US 5,290,424 AGranted

Method of making a shaped reflective aluminum strip, doubly-protected with oxide and fluoropolymer coatings

AssigneeAluminum Company of America

InventorsFrank A. Mozelewski, Daniel L. Serafin, Robert E. Bombalski, Romeo C. Pascasio, Donald L. Nock

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Abstract

A shaped strip of highly reflective aluminum protected by an anodic oxide coating and a light-permeable fluoropolymer coating which is non-adhesively interstitially mechanically bonded to the microscopic irregularities of the anodic oxide surface. There is no adhesive used to obtain chain entanglement. The highly reflective strip may be substituted for polished stainless steel and/or bi-metal and used under comparably aggressive conditions for a prolonged period without deleteriously affecting the initial D/I (distinctness of reflected image) of the shaped strip. The strip of arbitrary length is shaped in rolling dies so that at least a portion of the strip has a radius of less than 10 mm without damaging or separating the fluoropolymer coating. The specific steps of the claimed process require starting with a clean strip which is brightened to a nearmirror-like finish, then treated to carry a thin porous aluminum oxide coating in a phosphoric acid bath under direct current (DC). After rinsing and drying, the reflective surface is coated with the fluoropolymer while maintaining at least 80% D/I. The strip, now dual-coated, is then formed to a desired profile. The dual-coated strip, in turn, may be treated with a corona discharge to activate its surface so as to non-adhesively bond an adhesive chosen to bond a thermoplastic strip of synthetic resin to the activated fluoropolymer surface.

A process for converting a sheet of aluminum alloy in the range from about 0.010 inch (0.25 mm) to about 0.050 inch (1.25 mm) thick, into a decorative reflective sheet, doubly-protected with a combination of an oxide coating formed by phosphoric acid anodizing, and, a sequentially applied cured fluoropolymer coating, said doubly-protected sheet having a surface substantially free of degradation due to environmental exposure, said process comprising,

(a) cleaning said surface of said sheet of aluminum alloy to remove superficial contaminants and leave a clean surface;
(b) brightening said clean surface until said clean surface is a bright surface having substantially mirror-like characteristics with a distinctness of reflected image (D/I) of at least 80%;
(c) generating on said bright surface a porous aluminum oxide coating in the range from 100 nanometers (0.1 .mu.m) to 0.2 mil (5 .mu.m) thick, in a bath containing from about 5% to 20% by weight of phosphoric acid, at a temperature in the range from about 25.degree. C. to 75.degree. C., under direct current (DC) applied to said sheet at from about 5 to 50 amps/ft.sup.2 at constant voltage in the range from about 10 to 50 volts, said oxide coating being deposited within less than 3 min, without first etching said surface, so as to produce a phosphoric acid anodized reflective surface having at least 80% D/I;
(d) rinsing said phosphoric acid anodized surface and drying, to leave a dry reflective surface;
(e) contacting said dry reflective surface with a fluoropolymer in an amount such that, upon curing, a cured fluoropolymer is interstitially mechanically bonded to said oxide coating, so as to form said reflective sheet doubly-coated on at least one side which maintains at least 80% D/I;
and,
(f) shaping said doubly-coated sheet to conform to a profile having at least one radius which is less than 10 mm without debonding said cured matrix fluoropolymer from said oxide coating at the interface thereof.

4 more elements

Abstract

Claims12