Optical: systems and elements – Signal reflector – 3-corner retroreflective
Reexamination Certificate
2000-04-13
2001-11-20
Phan, James (Department: 2872)
Optical: systems and elements
Signal reflector
3-corner retroreflective
C359S529000
Reexamination Certificate
active
06318866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a triangular-pyramidal cube-corner retroreflective sheeting having a novel structure. More minutely, the present invention relates to a cube-corner retroreflective sheeting in which triangular-pyramidal reflective elements having a novel structure are arranged in a closest-packed state.
More minutely, the present invention relates to a cube-corner retroreflective sheeting constituted of triangular-pyramidal cube-corner retroreflective elements (hereafter referred to as triangular-pyramidal reflective elements or merely, elements) useful for signs including license plates of automobiles and motorcycles, safety materials of clothing and life jackets, markings of signboards, and reflectors of visible-light, laser-beam, and infrared-ray reflective sensors.
Still more minutely, the present invention relates to triangular-pyramidal cube-corner retroreflective sheeting in which a pair of triangular-pyramidal cube-corner retroreflective elements partitioned by three lateral faces (faces a
1
, b
1
, and c
1
; faces a
2
, b
2
, and C
2
; . . . ) almost perpendicularly intersecting each other because V-shaped grooves having substantially-symmetric cross sections intersect each other are arranged in a closest-packed state so as to protrude to one side on a common bottom plane (S-S′), faced lateral faces (faces c
1
and c
2
) of this pair of triangular-pyramidal retroreflective elements are paired by sharing a base (x), the bottom face (S-S′) is a common plane including bases (z and z) of one-side lateral faces (faces a
1
and a
2
) and bases (y and y) of the other-side lateral faces (faces b
1
and b
2
), and faced lateral faces (faces c
1
and c
2
) of the triangular-pyramidal retroreflective elements sharing the base (x) have shapes different from each other, and heights from the bottom face (S-S′) up to the apex are different from each other.
Still more minutely, the present invention relates to a triangular-pyramidal cube-corner retroreflective sheeting in which a pair of triangular-pyramidal cube-corner retroreflective elements partitioned by three lateral faces (faces a
1
, b
1
, and c
1
; faces a
2
, b
2
, and c
2
; . . . ) almost perpendicularly intersecting each other because V-shaped grooves having substantially-symmetric cross sections intersect each other have substantially optically analogous shapes and thereby, have angles &thgr; (hereafter also referred to as tilts of optical axes) formed between substantially same optical axes though different from each other in direction by 180° and a vertical line.
2. Description of the Related Art
A retroreflective sheeting for reflecting entrance light toward a light source has been well known so far and the sheeting using its retroreflective characteristic is widely used in the above fields. Particularly, a cube-corner retroreflective sheeting using the retroreflective theory of a cube-corner retroreflective element such as a triangular-pyramidal retroreflective element is extremely superior to a conventional retroreflective sheeting using micro glass beads in retroreflectivity and its purpose has been expanded year by year because of its superior retroreflective performance.
However, though a conventionally-publicly-known triangular-pyramidal retroreflective element shows a preferable retroreflectivity when an angle formed between an axis vertical to a sheet plane (axis passing through the apex of the triangular pyramid of the triangular-pyramidal retroreflective element equally separate from three faces constituting a triangular-pyramidal cube-corner retroreflective element and intersecting each other at an angle of 90°) and entrance light (the angle is hereafter referred to as entrance angle) is kept in a small range. However, the retroreflectivity rapidly deteriorates as the entrance angle increases (that is, the entrance angularity deteriorates).
Moreover, the light entering the triangular-pyramidal retroreflective element face at an angle less than a critical angle (&agr;
c
) satisfying an internal total-reflection condition determined by the ratio between the refractive index of a transparent medium constituting the triangular-pyramidal retroreflective element and the refractive index of air penetrates into the back of the element without totally reflecting on the interface of the element. Therefore, a retroreflective sheeting using a triangular-pyramidal retroreflective element generally has a disadvantage that it is inferior in entrance angularity.
However, because a triangular-pyramidal retroreflective element can reflect light in the light entrance direction almost over the entire surface of the element, retroreflected light is not diverged at a wide angle due to spherical aberration differently from the case of a micro-glass-bead reflective element.
However, the narrow dispersion angle of the retroreflected light practically easily causes a trouble that, when the light emitted from a head lamp of an automobile is retroreflected on a traffic sign, the retroreflected light hardly reaches, for example, a driver present at a position distant from the axis of the incident light. Particularly when the distance between an automobile and a traffic signal decreases, the above trouble more frequently occurs because the angle (observation angle) formed between the entrance axis of a light ray and the axis (observation axis) connecting a driver and a reflective point increases (that is, the observation angularity deteriorates).
For the above cube-corner retroreflective sheeting, particularly for the entrance angularity or observation angularity of a triangular-pyramidal cube-corner retroreflective sheeting, many proposals have been known so far and various improvements and studies are performed.
For example, Jungersen's U.S. Pat. No. 2,481,757 discloses a retroreflective sheeting constituted by arranging retroreflective elements of various shapes on a thin sheeting and a method for manufacturing the sheeting. Moreover it is described that triangular-pyramidal reflective elements disclosed in the above U.S. patent include a triangular-pyramidal reflective element in which the apex is located at the center of a base triangle and the optical axis does not tilt and a tilted triangular-pyramidal reflective element in which the apex is not located at the center of a base triangle to efficiently reflect light toward an approaching automobile.
Furthermore, it is described that the size of a triangular-pyramidal reflective element, that is, the depth of the element is {fraction (1/10)} in (2,540 &mgr;m) or less. Furthermore,
FIG. 15
in the U.S. patent illustrates a triangular-pyramidal reflective element whose optical axis tilts in the direction to be plus (+) as described later. The tilt angle (&thgr;) of the optical axis is estimated as approx. 6.5° when obtaining it from the ratio between the major and minor sides of the base triangle of the illustrated triangular-pyramidal reflective element.
Moreover, the above Jungersen's U.S. patent does not specifically disclose a very small triangular-pyramidal reflective element shown in FIG. the present invention or it does not disclose a size or an optical axis tilt a triangular-pyramidal reflective element must have in order to show superior observation angularity and entrance angularity.
Furthermore, Stamm's U.S. Pat. No. 3,712,706 discloses a retroreflective sheeting in which so-called equilateral triangular-pyramidal cube-corner retroreflective elements whose base triangles are equilateral triangles are arranged on a thin sheeting so that their bottom faces are brought into a closest-packed state on a common plane. Stamm's U.S. patent solves the problems that retroreflectivity is deteriorated and light entrance at an angle of less than an internal total reflection condition passes through an interface between elements and thereby it is not retroreflected by vacuum-depositing with a metal such as aluminum on the reflective surface of a reflective element, mirror-re
Hamada Yutaka
Mimura Ikuo
Takahashi Takehito
Fitzpatrick ,Cella, Harper & Scinto
Nippon Carbide Kogyo Kabushiki Kaisha
Phan James
LandOfFree
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