Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-01-05
2001-08-28
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S329000, C428S331000, C428S336000, C428S446000, C428S447000, C428S913000
Reexamination Certificate
active
06280838
ABSTRACT:
The invention relates to an optical element comprising a substrate provided with a transparent coating containing a photochromic material, the transmission of said optical element in the visible region varying in response to a variation in light.
The invention also relates to a display device provided with a display window which serves as the substrate for the optical element.
The invention further relates to a method of manufacturing an optical element comprising a substrate provided with a transparent coating containing a photochromic material, the transmission of said optical element in the visible region varying in response to a variation in light.
Optical elements for varying the transmission of light are used to influence the transmission and/or reflection of (visible) light, for example, of lamps, rear-view mirrors and sunroofs of cars, or of windows for buildings (“smart windows”) or of spectacle lenses. Said optical elements are also used at the viewing side of display windows of (flat) display devices, such as cathode ray tubes (CRTs), plasma-display panels (PDPs) and liquid-crystal display devices (LCDs, LC-TVs and plasma-addressed LCDs) to improve the contrast of the image reproduced. By virtue thereof, it is not necessary to change the glass composition of the display window, and the possibilities of bringing the light transmission to a desired value in a simple manner are increased.
The transparent coatings mentioned in the opening paragraph influence the intensity of both the reflected ambient light and the light originating from an (internal) light source, for example the phosphors in a CRT. The incident ambient light passes through the coating and is reflected at the substrate (for example at the CRT phosphors or color filters), whereafter the reflected light again traverses the coating. If the transmission of the coating is T, then the intensity of the reflected ambient light decreases by a factor of T
2
. However, the light originating from the internal light source(s) traverses the transparent coating only once, so that the intensity of this light decreases only by a factor of T. The combination of these effects causes an increase of the contrast by a factor of T
−1
.
Examples of optical elements for varying the transmission of light include, inter alia, electrochromic elements and photochromic elements.
The transmission of an optical element comprising a transparent coating with a photochromic material, hereinafter referred to as photochromic element, varies (automatically) as a result of electromagnetic radiation, for example light, such as sunlight, which is directly or indirectly incident on the coating. A large number of photochromic materials are known, and they can be subdivided into various classes (for example spiro-pyrans, spiro-oxazines or fulgides). Such an optical element enables, for example, the contrast of a (luminescent) image to be increased by applying a photochromic coating to the display window of a display device, the local transmission of the coating in the visible region being governed by the radiation which is (locally) incident on the coating. Such an optical element can also be provided on the lenses of sunglasses to reduce the transmission of (sun)light, so that disturbing radiation (blinding) and/or (UV-)radiation in the light, which is detrimental to the eye, can be reduced, while, at the same time, good vision is achieved.
An optical element of the type mentioned in the opening paragraph is known from European Patent Application EP-A 740845 (PHN 15.083, U.S. Ser. No. 08/548,936). The photochromic element described in said Patent Application is provided on a display window of a display device, and comprises a selectively transparent coating whose transmission decreases automatically as the intensity of the incident radiation increases, and is (preferably) governed by (electromagnetic) radiation incident on the coating and having a wavelength outside the region in which the display device emits light (for example (ambient) light in the so-called UV-A region).
A disadvantage of the known optical element is that, in general, the applicability of the above-described photochromic coatings is limited.
Therefore, it is an object of the invention to provide, inter alia, an optical element of the type mentioned in the opening paragraph, which has a wider applicability. The invention further aims at providing a simple method of manufacturing such optical elements.
To this end, the optical element in accordance with the invention is characterized in that the coating comprises an inorganic network of a silicon oxide, and in that the coating also contains an organic polymer which is chemically bonded to the inorganic network via Si—C bonds.
The invention is based on the insight that the photochromic material in the transparent coating is incorporated in a combination of an inorganic network and an orgarnic polymeric network, that is, a so-called hybrid network comprising silicon oxide and organic (carbon-containing) polymers. By incorporating the photochromic material in such a hybrid network, a photochromic coating is obtained which demonstrates a good switching behavior and which is scratch-resistant. In the known optical element, the photochromic material is incorporated in a (purely) organic network. In such networks, the photochromic material demonstrates a good switching behavior. However, these organic polymers have a poor mechanical strength (hardness, resistance to wear and scratch resistance). If the photochromic material is incorporated in a (purely) inorganic network, in general, two types of problems occur. On the one hand, there is the phenomenon that, as soon as the photochromic material is incorporated in an inorganic network, the photochromic effect becomes inverted, i.e. under the influence of light, the normal transition from (colorless) transparent to colored (for example color-neutral grey) changes to a reduction of the color of the photochromic material under the influence of light (the so-called “bleaching”), which is undesirable. On the other hand, once the photochromic material is incorporated in the purely inorganic network, a reduction or even (substantial) absence of the photochromic effect is often observed.
By incorporating the photochromic material in the hybrid network comprising a silicon oxide and polymers, a photochromic coating having the desired physical and chemical properties is achieved, in particular as regards the preservation of the switching behavior of the photochromic material. In addition, a mechanically strong and thermally stable coating is obtained having the desired density and mechanical strength (hardness, resistance to wear and scratch resistance). The hybrid network has such flexibility that the photochromic material has sufficient space for switching, whereas a purely inorganic network often is too compact and/or too tight, so that a photochromic material incorporated in such a network has insufficient possibilities (for example as a result of steric hindrance) of undergoing the (reversible)(chemical) structural changes necessary for the photochromic effect. By way of example of such a structural change, the photochromic act of a spiro-pyran comprises the heterolytic opening of the spiro C—O bond. By incorporating the photochromic material in a coating in accordance with the invention, an optical element having a good photochromic effect and the desired mechanical properties is obtained.
Photochromic coatings in accordance with the invention are used, for example, to improve the contrast of display windows of display devices, which coatings are sensitive to (sun)light which is directly incident on the display window provided with the electrochromic element as well as to (ambient) light or (sun)light which is incident on the coating via (double)(window)glass. Another field of application relates to providing lenses of sunglasses with a photochromic coating in accordance with the invention. The use of such coatings leads to a properly switching photochromic system, which also func
Bernards Thomas N. M.
Rietjens Gerardus H.
Severin-Vantilt Marijke M. E.
Snijkers-Hendrickx Ingrid J. M.
Hess Bruce H.
Shewareged B.
Spain Norman N.
U. S. Philips Corporation
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