Note: Descriptions are shown in the official language in which they were submitted.
20~~~~~~
Case 156-7114
PROCESS POR ELECTROLYTICALLy TREATING ALUMINIUM AND ALUMINIUM ALLOyS
Background of the Invention
The present invention relates to a method for anodising and elec-
trolytically colouring aluminium and aluminium alloys, and to compo-
sitions useful therein.
Various electrolytic colouring processes have been developed, and
can be viewed as fundamentally "two-stage" processes involving an
anodising stage followed by an electrolytic colouring stage.
In the anodising step, the aluminium workpiece is electrolysed
under conditions to result in the formation of a surface aluminium ,
oxide coating (commonly referred to as an "anodic oxide film"). The
electrolysis is generally performed by applying direct current to the
aluminium workpiece serving as the anode in an electrolytic bath
wherein a second metal source, such as aluminium, or graphite, serves
as the cathode. An aqueous strong acid electrolyte such as sulphuric
acid is generally employed to provide anodic oxide film of satisfac-
tory hardness, corrosion resistance and colouring ability.
The resulting anodic oxide film comprises an inner protective
"barrier" layer which is dielectric, thin (i.e. about 0.1-1 micron),
strong, and pore-free; and a nondielectric outer layer, of greater
thickness (i.e. from about 3 to 100 or more microns) which to varying
degrees depending on the conditions of anodisation is characterised by
a pattern of pores extending within the layer, see Hubner, W.W.E. and
A. Schiltknecht, The Practical Anodising of Aluminium, MacDonald &
Evans, London (1960), pp. 21-29. The porous outer layer of the anodic
oxide film provides a suitable substrate for deposition of colouring
agents.
- 2 - - ~~~~~~e 156-7114
The second stage of the two-stage electrolytic colouring processes
comprises electrolytic deposition of colouring agents, e.g., metal
salts or mixtures thereof, into the pores of the anodic oxide film,
typically in the presence of alternating current.
Various factors such as current density and duration, temperature
and composition of the anodisation and colouring baths, and special-
ised treatments may affect the morphology and properties of the re-
sulting anodic oxide film and its colouring.
For example, depending on the current density in the anodising
step, the anodic oxide film which is produced varies from a "soft" or
porous-type film to a "hard" dense film of lesser porosity. Generally,
the porous anodic oxide film is obtained by anodising at current den-
sities not exceeding about 25 amperes per square foot (ASF) (2.7
amps./dm2) at ambient temperature, i.e. about 55-95°F (ca. 13-
35°C).
Anodising at current densities above about 24 or 25 ASF (2.6-2.7
amps./dm2) under certain conditions provides hard, dense-type film of
lesser porosity, the hardness varying with the anodising temperature.
In U.S. Patents 4,180,443 and 4,179,342, hard, dense-type anodic
oxide coatings are produced at direct current densities of about 24 to
36 ASF (2.6-3.9 amps./dm2) at ambient temperature in an aqueous acid
electrolyte comprising sulphuric acid, a polyhydric alcohol and an
organic carboxylic acid. Such processes offer certain advantages in
hard coating technology but nevertheless apparently provide only
limited colours, i.e., deep red, bronze and black.
The present invention relates to improvements in porous anodic
oxide film technology including, in particular, processes which pro-
vide a variety of light to medium colours of the anodised aluminium or
aluminium alloy.
3 20204 ~~
Case 156-7114
Summary of the Invention
The process of the present invention comprises the steps of: (a)
anodising an aluminium or aluminium alloy workpiece in an aqueous
electrolyte solution comprising a strong acid, preferably about 90-300
grams per liter (g/1) thereof, by application of direct current at a
current density of about 5-25 ASF (0.54-2.7 amps./dmz) and a tempera-
ture of from 55-90°F (13-32°C) to form on the workpiece a porous
anodic oxide film having a thickness of at least about 3 microns;
(b) subjecting the resulting anodised workpiece to alternating current
at a voltage of about 5-25 volts for about 1-25 minutes in an aqueous
electrolyte solution comprising a strong acid and an organic carboxyl-
is acid containing at least one reactive group bound to the carbon
atom in the alpha-position, wherein said reactive group is- a hydroxy,
amino, keto or carboxyl group, preferably 120-250g/1 of the strong
acid and about 1-15% by volume of the organic carboxylic acid;
and (c) colouring the workpiece by subjecting it to substantially
alternating current in an aqueous electrolyte solution comprising at
least one metal salt as a colouring agent.
In certain preferred embodiments of the invention, a "waiting
period" is maintained at one or more stages in the above process,
during which essentially no current is passed to the workpiece in the
electrolyte solution. It has been found that such "currentless"
waiting periods advantageously can provide deeply coloured product
which is particularly suitable for architectural applications.
In a further embodiment of the invention resulting in product of
improved colour uniformity, the workpiece prior to electrolytic
colouring [step (c)] is subjected to a pre-treatment which comprises
application of substantially direct current thereto. '
Detailed Description of the Invention
The anodisation step may be preceded by known pre-treatments of
the aluminium workpiece such as by rinsing and degreasing, e'g., with
hot trichloroethylene or trisodium phosphate, and etching, e-g., with
caustic soda.
- 4 - Case 156-7114
The anodisation is performed by conventional means generally known
in the art. The aluminium workpiece, which is adapted to serve as the
anode of a power source, is immersed in an electrolyte bath, together
with another metal source, preferably also aluminium, or graphite,
which serves as the cathode. Direct current is applied to the work-
piece for a time and under conditions suitable for formation of the
anodic oxide film.
The anodizing bath comprises an aqueous strong acid electrolyte,
such as sulphuric or phosphoric acid, or a mixture thereof.
The acid concentration in the aqueous electrolyte bath is prefer-
ably from about 90-300 g/1 of bath and more preferably 120-250 g/1.
Sulphuric acid is preferred, because it provides film of "architec-
tural quality", i.e., having suitable hardness, thickness, and cor-
rosion resistance for outdoor use.
It is advantageous that a certain amount of aluminium also be
present in the anodising bath, which can be provided by the addition
of suitable aluminium compounds, such as aluminium sulphate. The
amount of aluminium which is present in the bath is about 1-10 g/1,
preferably 1-5 g/1.
Direct anodic current is applied to the workpiece at a current
density of about 5-25 ASF (0.54-2.7 amps./dmZ), more preferably 10-20
ASF (1.08-2.2 amps./dmZ), and even more preferably 15-20 ASF (1.6-2.2
amps./dm2).
The term "direct current" as used herein shall be understood to
comprise not only direct current in the strict sense of the term but
also other essentially identical currents such as, e-g., those pro-
duced by fullwave rectification of single-phase alternating current or
by rectification of three-phase alternating current.
The anodisation bath is desirably maintained at about room tempe-
rature, i.e. 55-90°F (13-32°C), preferably about 65-75°F
(18-24°C),
and more preferably about 68-72°F (20-22°C), and therefore it
may be
necessary to employ devices to regulate the temperature of the bath
during anodisation.
In the process of the present invention, anodising conditions are
preferably selected to provide a porous anodic oxide film of about
20-30 microns thickness, and it will be within the skill of the
- 5 - Case 156-7114
practitioner in the art to obtain such film by practicing within the
scope of the present invention.
According to the process of the invention, the resulting anodised
aluminium or aluminium alloy workpiece is then subjected to an alter
s nating current (AC) in an aqueous strong acid electrolyte solution
which comprises about 1-15%, preferably about 1-10% by volume of an
organic carboxylic acid containing at least one reactive group bound
to the carbon atom in the alpha-position, wherein said reactive group
is a hydroxy, amino, keto or carboxyl group.
It has been found that a treatment of the anodised workpiece with
AC current prior to electrolytic colouring, employing an electrolyte
solution comprising the said organic carboxylic acid compounds, per-
mits obtainment of medium to light colours of aluminium, including
colours in the blue and green range.
Examples of suitable organic carboxylic acid compounds include
glycolic (hydroxyacetic), lactic (hydroxypropionic), malic (hydroxy-
succinic), oxalic, pyruvic, and aminoacetic acids, and mixtures
thereof. Glycolic acid is preferred in the present process.
It has been further found that the use of certain polyhydric
alcohols together with the aforementioned organic carboxylic acid
compounds in the AC-treatment step provides additional light and
medium colour tones, particularly including colours in the the blue
and blue-gray range.
Therefore, in an embodiment of the process of the present inven-
tion, the AC-treatment electrolyte bath further comprises, in addition
to the organic carboxylic acid compound or compounds, about 1-15%, and
preferably 1-10% by volume of a polyhydric alcohol of 3 to 6 carbon
atoms. Examples of suitable polyhydric alcohols are glycerol, butane-
diol-1,4, pentanediol-1,5, mannitol and sorbitol, of which glycerol is
preferred.
Most preferably, the AC-treatment electrolyte bath comprises equal
parts by volume, e-g., 1-10 volume % each, of the organic carboxylic
acid and the polyhydric alcohol.
It has also been found that the desired light and medium colours
of aluminium can be achieved when the organic carboxylic acid and/or
polyhydric alcohol compounds which are employed in the AC-treatment
- 6 - ~ ~~ ~ ~ ~ ease 156-7114
step are also present in the anodisation bath, and accordingly in an
embodiment of the invention, a common bath may be used both for
anodisation and for the AC-treatment.
The preferred electrolyte for AC-treatment is sulphuric acid.
The voltage of the alternating current is about 5 to about 25
volts, preferably about 10-20 volts, more preferably about 12-18
volts, and most preferably about 12-15 volts to obtain colours in the
blue range and 15-18 volts to obtain colours in the green range.
Current is applied to the workpiece for about 1 to 25 minutes.
The wave form may, for example, be symmetric and/or asymmetric,
pulsed anodic and/or cathodic with a square or sinusoidal output. The
current may be applied continuously or non-continuously.
The AC-treatment bath is maintained at about 55-90°F (13-
32°C),
preferably about 65-75°F (18-24°C).
The thus-treated anodised aluminium workpiece is then subjected to
electrolysis under generally known conditions to deposit one or more
colouring agents into the pores of the anodic oxide film.
The electrolytic colouring bath comprises an aqueous strong acid,
preferably sulphuric acid, in a concentration of about 5-50 g/1 based
on the total bath.
An alternating current is generally employed to deposit the
colouring agent into the pores of the anodic oxide film. The applied
voltage is generally in the range of from about 5 to about 25 volts,
and preferably about 10-16 volts. The wave form is preferably
sinusoidal.
Prior to electrolytic colouring, the workpiece is preferably sub-
jected to an electrolytic "pre-treatment" which comprises application
of a substantially direct anodic current thereto. This DC pre-treat-
ment step has been found to provide product having improved colour
uniformity.
To effect such improvements, a current density of preferably about
0.5 ASF to about 5 ASF (0.054-0.54 amps./dm2) is maintained for about
0.5 minute to 10 minutes.
This direct current pre-treatment step may most conveniently be
carried out in the electrolytic colouring solution but can also be
carried out in a separate electrolytic bath having an acid concentra-
- Case 156-7114
tion substantially equivalent to the acid concentration of the
colouring solution.
After the DC pre-treatment step, the workpiece is then subjected
to electrolysis by conventional means as described above employing a
colouring agent in an aqueous electrolyte solution. Suitable colouring
agents are metals such as nickel, cobalt, silver, copper, selenium,
iron, molybdenum and tin, and the salts thereof, such as sulphates,
nitrates, phosphates, hydrochlorides, oxalates, acetates and tar-
trates.
Additives such as aromatic sulphonic acids and organic thio-
compounds may be used to aid in obtaining uniformity and depth of
colour.
Copper has been found useful as a colouring agent in the process
of the present invention. An example of a copper bath which may be
employed comprises:
Sulphuric acid 10-25
Copper sulphate 5-15
Magnesium sulphate 0-25
Tin salts, optionally in combination with the sulphates or ace-
tates of copper or nickel, are also desirably employed in the process.
A preferred electrolytic colouring bath which in the process of
the present invention has been found to provide anodised aluminium
product in light to medium colours comprises the following formula
tion:
sulphuric acid 5 50
-
copper sulphate 5 50
-
stannous sulphate 1 10
-
tartaric acid 1 10
-
nickel acetate 1 10
-
boric acid 1 10
-
- 8 ~ ~ ~ ~ ~ '~ ~ Case 156-7114
A further preferred bath comprises:
g/1
sulphuric acid 20 - 40
copper sulphate 10 - 25
stannous sulphate 5 - 10
tartaric acid 5 - 10
nickel acetate 5 - 10
boric acid 5 - 10
Varying colours of aluminium may be obtained depending on the con-
ditions of anodisation and electrolytic deposition.
For example, an aluminium workpiece having been anodised by direct
current in an anodisation bath at 68°F (20°C) comprising:
sulphuric acid 170 g/1
aluminium 5 g/1
glycerine 1.0 Y by vol.
glycolic acid 1.0 Y by vol.
at a voltage of 18V for 40 minutes and at a current density of 15 ASF
(1.61 amps./dm~), which is then subjected to AC-treatment in the same
bath at a voltage of 18V for 5 minutes, followed by electrolytic
colouring in a bath comprising the following formulation:
sulphuric acid 10
copper sulphate 5
stannous sulphate 5
tartaric acid 5
nickel acetate 5
boric acid 20
at a voltage of 18V, for 0.5 min., 1 minute, 2 and 3 minutes,
respectively, has the following colouration as a function of duration
of applied current in the electrolytic deposition step:
~Od~4~~
- 9 - Case 156-7114
duration of applied current colour
(minutes)
0.5 light blue
1.0 blue
Z0 light green
3.0 dark green
It has been found that deeper colours including those in the blue,
blue-gray, green and green-gray range, are obtainable by maintaining a
"waiting period" at one or more stages of the process, during which
essentially no current is passed to the workpiece in the electrolyte
solution.
The cumulative duration of the currentless waiting periods is pre-
ferably about 0.5 to 30 minutes.
Preferably such a waiting period is maintained following the AC
teatment step (b), and prior to the electrolytic colouring step (c),
of the process of the invention.
For example, the workpiece, having been recovered from the AC-
treatment solution of step (b), is then introduced into the electro-
lytic colouring solution of step (c) (or another electrolytic solution
having an acid strength substantially equivalent thereto), and main-
tained therein for a period of time during which essentially no cur-
rent is passed to the workpiece, after which the workpiece is sub-
jected to further electrolytic treatments according to the invention.
In the case where a direct current pre-treatment of the workpiece is
carried out prior to electrolytic colouring, as previously described
herein, the currentless "waiting period" is generally effected prior
to this DC pre-treatment step. (An additional such waiting period,
generally about 0.5 minute in duration, is also preferably maintained
between the DC pre-treatment step and the electrolytic colouring
step.)
More preferably, the workpiece, having been subjected to AC-treat-
ment in the electrolytic solution of step (b) is then maintained in
such solution (or in another electrolytic solution having substantial-
ly equivalent acid strength thereto) for an initial currentless wait-
ing period, and thereafter is transferred to the electrolytic colour-
- 10 - Case 156-7114
ing solution of step (c) (or another electrolytic solution having
substantially equivalent acid strength thereto), where one or more
additional such currentless waiting periods are maintained, as de-
scribed above, prior to electrolytic colouring according to step (c)
of the invention. It is preferred in this case that the initial wait-
ing period in the electrolytic solution of step (b) be about 1-20, and
preferably 10-15, minutes in duration, and that the subsequent period
or periods be about 4-10 minutes in cumulative duration. It has been
observed that deepened colours of the resulting product, including
deeper blue and blue-gray colour tones at lower AC-treatment voltages
and deeper green colours at higher AC-treatment voltages, can be ob-
tained by lengthening the duration of the waiting period in the AC-
treatment solution (or equivalent acid strength solution) within the
above-recited ranges.
The provision of blue, green and other colours of anodised alumi-
nium and aluminium alloy by the process of the invention responds to a
long-felt need in the art, particularly as concerns architectural alu-
minium product.
Following electrolytic colouring, the pores in the anodic oxide
film may be sealed by immersion in boiling water or by impregnation
with wax-like substances, or by other means such as with chemical
treatments, which are known in the art.
The process of the present invention can be applied to all
aluminium and aluminium alloys which may be conventionally anodised
and electrolytically coloured. Such alloys are well-known and contain
at least about 80%, and preferably at least about 95%, aluminium.
In each of the following examples, the aluminium workpiece com-
prises a panel of sheet stock type 1100 aluminium alloy about 10 x 15
cm, which has been pre-treated by degreasing with an alkaline cleaner
comprising 60-70% by weight borax, ca. 10% sodium tripolyphosphate,
ca. 5% trisodium phosphate, ca. 2% sodium gluconate with the balance
of a carboxylated surfactant, followed by immersion in aqueous 6%
sodium hydroxide etching solution at 60°C for about 5 minutes.
~~~v~c~,D~
- 11 - Case 156-7114
A 45-liter tank equipped with a power source and temperature con-
trol means which contains an electrolyte bath of the below-indicated
composition, is used for anodisation of the panel, and also for the
subsequent AC-treatment. An 18-liter tank also equipped with a power
source, containing an electrolytic colouring bath of the below-de-
scribed composition, is employed in the colouring step. In the
anodisation tank, the panel is adapted to serve as the anode of the
external power source, and six strips of aluminium extrusion alloy
6063T6, each approximately 2 x 25 cm, serve as counterelectrodes. The
counterelectrodes are arrayed in two parallel rows equidistant from
the panel on each side. The electrodes are completely immersed in the
bath, current is then applied.
In each of the examples, anodisation is performed by applying
direct current to one of the panels at the current density and for the
length of time also below-indicated.
Except where otherwise indicated, the panel is thereafter sub-
jected to the AC-treatment step of the process, wherein alternating
current is applied at the voltage and for the length of time indicated
in column (b) in the accompanying Table I.
The panel is then removed from the tank, rinsed with water, and
transferred to the electrolytic colouring bath, which has the below-
recited composition. Current is applied to the panel at the voltage
and for a length of time recorded in column (c) of Table I.
The obtained colours of the panels are recorded in the last column
of Table I.
Table II provides the results of standard testing of certain of
the panels for weatherability and corrosion resistance.
Unless otherwise indicated, the temperature of the baths is about
20-22.2°C.
- 12 - Case 156-7114
Examples 1-10
(a) Anodisation [step (a)] is carried out employing a direct cur-
rent voltage at a current density of 1.61 amps./dm2 for about 35 min-
utes in a bath as follows:
165 g/1 sulphuric acid
6 g/1 aluminium
2 vol. Y glycolic acid
(b) AC-treatment of the anodised workpiece [step (b)] is then
carried out in the bath employed in step (a) under the current con-
ditions given in Table I.
(c) Electrolytic colouring [step (c)] is conducted under the cur-
rent conditions given in Table I in a bath comprising:
g/1 sulphuric acid
10 g/1 copper sulphate
15 20 g/1 magnesium sulphate
Colours in the range of green-gray and blue-gray are obtained,
with green generally predominating at the higher alternating current
ranges, e-g., about 15 volts or above, and blue predominating at lower
current ranges. Reddish colours are observed in Examples 9 and 10
following treatments in step (b) wherein current strength is about 6
volts; however, color tones in the blue and green range can be
obtained at lower voltages by employing, e.g., increased acid
concentration solutions, higher operating temperatures, etc.
Co~parative Bxamples 11 and 12
The general procedure of Examples 1-10 is employed using baths of
the same composition, under the current conditions indicated in Table
I, except that no glycolic acid is present in the electrolytic bath
used in steps (a) and (b).
Reddish colours are obtained.
~~~~~r-~
- 13 - Case 156-7114
Example 13
The general procedure of Examples 1-10 is followed, an alternating
current of 26 volts being employed in step (b). (In addition, 2 vol.9~
glycolic acid is added to the bath used in steps (a) and (b), pro-
s viding a total of 4 vol.Y glycolic acid in the bath.)
The product is poorly coloured and exhibits spalling. However,
the desired colours of the invention may be obtainable under the given
voltage conditions by, e-g., lowering acid concentration, reducing
temperature, etc.
Examples 14-28
(a) Anodisation is carried out employing a direct current voltage
of 18 V for 40 minutes at a current density of 1.61 amps./dmz in a
bath comprising:
sulphuric acid 170 g/1
glycolic acid 2.0 vol.Y
glycerine 2.0 vol.Y
aluminium 5 g/1
(b) AC-treatment of the anodised workpiece [step (b)] is then
carried out in the bath employed in step (a) under the current
conditions given in Table I.
(c) Electrolytic colouring is then carried out under the current
conditions indicated in Table I in a bath comprising:
copper sulphate 10
stannous sulphate 5
nickel acetate 5
tartaric acid 5
boric acid 5
sulphuric acid 20
- 14 - Case 156-7114
Comparative Examples 29-33
The general procedure of steps (a) and (c) of Examples 14-28 is
repeated employing the same electrolytic baths and the same current
conditions for anodisation. (The current conditions.for electrolytic
colouring [step (c)] are provided in Table I.) However, step (b) is
omitted.
The resulting panels exhibit colours in the red to black colour
tones.
The resulting panels of Examples 14-28 and Comparative Examples
29-33 axe then subjected to tests of weatherability and corrosion
resistance as recorded in the accompanying Table II.
In Table I, the different columns indicated below have the
following meanings: -
(b) AC-treatment step (c) electrolytic colouring step
bl current (volts AC) cl current (volts)
bz duration (min.) cZ duration (min.)
- 15 - Case 156-7114
TABLE I
(b) (c)
Examples bl b2 C1 CZ Colour
1 15 10 18V-AC 2 dark green-gray
2 16 20 " 1 medium-dark
green-gray
3 15 5 " 1 dark green-gray
4 12 5 " 1 medium blue-gray
10 5 " 1 light blue-gray
6 20 5 " 0.5 medium-light
green-gray
7 20 5 20V-AC 1.0 medium-dark
green-gray
8 24 5 " 0.5 faint green/spalling
9 6 5 18V-AC 2 deep red
6 5 " 4 red-black
ComparativeExamples
11 16 5 18V-AC 1 light red
12 16 5 " 2 rose
Examples
13 26 5 18V-AC 4 no colour/spalling
14 18 5 " 2 light blue-gray
18 10 " 2 light green
16 18 15 " 5 light green,
some
spalling
17 23 5 " 0.5 light green
18 23 5 " 2 dark green
19 23 5 " 1 medium green-gray
23 10 " 0.5 light green
21 23 10 " 2 medium green
22 23 10 " 3 dark green gray
23 16 5 " 2 light gray
24 16 5 " 4 medium blue-gray
15 5 " 2 medium blue-gray
26 15 5 " 4 blue-green-gray
- 16 - Case 156-7114
TABLE I (continued)
(b) (c)
Examples bl bz cl c2 Colour
27 20 10 18V-AC 1 green-gray
28 20 10 " 3 dark
gray
ComparativeExamples
29 -- -- 16V-DC 15 deep
red
18V-AC 0.5 light
rose
1.0 light
red
2.0 medium
red
3.0 deep
red
5.0 black
30 -- -- 16V-DC 2 medium
red
18V-AC 1 light
red
31 -- -- 18V-AC 5 black
32 -- -- " 1 light
red
33 -- -- " 3 deep
red
TABLE II
Note Weight Loss~>Admittance3~
corresponding
to
Grey Scalel~ mg/dm= (uS)
9~ Loss Observed Corrosion
of
ColourColour e Resistance4>
Chang
Examples
23 <10 brighter 2.6 11.0 10 (no
attack)
24 <10 " 5.0 7.5 10 ( " )
25 <10 " 2.8 11.5 10 ( " )
26 10 " 2.2 8.0 10 ( " )
27 <10 " 3.2 12.5 10 ( "
28 <10 " 3.4 12.0 10 ( " )
ComparativeExamples
32 10 darker 2.6 8.5 10 ( " )
33 10 darker 4.0 12.5 10 ( " )
- 17 -~~~~~~~~ase 156-7114
Inscription to Table II:
1> Panels tested on Atlas Weather-0-meter 65 WRC for 7'000 hours
of total exposure.
The numeral "10" indicates a loss of colour of about 10%.
The observed change in colour of the panel after testing,
whether brighter or darker, is also indicated.
z' Procedure of ISO 3210 -1983(E): - Assessment of quality of
anodic oxide film by measurement of loss of mass after
immersion in phosphoric-chromic acid solution.
3~ Admittance value (uS) obtained according to the procedure of
ISO 2931 - 1983(E).
Results of Copper-accelerated acetic acid salt spray (CASS)
test [ISO-3770-1976(E)].
Examples 34-37 - General Procedure
(a) Employing the apparatus initially described above, anodisa-
tion of the workpiece is carried out by applying direct current to the
panel at a current density of 1.61 amps./dmZ for about 35 minutes in a
bath comprising:
165 g/1 sulphuric acid
6 g/1 aluminium
2.0 vol.% glycolic acid
2.0 vol.% glycerine
(b) AC-treatment of the anodised workpiece is then carried out in
the same bath employed in step (a) by passing 14 volts for 10 minutes.
(c) The panel is then removed from the anodisation tank, rinsed
with water, and transferred to an electrolytic colouring bath, which
comprises:
- 18 - Case 156-7114
15 g/1 sulphuric acid
g/1 copper sulphate
g/1 magnesium sulphate.
Alternating current is passed at a voltage of 14 volts for 2 min-
5 utes.
Example 34
(i) Prior to application of alternating current in step (c)
above, the panel is maintained in the colouring bath for a currentless
"waiting period" of 20 minutes.
10 The colour of the resulting panel is a deep blue.
Example 35
(i) Following the AC-treatment according to step (b) above, the
workpiece is maintained in the electrolyte solution used in step (b)
for a currentless "waiting period" of 5 minutes. The workpiece is then
15 removed from the anodisation bath and transferred to the colouring
bath.
(ii) Prior to application of alternating current in step (c)
above, the panel is maintained in the colouring bath for a currentless
"waiting period" of 10 minutes.
20 The resulting panel is observed to have a somewhat deeper blue
colouration than the panel of Example 34.
Example 36
The procedure of Example 35 is repeated, with the exception that
the aluminium workpiece comprises a panel of 6063-T6 aluminium alloy
about 5 x 50cm; the colouring tank comprises a 7-liter tank having
dimensions 15 x 15 x 60 cm; and the counterelectrodes comprise 2 rods
of stainless steel, 0.64 cm diameter, 15 cm in length, which are
placed about 1.3 em from one end of the tank. Thus current density
applied to the workpiece in the electrolytic colouring step (c) of the
process varies depending on distance from the counterelectrodes.
The resulting workpiece exhibits an intense blue colour in the
higher current density zone (i.e., nearest the counterelectrodes) and
2~~~,~s;t~
- 19 - Case 156-7114
a lighter blue colour in the low current density zone (furthest from
the counterelectrodes).
Example 37
The procedure of Example 36 is followed, except that after sub-
s jecting the anodic workpiece to a currentless waiting time of 10 min-
utes in the colouring tank, and prior to application of AC current for
electrolytic colouring under the conditions of Example 35, a direct
current of 16 V is applied to the workpiece for 2 minutes, and the
workpiece is then subjected to a currentless "waiting time" of 0.5
minute.
The resulting panel shows greater unifomity of blue colour, indi-
cating that improved throwing power is obtained as a result of appli-
cation of direct current in the electrolytic colouring bath prior to
application of alternating current. A green colour is also observed in
the high current density zone.
Example 38
Steps (a), (b) and (c) of the General Procedure described for
Examples 34-37 are carried out, employing the apparatus initially
described herein, with the exception that the workpiece and colouring
tank apparatus are as described in Example 36. The following addition-
al steps are carried out following step (b) (AC-treatment) and prior
to step (c) (electrolytic colouring) of the General Procedure, in the
order below-indicated:
(i) Following step (b), a panel is maintained in the AC-treatment
bath of step (b) for a currentless waiting time period having a dura-
tion of either of 0 min.; 2 min.; 10 min.; or 20 min.
(ii) The panel is then transferred to the colouring bath where it
is maintained for a currentless "waiting period" of 5 minutes.
(iii) A direct current of 16 V is then applied to the workpiece
for 2 minutes;
(iv) The workpiece is subjected to a currentless "waiting time" of
0.5 minute; and step (c) is then carried out.
- 20 - Case 156-7114
A primarily light blue colour of the resulting product is obtained
with good colour uniformity in the absence of a waiting period in step
(i). It was observed that deeper colours, including predominantly deep
blue colours, can be obtained by lengthening the waiting period of
step (i) from 0 to 20 minutes.
Example 39
The procedure of Example 38 is carried out, with the exception
that in the AC-treatment step (b), an alternating current of 18 volts
is employed.
A primarily light greenish-blue colour of the resulting product
with good colour uniformity is obtained in the absence of a waiting
period in step (i). It was observed that deeper greenish colours can
be obtained by lengthening the waiting period of step (i) from 0 to 20
minutes.
The above examples demonstrate that desirable colours of anodised
aluminium and aluminium alloy may be obtained by the process of the
invention, and that the thus-prepared coloured anodic oxide film has
satisfactory corrosion resistance and weatherability.
Of course, various changes and modifications may be made without
departing from the invention and it is intended, therefore, that all
matter contained in the foregoing description shall be interpreted as
illustrative only and not limitative of the invention.
