Note: Descriptions are shown in the official language in which they were submitted.
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GOLD COLORED WARE
The present invention is concerned with jewelry, flatware
and like items which are generally made of a copper-rich base metal
and which have a gold surface.
BACKGROUND OF THE INVENTION
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There is a market for gold surfaced jewelry, flatware,
cups, dishes, candle sticks holders, bowls~ platters and the like
which are inexpensive but which are of a better quality than the
common gold plated items. For purposes of convenience in this
specification and claims such items are called 'idecora~ive-utility"
items~.~ Some of the problems in~olved in~producing better quality
decorative-utility items ar1se~from~the use of copper-base materials
such as~brass, cupro-nickel and nickel-silver as the primary
str~uctural materlal of the item. The use of such materials is
dictated by cost and by~convenience~in cold forming the item.
However, such copper-base alloys~generally corrode severely in
contact with substances commonly found around people and households.
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For example, cartridge brass and nickel-silver are corroded severely
by human sweat, aqueous ammonia and sulfides, either airborne or in
solution.
A thin layer of gold, perhaps 0.2 to 0.6 micrometer thlck,
is sufficient to impart a satisfactory golden appearance to an item
~ade of copper-base alloy. However, a layer of gold that thin gives
essentially no corrosion protection to the underlying metal. In fact
in aqueous electrolytic systems, e~g. common salt water, a very thin
gold surface layer can accelerate corrosion of the underlying metal
by providing a built-in~ nicely coupled, cathode-anode system. The
copper-base alloy unfortunately serves as the anode and is consumed.
The art has learned to avoid this problem by interposing, between the
copper alloy of the base and the gold outer layer, an intermediate
layer of nickel of sufficient thickness to inhibit corrosion of the
copper alloy base. The use of such an intermediate layer solves the
corrosion problem without the use of very thick layers of gold which
would be uneconomical. It doesn't solve all the problems however.
Gold is soft and scratches easily. In very thin layers, e.g. 0.3-0.6
micrometer thick, scratches can easily go through to the base and
uncover the underlying white nickel. Such scratches then are very
unsightly. This problem can be solved by electrodepositing a
relatively hard gold alloy instead of gold but this solution is not
ideal. First, because of electrochemical factors such as the use of
insoluble anodes, it is difficult to plate consistent alloy
compositions item to item and batch to batch. Thus, there can be
observable differences in appearance between such items and such
batches. Secondly, the alloy plate is of uniform hardness through
the thickness of the deposit. If the plate deposit is made hard
enough to significantly inhibit scratching, there is danger that
through internal stress, adhesion to the nickel lnterlayer will be
weak~
Applican~ has now provided a process whereby improved gold
surfaced decorative-utility items can be produced.
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DESCRIPTION OF THE INVENTION
The present invention contemplates a composite material in
the form of a "decorative-utility" item, comprising a base made of a
metal from the group of copper-base alloys, i.e. alpha brasses,
cupro-nickels and alpha nickel-silvers, an intermediate layer of
nickel at leas~ about 3 micrometers thick and a surface layer of gold
at least about 0.3 micrometer thick up to e.g. about 0.6 micrometer
or even 0.8 micrometer thick. The nickel-gold coating can cover the
entire surfaces of the decorative-utility item or can be confined to
one surface or a portion of the entire surface. The gold contains a
varying amount of nickel such that the nickel content decreases from
the side of the gold abutting the nickel layer to about 1-10% by
weight at the outer surface. The gold layer is metallurgically
bonded to the nickel and contains at the outer surface an amount of
nickel sufficient to increase the hardness of the gold layer but
insufficient to significantly destroy the distinctive color of the
gold layer. In some instances, ~ickel as in the inter~ediate layer
can serve as the base.
The "decorative-utility" structure of the present invention
can be made by depositing, e.g. by electroplating, a layer of gold
onto a nickel surfaced base and thereafter annealing the composite
structure to provide a metallurgical bond therebetween and to
interdiffuse nickel of the intermediate layer and gold o the surface
layer.
DETAILS OF THE INVENTION
. .
In order to provide those skilled in the art with greater
detail with respect to the present invention, the following
paragraphs set forth particulars and alternatives contemplated to be
within the scope of the invention as hereinbefore described.
The base of the composlte structure of the present
invention is advantageously any alpha brass, i.e. a copper-~inc alloy
containing about 5 to about 30% zinc or an alpha nickel~silver, i.e.
an alloy containing greater than 65% nickel plus copper and less than
35% ~inc or a cupro-nickel, i.e. a copper-base alloy containing up
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to about 40~ nickel. Cartridge brass which generally contains 30~
zinc, balance copper, nickel-silver which contains about 65% copper,
10 to 18% nickel, balance zinc and cupro-nickel containing 5-40%
nickel, up to 3% iron, balance copper are quite suitable as base
materials for the composite structures of the present invention. As
those skilled in the art are aware, these metals are supplied in
sheet, rod, wire, tube and strip form. Shapes are fabricated from
these and other standard forms by stamping, cutting, bending,
rolling, drawing, hammering, spinning, machining 7 swaging and other
well-known manufacturing techniques. It is within the contemplation
of the present invention that the necessary nickel interlayer between
the base and the gold outer layer can be applied to a raw or semi-
fabricated form of the article and be worked along with the copper-
base material. The use of a composite sandwich of copper alloy and
nickel is not preferred because of the likelihood of production of
edge areas not covered with nickel. ~owever, if such edge areas are
not exposed, the use of a composite sandwich will be satisfactory.
There is advantage in providing a nickel deposit on the
structure by electrodeposition. While other means of providing a
nickel deposit such as chemical deposition, sputtering, ion
bombardment, etc. are within the contemplation of the present
invention, electroplating has been found to be an easy, reliable
method of providing a nickel deposit which is essentially free from
organic residue, sulfur and low melting phaæes. The nickel
electrodeposit is accomplished by standard procedures using
Watts-type, chloride, fluoborate and sulfamate baths such as those
disclosed in Electroplating Engineering Handbook, Graham, Van
Nostrand-Reinhold, 3rd Ed., 1971, pages 247 and 248.
In most cases, there is no upper limit to the thickness of
3~ a nickel coating or deposit on a structure e~capt that limit which
may be imposed by practicality, e.g. about 40 micrometers when nickel
is electrodeposited. It is important that the nickel on the surface
of the structure be at least about 3 micrometers thick and
advantageously in the range of ~ to 12 micrometers in thickness. The
nickel layer acts as a barrier coating to diffusion of unwanted
elements, e.g. copper and zinc, in the base into the gold and must be
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sufficlently thick to serve this function as well as to provide to
the gold the amount of nickel required for hardening.
The gold on the nickel surface of the base is
advantageously electrodeposited as pure (24 KT) gold from an
electroplating bath using conditions applicable to obtaining a pure
electrodeposit. For purposes of this specification and claims,
however, gold need not be 100% pure. For purposes of this invention,
the term "gold" includes not only pure gold but also yellow alloys
and reddish yellow alloys which may contain silver, copper, nickel, a
platinum group metal and comb-lnations thereof. Gold containing up to
about 8% to 10% by weight nickel will retain its gold color
equivalent to the color of 14 KT to 18 KT gold-silver-copper alloy.
The gold layer on the nickel surface of the base i9
advantageously electrodeposited from a cyanide type bath. Such baths
are usually of proprietary nature. However, the general types of
cyanide baths and conditions of operation are set forth in standard
reference sources such as Electroplating Engineering Handbook IBID,
page 242 and in References 1, 2, 29, 30, 31, 32 and 33 listed on page
255 of that work. It is also within the contemplation of the present
invention to provide gold layers of the requisite thickness by means
other than electroplating provided, of course, that the quality of
the adhesion of the gold layer to the nickel is at least equivalent
to that provided by electroplating. As those skilled in the art are
aware, the quality of adhesion of an electroplate depends to a large
extent on the care taken in surface preparation and cleaning of the
base to be plated. In this regard Chapter 3 of the aforecited
Electroplating Engineering ~andbook entitled "Metal Surface
Preparation and Cleaning" is recommended to those desiring to
practice ehe present invention.
In producing the composite structure of the present
invention, the annealing step to achieve the metallurgical bond
between gold and nickel and to harden the gold is an important
feature. Annealing can be carried out any time after deposition of
the gold layer, either before or after working or mechanical
operation on the composite material. The conditions of temperature
and time of annealing are selected so that an interdiffused layer of
gold and nickel is achieved without loss of the desired surface
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color. For example, with a gold deposit averaging 0.5 micrometers
thick, effective annealing in hydrogen at 450C may be achieved in a
short time, e.g. in the range of about 4 to 25 minutes. This
annealing time has been determined as residence time in a 5 cm tube
furnace under laboratory conditions. Those skilled in the art will
appreciate that commercial scale furnacing can vary in temperature
and time. Annealing to interdiffuse nickel and gold must be carried
out in such a fashion so as to avoid detrimental dissipation of
strength induced in the coated ob~ect by cold working. Various
copper-base alloys as set forth in the following table have ranges of
annealing temperature which are employed for softening the alloys
after cold working operations.
TABLE
Composition (% by Wt)
Alloy Cu Zn Ni Other Annealing Range (C)
Jewelry Bronze 87.5 12.5 -- -- 425-750
Red Brass 85 15 -- -- 425-750
: Cartridge Brass 70 30 -- -- 425-750
Nickel-Silver 65-18 65 1718 -- 593-815
Nickel-Silver 55-18 55 2718 ~- 593-815
Nickel-Silver 65-12 65 2312 -- 593-815
Cupro-Nickel 10% 88.7 ~- 10 1.3Fe 650-815
Cupro-Nickel 30% 70 -- 30 -- 600-815
A typical full annealing treatment for cartridge brass cold drawn 50%
involves heating for one hour at a temperature of about 425~C to
about 540C. A decorative-utility object made of cartridge brass
should be annealed for nickel-gold interdiffusion at a time at
temperature generally which is less than that which will achieve full
softening of work-hardened brass. The softening annealing range
applicable to the nickel-silvers and cupro-nickels makes these alloys
more amenable to use in the present invention because the gold-
nickel interdiffusion heat treatment has less softening effect on the
work-hardened nickel-silver.
In order to give those skilled in the art a greater
appreciation of the advan~agss of the present invention the following
examples are given:
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EXAMPLES
Copper-base alloys in the forms of ~utlery items, e.g.
forks and spoons and plates, costume jewelry and emblems are
provided. These are made of nickel-silver 65-12, jewelry bronze,
c~pro-nickel 10% and cartrldge brass. The items are thoroughly
cleaned and degreased and then electroplated in a Watts-type bath
with 10 micrometers of nickel followed after thorough rinsing, by
plating 0.5 micrometer of 24 KT gold from a proprietary complex
cyanide electroplating bath. Following plating, the rinsed and
thoroughly dry items are heat treated in an inert atmosphere as set
forth in the following ~able.
TABLE
Alloy of Item Time Temperature
Jewelry Bronze 15 min 450C
Cartridge Brass 15 min 450C
Cupro-Nickel 10~ 25 min 450C
Nickel-Silver 65-12 25 min 500C
In each instance, the final plated and heat treated items have an
attractive gold colored finish which is significantly harder and more
wear resistant than similar items plated with gold in the manner
customary in the trade. Because of their longer time heat treatment
at higher temperature, the items having a base of nickel-silver are
somewhat whiter in tinge than the other items in the preceding table
but are definitely of a golden color normally associated with yellow
14 KT gold.
While in accordance with the provisions of the statute,
there is illustrated and described herein specific embodiments of the
invention, those skilled in the art will understand that changes may
be made in the form of the invention covered by the claims and that
certain features of the invention may sometlmes be used to advantage
without a corresponding use of the other features.
