WO2009135766A1

WO2009135766A1 - Method of inhibiting biofouling on a surface in contact with water

Info

Publication number: WO2009135766A1
Application number: PCT/EP2009/054893
Authority: WO
Inventors: Frank Wilco Bartels; Thomas Frechen; Harald Keller; Wolfgang Schrepp; Parappuveetil Sarangadharan Suresh
Original assignee: Basf Se
Priority date: 2008-05-05
Filing date: 2009-04-23
Publication date: 2009-11-12

Abstract

The invention concerns a method of inhibiting biofouling on a surface in contact with water, wherein a polymer composition is applied to said surface, said polymer composition being accessible to water and comprising at least one elastomer having an elongation at break according to DIN 53455 of at least 400%. Furthermore, the invention concerns anti-fouling coatings and paints comprising the before mentioned polymer compositions and the use of these polymer compositions for antifouling coatings and paints, preferably marine antifouling coatings and paints.

Description

Method of inhibiting biofouling on a surface in contact with water

Description

The invention concerns a method of inhibiting biofouling on a surface in contact with water, wherein a polymer composition is applied to said surface, said polymer composition being accessible to water and comprising at least one elastomer having an elongation at break according to DIN 53455 of at least 400%.

Furthermore, the invention concerns anti-fouling coatings and paints comprising the before mentioned polymer compositions and the use of these polymer compositions for antifouling coatings and paints, preferably marine antifouling coatings and paints.

Biofouling is the accumulation of microorganisms, plants, algae, and animals on solid surfaces, in particular on submerged structures such as ships' hulls and devices for water treatment.

Biofouling is also found in membrane systems, such as membrane bioreactors and reverse osmosis spiral wound membranes. In the same manner it is found as fouling in cooling water cycles of large industrial equipments and power stations.

In marine environment, the process of biofouling is initiated with the formation of microbial biofilms on submerged surfaces, such as ship hulls. The presence of the biofilm facilitates the subsequent attachment and settlement of different marine organisms, such as barnacles and fungi.

Biofouling can also occur in groundwater wells where buildup can limit recovery flow rates, and in the exterior and interior of ocean-laying pipes. In the latter case it has been shown to retard the seawater flow through the pipe and has to be removed with the tube cleaning process.

Furthermore, microorganisms can colonize a wide variety of medical devices, putting patients at risk for local and systemic infectious complications, including local-site infections, catheter-related bloodstream infections, and endocarditis.

Biofouling is typically divided into microfouling, i.e., biofilm formation induced by bacterial adhesion, and macrofouling, i.e., the attachment of larger organisms, of which the main culprits are barnacles, mussels, polychaete worms, bryozoans, and seaweed.

It is known that accumulated biofoulers can form enormous masses that severely diminish ships' maneuverability and carrying capacity. Fouling causes huge material and economic costs in maintenance of mariculture, shipping industries, naval vessels, and seawater pipelines.

In order to minimize the impacts of foulers, many underwater structures are protected by antifouling coatings. Traditionally, tin or copper based antifouling paints are being used to control fouling, which work by slowly releasing substances toxic to the attaching organisms.

Coatings which comprise an inert binder with a biocidal ingredient which is leached from the paint are well known from the prior art. Among the binders which have been used are vinyl resins, particularly a vinyl chloride/vinyl acetate copolymer, and rosin. The vinyl resins are seawater-insoluble and paints based on them use a high pigment concentration so that there is contact between pigment particles to ensure leaching. Rosin is a hard brittle resin which is very slightly soluble in seawater. The biocidal pig- ment is very gradually leached out of the matrix of rosin binder in use, leaving a skeletal matrix of rosin which becomes washed off the hull surface to allow leaching of the biocidal pigment from deep within the paint film.

The state of the art coatings are based on thick self coatings containing CuO or organic biocides that have sustained release of biocides over a period of 1-2 years polishing (see i.e. EP-A-69559; EP-A-529693; WO-A-91/09915). The foul release coatings are mainly based on thick crosslinked silicones that are hydrophobic and elastomeric. In these coatings the microorganisms adhere to the surface but detach while the ship travels at a speed of about 15 knots.

The state of the art coatings, however, have been found to be toxic to marine organisms in many cases. For example, extremely low concentrations of tributyltin (TBT), the mostly commonly used anti-fouling agent, cause defective shell growth in the oyster Crassostrea gigas and development of male characteristics in female genitalia in the dog whelk Nucella lapillus. In response to the increased scientific evidence on the toxicity of such coatings in aquatic environment, the use of organotin based coatings were banned in many countries.

The ban of organotins such as TBT and triphenyltin (TPT), and other toxic biocides in marine coatings is a severe problem for the shipping industry; it presents a major challenge for the producers of coatings to develop alternative technologies to prevent fouling on ship hulls.

The most successful antifouling paints in recent years have been "self-polishing co- polymer" paints based on a polymeric binder to which biocidal triorganotin moieties are chemically bound and from which the biocidal moieties are gradually hydrolyzed by seawater, as described for example in British Patent GB-1457590. The polymer from which the triorganotin moieties have been hydrolyzed becomes soluble in seawater, so that as the outermost paint layer becomes depleted of biocide it is swept off the surface of the hull by the movement of the ship through seawater. Self-polishing copolymer paints which release non-biocidal moieties are described in European Patent EP- 069559 and European Patent Application EP-A 232006.

Japanese Patent Application JP-A 1 1-061002 describes tin-free antifouling paint compositions based on a film-forming resin component, a chlorinated ethylene/vinyl acetate copolymer or a chlorinated partial hydrolyzate of this copolymer and an antifoulant. The film-forming component can for instance be a vinyl chloride copolymer resin combined with rosin as the water-soluble resin. A copolymer of vinyl chloride and vinylisobutyl ether is mentioned as film-forming polymer. The antifoulant is a biocide leaching out gradually.

It was an object of the present invention to provide a polymer composition forming films that exhibit reduced biofouling without leaching out of compounds and without the addition of an inorganic or organic biocide. In particular, the coatings comprising these polymer compositions ought to exhibit reduced settlement of macroorganisms in seawater, in particular of barnacle cyprids, and exhibit increased release of marine biofilms from its surface. The polymer compositions and paint preparations containing these polymer compositions ought to form films that are durable, mechanically stable and crack free and stable in marine environment, in particular stable against sea water. It was yet another object to provide coatings that do not leach out compounds, in particular compounds toxic to living organisms, when in contact with water.

It has been possible to achieve these targets by providing the method of reducing the biofouling of surfaces submerged in water as defined above. Preferred embodiments are outlined in the following and in the claims. Combinations of preferred embodiments do not leave the scope of the present invention.

For the purpose of the present invention, the inhibition of biofouling on surfaces in contact with water is characterized by at least one of the following criteria:

(1 ) inhibition of biofilm formation with respect to a mixed marine bacterial biofilm composed of Cobetia marina, Marinobacter hydrocarbonoclasticus and Vibrio alginolyticus compared to an epoxy standard,

(2) increased biofilm release compared to the release of a PDMS standard, wherein a mixed marine bacterial biofilm composed of Cobetia marina, Marinobacter hydrocarbonoclasticus and Vibrio alginolyticus is used and wherein the biofilm re- lease is determined after having rotated the biofilm for 10 min at 12 knots in natural seawater, and (3) reduced settlement of barnacle cyprids compared to the settlement on a glass surface.

Inhibition of biofilm formation means that after 4h incubation and drying the biomass - preferably quantified by Tecan plate reader - is reduced compared to the bisphenol based epoxy standard Epikote® 1004. When the biofilm formation under these conditions on the epoxy standard surface is normalized to 100%, preferably the biofilm formation is reduced to below 70%, in particular to below 60%, more preferably to below 50%, much preferably to below 40%.

Biofilm release is expressed as % biofilm reduction (Δ biomass/biomass before release x 100%), normalized against the silicone based standard Silastic® T-2 (Dow Corning). Preferably, the biofilm release is below 80%, in particular below 70 %, preferably below 60%, much preferably below 50%.

Inhibition of the accumulation of barnacle cyprids means that the settlement 3-day-old barnacle cyprids in artificial seawater after incubation for 48 hours at 28 ⁰C is reduced compared to the accumulation on a standard glass surface. When the settlement under these conditions on the glass surface is normalized to 100%, preferably the settlement of barnacle cyprids is reduced to below 60%, in particular to below 50%, more preferably to below 40%, much preferably to below 30%.

According to the invention, the method of inhibiting biofouling on surfaces in contact with water comprises the application of a polymer composition to said surface such that the polymer composition is accessible to the water. Therefore, the polymer composition forms part of the outermost layer of the coating or the paint film applied to the surface. In other words, the polymer composition preferably shields the surface from the surrounding water. The person skilled in the art knows that the coating or parts of the coating may be swollen by the water though.

The term "water" for the purpose of the present invention shall comprise liquid water as such and water which is part of a humid environment, for instance in the form of particles, droplets or vapor.

Preferably, the polymer composition is applied to said surface in dry state, prior to putting the surface in contact with water. Preferably, the polymer composition is applied as part of a paint composition or a coating composition, preferably as part of a paint composition. Elastomer

An elastomer is a polymer with the property of elasticity. According to the invention, the polymer composition applied to the surface comprises at least one elastomer exhibiting an elongation at break according to DIN 53455 of at least 400%, preferably of at least 500%, in particular of at least 650%, much preferably at least 800%.

Preferably, the elastomers used in this invention furthermore exhibit a Youngs modulus of from 1 to 500 MPa. The value of Youngs modulus throughout the present invention refers to ISO 527-1 , determined at 23°C and 50% relative humidity in machine direction with a constant displacement rate of 0.5 mm/min. The elastomers according to the invention preferably exhibit a Youngs modulus of from 1 to 200 MPa, in particular from 1 to 150 MPa, more preferred from 1 to 100 MPa, very particularly preferred from 1 to 50 MPa.

The elastomers preferably have a Shore A hardness of between about 20 and about 90, or between about 50 and 80. Shore A hardness is a measure of softness, and can be measured according to ASTM D-5.

In principle, any rubber-like polymer having elastic properties as defined above can be used as elastomers in the method according to the invention. Preferably the elastomer or the elastomers according to the present invention are selected from rubbers and thermoplastic elastomers (TPE). A rubber is a polymeric precursor capable of forming a permanently crosslinked (i.e., cured) polymer through a process called vulcanization and a TPE is a polymer capable of forming a reversibly crosslinked polymer showing thermoplastic behaviour under suitable processing conditions.

Examples of rubbers suitable for the present invention include unsaturated rubbers that can be cured (vulcanized), preferably by sulfur vulcanization:

Natural Rubber (NR) Polyisoprene (IR)

Butyl rubber (copolymer of isobutylene and isoprene, NR) Halogenated butyl rubbers (chloro butyl rubber: CIIR; bromo butyl rubber: BIIR) - Polybutadiene (BR)

Styrene-butadiene rubber (copolymer of polystyrene and polybutadiene, SBR) Nitrile rubber (copolymer of polybutadiene and acrylonitrile, NBR) Hydrated nitrile rubbers (HNBR) including Therban® and Zetpol® Chloroprene rubber (CR), polychloroprene, including Neoprene® and Baypren®

Saturated rubbers suitable for the method according to the invention that are preferably crosslinked by other means than sulfur vulcanization: EPM (ethylene propylene rubber) and EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene) Epichlorohydrin rubber (ECO) - Polyacrylic rubber, in particular polyacrylate rubber ACM and acrylate butadiene rubber, ABR)

Silicone rubber, in particular Sl, Q, VMQ (ASTM nomenclature) Fluorosilicone rubber, in particular FVMQ (ASTM nomenclature) Fluoroelastomers (in particular FKM, FPM according to ASTM nomenclature), in particular Viton®, Tecnoflon®, Fluirel® and Dai-El®

Perfluoroelastomers (in particular FFKM according to ASTM), in particular KaI- rez®

Tetrafluoro ethylene/propylene rubbers (in particular FEPM according to ASTM nomenclature) - Chlorosulfonated Polyethylene (in particular CSM according to ASTM nomenclature), in particular Hypalon®

Thermoplastic elastomers suitable for the method according to the present invention are:

thermoplastic polyurethane elastomers, thermoplastic copolyester elastomers, thermoplastic polyamide elastomers, including polyetheramides and polyether- esteramides, and thermoplastic elastomeric styrenic block copolymers (S-TPE).

The elastomers used in the method according to the present invention are preferably selected from at least one polymer or copolymer of the group consisting of polybutadi- ene, polyisobutylene and block copolymers of vinyl aromatic monomers and dienes.

If the elastomer comprises polybutadiene, preference is given to:

polybutadiene with a number average molecular weight Mn of at least 1 ,000,000 g/mol determined by GPC, preferably having a cis-1 ,4-content of from

20 to 50 mol-%, a trans-1 ,4-content of from 30 to 70 mol-%, and a Tg of from - 105°C to -85°C and to mixtures of block copolymers of vinyl aromatic monomers and dienes with polybutadiene with Mn of from 1000 to 10,000 g/mol.

Butadiene rubbers are known to the person skilled in the art and are for instance described in Ullman's Encyclopedia of Industrial Chemistry. In a first preferred embodiment of the invention, the at least one elastomer comprises a thermoplastic elastomer (TPE).

Preferred thermoplastic elastomers for the purpose of the present invention are:

a) thermoplastic vulcanizates (TPVs), where the plastic phase may be a semicrys- talline polyolefin such as a propene copolymer, linear low-density polyethylene, ethylene methacrylate copolymer or ethylene-ethyl acrylate copolymer, and the rubber phase may consist of EPM, EPDM, isobutene-isoprene copolymer (butyl rubber), isobutene-p-methylstyrene copolymers, halogenated isobutene-p- methylstyrene copolymers, natural rubber, styrene-butadiene co-polymers, ni- trile-butadiene copolymers, styrene-isoprene-styrene block copoly-mers and their hydrogenated version, polyvinylchloride (PVC), copolymers of polyvinylchloride, polyvinylether, copolymers of polyvinyl ether, polyvinyl alcohol (PVA), polyvi- nylacetate, polyvinylbutyrate and polyacrylonitrile etc;

b) thermoplastic polyurethane elastomers, in general obtained from diisocyanates, like 4,4^'-diisocyanatodphenylmethane (MDI), 3,3^'-dimethyl-4,4^'- biphenyl/diisocyanate (TODI), 1 ,4-phenylene-diisocyanate (PPDI), 4,4^'- dicyclohexylmethane diisocy-anate (H12-MDI) and 1 ,6-diisocyanatohaxane (HDI), and short chain diols with molecular masses of 61 to ~ 600 and long-chain polyester and polyether diols with molecular masses between 600 and 4000;

c) thermoplastic copolyester elastomers, in general obtained from the condensation of an aromatic dicarboxylic acid or ester, e.g. terephthalic acid or 2,6- naphthalenedicarboxylic acid, and low molecular weight aliphatic diols, e.g. 1 ,4- butanediol, and polyalkyleneetherglycols, in particular such with a molecular weight between 1000 and 4000, e.g. poly-(ethyleneglycol), poly(propyleneglycol) or poly(butyleneglycol), like polyethylene terephthalate (PET), copolymers of

PET, polyethylene naphthalate (PEN) and copolymers of PEN;

d) thermoplastic polyamide elastomers, in general obtained from dicarboxylic acid terminated oligoamides, e.g. polylaurolactam with Mn ~ 600 - 4000, and poly- ether diols or diamines based on poly(ethylenglycol), poly(propylenglycol) or poly(tetramethyleneglycol), like nylon 6, nylon 66, nylon 6, 12 and copolymers thereof;

e) thermoplastic styrenic elastomers that are styrenic block copolymers (SBC), in general obtained by block copolymerisation of styrene and butadiene (SBS) or isoprene (SIS) and optional selective hydrogenation to form styrene- ethylene/butane-styrene (SEBS), respectively styrene-ethylene/propene-styrene (SEPS) copolymers, which may optionally be further functionalized with reactive comonomers such as maleic anhydride.

These thermoplastic elastomers (TPE) are well known in the art. The properties and manufacture of such compounds is described e.g. in T. Ouhadi et al., Thermoplastic Elastomers, in Ulman^'s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag Wein- heim 2004 and the references cited therein.

In a first particularly preferred embodiment of the invention, the at least one elastomer is selected from styrenic block copolymers (SBC), in particular from styrene-butadiene- styrene block copolymers (SBS). Preferred styrenic block copolymers according to this first particularly preferred embodiment of the invention are described in the following.

Preferably, the at least one elastomer is selected from thermoplastic elastomers based on styrenic block copolymers (SBC) comprising blocks having a Tg below room temperature and further comprising blocks having a Tg above room temperature, more preferably having a Tg of above 60 deg C. The ratio of the former to later block length is preferably in the range of 1-80%, more preferably in the range of 1-20%.

Preferred thermoplastic elastomeric SBCs have a Tg of at least 60⁰C.

In a particularly preferred embodiment, the elastomer comprises

A1 ) from 1 to 100%, preferably from 1 to 95% by weight of a thermoplastic elastomer based on styrene (S-TPE), and A2) from 0 to 99%, preferably from 5 to 99% by weight of a polyolefin.

Preferably, the ratio of A1) to A2) is from 1 to 20% by weight A1) to from 80 to 99% by weight A2). Also preferred is a ratio of A1 ) to A2) from 40 to 95% by weight A1 ) to from 5 to 60% by weight A2).

Particularly preferably, the elastomer according to the invention is at least one thermoplastic elastomer based on styrene (S-TPE).

These thermoplastic elastomers based on styrene preferably have the following proper- ties:

The S-TPE preferably has tensile strain at break of more than 300%, particularly preferably more than 500%, in particular more than 600%, measured to ISO 527, and the amount of this material admixed is from 1 to 20% by weight, preferably from 3 to 5% by weight, based on the polystyrene composition. The S-TPE more preferably used for admixing comprises a linear or star-shaped styrene-butadiene block copoly-mer with external polystyrene blocks S and, between these, styrene-butadiene copoly-mer blocks with random styrene/butadiene distribution (S/B)_random, or with a styrene gradient

(S/B)taper-

The total butadiene content is preferably in the range from 15 to 50% by weight, par- ticularly preferably in the range from 25 to 40% by weight, and the total styrene content is accordingly preferably in the range from 50 to 85% by weight, particularly preferably in the range from 60 to 75% by weight.

The styrene-butadiene block (S/B) is preferably composed of from 30 to 75% by weight of styrene and from 25 to 70% by weight of butadiene. A block (S/B) particularly preferably has a butadiene content of from 30 to 65% by weight.

The proportion of the polystyrene block S is preferably in the range from 5 to 40% by weight, in particular in the range from 25 to 35% by weight, based on the entire block copolymer. The proportion of the copolymer blocks S/B is preferably in the range from 60 to 95% by weight, in particular in the range from 65 to 75% by weight.

Particular preference is given to linear styrene-butadiene block copolymers of the general structure S-(S/B)-S having, situated between the two S blocks, one or more (S/B)random blocks having random styrene/butadiene distribution. These block copolymers are obtainable via anionic polymerization in a non-polar solvent with addition of a polar cosolvent or of a potassium salt, as described by way of example in WO 95/35335 or WO 97/40079.

Vinyl content is the relative proportion of 1 ,2-linkages of the diene units, based on the entirety of 1 ,2-, 1 ,4-cis and 1 ,4-trans linkages. The 1 ,2-vinyl content in the styrene- butadiene copolymer block (S/B) is preferably below 20%, in particular in the range from 10 to 18%, particularly preferably in the range from 12 to 16%.

Examples of suitable component B are semicrystalline polyolefins, such as homo- or copolymers of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1- pentene, and also ethylene copolymers with vinyl alcohol, ethyl acrylate, butyl acrylate, or methacrylate. Component B is preferably linear low-density polyethylene (LLDPE) or a ethylene-acrylic co-polymer.

A polymer film may be produced from the mixture of A) and B) by suitable processes, such as spraying, painting, dipping, plunging, coating or by mono- and coextrusion to give tubular films, chill-roll films, or other extruded films, or by calendaring, injection molding, or blow molding.

The above blends of compounds A) and B) are disclosed e.g. in US-A 2005/0282028 and US-A 2005/0282965. Particularly preferred as elastomers are S-TPEs having a total styrene content of from 40 to 80 % by weight, preferably 50 to 70 % by weight, and - a Youngs modulus of from 100 to 200 MPa, and comprising linear or star-shaped styrene-butadiene blocks with external polystyrene blocks S and, sandwiched between these, styrene-butadiene copolymer blocks with random styrene/butadiene distribution (S/B)_random, or with a styrene gradient

Preferably, the S-TPEs have a shore-A hardness (according to ISO868) of from 80 to 100 and a Tg of the soft phase in the range of -50 to -20 ⁰C, preferably from -45°C to - 30⁰C.

Methods of making these S-TPEs are well known to the person skilled in the art, for instance via anionic polymerization.

Suitable S-TPEs of this kind are for instance commercialized under the trade name Styroflex® by BASF Aktiengesellschaft, Ludwigshafen, Germany

A further suitable elastomer for use in the method according to the invention is polyiso- butylene.

Preferably, the polyisobutylene (PIB) has a number-average molecular weight of from 100.000 to 1.000.000 g/mol determined by gel permeation chromatography, which in the following is referred to as high-molecular weight PIB. Particularly preferred, the PIB has a number-weighted molecular weight of from 200.000 g/mol to 600.000 g/mol. Preferably, the average molecular weight of high molecular weight polyisobutylene used in the present invention is about 400,000 g/mol.

High-molecular polyisobutylenes having molecular weights of up to several 100,000 dalton have been known for a number of years, and the preparation thereof is described for example in H. Gueterbock: "Polyisobutylen and Mischpolymerisate", pp 77 to 104, Springer Verlag, Berlin 1959.

Such high molecular weight polyisobutylenes are obtainable, inter alia, by cationic polymerization of isobutylene by the belt method, isobutylene in pure, dried, liquid ethylene being subjected to cationic polymerization on a slightly inclined, continuous belt with the aid of boron trifluoride (DE-A 3 527 551). Furthermore, such high molecular weight polyisobutylenes are sold under the trade name Oppanol® by BASF Aktiengesellschaft. High molecular weight polyisobutylene alters the elasticity of the surface of the coating and helps reduce the tendency of biofilm adhesion. Polyisobutylene may be used in combination with polyvinyl chloride and/or copolymers of polyvinyl chloride. In a preferred embodiment, the polymer composition used in the method according to the invention comprises a mixture of from 80 to 95 wt% of a co- polymer (a1) of vinylchloride and vinylisobutylether and from 5 to 20 wt% of polyisobutylene (a2).

The polymer compositions according to the present invention may furthermore comprise a nanoparticulate component wherein the number median particle diameter (d50) is from 0,5 to 500 nm. Preferably, the number-weighted median particle diameter is from 1 to 200 nm, in particular from 2 to 200 nm, very particularly preferred from 2 to 100 nm, in particular from 5 to 50 nm.

The number median particle diameter is determined via image analysis of a TEM im- age that has been recorded from a microtome cut slice of the coating or of a film derived from the polymer composition according to the invention (subsequently referred to as "TEM image"). The person skilled in the art chooses the position of the slice cut out of the coating or the film such that a statistically meaningful value is derived. The number median particle diameter of nanoparticulate component (B) in this invention shall be the number-weighted median diameter (d50 value) determined within a group of at least 200 particles in the diameter range of up to 5000 nm in the TEM image.

For the determination of the mean particle diameter of the polymer composition, all individual nanoparticles visible in the "TEM image" and satisfying the criteria for the nanoparticulate component are taken into account if they have an individual particle diameter of up to 1000 nm. Otherwise they are not considered to be nanoparticulate and are therefore not comprised by the nanoparticulate component.

The particle diameter of an individual particle pursuant to this invention is the smallest diameter of the particle through its geometric center in the TEM image. By way of example, if the particle is a sphere, the particle will appear as a circle in the TEM image. The shortest diameter is twice the radius of the circle. If the particle is an ellipsoid, the particle will appear as an oval slice in the image. The particle diameter is the shortest diameter through the center of the oval. In case the particle is tube-shaped, the particle will appear as a "needle" in the image. The diameter of the particle then is the thickness of the needle. In case the particle is a platelet, the diameter of the particle then is the thickness of the layer or the layers.

If nanoparticles are clustered or partially touch each other in the image, the particle diameter shall refer to the shortest diameter of each individual particle as far as its shape can be determined by extrapolation. If a cluster does not allow the particles to be analyzed as individual particles due to strong agglomeration, then the particle diameter shall be the shortest diameter through the center of the agglomerated particle as long as it does not exceed the 1000 nm limit according to the definition of the nanoparticu- late component.

For the polymer composition according to this invention it is advantageous if the spacial distribution of the nanoparticles in the coating or in the film is relatively homogeneous.

The mean aspect ratio of the nanoparticulate component can vary over a broad range. The aspect ratio of an individual particle according to this invention shall be the ratio of the length and the width (l/w) through the geometric center of the particle. The mean aspect ratio is determined by transmission electron microscopy in combination with image analysis, analogously to the particle diameter and is quoted as a median value (d50).

The nanoparticulate component used in the present invention preferably has a mean aspect ratio from 1000 to 1 , in particular from 500 to 10, preferably from 400 to 20.

Examples of inorganic nanoparticles that can be used are silicates, in particular clay, carbonates, silica, metal oxides, or a mixture composed of two or more of these nanoparticulate materials.

In case a metal oxide is used as nanoparticulate material, titanium dioxide, zinc oxide, aluminum oxide, and magnesium oxide is preferred. Preferably, the nanoparticulate material is selected from earth metal carbonates, metal oxides, and clay. In a first pre- ferred embodiment, the nanoparticulate material (B) comprises an earth metal carbonate, preferably calcium carbonate, in particular precipitated calcium carbonate.

Precipitated or synthetic calcium carbonate (PCC) is often composed of particularly small particles of regular shape (smaller than 1 micrometer), which may have surface- modification. The particular particle size distribution of PCC makes it very particularly preferably suitable as component C.

The binding of the inorganic fillers into the material can moreover often be improved via addition of dispersing agents. The moldings preferably comprise from 0 to 8 parts by weight of dispersing agents, based on 100 parts by weight of the mixture composed of components A to C. The mixture particularly preferably comprises from 0.1 to 4 parts by weight of dispersing agents, based on 100 parts by weight of the mixture composed of components A to C. Suitable dispersing agents are low-molecular-waxes, e.g. polyethylene waxes, or stearates, such as magnesium stearate or calcium stearate.

In a particularly preferred embodiment, the nanoparticulate material comprises at least one clay ("nanoclay"). The inorganic clay in general is a silicate. The silicate can be a smectite clay, such as montmorillonite, nontronite, beidellite, bentonite, volkonskoite, laponite, hectorite, saponite, sauconite, magadite, kenyaite, stevensite, vermiculite, halloysite, hydrotalcite, and so on, or a combination thereof.

Useful clay materials include natural, synthetic, and modified phyllosilicates. Natural clays include smectite clays, such as montmorillonite, hectorite, mica, vermiculite, bentonite, nontronite, beidellite, volkonskoite, saponite, magadite, kenyaite, and the like. Synthetic clays include synthetic mica, synthetic saponite, synthetic hectorite, and the like. Modified clays include fluoronated montmorillonite, fluoronated mica, and the like. Suitable clays are available from various companies including Nanocor, Inc., Southern Clay Products, Kunimine Industries, Ltd., and Rheox.

Generally, the layered clay materials useful in this invention are an agglomeration of individual platelet particles that are closely stacked together like cards, in domains called tactoids. The individual platelet particles of the clays preferably have thickness of less than about 2 nm and diameter in the range of about 10 to about 3000 nm. Preferably, the clays are dispersed in the polymer so that most of the clay material exists as individual platelet particles, small tactoids, and small aggregates of tactoids. Preferably, a majority of the tactoids and aggregates in the polymer/clay nanocomposites of the present invention will have thickness in its smallest dimension of less than about 20 nm. Polymer/clay nanocomposite compositions with the higher concentration of individual platelet particles and fewer tactoids or aggregates are preferred.

According to this particularly preferred embodiment, the clay is preferably selected from smectite, vermiculite and halloysite.

The smectite clay in turn preferably is selected from montmorillonite, saponite, beidel- lite, nontrite, hectorite and mixtures thereof. Particular preference is given to montmorillonite clay, a layered alumino-silicate.

The nanoclay platelets generally have a thickness of about 0,3 to100 nm and a size in the planar direction ranging from about 0,01 micron to 100 microns. The aspect ratio is generally in the order of 10 to 10.000.

A particularly suitable material is Cloisite TM 10A (available from Southern Clay Products), its platelets having a thickness of about 1 nm (10 Angstroms) and a size in the planar direction of about 0,15 to 0,20 micron.

Moreover, the layered clay materials are typically swellable free flowing powders having a cation exchange capacity from about 0.3 to about 3.0 milliequivalents per gram of mineral (meq/g), preferably from about 0.9 to about 1.5 meq/g. The clay may have a wide variety of exchangeable cations present in the galleries between the layers of the clay, including, but not limited to, cations comprising the alkaline metals (group IA), the alkaline earth metals (group NA), and their mixtures. The most preferred cation is so- dium; however, any cation or combination of cations may be used provided that most of the cations may be exchanged for organic cations (onium ions). The exchange may occur by treating a individual clay for a mixture or a mixture of clays with organic cations.

Preferred clay materials, for at least one of the components of the clay mixture, are phyllosilicates of the 2:1 type having a cation exchange capacity of 0.5 to 2.0 meq/g.

The most preferred clay materials, for at least one of the components of the clay mixture, are smectite clay minerals, particularly bentonite or montmorillonite, more particu- larly Wyoming-type sodium montmorillonite or Wyoming-type sodium bentonite.

It is well known to the person skilled in the art that the before mentioned clays can be chemically modified. Typically, such modification is intended to improve the compatibility with the matrix material and makes the clay more hydrophobic. If a clay is used for the purpose of the present invention, it is preferred to apply surface modification of clay prior to its use by means of an organic modifier. Hydrophobic clays are preferably prepared by ionic modification using hydrogenated tallow (Cis-alkyl) dimethylquaternary ammonium salt followed by covalent modification by trimethoxysilanes.

Bacteriophobic Compound

The polymer compositions used in the method according to the present invention preferably comprise as further component at least one bacteriophobic compound, preferably from 1 to 10 wt% relative to the total weight of the elastomer.

A bacteriophobic additive is an additive that sustainably reduces the formation of bacteria containing biofilms on a coating containing such bacteriophobic additive. In principle any additive that does not wash out or otherwise decompose or disappear can be used. In general, any additive which does not contain heavy metals can be used. Pref- erably, the bacteriophobic additive is non-toxic to mammals.

In a preferred embodiment, the bacteriophobic additive is a polymer, preferably a fluoropolymer. A wide range of film-forming fluoropolymers such as those prepared from polymers and copolymers of trifluoroethylene, hexafluoropropylene, monochloro- trifluoroethylene, dichlorodifluoroethylene, tetrafluoroethylene, vinylidene fluoride, vinyl fluoride, among others can be used. For example, the fluoropolymer may be a fluorinated ethylene/propylene copolymer (commonly known as FEP resins); a copolymer of ethylene and chlorotrifluoroethylene, a copolymer of ethylene and tetrafluoroethylene ("ETFE"), a perfluorovinyl ether/tetrafluoroethylene copolymer ("PFA"), a vinylidene fluoride/hexafluoropropylene copolymer, vinylidene fluoride/perfluoro (alkyl vinyl ether) dipolymers and terpolymers with tetrafluoroethylene, polyvinylidene fluoride homopolymer (PVDF) or a blend of polyvinylidene fluoride with an acrylic polymer, or polyvinyl fluoride homopolymer (PVF), among others.

Examples of melt-processible fluoropolymers include but are not limited to ETFE, PFA, and FEP resins. Films of melt processible fluoropolymers are typically prepared by extrusion of the melt through a die. See, e.g., Eldridge M. Mount III, "Films, Manufacture" in Encyclopedia of Polymer Science and Technology, 3.sup.rd edition, vol. 6, Jacqueline I. Kroschwitz (exec, ed.), John Wiley & Sons, Inc. (2002), 283-305. Cast film or sheet is self-supporting and formed from the extruded melt. Multilayer structures can be formed by coextrusion of multiple melt streams or by extrusion coating a melt stream onto a preformed web. In blown film processes, the melt is extruded through an annular die into a tube subsequently blown into a bubble. The bubble may be blown immediately from the melt, or the tube may be quenched first, then reheated and blown into film.

The present invention is preferably employed with polyvinyl fluoride (PVF). Other preferred fluoropolymers for use in the present invention are made from polyvinylidene fluoride (PVDF) or from a blend of polyvinylidene fluoride (PVDF) and acrylic polymers. These fluoropolymer films can be made from fluid compositions that are either (1) solutions or (2) dispersions of fluoropolymer. Films are formed from such solutions or dispersions of fluoropolymer by casting or extrusion processes.

Typical solutions or dispersions for polyvinylidene fluoride or copolymers of vinylidene fluoride are prepared using solvents which have boiling points high enough to avoid bubble formation during the film forming/drying process. The polymer concentration in these solutions or dispersions is adjusted to achieve a workable viscosity of the solution and in general is less than about 25% by weight of the solution. A suitable fluoropolymer film is formed from a blend of polyvinylidene fluoride, or copolymers and ter- polymers thereof, and acrylic resin as the principal components as described in U.S. Pat. Nos. 3,524,906; 4,931 ,324; and 5,707,697.

Using films of polyvinyl fluoride (PVF), suitable films of the present invention can be made from dispersions of the fluoropolymer. The nature and preparation of such dis- persions are described in detail in U.S. Pat. Nos. 2,419,008; 2,510,783; and 2,599,300. Suitable PVF dispersions can be formed in, for example, propylene carbonate, N- methyl pyrrolidone, . gamma. -butyrolactone, sulfolane, and dimethylacetamide. The concentration of PVF in the dispersion will vary with the particular polymer and the process equipment and the conditions used. In general, the fluoropolymer will comprise from about 30 to about 45% by weight of the dispersion.

Films of polyvinyl fluoride may be formed by extrusion procedures such as those presented in U.S. Pat. Nos. 3,139,470 and 2,953,818, which describe the feeding of polyvinyl fluoride dispersion to a heated extruder connected to a slotted casting hopper. A tough coalesced extrudate of polyvinyl fluoride is extruded continuously in the form of a film containing latent solvent. The film can be merely dried or, alternately, can be heated and stretched in one or more directions while the solvent is volatilized from the film. When stretching is used, oriented film is produced. Alternatively, films of polyvinyl fluoride can be cast from dilute dispersions of the polymer in latent solvent. Cast, multilayer polyvinyl fluoride structures as those described in U.S. Pat. No. 4,877,683 may also be used in place of a single film of PVF.

In a particularly preferred embodiment, the at least one bacteriophobic compound making up the bacteriophobic component is at least one copolymer of vinylidene fluoride and hexafluoroprene.

Marine coatings comprise a binder and solvent and optionally other ingredients. The solvent may be either organic solvent or water. The compositions of the invention are suitable for use in both solvent and water based marine coatings. Solvent based marine coatings are preferred.

The marine coatings of the present invention may optionally contain one or more of the following: inorganic pigments, organic pigments or dyes, and natural resins, such as rosin. Water based coatings may also optionally contain: coalescents, dispersants, surface active agents, rheology modifiers or adhesion promoters. Solvent based coatings may also optionally contain extenders, plasticizers or rheology modifiers.

A typical marine coating comprises 2 to 20% binders, up to 15% rosins/modified rosins, 0.5 to 5% plasticizers, 0.1 to 2% antisettling agent, 5 to 60% solvent/diluent, and up to 30% pigments.

Marine coatings containing the compositions of the invention may be applied to a structure to be protected by any of a number of conventional means, such as, for example, spraying, rolling, brushing and dipping.

According to a particularly preferred embodiment, the paints and coatings according to the present invention do not contain a biocide. Preferably, the method for inhibiting biofouling according to the present invention does not involve a step, wherein a biocide is applied to the surface which is intended for use in contact with water.

Examples

The coatings listed in table 1 were prepared and their anti-fouling properties were studied according to the following procedures.

Components

A-1 : Styroflex® 2G66 supplied from BASF Aktiengesellschaft, a thermoplastic elastomer based on a SBS block copolymer with elongation at break according to DIN 53455 of more than 650%, a styrene content of at least 65% and a rubber fraction of at least 70%.

B-1 : Laponite RDS nanoclay, a peptized version of Laponite, supplied by Southern Clay Products, a division of Rockwood Additives Ltd. The median particle diameter is 25nm and the aspect ratio is about 25.

C-1 : copolymer of polyvinylidene fluoride and hexafluoropropylene (CAS No. 9011-17- 0) with Mn of 130,000 g/mol, procured from Sigma Aldrich.

Preparation of polymer compositions

Example 2

B-1 (5 parts with respect to the weight of A-1 dissolved in tetrahydrofuran) was dispersed into the solution to form the homogeneous dispersion with the help of sonicator and the solid content was adjusted to 15%.

Example 3

5 parts of C-1 and 95 parts of A-1 were weighed out and dissolved in tetrahydrofuran (Sigma-Aldrich) with the help of sonicator to form a polymer solution with a solid con- tent of 15%.

Example 4

5 parts of C-1 and 95 parts of A-1 were weighed out and dissolved in tetrahydrofuran (Sigma-Aldrich) with the help of sonicator to form a polymer solution with a solid con- tent of 15%. B-1 (2parts with respect to the weight of polymer in the solution [phr]) was dispersed into the solution, one after the other to form the homogeneous dispersion. Table 1 : Paint formulations (all amounts in % by weight)

Preparation of the coatings

The dispersion prepared according to the examples in Table 1 is then applied on pre- cleaned polycarbonate substrates (76 x 26 mm) by spin coating at 1000 rpm for 30 s, followed by baking on a hotplate at 110 ⁰C for 30 minutes. Finally, the films were heat- treated in an oven at 90, 100 and 1 10 ⁰C for 1 h, respectively.

Determination of antifouling performance in seawater: The performance against three different marine organisms was tested by static exposure tests.

1. Barnacle settlement (test 1 )

Slides were immersed in a tank of continuously-filtered RO water for 7 days and in ASW (artificial seawater) for 1 hour before the assay was started. 20 x 3-day-old barnacle cyprids were introduced to each slide contained within 1 ml ASW. The slides were incubated at 28 ⁰C for 48 hours. After this period, each slide was inspected to obtain the percentage settlement. Settlement on the practical coatings was normalized to the glass standard. The antifouling performance against barnacle cyprids is rated from 0 to 100, where 100 means no settlement on the test slide, while 0 means that the test slide has been fouled like the glass reference.

2. Release of marine biofilms (test 2)

Slides were pre-leached in a tank of artificial seawater for 14d. The three bacterial suspensions used for the testing were repetitively washed and centrifuged to remove excess EPS for optimal adhesion.

Slides were immersed for 1 h in Quadriperm® plates containing 8 ml suspension of the 3 bacteria mix with an OD of 0.2 at a wavelength of 595 nm. Slides were rinsed to remove non-adhered cells and transferred to 8 ml of growth medium. After 4h incubation and drying, two slides of each coating and Silastic® T2 were rotated on the rotor for 10 min at 12 knots in natural seawater. The remaining biofilm was then quantified as described above. Data are expressed as % biofilm removal (Δ biomass/biomass before release^*100%). Removal was normalised against Silastic® T-2 as a standard.

Table 2 summarizes the test results concerning barnacle cyprid settlement.

Table 2:

compared to glass standard after 48 hours and normalized to 100%

Claims

1. Method of inhibiting biofouling on a surface in contact with water, wherein a polymer composition is applied to said surface, said polymer composition being accessible to water and comprising at least one elastomer having an elongation at break according to DIN 53455 of at least 400%.

2. Method according to claim 1 , wherein said surface is in contact with sea water.

3. Method according to claim 1 or 2, wherein said at least one elastomer exhibits a Young's modulus according to ISO 527-1 of from 1 to 200 MPa.

4. Method according to claims 1 to 3, wherein said at least one elastomer is selected from at least one polymer or copolymer of the group consisting of polybu- tadiene, polyisobutylene and block copolymers comprising as monomers vinyl aromatic monomers and dienes.

5. Method according to claims 1 to 4, wherein said at least one elastomer is a thermoplastic elastomer.

6. Method according to claims 1 to 5, wherein said at least one elastomer is selected from at least one block copolymer comprising as monomers styrene and butadiene.

7. Method according to claims 1 to 6, wherein said at least one elastomer is selected from at least one block copolymer having at least one hard block based on vinylaromatic monomers, and at least one soft block based on a random copolymer of at least one vinylaromatic monomer and at least one diene.

8. Method according to claims 1 to 7, wherein said polymer composition further comprises at least one inorganic nanoparticulate material which has a number median particle diameter of from 1 to 500 nm.

9. Method according to claim 8, wherein said at least one inorganic nanoparticulate material consists of at least one selected from earth metal carbonates, metal oxides, and clay.

10. Method according to claims 8 or 9, wherein said at least one inorganic nanoparticulate material contains a clay.

1 1. Method according to claim 1 to 10, wherein said polymer composition further comprises at least one bacteriophobic compound.

12. Method according to claim 11 , wherein said at least one bacteriophobic compound is at least one fluorine containing polymer.

13. Method according to claim 11 or 12, wherein said at least one bacteriophobic compound is at least one copolymer of vinylidene fluoride and hexafluoroprene.

14. Method according to claims 1 to 13, wherein no biocide is applied to said surface.

15. An anti-fouling coating comprising a polymer composition as defined in any of claims 1 to 14.

16. An anti-fouling paint comprising a polymer composition as defined in any of claims 1 to 14.

17. Use of a polymer composition as defined in any of claims 1 to 14 for antifouling coatings or antifouling paints, preferably marine antifouling coatings or marine antifouling paints.