Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-12-11
2002-08-20
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S426000, C428S457000, C428S537100, C428S537500, C428S411100, C528S195000, C528S198000, C252S582000, C252S586000
Reexamination Certificate
active
06436525
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention relates to coatings comprising hydroxyl-functional components(s), polymeric anhydride-functional component(s) and photochromic components(s), hereinafter referred to as photochromic polyanhydride coatings, articles coated with such coatings and photochromic articles, i.e., polymerizates, made of such coating compositions. More particularly, this invention relates to certain photochromic polyanhydride coatings which when coated onto a substrate and exposed to activating light radiation exhibit improved photochromic performance properties. Further, this invention relates to photochromic polyanhydride 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.
It has now been discovered that photochromic coated articles having 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 meet optical coating “cosmetic” standards required by both the industry and the consuming public may be prepared using a photochromic polyanhydride coating. The novel coatings described herein exhibit a Fischer microhardness of from at least 50 to not more than 130 Newtons per mm
2
. These coatings also exhibit improved photochromic properties, i.e., formation of darker activated color and faster rates of photochromic activation and fade, when irradiated with the ultraviolet light, as compared to such coatings having a Fischer microhardness greater than 130 Newtons per mm
2
. Also, the composition used to form the coating may be used to form a photochromic polyanhydride polymerizate.
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 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 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 a photochromic compound incorporated in the plastic to function properly. The coating composition of the present invention enables preparation of photochromic articles using such plastics. Further, use of photochromic coatings results in more efficient utilization of photochromic compounds by avoiding the losses associated with more conventional transfer methods, e.g., imbibition or permeation, to produce photochromic articles.
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 hydroxyl-functional component(s) having at least two hydroxyl groups and polymeric anhydride-functional component(s) having at least two cyclic carboxylic acid anhydride groups in a composition including at least one organic photochromic component. Other optional ingredients include crosslinking agents, e.g., epoxy-functional components, acrylamide-functional components or melamine resins, and plasticizers in amounts necessary to adjust the Fischer microhardness levels as well as the photochromic performance properties to within the desired range. The coating composition may further include catalyst.
Solvents may also be present in the coating composition. However, as described herein, solvents 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 compositions of the present invention are applied as a coating and cured, they exhibit a Fischer microhardness of at least 50 Newtons per mm
2
, preferably at least 60, more preferably, at least 70 Newtons per mm
2
and not more than 130 Newtons per mm
2
, preferably, not more than 120 and more preferably not more than 110 Newtons per mm
2
. The Fischer microhardness may range between any combination of these values, inclusive of the recited values. The photochromic properties of the cured coatings of the present invention are characterized by a &Dgr;OD after 30 seconds of at least 0.15, preferably, at least 0.17 and most preferably, at least 0.18; and a &Dgr;OD after 15 minutes of at least 0.50, preferably, at least 0.60, and most preferably, at least 0.63; and a bleach rate of not more than 200 seconds, preferably, not more than 195, and most preferably, not more than 190 seconds—all as measured at 72° F. (22° C.), and as described in Part C of Example 8 herein.
Polyanhydride coatings having microhardness and photochromic performance properties within the aforestated ranges can be produced by balancing the components that contribute to the hardness and softness of the coating matrix. The specific properties of the components comprising the coating or polymerizate that will effect the microhardness and photochromic performance properties of the polyanhydride matrix are the glass transition temperature, molecular weight and crosslink density. Generally, using components having higher glass transition temperatures and molecular weights results in coatings and polymerizates having increased microhardness and vice versa. An increase in the number of reactive groups of the component will also cause an increase in the microhardness, provided that all of the groups are reacted. In this latter case, an increase in the number of reactive groups, i.e., crosslinking sites, increases the crosslinked density of the cured coating. It is believed however that the harder the coating or polymerizate, the slower the performance of the photochromic compound contained therein.
The contribution of a particular component, e.g., the hydroxyl-functional component, to either the hardness or softness of the polyanhydride coating can be readily determined-by measuring the Fischer microhardness of the resulting polyanhydride coating. The hardness-producing component, as defined herein, is a component that increases the microhardness of the polyanhydride coating as its concentration increases. Similarly, the softness-producing component, as defined herein, is a component that decreases the microhardness of the polyanhydride coating as its concentration increases. Examples of hardness-producing hydroxyl-functional components, e.g., organic polyols, include, but are not limited to, low molecular weight polyols, amide-containing polyols, epoxy polyols and urethane polyols. Softness-producing hydroxyl-functional components, e.g., organic polyols, include, but are not limited to, polyester polyols, polyacrylic polyols, and polyether polyols, e.g. polyoxyalkylenes and poly(oxytetr
Swarup Shanti
Walters Robert W.
Welch Cletus N.
Mallak Frank P.
PPG Industries Ohio Inc.
Rickman Holly C.
Thibodeau Paul
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