Note: Descriptions are shown in the official language in which they were submitted.
lZ9913S
The present invention relates to a process for elec-
trolytically coloring aluminum or an aluminum alloy hereafter
generally called "aluminum material~, in which, firstly, the
aluminum material is sub;ected to an anodizing treatment to
form an anodized aluminum material, and, secondly, the
anodized aluminum material is subjected to an electrolytic
coloring treatment simply by adjusting electrolytic
conditions, and thereby there is produced on the anodized
surface thereof a desired color ranging from any gray of a
gray series through the gray series, to black.
In U.S. Pat~nt No. 3,382,160 there is disclosed a
~ h~s beer~
'~ process in which after the aluminum material ~ subjected to
an electrolytic treatment in a sulfuric acid bath so as to
form an anodic coating thereon, the resultant anodized alu-
minum material is sub;ected to an electrolytic treatment in an
electrolytic coloring bath containing such metallic salts as a
nickel salt, a cobalt salt, or a stannous salt such that such
salts may be pr0cipitatad in innumerable fine pores of the
anodic coating thereof to produce a bronze color series
thereon.
This electrolytic coloring of the anodized aluminum
material is called a "secondary electrolytically coloring pro-
cess" and has been widely used for manufacturing colored alu-
minum material products for building, construction and other
applications. However, all of the colored aluminum products
obtained industrially by using various types of conventional
electrolytic coloring baths as mentioned above have only lim-
ited colors or tints ranging from a bronze series to black,
and consequently cannot meet the latest demand for diversified
or varied colored alumin~m products.
The present invention provides for an improvement in
electrolytic coloring bath compositions for achieving not only
-- 1 --
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improvement in the corrosion resisting properties and
abrasion resisting properties of aluminum products, but also
obtaining varied colored aluminum products. According to the
present invention the so-called second~ electrolytic
treatment is carried out using an electrolytic coloring hath
containing a combination of a nickel salt and a zinc salt, as
an essential coloring agent, preferably, in a specific weight
ratio thereo~, of l.0 to 0~5, additionally containing
chelating reagent for nickel ions and a suitable supporting
electrolyte.
According to the present invention there is
provided a process for electrolytically coloring an aluminum
material substrate comprising: (a) anodizing an aluminum
material substrate; (b) introducing said anodized aluminum
material into a bath comprising a nickel salt, a zinc salt, a
chelating reagent for nickel ions and magnesium sulfate, at a
pH of 4.5 or greater, and in which the compounding ratio of
nickel salt to zinc salt is 1:0.1 to 0.5; and (c)
electrolyzing said substrate.
Thus, according to the pre~ent invention, firstly
an aluminum material is subjected to an anodic treatment to
~em an anodic coating thereon, and, secondly, the resultant
anodized aluminum material is subjected to an electrolytic
coloring treatment in an electrolytic coloring bath
containing, as principal constituents, a nickel salt,
preferably, nickel sulfate, ammonium nickel sulfate, or
nickel sulphamate, and a zinc salt, preferably zinc sulfate
or zinc chloride, and additionally containing, as a chelating
reagent for nickel ions at least one type selected from the
group comprising gluconic
1299135
acid, malonic acid, sulfosalicylic acid, tartaric acid, citric
aci.d, sulfophthalic acid, sulfamlc acid and boric acid and as
a supporting electrolyte, ammonium sulfate and magnesium sul-
fate and adjusted to a pH of at least 4.5, so that the precip-
itated and dispersed degree of particles of the nickel salt
into the fine pores of the anodic coating can be increased,
and thereby there can be produced varied colored aluminum
products having such a color range of from a gray series
including a pure gray or a gray slightly tinged with blusish
green to black which range it has not been possible to produce
using the conventional electrolytic coloring process. In
addition, it has also been found that the corrosion resisting
properties of the colored coating of the aluminum product thus
r ~
produced io better than those of the colored aluminum product
having the bronze series colored coating obtained by the
conventional process as above, and the abrasion resisting
properties and the covering power produced by the process are
also excellent as compared with the conventional processes.
' " c ~- e lq ,l, .,~ .~
The term "mas]~ing reagent" for nickel ions has the
same meaning as that used in analytical chemistry, and refers
to any chemical compound that acts to stabilize nickel ions in
the base so that electrolytic deposition speed of nickel ions
may be appropriate when the nickel ions are deposited together
with the electrolytic deposition of the zinc ions as described
below.
Further, the nickel salt and the zinc salt consti-
tuting the principal constituents of the bath act to give to
the aluminum material a desired color selected from the colors
or tints in the range of from a gray series to black as a
result of being with the progress of the deposition thereof in
the fine pores of the anodic coating of the aluminum material
at the time of the secondary electrolytic coloring treatment.
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In this case, when a small amo~mt of molybdate is added
to the principal coloring constituents, this acts to assist
in giving the gray series to the aluminum material while the
secondary electrolytic treatment is being carried out.
Accordingly, it is effective to add, as the principal
constituents, in a bath a small amount of molybdate, such as
ammonium molybdate, beside the nickel salt and the zinc salt.
For carrying out the secondary electrolytic treatment,
there is used a direct current, an alternating current of
dual currents of ~C and DC. It has been found preferable
that the voltage used be about 10-30 V, and the bath
temperature about 15-30C.
When the pH value of the electrolytic coloring bath is
adjusted to below 4.5, it becomes difficult to effect the
codeposition of the metals into the fine pores of the anodic
coating, and consequently the coloring effect of this
invention cannot be fully obtained. Accordingly, it is
desirable that the pH value should be adjusted to be kept
above 4.5, and preferably within the range of 5-9.
The reason why the colored coating of aluminum material
ranging from a simple gray through a gray series to black
which has excellent corrosion resisting properties can be
obtained by the process of the present invention is
considered to be as follows:-
Aluminum itself is an extremely basic metal, and has a
strong negative polarity automatically at the time of use in
the electrolytic treatment. Accordingly, metallic positive
ions in the bath are strongly attracted to the aluminum,
while forming a concentration gradient thereof in the bath.
In this sense, the secondary electrolytic coloring process is
similar to a plating technique, and according to detailed
reports (Electrochemistry 45, No. 2, 1977 and 47 No. 2, 1979
129913S
by Mr. Kurachi Mitsuo et al. on codeposition from a plating
ba-th containing, as its princlpal constituents, nickel sulfate
and zinc sulfate, but adjusted to p~ 2-4, there is some
description relating to the codeposition of the nickel and
zinc metals, but there can hardly be obtained gray colored
plated products.
According to this invention, in spite of the fact
that where the electrolytic coloring bath is so prepared as to
contain a nickel salt and a zinc salt in the concentration
ratio of 1:0.25 and to adjust its pH to 6.5, for instance, it
has been found by a chemical analysis that the ratio or
deposited nickel metal and deposited zinc metal in the fine
pores or cells of the anodic coating of the aluminum material
w2~ 1:1 (atomic ratio) as a result of applying to the forego-
ing bath an alternating current at 14 v for 3 minutes, and a
gray colored aluminum product is obtained. From the above, it
is considered that on the codeposition of the zinc and nickel,
the deposition of zinc is superior to the deposition of
nickel, and when the AC electrolysis is further continued or
the deposition condition is properly ad~usted, the deposition
rate of the zinc is further increased and at the same tlme the
dispersibility of nickel salt is increased, and thereby a
desired varied color of a gray series can be obtained
adjustably.
Mr. Kurachi Mitsuo et al. reported his study about
the codeposited materials in the foregoing reports, in which
he presumed that they are intermetallic compounds, such as
NiZn3 or Ni5Zn21, and also in the foregoing process of this
invention these intermetallic compounds are considered to be
contained among such materials deposited in the anodic coating
that give thereto varied colors in the range of from a gray
series to black of this invention.
1299~5
The corrosion resisting properties of the colored
aluminum material obtained by the process of the present
invention are better than-~ha~ of the colored aluminum
material obtained by the conventional nickel salt electrolytic
bath. This is considered to be due to the fact that the
C~, ~ /" ,!, "~
presence of the m~6~-lng reagent for nickel ions in the bath
causes the zinc to deposit preferentially on the anodic
coating of the aluminum and protect the aluminum from
corrosion. The inventor has made a CASS anticorrosion test
according to JIS - H 8681, on the colored aluminum product
obtained by the process of this invention and the colored
aluminum product obtained by the conventional nickel salt
electrolytic bath, for 8 hours, 16 hours, 24 hours and 32
hours to obtain the results as shown in the following Table 1.
Each sample to be tested was 9 microns in coating thickness,
and the secondary electrolytic treatment for producing each
sample was carried out at 15 V of AC, for 3 minutes.
Table 1
CASS test time ¦ Bath of the process Conventional bath
of the present invention
8 hours R.N. 10 R.N. 10
16 hours R.N. 10 R.N. 10
24 hours R.N. 10 R.N. 9.8
32 hours ~ R.N. 10 R.N. 9.5
"R.N." stand for Rating Number.
It is appreciated from the results of Table 1 that
the colored aluminum material obtained by the process of this
invention was R.N. 10, even after 32 hours from the starting
of the test, and did not display any corrosion, whereas the
conventional one was R.N ! 9 . 8 after the lapse of time of 24
hours and displayed a slight corrosion, and thus the corrosion
~299~35
thereof was advanced with time.
The present invention will be further illustrated by way
of the following Examples.
Example 1
A sheet of 2S aluminum material was subjected to an
anodic treatment by a conventional method, for instance, in
sulfuric acid bath containing 15% by weight of sulfuric acid
at ambient temperature for 30 to 50 minutes, with a direct
current, to form thereon an anodic coating of 10 ~m in
thickness. Then, with nickel as the other polarity
electrode, the same was subjected to an AC secondary
electrolytic treatment in an electrolytic coloring bath (pH
6.5) comprising 30 g/~ of boric acid, 20 g/~ of nickel
sulfate, 6 g/Q of zinc sulfate, 25 g/Q of magnesium sulfate
and 40 g/Q of a~monium sulfate. There was produced a light
gray colored aluminum material finish at 17 V, for 2 minutes,
a slight blue-greenish gray colored one at the same voltage,
for 4 minutes, and a black colored one at 15 V for 12
minutes, respectively.
Example 2
A 43S aluminum material was subjected to an anodic
treatment in a sulfuric acid bath by the conventional method
as above to form thereon an anodic coating of 15 ~m in
thickness. Then, with carbon as the other polarity
electrode, the same was subjected to an AC secondary
electrolytic treatment in an electrolytic coloring bath (pH
7.3) comprising 20 g/~ of sulfamic acid, 25 g/~ of nickel
sulfamate, 5 g/~ of zinc chloride, 0.5 g/~ of ammonium
molybdate, 25 g/Q of magnesium sulfate and 30 g/~ of ammonium
p
~2991~5
sulfate. There was produced a light gray colored aluminum
material finish at 17 V for 30 seconds, a gray colored one at
the same voltage as above for 1 minute, a deep gray colored
one at the same voltage for 3
1299135
minutes, and a black colored one at 14 v for 13 minutes.
Example 3
An _ l,lO0 P - H 24 aluminum material was subjected
to an anodic treatment in a sulfuric acid bath by a conven-
tional method to form an anodic coating of 10 microns in
thickness. Then, with nickel as the other polarity electrode,
nr.~ I~e r I C~ I
,~^ the ~a~e was subjected to an AC secondary electrolytic
treatment in a coloring electrolytic bath (pH 7.8) comprising
20 g/Q of sulfosalicylic acid, 20 g/~ of nickel sulfate, 4
g/Q of zinc sulfate, 25 g/~ of magnesium sulfate and 40 g~R
of ammonium sulfate.
As a result, there was produced a light gray colored
aluminum material finish at 15 V for l minute, a simple gray
colored one at the same voltage as above for 2 minutes, a
slight blue-greenish deep gray colored one at the same voltage
for 3 minutes and a black colored one at the same voltage for
12 minutes.
Example 4
An _ 6,063S - T 5 aluminum material was subjected to
an anodic treatment in a sulfuric acid bath by a conventional
method to form an anodic coating of 15 micron thickness.
~ er ~
Then, with nickel as the other polarity electrode, the ~
was sub;ected to an AC secondary electrolytic treatment in an
electrolytic coloring bath (pH 5.3) comprising 15 g/~ of sul-
fophthalic acid 30 g/~ of nickel sulfate, 6 g~ of zinc sul-
fate, 30 g/~ of magnesium sulfate and 25 g/~Q of ammonium
sulfate. As a result, there was produced a simple gray
colored aluminum material finish at 18 V for 2 minutes, and a
black colored one at the same voltage as above for ten
minutes.
Example 5
The same aluminum material as used in Example 4 was
1299~35
used and the same was treated with the same manner as in
Example 4 except for that the anodized aluminum materlal was
subjected to a DC secondary electrolytic treatment at 10 V for
40 seconds. A colored aluminum material finish having gray
tinged with slight blue-green was obtained.
Example 6
A 2S aluminum material was sub;ected to an anodic
treatment in a sulfuric acid bath by a conventional method to
form an anodic coating of about 14 ~m in thickness. Then,
f er ~
with carbon as the other polarity electrode, the~e was sub-
jected to a secondary electrolytic treatment at an AC and DC
double currents in an electrolytic coloring bath (pH 7.5) com-
prising 30 g/~ of gluconic acid, 25 g/~ of nickel sulfate,
15 g/~ of ammonium sulfate, 25 g/JQ of magnesium sulfate and
5 g/~ of zinc sulfate. As a result, there was produced a
blue-greenish gray colored aluminum material finish at 10 V
for 2 minutes and a simple gray colored one at 12 V for 2
minutes and a black colored one at 14 V for 7 minutes.
