Note: Descriptions are shown in the official language in which they were submitted.
1 48,448I
PROTECTIVE COATING MEANS FOR ARTICLES SUCH AS
GOLD-PLATED JEWELRY AND WRISTWATCH COMPONENTS,
AND METHOD OF FORMING SUCH COATING MEANS
BACKGROUND OF THE INVENTION
This invention generally relates to the art of
protecting articles that have metallic surfaces which are
susceptible to abrasion damage or corrosion and has par-
ticular reference to proiecting gold-plated articles of
jewelry and wristwatch components (such as bracelets and
cases) with a transparent coating of one or more selected
inert materials. The invention also provides methods for
coating such articles with one or more overlying protec-
ti-ve films that are transparent and composed of abrasion-
resistant material.
As is well known, many articles of merchandise
have metallic surfaces which inherently become dull or
tarnished in the environment in which the article is used.
For example, hardware items such as building-identifica-
tion plaques, handrails, doorknobs, decorative door-
knockers~ etc. that are composed of brass or a similar
metal oxidize quite rapidly and require constant polishing
and waxing to maintain a brilliant pleasing appearance.
This is also an age old problem with articles such as
flatware, trays, trophies, etc. that are made of silver or
are silver plated.
'`~
,_..~ ,.r~
"- 2 48,448I
While articles such as ~ine jewelry and the like
that are m2de from solid gold or have gold-plated surfaces
do not tarnish and thus do not present such a maintenance
problem, they scratch easily and soon become unsightly
5 when subjected to the constant abrasion and "rubbing
action" encountered during normal everyday use. Since
gold is a relatively soft material, it also wears away
quite rapidly when subjected to such conditions. If the
article is gold-plated, this frequently exposes the base
lO metal and creates an unsightly corrocled appearance in the
case of articles (such as chains, rings, lockets, watch-
bands, etc.) that are in direct contact with the person's
body. These characteristics thus present serious problems
in the production and marketing of such items as gold-
15 plated jewelry and gold-plated bracelets and cases for
` wristwatches. In order to compensate for the loss of gold
, that occurs during use by the customer, relatively thick
gold plating is customarily used on high ~uality merchan-
dise of this type to ensure that the article will retain
r 20 its original pleasing appearance. However, in view of the
~iv extremely high cost of gold and the likelihood that it
will become even more expensive in the future, the use of
such heavy gold plating presents a serious economic prob-
lem in the watch and jewelry industries.
A practical and reliable means for protecting
gold and gold plated articles such as wristwatch compon-
ents and the like from rapid wear and unsightly scratching
(as well as corrosion if the gold plating has worn
through~ without materially changing its "natural" finish
~$ 30 or appearance would, accordingly, not only be very desir-
able from a quality and marketing standpoint but would be
very advantageous from a production and cost reduction
standpoint. Such protective means would also be very
useful in preventing skin reactions and similar problems
that are sometimes encountered by certain individuals when
they wear a ring, chain or similar article that is made
from a particular metal or alloy.
3 48,448I
SUMMARY OF T~E INVENTION
All of the foregoing objectives are achieved in
accordance with the present invention by coating the
metallic surface of the article with a thin substantially
transparent and colorless film of a selected inert and
non-metallic material which tenaciously adheres to the
surface and has sufficient "hardness" to provide a very
durable and abrasion-resistant protective finish and
covering. In accordance with a preferred embodiment, the
protective film is composed of a dielectric type material
such as silicon dioxide, magnesium oxide, aluminum oxide,
titanium dioxide, spinel, silicon nitride, silicon carbide
and various types of glasses that have the proper combina-
tion of hardness, transparency and thermal expansion
characteristics. Other dielectric type materials which
are substantially transparent in film thicknesses and are
also suitable are tantalum oxide, niobium oxide, and
germanium oxide. Certain types of glasses can also be
used as the protective covering or as "buffer" layers be-
tween the protective films and the substrates to compen-
sate for differences in the thermal expansion characteris-
tics of the substrate material and protective material.
The protective film of selected inert material
is preferably deposited by RF-sputtering techniques and
its thickness is controlled to prevent undesirable dis-
coloration of the article by optical interference effects
produced by incident light rays which enter the film.
Such interference effects are exhibited by transparent
films when the optical thickness (that is, the true thick-
ness of the film multiplied by the refractive index of thefilm material) is comparable to the wavelength of light
and thus falls within the range of from about 3,000 to
8,000 Angstroms (the visible portion of the spectrum).
Since the refractive index for the various film materials
is different, the optimum thickness range will also vary
depending upon the particular material used to form the
protective film.
4 48,44~I
Composite type films which include one or more
additional layers of another material are also employed in
accordance with another embodiment of the invention to
enhance the adhesion of the protective film as well as the
adhesion of a layer of a different metal that is sputtered
onto the substrate (as in the case of an article of base
metal such as a watchband that is first coated with a
sputtered layer of gold or another precious metal). A
composite coating consisting of very thin films of a
precious metal (such as gold) and interposed alternately-
arranged transparent films of a protective material are
employed in accordance with another embodimen-t to further
reduce the amount of precious metal required per article.
Various methods of forming the protective films and also
sequentially metal-coating and then protectively-coating
various articles composed of a base metal employing sput-
tering-deposition apparatus and techniques are also dis-
closed.
BRIEF DESCRIPTION OF THE DRAWING
A better understanding of the invention will be
obtained from the exemplary embodiments shown in the
accompanying drawing, wherein:
Figure 1 is a plan view of a gold-plated band or
bracelet for a wristwatch which has been protectively
coated in accordance with the invention;
Fig. 2 is a fragmentary cross-sectional view, on
a greatly enlarged scale, through a portion of the watch
bracelet shown in Fig. 1 and depicts the manner in which
the thin plating of gold is protected by an overlying
transparent film of inert abrasion-resistant material;
Fig. 3 is a similar cross-sectional view of a
conventional watch bracelet, on the same scale, and illus-
trates the much thicker gold plating commonly employed in
the prior art for such watch components in the absence of
the protective coating means of the present invention;
Eig. 4 is a similar cross-sectional view of
another embodiment wherein the substrate is provided with
s~
48,~48I
an adhesion-promoting primer layer before being coated
with a sputtered layer of gold or the like and then pro
tectively coated;
Fig. 5 is a fragmentary cross-sectional view on
an enlarged scale of still another embodiment wherein a
buffer or transition layer of a selected glass is employed
between the transparent protective fili~ and the plated
- surface o~ the substrate to compensate for the difference
in the thermal expansion coefficients of the plated sub-
strate and protective film;
Fig. 6 is a similar view of an alternative
embodiment in which two buffer or transition layers of
different glasses are employed;
Fig. 7 is a cross-sectional view of yet another
embodiment wherein a transparent protective film of a
selected inert material is deposited directly onto the
` unplated surface of a substrate or article that is com-
posed of tarnishable metal;
Fig. 8 is a cross-sectional view of another
embodiment of the invention wherein alternating very thin
films of a precious metal (such as gold) and a transparent
protective material are employed to further reduce the
amount of precious metal reguired to plate an article; and
Fig. 9 is a plan view of a case for a wristwatch
which is representative of other types of metallic arti-
cles that can be protectively coated in accordance with
the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
;, While the present invention can be used with
advantage to protectively coat various kinds of articles
having metallic surfaces that are subject to attack or
corrosion by the environment in which they are used as
well as pieces of jewelry and the like tha-t are plated
with a layer of a precious metal of a type which is easily
scratched or rapidly worn away during normal use of the
jewelry, it is especially adapted for use in conjunction
with gold-plated articles such as bracelets and cases for
6 48,4~8I
wristwatches and the like and it has accordingly been so
illustrated and will be so described.
A representative watchband or bracelet 10 is
shown in Fig. 1 and consists of the usual intercoupled
links L and a suitable latching member or clasp C. As
illustrated in Fig. 2, such components are typically
fabricated from a suitable base metal 12 (such as brass or
stainless steel) which serves as a substrate for a plating
14 of gold, a gold alloy, or other precious metal that
provides the desired attractive lustrous finish. As is
customary in the gold~plating art, a thin coating 13 of
nic~el or other suitable metal is deposited on the sub-
strate before the plating operation is performed by elec-
trode position or other well known means. Such an initial
coating is referred to as a "strike" in the art and is re-
quired to insure that the gold plating bonds properly to
the substrate and that a smooth lustrous gold finish is
produced if the substrate has a rough surface. Nickel
"strikes" on brass substrates typically. have a thickness
20 in the order of 0.10 micron (1,000 Angstroms) or so. How
; ever, the thickness of such bonding layers is not critical
and can be varied according to the plating requirements
and the composition and condition of the base metal.
In accordance with one of the important advan-
tages afforded by the present invention, the thickness of
the yold plating 14 is drastically reduced and the plated
surface of the watch bracelet 10 (or other article) is
protected from scratching and abrasion by a film 16 of a
selected inert and non-metallic material that tenaciously
adheres to the gold-plated surface of the substrate 12.
In order to provide adequate long-term protection for the
thin "soft" plating 14 of gold without altering its ap-
pearance, the protective film 16 must be formed from a
material which is much "harder" than gold and is substan-
tially transparent and substantially colorless in thinfilm form.
7 48,448I
Materials which meet all of these requirements
and are thus suitable for use as protective films in
accordance with the invention are silicon dioxide (SiO2~,
aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon
nitride (Si3N4), magnesium oxide (MgO), spinel
(MgO-3.5Al2O3), Corning Glass No. 0080 (soda-lime glass),
~';l Corning Glass No. 7070, Corning Glass No. 7740 (PYREX
glass), and Corning Glass No. 7059.
The various properties of these materials ~hich
make them suitable for use as protective coatings pursuant
to the invention are listed in Table I below. For compar-
ison, electroplated gold has a Knoop hardness of about 130
and the thermal expansion coefficients for stainless steel
and brass are 173 and 169 x 10 7/oC, respectively.
TABLE I
~ Protective Thermal Expansion
i Coating Hardness RefractiveCoefficient
Material ~ Index (n)(x10 /C)
_ .
f SiO2 741 1.46 8
A1203 1370 1.78 73
~'.
~ TiO2 879 2.71 96
. .
Si3N4 2500 1.87 45
MgO 692 1.69 120
Spinel 1140 1.73 59
25 Corning Glass 400 1.512 92
~j No. 0080(approx.)
Corning Glass 418 1.469 32
No. 7070(approx.)
Cornlng Glass 418 1.474 33
No. 7740
Corning Glass 424 1. 53 46
No. 7059
S~
8 48,448I
The hardness data given in Table I is the Knoop
microhardness for bulk materials and thus provides an
indication of the abrasion resistance of the various
materials and their ability to protect the underlying
plating of gold (or other precious metal).
Corning Glass No. 0080 is a soda-lime silicate
type glass that i5 used in the electric lamp industry for
lamp bulbs and the like. Such glasses typically contain
60 to 75% (by wt.) SiO2, 5 to 18% Na2O, 3 to 13% CaO or
MgO (or a mixture thereof~ and minor amounts of additional
materials such as A12O3, and K2O. A specific example of a
glass composition of this type is as follows: 73O6% SiO2,
16% Na2O, 3.6% ~gO, 5.2% CaO, 1% A12O3 and 0.6% K2O.
Corning Glass Nos. 7070 and 77~0 are borosili-
cate type glasses that contain major amounts of SiO2 and
B2O3 and various minor constituents. Glass No. 7740 is
marketed by Corning under the trade name "Pyrex" glass. A
specific example of a No. 7740 type glass is as follows:
80-5% (by wt-) Si2' 12-9% B2O3, 2-2~ A12O3, and 0.4% K2O.
A specific example of a No. 7070 type glass
composition is as follows: 70% (by wt.) SiO~, 28% B~03,
1-2% Li2O, 1.1% A12O3, 0.2% MgO, 0.5% K2O and o.l% CaO.
Corning Glass No. 7050 is an aluminoborosilicate
type glass which typically has the following composition;
50.2% (by wt.) SiO2, 25.1% BaO, 13.0% B2O3, 10.7% A12O3
and 0.4% As2O3.
Other dielectric type materials that are suit-
able for use as protective films in accordance with the
invention are silicon carbide (SiC) which has a Knoop
hardness of 2500, tantalum oxide (Ta2O5), niobium oxide
(Nb2O5) and germanium oxide (GeO2). Another glass which
; has also been found suitable is a high-lead-content solder
glass which has a thermal expansion coefficient of 117 x
10 7/oC and typically contains 85% (by wt.) PbO, 7.5% B2O3
and 7.5% SiO2.
As indicated by the data given in Table I, the
material which is used to form -the protective film 1~ should
have a refrac~ive index that is in the range of from about
1.~ to about 2.8.
S'~L~
8a 48,448I
In general, any material that has a Knoop hard
ness of 400 or more, is inert, and has the ability to be
o~
9 48,448I
deposited in thin adherent films that are of controlled
thickness and are also substantially transparent and
colorless in such thicknesses can be used as the protec-
tive coating. If the thermal expansion characteristic of
the protective material relative to the substrate is such
that flakiny, cracking or peeling o the film occurs, then
an intervening layer (or layers) of other materials must
be used as hereinafter disclosed to correct the mismatch.
Various types of clear glass compositions (such as the
aforesaid solder glass) that have thermal expansion co-
efficients which approximate that of stainless steel, for
example, can also be used.
While the protective film 16 can be formed on
the plated substrate 12 by various means including elec-
tron beam evaporation and chemical vapor-deposition tech-
niques, deposition by RF-sputtering is preferred because
sputtered films, in general, exhibit excellent adhesion,
t are dense and free from pinholes, provide satisfactory
substrate coverage, and have the proper stoichiometry.
20As is well-known, transparent films will produce
coloration due to optical interference or so-called "New-
ton ring" effects when the optical thickness (the product
of the true or mechanical thickness and the refractive
index) of the film is roughly of the same order of magni-
2Stude as the wavelength of light (from about 3,000 to 8,000
Angstroms). The film thickness range which enables inci-
dent light rays to produce such interference color effects
thus depends upon the refractive index of the coating
` material and generally lies between 0.05 micron (500
30Angstroms) and 1.5 microns (15,000 Angstroms) for the
materials which are listed in Table I or referred to as
being suitable. Hence, in order to avoid such undesirable
discoloration of the gold-plated surface of the watchband
10 (or other article which is being protectively coated~,
the thickness of the protective film 16 must either be
less than about 500 Angstroms or greater than about 15,000
Angstroms for these materials.
0~
48,448I
Since films with thicknesses less than 500
Angstroms would be too thin to provide adequate "long
term" abrasion protection, protective films formed from
the aforementioned materials must have thicknesses that
are greater than about 15,000 Angstroms. Protective films
that are too thick, however, must also be avoided since
they will tend to crack or peel away from the substrate.
Since the film thickness above which optical interference
coloration effects are not discernible varies inversely
with the refractive index of the coating material, a
thinner film of a high refractive index material can be
employed. This is desirable from a manufacturing stand
point since shorter ~ilm-deposition times will be required
and peeling will be inhibited. The following materials
are preferred in this respect since they have high indices
of refraction (shown in parenthesis): SiC (2.73), Nb2O5
(2-24), Ta2O5 (2-21), TiO2 (2.71), GeO (2.1) and Si3N4
(1.87).
The sputtering yield provides a relative indi-
cation of how easily a given material can be sputtered
.~ from a target and, hence, how rapidly a protective film of
that material can be formed by sputter-deposition. This
is an important consideration when coating in mass-produc-
tion quantities is involved. In general, the ideal mate-
rial for the protective coating from both a quality and
manufacturing standpoint is thus a material which has high
values for hardness, refractive index, and sputtering
yield.
TEST DATA AND SPECIFIC EXAMPLES
' 30 Preliminary tests performed on small stainless-
steel plates which were coated with a 2.5 microns (25,000
Angstroms) thick electroplated layer of 24 K gold have
indicated that protective coatings of SiO2, Al2O3, TiO2,
Si3N4 and SiC which were formed by RF-sputtering exhibited
excellent adhesion and protection of the substrates
against abrasion. A portion of each of the gold-plated
test plates was masked during deposition of the protective
11 48,448I
film to provide an uncoated "gold reference" surface for
evaluation. Film adhesion was checked by a so-called
"tape test" which consisted of firmly pressing a piece of
"Scotch'r-brand adhesive tape onto a film-coated portion of
the test plate and then stripping the tape away. This is
a very demanding test since any material which is not
firmly bonded or securely anchored to the substrate will
be lifted from its surface when the adhesive tape is
stripped away. Abrasion resistance was determined by
vigorously rubbing the coated and uncoated portions of the
test plates with a pencil eraser and then with steel wool.
The appearance of the coated portions of the plates was
evaluated visually by noting any discoloration effects or
undesirable altering of the natural color of the gold
plating.
These preliminary tests verified that very thin
films of the tested materials in the thickness range below
that were required to avoid optical interference effects
(that is, less than about 0.05 micron or 500 Angstroms)
would not provide adequate "long-term" abrasion protection
of the gold plated substrates. The sputtered films of SiC
had a yellowish-brown tint and altered the natural gold
color of the samples to a certain degree. Such films
would, accordingly, be satisfactory only where a slight
discoloration of the plated surface could be tolerated (or
might even be desirable). Although the sputtered films of
TiO2 were colorless and (due to their high refractive
index) were devoid of any optical interference coloration
even though they were only 1.5 microns or 15,000 Angstroms
thick, the high refractive index of this material caused
the film surface to have a high reflectivity which tended
to mute the gold color of the substrate and slightly
modify its appearance. The Al2O3 sputtered very slowly
and would thus probably not lend itself to mass production
operations.
Experiments have indicated that the sputtering
yield of Si3N4 is comparable to that of SiO2 (0.13 mole-
~3~
12 4~,448I
cule per ion at 1 kilovolt target voltage) and these two
materials are thus good selections for protectively coat-
ing gold plated substrates where coating times and costs
are critical factors.
Test data obtained with SiO2 films of varying
thickness on gold-plated stainless steel sample plates
have shown that protective films of this material that
were apprvximately 1.4 microns or 14,000 Angstroms thick
exhibited pale pink and green interference colors which
indicated that the films were too thin. When films of
SiO2 5 microns or 50,000 Angstroms thick were deposited on
such gold-plated sample substrates, the coatings cracked
and flaked from the substrates due to high stresses pre-
sent within the thick films. SiO2 films 3.4 microns
15 (34,000 Angstroms) thick adhered well to the gold plated
substrates and also had excellent abrasion resistance, on
the basis of the "eraser and steel wool" test. The color
of the coated plates was indistinguishable from the origi~
nal gold-plated substrate. Pursuant to these experimental
data, the optimum thic~ness range for SiO2 protective
films on gold-plated articles is accordingly within the
range of about 1.5 to about 4 microns (that is, from about
15,000 to about 40,000 Angstroms).
Similar tests conducted on gold-plated watch
bracelets 10 of the type shown in ~ig. 1 confirmed the
foregoing early test data obtained on plate samples.
These additional tests revealed that cleanliness of the
gold-plated substrates prior to deposition of the pro-
tective film is quite important. Some of the sample
: 30 watchbands apparently had an organic film or coating on
their surfaces which may have been intended to serve as a
protective coating by the manufacturer. This contamina
tion produced undesirable brown stains when SiO2 protec-
tive films were applied and also caused flaking of the
films. These coating problems were solved by subjecting
the watchbands to a cleaning procedure which consisted of
boiling the components in a suitable detergent, rinsing
5~
13 48,4~8I
them in deionized water and methyl alcohol, and then
drying them in air at around 120C.
The additional series of tests also indicated
that the optimum thickness of SiO2 protective films was
somewhat less for ~he gold-plated watchbands than for the
gold-plated test blanks of metal. Films between about 2
and 3~5 microns thick tended to flake from the watchbands
and no undesirable interference color effects were pro-
duced if the film thickness was greater than about 1.4
microns. The optimum thickness for protective films of
SiO2 in the case of gold-plated watchbands of the kind
shown in Fig. ] is accordingly within the range of from
about 1.4 to about 2 microns (that is, from about 14,000
to about 20,000 Angstroms~.
The differences in the observed interference
effects for SiO2 films deposited on the test blanks of
gold-plated metal and on the gold-plated watchbands may
have been due to the smooth surface finish of the test
blanks and the fact that the watchbands had a textured
surface finish.
A most important advantage afforded by the
present invention from a cost standpoin-t is the fact that
wristwatch bracelets and other components for fine watches
(as well as various articles of fine jewelry) can be
provided with a much thinner plating of gold without
detracting in any way from the quality or appearance of
the components or articles since the natural appearance of
the gold plating is preserved by the transparent film of
protective material. As shown in Figs. 1 and 2, a watch-
band 10 of high quality having a stainless steel substrate12 which is provided with a nickel "strike" 13 about 1,000
Angstroms thick and then plated with a layer 14 of gold
approximately 0.5 micron or 5,000 Angstroms thick (dimen-
sion "t1") can accordingly be made by protectively coating
the thin layer of gold with a film 16 of 5iO2 (or similar
transparent material) that is approximately four -times as
thick as the gold plating--that is, a protective film of
sj ~
14 48,448I
SiO2 approximately 2 microns or 20,000 Angstroms thick.
The relative thicknesses of the gold plating, the bonding
layer or "s-trike" and the protective film are substan~
tially as shown in Fig. 2. Hence, the gold plating 14 is
only one-fourth as thick as the protective film 16, and the
nickel "strike" 13, in turn, is only one-fifth as thlck as
the gold plating.
If the article or substrate is such that it can
be coated with a thinner layer o~ gold which still retains
the natural appearance and color of solid go:Ld, then gold
coatings in the order of about 0.2 or 0.3 micron (about
2,000 or 3,000 Angstroms) can be used in combination with
the protective film of the invention.
In contrast, conventional watch bracelets 11
(shown in Fig. 3) of good quality having similar sub-
strates 18 of stainless steel which is primed by a nickel
"strike" 19 about 1,000 Angstroms thick generally have a
gold plating 20 that is approximately 10 microns or
100,000 Angstroms thick (dimension "t2") -that is, twenty
times thicker than the gold plating 14 employed in accord-
ance with the invention. Figs. 2 and 3 are drawn to the
same scale so that the relative thicknesses of the two
gold platings 14 and 20 is accurately shown in and apparent
from the drawing.
Hence, the present invention permits the thick-
ness of the gold platings employed on such fine watch
components to be reduced by at least 95% (5,000 Angstroms
versus lO0,000 Angstroms) and up to 9~% or so (2,000
Angstroms versus 100,000 Angstroms) with a corresponding
reductions in the manufacturing cost of the watches. In
view of the high cost of gold and other precious metals,
the cost saving is very significant and constitutes an
important competitive advantage, not only in the watch
industry but in the manufacture of fine jewelry and simi-
lar articles that are composed of a base metal and pres-
ently require heavy coatings or platings of a precious
metal to preserve their appearance.
48,~48I
ALTERNATIVE "PRIMER LAYER" EMBODIMENT (FIG. 4)
Further tests on protective films for gold-
plated articles such as watch bracelets have shown that an
additional reduction in their manufacturing cost can be
reali~ed by depositing the gold layer on the watch brace-
lets by sputtering techniques (rather than electroplating)
so that both the gold-coating and protective~coating
operations can be performed sequentially within the vacuum
chamber of the RF-sputtering apparatus. Experiments con-
firmed that this could be achieved quite readily by pro-
~viding one target of gold and another target of SiO2 (or
other material from which the protective film is to be
formed) within the vacuum chamber and then simply operat-
ing the sputtering apparatus in two different modes which
selectively bombarded the targets to first deposit the
required layer of sputtered gold onto the watchbands of
ase metal and then coat the resulting gold-coated surface
with a film of sputtered SiO2, the required thicknesses
being obtained by properly controlling the target voltage,
power input and the length of the sputtering operation in
~, each mode.
A further advantage afforded by this method of
sequentially-coating was the ability to sputter-coat the
watchbands with a layer of 24K gold instead of the 14K
gold conventionally used in the electroplating process.
I'he sputtered-gold layers thus had a deeper and richer
. gold color (due to the higher gold content) compared to
watchbands with gold-electroplated coatings--even though
the sputtered-gold layers were much thinner and used less
gold.
During the course of these experiments, it was
also discovered that both the adherence and durability of
the sputtered-gold coatings could be improved by deposit-
ing a very thin layer of titanium (Ti) on the stainless
steel substrate before sputter-depositing the gold layer.
The use of a sputtered film of Ti about 200 Angstroms
thick permitted a layer of sputtered gold less than 0.5
16 48,448I
micron thick (5,000 Angstroms) to pass the "tape test" for
adhesion. Such a preliminary or "primer" layer of Ti
accordingly enables sputtered gold layers approximately
0.25 or 0.3 micron thick (2,500 or 3,000 Angstroms) to be
employed on substrates--thus providing a corresponding
further reduction in coating and material cost without
detracting from the appearance of the finished article as
regards its natural gold "finish" and appearance.
A watch bracelet lOa (or other article) having a
10 substrate 12a of a base metal (such as stainless steel or
the like) that is provided with the composite sputtered
coating according to this embodiment as shown in Fig. 4.
As will be noted, the substrate 12a has a thin primer
layer 21 of titanium deposited on its surface to promote
15 the adhesion of a layer 22 of sputtered gold which, in
turn, is protected by a film 16a of SiO2 or other suitable
material that is substantially transparent and does not
noticeably alter the natural appearance or finish of the
gold layer.
The film thickness of the adhesion-promoting
primer-layer 21 of titanium is not especially critical and
can be in the range of from about 50 to 400 Angstroms.
Suitable thin films of other metals such as chromium,
nickel and NichromeC~ype alloys that have a similar adhe-
25 sion-promoting effect can also be used. Nichrome alloys
are well known in the art and are composed of about 80%
(by wt.) nickel and about 20% chromium.
The manufacture of the watch bracelet lOa or
other article will also be facilitated if the primer layer
30 21 of titanium (or other metal) is sputter-deposited on
the substrate 12a in sequential fashion with the overlying
layers of gold and protective material in a common vacuum
chamber of a properly modified and controlled RF-sputter-
ing apparatus.
ALTERNATIVE "BUFFER LAYER7' EMBODIMENT (FIG. 5)
Anot:her form of composite protective coating for
gold-plated watch components and similar articles is shown
17 48,448I
in Fig. 5 and was developed to overcome an adherence
problem encountered during trial runs using a production
type sputtering system which operated at high deposition
rates. When sputtering protective films of SiO2 onto
gold-plated stainless steel watchbands using such a sys~
tem, it was discovered that the protective films sometimes
flaked from the watchbands upon removal from the sputter-
ing apparatus. While the exact cause of this problem is
unknown, it is believed that it may be due to excessive
heating of the watchbands produced by the high rate at
which the sputtered material was deposited--in combination
with the subsequent cooling and a thermal expansion co-
efficient mismatch between the SiO2 film and stainless
steel substrate which induced stresses in the fi.lms with
resultant flaking.
It was found that this problem could be solved
by using an additional transparent layer of a suitable
material between the SiO2 film and the gold-plated stain-
less steel substrate, which additional layer is composed
of a material that has a thermal expansion coefficient
between that of SiO2 (8 x lO 7/oC) and that of stainless
steel (173 x lO 7/oC). The additional layer thus serves
as a buffer or "transition" layer that compensates for the
expansion mismatch between the substrate and protective
SiO2 film without interfering with the ability of the film
to protect and preserve the natural appearance of the gold
plating.
The soda-lime silicate type glass marketed by
the Corning Glass Company under the trade designation
Corning Glass No. 0080 (listed in Table I) is a material
particularly suitable for use as such a buffer layer since
it has a thermal expansion coefficient of 92 x lO 7/oC
(about midway between that of stainless steel and ~iO2)
and is transparent and colorless in the thicknesses re-
~5 quired. This glass composition also has an index of re-
fraction of l.512 and a Knoop hardness of about 400 as
indicated in the Table. However, any of the glasses list-
~, ~
18 48,448I
ed in Table I (as well as the aforementioned solder glass)can be used as a buffer material since they all have
thermal expansion coefficients that are much higher than
that of SiO2. Since materials such as TiO2 and A1203 have
high coefficients of thermal expansion, they are also
especially suited for use as a buffer material.
Tests have shown that stainless steel watchbands
provided with a gold layer (either plated or sputtered)
approximately 5,000 Angstroms thick can be provided with a
sputtered composite transparent protective coating that
e~hibits excellent adhesion and durability and consists of
a layer of Corning No. 7059 Glass about 1.5 microns thick
(15,000 Angstroms) that was covered by a film of SiO2
approximately 0.5 micron (5,000 Angstrom) thick. The
relative thicknesses of the transition or buffer layer of
glass and the SiO2 film are not critical and can vary
considerably from the stated values. For example, the
film thickness of the SiO2 can be within the range of from
~; about 0.2 micron to about 2 microns (2,000 to 20,000
Angstroms) and the buffer layer of glass can be from about
1 to 4 microns thick (10,000 to 40,000 Angstroms). How-
ever, the combined thicknesses of the protective film and
buffer layer must be sufficient to prevent the occurrence
of optical interference effects and undesired coloration
of the gold-coated surface of the article.
As illustrated in Fig. 5, a watchband lOb or
other article according to this embodiment consists of a
substrate 12b of stainless steel (or other base metal), a
"strike" or bonding layer 13b of nickel or the like, a
thin plating 14b of gold (or other precious metal) that is
protectively shielded from scratching and other damage by
a substantially transparent and colorless composite coat-
ing which consists of the buffer layer 24 of a selected
glass and a much thinner layer 25 of SiO2 or other suit-
able abrasion-resistant material.
19 48,448I
ALTERNATIVE MULTIPLE "BUFFER-
LAYER" EMBODIMENT (FI~
The invention is not limited to the use of a
single layer of a buffer material to correct the mismatch
of the thermal expansion and contraction characteristics
of the gold-plated substrate and the protective film but
includes within its scope the use of two or more buffer
layers for this purpose. A multiple buffer-layer embodi-
ment 10c is shown in Fig. 6.
As illustrated, this embodiment comprises a sub
strate 12c of a base metal, the usual very thin "strike"
or bonding layer 13c of nickel or the like, a gold plating
14c of reduced thickness, two buffer layers 26, 27 of two
different substantially transparent colorless materials
that have thermal expansion coefficients which provide a
"two-step" transition from the high expansion coefficient
of the plated substrate 12c to the much lower expansion of
the transparent protective film 28.
In the case of a stainless steel gold-plated
substrate and a protective film of SiO2, a first buffer
layer of soda-lime silicate glass (No. 0080 glass) and a
second buffer layer of Corning No. 7059 Glass would be a
good combination of buffer materials since they would
provide a '7balanced" transition from 173 to 92 to 46 to 8
(in terms of the expansion coefficients of the respective
materials, starting with the substate).
The thickness of the buffer layers is not criti-
cal but they obviously should be thin enough to maintain
the composite coating below about 40,000 Angstroms or so.
They may be of equal thickness (as shown in Fig. 6) or
their relative thickness can be varied and correlated with
the expansion coefficients of the particular materials to
provide an optimum "gradation" of stress forces at the
interface of the substrate and protective film. However,
in Fig. 6 the total thickness of the illustrated composite
coating (that is, buffer layers 26, 27 and the protective
film 28) is the same as the thickness of the composite
20 48,448I
coating used in the single~buffer layer embodiment shown
in Fig. 5. This is preferred since it would reduce the
sputter~coating times to a minimum.
ALTERNATIVE SIN~LE-COATING EMBODIMENT (FIG. 7)
The invention is also suitable for use in pro-
tectively coating articles that are entirely composed of a
material (such as brass or silver) that is rapidly de-
graded or becomes tarnished by chemical attack from oxygen
or pollutants in the atmosphere in which they are used.
As shown in Fig. 7, in accordance with this
embodiment the unplated article 10d itself (a silver bow]
or tray, or a brass name~plate, for example) constitutes
the substrate 12d that is provided with the substantially
transparent and colorless protective film 30 of SiO2 (or
other suitable abrasion-resistant material such as those
listed in Table I and in the text immediately following
the Table). The thickness of the film 30, as in the pre-
vious embodiments, must be properly correlated with the
refractive index of the parti.cular protective material to
avoid ~optical interference effects and resultant undesir-
able coloration that would otherwise be produced by inci-
dent light rays. Since the aforementioned solder glass
has a thermal expansion coefficient of 117 x 10 7/oC, it
can also be used to form the protective film 30 in those
instances where the article is composed of a metal that
also has a high expansion coefficient. E'or example, a
protective film of this type glass (or any of the other
glasses listed in Table I) would be suitable for use on
silver trays, brass commemorative pla~ues or brass name-
plates used on bui.ldings and the like, especially sincesuch articles are not subjected to severe abrasion during
normal use.
If the protective film 30 is composed of a much
harder material such as TiO2, SiO2, MgO or the like, then
it can be used in conjunction with watchbands or watch
cases that are composed of solid brass and are thus not
coated or plated with gold or another precious metal.
21 48,448I
Experimental tests have demonstrated that sputtered SiO2
films adhere very well to brass articles and produce a
body color that is very similar to gold. SiO2 films 2.58
microns thick (25,800 Angstroms) were free of blemishes
and abrasion-resistant when sputter-deposited on a clean
brass watchcase.
ALTERNATIVE "MULTI-THIN-FILM"
EMBODIMENT (FIG. 8)
Another form of composite layer that permits
even thinner coatings and smaller amounts of gold or other
precious metals to be employed on substrates of a base
metal is shown in Fig. 8.
According to this embodiment, an article lOe
(such as a bracelet for a wristwatch or a piece of jewel-
ry) that is composed of a base metal (such as stainless
steel or the like that serves as a substrate 12e) is coat-
ed with a primer layer 13e of titanium or a similar mater-
ial and then with a plurality of very thin films 31,3~-
35,37 of sputtered gold (or other precious metal) and a
plurality of interposed thin films 32,~4--36,38 of sput-
tered SiO2 (or other transparent and inert protective
material). The series of alternately-disposed sputter-
deposited films of gold and SiO2 form a very hard and
durable composite coating whose outer surface consists of
an SiO2 film 38 and whose inner surface is a layer 31 of
gold that is bonded to the primer-coated substrate 12e.
While a total o~ eight interposed and overlapped films
31-38 are shown in Fig. 8, any suitable or required number
can be employed (as indicated by the "break-away" in the
composite coating). Tests conducted with substrates
having a total of ten such films gave satisfactory re
sults.
The alternating films can be very thin (for ex-
ample, less than about 100 Angstroms thick) and provide
several advantages in that they greatly reduce the sput-
tering times (and thus the overall coating cost) but still
produce an article 10e with a finish that has the natural
22 48,~48I
look of gold but has excellent abrasion~resistant proper-
ties and actually contains a very small total amount of
gold metal. As the top films "wear away" due to their
extreme thinness, the next layer (of gold or SiO2) provide
the desired gold "finish" appearance.
The total amount of gold in such multi-film
composite coatings can be further reduced by making the
gold films thinner than the films of protective material--
for example, gold films that are around 50 Angstroms thick
in combination with SiO2 films about 100 Angstroms thick.
Hence, a composite coating having a total of forty such
films would have an overall thickness of only 3,000 Ang-
stroms (with the aggregate or "total" film thickness of
the gold films being only 1,000 Angstroms and thus re-
quiring a very small quantity of gold).
Since the interposed protective films are sothin, they do not produce any optical interference effects
or discoloration of the underlying gold films and can be
sputter-deposited very rapidly. Flaking or peeling of the
films is also not a problem since the sputtered materials
are intimately bonded to one another and are not thick or
brittle enough to create stresses due to mismatches of
thermal expansion coefficients, either with respect to the
interposed films themselves or with respect to the base-
metal substrate.
While the combination of interposed films ofSiO2 and gold have been referred to in the embodiment just
described, it will be apparent to those skilled in the art
that various other combinations of materials can be used--
depending upon the type of article involved (for example,
alternating films of silver and spinel or a suitable
glass, alternating films of platinum and TiO2 or MgO,
etc.).
WATCHCASE EMBODIMENT (FIG. 9~
The invention is not limited to protectively
coating bracelets or bands for wristwatches but includes
within its scope the provision of transparent abrasion-
23 43,4~8I
resistant coatings (consisting of one or several films) on
other components for wristwatches such as watchcases 40 of
the type shown in Fig. 9. Such cases can either comprise
a gold-plated base metal (such as stainless steel or
brass) or they can be composed of a metal such as brass
that is not plated with gol.d but has a body color which is
very similar to gold.
The various protective films and composite pro-
tective coatings of the present invention can accordingly
be used on any article of manufacture that has a metallic
surface which is degraded or tarnished by chemical attack
from the atmosphere or from pollutants in the atmosphere
in which the article is used. The films and coating can
also be used on articles such as jewelry and decorative
components which have a substrate that is composed of a
base metal (such as stainless steel or the like) that is
coated with a relatively soft metal (such as gold) which
, is easily scratched and has poor 'iwearing" characteris-
, tics.
~X 20 Another more limited but important benefit
afforded by the protective films and coatings of the
present invention is in the prevention of "allergic" type
reactions which some persons experience when wearing rings
or chains, etc., that are composed of a certain metal or
alloy. Since all of the materials listed are chemically
inert and stable, a thin film of such material physically
- isolates the wearer's skin from the reaction-causing metal
and thus permits the ring or other article to be worn
without any undesirable biological effects or reactions.
3~ This is especially true in the case of the glass or glass-
like film~forming materials listed or mentioned previous-
ly .
SPECIFIC EXAMPLE OF SPUTTER-COATING PROCESS
Following is a specific example of the manner in
which the substantially transparent abrasion resistant
films or coatings of the present invention are applied to
articles or substrates by sputter-deposition using experi-
mental apparatus.
24 48,448I
The articles or substrates are loaded into an
RF-sputtering apparatus along with a suitable target of
the selected coating material, a 6~inch diameter target of
SiO~ for example. The sputtering chamber is then evac-
uated to a pressure of about 5 x 10 7 Torr and filled withapproximately 1.4 x 10 2 Torr of a mixture of 90% argon
and 10% oxygen which serves as the sputtering gas. An RF
target voltage of 750 volts is then applied to the target
so that the power input is around 200 watts. The sputter
ing apparatus was operated for approximately 10 hours
under these conditions and films of SiO2 having a thick~
ness of from 1.5 to 2.0 microns (15,000 to 20,000 Ang-
stroms) were deposited on the substrate. If a production
type magnetron RF-sputtering apparatus were used, the time
required to deposit SiO2 films of such thicknesses could
be reduced to approximately 1 or 2 hours.
As will be appreciated to those skilled in the
art, the operating parameters of the sputtering apparatus
can be adjusted in accordance with the sputtering yields,
etc., of the various coating materials so that films of
the thicknesses required for each of the described embodi-
ments can be readily and efficiently deposited.
; ADDITIONAL SPECIFIC E~AMPLES OF VARIOUS EMBODIMENTS
In addition to the experimental and test samples
and data described previously, following are specific
examples of additional embodiments that have been made and
evaluated:
Fig. 2 Embodiment ~ a stainless steel watchband
was first coated with a primer layer of Ti 260 Angstroms
thick which was sputter-deposited in a chamber evacuated
to a pressure of 4 x 10 7 Torr and then filled with argon
(the sputtering gas) to a pressure of 1.4 x 10 Torr.
The Ti film was deposited in approximately eleven minutes
using an RF target voltage of 950 volts and a power input
of around 200 watts. A gold film 4,900 Angstroms thick
was then sputter-deposited (without removing the watchband
from the chamber) by operating the sputtering apparatus
25 48,448I
for twenty minutes (with a 24K gold target) at a target
voltage of 750 volts and lO0 watts power input. A protec-
tive film of SiO2 approximately 20,000 Angstroms thick was
then sputter-deposited by operating the apparatus at a
target voltage of 750 volts and 200 watt power input for
ten hours (using an SiO2 target). The coatings adhered
very well to the substrate and the SiO2 film was colorless
and passed the abrasion and adhesion tests described
previously.
~0 Fig. 4 Embodiment - A stainless steel watchband,
which was previously electroplated with gold in the con-
ventional ~anner, was provided with a buffer layer of
Corning No. 7059 glass that was 1.5 microns (15,000 Ang-
stroms) thick and then coated with a protective film of
15 SiO2 0.5 micron (5,000 Angstroms) thick by operating an
RF-sputtering apparatus in sequential fashion with two
different targets. The sputtering chamber was first
evacuated to a pressure of 6 x lO 7 Torr and then filled
with a sputtering gas consisting of 90% argon and 10%
oxygen at a pressure of 1.4 x lO 2 Torr. The buffer layer
of glass was deposited by operating the apparatus at a
target voltage of 450 volts and a power input of 300 watts
for four and one-half hours, and the SiO2 film was depos-
ited by using a target voltage of 750 volts and operating
the apparatus for three hours at 200 watts input.
_g 7 Embodiment - A brass watchcase was coated
with a transparent colorless protective film of SiO2 2.58
microns (25,800 Angstroms) thick by first evacuating the
sputtering chamber to a pressure of 5 x 10 7 ~orr, then
filling it with a sputtering gas consisting of 90% argon
and 10% oxygen at a pressure of 1.4 x 10 2 Torr and oper-
ating the apparatus for fifteen hours at 200 watts input
and 750 volts applied to the SiO2 target. The SiO2 film
adhered well, had no visual defects and passed the afore-
mentioned "tape" and abrasion tests.
As will be apparent to those skilled in the art,when the precious metal coating or plating on the article
,
48,448I
consists of gold, it need not be composed of pure (24K)
gold but can comprise a suitable gold alloy (for example,
lOK or 14K gold, etc.).
