Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-11-09
2003-02-04
Truong, Duc (Department: 1711)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S040700, C428S690000, C428S917000, C430S056000, C430S060000, C430S068000, C430S075000, C525S09200D, C525S089000, C525S451000, C525S461000, C525S462000, C525S466000
Reexamination Certificate
active
06514594
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fluorescent multi-layer polymeric articles having an ultraviolet light screening layer to protect the fluorescence color stability of a fluorescent layer. More particularly, the invention is directed to articles, preferably comprising a plurality of retroreflective elements, in which a fluorescent polymeric layer is protected by a polymeric ultraviolet light screening layer fabricated from a U.V. light absorbing polymer, or a polymer capable of re-arrangement to a U.V. light absorbing polymer.
BACKGROUND OF THE INVENTION
Retroreflective sheeting is widely used for traffic and roadway safety signs. Such sheeting is typically provided as a polymeric monolayer or multilayer sheeting material having thousands of retroreflective elements, such as microprismatic comer cubes or glass microspheres, that reflect incident light. It is well known to incorporate one or more fluorescent dyes into a retroreflective sheeting in order to enhance the visibility of articles such as road signs manufactured from such sheeting material. Fluorescent colors enhance visual contrast, which makes fluorescent colored materials more conspicuous than nonfluorescent materials. Unfortunately, most fluorescent colorants have poor ultraviolet light stability. In some cases, fading of fluorescent sheeting due to ultraviolet light exposure can occur within six months. The loss of fluorescence caused by ultraviolet light exposure dramatically shortens the useful life of fluorescent traffic and roadway signs. Accordingly, there is a need in the art to stabilize fluorescent colorants in plastics and to find a means to reduce the fading of fluorescent dyes in order to provide articles such as retroreflective road signs that can remain in service for significantly longer periods.
To enhance the outdoor durability of fluorescent retroreflective sheeting, an ultraviolet light screening layer is often used to protect the base fluorescent polymeric matrix layer from the effects of ultraviolet radiation. Traditionally, the U.V. light screening layer is made by incorporating U.V. light absorbing compounds into a transparent polymer matrix. Japan Kokai No. 2-16042, Application No. 63-165914 (Koshiji et al.) and U.S. Pat. No. 5,387,458 (Pavelka et al.) each disclose fluorescent articles consisting of an ultraviolet screen layer disposed in front of a fluorescent layer. According to these references, the screening layer contains substantial amounts of ultraviolet light absorbing compounds, which absorb a defined range of U.V. light (wavelengths from 290 to 400 nm).
Such prior art multilayer structures in which a U.V. light absorbent additive-treated screening layer is disposed in front of a layer containing a fluorescent dye can give rise to several difficulties. One problem is that the U.V. light absorbent additives incorporated into the U.V. light screening layer may leach out with time, because most U.V. light absorbing compounds are relatively small molecules and the U.V. light screening layer is typically quite thin. As a result of this phenomenon, the screening layer may lose its protective function, and the fluorescent colorants in the fluorescent layer will quickly fade and lose their fluorescence when exposed to ultraviolet light. A further problem with the U.V. light absorbent additive-treated screening layers is that U.V. light absorbing compounds present therein can diffuse or migrate into the fluorescent layer. If the U.V. light absorbing compound is not carefully selected, this diffusion can actually accelerate the fading of the fluorescent colorant even though the diffused compound is one that absorbs U.V. light. The problem of additive migration requires that a U.V. light absorbing additive incorporated into a screening layer be carefully matched to the fluorescent colorant so as to minimize any tendency of the migrating U.V. light absorber to affect the color and fluorescence of the articles. The implication that one may randomly select any U.V. absorber capable of blocking most of U.V. light below 400 nm wavelength (see, e.g., Japan Kokai No. 2-16042, Application No. 63-165914 (Koshiji et al.) and U.S. Pat. No. 5,387,458 (Pavelka et al)) fails to take into account the potential interaction between the U.V. absorber in the screening layer, and the fluorescent dye(s) present in the colored layer.
Based on the problems described above, there is a strong need in the art for polymeric articles in which an ultraviolet light screening layer can provide longer lasting U.V. light protection to a polymeric layer containing a fluorescent dye. Moreover, there is a need in the art of manufacturing of such articles to be able to select a fluorescent colorant without regard to the type of U.V. light absorbing material present in the screening layer, and vice versa.
In view of the foregoing, a general object of the present invention is to provide a polymeric multilayer article in which a polymeric ultraviolet light screening layer is arranged in protective laminar fashion (with or without intervening layers) with a fluorescent dye-containing layer in order to provide a much higher degree of fluorescence and color stability in the dye-containing layer than is currently afforded by conventional U.V. light screening layers comprising a polymer and a U.V. light absorbing additive.
Another object of the invention is to provide a polymeric multilayer retroreflective article in which an ultraviolet light screening layer is fabricated from a polymer capable of absorbing ultraviolet radiation such that the retroreflective article can be used to fabricate fluorescent, outdoor-weatherable products that have greater durability in terms of both color and fluorescence.
Yet another object of the invention is to provide a polymeric multilayer retroreflective article in which an ultraviolet light screening layer is disposed in protective relation to a fluorescent layer having cube comers formed on a surface thereof, and the ultraviolet light screening layer is fabricated from one or more U.V. light absorbing polymers or polymers capable of undergoing re-arrangement to an ultraviolet light absorbing polymer.
Still a further object of the invention is to provide a polymeric retroreflective article in which an ultraviolet light screening layer fabricated from a U.V. light absorbing polymer, or from a polymer capable of re-arrangement to a U.V. light absorbing polymer, can be attached to, or otherwise arranged in protective laminar configuration with, a polymeric layer comprising a fluorescent dye to reduce loss of fluorescence upon exposure of the article to ultraviolet radiation, even if no additional U.V. light absorbing additives and/or light stabilizers are used in the screening layer and/or the colored layer.
Yet another object of the invention is to provide retroreflective sheeting material in which an enhanced ultraviolet light screening layer, fabricated from a U.V. light absorbing polymer, or from a polymer capable of re-arrangement to a U.V. light absorbing polymer, can provide a remarkable degree of fluorescence protection to an underlying fluorescent layer, thereby extending the useful life of such retroreflective sheeting material significantly beyond that currently attainable using conventional screening layers containing U.V. light absorbing additives.
These and other objects will become apparent hereinafter to those skilled in the art.
SUMMARY OF THE INVENTION
The present invention results from our discovery that a U.V. light screening layer fabricated from a U.V. light absorbing polymer, and/or a polymer capable of undergoing re-arrangement to a U.V. light absorbing polymer, can provide a remarkable level of protection to the fluorescence and color durability of a polymeric layer containing a fluorescent colorant. The level of protection is superior to that afforded by U.V. light screening layers in which one or more conventional U.V. light absorbent additives (e.g., benzophenones and/or benzotriazoles, either with or without hindered amine light stabilizers,
Buoni Drew J.
Dockus Kimberly A.
Wei Guang-Xue
Avery Dennison Corporation
Jones Day Reavis & Pogue
Truong Duc
LandOfFree
Fluorescent polymeric articles having screening layer formed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluorescent polymeric articles having screening layer formed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluorescent polymeric articles having screening layer formed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3122524