Optical: systems and elements – Signal reflector – 3-corner retroreflective
Reexamination Certificate
2002-07-31
2004-11-16
Phan, James (Department: 2872)
Optical: systems and elements
Signal reflector
3-corner retroreflective
C359S530000, C428S156000
Reexamination Certificate
active
06817724
ABSTRACT:
TECHNICAL FIELD
The present invention relates to triangular-pyramidal cube-corner retroreflective elements having a novel structure and a triangular-pyramidal cc retroreflective assembly in which the triangular-pyramidal cube-corner retroreflective elements are arranged. More minutely, the present invention relates to retroreflective elements (hereafter simply referred to as retroreflective elements or reflective elements) such as triangular-pyramidal cube-corner retroreflective elements constituting a retroreflective body useful for reflectors such as signs including traffic signs and construction work signs, visible tapes of vehicles and motorcycles, safety materials of clothing and life preservers, markings of signboards, and reflectors of visible light, laser beam, or infrared-ray reflective sensors, and an assembly of the retroreflective elements.
Still more minutely, the present invention relates to triangular-pyramidal cube-corner retroreflective elements characterized in that triangular-pyramidal cube-corner retroreflective elements protruding beyond a common bottom plane (S
x
-S
x
′) share one base edge (x) on the bottom plane (S
x
-S
x
′) and are arranged in the closest-packed state so as to be faced each other, the bottom plane (S
x
-S
x
′) is a common plane including a plurality of the base edges (x,x, . . . ) shared by the triangular-pyramidal reflective elements, two triangular-pyramidal reflective elements faced each other include the shared base edges (x,x, . . . ) on the bottom plane (S
x
-S
x
′) and form a substantially same-shape element pair faced each other so as to be symmetric to planes (L
x
—L
x
, L
x
—L
x
, . . . ) vertical to the bottom plane (S
x
-S
x
′), and when assuming the height from the bottom plane (S
x
-S
x
′) including the base edges (x,x, . . . ) shared by the two triangular-pyramidal reflective elements faced each other up to apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements as h
x
, the height from a bottom plane (S
y
-S
y
′) including other base edges (y,y, . . . ) of the triangular-pyramidal reflective elements up to the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements as h
y
, and the height from a bottom plane (S
z
-S
z
′) including still other base edges (z,z, . . . ) of the triangular-pyramidal reflective elements up to the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements as h
z
, at least any two of h
x
, h
y
, and h
z
are substantially different from each other and a mirror reflective layer is formed on reflective side faces of the triangular-pyramidal reflective 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 triangular-pyramidal cube-corner retroreflective elements (hereafter also simply referred to as triangular-pyramidal reflective elements or CC reflective elements) are remarkably superior to a retroreflective body using conventional micro glass beads in retroreflective efficiency of light and thereby, uses of the triangular-pyramidal cube-corner retroreflective elements have been increased year by year because of its superior retroreflective performance.
However, though conventional publicly-known triangular-pyramidal retroreflective elements show 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 triangular-pyramidal cube-corner retroreflective elements and inserting with each other at an angle of 90°) of the elements and an entrance ray is small because of the reflection theory of the elements, 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 elements 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 elements and that of air reaches the back of the elements without totally reflecting from the interface of the elements. Therefore, a retroreflective sheeting using triangular-pyramidal reflective elements generally has a disadvantage that it is inferior in entrance angularity.
However, because triangular-pyramidal retroreflective elements can reflect light in the direction in which the light enters over the almost entire surface of the elements, reflected light does not reflect by diverging at a wide angle due to spherical aberration like the case of micro-glass bead reflective elements. 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 frequency of 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, the specification of Jungersen's U.S. Pat. No. 2,481,757 discloses retroreflective elements assembly in which all base edges of triangular-pyramidal reflective elements are present on the same plane, the optical axis of each retroreflective elements tilts from the direction vertical to the basic plane, and a mirror reflective layer is formed on surfaces of prism side faces of the retroreflective elements. These retroreflective elements form a retroreflective element pair faced each other at the both sides of a shared base edge and the optical axis of the retroreflective element pair tilts in directions opposite to each other.
Moreover, the official gazette of Stamm's Japanese Patent Laid-Open No. Sho 49-106839 (specification of U.S. Pat. No. 3,712,706) discloses a retroreflective sheeting constituted by an assembly of normal triangular-pyramidal cube-corner retroreflective elements each of whose bottom planes is an equilateral triangle and on each of whose reflection-side surfaces a mirror reflective layer is formed. The optical axis of each of the retroreflective elements is vertical to the bottom plane of the elements.
The triangular-pyramidal cube-corner retroreflective elements in the above two proposals respectively have a mirror reflective layer on surfaces of their prism side faces. Therefore, incoming light hardly passes through retroreflective elements but it is substantially entirely reflected. Therefore, when comparing the above retroreflective elements with triangular-pyramidal cube-corner retroreflective elements having no mirror reflective layer according to only the internal total reflection theory, all rays to be retroreflected greatly increase and are superior in entrance angularity.
However, CC reflective elements designed so that the optical axis tilts have a problem that differences between areas of three reflective side faces (faces a, b, and c) excessively increase and the retroreflective performance is deteriorated.
The present inventor et al. have found in recent years that it is possible to improve the entrance angularity of a retroreflective sheeting constituted by the above retroreflective elements by substantially making the depth (h′)[equal to the height of apexes (H
1
and H
2
) from the bottom pla
Hamada Yutaka
Matsuda Akihiro
Mimura Ikuo
Yoshioka Takashi
Fitzpatrick ,Cella, Harper & Scinto
Nippon Carbide Kogyo Kabushiki Kaisha
Phan James
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