EP0015279B1 - Coating system - Google Patents

Coating system Download PDF

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Publication number
EP0015279B1
EP0015279B1 EP79900757A EP79900757A EP0015279B1 EP 0015279 B1 EP0015279 B1 EP 0015279B1 EP 79900757 A EP79900757 A EP 79900757A EP 79900757 A EP79900757 A EP 79900757A EP 0015279 B1 EP0015279 B1 EP 0015279B1
Authority
EP
European Patent Office
Prior art keywords
aluminum
process according
coloring
anodized
bath
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP79900757A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0015279A4 (en
EP0015279A1 (en
Inventor
George R. Darrow
Adam J. Walsh
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Reynolds Metals Co
Original Assignee
Reynolds Metals Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US05/972,928 external-priority patent/US4180443A/en
Priority claimed from US06/000,022 external-priority patent/US4179342A/en
Application filed by Reynolds Metals Co filed Critical Reynolds Metals Co
Publication of EP0015279A1 publication Critical patent/EP0015279A1/en
Publication of EP0015279A4 publication Critical patent/EP0015279A4/en
Application granted granted Critical
Publication of EP0015279B1 publication Critical patent/EP0015279B1/en
Expired legal-status Critical Current

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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.
  • Patents 3,669,856; 3,769,180 and 3,849,263 represent recent developments in the field of coloring aluminum or aluminum al!oys. These patents are, in general, directed towards the coloring of anodized aluminum by immersing said article in a bath containing a salt of a particular metal and passing an alternating current between the previously anodized article and a counter- electrode.
  • both processes produce an anodized layer which is relatively thick (customarily 38 ,um-1.5 mil-or heavier) in order to obtain high heat resistance and is of a darkish, muddied colour, thereby rendering it unsuitable for use in a process where light, un- muddied colours 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 described by this patentee.
  • This patent describes 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 and 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.
  • the electrolyte also contains an alkali salt of a titanic acid complex of a hydroxy- aliphatic carboxylic acid containing from 2 to 8 carbon atoms, such as, for example, titanium di- lactate ammonium salt.
  • 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 colouring bath at the same time.
  • spacing of the various workpieces in the colouring bath was a critical factor in successfully uniformly colouring aluminum extrusions, particularly for architectural purposes.
  • the present invention now provides a process for the production of coloured protective coatings on articles of aluminum or aluminum alloys wherein the article is first anodized and thereafter an alternating current is passed between the anodized article and a counter-electrode immersed in an acidic aqueous bath containing salts of metals capable of colouring the anodized layer, characterized in that the article is anodized in an electrolyte comprising from 12 to 24 weight percent sulfuric acid, from 1 to 4 volume percent of polyhydric alcohol of from 3 to 6 carbon atoms and from 1 to 4 volume percent of an organic carboxylic acid containing at least one reactive hydroxy, amino, keto or carboxyl group in the alpha-position in the absence of a titanic complex, at a temperature of 18-30°C (65-85°F) at a current density of 2.6-3.9 A/dm 2 (24-36 amperes/sq. ft.) until there is obtained an anodized layer having a thickness of from 5 to 2 ⁇ m (
  • the anodic layer be from 5 to 28 ⁇ m in the thickness, and preferably 15 to 28 pm (0.6 to 1.1 mils), as opposed to the 25-127 pm (1-5 mils) set forth at column 3, line 26 of said U.S. Patent 3,524,799.
  • 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 1 5%.
  • 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 the polyhydric alcohol employed ranges from 1% to 4% by volume of the anodized 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 between 1% and 4% by volume of the bath.
  • a preferred concentration when glycolic acid is used in combination with glycerol is between 1 and 2% by volume.
  • the temperature at which anodizing is carried out must range from 18 to 30°C (65-85°F) with room temperature conditions, i.e. 20-24°C (68-75°F) being preferred.
  • the current density which is used in the anodizing operation be in the range of from 24 to 36 amperes/sq. ft. (2.6 to 3.9 A/d M 2 ).
  • the time required to achieve the desired film thickness of between 5 and 28 pm (0.6 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 in 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 metal for 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 10-500 periods per second, preferably 50 periods per second, and a voltage of 2-50 volts and a current density of 0.2-1.0 A/dm 2 based on the surface of the aluminum article.
  • the counterelectrode which is employed is preferably made out of the same metal as the metal used in the electrolyte solution. Thus, for example, when utilizing a tin salt in order to impart a bronze color, it is preferred that the counterelectrode be made out of tin. As is known in the art, however, this is not necessary and 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 dyes or with processes involving simultaneous anodizing and coloring. According to this technique, after application 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.
  • 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
  • the metallic salts e.g., sulfates, chlorides, acetates, etc. desired to provide the particular color
  • 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 electrolyte can range from 0-12 grams/liter, and more desirably, from 4-8 grams/liter.
  • novel process of this invention is applicable to colour articles made from aluminum, as well as from aluminum base alloys of all kinds.
  • the colouring 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 colouring. This relates to both the starting up of the colouring and to a latter supply of another alternating voltage than the one initially used.
  • An aluminum article is anodised for about 24 minutes at 18°C (65°F) in an anodizing bath at 1.5 pH and having the following composition: with a constant current density of about 2.6 amperes/sq. dm (24 amps/sq. ft.) and a DC voltage rising to about 20 volts.
  • An anodic coating of about 20 ⁇ m (0.8 mils) is obtained.
  • the anodized aluminum article is electrically connected with a counterelectrode of tin in an aqueous electrolyte containing 2% by weight stannous sulfate and about 50 ml concentrated sulfuric acid per liter, an alternating current at 5-8 volts is supplied to the electrodes at room temperature for a period ranging from 5-15 minutes and the current density is varied from 0.2 to 0.8 a/dm 2. Very attractive bronze tones or black are obtained on the aluminum articles, depending on the duration of the supply of alternating current.
  • Example 1 The process of Example 1 is repeated with the exception that a deep red to black colour is obtained, depending on duration, using copper sulfate instead of tin sulfate, a pH of 4.0 and a counterelectrode of graphite.
  • Example 2 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 counter- electrode of nickel.
  • An aluminum article was anodized in accordance with normal anodizing techniques utilizing a current density of 2.6 amperes/sq. dm. (24 amps/sq. ft.) and an electrolytic bath comprising 20 weight percent sulfuric acid, and 8 grams/liter of oxalic acid.
  • the temperature utilized ranged from 18-21 °C, and the resulting aluminum article had an anodized layer of 25 microns. The results produced was not suitable for colouring due to that fact that it was darkish in colour.
  • 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 3.9 amperes/sq. dm. (36 amps/sq. ft.) at a temperature of about 19.5°C. After 13 minutes an anodized layer of approximately 21.1 pm (0.83 mils) was obtained.
  • the anodized aluminum article was then electrolytically coloured 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 A-naphthol and 0.4 grams of gelatin per liter.
  • the electrolytic colouring was carried out by applying alternating current through the electrolyte at a voltage of 8 volts for three minutes. Three minutes of half-wave alternating current was then applied.
  • An aluminum article was anodized utilizing the electrolyte solution of Example 6 at a current density of 4.3 amperes/sq. dm. (40 amps/sq. ft.) at a temperature of 20°C.
  • An aluminum article was anodized utilizing the anodizing solution set forth in Example 6 at a temperature of 20°C and at a current density of 5.2 amperes/sq. dm. (48 amps/sq. ft.). The anodizing was carried out until an anodized layer was obtained which had a thickness of about 41.9 pm (1.65 mils). Subsequent colour anodizing of this material in accordance with the techniques of this invention resulted in spalling on the anodic film.
  • An aluminum article was anodized utilizing the electrolyte solution of Example 6 at a temperature of 21 °C until an anodized layer having a thickness of about 20 pm (0.8 mils) was obtained.
  • This material was then electrolytically coloured utilizing the techniques of United States 3,669,856 and the colour solution of Example 6. Alternating current was applied for 11 2 minutes and thereafter a half-wave alternating current was applied for a half minute. The resulting material was coloured satisfactorily and was capable for use as an architectural material.
  • An aluminum article was anodized using the electrolytic solution of Example 6 at a temperature of 20°C for six minutes in order to obtain an article which had a thickness of approximately 10 ⁇ m (0.4 mils).
  • This material was then electrolytically coloured utilizing the solution of Example 6 by passing normal AC current between the aluminum article and a counterelectrode for two minutes, thereafter an alternating current having a minus half-wave which was asymmetrical was applied for one minute.
  • An aluminum article was anodized utilizing the solution of Example 6 at a temperature of 20°C, a current density of 3.9 amperes/sq. dm. (36 amps/sq. ft.) in order to obtain a material which had a thickness of 28 pm.
  • the material was thereafter colour anodized utilizing the tin solution set forth in Example 6 and the technique of United States 3,669,856. Alternating current was applied for 11 2 minutes followed by half-wave at one minute. A perfectly acceptable coloured article was obtained.
  • Example 9 The process of Example 9 is repeated with the exception that after the product was run to a bronze colour, it was immersed in an oxidizing acid, preferably 20-30 volume % nitric acid at room temperature, which resulted in a unfirm champagne colour. This colour 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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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
EP79900757A 1978-06-28 1980-02-01 Coating system Expired EP0015279B1 (en)

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
US92005378A 1978-06-28 1978-06-28
US92005778A 1978-06-28 1978-06-28
US920057 1978-06-28
US920053 1978-06-28
US972928 1978-12-26
US05/972,928 US4180443A (en) 1978-06-28 1978-12-26 Method for coloring aluminum
US06/000,022 US4179342A (en) 1978-06-28 1979-01-02 Coating system method for coloring aluminum
US22 1979-01-02

Publications (3)

Publication Number Publication Date
EP0015279A1 EP0015279A1 (en) 1980-09-17
EP0015279A4 EP0015279A4 (en) 1980-10-16
EP0015279B1 true EP0015279B1 (en) 1983-04-13

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ID=27484965

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Application Number Title Priority Date Filing Date
EP79900757A Expired EP0015279B1 (en) 1978-06-28 1980-02-01 Coating system

Country Status (10)

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EP (1) EP0015279B1 (it)
JP (1) JPS55500501A (it)
AR (1) AR222177A1 (it)
BE (1) BE877340A (it)
DE (1) DE2965186D1 (it)
DK (1) DK81680A (it)
ES (1) ES482021A1 (it)
IT (1) IT1125392B (it)
NL (1) NL7905049A (it)
WO (1) WO1980000158A1 (it)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4451335A (en) * 1980-11-24 1984-05-29 Woods Jack L Method for producing full color images on aluminum
ES2037578B1 (es) * 1991-04-10 1994-02-01 Novamax Technologies Holding I Metodo para la obtencion, por via electronica, sobre aluminio anodizado, de una gama de colores grises.
JP4660760B2 (ja) * 2005-06-02 2011-03-30 国立大学法人広島大学 アルミニウム又は／及びアルミニウム合金の陽極酸化皮膜の形成方法およびその方法により形成される陽極酸化皮膜
DK2665842T3 (en) * 2011-01-17 2015-03-23 Hydro Aluminium Rolled Prod Exterior facade metal plate made of aluminum with a high surface roughness
CN111876812B (zh) * 2020-08-01 2021-11-05 东莞市慧泽凌化工科技有限公司 一种无镍电解着色增黑添加剂及其使用方法

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1902983C3 (de) * 1968-06-21 1978-06-22 Keller, Eberhard, 7121 Freudental Verfahren zum elektrolytischen Färben von anodischen Oxidschichten auf Aluminium oder Aluminiumlegierungen
US3524799A (en) * 1969-06-13 1970-08-18 Reynolds Metals Co Anodizing aluminum
NO120248B (it) * 1969-06-25 1970-09-21 O Gedde
US3769180A (en) * 1971-12-29 1973-10-30 O Gedde Process for electrolytically coloring previously anodized aluminum using alternating current
JPS5249408B2 (it) * 1972-11-21 1977-12-17

Also Published As

Publication number Publication date
BE877340A (fr) 1979-10-15
EP0015279A4 (en) 1980-10-16
ES482021A1 (es) 1980-02-16
EP0015279A1 (en) 1980-09-17
DK81680A (da) 1980-02-26
JPS55500501A (it) 1980-08-07
IT7923954A0 (it) 1979-06-28
AR222177A1 (es) 1981-04-30
IT1125392B (it) 1986-05-14
NL7905049A (nl) 1980-01-03
WO1980000158A1 (en) 1980-02-07
DE2965186D1 (en) 1983-05-19

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