U.S. patent application number 13/925190 was filed with the patent office on 2013-10-31 for multi-layered light diffusion plate and liquid crystal display device comprising the same.
The applicant listed for this patent is LG Chem, Ltd.. Invention is credited to Seo-Hwa Kim, Bong-keun Lee, Ju-Hwa Lee, Jae-Chan Park, Hyun-Seok Yang.
Application Number | 20130286325 13/925190 |
Document ID | / |
Family ID | 38778777 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130286325 |
Kind Code |
A1 |
Yang; Hyun-Seok ; et
al. |
October 31, 2013 |
MULTI-LAYERED LIGHT DIFFUSION PLATE AND LIQUID CRYSTAL DISPLAY
DEVICE COMPRISING THE SAME
Abstract
Disclosed herein is a multi-layered light diffusion plate, in
which the multi-layered light diffusion plate is manufactured by
coextruding a transparent layer comprising an amorphous transparent
thermoplastic resin and a light diffusion layer comprising an
amorphous transparent thermoplastic resin and transparent
particles, so that the manufacturing process thereof is simple and
efficient, and which has excellent light transmissivity and light
diffusivity, high brightness, and high brightness uniformity,
thereby improving viewing angle characteristics, and to a liquid
crystal display device comprising the same.
Inventors: |
Yang; Hyun-Seok; (Daejeon,
KR) ; Lee; Bong-keun; (Daejeon, KR) ; Kim;
Seo-Hwa; (Daejeon, KR) ; Park; Jae-Chan;
(Daejeon, KR) ; Lee; Ju-Hwa; (Gyeonggi-Do,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Chem, Ltd. |
Seoul |
|
KR |
|
|
Family ID: |
38778777 |
Appl. No.: |
13/925190 |
Filed: |
June 24, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12084223 |
Apr 28, 2008 |
8508850 |
|
|
PCT/KR2007/001790 |
Apr 13, 2007 |
|
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13925190 |
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Current U.S.
Class: |
349/64 ;
359/599 |
Current CPC
Class: |
G02B 13/20 20130101;
G02F 1/133606 20130101; G02B 5/02 20130101; G02B 5/0242 20130101;
G02B 5/0278 20130101; G02B 5/0268 20130101 |
Class at
Publication: |
349/64 ;
359/599 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; G02B 5/02 20060101 G02B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2006 |
KR |
10-2006-0048679 |
Claims
1. A multi-layered light diffusion plate comprising a coextruded
transparent layer, and a light diffusion layer, wherein the
transparent layer comprises an amorphous transparent thermoplastic
resin and the light diffusion layer comprises an amorphous
transparent thermoplastic resin and transparent particles.
2. The multi-layered light diffusion plate of claim 1, wherein the
amorphous transparent thermoplastic resin is selected from the
group consisting of polyalkyl(meth)acrylate, an
alkyl(meth)acrylate-styrene copolymer, polycarbonate,
polyvinylchloride, a styrene-acrylonitrile copolymer, a
styrene-maleic anhydride copolymer, a styrene-maleic anhydride
derivative copolymer, a cycloolefin copolymer, polyacrylonitrile,
polystyrene, polysulfone, polyethersulfone, polyarylate and a
mixture thereof.
3. The multi-layered light diffusion plate of claim 2, wherein the
amorphous transparent thermoplastic resin is selected from the
group consisting of polymethyl(meth)acrylate, a
methyl(meth)acrylate-styrene copolymer, polycarbonate, polystyrene
and a mixture thereof.
4. The multi-layered light diffusion plate of claim 1, wherein the
transparent particles are inorganic particles, organic particles or
a mixture thereof.
5. The multi-layered light diffusion plate of claim 4, wherein the
organic particles are produced using one or more selected from the
group consisting of a polymethyl(meth)acrylate resin, a
methyl(meth)acrylate-styrene copolymer resin, a polystyrene resin
and a silicon resin.
6. The multi-layered light diffusion plate of claim 4, wherein the
organic particles are partially cross-linked.
7. The multi-layered light diffusion plate of claim 4, wherein the
inorganic particles are one or more selected from the group
consisting of calcium carbonate, barium sulfate, titanium oxide,
aluminum hydroxide, silica, a glass bead, talc, mica, white carbon,
magnesium oxide, and zinc oxide.
8. The multi-layered light diffusion plate of claim 1, wherein the
transparent particles have an average particle size of between 0.5
.mu.m and 50 .mu.m.
9. The multi-layered light diffusion plate of claim 1, wherein the
light diffusion layer comprises: from 80 to 99.9 parts by weight of
an amorphous transparent thermoplastic resin; and from 0.1 to 20
parts by weight of transparent particles.
10. The multi-layered light diffusion plate of claim 1, wherein the
transparent layer has a thickness of between 0.95 mm and 3.0
mm.
11. The multi-layered light diffusion plate of claim 1, wherein the
light diffusion layer has a thickness of between 50 .mu.m to 500
.mu.m.
12. The multi-layered light diffusion plate of claim 1, wherein the
multi-layered light diffusion plate is a two-layered structure or a
three-layered structure.
13. The multi-layered light diffusion plate of claim 12, wherein
the three-layered structure comprises: an intermediate layer formed
of the transparent layer; an uppermost layer formed of the light
diffusion layer; and a lowermost layer formed of the light
diffusion layer.
14. The multi-layered light diffusion plate of claim 1, wherein the
light diffusion plate has a total light transmissivity of 60% or
more.
15. A liquid crystal display comprising a direct backlight unit
comprising the multi-layered light diffusion plate according to
claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of U.S. patent
application Ser. No. 12/084,223, filed on Apr. 28, 2008, which
application is a national phase entry under 35 U.S.C. .sctn.371 of
International Application No. PCT/KR2007/001790 filed Apr. 13,
2007, which claims priority from Korean Patent Application No.
10-2006-0048679 filed on May 30, 2006, all of which are hereby
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a multi-layered light
diffusion plate and to a liquid crystal display device comprising
the same, and, more particularly, to a multi-layered light
diffusion plate, which is manufactured by coextruding a transparent
layer, including an amorphous transparent thermoplastic resin, and
a light diffusion layer, including an amorphous transparent
thermoplastic resin and transparent particles, so that the
manufacturing process thereof is simple and efficient, and which
has excellent light transmissivity and light diffusivity, high
brightness, and high brightness uniformity, thereby improving
viewing angle characteristics, and to a liquid crystal display
device comprising the same.
[0003] Generally, in a liquid crystal display device, such as a
monitor or a liquid crystal TV, a light diffusion sheet has been
used to form a point light source or a line light source into a
surface light source. This light diffusion sheet must have high
light diffusivity in order to prevent light sources or internal
objects, disposed posterior thereto, from being seen from the
exterior and in order to show uniform luminosity, and must have
high light transmissivity in order to increase light efficiency,
that is, high brightness and low power consumption. Furthermore,
this light diffusion sheet is required to have high brightness
uniformity in order to secure wide viewing angles.
[0004] Light diffusion sheets, which have been developed up to now,
are as follows: (1) a light diffusion sheet obtained by extruding a
transparent thermoplastic resin into a sheet shape, and then
physically forming protruded portions on the surfaces of the sheet
(Japanese Unexamined Patent Application Publication No.
Hei04-275501); (2) a light diffusion sheet or film obtained by
layering a light diffusion layer, formed of a transparent resin
including particles, on a transparent base film, such as a
polyester resin (Japanese Unexamined Patent Application Publication
No. Hei06-059108); (3) a light diffusion sheet obtained by mixing
inorganic particles in a transparent resin to form a mixture, and
then forming the mixture into a sheet having light diffusivity
(Japanese Unexamined Patent Application Publication No.
Hei06-347617); (4) an oriented polyester film, having excellent
light diffusivity, comprising at least two layers produced through
a coextrusion process (Japanese Unexamined Patent Application
Publication No. 2001-322218 and Korean Unexamined Patent
Application Publication No. 2002-48116); and (5) a light diffusion
sheet obtained by mixing beads in a melted transparent resin to
form a mixture, and then extruding the mixture (Japanese Unexamined
Patent Application Publication No. Hei06-123802).
[0005] The light diffusion sheets mentioned above in (1) and (2)
are surface light diffusive sheets obtaining light diffusivity by
forming protruded portions on the surfaces thereof or layering a
light diffusion layer on the surfaces thereof. However, in light
diffusion sheets in general, and the light diffusion sheets (1) and
(2), in particular, when the light diffusivity is obtained through
a surface treatment, there is a strong likelihood that the surfaces
of the sheet will be damaged upon treatment. Particularly, the
light diffusion sheet (2) that is now generally used in a
small-sized liquid crystal display of a notebook computer, etc. has
a problem in that it is difficult to form a layered structure,
which is required in order to realize a high-performance liquid
crystal display device and a multi-functional liquid crystal
display device. Further, this light diffusion sheet has a problem
in that a light diffusion layer applied on the surface thereof is
easily peeled off due to the difference in the thermal expansion
rate between the base film and the sheet.
[0006] Meanwhile, the light diffusion sheets mentioned above in (3)
and (5) have advantages in that sheets are imparted with light
diffusivity while the sheets are formed, thereby obtaining a high
light diffusivity. However, the light diffusion sheet (3) has
disadvantages in that, because inorganic particles are added to
impart light diffusivity, light transmissivity is decreased, and
therefore, the brightness and mechanical properties are greatly
decreased. Further, this sheet also has a problem in that a
processing machine becomes worn down when the sheets are processed
for a long time. In the light diffusion sheets (4), since a
crystalline polyester resin is used to manufacture the sheet, in
order to obtain a light diffusion sheet having a desired light
diffusivity and total light transmissivity, a process of
manufacturing the light diffusion sheet must include the steps of
preparing a non-stretched polyester sheet including at least two
layers, stretching the non-stretched polyester sheet by a
predetermined elongation percentage in a vertical or horizontal
direction at a predetermined temperature, and heat-treating the
stretched polyester sheet. In this case, when the process of
stretching the non-stretched polyester sheet is not performed,
transparency and optical characteristics are greatly decreased due
to the presence of crystals between polymer chains formed in a
process of cooling the sheet. Accordingly, there are disadvantages
in that the manufacturing process thereof is complex and the
productivity thereof is decreased, because the stretching process
is always required in order to secure the transparency and optical
characteristics. The light diffusion sheet (5) mentioned above is
now most widely used, but has a problem in that it exhibits neither
the brightness nor the brightness uniformity sufficient for
application to liquid crystal panels having increasingly wide
viewing angles, which have been developed recently.
BRIEF SUMMARY OF INVENTION
[0007] Accordingly, the present invention has been made in order to
solve the above problems occurring in the prior art, and an aspect
of the present invention is to provide a multi-layered light
diffusion plate, in which the manufacturing process thereof is
simple and efficient, and which has excellent light transmissivity
and light diffusivity, high brightness, and high brightness
uniformity, thereby improving viewing angle characteristics, and to
a liquid crystal display device comprising the same.
[0008] According to another aspect of the present invention, there
is provided a multi-layered light diffusion plate 1 manufactured by
coextruding a transparent layer 2, comprising an amorphous
transparent thermoplastic resin, and a light diffusion layer 3,
comprising an amorphous transparent thermoplastic resin and
transparent particles 4, as shown in FIGS. 1 and 2.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a schematic sectional view showing a two-layered
light diffusion plate according to an embodiment of the present
invention;
[0010] FIG. 2 is a schematic sectional view showing a three-layered
light diffusion plate according to another embodiment of the
present invention;
[0011] FIG. 3 is a plan view schematically showing an apparatus for
evaluating brightness and brightness uniformity; and
[0012] FIG. 4 is a schematic sectional view showing a liquid
crystal display device according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] In the light diffusion plate 1 of the present invention, the
amorphous transparent thermoplastic resin has a total light
transmissivity of 70% or more, and preferably 80% or more. Further,
in the amorphous transparent thermoplastic resin, unlike a
crystalline resin, since crystals are not formed between polymer
chains, an additional stretching process for imparting transparency
is not required. It is preferred that the amorphous transparent
thermoplastic resin be selected from the group consisting of
polyalkyl(meth)acrylate, an alkyl(meth)acrylate-styrene copolymer,
polycarbonate, polyvinylchloride, a styrene-acrylonitrile
copolymer, a styrene-maleic anhydride copolymer, a styrene-maleic
anhydride derivative copolymer, a cycloolefin copolymer,
polyacrylonitrile, polystyrene, polysulfone, polyethersulfone,
polyarylate and a mixture thereof. More particularly, it is
preferred that the amorphous transparent thermoplastic resin be
selected from the group consisting of polymethyl(meth)acrylate, a
methyl(meth)acrylate-styrene copolymer, polycarbonate, polystyrene
and a mixture thereof.
[0014] Further, in the light diffusion plate 1 of the present
invention, the light diffusion layer 3 includes an amorphous
transparent thermoplastic resin and transparent particles 4. The
above amorphous transparent thermoplastic resin is preferably used
as the amorphous transparent thermoplastic resin included in the
light diffusion layer 3. Inorganic particles, organic particles or
a mixture thereof are used as the transparent particles.
Preferably, organic particles are used as the transparent particles
4. It is preferred that the organic particles be produced using one
or more selected from the group consisting of a
polymethyl(meth)acrylate resin, a methyl(meth)acrylate-styrene
copolymer resin, a polystyrene resin and a silicon resin. Further,
it is preferred that the organic particles be partially
cross-linked because the shape of the particles is not changed, and
is thus maintained as it is. It is preferred that the inorganic
particles be one or more selected from the group consisting of
calcium carbonate, barium sulfate, titanium oxide, aluminum
hydroxide, silica, a glass bead, talc, mica, white carbon,
magnesium oxide, and zinc oxide.
[0015] Further, it is preferred that the transparent particles 4
have an average particle size of 0.5.about.50 .mu.m, and more
preferably 1.5.about.20 .mu.m. When the average particle size of
the transparent particles is below 0.5 .mu.m, sufficient light
diffusivity cannot be obtained, so that overall plane luminescence
intensity is decreased and a light source is visible through the
light diffusion plate. In contrast, when the average particle size
of the transparent particle is above 50 .mu.m, sufficient light
diffusivity cannot be obtained, so that plane luminescence
intensity is decreased, and light transmissivity and brightness are
decreased when a large quantity of transparent particles is added
in order to increase the light diffusivity.
[0016] Further, in the light diffusion plate 1 of the present
invention, preferably, the light diffusion layer 3 includes
80.about.99.9 parts by weight of an amorphous transparent
thermoplastic resin and 0.1.about.20 parts by weight of transparent
particles 4. More preferably, the light diffusion layer includes
9.about.99.5 parts by weight of an amorphous transparent
thermoplastic resin and 0.5.about.10 parts by weight of transparent
particles. Here, when the amount of transparent particles is below
0.1 parts by weight, light diffusivity is insufficient, so that a
rear light source is visible through the light diffusion plate. In
contrast, when the amount of the transparent particles is above 20
parts by weight, light transmissivity and brightness are
decreased.
[0017] Further, in the light diffusion plate 1 of the present
invention, the transparent layer 2 or the light diffusion layer 3,
if necessary, may further selectively include an additive such as
an ultraviolet stabilizer, a fluorescent brightening agent, a
impact resistant agent, an anti-electrostatic agent, a heat
stabilizer, a flame retardant, a lubricant, dye, or the like, in
addition to the above components, within the range that
accomplishes the objects and effects of the present invention.
[0018] In the light diffusion plate 1 of the present invention, it
is preferred that the transparent layer 2 have a thickness of
0.95.about.3.0 mm. More particularly, it is preferred that the
transparent layer have a thickness of 1..about.2.5 mm. When the
thickness of the transparent layer is below 0.95 mm, the mechanical
properties of the light diffusion plate are deteriorated and thus
unsuitable. In contrast, when the thickness of the transparent
layer is above 3.0 mm, the light diffusion plate becomes heavy, and
it is difficult to make the light diffusion plate thin, and thus
unpractical.
[0019] In the light diffusion plate 1 of the present invention, it
is preferred that the light diffusion layer 3 has a thickness of
50.about.500 .mu.m. More particularly, it is preferred that the
light diffusion layer have a thickness of 100.about.300 .mu.m. When
the thickness of the light diffusion layer is below 50 .mu.m, light
diffusivity is insufficient, and light transmissivity and
brightness are decreased when the amount of transparent particles
is increased in order to supplement the light diffusivity. In
contrast, when the thickness of the light diffusion layer is above
500 .mu.m, light transmissivity and brightness are decreased even
if light diffusivity is improved, and the light diffusion plate
becomes heavy, and it is difficult to make the light diffusion
plate thin, and thus unpractical.
[0020] The light diffusion plate 1 of the present invention is
manufactured by coextruding the transparent layer 2 and the light
diffusion layer 3. The apparatuses used in the coextrusion process
and the coextrusion conditions are not particularly limited. A
commonly known coextrusion apparatus, such as a double coextruder
or a triple coextruder, as well as any apparatus which can
coextrude a polymer resin sheet or a polymer resin film may used.
The coextrusion conditions can also be suitably adjusted depending
on the kind of resin and the thickness of each layer used in
commonly known coextrusion conditions. In a method of manufacturing
a multi-layered light diffusion plate according to an embodiment of
the present invention, the method includes the steps of mixing
80.about.99.9% by weight of the above amorphous transparent
thermoplastic resin with 0.1.about.20% by weight of the above
transparent particles using a Henschel mixer to form a mixture,
extruding the mixture using an extruder to prepare a pellet type
resin composition for a light diffusion layer, and melting and
coextruding the pellet type resin composition for a light diffusion
layer and the amorphous transparent thermoplastic resin for a
transparent layer using a coextruder provided with a T-die to
obtain a two-layered light diffusion plate or a three-layered light
diffusion plate. In this case, if necessary, an additive may be
further added at the time of preparing the resin composition of
each layer or at the time of coextruding the resin composition.
Further, the thickness of each layer can be adjusted by controlling
the screw rotation speed of an extruder and thus changing the
discharge amount of the extruder.
[0021] It is preferred that the multi-layered light diffusion plate
of the present invention be a two-layered structure or a
three-layered structure. Here, when the multi-layered light
diffusion plate 1 is a three-layered structure, it is preferred
that an intermediate layer thereof be a transparent layer 2, an
uppermost layer thereof be a light diffusion layer 3, and a
lowermost layer thereof be a light diffusion layer 3. Further, the
multi-layered light diffusion plate of the present invention has a
total light transmissivity of 60% or more, preferably 70% or more,
and, more preferably 80% or more.
[0022] Meanwhile, according to another aspect of the present
invention, there is provided a liquid crystal device including the
multi-layered light diffusion plate of the present invention.
[0023] According to the present invention, there can be realized a
multi-layered light diffusion plate, in which the manufacturing
process thereof is simple and efficient because no additional
stretching process is performed, and which has excellent light
transmissivity and light diffusivity, high brightness, and high
brightness uniformity, thereby improving viewing angle
characteristics, and a liquid crystal display including a direct
backlight unit including the light diffusion plate.
[0024] Hereinafter, a liquid crystal display device including a
direct backlight unit including the multi-layered light diffusion
plate of the present invention will be described in detail with
reference to the accompanying drawings.
[0025] Reference should now be made to the drawings, in which the
same reference numerals are used throughout the different drawings
to designate the same or similar components.
[0026] FIG. 4 is a schematic sectional view showing a liquid
crystal display device 100 according to an embodiment of the
present invention.
[0027] A liquid crystal display device 100 includes a liquid
crystal panel 110, which displays an image according to driving
signals and data signals applied from the outside, and a backlight
unit 120 arranged behind the liquid crystal panel 110 so as to
illuminate the liquid crystal panel 110.
[0028] In order to understand the present invention and carry out
the present invention, the precise structural characteristics of
the liquid crystal panel 110 are not important. A liquid crystal
panel having any structure, as long as it is generally used in a
liquid crystal display device, may be used in the liquid crystal
display device of the present invention.
[0029] The backlight unit 120 is placed behind the liquid crystal
panel 110, and supplies light, for example, white light, to the
liquid crystal panel 110. The backlight unit 120 includes a
plurality of light sources 150 supplying light for illuminating the
liquid crystal panel 110, a reflective sheet 180, a bottom chassis
190 containing the plurality of light sources 150 and the
reflective sheet 180, the light diffusion plate 140 of the present
invention, placed over the light sources 150, and an optical sheet
130.
[0030] A line light source, such as a Cold Cathode Fluorescent Lamp
(CCFL), generating light having a predetermined wavelength, for
example, white light, or an External Electrode Fluorescent Lamp
(EEFL), is used as the light source 150. However, not only the line
light source can be used as the light source 150, and a point light
source, such as a Light Emitting Diode (LED), may also be used as
the light source 150. In this case, the number of LEDs used as the
light source 150 may be suitably selected depending on the size of
the liquid crystal panel 110 to be illuminated. Further, the LEDs
used as the light source are not limited. One white LED or a
combination of three LEDs, generating red light (R), green light
(G) and blue light (B), respectively, may be used.
[0031] The reflective sheet 180 is placed under the light sources,
and improves the efficiency of use of light by reflecting light
radiated from the light sources 150 toward the liquid crystal panel
110. The reflective sheet 180 may be manufactured by applying
silver (Ag) on a sheet composed of SUS, brass, aluminum or PET, and
then coating the sheet with titanium in order to prevent the
deformation of the sheet due to the absorption of heat for a long
time, even if a very small amount of heat is generated. Further,
the reflective sheet 180 may be manufactured by dispersing bubbles
for scattering light on a sheet composed of a synthetic resin such
as PET.
[0032] The light sources 150 and the reflective sheet 180 are
contained in the bottom chassis 190.
[0033] The light generated from the light sources 150 is
transmitted to the multi-layered light diffusion plate 140 of the
present invention, which is placed over the light sources 150.
[0034] An optical sheet 130 is arranged over the light diffusion
plate. The optical sheet 130 includes a diffusion sheet 130a, a
prism sheet 130b and a protective sheet 130c. The light having
passed through the light diffusion plate 140 is transmitted to a
diffusion sheet 130a, and the diffusion sheet 130a serves to make
brightness uniform over the entire visible region of the liquid
crystal panel 110, and to widen the viewing angle. A prism sheet
130b is placed over the diffusion sheet 130a in order to improve
light efficiency and brightness, and serves to supplement the
brightness decreased by the diffusion sheet 130a. The prism sheet
130b increases the brightness within the effective viewing angle
because it refracts incoming light, which is transmitted from the
diffusion sheet 130a at a low incident angle, thus concentrating
the light forwardly. A protective sheet 130c is placed over the
prism sheet 130b. The protective sheet 130c serves to prevent the
prism sheet 130b from being damaged, and to re-widen the viewing
angle, reduced by the prism sheet 130b, within a predetermined
range.
[0035] In the liquid crystal display device of the present
invention, since the light generated from the light sources 150
passes through the multi-layered light diffusion plate 140 of the
present invention, the light can enter the light diffusion plate at
a wider range of incident angle and can be transmitted toward the
liquid crystal panel 110, placed at the front of the multi-layered
light diffusion plate 140, thereby providing a higher brightness,
compared to the conventional light diffusion plate.
EXAMPLES
[0036] A better understanding of the present invention may be
obtained through the following examples, which are set forth to
illustrate, but are not to be construed as the limit of the present
invention.
Examples 1 to 9 and Comparative Examples 1 to 3
[0037] A resin and transparent particles shown in Table 1 were put
into a Henschel mixer at the ratio shown in Table 1, and were then
mixed to form a mixture. Then, the mixture was formed into a pellet
type resin composition for a light diffusion layer.
[0038] The pellet type resin composition for a light diffusion
layer and a resin for a transparent layer shown in Table 1 were
melted and coextruded using a coextruder provided with a T die,
thereby manufacturing a multi-layered light diffusion plate.
(However, in Comparative Examples 1 and 2, the pellet type resin
composition for a light diffusion layer was independently extruded
alone, thereby manufacturing a single-layered light diffusion
plate.)
[0039] The thickness of each layer of the manufactured
multi-layered light diffusion plate was adjusted by controlling the
screw rotation speed of an extruder and thus changing the discharge
amount of the extruder, and the results thereof are given in Table
1. Further, the total light transmissivity, light diffusivity,
average brightness and brightness uniformity of the manufactured
multi-layered light diffusion plate were measured using the
following measurement methods, and the results thereof are given in
Table 2.
[0040] Material Property Measurement Methods
[0041] (1) Total Light Transmissivity and Light Diffusivity
[0042] The total light transmissivity and light diffusivity were
measured using a haze transmissometer (trademark name: HR-100,
Murakami Color Research Laboratory).
[0043] (2) Average Brightness
[0044] A sheet was cut to an area of 720 mm.times.420 mm, and the
cut sheet was placed on a 32 inch direct backlight unit. Then,
brightness was measured at 17 points (5-21 in FIG. 3) using a BM-7
(an apparatus for evaluating brightness and brightness uniformity,
manufactured by TOPCON LTD.), and average brightness was obtained
from the measured brightness. The apparatus for evaluating
brightness and brightness uniformity was shown in FIG. 3.
[0045] (3) Brightness Uniformity
[0046] Brightness uniformity was evaluated using the following
formula based on maximum brightness and minimum brightness in the
measurement results (2). According to the following formula, when
the value of the brightness uniformity is 1.00, the brightness
uniformity is best. Higher values indicate poor brightness
uniformity.
Brightness uniformity=maximum brightness/minimum brightness
TABLE-US-00001 TABLE 1 Light diffusion layer Transparent layer
Transparent Thickness Resin particle Thickness Layer resin (mm)
resin (wt. %) (wt. %) (.mu.m) number Example 1 PMMA 1.75 PS 97.1 A:
0.9 250 Two B: 2.0 layers Example 2 PMMA 1.75 MS200 96.8 A: 0.9 250
Two B: 2.3 layers Example 3 PMMA 1.75 MS600 96.5 A: 1.2 250 Two B:
2.3 layers Example 4 PMMA 1.75 PMMA 97.5 A: 2.5 250 Two B: 0 layers
Example 5 PMMA 1.75 PC 97.1 A: 0.9 250 Two B: 2.0 layers Example 6
PS 1.75 PS 97.1 A: 0.9 250 Two B: 2.0 layers Example 7 MS200 1.75
MS200 96.8 A: 0.9 250 Two B: 2.3 layers Example 8 PMMA 1.70 PS
(upper 97.1 A: 0.9 Upper Three (intermediate and lower B: 2.0
layer: 150 layers layer) layers) Lower layer: 150 Example 9 PC 1.75
PMMA 97.5 A: 2.5 250 Two B: 0 layers Comparative -- -- PMMA 99.5 A:
0.5 2000 Single Example 1 B: 0 layer Comparative -- -- MS200 99.5
A: 0.2 2000 Single Example 2 B: 0.3 layer Comparative PET 1.75 PET
97.1 A: 0.9 250 Two Example 3 B: 2.0 layers PMMA:
polymethylmethacrylate (LG MMA, EG920) PS: polystyrene (LG Chem,
Ltd., 25SP IDI) MS200: methylmethacrylate-styrene copolymer (Nippon
Steel Corporation) MS600: methylmethacrylate-styrene copolymer
(Nippon Steel Corporation) PC: polycarbonate (LG DOW polycarbonate,
Calibre 300-22) PET: polyethyleneterephthalate (SK Chemicals,
SKYPET BB7755) Transparent particle A: silicon organic particle (GE
Toshiba Silicon, Tospearl 120, average particle size: 2 .mu.m)
Transparent particle B: acrylic organic particle (Nippon Shokubai,
MA1002, average particle size: 2.5 .mu.m)
TABLE-US-00002 TABLE 2 Total light Light Average transmissivity
diffusivity brightness Brightness (%) [haze] (%) (cd/m.sup.2)
uniformity Example 1 80.2 84.3 5412 1.36 Example 2 80.7 84.3 5419
1.36 Example 3 81.1 84.2 5430 1.37 Example 4 81.3 84.2 5423 1.37
Example 5 79.1 84.3 5405 1.35 Example 6 80.0 84.3 5398 1.36 Example
7 79.1 84.3 5385 1.36 Example 8 78.4 84.4 5374 1.35 Example 9 77.8
84.3 5355 1.35 Comparative 69.4 84.4 5386 1.45 Example 1
Comparative 70.9 84.3 5380 1.47 Example 2 Comparative 67.4 84.4
4872 1.35 Example 3
[0047] As shown in Table 2, the multi-layered light diffusion
plates of the present invention in Examples 1 to 9 showed
remarkably good total light transmissivity and brightness
uniformity, compared to the single layered light diffusion plates,
which do not have an additional transparent layer and were not
coextruded (Comparative Examples 1 and 2). Further, the
multi-layered light diffusion plates of the present invention in
Examples 1 to 9 showed remarkably good total light transmissivity
and average brightness, compared to the non-stretched light
diffusion plate manufactured by coextruding
polyethyleneterephthalate, which is a crystalline resin
(Comparative Example 3).
[0048] According to the present invention, there can be realized a
multi-layered light diffusion plate, in which the manufacturing
process thereof is simple and efficient because no additional
stretching process is performed, and which has excellent light
transmissivity and light diffusivity, high brightness, and high
brightness uniformity, thereby improving viewing angle
characteristics, and a liquid crystal display including a direct
backlight unit including the light diffusion plate.
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