U.S. patent application number 10/785297 was filed with the patent office on 2005-08-25 for non-cyanide silver plating bath composition.
Invention is credited to Morrissey, Ronald J..
Application Number | 20050183961 10/785297 |
Document ID | / |
Family ID | 34861596 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183961 |
Kind Code |
A1 |
Morrissey, Ronald J. |
August 25, 2005 |
Non-cyanide silver plating bath composition
Abstract
Disclosed is an electroplating solution for the deposition of
silver; said solution containing silver in the form of a complex of
silver with hydantoin or a substituted hydantoin compound; said
solution also containing an excess of the hydantoin or substituted
hydantoin compound employed, together with an effective quantity of
a nonprecipitating electrolyte salt, and also an effective quantity
of 2,2' dipyridyl for the purpose of obtaining a mirror-bright to
brilliant deposit.
Inventors: |
Morrissey, Ronald J.;
(Cranston, RI) |
Correspondence
Address: |
BANNER & WITCOFF, LTD.
28 STATE STREET
28th FLOOR
BOSTON
MA
02109-9601
US
|
Family ID: |
34861596 |
Appl. No.: |
10/785297 |
Filed: |
February 24, 2004 |
Current U.S.
Class: |
205/263 |
Current CPC
Class: |
C25D 3/46 20130101 |
Class at
Publication: |
205/263 |
International
Class: |
C25D 003/46 |
Claims
What is claimed is:
1. An electroplating solution for the deposition of silver; said
solution comprising silver in the form of a complex of silver with
hydantoin or a substituted hydantoin compound; said solution also
comprising an excess of the hydantoin or substituted hydantoin
compound, together with an effective quantity of a nonprecipitating
electrolyte salt, and also an effective quantity of 2,2' dipyridyl
for the purpose of obtaining a mirror-bright to brilliant
deposit.
2. The electroplating solution of claim 1, further comprising an
effective quantity of a pyridine or substituted pyridine compound
for the purpose of improving the overall brightness of the deposit
obtained.
3. The electroplating solution of claim 1 or 2, further comprising
an effective quantity of surface-active material for the purpose of
further improving the overall brightness and brilliance of the
deposit obtained.
4. The electroplating solution of claim 3, wherein the
surface-active material is selected from the group consisting of
Hamposyl C, Hamposyl L, Hamposyl O, Blancol, Blancol N, Rhodacal,
and Rhodacal N.
5. The electroplating solution of claims 1 or 2, wherein the
pyridine or substituted pyridine compound is selected from the
group consisting of nicotinamide, isonicotinamide, 2-aminopyridine,
3-aminopyridine, nicotinic acid and its salts, and isonicotinic
acid and its salts.
6. The electroplating solution of claim 4, wherein the
surface-active material is selected from the group consisting of
Hamposyl C, Hamposyl L, Hamposyl O, Blancol, Blancol N, Rhodacal,
and Rhodacal N.
7. The electroplating solution of claim 1 or 2, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
8. The electroplating solution of claim 3, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
9. The electroplating solution of claim 4, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
10. The electroplating solution of claim 5, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
11. The electroplating solution of claim 6, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
12. A process for the formation of a mirror-bright to brilliant
electrodeposit of silver on a substrate comprising the step of:
electroplating said substrate in an electroplating solution, said
solution comprising silver in the form of a complex of silver with
hydantoin or a substituted hydantoin compound; said solution also
comprising an excess of the hydantoin or substituted hydantoin
compound, together with an effective quantity of a nonprecipitating
electrolyte salt, and an effective quantity of 2,2' dipyridyl for
the formation of a mirror-bright to brilliant deposit.
13. The process of claim 12, wherein the electroplating solution
further comprises an effective quantity of a pyridine or
substituted pyridine compound for the purpose of improving the
overall brightness of the deposit obtained.
14. The process of claim 12 or 13, wherein the electroplating
solution further comprises an effective quantity of surface-active
material for the purpose of further improving the overall
brightness and brilliance of the deposit obtained.
15. The process of claim 14, wherein the surface-active material is
selected from the group consisting of Hamposyl C, Hamposyl L,
Hamposyl O, Blancol, Blancol N, Rhodacal, and Rhodacal N.
16. The process of claim 13, wherein the pyridine or substituted
pyridine compound is selected from the group consisting of
nicotinamide, isonicotinamide, 2-aminopyridine, 3-aminopyridine,
nicotinic acid and its salts, and isonicotinic acid and its
salts.
17. The process of claim 16, wherein the surface-active material is
selected from the group consisting of Hamposyl C, Hamposyl L,
Hamposyl O, Blancol, Blancol N, Rhodacal, and Rhodacal N.
18. The process of claim 12 or 13, wherein the nonprecipitating
electrolyte salt is selected from the group consisting of the salts
of sulfamic, hydrofluoric, nitric, fluoboric, glycolic, and lactic
acids.
19. The process of claim 14, wherein the nonprecipitating
electrolyte salt is selected from the group consisting of the salts
of sulfamic, hydrofluoric, nitric, fluoboric, glycolic, and lactic
acids.
20. The electroplating solution of claim 15, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
21. The electroplating solution of claim 16, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
22. The electroplating solution of claim 17, wherein the
nonprecipitating electrolyte salt is selected from the group
consisting of the salts of sulfamic, hydrofluoric, nitric,
fluoboric, glycolic, and lactic acids.
Description
BACKGROUND OF THE INVENTION
[0001] Numerous non-cyanide silver plating processes have been
attempted (1). Of these, the only ones to have achieved commercial
success have been those employing succinimide, either as a
premanufactured silver complex (2, 3), or as a reagent. Succinimide
undergoes hydrolysis at pH values above neutrality, which in turn
causes the pH of the plating solution, normally in the range of 8
to 9 or so, to become unstable; and also to require frequent
replenishment of the succinimide.
[0002] Hydantoin (CAS Number 461-72-3) is a cyclic diimide
possessing structural features similar to succinimide, and
similarly effective as a complexing agent for silver. A series of
substituted hydantoins exist, of which the most commonly available
commercially is 5,5-dimethylhydantoin (CAS No. 77-71-4). As a
class, the hydantoins are soluble in moderate-to-strongly alkaline
(pH .gtoreq.8) solutions, are capable of forming complexes with
silver and other metals, and are more resistant to hydrolysis than
succinimide. Asakawa (4) patented non-cyanide plating solutions for
silver in which silver salts are added together with a hydantoin
compound and an inorganic or organic acid salt for the purpose of
providing electrical conductivity.
[0003] Asakawa teaches the use of various sulfur-containing
compounds as gloss-controlling agents for the deposits from the
plating solutions of his invention, and states that with the use of
such additives deposit appearance suitable for decorative
applications can be obtained. There is no mention of mirror-bright
appearance, however, and the Examples provided do not appear to
indicate that mirror-bright deposits would be obtained. In
particular, all of the Examples cited include significant
quantities of chloride ion, which is a known precipitant for silver
and highly likely to form insulating films at the anodes.
[0004] Since much commercial silver plating is for the purpose of
obtaining mirror-bright to brilliant deposits, it would clearly be
desirable to electroplate such deposits from a non-cyanide plating
solution, thus saving the costs of cyanide waste treatment, and
also of subsequent polishing and buffing.
SUMMARY OF THE INVENTION
[0005] Accordingly, it is an object of this invention to provide a
non-cyanide plating solution for the deposition of silver, said
solution being capable of yielding mirror-bright to brilliant
deposits. It is a further object that the plating solution thus
provided be as chemically stable as possible, and free of chemical
precipitants.
[0006] One preferred embodiment of the present invention is an
electroplating solution for the deposition of silver; said solution
comprising silver in the form of a complex of silver with hydantoin
or a substituted hydantoin compound; said solution also comprising
an excess (i.e., more than a stoichiometric amount based on the
silver) of the hydantoin or substituted hydantoin compound,
together with an effective quantity of a nonprecipitating
electrolyte salt, and also an effective quantity of 2,2' dipyridyl
for the purpose of obtaining a mirror-bright to brilliant deposit.
An excess amount of the hydantoin or substituted hydantoin compound
ensures the complete (or nearly complete) complexation of the
silver.
[0007] Preferably, the electroplating solution further comprises an
effective quantity of a pyridine or substituted pyridine compound
for the purpose of improving the overall brightness of the deposit
obtained. Advantageously, the electroplating solution further
comprises an effective quantity of surface-active material for the
purpose of further improving the overall brightness and brilliance
of the deposit obtained.
[0008] In certain preferred embodiments the surface-active material
is selected from the group consisting of Hamposyl C, Hamposyl L,
Hamposyl O, Blancol, Blancol N, Rhodacal, and Rhodacal N. In
certain preferred embodiments, the pyridine or substituted pyridine
compound is selected from the group consisting of nicotinamide,
isonicotinamide, 2-aminopyridine, 3-aminopyridine, nicotinic acid
and its salts, and isonicotinic acid and its salts. In certain
preferred embodiments, the nonprecipitating electrolyte salt is
selected from the group consisting of the salts of sulfamic,
hydrofluoric, nitric, fluoboric, glycolic, and lactic acids.
[0009] Another preferred embodiment of the present invention is a
process for the formation of a mirror-bright to brilliant
electrodeposit of silver on a substrate comprising the step of:
[0010] electroplating said substrate in an electroplating
solution,
[0011] said solution comprising silver in the form of a complex of
silver with hydantoin or a substituted hydantoin compound;
[0012] said solution also comprising an excess of the hydantoin or
substituted hydantoin compound, together with an effective quantity
of a nonprecipitating electrolyte salt, and an effective quantity
of 2,2' dipyridyl for the formation of a mirror-bright to brilliant
deposit.
[0013] Preferably, the electroplating solution used in the process
of the invention further comprises an effective quantity of a
pyridine or substituted pyridine compound for the purpose of
improving the overall brightness of the deposit obtained.
Advantageously, the electroplating solution used in the process of
the invention further comprises an effective quantity of
surface-active material for the purpose of further improving the
overall brightness and brilliance of the deposit obtained. In
certain preferred embodiments the surface-active material is
selected from the group consisting of Hamposyl C, Hamposyl L,
Hamposyl O, Blancol, Blancol N, Rhodacal, and Rhodacal N. In
certain preferred embodiments, the pyridine or substituted pyridine
compound is selected from the group consisting of nicotinamide,
isonicotinamide, 2-aminopyridine, 3-aminopyridine, nicotinic acid
and its salts, and isonicotinic acid and its salts. In certain
preferred embodiments, the nonprecipitating electrolyte salt is
selected from the group consisting of the salts of sulfamic,
hydrofluoric, nitric, fluoboric, glycolic, and lactic acids.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] It has been found that in moderately alkaline (pH .gtoreq.9)
plating solutions containing silver in the form of a complex formed
with hydantoin or a substituted hydantoin, together with a
nonprecipitating electrolyte salt, addition of 2,2'-dipyridyl (CAS
No. 366-18-7), either alone or in conjunction with other
substituted pyridines and/or surfactants, produces mirror-bright to
brilliant deposits.
[0015] As used herein, the terms "nonprecipitating electrolyte
salts" refer to salts of acids the silver salts of which are
soluble. Examples of such nonprecipitating electrolyte salts would
include the sodium, potassium, or ammonium salts of sulfamic,
hydrofluoric, nitric, fluoboric, glycolic and lactic acids. Such
materials do not cause film formation at the anodes, and in some
cases promote anode corrosion. Additionally, the silver-hydantoin
complexes of this invention arc premanufactured in that form to the
plating solution, together with an excess of the hydantoin and the
nonprecipitating electrolyte salt.
[0016] Addition of 2,2'-dipyridyl to the plating solutions of this
invention, usually in amounts in the range of about 0.1 to 10 grams
per liter, produces bright deposits over a current density range
from about 5-20 mA/cm.sup.2 for solutions operated at room
temperature. Addition of further quantities of various substituted
pyridine compounds, usually in amounts greater than that of the
2,2'-dipyridyl itself, expands the range of usable current density
from about 1 to 30 mA/cm.sup.2, and improves the uniformity and
whiteness of the entire deposit. Preferred substituted pyridine
compounds for the purposes of this invention include nicotinamide,
isonicotinamide, 2-aminopyridine, 3-aminopyridine, nicotinic acid
and its salts, and isonicotinic acid and its salts. These are added
in amounts from about 2.5 to 100 grams per liter, depending on
other parameters of the plating solution. It should be pointed out
that in the absence of 2,2'-dipyridyl, addition of substituted
pyridine compounds is generally ineffective for the purposes of
this invention. It should also be pointed out that additions of
4,4'-dipyridyl and 1,10-phenanthroline arc likewise ineffective for
the purposes of this invention.
[0017] Finally, it has been discovered that the addition of a
suitable surfactant to the plating solutions of this invention
containing both 2,2'-dipyridyl and a substituted pyridine compound,
produces an overall improvement of deposit brightness from
mirror-bright to brilliant. Surfactants suitable for the purposes
of this invention include the class of substituted glycine
derivatives known commercially as Hamposyls, and also the
sulfonated naphthalene-formaldehyde condensate known commercially
as Blancol N or Rhodacal N and their aqueous solutions. Both of
these classes of surfactants have been used previously for
conventional (cyanide based) silver plating.
[0018] The plating solutions of this invention produce
mirror-bright to brilliant deposits over a range of pH from about 9
to about 13. Certain practical considerations act to limit this
range somewhat. The corrosivity of the solutions toward silver
anodes increases generally with increasing pH from about pH 9.5 to
about pH 13. It also happens that 2,2'-dipyridyl is subject to
hydrolysis at pH values above about 10.5, the rate of hydrolysis
increasing with increasing pH. In order to obtain adequate
replenishment of silver from the anodes and to preserve the useful
life of the brightener chemicals, an optimum pH range of about
10-11 is arrived at.
[0019] Some Examples of plating solutions of this invention are
given as follows. In each of the Examples, silver is added as a
preformed complex formed by the reaction of silver oxide with
hydantoin, or with a substituted hydantoin, such as
5,5-dimethyl-hydantoin, as appropriate. No foreign ions are thus
introduced. Other substituted hydantoin compounds can likewise be
employed. Methyl-hydantoin, other alkyl-hydantoins, other
dialkyl-hydantoins, and the like are useful herein. See the
hydantoin compounds of U.S. Pat. No. 5,750,018 for additional
examples. This patent is hereby incorporated herein by
reference.
EXAMPLE 1
[0020] Sufficient water was used to form one liter of a solution
containing the following:
1 Potassium hydroxide 60 grams Sulfamic Acid 52.5 grams
5,5-dimethylhydantoin 60 grams Silver as complex with 25 grams Ag
5,5-dimethylhydantoin 2,2'-dipyridyl 0.8 grams
[0021] The solution pH was approximately 11.0. A test panel was
plated from this solution in a Hull cell at 0.5 ampere for 5
minutes at room temperature with moving-vane agitation. The deposit
obtained was white and mirror-bright at indicated current densities
from about 5-20 mA/cm.sup.2.
EXAMPLE 2
[0022] Sufficient water was used to form one liter of a solution
containing the following:
2 Potassium hydroxide 60 grams Sulfamic Acid 52.5 grams
5,5-dimethylhydantoin 60 grams Silver as complex with 25 grams Ag
5,5-dimethylhydantoin 2,2'-dipyridyl 0.40 grams Nicotinamide 4.0
grams
[0023] The solution pH was approximately 11.0. A test panel was
plated from this solution in a Hull cell at 0.5 ampere for 5
minutes at room temperature with moving-vane agitation. The deposit
obtained was white and mirror-bright at indicated current densities
from near zero to about 12.5 mA/cm .
EXAMPLE 3
[0024] A plating solution was made up as in Example 2, but
additionally containing approximately 0.6 grams of Rhodacal N in
the form of an aqueous solution. A test panel was plated from this
solution in a Hull cell at 0.5 ampere for 5 minutes at room
temperature with moving-vane agitation. The deposit obtained was
brilliant mirror-bright white at current densities from near zero
to greater that 20 mA/cm.sup.2.
EXAMPLE 4
[0025] A plating solution was made up as in Example 3 except
containing approximately 0.4 grams of Hamposyl L as an aqueous
solution solubilized by potassium hydroxide in place of the
Rhodacal N. A test panel was plated from this solution in a Hull
cell at 0.5 ampere for 5 minutes at room temperature with
moving-vane agitation. The deposit obtained was brilliant
mirror-bright white at current densities from near zero to greater
than 20 mA/cm.sup.2.
EXAMPLE 5
[0026] A plating solution was made up as in Example 3 except
containing 1.3 grams of 2-aminopyridine in place of nicotinamide. A
test panel was plated from this solution in a Hull cell at 0.5
ampere for 5 minutes at room temperature with moving-vane
agitation. The deposit obtained was brilliant mirror-bright white
at current densities from near zero to greater than 20
mA/cm.sup.2.
EXAMPLE 6
[0027] A plating solution was made up as in Example 5 except
containing 0.8 grams of 3-aminopyridine in place of
2-aminopyridine. A test panel was plated from this solution in a
Hull cell at 0.5 ampere for 5 minutes at room temperature with
moving-vane agitation. The deposit obtained was brilliant
mirror-bright white at current densities from near zero to greater
than 20 mA/cm.sup.2.
EXAMPLE 7
[0028] Sufficient water was used to form one liter of a solution
containing the following:
3 Potassium hydroxide 45 grams Sulfamic Acid 45 grains Hydantoin 45
grams Silver as complex 25 grams Ag with hydantoin 2,2' dipyridyl
2.64 grams
[0029] The solution pH was approximately 11.0. A test panel was
plated from this solution in a Hull cell at 0.5 ampere for 5
minutes at room temperature, with moving-vane agitation. The
deposit obtained was white and hazy-bright from near zero to about
5 mA/cm.sup.2.
EXAMPLE 8
[0030] A plating solution was made up as in Example 7 except
additionally containing 26.4 grams of nicotinamide. A test panel
was plated from this solution in a Hull cell at 0.5 ampere for 5
minutes at room temperature with moving-vane agitation. The deposit
obtained was white and mirror-bright at current densities from near
zero to greater than 20 mA/cm.sup.2.
EXAMPLE 9
[0031] A plating solution was made up as in Example 8 except
additionally containing 0.16 grams of Hamposyl L in the form of an
aqueous solution solubilized with potassium hydroxide. A test panel
was plated from this solution in a Hull cell at 0.5 ampere for 5
minutes at room temperature with moving-vane agitation. The deposit
obtained was brilliant mirror-bright white at current densities
from near zero to 20 mA/cm.sup.2.
[0032] It will be apparent to those skilled in the art that the
Examples provided herein are illustrative of the present invention,
but do not represent the totality of the useful embodiments
thereof.
[0033] The following documents, cited above, are hereby
incorporated herein by reference:
[0034] 1. Modem Electroplating, 4.sup.th Edition, M. Schelesinger
and M. Paunovic, Eds., John Wiley, New York 2000, pp. 227 ff.
[0035] 2. E. Hradil, H. Hradil, and A. M. Weisberg, U.S. Pat. No.
4,126,524 (1978).
[0036] 3. E. Hradil, H. Hradil and A. M. Weisberg U.S. Pat. No.
4,246,077 (1981).
[0037] 4. T. Asakawa, U.S. Pat. No. 5,601,696 (1997)
[0038] 5. W. Brasch, U.S. Pat. No. 5,750,018 (1998)
* * * * *