MX2008011825A - Silicone coating composition for protection from cathodic stress. - Google Patents

Abstract

This invention relates to a corrosion protection silicone coating system provides for easy and convenient application by conventional methods such as dipping, brushing or spraying. The coating provides a guard against environmental effects causing cathodic stress along with high physical strength and adhesion achieved with a suitable blend of reinforcing and extending fillers. The coating is an organopolysiloxane rubber coating composition containing between about 10 and 80 weight percent of a sacrificial metal filler to provide protection against environmental effects causing cathodic stress. Preferably, the coating is a one-part room temperature vulcanizing organopolysiloxane rubber coating composition to provide protection against cathodic stress. The present invention also provides for a method of coating metal surfaces to protect the metal surface from corrosion and cathodic stress. The method comprises applying to the surface a thin layer of the above one- part organopolysiloxane rubber composition and allowing the layer of the one-part organopolysiloxane rubber composition to cure at room temperature to a silicone elastomer.

Description

COMPOSITION OF SILICONE COATING FOR PROTECTION AGAINST CATHODIC TENSION FIELD OF THE INVENTION The present invention is directed to a silicone coating composition that protects metal surfaces from corrosion and cathodic stress.

BACKGROUND OF THE INVENTION A common coating is one that is used to protect metal surfaces against corrosion, especially caused by cathodic stress. Corrosion is an electrochemical process that causes' degradation of the metal through an oxidizing process. Environmental factors such as water, oxygen, salt and acid rain cause oxidative chemical reactions that slowly turn the metal into metallic oxide and wear it or scrape it off the surface. The coatings provide a barrier between the metal and the environmental factors that cause corrosion. The efficiency of the coating and its service life depend on its barrier properties against the penetration of moisture and other chemicals and its resistance to degradation caused by environmental factors such as salt, acid rain and ultraviolet (UV) radiation. The integrity of the coating can also be affected by chemical damage, which exposes the metal to the environment and initiates the electrochemical oxidation of the metal and subsequent delamination of the coating. The Sacrificial metals such as zinc, nickel and cadmium in the coating provide relief against cathodic stress caused by contact of moisture, salt and oxygen to the exposed metal. Most of the coating systems currently available provide cathodic protection to the substrate through a system of three covers. The first cover contains a sacrificial metal (metal-rich cover) followed by a second cover that helps to join the base and the top cover together and also helps to seal the sacrificial metal and finally a third organic cover to provide a barrier between the external environment and the base cover. Examples of three-deck systems are three epoxy or roof polyurethane systems, shown for example, in U.S. Pat. 6,866,941. The epoxy-based compositions use a two-part composition, which remains as a coating on the surface through brush, dip or spray application. Epoxy based coating compositions have the advantage of providing a coating with a high gloss surface. However, epoxy-based coatings generally require that the two separate parts be mixed together and used within a very short period of time. If the composition is not used within this period, it will be cured before it can be applied to the surface. In addition, epoxy-based compositions can emit volatile organic compounds (VOC) and they require careful handling. There is still a need for a coating that provides protection against cathodic stress, a moisture barrier and chemicals for protection against corrosion and UV resistance in a system with less sizing content, from a single coating.

BRIEF DESCRIPTION OF THE INVENTION This invention relates to a silicone coating system for protection against corrosion, which provides protection to a substrate against cathodic stress caused by a corrosive environment and has a longer service life by virtue of its resistance against environmental factors such as chemicals, heat and UV radiation. The coating provides an easy and convenient application through traditional methods such as dipping, brush application or spraying. The coating provides an insurance against environmental effects that cause cathodic stress along with high physical strength and adhesion achieved with an adequate mix of reinforcement and extension fillers. The present invention provides an organopolysiloxane rubber coating composition containing between about 10 and 80 by weight of a sacrificial metal filler to provide protection against environmental effects that cause cathodic stress.

In one aspect of the invention, the coating composition comprises: a) from about 5 to about 80 weight percent of one or more polyorganosiloxane fluids of the formula: R1 [(R) 2SiO] n (R) 2Si R wherein R is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, R each of which may be the same or different are OH, a monovalent alkyl or alkenyl radical having from 1 to 8 atoms of carbon or a phenyl radical, and n has an average value so that the viscosity is from about 10 to about 100,000 centipoises at 25 ° C, preferably from about 500 to about 20,000 centipoises at 25 ° C. In at least one of the polyorganosiloxane fluids, R1 is a reactive group such as OH or alkenyl, preferably OH, most preferably both R are OH; b) from about 10 to about 80 weight percent of a sacrificial metal filler; c) from about 0 to about 15 weight percent of a conductive filler; d) a catalyst suitable for the reactive group of the polyorganosiloxane of (a); and e) an interlacing agent suitable for the group polyorganosiloxane reagent of (a). In another aspect, the present invention provides a one-part vulcanization polyorganosiloxane vulcanization rubber coating composition to provide protection against cathodic stress. The composition consists essentially of the product obtained by mixing the following: a) from about 5 to about 80 weight percent of one or more polydiorganosiloxane fluids of the formula: HO [(R17) 2SiO] n (R 7) 2SiOH wherein R17 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms, or a phenyl radical, which has from 3 to 9 halogen atoms, and n has an average value such that the viscosity is about 10. about 100,000 centipoise at 25 ° C, preferably from about 500 to about 20,000 centipoise at 25 ° C; b) from 0 to about 8 weight percent of a bifunctional chain extender of the general formula: wherein X1 is an alkyl radical with a functional group linked directly to the silicone atom, of carboxyl presence, ketoximino, alkoxy, carbonyl or amine, most preferably alkoxy or ketoximino and R18 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical; c) from about 10 to about 80 weight percent of one or more sacrificial metal fillers; d) from about 0 to about 15 weight percent of one or more conductive fillers; e) from about 0 to about 20 weight percent of an amorphous SiO 2 reinforcement filler optionally treated on the surface, having a surface area of between about 50 to 250 m2 / g and a particle size scale of between about. 0.01 to 0.03 microns; f) from about 0.1 to about 35 weight percent of one or more crosslinking agents of the general formula: (X) 4-m "S i -R 12 m wherein R 12 is an alkyl, alkenyl or phenyl radical (preferably methyl or ethyl), X is an alkyl radical with a functional group selected from carboxyl, ketoximino, alkoxy, carbonyl or amine directly linked to the silicone atom, and m is an integer from 1 to 2; g) from about 0.2 to about 3 weight percent of an adhesion promoter of the formula: wherein R and R are independently selected from monovalent alkyl or akenyl radicals having from 1 to 8 carbon atoms, or a phenyl radical, which optionally may be substituted with an alkyl radical having from 1 to 8 carbon atoms and may also contain from 3 to 9 halogen atoms, b is an integer between 0 and 3, and R24 is a saturated, unsaturated or aromatic hydrocarbon radical having from 1 to 10 carbon atoms, which may optionally contain an organofunctional group; h) from about 0 to about 5 weight percent of an organometallic complex as a condensation catalyst of the formula: (R25) 2M (R26) 2 wherein R25 is an alkyl radical, monovalent akenyl having 1 to 10 carbon atoms or a phenyl radical, R26 is an alkyl, akenyl radical, having 1 to 10 carbon atoms or a phenyl radical having an organo-functional group and M is a metal; and i) from 0 to 80 weight percent of a suitable solvent or diluent. The present invention also provides a method for coating metal surfaces to protect the metal surface against corrosion and cathodic stress. The method comprises applying to the surface, a layer of an organopolysiloxane rubber composition containing from about 10 to about 80 weight percent of a sacrificial metal filler and allowing the layer of the organopolysiloxane rubber composition of a part to be cure at room temperature to a silicone elastomer ..

DETAILED DESCRIPTION OF THE INVENTION The organopolysiloxane rubber compositions of the present invention which contain a sacrificial metallic filler are ideally suited for the protection of surfaces against environmental effects. Said protection includes, in particular, cathodic stress caused by the exposure of metallic surfaces and structures against salt spraying and chemical environments including direct exposure to salt water, salt fog, gases and other industrial pollutants. The contact between two different metals can also cause cathodic tension, especially in the presence of humidity. The compositions of the present invention can also be used to coat metallic surfaces of motor vehicles, which can be exposed to a condition with high salt content during the winter season. Compositions with suitable additives also provide protection against the effects of climate against exposure to, among other things, UV radiation. The compositions of the present The invention is particularly useful in marine installations, such as ship hull coatings, marine platforms, dykes, pillars, buoys, water consumption pipes and various underwater structures. The coating composition of the present invention is also useful for coating electrical transmission towers and bridges for the protection of metallic structures against cathodic stress, directly exposed to salt water and industrial pollution, especially sulfur-based air pollutants. Since it is made of silicone, the resulting coating on the metal surface provides protection against the otherwise bad effects of environmental climate / UV exposure, hydrolysis, and other effects. Due to its nature: naturally hydrophobic, the outer layer of the silicone creates a highly hydrophobic coating of very low cost. The composition used in the present invention comprises a sacrificial metal filler and vulcanizable polyorganosiloxane, which provide the composition with protection against corrosion, particularly against cathodic stress. The vulcanizable polyorganosiloxane can be any of the vulcanization polyorganosiloxane compositions commonly used, using one-part or two-part catalytically cured systems, for example, through the addition of curing, or using moisture curing systems. The polyorganosiloxane is terminated with a reactive group, generally hydroxyl or alkenyl, as follows: R [(R) 2S0] n (R) 2Si R1 wherein R is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, R 1, each of which may be the same or different, is a reactive group selected from OH, or an alkenyl radical monovalent having from 1 to 8 carbon atoms, and n has an average value such that the viscosity is from about 10 to about 100,000 centipoises at 25 ° C, preferably from about 500 to about 20,000 centipoises at 25 ° C. The catalytically polymerizable polyorganosiloxane compositions utilizing addition curing systems are not controlled by atmospheric moisture. The high temperature can accelerate the healing process, although the entanglement addition reaction can also occur at room temperature. The base polymer is generally a polydiorganosiloxane of the general formula: R3 [(R2) 2SiO] n (R2) 2 If R3 wherein R2 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms, optionally substituted with 1 to 9 halogen atoms, or a phenyl radical, optionally substituted with 1 to 6 halogen atoms, R3 is a monovalent alkenyl radical (preferably a monovalent vinyl or ethylene radical) and n has an average value so that the viscosity is 100 to 100,000 centipoise. An example of said base polymer is: CH2 = CH-Si (CH3) 2-0-Si (CH3) 2-0 0-Si (CH3) 2-CH = CH2 The addition cure systems use an interlayer to polymerize the base polymer. The interlayer is generally a polydiorganosiloxane of the general formula: R5 [(R4) (H) SiO] m [(R4) 2SiO] nR5 wherein each of R4 and R5, which may be the same or different, is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms, optionally substituted with 1 to 9 halogen atoms, or a phenyl radical, optionally substituted coh 1 to 6 halogen atoms, and H is a hydride radical, m and n are integers and their total average value is such that the viscosity is 10 to 10,000 centipoise. The value of m is 10 to 50 percent of the value of m + n. For optimal entanglement, the ratio of the alkenyl radical, preferably an ethylene radical, to the hydride radical is from 1: 1 to 6: 1. The interlacing reaction of healing systems of addition requires a catalyst, generally an organometallic platinum complex of the formula: Pt [R7 (SiOR6) R7] 4 wherein R6 is alkyl or alkenyl and R7 is alkenyl. An example of said platinum catalyst is: Platinum-divinyltetramethyldisiloxane complex (CH2 = CH-S1 (CH3) 2-0-Si (CH3) 2-CH = CH2) 4Pt Entanglement through addition is an extremely rapid reaction. The reaction rate can be controlled by reducing the amount of catalyst or by using a reaction inhibitor such as a vinyl-terminated dimethylsiloxane which reduces the activity of the platinum catalyst. An adhesion promoter can also be used for the two part addition cure system to improve the adhesion of the elastomer to the surface. The adhesion promoter is generally a silane having the general formula: R8Si (R90) 3 wherein R8 is an alkenyl radical, preferably a vinyl radical, and R9 is an alkyl radical having from 1 to 6 carbon atoms carbon. Addition curing systems are generally provided in two parts with the base polymer, interlayer, adhesion promoter and inhibitor in one part and the base polymer and catalyst in the other part / Fillers and pigments are added in any of the parts to achieve an equivalent viscosity of both parts for a homogeneous mixer. The entanglement of the polyorganosiloxane terminated by an alkyl radical, such as a vinyl radical (also described for the addition curing system) can also be accelerated - by heat in the presence of organic peroxide, such as dichlorobenzoyl peroxide, trichlorobenzoyl peroxide or dicumyl peroxide as a catalyst. The peroxide-organic entanglement does not require a functional hydride interlayer (as described in the addition cure system). Moisture curing systems are generally vulcanizable at room temperature (RTV), although higher temperatures can also be used to accelerate the healing reaction. The moisture curing composition may also be provided as a two part system similar to the addition curing compositions or may be a one part composition containing all the components of the composition in a single container. Preferably, to facilitate handling and application, the RTV compositions are in one part. Moisture curing systems generally use a hydroxyl-terminated polyorganosiloxane as a base polymer. Preferably, the base polymer is one or more polyorganosiloxanes of the general formula: R11 [(10) 2SiO] n (R10) 2SiR11 where R 0 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, R 1 each of which may be the same or different, are OH, a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, and n has an average value so that the. The viscosity is from about 10 to about 100,000 centipoise at 25 ° C, preferably from about 500 to 1 about 20,000 centipoise at 25 ° C. At least one of R 1 is a reactive group such as OH or alkenyl, preferably OH, most preferably both R 11 are OH. Moisture healing systems use an interlacer that has the general formula: (X) 4.m-Si-R12m wherein R 12 is an alkyl, alkenyl or phenyl radical (preferably methyl or ethyl) and X is an alkyl radical with a functional group bonded directly to the silicone atom and n is an integer from 0 to 2. The functional group can be carboxyl, ketoximino , alkoxy, carbonyl or amine. The interlayers commonly used for one-part or two-part RTV moisture cure systems include: Acetoxy silane (CH3C (0) 0) 3-Si-R12 releases acetic acid as a by-product of curing. Oxime silane (C2H5 (CH3) C = NO) 3-SiR12 liberates methyl ethyl ketoxime as a by-product of curing. Alkoxy silane (R 30) 3-Si-R 12 wherein R 13 is an alkyl radical of 1 to 6 carbon atoms. Releases alcohol as a by-product of healing. Enoxi silane (CH3C (0) CH2) 3-S¡R12 releases acetone as a by-product of curing. Amine silane ((CH3) 2N) 3-Si-R12 liberates amine as a by-product of curing. It is the fastest reaction interlayer that does not require a catalyst. To improve the entanglement reaction, a catalyst is generally used. For moisture curing systems, a commonly used catalyst is an organotin salt, such as dibutyltin dilaurate, among others. To improve the adhesion of the elastomer to the surface on which it remains as a coating, an adhesion promoter can be used. The adhesion promoter is commonly a compound of the formula: wherein R15 and R16 are independently selected from monovalent alkyl or alkenyl radicals having from 1 to 8 carbon atoms or a phenyl radical which optionally can be substituted with an alkyl radical having from 1 to 8 carbon atoms, b in an integer of 0 and 3, and R 4 is a saturated, unsaturated or aromatic hydrocarbon radical having from 1 to 10 carbon atoms, which may optionally contain a functional group. The organopolysiloxane rubber compositions of a portion of the present invention for use as a protective coating contain from about 5 to about 80 weight percent of one or more polydiorganosiloxane fluids of the formula: HO [R17) 2SiO] n (R17) 2SiOH wherein R17 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical which may contain from 3 to 9 halogen atoms, and n has an average value such that the viscosity is from about 10 to about 100,000 centipoise at 25 ° C. Preferably, n has an average value so that the viscosity is between about 500 and about 20,000 centipoises at 25 ° C, most preferably between about 1,000 and 20,000 centipoises at 25 ° C. Polydimethylsiloxane is the most preferred silicone polymer fluid. The polydimethylsiloxanes may contain small amounts of small units of monoethylsiloxane and a methyl radical replaced with other radicals in small amounts as impurities as described. found in commercial products, but the preferred fluid contains only polydimethylsiloxane. When using low viscosity fluids, usually 1,000 centipoise or less, it may be advantageous to add bifunctional chain extenders of the general formula: wherein X1 is an alkyl radical with a functional group linked directly to the silicone atom, preferably alkoxy, ketoximino, carbonyl, carboxyl or amine, most preferably alkoxy or ketoximino and R18 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical. If chain extenders are used, these are generally present in an amount of up to about 8 weight percent, preferably between about 2 weight percent and about 8 weight percent. The composition of this preferred embodiment may contain a second linear low molecular weight dimethyl polysiloxane to act as a viscosity reducing diluent for the composition, to facilitate the application of the composition to the surface. The linear low molecular weight dimethyl polysiloxanes are oligomeric compounds blocked at the end of the previous form wherein the -OH terminal is replaced by blocking groups which may be the same or different, independently selected from a monovalent alkyl or alkenyl having 1 to 10 carbon atoms. to 8 carbon atoms or a phenyl radical. The average value of n varies between 4 and 24, preferably between 4 and 20. If the composition contains the two polysiloxanes presented above, the total polysiloxanes in general is about 40 to 60 weight percent, with relative amounts of the two polysiloxanes being selected based on the desired characteristics of the final coating. Generally, each of the polysiloxanes will be present in a ratio of about 30 weight percent to about 70 weight percent based on the total weight of the polysiloxane fluids. In addition to, or in place of the linear low molecular weight dimethyl polysiloxanes, the composition may contain up to about 40 weight percent, and preferably from 20 to 30 weight percent, of a cyclo-organosiloxane of the formula: [(R19) 2SiO] n wherein R 9 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, which optionally can be substituted with an alkyl radical having from 1 to 8 carbon atoms and n has an average value of 3 to 10. The preferred cycloorganosiloxane is a cyclic dimethylsiloxane and is used in a manner similar to linear low molecular weight dimethyl polysiloxanes as a diluent to lower the viscosity of the composition for convenient application by spraying, brushing or dipping. The composition also contains from 10 to 80 percent by weight, preferably from 30 to 60 percent by weight, most preferably from 40 to 50 percent by weight of sacrificial metal fillers to increase the resistance of the coating to the cathodic tension of the environmental effects The sacrificial metal fillers are preferably selected from zinc powder, zinc flakes, aluminum powder, aluminum flakes, nickel powder, nickel flakes, magnesium powder and magnesium flakes. In addition to the sacrificial filler, the composition may also contain from 0 to 15 weight percent of a conductive filler selected from conductive metallic powder, glass fibers coated with metal, or powder and mica. The composition may also contain from about 0 to 20 weight percent of an amorphous SiO 2 reinforcing filler having a surface area of between 50 and about 250 m2 / g and a scale of particle size between approximately 0.01 and 0.03 microns. Preferably, the surface area is between about 50 and about 150 m2 / g, most preferably from about 75 to about 150 m2 / g. The specific gravity of the filling is preferably around 2.2. The surface of the amorphous silica can also be treated with organic molecules such as hexamethyldisilasan or polydimethylsiloxane or silane. It has been found that using a surface treated with silica helps reduce the viscosity of the composition. Similary, the use of lower surface area fillers also helps reduce the viscosity of the composition. The composition also contains from about 0.1 to about 35 weight percent, preferably from about 3 to about 15 weight percent, most preferably from about 3 to 10 weight percent of an organo-functional crosslinking agent of the General Formula: wherein R 2 is an alkyl, alkenyl or phenyl radical (preferably methyl or ethyl), X is an alkyl radical with a functional group selected from carboxyl, ketoxymino, alkoxy, carbonyl or amine linked directly to the silicone atom, and n is an integer from 0 to 2. Preferably, the entanglement agent is an agent oximinosilane entanglement of the formula R20Si (ON = CR212) 3, wherein R20 and R21 each represents a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms, or a phenyl radical, preferably an alkyl radical such as methyl, ethyl, propyl, butyl or an alkenyl radical such as vinyl, allyl or a phenyl radical. Preferred groups R20 and R21 are alkyl or vinyl radicals, most preferably methyl and ethyl radicals. The composition also contains from about 0.2 to about 3 weight percent of an organofunctional silane as an adhesion promoter. Preferably, the organofunctional silane has the formula: R22b I (R230) 3.b SiR24 wherein R22 and R23 are independently selected from monovalent alkyl or alkenyl radicals having from 1 to 8 carbon atoms, or a phenyl radical, which optionally may be substituted with alkyl radicals having from 1 to 8 carbon atoms and containing from 1 to 8 carbon atoms; to 9 halogen atoms, b is an integer of 0 to 3, preferably 0, and R24 is a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 10 carbon atoms, which can also be functionalized through a member selected from the group consisting of amino, ether, epoxy, isocyanate, cyano, acryloxy and acyloxy, and combinations thereof.

R22 and R23 are preferably an alkyl radical such as, preferably, methyl, ethyl, propyl, butyl, or an alkenyl radical such as vinyl and allyl. Most preferably, R22 and R23 with alkyl radicals, preferably methyl, ethyl or propyl radicals. Preferably, R24 is an alkyl group, most preferably further functionalized by one or more amino groups. The most preferred organofunctional silane is N- (2-aminoethyl-3-aminopropyl) trimethoxysilane). The composition further contains from about 0 to about 5 weight percent of an organometallic complex such as a condensation catalyst, which accelerates the aging of the composition. The condensation catalyst is of the formula: (R ") 2M (R¿b) 2 wherein R is a monovalent alkyl or alkenyl radical having from 1 to 10 carbon atoms or a phenyl radical, R26 is an alkyl or alkenyl radical having from 1 to 10 carbon atoms or a phenyl radical having an organo functional group, and M is a metal. Preferably, the organometallic complex is an organotin complex of a carboxylic acid selected from the group consisting of dibutyltin diacetate, stannous octoate, dibutyltin dioctate and dibutyltin dilaurate. Preferably, the condensation catalyst is present at about 0.02 to about 3 weight percent. Most preferably, the organotin salt is dibutyltin dilaurate of the formula: (C4H9) 2Sn (OCOC10H20CH3) 2.

In all of the above compounds, the alkyl includes straight, branched or cyclic radicals. Among the alkyl groups are straight chain or branched chain alkyl of 1 to 10 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, fanyl, isopentyl, hexyl, etc., the cycloalkyl is cycloalkyl of 3 to 8 carbon atoms, for example, cyclopropyl, cyclobutyl, cyclohexyl, etc., the alkenyl groups are, alkenyl of 1 to 10 carbon atoms, such as, for example, vinyl and allyl. The above groups as well as the phenyl radicals can further be functionalized by including in the chain or ring structure, as the case may be, a group selected from the class consisting of amino, ether, epoxy, isocyanate, cyano, acryloxy, acyloxy and combinations, provided that the functionalization does not adversely affect the desired properties of the compound. The composition may contain from 0 to 80 weight percent of a solvent or diluent to allow for easier coating application. The amount of the solvent will be selected to allow the composition to be applied easily and quickly to the surface to be coated. The composition may contain other optional ingredients such as pigments and other fillers in lower amounts provided that the addition of the ingredients does not cause degradation of the desired properties of the cured coating made from the composition. The organopolysiloxane composition of the present invention is prepared by mixing the ingredients together in the absence of moisture. The silane is sensitive to moisture and will experience entanglement in the presence of moisture, so that the mixture must be essentially free of free moisture when the silane is added and maintained in a moisture free state until curing is desired. A preferred method of mixing comprises mixing the polysiloxane fluids with the fillers and pigments. Then, oximinosilane and organofunctional silane are added and mixed under a nitrogen atmosphere. The organotin salt is added to the mixture together with any solvent or diluent and the mixture is then filled into sealed containers for storage before use.

The surface that will be protected is covered with the composition through conventional methods such as immersion, brush application or spraying. Preferably, the surface to be protected is covered by spraying one or more application of the composition of the present invention. The composition can be adjusted to the proper consistency for use in these methods by heating or by the addition of a suitable solvent, particularly for spray application.

The thickness of the coating will depend on the specific requirements of the application and the desired level of protection. The coating preferably has an average thickness of 50 to 1000 microns, preferably an average thickness of 100 to 750 microns, most preferably around 250 to 500 microns. After the coating is formed on the surface, the surface is exposed to a normal atmosphere for entanglement and cure of the coating. The improved coating of the present invention is capable of protecting surfaces against environmental effects, particularly cathodic stress of metal surfaces as a result of corrosion in the presence of moisture such as rain or fog in combination with contaminated atmospheres, salt or mist spray or direct exposure to salt water. The improved coating of the present invention is particularly useful for protecting metal surfaces that are directly exposed to salt water. Such surfaces include ship hulls and other vessels, oil drilling platforms, marine port structures and pillars, etc. When the coating is used in the hulls of ships, other benefits such as resistance to incrustation as well as protection against corrosion are achieved. The coating does not allow marine animals, such as gullies or barnacles, to adhere easily to the surface. Any of these animals that attempt to bind or stick to the surface are usually removed from the surface through high pressure washers. In addition, surface cleaning is generally achieved through high-pressure washing and / or manual or mechanical rubbing and does not require scraping operations commonly used during the cleaning of ship hulls, or other marine installations. As the cleaning of the surfaces covered with the composition of the present invention is easily achieved, the composition can also be used as an anti-paint coating on the surfaces. The following examples are included to illustrate the preferred embodiments of the invention and to demonstrate the usability of the coating and are not intended to limit the scope of protection for the invention in any way.

EXAMPLE 1 A coating composition was prepared by mixing 24 parts by weight of polydimethylsiloxane fluid with a viscosity of 5,000 centipoises and 2 parts by weight of surface-treated amorphous silica, having a surface treatment with hexamethyldisilasan and a surface area of about 125 m2 / g, 10 parts by weight of glass fibers covered with metal. Then, 3 parts by weight of methyl tri s- (methylene methyl ketoxime) silane and 1 part by weight of N- (2-aminoethyl-3-aminopropyl) trimethoxy silane were added and mixed under a nitrogen atmosphere. Then, 50 parts by weight of zinc dust. The coating composition was diluted with 10 parts by weight of petroleum naphtha to obtain a viscosity of between 3,000 and 4,000 cP. The cured elastomeric coating provides excellent resistance against chemicals, galvanic corrosion, cathodic stress and cathodic delamination.

EXAMPLE 2 A coating composition was prepared by mixing 24 parts by weight of polydimethylsiloxane fluid with a viscosity of 5,000 centipoises and 2 parts by weight of surface treated amorphous silica, having a surface treatment with hexamethyldisilasan and a surface area of about -125 m2 / g, 10 parts by weight of aluminum flakes. Then 3 parts by weight of tris- (methyl ethyl ketoxime) silane were added. methyl and 1 part by weight of N- (2-aminoethyl-3-aminopropyl) trimethoxy silane and mixed under a nitrogen atmosphere. Then, 50 parts by weight of zinc flakes were also added and mixed. The coating composition was diluted with 10 parts by weight of petroleum naphtha to obtain a viscosity of between 3,000 and 4,000 cP. The cured elastomeric coating provides excellent resistance against chemicals, galvanic corrosion, cathodic stress and cathodic delamination.

CATODE SEPARATION TEST (ASTM G8) Test panels were prepared by applying the formulation of coating on steel pipes with an external diameter of 21 mm, an internal diameter of 12 mm and a length of 230 mm. One end of the pipe was sealed with silicone sealant and the pipe was covered to a length of 160 mm from the sealed end with a coating thickness of 500 microns. Electric contact was applied on the uncovered end using connecting clips (crocodile). An Instek Laboratory Model PS-3030 DC power supply was used to provide a constant potential supply to the coated electrodes. The coated ends of the test panels were suspended in a glass tank with a capacity of 35 liters;: The water in the glass tank was circulated through a pump. Aqua Clear 200. The electrical circuit was prepared as per circuit diagram in an ASTM G8 Method B for more than one specimen. Magnesium anodes were obtained from the company Interproyincial Corrosion Control Company Limited, Ontario, Canada. The surfaces of the anodes were cleaned periodically during the test to remove the deposition of salts. A standard Coromel Calomel Electrode (Individual Cell) was obtained and used to measure the electrode potential in each coated electrode. The chemicals for the preparation of the electrolyte solution were obtained from Alphachem. The electrolyte solution is prepared by mixing 1 mass percentage of sodium chloride, 1 mass percentage of sodium sulfate and 1 mass percentage of sodium carbonate. Three coating breaks or "Holidays" were made on the coated test panel along the circumference at an angle of 120 °, 30 mm above the lower end, drilling through the coating towards the metal. The drill (diameter 2 mm) was modified by grinding the flat drilling point to avoid drilling through the metal. Three more overlapping breaks or "Holidays" were made on the upper end of the coated electrode, which was not. immersed in the electrolyte. The purpose of Hollidays not submerged1 * 'was to compare the loss of adhesion as a result of the stress? »Cathodic. A sheet of high density polyethylene containing holes for the electrodes was mounted on top of the tank. The coated electrodes were passed through the holes and suspended in the electrolyte solution symmetrically such that only the coated end portion was immersed in the solution. Two magnesium electrodes were also inserted through the holes and suspended in the solution at both ends of the tank in order to maintain an equal distance from all the coated electrodes. A potential of 1.5 volts was applied from the DC Power Supply and the current was measured in the Ammeter. The potential of each electrode Coated was also measured through the Standard Calomel Electrode and recorded. The test was continued for 30 days. The cathodic delamination of the coating on the test panel was only 0 to 2 mm from the holliday. This showed excellent coating resistance against cathodic stress applied for 30 days. The compositions of the present invention are useful in many cases, where protection of the surfaces against environmental effects is desired. These compositions include the composition of the above examples as well as other compositions, the formulation of which is within the skill of those skilled in the art. The selection of the various, 1 components and their proportions could be immediately apparent * depending on the desired properties of the final coating. Although the invention has been described with reference to specific embodiments, it should be understood by those skilled in the art that various changes can be made and equivalents can be substituted without departing from the spirit and true scope of the invention. All these modifications are intended to be within the scope of the appended claims.

Claims (20)

1. An organopolysiloxane rubber composition for use as a cathodic protection, anti-corrosion coating on surfaces, the composition consists essentially of the product obtained by mixing of the following: a) from about 5 to about 80 weight percent of one or more polyorganosiloxane fluids of the formula:

R1 [(R) 2S0] n (R) 2Si R1 wherein R is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, each R 1, which may be the same or different are OH, a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical, and n has an average value so that the viscosity is from about 10 to about 100,000 centipoises at 25 ° C, and at least one of the polyorganosiloxane fluids, R both are the same reagent selected from the group of OH and alkenyl; b) from about 10 to about 80 weight percent of a sacrificial metal filler; c) from about 0 to about 15 weight percent of one or more conductive fillers; d) an organometallic catalyst suitable for crosslinking of the polyorganosiloxane of (á); and e) an organosilane interlacing agent suitable for crosslinking the polyorganosiloxane of (a). 2. A composition according to claim 1, which consists essentially of: a) from about 5 to about 80 weight percent of one or more polydiorganosiloxane fluids of the formula:

HO [(R17) 2SiO] n (R17) 2SiOH wherein R17 is a monovalent alkyl or alkenyl radical having 1 to 8 carbon atoms, or a phenyl radical, which may contain from 3 to 9 halogen atoms, and n has a value of. average so that the viscosity is about 10r approximately 100,000 centipoises at 25 ° C; b) from about 10 to about 80 weight percent of one or more sacrificial metal fillers; c) from about 0 to about 15 weight percent of one or more conductive fillers; d) from about 0 to about 5 weight percent of an organometallic complex as a condensation catalyst of the formula:

(R25) 2M (R25) 2 wherein R25 is a monovalent alkyl or alkenyl radical having from 1 to 10 carbon atoms or a phenyl radical, R26 is an alkyl or alkenyl radical having from 1 to 10 carbon atoms or a phenyl radical having an organo functional group and it's a metal; e) from about 0.1 to about 35 weight percent of one or more entanglement agents of the general formula: wherein R 2 is an alkyl, alkenyl or phenyl radical, X is an-: alkyl radical with a functional group selected from carboxyl, ketoximino, alkoxy, carbonyl or amine directly linked to the :, silicone atom, and m is an integer of 1; to 2; f) from about 0.2 to about 3 weight percent of an adhesion promoter of the formula: wherein R and R are independently selected from monovalent alkyl or alkenyl radicals having from 1 to 8 carbon atoms or a phenyl radical, which optionally may be substituted with an alkyl radical having from 1 to 8 carbon atoms and may also contain 3 to 9 halogen atoms, b is an integer between 0 and 3, and R24 is a saturated hydrocarbon radical, unsaturated or aromatic having from 1 to 10 carbon atoms, which may optionally contain an organofunctional group; g) from about 0 to about 20 weight percent of an amorphous surface treated SiO 2 reinforcing filler, having a surface area of between about 50 to 250 m2 / g and a particle size scale of between approximately 0.01 to 0.03 microns; h) from 0 to 80 weight percent of a suitable solvent or diluent; and i) from 0 to 8 weight percent of a chain extender, bifunctional of the general formula:

R ^ 2 ~ Si-X ^ 2 wherein X 1 is alkoxy or ketoximino and R 18 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical. 3. A composition according to claim 2, wherein n is selected such that the viscosity is from about 1,000 to about 20,000 centipoises at 25 ° C. 4. A composition according to claim 3, wherein R17 is alkyl. 5. A composition according to claim 4, wherein R17 is methyl.

6. A composition according to claim 5, wherein the interlayer is an oxosilane crosslinking agent of the formula: R20Si (ON = CR212) 3 wherein R20 and R21 are independently selected from monovalent alkyl or alkenyl radicals having from 1 to 8 carbon atoms or a phenyl radical, which optionally can be substituted with an alkyl radical having from 1 to 8 carbon atoms. 7. A composition according to claim 6, in which the adhesion promoter is a compound of the formula: NHCH2CH2NH2 I

CH2 i CH2CH2Si (OMe) 3 wherein Me is the methyl radical.

8. A composition according to claim 7, wherein the condensation catalyst is an organotin salt of a carboxylic acid selected from the group consisting of dibutyltin diacetate, stannous octoate and sodium dioctoate. dibutyltin.

9. A composition according to claim 8, wherein the organotin salt of a carboxylic acid is a compound of the formula: (C4H9) 2Sn (OCOC10H2oCH3) 2

10. A composition according to claim 9 ,. wherein the sacrificial metal filler is one or more materials selected from zinc powder, zinc flakes, nickel powder, nickel flakes, magnesium powder, magnesium flakes, aluminum powder and aluminum flakes.

11. A composition according to claim 10, wherein the conductive filler is one or more materials selected from metal powder, glass fibers covered with metal, metal flakes, coal dust or graphite, and mica.

12. A composition according to claim 11, wherein the surface of the amorphous Si02 reinforcement filler has been. treated with hexamethyldisilazane or polydimethylsiloxane or silane.

13. A composition according to claim 12, wherein the metallic sacrificial filler is zinc powder or zinc flakes, and the conductive filler is glass fibers coated with metal. A composition according to claim 2, consisting essentially of: a) about 24 weight percent of a dimethyl-terminated dimethyl polysiloxane fluid having a viscosity of about 5,000 centipoise at 25 ° C; b) about 50 weight percent of one or more sacrificial metal fillers selected from zinc powder, zinc flakes, aluminum powder and aluminum flakes; c) about 10 weight percent of glass fibers covered with metal as a conductive filler; d) about 0.1 weight percent butyltin dilaurate; e) about 3 weight percent methyl tris- (meth I ethyl ketoxime) silane; f) about 1 weight percent of N- (2-aminoethyl-3-aminopropyl) trimethylsilane; g) about 2 weight percent of a mixture of amorphous and crystalline SiO 2 fillers having a specific gravity of 2.2 and a surface area of about 50m2 / g to about 130m2 / g; and h) about 10 weight percent of a solvent. 15. A method to protect a surface from corrosion and cathodic stress, comprising: (1) applying to the surface, a thin layer of one. organopolysiloxane rubber composition on the one hand, consisting essentially of the product obtained by mixing the following: a) from about 5 to about 80 weight percent of one or more polydiorganosiloxane fluids of the formula: HO [(R17) 2SiO] n (R17) 2SiOH wherein R17 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms, or a phenyl radical, which may contain from 3 to 9 halogen atoms, and n has a value average so that the viscosity is about 10 about 100,000 centipoise at 25 ° C; b) from about 10 to about 80 weight percent of one or more sacrificial metal fillers providing cathodic protection; c) from about 0 to about 15 weight percent of one or more conductive fillers; d) from about 0 to about 5 weight percent of an organometallic complex as a condensation catalyst of the formula: (R25) 2M (R26) 2 wherein R25 is a monovalent alkyl or alkenyl radical having from 1 to 10 carbon atoms or a phenyl radical, R26 is an alkyl or alkenyl radical, having from 1 to 10 carbon atoms or a phenyl radical having an organo-functional group and M is a metal; e) from about 0.1 to about 35 weight percent of one or more entanglement agents of the general formula: (X) 4. m - S i - R 12 m wherein R 12 is an alkyl, alkenyl or phenyl radical, X is an alkyl radical with a functional group selected from carboxyl, ketoximino, alkoxy, carbonyl or amine bonded directly to the silicone atom, and m is an integer from 1 to 2; f) of. about 0.2 to about 3 weight percent of an adhesion promoter of the formula: R22b I (R230) 3-b SiR24 wherein R22 and R23 are independently selected from monovalent alkyl or alkenyl radicals having from 1 to 8 carbon atoms or a phenyl radical, which optionally may be substituted with an alkyl radical having from 1 to 8 carbon atoms, and also it may contain from 3 to 9 halogen atoms, b is an integer from 0 to 3, and R24 is a saturated, unsaturated or aromatic hydrocarbon radical having from 1 to 10 carbon atoms, which may optionally contain organ-functional group; g) from about 0 to about 20 weight percent of an amorphous SiO 2 reinforcement filler, optionally surface treated, having a surface area of between about 50 to 250 m2 / g and a particle size scale of between approximately 0.01 to 0.03 microns; h) from 0 to 80 weight percent of a suitable solvent or diluent; and i) from 0 to 8 weight percent of a bifunctional chain extender of the general formula: wherein X 1 is alkoxy or ketoximino and R 8 is a monovalent alkyl or alkenyl radical having from 1 to 8 carbon atoms or a phenyl radical; (2) allowing the layer of the organopolysiloxane rubber composition of one part to cure at room temperature to a silicone elastomer. 16. A method according to claim 15, wherein n is selected so that the viscosity is from about 1,000 to about 20,000 centipoises at 25 ° C. 17. A method according to claim 16, wherein R17 is alkyl. 18. A method according to claim 17, wherein the sacrificial metal filler is one or more materials selected from zinc powder, zinc flakes, nickel powder, nickel flakes, magnesium powder, magnesium flakes, powder of aluminum and aluminum flakes. 19. A method according to claim 18, wherein the sacrificial metal filler is one or more materials selected from zinc powder and zinc flakes, and the conductive filler is glass fiber coated with metal. 20. A method according to claim 15, wherein the composition consists essentially of: a) about 24 weight percent of a dimethyl-terminated dimethyl polysiloxane fluid having a viscosity of 1,000 to 5,000 centipoise at 25 ° C; b) about 50 weight percent of one or more sacrificial metal fillers selected from zinc powder, zinc flakes, aluminum powder and aluminum flakes; c) about 10 weight percent of glass fibers covered with metal as a conductive filler; d) about 0.1 weight percent butyltin dilaurate; e) about 3 weight percent of methyl tris- (methyl ethyl ketoxime) silane; f) about 1 weight percent N- (2-aminoethyl-3-aminopropyl) trimethylsilane; g) about 2 weight percent of a mixture of amorphous and crystalline SiO 2 fillers having a specific gravity of 2.2 and a surface area of up to about 130m2 / g; and h) about 10 weight percent of a solvent.