US3532607A - Production of anodised surfaces of aluminum or aluminum alloys - Google Patents

Description

United States Patent 3,532,607 PRODUCTION OF ANODISED SURFACES OF ALUMINUM OR ALUMINUM ALLOYS Kenneth Edward Roberts, Dorchester, Dorset, England, assignor to Anomate Products Corporation, Summit,

NJ. No Drawing. Filed Feb. 20, 1967, Ser. No. 617,056 Claims priority, application Great Britain, Feb. 26, 1966,

8,575/ 66 Int. Cl. C23b 9/02; B44c l/04 US. Cl. 204-18 4 Claims ABSTRACT OF THE DISCLOSURE a two-coloured or multi-coloured design on such an anodised plate using a photosensitive resist is described.

This invention relates to the anodising of surfaces of aluminum or aluminium alloys containing at least 99% of aluminum and more particularly to the anodising of such a surface prior to the production thereon of a twocolour or multi-colour design using a photosensitive resist and an appropriate dye or dyes. One of the two or more colours may be the natural colour of the anodised surface.

The production of such designs on anodised aluminum surfaces is of particular interest for the production of nameplates, for example, for attachment to machines, but it is of interest also in the other and wider fields, for example, the use of decorated aluminum panels in the construction of dwelling houses or other buildings. Hitherto, however, in order to avoid impairment of the anodised coating, it has been necessary either to seal the oxide coating by suitable treatment after anodising, either immediately after washing or after the oxide coating has been dyed, or to protect the oxide coating during the production of the design by a layer of a protective material such as gelatine. The introduction of the sealing step at this stage in a manufacture of the decorated surfaces is inconvenient, particularly where an entirely automatic process is required, and may, moreover, limit the methods which can be used for producing the design, or may produce an inferior product owing to partial destruction of the anodised layer during the process of producing the design. The use of a gelatine coating obviously complicates the production of the design by the introduction of the coating step.

It is an object of the present invention to provide a process for producing an anodised surface, of aluminum or an aluminum alloy containing at least 99% by weight of aluminum for use where a coloured design is subsequently to be produced on the anodised surface, by the use of which these disadvantages may be overcome or at least minimised.

According to the invention, there is provided a process for producing an anodised surface of aluminum or an aluminum alloy containing at least 99% by weight of aluminum, for use where a two-colour or multi-colour design is subsequently to be produced on the anodised surface using a photosensitive resist and one or more dyes, comprising the step of anodising the surface in an anodising solution consisting of dilute aqueous sulphuric acid containing 5-20% by volume of sulphuric acid, using a direct current at- 10.5 to 24 volts, the current being maintained within the range 9-20 amps per square foot, the temperature in the range 40-90 F. and the treatment time in the range -60 minutes.

3,532,607 Patented Oct. 6, 1970 It has been found that by suitable selection of the anodising conditions within the ranges specified above in accordance with the particular material being treated, the anodised surface can be used in the unsealed state for subsequent processing to produce the design without any danger of impairment of the anodised oxide layer, and without the necessity for adopting special and complicated techniques in the production of the design.

The particular values of each of the parameters involved will depend upon the nature of the material being treated, the parameters being mutually adjusted in accordance with the physical form and chemical composition of the metal.

Thus, for example, in the treatment of standard 99.5% aluminum sheet in gauges 10 SWG. to 30 SWG., manufactured by the British Aluminium Company Ltd., using a bath containing 20% by volume of sulphuric acid, a current density of 9.8 amps per sq. ft., at 12 volts, a bath temperature of 74 F. and a treatment time of 30 min utes have been found to be satisfactory.

For the same material, using a bath consisting of 5% by volume aqueous sulphuric acid, a temperature of 40 F., a current density of 20 amps per square foot at 24 volts and a treatment time of 60 minutes have also given satisfactory results.

Again, for sheets of from 10 SWG. to 22 SWG. manufactured by Birmetals Ltd. and sold under the name B.B.2, a current density of 9.4 amps per square foot at 10.5 volts consisting of 20% by volume aqueous sulphuric acid, a temperature of 72 F. and a treatment time of 30 minutes give satisfactory results; for sheets of from 24 SWG. to 30 SWG. sold by the same company under the name B.B.17, a current density of 9.4 amps per square foot at 10.5 volts, a bath of 20% by volume aqueous sulphuric acid, a temperature of 74 F. and a treatment time of 30 minutes are satisfactory; and for sheets sold under the name 550 manufactured by Impalco Ltd., a current density of 9.6 amps per square foot at volts, a bath temperature of 74 F. and a treatment time of 30 minutes give satisfactory results.

For aluminum foil of thickness 0.003 inch and using a 20% by volume sulphuric acid bath, a current density of 9.4 amps per square foot at 10.5 volts, a bath temperature of 88 F. and a treatment time of 20 minutes are satisfactory; whilst for aluminum foil thicknesses between 0.005 and 0.008 inch using the same bath, a current density of 10.5 amps per sq. ft. at 12 volts, a bath temperature of 90 F. and a treatment time of 20 minutes are satisfactory.

After the anodising treatment has been completed, the metal sheets are rinsed in cold running water and may be gently sponged over under cold running water, or are rinsed clear under reasonably powerful, cold water spray jets. 1

Depending on the particular method of producing the design on the anodised surface chosen, the anodised surfaces after cleansing may, if desired, be dyed by immersion in a hot or cold solution of the dye for the period indicated by the manufacturer of the dye. This period is usually between 7 and 30 minutes.

The sheets, either dyed, or of natural anodised aluminum are now dried by draining and airing in circulating slightly warmed air at a temperature not exceeding 80- F.

Various procedures may be adopted for the production of the final design on the anodised surface. In a preferred method of producing the design, the anodised surface of the sheet is dyed as described above before drying. The surface on which the design is to be formed is now coated with a suitable photosensitive resist resin, for example, Kodak P.C. or Kodak P.R. Photosensitive Resist, either by dipping or by spraying or whirling the resist on to the surface. If a design is to be produced on both sides of the metal sheet, it will preferably be coated with the resist by dipping and allowing surplus resist to drain off. The resist layer is then allowed to dry.

The coated surface is now exposed to ultra-violet light through a line or half-tone positive or negative stencil and developed using a developer appropriate to the particular resist employed. After development the surface is rinsed clean with cold water.

The colour is now removed from the uncovered areas of the anodised layer by immersing the sheet in a solution of 50 gms. per litre of potassium permanganate 50 100 gms. per litre of nitric acid and 50-100 gms. per litre of sodium bisulphite in water. The unwanted colour disappears after soaking and agitating for about 1 minute.

The remaining photosensitive resist which has been exposed and fixed on the sheet to protect the original dye is now removed by treatment with a suitable organic solvent, for example, xylene or trichlorethylene, and the sheet fully sealed by immersion in a heavy metal salt solution, such as nickel acetate solution, with or without boric acid crystals; or by sealing in hot water or steam. The result is a surface having a two-colour design (one colour being the natural colour of anodised aluminum and the other that of the original dye), in which the anodised oxide layer is intact and undamaged over the whole extent of the surface.

If the design is required to be in two colours other than one colour and natural anodised aluminum, the sheet can be immersed in a suitable dyefor the necessary time prior to removal of the remainder of the resist. If more than two colours, or two or more colours and natural anodised aluminum, are required, then the sheet may be recovered with resist and exposed through a second stencil, the procedure then being as before, further exposures being used as necessary.

Other methods of producing the desired design may, of course, be used with plates anodised in accordance with the invention; for example, the known method in which the plate is covered with a layer of protective material, for example, gelatine or carboxymethylcellulose, before deposition of the resist. This latter method is not, however, essential, since the anodised oxide coating obtained by the process of the present invention is sufliciently robust to be usable without scaling in the simpler method described above.

Whilst in the preceding description, reference has been made of the sake of clarity to the treatment of metal sheets, it will be appreciated that the anodising process of the present invention and the subsequent production of a design on the anodised surfaces can be applied to aluminum and aluminum alloys in forms other than sheets, for example, to foils, blocks, panels having an appreciable thickness, and to other shaped articles, made, for example, from metal sheet or foil.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A process for producing a two-colour or multicolour design on a surface of a to 30 SWG. 99.5% aluminum sheet which comprises the steps of:

(a) anodising said surface in a bath of by volume aqueous sulphuric acid at a temperature of 74 F. for 30 minutes with a current density of 9.8 amps per sq. ft. at 12 volts;

(b) washing the anodised surface with cold water;

(c) dyeing the anodised surface;

(d) drying the dyed anodised surface with warm air at 80120 F.;

(e) coating the dyed anodised surface with a photosensitive resist resin;

(f) exposing the coated surface to ultraviolet light through an appropriate positive or negative stencil;

(g) developing the exposed coating to remove areas of said coating which have not been exposed;

(h) rinsing said surface;

(i) decolorizing areas of said surface not covered by residual coating by treatment with a decolorizing solution;

(j) dyeing the decolorized areas in different colour to that of the original dyed surface prior to decolorizetion;

(k) removing residual coating; and

(l) sealing said surface.

2. A process as claimed in claim 1 wherein for the production of a multi-colour design, steps (e) to (k) are repeated at least once prior to step (I), a different stencil being used at each repetition in step (f); and decolorized areas produced by step (i) being at each repetition dyed a different colour.

3. A process for producing a two-colour or multi-colour design on a surface of aluminum foil of thickness between 0.005 and 0.008 inch which comprises the steps:

(a) anodising said surface in a bath of 20% by volume aqueous sulphuric acid at a temperature of F. for 20 minutes with a current density of 10.5 amps per sq. ft. at 12 volts;

(b) washing the anodised surface with cold Water;

(c) dyeing the anodised surface;

(d) drying the dyed anodised surface with warm air at 80 to F.;

(e) coating the dyed anodised surface with a photosensitive resist resin;

(f) exposing the coated surface to ultraviolet light through an appropriate positive or negative stencil;

(g) developing the exposed coating to remove areas of said coating which have not been exposed;

(h) rinsing said surface;

(i) decolorizing areas of said surface not covered by residual coating by treatment with a decolorizing solution;

(j) dyeing the decolorized areas in different colour to that of the original dyed surface prior to decolorization;

(k) removing residual coating; and

(l) sealing said surface.

4. A process as claimed in claim 3 wherein for the production of a multi-colour design, steps (e) to (k) are repeated at least once prior to step (1), a different stencil being used at each repetition in step (f); and decolorized areas produced by step (i) being at each repetition dyed a different colour.

References Cited UNITED STATES PATENTS 2,550,388 4/1951 Simon et al. 204--58 2,812,295 11/ 1957 Patrick 204-58 FOREIGN PATENTS 474,608 10/ 1937 Great Britain. 476,161 11/1937 Great Britain.

OTHER REFERENCES Production of Multi-Coloured Effects on Anodized Aluminum, V. F. Henley, The Metal industry, June 18, 1943, pp. 386-388.

HOWARD S. WILLIAMS, Primary Examiner T. 'IUFARIELLO, Assistant Examiner U.S. Cl. X.R. 204-5 8