl chloride, n-hexylbenzyl chloride, isohexylbenzyl chloride, n-octylbenzyl chloride, dodecylbenzyl chloride, tetradecylbenzyl chloride, and octodecylbenzyl chloride; alkylphenethyl chlorides such as butylphenethyl chloride, hexylphenethyl chloride, octylphenethyl chloride, dodecylphenethyl chloride, tetradecylphenethyl chloride, and hexadecylphenethyl chloride; and the dialkyl a-chlorosuccinates such as diamyl a-chlorosuccinate, dihexyl a-chlorosuccinate, diheptyl a-chlorosuccinate, dioctyl a-chlorosuccinate, dinonyl oz-chlorosuccinate, didecyl a-chlorosuccinate and didodecyl oz-chlorosuccinate. The corresponding bromides and iodides may be used instead of the chlorides.

The N-tetrasubstituted thioureas are represented by tetramethylthiourea, tetraethylthiourea, N,N,N',N'- tetrahydroxyethylthiourea, N,N,N ',N '-tetrahydroxypropylthiourea, N,N,N,N'-tetrahydroxybutylthiourea, N,N '-ethylene-N,N -dihydroxyethylthiourea, N,N dimethyl-N,N'-dibutylthiourea, N,N-dimethyl-N,N- diethylthiourea and N,N'-diethyl-N,N'- dipropylthiourea.

The particle size of the aqueous dispersion or latex, however obtained, is not critical to the electrodeposition process. However, the particle size (average diameter) usually is in the range of from about 500 Angstroms to about l0,000 Angstroms, preferably from about l,500 Angstroms to about 5,000 Angstroms.

The polymer particles have hydrophobic properties because of the nature of the polymer but have some hydrophilic character through positive charges, and hence some cationic character, because of the presence on the particle surface of isothiouronium groups such as from adsorbed emulsifiers or from copolymer ized monomers having isothiouronium groups wherein the amount of such groups attached to the polymer is sufficient to provide waterdispersibility but is insufficient to impart water-solubility or electrical conductivity to the dry organic, film-forming polymer. Thus, isothiouronium groups are present on the polymer because of adsorbed surfactants containing the groups, or because of copolymerization of monomers containing such groups, or because of conversion of other substituent groups on the polymer to isothiouronium groups. The isothiouronium group, i.e., cation, has the formula and the counterion is Z wherein R, R R", R and Z are as defined above for the isothiouronium surfactants. The total quantity of cation-active groups usually ranges from about 0.02 milliequivalent to about 0.4 milliequivalent per gram of polymer.

In this specification and the accompanying claims the term cation-active particles" as applied to the polymer particles refers to particles according to the foregoing description.

The process of this invention is used to coat any electroconductive surface, i.e., articles having an electroconductive surface. Examples of materials which furnish electroconductive surfaces are metals such as iron, steel, phosphated steel, copper, aluminum, chromium, magnesium, tin, titanium, nickel, lead, zinc, or a metal alloy consisting of any of the aforesaid metals, conductive gels, conductive polymers and various forms of carbon such as graphite. Such materials can be in various forms or articles such as automobiles, wire, appliances, metal cans, siding, conductive paper and the like.

In the preferred embodiments of this invention a smooth, unifonn coating is applied to the electroconductive surface.

The aqueous dispersions which are used in the electrocoating process are employed at a polymer concentration of from about 0.5 per cent to about 50 per cent by weight, preferably from about 2 per cent to about per cent. For operability the process is essentially pH independent. For example, the process gives good electrodeposition performance with aqueous dispersions having a range of pH of from about 2 to about 12. Because of corrosion problems below a pH of 6, however, operation above a pH of 6 is preferred. Although operable in the process above a pH of 10, some isothiouronium compounds decompose with time at such pH values. Therefore, a pH range of from about 6 to about l0 is especially preferred.

ln carrying out the electrodeposition process of this invention, an electrophoretic cell is utilized. In the process, the surface to be coated becomes a cathode, another electrode becomes an anode, the latex composition comprises the coating bath and a source of electric current is required. During the process, the article to be coated can be positioned and maintained so that the surface to be coated is stationary within the coating bath or can be passed through a coating bath in a con tinuous manner. With direct current, the source is connected to the electrodes so that the current flows in such a direction as to maintain the article to be coated as the cathode and the other electrode as the anode in an electrophoretic system. The anode and the cathode may each be a single member or either or both may constitute a plurality of joined members. If desired the anode may be separated by a diaphragm from the polymer dispersion. Thus, the anode per se is in electrical contact, but not necessarily physical contact, with the aqueous polymer dispersion. In the use of direct current the anode preferably should be inert for this cationic electrodeposition system and can be the tank in which the process is carried out, for example, if the tank is of metal which is graphite-coated on the interior surfaces. lf alternating current is used, then the charge on the electrodes alternates between positive and negative and a particular electrode becomes coated during the periods when it is negatively charged. During the electrodeposition, the electromotive force is applied in various ways:

1. constant source voltage which results in decreasing current as the electrodeposition proceeds;

2. constant current flow which requires increasing voltage as the process occurs;

3. constant cathode potential, and

4. pulse, i.e., high voltages for short, intermittent times.

The electromotive force which may be applied in the present process covers a wide range such as from about 10 volts to about 5,000 volts. With the first three of the above-listed methods of application, the applied potential generally is not greater than about 350 volts. With the fourth method of application, the potential used ranges from about 200 to about 5,000 volts, preferably to about 800 volts.

At the applied voltages with any of these methods, when the conducting surface of the article to be coated is maintained stationary in the coating bath, the flow of current stops, or becomes very low, when the article is coated.

The coating bath conveniently is operated at ambient temperature, preferably from about C. to about 35C. although temperatures from about 0C. to about 70C. or 80C. may be used.

In prior known electrocoating processes, supporting electrolytes ordinarily are not used. The presence of extraneous electrolyte is known to have a deleterious effect on such processes. However, to obtain optimum results in the practice of the present invention, certain types of water soluble inorganic salts are used to control conductivity. The salt concentration can affect film thickness, quantity of electricity used, efficiency (milligrams of coating deposited per coulomb), and appearance of the coating. Various kinds of salts may be used as supporting electrolytes. The anions of such salts may be selected from the same kinds which are suitable as the counterion for the isothiouronium cation required for the process. The cations of the supporting electrolyte salts should be selected so as not to interfere with the electrodeposition of the resin at the cathode. Unde sirable cations include the alkali metal ions and calcium ions, which can be tolerated, however, at low concentrations, i.e., less than about 0.002 normal. In general, such undesirable ions have electrode potentials more negative than 2.40 volts as defined at pages 414 and 415, with values being listed from page 415 through page 426, of The Encyclopedia of Electrochemisrry, Clifford A. Hampcl, Editor, Reinhold Publishing Corporation, New York, l964.

In the present process, a supporting electrolyte assists in some embodiments of the invention to improve efficiency, particularly at low emulsifier concentrations. The addition of supporting electrolyte increases throwing power at constant pH. Such supporting electrolytes are water-soluble and may be used in small amounts such as up to about 0.] normal based on the total vol urne of the aqueous dispersion of the coating bath. Ammonium salts of weak acids, such as ammonium acetate, ammonium borate, ammonium carbonate, ammonium bicarbonate, and ammonium maleate, are preferred. Diammonium hydrogen phosphate has been found to be especially effective. In addition to its conductive contribution, that salt also serves to buffer the aqueous medium and in general to assist in the deposition of smooth films.

The coating bath comprises the aqueous dispersion of polymer including the isothiouronium surfactant and various optional additives. Such additives include, for illustration, pH control agents and buffers as referred to above and also such materials as dyes, pigments, fillers, agents for improved flow, and standard plasticizers and/or crosslinking systems for the particular polymer being electrodeposited.

The polymer coating ordinarily is deposited on the electroconductive surface within from about 10 seconds to about 2 minutes, although under the extremes of conditions, the deposition can be accomplished in one second or less or in some instances deposition is still continuing for l0 minutes or more. During the electrodeposition process, it is advantageous that the coating bath should be circulated continuously.

The thickness of the film which is electrodeposited ranges from about 0.] mil to about 2 mils depending on the conductive substrate, the polymer composition, the soap concentration, the type of inorganic salt, the inorganic salt concentration, the applied voltage, the current density, the pH, the temperature of the coating bath, the deposition time and solids concentration in the coating bath.

The present invention provides an electrodeposition system which has excellent throwing power. By throwing power is meant that property whereby areas of the electrode being coated at varying distances from the other electrode receives substantially the same density and thickness of the coating material when coated at the same potential. Throwing power relates to the ability to coat hidden areas on irregular shaped objects. There are several methods for measuring throwing power. To obtain the results shown in the examples of this specification, a tank made of Plexiglas having a depth (inside) of 10 cm. was used which, viewed from the top, is L-shaped. The base of the L has a width of 3 cm. and the other arm of the L has a width of 1.5 cm. (all inside measurements) with no internal division between them. In the base of the L, two 4 inch square (10 X 10 cm.) panels are disposed opposite each other and parallel to each other and to the base of the L. One panel is a carbon plate and functions as a reference electrode, i.e., the anode. The other panel is phosphatized steel (Bonderite 37) and functions as the cathode. The other arm of the L is the throwing power" section and contains a phosphatized steel panel, 4 inches X l2 inches 10 X 33 cm.), which is connected by a shunt to the cathode in the base of the L. In carrying out a test, the tank is filled to a depth of about 9 cm. with the coating composition dispersion so that approximately three-quarters of each panel is immersed in the dispersion and a source of the desired voltage is connected to the anode and cathode in the base of the L for 2 minutes {unless otherwise specified). The throwing power coated distance, inches (or cm.)

12 inches (or 30 cm.) mock This apparatus, with one significant difference, is the of direct current at 200 volts was connected individually to the two anodes and to each of the samples which functioned as the cathode. After 2 minutes, the potential source was disconnected and the coating weight and efficiency were determined. The coating weights, coulombs, efficiencies and thicknesses are shown in Table I. These data are the average of the results for the number of panels shown.

The throwing power at 200 volts, determined accord same as that described by A. E. Gilchrist and D. O. ing to the method described supra, was found to be 100 Shuster at page 195 and illustrated in FIG. 1 in Electroper cent for Example 5.

TABLE I Example No. of Coating Efficiency Thickness No. Metal Pancls Tcstcd Wt. mg. Coulombs mg/Coul. mils l Magnesium 3 6.4 .97 8.) 0,18 2 Coppcr 3 9.8 .93 25.2 041 3 Lead 3 8.5 .26 32.2 0.65 4 CR8" 3 l4.7 .60 37.8 0.49 5 PCS" 2 8.7 0.185 47 0.33 6 Platinum 1 8.1 .23 35 5 .50 7 Aluminum 3 3.6 .16 27.8 .35

"CR5 (old Rolled Steel "PCS Phosphutcd Stccl (BONDERITE 37] deposition of Coatings, Advances in Chemistry Series, No. 119, American Chemical Society (1973) (Library of Congress Card No. 73-75713). The difference is that the polarity is reversed on the electrodes since Gilchrist and Shuster were measuring anodic electrodeposition whereas the present invention is concerned with cathodic electrodeposition.

In order to be acceptable, the throwing power should be at least per cent and preferably should be greater than about 40 per cent.

The following examples show ways in which the present invention can be practiced, but should not be construed as limiting the invention. All parts are parts by weight and all percentages are weight percentages, unless otherwise expressly indicated.

EXAMPLES 1-7 To a latex having a particle size of l 170 Angstroms and containing a copolymer of 40 weight per cent of styrene and 60 weight per cent of butyl acrylate which had been prepared by emulsion polymerization using S-p-dodecylbenzyl-N,N ,N ',N '-tetramethylisothiouronium chloride as surfactant were added sufficient dialyzed surfactant of the same kind and sufficient diammonium hydrogen phosphate to provide 0.06 milliequivalents of each per gram of polymer as well as sufficient water to dilute the solids content of the latex to 10 per cent. The pH of the resulting coating formulation was 5.6 and the conductivity was 890 micromhos per centimeter.

The above-described formulation was used to coat various metal panels by cathodic electrodeposition as summarized in Table I. For each series a rectangular polyethylene electrodeposition cell containing two graphite anodes of equal size located at the ends of the long axis was partially filled with the latex. A rectangular sample, about k inch by 4 inches by 1/16 inch, of the indicated metal was immersed in the latex to a depth sufficient to provide 729 square millimeters of metal surface in contact with the latex halfway between the two anodes with the flat inch by 4 inch plane nor mal to a straight line between the two anodes. A source EXAMPLES 8-10 OC-CH-CH N/\N B (CI-1 l was prepared by refluxing equimolar amounts of dinhexyl a-bromosuccinate and tetramethylthiourea in ethanol solution for five hours. Water was added to the resulting solution which was then extracted with hexane then with ether. An per cent yield was obtained and the identity of the product from the aqueous phase was confirmed by nuclear magnetic resonance spectra.

Surfactant B was obtained in the same manner by reacting equimolar amounts of p-dodecylbenzyl chloride and tetramethylthiourea except the reaction solvent was methanol and the refluxing time was 4 hours. The surfactant, p-dodecylbenzyl-N,N,N ,N '-tetramethylis0- thiouronium chloride, was obtained in per cent yield. Preparation of the Coating Formulation To a latex ofa copolymer of 60 weight percent of styrene and 40 weight percent of butadiene having a particle size of 1480 Angstroms and containing 0.03 milliequivalent of dodecylbenzyldimethylsulfonium chloride was added 0.17 milliequivalent of Surfactant A. Sufficient water to reduce the solids content of the latex to 10 per cent and sufficient diammonium hydrogen phosphate to raise the conductivity to 2480 micromhos per centimeter were then added and the pH was adjusted to 7.5 to provide the coating formulation for Example 8.

The coating formulation for Example 9 was prepared in the same manner except Surfactant B in the same amount was used instead of Surfactant A.

The coating formulation for Example was prepared in the same manner from a portion of the coating formulation for Example 9 by adding an additional 0.1 3 milliequivalent of the same surfactant per gram of polymer in that portion of the latex.

Electrodeposition of the Coating Formulations The above-described coating formulations were used to coat zinc phosphated steel panels (BONDERITE 37) in the same manner as described for Examples 17 except that the coating time was 30 seconds and larger panels were immersed in the latex to a depth sufficient to provide about 9500 square millimeters of surface. The results are shown in Table 11.

TABLE II Example No. 8 9 10 Surfactant kind A B B amount, meq. 017 0.17 0.30 Conductivity, micromhos/cm. 2205 2250 Efficiency. mglCoul. 19.8 16.2 12 Thickness, mils .32 ,18 .16

The deposited film was uniform for Examples 8, 9 and 10 with slight roughness in Example 8 but the films were very smooth for Examples 9 and 10.

EXAMPLES 11-15 The coating formulation was prepared as described for Example 9 except the copolymer in the latex was 50 weight per cent of styrene and 50 weight per cent of butadiene, the pH values and conductivities were adjusted to various levels as shown for each example in Table [11. The electrodeposition was carried out in the same manner as for Examples 8-10.

That which is claimed is: l. A method for applying a coating to an object having an electroconductive surface comprising 1, immersing the object in a coating bath comprising a latex having a pH in the range from about 2 to about 12 of cation-active particles of waterinsoluble, essentially electrically non-conductive, organic, film-forming polymer wherein a substantial portion of the cation-activity is provided by isothiouronium cations; said latex having a conductivity of from about 300 micromhos to about 3,500 micromhos per centimeter;

2v passing an electric current through said bath sufficient to effect deposition of a coating of said polymer on the object by providing a difference of electrical potential between the object and an electrode that is a. spaced apart from said object b. in electrical contact with said bath 0. electrically positive in relation to said object.

2. The method of claim 1 in which the electric current is direct current.

3. The process of claim 1 in which the aqueous dispersion has a solids content of from about 2 per cent to about 15 per cent by weight.

4. The process of claim 1 in which the dispersion is maintained at a pH of from about 6 to about 10.

5. The process of claim 1 in which the conductivity of the aqueous dispersion is from about 600 micromhos to about 1,800 micromhos per centimeter.

6. The process of claim 1 in which the aqueous dispersion contains a supporting electrolyte in a concentration up to about 0.1 normal.

7. The process of claim 1 in which some of the cation-activity is provided by sulfonium cations.

8. The process of claim 1 in which isothiouronium cation has the formula wherein R and R individually are alkyl or hydroxyalkyl having from 1 to 4 carbon atoms, R and R" individually are alkyl or hydroxyalkyl having from 1 to 4 carbon atoms or are combined in one divalent radical having 2 carbon atoms and Z is a water-soluble, electrolytically acceptable anion.

9. The process of claim 1 in which the isothiouronium cation is provided by an adsorbed isothiouronium compound.

10. The process of claim 9 in which the isothiouronium compound has the formula wherein R is a long chain, monovalent hydrophobic radical having from 8 to 25 carbon atoms, R and R individually are alkyl or hydroxyalkyl having from 1 to 4 carbon atoms, R and R individually are alkyl or hydroxyalkyl having from 1 to 4 carbon atoms or are combined in one divalent radical having 2 carbon atoms and Z' is a water-soluble, electrolytically acceptable anion.

Claims

1. A METHOD FOR APPLYING A COATING TO AN OBJECT HAVING AN ELECTROCONDUCTIVE SURFACE COMPRISING

1. IMMERSING THE OBJECT IN A COATING BATH COMPRISING A LATEX HAVING A PH IN THE RANGE FROM ABOUT 2 TO ABOUT 12 OF CATION-ACTIVE PARTICLES OF WATER-INSOLUBLE, ESSENTIALLY ELECTRICALLY NON-CONDUCTIVE, ORGANIC, FILM-FORMING POLYMER WHEREIN A SUBSTANTIAL PORTION OF THE CATION-ACTIVITY IS PROVIDED BY ISOTHIOURONIUM CATIONS; SAID LATEX HAVING A CONDUCTIVITY OF FROM ABOUT 300 MICROMHOS TO ABOUT 3,500 MICROMHOS PER CENTIMETER;

2. PASSING AN ELECTRIC CURENT THROUGH SAID BATH SUFFICIENT TO EFFECT DEPOSITION OF COATING OF SAID POLYMER ON THE OBJECT BY PROVIDING A DIFFERENCE OF ELECTRICAL POTENTIAL BETWEEN THE OBJECT AND AN ELECTRODE THAT IS A. SPACED APART FROM SAID OBJECT B. IN ELECTRICAL CONTACT WITH SAID BATH C. ELECTRICALLY POSITIVE IN RELATION TO SAID OBJECT.

2. passing an electric current through said bath sufficient to effect deposition of a coating of said polymer on the object by providing a difference of electrical potential between the object and an electrode that is a. spaced apart from said object b. in electrical contact with said bath c. electrically positive in relation to said object.

2. The method of claim 1 in which the electric current is direct current.

8. The process of claim 1 in which isothiouronium cation has the formula

10. The process of claim 9 in which the isothiouronium compound has the formula