Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1999-11-24
2003-01-14
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S411100, C428S412000, C428S423100, C428S426000, C428S436000, C428S457000, C428S500000, C428S501000, C428S502000, C428S506000, C428S532000, C428S537100, C428S923000, C428S926000
Reexamination Certificate
active
06506488
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention relates to coatings comprising an aminoplast resin, component(s) having hydroxyl functional groups and photochromic substance(s), hereinafter referred to as photochromic aminoplast resin coatings. In particular, this invention relates to articles coated with such photochromic coatings and photochromic articles, i.e., polymerizates, made from such polymerizable compositions. More particularly, this invention relates to certain photochromic aminoplast resin coatings which when present on a substrate and exposed to activating light radiation exhibit improved photochromic properties. Further, this invention relates to photochromic aminoplast 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 use of melamine resins as a potential matrix for photochromic compounds in multilayered articles has been disclosed in U.S. Pat. No. 4,756,973 and Japanese patent applications 62-226134, 3-2864 and 3-35236. In U.S. Pat. No. 4,756,973 and JP 62-226134, melamine resin is referred to in a list of different materials, but specific examples of melamines and reactants to produce photochromic coatings are not disclosed. JP 3-2864 and 3-35236 disclose examples of melamine photochromic coatings, but information necessary to duplicate the examples is not included in the applications.
JP 61-268788 discloses a photochromic coating composition consisting of spironaphthoxazine, polyol condensed melamine and a polymer or copolymer of a vinyl compound containing a hydroxyl group. Comparative Examples 6-10 herein represent the examples of JP 61-268788. Lenses prepared with the coatings of Comparative Examples 6-10 demonstrate cosmetic defects and/or have performance properties outside of the desired range. The photochromic aminoplast coatings prepared with the Examples of the present invention were prepared by mixing all of the ingredients together instead of using the additional step of JP 61-268788, which is to condense a polyol with the melamine resin prior to adding the other ingredients.
It has now been discovered that photochromic aminoplast resin coatings that demonstrate good photochromic properties, i.e., color and fade at acceptable rates and achieve a sufficiently dark colored state, and that meet optical coating “cosmetic” standards may be produced. Such coatings enable the production of photochromic articles using plastics in which photochromic compounds do not function properly, and avoids the use of thermal transfer processes.
The novel coatings described herein exhibit a Fischer microhardness of from at least 45 to 180 Newtons per mm
2
. Articles of the present invention having this range of hardness are suitable for manipulation by automated process equipment without being damaged. The photochromic aminoplast coating composition used to form the photochromic coating may also be used to form a photochromic aminoplast resin 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-a-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 associated with the article exhibit a high activated intensity and acceptable coloration and fade rates.
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. This is advantageous when the plastic, e.g., thermoplastic polycarbonate, does not have enough internal free volume or polymer chain flexibility for the photochromic compounds incorporated into the plastic to function properly. Further, use of photochromic coatings result in more efficient utilization of photochromic compounds. The losses associated with more conventional transfer methods, e.g., imbibition or permeation, are avoided as well as the costs associated with the disposal of spent photochromic dye solutions.
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”.
When the coating compositions of the present invention are applied as a coating and cured, the coating exhibits a Fischer microhardness of at least of 45 Newtons per mm
2
, preferably at least 55, more preferably at least 60 Newtons per mm
2
. Typically, the cured coating exhibits a Fischer microhardness of not more than 180 Newtons per mm
2
, preferably not more than 160 and more preferably not more than 150 Newtons per mm
2
. The Fischer microhardness of the coating may range between any combination of these values, inclusive of the recited range.
The photochromic properties of the cured coating of the present invention are characterized by a &Dgr;OD after 30 seconds of at least 0.15, preferably at least 0.16 and most preferably at least 0.17, and a &Dgr;OD after 8 minutes of at least 0.47, preferably 0.50, and most preferably at least 0.55. The photochromic properties also are characterized by a bleach rate of not more than 180 seconds, preferably not more than 140, and more preferably not more than 100 seconds—all as measured at 85° F. (29.4° C.), and as described in Part D of Example 16 herein.
Aminoplast resin coatings having microhardness and photochromic performance properties within the aforestated ranges can be produced by balancing the amounts of the components of the crosslinkable composition used to prepare the coating matrix. For example, the specific properties of the components comprising the coating matrix or polymerizate that will effect the microhardness and photochromic performance properties of the aminoplast resin matrix are the glass transition temperature and molecular weight of the components, and the crosslink density of the resultant matrix. Generally, using components having higher glass transition temperatures and molecular weights results in coatings and polymerizates having an increased microhardness and vice versa. An increase in the number of reactive groups of a component will also cause an increase in the microhardness, provided that all of the groups are reacted. In the latter case, the increase in the number of reactive groups, i.e., crosslinking sites, increases the 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., a hydroxyl-functional component such as an organic polyol, to either the hardness or softness of the coating can be readily determined by measuring the Fischer microhardness of the resulting aminoplast resin coating. The hardness-producing component, as defined herein, is a component that increases the microhardness of the aminoplast resin coating as its concentration increases. Similarly, the softness-producing component, as defined herein, is a component that decreases the microhardness of the aminoplast resin coating as its concentration increases. Examples of h
Conklin Jeanine A.
O'Dwyer James B.
Stewart Kevin J.
Swarup Shanti
Welch Cletus N.
Mallak Frank P.
PPG Industries Ohio Inc.
Resan Stevan A.
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