WO2009144495A2

WO2009144495A2 - Hydrophobic coating composition

Info

Publication number: WO2009144495A2
Application number: PCT/GB2009/050572
Authority: WO
Inventors: Keith Macgregor
Original assignee: Si Laboratories Limited
Priority date: 2008-05-28
Filing date: 2009-05-27
Publication date: 2009-12-03
Also published as: WO2009144495A3; GB0809629D0

Abstract

The present invention relates to a hydrophobic containing composition, which, when applied to a surface, prevents or reduces contamination of the surface. The composition comprises a hydroxy-terminated siloxane and a silane.

Description

Hydrophobic Coating Composition

The present invention relates to a hydrophobic coating composition applied to a surface to prevent or reduce contamination of the surface. Such contamination may include biological, microbiological, chemical, and/or radiological contamination.

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.

There is also a growing need in hospitals for a coating which prevents surfaces collecting, harbouring, and/or becoming a breeding ground for microorganisms, particularly those such as MRSA (Methicillin Resistant Staphylococcus Aureus) and C. diff (Clostridium difficile) , both of which are now a serious problem in hospital environments.

Moreover, there is a need in both a military and a non-military context to protect surfaces from chemical and biological contamination, particularly in defence against chemical and biological weapons. An anti-contamination coating that could be simply applied to existing surfaces would therefore be of high value.

Furthermore, there is a need again in both a military and a non-military context to protect surfaces from radiological contamination caused by exposure of surfaces to radiation or radioactive substances. An anti- contamination coating that could be simply applied to existing surfaces would again therefore be of high value, especially if such a coating also protected against chemical and biological contamination.

Finally, surfaces in many neighbourhoods and cities are vulnerable to being blighted by graffiti. Removal of such graffiti currently requires the use of chemicals which cause harm to the environment, especially when said chemicals make their way into rivers and the surrounding ecosystem. It is thereby desirable to coat certain surfaces with a coating which substantially resists the adherence of graffiti, thus enabling facile removal of the graffiti without the need for harmful chemicals.

In accordance with a first aspect of the present invention there is provided a hydrophobic coating composition for coating a surface, comprising a hydroxy- terminated siloxane; and at least one silane.

Preferably the composition does not comprise an aluminium component or a glass component.

By aluminium component is meant either aluminium metal, or a water-insoluble aluminium compound, for example aluminium oxide or an aluminium silicate.

By glass component is meant a particulate glass component comprising glass that has been particulated. This includes any kind of glass, including high-quartz glass (sometimes called just "quartz sand") , borosilicate glass, or soda-lime glass.

In this specification, a siloxane has the general formula:

where R¹ and R² may be any hydrocarbyl group optionally substituted, or a further siloxane branch in accordance with the above structure, and n may be any integer greater than 2. R¹ and R² are preferably the same, and are preferably branched or unbranched alkyl radicals.

A hydroxy-terminated siloxane has at least one free hydroxyl group in the molecule, preferably attached to a terminal silicon atom. This includes where the terminal silicon atom is comprised of a branched or cross-linked siloxane .

The composition, due to its extreme hydrophobic properties has, it is believed, an unusual marine antifouling property in that bacterial organisms, which are the base for marine growth contamination, will attempt to colonise an 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.

Preferably the at least one silane renders the composition curable.

Preferably the composition is curable to give a coating comprising a polymer matrix.

Preferably the at least one silane chemically crosslinks the hydroxy-terminated siloxane upon curing the composition. This has the advantage that the composition is stable on storage, and during application, so as to remain either sprayable or spreadable.

The composition is preferably "slippy" to the touch when in the form of a dried coating on a substrate. Preferably the composition is curable upon the surface to give a substantially non-stick coated surface such that water dropped onto a coated surface forms beads, which may readily run off it when it is tilted by 10° from the horizontal.

Preferably the composition further comprises an adhesion promoter. Preferably the at least one silane comprises the adhesion promoter. Preferably the composition adheres to aluminium, alloys, stainless steel, wood, GRP, painted surfaces, and rubber bitumen. Preferably the composition will adhere to a cured or partially cured layer of the same. This allows for the application of several layers, or reapplication of a partially depleted layer to maintain the effect imparted upon a surface by the present invention.

The hydroxy-terminated siloxane preferably comprises a polymer or a co-polymer, and more preferably comprises a polymer, most preferably a homopolymer. The hydroxy- terminated siloxane may comprise a polydialkylsiloxane, and most preferably comprises polydimethylsiloxane . The hydroxy-terminated siloxane preferably comprises a polymer which terminates with at least one hydroxyl group, and most preferably with a hydroxyl group at each terminus. A terminus may include the end/terminus of a branched or cross-linked siloxane chain. Preferably, however, the hydroxy-terminated siloxane comprises an unbranched polysiloxane .

The hydroxy-terminated siloxane preferably comprises from 20 to 75 wt% of the composition, preferably from 25 to 70 wt% of the composition, and more preferably from 45 to 65 wt% of the composition, and most preferably from 50 to 55 wt% of the composition.

The hydroxy-terminated siloxane preferably has a viscosity of at least 10 poise (P) (1 Pascal-seconds,

Pa. s), preferably at least 100 P (10 Pa. s), more preferably at least 250 P (25 Pa. s), most preferably at least 400 P (40 Pa. s) . Preferably the viscosity is no more than 1000 P (100 Pa. s), preferably no more than 750 P (75 Pa. s), most preferably no more than 600 P (60 Pa. s) .

The composition preferably further comprises a plasticizer. The plasticizer may be a siloxane, preferably a non-hydroxy-terminated siloxane. The non- hydroxy-terminated siloxane is preferably a polydialkylsiloxane . 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 .

The non-hydroxy-terminated siloxane preferably comprises no cross-linkable moieties, and preferably no free hydroxyl groups .

The non-hydroxy-terminated siloxane preferably has a viscosity of at least 1 poise (P) (0.1 Pascal-seconds, Pa. s), more preferably at least 5 P (0.5 Pa. s), most preferably at least 9 P (0.9 Pa. s) . Preferably the viscosity is no more than 100 P (10 Pa. s), more preferably no more than 50 P (5 Pa. s), and most preferably no more than 11 P (1.1 Pa. s) .

The at least one silane preferably comprises at least one leaving group, and more preferably at least two leaving groups. The at least one leaving group preferably comprises a group whose conjugate acid has a pK_a in water of between 8 and 17, preferably between 9 and 15, preferably between 11 and 13. The at least one leaving group may comprise a moiety selected from the group including aryloxy, haloalkoxy, oxime, ketooxime. The at least one silane may comprise a ketoxime silane.

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, N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane, trimethyl (vinyl) silane, tris (2-methoxyethoxy) (vinyl) silane, methyltris (dimethylketoxime) 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-methyl (3, 3, 3-trifluoropropyl) silane, vinyltrimethoxysilane .

Such silanes may typically comprise up to 20 wt% of the overall composition, but more preferably 1 to 10 wt%, and most preferably 2 to 8 wt%. The silanes suitably act as crosslinking agents, catalysts, tensile elasticity control, and adhesion promoters.

The weight ratio of the hydroxy-terminated siloxane to the at least one silane is preferably from 2:1 to 20:1, more preferably from 5:1 to 15:1 and most preferably from 7:1 to 9:1.

The composition 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 some embodiments the composition may also comprise an additional chemical compound, especially of copper, iron, tin, zinc or titanium, preferably selected from the group: copper (I) acetate, copper (II) acetate, copper (II) oxide, ferric oxide, titanium dioxide, zinc oxide, zinc acetate, zinc octoate, zinc chloride, zinc bromide, titanium tetrachloride, di-n-octyltin l-benzoyl-4-methyl- 2-pentanonate 2-ethylhexanoate and di-n-octyltin 1- benzoyl-4-methyl-2-pentanonate laurate. When such an additional compound is present 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, most preferably 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. Titanium dioxide participates in self-cleaning by generating ions when subjected to UV light.

The composition may further comprise a fluoropolymer . The fluoropolymer preferably leads to increased hydrophobicity of the overall composition. The fluoropolymer is preferably derived from an acrylate fluoromonomer . The fluoropolymer preferably 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. 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 5 wt%.

In preferred embodiments the composition contains alkanes, preferably Cu to Ci₅. When present these may constitute up to 65 wt% of the overall composition, but more preferably 20 to 55 wt%. Preferably the alkanes comprise isoparaffinic solvent. Alkanes are believed to be solvent carriers or diluents for the siloxane polymers; as they evaporate the hydrolysis gradually increases to form the final matrix.

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 (5-10 Pa. s), preferably 7000-10000 cP (7-10 Pa. s) . Herein, all viscosities are as 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%. According to a second aspect of the present invention there is provided a hydrophobic coating composition comprising:

- 35 to 55% w/w hydroxy terminated polydimethylsiloxane

- 1 to 15% w/w non-hydroxy terminated polydimethylsiloxane

- 1 to 15% w/w silane

- 20 to 65% w/w alkanes - 0.1 to 4% w/w titanium dioxide

- 0.1 to 6% w/w fluoropolymer

According to a third aspect of the present invention there is provided a coated substrate wherein the coating comprises at least one layer of the composition of either of the first or second aspect.

The coating may comprise more than one layer of the composition. 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 a fourth aspect of the present invention there is provided a method of preparing a hydrophobic coating composition, comprising mixing together a hydroxy- terminated siloxane and at least one silane to form a sprayable or spreadable composition according to either of the first or second aspect.

A fifth aspect of the present invention involves a method of preparing a coated substrate of the third aspect, comprising:

a) spraying or spreading the hydrophobic coating composition of the first or second aspect over a surface by a spraying or spreading means to form a layer; b) optionally spraying or spreading one or more 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), wood, painted surfaces, conventional antifouling paint, and rubber bitumen.

Preferably the method further comprises spraying or spreading the hydrophobic coating composition over the coating (s) .

Preferably the curing process is moisture activated in air as a result of the moisture content of the atmosphere. Preferably the applied coating (s) are left for 12 hours and more preferably 24 hours to cure. Preferably there is at least 4 hours between each coating application, more preferably at least 8 hours, and most preferably at least 12.

Preferably no more than four, and more preferably no more than two coats are applied in any one treatment program.

Preferably such compositions may tolerate temperatures from -4O⁰C, preferably from -6O⁰C, to 500⁰C after curing. More preferably the compositions tolerate temperatures between -60°C to 280°C. Preferably the compositions substantially retain their hydrophobicity, and preferably retain their flexibility, between -60°C to 280°C.

According to a sixth aspect of the present invention there is provided a method of combating bacteria on a surface, comprising preparing a coated substrate in accordance with the fifth aspect.

According to a seventh aspect of the present invention there is provided a method of protecting underwater structures, comprising preparing a coated substrate in accordance with the fifth aspect.

Preferably the coating prevents fouling on the 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. Applied correctly, the 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.

According to an eighth aspect of the present invention there is provided a method of protecting surfaces from chemical or biological contamination, comprising preparing a coated substrate in accordance with the fifth aspect.

According to an ninth aspect of the present invention there is provided a method of protecting surfaces from radioactive contamination, comprising preparing a coated substrate in accordance with the fifth aspect.

According to an tenth aspect of the present invention there is provided a method of preventing adherence of graffiti to a surface, comprising preparing a coated substrate in accordance with the fifth aspect.

According to an eleventh aspect of the present invention there is provided a method of protecting a substrate from degradation caused by chemicals, comprising preparing a coated substrate in accordance with the fifth aspect. The degradation may be corrosion. The chemicals may be acidic solutions, preferably aqueous acidic solutions. Preferably the aqueous acidic solutions have a pH of 5 or lower, more preferably 2 or lower, and most preferably 1 or lower. Therefore, the method preferably protects the substrate even at very low pH. Preferably the method protects the substrate from corrosion by acid rain. The chemicals may be alkaline solutions, preferably aqueous alkaline solutions. Preferably, the aqueous alkaline solutions have a pH of 9 or higher, more preferably 11 or higher, and most preferably 13 or higher. Preferably the method protects the substrate from both acidic and alkaline conditions.

According to a twelfth aspect of the present invention there is provided a method to prevent ice formation upon a substrate, comprising preparing a coated substrate according to the fifth aspect. Preferably the coated substrate is readily removable, with minimal friction, from a block of ice formed around the coated substrate when the coated substrate is partially submerged in water that is subsequently frozen. The coated substrate may be an internal component of a freezer or refrigerator. The internal component may be an inside surface. The inside surface may include an internal wall, an internal surface of a door, or a drawer. This leads to less ice build up within the freezer, and less need for regular thawing.

According to a thirteenth aspect of the present invention there is provided a cooling device comprising the coated substrate of the third aspect. Preferably the cooling device is a fridge or a freezer. According to a fourteenth aspect of the present invention there is provided a method of increasing water repellent properties of a fabric substrate, comprising preparing a coated substrate in accordance with the fifth aspect, where said substrate comprises fabric. The fabric substrate may be clothing, for example a swim-suit. The fabric substrate may be a coat. The fabric substrate may be a tent .

According to an fifteenth aspect of the present invention there is provided a use of a hydrophobic coating composition according to the first or second aspect, to combat bacteria on a surface, protect underwater structures, protect surfaces from chemical or biological contamination, protect surfaces from radioactive contamination, prevent adherence of graffiti to a surface, protect a substrate from degradation caused by chemicals, prevent ice formation upon a substrate, or increase water repellent properties of a fabric substrate.

Preferred features of any aspect are also preferred features of any other aspect.

The invention will now be further described with respect to the following examples.

EXAMPLE 1

A hydrophobic coating composition was made by blending the following components:

- 54.0% w/w hydroxy terminated polydimethylsiloxane

11.0% w/w non-hydroxy terminated polydimethylsiloxane 5.1% w/w methyltris (dimethylketoxime) silane

- 1.2% w/w vinyltrimethoxysilane

- 1.1% w/w amorphous silicon dioxide 0.5% w/w N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane 27.1% w/w isoparaffinic solvent

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.

The viscosity of all siloxanes in the Examples hereinafter are the same as for this Example.

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 . 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 .

Coatings formed from the composition are resistant to bio-fouling in marine environments. 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 2

27.5% w/w hydroxy terminated polydimethylsiloxane

- 5.8% w/w non-hydroxy terminated polydimethylsiloxane - 2.5% w/w methyltris (dimethylketoxime) silane

- 0.6% w/w vinyltrimethoxysilane 0.5% w/w amorphous silicon dioxide

- 0.3% w/w N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane - 62.8% w/w isoparaffinic solvent

The components were blended and the composition was then packaged in airtight paint tins, with the intention of later brushing from the tins onto a test surface to be the subject of graffiti.

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.

Surfaces coated with this coating were difficult to graffiti. Paint readily ran down the surface so that it was difficult to form a defined image. Such a surface would not suffice for a graffiti artist. Furthermore, paint which became partially adhered was easily 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 3

53.7% w/w hydroxy terminated polydimethylsiloxane

- 10.5% w/w non-hydroxy terminated polydimethylsiloxane 5.0% w/w methyltris (dimethylketoxime) silane - 1.1% w/w vinyltrimethoxysilane

1.1% w/w amorphous silicon dioxide

- 0.5% w/w N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane 25.1% w/w isoparaffinic solvent - 3.0% w/w titanium dioxide

The components were blended and 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. It is of note that the performance of the composition of this example was improved compared to that of Example 1. The titanium dioxide acts as a photocatalyst in the presence of UV light, to further create a hostile environment for bacteria and thus alleviate fouling. 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 4

52.7% w/w hydroxy terminated polydimethylsiloxane 10.5% w/w non-hydroxy terminated polydimethylsiloxane

- 5.0% w/w methyltris (dimethylketoxime) silane

- 1.1% w/w vinyltrimethoxysilane 1.1% w/w amorphous silicon dioxide - 0.5% w/w N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane

- 23.1% w/w isoparaffinic solvent 2.0% w/w titanium dioxide

- 4.0% w/w Ftone™ 105D (commercially available from Daikin Industries Limited)

Ftone™ 105D is a fluoropolymer derived from an acrylic monomer. Compositions were also made containing equal quantities (4.0% w/w) of the polymerised adduct of 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl acrylate (available from Sigma-Aldrich) , to the same effect. Examples of applicable polymerisation processes can be found in WO 93/20116.

Coatings formed form 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. Compositions of this example showed improved antifouling properties over those of Example 3, suggesting that the fluoropolymer is responsible for such an augmentation. Application of a second such coating, if wished, is easily achieved; the first and second coatings bond well together.

EXAMPLE 5

52.5% w/w hydroxy terminated polydimethylsiloxane

- 10.5% w/w non-hydroxy terminated polydimethylsiloxane 5.1% w/w methyltris (dimethylketoxime) silane - 1.2% w/w vinyltrimethoxysilane

1.1% w/w amorphous silicon dioxide

- 0.5% w/w N-beta- (aminoethyl) -gamma - aminopropylmethyldimethoxysilane

- 25.1% w/w isoparaffinic solvent - 4.0% w/w Ftone™ 105D (commercially available from Daikin Industries Limited)

Coatings formed form 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. Compositions of this example showed improved antifouling properties over those of Example 1, suggesting that the fluoropolymer is responsible for such an augmentation, presumably due to increased hydrophobicity . Application of a second such coating, if wished, is easily achieved; the first and second coatings bond well together.

EXAMPLE 6

Five tests were carried out, each using one of the coatings of Examples 1 to 5. Each test employed two test plates; one coated using one of the compositions of Examples 1 to 5, the other uncoated as a control. Each of the coated and uncoated plates of each test was exposed to bacteria by virtue of being completely submerged for 1 minute in water obtained from a roadside drain. Each plate was left vertically inclined for 3 hours, so that the bulk of the water drained from the surface of even the uncoated plates. The plates were also air dried at 35⁰C during this 3 hour period. A swab was taken from each plate by scraping each plate along its length once with the end of a cotton bud. The end of the cotton bud was then placed in an agar plate for 5 seconds and cultures of bacteria were left to incubate therein for 48 hours at 35⁰C. The relative growth of bacterial colonies was then assessed by eye. The results are compared in Table 1 below.

TABLE 1

VL - Very low growth of bacterial culture

L - Low growth of bacterial culture

M - Medium growth of bacterial culture

H - High growth of bacterial culture

VH - Very high growth of bacterial culture

After taking the first swab, all plates were left to incubate at 35⁰C for a further 10 days, after which time a second swab was taken for each plate in the same manner as the first swab, only from a different part of the plate. Cultures of bacteria were again grown for 48 hours and the results are compared in Table 2 below.

TABLE 2

Table 1 clearly shows that living bacteria do not readily adhere to the coated plates, unlike the uncoated plates where bacterial contamination is very high. Therefore such coated surfaces substantially combat bacteria .

Table 2 demonstrates that the coated plates are effective at combating the growth of bacteria from those bacteria which did successfully adhere in the first instance. Clearly the coating of Example 4 is the most effective, as expected given the presence of titanium dioxide and a fluoropolymer .

These results clearly demonstrate the effectiveness of the hydrophobic coating compositions of the present invention in respect of combating the adherence and growth of bacteria on a surface. For these reasons, such coatings are considered ideal for surfaces in hospitals.

For instance, when coatings of examples 1 to 5, especially examples, 1, 3, 4 and 5, were applied to one side of a hospital door which was regularly pushed open with microbially contaminated hands, it was found that the coated surface did not support microbial growth, whereas the other uncoated side of the door, which was also regularly pushed open, did support microbial growth. Such effectiveness is also applicable to any form of biological contamination, and can be extended to chemical contamination since most chemical agents will not adhere to the coated surface, but will instead run off or evaporate due to the repellent effect of the surface. As mentioned in the previous examples, underwater structures are also substantially protected against fouling by virtue of the coating compositions of the present invention.

EXAMPLE 7

Tests were conducted on the hydrophobic coating composition of Example 1 to assess the effectiveness of such a coating in protecting against radiological contamination. To this end, both coated (with one coat as described in Example 1) and uncoated (control) test pieces were submerged into highly radioactive alkaline soft sludge typical of any nuclear power or reprocessing plant.

Each of the coated and uncoated (control) test pieces consisted of three separate rectangular plates made from aluminium (Al) , stainless steel (SS) , and galvanised steel (GS) together with a carbon steel pipe (CSP) and a stainless steel pipe (SSP) , all attached to a holding frame to yield a 5 pronged fork. In the case of the coated test piece, all 5 prongs of the fork were coated with a single coat as outlined in Example 1. The control piece had no special preparation and was representative of structures currently put into a pond, containing such radioactive sludge, in a nuclear power or reprocessing plant . Both test pieces and corresponding sets of plates were recovered on a regular basis at the same time, and underwent washing using running water as they were withdrawn from the pond and suspended over a bay. This was carried out on a regular basis over a period of three months and the levels of radioactive contamination and radiation recorded for all materials on the test pieces, including Al, SS, GS, CSP, and SSP.

For all materials of the coated test piece, their radioactivity was indistinguishable from background radiation on the test site. In contrast, the materials of the uncoated test piece could not be removed from the test area owing to the high level of radioactive contamination pertaining thereto.

Later tests showed that coated test pieces exposed to radiation in the above manner sustained some radioactive contamination when washed using only slow-running water. Greater agitation of the surface during washing led to greater radioactive decontamination of the coated test pieces. However, no amount of washing and/or agitation of radiation exposed uncoated test pieces could significantly reduce the levels of radioactive contamination.

Therefore the ability to readily decontaminate surfaces, coated with compositions of the present invention, allows on-site decontamination which significantly saves on decontamination costs, and reduces the need to transport highly radioactively contaminated components. Furthermore, allowing items to be moved to low radiation dose areas, with minimal effort, reduces dosages to workers engaged in decontamination and storage operations, and reduces dose rates during maintenance operations. The operating life of certain equipment is also significantly extended.

EXAMPLE 8

A 2mm thick aluminium strip measuring 30cm by 3cm was coated with the coating of Example 1 to give a hydrophobically coated strip ("Strip A") . A second aluminium strip of the same dimensions was coated with a two-part epoxy resin to give an epoxy coated strip ("Strip B") . A third aluminium strip was an uncoated control strip ("Step C") . The three strips were exposed to different conditions by submerging them in acidic and alkaline aqueous solutions over various time periods. The results are tabulated below.

TABLE 3

Therefore, coatings of the present invention not only render metal surfaces corrosion resistant, but they even out-perform two-part epoxy resins.

The coatings of the invention may therefore be described as corrosion inhibitors, and could be used to prevent damage caused by acid rain on a variety of surfaces, but especially metal surfaces. Such coatings provide general chemical protection, especially against highly acidic or highly alkaline (or basic) conditions.

EXAMPLE 9

An aluminium strip as described in Example 8 was created with the coating of Example 1 to again give a coated strip as per "Strip A". The strip was then submerged into a cardboard carton filled with water before the carton containing the water and strip was placed within a freezer for 48 hours. Upon removing the carton from the freezer it was found that the strip could be easily removed from the resulting ice block without resistance. The ice therefore did not freeze onto the strip .

The coating is therefore highly suitable as a coating for the interior walls or interior of the drawers of a freezer or even a fridge. The advantage of the coating in a freezer is that defrosting/thawing will be required less often, which is a particular advantage in the case of commercial freezers. Moreover, the risk of bacterial contamination within the ice is reduced because ice will not stick to the coated walls.

EXAMPLE 10

A fabric cloth was coated with the coating of Example 1. The cloth was still breathable - i.e. water vapour and air could still pass through the fibres - but water resistance increased markedly. This has applications for water-proof clothes, swimwear, and even temporary fabric such as tents.

EXAMPLE 11

Strip A of Example 8 was cooled to -60°C for 24 hours before being allowed to warm back to room temperature. The coating remained both hydrophobic and flexible.

The strip was then heated to 280°C for 4 hours before allowing the strip to cool back to room temperature. The coating remained hydrophobic and flexible

Claims

1. A hydrophobic coating composition for coating a surface, comprising:

a hydroxy-terminated siloxane; and at least one silane.

2. The hydrophobic coating composition as claimed in any preceding claim wherein the at least one silane chemically cross-links the hydroxy-terminated siloxane upon curing the composition.

3. The hydrophobic coating composition as claimed in any preceding claim wherein the at least one silane comprises an adhesion promoter.

4. The hydrophobic coating composition as claimed in any preceding claim wherein the composition adheres to aluminium, alloys, stainless steel, wood, GRP, painted surfaces, and rubber bitumen.

5. The hydrophobic coating composition as claimed in any preceding claim wherein the composition will adhere to a cured or partially cured layer of the same.

6. The hydrophobic coating composition as claimed in any preceding claim wherein the hydroxy-terminated siloxane comprises a polydialkylsiloxane .

7. The hydrophobic coating composition as claimed in any preceding claim wherein the hydroxy-terminated siloxane comprises a polymer which terminates with a hydroxyl group at each terminus .

8. The hydrophobic coating composition as claimed in any preceding claim, further comprising a plasticizer.

9. The hydrophobic coating composition as claimed in any preceding claim wherein the at least one silane comprises at least one leaving group.

10. The hydrophobic coating composition as claimed in any preceding claim further comprising a fluoropolymer .

11. The hydrophobic coating composition as claimed in any preceding claim, wherein the composition is sprayable or spreadable.

12. A coated substrate wherein a coating comprises at least one layer of the composition of any preceding claim.

13. The coated substrate as claimed in claim 12 wherein the coating comprises more than one layer of the composition according to any of claims 1 to 11.

14. A method of preparing a coated substrate as claimed in claim 12, comprising:

a) spraying or spreading the hydrophobic coating composition as claimed in any of claims 1 to 11 over a surface by a spraying or spreading means to form a layer; b) optionally spraying or spreading one or more further layers of coating; and c) curing the said coating (s) .

15. The use of a hydrophobic coating composition as claimed in any of claims 1 to 11, to combat bacteria on a surface, protect underwater structures, protect surfaces from chemical or biological contamination, protect surfaces from radioactive contamination, prevent adherence of graffiti to a surface, protect a substrate from degradation caused by chemicals, prevent ice formation upon a substrate, or increase water repellent properties of a fabric substrate.