U.S. patent application number 10/055969 was filed with the patent office on 2002-08-22 for liquid crystal display device.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Ishida, Kazuhiro, Saito, Ken.
Application Number | 20020113924 10/055969 |
Document ID | / |
Family ID | 18902294 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020113924 |
Kind Code |
A1 |
Saito, Ken ; et al. |
August 22, 2002 |
Liquid crystal display device
Abstract
In a liquid crystal display device, a transparent sheet TPS is
provided to a surface of a diffusion plate SCT which faces a light
source (cold cathode fluorescent lamps CFL). The whole or at least
respective portions of four sides forming peripheries of the
transparent sheet TPS and the diffusion plate SCT are adhered to
each other using a pressure sensitive adhesive double-sided tape or
the like thus sealing a gap defined between them in a complete
state or in an incomplete state with respect to outside air so that
the drying conditions at a liquid-crystal-display element side and
a light-source side of the diffusing plate SCT become equal.
Inventors: |
Saito, Ken; (Mobara, JP)
; Ishida, Kazuhiro; (Mobara, JP) |
Correspondence
Address: |
Antonelli, Terry, Stout & Kraus, LLP
Suite 1800
1300 North Seventeenth Street
Arlington
VA
22209
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
18902294 |
Appl. No.: |
10/055969 |
Filed: |
January 28, 2002 |
Current U.S.
Class: |
349/112 |
Current CPC
Class: |
G02F 2201/54 20130101;
G02F 1/133504 20130101; G02F 1/133608 20130101; G02F 1/133604
20130101; G02F 1/133605 20130101; G02F 2202/28 20130101 |
Class at
Publication: |
349/112 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2001 |
JP |
2001-039522 |
Claims
What is claimed is:
1. A liquid crystal display device comprising a liquid crystal
display element, a light source, a substantially rectangular
diffusion plate which is interposed between the liquid crystal
display element and the light source, and at least one optical
sheet which is arranged between the diffusion plate and the liquid
crystal display element, wherein the liquid crystal display device
includes a transparent sheet which is arranged between the
diffusion plate and the light source and has a contour which is
substantially equal to a contour of the diffusion plate, and at
least one optical sheet is brought into contact with the diffusion
plate and respective major portions or respective whole portions of
four sides of the transparent sheet are adhered to the diffusion
plate.
2. A liquid crystal display device according to claim 1, wherein
the whole four sides of the transparent sheet are adhered to
diffusion plate.
3. A liquid crystal display device according to claim 1 or 2,
wherein the transparent sheet is adhered to the diffusion plate
using a pressure sensitive adhesive double-sided tape or a tacky
adhesive agent.
4. A liquid crystal display device according any one of claims 1 to
3, wherein at least one optical sheet is adhered to the diffusion
plate.
5. A liquid crystal display device according any one of claims 1 to
3, wherein the liquid crystal display device includes a spacer
which restricts a warp quantity of the diffusion plate in the
direction toward the light source.
6. A liquid crystal display device according claim 5, wherein at
least one optical sheet is adhered to the diffusion plate.
7. A liquid crystal display device comprising a liquid crystal
display element, a light source, a substantially rectangular
diffusion plate which is interposed between the liquid crystal
display element and the light source, and at least one optical
sheet which is arranged between the diffusion plate and the liquid
crystal display element, wherein the liquid crystal display device
includes a transparent sheet which is arranged between the
diffusion plate and the light source and has a contour which is
substantially equal to a contour of the diffusion plate and a
spacer which restricts a warp quantity of the diffusion plate in
the direction toward the light source, and at least one optical
sheet is brought into contact with the diffusion plate and at least
respective portions of four sides of the transparent sheet are
adhered to the diffusion plate.
8. A liquid crystal display device according to claim 7, wherein
the whole or major portions of four sides of the transparent sheet
are adhered to diffusion plate.
9. A liquid crystal display device according to claim 7 or 8,
wherein the transparent sheet is adhered to the diffusion plate
using a pressure sensitive adhesive double-sided tape or a tacky
adhesive agent.
10. A liquid crystal display device according any one of claims 7
to 9, wherein at least one optical sheet is adhered to the
diffusion plate.
11. A liquid crystal display device comprising a liquid crystal
display element, a light source, a substantially rectangular
diffusion plate which is interposed between the liquid crystal
display element and the light source, and at least one optical
sheet which is arranged between the diffusion plate and the liquid
crystal display element, wherein the liquid crystal display device
includes a transparent sheet which is arranged between the
diffusion plate and the light source and has a contour which is
substantially equal to a contour of the diffusion plate and a
spacer which restricts a warp quantity of the diffusion plate in
the direction toward the light source, and at least one optical
sheet is brought into contact with the diffusion plate and the
whole surface of the transparent sheet is adhered to the diffusion
plate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a liquid crystal display
device mounting a direct light source on a liquid crystal display
element, and more particularly, to a liquid crystal display device
which can irradiate the illumination light of the uniform
brightness with respect to the liquid crystal display element by
suppressing a warp of a diffusion plate which is arranged between
the direct light source and the liquid crystal display element.
[0003] 2. Description of the Related Art
[0004] There has been known a liquid crystal display device which
is provided with a light source which illuminates a liquid crystal
panel for observing an electronic latent image formed on a liquid
crystal panel as a clear visible image. This type of light source
is a so-called backlight which constitutes a light source which
illuminates the liquid crystal display element from a back surface
thereof. Hereinafter, the light source is also referred to as
"backlight".
[0005] As such a backlight, a side-edge backlight which arranges a
linear lamp (a fluorescent lamp, particularly a cold cathode
fluorescent lamp being used popularly) at a side surface of a light
guide plate made of a transparent plate formed by molding using
acrylic resin or the like, and a direct backlight which arranges
one or a plurality of linear lamps right below a back surface of
the liquid crystal panel have been known.
[0006] A notebook type computer which is required to be as thin as
possible adopts the side-edge backlight and a liquid crystal
display monitor for a liquid crystal display device also mainly
adopts the side-edge backlight to shorten a depth of the display
device.
[0007] With respect to a large-sized liquid crystal display device
such as a display monitor, the acquisition of a high contrast and
bright color display image and the prevention of the deterioration
of brightness even after the use for a long time constitute
inevitable requirements and hence, a liquid crystal display device
of a type (direct type) which arranges a plurality of linear lamps
right below the liquid crystal panel has been commercialized.
[0008] FIG. 14 is a cross-sectional view which is served for
explaining a constitutional example of the liquid crystal display
device which is provided with the direct backlight. In the drawing,
PNL indicates a liquid crystal display element (a liquid crystal
panel) which generates an image electronically. The liquid crystal
display element sandwiches a liquid crystal layer LC between a pair
of glass substrates SUB1, SUB2 and generates an image by
selectively applying voltage to electrodes or switching elements
for pixel selecting which are formed on either one or both of the
glass substrates SUB1, SUB2.
[0009] Further, the polarizers PL1, PL2 are laminated to respective
outer surfaces of the glass substrates SUB1, SUB2. The polarizers
PL1, PL2 control the polarization of the illumination light from a
backlight BL so as to make the light which passes through the
liquid crystal layer LC irradiate from the upper-side polarizer
(PL2) or interrupt the irradiation.
[0010] The backlight BL is constituted of a plurality of cold
cathode fluorescent lamps CFL, a reflection plate REF, a diffusion
plate SCT which controls the distribution of illumination light
irradiated from the cold cathode fluorescent lamps CFL, and an
optical sheet OPS which is constituted of a laminated body formed
of at least one diffusion sheet SC which controls the direction of
the illumination light and at least one prism sheet PRS. The
backlight BL is mounted on a back surface of the liquid crystal
display device PNL.
[0011] FIG. 15 is a cross-sectional view which is served for
schematically explaining a specific example of the backlight BL
shown in FIG. 14. In the direct backlight, the diffusion plate SCT
which has a relatively large thickness and is formed of an acrylic
resin plate, a polycarbonate resin plate or the like is arranged
above and close to a plurality of cold cathode fluorescent lamps
CFL which constitute the light source.
[0012] Further, on a surface of the diffusion plate SCT which is
disposed right above and faces the cold cathode fluorescent lamps
CFL in an opposed manner, a reflection light shielding pattern for
correcting the brightness irregularities is formed by printing or
the like. The reflection light shielding pattern is adjusted to
make the illumination light which illuminates the liquid crystal
display element obtain the optimum brightness distribution when the
diffusion plate is flat.
[0013] The cold cathode fluorescent lamps CFL which constitute the
backlight are mounted along valley portions of mountain-like
reflection plates REF arranged in the inside of a metal-made lower
frame FLM-D made of an aluminum plate or an iron plate. On the
diffusion plate SCT which is arranged above the cold cathode
fluorescent lamps CFL, the optical sheet OPS which is constituted
of a laminated body consisting of at least one diffusion sheet SC
and at least one prism sheet PRS is mounted in a superposed manner.
Then, an upper frame FLM-U is engaged with and integrally formed
with a lower frame FLM-D.
[0014] However, since the diffusion plate SCT is arranged close to
the cold cathode fluorescent lamps CFL, when a given time elapses
after the cold cathode fluorescent lamps CFL are turned on, a warp
which forms the diffusion plate SCT in a projected form toward the
liquid crystal display element side, for example, is generated so
that there is a possibility that the flatness of the diffusion
plate SCT is spoiled. When the flatness of the diffusion plate SCT
is spoiled, the brightness distribution adjustment using the
reflection light shielding pattern formed on the diffusion plate
SCT gives rise to irregularities so that the illumination light
irradiated to the liquid crystal display element cannot obtain the
uniform brightness distribution.
[0015] To cope with such an inconvenience, a liquid crystal display
device which arranges a light transmission sheet (hereinafter
called "a transmission sheet") at a back surface (a light source
side) of the diffusion plate has been proposed (Japanese Laid-open
Patent Publication 223812/1999). In this related art, a transparent
sheet is brought into close contact with a back surface of the
diffusion plate so as to decrease the contact of a light source
side of the diffusion plate with outside air whereby the drying of
the light source side of the diffusion plate is suppressed thus
preventing the deformation of the diffusion plate.
[0016] Further, with respect to the deformation of the diffusion
plate, Japanese Laid-open Patent Publication 326517/1998 discloses
a liquid crystal display device which installs support columns
(spacers) between a frame and a diffusion plate of a light source
to prevent the downward deflection of a center portion due to the
deadweight of the diffusion plate generated along with the lapse of
time due to the use of the liquid crystal display device for a long
period.
[0017] As other literatures which disclose the related art on the
direct liquid crystal display device, Japanese Accepted Patent
Publication 13666/1976, Japanese Laid-open Patent Publication
309921/1988 and the like can be named, for example.
SUMMARY OF THE INVENTION
[0018] As shown in FIG. 15, above (liquid-crystal-display element
side) the diffusion plate SCT, the optical sheet OPS which is
formed by sandwiching the prism sheet PRS with two diffusion sheets
SC-D, SC-U is laminated. The prism sheet PRS may be formed of a
single sheet or may be used in a form that other prism sheet is
superposed on the prism sheet PRS, wherein the groove directions of
these sheets intersect each other.
[0019] Here, the structure of the diffusion sheet and the prism
sheet is not limited to the above-mentioned example and only a
single diffusion sheet, a combination of one diffusion sheet and
two prism sheets which are laminated to each other, a combination
of one diffusion sheet and one prism sheet and other combinations
are known. On the other hand, a lower side (a light source side) of
the diffusion plate SCT is disposed close to the light source (cold
cathode fluorescent lamps CFL).
[0020] In such a constitution, it is considered that the
light-source-side surface of the diffusion plate is projected due
to the elevation of temperature and hence, the deformation of the
diffusion plate which makes the diffusion plate projected toward
the light source side occurs. However, the fact is that the
diffusion plate is projected toward the liquid crystal display
element side in most cases.
[0021] As a result of analysis of such a phenomenon, it has been
found that the light-source-side surface of the diffusion plate is
more liable to be easily dried than the
liquid-crystal-display-element side surface of the diffusion sheet
with which the optical sheet is brought into contact and the
diffusion plate is liable to be projected toward the
liquid-crystal-display-element side due to the difference of the
drying conditions of both surfaces.
[0022] It is considered that Japanese Laid-open Patent Publication
223812/1999 suppresses the drying of the light-source-side surface
of the diffusion plate by mounting a transparent sheet on the
light-source-side surface of the diffusion plate. However, in such
a constitution, it is understood that the transparent sheet is
brought into close contact with the diffusion plate. Since this
contact is not considered to constitute the adhesion, a gap is
formed between the diffusion plate and the transparent sheet
although the gap is minute. While the moisture leaks through this
gap, a gap defined between the optical sheet which is laminated to
the liquid-crystal-display-element side of the diffusion plate and
the diffusion plate is narrower than the gap between the diffusion
plate and the light-source-side transparent sheet due to the
deadweight of the optical sheet. Further, the circulation of air
through the gap defined between the optical sheet which is
laminated to the liquid-crystal-display-element side of the
diffusion plate and the diffusion plate is smaller than the
circulation of air through the gap between the diffusion plate and
the light-source-side transparent sheet whose temperature is liable
to be elevated faster, the moisture is difficult to escape
(difficult to be dried) and hence, the prevention of the projecting
of the diffusion plate toward the liquid-crystal-display element
side is less than optimal.
[0023] Further, with respect to the related art disclosed in
Japanese Laid-open Patent Publication 223812/1999, the description
that the optical sheet (the diffusion sheet or the prism sheet) or
the transparent sheet is brought into close contact with the
diffusion plate implies that the transparent sheet or the like is
simply superposed on the diffusion plate. That is, based on the
fact that the optical sheet (the diffusion sheet or the prism
sheet) which is arranged on the diffusion plate (the
liquid-crystal-display-element side) is usually simply superposed
on the diffusion plate without using a tacky adhesive agent or an
adhesive agent, the fact that no specific description is made with
respect to the arrangement of the diffusion plate and the
transparent sheet, and a comparison of such a constitution with an
embodiment which makes the humidity conditions of front and back
surfaces of a diffusion plate equal by providing support portions
which form a gap (an air layer) between the diffusion plate and the
optical sheet without using a transparent plate, it is understood
that the above-mentioned close contact of the optical sheet means
to simply superpose the optical sheet on the diffusion plate so as
to bring them into close contact with each other. Based on this
understanding, it is understood that the meaning of close contact
between the diffusion plate and the transparent sheet means to
simply superpose them each other and bringing them into close
contact with each other in the similar manner.
[0024] Accordingly, even when the transparent sheet is only
arranged at the light-source side of the diffusion plate as
mentioned above, the moisture leaks through the fine gap formed
between the diffusion plate and the transparent sheet and hence, it
is still less than optimal to prevent the diffusion plate from
being projected toward the liquid-crystal-display-element side.
[0025] Further, as mentioned above, there may be a case that, when
the diffusion plate is used for a long period, due to the
deadweight of the diffusion plate and the presence of the optical
sheet laminated to the diffusion plate, the center portion of the
diffusion plate is deflected downwardly and causes the
irregularities of brightness.
[0026] This constitutes another task to be solved in the technical
field of the present invention.
[0027] Accordingly, it is an object of the present invention to
provide a liquid crystal display device which can overcome the
above-mentioned problems and enables the irradiation of
illumination light of uniform brightness distribution to a liquid
crystal display element for a long time by suppressing a warp or a
downward deflection of a diffusion plate disposed between a direct
light source (backlight) and the liquid crystal display
element.
[0028] To achieve the above-mentioned object, according to the
present invention, a transparent sheet is provided to a surface (a
lower surface) of a diffusion plate which faces a light source in
an opposed manner, and the whole or at least respective portions of
four sides which constitute peripheries of the transparent sheet
and the diffusion plate (the diffusion plate and the transparent
sheet being formed in a rectangular shape) are adhered to each
other so that the drying conditions at a
liquid-crystal-display-element side and a light-source side of the
diffusion plate can be made substantially equal.
[0029] Further, according to the present invention, a transparent
sheet is provided to a surface (a lower surface) of a diffusion
plate which faces a light source in an opposed manner, and a spacer
is interposed between the diffusion plate and the light source.
Accordingly, the downward deflection of a center portion of the
diffusion plate brought about by the deadweight of the diffusion
plate and the superposed optical sheet when the liquid crystal
display device is used for a long period and hence, a warp of the
diffusion plate projected toward the light source side due to the
difference of the drying conditions can be prevented. Typical
constitutions of the present invention are listed hereinafter.
[0030] (1) In a liquid crystal display device comprising a
substantially rectangular diffusion plate which is interposed
between a liquid crystal display element and a light source, at
least one optical sheet which is arranged between the diffusion
plate and the liquid crystal display element, and a transparent
sheet which is arranged between the diffusion plate and the light
source and has a contour which is substantially equal to a contour
of the diffusion plate,
[0031] at least one optical sheet is arranged to be brought into
contact with the diffusion plate and the whole portions of four
sides of the optical sheet or respective major portions or
respective whole portions of four sides of the transparent sheet
are adhered to the diffusion plate.
[0032] Although the whole of the four sides can be adhered, that
is, although the four sides can be adhered without any gaps, even
when respective portions of the four sides are adhered, that is,
even when the four sides are adhered with the presence of some
gaps, such a constitution is still effective compared to a liquid
crystal display device which has no such a constitution.
[0033] Due to such a constitution, the drying conditions at the
optical-sheet side and the transparent-sheet side of the diffusion
plate become substantially equal and hence, it becomes possible to
prevent a warp of the diffusion plate whereby the brightness
distribution of the illumination light irradiated to the liquid
crystal display element can be held uniform. Further, even when a
warp is generated, the period until the warp occurs can be
prolonged.
[0034] (2) With respect to the constitution (1), the whole four
sides of the transparent sheet are adhered to the diffusion plate.
In the state that four sides of the transparent sheet and the
diffusion plate are adhered to each other, the degree of sealed
state between the transparent sheet and the diffusion plate is
classified as follows. That is, in the first state, the whole four
sides of the transparent sheet and the diffusion plate are adhered
to each other continuously without any gaps (this state being
referred to as "completely sealed state") and, in the second state,
neighboring portions of the four sides or respective portions of
the four sides of the transparent sheet and the diffusion sheet are
adhered to each other in an intermittent or in a discontinued
manner so that the inside defined between them is partially
communicated with outside air (this state being referred to as
"incompletely sealed state").
[0035] The surface of the diffusion plate which faces the light
source is more liable to be easily dried compared to the surface of
the diffusion plate which faces the liquid crystal display element.
Due to the above-mentioned constitution, it becomes possible to
suppress the occurrence of a warp of the diffusion plate projected
toward the liquid-crystal-display-element side which is caused by a
phenomenon that the drying of the transparent sheet side of the
diffusion plate progresses faster than the drying of the
liquid-crystal-display-element side of the diffusion plate when the
light source is lit for a long time. Accordingly, the brightness
distribution of the illumination light irradiated to the liquid
crystal display element can be held uniform. By setting the degree
of the sealed state between the transparent sheet and the diffusion
plate to the completely sealed state, the occurrence of the warp
can be suppressed for a long time.
[0036] (3) With respect to the constitution (1) or (2), the
transparent sheet is adhered to the diffusion plate using a
pressure sensitive adhesive double-sided tape or a tacky adhesive
agent.
[0037] As means for adhering two plate-like or sheet-like members,
a pressure sensitive adhesive double-sided tape or a tacky adhesive
agent can be used. Using such a member as the means for adhering
the transparent sheet to the diffusion plate, the degree of the
sealed state between the transparent sheet and the diffusion plate
can be set to the completely sealed state or the incompletely
sealed state with respect to the outside air without necessitating
special adhering means.
[0038] (4) With respect to any one of the constitutions (1) to (3),
at least one optical sheet is adhered to the diffusion plate.
[0039] By adhering the optical sheet which is mounted on the
liquid-crystal-display element side of the diffusion plate in the
same manner as the transparent sheet, it becomes possible to
reliably make the drying conditions at both sides, that is, the
upper and lower sides of the diffusion plate equal so that a warp
of the diffusion plate can be suppressed even when the liquid
crystal display device is used for a long time.
[0040] (5) With respect to the constitutions (1) to (3), the liquid
crystal display device is provided with a spacer for restricting a
warp quantity of the diffusion plate in the direction toward the
light source. The warp of the diffusion plate which is projected
toward the light source side can be suppressed by providing the
spacer between the light source and the diffusion plate.
[0041] Unless the transparent sheet is provided to the light source
side of the diffusion plate, the diffusion plate generates a warp
which is projected toward the liquid-crystal-display-element side.
The above-mentioned spacer cannot restrict such a warp.
Accordingly, by adhering the above-mentioned transparent sheet to
the light source side of the diffusion plate, the occurrence of the
warp which is projected toward the liquid-crystal-display-element
side can be suppressed.
[0042] Here, depending on the adhering method of the transparent
sheet (the whole four sides which constitute the peripheries of the
transparent sheet and the diffusion plate or respective portions of
these four sides) or the environment in which the liquid crystal
display device is used, there may be a case in which the occurrence
direction of the warp is projected toward the light source side.
Further, there may be a case in which the liquid crystal display
device is designed such that the degree of sealed state between the
transparent sheet and the diffusion plate is adjusted such that the
occurrence direction of the warp is projected toward the light
source side by predicting the environment in which the liquid
crystal display device is used. Further, the diffusion plate tends
to be projected toward the light source side due to the dead weight
of the diffusion plate along with the lapse of time.
[0043] To suppress the distance between the diffusion plate and the
light source to a predetermined value in such a case, the spacer
which restricts the diffusion plate from projecting toward the
light source side is provided between the light source and the
diffusion plate. That is, by preventing at least the occurrence of
the warp of the diffusion plate which is projected toward the
liquid-crystal-display-element side and by restricting the warp of
the diffusion plate toward the light source side using the spacer,
the tolerance of the design can be enhanced and the warp can be
reliably prevented.
[0044] (6) With respect to the constitutions (1) to (3), a spacer
which suppresses an a quantity of a warp of the diffusion plate in
the light source direction is provided and at least one optical
sheet is adhered to the diffusion sheet.
[0045] Even when the optical sheet to be mounted on the
liquid-crystal-display-element side of the diffusion plate and the
transparent sheet to be mounted on the light-source side of the
diffusion plate are respectively adhered to the diffusion plate so
as to make the drying conditions at both sides equal, there may be
a case that the warp which is projected toward the light source
side may occur due to the deadweight of the diffusion plate.
Further, there may be a case that the diffusion plate is swelled or
expanded due to heat. The provision of thee spacer can prevent the
occurrence of such a warp.
[0046] (7) In a liquid crystal display device comprising a
substantially rectangular diffusion plate which is interposed
between a liquid crystal display element and a light source, at
least one optical sheet which is arranged between the diffusion
plate and the liquid crystal display element, a transparent sheet
which is arranged between the diffusion plate and the light source
and has a contour which is substantially equal to a contour of the
diffusion plate, and a spacer which restricts a warp quantity of
the diffusion plate in the direction toward the light source,
[0047] at least one optical sheet is brought into contact with the
diffusion plate and at least respective portions of four sides of
the transparent sheet are adhered to the diffusion plate.
[0048] By combining the above-mentioned constitutions (5) to the
above-mentioned constitutions (1) to (3), that is, due to the
combination of adhesion of transparent sheet and the spacer, the
warp of the diffusion plate can be further efficiently suppressed
even when the liquid crystal display device is used for a long
time.
[0049] (8) With respect to the constitutions (7), the whole or
major portions of four sides of the transparent sheet are adhered
to diffusion plate. By setting the whole four sides of the
transparent sheet and the diffusion plate into the completely
sealed state or the incompletely sealed state as the adhesion
method in the constitution (7), the warp of the diffusion plate can
be suppressed even when the liquid crystal display device is used
for a long time.
[0050] (9) With respect to the constitution (7) or (8), the
transparent sheet is adhered to the diffusion plate using a
pressure sensitive adhesive double-sided tape or a tacky adhesive
agent. With the use of such member in the constitution (7), the
degree of the sealed state between the transparent sheet and the
diffusion plate can be set to the completely sealed state or the
incompletely sealed state with respect to the outside air without
necessitating special adhering means.
[0051] (10) With respect to the constitutions (7) to (9), at least
one optical sheet is adhered to the diffusion plate. By adhering
the optical sheet which is mounted on the
liquid-crystal-display-element side of the diffusion plate in the
same manner as the transparent sheet, it becomes possible to
reliably make the drying conditions at both surfaces, that is, the
upper and lower surfaces of the diffusion plate equal so that the
warp of the diffusion plate can be suppressed even when the liquid
crystal display device is used for a long time.
[0052] (11) In a liquid crystal display device comprising a
substantially rectangular diffusion plate which is interposed
between a liquid crystal display element and a light source, and at
least one optical sheet which is arranged between the diffusion
plate and the liquid crystal display element, a transparent sheet
which is arranged between the diffusion plate and the light source
and has a contour which is substantially equal to a contour of the
diffusion plate, and a spacer which restricts a warp quantity of
the diffusion plate in the direction toward the light source,
[0053] at least one optical sheet is brought into contact with the
diffusion plate and the whole surface of the transparent sheet is
adhered to the diffusion plate.
[0054] By adhering the diffusion plate to the whole surface of the
transparent sheet, the drying of the light-source side of the
diffusion plate is remarkably reduced so that a warp of the
diffusion plate projecting toward the light-source side can be
suppressed. Further, with the provision of the spacer between the
light source and the diffusion plate, even when a warp of the
diffusion plate which is projected toward the light-source side
occurs due to the environment in which the liquid crystal display
device is used or the deadweight of the diffusion plate, the
brightness distribution of the illumination light irradiated to the
liquid crystal display element can be uniformly held.
[0055] It is needless to say that the present invention is not
limited to the above-mentioned constitutions and constitutions of
embodiments which will be explained hereinafter and various
modifications can be made without departing from the technical
concept of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a cross-sectional view of a direct backlight for
schematically explaining a first embodiment of a liquid crystal
display device according to the present invention.
[0057] FIG. 2 is a plan view for schematically explaining the
adhering state of a diffusion plate and a transparent sheet of the
first embodiment of the liquid crystal display device according to
the present invention.
[0058] FIG. 3 is a partial cross-sectional view taken along a line
A-A' of FIG. 2 for schematically explaining the first embodiment of
the liquid crystal display device according to the present
invention.
[0059] FIG. 4 is a plan view for schematically explaining the
adhering state of the diffusion plate and the transparent sheet
which constitute the direct backlight for schematically explaining
the sixth embodiment of the liquid crystal display device according
to the present invention.
[0060] FIG. 5 is a side view as viewed from the direction of an
arrow B in FIG. 4 for schematically explaining the sixth embodiment
of the liquid crystal display device according to the present
invention.
[0061] FIG. 6 is a cross-sectional view of the direct backlight for
schematically explaining the seventh embodiment of the liquid
crystal display device according to the present invention.
[0062] FIG. 7 is a plan view as viewed from the direction of an
arrow D in FIG. 6 for schematically explaining the seventh
embodiment of the liquid crystal display device according to the
present invention.
[0063] FIG. 8 is a perspective view of an essential part for
schematically explaining the seventh embodiment of the liquid
crystal display device according to the present invention.
[0064] FIG. 9 is a cross-sectional view for schematically
explaining a device for measuring a warp of a diffusion plate
structure.
[0065] FIG. 10 is an explanatory view of a result obtained by
measuring the warp of a diffusion plate structure to which a
transparent sheet is adhered and the warp of a diffusion plate
structure to which a transparent sheet is not adhered which
constitutes a comparison example.
[0066] FIG. 11 is a developed perspective view for explaining the
constitution of the backlight according to the present
invention.
[0067] FIG. 12 is a cross-sectional view of an essential part taken
along a line E-E of FIG. 11 for explaining the constitution of the
backlight according to the present invention.
[0068] FIG. 13 is an appearance view showing an example of a
display monitor, on which a liquid crystal display device provided
with the backlight according to the present invention is
mounted.
[0069] FIG. 14 is a cross-sectional view for schematically
explaining a constitutional example of a liquid crystal display
device provided with a direct backlight.
[0070] FIG. 15 is a cross-sectional view for schematically
explaining a specific example of the backlight shown in FIG.
14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] Embodiments of a liquid crystal display device according to
the present invention are explained in detail in conjunction with
drawings showing the embodiments.
[0072] FIG. 1 is a cross-sectional view of a direct backlight for
schematically explaining a first embodiment of a liquid crystal
display device according to the present invention, FIG. 2 is a plan
view for schematically explaining the adhering state of a diffusion
plate and a transparent sheet shown in FIG. 1, and FIG. 3 is a
partial cross-sectional view taken along a line A-A' in FIG. 2.
[0073] Here, although a liquid crystal display element is arranged
above the direct backlight shown in Fi 1, such a liquid crystal
display element is omitted from the drawings.
[0074] In FIG. 1, the direct backlight of this embodiment is
constituted by arranging a diffusion plate SCT having a relatively
large thickness (approximately 2 mm, for example) formed of acrylic
resin (or possibly polycarbonate resin) above and close to a
plurality of cold cathode fluorescent lamps CFL which constitute a
light source. The diffusion plate SCT is formed of a rectangular
plate in the same manner as the liquid crystal display element.
[0075] Further, on a surface of the diffusion plate SCT which is
disposed right above and faces the cold cathode fluorescent lamps
CFL in an opposed manner, a reflection light shielding pattern for
correcting the brightness irregularities is formed by printing or
the like. The reflection light shielding pattern is adjusted such
that the optimal brightness distribution can be obtained when the
diffusion plate SCT is made flat.
[0076] The cold cathode fluorescent lamps CFL which constitute the
backlight are mounted along valley portions of a mountain-like
reflection plate REF which is arranged in the inside of a
metal-made lower frame FLM-D which is preferably formed of an
aluminum plate. Above the diffusion plate SCT which is arranged
above these cold cathode fluorescent lamps CFL, an optical sheet
OPS which is constituted of a diffusion sheet SC and a prism sheet
PRS is arranged in a superposed manner. Further, an upper frame
FLM-U is engaged with and integrally formed with a lower frame
FLM-D.
[0077] Further, to the surface of the diffusion plate SCT which
faces the cold cathode fluorescent lamps CFL in an opposed manner,
a transparent sheet TPS having a shape and a size approximately
equal to a shape and a size of the diffusion plate SCT is
adhered.
[0078] The transparent sheet TPS is formed of a resin film, a PET
film or the like as in the case of the optical sheet OPS. It is
preferable to set a thickness of the transparent sheet TPS to 0.15
mm or more, for example, in view of the moisture permeability. The
adhering state is shown in FIG. 2 and FIG. 3.
[0079] In this embodiment, all four sides, that is, the entire
peripheries of the diffusion plate SCT and the transparent sheet
TPS are adhered to each other using a pressure sensitive adhesive
double-coated tape BA such that the inside of the adhered entire
peripheries is completely sealed. Accordingly, the leaking of
moisture from the inside of the adhered entire peripheries can be
suppressed.
[0080] The optical sheet OPS which is mounted on the
liquid-crystal-display-element side, that is, an upper surface of
the diffusion plate SCT is formed of a laminated body consisting of
at least one diffusion sheet SC or one prism sheet PRS.
Accordingly, the optical sheet OPS is brought into close contact
with the diffusion plate SCT. Further, the optical sheet OPS may
have four peripheral sides thereof adhered to the diffusion plate
SCT using a pressure sensitive adhesive double-coated tape or a
tacky adhesive agent or may have the whole area thereof adhered to
the diffusion plate SCT using a tacky adhesive agent. With respect
to the manner of adhesion of the optical sheet OPS and the
diffusion plate SCT, the similar manner of operation is adopted by
respective embodiments which will be explained hereinafter.
[0081] In this manner, according to this embodiment, the drying
conditions at the optical sheet side and the transparent sheet side
of the diffusion plate can be made substantially equal so that it
becomes possible to prevent the occurrence of the warp of the
diffusion plate whereby the luminance distribution of the
illumination light to the liquid crystal display element can be
held uniform.
[0082] In a second embodiment of the liquid crystal display device
according to the present invention, in place of using the pressure
sensitive adhesive double-coated tape BA in the first embodiment, a
tacky adhesive agent is coated on the whole periphery between the
whole four sides of the diffusion plate SCT and the transparent
sheet TPS by printing or using a dispenser and then they are
adhered to each other.
[0083] Also according to this embodiment, the drying conditions at
the optical sheet side and the transparent sheet side of the
diffusion plate can be made substantially equal so that it becomes
possible to prevent the occurrence of the warp of the diffusion
plate whereby the luminance distribution of the illumination light
to the liquid crystal display element can be held uniform.
[0084] In a third embodiment of the liquid crystal display device
according to the present invention, a tacky adhesive agent is
coated on the whole surfaces of the diffusion plate SCT and the
transparent sheet TPS which face each other in an opposed manner
using means similar to the means described above and then they are
laminated to each other by adhesion.
[0085] Also according to this embodiment, the drying conditions at
the optical sheet side and the transparent sheet side of the
diffusion plate can be made substantially equal so that it becomes
possible to prevent the occurrence of the warp of the diffusion
plate whereby the luminance distribution of the illumination light
to the liquid crystal display element can be held uniform.
[0086] In a fourth embodiment of the liquid crystal display device
according to the present invention, the whole peripheries formed
between the whole four sides of the diffusion plate SCT and a
transparent sheet TPS are adhered to each other using a pressure
sensitive adhesive double-coated tape BA. At the same time, a tacky
adhesive agent is coated on the whole surfaces of the diffusion
plate SCT and the transparent sheet TPS which face each other in an
opposed manner so as to laminate them by adhesion using means
similar to the above-mentioned means.
[0087] Also according to this embodiment, the drying conditions at
the optical sheet side and the transparent sheet side of the
diffusion plate can be made substantially equal so that it becomes
possible to prevent the occurrence of the warp of the diffusion
plate whereby the luminance distribution of the illumination light
to the liquid crystal display element can be held uniform.
[0088] In a fifth embodiment of the liquid crystal display device
according to the present invention, a pressure sensitive adhesive
double-sided tape or a tacky adhesive agent which is provided
between the whole peripheries respectively formed by four sides of
the diffusion plate SCT and the transparent sheet TPS which face
each other in an opposed manner is interposed such that the tape or
the agent is discontinued at some portions thereof so that the
inside formed by the adhesion is slightly communicated with outside
air. That is, at least portions of respective four sides of the
diffusion plate SCT and the transparent sheet TPS are adhered to
each other. The magnitude of discontinued portions can be designed
corresponding to the degree of warp by taking the material and the
environment in which the liquid crystal display device is used into
consideration. Here, to minimize the discontinued portions, the
major portions of respective four sides of the diffusion plate SCT
and the transparent sheet TPS are adhered to each other.
[0089] Here, usually, when the cut pressure sensitive adhesive
double-sided tapes are respectively adhered to the above-mentioned
four sides or when the adhesive agent is respectively coated on the
four sides, there may be a case that a gap is formed more or less
between the pressure sensitive adhesive double-sided tapes or the
tacky adhesive agents on the neighboring sides. According to the
fifth embodiment, by making use of this gap, the inside formed
between the diffusion plate SCT and the transparent sheet TPS can
be made partially communicated with outdoor air (incompletely
sealed state) so that the drying condition inside can be
arbitrarily adjusted.
[0090] FIG. 4 is a plan view for schematically explaining the
adhering state of the diffusion plate and the transparent sheet
which constitute a direct backlight for schematically explaining
the sixth embodiment of the liquid crystal display device according
to the present invention. FIG. 5 is a schematic side view as viewed
from the direction of an arrow B shown in FIG. 4.
[0091] In this embodiment, at portions of outer peripheries of a
diffusion plate SCT and a transparent sheet TPS, notches AL are
formed so as to position them with respect to a lower frame FLM-D.
In this embodiment, one notch AL is formed at each short side of
the diffusion plate SCT and the transparent sheet TPS.
[0092] On respective four sides of the diffusion plate SCT,
individual pressure sensitive adhesive double-sided tapes BA are
mounted. The pressure sensitive adhesive double-sided tapes BA are
mounted on portions of the short sides while avoiding portions
where the notches AL are formed. Accordingly, at the portions where
the notches AL are formed, the gaps indicated by an arrow C in FIG.
4 and FIG. 5 are formed.
[0093] In this embodiment, the inside of the diffusion plate SCT
and the transparent sheet TPS becomes the incompletely sealed state
with respect to outside air and the minute gaps which make the
inside communicated with the outside air are formed. In the same
manner as the constitution explained in the fifth embodiment, the
drying condition of the inside of the diffusion plate SCT and the
transparent sheet TPS can be adjusted in response to the magnitude
of the gaps.
[0094] According to this embodiment, the drying conditions at the
optical sheet side and the transparent sheet side of the diffusion
plate can be made substantially equal so that it becomes possible
to prevent the occurrence of the warp of the diffusion plate
whereby the luminance distribution of the illumination light to the
liquid crystal display element can be held uniform.
[0095] In this embodiment, in place of the pressures sensitive
adhesive double-sided tape BA, a tacky adhesive agent can be used.
Since an advantageous effect brought about by this constitution is
similar to the advantageous effect obtained by the previous
embodiment, the repeated explanation is omitted here.
[0096] FIG. 6 is a cross-sectional view of the direct backlight for
schematically explaining the seventh embodiment of the liquid
crystal display device according to the present invention, FIG. 7
is a plan view of the backlight as viewed from the direction of an
arrow D in FIG. 6, and FIG. 8 is a perspective view of an essential
part of the backlight. Here, FIG. 7 is a plan view as viewed in the
state that an optical sheet OPS shown in FIG. 6 is removed.
Reflection surfaces of a reflection plate REF mounted on an inner
surface of a lower frame FLM-D form a plurality of parallel
mountain shapes and cold cathode fluorescent lamps CFL are arranged
along valley portions thereof.
[0097] According to this embodiment, in the same manner as the
above-mentioned respective embodiments, a transparent sheet TPS is
adhered to a diffusion plate SCT using a pressure sensitive
adhesive double-sided tape or a tacky adhesive agent so as to
insulate the inside thereof from the outside thereof whereby the
drying conditions on both of upper and lower surfaces of the
diffusion plate SCT and the transparent sheet TPS can be made
equal.
[0098] Further, according to this embodiment, to suppress a
distance between the diffusion plate SCT and a light source to a
predetermined value even when the diffusion plate SCT is projected
toward the light source (the cold cathode fluorescent lamp) due to
the deadweight thereof as time lapses, a spacer HLD is disposed
between the light source and the diffusion plate SCT. Further, the
degree of adhesion, that is, the degree of the sealed state is
adjusted such that, even when the warp is generated, the direction
of the warp is intentionally designed to be projected toward the
light source side. Accordingly, the warp can be restricted by the
spacer HLD so that the occurrence of the warp can be
suppressed.
[0099] As shown in FIG. 8, in this embodiment, the spacer HLD is
formed of a column shape which is preferably made of hard resin.
Here, the spacer HLD has a circular conical shape. However, even
when the shape of the spacer HLD is a trigonal pyramid, a
quadrangular pyramid, other multipyramid, a circular column or a
rectangular column, the same advantageous effect can be obtained.
When the spacer HLD is formed in the circular conical shape, light
irradiating from the cold cathode fluorescent lamps can be
reflected in a specific direction so that the irregularity of the
brightness distribution can be reduced.
[0100] The spacer HLD is arranged such that the single spacer HLD
is provided to the center of the plane of the backlight and has a
base bottom portion thereof fixed to a lower frame FLM-D in an
erected posture using an adhesive agent, wherein a distal end of
the spacer HLD penetrates a crest portion of the mountain of the
reflection plate REF and is brought into contact with the diffusion
plate SCT so as to support the downward deflection (the warp
projected toward the light source side) of the diffusion plate
SCT.
[0101] The spacer HLD is not limited the case shown in FIG. 8 where
one spacer HLD is formed on the center of the plane of the
backlight. That is, when the size of a screen is large, the weight
of the diffusion plate also becomes large. In such a case, the
distance between the diffusion plate SCT and the light source can
be suppressed to the predetermined value by uniformly arranging a
plurality of spacers HLD which support the diffusion plate on a
plane of a backlight.
[0102] According to this embodiment, the deformation of the
diffusion plate can be prevented and hence, the brightness
distribution of the illumination light to a liquid crystal display
element can be held uniform.
[0103] Subsequently, the evaluation obtained by reviewing the
result of suppression effect of the warp of the diffusion plate
used in the backlight of the liquid crystal display device
according to the present invention is explained hereinafter. Here,
the result of measurements of warp respectively obtained with
respect to the constitution of the above-mentioned embodiment (the
embodiment in which the diffusion plate and the transparent sheet
are adhered to each other at four sides while forming gaps at
portions thereof as shown in FIG. 4) (hereinafter referred to as
"diffusion plate structure with the adhered transparent sheet") and
a comparison example in which although the transparent sheet is
provided, the transparent sheet is simply superposed on the
diffusion plate and is not adhered (hereinafter referred to as
"diffusion plate structure with the non-adhered transparent sheet")
are shown in comparison. Here, optical sheets are adhered to and
are brought into close contact with respective upper surfaces of
both diffusion plate structures, that is, respective surfaces of
both diffusion plate structures which face the liquid crystal
display element in an opposed manner.
[0104] FIG. 9 is a cross-sectional view for schematically
explaining a measuring device of a warp of a diffusion plate
structure. In the measuring device shown in the drawing, a
diffusion plate structure SCTS is mounted on a lower frame FLM-D
and a planar plate PLR (a scale) is mounted on the diffusion plate
structure SCTS by way of spacers SPC and the change of the distance
between an upper surface of the diffusion plate structure SCTS and
a lower surface of the planar plate PLR is measured as a warp W.
The measuring device is also provided with a spacer HLD so as to
restrict a warp quantity when the diffusion plate structure SCTS is
projected toward a side opposite to the planer plate PLR.
[0105] FIG. 10 is an explanatory view of a result which is obtained
by measuring the warp of the diffusion plate structure with the
adhered transparent sheet and the warp of the diffusion plate
structure with the non-adhered transparent sheet using the
measurement device explained in FIG. 9. Time (h) is taken on an
axis of abscissas and a warp quantity (mm) is taken on an axis of
ordinates. A lower surface of the planar plate PLR is set as the
reference level [0] and the relative upwardly projecting warp is
indicated by [+] and the relative downwardly projecting warp is
indicated by [-] with respect to the reference level [0].
[0106] In FIG. 10, a graph plotted by [0] indicates a change of a
warp quantity of the diffusion plate structure (adhered at four
sides) of the present invention and a graph plotted by [x]
indicates a change of a warp quantity of the diffusion plate
structure of the comparison example (no adhesion).
[0107] By mounting the diffusion plate structure on the
above-mentioned measuring device and then by holding this state for
250 hours at maximum, while a warp quantity of the diffusion plate
structure according to the present invention was hardly changed,
the warp of the conventional diffusion plate structure exhibited a
large change which is projected upwardly. In the drawing, the warp
observed around 220 hours is considered to be an error in
measurement.
[0108] As apparent from the result of this evaluation, it is
understood that the diffusion plate structure with the adhered
transparent sheet of the present invention does not generate the
warp during the use thereof for a long time. Accordingly, the
brightness distribution of the illumination light to the liquid
crystal display element can be held uniform.
[0109] A specific example of a backlight into which the diffusion
plate structure explained in the above-mentioned embodiments of the
present invention is incorporated is explained hereinafter.
[0110] FIG. 11 is a developed perspective view for explaining the
constitution of the backlight according to the present invention.
In general, on an upper surface of a lower frame FLM-D which is
made of metal material, a plurality of cold cathode fluorescent
lamps CFL are arranged such that their longitudinal directions are
parallel to each other. The lower frame FLM-D is covered with an
upper frame FLM-U and both frames are coupled using pawls NL. Then,
both sides (left and right sides) of the lower frame FLM-D and the
upper frame FLM-U are sandwiched by a mold MLD-L (a left mold) and
a mold MLD-R (a right mold) which are made of resin material thus
integrally forming the backlight. The lower frame FLM-D is provided
with a reflection plate REF at a cold-cathode-fluorescent-lamp CFL
side thereof.
[0111] Then, on the upper frame FLM-U, a diffusion plate SCT which
adheres a transparent sheet TPS to a cold-cathode fluorescent-lamp
CFL side, and an optical sheet OPS which laminates a prism sheet
PRS between two diffusion sheets SC-D and SC-U are mounted. The
adhered structure of the diffusion plate SCT and the transparent
sheet TPS and the adhered structure of the diffusion plate SCT and
the optical sheet OPS adopt any one of constitutions of the
above-mentioned embodiments.
[0112] A liquid crystal panel (not shown in the drawing) is mounted
above the backlight and a power source for driving cold cathode
fluorescent lamps CFL, other necessary circuits and structural
members are mounted on the liquid crystal panel.
[0113] FIG. 12 is a cross-sectional view of an essential part taken
along a line E-E in FIG. 11. A reflection plate REF having
mountain-like reflection surfaces and a plurality of linear light
sources CFL are fixed to an inner surface of the lower frame FLM-D.
Then, the lower frame FLM-D and the upper frame FLM-U are laminated
and, thereafter, both frames are fixed to each other at a given
position using pawls NL shown in FIG. 11 and they are integrally
formed by left and right molds MLD-L and MLD-R.
[0114] Then, on an upper surface of the upper frame FLM-U, a
diffusion plate SCT which adheres a transparent sheet TPS to a
lower surface thereof and an optical sheet OPS to which a diffusion
sheet and a prism sheet are laminated are aligned and, thereafter,
the laminated structure is fixed to left and right molds MLD-L,
MLD-R using screws BT.
[0115] FIG. 13 is an appearance view showing one example of a
display monitor which mounts the liquid crystal display device
provided with the backlight according to the present invention
thereon. A backlight which constitutes a liquid crystal display
device mounted on a screen, that is, a display part of the monitor
has the constitution of the above-mentioned embodiment of the
present invention. Since the drying conditions on the front and
back surfaces of the diffusion plate brought about by turning on
the cold cathode fluorescent lamps can be made substantially equal,
a warp of a diffusion plate can be suppressed and the brightness
distribution of the illumination light irradiated to a liquid
crystal display element when the liquid crystal display device is
used for a long time can be uniformly maintained thus realizing the
display of high image quality.
[0116] As has been described heretofore, according to the present
invention, it becomes possible to provide a liquid crystal display
device which enables the irradiation of illumination light of
uniform brightness distribution to a liquid crystal display element
for a long period by suppressing a warp or a downward deflection of
a diffusion plate disposed between a direct light source
(backlight) and the liquid-crystal display element.
* * * * *