Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1998-02-27
2002-02-12
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S447000, C428S450000, C428S451000, C428S452000, C428S540000, C428S541000
Reexamination Certificate
active
06346331
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coating compositions, and more particularly but not by way of limitation, to coating compositions which, when cured, provide substantially transparent coatings having enhanced abrasion resistance. In one aspect, the present invention relates to a coating composition having improved stability wherein the coating compositions are derived from aqueous-organic solvent mixtures containing effective amounts of epoxy functional silanes, tetrafunctional silanes and multifunctional compounds such as multifunctional carboxylic acids, multifunctional anhydrides, and mixtures thereof.
2. Description of Prior Art
The prior art is replete with compositions which, when applied to substrates and cured, provide transparent, abrasion resistant coatings for the substrates. Such coatings are especially useful for polymeric substrates where it is highly desirable to provide substrates with abrasion resistant surfaces, with the ultimate goal to provide abrasion resistant surfaces which are comparable to glass. While the compositions of the prior art have provided transparent coating compositions having improved abrasion resistant properties, such prior art compositions are generally lacking when compared to glass. Thus, a need has long existed for improved compositions having improved stability and which, when applied to a substrate, such as a polymeric substrate, and cured provide transparent, highly abrasion resistant coatings. It is to such compositions and processes by which such compositions are manufactured and applied to substrates that the present invention is directed.
BRIEF SUMMARY OF THE INVENTION
The present invention provides compositions having improved stability which, when applied to a variety of substrates and cured, form transparent coatings having superior abrasion resistant properties. Broadly, the coating compositions of the present invention comprise an aqueous-organic solvent mixture containing from about 10 to about 99.9 weight percent, based on the total solids of the composition, of a mixture of hydrolysis products and partial condensates of an epoxy functional silane and a tetrafunctional silane and from about 0.1 to about 30 weight percent, based on the total solids of the composition, of a multifunctional compound selected from the group consisting of multifunctional carboxylic acids, multifunctional anhydrides and combinations thereof. The epoxy functional silane and the tetrafunctional silane are present in the aqueous-organic solvent mixture in a molar ratio of from about 0.1:1 to about 5:1. The coating compositions of the present invention may further include from about 0.1 to about 50 weight percent of a mixture of hydrolysis products and partial condensates of one or more silane additives, based on the total solids of the composition, and/or an amount of colloidal silica or a metal oxide or combinations thereof equivalent to from about 0.1 to about 50 weight percent solids, based on the total solids of the composition.
It is an object of the present invention to provide coating compositions having improved stability which form transparent coatings upon curing. It is a further object of the present invention to provide stable coating compositions which form transparent coatings upon curing having improved abrasion resistance.
Other objects, advantages and features of the present invention will become apparent upon reading the following detailed description in conjunction with the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to coating compositions having improved stability which, when applied to a variety of substrates and cured, form substantially transparent abrasion resistant coatings having a Bayer number of at least 5 when tested in accordance with the variation of the Oscillating Sand Test (ASTM F735-81) hereinafter described.
For testing abrasion resistance of coated substrates, any of a number of quantitative test methods may be employed, including the Taber Test (ASTM D-4060), the Tumble Test and the Oscillating Sand Test (ASTM F735-81). In addition, there are a number of qualitative test methods that may be used for measuring abrasion resistance, including the Steel Wool Test and the Eraser Test. In the Steel Wool Tests and the Eraser Test, sample coated substrates are scratched under reproducible conditions (constant load, frequency, etc.). The scratched test samples are then compared and rated against standard samples. A semi-quantitative application of these test methods involves the use of an instrument, such as a Spectrophotometer or a Colorimeter, for measuring the scratches on the coated substrate as a haze gain.
The measured abrasion resistance of a cured coating on a substrate, whether measured by the Bayer Test, Taber Test, Steel Wool Test, Eraser Test, Tumble Test, etc. is a function, in part, of the cure temperature and cure time. In general, higher temperatures and longer cure times result in higher measured abrasion resistance. Normally, the cure temperature and cure time are selected for compatibility with the substrate; although, sometimes less than optimum cure temperatures and cure times are used due to process and/or equipment limitations. It will be recognized by those skilled in the art that other variables, such as coating thickness and the nature of the substrate, will also have an effect on the measured abrasion resistance. In general, for each type of substrate and for each coating composition there will be an optimum coating thickness. The optimum cure temperature, cure time, coating thickness, and the like, can be readily determined empirically by those skilled in the art.
Within the Ophthalmic Industry, the Oscillating Sand Test is presently the most widely used and accepted method for measuring abrasion resistance. Since the original ASTM application of the Oscillating Sand Test was for testing flat polymeric sheets, the test method has necessarily been modified for use with ophthalmic lenses. There is currently no ASTM accepted standard (or other industry standard) for this test as applied to ophthalmic lenses; therefore, there are a number of basic variations of the Oscillating Sand Test in practice.
In one particular variation of the Oscillating Sand Test, a sand cradle is modified to accept coated sample lenses and uncoated reference lenses. Typically, poly(diethylene glycol-bis-allyl carbonate) lenses, hereinafter referred to as ADC lenses, are used as the reference lenses. The lenses are positioned in the cradle to allow a bed of abrasive material, either sand or a synthetically prepared metal oxide, to flow back and forth across the lenses, as the cradle oscillates back and forth at a fixed stroke, frequency and duration.
In the test method employed to determine the abrasion resistance of the coating compositions of the present invention, a commercially available sand sold by CGM, Inc., 1463 Ford Road, Bensalem, Pa., was used as the abrasive material. In this test, 877 grams of sifted sand (600 ml by volume) was loaded into a 9 {fraction (5/16)}″×6 ¾″ cradle fitted with four lenses. The sand was sifted through a #5 Mesh screen (A.S.T.M.E.-11 specification) and collected on a #6 Mesh screen. Each set of four lenses typically two ADC lenses and two coated lenses, was subjected to a 4 inch stroke (the direction of the stroke coinciding with the 9 {fraction (5/16)}″ length of the cradle) at a frequency of 300 strokes per minute for a total of 3 minutes. The lens cradle was then repositioned by turning 180 degrees and then subjected to another 3 minutes of testing. Repositioning of the cradle was used to reduce the impact of any inconsistencies in the oscillating mechanism. The ADC reference lenses used were Silor 70 mm plano FSV lenses, purchased through Essilor of America, Inc. of St. Petersburg, Fla.
The haze generated on the lenses was then measured on a Gardner XL-835 Colorimet
Guest Allen M.
Harvey Janet L.
Ho Tuan H.
Sollberger Mark S.
Terry Karl W.
Dunlap Codding & Rogers P.C.
Nakarani D. S.
SDC Coatings Inc.
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