Title: Planar light source device and liquid-crystal display device
Abstract: Provided is a planar light source device, which comprises a light guide having at least one side end serving as a light incident side and having one surface serving as a light-emitting side, a light source disposed in the vicinity of the side end of the light guide, and a light reflector disposed on the other side opposite to the light-emitting side, and which is characterized in that the light guide is essentially formed of a polyolefin resin, the light reflector is also essentially formed of a polyolefin resin, and when a piece of the light reflector having a face size of 1.5 cm×1.5 cm is prepared, and it is pressed against the surface of the light guide with its reflective face being in contact with the surface of the light guide under a load of 135 g/cm2 thereto, and, in that condition, when it is reciprocated 10 times on the surface of the light guide to a width of 5 cm every time at a speed of 2.5 cm/sec, then the surface of the light guide is not substantially scratched by it. The planar light source device is characterized in that the light guide therein is hardly scratched and the device is lightweight.
Patent Number: 7,004,612 Issued on 02/28/2006 to Takahashi, et al.
| Inventors:
|
Takahashi; Tomotsugu (Tokyo, JP);
Ueda; Takahiko (Ibaraki, JP);
Koyama; Hiroshi (Ibaraki, JP)
|
| Assignee:
|
Yupo Corporation (Tokyo, JP)
|
| Appl. No.:
|
003732 |
| Filed:
|
December 6, 2004 |
Foreign Application Priority Data
| Jun 06, 2002[JP] | 2002-165622 |
| Current U.S. Class: |
362/615; 362/603 |
| Current Intern'l Class: |
F21V 7/04 (20060101) |
| Field of Search: |
362/600,603,608,615,582
|
References Cited [Referenced By]
U.S. Patent Documents
| 6914719 | Jul., 2005 | Koyama et al.
| |
| 2001/0033482 | Oct., 2001 | Funamoto et al.
| |
| 2002/0015299 | Feb., 2002 | Koyama et al.
| |
| Foreign Patent Documents |
| 1 111 440 | Jun., 2001 | EP.
| |
| 61-99187 | May., 1986 | JP.
| |
| 63-62014 | Mar., 1988 | JP.
| |
| 7-230004 | Aug., 1995 | JP.
| |
| 7-287110 | Oct., 1995 | JP.
| |
| 2001-74940 | Mar., 2001 | JP.
| |
| 2001/-183532 | Jul., 2001 | JP.
| |
| 2002/-109928 | Apr., 2002 | JP.
| |
| 2002/-148443 | May., 2002 | JP.
| |
Primary Examiner: Alavi; Ali
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Parent Case Text
The present application is a continuation of PCT/JP03/07118 filed on Jun. 5,
2003 and claims priority under 35 U.S.C. §119 of Japanese Patent Application
No. 165622/2002 filed on Jun. 6, 2002.
Claims
What is claimed is:
1. A planar light source device, which comprises a light guide having at least
one side end serving as a light incident side and having one surface serving as
a light-emitting side, a light source disposed in the vicinity of the side end
of the light guide, and a light reflector disposed on the other side opposite to
the light-emitting side, wherein
the light guide is essentially formed of a polyolefin resin,
the light reflector is also essentially formed of a polyolefin resin, and
when a piece of the light reflector having a face size of 1.5 cm×1.5 cm
is prepared, and it is pressed against the surface of the light guide with its
reflective face being in contact with the surface of the light guide under a load
of 135 g/cm
2 thereto, and, in that condition, when it is reciprocated
10 times on the surface of the light guide to a width of 5 cm every time at a speed
of 2.5 cm/sec, then the surface of the light guide is not substantially scratched
by it.
2. The planar light source device as claimed in claim 1, wherein the light guide
has a surface hardness of from 3B to 5H in terms of the pencil hardness on the
side thereof facing to the light reflector.
3. The planar light source device as claimed in claim 1, wherein the light guide
has a density of from 0.7 to 1.5 g/cm
3.
4. The planar light source device as claimed in claim 1, wherein the light guide
is essentially formed of a cyclic polyolefin.
5. The planar light source device as claimed in claim 4, wherein the cyclic polyolefin
has a cycloalkane structure or a cycloalkene structure as the backbone chain thereof.
6. The planar light source device as claimed in claim 1, wherein the light reflector
contains a layer that is at least monoaxially stretched and shaped.
7. The planar light source device as claimed in claim 1, wherein the pencil hardness
of the surface of the light reflector that faces the light guide is 5H or lower.
8. The planar light source device as claimed in claim 1, wherein the light reflector
has a porosity of from 5 to 50%.
9. The planar light source device as claimed in claim 1, wherein the light reflector
has a 2% deformation compression stress in the thickness direction thereof of from
300 to 3000 gf/cm
2.
10. A liquid-crystal display device characterized by comprising the planar light
source device of claim 1 as a backlight source thereof.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a planar light source device and to a liquid-crystal
display device comprising it, More precisely, the invention relates to a technique
for reducing the weight of a planar light source device, and to a liquid-crystal
display device that comprises the planar light source device favorably as the backlight
system therein.
2. Description of the Related Art
Transmission-type liquid-crystal display devices are much used
these days as monitors for personal computers and as display devices for thin TVs,
and in such liquid-crystal display devices, in general, a planar lighting device,
or that is, a backlight is disposed on the back of the liquid-crystal element therein.
The backlight has the function of converting the linear light from a linear light
source such as a cold-cathode tube into planar light, Typical examples of the concrete
structure of backlight are mentioned. One comprises a light source disposed just
below the back of a liquid-crystal element; and the other comprises a light source
disposed on the side thereof in which the light from the light source is converted
into planar light though a transparent light guide such as an acrylic plate to
obtain a planar light source (sidelight system). An optical element such as prism
array or diffusion sheet is disposed on the light output side of the device, and
a light reflector formed of a foamed polyester or the like is disposed oh the other
side opposite to the light output side thereof to thereby obtain the desired optical characteristics.
The sidelight system is disclosed in, for example, JP-A 61-99187 and 63-62014.
In particular, in order to more effectively utilize the general properties of lightweight
and thin liquid-crystal display devices, it is desirable to use the sidelight system
in which the backlight may be thin. Accordingly, sidelight-system backlights are
much used in liquid-crystal display devices such as portable personal computers.
The necessary properties of such backlights are being to be on a higher level
these days. In particular, in monitor display devices for notebook-side personal
computers and desk-top personal computers and in large-panel thin TVs, generally
used are transmission-type full-color liquid-crystal display devices. In this case,
since the light transmittance of the color liquid-crystal cell is extremely low
by itself, the necessary brightness of the backlight source must be inevitably high.
Accordingly, in the above-mentioned sidelight-system backlight, generally
but much used is a sheet of prism array or the like so as to ensure the front brightness
of the device owing to the optical light-condensing effect thereof, or a special
photofunctional sheet having a light-deflecting and converting function so as to
effectively utilize the output light of the device. However, much using it inevitably
results in the increase in the weight of the planar light source device and therefore
the increase in the weight of the liquid-crystal display device comprising it.
For solving the problem, it may be taken into consideration to use a resin that
is more lightweight than ordinary acrylic resin for light guides.
However, when the light guide formed of a lightweight material is contacted
with an optical reflector, then there occurs a problem in that the light guide
is scratched and could not be in practical use.
SUMMARY OF THE INVENTION
Taking the prior-art problems into consideration, an object of the present
invention is to provide a planar light source device in which the light guide is
lightweight but is hardly scratched. Another object is to provide a liquid-crystal
display device in which the backlight is stable and lightweight.
We, the present inventors have assiduously studied, and, as a result, have found
that the planar light source device of the invention can attain the above-mentioned
objects, which comprises a light guide having at least one side end serving as
a light incident side and having one surface serving as a light-emitting side,
a light source disposed in the vicinity of the side end of the light guide, and
a light reflector disposed on the other side opposite to the light-emitting side,
and which is characterized in that the light guide is essentially formed of a polyolefin
resin, and the light reflector is also essentially formed of a polyolefin resin,
and when a piece of the light reflector having a face size of 1.5 cm×1.5 cm
is prepared, and it is pressed against the surface of the light guide with its
reflective face being in contact with the surface of the light guide under a load
of 135 g/cm
2 thereto, and, in that condition, when it is reciprocated
10 times on the surface of the light guide to a width of 5 cm every time at a speed
of 2.5 cm/sec, then the surface of the light guide is not substantially scratched
by it.
Preferably, the light guide to constitute the planar light source device
of the invention has a surface hardness of from 3B to 5H in terms of the pencil
hardness on the side thereof facing to the light reflector, and has a density of
from 0.7 to 1.5 g/cm
3. Also preferably, the essential ingredient of
the light guide, polyolefin resin is a cyclic polyolefin (especially having a cycloalkane
structure or a cycloalkene structure as the backbone chain thereof).
Preferably, the light reflector to constitute the planar light source
device of the invention contains a layer that is at least monoaxially stretched
and shaped. Also preferably, the pencil hardness of the surface of the light reflector
that faces the light guide is 5H or lower, and the light reflector has a porosity
of from 5 to 50%. Also preferably, the light reflector has a 2% deformation compression
stress in the thickness direction thereof of from 300 to 3000 gf/cm
2.
The invention also provides a liquid-crystal display device that comprises the
above-mentioned planar light source device as the backlight source unit thereof.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic cross-sectional view of a planar light source device of
one embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The constitution and the effect of the planar light source device and the liquid-crystal
display device of the invention are described in detail hereinunder. In this description,
the numerical range expressed by the wording "a number to another number" means
the range that falls between the former number indicating the lowermost limit of
the range and the latter number indicating the uppermost limit thereof.
The planar light source device of the invention comprises a light guide having
at least one side end serving as a light incident side and having one surface serving
as a light-emitting side, a light source disposed in the vicinity of the side end
of the light guide, and a light reflector disposed on the other side opposite to
the light-emitting side.
The planar light source device of the invention is characterized in that, even
when the light guide and the light reflector that constitute the device are rubbed
against each other, the light guide is hardly scratched. Concretely, when a piece
of the light reflector having a face size of 1.5 cm×1.5 cm is prepared, and
it is pressed against the surface of the light guide with its reflective face being
in contact with the surface of the light guide under a load of 135 g/cm
2 thereto,
and, in that condition, when it is reciprocated 10 times on the surface of the
light guide to a width of 5 cm every time at a speed of 2.5 cm/sec, then the surface
of the non-light-emitting surface of the light guide is not substantially scratched
by it. In this description, the wording "not substantially scratched" means that,
when the surface of the light guide is observed with an optical microscope, Olympus
Optical Industry's SZX12 at a 10-time power, then the total length of the scratches
seen on it is less than 2 mm. Preferably, the total length of the scratches is
at most 1 mm, more preferably at most 0.5 mm, but most preferably no scratch is
seen at all.
The light guide of the planar light source device of the invention has such excellent
scratch resistance. Therefore, when the device is utilized in liquid-crystal display
devices and when the light guide and the light reflector therein are rubbed against
each other owing to the vibration they receive in service of the device, the light
guide is not scratched. Accordingly, the planar light source device of the invention
is extremely useful as stable backlights for liquid-crystal display devices and
its practicability is high.
Light Guide
The light guide to constitute the planar light source device of the invention
is essentially formed of a polyolefin resin.
The polyolefin resin includes cyclic polyolefin; ethylenic resin such as linear
low-density polyethylene, high-density polyethylene, middle-density polyethylene;
propylene resin; polymethyl-1-pentene. Above all, cyclic polyolefin is preferred.
The cyclic polyolefin is a polyolefin having an alicyclic structure in the backbone
chain thereof. The alicyclic structure in the backbone chain includes a cycloalkane
structure and a cycloalkene structure. Specific examples of the cyclic polyolefin
are norbornene polymer, monocyclic olefin polymer, cyclic conjugated diene polymer
and its hydrogenated derivatives, vinyl-alicyclic hydrocarbon polymer and its hydrogenated
derivatives, addition polymer of cyclic olefin monomer and ethylene, and these
are preferred examples.
The light guide is essentially formed of such a polyolefin resin, and the polyolefin
resin content of the light guide is preferably from 80 to 100% by weight, more
preferably from 90 to 100% by weight, even more preferably from 95 to 100% by weight.
The light guide may contain any other component than polyolefin resin, not too
much detracting from the function thereof.
For example, the light guide may suitably contain an inorganic pigment and/or
an organic filler for controlling the transparency thereof. Preferably, the amount
of the inorganic fine powder and/or the organic filler that may be in the light
guide is from 0 to 20% by weight, more preferably from 0 to 10% by weight, even
more preferably from 0 to 5% by weight.
The inorganic fine powder includes heavy calcium carbonate, light calcium carbonate,
calcined clay, silica, diatomaceous earth, talc, mica, synthetic mica, sericite,
kaolinite, titanium oxide, barium sulfate, and alumina. Of those, preferred are
heavy calcium carbonate, light calcium carbonate and barium sulfate.
For the organic filler, preferably selected is a resin not compatible with the
polyolefin resin, the essential ingredient of the light guide. Concretely, the
resin for the organic filler includes polyethylene terephthalate, polybutylene
terephthalate, polycarbonate, nylon-6, nylon-6,6, cyclic olefin homopolymer, cyclic
olefin-ethylene copolymer and the like having a melting point of from 120°
C. to 300° C. or having a glass transition point of from 120° C. to 280°
C. For example, when a polyester resin film is used for the polyolefin resin for
the light guide, then the organic filler is preferably polystyrene, polycarbonate,
nylon-6, nylon-6,6, polymethyl-1-pentene, cyclic olefin homopolymer, cyclic olefin-ethylene
copolymer or the like having a melting point of from 120° C. to 300°
C. or having a glass transition point of from 120° C. to 280° C.
One or more different types of the inorganic fine powders and the organic fillers
mentioned above may be selected and used in the light guide, either singly or as
combined therein. When two or more different types of them are used as combined,
the inorganic fine powder and the organic filler may be mixed and used.
The light guide may be produced by kneading the polyolefin resin or a resin composition
containing the polyolefin resin and the additive and then shaping it. For kneading
it, employable are a single-screw extruder, a double-screw extruder, a roll, a
kneader, etc. For shaping it, for example, employable is extrusion molding, injection
molding, calender molding, inflation molding, pressing, blow molding or their combination.
Of those, especially preferred is injection molding.
The shape of the light guide may be suitably determined depending on the use,
the object and the service mode of the planar light source device of the invention.
In general, it is tabular.
Preferably, the light guide in the planar light source device of the
invention has a surface hardness of from 3B to 5H in terms of the pencil hardness
on the side thereof facing to the light reflector, more preferably from 3B to F.
If the pencil hardness thereof is over 5H, then the light guide may scratch the
light reflector. If the pencil hardness thereof is lower than 3B, then the light
guide may be readily scratched during manufacture or use of the planar light source
device. The "pencil hardness" as referred to herein is measured under a load of
10 g, according to the method described in JIS-K-5401-69.
Preferably, the light guide in the planar light source device of the
invention has a density of from 0.7 to 1.5 g/cm
3, more preferably from
0.8 to 1.3 g/cm
3. If the density of the light guide is over 1.5 g/cm
3,
then the planar light source device may be heavy and the light guide may be a bar
to weight reduction of the planar light source device. If the density thereof is
less than 0.70 g/cm
3, then the light guide may be readily deformed by
external force or the like. The "density" as referred to herein is measured according
to JIS-P-8118.
In a specific area of any surface of the light guide, a dot pattern may be formed
for toning the light through it. For the formation, employable is shaping, engraving
or printing.
Light Reflector
The light reflector to constitute the planar light source device of the invention
is essentially formed of a polyolefin resin. The polyolefin resin includes ethylenic
resin such as linear low-density polyethylene, high-density polyethylene, middle-density
polyethylene; propylene resin; polymethyl-1-pentene; ethylene-cyclic olefin copolymer.
The propylene resin may be, for example, propylene homopolymer, or copolymer
of the essential ingredient, propylene and α-olefin such as ethylene, 1-butene,
1-hexene, 1-heptene, and 4-methyl-1-pentene. The stereospecificity of the polymer
is not specifically defined, and the polymer may be isotactic or syndiotactic,
or may have a different degree of stereospecificity. The copolymer may be binary,
ternary, or quaternary, and may be a random copolymer or a block copolymer.
Of the propylene resin, preferred for use herein are propylene homopolymer, and
propylene copolymer having a melting point not lower than 140° C. If a resin
having a melting point lower than 140° C. is in the light reflector, then
the molten sheet for the light reflector may stick to chill rolls when the light
reflector is formed through extrusion and then cooled with chill rolls, and, if
so, the surface of the light reflector may be scratched or may have white mottles,
and the optical properties of the light reflector may be thereby worsened.
The polyolefin resin content of the light reflector is preferably from 30 to
99% by weight, more preferably from 35 to 97% by weight.
The light reflector may contain any other component than polyolefin resin, not
too much detracting from the function thereof.
For example, the light reflector may suitably contain an inorganic pigment and/or
an organic filler. Preferably, the amount of the inorganic fine powder and/or the
organic filler that may be in the light reflector is from 1 to 70% by weight, more
preferably from 3 to 65% by weight. If the amount of the inorganic fine powder
and/or the organic filler is larger than 70% by weight, then the surface strength
of the light reflector may lower. If the amount is smaller than 1%, then the light
reflector may readily cause blocking.
Regarding the details of the inorganic fine powder and the organic filler
for use in the light reflector, the same as those mentioned hereinabove for the
light guide may be referred to.
If further desired, the light reflector to constitute the planar light source
device of the invention may contain a stabilizer, a light stabilizer, a dispersant,
a lubricant, etc.
For example, the light reflector may contain from 0.001 to 1% by weight of a
stabilizer such as a steric-hindered phenol, phosphorus, or amine compound, from
0.001 to 1% by weight of a light stabilizer such as a steric-hindered amine, benzotriazole
or benzophenone compound, and from 0.01 to 4% by weight of a dispersant for inorganic
fine powder (e.g., silane coupling agent), a higher fatty acid such as oleic acid
or stearic acid, metal soap, polyacrylic acid, polymethacrylic acid or a salt thereof.
The light reflector to constitute the planar light source device of the invention
may have a single-layered structure, or a two-layered structure comprising a substrate
layer and a surface layer, or a three-layered structure comprising a surface layer
and a back layer formed on the substrate layer thereof, or a multi-layered structure
having an additional resin film layer formed between the substrate and the surface
layer and/or the back layer thereof. When the light reflector has a two-layered
or more multi-layered structure, the it is desirable that all the constitutive
layers contain a polyolefin resin.
In order to toughen the light reflector and to reduce the weight thereof and
to
improve the reflectivity thereof by making its inside porous, it is desirable that
the light reflector has an at least mono-axially stretched layer. Regarding the
number of axes for stretching, the single-layered structure may be stretched monoaxially
or biaxially; the two-layered structure maybe stretched monoaxially/monoaxially,
monoaxially/biaxially, or biaxially/monoaxially; the three-layered structure may
be stretched monoaxially/monoaxially/biaxially, monoaxially/biaxially/monoaxially,
biaxially/monoaxially/monoaxially, monoaxially/biaxially/biaxially, or biaxially/biaxially/monoaxially.
In further multi-layered structures, the number of axes for stretching may be combined
in any desired manner.
The stretching method is not specifically defined, and may be any known method.
For example, herein employable is machine-direction stretching to be attained by
utilizing the peripheral speed difference between rolls; cross-direction stretching
to be attained by the use of a tenter oven; or simultaneous biaxial stretching
to be attained by combination of rolling, tenter oven and linear motor.
The stretching ratio is not specifically defined, and may be suitably determined
depending on the use and the object of the planar light source device and on the
properties of the resin used, when a propylene homopolymer or copolymer is used
for the polyolefin resin and when the sheet is stretched in one direction, then
the stretching ratio is preferably from about 2 to 25 times, more preferably from
3 to 20 times. When the sheet is stretched biaxially, then the areal stretching
ratio is from 9 to 80 times, more preferably from 30 to 60 times. If further desired,
the stretched structure may be subjected to heat treatment as high temperature.
When the resin to be stretched is a crystalline resin, it is desirable that
the resin is stretched at a temperature not lower than the glass transition point
of the non-crystal part thereof and not higher than the melting point of the crystalline
part thereof. The concrete stretching temperature may be suitably selected from
the known temperature range suitable to the resin selected.
In general, thermoplastic resin is stretched most suitably at a temperature lower
by from 2 to 60° C. than the melting point of the resin. When the resin is
propylene homopolymer (melting point, 155 to 167° C.), then it is preferably
stretched at 95 to 165° C.; and high-density polyethylene (melting point,
121 to 134° C.) is preferably stretched at 61 to 132° C.
Preferably, the stretching speed is selected within a range of from 20
to 350 m/min.
When a resin composition containing an inorganic fine powder and/or an organic
filler is stretched, the resulting film may have fine cracks in its surface and
have fine pores inside it. The pores effectively act for improving the light reflectivity
of the film, for controlling the compressive elasticity in the direction of the
thickness thereof and for reducing the weight of the film.
Preferably, the thickness of the stretched resin film is from 50 to 500
μm, more preferably from 80 to 350 μm.
When the light reflector has a two-layered or more multi-layered structure and
when a stretched film layer and a non-stretched film layers are layered or laminated
to form it, then employable is any method of casting, extrusion lamination, dry
lamination or the like.
The method of forming the resin film to constitute the light reflector is not
specifically defined, and may be any known method. Concretely, herein employable
is cast molding of sheetwise extruding resin melts through a single-layered or
multi-layered T-die or I-die connected to a screw-type extruder; calender molding,
roll molding, inflation molding; removal of solvent and oil from cast-molded or
calender-molded sheet of a mixture of thermoplastic resin, organic solvent and
oil; or molding of thermoplastic resin solution followed by removal of solvent
from it.
The shape of the light reflector for use in the invention is not specifically
defined. In general, it is sheet, but may have any other shape depending on the
use, the object and the service mode thereof.
Preferably, the pencil hardness of the surface of the light reflector
for use in the invention that faces the light guide is 5H or lower, more preferably
3 H or lower, even more preferably 1 H or lower. If the pencil hardness thereof
is higher than 5 H, then the light reflector may scratch the surface of the light
guide during manufacture or use of the planar light source device.
Also preferably, the light reflector has a porosity of from 5 to 50%, more preferably
from 10 to 45%, even more preferably from 15 to 40%. If the porosity thereof is
larger than 50%, then the strength of the light reflector may lower. If the porosity
thereof is smaller than 5%, then the light reflector may be a bar to weight reduction
of the planar light source device.
The "porosity" as referred to herein means a value calculated according to the
following equation (1):
Porosity (%)=[(ρ
0-ρ)/ρ
0]×100 (1).
In the formula, ρ
0 indicates the true density of the film, and
ρ indicates the density of the stretched film (JIS-P-8118). So far as the
unstretched material does not contain a large amount of air, the true density of
the film is almost equal to the density of the unstretched film. The density of
the stretched film may be obtained by determining the unit weight (g/m
2)
of the light reflector followed by dividing it by the thickness (μm) of the
light reflector determined with a micrometer or through electronic microscope observation
(unit weight/thickness).
Preferably, the light reflector for use in the invention has a 2% deformation
compression stress in the thickness direction thereof of from 300 to 3000 gf/cm
2,
more preferably from 350 to 2800 gf/cm
2, even more preferably from 400
to 2500 gf/cm
2.
If the 2% deformation compression stress in the thickness direction thereof is
smaller than 300 gf/cm
2, then the light reflector may be readily wrinkled.
If the 2% deformation compression stress in the thickness direction thereof is
larger than 3000 gf/cm
2, then the light reflector may scratch the surface
of the light guide during manufacture or use of the planar light source device.
The "2% deformation compression stress in the thickness direction" as referred
to herein is a value measured according to the method mentioned below.
Concretely, a pressure unit is fitted to a tensile tester, Autograph
AGS-5kND (by Shimadzu), and the sample to be analyzed is compressed with it at
a compression speed of 1 mm/min, whereupon the compression stress under which the
sample shows 2% deformation as determined with a CCD laser displacement sensor
LK3100 (by Keyence) is read in the tensile tester.
The "2% deformation" as referred to herein means that the degree of displacement
of the compressed light reflector is 2% of the thickness of the non-compressed
light reflector.
Planar Light Source Device and Liquid-Crystal Display Device
Using the light guide and the light reflector formed according to the methods
mentioned above, the planar light source device of the invention may be produced.
The planar light source device of the invention is a sidelight-type planar light
source device. A concrete constitution example of the planar light source device
of the invention is shown in FIG. 1.
In the planar light source device of FIG. 1, the upper face of the light guide
(
2) is a light-emitting side thereof; and the left-side face thereof is
a light incident side thereof. A light reflector (
1) is disposed on the
other side opposite to the light-emitting side of the light guide (
2); and
a light source (
3) is disposed in the vicinity of the light incident side
of the light guide (
2). The light emitted by the light source runs into
the light guide through its light incident side, and goes out through its light-emitting
side along with the light reflected by the light reflector.
The light reflector (
1) is so disposed that it may reflect light inside
the light guide (
2) and may efficiently emit light through the light-emitting
side of the light guide. Preferably, the light reflector (
1) entirely covers
the other side opposite to the light-emitting side of the light guide, but may
partly cover it in consideration of the use, the object and the service mode thereof.
The light source (
3) for use in the planar light source device of the
invention may be suitably selected from any ordinary ones generally used in planar
light source devices. One typical example of the light source is a linear light
source such as a cold-cathode lamp.
A diffusion sheet may be disposed on the light-emitting side of the planar light
source device of the invention. For the material of the diffusion sheet, mentioned
are cyclic polyolefin, ethylene resin, propylene resin, and polyethylene resin.
Preferably, the thickness of the diffusion sheet is from 50 to 500 μm, more
preferably from 70 to 300 μm.
Since the light reflector (
1) and the light guide (
2) in the
planar light source device of the invention are both formed of a polyolefin resin
as the essential ingredient thereof, the device is more lightweight than conventional
devices. In addition, since the light guide is hardly scratched even when the light
reflector and the light guide are rubbed against each other owing to vibration
or the like, another advantage of the light source device of the invention is that
its stability as a light source is high.
Using the planar light source device of the invention, a liquid-crystal display
device can be produced.
The liquid-crystal display device as referred to herein is for image display
by the use of liquid-crystal cells as arrays of optical shutters, in which the
orientation condition of the liquid crystal is varied owing to the electro-optical
effect, or that is, the optical anisotropy (refractive anisotropy) of the liquid-crystal
molecules and by applying an electric field to any desired display units or by
passing electric current through them to thereby change the optical transmittance
or the reflectance of the units so as to drive the device.
The liquid-crystal display device is constructed by disposing, for example, a
diffusion sheet, a lens film, a brightness-improving film, a polarizer, an optically-compensatory
plate, a liquid-crystal cell, an optically-compensatory plate and a polarizer in
that order on the light-emitting side of the planar light source device.
Concretely, the liquid-crystal display device includes a transmission-type
simple matrix-drive super-twisted nematic mode device, a transmission-type active
matrix-drive twisted nematic mode device, a transmission-type active matrix-drive
in-plane switching mode device, a transmission-type active matrix-drive multi-domain
vertical align mode device.
When the planar light source device of the invention is used as a backlight
source to construct a liquid-crystal display device, then its brightness is essentially
high and it may be a more lightweight device than the backlight source unit in
ordinary liquid-crystal display devices.
The invention is described more concretely with reference to the following Examples,
Comparative Example and Test Example. Not overstepping the scope of the invention,
the materials and their amount and ratio and the operations mentioned below may
be suitably changed. Accordingly, the scope of the invention should not be limited
to the following examples.
The details of the materials used in the examples are shown in the following Table.
| TABLE 1 |
|
| Compound |
Details |
|
| PP1 |
propylene homopolymer [Nippon Polychem's |
| |
Novatec PP:EA8] (MFR (230° C., 2.16 kg load) = |
| |
0.8 g/10 min), melting point (167° C., DSC peak |
| |
temperature) |
| PP2 |
propylene homopolymer [Nippon Polychem's |
| |
Novatec PP:MA4] (MFR (230° C., 2.16 kg load) = |
| |
5 g/10 min), melting point (167° C., DSC peak |
| |
temperature) |
| HDPE |
high-density polyethylene [Nippon Polychem's |
| |
Novatec HD:HJ360] (MFR (190° C., 2.16 kg load) = |
| |
5.5 g/10 min), melting point (134° C., DSC peak |
| |
temperature) |
| (a) heavy calcium |
heavy calcium carbonate having a mean particle |
| carbonate |
size of 0.97 μm (Maruo Calcium's Caltex 7) |
| (b) heavy calcium |
heavy calcium carbonate having a mean particle |
| carbonate |
size of 1.8 μm (Bihoku Funka Kogyo's Softon |
| |
1800) |
| (c) light calcium |
light calcium carbonate having a mean particle |
| carbonate |
size of 0.07 μm (Maruo Calcium's MC-5) |
| (d) barium |
barium sulfate having a mean particle size of |
| sulfate |
0.5 μm (Sakai Chemical Industry's B-54) |
| titanium oxide |
titanium dioxide having a mean particle size |
| |
of 0.2 μm (Ishihara Sangyo's CR-60) |
|
EXAMPLE 1
A composition (B) comprising PP1, HDPE, and filler of heavy calcium carbonate
and
titanium dioxide; and compositions (A) and (C) each comprising PP2, HDPE and filler
of heavy calcium carbonate and titanium dioxide were melt-kneaded in different
three extruders at 250° C. The blend ratio by weight of each composition is
as in Table 2. Next, the resulting melts were fed into one coextrusion die, in
which (A) and (C) were laminated on both sides of (B), and these were sheetwise
extruded out and cooled with a chill roll to about 60° C. to prepare a laminate (A/B/C).
The laminate was re-heated at 145° C. and then stretched to the draw ratio
as in Table 2, in the machine direction by utilizing the peripheral speed difference
between a large number of rolls, and thereafter this was annealed at 160°
C., and its edges were trimmed away to obtain a light reflector formed of a multi-layered
stretched resin film.
A cyclic polyolefin (Nippon Zeon's trade name, Zeonoa 1060R) was used for a light guide.
The light guide and the light reflector were combined to construct a planar light
source device having the light guide disposed on the side of the surface layer
(A) of the light reflector (FIG. 1),
EXAMPLE 2
A composition (B) comprising PP1, HDPE, and filler of heavy calcium carbonate
and
titanium dioxide; and compositions (A) and (C) each comprising PP2, HDPE and filler
of heavy calcium carbonate and titanium dioxide were melt-kneaded in different
three extruders at 250° C. The blend ratio by weight of each composition is
as in Table 2. Next, the resulting melts were fed into one coextrusion die, in
which (A) and (C) were laminated on both sides of (B), and these were sheetwise
extruded out and cooled with a chill roll to about 60° C. to prepare a laminate (A/B/C).
The laminate was re-heated at 145° C., then stretched to the draw ratio
as in Table 2, in the machine direction by utilizing the peripheral speed difference
between a large number of rolls, then again re-heated at about 150° C. and
stretched by the use of a tenter in the cross direction to the draw ratio as in
Table 2. Next, this was annealed at 160° C. and then cooled to 60° C.,
and its edges were trimmed away to obtain a light reflector formed of a multi-layered
stretched resin film. The surface layer (A) is to be in contact with the light
guide when a liquid-crystal display is constructed.
Using the light reflector obtained herein and the light guide described in
Example 1, a planar light source device was constructed in the same manner as in
Example 1.
EXAMPLE 3
A composition (B) comprising PP1, HDPE, and filler of heavy calcium carbonate
and
titanium dioxide was melt-kneaded in an extruder at 250° C. The blend ratio
by weight of the composition (B) is as in Table 2. Next, this was sheetwise extruded
out and cooled with a chill roll to about 60° C. to obtain a non-stretched
sheet. Thus obtained, the non-stretched sheet was re-heated at 145° C. and
stretched to the draw ratio as in Table 2, in the machine direction by utilizing
the peripheral speed difference between a large number of rolls.
Compositions (A) and (C) each comprising PP2, HDPE and filler of heavy
calcium carbonate and titanium dioxide were melt-kneaded in different extruders
at 250° C. The blend ratio by weight of each composition is as in Table 2.
Next, each melt was sheetwise extruded out and laminated on both faces of the stretched
film of the composition (B) obtained in the previous step as above, as in the constitution
shown in Table 2. Next, this was cooled with a chill roll to about 60° C.
to obtain a laminate (A/B/C).
The laminate was re-heated at about 150° C., then stretched to the draw
ratio as in Table 2, in the cross direction by the use of a tenter. Next, this
was annealed at 160° C. and then cooled to 60° C., and its edges were
trimmed away to obtain a light reflector formed of a multi-layered stretched resin
film. The surface layer (A) is to be in contact with the light guide when a liquid-crystal
display is constructed.
Using the light reflector obtained herein and the light guide described in
Example 1, a planar light source device was constructed in the same manner as in
Example 1.
EXAMPLE 4
A composition (B) comprising PP1, HDPE, and filler of light calcium carbonate
and
titanium dioxide; and compositions (A) and (C) each comprising PP2, HDPE and filler
of light calcium carbonate and titanium dioxide were melt-kneaded in different
three extruders at 250° C. The blend ratio by weight of each composition is
as in Table 2. Next, the resulting melts were fed into one coextrusion die, in
which (A) and (C) were laminated on both sides of (B), and these were sheetwise
extruded out and cooled with a chill roll to about 60° C. to prepare a laminate (A/B/C).
The laminate was re-heated at 145° C., then stretched to the draw ratio
as in Table 2, in the machine direction by utilizing the peripheral speed difference
between a large number of rolls, then again re-heated at about 150° C. and
stretched by the use of a tenter in the cross direction to the draw ratio as in
Table 2. Next, this was annealed at 160° C. and then cooled to 60° C.,
and its edges were trimmed away to obtain a light reflector formed of a multi-layered
stretched resin film. The surface layer (A) is to be in contact with the light
guide when a liquid-crystal display is constructed.
Using the light reflector obtained herein and the light guide described in
Example 1, a planar light source device was constructed in the same manner as in
Example 1.
EXAMPLE 5
A composition (B) comprising PP1, HDPE, and filler of barium sulfate and titanium
dioxide; and compositions (A) and (C) each comprising PP2, HDPE and filler of barium
sulfate and titanium dioxide were melt-kneaded in different three extruders at
250° C. The blend ratio by weight of each composition is as in Table 2. Next,
the resulting melts were fed into one coextrusion die, in which (A) and (C) were
laminated on both sides of (B), and these were sheetwise extruded out and cooled
with a chill roll to about 60° C. to prepare a laminate (A/B/C).
The laminate was re-heated at 145° C., then stretched to the draw ratio
as in Table 2, in the machine direction by utilizing the peripheral speed difference
between a large number of rolls, then again re-heated at about 150° C. and
stretched by the use of a tenter in the cross direction to the draw ratio as in
Table 2. Next, this was annealed at 160° C. and then cooled to 60° C.,
and its edges were trimmed away to obtain a light reflector formed of a multi-layered
stretched resin film. The surface layer (A) is to be in contact with the light
guide when a liquid-crystal display is constructed.
Using the light reflector obtained herein and the light guide described in
Example 1, a planar light source device was constructed in the same manner as in
Example 1.
COMPARATIVE EXAMPLE 1
A commercially-available white polyester film (Toray's trade name, E60L) was
used
for a light reflector.
Using the light reflector and the light guide described in Example 1, a planar
light source device was constructed in the same manner as in Example 1.
TEST EXAMPLE
The light reflectors produced in Examples 1 to 5 and in Comparative Example 1
were tested for the friction, the 2% deformation compression stress, the pencil
hardness and the porosity thereof.
<1> Friction Test:
A piece of the light reflector having a size of 1.5 cm×1.5 cm was fitted
to
the back side (non-light-emitting side, pencil hardness B) of the light guide formed
of a cyclic polyolefin resin (Nippon Zeon's trade name, Zeonoa 1060R) having a
density of 1.01 g/cm
3 in such a manner that the reflective side of the
reflector could be in contact with the back side of the light guide, and this was
reciprocated 10 times to a width of 5 cm each, at a speed of 2.5 cm/sec and under
a load of 135 g/cm
2. The surface of the light guide was observed with
an optical microscope, Olympus Optical Industry's SZX12 at a 10-time power, and
checked for scratches. When some scratches were found on the surface, then the
length of each scratch was measured, and the data of all scratches were summed
up. The samples thus tested were evaluated according to the following 3 ranks.
∘: No scratch was found.
Δ: Substantial scratches were not found (the total length of the scratches
was less than 2 mm).
x: Great scratches were found, and practical use of the sample is problematic
(the total length of the scratches was 2 mm or more).
<2> Determination of 2% Deformation Compression Stress:
A pressure unit was fitted to a tensile tester, Autograph AGS-5kND (by Shimadzu),
and the light reflector sample to be analyzed was compressed with it at a compression
speed of 1 mm/min, whereupon the compression stress under which the sample showed
2% deformation as determined with a CCD laser displacement sensor LK3100 (by Keyence)
was read in the tensile tester.
<3> Pencil Hardness Test:
According to the method described in JIS-K5401-69, a pencil was applied
under a load of 10 g to the sample to be tested, and the surface of the sample
was visually checked for scratches.
<4> Determination of Porosity:
According to JIS-P-8118, the density and the true density of the stretched
film were measured, and the porosity of the film was obtained according to the
above-mentioned equation (1).
The measured data are shown in Table 2 and Table 3.
| |
TABLE 2 |
| |
|
| |
Composition of Surface |
Composition of Substrte |
Composition of Back Layer |
| |
Layer (A) (% by weight) |
Layer (B) (% by weight) |
(C) (% by weight) |
| |
PP 2 |
HDPE |
Filler |
TiO2 |
PP 1 |
HDPE |
Filler |
TiO2 |
PP 2 |
HDPE |
Filler |
TiO2 |
|
| Example 1 |
97 |
— |
(a) 2.5 |
0.5 |
29 |
6 |
(a) 60 |
5 |
97 |
— |
(a) 2.5 |
0.5 |
| Example 2 |
70 |
— |
(a) 29.5 |
0.5 |
61 |
6 |
(a) 30 |
3 |
97 |
— |
(a) 2.5 |
0.5 |
| Example 3 |
55 |
— |
(b) 44.5 |
0.5 |
71 |
6 |
(b) 20 |
3 |
55 |
— |
(b) 44.5 |
0.5 |
| Example 4 |
97 |
— |
(c) 2.5 |
0.5 |
59 |
6 |
(c) 30 |
5 |
97 |
— |
(c) 2.5 |
0.5 |
| Example 5 |
97 |
— |
(d) 2.5 |
0.5 |
59 |
6 |
(d) 30 |
5 |
97 |
— |
(d) 2.5 |
0.5 |
| Comp. |
White Polyester Film |
| Example 1 |
|
| |
Layer |
Stretch |
|
|
|
| |
Thickness |
Magnification |
Draw Ratio |
Areal Ratio |
Porosity |
| |
|
A/B/C (μm) |
MD |
CD |
MD/CD |
MD * CD |
(%) |
| |
|
| |
Example 1 |
1/168/1 |
8.0 |
1.0 |
8.00 |
8.0 |
45 |
| |
Example 2 |
1/168/1 |
4.2 |
8.5 |
0.49 |
35.7 |
43 |
| |
Example 3 |
41/168/41 |
4.2 |
8.5 |
0.49 |
35.7 |
45 |
| |
Example 4 |
1/168/1 |
4.2 |
8.5 |
0.49 |
35.7 |
30 |
| |
Example 5 |
1/168/1 |
4.2 |
8.5 |
0.49 |
35.7 |
45 |
| |
Comp. |
White Polyester Film |
| |
Example 1 |
| |
|
| |
TABLE 3 |
| |
|
| |
Scratch |
2% Compression |
Pencil |
| |
Resistance |
Stress |
Hardness Test |
| |
of Light Guide |
(gf/cm2) |
(10 g load) |
| |
|
| |
| Example 1 |
◯ |
800 |
6B or less |
| Example 2 |
◯ |
1200 |
6B |
| Example 3 |
◯ |
1000 |
6B |
| Example 4 |
Δ |
2300 |
3H |
| Example 5 |
◯ |
1300 |
5B |
| Comp. Example 1 |
X |
4700 |
6H or more |
|
INDUSTRIAL APPLICABILITY
According to the invention, the light guide is not scratched even when
it is rubbed against the light reflector owing to vibration or the like while the
planar light source device is manufactured or is built in a liquid-crystal display
device and used therein, In addition, the invention realizes weight reduction of
the planar light source device and the liquid-crystal display device comprising it.
The present disclosure relates to the subject matter contained in Japanese Patent
Application No. 165622/2002 filed on Jun. 6, 2002, which is expressly incorporated
herein by reference in its entirety.
The foregoing description of preferred embodiments of the invention has been
presented for purposes of illustration and description, and is not intended to
be exhaustive or to limit the invention to the precise form disclosed. The description
was selected to best explain the principles of the invention and their practical
application to enable others skilled in the art to best utilize the invention in
various embodiments and various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention not be limited by
the specification, but be defined claims set forth below.
*
