Electrodeposition process

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.

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Description
FIELD OF THE INVENTION

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

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.

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.

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.

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.

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.

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:

    • 1. Chemical cleaning (such as with alkaline solution) of the metal substrate to remove oils, greases, and other contaminants;
    • 2. Polishing and buffing of the substrate to remove parting lines, smooth the surface, and otherwise remove surface imperfections;
    • 3. Applying a copper strike plating layer to improve plating adhesion and protect against corrosion from subsequent plating operations;
    • 4. Applying a bright acid copper plating layer to provide leveling and good thermal cycling;
    • 5. Applying a bright nickel plating layer to provide corrosion resistance and provide a highly reflective finish;
    • 6. Applying a satin steel plating layer to provide a less reflective satin appearance; and
    • 7. Applying the final chromium plating layer to protect the nickel layer against corrosion and provide a clean final finish.

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:

    • 1. Clean using any standard aluminum cleaner, such as alkaline cleaner, to obtain a consistent and uniform deposit by producing a clean active surface;
    • 2. Rinse in deionized water;
    • 3. Rinse a second time in deionized water;
    • 4. Acid wash (e.g. with 50% nitric acid) to de-smut (i.e. remove excess grime from the surface);
    • 5. Apply a first zinc-nickel-copper (zincate) coating;
    • 6. Rinse in deionized water;
    • 7. Rinse a second time in deionized water;
    • 8. Remove first zincate coating using room temperature nitric acid;
    • 9. Rinse in deionized water;
    • 10. Rinse a second time in deionized water;
    • 11. Apply second zincate coating;
    • 12. Rinse in deionized water;
    • 13. Rinse a second time in deionized water;
    • 14. Perform a thin strike of a metal, such as copper or nickel; and
    • 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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

The liquid coating composition, according to the present invention, comprises a material selected from the group consisting of polymeric materials, polar liquids, non-polar liquids, surface tension-modifying compounds, antioxidants, organic liquids, petroleum-based substances, waxes, buffering materials, particulate suspensions, colloidal materials, resins, and mixtures thereof.

In one particular embodiment of the present invention, the liquid coating composition comprises a lower alkyl carboxylic acid moiety. The lower alkyl carboxylic acid moiety can, in particular, be derived from a C1 to C6 carboxylic acid, salt, or derivative thereof. Preferentially, the lower alkyl carboxylic acid moiety is derived from a C1 to C6 carboxylate. In a particularly preferred embodiment, the lower alkyl carboxylic acid moiety is derived from sodium propionate.

Where the liquid coating composition comprises a lower alkyl carboxylic acid moiety, the liquid coating composition can further comprise at least one additional moiety. Preferentially, the at least one additional moiety is selected from the group consisting of a 2,4-trans, trans-hexanienoic moiety, a benzoic moiety, a phosphate moiety, a citrate moiety, acids and salts thereof, and mixtures thereof.

Various materials can be used as the electrodeposition material according to the present invention. In one embodiment, the electrodeposition material comprises a metal, preferentially a transition metal. In another embodiment of the invention, the electrodeposition material comprises a conductive polymer or other materials known as organic metals or synthetic metals.

The electrodeposition process of the present invention further allows for improving electrodeposition coating properties through adjusting the composition of the electrodeposition bath. Accordingly, in addition to the electrodeposition material, the bath can further comprise one or more additives. Preferably, the one or more additives are selected from the group consisting of anticorrosive agents, brighteners, wetting agents, adhesion improvers, and pH buffers.

Various electrodeposition substrates can also be used according to the present invention. In one embodiment of the invention, the electrodeposition substrate comprises a metal. Additional conductive materials can also be used as the electrodeposition substrate. In one embodiment, the electrodeposition substrate comprises a conductive polymer or other materials known as organic metals or synthetic metals.

According to another aspect of the present invention, there is provided an electrodeposition process for preparing a coated substrate wherein the coating is etched to provide a textured surface. According to this aspect of the invention, the electrodeposition process comprises the following steps: coating a substrate with a liquid coating composition; immersing the coated substrate in a bath comprising a material for electrodeposition; applying for a first period of time an electrical current of specified voltage having a beginning polarity to form an initial electrodeposition coating on the substrate; reducing the voltage of the electrical current; applying an electrical current for a second period of time to form a final electrodeposition coating of a desired thickness; and etching the final electrodeposition coating.

In one embodiment of the present invention according to this aspect of the invention, the etching step comprises applying an electrical current that is the reverse of the beginning polarity followed by applying an electrical current of the beginning polarity. Preferentially, the electrical current of reverse polarity and the electrical current of beginning polarity are each applied for a period of time of about 0.1 seconds to about 1 minute.

In a preferred embodiment according to the present invention, the step of applying the current of beginning polarity is repeated at least once. In another embodiment, both the step of applying the electrical current of reverse polarity and the step of applying the electrical current of beginning polarity are each repeated at least once.

According to another aspect of the present invention, there is provided a process for improving lubricity of a substrate. The method according to this aspect of the present invention comprises applying an electrodeposition layer to the substrate and etching the electrodeposition layer.

According to yet another aspect of the present invention, there is provided a process for improving adhesion on a substrate. The method according to this aspect of the present invention comprises applying an electrodeposition layer to the substrate and etching the electrodeposition layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a microscopic cross-sectional view at 1000× magnification of an aluminum plate that has been coated with the electrodeposition process according to an embodiment of the present invention, the cross-section being taken at the center of the plate;

FIG. 2 provides a microscopic cross-sectional view at 1000× magnification of the same sample shown in FIG. 1, the cross-section of the present figure being taken at the edge of the plate;

FIG. 3 provides a microscopic cross-sectional view at 500× magnification of an aluminum substrate that has been coated with the electrodeposition process according to an embodiment of the present invention;

FIG. 4 provides a microscopic cross-sectional view at 1000× magnification of the same sample illustrated in FIG. 3;

FIG. 5 provides a microscopic cross-sectional view at 500× magnification of an aluminum substrate that has been coated with the electrodeposition process according to an embodiment of the present invention;

FIG. 6 provides a microscopic cross-sectional view at 1000× magnification of an aluminum plate that has been coated with the electrodeposition process according to an embodiment of the present invention, the cross-section being taken at the center of the plate;

FIG. 7 provides a 250× magnification surface view taken with a scanning electron microscope of the sample from FIG. 6, the surface view being taken at the center of the plate;

FIG. 8 provides a 250× magnification surface view taken with a scanning electron microscope of an electrodeposition coating applied with the electrodeposition process according to an embodiment of the present invention; and

FIG. 9 provides a 250× magnification surface view taken with a scanning electron microscope of an electrodeposition coating applied with the electrodeposition process according to an embodiment of the present invention including application of an etch.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

The present invention is directed to a process for the electrodeposition of a coating onto a substrate. The term electrodeposition as used herein is intended to refer to the process of producing a coating, usually (but not necessarily) metallic, on a surface by the action of an electric current. The term electrodeposition is commonly used interchangeably with the term electroplating. As used herein, the term electrodeposition is intended to be used in its broadest sense, encompassing the term electroplating.

As noted above, the electroplating methods currently known in the art are plagued by multiple drawbacks. Such known methods require chemical and/or mechanical pretreatment of the substrate to be electroplated to ensure the substrate surface is smooth and free from contaminants. The electroplating processes themselves are often laborious, requiring multiple cleaning, washing, and plating steps to apply undercoats for imparting particular properties. The known processes further suffer from an inability to provide a uniform, complete coating. These problems, however, are solved by the electrodeposition process of the present invention, which combines the previously unrecognized steps of coating the substrate with a liquid coating and applying an electrical current at relatively high voltage for a short period to time to form a “flash” electrodeposition coating on the substrate that is complete and uniform across the surface of the substrate. In addition, the electrodeposition process of the present invention can also utilize the practice of “entering the tank hot,” also known as “live entry.” This practice is generally understood to mean placing the electrodeposition substrate into the electrodeposition bath (i.e. the tank) with an electrical current already applied, either to the substrate, the bath, or both. As such, the electrodeposition apparatus already has an applied current (i.e. is “hot”) prior to introducing the substrate into the bath with the material for electrodeposition. This process of entering the tank hot is an alternative to the standard process of immersing the substrate into the bath and then applying the current. The combination of process steps described above provides an increased throwing power that has been heretofore unseen in the electrodeposition industry. Accordingly, the process is surprisingly effective at providing a complete, uniform electrodeposition coating in a short period of time without extensive substrate pretreatment.

The electrodeposition process according to the present invention generally comprises 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 electrodeposition coating on the substrate.

The process of the present invention is characterized by the application of a liquid coating composition to the substrate prior to immersing the substrate in the electrodeposition bath. This is a novel process step leading to surprising results, particularly in light of the present wisdom relating to surface preparation in the field of electrodeposition. Along this line, it has been stated that one can make a poor coating perform with excellent pretreatment, but one cannot make an excellent coating perform with poor pretreatment. This statement is supported by U.S. Pat. No. 6,692,630, which teaches that a part for electrodeposition should have a clean surface (i.e. free from any dirt, grease, or oil) in order to obtain a consistent and uniform deposit. The process of the present invention is completely adverse to the previous teaching in the art, actually introducing a component that, according to the known plating methods, would be considered a contaminant.

While not wishing to be bound by theory, it is believed that the liquid coating composition used according to the present invention improves the electrodeposition process by reducing surface tension at the interface between the electrodeposition substrate and the electrodeposition bath. This reduction in the surface tension increases and equalizes conductivity at the interface facilitating even dispersal of charge and uniform, complete coating of the substrate with the electrodeposition material. The liquid coating, in addition to the believed mode of activity described above, allows for the application of electrical currents of high voltage that would conventionally be expected to partially or totally damage the substrate.

The liquid coating composition further improves the electrodeposition process by altering the texture of the surface of the substrate being coated. This mechanical effect provides a smoothing advantage reducing the friction on the substrate surface and effectively evening the textured surface to allow better flow of the electrodeposition coating. In other words, the liquid coating composition can be characterized as acting as a guide for the application of the electrodeposition material. All of the above act together to improve the throwing power of the system and provide a complete, even electrodeposition coating on the substrate.

The application of the liquid coating can be by any method generally known in the art. In particular, the liquid coating can be applied by dipping the substrate in the coating liquid. Alternately, the liquid coating can be applied by spraying, brushing, rolling, or any other method that would be readily obvious to one of ordinary skill in the art.

The liquid coating composition used according to the present invention can include any liquid material that will not substantially interfere with the conductivity of the electrical current around the electrodeposition substrate. Preferentially, the liquid coating composition is a substance selected from the group consisting of polymeric materials, polar liquids, non-polar liquids, surface tension-modifying compounds, antioxidants, organic liquids, petroleum-based substances, waxes, buffering materials, particulate suspensions, colloidal materials, resins, and mixtures thereof.

According to one preferred embodiment of the present invention, the liquid coating composition comprises an anticorrosive agent. Particularly preferred anticorrosive agents are lower alkyl carboxylic acids and salts or other derivatives thereof as disclosed in co-pending U.S. patent application Ser. No. 10/606,946, which is incorporated herein by reference in its entirety. These preferred anticorrosive agents structurally conserve or embody a lower alkyl carboxylic acid moiety that can be represented as R—COO−, in which R is hydrogen or C1-C6 alkyl.

The lower alkyl carboxylic acid moiety can be derived from a C1-C6 carboxylic acid, or from a salt or other derivative thereof. Exemplary lower alkyl carboxylic acids useful in liquid coating composition in the present invention include without limitation formic acid, acetic acid, propionic acid, butyric acid, 2-methyl propionic acid, and the like, as well as mixtures thereof. Exemplary lower alkyl carboxylate salts useful in the liquid coating composition in the present invention include without limitation formate, acetate, propionate, butyrate, and 2-methyl propionate, as well as mixtures thereof. Mixtures of one or more lower alkyl carboxylic acids with one or more salts and/or other derivatives thereof may also be useful in the liquid coating composition in the present invention.

When present as a salt, the cation of the lower alkyl carboxylate salt may be selected from a wide variety of mono- and di-valent cations. Advantageously, the cation is selected from alkali metal or alkaline earth metal cations. A particularly advantageous cation for use in the liquid coating composition of the present invention is sodium.

In embodiments wherein the liquid coating composition comprises an anticorrosive agent such as described above, the liquid coating composition can further comprise other compounds, including other anticorrosive agents known in the art. Particularly useful additional agents include compounds that conserve or embody a 2,4-trans, trans-hexadiene moiety in their molecular structure. Such compounds include 2,4-trans, trans-hexadienoic acid and alkali salts and/or other derivatives thereof, such as the alkali salt potassium sorbate.

Other compounds useful in combination with the anticorrosive agents described above include acids and/or salts or other derivatives thereof that are capable of increasing the solubility of the anticorrosive agent in water. One non-limiting example of such a compound is benzoic acid and its alkali salts and/or other derivatives thereof. Particularly useful are alkali salts of benzoic acid, such as sodium benzoate. Additional non-limiting examples of compounds useful in combination with the anticorrosive agents described above include compounds comprising a phosphate moiety or citrate moiety, acids and salts thereof, and mixtures thereof.

According to another preferred embodiment, the liquid coating composition as used according to the electrodeposition process of the present invention comprises at least one polymeric material. The polymeric materials used in the liquid coating composition can be either natural or synthetic. Further, it is not necessary that the polymeric material be generally found in a liquid state so long as the polymeric material is capable of being in a liquid form. For example, the liquid coating composition according to the present invention can comprise as solution comprising at least one polymeric material that has been solubilized in a suitable solvent.

Particularly preferred according to the present invention are polymeric materials having incorporated therein an ionic component. Such polymeric materials can have a net positive charge or a net negative charge, and can be referred to as polyelectrolytes.

The liquid coating composition according to the present invention can also include materials that are solid at room temperature but capable of easy transition to a liquid state. A particularly preferred group of materials for use as the liquid coating composition is polyethylene glycol materials. One example of polyethylene glycols useful in the present invention are those sold under the tradename Carbowax™. Carbowax 8000, for example, has an average molecular weight of about 8000 and a melting point of about 60° C. Such products can by used by transitioning the material from a solid to a liquid state and using the material in its liquid state as the liquid coating composition according to the process of the present invention. Once the electrodeposition substrate has been coated with the liquid coating composition, the substrate can be immediately immersed in the electrodeposition bath according to the remaining process steps, or the material used as the liquid coating composition can be allowed to transition back to its solid state. Such materials can also be used in admixture with other coating materials, including materials that are generally liquid at room temperature.

According to a particularly preferred embodiment of the present invention, the liquid coating composition comprises an electrically conductive material. Preferentially, the electrically conductive material is an aqueous material. While it is not necessary that the liquid coating composition be electrically conductive, the incorporation of electrically conductive materials is particularly useful for improving the flow of the electrodeposition coating material, particularly on highly textured surfaces. The electrically conductive material can include materials, particularly aqueous materials, incorporating an ionic component. Accordingly, in one preferred embodiment, the electrically conductive material is a conductive salt. In another preferred embodiment, the electrically conductive material is a salt of a polymeric material. Preferentially, the electrically conductive material is charged, with preference being for positively charged materials.

In a further embodiment according to the present invention, the liquid coating composition is applied to the electrodeposition substrate, and the liquid coating is allowed to cure prior to proceeding with the remaining steps of the electrodeposition process. The term cure is generally intended in include any active or passive process whereby the coating is altered, by chemical or physical means, for keeping or use. Accordingly, curing could encompass allowing a room temperature solid material that has been transitioned into a liquid state to transition back into a solid state after application to the electrodeposition substrate. Curing could further encompass the situation where a liquid coating comprising a solubilized material is processed such that the solvent is evaporated leaving a coating of the solubilized material. Curing could also encompass the situation where the liquid coating material comprises a material capable of forming a “skin” or substantially solid surface layer while remaining substantially liquid underneath the skin and the formation of such a skin is allowed or facilitated. Curing could also encompass the situation where one or more polymeric materials are used and allowed to crosslink, with or without the use of separate crosslinking agents. Other examples of curing would be readily recognized by one of skill in the art and likewise are encompassed by the present invention.

The liquid coating composition can be applied as a single coating layer or as multiple coating layers. In one embodiment of the invention, a liquid coating composition is applied and allowed to cure, and at least one additional liquid coating composition is applied over the cured liquid coating composition. Other methods for applying multiple layers of at least one liquid coating composition would by known by one of skill in the art and are also encompassed by the present invention.

In one embodiment of the present invention, the liquid coating material is incorporated into the electrodeposition bath. According to this embodiment of the invention, the liquid coating composition can be applied to the electrodeposition substrate separately and comprise at least a portion of the electrodeposition bath or can be present in the process solely as part of the electrodeposition bath.

The electrodeposition bath as used in the process of the present invention can be comprised of bath materials as generally known to one of skill in the art. Minimally, the bath as used in the present invention should comprise at least one material for electrodeposition. As noted above, the electrodeposition bath can further comprise at least one material also useful as the liquid coating composition of the present invention. The bath can further comprise additional agents commonly used in electrodeposition process, such as anticorrosive agents, brighteners, wetting agents, adhesion improvers, pH buffers, and the like.

The present invention is further characterized in that the materials commonly incorporated into the electrodeposition bath can be incorporated into the liquid coating composition. According to known plating methods, it is common to prepare complicated bath mixtures comprising multiple property enhancing agents for a desired plating process, and then adjust the bath mixture, or prepare a completely new bath mixture, having different property enhancing agents for a different desired plating process. According to the present invention, however, it is possible to prepare a single, standard bath that can be used in multiple plating processes since the property enhancing agents are used in the liquid coating composition rather than the electrodeposition bath. In other words, the process of the present invention allows for incorporating the specialized characteristics of the electrodeposition bath into the liquid coating composition, which is more easily adjusted than the electrodeposition bath.

In addition to the above, the electrodeposition process of the present invention is characterized by the ability to incorporate desirable properties into the final part comprising the electrodeposition coating. Accordingly, it is possible to use liquid coating compositions having particularly preferred properties and incorporate those properties into the electrodeposition coating applied with the process of the present invention. As already noted, the liquid coating composition can be an anticorrosive agent. When such an agent is used, the final part having the electrodeposition coating applied over the anticorrosive liquid coating composition is particularly imparted with improved anticorrosive attributes. A similar effect can be achieved through the use of other materials as the liquid coating composition. Accordingly, the electrodeposition process of the present invention particularly encompasses processes for improving specific desirable product qualities, such as anticorrosiveness, adhesion, lubricity, and the like.

The present invention also encompasses adding further properties to the electrodeposition coated substrate that are not readily envisioned by one of skill in the art. For example, with the process of the present invention, it is possible to incorporate polymeric-type properties into the electrodeposition coating that have heretofore been unknown in the art. This is achievable through use of polymeric materials as the liquid coating composition. The polymeric material is thus at least partially incorporated into the electrodeposition coating providing a coating having the properties of known electroplating methods, but also having at least some of the properties of the liquid coating composition. Therefore, using the electrodeposition process of the present invention it is possible to provide coatings having properties heretofore unknown in the art.

The use of multiple layers of at least one liquid coating composition allows for further customization of the properties and characteristics of the final part with the electrodeposition coating of the process of the present invention. Different liquid coating compositions with different desirable properties could be used as multiple layers to impart beneficial characteristics to the electrodeposition coated substrate. Additionally, the combination of different liquid coating compositions could encompass a synergistic effect providing properties and characteristics that are improved even over the individual characteristics provided by the individual liquid coating compositions.

The present invention also encompasses other types and modes of treatment of the electrodeposition substrate prior to coating the substrate with the liquid coating composition. For example, the substrate could be treated to texture the part for improved lubricity prior to coating with the liquid coating composition. Such treatment could encompass generally roughing the surface of the substrate, such as with sandpaper. However, such treatment could also include other texturing process such as could impart a specifically patterned texture to the surface of the substrate. Accordingly, if it was known to be useful to have a surface with a specific series of pores or ridges or other types of texturing, such a texture could be imparted and then an electrodeposition coating applied according to the electrodeposition process of the present invention. Other methods for improving the qualities and characteristics of the finished part with the electrodeposition coating are also encompassed by the present invention.

As previously noted, the electrodeposition bath comprises at least one material for electrodeposition. The material for electrodeposition can comprise any such material that is generally known in the field of electrodeposition. Preferentially, the material for electrodeposition comprises at least one metal. More preferentially, the material for electrodeposition comprises a transition metal. The electrodeposition process of the present invention is particularly useful in the electrodeposition of metals including, but not limited to, titanium, vanadium chromium, manganese, cobalt, nickel, copper, zinc, zirconium, ruthenium, rhodium, palladium, silver, platinum, and gold.

The material for electrodeposition in the process of the present invention can further comprise conductive polymers and like materials commonly referred to as organic metals or synthetic metals. The conductive polymers used according to the present invention include intrinsically conductive polymers as well as polymers that have been chemically or physically modified to be conductive. Polymers that have been modified to be conductive include polymers that include filler materials, such as carbon particles or metallic fibers.

Intrinsically conductive polymers, or organic metals, are materials that are polymeric in nature (i.e. are organic compounds comprising chains of repeating units) yet exhibit semi-metallic properties and pure metallic properties. Intrinsically conductive polymers are also referred to as conjugated polymers due to the polymer backbone generally comprising a conjugated bond system (e.g. aromatic or heteroaromatic rings, alternating double bonds, or triple bonds). Such polymers combine the electrical properties of a conventional semiconductor like silicon with the processing properties of conventional polymers and coatings.

An overview of intrinsically conductive polymers generally useful as the material for electrodeposition according to the present invention is provided in Synthetic Metals, volumes 17-19 (1987) and volumes 84-86 (1997), which is incorporated herein by reference. Specific non-limiting examples of intrinsically conductive polymers useful as the material for electrodeposition according to the present invention include polyaniline (PAni), polydiacetylene, polyacetylene (PAc), Polypyrrole (PPy), polythiophene (PTh), polyalkylthiophene, polyisothianaphthene (PITN), polyphenylenevinylene, polyheteroarylenevinylene (PArV) (wherein the heteroarylene group can be, for example, thiophene, furan, or pyrrole), poly-p-phenylene (PpP), polyphenylene sulfide (PPS), polyperinaphthalene (PPN), polyindole, polyquinoline, poly-3-thienylethylacetate, and derivatives thereof, copolymers thereof with other monomers, and physical mixtures thereof.

Intrinsically conductive polymers can exist in various states described by different empirical formulae and can be converted into one another, usually substantially reversibly, by (electro)chemical reactions, such as oxidation, reduction, acid/base reactions, or complex formation. These reactions can also be described as “doping” or “compensation”. For example, polyaniline can exist in a reduced state (leucoemaraldine), a partially oxidized state (emeraldine), and a fully oxidized state (pernigraniline), but it is most conductive in its emeraldine form. This state can be achieved by doping the polyaniline with any suitable organic acid to form the salt of the intrinsically conductive polymer.

The electrodeposition process of the present invention is suited for applying an electrodeposition coating to any type of substrate that is generally accepted as being amenable to electrodeposition coating. The process can be used for coating electrically conductive materials, such as metals and conductive polymers. Further, the process can be used for coating non-conductive materials. In one embodiment of the invention, the substrate comprises a non-conductive material and the liquid coating composition comprises an electrically conductive material.

The process of the present invention is particularly useful for coating parts used in high performance applications, such as machining applications, automobile applications, and aerospace applications. The process is further particularly useful for coating lightweight materials requiring an ultra-thin, yet complete and durable coating so as to provide protection without appreciably increasing the overall weight of the part.

The electrodeposition process of the present invention generally comprises 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 having a specified voltage to form an electrodeposition coating on the substrate. According to one embodiment of the present invention, the substrate coated with the liquid coating composition is immersed in the bath prior to application of the electrical current. In this embodiment, the electrical current is generally applied immediately upon immersion into the bath of the substrate coated with the liquid coating composition. It is generally preferred that the substrate coated with the liquid coating composition not be allowed to sit for prolonged periods of time in the bath prior to the application of the electrical current as such prolonged contact with the bath could facilitate movement of the liquid coating composition away from the coated substrate. If the liquid coating composition has been allowed to cure on the substrate prior to immersion of the coated substrate into the electrodeposition bath, it may be useful to allow the substrate with the cured liquid coating composition to sit in the bath for a period of time prior to application of the electrical current to allow the cured liquid composition to at least partially transition to a liquid or uncured state.

In a particularly preferred embodiment of the electrodeposition process according to the present invention, the process further comprises live entry of the electrodeposition substrate into the electrodeposition bath. In one embodiment, live entry is achieved by applying an electrical current to the electrodeposition substrate coated with the liquid coating composition prior to immersing the coated substrate into the electrodeposition bath. In another embodiment, live entry is achieved by applying an electrical current to the electrodeposition bath prior to immersing the electrodeposition substrate coated with the liquid coating composition into the bath. Live entry is a particularly preferred aspect of the present invention as it has been found to further facilitate the rapid application of an electrodeposition coating that is complete and uniform. The use of live entry to facilitate an improved electrodeposition coating represents yet another aspect of the present invention that is surprising in view of the known art. For example, U.S. Pat. No. 6,692,630 specifically states live entry is an electrodeposition process step that should be avoided.

The electrical current applied according to the process of the present invention should be of a voltage that is sufficiently high to form an electrodeposition coating on the substrate. The voltage applied can vary depending upon the nature of the electrodeposition substrate; however, it has been found that the process of the present invention is generally most effective when the voltage applied is considerably higher than the voltage that would generally be applied according to prior art methods.

An example of the ability of the process of the present invention to incorporate electrical current of a voltage generally greater than would be acceptable in currently known methods is as follows. For providing an electrodeposition coating on an aluminum plate (for example, 12 in.×12 in.×0.25 in.), currently known methods would begin with an electrical current of relatively low voltage (e.g. 0.5 V to 1 V) and slowly increase the electrical current to a maximum voltage of about 4 V to about 5 V. Currently known methods would not be expected to exceed such voltage, though, as damage to the part would be expected. According to the process of the present invention, however, the same type of aluminum plate, after being coated with a liquid coating composition according to the invention, would have applied thereto an electrical current having a beginning voltage of about 8 V to about 15 V. Such high voltage would generally be applied for only a limited time, and the voltage of the electrical current could then be reduced for continued electrodeposition. For larger parts, an electrical current of even greater voltage could be used without risk of damaging the electrodeposition substrate.

The ability to use an electrical current of increased voltage is due in part to the presence of the liquid coating composition that instantly and evenly distributes the electrical current to all parts of the substrate, as well as acting as a protective barrier between the electrodeposition bath components and the electrodeposition substrate. Such effect is noticeably not provided in the current electroplating methods, where uneven distribution of the electrical current leads to, among other disadvantages, uneven coating and increased risk of damage to the electrodeposition substrate, even with electrical current having a voltage that is considerably less than what is beneficial according to the process of the present invention.

Generally, the voltage applied according to the process of the present invention is at least 20% greater than the voltage typically applied according to prior art plating methods. Preferably, the voltage applied according to the process of the present invention is at least 50% greater than the voltage typically applied according to the prior art plating methods. Most preferably, the voltage applied according to the process of the present invention is at least 75% greater than the voltage typically applied according to the prior art plating methods.

Depending upon the nature of the electrodeposition substrate, and the electrodeposition method being used, the voltage applied according to the process of the present invention can be considerably greater than described above. For example, according to one embodiment of the invention, the electrical current could have a voltage of up to about 1000 V. Preferably, the voltage applied is up to about 700 volts. In one preferred embodiment, the applied electrical current has a voltage of about 1 mV to about 500 V.

Given the unusually high voltages used in the present invention, the electrical current applied in the electrodeposition process is preferably only applied for only a limited time period. In fact, only a limited duration of application of the current is generally necessary to impart a complete, even electrodeposition coating on the substrate. The duration of the application of the electrical current can vary depending upon the nature of the electrodeposition substrate. For example, for a relatively small substrate, particularly a substrate comprised of a material readily susceptible to damage, the electrical current could be applied for as little as about 0.1 seconds. Conversely, for a relatively large substrate, particularly a substrate comprised of a material that is not easily susceptible to damage, the electrical current could be applied for up to 3 hours.

A non-limiting example of the reduced plating time required according to the process of the present invention is as follows. As previously described, an aluminum plate having dimensions of approximately 12 in.×12 in.×0.25 in., when using currently known electroplating methods, would be plated using an electrical current of relatively low voltage applied, with the voltage of the current being slowly increased. To achieve complete coating of the substrate, the electrical current with increasing voltage would be applied, generally, for about 7 minutes to about 10 minutes. Of course, for larger parts, this time would be increased. Also as previously described, it would be expected that the coating applied with such previously known methods would be uneven, having noticeable buildup at the edges and at any non-smooth portions of the substrate surface. Also, for a highly textured substrate, it would be expected that the coating applied would not have thorough coverage in the highly textured areas. When using the process of the present invention, however, the same aluminum substrate could have an electrodeposition coating applied (after application of the liquid coating composition) by applying an electrical current of relatively high voltage (e.g. about 10 V) for about 1 minute. If desired, the electrical current could then be reduced to a lesser voltage (e.g. about 4-5 V) and the electrodeposition process continued for about 1 minute. Accordingly, the electrodeposition coating applied according to the process of the present invention, in addition to being even and complete (even in any highly textured areas), is applied in approximately one quarter to one tenth of the time normally required according to the currently known electroplating methods.

Accordingly, in one preferred embodiment, the electrical current is applied for a period of time of about 0.1 seconds to about 3 hours. Even more preferably, the electrical current is applied for a period of time of about 1 second to about 30 minutes. In one particularly preferred embodiment, the electrical current is applied for a period of time of about 5 seconds to about 2 minutes.

The electrodeposition process of the current invention is further characterized by the ability of the process to form an ultra-thin electrodeposition coating on a substrate wherein the coating is uniform across the surface of the substrate and provides complete coverage of the substrate surface. The combination of the liquid coating composition and the application of a high voltage electrical current provide a “flash” coating effect wherein the material for electrodeposition is immediately and uniformly deposited across the surface of the electrodeposition substrate.

A particularly surprising effect of the liquid coating composition according to the present invention is the ability of the liquid coating composition to remain on the coated substrate, even after being immersed in the electrodeposition bath solution. While this effect is generally observed with all materials useful as the liquid coating composition, as described herein, the effect is particularly observed when the liquid coating composition comprises an electrically conductive material, particularly when the electrically conductive carries a charge. The liquid coating composition strongly adheres to the substrate before and during introduction of the coated substrate in the electrodeposition bath solution.

Once the coated substrate is immersed in the electrodeposition bath, the liquid coating composition provides an interface zone with the electrodeposition bath solution, wherein the liquid coating composition intimately blends with the electrodeposition bath solution while remaining tightly adhered to the surface of the electrodeposition substrate. Therefore, the substrate coated with the liquid coating composition has an unobstructed electrodeposition interface with the electrodeposition bath solution at all points along the surface of the substrate. Furthermore, the liquid coating composition, being both adhered to the substrate surface and intimately blended with the electrodeposition bath solution, is effectively incorporated into the electrodeposition coating without altering the chemical makeup of the electrodeposition coating. Accordingly, the liquid coating composition acts as a guide for the electrodeposition coating, uniformly guiding the electrodeposition coating material to all point of the substrate surface, on a nano scale, providing instant application of the electrodeposition material at all areas of the substrate surface rather than a gradual movement of the electrodeposition coating from the more highly conductive areas to the less conductive areas, as would be expected according to the presently known electroplating methods. Therefore, the process of the present invention can be viewed as facilitating application of an electrodeposition coating as a nanoparticulate coating, the electrodeposition coating material being electrically deposited as nanoparticles at all points on the surface of the substrate.

The average thickness of this flash coating is controllable through variation of the applied voltage and the duration of application. A rapid, complete electrodeposition coating having an average thickness of as little as 0.1 μm can be applied using the electrodeposition process described herein. Accordingly, in one preferred embodiment of the present invention, the electrodeposition coating has a thickness of at least about 0.1 μm.

A particularly surprising aspect of the present invention is the ability to apply an electrodeposition coating having an average thickness as described above wherein the coating is uniform across the surface of the electrodeposition substrate. This aspect of the invention is illustrated in FIG. 1 and FIG. 2, which provide microscopic views at 1000× magnification of an electrodeposition coating applied to a substrate (a 12″×12″×0.25″ grade 6061 aluminum plate) according to one embodiment of the present invention. The plate had no pretreatment prior to the electrodeposition process (i.e. the plate was not chemically or mechanically treated to clean or smooth the surface). Further, the edges of the plate were also left untreated (i.e. were not chemically or mechanically smoothed or rounded).

FIG. 1 is a cross-section of the substrate coated with an electrodeposition coating according to the present invention applied thereto. The cross-section of FIG. 1 was taken at the center of the plate, and the electrodeposition coating thickness was quantitatively measured to have an average thickness of about 1.4 μm. FIG. 2 is a cross-section of the same substrate coated with the same electrodeposition coating of FIG. 1. The cross-section shown in FIG. 2 was taken at the edge of the plate, and the electrodeposition coating thickness was quantitatively measured to have an average thickness of about 1.6 μm. Accordingly, average coating thickness at the center of the plate is only approximately 0.2 μm less than the average coating thickness at the edge of the plate.

The uniformity of electrodeposition coating thickness illustrated in FIG. 1 and FIG. 2 is particularly surprising in comparison to the results that would be expected if the same coating was applied using the electroplating methods currently known in the industry. According to known methods, the substrate would generally be immersed in the electroplating bath and an electrical current applied, the voltage slowly being increased until the desired coating thickness is achieved. In such methods, it is common to have excessive buildup at the edges of the plate, as the electrical current is generally unevenly distributed across the plate, generally being greater at the edges of the plate. Further, with the edges of the plate left as sharp corners, it would generally be expected that additional buildup would occur due to the inability of the coating to “flow” over the edges. Accordingly, it would be expected that the same plate used in the process illustrated in FIG. 1 and FIG. 2, if used in a currently known plating method, would have a much greater coating thickness at the edges. For example, in order to obtain a coating thickness of about 1.4 μm at the center of the plate using currently known plating methods, the thickness at the edge of the plate would be expected to be in excess of 2 μm or greater. This non-uniformity observed in the currently known plating methods becomes even more exaggerated as the desired plating thickness increases. For example, if the desired thickness at the center of the plate was, for example, 100 μm, it would be expected that the applied thickness at the edges of the plate to achieve the desired thickness at the middle of the plate would be as much as 200 μm or greater. This problem is solved in part, however, by the electrodeposition process of the present invention, where substantial uniformity of coating thickness across the entire surface of the electrodeposition substrate is observed.

The electrodeposition process of the present invention is further characterized by its ability to apply an electrodeposition coating having complete coverage of the entire landscape of the electrodeposition substrate surface. Currently known electroplating methods are plagued by an inability to quickly and reliably cover all points on the surface of a substrate. Typically, the known methods are effective at coating completely smooth surfaces or the raised aspects of the surface; however, the known methods lack the ability to reliably provide a coating that will coat down into pitted or porous aspects of a substrate surface. These missed areas result in the presence of “holes” in the electroplated coating.

The electrodeposition process of the present invention overcomes this problem faced by the prior art electroplating methods. As previously noted, the combination of the liquid coating composition and the application of a high voltage electrical current provide a “flash” coating effect wherein the material for electrodeposition is immediately and uniformly deposited across the surface of the electrodeposition substrate. The same characteristics of the electrodeposition process of the present invention that allow for a flash coating that is uniform also facilitate complete coverage of the electrodeposition coating, even down into pits, grooves, pores, embossing, and other recessed aspects of the surface of a substrate. Accordingly, a substrate to be coated according to the electrodeposition process of the present invention does not require extensive processing to smooth the surface, removing raised portions and generally smoothing the surface to a uniform state. On the contrary, in one embodiment of the present invention the surface of a substrate is roughed prior to application of the liquid coating composition, further providing a textured surface that would generally be unacceptable for coating under known electroplating methods.

The ability to provide a complete coating using the electrodeposition process of the present invention is illustrated in FIG. 3, which shows a microscopic view at 500× magnification of a cross-section of a grade 6061 aluminum plate that has been coated with the electrodeposition process according to one embodiment of the present invention. The electrodeposition coating was quantitatively measured to have an average thickness of about 5.08 μm. As seen in FIG. 3, the surface of the substrate is relatively rough (about 110-115 micron) having multiple raised and pitted areas. The roughness of the surface of the substrate illustrates the ability of the process of the present invention for completely and evenly coating rough surfaces (e.g. about 120 micron or greater), as well as smooth surfaces (e.g. about 2 micron).

As generally understood in the art, the roughness of a surface is measured in micro inches (μin) or microns (μm). One micro inch is equal to 0.025 microns, and one micron is equal to 40 micro inches. Within this scale, every surface can have its roughness characterized by a number. Surface roughness can be measured with a surface analyzer, such as a profilometer, and readings are usually given in values of roughness average (μm Ra) or roughness Root Mean Square (μm RMS). The International Standards Organizations (ISO) has designated Ra as the correct medium for measuring the roughness of a machined surface. Roughness average is established by finding an average centerline between the valleys and the peaks of the surface, and Ra can be mathematically determined as the average height of the peaks above the centerline and the valleys below the centerline. Accordingly, an Ra of zero indicates a perfectly smooth surface having no deviation from the centerline. Increasing Ra values indicate increasingly rougher surfaces.

As further seen in FIG. 3, the electrodeposition coating is evenly and completely present at all aspects of the substrate surface, covering the raised portions and also covering the surface in the pitted areas. FIG. 4 provides a microscopic view at 1000× magnification of the same area of the same sample illustrated in FIG. 3. FIG. 4 illustrates in greater detail the complete coverage of the substrate surface.

The ability of the electrodeposition process of the present invention to provide complete coverage of relatively uneven, pitted surfaces is even further illustrated in FIG. 5, which shows a microscopic view at 1000× magnification of a cross-section of a grade 2024 aluminum plate that has been coated with the electrodeposition process according to one embodiment of the present invention. The electrodeposition coating was quantitatively measured to have an average thickness of about 12.7 μm. As seen in FIG. 5, the electrodeposition process of the present invention provides such complete coverage of the substrate surface that the coating shows full coverage even in pitted areas extending inward and downward into the substrate surface.

The ability of the electrodeposition process of the present invention to provide complete, uniform coverage of even relatively rough substrate surfaces is even more surprising considering such coverage is possible, even at extremely ultra-thin coverage rates. FIG. 6 shows a microscopic view at 1000× magnification of a cross-section of a grade 6061 aluminum plate that has been coated with the electrodeposition process according to one embodiment of the present invention, wherein the plate was “flash” coated for 15 seconds. Microscopic analysis, even at 1000× magnification, revealed no optically measurable coating at the surface of the plate, according to independent analysis at a metallurgical testing laboratory. In actuality, however, the plate has been provided with a complete, uniform electrodeposition coating of an average thickness too small to be measured through use of optical devices. Accordingly, the electrodeposition coating would be of an estimated thickness of less than about 0.5 micron. In other words, the electrodeposition coating in the cross-section shown in FIG. 6 has a thickness that is optically immeasurable.

FIG. 7 shows a surface view at 250× magnification taken with a scanning electron microscope (SEM) of the sample from FIG. 6. The SEM micrograph of FIG. 7 clearly shows that while the coating is optically immeasurable, the coating is in fact present, being SEM detectable, and evenly dispersed across the surface of the substrate.

In addition to the “flash” coating technology provided by the electrodeposition process of the present invention, the process can further comprise reducing the voltage of the applied electrical current and applying the electrical current for a second period of time to form a final electrodeposition coating of a desired thickness. As previously noted, the electrodeposition process of the present invention is characterized by the application of a relatively high voltage. This high voltage facilitates the application of the “flash” coating as described above. However, the process of the present invention further comprises reducing the voltage and continuing the electrodeposition process. This allows for the customization of the electrodeposition coating to various desired thicknesses.

The amount by which the voltage of the electrical current is reduced is dependent upon the nature of the substrate and the final desired coating thickness. According to one embodiment of the invention, the voltage of the electrical current is reduced by at least 30%. In another embodiment of the invention, the voltage of the electrical current is reduced by at least 50%. According to yet another embodiment of the invention, the voltage of the electrical current is reduced by at least 70%.

The second period of time in which the electrical current is applied can vary depending upon the nature of the substrate and the desired properties of the final part with the electrodeposition coating applied thereto. Accordingly, the second period of time can vary from 0 seconds to several days. In one embodiment of the invention, the second period of time is about 0 seconds to about 24 hours, preferably about 0 seconds to about 12 hours.

The electrodeposition process of the present invention greatly improves upon the known electroplating methods in its ability to provide ultra-thin coatings that are complete and uniform. The electrodeposition process of the present invention is further an improvement over the known electroplating methods in its ability to provide even thicker coatings that are still uniform and complete.

With the electroplating methods currently known in the art, the initial coating goes on the substrate in an uneven fashion. This can be due to standard plating occurrences, such as uneven surface texture and buildup at the edges of the substrate. Once a non-uniform coating is applied, further electroplating of the substrate magnifies and exaggerates the non-uniformity of the coating. This problem is eliminated with the electrodeposition process of the present invention.

With the electrodeposition process of the present invention, the initial “flash” coating is complete and uniform in nature. Accordingly, if the voltage of the electrical current is optionally reduced and the electrodeposition process is continued with application of an electrical current for a second period of time, the additional electrodeposition coating that is applied is also uniform in nature. Accordingly, a finished part prepared according to the electrodeposition process of the present invention generally requires no further processing, such as mechanical processing, to remove excess coating to provide a uniform average thickness, which is commonplace according to the presently known electroplating methods.

As would be immediately recognizable to one of skill in the art, additional electrodeposition steps could be useful for preparing a part having an electrodeposition coating of specific qualities and characteristics. Accordingly, the electrodeposition process of the present invention is also amenable to further electrodeposition steps as would be advantageous.

The continued application of the electrodeposition coating under the electrodeposition process of the present invention is further advantageous in that the process can further comprise adjusting the voltage of the electrical current during the second period of time in which the electrical current is applied. This is particularly advantageous in further facilitating the customization of the electrodeposition coating. Accordingly, the voltage of the electrical current can be increased, decreased, held constant, or any combination of these as would useful for customizing the overall average thickness of the electrodeposition coating.

While the electrical current used in the electrodeposition process of the present invention is generally described herein in terms of applied voltage, it would be recognizable by one of skill in the art that an electrical current as applied in the process of the present invention includes additional inherent measurable properties, such as amperage. Therefore, the process of the present invention fully encompasses the manipulation of these additional inherent properties in accordance with the disclosure provided herein. Accordingly, the present invention also encompasses electrodeposition processes of like nature wherein the process is defined in terms of said additional electrical properties.

According to another aspect of the electrodeposition process of the present invention, the electrodeposition coating can be etched to provide additional desirable properties. The etch process is generally carried out after the final desired average thickness of the electrodeposition coating has been achieved. Accordingly, the etch process steps can be applied immediately after application of the “flash” electrodeposition coating as described above. Further, the etch process steps can be applied after additional electrodeposition steps have been carried out. Accordingly, the etch process steps can be viewed as an independent process useful for imparting specific properties described more thoroughly below. Thus, in one embodiment of the invention, the etch is applied to the electrodeposition coating of a substrate that was previously coated by the methods described herein, or by other known methods in the art.

The etch process steps can also be viewed as additional process steps of the electrodeposition process described above. As such, the etch process as described herein can include each and every aspect of the electrodeposition process as previously described.

In one embodiment of this aspect, the electrodeposition process comprises the steps of: coating a substrate with a liquid coating composition; immersing the coated substrate in a bath comprising a material for electrodeposition; applying for a first period of time an electrical current having a beginning polarity and having a specified voltage to form an initial electrodeposition coating on the substrate; reducing the voltage of the electrical current; applying an electrical current for a second period of time sufficient to form a final electrodeposition coating of a desired thickness; and etching the final electrodeposition coating.

In a preferred embodiment of the present invention, the etching process comprises the steps of applying an electrical current of reverse polarity for a period of time and applying an electrical current of beginning polarity for a period of time.

According to one particularly preferred aspect of the present invention, the application of an electrical current of beginning polarity for a period of time is repeated at least once. According to this embodiment, it is preferred that the application of the electrical current be in the form of current pulses wherein the current is applied, stopped, applied again, stopped again, and so on until the desired number of pulses of electrical current of beginning polarity have been applied. In one particularly preferred embodiment, the application of an electrical current of beginning polarity for a period of time is repeated twice.

The time period for which the electrical current of reverse polarity is applied can vary depending upon the nature of the substrate and the particularly desired properties of the finished part with the etched electrodeposition coating according to the present invention. In one embodiment, the period of time for application of the electrical current of reverse polarity is about 0.1 second to about 1 minute. Such time could be increased, however, particularly for an electrodeposition substrate that is relatively large or for an electrodeposition coating that has a relatively large average thickness.

The time period for which the electrical current of beginning polarity is applied can likewise vary depending upon the nature of the substrate and the particularly desired properties of the finished part with the etched electrodeposition coating according to the present invention. In one embodiment, the period of time for application of the electrical current of beginning polarity is about 0.1 second to about 1 minute. As before, however, such time could be increased, particularly for an electrodeposition substrate that is relatively large or for an electrodeposition coating that has a relatively large average thickness.

In another embodiment of the present invention, the etching steps, as a group, are repeated at least once. In a particularly preferred embodiment, the etching steps are repeated twice.

The etching process is particularly beneficial for improving substrate characteristics, such as lubricity. As previously noted, the currently known electroplating methods require extensive processing of the substrate to smooth the surface to improve application of the coating. While such parts have a smooth finish, the surface is devoid of the ability to retain fluids. The opposite effect is achieved with the electrodeposition and etching process of the present invention.

Electrodeposition and etching according to the process of the present invention provide a finished part with an electrodeposition coating that is beneficially textured having a porous finish capable of retaining lubricating fluids. The electrodeposition coating applied according to the process of the present is surprisingly uniform, providing a finish that is generally unexpectedly smooth, even when applied over a rough surface. The electrodeposition process of the present invention, however, is further useful for its optional etching steps that are capable of transforming the generally smooth finish to a uniquely textured finish that can be characterized as porous or dimpled.

The etching process of the present invention is particularly useful for the preparation of parts for use in the presence of fluids, especially lubricating fluids, such as hydraulic fluids, oils, and the like. The etching process is further useful for the preparation of parts for use in applications where a selective fit is desirable or required. This is of particular interest in industries, such as the automotive industry, where motor parts must be made to precise dimensions having specific surface roughness values. Further, the moving parts in the engine must be properly lubricated to ensure long life. Parts prepared according to the present invention, particularly using embodiments incorporating the etching steps, can be used to facilitate the advantages of wear and lubricity.

The etch process of the present invention also provides a surface texture that will tend to “give” enough to achieve desired clearance between inner dimension (ID) and outer dimension (OD) of fitted parts. Further, such fit can include fits ranging from a loose “slip fit”, to a “no-shake fit”, to a “press fit”. This variability is partially due to the rougher surface texture that has the correct amount and proportions of hardness, lubricity, and give to wring into any desired fit. Accordingly, when the electrodeposition coating according to the present invention is applied to fitted parts, the coating can be applied to the OD of the inner fit part, the ID of the outer fit part, or both.

The electrodeposition process of the present invention, including the etch process, is particularly beneficial for use in coating parts, such as nuts, bolts, screws, rivets, and the like. The process is also useful for coating part where usage requires corrosion protection or where it is desirable that the part or assembly not be exposed to the surrounding elements. This is particularly possible due to the fit properties previously described. The etched parts, and the associated “give” of the coating, enables production of parts having a tight fit that blocks out invasive corrosion elements. Such tight fit further eliminates dangerous vibration and provides longer life to assemblies thus coated. This corresponds to reduced maintenance and time lost to repairs.

The surface condition of the coating applied to the substrate using the general electrodeposition process of the present invention is illustrated in FIG. 8, which shows a SEM micrograph at 250× magnification of such a coating. As shown in FIG. 8, the coating is generally smooth and uniform. A similar coating having undergone the etch process of the present invention is provided in FIG. 9. As seen in FIG. 9, the etched surface is generally rougher in appearance than the surface shown in FIG. 8. The surface as shown in FIG. 8 has multiple “swirls”, which are indicative of a compressed and smooth surface. The etched surface in FIG. 9, however, is visibly textured having a nodule structure (i.e. raised “bumps”) along the surface, but also having pores capable of retaining fluids, which is indicative of a coarse texture. The surface shown in FIG. 9 was prepared according a regular etch process. The process also encompasses a heavy etch, wherein the etch steps can be repeated for a greater number of cycles. Accordingly, the etch can be customized according to the desired finish and the desired properties of the finished part.

Etching the surface of a coating applied according to the electrodeposition process of the present invention is particularly beneficial because of the useful properties imparted to the coated part. In particular, an etched coating according to the present invention exhibits improved adhesion and improved lubricity.

Accordingly, in another aspect of the present invention, there is provided a process for improving lubricity of a substrate comprising applying an electrodeposition layer to the substrate and etching the electrodeposition layer. According to this aspect of the invention, the substrate has a finished coating surface that is textured for receiving and retaining lubricating materials, particularly lubricating oils and the like. The textured surface preferentially has a porous texture having a series of micro and nano pores that are particularly beneficial for their ability to accept and retain the lubricating material applied thereto. The lubricating material retained in the micro and nano pores of the etched surface is available for moving out of the pores and over the raised portions of the etched surface. On a smooth surface without the micro and nano pores, the lubricating material cannot be retained on the surface, and the material is moved away from the surface, decreasing lubricity of the coated part. The etched coating according the present invention, however, has increased lubricity resulting from the micro and nano pores of the etched surface.

According to yet another aspect of the present invention, there is provided a process for improving adhesion on a substrate comprising applying an electrodeposition layer to the substrate and etching the electrodeposition layer. According to this aspect of the invention, the substrate has a finished coating surface that is textured for receiving additional coating layers, such as paints. As previously noted, surfaces prepared according to known electroplating methods, because of the limitations of the methods in being unable to coat over rough surfaces, are particularly smooth, either because of the chemical or mechanical pre-preparation of the substrate surface or because of the sanding and other smoothing of the plated surface to provide uniformity. Such smooth surfaces have particularly poor adhesion and are not well suited for receiving further coatings, such as paints, which is common in the industry. This problem, however, is solved by the process of the present invention.

According to another aspect of the present invention, there is provided a process for improving corrosion resistance of a substrate. According to this aspect of the invention, the process comprises providing a substrate for which improved corrosion resistance is desirable, coating the substrate with a liquid anti-corrosive agent, immersing the substrate coated with the liquid anti-corrosive agent in an electrodeposition bath, and applying an electrical current of specified voltage to form an electrodeposition coating on the substrate.

EXPERIMENTAL

The present invention is more fully illustrated by the following examples, which are set forth to illustrate the present invention and are not to be construed as limiting thereof.

Example 1 Electrodeposition Process

A 12 in.×12 in.×0.25 in. 6061 aluminum plate had an electrodeposition coating applied thereto using a process according to the present invention. The plate was prepared for the electrodeposition process according to the following optional steps. The plate was cleaned with methyl ethyl ketone (MEK), and the sharp edges on the plate were removed through sanding. The plate was then prepped for attachment to the plating rack by drilling a ⅜″ hole in one corner of the plate, and the plate was cleaned again with MEK to remove loose shavings. The plate was abrasive blasted to rough the surfaces to be plated and cleaned again with MEK to remove blast residue. The plate was then attached to the plating rack with a 2 inch copper hook bolted through the hole with a ¼-20 bolt.

The prepped and racked plate was then chrome plated according to the following process. A liquid coating composition comprising 10% carbowax 8000 and 5% sodium propionate in deionized water was applied to the plate. The cable for providing the electrical current was connected to the plating rack. An electrical current having a negative charge of 10.2 V was applied to the plate, and the plate with the liquid coating composition applied thereto and the electrical current applied thereto was immersed in the electrodeposition bath. The electrodeposition bath was comprised of sulfuric acid, chromic acid, and water. The plate in the electrodeposition bath had the −10.2 V electrical current applied for 1 minute, and the voltage of the electrical current was reduced to −5.0 V and the current applied for 4 minutes. The electrical current was then discontinued, and the plate was taken out of the electrodeposition bath. The plate was then taken from the rack, rinsed in hot water, and air dried to provide the completed electrodeposition coating.

Example 2 Electrodeposition Process with Etch

A 12 in.×12 in.×0.25 in. 6061 aluminum plate had an electrodeposition coating applied thereto using a process according to the present invention incorporating steps to provide an etch finish. The plate was prepared for the electrodeposition process according to the optional steps described above in Example 1.

The liquid coating composition described in Example 1 was applied to the plate, and the cable for providing the electrical current was connected to the plating rack. An electrical current having a negative charge of 10.2 V was applied to the plate, and the plate with the liquid coating composition applied thereto and the electrical current applied thereto was immersed in the electrodeposition bath of the composition as described in Example 1. The plate in the electrodeposition bath had the −10.2 V electrical current applied for 1 minute, and the voltage of the electrical current was reduced to −5.0 V and the current applied for 4 minutes to provide the electrodeposition coating.

To provide the etch finish on the electrodeposition coating, the voltage of the electrical current was increased to 9.0 V and the polarity of the current was reversed (i.e. changed to a positive charge). The +9.0 V electrical current was applied for 1-2 seconds. The charge of the electrical current was changed back to the original negative charge, and a −9.0 V electrical current was applied three times (3 second duration each time) with 5 second intervals between. This provided a regular etch to the electrodeposition coating on the plate.

Additional, optional, etching steps were performed to provide a heavy etch to the electrodeposition coating. The additional, optional, steps comprised repeating the application of the +9.0 V electrical current for 1-2 seconds followed by application of the −9.0 V electrical current three times for a 3 second duration each time, with 5 second intervals between. These additional steps were then repeated a second time to complete the etch process steps. After the electrical current was finally discontinued, the plate was taken out of the electrodeposition bath. The plate was then taken from the rack, rinsed in hot water, and air dried to provide the completed heavy etch electrodeposition coating.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. An electrodeposition process comprising:

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 having a specified voltage to form an electrodeposition coating on the substrate.

2. The electrodeposition process according to claim 1, further comprising reducing the voltage of the electrical current after said applying step, and then applying an electrical current for a second period of time to form a final electrodeposition coating of a desired thickness.

3. The electrodeposition process according to claim 2, further comprising adjusting the electrical current during the second period of time.

4. The electrodeposition process according to claim 1, further comprising roughing a surface of the substrate prior to said step of coating the substrate with a liquid coating composition.

5. The electrodeposition process according to claim 1, further comprising curing the liquid coating composition prior to said immersing step.

6. The electrodeposition process according to claim 1, wherein said step of applying an electrical current takes place prior to said immersing step.

7. The electrodeposition process according to claim 6, wherein the electrical current is applied to the coated substrate or to the bath.

8. The electrodeposition process according to claim 1, wherein the liquid coating composition comprises a material selected from the group consisting of polymeric materials, polar liquids, non-polar liquids, surface tension-modifying compounds, antioxidants, organic liquids, petroleum-based substances, waxes, buffering materials, particulate suspensions, colloidal materials, resins, and mixtures thereof.

9. The electrodeposition process according to claim 1, wherein the liquid coating composition comprises a lower alkyl carboxylic acid moiety.

10. The electrodeposition process according to claim 9, wherein the lower alkyl carboxylic acid moiety is derived from a C1 to C6 carboxylic acid, salt, or derivative thereof.

11. The electrodeposition process according to claim 9, wherein the lower alkyl carboxylic acid moiety is derived from a C1 to C6 carboxylate.

12. The electrodeposition process according to claim 11, wherein the carboxylate is selected from the group consisting of formate, acetate, propionate, butyrate, 2-methyl propionate, and mixtures thereof.

13. The electrodeposition process according to claim 9, wherein the lower alkyl carboxylic acid moiety is derived from sodium propionate.

14. The electrodeposition process according to claim 9, wherein the liquid coating composition further comprises at least one moiety selected from the group consisting of a 2,4-trans, trans-hexadienoic moiety, a benzoic moiety, a phosphate moiety, a citrate moiety, acids and salts thereof, and mixtures thereof.

15. The electrodeposition process according to claim 1, wherein the liquid coating composition comprises an electrically conductive material.

16. The electrodeposition process according to claim 1, wherein the liquid coating composition comprises a positive charge.

17. The electrodeposition process according to claim 1, wherein the material for electrodeposition comprises a metal.

18. The electrodeposition process according to claim 17, wherein the metal comprises a transition metal.

19. The electrodeposition process according to claim 1, wherein the material for electrodeposition comprises a conductive polymer.

20. The electrodeposition process according to claim 1, wherein the bath further comprises one or more additive.

21. The electrodeposition process according to claim 20, wherein the one or more additive is selected from the group consisting of anticorrosive agents, brighteners, wetting agents, adhesion improvers, and pH buffers.

22. The electrodeposition process according to claim 1, wherein the substrate comprises a metal.

23. The electrodeposition process according to claim 1, wherein the substrate comprises a conductive polymer.

24. The electrodeposition process according to claim 1, wherein the period of time is a period of about 0.1 second to about 3 hours.

25. The electrodeposition process according to claim 24, wherein the period of time is a period of about 1 second to about 30 minutes.

26. The electrodeposition process according to claim 24, wherein the period of time is a period of about 5 seconds to about 2 minutes.

27. The electrodeposition process according to claim 1, wherein the current creates a voltage of about 1 mV to about 500 V.

28. The electrodeposition process according to claim 1, wherein the electrodeposition coating has a thickness of at least about 0.1 micron.

29. The electrodeposition process according to claim 1, wherein the electrodeposition coating has a uniform thickness on the substrate.

30. The electrodeposition process according to claim 2, wherein the voltage of the electrical current is reduced by at least 30%.

31. The electrodeposition process according to claim 30, wherein the voltage of the electrical current is reduced by at least 50%.

32. The electrodeposition process according to claim 30, wherein the voltage of the electrical current is reduced by at least 70%.

33. An electrodeposition process comprising:

coating a substrate with a liquid coating composition;
immersing the coated substrate in a bath comprising a material for electrodeposition;
applying for a first period of time an electrical current of specified voltage having a beginning polarity to form an initial electrodeposition coating on the substrate;
reducing the voltage of the electrical current;
applying an electrical current for a second period of time to form a final electrodeposition coating of a desired thickness; and
etching the final electrodeposition coating.

34. The electrodeposition process according to claim 33, further comprising adjusting the electrical current during the second period of time.

35. The electrodeposition process according to claim 33, further comprising roughing a surface of the substrate prior to said step of coating the substrate with a liquid coating composition.

36. The electrodeposition process according to claim 33, further comprising curing the liquid coating composition prior to said immersing step.

37. The electrodeposition process according to claim 33, wherein said step of applying an electrical current takes place prior to said immersing step.

38. The electrodeposition process according to claim 37, wherein the electrical current is applied to the coated substrate or to the bath.

39. The electrodeposition process according to claim 33, wherein the second period of time is a period of 0 seconds to about 12 hours.

40. The electrodeposition process according to claim 33, wherein said etching step comprises:

applying an electrical current of reverse polarity for a period of time, and applying an electrical current of beginning polarity for a period time.

41. The electrodeposition process according to claim 40, further comprising repeating said step of applying an electrical current of beginning polarity.

42. The electrodeposition process according to claim 40, wherein the period of time of applying an electrical current of reverse polarity is a period of about 0.1 second to about 1 minute.

43. The electrodeposition process according to claim 40, wherein the period of time of applying an electrical current of beginning polarity is a period of about 0.1 second to about 1 minute.

44. The electrodeposition process according to claim 41, wherein said repeating step is carried out at least once.

45. The electrodeposition process according to claim 41, wherein said repeating step is carried out two times.

46. The electrodeposition process according to claim 33, wherein said etching step is repeated at least once.

47. The electrodeposition process according to claim 33, wherein the liquid coating composition comprises a material selected from the group consisting of polymeric materials, polar liquids, non-polar liquids, surface tension-modifying compounds, antioxidants, organic liquids, petroleum-based substances, waxes, buffering materials, particulate suspensions, colloidal materials, resins, and mixtures thereof.

48. The electrodeposition process according to claim 33, wherein the liquid coating composition comprises a lower alkyl carboxylic acid moiety.

49. The electrodeposition process according to claim 48, wherein the lower alkyl carboxylic acid moiety is derived from sodium propionate.

50. The electrodeposition process according to claim 48, wherein the liquid coating composition further comprises at least one moiety selected from the group consisting of a 2,4-trans, trans-hexadienoic moiety, a benzoic moiety, a phosphate moiety, a citrate moiety, acids and salts thereof, and mixtures thereof.

51. The electrodeposition process according to claim 33, wherein the liquid coating composition comprises an electrically conductive material.

52. The electrodeposition process according to claim 33, wherein the liquid coating composition comprises a positive charge.

53. The electrodeposition process according to claim 33, wherein the material for electrodeposition comprises a metal.

54. The electrodeposition process according to claim 53, wherein the metal comprises a transition metal.

55. The electrodeposition process according to claim 33, wherein the material for electrodeposition comprises a conductive polymer.

56. The electrodeposition process according to claim 33, wherein the substrate comprises a metal.

57. The electrodeposition process according to claim 33, wherein the substrate comprises a conductive polymer.

58. An electrodeposition process comprising:

coating a substrate with a liquid coating composition;
immersing the coated substrate in a bath comprising a material for electrodeposition;
applying for a first period of time an electrical current of specified voltage to form an initial uniform electrodeposition coating on the substrate;
reducing the voltage of the electrical current; and
applying the reduced voltage electrical current for a second period of time to form a final electrodeposition coating of a desired thickness.

59. The electrodeposition process according to claim 58, further comprising adjusting the electrical current during the second period of time.

60. An electrodeposition process comprising:

coating a substrate with a liquid coating composition comprising a lower alkyl carboxylic acid moiety;
immersing the coated substrate in a bath comprising a material for electrodeposition;
applying for a first period of time an electrical current of specified voltage to form an initial uniform electrodeposition coating on the substrate;
reducing the voltage of the electrical current; and
applying the reduced voltage electrical current for a second period of time to form a final electrodeposition coating of a desired thickness.

61. The electrodeposition process according to claim 60, further comprising adjusting the electrical current during the second period of time.

62. An electrodeposition process comprising:

coating a substrate with a liquid coating composition;
applying to the coated substrate an electrical current having a specified voltage;
immersing the coated substrate with the electrical current applied thereto in a bath comprising a material for electrodeposition;
continuing application of the electrical current for a first period of time;
reducing the voltage of the electrical current; and
continuing the application of the electrical current for a second period of time to form a final electrodeposition coating of a desired thickness.

63. The electrodeposition process according to claim 58, further comprising adjusting the electrical current during the second period of time.

64. An electrodeposition process comprising:

a) coating a substrate with a liquid coating composition;
b) immersing the coated substrate in a bath comprising a material for electrodeposition;
c) applying for a first period of time an electrical current of specified voltage having a beginning polarity to form an initial electrodeposition coating on the substrate;
d) reducing the voltage of the electrical current;
e) applying the reduced voltage electrical current for a second period of time to form a final electrodeposition coating of a desired thickness;
f) applying an electrical current of reverse polarity for a period of time;
g) applying an electrical current of beginning polarity for a period of time;
h) repeating at least once said step of applying an electrical current of beginning polarity; and
i) optionally repeating steps f) through h).

65. A process for improving lubricity of a substrate comprising:

coating the substrate with a liquid coating composition;
applying an electrodeposition layer to the coated substrate; and
etching the electrodeposition layer.

66. The process for improving lubricity of a substrate according to claim 65, wherein said etching step comprises

applying an electrical current of positive polarity for a period of time, and
applying an electrical current of negative polarity for a period of time.

67. The process for improving lubricity of a substrate according to claim 66, further comprising repeating said step of applying an electrical current of negative polarity.

68. The process for improving lubricity of a substrate according to claim 66, wherein the period of time for applying an electrical current of positive polarity is a period of about 0.1 second to about 1 minute.

69. The process for improving lubricity of a substrate according to claim 66, wherein the period of time for applying an electrical current of negative polarity is a period of about 0.1 second to about 1 minute.

70. A process for improving adhesion on a substrate comprising:

coating the substrate with a liquid coating composition;
applying an electrodeposition layer to the substrate; and
etching the electrodeposition layer.

71. The process for improving adhesion of a substrate according to claim 70, wherein said etching step comprises

applying an electrical current of positive polarity for a period of time, and
applying an electrical current of negative polarity for a period of time.

72. The process for improving adhesion of a substrate according to claim 71, further comprising repeating said step of applying an electrical current of negative polarity.

73. The process for improving adhesion of a substrate according to claim 71, wherein the period of time of applying an electrical current of positive polarity is a period of about 0.1 second to about 1 minute.

74. The process for improving adhesion of a substrate according to claim 71, wherein the period of time for applying an electrical current of negative polarity is a period of about 0.1 second to about 1 minute.

75. A process for improving corrosion resistance of a substrate comprising:

coating the substrate with a liquid anti-corrosive composition;
immersing the coated substrate in a bath comprising a material for electrodeposition; and
applying an electrical current of a specified voltage to form an electrodeposition coating on the substrate.
Patent History
Publication number: 20060037861
Type: Application
Filed: Aug 23, 2004
Publication Date: Feb 23, 2006
Inventors: Paul Manos (Pinehurst, NC), Kerry Ryan (Garden City, MI)
Application Number: 10/924,085
Classifications
Current U.S. Class: 204/471.000; 204/484.000
International Classification: C25B 7/00 (20060101); C25D 13/00 (20060101);