POLYMERIC ANTIFOULING COMPOSITIONS

Abstract: Polymeric antifouling composition comprising a high-built layer containing a vulcanized silicone rubber and an exuding liquid, and a substantially water-impermeable layer, which layers are joined together through an acrylate-type bonding film, and which composition contains at least 60% by volume of the high-­ built layer. The polymeric antifouling composition may also contain one or more characters consisting of a vulcanized silicone rubber and a fluorescent pigment.

Description: POLYMERIC ANTIFOULING CQMPOSITIONS The present invention relates to polymeric anti fouling oompositions as well as to a method for the manufacture of coated structures using the polymeric antifouling compositions according to the present invention and to structures thus coated. The prevention of structures against fouling by various organisms such as grasses, algae, barnacles, tube worms, sepula, oysters, ascidia, bryozoa and the like has gained in importance in the last decade because of the soaring development of, in particular, off-shore facilities. The early conventional antifouling coatings were based on paints containing poisonous substances such as copper, tin, mercury, arsenic and lead and derivatives thereof. They are now becoming obsolete because of the limited useful lifetime and the ecological problems connected therewith. They are being replaced by coatings based on vulcanizable silicone rubbers, preferably room-temperature-vulcanizable silicone rubbers as described in British Patent Specification 1,307,001, which basically prevent organisms from adhering to structures coated with such rubbers. In order to improve the anti-fouling properties of coatings based on silicone rubbers it has already been suggested to incorporate into the anti fouling coatings certain fluids which are released very slowly through the silicone rubber so that the build-up of undesired organisms is even more retarded. Suitable fluids comprise silicone oils as described in British Patent Specification 1,470,465 and low molecular weight polyolefins, polyesters, polyisocynates, polyurethanes, polyepoxides, lubricating oils as well as plasticizers as described in British Patent Specification 1,581,727. Although the silicone rubbers, and in particular the room temperature vucanizable silicone rubbers have excellent water-repelling properties, they are nevertheless rather porous so that water may pass through their structure. It would therefore be advantageous to have a substantially water-ippermeable layer present within the antifouling composition to prevent access of water to the body underlying the antifouling coating. In order to cope with the tendency to use high-built layers of siliconerubbers on fixed structures - which layers can be suitably prefabricated - it becomes also of great importance to secure an optimum bonding between the silicone-rubber layer and the substantially water-inpermeable layer whilst using a very small amount of bonding agent which facilitates handling during manufacture, storage and transport. Surprisingly, it has now been found that high-built layers of a silicone-rubber containing an exuding liquid can be secured to a layer of substantially water-impermeable material when use is made of a particular bonding agent which is applied in the form of a very thin film. The e present invention thus relates to a polymeric anti fouling composition comprising a high-built layer containing a vulcanized silicone rubber and an exuding liquid and a substantially water impermeable layer, which layers are joined together through an acrylate-type bonding film, and which composition contains at least 60% by volume of the high-built layer. Vulcanized silicone rubbers to be used in the polymeric antifouling compositions according to the present invention can be prepared fram silicone gums, which are highly linear highmolecular weight organosiloxane polymers consisting essentially of alternating atoms of silicone and oxygen as a polymeric backbone with organic substituents attached to the silicone atoms of the polymeric backbone. Vulcanized silicone rubber may be prepared by heat curing with various catalysts (such as peroxides) or by radiation curing of a silicone gum which, e.g., substantially consists of a polydisubstituted siloxane. All or the predcminant part of the organic substituents may be methyl units, the remainder being vinyl- and/or phenyl units. vulcanized silicone rubbers may also be prepared by vulcanizing at ambient temperature silicone gums which contain silanol end groups (the so-called RIV gums). All or the predaninant part of the substituents in the RIV gums may be hydrocarbyl groups, (in particular methyl groups), the remainder may be ethyl-, phenyl- or substituted hydrocarbyl groups, such as chlorophenyl-, fluoropropyl- or cyanoethyl groups. Preference is given to the use of silicone rubbers which are rosm-temperature vulcanizable RIV gums in which the organic substituents contain or consist of silicone-free segments which are constituted of recurrent units (in particular polymeric segments) as described in European Patent Publication 0032597;they are very suitable to be vulcanized to silicone rubbers to form part of the polymeric antifouling ccmposition. The polymeric segments are preferably linked to the silicone atoms via alkylene or alkylidene groups, and very suitably are derived from monomers containing ethylenic unsaturation. The said monomers may, e.g., consist at least partly of unsaturated acids or derivatives thereof (such as esters, e.g. esters of acrylic and/or methacrylic acid and monovalent alcohols) and/or include styrene. Polymeric segments based on copolymers of styrene and butylacrylate are very suitable. The preparation of vulcanized silicone rubbers from silicone gums at ambient temperatures may be carried out by two different methods, viz. the one-pack WN-system and the two-pack RTV-systen as described in the British Patent Specification 1,581,727. The polymeric anti fouling compositions according to the present invention contain a fluid organic compound which is part of the high-built layer in order to optimize the period in which the coating according to the invention is not fouled. Fluid organic compounds which act as exuding liquids include compounds having a boiling point at atmospheric pressure of at least 2500C. Examples of such liquids are silicone fluids, which consist of poly-dihydrocarbyl siloxanes (of which the hydrocarbyl groups may be substituted with hetero-atoms). The hydrocarbyl groups may be alkyl groups (in particular methyl groups) or all or part thereof may be aryl groups (in particular phenyl groups). A further group of fluid organic compounds comprises low molecular weight polyolefins, such as ethylene/propylene copolymers, and in particular polyisobutene with a molecular weight up to about 5,000, e.g. fram 300-500. Other types of fluid organic compounds which can be applied comprise low molecular weight polydienes, polyesters, polyisocyanates, polyepoxides, lubricating oils such as technical white oils and plasticizers (e.g. esters of fatty acids, which may be substituted with hetero atoms or- groups, esters of phosphoric acid and halogenated hydrocarbons). Preference is given to the use of polyolefins, in particular polybutene since the presence of such materials substantially improves the tear strength, the tensile strength, the elongation at break and the shore hardness of the polymeric anti fouling compositions containing them. The amounts of fluid organic compounds present may vary between wide limits. Amounts fram 0.1 to 100 pbw per 100 pew of vulcanized silicone rubber are suitably applied, preference being given to the use of 10-50 pbw of fluid organic carpound per 100 pbw of vulcanized silicone rubber. The substantially water-impermeable layer suitably contains or consists of polyvinylchloride, an epoxy resin or a polyurethane. Preference is given to the use of polyvinylchloride as the material to form the water-iitermeable layer. Since the vulcanized silicone rubber layer is a high-built layer, it is possible to substantially reduce the thickness of the waterimpermeable layer, e.g. to well below 1 itm without unduly reducing the handleability of the total composition. Water-impermeable layers between 50 V and 700 p can be suitably applied, preferably being given to layers having a thickness between 200 V and 600 . As discussed hereinbefore, it is of great importance to have sufficient bonding strength between the high-built layer and the substantially water-impermeable layer since the life expectancy of the polymeric antifouling composition will be largely governed by this feature. The fact that acrylate-type materials exhibit excellent bonding properties has solved the problem of obtaining a very thin but also a very strong bond between the two base layers of the polymeric antifouling compositions according to the present invention. It has been found that acrylate-type materials can be applied in the form of a film, i.e. as an ultrathin layer which may even be monomolecular. Good results can be obtained using silicone esters of (meth)acrylic acid, in particular when using lower alkyl silicone esters of acrylic acid, e.g. C1 6 alkyl silicone esters. Many of them are ccmmercially available as acrylate primers. It should be noted that bonding the high-built layer and the substantially water-impermeable layer by means of an elastomeric bonding agent (a solution of silicone rubber in toluene) failed to give any appreciable bonding strength. The high-built layers in the polymeric antifouling compositions according to the present invention typically have a thickness between 3 iirn and 10 mm. They form at least 60% by volume, and preferably at least 80% by volume, of the total volume of the compositions. It is possible to include one or more fluorescent pigments in the high-built layers, preferably in the form of one or more specific characters, which render the polymeric antifouling compositions also suitable to serve as markers to identify individual areas of, in particular underwater parts of, marine structures such as ships, buoys, fuel tanks, floating and fixed offshore platforms and pipelines. Fluorescent compounds are inorganic or organic compounds (in particular dyes) which convert onfalling light of a certain wave length (the exciting light) to light of a longer wave length which is emitted after a short period of time (e.g. less than 10 sec.). In general, the exciting light consists of ultraviolet light or visible light of the blue end of the spectrum, and the light emitted has wave lengths in the visible part of the spectrum. In the preferred cases the emitted light has the same hue as light reflected by the dye, because the reflected colour is thus reinforced with the emitter colour producing hues which appear extraordinarily bright to the eye. This effect is achieved by incorporating a suitable organic dye in the fluorescent pigment which is to be used in the polymeric antifouling compositions according to the invention. It is of advantage that the dye incorporated fluoresces under the influence of exciting light in the visible part of the spectrum nsm (in other words: shows daylight fluorescence) because in that case by irradiation with electric torch light as used during working under water (e.g. by divers), the marked areas of the surface of the marine structures are clearly visible and identifiable. Very suitably the pigments consist for the greater part of organic resins in which the dyes have been incorporated, in general in low concentrations (e.g. 1-5%w). Such pigments are commercially available. The choice of the pigment to be used will depend on the type of colour and intensity thereof which is desired under the prevailing circumstances at the underwater parts of the marine structure. The amount of fluorescent pigments present in the polymeric anti fouling compositions according to the invention may vary between wide limits. Amounts from 0.1 to 20% w, on vulcanized silicone rubber are very suitable. The characters to serve as (part(s) of the) markers are preferably made of the same silicone rubber as used in; the polymeric antifouling compositions so that the total outerlayer of the composition exhibits antifouling properties. The compositions according to the present invention may be provided with an adhesive undercoat which is capable of securing the polymeric antifouling compositions to the desired location. Conventional adhesives such as certain polyurethanes and bitemen-based compounds such as bitumastic can be suitably applied. The outer surface of the conventional adhesive may be covered with self-adhesive tape which is released prior to application. The layer of conventional adhesive will generally have a thickness between 200 V and 2 rtm depending on the type of material used and the application envisaged. The present invention also relates to a method for the manufacture of coated structures by using polymeric anti fouling compositions according to the present invention and to structures thus coated. A suitable method for applying the polymeric antifouling compositions to the appropriate structures comprises cleaning the surface of the structure to be coated and optionally providing it with an anticorrosion coat and fixing the polymeric antifouling composition, which has been pre-made by means of conventional techniques such as casting, directly to an adhesive layer present on the surface or by releasing the self-adhesive tape fran the pre-made polymeric antifouling composition provided with an adhesive undercoat and pressing it onto the surface to be protected. It is also possible, and preferred when existing underwater structures are to be protected, to use clamping bands to which the pre-made polymeric antifouling compositions which may contain one or several characters, are secured and to strap or wrap the clamping bands around the parts of the structures to be protected. Both onshore structures such as pipelines for power stations, structures used in fish farming and offshore structures can be coated with the polymeric anti fouling composition according to the present invention. The present non-toxic polymeric antifouling compositions are especially advantageous because of their extended life expectancy which is of prime importance in rather inaccessible environments. EXAMPLE 1 An intimate mixture was prepared by blending 150 parts by weight of a commercial organo-polysiloxane which contained grafted polymeric segments based on styrene (about 20-25% w) and butylacrylate (about 30-40% w), 6 parts by weight of a catalyst consisting of a blend of an organic tin compound and an alkyl silicate, and 30 parts by weight of a polyisobutene having an average molecular weight of 350. The mixture thus prepared was attached to a layer of polyvinylchloride by means of 0.4 parts by weight of an acrylate bonding agent (available fran Wacker Chemie, Munich, Germany) and the composition was allowed to cure at roam temperature. The thickness of the final composition (in the form of a sheet) was about 7 itrn and the volume of the silicone top coat amounted to about 90% of the total volume. The anti fouling properties of the composition were tested by securing the composition to a panel by means of bitumastic. The anti fouling performance of the composition was highly satisfactorily as was the bonding between the polyvinylchloride layer and the high-built silicone rubber top coat. EXAMPLE 2 The experiments described in Example 1 were repeated whilst incorporating 15 parts by weight of a commercial daylight fluorescent orange pigment in the top coat to be cured. The final product showed both a very good overall anti fouling performance and very good visibility when illuminated. COEIPARATIVE EXEE The preparation of the composition as described in Example 1 was repeated but using a solution of a curable rubber in toluene as a prospective elastomeric bonding agent. After curing at roan temperature, the two layers could be easily torn apart by exerting slight manual force, which made the composition unsuitable for further processing/testing.

Claims: CLAIMS 1. Polymeric antifouling composition comprising a high-built layer containing a vulcanized silicone rubber and an exuding liquid, and a substantially water-impermeable layer, which layers are joined together through an acrylate-type bonding film, and which composition contains at least 60% by volume of the highbuilt layer. 2. Composition according to claim 1, wherein the high-built layer contains a roam temperature vulcanized silicone rubber which rubber contains silicon-free segments which are constituted of recurrent units. 3. Composition according to claim 1 or 2, wherein the substantially water-lirpermeable layer comprises a layer of polyvinyl chloride or an epoxy resin. 4. Composition according to any one of claims 1-3, wherein the bonding film is based on a silicone ester of (meth) acrylic acid. 5. Composition according to any one of claims 1-4, wherein the thickness of the high-built layer is between 3 and 10 iron. 6. Composition according to any one of claims 1-5, wherein the high-built layer carpflses one or more characters consisting of a vulcanized silicone rubber and a fluorescent pigment. 7. Composition according to any one of claims 1-6, wherein the substantially water-impermeable layer is coated with a layer of a conventional adhesive which may be covered with a self-adhesive tape. 8. A method for the manufacture of a coated structure by coating at least part of the outer surface with a polymeric antifouling composition according to any one of claims 1-7. 9. A method according to claim 8, wherein at least part of the outer surface is coated with a polymeric antifouling composition according to any one of claims 1-7, either by means of a conventional adhesive or by means of clamping bands. 10. A structure which has been coated at least partially with a composition according to any one of claims 1-7.

Inventors: MILLER, DOUGLAS, RICHES, KENNETH MAURICE, SHONE, EDWARD BRIAN
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1985
Main classification: C09D5
IPC codes: C09D5, B32B25