U.S. patent application number 15/134469 was filed with the patent office on 2017-10-26 for dark colored chromium based electrodeposits.
The applicant listed for this patent is MacDermid Acumen, Inc. Invention is credited to Masahiro Hara, Tatsuya Nishiyama.
Application Number | 20170306515 15/134469 |
Document ID | / |
Family ID | 60089417 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170306515 |
Kind Code |
A1 |
Hara; Masahiro ; et
al. |
October 26, 2017 |
Dark Colored Chromium Based Electrodeposits
Abstract
An aqueous trivalent chromium electrolyte comprising trivalent
chromium ions and amino acids that allow for producing a dark
colored hue in the trivalent chromium coating which is plated on a
substrate. The amino acids described herein comprise a cationic
side chain and are at least essentially free of sulfur. The
cationic side chain of the amino acid further comprises nitrogen.
When used in the trivalent chromium electrolyte, these amino acids
allow for producing significantly darker trivalent chromium
deposits. The trivalent chromium electrolyte is used in a method
for producing the desired dark colored hue in the trivalent
chromium coating that is produced on a substrate using
electrodeposition.
Inventors: |
Hara; Masahiro; (Kanagawa,
JP) ; Nishiyama; Tatsuya; (Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MacDermid Acumen, Inc |
Waterbury |
CT |
US |
|
|
Family ID: |
60089417 |
Appl. No.: |
15/134469 |
Filed: |
April 21, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/10 20130101; C25D
3/06 20130101 |
International
Class: |
C25D 3/10 20060101
C25D003/10; C25D 7/00 20060101 C25D007/00; C25D 3/06 20060101
C25D003/06 |
Claims
1. A trivalent chromium electrolyte comprising: i) trivalent
chromium ions, ii) one or more complexants capable of maintaining
the trivalent chromium ions in solution; and iii) one or more amino
acids; wherein the amino acids comprise a cationic side chain
comprising nitrogen and wherein the cationic side chain is at least
essentially free of sulfur; and wherein the electrolyte is
substantially free of hexavalent chromium salts; wherein the
electrolyte further comprises thiocyanate ions; wherein
concentration of the amino acids in the electrolyte is such that a
dark colored chromium deposit produced on a substrate, when the
electrolyte is used to plate chromium on said substrate, has an L*
value of 78.47 or lower as measured according to an L*a*b*
colorspace system.
2. A trivalent chromium electrolyte according to claim 1, wherein
the one or more amino acids are selected from the group consisting
of arginine, histidine, lysine, tryptophan, and combinations
thereof.
3. (canceled)
4. (canceled)
5. A trivalent chromium electrolyte according to claim 1, wherein
the total concentration of amino acids is between about 5 g/L and
about 10 WI.
6. (canceled)
7. The trivalent chromium electrolyte according to claim 1, wherein
the thiocyanate ions are present in a concentration between about
0.2 g/L and about 5 g/L.
8. The trivalent chromium electrolyte according to claim 2, wherein
the amino acid comprises histidine.
9. The trivalent chromium electrolyte according to claim 2, wherein
the amino acid comprises arginine.
10. The trivalent chromium electrolyte according to claim 2,
wherein the amino acid comprises a mixture of histidine and
arginine.
11. A method of producing a dark colored chromium deposit on a
substrate comprising the steps of: i) providing a trivalent
chromium based electrolyte comprising: a) trivalent chromium ions,
b) one or more complexants capable of maintaining the trivalent
chromium ions in solution, and c) one or more amino acids, wherein
the amino acids comprise a cationic side chain comprising nitrogen
and wherein the cationic side chain is at least essentially free of
sulfur; and wherein the electrolyte is substantially free of
hexavalent chromium salts; and adding such a concentration of the
amino acids to the electrolyte such that the dark colored chromium
deposit produced on the substrate, after electrodepositing, has an
L* value of 78.47 or lower as measured according to an L*a*b*
colorspace system; and ii) electrodepositing the dark colored
chromium deposit on the substrate using the trivalent chromium
based electrolyte.
12. The method according to claim 11, wherein the one or more amino
acids are selected from the group consisting of arginine,
histidine, lysine, tryptophan, and combinations thereof.
13. (canceled)
14. (canceled)
15. The method according to claim 11, wherein the total
concentration of amino acids is between about 5 g/L and about 10
el.
16. The method according to claim 11, wherein the trivalent
chromium based electrolyte further comprises thiocyanate ions.
17. The method according to claim 16, wherein the thiocyanate ions
are present in a concentration between about 0.2 g/L and about 5
g/L.
18. The method according to claim 12, wherein the one or more amino
acids comprises histidine.
19. The method according to claim 12, wherein the one or more amino
acid comprises arginine.
20. The method according to claim 12, wherein the one or more amino
acids comprises a mixture of histidine and arginine.
21. (canceled)
22. The method according to claim 11, wherein the substrate
comprises a nickel deposit on the substrate and the trivalent
chromium is plated on the nickel deposit.
23. The method according to claim 11, wherein the pH of the
trivalent chromium electrolyte is between about 2.0 and about
5.0.
24. The method according to claim 23, wherein the pH of the
trivalent chromium electrolyte is about 3.5.
25. A method of producing a dark colored chromium deposit on a
substrate comprising the steps of: i) providing a trivalent
chromium based electrolyte comprising: a) trivalent chromium ions,
b) one or more complexants capable of maintaining the trivalent
chromium ions in solution, and c) one or more amino acids, wherein
the amino acids comprise a cationic side chain comprising nitrogen
and wherein the cationic side chain is at least essentially free of
sulfur; and wherein the electrolyte is substantially free of
hexavalent chromium salts; and ii) electrodepositing the dark
colored chromium deposit on the substrate using the trivalent
chromium based electrolyte; wherein the dark colored chromium
deposit produced on the substrate has an L* value, measured
according to an L*a*b* colorspace system, at least 5.3% lower than
the trivalent chromium deposit produced by the same trivalent
chromium electrolyte that does not comprise the one or more amino
acids.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to a composition and
method for producing dark coloured chromium coatings by
electrodeposition.
BACKGROUND OF THE INVENTION
[0002] Chromium has been used for many years as a decorative
coating and has many applications. For decorative purposes, the
chromium is generally applied as a thin coating, which is typically
less than 1 micrometre in thickness, over a coating of nickel. The
chromium provides a hard, wear resistant layer and excellent
corrosion performance is also obtained due to the chromium layer
being cathodic with respect to the underlying nickel deposit. Thus
the underlying nickel becomes the anode in the corrosion cell and
corrodes preferentially leaving the chromium layer uncorroded.
[0003] Typically, these thin decorative chromium layers have been
applied by electrodeposition from electrolytes based on hexavalent
chromium, which typically comprise chromic acid. The chromium
deposits obtained from these electrolytes are essentially pure
chromium and have a uniform and invariant colour. A thin oxide
layer forms on the top of the coatings giving a blue/white
appearance which is very well known. In addition to the incentive
to use alternative electrolytes due to serious health and
environmental hazards associated with chromic acid, there is also a
market demand for coatings having a darker hue.
[0004] An initial solution to providing a darker hued deposit from
chromium electrolytes can be obtained by electrodepositing the
chromium coatings from electrolytes based on trivalent chromium.
Due to the nature of the deposition mechanism from these
electrolytes, the chromium coating produced is less pure than that
produced from hexavalent electrolytes. This is due to co-deposition
of other elements within the coating. Most commonly, these
co-deposited elements are iron, sulphur and carbon or combinations
thereof. By adjusting the electrolyte formulation of trivalent
chromium based processes to maximize the darkness of the deposit
produced by the incorporation of these co-deposited elements,
coatings of a fairly dark hue can be obtained.
[0005] While coatings provided by trivalent chromium electrolytes
typically produce darker hued deposits than that of hexavalent
chromium electrolytes, the resulting coatings from the prior art
are still not dark enough to fulfill the needs of the market and a
demand exists to produce darker chromium based coatings. It is the
object of this invention to provide a means of producing these
coatings.
SUMMARY OF THE INVENTION
[0006] It is an object of the invention to provide a trivalent
chromium plating electrolyte that is capable of providing dark
colored chromium deposits on a substrate.
[0007] It is an object of the invention to provide amino acids in
the trivalent chromium electrolyte that are capable of creating a
dark hue in the resulting trivalent chromium deposit.
[0008] It is another object of the invention to provide amino acids
in the trivalent chromium electrolyte that have nitrogen containing
side chains.
[0009] It is another object of the invention to provide amino acids
that do not contain sulfur in the trivalent chromium electrolyte to
provide darker hues of chromium deposits on substrates.
[0010] It is yet another object of the invention to provide a
darker hued deposit on a substrate using a trivalent chromium
electrolyte with select amino acids than the prior art trivalent
chromium plating electrolytes can achieve.
[0011] It is still another object of the invention to provide a
method of plating a trivalent chromium deposit with a dark hue over
a nickel deposit.
[0012] In one embodiment, a composition is provided for a trivalent
chromium electrolyte comprising: [0013] i) trivalent chromium ions,
[0014] ii) one or more complexants capable of maintaining the
trivalent chromium ions in solution; and [0015] iii) one or more
amino acids; wherein the amino acids comprise a cationic side chain
comprising nitrogen and wherein the cationic side chain is at least
essentially free of sulfur; and [0016] wherein the electrolyte is
substantially free of hexavalent chromium salts.
[0017] In another embodiment, a method is provided for producing a
dark colored chromium deposit on a substrate, comprising the steps
of: [0018] i) providing a trivalent chromium based electrolyte
comprising: [0019] a) trivalent chromium ions, [0020] b) one or
more complexants capable of maintaining the trivalent chromium ions
in solution, and [0021] c) one or more amino acids, wherein the
amino acids comprise a cationic side chain comprising nitrogen and
wherein the cationic side chain is at least essentially free of
sulfur; and [0022] wherein the electrolyte is substantially free of
hexavalent chromium salts; and [0023] ii) electrodepositing a dark
colored chromium deposit on the substrate using the trivalent
chromium based electrolyte.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 depicts various classes of amino acids.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The inventors have surprisingly found that the incorporation
of select amino acids which comprise nitrogen containing side
chains into the trivalent chromium electrolyte results in coatings
which are substantially darker than those obtained from the same
electrolyte in the absence of these compounds. The amino acids
useful in the current invention are additionally at least
essentially free of sulfur. By essentially free of sulfur, it is
meant that sulfur is not present in any concentration, aside from
trace amounts that may occur as contaminants in such compounds. The
darkest coatings are obtained when select amino acids are added to
electrolytes which have already been optimised to produce dark
coatings by the incorporation of other elements such as sulfur,
iron, carbon or combinations thereof.
[0026] The use of amino acids as complexants in trivalent chromium
plating baths has been described in U.S. Pat. No. 4,107,004 to Ward
et al. and U.S. Pat. No. 4,157,945 to Barnes et al., which describe
the use of glycine as a complexant. U.S. Pat. No. 4,161,432 to
Barclay et al. describes the use of glycine, aspartic acid,
arginine and histidine as complexants. U.S. Pat. No. 4,448,648 and
U.S. Pat. No. 4,448,649 both to Barclay et al., describe the use of
aspartic acid as a complexant. The subject matter of each of these
patents of which is herein incorporated by reference in its
entirety. These patents are all focused on producing coatings which
are light in color and do not provide for changing the color of the
deposit produced or variation of deposit color associated with
different amino acids.
[0027] Amino acids fall into several groups as shown in FIG. 1. The
amino acids methionine and cysteine (and cystine) contain bivalent
sulphur in their side chains. The use of these sulphur-containing
compounds as darkening agents in trivalent chromium baths has been
previously disclosed, as for example in WO 2012/150198A1 to Schulz
et al., which is hereby incorporated herein by reference in its
entirety. This is understood to be a function of the presence of
sulfur in the compound, as sulfur is known to cause darker hues in
trivalent chromium deposits as compared to the more pure deposits
produced from hexavalent chromium electrolytes.
[0028] The inventors of the present invention have surprisingly
found that sulfur-free amino acids, including those selected from
the group having nitrogen containing cationic side chains, have the
desired effect of darkening the deposit in a uniform manner. The
side chains are cationic under the normal pH conditions of most
commercially available trivalent chromium electroplating baths (pH
2.5-4.0) due to the presence of a nitrogen-containing (amine)
functional group in the side chain.
[0029] The amino acids that are useful in the current invention
include, for example, arginine, histidine, lysine and combinations
thereof. It was found that these amino acids will produce
significant darkening of the trivalent chromium deposits.
Additionally tryptophan, although not listed under the amino acids
containing a positively charged group in FIG. 1, has a
nitrogen-containing side chain and is also found to have enhanced
darkening effects. From this result, while not wishing to be bound
by theory, it is also believed that the side chain of tryptophan is
cationic under the normal pH conditions in the trivalent chromium
electroplating bath.
[0030] The effective concentration range of the preferred amino
acids in the trivalent chromium electrolyte is preferably between
about 1 g/L and about 50 and more preferably between about 2 g/L
and about 20 g/l. The concentration of amino acids in the trivalent
chromium electrolyte is most preferably between about 5 g/L and
about 10 g/L.
[0031] When electroplating from electrolyte solutions described
herein, inert anodes, such as carbon anodes, are typically used.
Other inert anodes such as platinized titanium, platinum, iridium
oxide coated titanium, or tantalum oxide coated titanium may also
be used.
[0032] The temperature of the trivalent chromium based electrolyte
is in the range of 40.degree. C. to 60.degree. C., most preferably
around 50.degree. C. The pH of the electrolyte is in the range from
about 2 to about 5, most preferably about 3.5. The current used
during plating is in the range of about 1 amp to about 10 amps,
most preferably about 4 amps. Agitation is not required during the
plating of substrates in the trivalent chromium electrolyte.
[0033] As used herein, the term "about" refers to a measurable
value such as a parameter, or a concentration or the like and is
meant to include variations of +/-15% or less, preferably
variations of +/-10% or less, more preferably variations of +/-5%
or less, and most preferably variations of +/-0.1% or less from the
particularly recited value in so far as such variations are
appropriate to carry out the invention as described herein.
Furthermore, it is also to be understood that the value to which
the modifier "about" refers is itself specifically disclosed
herein.
[0034] In a preferred embodiment, the substrate comprises nickel
deposited on the underlying substrate and the chromium is
electroplated on the nickel deposit.
[0035] In order to demonstrate the scope of the invention, a Konica
Minolta CM2600d spectrophotometer was used to determine the
"lightness" values of the various deposits by measuring the L*
value according to the L*a*b* colorspace system. The colorspace
system gives a quantitative value (L*), which can be used to
compare the degree of darkening obtained by the various
combinations of amino acid additives. The higher the L* value, the
lighter the deposit and the lower the L* value the darker the
deposit. An L* value of 0 is black and an L* of 100 is white. Lower
L* values are the desire of the current invention.
[0036] Dark hued coatings produced by the electrodeposition of
trivalent chromium using the electrolytes described herein
preferably have an L* value, measured according to an L*a*b*
colorspace system, of less than that of typical trivalent chromium
deposits that produce light colored coatings and those that have
already been maximized for darkness in the resulting deposits.
[0037] The trivalent chromium based electrolytes may contain
thiocyanate ions. The thiocyanate ions may be present in a
concentration anywhere from about 0.2 g/L up to about 5.0 g/L.
[0038] The trivalent chromium based electrolytes presented herein
are at least substantially free of hexavalent chromium salts,
wherein no Cr(VI) ions can be detected in the electrolyte by
ordinary measurement techniques.
[0039] The trivalent chromium electrolyte comprises a source of
trivalent chromium ions, one or more complexants (complexing
agents) capable of maintaining the trivalent chromium ions in
solution, and the select amino acids as described herein. The amino
acids have provided darker hues in the plated deposit compared to
the use of the same electrolyte without such amino acids.
[0040] The trivalent chromium electrolyte used as a standard is an
electrolyte designed to produce light colored chromium deposits.
The electrolyte and plating process is based on U.S. Pat. No.
4,473,448 to Deeman. This patent is hereby incorporated by
reference in its entirety.
[0041] Additionally, inventive examples are also provided based on
a trivalent chromium electrolyte solution that has already been
formulated to produce dark deposits, based on U.S. Pat. No.
4,161,432 to Barclay et al. The amino acid used in the electrolyte
composition is aspartic acid. This reference is hereby incorporated
by reference in its entirety.
[0042] The following non-limiting examples illustrate the
effectiveness of the invention. All of the examples were prepared
by electroplating a trivalent chromium deposit onto Hull cell
panels. The Hull Cell panels had previously been electroplated with
10 microns of a bright nickel deposit and are then placed in a Hull
Cell with the trivalent chromium electrolyte being tested. For the
trivalent chromium plating step, the conditions are as shown in
Table 1. Conditions for the trivalent chromium plating remained
consistent regardless of the composition being tested.
[0043] The lightness or L* value of the trivalent chromium deposit
was measured at a point on the Hull Cell panel corresponding to a
current density of 8 amps per square decimeter in all cases, which
is representative of a normal working range for chromium
plating.
TABLE-US-00001 TABLE 1 Trivalent Chromium Plating Hull Cell
Conditions Parameter Value Temperature 50.degree. C. pH 3.5 Plating
time 5 minutes Plating current 4 Amps Agitation none Anode titanium
coated with a conductive mixed metal oxide film
Comparative Example 1
[0044] Table 2 provides the L* values measured using the
electrolyte based on U.S. Pat. No. 4,473,448 to Deeman as a
Standard (1), with various amino acids added that were not
effective darkening agents.
TABLE-US-00002 TABLE 2 Electrolyte Composition L* Value Standard
(1) with no additional amino acids 82.84 Standard (1) plus 5 g/l
Glycine 81.15 Standard (1) plus 5 g/l Alanine 81.9 Standard (1)
plus 5 g/l Valine 82.83 Standard (1) plus 5 g/l Isoleucine 82.47
Standard (1) plus 5 g/l Proline 82.23 Standard (1) plus 5 g/l
Phenylalanine 82.25 Standard (1) plus 5 g/l Serine 80.7 Standard
(1) plus 5 g/l Threonine 82.78 Standard (1) plus 5 g/l Tyrosine
83.72 Standard (1) plus 5 g/l Glutamine 80.51 Standard (1) plus 5
g/l Aspartic acid 80.05
[0045] As can be seen from the results set forth in Table 2, none
of the amino acids tested produced any significant reduction in the
L* values when compared to the trivalent chromium electrolyte
without amino acids added. The average reduction in L* value was
1.17%.
Example 1
[0046] Table 3 provides the L* values obtained when the amino acids
described herein are added to the electrolyte based on U.S. Pat.
No. 4,473,448 to Deeman. The same Standard (1) electrolyte is used
as in the comparative example above. As previously noted, this
electrolyte typically produces light colored trivalent chromium
deposits.
TABLE-US-00003 TABLE 3 Electrolyte Composition L* Value Standard
(1) with no additional amino acids 82.84 Standard (1) with 5 g/l
Arginine 75.26 Standard (1) with 5 g/l Histidine 69.33 Standard (1)
with 5 g/l Lysine 78.47 Standard (1) with 5 g/l Tryptophan 46.31
(but deposit cosmetically unacceptable)
[0047] In this case, the average reduction in L* value was 12.7%
using the examples of the invention of arginine and histidine. This
is a significant difference which can easily be seen by eye. The
addition of arginine, histidine or lysine gave uniform color across
the entire deposit. The addition of tryptophan gave a dramatic
effect but produced very uneven and streaky deposits, which
although significantly darker, were commercially unacceptable.
Example 2
[0048] Table 4 gives the L* values obtained when amino acids of the
invention are added to the electrolyte based on U.S. Pat. No.
4,161,432 to Barclay et al. This electrolyte was used as the
Standard (2) to compare the L* values after the amino acids are
added. As previously noted, deposits produced using this
electrolyte process were previously formulated to provide dark
colored trivalent chromium deposits.
TABLE-US-00004 TABLE 4 Electrolyte Composition L* Value Standard
(2) with no additional amino acids 69.33 Standard (2) with 5 g/l
Arginine 60.32 Standard (2) with 5 g/l Histidine 58.71 Standard (2)
with 2.5 g/l Histidine and 2.5 g/l Arginine 59.41 Standard (2) with
5 g/l Histidine and 5 g/l Arginine 57.21
[0049] In this case, the average reduction in the L* value was
15.02%. This is a very noticeable difference in color. While the
electrolyte based on U.S. Pat. No. 4,161,432 to Barclay et al.
naturally produces a dark deposit, it was possible to increase the
deposit darkness by the addition of the amino acids as described
herein.
[0050] As it has been shown by way of the examples presented
herein, the inventors have surprisingly found that darker hued
deposits can be obtained from trivalent chromium electrolytes that
contain the amino acids as described within. The result was
unexpected as the effective amino acids did not contain sulfur, but
the presence of cationic nitrogen containing side chains allowed
for darker hues in the deposits obtained using the trivalent
chromium electrolyte of the current invention.
[0051] It should also be understood that the following claims are
intended to cover all of the generic and specific features of the
invention as described herein and all statements of the scope of
the invention that as a matter of language might fall there
between.
* * * * *