Optical: systems and elements – Signal reflector – 3-corner retroreflective
Reexamination Certificate
2000-10-23
2002-05-21
Phan, James (Department: 2872)
Optical: systems and elements
Signal reflector
3-corner retroreflective
C359S529000
Reexamination Certificate
active
06390629
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 triangular-pyramidal cube-corner retroreflective sheeting in which triangular-pyramidal reflective elements having a novel structure are arranged in the closest-packed state.
Still more minutely, the present invention relates to a cube-corner retroreflective sheeting constitute of triangular-pyramidal cube-corner retroreflective elements (hereafter referred to as triangular-pyramidal reflective elements or merely, elements) useful for signs including traffic signs and construction work signs, license plates of automobiles and motorcycles, safety materials of clothing and life preservers, markings of signboards, and reflectors of visible-light, laser-beam, and infrared-ray reflective sensors.
Still further minutely, the present invention relates to a triangular-pyramidal cube-corner retroreflective sheeting characterized in that triangular-pyramidal cube-corner retroreflective elements protruded beyond a common base plane (X-X′) are faced each other and arranged on the base plane (X-X′) in the closest-packed state by sharing one base edge on the base plane (X-X′), the base plane (X-X′) is a common plane including many base edges (x, x, . . . ) shared by the triangular-pyramidal reflective elements, the two triangular-pyramidal reflective elements faced each other constitute an element pair having substantially same shape faced so as to be respectively substantially symmetric to planes (Y-Y′, Y-Y′, . . . ) vertical to the base plane (X-X′) including many shared base edges (x, x, . . . ) on the base plane (X-X′), the triangular-pyramidal reflective elements are constituted of substantially same hexagonal or triangular lateral faces (prism faces) (faces c
1
and c
2
) using the shared base edges (x, x, . . . ) as one sides and substantially same quadrangular lateral faces (faces a
1
and b
1
and faces a
2
and b
2
) substantially orthogonal to the face c
1
or the face c
2
by using two upper sides of the face c
1
or c
2
starting with apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements as one sides and sharing one ridge line of the triangular-pyramidal reflective elements and using the ridge line as one side, and when assuming the height from the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements up to the base plane (X-X′) including the base edges (x, x, . . . ) of the hexagonal or triangular lateral faces (faces c
1
and c
2
) of the triangular-pyramidal reflective elements as (h), the height from the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements up to a substantially horizontal plane (Z-Z′) including base edges (z and w) of other lateral faces (faces a
1
and b
1
and faces a
2
and b
2
) of the triangular-pyramidal reflective elements as (h
0
), the intersection between a vertical line from the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements to the base plane (X-X′) and the base plane (X-X′) as P, the intersection between an optical axis passing through the apexes (H
1
and H
2
) and the base plane (X-X′) as Q, and moreover, expressing distances from the intersections (P) and (Q) up to planes (Y-Y′, Y-Y′, . . . ) including the base edges (x, x, . . . ) shared by the triangular-pyramidal reflective elements and vertical to the base plane (X-X′) as p and q, and assuming the angle formed between the optical axis and the vertical plane (Y-Y′) as (&thgr;), the above h and h
0
are not substantially equal and meet the following expression (1).
0.5
R
≦
h
h
0
≦
1.5
R
(
1
)
(In the above expression, R is defined by the following expression.)
R
=
sin
(
35.2644
*
-
θ
)
+
1.2247
sin
θ
sin
(
35.2644
*
-
θ
)
(In the above expression, it is assumed that when the value of the above (p−q) is negative, &thgr; takes a negative (−) value.)
BACKGROUND ART
A retroreflective sheeting for reflecting incoming 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 retroreflective sheeting using the retroreflective principle (theory) of a cube-corner retroreflective element such as a triangular-pyramidal reflective 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 the angle formed between the optical axis of the element {axis passing through the apex of the triangular pyramid of the triangular-pyramidal retroreflective element equally separate from three lateral faces (faces a, b, and c)} constituting a triangular-pyramidal cube-corner retroreflective element and intersecting each other at an angle of 90° and an incident light (the angle is hereafter referred to as entrance angle) is kept in a small range, the retro-reflectivity rapidly deteriorates as the entrance angle increases (that is, the entrance angularity deteriorates).
Moreover, the reflection principle (theory) of a triangular-pyramidal retroreflective element uses internal total reflection caused on the interface between air and a transparent medium constituting the triangular-pyramidal reflective element when light is emitted to air from the transparent medium at a specific angle {critical angle (&agr;
c
)} or more. The critical angle (&agr;
c
) is shown as the following expression by a refractive index (n) of a transparent medium constituting a triangular-pyramidal reflective element and a refractive index (n
0
) of air.
sin
α
c
=
n
0
n
In this case, it is allowed to consider the refractive index (n
0
) of air is almost equal to 1 and constant. Therefore, the critical angle (&agr;
c
) decreases as the value of the refractive index (n) of the transparent medium increases and light easily reflects from the interface between the transparent medium and air. When using a synthetic resin for a transparent medium, the critical angle (&agr;
c
) shows a comparatively large value of approx. 42° because most synthetic resins have a refractive index of approx. 1.5.
Light incoming to the surface of a retroreflective sheeting using the above triangular-pyramidal reflective element at a large entrance angle reaches the interface between the triangular-pyramidal reflective element and air at a comparatively small angle from a lateral face (reflecting surface) of the reflective element after passing through the triangular-pyramidal reflective element. When the comparatively small angle is smaller than the critical angle (&agr;
c
), the light passes through the back of the element without totally reflecting from the interface. Therefore, a retroreflective sheeting using a triangular-pyramidal reflective element has a disadvantage that it is generally inferior in entrance angularity.
However, because a triangular-pyramidal retroreflective element is able to reflect light in the light incoming direction over almost entire surface of the element, reflected light does not reflect by emanating to a wide angle due to spherical aberration like a micro-glass-bead reflective element. However, in practical use, the narrow divergence angle of retroreflected light easily causes a trouble that the light emitted from a head lamp of an automobile does not easily reach eyes of a driver present at a position separate from the optical axis of the light such as eyes of the driver when the light is retroreflected from a traffic sign. The above trouble more frequently occurs particularly when an automobile approac
Adachi Keiji
Mimura Ikuo
Nippon Carbide Kogyo Kabushiki Kaisha
Phan James
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