Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
1998-11-06
2001-07-31
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C252S586000, C528S112000
Reexamination Certificate
active
06268055
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention relates to photochromic epoxy resin coatings and articles coated with such coatings. More particularly, this invention relates to certain photochromic epoxy resin coatings prepared with polyacid curing agents which when coated onto a substrate and exposed to activating light radiation exhibit improved photochromic performance properties. Further, this invention relates to photochromic epoxy resin coatings that meet commercially acceptable “cosmetic” standards for optical coatings applied to optical elements, e.g., lenses.
Photochromic compounds exhibit a reversible change in color when exposed to light radiation involving ultraviolet rays, such as the ultraviolet radiation in sunlight or the light of a mercury lamp. Various classes of photochromic compounds have been synthesized and suggested for use in applications in which a sunlight-induced reversible color change or darkening is desired. The most widely described classes of photochromic compounds are oxazines, pyrans and fulgides.
The general mechanism responsible for the reversible change in color, i.e., a change in the absorption spectrum in the visible range of light (400-700 nm), exhibited by different types of photochromic compounds has been described and categorized. See John C. Crano, “Chromogenic Materials (Photochromic)”,
Kirk-Othmer Encyclopedia of Chemical Technology
, Fourth Edition, 1993, pp. 321-332. The mechanism for the reversible change in color for indolino spiropyrans and indolino spirooxazines is believed to involve an electrocyclic mechanism. When exposed to activating radiation, these compounds transform from a colorless closed ring compound into a colored open ring species. In contrast, the colored form of fulgide photochromic compounds is believed to be produced by an electrocyclic mechanism involving the transformation of a colorless open ring form into a colored closed ring form.
In the aforedescribed electrocyclic mechanisms, the described photochromic compounds require an environment in which they can reversibly transform. In solid polymer matrices, the rates at which the photochromic processes of activation, i.e., formation of color or darkening, and fading, i.e., the return to the original or colorless state, occur are believed to be dependent on the free volume in the polymer matrix. The free volume of the polymer matrix is dependent upon the flexibility of the chain segments of the polymer environment surrounding the photochromic compound, i.e., the local mobility or local viscosity of the chain segments comprising the matrix. See Claus D. Eisenbach, “New Aspects of Photochromism in Bulk Polymers”, Photographic Science and Engineering, 1979, pp. 183-190. One of the main obstacles reported by Claus D. Eisenbach, for the larger commercial application of photochromic systems, is the slow rate of photochromic activation and fade in a solid polymer matrix.
UK Patent No. 1,419,985 describes a sunlight photochromic filter for human spectacles prepared from an epoxy resin containing photochromic material. The photochromic epoxy resin is free of molecular oxygen and protected from atmospheric oxygen by an oxygen-impermeable barrier. U.S. Pat. No. 4,556,605 describes photochromic coating compositions comprising spiropyrans, hydrolysates of organosilanes, an epoxy compound and curing catalyst. U.S. Pat. No. 4,756,973 describes a plastic lens having an epoxy resin layer containing a spirooxazine along with a phenol resin and/or a phenolic compound. However, articles coated with a photochromic epoxy resin coating that have coating thicknesses necessary to demonstrate good photochromic properties, i.e., to color and fade at acceptable rates and to achieve a dark enough colored state, and that meet optical coating “cosmetic” standards required by the industry and the consuming public are currently not commercially available.
In accordance with the present invention, there has now been developed novel photochromic epoxy resin coatings that have acceptable Fischer microhardness and photochromic properties. These novel coatings exhibit a Fischer microhardness of from 50 to 150 Newtons per mm
2
, and improved photochromic properties, i.e., the formation of darker activated colors and faster rates of photochromic activation and fade when irradiated with ultraviolet light.
DETAILED DESCRIPTION OF THE INVENTION
In recent years, photochromic articles, particularly photochromic plastic materials for optical applications, have been the subject of considerable attention. In particular, photochromic ophthalmic plastic lenses have been investigated because of the weight advantage they offer, vis-à-vis, glass lenses. Moreover, photochromic transparencies for vehicles, such as cars and airplanes, have been of interest because of the potential safety features that such transparencies offer. Photochromic articles that are most useful are those in which the photochromic compounds exhibit a high activated intensity, a high coloration rate and an acceptable fade rate.
The use of photochromic epoxy resin coatings enables the preparation of photochromic plastic articles without the need to incorporate the photochromic compound(s) into the plastic substrate, which avoids the need to develop special organic optical resin materials for use with photochromic compounds. This is advantageous when the plastic, e.g., thermoplastic polycarbonate, does not have enough internal free volume for the photochromic compounds to function properly. Coating such plastics with the coating composition of the present invention enables preparation of photochromic articles using these plastics. Another advantage that a photochromic coating provides is the more efficient utilization of photochromic compounds when preparing photochromic articles, i.e., avoiding the loss of photochromic compounds associated with more conventional transfer methods of incorporating such materials into plastics, e.g., imbibition or permeation.
Other than in the operating examples, or where otherwise indicated, all values, such as those expressing wavelengths, quantities of ingredients, ranges or reaction conditions, used in this description and the accompanying claims are to be understood as modified in all instances by the term “about”.
The photochromic coatings of the present invention may be prepared by the reaction of a composition comprising an epoxy resin and a curing agent, e.g., a polyacid comprising a half-ester formed from reacting an acid anhydride with an organic polyol, wherein the composition includes at least one organic photochromic substance. The coating composition may further include a catalyst. Regarding other possible conventional ingredients or adjuvants in the coating composition, it is known in the coating art that solvents are typically used to dissolve certain of the ingredients in the coating composition, act as carriers and/or adjust the viscosity of the coating composition for different application methods. Therefore while solvents may be present in the coating composition described herein, they are not factored into the weight ratios and weight percents stated herein. All weight ratios and weight percents used herein are based on the total solids in the coating composition, unless stated otherwise.
When the coating composition of the present invention is applied as a coating and cured, it exhibits a Fischer microhardness in the range of from 50 to 150 Newtons per mm
2
and improved photochromic performance properties. The improved photochromic performance properties contemplated herein are a &Dgr;OD of at least 0.15 after 30 seconds and at least 0.50 after 15 minutes, and a Bleach rate of less than 200 seconds—all as measured at 72° F. (22° C.) , and as described in Part C of Example 9 herein. Preferably, the Fischer microhardness is between 60 and 140 Newtons per mm
2
, the &Dgr;OD is at least 0.17 after 30 seconds and at least 0.60 after 15 minutes, and the Bleach rate is less than 190 seconds. Most preferably, the Fischer microhardness is in the range of from 80 to 130 Newtons per mm
2
, t
Burgman John W.
Singer Debra L.
Swarup Shanti
Walters Robert W.
Welch Cletus N.
Le H. Thi
Mallak Frank P.
PPG Industries Ohio Inc.
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