AU676726B2 - Metal coating process - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: PETER BYRNE CONCEPTS PTY.LTD.

Actual Inventor(s): BYRNE, Peter Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Invention Title: Metal Coating Process Details of Associated Provisional Application(s): No(s): PL9184/93 filed 4 June, 1993 The following statement is a full description of this invention, including the best method of performing it known to me/us: -1- METAL COATING PROCESS The present invention relates to a metal coating process and more particularly to a process for applying a metal finish to a range of substrates for use in the manufacturing and construction industries.

A requirement exists for a process for applying a metallic coating to a wide range of substrates in order to provide a metallic finish to the substrate. This may be required for example in interior or exterior building design where a metallic decorative appearance is required on the surface of a substrate which is not itself a metal. Similar considerations apply when the substrate is used in manufacture.

Although in both cases the metal finish is usually provided for aesthetic rather than functional reasons, nevertheless it is important that the finish is a durable finish which remains firmly affixed to the substrate.

According to the present invention there is provided a process of applying a metallic coating to a substrate, comprising the steps of applying an adhesive layer to the substrate and, whilst the adhesive layer is in a tacky state, applying a base coat of a relatively low melting point metallic material using an arc spray process to form a base layer, and then applying one or more metallic top coats to the base layer by means of an arc spray process.

The base coat is preferably formed from zinc.

25 If required, the metallic top coat may be finished to a desired finish by means of a surface treatment which may be a mechanical treatment and/or a hand treatment and/or a chemical treatment.

Prior to application of the adhesive, the surface of the substrate may be textured to provide a textured appearance for the finished metallic surface.

940525,p:\oper\rst~me tal-coatspe,I -2- The invention will now be further described by way of example only.

In accordance with the preferred embodiments of the invention a metallic finish is applied to a substrate by an arc spray deposition process involving the use of two metallic wires between which an arc is struck with a stream of air being directed through the zone of the arc to carry metallic particles from the two wires onto a substrate. Arc spray guns for this purpose are per se known. It is to be noted that the air stream does not form a high temperature plasma but is a cool air stream which carries molten particles onto the substrate and actually cools the particles.

The appearance of the coating will be dependent on whether the two wires are of substantially similar metals or are of dissimilar metals. The applied coating can be finished as required, for example to provide a mirror finish, a flat finish or a coarse S"grainy finish. Other finishing treatments for the coating may involve the application of paints or chemical ageing solutions. A wide range of metals can be sprayed in this 15 manner, including zinc, tin, copper, aluminium, bronze, brass and steel.

In accordance with the invention the metallic finish can be applied to a wide range of substrates including plastics, timber, stone, concrete, fibre-reinforced plastics, particle boards, fibre boards and ferrous or non-ferrous metals. Prior to S 20 application of the finish, the surface of the substrate must be cleaned so that it is free from all dirt and grease and in some instances some surface roughening either by sanding or sand blasting may be desirable. A layer of adhesive is applied, for example by spraying, to the surface to be coated. The adhesive must be compatible with the material of the substrate so as to form a firm bond between the substrate and a low melting point metallic base layer to be subsequently applied. The adhesive should remain in a "tacky" state after application for a time sufficient to allow application of the metallic base coat. The adhesive must also be heat resistant at least to the temperature at which the base coat is applied. We have determined that an acrylic-based contact cement is suitable for use with a broad range of substrates. An example of a suitable acrylic-based contact cement is that sold as "Selleys Quick Grip". The metallic base coat is applied by the arc spray pocess whilst the adhesive is still tacky. The base coat is composed of a relatively low 940525,p:\oper\rshmeta1-coaLspe2 s -3melting point metal which is not likely to cause heat damage when applied to the substrate. A suitable metal for forming the base coat is zinc or an alloy thereof although other metals having a relatively low melting point may be used. As described previously the nature of the arc spray process is that the air stream which carries the molten particles onto the substrate is a cool air stream. The air stream cools the surface layer of the particles during transport and when impinging on the substrate the molten particles will spread and will rapidly cool so as to avoid heat damage to the substrate. The use of the initial adhesive layer prior to application of the base metal coat considerably improves the adhesion of the base coat to the substrate. The base coat provides a keying layer for the subsequent top coat and also acts as a heat sink so that a top coat of a higher temperature melting point metal can be ap-lied without causing heat damage to the substrate.

:i When the base layer consisting of the metal base coat applied to the adhesive layer has fully cured, and which may typically take 24 hours, one or more metal top coats are then applied using the arc spray process and, usually, this will consist of a metal or combination of metals having a significantly higher melting point than that of the zinc used for the base coat. The number of passes of the spray gutm will •"determine the thickness of the top coat and will be dependant on the requirements 20 of the particular application. The metal top coat may then be worked to achieve the required finish. It may be machine or hand finished with appropriate finishing disks or pads, and may finally be polished if a reflective or mirror finish is required. Many variations can be achieved in the nature of the finish by varying such factors as the air pressure, and the current and voltage of the arc. A flecked appearance can be S. 25 obtained by using different wires in the spray gun, or alternatively by the application of a spray of a different metal over the top coat.

A cast and pressed metal effect can be achieved by first coating the substrate with a settable viscous compound such as an acrylic or epoxy based wall filler which can b2 trowelled or screeded directly onto the substrate. The surface of the viscous material may be embossed or otherwise conditioned while it is still wet, When it has fully cured the metal coating process described above, commencing with the adhesive 940525,p:\operrshretal-cat-spe,3 -4underlayer, then takes place.

A raised textured effect can alternatively be achieved on the substrate by initially applying a brush coat of a polyurethane-based adhesive onto the substrate.

When the adhesive is at a tacky stage a fine mist of water is applied which causes the surface to slightly foam. Hand painted textured designs can be achieved in this way. When the adhesive has fully cured, the metal coating process described above, starting with the application of the adhesive underlayer, takes place.

The process particularly described involving arc spray coating, possibly in conjunction with pre-texturing treatments of a substrate, enables a wide variety of metallic surface finishes to be applied to a wide range of substrates relatively inexpensively. By way of non-limiting example, the process can be used to provide a decorative metallic finish to doors, wall panels, door and window frames, facias, signs, posts, columns, ornaments, sculptures.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention.

ot oo a 940525p:\operhmtal-coatsp,4 -3L~PIY LL II

Claims (9)

1. A process of applying a metallic coating to a substrate, comprising the steps of applying an adhesive layer to the substrate and, whilst the adhesive layer is in a tacky state, applying a base coat of a relatively low melting point metallic material using an arc spray process to form a base layer, and then applying one or more metallic top coats to the base layer by means of an arc spray process.

2. A process according to claim 1, wherein the base coat consists of zinc or a zinc alloy.

3. A process according to claim 1 or claim 2, comprising the step of surface treating the metallic top coat to a required finish.

4. A process according to claim 3, wherein the surface treatment is a mechanical treatment and/or a hand treatment and/or a chemical treatment.

A process according to claim 3 or claim 4, wherein the surface treatment provides a reflective finish.

6. A process according to any one of claims 1 to 5, wherein the metallic top coat consists of a metal or combination of metals having a higher melting point than that of the base coat.

7. A process according to any one of claims 1 to 6, comprising texturing a surface of the substrate prior to application of the adhesive layer.

8. A process according to any one of claims 1 to 7, wherein the adhesive layer consists of an acrylic-based contact cement. 940526,p:\oper~rshneta-coatspe,5 -6-

9. A substrate when coated by a process according to any one of the preceding claims. DATED this 26th day of May, 1994. PETER BYRNE CONCEPTS PTY.LTD. By their Patent Attorneys: DAVIES COLLISON CAVE 940526,p\operkrsl,metal-coatspe,6 -7- ABSTRACT A metallic finish, for example a decorative finish, is applied to a substrate by first applying an adhesive layer, and while the adhesive is still tacky applying a base coat of low melting point metallic material by means of an arc spray process. One or more metallic top coats are then applied to the base coat also by means of an arc spray process, the top coat then being subjected to a finishing treatment. e 9 *S 5 940525,p:\oper\rshretal-coaspe,7