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  Electrodeposition processUSPTO Application #: 20060037861Title: Electrodeposition process Abstract: The present invention is directed to an electrodeposition process for producing a coated substrate having improved properties. The electrodeposition process comprises coating a substrate with a liquid coating composition, immersing the substrate with the liquid coating composition in an electrodeposition bath, and applying an electrical current having a specified voltage to form an electrodeposition coating to the substrate. In a preferred embodiment, the electrical current is applied prior to immersing the coated substrate in the bath. The coating can further be etched to beneficially texture the surface of the coated substrate. The substrate coated with the process of the invention exhibits improved corrosion resistance, durability, lubricity, adhesion, as well as other favorable characteristics. (end of abstract) Agent: Alston & Bird LLP Bank Of America Plaza - Charlotte, NC, US Inventors: Paul D. Manos, Kerry A. Ryan USPTO Applicaton #: 20060037861 - Class: 204471000 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Non-distilling Bottoms Treatment, Electrophoresis Or Electro-osmosis Processes And Electrolyte Compositions Therefor When Not Provided For Elsewhere, Coating Or Forming Of Object The Patent Description & Claims data below is from USPTO Patent Application 20060037861. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention is related to an electrodeposition process having improved uniformity of coating and providing improved adhesion and lubricity, in addition to further improved properties. More specifically, the present invention is related to a process for the electrodeposition of an electrodeposition species onto a substrate wherein an electrical current of high voltage is applied to the substrate that has been previously coated with a liquid coating composition leading to a flash electrodeposition coating that is uniform and complete along the surface of the substrate. BACKGROUND [0002] Electrodeposition is a well-known process of producing a coating on a surface through use of an electric current. Over recent decades, electrodeposition has evolved from somewhat of an art to an exact science. Not surprisingly, the number and types of applications of this practice are continually increasing. For example, electrodeposition is widely used in the electronics industry, including printed wiring and circuit boards, sensors, optics, electrolytic foil, silicon wafer plating, and other areas of micro and macro electronics. Additionally, electrodeposition is used in the manufacture of materials for everyday use, such as jewelry, furniture fittings, utensils, decorative pieces, and the like. [0003] In addition to the above uses, a number of key industries, such as the automobile and aerospace industries, rely heavily on electrodeposition processes, even where other methods, such as evaporation, sputtering, and chemical vapor deposition (CVD), are options. For example, in the automobile industry, metal parts to be exposed to the environment are commonly coated with a thin layer of chromium through an electrodeposition process (i.e. chrome plated) to enhance corrosion resistance. Such industries rely on electrodeposition processes in part because they are both economical and convenient. Accordingly, economy and convenience surrounding an electrodeposition process are of great concern in the electrodeposition industry. [0004] Of at least equally great concern, however, is the ability to provide a high quality coating that is durable and that will improve substrate qualities. It is a generally held standard in the electrodeposition industry that surface preparation is important to providing a quality electrodeposition coating. Under known electrodeposition processes, surface pretreatment by chemical and/or mechanical means is required prior to the actual electrodeposition coating. One preparation method is surface cleaning, wherein various agents, such as solvents, alkaline cleaners, acid cleaners, abrasives, and water, are used to remove all contaminants from the surface of the electrodeposition substrate. Alternately, or in addition to the above, surface modification is also employed. Such surface modification includes various methods leading to changes in surface attributes, such as application of metal coatings or hardening of the surface. [0005] The generally held importance of surface preparation prior to electrodeposition is clearly stated in the Electrochemistry Encyclopedia provided by the Yeager Center for Electrochemical Sciences available online at http://electrochem.cwru.edu/ed/encycl/. According to the encyclopedia, the success of electroplating depends on removing contaminants and films from the substrate. This is stated to arise from the interference of organic and nonmetallic films with bonding by causing poor adhesion and even preventing deposition. Surface preparation also extends, however, to surface smoothing. Imperfections in the surface to be coated are problematic using standard electrodeposition methods because of the problems of buildup and incomplete coating. If the imperfection is a raised imperfection, excess coating can be applied at the raised area further exaggerating the imperfection. Conversely, if the imperfection is a pitted or depressed imperfection, the electrodeposition coating can fail to coat into the pit or depression causing an incomplete coating. [0006] Simply stated, the accepted wisdom in the industry is that a substrate for electrodeposition coating must be perfectly clean and free from any kind of contaminant and must be as uniform and free from surface imperfections as possible prior to electrodeposition. [0007] This perceived necessity has lead to electrodeposition processes that are cumbersome at best requiring multiple steps that are costly, time consuming, and produce unnecessary exposure of the worker to multiple chemical compositions. For example, a standard electrodeposition process for plating a metal substrate to provide corrosion resistance might be expected to involve the following steps: [0008] 1. Chemical cleaning (such as with alkaline solution) of the metal substrate to remove oils, greases, and other contaminants; [0009] 2. Polishing and buffing of the substrate to remove parting lines, smooth the surface, and otherwise remove surface imperfections; [0010] 3. Applying a copper strike plating layer to improve plating adhesion and protect against corrosion from subsequent plating operations; [0011] 4. Applying a bright acid copper plating layer to provide leveling and good thermal cycling; [0012] 5. Applying a bright nickel plating layer to provide corrosion resistance and provide a highly reflective finish; [0013] 6. Applying a satin steel plating layer to provide a less reflective satin appearance; and [0014] 7. Applying the final chromium plating layer to protect the nickel layer against corrosion and provide a clean final finish. [0015] A similar process for electroplating aluminum parts is provided in U.S. Pat. No. 6,692,630, which is directed to a pretreatment process for electroplating aluminum parts or strip. The process is described as including the following steps: [0016] 1. Clean using any standard aluminum cleaner, such as alkaline cleaner, to obtain a consistent and uniform deposit by producing a clean active surface; [0017] 2. Rinse in deionized water; [0018] 3. Rinse a second time in deionized water; [0019] 4. Acid wash (e.g. with 50% nitric acid) to de-smut (i.e. remove excess grime from the surface); [0020] 5. Apply a first zinc-nickel-copper (zincate) coating; [0021] 6. Rinse in deionized water; [0022] 7. Rinse a second time in deionized water; [0023] 8. Remove first zincate coating using room temperature nitric acid; [0024] 9. Rinse in deionized water; [0025] 10. Rinse a second time in deionized water; [0026] 11. Apply second zincate coating; [0027] 12. Rinse in deionized water; [0028] 13. Rinse a second time in deionized water; [0029] 14. Perform a thin strike of a metal, such as copper or nickel; and [0030] 15. Plate with one or more layers of final desired metal. In addition to the above process, the patent further includes a figure depicting a flow chart for an additional process including 18 steps related to electrodeposition. [0031] Processes, such as those described above, requiring multiple steps are neither efficient nor cost effective. Additionally, they can actually be detrimental to the electrodeposition substrate both in terms of physical integrity and in acceptability for the intended end use. For example, a part to be electroplated can be made to exacting measurements, and the initial manufacturing process requires consideration of each of the preparation layers that are applied prior to the application of the actual desired coating. As another example, each layer that is electrodeposited increases the overall mass of the substrate. In a large part, the additional preparation coatings can make a part prohibitively heavy for the intended use. [0032] These multi-step processes involving the application of multiple plating layers, in addition to the desired final layer, are further detrimental in the unnecessary application of excess stress to the electrodeposition substrate. One type of stress is hydrogen embrittlement, which involves the ingress of hydrogen into a component. This ingress of hydrogen can seriously reduce the ductility and load-bearing capacity of a material and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. It is commonly known that electroplating (along with other manufacturing processes, such as welding, electroplating, and pickling) facilitates the entry of hydrogen into a material. If a material that is susceptible to hydrogen embrittlement is the substrate used in an electrodeposition process, it is often recommended that a final, baking heat treatment be included to expel the hydrogen. This further increases the cost of the electrodeposition process and increases the required electrodeposition time. [0033] Standard electroplating processes are further limited in their ability to form a uniform coating. This is due in part to a limited ability to maximize throwing power without damaging the substrate. Throwing power is understood in the art to be a qualitative term used to describe the ability of an electrodeposition system to produce a uniformly thick deposit on the substrate surface. Throwing power is considered to be good when the current distribution is uniform, even on an irregularly shaped substrate. Throwing power of the system is a limiting factor in coating uniformity, and many efforts have been made to increase the throwing power of an electrodeposition system. Even in standard electrodeposition systems with good throwing power, though, substrates that are irregularly shaped, have sharp edges, or have surface imperfections often get non-uniform coatings, and sometimes get incomplete coatings. It is commonly understood in the electrodeposition industry that in order to get a desired coating thickness on all parts of a substrate, some parts of the substrate will have a thickness that is as much as 50% greater than the desired thickness. This once again leads to additional process steps in grinding the part to a uniform thickness. [0034] All of the above limitations in the standard electrodeposition methods presently known in the industry lead to the production of electroplated parts of insufficient quality. The electrodeposition process itself is intended to produce parts having improved properties, but the inherent problems described above underscore the insufficiency of the presently known methods. [0035] One example of such insufficiency is in the area of corrosion prevention. As noted above, one major use of electrodeposition is as a corrosion preventative. Corrosion is a serious problem that not only affects and undermines endurance of the industrial world, but all aspects of the quality of everyday life. The usable lifetime of many products and structures is defined not by the inherent properties of the materials used but by the duration of time for which corrosion can be inhibited. Incomplete electrodeposition, such as in the failure to coat in a pit or other depression in the surface of the substrate, provides an open area of attack for corrosion. Therefore, a part that is supposed to be protected from corrosion by application of an electrodeposition coating has one or more weak spots where corrosion can undermine the protective effect. Accordingly, there is a need in the field for an electrodeposition process that can provide a generally complete coating across the surface of a substrate, even coating down into surface imperfections, such as pits or other depressions. [0036] Lubricity is another property desired in many industrial parts that is limited by the current electrodeposition methods. Moveable parts, such as hydraulic parts, aircraft and automobile engine parts, and other types of machinery parts, generally require some type of lubricating fluid to facilitate smooth movement of the parts and to avoid seizure upon heating. Lubricity is a quantitative term generally used to describe the ability of a fluid to affect friction between surfaces that are in relative motion, but the term can also refer to the inherent ability of the parts themselves to interact with the friction affecting fluid. Current electrodeposition processes inherently produce coated parts that exhibit poor lubricity. [0037] As previously noted, the current practice in the electrodeposition field is to prepare a substrate for electrodeposition by smoothing the surface to remove all imperfections. This is required in the current methods in order to ensure complete and uniform coverage. For example, U.S. Pat. No. 5,543,084 teaches the use of a base coat for serving a metal-filling function to cover the roughness of a steel surface and to mask the imperfections from the pressing and assembly operations. Electroplated parts produced with such methods have a final surface coating that is extremely smooth. While it is somewhat counterintuitive, such parts exhibit poor lubricity because they lack the ability to retain the lubricating fluid on the surface for a sufficient time period to allow the fluid to affect friction. Parts having a surface that is somewhat textured, i.e. having areas for retaining lubricating fluids on the surface, have a greater inherent lubricity. Complete coating of such textured parts is not possible with current electrodeposition methods because the texturing of the surface leads to incomplete coating or non-uniform coatings. Accordingly, it would be useful to have an electrodeposition process enabling complete, uniform coating of substrates having substantially rough surfaces. Further, it would be useful to have an electrodeposition process enabling etching of an otherwise smooth electrodeposition coating. Such a process would allow for the production of coated parts having improved lubricity. [0038] Similarly, current electrodeposition processes produce coated parts with low adhesive qualities. It is often useful to apply further coatings, such as paint, to a substrate having an electrodeposition coating already applied. Under current electrodeposition processes, though, as noted above, the coated parts are extremely smooth. Accordingly, the additional coating to be applied, such as paint, is unable to sufficiently adhere to the electrodeposition coating. Therefore, it is necessary to further process the part, such as chemically treating the part to partially remove the electrodeposition coating or mechanically treating the part, such as sanding, to rough the surface sufficiently to allow adhesion of the additional coating. Accordingly, it would be useful to have an electrodeposition process enabling preparation of coated parts having improved adhesion, i.e., being immediately ready for accepting further coatings, such as paint. [0039] The foregoing illustrates but a few of the shortcomings of the presently known electrodeposition methods. There currently exists a need in the field of electrodeposition for a process that improves not only corrosion resistance, lubricity, and adhesion, but also is capable of improving surface hardness, uniformity of coating, and durability. These needs are met by the process of the current invention. SUMMARY OF THE INVENTION [0040] The present invention provides an electrodeposition process allowing for application of electrodeposition coatings that are uniform and complete. The electrodeposition coating can be applied rapidly as an initial, ultra-thin coating, and coating thickness can be customized based upon individual requirements. The electrodeposition process eliminates multiple substrate surface preparation steps, thereby reducing time and cost. The process of the present invention combines attributes of nickel, electroless nickel, hard chrome plating, and anodizing all into one coating. [0041] According to one aspect of the present invention, there is provided an electrodeposition process comprising the steps of coating a substrate with a liquid coating composition, immersing the coated substrate in a bath comprising a material for electrodeposition, and applying for a period of time an electrical current to form an initial electrodeposition coating on the substrate. Preferentially, the voltage of the electrical current is substantially greater than generally used in currently known electroplating methods. [0042] In one embodiment of the present invention, the electrodeposition process further comprises reducing the voltage of the electrical current and applying the electrical current for a second period of time to form a final electrodeposition coating of a desired thickness. The voltage of the electrical current can be adjusted during the second period of time. During such adjustment, the voltage can be further reduced, or increased, or both reduced and increased. This allows for customization of the electrodeposition coating. [0043] The present invention also encompasses further embodiments of the above described process. In one embodiment, at least a portion of the surface of the substrate is roughed prior to the step of coating the substrate with the liquid coating composition. In another embodiment, an electrical current is applied to the substrate prior to the step of immersing the substrate in the bath. In yet another embodiment, an electrical current is applied to the bath prior to the step of immersing the substrate in the bath. In still another embodiment, the liquid coating can be cured prior to the step of immersing the coated substrate in the bath. Continue reading... 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