Antifouling coating composition

[0002] This present application is a continuation-in-part of U.S. Ser. No. 09/586,378 filed Jun. 2, 2000, now U.S. Pat. No. 6,313,193 entitled “Antifouling Coating Composition” the disclosure of which is incorporated herein by reference in its entirety

[0003] The present invention relates to an antifouling coating composition, and more particularly to an antifouling coating composition for use with underwater structures such as ships, port facilities, buoys, pipelines, bridges, submarine stations, submarine oil field excavation facilities, water conduit raceway tubes in power plants, cultivating fishing nets, stationary fishing nets. Such coating composition is suitable for preventing underwater living things from adhering and growing on the surface of the underwater structure.

[0004] Biofouling, the growth of barnacles, seaweeds, tubeworms and other marine organisms on the hulls of ocean-going vessels, and other underwater structures, cause the international marine community billions of dollars a year. In the case of ocean-going vessels, most of this money goes for the extra fuel needed to overcome the increased drag on vessels. Some of it is spent for hull cleaning and repainting and for the upkeep on propulsion equipment. Of the total amount of money, a tiny amount is invested in the search for better antifouling inhibitors.

[0005] One currently used hull antifouling coating contains species such as tributyltin compounds or copper oxide and function through leaching of the toxicant into the marine environment. The resulting environmental hazards of introducing such toxicants into the marine ecosystem include disruption of natural ecocycles for many commercially important shellfish and pollution of entire food chains. The removal and disposal of toxicant-containing coatings from ships and other structures also pose separate environmental hazards, driving up the cost of refurbishment.

[0006] An alternative approach is to use acrylic acid monomer compositions which are water soluble, i.e., a polyester resin with an acrylic acid group. Such coatings include a biocide, which after a certain amount of time becomes inactive. The composition, because it is water soluble, wears off over time, i.e., is ablative, and exposes new and active biocide at the surface. Such a composition is known as a self-polishing composition. Thus the alternative approach has been to employ a polymeric coating to function as a fouling release coating. Poly(dimethylsiloxane) (PDMS)based coatings have properties which meet some of those requirements. On the other hand, as noted, studies have shown that such a cured PDMS material becomes unstable when immersed in water for three months.

[0007] Another specific approach involves the use of a composition containing a majority by weight as resin-solid content a reaction-curable silicone resin composition, a silicone resin having the specific average molecular weight and viscosity and an alkoxy group at its molecular terminal. While such a composition exhibits non-toxic characteristics, it is silicone based and in addition to the discussed disadvantages, subject to premature wear requiring frequent maintenance in the form of reapplication of the coating.

[0008] In accordance with the invention, an antifouling coating composition, which is a silicone modified glass, is provided which is extremely effective in preventing fouling, and which is highly durable over time.

[0009] The antifouling composition of the present invention compromises a glassy matrix formed by crosslinking a mixture of a silanol-terminated silicone and an alkoxy functionalized siloxane to provide an interpenetrating polymer network of glass and silicone and at least two materials capable of microphase separation, at least one of which is graftable to the glassy matrix.

[0010] The present invention also provides a method of treating a substrate to prevent fouling thereof. The method includes applying to the substrate a mixture of a silanol-terminated silicone and an alkoxy functionalized siloxane, and at least two materials capable of microphase separation. Thereafter crosslinking the mixture to provide an interpenetrating polymer network of glass and silicone to which is grafted at least one of the materials capable of microphase separation.

[0011] Optionally the mixture/antifouling composition can include an agent capable of preventing or inhibiting slime (e.g., algae, bacteria, protozoa, diatoms, etc.) from growing on the surface of the coating. While in most cases, such agent will be included in the composition, there are instances when slime is not an issue, and the anti-slime agent can be omitted. Suitable agents capable of preventing or inhibiting slime include surfactants, emulsifiers, enzymes, silver compounds, quaternary amine compounds, sulfa-based antimicrobial compounds, saponin and cholesterol, and mixtures and blends thereof.

[0012] The present invention will be more fully understood by reference to the following description and examples. Variations and modifications of the embodiments of the invention can be substituted without departing from the principles of the invention, as will be evident to those skilled in the art.

[0013] The present invention is based on the discovery that a modified glassy matrix can be combined with at least two materials capable of microphase separation to make a uniform and tough antifouling coating for use on surfaces, particularly marine surfaces in an underwater environment.

[0014] The glassy matrix serves to provide a carrier or support material composition. The matrix provides critical properties such as good adhesion to the substrate on which the formulation is applied as a coating, toughness, crack resistance, durability, abrasion resistance and stability in an aqueous environment. The glassy matrix is formed by crosslinking a mixture of a silanol-terminated silicone and alkoxy functionalized siloxane to provide a silicate glass. Typically, the glassy matrix is crosslinked using an organotitanate or tin catalyst agent.

[0015] Suitable functionally-terminated silicones include polydimethylsiloxane silanol terminated, vinyl terminated and amino terminated. Such silicones have low tear strength and can be toughened by incorporating glass (SiO₂) into the structure. Thus, an alkoxy functionalized siloxane can be included. Suitable alkoxy functionalized siloxanes include polydimethylsiloxane, tetraethoxy silane, tetramethoxy silane, and polydimethoxy siloxane.

[0016] One manner of forming the glassy matrix is using a Sol-Gel process employing an organotitanate compound, for example, a titanium alkoxide compound such as titanium methoxide, titanium ethoxide, titanium isopropoxide, titanium propoxide, titanium butoxide, titanium ethylhexoxide, titanium diisopropoxide (bis 2,4 pentanedionate), titanium diisopropoxide bis(ethylacetoacetate), or any other type of titanium alkoxide compound. These titanium alkoxide compounds can be used separately or in any combination. Although titanium alkoxides are given as examples, other organotitanate compounds can be used. The glassy matrix can also include a carboxylic acid compound. Silica gel is optional to inhibit the crosslinking reaction. Silica gel is used if storage over a long period of time is an issue. This is because it stores moisture. Alternatively, only silica gel can be used in place of the carboxylic acid compound. However, this does not work as well and a lot of silica gel is required.

[0017] With respect to the Sol-Gel process, as is well know to those of ordinary skill in the art, the Sol-Gel process is conventional, and typically produces a Sol-Gel glass which results from an optically transparent amorphous silica or silicate material produced by forming interconnections in a network of colloidal submicrometer particles under increasing viscosity until the network becomes completely rigid, with about one-half the density of glass.

[0018] In addition, the matrix can also include means for inhibiting or slowing the crosslinking reaction. Exemplary means for inhibiting include propionic or octonoic acid. Such agents permit the surface of the substrate to be coated to be painted before the formulation cures or crosslinks. The matrix can include various fillers and viscosity control agents such as mica, fumed silica, silica, kaolin, bentonite, zinc oxide, iron oxide, polytetrafluoroethylene powder, ultra high molecular weight polyethylene powder, high, medium and low molecular weight polyethylene powder, or other appropriate fillers, as will be readily apparent to those of ordinary skill in the art, can be used.

[0019] The two materials capable of microphase separation serve to prevent barnacles or other organisms from attaching or staying attached to the coating and thus the substrate. The material comprises at least one material, preferably a liquid, which in addition to its separation aspects, one of which is capable of being grafted into the glassy matrix. A material capable of microphase separation is a material that because of physical or chemical interactions between (among) the materials substantially continuously phase separates or moves. Such separation or movement in effect provides a substantially constant scraping motion thereby preventing the build up of slim or foul on the surface of the substrate.

[0020] One of the materials capable of microphase separation and graftable into the glassy matrix may be a vinyl terminated polydimethyl siloxane polymer reacted with dimethylethoxy silane and triethyl silane using a hydrosilylation reaction. Another microphase separatable material which can be employed is a methylhydrosiloxane polymer which is side-chain grafted with octene and vinyltriethoxy silane using a platinum-activated hydrosilylation reaction. Similarly, any hydrocarbon compound having a carbon atom chain of up to C20 can be used. Yet still further a methylhydrosiloxane polymer which is side-chain grafted with styrene and vinyltriethoxy silane using a platinum-activated hydrosilylation reaction can also be used. In this regard, it is noted that the platinum catalyst serves to react the hydride and the vinyl in the initial formulation. No platinum curing occurs in the final product provided in the field. Yet still further, a liquid hydrocarbon, such as polydecene, can also be used. In addition, other materials such as octanoic acid, heptanoic acid, hexanoic acid, decanoic acid, lauric acid, oleic acid, linoleic acid, linolenic acid, stearic acid, or any carboxylic acid containing a linear carbon chain of up to about C20 can be employed. Similarly, aluminum oleate, aluminum stearate, copper oleate, copper stearate, calcium stearate, magnesium stearate, or any fatty acid salt complex can be employed. In this regard, it is noted that of the above components, oleic acid is preferred as is aluminum oleate and aluminum stearate. Another microphase separatable material which can be employed is fluorotelomer intermediate available as Zonyl® from duPont.

[0021] The antifouling composition optionally may include an agent capable of preventing slime growth such as algae, bacteria, protozoa, diatoms and the like. Particularly preferred are surfactants and emulsifiers such as sorbitan mono- and tri-oleate (Span® products), polyoxyethylene sorbitan mono-oleate, polyoxyethylene sorbitan tri-oleate, and polyoxyethylene sorbitan mono-sterate (Tween® products), saponin, and cholesterol. Other suitable antifouling agents include silver compounds such as silver powder, silver oxide, silver chloride, silver carbonate, silver acetate and silver citrate; quaternary amine compounds such as cetrimide; isoniazid; benzalkonium chloride; sulfa-based antimocrobial compounds such as sulfanilamide, sulfaguanidine, sulfathiazole, sulfacetamide, sulfabenzamide and sulfamethiazole; saponin; and cholesterol. An exemplary antimicrobial compound is Irgarol™, which is a slime inhibitor manufactured by, and commercially available from Ciba Geigy.

[0022] Additional additives which can be added to the formulation and can include aminopropyltriethoxy silane which serves to increase adhesion and can be used, for example, when the coating composition is used on the running gear of a vessel. Fumed silica can be used for thixotropic control, i.e., to increase viscosity. Pigments can be used to alter the color, and certain phosphates can also be added for anticorrosion properties.

[0023] The glassy matrix preferably comprises about 20 to 90 percent by weight of the composition; the liquid material capable of liquid phase separation preferably comprises about 1 to 30 percent by weight of the composition; and the agent capable of preventing slime preferably comprises about 0.1 to 25 percent by weight of the composition.

[0024] In operation, the antifouling composition of the present invention can be applied to a substrate by roll-coating, brush, spray coating dipping and the like. As discussed above, it is preferred that the user mix the catalyst with the other components right before or substantially contemporaneously with application to form the interpenetrating polymer network of glass and silicone on the surface of the substrate.

[0025] The present invention is illustrated in greater detail by the following examples and comparative examples, in which “part” means “part by weight” unless otherwise expressed. The examples are not to be construed as limiting the scope of the present invention.

[0026] As may be appreciated, in order to commercially provide the components for the coating, they must be kept separated so that a reaction does not occur prior to application on a surface. Thus, a typical commercial product is provided in two parts as follows:

[0027] In preparing the mixture for being applied, parts A and B, for all formulations, should be combined and mixed using a mechanical mixing device for about three (3) to about five (5) minutes. Such a device can be a paint shaker, electrically powered stirrer or like device. After mixing, the coating can be kept in a scaled container for up to about six (6) hours before use. When applied, for example, with brush, roller, or sprayer, curing of the coating occurs rapidly as it is fashioned into a thin layer on the surface. The coating will be substantially tack free in about fifteen (15) to about thirty (30) minutes, and will be serviceable after about twenty-four (24) hours. Increased temperature and/or humidity will increase the cure rate, but the coating can still be applied at temperatures of about 32° F. to about 100° F.

[0028] In the previous discussion specific viscosities have been given for the hydro or hydroxy functionalized silicones. However, the formulation for the hydro or hydroxy functional silicones is not limited to those viscosities and can range from about 20 to about 115,000 centistokes. In terms of molecular weight, this corresponds to a molecular weight of about 400 g/mol to about 140,000 g/mol. The vinyl functionalized silicone polymers are typically described previously as being 1000 centistokes, but can also range from about 0.7 centistokes to about 165,000 centistokes, or about 186 g/mol to about 155,000 g/mol.

[0029] With respect to titanate silicate ratios, the ratio of the titanate to silicate can vary from about 1 mol % of the reactive titanate groups to about 99 mol % reactive silicate groups to about 99 mol % of the reactive titanate groups to about 1 mol % of the reactive silicate groups. An example of this is as follows. Polydiethoxy siloxane contains two reactive groups per molecular repeat unit. Titanium isopropoxide contains four (4) reactive molecular groups per molecule. A fifty percent (50%) ratio of the reactive groups would mean that there would be one half (½) mole of titanium isopropoxide per 1 mole polydiethoxy siloxane molecular repeat units. A twenty-five percent (25%) ratio would mean that there would be one (1) mole of titanium isopropoxide per six (6) moles of polydiethoxy siloxane repeat units. In this regard a preferred ratio would be about 50/50, with a most preferred ratio being about 25 titanate and about 75 silicate. The most preferred ratio enhances bonding to the filler material.

[0030] In terms of two-part commercial availability as discussed above, other two-part formulations are set forth in the following additional examples.

[0031] This commercial embodiment corresponds to Example 5 as previously described.

[0032] This commercial embodiment corresponds to Example 6 as previously described.

[0033] This commercial embodiment corresponds to Example 7 as previously described.

[0034] This commercial embodiment corresponds to Example 8 as previously described.

[0035] This commercial embodiment corresponds to Example 1 as previously described.

[0036] This commercial embodiment corresponds to Example 2 as previously described.

[0037] This commercial embodiment corresponds to Example 3 as previously described.

[0038] This commercial embodiment corresponds to Example 4 as previously described.

[0039] This total formulation would be provided commercially in two parts as follows:

[0040] This total formulation would be provided commercially in two parts as follows:

[0041] This total formulation would be provided commercially in two parts as follows:

[0042] This total formulation would be provided commercially in two parts as follows:

[0043] This total formulation would be provided commercially in two parts as follows:

[0044] A hard composition can be formulated as follows:

[0045] A rubbery composition can be formulated as follows:

[0046] As may be appreciated, in providing the formulation to an end user, the organotitanate is maintained separate from the other components, particularly the polydimethyl siloxane silanol terminated and the polydiethoxy siloxane, to prevent the matrix from crosslinking and setting, such that all of the other components making up the formulation, can later be mixed together by an end user, in whatever mixture is appropriate provided the above-mentioned components are kept separate and the formulation can then either be brushed, rolled or sprayed onto the surface which is being coated.

[0047] The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.