Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2002-06-13
2004-08-17
Tucker, Philip (Department: 1712)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S299000, C427S327000, C427S386000, C427S402000, C427S409000, C428S416000, C428S418000
Reexamination Certificate
active
06777034
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to weldable, corrosion-resistant coated metal substrates and, more particularly, to metal substrates having chrome-free coatings thereon which inhibit corrosion and facilitate forming and welding of the metal substrate.
BACKGROUND OF THE INVENTION
Weldable coatings containing an electrically conductive material, such as zinc, are often used to provide an electroconductive layer on metal substrates. Zinc-rich weldable coatings can be applied directly to ferrous metal surfaces or over ferrous metal which has been treated with a chromium-containing solution. For example, U.S. Pat. No. 4,346,143 discloses a process for providing corrosion protection to ferrous metal substrates comprising etching the surface of the substrate with nitric acid followed by applying a zinc-rich coating including a binder material to the etched surface.
U.S. Pat. Nos. 4,157,924 and 4,186,036 disclose a weldable coating for metallic substrates which contains an epoxy or phenoxy resin, electroconductive pigment such as zinc and a diluent such as glycol ether. As discussed at column 7, lines 37-42, the substrate can be pretreated with a pulverulent metal-free composition containing chromate and/or phosphate ions.
Similarly, European Patent Application No. 0157392 discloses an anti-corrosive primer for metal phosphate- or chromate-treated steel which consists of a mixture of 70 to 95 weight percent zinc, aluminum, a gliding agent and a binding agent.
U.S. Pat. No. 3,687,739 discloses a weldable composite coating comprising (1) an undercoating of pulverulent metal and a hexavalent chromium-containing liquid composition and (2) a topcoating comprising a particulate, electrically conductive pigment and a binder material.
Although chromium-containing coatings provide excellent corrosion protection, particularly under zinc-rich coatings, they are toxic and present waste disposal problems. Therefore, there is a need for chromium-free treatment solutions for treating metal substrates prior to the application of a weldable coating. The treatment solution should provide corrosion resistance, maintain substrate electroconductivity for welding and provide lubricity to assist in forming and stamping.
SUMMARY OF THE INVENTION
One aspect of the present invention is a weldable, coated metal substrate comprising: (a) a metal substrate; (b) a pretreatment coating comprising a reaction product of at least one epoxy-functional material and at least one material selected from the group consisting of phosphorus-containing materials, amine-containing materials and mixtures thereof deposited upon at least a portion of a surface of the metal substrate; and (c) a weldable coating comprising an electroconductive pigment and a binder deposited upon at least a portion of the pretreatment coating.
Another aspect of the present invention is a weldable, coated metal substrate comprising: (a) a metal substrate; (b) a pretreatment coating comprising at least one ester of a phosphorus-containing material deposited upon at least a portion of a surface of the metal substrate; and (c) a weldable coating comprising an electroconductive pigment and a binder deposited upon at least a portion of the pretreatment coating.
Yet another aspect of the present invention is a method for preparing a weldable, coated metal substrate, comprising the steps of: (a) treating a surface of a metal substrate with a pretreatment coating comprising a reaction product of at least one epoxy-functional material and at least one material selected from the group consisting of phosphorus-containing materials, amine-containing materials and mixtures thereof to form a substrate having a pretreated surface; and (b) applying a weldable coating to the pretreated surface to form a weldable, coated metal substrate, the weldable coating comprising an electroconductive pigment and a binder.
Another aspect of the present invention is a method for inhibiting corrosion of a metal substrate comprising: (a) treating a surface of a metal substrate with pretreatment coating comprising a reaction product of at least one epoxy-functional material and at least one material selected from the group consisting of phosphorus-containing materials, amine-containing materials and mixtures thereof to form a substrate having a pretreated surface; and (b) applying a weldable coating to the pretreated surface to form a corrosion-resistant coated metal substrate, the weldable coating comprising an electroconductive pigment and a binder.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The metal substrates used in the practice of the present invention include ferrous metals, non-ferrous metals and combinations thereof. Suitable ferrous metals include iron, steel, and alloys thereof. Non-limiting examples of useful steel materials include cold rolled steel, galvanized (zinc coated) steel, electrogalvanized steel, stainless steel, pickled steel, zinc-iron alloy such as GALVANNEAL, and combinations thereof. Useful non-ferrous metals include aluminum, zinc, magnesium and alloys thereof, such as GALVALUME and GALFAN zinc-aluminum alloys. Combinations or composites of ferrous and non-ferrous metals can also be used.
The shape of the metal substrate can be in the form of a sheet, plate, bar, rod or any shape desired. Preferably, the shape of the metal substrate is an elongated strip wound about a spool in the form of a coil. The thickness of the strip preferably ranges from about 0.254 to about 3.18 millimeters (mm) (about 10 to about 125 mils), and more preferably about 0.3 mm, although the thickness can be greater or less, as desired. The width of the strip generally ranges from about 30.5 to about 183 centimeters (about 12 to about 72 inches), although the width can vary depending upon its intended use.
Before depositing the coatings upon the surface of the metal substrate, it is preferred to remove foreign matter from the metal surface by thoroughly cleaning and degreasing the surface. The surface of the metal substrate can be cleaned by physical or chemical means, such as mechanically abrading the surface or cleaning/degreasing with commercially available alkaline or acidic cleaning agents which are well known to those skilled in the art, such as sodium metasilicate and sodium hydroxide. A non-limiting example of a preferred cleaning agent is CHEMKLEEN 163 phosphate cleaner which is commercially available from PPG Industries, Inc. of Pittsburgh, Pa.
Following the cleaning step, the metal substrate is usually rinsed with water, preferably deionized water, in order to remove any residue. The metal substrate can be air dried using an air knife, by flashing off the water by brief exposure of the substrate to a high temperature or by passing the substrate between squeegee rolls.
In the present invention, a pretreatment coating is deposited upon at least a portion of the outer surface of the metal substrate. Preferably, the entire outer surface of the metal substrate is coated with the pretreatment coating.
The pretreatment coating facilitates adhesion of the subsequently applied weldable coating to the metal substrate. The pretreatment coating should be sufficiently thin and/or deformable to permit the heat and force applied to the weldable coating by the welding tool to drive at least a portion of the electroconductive pigment therein through the pretreatment coating to contact or essentially contact the metal substrate and provide an electrically conductive path to permit welding of the coated substrate. As used herein “essentially contact” means that the electrical resistance provided by the pretreatment coating is less than about 1 ohm. The thickness of the pretreatment coating can vary, but is generally less than about 1 micrometer, preferably ranges from about 1 to about 500 nanometers, and more preferably is about 10 to about 300 nanometers.
In a preferred embodiment, the pretreatment coating comprises a reaction product of one or more epoxy-functional materials and one or more materials selected from phosphorus-containing materials, amine-conta
Berger Valentin
Gray Ralph C.
Nugent, Jr. Richard M.
Pawlik Michael J.
Altman Deborah M.
Feely Michael J
Meyers Diane R.
PPG Industries Ohio Inc.
Tucker Philip
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