Optical: systems and elements – Signal reflector – 3-corner retroreflective
Reexamination Certificate
1998-02-05
2001-08-28
Phan, James (Department: 2872)
Optical: systems and elements
Signal reflector
3-corner retroreflective
C359S518000, C359S530000, C359S531000, C359S532000, C359S539000, C359S900000
Reexamination Certificate
active
06282026
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of retroreflective articles that have two optical surfaces.
BACKGROUND
Nighttime visibility of objects and people is a continuing problem, particularly for the operators of vehicles such as trucks and automobiles. Approaches to increasing their nighttime visibility can be either active or passive. Active systems provide conspicuity by providing a steady light source, flashing light source, or a combination of steady and flashing light sources. Although active systems do provide conspicuity, they must be provided with energy, typically electrical energy, to provide the desired light. Energy sources are not always available or they may be depleted such that the light sources will not operate. As a result, active systems find limited application for providing long term conspicuity.
Examples of passive systems include diffuse reflectors, specular reflectors, and/or retroreflectors. Retroreflectors can return a significant portion of incident light, that would otherwise be reflected elsewhere, back towards a light source, such as the headlights of a car or truck. Retroreflectors are typically constructed of beads (see, e.g., U.S. Pat. Nos. 4,025,159 to McGrath; 4,983,436 to Bailey et al.; and 5,066,098 to Kult et al.) or they can include cube corner elements (see, e.g., U.S. Pat. Nos. 5,272,562 to Coderre and 5,450,235 to Smith et al.). With many retroreflectors, the amount of returned light can make the retroreflective article appear as though it has a light source of its own when, in reality, at least a portion of the light directed at the retroreflector from the light source is merely being returned towards the source. Although retroreflectors return a significant portion of light, the incident light is typically from a steady source such as headlights. Steady incident light yields generally steady returned light from the retroreflectors, that is, the intensity of the returned light does not appreciably vary.
Investigators have made various strides towards improving the conspicuity of retroreflective articles. For example, Shusta et al. in PCT publications WO 97/41465 and 97/41464 (U.S. patent application Ser. Nos. 08/640,326 and 08/640,383) describe a retroreflective article that glitters when exposed to light. Fluorescent dyes have also been used to improve conspicuity—see for example, U.S. Pat. Nos. 5,387,458 and 3,830,682. U.S. Pat. No. 4,726,134 describes a retroreflective sign which has areas that vary in retroreflectivity to improve the sign's conspicuity.
SUMMARY OF THE INVENTION
The present invention provides an alternative approach to improving conspicuity of retroreflective articles. In accordance with the present invention, a retroreflective article is provided that has varying retroreflectivity using a first surface that includes a plurality of light redirecting structures and a second surface that includes retroreflective areas and separation areas. The light redirecting structures on the first surface are preferably arranged relative to the retroreflective areas and the separation areas on the second surface such that a substantial portion of light incident on the light redirecting structures is superimposed on areas of the second surface. At some angles, it is preferred that substantially all of the light is superimposed on either the retroreflective areas or the separation areas, resulting in varying retroreflection from the retroreflective articles.
Together, the two optical surfaces of the retroreflective articles provide varying retroreflection of incident light where the variations can be between, for example, retroreflection or no retroreflection, retroreflection of different colors, retroreflection at different brightness levels, etc. In other words, when subjected to incident light from a steady light source, relative movement between the retroreflective article and the light source will result in variations in retroreflection. When retroreflective articles provide varying retroreflection, the variations or changes tends to increase the conspicuity of the retroreflective articles.
In one aspect, the present invention provides a retroreflective article having a first surface including a plurality of light redirecting structures; a second surface opposite the first surface, the second surface including a plurality of retroreflective areas retroreflecting light towards the first surface; and a plurality of separation areas on the second surface, each of the separation areas located between the retroreflective areas; wherein a substantial portion of light incident on the plurality of light redirecting structures on the first surface of the retroreflective article at a given angle is superimposed on the second surface of the retroreflective article.
In another aspect, the present invention provides a retroreflective article having a first surface including a plurality of light redirecting structures, each of the light redirecting structures comprising a facet pair including two facets located in facet planes, the facet planes of each facet pair intersecting along a line of intersection, wherein the lines of intersection for each of the facet pairs are generally aligned with a first axis; a second surface including a plurality of retroreflective areas, each of the retroreflective areas having a plurality of retroreflective structures retroreflecting light towards the first surface, wherein the retroreflective areas comprise columns generally aligned with the first axis; and a plurality of separation areas on the second surface, each of the separation areas located between the retroreflective areas; wherein at least a portion of light incident on each of the facet pairs on the first surface of the retroreflective article at a given angle is superimposed on the second surface of the retroreflective article.
In another aspect, the present invention provides a retroreflective article including a body having a first surface and a second surface opposite the first surface; a plurality of retroreflective areas on the second surface of the body, the retroreflective areas including a plurality of retroreflective structures, wherein the retroreflective areas are provided in columns generally aligned with a first axis; a plurality of separation areas on the second surface of the body, each of the separation areas located between the retroreflective areas; an optical window located between the first and second surfaces, the optical window transmitting light into the body; and a plurality of light directing structures located on the first surface of the body, wherein a substantial portion of light incident on the plurality of light redirecting structures at a given angle from the optical window is superimposed on the second surface of the retroreflective article.
In another aspect, the present invention provides a method of manufacturing a retroreflective article by providing a first surface including a plurality of light redirecting structures and a second surface opposite the first surface, the second surface being separated from the second surface by an optically transmissive medium; providing a light curable binder solution on the second surface; providing a plurality of retroreflective beads proximate the second surface, each of the plurality of retroreflective beads at least partially immersed in the binder solution; forming retroreflective areas on the second surface by directing light energy through the first surface to cure selected areas of the binder solution on the second surface, wherein the binder solution in the selected areas is sufficiently cured to retain a substantial portion of the retroreflective beads; and removing the retroreflective beads from the uncured binder solution on the second surface to form separation areas between the retroreflective areas; wherein a substantial portion of light incident on the plurality of light redirecting structures on the first surface of the retroreflective article at a given angle is superimposed on the second surface of the retroreflective artic
Dreyer John F.
Fleming Madeleine B.
3M Innovative Properties Company
Hofmann, Jr. Rudolph P.
Phan James
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