Optical: systems and elements – Projection screen – Unitary sheet comprising plural refracting areas
Reexamination Certificate
1999-12-21
2001-10-23
Mahoney, Christopher E. (Department: 2851)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural refracting areas
C359S460000, C348S744000
Reexamination Certificate
active
06307675
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rear-projection screen and, more particularly, to a screen used as the display of a rear-projection TV using a liquid crystal panel as a video source.
FIG. 7
is a sectional plan view showing a conventional rear-projection screen generally used for a CRT rear-projection TV. This screen comprises, from the projection side (rear side), a Fresnel lens sheet
110
, double-side lenticular sheet
120
, and protective plate
130
.
The Fresnel lens sheet
110
has a transparent resin substrate
111
, and Fresnel lens
112
on its front side. The protective plate
130
has a transparent resin substrate
131
and, normally, a surface-treated layer
138
formed on its front side. The protective plate
130
prevents dust from sticking to the three-dimensional surface of the double-side lenticular sheet
120
on the front side and protects a light-shielding layer
125
. The surface-treated layer
138
of the protective plate
130
is formed as an abrasion-resistant hard coat or an antistatic treatment.
The lenticular sheet
120
has a resin substrate
121
and lenticular portions
122
and
123
on both surfaces of the substrate. The lenticular portion
122
on the rear side is constructed by horizontally juxtaposing a plurality of cylindrical lenses extending in the vertical direction. The lenticular portion
122
is provided to refract/diffuse video light in the horizontal direction. The lenticular portion
123
on the observation side (front side) is also constructed by horizontally juxtaposing a plurality of cylindrical lenses extending in the vertical direction. The lenticular portions
122
and
123
have the function of correcting a color shift (to be described later).
A light diffusing material
124
is mixed into the resin substrate
121
of the lenticular sheet
120
to refract/diffuse video light in the vertical direction. The resin substrate
121
has on its front side protruding portions alternating with the cylindrical lenses of the lenticular portion
123
. Each protruding portion has a flat top on which a light-shielding layer
125
is formed by printing black ink or the like. The light-shielding layer
125
is provided to improve external light contrast.
Recently, CRT rear-projection TVs are being replaced with liquid crystal rear-projection TVs with characteristic features such as small power consumption, high-image-quality, and lightweight/low-profile structure. In a CRT rear-projection TV, an image is projected from three tubes of R, G, and B, and the positional difference between the three tubes generates a color shift. To correct the color shift, the rear-projection screen must have a double-side lenticular sheet. However, in a liquid crystal rear-projection TV, video light from the liquid crystal is projected through a monocular lens, and no color shift due to the position difference occurs. Hence, the rear-projection screen can use a single-side lenticular sheet.
FIG. 8
is a sectional plan view showing a conventional rear-projection screen used for a liquid crystal rear-projection TV. This screen comprises, from the rear side, a Fresnel lens sheet
140
and horizontal lenticular sheet
150
.
The Fresnel lens sheet
140
has a resin substrate
141
, and Fresnel lens
142
on its front side. The lenticular sheet
150
has a resin substrate
151
, lenticular portion
152
on its rear side, and surface-treated layer
158
on its front side. The lenticular portion
152
is constructed by horizontally juxtaposing a plurality of cylindrical lenses in the vertical direction. The lenticular portion
152
is disposed to refract/diffuse video light in the horizontal directions
This screen has no light-shielding layer as shown in
FIG. 7
, so low contrast due to external light poses a problem. To refract/diffuse video light in the vertical direction and increase the contrast, light diffusing material
154
and dark colorant
154
are mixed into the resin substrate
151
of the lenticular sheet
150
. The effect provided is not sufficient, and therefore, a light diffusing material
144
is mixed into the resin substrate
141
of the Fresnel lens sheet
140
.
A considerably large amount of light diffusing materials
144
and
154
and dark colorant
154
need be added to obtain a sufficient addition effect. As a result, the screen luminance becomes low in proportion to the content of the added materials. If the content is small, the video light refraction/diffusion function in the vertical direction is insufficient, resulting in a narrow vertical viewing angle of the screen.
FIG. 9
is a sectional plan view showing another example of the conventional rear-projection screen used for a liquid crystal rear-projection TV. This screen comprises, from the rear side, a Fresnel lens sheet
160
and horizontal lenticular sheet
170
.
The Fresnel lens sheet
160
has a resin substrate
161
, and Fresnel lens
162
on its front side. A light diffusing material
164
is mixed into the resin substrate
161
of the Fresnel lens sheet
160
.
The horizontal lenticular sheet
170
has a resin substrate
171
, and lenticular portion
172
on its rear side. The lenticular portion
172
on the rear side is constructed by horizontally juxtaposing a plurality of cylindrical lenses extending in the vertical direction. A UV curing resin layer
176
and light-shielding layer
175
are formed on the front side of the resin substrate
171
. The light-shielding layer
175
consists of black stripes formed in regions except the light focusing portions of the cylindrical lenses of the lenticular portion
172
.
The horizontal lenticular sheet
170
also has a protective resin substrate
181
bonded to the front side of the light-shielding layer
175
via an adhesive layer
177
. A light diffusing material
184
and dark colorant
184
are mixed into the resin substrate
181
. A surface-treated layer
188
is formed as an anti-reflection treatment, antistatic treatment, and hard coat treatment on the front side of the resin substrate
181
.
According to the screen shown in
FIG. 9
, the contrast is improved, and the content of the above-described colorant or light diffusing material can be reduced because of the effect of the black light-shielding layer
175
. In this case, however, a phenomenon called “hot bar” inherent to the liquid crystal rear-projection TV is observed. In the “hot bar” phenomenon, light from the projector light source is observed locally bright, on the screen surface, as a long bar which extends in the horizontal direction perpendicular to the length of the cylindrical lenses of the lenticular portion
172
. To solve this phenomenon, light diffusing materials and colorants
164
and
184
are mixed into the resin substrate
161
of the Fresnel lens sheet
160
and the protective resin substrate
181
, respectively, to subject them to a light diffusion treatment. For this screen, however, the screen luminance lowers, and the manufacturing cost increases because of preparation of the resin substrates
161
and
181
.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to improve both the contrast and luminance of a screen used as the display of a rear-projection TV and also reduce the manufacturing cost.
It is another object of the present invention to increase the viewing angle in an improved screen.
According to the first aspect of the present invention, there is provided a rear-projection screen for which a projection side is defined as a rear side, and an observation side is defined as a front side, comprising:
a first lenticular portion having a plurality of cylindrical lenses extending in a first direction and juxtaposed in a second direction perpendicular to the first direction;
a first substrate disposed on the front side of the first lenticular portion, the first substrate having a thickness of 0.5 to 3 mm, a total light transmittance Tt1 of 75 to 95%, a diffusion transmittance Dt1 of 40 to 70%, and a haze value H1 of 50 to 80;
a Fresnel lens disposed on the front side of the first substra
Abe Takashi
Nishikawa Yuichi
Ono Yoshiyuki
Yoshida Tsutomu
Mahoney Christopher E.
Staas & Halsey , LLP
Toppan Printing Co. Ltd.
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