SELF-HEALING CERAMIC COATING AND PROCESS FOR ITS FORMATION.

Abstract

An exterior body panel is provided, including a substrate shaped like the panel. A clear topcoat is applied over the panel. A moisture-cured polysilazane composition with intercalated disulfide fractions derived from disulfide monomers covers the topcoat. A ceramic-generating composition kit is also provided. One method for creating a ceramic coating over a topcoat covering an exterior panel involves combining a first part comprising a polysilazane and a solvent in which the polysilazane is dissolved, with a second part, stored separately from the first part, comprising a disulfide monomer to form a reactive gel. The reactive gel is applied to the topcoat in open air. After sufficient time, moisture curing of the reactive gel occurs, and with the evaporation of the solvent, the ceramic coating with disulfide bonds within it is formed.

Description

SELF-HEALING CERAMIC COATING AND PROCESS FOR ITS FORMATION FIELD OF INVENTION The present invention relates generally to the protection of surfaces for equipment and vehicles and, in particular, to a composition and a process for imparting a durable, self-healing ceramic coating to the surface of the equipment or vehicle. BACKGROUND OF THE INVENTION Exterior paint protection for vehicles has evolved to include base coats, a pigmented color coat, and a clear topcoat. As a result, a vehicle's exterior has a high-gloss finish. However, as the topcoat degrades through mechanical abrasion and chemical processes, the finish diminishes. To restore the finish and provide an additional layer of protection, waxes have traditionally been used. While waxes do offer some protection, that protection is typically short-lived, attracts dirt, and requires considerable labor to apply. Although reactive siloxane wax sealants have improved upon natural wax-based formulations, the durability of such sealants remains less than desirable, and streaks in them are difficult to correct. Another type of surface protection product is ceramic spray coatings. These products polish hard coatings that are difficult to refinish. The ceramic coating adds silica or titanium dioxide for a harder, longer-lasting protective layer. The purpose of these combined elements in a ceramic spray is to create a ceramic coating that keeps the car clean and shiny for a long time. Refinishing ceramic coatings is possible, but it can be costly for many users. As a result, a user should be familiar with a wide variety of materials used for exterior vehicle surfaces, including painted surfaces and glass. Although numerous ceramic coatings for automobiles are currently on the market, few are self-healing. As a result, any chipping or scratching of the coating must be repaired, which is time-consuming and expensive. Furthermore, if any damage penetrates the coating completely, the vehicle's clear coat is no longer protected and is exposed to the elements. Again, manual repair would be required to correct this defect, in addition to any damage that occurs to the clear coat and / or paintwork in the meantime. Those with self-healing properties only do so under conditions of high temperatures and / or harsh solvents that could damage the underlying substrate. Therefore, there is a need for a formulation and application process that overcomes the aforementioned limitations of the prior art by providing a ceramic coating to a vehicle's surface to retain the attributes of a ceramic coating while self-healing under less stringent conditions. There is also a need for the resulting coating. BRIEF DESCRIPTION OF THE INVENTION An exterior body panel is provided, including a substrate shaped to the panel. A clear topcoat is applied to the panel. A cured polysilazane or polysiloxane composition with intercalated disulfide fractions derived from disulfide monomers covers the final layer. A ceramic-generating composition kit is also provided, comprising a first part containing a polysilazane and a solvent in which the polysilazane dissolves. A second part, stored separately, contains monomer disulfide. Instructions are provided for combining the parts to form a moisture-reactive coating composition. One method for creating a ceramic coating over a top layer covering an exterior panel involves combining a first part containing a polysilazane or polysiloxane and a solvent in which the polysilazane or polysiloxane is dissolved, with a second part, stored separately from the first part, containing a disulfide monomer to form a reactive gel. The reactive gel is then applied to the top layer in open air. After sufficient time, moisture curing of the reactive gel occurs, and with the evaporation of the solvent, the ceramic coating with internal disulfide bonds is formed. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention is useful in forming a protective ceramic layer over a polymerized or resinous topcoat. A coating of the invention exhibits self-healing properties at reasonable temperatures, while also providing a high water contact angle of over 90° and high gloss. In the context of a vehicle, the topcoat is in turn overlaid with a pigmented color layer. Although the present invention will be detailed further with respect to a high-gloss vehicle exterior surface, it is appreciated that it is equally applicable to commercial equipment, furniture, countertops, and kitchen appliances where the topcoats also include polyurethane varnishes. The formation of a ceramic layer is halted by the formation of an intermediate that is subsequently activated to form a silicate, thus providing an opportunity for re-evaluation.In addition to saving the time and money needed to repair or reapply a damaged ceramic coating, an inventive coating provides superior long-lasting protection to the underlying surface. The numerical ranges cited in this document are intended to enumerate not only the final values ​​of said ranges, but also the individual values ​​included within the range and varying by individual units of the last significant digit. By way of example, a range from 0.1 to 1.0 in arbitrary units according to the present invention also encompasses 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9; each independently as lower and upper limit values ​​for the range. Table 1 lists the main components of a polysilizane modality of the ceramic coating composition of the invention. Table 1 - Formulation of a fully formulated inventive polysilizane composition of the invention Ingredient Percentage by Total Weight Polysilazane 10-remainder Solvent 0-10 Organic Disulfide* Stoichiometric Excess of Si-N Bonds Coupling Agent 0-5 Solvent 0-10 Wetting Agent 0-60 Volatile oil 0-5 Additives Each: 0-5 Stuffed 0-20 -stored separately from polysilazane until curing is desired A polysilazane is present in some inventive embodiments and is characterized by silicon-nitrogen linkages forming chains, rings, or combinations thereof, and is characterized by the formula [R1R2Si-NR3]n, where R1, R2, and R3 are each independently H, Ci-Cg alkyl, Cg-Cw aryl, and fluorinated alkyl and its aryls; and n is an integer from 2 to 30. Methylated polysilazanes and polysilazanes having trifluoropropyl constituents have been well studied for the modified hydrophobicity conferred relative to perhydropolysilazane. Rochow, E. G., Polymeric Methylsilazanes Pure and Applied Chemistry, vol. 13, no. 1-2, 1966, pp. 247-262; and Breed. LW et al “New Synthetic Methods for Silicon-Nitrogen Polymers, AD0908905, AFML-TR-69-20, Part IV, (Nov. 1972), pp. 16-20. Table 2 lists the main components of a polysiloxane modality of the ceramic coating composition of the invention. Table 2 - Formulation of a composition formulated entirely with polysiloxane of the invention Ingredient Percentage by Total Weight Polysiloxane 10-remainder Solvent 0-10 Organic Disulfide 1-5 Coupling Agent 0-5 Wetting agent Volatile oil 0-60 0-5 Additives Each: 0-5 Filler ______ 0-20 In still other embodiments, the coating is based on a polysiloxane present as a coating polymer. The polysiloxane is formed by the reaction of an organopolysiloxane containing ethylenic unsaturation with an organohydropolysiloxane and a disulfide-containing monomer or oligomer. The crosslinking polymer is generally a hydride-functionalized siloxane. Hydride-functionalized siloxanes used here for illustrative purposes include methylhydrosiloxane copolymer with 15–50 mol% methylhydrosiloxane, SiH-terminated polydimethylsiloxanes, and combinations thereof. The operational catalysts used herein include, among others suitable for promoting the reaction to form the polysiloxane, acids, bases, or a platinum complex in alcohol, xylene, divinylsiloxanes, or cyclic vinylsiloxanes. Part A contains the silicone with ethylene unsaturation and the catalyst, and Part B contains the hydride functional siloxane. It can be seen that a disulfide-containing monomer can be present in a silicone with ethylene unsaturation or in a hydride functional siloxane, either Part A or Part B. A solvent or solvent system is selected that is chemically compatible with polysilazane and in which the polysilazane is soluble or at least suspended. The solvents used here include, but not limited to, butyl acetate, xylene, n-butyl ether, diethylene glycol butyl ether acetate, methylcyclohexane, n-octane, and butyl titanate. It is observed that the film-forming properties of polysilazane as the solvent evaporates influence the quality of the polysilazane film; a film that is too thin is incomplete, while a film that is too thick tends to crack and craze upon heating. A disulfide monomer is present to crosslink with the polysilazane and is believed to be the functionality that imparts the self-healing attributes of the present invention. An operative disulfide in the present document is selected to include at least two reactive moieties under ambient humidity curing conditions separated by a sulfur-sulfur bond backbone. The operative disulfides in this document include, but are not limited to: allithiamine, cystine, dithionitrobenzoic acid, fursultiamine, glutathione disulfide, homocysteine, C2-C6 hydroxy(alkyl) disulfides, C2-C6 bis[(C2-C6 trialkoxysilyl)alkyl disulfides], dipentamethylenethiuram tetrasulfide, tetramethylthiuram disulfide, 2,2'-dithiobis(benzothiazole), thiram, C2-C6 alkyl thiram disulfide, prosultiamine, pyritinol, and combinations thereof. A coupling agent is present to promote adhesion to the underlying layers of the surface imperfection, namely the top layer alone, or the top layer and the underlying pigmented color layer; as well as improved bonding to an overlying ceramic coating.Coupling agents operative herein illustratively include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (3-glycidoxypropyl)bis(trimethylsiloxy)methylsilane, (3-glycidoxypropyl)methyldiethoxysilane, (3-glycidoxypropyldimethylethoxysilane, 3-(mercaptopropyl)triethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxypropyldimethylethoxysilane, methacryloxypropyldimethylmethoxysilane, etacryloxypropylmethyldimethoxysilane, methacryloxypropyltriethoxysilane, methoxymethyltrimethylsilane, 3-methoxypropyltrimethoxysilane, 38 methacryloxypropyldimethylchlorosilane, methacryloxypropylmethyldichlorosilane, methacryloxypropyltrichlorosilane, 3-isocyanatopropyldimethylchlorosilane, 3-isocyanatopropyltriethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfide, and combinations thereof. A volatile oil is present to provide a solution, a curable composition that flows onto a surface and, upon drying, creates a paste that can be polished to form a moisture-cured polysilazane layer with the disulfide. The volatile oils used here include C8-C1c alkanes, such as branched alkanes including, for example, isododecane, isodecane, and isohexadecane; and linear or cyclic silicone oils, which have 2 to 10 silicon atoms with substituents that in each occurrence are independently H, Cj-Cw alkyl, or Ci-Ciq alkoxy. The specific volatile silicone oils operating here include, but are not limited to, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, heptamethylhexyltrisiloxane, methyloctyltrisiloxane, hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, and dodecamethylpentasiloxane; and mixtures of any of the above. Various additives are readily incorporated into an inventive formulation, including, for example, light and heat stabilizers to maintain the clarity of the cured filler, adhesion promoters, flow control additives, pigments and colorants, and combinations thereof. Generally, each of the aforementioned additives is present independently at 0 to 5 percent by total weight. Although fillers are typically unnecessary in an inventive repair composition due to the small size of the microabrasions and surface imperfections being corrected, such fillers are optionally present to impart hardness and visual effects. The inclusion of fillers is particularly beneficial if a ceramic coating is not used to protect the UV-cured filler. The operative filler particles in the present invention include, but are not limited to, mica flakes, pigments, talc, alumina, silica, titania, microspheroids, and combinations thereof. An inventive repair composition typically has a fully formulated viscosity in the range of 100 to 1000 cps at 20°C and may flow before curing. It is understood that a substrate requiring repair is often mounted vertically or even inverted, so while the repair composition should flow slightly before drying to a paste consistency, it must also have sufficient viscosity to prevent excessive runoff from a vertical or inverted substrate. After application, the coating adheres to the polar residues extending from the substrate surface, such as the topcoat of a vehicle. The polysilazane then cures through a hydrolysis reaction with ambient moisture. Depending on environmental conditions, curing is complete between 8 and 72 hours after the initial application, while an initial curing step before polishing requires approximately 3 minutes. While not intended to be tied to any particular theory, it is believed that a polymer network composed of polysilazane and the organic disulfide forms to impart the self-healing characteristics to the resulting coating. Reversible disulfide bonds within the cured polymer network are readily formed under certain reaction conditions, thus providing the self-healing property to the coating of the invention. The reaction conditions for inducing disulfide cleavage include chemical exposures to reducing agents including monothiols, such as β mercaptoethanol (BME), dithiotritol (DTT); basic pH solutions such as NaOH solutions; basic surfactants; exposure to ultraviolet light; heat; or a combination thereof. After exposure to air expelled by a hot air gun for 1 to 10 minutes, the coating is capable of achieving a self-healing efficiency of up to 100%, which is defined by the following equation: where SHE is defined as the self-healing efficiency, where 0% represents a completely unhealed scratch and 100% represents a completely healed scratch; w0 is the initial width of a scratched / damaged region and w is the final width of a scratched / damaged region. Once the coating is in place and has been damaged, self-healing in this system occurs through three main steps: 1. The bulk lining undergoes viscous flow or slippage to fill the damaged region of the lining. To facilitate this process, a heat gun or other disulfide cleavage reaction inducer is used. 2. The polymer chains diffuse across the resulting interface. These first two steps are driven primarily by bulk transport phenomena. 3. Covalent bonds reform between unpaired sulfur atoms in the polymer chains (resulting from the breaking of covalent bonds upon coating damage) in adjacent chains, thereby restoring the overall mechanical properties of the material. This process is defined here as self-healing. For the first two phases to occur in the context of disulfide thermal scintillation, the temperature must be above a critical threshold of the glass transition temperature, Tg. Below Tg, the polymer chains within the coating are held in place and cannot move, resulting in either chain diffusion or limited bulk flow. Above Tg, the polymer chains become mobile, and chain diffusion / bulk flow is possible. To ensure that Tg is exceeded, a hot air gun is used. Typical Tg temperatures for inventive coatings range from 70 to 140 °C. Due to the crosslinking reaction between the polysilazane and the disulfide, the disulfide is packaged as a second part, while the polysilazane is packaged as a first part. The two parts are combined immediately before application, as gel formation begins at that point. The remaining components are divided between the two parts based solely on storage compatibility. An exemplary method for application includes: 1. Ensure the vehicle has been thoroughly washed, degreased and free of dirt / contaminants before applying the composition. 2. Combine a mixture of the first part containing a polysilazane or polysiloxane composition and a second part of disulfide solution, and mix well. Be sure to use only a small amount of each component, as the system can gel quickly. 3. Place the mixed coating onto a suede applicator pad or applicator sponge, 4. Rub the applicator over a small area of ​​the vehicle, noting where the application limits are. 5. Wait 3 minutes, 6. With a clean, dry microfiber towel, lightly polish the coated area until no more "cloudiness" is visible on the coated surface, and 7. Repeat steps 3 through 6 until the entire vehicle has been coated. If the mixed coating becomes too viscous for application, repeat step 2 with a smaller area to be coated. EXAMPLES These examples demonstrate the processes claimed in this patent application. It should be noted that other additions and modifications known in the art must also be covered. Example 1 An inventive composition is provided based on the first part containing: 10 percent by weight of butyl acetate, 24.5 percent by weight of octamethylcyclotetrasiloxane, 24.5 percent by weight of decamethylcyclopentasiloxane, 0.5 percent by weight of diethylene glycol monobutyl ether, 0.5 percent by weight of 3-(aminopropyl)tethoxysilane, and 22 percent by weight of polysilazane; with a second part containing 7 percent by weight of 2-hydroxyethyl disulfide and a butyl acetate residue. When the two parts are combined, a ceramic gel is formed which, when applied to a vehicle surface, forms a coating intentionally shaped to include spatter drips. Three minutes after application, the coating is polished to provide a hard ceramic layer with a contact angle with the surface of more than 90°. Example 2 The process from Example 1 is repeated with 6 percent by total weight of mica instead of a similar amount of decamethylcyclopentasiloxane. A similar curing profile results. Example 3 The coating of claim 1 is exposed to the output of a heat gun until the coating softens and flows to self-repair the drops. Example 4 An inventive composition based on the first part is provided, comprising: 29.3 percent by weight of diethyldithoxysilane, 11.7 percent by weight of tetraethyl orthosilane, 1.7 percent by weight of silicon tetrachloride, 0.9 percent by weight of tetrabutyl orthotitanate, and 2.5 percent by weight of bis[(triethoxysilyl)propyl] disulfide, combined with 50 percent by weight of butyl acetate and a polyether siloxane copolymer residue (approximately 4 percent by weight). Following acid curing, a ceramic gel is formed which, when applied to a vehicle surface, forms a coating intentionally shaped to include spattered drips. Three minutes after application, the coating is polished to provide a hard ceramic layer with a contact angle to the surface of more than 90°. Example 5 The process of Example 4 is repeated with the exclusion of silicon tetrachloride and a base catalyst with an increased molar equivalent of tetraethyl orthosilicate. The resulting coating has similar properties. Example 6 The process from Example 5 is repeated with a platinum catalyst instead of the base. The resulting coating has similar properties. The patent documents and publications mentioned in this specification are indicative of the skill levels of those skilled in the art to which the invention belongs. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication were specifically and individually incorporated by reference. The foregoing description is illustrative of particular embodiments of the invention, but is not intended to limit its practice. The following claims, including all their equivalents, are intended to define the scope of the invention.

Claims

1. An exterior body panel characterized in that it comprises: a substrate having a panel shape; a transparent top layer on said substrate; a cured composition of polysilazane or polysiloxane with intercalated disulfide moieties derived from disulfide monomers.

2. The panel according to claim 1, characterized in that said polysilazane is present and is a perhydrosilazane.

3. The panel according to claim 1, characterized in that said polysilazane has the formula [R1R2Si-NR3]n wherein R1, R2 and R3 are each independently CrC6 alkyl, C6-C10 aryl, fluorinated Ct-C6 alkyl, fluorinated C6-C10 aryl; and n is an integer value from 2 to 30.

4. The panel according to claim 1, characterized in that said polysiloxane is present.

5. The panel according to any of claims 1 to 3, characterized in that it further comprises a silane coupling agent.

6. The panel according to any one of claims 1 to 4, characterized in that said disulfide monomers include at least one of: allithiamine, cystine, dithionitrobenzoic acid, fursultiamine, glutathione disulfide, homocysteine, C2-C6 hydroxy(alkyl) disulfides, C2-C6 bis[(trialkoxysilyl)alkyl] disulfides, dipentamethylenethiuram tetrasulfide, tetramethylthiuram disulfide, 2,2'-dithiobis(benzothiazole), thiram, C2-C6 alkyl thiram disulfide, prosultiamine, pyritinol, and combinations thereof.

7. A ceramic generating composition kit characterized in that it comprises: a first part comprising: a polysilazane or polysiloxane; and a solvent in which said polysilazane or said polysiloxane is dissolved; a second part stored separately from said first part and comprising a disulfide monomer; and instructions for combining said part A and said part B to form a coating composition.

8. The composition according to claim 6, characterized in that it further comprises a silane coupling agent.

9. The composition according to claim 6 or 7, characterized in that it further comprises at least one additive of a photostabilizer, a thermostabilizer, an adhesion promoter, a flow control additive, a pigment, a colorant or a combination thereof.

10. The composition according to any of claims 6 to 8, characterized in that it further comprises a particulate filler.

11. The composition according to any of claims 6 to 9, characterized in that it further comprises a volatile oil miscible with said solvent; 12. A method for creating a ceramic coating on a top layer covering an exterior panel, characterized in that it comprises: combining a first part comprising: a polysilazane or a polysiloxane, a solvent in which said polysilazane or said polysiloxane is dissolved, with a second part stored separately from said first part and comprising a disulfide monomer to form a reactive gel; applying said reactive gel to the top layer outdoors; and allowing sufficient time for moisture curing of said reactive gel and evaporation of said solvent to form the ceramic coating with disulfide bonds therein.

13. The method according to claim 11, characterized in that the sufficient time is from 1 to 10 minutes.

14. The method in accordance with any of claims 11 or 12, characterized in that it further comprises cleaning the final layer before said application.

15. The method according to any of claims 11 to 13, characterized in that the disulfide monomer is present in a solution and a silane coupling agent is present in said reactive gel.

16. The method in accordance with any of claims 11 to 14, characterized in that it further comprises a volatile oil in said reactive gel.

17. The method in accordance with any of claims 11 to 15, characterized in that it further comprises a self-healing ceramic coating.

18. The method according to claim 16, characterized in that said self-repair comprises breaking the disulfide bonds and allowing said ceramic coating to flow, further comprising forming a dam around said repair composition prior to said exposure.

19. The method according to claim 17, characterized in that the breaking of the disulfide bonds occurs under the reaction conditions of at least one of the following: chemical exposures to reducing agents, basic pH solutions; exposure to ultraviolet light; heat; or a combination thereof.

20. The method according to claim 18, characterized in that the reaction condition is the application of heat above the glass transition temperature of said ceramic coating.

21. The method according to claim 19, characterized in that the heat is applied with a heat gun.