Conversion Coating Application System Including Hydrogels and Methods of Using Same

This application is a continuation of Applicant's U.S. Non-Provisional patent application Ser. No. 18/735,822, filed Jun. 6, 2024, and entitled CONVERSION COATING APPLICATION SYSTEM INCLUDING HYDROGELS AND METHODS OF USING SAME, which claims priority to Applicant's prior U.S. Non-Provisional patent application Ser. No. 18/209,123, filed Jun. 13, 2023, and entitled CONVERSION COATING APPLICATION SYSTEM INCLUDING HYDROGELS AND METHODS OF USING SAME, which claims priority to and the benefit of Applicant's U.S. Provisional Patent Application No. 63/351,771, filed Jun. 13, 2022, and entitled CONVERSION COATING APPLICATION SYSTEM INCLUDING HYDROGELS AND METHODS OF USING SAME, all of which prior applications are hereby incorporated by reference in their entirety. It is to be understood, however, that in the event of any inconsistency between this specification and any information incorporated by reference in this specification, this specification shall govern.

Conversion coatings are widely used to treat metal surfaces to improve corrosion resistance, increase adhesion of subsequent coatings such as paint, form a decorative finish, or retain electrical conductivity. Conversion coatings are formed by applying a conversion coating solution to the metal. The conversion coating solution and the metal react to convert or modify the metal surface into a thin film with the desired functional characteristics. Conversion coatings are particularly useful for the surface treatment of metals such as aluminum, zinc, and magnesium.

Metal surfaces may be subject to corrosion or other types of degradation as the metal surfaces are exposed to the elements or other operational conditions. For example, metal pipes in industrial facilities may be exposed to the elements or may be exposed to harsh operating environments that may degrade or corrode the metal surface. Replacing the degraded or corroded metals pipes is costly and often requires the industrial facility to shut down during repairs. Furthermore, applying conversion coatings during operations typically involves manually brushing on the conversion coating with brushes or sprayers that may cause workers to be exposed to chemicals within the conversion coatings. Additionally, the brushes and sprayers typically apply excess conversion coating that may spread to other areas of the industrial facility that were not intended to be coated, requiring extensive clean up. Accordingly, there is a need for a system that applies conversion coatings to metal surfaces that minimizes exposure to the chemicals within the conversion coatings, minimizes the clean up required after the conversion coating has been applied, and reduces costs to apply a conversion coating.

A number of embodiments of a chemical applicator that is configured to apply a reactive chemical solution or a reactive chemistry to a surface. The chemical applicators described herein typically include a hydrogel that contains the reactive chemical solution until the hydrogel and the reactive chemical solution contact the surface. The hydrogel enables the reactive chemical solution to contact the surface such that the reactive chemical solution reacts with the surface to complete a desired chemical, physical, and/or mechanical transformation. The hydrogel may be configured to contain any reactive chemistry, including hazardous chemistries, provided the hydrogel does not unfavorably react with the reactive chemistry prior to application on the surface and enables the reactive chemistry to contact and react with the surface. The chemical applicators described herein contain the reactive chemical solution in the hydrogel, apply the reactive chemical solution to the surface such that the reactive chemical solution reacts and/or operates as if the surface had been into the reactive chemical solution, and/or applied the reactive chemical solution in a manner that reduces waste, reduces mess, and reduces exposure to the reactive chemical solution. Contact between the hydrogel and the surface to be coated allows the reaction to take place often without heat or other forms of energy such as mechanical scrubbing.

In the embodiments described herein, the reactive chemical solution typically includes a conversion coating solution that can be used to form such conversion coatings are disclosed. The conversion coating solution broadly includes trivalent chromium, hexavalent chromium, and/or non-hexavalent chromium compounds and the conversion coating applicator also broadly includes a hydrogel configured to selectively contain the conversion coating solution. In some embodiments, the conversion coating solution includes a chromium compound, a dye compound, and a zirconate compound. Methods for using the conversion coating applicator to protect metal substrates are also disclosed.

The conversion coating solution is used to form a protective coating on a metal substrate and the conversion coating applicator is used to apply the conversion coating solution to the metal substrate. The coating generally passivates the metal surface or, in other words, makes it less susceptible to corrosion and/or other undesirable reactions in the future.

The chromium compound can be any suitable chromium compound. One example of a suitable chromium compound is trivalent chromium sulfate. It should be appreciated that other chromium compounds can also be used.

Conversion coatings may be formed on the surface of metals through the use of hydrogels that have been infused with a conversion coating solution. The conversion coating solution is infused into the hydrogel. The conversion coating may then be formed on the metal substrate by placing the hydrogel on the surface of the metal substrate for a period of time, allowing the conversion coating solution to diffuse out of the hydrogel, onto the surface, react, and form the conversion coating.

The conversion coating applicator is easy to use and minimizes cleanup. A hydrogel infused with an active substance is easy to handle and use. It eliminates the need for liquid containers of the conversion coating, reduces or eliminates chemicals running off (dripping off) the surface. The system is applicable to preparatory chemistries as well-cleaners, activators, etc., so that the application and ultimate formation of the coating does not waste chemicals and improves the safety of forming the coating because the materials are relatively contained and minimize the chance that the chemistry will spill on the user.

There are other novel aspects and features of this disclosure. They will become apparent as this specification proceeds. Accordingly, this brief summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. The summary and the background are not intended to identify key concepts or essential aspects of the disclosed subject matter, nor should they be used to constrict or limit the scope of the claims. For example, the scope of the claims should not be limited based on whether the recited subject matter includes any or all aspects noted in the summary and/or addresses any of the issues noted in the background.

A number of embodiments of a reactive chemical applicator or a conversion coating applicator are disclosed along with hydrogels, conversion coatings, and additives that can be used to form the conversion coating applicator and methods for treating a substrate with the conversion coating applicator. In general, the conversion coating applicator includes a hydrogel infused with a reactive chemical solution. In the illustrated embodiments, the reactive chemical solution includes a conversion coating solution. In alternative embodiments, the reactive chemical solution may be any chemical solution that enables the conversion coating applicator to operate as described herein. The hydrogel enables the conversion coating solution to be applied to a limited area of the substrate such that only the limited area of the substrate contacts the conversion coating solution, minimizing contamination of other areas and minimizing worker contamination. The conversion coating solution may include a trivalent chromium compound, a hexavalent chromium compound, a non-hexavalent chromium compound, a zirconate compound, and/or a dye compound. The conversion coating solution may be used to improve the metal's corrosion resistance, abrasive properties, and adhesion bonding properties as well as dye a metal surface or part.

The conversion coating applicator may provide one or more of the following improvements/advantages over conventional application systems: 1) simpler and easier application that reduces the amount of training required for a worker to safely apply the conversion coating to a substrate, 2) limited application area that reduces excess conversion coating solution application and conversion coating solution waste, 3) reduced cleanup, and/or 4) reduced exposure of workers to the conversion coating solution.

Hydrogel typically include three-dimensional networks of hydrophilic polymers that swell in water and contain a large amount of water relative to their volume while maintaining the structure due to chemical or physical cross-linking of individual polymer chains. Hydrogels typically include at least 10% water of the total weight (or volume), are hydrophilic, and are flexible such that hydrogels can conform to the shape of a surface they are positioned on. The hydrophilicity of the network is due to the presence of hydrophilic groups such as —NH2, —COOH, —OH, —CONH2, —CONH—, and —SO3H.

Hydrogels typically may undergo a volume phase transition or gel-sol phase transition in response to certain physical and chemical stimuli. The physical stimuli may include temperature, electric and magnetic fields, solvent composition, light intensity, and pressure, and the chemical stimuli may include chemical reactions, pH, ions, and specific chemical compositions. Most conformational transitions are reversible, and the hydrogels are capable of returning to their initial state after a reaction as soon as the trigger is removed. The response of hydrogels to external stimuli is typically determined by the nature of the monomer, charge density, pendant chains, and the degree of cross-linkage. The magnitude of response is also typically directly proportional to the applied external stimulus.

illustrates a side schematic view of a conversion coating applicatorin accordance with aspects of the present disclosure. The conversion coating applicatorincludes a first liner, a hydrogel, and a second liner or cover. In addition, the conversion coating applicatormay include additional layers not illustrated in. For example, the hydrogelmay include a plurality of hydrogel layers to absorb and deposit a plurality of conversion coating chemicals. Additionally, the first linerand the second linermay also include plurality of layers configured for strength, moisture retention, and adhesion such as, but not limited to, a scrim and/or a non-woven scrim. The scrim and/or the non-woven scrim may be part of the first liner, the hydrogel, and/or the second liner or coverto provide additional support for the conversion coating applicator.

The first lineris configured to hold and maintain the hydrogelin place. The first linerincludes an inert plastic or polymer that does not absorb the hydrogel or the conversion coating chemicals. The first lineris flexible but strong enough to hold the hydrogel and withstand the elements for short durations while the conversion coating chemicals react with the metal substrate. As such, the first linermay include any material that is strong enough to hold the hydrogel, flexible enough to apply the hydrogel over a metal substrate, resistant to absorption of the conversion chemicals, and inert to the conversion coating solution. In the illustrated embodiment, the first linermay include polyethylene, polyester, polypropylene, polyethylene terephthalate, medium-density polyethylene, and/or polytetrafluoroethylene.

Similarly, the second lineris also configured to hold and maintain the hydrogelin place. However, the second lineris configured to be removed from the hydrogelprior to application of the hydrogelto the metal substrate. The second lineralso includes an inert plastic or polymer that does not absorb the hydrogel or the conversion coating chemicals. Typically, the second lineris also flexible but strong enough to hold the hydrogel and withstand the elements for short durations. As such, the second linermay include any material that is strong enough to hold the hydrogeland resistant to absorption of the conversion chemicals. In some embodiments, the second linermay include the same material as the first liner. In the illustrated embodiment, the second linermay include polyethylene, polyester, polypropylene, polyethylene terephthalate, medium-density polyethylene, and/or polytetrafluoroethylene.

The hydrogelincludes a polymer hydrogel that is configured to: (1) absorb the conversion chemicals, (2) desorb the conversion chemicals when the hydrogelcontacts a metal substrate, and (3) is inert with respect to the conversion chemicals. As such, the hydrogelmay include any network of hydrophilic polymers that can swell and hold the conversion chemicals.

For example, the hydrogelmay include any of the following hydrogel types: homopolymeric hydrogels, cationic hydrogels, natural hydrogels, physically cross linked hydrogels, amorphous hydrogels, copolymeric hydrogels, anionic hydrogels, synthetic hydrogels, chemically cross linked hydrogels, semicrystalline hydrogels, interpenetrating hydrogels, nonionic hydrogels, hybrid hydrogels, crystalline hydrogels, hydrocolloid aggregate hydrogels, and/or any other type of hydrogel. If the hydrogel is a synthetic hydrogel, the hydrogelmay include poly(vinyl alcohol), polyethylene oxide, poly(acrylic acid), poly(hydroxyethyl methacrylate), poly(glyceryl methacrylate), poly(hydroxypropyl methacrylate), polyacrylamide, poly(ethylene glycol), poly(vinylpyrrolidone), poly(ethyleneimine), polyhydric alcohol, polyacrylamide, polysaccharide, and/or any other type of polymer. If the hydrogelincludes a natural hydrogel, the hydrogelmay include chitosan, alginate, collagen, silk fibroin, hyaluronic acid, fibrin, gelatin, agarose, and/or any other type of natural hydrogel. The hydrogelmay include some commercially available hydrogels including Actiformcool®, Aquaflo®, Clearsite®, Geliperm®, Hydrosorb®, Novogel®, Primskin®, Suprasorb G®, AquaDerm®, Tegraderm®, and/or any other commercially available hydrogel.

As described herein, the conversion coating applicatoris configured to hold the conversion coating solution until the second linerhas been removed and the hydrogelcontacts a metal substrate. The conversion coating solution then reacts with the metal substrate, diffuses toward the metal substrate as the reaction consumes the conversion coating solution, and desorbs from the hydrogelonto the metal substrate to react with the metal substrate.

In the illustrated embodiment, the reactive chemical solution includes a chromium compound for forming a conversion coating on the metal substrate. The chromium compound may be any type of chromium compound including, but not limited to, a trivalent chromium compound, a hexavalent chromium compound, and a non-hexavalent chromium compound. In alternative embodiments, the reactive chemical solution may include a non-chromium compound that is capable of forming a conversion coating on the metal substrate. More specifically, in the illustrated embodiment and in the Examples described herein, the reactive chemical solution includes a trivalent chromium compound.

The trivalent chromium compound can be any suitable trivalent chromium compound capable of forming a conversion coating on the metal substrate. Examples of suitable trivalent chromium compounds can be found in the patents incorporated by reference at the end of the description.

The trivalent chromium compound can be a water-soluble trivalent chromium compound such as a trivalent chromium salt. It is generally desirable to use chromium salts that provide anions that are not as corrosive as chlorides. Examples of such anions include nitrates, sulfates, phosphates, and acetates. In a preferred embodiment, the trivalent chromium compound is a trivalent chromium sulfate. Examples of such compounds include Cr(SO), (NH)Cr(SO), or KCr(SO).

It should be appreciated that the conversion coating solution can include one or multiple trivalent chromium compounds. For example, in one embodiment, the conversion coating solution includes a single trivalent chromium compound. In another embodiment, the conversion coating solution includes two, three, four, or more trivalent chromium compounds.

The conversion coating solution can include any suitable quantity of the trivalent chromium compound. Examples of suitable quantities can be found in the patents incorporated by reference at the end of the description. In some embodiments, the conversion coating solution includes approximately 0.1 g/liter (0.01 wt %) to approximately 20 g/liter (2 wt %) of the trivalent chromium compound, approximately 0.2 g/liter (0.02 wt %) to approximately 10 g/liter (1 wt %) of the trivalent chromium compound, or approximately 0.5 g/liter (0.05 wt %) to approximately 8 g/liter (0.8 wt %) of the trivalent chromium compound.

In other embodiments, the conversion coating solution includes at least approximately 0.1 g/liter (0.01 wt %) of the trivalent chromium compound, at least approximately 0.2 g/liter (0.02 wt %) of the trivalent chromium compound, or at least approximately 0.5 g/liter (0.05 wt %) of the trivalent chromium compound. In still other embodiments, the conversion coating solution includes no more than 20 g/liter (2 wt %) of the trivalent chromium compound, no more than 10 g/liter (1 wt %) of the trivalent chromium compound, or no more than 8 g/liter (0.8 wt %) of the trivalent chromium compound.

The dye compound (alternatively referred to as a pigment compound or colorant compound) can be any material that is compatible with the conversion coating solution and the hydrogel chemistry and is capable of imparting a color to the metal substrate. In some embodiments, the dye compound includes one or more metal atoms and in other embodiments it does not. In those embodiments where the dye compound includes one or more metal atoms, the metal atom can be present as part of a metal complex.

In some embodiments, the dye compound can include an azo dye, a chromium complex dye, an anthraquinoid dye, and/or a methine dye. In a preferred embodiment, the dye compound includes a metal complex azo dye, a chromium complex dye, and/or metal free azo dye. It should be appreciated that azo dyes include monoazo dyes, disazo dyes, and/or trisazos dyes.

Numerous other dye compounds can be used as long as they are compatible with the other constituents in the conversion coating solution and the hydrogel. Examples of such dyes include those used to anodize aluminum and colorize textiles. Other examples include acid dyes, mordant dyes, metal-complex dyes, triphenylmethane dyes, xanthene dyes, wool dyes, silk dyes, direct dyes, reactive dyes, vat dyes, and the like. It is understood that these dyes may be classified in more than one way such as by structure or by typical use—e.g., a dye may be referred to as a chrome dye, a mordant dye, a wool dye, etc.

It should be appreciated that the conversion coating solution can include one or multiple dye compounds including any quantity and/or combination of the dyes described above. In some embodiments, the trivalent chromium conversion coating solution comprises approximately 0.1 g/liter (0.01 wt %) to approximately 20 g/liter (2 wt %) of the dye compound, approximately 0.2 g/liter (0.02 wt %) to approximately 10 g/liter (1 wt %) of the dye compound, or approximately 0.5 g/liter (0.05 wt %) to approximately 5 g/liter (0.5 wt %).

In some other embodiments, the conversion coating solution comprises at least approximately 0.1 g/liter (0.01 wt %) of the dye compound, at least approximately 0.2 g/liter (0.02 wt %) of the dye compound, or at least approximately 0.5 g/liter (0.05 wt %) of the dye compound. In yet other embodiments, the conversion coating solution comprises no more than 20 g/liter (2 wt %) of the dye compound, no more than 10 g/liter (1 wt %) of the dye compound, or no more than 5 g/liter (0.5 wt %) of the dye compound.

The zirconate compound can be any suitable zirconate compound that is capable of facilitating the formation of a protective coating on a substrate. Examples of suitable zirconate compounds include alkali metal hexafluorozirconate compounds such as potassium hexafluorozirconate, sodium hexafluorozirconate, and fluorozirconic acid.

In some embodiments, the conversion coating solution comprises approximately 0.2 g/liter (0.02 wt %) to approximately 20 g/liter (2 wt %) of the zirconate compound, approximately 0.5 g/liter (0.05 wt %) to approximately 18 g/liter (1.8 wt %) of the zirconate compound, or approximately 1 g/liter (0.1 wt %) to approximately 15 g/liter (1.5 wt %) of the zirconate compound.

In some other embodiments, the conversion coating solution comprises at least approximately 0.2 g/liter (0.02 wt %) of the zirconate compound, at least approximately 0.5 g/liter (0.05 wt %) of the zirconate compound, or at least approximately 1 g/liter (0.1 wt %) of the zirconate compound. In yet other embodiments, the conversion coating solution comprises no more than approximately 20 g/liter (2 wt %) of the zirconate compound, no more than approximately 18.0 g/liter (1.8 wt %) of the zirconate compound, or no more than approximately 15 g/liter (1.5 wt %) of the zirconate compound.

The trivalent chromium conversion coating solution can include a variety of additional compounds. Examples of additional compounds can be found in the patents incorporated by reference at the end of the description. Any individual compound or combination of compounds disclosed in the patents can be included in the conversion coating solution in any of the disclosed quantities.

In some embodiments, the trivalent chromium conversion coating solution includes a phosphorous compound that further enhances corrosion protection of the metal substrate. The improved corrosion protection is provided by adsorption of phosphonate groups from an organic amino-phosphonic acid compound on a surface of the metal substrate to form a M-O-P covalent bond and subsequent formation of a network hydrophobic layer over any active corrosion site on the metal substrate.

Examples of suitable phosphorous compounds include derivatives of amino-phosphonic acids such as the salts and esters of nitrilotris(methylene)triphosphonic acid (NTMP), hydroxy-, amino-alkylphosphonic acids, ethylimido(methylene)phosphonic acids, diethylaminomethylphosphonic acid, and the like. Preferably, the derivative is soluble in water. A particularly suitable phosphorous compound for use as a corrosion inhibitor and solution stabilizer is nitrilotris(methylene)triphosphonic acid (NTMP).

The phosphorous compound can be present in the conversion coating solution in any suitable amount. In some embodiments, the conversion coating solution comprises approximately 5 ppm to approximately 100 ppm of the phosphorous compound or approximately 10 ppm to approximately 30 ppm of the phosphorous compound. In other embodiments, the conversion coating solution comprises at least approximately 5 ppm of the phosphorous compound or at least approximately 10 ppm of the phosphorous compound. In still other embodiments, the conversion coating solution comprises no more than approximately 100 ppm of the phosphorous compound or no more than 30 ppm of the phosphorous compound.

The trivalent chromium conversion coating solution can also comprise a fluoride compound. Examples of suitable fluoride compounds include alkali metal tetrafluoroborates (e.g., potassium tetrafluoroborate), alkali metal hexafluorosilicates (e.g., potassium hexafluorosilicate), and the like. The fluoride compound is preferably water soluble.

The fluoride compound can be present in the conversion coating solution in any suitable amount. In some embodiments, the conversion coating solution comprises approximately 0.2 g/liter (0.02 wt %) to approximately 20 g/liter (2 wt %) of the fluoride compound or approximately 0.5 g/liter (0.05 wt %) to approximately 18 g/liter (1.8 wt %) of the fluoride compound. In other embodiments, the trivalent chromium conversion coating solution comprises at least approximately 0.2 g/liter (0.02 wt %) of the fluoride compound or at least approximately 0.5 g/liter (0.05 wt %) of the fluoride compound. In still other embodiments, the trivalent chromium conversion coating solution comprises no more than 20 g/liter (2 wt %) of the fluoride compound or no more than 18 g/liter (1.8 wt %) of the fluoride compound.

In some embodiments, the trivalent chromium conversion coating solution includes a corrosion inhibitor additive that increases the corrosion resistance provided by the coating. Examples of suitable corrosion inhibitor compounds include any of those disclosed in CN 102888138. Other examples include 2-mercaptobenzothiazole (MBT), 2-mercaptobenzimidazole (MBI), 2-mercaptobenzoxazole (MBO) and/or benzotriazole (BTA). The addition of the corrosion inhibitor compound can increase the corrosion resistance of the coating so that it satisfies the requirements of MIL-DTL-81706B Class 1A and Class 3 or the less stringent requirements of MIL-DTL-5541F Class 1A and Class 3.

It should be appreciated that although the corrosion inhibitor additive serves to substantially increase the coating's corrosion resistance, the coating can also satisfy the MIL corrosion resistance requirements even in the absence of such an additive.

The trivalent chromium conversion coating solution can also include other materials such as thickeners, surfactants, and the like. Examples of these materials can be found in the patents incorporated by reference at the end of the description. These materials can be included in the trivalent chromium conversion coating solution in any of the quantities disclosed in the patents.

Certain impurities can reduce the corrosion resistance/color vibrance of the trivalent chromium conversion coating solution. One example of such an impurity is iron (Fe). Iron impurities present in the dye may reduce the effectiveness so the coating. For example, dye containing 0 ppm of iron can produce test plates (aluminum) that show no corrosion for 800+ hours. However, dye containing 10 ppm of iron can produce plates (aluminum) that show no corrosion for 216 hours. The corrosion resistance of the latter can be increased by adjusting other parameters of the solution such as the chromium content and/or corrosion inhibitor content, but the result is still not as good as those situations where the dye contains 0 ppm of iron.

In some embodiments, the dye and/or the trivalent chromium conversion coating solution have no more than 100 ppm iron, no more than 50 ppm iron, no more than 25 ppm iron, no more than 10 ppm iron, no more than 5 ppm iron, no more than 2 ppm iron, no more than 1 ppm iron, or, preferably, no iron. The dye and/or the trivalent chromium conversion coating solution can have 0-100 ppm iron.

In some embodiments, the trivalent chromium conversion coating solution has no more than 750 ppb iron, no more than 500 ppb iron, no more than 300 ppb iron, no more than 100 ppb iron, no more than 50 ppb iron, or, preferably no iron.

The conversion coating solution can take a variety of forms. In some embodiments, the conversion coating solution is the final mixed solution having the concentrations of the various compounds described above. A typical example of a final mixed solution includes one part trivalent chromium conversion coating solution concentrate, one part dye additive, and two parts water. The final mixed solution is then absorbed into the hydrogel as described herein and the conversion coating applicatorcan be sold as an already mixed ready to use product.

The trivalent chromium conversion coating solution can be used to treat any suitable metal substrate. In some embodiments, the trivalent chromium conversion coating solution can be used to treat substrates comprising aluminum, magnesium, and/or zinc. The substrates can be pure or commercially pure aluminum, magnesium, or zinc. The substrates can also be an alloy of these metals or an alloy that includes these metals.

In other embodiments, the conversion coating solution can be used to treat substrates comprising valve metals such as vanadium, tantalum, hafnium, niobium, and/or titanium. The substrates can be a pure or commercially pure elemental valve metal. The substrates can also be an alloy of a valve metal or an alloy that includes a valve metal.

The metal substrate can be subjected to another treatment prior to being treated with the conversion coating solution. For example, the metal substrate can be anodized before being treated with the conversion coating solution.