GB2233333A - Anti-fouling paints - Google Patents

Abstract

A marine paint composition contains a divalent metal salt of a hydroxycarboxylic acid which contains a fused ring system. The marine paint composition is any film forming material proposed for use in such systems. The metal salt is conveniently zinc 3-hydroxy-naphthoate. The metal salt is typically present in an amount of at least 5% by weight of the paint composition. The paint has anti-fouling characteristics, especially in respect of algae.

Description

MARINE PAINT COMPOSITION The present invention relates to marine paint compositions and in particular to such compositions which have improved antifouling characteristics.

The growth of marine organisms such as algae and barnacles on a surface in contact with water is undesirable, particularly if the surface is the hull of a vessel. The presence of the organisms on the hull can cause increased drag and thus results either in loss of speed or an increase in fuel consumption or both. Furthermore, the growth of the rorganisms can lead to penetration of any protective coating on a metal and an increase in corrosion.

To overcome such problems, it has been proposed to coat surfaces in contact with a marine environment with an "anti-fouling1 composition to reduce the formation of organisms on the surface.

Materials which have been proposed for use in anti-fouling compositions include organic mercury, lead and arsenic compounds.

However, compounds of this type are not used in view of environmental hazards associated with the use of such compounds. Currently compounds of tin are used but these compounds are now regarded as undesirable on toxicity grounds.

In our European Patent Application publication No 289155 we disclose that salts of certain hydroxycarboxylic acids give useful protection against corrosion. We have now found that these compounds are surprisingly effective in providing anti-fouling characteristics to a surface coating composition and also provide bactericidal characteristics to the surface coating composition.

According to the present invention there is provided an anti-fouling composition which comprises (a) a salt of a metal (H) of a hydroxycarboxylic acid in which the hydroxy group and the carboxylic acid group are attached to the ring atoms of a fused ring system and wherein the metal M is at least divalent; and (b) a surface coating composition which is a marine paint composition.

Hereafter the salt of a metal (M) of a hydroxycarboxylic acid in which the hydroxy group and the carboxylic acid group are attached to the ring atoms of a fused ring system will be referred to simply as "the salt".

The fused ring system may be substituted or unsubstituted.

Suitable substituents include halogen atoms, hydroxyl groups, hydrocarbyl groups, hydrocarbonoxy groups, hydrocarbonyl groups or hydrocarbonyloxy groups. Any substituent groups which are present in the fused ring system are additional to the hydroxy and carboxylic acid groups. The substituent groups may be such as to modify the solubility characteristics of the salt. Thus, the substituent may be an alkyl, alkenyl, alkoxy or acyl group for example one which contains up to 20 carbon atoms.

The fused ring system contains at least two rings fused together. One or more of the rings may contain a heteroatom, for example a nitrogen atom. Salts in accordance with the present invention are particularly those in which at least one ring of the fused ring system is a hydrocarbon ring. Convenient compounds are those in which the fused ring system is a hydrocarbon ring system, for example a fused aromatic hydrocarbon ring system. The salt is preferably one in which the hydroxy group and the carboxylic acid group are attached to adjacent carbon atoms of the fused ring system, and especially of a fused hydrocarbon ring system. We have obtained useful results when the fused ring system is a naphthalene ring system, as in the salt derived from 3-hydroxy-2-naphthoic acid, 2-hydroxy-1-naphthoic acid or 1-hydroxy-2-naphthoic acid.

The metal (M) is conveniently divalent but metals of higher valency may be used. Suitable metals are the metals of Group II of the Periodic Table such as magnesium, calcium, barium and zinc. A trivalent metal which may be used as the metal (M) is aluminium. We have obtained useful results using zinc 3-hydroxy-2-naphthoate.

The compositions of the present invention can be coated onto a surface which is, or which is intended to be, in contact with a marine, fresh or salt-water, environment. The surface can be metal, wood or a plastics material.

As a further aspect of the present invention there is provided a method of reducing the susceptibility of a surface to the formation of a coating of marine organisms which comprises applying to the surface a composition which is, or which contains, a salt of a metal (M) of a hydroxycarboxylic acid in which the hydroxy group and the carboxylic acid group are attached to the ring atoms of a fused ring system and wherein the metal M is at least divalent.

As a yet further aspect of the present invention there is provided a surface which is, or which is intended to be, in contact with a marine environment and which has applied thereto a salt as hereinbefore defined.

The salt may be applied to the surface using any suitable solvent or dispersant. It is preferred that the surface is also provided with a coating of a marine paint composition. The salt and the marine paint composition may be applied separately to the surface but it is convenient to use a marine paint composition which contains the salt.

The marine paint composition may be any composition known for this purpose. The composition is very preferably one which is capable of forming a continuous layer of a film-forming material on the surface. Hence, the preferred composition is one which contains a film-forming material.

The film-forming material may be a synthetic material, a natural material or a mixture thereof. Synthetic materials which may be used include vinyl resins, for example vinyl chloride-vinyl acetate-vinyl alcohol copolymers, epoxy resins such as polyamide-cured epoxy resins, urethane polymers and chlorinated rubber, for example chlorinated synthetic rubber. Natural materials which can be used include rosin and bituminous materials such as coal tar pitch. Coal tar epoxy resins may also be used as coating materials.

Chlorinated synthetic rubbers which may be used include polyisoprene, polybutadiene, copolymers of isoprene and butadiene and mixtures of polyisoprene and polybutadiene. Suitable chlorinated synthetic rubbers are available from ICI Chemicals and Polymers Limited under the Registered Trade Mark tAlloprene".

The coating composition is such that, after application and drying, the resulting coating contains at least lOZ by weight of the film-forming material.

In addition to the film-forming material and the salt, the coating composition may also include extenders andlor pigments and plasticisers. Pigments include iron oxide, titanium dioxide, silica and carbon black. Plasticisers include tricresyl phosphate and chlorinated paraffin wax, the latter being available from ICI Chemicals and Polymers Limited under the Registered Trade Mark "Cereclor".

In addition to the salt, the composition may also contain other anti-fouling materials such as cuprous oxide or zinc oxide.

The zinc oxide may be used together with a zinc salt, for example the zinc salt 3-hydroxy-2-naphthoic acid. The zinc salt and the zinc oxide may be in the form of a basic salt which is conveniently prepared by the reaction of an excess of zinc oxide with the appropriate hydroxycarboxylic acid.

The anti-fouling composition preferably contains at least 5Z by weight of the salt. The proportion of the salt preferably does not exceed 70Z by weight of the composition and more preferably does not exceed 50Z by weight of the composition. It is especially preferred that the composition contains not more than 25Z by weight of the salt. It is particularly preferred that the composition contains at least loz by weight of the salt.

The composition preferably contains a film-forming binder and this is typically a solution, emulsion or dispersion in a suitable liquid medium. The liquid medium is preferably one which is a solvent for the film-forming binder and which evaporates readily once the composition has been applied to the surface. Suitable liquids are aromatic hydrocarbons, ketones and esters.

The polymer or polymers, which is, or are, used when component (b) is a film-forming binder, is usually used in an amount of from 5 to 60Z (based on the weight in grams of the polymer per 100cm3 of the composition), and is more usually 10 to 40Z. The polymer may be dissolved or colloidally dispersed (that is exist as an emulsion, with an average particle size usually below two micrometres) in a suitable liquid carrier medium.

In addition to the salt, the composition may contain further components as noted previously herein or additional components commonly employed in film-forming compositions such as defoamers, rheology control agents, thickeners, dispersing and stabilising agents, (usually surfactants), wetting agents, fungicides, coalescing solvents and anti-freeze agents.

The composition of the present invention may be prepared using any of the techniques which have been used for incorporating solids into a liquid or plastic medium in which the solid is essentially insoluble. Thus, if component (b) is a film-forming binder, techniques for preparing paint compositions may be used, for example by mixing the components either in a grinding apparatus or pre-mixing the components and then grinding. The salt, and any optional metal oxide, may be incorporated into the surface coating composition at any convenient stage, for example during the grinding together of the components of the paint formulation.

As noted previously herein, the compositions of the present invention may be coated onto metal, wood or plastic surface, to provide an anti-fouling surface. The coated surface also shows a reduced build-up of bacterial slime.

The composition may be applied to the surface in conventional manner, for example by dipping, spraying or brushing.

The temperature of the application may be any suitable temperature, for example from 0 to 500C.

Various aspects of the present invention are set out in more detail hereafter in the following illustrative examples in which all parts and percentages are by weight unless otherwise stated.

Preparation of Zinc salt of 3-hydroxv-2-nanhthoic acid 27.3g of 3-hydroxy-2-naphthoic acid was stirred at room temperature in 145cm3 M sodium hydroxide solution plus 50cm3 water until the bulk of the acid had dissolved.

To the above well stirred suspension was added dropwise a solution of 20.9g zinc sulphate heptahydrate in about 100cm3 water.

Further aliquots of water were added during the addition to make the mixture more stirrable. When the addition had been completed the mixture was stirred a further one hour, then filtered and the solid product was washed well with water and dried at 450C to constant weight.

A yield of 32.it of a solid having a melting point in excess of 3O00C was obtained.

By micro-analysis, the product was found to contain C 55.6Z wt; H 3.9Z wt; and Zn 13.5Z wt.

Theory for C22H14O6Zn.2H2O is C 55.6Z wt; H 3.8Z wt; and Zn 13.7Z wt.

The proportion of water was determined by Karl Fischer analysis and found to be 7.3Z wt. Theory for zinc 3-hydroxy-2-naphthoate dihydrate is 7.6Z wt.

Examples 1 to 4 The zinc salt of 3-hydroxy-2-naphthoic acid was incorporated into a paint by shaking a mixture of the salt and the paint for 30 minutes in the presence of glass beads using a "Red Devil" paint blender. The zinc salt was added to the paint in amounts to give levels of 10, 5, 2.5 and 1.25Z by weight of the zinc salt in the paint.

The paint used had the following composition: Alloprenew R10 14.3Z wt "Cereclor" 42 9.4Z wt Zinc Oxide 28.2Z wt Titanium dioxide 15.2Z wt Xylene 32.9Z wt The paint was brushed on to one face of a 15.24cm x 2.54cm stainless steel strip. A total of three coats of the paint were applied, with extended drying (at least two days) after each application of paint.

Each painted strip was leached by immersion in a container of tap water and maintaining a circulation of tap water past the surface. Leaching was continued for a total of 10 weeks. 50Z, by volume, of the water was replaced by fresh water five days in each week.

Each leached, painted strip was then transferred to a glass vessel containing 500cm3 of tap water to which had been added 12.5g per dm3 of a marine salts mixture (available as Ultramarine Synthetica Sea Salts from Waterlife Research Industries) and 10cm3 per dm3 of E25 solution. Each strip was inclined at about 600 to the horizontal with the paint side uppermost. E25 is a nutrient mixture described by Scottish Marine Biological Station, Oban, Argyl PA34 4AD, Scotland.The E25 solution has the following composition: Soil extract 10cm3 Potassium nitrate 200mg Dipotassium hydrogen phosphate 20mg Magnesium sulphate heptahydrate 20mg Vitamin B12 400mg Thiamine hydrochloride 200mg3 Distilled Water to 1000cm An algal suspension was obtained by homogenising for 20 seconds about lg of Enteromorpha intestinalis filamentous growth with 100cm3 of a 12.5g per dm3 aqueous solution of the marine salts mixture. 5cm3 of this suspension were inoculated into each test system. The systems were maintained at room temperature under artificial daylight (12 hours light and 12 hours dark cycle).

After 2 weeks, 250cm3 of the water was removed and replaced by 250cm3 of a fresh aqueous solution containing the marine salts mixture and E25 in tap water. Each system was re-inoculated and the systems incubated for a further two weeks under the same conditions. The strips were then removed, and the extent of algal colonisation of each paint film was visually assessed and recorded.

The results obtained are set out in Table One.

TABLE ONE

Ex Ex or I Amount of I Algal I ComD i ZHN (Z) (a) I Growth (b) I I I I I I 1 1 10 1 1 1 121 5 5 2 1 3 3 I 2.5 1 3 I 1 4 1 1.25 1 3 A NIL 4 Notes to Table One (a) ZHN is zinc salt of 3-hydroxy-2-naphthoic acid.

Z is Z by weight of ZHN in the paint.

(b) 1 indicates that no algal colonisation was visible.

2 indicates that slight algal colonisation was visible with less than 10Z coverage of the surface with algae.

3 indicates that moderateimarked algal colonisation was visible with 10 - 50Z coverage of the surface with algae.

4 indicates that heavy colonisation was visible with 50 - 100Z coverage of the surface with algae.

Example 5 A sample of the paint composition of Example 2, that is one containing 5Z by weight of the zinc salt of 3-hydroxy-2-naphthoic acid, was applied by brush, in.two coats, to a 15.24cm length on both sides of a 30.48cm x 2.54cm stainless steel strip.

The painted surfaces were immersed in a reservoir containing 5dm3 of tap water which was being circulated at a rate of IOdm3lminute to provide a flow of water over the painted surface.

2dm3 of water were removed and replaced by fresh water for five days of each week. The water was inoculated with 5cm3 of a nutrient broth culture containing about 109 cells 1cm3 of Pseudomonas fluorescens NCIB 9046 and a corresponding inoculation was made once per week.

The water was supplemented daily with 200 ppm of glucose and 2 ppm of ammonium nitrate.

The painted steel strips were weighed every two weeks during a total incubation period of eight weeks. The weight of slime accumulated on the paint film at various times is set out in Table Two together with the weight of slime accumulated on a paint film not containing the zinc salt.

Table Two

I Ex or I Additive I Wt of slime (g) after | Relative I I Comp | (a) I Incubation Period of | amount of I Ex 2w(c) 4w(c) 6w(c) 8w(c) Slime (d) B NIL 1.7 3.5 5.1 5.2 100 5 ZHN 0.9 1.5 2.0 2.2 42 Notes to Table Two (a) is as defined in Notes to Table One.

(c) w indicates weeks.

(d) Z relative to weight of slime in Comp Ex B after 8 weeks.

Claims (21)

1. An anti-fouling composition which comprises (a) a salt of a metal (M) of a hydroxycarboxylic acid in which the hydroxy group and the carboxylic acid group are attached to the ring atoms of a fused ring system and wherein the metal M is at least divalent; and (b) a surface coating composition which is a marine paint composition.

2. A composition as claimed in claim 1 wherein the fused ring system is further substituted with at least one group which is a halogen atom, a hydrocarbyl group, a hydrocarbonoxy group or a hydrocarbonoyl group.

3. A composition as claimed in either claim 1 or claim 2 wherein the fused ring system is a fused aromatic hydrocarbon ring system.

4. A composition as claimed in any one of claims 1 to 3 wherein the metal (M) is a divalent metal.

5. A composition as claimed in any one of claims 1 to 4 in which the salt is one in which the hydroxy group and the carboxylic acid group are attached to adjacent carbon atoms of the fused ring system.

6. A composition as claimed in any one of claims 1 and 3 to 5 wherein the salt is zinc-3-hydroxy-2-naphthoate.

7. A composition as claimed in any one of claims 1 to 6 wherein the marine paint composition contains a film-forming material.

8. A composition as claimed in claim 7 wherein the film-forming material contains a vinyl resin, an epoxy resin, polyurethane, or a chlorinated rubber.

9. A composition as claimed in claim 8 wherein the filmforming material is a chlorinated synthetic rubber which is polyisoprene, polybutadiene, or copolymers or mixtures thereof.

10. A composition as claimed in any one of claims 1 to 9 which also contain extenders andlor pigments and plasticisers.

11. A composition as claimed in any one of claims 1 to 10 which also contains other anti-fouling materials.

12. A composition as claimed in any one of claims 1 to 11 which contains at least 5Z by weight of component (a).

13. A composition as claimed in any one of claims 1 to 12 which contains not more than 70Z by weight of component (a).

14. A composition as claimed in any one of claims 1 to 14 which contains from 5 to 60Z by weight of film-forming material per 100cm3 of the composition.

15. A composition as claimed in any one of claims 1 to 14 which contains the zinc salt of the hydroxycarboxylic acid and zinc oxide.

16. A composition as claimed in claim 15 which contains a basic zinc salt which is the product of reacting an excess of zinc oxide with a hydroxycarboxylic acid.

17. A method of reducing the susceptibility of a surface to the formation of a coating of marine organisms which comprises applying to the surface a composition which is, or which contains, a salt of a metal (M) of a hydroxycarboxylic acid in which the hydroxy group and the carboxylic acid group are attached to the ring atoms of a fused ring system and wherein the metal M is at least divalent.

18. A method as claimed in claim 17 wherein the composition is a marine paint composition which contains the salt.

19. A method as claimed in either claim 17 or claim 18 wherein the composition is applied to the surface by dipping, spraying or brushing.

20. A method as claimed in any one of claims 17 to 19 wherein the composition is applied to the surface at a temperature of from 0 to 500C.

21. A surface which is, or which is intended to be, in contact with a marine environment and which has applied thereto a salt of a metal (M) of a hydroxycarboxylic acid in which the hydroxy group and the carboxylic acid group are attached to the ring atoms of a fused ring system and wherein the metal M is at least divalent.