GB2127849A - Electrocoloring aluminum or alloy thereof in a yellow to orange color - Google Patents

Electrocoloring aluminum or alloy thereof in a yellow to orange color Download PDF

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Publication number
GB2127849A
GB2127849A GB08321734A GB8321734A GB2127849A GB 2127849 A GB2127849 A GB 2127849A GB 08321734 A GB08321734 A GB 08321734A GB 8321734 A GB8321734 A GB 8321734A GB 2127849 A GB2127849 A GB 2127849A
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United Kingdom
Prior art keywords
aluminum
alloy
electrocoloring
bath
acid
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Granted
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GB08321734A
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GB2127849B (en
GB8321734D0 (en
Inventor
Fabio Tegiacchi
Antonio Dito
Pietro Cavallotti
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WR Grace and Co
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WR Grace and Co
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    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02Anodisation
    • C25D11/04Anodisation of aluminium or alloys based thereon
    • C25D11/18After-treatment, e.g. pore-sealing
    • C25D11/20Electrolytic after-treatment
    • C25D11/22Electrolytic after-treatment for colouring layers
    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02Anodisation
    • C25D11/04Anodisation of aluminium or alloys based thereon
    • C25D11/12Anodising more than once, e.g. in different baths

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Chemical Treatment Of Metals (AREA)
  • ing And Chemical Polishing (AREA)
  • Electroplating Methods And Accessories (AREA)

Abstract

Aluminum or an alloy thereof is electrocolored in a yellow to orange color by first subjecting previously anodized aluminum or alloy thereof to a pre-treatment in a highly concentrated phosphoric acid (H3PO4) bath while passing an alternating current therethrough. The aluminum or alloy thereof is then colored in an electrolytic bath comprising SeO2 or an alkaline selenite by passing therethrough an alternating current at 8-20 volts.

Description

SPECIFICATION A method for electrocoloring aluminum or alloy thereof in a yellow to orange color This invention relates to electrocoloring aluminum and its alloys.
Various electrocoloring processes are currently known which are applicable to previously anodized aluminum and its alloys to achieve a wide range of colors, including such colors as bronze, gold, yellow and orange, and red.
Thus, as an example, processes are known wherein the aluminum or alloy thereof, which has been coated with a layer of porous oxide by anodic oxidation (i.e. by anodization), is treated in a phosphoric acid bath with direct or alternating current, and subsequently subjected to electrocoloring, e.g. with an electrolyte containing nickel or tin, to produce, as a function of the duration of the electrocoloring step, a yellow to gold to orange to red color shade.
Such a process is disclosed, for example, in U.S. Patent No. 4,251,330, wherein the resulting colors can be attributed to so-called optical interference effects.
The process of this prior patent involves problems connected with the final color achieved, since color fading may occur after electrocoloring and prior to the final fixing step such as is normally carried out in this type of process.
Color fading has been attributed to the electrodeposited pigment being re-dissolved by acid electrolyte residues which are left in the pores of the anodic oxide layer. While U.S. Patent No.
4,251,330 mentions previously proposed techniques for obviating color fading, in particular that of using a stabilizing treatment before fixing by immersion of the electrocolored workpiece in a chromate bath, it proposes, in turn, a novel technique of electrolytically co-depositing two metals which are capable of forming alloys resistant to acid attack. Of course, this technique, while apparently obviating the drawbacks connected with color fading after the coloring step, also introduces some disadvantages connected with increased operative difficulties and a higher material consumption.
Another prior patent, namely U.S. Patent No. 3,382,160, discloses the electrodeposition of selenium onto anodized aluminum to impart a yellow-gold or red-gold color to the aluminum. The process described therein involves a prolonged electrodeposition extended for about 10 minutes at a potential of 13 to 20 Volts. In such conditions, the amounts of acidic electrolyte left in the pores of the aluminum oxide layer are quite large, so that increased residues are released in the course of the fixing operation which follows. The net result is that the selenium electrocolored aluminum, produced by the method of this U.S. patent, is liable to advanced corrosion and cannot pass the corrosion tests required for certain architectural applications.
This invention provides a method for electrocoloring aluminum or an alloy thereof in a yellow to orange color, which avoids the cited disadvantages of conventional techniques.
The colors obtained by the new method are stable and not liable to variation, e.g. on exposure to light. No stabilization treatment before the final fixing is required.
The final products have high resistance to corrosion.
The method of the present invention, for electrocoloring aluminum or an alloy thereof with a yellow to orange color of improved color stability, comprises subjecting anodized aluminum or an alloy thereof to an electrolytic pre-treatment in a bath containing phosphoric acid in a concentration of 1 50 to 300 g/liter, while passing an alternating current therethrough, electrocoloring the thus pre-treated aluminum or alloy thereof in a bath containing a selenium electrolyte using an alternating current at a voltage of 8 to 20 Volts for less than 10 minutes, and then subjecting the thus electrocolored aluminum or alloy thereof directly to a final fixing without using any intermediate color stabilizing step.
It has been unexpectedly found that, by the method of this invention, aluminum and its alloys can be colored in colors ranging from various shades of yellow to orange, which are particularly stable against variations caused by dissolving by the acidic electrolyte, and by light and weather exposure, that is by corrosion in general.
In the new method previously anodized aluminum, or alloy thereof onto which a porous layer of anodic aluminum oxide, having generally a thickness of at least 3 microns, has been formed, is used.
The anodization of aluminum and its alloys is effected in a conventional manner, generally in a sulphuric acid bath, while a direct current is passed at a voltage and for a duration which depend on the sulphuric acid concentration in the bath and on the temperature. In general, concentrations in the 100 to 200 g/liter and voltages in the 10 to 20-Volt range, at room temperature and for times of 20-50 minutes, are used.
The anodized aluminum or alloy thereof is then subjected to an electrolytic pre-treatment step, which tends to optimize the subsequent electrolytic deposition of the pigment. It is believed that such pre-treatment acts to modify the size and geometry of the pores in the anodic oxide layer.
In this step an acid bath is used, in particular a bath of phospheric acid or a mixture thereof with an organic or inorganic acid, such as sulphuric acid, oxalic acid, or tartaric acid. The phosphoric acid concentration is a critical factor in the method of the invention, and is in the 1 50 to 300 g/liter range.
Where other acids are added to the phosphoric acid, the latter should be provided in amounts greater than 50 percent of the mixture of acids present in the bath.
During this pre-treatment step, an alternating current is passed through the treatment bath at a voltage of 9 to 1 5 Volts for usually from 1 to 5 minutes. The treatment is carried out at a temperature in the 100C to 350C range, and generally at room temperature.
The pre-treatment step, which is believed to enlarge the pores in the anodic oxide layer, is followed, in the method of this invention, by the electrocoloring step proper, in a bath containing a selenium electrolyte. In general, either selenium dioxide or an alkaline selenite is used in a concentration from 1 to 30 g/liter. In addition to the selenium compound, the electrocoloring bath should include an acid, preferably H2SO4, in a concentration of 1 to 30 g/liter. Electrocoloring is effected with an alternating current at 8-20 Volts for a time of up to 10 minutes. The temperature should be in the 1 0-350C range, preferably room temperature.
In the new method, the pre-treatment and electrocoloring steps are carried out as two discrete steps in two separate baths. Preferably, during the pre-treatment step of pore modification, H3P is used in a concentration from 200 to 300 g/l. The electrocoloring step which follows in the bath containing the selenium electrolyte is preferably carried out at a voltage of 8-1 6 Volts for 3-4 minutes.
The method of this invention yields, after the electrocoloring, a stable color which remains unaffected during the interval between the completion of the electrocoloring step and the final, conventional, color fixing treatment, such as is required with this type of process. Thus, no preliminary operations for fixing for color stabilization are required, such as immersion in chromate baths or codeposition of two metals, as become necessary with conventional techniques.
Accordingly, after the electrocoloring step, an ordinary fixing operation is carried out, e.g. by boiling in deionized water, with the possible addition of an additive such as a nickel salt.
The resulting selenium-electrocolored aluminum or alloy thereof has a color in a shade of yellow to orange, which will vary depending on the duration of the pre-treatment step in the phosphoric acid. The colors obtained are unaffected by exposure to light and weather, so that aluminum articles so colored are particularly suitable for architectural and other applications having high corrosion-resistance requirements.
The invention will be more clearly understood by reference to the following examples.
EXAMPLE 1 An aluminum sample which has been oxidized in a H2SO4 bath at 1 80 g/l, 1 5 Volts, and 1.5 A/dm2 with direct current for 30 minutes, was subjected to treatment with an alternating current (10 Volts for 1 minute) in a H3PO4 250 g/l solution at room temperature. After rinsing in deionized water, electrocoloring was carried out in a bath containing SeO2 (10 g/l) and H2S04 (20 g/i) at 12 Volts for 3 minutes. A pinky yellow color was obtained. The sample, after fixing in a solution of nickel salts at 950C, showed no discoloration.
EXAMPLE 2 An aluminum sample oxidized in a H2S04 bath at 1 80 g/l, 1 5 Volts, and 1.5 A/dm2 with direct current for 30 minutes, was subjected to treatment with alternating current (10 Volts for 1.5 minutes) in a solution of H3PO4 at 250 g/l and sulphuric acid at 50 g/l at room temperature. After rinsing with deionized water, electrocoloring was carried out using a solution of SeO2 (10 g/l), and H2SO4 (20 gl) at 12 Volts for 3 minutes. A golden yellow color was obtained. Following fixing in a solution of nickel salts at 950C, the sample showed no discoloration.
EXAMPLE 3 An aluminum sample oxidized in a bath of H2S04 at 1 80 g/l, 15 Volts, and 1.5 A/dm2 with direct current for 30 minutes, was then subjected to treatment with alternating current at 1 0 Volts for 2.5 minutes in a H3PO4 (300 g/l) solution at ambient temperature. Following rinsing with deionized water, electrocoloring was carried out in a solution of SeO2 (10 g/l), and H2S04 (20 g/l), at 12 Volts for 3 minutes using a stainless steel counterelectrode.
An orange color was obtained. The sample, upon fixing in a nickel salt solution at 950C, showed no discoloration.
Tabie 1 which follows illustrates some Examples of the colors to be obtained with the method of this invention, as a function of the duration of the pore modification pre-treatment.
TABLE 1 Thickness of the Duration times of Alternating current Color fixing oxide layer formed pre-treatment with electrocoloring with with nickel by direct current 250 91- H3PO4 10 gel ' SeO2 salt at 950C anodization in and alternating and 20 91- and 3 minim H2SO4(microns) current (min.) H2SO4 oxide 12 1.0 pinky yellow No discoloration observed 12 1.5 golden yellow No discoloration observed 12 2.5 orange No discoloration observed 18 1.0 pinky yellow No discoloration observed 1 8 2.0 golden yellow No discoloration observed 18 3.0 orange No discoloration observed 20 1.5 pinky yellow No discoloration observed 20 2.5 golden yellow No discoloration observed 20 3.5 orange No discoloration observed Aluminum articles electrocoiored by the method of this invention have been subjected to testing for resistance to light exposure in conformity with standard UNI 4529 (Xeno test).
The results obtained are as shown below: Oxide Evaluated resistance thickness Color to light exposure 12 Mm pinky yellow 8 golden yellow 8 orange 6-7 12 um pinky yellow 8 golden yellow 8 orange 6-7 The above results relate to aluminum articles having an anodic oxide layer 1 2 Mm or 1 8 *4m, thick, and show that electrocoloring with selenium in accordance with this invention yields colors having maximum or next-to-maximum resistance to light. For the Xeno Test a rating of 8 represents the maximum rating of resistance to light.
The new method is particularly effective for treatment of aluminum alloys, such as aluminum magnesium-silicon and aluminum-magnesium-silicon manganese alloys. Information about Al-Mg-Si and A-Mg-Si-Mn alloys may be collected from UNI-3571 and UNI-3569 data.

Claims (10)

1. A method for electrocoloring aluminum or an alloy thereof in a yellow to orange color, which comprises subjecting anodized aluminum or alloy thereof to an electrolytic pre-treatment in a bath containing phosphoric acid in a concentration of 1 50-300 g/l while passing an alternating current therethrough, electrocoloring the thus pre-treated aluminum or alloy thereof in a bath containing a selenium electrolyte using an alternating current at a voltage of 8-20 Volts for less than 10 minutes, and subjecting the thus electrocolored aluminum or alloy thereof directly to a final fixing without using any intermediate color stabilizing step.
2. A method according to claim 1, wherein the pre-treatment bath contains, as electrolyte, phosphoric acid or a mixture thereof with an organic or inorganic acid, the said mixture containing over 50 percent by weight of phosphoric acid.
3. A method according to claim 2, wherein the said mixture contains oxalic acid, tartaric acid, and/or sulphuric acid, in addition to the phosphoric acid.
4. A method according to any of the preceding claims, wherein the pre-treatment is carried out in a bath containing H3PO4 in a concentration from 200 to 300 g/l, and at a voltage of 9 to 1 5 Volts for a period of 1-5 minutes.
5. A method according to any of the preceding claims, wherein the said electrocoloring step is carried out at a voltage of 8 to 1 6 Volts for a time not exceeding 3-4 minutes.
6. A method according to any of the preceding claims, wherein the said selenium electrolyte is SeO2 or an alkaline selenite.
7. A method according to any of the preceding claims, wherein the said electrocoloring bath contains the said selenium electrolyte in a concentration from 1 to 30 g/l and sulphuric acid in concentration from 1 to 30 g/l.
8. A method according to any of the preceding claims, wherein the said final fixing step is carried out by boiling the electrocolored aluminum or alloy thereof in a bath of deionized water optionally containing a nickel salt.
9. A method according to claim 1 substantially as herein described in any one of the Examples.
10. Electrocolored aluminum or alloy thereof produced by the process of any of claims 1 to 9.
GB08321734A 1982-10-07 1983-08-12 Electrocoloring aluminum or alloy thereof in a yellow to orange color Expired GB2127849B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
IT23657/82A IT1153213B (en) 1982-10-07 1982-10-07 ELECTRO-COLORING PROCESS OF ALUMINUM AND ITS ALLOYS IN YELLOW-ORANGE TONES

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GB8321734D0 GB8321734D0 (en) 1983-09-14
GB2127849A true GB2127849A (en) 1984-04-18
GB2127849B GB2127849B (en) 1985-10-16

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DE (1) DE3331857A1 (en)
FR (1) FR2534281B1 (en)
GB (1) GB2127849B (en)
IT (1) IT1153213B (en)
SE (1) SE458207B (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2654118A1 (en) * 1989-11-08 1991-05-10 Sandoz Sa PROCESS FOR THE ELECTROLYTIC TREATMENT OF ALUMINUM AND ALUMINUM ALLOYS.
CN1059476C (en) * 1996-08-21 2000-12-13 邓维鹏 Eletrolytic colouring technology for golden colour aluminium alloy selenide
WO2001018281A1 (en) * 1999-09-07 2001-03-15 Alcan International Limited Rapid colouring process for aluminum products

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3382160A (en) * 1960-03-31 1968-05-07 Asada Tahei Process for inorganically coloring aluminum
US4251330A (en) * 1978-01-17 1981-02-17 Alcan Research And Development Limited Electrolytic coloring of anodized aluminium by means of optical interference effects

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2654118A1 (en) * 1989-11-08 1991-05-10 Sandoz Sa PROCESS FOR THE ELECTROLYTIC TREATMENT OF ALUMINUM AND ALUMINUM ALLOYS.
GB2237817A (en) * 1989-11-08 1991-05-15 Sandoz Ltd Electrolytic colouring of anodized aluminium
GB2237817B (en) * 1989-11-08 1994-03-02 Sandoz Ltd Process for electrolytically treating aluminium and aluminium alloys
CN1059476C (en) * 1996-08-21 2000-12-13 邓维鹏 Eletrolytic colouring technology for golden colour aluminium alloy selenide
WO2001018281A1 (en) * 1999-09-07 2001-03-15 Alcan International Limited Rapid colouring process for aluminum products

Also Published As

Publication number Publication date
GB2127849B (en) 1985-10-16
IT8223657A0 (en) 1982-10-07
SE458207B (en) 1989-03-06
IT1153213B (en) 1987-01-14
FR2534281B1 (en) 1986-12-26
SE8304416L (en) 1984-04-08
GB8321734D0 (en) 1983-09-14
SE8304416D0 (en) 1983-08-15
FR2534281A1 (en) 1984-04-13
DE3331857A1 (en) 1984-04-12

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PCNP Patent ceased through non-payment of renewal fee