U.S. patent application number 13/377017 was filed with the patent office on 2012-04-05 for surface light source device, lighting device, and backlight device.
Invention is credited to Toshihiko Hori, Hiroyasu Inoue.
Application Number | 20120080710 13/377017 |
Document ID | / |
Family ID | 43308960 |
Filed Date | 2012-04-05 |
United States Patent
Application |
20120080710 |
Kind Code |
A1 |
Inoue; Hiroyasu ; et
al. |
April 5, 2012 |
SURFACE LIGHT SOURCE DEVICE, LIGHTING DEVICE, AND BACKLIGHT
DEVICE
Abstract
A surface light source device is provided that has high light
extraction efficiency and high mechanical strength and can suppress
a change in color tone at different viewing angles. To that end,
the surface light source device includes: an organic EL element
including a luminescent layer; and a light-emitting surface
structure layer that is disposed in contact with one of the
surfaces of the organic EL element and defines a concave-convex
structure on the surface on the device light-emitting surface side.
The concave-convex structure includes a plurality of concave
portions having oblique surfaces and flat portions disposed around
the concave portions. The surface light source device further
includes a diffusing member on which the light emitted from the
luminescent layer is incident, the diffusing member allowing the
incident light to pass therethrough or reflecting the incident
light in a diffused manner.
Inventors: |
Inoue; Hiroyasu; (Tokyo,
JP) ; Hori; Toshihiko; (Tokyo, JP) |
Family ID: |
43308960 |
Appl. No.: |
13/377017 |
Filed: |
June 11, 2010 |
PCT Filed: |
June 11, 2010 |
PCT NO: |
PCT/JP2010/059903 |
371 Date: |
December 8, 2011 |
Current U.S.
Class: |
257/98 ; 257/40;
257/E51.018 |
Current CPC
Class: |
G02B 6/0036 20130101;
G02F 1/133607 20210101; H01L 51/5237 20130101; H01L 51/5268
20130101; H01L 51/5271 20130101; G02F 1/133603 20130101; H01L
51/5275 20130101; G02B 5/045 20130101 |
Class at
Publication: |
257/98 ;
257/E51.018; 257/40 |
International
Class: |
H01L 51/52 20060101
H01L051/52 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2009 |
JP |
2009-139818 |
Jun 24, 2009 |
JP |
2009-149944 |
Claims
1. A surface light source device, comprising: an organic
electroluminescent element including a luminescent layer; and a
light-emitting surface structure layer disposed in contact with at
least one of surfaces of the organic electroluminescent element,
wherein: the light-emitting surface structure layer includes a
concave-convex structure provided on a surface thereof on a side
toward a light-emitting surface of the device, the concave-convex
structure includes a plurality of concave portions having oblique
surfaces and flat portions disposed around the concave portions,
the surface light source device further comprises a diffusing
member on which light emitted from the luminescent layer is
incident, the diffusing member allowing the incident light to pass
therethrough or reflecting the incident light in a diffused manner,
and the surface light source device includes the diffusing member
as a member that constitutes at least one of: a layer constituting
all or part of the light-emitting surface structure layer, and a
layer disposed at a position farther from the light-emitting
surface structure layer than the organic electroluminescent
element.
2. The surface light source device according to claim 1, wherein
the diffusing member is a member provided as the layer constituting
all or part of the light-emitting surface structure layer, and is a
member that allows the incident light to pass therethrough in a
diffused manner.
3. The surface light source device according to claim 2, wherein
the diffusing member is a bonding layer interposed between two
layers included in the light-emitting surface structure layer.
4. The surface light source device according to claim 3, wherein
the light-emitting surface structure layer includes: a substrate
disposed in contact with the organic electroluminescent element, a
concave-convex structure layer disposed at a position closer to the
device light-emitting surface than the substrate, the
concave-convex structure layer including the concave-convex
structure on a surface thereof, the surface being on a side close
to the device light-emitting surface, and a bonding layer for
bonding the substrate and the concave-convex structure layer, and
wherein: the surface light source device includes the bonding layer
as the diffusing member.
5. The surface light source device according to claim 1, wherein
the diffusing member is formed from a material containing particles
that impart light diffusibility.
6. The surface light source device according to claim 1, wherein
the diffusing member is a member disposed at a position farther
from the light-emitting surface structure layer than the organic
electroluminescent element, and is a member that reflects the
incident light in a diffused manner.
7. The surface light source device according to claim 1, wherein,
when the concave-convex structure is observed in a direction
perpendicular to the device light-emitting surface, a ratio of an
area occupied by the flat portions relative to the sum of the area
occupied by the flat portions and an area occupied by the concave
portions is 10 to 75%.
8. The surface light source device according to claim 1, wherein
the concave portions have a pyramid shape, a conical shape, a shape
of part of a sphere, or a shape of a combination thereof, the
plurality of concave portions are aligned on the device
light-emitting surface in two or more directions crossing each
other, and spacings are provided between adjacent concave portions
in all of the two or more directions, the spacings constituting the
flat portions.
9. The surface light source device according to claim 1, wherein
the concave portions have a pyramid shape, a conical shape, a shape
of part of a sphere, or a shape of a combination thereof, the
plurality of concave portions are aligned on the device
light-emitting surface in two or more directions crossing each
other, and spacings are provided between adjacent concave portions
in only one of the two or more directions, the spacings
constituting the flat portions.
10. The surface light source device according to claim 1, wherein
the concave portions have a groove shape, the plurality of concave
portions are aligned in parallel to each other on the device
light-emitting surface, and spacings are provided between adjacent
concave portions, the spacings constituting the flat portions.
11. A surface light source device, comprising: an organic
electroluminescent element including, in the following order, a
first electrode layer, a luminescent layer, and a second electrode
layer; and a light-emitting-side member that is disposed in contact
with at least one of surfaces of the organic electroluminescent
element and has a light-emitting surface from which light is
emitted to the outside, wherein: the light-emitting-side member
includes: a light-distribution conversion unit that converts a
distribution of light emitted from the organic electroluminescent
element so as to reduce a difference between a chromaticity of
light emitted from the light-emitting surface in a normal direction
with respect to the light-emitting surface and a chromaticity of
light emitted from the light-emitting surface in an oblique
direction crossing the normal direction, and a diffusing section
that diffuses the light emitted from the organic electroluminescent
element.
12. The surface light source device according to claim 11, wherein
the diffusing section is a layer that is disposed between the
light-distribution conversion unit and the organic
electroluminescent element and is formed of a composition
containing particles that impart light diffusibility.
13. The surface light source device according to claim 11, wherein
the diffusing section is a layer that is disposed on a
light-emitting side of the light-distribution conversion unit and
is formed of a composition containing particles that impart light
diffusibility.
14. The surface light source device according to claim 11, wherein
the light-distribution conversion unit includes a concave-convex
structure layer having a concave-convex structure formed on a
surface thereof.
15. The surface light source device according to claim 14, wherein
the concave-convex structure layer is formed of a composition
containing particles that impart light diffusibility and serves
also as the diffusing section.
16. The surface light source device according to claim 11, wherein
the light-distribution conversion unit includes a substrate and a
concave-convex structure layer disposed on a surface of the
substrate, the concave-convex structure layer having a
concave-convex structure formed on a surface thereof on a side
opposite to the substrate.
17. The surface light source device according to claim 16, wherein
the substrate and/or the concave-convex structure layer is formed
of a composition containing particles that impart light
diffusibility and serves also as the diffusing section.
18. The surface light source device according to claim 11, wherein
the light-distribution conversion unit includes a substrate film
and a selective reflecting layer disposed on at least one of
surfaces of the substrate film.
19. The surface light source device according to claim 18, wherein
the selective reflecting layer includes a layer containing a resin
having cholesteric regularity.
20. The surface light source device according to claim 18, wherein
the substrate film is formed of a composition containing particles
that impart light diffusibility and serves also as the diffusing
section.
21. A lighting device comprising the surface light source device
according to claim 1.
22. A backlight device comprising the surface light source device
according to claim 1.
23. A lighting device comprising the surface light source device
according to claim 11.
24. A backlight device comprising the surface light source device
according to claim 11.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface light source
device, a lighting device provided with the surface light source
device, and a backlight device provided with the surface light
source device.
BACKGROUND ART
[0002] The luminescent bodies of organic electroluminescent
elements (hereinafter may be referred to as "organic EL elements")
can be formed in a planar shape, and the color of light emitted
therefrom can be white or a color close to white. Therefore, it is
contemplated that such organic EL elements are used as light
sources of lighting devices for illuminating areas in living
environments etc. or in applications for backlights of display
devices.
[0003] As an example of the organic EL elements used in lighting
applications, white organic EL elements are being manufactured.
Many of such white elements are of the stacked or tandem type in
which luminescent layers that emit light with complimentary colors
are stacked. The stacks of such luminescent layers are mainly
stacks of yellow/blue luminescent layers or green/blue/red
luminescent layers.
[0004] However, currently known organic EL elements are
unsatisfactory in terms of efficacy for the aforementioned lighting
applications. Therefore, when an organic EL element is used as a
surface light source, it is required to improve its light
extraction efficiency. For example, although the luminescent
efficiency of the luminescent layer itself of an organic EL element
is high, the amount of light is reduced due to, for example,
interference in the layers in the stacked structure constituting
the element when the light passes through the stacked structure and
is emitted to the outside. Therefore, it is required to reduce such
a loss of light as much as possible.
[0005] One known method for improving the light extraction
efficiency of organic EL elements is to provide various structures
on their light-extraction substrates. For example, it is proposed
to provide prisms containing a fluorescent compound on the
light-emitting surface of a light source device (Patent Document
1). It is also proposed to provide a micro-lens array on the
light-emitting surface of a light source device (Patent Document
2). With these structures, light can be gathered in a favorable
manner, and the efficiency is thereby improved. As another example
of means for improving the light extraction efficiency of an
organic EL element, Patent Document 3 discloses that a light
diffusing medium is provided on the light-emitting side of the
organic EL element to improve the overall brightness.
LIST OF PRIOR ART DOCUMENTS
Patent Documents
[0006] Patent Document 1: Japanese Patent Application Laid-Open No.
2002-237381 A [0007] Patent Document 2: Japanese Patent Application
Laid-Open No. 2003-59641 A [0008] Patent Document 3: Japanese
Patent Application Laid-Open No. 2006-528825 A (WO2005-18010)
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0009] As a result of intensive studies by the present inventors,
it has been found out that, when an organic EL element is used as a
surface light source device, there is another demand for a
reduction in the change in color tone (color unevenness) at
different viewing angles, in addition to the demand for an
improvement in the light extraction efficiency described above.
More specifically, the problem is that the light spectrum observed
in the front direction of the light-emitting surface of the surface
light source device (in the normal direction with respect to the
light-emitting surface) can be different from the light spectrum
observed in an oblique direction that crosses the front direction.
In such a case, a change in color tone at different viewing angles
occurs, and therefore the surface light source device is not always
suitable as a light source. Note that a certain direction that
crosses another direction means that the former direction is not
parallel to the latter direction.
[0010] Such color unevenness can also occur when the structure
described in any of Patent Documents 1 and 2 is adopted in a
stacked-type organic EL element for lighting applications. In such
a case, the color unevenness is observed as a phenomenon in which
the color tone of the light-emitting surface when observed from the
front is significantly different from the color tone of the
light-emitting surface when observed in a direction oblique with
respect to the front. This phenomenon is due to the difference in
the depth from the light-emitting surface to each luminescent layer
for each color.
[0011] Such a problem of color unevenness can be improved also by
the technology described in Patent Document 3. However, in this
case, the diffusion performance must be significantly improved.
Therefore there arises a necessity to, for example, increase the
amount of a diffusing agent to be added. In this case, the
thickness of the diffusing layer must be increased to a maximum.
This causes problems such as warpage of the product which leads to
reduction in productivity. In addition, the thick diffusing layer
cannot contribute to a reduction in the thickness (downsizing) of
the device.
[0012] In addition, when the structure described in any of Patent
Documents 1 and 2 is adopted for a stacked-type organic EL element
for lighting applications and a concave-convex structure such as
prisms is provided on the light-emitting surface of the light
source device, the apex portions of the concave-convex structure
are easily broken off, which causes difficulty in increasing the
mechanical strength of the device.
[0013] The present invention has been made in view of the foregoing
issues. It is a first object of the present invention to provide a
surface light source device, a lighting device, and a backlight
device that have high light extraction efficiency and high
mechanical strength and can reduce the change in color tone at
different viewing angles.
[0014] It is a second object of the present invention to provide a
surface light source device that can be produced with high
productivity, can contribute to a reduction in the size of devices,
and can suppress the change in color tone at different viewing
angles and to provide a lighting device that uses the surface light
source device and a backlight device that uses the surface light
source device.
Means for Solving the Problem
[0015] The present inventors have made intensive studies to solve
the foregoing problems. The inventors have then found out that the
first object can be achieved by giving the light-emitting surface
of a surface light source device a specific structure, and
providing a diffusing member in the surface light source device.
The first invention has been completed based on this finding.
[0016] The present inventors have also found out that the second
object can be achieved by providing both a diffusing section and a
light-distribution conversion unit. The second invention has been
completed based on this finding.
[0017] Accordingly, the first invention provides the following (1)
to (10), (21), and (22).
(1) A surface light source device, comprising: an organic
electroluminescent element including a luminescent layer; and a
light-emitting surface structure layer disposed in contact with at
least one of surfaces of the organic electroluminescent element,
wherein:
[0018] the light-emitting surface structure layer includes a
concave-convex structure provided on a surface thereof on a side
toward a light-emitting surface of the device,
[0019] the concave-convex structure includes a plurality of concave
portions having oblique surfaces and flat portions disposed around
the concave portions,
[0020] the surface light source device further comprises a
diffusing member on which light emitted from the luminescent layer
is incident, the diffusing member allowing the incident light to
pass therethrough or reflecting the incident light in a diffused
manner, and
[0021] the surface light source device includes the diffusing
member as a member that constitutes at least one of:
[0022] a layer constituting all or part of the light-emitting
surface structure layer, and
[0023] a layer disposed at a position farther from the
light-emitting surface structure layer than the organic
electroluminescent element.
(2) The aforementioned surface light source device, wherein the
diffusing member is a member provided as the layer constituting all
or part of the light-emitting surface structure layer, and is a
member that allows the incident light to pass therethrough in a
diffused manner. (3) The aforementioned surface light source
device, wherein the diffusing member is a bonding layer interposed
between two layers included in the light-emitting surface structure
layer. (4) The aforementioned surface light source device, wherein
the light-emitting surface structure layer includes:
[0024] a substrate disposed in contact with the organic
electroluminescent element,
[0025] a concave-convex structure layer disposed at a position
closer to the device light-emitting surface than the substrate, the
concave-convex structure layer including the concave-convex
structure on a surface thereof, the surface being on a side close
to the device light-emitting surface, and
[0026] a bonding layer for bonding the substrate and the
concave-convex structure layer, and wherein:
[0027] the surface light source device includes the bonding layer
as the diffusing member.
(5) The aforementioned surface light source device, wherein the
diffusing member is formed from a material containing particles
that impart light diffusibility. (6) The aforementioned surface
light source device, wherein the diffusing member is a member
disposed at a position farther from the light-emitting surface
structure layer than the organic electroluminescent element, and is
a member that reflects the incident light in a diffused manner. (7)
The aforementioned surface light source device, wherein, when the
concave-convex structure is observed in a direction perpendicular
to the device light-emitting surface, a ratio of an area occupied
by the flat portions relative to the sum of the area occupied by
the flat portions and an area occupied by the concave portions is
10 to 75%. (8) The aforementioned surface light source device,
wherein the concave portions have a pyramid shape, a conical shape,
a shape of part of a sphere, or a shape of a combination
thereof,
[0028] the plurality of concave portions are aligned on the device
light-emitting surface in two or more directions crossing each
other, and
[0029] spacings are provided between adjacent concave portions in
all of the two or more directions, the spacings constituting the
flat portions.
(9) The aforementioned surface light source device, wherein the
concave portions have a pyramid shape, a conical shape, a shape of
part of a sphere, or a shape of a combination thereof,
[0030] the plurality of concave portions are aligned on the device
light-emitting surface in two or more directions crossing each
other, and
[0031] spacings are provided between adjacent concave portions in
only one of the two or more directions, the spacings constituting
the flat portions.
(10) The aforementioned surface light source device, wherein the
concave portions have a groove shape,
[0032] the plurality of concave portions are aligned in parallel to
each other on the device light-emitting surface, and
[0033] spacings are provided between adjacent concave portions, the
spacings constituting the flat portions.
(21) A lighting device comprising the surface light source device
according to any one of (1) to (10). (22) A backlight device
comprising the surface light source device according to any one of
(1) to (10).
[0034] The second invention provides the following inventions.
(11) A surface light source device, comprising: an organic
electroluminescent element including, in the following order, a
first electrode layer, a luminescent layer, and a second electrode
layer; and a light-emitting-side member that is disposed in contact
with at least one of surfaces of the organic electroluminescent
element and has a light-emitting surface from which light is
emitted to the outside, wherein:
[0035] the light-emitting-side member includes:
[0036] a light-distribution conversion unit that converts a
distribution of light emitted from the organic electroluminescent
element so as to reduce a difference between a chromaticity of
light emitted from the light-emitting surface in a normal direction
with respect to the light-emitting surface and a chromaticity of
light emitted from the light-emitting surface in an oblique
direction crossing the normal direction, and
[0037] a diffusing section that diffuses the light emitted from the
organic electroluminescent element.
(12) The aforementioned surface light source device, wherein the
diffusing section is a layer that is disposed between the
light-distribution conversion unit and the organic
electroluminescent element and is formed of a composition
containing particles that impart light diffusibility. (13) The
aforementioned surface light source device, wherein the diffusing
section is a layer that is disposed on a light-emitting side of the
light-distribution conversion unit and is formed of a composition
containing particles that impart light diffusibility. (14) The
aforementioned surface light source device, wherein the
light-distribution conversion unit includes a concave-convex
structure layer having a concave-convex structure formed on a
surface thereof. (15) The aforementioned surface light source
device, wherein the concave-convex structure layer is formed of a
composition containing particles that impart light diffusibility
and serves also as the diffusing section. (16) The aforementioned
surface light source device, wherein the light-distribution
conversion unit includes a substrate and a concave-convex structure
layer disposed on a surface of the substrate, the concave-convex
structure layer having a concave-convex structure formed on a
surface thereof on a side opposite to the substrate. (17) The
aforementioned surface light source device, wherein the substrate
and/or the concave-convex structure layer is formed of a
composition containing particles that impart light diffusibility
and serves also as the diffusing section. (18) The aforementioned
surface light source device, wherein the light-distribution
conversion unit includes a substrate film and a selective
reflecting layer disposed on at least one of surfaces of the
substrate film. (19) The aforementioned surface light source
device, wherein the selective reflecting layer includes a layer
containing a resin having cholesteric regularity. (20) The
aforementioned surface light source device, wherein the substrate
film is formed of a composition containing particles that impart
light diffusibility and serves also as the diffusing section. (21)
A lighting device comprising the aforementioned surface light
source device. (22) A backlight device comprising the
aforementioned surface light source device.
Effect of the Invention
[0038] The surface light source device of the first invention has
high light extraction efficiency and can reduce the change in color
tone at different viewing angles, and the light-emitting surface of
the device has high mechanical strength. Therefore, the surface
light source device is useful as the light source of a lighting
device and the backlight of a display device such as a liquid
crystal display device.
[0039] The lighting device and backlight device of the first
invention include the surface light source device of the first
invention. Therefore, the lighting device and the backlight device
can have high light extraction efficiency and high mechanical
strength and can reduce the change in color tone at different
viewing angles.
[0040] The surface light source device of the second invention has
advantages in that it can be produced with high productivity
because problems such as warpage of the product do not occur, can
contribute to a reduction in the size of the device, and can
suppress the change in color tone at different viewing angles.
Since the surface light source device has such advantages, it is
useful as the light source of a lighting device and the backlight
device for a liquid crystal display device.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1 is a perspective view schematically showing a surface
light source device according to Embodiment 1-1.
[0042] FIG. 2 is a cross-sectional view showing a cross-section
obtained by cutting the surface light source device shown in FIG. 1
along a plane that passes through line 1a-1b in FIG. 1 and is
perpendicular to a device light-emitting surface.
[0043] FIG. 3 is an enlarged partial top view showing the structure
of the device light-emitting surface 10U of the surface light
source device 10 shown in FIG. 1.
[0044] FIG. 4 is a partial cross-sectional view showing a
cross-section obtained by cutting a concave-convex structure layer
111 shown in FIG. 3 along a vertical plane passing through line 10a
in FIG. 3.
[0045] FIG. 5 is a partial cross-sectional view showing a
modification of concave portions shown in FIG. 4.
[0046] FIG. 6 is a partial cross-sectional view showing another
modification of the concave portions shown in FIG. 4.
[0047] FIG. 7 is a top view schematically showing a surface light
source device according to Embodiment 1-2.
[0048] FIG. 8 is a cross-sectional view showing a cross-section
obtained by cutting the surface light source device shown in FIG. 7
along a plane that passes through line 2a in FIG. 7 and is
perpendicular to a device light-emitting surface.
[0049] FIG. 9 is a perspective view schematically showing a surface
light source device according to Embodiment 1-3.
[0050] FIG. 10 is a top view schematically showing a surface light
source device according to Embodiment 1-4.
[0051] FIG. 11 is a cross-sectional view showing a cross-section
obtained by cutting the surface light source device shown in FIG.
10 along a plane that passes through line 3a in FIG. 10 and is
perpendicular to a device light-emitting surface.
[0052] FIG. 12 is a cross-sectional view showing a cross-section
obtained by cutting a surface light source device according to
Embodiment 1-5 along a plane perpendicular to a device
light-emitting surface.
[0053] FIG. 13 is a top view schematically showing a surface light
source device according to Embodiment 1-6.
[0054] FIG. 14 is a cross-sectional view showing a cross-section
obtained by cutting the surface light source device shown in FIG.
13 along a plane that passes through line 4a in FIG. 13 and is
perpendicular to a device light-emitting surface.
[0055] FIG. 15 is a top view schematically showing a concave-convex
structure layer according to a modification of Embodiment 1-6.
[0056] FIG. 16 is a top view schematically showing a surface light
source device according to Embodiment 1-7.
[0057] FIG. 17 is a cross-sectional view showing a cross-section
obtained by cutting the surface light source device shown in FIG.
16 along a plane that passes through line 11a-11b in FIG. 16 and is
perpendicular to a device light-emitting surface.
[0058] FIG. 18 is a cross-sectional view schematically showing a
cross-section obtained by cutting a surface light source device
according to Embodiment 1-8 along a plane perpendicular to a device
light-emitting surface.
[0059] FIG. 19 is a vertical cross-sectional view illustrating a
surface light source device according to Embodiment 2-1.
[0060] FIG. 20 is a vertical cross-sectional view illustrating a
surface light source device according to Embodiment 2-2.
[0061] FIG. 21 is a graph showing the spectrum from a luminescent
layer used in the surface light source device.
[0062] FIG. 22 is a graph showing the selective reflection
characteristics of a selective reflecting layer used in the surface
light source device according to Embodiment 2-2.
[0063] FIG. 23 is a graph showing the distributions of light from a
surface light source device used for comparison with the surface
light source device according to Embodiment 2-2.
[0064] FIG. 24 is a graph showing the distributions of light from a
surface light source device used for comparison with the surface
light source device according to Embodiment 2-2.
[0065] FIG. 25 is a graph showing the distributions of light from
the surface light source device according to Embodiment 2-2.
[0066] FIG. 26 is a vertical cross-sectional view illustrating a
surface light source device according to an embodiment of the
second invention.
[0067] FIG. 27 is a vertical cross-sectional view illustrating a
surface light source device according to an embodiment of the
second invention.
[0068] FIG. 28 is a graph showing the relationships between the
angle at which chromaticity is measured and the chromaticity values
x and Y in the measurement results in Comparative Example 1-1.
[0069] FIG. 29 is a graph showing the relationships between the
angle at which chromaticity is measured and the chromaticity values
x and Y in the measurement results in Example 1-1.
[0070] FIG. 30 is a graph showing the relationships between the
angle at which chromaticity is measured and the chromaticity values
x and Y in the measurement results in Example 1-2.
[0071] FIG. 31 is a graph showing the relationship between a flat
portion ratio and a load in the results of measurement in Reference
Example 1-1.
DESCRIPTION OF EMBODIMENTS
I. Description of First Invention
[0072] The first invention will be described in detail by way of
embodiments and exemplifications. However, the first invention is
not limited to the following embodiments and exemplifications.
Embodiment 1-1
[0073] The first invention will be described in more detail with
reference to the drawings.
[0074] A surface light source device of the first invention
includes: an organic EL element including a luminescent layer; and
a light-emitting surface structure layer that is disposed in
contact with at least one surface of the organic EL element and
defines a concave-convex structure on the surface on the device
light-emitting surface side.
[0075] The device light-emitting surface is the light-emitting
surface of the surface light source device, i.e., the
light-emitting surface from which the light from the surface light
source device is emitted to the outside of the device. The device
light-emitting surface is a surface parallel to the luminescent
layer of the organic EL element and is parallel to the principal
surface of the surface light source device. However, in a
microscopic sense, the surfaces of concave portions described later
may form a non-parallel angle with respect to the luminescent
layer. Hereinafter, unless otherwise specifically mentioned, the
phrase "parallel (or perpendicular) to the device light-emitting
surface" simply means that an object is parallel (or perpendicular)
to the device light-emitting surface with the concave portions
being neglected. Unless otherwise mentioned, a description will be
given of the surface light source device placed with its device
light-emitting surface being parallel to the horizontal direction
and facing upward.
[0076] In the first invention, when components are "parallel" or
"perpendicular" to each other, a deviation in the range in which
the effects of the first invention are not impaired may be present.
For example, a tolerance of .+-.5.degree. with respect to the
parallel or perpendicular angle may be allowable.
[0077] Embodiment 1-1 is a first embodiment of the first invention.
FIG. 1 is a perspective view schematically showing the surface
light source device according to Embodiment 1-1. In Embodiment 1-1,
the surface light source device 10 is a device including a device
light-emitting surface 10U and having a flat rectangular plate-like
structure. FIG. 2 is a cross-sectional view showing a cross-section
obtained by cutting the surface light source device 10 shown in
FIG. 1 along a plane that passes through line 1a-1b in FIG. 1 and
is perpendicular to the device light-emitting surface.
[0078] The surface light source device 10 includes an organic EL
element 140 and a light-emitting surface structure layer 100
disposed in contact with a surface 144 of the organic EL element
140. The surface 144 is toward the device light-emitting surface
10U. The surface light source device 10 further includes, as an
optional component, a sealing substrate 151 disposed on a surface
145 of the organic EL element 140. The surface 145 is on the side
opposite to the device light-emitting surface 10U. Although not
shown in the figures, any optional material such as a filler or an
adhesive agent may be present between the surface 145 and the
sealing substrate 151. A gap may also be present therebetween. In
the gap, air or any other gas may be present so long as a problem
such as significant deterioration of the durability of a
luminescent layer 142 does not occur. Alternatively, the gap may be
a vacuum gap.
[0079] The organic EL element 140 includes a first electrode layer
141, a luminescent layer 142, and a second electrode layer 143. In
the Embodiment 1-1, the first electrode layer 141 is a transparent
electrode, and the second electrode layer 143 is a reflecting
electrode. With this configuration, the light from the luminescent
layer 142 passes through the first electrode layer 141, or is
reflected on the second electrode layer 143 and then passes through
the luminescent layer 142 and the first electrode layer 141,
whereby the light can be directed toward the light-emitting surface
structure layer 100.
[0080] The light-emitting surface structure layer 100 includes: a
multi-layered body 110 including a concave-convex structure layer
111 and a substrate film layer 112; a glass substrate 131 serving
as a substrate and disposed in contact with the organic EL element
140; and a bonding layer 121 that bonds the multi-layered body 110
to the glass substrate 131. In the surface light source device 10,
one or more of the concave-convex structure layer 111, the
substrate film layer 112, the bonding layer 121, and the glass
substrate 131 are formed of a material containing a diffusing agent
(particles that impart light diffusibility). This configuration
thus constitutes a diffusing member that allows the incident light
to pass therethrough or reflects the incident light in a diffused
manner, wherein the incident light is a light that has been emitted
(this emission is also referred to as discharge) from the
luminescent layer 142 and incident on the diffusing member. In the
configuration of the present embodiment, the organic EL element 140
is in direct contact with the glass substrate 131. However, another
layer such as a diffusing layer may be interposed therebetween.
[0081] The concave-convex structure layer 111 is located at the top
surface of the surface light source device 10 (i.e., the outermost
layer of the surface light source device 10 that is on the
light-emitting surface side). Therefore, the concave-convex
structure layer 111 is disposed at a position closer to the device
light-emitting surface 10U than the glass substrate 131. In
addition, the concave-convex structure layer 111 has a
concave-convex structure provided on its surface that is on the
side close to the device light-emitting surface 10U. The
concave-convex structure includes a plurality of concave portions
113 and flat portions 114 disposed around the concave portions 113.
In the present embodiment, the surface of the concave-convex
structure layer 111 that is on the side close to the device
light-emitting surface 10U is indeed the device light-emitting
surface 10U. Therefore, the concave-convex structure defines the
device light-emitting surface 10U. In a macroscopic sense, i.e.,
with the concave portions 113 being neglected, the device
light-emitting surface 10U is a flat surface parallel to other
layers, such as the flat portions 114 and the glass substrate 131,
in the device. However, in a microscopic sense, the device
light-emitting surface 10U is a concave-convex surface including
oblique surfaces defined by the concave portions 113. In the
present application, the figures are schematic diagrams, and
illustrate only a small number of concave portions on the device
light-emitting surface. However, in an actual device, a much larger
number of concave portions may be provided on one device
light-emitting surface.
(Organic EL Element)
[0082] In the first invention, the organic EL element may be an
element including two or more electrode layers and a luminescent
layer that is disposed between these electrode layers and emits
light when a voltage is applied from the electrodes, as exemplified
as the organic EL element 140.
[0083] Generally, an organic EL element has a structure in which
electrodes and layers such as a luminescent layer that constitute
the element are formed on a substrate and a sealing member that
covers these layers is then provided so that the layers such as the
luminescent layer are sealed with the substrate and the sealing
member. Generally, a device that emits light from its substrate
side is referred to as a bottom emission type, and a device that
emits light from its sealing member side is referred to as a top
emission type. The surface light source device of the first
invention may be any of the top emission type and the bottom
emission type. When the surface light source device is of the
bottom emission type, a combination including a substrate used to
form layers and, if necessary, an optional layer forms the
light-emitting surface structure layer. When the surface light
source device is of the top emission type, a combination including
a structural member on the light-emitting surface side, such as the
sealing member, and, if necessary, an optional layer constitutes
the light-emitting surface structure layer.
[0084] In the first invention, no particular limitation is imposed
on the luminescent layer constituting the organic EL element, and
any of the known luminescent layers may be suitably selected. The
number of types of luminescent materials in the luminescent layer
is not limited to one, and also the number of luminescent layers is
not limited to one. In order to adapt to the use of the device as a
light source, the luminescent layer may be a single layer or a
combination of a plurality of layers. In this manner, white light
or light of a color close to white can be emitted.
[0085] In addition to the luminescent layer, the organic EL element
may further include another layer such as a hole injection layer, a
hole transport layer, an electron transport layer, an electron
injection layer, and a gas barrier layer that are disposed between
the electrodes. The organic EL element may further include any
optional components such as wiring leads for supplying an electric
current to the electrodes and a peripheral structure for sealing
the luminescent layer.
[0086] No particular limitation is imposed on the electrodes of the
organic EL element, and any of the known electrodes may be
appropriately selected. As in the organic EL element 140 in
Embodiment 1-1, when a transparent electrode is employed as the
electrode on a side toward the light-emitting surface structure
layer and a reflecting layer is employed as the electrode on the
opposite side, the organic EL element may be configured to emit
light toward the light-emitting surface structure layer. When
transparent electrode layers are employed as both the electrodes
and a reflecting member or a scattering member (such as a white
scattering member disposed through an air layer) is provided on the
side opposite to the light-emitting surface structure layer, light
emission toward the light-emitting surface structure layer may be
achieved.
[0087] No particular limitation is imposed on the materials for
forming the electrode layers and the layers disposed therebetween.
Specific examples of such materials are as follows.
[0088] Examples of the material for the transparent electrode may
include ITO.
[0089] Examples of the material for the hole injection layer may
include starburst aromatic diamine compounds.
[0090] Examples of the material for the hole transport layer may
include triphenyldiamine derivatives.
[0091] Examples of the host material for a yellow luminescent layer
may also include triphenyldiamine derivatives.
[0092] Examples of the dopant material for the yellow luminescent
layer may include tetracene derivatives.
[0093] Examples of the material for a green luminescent layer may
include pyrazoline derivatives.
[0094] Examples of the host material for a blue luminescent layer
may include anthracene derivatives, and examples of the dopant
material for the blue luminescent layer may include perylene
derivatives.
[0095] Examples of the material for a red luminescent layer may
include europium complexes.
[0096] Examples of the material for the electron transport layer
may include aluminum quinoline complexes (Alq).
[0097] Examples of the material for a cathode may include a stack
of lithium fluoride and aluminum layers that is produced by
sequential vacuum deposition.
[0098] The aforementioned luminescent layer and other luminescent
layers may be suitably combined to obtain a stacked or tandem type
luminescent layer that generates light with complementary colors.
The combination of complementary colors may be yellow/blue,
green/blue/red, etc.
(Light-Emitting Surface Structure Layer)
[0099] In the first invention, the light-emitting surface structure
layer may be composed of a plurality of layers, as exemplified as
the light-emitting surface structure layer 100, but may also be
composed of a single layer. It is preferable, from the viewpoint of
easily obtaining a light-emitting surface structure layer having
the desired characteristics, to use a plurality of layers. For
example, as in the light-emitting surface structure layer 100, the
multi-layered body including a combination of the concave-convex
structure layer and the substrate film layer may be used. In this
manner, a high-performance light-emitting surface structure layer
can be easily obtained.
[0100] The resin composition constituting the concave-convex
structure layer and the substrate film may be a composition
containing a transparent resin. The term "transparent" in the
transparent resin means that it has a light transmittance suitable
for use as an optical member. In the first invention, each of the
layers constituting the light-emitting surface structure layer may
have a light transmittance suitable for use as an optical member,
and the total light transmittance of the light-emitting surface
structure layer as a whole may be 80% or larger.
[0101] No particular limitation is imposed on the types of the
transparent resins contained in the resin compositions. Any of
various resins that can form a transparent layer may be used
therefor. Examples of such a resin may include thermoplastic
resins, thermosetting resins, ultraviolet curable resins, and
electron ray-curable resins. Of these, thermoplastic resins can be
easily deformed by heat, and ultraviolet curable resins have high
curability and high efficiency. Therefore, these resins are
preferred because the concave-convex structure layer can be
efficiently formed. Examples of the thermoplastic resins may
include polyester-, polyacrylate-, and cycloolefin polymer-based
resins. Examples of the ultraviolet curable resins may include
epoxy-, acrylic-, urethane-, ene/thiol-, and isocyanate-based
resins. Resins having a plurality of polymerizable functional
groups may be preferably used as the aforementioned resins.
[0102] As the material for the concave-convex structure layer
included in the multi-layered body, a material having high hardness
after curing is preferred because such a material can easily form
the concave-convex structure of the device light-emitting surface
and can easily provide abrasion resistance of the concave-convex
structure. More specifically, it is preferable to use a material
having a pencil hardness of HB or higher when a resin layer having
a thickness of 7 .mu.m is formed on a substrate with no
concave-convex structure provided thereon. A material having a
pencil hardness of H or higher is more preferred, and a material
having a pencil hardness of 2H or higher is still more preferred.
As the material for the substrate film layer, it is preferable to
use a material having some degree of flexibility, because thereby
handling of the multi-layered body can be facilitated during the
formation of the concave-convex structure layer and/or after
completing the formation of the multi-layered body. Use of a
combination of the aforementioned materials results in production
of a multi-layered body that can be handled easily and that has
high durability, whereby a high-performance surface light source
device can be easily manufactured. Such a combination of materials
may be obtained by appropriately selecting, as the resins contained
in the materials, the transparent resins exemplified above. More
specifically, a ultraviolet curable resin such as acrylate may be
used as the transparent resin constituting the material for the
concave-convex structure layer, and a film made of an alicyclic
olefin polymer (such as ZEONOR Film which will be described later)
or a polyester film may be used as the transparent resin
constituting the material for the substrate film. A preferred
combination of materials may thereby be obtained.
[0103] When the light-emitting surface structure layer includes a
concave-convex structure layer and a substrate film layer as in the
light-emitting surface structure layer 100, the refractive indexes
of the concave-convex structure layer and the substrate film may be
as close to each other as possible. In such a case, the difference
in refractive index is preferably 0.1 or smaller and more
preferably 0.05 or smaller.
[0104] When any of the layers used as the components of the
light-emitting surface structure layer, such as the concave-convex
structure layer and the substrate film layer, serves as the
diffusing member, the resin composition used as the material for
such a layer may contain a component that can impart light
diffusibility, such as particles that will be described later. If
necessary, the resin composition may contain any optional
components. Examples of such optional components may include
additives such as antidegradants such as phenol-based and
amine-based antidegradants; antistatic agents such as
surfactant-based and siloxane-based antistatic agents; and
light-proofing agents such as triazole-based and
2-hydroxybenzophenone-based light-proofing agents.
[0105] In the first invention, no particular limitation is imposed
on the thickness of the concave-convex structure layer, but the
thickness is preferably 1 to 70 .mu.m. The thickness of the
concave-convex structure layer is the distance between its surface
on the substrate side on which the concave-convex structure is not
formed and the flat portions of the concave-convex structure. The
thickness of the substrate film layer is preferably 20 to 300
.mu.m.
[0106] In the first invention, the light-emitting surface structure
layer may further include a substrate such as the glass substrate
131 in the light-emitting surface structure layer 100 described
above. Having such a substrate, the surface light source device may
have stiffness for suppressing warpage. When a substrate having a
good ability to seal the organic EL element and easily allowing
successive formation of the layers constituting the organic EL
element on the substrate in the production process is used as the
aforementioned substrate, the durability of the surface light
source device can be improved, and the manufacture of the surface
light source device can be facilitated.
[0107] Examples of the material constituting the substrate may
include, in addition to glass, resins. No particular limitation is
imposed on the refractive index of the substrate. The refractive
index may be 1.4 to 2.0. In the first invention, no particular
limitation is imposed on the thickness of the substrate. The
thickness is preferably 0.1 to 5 mm.
[0108] The light-emitting surface structure layer may further
include a bonding layer interposed between two layers in the
light-emitting surface structure layer such as between the
multi-layered body and the substrate. An adhesive agent used as the
material for the bonding layer is not limited to an adhesive agent
in a narrow sense (a so-called hot-melt adhesive agent having a
shear storage modulus at 23.degree. C. of 1 to 500 MPa and
exhibiting no adhesion at room temperature) but also encompasses a
tacky agent having a shear storage modulus at 23.degree. C. of
smaller than 1 MPa. Specifically, an adhesive agent having a
refractive index close to those of the substrate and the
transparent resin layer and having transparency may be
appropriately used. More specific examples may include
acrylic-based adhesive agents or acrylic-based tacky agents.
Preferably, the thickness of the bonding layer is 5 to 100
.mu.m.
(Diffusing Member)
[0109] The surface light source device of the first invention
further includes a diffusing member for allowing the incident light
to pass therethrough in a diffused manner or reflecting the
incident light in a diffused manner. The diffusing member may be
provided as a layer that constitutes all or part of the
light-emitting surface structure layer, as a member disposed at a
position farther from the light-emitting surface structure layer
than the organic EL element, or as both of them. More specifically,
in the first invention, all or part of the light-emitting surface
structure layer may have the function of a diffusing member, or a
diffusing member may be provided as a member different from the
light-emitting surface structure layer.
[0110] When one of the electrode layers of the organic EL element
is a reflecting electrode and the other is a transparent electrode
as in the surface light source device 10 in Embodiment 1-1, the
diffusing member may be a member that is provided as a layer
constituting all or part of the light-emitting surface structure
layer and that allows the incident light to pass therethrough in a
diffused manner. More specifically, all or part of the layers
constituting the light-emitting surface structure layer, such as
the concave-convex structure layer, the substrate film, the bonding
layer, the glass substrate, etc. that can form the light-emitting
surface structure layer, may be formed as layers that diffuse
light. In this manner, all or part of these layers can serve as the
diffusing member.
[0111] Examples of the material for the layer that diffuses light
may include materials containing particles and alloy resin
materials having light diffusibility that are prepared by mixing
two or more resins. In terms of facilitating control of light
diffusibility, a material containing particles is preferred, and a
resin composition containing particles is particularly preferred.
In these cases, since the particles serves to impart light
diffusibility, the composition containing such particles has light
diffusibility.
[0112] The particles contained in the diffusing member may be
transparent or opaque. The material of the particle may be metals,
metal compounds, and resins. Examples of the metal compounds may
include oxides and nitrides of metals. Specific examples of the
metals and metal compounds may include metals having high
reflectivity such as silver and aluminum, and metal compounds such
as silicon oxide, aluminum oxide, zirconium oxide, silicon nitride,
tin-doped indium oxide, and titanium oxide. Examples of the resins
may include methacrylic resins, polyurethane resins, and silicone
resins.
[0113] The shape of the particles may be a spherical, cylindrical,
cubic, rectangular prism, pyramid, conical, or star shape.
[0114] In the diffusing member, the ratio of the volume of the
particles relative to the total volume of the materials
constituting the diffusing member is preferably 1 to 80% and more
preferably 5 to 50%. When the ratio of the particles is equal to or
larger than the aforementioned lower limit, the desired effects
such as a reduction in the change in color tone at different
viewing angles can be obtained. When the volume ratio is equal to
or smaller than the aforementioned upper limit, the aggregation of
the particles in the diffusing member can be prevented, so that a
diffusing member in which the particles are favorably dispersed can
be easily obtained.
[0115] The diameter of the particles is preferably 0.1 .mu.m or
larger and 10 .mu.m or smaller and more preferably 5 .mu.m or
smaller. The diameter of the particles is a 50% particle diameter
in the cumulative distribution of the volume of the particles with
the particle size plotted on the horizontal axis. The larger the
particle diameter, the smaller the amount of the particles
necessary to obtain the desired effects. The smaller the particle
diameter, the smaller the necessary amount of the particles.
Therefore, the smaller the particle diameter, the smaller the
amount of particles necessary to obtained the desired effects such
as a reduction in the change in color tone at different viewing
angles and an improvement in light extraction efficiency. When the
particles have a shape other than a spherical shape, the diameters
of spheres having volumes equal to the volumes of the particles are
considered as the diameters of the particles.
[0116] When the particles are transparent and are contained in a
transparent resin, the difference in refractive index between the
particles and the transparent resin is preferably 0.05 to 0.5 and
more preferably 0.07 to 0.5. The refractive index of the particles
may be larger than or smaller than the refractive index of the
transparent resin. When the refractive index of the particles is
too close to that of the transparent resin, the diffusing effect
may not be obtained, so that color tone unevenness is not
suppressed. When the difference in refractive index is too large,
although the degree of diffusion becomes high and therefore the
color tone unevenness is suppressed, the light extraction effect
may be reduced.
[0117] When all or part of the layers constituting the
light-emitting surface structure layer are formed as the diffusing
member, there is no particular limitation as to which of the layers
constituting the light-emitting surface structure layer is used as
the diffusing member. The selection may be made from various points
of view. For example, it is preferable, from the viewpoint of
facilitating adjustment of the degree of diffusion, to use a layer
containing a transparent resin as the diffusing member.
[0118] It is also preferable to use a layer having a certain degree
of thickness (e.g., 5 .mu.m or larger) as the diffusing member,
from the viewpoint of ensuring sufficient light diffusibility
without using an excessively large amount of particles in such a
layer.
[0119] Preferably, the concave-convex structure layer is formed of
a material having high hardness, as described above. However, when
the thickness of the high-hardness material layer used in the
surface light source device is large, undesirable warpage of the
device light-emitting surface may occur with the lapse of time.
Therefore, from this point of view, it is preferable to use, as the
diffusing member, a layer that is other than the concave-convex
structure layer and has properties that facilitate plastic
deformation, examples of which may be the substrate film and the
bonding layer.
[0120] When a layer that is produced by a process that does not
include a step of heating the material thereof (for example, a
transparent resin) is used as the diffusing member, the production
process can be easily managed. For example, a problem such as
clogging of a resin conveying passage with particles can be easily
addressed. From this point of view, it is preferable to use the
bonding layer as the diffusing member. It is also preferable to use
the bonding layer and a layer other than the bonding layer as the
diffusing members. For example, when the bonding layer and the
substrate film are used as the diffusing members and the ratio of
the particles added to the substrate film is reduced, the process
of producing the substrate film can be easily managed (for example,
the frequency of occurrence of clogging can be reduced).
[0121] An additional layer other than the concave-convex structure
layer, the substrate film layer, the bonding layer, and the glass
substrate may be provided in the light-emitting surface structure
layer, and the additional layer may be used as the diffusing
member. For example, such an additional layer may be formed between
the concave-convex structure layer and the substrate film layer,
between the bonding layer and the glass substrate, or on the
surface of the glass substrate that is toward the luminescent layer
(for example, between the glass substrate and an electrode layer of
the luminescent layer). Alternatively, the additional layer and one
or more of the concave-convex structure layer, the substrate film
layer, the bonding layer, and the glass substrate may be used as
the diffusing members.
[0122] When the diffusing member is provided as a layer
constituting all or part of the light-emitting surface structure
layer, no particular limitation is imposed on the degree of
diffusion. However, for example, when all or part of the layers
from the concave-convex structure layer to the bonding layer serve
as the diffusing members, the total light transmittance of the
layers from the concave-convex structure layer to the bonding layer
wherein the concave-convex surface structure of the concave-convex
structure layer is not formed is preferably 70 to 95% and more
preferably 75 to 90%.
[0123] No particular limitation is imposed on the refractive index
of the diffusing member. The refractive index is preferably 1.45 to
2, more preferably 1.6 to 2, and still more preferably 1.7 to 2. It
is preferable that the refractive index of any layer on the
light-emitting side of the diffusing member is smaller than the
refractive index of the diffusing member. When the diffusing member
has a large refractive index as described above, the range of
selection of the refractive index of any layer on the
light-emitting side of the diffusing member is widened, and
therefore the material for such a layer may be more freely
selected.
(Concave-Convex Structure)
[0124] In the first invention, the concave-convex structure on the
light-emitting surface structure layer includes a plurality of
concave portions including oblique surfaces and flat portions
disposed around the concave portions. The "oblique surface" is a
surface forming a non-parallel angle with respect to the device
light-emitting surface. The surfaces of the flat portions may be
parallel to the device light-emitting surface.
[0125] As an example of the concave-convex structure, the
concave-convex structure on the device light-emitting surface of
the surface light source device 10 shown in FIGS. 1 and 2 will be
described in detail with reference to FIGS. 3 and 4. FIG. 3 is an
enlarged partial top view illustrating the structure of the device
light-emitting surface 10U of the surface light source device 10
that is defined by the concave-convex structure layer 111. FIG. 4
is a partial cross-sectional view showing a cross-section obtained
by cutting the concave-convex structure layer 111 shown in FIG. 3
along a vertical plane that passes through line 10a in FIG. 3.
[0126] Each of the plurality of concave portions 113 is a regular
quadrangular pyramid-shaped recess. Therefore, oblique surfaces 11A
to 11D of the concave portion 113 have the same shape, and the base
edges 11E to 11H form a square. The line 10a is a line passing
through all the apexes 11P of a row of concave portions 113 and
parallel to the base edges 11E and 11G of the concave portions
113.
[0127] The concave portions 113 are continuously aligned at regular
intervals in two mutually orthogonal alignment directions. One
direction X of the two arrangement directions is parallel to the
base edges 11E and 11G. In the direction X, a plurality of concave
portions 113 are aligned with a constant spacing 11J therebetween.
The other direction Y of the two alignment directions is parallel
to the base edges 11F and 11H. Also in the direction Y, a plurality
of concave portions 113 are aligned with a constant spacing 11K
therebetween.
[0128] The angles between a flat portion 114 and each of the
oblique surfaces 11A to 11D constituting a concave portion 113
(angles 11L and 11M shown in FIG. 4 for the oblique surfaces 11B
and 11D, respectively) are set to, for example, 60.degree..
Therefore, the vertex angle of the regular quadrangular pyramid
constituting the concave portion 113, i.e., the angle at the apex
11P formed by oblique surfaces facing each other (an angle 11N
shown in FIG. 4 for the angle formed by the oblique surfaces 11B
and 11D) is also 60.degree..
[0129] As described above, the surface light source device has a
structure including, on the device light-emitting surface, a
plurality of concave portions and flat portions disposed
therearound and includes a predetermined diffusing member in
combination with the aforementioned structure. This can improve the
light extraction efficiency and can reduce the change in color tone
at different viewing angles. In addition, these features can
prevent the concave-convex structure from, for example, being
broken off by an external impact, and therefore the mechanical
strength of the device light-emitting surface can be improved.
[0130] Since the surface light source device of the first invention
has the aforementioned features, variations in at least one of x-
and y-chromaticity coordinates in all directions in a hemisphere on
the light-emitting surface can be reduced, for example, by half as
compared to those which does not have the aforementioned features.
Therefore, in the surface light source device, the change in color
tone at different viewing angles can be suppressed. To measure the
variations in chromaticity in all directions in the hemisphere, for
example, a spectral radiance meter is placed on the normal
direction with respect to (placed in front of) the device
light-emitting surface, and a mechanism for rotating the device
light-emitting surface from -90 to 90.degree. with respect to the
direction of the normal being defined as 0.degree. is provided. In
this manner, the emission spectra can be measured in various
directions to calculate the chromaticity coordinates, and the
variations in the chromaticity coordinates can thereby be
calculated.
[0131] The light extraction efficiency of the surface light source
device can be improved by appropriately adjusting the ratio of the
area occupied by the flat portions relative to the sum of the area
occupied by the flat portions and the area occupied by the concave
portions when the concave-convex structure layer is observed in a
direction perpendicular to the device light-emitting surface
(hereinafter this ratio is referred to as a "flat portion ratio").
More specifically, when the flat portion ratio is adjusted to 10 to
75%, favorable light extraction efficiency can be obtained, and the
mechanical strength of the device light-emitting surface can be
improved.
[0132] In the first invention, the concave portions may have, in
addition to the pyramid shape described above, for example, a
conical shape, a shape of part of a sphere, a groove shape, or a
combination of any of the aforementioned shapes. The pyramid shape
may be a quadrangular pyramid shape with a square bottom, as
exemplified as the concave portions 113 described above, but the
present invention is not limited thereto. The pyramid shape may be
any of triangular, pentagonal, and hexagonal pyramid shapes and
quadrangular pyramid shapes with non-square bottoms.
[0133] The terms cone and pyramid used in the present application
encompass not only ordinary conical and pyramid shapes having a
sharp apex but also conical and pyramid shapes having rounded
apexes and conical and pyramid shapes having flat truncated apexes
(such as frustum shapes). For example, although the apexes 11P of
the quadrangular pyramids are sharp in the concave portions 113
shown in FIG. 4, the apexes of the quadrangular pyramids may have a
rounded shape as in an apex 61P of a concave portion 613 shown in
FIG. 5. As exemplified by concave portions 713 shown in FIG. 6, a
flat portion 71P may be provided at the apex of each pyramid to
form a flat truncated shape.
[0134] When the apex of each pyramid has a rounded shape as shown
in FIG. 5, the difference 61R in height between the apex 61P and an
apex 61Q, which is the non-rounded sharp apex of the pyramid, may
be equal to or smaller than 20% of the height 61S of the pyramid
with the non-rounded sharp apex. When the apex of each pyramid has
a flat truncated shape as shown in FIG. 6, the difference 71R in
height between a flat portion 71P and an apex 71Q, which is the
non-flat sharp apex of the pyramid, may be equal to or smaller than
20% of the height 71S of the pyramid with the non-flat sharp
apex.
[0135] No particular limitation is imposed on the depth of the
concave portions in the concave-convex structure. The maximum value
(Ra(max)) of the center line mean roughness measured in various
directions (various directions in a plane parallel to the device
light-emitting surface) on the surface having the concave-convex
structure formed thereon may be in the range of 1 to 50 .mu.m. When
the concave-convex structure is formed on the concave-convex
structure layer, the depth of the concave portions can be set to a
preferred value relative to the thickness of the concave-convex
structure layer. For example, when a hard material advantageous for
maintaining the durability of the concave-convex structure layer is
used as the material for the concave-convex structure layer, the
smaller the thickness of the concave-convex structure layer, the
higher the flexibility of the multi-layered body, and the more
easily the multi-layered body can be handled in the process of
manufacturing the surface light source device. More specifically,
the difference between the depth 16D of the concave portion shown
in FIG. 4 and the thickness 16E of the concave-convex structure
layer 111 is preferably 0 to 30 .mu.m.
[0136] In the first invention, the angle formed by the device
light-emitting surface and the oblique surfaces of the concave
portions is preferably 40 to 70.degree. and more preferably 45 to
60.degree.. For example, when the shape of the concave portions is
a quadrangular pyramid as shown in FIGS. 1, 2, 3, and 4, the vertex
angle (the angle 11N in FIG. 4) is preferably 60 to 90.degree..
From the viewpoint of minimizing the change in color tone at
different viewing angles and improving the light extraction
efficiency, the larger the angle between the device light-emitting
surface and the oblique surface, the more preferable. Specifically,
the angle is preferably, for example, 55.degree. or larger and more
preferably 60.degree. or larger. In such a case, the upper limit of
the angle may be about 70.degree., in consideration of maintaining
the durability of the concave-convex structure layer.
[0137] When the shape of the concave portions is a pyramid,
conical, or groove shape with a rounded or flat truncated apex, the
angles of the oblique surfaces other than the rounded or truncated
portions are regarded as the angles of the aforementioned oblique
surfaces. For example, in the examples shown in FIGS. 5 and 6,
surfaces 613a, 613b, 713a, and 713b are regarded as the oblique
surfaces. By setting the angles of the oblique surfaces in this
manner, the light extraction efficiency can be improved. The angles
of all oblique surfaces in the concave-convex structure are not
necessarily the same, and oblique surfaces having different angles
within the aforementioned range may coexist. The angle formed by
the oblique surface of a conical shape and the device
light-emitting surface may be the angle formed by the generating
line of the cone and the device light-emitting surface.
[0138] The plurality of concave portions may be aligned on the
device light-emitting surface in any appropriate form. For example,
the plurality of concave portions may be aligned in two or more
mutually crossing directions on the device light-emitting surface.
More specifically, the plurality of concave portions may be aligned
in two mutually orthogonal directions, as in the concave portions
113 shown in FIGS. 1 and 3.
[0139] When the concave portions are aligned in two or more
directions, spacings may be provided between concave portions
adjacent in one or more directions. By providing such spacings,
flat portions are formed. For example, in the alignment of the
concave portions 113 shown in FIG. 3, spacings 11J and 11K are
provided in the two mutually orthogonal directions X and Y so as to
form the flat portions 114. With this configuration, both favorable
light extraction efficiency and high mechanical strength of the
device light-emitting surface can be obtained.
(Manufacturing Method)
[0140] No particular limitation is imposed on the method of
manufacturing the surface light source device of the first
invention. Manufacture of the above exemplified surface light
source device having the light-emitting surface structure layer
including the concave-convex structure layer, the substrate film,
the bonding layer, and the glass substrate may be performed as
follows. The layers constituting the organic EL element may be
formed on one surface of the glass substrate. Before or after the
formation of these layers, the multi-layered body including the
concave-convex structure layer and the substrate film may be
attached to the other surface of the glass substrate via a bonding
layer. The surface light source device may thereby be
manufactured.
[0141] The multi-layered body including the concave-convex
structure layer and the substrate film may be manufactured by
preparing a mold such as a metal mold having a desired shape and
transferring this shape to the layer of a material for forming the
concave-convex structure layer. Specific examples of the method may
include:
[0142] (Method 1) a method that includes preparing an unprocessed
multi-layered body having a layer of a resin composition A that
constitute the substrate film and a layer of a resin composition B
for forming the concave-convex structure layer (the concave-convex
structure has not been formed at this point) by, e.g.,
co-extrusion, and forming the concave-convex structure on the
surface on the resin composition B side of the unprocessed
multi-layered body; and
[0143] (Method 2) a method that includes applying the resin
composition B in liquid form to the substrate film, putting a mold
on the layer of the applied resin composition B, and curing the
resin composition B with the mold put thereon to form the
concave-convex structure layer.
[0144] In Method 1, the unprocessed multi-layered body may be
obtained by, for example, extrusion molding in which the resin
composition A and the resin composition B are co-extruded. Then a
mold having a desired surface shape may be pressed against the
surface on the resin composition B side of the unprocessed
multi-layered body, whereby the concave-convex structure is
formed.
[0145] More specifically, an unprocessed multi-layered body in a
lengthy shape is formed continuously by extrusion molding and is
then pressed between a transcription roller having the desired
surface shape and a nip roller. This allows continuous
manufacturing in an efficient manner. Preferably, the nipping
pressure between the transcription roller and the nip roller is
several MPa to several tens of MPa. Preferably, the temperature
during transcription is equal to or higher than Tg and equal to or
lower than (Tg+100.degree. C.) where Tg is the glass transition
temperature of the resin composition B. The contacting time the
unprocessed multi-layered body with the transcription roller may be
controlled by adjusting the feeding speed of the film, i.e., the
rotation speed of the rollers and is preferably 5 seconds or longer
and 600 seconds or shorter.
[0146] In Method 2, it is preferable to use, as the resin
composition B that forms the concave-convex structure layer, a
composition that is curable with energy rays such as ultraviolet
rays. Such a resin composition B is applied to the substrate film
and cured by irradiation with energy rays such as ultraviolet rays
from a light source positioned on the back side of the coated
surface (the side opposite to the surface of the substrate film to
which the resin composition B has been applied) with the mold put
on the resin composition B. Then the mold is removed, whereby the
multi-layered body in which the coating of the resin composition B
serves as the concave-convex structure layer can be formed.
Embodiment 1-2
[0147] In the surface light source device of the first invention,
the shape of the concave portions constituting the device
light-emitting surface is not limited to the pyramid shape
exemplified in Embodiment 1-1 described above. For example, the
concave portions may have a shape that is part of a sphere as in
Embodiment 1-2 which will be described below.
[0148] Embodiment 1-2 is a second embodiment according to the first
invention. FIG. 7 is a top view schematically showing a surface
light source device according to Embodiment 1-2, and FIG. 8 is a
cross-sectional view showing a cross-section obtained by cutting
the surface light source device shown in FIG. 7 along a plane that
passes through line 2a in FIG. 7 and is perpendicular to the device
light-emitting surface. As shown in FIGS. 7 and 8, the surface
light source device 20 according to Embodiment 1-2 has the same
configuration as that of Embodiment 1-1 except that the shape of
the device light-emitting surface, i.e. the surface shape of a
concave-convex structure layer 211 in a multi-layered body 210
constituting a light-emitting surface structure layer 200, is
different from that in Embodiment 1-1.
[0149] The concave portions 213 formed on the surface of the
concave-convex structure layer 211 have a hemispherical shape and
are aligned successively on the device light-emitting surface 20U
at regular intervals in three alignment directions parallel to
lines 2a, 2b, and 2c. The angles between lines 2a, 2b, and 2c are
60.degree.. Spacings are provided between concave portions 213
adjacent in the directions of the lines 2a, 2b, and 2c, and these
spacings form flat portions 214.
[0150] With the device light-emitting surface having the structure
including the hemispherical concave portions and the flat portions
formed as the spacings therebetween, the light extraction
efficiency can also be improved, and the change in color tone at
different viewing angles can also be reduced, as in the
pyramid-shaped concave portions in Embodiment 1-1. In addition, the
mechanical strength of the device light-emitting surface can be
improved.
Embodiment 1-3
[0151] In the surface light source device of the first invention,
the shape of the concave portions constituting the device
light-emitting surface may also be a groove shape as in Embodiment
1-3 which will be described below.
[0152] Embodiment 1-3 is a third embodiment according to the first
invention. FIG. 9 is a perspective view schematically showing the
surface light source device according to Embodiment 1-3. As shown
in FIG. 9, the surface light source device 30 according to
Embodiment 1-3 has the same configuration as that of Embodiment 1-1
except that the shape of the device light-emitting surface, i.e.
the surface shape of a concave-convex structure layer 311 in a
multi-layered body 310 constituting a light-emitting surface
structure layer 300, is different from that in the first
embodiment.
[0153] Each of a plurality of concave portions 313 formed on the
surface of the concave-convex structure layer 311 has a linear
groove shape and includes two flat oblique surfaces. Therefore, a
cross-section obtained by cutting a concave portion 313 along a
plane perpendicular to the extending direction of the grooves has a
triangular shape with two oblique sides. The plurality of concave
portions 313 are aligned in parallel to each other on a device
light-emitting surface 30U. At each gap between adjacent concave
portions 313, Spacings 314 are provided. These spacings 314
constitute flat portions on the device light-emitting surface
30U.
[0154] With the device light-emitting surface having a structure
including the groove-shaped concave portions and the flat portions
formed as the spacings therebetween, the light extraction
efficiency can also be improved, and a change in color tone at
different viewing angles can also be reduced, as in the
pyramid-shaped concave portions in the Embodiment 1-1. In addition,
the mechanical strength of the device light-emitting surface can be
improved.
[0155] No particular limitation is imposed on the groove shape of
the concave portions so long as it includes oblique surfaces. The
cross-sectional shape of the concave portions is not limited to a
triangular shape exemplified above and may be any of various
shapes. For example, the cross-sectional shape of the grooves may
be any of other polygonal shapes such as pentagonal and heptagonal
shapes and shapes other than polygonal shapes such as a part of a
circle. Similar to the aforementioned Embodiment 1-1 wherein the
apexes of the pyramids or cones may be a deformed to be a rounded
shape or a flat truncated shape, the shape of the cross-section of
each groove may be deformed to be a shape with a rounded apex or a
flat truncated shape.
Embodiment 1-4
[0156] In the surface light source device of the first invention,
when the shape of the concave portions constituting the device
light-emitting surface is a pyramid shape, the pyramid shape is not
limited to the simple pyramid shape exemplified in Embodiment 1-1
described above. For example, the shape of the concave portions may
be a combination of a plurality of pyramid shapes as in Embodiment
1-4 which will be described below.
[0157] Embodiment 1-4 is a fourth embodiment according to the first
invention. FIG. 10 is a top view schematically showing a surface
light source device according to Embodiment 1-4, and FIG. 11 is a
cross-sectional view showing a cross-section obtained by cutting
the surface light source device shown in FIG. 10 along a plane that
passes through line 3a in FIG. 10 and is perpendicular to a device
light-emitting surface. As shown in FIGS. 10 and 11, the surface
light source device 40 according to Embodiment 1-4 has the same
configuration as that of Embodiment 1-1 except that the shape of
the device light-emitting surface 40U, i.e. the shape of concave
portions 413 in a concave-convex structure layer 411 in a
multi-layered body 410 constituting a light-emitting surface
structure layer 400, is different from the shape of the concave
portions 113 in Embodiment 1-1.
[0158] Each of the plurality of concave portions 413 formed on the
surface of the concave-convex structure layer 411 has three types
of oblique surfaces 41T, 41U, and 41V having different inclination
angles with respect to the device light-emitting surface. The
oblique surface 41V has the steepest inclination, and four oblique
surfaces 41V form a quadrangular pyramid. The inclination of the
oblique surfaces 41U is less steep than that of the oblique
surfaces 41V, and the inclination of the oblique surfaces 41T is
less steep than that of the oblique surfaces 41U. Four oblique
surfaces 41U form a part of a quadrangular pyramid, and four
oblique surfaces 41T also constitute a part of a quadrangular
pyramid. The combination of these oblique surfaces constitutes the
shape of each concave portion 413 in which three types of
quadrangular pyramids or parts thereof are combined. Flat portions
414 located around the concave portions 413 are formed of spacings
provided between concave portions aligned in two mutually
orthogonal directions, as in the flat portions 114 in Embodiment
1-1.
[0159] With these concave portions having a shape formed of a
combination of a plurality of pyramids, the change in color tone at
different viewing angles may be further reduced as compared to that
with the pyramid shaped concave portions in Embodiment 1-1. In
addition, as in Embodiment 1-1, the light extraction efficiency can
be improved, and the mechanical strength of the device
light-emitting surface can be improved.
Embodiment 1-5
[0160] In Embodiments 1-1 to 1-4 described above, the diffusing
member is a member that is provided as a layer that constitutes all
or part of the light-emitting surface structure layer so as to
allow the incident light to pass therethrough in a diffused manner.
However, the diffusing member in the surface light source device of
the first invention is not limited thereto. As exemplified in
Embodiment 1-5 below, the diffusing member may also be a member
that is disposed at a position farther from the light-emitting
surface structure layer than the organic EL element and reflects
the incident light in a diffused manner.
[0161] Embodiment 1-5 is a fifth embodiment according to the first
invention. FIG. 12 is a cross-sectional view showing a
cross-section obtained by cutting a surface light source device
according to Embodiment 1-5 along a plane perpendicular to a device
light-emitting surface. As shown in FIG. 12, Embodiment 1-5 is
different from Embodiment 1-1 in that the surface light source
device 50 includes, as the second electrode layer, an electrode
layer 146 serving as a second transparent electrode in place of the
reflecting electrode 143 and includes a reflecting member 551 and a
reflecting member substrate 552 in place of the sealing substrate
151. The rest of the configuration is the same as that in
Embodiment 1-1.
[0162] In the surface light source device 50, the reflecting member
551 has a property to reflect on a reflecting surface 551U the
light incident on the reflecting member 551, and the reflecting
surface 551U is not flat but has a concave-convex shape. Therefore,
the reflecting member 551 can reflect the incident light in a
diffused manner.
[0163] The reflection on the reflecting surface 551U of the
reflecting member 551 in a diffused manner means that at least part
of the incident light is reflected in a non-specularly manner
(reflected in a direction different from that of specular
reflection). By this reflection, at least a part of the light from
the luminescent layer 142 is diffused before the light reaches the
device light-emitting surface 10U.
[0164] In the surface light source device 10 in Embodiment 1-1, a
layer constituting all or part of the light-emitting surface
structure layer serves as the diffusing member. However, in the
surface light source device 50 in Embodiment 1-5, the reflection of
light by the reflecting member 551 in a diffused manner brings
about the same effects as those by the diffusing member in the
light-emitting surface structure layer. Therefore, the effects of
the first invention can be obtained without providing the diffusing
member in the light-emitting surface structure layer. However, if
desired, a diffusing member similar to that used in Embodiment 1-1
may be provided in the light-emitting surface structure layer as an
additional diffusing member in addition to the reflecting member
551.
[0165] A gap 553 between the second transparent electrode 146 and
the reflecting surface 551U of the reflecting member 551 may be
filled with any optional material such as a filler or an adhesive
agent that does not significantly impair the transmission of light.
The gap may be a gap in which air or any other gas is present, or
the gap may be a vacuum gap, so long as a problem such as
significant deterioration of the durability of the luminescent
layer 142 does not occur.
[0166] No particular limitation is imposed on the material for the
reflecting member 551. The reflecting member 551 may be a member
including at least a layer of material having a property of
reflecting incident light, such as aluminum and silver. More
specifically, a reflecting member having a fine concave-convex
structure may be obtained by forming one or a plurality of layers
of such a metal on a substrate having a fine concave-convex
structure. A reflecting member having a fine concave-convex
structure may also be obtained by forming a layer of such a metal
on a flat substrate and then processing the metal layer. A
reflecting member having a fine concave-convex structure may also
be obtained by forming a layer of such a metal on a flat resin
substrate and then causing corrugation of the resin substrate. For
the purpose of improving adhesion properties, corrosion resistance,
and abrasion resistance, the reflecting member may have a structure
in which a functional layer such as an inorganic thin film or an
organic thin film is deposited on the surface of the metal
layer.
[0167] The material of the reflecting member 551 is not limited to
a metal. For example, it is possible to use a diffusing plate
formed of any arbitrary material and having a white surface by
which the incident light is reflected in a diffused manner.
Embodiment 1-6
[0168] In Embodiment 1-1 and other Embodiments described above, the
quadrangular pyramids are aligned in two directions on the device
light-emitting surface, wherein the flat portions are formed by
providing spacings between quadrangular pyramids adjacent in both
two directions. However, the first invention is not limited
thereto. For example, spacings may be provided only in one of the
two directions, as in Embodiment 1-6 which will be described
below.
[0169] Embodiment 1-6 is a sixth embodiment according to the first
invention. FIG. 13 is a top view schematically showing a surface
light source device according to Embodiment 1-6, and FIG. 14 is a
cross-sectional view showing a cross-section obtained by cutting
the surface light source device shown in FIG. 13 along a plane that
passes through line 4a in FIG. 13 and is perpendicular to the
device light-emitting surface. As shown in FIGS. 13 and 14, the
surface light source device 80 according to Embodiment 1-6 has the
same configuration as that of Embodiment 1-1 except that the shape
of the device light-emitting surface 80U, i.e. the surface shape of
a concave-convex structure layer 811 in a multi-layered body 810
constituting the light-emitting surface structure layer 800, is
different from that of Embodiment 1-1.
[0170] The shape of each of concave portions 813 formed on the
surface of the concave-convex structure layer 811 is the same as
that of the concave portions 113 in Embodiment 1-1. However,
spacings between concave portions 813 are provided only between
concave portions 813 adjacent in a direction orthogonal to line 4a
in FIG. 13. Therefore, flat portions 814 extending in a direction
parallel to line 4a are formed. In such an instance, the abrasion
resistance when the device light-emitting surface undergoes
abrasion in a certain direction, for example, in a direction
parallel to the extending direction of the flat portions 814, may
be lowered more than that in Embodiment 1-1. However, the light
extraction efficiency may be improved. Therefore, this
configuration may be preferred in some cases.
[0171] As to the shape of the concave portions 813 in the present
embodiment, the height of boundary portions 815 between adjacent
concave portions 813 is the same as the height of the flat portions
814. However, the height of the boundary portions 815 may be
different from the height of the flat portions 814.
[0172] In the example described above, the concave portions 813
have only a quadrangular pyramid shape. However, the concave
portions 813 may have a shape other than the quadrangular pyramid
shape. For example, as shown in FIG. 15, a plurality of concave
portions 816 having a hip-roof shape may be aligned. A
concave-convex structure layer 821 shown in FIG. 15 is a
modification of the concave-convex structure layer 811 according to
Embodiment 1-6 and has the same structure as that of the
concave-convex structure layer 811 according to Embodiment 1-6
except that the shape of the concave portions is different.
Embodiment 1-7
[0173] In Embodiments 1-1 to 1-6, the flat portions on the
concave-convex structure layer do not have a variety in height (the
height when the device is placed with the device light-emitting
surface facing upward and being parallel to the horizontal
direction) but have a uniform height. However, the first invention
is not limited thereto. For example, as in Embodiment 1-7 which
will be described below, the flat portions may have a variety in
height.
[0174] Embodiment 1-7 is a seventh embodiment according to the
first invention. FIG. 16 is a top view schematically showing a
surface light source device according to Embodiment 1-7, and FIG.
17 is a cross-sectional view showing a cross-section obtained by
cutting the surface light source device shown in FIG. 16 along a
plane that passes through line 11a-11b in FIG. 16 and is
perpendicular to a device light-emitting surface. As shown in FIGS.
16 and 17, the surface light source device 90 according to
Embodiment 1-7 has the same configuration as that of Embodiment 1-1
except that the shape of the device light-emitting surface 90U,
i.e. the surface shape of a concave-convex structure layer 911 in a
multi-layered body 910 constituting a light-emitting surface
structure layer 900, is different from that in Embodiment 1-1.
[0175] Each of concave portions 913 formed on the surface of the
concave-convex structure layer 911 has approximately the same shape
as the shape of the concave portions 113 in Embodiment 1-1.
However, between the concave portions 913, two types of flat
portions including lower flat portions 914 and higher flat portions
915 are provided, and the flat portions 914 and 915 are connected
by oblique surfaces 91W.
[0176] In the present embodiment, two rows of flat portions 914 and
one row of flat portions 915 are disposed in an alternate manner,
whereby a repeating unit composed of two flat portions 914, one
flat portion 915, and the oblique surfaces (including the oblique
surfaces 91W) of three concave portions 113 between these flat
portions is repeated on the cross-section of the light-emitting
surface structure layer 900. Such repetitions may also appear on a
cross-section perpendicular to the lines 11a and 11b shown in FIG.
16 and to the device light-emitting surface, as well as on the
cross-section passing through the lines 11a and 11b.
[0177] When the flat portions have such a variety in height, the
abrasion resistance of the device light-emitting surface is
slightly reduced. However, such variety also brings about a
preferable effect of reducing a rainbow unevenness which appears
upon observing the device light-emitting surface. More
specifically, when a surface light source device is produced with
its device light-emitting surface being designed such that the flat
portions do not have a variety in height, the heights of the flat
portions may contain errors due to the errors caused during
formation of the flat portions. Such errors may cause interference
of the light from the device light-emitting surface (i.e., one or
both of the light emitted from the device and external light
reflected by the device light-emitting surface), and this may cause
a rainbow unevenness. When the difference in height between the two
types of flat portions 914 and 915 is intentionally set to a size
difference larger than the difference that causes interference of
light, the interference can be prevented, and the rainbow
unevenness can be suppressed. The size difference larger than the
difference that causes interference of light is, for example, equal
to or larger than 0.62 times and preferably equal to or larger than
1.5 times the center wavelength of the light emitted from the
surface light source device.
[0178] In the present embodiment, the flat portions have a
predetermined variety in height (a size difference larger than the
difference that causes interference). However, there may be another
possible structure wherein, for example, the height positions of
the flat portions is the same, but the concave portions have a
predetermined difference in depth (a size difference larger than
the difference that causes interference). Also in this case, the
same effects as that of the previously mentioned embodiment can be
obtained. Alternatively, the variety may be present as to both the
heights of the flat portions and the depths of the concave
portions. The aforementioned configuration in which the flat
portions or the concave portions have a predetermined variety is
applicable not only to the present embodiment but also to all
embodiments in the scope of the present invention.
[0179] The aforementioned numerical range has been verified by the
following findings. In an instance of a concave-convex structure
layer designed such that all the flat portions have the same
height, when the height of the flat portions includes an error of
170 nm or larger, interference occurs and the rainbow unevenness is
observed. In such an instance, it has been found out that the
occurrence of the rainbow unevenness can be suppressed by
intentionally providing a size difference in height equal to or
larger than 2 times the minimum error that causes the rainbow
unevenness. In another instance of a concave-convex structure layer
designed such that all the flat portions have the same height, when
the height of the flat portions fluctuates with a standard
deviation of .sigma.1 nm (.apprxeq.60 nm), interference occurs and
the rainbow unevenness is observed. In such an instance, it has
been found out that the occurrence of the rainbow unevenness can be
suppressed by intentionally providing a size difference in height
equal to or larger than 6.times..sigma.1 nm (=360 nm). The
aforementioned two findings show that the size difference larger
than the difference that causes interference of light is equal to
or larger than 0.62 times the center wavelength of the light
emitted from the surface light source device.
Embodiment 1-8
[0180] In the surface light source device of the first invention,
the device light-emitting surface may not be provided only on one
side of the surface light source device. For example, as in
Embodiment 1-8 which will be described below, both surfaces of the
surface light source device may be device light-emitting
surfaces.
[0181] Embodiment 1-8 is an eighth embodiment according to the
first invention. FIG. 18 is a cross-sectional view schematically
showing a cross-section obtained by cutting a surface light source
device according to Embodiment 1-8 along a plane perpendicular to a
device light-emitting surface. As shown in FIG. 18, Embodiment 1-8
is different from Embodiment 1-1 in that the surface light source
device 1000 includes an electrode layer 146 serving as a second
transparent electrode in place of the reflecting electrode 143 and
further includes another light-emitting surface structure layer 100
in place of the sealing substrate 151. The rest of the
configuration is the same as that in Embodiment 1-1. Any optional
material such as a filler or an adhesive agent or a gap may be
present between the second transparent electrode 146 and the
light-emitting surface structure layer 100 on the lower side in the
figure. In the gap, air or any other gas may be present so long as
a problem such as significant deterioration of the durability of
the luminescent layer 142 does not occur. Alternatively, the gap
may be a vacuum gap.
[0182] Since the second electrode layer 146 is a transparent
electrode, the light from the luminescent layer 142 passes through
the first electrode layer 141 and the second electrode layer 146
and is then emitted from both the device light-emitting surfaces
10U on the upper and lower sides in the figure. When light is
emitted from both the front and back sides as described above, the
light extraction efficiency can also be improved, and the change in
color tone at different viewing angles can also be reduced, in a
similar manner as in Embodiment 1-1. In addition, the mechanical
strength of the device light-emitting surface can also be
improved.
[0183] In the surface light source device 1000 of the present
embodiment, generally, the light that enters one of the device
light-emitting surfaces 10U passes through the surface light source
device 1000 and is emitted from the other device light-emitting
surface 10U. Therefore, the opposite side can be viewed with naked
eyes through the surface light source device 1000, and the surface
light source device can be of a see-through type. This allows
diversification of the design.
[0184] In the example shown in the present embodiment, the
light-emitting surface structure layers 100 having the same
structure are disposed on both the upper and lower sides in the
figure of the surface light source device 1000. However, a
combination of different light-emitting surface structure layers
may be provided. For example, the light-emitting surface structure
layer 100 may be provided on the surface of the first electrode
layer 141, and the light-emitting surface structure layer 200 may
be provided on the surface of the second electrode layer 146.
<Lighting Device and Backlight Device>
[0185] Each of the lighting device of the first invention and the
backlight device of the first invention includes the surface light
source device of the first invention.
[0186] The lighting device of the first invention includes the
surface light source device of the first invention as a light
source and may further include any optional components such as a
member for holding the light source and a circuit for supplying
electric power. The backlight device of the first invention
includes the surface light source device of the first invention as
a light source and may further include any optional components such
as a casing, a circuit for supplying electric power, a diffusion
plate for making the emitted light more uniform, a diffusing sheet,
and a prism sheet. The applications of the backlight device of the
first invention include display devices, such as liquid crystal
display devices, for displaying images by controlling pixels and
backlights for display devices, such as signboards, for displaying
still images.
[0187] The first invention is not limited to the examples shown in
the aforementioned embodiments, and modifications may be made
within the scope of the claims of the present application and the
scope of equivalents thereto.
[0188] For example, in the description of the examples of the
aforementioned embodiments, the light-emitting surface structure
layers that are composed of a concave-convex structure layer, a
substrate film layer, a bonding layer, and a glass substrate have
been exemplified. However, the light-emitting surface structure
layer may be composed of a smaller number of layers, or
alternatively may further include, in addition to these layers, an
optional layer. For example, a coating layer may be provided on the
concave-convex structure layer and may define the concave-convex
structure of the device light-emitting surface.
[0189] In the examples shown in the aforementioned embodiments, all
the concave portions distributed over the entire device
light-emitting surface have the same shape. However, concave
portions having different shapes may also coexist on the device
light-emitting surface. For example, pyramid-shaped concave
portions having different sizes may coexist. Pyramid-shaped concave
portions and conical concave portions may also coexist. Concave
portions having a shape of a combination of a plurality of pyramids
and concave portions having a simple pyramid shape may also be
coexist.
[0190] In the examples shown in the aforementioned embodiments, the
widths of the flat portions and the spacings between adjacent flat
portions are always constant. However, flat portions having a small
width and flat portions having a large width may coexist. Narrow
spacings between the flat portions and wide spacings between the
flat portions may also coexist. When the flat portions have a size
difference in at least one of their height, width, and spacing that
is larger than the difference that causes interference of emitted
light or reflected light in this manner, the rainbow unevenness
caused by interference can be suppressed.
[0191] In the examples shown in the aforementioned embodiments
which include a reflecting electrode layer, the reflecting
electrode layer may be replaced with a combination of a transparent
electrode and a reflecting layer. Also in such a case, a device
having the same effect as that with the reflecting electrode can be
configured.
II. Description of Second Invention
[0192] The second invention will be described in detail by way of
embodiments and exemplifications, but the second invention is not
limited to the following embodiments and exemplifications.
Embodiment 2-1
[0193] A surface light source device according to a first
embodiment of the second invention will be described
hereinbelow.
[0194] Embodiment 2-1 is a first embodiment according to the second
invention. FIG. 19 is a vertical cross-sectional view illustrating
the surface light source device according to Embodiment 2-1. As
shown in FIG. 19, the surface light source device 2001 according to
the present embodiment has a light-emitting surface 2040A having a
rectangular shape in a plan view and includes an organic EL element
2020 and a concave-convex structure body 2040 serving as a
light-emitting-side member that is disposed directly or indirectly
on at least one surface of the organic EL element 2020.
[0195] The organic EL element 2020 includes, in the following
order, a first electrode layer 2022 constituting a reflecting
electrode, a luminescent layer 2024, and a second electrode layer
2026 serving as a transparent electrode. When a voltage is applied
between the first electrode layer 2022 and the second electrode
layer 2026, the luminescent layer 2024 emits light, so that the
organic EL element 2020 can be used as a light source. Such an
organic EL element 2020 can be preferably used for a lighting
device and a display device.
[0196] As the luminescent layer 2024, any known luminescent layer
may be used. The number of types of luminescent materials used in
the luminescent layer 2024 is not limited to one, and the number of
luminescent layers is not limited to one. In order to adapt to the
use as a light source, the luminescent layer may be a single type
of layer or a combination of a plurality of types of layers. In
this manner, white light or light of a color close to white can be
emitted.
[0197] No particular limitation is imposed on the electrodes of the
organic EL element 2020, and any of known electrodes may be
appropriately selected. The first electrode layer 2022 is a metal
electrode layer. The second electrode layer 2026 is a transparent
electrode layer. With this configuration, the light emitted from
the luminescent layer 2024 passes through the second electrode
layer 2026, or is reflected on the first electrode layer 2022 and
then passes through the luminescent layer 2024 and the second
electrode layer 2026, whereby the light can be emitted to the
outside of the organic EL element 2020. The first electrode layer
2022 may also be formed as a transparent electrode layer. In such a
case, light may be emitted from both surfaces of the organic EL
element. When the first electrode layer 2022 is a transparent
electrode layer, a reflecting member or a scattering member (such
as a white scattering member disposed via an air layer) may be
disposed on the side opposite to the luminescent layer 2024.
[0198] If necessary, the organic EL element 2020 may further
include, between the first electrode layer 2022 and the second
electrode layer 2026, other layers such as a hole injection layer,
a hole transport layer, an electron transport layer, an electron
injection layer, and a gas barrier layer, in addition to the
luminescent layer 2024. The organic EL element 2020 may further
include an optional component such as wiring leads for supplying
electric current to the electrode layers 2022 and 2026, and a
peripheral structure for sealing the luminescent layer.
[0199] No particular limitation is imposed on the materials that
constitute the electrode layers and other layers disposed
therebetween. Specific examples of such materials may include the
materials exemplified in the description of the first
invention.
[0200] The aforementioned luminescent layer and other luminescent
layers may be suitably combined to obtain a stacked or tandem type
luminescent layer that generates light with complementary colors.
The combination of complementary colors may be yellow/blue,
green/blue/red, etc.
[0201] The concave-convex structure body 2040 is disposed on the
surface of the second electrode layer 2026. The surface of the
concave-convex structure body 2040 that is on the side opposite to
the second electrode layer 2026 is the light-emitting surface 2040A
from which light emits to the outside. On the light-emitting
surface 2040A, a concave-convex structure 2041 is formed. The
light-emitting surface 2040A is a surface parallel to the surface
of the luminescent layer 2024 of the organic EL element 2020 and is
also parallel to the principal surface of the surface light source
device. However, in a microscopic sense, the concave-convex
structure 2041 is formed on the light-emitting surface 2040A as
described above, and therefore the light-emitting surface 2040A may
be non-parallel to the surface of the luminescent layer. However,
unless otherwise specifically mentioned, the phrase "parallel (or
perpendicular) to the light-emitting surface" simply means that an
object is parallel (or perpendicular) to the light-emitting surface
with the concave-convex structure etc. being neglected. Unless
otherwise mentioned, a description will be given of the surface
light source device placed with its light-emitting surface being
parallel to the horizontal direction and facing upward. In the
second invention, when components are "parallel" or "perpendicular"
to each other, a deviation in the range in which the effects of the
second invention are not impaired may be present. For example, an
tolerance of .+-.5.degree. with respect to the parallel or
perpendicular angle may be allowable.
[0202] The concave-convex structure body 2040 includes a substrate
2042 made of, for example, glass and disposed on the surface of the
second electrode layer 2026, a concave-convex structure main body
2044, and a bonding layer 2046 that bonds the substrate 2042 to the
concave-convex structure main body 2044. The concave-convex
structure main body 2044 includes a base substrate 2045 and a
concave-convex structure layer 2047 disposed on the surface of the
base substrate 2045 and serving as a light-distribution conversion
unit. In the surface light source device 2001, at least one of the
substrate 2042, the base substrate 2045, the bonding layer 2046,
and the concave-convex structure layer 2047 is formed of a
composition containing, for example, particles that impart light
diffusibility. The layer having the light diffusibility diffuses
the light from the luminescent layer 2024 and allows the resultant
light to pass through the layer or to be reflected therein.
Therefore, this layer functions as a disusing section in the second
invention.
[0203] The substrate 2042 functions as a plate member that imparts
stiffness for suppressing the warpage to the surface light source
device 2001. The substrate 2042 has a good ability to seal the
organic EL element 2020 and to facilitate successive formation of
the layers constituting the organic EL element 2020 on the
substrate 2042 in the production process. Therefore, the substrate
2042 has advantages in improving the durability of the surface
light source device 2001 and for facilitating the production
process. No particular limitation is imposed on the thickness of
the substrate 2042. Preferably, the thickness is 0.1 to 5 mm. In
the present embodiment, the substrate 2042 is made of glass.
However, the substrate may be made of resin. In such a case, the
refractive index of the resin or glass constituting the substrate
2042 may be 1.4 to 2.
[0204] The base substrate 2045 may be formed of a composition
containing a transparent resin. The term "transparent" in the
transparent resin means that it has a light transmittance suitable
for use as an optical member. In the second invention, each of the
layers constituting the light-emitting-side member may have a light
transmittance suitable for use as an optical member, and the total
light transmittance of the light-emitting-side member as a whole
may be 80% or larger.
[0205] Examples of the transparent resin are the same as those
described in the description of the light-emitting surface
structure layer of the first invention.
[0206] The concave-convex structure layer 2047 is located at the
outermost portion on the light-emitting surface side of the surface
light source device 2001, and the surface of the concave-convex
structure layer 2047 that is opposite to the base substrate 2045 is
the light-emitting surface 2040A. The concave-convex structure
layer 2047 has a concave-convex structure including a plurality of
concave portions 2048 having oblique surfaces and flat portions
2049 disposed around the concave portions 2048 and formed into a
flat shape so that adjacent concave portions 2048 are spaced apart.
The same material as that for the base substrate 2045 described
above may be used as the material constituting the concave-convex
structure layer 2047. The concave-convex structure defines the
light-emitting surface. When the structure including a plurality of
concave portions and flat portions disposed around the concave
portions is provided as described above, light extraction
efficiency can be improved. In addition, the concave-convex
structure is prevented from, for example, being broken off by an
external impact, and therefore the mechanical strength of the
light-emitting surface can be improved. The "oblique surface" is a
surface forming a non-parallel angle with respect to the
light-emitting surface. The surfaces of the flat portions may be
parallel to the light-emitting surface.
[0207] The light extraction efficiency of the surface light source
device 2001 can be improved by appropriately adjusting the ratio of
the area occupied by the flat portions 2049 relative to the sum of
the area occupied by the flat portions 2049 and the area occupied
by the concave portions 2048 when the concave-convex structure
layer 2047 is observed in a direction perpendicular to the
light-emitting surface 2040A (hereinafter this ratio is referred to
as a "flat portion ratio"). More specifically, when the flat
portion ratio is adjusted to 10 to 75%, favorable light extraction
efficiency can be obtained, and the mechanical strength of the
light-emitting surface 2040A can be improved.
[0208] Each of the plurality of concave portions 2048 is a recess
having a regular quadrangular pyramid shape. Therefore, oblique
surfaces 2048A constituting each concave portion 2048 are identical
isosceles triangles. The plurality of concave portions 2048 are
aligned at regular intervals in two mutually orthogonal alignment
directions and are oriented in the same direction. The angles
formed by the flat portions 2049 and the oblique surfaces 2048A
constituting each concave portion 2048 may be set to, for example,
60.degree.. Therefore, the vertex angle of the regular quadrangular
pyramid forming the concave portion 2048 is 60.degree.. However,
the angles formed by the oblique surfaces of the concave portions
and the flat portions are preferably 40 to 70.degree. on average in
terms of further improving the light extraction efficiency while
minimizing the change in color tone at different viewing
angles.
[0209] As the material constituting the concave-convex structure
layer 2047, a material having high hardness after curing is
preferred because such a material can easily form the
concave-convex structure of the light-emitting surface and can
easily provide abrasion resistance of the concave-convex structure.
More specifically, it is preferable to use a material having a
pencil hardness of HB or higher when a resin layer having a
thickness of 7 .mu.m is formed on a base substrate with no
concave-convex structure provided thereon. A material having a
pencil hardness of H or higher is more preferred, and a material
having a pencil hardness of 2H or higher is still more preferred.
As the material for the base substrate 2045, it is preferable to
use a material having some degree of flexibility, because thereby
handling of the concave-convex structure main body 2044 can be
facilitated during the formation of the concave-convex structure
layer 2047 and/or the completed concave-convex structure main body
2044. Use of a combination of the aforementioned materials results
in production of a concave-convex structure main body 2044 that can
be handled easily and that has high durability, whereby a
high-performance surface light source device can be easily
manufactured.
[0210] Such a combination of materials may be obtained by
appropriately selecting, as the resins contained in the materials,
the transparent resins exemplified above. More specifically, a
ultraviolet curable resin such as acrylate may be used as the
transparent resin constituting the material for the concave-convex
structure layer 2047, and a film made of an alicyclic olefin
polymer (such as ZEONOR Film which will be described later) or a
polyester film may be used as the transparent resin constituting
the material for the base substrate 2045. A preferred combination
of materials may thereby be obtained.
[0211] In the present embodiment, the difference in refractive
index between the base substrate 2045 and the concave-convex
structure layer 2047 may be as small as possible. In such a case,
the difference in refractive index is preferably equal to or
smaller than 0.15 and more preferably equal to or smaller than
0.05.
[0212] When any of the layers that constitute the base substrate
2045, the concave-convex structure layer 2047, etc. serve as a
diffusing section, the composition used as the material for such a
layer may contain particles, described later, that impart light
diffusibility. For example, when one or both of the base substrate
2045 and the concave-convex structure layer 2047 are formed of a
composition containing particles that provide light diffusibility,
the base substrate 2045 and the concave-convex structure layer 2047
serve also as the diffusing section. In necessary, such a
composition may further contain any optional component. Examples of
such an optional component may include the same components as those
described in the description of the light-emitting surface
structure layer of the first invention.
[0213] In the present embodiment, no particular limitation is
imposed on the thickness of the concave-convex structure layer
2047, but the thickness thereof is preferably 1 to 70 .mu.m. The
thickness of the concave-convex structure layer 2047 is the
distance between its surface on the substrate side on which the
concave-convex structure 2041 is not formed and the flat portions
2049 of the concave-convex structure body 2040. The thickness of
the base substrate 2045 is preferably 20 to 300 .mu.m.
[0214] As the material for the bonding layer 2046, any adhesive
agent (encompassing a tacky agent) having a refractive index close
to that of the base substrate 2045 or the concave-convex structure
layer 2047 and having a transparency may be used. Specific examples
of the adhesive agent may include acrylic-based adhesive agents (or
acrylic-based tacky agents). The thickness of the bonding layer
2046 is preferably 5 to 100
[0215] In the surface light source device 2001 in the present
embodiment, all or part of the layers constituting the
concave-convex structure body 2040 may be layers that diffuse light
and therefore can serve as the diffusing section. Examples of the
material for the layer that diffuses light may include materials
containing particles and alloy resin materials having light
diffusibility that are prepared by mixing two or more types of
resin. In terms of facilitating control of light diffusibility, a
material containing particles is preferred, and a resin composition
containing particles is particularly preferred.
[0216] The particles are the same as the particles described in the
description of the diffusing member of the first invention.
Therefore, the material, ratio of the amount added, diameter,
refractive index, etc. of the particles are the same as those of
the particles described in the description of the diffusing member
of the first invention.
[0217] As described above, all or part of the layers constituting
the concave-convex structure body may serve as the diffusing
section. In such a case, no particular limitation is imposed on the
selection of which of the layers constituting the concave-convex
structure body is used as the diffusing section. The selection may
be made from various points of view. For example, from the
viewpoint of facilitating adjustment of the degree of diffusion, it
is preferable that a layer containing a transparent resin serves as
the diffusing section. From the viewpoint of ensuring sufficient
light diffusibility without using an excessively large amount of
particles in such a layer, it is preferable that a layer having a
thickness of more than a certain degree, for example, 5 .mu.m or
larger, serves as the diffusing section.
[0218] Preferably, the concave-convex structure layer is formed of
a material having high hardness, as described above. However, when
the thickness of the high-hardness material layer used in the
surface light source device is large, undesirable warpage of the
light-emitting surface may occur with the lapse of time. Therefore,
from this point of view, it is preferable that a layer (for
example, a base substrate and/or a bonding layer) that is different
from the concave-convex structure layer and has properties that
facilitate plastic deformation is provided in addition to the
concave-convex structure layer, and this layer serves as the
diffusing section.
[0219] When a layer that is produced by a process that does not
include a step of heating the material thereof (for example, a
transparent resin) is used as the diffusing section, the production
process can be easily managed. For example, a problem such as
clogging of a resin conveying passage with particles can be easily
addressed. From this point of view, it is preferable to use the
bonding layer as the diffusing section. It is also preferable to
use the bonding layer and a layer other than the bonding layer as
the diffusing section. For example, when the bonding layer and the
base substrate are used as the diffusing section and the ratio of
the particles added to the base substrate is reduced, the process
of producing the base substrate can be easily managed (for example,
the frequency of occurrence of clogging can be reduced). No
particular limitation is imposed on the refractive index of the
diffusing section. The refractive index is preferably 1.45 to 2,
more preferably 1.6 to 2, and still more preferably 1.7 to 2. It is
preferable that the refractive index of any layer on the
light-emitting side of the diffusing section is smaller than the
refractive index of the diffusing section. When the diffusing
section has a large refractive index as described above, the range
of selection of the refractive index of any layer on the
light-emitting side of the diffusing section is widened, and
therefore the material for such a layer may be more freely
selected.
[0220] An additional layer other than the concave-convex structure
layer, the base substrate, the bonding layer, and the glass
substrate may be provided in the concave-convex structure body, and
the additional layer may be used as the diffusing section. For
example, the additional layer may be formed between the
concave-convex structure layer and the substrate film layer,
between the bonding layer and the glass substrate, or on the
surface of the glass substrate that is toward the luminescent layer
(for example, between the glass substrate and an electrode layer of
the luminescent layer). Alternatively, the additional layer and one
or more of the concave-convex structure layer, the base substrate,
the bonding layer, and the glass substrate may be used as the
diffusing section.
[0221] When the diffusing section is provided as a layer
constituting all or part of the concave-convex structure body, no
particular limitation is imposed on the degree of diffusion.
However, for example, when all or part of the layers from the
concave-convex structure layer to the bonding layer serve as the
diffusing section, the total light transmittance of the layers from
the concave-convex structure layer to the bonding layer wherein the
concave-convex surface portion of the concave-convex structure
layer is not formed is preferably 70 to 95% and more preferably 73
to 90% because thereby a color unevenness elimination effect can be
sufficiently ensured.
[0222] Since the surface light source device 2001 of the second
invention has the aforementioned features, variations in at least
one of x- and y-chromaticity coordinates in all directions in a
hemisphere on the light-emitting surface 2040A can be reduced, for
example, by half as compared to those which does not have the
aforementioned features. Therefore, in the surface light source
device 2001, the change in color tone at different viewing angles
can be suppressed. To measure the variations in chromaticity in all
directions in the hemisphere, for example, a spectral radiance
meter is placed on the normal direction with respect to (placed in
front of) the light-emitting surface 2040A, and a mechanism for
rotating the light-emitting surface from -90 to 90.degree. (the
direction of the normal is defined as 0.degree.) is provided. In
this manner, the emission spectra can be measured in various
directions to calculate the chromaticity coordinates, and the
variations in the chromaticity coordinates can thereby be
calculated.
[0223] In addition, the concave-convex structure layer 2047 formed
in the concave-convex structure main body 2044 functions as a
light-distribution conversion unit. When the light emitted from the
organic EL element 2020 is incident on the concave-convex structure
2041, this light-distribution conversion unit converts the
distribution of the incident light so as to reduce the difference
between the chromaticity of the light emitted from the
light-emitting surface 2040A in the direction normal to the
light-emitting surface 2040A and the chromaticity of the light
emitted from the light-emitting surface 2040A in an oblique
direction crossing the normal direction. Such a concave-convex
structure 2041 can control the chromaticity that varies depending
on the observation direction, and the diffusing effect by the
aforementioned diffusing section can thereby be complemented.
Therefore, for example, the amount of the particles added to the
layer constituting the diffusing section can be reduced more than
that used conventionally. In this manner, this feature enables
reduction of the thickness and weight of the layer constituting the
diffusing section. Therefore, this feature can contribute to the
reduction in thickness and size of the surface light source device
2001.
[0224] No particular limitation is imposed on the method of
manufacturing the surface light source device 2001 according to the
present embodiment. Manufacture of the above exemplified surface
light source device having the concave-convex structure body
including the concave-convex structure layer, the base substrate,
the bonding layer, and the glass substrate may be performed as
follows. The layers constituting the organic EL element may be
formed on one surface of the glass substrate. Before or after the
formation of these layers, the concave-convex structure main body
may be attached to the other surface of the glass substrate via a
bonding layer. The surface light source device may thereby be
manufactured.
[0225] The concave-convex structure main body may be manufactured
by preparing a mold such as a metal mold having a desired shape,
and transferring this shape to the layer of a material for forming
the concave-convex structure layer. More specific examples of the
method may include Method 1 and Method 2 exemplified in the
manufacturing method in the description of the first invention.
[0226] Each of the lighting device of the second invention and the
backlight device of the second invention includes the surface light
source device described above. The lighting device of the second
invention includes the surface light source device of the second
invention as a light source and may further include any optional
components such as a member for holding the light source and a
circuit for supplying electric power. The backlight device of the
second invention includes the surface light source device of the
second invention as a light source and may further include any
optional components such as a casing, a circuit for supplying
electric power, a diffusion plate for making the emitted light more
uniform, a diffusing sheet, and a prism sheet. The applications of
the backlight device of the second invention include display
devices, such as liquid crystal display devices, for displaying
images by controlling pixels and backlights for display devices,
such as signboards, for displaying still images.
Embodiment 2-2
[0227] A surface light source device according to a second
embodiment of the second invention will be described.
[0228] Embodiment 2-2 is the second embodiment according to the
second invention. Components that are the same as or that
correspond to those in Embodiment 2-1 are denoted by the same
reference numerals, and the description will be omitted or
simplified. FIG. 20 is a vertical cross-sectional view illustrating
the surface light source device according to Embodiment 2-2. As
shown in FIG. 20, the surface light source device 2002 according to
the present embodiment has a light-emitting surface 2040A having a
rectangular shape in a plan view and includes an organic EL element
2020 and a light-emitting-side member 2060 disposed in contact with
at least one surface of the organic EL element 2020.
[0229] The light-emitting-side member 2060 includes a selective
reflecting member 2062, a glass substrate 2042, and a diffusing
layer 2070 serving as a diffusing section and disposed between the
selective reflecting member 2062 and the glass substrate 2042. The
selective reflecting member 2062 includes a substrate film 2064 and
a selective reflecting layer 2066 disposed on the surface of the
substrate film 2064.
[0230] The diffusing layer 2070 is a layer for diffusing the light
from the organic EL element 2020. Examples of the material
constituting the diffusing layer may include materials containing
particles and alloy resin materials having light diffusibility that
are formed by mixing two or more types of resins. In terms of
facilitating control of light diffusibility, a material containing
particles is preferred, and a resin composition containing
particles is particularly preferred.
[0231] The selective reflecting layer 2066 is a layer having a
property that allows specific polarized light in a certain
wavelength range to pass therethrough and reflects or absorbs other
polarized light. A selective reflection range is a wavelength range
in which the selective reflecting layer exhibits the aforementioned
properties. The base substrate 2064 may be configured similarly to
the base substrate 2045 described above.
[0232] The configuration of the selective reflecting layer 2066 is
appropriately selected depending on the intensity peak of the light
emitted from the luminescent layer because the selective reflection
properties generally vary depending on the wavelength. For example,
a luminescent layer having two or more luminescence intensity peaks
may be used as the luminescent layer for the present embodiment.
Preferably, one or more of the two or more luminescence intensity
peaks are in the wavelength range of 500 nm to 650 nm. An example
of the spectrum of the light from the luminescent layer having such
intensity peaks is shown in FIG. 21. The spectrum shown in FIG. 21
has two peaks at wavelengths of 480 nm and 575 nm. Such two or more
luminescence intensity peaks may be obtained by forming the
luminescent layer as a stack of a plurality of layers capable of
emitting light with different colors or as a mixed layer formed by
doping a coloring agent into a layer of another coloring agent.
[0233] The selective reflecting layer 2066 has a selective
reflection range for transmitted light in the front direction
within which range the wavelength of at least one of the
aforementioned luminescence intensity peaks falls. An example will
be described in conjunction with the spectrum of the luminescent
element shown in FIG. 21. The selective reflecting layer may have a
selective reflection range for transmitted light in the front
direction within which range at least one of wavelengths of 480 nm
and 575 nm falls.
[0234] The selective reflection range is a wavelength range in
which transmittance (.lamda.)[%] satisfies
{a-transmittance(.lamda.)}/{a-b}.gtoreq.0.3
where a[%] is the maximum transmittance and b[%] is the minimum
transmittance in a visible light range from 380 to 780 nm.
[0235] Preferably, the selective reflecting layer 2066 has a
transmittance T.sup.F.sub.Y,N at a wavelength of 575 nm in the
front direction, a mean transmittance T.sup.F.sub.Y,60 at a
wavelength of 575 nm in a direction at an angle of 60.degree. with
respect to the polar direction, a transmittance T.sup.F.sub.B,N at
a wavelength of 480 nm in the front direction, and a mean
transmittance T.sup.F.sub.B,60 at a wavelength of 480 nm in a
direction at an angle of 60.degree. with respect to the polar
direction, all of which satisfy the relationship given by
inequality [1]. When the selective reflecting layer 2066 has such a
selective reflection range, the change in color tone at different
viewing angles can be reduced.
(T.sup.F.sub.Y,60/T.sup.F.sub.Y,N)>(T.sup.F.sub.B,60/T.sup.F.sub.B,N)
[1]
[0236] More preferably, the selective reflecting layer 2066 has, as
the selective reflection range for transmitted light in the front
direction, one or more selective reflection ranges lying in the
wavelength range of 500 nm to 650 nm. Still more preferably, the
selective reflecting layer 2066 has, as the selective reflection
range for transmitted light in a direction at an angle of
60.degree. with respect to the polar direction, i.e. in a direction
at an angle of 60.degree. with respect to the front direction, one
or more selective reflection ranges lying in the wavelength range
of 400 nm to 600 nm.
[0237] An example of selective reflection characteristics with the
selective reflection ranges described above is shown in FIG. 22 in
conjunction with the spectrum of the luminescent element shown in
FIG. 21. As shown in FIG. 22, in the selective reflection
characteristics of the transmitted light at an angle of 0.degree.,
i.e. in the front direction, the strongest reflection occurs at a
wavelength of 575 nm, and the selective reflection range for the
transmitted light in the front direction is not less than 525 nm
and not more than 635 nm. As the angle of the transmitted light
increases, the maximum absorption wavelength is shifted to a
shorter wavelength side. Therefore, the aforementioned inequality
[1] is satisfied. In a direction at an angle of 60.degree. with
respect to the polar direction, the maximum absorption wavelength
is 490 nm, and the selective reflection range is not more than 580
nm.
[0238] Examples of the suppression of the change in color tone at
different viewing angles by the selective reflecting layer 2066
having the aforementioned selective reflection characteristics are
shown in FIGS. 23 to 25. FIG. 25 is a graph showing the
distributions of blue light having a wavelength of 480 nm and
yellow light having a wavelength of 575 nm emitted from the
light-emitting surface 2040A of the surface light source device of
the second invention shown in FIG. 20. In this instance, the
surface light source device includes an element having the spectrum
shown in FIG. 21 as the luminescent element and also includes a
selective reflecting layer having the selective reflection
characteristics shown in FIG. 22 as the selective reflecting layer
2066. FIG. 24 is a graph showing the light distributions of the
blue light and yellow light emitted from the glass substrate when
the light distributions are observed without the provision of the
diffusing layer 2070. FIG. 23 is a graph showing the light
distributions when the observation is made with provision of none
of the diffusing layer 2070 and the selective reflecting member
2062.
[0239] As shown in FIG. 23, the distributions of the blue light and
yellow light emitted from the glass substrate 2042 deviate from
each other. However, as shown in FIG. 24, the deviation is reduced
when the light passes through the selective reflecting member 2062
and is then emitted from the light-emitting surface 2040A.
Therefore, the selective reflecting member 2062 functions as a
light-distribution conversion unit that converts the distribution
of light emitted from the organic EL element 2020 so as to reduce
the difference between the chromaticity of the light emitted from
the light-emitting surface 2040A in a direction normal thereto and
the chromaticity of the light emitted from the light-emitting
surface 2040A in an oblique direction crossing the normal
direction.
[0240] As shown in FIG. 23, the distributions of the blue light and
yellow light emitted from the glass substrate 2042 deviate from
each other. However, as shown in FIG. 25, the deviation is further
reduced when the light passes through the diffusing layer 2070 and
the selective reflecting member 2062 and is then emitted from the
light-emitting surface 2040A. Therefore, the selective reflecting
member 2062 can suppress the color unevenness at different viewing
angles, and the diffusing layer 2070 can further suppress the color
unevenness. In this manner, the combined use of the selective
reflecting member 2062 and the diffusing layer 2070 can further
improve the color unevenness elimination effect as compared to the
case in which only the diffusing layer 2070 or only the selective
reflecting member 2062 is used, and the diffusing layer 2070 can
have a reduced diffusing effect. This is advantageous in that the
ratio of the amount of diffusing particles etc. added can be
reduced and therefore the thickness of the diffusing layer can be
reduced.
[0241] In the surface light source device 2002 in the present
embodiment, a part of the light generated in the luminescent layer
2024 passes directly through the second electrode layer 2026, and
another part of the light is reflected on the first electrode layer
2022 and then passes through the second electrode layer 2026. The
light that passes through the second electrode layer 2026 passes
through the glass substrate 2042, the diffusing layer 2070, the
selective reflecting layer 2066, and the substrate film 2064 and is
then emitted to the outside. The light reflected on any of the
boundaries between the layers from the luminescent layer 2024 to
the glass substrate 2042 goes in downward direction in the figure
and is then reflected on the first electrode layer 2022 or another
boundary, to emit outside. Since the light is emitted through such
a variety of paths, interference of light occurs. The increase or
decrease of the amount of light caused by the interference varies
depending on the wavelength, and therefore the relationship between
the viewing angle and the brightness varies depending on the
wavelength. This results in a change in color tone at different
viewing angles. When such light passes through the aforementioned
diffusing layer 2070 and further through the selective reflecting
layer 2066 having the aforementioned specific selective reflection
characteristics, the change in color tone at different viewing
angles may be reduced. In the present embodiment, the selective
reflecting layer 2066 is provided on one surface of the substrate
film 2064. However, also when the selective reflecting layers 2066
are provided on both surfaces of the substrate film 2064, similar
advantages may be obtained.
[0242] Any material may be used for the selective reflecting layer
2066, and the selective reflection may be based on any principle,
so long as the selective reflecting layer 2066 has the
aforementioned selective reflection range. A preferable example of
the selective reflecting layer may be a layer including a circular
polarization separating sheet. When the selective reflecting layer
includes a circular polarization separating sheet, the selective
reflecting layer allows only specific circularly polarized light in
the selective reflection range to pass therethrough and reflects
the remainder of the light (such as the remainder of the circularly
polarized light and linearly polarized light).
[0243] Examples of the circular polarization separating sheet may
include a layer containing a resin having cholesteric regularity.
One example thereof may be a circular polarization separating sheet
obtained by coating a transparent resin substrate with a
composition that can form a cholesteric liquid crystal phase (a
cholesteric liquid crystal composition) to obtain a liquid crystal
layer and then subjecting the layer to light irradiation and/or
heat treatment at least once to cure the composition. As the
cholesteric liquid crystal composition, a composition containing a
rod-shaped liquid crystal compound that is self-curable or curable
with another material may be used. Specific examples of the
cholesteric liquid crystal composition may include a rod-shaped
liquid crystal compound having a refractive index anisotropy value
.DELTA.n of 0.10 or larger and including two or more reactive
groups in one molecule.
[0244] No particular limitation is imposed on the method of
manufacturing the cholesteric liquid crystal composition, and the
cholesteric liquid crystal composition may be manufactured by
mixing the aforementioned essential component and an optional
component. Manufacture of the selective reflecting layer using the
cholesteric liquid crystal composition may be performed as follows.
The substrate film 2064 may be coated with the aforementioned
cholesteric liquid crystal composition to obtain a liquid crystal
layer, and then the layer is subjected to light irradiation and/or
heat treatment at least once to cure the composition.
[0245] No particular limitation is imposed on the material for the
substrate film 2064, and any substrate having a total light
transmittance of 80% or larger at a thickness of 1 mm. Specific
examples thereof may include single-layer and stacked films made of
synthetic resins such as alicyclic olefin polymers, chain olefin
polymers, for example, polyethylene and polypropylene,
triacetylcellulose, polyvinyl alcohol, polyimide, polyarylate,
polyester, polycarbonate, polysulfone, polyethersulfone, modified
acrylic polymers, epoxy resins, polystyrene, and acrylic resins. Of
these, alicyclic olefin polymers or chain olefin polymers are
preferred. Particularly, alicyclic olefin polymers are preferred
because of their transparency, low hygroscopicity, size stability,
light weight, etc. As in the diffusing layer 2070, particles that
impart light diffusibility may be added to the substrate film 2064.
With this configuration, the substrate film 2064 is formed of a
composition containing particles that provide light diffusibility
and serves also as the diffusing section. This is advantageous in
reducing thickness of the diffusing layer 2070.
[0246] If necessary, the substrate film may include an orientation
film. When the substrate film includes an orientation film, the
cholesteric liquid crystal composition applied thereto can be
aligned in the desired direction. The orientation film may be of a
thickness that is capable to give the liquid crystal layer the
desired orientation uniformity, and the thickness is preferably
0.001 to 5 .mu.m and more preferably 0.01 to 2 .mu.m. The liquid
crystal composition may be applied to the substrate film by any
know method such as reverse gravure coating, direct gravure
coating, die coating, or bar coating. If necessary, the coating
layer obtained by the application may be subjected to orientation
treatment before the coating layer is cured. The orientation
treatment may be performed by heating the coating layer at 50 to
150.degree. C. for 0.5 to 10 minutes. The orientation treatment can
give precise orientation to the cholesteric liquid crystal
layer.
[0247] After the optionally performed orientation treatment, the
cholesteric liquid crystal composition may be cured, for obtaining
a cured liquid crystal layer that is a cured produce of the
cholesteric liquid crystal composition. The curing process may be
performed as a combination of one or more times of light
irradiation and heat treatment. More specifically, the heating may
be performed under conditions at a temperature of, for example, 40
to 200.degree. C., preferably 50 to 200.degree. C., and more
preferably 50 to 140.degree. C. and for a time period of 1 second
to 3 minute and preferably 5 to 120 seconds. In the second
invention, the light used for the light irradiation encompasses not
only visible light but also ultraviolet light and any other
electromagnetic waves. Specifically, the light irradiation may be
performed as, for example, irradiation with light having a
wavelength of 200 to 500 nm for 0.01 seconds to 3 minutes. For
example, irradiation with weak ultraviolet light of 0.01 to 50
mJ/cm.sup.2 and heating may be alternately repeated a plurality of
times to form a circular polarization separating sheet having a
wide reflecting range. After performing the reflecting range
expansion by the aforementioned irradiation with weak ultraviolet
light etc., the liquid crystal compound may then be completely
polymerized by irradiation with relatively strong ultraviolet light
of, for example, 50 to 10,000 mJ/cm.sup.2 to form a cured liquid
crystal layer. The reflecting range expansion and the irradiation
with strong ultraviolet light may be performed in air, or all or
part of these processes may be performed in an atmosphere with a
controlled oxygen concentration (for example, a nitrogen
atmosphere).
[0248] In the second invention, the number of repetitions of the
sequence of the steps of applying the cholesteric liquid crystal
composition to the transparent resin substrate and curing the
composition is not limited to one. The sequence of application and
curing may be repeated a plurality of times to form two or more
cured liquid crystal layers.
[0249] In the selective reflecting layer described above, the dry
thickness of the cured liquid crystal layer is preferably 0.5 .mu.m
to 10.0 .mu.m and more preferably 1.0 .mu.m to 5.0 .mu.m. A dry
thickness of the cured liquid crystal layer of smaller than 0.5
.mu.m is not preferred because thereby sufficient reflecting
performance is not obtained. A dry thickness of larger than 10.0
.mu.m is also not preferred because thereby the amount of light
absorption by the cured liquid crystal layer increases. When the
cured liquid crystal layer includes two or more layers, the dry
thickness is the sum of the thicknesses of these layers. When the
cured liquid crystal layer includes only one layer, the dry
thickness is the thickness of that one layer.
[0250] By the aforementioned process, a stacked structure including
the substrate film 2064 and the selective reflecting layer 2066 may
be obtained. The stacked structure may be attached to the glass
substrate 2042 via the diffusing layer 2070, and the surface light
source device 2002 shown in FIG. 20 may thereby be obtained.
[0251] As in Embodiment 2-1, each of a lighting device of the
second invention and a backlight device of the second invention
includes the surface light source device, and the same effects as
those in Embodiment 2-1 can be obtained.
<Modifications>
[0252] The second invention is not limited to the aforementioned
embodiments.
[0253] In the configuration of Embodiment 2-1 described above, the
concave-convex structure includes concave portions. However, the
present invention is not limited thereto, and the concave-convex
structure may be configured to include convex portions. When the
concave-convex structure is configured to include convex portions,
flat portions similar to those described above may be or may not be
provided between adjacent convex portions.
[0254] In Embodiment 2-1 described above, the shape of the concave
portions is a regular quadrangular pyramid shape. However, the
shape of the concave portions may be any of polygonal pyramid
shapes such as triangular pyramid and octagonal pyramid shapes, a
conical shape, truncated polygonal pyramid shapes, a truncated
conical shape, a hemispherical shape, a groove shape, and
combinations thereof. When the concave-convex structure is
configured to include polygonal pyramids or truncated polygonal
pyramids, the oblique surfaces of the respective polygonal pyramids
need not be strictly flat surfaces and may be formed as curved
surfaces with slight fluctuations. When the concave-convex
structure is configured to include cones, their generating line is
not necessarily a completely straight line, as in the case of the
polygonal pyramids, and may be a curved line with slight
fluctuations. When polygonal pyramids or cones are employed as any
of the concave or convex portions, their apexes may have rounded
shapes. When polygonal pyramids or cones are employed, these are
not limited to right pyramids or right cones and may be oblique
pyramids or oblique cones.
[0255] In Embodiment 2-1 described above, all of the plurality of
concave portions have the same shape. However, different shapes may
coexist. For example, pyramid-shaped concave portions having
different sizes may coexist, or pyramid-shaped concave portions and
conical concave portions may coexist. Alternatively, concave
portions having a shape of a combination of a plurality of pyramids
and concave portions having a simple pyramid shape may coexist.
[0256] In Embodiment 2-1 described above, the concave portions are
aligned in two mutually orthogonal directions. However, the concave
portions may be aligned in non-orthogonal directions or in one or
three or more directions. In the embodiment, the flat portions are
provided between concave portions adjacent in any of the
aforementioned two directions. However, the flat portions may be
provided in only one direction or may be provided in none of
directions. However, the configuration with the flat portions is
advantageous in obtaining better light extraction efficiency and
also better mechanical strength of the light-emitting surface.
[0257] In Embodiment 2-2 described above, a layer containing a
resin having cholesteric regularity is used as the selective
reflecting layer. However, the present invention is not limited
thereto, and the selective reflecting layer may be a dielectric
multilayer film. Examples of the dielectric multilayer film may
include a band-pass filter formed using TiO.sub.2 as a
high-refractive index material and SiO.sub.2 as a low-refractive
index material and showing strong reflecting or transmitting
characteristics at specific wavelengths. These selective reflecting
layers have a common feature in that the wavelength range having
selective reflection characteristics is shifted when the viewing
angle is changed. These selective reflecting layers utilize the
characteristics that the transmittance of light having a wavelength
in the visible range changes in association with the aforementioned
shift.
[0258] In each of the aforementioned embodiments, the surface light
source device may include an optional layer. For example, a coating
layer may be provided on the concave-convex structure layer and the
coating layer may define the concave-convex structure of the
light-emitting surface. In addition, a sealing substrate may be
provided on the surface of the organic EL element that is on the
side opposite to the light-emitting surface 2040A.
[0259] In each of the aforementioned embodiments, the
concave-convex structure body or the selective reflecting member is
used as the light-distribution conversion unit. However, the
present invention is not limited thereto. For example, a
diffraction structure may also be used. A diffraction structure has
an ability for diffusing a specific wavelength strongly when an
appropriate pitch is selected. Also in this case, a combination
with another diffusing layer provides the effect of further
reducing color unevenness, as in each of the aforementioned
embodiments.
[0260] In the aforementioned embodiments, the light-emitting-side
member is provided only on one surface of the organic EL element
2020. However, light-emitting-side members may be provided on both
sides. In this case, it is preferable that the first electrode
layer described above is also formed as a transparent electrode.
Examples of this configuration are shown in FIGS. 26 and 27.
[0261] FIGS. 26 and 27 are vertical cross-sectional views
illustrating surface light source devices of embodiments of the
second invention. The surface light source device 2003 shown in
FIG. 26 is different from the surface light source device in
Embodiment 2-1 in that a first electrode 2028 serving as a
transparent electrode is provided in place of the first electrode
2022 serving as a reflecting electrode and that concave-convex
structure bodies 2040 are provided on both sides of the organic EL
element 2020, and the rest of the configuration is the same as that
in Embodiment 2-1. The surface light source device 2004 shown in
FIG. 27 is different from the surface light source device in
Embodiment 2-2 in that a first electrode 2028 serving as a
transparent electrode is provided in place of the first electrode
2022 serving as a reflecting electrode and that light-emitting-side
members 2060 are provided on both sides of the organic EL element
2020, and the rest of the configuration is the same as that in
Embodiment 2-2. An optional material such as a filler or an
adhesive agent may be present between the first electrode 2028 and
a substrate 2042, or a gap may be present therebetween. In the gap,
air or any other gas may be present so long as a problem such as
significant deterioration of the durability of the luminescent
layer 142 does not occur. Alternatively, the gap may be a vacuum
gap.
[0262] In each of the surface light source devices 2003 and 2004,
the first electrode layer 2028 is a transparent electrode.
Therefore, the light from the luminescent layer 2024 passes through
the first electrode layer 2028 and the second electrode layer 2026
and is then emitted from the light-emitting surfaces 2040A on the
upper and lower sides in the figures. Also in the surface light
source devices 2003 and 2004 in which light is emitted from both
the front and back surfaces, the same effects as those in
Embodiments 2-1 and 2-2 can be obtained.
[0263] In each of the surface light source devices 2003 and 2004,
the light incident on one of the light-emitting surfaces 2040A
generally passes through the surface light source device 2003 or
2004 and is emitted from the other light-emitting surface 2040A.
Therefore, the opposite side can be viewed with naked eyes through
the surface light source device 2003 or 2004, and the surface light
source device can be of a see-through type. This allows
diversification of the design.
[0264] In the aforementioned examples, identical
light-emitting-side members (concave-convex structure bodies 2040
or light-emitting-side members 2060) are disposed on the upper and
lower sides in the figures of the surface light source devices 2003
and 2004. However, a combination of different light-emitting-side
members may be provided. For example, the concave-convex structure
body 2040 may be provided on the surface of the first electrode
2028, and the light-emitting-side member 2060 may be provided on
the surface of the second electrode layer 2026.
[0265] For example, a layer formed of a composition containing
particles that impart light diffusibility may be disposed on the
light emitting side of a concave-convex structure layer 2047 or a
selective reflecting member 2062, to be used as the diffusing
section.
EXAMPLES
[0266] The present invention will be described in more detail by
way of Examples and Comparative Examples. However, the present
invention is not limited to the following Examples. In the
following, the refractive indexes of resins used are the refractive
indexes after curing.
Description of Examples and Comparative Examples with Regard to the
First Invention
Comparative Example 1-1
[0267] (C1-1: Formation of Organic EL Element and Production of
Surface Light Source Device (without Multi-Layered Body))
[0268] A transparent electrode layer with a thickness of 100 nm, a
hole transport layer with a thickness of 10 nm, a yellow
luminescent layer with a thickness of 20 nm, a blue luminescent
layer with a thickness of 15 nm, an electron transport layer with a
thickness of 15 nm, an electron injection layer with a thickness of
1 nm, and a reflecting electrode layer with a thickness of 100 nm
were formed in this order on one principal surface of a glass
substrate (refractive index: 1.53) with a thickness of 0.7 mm. All
the layers from the hole transport layer to the electron transport
layer were formed of organic materials. The yellow luminescent
layer and the blue luminescent layer have different luminescence
spectra.
[0269] The materials for forming the respective layers from the
transparent electrode layer to the reflecting electrode layer were
as follows.
[0270] Transparent electrode layer: tin-doped indium oxide
(ITO)
[0271] Hole transport layer:
4,4'-bis[N-(naphthyl)-N-phenylamino]biphenyl (.alpha.-NPD)
[0272] Yellow luminescent layer: .alpha.-NPD containing 1.5 wt % of
rubrene
[0273] Blue luminescent layer: 4,4'-dicarbazolyl-1,1'-biphenyl
(CBP) containing 10 wt % of iridium complex
[0274] Electron transport layer: phenanthroline derivative
(BCP)
[0275] Electron injection layer: lithium fluoride (LiF)
[0276] Reflecting electrode layer: Al
[0277] The transparent electrode layer was formed by reactive
sputtering with an ITO target, and the surface resistance was
100.OMEGA./.quadrature. or smaller. To form the layers from the
hole injection layer to the reflecting electrode layer, the glass
substrate having the transparent electrode layer formed thereon was
placed in a vacuum deposition apparatus, and the materials for the
layers from the hole injection layer to the reflecting electrode
layer were successively vapor-deposited by resistance heating. The
inner pressure of the system was 5.times.10.sup.-3 Pa, and the
evaporation rates were 0.1 to 0.2 nm/s.
[0278] Wiring leads for supplying an electric current were attached
to the electrode layers. The layers from the hole transport layer
to the reflecting electrode layer were sealed with a sealing
member, to thereby produce a surface light source device (without
multi-layered body). The obtained surface light source device had a
rectangular light-emitting surface that was capable of emitting
white light from the glass substrate side.
(C1-2: Evaluation)
[0279] As to the surface light source device obtained in (C1-1),
color unevenness at different viewing angles was measured in
accordance with the following.
[0280] A spectral radiance meter (BM-5, product of TOPCON
Corporation) was placed in front of (on the normal to) the
light-emitting surface (device light-emitting surface). A constant
current of 100 mA/m.sup.2 was applied to the surface light source
device, and chromaticity (x, y) was measured while the
light-emitting surface was rotated to change the observing
direction of the spectral radiance meter with respect to the
light-emitting surface. The observation direction was changed in a
direction parallel to the long edge of the light-emitting surface
in the range of -90 to 90.degree. with respect to the front
(normal) direction being set to 0.degree.. The measurement results
are shown in FIG. 28. In the observation angle range of
.+-.80.degree., (.DELTA.x, .DELTA.y) was (0.050, 0.058). .DELTA.x
is the amount of change in the coordinate value x, and .DELTA.y is
the amount of change in the coordinate value y.
Example 1-1
[0281] A multi-layered body 110 prepared by the following procedure
was attached to the surface light source device obtained in
Comparative Example 1-1 to produce the surface light source device
schematically shown in FIGS. 1 and 2, and the device was evaluated.
Although the organic EL element 140 schematically shown in FIG. 1
includes only three layers, the surface light source device
produced in this Example includes an organic EL element having a
larger number of luminescent layers.
(1-1: Preparation of Multi-Layered Body 110)
[0282] To a UV (ultraviolet) curable resin (urethane acrylate
resin, refractive index: n=1.54), a diffusing agent (silicone
resin, refractive index n=1.43) being spherical particles having a
mean diameter of 2 .mu.m was added in an amount of 10% (volume
ratio) based on the total amount of the composition. The mixture
was stirred for dispersing the particles. A resin composition was
thus obtained.
[0283] The obtained resin composition was applied to a substrate
film (ZEONOR Film, product of ZEON Corporation, refractive index:
1.53). Then a metal mold having a predetermined shape was pressed
against the coating layer of the resin composition, and the resin
composition was irradiated with ultraviolet rays from the substrate
film side at a cumulative light quantity of 1000 mJ/cm.sup.2, to
form a concave-convex structure layer on the substrate film, to
thereby obtain a multi-layered body 110 that was a rectangular film
with a layer structure of (the substrate film layer 112)-(the
concave-convex structure layer 111).
[0284] In the multi-layered body 110, the concave-convex structure
on the concave-convex structure layer 111 was composed of a
plurality of concave portions 113 having a regular quadrangular
pyramid shape and flat portions 114 disposed around the concave
portions, as shown in FIGS. 3 and 4. The angles (such as 11L and
11M) between the flat portions and the oblique surfaces
constituting the concave portions 113 were 60.degree.. The length
of the base edges (11E to 11H) of the concave portions 113 was 16
.mu.m. The spacings 11J and 11K between the concave portions 113
were 4 .mu.m and were constant intervals. The base edges of the
concave portions 113 were parallel to the long edge direction or
short edge direction of the multi-layered body 110. The thickness
of the concave-convex structure layer 111 (the thickness from the
flat portions 114 to a plane in contact with the substrate film)
was 34 .mu.m, and the thickness of the substrate film layer 112 was
100 .mu.m. The flat portion ratio was 36%.
(1-2: Surface Light Source Device (with Multi-Layered Body))
[0285] The multi-layered body 110 obtained in (1-1) was attached to
the surface of the glass substrate 131 in the surface light source
device obtained in (C1-1) in Comparative Example 1-1 via an
adhesive agent (CS9621, acrylic resin, refractive index: 1.49,
product of NITTO DENKO Corporation), to thereby obtain a surface
light source device having the layer structure of (the
multi-layered body 110)-(the bonding layer 121)-(the glass
substrate 131)-(the organic EL element 140). The thickness of the
bonding layer was 25 .mu.m.
(1-3: Evaluation)
[0286] As to the obtained surface light source device, color
unevenness was measured in the same manner as in (C1-2) of
Comparative Example 1-1. The results of the determination of x and
y values at different viewing angles are shown in FIG. 29. In the
viewing angle range of .+-.80.degree., (.DELTA.x, .DELTA.y) was
(0.011, 0.013). As can be seen from these results, the color
unevenness was significantly reduced as compared to that in
Comparative Example 1-1.
Comparative Example 1-2
[0287] A multi-layered body 110 was prepared and then a surface
light source device was obtained in the same manner as in Example
1-1 except that the diffusing agent for preparing the multi-layered
body 110 in (1-1) was not added to the material for the
concave-convex structure layer.
<Light Extraction Amount>
[0288] The light extraction amount of each of the surface light
source devices in Comparative Example 1-1, Example 1-1, and
Comparative Example 1-2 was determined from the results of the
measurement of the Y value in tristimulus values, and relative
amounts with respect to the light extraction amount in Comparative
Example 1-1 being set to 1 were determined. As a result, the light
extraction amount in Example 1-1 was 1.43 and the light extraction
amount in Comparative Example 1-2 was 1.37.
[0289] The surface light source device of Example 1-1 had
significantly improved light extraction efficiency as compared to
the surface light source device of Comparative Example 1-1 having
no concave-convex structure for improving light extraction
efficiency. The light extraction amount of the surface light source
device of Example 1-1 was also improved significantly as compared
to that of the surface light source device of Comparative Example
1-2 that had the same concave-convex structure as that of Example
1-1 but had no diffusing member.
Example 1-2
[0290] A multi-layered body 110 was prepared and then a surface
light source device was obtained in the same manner as in Example
1-1 except for the following modification.
[0291] Upon the preparation of the multi-layered body 110 in (1-1),
no diffusing agent was added to the material for the concave-convex
structure layer. Instead, an adhesive agent was prepared by adding
the same diffusing agent as that used in (1-1) to an acid-modified
polyolefin resin (COLNOVA MPO-B1300, product of NIHON LIMA Co.,
Ltd., refractive index: 1.49) in an amount of 10% (volume ratio)
based on the total amount of the adhesive agent. This adhesive
agent was used in (1-2) in place of the acrylic adhesive agent.
[0292] As to the obtained surface light source device, color
unevenness was measured in the same manner as in (C1-2) of
Comparative Example 1-1. The results of the determination of x and
y values at different viewing angles are shown in FIG. 30. In the
viewing angle range of .+-.80.degree., (.DELTA.x, .DELTA.y) was
(0.024, 0.034). As can be seen from these results, the color
unevenness was significantly reduced as compared to that in
Comparative Example 1-1.
Comparative Example 1-3
[0293] A multi-layered body 110 was prepared and then a surface
light source device was obtained in the same manner as in Example
1-2 except that the diffusing agent for preparing the multi-layered
body 110 in (1-1) was not added to the adhesive agent.
[0294] As to the obtained surface light source device, color
unevenness was measured in the same manner as in (C1-2) of
Comparative Example 1-1. The x and y values at different viewing
angles were determined. In the viewing angle range of
.+-.80.degree., (.DELTA.x, .DELTA.y) was (0.027, 0.041).
Comparative Example 1-4
[0295] A multi-layered body was prepared and then a surface light
source device was obtained in the same manner as in Example 1-2
except that, upon preparing the multi-layered body 110 in (1-1),
irradiation with ultraviolet rays was performed without using the
pressing metal mold for forming the concave-convex structure layer.
As a result, in place of the concave-convex structure layer, a
layer (thickness: 34 .mu.m) made of the same material as that for
the concave-convex structure layer but having no concave-convex
structure (i.e., a layer with a flat portion ratio of 100%) was
formed.
[0296] As to the obtained surface light source device, color
unevenness was measured in the same manner as in (C1-2) of
Comparative Example 1-1. The x and y values at different viewing
angles were determined. In the viewing angle range of
.+-.80.degree., (.DELTA.x, .DELTA.y) was (0.043, 0.053).
<Light Extraction Amount>
[0297] The light extraction amount of each of the surface light
source devices in Example 1-2, Comparative Example 1-3, and
Comparative Example 1-4 was determined from the results of the
measurement of the Y value in the tristimulus values, and relative
amounts with respect to the light extraction amount in Comparative
Example 1-1 being set to 1 were determined. As a result, the light
extraction amount in Example 1-2 was 1.38, the light extraction
amount in Comparative Example 1-3 was 1.29, and the light
extraction amount in Comparative Example 1-4 was 1.24.
[0298] The surface light source device of Example 1-2 had
significantly improved light extraction efficiency as compared to
the surface light source device of Comparative Example 1-1 having
no concave-convex structure for improving the light extraction
efficiency. The light extraction amount of the surface light source
device of Example 1-2 was also found to be improved significantly
as compared to that of the surface light source device of
Comparative Example 1-3 having the same concave-convex structure as
that of Example 1-2 but having no diffusing member and also to that
of the surface light source device of Comparative Example 1-4
having the same diffusing member as that of Example 1-2 but having
no concave-convex structure.
Reference Example 1-1
Abrasion Resistance
[0299] Several multi-layered bodies with different concave-convex
structure shapes were obtained in the same manner as in (1-1) in
Example 1-1 except that the shape of the metal mold was changed.
The obtained multi-layered bodies had the same shapes of the
concave portions, but the spacings 11J and 11K between the concave
portions were changed to obtain a variety of flat portion
ratios.
[0300] Each of the obtained several multi-layered bodies was placed
horizontally. The multi-layered body was vertically pressed against
a sapphire needle having a tip end with a diameter of 2 mm with a
load applied to the multi-layered body, and was moved in the
horizontal direction. Whether or not any scratch was formed by the
needle after the movement was visually determined. The load was
gradually reduced, and the load (g) at which no scratch was formed
was determined. The relationship between the load at which no
scratch is formed and the flat portion ratio is plotted in FIG. 31.
As can be seen from the results in FIG. 31, the larger the flat
portion ratio, the better the abrasion resistance.
Reference Example 1-2
Light Extraction Efficiency (Pyramids)
[0301] Light extraction efficiency of a surface light source device
was calculated by simulation, assuming that the device consists of
an organic EL element and a light-emitting surface structure layer
which are as follows.
[0302] The organic EL element was assumed to have a luminescent
layer, a transparent electrode, and a reflecting electrode. The
reflectivity of the reflecting electrode was set to 85%, and the
luminescent characteristics of the luminescent layer were assumed
to be in accordance with the Lambert distribution.
[0303] The light-emitting surface structure layer was assumed to be
a plate-like body having a thickness of 20 .mu.m and to consist of
a transparent material having a refractive index of 1.53 or a
material prepared by adding to the transparent material a diffusing
agent having a particle diameter of 2 .mu.m and a refractive index
of 1.43 in an amount of 7.5% based on the total volume. The
concave-convex structure on the light-emitting surface structure
layer was assumed to be a structure of concave portions having a
regular quadrangular pyramid shape (vertex angle: 60.degree., base
edges: 20 .mu.m) aligned as in the concave-convex structure layer
in FIG. 1. The spacings 11J and 11K between the concave portions
were changed so as to cause variety in the flat portion ratio.
[0304] Each light-emitting surface structure layer was placed on
the transparent electrode-side surface of the aforementioned
organic EL element to thereby constitute a surface light source
device.
[0305] Relative light extraction efficiencies with respect to an
instance wherein no diffusing agent was added and the flat portion
ratio was 100% being set to 1.00 were determined. The results are
shown in Table 1.
TABLE-US-00001 TABLE 1 60.degree. pyramid Light extraction
efficiency (relative value) Flat portion ratio Without diffusing
With diffusion (%) agent agent 0 1.84 1.90 36 1.83 1.89 64 1.76
1.85 84 1.57 1.76 100 1.00 1.60
Reference Example 1-3
Light Extraction Efficiency (Hemispheres)
[0306] Light extraction efficiency of a surface light source device
was calculated by simulation, assuming that the device consists of
an organic EL element and a light-emitting surface structure layer
which are as follows.
[0307] The organic EL element was assumed to have a luminescent
layer, a transparent electrode, and a reflecting electrode. The
reflectivity of the reflecting electrode was set to 85%, and the
luminescent characteristics of the luminescent layer were assumed
to be in accordance with the Lambert distribution.
[0308] The light-emitting surface structure layer was assumed to be
a plate-like body having a thickness of 20 .mu.m and to consist of
a transparent material having a refractive index of 1.53 or a
material prepared by adding to the transparent material a diffusing
agent having a particle diameter of 2 .mu.m and a refractive index
of 1.43 in an amount of 10.0% based on the total volume. The
concave-convex structure on the light-emitting surface structure
layer was assumed to be a structure of concave portions having a
hemispherical shape (diameter: 20 .mu.m) aligned as in the
concave-convex structure layer in FIG. 7. The spacing between the
concave portions was changed so as to cause variety in the flat
portion ratio.
[0309] Each light-emitting surface structure layer was placed on
the transparent electrode-side surface of the aforementioned
organic EL element to thereby constitute a surface light source
device.
[0310] Relative light extraction efficiencies with respect to an
instance wherein no diffusing agent was added and the flat portion
ratio was 100% being set to 1.00 were determined. The results are
shown in Table 2.
TABLE-US-00002 TABLE 2 Hemisphere Light extraction efficiency
(relative value) Flat portion ratio Without diffusing With
diffusion (%) agent agent 10 1.90 1.91 27 1.89 1.91 49 1.84 1.87 77
1.66 1.78 100 1.00 1.60
[0311] As can be seen from the results in Tables 1 and 2, when the
light-emitting surface structure layer contains no diffusing agent,
the light extraction efficiency significantly decreases as the flat
portion ratio increases. However, when the light-emitting surface
structure layer contains the diffusing agent, the significant
decrease in light extraction efficiency is suppressed, and
therefore high light extraction efficiency and high abrasion
resistance can be achieved simultaneously.
Example 1-3
[0312] A multi-layered body 110 was prepared and then a surface
light source device was obtained in the same manner as in Example
1-1 except that the shape of the metal mold for preparing the
multi-layered body 110 in (1-1) was changed. The obtained
multi-layered body had almost the same shape of the concave
portions as that in Example 1-1. However, the flat portions had
flat portions having two different heights as in the flat portions
914 and 915 shown in FIG. 16. The difference in height between the
two types of flat portions was 2 .mu.m.
[0313] An image reflected from the surface of the obtained surface
light source device with electric power turned off was observed. It
was observed that the rainbow unevenness was reduced.
[Example for Refractive Index of Bonding Layer]
[0314] In the embodiments according to the first invention, the
light-emitting surface structure layer is configured to include a
multi-layered body including a concave-convex structure layer and a
substrate film layer, a glass substrate, and a bonding layer for
bonding the multi-layered body and the glass substrate. When the
bonding layer is a layer having light diffusibility, it is
preferable that the refractive index of a matrix material
constituting the bonding layer is larger than the refractive index
of a matrix material constituting the bonding surface of the
multi-layered body (in this case, the substrate film layer). The
term "larger" means that the difference is at least 0.01. The
difference is preferably 0.05 or larger and more preferably 0.15 or
larger. In such a case, it is preferable that the difference
between the refractive index of the glass substrate and the
refractive index of the bonding layer is small. The term "small"
means that the difference is equal to or smaller than 0.15. The
difference is preferably 0.1 or smaller and more preferably 0.05 or
smaller. The advantages of such a configuration were calculated by
the following simulations.
[0315] The aforementioned configuration is applicable not only to
the first invention but also to the second invention. More
specifically, in the embodiments according to the second invention,
the concave-convex structure body is configured to include a
substrate made of, for example, glass and disposed on the surface
of the second electrode, a concave-convex structure main body, and
a bonding layer for bonding the substrate and the concave-convex
structure main body. When the bonding layer is a layer having light
diffusibility, it is preferable that the refractive index of a
matrix material constituting the bonding layer is larger than the
refractive index of a matrix material constituting the bonding
surface of the concave-convex structure main body. The term
"larger" means that the difference is at least 0.01. The difference
is preferably 0.05 or larger and more preferably 0.15 or larger. In
such a case, it is preferable that the difference between the
refractive index of the glass substrate and the refractive index of
the bonding layer is small. The term "small" means that the
difference is equal to or smaller than 0.15. The difference is
preferably 0.1 or smaller and more preferably 0.05 or smaller.
Example 1-4
[0316] Light extraction efficiency of a surface light source device
was calculated by simulation, assuming that the device corresponds
to those in FIG. 2 and consists of an organic EL element and a
light-emitting surface structure layer as follows.
[0317] The organic EL element was assumed to have a luminescent
layer having a refractive index of 1.9, a transparent electrode
also having a refractive index of 1.9, and a reflecting electrode.
The reflectivity of the reflecting electrode was set to 100%, and
the luminescent characteristics of the luminescent layer were
assumed to be in accordance with the Lambert distribution.
[0318] The concave-convex structure layer was assumed to be a
plate-like body having a thickness of 20 .mu.m and to consist of a
transparent material having a refractive index of 1.53, wherein
concave portions having a regular quadrangular pyramid shape
(vertex angle: 60.degree., base edges: 20 .mu.m) were aligned at a
pitch of 25 .mu.m as in the concave-convex structure layer in FIG.
1.
[0319] The substrate film layer was assumed to be a plate-like body
having a thickness of 100 .mu.m and a refractive index of 1.53.
[0320] The glass substrate was assumed to have a thickness of 500
.mu.m and to consist of a material having a refractive index of
1.7.
[0321] As the bonding layers, the following formulations 1 and 2
were simulated.
(Formulation 1) A plate-like body having a thickness of 15 .mu.m.
In the material used for the plate-like body in formulation 1, a
transparent material having a refractive index of 1.7 was used as a
matrix material, and a diffusing agent having a particle diameter
of 2 .mu.m and a refractive index of 1.43 was added to the
transparent material in a ratio of 30% based on the total volume.
(Formulation 2) A plate-like body having a thickness of 15 .mu.m.
In the material used for the plate-like body in formulation 2, a
transparent material having a refractive index of 1.53 was used as
a matrix material, and a diffusing agent having a particle diameter
of 2 .mu.m and a refractive index of 1.43 was added to the
transparent material in a ratio of 30% based on the total
volume.
[0322] In formulation 1, the difference between the refractive
index of the matrix material constituting the bonding layer and the
refractive index of the material constituting the substrate film
layer was 0.17 (=1.7-1.53), and the difference between the
refractive index of the matrix material constituting the bonding
layer and the refractive index of the material constituting the
glass substrate was 0 (=1.7-1.7).
[0323] In formulation 2, the difference between the refractive
index of the matrix material constituting the bonding layer and the
refractive index of the material constituting the substrate film
layer was 0 (=1.53-1.53), and the difference between the refractive
index of the matrix material constituting the bonding layer and the
refractive index of the material constituting the glass substrate
was 0.17 (=1.7-1.53).
[0324] In the aforementioned configurations, relative light
extraction efficiencies with formulation 1 and formulation 2 were
calculated. The light extraction efficiency with formulation 1 was
1.3 times the light extraction efficiency with formulation 2. As
can be seen from these results, the aforementioned configuration
realizes a further improvement of the light extraction
efficiency.
Description of Examples and Comparative Examples in Second
Invention
Comparative Example 2-1
(C1-1: Production of Organic EL Element and Production of Surface
Light Source Device)
[0325] A surface light source device was produced in the same
manner as in Comparative Example 1-1. The obtained surface light
source device is referred to as a surface light source device A.
The surface light source device A had a rectangular light-emitting
surface capable of emitting white light from the glass substrate
side.
(C1-2: Evaluation)
[0326] As to the obtained surface light source device A, color
unevenness at different viewing angles was measured in the same
manner as in Comparative Example 1-1.
[0327] In the viewing angle range of .+-.80.degree., (.DELTA.x,
.DELTA.y) was (0.050, 0.058).
[0328] In the second invention, the color unevenness of the surface
light source device is evaluated based on the difference in
chromaticity. The criterion of judgment of the difference in
chromaticity is (.DELTA.x, .DELTA.y)=(0.025, 0.025) or lower
because no practical problem occurs under this criterion.
Example 2-1
[0329] A concave-convex structure main body 2044 prepared by the
following procedure was attached to the surface light source device
A obtained in Comparative Example 2-1 to produce the surface light
source device schematically shown in FIG. 19, and the device was
evaluated. Although the organic EL element schematically shown in
FIG. 19 includes only three layers, the surface light source device
produced in this Example includes an organic EL element having a
larger number of luminescent layers.
(1-1: Production of Concave-Convex Structure Main Body 2044)
[0330] To a UV (ultraviolet) curable resin (urethane acrylate
resin, refractive index: n=1.54), a diffusing agent (silicone
resin, refractive index n=1.43) being spherical particles having a
mean diameter of 2 .mu.m was added in an amount of 10% (volume
ratio) based on the total amount of the composition. The mixture
was stirred for dispersing the particles. A resin composition was
thus obtained.
[0331] The obtained resin composition was applied to a substrate
film (ZEONOR Film, product of ZEON Corporation). Then a metal mold
having a predetermined shape was pressed against the coating layer
of the resin composition, and the resin composition was irradiated
with ultraviolet rays from the substrate film side at a cumulative
light quantity of 1000 mJ/cm.sup.2, to form a concave-convex
structure layer on the substrate film, to thereby obtain a
concave-convex structure main body 2044 that was a rectangular film
with a layer structure of (the substrate film)/(the concave-convex
structure layer).
[0332] In the concave-convex structure main body 2044, the
concave-convex structure 2041 on the concave-convex structure layer
2047 was composed of a plurality of concave portions having a
regular quadrangular pyramid shape and flat portions disposed
around the concave portions. The angles between the flat portions
and the oblique surfaces constituting the concave portions were
60.degree.. The length of the base edges of the concave portions
was 16 .mu.m. The spacings between the concave portions were 4
.mu.m and were constant intervals. The base edges of the concave
portions were parallel to the long edge direction or short edge
direction of the concave-convex structure main body 2044. The
thickness of the concave-convex structure layer 2047 (corresponding
to the thickness of the diffusing section) was 34 .mu.m, and the
thickness of the substrate film 2045 was 100 .mu.m. The flat
portion ratio was 36%.
(1-2: Production of Surface Light Source Device)
[0333] The concave-convex structure main body 2044 was attached to
the glass substrate of the surface light source device obtained in
Comparative Example 2-1 via an adhesive agent (CS9621, acrylic
resin, refractive index: 1.49, product of NITTO DENKO Corporation)
to obtain a surface light source device B. The thickness of the
bonding layer 2046 was 25 .mu.m.
(1-3: Evaluation)
[0334] As to the obtained surface light source device B, color
unevenness was measured in the same manner as in Comparative
Example 2-1. In the viewing angle range of .+-.80.degree.,
(.DELTA.x, .DELTA.y) was (0.011, 0.013). As can be seen from these
results, the color unevenness was significantly reduced as compared
to that in Comparative Example 2-1.
Comparative Example 2-2
[0335] A concave-convex structure main body 2044 was produced and
then a surface light source device C was obtained in the same
manner as in Example 2-1 except that the diffusing agent for
preparing the aforementioned concave-convex structure main body
2044 was not added to the material for the concave-convex structure
layer (i.e., embodiment with no diffusing section). The measurement
was then performed in the same manner as described above. In the
viewing angle range of .+-.80.degree., (.DELTA.x, .DELTA.y) was
(0.028, 0.040). As can be seen from these results, the color
unevenness was slightly reduced as compared to that in Comparative
Example 2-1
<Light Extraction Amount>
[0336] The light extraction amount of each of the surface light
source devices A to C in Comparative Example 2-1, Example 2-1, and
Comparative Example 2-2 was determined from the Y value in the
tristimulus values calculated based on the measurement results
described above, and relative amounts with respect to the light
extraction amount in Comparative Example 2-1 being set to 1 were
determined. As a result, the light extraction amount in Example 2-1
was 1.43 and the light extraction amount in Comparative Example 2-2
was 1.37. The surface light source device B of Example 2-1 had
significantly improved light extraction efficiency as compared to
the surface light source device A of Comparative Example 2-1 having
no concave-convex structure for improving light extraction
efficiency. The light extraction amount of the surface light source
device B of Example 2-1 was improved significantly also as compared
to that of the surface light source device C of Comparative Example
2-2 that had the same concave-convex structure 2041 as that of
Example 2-1 but had no layer for imparting light diffusibility.
Example 2-2
(2-1: Production of Transparent Resin Substrate Film)
[0337] Both sides of a film made of an alicyclic olefin polymer
(ZEONOR Film, product of ZEON Corporation) were subjected to corona
discharge treatment. One side of the treated film was coated with a
5% aqueous solution of polyvinyl alcohol using a #2 wire bar. The
coating layer was dried to form an orientation film having a
thickness of 0.1 .mu.m. Then the orientation film was subjected to
rubbing processing to prepare a transparent resin substrate film
including the orientation film.
(2-2: Formation of Cured Liquid Crystal Layer)
[0338] A cholesteric liquid crystal composition for forming a cured
liquid crystal layer was prepared with the following
composition.
[0339] Ratio of solids: 40% by weight
[0340] Liquid crystal compound (rod-shaped liquid crystal compound
with .DELTA.n (ne-no))=0.13): 95.70 parts by weight
[0341] Photo-polymerization initiator (product name: IRG907,
product of Ciba Specialty Chemicals): 3.1 parts by weight
[0342] Surfactant (product name: KH-40, product of AGC SEIMI
CHEMICAL Co., Ltd.): 0.11 parts by weight
[0343] Chiral agent (product name: LC756, product of BASF): 4.03
parts by weight
[0344] Solvent methyl ethyl ketone: 154.82 parts by weight
[0345] The cholesteric liquid crystal composition was applied using
a #4 wire bar to the surface of the transparent resin substrate
film prepared in (2-1) having the orientation film, said surface
having the orientation film formed thereon. The coating layer was
dried at 100.degree. C. for 5 minutes for orientation and ripening.
Then the coating layer was irradiated with ultraviolet rays at 1.0
mJ/cm.sup.2 (UV-A: 365 nm.+-.5 nm), held at 100.degree. C. for 1
minute, and then irradiated with ultraviolet rays at 500
mJ/cm.sup.2 to cure the coating layer. A circular polarization
separating sheet in which a selective reflecting layer having a dry
thickness of 2 .mu.m was disposed on the substrate film via the
orientation film was thereby produced. The reflection spectrum of
the obtained circular polarization separating sheet was measured
using a spectrophotometer (JASCO V-550, product of JASCO
Corporation). The circular polarization separating sheet had
selective reflection characteristics shown in FIG. 22.
(2-3: Production of Organic EL Element)
[0346] An organic EL element including a second electrode layer, a
luminescent layer, and a first electrode layer was disposed on one
surface of a glass substrate having a thickness of 1.1 mm to obtain
a surface light source device E. At this stage, an electric current
was applied to the organic EL element in the surface light source
device E, and the distributions of blue light having a wavelength
of 480 nm and yellow light having a wavelength of 575 nm emitted
from the glass substrate were measured. The results shown in FIG.
23 were obtained. As to the obtained surface light source device E,
color unevenness was measured in the same manner as in Comparative
Example 2-1. In the viewing angle of .+-.80.degree., (.DELTA.x,
.DELTA.y) was (0.129, 0.128).
(2-4: Preparation of Diffusing Layer)
[0347] To an acid-modified polyolefin resin (refractive index:
1.49, COLNOVA MPO-B130C, product of NIHON CIMA Co., Ltd.), the same
diffusing agent as that used in (1-1) of Example 2-1 was added in
an amount of 20% (volume ratio) based on the total amount of the
adhesive agent, to prepare an adhesive agent (diffusing layer).
(2-5: Production of Surface Light Source Device)
[0348] The adhesive agent prepared in (2-4) was applied to the
other surface of the glass substrate to a thickness of 30 .mu.m
(the adhesive agent layer acts as the diffusing section), and then
the circular polarization separating sheet was attached thereto so
that the selective reflecting layer faces the adhesive agent, to
produce a surface light source device D having the structure shown
in FIG. 20. An electric current was applied to the obtained surface
light source device D, and the distributions of blue light having a
wavelength of 480 nm and yellow light having a wavelength of 575 nm
emitted from the light-emitting surface 2040A were measured. The
results shown in FIG. 25 were obtained.
(2-6: Evaluation)
[0349] As to the obtained surface light source device D, color
unevenness was measured in the same manner as in Comparative
Example 2-1. In the viewing angle range of .+-.80.degree.,
(.DELTA.x, .DELTA.y) was (0.017, 0.017). As can be seen from these
results, the color unevenness was significantly reduced as compared
to that in the surface light source device E.
Comparative Example 2-3
[0350] A surface light source device F was obtained in the same
manner as in Example 2-2 except that the diffusing agent was not
added to the adhesive agent in (2-4), and the same measurement as
above was performed. In the viewing angle range of .+-.80.degree.,
(.DELTA.x, .DELTA.y) was (0.092, 0.091). As can be seen from these
results, the color unevenness was slightly improved as compared to
that in the surface light source device E. However, the improvement
was not as high as that in the surface light source device D, and
the color unevenness elimination effect was not sufficient. An
electric current was applied to the obtained surface light source
device E, and the distributions of blue light having a wavelength
of 480 nm and yellow light having a wavelength of 575 nm emitted
from the light-emitting surface were measured. The results shown in
FIG. 24 were obtained.
[0351] As is clear from the comparison between the results in FIGS.
23 to 25, with the surface light source device of the present
invention that includes, in addition to the luminescent element,
the diffusing layer (adhesive agent layer) and the circular
polarization separating sheet, the difference between the
distribution of blue light and the distribution of yellow light is
smaller than that in a luminescent element provided without a
circular polarization separating sheet or without a diffusing
layer, and the change in color tone at different viewing angles is
small.
Reference Example 2-1
[0352] A description will be given of the evaluation of color
unevenness when the concave-convex structure and selective
reflecting layer used in the present invention are not provided but
a diffusing layer is provided on the light emitting side of the
organic EL element. The evaluation was performed with a variation
in the amount of diffusing agent added.
[0353] To a UV (ultraviolet) curable resin (urethane acrylate
resin, refractive index: n=1.54), a diffusing agent (silicone
resin, refractive index n=1.43) being spherical particles having a
mean diameter of 2 .mu.m was added in an amount of 10% (volume
ratio) based on the total amount of the composition. The mixture
was stirred for dispersing the particles. A resin composition was
thus obtained. The obtained resin composition was applied to the
glass substrate of the surface light source device used in Example
2-1 and was cured by irradiation with ultraviolet rays to form a
diffusing layer having a predetermined thickness on the surface of
the organic EL element. More specifically, the amount of the
applied resin composition, for example, was changed to produce
three diffusing layers having thicknesses of 30 .mu.m, 50 .mu.m,
and 100 .mu.m, respectively. For each of the surface light source
devices having these diffusing layers, difference in chromaticity
was determined. Separately, diffusing layers were formed on the
glass substrates so as to have thicknesses of 30 .mu.m, 50 .mu.m,
and 100 .mu.m, and the total light transmittances were measured.
The results are shown in Table 3.
TABLE-US-00003 TABLE 3 1 2 3 Thickness .mu.m 30 50 100 Chromaticity
.DELTA.x -- 0.026 0.025 0.016 difference .DELTA.y -- 0.046 0.029
0.021 Total light % 87 81 73 transmittance
[0354] As shown in Reference Example 2-1, in order to improve the
difference in chromaticity to the same extent as that in Examples
2-1 and 2-2 (to meet the pass criterion), the thickness of the
diffusing layer must be increased to about 100 .mu.m. However, in
each of Examples 2-1 and 2-2, the thickness of the layer
constituting the diffusing section is about 30 .mu.m. Therefore,
the diffusing section can be in a thin thickness that does not
impair productivity and does not hinder a reduction in total
thickness.
EXPLANATION OF NUMERALS
[0355] 10: Surface light source device [0356] 10U: Device
light-emitting surface [0357] 100: Light-emitting surface structure
layer [0358] 110: Multi-layered body [0359] 111: Concave-convex
structure layer [0360] 112: Substrate film layer [0361] 113:
Concave portion [0362] 114: Flat portion [0363] 11A-11D: Oblique
surface [0364] 11E-11H: Base edge [0365] 11P: Apex [0366] 121:
Bonding layer [0367] 131: Glass substrate [0368] 140: Organic EL
element [0369] 141: Electrode layer [0370] 142: Luminescent layer
[0371] 143: Electrode layer [0372] 146: Electrode layer [0373] 151:
Sealing substrate [0374] 20: Surface light source device [0375]
20U: Device light-emitting surface [0376] 200: Light-emitting
surface structure layer [0377] 210: Multi-layered body [0378] 211:
Concave-convex structure layer [0379] 213: Concave portion [0380]
214: Flat portion [0381] 30: Surface light source device [0382]
30U: Device light-emitting surface [0383] 300: Light-emitting
surface structure layer [0384] 310: Multi-layered body [0385] 311:
Concave-convex structure layer [0386] 313: Concave portion [0387]
314: Flat portion [0388] 40: Surface light source device [0389]
40U: Device light-emitting surface [0390] 400: Light-emitting
surface structure layer [0391] 410: Multi-layered body [0392] 411:
Concave-convex structure layer [0393] 413: Concave portion [0394]
41T, 41U, 41V: Oblique surface [0395] 414: Flat portion [0396] 50:
Surface light source device [0397] 551: Reflecting member [0398]
552: Reflecting member substrate [0399] 553: Gap [0400] 80: Surface
light source device [0401] 80U: Device light-emitting surface
[0402] 800: Light-emitting surface structure layer [0403] 810:
Multi-layered body [0404] 811: Concave-convex structure layer
[0405] 813: Concave portion [0406] 814: Flat portion [0407] 815:
Boundary portion between adjacent concave portions [0408] 816:
Concave portion [0409] 821: Concave-convex structure layer [0410]
90: Surface light source device [0411] 90U: Device light-emitting
surface [0412] 900: Light-emitting surface structure layer [0413]
910: Multi-layered body [0414] 911: Concave-convex structure layer
[0415] 913: Concave portion [0416] 914, 915: Flat portion [0417]
1000: Surface light source device [0418] 2001, 2002, 2003, 3004:
Surface light source device [0419] 2020: Organic EL element [0420]
2022: First electrode layer [0421] 2024: Luminescent layer [0422]
2026: Second electrode layer [0423] 2028: First electrode layer
[0424] 2040: Concave-convex structure body [0425] 2040A:
Light-emitting surface [0426] 2041: Concave-convex structure [0427]
2042: Substrate [0428] 2044: Concave-convex structure main body
[0429] 2045: Base substrate [0430] 2046: Bonding layer [0431] 2047:
Concave-convex structure layer [0432] 2048: Concave portion [0433]
2048A: Oblique surface [0434] 2049: Flat portion [0435] 2060:
Light-emitting-side member [0436] 2062: Selective reflecting member
[0437] 2064: Substrate film [0438] 2066: Selective reflecting layer
[0439] 2070: Diffusing layer
* * * * *