U.S. patent application number 12/988764 was filed with the patent office on 2011-02-17 for flexible substrate.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Daisuke Hattori, Takeshi Murashige, Tatsuki Nagatsuka, Yoshimasa Sakata, Takashi Yamaoka.
Application Number | 20110039097 12/988764 |
Document ID | / |
Family ID | 41216803 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110039097 |
Kind Code |
A1 |
Murashige; Takeshi ; et
al. |
February 17, 2011 |
FLEXIBLE SUBSTRATE
Abstract
There is provided a flexible substrate having excellent
flexibility and gas barrier properties. A flexible substrate 100
according to the present invention includes: a base material 20
including an inorganic glass 10 and resin layers 11 and 11' placed
on both sides of the inorganic glass 10; and an inorganic thin film
12 placed on a side of one of the resin layers where the inorganic
glass is not placed, wherein the inorganic thin film 12 is formed
on at least a peripheral edge of one surface of the base
material.
Inventors: |
Murashige; Takeshi; ( Osaka,
JP) ; Yamaoka; Takashi; (Osaka, JP) ; Hattori;
Daisuke; ( Osaka, JP) ; Sakata; Yoshimasa;
(Osaka, JP) ; Nagatsuka; Tatsuki; (Osaka,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
41216803 |
Appl. No.: |
12/988764 |
Filed: |
April 17, 2009 |
PCT Filed: |
April 17, 2009 |
PCT NO: |
PCT/JP2009/057737 |
371 Date: |
November 3, 2010 |
Current U.S.
Class: |
428/337 ;
428/426; 428/441 |
Current CPC
Class: |
H05K 1/11 20130101; H05K
5/0017 20130101; Y02E 10/549 20130101; H01L 51/0097 20130101; Y10T
428/266 20150115; H01L 51/5256 20130101; Y10T 428/31645 20150401;
H05K 1/0306 20130101; H01L 51/5253 20130101; H05K 1/0353 20130101;
B32B 17/064 20130101; H01L 2251/5338 20130101 |
Class at
Publication: |
428/337 ;
428/426; 428/441 |
International
Class: |
B32B 17/06 20060101
B32B017/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2008 |
JP |
2008-114372 |
Claims
1. A flexible substrate, comprising: a base material including an
inorganic glass and resin layers placed on both sides of the
inorganic glass; and an inorganic thin film placed on a side of one
of the resin layers where the inorganic glass is not placed,
wherein the inorganic thin film is formed on at least a peripheral
edge of one surface of the base material.
2. A flexible substrate according to claim 1, wherein the inorganic
thin film is formed on an entire surface of the one surface of the
base material.
3. A flexible substrate according to claim 1, further comprising a
smoothing layer, the smoothing layer being placed on a side of the
inorganic thin film where the resin layers are not placed.
4. A flexible substrate according to claim 3, further comprising
another inorganic thin film, wherein the another inorganic thin
film is placed on a side of the smoothing layer where the resin
layers are not placed.
5. A flexible substrate according to claim 1, wherein the flexible
substrate has a thickness (total thickness) of 600 .mu.m or
less.
6. A flexible substrate according to claim 1, wherein the resin
layers are each formed of a resin composition containing an
epoxy-based resin and/or an oxetane-based resin as a main
component.
7. A flexible substrate according to claim 1, wherein the resin
layers each contain a thermoplastic resin having repeating units
represented by a general formula (X) and/or a general formula (Y):
##STR00013## where: R.sub.1 represents a substituted or
unsubstituted aryl group having 6 to 24 carbon atoms, a
cycloalkylene group having 4 to 14 carbon atoms, or a linear or
branched alkylene group having 1 to 8 carbon atoms; R.sub.2
represents a substituted or unsubstituted aryl group having 6 to 24
carbon atoms, a linear or branched alkyl group having 1 to 8 carbon
atoms, a linear or branched alkylene group having 1 to 8 carbon
atoms, a cycloalkyl group having 5 to 12 carbon atoms, a
cycloalkylene group having 5 to 12 carbon atoms, or a hydrogen
atom; R.sub.3 and R.sub.4 each independently represent a linear or
branched alkyl group having 1 to 8 carbon atoms, a hydrogen atom, a
linear or branched alkylene group having 1 to 8 carbon atoms, a
cycloalkyl group having 5 to 12 carbon atoms, or a cycloalkylene
group having 5 to 12 carbon atoms; A represents a carbonyl group,
or a linear or branched alkylene group having 1 to 8 carbon atoms;
m represents an integer of 0 to 8; and n represents an integer of 0
to 4.
8. A flexible substrate according to claim 1, wherein the resin
layers each contain a thermoplastic resin having one or more
repeating units represented by a general formula (Z): ##STR00014##
where: R.sup.1 represents a substituted or unsubstituted aryl group
having 6 to 24 carbon atoms, a linear or branched alkylene group
having 1 to 8 carbon atoms, or a cycloalkylene group having 4 to 14
carbon atoms, or an oxygen atom; and R.sup.2 represents a
substituted or unsubstituted aryl group having 6 to 24 carbon
atoms, a linear or branched alkyl group having 1 to 8 carbon atoms,
a linear or branched alkylene group having 1 to 8 carbon atoms, a
cycloalkyl group having 5 to 12 carbon atoms, a cycloalkylene group
having 5 to 12 carbon atoms, or a hydrogen atom.
9. A flexible substrate according to claim 1, wherein the resin
layers each contain a polyether sulfone-based resin.
10. A flexible substrate according to claim 1, wherein the
inorganic thin film contains at least one kind of an inorganic
compound selected from the group consisting of oxides, nitrides,
hydrides, and composite compounds of them.
11. A flexible substrate according to claim 10, wherein the
inorganic compound has an amorphous structure.
12. A flexible substrate according to claim 1, wherein the
inorganic thin film is of a three-layer configuration having an
inorganic oxide layer, an inorganic nitride layer, and an inorganic
oxide layer.
13. A flexible substrate according to claim 1, further comprising a
transparent electrode placed on a side of the inorganic thin film
where the resin layers are not placed.
14. An organic electroluminescence display apparatus comprising the
flexible substrate according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a flexible substrate, and
more specifically, to a flexible substrate having excellent gas
barrier properties.
BACKGROUND ART
[0002] In association with the development of an image
communication technology, the thinning of flat panel displays
(FPDs) has been advanced in recent years. A substrate that brings
together flexibility and impact resistance will be indispensable
for the realization of a curved surface display of a large panel
seeking for a high realistic sensation and an improvement in
flexibility of a take-up type portable terminal or the like
pursuing portability and convenience.
[0003] Glass substrates have been widely used as substrates for the
FPDs. However, when one attempts to perform the thinning of any
such glass substrate for imparting flexibility to the glass
substrate, impact resistance becomes insufficient, and hence, for
example, the following problem arises. That is, the glass substrate
is apt to crack in a production process for an FPD.
[0004] In view of the foregoing, investigations have been conducted
on the use of resin films each of which has excellent impact
resistance and has a lightweight and excellent flexibility as
substrates for the FPDs instead of the glass substrates. However,
none of the resin films can provide sufficient gas barrier
properties (such as oxygen-blocking property and water
vapor-blocking property) requested of a substrate for an FPD
alone.
[0005] A gas barrier laminate material obtained by laminating a
metal oxide film or the like and an organic layer on a base
material has been proposed for improving the gas barrier properties
(see Patent Document 1). However, the gas barrier properties of the
laminate material of Patent Document 1 are still not enough for the
laminate material to be used in an organic electroluminescence
display apparatus of which high gas barrier properties are
requested out of the FPDs.
Prior Art Document
Patent Document
[0006] [Patent Document 1] JP 2004-82598 A
SUMMARY OF THE INVENTION
Problems to be solved by the invention
[0007] The present invention has been made to solve the
above-mentioned conventional problems, and an object of the present
invention is to provide a flexible substrate having excellent
flexibility and gas barrier properties.
Means for Solving the Problems
[0008] A flexible substrate according to an embodiment of the
present invention includes: a base material including an inorganic
glass and resin layers placed on both sides of the inorganic glass;
and an inorganic thin film placed on a side of one of the resin
layers where the inorganic glass is not placed, wherein the
inorganic thin film is formed on at least a peripheral edge of one
surface of the base material.
[0009] In a preferred embodiment of the invention, the inorganic
thin film is formed on an entire surface of the one surface of the
base material.
[0010] In a preferred embodiment of the invention, the flexible
substrate further includes a smoothing layer, the smoothing layer
being placed on a side of the inorganic thin film where the resin
layers are not placed.
[0011] In a preferred embodiment of the invention, the flexible
substrate further includes another inorganic thin film, wherein the
another inorganic thin film is placed on a side of the smoothing
layer where the resin layers are not placed.
[0012] In a preferred embodiment of the invention, the flexible
substrate has a thickness (total thickness) of 600 .mu.m or
less.
[0013] In a preferred embodiment of the invention, the resin layers
are each formed of a resin composition containing an epoxy-based
resin and/or an oxetane-based resin as a main component.
[0014] In a preferred embodiment of the invention, the resin layers
each contain a thermoplastic resin having repeating units
represented by a general formula (X) and/or a general formula
(Y):
##STR00001##
where:
[0015] R.sub.1 represents a substituted or unsubstituted aryl group
having 6 to 24 carbon atoms, a cycloalkylene group having 4 to 14
carbon atoms, or a linear or branched alkylene group having 1 to 8
carbon atoms; R.sub.2 represents a substituted or unsubstituted
aryl group having 6 to 24 carbon atoms, a linear or branched alkyl
group having 1 to 8 carbon atoms, a linear or branched alkylene
group having 1 to 8 carbon atoms, a cycloalkyl group having 5 to 12
carbon atoms, a cycloalkylene group having 5 to 12 carbon atoms, or
a hydrogen atom; R.sub.3 and R.sub.4 each independently represent a
linear or branched alkyl group having 1 to 8 carbon atoms, a
hydrogen atom, a linear or branched alkylene group having 1 to 8
carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or a
cycloalkylene group having 5 to 12 carbon atoms; A represents a
carbonyl group, or a linear or branched alkylene group having 1 to
8 carbon atoms; m represents an integer of 0 to 8; and n represents
an integer of 0 to 4.
[0016] In a preferred embodiment of the invention, the resin layers
each contain a thermoplastic resin having one or more repeating
units represented by a general formula (Z):
##STR00002##
where:
[0017] R.sup.1 represents a substituted or unsubstituted aryl group
having 6 to 24 carbon atoms, a linear or branched alkylene group
having 1 to 8 carbon atoms, or a cycloalkylene group having 4 to 14
carbon atoms, or an oxygen atom; and R.sup.2 represents a
substituted or unsubstituted aryl group having 6 to 24 carbon
atoms, a linear or branched alkyl group having 1 to 8 carbon atoms,
a linear or branched alkylene group having 1 to 8 carbon atoms, a
cycloalkyl group having 5 to 12 carbon atoms, a cycloalkylene group
having 5 to 12 carbon atoms, or a hydrogen atom.
[0018] In a preferred embodiment of the invention, the resin layers
each contain a polyether sulfone-based resin.
[0019] In a preferred embodiment of the invention, the inorganic
thin film contains at least one kind of an inorganic compound
selected from the group consisting of oxides, nitrides, hydrides,
and composite compounds of them. In a preferred embodiment of the
invention, the inorganic compound has an amorphous structure.
[0020] In a preferred embodiment of the invention, the inorganic
thin film is of a three-layer configuration having an inorganic
oxide layer, an inorganic nitride layer, and an inorganic oxide
layer.
[0021] In a preferred embodiment of the invention, the flexible
substrate further includes a transparent electrode placed on a side
of the inorganic thin film where the resin layers are not
placed.
[0022] According to another aspect of the present invention, an
organic electroluminescence display apparatus is provided. The
organic electroluminescence display apparatus includes the flexible
substrate as described above.
EFFECTS OF THE INVENTION
[0023] According to the present invention, there can be provided a
flexible substrate having excellent flexibility and gas barrier
properties as a result of the possession of an inorganic glass,
resin layers, and an inorganic thin film. To be specific, the
inorganic glass placed at the center can function as a gas barrier
layer. In addition, a gas or moisture which penetrates from an end
of each resin layer can be blocked by the inorganic thin film. As a
result, the flexible substrate can be excellent in gas barrier
properties. The use of such flexible substrate can realize an
organic electroluminescence (EL) display apparatus capable of
continuing a good emission state for a long time period (that is,
having excellent storage stability). Meanwhile, the inorganic glass
can suppress the thermal expansion of each resin layer having a
high coefficient of linear expansion, and can provide a substrate
having a small coefficient of linear expansion. The rupture of the
inorganic glass is generally considered to be caused by the
concentration of a stress on minute defects on its surface, and the
thinning of the inorganic glass is difficult because the smaller
the thickness of the inorganic glass, the higher the possibility
that the rupture occurs. In the flexible substrate of the present
invention, the resin layers placed on both sides of the inorganic
glass alleviate a stress in the direction in which the inorganic
glass is torn toward the defects at the time of its deformation.
Accordingly, the thinning and weight reduction of the inorganic
glass can be achieved. As a result, the flexible substrate can be
excellent in flexibility, secondary processability, and
operability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic sectional view of a flexible substrate
according to one embodiment of the present invention.
[0025] FIG. 2 is a schematic plan view of a flexible substrate
according to another embodiment of the present invention.
[0026] FIG. 3 is a schematic sectional view of a flexible substrate
according to still another embodiment of the present invention.
[0027] FIG. 4 is a schematic sectional view of a flexible substrate
according to still another embodiment of the present invention.
[0028] FIG. 5 is a schematic sectional view of an organic EL
display apparatus according to one embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
A. Entire Configuration of Flexible Substrate
[0029] FIG. 1 is a schematic sectional view of a flexible substrate
according to a preferred embodiment of the present invention. The
flexible substrate 100 includes a base material 20 and an inorganic
thin film 12 formed on at least one surface of the base material
20. The base material 20 includes an inorganic glass 10, and resin
layers 11 and 11' placed on both sides of the inorganic glass 10.
The inorganic thin film 12 is placed on the side of the resin layer
11 where the inorganic glass 10 is not placed. FIG. 2 is a plan
view of the flexible substrate according to another preferred
embodiment of the present invention. In the flexible substrate 100,
the inorganic thin film 12 is placed on the peripheral edge of one
surface of the base material 20. The inorganic thin film may be
formed only on the peripheral edge of the one surface of the base
material as illustrated in FIG. 2, or may be formed on the entire
surface of the one surface of the base material as illustrated in
FIG. 1. Such configuration provides a flexible substrate having
excellent flexibility and gas barrier properties. When the resin
layer on the side of the flexible substrate where an organic EL
device is formed contains a component responsible for outgassing
such as a monomer of the resin, a solvent, moisture, or an
additive, the inorganic thin film is preferably formed so as to
cover not only the entire surface of the one surface of the base
material (substantially the surface of the resin layer) but also
the entirety of the base material.
[0030] FIG. 3 is a schematic sectional view of a flexible substrate
according to still another preferred embodiment of the present
invention. The flexible substrate 100' further includes a smoothing
layer 13 in addition to the inorganic glass 10, the resin layers 11
and 11', and the inorganic thin film 12. The smoothing layer 13 is
placed on the side of the inorganic thin film 12 where the resin
layer 11 is not placed. Providing the smoothing layer smoothes
unevenness on the surface of the inorganic thin film, and hence a
flexible substrate having excellent surface smoothness can be
obtained. FIG. 4 is a schematic sectional view of a flexible
substrate according to still another preferred embodiment of the
present invention. The flexible substrate 100'' further includes
another inorganic thin film 12' and another smoothing layer 13' on
the surface of the smoothing layer 13. In this embodiment, the
other inorganic thin film 12' is placed on the side of the
smoothing layer 13 where the resin layer 11 is not placed. As
described above, the flexible substrate of the present invention
can include a plurality of inorganic thin films. Providing the
plurality of inorganic thin films can provide additionally
excellent gas barrier properties. In addition, the flexible
substrate of the present invention can include a plurality of
smoothing layers. A smoothing layer is preferably placed on the
side of the adjacent inorganic thin film where no resin layer is
placed like the illustrated example.
[0031] The resin layers 11 and 11' placed on both sides of the
inorganic glass 10 may be formed of the same material, or may be
formed of different materials. The resin layers are preferably
formed of the same material. The thickness of each of the resin
layers 11 and 11' can be set to any appropriate thickness. To be
specific, the resin layers may be substantially identical to each
other in thickness, or may be different from each other in
thickness in consideration of, for example, a stress applied to the
base material at the time of the step of forming the inorganic thin
film. The thickness of the resin layer on the side where the
inorganic thin film is formed is preferably made large because of,
for example, the following reason. That is, the resin layer can be
prevented from being convexed toward the inorganic thin film in the
step of forming the inorganic thin film. Such configuration can
provide a flexible substrate having a small coefficient of linear
expansion, and having extremely excellent operability and secondary
processability.
[0032] It is preferred that the resin layers 11 and 11' be directly
formed on the inorganic glass 10. To be specific, the resin layers
11 and 11' are each formed on the inorganic glass without through
any adhesion layer. Such configuration can provide an additionally
thin flexible substrate. It should be noted that the resin layers
11 and 11' may each be fixed to the inorganic glass through an
adhesion layer. The adhesion layer is formed of any appropriate
adhesive or pressure-sensitive adhesive.
[0033] The inorganic glass has a thickness d.sub.g of preferably 1
to 400 .mu.m, more preferably 10 to 200 .mu.m, and particularly
preferably 30 to 100 .mu.m. The thickness of the inorganic glass
can be reduced by placing the resin layers on both sides of the
inorganic glass.
[0034] The resin layers each have a thickness d.sub.r of preferably
1 to 250 .mu.m, and more preferably 10 to 125 .mu.m. As described
above, the resin layers 11 and 11' may be identical to or different
from each other in thickness. The resin layers have a total
thickness d.sub.rsum of preferably 2 to 250 .mu.m, and more
preferably 20 to 250 .mu.m.
[0035] A ratio d.sub.rsum/d.sub.g of the total thickness d.sub.rsum
of the resin layers to the thickness d.sub.g of the inorganic glass
is preferably 0.01 to 10, more preferably 0.1 to 5, and
particularly preferably 0.8 to 2.5. When the total thickness of the
resin layers and the thickness of the inorganic glass have such
relationship, the thermal expansion of each resin layer can be
suppressed by the inorganic glass, and at the same time, the
inorganic glass can be reinforced. As a result, coexistence of low
linear expansion and a mechanical strength can be achieved. A ratio
{(d.sub.r-d.sub.g)/d.sub.g} of a difference (d.sub.r-d.sub.g)
between the thickness d.sub.r of each resin layer and the thickness
d.sub.g of the inorganic glass to the thickness d.sub.g of the
inorganic glass is preferably -0.95 to 1.5, and more preferably
-0.6 to 0.3. When the thicknesses have such relationship, the
warping or wave of the resultant flexible substrate can be
extremely suppressed because thermal stresses are uniformly applied
to both surfaces of the inorganic glass even at the time of a heat
treatment.
[0036] The inorganic thin film has a thickness of preferably 1 nm
to 20 .mu.m, more preferably 5 nm to 15 .mu.m, and particularly
preferably 10 nm to 10 .mu.m. When the inorganic thin film has such
thickness, additionally excellent gas barrier properties can be
obtained.
[0037] The smoothing layer has a thickness of preferably 1 nm to 20
.mu.m, more preferably 5 nm to 10 .mu.m, and particularly
preferably 10 nm to 5 .mu.m. Providing a smoothing layer having
such thickness smoothes the unevenness on the surface of the
inorganic thin film, and hence a flexible substrate additionally
having excellent surface smoothness can be obtained.
[0038] The thickness (total thickness) of the above-mentioned
flexible substrate can be set to any appropriate value depending on
the configuration of the flexible substrate. The thickness is
preferably 600 .mu.m or less, more preferably 1 to 400 .mu.m, and
particularly preferably 20 to 200 .mu.m.
[0039] The average coefficient of linear expansion at 170.degree.
C. of the flexible substrate is preferably 20 ppm.degree. C..sup.-1
or less, and more preferably 10 ppm.degree. C..sup.-1 or less. When
the average coefficient of linear expansion falls within the
above-mentioned range, for example, even if the substrate is
subjected to a plurality of heat treatment steps, the displacement
of pixels, and the rupture and cracks of wiring are unlikely to
occur.
[0040] The rupture diameter of the flexible substrate when curved
is preferably 30 mm or less, and more preferably 10 mm or less.
[0041] The transmittance of the flexible substrate at a wavelength
of 550 nm is preferably 85% or more, and more preferably 90% or
more. The reduction ratio of light transmittance of the flexible
substrate after the heat treatment at 180.degree. C. for 2 hours is
preferably within 5%. This is because, with such reduction ratio,
the practically acceptable light transmittance can be kept, for
example, even if a heat treatment required in a FPD production
process is conducted. One of the effects of the present invention
is that such characteristics are realized while adopting a resin
layer.
[0042] A surface roughness Ra of the flexible substrate
(substantially, a surface roughness Ra of each of a resin layer, an
inorganic thin film, or a smoothing layer) is preferably 5 nm or
less, and more preferably 2 nm or less. The wave of the flexible
substrate is preferably 0.5 .mu.m or less, and more preferably 0.1
.mu.m or less. The flexible substrate with such characteristics has
excellent quality.
B. Inorganic Glass
[0043] A shape of the inorganic glass used in the flexible
substrate of the present invention is typically a plate shape.
Examples of the inorganic glass include soda-lime glass, borate
glass, aluminosilicate glass, and quartz glass according to the
classification based on a composition. Further, according to the
classification based on an alkali component, examples of the
inorganic glass include no-alkali glass and low alkali glass. The
content of an alkali metal component (e.g., Na.sub.2O, K.sub.2O,
Li.sub.2O) of the inorganic glass is preferably 15 wt % or less,
and more preferably 10 wt % or less.
[0044] The transmittance of the inorganic glass at a wavelength of
550 nm is preferably 90% or more. A refractive index n.sub.g of the
inorganic glass at a wavelength of 550 nm is preferably 1.4 to
1.6.
[0045] An average coefficient of thermal expansion of the inorganic
glass is preferably 10 ppm.degree. C..sup.-1 to 0.5 ppm.degree.
C..sup.-1, and more preferably 5 ppm.degree. C..sup.-1 to 0.5
ppm.degree. C..sup.-1. The inorganic glass in the above-mentioned
range can effectively suppress a change in dimension of a resin
layer in a high-temperature or low-temperature environment.
[0046] The density of the inorganic glass is preferably 2.3
g/cm.sup.3 to 3.0 g/cm.sup.3, and more preferably 2.3 g/cm.sup.3 to
2.7 g/cm.sup.3. With the inorganic glass in the above-mentioned
range, a light-weight flexible substrate is obtained.
[0047] As a method of forming the inorganic glass, any appropriate
method can be adopted. The inorganic glass is typically produced by
melting a mixture containing a main material such as silica and
alumina, an antifoaming agent such as salt cake and antimony oxide,
and a reducing agent such as carbon at a temperature of
1400.degree. C. to 1600.degree. C. to form a thin plate, followed
by cooling. Examples of the method of forming a thin plate of the
inorganic glass include a slot down draw method, a fusion method,
and a float method. The inorganic glass formed into a plate shape
by any one of those methods may be chemically polished with a
solvent such as hydrofluoric acid, if required, in order to reduce
the thickness and enhance smoothness.
[0048] As the inorganic glass, commercially available glass may be
used as it is, or commercially available inorganic glass may be
polished so as to have a desired thickness and used. Examples of
the commercially available inorganic glass include "7059," "1737,"
and "EAGLE 2000" each manufactured by Corning Incorporated, "AN100"
manufactured by Asahi Glass Co., Ltd., "NA-35" manufactured by NH
Technoglass Corporation, "OA-10" manufactured by Nippon Electric
Glass Co., Ltd., and "D263" and "AF45" each manufactured by SCHOTT
AG.
C. Resin Layer
[0049] A transmittance of each of the resin layers at a wavelength
of 550 nm is preferably 85% or more. A refractive index (n.sub.r)
of each of the resin layers at a wavelength of 550 nm is preferably
1.3 to 1.7. The difference between the refractive index (n.sub.r)
of each of the resin layers and a refractive index (n.sub.g) of the
inorganic glass is preferably 0.2 or less, and more preferably 0.1
or less. When the difference in refractive index falls within such
range, the adverse effect on the display characteristics caused by
the difference in refractive index between the inorganic glass and
the resin layers can be prevented.
[0050] The elastic moduli (Young's moduli) of the resin layers are
each preferably 1 GPa or more, and more preferably 1.5 GPa or more.
When the elastic moduli each fall within the above-mentioned range,
even if the inorganic glass is made thin, a stress in the direction
in which the inorganic glass is torn toward the defects at the time
of its deformation is alleviated by the resin layers, so cracks and
rupture of the inorganic glass are unlikely to occur.
[0051] As a resin composition for forming each of the resin layers,
any appropriate resin composition can be adopted. The resin
composition preferably includes a resin having excellent heat
resistance. The resin may be a thermosetting or UV-curable resin,
or may be a thermoplastic resin. Examples of the thermosetting or
UV-curable resin include a polyarylate-based resin, a
polyimide-based resin, a polyethylene naphthalate-based resin, a
polyether sulfone-based resin, a polycarbonate-based resin, an
epoxy-based resin, an oxetane-based resin, an aclyric resin, and a
polyolefin-based resin. Any appropriate site (such as a terminal of
the main chain) of each of those resins may be subjected to
modification according to any appropriate mode (such as
modification with a hydroxyl group). In addition, those resins may
be used alone or in combination. When a thermosetting or UV-curable
resin is used, the resin layers are each particularly preferably
formed of a resin composition containing an epoxy-based resin
and/or an oxetane-based resin as a main component. This is because
resin layers each of which has excellent surface smoothness and has
a good hue are obtained. In addition, the resin layers are each
preferably formed of a resin composition containing a polyether
sulfone-based resin a terminal of which is modified with a hydroxyl
group and/or an oxetane-based resin as a main component.
[0052] As the epoxy-based resin, any appropriate resin can be used
as long as the resin has an epoxy group in its molecule. Examples
of the epoxy-based resin include bisphenol types such as a
bisphenol A type, a bisphenol F type, a bisphenol S type, and a
hydrogenated substance thereof; novolac types such as a phenol
novolac type and a cresol novolac type; nitrogen-containing cyclic
types such as a triglycidylisocyanurate type and a hydantoin type;
alicyclic types; aliphatic types; aromatic types such as a
naphthalene type and a biphenyl type; glycidyl types such as a
glycidyl ether type, a glycidyl amine type, and a glycidyl ester
type; dicyclo types such as a dicyclopentadiene type; ester types;
ether ester types; and modified types thereof. These epoxy-based
resins may be used alone or in combination.
[0053] The epoxy-based resin is preferably a bisphenol A-type
epoxy-based resin, an alicyclic-type epoxy-based resin, a
nitrogen-containing cyclic-type epoxy-based resin, or a
glycidyl-type epoxy-based resin. When the above-mentioned
epoxy-based resin is of a nitrogen-containing cyclic type, the
epoxy-based resin is preferably any one of the
triglycidylisocyanurate-type epoxy-based resins. Those epoxy-based
resins each have excellent discoloration-preventing property.
[0054] Each of the resin layers is preferably a cured layer of at
least one kind of an epoxy-based prepolymer selected from the group
consisting of the following general formulae (I), (II), (III), and
(IV).
##STR00003##
[0055] In the above formula (I): X.sub.1 and X.sub.2 each
independently represent a covalent bond, a CH.sub.2 group, a
C(CH.sub.2).sub.2 group, a C(CF.sub.3).sub.2 group, a CO group, an
oxygen atom, a nitrogen atom, a SO.sub.2 group, a
Si(CH.sub.2CH.sub.2).sub.2 group, or a N(CH.sub.2) group; Y.sub.1
to Y.sub.4 each represent substituents, and a to d each represent a
substitution number; Y.sub.1 to Y.sub.4 each independently
represent a hydrogen atom, a halogen atom, an alkyl group having 1
to 4 carbon atoms, a substituted alkyl group having 1 to 4 carbon
atoms, a nitro group, a cyano group, a thioalkyl group, an alkoxy
group, an aryl group, a substituted aryl group, an alkyl ester
group, or a substituted alkyl ester group; a to d each represent an
integer of 0 to 4; and l represents an integer of 2 or more.
##STR00004##
[0056] In the above formula (II): X.sub.3 and X.sub.4 each
independently represent a CH.sub.2 group, a C(CH.sub.3).sub.2
group, a C(CF.sub.3).sub.2 group, a CO group, an oxygen atom, a
nitrogen atom, a SO.sub.2 group, a Si(CH.sub.2CH.sub.3).sub.2
group, or a N(CH.sub.3) group; Y.sub.5 to Y.sub.7 each represent
substituents; e to g represent a substitution number; Y.sub.5 to
Y.sub.7 each independently represent a hydrogen atom, a halogen
atom, an alkyl group having 1 to 4 carbon atoms, a substituted
alkyl group having 1 to 4 carbon atoms, a nitro group, a cyano
group, a thioalkyl group, an alkoxy group, an aryl group, a
substituted aryl group, an alkyl ester group, or a substituted
alkyl ester group; e and g each represent an integer of 0 to 4; f
represents an integer of 0 to 3; and m represents an integer of 2
or more
##STR00005##
[0057] In the above formula (III): X.sub.5 and X.sub.7 each
independently represent a covalent bond, a CH.sub.2 group, a
C(CH.sub.3).sub.2 group, a C(CF.sub.3).sub.2 group, a CO group, an
oxygen atom, a nitrogen atom, a SO.sub.2 group, a Si
(CH.sub.2CH.sub.3).sub.2 group, or a N(CH.sub.3) group; and Y.sub.8
represents any one of the above formulas (a) to (d).
##STR00006##
[0058] In the above formula (IV): n and m each represent an integer
of 1 to 6; and Y.sub.9 is a portion represented by the above
formula (a) or (b).
[0059] An epoxy resin represented by the following general formula
(V) is preferably used as the epoxy-based resin.
##STR00007##
[0060] In the above formula (V): R represents a residue of an
organic compound having z active hydrogens, and the organic
compound is at least one selected from compounds each containing at
least one hydroxyl group alone as an active hydrogen group, and
unsaturated alcohols each containing at least one hydroxyl group
alone as an active hydrogen group and each simultaneously
containing an unsaturated double bond-containing group; n.sub.1,
n.sub.2, . . . n.sub.z each represent an integer of 0 or 1 to 30,
and their sum equals 1 to 100; z represents an integer of 1 to 10
representing the number of active hydrogen groups of R; and A
represents an oxycyclohexane skeleton having a substituent X, the
skeleton being a group represented by the following formula (VI)
(in the formula (VI), X represents an epoxy group).
##STR00008##
[0061] Specific examples of R in the above formula (V) include the
respective residues of ethylene glycol, diethylene glycol,
triethylene glycol, trimethylolpropane, trimethylol melamine, and
isocyanuric acid. Of those, the trimethylolpropane residue is
preferably used in terms of the ease of availability and the ease
of handling of the resin. The maximum z out of the subscripts of
n.sub.1, n.sub.2, . . . n.sub.z represents the number of active
hydrogen groups of R, and for example, the value for z is 2 in the
case of ethylene glycol or 3 in the case of trimethylolpropane. In
the case where z equals 0, no epoxy group can be incorporated, and
hence an improving effect on a viscosity is hardly obtained. On the
other hand, the case where z is equal to or larger than 11 is not
economical because a compound to serve as the skeleton is hardly
available and has a high price.
[0062] The numbers n.sub.1, n.sub.2, . . . n.sub.z of bonded epoxy
group-containing cyclohexyl ether groups each represented by A
(chain lengths) each represent an integer of 0 or 1 to 30, and
their sum equals 1 to 100. When any one of n.sub.1, n.sub.2, . . .
n.sub.z exceeds 30, the viscosity of the epoxy resin increases, and
hence the handleability may deteriorate. In addition, when the sum
of n.sub.1, n.sub.2, . . . n.sub.z equals 0, no reactivity is
obtained. When the sum exceeds 100, the extent to which the
viscosity increases at the time of melting and kneading is
difficult to control. When R represents the trimethylolpropane
residue, it is preferred that n.sub.1, n.sub.2, and n.sub.3 each
represent an integer of 5 to 30 and their sum equal 15 to 90.
[0063] The epoxy equivalence (mass per epoxy group) of the
epoxy-based resin is preferably 100 g/eqiv. to 1000 g/eqiv. When
the epoxy equivalence falls within the above-mentioned range, the
flexibility and strength of a resin layer to be obtained can be
enhanced.
[0064] The softening point of the epoxy-based resin is preferably
120.degree. C. or less. Further, the epoxy-based resin is
preferably a liquid at room temperature (e.g., 5 to 35.degree. C.).
The epoxy-based resin is more preferably a two-liquid mixed type
epoxy-based resin that is a liquid at an application temperature or
less (particularly at room temperature). This is because such resin
has excellent spreading characteristics and application
characteristics when a resin layer is formed.
[0065] Any appropriate compound having an oxetane ring in its
molecule is used as the oxetane-based resin. Specific examples of
the compound include oxetane compounds represented by the following
formulae (1) to (5).
##STR00009##
[0066] The resin composition can further contain any appropriate
additive depending on purposes. Examples of the additive include a
curing agent, a curing-accelerating agent, a diluent, an
antioxidant, adenaturant, a surfactant, a dye, a pigment, a
discoloration preventing agent, a UV absorber, a softening agent, a
stabilizer, a plasticizer, and an antifoaming agent. The kind,
number, and amount of an additive to be contained in a resin
composition can be set appropriately depending on purposes.
[0067] As the resin composition, a commercially available product
may be used as it is, and a commercially available product to which
any appropriate additive and/or resin is/are added may be used.
Examples of the commercially available epoxy-based resin (resin
composition) include Grade 827 and Grade 828 each manufactured by
Japan Epoxy Resin Co., Ltd., EP Series and KR Series each
manufactured by Adeka Corporation, and Celoxide 2021P and EHPE 3150
each manufactured by Daicel Chemical Industries Limited. Examples
of the commercially available oxetane resin include OXT221
manufactured by Toagosei Company, Limited.
[0068] The thermoplastic resin is, for example, a thermoplastic
resin (A) having repeating units represented by the following
general formula (X) and/or the following general formula (Y). The
incorporation of such thermoplastic resin can provide resin layers
each of which has excellent adhesiveness with the above-mentioned
inorganic glass and toughness. As a result, a flexible substrate in
which a crack hardly progresses at the time of cutting can be
obtained.
##STR00010##
In the formula (X): R.sub.1 represents a substituted or
unsubstituted aryl group having 6 to 24 carbon atoms, a
cycloalkylene group having 4 to 14 carbon atoms, or a linear or
branched alkylene group having 1 to 8 carbon atoms, preferably a
substituted or unsubstituted aryl group having 6 to 20 carbon
atoms, a cycloalkylene group having 4 to 12 carbon atoms, or a
linear or branched alkylene group having 1 to 6 carbon atoms, more
preferably a substituted or unsubstituted aryl group having 6 to 18
carbon atoms, a cycloalkylene group having 5 to 10 carbon atoms, or
a linear or branched alkylene group having 1 to 4 carbon atoms; and
R.sub.2 represents a substituted or unsubstituted aryl group having
6 to 24 carbon atoms, a linear or branched alkyl group having 1 to
8 carbon atoms, a linear or branched alkylene group having 1 to 8
carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, a
cycloalkylene group having 5 to 12 carbon atoms, or a hydrogen
atom, preferably a substituted or unsubstituted aryl group having 6
to 20 carbon atoms, a linear or branched alkyl group having 1 to 6
carbon atoms, a linear or branched alkylene group having 1 to 4
carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, a
cycloalkylene group having 5 to 10 carbon atoms, or a hydrogen
atom. In the formula (Y): R.sub.3 and R.sub.4 each independently
represent a linear or branched alkyl group having 1 to 8 carbon
atoms, a hydrogen atom, a linear or branched alkylene group having
1 to 8 carbon atoms, a cycloalkyl group having 5 to 12 carbon
atoms, or a cycloalkylene group having 5 to 12 carbon atoms,
preferably a linear or branched alkyl group having 1 to 5 carbon
atoms, a hydrogen atom, a linear or branched alkylene group having
1 to 5 carbon atoms, a cycloalkyl group having 5 to 10 carbon
atoms, or a cycloalkylene group having 5 to 10 carbon atoms, more
preferably a linear or branched alkyl group having 1 to 4 carbon
atoms, a hydrogen atom, a linear or branched alkylene group having
1 to 4 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms,
or a cycloalkylene group having 5 to 8 carbon atoms; A represents a
carbonyl group, or a linear or branched alkylene group having 1 to
8 carbon atoms, preferably a carbonyl group, or a linear or
branched alkylene group having 1 to 6 carbon atoms, more preferably
a carbonyl group, or a linear or branched alkylene group having 1
to 4 carbon atoms; m represents an integer of 0 to 8, preferably an
integer of 0 to 6, more preferably an integer of 0 to 3; and n
represents an integer of 0 to 4, preferably an integer of 0 to
2.
[0069] The thermoplastic resin (A) has a polymerization degree of
preferably 10 to 6000, more preferably 20 to 5000, and particularly
preferably 50 to 4000.
[0070] Specific examples of the thermoplastic resin (A) include
styrene-maleic anhydride copolymers and ester group-containing
cycloolefin polymers. Those thermoplastic resins may be used alone
or in combination.
[0071] The thermoplastic resin (A) has a glass transition
temperature of preferably 110.degree. C. or more, more preferably
120.degree. C. or more, and particularly preferably 120 to
350.degree. C. When the glass transition temperature falls within
such range, a flexible substrate having excellent heat resistance
can be obtained.
[0072] Another specific example of the thermoplastic resin is a
thermoplastic resin (B) having one or more repeating units each
represented by the following general formula (Z). The incorporation
of such thermoplastic resin can provide resin layers each of which
has excellent adhesiveness with the above-mentioned inorganic glass
and toughness. As a result, a flexible substrate in which a crack
hardly progresses at the time of cutting can be obtained.
##STR00011##
In the formula (Z): R.sup.1 represents a substituted or
unsubstituted aryl group having 6 to 24 carbon atoms, a linear or
branched alkylene group having 1 to 8 carbon atoms, or a
cycloalkylene group having 4 to 14 carbon atoms, or an oxygen atom,
preferably a substituted or unsubstituted aryl group having 6 to 20
carbon atoms, a linear or branched alkylene group having 1 to 6
carbon atoms, a cycloalkylene group having 4 to 12 carbon atoms, or
an oxygen atom, more preferably a substituted or unsubstituted aryl
group having 6 to 18 carbon atoms, a linear or branched alkylene
group having 1 to 4 carbon atoms, a cycloalkylene group having 5 to
10 carbon atoms, or an oxygen atom; and R.sup.2 represents a
substituted or unsubstituted aryl group having 6 to 24 carbon
atoms, a linear or branched alkyl group having 1 to 8 carbon atoms,
a linear or branched alkylene group having 1 to 8 carbon atoms, a
cycloalkyl group having 5 to 12 carbon atoms, a cycloalkylene group
having 5 to 12 carbon atoms, or a hydrogen atom, preferably a
substituted or unsubstituted aryl group having 6 to 20 carbon
atoms, a linear or branched alkyl group having 1 to 6 carbon atoms,
a linear or branched alkylene group having 1 to 4 carbon atoms, a
cycloalkyl group having 5 to 10 carbon atoms, a cycloalkylene group
having 5 to 10 carbon atoms, or a hydrogen atom.
[0073] The thermoplastic resin (B) has a polymerization degree of
preferably 10 to 6000, more preferably 20 to 5000, and particularly
preferably 50 to 4000.
[0074] Specific examples of the thermoplastic resin (B) include a
polyarylate, a polyester, and a polycarbonate. Those thermoplastic
resins may be used alone or in combination.
[0075] The thermoplastic resin (B) has a glass transition
temperature of preferably 120.degree. C. or more, more preferably
150.degree. C. or more, and particularly preferably 180 to
350.degree. C. When the glass transition temperature falls within
such range, a flexible substrate having excellent heat resistance
can be obtained.
D. Inorganic Thin Film
[0076] The inorganic thin film is formed of any appropriate
inorganic compound. The inorganic thin film preferably contains at
least one kind of an inorganic compound selected from the group
consisting of oxides, nitrides, hydrides, and composite compounds
of them. To be specific, the inorganic compound may be a composite
compound of an oxide, a nitride and/or a hydride as well as an
oxide, nitride, or hydride simple substance. The use of such
compound can provide additionally excellent transparency. The
inorganic compound for forming the inorganic thin film can have any
appropriate structure. To be specific, the compound may have a
complete crystal structure, or may have an amorphous structure.
[0077] Examples of the element forming the inorganic compound
include carbon (C), silicon (Si), aluminum (Al), magnesium (Mg),
calcium (Ca), potassium (K), tin (Sn), sodium (Na), boron (B),
titanium (Ti), lead (Pb), zirconium (Zr), and yttrium (Y). Those
elements may be used alone or in combination. Of those, carbon,
silicon, and aluminum are preferably used. Specific examples of the
inorganic compound include diamond-like carbon (DLC), SiN.sub.x,
SiO.sub.y, and AlO.sub.z. The value for x in SiN.sub.x is
preferably 0.3 to 2. The value for y in SiO.sub.y is preferably 1.3
to 2.5. The value for z in AlO.sub.z is preferably 0.7 to 2.3.
[0078] Any appropriate configuration can be adopted for the
inorganic thin film. To be specific, the inorganic thin film may be
formed of a single layer, or may be a laminate of a plurality of
layers. A configuration when the inorganic thin film is a laminate
is, for example, a three-layer configuration having an inorganic
oxide layer, an inorganic nitride layer, and an inorganic oxide
layer (such as a laminate of an SiO.sub.y layer, an SiN.sub.x
layer, and an SiO.sub.y layer).
E. Smoothing Layer
[0079] The smoothing layer is formed of any appropriate forming
material. To be specific, the smoothing layer is formed of any
appropriate resin composition. The resin composition preferably
contains a thermosetting resin or a photocurable resin.
[0080] As the thermosetting resin, there is exemplified a resin
which can be cured by applying thermal energy, and form a
transparent and flat surface after being cured. Representative
examples of the thermosetting resin include polycarbonate,
polymethylmethacrylate, polyacrylate, a methyl phthalate
homopolymer or copolymer, polyethylene terephthalate, polystyrene,
diethylene glycol bis(allyl carbonate), an acrylonitrile-styrene
copolymer, poly(-4-methylpentene-1), a phenolic resin, an epoxy
resin, a cyanate resin, a maleimide resin, and a polyimide resin.
Also included are a thermosetting resin obtained by modifying those
resins with polyvinyl butyral, acrylonitrile-butadiene rubber, a
polyfunctional acrylate compound, or the like, a thermosetting
resin obtained by modifying those resins with a thermoplastic resin
such as a crosslinked polyethylene resin, a crosslinked
polyethylene/epoxy resin, a crosslinkedpolyethylene/cyanate resin,
a polyphenylene ether/epoxy resin, and a polyphenylene
ether/cyanate resin, and the like. Those thermosetting resins may
be used alone or in combination.
[0081] Examples of the photocurable resin include a resin
composition composed of an acrylate compound containing a
radical-reactive unsaturated compound, a resin composition composed
of an acrylate compound and a mercapto compound having a thiol
group, and a resin composition obtained by dissolving an oligomer
such as epoxy acrylate, urethan acrylate, polyester acrylate, and
polyether acrylate in a polyfunctional acrylate monomer. Those
resins may be used alone or in combination.
[0082] The resin composition for forming the smoothing layer can
contain an additive such as an antioxidant, a UV absorber, or a
plasticizer as required. In addition, the resin composition can
contain an appropriate resin or additive for the purposes of, for
example, improving film formability and preventing pinholes.
F. Method of Producing Flexible Substrate
[0083] The flexible substrate of the present invention is typically
produced by a method including the steps of: applying a resin
composition onto the above-mentioned inorganic glass and curing or
drying and heat-treating the resin composition to form each of the
resin layers; and forming the above-mentioned inorganic thin film
on the surface of one of the resultant resin layers. In addition,
when a smoothing layer is provided, the method further includes a
step of forming the smoothing layer on the surface of the inorganic
thin film.
[0084] Examples of a method of applying the resin composition in
the formation of the resin layers include: coating methods such as
air doctor coating, blade coating, knife coating, reverse coating,
transfer roll coating, gravure roll coating, kiss coating, cast
coating, spray coating, slot orifice coating, calender coating,
electrodeposition coating, dip coating, and die coating; and
printing methods including relief printings such as flexographic
printing, intaglio printings such as direct gravure printing and
offset gravure printing, planographic printings such as offset
printing, and stencil printings such as screen printing.
[0085] In the above-mentioned application, a leveling agent such as
silicone oil and an additive such as a curing agent are added to a
resin composition, if required, whereby the application suitability
of an application liquid and the printing suitability of ink can be
enhanced. Further, by subjecting an inorganic glass surface to
silane treatment or mixing a silane coupling agent with a resin
composition, the adhesiveness between the inorganic glass and the
resin composition (finally, resin layers) can be enhanced.
[0086] As the silane coupling agent, for example, a vinyl-based,
epoxy-based, styryl-based, methacryloxy-based, acryloxy-based,
amino-based, ureido-based, chloropropyl-based, mercapto-based,
sulfide-based, or isocyanate-based silane coupling agent is used.
In the case where the thermoplastic resin (A) and/or (B) is/are
used as the resin forming the resin layer, the amino-based,
epoxy-based, and isocyanate-based silane coupling agents are
preferably used.
[0087] A method of curing the resin composition can be selected
depending on the kind of the resin in the resin composition. When a
thermosetting resin is used, the resin composition is cured by
heating. Any appropriate conditions can be adopted as heating
conditions. To be specific, a heating temperature is preferably 80
to 250.degree. C., and a heating time is preferably 1 to 30
minutes. When a UV-curable resin is used, the resin composition is
cured by UV irradiation. Any appropriate condition can be adopted
as an irradiation condition. To be specific, a dose is preferably
100 to 600 mJ/cm.sup.2.
[0088] Any appropriate drying method (such as natural drying, blast
drying, or heat drying) can be adopted for the above-mentioned
drying. In the case of, for example, the heat drying, a drying
temperature is typically 100 to 200.degree. C., and a drying time
is typically 1 to 10 minutes. Any appropriate heat treatment method
can be adopted for the heat treatment. A heat treatment temperature
is typically 100.degree. C. to 300.degree. C., and a heat treatment
time is typically 5 to 45 minutes. When the silane coupling agent
is used, it is assumed that the coupling agent and the
thermoplastic resin can be chemically bonded to, or caused to
interact with, each other by the heat treatment.
[0089] Any appropriate method can be adopted as a method of forming
the inorganic thin film. Examples of the method include: physical
vapor deposition methods such as a vacuum deposition method, an
oxidation reaction deposition method, a sputtering method, and an
ion plating method; and a plasma chemical vapor deposition method.
To be specific, when an inorganic thin film containing a silicon
compound is formed, a plasma CVD method involving the use of an
organosilicon compound such as SiH.sub.4 or tetramethoxysilane
(TMOS) as a raw material can be employed. When an inorganic thin
film containing DLC is formed, a plasma CVD method involving the
use of a hydrocarbon such as methane, acetylene, ethylene, or
butadiene as a raw material can be employed.
[0090] Any appropriate method can be adopted as a method of forming
the smoothing layer. Examples of the method include a spin coating
method, a spray method, a blade coating method, a dipping method,
and a deposition method. Upon formation of the smoothing layer, a
thin film is typically formed by dissolving or dispersing the
above-mentioned resin composition in an appropriate diluent such as
ethanol, chloroform, tetrahydrofuran, or dioxane.
G. Applications
[0091] The flexible substrate of the present invention can be
typically used in, for example, a self-luminous display apparatus
such as an electroluminescence (EL) display, a plasma display (PD),
or a field emission display (FED), or a liquid crystal display
apparatus. The flexible substrate of the present invention can be
suitably used in an organic electroluminescence (EL) display
apparatus of which high gas barrier properties are requested out of
those display apparatuses.
[0092] FIG. 5 is a schematic sectional view of an organic EL
display apparatus according to a preferred embodiment of the
present invention. The organic EL display apparatus 200 includes
the flexible substrate 100 of the present invention, a transparent
electrode 80, an organic light-emitting layer 30, and a counter
electrode 40 sequentially formed on the flexible substrate 100, and
an inorganic protective film 60 and a resin protective film 70
placed to cover them. The transparent electrode 80 is placed on the
side of the inorganic thin film of the flexible substrate 100 where
no resin layer is placed (upper side in the illustrated example).
The transparent electrode 80, the organic light-emitting layer 30,
and the counter electrode 40 in a region where the transparent
electrode 80 and the counter electrode 40 overlap each other serve
as a pixel 50. Although not illustrated, a hard coat layer may be
placed on the side of the flexible substrate 100 where the
transparent electrode 80 is not placed. The configuration of the
organic EL display apparatus of the present invention is not
limited to the illustrated example, and any appropriate
configuration can be adopted. For example, the flexible substrate
of the present invention may be used as a sealing member by being
placed to cover the inorganic protective film 60 and the resin
protective film 70. In addition, for example, the organic EL
display apparatus may be a top emission system, or may be a bottom
emission system.
[0093] At least one electrode (typically the anode) of the organic
EL display apparatus must be transparent in order that light
emitted from the organic light-emitting layer 30 may be extracted.
As the forming material for the transparent electrode, there are
used indium tin oxide (ITO), indium zinc oxide (IZO), indium tin
oxide doped with silicon oxide (ITSO), indium oxide containing
tungsten oxide (IWO), indium zinc oxide containing tungsten oxide
(IWZO), indium oxide containing titanium oxide (ITiO), indium tin
oxide containing titanium oxide (ITTiO), indium tin oxide
containing molybdenum (ITMO), and the like. Meanwhile, the use of a
substance having a small work function in the cathode plays an
important role in facilitating electron injection to improve
luminous efficiency. Therefore, the counter electrode 40 is
typically formed of a metal film such as an Mg--Ag or Al--Li film
and used as the cathode.
[0094] The organic light-emitting layer 30 is a laminate of various
organic thin films. In the illustrated example, the organic
light-emitting layer 30 has: a hole-injecting layer 31 formed of a
hole-injectable organic material (such as a triphenylamine
derivative) and provided for improving the efficiency with which a
hole is injected from the anode; a light-emitting layer 32 formed
of a luminous organic substance (such as anthracene); and an
electron-injecting layer 33 formed of an electron-injectable
material (such as a perylene derivative) and provided for improving
the efficiency with which an electron is injected from the cathode.
The organic light-emitting layer 30 is not limited to the
illustrated example, and any appropriate combination of organic
thin films in which light emission can be caused by the
recombination of an electron and a hole in the light-emitting layer
32 can be adopted. For example, a configuration formed of a first
hole-transporting layer (made of, for example, copper
phthalocyanine), a second hole-transporting layer (made of, for
example, N,N'-diphenyl-N,N'-dinaphthylbenzidine), and an
electron-transporting layer-cum-light-emitting layer (made of, for
example, tris(8-hydroxyquinolinato)aluminum) can be adopted.
[0095] When a voltage equal to or higher than a threshold is
applied between the transparent electrode and the counter
electrode, a hole is supplied from the anode to reach the
light-emitting layer 32 through the hole-injecting layer 31.
Meanwhile, an electron is supplied from the cathode to reach the
light-emitting layer 32 through the electron-injecting layer 33.
Energy generated by the recombination of the hole and the electron
in the light-emitting layer 32 excites the luminous organic
substance in the light-emitting layer, and the excited luminous
organic substance radiates light upon return to its ground state.
Thus, light emission occurs. An image can be displayed by applying
a voltage to every desired pixel to cause the organic
light-emitting layer to emit light. When color display is
performed, for example, the light-emitting layers of three adjacent
pixels may be formed of luminous organic substances that emit red
(R) light, green (G) light, and blue (B) light, or any appropriate
color filter may be provided on each of the light-emitting
layers.
[0096] In such organic EL display apparatus, the thickness of the
organic light-emitting layer 30 is preferably as small as possible.
This is because emitted light is preferably transmitted as much as
possible. The organic light-emitting layer 30 can be formed of, for
example, an extremely thin film having a thickness of about 10 nm.
As a result, at the time of non-emission (black state), light
incident from the lower surface side of the flexible substrate 100
to transmit through the transparent electrode 80 and the organic
light-emitting layer 30 and then reflected at the counter electrode
40 is emitted toward the lower surface side of the flexible
substrate 100 again.
[0097] The hard coat layer is formed of any appropriate forming
material. The layer is typically formed of the same resin
composition as that of the above-mentioned smoothing layer.
EXAMPLES
[0098] Hereinafter, the present invention is described specifically
by way of examples. However, the present invention is not limited
to those examples.
Example 1
Production of Base Material (Resin Layer/Inorganic Glass/Resin
Layer)
[0099] A plate-like inorganic glass having a thickness of 50 .mu.m
("D263" manufactured by SCHOTT AG) was washed with methyl ethyl
ketone (MEK), and both of its surfaces were subjected to a corona
treatment. After that, a silane coupling agent (KBM-403
manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to each
of both surfaces of the inorganic glass, and then the resultant was
heat-treated at 110.degree. C. for 5 minutes.
[0100] Next, a mixed liquid of an epoxy resin 1 represented by the
following formula (a) (Celoxide 2021P manufactured by Daicel
Chemical Industries Limited.), an epoxy resin 2 (a
1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of
2,2-bis(hydroxymethyl)-1-butanol, manufactured by Daicel Chemical
Industries Limited., EHPE3150), an oxetane resin represented by the
following formula (5) (OXT221 manufactured by Toagosei Company,
Limited), and a polymerization initiator (SP-170 manufactured by
ADEKA CORPORATION) was prepared. The resultant mixed liquid was
applied to the front surface of the inorganic glass, and was then
irradiated with UV light at 300 mJ/cm.sup.2 or more so that the
resins were cured. Thus, a resin layer having a thickness of 25
.mu.m was formed. A resin layer having a thickness of 25 .mu.m was
similarly formed on the rear surface of the inorganic glass. After
that, the resultant was heat-treated at 150.degree. C. for 30
minutes.
[0101] Thus, a base material having a thickness of 100 .mu.m was
produced.
##STR00012##
[0102] (Formation of Inorganic Thin Film)
[0103] An SiN.sub.X film (having a thickness of 100 nm) was formed
on one surface of the base material obtained in the forgoing by a
plasma CVD method. Conditions for the formation of the SiN.sub.X
film are as described below. Thus, a flexible substrate was
produced.
TABLE-US-00001 Degree of vacuum: 0.3 Pa (2.25 .times. 10.sup.-3
Torr) SiH.sub.4 gas flow rate: 50 sccm Nitrogen gas flow rate: 50
sccm Frequency: 13.56 MHz Electric power: 700 W
Example 2
[0104] A flexible substrate was produced in the same manner as in
Example 1 except that an SiO.sub.y film (having a thickness of 100
nm) was formed on one surface of the base material by a plasma CVD
method. Conditions for the formation of the SiO film are as
described below.
TABLE-US-00002 Degree of vacuum: 0.3 Pa (2.25 .times. 10.sup.-3
Torr) SiH.sub.4 gas flow rate: 10 sccm Oxygen gas flow rate: 20
sccm Nitrogen gas flow rate: 50 sccm Frequency: 13.56 MHz Electric
power: 500 W
Example 3
[0105] A flexible substrate was produced in the same manner as in
Example 1 except that a diamond-like carbon (DLC) film (having a
thickness of 100 nm) was formed on one surface of the base material
by a plasma CVD method. Conditions for the formation of the DLC
film are as described below.
TABLE-US-00003 Degree of vacuum: 0.3 Pa (2.25 .times. 10.sup.-3
Torr) CH.sub.4 gas flow rate: 200 sccm Frequency: 13.56 MHz
Electric power: 1000 W Electrode DC voltage: 300 V
Example 4
[0106] A flexible substrate was produced in the same manner as in
Example 1 except that an SiO.sub.y film (having a thickness of 100
nm), an SiN.sub.X film (having a thickness of 100 nm), and an
SiO.sub.y film (having a thickness of 100 nm) were formed in the
stated order on one surface of the base material by a plasma CVD
method to form an SiO.sub.y/SiN.sub.x/SiO.sub.y laminate. It should
be noted that conditions for the formation of the SiO.sub.y films
and the SiN.sub.X film are as described above.
Example 5
[0107] A flexible substrate was produced in the same manner as in
Example 1 except that the following base material was used.
(Base Material)
[0108] A styrene-maleic anhydride copolymer (manufactured by
Sigma-Aldrich Corporation and having a weight-average molecular
weight of 220,000) was dissolved in methyl isobutyl ketone so that
the resultant solution had a concentration of 20 wt %.
[0109] Separately, one surface of an inorganic glass measuring 50
.mu.m thick by 10 cm long by 4 cm wide ("D263" manufactured by
SCHOTT AG) was washed with methyl ethyl ketone, and was then
subjected to a corona treatment. Subsequently, an amine
group-containing coupling agent (KBM-603 manufactured by Shin-Etsu
Chemical Co., Ltd.) was applied to the surface, and then the
resultant was heat-treated at 110.degree. C. for 5 minutes. The
above-mentioned styrene-maleic anhydride solution was applied to
the surface of the inorganic glass subjected to the coupling
treatment, and then the resultant was dried at 160.degree. C. for
10 minutes. After that, the resultant was heat-treated at
200.degree. C. for 30 minutes. The other surface of the inorganic
glass was subjected to similar treatments. Thus, a laminate of the
inorganic glass, amine group-containing coupling agent layers, and
thermoplastic resin layers having a total thickness of 60 .mu.m was
obtained.
[0110] Further, a 7-wt % solution of a polyamideimide synthesized
in Reference Example 1 below in methyl isobutyl ketone was applied
to one surface of the laminate, and then the resultant was dried at
160.degree. C. for 10 minutes. After that, the resultant was
heat-treated at 200.degree. C. for 30 minutes. The other surface of
the inorganic glass was subjected to similar treatments. Thus, a
base material having a total thickness of 120 .mu.m was
obtained.
Reference Example 1
Synthesis of Polyamideimide
[0111] The polyamideimide was synthesized from
2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA),
trimellitic anhydride (TMA), and
2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB). The
polyamideimide had a weight-average molecular weight of about
110,000.
Example 6
[0112] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 5 in the same manner
as in Example 2.
Example 7
[0113] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 5 in the same manner
as in Example 3.
Example 8
[0114] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 5 in the same manner
as in Example 4.
Example 9
[0115] A flexible substrate was produced in the same manner as in
Example 1 except that the following base material was used.
(Base Material)
[0116] A 14.5-wt % casting solution was obtained by mixing a 20-wt
% solution of a polyarylate (U-Polymer U-100 manufactured by
Unitika Limited.) in methylene chloride and cyclopentanone.
[0117] Separately, one surface of an inorganic glass having a
thickness of 50 .mu.m ("D263" manufactured by SCHOTT AG) was washed
with methyl ethyl ketone, and was then subjected to a corona
treatment. Subsequently, an amine group-containing coupling agent
(KBM-603 manufactured by Shin-Etsu Chemical Co., Ltd.) was applied
to the surface, and then the resultant was heat-treated at
110.degree. C. for 5 minutes. The above-mentioned casting solution
was applied to the surface of the inorganic glass subjected to the
coupling treatment, and then the resultant was dried at 160.degree.
C. for 10 minutes. After that, the resultant was heat-treated at
200.degree. C. for 30 minutes. The other surface of the inorganic
glass was subjected to similar treatments. Thus, a substrate having
a total thickness of 120 .mu.m was obtained.
Example 10
[0118] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 9 in the same manner
as in Example 2.
Example 11
[0119] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 9 in the same manner
as in Example 3.
Example 12
[0120] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 9 in the same manner
as in Example 4.
Example 13
[0121] A flexible substrate was produced in the same manner as in
Example 1 except that the following base material was used.
(Base Material)
[0122] A casting solution was obtained by mixing a polyether
sulfone a terminal of which had been modified with a hydroxyl group
(Sumika Excel 5003P manufactured by Sumitomo Chemical Company,
Limited), cyclopentanone, dimethyl sulfoxide, and a leveling agent
(BYK-307 manufactured by BYK-Chemie) at a weight ratio of
140:658:42:0.105.
[0123] Separately, one surface of an inorganic glass measuring 50
.mu.m thick by 10 cm long by 4 cm wide ("D263" manufactured by
SCHOTT AG) was washed with methyl ethyl ketone, and was then
subjected to a corona treatment. Subsequently, an epoxy group end
coupling agent (KBM-403 manufactured by Shin-Etsu Chemical Co.,
Ltd.) was applied to the surface, and then the resultant was
heat-treated at 110.degree. C. for 5 minutes. The above-mentioned
casting solution was applied to the surface of the inorganic glass
subjected to the coupling treatment, and then the resultant was
dried at 160.degree. C. for 10 minutes. After that, the resultant
was heat-treated at 200.degree. C. for 30 minutes. Thus, a resin
layer having a thickness of 35 .mu.m was formed.
[0124] The other surface of the inorganic glass was subjected to
similar treatments. Thus, a base material having a total thickness
of 120 .mu.m was obtained.
Example 14
[0125] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 13 in the same
manner as in Example 2.
Example 15
[0126] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 13 in the same
manner as in Example 3.
Example 16
[0127] A flexible substrate was produced by forming an inorganic
thin film on the base material used in Example 13 in the same
manner as in Example 4.
Example 17
[0128] An organic EL device was produced by the following method,
and was then sealed with the flexible substrate of Example 11.
Thus, an organic EL display apparatus was obtained.
[0129] The surface of the indium tin composite oxide (ITO) layer of
a glass substrate having the ITO layer (surface resistance:
10.OMEGA./.quadrature.) was washed with isopropyl alcohol. After
that, the ITO layer was subjected to a UV-ozone treatment for 15
minutes so as to be turned into a transparent electrode (anode).
The following organic compound layers were sequentially formed on
the anode by employing a vacuum deposition method.
[0130] First Hole-Transporting Layer: [0131] Copper phthalocyanine
(thickness: 10 nm)
[0132] Second Hole-Transporting Layer: [0133]
N,N'-diphenyl-N,N'-dinaphthylbenzidine (thickness: 40 nm)
[0134] Electron-Transporting Layer-Cum-Light-Emitting Layer: [0135]
Tris(8-hydroxyquinolinato) aluminum (thickness: 60 nm)
[0136] Next, lithium fluoride and aluminum were sequentially
deposited from the vapor so as to have thicknesses of 1 nm and 100
nm, respectively. Thus, a counter electrode (cathode) was formed.
The aluminum surface was sealed with the flexible substrate
obtained in Example 11 (subjected to an annealing treatment at
110.degree. C. for 15 minutes) through a UV-curable epoxy-based
adhesive. Then, UV light was applied from the side of the flexible
substrate to cure the adhesive. Thus, the organic EL display
apparatus was obtained.
Example 18
[0137] An organic EL display apparatus was produced in the same
manner as in Example 17 except that sealing was performed with the
flexible substrate obtained in Example 15 (subjected to an
annealing treatment at 110.degree. C. for 15 minutes).
Comparative Example 1
[0138] A laminate was obtained in the same manner as in Example 11
except that the inorganic thin film (DLC film) was not formed.
Comparative Example 2
[0139] A laminate was obtained in the same manner as in Example 15
except that the inorganic thin film (DLC film) was not formed.
Comparative Example 3
[0140] An organic EL display apparatus was produced in the same
manner as in Example 17 except that sealing was performed with the
laminate obtained in Comparative Example 1 (subjected to an
annealing treatment at 110.degree. C. for 15 minutes).
Comparative Example 4
[0141] An organic EL display apparatus was produced in the same
manner as in Example 17 except that sealing was performed with the
laminate obtained in Comparative Example 2 (subjected to an
annealing treatment at 110.degree. C. for 15 minutes).
[0142] [Evaluation]
(1) Water Vapor Permeability
[0143] Each of the flexible substrates obtained in Examples 1 to 16
was evaluated for its water vapor permeability by an MOCON
measurement method in conformity with JIS K 7129B. To be specific,
measurement was performed with a water vapor permeability-measuring
apparatus "PERMATRAN-W3/33MG (with an HRH-1D type high-precision
flow rate controller)" manufactured by MOCON. The measurement was
performed under humidity conditions of 40.degree. C. and 90% RH at
a gas flow rate of 10.0.+-.0.5 cc/min for a measurement time of 20
hours or more.
[0144] In each case, the water vapor permeability was lower than a
measurement limit (10.sup.-2 g/m.sup.2day).
(2) Storage Stability
[0145] The organic EL display apparatuses of Examples 17 and 18,
and Comparative Examples 3 and 4 were each caused to emit light by
applying a DC voltage of 7 V. In each display apparatus, no dark
spots were observed, and a uniform emission state was achieved.
After that, each display apparatus was stored under a
normal-temperature, normal-pressure atmosphere, and its emission
state was periodically observed. Table 1 shows emission states
after 7 days, after 30 days, and after 60 days. Evaluation criteria
are as described below.
[0146] .smallcircle.: Uniform emission state
[0147] .DELTA.: Generation of dark spots
[0148] x: No lighting
TABLE-US-00004 TABLE 1 After 7 days After 30 days After 60 days
Example 17 .smallcircle. .smallcircle. .smallcircle. Example 18
.smallcircle. .smallcircle. .smallcircle. Comparative .smallcircle.
.DELTA. x Example 3 Comparative .smallcircle. .DELTA. x Example
4
[0149] As is apparent from Table 1, the organic EL display
apparatuses using the flexible substrates of the examples of the
present invention are markedly excellent in storage stability as
compared with the organic EL display apparatuses of the comparative
examples. To be specific, each of the organic EL display
apparatuses of the examples maintained a uniform emission state
even after 60 days while each of the organic EL display apparatuses
of the comparative examples showed the generation of dark spots
after 30 days and did not light after 60 days. The foregoing shows
that the formation of an inorganic thin film on a flexible
substrate significantly improves the storage stability.
INDUSTRIAL APPLICABILITY
[0150] The flexible substrate of the present invention can be
suitably used in an organic electroluminescence (EL) display
apparatus.
LIST OF REFERENCE NUMERALS
[0151] 10 inorganic glass [0152] 11, 11' resin layer [0153] 12
inorganic thin film [0154] 13 smoothing layer [0155] 20 base
material [0156] 100 flexible substrate [0157] 200 organic EL
display apparatus
* * * * *