Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-01-29
2003-09-09
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S354000, C428S035300, C428S379000, C442S059000
Reexamination Certificate
active
06617019
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to protective coatings for metal surfaces, more particularly to protective coatings that maintain adhesion to such metal surfaces through cold forming. This invention also relates to cold-formable protected metal surfaces. This invention still more particularly relates to cold-formable metal substrates having a protective coating applied to at least one major planar surface thereof, and to articles of manufacture fabricated from such substrates. The articles of manufacture include, for example, pipes for a variety of end use applications as well as wire and cable products.
Metal surfaces are susceptible to corrosion from various sources such as moisture, air and a wide variety of chemical compounds. This susceptibility tends to limit use of metal in a number of applications, including sanitary or storm sewer systems and industrial processes involving acidic chemical compounds.
One means of improving corrosion resistance of metal surfaces, such as the interior surfaces of metal pipe, uses a concrete liner. This approach meets with limited success because concrete fails to form a secure bond to such metal surfaces. Concrete also cracks, chips, and pulls away from the metal surface, effectively leaving the metal exposed. Another approach focuses upon forming metal pipe from plastic laminated steel sheet. WCI Steel Company of Warren, Ohio uses this approach in making a product that is known as Poly-Coat®. In general, one first laminates a plastic or polymer material, such as a carbon black filled ethylene/acrylic acid (EAA) copolymer compound, onto a surface of a suitable metal such as sheet steel. One then converts the laminate into a pipe, causing a polymer coated surface to form an inner pipe wall. The polymer coating typically has a thickness of no more than 0.10 inch (0.25 centimeter (cm)).
U.S. Pat. No. 4,975,138 discloses a method for forming a coated metal object. The method comprises three sequential steps. One first prepares a laminate that comprises an unformed metal substrate bonded to an uncoated fabric by way of a thermoplastic adhesive layer. Second, one forms the laminate into a desired shape while retaining adhesion between the substrate, fabric and thermoplastic adhesive layer. Last, one applies a coating over the fabric. Such coatings tend to lack uniformity of thickness, at least when applied to interior surfaces of the shape, such as inner pipe surfaces. In order to ensure a minimum coating thickness, one typically uses an excess of coating material, thereby increasing cost and possibly interfering with flow dynamics within the pipe.
U.S. Pat. No. 5,316,606 discloses a method for forming polymer laminated metal pipe. The method starts with sheet steel that has a co-extruded polymer layer of EAA copolymer and a polyethylene/acrylic acid blend applied to at least one of its surfaces. The coated steel sheet, after being passed through a profile former to form channels and seam members, is placed in contact with a heated polyethylene liner. Applied pressure effects bonding between the heated polyethylene liner and the coated steel sheet. The method concludes by forming the sheet steel into a section of pipe.
SUMMARY OF THE INVENTION
A first aspect of this invention is a composite protective coating for a metal surface comprising:
a. an inner adhesive film for adhering the coating to the metal surface, the inner film comprising:
1) a first layer of a copolymer of ethylene and acrylic acid, and
2) a second layer of an EAA copolymer, the first layer adhering to the metal surface and the second layer adhering to the first layer;
b. a reinforcing layer adjacent to the second layer of the inner adhesive film and bonded thereto; and
c. an outer adhesive film adjacent to the reinforcing layer, the outer layer comprising:
1) a first layer of an EAA copolymer, and
2) a second layer of an EAA copolymer, the first layer adhering to the reinforcing layer and the second layer adhering to the first layer.
A second aspect of this invention is a composite protective coating for a metal surface comprising:
a. an inner adhesive film for adhering the coating to the metal surface, the inner film comprising:
1) a first layer of a hydroxy-phenoxyether polymer, and
2) a second layer of a hydroxy-phenoxyether polymer, the first layer adhering to the metal surface and the second layer adhering to the first layer;
b. a reinforcing layer adjacent to the second layer of the inner adhesive film and bonded thereto; and
c. an outer adhesive film adjacent to the reinforcing layer, the outer layer comprising:
1) a first layer of a hydroxy-phenoxyether polymer, and
2) a second layer of a hydroxy-phenoxyether polymer, the first layer adhering to the reinforcing layer and the second layer adhering to the first layer.
The first layer of the outer adhesive film of the composite coatings of either the first or second aspect preferably has a surface energy that exceeds that of the second layer of the outer adhesive film. Exposure of the first layer to corona discharge, flame treatment or some other conventional surface modification provides an increase in surface energy for the first layer.
In a third aspect, this invention comprises a cold-formable coated metal object comprising:
a. a metal substrate;
b. the composite protective coating of either the first aspect or the second aspect.
DETAILED DESCRIPTION OF THE INVENTION
The term “interpolymer”, as used herein, means a polymer having polymerized therein two or more polymerizable monomers. As such, it includes copolymers (often thought of as including two polymerizable monomers), terpolymers (three polymerizable monomers) and tetrapolymers (four polymerizable monomers). The terms “copolymer” and “interpolymer” are used interchangeably throughout this application.
The composite protective coating of the present invention comprises at least three layers. In simple terms, the coating is a sandwich of a reinforcing layer between two adhesive films, nominally an inner adhesive film and an outer adhesive film.
The inner adhesive film preferably comprises at least two layers, a first or metal adhesive layer and a second or inner base layer. The metal adhesive layer effects a bond between the composite coating and a metal substrate when the coating is applied to the substrate. The metal adhesive layer desirably comprises from 10 to 50 percent, preferably from 10 to 30 percent, and more preferably from 15 to 25 percent of total film layer thickness. With only two layers, the second layer makes up any difference between total film thickness and the metal adhesive layer thickness. If desired, the inner base layer may itself comprise two or more layers. In addition, although the first layer is nominally a metal adhesive layer, the first layer can also bond to other substrates.
Both the metal adhesive and base layers of the inner adhesive film preferably comprise a copolymer of ethylene and an ethylenically unsaturated carboxylic acid, more preferably an EAA copolymer. The EAA copolymer preferably has an acrylic acid content within a range of from 3 to 9 percent by weight (wt %) of total copolymer weight. A carboxylic acid, especially an acrylic acid, content outside the range may be used provided one accepts property variations that accompany such contents. In addition, one may use blends of two or more copolymers with differing carboxylic acid contents without departing from the scope or spirit of the present invention.
Preferred polymers for use in the first and second layers of the inner adhesive film include interpolymers of ethylene and at least one copolymerizable comonomer containing carboxyl functionality and further derivatives thereof and anhydride modified polyolefins. Suitable polymers include interpolymers of ethylene with from 1.0 to 50.0 wt % of an ethylenically unsaturated carboxylic acid such as acrylic or methacrylic acid or a C
1-4
alkyl ester thereof. Other suitable polymers include homopolymers and interpolymers of ethylene, including the above-described interpolymers, modified by reaction wi
Cohen Benjamin Robert
Danner Mark Carl
Chang Victor S.
Dow Global Technologies Inc.
Zirker Daniel
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