EP1207221A1 - Method for electrolytic coloring of aluminum material - Google Patents
Method for electrolytic coloring of aluminum material Download PDFInfo
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- EP1207221A1 EP1207221A1 EP00939163A EP00939163A EP1207221A1 EP 1207221 A1 EP1207221 A1 EP 1207221A1 EP 00939163 A EP00939163 A EP 00939163A EP 00939163 A EP00939163 A EP 00939163A EP 1207221 A1 EP1207221 A1 EP 1207221A1
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- Prior art keywords
- coloring
- voltage
- aluminum material
- current
- alternating current
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/04—Anodisation of aluminium or alloys based thereon
- C25D11/18—After-treatment, e.g. pore-sealing
- C25D11/20—Electrolytic after-treatment
- C25D11/22—Electrolytic after-treatment for colouring layers
Definitions
- This invention relates to a process for electrolytically coloring an aluminum material consisting of anodized aluminum or an anodized aluminum alloy (hereinafter simply referred to as "aluminum material"); more particularly, this invention relates to a process for electrolytically coloring an aluminum material which can attain uniformity in color tone during alternating current electrolytic coloring and, still more, to a process for electrolytically coloring an aluminum material which can keep the color tone from changing irregularly not only in a given energizing lot but also in different energizing lots during electrolytic coloring thereby producing an aluminum material colored in a uniform tone.
- aluminum material an aluminum material consisting of anodized aluminum or an anodized aluminum alloy
- An aluminum material is used frequently in many areas such as construction materials, vehicle parts and furniture on account of its good processability and corrosion resistance and, for the purpose of enhancing the aesthetic effect of the material, electrolytic coloring has been practiced wherein an aluminum material is subjected to electrolysis in an electrolyte containing a soluble salt of metal such as Ni, Co, Cu, and Sn thereby causing the electrolysis product of the metal salt to deposit in the porous anodic oxide film.
- a soluble salt of metal such as Ni, Co, Cu, and Sn
- alternating current electrolytic coloring (Asada process) wherein an alternating current is passed through an electrolyte to effect electrolysis and direct current electrolytic coloring wherein a direct current is passed through an electrolyte.
- Ada process alternating current electrolytic coloring
- direct current electrolytic coloring wherein a direct current is passed through an electrolyte.
- This pretreatment prior to coloring by constant voltage electrolysis aims at eliminating irregular coloring by passing a direct current at constant voltage for a certain length of time thereby making the resistance of the anodic oxide film uniform in various parts and creating a condition for a relatively uniform current to flow through the oxide film during alternating current electrolytic coloring which follows the pretreatment; this process is commercially admissible in the cases in which an aluminum material is electrolytically colored in a relatively dark tone.
- Another process proposes the following procedure for electrolytic coloring of an aluminum material; a stable color tone is attained by repeating passage and stoppage of electric current in multiple stages intermittently and meanwhile setting the voltage successively higher from one stage to the subsequent stage [Japan Kokai Tokkyo Koho Hei 8-41,685 (1996)]. It is said that the process undoubtedly attains a stable color tone and additionally shortens the time required for coloring in black, and controls the influence of trace amounts of impurities thereby preventing white streak defects.
- Any of the aforementioned processes can attain a relatively stable color tone in a given energizing lot, but is unable to control irregularities in color tone in different energizing lots completely and, in consequence, produces with difficulty an aluminum material colored in a uniform tone in different energizing lots.
- alternating current electrolytic coloring which is effected by changing the total current density that is the sum total of the absolute values of positive and negative current densities of the current waveform stepwise from the first step to at least the fourth step [Japan Tokkyo Koho Hei 3-32,637 (1991)].
- This process can somehow manage to do as much as keeping the difference in color tone from becoming real in the case of electrlolytic coloring of an aluminum material in a relatively light tone.
- the present inventors have conducted studies to develop a process for producing an aluminum material colored in a uniform tone stably and commercially advantageously while preventing irregular coloring in different energizing lots as much as possible in alternating current electrolytic coloring and found that a uniform color tone can be attained in different energizing lots even in electrolytic coloring in a relatively light tone by performing a pretreatment prior to coloring that precedes alternating current electrolytic coloring until the voltage and current respectively reach the preset ultimate values.
- the bath voltage in the pretreatment prior to coloring is affected by the temperature and pH of the electrolytic coloring bath and, still more, by the water washing time and the pH of the water washing bath during the step for water washing of the anodized aluminum material before immersion in the electrolytic coloring bath (the aforementioned conditions are hereinafter collectively referred to as "the bath conditions") and the bath voltage changes with the bath conditions.
- the bath voltage in the pretreatment prior to coloring by constant current electrolysis is decided primarily by the resistance of the electrolytic coloring bath and the resistance of the anodic oxide film on the surface of aluminum material immersed in the bath.
- changes in the resistance of the electrolytic coloring bath from energizing lot to energizing lot are not very large, at most 0.1-0.2 V in terms of the corresponding voltage, changes in the bath voltage in the pretreatment prior to coloring are considered to be due chiefly to the resistance of the anodic oxide film.
- the anodic oxide film on the surface of aluminum material consists of the so-called "barrier layer” which is a fine aluminous layer formed on the aluminum substrate of an aluminum material and a porous layer formed on the barrier layer and the resistance of the anodic oxide film is practically that of the barrier layer.
- the efficiency for formation of the barrier layer in the pretreatment prior to coloring by constant current electrolysis is considered to be 60% or so in terms of apparent efficiency that is the ratio of the theoretical amount formed with the current efficiency assumed to be 100% to the actual amount increased with the dissolution of the barrier layer taken into account (amount increased/theoretical amount formed).
- apparent efficiency changes under the influence of the bath conditions like the aforementioned bath voltage in the pretreatment prior to coloring; as a result, the resistance of the anodic oxide film on the surface of aluminum material changes from energizing lot to energizing lot.
- the present inventors have conducted studies to find a commercially adequate solution to the aforementioned problem, found that the thickness of the barrier layer of the anodic oxide film to be formed and adjusted in the pretreatment prior to coloring is dependent on the ultimate voltage and current to be reached finally in the pretreatment, for example, the thickness in question is proportional to the ultimate voltage in the case of the pretreatment prior to coloring by constant current electrolysis, and, as a result, the thickness of the barrier layer is directly related to the color tone given to the aluminum material by alternating current electrolytic coloring, and completed this invention.
- an object of this invention is to provide a process for electrolytically coloring an aluminum material which is capable of preventing as much as possible irregularities in coloring not only in a given energizing lot but also in different energizing lots in alternating current electrolytic coloring of an aluminum material and producing an aluminum material colored in a uniform tone stably and easily on a commercial scale.
- this invention relates to an improved process for electrolytically coloring an aluminm material which comprises performing said pretreatment prior to coloring until the voltage and current respectively reach the preset ultimate voltage and current.
- a particularly desirable mode of execution of the process for electrolytically coloring an aluminum material comprises performing a pretreatment prior to coloring by constant current electrolysis wherein a direct current is passed until the voltage reaches the ultimate value while maintaining the current at the preset ultimate value and then performing alternating current electrolytic coloring wherein a voltage-controlled alternating current waveform that has the peak voltage 0.55-0.8 times the final voltage in the pretreatment prior to coloring by constant current electrolysis is passed through the aluminum material.
- an aluminum material to be electrolytically colored in this invention there is no specific restriction on an aluminum material to be electrolytically colored in this invention and, as in the conventional anodizing, a direct current, an alternating current, or an alternating current superimposed on a direct current is passed through an electrolytic bath containing an aqueous solution of acid such as sulfuric acid, oxalic acid, sulfonic acid, and chromic acid with an aluminum raw material consisting of ordinary aluminum or an aluminum alloy serving as the anode to form an anodic oxide film on the surface of the aluminum raw material.
- acid such as sulfuric acid, oxalic acid, sulfonic acid, and chromic acid
- Soluble metal salts include inorganic salts such as sulfates, nitrates, phosphates, chlorides, and chromates and organic salts such as oxalates, acetates, and tartrates of metals such as nickel (Ni), cobalt (Co), copper (Cu), tin (Sn), chromium (Cr), magnesium (Mg), iron (Fe), cadmium (Cd), titanium (Ti), manganese (Mn), molybdenum (Mo), calcium (Ca), vanadium (V), lead (Pb), and zinc (Zn).
- Soluble metal salts include inorganic salts such as sulfates, nitrates, phosphates, chlorides, and chromates and organic salts such as oxalates, acetates, and tartrates of metals such as nickel (Ni), cobalt (Co), copper (Cu), tin (Sn), chromium (Cr), magnesium
- dithionites such as sodium dithionite and zinc dithionite
- thiosulfates such as ammonium thiosulfate and sodium thiosulfate
- hydrogen sulfites such as sodium hydrogen sulfite, sulfurous acid
- sulfites such as sodium sulfite, thioglycolic acid
- thioglycolates such as ammonium thioglycolate.
- the pretreatment prior to coloring preceding alternating current electrolytic coloring in this invention is performed by immersing an aluminum material in the electrolytic coloring bath, passing a direct current waveform (that is, direct current or an alternating current superimposed on a direct current) with the aluminum material serving as the anode, and completing the operation at the point when the voltage (the peak voltage in case the direct current waveform is that of an alternating current superimposed on a direct current) and the current respectively reach the preset ultimate values.
- a direct current waveform that is, direct current or an alternating current superimposed on a direct current
- a concrete procedure is to pass a direct current while keeping the current at the preset value of ultimate current and terminate the pretreatment when the voltage reaches the preset value of ultimate voltage.
- the current flows preferentially to the portion where the barrier layer of the anodic oxide film on the surface of aluminum material is relatively thin and offers a low resistance and to the portion near the cathode where the resistance of the bath is low; the barrier layers either get compensated for small thickness or grow relatively thicker by the amount corresponding to the difference in resistance of the bath in these portions and a constant anodic current distribution is obtained when the voltage reaches the ultimate value.
- the ultimate voltage and current in the pretreatment prior to coloring varies with what color tone is required for the aluminum material as product; the ultimate voltage is preferably set at 30-50 V for electrolytic coloring in a relatively light tone or at 20-30 V for electrolytic coloring in a relatively dark tone and the ultimate current is preferably set in the range 20-50 A/m 2 .
- this invention Upon completion of the pretreatment prior to coloring in this manner, this invention performs alternating current electrolytic coloring in the same electrolytic coloring bath by passing an alternating current waveform or a superimposed AC-DC waveform through the aluminum material.
- the peak voltage of the alternating current waveform or superimposed AC-DC waveform in use is set at a value preferably 0.55-0.8 times, more preferably 0.65-0.75 times, the value of the preset ultimate voltage in the pretreatment prior to coloring. If the peak voltage is lower than 0.55 times, coloring does not occur or the rate of coloring becomes extremely low. On the other hand, if the peak voltage exceeds 0.8 times, the current becomes difficult to stay constant in alternating current electrolytic coloring and a uniform color tone cannot be obtained even if the time for treatment is fixed.
- making the color tone uniform is nothing less than making the current distribution in the aluminum material uniform when electrolytic coloring is performed with the aluminum material serving as the anode.
- the film resistance corresponding to the bath resistance in each part is generated and the current distribution of the aluminum material can be made constant and nearly uniform at the end of the pretreatment prior to coloring.
- the present inventors have found that the changes in film resistance in alternating current electrolytic coloring is dependent on and closely related to the ratio of the final voltage in the current-controlled pretreatment prior to coloring to the peak voltage of the alternating current waveform in alternating current electrolytic coloring. That is, the current-controlled pretreatment prior to coloring is performed first by passing a direct current while regulating the final voltage and then alternating current electrolytic coloring is performed in the same electrolytic coloring bath by passing a voltage-controlled alternating current waveform having the peak voltage 0.55-0.8 times the final voltage in the aforementioned current-controlled pretreatment prior to coloring and this procedure makes it possible to obtain a uniform current distribution corresponding to the changes in film resistance at the end of the pretreatment prior to coloring and obtain a uniform color tone.
- a preferable procedure is to scan the aluminum material pretreated and placed in the electrolytic coloring bath with alternating current voltage to plot a voltage-current curve, determine the boundary voltage E 0 that is the intersection of the respective extension lines of the flat region and the rising region in the curve, and set the peak voltage in alternating current electrolytic coloring at this boundary voltage E 0 .
- the boundary voltage E 0 thus determined is normally 0.65-0.75 times the ultimate voltage preset in the current-controlled pretreatment prior to coloring and, although varying somewhat with the conditions for the pretreatment prior to coloring or other conditions (such as treatment of anodic oxide film and the subsequent water washing), it can be determined unambiguously as a suitable peak voltage of an alternating current waveform or a superimposed AC-DC waveform.
- an electric current flows with ease in the parts near the counter electrode in the initial and intermediate stages of the pretreatment prior to coloring and the barrier layer grows there preferentially.
- the film resistance increases as the barrier layer grows and the ease of flow of the current in this part is held in check. That is, preferential growth of the barrier layer in the part where the current flows with ease in the pretreatment prior to coloring helps to eliminate the difference in site-dependent ease of current flow in alternating current electrolytic coloring thereby causing the current to flow with a nearly uniform current distribution over the whole surface of the aluminum material in a given energizing lot and eliminating irregularities in color tone in a given energizing lot.
- the aforementioned pretreatment prior to coloring is peformed until the voltage and current reach the preset ultimate values and, even if the bath conditions change in different energizing lots, the condition of the barrier layer finally adjusted by the pretreatment prior to coloring becomes constant in different energizing lots and the current flows with a nearly uniform current distribution over the whole surface of the aluminum material in different energizing lots and this eliminates irregularities in color tone in different energizing lots.
- Fig. 1 is a voltage-current curve plotted in the determination of the boundary voltage E 0 in Example 1.
- An aluminum raw material A6063S-T5
- 20% H 2 SO 4 at a current density of 100 A/m 2 for 30 minutes to form an anodic oxide film with a thickness of 10 ⁇ m on the surface of the aluminum raw material and then washed in an acid bath at pH 1 for 5 minutes to prepare an aluminum material.
- An electrolytic coloring bath composed of 25 g/l of CuSO 4 and 5 g/l of H 2 SO 4 was prepared and the aforementioned aluminum material was submitted to the current-controlled pretreatment prior to coloring with the aluminum material serving as the anode at a current density of 25 A/m 2 , a bath temperature of 25°C, and an ultimate voltage of 20 V for approximately 20 seconds.
- the pretreated aluminum material was scanned with alternating current voltage in the same coloring bath while raising the peak voltage from 0 V at a rate of 1 V/sec and a voltage-current curve was plotted.
- Alternating current electrolytic coloring was performed in the same coloring bath by setting the peak voltage of a commercial alternating current at this boundary voltage which is 14 V and passing the current for 50 seconds, 100 seconds, and 150 seconds to give the aluminum material electrolytically colored pink.
- the current-controlled pretreatment prior to coloring and alternating current electrolytic coloring were performed as in the aforementioned Example 1 except using the the conditions and the peak voltage of a commercial alternating current shown in Table 1 to give the electrolytically colored aluminum material.
- the constant voltage pretreatment prior to coloring was performed by placing the aluminum material as the anode, passing a direct current at a voltage of 15 V initially, switching the voltage over to 20 V thereafter at the point when the current density dropped to 32 A/m 2 , and continuing the operation until the final current density became 25 A/m 2 .
- Example 2 Upon completion of the constant voltage pretreatment prior to coloring, the material was scanned with commerical alternating current voltage in the same electrolytic coloring bath as in Example 1 and a voltage-current curve was plotted. The results are similar to those in Example 1 and the boundary voltage E 0 determined from the intersection of the respective extension lines of the flat and rising region was 14 V.
- Alternating current electrolytic coloring was performed in the same electrolytic coloring bath by setting the peak voltage of a commercial alternating current at this boundary voltage E 0 of 14 V and passing the current for 100 seconds to give the aluminum material electrolytically colored pink.
- the colored aluminum material was submitted to color measurement to examine the uniformity of color tone (color difference; ⁇ E * ab ) in a given energizing lot. The results are shown in Table 1.
- Example 1 The current-controlled pretreatment prior to coloring and alternating current electrolytic coloring were performed as in the aforementioned Example 1 except applying the peak voltage of a commercial alternating current shown in Table 1 and the electrolytically colored aluminum material thus obtained was examined for the uniformity of color tone as in Example 1. The results are shown in Table 1.
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Abstract
This invention relates to an improvement of a process for electrolytically
coloring an aluminum material comprising immersing an aluminum material
consisting of anodized aluminum or an anodized aluminum alloy in an
electrolytic coloring bath containing a soluble metal salt, performing a
pretreatment prior to coloring by passing a direct current waveform with said
aluminum material serving as the anode, and performing alternating current
electrolytic coloring in the same electrolytic coloring bath and the improved
process comprises performing said pretreatment prior to coloring until the
voltage and current respectively reach the preset ultimate values. It is possible
to prevent as much as possible an occurrence of irregular coloring not only in
one energizing lot but also in different energizing lots and produce an
aluminum material colored in a uniform tone stably and readily on a
commercial scale.
Description
This invention relates to a process for electrolytically coloring an
aluminum material consisting of anodized aluminum or an anodized
aluminum alloy (hereinafter simply referred to as "aluminum material");
more particularly, this invention relates to a process for electrolytically
coloring an aluminum material which can attain uniformity in color tone
during alternating current electrolytic coloring and, still more, to a process
for electrolytically coloring an aluminum material which can keep the color
tone from changing irregularly not only in a given energizing lot but also in
different energizing lots during electrolytic coloring thereby producing an
aluminum material colored in a uniform tone.
An aluminum material is used frequently in many areas such as
construction materials, vehicle parts and furniture on account of its good
processability and corrosion resistance and, for the purpose of enhancing the
aesthetic effect of the material, electrolytic coloring has been practiced wherein
an aluminum material is subjected to electrolysis in an electrolyte containing a
soluble salt of metal such as Ni, Co, Cu, and Sn thereby causing the
electrolysis product of the metal salt to deposit in the porous anodic oxide film.
The following processes are known for electrolytic coloring of an aluminum
material; alternating current electrolytic coloring (Asada process) wherein an
alternating current is passed through an electrolyte to effect electrolysis and
direct current electrolytic coloring wherein a direct current is passed through
an electrolyte. Each process has its own advantages and the former can utilize
a low-cost power source to reduce the equipment cost while the latter can
perform electrolytic coloring in a relatively short time and, in particular, is
known to attain sufficiently uniform coloring in the case of electrolytic coloring
in dark tone such as black.
A problem arises, however, in the aforementioned electrolytic coloring of an
aluminum material, particularly in the cases in which an aluminum material
has a complicated shape or aluminum materials of various shapes are treated
simultaneously; irregular coloring tends to occur in the depressed and
projected parts, the color tone lacks uniformity and deviates from the range
approved by clients, the product yield drops and, as a result, the product cost
runs up.
Such being the case, a variety of processes have been proposed to solve this
problem. For example, one of them performs a pretreatment of an aluminum
material prior to alternating current electrolytic coloring by passing a direct
current in the same electrolytic coloring bath with the aluminum material
used as the anode; constant voltage electrolysis is known as such wherein a
direct current is passed for a given length of time while maintaining the
voltage at a constant value [Japan Tokkyo Koho Sho 54-23,664 (1979)].
This pretreatment prior to coloring by constant voltage electrolysis aims at
eliminating irregular coloring by passing a direct current at constant voltage
for a certain length of time thereby making the resistance of the anodic oxide
film uniform in various parts and creating a condition for a relatively uniform
current to flow through the oxide film during alternating current electrolytic
coloring which follows the pretreatment; this process is commercially
admissible in the cases in which an aluminum material is electrolytically
colored in a relatively dark tone.
Another process proposes the following procedure for electrolytic coloring of
an aluminum material; a stable color tone is attained by repeating passage
and stoppage of electric current in multiple stages intermittently and
meanwhile setting the voltage successively higher from one stage to the
subsequent stage [Japan Kokai Tokkyo Koho Hei 8-41,685 (1996)]. It is said
that the process undoubtedly attains a stable color tone and additionally
shortens the time required for coloring in black, and controls the influence of
trace amounts of impurities thereby preventing white streak defects.
Any of the aforementioned processes can attain a relatively stable color
tone in a given energizing lot, but is unable to control irregularities in color
tone in different energizing lots completely and, in consequence, produces with
difficulty an aluminum material colored in a uniform tone in different
energizing lots.
This tendency to irregularity does not matter very much in electrolytic
coloring in a relatively dark tone, but becomes pronouced in electrolytic
coloring in a relatively light tone and poses a problem in commercial
production of an electrolytically colored aluminum material.
Another process proposed to solve the aforementioned problem is
alternating current electrolytic coloring which is effected by changing the total
current density that is the sum total of the absolute values of positive and
negative current densities of the current waveform stepwise from the first step
to at least the fourth step [Japan Tokkyo Koho Hei 3-32,637 (1991)]. This
process can somehow manage to do as much as keeping the difference in color
tone from becoming real in the case of electrlolytic coloring of an aluminum
material in a relatively light tone.
This process, however, faces another problem in that the control of current
becomes extremely complicated and the equipment cost goes up to its
economical disadvantage. Moreover, in electrolytic coloring of an aluminum
material in a relatively light tone such as bronze, a slight difference in color
tone becomes emphasized and conspicuous depending upon the condition of
light and greatly affects the value of commodities. A case of this kind presents
a big problem in commerical production of an electrolytically colored aluminum
material.
Under these circumstances, the present inventors have conducted studies
to develop a process for producing an aluminum material colored in a uniform
tone stably and commercially advantageously while preventing irregular
coloring in different energizing lots as much as possible in alternating current
electrolytic coloring and found that a uniform color tone can be attained in
different energizing lots even in electrolytic coloring in a relatively light tone
by performing a pretreatment prior to coloring that precedes alternating
current electrolytic coloring until the voltage and current respectively reach
the preset ultimate values.
According to the literature survey and research works of the present
inventors, irregularity in color tone in different energizing lots in alternating
current electrolytic coloring of an aluminum material seems to occur for the
following reasons.
For example, in case a pretreatment prior to coloring is performed by
constant current electrolysis in the same electrolytic coloring bath as used for
alternating current electrolytic coloring of an aluminum material, the bath
voltage in the pretreatment prior to coloring is affected by the temperature
and pH of the electrolytic coloring bath and, still more, by the water washing
time and the pH of the water washing bath during the step for water washing
of the anodized aluminum material before immersion in the electrolytic
coloring bath (the aforementioned conditions are hereinafter collectively
referred to as "the bath conditions") and the bath voltage changes with the
bath conditions.
Now, the bath voltage in the pretreatment prior to coloring by constant
current electrolysis is decided primarily by the resistance of the electrolytic
coloring bath and the resistance of the anodic oxide film on the surface of
aluminum material immersed in the bath. As changes in the resistance of the
electrolytic coloring bath from energizing lot to energizing lot are not very
large, at most 0.1-0.2 V in terms of the corresponding voltage, changes in the
bath voltage in the pretreatment prior to coloring are considered to be due
chiefly to the resistance of the anodic oxide film. The anodic oxide film on the
surface of aluminum material consists of the so-called "barrier layer" which is
a fine aluminous layer formed on the aluminum substrate of an aluminum
material and a porous layer formed on the barrier layer and the resistance of
the anodic oxide film is practically that of the barrier layer.
The efficiency for formation of the barrier layer in the pretreatment prior to
coloring by constant current electrolysis is considered to be 60% or so in terms
of apparent efficiency that is the ratio of the theoretical amount formed with
the current efficiency assumed to be 100% to the actual amount increased with
the dissolution of the barrier layer taken into account (amount
increased/theoretical amount formed). Moreover, since the rate of chemical
dissolution of the barrier layer is affected by changes in the bath conditions,
the apparent efficiency changes under the influence of the bath conditions like
the aforementioned bath voltage in the pretreatment prior to coloring; as a
result, the resistance of the anodic oxide film on the surface of aluminum
material changes from energizing lot to energizing lot.
On the other hand, in the pretreatment prior to coloring by the
conventional constant current electrolysis which is effected by passing a direct
current at a constant value for a given length of time, the bath voltage changed
in a given energizing period under the influence of "the changes in the bath
voltage in the pretreatment prior to coloring" and "the changes in the
resistance of the anodic oxide film on the surface of aluminum material"
caused by the changes in the aforementioned bath conditions; as a result, it
was not possible to control completely the formation of the barrier layer on the
surface of aluminum material and to keep the current distribution in the
anodic oxide film of aluminum material constant.
In order to obtain a uniform color tone in different energizing lots, a
conceivable approach is to control the aforementioned bath conditions strictly
and eliminate their influence. In reality, however, strict control of the bath
conditions is difficult to perform on a commercial scale and changes of the bath
conditions are unavoidable within the range of control and, in particular, it is
impossible to suppress completely the unevenenss in color tone in different
energizing lots in the case of electrolytic coloring in a relatively light tone.
The present inventors have conducted studies to find a commercially
adequate solution to the aforementioned problem, found that the thickness of
the barrier layer of the anodic oxide film to be formed and adjusted in the
pretreatment prior to coloring is dependent on the ultimate voltage and
current to be reached finally in the pretreatment, for example, the thickness in
question is proportional to the ultimate voltage in the case of the pretreatment
prior to coloring by constant current electrolysis, and, as a result, the thickness
of the barrier layer is directly related to the color tone given to the aluminum
material by alternating current electrolytic coloring, and completed this
invention.
Accordingly, an object of this invention is to provide a process for
electrolytically coloring an aluminum material which is capable of preventing
as much as possible irregularities in coloring not only in a given energizing lot
but also in different energizing lots in alternating current electrolytic coloring
of an aluminum material and producing an aluminum material colored in a
uniform tone stably and easily on a commercial scale.
In a process for electrolytically coloring an aluminum material which
comprises immersing an aluminum material consisting of anodized aluminum
or an anodized aluminum alloy in an electrolytic coloring bath containing a
soluble metal salt, performing a pretreatment prior to coloring by passing a
direct current waveform with the aluminum material serving as the anode,
and performing alternating current electrolytic coloring in the same
electrolytic coloring bath, this invention relates to an improved process for
electrolytically coloring an aluminm material which comprises performing said
pretreatment prior to coloring until the voltage and current respectively reach
the preset ultimate voltage and current.
In this invention, a particularly desirable mode of execution of the process
for electrolytically coloring an aluminum material comprises performing a
pretreatment prior to coloring by constant current electrolysis wherein a direct
current is passed until the voltage reaches the ultimate value while
maintaining the current at the preset ultimate value and then performing
alternating current electrolytic coloring wherein a voltage-controlled
alternating current waveform that has the peak voltage 0.55-0.8 times the
final voltage in the pretreatment prior to coloring by constant current
electrolysis is passed through the aluminum material.
There is no specific restriction on an aluminum material to be
electrolytically colored in this invention and, as in the conventional anodizing,
a direct current, an alternating current, or an alternating current
superimposed on a direct current is passed through an electrolytic bath
containing an aqueous solution of acid such as sulfuric acid, oxalic acid,
sulfonic acid, and chromic acid with an aluminum raw material consisting of
ordinary aluminum or an aluminum alloy serving as the anode to form an
anodic oxide film on the surface of the aluminum raw material.
There is also no specific restriction on the electrolytic coloring bath
containing a soluble metal salt intended for the pretreatment prior to coloring
and for alternating current electrolytic coloring of the aluminum material
obtained in the aforementioned manner and any electrolytic coloring bath
similar to the conventional one is acceptable. Soluble metal salts include
inorganic salts such as sulfates, nitrates, phosphates, chlorides, and chromates
and organic salts such as oxalates, acetates, and tartrates of metals such as
nickel (Ni), cobalt (Co), copper (Cu), tin (Sn), chromium (Cr), magnesium (Mg),
iron (Fe), cadmium (Cd), titanium (Ti), manganese (Mn), molybdenum (Mo),
calcium (Ca), vanadium (V), lead (Pb), and zinc (Zn).
For the purpose of improving the degree of coloring, it is allowable, if
necessary, to add the following compounds including strong reducing agents as
additives to the electrolytic coloring bath: dithionites such as sodium dithionite
and zinc dithionite, thiosulfates such as ammonium thiosulfate and sodium
thiosulfate, hydrogen sulfites such as sodium hydrogen sulfite, sulfurous acid,
sulfites such as sodium sulfite, thioglycolic acid, and thioglycolates such as
ammonium thioglycolate.
The pretreatment prior to coloring preceding alternating current
electrolytic coloring in this invention is performed by immersing an aluminum
material in the electrolytic coloring bath, passing a direct current waveform
(that is, direct current or an alternating current superimposed on a direct
current) with the aluminum material serving as the anode, and completing the
operation at the point when the voltage (the peak voltage in case the direct
current waveform is that of an alternating current superimposed on a direct
current) and the current respectively reach the preset ultimate values.
In performing the pretreatment prior to coloring, for example, by constant
current electrolysis which is effected by passing a current of a constant value,
a concrete procedure is to pass a direct current while keeping the current at
the preset value of ultimate current and terminate the pretreatment when the
voltage reaches the preset value of ultimate voltage. In the initial stage of this
constant current pretreatment, the current flows preferentially to the portion
where the barrier layer of the anodic oxide film on the surface of aluminum
material is relatively thin and offers a low resistance and to the portion near
the cathode where the resistance of the bath is low; the barrier layers either
get compensated for small thickness or grow relatively thicker by the amount
corresponding to the difference in resistance of the bath in these portions and a
constant anodic current distribution is obtained when the voltage reaches the
ultimate value.
On the other hand, in case the pretreatment prior to coloring is performed
by constant voltage electrolysis by passing a current at constant voltage, there
is normally a danger of overcurrent if a current of the preset ultimate voltage
is passed from the start in the initial stage. To prevent the flow of overcurrent,
a direct current waveform is passed at a lower voltage than the preset ultimate
voltage in the initial stage and, when the current stabilizes, the voltage is
switched over to the ultimate voltage and the constant voltage electrolysis is
continued until the current reaches the preset ultimate value.
Setting of the ultimate voltage and current in the pretreatment prior to
coloring varies with what color tone is required for the aluminum material as
product; the ultimate voltage is preferably set at 30-50 V for electrolytic
coloring in a relatively light tone or at 20-30 V for electrolytic coloring in a
relatively dark tone and the ultimate current is preferably set in the range 20-50
A/m2.
Upon completion of the pretreatment prior to coloring in this manner, this
invention performs alternating current electrolytic coloring in the same
electrolytic coloring bath by passing an alternating current waveform or a
superimposed AC-DC waveform through the aluminum material.
In this case, there is no specific restriction on the procedure for alternating
current electrolytic coloring and the conventional procedure can be adopted.
For the reason given below, the peak voltage of the alternating current
waveform or superimposed AC-DC waveform in use is set at a value preferably
0.55-0.8 times, more preferably 0.65-0.75 times, the value of the preset
ultimate voltage in the pretreatment prior to coloring. If the peak voltage is
lower than 0.55 times, coloring does not occur or the rate of coloring becomes
extremely low. On the other hand, if the peak voltage exceeds 0.8 times, the
current becomes difficult to stay constant in alternating current electrolytic
coloring and a uniform color tone cannot be obtained even if the time for
treatment is fixed.
This situation can be understood as follows according to the studies of the
present inventors.
In electrolytic coloring, a metal species in the bath is reduced and deposited
inside the oxide film to produce a color tone. Therefore, making the color tone
uniform is nothing less than making the current distribution in the aluminum
material uniform when electrolytic coloring is performed with the aluminum
material serving as the anode.
In case the pretreatment prior to coloring is performed with the aluminum
material as the anode by controlling the current and regulating the final
voltage, the film resistance corresponding to the bath resistance in each part is
generated and the current distribution of the aluminum material can be made
constant and nearly uniform at the end of the pretreatment prior to coloring.
However, in case alternating current electrolytic coloring is performed
thereafter by passing an alternating current waveform, the current
distribution in the aluminum material becomes nonuniform and the color tone
becomes nonuniform in spite of the fact that the current distribution in the
aluminum material is nearly uniform at the end of the pretreatment prior to
coloring if the peak voltage of the alternating current waveform is equal to or
higher than the final voltage in the current-controlled pretreatment prior to
coloring. This is because the film resistance itself has a property of varying
with the direction of current and the resistance in the case of the aluminum
material serving as the cathode is less than in the case of the aluminum
material serving as the anode.
As a result of studies of this problem, the present inventors have found that
the changes in film resistance in alternating current electrolytic coloring is
dependent on and closely related to the ratio of the final voltage in the current-controlled
pretreatment prior to coloring to the peak voltage of the alternating
current waveform in alternating current electrolytic coloring. That is, the
current-controlled pretreatment prior to coloring is performed first by passing
a direct current while regulating the final voltage and then alternating current
electrolytic coloring is performed in the same electrolytic coloring bath by
passing a voltage-controlled alternating current waveform having the peak
voltage 0.55-0.8 times the final voltage in the aforementioned current-controlled
pretreatment prior to coloring and this procedure makes it possible
to obtain a uniform current distribution corresponding to the changes in film
resistance at the end of the pretreatment prior to coloring and obtain a
uniform color tone.
In actual operations, it is necessary for the purpose of improving
productivity to select a voltage as high as possible within the range 0.55-0.8
times the final voltage. In order to satisfy the two requirements of uniform
color tone and improved productivity, a preferable procedure is to scan the
aluminum material pretreated and placed in the electrolytic coloring bath with
alternating current voltage to plot a voltage-current curve, determine the
boundary voltage E0 that is the intersection of the respective extension lines of
the flat region and the rising region in the curve, and set the peak voltage in
alternating current electrolytic coloring at this boundary voltage E0. The
boundary voltage E0 thus determined is normally 0.65-0.75 times the ultimate
voltage preset in the current-controlled pretreatment prior to coloring and,
although varying somewhat with the conditions for the pretreatment prior to
coloring or other conditions (such as treatment of anodic oxide film and the
subsequent water washing), it can be determined unambiguously as a suitable
peak voltage of an alternating current waveform or a superimposed AC-DC
waveform.
According to the process of this invention, an electric current flows with
ease in the parts near the counter electrode in the initial and intermediate
stages of the pretreatment prior to coloring and the barrier layer grows there
preferentially. The film resistance increases as the barrier layer grows and the
ease of flow of the current in this part is held in check. That is, preferential
growth of the barrier layer in the part where the current flows with ease in the
pretreatment prior to coloring helps to eliminate the difference in site-dependent
ease of current flow in alternating current electrolytic coloring
thereby causing the current to flow with a nearly uniform current distribution
over the whole surface of the aluminum material in a given energizing lot and
eliminating irregularities in color tone in a given energizing lot.
Moreover, according to the process of this invention, the aforementioned
pretreatment prior to coloring is peformed until the voltage and current reach
the preset ultimate values and, even if the bath conditions change in different
energizing lots, the condition of the barrier layer finally adjusted by the
pretreatment prior to coloring becomes constant in different energizing lots
and the current flows with a nearly uniform current distribution over the
whole surface of the aluminum material in different energizing lots and this
eliminates irregularities in color tone in different energizing lots.
Fig. 1 is a voltage-current curve plotted in the determination of the
boundary voltage E0 in Example 1.
A preferable mode of execution of this invention will be described concretely
with reference to test examples, examples, and comparative examples below.
An aluminum raw material, A6063S-T5, was anodized in 20% H2SO4 at a
current density of 100 A/m2 for 30 minutes to form an anodic oxide film with a
thickness of 10 µm on the surface of the aluminum raw material and then
washed in an acid bath at pH 1 for 5 minutes to prepare an aluminum
material.
An electrolytic coloring bath composed of 25 g/l of CuSO4 and 5 g/l of H2SO4
was prepared and the aforementioned aluminum material was submitted to
the current-controlled pretreatment prior to coloring with the aluminum
material serving as the anode at a current density of 25 A/m2, a bath
temperature of 25°C, and an ultimate voltage of 20 V for approximately 20
seconds.
Upon completion of the pretreatment in this manner, the pretreated
aluminum material was scanned with alternating current voltage in the same
coloring bath while raising the peak voltage from 0 V at a rate of 1 V/sec and a
voltage-current curve was plotted.
The results are shown in Fig. 1 and the boundary voltage E0 was 14 V when
the flat region and the rising region of the curve were respectively extended
and the intersection of the two extension lines was read.
Alternating current electrolytic coloring was performed in the same
coloring bath by setting the peak voltage of a commercial alternating current
at this boundary voltage which is 14 V and passing the current for 50 seconds,
100 seconds, and 150 seconds to give the aluminum material electrolytically
colored pink.
Color measurement was made on the electrolytically colored aluminum
material thus obtained and the uniformity of color tone (color difference; ΔE *
ab) in a given energizing lot was examined.
The treatment of the anodic oxide film, current-controlled pretreatment
prior to coloring, and alternating current electrolytic coloring were repeated
under the aforementioned conditions and the electrolytically colored aluminum
material was submitted to color measurement to examine the uniformity of
color tone (color difference; ΔE * ab) in different energizing lots. The results
are shown in Table 1.
The current-controlled pretreatment prior to coloring and alternating
current electrolytic coloring were performed as in the aforementioned Example
1 except using the the conditions and the peak voltage of a commercial
alternating current shown in Table 1 to give the electrolytically colored
aluminum material.
The uniformity of color tone was examined as in Example 1 on the
electrolytically colored aluminum material thus obtained. The results are
shown in Table 1.
Using the aluminum material prepared by anodizing the same raw materil
by the same method as in Example 1 and the same electrolytic coloring bath as
in Example 1, the constant voltage pretreatment prior to coloring was
performed by placing the aluminum material as the anode, passing a direct
current at a voltage of 15 V initially, switching the voltage over to 20 V
thereafter at the point when the current density dropped to 32 A/m2, and
continuing the operation until the final current density became 25 A/m2.
Upon completion of the constant voltage pretreatment prior to coloring, the
material was scanned with commerical alternating current voltage in the same
electrolytic coloring bath as in Example 1 and a voltage-current curve was
plotted. The results are similar to those in Example 1 and the boundary
voltage E0 determined from the intersection of the respective extension lines of
the flat and rising region was 14 V.
Alternating current electrolytic coloring was performed in the same
electrolytic coloring bath by setting the peak voltage of a commercial
alternating current at this boundary voltage E0 of 14 V and passing the
current for 100 seconds to give the aluminum material electrolytically colored
pink.
The colored aluminum material was submitted to color measurement to
examine the uniformity of color tone (color difference; ΔE * ab) in a given
energizing lot. The results are shown in Table 1.
Alternating current electrolytic coloring was performed under the same
conditions as in Example 1 without the current-controlled pretreatment prior
to coloring and the electrolytically colored aluminum material thus obtained
was examined for the uniformity of color tone as in Example 1. The results are
shown in Table 1.
The current-controlled pretreatment prior to coloring and alternating
current electrolytic coloring were performed as in the aforementioned Example
1 except applying the peak voltage of a commercial alternating current shown
in Table 1 and the electrolytically colored aluminum material thus obtained
was examined for the uniformity of color tone as in Example 1. The results are
shown in Table 1.
The constant voltage pretreatment prior to coloring was performed at a
bath voltage of 30 V for 30 seconds and alternating current electrolytic coloring
was performed as in Example 2 and the electrolytically colored aluminum
material thus obtained was examined for the uniformity of color as in Example
1. The results are shown in Table 1.
According to this invention, it is possible not only to secure uniformity in
color tone in a given energizing lot but also prevent irregular coloring in
different energizing lots as much as possible in alternating current electrolytic
coloring of aluminum materials and produce aluminum materials colored in a
uniform tone commerically and stably.
Claims (5)
- In a process for electrolytically coloring an aluminum material which comprises immersing an aluminum material consisting of anodized aluminum or an anodized aluminum alloy in an electrolytic coloring bath containing a soluble metal salt, performing a pretreatment prior to coloring by passing a direct current waveform with said aluminum material serving as the anode, and performing alternating current electrolytic coloring in the same electrolytic coloring bath, an improved process for electrolytically coloring an aluminum material which comprises performing said pretreatment prior to coloring until the voltage and current respectively reach the preset ultimate values.
- A process for electrolytically coloring an aluminum material as described in claim 1 wherein said pretreatment prior to coloring is constant current electrolysis effected by passing a direct current waveform while maintaining the current at the preset ultimate value and the constant current electrolysis is continued until the voltage reaches the preset ultimate value.
- A process for electrolytically coloring an aluminum material as described in claim 2 wherein said alternating current electrolytic coloring is performed by passing to the aluminum material a voltage-controlled alternating current waveform having the peak voltage which is 0.55-0.8 times the final voltage in the pretreatment prior to coloring.
- A process for electrolytically coloring an aluminum material as described in claim 1 wherein said pretreatment prior to coloring is constant voltage electrolysis effected by starting the passage of a direct current waveform at a voltage lower than the preset ultimate value, then switching over to the ultimate value, and passing a direct current waveform and the constant voltage electrolysis is continued until the current reaches the preset ultimate value.
- A process for electrolytically coloring an aluminum material as described in any one of claims 1 to 4 wherein the aluminum material pretreated prior to coloring and placed in the electrolytic coloring bath is scanned by alternating current voltage to plot a voltage-current curve, the boundary voltage E0 is determined from the intersection of the respective extension lines of the flat and rising regions of the voltage-current curve, and the peak voltage in alternating current electrolytic coloring is controlled below the boundary voltage E0.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP17956499 | 1999-06-25 | ||
| JP17956499A JP3379482B2 (en) | 1999-06-25 | 1999-06-25 | Electrolytic coloring of aluminum material |
| JP17956399 | 1999-06-25 | ||
| JP17956399A JP3379481B2 (en) | 1999-06-25 | 1999-06-25 | Electrolytic coloring method of aluminum material |
| PCT/JP2000/004179 WO2001000904A1 (en) | 1999-06-25 | 2000-06-26 | Method for electrolytic coloring of aluminum material |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP1207221A1 true EP1207221A1 (en) | 2002-05-22 |
| EP1207221A4 EP1207221A4 (en) | 2002-09-11 |
Family
ID=26499374
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP00939163A Withdrawn EP1207221A4 (en) | 1999-06-25 | 2000-06-26 | ELECTROLYTIC COLORING PROCESS OF AN ALUMINUM MATERIAL |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP1207221A4 (en) |
| KR (1) | KR100718427B1 (en) |
| CN (1) | CN1200146C (en) |
| AU (1) | AU5430200A (en) |
| CA (1) | CA2377953A1 (en) |
| NO (1) | NO20016306L (en) |
| WO (1) | WO2001000904A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101509891B (en) * | 2009-04-01 | 2012-05-30 | 西南铝业（集团）有限责任公司 | Method for detecting uniformity of tank cover material conversion film |
| CN101831681B (en) * | 2010-06-04 | 2012-02-01 | 天津大学 | A kind of preparation method of colored composite film of aluminum alloy |
| CN102330137B (en) * | 2011-09-03 | 2015-07-08 | 广亚铝业有限公司 | Inorganic colorful electrolysis coloring technology for aluminium profile anodic oxide film |
| CN102534722B (en) * | 2011-11-28 | 2014-09-10 | 珠海市奥美伦精细化工有限公司 | Pre-dyeing treatment agent for surface of blind hole workpiece in aluminum alloy welding area and application technology thereof |
| CN103076487B (en) * | 2013-01-10 | 2015-05-27 | 安徽省临泉县嘉柏列科技有限公司 | Algorithm for sampling voltage peak in sudden change of load of high-power battery test equipment |
| CN106480486A (en) * | 2015-08-26 | 2017-03-08 | 侊东Hitech株式会社 | The classification color method of aluminium and utilize its aluminium |
| CN110592638A (en) * | 2019-09-17 | 2019-12-20 | 佛山市海化表面处理科技有限公司 | Anodic oxidation electrolytic coloring process for aluminum and aluminum alloy |
| CN111876812B (en) * | 2020-08-01 | 2021-11-05 | 东莞市慧泽凌化工科技有限公司 | Nickel-free electrolytic coloring blackening additive and use method thereof |
| CN112301398B (en) * | 2020-09-29 | 2022-02-18 | 九牧厨卫股份有限公司 | Preparation method of golden film |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1022927A (en) * | 1966-12-12 | 1966-03-16 | Tahei Asada | Improvements in and relating to coloring aluminium articles by electrolytic depositions of colored compounds |
| JPS5423664B2 (en) * | 1975-03-06 | 1979-08-15 | ||
| JPS5825495A (en) * | 1981-08-05 | 1983-02-15 | Mitsubishi Keikinzoku Kogyo Kk | Aluminum electrolytic coloring method |
| JPS59173294A (en) * | 1983-03-23 | 1984-10-01 | Pilot Pen Co Ltd:The | Electrolytic coloration of aluminum or its alloy |
| DE3741456A1 (en) * | 1987-12-08 | 1989-06-22 | Erbsloeh Julius & August | Method for the electrolytic colouring of anodically generated oxide layers on aluminium and aluminium alloys |
| IT1240224B (en) * | 1989-08-17 | 1993-11-27 | Eliseo Benitez-Garriga | ELECTROLYTIC PROCEDURE FOR COLORING ANODIZED ALUMINUM AND ITS PRODUCT. |
| US5674371A (en) * | 1989-11-08 | 1997-10-07 | Clariant Finance (Bvi) Limited | Process for electrolytically treating aluminum and compositions therefor |
| DE4034854C2 (en) * | 1989-11-08 | 2000-08-17 | Clariant Finance Bvi Ltd | Process for the electrolytic dyeing of aluminum and aluminum alloys |
| JP3266084B2 (en) * | 1997-12-26 | 2002-03-18 | 日本軽金属株式会社 | Method for electrolytic coloring of aluminum or aluminum alloy |
-
2000
- 2000-06-26 EP EP00939163A patent/EP1207221A4/en not_active Withdrawn
- 2000-06-26 WO PCT/JP2000/004179 patent/WO2001000904A1/en not_active Ceased
- 2000-06-26 KR KR1020017016461A patent/KR100718427B1/en not_active Expired - Fee Related
- 2000-06-26 CA CA002377953A patent/CA2377953A1/en not_active Abandoned
- 2000-06-26 AU AU54302/00A patent/AU5430200A/en not_active Abandoned
- 2000-06-26 CN CNB008094543A patent/CN1200146C/en not_active Expired - Fee Related
-
2001
- 2001-12-21 NO NO20016306A patent/NO20016306L/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP1207221A4 (en) | 2002-09-11 |
| CN1200146C (en) | 2005-05-04 |
| CA2377953A1 (en) | 2001-01-04 |
| KR100718427B1 (en) | 2007-05-14 |
| KR20020029870A (en) | 2002-04-20 |
| CN1358239A (en) | 2002-07-10 |
| AU5430200A (en) | 2001-01-31 |
| WO2001000904A1 (en) | 2001-01-04 |
| NO20016306D0 (en) | 2001-12-21 |
| NO20016306L (en) | 2002-02-15 |
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