Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1998-05-22
2001-02-13
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S480000, C428S500000
Reexamination Certificate
active
06187444
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention relates to photochromic polyurethane coatings and articles having such coatings. More particularly, this invention relates to certain photochromic polyurethane coatings that when applied onto a substrate and exposed to activating light radiation exhibit improved photochromic performance properties. Furthermore, this invention relates to photochromic polyurethane 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 general mechanism for the most common classes of photochromic compounds, e.g., indolino spiropyrans and indolino spirooxazines, involves 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 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 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.
The use of photochromic compounds in polyurethanes has been disclosed. German Democratic Republic Patent No. 116 520 describes a method of preparing photochromic polymer systems which include photochromic ortho-nitrobenzyl compounds added to reaction systems which lead to polyurethanes. European Patent Application Number 0 146 136 describes an optical element with a photochromic coating, such as a polyurethane lacquer in which are incorporated one or more phototropic substances. U.S. Pat. No. 4,889,413 describes a process for producing a polyurethane plastic having photochromic properties. Japanese Patent Application 3-269507 describes a light adjusting plastic lens composed of a plastic base material, a primer layer consisting of a thermosetting polyurethane containing a photochromic substance placed over the base material and a silicone resin hardcoat layer covering the polyurethane layer. Japanese Patent Application 5-28753 describes a coating material with photochromic properties containing urethane products for formation of the coating matrix and organic photochromic compounds.
Although the use of photochromic compounds in polyurethanes has been described in the literature, photochromic polyurethane coated articles 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, that meet optical coating “cosmetic” standards required by the industry and the consuming public have not been attained, which may explain why there are no commercial photochromic polyurethane coatings for optical applications, e.g., lenses, currently available.
A photochromic polyurethane coating that has acceptable Fischer microhardness and photochromic properties has now been discovered. This novel coating exhibits 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-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 exhibit a high activated intensity, a high coloration rate and an acceptable fade rate.
The use of photochromic polyurethane coatings enables the preparation of photochromic plastic articles without the need to incorporate the photochromic compound(s) into the plastic. 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 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”.
Polyurethanes that may be used to prepare the photochromic polyurethane coating of the present invention are those produced by the catalyzed or uncatalyzed reaction of an organic polyol component and an isocyanate component that when combined to provide a polyurethane composition and when applied as a coating and cured, 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 0.44 after 30 minutes, and a Bleach rate of less than 200 seconds—all as measured in the 72° F. (22° C.) Photochromic Performance Test defined in Part D of Example 11 herein. Preferably, the Fischer microhardness is between 70 and 140 Newtons per mm
2
1
the &Dgr;OD is at least 0.17 after 30 seconds and at least 0.45 after 30 minutes, and the Bleach rate is less than 180 seconds. Most preferably, the Fischer microhardness is in the range of from 100 to 130 Newtons per mm
2
, the &Dgr;OD is at least 0.18 after 30 seconds and at least 0.46 after 30 minutes, and the Bleach rate is less than 150 seconds.
The aforedescribed photochromic performance properties of the polyurethane coating of the present invention are a function of the temperature at which testing is
Bowles, III Robert J.
Conklin Jeanine A.
Gruchacz Nancyanne
Hunt Robin
Swarup Shanti
Hess Bruce H.
Mallak Frank P.
PPG Industries Ohio Inc.
Shewareged B.
Stein Irwin M.
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