US3663399A - Treatment of electrodeposition bath - Google Patents

Abstract

This invention relates to a method of rinsing articles coated by electrodeposition process which comprises using as the rinsing agent the effluent obtained from a selective separation process such as a filtration process, for example, ultrafiltration, utilized to control electrodeposition bath composition.

Description

United States Patent Loop 5] May 16, 1972 [54] TREATMENT OF [56] References Cited ELECTRODEPOSITION BATH UNITED STATES PATENTS [72] Inventor: Frederick M. Loop, North Olmsted, Ohio 3,355,373 11/1967- Brewer et a1 ..204/181 I 3,419,488 12/1968 Cooke ...204/181 [731 Asslgnw PPG lndustrles Pmsburgh, 3,556,970 1/1971 Wallace et a1. ..204/181 [221 Filed: FOREIGN PATENTS OR APPLICATIONS pp ,093 l,071,458 6 1967 Great Britain ..204/181 Primary Examiner-Howard S. Williams Related U.S. Application Data and Spencer [63] Continuation-impart of Ser. No. 881,259, Dec. l, [57] ABSTRACT 1969* abandoned This invention relates to a method of rinsing articles coated by electrodeposition process which comprises using as the rinsing U.S. agent the emuen obtained from a selective eparation process [51 l Int Clk ,C 13/00 such as a filtration process, for example, ultrafiltration, util- [58] Field of Search ..204/181 ized to control electrodeposition bath composition.

15 Claims, 3 Drawing Figures EEFIEFEEEEJ 0R. RETENTATE Patented May 16, 1972 v2 Sheets-Sheet I INVENTOR Heaven/ax M- .zoaP

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INVENTOR 5 -505mm ML. mop

ATTORNEY TREATMENT OF ELECTRODEPOSITION BATH CROSS-REFERENCES TO RELATES APPLICATIONS This application is a continuatin-in-part of copending Application Ser. No. 881,259, filed Dec. 1, 1969 now abandoned.

STATE OF THE ART 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 oh 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.

In the electrodeposition process, 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 counter-electrode 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.

In the electrodeposition process, when the article has been coated and is being withdrawn from the coating bath, a portion of the bath material which is not electrocoated to the article but merely adherent thereto, or pocketed by complexshaped articles, is withdrawn with the article. This material is commonly called dragout." This dragout is generally rinsed from the article, leaving an adherent electrocoated film which is then dried or baked in the conventional manner. This dragout represents wasted material and reduces efiiciency of the system. Further, the rinse water containing the dragout comprises a waste disposal problem. Typically, in the past the rinsing has been conducted with tap water and/or deionized water.

It has now been found that 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 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. Various advantages are derived from this technique. These advantages include the following: the use of the effluent achieves economies in water use; where the rinse is conducted in a manner so that the rinse water containing dragout is returned to the bath, the use of efiluent or filtrate in the rinsing process achieves removal of dragout without unduly changing or diluting the composition of the bath due to the addition of relatively pure water, which is the chief reason why rinsing is typically not conducted over the bath in such -a manner that the rinse water is returned to the bath. The process of the invention further reduces environmental pollution by the total electrodeposition system.

The use of the technique herein described is highly flexible. As previously stated, the rinsing may be accomplished in such a way that the effluent or filtrate and dragout are either collected separate from the bath or immediately returned to the bath. Likewise, since selective filtration and particularly ultrafiltration is a method of bath control,'it may be 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. Thus, the rinsing of dragout may intermittently 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. Likewise, a mixture of ultrafiltrate and other water may be employed as the rinsing media.

In the attached drawing (FIG. 3), an apparatus used to carry out the method of this invention is schematically illustrated. The electrodeposition bath 1 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. Here, in the ultrafiltration process, 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, where 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 control of an electrodeposition bath by an ultrafiltration process has been described in copending Application Ser. No. 814,789, filed Apr. 9, 1969. In the ultrafiltration process, exceptional control of a bath composition and removal of objectional accumulated materials has been achieved by a selective filtration process, that is, a process which selectively removes low molecular weight materials from the bath composition. This selective filtration process removes excess counter-ion and thus serves as a method of conventional bath control, but, in addition, this method further removes other excess materials or contaminants from the bath, thus permitting more complete control over bath constituents than has heretofore been possible.

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, is 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 thus 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 ultrafiltration" 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 principles of ultrafiltration and filters are discussed in a chapter entitled Ultrafiltration" in the Spring, 1968, volume of ADVANCES IN SEPARATIONS AND PURIFICATIONS, E. S. Perry, Editor, John Wiley & Sons, New York, as well as in CHEMICAL ENGINEERING PROGRESS, Volume 64, December, 1968, pages 31 through 43, which are hereby incorporated by reference.

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 or solvent plus dissolved low molecular weight solute is removed. A suitable apparatus for conducting ultrafiltration is described in U. S. Pat. No. 3,494,465, which is hereby incorporated by reference.

There are two types of ultrafiltration membrane. One is the microporous ultrafilter, which is a filter in the traditional sense, that is, a rigid, highly voided structure containing interconnected random pores of extremely small average size. Through such a structure, solvent (in the case of electrodeposition, water) flows essentially viscously under a hydraulic pressure gradient, the flow rate proportional to the pressure difference, dissolved solutes, to the extent that their hydrated molecule dimensions are smaller than the smallest pores within the structure, will pass through, little impeded by the matrix. Larger size molecules, on the other hand, will become trapped therein or upon the external surface of the membrane and will thereby be retained. Since the microporous ultrafilters 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.

In contrast, 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. In such a structure, 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 ultrafilter 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 solvent 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 micron layer, of a homogenous 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. If desired, 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 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 described 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.

The choice of a specific chemical composition for the membrane is determined to a large extent by its resistance to the chemical environment. Membranes can be typically prepared from thermoplastic polymers such as polyvinyl chloride, polyacrylonitrile, polysulfones, poly(methyl methacrylate), polycarbonates, poly(n-butyl methacrylate), nylons, as well as a large group of copolymers formed from any of the monomeric units of the above polymers, including Polymer 360, a polysulfone copolymer. Cellulose materials such as cellulose acetate may also be employed as membrane polymers.

Some examples of specific 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 penneability characteristics:

Solute Retention Characteristics Solute Molecular Weight Retention Bacitracin 1,400 0 Cytochrome C 14,500 0 Pepsin' 35,000 100 Albumin 67,000 100 Dextran 1 l0 1 10,000 60 Flow Rate-mL/min.

0.25% Cytochrome C 0.25% Pepsin 12,400 mw) -35,000

mw) in distilled in distilled Membrane Pressure Distilled Diameter P.S.I. water water water I50 mm. 50 600 24.0 80.0

Flux

Molecular Re (gal.lsq.ft./day at Solute weight tention 30 psi., 1 .0% solute) Cytochrome 0 12,600 so 100 a Chymotripsinagen 24,000 22 Ovalbumin 45,000 45 This membrane is hereinafter referred to as Membrane B.

Dorr-Oliver BPA membrane, the membrane chemical composition of which is phenoxy resin (polyhydroxy ether) and which has the following permeability characteristics:

Flux

Molecular Re- (gal./sq.ft./day at Solute weight tention 30 psi., 1 .0% solute) Cytochrome C 12,600 50 30 This membrane is hereinafter referred to as Membrane C."

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. In 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 rovided by a stirrer, for example, a magnetic stirrer. Obviously, this system is best used for small batches of material. In a process requiring continuous separation, a continuous selective filtration process is 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.

Likewise, 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, on the other hand, 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 vary widely and is not limiting to the operation of the process. The filter or membrane may, for example, be in the form of sheets, tubes or hollow fiber bundles, among other configurations.

Under ideal conditions, selected low molecular weight solutes would be filtered as readily as solvent and their concentration in the filtrate is equal to that in the retentate. Thus, for example, if a material is concentrated to equal volumes of filtrate and retentate, the concentration of low molecular weight solute in each would be the same.

Using diafiltration, retentate solute concentration is not constant and the mathematical relationship is as follows:

where 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), and 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 physical relationship. For example, the pigments are usually ground in a resin medium and are thus wetted" with the vehicle resin. As can be readily appreciated then, 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.

bonate), neutralizing agent, organic solvent and ions such as 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 about 500. As previously indicated, 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. Likewise, as previously indicated, the retained solutes may, in fact, be colloidal dispersions ormolecular dispersions rather than true solutes.

In practice, 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. Obviously, if desired, the egress side of the filter may be maintained at a reduced pressure to create the pressure difierence.

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. With the presently preferred membranes, the operating pressures are between about 10 and p.s.i., preferably between about 25 and 75 p.s.i. Under most circumstances, the ultrafilter should have an initial flux rate, measured with the composition to be treated of at least about 3 gal./ft/day (24 hours) and preferably at least about 4.5 gal./ft /day.

As previously indicated, 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 parallel to the filter surface.

The retained solutes comprising the vehicle resin are then returned to the electrodeposition bath. Ifdesired, the concentrate may be reconstituted by the addition of water either before entry to the bath or by adding water directly to the bath.

If there is present in the bath desirable materials which, because of their molecular size, are removed in the ultrafiltra- "tion process, these may likewise be returned to the bath either directly to the retained solute before entry to the bath, in the makeup feed as required, or independently.

A number of electrodepositable 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 used electrodeposition satisfactory for certain specialized uses.

Presently, 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. By 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. Preferably, the drying oil or semi-drying oil per se is employed.

Also included among such 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 transesterification of the ester, as by forming a dior mono-glyceride 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. In addition to glycerol, a1- coholysis can be carried out using the other polyols such as trimethylolpropane, pentaerythritol, sorbitol and the like. If desired, the esters can also be modified with monomers such as cyclopentadiene or styrene and the modified esters produced thereby can be utilized herein. Similarly, other esters or unsaturated fatty acids, for example, those prepared by the esterification of tall oil fatty acids with polyols, are also useful.

Also included within the terms 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-, di-and poly-epoxides, semi-drying or drying oil fatty acid esters of polyols, such as butanediol, trimethylolethane, trimethylol-propane, trimethylolhexane, pentaerythritol, and the like; and semi-drying or drying fatty acid esters of resinous polyols such as homopolymers of 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 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 any of the above acids or anhydrides may also be utilized. Generally speaking, the anhydride or acid employed contains from 4 -l2 carbon atoms, although longer chain compounds can be used if so desired.

While the reaction products can be comprises 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.

As shown in the art, it is preferred that in certain instances the neutralization reaction becarried 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.

Essentially any polyol can be employed, but diols are preferred. When 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)div2-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.

In many instances, only part of the anhydride groups of the adduct, e.g., about 10 percent, are reacted with the polyol. Of those anhydride groups reacted, it is preferred that only one of the carboxyl groups is esterified in each instance.

The product contains a substantial part of the oriiginal acidity derived from the dicarboxylic acid or anhydride; ordinarily the product should have an acid number of at least about 20. To provide 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.

The polyol reaction products and reaction conditions are more fully described in Application Ser. No. 450,205, filed Apr. 22, 1965, now US. Pat. No. 3,565,781, as well as the art cited above.

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. 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. 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. A number of these are known in the art and may be employed. Preferred are water-dispersible alkyds such as those in which a conventional alkyd (such as a glyceryl phthalate resin), which may be modified with drying oil fatty acids, is made with a high acid number (e.g., 50 to 70) and solubilized with ammonia or an amine, or those in which 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.

The above alkyds are combined with an 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 alltanol. 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.

Yet another electrodepositable composition of desirable properties comprises mixed esters of a resinous polyol. These resin esters comprise mixed esters of an unsaturated fatty acid adduct. Generally 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. The remaining functionality is then reacted with the unsaturated fatty acid adduct of an olefinically unsaturated dicarboxylic anhydride, such as maleic anhydride, this second esterifrcation reaction being conducted under conditions so that esterification occurs through the anhydride ring, thereby introducing free acid groups into the molecule. Mixed acids of the class described are disclosed in Belgian Pat. No. 641,642, as well as in Copending Applicatriethylamine, tributylamine, methyldiethylamine, dimethylbutylamine, and the like; cyclic amines such as morpholine, pyrrolidine, piperidine; diarnines such as hydrazine, methylhydrazine, 2,3-toluene diamine, ethyl diamine and piperizine and substituted amines such as hydroxylamine, ethanolamine, diethanolamine, butanolamine, hexanolamine and methyldiethanolamine, octanolamine, diglycolamine and other polyglycolamines, triethanolamine, and methylethanolamine, n-amino-ethanolamine and methyldiethanolamine and polyamines such as diethylene triamine.

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 surfaceactive 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 composition.

In many instances, it is preferred to add to the bath in order to aid dispersibility, viscosity and/or film' quality, a non-ionic modifier or solvent. Examples of such materials are aliphatic, naphthenic and aromatic hydrocarbons or mixtures of the same; monoand dialkyl ethers or glycols, pine oil, and other solvents compatible with the resin system. The presently preferred modifier is 4-methoxy-4-methyl pentanone-Z (Pent- Oxone There may also be included in the coating composition, if

desired, additives such as antioxidants. For example, I

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.

Other additives which may be included in coating compositions, if desired, include, for example, wetting agents such as petroleum sulfonates,.sulfated fatty amines, or their amides, esters of sodium isothionates, alkyl phenoxypolyethylene alltanols, or phosphate esters including ethoxylated alkylphenol phosphate. Other additives which may be employed include anti-foaming agents, suspending agents, bactericides, and the like. r

in formulating the coating composition, ordinary tap water may be employed. However, 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. Thus, in common practice, 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.

In addition to the electrodepositable vehicle resins described above, there may be present in the electrodepositable composition other resinous materials which are noncarboxylic acid materials. For example, as shown above, there may be added up to about 50 percent by weight of an aminealdehyde condensation product.

Other 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.

The process of the instant invention is equally applicable to cationic type vehicle resins, that is, polybases solubilized by means of an acid, for example, an amineterminated polyamide or an acrylic polymer solubilized with acetic acid. Another case of such cationic polymers is described in copending A plication Ser. No. 772,366, filed Oct. .28, 1968 now abandoned.

In a manner similar to the anionic resins described above, 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. 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 invention is further described in conjunction with the following examples, which are to be considered illustrative rather than limiting. All parts and percentages in the examples and throughout the specification are by weight unless otherwise specified.

EXAMPLE I The vehicle resin in this example is a malenized tall oil fatty acid adipic acid ester of a styrene-allyl alcohol copolymer of Non-Volan'les Solubilizing amine diethyl/triethylamine. The compositionv was reduced to 12 percent solids with deionized water. The solvent comprises 2.6 percent of the total composition.

The bath treated in this example was the above composition after approximately 6 months aging and three turnovers.

This bath was subjected to selective filtration utilizing a Diaflow Membrane Ultrafilter PM 30 described above as Membrane A.

The bath was filtered by a batchgprocess using membrane PM-30 at 50 p.s.i.

A 50 percent separation of bath material was accomplished as follows:

1,000 parts of the above bath composition was subjected to ultrafiltration, removing 500 parts of ultrafiltrate. Steel panels were coated from the uitrafiltered bath material. rinsing the panels to remove dragout with the above ultraiiltrate in such a manner that the rinse containing dragout is returned to the electrodeposition bath. The coating of panels was continued until all the ultraiiltrate had been utilized for rinsing.

The properties of the starting and reconstituted bath materials were as follows:

Panels coated from both materials. for example. at 250 volts for 2 minutes at a bath temperature of 75' were equivalent in appearance and properties.

EXAMPLE ii The vehicle resin in this Example is an Epon lOO4-tall oil fatty acid mixed partial ester with a maleinized tall oil fatty acid adduct comprising 45 percent Epon i004, 48 percent tall oil fatty acid and 7 percent maleic anhydride, having an acid value of 59 and a viscosity of 230,000 at 85 percent solids in butyi Cellosolve. The eiectrodepositable material had the following composition at 12 percent solids:

Parts by Weight Surfactant (Witco 9 l 2 Vehicle resin solids (above) maleinized linseed oil Anthracite coal (plgmentary) 2 Strontium ehromate Basic lead silicate Montmorillonite clay, modified with trimethyi octyl ammonium ions and containing 0.65% nitrogen (Bentone ll) Potassium hydroxide Butyl Cellosolve Diethylamine Cresylic acid Deionized water i715.

2,000 parts of the above composition were charged into an electrodepodtion bath. The bath was subjected to ultrafiltration through a PM-30 membrane (Membrane A above) at 50 p.s.i. After four hours, 1,000 parts of ultrafiltrate were col-' lected.

Phosphatized steel panels were then coated from the electrodeposition bath at 250 volts for 2 minutes at a bath temperature of F. The panelswere rinsed with the ultrafiltrate collected above in such a manner that the rinse containing dragout returned to the electrodeposition bath. Fourteen panels were coated and rinsed in order to utilize all of the ultrafiltrate.

The properties of the starting and reconstituted bath materials were as follows:

Panels coated from the initial bath and the reconstituted bath. for example, at 250 volts for 2 minutes at 75 F., were equivalent in appearance and properties.

Other 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.

According to the provisions of the Patent Statutes, there are described above theinvention and what are now considered its best embodiments; however, within the scope of the ap-v pended claims, it is to be understood that the invention can be produced otherwise than specifically described.

I claim:

1. A method of rinsing dragout from an eleetrocoated article with a rinsing agent, said article having been electrocoated in an eiectrodeposition bath comprising synthetic resin ionically solubilized in aqueous medium, which comprises subjecting at least a portion of the electrodeposition bath to an ultrafiltration process wherein the ultrafiltration membrane passes an effluent comprising water and solute of substantially lower molecular size than the solubilized resin, returning retentate from the ultrafiltrati'on process to the electrodeposition bath and employing the resultant efiluentas at least a portion of the rinsing agent for said electrocoated article.

2. A method as in claim 1 wherein the resin is a base-solubilized synthetic polyacid resin.

3. A method as in claim 2 wherein the resin is a base-solubiL' ized polycarboxylic acid resin.

4. A method as in claim 3 wherein the base is a water-soluble amine.

5. A methodas in claim 3 wherein the base is potassium hydroxide.

' 6. A method as in claim 1 wherein the resin is an ionically solubilized synthetic polybasic resin. I

7. A method as in claim 1 wherein the ultrafiltration process is operated at a pressure gradient between about l0 anti about .150 p.s.i. and the ultrafiltration membrane has a flux rate of at least about 4.5 gallons per square foot per pay.

8. A method as in claim 1 wherein rinsing is conducted in 1 such a manner that the resultant dragout-containing rinse is returned to the electrodeposition bath.

9. A method as in claim 8 wherein the resin is base-solubilized synthetic polyacid resin.

10. 'A method as in claim 8 wherein the resin is base-solubilized polyacrboxylic acid resin.

11. A method as in claim 10 wherein the base is a watersoluble amine. V

12. A method as in claim 10 wherein the hydroxide.

base is potassium 13. A method as in claim 8 wherein the resin is ionically solubilized synthetic polybasic resin.

14. A method as in claim 8 wherein the ultrafiltration process is operated at a pressure gradient between about 10 and about 150 p.s.i. and the ultrafiltration membrane has a flux rate of at least about 4.5 gallons per square foot per day.

15. A method as in claim 14 wherein the pressure gradient is between about 25 and about 75 p.s.i.

l t i UNTTED ST *TES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,663,399 Dated May 16, 1972 Inventor-( M- It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 3, "relates" should read --related Column 6, line 62, after the word "entirely", the words "used electrodeposition" should be deleted.

Column 7, line 55, the word "becarried" should read -be carried-- Column 8, line 11, the word "oriiginal" should read --original- Claim 7, Column 12, line 64, the word "pay" should read day- Claim 10, Column 12, line 71, the word "polyacrboxylic" should read polycarboxylic- Signed and sealed this 23rd day of January 1973,

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PC4050 uscomm-oc 60376-P69 i U.5. GOVERNMENT PRINTING OFFICE} 9.9 0-386-534.

Claims (14)

1. 2. A method as in claim 1 wherein the resin is a base-solubilized synthetic polyacid resin.
2. 3. A method as in claim 2 wherein the resin is a base-solubilized polycarboxylic acid resin.
3. 4. A method as in claim 3 wherein the base is a water-soluble amine.
4. 5. A method as in claim 3 wherein the base is potassium hydroxide.
5. 6. A method as in claim 1 wherein the resin is an ionically solubilized synthetic polybasic resin.
6. 7. A method as in claim 1 wherein the ultrafiltration process is operated at a pressure gradient between about 10 and about 150 p.s.i. and the ultrafiltration membrane has a flux rate of at least about 4.5 gallons per square foot per pay.
7. 8. A method as in claim 1 wherein rinsing is conducted in such a manner that the resultant dragout-containing rinse is returned to the electrodeposition bath.
8. 9. A method as in claim 8 wherein the resin is base-solubilized synthetic polyacid resin.
9. 10. A method as in claim 8 wherein the resin is base-solubilized polyacrboxylic acid resin.
10. 11. A method as in claim 10 wherein the base is a water-soluble amine.
11. 12. A method as in claim 10 wherein the base is potassium hydroxide.
12. 13. A method as in claim 8 wherein the resin is ionically solubilized synthetic polybasic resin.
13. 14. A method as in claim 8 wherein the ultrafiltration process is operated at a pressure gradient between about 10 and about 150 p.s.i. and the ultrafiltration membrane has a flux rate of at least about 4.5 gallons per square foot per day.
14. 15. A method as in claim 14 wherein the pressure gradient is between about 25 and about 75 p.s.i.

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