U.S. patent application number 12/560749 was filed with the patent office on 2010-01-07 for view angle control sheet.
Invention is credited to Masahiro GOTO.
Application Number | 20100002306 12/560749 |
Document ID | / |
Family ID | 35451008 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100002306 |
Kind Code |
A1 |
GOTO; Masahiro |
January 7, 2010 |
VIEW ANGLE CONTROL SHEET
Abstract
A view angle control sheet which can suppress a decrease in
screen brightness is provided. Lens portions having trapezoidal
shapes in cross section are arranged at predetermined intervals,
and a wedge-shaped portion between the lens portions adjacent to
each other is filled with the same material as the lens portion or
with a material different from the lens portion. In the
wedge-shaped portion, a bottom surface is provided on a screen
image side while a leading edge is provided on an observer side,
and at least a slope portion of the wedge-shaped portion is made of
a material having a refractive index lower than that of a lens
portion material.
Inventors: |
GOTO; Masahiro; (Tokyo-to,
JP) |
Correspondence
Address: |
LADAS & PARRY LLP
224 SOUTH MICHIGAN AVENUE, SUITE 1600
CHICAGO
IL
60604
US
|
Family ID: |
35451008 |
Appl. No.: |
12/560749 |
Filed: |
September 16, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10562516 |
Dec 28, 2005 |
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PCT/JP2005/007911 |
Apr 26, 2005 |
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12560749 |
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Current U.S.
Class: |
359/613 ;
359/614 |
Current CPC
Class: |
G02F 1/133524 20130101;
G02F 1/133562 20210101; G02B 5/003 20130101 |
Class at
Publication: |
359/613 ;
359/614 |
International
Class: |
G02B 27/00 20060101
G02B027/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2004 |
JP |
2004-154911 |
Claims
1. A display device having a view angle control sheet being bonded
to a liquid crystal display panel wherein the view angle control
sheet comprising lens portions having trapezoidal shapes in cross
section arranged a predetermined intervals, a wedge-shaped portion
between the lens portion adjacent to each other is filled with the
same material as that of the lens portions or with a material
different from the lens portions, the wedge-shaped portion has a
bottom surface on the liquid crystal display panel side while
having a leading edge on an observer side with an outside light
beam absorption effect, and the following relationships are held at
least between a refractive index (N2) of a material constituting a
slope portion of the wedge-shaped portion and a refractive index
(N1) of a material constituting the lens portions: N2.ltoreq.N1,
N1-0.01.ltoreq.N2
2. A display device according to claim 1, wherein an angle
(.theta.) (degree) formed by the slope portion and a normal line of
a light beam outgoing plane exists in the following range:
3.ltoreq..theta..ltoreq.20.
3. A display device according to claim 1, wherein the following
relationship is held further between the refractive indexes (N1)
and (N2): 0.8N1.ltoreq.N2.ltoreq.0.98N1.
4. A display device according to claim 1, wherein a cross-sectional
shape of the wedge-shaped portion is a substantial isosceles
triangle.
5. A display device according to claim 1, wherein one of angles
formed by two slopes of the wedge-shaped portion and the normal
line of the light beam outgoing plane of the view angle control
sheet is larger than the other.
6. A display device according to claim 1 wherein the slope portion
of the view angle control sheet has a curved cross-sectional shape
or a polygonal-line cross-sectional shape such that the liquid
crystal display panel side differs from the observer side in an
angle formed by the slope portion and an observer side surface.
7. A display device according to claim 1, wherein light beam
absorption particles of the view angle control sheet are added to
the wedge-shaped portion.
8. A display device according to claim 7, wherein an average
particle size of the light beam absorption particles is at least 1
.mu.m and the average particle size is not more than two-thirds of
a width of the bottom surface.
9. A display device according to claim 7, wherein an addition
amount of the light beam absorption particle ranges from 10 to 50%
by volume.
10. A display device according to claim 1, wherein a function of
any one of anti-reflection (AR), anti-static (AS), anti-glaring
(AG), and a touch sensor or a plurality of functions thereof are
impacted to at least one surface side of the view angle control
sheet.
11. A display device according to claim 1, wherein the view angle
control sheet is arranged in a crosswise stripe.
12. A display device according to claim 1, wherein one view angle
control sheet is laminated on the observer side of the liquid
crystal display panel or two view angle control sheets are
laminated on the observer side of the liquid crystal display panel
while being substantially orthogonal to each other.
13. A display device according to claim 12, wherein the width of
the bottom surface of the view angle control sheet is not more than
1/1.5 of a size of one pixel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a view angle control sheet
which is suitably used for display devices such as an organic light
emitting diode (hereinafter referred to as an "OLED") display and a
liquid crystal display (hereinafter referred to as an "LCD").
BACKGROUND ART
[0002] Usually it is preferable that an OLED display, an LCD, and
the like have a wide view angle such that a good image is obtained
when an observer sees the image from any position. For example,
Patent Document 1 discloses a light diffusion sheet, in which
plural unit lenses are formed in a one-dimensional direction or a
two-dimensional direction, the unit lens includes a total
reflection portion where total reflection of a part of an incident
light beam is generated in an inner plane of the total reflection
portion, the unit lens is made of a material having a predetermined
refractive index N1, and a portion located between the adjacent
unit lenses is filled with a material having a predetermined
refractive index N2.
[0003] On the other hand, for example, when a person performs work
in a commuter train, sometimes the person needs to prevent other
people from taking a look inside a screen. In such cases, it is
desirable that the view angle be controlled such that the screen
can be seen only from the observer of the display while the screen
cannot be seen from other people. In order to meet such the demand,
for example, a louver type view angle control sheet is developed
and used as shown in FIG. 15.
[0004] Patent Document 1: Japanese Patent Application Laid-Open No.
2003-50307
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0005] However, in the louver type view angle control sheet,
because screen image light in an oblique direction is simply cut,
there is a problem that screen brightness is decreased.
[0006] In view of the foregoing, an object of the invention is to
provide a view angle control sheet that can control the decrease in
screen brightness.
Means for Solving the Problem
[0007] The invention will be described below.
[0008] In the invention according to claim 1, the problem is solved
by a view angle control sheet characterized in that lens portions
having trapezoidal shapes in cross section are arranged at
predetermined intervals, a wedge-shaped portion between the lens
portions adjacent to each other is filled with the same material as
the lens portion or with a material different from the lens
portion, the wedge-shaped portion has a bottom surface on a screen
image side while having a leading edge on an observer side, and the
following relationship holds at least between a refractive index N2
of a material constituting a slope portion of the wedge-shaped
portion and a refractive index N1 of a material constituting the
lens portion:
N2.ltoreq.N1.
[0009] In the view angle control sheet according to claim 1, the
invention according to claim 2 is characterized in that an angle
.theta. (degree) formed by the slope portion and a normal line of a
light beam outgoing plane exists in the following range:
3.ltoreq..theta..ltoreq.20.
[0010] In the view angle control sheet according to claim 2, the
invention according to claim 3 is characterized in that the
following relationship holds further between the refractive indexes
N1 and N2:
0.8N1.ltoreq.N2.ltoreq.0.98N1.
[0011] In the view angle control sheet according to claim 1 or 2,
the invention according to claim 4 is characterized in that the
following relationship holds still further between the refractive
indexes N1 and N2:
N1-0.01.ltoreq.N2.
[0012] In the view angle control sheet according to any one of
claims 1 to 4, the invention according to claim 5 is characterized
in that, when a ratio of the refractive indexes N1 and N2 is
N2/N1=R, the following relationship holds further in the angle
.theta. (degree) formed by the slope portion of the wedge-shaped
portion and the normal line of the light beam outgoing plane:
-0.01<R-cos .theta.<0.002.
[0013] In the view angle control sheet according to any one of
claims 1 to 5, the invention according to claim 6 is characterized
in that a cross-sectional shape of the wedge-shaped portion is a
substantial isosceles triangle.
[0014] In the view angle control sheet described in any one of
claims 1 to 5, the invention according to claim 7 is characterized
in that one of angles formed by two slopes of the wedge-shaped
portion and the normal line of the light beam outgoing plane is
larger than the other.
[0015] In the view angle control sheet according to any one of
claims 1 to 7, the invention according to claim 8 is characterized
in that the slope portion has a curved cross-sectional shape and/or
a polygonal-line cross-sectional shape such that the screen image
side differs from the observer side in an angle formed by the slope
portion and an observer side surface.
[0016] In the view angle control sheet according to any one of
claims 1 to 8, the invention according to claim 9 is characterized
in that the wedge-shaped portion has a light beam absorption
effect.
[0017] In the view angle control sheet according to any one of
claims 1 to 9, the invention according to claim 10 is characterized
in that light beam absorption particles are added to the
wedge-shaped portion.
[0018] In the view angle control sheet according to claim 10, the
invention according to claim 11 is characterized in that an average
particle size of the light beam absorption particles is at least 1
.mu.m and the average particle size is not more than two-thirds of
a width of the bottom surface.
[0019] In the view angle control sheet according to claim 10 or 11,
the invention according to claim 12 is characterized in that an
addition amount of the light beam absorption particle ranges from
10 to 50% by volume.
[0020] In the view angle control sheet according to any one of
claims 1 to 12, the invention according to claim 13 is
characterized in that a function of any one of AR, AS, AG, and a
touch sensor or plurality functions there of are imparted to at
least one surface side.
[0021] The invention according to claim 14 is a display device
characterized in that a view angle control sheet according to any
one of claims 1 to 13 is bonded.
[0022] The invention according to claim 15 is a display device
characterized in that a view angle control sheet according to any
one of claims 1 to 13 is arranged in a crosswise stripe.
[0023] The invention according to claim 16 is a display device
characterized in that one view angle control sheet according to any
one of claims 1 to 13 is laminated on the observer side of a screen
image source or two view angle control sheets according to any one
claims 1 to 13 are laminated on the observer side of the screen
image source while being substantially orthogonal to each
other.
[0024] In the display device according to claim 16, the invention
according to claim 17 is characterized in that the width of the
bottom surface is not more than 1/1.5 of a size of one pixel.
EFFECT OF THE INVENTION
[0025] According to the invention, the view angle control sheet
that can suppress the decrease in brightness can be obtained.
Further, according to the view angle control sheet of the
invention, image contrast can be improved. These features and
advantages of the invention will be apparent from the following
best mode for carrying out the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a view showing a cross section in a direction of a
view angle control sheet according to a first embodiment of the
invention;
[0027] FIG. 2 is a view showing a cross section in a direction of a
view angle control sheet according to a second embodiment of the
invention;
[0028] FIG. 3 is a view showing a cross section in a direction of a
view angle control sheet according to a third embodiment of the
invention;
[0029] FIG. 4 is a view showing a cross section in a direction of a
view angle control sheet according to a fourth embodiment of the
invention;
[0030] FIG. 5 is a view showing a cross section in a direction of a
view angle control sheet according to a fifth embodiment of the
invention;
[0031] FIG. 6 is a schematic sectional view illustrating a status
in which a light beam reflected from a slope of a wedge-shaped
portion of the view angle control sheet reaches an observer
side;
[0032] FIG. 7 is a view for examining a condition that the light
beam is incident to a lens portion such that the light beam is
emitted toward a direction perpendicular to the view angle control
sheet;
[0033] FIG. 8 is a view for examining a condition that the light
beam is incident to the lens portion so as to be emitted at a
10.degree. angle with respect to the view angle control sheet;
[0034] FIG. 9 is a view showing various shape modes of a
low-refractive index portion;
[0035] FIG. 10 is a view showing the cross section of the view
angle control sheet in which a slope shape of the wedge-shaped
portion exhibits another mode;
[0036] FIG. 11 is a view showing an example of a configuration of
the view angle control sheet;
[0037] FIG. 12 is a view showing another example of the
configuration of the view angle control sheet;
[0038] FIG. 13 is a view showing still another example of a
configuration of the view angle control sheet;
[0039] FIG. 14 is a view showing an example of the configuration of
a display device provided with the view angle control sheet;
and
[0040] FIG. 15 is a view showing an example of the conventional
view angle restriction sheet.
DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS
[0041] S1, S2, S3, S4, S5, S9, S10, and S11 view angle control
sheet [0042] 11, 21, 31, 41, 51, 61, 71, and 91 screen image-side
base sheet [0043] 12, 22, 32, 42, 52, 62, 72, and 92 lens portion
[0044] 13, 23, 33, 43, 53, 63, 73, and 93 observer-side base sheet
[0045] 14, 24, 34, 44, and 54 wedge-shaped portion [0046] 35 and 55
inter-lens portion [0047] 17, 27, 37, 47, and 57 bottom surface
[0048] 120 display device
[0049] L11, L12, L13, L21, L22, L23, L31, L32, L33, L41, L42, L43,
L51, L52, and L53 light beam [0050] L14, L24, L34, L44, and L54
light incident to bottom surface [0051] L15, L25, L37, L45, and L55
outside light beam
BEST MODE FOR CARRYING OUT THE INVENTION
[0052] The invention will be described below based on preferred
embodiments shown in the drawings.
[0053] FIG. 1 is a view showing a cross section in a direction of a
view angle control sheet S1 according to a first embodiment of the
invention. In FIG. 1, a screen image light source is arranged on
the left side in the drawing, and an observer lies on the right
side in the drawing. The view angle control sheet S1 is formed by
gluing a screen image-side base sheet 11, a lens portion 12, and an
observer-side base sheet 13 in order from the screen image side to
the observer side. The lens portion 12 is made of a material whose
refractive index is N1. In FIG. 1, a portion having a triangular
shape in cross section sandwiched by hypotenuses of the lens
portions 12 and 12 vertically adjacent to each other is filled with
a material having the refractive index N2 lower than the refractive
index N1 of the lens portion 12. Here in after the portion filled
with the low-refractive index material is referred to as
"wedge-shaped portion 14". The wedge-shaped portion 14 has a
leading edge on the observer side, and the wedge-shaped portion 14
has a bottom surface 17 on the screen image side.
[0054] A ratio of the refractive index N1 of the lens portion 12 to
the refractive index N2 of the wedge-shaped portion 14 is set in a
predetermined range in order to secure optical characteristics of
the view angle control sheet S1. An angle formed by the hypotenuse
where the wedge-shaped portion 14 and the lens portion 12 are in
contact with each other and a normal line V (line parallel to a
normal-incidence light beam to the view angle control sheet S1) of
an outgoing light beam plane is formed at a predetermined angle
.theta..sub.1.
[0055] In the invention, the angle .theta..sub.1 is set in the
range of 3 to 20 degrees in order to totally reflect the screen
image light beam at the slope portion of the wedge-shaped portion
to narrow the view angle. In the angle setting of the total
reflection plane, an optimum value depends on a distance between a
imaging surface and the view angle control sheet, resolution of the
image screen, necessary view angle brightness, and the like. In
order to suppress the decrease in resolution caused by ghost
generation or the like, it is necessary that positional
displacement between the totally reflected screen image and the
directly transmitted screen image be decreased by setting angle
.theta..sub.1 in the range of about 3 to about 5 degrees. Because
the decrease in resolution caused by the ghost generation or the
like becomes remarkable when the distance between the imaging
surface and the sheet is broadened, similarly it is necessary to
decrease the angle .theta..sub.1. On the contrary, it is thought
that the angle .theta..sub.1 ranging from about 5 to about 20
degrees is also required in order to sufficiently exert brightness
increase effect. Thus, it is necessary that the optimum value is
determined as the angle .theta..sub.1by performing design in
appropriate consideration of the view angle and the distance
between the imaging surface and the view angle control sheet. With
reference to a refractive index difference, similarly the
refractive index difference is increased in order to obtain the
brightness increase effect in the wide range. On the other hand,
when the decrease in resolution caused by the ghost is suppressed
rather than obtaining the brightness increase effect only near a
front face, it is necessary to decrease the refractive index
difference. That is, in the broad distance between the imaging
surface and the view angle control sheet, in the case of emphasis
on the resolution, it is advantageous that the angle .theta..sub.1
is decreased while the refractive index difference is decreased. On
the other hand, in the narrow distance between the imaging surface
and the view angle control sheet, in order to obtain the brightness
increase effect in the wide range, it is advantageous that the
angle .theta..sub.1 is increased while the refractive index
difference is increased.
[0056] In consideration of all the above things, usually the angle
.theta..sub.1 is set in the range of 3 to 20 degrees. When the
angle .theta..sub.1 exceeds 20 degrees, the sufficient brightness
increase effect is decreased in the front face and only the
decrease in resolution becomes remarkable. The ghost is also easily
generated. When the angle .theta..sub.1 is set lower than 3
degrees, because the diffusion light beams do not reach the
observer-side front face, the brightness increase effect is not
obtained. From the viewpoint of difficulty of die production, in
the range in which the production can stably be performed, it is
preferable that the angle .theta..sub.1 be at least 5 degrees. When
the angle .theta..sub.1 is set near the range of 3 to 5 degrees, an
aperture ratio can be increased to improve the contrast. However,
the effect that the brightness at zero degree is improved is
weakened because the angle .theta..sub.1 focuses the diffusion
light beams near zero degree. That is, when the angle .theta.1
ranges from 3 to 5 degrees, the brightness increase effect is
slightly decreased because the focus effect is decreased, and the
ghost is hardly generated due to the influence of the decrease in
brightness increase effect. Since the aperture can be increased
even if the angle .theta..sub.1 is decreased to the level of the
range of 3 to 5 degrees, the front-face brightness is decreased
only slightly. However, from the viewpoints of die production and
difficulty of lens molding, it is further preferable that the angle
.theta..sub.1 be at least 5 degrees. The description of the angle
.theta..sub.1 in the first embodiment shall also hold in the
following angles .theta..sub.2 to .theta..sub.6. In the embodiments
of the description including the first embodiment, the wedge-shaped
portion has the triangular cross-sectional shape. The invention is
not limited to the embodiment. For example, the cross-sectional
shape of the wedge-shaped portion may be formed in a trapezoid.
[0057] The wedge-shaped portion 14 is colored in predetermined
density with pigment such as carbon or with predetermined dye. The
screen image-side base sheet 11 and the observer-side base sheet 13
are made of the material whose refractive index is substantially
similar to the refractive index of the lens portion 12. An outside
surface of the observer-side base sheet 13 has a function of at
least one of AR, AS, and AG on the observer side. "AR" is the
abbreviation of anti-reflection, and the "AR" shall mean the
function of suppressing reflectance of the light beam incident to
the lens surface. "AS" is the abbreviation of anti-static, and the
"AS" shall mean the antistatic function. "AG" is the abbreviation
of anti-glare, and the "AG" shall mean the anti-glaring function of
the lens. The view angle control sheet S1 according to the first
embodiment may have only one of these functions, or the view angle
control sheet S1 may have the plural functions.
[0058] An optical path of the light beam incident to the lens
portion 12 of the view angle control sheet S1 will briefly be
described with reference to FIG. 1. The optical paths of the light
beams L11 to L15 are schematically shown in FIG. 1. The normal
light beam L11 incident near a center portion of the lens portion
12 from the screen image light source side goes straight in and
passes through the view angle control sheet S1 to reach the
observer. The light beam L12 incident near an end portion of the
lens portion 12 from the screen image light source side with a
predetermined angle is totally reflected at the hypotenuse due to
the refractive index difference between the refractive index N1 of
the lens portion 12 and the refractive index N2 of the wedge-shaped
portion 14, and the light beam L12 is output onto the observer side
as the normal light beam. The light beam L13 incident near the end
portion of the lens portion 12 from the screen image light source
side with the large angle is totally reflected at the hypotenuse,
and the light beam L13 is output onto the observer side with the
small angle close to the normal light beam unlike the incident
light beam in the opposite direction of the incident light beam.
The light beam L14 which directly impinges on the wedge-shaped
portion 14 from the bottom surface 17 is incident to the inside of
the wedge-shaped portion 14. Since the wedge-shaped portion 14 is
colored, the light beam L14 is absorbed by the wedge-shaped portion
14 and the light beam L14 never reaches the observer side. The
outside light beam L15 incident to the hypotenuse from the observer
side with the angle larger than the predetermined angle is not
totally reflected irrespective of the refractive index difference
between the lens portion 12 and the wedge-shaped portion 14, and
the outside light beam L15 is incident to the inside of the
wedge-shaped portion 14. The outside light beam L15 is absorbed by
the colored wedge-shaped portion 14. Accordingly, the image
contrast is improved in a visual field from the observer side.
Thus, the view angle can be controlled in the cross-sectional
direction and the decrease in brightness can be suppressed, so that
the high-contrast view angle control sheet can be obtained.
[0059] FIG. 2 is a view showing a cross section in a direction of a
view angle control sheet S2 according to a second embodiment. In
FIG. 2, similarly the screen image light source is arranged on the
left side in the drawing, and the observer lies on the right side
in the drawing. The view angle control sheet S2 is formed by gluing
a screen image-side base sheet 21, a lens portion 22, and an
observer-side base sheet 23 in order from the screen image side to
the observer side. The lens portion 22 is made of the material
whose refractive index is N1. In FIG. 2, a portion having the
triangular shape in cross section sandwiched by the hypotenuses of
the lens portions 22 and 22 vertically adjacent to each other is
filled with the material having the refractive index N2 lower than
the refractive index N1 of the lens portion 22. Here in after the
portion filled with the low-refractive index material is referred
to as "wedge-shaped portion 24". The wedge-shaped portion 24 has
the leading edge on the observer side, and the wedge-shaped portion
24 has a bottom surface 27 on the screen image side.
[0060] A ratio of the refractive index N1 of the lens portion 22 to
the refractive index N2 of the wedge-shaped portion 24 is set in
the predetermined range in order to secure the optical
characteristics of the view angle control sheet S2. An angle formed
by the hypotenuse where the wedge-shaped portion 24 and the lens
portion 22 are in contact with each other and the normal line V
(line parallel to the normal-incidence light beam relative to the
view angle control sheet S2) of the outgoing light beam plane is
formed at a predetermined angle .theta..sub.2.
[0061] The wedge-shaped portion 24 is colored in the predetermined
density with the pigment such as carbon or with the predetermined
dye. The screen image-side base sheet 21 and the observer-side base
sheet 23 are made of the material whose refractive index is
substantially similar to the refractive index of the lens portion
22. The outside surface of the observer-side base sheet 23 has the
function of at least one of AR, AS, and AG on the observer side. In
the second embodiment, the view angle control sheet S2 may have
only one of these functions, or the view angle control sheet S2 may
have the plural functions.
[0062] In the view angle control sheet S2 shown in FIG. 2, when the
lens portions 22 are arranged in the one-dimensional direction, a
black stripe BS is formed in the bottom surface 27 (many circular
black faces are formed when the lens portions 22 are arranged in
the two-dimensional direction). The inside of the wedge-shaped
portion 24 is filled with the material having the refractive index
N2 lower than the refractive index N1 of the lens portion 22. In
the view angle control sheet S2 having the above-described
configuration, light beams L21 to L23 incident from the screen
image light source side pass through the same optical paths as the
incident light beams L11 to L13 in the view angle control sheet S1
according to the first embodiment. A light beam L24 incident to the
black stripe BS of the bottom surface 27 is absorbed by the black
stripe BS. Further, an outside light beam L25 incident to the
hypotenuse from the observer side with the angle larger than the
predetermined angle is not totally reflected irrespective of the
refractive index difference between the lens portion 22 and the
wedge-shaped portion 24, and the outside light beam L25 is incident
to the inside of the wedge-shaped portion 24. The outside light
beam L25 is absorbed by the colored wedge-shaped portion 24.
Accordingly, the image contrast is improved in the visual field
from the observer side. Thus, the view angle control sheet S2 can
obtain the same effect as the view angle control sheet S1 according
to the first embodiment. That is, the view angle can be controlled
in the cross-sectional direction and the decrease in brightness can
be suppressed, so that the high-contrast view angle control sheet
can be obtained.
[0063] FIG. 3 shows a view angle control sheet S3 according to a
third embodiment of the invention. The view angle control sheet S3
is arranged by gluing a screen image-side base sheet 31, a lens
portion 32, and an observer-side base sheet 33 in order from the
screen image side to the observer side. The lens portion 32 is made
of the material having the high refractive index N1. Moreover, in
FIG. 3, a layer 34 (hereinafter referred to as "transparent
low-refractive index layer 34") is formed in the hypotenuses of the
lens portions 32 and 32 vertically adjacent to each other. The
transparent low-refractive index layer 34 is made of the
transparent material having the refractive index N2 lower than the
refractive index N1. A portion having the triangular shape in cross
section sandwiched by the hypotenuses of the adjacent lens portions
32 and 32 is filled with the material having the substantially same
refractive index as the refractive index N1 of the lens portion 32.
Hereinafter sometimes the portion having the triangular shape in
cross section is referred to as "inter-lens portion 35".
[0064] A ratio of the refractive index N1 of the lens portion 32 to
the refractive index N2 of the transparent low-refractive index
layer 34 is set in the predetermined range in order to secure the
optical characteristics of the view angle control sheet S3. An
angle formed by the hypotenuse where the transparent low-refractive
index layer 34 and the lens portion 32 are in contact with each
other and the normal line V (line parallel to the normal-incidence
light beam relative to the view angle control sheet S3) of the
outgoing light beam plane is formed at a predetermined angle
.theta..sub.3. The ratio and the angle .theta..sub.3 will be
described in detail later.
[0065] The lens portion 32 is usually made of the material such as
epoxy acrylate having an ionizing radiation-curable property. The
transparent low-refractive index layer 34 is made of the material
having the refractive index lower than the refractive index of a
transparent resin such as silica. In addition, the inter-lens
portion 35 is colored in the predetermined density with carbon, the
pigment or with the predetermined dye. The screen image-side base
sheet 31 and the observer-side base sheet 33 are made of the
material whose refractive index is substantially similar to the
refractive index of the lens portion 32. Similarly to the view
angle control sheet S1 according to the first embodiment, the
outside surface of the observer-side base sheet 33 has the function
of at least one of AR, AS, and AG on the observer side.
[0066] In the view angle control sheet S3 having the
above-described configuration, light beams L31 to L33 incident from
the screen image light source side pass through the same optical
paths as the incident light beams L11 to L13 in the view angle
control sheet S1 according to the first embodiment. A light beam
L34 which impinges on a bottom surface 37 of the colored inter-lens
portion 35 is incident to the inside of the colored inter-lens
portion 35, and the light beam L34 is absorbed by the colored
inter-lens portion 35 and the light beam L34 never reaches the
observer side. Further, an outside light beam L37 incident to the
hypotenuse from the observer side with the angle larger than the
predetermined angle is not totally reflected irrespective of the
refractive index difference between the lens portion 32 and the
transparent low-refractive index layer 34, the outside light beam
L37 is transmitted through the transparent low-refractive index
layer 34. Then, the outside light beam L37 is incident to the
inside of the colored inter-lens portion 35, and the outside light
beam L37 is absorbed by the colored inter-lens portion 35.
Accordingly, the image contrast is improved in the visual field
from the observer side. Thus, the view angle control sheet S3 can
obtain the same effect as the view angle control sheet S1 according
to the first embodiment. That is, the view angle can be controlled
in the cross-sectional direction and the decrease in brightness can
be suppressed, so that the high-contrast view angle control sheet
can be obtained.
[0067] FIG. 4 shows a cross section of a view angle control sheet
S4 according to a fourth embodiment of the invention. The view
angle control sheet S4 is arranged by gluing a screen image-side
base sheet 41, a lens portion 42, and an observer-side base sheet
43 in order from the screen image side to the observer side. The
lens portion 42 is made of the material having the high refractive
index N1. In FIG. 4, a portion having the triangular shape in cross
section sandwiched by the lens portions 42 and 42 vertically
adjacent to each other is filled with the material in which light
beam absorption particles 49 are added into a transparent material
(hereinafter referred to as "transparent low-refractive index
material 46") having the refractive index N2 lower than the
refractive index N1. Hereinafter the portion filled with the
low-refractive index material 46 is referred to as "wedge-shaped
portion 44". The wedge-shaped portion 44 has the leading edge on
the observer side, and the wedge-shaped portion 44 has a bottom
surface 47 on the screen image side.
[0068] A ratio of the refractive index N1 of the lens portion 42 to
the refractive index N2 of the low-refractive index material 46 is
set in the predetermined range in order to secure the optical
characteristics of the view angle control sheet S4. An angle formed
by the hypotenuse where the wedge-shaped portion 44 and the lens
portion 42 are in contact with each other and the normal line V
(line parallel to the normal-incidence light beam relative to the
view angle control sheet S4) of the outgoing light beam plane is
formed at a predetermined angle .theta..sub.4.
[0069] The lens portion 42 is usually made of the material such as
epoxy acrylate having the ionizing radiation-curable property. The
material such as urethane acrylate having the ionizing
radiation-curable property is usually used as the transparent
low-refractive index material 46. Commercially available color
resin fine particles can be used as the light beam absorption
particles 49. Further, the screen image-side base sheet 41 and the
observer-side base sheet 43 are made of the material whose
refractive index is substantially similar to the refractive index
of the lens portion 42. Similarly to the view angle control sheet
S1 according to the first embodiment, in the fourth embodiment, the
outside surface of the observer-side base sheet 43 has the function
of at least one of AR, AS, and AG on the observer side.
[0070] The optical path of the light beam incident to the lens
portion 42 of the view angle control sheet S4 will briefly be
described with reference to FIG. 4. The optical paths of the light
beams L41 to L43 and L44 are schematically shown in FIG. 4. In FIG.
4, the normal light beam L41 incident near the center portion of
the lens portion 42 from the screen image light source side goes
straight in and passes through the view angle control sheet S4 to
reach the observer. The light beam L42 obliquely incident near the
end portion of the lens portion 42 from the screen image light
source side is totally reflected at the hypotenuse due to the
refractive index difference between the lens portion 42 and the
transparent low-refractive index material 46, and the light beam
L42 is output onto the observer side as the normal light beam. The
light beam L43 incident near the end portion of the lens portion 42
from the screen image light source side with the angle larger than
that of the light beam L42 is totally reflected at the hypotenuses
and the light beam L43 is output onto the observer side with the
small angle close to the normal light beam unlike the incident
light beam in the opposite direction to the direction of the
incident light beam. The light beam L44 which impinges on the
bottom surface 47 of the wedge-shaped portion 44 is incident to the
inside of the wedge-shaped portion 44. The light beam L44 is
absorbed by the light beam absorption particles 49 and the light
beam L44 never reaches the observer side. Furthermore, the outside
light beam L45 incident to the hypotenuse from the observer side
with the angle larger than the predetermined angle is not totally
reflected irrespective of the refractive index difference between
the lens portion 42 and the wedge-shaped portion 44, and the
outside light beam L45 is incident to the inside of the
wedge-shaped portion 44. The outside light beam L45 is absorbed by
the light beam absorption particles 49 of the wedge-shaped portion
44. Accordingly, the image contrast is improved in the visual field
from the observer side. Thus, since the light incident with various
angles from the screen image side is output onto the observer side
in the direction of the normal line of the outgoing light beam
plane or the direction close to it, the view angle can be
controlled and the decrease in brightness can be suppressed, so
that the high-contrast view angle control sheet can be
obtained.
[0071] FIG. 5 shows a view angle control sheet S5 according to a
fifth embodiment of the invention. The view angle control sheet S5
is arranged by gluing a screen image-side base sheet 51, a lens
portion 52, and an observer-side base sheet 53 in order from the
screen image side to the observer side. The lens portion 52 is made
of the material having the high refractive index N1. In FIG. 5, a
layer 54 (hereinafter referred to as "transparent low-refractive
index layer 54") is formed in the hypotenuses of the lens portions
52 and 52 vertically adjacent to each other. The transparent
low-refractive index layer 54 is made of the transparent material
having the refractive index N2 lower than the refractive index N1.
Further, a portion having the triangular shape in cross section
sandwiched by the hypotenuses of the adjacent lens portions 52 and
52 is filled with the material in which light beam absorption
particles 59 are added into a transparent material 58 having the
refractive index higher than the refractive index N2. Hereinafter
the portion having the triangular shape in cross section is
referred to as "inter-lens portion 55".
[0072] A ratio of the refractive index N1 of the lens portion 52 to
the refractive index N2 of the transparent low-refractive index
layer 54 is set in the predetermined range in order to secure the
optical characteristics of the view angle control sheet S5. An
angle formed by the hypotenuse where the transparent low-refractive
index layer 54 and the lens portion 52 are in contact with each
other and the normal line V (line parallel to the normal-incidence
light beam relative to the view angle control sheet S5) of the
outgoing light beam plane is formed at a predetermined angle
.theta..sub.5.
[0073] The lens portion 52 is usually made of the material such as
epoxy acrylate having the ionizing radiation-curable property. The
transparent low-refractive index layer 54 is made of the material
having the refractive index lower than the refractive index of the
transparent resin such as silica. The commercially available color
resin fine particles can be used as the light beam absorption
particles 59. The screen image-side base sheet 51 and the
observer-side base sheet 53 are made of the material whose
refractive index is substantially similar to the refractive index
of the lens portion 52. Similarly to the view angle control sheet
S1 according to the first embodiment, in the fifth embodiment, the
observer side of the observer-side base sheet 53 has the function
of at least one of AR, AS, and AG on the observer side.
[0074] The optical path of the light beam incident to the lens
portion 52 of the view angle control sheet S5 will briefly be
described with reference to FIG. 5. The optical paths of the light
beams L51 to L54 are also schematically shown in FIG. 5. In FIG. 5,
the normal light beam L51 incident near the center portion of the
lens portion 52 from the screen image light source side goes
straight in and passes through the view angle control sheet S5 to
reach the observer.
[0075] The light beam L52 obliquely incident near the end portion
of the lens portion 52 from the screen image light source side is
totally reflected at the hypotenuse due to the refractive index
difference between the lens portion 52 and the transparent
low-refractive index material 54, and the light beam L52 is output
onto the observer side as the normal light beam. The light beam L53
incident near the end portion of the lens portion 52 from the
screen image light source side with the angle larger than that of
the light beam L52 is totally reflected at the hypotenuse, and the
light beam L53 is output onto the observer side with the small
angle close to the normal light beam unlike the incident light beam
in the opposite direction of the incident light beam. The light
beam L54 incident to the inside of the inter-lens portion 55 from
the screen image side is also absorbed by the light beam absorption
particles 59 and the light beam L54 is never output to the observer
side as the reflection light beam. Further, the outside light beam
L55 incident to the hypotenuse from the observer side with the
angle larger than the predetermined angle is not totally reflected
irrespective of the refractive index difference between the lens
portion 52 and the transparent low-refractive index material 54,
and the outside light beam L55 is incident to the inter-lens
portion 55. The outside light beam L55 is absorbed by the light
beam absorption particles 59 of the inter-lens portion 55.
Accordingly, the image contrast is improved in the visual field
from the observer side. Thus, wide view angle can be obtained and
the decrease in brightness can be suppressed, so that the
high-contrast view angle control sheet S5 can be obtained.
[0076] In the light beam absorption particles 49 and 59 in the view
angle control sheets S4 and S5 according to the fourth and fifth
embodiments, an average particle size preferably ranges from 1
.mu.m to two-thirds of a width of the bottom surface 47 of the
wedge-shaped portion 44 or the bottom surface 57 of the inter-lens
portion 55. When the sizes of the light beam absorption particles
49 and 59 are too small, the sufficient light beam absorption
effect cannot be obtained. On the other hand, the excessively large
sizes of the light beam absorption particles 49 and 59 are
undesirable, because the inside of the wedge-shaped portion 44 or
the inter-lens portion 55 is hardly filled with the light beam
absorption particles 49 or 59 from the bottom surface 47 or 57
during the production. Moreover, the light beam absorption
particles 49 and 59 in the view angle control sheets S4 and S5
according to the fourth and fifth embodiments preferably have a 10
to 50% by volume of the whole volume of the wedge-shaped portion 44
or the inter-lens portion 55. Maintaining the above volume ratio
enables to keep the sufficient light beam absorption effect and to
give simple production process.
[0077] FIG. 6 is a schematic sectional view illustrating a status
in which the light beam reflected at the slope of the wedge-shaped
portion of the view angle control sheet reaches the observer side.
In view angle control sheets 60A, 60B, and 60C shown in an upper
portion, a middle portion, and a lower portion of FIG. 6, the
screen image side is set to the left side in FIG. 6 and the
observer side is set to the right side. In each sheet, a screen
image-side base sheet 61, a lens portion 62, and an observer-side
base sheet 63 are arranged in order from the left side of FIG. 6.
The wedge-shaped portion 64 is provided in the lens portion 62
while the leading edge (apex) of the wedge-shaped portion 64 is
orientated toward the observer side. An angle .theta..sub.6 formed
by the slope of each wedge-shaped portion 64 and the normal line V
of the light beam outgoing plane is formed in the range of 3 to 20
degrees.
[0078] The view angle control sheets 60A, 60B, and 60C shown in the
upper portion, the middle portion, and the lower portion of FIG. 6
compare three cases, where the ratios of the refractive index N1 of
the material constituting the lens portion to the refractive index
N2 of the material constituting the slope portion differ from one
another, to one another. The view angle control sheet 60A of the
upper portion is the case where the value of R=N2/N1 is small,
i.e., the case where a level in which the refractive index N1 of
the lens portion 62 is larger than the refractive index N2 of the
slope portion is larger than the levels of the following view angle
control sheets 60B and 60C, and the total reflection is generated
in a range A shown in FIG. 6.
[0079] The view angle control sheet 60B of the middle portion is
the case of R-cos .theta..sub.6=0. The view angle control sheet 60B
shows a boundary in which the totally reflected light beam reaches
the front face, and the total reflection is generated in a range B
shown in FIG. 6.
[0080] The view angle control sheet 60C of the lower portion is the
case where R has the large value. The reflected light beam does not
reach the front face, and the total reflection is generated in a
range C shown in FIG. 6. In the invention, in consideration of the
practical characteristics, the following relationship is preferably
satisfied:
-0.01<R-cos .theta..sub.6<0.002
[0081] When the value of (R-cos .theta..sub.6) is not more than
-0.01, the number of totally reflected light beams is increased,
and the totally reflected light beam is observed in the wide angle.
Therefore, particularly when the totally reflected light beam is
observed from the oblique direction, the distance between the ghost
image and the real screen image is increased, which causes the
ghost image to become conspicuous, consequently the ghost image
degrades screen image quality.
[0082] On the other hand, when the value of (R-cos .theta..sub.6)
is at least 0.002, the small number of light beams is totally
reflected, and the effective screen image light beam hardly reaches
the observer. Therefore, the brightness increase effect cannot
sufficiently be obtained.
[0083] Then, the condition that all the light beams in the view
angle control sheet S3 incident to the unit lens portion 32 of the
view angle control sheet S3 according to the third embodiment are
totally reflected by the hypotenuse will be studied with reference
to FIG. 7 and FIG. 8.
[0084] As the incident angle from the screen image side into the
sheet is brought close to 90 degrees, the total reflection hardly
occurs at the hypotenuse of the view angle control sheet S3.
Therefore, when the condition that the light beam is totally
reflected at the smaller angle is determined, i.e., when the
condition that the light beam which is incident into the sheet is
totally reflected by the hypotenuse in extremely parallel with the
screen image-side light beam incident plane, other incident light
beams are totally reflected by the hypotenuse.
[0085] FIG. 7 is a view showing the optical path when the light
beam L32 reflected at the hypotenuse of the view angle control
sheet S3 is output at right angle to the outgoing plane in the view
angle control sheet 3. In FIG. 7, it is assumed that the screen
image light source is positioned in the lower portion and the
observer is positioned in the upper portion. The screen image-side
base sheet 31 and the observer-side base sheet 33 are omitted for
the sake of the simple description (the same to FIG. 8).
[0086] In FIG. 7, the condition (critical condition) that the total
reflection of the light beam L32 incident to the hypotenuse is
started at a point A of the hypotenuse is given as follows by
Snell's law:
sin(90.degree.-.theta..sub.3)=N2/N1.
Therefore, in order to always generate the total reflection of the
normal light beam L32, it is necessary to satisfy the following
condition represented by expression 1:
sign(90.degree.-.theta..sub.3).gtoreq.N2/N1. Expression 1
At this point, because the value of sin(90.degree.-.theta..sub.3)
is always smaller than 1.0, the expression 1 becomes substantially
N2.ltoreq.N1.
[0087] Assuming that the refractive index of atmosphere is 1, the
condition (critical condition) that the light beam L32 totally
reflected at the point A of the hypotenuse is the light beam which
is incident into the sheet at a point B of the light beam incident
plane in extremely parallel with the screen image-side light beam
incident plane is given as follows by the Snell's law:
sin 2.theta..sub.3=1/N1.
Therefore, all the light beams incident into the sheet from the
point B satisfy the following condition represented by expression
2:
sin 2.theta..sub.3<1/N1. Expression 2
[0088] That is, the expression 1 and the expression 2 become the
condition that all the light beams in the view angle control sheet
S3 incident to the unit lens portion 32 of the view angle control
sheet S3 are totally reflected by the hypotenuse.
[0089] The optical path of the light beam L35 which forms the
inclination of 10.degree. relative to the outgoing light beam plane
normal line by impinging on the lens portion of the view angle
control sheet S3 to be reflected from the hypotenuse will briefly
be described below with reference to FIG. 8 for the purpose of
reference.
[0090] In FIG. 8, the condition (critical condition) that the total
reflection of the light beam L35 incident to the hypotenuse in the
view angle control sheet S3 is started at the point A of the
hypotenuse is given as follows by the Snell's law:
sin(80.degree.-.theta..sub.3)=N2/N1.
Therefore, in order to always generate the total reflection of the
normal light beam L35, it is necessary to satisfy the following
condition represented by expression 3:
sin(80.degree.-.theta..sub.3)>N2/N1. Expression 3
[0091] Assuming that the refractive index of atmosphere is 1, the
condition (critical condition) that the light beam is the light
beam which is incident into the sheet at a point B of the light
beam incident plane in extremely parallel with the screen
image-side light beam incident plane is given as follows by the
Snell's law:
sin(2.theta..sub.3+10.degree.)=1/N1.
Therefore, the light beams incident into the sheet from the point B
is always given as follows:
sin(2.theta..sub.3+10.degree.)<1/N1.
That is, the light beams incident into the sheet from the point B
always satisfies the following condition represented by expression
4:
N1<1/sin(2.theta..sub.3+10.degree.). Expression 4
[0092] Assuming that the angle .theta..sub.3 is set in the range of
5.degree. to 20.degree. which is preferable in consideration of
production conditions and the like, the value of N1 and N2 will
specifically be studied in the angle .theta..sub.3 ranging from
5.degree. to 20.degree.. In the ranging of
5.degree.<.theta..sub.3<20.degree., the following
relationship is held:
0.940<sin(90.degree.-.theta..sub.3)<0.996.
Therefore, as can be seen from the expression 1, the value of N2/N1
is smaller than 0.940, so that the following expression 5 is
obtained:
N2/N1<0.940. Expression 5
[0093] In the ranging of 5.degree.<.theta..sub.3<20.degree.,
the following relationship is held:
1.56<1/sin 2.theta..sub.3<5.76.
Therefore, as can be seen from the expression 2, the following
expression 6 is obtained:
N1<1.56. Expression 6
When the actually available material is considered, the minimum
value of N2 is 1.30, so that the following relationship is
held:
N2/N1>1.30/1.56=0.83.
Accordingly, the following expression 7 is given from the above
relationship and the expression 6:
0.83<N2/N1<0.940. Expression 7
The value of N2/N1 can be set in the range represented by the
expression 6 and the expression 7, in order that all the light
beams incident into the sheet from the screen image side in the
range of 5.degree.<.theta..sub.3<20.degree. are totally
reflected by the hypotenuse. In the invention, the range of N2/N1
is defined as follows from the viewpoints of the sheet production
conditions and the actual characteristics:
0.80<N2/N1<0.98.
[0094] FIG. 9 is a view showing various shape modes of the
low-refractive index portion 4. The low-refractive index portion 4
has the substantially triangular shape formed by the hypotenuses of
the two adjacent unit lenses 2 and 2. FIG. 9A shows the case where
the hypotenuse is formed by a straight line. In this case, an angle
.theta..sub.11 formed by the hypotenuse and the outgoing light beam
plane normal line is kept constant at any point on the hypotenuse.
FIG. 9B shows the case where the hypotenuse is formed by a smoothly
curved line. FIG. 9C shows the case where the hypotenuse is formed
by the two straight lines. In these cases, angles .theta..sub.12,
.theta..sub.13, and .theta..sub.14 formed by the hypotenuses and
the outgoing light beam plane normal lines depend on the position
on the hypotenuse. In the invention, when the angle formed by the
hypotenuse and the outgoing light beam plane normal line is not
constant as shown in FIGS. 9B and 9C, the effect of the invention
can be obtained by satisfying the conditions of the above-described
expressions 1 to 7 in the range at least a 90% length of the
hypotenuse.
[0095] FIG. 10 shows the cross section of a view angle control
sheet 70 in which the slope shape of the wedge-shaped portion
exhibits another mode. The cross-sectional shape of a wedge-shaped
portion 74 has an acute-angled triangle whose apex is orientated
toward the observer side. An angle formed by an upper-side slop of
the acute-angled triangle and an outgoing light beam plane normal
line V1 is zero degree. On the other hand, an angle .theta..sub.7
formed by a lower-side slope of the acute-angled triangle and an
outgoing light beam plane normal line V2 is about 10 degrees. As
shown in FIG. 10, when the lower-side slope is larger than the
upper-side slope in the angle relative to the outgoing light beam
plane normal line, the display device is formed by a crosswise
stripe in which the wedge-shaped portions are horizontally arranged
(see FIG. 11). Therefore, since the display device is usually seen
from slightly upper side, the transmittance is high for the light
beam going upward from the screen image source, and the brightness
can be further improved on the observer side.
[0096] FIGS. 11 to 13 are a view showing an example of the
configuration of the view angle control sheet according to the
invention. A view angle control sheet S90 shown in FIG. 11 includes
a unit lens 92 whose vertically cross-sectional shape is constant
in the horizontal direction. A base sheet 91 is arranged on the
screen image side and a base sheet 93 is arranged on the observer
side. In FIG. 11, although the three components are shown while
separated from one another for the purpose of understanding,
actually the components are bonded to one another.
[0097] A view angle control sheet S0 shown in FIG. 12 includes a
unit lens 102 whose horizontally cross-sectional shape is constant
in the vertical direction. Abase sheet 101 is arranged on the
screen image side and a base sheet 103 is arranged on the observer
side.
[0098] In a view angle control sheet S11 shown in FIG. 13, unit
lenses having circular truncated conical shapes are
two-dimensionally arrayed on the vertical plane. Top surfaces of
the circular truncated conical unit lenses are formed in the same
plane, and a base sheet 111 is bonded to the plane. A cavity
between the base sheet 111 and the unit lens 112 is filled with the
low-refractive index material to form a low-refractive index
portion 114. The effect of the invention can be obtained by any one
of the configurations of the view angle control sheets S9, S10, and
S11 shown in FIGS. 11 to 13.
[0099] FIG. 14 shows a configuration of a display device 120
provided with the view angle control sheet according to the
invention. In FIG. 14, the screen image side is set in a front left
lower direction and the observer side is set in a back-side right
upper direction. The display device 120 of the invention includes a
liquid crystal display panel 121, a view angle control sheet 122 in
which the lens portions are vertically arranged, a view angle
control sheet 123 in which the lens portions are horizontally
arranged, a Fresnel lens 124, and a functional sheet 125 having at
least one of the functions AR, AS, and AG in order from the screen
image side. The arrangement between the view angle control sheet
122 and the view angle control sheet 123 may be arranged. In FIG.
14, although the components are shown while separated from one
another for the purpose of understanding, actually the components
are in contact with one another or the components are bonded to one
another.
[0100] In the display device 120 of the invention, the width of the
edge-shaped portion bottom surface in the view angle control sheet
is preferably not more than 1/1.15of the size of one pixel of the
display device 120. The generation of a moire pattern can be
suppressed by keeping the above ratio. Further, in the invention,
"view angle control sheet" mainly means the configuration on a
combination of the view angle control sheet 122 and the view angle
control sheet 123. However, when the Fresnel lens 124 and the
functional sheet 125 are arranged on the outgoing light beam side
as shown in FIG. 14, the "view angle control sheet" shall be a
concept including the Fresnel lens 124 and the functional sheet
125.
Example 1
[0101] The view angle control sheet having the wedge-shaped portion
shown in FIG. 9C was produced with the following specifications.
The view angle was able to be controlled at 15.degree..
[0102] aperture ratio: 50% (in this case, "aperture ratio" means a
ratio of an area of light transmission portion (lens portion) to
the whole area in the light beam incident plane)
.theta..sub.13=8.degree.
.theta..sub.14=12.degree.
[0103] inter-lens pitch: 0.05 mm
[0104] lens portion material (resin) refractive index: 1.56
[0105] wedge-shaped portion material refractive index: 1.48
[0106] Thus, the invention is described with reference to the
embodiments which are considered to be currently most practical and
preferable. However, the invention is not limited to the
embodiments disclosed in the description, but the various
modifications could be made without departing from the summary or
thought of the invention which can be read from claims of the
invention and the whole description. Therefore, it is understood
that the modified view angle control sheet is also included in the
technical scope of the invention.
* * * * *