JP3140165B2 - Method for electrolytic coloring of anodized aluminum surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to a method for electrolytically coloring anodized aluminum surfaces.

[0002]

BACKGROUND OF THE INVENTION U.S. Pat. No. 4,310,586 discloses a method for forming a colored anodic oxide film on aluminum and anodizable aluminum alloys. In this method, a porous anode film having a thickness of at least 3 microns is first formed on a surface of an object made of aluminum or an anodizable aluminum alloy, the metal being contained in pores in the anode film containing the metal salt. Deposition is performed by electrodeposition from the electrolyte, followed by further anodic oxidation to increase the thickness of the anode film between the inner edge of the deposit and the underlying surface of the metal object. The film thus formed becomes colored by the light interference effect. Light incident on this film is partially reflected by the discontinuous surface formed by the outer edges of the metal deposit, and partially reaches the underlying surface of the object through the film, where the arriving light causes reflection. . The light reflected from the attached matter and the light reflected from the object optically interfere with each other, and when the difference in the optical path length is on the order of the wavelength of the light, the light is colored. Anodization following the deposition of metal in the pores increases the optical path length (between light reflected from the deposit and light reflected from the object) without increasing the This is done to increase the volume. This increases the absorption of light by the deposits and leads to relatively large muddiness of visible light. In U.S. Pat. No. 4,310,586, it was recognized that metal deposits were easily dissolved during the re-anodization step, in some cases causing fading, and in some cases the color disappeared completely. . For example, leaching resistant alloyed deposits such as tin-nickel have been proposed for use with non-agglomerated reanodizing electrolytes. These solutions have not been fully satisfactory. Electrolytes based on non-cohesive acids, for example, preferably sulfosalicylic acid, have relatively low electrical conductivity. Prolonging the re-anodization of the deposit in these electrolytes results in non-uniform coloring. This is because anodic oxide growth occurs at different rates throughout the aluminum surface being colored. The use of only alloyed deposits does not solve the leaching problem to a degree sufficient to re-anodize in a more commercially acceptable conductive electrolyte. In addition, their use adds a rather complex problem related to process control. It is also known to make the metal deposit more resistant to dissolution by replacing the initially deposited metal with precious metals having corrosion resistance (gold and palladium disclosed). However, this method is only used where the anode film is very thin. This is because new access to the deposit by the noble metal in the solution is possible. This was considered important. This is because the redox reaction occurring in the pores causes substantial depletion of precious metal ions physically close to the deposit. It was thought necessary to limit the film thickness to about 3 microns.

[0003]

Accordingly, there is a need to provide an improved method of providing interference colored products with relatively thick anode films, such as those used in architectural and automotive applications.

[0004]

SUMMARY OF THE INVENTION The present invention provides at least about 3
A method for producing an interference colored product comprising a porous anode film having a thickness of microns. The method comprises porous anodizing a surface of an object made or coated with aluminum or an anodizable aluminum alloy to form an anode film having a thickness of at least about 3 microns, and depositing a metal within pores of the anode film. Forming a metal deposit by electrodeposition. The electrodeposited metal may be either a noble metal or a non-noble metal. If a non-noble metal, the film is contacted with a solution of a noble metal salt to at least partially convert the non-noble metal to a noble metal. If the deposited metal is a noble metal, this extra step is of course not necessary. Thereafter, the object is further anodized in an electrolyte containing a strong acid to increase the separation between the deposit and the object. A small amount of the deposit is electrodeposited in the hole so that the next anodization can be performed uniformly over the entire surface. The present invention also provides
The present invention relates to a product having uniform coloring produced by the method of the present invention. The term "precious metal" as used herein means gold, platinum, palladium, ruthenium, rhodium, terium, iridium, rhenium, osmium, combinations thereof, or alloys thereof. Also,
The term "non-noble metal" as used herein means tin, nickel, cobalt, copper, silver, cadmium, iron, lead, manganese, molybdenum, or a combination or alloy thereof. In addition, the term strong acid means an acid capable of forming a highly electrically conductive electrolyte when used in a standard amount that allows anodic oxidation to be performed by conventional methods at conventional rates. Specific examples of these acids are sulfuric acid and phosphoric acid.

[0005]

In the present invention, the formation of deposits on the structure disclosed in U.S. Pat. No. 4,310,586 by the careful use of noble metals allows the formation of a high grade anode film having a thickness greater than about 3 microns. It has been found that interference colors with color uniformity can be formed. Generally, the method of the present invention is a different building batch process than the so-called web process. This may be because the workpiece may be complex (e.g., a complex extrusion rather than a flat foil or plate), and the spacing between the workpiece and the electrode may vary from batch to batch, resulting in a flat web. It becomes more difficult to maintain uniform coloring than in a process for coloring.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific examples. FIGS. 1A to 1E illustrate preferred specific examples. FIG. 1A shows an object 10 made of aluminum or an anodizable aluminum alloy or coated adjacent an outer surface 11 thereof. The object 10 may be, for example, a thin flexible foil, a laminate, a plate, a sheet,
It can be an extruded product, a cast product, a molded part or a product of the type normally subjected to anodization for protection or decoration.

As shown in FIG. 1B, an article 10 is first
The porous anode film 12 is formed on the surface 11 of the object by being subjected to a porous ancdization process. The film 12 has a hole 14 extending from the outer surface 15 of the film to the metal object 10 inward. The film 12 is immersed in a conventional method, for example, immersing the surface in an electrolyte containing a strong acid (usually an inorganic acid) such as sulfuric acid or phosphoric acid or a mixture of a strong acid and a relatively weak organic acid (oxalic acid). It is formed by bringing an electrode into contact with a liquid and applying a voltage between the electrode and the object. The applied voltage is AC, DC,
It may be AC / DC, pulsed high voltage, low voltage, ramped voltage, etc., and is typically in the range of 10-110V. However, in the final stage of anodization, the inner end 16
Barrier layer 1 of non-perforated anodic oxide
Separated from the object 10 by 7 and implemented to allow subsequent electrodeposition of metal in the hole 14. This can be achieved, for example, by anodizing at a DC voltage of 2 to 50 V, preferably 5 to 20 V. This electrolysis is preferably continued until the overall thickness of the anode film 12 is at least 3 microns and the film is protected against weathering or the like of the object 10. In fact, film 12 is 3
It can be manufactured to have a thickness of up to 0 or 40 microns. The barrier layer 17 is usually 20 to 500
Å, preferably in the range of 50-200Å.

As shown in FIG. 1B, the hole 14 preferably has a uniform thickness over its entire length, but a hole having a narrow inner portion and a wide inner portion (not shown). It is more preferred to manufacture. So-called bottleneck holes can be formed by changing the acid of the electrolyte from a relatively non-corrosive acid (eg, sulfuric acid) to a relatively corrosive acid (eg, phosphoric acid) throughout the electrolytic process. The details of this method are described in US Patent No. 4,066,816 to Sheasby et al.

As shown in FIG. 1B, a deposit composed entirely or partially of the noble metal 20 is formed in the hole 14. This can be achieved by one of the following methods. The first can be formed directly by electrodepositing the deposit 20 from an electrolyte containing a soluble salt of a noble metal. This involves, for example, immersing the surface 15 at least partially in a suitable noble metal salt (e.g., palladium nitrosylsulfate) and contacting the electrolyte directly or indirectly with an electrode (e.g., graphite) to form the object 10 And by applying an electrical program between the electrodes. This electrical program may be current or voltage controlled, AC, DC, AC / D
C, pulse, lamp, etc.

In the other, as shown in FIG. 1C, a non-precious metal is electrodeposited in the hole 14 to form a non-precious metal deposit 19. This involves, for example, immersing the surface in an electrolyte containing one or more non-precious metal salts (eg, nickel sulfate), bringing the electrolyte into contact with an electrode (eg, made of graphite), and applying an electric current between the object 10 and the electrode. Can be achieved by applying a strategic program. This electrical program may be current or voltage controlled, AC, DC, AC /
Including DC, pulse, lamp, etc. The non-noble metal deposit is then at least partially converted to a noble metal deposit 20.
This is done by bringing the surface 15 into contact with a dilute solution of a noble metal by dipping or spraying. This solution preferably contains at least one noble metal in less than 5000 ppm, and may be as low as 50 ppm. For example, a suitable solution can be prepared by dissolving 300 mg / l or more of palladium sulfate in water.
If desired, the above methods may be combined by direct electrodeposition / substitution from an electrolyte containing both noble and non-noble metals. This combination process has the advantage of reducing starting material costs.

It should be noted that it is surprising that noble metal solutions can be used to replace non-noble metal deposits 19. Thick anode film 1
2 (e.g., up to 25 microns), the pores 14 are very long and narrow (e.g., 25 microns long, typically having an average diameter of 250 DEG), so that the length to diameter ratio is typically about 1
000: 1. Once this hole is filled with liquid
This liquid appears to be very inert in the pores.
The concentration of precious metals in the processing solution is very low (average 3
(50 ppm), it is surprising that enough noble metal diffuses to the lower end of the pores (where the deposits are located) to replace the noble metal. According to the measurement (ICP atomic absorption spectroscopy), the resulting noble metal deposit showed that the consumption of the entire noble metal in the solution contained in the 25-micron long hole was 35
Have the amount you need more than once. That is, the holes must be filled 35 equivalents and consumed.

The method used to provide the noble metal deposit 20 in the hole 14 may be any of the above, but it is important to minimize the amount or volume of the deposit as much as possible. Otherwise, it is difficult to achieve good coloring uniformity.
An advantage of the method of the present invention is that very small amounts of metal deposits can be used since the subsequent leaching step is minimal since the corrosion resistance of the noble metal is very high. Theoretically, if the deposits 20 are very large, they will act as obstacles to the next anodizing step, which is described below, with consequent color nonuniformity. The deposit 20 is porous but in an amount sufficient to prevent the next anodization, or at best uncontrollable and not uniform over the entire metal surface.

The maximum allowable size or amount for good color uniformity of the deposit 20 depends on the voltage used in the subsequent anodizing step and the conditions used in the electrodeposition step, and is suitable in all cases. The prescribed amount cannot be explained. However, the deposit 20 is generally not greater than 250 nm in depth (vertical thickness), and preferably 20-70 nm in depth. Suitable deposits include electrodeposition (non-noble metal deposits 19), usually performed at a current density in the range of 0.05 to 0.5 A / dm ² for 5 to 500 seconds.
Or any of the noble metal deposits 20).

Once a suitable noble metal deposit is one of the techniques described above,
When they are formed by one, as shown in FIG.
The following anodization step is performed to thicken the anode film 12 below the anode film 12. This anodic oxidation step further oxidizes the metal surface 11 and extends the hole 14 below the deposit 20. This increases the separation between the semi-reflective surface 20 formed by the outer edge of the deposit 20 and the reflective surface 11 of the object 10. This increased separation increases the range of coloration displayed by the film, approaching dichroic colors (ie, the coloration varies with viewing angle). In a complete sense, the increased separation is still the realm of the optical interference distance
m] (ie, in the order of the light wavelength). In order to achieve uniform coloring, it is important that the porous oxide optical interference layer 12b be formed at a uniform rate over the entire surface of the material being processed.
A particular advantage of the method of the present invention is that by providing the deposit 20 of a noble metal such as palladium, an electrolyte containing a strong acid (e.g., sulfuric acid or phosphoric acid) can be dissolved without partial or complete dissolution of the deposit 20. It can be used for the next anodizing step. This has the advantage that the use of a strong acid results in a highly conductive electrolyte, which causes a uniform anodic oxidation below the deposit 20 necessary for the formation of a uniformly colored surface. It is also possible to use a mixture of a strong acid and a weak acid, such as a mixture of sulfuric acid and oxalic acid. The use of a relatively weak acid, such as sulfosalicylic acid, must avoid significant dissolution of non-noble metal deposits in advance, resulting in a relatively poorly conductive electrolyte that results in non-uniform anodic oxidation. Become. The effect of varying oxide growth rate on color uniformity is shown graphically in FIG.
Color uniformity (from good to poor) is shown on the Y-axis. The available range of coloration is plotted on the X-axis (the X value is in fact proportional to the oxide thickness, each thickness being associated with an independent interference color, for example, 40 = violet). The dashed curves show the different color sensitivity when the final anodization rate is changed by 13% (typically with sulfosalicylic acid). The solid curve shows the sensitivity when the final anodization rate changes by 2% (in the case of sulfuric acid). Horizontal double line should not be exceeded Industrial standard color uniformity
(Or sensitivity) limits. The portion of the curve that falls below this line indicates a color with acceptable color uniformity. As can be seen from the solid curves, all available colors are acceptable when sulfuric acid is used. This is not the gray and blue gray obtainable by the prior art. In addition to the choice of acid contained in the final anodizing electrolyte, improvements to film pressure uniformity can be achieved by the following additional factors. One is to optimize the chemistry and temperature of the electrolyte (to maximize conductivity), such as the addition of salts and other compounds. Another is an electrical program, such as reduced current density, current or voltage control, DC, AC, AC / DC, waveform changes,
Optimize pulse DC, ramp, frequency, etc. Upon completion of the next anodization, normal finishing steps can be performed if desired. However, conventional chromating, which is commonly used to prevent migration or leaching of deposits during subsequent processing steps or during use of the product, is not required. This is because when the deposit 20 is at least partially composed of a noble metal, it is ready for such leaching or migration. Typical final processing involves overstaining
yeing), hot water sealing, electrophoretic organic coating, and lacquering. The present invention is further described by the following non-limiting examples. EXAMPLE 1 A chemically glossed sheet of aluminum alloy AA5657 is anodized in 3500 ml at 15 volts for 10 minutes with sulfuric acid at a concentration of 156 g / l at 21 ° C. to form a 3.4 mm thick anode film. The sheet is washed with water and anodized again in a warm 100 g / l phosphoric acid solution for 5 minutes using 8 V DC (during which time the pores and barrier layer are modified). Following rinsing, the sheet is immersed in a standard nickel ANOLOK ™ solution in contact with a single graphite electrode. Nickel is electrodeposited from this solution for 60 seconds using AC with an applied voltage of 7V peak. Subsequent to the water washing, the substrate is immersed in a 400 ppm Pd (palladium sulfate) solution for 5 minutes, and anodized again in the original sulfuric acid solution with a DC voltage of 10 V applied. Table 1 shows the colorations obtained after various anodization times.

[Table 1] The resulting coloration was highly desirable with uniformity from back to front and edge to center. Example 2 The same method as in Example 1 was carried out as a whole using an 8-inch extruded aluminum alloy AA6063. The cross section was a complex shape with an outer circumference of about 10 inches. The difference from the method of Example 1 is that the film is 15
It has grown to a micron thickness and has increased the size of the graphite counter electrode in the ANOLOK ™ beaker. Similar results were achieved, with excellent color uniformity over the entire surface of the product. EXAMPLE 3 Clean AA6063T4 aluminum alloy subjected standard pre-etching _{treatment, 165g / l H 2 SO 4} , 10
Anodized with stirring at 17 ° C. DC in g / l (COOH) ₂ for 60 minutes. The panel was subjected to pickling (pH〜2) and initially 10 VrmsA at 15 ° C. in 100 g / l H ₃ PO _4.
C (60 Hz) was applied for 4.5 minutes, then 10 V DC
Was applied with stirring for 1 minute. Pickle this panel (p
H-2) and neutral washing. Nickel was deposited in the pores from a solution containing 150 g / l magnesium sulfate pentahydrate and 35 g / l boric acid, using 21 g / l of nickel as nickel sulfate. The pH was adjusted to 5.5 using magnesium oxide and sulfuric acid. 10Hz with current control
AC square wave power supply was used for electrodeposition. The current density was maintained at 0.12 A / dm ² for 25 seconds without stirring. The panel was neutrally washed and immersed in a solution containing palladium for about 2 minutes with slight agitation. About 0.7 g of this solution
Of Pd (II) SO ₄ was dissolved in 5 ml of 18M sulfuric acid and made up to 1 l with deionized water. The panel was neutrally washed and subjected to normal pre-sealing and sealing treatments. The resulting panel had a clean uniform coloration. Table 2 shows the colorations obtained after various anodization times.

[Table 2]

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing the progress (A) to (E) of an aluminum-containing object and an anode film in a preferred method of the present invention.

FIG. 2 is a graph showing the color uniformity of available colors formed by the method of the present invention and the conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Object 11 Surface 12 Film 14 Hole 17 Barrier layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mike Patrick Thomas Canada, No. 29, Ellebeck Street, Kingston, Ontario, K7EL4H5 (56) References JP-A-54-112347 JP, A) JP-A-57-85995 (JP, A) JP-T-Hei 6-506985 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 11/22, 11/18

Claims (10)

(57) [Claims] 1. A method of making an interference colored product having a porous anode surface film having a thickness of at least about 3 microns, wherein the product is made of a material selected from the group consisting of aluminum and anodizable aluminum alloys. A step of porous anodizing the surface of the coated object to form a porous anode film, and electrodepositing a material containing a noble metal or a non-noble metal in pores in the porous anode film, When contains a non-noble metal, further contacting the porous anode film with a noble metal salt solution to replace at least a portion of the non-noble metal with a noble metal, forming a metal-containing deposit in the pores, In order to increase the separation distance between the metal-containing deposits and the surface of the object, the method includes anodizing the object in an electrolytic solution containing a strong acid, The anodic oxidation is performed uniformly by forming the metal-containing deposit to be thin, and the porous anodic oxidation and the anodic oxidation are performed so that the anode film has a thickness of at least about 3 microns. A manufacturing method characterized in that: 2. The method of claim 1 wherein said metal-containing deposit is electrodeposited in said pores to a thickness of 250 nm or less. 3. The method of claim 1 wherein said metal-containing deposit is electrodeposited in said pores to a thickness of 20-70 nm. 4. The method of claim 1, wherein the material deposited in the pores comprises a non-precious metal. 5. The non-noble metal is nickel, cobalt,
5. The method of claim 4, wherein the method is selected from the group consisting of silver, tin, copper, iron, cadmium, lead, manganese, molybdenum, or alloys thereof, or a combination thereof. 6. The noble metal salt is a metal salt selected from the group consisting of palladium, platinum, gold, ruthenium, rhodium, terium, iridium, rhenium, osmium or an alloy thereof, or a combination thereof. 4. The method according to 4. 7. The non-noble metal is nickel, cobalt,
The method according to claim 4, wherein the noble metal salt is selected from the group consisting of copper and tin, and the salt is a palladium salt. 8. The method according to claim 1, wherein the material deposited in the holes is a noble metal. 9. A reflective object having a surface, a porous anode film covering the surface of the object and having a thickness of at least 3 microns, and a deposit containing a noble metal located in a hole of the porous film. A uniformly colored structure wherein the deposits are equally spaced from the object over the entire surface. 10. A process for forming a porous anode film by porous anodizing a surface of an object manufactured or coated with a material selected from the group consisting of aluminum and an anodizable aluminum alloy; A material containing a noble metal or a non-noble metal is electrodeposited in the pores of the porous anode film, and when the material contains a non-noble metal, the porous anode film is further contacted with a noble metal salt solution to at least partially remove the non-precious metal. Replacing the noble metal with a noble metal to form a metal-containing deposit in the pores, and increasing the separation distance between the metal-containing deposit and the object surface, in an electrolyte containing a strong acid. A step of performing anodization of the object; forming the metal-containing deposit in a thin thickness so that the anodization is performed uniformly; The anodic oxidation, the anode film of at least about 3 microns as claimed in claim 9, wherein formed by a method of performing so as to have a thickness structure.