The invention is an article formed of a metal substrate with a protective, weather-resistant, transparent film overlying the surface of the metal substrate. The film is formed of a polymer that contains vinylidene fluoride and which imparts weather resistant properties to the workpiece. An adhesive layer is positioned between the protective film and the metal substrate and bonds the protective film to the metal substrate. The adhesive layer comprises an acrylic resin adhesive and a zircoaluminate adhesion promoter which enhances the bond between metals such as aluminum and the vinylidene fluoride containing polymer.

FIELD OF THE INVENTION 
The present invention relates to articles having a metal surface appearance 
and in particular relates to a workpiece of a fluoropolymer film over a 
metal substrate such as sheet aluminum, which has a weather-resistant 
metal surface appearance. 
BACKGROUND OF THE INVENTION 
Polished or plated metal has been used for many years to provide durable 
and decorative surfaces in a number of applications. For example, chromium 
metal has been used to provide such a bright decorative surface to 
designated parts such as car bumpers and trim. Chromium is, however, being 
designed out of current applications because of its weight, uncertain 
availability and expense. 
In a number of applications, other bright polished metals such as aluminum 
can provide a similar appearance to chromium while avoiding the weight, 
expense and uncertain availability associated with chromium. Aluminum is 
abundantly available, relatively light in weight, durable, and forms a 
protective coating of aluminum oxide about 50 angstroms thick which makes 
it highly resistant to ordinary corrosion. 
Aluminum is, however, susceptible to attack by acids and bases, and 
polished aluminum surfaces do not resist weathering, but instead develop a 
milky appearance that generally results from the aluminum oxide coating. 
Because of aluminum's advantages in weight and durability, however, a 
number of techniques have been developed to attempt to protect aluminum, 
and these techniques have met with varying degrees of success. 
One technique is chemical anodization which provides improved protection 
and the option of color tinting. Anodization, however, has not been 
demonstrated to result in long-term protection on exposed parts under many 
environmental conditions, and the use of the process itself is under 
increasing environmental pressure because of the problems associated with 
waste disposal requirements for the spent chemicals used in the surface 
anodization process. Anodization also tends to embrittle the aluminum, 
limiting the extent to which post-anodization forming techniques can be 
successfully used. 
Another technique for protecting aluminum is the direct coating of the 
aluminum with a polymer. This generally provides some advantages over 
anodization in terms of protection. Typical polymer coating processes, 
however, require extensive solvent handling, followed by baking or curing 
of the polymer after its application. Furthermore, polymer coatings often 
either are or become brittle, may delaminate, and may show "orange peel," 
"cracking", "crazing", or "blushing" effects after exterior exposure. 
Coatings such as the clear vinyl coatings which are sometimes used to face 
a bright metal can also mold, mildew or stain. 
Yet another technique is the lamination of a polymeric film to an aluminum 
surface using an adhesive. Such laminates can demonstrate some of the same 
theoretical advantages as polymer coatings. Typically, however, such 
laminates lack clarity, do not exhibit long-term bond durability, and 
exhibit poor formability. As will be understood to those familiar with the 
working of decorative metals, formability means that the finished metal 
may be worked, whether by stamping, pulling, or bending, without affecting 
the decorative surface. As is known to chemists, metallurgists, and 
engineers, one of the advantages of metals is their malleability, 
ductility, and flexibility. Accordingly, coatings or treatments of metals 
which will not withstand such metal-working techniques are inappropriate, 
disadvantageous, or even useless, depending upon the needed application. 
Other problems which such a surface treatment should address include 
adhesion, and resistance to heat, water, solvent, mechanical scrubbing and 
biological attack. 
SUMMARY OF THE INVENTION 
The present invention provides a bright metal surface with a film 
lamination that will withstand weather exposure without cracking, crazing 
or blushing, will exhibit water clarity, and will maintain its clarity and 
lamination when stamped, bent or drawn, which is suitable for tinting with 
pigments or dyes or both, and which avoids development of an objectionable 
surface appearance after typical environmental exposure. 
More specifically, the present invention comprises a metal substrate with a 
protective weather-resistant surfacing layer overlying the surface of the 
metal substrate. The surfacing layer is formed of a polymer which contains 
vinylidene fluoride, and preferably comprises a film of the polymer. An 
adhesive layer is positioned between the protective film and the metal 
substrate and bonds the protective film to the metal substrate. The 
adhesive layer comprises an acrylic resin adhesive and a zircoaluminate 
adhesion promoter. 
The foregoing and other objects and advantages of the invention will be 
more clearly understood when taken in conjunction with the detailed 
description and the accompanying drawings in which

DETAILED DESCRIPTION 
The invention comprises an article, broadly designated at 10 in FIG. 4, 
which has a metal surface appearance that is resistant to weathering. The 
article comprises a metal substrate Il which in a preferred embodiment is 
aluminum. The present invention can comprise metal substrates which have 
been polished, textured or brushed depending upon the desired final 
appearance, and can be formed of other metals in addition to aluminum. A 
protective weather-resistant surfacing layer, preferably a film 12, 
overlies the surface of the metal substrate and is formed of a polymer 
which contains vinylidene fluoride. As is known to those familiar with 
such materials, vinylidene fluoride polymer (or "polyvinylidene fluoride") 
is a polymer of 1,1-difluoroethylene (H.sub.2 C=CF.sub.2). A particular 
preferred film for use in the present invention is formed of a polymer 
alloy of polyvinylidene fluoride and one or more other polymers such as 
acrylic polymers. One such suitable film is produced by Rexham Corporation 
industrial film division and identified by the trademark Fluorex A and is 
an alloy of polyvinylidene fluoride polymer and methylmethacrylate. 
The polyvinylidene fluoride film provides primary protection to underlying 
materials, in this case the aluminum, from the direct affects of 
atmosphere, sunlight, solvents, pollution, moisture, and abrasion present 
in the elements to which such materials are exposed in an outdoor 
environment. 
In order to join the polymer film of the present invention to the aluminum 
substrate, an adhesive layer 13 is positioned between the protective film 
and the metal substrate and bonds the protective film to the metal 
substrate, forming a laminate. The adhesive layer comprises an acrylic 
resin adhesive and a zircoaluminate adhesion promoter. 
Acrylic polymers are thermoplastic polymers or copolymers of acrylic acid, 
methacrylic acid, esters of these acids, or acrylonitrile. Because one of 
the objects of the present invention is to provide and maintain a bright, 
metal surface appearance, acrylic adhesives are chosen for their clarity. 
In other words, the acrylic adhesive does not interfere with or obstruct 
the appearance of the metal or the polyvinylidene fluoride film. Moreover, 
in addition to being transparent to start with, the adhesive must remain 
transparent under the same conditions of manufacture, metal working and 
environmental exposure that the metal and film themselves must be exposed 
to. In this regard, only about one to five percent of all adhesives are 
colorless and transparent. Thus, a desirable adhesive must be flexible, 
colorless and transparent to both incident light and reflected light, must 
bond securely to the metal, must bond securely to the fluorinated polymer, 
and must maintain these properties under conditions of manufacture and 
environmental use. 
Although they are excellent adhesives in many respects, acrylic adhesives 
generally will not, by themselves, form as good a bond as may be desired 
or necessary between materials as dissimilar as a metal and a 
fluoropolymer. Therefore, in order to obtain the desired properties, the 
adhesive layer of the present invention includes an adhesion promoter in 
addition to the acrylic resin. Adhesion promoters are chemical additives 
which, when added to an adhesive in a small quantity (typically less than 
two percent based on resin solids), greatly increase the work required to 
separate the adhering materials. 
Zircoaluminate adhesion promoters are well suited to the purpose of 
promoting the adhesion of polyvinylidene fluoride and polyvinylidene 
fluoride alloys to metal substrates such as aluminum. In particular, 
zircoaluminate organo metallic adhesion promoters are surface modifiers 
which are hydrolytically and thermally stable coordinate covalent 
complexes which are dominated by aluminum and zirconium chemistry. The 
compositions are highly reactive with various metals and resins and 
thereby enhance the adhesion of coatings to metals. Zircoaluminates 
typically are formed of a zirconium building block, an aluminum building 
block, and an organic functional portion. In the present invention, 
preferred embodiments include amino functional zircoaluminate compounds 
supplied in a propylene glycol solvent, such as the promoter available 
from Cavedon Chemical Company, Inc. under the designation CAVCO MOD APG, 
and carboxy functional zircoaluminate compounds in propylene 
glycol--methyl ether solvent mixtures available from the same source under 
the designation CAVCO MOD CPM. 
Preferably the adhesive also includes one or more ultraviolet light 
stabilizers. These stabilizers are useful because the polyvinylidene 
fluoride is transparent to ultraviolet light and the underlying metal is 
reflective to it. As a result, the adhesive and the adhesion promoter are 
both constantly exposed to both incident and reflected ultraviolet light 
in outdoor environmental applications. As known to those familiar with 
such materials, light stabilizers generally function by absorbing enough 
ultraviolet light to prevent significant or extensive interference with 
the adhesive or adhesion promoter by ultraviolet light, and by quenching 
the degradation reactions that ultraviolet light typically initiates in 
such materials. In one particular preferred embodiment of the invention, 
an absorbing type of molecule such as a benzophenone can be blended with a 
quenching type molecule such as a hindered amine to achieve the desired 
level of stabilization. 
Nevertheless, it should be noted that the protective films of the laminates 
of the present invention can be pigmented, as well as transparent, 
although it will be understood that pigmented films, because they tend to 
block ultraviolet light, are not as sensitive to such exposure to 
ultraviolet light. Similarly, the films can include otherwise conventional 
additives and the adhesives can be mixed and applied using conventional 
solvents. 
FIGS. 1 through 3 illustrates contoured articles such as automotive trim 
pieces according to the present invention. FIG. 2 shows a portion 16 of 
side panel trim formed of a metal sheet having a contoured, nonplanar 
configuration. The weather resistant protective transparent surfacing film 
formed of the vinylidene fluoride-containing polymer overlies and is 
coextensive with one surface of the contoured sheet. As in the other 
embodiments of the invention, a transparent acrylic resin adhesive and a 
zircoaluminate adhesion promoter bond the protective film to the metal 
sheet. A stabilizing filling material such as a polymer backing 18 is 
injection molded on the other surface of the metal sheet and serves to 
reinforce and maintain the shape of the contoured metal sheet. FIG. 3 is a 
larger view of a portion of the window molding 17 and illustrates how an 
article according to the present invention can be successfully formed 
along somewhat gentler contours than those illustrated in FIG. 2. 
The invention further comprises the method of forming an article having the 
metallic surface appearance that is both weather-resistant and workable. 
Where a laminate is preferred, the method comprises laminating a 
protective vinylidene fluoride polymer film to the surface of the metal 
substrate using an acrylic resin adhesive which contains a zircoaluminate 
adhesion promoter. 
In one embodiment, the method comprises applying the acrylic resin adhesive 
containing the zircoaluminate promoter to the surface of the vinylidene 
fluoride polymer film following which the protective film is laminated to 
the metal substrate with the adhesive therebetween. In such circumstances, 
the metal substrate can be in a heated condition when the protective film 
is being laminated thereto. In a preferred embodiment, the protective film 
is applied to the metal substrate by nipping the film onto the substrate 
with a nipping roll. 
In another embodiment, the method of the invention comprises applying the 
acrylic resin adhesive containing the zircoaluminate adhesion promoter to 
the surface of the metal substrate following which the protective 
vinylidene fluoride polymer film is laminated to the surface of the metal 
substrate upon which the adhesive was applied. In this embodiment the 
protective film may be similarly laminated to the metal substrate while 
the metal substrate is in a heated condition and can be applied by nipping 
the film onto the substrate with a nipping roll. 
In yet another embodiment, the finished article can be produced by applying 
a primer coating comprised of a dilute solution of an acrylic material and 
a zircoaluminate adhesion promoter to the surface of a metal substrate, 
then applying an acrylic resin adhesive to the surface of a film formed of 
a polymer which contains polyvinylidene fluoride, and then laminating the 
coated surface of the protective film to the primer-coated metal 
substrate. If desired, a small amount of the adhesion promoter may also be 
added to the resin adhesive. In such cases it is preferred to use a larger 
concentration of the promoter in the primer coating than in the acrylic 
resin adhesive. As in the previous embodiments, the protective film may be 
laminated to the metal substrate while the metal substrate is in a heated 
condition and by using a nipping roll. 
It will be recognized those familiar with such materials that although the 
laminating of a film to a substrate is a convenient method of practicing 
the present invention, it is not the only method. In particular, another 
method comprises coating the acrylic adhesive and zircoaluminate adhesion 
promoter onto the metal substrate, over which the resin containing the 
polyvinylidene fluoride and acrylic polymers is then cast to form the 
film. 
The following examples illustrate some of the preferred techniques, and the 
characteristics of the resulting products. 
EXAMPLE I 
An adhesive composition was prepared by mixing 114.9 grams of a methyl 
methacrylate copolymer supplied at 45 percent solids in toluene (Rohm and 
Haas B48S) with 44.9 grams of monopropylene glycol monomethyl ether (Union 
Carbide UCAR PM), 1.37 grams of an amino functional zircoaluminate 
adhesion promoter supplied in propylene glycol solvent (CAVCO MOD APG) and 
0.23 grams of a hindered amine light stabilizer (T-292 from Ciba-Geigy). 
The adhesive was coated onto a bright chromate-treated aluminum panel 
using a No. 18 wire wound rod at a wet solid of 30 percent to yield dry 
coating thickness of 0.5 mils. The coated aluminum panel was dried for 
three minutes at 400.degree. F. and quickly nip-bonded to 2 mil clear film 
of a vinylidene fluoride polymer/acrylic polymer alloy (Fluorex A from 
Rexham Corporation, Industrial Films Division, Matthews, North Carolina). 
The laminate was tested for bond strength and the bond of the Fluorox A 
film to the aluminum was found to be film destructive, meaning that when 
an effort is made to separate the film from the aluminum, the film fails 
before the bond does. 
The coating was tested to determine its integrity during forming operations 
by using ball indentation (Gardener impact) to achieve approximately 18 
percent metal elongation. Both direct and indirect impact showed no 
blushing or rupture of the clear film. The film was exposed to 
temperatures of 158.degree. F. for three weeks, following which no lifting 
of the film from the impacted areas was observed. 
The samples were also exposed to 2,000 hours of exposure in a carbon arc 
weatherometer, following which no change in gloss was observed (reading of 
140 on a Gardener gloss meter with 60 head); no change in distinctiveness 
of image (DOI) was observed as measured on a Hunter Dorigon meter; no 
change in spectral reflectance was observed measured on a Hunter Dorigon 
meter; no significant color changes were observed (as measured on a Model 
500 color computer from Applied Color Systems); and no change in visible 
appearance was observed. In comparison, samples of clear Fluorex A bonded 
with a blended adhesive of methyl methacrylate and bisphenol-A to a bright 
aluminum panel showed objectionable visual defects after this exposure. In 
particular, the aluminum exhibited the whitening characteristic of its 
oxidation, and the adhesive discolored, exhibiting a yellowish or brownish 
tint. 
The samples were also exposed in a UV-CON weatherometer for 2,000 hours 
with the same favorable results as observed in the carbon arc 
weatherometer. 
The samples were also exposed to 300 hours of condensing humidity 
(95.degree. F., 95 percent relative humidity) followed by 300 hours in a 
salt spray corrosive environment. These samples showed no visual change 
and no loss of bond when cut with a cross-hatch pattern and then tape 
tested with 3M tape No. 710. 
Finally, the samples were tested by bending the metal and film laminate 
back on itself with the film on the outside surface (a zero T-bend) and 
showed no blushing or cracking. 
EXAMPLE II 
An adhesive composition was formed from 115.02 grams of the methyl 
methacrylate copolymer, 43.81 grams of the monopropylene glycol 
monomethylether, and 0.51 grams of the hindered amine stabilizer, all as 
set forth in Example I. To these were added 0.11 grams of an antioxidant 
(I1010 by Ciba-Geigy) and 0.22 grams of a carboxy functional 
zircoaluminate adhesion promoter supplied in a propylene glycol and methyl 
ether solvent (CAVCO MOD CPM). 
A primer was formed of 4.71 grams of the methyl methacrylate copolymer, 
50.3 grams of the monopropylene glycol monomethylether solvent, 0.61 grams 
of the zircoaluminate adhesive promoter, and 0.02 grams of the 
antioxidant. 
In this example, bright chromate treated aluminum was coated with the 
described primer by hand-wiping using a saturated tissue. The sample was 
dried at 475.degree. F. for 1 minute. The adhesive mixture was then 
applied to the primer using a No. 18 wire wound rod to spread the adhesive 
and the film was laminated to the surface. The sample was dried at 
400.degree. F. for 2.5 minutes. The sample was tested as in Example I. The 
bond was film-destructive, and the sample exhibited all of the properties 
noted with respect to Example I. 
EXAMPLE III 
The preparation and application of the adhesive mixture, primer mixture, 
and laminated film of Example II were identically repeated on bright, 
clear non-chromate treated aluminum. The bond was again observed to be 
film destructive, and the properties of the sample were substantially 
identical to those of Example I and Example II. 
EXAMPLE IV 
An adhesive was formed by mixing 20 grams methyl methacrylate copolymer 
supplied as dried pellets, 23.89 grams of toluene, 17.83 grams of the 
monopropylene glycol monomethylether solvent, 0.6 grams of the amino 
functional zircoaluminate promoter in propylene glycol solvent, and 0.12 
grams of the hindered amine stabilizer. This adhesive was applied to 
bright chromate-treated aluminum to which the polyvinylidene-containing 
film was then laminated. A film-destructive bond was formed between the 
film and the aluminum and exhibited substantially all of the properties 
set forth with respect to Examples I-III. 
The foregoing description and examples have been set forth by way of 
explanation and not by way of limitation, the scope of the invention being 
set forth in the following claims.