WO1983003804A1

WO1983003804A1 - Anti-fouling treatment of boats, ships, buoys and other structures exposed to water

Info

Publication number: WO1983003804A1
Application number: PCT/GB1983/000124
Authority: WO
Inventors: Christopher William Shaw
Original assignee: Shaw C W
Priority date: 1982-04-27
Filing date: 1983-04-27
Publication date: 1983-11-10
Also published as: JPS59500662A; NO834813L; AU1512483A; EP0106897A1; FI834810A0; FI834810A

Abstract

An anti-fouling coating for vessels and marine structures comprises alternate layers of paint and particulate metallic material, preferably copper or copper-nickel alloy powder. The coating is commenced and finished with a layer of paint and the or each layer of particulate metallic material is applied to the preceding paint layer whilst the latter is sufficiently wet or tacky for the particulate material to adhere to it. After application of the final paint layer, this is allowed to harden and is then treated, for example by abrading, to expose sufficient metal to produce an anti-fouling characteristic.

Description

ANTI-FOULING TREATMENT OF BOATS , SHIPS , BUOYS

AND OTHER STRUCTURES EXPOSED TO WATER The present invention relates to an anti-fouling treatment for protecting boats, ships, buoys and other structures (hereinafter referred to generally as vessels and marine structures) exposed to sea or fresh water against fouling by weed, slime, barnacles and other marine growth and organisms.

It is well known that, in most circumstances, the hulls of vessels and the surfaces of marine structures exposed to water attract such growth. The effect of this so-called bio-fouling is to cause extra weight and increased friction with flowing water and certain types of corrosion or decay in both vessels and marine, structure and increased fuel consumption or reduced speed in the case of vessels. Special paints have been prepared for several centuries in an effort to combat the bio-fouling problem. In recent years these paints have included copper-based, tin-based or mercury based toxic compounds which inhibit marine growth. Such paints tend to last for up to a year, and sometimes less. Most tend to increase surface roughness year by year as each successive layer is applied. However, a recent paint, marketed by International Paint Co., under the trade name Micron 25, tends to leach away completely thereby minimising this problem. Even so, the disadvantages of toxic paints are shortness of life, environmental damage, and danger to those working with them

It has been known for at least 200 years that copper- coated hulls do not suffer bio-fouling. However, copper has a tendency to dissolve gradually in sea water. Further-more, the business of cladding a hull or structure with copper is slow and time-consuming and requires special care to eliminate galvanic corrosion.

More recently, it has been shown that additions of nickel up to 30%, and ideally 5% to 15%, and specifically 10% provide resistance to the dissolving action of sea-water without destroying the powerful anti-bio-fouling effect. Hulls have been built using copper-nickel plate as an exterior surface. Steel hulls have been clad with copper nickel plate by a system of welding. Hulls have also been built using plate which is a combination of steel and copper-nickel rolled together to form a single material. These methods have shown the success of copper-nickel as an outer layer for a hull with respect to erosive resistance, corrosion resistance, and bio-fouling resistance. Nevertheless, they are debatable techniques economically because of general expense and apply, in the main, to heavy duty shipping and structures.

More recently still, it has been shown that a mesh or net of copper-nickel wire, embedded in a suitable material, such as, an epoxy or polyester resin, to form a sheet and fixed by glueing to a ship's hull, and abraded on the outside side to expose the metallic mesh, provides bio-fouling protection. The mesh needs to be of a fineness such that some metallic material is visible every 0.1" (2.54mm) or so. This method has the advantage that it can be retrospectively fitted to an existing surface. It is also relatively light in weight. However, the material will not conform to many three-dimensional surfaces and resort must then be had to applying it in a patchwork manner which is unsightly, time-consuming, and a great deal more difficult because of the need for good tailoring of the patches and because of the difficulty of joining the patches one with another.

Another recent proposal is an anti-fouling material consisting of a polyester resin with a high percentage of copper or other metallic particles mixed with it. The material, marketed by Scott Bader Co. under the trade name Coppergel, is designed to form the outer layer of the underwater part of a boat which is to be built by successive laminations in a female mould. Accordingly, the underwater surface of the boat is as smooth as is permitted by the mould and the skill of the applicator. This seems an excellent solution to the problem of anti-fouling structures built in female moulds. However the material is difficult, if not impossible, to apply evenly and smoothly to an already-formed structure. In the case of a metal structure, this material would need to be applied after suitable insulating coats of paint had been applied to prevent galvanic corrosion between particles and the metal of the structure. It is not easy, in practice, to devise a paint system to which a loaded polyester resin will satisfactorily adhere.

It is an object of the present invention to provide an anti-fouling coating for vessels and marine structures, which can be applied to any surface of a vessel or structure that can be painted and which has a relatively long life.

From one aspect the invention consists in an anti-fouling coating on a surface of a vessel or marine structure, characterised by alternate layers of paint and particulate metallic material applied to the surface, commencing with a layer of paint, the or each layer of particulate metallic material being adhered to the surface by the paint, and the outer surface of the coating being treated to expose sufficient metallic material to produce an anti-fouling characteristic. From another aspect, the invention consists in a method of applying an anti-fouling coating to a surface of a vessel or marine structure, characterised by the steps of alternately applying layers of paint and one or more layers of particulate metallic material to the surface, said application commencing and finishing with a layer of paint, and the or each layer of particulate metallic material being applied to a preceding paint layer whilst the latter is sufficiently wet or tacky to adhere the particulate material to the surface, and treating the final or outer paint layer, when hard, to expose sufficient metal to produce an anti-fouling characteristic.

The invention provides a thin conformable coating which may be readily applied to surfaces subject to bio-fouling. The paint and particulate metallic material may be separately and easily applied by spraying techniques. Alternatively, the particulate metal can be sieved or thrown onto the wet or tacky paint, but has been found not to adhere so well as if sprayed. Further-more, the paint can be brushed on instead of being sprayed, and this is entirely adequate, although there is a greater requirement to ensure that preceding layers are completely dry before brush application. In any event, the resulting anti-fouling coating can be as light as a single application of paint and particulate metal or can be as heavy as desired dependent on the number of paint and multiple powder layers, the size of the metallic powder particles, the consistency of the paint, and the mode of application. The particulate metallic material is preferably in finely divided or powder form and may, for example, have a particle size in the range from 100 to 300 British standard mesh and, preferably, 180 to 220 mesh. However, coarser powder also works well and, fundamentally, the particle size utilised depends on the thickness of a paint layer which can be satisfactorily applied. In this regard, the particle size should be such that the particles are almost entirely embedded in the preceding wet paint layer. Preferably, the particulate metallic material comprises copper or a copper-nickel alloy. The latter may have a nickel content in the range from 5% to 35% by weight. The paint may be any suitable marine paint, such as a synthetic resin based marine paint. An advantage of the invention, which is based on the use of paint, is that a paint can be obtained suitable for coating practically any known surface. It is therefore easy to build up protection for structures to any known presently acceptable standard by the use of paint layers alone, before applying an anti-fouling coating according to the invention and including further paint layers to accept the particulate metallic material. In this way, also, an electrically insulating layer may be formed between the particulate metallic material and any metallic structure, which insulating layer inhibits the galvanic corrosion which would occur if dissimilar metals in the galvanic scale are used.

In one particular embodiment, copper or a copper- nickel alloy powder is sprayed onto a surface painted with a layer of two-pot polyurethane paint (that is a polyurethane based paint with a separate curing component), as marketed by International Paint Co.. It is sprayed onto the surface whilst the paint is still wet or tacky. The powder may be copper having a particle size such as mainly to pass through a 100 British standard mesh sieve whilst mainly not passing through a 300 British standard mesh sieve. Alternatively, it may be a copper-10% nickel alloy powder of similar size or a copper-25% nickel powder with 5% tin added. The powder forms a well defined layer on the paint taking on an appearance something like emery paper.

After application of the metal powder layer, a further layer of paint is applied, when the first paint layer has dried adequately, and this fills most of the spaces between the metal powder particles and serves further to bond the powder into a strong coating. When this final paint layer has hardened, the surface of the resulting coating is lightly abraded with an abrasive paper, for example, with 600 mesh wet or dry emery paper, and this exposes sufficient metal to produce an anti-bio-fouling effect whilst, at the same time, providing a smooth and relatively friction free surface.

The steps may be repeated so that alternate layers of paint and powder are built-up on the structure to be protected. With such an anti-fouling coating having multiple metal powder layers, it is generally unnecessary to abrade the layers of powder or paint except for the final or outer layer.

Claims

1. An anti-fouling coating on a surface of a vessel or marine structure, characterised by alternate layers of paint and particulate metallic material applied to the surface, commencing with a layer of paint, the or each layer of particulate metallic material being adhered to the surface by the paint, and the outer surface of the coating being treated to expose sufficient metallic material to produce an anti-fouling characteristic .

2. An anti-fouling coating according to claim 1 , characterised in that the particulate metallic material comprises copper or a copper-nickel alloy.

3. An anti-fouling coating according to claim 2, characterised in that the copper-nickel alloy includes 5% to 35% nickel.

4. An anti-fouling coating according to claim 2 or 3, characterised in that the copper-nickel alloy has a minor portion of tin added.

5. An anti-fouling coating according to any preceding claim, characterised in that the particle size of the particulate metallic material is in the range from 100 to 300 British standard mesh.

6. An anti-fouling coating according to any preceding claim, characterised in that the paint is a synthetic resin based paint, for example, a polyurethane paint.

7. A method of applying an anti-fouling coating to a surface of a vessel or marine structure, characterised by the steps of alternately applying layers of paint and one or more layers of particulate metallic material to the surface, said application commencing and finishing with a layer of paint, and the or each layer of particulate metallic material being applied to a preceding paint layer whilst the latter is sufficiently wet or tacky to adhere the particulate material to the surface, and treating the final or outer paint layer, when hard, to expose sufficient metal to produce an anti-fouling characteristic.

8. A method according to claim 7, characterised in that the paint and particulate metallic material are applied by spraying.

9. A method according to claim 7 or 8, characterised in that the treating step includes abrading the hardened outer paint layer, for example, with abrasive paper.

10. A method according to any preceding claim 7 to 9, characterised in that the particulate material comprises copper or copper-nickel alloy powder.

11. A method according to any preceding claim 7 to 10, characterised in that the paint is a synthetic resin based marine paint.