CA1049949A - Process for the production of combination dyeing on workpieces of aluminum or aluminum alloys - Google Patents
Process for the production of combination dyeing on workpieces of aluminum or aluminum alloysInfo
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- CA1049949A CA1049949A CA228,800A CA228800A CA1049949A CA 1049949 A CA1049949 A CA 1049949A CA 228800 A CA228800 A CA 228800A CA 1049949 A CA1049949 A CA 1049949A
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Abstract
ABSTRACT OF THE DISCLOSURE
The specification describes a process for producing coloured, protective coatings on objects made of aluminum or aluminum alloys, to which a protective oxide layer has already been added. The process involves anodically oxidizing the object, electrolytically dyeing the object in an acid solution of a metal salt, for between 0.1 to 15 minutes with an alternating current of between 1 to 50 volts, immersing the object in an aqueous solution of a hetero-polybasic acid of silicon or phosphorus with molybdenum, and treating the object in boiling water.
The specification describes a process for producing coloured, protective coatings on objects made of aluminum or aluminum alloys, to which a protective oxide layer has already been added. The process involves anodically oxidizing the object, electrolytically dyeing the object in an acid solution of a metal salt, for between 0.1 to 15 minutes with an alternating current of between 1 to 50 volts, immersing the object in an aqueous solution of a hetero-polybasic acid of silicon or phosphorus with molybdenum, and treating the object in boiling water.
Description
- 10499~9 The invention relates to a process for producing coloured, protective coatings on workpieces made of aluminum or alloys thereof, to which a protective layer of oxide has already been applied.
The increasing use of aluminum or alumlnum alloys for internal and external applications has resulted in the development of numerous processes for the surface treatment of anodically produced layers of oxide on aluminum and alloys thereof, in order to increase the decorative effect and/or stability of such products.
A process for dyeing anodically oxidized aluminum objects with aniline dyestuffs was developed at an early stage.
However, ob~ects thus dyed had poor resistance to atmospheric action.
Italian Patent 339,232 discloses a dyeing process whereby anodized aluminum is immersed in the solution of a metal salt which is more highly electro-positive than aluminum. The metal is reduced by the aluminum and is precipitated on the surface thereof.
In practice, this method produced no useful results.
According to another known process, the aluminum workpiece is anodized and is immersed in chemicals which penetrate ; into the pores of the oxide layer. The workpiece thus treated is then immersed in an aqueous solution of metal salts which also enter the pores and unite with the chemical substance first used. It has been found that, in practice, this process easily leads to different shades, q~
--~ 1/ --1--,._. . : , when applied -to large areas: it is also difficult to reproduce.
Also known are processes for simultaneously anodiz-ing and dyeing alumnum workpieces. However, the choice of colours afforded by these processes is limited. Fur-thermore they are expensive and difficult to carry out, since the metallic structure and composition of the aluminum is extremely important in achieving the desired results. For instance, it it is desired to produce a grey, aluminum alloys containing a relatively large amount of silicon must be used. Alloys of this kind are dfficult to form by pressure and the producer is faced with storage problems.
Aslo known are numerous processes for dyeing anod-ized aluminum electrolytically. In these processes, the anodized workpiece is immersed in an acid bath contain-ing the dissolved salt of a metal adapted to precipitate electrolytically in the pores of the layer of aluminum oxide, thus forming coloured compounds. At the present time, this is the process most commonly used for dye-ing anodized workpieces, especially if alternating cur-rent is to be used. The electrolyte proposed for-such processes is an aqueous solution of the metal vanadium, chromium, manganese, iron, cobalt, nickel, copper, sel-enium, silver, cadmiun, tin, tellurium, gold and lead.
Some of these salts procues colours varying between a black bronze and black, depending upon the current in-tensity and the dyeing time, whereas others produce yellow and red colours.
Norwegian Patent 125,236 discloses a process for producing blue colours, in which the anodized aluminum or aluminum-alloy workpiece is dyed electrolytically w with the aid of an acid aqueous solution of a hetero-t~ .
~ - 2 -: - - . . .. .
. . . - . ~ :. . .
~04994~
polybasic acid of` silicon or phosphorus with molyb-denum or tungsten, of the formula H85i(mo207)6 or H8 Si(W207)6~ It was .
- 2a -~ . !
~" ' .
also proposed in this patent to use a dyeing electroly-sis bath of this kind for over-dyeing anodized aluminum which has been dyed, after anodizing, with aqueous sol-ution of salts of the above-mentioned metals, using the electrolytic method. Depending upon the metal salts used for the initial electrolytic deying, this produced mixed colours, e.g. grey-green, yellow-green and violet in a number of attractive shades. After the conventional treatment in boiling water, these colours proved to be extremely fast and durable.
In the case of large workpieces, however, this pro- ~-cess had its disadvantages, since the electrolysis bath of hetero-polybasic acids of silicon or phosphorus with molybdenum or tungsten gave off gas bubbles which, in ascending, left vertical strips on the workpiece. Further-more the known difficulties associated with two-stage dyeing processes were increased still further by the two fold electtrolytic treatment, as a result of occasional secondary precipitations of silicon, which bring about differences in colour.
It is therefore the purpose of this present inven-tion to provide a process for the production of combin ation dyeing on workpieces of oxidized aluminum or aluminum alloys, which will el2minate the disadvantages outline above. ;
This purpose is achieved in that, after being anod-ized, workpieces of aluminum or aluminum alloys are dyed electrolytically, with an alternating current, using a aqueous bath consisting of solutions of metal salts, after which they are imrnersed in an aqueous bath contain-ing hetero-polybasic acids of silicon or phosphorus with molybdenum or tungsten. Examples of such metals salts ~ - 3 -: .
are the salts of the me-tals nickel, manganese, cobalt, cadmium, iron and lead. In the case of sa:L-ts of copper, and o:f metals nobler than copper - 3a -~049949 it is desirable to add a small amoun-t of an appropriate metal salt -to the elec-trolysis bath, appropr:iate metals salts being, for example, stannous salts, or nickeL, cobalt and zinc salts, in amount of about 0.5% by weight .
The admixture of small amount of a stannous salt, for instance, apparently causes very small particles of tin to be incorporated into the oxide layer during the electrolytic treatment. Although this does effect the dyeing action of -the noble-metal salts, for example silver sulphate, it brings about a change in colour upon immersion in the hetero-polybasic acid solution, which is not brought about by the noble-metal salt i-tself.
The invention therefore relates to a proce.ss for the production of combination dyeing on workpieces of aluminum or aluminum alloys, whereby the workpiece, I
which has been anodized and possibley dyed electrolyti-cally with the addition of a small quantity of an appropriate metal salt, is immersed in an aqueous solu-tion of a hetero-polybasic acid of silicon or phosphorus with molybdenum or phosphorus 9 as a result of wh~ch an electro-chemical reaction takes place, evidently withcut a supply of current, with the metal ions previously embedded electrolytically, the said reaction leading to the desired combination dyeing.
In one particular aspect the present invention pro-vides a process for the production of combination dyeing on a workpiece of aluminum or aluminum alloys previously anodically oxidized and then dyed electrolytically in an acid solution of a metal salt, for between 0.1 and 15 minutes, with alternating current of 1 - 50 V, charac--te-rized in that the anodically oxidized and electrolyti-cally dyed workpiece is immersed in an aqueous solution of a heteropolybasic acid of silicon or phosphorus with molybdenum, after which .
it is re-condensed in boiling wa-ter.
reStS have shown that if aluminum which has been merely anodically oxidized is immersed in a dyeing bath of this kind does not produce colour in the layer of aluminum oxide, and it was therefore surprising that it was possible to achieve chemcial dyeing after the anod-ically oxidized aluminum had been dyed electrolytically, using a bath consisting of dissolved salts of the above-mentioned metals.
It has also been found, surprisingly enough, that, with the process according to the invention - in cont-rast to the process according to N~rwegian Patent 125,236 - it is unnecessary to use sufficiently pure hetero-polybasic acids, which are very expensive to manufact~e instead, in the process according to the invention, these hetero-polybasic acids may be produced in situ in the dyebath, in that sodium molybdate or sodium tungstate may be caused to react, in an aqueous solution, with soldium silicate or sodium phosphate and hydrochlor-ic acid in an approximately stoichiometric ratio, for example in accordance with the following equations:
12Na2ZO + Na2SiO3 + 26HCL + H20 r H4SiZ12040 X H20 +
26NaCl + llH20 or 12Na2Z04 + NaHP04 + 26HCL + H20~ H7P(Z207)6 x H20 +
26NaCl +llH20 wherein Z signifies Mo ore W.
The above reaction equations indicate that consid-erable quantities of sodium chloride are formed duringthe production of hetero-polybasic acids. It was found, surprisingly enough, this sodium-chloride content leads to improved dyeing results, as is the case in a bath to which pure manufactured hetero-polybasic acids have been added. Furthermore, tests have shown that these improved dyeing results are also obtained if sodium chloride is ~ _ 5 _ ~049~9 added t~ a dye-bath in which pure manufactured hetero-polybasic acids have been dissolved.
- 5a -:. . . : - .
~049949 These improved results may be recognized by the more pronounced grey shade of -the electrolytically applied base colour. However, the sodium-chloride addition must not be too large, since it has been found in practice hat a sodium-chloride content more than double that formed during the stoichiometric reaction, in relation to the heteropholybasic acid, leads to a more brownish grey~colour The concentration of het~ro-polybasic acid in the dyebath used may vary withih wide limits, concentrations between 0.1 and 20% by weight having been found to give good results. A concnetration of between 0.5 and 2% by weight has been found preferable.
Particularly good dyeing results were obtained after electrolytic dyeing in an acid, aqueous bath of a dis-solved tin salt. Depending upon current density, tin-salt concentration and dyeing time, the colours obtained varied between from a weak bronze to a black. After a workpiece so dyed electrolytically had been immersed in a bath containing one of the above mentioned hetero polybasic acids with tungsten or molybdenum, grey shades were obtained, varying between dark grey - when the tin base-colour was very dark, to a light grey - when the base colour was a weak bronze. The period of immersion also affected the colour obtained, a very long period resulting in an unwanted colour change to blue. Good results were obtained with immersion periods of between 1 and 10 minutes.
The grey colours obtained by the process according tothe invention are extremely resistant to wear, light-fast, and weatherproof and are therefore outstandingly suitable for producing, on aluminum or aluminum-alloy workpieces, the durable greys demanded for numerous applications.
~ - 6 _ Since the condition~ to be maintained during the anodic oxidation of aluminum and the electrolytic dyeing of anodically - 6a -:
, ' . ~ ' . :. :
oxidized alumin~ are already described in detail in t the relevant literature, they require no further ex- .
planation herein. A summary of the prior art may be found in an article entitle "Electrolytic dyeing of an-odized aluminum", Galvanotechnik 7968 Saulgau, 63 (1972) No. 2 pages 110 to 121.~
The invention is explained hereinafter with the aid of some examples.
As aluminum workpiece, previously anodically oxid-ized in a 15% aqueous solution of sulphuric acid, was connected to a tin counter-electrode in an aqueous electrolyte containing 2% of stannic chloride and 2%
of concentrated sulphuric acid per litre. An alter-nating voltage of between 5 and 8 V was applied to the electrodes at room temperature for a period of time varying between 5 and 15 minutes, while the current density used varied between 0.2 and 0.8 amp/dm .
Depending on the length of time during which the alter-nating current was applied, highly attractive bronze tones were obtained. The bronze tone became deeper as the period during which the alternating current was applied was increased.
Workpieces thus electrolytically dyed were washed with water and were immersed in a bath containing 2%
by weight of dissolved hetero-polybasic acid made of silicon with molybdenum. The immersion period varied between 1 and 10 minutes. Depending upon the electro-lytically applied base colour and the length of the immersion period, grey colours were obtained, varying between light and dark grey, buth with a tine go green in the lighter greys and a brownish-green tinge in the ~, darker greys. After the conventional treatment in boiling water, the greys obtained were highly resistant to weathering.
EXAMPL.E 2 : 7 .. . .
Anodically oxidized workpieces electrolytically dyed as in Example 1, were immersed in a bath -to which was added about 80C~o by weight ol` NaCl of the stoichio-metric amount in relation to the hetero-polybasic acid ,.
The grey colours obtained were purer than in Example 1.
An aluminum workpiece, previously anodically oxi-dized as in Example 1, was connected to a graphite counter-electrode in an aqueous electrolyte containing 30 g/l of boric acid and 50 g/l of cobalt acetate.
Alternating current at 14V and about 0.5 amps/dm was passed through the electrolyte between the workpiece to be dyed and the counter-electrode Dyeing was carried on for 10 minutes, and the colour obtained was brown.
The workpiece was rinsed and was immersed in a dyebath of the above-mentioned composition, with and with,out the addition of sodium chloride. The colour obtaned was an attractive grey with a green-brown shimmer, which became purer after the workpiece was immersed in a bath containing sodium chloride. After the ususal treatment in boiling water, the colors thus obtained were highly weatherproof.
The same results were obtained after basic electro-lytic dyeing with dissolved nickel salts and subsequent immersion in a bath containing the hetero-polybasic acid of silicon with molybdenum or tungsten in the given conentration, both with and t~ithout the addition of sodium chloride.
Sodium molybdate in approximately stoichiometric ratio to sodim silicate and hydrochloric acid was reacted in an aqueous solution. The concentration of the hetero-polybasic acid produced from silicon with molybdenum in the aqueous bath amount to about 0.5%, and when aluminum objects, previously dyed electro~
lytically as described in the foregoing examples - were immersed in this bath, very pure and durable colours were obtained after the usual treatment in boiling water.
This example shows that better dyeing was obtained in this bath than in a bath in which pure manufactured hetero-polybasic acids from silicon and molybdenum or tungsten were dissolved.
These tests according to Examples l to 4 were re-peated, but with hetero-polybasic acids from phosphorus with molybdenum or tungsten. Substantially the same results were obtained, but a somewhate longer period of immersion was required to obtain the same chemical dyeing.
A strip measuring approximately 5 x 12 cm of the standard AlMg3 alloy was pickled in caustic soda, rinsedm and anodized in a conventional sulphuric-acid electrolyre according to German Industrial Standard 17 612, with a minimal coating thickness of 20/um.
The test piece was then well rinsed and dyed in a 0.5% sulphuric silver-sulphate solution with no further additions.
Voltage: 8V
Time: 0.25 minute Colour: intense lemon yellow The test piece was then well rinsed and immersed for about 3.5 minutes, to a depth of a few centimeters in a 2% molybdate-silicic-acid solution.
The immersed portion of the test piece was not of the mixed colour desired, but~lwas merely lighter than before, as would occur had it been immersed in another acid solution.
_ g _ :. - . . ~ : : . ..
~049949 EXAMPI.E 7 A test piece was anodized as in Example 6, rinsed and dyed in a 0.5% sulphuric silver-sulphate solution to which 2.5 g/1 of` stannic sulphate has been added.
In order to prevent the silver from being completely reduced to metal and precipitating, l~ of cresol sulph-uric acid and 0.5% of gelatine were added.
Voltage: 8V
Time: l minute Colour: dark brass shade The test peice was then rinsed and immersed for 12 minutes in a molybdato-silicic-acid solution.
The immersed portion of the test piece showed a change of colour towards green, but not the desired com-bination colour.
Example 7 was repeated except that 5 g/l of stannic sulphate were added to the electrolytic dyebath. However this amount is so small that the carrier still consisted substnatially of silver.
The test piece was immersed for 3 minutes in a molybdatosilicic-acid solution, after which the brass shade changed to a distinctly greenish shade.
E~AMPLE 9 Example 8 was repeated, except that the electrolytic dyeing was carried out in a 2% sulphuric copper-sulphate solution also containing 5 g/l of stannic sulphate.
The test piece was reddish brown. After rinsing and im-mersion in a 2% molybdator-silicic acid solution, an intense blue-grey colour was obtained after an immersion time of 0.5 minutes.
Further tests have shown that combination dyeing with .
.
, ~049949 copper and noble-metal salts is also possible by adding small quantities, prererably between 0.5 and 1.~% of metal salts other than the stannic salts mentioned above for example nickel, cobalt and zinc salts.
In the case of thin, fine-pored layers of oxide, the subsequent second dyeing in hetero-polybasic acid may possibly turn out too weak. In order to counter-act this, it has been found advantageous to immerse the dyed aluminum objects in a solution of a reducing agent.
A highly dilute solution of a bivalent tin salt has been found particularly suitable for this purpose.
. ~ - - :, . . .
The increasing use of aluminum or alumlnum alloys for internal and external applications has resulted in the development of numerous processes for the surface treatment of anodically produced layers of oxide on aluminum and alloys thereof, in order to increase the decorative effect and/or stability of such products.
A process for dyeing anodically oxidized aluminum objects with aniline dyestuffs was developed at an early stage.
However, ob~ects thus dyed had poor resistance to atmospheric action.
Italian Patent 339,232 discloses a dyeing process whereby anodized aluminum is immersed in the solution of a metal salt which is more highly electro-positive than aluminum. The metal is reduced by the aluminum and is precipitated on the surface thereof.
In practice, this method produced no useful results.
According to another known process, the aluminum workpiece is anodized and is immersed in chemicals which penetrate ; into the pores of the oxide layer. The workpiece thus treated is then immersed in an aqueous solution of metal salts which also enter the pores and unite with the chemical substance first used. It has been found that, in practice, this process easily leads to different shades, q~
--~ 1/ --1--,._. . : , when applied -to large areas: it is also difficult to reproduce.
Also known are processes for simultaneously anodiz-ing and dyeing alumnum workpieces. However, the choice of colours afforded by these processes is limited. Fur-thermore they are expensive and difficult to carry out, since the metallic structure and composition of the aluminum is extremely important in achieving the desired results. For instance, it it is desired to produce a grey, aluminum alloys containing a relatively large amount of silicon must be used. Alloys of this kind are dfficult to form by pressure and the producer is faced with storage problems.
Aslo known are numerous processes for dyeing anod-ized aluminum electrolytically. In these processes, the anodized workpiece is immersed in an acid bath contain-ing the dissolved salt of a metal adapted to precipitate electrolytically in the pores of the layer of aluminum oxide, thus forming coloured compounds. At the present time, this is the process most commonly used for dye-ing anodized workpieces, especially if alternating cur-rent is to be used. The electrolyte proposed for-such processes is an aqueous solution of the metal vanadium, chromium, manganese, iron, cobalt, nickel, copper, sel-enium, silver, cadmiun, tin, tellurium, gold and lead.
Some of these salts procues colours varying between a black bronze and black, depending upon the current in-tensity and the dyeing time, whereas others produce yellow and red colours.
Norwegian Patent 125,236 discloses a process for producing blue colours, in which the anodized aluminum or aluminum-alloy workpiece is dyed electrolytically w with the aid of an acid aqueous solution of a hetero-t~ .
~ - 2 -: - - . . .. .
. . . - . ~ :. . .
~04994~
polybasic acid of` silicon or phosphorus with molyb-denum or tungsten, of the formula H85i(mo207)6 or H8 Si(W207)6~ It was .
- 2a -~ . !
~" ' .
also proposed in this patent to use a dyeing electroly-sis bath of this kind for over-dyeing anodized aluminum which has been dyed, after anodizing, with aqueous sol-ution of salts of the above-mentioned metals, using the electrolytic method. Depending upon the metal salts used for the initial electrolytic deying, this produced mixed colours, e.g. grey-green, yellow-green and violet in a number of attractive shades. After the conventional treatment in boiling water, these colours proved to be extremely fast and durable.
In the case of large workpieces, however, this pro- ~-cess had its disadvantages, since the electrolysis bath of hetero-polybasic acids of silicon or phosphorus with molybdenum or tungsten gave off gas bubbles which, in ascending, left vertical strips on the workpiece. Further-more the known difficulties associated with two-stage dyeing processes were increased still further by the two fold electtrolytic treatment, as a result of occasional secondary precipitations of silicon, which bring about differences in colour.
It is therefore the purpose of this present inven-tion to provide a process for the production of combin ation dyeing on workpieces of oxidized aluminum or aluminum alloys, which will el2minate the disadvantages outline above. ;
This purpose is achieved in that, after being anod-ized, workpieces of aluminum or aluminum alloys are dyed electrolytically, with an alternating current, using a aqueous bath consisting of solutions of metal salts, after which they are imrnersed in an aqueous bath contain-ing hetero-polybasic acids of silicon or phosphorus with molybdenum or tungsten. Examples of such metals salts ~ - 3 -: .
are the salts of the me-tals nickel, manganese, cobalt, cadmium, iron and lead. In the case of sa:L-ts of copper, and o:f metals nobler than copper - 3a -~049949 it is desirable to add a small amoun-t of an appropriate metal salt -to the elec-trolysis bath, appropr:iate metals salts being, for example, stannous salts, or nickeL, cobalt and zinc salts, in amount of about 0.5% by weight .
The admixture of small amount of a stannous salt, for instance, apparently causes very small particles of tin to be incorporated into the oxide layer during the electrolytic treatment. Although this does effect the dyeing action of -the noble-metal salts, for example silver sulphate, it brings about a change in colour upon immersion in the hetero-polybasic acid solution, which is not brought about by the noble-metal salt i-tself.
The invention therefore relates to a proce.ss for the production of combination dyeing on workpieces of aluminum or aluminum alloys, whereby the workpiece, I
which has been anodized and possibley dyed electrolyti-cally with the addition of a small quantity of an appropriate metal salt, is immersed in an aqueous solu-tion of a hetero-polybasic acid of silicon or phosphorus with molybdenum or phosphorus 9 as a result of wh~ch an electro-chemical reaction takes place, evidently withcut a supply of current, with the metal ions previously embedded electrolytically, the said reaction leading to the desired combination dyeing.
In one particular aspect the present invention pro-vides a process for the production of combination dyeing on a workpiece of aluminum or aluminum alloys previously anodically oxidized and then dyed electrolytically in an acid solution of a metal salt, for between 0.1 and 15 minutes, with alternating current of 1 - 50 V, charac--te-rized in that the anodically oxidized and electrolyti-cally dyed workpiece is immersed in an aqueous solution of a heteropolybasic acid of silicon or phosphorus with molybdenum, after which .
it is re-condensed in boiling wa-ter.
reStS have shown that if aluminum which has been merely anodically oxidized is immersed in a dyeing bath of this kind does not produce colour in the layer of aluminum oxide, and it was therefore surprising that it was possible to achieve chemcial dyeing after the anod-ically oxidized aluminum had been dyed electrolytically, using a bath consisting of dissolved salts of the above-mentioned metals.
It has also been found, surprisingly enough, that, with the process according to the invention - in cont-rast to the process according to N~rwegian Patent 125,236 - it is unnecessary to use sufficiently pure hetero-polybasic acids, which are very expensive to manufact~e instead, in the process according to the invention, these hetero-polybasic acids may be produced in situ in the dyebath, in that sodium molybdate or sodium tungstate may be caused to react, in an aqueous solution, with soldium silicate or sodium phosphate and hydrochlor-ic acid in an approximately stoichiometric ratio, for example in accordance with the following equations:
12Na2ZO + Na2SiO3 + 26HCL + H20 r H4SiZ12040 X H20 +
26NaCl + llH20 or 12Na2Z04 + NaHP04 + 26HCL + H20~ H7P(Z207)6 x H20 +
26NaCl +llH20 wherein Z signifies Mo ore W.
The above reaction equations indicate that consid-erable quantities of sodium chloride are formed duringthe production of hetero-polybasic acids. It was found, surprisingly enough, this sodium-chloride content leads to improved dyeing results, as is the case in a bath to which pure manufactured hetero-polybasic acids have been added. Furthermore, tests have shown that these improved dyeing results are also obtained if sodium chloride is ~ _ 5 _ ~049~9 added t~ a dye-bath in which pure manufactured hetero-polybasic acids have been dissolved.
- 5a -:. . . : - .
~049949 These improved results may be recognized by the more pronounced grey shade of -the electrolytically applied base colour. However, the sodium-chloride addition must not be too large, since it has been found in practice hat a sodium-chloride content more than double that formed during the stoichiometric reaction, in relation to the heteropholybasic acid, leads to a more brownish grey~colour The concentration of het~ro-polybasic acid in the dyebath used may vary withih wide limits, concentrations between 0.1 and 20% by weight having been found to give good results. A concnetration of between 0.5 and 2% by weight has been found preferable.
Particularly good dyeing results were obtained after electrolytic dyeing in an acid, aqueous bath of a dis-solved tin salt. Depending upon current density, tin-salt concentration and dyeing time, the colours obtained varied between from a weak bronze to a black. After a workpiece so dyed electrolytically had been immersed in a bath containing one of the above mentioned hetero polybasic acids with tungsten or molybdenum, grey shades were obtained, varying between dark grey - when the tin base-colour was very dark, to a light grey - when the base colour was a weak bronze. The period of immersion also affected the colour obtained, a very long period resulting in an unwanted colour change to blue. Good results were obtained with immersion periods of between 1 and 10 minutes.
The grey colours obtained by the process according tothe invention are extremely resistant to wear, light-fast, and weatherproof and are therefore outstandingly suitable for producing, on aluminum or aluminum-alloy workpieces, the durable greys demanded for numerous applications.
~ - 6 _ Since the condition~ to be maintained during the anodic oxidation of aluminum and the electrolytic dyeing of anodically - 6a -:
, ' . ~ ' . :. :
oxidized alumin~ are already described in detail in t the relevant literature, they require no further ex- .
planation herein. A summary of the prior art may be found in an article entitle "Electrolytic dyeing of an-odized aluminum", Galvanotechnik 7968 Saulgau, 63 (1972) No. 2 pages 110 to 121.~
The invention is explained hereinafter with the aid of some examples.
As aluminum workpiece, previously anodically oxid-ized in a 15% aqueous solution of sulphuric acid, was connected to a tin counter-electrode in an aqueous electrolyte containing 2% of stannic chloride and 2%
of concentrated sulphuric acid per litre. An alter-nating voltage of between 5 and 8 V was applied to the electrodes at room temperature for a period of time varying between 5 and 15 minutes, while the current density used varied between 0.2 and 0.8 amp/dm .
Depending on the length of time during which the alter-nating current was applied, highly attractive bronze tones were obtained. The bronze tone became deeper as the period during which the alternating current was applied was increased.
Workpieces thus electrolytically dyed were washed with water and were immersed in a bath containing 2%
by weight of dissolved hetero-polybasic acid made of silicon with molybdenum. The immersion period varied between 1 and 10 minutes. Depending upon the electro-lytically applied base colour and the length of the immersion period, grey colours were obtained, varying between light and dark grey, buth with a tine go green in the lighter greys and a brownish-green tinge in the ~, darker greys. After the conventional treatment in boiling water, the greys obtained were highly resistant to weathering.
EXAMPL.E 2 : 7 .. . .
Anodically oxidized workpieces electrolytically dyed as in Example 1, were immersed in a bath -to which was added about 80C~o by weight ol` NaCl of the stoichio-metric amount in relation to the hetero-polybasic acid ,.
The grey colours obtained were purer than in Example 1.
An aluminum workpiece, previously anodically oxi-dized as in Example 1, was connected to a graphite counter-electrode in an aqueous electrolyte containing 30 g/l of boric acid and 50 g/l of cobalt acetate.
Alternating current at 14V and about 0.5 amps/dm was passed through the electrolyte between the workpiece to be dyed and the counter-electrode Dyeing was carried on for 10 minutes, and the colour obtained was brown.
The workpiece was rinsed and was immersed in a dyebath of the above-mentioned composition, with and with,out the addition of sodium chloride. The colour obtaned was an attractive grey with a green-brown shimmer, which became purer after the workpiece was immersed in a bath containing sodium chloride. After the ususal treatment in boiling water, the colors thus obtained were highly weatherproof.
The same results were obtained after basic electro-lytic dyeing with dissolved nickel salts and subsequent immersion in a bath containing the hetero-polybasic acid of silicon with molybdenum or tungsten in the given conentration, both with and t~ithout the addition of sodium chloride.
Sodium molybdate in approximately stoichiometric ratio to sodim silicate and hydrochloric acid was reacted in an aqueous solution. The concentration of the hetero-polybasic acid produced from silicon with molybdenum in the aqueous bath amount to about 0.5%, and when aluminum objects, previously dyed electro~
lytically as described in the foregoing examples - were immersed in this bath, very pure and durable colours were obtained after the usual treatment in boiling water.
This example shows that better dyeing was obtained in this bath than in a bath in which pure manufactured hetero-polybasic acids from silicon and molybdenum or tungsten were dissolved.
These tests according to Examples l to 4 were re-peated, but with hetero-polybasic acids from phosphorus with molybdenum or tungsten. Substantially the same results were obtained, but a somewhate longer period of immersion was required to obtain the same chemical dyeing.
A strip measuring approximately 5 x 12 cm of the standard AlMg3 alloy was pickled in caustic soda, rinsedm and anodized in a conventional sulphuric-acid electrolyre according to German Industrial Standard 17 612, with a minimal coating thickness of 20/um.
The test piece was then well rinsed and dyed in a 0.5% sulphuric silver-sulphate solution with no further additions.
Voltage: 8V
Time: 0.25 minute Colour: intense lemon yellow The test piece was then well rinsed and immersed for about 3.5 minutes, to a depth of a few centimeters in a 2% molybdate-silicic-acid solution.
The immersed portion of the test piece was not of the mixed colour desired, but~lwas merely lighter than before, as would occur had it been immersed in another acid solution.
_ g _ :. - . . ~ : : . ..
~049949 EXAMPI.E 7 A test piece was anodized as in Example 6, rinsed and dyed in a 0.5% sulphuric silver-sulphate solution to which 2.5 g/1 of` stannic sulphate has been added.
In order to prevent the silver from being completely reduced to metal and precipitating, l~ of cresol sulph-uric acid and 0.5% of gelatine were added.
Voltage: 8V
Time: l minute Colour: dark brass shade The test peice was then rinsed and immersed for 12 minutes in a molybdato-silicic-acid solution.
The immersed portion of the test piece showed a change of colour towards green, but not the desired com-bination colour.
Example 7 was repeated except that 5 g/l of stannic sulphate were added to the electrolytic dyebath. However this amount is so small that the carrier still consisted substnatially of silver.
The test piece was immersed for 3 minutes in a molybdatosilicic-acid solution, after which the brass shade changed to a distinctly greenish shade.
E~AMPLE 9 Example 8 was repeated, except that the electrolytic dyeing was carried out in a 2% sulphuric copper-sulphate solution also containing 5 g/l of stannic sulphate.
The test piece was reddish brown. After rinsing and im-mersion in a 2% molybdator-silicic acid solution, an intense blue-grey colour was obtained after an immersion time of 0.5 minutes.
Further tests have shown that combination dyeing with .
.
, ~049949 copper and noble-metal salts is also possible by adding small quantities, prererably between 0.5 and 1.~% of metal salts other than the stannic salts mentioned above for example nickel, cobalt and zinc salts.
In the case of thin, fine-pored layers of oxide, the subsequent second dyeing in hetero-polybasic acid may possibly turn out too weak. In order to counter-act this, it has been found advantageous to immerse the dyed aluminum objects in a solution of a reducing agent.
A highly dilute solution of a bivalent tin salt has been found particularly suitable for this purpose.
. ~ - - :, . . .
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the production of combination dyeing on a workpiece of aluminum or aluminum alloys previously anodically oxidized and then dyed electroly-tically in an acid solution of a metal salt, for between 0.1 and 15 minutes, with alternating current of 1 - 50 V, characterized in that the anodically oxidized and elec-trolytically dyed workpiece is immersed in an aqueous solution of a hetero-polybasic acid of silicon or phos-phorus with molybdenum, after which it is re-condensed in boiling water.
2. A process according to Claim 1, characterized in that sodium chloride is added to the aqueous bath containing the heteropholybasic acid.
3. A process according to Claim 1, characterized in that the workpiece is immersed in a bath in which the hetero-polybasic acid is produced in situ.
4. A process according to Claims 1 to 3, character-ized in that the workpiece is immersed in an aqueous bath containing between 0.1 and 20% of the hetero-polybasic acid.
5. A process according to Claims 1 to 3, charac-terized in that the workpiece is immersed in an aqueous bath containing between 0.5 and 2% of the hetero-poly-basic acid.
6. A process according to Claim 1, characterized in that the workpiece dyed according to the process of Claim 1 is subsequently immersed in an aqueous solution of a reducing agent, in order to deepen the colour obtained.
7. A process according to Claim 6, characterized in that the workpiece is immersed in an aqueous solution of a bivalent tin salt.
8. A process according to Claim 1 characterized in that the bath liquid for electrolytic dyeing contains a sulphuric copper-sulphate solution.
9. A process according to Claim 8, characterized in that the bath liquid for electrolytic dyeing additionally contains about 5 g/l of stannic sulphate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA228,800A CA1049949A (en) | 1975-06-09 | 1975-06-09 | Process for the production of combination dyeing on workpieces of aluminum or aluminum alloys |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA228,800A CA1049949A (en) | 1975-06-09 | 1975-06-09 | Process for the production of combination dyeing on workpieces of aluminum or aluminum alloys |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1049949A true CA1049949A (en) | 1979-03-06 |
Family
ID=4103269
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA228,800A Expired CA1049949A (en) | 1975-06-09 | 1975-06-09 | Process for the production of combination dyeing on workpieces of aluminum or aluminum alloys |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1049949A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4756772A (en) * | 1983-10-31 | 1988-07-12 | Alcan International Limited | Method of coloring a porous anodic oxide film on the surface of an aluminum article |
| CN110359072A (en) * | 2018-04-09 | 2019-10-22 | 德韧营运有限责任公司 | Produce the method with the aluminium parts of colored surface |
-
1975
- 1975-06-09 CA CA228,800A patent/CA1049949A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4756772A (en) * | 1983-10-31 | 1988-07-12 | Alcan International Limited | Method of coloring a porous anodic oxide film on the surface of an aluminum article |
| CN110359072A (en) * | 2018-04-09 | 2019-10-22 | 德韧营运有限责任公司 | Produce the method with the aluminium parts of colored surface |
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