WO2008149134A2

WO2008149134A2 - Antifouling composition

Info

Publication number: WO2008149134A2
Application number: PCT/GB2008/050385
Authority: WO
Inventors: Keith Martin Macgregor
Original assignee: Si Laboratories Limited
Priority date: 2007-06-02
Filing date: 2008-05-28
Publication date: 2008-12-11
Also published as: GB0710574D0; WO2008149134A3

Abstract

The present invention relates to an antifouling composition applied to a surface to prevent or reduce fouling, in particular in a marine environment. The present invention further relates to an antifouling composition comprising a marine bacteria combating material, wherein the marine bacteria combating material has a negative zeta potential. Antifouling compositions of the present invention substantially combatmarine bacteria through electrostatic forces.

Description

Antifouling Composition

The present invention relates to an antifouling composition applied to a surface to prevent or reduce fouling, in particular in a marine environment.

Fouling on underwater surfaces of seaborne vessels such as boats can seriously affect their performance, in particular their speed, acceleration and fuel efficiency, as well as in some cases hasten surface corrosion, which can reduce lifetime and encourage further fouling. Once fouling has taken hold it will not be removed through motion of the boat whereto it is attached, and prolonged fouling will damage the substrata of a boat.

Accordingly many efforts have been made to reduce fouling. In many cases these have involved applying a coating that repels marine fouling organisms and/or slime or reduces their ability to adhere to the surface.

The repulsion approach has often involved coatings containing toxic materials, such as organotin compounds and copper compounds, discussed in US 6,559,201. Such compounds may leach into the environment, reducing the effectiveness of the coating and polluting the environment .

Existing non-toxic antifouling coatings which seek to reduce the ability of marine organisms and/or slime to adhere to the surface have proved only moderately effective . There remains a need for an antifouling coating which is safe to apply, effective across a worthwhile time span and environmentally acceptable.

In accordance with a first aspect of the present invention there is provided an antifouling composition comprising a marine bacteria combating material; wherein the marine bacteria combating material has a negative zeta potential.

The marine bacteria combating material preferably has a permanent surface negative charge.

Zeta potential is essentially a measure of surface electrostatic properties, and is a theoretical property exhibited by all colloid particles and surfaces within a dispersion medium (eg. sea water) . Zeta potential is a universal measure of the electrical potential difference between a dispersion medium and the stationary layer (or interfacial double layer) of fluid associated with the dispersed particle or surface.

The zeta potential of the marine bacteria combating material may be more negative than -25mV, is preferably more negative than -3OmV, preferably more negative than -

4OmV, more preferably more negative than -5OmV, and most preferably more negative than -6OmV.

The marine bacteria combating material is preferably a marine bacteria repelling material. Preferably marine bacteria is repelled through electrostatic forces. The combating material is also believed to exhibit catalytic activity which serves to dissociate molecules such as water and oxygen to form highly reactive free radicals.

The radicals cause a redox reaction with organic molecules, such as those present in the cell wall of marine bacteria. The marine bacteria combating material is therefore self-sterilizing and actively resists biofouling .

The marine bacteria combating material may be a siliceous component, preferably comprising silicon dioxide. Preferably the siliceous component is in particulate form.

A suitable average particle size for the particulate siliceous component may be from 0.001 to 1000 microns, preferably from 0.01 to 500 microns, more preferably from 0.1 to 100 microns, and most preferably from 5 to 40 microns, as measured by use of a particle image analyser. Preferably the particulate siliceous component may be described as a powder.

The siliceous component may comprise up to 80 wt% of the antifouling composition, preferably up to 50 wt%, preferably up to 20 wt%, more preferably 0.001 to 20 wt%, preferably 0.01 to 12 wt%, most preferably 0.1 to 8 wt%.

The siliceous component may have the required zeta potential following mechanical treatment to form particles of the preferred particulate size. The siliceous component may have the required zeta potential as a result of chemical processing, most preferably by treatment of a suitable precursor with a base, preferably hydroxide ions. The siliceous component preferably comprises a glass component .

The glass component may comprise any kind of glass, including high-quartz glass (sometimes called just "quartz sand"), borosilicate glass, or soda-lime glass.

Preferably the glass is conventionally coloured, e.g. by addition of certain chemical compounds, for example metal oxides such as manganese oxide, cobalt oxide, chromium oxide, sulphur compounds and iron oxides, especially ferric oxide.

Coloured glasses containing one or more of the preceding additive compounds are especially preferred glass components for use in the present invention.

Particularly preferred are iron oxides, especially ferric oxide .

Although we are not bound by theory, it is believed that the presence of chemical compounds, responsible for the colouring of glass, are responsible for an enhancement of efficacy of the present invention, as an antifouling coating. Further, we believe that glasses with a negative surface charge give especially good enhancement of efficacy, owing to a bacteria repelling effect. Preferred glass particles have a zeta potential more negative than - 30 mV.

Accordingly glass particles for use in the present invention preferably have a negative surface charge. A negative surface charge may arise in glass particles due to the chemical nature of the glass, and/or chemical treatment (e.g. with acid or alkali), and/or mechanical treatment, for example when pulverising glass pieces to form the particles or when subjecting glass particles to shear forces. One example of the latter is when glass particles are injected into the air stream of a jet engine for the purpose of cleaning the jet engine. Another is when glass particles are passed tangentially between the adjacent edges of two rapidly counter-rotating ceramic circular plates.

Negatively charged glass particles may simply be purchased on the open market. One example is glass cullet material used to manufacture insulating material.

A particulate glass component for use in the present invention may be made by grinding pieces of glass in an industrial grinding apparatus. The pieces of glass may be made by breaking glass artefacts, for example bottles and j ars .

Recycled glass is very suitable as a base material for a particulate glass component of the present invention.

Whilst plain glass may produce a negatively charged surface due to reaction of (SiOH) species in the glass with hydroxyl ions in the water, forming Si(OH)₂- species on the surface, glass having a pre-charged negative surface is preferred.

In some embodiments the composition may also comprise an additional chemical compound, especially of iron, tin, zinc or titanium, preferably selected from the group: ferric oxide, titanium dioxide, zinc oxide, zinc acetate, zinc octoate, zinc chloride, zinc bromide, titanium tetrachloride, u-n-cclvlti.. ^-b-^.zoyl-^-nc L hyl-2-

4-^vf"^r ,v -/-p«r- , arιuna^r _^- ]''':rri,^Ω, ^ΓΛI ,^" s_^," an ado t ._^"ai ^orpr^nc s p^ese^*^ it constitutes typically 0.001 to 5 wt%, but more preferably 0.01 to 2 wt% of the overall composition. Transition metal compounds are especially preferred. Photocatalysts such as titanium oxide and zinc oxide are especially preferred, particularly titanium dioxide. Such additional chemical compounds may be introduced into the composition in their particulate form, preferably having mean particle size in the range 0.001 to 1000 microns, preferably from 0.01 to 500 microns, more preferably from 0.1 to 100 microns. Alternatively or additionally such chemical compounds may be introduced to the composition by being present in the glass component. Titanium dioxide participates in self-cleaning by generating ions when subjected to UV light.

The antifouling composition may further comprise a fluoropolymer component, especially a fluoropolymer component which increases the hydrophobicity of the polymer matrix composition. The fluoropolymer component may comprise a fluoropolymer selected from the group including: Teflon®, polyvinylfluoride, and polymers of 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7-Dodecafluoroheptyl acrylate, 2,2, 3, 3, 4, 4, 4-Heptafluorobutyl acrylate, 1,1,1,3,3,3- Hexafluoroisopropyl acrylate, 2,2,3,3,4,4,5,5- Octafluoropentyl acrylate, 2,2,3,3,4,4,5,5- Octafluoropentyl methacrylate, 2, 2, 3, 3, 3-Pentafluoropropyl acrylate, 2, 2, 3, 3-Tetrafluoropropyl acrylate or mixtures thereof. Particularly preferred is the polymer of 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl acrylate. All such fluoropolymers are readily available commercially, or easily synthesised through standard polymerisation of the respective fluoromonomers . Preferably the fluoropolymer component comprises a fluoroalkyl acrylate copolymer, preferably including any of the above monomers, or copolymers of any two or more of the above species. Most preferably the fluoropolymer component comprises a homopolymer. The fluoropolymer component preferably comprises 0.01 to 10 wt% of the antifouling composition, preferably 0.01 to 2 wt%, more preferably 0.1 to 1.5 wt%, most preferably 0.5 to 1.0 wt%.

The antifouling composition preferably comprises a matrix material.

Preferably the matrix comprises a polymer matrix.

Preferably the matrix comprises a water-repelling material .

The composition is preferably "slippy" to the touch when in the form of a dried coating on a substrate.

Preferably water dropped onto a coating formed from the composition forms beads, which may readily run off it, for example when it is tilted by 10° from the horizontal.

The composition may comprise as particulate material an aluminium component. Alternatively the composition may comprise a carbon component such as carbon black.

The aluminium component may comprise aluminium metal. The aluminium component may comprise a water-insoluble compound, for example aluminium oxide or an aluminium silicate .

Preferably the particulate aluminium or carbon component is in a suitable particulate form that it can be readily dispersible within a coating composition.

A suitable particle size of the particulate aluminium or carbon component may be from 1 to 25 microns, more preferably from 2 to 20 microns, preferably from 5 to 10 microns .

Particle sizes herein are measured by use of a particle image analyser.

Preferably the particulate aluminium or carbon component may be described as a powder. Preferably the aluminium or carbon component comprises aluminium or carbon platelets, which further enhance the "slippiness" of the composition, when coated, and also coat the substrate such that the platelets mutually overlap to form a barrier, giving protection against water ingress into and osmosis through the said substrate.

Preferably the aluminium or carbon component is delivered into the composition in a liquid vehicle, preferably a hydrocarbon solvent, preferably C5-C12, more preferably white spirits.

Preferably the weight ratio, aluminium or carbon component to vehicle, is between 9:1 and 1:9, more preferably between 7:3 and 3:7, and most preferably between 6:4 and 4:6, so as to form a mobile slurry with the aluminium or carbon prior to mixing with other components of the antifouling composition.

When the antifouling composition comprises an aluminium or carbon component it preferably comprises up to 5 wt% of the aluminium or carbon component and more preferably 0.01 to 2.5 wt%, and most preferably 0.05 to

0.4 wt% (not including any solvent present).

The matrix preferably comprises a polymeric silicon- containing compound, and preferably two or more such compounds. Preferably the compositions comprise at least one siloxane and at least one silane. Preferably a polymerisable siloxane or siloxane polymer or oligomer (including disiloxanes, trisiloxanes and tetrasiloxanes) is present. Preferably the curing process is moisture activated in air as a result of the moisture content of the atmosphere.

Suitable siloxane polymers or oligomers may include dimethylpolysiloxane, diethylpolysiloxane, diphenylpolysiloxane, dimethoxypolysiloxane, diethoxypolysiloxane, dimethylpolysiloxane ethoxylate, poly [methyl (3, 3, 3-trifluoropropyl) siloxane] , hexamethyldisiloxane, hexaethyldisiloxane, hexaphenyldisiloxane, 1,1,3, 3-tetramethyldisiloxane, 1,1,3, 3-tetraethyldisiloxane, 1,1,3,3- tetraisopropyldisiloxane, 1, 3-diethoxy-l, 1,3,3- tetramethyldisiloxane, 1, 3-dimethyltetravinyldisiloxane, pentamethyldisiloxane, 1, 1, l-trimethyl-3, 3, 3- triphenyldisiloxane, 1,1, l-triphenyl-3, 3, 3-tris (m- tolyl) disiloxane, 1, 3-dimethyl-l, 1,3,3- tetraphenyldisiloxane, 1,1,3, 3-tetramethyl-l, 3- diphenyldisiloxane, 1, 3-dibenzyl-l, 1,3,3- tetramethyldisiloxane, 1, 3-dimethyltetramethoxydisiloxane, octamethyltrisiloxane, 1,1,1,3,5,5,5- heptamethyltrisiloxane, 1,1,3,3,5, 5-hexamethyltrisiloxane, decamethyltetrasiloxane, 1,1,1,3,5,7,7,7- octamethyltetrasiloxane .

Such siloxane polymers may comprise up to 70 wt% of the overall antifouling composition, preferably up to 65 wt%, and more preferably 35 to 55 wt%.

Suitable silanes may include tetraethyl silane, tetraallyl silane, tetraphenyl silane, tetrakis (3- fluorophenyl) silane, tetrakis (p-tolyl) silane, ethyltriacetoxysilane, isobutyl (trimethoxy) silane, triacetoxy (vinyl) silane, triethoxy (ethyl) silane, triethyl (trifluoromethyl) silane, trimethoxy (vinyl) silane, trimethyl (phenyl) silane, trimethyl (vinyl) silane, tris (2- methoxyethoxy) (vinyl) silane, l-phenyl-2- trimethylsilylacetylene, 3-trimethylsiloxy-l-propyne, 3- [ tris (trimethylsiloxy) silyl] propyl methacrylate, allyl (4- methoxyphenyl) dimethylsilane, butyldimethyl (dimethylamino) silane, diisopropyl (3, 3,4,4,5,5,6, 6, 6-nonafluorohexyl) silane, dimethoxy-methy1 (3, 3, 3-trifluoropropyl) silane .

Such silanes may typically comprise up to 20 wt% of the overall antifouling coating composition, but more preferably 1 to 10 wt%. The silanes suitably act as crosslinking agents, catalysts, tensile elasticity control, and adhesion promoters. The polymer matrix may further comprise a siloxanolate of the formula:

M₂O[R₂SiO]_x

whereby M can be any monovalent metal ion, preferably an alkali metal; or an ammonium ion, preferably tetraalkylammonium, more preferably tetramethylammonium. Preferably a siloxanolate comprises up to 10% wt/wt of composition, preferably 1-5%.

In preferred embodiments the composition contains alkanes, preferably Cu to Ci₅. Preferably the alkanes are isoparaffins When present the alkanes may constitute up to 55 wt% of the overall composition, but more preferably 20 to 55 wt%. Alkanes are believed to be solvent carriers or diluents for the polymer; as they evaporate the hydrolysis gradually increases to form the final matrix.

The matrix composition, due to its extreme hydrophobic properties has, it is believed, an unusual antifouling property in that bacterial organisms, which are the base for marine growth contamination, will attempt to colonise the underwater surface. However, not being able to adhere, the lipids which are part of the bacterial membrane will spread attempting to secure adhesion. Ultimately this action will result in bursting of the bacterial membrane and deactivation of the microorganism. This effect is enhanced by inclusion into the matrix of the component with high zeta potential.

Compositions may be sprayable but are preferably spreadable by means of an implement such as a roller or brush. Preferably the viscosity of the composition

(before curing) is in the range 5000-10000 cP, preferably

7000-10000 cP, measured on a Brookfield viscometer, using spindle No. 1, at 22.5°C at a speed of 60 rpm at a torque setting of 36.2%.

Preferred features of any aspect are also preferred features of all other aspects of the present invention.

According to a second aspect of the present invention there is provided an antifouling composition with a negative zeta potential.

According to a third aspect of the present invention there is provided an antifouling composition which substantially repels marine bacteria through electrostatic forces .

Preferably the electrostatic forces result from the antifouling composition having a negative zeta potential. Preferably the electrostatic forces result from a marine bacteria combating material.

According to a fourth aspect of the present invention, there is provided an antifouling composition comprising a marine bacteria combating material; wherein the marine bacteria combating material repels bacteria through electrostatic forces.

According to a fifth aspect of the present invention there is provided an antifouling composition comprising a glass component. The glass component preferably has a negative zeta potential as defined above in relation to the first aspect, but this is not essential in this fifth aspect. It may not be material in all embodiments.

Preferably the antifouling composition further comprises a matrix material.

According to a sixth aspect of the present invention there is provided an antifouling composition comprising:

a matrix material comprising:

- 35 to 55 wt% siloxane; and

- 1 to 20 wt% silane; and

- 20 to 55 wt% alkanes; and a particulate material comprising: - 0.01 to 2.5 wt% aluminium or aluminium oxide or aluminium silicate; and/or

- 0.001 to 20 wt% glass.

The glass component preferably has a negative zeta potential as defined above in relation to the first aspect, but this is not essential in this sixth aspect. It may not be material in all embodiments.

According to a seventh aspect of the present invention there is provided a coated substrate, wherein the coating comprises a composition of any of the first to sixth aspects .

The coating may be applied in one pass, or preferably one or more passes, and most preferably from two to four passes . The coating may undergo further processing once applied; preferably curing in air.

The thickness of the final coating is preferably between 50 microns to 2000 microns, more preferably between 100 microns to 1000 microns, and most preferably between 250 microns and 650 microns.

According to an eighth aspect of the present invention there is provided a method of preparing a marine bacteria combating material, comprising particulating a siliceous component .

Preferably the method comprises particulating the siliceous component so as to exhibit a negative zeta potential, preferably more negative than -25mV, preferably more negative than -3OmV, more preferably -4OmV, more preferably -5OmV, and most preferably -6OmV.

Preferably the siliceous component requires no chemical treatment when particulating.

Preferably the siliceous component is derived from glass. The glass may be waste glass, such as waste bottles.

According to a ninth aspect of the present invention there is provided a method for preparing an antifouling composition, comprising mixing together the marine bacteria combating material and additional components of the antifouling compositions of any of the first to sixth aspects, to form a sprayable or spreadable product. The marine bacteria combating material may be prepared separately, premixing the marine bacteria combating material with a hydrocarbon solvent to form a mobile slurry which may then be further mixed with the additional components to give a uniform antifouling composition.

A tenth aspect of the present invention involves a method of protecting underwater structures from fouling, and preferably corrosion, comprising:

a) spraying or spreading the antifouling composition of any of the first to sixth aspect over the surface of an underwater structure by a spraying or spreading means to form a layer; b) optionally spraying or spreading further layers of coating; and c) curing the said coating (s).

Preferably the substrate to be treated is clean (for example grease free) and without corrosion damage (for example perforations or crusting) .

The composition is suitable for the treatment of any surface, though a surface would preferably be selected from the group: fibreglass, metal alloys (including aluminium/aluminium alloy), steel, iron, wood, painted surfaces, conventional antifouling paint, and rubber bitumen .

Preferably no more than four, and more preferably no more than two coats are applied in any one antifouling treatment program. Preferably there should be at least 4 hours between each coating application, more preferably at least 8 hours, and most preferably at least 12.

Preferably the applied coating (s) should be left for 24 hours and more preferably 48 hours to cure.

Preferably such antifouling compositions may tolerate temperatures from -40⁰C to 200⁰C after curing.

An eleventh aspect of the invention involves the use of the compositions described in any of the first to sixth aspects to prevent fouling on underwater structures, and preferably those from the group including boats, ships, submarines, submarine oil field facilities, underwater tunnels, fishing nets, water intakes, pipelines, jetties, breakwaters, groynes, buoys and bridges.

Applied correctly, the antifouling coatings herein disclosed should last for at least 5 years, more likely at least 10 years and most likely at least 20 years.

On static underwater structures the propensity of organisms and soils to adhere to the surface is reduced. The frequency of cleaning can be reduced and cleaning requires minimal effort.

The same is true on mobile underwater structures, but an additional benefit may occur: fouling may be washed off by movement through the water. A boat or ship may in effect become self-cleaning. The invention will now be further described with respect to the following examples.

EXAMPLES

Examples of antifouling compositions of the present invention include:

a polymer matrix material; - a particulate marine bacteria combating material; and an optional metal component.

The particulate marine bacteria combating material is a siliceous component, whereas the optional metal component is an aluminium component.

The siliceous component has particles with a negative surface charge. This negative surface charge is believed to provide a source of electrostatic repulsion to colloidal bacteria particles, which themselves appear generally to exhibit a negative surface charge. Since fouling and the accumulation of marine growth typically starts with bacterial fouling, the repulsion of bacteria is considered to be a crucial factor in the development of improved antifouling compositions.

Surface charge may generally be measured using zeta potentials, a theoretical property exhibited by all colloid particles and surfaces within a dispersion medium (eg. sea water) . Zeta potential is a universal measure of the electrical potential difference between a dispersion medium and the stationary layer (or interfacial double layer) of fluid associated with the dispersed particle or surface .

The polarity and magnitude of a zeta potential (positive or negative) essentially reflects the polarity and magnitude of the charge at the actual surface of a dispersed particle. Therefore, two particles having a high zeta potential of the same polarity will tend to repel. Two particles having either low zeta potentials or zeta potentials of opposite polarity will tend to attract, thus accounting for their tendency to coagulate or flocculate. Zeta potentials are therefore also a useful indication of whether two types of particles will form a stable emulsion or not.

In the context of the present invention, zeta potential is seen as an important measure of the affinity of bacteria, dispersed in marine environments, for surfaces coated with antifouling compositions. To this end, siliceous components have been produced which exhibit highly negative zeta potentials. Such siliceous components are then ideal for use in antifouling compositions .

EXAMPLE 1

The siliceous component is generated through compacting coloured glass bottles, flushing with 2M citric acid, and processing in a high speed cyclone to produce glass particles between 5 and 40 microns in size.

An equally useful siliceous component is generated through feeding powdered glass (preferably derived from coloured glass bottles) through two grooved metal or ceramic circular plates separated by 20 microns and spinning at high speed in opposite directions.

Both methods yield glass particles of approximately 20 microns with highly negative zeta potential.

It will be understood by those skilled in the art that other methods of producing glass fines are also available, including retrieving exhaust waste glass from injecting glass particles in the air stream of jet engines for the purpose of cleaning. Subjecting glass to high shear forces will in general result in glass with high negative surface charge.

EXAMPLE 2

The siliceous component is generated through the hydrolysis of tetraethyl orthosilicate (TEOS) obtained from Sigma-Aldrich.

A sol-gel is formed between TEOS and hydrochloric acid solution, by heating the two components together at 50⁰C for 1 hour. The sol-gel is then dried at 150⁰C to produce a fine powder of silicon dioxide having an average particle size of below 20 microns.

It will be understood by those skilled in the art that the sol-gel may also be formed using ammonia or ethyl alcohol and/or a process of air drying.

EXAMPLE 3 The zeta potentials of the siliceous components formed from Examples 1 and 2 were subsequently measured.

A sample of each of Example 1 and 2 silicon dioxide product was made up in a Zetasizer Nano cell (folded capillary cell) as a 0.5% w/v dispersion in deionised water. In each case the dispersant had an RI (refractive index) of 1.33, a viscosity of 0.8872 cP at ambient temperature, and a dielectric constant of 78.5. Each sample was at pH 6.8 and was analysed at 25°C.

Samples were analysed using a Zetasizer Nano Z system available from Malvern Instruments (www.malvern.co.uk), which employs M3-PALS technology based on the well-known technique of phase analysis light scattering (PALS) with a mixed mode measurement (M3) technique to enable accurate measurements of zeta potential. In each case, 12 zeta runs were carried out and average zeta potentials were as follows :

Example 1 sample: -47.2 mV Example 2 sample: -25.0 mV

Therefore the siliceous component formed from ground coloured glass was deemed preferable for compositions of the present invention.

EXAMPLE 4

A control antifouling composition was made by blending the following components: - 3 . 0 % w/w tetraethyl s i lane 54 . 8 % w/w i soparaf f ins , Cn-Ci₅

- 39.5% w/w polydiethoxysiloxane

- 2.34% w/w dipotassium dimethylsiloxanolate - 0.36% w/w aluminium fines (0.18% w/w aluminium platelets in 0.18% w/w white spirit)

The first four components were blended, followed by the aluminium fines.

Two additional antifouling compositions were formed: the first by blending 10% w/w of the siliceous component of Example 1 into the control antifouling composition; and the second by blending 10% w/w of the siliceous component of Example 2 into the control antifouling composition.

The three compositions were then individually packaged in airtight paint tins, with the intention of later brushing from the tins onto a suitable substrate, e.g. a boat hull, or conveying to a sprayer apparatus.

In use, the thickness of a typical coat after application of two layers and curing in air is 150 to 400 microns. The composition feels "slippy" and is not wetted by water: water dropped onto the coated substrate held horizontally forms beads; inclining the substrate even a small amount, e.g. 10°, causes the beads to run off the surface .

EXAMPLE 5

Three test plates were coated using the compositions of Example 4: the first with the control antifouling composition; the second with the coating containing silicon dioxide of Example 1; and the third with the coating containing silicon dioxide of Example 2.

After six weeks of immersion in sea water, both the Example 1 and Example 2 coatings were found to be substantially free of bacterial marine growth (as assessed by eye) , albeit Example 2 showed signs of minor accumulation of bacteria. The control antifouling composition clearly had bacterial accumulations.

Furthermore, coatings formed from all the compositions are resistant to fouling. Such fouling as does form is poorly adhered and can be quickly removed, for example, by mild rubbing or by spraying with water. Application of a second such coating, if wished, is easily achieved; the first and second coatings bond well together.

EXAMPLE 6

An antifouling composition was made by blending the following components:

- 2.9 % w/w tetraethyl silane _ 4 0 . 9 % w/w i s oparaf f ins , Cn -Ci₅

- 43.3 % w/w polydiethoxysiloxane

10.0 % w/w dipotassium dimethylsiloxanolate 2.2 % w/w ground glass powder.

The first four components were blended, followed by the ground glass powder. The composition was then packaged in airtight paint tins, with the intention of later brushing from the tins onto a suitable substrate, e.g. a boat hull, or conveying to a sprayer apparatus .

In use, the thickness of a typical coat after application of two layers and curing in air is 150 to 420 microns. The composition feels "slippy" and is not wetted by water: water dropped onto the coated substrate held horizontally forms beads; inclining the substrate even a small amount, e.g. 10°, causes the beads to run off the surface.

Coatings formed from the composition did not have any marine growth during six months' immersion in seawater. Such fouling as does form is poorly adhered and can be quickly removed, for example, by mild rubbing or by spraying with water. Application of a second such coating, if wished, is easily achieved; the first and second coatings bond well together.

EXAMPLE 7

An antifouling composition was made by blending the following components:

- 3.0% w/w tetraethyl silane

51.9% w/w isoparaffins, Cn-Ci₅

- 38.5% w/w polydiethoxysiloxane

2.4% w/w dipotassium dimethylsiloxanolate

- 0.6% w/w titanium dioxide powder - 3.3% w/w ground glass powder (from recycled coloured glass ground to a finer grade of about 50 microns) . - 0.3% w/w aluminium fines (0.15% w/w aluminium platelets in 0.15% w/w white spirit) .

The first six components were blended, followed by the aluminium fines. The composition was then packaged in airtight paint tins, with the intention of later brushing or spraying onto a hull or undersurface intallation, for example of a jetty, breakwater, buoy or bridge.

In use, the thickness of a typical coat after application of two layers and curing in air is 150 to 400 microns. The composition feels "slippy" and is not wetted by water: water dropped onto the coated substrate held horizontally forms beads.

Coatings formed from the composition are resistant to fouling. Such fouling as does form is poorly adhered and can be quickly removed, for example, by mild rubbing or by spraying with water. Application of further coating, if wished, is easily achieved; successive coatings bond well together .

EXAMPLE 8

Compositions of Examples 4 to 7 are all found to have enhanced antibacterial and antifouling properties when blended with 2% w/w titanium dioxide. The titanium dioxide acts as a photocatalyst in the presence of UV light, to further create a hostile environment for bacteria. This is believed to be the result of the localised generation of oxygen gas, especially whilst the coating is exposed to UV light such as from the sun. EXAMPLE 9

Compositions of Examples 4 to 8 were further enhanced in terms of their hydrophobic properties through the addition of 1% w/w of a fluoropolymer such as the polymerised adduct of 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl acrylate (available from Sigma-Aldrich) . Examples of applicable polymerisation processes can be found in WO

93/20116. Such fluoropolymers particularly improved the compositions of Example 4 in terms of their bacteria combating properties and also their general hydrophobicity .

Other advantageous fluoropolymers used in accordance with the present invention are those sold commercially as

Ftone™ 105D from Daikin Industries Limited. When used in

2% wt/wt quantities, these fluoropolymers are especially effective .

EXAMPLE 10

An antifouling composition was made by blending the following components:

- 48.6% w/w hydroxy-terminated polydimethylsiloxane

9.9% w/w non-hydroxy-terminated polydimethylsiloxane

- 4.6% w/w methyltris (dimethylketoxime) silane 1.1% w/w vinyltrimethoxysilane

- 1.0% w/w amorphous silicon dioxide - 0.4% w/w N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane 24.4% w/w isoparaffinic solvent - 10.0% w/w ground glass powder (from recycled coloured glass ground to a finer grade of about 50 microns) .

The components were blended and then packaged in airtight paint tins, with the intention of later brushing from the tins onto a suitable substrate, e.g. a boat hull, or conveying to a sprayer apparatus .

Hydroxy-terminated polydimethylsiloxane has a viscosity of 500 P (50 Pa. s) and serves as the foundation of the composition and is cross-linked on curing by the various silanes present.

Non-hydroxy terminated polydimethylsiloxane has a viscosity of 10 P (1 Pa. s) and is a plasticizer which allows a flexible substrate coated with the above composition to be flexed without cracking the coating.

N-beta- (aminoethyl) -gamma- aminopropylmethyldimethoxysilane is an adhesion promoter which helps the composition initially adhere to a substrate to be coated before curing takes place.

The isoparaffinic solvent acts as a diluent or thinning agent to provide the composition with a consistency conducive to spreadability .

Coatings formed from the composition are resistant to bio-fouling in marine environments and did not have any marine growth during six months' immersion in seawater.

Such fouling as does form is poorly adhered and can be quickly removed, for example, by mild rubbing or by spraying with water. Application of a second such coating, if wished, is easily achieved; the first and second coatings bond well together.

Claims

1. An antifouling composition comprising:

a marine bacteria combating material;

wherein the marine bacteria combating material has a negative zeta potential.

2. The antifouling composition as claimed in claim 1 wherein the zeta potential of the marine bacteria combating material is more negative than -25mV.

3. The antifouling composition as claimed in claim 1 wherein the zeta potential of the marine bacteria combating material is more negative than -3OmV.

4. The antifouling composition as claimed in claim 1 wherein the zeta potential of the marine bacteria combating material is more negative than -4OmV.

5. The antifouling composition according to any preceding claim, wherein the marine bacteria combating material is a siliceous component.

6. The antifouling composition as claimed in claim 5 wherein the siliceous component comprises up to 80 wt% of the antifouling composition.

7. The antifouling composition as claimed in any of claims 5 or 6, wherein the siliceous component has an average particle size from 0.001 to 1000 microns.

8. The antifouling composition as claimed in any of claims 5 to 7, wherein the siliceous component comprises a glass component.

9. The antifouling composition as claimed in claim 8, wherein the glass component comprises glass which is coloured.

10. The antifouling composition as claimed in either of claim 8 or 9, wherein the glass component has been subjected to shear forces.

11. The antifouling composition as claimed in any of claims 8 to 10, wherein the glass component comprises recycled glass.

12. The antifouling composition according to any preceding claim, comprising a photocatalyst .

13. The antifouling composition as claimed in claim 12, wherein the photocatalyst comprises from 0.01 to 2 wt% of the overall composition.

14. The antifouling composition as claimed in either claim 12 or 13, wherein the photocatalyst comprises titanium dioxide and/or zinc oxide.

15. The antifouling composition according to any preceding claim, comprising a fluoropolymer component.

16. The antifouling composition as claimed in claim 15, wherein the fluoropolymer component leads to increased hydrophobicity of the overall composition.

17. The antifouling composition as claimed in any of claims 15 or 16, wherein the fluoropolymer component comprises 0.01 to 2 wt% of the antifouling composition.

18. The antifouling composition as claimed in any of claims 15 to 17, wherein the fluoropolymer component comprises a fluoropolymer selected from the group including: polyfluoroalkanes (for example PTFE), polyvinylfluoride, and polymers of 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7-Dodecafluoroheptyl acrylate, 2,2, 3, 3, 4, 4, 4-Heptafluorobutyl acrylate, 1,1,1,3,3,3- Hexafluoroisopropyl acrylate, 2,2,3,3,4,4,5,5- Octafluoropentyl acrylate, 2,2,3,3,4,4,5,5- Octafluoropentyl methacrylate, 2, 2, 3, 3, 3-Pentafluoropropyl acrylate, 2, 2, 3, 3-Tetrafluoropropyl acrylate, or mixtures thereof.

19. The antifouling composition according to any preceding claim, comprising a matrix material.

20. The antifouling composition as claimed in claim 19, wherein the matrix material is a polymer matrix.

21. The antifouling composition as claimed in any of claims 19 to 20, wherein the matrix material comprises a polymeric silicon-containing compound.

22. The antifouling composition as claimed in any of claims 19 to 21, wherein the matrix material comprises a siloxane .

23. The antifouling composition as claimed in any of claims 19 to 22, wherein the matrix material comprises a silane .

24. The antifouling composition according to any preceding claim, comprising an aluminium component.

25. The antifouling composition as claimed in claim 24 wherein the aluminium component comprises aluminium metal or aluminium oxide or an aluminium silicate.

26. The antifouling composition as claimed in any of claims 24 to 25, comprising up to 5 wt% of the aluminium component .

27. The antifouling composition as claimed in any of claims 24 to 26, wherein the particle size of the aluminium component is from 1 to 25 microns.

28. An antifouling composition with a negative zeta potential.

29. An antifouling composition which substantially repels marine bacteria through electrostatic forces.

30. An antifouling composition comprising:

a marine bacteria combating material; wherein the marine bacteria combating material repels bacteria through electrostatic forces.

31. An antifouling composition comprising a glass component .

32. An antifouling composition comprising:

a matrix material comprising: - 35 to 55 wt% siloxane; and

- 1 to 20 wt% silane; and

- 20 to 55 wt% alkanes; and a particulate material comprising:

- 0.01 to 2.5 wt% aluminium or aluminium oxide or aluminium silicate; and/or

- 0.001 to 20 wt% glass.

33. A coated substrate, wherein the coating comprises a composition of any preceding claim.

34. A method of preparing a marine bacteria combating material, comprising particulating a siliceous component.

35. The method as claimed in claim 34, comprising particulating the siliceous component so as to exhibit a negative zeta potential.

36. A method for preparing an antifouling composition as claimed in any of claims 1 to 32, comprising mixing together the marine bacteria combating material and additional components of the antifouling composition to form a sprayable or spreadable product.

37. The method as claimed in claim 36 comprising preparing the marine bacteria combating material separately; premixing the marine bacteria combating material with a hydrocarbon solvent to form a mobile slurry; and further mixing with the additional components to give a uniform antifouling composition.

38. A method of protecting underwater structures from fouling, comprising:

a) spraying or spreading an antifouling composition as claimed in any of claims 1 to 32 over the surface of an underwater structure by a spraying or spreading means to form a layer; b) optionally spraying or spreading further layers of coating; and c) curing the said coating (s).

39. The use of a composition according to any of claims 1 to 32, to prevent fouling on underwater structures, and preferably those from the group including boats, ships, submarines, submarine oil field facilities, underwater tunnels, pipelines, jetties, breakwaters, groynes, buoys and bridges.

40. An antifouling composition as substantially hereinbefore described with reference to the Examples.

41. A coated substrate as substantially hereinbefore described with reference to the Examples.

42. A method of preparing a marine bacteria combating material as substantially hereinbefore described with reference to the Examples.

43. A method of preparing an antifouling compositions as substantially hereinbefore described with reference to the Examples .

44. A method of protecting underwater structures as substantially hereinbefore described with reference to the

Examples .

45. A use of an antifouling composition as substantially hereinbefore described with reference to the Examples.