Patent Application
20170327955
This disclosure relates to coatings for corrosion protection, and more specifically to conversion coatings for corrosion protection of metal substrates.
Many metals are subject to corrosion, which can be exacerbated by exposure to corrosion-promoting environmental conditions such as high-chloride environments found in proximity to marine environments. Surface coatings have been used to provide protection against corrosion by imposing a physical barrier between the metal substrate and the surrounding environment. However, conventional polymer surface coatings can suffer from a number of problems such as inadequate or uneven thickness, pinholes and other gaps in coating coverage, and the necessity of extensive surface preparation of the substrate prior to application of the coating in order to provide adequate bonding between the coating and the substrate, in addition to the cost, time and complexity of applying the polymer coating.
Metal surface treatments such as conversion coatings have been used to protect metals such as aluminum, zinc, cadmium, tin, magnesium, iron, copper, silver, and their alloys such as zinc-nickel, tin-zinc, etc. Conversion coating compositions have been commonly applied to large surface area substrates by immersion or spray application. Such techniques, however, can be cumbersome for touch-up application such as to repair abraded surfaces or at connection interfaces between assembled metal components. Small scale handheld application of conversion coatings has been performed with felt pen-style applicators. Historically, chromate conversion coatings utilizing hexavalent chromium have been effectively used to provide corrosion protection. However, the use of hexavalent chromium is largely in the process of being discontinued due to toxicity concerns. Touch-up conversion coatings based on trivalent chromium have been applied with felt pen-style applicators; however, such trivalent conversion coatings have been found to be less effective at preventing corrosion than conversion coatings based on hexavalent chromium.
According to some aspects of this disclosure, a kit for applying a coating comprises a first handheld container comprises a first liquid composition disposed therein that comprises a trivalent chromium salt. A first applicator is disposed in fluid communication with the first container and is configured to dispense the first composition. The kit also includes a second handheld container comprises a second liquid composition disposed therein comprising an oxidizing agent. A second applicator is disposed in fluid communication with the second container and is configured to dispense the second composition.
In some aspects, a method of using the above-described kit comprises applying a coating of the first composition to a substrate, allowing a drying period of time to pass, applying the second composition to the coated substrate, and maintaining a wet layer of the second composition on the coated substrate for at least 0.5 minutes.
In some aspects, a method of protecting a trivalent chromium conversion-coated substrate from corrosion comprises contacting the substrate with a porous pad disposed on an end of an oblong handheld housing in fluid communication with a chamber disposed within the housing, and dispensing a liquid composition comprising an oxidizing agent disposed in the chamber onto the substrate through the porous pad.
The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
With reference now to the Figures,
In some embodiments, the trivalent chromium salt composition can be an aqueous solution or a non-aqueous solution comprising trivalent chromium and various anions. Exemplary anions include nitrate, sulfate, phosphate, and/or acetate. Specific exemplary trivalent chromium salts can include Cr2(SO4)3, (NH)4Cr(SO4)2, KCr(SO4)2, CrF3Cr(NO3)3, and mixtures comprising any of the foregoing. The concentration of the trivalent chromium salt in the composition, per liter of solution, can range from about 0.01 g to about 22 g, more specifically from about 3 g to about 12 g, and even more specifically from about 4 g to about 8.0 g. Embodiments of compositions and the application thereof to substrates are described in U.S. Pat. Nos. 5,304,257, 5,374,347, 6,375,726, 6,511,532, 6,521,029, and 6,511,532, the disclosures of which are incorporated herein by reference in their entirety. Various additives and other materials can be included in the composition comprising trivalent chromium as disclosed in the patent literature, and the trivalent chromium salt composition can be selected from any of a number of known commercially-available compositions.
In some embodiments, the oxidizing agent can be a peroxide or a permanganate salt. In some embodiments, the oxidizing agent is hydrogen peroxide (H2O2). Examples of peroxides other than hydrogen peroxide include inorganic peroxides (e.g. Li2O2, Na2O2, K2O2, BaO2), and organic peroxides (e.g., R—OO—R′, R—OO—H, or RCO—OO—R′, where R, and R′ are organic groups). The oxidizing agent can be in aqueous or non-aqueous solutions at concentrations in ranges having a lower endpoint of 0.1 wt. %, more specifically 0.5 wt. %, more specifically 1.0 wt. %, more specifically 2.0 wt. %, more specifically 3.0 wt. %, and more specifically 4.0 wt. %, and an upper endpoint of 10.0 wt. %, more specifically 9.0 wt. %, more specifically 8 wt. %, more specifically 7 wt. %, more specifically 6 wt. %, more specifically 4 wt. %, and even more specifically 3.5 wt. %. The above upper and lower endpoints can be independently combined to disclose various different ranges.
The compositions in the chambers 11a, 11b can be dispensed by bringing the liquid compositions in the chambers 11a, 11b into contact with the dispensing applicators 14a, 14b, respectively. Each dispensing applicator 14a, 14b can independently be selected as a porous material configured to transport the liquid composition from the respective chamber 11a, 11b to a substrate in contact with the outer surface of the applicator 14a, 14b. The liquid composition can be brought into contact with the applicator 14a, 14b by bringing the dispensing applicator 14a, 14b into contact with a fixed-position surface (which can but does not have to be the substrate to be coated) and applying hand pressure on the housing 10a, 10b toward the surface to open the poppet valve 15a, 15b. The dispensing applicators 14a, 14b are slideably mounted in the housing 10a, 10b. At rest, the dispensing applicators 14a, 14b are biased away from the main body of the housing 10a, 10b by applicator biasing members (not shown) to an at-rest position as shown in
Another example embodiment of a kit is schematically depicted in
In some embodiments, avoidance of contamination from chromium salts on the substrate being coated into the second container comprising the oxidizing agent composition is promoted by contamination-avoiding materials or components. In some embodiments, the applicator 14b can be formed from a material that is resistant to wicking of material from the coated substrate into the chamber 17b from which it could potentially infiltrate to the chamber 11b when the poppet valve 15b is open. Such materials can include surfaces that are resistant to wetting by the coated chromium salt composition. In some embodiments, the poppet valve 15b can include check-valve features (not shown, but known in the valve art) to prevent migration of fluid from chamber 17b into chamber 11b. In some embodiments, anti-contamination procedures can be followed such as draining or flushing the chamber 17b after application is complete, or using a surface other than the coated substrate for displacing the applicator 14b to charge the chamber 17b so that the poppet valve 15b is closed before the applicator 14b comes into contact with the coated substrate. Combinations of the above materials or procedures can be used as well.
In some embodiments, the first liquid composition comprising the trivalent chromium salt can be allowed to contact the substrate for a period of time before applying the second composition comprising the oxidizing agent, and in some embodiments the kit can include instructions to that effect. The amount of contact time can vary considerably depending on the ambient temperature and humidity, the specific properties of the applicator and the liquid composition, and the thickness with which it is applied. Any amount of contact time greater than zero can be used. In some embodiments, contact times can range from 1 minute to 5 minutes. In some embodiments, contact times can range from 1 minute to 3 minutes.
In some embodiments, a wet layer of the second liquid composition comprising the oxidizing agent is maintained on the coated substrate for a minimum period of time. Although this disclosure is not bound by any theory of operation, it is believed that the wet layer promotes chemical interaction of the oxidizing agent with the trivalent chromium salt composition. Examples of minimum wet layer time limits can include 0.5 minutes, more specifically 1 minute, more specifically 1.5 minutes, more specifically 2 minutes, more specifically 3 minutes, more specifically 4 minutes, and even more specifically 5 minutes. Theoretically there is no maximum wet layer time; however, minimization of the opportunity costs of lost efficiency typically results in drying times that do not drastically exceed the specified minimum wet layer time. In some embodiments, a wet layer of the second liquid composition comprising the oxidizing agent is maintained by making a plurality of passes over the substrate with the applicator 14b, and in some embodiments the kit can include instructions to that effect. In some embodiments, the second liquid composition can be configured to maintain a wet layer for a target duration, e.g., through the inclusion of additives such as gel or thickening agents (e.g., fused silica, water soluble polymers) or lower volatility solvents. Moisture can also be retained by film-forming agents in the first composition such as sodium or potassium salts of hexafluorotitanic acid or hexafluorozirconic acid, or the selection of a chromium salt with colligative properties such as high solubility that render it inherently slow-drying.
While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
