U.S. patent application number 11/575320 was filed with the patent office on 2009-01-08 for chromium plating.
Invention is credited to Waiman Chan.
Application Number | 20090008259 11/575320 |
Document ID | / |
Family ID | 32247829 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090008259 |
Kind Code |
A1 |
Chan; Waiman |
January 8, 2009 |
Chromium Plating
Abstract
A method of chromium coating a substrate is described, which
method comprises: a) depositing, preferably electrodepositing, a
metallic layer onto the substrate comprising chromium from a
plating bath that includes trivalent chromium and no, or
substantially no, hexavalent chromium; b) physical vapor depositing
a layer comprising chromium cn the layer deposited from step a). In
one embodiment, in step a), the layer is chromium and is
electrodeposited from a plating bath that includes trivalent
chromium and no, or substantially no, hexavalent chromium. The
metallic layer deposited in step a) is preferably a metal or an
alloy of two or more metals and may be selected from the group
consisting of chromium, copper, nickel, cobalt, zinc, lead iron,
palladium and tin and alloys thereof, e.g. copper tin, copper zinc,
tin lead, tin nickel, tin cobalt, tin zinc, iron nickel, cobalt
nickel, zinc nickel, zinc iron, zinc iron nickel, zinc iron cobalt
or palladium nickel. Copper and nickel are especially preferred.
The coating formed by the method has a blue sheen that is usually
associated with chromium electrodeposited from hexavalent chromium
baths without having to use a hexavalent chromium bath, which is
highly toxic.
Inventors: |
Chan; Waiman; (Hong Kong,
CN) |
Correspondence
Address: |
ANDRUS, SCEALES, STARKE & SAWALL, LLP
100 EAST WISCONSIN AVENUE, SUITE 1100
MILWAUKEE
WI
53202
US
|
Family ID: |
32247829 |
Appl. No.: |
11/575320 |
Filed: |
April 1, 2005 |
PCT Filed: |
April 1, 2005 |
PCT NO: |
PCT/CN2005/000435 |
371 Date: |
September 16, 2008 |
Current U.S.
Class: |
205/192 |
Current CPC
Class: |
C23C 28/021 20130101;
C23C 28/025 20130101; C25D 5/48 20130101; C25D 3/06 20130101; C23C
28/023 20130101 |
Class at
Publication: |
205/192 |
International
Class: |
C23C 28/02 20060101
C23C028/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2004 |
GB |
0407619.6 |
Claims
1. A method of chromium coating a substrate to provide a chromium
deposit having a blue sheen, which method comprises: a) depositing
a metallic layer on the substrate; and b) physical vapor depositing
a layer comprising chromium on the layer deposited from step
a).
2. A method as claimed in claim 1 wherein step a) comprises
electrodepositing a layer comprising chromium from a plating bath
that includes trivalent chromium and no, or substantially no,
hexavalent chromium.
3. A method as claimed in claim 1 wherein the metal deposited in
step a) is a single metal or an alloy of two or more metals.
4. A method as claimed in claim 3, wherein the metal deposited in
step a) is selected from the group consisting of chromium, copper,
nickel, cobalt, zinc, lead iron, palladium and tin and copper tin,
copper zinc, tin lead, tin nickel, tin cobalt, tin zinc, iron
nickel, cobalt nickel, zinc nickel, zinc iron, zinc iron nickel,
zinc iron cobalt or palladium nickel.
5. A method as claimed in claim 3, wherein the metal deposited in
step a) is selected from chromium, copper and nickel.
6. A method as claimed in claim 1, wherein the metal deposited in
step a) is electrodeposited.
7. A method as claimed in claim 1, wherein the metal deposited in
step a) has a thickness of 0.05 to 1 .mu.m.
8. A method as claimed in claim 7, wherein the metal deposited in
step a) has a thickness of 0.3 to 0.9 .mu.m.
9. A method as claimed in claim 8, wherein the metal deposited in
step a) has a thickness of 0.5 to 0.8 .mu.m.
10. A method as claimed in claim 1, wherein the vapor deposited
chromium layer (step b) has a thickness of 0.05 to 1.5 .mu.m.
11. A method as claimed in claim 11, wherein the vapor deposited
chromium layer (step b)) has a thickness of 0.05 to 1 .mu.m.
12. A method as claimed in claim 12, wherein the layers vapor
deposited chromium layer (step b)) has a thickness of 0.1 to 1
.mu.m.
13. A method as claimed in claim 1, wherein the layers formed in
steps a) and b) consist substantially wholly of chromium and the
layer formed in step a) is formed by electrodeposition.
14. A method as claimed in claim 1, wherein step b) deposits the
chromium layer directly on top of the layer formed in step a).
15. A product having a chromium coating made by the method of claim
1.
Description
TECHNICAL FIELD
[0001] The present invention relates to chromium plating of
substrates, including metal and plastic substrates.
BACKGROUND ART
[0002] Chromium plating is a well known technique for protecting
substrates and giving them an attractive appearance. It is known to
electroplate both metallic and plastic substrates using an
electroplating bath containing hexavalent chromium, typically
chromic acid or chromates (H.sub.2CrO.sub.4 and CrO.sub.4.sup.2-).
Electroplated deposits from hexavalent plating baths provide a
strong, abrasion-resistant layer that will protect the underlying
substrate from corrosion and provide an attractive decorative
finish. One feature that is seen to be particularly attractive is
the "blue sheen" of the chromium layer that is electrodeposited
from hexavalent chromium baths.
[0003] Hexavalent chromium, however, is believed to be toxic and
carcinogenic and its use is being phased out. Accordingly,
alternatives are being sought. One alternative that has been
proposed is a bath based on trivalent chromium, which does not give
rise to the same health problems as hexavalent chromium, see for
example U.S. Pat. No. 5,415,763, U.S. Pat. No. 5,413,646 U.S. Pat.
No. 524,326 and U.S. Pat. 5,196,109.
[0004] However, trivalent chromium electroplating baths are not
stable and are difficult to control. Thus it is not easy to obtain
a consistently smooth finish using a trivalent chromium bath;
furthermore electrodeposits from trivalent chromium baths do not
have the characteristic blue sheen of electrodeposits from
hexavalent chromium baths, which is seen to be highly
desirable.
[0005] Physical vapor deposition (often abbreviated "PVD") is a
well known technique for forming layers on substrates and involve
the evaporation of the coating material by bombarding a target with
a high energy source, such as a beam of electrons or ions. This
beam dislodges atoms from the surface of the target thereby
vaporising them. The vaporised atoms are transported from the
target to the substrate, where they form a deposit on the
substrate.
[0006] JP-63-230189 describes a cutter for a razor in which the
outer part of the cutter blade has a nickel layer formed by
electrodeposition from a nickel sulphamate bath, a layer of a
phosphorus-containing alloy, e.g. Ni--P, and a layer of chromium
less than 0.2 .mu.m thick and formed by sputtering.
[0007] U.S. Pat. No. 4,906,533 describes a method of plating steel
for use in making tin cans; the steel is electroplated with
chromium, removing chromium oxide from the deposited layer and
depositing a layer of aluminium by vacuum deposition.
[0008] CH 660278 describes a steel watch case that is electroplated
with chromium and the a layer of TiC is applied by PVD.
[0009] JP 6-192853 and JP 3-197688 describe a method of applying a
hardened surface to an object by electroplating it with chromium
and applying a ceramic layer, e.g. TiN, by PVD.
[0010] JP 59-215483 describes a method of applying a hardened
gold-coloured surface to an object by electroplating it with
chromium and sputtering Ti onto in a nitrogen atmosphere to form a
gold-coloured TiN layer.
[0011] DE-A-1514668 describes a method of making electrical
contacts for semrconductors by depositing successively by PVD a Cr
layer, a Cr and Ag layer and a layer of Ag alone; the layers can be
thickened by electrodeposition.
[0012] GB 2327091 describes a method of applying a decorative and
protective coating on an object by electroplating a layer of Cu, Ni
or Cr, e.g. from a hexavalent chromium bath, pulse blow drying the
electrodeposited layer and depositing a refractory metal (Zr, Ti,
Hf or Zr/Ti) by PVD. The method can produce a brass colour.
DISCLOSURE OF INVENTION
[0013] It has now been found that coatings having a blue sheen can
be obtained without using hexavalent chromium baths.
[0014] According to the present invention, there is provided a
method of coating a substrate to provide a decorative and
protective chromium deposit having a blue sheen without having to
use hexavalent chromium electrodeposition, which method comprises:
[0015] a) depositing a metallic layer onto the substrate, and;
[0016] b) physical vapor depositing a layer comprising chromium on
the layer deposited from step a).
[0017] Preferably in step a), the layer is chromium and is
electrodeposited from a plating bath that includes trivalent
chromium and no, or substantially no, hexavalent chromium.
[0018] The metallic layer deposited in step a) is preferably a
metal or an alloy of two or more metals and may be selected from
the group consisting of chromium, copper, nickel, cobalt, zinc,
lead iron, palladium and tin and alloys thereof, e.g. copper tin,
copper zinc, tin lead, tin nickel, tin cobalt, tin zinc, iron
nickel, cobalt nickel, zinc nickel, zinc iron, zinc iron nickel,
zinc iron cobalt or palladium nickel. Copper and nickel are
especially preferred. Preferably the layer deposited in step a)
contains at most only traces of non-metals that are common in the
electroplating art, e.g. nickel deposits often contain sulphur.
[0019] The invention is primarily directed at decorative and
protective coatings rather than coatings to provide hardness and
wear resistance that are used in cutting and tooling applications
and so the layers deposited on the substrate, including in step a),
preferably do not include a hard ceramic, e.g. a nitride or
phosphide, or a phosphorus containing alloy.
[0020] It has also been found that the method of the present
invention provides a chromium coating that is highly effective in
preventing corrosion of the substrate.
[0021] Preferably, the electrodeposited chromium layer (step a) has
a thickness of 0.1 to 1 .mu.m, e.g. 0.3 to 0.9 .mu.m, such as 0.5
to 0.8 .mu.m. Preferably the step a) layer is greater than 0.2
.mu.m thick. The preferred thickness of the PVD layer is 0.01 to 2
.mu.m, e.g. 0.05 to 1.5 .mu.m, such as 0.1 to 1 .infin.m.
[0022] Before the article is coated in step a), e.g. electroplated
with chromium, it may be provided with one or more protective or
barrier layers, e.g. a base layer of nickel, preferably formed by
electrodeposition. If the substrate is plastic, its surface should
be rendered conductive, which can be achieved using well-known
techniques for electroplating plastic and other non-conductive
substrates.
[0023] It is not necessary that the chromium PVD deposit is formed
directly on the metal, e.g. chromium, deposited in step a) and an
intermediate layer, e.g. of white metal such as nickel, may be laid
down between the step a) layer and the PVD layer.
[0024] Both electrodeposition from trivalent chromium baths and PVD
are well-known techniques and so their operation will be entirely
apparent to the skilled person.
[0025] The substrate may be plastic. Electroplating of plastic
substrates is well-known and involves subjecting the insulating
plastic to a series of known pre-treatment steps that render the
surface electrically conductive. These steps involve the
non-electric deposition of a conductive material, e.g. nickel, and
the deposition of a layer of nichrome (nickel-chromium alloy). The
metallic layer may be thickened through electroplating of
cupronickel, using the following process steps: [0026]
pre-treatment.fwdarw.acid cleaning
water.fwdarw.cleaning.fwdarw.pyrophosphoric copper.fwdarw.water
cleaning.fwdarw.acid cleaning.fwdarw.bright copper.fwdarw.water
cleaning.fwdarw.activation.fwdarw.water cleaning.fwdarw.semi-bright
nickel.fwdarw.bright nickel.fwdarw.seal nickel.fwdarw.water
cleaning.fwdarw.drying
[0027] The plastic has thereby become conductive and is suitable
for general electroplating.
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] Although electrodeposition from a trivalent chromium bath
and PVD are well-known individually, we have found that the
following are the optimum conditions for achieving the required
blue sheen to a chromium deposit using the present invention.
However, these conditions are not intended to limit the claims.
[0029] A substrate may be pre-treated with one or more base layers,
e.g. at least one nickel layer; in the case of a substrate made of
plastic, an electrically conductive surface layer must be applied
to the insulating plastic surface as described above. The substrate
may be, for example, a plastic moulding, a zinc die cast, a cast or
machined brass part or a machined steel part. The substrate is then
subjected to trivalent chromium plating followed by PVD of chromium
under the conditions described below:
TABLE-US-00001 Trivalent Chromium Plating Bath composition:
trivalent chromium Temperature: 20.degree. C.-50.degree. C. Bath
Acidity (pH): 2.8-3.8 Current Density: 5-20 A/dm.sup.2
Electroplating Time: 2-6 mins Thickness of the electrodeposit:
0.1-1 .mu.m
[0030] The resulting chromium electrodeposit 99.99% Metallic
Chromium meets the following tests as a result of the trivalent
chromium plating process:--
TABLE-US-00002 (1) Temperature test: 72.degree. C..fwdarw.
25.degree. C..fwdarw. -30.degree. C. (3 cycles) (2) CASS test: 8-16
HR
[0031] Physical Vapor Deposition (PVD)
TABLE-US-00003 Technique: Electric Arc Style Physical Vapor
Deposition Material being deposited: Metallic Chromium Deposit
Content: 99% Metallic Chromium Deposition Temperature:
<70.degree. C. (plastic substrate) 70-120.degree. C. (Zinc die
cast substrate) 120-180.degree. C. (Brass, Steel or other materials
substrate) Deposit thickness: 0.01-2 .mu.m, preferably
0.1-0.5/.mu.m Pressure: 2 .times. 10.sup.-5- 2 .times. 10.sup.-7
Torr Colour: Silver-white Process Steps: Venting (2 .times. 10
Torr) 20-30 mins glow discharge 5-10 mins high bias 1-3 mins metal
layer (99.99% Chromium) 1-100 mins
[0032] The resulting deposit had a blue sheen. The "L*" (black to
white), "a*" (green to red), "b*" (blue to yellow) values of the
colour measurement for the blue sheen effect of chromium are:
TABLE-US-00004 i. Measurement Instrument: Spectrophotometer ii.
Setting of the Instrument: D65/10, SCI iii. L* 82.4 to 88.4 iv. a*
-1.5 to 0 v. b* -2 to 0
* * * * *