Coating processes – Optical element produced – Transparent base
Reexamination Certificate
2000-06-22
2002-12-31
Moore, Margaret G. (Department: 1712)
Coating processes
Optical element produced
Transparent base
C427S386000, C427S387000, C106S287110
Reexamination Certificate
active
06500486
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to coating compositions, and more particularly, to polyorganosiloxane compositions forming mar-resistant coatings on substrates and to controlling the tintability of the mar-resistant coatings after formation on a substrate.
2. Background of the Art
A variety of substrates, including those made of glass, plastic, metal, or concrete, are usefully coated with protective films. It is generally desirable that protective film coatings have good weathering properties, strong adhesion to the substrate, as well as resistance to thermal shock, mechanical shock, heat, humidity, and common chemicals. It is also desirable that the protective film coatings be practical to apply, dry, and cure. These properties are more difficult to achieve when the protective film coating is applied to polymeric or plastic substrates than when applied to many other substrates because of the greater susceptibility of these synthetic substrates, especially where the need for mar resistance is highest.
Some plastic substrates are desirable substitutes for glass due to a lower density than glass, economically advantageous fabrications, and breakage resistance. However, commercially available plastic substrates tend to have a reduced resistance to surface damage such as abrasion, marring, and scratching when compared to glass. Therefore, protective film coatings for plastic substrates are of particular interest to a wide range of industries where plastics are used.
Several technical approaches have been attempted in an effort to coat plastic substrates to improve resistance to abrasion, marring and scratching of the plastic substrates. Among the various classes of materials used to provide protection to polymeric substrates have been polysiloxanes, epoxy resins, acrylic (both acryloyl and methacryloyl) resins, urethanes, titanate esters, and ambifunctional polymeric compositions with multiple classes of polymer functionalities (e.g., acryloylsilanes, epoxysilanes, etc.). In particular, substantial work has been carried out to develop coatings of polyorganosiloxanes cross-linked by a condensation of silane or silanol groups.
U.S. Pat. No. 3,837,876 (Mayasumi et al.) describes a reaction of an aminosilane with an epoxysilane to produce a substance dissolvable in a solvent. Once dissolved, the substance was applied to various substrates to coat the substrates and form a mar-resistant coating on the surface.
U.S. Pat. No. 3,166,527 (Ender) describes mixing an epoxysilane with an aminosilane to make an unpolymerized mixture and a polymerized mixture. Each of the mixtures was applied to a surface to coat the surface. The coating made by each mixture was cured either by standing at ambient temperature or by heating.
U.S. Pat. No. 3,961,977 (Koda) describes a use of an aminoalkoxysilane hydrolyzed within a range of 10 to 40% of hydroxyl groups and an epoxyalkoxysilane to make a coating mixture. The hydrolyzed aminoalkoxysilane and epoxyalkoxysilane were dissolved in a solvent. Solvents described included a ketone.
U.S. Pat. No. 4,378,250 (Treadway) describes the use of ketones or aldehydes in making a mar-resistant coating. In particular, Treadway describes hydrolyzing at least two different silane materials to above 40% hydrolysis to form a reaction mixture. Treadway also describes adding the ketone to the reaction mixture to form a ketimine. The reaction mixture is then applied to a substrate and cured.
U.S. Pat. No. 5,786,032 describes a process for manufacturing an abrasion-resistant coating that adheres well to the substrate and is clear, transparent, colorless, and free of visible specs. The coating is also highly tintable and is strongly adherent to the substrate even after tinting or exposure to heat and humidity. The process comprises partially hydrolyzing an aminosilane having hydrolyzable groups to form an aminosilane hydrolyzate; adding a non-silane epoxy prepolymer to the aminosilane hydrolyzate to form a first mixture; partially polymerizing the first mixture to form a second mixture; adding a solvent to the second mixture to form a third mixture; applying the third mixture to a substrate and curing the third mixture on the substrate to make the tintable and abrasion resistant coating. The first mixture may consist essentially of the aminosilane hydrolyzate and the non-silane epoxy prepolymer. Although this composition provided a unique capability of mar-resistance and tintability after formation, the coating tended to be too tintable with certain materials, making application of a full range of colors to a single lens type more difficult.
SUMMARY OF THE INVENTION
The present invention comprises an abrasion-resistant coating that adheres well to the substrate and is clear, transparent, colorless, and free of visible specs. The coating is also controllably tintable and is strongly adherent to the substrate even after tinting or exposure to heat and humidity. The coating composition includes a solvent, an epoxy resin composition, an aminosilane, and an hydrocarbyltrihydrocarboxysilane, such as an alkyltrialkoxysilane. The aminosilane may be a partially hydrolyzed aminosilane that is effectively blocked from reacting with the epoxy resin composition at ambient temperature. The coating composition is applied to the substrate and then treated to remove any block from the hydrolyzable aminosilane such that the aminosilane and the epoxy resin composition react to form an abrasion-resistant coating.
DETAILED DESCRIPTION OF THE INVENTION
It is not easy to modify only a single significant property of a film without adverse modification of other properties of films. This is particularly true where some significant properties of the film are related by the underlying nature of the properties or the components of the film that contribute to these properties. This is particularly the case when dealing with a film such as an abrasion resistant mar-resistant coating where many of the properties are tied to the structure of the polymeric network. For example, both chemical resistance and mar resistance are in part tied to the tightness and surface organization of the polymer chains. To whatever degree that tightness and organization is altered to modify one property, the other property is likely to be affected. There is also no assurance that one property can be adjusted within the desired range while maintaining one or a myriad of properties that are necessary for a specific type of commercial product. Such is the case where the high quality, tintable mar-resistant coating of the prior art represented by U.S. Pat. No. 5,786,032 was found to have too rapid a rate of absorption of dye from tinting solutions. Even having discovered this limitation on the use of that composition, there was no assurance that any chemical modification of the composition could have been predicted to provide reduced tintability, maintain an acceptable level of abrasion resistance, and maintain the high level of optical quality and other attributes essential across a wide range of properties that are necessary in a composition to be used as a coating on an ophthalmic lens.
The present invention includes a coating composition that includes a solvent, an epoxy resin that undergoes epoxy polymerization, and an aminosilane in combination with 2 to 60% by weight of a hydrocarbyltrihydrocarbyloxysilane. A particularly desirable coating composition utilizes a partially hydrolyzed aminosilane that is effectively blocked from reacting with the epoxy resin at ambient temperature to provide an exceptionally durable coating that is cross-linked by silanol condensation in combination with the hydrocarboxytrihydrocarbyloxysilane. The present invention also includes a method for making a coating cross-linked by silanol condensation that includes partially hydrolyzing an aminosilane to a degree that is greater than 10% of complete molar reaction, mixing the partially hydrolyzed aminosilane with an agent blocking epoxy polymerization such as a ketone or an aldehyde to f
Anderson Elaine M.
Hage Martin L.
Hughes Frank J.
Koev Luben G.
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