Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
2001-08-01
2004-05-25
Oltmans, Andrew L. (Department: 1742)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C428S570000, C148S247000, C148S253000, C148S261000, C148S265000, C106S014120, C252S387000
Reexamination Certificate
active
06740424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aluminum fine powder suitable for use in an aqueous phosphate-based coating composition which takes advantage of a sacrificial corrosion inhibiting effect of aluminum and to an aqueous chromium-free corrosion inhibiting coating composition which does not contain harmful chromium components and which is formed with the aluminum fine powder suspended in an aqueous phosphate-based bonding solution, in order to inhibit corrosion of a metal surface, especially a surface of iron-based material.
2. Description of the Related Art
There are a variety of conventional corrosion inhibiting coating compositions depending on mechanisms of corrosion inhibition and based on corrosion inhibiting components. As such corrosion inhibiting coating compositions, coating compositions that are excellent in a corrosion inhibiting effect, taking advantage of a sacrificial corrosion inhibiting effect of zinc or aluminum, have been known as in the case of plating. Further, there are different kinds of bonding solutions (binders) for the corrosion inhibiting coating compositions, which are roughly classified into two categories, those with an inorganic aqueous bonding solution and those with an organic bonding solution. Well-known corrosion inhibiting coating compositions using the inorganic aqueous bonding solution include an alkali-silicate type of corrosion inhibiting coating composition such as a zinc-rich paint and a phosphate-based corrosion inhibiting coating composition such as a Sermetel coating composition available from SERMATECH INTERNATIONAL, INC. of the U.S. taking advantage of the sacrificial corrosion inhibiting effect of aluminum which is used for surface treatment of turbine blades of aircraft engines.
Many of these corrosion inhibiting coating compositions usually contain hexavalent chromium components that have a specific corrosion inhibiting effect. For example, a fundamental technology of the Sermetel coating composition from SERMATECH, INC. is disclosed in U.S. Pat. No. 3,248,251 filed in 1963 by Teleflex Incorporated that is a parent company of the SERMATECH. Although the patent describes that molybdate has the same corrosion inhibiting effect as that of chromate, hexavalent chromium (chromate ion) having a significant corrosion inhibiting effect is actually included in the Sermetel coating composition as an essential component.
Hexavalent chromium in the corrosion inhibiting coating composition would lead to formation of a conversion coating on a metal surface or to passivation of the metal surface. That is, the hexavalent chromium component in the Sermetel coating composition forms the conversion coating even on a particle surface of aluminum fine powder which is suspended in the coating composition so as to effectively prevent a reaction generating a hydrogen gas between an acidic phosphate-based bonding solution, the pH of which is around 3, and the aluminum fine powder. Therefore, it becomes possible to achieve a several-months pot life of the corrosion inhibiting coating composition.
Further, the corrosion inhibiting effect of the hexavalent chromium component also effects a metal substrate to be coated as well. The conversion coating or passivation coating including hexavalent chromium is formed on a surface of the metal substrate and prevents a reaction between the acidic phosphate-based bonding solution and substrates (hydrogen is generated when steel products are dipped). This conversion coating has the effect of protecting the substrate material from rust even after the coating has been baked. The Sermetel coating composition has excellent properties resulted from combining the sacrificial corrosion inhibiting effect of aluminum and the corrosion inhibiting function of the hexavalent chromium component and also has a reputation as an excellent corrosion inhibiting coating with a heat resistance up to around 600° C.
However, it has been commonly known that the hexavalent chromium component is carcinogenic, and even if trivalent chromium is used, it is not easy to prevent oxidation of trivalent chromium to hexavalent chromium. Therefore, it is preferable to use a corrosion inhibiting coating composition that is completely free of chromium components with consideration of their influences on the global environment. The first-ever non-chromium corrosion inhibiting coating composition, which is completely free of chromium components, has been developed by Solar Turbines Incorporated of the U.S. and is disclosed in U.S. Pat. No. 5,242,488. Thereafter, U.S. Pat. No. 5,478,413 titled “Environmentally friendly coating compositions” was filed from the SERMATECH INTERNATIONAL INC., which is an manufacturer of the Sermetel coating, and issued.
SUMMARY OF THE INVENTION
A problem in practical utilization of these non-chromium corrosion inhibiting coating compositions is that aluminum fine powder dispersed in the coating composition reacts with an acidic phosphate-based bonding solution to produce hydrogen, so that the coating composition becomes unusable within 1-2 days due to an increase in its viscosity and has a short pot life. The inventors have assumed that the pot life can be increased by forming an overcoat, alternative to a conversion coating formed by hexavalent chromium, on a surface of the aluminum fine powder, and now consequently found a solution as a result of various studies.
An object of the present invention is to provide aluminum fine powder having an overcoat, alternative to a conversion coating formed by harmful hexavalent chromium, on its surface and a phosphate-based aqueous chromium-free corrosion inhibiting coating composition having a practical pot life in which the aluminum fine powder is suspended in a bonding solution.
According to the present invention, the surface of the aluminum fine powder is treated with a hydrophilic coupling agent. A titanium-coupling agent can be used as the hydrophilic coupling agent.
Further, in the present invention, the aluminum fine powder which is surface treated with the hydrophilic coupling agent can be obtained by preparing ethyl alcohol to which 3 to 12% by weight of water is added, dissolving 0.3 to 1.5 parts by weight of the hydrophilic coupling agent relative to 100 parts by weight of the aluminum fine powder to be added in this solution, suspending the aluminum fine powder to be treated in this solution, forming a thin film of the coupling agent on a particle surface of the aluminum fine powder by heating and keeping the solution at 50 to 70° C. for 2 to 7 hours with the aluminum fine powder suspended therein, filtrating the solution which contains hydrolytic products of the coupling agent to recover the aluminum fine powder, rinsing the recovered aluminum fine powder with ethyl alcohol having a purity of 99% by weight or more, and heating the rinsed aluminum fine powder to a temperature which is lower than a boiling point 78.3° C. of ethyl alcohol to dry it under reduced pressure.
An aqueous corrosion inhibiting coating composition according to the present invention is a composition in which 25 to 40% by weight of the aluminum fine powder which is surface treated with the hydrophilic coupling agent is suspended in the acidic phosphate-based aqueous bonding solution. In this case, a titanium-coupling agent can be used as the hydrophilic coupling agent.
In the above-described case, the phosphate-based aqueous bonding solution can contain phosphate ions, aluminum ions, zinc ions, and two or more kinds of alkaline earth metal ions, and further contain 0.2 to 1% by weight of polyphosphate ions.
A surface of the aluminum fine powder used in the present invention is treated with the coupling agent and a surface of the particle is covered with a thin overcoat of the coupling agent. Although there are many kinds of coupling agents, it has been found that the only limited kinds of coupling agents can be effective for this purpose. An effective coupling agent is within a class in which the treated surface exhibits hydrophilic property, so tha
Endo Yasuhiko
Sakai Tomio
Shimada Saburo
McGlew and Tuttle , P.C.
Oltmans Andrew L.
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