US3491011A - Method of electrodepositing coating compositions with reduced soluble chromate ions - Google Patents

Method of electrodepositing coating compositions with reduced soluble chromate ions Download PDF

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US3491011A
US3491011A US3491011DA US3491011A US 3491011 A US3491011 A US 3491011A US 3491011D A US3491011D A US 3491011DA US 3491011 A US3491011 A US 3491011A
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percent
acid
composition
electrodeposition
resin
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Louis R Le Bras
Frederick M Loop
Donald P Hart
Joseph E Plasynski
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PPG Industries Inc
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
    • C09D5/4484—Anodic paints
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
    • C09D5/4419—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications with polymers obtained otherwise than by polymerisation reactions only involving carbon-to-carbon unsaturated bonds
    • C09D5/4423—Polyesters, esterified polyepoxides
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31504—Composite [nonstructural laminate]
    • Y10T428/31678—Of metal

Definitions

  • This invention relates to aqueous chromate-containing coating compositions having reduced levels of soluble chromate ions to concentrates of electrodepositable compositions, to the method of electrodeposition and to the articles so coated.
  • the compositions are formed by ageing a composition comprising a polycarboxylic acid vehicle resin, strontium chromate pigment and Water at a pH below 7.0, thereby reducing the soluble chromate ion concentration, preferably to a level less than about 300 parts per million.
  • This invention relates to a method of making electrodeposition concentrates and to the electrodepositable compositions derived from said concentrates. More particularly, this invention relates in part to a method of preparing electrodepositable compositions containing a controlled level of soluble chromate ions.
  • Electrodeposition is a relatively new coating technique, which, although based on well-known principles, has only recently become technically feasible through the development of electrodepositable compositions which have the desired characteristics to meet the demands placed on a modern coating material.
  • the coatings achieved have excellent properties for many applications and electrodeposition results in a coating which does not run or Wash off during baking.
  • Virtually any conductive substrate may be coated by electrodeposition.
  • Most commonly employed substrates include base metals such as iron, steel, copper, zinc, brass, tin, nickel, chromium and aluminum, as well as other metals and pretreated metals. Impregnated paper or other substrates rendered conductive under the conditions employed may also be coated.
  • a pigskin pattern is found on the article being coated; and/or that there is a reduction in throwing power of the electrodeposition composition and the ruptured voltage of the electrodeposition composition is lowered.
  • the presence of soluble chromate ions reduces the wet adhesion of the electrodeposition film prior to drying, which is usually accomplished by baking.
  • a freshly-deposited film appears quite dry and feels only slightly tacky.
  • Such a film is relatively resistant to physical distortion and is relatively water-insoluble. This water insolubility permits the film to be rinsed with water in order to remove bath dragout. Dragout consists of non-deposited paint which adheres to the coated article upon its removal from the bath.
  • compositions of high solids content preferably one in which the vehicle has been slightly neutralized since this aids in disbursing the additional composition throughout the electrodeposition bath.
  • Compositions made from vehicles which have up to 20 percent of their acidity neutralized have generally been employed for this purpose.
  • a method has now been found of producing concentrates containing chromates which in turn produce, on one hand, electrodepositable compositions when employed in electrodepositions baths yield improved properties and, on the other hand, when employed to replenish the supply of electrodepositable composition in the bath are more readily dispersible and which prolong the stability of the electrodeposition bath and which, when chromate ions are present in electrodepositable composition, control the level of soluble chromate ions.
  • Electropositable resins are known and can be employed to provide the electrodepositable composition of this invention.
  • Virtually any water-soluble, water-dispersible or water-emulsifiable polycarboxylic resinous material can be electrodeposited and, if filmforming, provides a coating which may be suitable for certain purposes. Any such electrodepositable is included among those which can be employed in the present invention, even though the coating obtained may not be entirely satisfactory for certain specialized uses.
  • the preferred resins which may be employed in the process invention comprise a reaction product or adduct of the drying oil or semi-drying oil fatty acid ester with a dicarboxylic acid or anhydride.
  • drying oil or semidrying oil fatty acid esters are meant esters of fatty acids which are or can be derived from drying oils or semidrying oils, or from such sources as tall oil.
  • Such fatty acids are characterized by containing at least a portion of polyunsaturated fatty acids.
  • the drying oil or semi-drying oil per se is employed.
  • drying oils are those oils which have an iodine value of above about 130
  • the semi-drying oils are those which have an iodine value of about 90 to 130, as determined by method ASTMDl467-57T.
  • esters include linseed oil, soya oil, saifiower oil, perilla oil, tung oil, citicica oil, poppyseed oil, sunflower oil, tall oil esters, Walnut oil, dehydrated castor oil, herring oil, menhadan oil, sardine oil and the like.
  • esters also included among such esters are those in which the esters themselves are modified with other acids, including saturated, unsaturated or aromatic acids such as butyric acid, stearic acid, linoleic acid, phthalic acid, isophthalic acid, terophthalic acid or benzoic acid, or an anhydride of such an acid.
  • One inexpensive acid material which has been found to produce good results in many instances is resin, which is composed of chiefly abiotic acid and other resin acids.
  • the acid modified esters are made by transesterification of the ester, as by forming a dior monoglyceride by alcoholysis, followed by esterification with the acid; they may also be obtained by reacting oil acids with a polyol and reacting the acid with the partial ester.
  • alcoholysis can be carried out using other polyols such as trimethylolpropane, pentaerythritol, sorbitol, and the like.
  • the esters can also be modified with monomers such as cyclopentadiene or styrene and the modified esters produced thereby can be utilized herein.
  • other esters of unsaturated fatty acids for example, those prepared by the esterification of tall oil fatty acids with polyols, are also useful.
  • drying oil fatty acid esters and semi-drying oil fatty acid esters as set forth herein are alkyd resins prepared utilizing semi-drying or drying oils; esters of epoxides with such fatty acids, including esters of diglycidyl ethers of polyhydric compounds as well as other mono-, diand polyepoxides; semi-drying or drying oil fatty acid esters of polyols, such as butanediol, trimethylolethane, trimethylolpropane, trimethylolhexane, pentaerythritol, and the like; and semidrying or drying fatty acid esters of resinous polyols such as homopolymers or copolymers of unsaturated aliphatic alcohols, e.g., allyl alcohol or methallyl alcohol, including copolymers of such alcohols with styrene or other ethylenically unsaturated monomers or with non-oil modified alky
  • Any alpha, beta-ethylenically unsaturated dicarboxylic acid or anhydride can be employed to produce the reaction products described herein. These include such anhydrides as maleic anhydride, itaconic anhydride, and other similar anhydrides. Instead of the anhydride, there may also be used ethylenically unsaturated dicarboxylic acids which form anhydrides, for example, maleic acid or itaconic acid. These acids appear to function by first forming the anhydride. Fumaric acid, which does not form an anhydride, may also be utilized, although in many instances it requires more stringent conditions than the unsaturated dicarboxylic acid anhydrides or acids which form such anhydrides. Mixtures of any of the above acids or anhydrides may also be utilized. Generally speaking, h anhydride or acid employed 9Qrtt in from 4 to 12 carbon atoms, although longer chain compounds can be used if so desired.
  • reaction product of the acid or anhydride with the fatty acid ester is not known with certainty, it is believed that the reaction takes place by addition of the unsaturated linkage of the acid or anhydride to the carbon chain of the oil.
  • unsaturated linkage of the acid or anhydride to the carbon chain of the oil.
  • the reaction may take place with the methylene group adjacent the nonconjugated double bond.
  • oils having conjugated double bonds such as tung oil
  • the reaction is probably of the Diels-Alder type.
  • reaction between the acid or acid anhydride and the drying oil or semi-drying oil fatty acid ester takes place readily without the use of a catalyst and at temperatures in the range of about C. to about 300 C. or higher, with the reaction generally being carried out between about 200 C. and about 250 C.
  • reaction products can be comprised solely of adducts of the fatty acid ester and the dicarboxylic acid or anhydride
  • the use of such monomer often produces films and coatings which are harder and more resistant to abrasion and which may have other similar desirable characteristics.
  • any ethylenically unsaturated monomer can be employed.
  • Such monomers include monoolefinic and diolefinic hydrocarbons such as styrene, alpha-methyl styrene, alpha-butyl styrene, vinyl toluene, butadiene-l,3, isoprene, and the like; halogenated monoolefinic and diolefinic hydrocarbons, such as alpha-chlorostyrene, alphabromostyrene, chlorobutadiene and similar compounds; esters of organic and inorganic acids, such as vinyl acetate, vinyl propionate, vinyl 2-chlorobenzoate, methyl acrylate, ethyl methacrylate, butyl methacrylate, heptyl acrylate, decyl methacrylate, methyl croton ate, isopropenyl acetate, vinyl alpha-bromopropionate, vinyl alpha-chlorovalerate, allyl chloride, allyl cyanide, allyl
  • R and R are hydrogen or alkyl, R; is hydrogen, alkyl or carboxyalkyl and R is cyano, aryl, alkyl, alkenyl, aralkyl, alkaryl, alkoxycarbonyl or aryloxycarbonyl.
  • the preferred compounds are styrene, substituted styrenes, alkyl acrylates, alkyl methacrylates, diolefins and acrylonitrile.
  • the reaction of the fatty acid ester, the acid or anhydride and any additional monomer or monomers can be carried out concurrently, that is, with each of the components of the reaction product being mixed together and heated to reaction temperature.
  • the oil or other fatty acid ester is preferably first reacted with the acid or acid anhydride, and then this product is subsequently reacted with any ethylenically unsaturated monomer or monomers employed.
  • a reaction product of linseed oil, maleic anhydride and styrene is made by first reacting maleic anhydride with linseed oil and then reacting the maleinized oil with styrene.
  • the reaction of the additional monomer with the initial reaction product is usually carried out at somewhat lower temperatures, usually between about 25 C. and 200 C.
  • each of the components gOing to make up the reaction product are ordinarily not critical. Generally speaking, between about percent and about 45 percent by weight of the unsaturated acid or acid anhydride is reacted with from about 55 percent to about 90 percent by weight of fatty acid ester. In the presently preferred products, usually percent to percent of anhydride and 70 percent to 85 percent of oil ester are employed. If an ethylenically unsaturated monomer is incorporated in the reaction product, it is typically used in amounts between about 5 percent and about percent by weight, based upon the total weight of acid or anhydride and ester, with between 10 percent and 25 percent being used in those products preferred at present.
  • the total composition of the reaction product may comprise from about 35 percent to about 90 percent by weight of the fatty acid ester and from about 10 percent to about 65 percent of the acid or anhydride and other monomer combined, with between about 6 percent and about percent of the acid or anhydride always present.
  • the products produced in the above manner are comprised of polymeric chains of moderate length.
  • the average molecular weight of the products to be used in electrodeposition should be low enough so that its flow characteristics at high solids are maintained, but high enough to provide adequate throwing power.
  • the desirable molecular weight levels vary with the coating composition and conditions employed. Generally those products having molecular weights of up to 10,000 or somewhat higher have given the best results.
  • Neutralization of these products is accomplished by reaction of all or part of the dicarboxylic anhydride groups with a base. Usually up to about half of such groups are neutralized in unesterified adducts; the partially esterified products are often neutralized to a greater extent, based on unesterified acid groups remaining.
  • amido groups are attached to part of the carbonyl carbon atoms derived from the dicarboxylic acid or anhydride.
  • amido groups are meant trivalent nitrogen atoms attached with one valence to the carbonyl carbon atom with the other two valences being linked to hydrogen or carbon atoms in the same or different organic radicals.
  • Amido groups are formed, for example, when the reaction with the neutralizing base is carried out with a water solution of ammonia, a primary amine or a secondary amine, or when the product is reacted with such an amine in the absence of water.
  • compositions within this general class are described in copending applications, Ser. No. 222,674, filed Sept. 10, 1962, now US. 3,366,563; and Ser. No. 282,880, filed May 24, 1963, now US. 3,369,938.
  • Another type of electrodepositable coating composition which gives desirable results are the water-dispersible coating compositions comprising at least partially neutralized interpolymers of hydroxyalkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acids and at least one other ethylenically unsaturated monomer. These are employed in the composition along with an amine-aldehyde condensation product or a polyepoxide, or both, with the interpolymer usually making from about percent to about 95 percent by weight of the resinous composition.
  • the acid monomer of the interpolymer is usuall acrylic acid or methacrylic acid, but other ethylenically unsaturated monocarboxylic and dicarboxylic acids, such as ethacrylic acid, crotonic acid, maleic acid, or other acids of up to about 6 carbon atoms can also be employed.
  • hydroxyalkyl ester is usually hydroxyethyl or hydroxypropyl acrylate or methacrylate, but also desirable are the various hydroxyalkyl esters of the above acids having, for example, up to about 5 carbon atoms in the hydroxyalkyl radical. Monoor diesters of the dicarboxylic acids mentioned are included. Ordinarily, the acid and ester each comprise between about 1 percent and about 20 percent by weight of the interpolymer, with the remainder being made up of one or more other copolymerizable ethylenically unsaturated monomers.
  • alkyl acrylates such as ethyl acrylate
  • alkyl methacrylates such as methyl methacrylate
  • vinyl aromatic hydrocarbons such as styrene
  • the above interpolymer is at least partially neutralized by reaction with a base as described above; at least about 10 percent, and preferably 50 percent or more of the acidic groups are neutralized, and this can be carried out either before or after the incorporation of the interpolymer in the coating composition.
  • the bases above can be used, with ammonia and amines being preferred; except when a polyepoxide is present, in which case there is preferably employed a hydroxide, such as sodium hydroxide, or if an amine, a tertiary amine.
  • the amine-aldehyde condensation products included in these compositions are, for example, condensation products of melamine, benzoquanamine, or urea with formaldehyde, although other amino-containing amines and amides, including triazines, diazines, triazoles, guanadines, guanamines and alkyl and aryl-substituted derivatives of such compounds can be employed, as can other aldehydes, such as acetaldehyde.
  • the alkylol groups of the products can be etherified by reaction with an alcohol, and the products utilized can be water-soluble or organic solvent-soluble.
  • the electrodepositable compositions can also include a polyepoxide, which can be any epoxide compound or mixture with an epoxy functionality of greater than 1.0. Numerous such polyepoxides are known and are described in patents such as US. Patents Nos. 2,467,171; 2,615,007; 2,716,123; 2,786,067; 3,030,336; 3,053,855; and 3,075,999.
  • polyglycidyl ethers of polyphenols such as bisphenol A, or aliphatic polyhydric alcohols, such as 1,4-butanediol
  • polyglycidyl esters of polycarboxylic acids such as diglycidyl adipate
  • polyepoxides from the epoxidation of unsaturated alicylic compounds such as 3,4-epoxy-6-methylcyclohexylmethyl- 3,4-epoxy-6-methylcyclohexanecarboxylate.
  • Electrodepositable compositions comprising the above interpolymers and an amine-aldehyde resin or a polyepoxide, or both, are more fully describedin copending application Serial No. 368,394, filed May 18, 1964, now
  • Still another electrodepositable composition of desirable properties comprises an alkyd-amine vehicle, that -is, a vehicle containing an alkyd resin and an aminealdehyde resin.
  • a conventional alkyd such as a glyceryl phthalate resin
  • a high acid number e.g. 50 to 70
  • a surface active agent such as a polyalkylene glycol (e.g. Carbowax)
  • High acid number alkyds are also made by employing a tricarboxylic acid, such as trimellitic acid or anhydride, along with a polyol in making the alkyd.
  • aminealdehyde resin such as those described hereinabove.
  • Preferred are water-soluble condensation products of melamine or a similar triazine with formaldehyde with subsequent reaction with an alkanol.
  • An example of such a product is hexakis (methoxymethyl)melamine.
  • the alkyd-amine compositions are dispersed in water and they ordinarily contain from about 10 percent to about 50 percent by weight of amine resin based on the total resinous components.
  • compositions of this class are described in US. Patents Nos. 2,852,475; 2,852,476; and 2,853,459.
  • the neutralization and solubilization of the above vehicles is accomplished by the use of a base.
  • Inorganic bases such as metal hydroxides or, more desirably, ammonia can be used for this purpose, as can organic bases, particularly amines.
  • organic bases particularly amines.
  • neutralizing bases are ammonia and any basic amine.
  • amine examples include primary and secondary amines including alkyl amines, such as methylamine, ethylamine, propylamine, butylamine, amylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, and N-methylbutylamine; cycloalkyl amines, such as cyclohexylamine; unsaturated amines, such as allylamine, 1,Z-dimethylpentenylamine and pyrrole; aryl amines, such as aniline; aralkyl amines such as benzylamine and phenethylamine; alkaryl amines, such as m-toluidine; cyclic amines, such as morpholine, pyrrolidine and piperidine; diamines, such as hydrazine, methylhydrazine, 2,3-toluenediamine, ethylenediamine, 1,2-naphthalenediamine and piperazine;
  • the electrodepositable coating compositions of the instant invention comprise the above vehicles, containing a strontium chromate-containing pigment composition.
  • the pigment composition in addition to strontium chromate, may be of any conventional type, comprising, for example, iron oxides, lead oxides, carbon black, titanium dioxide, talc, barium sulfate and the like, as well as combinations of these and similar pigments.
  • Color pigments such as cadmium yellow, cadmium red, phthalocyanine blue, chromic yellow, toluidine red, hydrated iron oxide and the like may be included if desired.
  • Better results with pigmented compositions are attained if the weight ratio of pigment solids to vehicle solids is not higher than about 1.5 to 1, and preferably not higher than about 1 to 1.
  • antioxidants for example, orthoamyl phenol or cresol (the commercial mixture of isomeric cresols is satisfactory). It is found especially advantageous to include such antioxidants in coating compositions which are used in baths which may be exposed to atmospheric oxygen at elevated temperatures and with violent agitation over extended periods of time.
  • ordinary tap water may be employed.
  • such water may contain a relatively high level of metals and cations; while not rendering the process in operative, the use of water containing these cations may result in variations in the properties of the bath when used for electrodeposition.
  • deionized water i.e., water from which free ions have been removed as by passage through an ion exchange resin, in making up the coating compositions of the invention.
  • additives which may be included in the coating composition if desired include for example, wetting agents such as petroleum sulfonates, sulfated fatty amides,
  • driers such as the linoleates, the naphthenates, the octanates and the tallates of such metals as lead, cobalt, manganese, iron, copper and zirconium.
  • Other additives which may be employed include antifoaming agents, suspending agents, bactericides and the like.
  • an aqueous bath containing the coating composition is placed in contact with an electrically conductive anode and an electrically conductive cathode.
  • the surface to be coated is employed as one of the electrodes.
  • the surface to be coated is employed as the anode.
  • an adherent film of the coating composition is deposited.
  • the conditions under which the electrodeposition step herein is carried out are those conventionally used in electrodeposition of coatings.
  • the applied voltage may be varied greatly and can be, for example, as low as 1 volt or as high as several thousand volts, although typically between 50 volts and 500 volts.
  • the current density is usually between about 0.1 ampere and 15 amperes per square foot, and is high initially and tends to decrease during the electrodeposition of a single article.
  • the concentration of the non-volatile components (i.e., vehicle and any pigments and the like) in the aqueous bath is not critical and relatively high levels can be employed. However, it is ordinarily desirable to use as low a concentration as gives satisfactory results, and in the cases of the above-described compositions, aqueous compositions containing as little as 1 percent by weight of non-volatile solids can be employed, while those containing between 5 percent and 20 percent by weight are preferred.
  • the process of this invention comprises forming a pigment paste by grinding a vehicle resin and pigment, and then, in order to obtain the proper pigment-binder ratio, adding additional resins of such a degree of neutralization that the final concentrate has a pH of below 7, thus obtaining the dispersion of high solids content which may be let down to form the electrodeposition composition or used as a concentrate to replenish the bath.
  • the essential step of the instant invention comprises aging the concentrate thus formed at least to some extent prior to letting down the concentrate, thereby obtaining appreciable reductions in the amount of soluble chromate ions present in the electrodeposition bath.
  • the grinding of the pigment paste may be done by the conventional methods known to the arts, such as a ball mill, pebble mill, sand mill, or an attritor.
  • the vehicle used in the grinding step may be the unneutralized resin or a partially neutralized resin.
  • the grinding resin is an aqueous dispersion of neutralized resin having a pH above 7 and preferably about 9.
  • the amount of water present in such an aqueous grind is not critical, however, commonly the resin employed in the grinding step is about 30 to 70 percent solids.
  • the use of more water merely reduces the effective capacity of the mills and although less water may be employed, there is an increase in viscosity of the material, with the attendant problems inherent in a high-viscosity material.
  • the pigment-binder ratio in the grinding step is not critical; however, levels between about 3.5/1 to 7/1 are frequently employed, although other levels may be utilized.
  • the resin used to let down the pigment paste to obtain the desired pigment-binder ratio desired in the final electrodeposition composition should have a degree of neutralization such that the final concentrate composition will have a pH below 7 and preferably between 5.5 and 6.5.
  • let down resin is at least neutralized to some extent to facilitate dispersion, although unneutralized resin may be employed.
  • the total solids of the final concentrate may be adjusted with the addition of water, preferably deionized water.
  • the total solids of the final concentrate is between about 50 percent to about 95 percent. At least about 1 percent water should be present in the final concentrate composition in order to promote the reduction of soluble chromate ions.
  • the essential step of this invention comprises aging the concentrate, under acid conditions, at a temperature and for a time sufiicient to substantially lower the level of soluble chromate ions in the composition.
  • the time required is temperature dependent, at least to some extent. Usually, the higher the temperature, the shorter the time. For example, if the concentrate is aged at a temperature of about 140 F. to 160 F. or higher, from 12 to 24 hours is usually sufficient to reduce the soluble chromate ions to the preferred level. At room temperature, a period of a few days (usually at most about 6 to days) is necessary to reduce the soluble chromate ion level to the preferred level.
  • the level of soluble chromate ions is necessary to reduce the level of soluble chromate ions to below about 300 parts per million.
  • the soluble chromate ion concentration is 'below about 200 parts per million.
  • Strontium chromate is highly effective as a corrosion-inhibitive pigment, even when present in only relatively minor amounts in the pigment composition of a coating being applied to a metal surface.
  • strontium chromate it was found that when about one percent of the deposited film was strontium chromate, the film, coated on zinc phosphate treated steel, failed to withstand 250 hours in the standard salt-spray test; which is exposure at 100 F. to a 100 percent relative humidity atmosphere of a five percent sodium chloride solution, the panel being scribed with an X to the metal below the film; A inch corrosion creepage from the scribe being considered failure.
  • the electrodeposition compositions prepared by the method of this invention can readily contain 8 percent or more strontium chromate based on the total pigment solids and yet have a soluble chromate ion level such that the composition may be electrodeposited free from the expected difiiculties. It is possible by the method of this invention to electrodeposit a polycarboxylic acid resin vehicle-based composition containing up to about 8 percent or more strontium chromate based on the total solids without encountering severe Wet adhesion problems, pigskinning, film rupture, excessive high conductivity, etc.
  • strontium chromate is deposited in the film in approximately the same proportions as it is contained in the total depositable solids of the electrodeposition bath.
  • some minor deviation from this ratio may become apparent in a continuous electrodeposition process, Where a large number of articles are coated in a continuous process, the bath being replenished by the addition of concentrates. Therefore, in practice 10 from time to time minor corrections in the strontium chromate level of the bath may be necessary.
  • the 1 to 1 ratio is a valid approximation, the deviation being quite small.
  • the level of soluble chromate ion as mentioned herein is determined by a specific procedure, which, although not necessarily providing an absolute measure, does establish a scientifically significant, readily determinable standard.
  • the procedure involves taking a sample of the electrodeposition composition to be examined and letting it down to 8 percent solids with deionized water. To 50 grams of this material is then added 50 grams of glacial acetic acid and the mixture stirred well. The mixture is then centrifuged for one half hour. The supernatent aqueous layer is then carefully decanted through a filter. The soluble chromate content of this serum is then determined in the following manner:
  • a graph is then prepared plotting concentration of CrO in parts per million versus milliliters of thiosulfate used and the best straight line drawn through the points obtained on the graph. This straight line is used as the standard curve when analyzing the serum.
  • the serum is then titrated in the following manner:
  • the concentration of CrO in the sample is read off in accordance with the number of milliliters of sodium thiosulfate required to titrate the sample.
  • the number obtained from the graph is multiplied by 2 to arrive at the actual concentration of CIO in the sample.
  • the figure obtained using this procedure is the figure recited as parts per million soluble chromate ions throughout the specification.
  • the starch solution used in the above procedure is the same starch solution that is generally used as the standard for determining iodine value by titration. It was prepared as follows:
  • soluble starch powder C H OQ for example Mallinckrodt 8188
  • This paste is then added to 1 liter of boiling water slowly so that the boiling is not interrupted, to form a clear solution, that is, one in which no precipitate is apparent.
  • 0.5 gram of mercuric chloride is added as a preservative. The solution is then cooled and used as needed.
  • a vehicle resin (Resin A) composition was produced by heating a 4 to 1 weight mixture of linseed oil and 1 1 maleic anhydride to 250 C. over a two hour period, and then holding this mixture at this temperature.
  • a solubilized resin (Resin Asolubilized) was prepared by mixing Resin A (above) with deionized water and diethylene amine to give a solution with a pH of about 7.2 and a solids content of 40 percent.
  • a pigment paste (Paste B) was made by grinding the following in a steel ball mill:
  • the above concentrate has approximately 75 percent solids content and a pH of 5.8.
  • Concentrate Xfresh Concentrate Y--aged at room temperature for 6 days. Concentrate Zaged at room temperature for 30 days.
  • Example II shows a composition as in Example I with a 25 percent increase in strontium chromate content.
  • a pigment paste (Paste C) was made by grinding the following in a steel ball mill:
  • Dispersing agent (combination oil soluble sulfonate and non-ionic surfactantWitco 912) 6.0
  • Cresylic acid (dissolved in an additional 7.0 parts 4-methoxy-4-methylpentanone-2) 3.5 Paste C (above) 534.9 Deionized water 28.61
  • the above concentrate had approximately 75 percent solids content and a pH of 5 .8.
  • Soluble Bath chromate temperion ature Film parts per Baked film ap- Electrodeposition composition derived (degrees thlckness million pearanee (350 F., from F.) Voltage Amperes (mils) as CrOr') Wet film appearance 20 minutes) Concentrate M (fresh) 79 1. 5-0. 35 0. 7-0. 75 530 Poor wet adhesion, greasy Slight orange peel. Concentrate N (aged 30 days) 78 100 1.4-0. 34 65 200 Wet adhesion good, not greasy- No orange peel.
  • EXAMPLE III The following example shows a composition as in Example I with a 60 percent increase in strontium chromate content.
  • Paste H was let down to electrodeposition g solids of approximately 8 percent in the usual manner Parts by Weight and soluble chromate ion determined.
  • Paste H was heat aged at 150 F. reading on the Hegmann Grind Gauge. There was then for 16 hours and then let down as above and soluble added to the mill and mixed 30 minutes: chromate ion determined. The soluble chromate ion concentration was 330 parts per million. Resin A solubilized (above) ji i 20 Additional portions of Paste H were formulated with Deionized Water 83D varying percentages of added water and heat aged at 150 F. for 16 hours and the soluble chromate ion was T above paste was then letdown as follows: determined at the end of this time.
  • the mix- T e a ove concentrate was t en sp it lnto portions. ture was heated to C. and .48 gram of Hthage Concentrate O-fresh. (lead oxide) Was added. The reaction mixture was then Concentrate Paged at room temperature for 24 days. heated to 238 C. and held at that temperature for one hour. The reaction mixture was cooled to 190 C. and After the above-indicated times the concentrates were all there was then added to the reactor 888 parts phthalic reduced to 7.5 percent operating solids as follows. anhydride, 274 parts dimethyolpropionic acid and 85 Parts by weight parts of xylene and the reaction mixture was then heated Concen rate 21 to 205 C.
  • Iron oxlde 3800 placed Iron oxlde 3800 in a canister containing steel balls and shaken for 25
  • the above mixture was shaken on a Red Devil Shaker minutes on a Red Devil Shaker, a rapidly vibrating (a rapidly vibrating shaker, such as those commonly shaker such as those commonly used to mix paints, at used to mix paints), for 30 minutes, at which time a 15 Hegmann fineness reading of at least about 6 /2 was obtained.
  • a concentrate (J) was prepared as follows:
  • the above electrodeposition composition had a percent content and has a specific conductivity at 75F. of 350.
  • the soluble chromate ion level was 120 parts per million.
  • a similar electrodeposition composition was prepared without aging at a pH below 7, as follows:
  • a pigment paste (Paste K) was prepared by charging the following into a steel canister containing steel balls:
  • the above mixture had a pH of 7.6.
  • the final electrodepositable composition was prepared as follows:
  • this electrodeposition composition had a specific conductivity at 75 F. of 1300 as against 350 for the previously described composition.
  • the soluble chromate ion concentration of this composition was 360 parts per million.
  • a method of coating a metal substrate which comprises passing electric current between an electrically conductive cathode in contact with an aqueous bath containing an electrodepositable composition comprising a solubilized polycarboxylic acid resin vehicle and strontium chromate pigment, said solubilized electrodeposition composition containing less than about 300 parts per million soluble chromate ion.
  • a method of coating a metal substrate which comprises passing electric current between an electrically conductive cathode in contact with an aqueous bath containing an electrodepositable composition
  • a vehicle which comprises a solubilized reaction product of a drying oil fatty acid ester with a member of the group consisting of alpha, beta-ethylenically unsaturated dicarboxylic acids and an anhydride of said acids, and strontium chromate pigment, said solubilized electrodeposition composition containing less than about 300 parts per million soluble chromate ion.
  • a method of coating a metal substrate which comprises passing electric current between an electrically conductive metal anode and an electrically conductive cathode in contact with an aqueous bath containing electrodepositable composition comprising a solubilized alkyd resin and strontium chormate pigment, said solubilized electrodeposition composition containing less than about 300 parts per million soluble chromate ion.

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US3491011D 1965-05-04 1965-05-04 Method of electrodepositing coating compositions with reduced soluble chromate ions Expired - Lifetime US3491011A (en)

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BE (1) BE680488A (de)
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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3622485A (en) * 1968-03-09 1971-11-23 Goodlass Wall & Co Ltd Electrodeposition
US3819548A (en) * 1971-12-03 1974-06-25 Basf Ag An electrocoating composition containing an acid binder present as the salt of an arylamine, alkynyl amine, quaternary ammonium hydroxide or phosphonium hydroxide
USRE30612E (en) * 1979-11-13 1981-05-12 International Minerals & Chemical Corp. Polyurethane-modified alkyd resin
US4310390A (en) * 1977-08-10 1982-01-12 Lockheed Corporation Protective coating process for aluminum and aluminum alloys
US4507360A (en) * 1983-10-13 1985-03-26 United States Steel Corporation Corrosion resistant core-plate and coatings therefor
US4517325A (en) * 1983-10-13 1985-05-14 United States Steel Corporation Corrosion resistant core-plate and coatings therefor
US20080051499A1 (en) * 2006-08-23 2008-02-28 Kania Charles M Aqueous-based polymers for sound deadening applications
US11518960B2 (en) 2016-08-24 2022-12-06 Ppg Industries Ohio, Inc. Alkaline molybdenum cation and phosphonate-containing cleaning composition

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3404079A (en) * 1965-01-11 1968-10-01 Ashland Oil Inc Process for preparing an electrocoating bath

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3404079A (en) * 1965-01-11 1968-10-01 Ashland Oil Inc Process for preparing an electrocoating bath

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3622485A (en) * 1968-03-09 1971-11-23 Goodlass Wall & Co Ltd Electrodeposition
US3819548A (en) * 1971-12-03 1974-06-25 Basf Ag An electrocoating composition containing an acid binder present as the salt of an arylamine, alkynyl amine, quaternary ammonium hydroxide or phosphonium hydroxide
US4310390A (en) * 1977-08-10 1982-01-12 Lockheed Corporation Protective coating process for aluminum and aluminum alloys
USRE30612E (en) * 1979-11-13 1981-05-12 International Minerals & Chemical Corp. Polyurethane-modified alkyd resin
US4507360A (en) * 1983-10-13 1985-03-26 United States Steel Corporation Corrosion resistant core-plate and coatings therefor
US4517325A (en) * 1983-10-13 1985-05-14 United States Steel Corporation Corrosion resistant core-plate and coatings therefor
US20080051499A1 (en) * 2006-08-23 2008-02-28 Kania Charles M Aqueous-based polymers for sound deadening applications
US7816470B2 (en) * 2006-08-23 2010-10-19 Ppg Industries Ohio, Inc. Aqueous-based polymers for sound deadening applications
US11518960B2 (en) 2016-08-24 2022-12-06 Ppg Industries Ohio, Inc. Alkaline molybdenum cation and phosphonate-containing cleaning composition

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GB1117875A (en) 1968-06-26
NL6606066A (de) 1966-11-07
DE1669247A1 (de) 1971-08-05
AT281232B (de) 1970-05-11
DE1669247B2 (de) 1972-11-16
BE680488A (de) 1966-11-04
DE1669247C3 (de) 1978-09-28
CH465992A (fr) 1968-11-30
FR1476214A (fr) 1967-04-07

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