Thixotropic stripping compositions and related methods and kits

Abstract

A thixotropic stripping composition may include a stripping component, a thickener, and a solvent. Said thixotropic stripping composition may have a viscosity of about 200 cP or greater. The stripping component can include ammonium nitrate or a combination of a base and an amine. Advantageously, said thixotropic stripping compositions may be useful, among other things, for stripping cadmium-containing coatings and / or zinc-nickel alloy containing coatings from substrates. The exposed substrates may then be inspected for damage, which may be useful for inspecting the underlying substrate in parts of vehicles (e.g., aircraft, water-borne vehicles, and the like) and other structures.

Description

THIXOTROPIC STRIPPING COMPOSITIONS AND RELATEDMETHODS AND KITSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 644,071, filed May 8, 2024, which is hereby incorporated by reference in its entirety for all intents and purposes.FIELD

[0002] The present disclosure relates to thixotropic stripping compositions. Also included in the present disclosure are methods and kits relating to thixotropic stripping compositions. The thixotropic stripping compositions of the present disclosure may be useful, among other things, for stripping cadmium-containing coatings and / or zinc-nickel alloy containing coatings from substrates. The exposed substrates may then be inspected for damage, which may be useful for inspecting the underlying substrate in parts of vehicles (e.g., aircraft, water-borne vehicles, and the like) and other structures.BACKGROUND

[0003] Electroplating a metal or metal alloy coating on a surface is commonly used to enhance the durability, corrosion resistance, and lubricity compared to the underlying substrate. The technique is used in a variety of industries, including aerospace, defense, electronics, and oil and gas. Two of the more common electroplated metal coatings are cadmium and zincnickel alloy.

[0004] While the coatings protect the underlying substrate from damage, the substrate can still be damaged, for example, from mechanical wear, which may not be visible with the coating present on the substrate surface. Accordingly, inspections of the underlying substrate are common. Typically, a small area of the coating is removed to expose the substrate, which is then inspected for damage. Current practices used to remove cadmium or zinc-nickel alloy coatings include mechanical removal methods using either a media blast or abrasive sanding. Both of these methods produce dust containing cadmium and zinc-nickel alloy, which is an airborne contaminant that primarily affects the immediate area but can be transported to other areas, furthering the contamination. There are concerns for both human health and safety andenvironmental impact relating to airborne metal particles. Cadmium, in particular, is a hazardous material targeted for reduction in use by the Environmental Protection Agency.

[0005] One alternative technology to the mechanical removal of this coating is chemical removal with a stripping solution. These stripping solutions include acids or other compounds that are sprayed, wiped, or poured onto the surface until the coating is chemically stripped from the substrate. The resulting spent fluid comprises reaction products including metal compounds and thus needs to be properly disposed of according to environmental guidelines. While this method eliminates the airborne contaminants discussed above, the method does produce spent fluid with waterborne contaminants. Further, because the chemical reaction needs to be sufficiently mild to mitigate chemical reaction with the underlying substrate, large volumes of stripping solution can be used. Additionally, substrates in certain areas, like the under-portion of an aircraft wing, need to be inspected. Removal of the corresponding coating via chemical stripping requires continuous application of the stripping solution. Therefore, in many instances, large volumes of spent stripping solution having metal compound contaminants are produced and require proper disposal, which is costly.BRIEF SUMMARY

[0006] In some embodiments of the present disclosure, a thixotropic stripping composition may comprise: a stripping component comprising ammonium nitrate or a combination of a base and an amine; a thickener; and a solvent, wherein a viscosity of the thixotropic stripping composition is about 200 cP or greater.

[0007] In some embodiments of the present disclosure, a kit may comprise: a container containing the foregoing thixotropic stripping composition and a set of instructions for using the thixotropic stripping composition.

[0008] In some embodiments of the present disclosure, a method may comprise: stripping at least a portion of a coating on a substrate using the foregoing thixotropic stripping composition.

[0009] In some embodiments of the present disclosure, a kit may comprise: a stripping component comprising ammonium nitrate or a combination of a base and an amine; one or more of a thickener, a solvent, and one or more additives; a container; and a set of instructions for producing and / or using a thixotropic stripping composition comprising the stripping component, the thickener, the solvent, and, optionally, one or more additives.

[0010] In some embodiments of the present disclosure, a method may comprise: treating a substrate with a thixotropic stripping composition to strip at least a portion of a coating from the substrate, the thixotropic stripping composition comprising: a stripping componentcomprising ammonium nitrate or a combination of a base and an amine; a thickener; and a solvent; wherein a viscosity of the thixotropic stripping composition is about 200 cP or greater; and removing the thixotropic stripping composition from the substrate.DETAILED DESCRIPTION

[0011] The present disclosure relates to thixotropic stripping compositions useful in removing cadmium and zinc-nickel coatings from substrates. The thixotropic stripping composition of the present disclosure is a thick composition that can be applied to the coating and remains in place while the stripping reaction occurs. Advantageously, while the stripping reaction is occurring, the thixotropic stripping composition also absorbs the cadmium and / or zinc-nickel products of said stripping reaction. Further, because the thixotropic stripping composition can be a thick paste, the thixotropic stripping composition can be applied in areas, like the under-portion of an airplane wing, and maintain contact with the coating without having to be continuously replenished, which would be required with a conventional stripping solution. Accordingly, the thixotropic stripping composition produces less volume of spent material that requires proper disposal.

[0012] Additionally, less viscous stripping solutions have a greater opportunity to escape collection and containment systems when being applied to the coating, which could result in runoff of the spent stripping solutions into the local environment. In contrast, the thickness of the thixotropic stripping composition of the present disclosure mitigates the production of runoff to the local environment.

[0013] Also included in the present disclosure are methods and kits relating to thixotropic stripping compositions. Advantageously, the kits may include a subset of the components of the thixotropic stripping composition to which a solvent like water can be added on-site. Accordingly, less space is needed for transportation and storage. Further, by freshly mixing the thixotropic stripping composition, the components thereof may be more potent because aging from hydrolysis or other reactions may be mitigated. Accordingly, the resultant thixotropic stripping compositions may have a more consistent performance, irrespective of the storage time of the kit.

[0014] Thixotropic Stripping Compositions

[0015] Thixotropic stripping compositions of the present disclosure include a stripping component, a thickener, a solvent, and optionally an additive. The thixotropic stripping solution is preferably suitable for stripping coatings that comprise cadmium or a zinc-nickel alloy.

[0016] The thixotropic stripping composition may have a viscosity of about 200 cP or greater (e.g., from 200 cP to 100,000 cP, from 200 cP to 1000 cP, from 500 cP to 5,000 cP, from 1,000 cP to 10,000 cP, from 5,000 cP to 25,000 cP, from 10,000 cP to 50,000 cP, from 25,000 cP to 75,000 cP, or from 50,000 cP to 100,000 cP). Examples of stripping components may include, but are not limited to, ammonium nitrate, a combination of a base and an amine, the like, and any combination thereof.

[0017] The ammonium nitrate may be present in the thixotropic stripping composition in an amount ranging from about 5 wt% to about 30 wt% (e.g., from 5 wt% to 15 wt%, from 8 wt% to 17 wt%, from 10 wt% to 20 wt%, from 10 wt% to 16 wt%, from 15 wt% to 25 wt%, or from 20 wt% to 30 wt%), based on a total weight of the thixotropic stripping composition.

[0018] As outlined above, the thixotropic stripping composition can include a combination of a base and an amine. Examples of bases may include, but are not limited to, sodium hydroxide, potassium hydroxide, the like, and any combination thereof. The base may be present in the thixotropic stripping composition in an amount ranging from about 10 wt% to about 35 wt% (e.g., from 10 wt% to 20 wt%, from 15 wt% to 25 wt%, from 20 wt% to 30 wt%, or from 25 wt% to 35 wt%), based on a total weight of the thixotropic stripping composition.

[0019] Examples of amines may include, but are not limited to, triethanolamine (TEA), N- aminoethylethanolamine, ethylenediamine, diethylenetriamine, triethylene tetramine, tetraethylenepentamine, pentaethylenehexamine, the like, and any combination thereof. The amine may be present in the thixotropic stripping composition in an amount ranging from about 1 wt% to about 25 wt% (e.g., from 1 wt% to 10 wt%, from 5 wt% to 15 wt%, or from 10 wt% to 20 wt%), based on a total weight of the thixotropic stripping composition.

[0020] The thickener may include a particle, a polymer, or any combination thereof. Particles may include a material that includes, but is not limited to, silica, alumina, titania, clay, polymer (e.g., latex particles), the like, and any combination thereof. The particles may have an average diameter from about 5 nm to about 10 pm (e.g., from 5 nm to 150 nm, from 50 nm to 500 nm, from 250 nm to 2 pm, or from 1 pm to 10 pm). Unless otherwise specified, “average diameter” refers to a number average diameter determined via light scattering. For non-spherical particles, the diameter used for calculating average diameter is the diameter of the smallest sphere that fully encapsulates the particle.

[0021] Examples of polymers may include, but are not limited to, polyacrylamides; hydrolyzed polyacrylamides; xanthan; scleroglucan; cellulose; carboxymethyl hydroxymethyl cellulose; carboxymethyl hydroxyethyl cellulose; polysaccharides; amphoteric polymers made from at least one of acrylamide, acrylic acid, and diallyldimethylammonium chloride; vinylsulfonate / vinyl amide / acrylamide terpolymers; vinyl sulfonate / acrylamide copolymers; acrylamide / acrylamido-methylpropanesulfonic acid copolymers; acrylamide / vinylpyrrolidone copolymers; sodium carboxymethyl cellulose; poly[dialkylaminoacrylate-co-acrylate- graftpoly (ethyleneoxide)] ; acrylamide / octadecyldimethylammoniummethyl methacrylate bromide copolymer; dimethylaminoethyl; methacrylate / vinyl pyrrolidone / hexadecyldimethylammoniumethyl methacrylate bromide terpolymer; acrylamide / 2-acrylamido-2-methyl propane sulfonic acid / 2-ethylhexyl methacrylate terpolymer; a cross-linked polyacrylamide, a crosslinked poly(meth)acrylate, a cross-linked polyacrylate, a cross-linked copolymer of acrylamide and acrylate monomer, a starch grafted with acrylonitrile and acrylate, a cross-linked polymer of two or more of allylsulfonates, 2- acrylamido-2-methyl- 1 -propanesulfonic acid, 3 -allyloxy-2-hydroxy- 1 -propanesulfonic acid, acrylamide, the like, and any combination thereof. In some instances, the polymer may be a swellable polymer. Examples of polymers may include, but are not limited to, a cross-linked polyacrylamide, a crosslinked poly(meth)acrylate, a cross-linked polyacrylate, a cross-linked copolymer of acrylamide and acrylate monomer, a starch grafted with acrylonitrile and acrylate, a cross-linked polymer of two or more of allylsulfonates, 2-acrylamido-2-methyl-l- propanesulfonic acid, 3 -allyloxy-2-hydroxy-l -propanesulfonic acid, acrylamide, the like, and any combination thereof.

[0022] The thickener may be present in the thixotropic stripping composition in an amount ranging from about 1 wt% to about 20 wt% (e.g., from 1 wt% to 5 wt%, from 3 wt% to 10 wt%, from 5 wt% to 12 wt%, or from 10 wt% to 20 wt%), based on a total weight of the thixotropic stripping composition.

[0023] Suitable solvents can be aqueous solvents that comprise water and optionally another solvent. Examples of solvents may include, but are not limited to, water, alcohols (e.g., methanol, ethanol, propanol, etc.), nitric acid, urea, the like, and any combination thereof. When water and one or more additional solvents are present, the weight ratio of water to the one or more additional solvents (cumulatively) ranges from about 1 : 1 to about 100: 1 (e.g., from 1:1 to 10:1, from 5:1 to 25:1, from 20:1 to 60:1, or from 50:1 to 100:1).

[0024] The solvents may be present in the thixotropic stripping composition in a sufficient amount to achieve a desired viscosity. For example, the solvent may be present in the thixotropic stripping composition in an amount ranging from about 25 wt% to about 90 wt% (e.g., from 25 wt% to 50 wt%, from 45 wt% to 65 wt%, from 50 wt% to 80 wt%, or from 65 wt% to 90 wt%), based on a total weight of the thixotropic stripping composition. However,amounts outside the foregoing range may be suitable, if needed, as determined by one of skill in the art, for attaining the desired viscosity.

[0025] The thixotropic stripping composition may also include one or more additives. Examples of additives may include, but are not limited to, a surfactant, a stripping enhancement additive, an abrasive additive, a buffer, a corrosion inhibitor, a hydrogen inhibitor, the like, and any combination thereof. Individual additives should be chosen to minimally react, and preferably not react, with the other components of the thixotropic stripping composition, especially the stripping component. In some instances, an additive (e.g., specific surfactants) may be prone to hydrolysis over time when exposed to water. Accordingly, how the thixotropic stripping composition is produced and stored and should be considered when deciding whether or not to use said additive. For example, the thixotropic stripping composition may be produced on-site from a kit where a hydrolysis-prone additive is in dry form and then mixed with water within a few hours of using the resultant thixotropic stripping composition. Accordingly, inclusion of the hydrolysis-prone additive is likely suitable. In contrast, a thixotropic stripping composition prepared days to months before use may not include the hydrolysis-prone additive.

[0026] Surfactants may, among other things, assist wetting the coating being stripped. Surfactants may be anionic, cationic, nonionic, or zwitterionic. A combination of the foregoing may be used. Examples of anionic surfactants may include, but are not limited to, alkyl sulfates, alkyl ether sulfates, alkylamido ether sulfates, alkylaryl polyether sulfates, monoglyceride sulfates, alkylsulfonates, alkylamidesulfonates, alkylarylsulfonates, a-olefm sulfonates, paraffmsulfonates, alkylsulfosuccinates, alkyl ether sulfosuccinates, alkylamidesulfosuccinates, alkylsulfoacetates, acylsarcosinates, acylglutamates, the like, and any combination thereof. The alkyl and acyl groups of the foregoing compounds may contain 6 to 24 carbon atoms and the aryl group optionally being chosen from phenyl and benzyl groups. Examples of cationic surfactants may include, but are not limited to, alkyl quaternary ammonium salts (e.g., cetyltrimethylammonium chloride, behenyltrimethylammonium chloride, and palmitylamidopropyltrimethylammonium chloride), the like, and any combination thereof. The foregoing alkyl groups apply to the cationic surfactants. Examples of nonionic surfactants may include, but are not limited to, alcohols, alpha-diols, alkyl(Cn 2o)phenols, and fatty acids that are polyethoxylated, polypropoxylated, or polyglycerolated, having a fatty chain containing, for example, 8 to 18 carbon atoms, the like, and any combination thereof. The number of ethylene oxide or propylene oxide groups may range from 2 to 50, and the number of glycerol groups to range from 2 to 30. Examples of zwitterionicsurfactants may include, but are not limited to, cocoamido propyl betaine, cocoamphoacetate, the like, and any combination thereof.

[0027] When included, the surfactants may be present in the thixotropic stripping composition in an amount ranging from about 0.01 wt% to about 5 wt% (e.g., from 0.01 wt% to 1 wt%, from 0.05 wt% to 0.5 wt%, from 0.5 wt% to 3 wt%, or from 2 wt% to 5 wt%), based on a total weight of the thixotropic stripping composition.

[0028] Stripping enhancement additives may increase the rate of stripping, which may, for example, be achieved by enhancing the activity of the stripping component and / or by stripping via a different reaction. Examples of stripping enhancement additives may include, but are not limited to, an acid (e.g., nitric acid and / or hydrochloric acid), hydrogen peroxide, cyanide, the like, and any combination thereof.

[0029] When included, the acid stripping enhancement additives (e.g., nitric acid and / or hydrochloric acid) may be present in the thixotropic stripping composition in an amount sufficient to achieve a molarity ranging from about 0.01 M to about 1 M (e.g., from 0.01 M to 0.1 M, from 0.05 M to 0.5 M, or from 0.1 M to 1 M), based on a total weight of the thixotropic stripping composition. When included, other stripping enhancement additives (e.g., hydrogen peroxide and / or cyanide) may be present in the thixotropic stripping composition in an amount ranging from about 0.01 wt% to about 1 wt% (e.g., from 0.01 wt% to 0.1 wt%, from 0.05 wt% to 0.5 wt%, or from 0.1 wt% to 1 wt%), based on a total weight of the thixotropic stripping composition.

[0030] Abrasive additives are particulates that may be useful for causing physical degradation of the coating, which may expose more surface area of the coating to the thixotropic stripping composition and decrease the time for stripping the coating. Preferably, abrasive additives are particles composed of materials having a Mohs hardness of about 4 or greater (e.g., from 4 to 10). Depending on the hardness of the particle thickeners, the particle thickeners may provide at least some abrasive qualities to the thixotropic stripping composition. Examples of materials suitable for use in abrasive additives may include, but are not limited to, silica, alumina, titania, magnesium oxide, boron, nitride, sand, steel, the like, and any combination thereof. The material should be chosen to not react with other components in the thixotropic stripping composition including the stripping component and the stripping enhancement additive.

[0031] Abrasive additives may be larger than particle thickeners. For example, abrasive additives may include particles having an average diameter from about 5 pm to about 20 pm (e.g., from 5 pm to 15 pm, 7 pm to 13 pm, or 10 pm to 20 pm).

[0032] When included, the abrasive additives (other than particle thickeners) may be present in the thixotropic stripping composition in an amount ranging from about 0.01 wt% to about 1 wt% (e.g., from 0.01 wt% to 0.1 wt%, from 0.05 wt% to 0.5 wt%, or from 0.1 wt% to 1 wt%), based on a total weight of the thixotropic stripping composition.

[0033] Corrosion inhibitors may be added to the solution to protect the substrate after stripping procedures are completed. Corrosion inhibitors are substances that, when added in a proper amount to the aggressive solutions that can cause metal corrosion, may prevent and / or slow down corrosion phenomena without causing a significant alteration of the solution composition. Examples of corrosion inhibitors may include, but are not limited to, organic corrosion inhibitors (e.g., fatty amides, pyridines, polymers, and imidazolines), inorganic corrosion inhibitors (e.g., chromates, dichromates, phosphates, and arsenates), the like, and any combination thereof.

[0034] When included, the corrosion inhibitor may be present in the thixotropic stripping composition in an amount ranging from about 0.01 wt% to about 1 wt% (e.g., from 0.01 wt% to 0.1 wt%, from 0.05 wt% to 0.5 wt%, or from 0.1 wt% to 1 wt%), based on a total weight of the thixotropic stripping composition.

[0035] Buffers may be useful in maintaining a desired pH or pH range for the thixotropic stripping compositions while the stripping reaction occurs. The pH of the thixotropic stripping composition using ammonium nitrate may preferably range from about 3.0 to about 6.0 before application of the thixotropic stripping composition. The pH of the thixotropic stripping composition using a combination of a base and an amine may preferably range from about 11.0 to about 14.0 before application of the thixotropic stripping composition. Preferably, said pH is maintained while the thixotropic stripping composition is in contact with the coating. Additionally, solutions may be pH adjusted to alter stripping speed (e.g., ammonium nitrate may be pH adjusted to 8-9 using sodium hydroxide).

[0036] Hydrogen inhibitors may react with hydrogen produced during the stripping reaction to mitigate hydrogen embrittlement of the substrate having the coating thereon. Hydrogen inhibitors are preferably used with ammonium nitrate stripping components. When included, the hydrogen inhibitors may be present in the thixotropic stripping composition in an amount ranging from about 0.01 wt% to about 1 wt% (e.g., from 0.01 wt% to 0.1 wt%, from 0.05 wt% to 0.5 wt%, or from 0.1 wt% to 1 wt%), based on a total weight of the thixotropic stripping composition.

[0037] Methods

[0038] The thixotropic stripping compositions of the present disclosure may be useful for stripping coatings that comprise cadmium, a zinc-nickel alloy, or a combination thereof from the surface of a substrate. Depending on the purpose of removing the coating, the coating across the entire substrate may be removed, or the coating at only a portion of the substrate may be removed. The area across the entire substrate removed using the methods and the thixotropic stripping compositions of the present disclosure may be 1 mm2or greater (e.g., 25 mm2or greater, 100 mm2or greater, from 1 mm2to 1 m2, from 1 mm2to 10 cm2, from 1 cm2to 100 cm2, from 10 cm2to 250 cm2, or from 100 cm2to 1 m2). Herein, when referring to removing a coating from a substrate, both of the foregoing are encompassed, unless otherwise specified. The various methods herein may remove the entire thickness of the coating or a portion of the thickness of the coating (e.g., 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more) from the substrate. Herein, when referring to removing at least a portion of the coating, both of the foregoing are encompassed, unless otherwise specified.

[0039] Said substrate may be one or more of the following materials: stainless steel, high strength steel, low grade steel, aluminum, aluminum alloy, titanium, titanium alloy, copper, copper alloy, nickel, nickel alloy, uranium, and the like. The substrate may be at least a portion of a vehicle (e.g., an aircraft, an automotive vehicle, a water-borne vehicle, a subsurface vehicle, a non-terrestrial vehicle, and the like), support equipment, a metal structure, a subsea structure, a solar cell, or a structure within an electrical device (e.g., electrical components, electrical connectors, electrical grounding, and the like).

[0040] The thixotropic stripping composition of the present disclosure may be used for removing coatings having a thickness ranging from about 0.1 pm or greater (e.g., 0.1 pm to 3 pm, 0.5 pm to about 5 pm, 3 pm to about 10 pm, or 10 pm to 30 pm). Depending on the original thickness of the coating, the thixotropic stripping composition of the present disclosure (e.g., applied one or more times) may be used alone for removing the coating, or a mechanical method may be used for reducing the coating thickness before application of the thixotropic stripping composition of the present disclosure. For example, before treating a coating with a thixotropic stripping composition of the present disclosure, a portion of the coating may be physically removed, for example, via sand blasting and / or grinding. The thixotropic stripping composition of the present disclosure may be used for removing the remaining portion of the coating (e.g., up to about 10 pm thick of coating).

[0041] Depending on the amount of time the thixotropic stripping composition of the present disclosure is allowed to interact with the coating and underlying substrate, a portion of the substrate may also be consumed in the stripping method. Preferably, the substrate may be etched by about 25 pm or less (e.g., from 0.1 pm to 25 pm, from 0.1 pm to 15 pm, from 0.1 pm to 5 pm, or from 0.1 pm to 1 pm). In some instances, there may be no etching of the substrate.

[0042] Generally, methods of the present disclosure may include stripping a coating from at least a portion a surface of a substrate using a thixotropic stripping composition of the present disclosure. Stripping may include treating a substrate with a thixotropic stripping composition of the present disclosure to strip at least a portion of a coating from the surface of the substrate. During treating, contact between the thixotropic stripping composition and the coating may be maintained for a desired amount of time. Herein, the term “contact time” refers to the amount of time the thixotropic stripping composition is in contact with the coating.

[0043] As discussed herein, the thixotropic stripping composition of the present disclosure advantageously serves the purpose of allowing the stripping component to contact the coating for the stripping reaction, as well as absorbing the cadmium and / or zinc-nickel products of said stripping reaction. Keeping the cadmium and / or zinc-nickel products in the thixotropic stripping composition may mitigate environmental exposure to said products, as compared to less viscous stripping solutions. Further, the total amount of spent material containing said products may be reduced because the thixotropic stripping composition of the present disclosure can maintain contact with the coating for longer periods of time, as compared to less viscous stripping solutions.

[0044] As used herein, the terms “cadmium products” and “zinc-nickel products” refer to the reaction products containing cadmium, zinc, nickel, or a combination thereof resulting from the reaction of one or more components of the thixotropic stripping composition with coatings comprising cadmium or zinc-nickel alloy. The terms do not limit the exact composition of said reaction products. For example, when treating a coating comprising a zinc-nickel alloy, zinc- nickel reaction products encompass chemical compounds that include zinc but not nickel, nickel but not zinc, and zinc and nickel.

[0045] Methods of the present disclosure may include applying a thixotropic stripping composition of the present disclosure to a coating on a substrate; maintaining the thixotropic stripping composition thereon for a contact time; and removing the spent thixotropic stripping composition from the substrate. The spent thixotropic stripping composition is the thixotropicstripping composition after reacting with the coating and, therefore, includes cadmium products and / or zinc-nickel products.

[0046] Preferably, the contact time may be about 10 seconds or longer (e.g., from 10 seconds to 36 hours or longer, from 10 seconds to 10 minutes, from 5 minutes to 45 minutes, from 30 minutes to 3 hours, from 1 hour to 12 hours, from 6 hours to 24 hours, or from 12 hours to 36 hours or longer). Shorter and longer contact times are contemplated. The contact time may depend on, among other things, the concentration of the stripping component, the thickness of the coating, the composition of the coating, the desired thickness to be removed from the coating, the temperature, the inclusion or absence of certain additives like abrasion additives, and the like. The contact time may be sufficiently long to remove the coating and, potentially, a portion (e.g., about 25 pm or less) of the substrate. Alternatively, the contact time may be sufficiently long to remove only a portion of the coating such that the method of applying, maintaining contact, and removing is performed more than once to remove the entirety of the coating thickness.

[0047] For example, in some instances, a method of the present disclosure may include performing a stripping cycle at least once (e.g., at least twice, at least 5 times, at least 15 times, 1 time to 50 times, 2 times to 50 times, 1 time to 10 times, 2 times to 15 times, 5 times to 20 times, 15 times to 30 times, or 25 times to 50 times), the stripping cycle comprising: applying a thixotropic stripping composition of the present disclosure to a coating on a substrate; maintaining the thixotropic stripping composition thereon for a contact time; and removing the spent thixotropic stripping composition from the substrate.

[0048] The thixotropic stripping composition, while contacting with the coating, may be at ambient temperature or above ambient temperature (e.g., by purposefully applying heat). The temperature of the thixotropic stripping composition, while contacting with the coating, may be 20°C or greater (e.g., 25°C or greater, 30°C or greater, from 20°C to 50°C, from 20°C to 35°C, from 30°C to 40°C, or from 35°C to 50°C). For example, the thixotropic stripping composition may be preheated before application. In another example, the thixotropic stripping composition may be actively heated (e.g., with a heat gun or other radiant heat device) while in contact with the coating. Heating may increase the rate of the stripping reaction.

[0049] In some instances, abrasive additives may be included in the thixotropic stripping composition where applying the thixotropic stripping composition includes applying sufficient pressure to cause physical degradation (e.g., scratches) in the coating. The physical degradation may increase the surface area of the coating that is accessible to the thixotropic stripping composition and, consequently, decrease the stripping time.

[0050] Removing the thixotropic stripping composition from the substrate may be by any suitable method. Examples of methods include, but are not limited to, washing with a solvent (different from or the same as in the thixotropic stripping composition), wiping, scraping, the like, and any combination thereof. Preferably, the method of removing includes wiping the thixotropic stripping composition from the substrate with a cloth or the like. Preferably, the cloth is moistened with a solvent.

[0051] After removal, the thixotropic stripping composition (and cloth or the like) may be placed in a container suitable for proper disposal.

[0052] The substrate exposed by the stripping method may be inspected for damage from corrosion, mechanical wear, and the like. Further, if damage is found, the substrate may be repaired and optionally recoated (e.g., with a cadmium-containing coating and / or zinc-nickel alloy containing coating).

[0053] In at least a portion of the time between stripping and recoating, a preservation coating or oil may be applied to the substrate to mitigate damage from the local environment. For example, in marine environments, the preservation coating or oil may be applied to mitigate corrosion of the substrate.

[0054] Kits

[0055] Kits of the present disclosure may include a container containing one or more components of a thixotropic stripping composition of the present disclosure and a set of instructions for preparing and / or using the thixotropic stripping composition. In some instances, the container may be suitable for mixing the components of the thixotropic stripping composition to produce said thixotropic stripping composition. In other instances, the container may be disposable. In other instances, the container may be suitable for use as a disposal container for the spent thixotropic stripping composition. In another instance, the container may be suitable for both mixing the thixotropic stripping composition and disposing of the spent thixotropic stripping composition.

[0056] Optionally, other parts of the kit may include, but are not limited to, an applicator, a disposal container, an environmental health and safety label for the spent thixotropic stripping composition, a cleaning cloth, personal protective equipment (e.g., nitrile gloves, latex gloves, and the like), the like, and any combination thereof.

[0057] The one or more components of a thixotropic stripping composition may be premixed, separate, or a combination thereof. Further, all or some of the one or more components of a thixotropic stripping composition may be in a dry form (e.g., having a water content of lessthan 1 wt%) where the instructions include steps for adding a solvent and mixing to produce the thixotropic stripping composition having a desired viscosity.

[0058] For example, a kit may include the stripping composition at a high concentration in a solvent and a thickener (dry or wet) separate from the stripping composition. The instructions, for example, may include steps for (i) diluting the highly concentrated stripping composition with additional solvent (which may be the same or different than the solvent in which the stripping composition is concentrated) and (ii) mixing the thickener into the diluted stripping composition. The instructions may include different volumes of additional solvents that can be used for dilution based on the desired final viscosity.

[0059] In another example, a kit may include a dry mixture of the stripping composition, the thickener, and one or more additives (e.g., a surfactant, an abrasive additive, etc.). The instructions, for example, may include steps for mixing the dry mixture with a solvent to produce the thixotropic stripping composition. Again, the instructions may include different volumes of solvent that can be used for dilution based on the desired final viscosity.

[0060] In another example, a kit may include the following (each wet or dry) separated from each other: a stripping composition, a thickener, a surfactant, and, optionally, a hydrogen inhibitor. The instructions, for example, may include steps for mixing the foregoing with a solvent and, optionally, a buffer to produce the thixotropic stripping composition. Again, the instructions may include different volumes of solvent that can be used for dilution based on the desired final viscosity.

[0061] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties (e.g., molecular weight), reaction conditions, and the like used in the present disclosure and associated claims are to be understood as being modified in all instances by the term “about.” At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, the term “about” relative to each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0062] A concentration range listed or described as being useful, suitable, or the like is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, a range “from 1 to 10” or “of 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific data points, it is to be understood that inventors appreciate and understand that any and all data points within the range are to beconsidered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.

[0063] The term “and / or” refers to both the inclusive “and” case and the exclusive “or” case, and is used herein for brevity. For example, a mixture comprising acetic acid and / or methyl acetate may comprise acetic acid alone, methyl acetate alone, or both acetic acid and methyl acetate.

[0064] A listing following “one or more of’ or “at least one of’ using “and” to connect the listing is intended in the alternative or conjunctive rather than the disjunctive. For example, “at least one of A, B, and C” and “one or more of A, B, and C” are each considered to disclose embodiments of A alone, B alone, C alone, A and B in combination, A and C in combination, B and C in combination, and all three of A, B, and C in combination.

[0065] Room temperature is 25°C, and atmospheric pressure is 101.325 kPa unless otherwise noted.

[0066] While compositions, systems, and methods are described herein in terms of “comprising” various components or steps, the compositions, systems, and methods can also “consist essentially of’ or “consist of’ the various components and steps.

[0067] Illustrative embodiments of the invention are described herein. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer’s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0068] Example Embodiments

[0069] Embodiment 1. A thixotropic stripping composition comprising: a stripping component comprising ammonium nitrate or a combination of a base and an amine; a thickener; and a solvent, wherein a viscosity of the thixotropic stripping composition is about 200 cP or greater.

[0070] Embodiment 2. The thixotropic stripping composition of Embodiment 1, wherein the stripping component comprises the ammonium nitrate at about 5 wt% to about 30 wt%, based on a total weight of the thixotropic stripping composition.

[0071] Embodiment s. The thixotropic stripping composition of Embodiment 1, wherein the stripping component comprises the combination of a base and an amine with thebase at about 10 wt% to about 35 wt% and the amine at about 1 wt% to about 25 wt%, each based on a total weight of the thixotropic stripping composition.

[0072] Embodiment 4. The thixotropic stripping composition of any one ofEmbodiments 1-3, wherein the thickener comprises particles.

[0073] Embodiment 5. The thixotropic stripping composition of any one ofEmbodiments 1-3, wherein the thickener comprises a polymer.

[0074] Embodiment 6. The thixotropic stripping composition of any one ofEmbodiments 1-3, wherein the thickener comprises a swellable polymer.

[0075] Embodiment 7. The thixotropic stripping composition of any one ofEmbodiments 1-6, wherein the thickener is present at about 1 wt% to about 20 wt%, based on a total weight of the thixotropic stripping composition.

[0076] Embodiment 8. The thixotropic stripping composition of any one ofEmbodiments 1-7, further comprising a surfactant.

[0077] Embodiment 9. The thixotropic stripping composition of Embodiment 8, wherein the surfactant is present at about 0.01 wt% to about 5 wt%, based on a total weight of the thixotropic stripping composition.

[0078] Embodiment 10. The thixotropic stripping composition of any one of Embodiments 1-9, further comprising one or more additives selected from the group consisting of: a stripping enhancement additive, an abrasive additive, a buffer, a corrosion inhibitor, and a hydrogen inhibitor.

[0079] Embodiment 11. A kit comprising: a container containing the thixotropic stripping composition of any one of Embodiments 1-10 and a set of instructions for using the thixotropic stripping composition.

[0080] Embodiment 12. The kit of Embodiment 11, further comprising one or more of: an applicator, a disposal container, an environmental health and safety label for the spent thixotropic stripping composition, a cleaning cloth, and personal protective equipment.

[0081] Embodiment 13. A method comprising: stripping at least a portion of a coating on a substrate using the thixotropic stripping composition of any one of Embodiments 1-10.

[0082] Embodiment 14. The method of Embodiments 13, wherein the substrate is at least a portion of vehicle, a support equipment, a metal structure, a subsea structure, a solar cell, or a structure within an electrical device.

[0083] Embodiment 15. The method of Embodiments 13 or 14, wherein the coating comprises cadmium, a nickel / zinc alloy, or any combination thereof.

[0084] Embodiment 16. The method of any one of Embodiments 13-15, wherein the substrate comprises stainless steel, high strength steel, low grade steel, aluminum, aluminum alloy, titanium, titanium alloy, copper, copper alloy, nickel, nickel alloys, uranium, or any combination thereof.

[0085] Embodiment 17. A kit comprising: a stripping component comprising ammonium nitrate or a combination of a base and an amine; one or more of a thickener, a solvent, and one or more additives; a container; and a set of instructions for producing and / or using a thixotropic stripping composition comprising the stripping component, the thickener, the solvent, and, optionally, one or more additives.

[0086] Embodiment 18. The kit of Embodiment 17, wherein the solvent is not present in the kit.

[0087] Embodiment 19. The kit of Embodiment 17 or 18, further comprising one or more of: an applicator, a disposal container, an environmental health and safety label for spent thixotropic stripping composition, a cleaning cloth, and personal protective equipment.

[0088] Embodiment 20. The kit of any one of Embodiments 17-19, wherein the container is a first container that contains the stripping component in the solvent at a higher concentration than in the thixotropic stripping composition; wherein the kit further comprises a second container comprising the thickener and, optionally, one or more additives; and wherein the set of instructions includes a step for diluting the stripping component with an additional solvent.

[0089] Embodiment 21. The kit of Embodiment 20, wherein the components in the second container are dry.

[0090] Embodiment 22. A method comprising: treating a substrate with a thixotropic stripping composition to strip at least a portion of a coating from the substrate, the thixotropic stripping composition comprising: a stripping component comprising ammonium nitrate or a combination of a base and an amine; a thickener; and a solvent; wherein a viscosity of the thixotropic stripping composition is about 200 cP or greater; and removing the thixotropic stripping composition from the substrate.

[0091] Embodiment 23. The method of Embodiment 22, wherein the treating comprises: applying the thixotropic stripping composition to the coating; and maintaining the thixotropic stripping composition thereon until the coating is removed from the substrate.

[0092] Embodiment 24. The method of Embodiment 22 or 23, wherein the treating comprises: performing two or more stripping cycles, each stripping cycle comprising: (i) applying the thixotropic stripping composition to the coating; (ii) maintaining the thixotropic stripping composition thereon to remove at least a portion of the remaining coating; and (iii)removing the thixotropic stripping composition from the substrate and / or the remaining coating.

[0093] Embodiment 25. The method of any one of Embodiments 22-24, wherein the thixotropic stripping composition is at an elevated temperature during at least a portion of the treating.

[0094] Hereinafter, the present invention will be better understood in view of the following nonlimiting examples.

[0095] Examples

[0096] A series of thixotropic stripping composition were prepared with the compositions of Table 1.Table 1

[0097] The thixotropic stripping compositions prepared within the scope of Examples 2 and 3 were less aggressive at stripping a cadmium-containing coating.

Claims

WHAT IS CLAIMED IS:

1. A thixotropic stripping composition comprising: a stripping component comprising ammonium nitrate or a combination of a base and an amine; a thickener; and a solvent, wherein a viscosity of the thixotropic stripping composition is about 200 cP or greater.

2. The thixotropic stripping composition of claim 1, wherein the stripping component comprises the ammonium nitrate at about 5 wt% to about 30 wt%, based on a total weight of the thixotropic stripping composition.

3. The thixotropic stripping composition of claim 1, wherein the stripping component comprises the combination of a base and an amine with the base at about 10 wt% to about 35 wt% and the amine at about 1 wt% to about 25 wt%, each based on a total weight of the thixotropic stripping composition.

4. The thixotropic stripping composition of claim 1, wherein the thickener comprises particles.

5. The thixotropic stripping composition of claim 1, wherein the thickener comprises a polymer.

6. The thixotropic stripping composition of claim 1, wherein the thickener comprises a swellable polymer.

7. The thixotropic stripping composition of claim 1, wherein the thickener is present at about 1 wt% to about 20 wt%, based on a total weight of the thixotropic stripping composition.

8. The thixotropic stripping composition of claim 1, further comprising a surfactant.

9. The thixotropic stripping composition of claim 8, wherein the surfactant is present at about 0.01 wt% to about 5 wt%, based on a total weight of the thixotropic stripping composition.

10. The thixotropic stripping composition of claim 1, further comprising one or more additives selected from the group consisting of: a stripping enhancement additive, an abrasive additive, a buffer, a corrosion inhibitor, and a hydrogen inhibitor.

11. A kit comprising: a container containing the thixotropic stripping composition of claim 1 and a set of instructions for using the thixotropic stripping composition.

12. The kit of claim 11, further comprising one or more of: an applicator, a disposal container, an environmental health and safety label for spent thixotropic stripping composition, a cleaning cloth, and personal protective equipment.

13. A method compri sing : stripping at least a portion of a coating on a substrate using the thixotropic stripping composition of claim 1.

14. The method of claim 13, wherein the substrate is at least a portion of vehicle, a support equipment, a metal structure, a subsea structure, a solar cell, or a structure within an electrical device.

15. The method of claim 13, wherein the coating comprises cadmium, a nickel / zinc alloy, or any combination thereof.

16. The method of claim 13, wherein the substrate comprises stainless steel, high strength steel, low grade steel, aluminum, aluminum alloy, titanium, titanium alloy, copper, copper alloy, nickel, nickel alloys, uranium, or any combination thereof.

17. A kit comprising: a stripping component comprising ammonium nitrate or a combination of a base and an amine;one or more of a thickener, a solvent, and one or more additives; a container; and a set of instructions for producing and / or using a thixotropic stripping composition comprising the stripping component, the thickener, the solvent, and, optionally, one or more additives.

18. The kit of claim 17, wherein the solvent is not present in the kit.

19. The kit of claim 17, further comprising one or more of: an applicator, a disposal container, an environmental health and safety label for spent thixotropic stripping composition, a cleaning cloth, and personal protective equipment.

20. The kit of claim 17, wherein the container is a first container that contains the stripping component in the solvent at a higher concentration than in the thixotropic stripping composition; wherein the kit further comprises a second container comprising the thickener and, optionally, one or more additives; and wherein the set of instructions includes a step for diluting the stripping component with an additional solvent.

21. The kit of claim 20, wherein the components in the second container are dry.

22. A method comprising: treating a substrate with a thixotropic stripping composition to strip at least a portion of a coating from the substrate, the thixotropic stripping composition comprising: a stripping component comprising ammonium nitrate or a combination of a base and an amine; a thickener; and a solvent; wherein a viscosity of the thixotropic stripping composition is about 200 cP or greater; and removing the thixotropic stripping composition from the substrate.

23. The method of claim 22, wherein the treating comprises: applying the thixotropic stripping composition to the coating; andmaintaining the thixotropic stripping composition thereon until the coating is removed from the substrate.

24. The method of claim 22, wherein the treating comprises: performing two or more stripping cycles, each stripping cycle comprising:(i) applying the thixotropic stripping composition to the coating;(ii) maintaining the thixotropic stripping composition thereon to remove at least a portion of the remaining coating; and(iii) removing the thixotropic stripping composition from the substrate and / or the remaining coating.

25. The method of claim 22, wherein the thixotropic stripping composition is at an elevated temperature during at least a portion of the treating.

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