Triangular-pyramidal cube-corner retroreflective sheeting

Details Triangular-pyramidal cube-corner retroreflective sheeting Triangular-pyramidal cube-corner retroreflective sheeting

2001-08-27

2004-02-03

Nguyen, Thong (Department: 2872)

Optical: systems and elements

Signal reflector

3-corner retroreflective

C359S529000

Reexamination Certificate

active

06685323

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 characterized in that triangular-pyramidal reflective elements respectively having a novel structure are arranged in the closest-packed state.
Still more minutely, the present invention relates to a triangular-pyramidal cube-corner retroreflective sheeting constituted of triangular cube-corner retroreflective elements (hereafter also referred to as triangular-pyramidal reflective elements or merely referred to as 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 beams, and infrared-ray reflective sensors.
Still more 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 first common bottom plane (virtual plane X-X′) are arranged so as to be faced each other in the closest-packed state on the first bottom plane (virtual plane X-X′) by sharing each base edge on the first bottom plane (virtual plane X-X′), the first bottom plane (virtual plane X-X′) is a common plane including the base edges (x, x, . . . ) shared by the triangular-pyramidal reflective elements, two opposite triangular-pyramidal reflective elements form a substantially-same-shape element pair faced each other so as to be substantially symmetric to planes (Y-Y′, Y-Y′, . . . ) vertical to the first bottom plane including the shared base edges (x, x, . . . ) on the first bottom plane (virtual plane X-X′), the triangular-pyramidal reflective elements are formed by substantially same triangular lateral faces (faces c
1
and c
2
) using each of the shared base edges (x, x, . . . ) as one side and two substantially same quadrangular lateral faces (faces a
1
and b
1
or faces a
2
or b
2
) substantially perpendicularly crossing the lateral faces (faces c
1
and c
2
), which (the above lateral faces a
1
and b
1
or lateral faces a
2
or b
2
) use each of two upper sides of the triangular lateral faces (faces c
1
and c
2
) started from apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements as one side and share one ridge line of the triangular-pyramidal reflective elements as one side, and the height (h′) from the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements up to the first bottom plane (virtual plane X-X′) including the base edges (x, x, . . . ) of the triangular lateral faces (faces c
1
and c
2
) of the triangular-pyramidal reflective elements is substantially smaller than the height (h) from the apexes (H
1
and H
2
) of the triangular-pyramidal reflective elements up to a substantilly-horizontal second bottom plane (Z-Z′) including base edges (z and w) of other lateral faces (faces a
1
and b
1
or faces a
2
or b
2
) of the triangular-pyramidal reflective elements.
BACKGROUND ART
A retroreflective sheeting is well known which reflects incoming light toward a light source and the sheeting using its retroreflective performance is widely used for the above application fields. Particularly, a retroreflective sheeting using the retroreflection principle of a cube-corner retroreflective element such as a triangular-pyramidal reflective element is exceptionally superior to a conventional retroreflective sheeting using micro-glass-beads in retroreflective efficiency of light and its purpose has expanded year by year because of its superior retroreflective performance.
However, though a conventionally publicly-known triangular-pyramidal retroreflective element shows a preferable retroreflective efficiency in a range of a small angle formed between the optical axis of the element (axis passing through the apex of a triangular pyramid which is present at the equal distance from three faces crossing each other at 90° and which constitutes a triangular-pyramidal cube-corner retroreflective element) and an entrance ray (this small angle is hereafter referred to as entrance angle), the retroreflective efficiency is suddenly deteriorated as the entrance angle increases (that is, entrance angularity is deteriorated).
Moreover, the reflection principle of a triangular-pyramidal retroreflective element conforms to the internal total reflection caused at the interface between air and a transparent medium constituting the triangular-pyramidal reflective element when light is transmitted into the air from the transparent medium at a specified angle {critical angle (&agr;
c
)} or more. The critical angle (&agr;
c
) is shown by the following expression in accordance with the refractive index (n) of the transparent medium and the refractive index (n′) of the air.
sin
⁢
 
⁢
α
c
=
n
′
n
In the above expression, because it is assumed that the refractive index (n′) of the air is almost equal to 1 and constant, the critical angle (&agr;
c
) decreases as the value of the refractive index (n) of the transparent medium increases and thereby, light more easily reflects at the interface between the transparent medium and the air. In general, because most synthetic resins have a refractive index of approx. 1.5, the critical angle (&agr;
c
) becomes a comparatively large value of approx. 42°.
Light incoming to the surface of a retroreflective sheeting using the above triangular-pyramidal reflective element at a large entrance angle passes through the triangular-pyramidal reflective element and reaches the interface between the element and air at a comparatively small angle. When the angle is less than the critical angle (&agr;
c
), the light is transmitted to the back of the element without totally reflecting from the interface. Therefore, a retroreflective sheeting using a triangular-pyramidal reflective element generally has a disadvantage that the entrance angularity is inferior.
However, because a triangular-pyramidal retroreflective element can reflect light in the direction from which the light enters almost over the entire surface of the element, reflected light does not diverge in a wide angle due to spherical aberration like the case of a micro-glass-bead reflective element.
However, the narrow divergent angle of the retroreflected light easily practically causes a trouble that when the light emitted from the head lamp of an automobile retroreflects from a traffic sign, the retroreflected light doe not easily reach eyes of a driver present at a position separate from the optical axis of the light. The trouble of this type more frequently occurs (that is, an observation angle is deteriorated) because the angle (observation angle) formed between the entrance axis of rays and the axis (observation axis) connecting a driver with a reflection point increases particularly when an automobile approaches a traffic sign.
For the above cube-corner reflective sheeting, particularly a triangular-pyramnidal cube-corner retroreflective sheeting, many proposals have been known and various improvements and studies have been made.
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 sheet and a method for manufacturing the sheeting. The above U.S. patent discloses a triangular-pyramidal reflective element whose apex is located at the center of a bottom-plane triangle and a tilted triangular-pyramidal reflective element whose apex is not located at the center of a bottom-plane triangle and that light is efficiently reflected toward an automobile coming nearer. Moreover, it is disclosed that a triangular-pyramidal reflective element has a depth of {fraction (1/10)} in (2,540 &mgr;m) or less. Moreover, FIG. 15 of the above U.S. patent illustrates a triangular-pyramidal reflective

Affiliated with

Also associated with

Rating

Triangular-pyramidal cube-corner retroreflective sheeting does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Triangular-pyramidal cube-corner retroreflective sheeting, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Triangular-pyramidal cube-corner retroreflective sheeting will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3292740