GB2084488A - Biofouling of surfaces - Google Patents

Abstract

To diminish biofouling of the surface of a structure in water, a coating of a resin containing particulate copper is applied to the preferred structure, or may be integrally formed during lay-up of a glass reinforced plastic structure other than a ship's hull.

Description

SPECIFICATION Biofouling of surfaces This invention relates to providing a surface to plastic mouldings, metal and other materials to resist biofouling when immersed in sea water or fresh water.

It is known that if boats and structures are sheathed with copper or copper alloys, the surface is resistant to biofouling and that the copper or copper alloy surface will prevent the attachment of marine plants and animals. If no treatment is given to ferrous metal when immersed in water the fouling will cause pitting and accelerated corrosion to the surface.

It is also known that marine anti-fouling paints when applied to an immersed surface will resist biofouling. Such paint compositions used to prevent fouling consisting mainly of cuprous oxide.

In these known methods there are disadvantages with copper or copper alloy sheathing in that the cost of welding sheets to form the sheathing of this structure is high, whereas anti-fouling paints generally need to be replaced every twelve months, it being necessary to remove the coated structure from the water, scrape off the old coating and apply several more coats to provide a satisfactory surface to resist biofouling; the finished coating is usually not smooth which in some cases can be a further disadvantage.

The present invention seeks to facilitate the manufacture of moulded articles when immersed in water to resist biofouling by the inclusion of copper or copper alloys in the surface of such articles, and also to provide a surface coating comprising a composition which has copper or copper alloy particles included therein and which will provide anti-fouling properties over an extended period and can have a smooth surface.

According to the invention, in a first aspect, in a method of moulding a glass reinforced article which will resist biofouling when immersed in water, a layer comprising a mixture of copper or copper alloy powder and a catalysed fluid resin is applied to the surface of the mould, a backing of glass fibres and resins is applied to the layer, and when the moulding hardens, it is removed from the mould and its surface is abraded to expose the copper or copper alloy.

It has been found by experiment that mouldings produced by this method have prevented biofouling when immersed in U.K. coastal waters for over three years and will continue to prevent fouling for a considerable period. A typical formation of the layer applied to the surface of a mould comprises a mixture of 75% by weight of water atomised irregular shaped copper powder and 25% by weight of catalysed resin, the resin being a polyester resin and the copper powder having a minimum particle size of 1 50 microns.

The layer of copper/resin mixture having a thickness of generally 1.5 mm and a backing of glass fibre and polyester resin to give an overall thickness of 5 mm, after removal from the mould the copper/resin surface of the moulding so formed was abraded and polished to give a smooth copper metal surface.

In a second test the copper powder had a maximum particle size of 1 50 microns with 45/55% by weight of the powder being less than 45 microns. The layer of copper/resin mixture having a thickness of generally 1.1 mm and a backing of glass fibre and polyester resin to give an overall thickness of 4 mm, after removal from the mould the copper/resin surface of the moulding so formed was abraded and polished to give a smooth copper metal surface.

In a third test the copper powder had a maximum particle size of 50 microns. The layer of copper/resin mixture having a thickness of generally 1 mm and a backing of glass fibre and polyester resin to give an overall thickness of 4.5 mm, after removal from the mould the copper/resin surface of the moulding so formed was abraded and polished to give a smooth copper metal surface.

A microscopic examination of the test mouldings shows that after two years and eight months immersion in U.K. coastal waters a great number of free copper particles are available in the surface to provide anti-fouling. From these'tests it is expected that the mouldings will prevent biofouling for a period 6-10 years for the coarse particles (of the order of 1 50 microns) and 5-8 years for the fine particles (of the order of 50 microns) in U.K. coastal waters. After this period the surface can then be further abraded or polished to expose further free copper particles to provide a similar period of protection.

This method can be used for any plastic mouldings immersed in water apart from boat hulls already described in Patent Application No.

50835/76.

According to the invention in a second aspect a copper or copper alloy/resin mixture is applied as a surface coating to a preformed structure constructed of any material to resist biofouling when immersed in sea water or fresh water. The structure may be a ship's hull.

The composition of the mixture to be so applied may comprise copper or copper alloy powder of fine or coarse particle size the particles being of an irregular or spherical shape, mixed with a catalysed resin of sufficient viscosity to hold the particles in suspension in a sufficient quantity to provide biofouling protection to the surface of the treated article or structure. Specific examples of the coating material are given above.

A method of applying such a coating to the steel hull of a ship to resist biofouling will now be described, by way of example. If the ship has been in use it will be necessary to clean the surface below the water line; this cleaning operation can be conveniently undertaken by abrasive blasting of the surface using abrasive particles, for example crushed flint, or angular steel grit, or metal oxide, conveyed in a stream of compressed air, to remove the marine life and plants from the surface. With this method of cleaning the surface of the steel hull it will be given an irregular surface which will provide a satisfactory bond for the surface coating.

The copper or copper alloy/resin mixture previously described can then be applied to the cleaned surface of the hull by brush or roller, or by spraying or any other convenient method, this coating to be applied by one or more applications until sufficient thickness has been achieved, typically a thickness of 0.8 mm. When this coating has hardened the surface is to be abraded to expose the copper and to give the appearance of a copper sheet.

If spraying of the coating is preferred, the apparatus may have separate nozzles for the resin and the copper or copper alloy powder. The nozzles apply the resin and powder at the same time in separate streams. Alternatively the spraying method can be undertaken by applying the resin to the surface and then spraying the copper or copper alloy powder conveyed in a stream of high velocity air or other gas so that the powder penetrates the surface of the soft resin and forms the copper or copper alloy surface. With this method, when the coating has hardened the final treatment of abrading the surface may be reduced.

For the application of the coating to a glass reinforced plastics surface, it will be necessary for the surface to be cleaned with a solvent and roughened, for example with abrasive paper, to provide a satisfactory surface for the application of the coating.

With other surfaces, for example, wood or concrete it may be necessary, after cleaning the surface for this to be sealed with a priming solution to provide a satisfactory base for the application of the copper or copper alloy/resin coating.

The thickness of the coating can be varied to suit the life required for the anti-fouling properties.

Claims (8)

1. A method of combatting biofouling of a structure which includes forming on the structure a coating of a resin containing particulate copper or copper alloy.

2. A method according to Claim 1, wherein the coating is applied to a preformed structure.

3. A method according to Claim 1 or Claim 2, including abrading the coating after it has cured.

4. A method according to Claim 1, Claim 2 or Claim 3, wherein the coating is applied by spraying.

5. A method according to any one of the preceding claims, wherein the structure is a ship's hull.

6. A method according to Claim 1, wherein the coating is formed as a surface layer during lay-up of the structure.

7. A method according to Claim 6, wherein the structure is other than a ship's hull.

8. Methods of combatting biofouling substantially as herein described.