Optical: systems and elements – Signal reflector
Patent
1995-09-25
1998-10-13
Phan, James
Optical: systems and elements
Signal reflector
359530, 359532, 359534, 359546, 359552, 116 63R, 404 12, 404 16, G02B 5124
Patent
active
058221190
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a retroreflective sheeting material; methods of making this retroreflective sheeting material, and its use for the manufacture of signs, markers, and decorations.
1. The Technical Field
For the visible light region of the electromagnetic spectrum, retroreflective sheeting materials are used in a broad range of applications including but not limited to signs and markers of the reflex type. These reflex type materials provide a greater visibility at night compared to ordinary reflective materials such as mirror type or diffusing type reflectors because the retroreflected light is automatically returned toward the light source in a concentrated, more narrow cone in the field of viewing than ordinary reflected light.
Retroreflective sheeting materials are not limited to applications in the visible region of the electromagnetic spectrum. They may also be applied e.g. in the infrared region of the spectrum to retroreflect guidance light for aeroplanes. Therefore, retroreflective sheeting materials may not only comprise retroreflective optical systems reflecting light retroreflectivily but may generally comprise retroreflective electromagnetic systems reflecting electromagnetic radiation retroreflectively.
A known retroreflective sheeting material of the "open surface" type is based on micro glass spheres the exposed transparent surface of which is not covered with a protective layer. This material is prepared by cascading transparent micro glass spheres with a high refractive index and ranging in diameter from 70 to 100.mu. onto a carrier sheet which is covered with a heat-softenable layer of low-density polyethylene; thermally sinking the micro glass spheres to about 50% of their diameters by passing the carrier through a tunnel oven; and coating the exposed surfaces of the micro glass spheres with a vapor coated aluminium layer. The exposed parts of the micro glass spheres are then bonded into a polymeric bead bond layer on a sheeting material such as textile or adhesive paper, and the carrier liner is stripped away.
Functionally, these retroreflective optical systems consist of an entrance transmission optical element for receiving and focusing incident electromagnetic radiation from an irradiation source which is specifically constituted by the optionally transparent solid covering in combination with the transparent spheres refracting the incident light, and they further consist of a reflective optical element for reflecting the incident electromagnetic radiation back toward the irradiation source which is constituted by the transparent spacer film in combination with the back reflector; said reflective optical element being positioned in or near the focal point of the entrance transmission optical element, i.e. the focal point defined by spheres and spacing film in combination is located in or near the back surface of the spheres embedded in a reflective binder, or in or near the back reflector.
Generally, a spherical type retroreflective sheeting material has a good retroreflectivity for small as well as for large angles of incidence. However, maximum retroreflectivity is obtained for an angle of incidence close to zero, i.e. when the light is incident normal to the plane of the sheeting material. For increasing angles of incidence the retroreflectivity slowly decreases.
A disadvantage of the spherical type retroreflective optical system is that the angle of reflected rays is scattered significantly due to spherical aberration. Thus, a spot diagram obtained by raytracing a spherical type retroreflector having a refractive index of 1.9 showed that the angle of reflected rays scattered.+-.10 degrees for an angle of incidence of zero degrees.
Ideally, a perfect retroreflection without spherical aberration can only be obtained for paraxial rays incident on a transparent sphere having an index of refraction equal to two. However, transparent materials of e.g. glass or plastic having an index of refraction of 2.0 are not readily available.
Another di
REFERENCES:
patent: 2354018 (1944-07-01), Heltzer et al.
patent: 2354049 (1944-07-01), Palmquist
patent: 2407680 (1946-09-01), Palmquist et al.
patent: 3758192 (1973-09-01), Bingham
patent: 3993401 (1976-11-01), Strehlow
patent: 4036552 (1977-07-01), Lee et al.
patent: 4244683 (1981-01-01), Rowland
patent: 4332847 (1982-06-01), Rowland
patent: 4526439 (1985-07-01), Okoshi et al.
patent: 4758296 (1988-07-01), McGrew
patent: 5171624 (1992-12-01), Walter
Ibsen Per Eld
Rasmussen Michael
Stensborg Jan
Kell Erik Franke
Phan James
LandOfFree
Retroreflective sheeting material, a method of its production an does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Retroreflective sheeting material, a method of its production an, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Retroreflective sheeting material, a method of its production an will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-319113