US3467588A - Production of uniformly gradated coatings - Google Patents

Description

p 1969 K. A. GEBLER ETAL PRODUCTION OF UNIFORMLY GRADATED COATINGS Filed Oct. 24. 1965 INVENTORS. I KENNETH A. GEBLER 8 MARTIN H. ORTNER BY aw,

than ATTOR/VE' United States Patent 3,467,588 PRODUCTION OF UNIFORMLY GRADATED COATINGS Kenneth A. Gebler, Dover, and Martin H. Ortner, Kinnelon, N.J., assignors to Vitro Corporation of America,

New York, N.Y., a corporation of Delaware Filed Oct. 24, 1965, Ser. No. 504,919 Int. Cl. C23b 13/00 US. Cl. 204l81 11 Claims ABSTRACT OF THE DISCLOSURE Electrophoretically coating an article; the coating having a plurality of graduated materials, each being fed to the coating bath from different reservoirs; the ratio of the feeding of the materials is gradually changed during the coating process giving gradation which is continuous and nonlamnar from the article surface to the outside surface of the applied coating.

This invention relates to the production of uniformly gradated coating and has particular reference to method and apparatus for electrophoretically depositing a multicomponent coating on a suitable substrate in such a manner that the composition of the coating is variably controlled during deposition. This invention also includes the resulting product.

Electrophoretic deposition occurs when an electrostatic field is established between two electrodes immersed within a colloidal or gross dispersion of charged particles, thus causing migration of the suspended particles toward one of the electrodes and producing the deposit of an adherent coating on that electrode.

Electrophoretic coatings and various methods and apparatus for applying them are known, examples being disclosed in US. Patents Nos. 2,848,391 and 2,861,935. However, no method or apparatus has been developed for producing coatings having continuously gradated compositions which shade insensibly from base to outer surface without steps or boundary or laminated structure involving discrete well-defined layers of a consistent composition such as painted, sprayed, dipped or electroplated coatings or layers. Thus in electroplating metals on metal or other electrolytic-responsive conducting surface or substrate of similar characteristic, the structure is invariable as to density or metallic characteristic unless difierent discrete metal layers are applied one upon the other, such as nickel on copper and chromium on the nickel layer and similar combinations of electrolytically compatible metals.

In accordance with the present invention, methods and apparatus are provided for electrophoretically applying a multicomponent coating graded at will to the exact composition desired on a suitable substrate by changing the proportions of two or more different electrophoretic materials supplied during deposition as the dispersion material to the electrophoretic deposition or coating tank in which is mounted the article to be coated. Thus, two dispersions of different particulate inorganic materials can be deposited continuously and simultaneously from, say, a 20-80 ratio to 40-60 or 5050 and ultimately to 100-0, or to any other ratio. The resulting deposition and product has no boundary or step or laminated or other transitional structure since the deposition is effected by individual particles approximately microns in diameter and the composition ratio of the coating components is infinitesimally and constantly changing during the depo ition interval. Hence, according to this invention such gradated coatings are useful when a potentially attractive or otherwise desirable coating material was not heretofore usable on a particular substrate because of the 3,467,588 Patented Sept. 16, 1969 lack of bonding affinity between the coating material and the selected substrate or because of Widely different coeflicients of thermal expansion between the coating material and the substrate.

The aforementioned difiiculties with respect to bonding of a coating material which we characterize as A to a different substrate which we characterize as B when the coating material is nonadherent due to lack of metallurgical or chemical reaction with the substrate, or when the coefficients of thermal expansion of A and B are so widely separated that the tensile or compressive strength of the coating is exceeded upon heating to an elevated temperature and cooling may be overcome by providing an intermediate material which we characterize as C and which bonds to both the substrate B and to the coating A or which possesses a coefiicient of thermal expansion intermediate between that of the coating A and substrate B. The intermerdiate material C could be deposited by numerous methods in single layer or a multiplicity of layers of uniform composition; however, the strength and effectiveness of such a laminar structure is reduced considerably from that of a homogeneously gradated structure. Typical examples of substrates, coatings, and homo geneously gradated intermediate materials which can be prepared by the method of this invention to yield an effective composite are:

pounds such as metal alloys, and nickel nickel-chromium,

silicides, borides, and cobalt base tungsten, molybberyllides and alloys. denum, etc. aluminides.

Oxide pigments Ferrous and non- Metal and ceramic ferrous alloys. binders.

Refractory oxide Tantalum and Intermetallic comoxidation resistant tungsten alloys. pounds such as compounds such as tungsten silicide zirconia, alumina, and zirconium thoria, hatnia, etc. boride.

Ferroelectric and Any electrically Metallic and ceramic magnetic compounds conductive surface. binders.

such as borium titanate and magnesium zinc ferrite. Erosion resistant compounds such as oxides and carbides.

Cobalt, nickel,

phosphates, silicates, etc.

Ferrous and nonierrous metals.

In addition to improving bonding of a coating or providing a match of coeflicients of thermal expansion, the homogeneously gradated coating may be utilized to modify some undesirable physical or chemical property of an otherwise suitable coating material. For example, the thermal conductivity of a low conductivity coating may be improved by the addition of metal particles throughout its structure. Conversely, the thermal conductivity of a high conductivity coating may be reduced by the use of a gradated concentration of a thermal insulator. In this example, and in the aforementioned examples, it is un derstood that the gradated zone may, by the apparatus of this invention, be produced throughout the entire coating thickness or throughout any desired cross section of the total coating. Other examples of the modification of one or more physical or chemical properties of a coating will be apparent to those skilled in the coating art.

The preferred apparatus of this invention comprises essentially a plurality of tanks each containing a supply dispersion of one of the coating materials to be blended and deposited electrophoretically on the article or surface to be coated. Pumps, one for each supply dispersion tank, are severally connected thereto and to a common discharge pipe leading to the vessel wherein the deposited material is to be applied electrophoretically to the article positioned withint he coating vessel. The proportions of the two or more dispersion materials are regulated at will by gradually changing the discharge volume of the pumps by means of an infinitely variable speed drive interposed between a power source and the individual pumps whereby the proportion of the dispersion materials is changed at will. As the thus proportioned supply dispersions are introduced into the electrophoretic coating vessel, the desired gradated deposition takes place smoothly and continuously in the manner described.

It will be seen that the present invention provides method and apparatus for producing a gradated layer of bonding material and product, the thermal and bonding characteristics of which may be varied at will during deposition, whereby the layer is not of a consistent composition or has any finite boundary but may be adjusted during its deposition interval to accommodate the ditfering characteristics of two or more surfaces to be united or otherwise placed into cooperative relation.

For a more complete understanding of the invention, reference my be had to the accompanying drawings in which:

FIGURE 1 illustrates a preferred form of apparatus of this invention for conducting the novel process and producing the product of this invention; and

FIGURE 2 is a diagrammatic representation of an enlarged cross-section of the article of this invention.

Referring to FIG. 1 of the drawing, numeral designates an electric motor mounted on base 11 and connected through a variable speed reduction device 12 controlled by knob 13 as to speed. A suitable speed reduction device is Vickers model No. TR3 variable speed hydraulic drive.

Also mounted on base 11 and driven by chain belt, or equivalent positive drive 14 from the output shaft of speed reduction device 12 are two variable speed drive devices 15 and 16 having a common differential control handle 17 whereby device 15 is driven at will at a proportionally higher speed as the speed of device 16 is decreased and vice versa. Graham model BD4R4 variable speed drive is a suitable diiferential device. Alternatively a continuously variable speed electric motor, not shown, may be substituted for handle 17.

Two pumps 18 and 19, preferably positive displacement pumps, are respectively driven by variable speed drive devices 15 and 16 at the corresponding differential speeds selected by speed control handle 17. Pumps 18 and 19 are connected respectively to dispersion tanks 20 and 21 by pipes 22 and 22. Tanks 20 and 21 are provided with suitable agitating means, such as motor driven stirrers or recirculating pumps 20 and 21', respectively, and contain dispersions of the coating materials which are pumped therefrom by pumps 18 and 19 and mixed in pipe 24 which is continuously supplied by branch pipes 23 and 23' leading from pumps 18 and 19. The predetermined proportions of mixed dispersion from tanks 20 and 21 are discharged from mixing pipe 24 into coating vessel 25 to be deposited electrophoretically on an article immersed in the coating vessel 25 preferably provided with an overflow pipe 26 in the manner described in aforementioned Patent No. 2,848,391.

In operation of the apparatus and in conducting the method of this invention to produce the novel product, tanks 20 and 21 are filled with, respectively, the desired dispersions of the particles to be electrophoretically deposited on the electroconductive surface of the article to be coated in the vessel 25. By way of example, assuming that the desired coating is to be composed of different metal compounds such as metal oxides, carbonates, sulfates or halides, the selected compound is first dispersed in a suitable fluid vehicle. One such compound, e.g., chromium oxide of from 0.01 to 50 micron particle size, may

be dispersed in an anhydrous electrically nonconducting fluid, such as ethyl, methyl or isopropyl alcohol, acetone, ethyl acetate, nitrobenzene or in water and maintained in uniform dispersion in tank 20 by the stirrer 20. A different metallic material, such as nickel oxide, also of from 0.01 to 50 micron particle size, may be dispersed in one of the aforementioned anhydrous electrically nonconducting fluid vehicles or in water and maintained in uniform dispersion in tank 21 by stirrer 21.

Having predetermined the initial mixture of dispersions for tanks 20 and 21 to be delivered to the electrophoretic coating vessel 25, the operator sets that initial proportion by control 17, say 20 parts from tank 20 and parts from tank 21, and starts the driving motor 10. Pumps 18 and 19, driven at the preselected speed by corresponding variable speed drivers 15 and 16, draw the proper amounts of dispersions from the tanks 20 and 21 by suction pipes 22 and 22' and delivered by pipes 23 and 23 to mixing pipe 24 and coating vessel 25. As the electrophoretic deposition begins in the known manner in vessel 25, the operator turns handle 17 gradually to change the differential drives by 15 and 16 and thus the mixed proportion of the dispersions delivered from tanks 20 and 21, or that may be done automatically by a constant speed motor in place of handle 17, so that variable speed drives 15 and 16 vary differentially to change the pump 18 and 19 speeds gradually and uniformly. Since pumps 18 and 19 determine the ratio of the volumes of dispersions delivered from tanks 20 and 21, the dispersion proportion gradually changes in the same way. The rate of speed of handle 17 may be changed at will by the operator or a variable speed motorized drive may be substituted for manual operation. The total volumetric throughput of the system is adjusted by means of speed reduction device 12 and the coating thickness on the article in vessel 25 is controlled by handle 17 as well as by the applied voltage during coating and by the solids concentrations of one of the dispersions in vessels 20 and 21.

By way of example of preparation of a substrate a metal panel 0.020" x b x 1" is grit blasted with mesh A1 0 grain. It is then acid etched for two seconds in a 1:1:% mixture by volume of HNO :HF:H SO rinsed with water and dried. Dispersions of glass powders of the same composition but one white and one colored (i.e., blue), are prepared by making the following mixtures:

Glass powder solids (white or colored), (-325 mesh particles) gm 42.5

Isopropyl alcohol ml 575 Nitromethane m1 275 Protein solution (30 mg./ml. in 60 isopropyl alcohol/40 nitromethane mixture) by volume ml 17 Cobalt nitrate solution (0.1 gm./ml. in isopropyl alcohol) ml 1 The metal panel specimen after cleaning is suspended in the minimum volume electrophoretic coating vessel 25. The specimen is made the cathode of this coating system and the cell acts as the anode. A dispersion of white glass is placed in the dispersion tank 21 in the attached sketch of the pumping system. A dispersion of colored glass is placed in the dispersion tank 20. The speed control 12 is set at 50. This setting results in an output shaft speed of 840 r.p.m. to the input shafts of the cross-linked variable speed drives 15 and 16. The power to the open motor 10 is turned on and pumping of white glass dispersion through the system and coating cell begins. Simultaneously a constant potential difference of volts DC is introduced between the specimen and coating cell by means of a standard power supply such as Hewlett-Packard model 712A not shown.

During a period of 55 seconds the variable speed drive control handle 17 is turned at a constant rate of 43 rpm. This causes both the composition of solids being pumped and that being coated onto the specimen to change gradually from 100% white glass to virtually 100% blue glass. The power is then shut off and the coated article removed from the cell. The resultant coating is 0.007" to 0.010" thick with 100% white glass at the surface of the substrate gradated to virtually 100% blue glass at the surface of the coating.

By varying the proportions delivered from dispersion tanks 20 and 21 in the manner described, a gradated coating which is shaded insensibly from the surface of the base article to the outer surface is deposited to the desired thickness from the initial to the finished proportion.

FIG. 2 illustrates diagrammatically the structure of the article 30 of this invention as visualized in enlarged particle cross-section, wherein numeral 27 designates the electroconductive base or substrate which may be copper with gradated particles deposited thereon shown as tiny triangles of one material and the different material by tiny circles. Thus, in the simple illustrative example given above the coating deposited on the surface of the article substrate 27 initially is a mixture of 20% chromium oxide identified by triangles 28 and 80% nickel oxide identified by circles 29. Then, as the handle 17 is turned the proportions of the deposited materials change gradually and imperceptibly as indicated by the gradually increasing density of the triangles 28 and the Proportionally decreasing density of the circles 29. Thus, if the ultimate proportions are reversed at the surface of substrate 27, the relative proportions at the surface would be 80% chromium oxide and 20% nickel oxide. These proportions may be changed at will as stated.

It will be seen that the gradated electrophoretic deposition process and the product (FIG. 2) of the invention differ from those processes and products where two or more materials are codeposited in a heterogeneous but fixed and uniform proportional manner such as described in aforementioned Patent No. 2,848,391. Also, although two different dispersions are described herein as mixed and electrophoretically deposited, three or more mixtures in proportional division between three or more dispersion tanks 20, 21, e.g., 20%, 30%, 50% and the like; may be effected in the same manner and with apparatus having three variable speed drives like and 16, whose speed is proportioned by the control 17 for driving three corresponding pumps like 18, 19 to supply to the mixing tube 24 the corresponding proportions from three dispersion tanks like 20, 21.

Although certain preferred embodiments of the inven tion have been described herein, it is to be understood that the invention is not limited thereby except within the scope of the appended claims.

We claim:

1. The method of forming a gradated coating on a base having an electrically conductive surface, which comprises separately supplyin to an electrophotetic deposition unit at least two dispersions of different particles in a non conducting fluid vehicle, and progressively changing the relative proportions of said dispersions supplied to said unit, whereby there is electrophoretically deposited on said base a layer comprising progressively varying proportions of said different particles from the base to the surface of the layer.

2. The method of forming a gradated coating on a base having an electrically conductive surface, which comprises separately supplying to an electrophoretic deposition unit at least two dispersions of different particles in a nonconducting fluid vehicle, and progressively and uniformly changing the relative proportions of said dispersions supplied to said unit, whereby there is electrophoretically deposited on said base a layer comprising progressively varying proportions of said different particles from the base to the surface of the layer.

3. The method of forming a gradated coating on a base having ann electrically conductive surface, which comprises separately supplying to an electrophoretic deposition unit at least two dispersions of different particles in a nonconducting fluid vehicle, and progressively mutually inversely changing the relative portions of said dispersions supplied to said unit, whereby there is electrophoretically deposited on said base a layer comprising progressively varying proportions of said different particles from the base to the surface of the layer.

4. The method of forming a gradated coating on a base having an electrically conductive surface, which comprises separately supplying to an electrophoretic deposition unit at least two dispersions of different particles in a nonconducting fluid vehicle, and progressively and uniformly changing the inverse proportions of said dispersions supplied to said unit, whereby there is electrophoretically deposited on said base a layer comprising progressively varying proportions of said different particles from the base to the surface of the layer.

5. A method as defined in claim 1, wherein the particles in at least one of the dispersions are electroconductive.

6. A method as defined in claim 2, wherein the particles in at least one of the dispersions are electroconductive.

7. A method as defined in claim 3, wherein the particles in at least one of the dispersions are electroconductive.

8. A method as defined in claim 4, wherein the particles in at least one of the dispersions are electroconductive.

9. A new product comprising an article having an electroconductive surface, and a gradated electrophoretic layer of at least two electroresponsive materials on said surface, the gradation of which is imperceptible from said article surface to the surface of the layer, said layer being formed on said surface by the method of claim 1.

10. A new product comprising an article having an electroconductive surface, and a gradated electrophoretic layer of at least two metals on said surface, the gradation of which is imperceptible from said article surface to the surface of the layer, said layer being formed on said surface by the method of claim 1.

11. A new product comprising an article having an electroconductive surface, and a gradated electrophoretic coating deposited on said surface, said coating comprising a plurality of gradated materials, the gradation of which is continuous and nonlaminar from the article surface through the thickness of the coating, and being formed on said surface by the method of claim 1.

No references cited.

JOHN H. MACK, Primary Examiner A. C. PRESCOTT, Assistant Examiner US. Cl. X.R. 29l94; 204299

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