Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-11-01
2004-02-10
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S515000
Reexamination Certificate
active
06689831
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to curable, protective coating compositions for metal substrates prior to the application of one or more decorative coatings.
Conversion coatings used alone, or prior to the application of a protective or decorative coating, are well known for promoting corrosion resistance. The conversion coatings are usually applied by immersion, spray, or roller, and are dried in place at room temperature. Chrome-containing, film-forming protective coating compositions are also known and are disclosed, for example, in U.S. Pat. No. 4,069,187. Such compositions may be suitable for use in pretreatment processes as conversion coatings and/or as primers. They are highly suitable in the electronics industry because of their “anti-fingerprint” properties, providing enhanced adhesion to subsequently applied coatings.
A drawback of these conventional pretreatment compositions is that they typically contain chromium and other heavy metals, such as nickel, producing waste streams that require expensive treatment and disposal due to environmental concerns.
Chrome-free pretreatment coatings have been developed but are typically not curable and are effective for corrosion inhibition only over a limited variety of substrates.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a curable coating composition, which is substantially free of chrome, for use as a conversion coating or primer on metal substrates prior to the application of a decorative coating. It is a further object of the invention to provide a composition that is effective for use on a number of metal substrates, particularly metal objects fabricated with more than one substrate type, so that the need to perform separate passivating treatments would be eliminated. It is a further object of the invention to provide a composition that is effective for use on untreated (i.e. non-phosphated) metal substrates as a direct-to-metal primer, providing enhanced corrosion resistance while maintaining adhesion to subsequently applied coating layers. Such compositions may find utility in the electronics industry.
In accordance with the present invention, a curable emulsion coating composition, essentially free of chromium, is provided. The composition comprises a continuous waterborne phase and a discontinuous phase. The discontinuous phase comprises at least one water-insoluble, particulate film-forming thermoplastic resin, at least one water-insoluble, film-forming thermosetting resin, and at least one water-insoluble alkali metal salt of a heavy metal-containing acid. The heavy metal may be selected from titanium, zirconium, and mixtures thereof. The heavy metal salt is present in the coating composition in an amount of 0.05 to 15 percent by weight, based on the total weight of the composition. Also provided is a process for coating a metal substrate by contacting the substrate with the composition of the present invention and heating the coated substrate to a peak metal temperature of 170 to 350° F. (77 to 177° C.). The coated metal substrate has a cured coating weight of 250-400 mg/ft
2
.
DETAILED DESCRIPTION
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used in the specification and claims are to be understood as modified in all instances by the term “about”.
The composition of the present invention is typically used to treat steel surface-treated with any of zinc metal, zinc compounds and zinc alloys (including electrogalvanized steel, hot-dipped galvanized steel, GALVANNEAL steel, and steel plated with zinc alloy). Also, aluminum, aluminum alloys, zinc-aluminum alloys such as GALFAN, GALVALUME, aluminum plated steel and aluminum alloy plated steel substrates may be used.
The substrate may alternatively comprise more than one metal or metal alloy, in that the substrate may be a combination of two or more metal substrates assembled together, such as hot-dipped galvanized steel assembled with aluminum substrates. Other substrate combinations that are commonly used in the coil industry and in other industrial applications are suitable as well.
The composition used in the process of the present invention may be applied to either bare metal or pretreated metal in the process of the present invention. By “bare” is meant a virgin metal substrate that has not been treated with any pretreatment compositions such as conventional phosphating baths, heavy metal rinses, etc. Additionally, bare metal substrates being coated with the composition of the present invention may be a cut edge of a substrate that is otherwise treated and/or coated over the rest of its surface.
The substrate to be coated is usually first cleaned to remove grease, dirt, or other extraneous matter. Conventional cleaning procedures and materials may be employed. These would include mild or strong alkaline cleaners such as are commercially available and conventionally used in metal pretreatment processes. Examples of alkaline cleaners include BASE Phase Non-Phos or BASE Phase #6, both of which are available from PPG Industries, Pretreatment and Specialty Products. Such cleaners are generally followed and/or preceded by a water rinse.
Optionally, the metal surface may be rinsed with an aqueous acidic solution after cleaning with the alkaline cleaner and before contact with the composition. Examples of rinse solutions include mild or strong acidic cleaners such as the dilute nitric acid solutions commercially available and conventionally used in metal pretreatment processes.
Although pretreatment of the metal substrate is not necessary, the metal substrate may optionally be pretreated with a solution selected from the group consisting of a metal phosphate solution, an organophosphate solution, an organophosphonate solution, and combinations thereof. Suitable metal phosphate coating compositions may be any of those known in the art. Examples include zinc phosphate, iron phosphate, manganese phosphate, calcium phosphate, magnesium phosphate, cobalt phosphate, zinc-iron phosphate, zinc-manganese phosphate, zinc-calcium phosphate, and layers of other types, which may contain one or more multivalent cations. Phosphating compositions are known to those skilled in the art and are described in U.S. Pat. Nos. 4,941,930, 5,238,506, and 5,653,790. Preferred compositions include organophosphate and organophosphonate pretreatment compositions such as those disclosed in U.S. Pat. Nos. 5,294,265 and 5,306,526.
Following the optional cleaning and pretreating steps, the metal surface is contacted with the curable coating composition of the present invention. The composition of the present invention may be applied to the metal substrate by known application techniques, such as dipping or immersion, spraying, intermittent spraying, dipping followed by spraying, spraying followed by dipping, brushing, or by roll-coating. Roller application is preferred.
The composition of the present invention is an emulsion. It is essentially free of chromium and comprises a continuous waterborne phase and a discontinuous phase. The discontinuous phase comprises at least one water-insoluble, particulate film-forming thermoplastic resin, at least one water-insoluble, film-forming thermosetting resin, and at least one water-insoluble alkali metal salt of a heavy metal-containing acid. The heavy metal may be selected from titanium, zirconium, and mixtures thereof. With respect to the heavy metal salt, by “water-insoluble” is meant that the salt has a solubility in water of no more than about 1.3 g/100 ml at a temperature of 20° C.
Suitable thermoplastic resins may be selected from acrylic polymers, vinyl polymers, polyesters, polyepoxides, and mixtures thereof. Acrylic polymers may be copolymers of one or more alkyl esters of acrylic and/or methacrylic acid optionally together with one or more other polymerizable ethylenically unsaturated (vinyl or allylic) monomers. Suitable alkyl esters of acrylic acid or methacrylic acid (“(meth)acrylates”) includ
Hernandez Emmanuel T.
Krippes William D.
McMillen Mark
Altman Deborah M.
Lipman Bernard
Meyers Diane R.
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