U.S. patent number RE48,844 [Application Number 16/923,570] was granted by the patent office on 2021-12-07 for liquid crystal display apparatus.
This patent grant is currently assigned to Saturn Licensing LLC. The grantee listed for this patent is Saturn Licensing LLC. Invention is credited to Toru Abiko, Makoto Aoki, Kiyohiro Kimura, Jun Sasaki.
United States Patent |
RE48,844 |
Kimura , et al. |
December 7, 2021 |
Liquid crystal display apparatus
Abstract
A liquid crystal display apparatus is provided in which
occurrence of a moire pattern can be prevented without largely
reducing front luminance. A liquid crystal display apparatus 1
includes a surface light source 4, a liquid crystal display panel
2, and first and second prism sheets 5 and 6 for condensing light
emitted from the surface light source 4 and guiding the light
toward the liquid crystal display panel. The first and second prism
sheets 5 and 6 are disposed such that prism array directions
thereof are orthogonal to each other. When a pixel pitch of the
liquid crystal display panel 2 is defined as Pp [.mu.m]; a prism
array pitch of the first prism sheet 5 is defined as Px [.mu.m];
and a prism array pitch of the second prism sheet 6 is defined as
Py [.mu.m], relationships of Px.ltoreq.Pp/(14-0.045 Pp) and
Py.ltoreq.Pp/(11.5-0.032 Pp) are satisfied.
Inventors: |
Kimura; Kiyohiro (Miyagi,
JP), Aoki; Makoto (Miyagi, JP), Sasaki;
Jun (Miyagi, JP), Abiko; Toru (Miyagi,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Saturn Licensing LLC |
New York |
NY |
US |
|
|
Assignee: |
Saturn Licensing LLC (New York,
NY)
|
Family
ID: |
1000005719049 |
Appl.
No.: |
16/923,570 |
Filed: |
July 8, 2020 |
PCT
Filed: |
March 29, 2007 |
PCT No.: |
PCT/JP2007/056793 |
371(c)(1),(2),(4) Date: |
August 29, 2008 |
PCT
Pub. No.: |
WO2007/119584 |
PCT
Pub. Date: |
October 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15704925 |
Sep 14, 2017 |
RE48143 |
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14603284 |
Jan 22, 2015 |
RE46601 |
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13963267 |
Aug 9, 2013 |
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Reissue of: |
11920886 |
Mar 29, 2007 |
7995158 |
Aug 9, 2011 |
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Reissue of: |
11920886 |
Mar 29, 2007 |
7995158 |
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Foreign Application Priority Data
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Mar 29, 2006 [JP] |
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JP2006-090709 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F
1/133606 (20130101); G02B 6/0053 (20130101); G02F
1/133607 (20210101) |
Current International
Class: |
G02F
1/1335 (20060101); F21V 8/00 (20060101); G02F
1/13357 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0942227 |
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Sep 1999 |
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EP |
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1550886 |
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Jul 2005 |
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EP |
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08-036179 |
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Feb 1996 |
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JP |
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2004-046076 |
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Feb 2004 |
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JP |
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2005-234538 |
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Sep 2005 |
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JP |
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10-506500 |
|
Jun 2007 |
|
JP |
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WO 96/10148 |
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Apr 1996 |
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WO |
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WO 2003/065083 |
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Aug 2003 |
|
WO |
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Other References
International Search Report and Written Opinion for International
Application No. PCT/JP2007/056793 dated May 15, 2007. cited by
applicant .
International Preliminary Report on Patentability for International
Application No. PCT/JP2007/056793 dated Oct. 21, 2008. cited by
applicant.
|
Primary Examiner: Hughes; Deandra M
Attorney, Agent or Firm: Wolf, Greenfield & Sacks,
P.C.
Parent Case Text
.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS .Iaddend.
.Iadd.Notice is hereby provided that more than one reissue
application has been filed: this application is a reissue
continuation of U.S. application Ser. No. 15/704,925, filed Sep.
14, 2017, which is a reissue continuation of U.S. application Ser.
No. 14/603,284, filed Jan. 22, 2015, which is a reissue
continuation of U.S. application Ser. No. 13/963,267, filed on Aug.
9, 2013, which is a reissue of U.S. Pat. No. 7,995,158, filed Aug.
29, 2008, which is a National Stage of International Application
PCT/JP2007/056793, filed Mar. 29, 2007, which claims the benefit of
and priority to Japanese Patent Application 2006-090709, filed on
Mar. 29, 2006..Iaddend.
Claims
The invention claimed is:
.[.1. A liquid crystal display apparatus comprising: a light
source; a liquid crystal display panel; and condenser sheets for
condensing light emitted from the light source and guiding the
light toward the liquid crystal display panel, the condenser sheets
including: a first condenser sheet in which ridges of a first
corrugated structure having a first light-condensing characteristic
are periodically arranged on one surface of the first condenser
sheet in a longitudinal direction of the liquid crystal display
panel; and a second condenser sheet in which ridges of a second
corrugated structure having a second light-condensing
characteristic are periodically arranged on one surface of the
second condenser sheet in a lateral direction of the liquid crystal
display panel, wherein, when a longitudinal, lateral, or sub-pixel
pitch of the liquid crystal display panel is defined as Pp, an
array pitch of the first corrugated structure is defined as Px, and
an array pitch of the second corrugated structure is defined as Py,
the following relationships are satisfied: Px is approximately
equal to Pp/(14-0.045Pp) and Py is approximately equal to
Pp/(11.5-0.032Pp) such that moire patterns are not produced by the
condenser sheets and the liquid crystal display panel, and the
condenser sheets do not significantly reduce the luminance from the
liquid crystal display..].
.[.2. The liquid crystal display apparatus according to claim 1,
wherein each of the first and second corrugated structures is a
prism structure having ridges of a triangular shape in cross
section..].
.[.3. The liquid crystal display apparatus according to claim 1,
wherein at least one of the ridges of the first corrugated
structure or the ridges of the second corrugated structure have a
shape of an aspheric lens..].
.[.4. The liquid crystal display apparatus according to claim 1,
wherein Px.ltoreq.50, Py.ltoreq.50, and |Px-Py|<50 are satisfied
when Pp.gtoreq.222..].
.[.5. The liquid crystal display apparatus according to claim 1,
wherein Px.ltoreq.20, Py.ltoreq.20, and |Px-Py|<20 are satisfied
when 222>Pp.gtoreq.144..].
.[.6. The liquid crystal display apparatus according to claim 1,
wherein Px.ltoreq.15, Py.ltoreq.20, and -20<Px-Py<15 are
satisfied when 114>Pp.gtoreq.136.5..].
.[.7. The liquid crystal display apparatus according to claim 1,
wherein Px is slightly less than or equal to Pp/(14-0.045Pp) and Py
is slightly less than or equal to Pp/(11.5-0.032Pp)..].
.[.8. A liquid crystal display apparatus comprising: a liquid
crystal display panel; and condenser sheets for condensing light
emitted from a light source and guiding the light toward the liquid
crystal display panel, the condenser sheets including: a first
condenser sheet in which ridges of a first corrugated structure
having a first light-condensing characteristic are periodically
arranged on one surface of the first condenser sheet in a
longitudinal direction of the liquid crystal display panel; and a
second condenser sheet in which ridges of a second corrugated
structure having a second light-condensing characteristic are
periodically arranged on one surface of the second condenser sheet
in a lateral direction of the liquid crystal display panel,
wherein, when a longitudinal, lateral, or sub-pixel pitch of the
liquid crystal display panel is defined as Pp, an array pitch of
the first corrugated structure is defined as Px, and an array pitch
of the second corrugated structure is defined as Py, the following
relationships are satisfied: Px is approximately equal to
Pp/(14-0.045Pp) and Py is approximately equal to Pp/(11.5-0.032Pp)
such that moire patterns are not produced by the condenser sheets
and the liquid crystal display panel, and the condenser sheets do
not significantly reduce the luminance from the liquid crystal
display..].
.[.9. The liquid crystal display apparatus according to claim 8
incorporated in a device selected from the following group: a
mobile phone, a digital camera, a liquid crystal television..].
.[.10. The liquid crystal display apparatus according to claim 8,
wherein each of the first and second corrugated structures is a
prism structure having ridges of a triangular shape in cross
section..].
.[.11. The liquid crystal display apparatus according to claim 8,
wherein at least one of the ridges of the first corrugated
structure or the ridges of the second corrugated structure have a
shape of an aspheric lens..].
.[.12. The liquid crystal display apparatus according to claim 8,
wherein Px.ltoreq.50, Py.ltoreq.50, and |Px-Py|<50 are satisfied
when Pp.gtoreq.222..].
.[.13. The liquid crystal display apparatus according to claim 8,
wherein Px.ltoreq.20, Py.ltoreq.20, and |Px-Py|<20 are satisfied
when 222>Pp.gtoreq.144..].
.[.14. The liquid crystal display apparatus according to claim 8,
Wherein Px.ltoreq.15, Py.ltoreq.20, and -20<Px-Py<15 are
satisfied when 114>Pp.gtoreq.136.5..].
.[.15. The liquid crystal display apparatus according to claim 8,
wherein Px is slightly less than or equal to Pp/(14-0.045Pp) and Py
is slightly less than or equal to Pp/(11.5-0.032Pp)..].
.Iadd.16. A condenser sheet for condensing light emitted from a
light source and guiding a light toward a liquid crystal display
panel having a pitch defined as Pp in micrometers comprising ridges
of a first corrugated structure having a first light-condensing
characteristic that are periodically arranged on a first surface of
the condenser sheet in a first direction of the liquid crystal
display panel, wherein the first corrugated structure has an array
pitch in micrometers defined as Px such that Px has a value greater
than or equal to 10 microns and less than or equal to
Pp/(14-0.045Pp)..Iaddend.
.Iadd.17. The condenser sheet of claim 16, wherein the first
corrugated structure is a prism structure having ridges of a
triangular shape in cross section..Iaddend.
.Iadd.18. The condenser sheet of claim 16, wherein the first
corrugated structure includes aspheric lens
structures..Iaddend.
.Iadd.19. The condenser sheet of claim 16, wherein 10
microns.ltoreq.Px.ltoreq.50 microns and Pp.gtoreq.222
microns..Iaddend.
.Iadd.20. The condenser sheet of claim 16, wherein 10
microns.ltoreq.Px.ltoreq.20 microns and Pp.gtoreq.144
microns..Iaddend.
.Iadd.21. A condenser sheet for condensing light emitted from a
light source and guiding a light toward a liquid crystal display
panel having a pitch defined as Pp in micrometers comprising ridges
of a second corrugated structure having a second light-condensing
characteristic that are periodically arranged on a first surface of
the condenser sheet in a second direction of the liquid crystal
display panel, wherein the second corrugated structure has an array
pitch in micrometers defined as Py such that Py has a value greater
than or equal to 10 microns and less than or equal to
Pp/(11.5-0.032Pp)..Iaddend.
.Iadd.22. The condenser sheet of claim 21, wherein the second
corrugated structure is a prism structure having ridges of a
triangular shape in cross section..Iaddend.
.Iadd.23. The condenser sheet of claim 21, wherein the second
corrugated structure includes aspheric lens
structures..Iaddend.
.Iadd.24. The condenser sheet of claim 21, wherein 10
microns.ltoreq.Py.ltoreq.50 microns and Pp.gtoreq.222
microns..Iaddend.
.Iadd.25. The condenser sheet of claim 21, wherein 10
microns.ltoreq.Py.ltoreq.20 microns and Pp.gtoreq.144
microns..Iaddend.
Description
TECHNICAL FIELD
The present invention relates to a liquid crystal display apparatus
including a light-transmissive condenser sheet, and more
particularly to a liquid crystal display apparatus including a
first condenser sheet and a second condenser sheet that are
arranged in a stack.
BACKGROUND ART
Liquid crystal display (LCD) apparatuses have a lower power
consumption and can be made smaller and thinner than
cathode-ray-tube (CRT) apparatuses. Nowadays, various sizes of
liquid crystal display apparatuses are widely used, ranging from
small apparatuses such as mobile phones and digital cameras to
large apparatuses such as large liquid crystal televisions.
Liquid crystal display apparatuses are classified into a
transmissive type, a reflective type, and the like. Particularly, a
transmissive liquid crystal display apparatus includes a liquid
crystal display panel constituted by a pair of transparent
substrates with a liquid crystal layer therebetween and a backlight
unit serving as an illumination light source. Backlight units are
classified into a direct-lighting type, in which a light source is
provided directly under a liquid crystal display panel, and an
edge-lighting type.
In general, a backlight unit for liquid crystal display apparatuses
employs a condenser sheet, such as a prism sheet, a lens sheet, or
the like, for orienting light emitted from a light source toward
the front.
For example, a prism sheet includes a number of prisms each having
a triangular cross section on a light-output surface thereof. The
prism sheet condenses and orients light incident thereon toward the
front by refracting and transmitting the incident light through
inclined planes of the prisms. Particularly, for use in mobile
apparatuses, an exemplary structure is known in which two prism
sheets are arranged in a stack such that respective prism arrays of
the two sheets are oriented orthogonally to each other, whereby
light spreading in the two directions are efficiently condensed to
improve front luminance (refer to Patent Document 1 below).
[Patent Document 1] PCT Japanese Translation Patent Publication No.
10-506500
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
A contrast pattern (moire pattern) may occur due to interference
depending on the prism array pitch of a prism sheet and the pixel
array pitch of a liquid crystal display panel. In order to prevent
the occurrence of such a moire pattern, it is effective to reduce
the prism array pitch.
However, there is a problem in that simply reducing the prism array
pitch may considerably reduce the front luminance and,
consequently, degrade the image quality. The same problem applies
to the case where two prism sheets are arranged in a stack, as
described above.
In view of the above problem, the present invention aims to provide
a liquid crystal display apparatus in which occurrence of a moire
pattern can be prevented without largely reducing front
luminance.
Means for Solving the Problem
In solving the above problem, the inventors have found that a
liquid crystal display apparatus causing no moire pattern can be
produced, while reduction of front luminance is minimized, by
determining the optimum combination of prism array pitches of prism
sheets in accordance with the pixel pitch of a liquid crystal
display panel.
That is, a liquid crystal display apparatus according to the
present invention includes a light source, a liquid crystal display
panel, and condenser sheets for condensing light emitted from the
light source and guiding the light toward the liquid crystal
display panel. The condenser sheets include a first condenser sheet
in which ridges of a first corrugated structure having a
light-condensing characteristic are periodically arranged on one
surface the first condenser sheet in a longitudinal direction of
the liquid crystal display panel, and a second condenser sheet in
which ridges of a second corrugated structure having a
light-condensing characteristic are periodically arranged on one
surface the of the second condenser sheet in a lateral direction of
the liquid crystal display panel. When a pixel pitch of the liquid
crystal display panel is defined as Pp [.mu.m], an array pitch of
the first corrugated structure is defined as Px [.mu.m], and an
array pitch of the second corrugated structure is defined as Py
[.mu.m], the following relationships are satisfied:
Px.ltoreq.Pp/(14-0.045Pp), and Py.ltoreq.Pp/(11.5-0.032Pp).
As described above, by determining the array pitches of the
respective corrugated structures of the first and second condenser
sheets in accordance with the pixel pitch of the liquid crystal
display panel, occurrence of a moire pattern can be prevented
without largely reducing front luminance of the liquid crystal
display panel.
Preferably, Px.ltoreq.50, Py.ltoreq.50, and |Px-Py|<50 are
satisfied when Pp.gtoreq.222; Px.ltoreq.20, Py.ltoreq.20, and
|Px-Py|<20 are satisfied when 222>Pp.gtoreq.144; and
Px.ltoreq.15, Py.ltoreq.20, and -20<Px-Py<15 are satisfied
when 114>Pp.gtoreq.136.5.
The first and second corrugated structures correspond to prism
structures having ridges of a triangular shape in cross section if
the condenser sheets are prism sheets. If the condenser sheets are
lens sheets, the first and second corrugated structures have ridges
of a lens shape, such as an aspheric lens, with a curved cross
section.
Advantages of the Invention
As described above, according to the liquid crystal display
apparatus of the present invention, occurrence of a moire pattern
can be prevented without largely reducing front luminance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view showing the schematic
structure of a liquid crystal display apparatus according to an
embodiment of the present invention.
FIG. 2 is a diagram showing occurrence of a moire pattern in
various combinations of prism array pitches Px and Py when the
pixel pitch is 222 .mu.m.
FIG. 3 is a diagram showing occurrence of a moire pattern in
various combinations of prism array pitches Px and Py when the
pixel pitch is 144 .mu.m.
FIG. 4 is a diagram showing occurrence of a moire pattern in
various combinations of prism array pitches Px and Py when the
pixel pitch is 136.5 .mu.m.
FIG. 5 is a diagram showing values of front luminance in various
combinations of prism array pitches Px and Py.
FIG. 6 is a schematic perspective view showing an exemplary
structure in which a first prism sheet and a second prism sheet are
combined together with an adhesive layer therebetween.
FIG. 7 is a schematic perspective view showing an exemplary
combination of a first condenser sheet constituting a prism sheet
and a second condenser sheet constituting a lens sheet.
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will now be described with
reference to the drawings. The invention is not limited to the
following embodiment, and various modifications can be made within
the scope of the invention.
FIG. 1 is an exploded perspective view showing the schematic
structure of a liquid crystal display apparatus 1 according to an
embodiment of the present invention. The liquid crystal display
apparatus 1 in the figure includes a liquid crystal display panel 2
and a backlight unit 3. The backlight unit 3 includes a surface
light source 4, a first prism sheet 5, a second prism sheet 6, and
a diffusion plate 7 arranged in that order.
The liquid crystal display panel 2 includes pixels arranged in the
longitudinal direction (X-direction in FIG. 1) and the lateral
direction (Y-direction in FIG. 1) thereof at a predetermined pitch,
and displays a predetermined image on the front surface thereof by
controlling the transmittance of light applied from the backlight
unit 3 for each of the pixels. The image displayed is a color image
but not limited thereto, of course. The liquid crystal display
panel 2 includes a liquid crystal cell constituted by a pair of
transparent substrates facing each other with a liquid crystal
layer provided therebetween, a pair of polarizing plates
sandwiching the liquid crystal cell, and the like. The liquid
crystal material constituting the liquid crystal layer is not
particularly limited but is appropriately selected according to the
method for driving liquid crystal, such as the TN method, the VA
method, or the like.
The surface light source 4 is either a direct-lighting type in
which a plurality of light sources are disposed on a surface or an
edge-lighting type in which a light-guiding plate is used. The
surface light source 4 irradiates the entire back surface of the
liquid crystal display panel 2 with backlight. As the light
sources, linear light sources such as fluorescent tubes or point
light sources such as light-emitting diodes are used.
The first and second prism sheets 5 and 6 serve as "condenser
sheets" of the invention for condensing light emitted from the
surface light source 4 toward the front (in the Z-direction) so as
to improve front luminance. The diffusion plate 7 is an optically
functional element for diffusing and delivering the backlight so as
to produce uniform luminance. The diffusion plate 7 may be provided
between the first prism sheet 5 and the surface light source 4.
Optically functional elements other than the first and second prism
sheets 5, 6, and the diffusion plate 7 may also be provided, such
as a polarization separation element that transmits one polarized
component and reflects another polarized component, for
example.
Each of the first and second prism sheets 5 and 6 is provided with
a prism structure having ridges of a triangular shape in cross
section on a light-output surface thereof. The prism structure
correspond to a "corrugated structure" of the present
invention.
On the first prism sheet 5, prisms 5P are arranged successively at
a predetermined pitch in the longitudinal direction of the liquid
crystal display panel 2 (the X-direction in FIG. 1). On the second
prism sheet 6, prisms 6P are arranged successively at a
predetermined pitch in the lateral direction of the liquid crystal
display panel 2 (the Y-direction in FIG. 1). In this embodiment,
cross sections of the prisms 5P and the prisms 6P are both
isosceles triangles each having a vertex angle of 90.degree..
The first prism sheet 5 condenses light spreading in the
X-direction, among the backlight emitted from the surface light
source 4, toward the Z-direction. The second prism sheet 6
condenses light spreading in the Y-direction toward the
Z-direction. Since the light spreading in the X- and Y-directions
are condensed toward the front (in the Z-direction) by the first
and second prism sheets 5 and 6, front luminance of the liquid
crystal display apparatus 1 is more improved than in the case where
only one prism sheet is provided.
The prism array pitch of the first prism sheet 5 and the prism
array pitch of the second prism sheet 6 may be either the same or
different. In general, the smaller the prism array pitch is, the
lower the resultant front luminance becomes. Moreover, a moire
pattern of interference fringes may occur due to the periodic
structures provided on the first and second prism sheets 5 and 6
and the display pixels provided on the liquid crystal display panel
2. The occurrence of such a moire pattern can be prevented by
reducing the prism array pitches of the first and second prism
sheets 5 and 6. However, if the prism array pitches are excessively
reduced, front luminance will be reduced considerably.
Hence, the liquid crystal display apparatus 1 of this embodiment is
configured so that, when the pixel pitch of the liquid crystal
display panel 2 is defined as Pp [.mu.m], the prism array pitch of
the first prism sheet 5 is defined as Px [.mu.m], and the prism
array pitch of the second prism sheet 6 is defined as Py [.mu.m],
the following relationships are satisfied:
Px.ltoreq.Pp/(14-0.045Pp), and Py.ltoreq.Pp/(11.5-0.032Pp) (1)
By setting the first prism array pitch Px and the second prism
array pitch Py in accordance with the pixel pitch Pp of the liquid
crystal display panel 2 so as to satisfy the above expression (1),
a liquid crystal display apparatus in which occurrence of a moire
pattern can be prevented without largely reducing front luminance
can be obtained.
For example, when the pixel pitch Pp is 222 .mu.m, the upper limits
of Px and Py are about 55 .mu.m and 56 .mu.m, respectively; when
the pixel pitch is 144 .mu.m, the upper limits of Px and Py are
about 19 .mu.m and about 20 .mu.m, respectively; and when the pixel
pitch is 136.5 .mu.m, the upper limits of Px and Py are about 17
.mu.m and 19 .mu.m, respectively.
Preferably, in the case of Pp.gtoreq.222, Px.ltoreq.50,
Py.ltoreq.50, and |Px-Py|<50 are satisfied; in the case of
222>Pp.gtoreq.144, Px.ltoreq.20, Py.ltoreq.20, and |Px-Py|<20
are satisfied; and in the case of 144>Pp.gtoreq.136.5,
Px.ltoreq.15, Py.ltoreq.20, and -20<Px-Py<15 are
satisfied.
FIGS. 2 to 4 show the results of an experiment for checking
occurrence of a moire pattern for each of combinations of the prism
array pitches of the first and second prism sheets 5 and 6 when the
pixel pitches (Pp) of the liquid crystal display panel 2 are 222
.mu.m, 144 .mu.m, and 136.5 .mu.m, respectively. In each of the
figures, numbers in the table indicate the value of "Px-Py", a
symbol "O" indicates that no moire pattern occurred, and a symbol
"x" indicates that a moire pattern occurred. The occurrence of a
moire pattern was examined visually.
Referring to FIG. 2, in the case of the 222 .mu.m pixel pitch, it
was found that no moire pattern occurred in all the combinations
where the prism array pitches Px and Py of the first and second
prism sheets 5 and 6 are 50 .mu.m or less. In contrast, referring
to FIG. 3, in the case of the 144 .mu.m pixel pitch, occurrence of
a moire pattern could be prevented only in the combinations where
Px and Py are both 19 .mu.m or less. Further, in the case of the
136.5 .mu.m pixel pitch, occurrence of a moire pattern could be
prevented only in the combinations of Px.ltoreq.14 .mu.m and
Py.ltoreq.19 .mu.m.
As described above, by setting the pixel pitch Pp of the liquid
crystal display panel 2 and the prism array pitches Px and Py of
the first and second prism sheets 5 and 6 so as to satisfy the
relationships of the expression (1), the liquid crystal display
apparatus 1 causing no moire pattern can be obtained.
FIG. 5 shows exemplary combinations of the prism array pitches Px
and Py (50 .mu.m, 19 .mu.m, 14 .mu.m, and 10 .mu.m) of the first
and second prism sheets 5 and 6 and values of front luminance in
those combinations. Front luminance is expressed as the measured
luminance of light transmitted through the prism sheets 5 and 6. In
FIG. 5, the ranges of the above-mentioned combinations of the prism
pitches Px and Py where no moire pattern occurred are indicated by
rectangles of different lines for the cases of the pixel pitches of
222 .mu.m, 144 .mu.m, and 136.5 .mu.m.
As shown in FIG. 5, it is understood that combinations of larger
prism array pitches Px and Py produce higher front luminance.
Further, by referring to the exemplary combinations in FIG. 5, the
optimum selection for the prism sheets 5 and 6 capable of
preventing reduction of front luminance caused by reduction of the
prism pitches can be made in accordance with the pixel pitch of the
liquid crystal display panel 2 to be used.
Thus, according to this embodiment, the array pitches of the
respective prisms 5P and 6P on the first and second prism sheets 5
and 6 are determined in accordance with the pixel pitch of the
liquid crystal display panel 2 as shown in the expression (1).
Accordingly, occurrence of a moire pattern can be prevented,
without largely reducing front luminance of the liquid crystal
display panel.
Furthermore, since the upper limits of the prism array pitches Px
and Py producing a high front luminance without causing a moire
pattern can be obtained easily according to the expression (1), the
combination of the prism sheets 5 and 6 can be optimized and the
degree of design flexibility can also be improved.
Next, detailed configurations of the first and second prism sheets
5 and 6 and modifications thereof will be described below.
Each of the first and second prism sheets 5 and 6 is configured to
have a prism structure on one surface of a base film made of
light-transmissive resin such as polyethylene terephthalate (PET)
or polycarbonate (PC). The prism structure may be directly formed
on the base film by a method such as casting or melt extrusion.
Alternatively, a surface having the shape of the prism structure
may be formed using an ultraviolet-curable resin material and then
be transferred onto the surface of the base film.
In an exemplary configuration in which the prism structure is
transferred onto the base film, the prism sheet can be made thinner
by configuring the prism structure to be later separable from the
base film. Specifically, the thickness of the prism sheet can be
made thinner in the following manner, for example: the thickness of
a 50-.mu.m-pitch prism sheet becomes 50 .mu.m, the thickness of a
19-.mu.m-pitch prism sheet becomes 35 .mu.m, the thickness of a
14-.mu.m-pitch prism sheet becomes 32 .mu.m, and the thickness of a
10-.mu.m-pitch prism sheet becomes 30 .mu.m.
If usability of the first and second prism sheets is expected to be
degraded because of such thinning, the first and second prism
sheets 5 and 6 may be bonded together with an adhesive layer 8
therebetween, as shown in FIG. 6. The adhesive layer 8 is
preferably made of a material having a refractive index lower than
those of the first and second prism sheets 5 and 6. For example,
when the prism sheets 5 and 6 are made of polycarbonate having a
refractive index of about 1.6, the adhesive layer 8 can be formed
of an acrylic ultraviolet-curable resin having a refractive index
of about 1.3 to 1.4.
The liquid crystal display apparatus 1 having an improved front
luminance can be obtained by employing two prism sheets including
the first and second prism sheets 5 and 6 as shown in FIG. 1. In
this case, the vertex angle of each of the prisms 5P of the first
prism sheet 5 provided on the lower position and the vertex angle
of each of the prisms 6P of the second prism sheet 6 provided on
the upper position are not necessarily the same, but may be
different. For example, when the vertex angle of each of the prisms
6P is set larger than that of each of the prisms 5P, the viewing
angle can be widened.
In the case where a single pixel includes sub-pixels having colors
of R, G, and B as in the case of a color liquid crystal display
panel, the prism array pitch Px of the first prism sheet 5 having
the prisms 5P arranged in the longitudinal direction (X-direction)
of the screen may be set to one-third of the prism array pitch Py
of the second prism sheet 6 having the prisms 6P arranged in the
lateral direction (Y-direction) of the screen.
The condenser sheets according to the present invention are not
limited to the above-described prism sheets 5 and 6. FIG. 7
illustrates an example in which the first condenser sheet is formed
of the first prism sheet 5 and the second condenser sheet is formed
of a lens sheet 9. The lens sheet 9 includes a number of
cylindrical lenses 9L each having, for example, an aspheric cross
section successively arranged in one direction on a light-output
surface thereof. In this example, the cylindrical lenses 9L are
arranged in a crosswise direction relative to the direction in
which the prisms 5P are arranged (orthogonal to the direction in
which the prisms 5P are arranged in the figure).
Also in this example, by setting the pixel pitch Pp of the liquid
crystal display panel, the prism array pitch Px of the prism sheet
5, and a lens array pitch Py of the lens sheet 9 so as to satisfy
the relationships of the expression (1), the advantages of the
invention can be obtained. Further, by placing the lens sheet 9 on
the upper position, a liquid crystal display apparatus having a
wider viewing angle can be produced. Also when the first and second
condenser sheets are both lens sheets, the same advantages as those
described above can be obtained.
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