U.S. patent application number 16/770357 was filed with the patent office on 2021-06-10 for trivalent chromium plating solution and method for chromium-plating using same.
This patent application is currently assigned to JCU CORPORATION. The applicant listed for this patent is JCU CORPORATION. Invention is credited to Masao HORI, Yuto MORIKAWA, Madoka NAKAGAMI.
Application Number | 20210172081 16/770357 |
Document ID | / |
Family ID | 1000005415822 |
Filed Date | 2021-06-10 |
United States Patent
Application |
20210172081 |
Kind Code |
A1 |
HORI; Masao ; et
al. |
June 10, 2021 |
TRIVALENT CHROMIUM PLATING SOLUTION AND METHOD FOR CHROMIUM-PLATING
USING SAME
Abstract
A trivalent chromium plating solution having a high plating
deposition rate and being practical is provided with a trivalent
chromium plating solution containing a trivalent chromium compound,
a complexing agent, potassium sulfate and ammonium sulfate as a
conductive salt, a pH buffer, and a sulfur-containing organic
compound, containing a carboxylic acid having two or more hydroxy
groups and two or more carboxy groups or a salt thereof as the
complexing agent, and containing a combination of saccharin or a
salt thereof and a sulfur-containing organic compound having an
allyl group as the sulfur-containing organic compound.
Inventors: |
HORI; Masao; (Wixom, MI)
; NAKAGAMI; Madoka; (Kawasaki-shi, JP) ; MORIKAWA;
Yuto; (Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JCU CORPORATION |
Taito-ku |
|
JP |
|
|
Assignee: |
JCU CORPORATION
Taito-ku
JP
|
Family ID: |
1000005415822 |
Appl. No.: |
16/770357 |
Filed: |
December 12, 2018 |
PCT Filed: |
December 12, 2018 |
PCT NO: |
PCT/JP2018/045593 |
371 Date: |
June 5, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/06 20130101 |
International
Class: |
C25D 3/06 20060101
C25D003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2017 |
JP |
2017-238232 |
Apr 25, 2018 |
JP |
2018-083550 |
Claims
1. A trivalent chromium plating solution, comprising: a trivalent
chromium compound, a first complexing agent, potassium sulfate and
ammonium sulfate as a conductive salt, a pH buffer, and a first
sulfur-containing organic compound, wherein the first complexing
agent is a carboxylic acid having two or more hydroxy groups and
two or more carboxy groups or a salt thereof, and the first
sulfur-containing organic compound is a combination of saccharin or
a salt thereof and a sulfur-containing organic compound having an
allyl group.
2. The trivalent chromium plating solution according to claim 1,
wherein the carboxylic acid having two or more hydroxy groups and
two or more carboxy groups or a salt thereof is diammonium
tartarate.
3. The trivalent chromium plating solution according to claim 1,
wherein the trivalent chromium plating solution has a mass ratio of
potassium sulfate and ammonium sulfate ((potassium
sulfate)/(ammonium sulfate)) of from 1.0 to 30.
4. The trivalent chromium plating solution according to claim 1,
wherein the sulfur-containing organic compound having an allyl
group is sodium allylsulfonate and/or allylthiourea.
5. The trivalent chromium plating solution according to claim 1,
further comprising: a second complexing agent, and a second
sulfur-containing organic compound, wherein the second complexing
agent is a carboxylic acid having two or more carboxy groups having
a number of carbon atoms of 4 or more or a salt thereof, and the
second sulfur-containing organic compound is a sulfonic acid having
a vinyl group or a salt thereof.
6. The trivalent chromium plating solution according to claim 5,
wherein the carboxylic acid having two or more carboxy groups
having a number of carbon atoms of 4 or more or a salt thereof is
phthalic acid or adipic acid.
7. The trivalent chromium plating solution according to claim 5,
wherein the sulfonic acid having a vinyl group or a salt thereof is
sodium vinylsulfonate.
8. The trivalent chromium plating solution according to claim 1,
wherein the trivalent chromium plating solution comprises
substantially no iron and/or cobalt.
9. A method for chromium-plating on an article, the method
comprising: electroplating an article with the trivalent chromium
plating solution according to claim 1.
10. A chromium-plated product, comprising: an article,
electroplated with the trivalent chromium plating solution
according to claim 1.
11. The chromium-plated product according to claim 10, wherein the
chromium plating comprises substantially no iron and/or cobalt.
Description
TECHNICAL FIELD
[0001] The present invention relates to a trivalent chromium
plating solution and a method for chromium-plating using the
same.
BACKGROUND ART
[0002] Chromium plating is used as a coating film for decoration
owing to the silvery white color thereof. Hexavalent chromium has
been used for the chromium plating, but the use of hexavalent
chromium is restricted in recent years due to the environmental
implications thereof, and the technology is shifted to the use of
trivalent chromium.
[0003] Many reports have been made for the technique using
trivalent chromium, and for example, a chromium electrolytic
plating solution containing a water soluble trivalent chromium
salt, a complexing agent for a trivalent chromium ion, such as
malic acid, a pH buffering compound, a sulfur-containing organic
compound, such as thiourea, and a water soluble compound, such as
saccharin, and having pH of from 2.8 to 4.2 has been known (PTL
1).
[0004] However, this trivalent chromium plating solution has a low
plating deposition rate and thus is not practical.
CITATION LIST
Patent Literature
[0005] PTL 1: Japanese Patent No. 5,696,134
SUMMARY OF INVENTION
Technical Problem
[0006] An object of the present invention is to provide a trivalent
chromium plating solution that has a high plating deposition rate
and is practical.
Solution to Problem
[0007] As a result of the earnest investigations by the present
inventors, it has been found that a trivalent chromium plating
solution can have a high plating deposition rate and can be
practical by using a carboxylic acid having two or more hydroxy
groups and two or more carboxy groups or a salt thereof as a
complexing agent for a trivalent chromium ion, and in addition,
using a combination of saccharin or a salt thereof and a compound
having an allyl group as a sulfur-containing organic compound, and
thus the present invention has been completed.
[0008] Accordingly, the present invention relates to a trivalent
chromium plating solution containing a trivalent chromium compound,
a complexing agent, potassium sulfate and ammonium sulfate as a
conductive salt, a pH buffer, and a sulfur-containing organic
compound,
[0009] containing a carboxylic acid having two or more hydroxy
groups and two or more carboxy groups or a salt thereof as the
complexing agent, and
[0010] containing a combination of saccharin or a salt thereof and
a sulfur-containing organic compound having an allyl group as the
sulfur-containing organic compound.
[0011] The present invention also relates to a method for
chromium-plating on an article to be plated, including
electroplating an article to be plated with the trivalent chromium
plating solution.
[0012] The present invention further relates to a chromium-plated
product including an article to be plated, electroplated with the
trivalent chromium plating solution.
Advantageous Effects of Invention
[0013] The trivalent chromium plating solution of the present
invention provides an appearance that is equivalent to plating with
hexavalent chromium despite the plating with trivalent chromium,
and furthermore has a high plating deposition rate and is
practical.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is an illustration showing the position where the
throwing distance is measured in the Hull cell test of Example
1.
[0015] FIG. 2 is a graph showing the relationship between the ratio
of potassium sulfate and ammonium sulfate contained in the
trivalent chromium plating solution and the throwing power in the
Hull cell test of Example 1.
[0016] FIG. 3 is images showing the results of the corrosion
resistance test (CASS test).
DESCRIPTION OF EMBODIMENTS
[0017] The trivalent chromium plating solution of the present
invention (which may be hereinafter referred to as a "plating
solution of the present invention") is a trivalent chromium plating
solution that contains a trivalent chromium compound, a complexing
agent, potassium sulfate and ammonium sulfate as a conductive salt,
a pH buffer, and a sulfur-containing organic compound,
[0018] contains a carboxylic acid having two or more hydroxy groups
and two or more carboxy groups or a salt thereof as the complexing
agent, and
[0019] contains a combination of saccharin or a salt thereof and a
sulfur-containing organic compound having an allyl group as the
sulfur-containing organic compound.
[0020] The trivalent chromium compound used in the plating solution
of the present invention is not particularly limited, examples of
which include basic chromium sulfate, chromium sulfate, chromium
chloride, chromium sulfamate, and chromium acetate, and basic
chromium sulfate and chromium sulfate are preferred. The trivalent
chromium compound may be used alone or as a combination of two or
more kinds thereof. The content of the trivalent chromium compound
in the plating solution of the present invention is not
particularly limited, and for example, is from 1 to 25 g/L, and
preferably from 5 to 15 g/L, in terms of metallic chromium.
[0021] The complexing agent used in the plating solution of the
present invention is a carboxylic acid having two or more hydroxy
groups and two or more carboxy groups or a salt thereof. Examples
of the complexing agent include a carboxylic acid, such as tartaric
acid, and a salt of the carboxylic acid, such as diammonium
tartarate, Rochelle salt, and sodium tartarate. The complexing
agent may be used alone or as a combination of two or more kinds
thereof. The content of the carboxylic acid or a salt thereof in
the plating solution of the present invention is not particularly
limited, and for example, is from 5 to 90 g/L, and preferably from
10 to 60 g/L. In the present invention, the hydroxy group in the
carboxy group is not counted as the hydroxy group.
[0022] The conductive salt used in the plating solution of the
present invention is potassium sulfate and ammonium sulfate. The
content of potassium sulfate and ammonium sulfate in the plating
solution of the present invention is not particularly limited, and
for example, is from 100 to 300 g/L, and preferably from 120 to 240
g/L, in terms of total amount. The mass ratio of potassium sulfate
and ammonium sulfate ((potassium sulfate)/(ammonium sulfate)) may
be from 0.5 to 60, and preferably from 1.0 to 30. In the case where
the mass ratio (potassium sulfate)/(ammonium sulfate) is in the
range, good covering power can be obtained, and a chromium plating
film can be formed on an article having a complicated shape to be
plated over a low current density portion.
[0023] The pH buffer used in the plating solution of the present
invention is not particularly limited, examples of which include
boric acid, sodium borate, potassium borate, phosphoric acid, and
dipotassium hydrogen phosphate, and boric acid and sodium borate
are preferred. The pH buffer may be used alone or as a combination
of two or more kinds thereof. The content of the pH buffer in the
plating solution of the present invention is not particularly
limited, and for example, is from 30 to 150 g/L, and preferably
from 50 to 110 g/L.
[0024] The sulfur-containing organic compound used in the plating
solution of the present invention is a combination of saccharin or
a salt thereof and a sulfur-containing organic compound having an
allyl group. Examples of the saccharin or a salt thereof include
saccharin and sodium saccharinate. Examples of the
sulfur-containing organic compound having an allyl group include
sodium allylsulfonate, allylthiourea, ammonium
2-methylallylsulfonate, and allyl isothiocyanate. The
sulfur-containing organic compound having an allyl group maybe used
alone or as a combination of two or more kinds thereof, and sodium
allylsulfonate and/or allylthiourea are preferred. Preferred
examples of the combination as the sulfur-containing organic
compound include sodium saccharinate and sodium allylsulfonate. The
content of the sulfur-containing organic compound in the plating
solution of the present invention is not particularly limited, and
for example, is from 0.5 to 10 g/L, and preferably from 2 to 8
g/L.
[0025] The plating solution of the present invention may further
contain ascorbic acid, sodium ascorbate, hydrogen peroxide,
polyethylene glycol, and the like.
[0026] The pH of the plating solution of the present invention is
not particularly limited, as far as the solution is acidic, and for
example, is preferably from 2 to 4.5, and more preferably from 2.5
to 4.0.
[0027] The preparation method of the plating solution of the
present invention is not particularly limited, and for example, the
solution can be prepared in such a manner that the trivalent
chromium compound, the complexing agent, the conductive salt, and
the pH buffer are added to water at from 40 to 50.degree. C. and
dissolved therein by mixing, then the sulfur-containing organic
compound is added thereto and mixed therein, and finally the pH
thereof is controlled with sulfuric acid, aqueous ammonia, or the
like.
[0028] Chromium plating can be formed on an article to be plated by
electroplating the article to be plated with the plating solution
of the present invention in the same manner as for the ordinary
chromium plating solution.
[0029] The condition of the electroplating is not particularly
limited, and for example, the electroplating may be performed at a
bath temperature of from 30 to 60.degree. C., with carbon or
iridium oxide as an anode, at a cathode current density of from 2
to 20 A/dm.sup.2, for a period of from 1 to 15 minutes.
[0030] Examples of the article to be plated capable of being
electroplated include a metal, such as iron, stainless steel, and
brass, and a resin, such as ABS and PC/ABS. The article to be
plated may be subjected to a treatment, such as copper plating and
nickel plating, in advance before the treatment with the plating
solution of the present invention.
[0031] The chromium-plated product thus obtained becomes a
chromium-plated product having an appearance, throwing power, and a
deposition rate that are equivalent to the use of hexavalent
chromium.
[0032] As another embodiment of the plating solution of the present
invention, a trivalent chromium plating solution that has a high
plating deposition rate, has good color tone and good corrosion
resistance, and is practical is then described.
[0033] As the complexing agent of the aforementioned plating
solution of the present invention, a carboxylic acid having two or
more carboxy groups having a number of carbon atoms of 4 or more or
a salt thereof is further used in combination, in addition to the
aforementioned compound. Examples of the carboxylic acid having two
or more carboxy groups having a number of carbon atoms of 4 or more
or a salt thereof include a carboxylic acid, such as adipic acid,
phthalic acid, pimelic acid, and sebacic acid, and a salt of the
carboxylic acid. In the case where a combination of the carboxylic
acid having two or more hydroxy groups and two or more carboxy
groups or a salt thereof and the carboxylic acid having two or more
carboxy groups having a number of carbon atoms of 4 or more or a
salt thereof is used as the complexing agent, the two kinds of the
complexing agents each may be used alone or as a combination of two
or more kinds thereof. In the case where a combination of the
carboxylic acid having two or more hydroxy groups and two or more
carboxy groups or a salt thereof and the carboxylic acid having two
or more carboxy groups having a number of carbon atoms of 4 or more
or a salt thereof is used as the complexing agent, the total
content of the complexing agents in the plating solution of the
present invention is not particularly limited, and for example, is
from 5 to 90 g/L, and preferably from 10 to 60 g/L, in terms of
total of all the complexing agents.
[0034] As the sulfur-containing organic compound of the
aforementioned plating solution of the present invention, a
sulfonic acid having a vinyl group or a salt thereof may further be
used in combination, in addition to the aforementioned compounds.
Examples of the sulfonic acid having a vinyl group or a salt
thereof include sodium vinylsulfonate, methyl vinylsulfonate, and
polyvinylsulfonic acid. In the case where a combination of the
saccharin or a salt thereof, the sulfonic acid having an allyl
group or a salt thereof, and the sulfonic acid having a vinyl group
or a salt thereof is used as the sulfur-containing organic
compound, the three kinds of the sulfur-containing organic
compounds each may be used alone or as a combination of two or more
kinds thereof. The content of the sulfur-containing organic
compounds in the plating solution of the present invention is not
particularly limited, and for example, is from 0.5 to 10 g/L, and
preferably from 2 to 8 g/L, in terms of total of all the
sulfur-containing organic compounds.
[0035] The plating solution of the present invention that uses the
complexing agents and the sulfur-containing organic compounds
described above can be prepared in the preparation method described
above. Chromium plating can be formed therewith on an article to be
plated in the method described above.
[0036] The chromium-plated product thus obtained becomes chromium
plating having a color tone that is equivalent to the use of
hexavalent chromium, and having high corrosion resistance and high
practicality. Accordingly, the chromium-plated product is favorably
applied to components of automobiles, motorcycles, faucets, and the
like, which are demanded to have corrosion resistance.
[0037] An ordinary trivalent chromium plating solution contains
iron or cobalt for the enhancement of the throwing power for a low
current density, but the plating solution of the present invention
can have enhanced throwing power without the addition of iron
and/or cobalt. A plating solution containing iron or cobalt has a
tendency that the corrosion resistance of the plating film is
decreased due to codeposition of iron or cobalt therein.
Accordingly, it is preferred that the plating solution of the
present invention contains substantially no iron and/or cobalt. The
plating solution of the present invention that contains
substantially no iron and/or cobalt means that the content of iron
and/or cobalt is 2 ppm or less, preferably 1 ppm or less, and more
preferably 0.5 ppm or less. The amount of iron and/or cobalt can be
analyzed by the ICP-MS method, the atomic absorption spectrometry,
or the like.
[0038] In the case where the plating solution of the present
invention contains substantially no iron and/or cobalt, the
resulting chromium-plated product also contains substantially no
iron and/or cobalt. The chromium-plated product of the present
invention that contains substantially no iron and/or cobalt means
that the content of iron and/or chromium in the chromium plating is
less than 0.5% by atom, and preferably 0.4% by atom or less. The
amount of iron and/or cobalt can be analyzed by EDS, XPS, or the
like.
EXAMPLES
[0039] The present invention will be described in detail with
reference to examples and comparative examples below, but the
present invention is not limited to the examples.
Example 1
Chromium Plating
[0040] The components shown in Table 1 were dissolved in water to
prepare a trivalent chromium plating solution. The trivalent
chromium plating solution was subjected to the Hull cell test using
a brass plate having nickel plating formed thereon. The condition
of the Hull cell test was a current of 4 A and a plating time of 3
minutes. After plating, the distance of the deposition of the
plating film from the left end of the brass plate was measured as
shown in FIG. 1, and was designated as the throwing power. The film
thickness at the position of the brass plate corresponding to a
current density of 8 ASD was measured by the X-ray fluorescent
spectrometry. The appearance after plating was evaluated in terms
of the L value, the a value, and the b value with a
color-difference meter (produced by Konica Minolta, Inc.). The
results are shown in Table 1.
TABLE-US-00001 TABLE 1 Composition Composition Composition
Composition Composition Composition Composition of plating solution
1 2 3 4 5 6 Basic chromium sulfate (g/L) 64 64 64 64 64 64
Diammonium tartarate (g/L) *.sup.1 30 30 30 30 30 -- Ammonium
lactate (g/L) *.sup.2 -- -- -- -- -- 30 Potassium sulfate (g/L) 150
150 150 150 150 150 Ammonium sulfate (g/L) 20 20 20 20 20 20 Boric
acid (g/L) 80 80 80 80 80 80 Sodium Saccharate (g/L) 4 4 4 4 4 4
Sodium allylsulfonate (36%) (ml/L) 1.58 -- -- -- -- 1.58 Sodium
vinylsulfonate (27.5%) (m/L) -- 1 -- -- -- -- Sodium
propinesulfonate (20%) (ml/L) -- -- 1 -- -- -- Allylthiourea (ppm)
-- -- -- 10 20 -- pH of plating solution 3.4 3.4 3.4 3.4 3.4 3.4
Bath temperature (.degree. C.) 45 45 45 45 45 45 Throwing power
(mm) 75 75 --* 75 74 74 Film thickness (.mu.m) 0.15 0.07 --* 0.13
0.15 0.08 Appearance L value 82.38 75.47 --* 82.60 82.40 80.01
Appearance a value -0.76 -0.29 --* -0.76 -0.72 -0.75 Appearance b
value -0.42 1.94 --* -0.22 -0.33 0.23 --*: no plating deposited
*.sup.1 two hydroxy groups and two carboxy groups *.sup.2 one
hydroxy group and one carboxy group note: Hexavalent chromium
plating has L value of 84, a value of -1.0, and b value of
-1.0.
[0041] It was found from the results that in the case where the
trivalent chromium plating solution used diammonium tartarate
(having two hydroxy groups and two carboxy group) as the complexing
agent, and a combination of sodium saccharate and sodium
allylsulfonate or allylthiourea (i.e., the sulfur-containing
organic compound having an allyl group) as the sulfur-containing
organic compound (Compositions 1, 4, and 5), the appearance was
equivalent to hexavalent chromium plating, and the film thickness
(i.e., the deposition rate) was approximately twice the case where
these compounds were not used.
[0042] The contents of iron and cobalt in the trivalent chromium
plating solutions each were less than 0.5 ppm, as measured by the
ICP-MS method. The contents of iron and cobalt in the resulting
chromium plating each were less than 0.4% by atom, as measured by
the EDS elemental analysis.
Example 2
Chromium Plating
[0043] The components shown in Table 2 were dissolved in water to
prepare a trivalent chromium plating solution. The trivalent
chromium plating solution was subjected to the Hull cell test using
a brass plate having nickel plating formed thereon. The condition
of the Hull cell test was a current of 4 A and a plating time of 3
minutes. After plating, the distance of the deposition of the
plating film from the left end of the brass plate was measured. The
results are shown in Table 2. The relationship between the ratio
(potassium sulfate)/(ammonium sulfate) and the throwing power is
shown in FIG. 2
TABLE-US-00002 TABLE 2 Compo- Compo- Compo- Compo- Compo- Compo-
Compo- Compo- Compo- sition sition sition sition sition sition
sition sition sition Composition of plating solution 7 8 9 10 11 12
13 14 15 Basic chromium sulfate (g/L) 64 64 64 64 64 64 64 64 64
Diammonium tartarate (g/L) 30 30 30 30 30 30 30 30 30 Potassium
sulfate (g/L) 150 150 150 120 85 60 40 20 5 Ammonium sulfate (g/L)
20 5 40 60 85 120 150 150 150 Boric acid (g/L) 80 80 80 80 80 80 80
80 80 Sodium Saccharate (g/L) 4 4 4 4 4 4 4 4 4 Sodium
allylsulfonate (36%) (ml/L) 1.58 1.58 1.58 1.58 1.58 1.58 1.58 1.58
1.58 pH of plating solution 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4
Bath temperature (.degree. C.) 45 45 45 45 45 45 45 45 45 Throwing
power (mm) 75 79 71 70 69 67 64 62 62
[0044] It was found that in the case where plating was performed
with the aforementioned trivalent chromium plating solutions, the
appearance and the film thickness were substantially the same in
all the compositions, but the throwing power became better with a
larger ratio (potassium sulfate)/(ammonium sulfate), and the
throwing power became particularly good with the ratio of from 1.0
to 30.
[0045] The contents of iron and cobalt in the trivalent chromium
plating solutions each were less than 0.5 ppm, as measured by the
ICP-MS method. The contents of iron and cobalt in the resulting
chromium plating each were less than 0.4% by atom, as measured by
the EDS elemental analysis.
Example 3
Chromium Plating
[0046] The components shown in Table 3 were dissolved in water to
prepare a trivalent chromium plating solution. The trivalent
chromium plating solution was subjected to the Hull cell test using
a brass plate having nickel plating formed thereon. The condition
of the Hull cell test was a current of 4 A and a plating time of 3
minutes. After plating, the distance of the deposition of the
plating film from the left end of the brass plate was measured as
shown in FIG. 1, and was designated as the throwing power. The film
thickness at the position of the brass plate corresponding to a
current density of 8 ASD was measured by the X-ray fluorescent
spectrometry. The appearance after plating was evaluated in terms
of the L value, the a value, and the b value with a
color-difference meter (produced by Konica Minolta, Inc.). The
results are shown in Table 3.
TABLE-US-00003 TABLE 3 Composition Composition Composition
Composition Composition Composition Composition of plating solution
16 17 18 19 20 21 Basic chromium sulfate (g/L) 64 64 64 64 64 64
Diammonium tartarate (g/L) 30 30 30 30 30 30 Adipic acid (g/L) --
-- 1 5 -- -- Phthalic acid (g/L) 1 5 -- -- -- -- Glycine (g/L) --
-- -- -- -- 1 Potassium sulfate (g/L) 150 150 150 150 150 150
Ammonium sulfate (g/L) 20 20 20 20 20 20 Boric acid (g/L) 80 80 80
80 80 80 Sodium Saccharate (g/L) 4 4 4 4 4 4 Sodium allylsulfonate
(36%) (ml/L) 3.6 3.6 7.2 7.2 3.6 3.6 Sodium vinylsulfonate (25%)
(ml/L) 3 3 5 5 3 3 pH of plating solution 3.4 3.4 3.4 3.4 3.4 3.4
Bath temperature (.degree. C.) 45 45 45 45 45 45 Throwing power
(mm) 76 75 75 74 75 75 Film thickness (.mu.m) 0.14 0.11 0.14 0.12
0.15 0.13 Appearance L value 82.0 81.8 82.2 82.0 82.8 81.7
Appearance a value -0.78 -0.72 -0.77 -0.74 -0.64 -0.74 Appearance b
value -0.25 -0.10 -0.33 -0.17 -0.58 -0.14 note: Hexavalent chromium
plating has L value of 84, a value of -1.0, and b value of
-1.0.
[0047] It was found from the results that in the case where the
trivalent chromium plating solution used a combination of a
carboxylic acid having two or more hydroxy groups and two or more
carboxy groups or a salt thereof and a carboxylic acid having two
or more carboxy groups having a number of carbon atoms of 4 or more
or a salt thereof as the complexing agent, and a combination of
saccharate or a salt thereof, a sulfonic acid having an allyl group
or a salt thereof, and a sulfonic acid having a vinyl group or a
salt thereof as the sulfur-containing organic compound, the
appearance was equivalent to hexavalent chromium plating.
[0048] The contents of iron and cobalt in the trivalent chromium
plating solutions each were less than 0.5 ppm, as measured by the
ICP-MS method. The contents of iron and cobalt in the resulting
chromium plating each were less than 0.4% by atom, as measured by
the EDS elemental analysis.
Example 4
CASS Test
[0049] Trivalent chromium plating solutions having the compositions
16, 18, 20, and 21 shown in Table 3 were prepared. With each of the
trivalent chromium plating solutions, chromium plating was formed
on a copper plate having nickel plating (2 .mu.m) thereon under
condition of a bath temperature of 45.degree. C. and a current
density of 8 A/dm.sup.2 for 3 minutes, so as to prepare a test
piece. The test piece was subjected to the CASS test (according to
JIS H8502). The micrographs of the test pieces after the CASS test
for 24 hours are shown in FIG. 3.
[0050] It was found from the results of the CASS test that in the
case where the trivalent chromium plating solution used a
combination of a carboxylic acid having two or more hydroxy groups
and two or more carboxy groups or a salt thereof and a carboxylic
acid having two or more carboxy groups having a number of carbon
atoms of 4 or more or a salt thereof as the complexing agent, and a
combination of saccharate or a salt thereof, a sulfonic acid having
an allyl group or a salt thereof, and a sulfonic acid having a
vinyl group or a salt thereof as the sulfur-containing organic
compound, the corrosion pores were finely dispersed to enhance the
corrosion resistance.
INDUSTRIAL APPLICABILITY
[0051] The trivalent chromium plating solution of the present
invention can be applied to various purposes as similar to plating
with hexavalent chromium.
* * * * *