Optical: systems and elements – Projection screen – Rear projection screen
Reexamination Certificate
2003-01-24
2004-12-28
Mack, Ricky (Department: 2873)
Optical: systems and elements
Projection screen
Rear projection screen
C359S456000, C359S457000, C359S453000
Reexamination Certificate
active
06836363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rear projection screen including a Fresnel lens sheet. More particularly, the present invention relates to a rear projection screen capable of displaying sharp images without producing ghost or double images, and to a rear projection type display including such a rear projection screen.
2. Description of Related Art
So-called rear projection type displays, which include rear projection screens on which light (imaging light) is projected from their back sides, are known as displays having large-sized screens.
As shown in
FIG. 3
, a conventional rear projection type display
101
is composed of: a rear projection screen
103
; a projector
105
for projecting light
106
on the rear projection screen
103
; and a reflector
104
for reflecting the projected light
106
into the back-side surface of the rear projection screen
103
. The rear projection screen
103
, the projector
105
and the reflector
104
, which are positioned as shown in
FIG. 3
, are contained within a cabinet
102
. Namely, the rear projection screen
103
is set in a bored window made in the upper part of the front (observation-side) surface of the cabinet
102
, and the projector
105
is placed at the lower part in the cabinet
102
. The reflector
104
is placed at the upper part in the cabinet
102
so that it can reflect the light
106
projected from the projector
105
, into the back-side surface of the rear projection screen
103
.
FIG. 4
is a view showing a typical rear projection screen
103
for use in the rear projection type display
101
shown in FIG.
3
. As shown in this drawing, the typical rear projection screen
103
includes a Fresnel lens sheet
111
on its back side and a lenticular lens sheet
121
on its observation side. The Fresnel lens sheet
111
and the lenticular lens sheet
121
are positioned in close proximity in the rear projection screen
103
; in general, they are closely fitted. The Fresnel lens sheet
111
has a Fresnel lens
112
on its observation-side surface and a flat surface
114
as its back-side surface. The lenticular lens sheet
121
has lenticular lenses
122
on its back-side surface (the surface facing to the Fresnel lens sheet
111
) arranged so that grooves will be vertically formed between the lenticular lenses. Further, on the observation-side surface of the lenticular lens sheet
121
, black stripes
123
for preventing the reflection of light entering from the observation side of the lenticular lens sheet
121
are formed on those parts corresponding to the non-light-converging parts of the lenticular lenses
122
provided on the back-side surface of the lenticular lens sheet
121
.
In the rear projection type display
101
having the above-described arrangements, when light
106
projected from the projector
105
is reflected from the reflector
104
into the back-side surface of the rear projection screen
103
, most of the incident light passes through the rear projection screen
103
and becomes imaging light
107
. However, the back-side surface of the rear projection screen
103
reflects a part of the incident light, and the reflector
104
reflects this reflected light
108
into the rear projection screen
103
. The reflected light
108
thus re-enters into the rear projection screen
103
at the point different from the one at which the projected light
106
has firstly entered, and finally emerges as ghost light
109
from the observation side. For this reason, when the rear projection screen
103
in the rear projection type display
101
is observed, ghost images are seen in addition to the properly reflected image in a position deviated from that of the properly reflected image. Such ghost images tend to appear when the optical path length between the projector
105
and the rear projection screen
103
(i.e., projection distance) is shorter and when the distance between the rear projection screen
103
and the reflector
104
is shorter. The appearance of ghost images is therefore a big problem encountered in attempts to make the rear projection type display
101
thinner.
A conventionally proposed measure for preventing the appearance of ghost images is such that an antireflection layer is formed on the back-side surface of a rear projection screen. With this measure, however, it is difficult to perfectly prevent the appearance of ghost images although it is possible to make the intensity of ghost images lower. Moreover, it is necessary to conduct vacuum deposition or the like to form an antireflection layer on the back-side surface of a rear projection screen. This process is poor in production efficiency, so that the above-described measure is inadequate from an industrial point of view.
On the other hand, Japanese Laid-Open Patent Publication No. 158153/1993 discloses the following measure of preventing the appearance of ghost images: the back-side surface of a Fresnel lens sheet to be used for a rear projection screen is roughened by forming crepe finish, hair lines, lenticular lenses or the like; in particular, lenticular lenses are provided in such a direction that grooves will be horizontally formed between the lenticular lenses. However, if the back-side surface of a Fresnel lens sheet is simply roughened in the manner as disclosed in this publication, the projected image tends to have lowered definition and contrast. Moreover, the formation of lenticular lenses on the back-side surface of a Fresnel lens sheet promotes the appearance of a moire pattern.
SUMMARY OF THE INVENTION
The present invention was accomplished in the light of the foregoing drawbacks in the related art. Namely, an object of the present invention is to provide a rear projection screen that can effectively prevent the appearance of ghost images which is caused by projected light reflected from the back-side surface of the rear projection screen, that can be excellent in production efficiency, that can display an image having satisfactorily high definition and contrast, and that does not promote the appearance of moire patterns; and a rear projection type display including such a rear projection screen.
Another object of the present invention is to provide a rear projection screen that scarcely undergoes curling, which leads to the lowering of image definition, with changes in environmental conditions such as change in humidity; and a rear projection type display including such a rear projection screen.
The present invention provides a rear projection screen comprising a Fresnel lens sheet that converges projected light entering from a back side thereof and allows the converged light to emerge from an observation side thereof, wherein the Fresnel lens sheet has an observation-side surface forming a Fresnel lens and a back-side surface forming a matte surface.
In the present invention, the Fresnel lens sheet preferably has a haze value defined in JIS (Japanese Industrial Standards) K7105 of 15 to 40%. Further, the matte surface of the Fresnel lens sheet preferably has a 60° specular gloss defined in JIS K 7105 of 20 to 45% and a 20° specular gloss defined in JIS K7105 of 5 to 15%.
Further, in the present invention, it is preferable that the Fresnel lens sheet includes a cured material layer formed by curing an ionizing-radiation-curing resin and a transparent substrate sheet laminated to the cured material layer; the Fresnel lens is formed in the cured material layer; and at least a surface of the transparent substrate sheet not facing to the cured material layer is matted to give the matte surface.
Furthermore, in the present invention, the transparent substrate sheet in the Fresnel lens sheet preferably shows a water absorption of not more than 0.2% when determined by immersing it in water at 23° C. for 24 hours under JIS K7209.
Furthermore, in the present invention, the Fresnel lens sheet preferably has a thickness between 0.2 mm and 1.5 mm.
Furthermore, in the present invention, it is preferable to subject the matte surface of the Fresnel lens sheet to antistatic
Goto Masahiro
Sekiguchi Hiroshi
Dai Nippon Printing Co. Ltd.
Mack Ricky
Parkhurst & Wendel L.L.P.
Thomas Brandi
LandOfFree
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