AQUEOUS SILICONE ELASTOMERS AS ANTI-GRAFFITI COATINGS

Abstract

A method that includes coating a composition containing liquid aqueous silicone elastomer onto an architectural surface, a signage surface, a constructed landscape surface, or a commercial superstructure surface, and then drying the composition containing liquid aqueous silicone elastomer to the point of forming an anti-graffiti coating containing silicone elastomer on the architectural surface, signage surface, constructed landscape surface, or commercial superstructure surface.

Description

AQUEOUS SILICONE ELASTOMERS AS ANTI-GRAFFITI COATINGS BACKGROUND Current anti-graffiti coatings fall into two categories: sacrificial and permanent. Sacrificial coatings are removed along with the graffiti during any cleaning process and require reapplication after each graffiti removal. Permanent anti-graffiti coatings remain after graffiti removal and continue to provide graffiti protection to the substrate through multiple cleaning and labeling cycles. Silicone-based coatings are considered premier permanent anti-graffiti products because their low surface energy makes them difficult for non-silicone-based paints to adhere to. Current silicone-based anti-graffiti coatings are room-temperature vulcanizing (RTV) silicone rubbers diluted in solvents with high volatile organic compounds (VOCs) and require solvents for equipment cleaning.This increases environmental problems, exposes workers to hazardous solvents, and is more dangerous to transport and store since most organic solvents are flammable. BRIEF DESCRIPTION A method is described herein comprising: coating an architectural surface with a composition containing a liquid aqueous silicone elastomer, CARI CARI a signage surface, a constructed landscape surface, or a commercial superstructure surface, and then dry the composition containing liquid aqueous silicone elastomer that results in the formation of an anti-graffiti coating containing silicone elastomer on the architectural surface, signage surface, constructed landscape surface, or commercial superstructure surface. The above will become more evident from the following detailed description. DETAILED DESCRIPTION This document describes the use of a composition containing aqueous silicone elastomer in anti-graffiti coatings for a surface. The aqueous silicone anti-graffiti coating reduces VOC emissions, is water-based, and is non-flammable for easier storage and handling. Illustrative surfaces include an architectural surface, a signage surface, a built landscape surface, or a commercial superstructure surface. For example, an architectural surface might be the surface of a building. For example, a signage surface might be the surface of a sign (e.g., a highway sign). For example, a built landscape surface might be the surface of a wall. CARI is a type of sealant used to seal surfaces, decorative walls, or statues. For example, a commercial superstructure surface might be a bridge or overpass. The silicone-containing composition is applied directly to a surface as a sprayable, brushable, or rollerable liquid. In certain applications, the surface may be wood, engineered wood composite, plastic, concrete, metal, glass, brick, masonry, an exterior insulation and finish system (EIFS), stone, or fiberglass. The silicone-containing composition can also be applied to painted surfaces (e.g., painted concrete walls). Such paints are typically architectural paints (e.g., from Sherwin-Williams, Home Depot, etc.) that are usually acrylic latex-based. The aqueous silicone elastomer can be used as the sole binder in the coating composition, meaning that the aqueous silicone elastomer does not need to be mixed with another binder. In certain embodiments, the coating described herein is applied on-site to a supporting surface. In certain embodiments, the supporting surface may be a building surface, sign, or wall. The coating containing silicone elastomer exhibits advantageous weather resistance, water resistance, flexibility, and elongation even at extreme temperatures. I BELIEVED The coating containing silicone elastomer exhibits superior elongation and high tensile strength, even at temperatures as low as -20°C. For example, the coating containing silicone elastomer can have an elongation of at least 500%, and more specifically at least 700%, at room temperature. The coating containing silicone elastomer can have an elongation of at least 500%, and more specifically at least 700%, at -20°C. The coating containing silicone elastomer can have a tensile strength of at least 500 psi, and more specifically at least 600 psi, at room temperature. The coating containing silicone elastomer can have a tensile strength of at least 500 psi, and more specifically at least 600 psi, at -20°C. In certain forms, the anti-graffiti coating has a dry thickness of 0.1 to 30 mils. The coating containing silicone elastomer also exhibits superior weather and UV stability when tested in the QUV accelerated climatometer. For example, the coating containing silicone elastomer can have a mass retention of at least 95%, and more specifically at least 97%, over a 2000-hour QUV period. The coating containing silicone elastomer can have a gloss retention of at least 90%, and more CARI, in particular, at least 95%, during a 2000-hour QUV period. The coating containing silicone elastomer may have a color loss of less than ΔE during a 2000-hour QUV period. The improved weather resistance and physical properties are beneficial for the coating to retain its physical properties under extreme cold for regions that regularly experience harsh winters. Additionally, the composition containing silicone elastomer is naturally clear. This natural clarity allows for the option of formulating the silicone elastomer composition to any desired color by adding color additives. Aqueous silicone elastomer and compositions containing the elastomer. An aqueous silicone elastomer can be any silicone that forms an elastomer in an aqueous system. An aqueous silicone elastomer is free of any solvents, particularly volatile organic compounds (VOCs), other than water. Several illustrative aqueous silicone elastomers are described below. In one embodiment, an aqueous silicone elastomer can be manufactured using cyclic monomer(s) as a starting reagent via ring-opening polymerization. This method uses cyclic siloxane monomers such as hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), or decamethylcyclopentasiloxane (D5). They differ only in the number of siloxane units on the ring. D3 has three siloxane units, D4 has four, and D5 has five. D4 is the most commonly used cyclic monomer for ring-opening polymerization (ROP). Cyclic monomers are polymerized by a strong acid catalyst that also acts as an emulsifying agent, known as a surfcat. A surfcat is typically any sulfuric or sulfonic acid, or a salt thereof, that includes a fatty acid or fatty ester portion. Illustrative surfcats include dodecylbenzenesulfonic acid, sodium lauryl sulfate, sodium olefin sulfonate, and sodium dioctyl sulfosuccinate. If the surfcat is in its acidic form, it can be used as is. If it is neutralized to form a salt, then the acidic form of the catalyst must be regenerated using another strong acid similar to HCl or H₂SO₄. Surfactants other than the surfcat may be used (optional), such as nonionic surfactants or anionic surfactants that are not strong acids. The cyclic monomer and the surfactant are emulsified together with water and any optional surfactants or crosslinkers. If the salt form of a surfactant is used (such as sodium lauryl sulfate), then the acidic form of the surfactant is regenerated by adding a stronger acid. CARI CARI is similar to HCl or H₂SO₄. The emulsion is then allowed to polymerize either at room temperature or by heating the mixing vessel to 60–90°C. This opens the ring of the cyclic monomer and the chain extends, creating the very high molecular weight linear polydimethylsiloxane. For example, polydimethylsiloxane can have a molecular weight of 250,000–500,000 g / mol. In certain forms, 85-90% of the cyclic monomers are converted into a linear polydimethylsiloxane, and polymerization can take as much as three weeks under ambient conditions. Optionally, a crosslinking agent such as a silane or colloidal silica can be added during polymerization. The surfactant is then neutralized to stop polymerization by adding a base. This can be any base such as an amine, a metal hydroxide, or a metal carbonate. The emulsion is then converted from a silicone oil emulsion to a silicone rubber dispersion via crosslinking by adding a colloidal silica-like filler, a silane-like crosslinker (optional), and an organotin catalyst. Methyltrimethoxysilane is the preferred silane. The organotin catalyst can be either divalent or tetravalent tin. A divalent CARI can be any organotin with an oxidation state of 2+ and organic ligands. Examples include tin(II) ethylhexanoate, tin(II) acetylacetonate, and tin(II) acetate. A tetravalent tin catalyst can be any organotin with an oxidation state of 4+, two covalently bonded organic groups, and two ligands. Examples include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate. The resulting product is an aqueous dispersion of crosslinked polydimethylsiloxane. In certain embodiments, the resulting product is a dimethylsiloxysilsesquioxane. In certain embodiments, the resulting product has a molecular weight of 100,000 to 500,000 g / mol. In certain embodiments, the resulting product has a solids content of 5–75% by weight, preferably 40–60%. In certain forms, the resulting product may have a viscosity of 100 cPs to 10000 cPs, preferably 100 to 500 cPs, at 23°C. In a second modality, an aqueous silicone elastomer can be manufactured via linear monomer(s) as a starting material. In this modality, the starting material is a linear polydimethylsiloxane terminated with silanol (Si-OH) groups, which allow polymerization via acid-catalyzed condensation. These silanol fluids are classified based on their viscosity, and much more. Useful CARI for this polymerization method are those in the range of 1 - 200 cPs at 23°C. This modality may include an optional crosslinking agent as in the ROP method described above. This method also uses a surfcat, as in the ROP method described above. Other surfactants, such as non-ionic surfactants, etc., can be used optionally in addition to the surfcat. The silanol fluid, any of the optional ingredients, the surfcat, and water are emulsified together. If the salt form of a surfcat is used, the surfcat is activated by the addition of a strong acid such as HCl or H₂SO₄. The emulsion is then allowed to polymerize either at room temperature or by heating the container. Polymerization is stopped by the addition of a base such as an amine, metal hydroxide, or metal carbonate. The emulsion is then converted from a silicone oil emulsion to a silicone rubber dispersion via crosslinking by adding a colloidal silica-like filler, a silane-like crosslinker (optional), and an organotin catalyst. Methyltrimethoxysilane is the preferred silane. The organotin catalyst can be either a divalent tin or a tetravalent tin catalyst. The divalent tin catalyst can be any organotin with an oxidation state of +2 and organic bonds. Examples include tin(II) ethylhexanoate, tin(II) acetylacetonate, and tin(II) acetate. The tetravalent tin catalyst can be any organotin with an oxidation state of +4, two covalently bonded organic groups, and two other bonds. Examples include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate.The emulsion is then converted from a silicone oil emulsion to a silicone rubber dispersion via crosslinking by adding a colloidal silica-like filler, a silane-like crosslinker (optional), and an organotin catalyst. Methyltrimethoxysilane is the preferred silane. The organotin catalyst can be either a divalent tin or a tetravalent tin catalyst. The divalent tin catalyst can be any organotin with an oxidation state of 2+ and organic ligands. Examples include tin(II) ethylhexanoate, tin(II) acetylacetonate, and tin(II) acetate. The tetravalent tin catalyst can be any organotin with an oxidation state of 4+, two covalently bonded organic groups, and two ligands. Examples include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate. In certain forms, 99-100% of the monomers Linear CRRI molecules are converted into a polymer, and polymerization takes 8-24 hours under ambient conditions. The resulting product is an aqueous dispersion of crosslinked polydimethylsiloxane. A third method involves direct emulsification without polymerization. In this method, a linear, silane-terminated polydimethylsiloxane fluid, similar to the second method, is used. However, the MW / viscosity of the starting fluid is much higher (10,000–100,000 cPs at 23°C), and no polymerization takes place. No surfactant is used in the third method; only a nonionic surfactant(s) are employed. The fluid of silanol, surfactant(s), and water are emulsified. The emulsion is then converted from a silicone oil emulsion to a silicone rubber dispersion via crosslinking by adding a colloidal silica-like filler, a silane-like crosslinker (optional), and an organotin catalyst. Methyltrimethoxysilane is the preferred silane. The organotin catalyst can be either a divalent tin or a tetravalent tin catalyst. The divalent tin catalyst can be any organotin with a 2+ oxidation state and organic bonds. Examples include tin(II) ethylhexanoate, tin(II) acetylacetonate, and CARI CARI tin(II) acetate. The tetravalent tin catalyst can be any organotin with an oxidation state of 4+, two covalently bonded organic groups, and two ligands. Examples include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate. The emulsion is then converted from a silicone oil emulsion to a silicone rubber dispersion via crosslinking by adding a colloidal silica-like filler, a silane-like crosslinker (optional), and an organotin catalyst. Methyltrimethoxysilane is a preferred silane. The organotin catalyst can be either divalent tin or tetravalent tin. The divalent tin catalyst can be any organotin with an oxidation state of 2+ and organic ligands. Examples include tin(II) ethylhexanoate, tin(II) acetylacetonate, and tin(II) acetate.The tetravalent tin catalyst can be any organotin with an oxidation state of 4+, two covalently bonded organic groups, and two ligands. Examples include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate. The resulting product is an aqueous dispersion of crosslinked polydimethylsiloxane. Additives can be included with the aqueous silicone elastomer to formulate a coating composition > your final NCNNC. Illustrative additives include fillers, pigments, binders, defoamers, rheology modifiers, or other common paint additives. For example, aqueous silicone elastomer can optionally be mixed with at least one filler such as calcium carbonate, nepheline syenite, barium sulfate, diatomaceous earth, kaolin clay, pumice, etc. The composition can be tinted any color by mixing the aqueous silicone elastomer with a pigment. For example, the aqueous silicone elastomer can be optionally mixed with titanium dioxide, or other white pigments, making the coating bright white. In another example, the aqueous silicone elastomer can be optionally mixed with aluminum flake pigments, making the coating silver. The coating composition may also optionally include a binder. For example, the aqueous silicone elastomer can be blended with a water-based, organic binder such as an acrylic or polyurethane. The acrylic or polyurethane binder can be an acrylic latex or a polyurethane dispersion with a pH >7. The amount of binder included in the composition can vary from 5–30% by weight, based on the wet weight of the total composition. CARI In certain forms, the silicone elastomer Aqueous CREI in the final coating composition is present in an amount of 35-99% by weight, based on the wet weight of the total composition. Examples Property Value Unit of Measurement Test Method Graffiti Removal Cleanability 1 Graffiti completely removed by high-pressure cold water wash ASTM D7089 Graffiti Removal Wipe clean Permanent marking ASTM D6578 Graffiti Removal Isopropyl alcohol wipeable Acrylic spray paint ASTM D6578 Graffiti Removal Isopropyl alcohol wipeable Alkyd spray paint ASTM D6578 Graffiti Removal Wipe clean Wax crayon ASTM D6578 Graffiti Removal Detergent wipeable Ballpoint pen ASTM D6578 Graffiti Removal Wipe clean Water-based marker ASTM D6578 ASTM D6578 The coating was applied to a wood substrate using a brush and allowed to cure at room temperature for 7 days. The panels were tagged with graffiti in 1x1 squares and allowed to settle at room temperature for 24 hours, then evaluated for graffiti removal. An attempt was made to remove each marking material from the panel using a cotton cloth alone, then using a cotton cloth moistened with the following cleaning agents, working through them in the order listed (increasing resistance): (a) mild detergent (b) isopropyl alcohol (IPA) > your NCNNC CARI (c) mineral spirits (d) xylene (e) methyl ethyl ketone (MEK) The results for each of the 5 graffiti marking materials are listed in the table above. ASTM D7089 The coating was applied to the concrete substrate by spraying and allowed to cure naturally for 7 days. The graffiti was then applied by spraying with a 10-can can (Fred Meyers Krylon Exterior Gloss Enamel) and allowed to cure for 7 days. The wall was then pressure washed at 2500 PSI. The graffiti was completely removed without damaging the silicone coating underneath. In view of the many possible embodiments to which the principles of the described invention can be applied, it should be recognized that the embodiments illustrated are only preferred examples of the invention and should not be taken as limiting the scope of the invention.

Claims

1. A method, characterized in that it comprises: coating a composition containing liquid aqueous silicone elastomer onto an architectural surface, a signage surface, a built landscape surface, or a commercial superstructure surface, and then drying the composition containing liquid aqueous silicone elastomer resulting in the formation of an anti-graffiti coating containing silicone elastomer on the architectural surface, the signage surface, the built landscape surface, or the commercial superstructure surface.

2. The method according to claim 1, characterized in that the anti-graffiti coating has a dry thickness of 0.1 to 30 mils.

3. The method according to claim 1 or 2, characterized in that the coating comprises spraying a composition containing liquid aqueous silicone elastomer.

4. The method according to claim 1 or 2, characterized in that the coating comprises a roller coating of the composition containing liquid aqueous silicone elastomer.

5. The method according to any of claims 1 to 4, characterized in that the liquid aqueous silicone CREI elastomer comprises a dimethyl siloxy silsesquioxane produced from the ring-opening polymerization of at least one cyclic siloxane monomer.

6. The method according to any of claims 1 to 4, characterized in that the liquid aqueous silicone elastomer is produced from at least one linear polydimethylsiloxane that is terminated with at least one silanol group.

7. The method according to any of claims 1 to 6, characterized in that the aqueous silicone elastomer is the only film-forming polymer present in the composition.

8. The method according to any of claims 1 to 7, characterized in that the aqueous silicone elastomer in the composition is present in an amount of 35-99% by weight, based on the wet weight of the total composition.

9. The method according to claim 5, characterized in that the cyclic siloxane monomer is hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane or decamethylcyclopentasiloxane.