Classifications

• • 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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
• • 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

• the present invention relates to a process for the production of colored protective coatings on articles of aluminum or aluminum alloys which have been previously anodized in a very special way in order to obtain products which are particularly suitable to be used in architectural applications.
• both processes produce an anodized layer which is relatively thick (customarily 1.5 mil or heavier) in order to obtain high heat resistance and is of a darkish, muddied color, thereby rendering it unsuitable for use in a process where light, unmuddied colors are desired.
• U.S. Patent 3,524,799 is directed towards a room temperature process for anodizing aluminum in order to produce hard, dense anodic coatings and the novel process of the present invention utilizes as one step thereof a modification of the process disclosed by this patentee.
• the specification and claims of this patent are directed to the formation of hard, dense anodic coatings on aluminum or aluminum alloys by anodizing the aluminum in an aqueous electrolyte containing a mineral acid, such as sulfuric acid, a polyhydric alcohol of 3 to 6 carbon atoms, an organic carboxylic acid containing at least one reactive group in the alpha-position to the carboxylic acid group, such as lactic acid or glycine, and an alkali salt of a titanic acid complex of a hydroxyaliphatic carboxylic acid containing from 2 to 8 carbon atoms, such as, for example, titanium dilactate ammonium salt.
• a mineral acid such as sulfuric acid, a polyhydric alcohol of 3 to 6 carbon atoms
• a process and bath which demonstrates high throwing power provides uniform color to small creases, cracks, nooks, detents, etc., as well as the larger uniform surfaces of an aluminum or aluminum alloy workpiece being colored.
• High throwing power also permits the introduction into the coloring bath of a mix of workpieces in terms of their alloy composition and overall physical configuration to obtain uniform color of all such workpieces.
• prior art coloring techniques it was often difficult, if not impossible, to obtain uniform coloring of workpieces of different alloys or shapes in a single coloring bath at the same time.
• spacing of the various workpieces in the coloring bath was a critical factor in successfully uniformly coloring aluminum extrusions, particularly for architectural purposes.
• a novel process for the production of colored coatings on articles of aluminum or aluminum alloys which are particularly adapted to be employed for architectural uses which involves first forming a hard, dense anodic coating on aluminum and aluminum base alloys by anodizing the aluminum in a specific electrolyte comprising sulfuric acid, a polyhydric alcohol of 3 to 6 carbon atoms and an organic carboxylic acid containing at least one reactive group in the alpha position in order to obtain a material having a film thickness of 5-28 microns (0.2 to 1..1 mils) and thereafter electrolytically coloring said anodized aluminum by passing alternating current between said anodized aluminum and a counter-electrode in an aqueous bath containing acid and a metal salt
• the anodic layer be between about 6 and about 1.1. mils in thickness, as opposed to the 1-5 mils set forth at column 3, line 26 of said U.S. Patent 3,524,799
• the electrolyte used to anodize the aluminum must be of the type described in U.S. Patent No. 3,524,799 without any alkali salt of titanic acid complex.
• the combination is an anodizing bath of a polyhydric alcohol containing from 3 to 6 carbon atoms, and an organic carboxylic acid containing a reactive group in alpha-position to the carboxylic acid group will react with the hot reaction products formed during anodizing with or adjacent to the surface of the pore base, and thereby suppress the attack or dissolution of the forming oxide film by these products.
• the mineral acid component of the electrolyte is sulfuric acid.
• the anodizing bath concentration of sulfuric acid is generally maintained between about 12% and about 20% by weight, preferably about 15%.
• Polyhydric alcohols containing from 3 to 6 carbon atoms which may be employed in the practice of the invention, singly or in admixture, include glycerol, butane-diol 1, 4, pentanediol-1, 5, mannitol and sorbitol.
• the total amount of polyhydric alcohol employed ranges from about 1% to about 4% by volume of the anodizing electrolyte.
• the preferred polyhydric alcohol is glycerol at a concentration of between about 1% to about 2%.
• the organic carboxylic acids containing a reactive group in alpha-position to the carboxylic acid group include acids in which the reactive group is hydroxy, amino, keto, or carboxyl.
• examples of such acids include glycolic (hydroxyacetic), lactic (hydroxypropionic), malic (hydroxysuccinic), oxalic, pyruvic, and aminoacetic acids.
• Acyclic carboxylic acids such as lactic, malic, and glycolic amino-acetic (glycine) acids are preferred.
• Glycolic acid is specifically preferred in combination with glycerol.
• a mixture of two or more of these acids may be employed in combination with the mineral acid and the polyhydric alcohol.
• the amount of carboxylic acid included in the electrolyte is preferably between about 1% and about 4% by volume of the bath.
• a preferred concentration when glycolic acid is used in combination with glycerol is between about 1 and 2% by volume.
• the temperature at which anodizing is carried out must range from 18 to 30°C (65.-85° ⁇ 0 with room temperature condition, i.e., 68-75°, F, being preferred.
• the current density which is used in the anodizing operation be in the range of from about 24 to about 36 amperes/sq. ft. (2.6 to 3.9A/dm 2 ) .
• the time required to achieve the desired film thickness of between about 0.2 and 1.1 mils will vary with the other parameters of temperature, current density, chemical composition of the bath, etc., but generally anodizing times on the order of from about 8 to about 30 minutes produce acceptable results.
• the aluminum article is thereafter colored electrolytically by passing alternating current between said article and a counterelectrode an aqueous acidic solution containing a water soluble metal salt.
• the electrolytic coloring process is extremely well known in the art, and in this connection, is disclosed in the technical and patent literature, including U.S. Patent 3,669,856; 3,849,263 and 3,869,180; the disclosure of which is herein incorporated by reference.
• the preferred metallic salt is a salt of tin, although salts of nickel, cobalt, copper and silicomolybdic acid and silicotungstic acid can also be employed, individually or in combination.
• the salts of these metals could be formed by adding the metal to the sulfuric acid in. the bath, but, preferably a sulfate salt of the metal is added to the bath for better control of the amount of the metal in solution in the electrolyte.
• the metallic salts desired to provide the particular color can be utilized at a concentration of from 0.5 to 20% by weight, preferably about 2% by weight based on the electrolyte.
• the salts modify the pH of the electrolyte to which they are added, and the pH of the complete bath may ordinarily range from about 3.5 to 5.
• the pH may be as low as 1, preferably 1.5. Tin in the preferred metalibr the salt because of the high throwing power of the bath and resultant improved colour effects at such low pH values.
• the alternating current may have a frequency of 10-
• the counterelectrode which is employed is preferably made out of the same metal as the metal used in the electrolyte solution.
• the counterelectrode be made out of tin.
• counterelectrodes made of other materials, such as graphite, stainless steel or titanium can also be used.
• Another advantage of the novel process of this invention resides in the fact that it is possible to correct for too dark a color electrolytically which has heretofore been impossible with processes utilizing dyesor with processes involving simultaneous anodizing and coloring. According to this technique, after appliccation of an excess of color the polarity of the coloring system is reversed and color can be subtracted from the anodized layer.
• the electrolytic coloring process is carried out by passing an alternating current between the anodized article of aluminum or aluminum alloy which has been carried out in the manner above-described, and a counterelectrode immersed in an acid aqueous bath containing metal salts having coloring cations, wherein the colored tones of the coatings can be controlled in a simple manner by modulating the shape of the curve of the applied alternating voltage in such a manner that during the coloring process the alternating voltage will provide a suitable ratio between the two current directions for an advantageous transport of material and course of reaction with regard to said anodized aluminum article.
• the alternating voltage supplied is modulated as regarding its amplitude and/or frequency so as to make asymmetrical, thereby to control the color tone of the aluminum article.
• the modulation of the alternating- voltage can be carried out in several ways, such as simultaneously supplying two or more different alternating voltages or a superimposed direct voltage or by generating an alternating voltage having the desired frequency and curve shape.
• the material for the counterelectrodes can be stainless steel, titanium, copper, nickel, but preferably tin because they lead to advantageously low energy consumption.
• the strength of the alternating voltage in the modulation of the amplitude and/or frequency thereof according to the present process is from 5-50 volts, depending upon the composition of the electrolyte and the properties of the oxide layer previously formed.
• a current density of from 0.1 to 0.5 A/dm 2 , dependent on the electrolyte employed and a low treatment period of from 1 to 10 minutes.
• various soluble metallic salts can be employed.
• the preferred salts are those of tin, although salts of nickel, cobalt, copper, silicomolybdic acid and silicotungstic acid can also be employed.
• the electrolytic coloring bath also contains a strong acid which is desirably either sulfuric or hydrochloric.
• the metallic salts . e.g., sulfates, chlorides, acetates, etc. desired to provide the particular color can be utilized at a concentration of from 0.5 to 20% by weight, preferably about 2% by weight based on the electrolyte.
• the pH of the electrolyte may vary considerably within the acid range, but pHs of about 1.5 have been found to be useful.
• a particularly preferred embodiment resides in having present in the electrolyte a certain amount of aluminum.
• the aluminum can be provided by the addition of suitable aluminum compounds, such as aluminum sulfate or a certain part of a previously used electrolytic bath can also be used.
• suitable aluminum compounds such as aluminum sulfate or a certain part of a previously used electrolytic bath can also be used.
• the amount of aluminum which is present in the electro- lyte can range from 0-12 grams/liter, and more desirably, from 4-8 grams/liter.
• novel process of this invention is applicable to color articles made from aluminum, as well as from aluminum base alloys of all kinds.
• the coloring takes place faster, more efficiently if the alternating current is regulated relatively slowly of the order of a few seconds from 0 to the voltage which is desired for the coloring. This relates toboth the starting up of the coloring and to a latter supply of another alternating voltage than the one initially used.
• An aluminum article is anodized for about 24 minutes at 65°F in an anodizing bath at 1.5 pH and having the following composition:
• Example 2 The process of Example 1 is repeated with the exception that a deep red to black color is obtained, depending on duration, using copper sulfate instead of tin sulfate, a pH of 4.0 and a counterelectrode of graphite.
• Example 3 The process of Example 2 is repeated with the exception that bronze tones to black are obtained using cobalt sulfate as the salt.
• Example 2 The process of Example 2 is repeated with the exception that bronze tones are obtained using nickel sulfate as the salt and a counterelectrode of nickel.
• EXAMPLE 5 An aluminum article was anodized in accordance with normal anodizing techniques utilizing a current density of 24 amperes/sq. ft. and an electrolytic bath comprising 20 weight percent surfuric acid, and 8 grams/liter of oxalic acid. The temperature utilize ranged from 18-21°C, and the resulting aluminum article had an anodized layer of 25 microns. The results product was not suitable for coloring due to the fact that it was darkish in color.
• EXAMPLE 6 An aluminum article was anodized using a solution comprising 18 weight percent sulfuric acid, 1% glycolic acid and 1% glycerol. The anodizing was carried out at a current density of 36 amperes/sq. ft. at a temperature of about 19.5°C. After 13 minutes an anodized layer of approximately 0.83 mils was obtained.
• the anodized aluminum article was then electrolytically colored by immersing the same into a bath comprising 25 grams/liter sulfuric acid, 22 grams/liter sulfonic acid, 25 grams/liter tin sulfate, 5 grams/liter aluminum sulfate, 0.2 grams/liter of 8- naphthol and 0.4 grams of gelatin per liter.
• the electrolytic coloring was carried out by applying alternating current through the electrolyte at a voltage of 8 volts for three minutes. Three minutes of alternating current of half-wave was then applied. An aluminum article having a blackish color was obtained.
• EXAMPLE 7 An aluminum article was anodized utilizing the electrolyte solution of Example 2 at a current density of -40 amperes/sq. ft. at a temperature of 20°C.
• the anodized article which was obtained was thereafter electrolytically colored in accordance with the techniques of United States 3,669,856. This resulted in an article having poor color.
• EXAMPLE 8 An aluminum article was anodized utilizing the anodixing solution set forth in Example 2 at a temperature of 20°C and at a current density of 48. amperes/sq. ft. The anodizing was carried out until an anodized layer was obtained which had a thickness of about 1.65 mils. Subsequent color anodizing of this material in accordance with the techniques of this invention resulted in spalling on the anodic film.
• EXAMPLE 9 An aluminum article was anodized utilizing the electrolyte solution of Example 2 at a temperature of 21°C until an anodized layer having a thickness of about 8 mils was obtained.
• This material was then electrolytically colored utilizing the techniques Of United States 3,669,856 and the color solution of Example 2. Alternating current was applied for 1 1/2 minutes and thereafter a half-wave alternating current was applied for a half-minute. The resulting material was colored satisfactorily and was capable for use as an architectural material.
• An aluminum article was anodized using the electrolytic solution of Example 2 at a temperature of 20°C for six minutes in order to obtain an article which had a thickness of approximately 0.4 mils.
• This material was then electrolytically colored utilizing the solution of Example 2 by passing normal AC current between the aluminum article and a counter- electrode for two minutes, thereafter an alternating current having a minus half-wave which was asymmetrical was applied for one minute.
• Example 12 An aluminum article was anodized utilizing the solution of Example 2 at a temperature of 20°C, a current density of 36 amperes/sq. ft. in order to obtain a material which had a thickness of 1.1 mils. The material was thereafter color anodized utilizing the tin solution set forth in Example 2 and the technique of United States 3,669,856. Alternating current was applied for 1 1/2 minutes followed by half-wave at one minute. A perfectly acceptable colored article was obtained. EXAMPLE 12
• Example 5 The process of Example 5 is repeated with the exception that after the product was run to a bronze color, it was immersed in an oxidizing acid, preferably 20-30 volume % nitric acid at room temperature, which resulted in a uniform champagne color. This color is virtually impossible to produce in a uniform manner by any other known process.
• an oxidizing acid preferably 20-30 volume % nitric acid at room temperature

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Citations (5)

• 1979
  • 1979-06-14 JP JP50109579A patent/JPS55500501A/ja active Pending
  • 1979-06-14 WO PCT/US1979/000417 patent/WO1980000158A1/en unknown
  • 1979-06-14 DE DE7979900757T patent/DE2965186D1/de not_active Expired
  • 1979-06-27 AR AR277079A patent/AR222177A1/es active
  • 1979-06-28 NL NL7905049A patent/NL7905049A/nl not_active Application Discontinuation
  • 1979-06-28 IT IT23954/79A patent/IT1125392B/it active
  • 1979-06-28 ES ES482021A patent/ES482021A1/es not_active Expired
  • 1979-06-28 BE BE0/196018A patent/BE877340A/xx not_active IP Right Cessation
• 1980
  • 1980-02-01 EP EP79900757A patent/EP0015279B1/en not_active Expired
  • 1980-02-26 DK DK81680A patent/DK81680A/da not_active Application Discontinuation

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