GB2266895A

GB2266895A - Priming surfaces to receive electrophoretic paint coatings

Info

Publication number: GB2266895A
Application number: GB9309877A
Authority: GB
Inventors: Brian Hems
Original assignee: WEDNESBURY DIECASTING AND META
Current assignee: WEDNESBURY DIECASTING AND META
Priority date: 1992-05-15
Filing date: 1993-05-13
Publication date: 1993-11-17
Anticipated expiration: 2013-05-13
Also published as: GB9309877D0; GB9211567D0; GB2266895B

Abstract

A process for depositing an electrophoretic paint coating on a substrate such as otherwise incompatible metal eg. zinc alloy, comprising the step of first depositing on said metal at least one metallic or metalised primer coating eg. an electroplated coating of copper, nickel and/or chromium or a lacquer containing aluminium oxide, and then depositing the electrophoretic paint by electrophoretic deposition.

Description

Title: "Improvements relating to electrophoretic coatings" Description of Invention This invention is concerned with improvements relating to electrophoretic coatings.

The process of electrophoretic deposition of lacquer coatings onto most metals, the lacquer coatings being either clear or dyed to simulate finishes such as gold or brass, is well known and is used extensively in the metal finishing industry.

The coatings so applied are quite regular and of even thickness, and the thickness is a predictable function of the deposition time. Thus by control of the deposition time, an even coating of a desired thickness can be achieved.

There has been available for a number of years an electrophoretic paint offering a "solid" coloured finish, typically white, rather than the clear lacquer or metal-simulating lacquer finishes referred to above.

This electrophoretic paint has been applied successfully to aluminium alloys, but prior to the present invention the applicants' attempts to apply such paint to zinc alloys have been unsuccessful, suffering from problems of poor adhesion and poor opacity.

It is to be understood that many fittings for doors and windows, including fasteners, operating handles and other door and window "furniture", are customarily formed from zinc alloy castings, and successful electrophoretic deposition of a "solid" paint colour, which is achieved by the present invention, offers a substantial advantage over the electrostatic powder coating techniques which have hitherto had to be used for zinc alloys and which have resulted in undesirable extreme and random variations in coating thickness.

Thus, according to a first aspect of the present invention there is provided a process for depositing an electrophoretic paint coating on substrate such as an otherwise incompatible metal, comprising the step of first depositing on said substrate at least one metallic or metalised primer coating, and then depositing the electrophoretic paint.

Said substrate may be a zinc alloy.

Said electrophoretic paint may be an electrophoretic paint offering a "solid" coloured finish.

Where a metallic primer coating is deposited, the or each such metallic primer coating may be a coating of at least one different metal (i.e. different to said incompatible metal) deposited by an electroplating process.

Said primer coating(s) may comprise at least one coating of copper ånd/or at least one coating of nickel and/or at least one coating of chromium.

Preferably chromium affords the primer coating onto which the electrophoretic paint is actually deposited.

In a preferred process in accordance with the invention, there is applied at least one primer coating of copper, followed by a primer coating of nickel, followed by a primer coating of chromium, followed by said electrophoretic paint.

Where a "metallised" primer coating is deposited, this may be in the form of a lacquer containing a metallic oxide (e.g. aluminium oxide, or other).

According to a second aspect of the invention, the invention provides an article coated by a process in accordance with the first aspect of the invention.

One preferred process in accordance with the invention, for providing a coated article in accordance with the invention, will now be described in detail, by way of example only with reference to the accompanying drawing, which is a schematic illustration of an electrophoretic paint process used in a process embodying the invention. In this example, a zinc alloy die-casting is an otherwise incompatible metal article to be coated, with, as an example, an electrophoretic paint offering a solid coloured finish.

The zinc alloy casting may be a component for a door or window fitting, and said "solid" coloured finish may for example be white in colour, white being presently a popular colour for such fittings, and an electrophoretic paint of that colour being available for example from the "LVH Coatings" Company based in the United Kingdom.

The zinc alloy casting may be in the "as cast" condition, or may be mechanically abraded, or finished or brightly polished by conventional processes.

In said preferred process in accordance with the invention, a first primer coating, of copper, is deposited on the zinc alloy casting by an electroplating process in a cyanide strike bath, followed by a second primer coating, also of copper, which is deposited by an electroplating process in a pyrophosphate solution. Next, a third primer coating, of nickel, is applied by an electroplating process. Then a final primer coating, of chromium, is applied by an electroplating process.The electroplating with chromium is carried out with a standard electroplating technique but with the hexavalent solution having a chromic acid content of 320 gms. per litre and in an operating temperature of 38"C. It is desirable, if not essential, that the castings are completely coated with chromium since optimum adhesion of the electrophoretic paint film depends on the presence of the complete coating of chromium.

The first and second primer coatings, of copper, are each not less than 0.0002 ins. thick. The third primer coating, of nickel, are not less than 0.00010 ins. thick and the final primer coating, of chromium, are not less than 0.00001 ins.

thick.

If desired, only a first primer coating, of copper, may be provided, the second primer coating of copper being omitted.

Referring now to the Figures, the castings, after being thus electroplated, are dipped into alkaline cleaner so that residual chrome acid is neutralised (as shown at A in stage 1 in the Figure) followed by efficient rinsing (stage 2) and then immersion in cold 2% hydrochloric acid for not more than 15 seconds (stage 3) followed by thorough rinsing in clean water (stage 4).

The thus cleaned chromium plated castings are then hung on the anode bar of an electrophoretic paint bath held at 250C to 300C and deposition is continued for 60 seconds at 5 - 6 amps per square foot. The paint solution is constantly circulated and filtered as shown at stage 5. Thereafter, the castings are rinsed in de-mineralised water (stages 6 - 9) and then hung in a clean atmosphere for 15 - 20 minutes so that the rinse water can drain off the castings.

When the castings are free from surface water they are placed in an electrically heated oven and stored with circulating air for 15 minutes at 1800C (stage 10).

The resulting coating provided by the solid-colour electrophoretic paint is of excellent opacity and even thickness, and exhibits excellent adhesion and hence exceptional resistance to weathering and corrosion (tests have shown the paint coating so applied to be 4 to 6 times more durable than powder coatings on zinc alloy castings).

In an alternative preferred process in accordance with the invention, only one primer coating is deposited, in the form of a lacquer metalised by incorporation of a metallic oxide (e.g. aluminium oxide), and then the solid-colour electrophoretic paint is deposited as described hereinbefore.

It will be appreciated that the details of the process may be varied, in particular in relation to the number of primer coatings applied (which number may be increased or decreased) while remaining within the scope of the invention.

Also, it is to be understood that the invention is not limited to door and window fittings but may be used in any technical context or environment. Moreover, the substrate may be other than an otherwise incompatible metal and may comprise any suitable substrate which can be coated with one or more metallic or primer coatings as described hereinbefore.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

1. A process for depositing an electrophoretic paint coating on a substrate such as otherwise incompatible metal, comprising the step of first depositing on said metal at least one metallic or metalised primer coating, and then depositing the electrophoretic paint.

2. A process according to claim 1 wherein said substrate is a zinc alloy.

3. A process according to claim 1 or claim 2 wherein said electrophoretic paint is an electrophoretic paint offering a "solid" coloured finish.

4. A process according to any one of the preceding claims wherein a metallic primer coating is deposited and the or each such metallic primer coating is a coating deposited by an electroplating process of at least one metal different to said substrate.

5. A process according to any one of the preceding claims wherein said at least one primer coating comprises at least one coating of copper and/or at least one coating of nickel and/or at least one coating of chromium.

6. A process according to any one of the preceding claims wherein chromium affords the primer coating onto which the electrophoretic paint is deposited.

7. A process according to any one of the preceding claims wherein there is applied at least one primer coating of copper, followed by a primer-coating of nickel, followed by a primer coating of chromium, followed by said electrophoretic paint.

8. A process according to any one of the preceding claims wherein the substrate is provided with a primer coating of chromium applied by an electroplating process carried out with a solution having a chromic acid content of 300 to 320 gms. per litre and an operating temperature of 36"C to 38"C.

9. A process according to any one of the preceding claims wherein at least one copper primer layer is deposited having a thickness of not less than 0.0002 ins. and preferably not greater than 0.0003 ins.

10. A process according to any one of the preceding claims wherein a nickel primer layer is deposited having a thickness of not less than 0.00010 ins.

and preferably not greater than 0.0003 ins.

11. A process according to any one of the preceding claims wherein a chromium primer layer is deposited having a thickness of not less than 0.00001 ins.

12. A process according to any one of claims 1 to 3 wherein a "metallised" primer coating is deposited in the form of a lacquer containing a metallic oxide.

13. A process according to claim 12 wherein the metallic oxide is aluminium oxide.

14. A process according to any one of the preceding claims wherein the substrate comprises a zinc alloy casting which may be in at least one of the following conditions; as cast; mechanically upbraded; finished; brightly polished.

15. A process according to any one of the preceding claims wherein the metal, after being electroplated with a copper primer coating, is cleaned.

16. A process according to any one of the preceding claims wherein the metal is electrically connected to an anode of an electrophoretic paint bath to deposit the electrophoretic paint.

17. A process according to any one of the preceding claims wherein the electrophoretic paint is deposited on the substrate in a bath held at a temperature lying in the range 250C to 300C and deposition is continued for 3 minutes to 3.5 minutes at 30 to 35 volts.

18. A process according to any one of the preceding claims wherein, after deposition of the electrophoretic paint the substrate is heated for 10 minutes to 15 minutes at 100"C to 1500C.

19. A process substantially as hereinbefore described.

20. An article coated by a process in accordance with any one of the preceding claims.

21. An article according to claim 20 wherein the article is a zinc alloy die casting.

22. An article according to claim 21 wherein the zinc alloy casting is a component for a door or window fitting.

23. An article substantially as hereinbefore described.

24. Any novel feature or novel combination of features disclosed herein and/or in the accompanying drawings.