U.S. patent application number 17/257348 was filed with the patent office on 2021-10-14 for trivalent chromium plating solution and chromium plating method 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 | 20210317589 17/257348 |
Document ID | / |
Family ID | 1000005712047 |
Filed Date | 2021-10-14 |
United States Patent
Application |
20210317589 |
Kind Code |
A1 |
NAKAGAMI; Madoka ; et
al. |
October 14, 2021 |
TRIVALENT CHROMIUM PLATING SOLUTION AND CHROMIUM PLATING METHOD
USING SAME
Abstract
A trivalent chromium plating solution containing a trivalent
chromium compound, a complexing agent, a conductive salt, and a
pH-buffering agent, and further containing an organic compound
having 2-4 carbon atoms and three or more chloro groups, and a
trivalent chromium plating method using the same provide a
practical trivalent chromium plating with enhanced corrosion
resistance as compared to the ordinary trivalent chromium
plating.
Inventors: |
NAKAGAMI; Madoka;
(Kawasaki-shi, JP) ; HORI; Masao; (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: |
1000005712047 |
Appl. No.: |
17/257348 |
Filed: |
July 2, 2019 |
PCT Filed: |
July 2, 2019 |
PCT NO: |
PCT/JP2019/026246 |
371 Date: |
December 31, 2020 |
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 3/06 20060101 C25D003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2018 |
JP |
2018-126508 |
Claims
1. A trivalent chromium plating solution, comprising: a trivalent
chromium compound, a complexing agent, a conductive salt, a
pH-buffering agent, and an organic compound having 2-4 carbon atoms
and three or more chloro groups.
2. The trivalent chromium plating solution of claim 1, wherein the
organic compound having 2-4 carbon atoms and three or more chloro
groups is chloral hydrate and/or trichloroethylene.
3. The trivalent chromium plating solution of claim 1, wherein the
conductive salt is a sulfate.
4. The trivalent chromium plating solution of claim 3, further
comprising a sulfur-containing organic compound.
5. The trivalent chromium plating solution according to of claim 4,
wherein: the complexing agent is a carboxylic acid having two or
more hydroxy groups and two or more carboxy groups or a salt
thereof, and the sulfur-containing organic compound is a
combination of saccharin or a salt thereof and at least one
selected from the group consisting of a sulfur-containing organic
compound having an allyl group and a carboxylic acid having a
carbamimidoylthio group and/or a dehydration reaction product
thereof.
6. The trivalent chromium plating solution of claim 5, wherein the
carboxylic acid having two or more hydroxy groups and two or more
carboxy groups or a salt thereof is tartaric acid or diammonium
tartrate.
7. The trivalent chromium plating solution of claim 5, wherein the
sulfur-containing organic compound having an allyl group is sodium
allylsulfonate and/or allylthiourea.
8. The trivalent chromium plating solution of claim 5, further
comprising a carboxylic acid having two or more carboxy groups and
4 or more carbon atoms or a salt thereof as the complexing
agent.
9. The trivalent chromium plating solution of claim 8, wherein the
carboxylic acid having two or more carboxy groups and 4 or more
carbon atoms or a salt thereof is phthalic acid and/or adipic
acid.
10. The trivalent chromium plating solution of claim 1, wherein the
conductive salt is a chloride.
11. An additive for a trivalent chromium plating solution,
comprising an organic compound having 2-4 carbon atoms and three or
more chloro groups as an active ingredient.
12. A chromium plating method for an article to be plated,
comprising electroplating the article to be plated with the
trivalent chromium plating solution of claim 1.
13. The chromium plating method of claim 12, further comprising
performing a chromate treatment after the electroplating the
article to be plated.
14. A method for enhancing corrosion resistance of an article to be
plated, comprising electroplating the article to be plated with the
trivalent chromium plating solution of claim 1.
15. The method of claim 14, further comprising performing a
chromate treatment after the electroplating the article to be
plated.
16. A chromium plated product obtained by electroplating an article
to be plated with the trivalent chromium plating solution of claim
1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a trivalent chromium
plating solution and a chromium plating method using the same.
BACKGROUND ART
[0002] A chromium plating has been used as a decorative coating
film due to the silver-white appearance thereof. Hexavalent
chromium has been used for the chromium plating, but the use of
hexavalent chromium is being restricted in recent years since
hexavalent chromium adversely affects the environments, and the
technologies are being shifted to the use of trivalent
chromium.
[0003] However, a trivalent chromium plating is inferior in
corrosion resistance to a hexavalent chromium plating. Under the
circumstances, the techniques for enhancing the corrosion
resistance of the trivalent chromium plating have been reported.
For example, PTL 1 reports the technique of the enhancement of
corrosion resistance in a calcium chloride environment.
[0004] However, this trivalent chromium plating is still inferior
in CASS corrosion resistance to the hexavalent chromium plating,
and is not practical.
CITATION LIST
Patent Literature
[0005] PTL 1: JP-A-2012-521495
SUMMARY OF INVENTION
Technical Problem
[0006] A problem of the present invention is to provide a practical
trivalent chromium plating with enhanced corrosion resistance as
compared to the ordinary trivalent chromium plating.
Solution to Problem
[0007] As a result of earnest investigations for solving the
problem by the present inventors, it has been found that a
trivalent chromium plating obtained with a trivalent chromium
plating solution having added thereto an organic compound having
2-4 carbon atoms and three or more chloro groups has high corrosion
resistance and is practical, and thus the present invention has
been completed.
[0008] The present invention relates to a trivalent chromium
plating solution containing a trivalent chromium compound, a
complexing agent, a conductive salt, and a pH-buffering agent,
[0009] the trivalent chromium plating solution further containing
an organic compound having 2-4 carbon atoms and three or more
chloro groups.
[0010] The present invention also relates to an additive for a
trivalent chromium plating solution, containing an organic compound
having 2-4 carbon atoms and three or more chloro groups as an
active ingredient.
[0011] The present invention further relates to a chromium plating
method for an article to be plated, including electroplating the
article to be plated with the trivalent chromium plating
solution.
[0012] The present invention still further relates to a method for
enhancing corrosion resistance of an article to be plated,
including electroplating the article to be plated with the
trivalent chromium plating solution.
[0013] The present invention still further relates to a chromium
plated product obtained by electroplating an article to be plated
with the trivalent chromium plating solution.
Advantageous Effects of Invention
[0014] The trivalent chromium plating solution of the present
invention can provide a plating that has an appearance equivalent
to a plating formed by using hexavalent chromium, irrespective of
the use of trivalent chromium, and further has enhanced corrosion
resistance and practicality.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a figure showing results of a corrosion resistance
test (CASS test) performed (Examples 1 to 5).
[0016] FIG. 2 is a figure showing results of the corrosion
resistance test (CASS test) performed (Comparative Examples 1 and 2
and Reference Example).
[0017] FIG. 3 is a figure showing results of the corrosion
resistance test (CRSS test) performed (Examples 6 to 8).
DESCRIPTION OF EMBODIMENTS
[0018] The trivalent chromium plating solution of the present
invention (hereinafter referred to as a "plating solution of the
present invention") is obtained by adding an organic compound
having 2-4 carbon atoms and three or more chloro groups, to a
trivalent chromium plating solution containing a trivalent chromium
compound, a complexing agent, a conductive salt, and a pH-buffering
agent.
[0019] The organic compound having 2-4 carbon atoms and three or
more chloro groups used in the plating solution of the present
invention (which may be hereinafter referred simply to as an
"organic compound") is not particularly limited, and examples of
which include chloral hydrate, trichloroethylene, trichloroacetic
acid, trichloroacetonitrile, and trichloroethanol. The organic
compound may be used alone, or two or more kinds thereof may be
used. Among these organic compounds, chloral hydrate and/or
trichloroethylene are preferred, and chloral hydrate is more
preferred. The content of the organic compound in the plating
solution of the present invention is not particularly limited, and
is, for example, 10 to 5,000 mg/L, preferably 20 to 2,000 mg/L, and
more preferably 50 to 1,000 mg/L.
[0020] The organic compound can form an additive for a trivalent
chromium plating solution using the organic compound as an active
ingredient. The additive for a trivalent chromium plating solution
may be added to the ordinary trivalent chromium plating
solution.
[0021] 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 two or more kinds thereof
may be used in combination. The content of the trivalent chromium
compound in the plating solution of the present invention is not
particularly limited, and is, for example, 1 to 25 g/L, and
preferably 1 to 15 g/L, in terms of metallic chromium.
[0022] The complexing agent used in the plating solution of the
present invention is not particularly limited, examples of which
include an aliphatic monocarboxylic acid, such as formic acid,
ammonium formate, and potassium formate, an aliphatic dicarboxylic
acid, such as succinic acid, maleic acid, malic acid, citric acid,
and triammonium citrate, and a carboxylic acid having two or more
hydroxy groups and two or more carboxy groups, such as tartaric
acid, diammonium tartrate, and sodium tartrate. The complexing
agent may be used alone, or two or more kinds thereof may be used
in combination. The content of the complexing agent in the plating
solution of the present invention is not particularly limited, and
is, for example, 0.1 to 50 g/L, and preferably 1 to 30 g/L.
[0023] The conductive salt used in the plating solution of the
present invention is not particularly limited, examples of which
include a sulfate, such as potassium sulfate, ammonium sulfate, and
sodium sulfate, a chloride, such as potassium chloride, ammonium
chloride, and sodium chloride, and a sulfamate, such as potassium
sulfamate, ammonium sulfamate, and sodium sulfamate. These
conductive salts are used as each of the groups, for example,
groups of sulfates, chlorides, and the like. Among the conductive
salts, a sulfate and a chloride are preferred. The conductive salt
may be used alone, or two or more kinds thereof may be used in
combination. The content of the conductive salt in the plating
solution of the present invention is not particularly limited, and
is, for example, 100 to 500 g/L, and preferably 150 to 300 g/L.
[0024] The pH-buffering agent used in the plating solution of the
present invention is not particularly limited, and may be boric
acid, sodium borate, potassium borate, phosphoric acid, dipotassium
hydrogen phosphate, or the like. Among these, boric acid and sodium
borate are preferred. The pH-buffering agent may be used alone, or
two or more kinds thereof may be used in combination. The content
of the pH-buffering agent in the plating solution of the present
invention is not particularly limited, and is, for example, 25 to
200 g/L, and preferably 50 to 100 g/L.
[0025] The plating solution of the present invention may further
contain ascorbic acid, sodium ascorbate, hydrogen peroxide,
polyethylene glycol, a tin salt, such as tin sulfate and tin
chloride, and the like.
[0026] The pH of the plating solution of the present invention is
not particularly limited, as far as the pH is in an acidic range,
and is, for example, preferably 2 to 4.5, and more preferably 2.5
to 4.0.
[0027] In the case where the conductive salt of the plating
solution of the present invention is a sulfate, the complexing
agent used is preferably 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 the carboxylic acid, such
as tartaric acid, and the salt of the carboxylic acid, such as
diammonium tartrate, Rochelle salt, and sodium tartrate. Among
these complexing agents, tartaric acid and diammonium tartrate are
preferred, and diammonium tartrate is more preferred. The
complexing agent may be used alone, or two or more kinds thereof
may be used in combination. The content of the carboxylic acid or
the salt thereof in the plating solution of the present invention
is not particularly limited, and is, for example, 0.1 to 90 g/L,
and preferably 1 to 60 g/L. In the present invention, a hydroxy
group in the carboxy group is not counted as the hydroxy group.
[0028] In the case where the conductive salt of the plating
solution of the present invention is a sulfate, furthermore, a
carboxylic acid having two or more carboxy groups and 4 or more
carbon atoms or a salt thereof is preferably used in combination
with the complexing agent. Examples of the carboxylic acid having
two or more carboxy groups and 4 or more carbon atoms or a salt
thereof include a carboxylic acid, such as adipic acid, phthalic
acid, pimelic acid, and sebacic acid, and salts of the carboxylic
acids. The complexing agent may be used alone, or two or more kinds
thereof may be used in combination, and phthalic acid and/or adipic
acid are preferred. The content of the carboxylic acid having two
or more carboxy groups and 4 or more carbon atoms or a salt thereof
in the plating solution of the present invention is not
particularly limited, and the carboxylic acid having two or more
carboxy groups and 4 or more carbon atoms or a salt thereof may be
used as a part of the carboxylic acid having two or more hydroxy
groups and two or more carboxy groups or a salt thereof within the
range of the content thereof. The use of the carboxylic acid having
two or more carboxy groups and 4 or more carbon atoms or a salt
thereof enhances the corrosion resistance without a chromate
treatment described later performed.
[0029] In the case where the conductive salt of the plating
solution of the present invention is a sulfate, furthermore, a
sulfur-containing organic compound is preferably contained. The
sulfur-containing organic compound used in the plating solution of
the present invention is not particularly limited, and examples of
which include saccharin or a salt thereof, a sulfur-containing
organic compound having an allyl group, a carboxylic acid having a
carbamimidoylthio group and a dehydration reaction product thereof,
thiourea, and sodium thiocyanate.
[0030] Examples of the saccharin or a salt thereof include
saccharin and sodium saccharate. Among these, sodium saccharate is
preferred.
[0031] Examples of the sulfur-containing organic compound having an
allyl group include sodium allylsulfonate, allylthiourea, ammonium
2-methylallylsulfonate, and allyl isothiocyanate. Among these,
sodium allylsulfonate and/or allylthiourea are preferred.
[0032] Examples of the carboxylic acid having a carbamimidoylthio
group and a dehydration reaction product thereof include a
carboxylic acid having a carbamimidoylthio group represented by the
general formula (1) and a dehydration reaction product of a
carboxylic acid having a carbamimidoylthio group represented by the
general formula (2).
##STR00001##
[0033] In the formula (1), n represents an integer of 1 to 5,
preferably 1 to 2.
##STR00002##
[0034] In the formula (2), m represents an integer of 1 or 2.
[0035] Specific examples of the carboxylic acid having a
carbamimidoylthio group and a dehydration reaction product thereof
include [[amino(imino)methyl]thio]acetic acid,
3-[[amino(imino)methyl]thio]propanoic acid,
2-iminothiazolidin-4-one, and
2-amino-5,6-dihydro-4H-1,3-thiazin-4-one.
[0036] The sulfur-containing organic compound may be used alone, or
two or more kinds thereof may be used in combination. Among the
sulfur-containing organic compounds, a combination of saccharin or
a salt thereof and one or more kind selected from the group
consisting of a sulfur-containing organic compound having an allyl
group and a carboxylic acid having a carbamimidoylthio group and/or
a dehydration reaction product thereof is preferred, and a
combination of sodium saccharate and sodium allylsulfonate is
particularly preferred. The content of the sulfur-containing
organic compound in the plating solution of the present invention
is not particularly limited, and is, for example, 0.5 to 10 g/L,
and preferably 2 to 8 g/L.
[0037] In the case where the conductive salt of the plating
solution of the present invention is a sulfate, it is particularly
preferred that a carboxylic acid having two or more hydroxy groups
and two or more carboxy groups or a salt thereof is used as the
complexing agent, and a combination of saccharin or a salt thereof
and one or more kind selected from the group consisting of a
sulfur-containing organic compound having an allyl group and a
carboxylic acid having a carbamimidoylthio group and/or a
dehydration reaction product thereof is used as the
sulfur-containing organic compound.
[0038] The preparation method of the plating solution of the
present invention described above is not particularly limited, and
the plating solution may be prepared, for example, in such a manner
that the trivalent chromium compound, the complexing agent, the
conductive salt, and the pH-buffering agent are added to water at
40 to 60.degree. C. and mixed and dissolved therein, then the
organic compound having 2-4 carbon atoms and three or more chloro
groups and depending on necessity the sulfur-containing organic
compound are added thereto and mixed therein, and finally the pH is
regulated with sulfuric acid, aqueous ammonia, or the like.
[0039] The plating solution of the present invention can provide a
chromium plating on an article to be plated by electroplating the
article to be plated with the plating solution of the present
invention, similarly to the ordinary chromium plating solution.
Further, corrosion resistance is enhanced by the
electroplating.
[0040] The condition of the electroplating is not particularly
limited, and the electroplating may be performed, for example, at a
bath temperature of 30 to 60.degree. C., with an anode formed of
carbon or iridium oxide, at a cathode current density of 2 to 20
A/dm.sup.2, for 1 to 15 minutes.
[0041] 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.
[0042] In the case where the article to be plated is subjected to a
nickel plating treatment, three layers or four layers of nickel
plating layers are preferably provided by the ordinary method. In
the case of three layers, a semibright nickel plating, a bright
nickel plating, and a microporous nickel plating may be provided in
this order. In this case, the potential differences among the
layers are not particularly limited, and for example, it is
preferred that the potential difference of the bright nickel
plating is -200 to -60 mV with respect to the semibright nickel
plating, and the potential difference of the microporous nickel
plating is 20 to 100 mV with respect to the bright nickel plating.
In the case of four layers, a semibright nickel plating, a high
sulfur content nickel plating, a bright nickel plating, and a
microporous nickel plating may be provided in this order. In this
case, the potential differences among the layers are not
particularly limited, and for example, it is preferred that the
potential difference of the bright nickel plating is -200 to -60 mV
with respect to the semibright nickel plating, the potential
difference of the high sulfur content nickel plating is -50 to -5
mV with respect to the bright nickel plating, and the potential
difference of the microporous nickel plating is 20 to 100 mV with
respect to the bright nickel plating.
[0043] The chromium plated product thus obtained has enhanced
corrosion resistance. The enhancement of the corrosion resistance
herein means that the rating number (R. N.) is enhanced in the
evaluation according to JIS H8502.
[0044] The chromium plating may be further subjected to a chromate
treatment, and thereby the corrosion resistance is further
enhanced.
[0045] The condition of the chromate treatment is not particularly
limited, and for example, electroplating may be performed at a bath
temperature of 25 to 70.degree. C., with an insoluble anode, such
as a lead-tin alloy, as an anode, at a cathode current density of
0.1 to 1 A/dm.sup.2, for 1 minute.
EXAMPLES
[0046] The present invention will be described in detail with
reference to examples below, but the present invention is not
limited to the examples.
Examples 1 to 5
Trivalent Chromium Plating
[0047] The trivalent chromium compound, the complexing agent, the
conductive salt, and the pH-buffering agent shown in Table 1 were
added to water at 60.degree. C. and mixed and dissolved therein,
then the organic compound having 2-4 carbon atoms and three or more
chloro groups and the sulfur-containing organic compound were added
thereto and mixed therein, and finally the pH was regulated with
sulfuric acid, aqueous ammonia, or the like, thereby preparing a
trivalent chromium plating solution. A chromium plating was formed
on an article of an ABS resin having formed thereon a copper
plating ("CU-BRITE EP-30", produced by JCU Corporation), a
semibright nickel plating ("CF-24T", produced by JCU Corporation),
a bright nickel plating ("HI-BRITE #88", produced by JCU
Corporation), and a microporous nickel plating ("MP-NI 308",
produced by JCU Corporation) under condition of the bath
temperature shown in Table 1 and a current density of 10 A/dm.sup.2
for 3 minutes, so as to provide a test piece. The test piece was
subjected to a CASS test (JIS H8502). The micrographs of the test
pieces after the CASS test for 80 hours are shown in FIGS. 1 and 2.
The rating numbers (R. N.) shown in the figures are evaluation in
terms of total corrosion rate. The chromate treatment was performed
with "EBACHRO-500", produced by JCU Corporation, under condition of
a bath temperature of 40.degree. C. and a cathode current density
of 0.2 A/dm.sup.2 for 1 minute.
TABLE-US-00001 TABLE 1 Example Example Example Example Example
Comparative Comparative Reference Composition of plating solution 1
2 3 4 5 Example 1 Example 2 Example Basic chromium sulfate g/L 64
64 64 64 64 64 64 -- Chromium anhydride g/L -- -- -- -- -- -- --
250 Sulfuric acid (98%) g/L -- -- -- -- -- -- -- 2.5 Malic acid g/L
15 -- -- -- -- 15 -- -- Diammonium tartrate g/L -- 30 30 30 30 --
30 -- Adipic acid g/L -- -- -- 1 -- -- -- -- Sodium sulfate g/L 35
-- -- -- -- 35 -- -- Potassium sulfate g/L 140 150 150 150 150 --
150 -- Ammonium sulfate g/L 30 20 20 20 20 30 20 -- Boric acid g/L
90 80 80 80 80 90 80 -- Sodium saccharate g/L 2.5 4 4 4 4 2.5 4 --
Thiourea mg/L 10 -- -- -- -- 10 -- -- Sodium allylsulfonate (36%)
mL/L -- 2 2 2 2 -- 2 -- Chloral hydrate (810 g/L) mL/L 0.1 0.1 0.1
0.1 -- -- -- -- Trichloroethylene mL/L -- -- -- -- 26 -- -- -- pH
of plating solution 3.4 3.4 3.4 3.4 3.4 3.4 3.4 -- Bath temperature
.degree. C. 60 55 55 55 55 60 45 40 Chromate treatment no no yes no
no no yes --
[0048] It was understood from the results of the CASS test that the
addition of the organic compound having 2-4 carbon atoms and three
or more chloro groups to the trivalent chromium plating solution
enhanced the corrosion resistance. Some of the plating solutions of
the present invention provided a high corrosion resistant film
without the chromate treatment performed.
Examples 6 to 8
Trivalent Chromium Plating
[0049] The trivalent chromium compound, the complexing agent, the
conductive salt, and the pH-buffering agent shown in Table 2 were
added to water at 60.degree. C. and mixed and dissolved therein,
then the organic compound having 2-4 carbon atoms and three or more
chloro groups and the sulfur-containing organic compound were added
thereto and mixed therein, and finally the pH was regulated with
sulfuric acid, aqueous ammonia, or the like, thereby preparing a
trivalent chromium plating solution. A chromium plating was formed
on an article of an ABS resin having formed thereon a copper
plating ("CU-BRITE EP-30", produced by JCU Corporation), a
semibright nickel plating ("CF-24T", produced by JCU Corporation),
a bright nickel plating ("HI-BRITS #88", produced by JCU
Corporation), and a microporous nickel plating ("MP-NI 308",
produced by JCU Corporation) under condition of the bath
temperature shown in Table 2 and a current density of 10 A/dm.sup.2
for 3 minutes, so as to provide a test piece. The test piece was
subjected to a CASS test (JIS H8502). The micrographs of the test
pieces after the CASS test for 80 hours are shown in FIG. 3. The
rating numbers (R. N.) shown in the figure are evaluation in terms
of total corrosion rate. The results are also shown in Table 2.
TABLE-US-00002 TABLE 2 Composition of plating Example Example
Example Comparative solution 6 7 8 Example 3 Basic chromium sulfate
g/L 19.5 19.5 19.5 19.5 Diammonium tartrate g/L 3 3 3 3 Potassium
sulfate g/L 150 150 150 150 Boric acid g/L 70 70 70 70 Sodium
saccharate g/L 3 3 3 3 [[amino(imino)methyl] 50 -- 20 50
thio]acetic acid mg/L 2-Iminothiazolidin-4-one -- 50 30 -- mg/L
Chloral hydrate (810 g/L) 0.25 0.25 0.25 -- mL/L pH of plating
solution 3.7 3.7 3.7 3.7 Bath temperature .degree. C. 55 55 55 55
Chromate treatment no no no no Rating number (R. N.) 9 9 9 8
[0050] It was understood from the results of the CASS test that the
corrosion pitting was smaller in Example 6 than in Comparative
Example 3. The similar result was obtained in Examples 7 and 8. It
was understood therefrom that the addition of the organic compound
having 2-4 carbon atoms and three or more chloro groups to the
trivalent chromium plating solution enhanced the corrosion
resistance.
Example 9
Trivalent Chromium Plating Bath
[0051] The trivalent chromium compound, the complexing agent, the
conductive salt, and the pH-buffering agent shown in the following
compositions 1 to 3 were added to water at 50.degree. C. and mixed
and dissolved therein, then the organic compound having 2-4 carbon
atoms and three or more chloro groups was added thereto and mixed
therein, and finally the pH was regulated with hydrochloric acid,
aqueous ammonia, or the like, thereby preparing a trivalent
chromium plating solution.
<Composition 1>
TABLE-US-00003 [0052] Basic chromium sulfate 64 g/L Ammonium
formate 16 g/L Potassium chloride 165 g/L Ammonium chloride 100 g/L
Ammonium bromide 6 g/L Boric acid 67 g/L Chloral hydrate (810 g/L)
0.1 mL/L
<Composition 2>
TABLE-US-00004 [0053] Basic chromium sulfate 64 g/L Ammonium
formate 16 g/L Sodium chloride 75 g/L Potassium chloride 165 g/L
Ammonium chloride 100 g/L Ammonium bromide 6 g/L Boric acid 67 g/L
Chloral hydrate (810 g/L) 0.1 mL/L
<Composition 3>
TABLE-US-00005 [0054] Basic chromium sulfate 64 g/L Ammonium
tartrate 30 g/L Potassium sulfate 150 g/L Ammonium sulfate 20 g/L
Boric acid 80 g/L Chloral hydrate (810 g/L) 0.1 mL/L
Examples 10 and 11
Trivalent Chromium Plating
[0055] The trivalent chromium compound, the complexing agent, the
conductive salt, and the pH-buffering agent shown in Table 3 were
added to water at 60.degree. C. and mixed and dissolved therein,
then the organic compound having 2-4 carbon atoms and three or more
chloro groups was added thereto and mixed therein, and finally the
pH was regulated with hydrochloric acid or aqueous ammonia, thereby
preparing a trivalent chromium plating solution. A chromium plating
was formed on an article of an ABS resin having formed thereon a
copper plating ("CU-BRITE EP-30", produced by JCU Corporation), a
semibright nickel plating ("CF-24T", produced by JCU Corporation),
a bright nickel plating ("HI-BRITE #88", produced by JCU
Corporation), and a macroporous nickel plating ("MP-NI 308",
produced by JCU Corporation) under condition of the bath
temperature shown in Table 3 and a current density of 10 A/dm.sup.2
for 3 minutes, so as to provide a test piece. The test piece was
subjected to a CASS test (JIS H8502). The rating numbers (R. N.)
after the CASS test for 80 hours are evaluation in terms of total
corrosion rate. The results are also shown in Table 3. The chromate
treatment was performed with "EBACHRO-500", produced by JCU
Corporation, under condition of a bath temperature of 40.degree. C.
and a cathode current density of 0.2 A/dm.sup.2 for 1 minute.
TABLE-US-00006 TABLE 3 Composition of plating Example Example
Comparative Comparative solution 10 11 Example 4 Example 5 Basic
chromium sulfate 64 64 64 64 g/L Ammonium formate g/L 16 16 16 16
Sodium chloride g/L 70 70 70 70 Potassium chloride g/L 140 140 140
140 Ammonium chloride g/L 85 85 85 85 Ammonium bromide g/L 6 6 6 6
Boric acid g/L 67 67 67 67 Chloral hydrate 0.8 0.8 -- -- (810 g/L)
mL/L pH of plating solution 2.7 2.7 2.7 2.7 Bath temperature
.degree. C. 32 32 32 32 Chromate treatment no yes no yes Rating
number (R. N.) 9 9.3 8 9
[0056] It was understood from the results of the CASS test that the
addition of the organic compound having 2-4 carbon atoms and three
or more chloro groups to the trivalent chromium plating solution
enhanced the corrosion resistance.
INDUSTRIAL APPLICABILITY
[0057] The trivalent chromium plating solution of the present
invention can be applied to various purposes similarly to a plating
using hexavalent chromium.
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