Abstract:
A protective layer which prevents marine fouling when attached to a boat hull or other structure intended to be submerged underwater. The protective layer achieves its anti-fouling characteristic by incorporating anti-fouling compounds uniformly dispersed throughout either a plastic film or an adhesive used to bond the film to a surface to be protected which slowly leach into the surrounding marine environment. The film is removably adhered to a boat hull or other structure by a thermally sensitive thermoplastic adhesive. The film may be removed by simply reheating until the adhesive softens to thereby allow the film and any undesired marine organisms attached thereon to be peeled away from the boat hull.

Description:
FIELD OF THE INVENTION 
     This invention relates to anti-fouling materials for inhibiting marine growth on submerged articles, particularly boat hulls. Specifically, this invention utilizes a plastic anti-fouling film for controlling the growth of algae, barnacles, mussels, fungi and other marine organisms on a boat hull in salt and/or fresh water. 
     BACKGROUND OF THE INVENTION 
     The growth of algae, fungi, barnacles, mussels and other marine organisms on submerged structures, such as boat hulls, is referred to as marine “fouling” and results in rough, biologically encrusted surfaces. Marine fouling of boat hulls causes many problems such as fuel waste, difficulty of boat steering and maneuvering due to increased drag, as well as damage to the boat hull itself. The rougher the hull, the more fuel the boat requires to maintain its speed through water. It is estimated that fuel savings alone could amount to several hundred million dollars annually through the use of anti-fouling techniques. 
     The rapid growth of marine organisms on underwater surfaces has long been a problem in the marine industry. Various chemically treated anti-fouling paints have traditionally been used to combat this kind of unwanted growth However, many of the chemicals incorporated with anti-fouling paints have been found to be toxic to non-target organisms, thereby mandating severe restrictions as to the use and application of such chemicals. 
     Anti-fouling paints have a myriad of problems associated with their use. For example, as anti-fouling paint ages, toxic chemicals leach out of the paint and the paint subsequently becomes a less effective deterrent to marine growth and must be replaced. Anti-fouling paint coatings are typically about 1.5 mm thick and thus need to be replaced annually in harsh salt water environments such as those around Florida and California. Before the old anti-fouling paint can be sanded or scraped off the hull, however, it is often necessary to scrape off the plentiful growth of barnacles, mussels, and any other marine organisms which have accumulated due to the decreased effectiveness of the paint over time. The removal of these organisms is quite time consuming and extremely laborious due to these organism&#39;s great adhesive strength. The boat hull must then be repainted with a fresh coat of anti-fouling paint. 
     A major drawback of this tedious work is that these anti-fouling paints contain ingredients that are highly toxic not only to barnacles and other marine growth, but also to the individuals applying the paint and subsequently removing it years later. The effect of paint dust or particles on the worker&#39;s health has thus become an important issue and a major concern associated with anti-fouling paints. 
     Anti-fouling paints also pose environmental hazards. Overspray during application, water run-off occurring during paint removal, and disposal of paint waste must be closely monitored and controlled to avoid long term environmental and ground water pollution. 
     Another disadvantage is that these anti-fouling paints are extremely expensive due to special precautions that need to be taken in their application, removal and disposal. In Florida, for instance, individuals must drape plastic tarps under and around a boat hull to catch the ground-off paint dust, new paint overspray and drippings. These tarps must then be bagged and specially marked as hazardous materials and shipped off site to a proper, pre-approved disposal location. Due to such special handling, extra shipping precautions and added disposal requirements, these anti-fouling paints are expensive to utilize. 
     A common anti-foulant ingredient utilized in these paints is copper and copper based compounds. The major disadvantage of copper based paint is that it can cause galvanic corrosion of aluminum vessels. Even with high quality anti-corrosive primers, flaws in the primer coat may result in corrosion of an aluminum hull, especially those with extended periods between dry dockings. Therefore, copper based anti-foulant paints are impractical for aluminum boats. 
     Another anti-fouling compound is tributyltin (TBT). Currently, owners of aluminum based boats use tributyltin based paints to inhibit marine fouling. A common TBT compound utilized is tributyltin methacrylate. Although use of TBT avoids the corrosive effects of copper on aluminum, paints utilizing TBT still retain all of the disadvantages of anti-fouling paint previously mentioned. 
     Due to the problems associated with anti-fouling paints, other anti-fouling techniques have been utilized, albeit with very limited success. For example, another anti-fouling method used is to “plant” a multiplicity of filaments on the surface of the boat hull or marine structure. The filaments flutter in the seawater so as to effectively prevent marine growth. However, it has been found that filaments which are fine enough to ensure sufficient fluttering to inhibit marine growth tend to get deformed, damaged, and entangled with one another in a short period. This results in the impairment of the fluttering characteristic, which in turn reduces the anti-fouling effect of the filaments. 
     SUMMARY OF THE INVENTION 
     The present invention provides an anti-fouling protective layer for preventing attachment of marine organisms to an underwater surface. More specifically, the anti-fouling protective layer comprises a plastic film having inner and outer surfaces, and a thermoplastic adhesive disposed between a structure intended to be submerged underwater and the inner surface of the film, said adhesive being of the type that upon heating removably adheres the film to the underwater surface of said structure. Either the plastic film or the thermoplastic adhesive is impregnated with an anti-fouling compound so that when attached to said structure, the anti-fouling compound prevents growth of marine organisms on the plastic film. 
     In one form, the plastic film is impregnated with an anti-fouling compound so as to prevent marine organisms from attaching to the plastic film. A hygroscopic plastic film may best allow a slow release of the anti-fouling compound into the surrounding aqueous environment and thus prevent the growth of marine organisms on the film. 
     In another embodiment, the thermoplastic adhesive is impregnated with the anti-fouling compound. In this embodiment, the outer plastic film must be permeable to allow release of the anti-fouling compound and prevent the growth of marine organisms on the outer plastic film. 
     Preferably, the outer plastic film includes a plurality of minute openings formed therethrough to allow the slow release of said anti-fouling compounds. 
     In yet another embodiment, an insulating film is disposed between the substrate containing the anti-fouling compound and the underwater surface. The insulating film is used to provide a barrier to prevent corrosion of the submerged structure by the anti-fouling compound. This embodiment would typically be utilized if a copper based anti-foulant ingredient was utilized on an aluminum boat hull. Preferably, the insulating film would be coextruded with the plastic film which is impregnated with the anti-fouling compound so as to be located between the plastic film and the adhesive. Alternately, the insulating film could be located between the adhesive layer and the surface to be protected if the adhesive layer is the substrate impregnated with the anti-fouling compound. 
     Preferably, the anti-fouling film has the heat sensitive thermoplastic adhesive pre-applied to its inner surface for ease of handling, but the film and adhesive may be separate components if desired. The film may be applied to a structure such as a boat hull by stretching the film over the hull and preferably taping it in place. Utilizing a heat gun and roller, the film and adhesive is heated, rolled onto the hull surface, and then allowed to cool. The anti-fouling film is thus adhesively bonded to the hull and will remain bonded until later removed. To replace old film, the film and adhesive is re-heated to soften the adhesive. The film is then stripped from the hull along with any barnacles, mussels and other marine growth which may be attached to the film. This eliminates the need for scraping organisms off the hull since they are simply removed when peeling off the film. This invention thus reduces the time and effort associated with removing marine growth directly from the boat hull. The invention also advantageously leaves no dust, overspray or toxic particles in the environment upon removal of the film. The used film may be placed in a plastic bag after removal for proper disposal or can be sent to a manufacturer for re-fabricating or recycling. A new plastic anti-fouling film can then be applied. 
     In still another embodiment, a laminate comprising a plastic film and a first adhesive impregnated with the anti-fouling compound is applied to the underwater surface of the structure. However, in this embodiment, the plastic film is peeled off of the first adhesive after application to the structure, leaving only the first adhesive containing the anti-fouling compound in direct contact with the outside environment. The first adhesive is removed after the anti-fouling agent has lost effectiveness by applying a removing laminate comprised of a carrier film and a second adhesive over the first adhesive, heating the carrier film and first and second adhesives to soften and bond the first adhesive to the second adhesive, and peeling off the carrier film together with the first adhesive now bonded to the second adhesive. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a fragmentary schematic view of a boat hull incorporating the anti-fouling layer of the present invention; 
     FIG. 2 is a fragmentary cross-sectional view of a boat hull to which a plastic film containing the anti-fouling ingredient has been adhesively applied; 
     FIG. 3 is a view similar to FIG. 2 except illustrating a second embodiment wherein the anti-fouling ingredient is incorporated in the adhesive instead of the film; 
     FIG. 4 is a view similar to FIG. 3 illustrating a third embodiment of the invention wherein the anti-fouling ingredient is incorporated in the adhesive and the plastic film is permeable; 
     FIG. 5 is a view similar to FIGS. 2-4 except illustrating a fourth embodiment incorporating an insulating barrier film between the a plastic film containing the anti-fouling ingredient and the adhesive layer bonding the film to a boat hull; 
     FIG. 6 is a view similar to FIG. 5 except illustrating a fifth embodiment wherein the insulating barrier film is located between the adhesive layer, which is impregnated with the anti-fouling ingredient, and the surface of the boat hull; 
     FIG. 7 is a view similar to FIGS. 3-4 except illustrating a sixth embodiment wherein only an adhesive layer containing the anti-fouling ingredient is provided; and 
     FIG. 8 is a view illustrating the removal of the adhesive layer of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, FIG. 1 illustrates an anti-fouling protective layer  10  for preventing attachment of marine organisms to a surface of a structure intended to be submerged underwater, such as hull  12  of boat. Specifically, the protective layer  10  may be utilized to control the growth of algae, barnacles, mussels, fungi and other undesirable marine organisms on boat hull  12  and may be utilized in both salt and/or fresh water. Further, it should be noted that although the drawings illustrate the use of protective layer  10  on hull  12  of a boat, protective layer  10  may be utilized to protect other structures intended to be submerged underwater, such as boat hulls, docks, dock floats, buoys and channel markers, and any other structures exposed to marine growth. 
     Referring now to FIG. 2, protective layer  10  is illustrated as including a plastic film  14  having an inner surface  16  and an outer surface  18  together with a thermoplastic adhesive  20  disposed between outer surface  22  of hull  12  and inner surface  16  of film  14 . Adhesive  20  and film  14  may be supplied as separate components and thus sequentially applied to outer surface  22  of hull  12 , as will hereinafter be described, but are preferably combined in a single laminate structure so that the film  14  is supplied with adhesive  20  incorporated thereon for ease of handling and application onto hull  12 . In this embodiment, an anti-fouling compound  24  is impregnated within film  14  so as to be uniformly dispersed therein. Generally, this can be accomplished during extrusion of film  14  by mixing an appropriate and effective amount of compound  24  into film  14  prior to its extrusion. 
     Any plastic film  14  that is compatible with anti-fouling compound  24  and has sufficient strength, durability, and flexibility to be applied to a variety of shapes and forms of hull  12  of a boat, may be utilized and is within the scope of the present invention. These films can be selected from the groups comprising ethylene based polymers and copolymers, such as ethylene/vinyl acetate, ethylene acrylate, ethylene methacrylate, ethylene methyl acrylate, ethylene methyl methacrylate, high and low density polyethylene, polyethylene blends and chemically modified polyethylene, copolymers of ethylene and 1-6 mono- or di-unsaturated monomers, polyamides, polybutadiene rubber, polyesters such as polyethylene terephthalate, polybutylene terephthalate; thermnoplastic polycarbonates, atactic poly-alpha-olefins, including atactic polypropylene, and others; thermnoplastic polyacrylamides, polyacrylonitrile, copolymers of acrylonitrile and other monomers such as butadiene styrene; polymethyl pentene, polyphenylene sulfide, aromatic polyurethanes; styrene-acrylonitrile, acrylonitrile-butadiene-styrene, styrene-butadiene rubbers, polyethylene terephthalate, acrylonitrile-butadiene-styrene elastomers, polyphenlene sulfide, A—B, A—B—A, A—(B—A) n —B, (A—B) n —Y block copolymers wherein the A comprises a polyvinyl aromatic block, the B block comprises a rubbery midblock which can be partly hydrogenated, and mixtures of said substances, but other similar materials can be used as well, to match the properties of the adhesive packaged. More specifically, nylon, polyethylene and polypropylene based films are preferred examples of the types of plastic material that may be employed as film  14 . It should be noted that it may be necessary to utilize dispersants, stabilizers, or other similar compounds to ensure the anti-fouling compound  24  utilized is uniformly distributed throughout film  14 . The plastic film  14  is preferably 6 mils or thicker which enables the film  14  to be easily applied, yet provides significant scratch protection to hull  12 . In addition, the film  14  may be transparent which allows it to be used directly over hull  12  of any color, as well as to be applied directly over decals that may already be incorporated onto hull  12 . Thus, film  14  can be applied either as original equipment or in the after market. 
     A wide range of heat activated, thermoplastic adhesive formulations may also be utilized for adhesive layer  20 . Adhesive  20  should be strong enough to ensure that if a scratch, tear or rip occurs in film  14 , film  14  does not become stripped from hull  12  as hull  12  is propelled through water. Adhesive  20  preferably has a thermno bonding temperature, i.e. the temperature at which the adhesive bonds to outer surface  22  of hull  12 , lower than the melting point of plastic film  14 . In other words, adhesive  20  should be able to adhere to boat hull  12  or other structure at a temperature such that when applied, plastic film  14  does not melt. Accordingly, plastic film  14  should have a higher melting point than the melting point of adhesive  20 . 
     Thermoplastic base polymers that can be used in the manufacture of the adhesive  20  of the invention are thermoplastic polymers that are sufficiently compatible with tackifier, plasticizer, and other thermoplastic or thermosetting components to formn a substantial homogenous melt and solid. Typically in the adhesive  20  of the invention, the polymer provides mechanical strength and a cohesively competent adhesive bonding mass. 
     Any of a variety of available thermoplastic materials can be used in the compositions of the invention. Examples of such thermoplastics are ethylene based polymers such as polyethylene and its co- and terpolymers, ethylene/vinyl acetate, ethylene acrylate, ethylene methacrylate, ethylene methyl acrylate, ethylene methyl methacrylate, copolymers of ethylene and  1 - 6  mono- or di-unsaturated monomers etc., polyamides, polybutadiene rubber, polyesters such as polyethylene terephthalate, polybutylene terepthalate, etc., thermoplastic polycarbonates, atactic poly-alpha-olefins, including atactic polypropylene, and others; thermoplastic polyacrylamides, polyacrylonitrile, copolymers of acrylonitrile and other monomers such as butadiene, styrene, etc., polymethyl pentene, polyphenylene sulfide, aromatic polyurethanes; styrene-acrylonitrile, acrylonitrile-butadiene-styrene, styrene-butadiene rubbers, polyethylene terephthalate, acrylonitrile-butadiene-styrene elastomers, polyphenylene sulfide. Also, A—B, A—B—A, A—(B—A) n —Y block copolymers wherein the A comprises a polyvinyl aromatic block, the B block comprises a rubbery midblock which can be partly hydrogenated, and others can be used. 
     Preferred polymers for use in the adhesive  20  of this invention comprise EVA, APP, linear A—B—A block, linear A—(B—A) n —B multiblock copolymers, and radial or teleblock copolymers of the formula (A—B)— n —y wherein A comprises a polystyrene block, B comprises a substantially rubbery polybutadiene or polyisoprene block, Y comprises a multivalent compound, and n is an integer of at least 3. The midblocks can be post-treated to improve their heat stability through hydrogenation or other post-treatment removing residual unsaturation. 
     The adhesive layer  20  of the invention can also contain other compatible polymers, plasticizers, tackifying, resin fillers, pigments, dyes, oils, catalysts, inhibitors, antioxidants, UV absorbers, waxes, and other conventional additives. A preferred adhesive is an adhesive such as Bostick 7064 available from Bostick. This adhesive has a melting point of approximately 250° F. Preferably, this adhesive would be utilized with a nylon film which has a melting point of approximately 350° F. which is well above the adhesive&#39;s melting point. 
     Hot melt adhesives can also be utilized as adhesive  20 . Briefly, thermoplastic synthetic resin materials used in hot melt adhesives comprise a variety of polymerized material. These polymers are blended with other ingredients such as plasticizers, tackifiers and extenders, to formn an adhesive. Such polymers include polyethylene, polypropylene, polyvinyl acetate, polyvinyl butyral, polyvinylalcohol, ethylene-vinylalcohol polymers and other polyvinyl resins; polystyrene resins, A—B—A block copolymers comprising polymers wherein A is a polystyrene block and B is a rubbery midblock section; acrylic and methacrylic acid ester resins; various other materials compounded from synthetic resins such as polyisobutylene, polyamides, cumarone-indene products and silicones. Such thermoplastic resins usually have permanent solubility and fusability so that when hot, they can flow or creep under stress and soften to some extent to form a bond. After cooling, the materials preferably resist creep and bond deformation. Tfhey are used in the manufacture of tape, safety glass, shoe cements, for the bonding or lamination of film, foil or non-woven laminates, metals, woods, rubber, paper and many other materials. The aforementioned hot melt adhesives are well known in the art, and are readily commnercially available. 
     Any of the known anti-fouling compounds can be utilized in the protective layer  10 . The only criteria is that such compounds are compatible with film  14 , and are effective to control the growth of algae, barnacles, mussels, fungi and other marine organisms. Typical examples of anti-fouling compounds includes furan based compounds, copper compounds, lactone compounds, capsaicin or capsicum compounds, polyurethanes, peppercorn derivatives, alkyl-phenols derivatives, antibiotics (such as chloramphenicol, erythromycin, neomycin, and streptomycin), TBT, organotin polymers, and any compound which can effectively inhibit marine growth and be effectively dispersed throughout a plastic film. The aforementioned compounds are well known anti-fouling compounds, and are readily commercially available. 
     Referring now to FIG. 3, there is illustrated a second embodiment of the protective layer  10 . In this embodiment, protective layer  10  once again includes a plastic film  26  having an inner surface  28  and an outer surface  30 , as well as an adhesive layer  32  disposed between inner surface  28  of film  26  and outer surface  34  of hull  36 . In this embodiment, however, anti-fouling compound  38  is impregnated in adhesive  32 . As a result, anti-fouling compound  38  dispersed in adhesive  32  may slowly leach out into the surrounding environment through film  26  and thus prevent the growth and/or attachment of undesirable marine organisms to film  26 . Thus, film  26  provides a slow release of anti-fouling compound  38  from adhesive  32  in order to repel mussels, barnacles and the like. 
     FIG. 4 illustrates a third embodiment for protective layer  10  which comprises a plastic film  56  having an inner surface  58  and an outer surface  60  together with an adhesive layer  62  disposed between inner surface  58  and outer surface  64  of boat hull  66 . In this embodiment, anti-fouling compound  68  is uniformly dispersed within adhesive layer  62  as in the embodiment of FIG.  3 . However, in this embodiment, film  56  is impervious to water. Therefore, in order to permit anti-fouling compound  68  to inhibit growth of marine organisms on outer surface  60  of film  56 , it is necessary that film  56  be permeable. In order to accomplish this, film  56  includes a plurality of openings  70  formed therethrough. Openings  70  enable compound  68  to pass through film  56  and function to prevent marine growth and/or attachment of marine organisms to film  56 . 
     Referring now to FIG.  5 . there is illustrated a fourth embodiment for protective layer  10 . In this embodiment, protective layer  10  is employed and applied to outer surface  40  of an aluminum hull  42 . As with the first embodiment shown in FIG. 2, this embodiment employs a plastic film  44  impregnated with anti-fouling compound  46 , having an inner surface  48  and an outer surface  50  together with an adhesive layer  52  for removably attaching protective layer  10  to surface  40  of hull  42 . In this embodiment, however, an insulating film  54  is employed as a barrier to prevent corrosion of aluminum hull  42  caused by anti-fouling compound  46 . As illustrated, insulating film  54  is disposed between inner surface  48  of plastic film  44  and adhesive layer  52 . Insulating film  54  is preferably composed of either polyethylene or polypropylene. However, film  54  can be composed of any material whidch effectively prevents anti-foulant  46  from causing corrosion of hull  42 . Preferably, insulating film  54  and outer plastic film  44 , are coextruded to formn an integral laminate structure for ease of handling and application. Many different plastic film s, as earlier described, may be utilized due to the existence of compatabilizers, which are complex chemical compounds used to co-extrude and thus laminate plastic films that are normally incompatible. 
     The film  14 ,  26 ,  44  or  56  may be applied to boat hull  12  by stretching the film over hull  12  and preferably taping it in place. Then, utilizing a heat gun  72  and roller (not shown), the film and adhesive is heated, rolled onto the boat hull&#39;s surface, and then allowed to cool. The film and adhesive is thus bonded to the surface of hull  12  and will remain bonded until later removed. To replace old film and adhesive, the film and adhesive is re-heated to soften the adhesive. The film and adhesive is then stripped from hull  12  along with any barnacles, mussels and other marine growth which happens to be attached to the film. 
     FIG. 6 illustrates a fifth embodiment for protective layer  10 . In this embodiment, protective layer  10  is again employed and applied to outer surface  74  of an aluminum hull  76 . As with the second embodiment shown in FIG. 3, this embodiment employs a plastic film  78  having an inner surface  80  and an outer surface  82  together with an adhesive layer  84  impregnated with anti-fouling compound  86 . In this embodiment, an insulating film  88  is employed as a barrier to prevent corrosion of aluminum hull  76  caused by anti-fouling compound  86 , and is disposed between adhesive layer  84  and the outer surface  74  of hull  76 . An adhesive layer  90  is employed to bond insulating film  88  to the outer surface  74  of hull  76 . As with the embodiment of FIG. 5, insulating film  88  is preferably composed of either polyethylene or polypropylene, but may be composed of any material which effectively prevents anti-fouling compound  86  from causing corrosion of hull  76 . 
     Referring now to FIG. 7, there is illustrated a sixth embodiment for protective layer  10 . However, in this embodiment, protective layer  10  comprises only an adhesive layer  92  which is impregnated with anti-fouling compound  94 . As illustrated, plastic film  96  having an inner surface  98  and an outer surface  100  is used to apply adhesive  92  onto outer surface  102  of boat hull  104 . As noted, adhesive  92  is impregnated with anti-fouling compound  94 . However, plastic film  96  is removable from adhesive  92  after applying the adhesive layer  92  to the outer surface  102  of boat hull  104 . Thus, the impregnated adhesive  92  comes into direct contact with the surrounding environment and compound  94  leaches from adhesive  92  to prevent marine growth and/or attachment of marine organisms to hull  104 . The adhesive  92  is applied to boat hull  104  in the same manner as the previous embodiments except for the additional step of removing film  96 . 
     Adhesive  92  is removed from outer surface  108  of boat hull  104  by applying a removing laminate over adhesive  92 , as shown in FIG.  8 . The removing laminate comprises a carrier film  106  having an inner surface  108  and adhesive  110  disposed on the inner surface  108 . Adhesive  110  is a thermoplastic or hot melt adhesive of a similar type as adhesive  92 . When heated, however, adhesive  110  chemically bonds with adhesive  92  while at the same time substantially destroying or weakening the bond between adhesive  92  and exterior surface  108  of boat hull  104 . The bond, however, between carrier film  106  and adhesive  110  remains intact thus allowing adhesive  92  to be separated from exterior surface  102  of boat hull  104 .