Optical: systems and elements – Projection screen – Embedded particles
Reexamination Certificate
1998-08-14
2001-09-25
Mahoney, Christopher E. (Department: 2851)
Optical: systems and elements
Projection screen
Embedded particles
Reexamination Certificate
active
06295162
ABSTRACT:
TECHNICAL FIELD
The present invention relates to rear projection screens chiefly used for rear-projection-type projectors such as video projectors and slide projectors.
BACKGROUND ART
As rear projection screens of this type, there have conventionally been known those screens composed of a single lenticular lens sheet comprising as a base material a synthetic resin such as polymethyl methacrylate, and an inorganic material such as glass or aluminum hydroxide, or beads of an organic material such as polymethyl methacrylate or polystyrene, incorporated into the base material, and those screens composed of such a lenticular lens sheet and other lens sheets. In the case of these rear projection screens, imaging light is projected on the screens by using a light source such as a CRT.
In addition to CRTs, single-tube light sources such as LCDs, DMDs and ILAs have recent y been used as the light sources for projection. Further, images projected are also becoming very clear and distinct, like those images formed on high-definition televisions or the like.
DISCLOSURE OF THE INVENTION
As in the case of the conventional broadcasting systems such as the NTSC and PAL color television systems, the aforementioned conventional rear projection screens have such a problem that, especially when very clear and distinct images are projected on the screens, the displayed images undergo roughening. Specifically, the surfaces of the screens look as if they are covered with a very fine net, so that the images displayed on the screens are seem to be deteriorated. It is known that this problem becomes more serious when single-tube light sources are used for the formation of the images.
Further, the conventional rear projection screens cannot so well reproduce the gloss of metals, etc. as direct-view tubes. Moreover, the images displayed on the screens have low contrast; and they are observed to be whitish and to be insufficient in sharpness especially under strong extraneous light.
Furthermore, it has also been known that the surfaces of the conventional rear projection screens readily receive fine scratches and that -the above-described problems become more serious due to these scratches.
The present invention was accomplished in view of the aforementioned facts. An object of the present invention is therefore to provide a rear projection screen capable of providing an image which is free from roughening, which has gloss reproduced with high fidelity and which is excellent in contrast and sharpness.
Another object of the present invention is to provide a rear projection screen whose surface does not receive fine scratches which will be the cause of the deterioration of an image displayed on the screen.
The first feature of the present invention is a rear projection screen comprising a lens sheet or flat sheet having such an optical function as light-condensing or light-diffusing function, wherein at least a surface of an imaging-light-transmitting area in the light-emerging-side surface of the lens sheet or flat sheet is made smooth so that a surface roughness of the imaging-light-transmitting area will be from 0 to 0.40 micrometers.
In the first feature of the present invention, it is preferable that the surface of the imaging-light-transmitting area be made smooth by coating thereto a transparent material. Further, it is preferable that the surface of the imaging-light-transmitting area be made smooth by coating thereto a transparent material whose refractive index is lower than that of a base material of the lens sheet or flat sheet. Furthermore, it is preferable that the surface of the imaging-light-transmitting area be coated with a layer of the transparent material having a thickness d which can fulfill the equation d =&lgr;/4n, where n is a refractive index of the transparent material, d is a thickness, and &lgr; is a theoretical design wavelength. It is also preferable that the surface of the imaging-light-transmitting area be made smooth by coating thereto a transparent material whose hardness is higher than that of a base material of the lens sheet or flat sheet. In addition, it is preferable that a light-shielding layer be provided on the light-emerging-side surface of the lens sheet or flat sheet, excluding the surface of the imaging-light-transmitting area and that the light-shielding layer be coated with a transparent material.
The second feature of the present invention is a rear projection screen comprising a plurality of lens sheets or flat sheets having such an optical function as light-condensing or light-diffusing function, wherein at least a surface of an imaging-light-transmitting area in a light-emerging-side surface of at least the outermost sheet on an observation side of the lens sheets or flat sheets is made smooth.
According to the first and second features of the present invention, at least the surface of the imaging-light-transmitting area in the light-emerging-side surface of the lens sheet or flat sheet is made smooth. Therefore, the screen can provide an image that is free from roughening, which has gloss reproduced with high fidelity and which is excellent in contrast and sharpness. Further, the surface of the imaging-light-transmitting area is made smooth by coating thereto a transparent material whose hardness is higher than that of the base material of the lens sheet or flat sheet. Therefore, the image displayed on the screen is free from deterioration which is brought about by fine scratches formed on the screen.
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Dai Nippon Printing Co. Ltd.
Mahoney Christopher E.
Parkhurst & Wendel L.L.P
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