Optical: systems and elements – Signal reflector – 3-corner retroreflective
Reexamination Certificate
2002-06-13
2004-10-12
Cherry, Euncha (Department: 2872)
Optical: systems and elements
Signal reflector
3-corner retroreflective
C359S529000
Reexamination Certificate
active
06802616
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a triangular-pyramidal cube-corner retroreflective sheeting having a novel structure. More minutely, the present invention relates to a retroreflective element such as a triangular-pyramidal cube-corner retroreflective element (hereafter merely referred to as a retroreflective element or a reflective element) constituting a retroreflective body useful for reflectors such as signs including traffic signs and construction work signs, license plates of vehicles such as automobiles and motorcycles, safety materials of clothing and life preservers, markings of signboards, and reflectors of visible-light, laser beams, or infrared-ray reflective sensors, and an assembly of the retroreflective elements.
BACKGROUND ART
A retroreflective body for reflecting entrance light toward a light source has been well known so far and the reflective body using its retroreflectivity is widely used in the above industrial fields. Particularly, a triangular-pyramidal cube-corner retroreflective body (hereafter also referred to as a CC reflective body) using the internal-total-reflection theory such as a triangular-pyramidal cube-corner retroreflective element (hereafter also merely referred to as a triangular-pyramidal reflective element or CC reflective element) is remarkably superior to a retroreflective body using conventional micro glass beads in retroreflective efficiency of light and thereby, purposes of the triangular-pyramidal cube-corner retroreflective element have been increased year by year because of its superior retroreflective performance.
However, though a conventional publicly-known triangular-pyramidal retroreflective element shows a preferable retroreflective efficiency when an angle formed between the optical axis (axis passing through the apex of a triangle equally separate from three faces constituting a triangular-pyramidal cube-corner retroreflective element and intersecting with each other at an angle of 90°) of the element and an entrance ray is small because of the reflection theory of the element, the retroreflective efficiency is suddenly lowered (that is, the entrance angle characteristic is deteriorated) as the entrance angle increases. Moreover, the light entering the face of the triangular-pyramidal reflective element at an angle less than the critical angle (&agr;
c
) meeting an internal-total-reflection condition decided in accordance with the refractive index of a transparent medium constituting the triangular-pyramidal reflective element and that of air reaches the back of the element without totally reflecting from the interface of the element. Therefore, a retroreflective sheeting using a triangular-pyramidal reflective element generally has a disadvantage that it is inferior in entrance angularity.
However, because a triangular-pyramidal retroreflective element can reflect light in the direction in which the light enters over the almost entire surface of the element, reflected light does not reflect by diverging at a wide angle due to spherical aberration like the case of a micro-glass-bead reflective element. However, the narrow divergent angle of the reflected light easily causes a trouble that when the light emitted from a head lamp of an automobile retroreflects from a traffic sign, it does not easily reach, for example, eyes of a driver present at a position separate from the optical axis of the head lamp. The above type of the trouble increases more and more (that is, observation angularity is deteriorated) because an angle (observation angle) formed between the entrance axis of rays and the axis connecting a driver with a reflection point increases.
Many proposals have been made so far for the above cube-corner retroreflective sheeting, particularly for a triangular-pyramidal cube-corner retroreflective sheeting and various improvements are studied.
For example, Jungersen's U.S. Pat. No. 2,310,790 discloses a retroreflective sheeting constituted by arranging various shapes of retroreflective elements on a thin sheeting and a method for manufacturing the sheeting. The 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 bottom-plane triangle and the optical axis does not tilt (that is, the optical axis is vertical to the bottom plane) and a triangular-pyramidal reflective element in which the apex is not located at the center of a bottom-plane triangle, and it is described in the U.S. patent to efficiently reflect light to an approaching automobile. Moreover, it is described that the depth of a triangular-pyramidal reflective element is kept within {fraction (1/10)} in (2,540 &mgr;m). Furthermore, FIG. 15 in the U.S. patent shows a triangular-pyramidal reflective element whose optical axis has a tilt angle (&thgr;) of approx. 6.5° obtained from the ratio between the major side and the minor side of the bottom-plane triangle of the illustrated triangular-pyramidal reflective element.
However, the above Jungersen's U.S. patent does not specifically disclose a very-small triangular-pyramidal reflective element disclosed by the present invention or does not describe or suggest a size of a triangular-pyramidal reflective element or a tilt angle the optical axis of the element necessary for superior observation angularity and entrance angularity.
Moreover, in the present specification, the expression “optical axis tilts in the plus (+) direction” denotes that the optical axis tilts in the direction in which the difference between the distance (q) from the intersection (Q) of the optical axis of a triangular-pyramidal reflective element and the bottom plane (S
x
-S
x
′) of the triangular-pyramidal reflective element up to the base edges (x,x, . . . ) shared by the element pair {the distance (q) is equal to the distance from the intersection (Q) up to a plane (L
x
—L
x
) vertical to the bottom plane (S
x
-S
x
′) including the bottom edges (x,x, . . . ) shared by the element pair} and the distance (p) from the vertical line extended from the apex of the element to the bottom plane (S
x
-S
x
′) and the bottom plane (S
x
-S
x
′) up to the base edges (x,x, . . . . ) {the distance (p) is equal to the distance from the intersection (P) up to the vertical plane (L
x
—L
x
)} becomes plus (+) as described later. On the contrary, when the optical axis tilts in the direction in which (q−p) becomes minus (−), the expression “optical axis tilts in the direction for the optical axis to become minus (−)” is displayed.
Moreover, Stamm's U.S. Pat. No. 3,712,706 discloses a retroreflective sheeting in which the so-called triangular-pyramidal cube-corner retroreflective elements respectively having an equilateral bottom-plane triangle (therefore, the optical axis is vertical to a bottom plane) are arranged on a thin sheeting so that bottom planes of the elements become the closest-packed state on a common plane. In the Stamm's U.S. patent, means for improving the wide angularity in accordance with the tilt of an optical axis is not described at all.
Furthermore, Hoopman's European Patent No. 137,736B1 discloses a retroreflective sheeting in which tilted triangular-pyramidal cube-corner retroreflective elements whose bottom-plane triangles are isosceles triangles are arranged on a common plane so that bottom planes of the elements become the closest-packed state. Moreover, it is described that the optical axis of the triangular-pyramidal cube-corner retroreflective element disclosed in the patent tilts in the minus (−) direction and its tilt angle approximately ranges between 7° and 13°.
Furthermore, Szczech's U.S. Pat. No. 5,138,488 similarly discloses a retroreflective sheeting in which tilted triangular-pyramidal cube-corner retroreflective elements whose bottom-plane triangles are isosceles triangles are arranged on a common plane so that bottom planes of the elements become the closest-packed state. In t
Cherry Euncha
Fitzpatrick ,Cella, Harper & Scinto
Nippon Carbide Kogyo Kabushiki Kaisha
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