US3663404A - Treatment of electrodeposition bath - Google Patents

Treatment of electrodeposition bath Download PDF

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US3663404A
US3663404A US94023A US3663404DA US3663404A US 3663404 A US3663404 A US 3663404A US 94023 A US94023 A US 94023A US 3663404D A US3663404D A US 3663404DA US 3663404 A US3663404 A US 3663404A
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effluent
bath
rinsing agent
ultrafiltration
electrodeposition
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Frederick M Loop
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PPG Industries Inc
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025—Reverse osmosis; Hyperfiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/145—Ultrafiltration
    • 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
    • C25D13/22—Servicing or operating apparatus or multistep processes

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  • This invention relates to a method of rinsing articles coated by an elcctrodeposition process which comprises employing as at least a portion ofthe rinsing agent the effluent obtained from a selective separation process such as an ultrafiltration process, while withdrawing a portion of said effluent which contains excess and/or undesirable low molecular weight species present in the electrodepositable composition, thereby, first, conserving bath material and, second, controlling the composition of the electrodepositable composition.
  • Electrodeposition has become a widely commercially accepted industrial coating technique. 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 are metal substrates including 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 substances rendered conductive under the conditions of the coating process may also be employed as substrates.
  • the articles to be electrocoated are immersed in an aqueous dispersion of a solubilized, ionized, film-forming material such as a synthetic organic vehicle resin.
  • An electric current is passed between the article to be coated, serving as an electrode, and a counterelectrode to cause deposition of a coating of the vehicle resin on the articles.
  • the articles are then withdrawn from the bath, usually rinsed, and then the coating either air-dried or baked in the manner of a conventional finish.
  • the rinsing to remove dragout of an electrodeposited article may be accomplished by employing the effluent or filtrate derived from a selective separation process such as a filtration process, for example, ultrafiltration, utilized to control the bath composition. It has been found further that this rinsing of dragout may be accomplished in such a manner that the rinse returns to the electrodeposition bath, thus conserving materials to an even greater extent.
  • a selective separation process such as a filtration process, for example, ultrafiltration
  • the rinsing is accomplished in such a way that the efiluent or filtrate and dragout are either collected separate from the bath or immediately returned to the bath.
  • selective filtration and particularly ultrafiltration is a method of bath control, it is desirable, in order to maintain or change the composition of the bath, to intermittently or concurrently remove at least a portion of the ultrafiltrate from the system.
  • the rinsing of dragout may intermittently or proportionately be conducted with tap water or, preferably, deionized water, either separate from the bath or in a manner so that this rinse returns to the bath.
  • the electrodeposition bath 1 of FIG. 3 from which films are deposited uses suitable apparatus (not shown).
  • a portion of the bath may be continuously or intermittently withdrawn through an outlet and valve 2 and passed through line 3 to a selective filter, in this case an ultrafilter 4.
  • a selective filter in this case an ultrafilter 4.
  • water, free counter-ions and counter-ions present as low molecular weight salts, for example, carbonates, as well as other low molecular weight species, if present, are separated from the vehicle resin, pigment and other high molecular weight components of the bath composition.
  • the ultrafiltrate is removed from the ultrafilter, passing through line 5, through the use of valve 6, while the concentrate or retentate is returned to the bath through line 15 and valve 16.
  • the ultrafiltrate may be directed either unidirectionally or proportionally in either an intermittent or continuous fashion to drain 7 or for use as rinse material. In the latter case, the ultrafiltrate is then passed through line 8 when it is directed through valves 9 or 13 to either a rinse station 14 for rinsing dragout in a manner that the dragout-containing rinse returns to the bath or 10 for rinsing dragout in a manner so that it does not return directly to the bath. Valves 9 and 13 likewise accommodate the intermittent or proportional use of water 11 and 12 other than ultrafiltrate for rinsing. Line 17 allows for return of ultrafiltrate to the bath if and when desired. As stated, this drawing is schematic and does not purport to describe the necessary pumping means or apparatus which are known in the art.
  • the selective filtration process employed in the process of the instant invention is any process which separates water from the electrodeposition bath through a physical barrier while retaining the solubilized resin components.
  • any means may be utilized which accomplishes this purpose.
  • Means may pass not only water but also solute of substantially lower molecular weight than the vehicle resin such as excess amine, carbonates, low molecular weight solvent and simple organic or inorganic anions and cations which may be present in the bath.
  • Examples of means for accomplishing this separation are reverse osmosis, where water of high purity may be obtained, and ultrafiltration, as well as other means which accomplish the intended result. Because ultrafiltration is particularly useful in bath control, this means is especially preferred.
  • the selective filtration process is an ultrafiltration process which separates materials below a given molecular weight size from the electrodeposition bath. With properly selected membranes, this treatment does not remove any product or desirable resin from the paint in the tank but does remove anionic, cationic and non-ionic materials from the paint in a ratio proportional to their concentration in the water phase of the paint. Thus, for example, it is possible to remove amines, alkaline metal ions, phosphates, chromates, sulfates, solvents and dissolved carbon dioxide, among others.
  • Ultrafiltration may be defined as a method of concentrating solute while removing solvent, or selectively removing solvent and low-molecular weight solute from a significantly higher molecular weight solute. From another aspect, it is a process of separation whereby a solution containing a solute of molecular dimensions significantly greater than the solvent is depleted of solute by being forced under a hydraulic pressure gradient to flow through a suitable membrane.
  • the first definition is the one which most fittingly describes the term ultrafiltration" as applied to an electrodeposition bath.
  • Ultrafiltration encompasses all membrane-moderated, pressure-activated separations wherein solvent or solvent and smaller molecules are separated from modest molecular weight macromolecules and colloids.
  • the term ultrafiltra tion is generally broadly limited to describing separations involving solutes of molecular dimensions greater than about ten solvent molecular diameters and below the limit of resolution of the optical microscope, that is, about 0.5 micron. In the present process, water is considered the solvent.
  • the basic ultrafiltration process is relatively simple. Solution to be ultrafiltered is confined under pressure, utilizing, for example, either a compressed gas or liquid pump in a cell, in contact with an appropriate filtration membrane supported on a porous support. Any membrane or filter having chemical integrity to the system being separated and having the desired separation characteristic may be employed. Preferably, the contents of the cell should be subjected to at least moderate agitation to avoid accumulation of the retained solute on the membrane surface with the attendant binding of the membrane. Ultrafiltrate is continually produced and collected until the retained solute concentration in the cell solution reaches the desired level, or the desired amount of solvent plus dissolved low molecular weight solute is removed.
  • a suitable apparatus for conducting ultrafiltration is described in U.S. Pat. No. 3,495,465, which is hereby incorporated by reference.
  • ultrafiltration membranes There are two types of ultrafiltration membranes.
  • solvent in the case of electrodeposition, water
  • microporous ultra-filters are inherently susceptible to internal plugging or fouling by solute molecules whose dimensions lie within the pore size distribution of the filter, it is preferred to employ for a specific solute a microporous ultrafilter whose mean pore size is significantly smaller than the dimensions of the solute particle being retained.
  • the diffusive ultrafilter is a gel membrane through which both solvent and solutes are transported by molecular diffusion under the action of a concentration or activity gradient.
  • solute and solvent migration occurs via random thermal movements of molecules within and between the chain segments comprising the polymer network.
  • Membranes prepared from highly hydrophilic polymers which swell to eliminate standard water are the most useful diffusive aqueous ultrafiltration membranes. Since a diffusive ultrafilter contains no pores in the conventional sense and since concentration within the membrane of any solute retained by the membrane is low and time-independent, such a filter is not plugged by retained solute, that is, there is no decline in solbent permeability with time at a constant pressure. This property is particularly important for a continuous concentration or separation operation. Both types of filters are known in the art.
  • the presently preferred ultrafilter is an anisotropic membrane structure such as illustrated in FIG. 1.
  • This structure consists of an extremely thin, about one-tenth to about ten micron layers of a homogeneous polymer 1 supported upon a thicker layer of a microporous open-celled sponge 2, that is, a layer of about 20 microns to about 1 millimeter, although this dimension is not critical.
  • this membrane can be further supported by a fibrous sheet, for example, paper, to provide greater strength and durability.
  • These membranes are used with a thin film or skin side exposed to the high pressure solution. The support provided to the skin by the spongy substrate is adequate to prevent film rupture.
  • Membranes useful in the process are items of commerce and can be obtained by several methods.
  • One general method is described in Belgian Pat. No. 721,058.
  • This patent describes a process which, in summary, comprises (a) forming a casting dope of the polymer in an organic solvent, (b) forming a film of the casting dope, and (c) preferentially contacting one side of said film with a diluent having high compatibility with the casting dope to effect precipitation of the polymer immediately upon coating the cast film with the diluent.
  • Membranes can be typically prepared from thermoplastic polymers such as polyvinyl chloride, polyacrylonitrile, polysulfones, poly(methyl methacrylate), polycarbonates, poly(n-butyl methacrylate as well as a large group of polymers formed from any of the monomeric units of the above polymers, including Polymer 360, a polysulfone copolymer. Cellulosic materials such as cellulose acetate may also be employed as membrane polymers.
  • thermoplastic polymers such as polyvinyl chloride, polyacrylonitrile, polysulfones, poly(methyl methacrylate), polycarbonates, poly(n-butyl methacrylate as well as a large group of polymers formed from any of the monomeric units of the above polymers, including Polymer 360, a polysulfone copolymer.
  • Cellulosic materials such as cellulose acetate may also be employed as membrane polymers.
  • anisotropic membranes operable in the process of the invention include Diaflow membrane ultrafilter PM-30, the membrane chemical composition of which is a polysulfone copolymer, Polymer 360, and which has the following permeability characteristics:
  • the membrane is chemically-resistant to acids (l-lCl, H H PO,,, all concentrates, alkalies, high phosphate buffer, and solutions of common salts as well as concentrated urea and quanadine hydrochloride.
  • the membrane is solvent-resistant to alcohol, acetone and dioxane.
  • the membrane is not solvent-resistant to dimethyl formamide or dimethyl sulfoxide. This membrane is hereinafter referred to as Membrane A.
  • Dorr-Oliver XPA membrane the membrane chemical composition of which is Dynel (an acrylonitrile-vinyl chloride copolymer) and which has the following permeability characteristics:
  • Membrane B Flux Molecular Percent gal./sq.ft./day at This membrane is hereinafter referred to as Membrane B.
  • Dorr-Oliver BPA type membrane the membrane chemical composition of which is phenoxy resin (polyhydroxy ether), and which has the following permeability characteristics:
  • the microporous ultrafilters are generally isotropic structures, thus flow and retention properties are independent of flow direction. It is preferred to use an ultrafilter which is anisotropic in its microporous membrane structure, FIG. 2. In such a membrane, the pore size increases rapidly from one face to the other. When the fine-textured side 4 is used in contact with the feed solution, this filter is less susceptible to plugging since a particle which penetrates the topmost layer cannot become trapped in the membrane because of the larger pore size 5 in the substrate.
  • the process of the invention may be operated as either a batch or a continuous process.
  • batch selective filtration or batch ultrafiltration a finite amount of material is placed in a cell which is pressurized. A solvent and lower molecular weight solutes are passed through the membrane. Agitation is provided by a stirrer, for example, a magnetic stirrer. Obviously this system is best used for small batches of material.
  • a continuous selective filtration process if preferred. Using this technique, material is continuously recirculated under pressure against a membrane or series of membranes through interconnecting flow channels, for example, spiral flow channels.
  • the ultrafiltration process may be conducted as either a concentration process or a diafiltration process.
  • Concentration involves removing solvent and low molecular weight solute from an increasingly concentrated retentate. Filtration flow rate will decrease as the viscosity of the concentrate increases.
  • Diafiltration is a constant volume process whereby the starting material is connected to a reservoir of pure solvent, both of which are placed under pressure simultaneously. Once filtration begins, the pressure source is shut off in the filtration cell and thus, as the filtrate is removed, an equal volume of new solvent is introduced into the filtration cell to maintain the pressure balance.
  • the configuration of the filter may also vary widely and is not limiting to the operation of the process.
  • the filter or membrane may, for example, be in the form of a sheet, tubes or hollow fiber bundles, among other configurations.
  • C is the initial solute concentration
  • C is the final solute concentration of the retentate
  • V is the volume of solute delivered to the cell (or the volume of the filtrate collected)
  • V is the initial solution volume (which remains constant).
  • Electrodepositable compositions while referred to as solubilized. in fact are considered a complex solution, dispersion or suspension or combination of one or more of these classes in water, which acts as an electrolyte under the influence of an electric current. While, no doubt, in some circumstances the vehicle resin is in solution, it is clear that in some instances and perhaps in most the vehicle resin is a dispersion which may be called a molecular dispersion of molecular size between a colloidal suspension and a true solution.
  • the typical industrial electrodepositable composition also contains pigments, crosslinking resins and other adjuvants which are frequently combined with the vehicle resin in a chemical and a physical relationship.
  • the pigments are usually ground in a resin medium and are thus wetted with the vehicle resin.
  • an electrodepositable composition is complex in terms of the freedom or availability with respect to removal of a component or in terms of the apparent molecular size of a given vehicle component.
  • ultrafiltration comprises subjecting an electrodepositable composition, especially after it has been employed in a coating process or aged, which inherently causes contaminants and other low molecular weight materials to accumulate in the bath, such as metal pretreatment chemicals, water, absorbed CO (either dissolved, or more likely, combined as an aminic salt or carbonate), neutralizing agent, organic solvent and ions such as forrnate, chromate, phosphate, chloride and sulfate, for example, to an ultrafiltration process employing an ultrafilter, preferably a difiusive membrane ultrafilter selected to retain the solubilized vehicle resin while passing water and low molecular weight solute, especially those with a molecular weight below a out 500.
  • an ultrafilter preferably a difiusive membrane ultrafilter selected to retain the solubilized vehicle resin while passing water and low molecular weight solute, especially those with a molecular weight below a out 500.
  • the filters discriminate as to molecular size rather than actual molecular weight, thus, these molecule weights merely establish an order of magnitude rather than a distinct molecular weight cut-off.
  • the retained solutes may, in fact, be colloidal dispersions or molecular dispersions rather than true solutes.
  • a portion of the electrodepositable composition may be continuously or intermittently removed from the electrodeposition bath and passed under pressure created by a pressurized gas or by means of pressure applied to the contained fluid in contact with the ultrafilter.
  • the egress side of the filter may be maintained at a reduced pressure to create the pressure difference.
  • the pressures necessary are not severe.
  • the maximum pressure in part, depends on the strength of the filter.
  • the minimum pressure is that pressure required to force water and low molecular weight solute through the filter at a measurable rate.
  • the operating pressures are between about 10 and p.s.i., preferably between about 25 and 75 p.s.i.
  • the ultrafilter should have an initial flux rate, measured with the composition to be treated of at least about 3 gal./sq.ft./day (24 hours) and preferably at least about 4.5 gal./sq.ft./day.
  • the bath composition should be in motion at the face of the filter to prevent the retained solute from impeding the flow through the filter. This may be accomplished by mechanized stirring or by fluid flow with a force vector to the filter surface.
  • the retained solutes comprising the vehicle resin are then returned to the electrodeposition bath.
  • the concentrate may be reconstituted by the addition of water either before entry to the bath or by adding water directly to the bath.
  • Electropositable resins are known and can be employed to provide the electrodepositable compositions which may be utilized within the scope of this invention.
  • Virtually any water-soluble, water-dispersible or water-emulsifiable polyacid or polybasic resinous material can be electrodeposited and, if film-forming, provides coatings which may be suitable for certain purposes.
  • Any such electrodepositable composition is included among those which can be employed in the present invention, even though the coating obtained might not be entirely satisfactory for certain specialized uses.
  • the most widely used electrodeposition vehicle resins are synthetic polycarboxylic acid resinous materials. Numerous such resins are described in U.S. Pat. Nos. 3,441,489; 3,422,044; 3,403,088; 3,369,983 and 3,366,563, which all include 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 semi-drying oil fatty acid esters are meant esters of fatty acids which are or can be derived from drying oils or semi-drying 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.
  • esters are those in which the esters themselves are modified with other acids, including saturated, unsaturated or aromatic acids or an anhydride thereof.
  • the acid-modified esters are made by trans-esterification 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 the other polyols such as trimethylol propane, pentaerythritol, sorbitol and the like.
  • esters can also be modified with monomers such as cyclopentadiene or styrene and the modified esters produced thereby can be utilized herein.
  • 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 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 semi-drying or drying fatty acid esters of resinous polyols such as homopolymers or copolymers of unsaturated aliphatic alcohols, e.g., ally] alcohol or methallyl alcohol, including copolymers of such alcohols with styrene or other ethylenically unsaturated monomers or with non-oil modified alkyd resins containing free hydroxyl groups
  • 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 the above acids or anhydrides may also be utilized. Generally speaking, the anhydride or acid employed contains from four to 12 carbon atoms, although longer chain compounds can be used if so desired.
  • reaction products can be comprised solely of adducts of the fatty acid ester and the dicarboxylic acid or anhydride, in many instances it is desirable to incorporate into the reaction product another ethylenically unsaturated monomer.
  • 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.
  • the neutralization reaction be carried out in such a manner that amido groups are attached to part of the carbonyl carbon atoms derived from the dicarboxylic acid or anhydride.
  • compositions within this general class are described in U.S. Pat. Nos. 3,366,563 and 3,369,983.
  • Another vehicle comprises the fatty acid ester, unsaturated acid or anhydride reaction products and any additional unsaturated modifying materials (as described above) which are further reacted with the polyol.
  • any polyol can be employed, but diols are preferred.
  • higher polyols such as trimethylolpropane, glycerol, pentaerythritol, and the like are utilized, they are employed in small amounts, or in conjunction with the diol, or in the presence of a monohydric alcohol, and are used with adducts having a relatively low proportion of acidic component.
  • Water-insoluble diols are often preferable, and especially desirable water-dispersed compositions for electrodeposition are obtained using 2,2-bis(4-hydroxycyclohexyl)propane which has given the best results), neopentyl glycol, 1,1- isopropylidene-bis(p-phenyleneoxy)di-2-propanol, and similar diols.
  • the proportions of the polyol and ester-anhydride adduct which are employed depend upon various factors, but are in general limited only by the need to avoid gelation of the product.
  • the total functionality of the reactants is a guide to determining the optimum proportions to be employed, and in most instances should not be greater than about 2.
  • the product contains a substantial part of the original acidity derived from the dicarboxylic acid or anhydride; ordinarily the product should have an acid number of at least about 20.
  • a water-dispersed product such as is used in electrodeposition processes, at least part of the remaining acidic groups are neutralized by reaction of the partially esterified product with a base.
  • 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 with the interpolymer usually making from about 50 percent to about percent by weight of the resinous composition.
  • the acid monomer of the interpolymer is usually acrylic acid or methacrylic acid, but other ethylenically unsaturated monocarboxylic and dicarboxylic acids of up to about six carbon atoms can also be employed.
  • the 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 five carbon atoms in the hydroxyalkyl radical. Mono or diesters of the dicarboxylic acids mentioned are included.
  • the acid and ester each comprise between about one 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.
  • the most often used are the alkyl acrylates, such as ethyl acrylate; the alkyl methacrylates, such as methyl methacrylate; and the vinyl aromatic hydrocarbons, such as styrene, but others can be utilized.
  • 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 amine-aldehyde condensation products included in these compositions are, for example, condensation products of melamine, benzoguanamine, or urea with formaldehyde, although other amine-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 watersoluble or organic solvent-soluble.
  • Electrodeposition compositions comprising the above interpolymers and an amine-aldehyde resin are more fully described in U.S. Pat. No. 3,403,088.
  • Still another electrodepositable composition of desirable properties comprises an alkyd-amine vehicle, that is, a vehicle containing an alkyd resin and an amine-aldehyde resin.
  • an alkyd-amine vehicle that is, a vehicle containing an alkyd resin and an amine-aldehyde 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) is incorporated.
  • 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.
  • amine-aldehyde 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 percent to about 50 percent by weight of amine resin based on the total resinous components.
  • Yet another electrodepositable composition of desirable properties comprises mixed esters of an unsaturated fatty acid adduct.
  • the polyols which are utilized with these resins are essentially any polyol having a molecular weight between about 500 and 5,000.
  • Such resinous polyols include those resinous materials containing oxirane rings which can be opened in, prior to, or during the esterification reaction to provide an apparent hydroxy site.
  • the vehicle resins are formed by reacting a portion of the hydroxyl groups of the polyol with the fatty acid, the ratio of the reactions being such that at least an average of one hydroxyl group per molecule of the polyol remains unreacted.
  • Inorganic bases such as metal hydroxides, especially potassium hydroxide, can be used.
  • ammonia or organic bases especially watersoluble amines, such as, for example, the mono-, diand trilower alkyl amines such as methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, and m-methyl-butylamine, triethylamine, tributylamine, methyldiethylamine, dimethylbutylamine, and the like; cyclic amines such as morpholine, pyrrolidine, pipen'dine; diamines such as hydrazine, methylhydrazine, 2,3-toluene diamine, ethyl diamine and piperiz
  • n-amino-ethanolamine and methyldiethanolamine polyamines such as diethylene triamine.
  • the electrodepositable composition there may be present in the electrodepositable composition any of the conventional types of pigments employed in the art. There is often incorporated into the pigment composition a dispersing or surface-active agent. Usually the pigment and surface-active agent, if any, are ground together in a portion of the vehicle, or alone, to make a paste and this is blended with the vehicle to produce a coating compositions.
  • a non-ionic modifier or solvent examples include aliphatic, naphthenic and aromatic hydrocarbons or mixtures of the same; monoand dialkyl ethers of glycols, pine oil and other solvents compatible with the resin system.
  • the presently preferred modifier is 4-methoxy-4-methyl pentanone-2 (Pent- Oxone).
  • antioxidants there may also be included in the coating composition, if desired, additives such as antioxidants.
  • additives such as antioxidants.
  • antioxidants for example, orthoamylphenol or cresol. It is 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 agitation over extended periods of time.
  • additives which may be included in coating compositions include, for example, wetting agents such as petroleum sulfonates, sulfated fatty amines, or their amides, esters of sodium isothionates, alkyl pheoxypolyethylene alkanols, or phosphate esters including ethoxylated alkylphenol phosphates.
  • wetting agents such as petroleum sulfonates, sulfated fatty amines, or their amides
  • esters of sodium isothionates such as petroleum sulfonates, sulfated fatty amines, or their amides
  • esters of sodium isothionates such as petroleum sulfonates, sulfated fatty amines, or their amides
  • esters of sodium isothionates such as petroleum sulfonates, sulfated fatty amines, or their amides
  • esters of sodium isothionates such as petroleum
  • ordinary tap water may be employed.
  • such water may contain a relatively high level of metals and cations which, while not rendering the process inoperative, these cations may result in variations of properties of the baths when used in electrodeposition.
  • deionized water i.e., water from which free ions have been removed by the passage through ion exchange resins, is invariably used to make up coating compositions of the instant invention.
  • the electrodepositable composition may be present in the electrodepositable composition other resinous materials which are non-carboxylic acid materials.
  • resinous materials which are non-carboxylic acid materials.
  • base-solubilized polyacids which may be employed as electrodeposition vehicles include those taught in U.S. Pat. No. 3,392,165, which is incorporated herein by reference, wherein the acid groups rather than being solely polycarboxylic acid groups contain mineral acid groups such as phosphonic, sulfonic, sulfate and phosphate groups.
  • cationic type vehicle resins that is, polybases solubilized by means of an acid, for example, an amine-terminated polyamide or an acrylic polymer solubilized with acetic acid.
  • an acid for example, an amine-terminated polyamide or an acrylic polymer solubilized with acetic acid.
  • cationic polymers is described in copending application Ser. No. 772,366, filed Oct. 28, 1968 now abandoned.
  • the cationic resins may be formulated with adjuvants, such as pigments, solvents, surfactants, crosslinking resins, and the like.
  • the polyacids are anionic in nature and are dispersed or dissolved in water with alkaline materials such as amines or alkaline metal hydroxides and, when subjected to an electric current, they migrate to the anode.
  • alkaline materials such as amines or alkaline metal hydroxides and, when subjected to an electric current, they migrate to the anode.
  • the polybasic resins, solubilized by acids, are cationic in character and when these resins are water-dispersed or solubilized with an acid such as acetic acid, the material deposits on the cathode under an electric current.
  • the electrodeposition bath contained:
  • the electrodeposition bath above while utilized in a continuous coating operation of metal parts at one turnover per six days was continuously subjected to ultrafiltration utilizing the XPA membrane described hereinabove.
  • the membrane removed 0.54 percent per hour of the bath volume as ultrafiltrate, one-third of which was sent to drain and two-thirds of which were utilized in rinsing l:l.5 ultrafiltrate to deionized water in a manner so that the rinse water containing paint dragout was returned to the electrodeposition bath, 10 percent of the rinse water being carried out by the parts.
  • the coating operation was conducted on a 16 hour a day basis. The remaining eight hours the entire ultrafiltrate was directed to drain. At the end of each 24 hour day, the electrodeposition bath had a consistent pH and solids properties:
  • the amount of ultrafiltrate produced can be varied as desired; it is most readily increased by increasing the area of the filter surface employed. if desired, sufficient ultrafiltration capacity may be employed to provide sufficient ultrafiltrate to drain for bath control while, in addition, providing sufficient ultrafiltrate to the rinsing head to allow rinsing with ultrafiltrate alone, above the tank, on a continuous 24 hour/day basis.
  • the process of the invention provides great flexibility in both bath control and dragout conservation and typically from about 5 to about percent of the ultrafiltrate may be removed from the system during a given period, such as a day, to effect bath control, depending on ultrafiltrate volume, bath turnover rate, rinse water entering the bath, and the particular electrodepositable composition employed, among other factors.
  • additional rinsing of the relatively paint solidsfree part may be subsequently conducted with, for example, tap water or deionized water.
  • Electrodepositable compositions such as those hereinabove described, can be substituted for those exemplified, Likewise, various ultrafilters and method variations may be employed to obtain the improvements hereinabove described.
  • a method of operating an electrodeposition process wherein the electrocoated articles are rinsed after coating comprising subjecting at least a portion of an electrodeposition bath comprising ionically solubilized synthetic resin to an ultrafiltration process wherein the ultrafiltration membrane passes an aqueous efiluent comprising water and solute of substantially lower molecular weight than the solubilized resin, while retaining said solubilized resin, and proportionately or intermittently utilizing said aqueous effluent as at least a portion of the rinsing agent in the electrodeposition process in a manner that the rinsing agent returns to the electrodeposition bath while proportionately or intermittently removing at least a portion of said effluent from the system.
  • a method of operating an electrodeposition process wherein electrically conductive substrate is electrocoated from an aqueous electrodeposition bath and subsequently rinsed with a rinsing agent to remove dragout comprising subjecting at least a portion of said aqueous electrodeposition bath comprising ionically solubilized synthetic resin, to an ultrafiltration process wherein an ultrafiltration membrane passes an aqueous effluent comprising water and solute of substantiaily lower molecular weight than the solubilized resin, while retaining said solubilized resin, and utilizing at least a portion of said effluent as at least a portion of the rinsing agent in the electrodeposition process in a manner that said rinsing agent, after use, returns to the electrodeposition bath while least 4.5 gallons per square foot per day. continuously or intermittently removing a portion of said effluent from the system.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Nanotechnology (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Paints Or Removers (AREA)
US94023A 1970-12-01 1970-12-01 Treatment of electrodeposition bath Expired - Lifetime US3663404A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4201644A (en) * 1978-09-29 1980-05-06 Shinto Paint Co., Ltd. Replenishment of electrodeposition coating bath
US4222837A (en) * 1979-07-10 1980-09-16 E. I. Du Pont De Nemours And Company Electrodeposition process with ultrafiltration
US4231850A (en) * 1978-04-12 1980-11-04 Nissan Motor Company, Limited Process for a cationic cathodic electrocoat
EP0255669A1 (de) * 1986-07-25 1988-02-10 Herberts Gesellschaft mit beschränkter Haftung Verfahren und Vorrichtung zur Tauchbeschichtung von Objekten mit flüssigen Beschichtungsmaterialien mit anschliessender Spülung unter Verwendung von Ultrafiltrat
US10006134B1 (en) * 2014-11-07 2018-06-26 University Of South Florida Electrodeposition of metal microstructures

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4138088A1 (de) * 1991-06-04 1992-04-16 Unicolor Ag Verfahren zum umweltschonenden farbspritzlackieren mit einem in wasser verduennbaren zweikomponentenlack und vorrichtung zur durchfuehrung des verfahrens
DE4223181A1 (de) * 1992-07-15 1994-01-20 Herberts Gmbh Verfahren zur Wiederaufbereitung von Elektrotauchlackbädern

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1071458A (en) * 1965-05-31 1967-06-07 Pressed Steel Fisher Ltd A process for treating the effluent from plants for the electro-deposition of paint
US3556970A (en) * 1967-03-22 1971-01-19 Pressed Steel Fisher Ltd Treatment of effluents by the reverse osmosis process

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3444064A (en) * 1966-12-06 1969-05-13 Ford Motor Co Method for improving operational stability of electrocoating bath
GB1143686A (it) * 1966-12-06
GB1305707A (it) * 1969-06-02 1973-02-07

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1071458A (en) * 1965-05-31 1967-06-07 Pressed Steel Fisher Ltd A process for treating the effluent from plants for the electro-deposition of paint
US3556970A (en) * 1967-03-22 1971-01-19 Pressed Steel Fisher Ltd Treatment of effluents by the reverse osmosis process

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4231850A (en) * 1978-04-12 1980-11-04 Nissan Motor Company, Limited Process for a cationic cathodic electrocoat
US4201644A (en) * 1978-09-29 1980-05-06 Shinto Paint Co., Ltd. Replenishment of electrodeposition coating bath
US4222837A (en) * 1979-07-10 1980-09-16 E. I. Du Pont De Nemours And Company Electrodeposition process with ultrafiltration
EP0255669A1 (de) * 1986-07-25 1988-02-10 Herberts Gesellschaft mit beschränkter Haftung Verfahren und Vorrichtung zur Tauchbeschichtung von Objekten mit flüssigen Beschichtungsmaterialien mit anschliessender Spülung unter Verwendung von Ultrafiltrat
US10006134B1 (en) * 2014-11-07 2018-06-26 University Of South Florida Electrodeposition of metal microstructures

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JPS5119455B1 (it) 1976-06-17
DE2158668A1 (de) 1972-06-15
CA968742A (en) 1975-06-03
FR2116412B1 (it) 1974-08-19
BE776038A (fr) 1972-05-30
DE2158668C2 (de) 1983-04-28
AU3493871A (en) 1973-05-03
FR2116412A1 (it) 1972-07-13

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