U.S. patent application number 13/538893 was filed with the patent office on 2012-11-01 for method for production of transparent conductive film and touch panel therewith.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Tomotake Nashiki, Hideo Sugawara.
Application Number | 20120273344 13/538893 |
Document ID | / |
Family ID | 40122352 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120273344 |
Kind Code |
A1 |
Nashiki; Tomotake ; et
al. |
November 1, 2012 |
METHOD FOR PRODUCTION OF TRANSPARENT CONDUCTIVE FILM AND TOUCH
PANEL THEREWITH
Abstract
There is provided a transparent conductive film having a
transparent conductor layer with a high level of pen input
durability and high-temperature, high-humidity reliability. The
transparent conductive film of the present invention is a
transparent conductive film, comprising: a transparent film
substrate; a transparent conductor layer that is provided on one
side of the transparent film substrate and has a thickness d of 15
nm to 35 nm and an average surface roughness Ra of 0.37 nm to 1 nm;
and at least a single layer of an undercoat layer interposed
between the transparent film substrate and the transparent
conductor layer.
Inventors: |
Nashiki; Tomotake;
(Ibaraki-shi, JP) ; Sugawara; Hideo; (Ibaraki-shi,
JP) |
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
40122352 |
Appl. No.: |
13/538893 |
Filed: |
June 29, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12250645 |
Oct 14, 2008 |
|
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13538893 |
|
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|
Current U.S.
Class: |
204/192.29 |
Current CPC
Class: |
G02F 2202/022 20130101;
Y10T 428/265 20150115; G02F 1/13338 20130101; G02F 2202/09
20130101; C08J 7/0423 20200101; G06F 3/045 20130101; G02F
2001/133331 20130101; G02F 2202/16 20130101 |
Class at
Publication: |
204/192.29 |
International
Class: |
C23C 14/34 20060101
C23C014/34 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2007 |
JP |
2007-274045 |
Claims
1. A method for manufacturing a transparent conductive film,
wherein said transparent conductive film comprises: a transparent
film substrate; a transparent conductor layer that is provided on
one side of the transparent film substrate and has a thickness d of
15 nm to 35 nm and an average surface roughness Ra of 0.37 nm to 1
nm; and a layer of an undercoat layer interposed between the
transparent film substrate and the transparent conductor layer,
said method comprising: forming a layer of an undercoat layer on
one side of a transparent film substrate; and forming a transparent
conductor layer on the undercoat layer by sputtering a target under
a discharge power condition of 4 W/cm.sup.2 to 7 W/cm.sup.2.
2. The method according to claim 1, further comprising performing
annealing treatment to crystallize at a temperature of 120.degree.
C. to 160.degree. C. after the step of forming the transparent
conductor layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 12/250,645, filed on Oct. 14, 2008 which is based upon and
claims the benefit of priority from the prior Japanese Patent
Application No. 2007-274045, filed on Oct. 22, 2007, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a transparent conductive
film that has transparency in the visible light range and includes
a film substrate and a transparent conductor layer provided on the
substrate with an undercoat layer interposed therebetween, and also
to a method for production thereof. The invention also relates to a
touch panel including the transparent conductive film.
[0004] The transparent conductive film of the present invention may
be used for transparent electrodes in touch panels and display
systems such as liquid crystal displays and electroluminescence
displays and also used for electromagnetic wave shielding or
prevention of static charge of transparent products. In particular,
the transparent conductive film of the present invention is
preferably used for touch panels. The transparent conductive film
of the invention is particularly suitable for use in resistive film
type touch panels.
[0005] 2. Description of the Related Art
[0006] Touch panels may be classified according to a position
sensing method into an optical type, an ultrasonic type, a
capacitive type, a resistive film type, and the like. Resistive
film type touch panels are configured to include a pair of
transparent conductive films arranged opposite to each other with
spacers interposed therebetween, in which an electric current is
allowed to flow through an upper transparent conductive film, while
a voltage at a lower transparent conductive film is measured. When
the upper transparent conductive film is brought into contact with
the lower transparent conductive film by pressing with a finger, a
pen or the like, the electric current flows through the contact
portion so that the position of the contact portion is detected.
Therefore, the transparent conductive films are required to have
pen input durability.
[0007] In recent years, therefore, various types of plastic films
such as polyethylene terephthalate films have been used as a
substrate of such transparent conductive films, because of their
advantages such as good impact resistance and light weight as well
as flexibility and workability. Touch panels including such
transparent conductive films are frequently used outdoors.
Therefore, the transparent conductive films are required to have
high-temperature, high-humidity reliability as well as pen input
durability.
[0008] Incidentally, it is proposed that a transparent conductive
film should include a transparent conductor layer with a controlled
thickness of 12 to 2 nm, a controlled maximum surface roughness of
1 to 20 nm and a controlled average surface roughness of 0.1 to 10
nm (WO 2004/105055 Pamphlet). It is also proposed that the
transparent conductive film should include two transparent
conductor layers such that the surface roughness Ra may be
controlled to be 0.5 to 2.0 nm and that the maximum height Ry may
be controlled to be 8 to 20 nm (Japanese Patent Application
Laid-Open (JP-A) No. 2005-268616). It is also proposed that the
transparent conductive film should include a transparent conductor
layer whose center line-average roughness Ra, ten-point-average
roughness Rz and maximum height Ry are adjusted to 1 nm or less, 10
nm or less, and 10 nm or less, respectively, by polishing (Japanese
Patent Application Laid-Open (JP-A) No. 2005-93318). WO 2004/105055
Pamphlet discloses that the transparent conductor layer may be
obtained in a form of a very thin continuous film. Japanese Patent
Application Laid-Open (JP-A) No. 2005-268616 discloses that the
transparent conductor layer has low resistance and high surface
smoothness. Japanese Patent Application Laid-Open (JP-A) No.
2005-93318 discloses that the surface of the transparent conductor
layer has high smoothness. However, the transparent conductor layer
described in each of the above documents does not provide both pen
input durability and high-temperature, high-humidity
reliability.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
transparent conductive film having a transparent conductor layer
with a high level of pen input durability and high-temperature,
high-humidity reliability and to provide a method for production
thereof. It is another object of the invention to provide a touch
panel including such a transparent conductive film.
[0010] As a result of investigations for solving the problems, the
inventors of the present invention have found that the objects can
be achieved using the features described below, and finally
completed the invention.
[0011] Namely, the transparent conductive film of the present
invention is a transparent conductive film, comprising: a
transparent film substrate; a transparent conductor layer that is
provided on one side of the transparent film substrate and has a
thickness d of 15 nm to 35 nm and an average surface roughness Ra
of 0.37 nm to 1 nm; and at least a single layer of an undercoat
layer interposed between the transparent film substrate and the
transparent conductor layer.
[0012] In the above, it is preferable that the ratio (Ra/d) of the
average surface roughness Ra to the thickness d is from 0.017 to
0.045.
[0013] In the above, it is preferable that the transparent
conductor layer has a maximum surface roughness Ry of 7.5 nm to 15
nm.
[0014] In the above, it is preferable that the ratio (Ry/d) of the
maximum surface roughness Ry to the thickness d is from 0.34 to
1.
[0015] In the above, it is preferable that a first undercoat layer
that is formed on the transparent film substrate side is made of an
organic material.
[0016] In the above, it is preferable that there are at least two
layers of the undercoat layers and at least the undercoat layer
most distant from the transparent film substrate side is made of an
inorganic material. It is preferable that the undercoat layer made
of the inorganic material is a SiO.sub.2 film.
[0017] In the above, it is preferable that the transparent
conductive film further comprises a transparent substrate that is
bonded to the other side of the transparent film substrate with a
transparent pressure-sensitive adhesive layer interposed
therebetween.
[0018] In the above, it is preferable that the transparent
conductive film is for use in a touch panel. It is preferable that
the touch panel is a resistive film type touch panel.
[0019] Also, the method for producing a transparent conductive film
of the present invention is a method for producing the
above-mentioned transparent conductive film, comprising the steps
of: forming at least a single layer of an undercoat layer on one
side of a transparent film substrate; and forming a transparent
conductor layer on the undercoat layer by sputtering a target under
a discharge power condition of 4 W/cm.sup.2 to 7 W/cm.sup.2.
[0020] In the above, it is preferable that the method further
comprises a step of performing annealing treatment to crystallize
at a temperature of 120.degree. C. to 160.degree. C. after the step
of forming the transparent conductor layer.
[0021] Also, the touch panel of the present invention is a touch
panel, comprising the above-mentioned transparent conductive
film.
[0022] In the transparent conductive film of the present invention,
the thickness d and the average surface roughness Ra of the
transparent conductor layer are each controlled to fall within a
specific range. According to the invention, such control of the
transparent conductor layer allows the production of a transparent
conductive film with a high level of pen input durability and
high-temperature, high-humidity reliability. According to the
invention, it has also been found that when the transparent
conductor layer is formed by sputtering at a discharge power
controlled within a specific range in the process of manufacturing
the transparent conductive film, the average surface roughness Ra
can easily increase relative to the thickness d, as compared with
when the discharge power is low. Such a manufacturing method allows
an efficient formation of a transparent conductor layer with a
satisfactory level of the thickness d and the average surface
roughness Ra according to the invention. The resulting transparent
conductive film is suitable for use in touch panels and
particularly suitable for use in resistive film type touch
panels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a cross-sectional view showing a transparent
conductive film according to an embodiment of the invention;
[0024] FIG. 2 is a cross-sectional view showing a transparent
conductive film according to an embodiment of the invention;
[0025] FIG. 3 is a cross-sectional view showing a transparent
conductive film according to an embodiment of the invention;
and
[0026] FIG. 4 is a schematic diagram showing an outline of
measurement of linearity.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Embodiments of the present invention are described below
with reference to the drawings. FIG. 1 is a cross-sectional view
showing an example of the transparent conductive film of the
invention. The transparent conductive film of FIG. 1 includes a
transparent film substrate 1 and a transparent conductor layer 3
provided on one side of the substrate 1 with an undercoat layer 2
interposed therebetween. The transparent conductive film of FIG. 2
includes two undercoat layers (indicated by 2). In FIG. 2,
undercoat layers 21 and 22 are formed in this order from the
transparent film substrate 1 side.
[0028] As shown in FIG. 3, a transparent substrate 5 may also be
bonded to the other side (where the transparent conductor layer 3
is not provided) of the transparent film substrate 1 of the
transparent conductive film with a transparent pressure-sensitive
adhesive layer 4 interposed therebetween. The transparent substrate
5 may be made of a single substrate film or a laminate of two or
more substrate films (with transparent pressure-sensitive adhesive
layer(s) interposed therebetween). FIG. 3 also shows a case where a
hard coat layer (resin layer) 6 is provided on an outer surface of
the transparent substrate 5.
[0029] There is no particular limitation to the film substrate 1,
and various types of plastic films having transparency may be used.
Examples of the material for the film substrate 1 include polyester
resins, acetate resins, polyethersulfone resins, polycarbonate
resins, polyamide resins, polyimide resins, polyolefin resins,
(meth)acrylic resins, polyvinyl chloride resins, polyvinylidene
chloride resins, polystyrene resins, polyvinyl alcohol resins,
polyarylate resins, and polyphenylene sulfide resins. In
particular, polyester resins, polycarbonate resins, and polyolefin
resins are preferred.
[0030] Examples thereof also include polymer films as disclosed in
JP-A No. 2001-343529 (W001/37007) and a resin composition that
contains (A) a thermoplastic resin having a side chain of a
substituted and/or unsubstituted imide group and (B) a
thermoplastic resin having a side chain of substituted and/or
unsubstituted phenyl and nitrile groups. Specifically, a polymer
film of a resin composition containing an alternating copolymer
made of isobutylene and N-methylmaleimide, and an
acrylonitrile-styrene copolymer may be used.
[0031] The thickness of the film substrate 1 is preferably in the
range of 2 to 200 .mu.m, more preferably in the range of 2 to 100
.mu.m. If the thickness of the film substrate 1 is less than 2
.mu.m, the film substrate 1 can have insufficient mechanical
strength so that it can be difficult to use the film substrate 1 in
the form of a roll in the process of continuously forming the
undercoat layer 2 and the transparent conductor layer 3 in some
cases. If the thickness exceeds 200 .mu.m, it can be impossible to
improve the scratch resistance of the transparent conductor layer 3
or the tap properties thereof for touch panels in some cases.
[0032] The surface of the film substrate 1 may be previously
subject to sputtering, corona discharge treatment, flame treatment,
ultraviolet irradiation, electron beam irradiation, chemical
treatment, etching treatment such as oxidation, or undercoating
treatment such that the adhesion of the undercoat layer 2 formed
thereon to the film substrate 1 can be improved. If necessary, the
film substrate may also be subjected to dust removing or cleaning
by solvent cleaning, ultrasonic cleaning or the like, before the
undercoat layer 2 is formed.
[0033] The undercoat layer 2 may be made of an inorganic material,
an organic material or a mixture of inorganic and organic
materials. The undercoat layer 2 generally has a refractive index
of 1.3 to 2.5, preferably of 1.38 to 2.3, and more preferably of
1.4 to 2.3. Examples of the inorganic material include NaF (1.3),
Na.sub.3AlF.sub.6 (1.35), LiF (1.36), MgF.sub.2 (1.38), CaF.sub.2
(1.4), BaF.sub.2 (1.3), SiO.sub.2 (1.46), LaF.sub.3 (1.55),
CeF.sub.3 (1.63), and Al.sub.2O.sub.3 (1.63), wherein each number
inside the parentheses indicates the light refractive index of each
material. In particular, SiO.sub.2, MgF.sub.2, Al.sub.2O.sub.3 or
the like is preferably used, and SiO.sub.2 is particularly
preferred. Besides the above, a complex oxide may also be used that
comprises about 10 to about 40 parts by weight of cerium oxide and
0 to about 20 parts by weight of tin oxide based on indium
oxide.
[0034] Examples of the organic material include acrylic resins,
urethane resins, melamine resins, alkyd resins, siloxane polymers,
and organosilane condensates. At least one selected from the above
organic materials may be used. In particular, a thermosetting resin
comprising a mixture of a melamine resin, an alkyd resin and an
organosilane condensate is preferably used as the organic
material.
[0035] The undercoat layer 2 is provided between the transparent
film substrate 1 and the transparent conductor layer 3 and does not
function as a conductor layer. Specifically, the undercoat layer 2
is provided as a dielectric layer. Therefore, the undercoat layer 2
generally has a surface resistance of 1.times.10.sup.6
.OMEGA./square or more, preferably of 1.times.10.sup.7
.OMEGA./square or more, and more preferably of 1.times.10.sup.8
.OMEGA./square or more. Here, the surface resistance of the
undercoat layer 2 does not have any particular upper limit. While
the surface resistance of the undercoat layer 2 may generally has
an upper limit of about 1.times.10.sup.13 .OMEGA./square, which
corresponds to a measuring limit, it may be higher than
1.times.10.sup.13 .OMEGA./square.
[0036] In view of productivity and flexibility, a first undercoat
layer formed on the transparent film substrate 1 side is preferably
made of an organic material. Therefore, when the undercoat layer 2
is a single layer, the undercoat layer 2 is preferably made of an
organic material.
[0037] When the undercoat layer 2 is composed of at least two
layers, at least a layer that is most distant from the transparent
film substrate 1 is preferably made of an inorganic material in
terms of pen input durability. When the undercoat layer 2 is
composed of three or more layers, a layer or layers that are above
the second layer from the transparent film substrate 1 are also
preferably made of an inorganic material.
[0038] The undercoat layer made of an inorganic material may be
formed by a dry process such as vacuum deposition, sputtering, and
ion plating or a wet process (coating). The inorganic material for
forming the undercoat layer is preferably SiO.sub.2 as described
above. In a wet process, a silica sol or the like may be applied to
form a SiO.sub.2 film.
[0039] Under the foregoing, when two layers of the undercoat layers
2 are formed, it is preferred that the first undercoat layer 21
should be made of an organic material and that the second undercoat
layer 22 should be made of an inorganic material.
[0040] The thickness of the undercoat layer 2 is generally, but not
limited to, from about 1 to about 300 nm, preferably from 5 to 300
nm, in view of optical design and the effect of preventing oligomer
production from the film substrate 1. When two or more undercoat
layers 2 are formed, the thickness of each layer may be from about
5 to about 250 nm, preferably from 10 to 250 nm.
[0041] Examples of materials that may be used to form the
transparent conductor layer 3 include, but are not limited to,
oxides of at least one metal selected from the group consisting of
indium, tin, zinc, gallium, antimony, titanium, silicon, zirconium,
magnesium, aluminum, gold, silver, copper, palladium, and tungsten.
Such metal oxides may be optionally doped with any metal atom
selected from the above group. For example, indium oxide doped with
tin oxide or tin oxide doped with antimony is preferably used. The
refractive index of the transparent conductor layer 3 is generally
about from 1.95 to about 2.05.
[0042] The thickness d of the transparent conductor layer 3 is from
15 to 35 nm. When the thickness d is controlled to fall within this
range, pen input durability and high-temperature, high-humidity
reliability can be achieved, and the transparent conductor layer 3
can be formed as a continuous coating with good electrical
conductivity and a surface resistance of 1.times.10.sup.3
.OMEGA./square or less. If the thickness d is less than 15 nm, pen
input durability and high-temperature, high-humidity reliability
cannot be achieved. If the thickness d is more than 35 nm, the
layer can be so thick that the transparency may be reduced, and
cracks can be easily formed to reduce pen input durability, which
is not so preferred. The thickness d is preferably from 17 to 35
nm, and more preferably from 17 to 30 nm.
[0043] The transparent conductor layer 3 has an average surface
roughness Ra of 0.37 to 1 nm. The control of the average surface
roughness Ra within this range gives pen input durability. If the
average surface roughness Ra is less than 0.37 nm, pen input
durability cannot be achieved even with the thickness d falling
within the range. On the other hand, if the average surface
roughness Ra is more than 1 nm, high-temperature, high-humidity
reliability cannot be achieved even with the thickness d falling
within the range, which is not preferred. The average surface
roughness Ra is preferably from 0.37 to 0.95 nm, more preferably
from 0.37 to 0.9 nm.
[0044] Concerning the relationship between the thickness d and the
average surface roughness Ra of the transparent conductor layer,
the inventors have also found that controlling the ratio (Ra/d) of
the average surface roughness Ra to the thickness d within a
specific range contributes to achievement of both pen input
durability and high-temperature, high-humidity reliability.
Specifically, in the transparent conductor layer, the ratio (Ra/d)
of the average surface roughness Ra to the thickness d is
preferably from 0.017 to 0.045 in order to achieve pen input
durability and high-temperature, high-humidity reliability. The
ratio (Ra/d) is more preferably from 0.017 to 0.043, and even more
preferably from 0.017 to 0.04.
[0045] The transparent conductor layer preferably has a maximum
surface roughness Ry of 7.5 to 15 nm in order to achieve pen input
durability and high-temperature, high-humidity reliability. The
maximum surface roughness Ry is more preferably from 7.5 to 14 nm,
and even more preferably from 7.5 to 13 nm.
[0046] Concerning the relationship between the thickness d and the
maximum surface roughness Ry of the transparent conductor layer,
the inventors have also found that controlling the ratio (Ry/d) of
the maximum surface roughness Ry to the thickness d within a
specific range contributes to achievement of both pen input
durability and high-temperature, high-humidity reliability.
Specifically, in the transparent conductor layer, the ratio (Ry/d)
of the maximum surface roughness Ry to the thickness d is
preferably from 0.34 to 1 in order to achieve pen input durability
and high-temperature, high-humidity reliability. The ratio (Ry/d)
is more preferably from 0.34 to 0.9, even more preferably from 0.34
to 0.8.
[0047] The transparent conductor layer 3 may be formed by any
method capable of satisfying the thickness d and average surface
roughness Ra range requirements, examples of which include a vacuum
deposition method, a sputtering method, and an ion plating method.
In particular, a sputtering method is preferred in view of
productivity and uniformity. The sputtering method may include
sputtering a target to deposit the transparent conductor layer 3 on
the undercoat layer 2.
[0048] The target may be any of a metal oxide target and a metal
target. In the invention, a metal oxide target is preferably used.
The metal oxide target to be used is preferably a sintered
material. Here, when the material for constituting the transparent
conductor layer is tin oxide-doped indium oxide, tin oxide-indium
oxide may be used as a metal oxide target, or a tin-indium alloy
may be used as a metal target. Here, sintered tin oxide-indium
oxide is preferably used as a metal oxide target.
[0049] The sputtering method may use any of a method of performing
sputtering under an argon gas atmosphere mainly composed of argon
gas and a method of performing reactive sputtering under an
oxygen-containing argon gas atmosphere. In the case of the former
sputtering method, a metal oxide target should be used. On the
other hand, in the case of the latter reactive sputtering method, a
metal oxide target or a metal target should be used. The invention
preferably uses a reactive sputtering method, and in particular,
preferably uses the reactive sputtering method with a metal oxide
target (preferably a sintered material). Here, in the reactive
sputtering method, the content of the oxygen gas in the argon gas
atmosphere may be from about 0.2 to 5% by volume, preferably from
0.2 to 3% by volume, based on the volume of the argon gas.
[0050] The sputtering method is preferably performed under a
discharge power condition of 4 to 7 W/cm.sup.2, in order to form
the transparent conductor layer 3 with the thickness d and the
average surface roughness Ra each falling within the above range.
If the discharge power is less than 4 W/cm.sup.2, there is a case
where irregularities could not be sufficiently formed. If the
discharge power is more than 7 W/cm.sup.2, there is a case where
nodules could be produced on the target surface so that stable
discharge could be impossible. The discharge power is more
preferably from 4 to 6.8 W/cm.sup.2, and even more preferably from
4 to 6.5 W/cm.sup.2. In addition, the sputtering method is
preferably performed with the transparent film substrate 1 heated
at a temperature of 80 to 160.degree. C. in order to form the
transparent conductor layer 3 with the thickness d and the average
surface roughness Ra each falling within the above range. Examples
of means for heating the transparent film substrate include such as
a heating roll and an IR heater. If the transparent film substrate
is heated at a temperature less than 80.degree. C., there is a case
where irregularities could not be sufficiently formed, and high
durability could not be provided. Here, the upper limit of the
temperature, 160.degree. C., is determined from the highest
temperature which the transparent film substrate can withstand. The
transparent film substrate 1 is preferably heated at a temperature
of 80 to 150.degree. C., and more preferably of 90 to 150.degree.
C.
[0051] The sputtering method may also be performed under the
atmospheric pressure or reduced pressure. The pressure is generally
from about 0.01 to 1 Pa, and preferably from 0.1 to 0.6 Pa.
[0052] After the transparent conductor layer 3 is formed, if
necessary, annealing treatment may be performed to crystallize at a
temperature in the range of 120 to 160.degree. C. The annealing
temperature is preferably from 130 to 155.degree. C. Therefore, the
film substrate 1 preferably has a heat resistance of 100.degree. C.
or more, and more preferably of 150.degree. C. or more. In
addition, the crystallization is preferably performed for 0.5 to 5
hours, and more preferably for 0.5 to 4 hours.
[0053] A transparent substrate 5 may also be bonded to the side of
the film substrate 1 where the transparent conductor layer 3 is not
provided, with the transparent pressure-sensitive adhesive layer 4
interposed therebetween. The transparent substrate 5 may be a
composite structure including at least two transparent substrate
films bonded with transparent pressure-sensitive adhesive
layer(s).
[0054] In general, the thickness of the transparent substrate 5 is
preferably from 90 to 300 .mu.m and more preferably controlled to
be from 100 to 250 .mu.m. When the transparent substrate 5 is
composed of a plurality of substrate films, the thickness of each
substrate film is preferably from 10 to 200 .mu.m, more preferably
from 20 to 150 .mu.m, and may be controlled such that the total
thickness of the transparent substrate 5 including these substrate
films and a transparent pressure-sensitive adhesive layer(s) can
fall within the above range. Examples of the substrate film may
include those described above for the film substrate 1.
[0055] The film substrate 1 and the transparent substrate 5 may be
bonded by a process including the steps of forming the
pressure-sensitive adhesive layer 4 on the transparent substrate 5
side and bonding the film substrate 1 thereto or by a process
including the steps of forming the pressure-sensitive adhesive
layer 4 contrarily on the film substrate 1 side and bonding the
transparent substrate 5 thereto. The latter process is more
advantageous in view of productivity, because it enables continuous
production of the pressure-sensitive adhesive layer 4 with the film
substrate 1 in the form of a roll. Alternatively, the transparent
substrate 5 may be formed on the film substrate 1 by sequentially
laminating a plurality of substrate films with the
pressure-sensitive adhesive layers. The transparent
pressure-sensitive adhesive layer for use in laminating the
substrate films may be made of the same material as the transparent
pressure-sensitive adhesive layer 4 described below. When the
transparent conductive films are bonded to each other, appropriate
transparent conductive films on which the transparent
pressure-sensitive adhesive layer 4 is laminated may be selected
and the transparent conductive films are bonded to each other.
[0056] Any transparent pressure-sensitive adhesive may be used for
the pressure-sensitive adhesive layer 4 without limitation. For
example, the pressure-sensitive adhesive may be appropriately
selected from adhesives based on polymers such as acrylic polymers,
silicone polymers, polyester, polyurethane, polyamide, polyvinyl
ether, vinyl acetate-vinyl chloride copolymers, modified
polyolefins, epoxy polymers, fluoropolymers, and rubbers such as
natural rubbers and synthetic rubbers. In particular, acrylic
pressure-sensitive adhesives are preferably used, because they have
good optical transparency and good weather or heat resistance and
exhibit suitable wettability and adhesion properties such as
cohesiveness and adhesiveness.
[0057] The anchoring strength can be improved using an appropriate
pressure-sensitive adhesive primer, depending on the type of the
pressure-sensitive adhesive as a material for forming the
pressure-sensitive adhesive layer 4. In the case of using such a
pressure-sensitive adhesive, therefore, a certain
pressure-sensitive adhesive primer is preferably used.
[0058] The pressure-sensitive adhesive primer may be of any type as
long as it can improve the anchoring strength of the
pressure-sensitive adhesive. For example, the pressure-sensitive
adhesive primer that may be used is a so-called coupling agent such
as a silane coupling agent having a hydrolyzable alkoxysilyl group
and a reactive functional group such as amino, vinyl, epoxy,
mercapto, and chloro in the same molecule; a titanate coupling
agent having an organic functional group and a titanium-containing
hydrolyzable hydrophilic group in the same molecule; and an
aluminate coupling agent having an organic functional group and an
aluminum-containing hydrolyzable hydrophilic group in the same
molecule; or a resin having an organic reactive group, such as an
epoxy resin, an isocyanate resin, a urethane resin, and an ester
urethane resin. In particular, a silane coupling agent-containing
layer is preferred, because it is easy to handle industrially.
[0059] The pressure-sensitive adhesive layer 4 may contain a
crosslinking agent depending on the base polymer. If necessary, the
pressure-sensitive adhesive layer 4 may also contain appropriate
additives such as natural or synthetic resins, glass fibers or
beads, or fillers comprising metal powder or any other inorganic
powder, pigments, colorants, and antioxidants. The
pressure-sensitive adhesive layer 4 may also contain transparent
fine particles so as to have light diffusing ability.
[0060] The transparent fine particles to be used may be one or more
types of appropriate conductive inorganic fine particles of silica,
calcium oxide, alumina, titania, zirconia, tin oxide, indium oxide,
cadmium oxide, antimony oxide, or the like with an average particle
size of 0.5 to 20 .mu.m or one or more types of appropriate
crosslinked or uncrosslinked organic fine particles of an
appropriate polymer such as poly(methyl methacrylate) and
polyurethane with an average particle size of 0.5 to 20 .mu.m.
[0061] The pressure-sensitive adhesive layer 4 is generally formed
using a pressure-sensitive adhesive solution that includes a base
polymer or a composition thereof dissolved or dispersed in a
solvent and has a solid content concentration of about 10 to 50% by
weight. An organic solvent such as toluene or ethyl acetate, water
or the like may be appropriately selected depending on the type of
the pressure-sensitive adhesive and used as the solvent.
[0062] After the bonding of the transparent substrate 5, for
example, the pressure-sensitive adhesive layer 4 has a cushion
effect and thus can function to improve the scratch resistance of
the transparent conductor layer formed on one side of the film
substrate 1 or to improve the tap properties thereof for touch
panels, such as so called pen input durability and surface pressure
durability. In terms of performing this function better, it is
preferred that the elastic modulus of the pressure-sensitive
adhesive layer 4 is set in the range of 1 to 100 N/cm.sup.2 and
that its thickness is set at 1 .mu.m or more, generally in the
range of 5 to 100 .mu.m. If the thickness is as described above,
the effect can be sufficiently produced, and the adhesion between
the transparent substrate 5 and the film substrate 1 can also be
sufficient. If the thickness is lower than the above range, the
durability or adhesion cannot be sufficiently ensured. If the
thickness is higher than the above range, outward appearances such
as transparency can be degraded. Here, in other aspects, the
elastic modulus and the thickness of the pressure-sensitive
adhesive layer 4 to be applied to the transparent conductive film
may be the same as those described above.
[0063] If the elastic modulus is less than 1 N/cm.sup.2, the
pressure-sensitive adhesive layer 4 can be inelastic so that the
pressure-sensitive adhesive layer 4 can easily deform by pressing
to make the film substrate 1 irregular and further to make the
transparent conductor layer 3 irregular. If the elastic modulus is
less than 1 N/cm.sup.2, the pressure-sensitive adhesive can be
easily squeezed out of the cut section, and the effect of improving
the scratch resistance of the transparent conductor layer 3 or
improving the tap properties of the transparent conductor layer 3
for touch panels can be reduced. If the elastic modulus is more
than 100 N/cm.sup.2, the pressure-sensitive adhesive layer 4 can be
hard, and the cushion effect cannot be expected, so that the
scratch resistance of the transparent conductor layer 3 or the pen
input durability and surface pressure durability of the transparent
conductor layer 3 for touch panels tends to be difficult to be
improved.
[0064] If the thickness of the pressure-sensitive adhesive layer 4
is less than 1 .mu.m, the cushion effect also cannot be expected so
that the scratch resistance of the transparent conductor layer 3 or
the pen input durability and surface pressure durability of the
transparent conductor layer 3 for touch panels tends to be
difficult to be improved. If it is too thick, it can reduce the
transparency, or it can be difficult to obtain good results on the
formation of the pressure-sensitive adhesive layer 4, the bonding
workability of the transparent substrate 5, and the cost.
[0065] The transparent substrate 5 bonded through the
pressure-sensitive adhesive layer 4 as described above imparts good
mechanical strength to the film substrate 1 and contributes to not
only the pen input durability and the surface pressure durability
but also the prevention of curling.
[0066] The pressure-sensitive adhesive layer 4 may be transferred
using a separator. In such a case, for example, the separator to be
used may be a laminate of a polyester film of a
migration-preventing layer and/or a release layer, which is
provided on a polyester film side to be bonded to the
pressure-sensitive adhesive layer 4.
[0067] The total thickness of the separator is preferably 30 .mu.m
or more, more preferably in the range of 60 to 100 .mu.m. This is
to prevent deformation of the pressure-sensitive adhesive layer 4
(dents) in a case where the pressure-sensitive adhesive layer 4 is
formed and then stored in the form of a roll, in which the
deformation (dents) can be expected to be caused by foreign
particles or the like intruding between portions of the rolled
layer.
[0068] The migration-preventing layer may be made of an appropriate
material for preventing migration of migrant components in the
polyester film, particularly for preventing migration of low
molecular weight oligomer components in the polyester. An inorganic
or organic material or a composite of inorganic and organic
materials may be used as a material for forming the
migration-preventing layer. The thickness of the
migration-preventing layer may be set in the range of 0.01 to 20
.mu.m as needed. The migration-preventing layer may be formed by
any method such as coating, spraying, spin coating, and in-line
coating. Vacuum deposition, sputtering, ion plating, spray thermal
decomposition, chemical plating, electroplating, or the like may
also be used.
[0069] The release layer may be made of an appropriate release
agent such as a silicone release agent, a long-chain alkyl release
agent, a fluorochemical release agent, and a molybdenum sulfide
release agent. The thickness of the release layer may be set as
appropriate in view of the release effect. In general, the
thickness is preferably 20 .mu.m or less, more preferably in the
range of 0.01 to 10 .mu.m, particularly preferably in the range of
0.1 to 5 .mu.m, in view of handleability such as flexibility. A
production method of the release layer is not particularly limited,
and may be formed in the same manner as in the case of the
migration-preventing layer.
[0070] An ionizing radiation-curable resin such as an acrylic
resin, a urethane resin, a melamine resin, and an epoxy resin or a
mixture of the above resin and aluminum oxide, silicon dioxide,
mica, or the like may be used in the coating, spraying, spin
coating, or in-line coating method. When the vacuum deposition,
sputtering, ion plating, spray thermal decomposition, chemical
plating, or electroplating method is used, a metal such as gold,
silver, platinum, palladium, copper, aluminum, nickel, chromium,
titanium, iron, cobalt, or tin or an oxide of an alloy thereof or
any other metal compounds such as metal iodides may be used.
[0071] If necessary, a hard coat layer (resin layer) 6 for
protecting the outer surface may be formed on the outer surface of
the transparent substrate 5 (on the side opposite to the
pressure-sensitive adhesive layer 4). For example, the hard coat
layer 6 is preferably made of a cured coating film of a curable
resin such as a melamine resin, a urethane resin, an alkyd resin,
an acrylic resin, and a silicone resin. The hard coat layer 6
preferably has a thickness of 0.1 to 30 .mu.m. If its thickness is
less than 0.1 .mu.m, its hardness can be inadequate. If its
thickness exceeds 30 .mu.m, the hard coat layer 6 can be cracked,
or curling can occur in the whole of the transparent substrate
5.
[0072] The transparent conductive film of the present invention may
be provided with an antiglare layer or an antireflection layer for
the purpose of increasing visibility. When the transparent
conductive film is used for a resistive film type touch panel, an
antiglare layer or an antireflection layer may be formed on the
outer surface of the transparent substrate 5 (on the side opposite
to the pressure-sensitive adhesive layer 4) similarly to the hard
coat layer 6. An antiglare layer or an antireflection layer may
also be formed on the hard coat layer 6. On the other hand, when
the transparent conductive film is used for a capacitive type touch
panel, an antiglare layer or an antireflection layer may be formed
on the transparent conductor layer 3.
[0073] For example, the material to be used to form the antiglare
layer may be, but not limited to, an ionizing radiation-curable
resin, a thermosetting resin, a thermoplastic resin, or the like.
The thickness of the antiglare layer is preferably from 0.1 to 30
.mu.m.
[0074] The antireflection layer may use titanium oxide, zirconium
oxide, silicon oxide, magnesium fluoride, or the like. In order to
produce a more significant antireflection function, a laminate of a
titanium oxide layer(s) and a silicon oxide layer(s) is preferably
used. Such a laminate is preferably a two-layer laminate comprising
a high-refractive-index titanium oxide layer (refractive index:
about 2.35), which is formed on the hard coat layer 6, and a
low-refractive-index silicon oxide layer (refractive index: about
1.46), which is formed on the titanium oxide layer. Also preferred
is a four-layer laminate which comprises the two-layer laminate and
a titanium oxide layer and a silicon oxide layer formed in this
order on the two-layer laminate. The antireflection layer of such a
two- or four-layer laminate can evenly reduce reflection over the
visible light wavelength range (380 to 780 nm).
[0075] For example, the transparent conductive film of the present
invention is suitable for use in optical type, ultrasonic type,
capacitive type, or resistive film type touch panels. In
particular, the transparent conductive film of the invention is
suitable for use in resistive film type touch panels.
EXAMPLES
[0076] The invention is more specifically described with some
examples below. It will be understood that the invention is not
limited to the examples below without departing from the gist of
the invention. In each example, the term "part or parts" means part
or parts by weight, unless otherwise stated.
Refractive Index
[0077] The refractive index of each layer was measured with a
measuring beam incident on the measurement surface of each object
in an Abbe refractometer manufactured by Atago Co., Ltd., according
the measurement method specified for the refractometer.
Thickness of Each Layer
[0078] The thickness of the layer with a thickness of at least 1
.mu.m, such as the film substrate, the transparent substrate, the
hard coat layer, and the pressure-sensitive adhesive layer, was
measured with a microgauge type thickness gauge manufactured by
Mitutoyo Corporation. The thickness of the layer whose thickness
was difficult to directly measure, such as the hard coat layer and
the pressure-sensitive adhesive layer, was calculated by
subtracting the thickness of the substrate from the measured total
thickness of the substrate and each layer formed thereon.
[0079] The thickness of the undercoat layer or the transparent
conductor layer was calculated using an instantaneous multichannel
photodetector system MCPD-2000 (trade name) manufactured by Otsuka
Electronics Co., Ltd., based on the waveform data of the resulting
interference spectrum.
Example 1
Formation of Undercoat Layer
[0080] A thermosetting resin (with a light refractive index n of
1.54) composed of a melamine resin, an alkyd resin and an
organosilane condensate (2:2:1 in weight ratio) was used to form a
first undercoat layer having a thickness of 185 nm on one side of a
film substrate made of a polyethylene terephthalate film
(hereinafter referred to as "PET film") having a thickness of 25
.mu.m. Then a silica sol (Colcoat P, manufactured by Colcoat Co.,
Ltd.) was diluted with ethanol to a solid content concentration of
2% by weight. The diluted silica sol was applied to the first
undercoat layer by a silica coating method and then dried and cured
at 150.degree. C. for 2 minutes to form a second undercoat layer (a
SiO.sub.2 film with a light refractive index of 1.46) having a
thickness of 33 nm.
Formation of Transparent Conductor Layer
[0081] While the PET film was heated at a temperature of
100.degree. C., an ITO film (with a light refractive index of 2.00)
having a thickness of 22 nm was formed on the second undercoat
layer by a reactive sputtering method with a sintered material of
97% by weight of indium oxide and 3% by weight of tin oxide at a
discharge power of 6.35 W/cm.sup.2 in a 0.4 Pa atmosphere composed
of 99% by volume of argon gas and 1% by volume of oxygen gas.
Formation of Hard Coat Layer
[0082] A toluene solution for use as a hard coat layer-forming
material was prepared by adding 5 parts of hydroxycyclohexyl phenyl
ketone (Irgacure 184, manufactured by Ciba Specialty Chemicals
Inc.) for serving as a photopolymerization initiator to 100 parts
of an acrylic urethane-based resin (Unidic 17-806, manufactured by
DIC Corporation) and diluting the mixture to a concentration of 30%
by weight.
[0083] The hard coat layer-forming material was applied to one side
of a transparent substrate made of a PET film having a thickness of
125 .mu.m and dried at 100.degree. C. for 3 minutes. The coating
was then immediately irradiated with light from two ozone-type
high-pressure mercury lamps (80 W/cm.sup.2 in energy density, 15 cm
focused radiation) to form a hard coat layer having a thickness of
5 .mu.m.
Preparation of Transparent Conductive Film
[0084] A transparent acrylic-based pressure-sensitive adhesive
layer with a thickness of about 20 .mu.m and an elastic modulus of
10 N/cm.sup.2 was then formed on the surface of the transparent
substrate opposite to the surface where the hard coat layer was
formed. A mixture of 100 parts of an acrylic-based copolymer of
butyl acrylate, acrylic acid and vinyl acetate (100:2:5 in weight
ratio) and 1 part of an isocyanate-based crosslinking agent was
used as a composition of the pressure-sensitive adhesive layer. The
film substrate (the surface on which the transparent conductor
layer was not formed) was bonded to the pressure-sensitive adhesive
layer side to form a transparent conductive film.
Crystallization of the Transparent Conductor Layer
[0085] After the transparent conductive film was prepared, heat
treatment was performed at 140.degree. C. for 90 minutes so that
the ITO film was crystallized.
Preparation of Touch Panel
[0086] The transparent conductive film was used as one of the panel
plates, and a glass plate on which an ITO thin film having a
thickness of 30 nm was formed was used as the other panel plate.
Both panel plates were arranged opposite to each other with spacers
having a thickness of 10 .mu.m interposed therebetween in such a
manner that the ITO thin films faced each other, so that a touch
panel for serving as a switch structure was prepared.
Examples 2 to 4 and Comparative Examples 1 to 4
[0087] Transparent conductive films were prepared using the process
of Example 1, except that the temperature at which the PET film was
heated, the discharge power, and the thickness of the transparent
conductor layer was changed as shown in Table 1 when the
transparent conductor layer was formed. Further, in the same manner
as in Example 1, the ITO film of the transparent conductive film
was crystallized, and then each touch panel was prepared.
[0088] The transparent conductive film and the touch panel (sample)
prepared in each of Examples and Comparative Examples were
evaluated as described below. The results are shown in Table 1.
Surface Characteristics of the Transparent Conductor Layer
[0089] AFM observation was performed with a scanning probe
microscope (SPI 3800, manufactured by SII Nano Technology Inc.).
The measurement was performed with a Si.sub.3N.sub.4 probe (0.09
N/m in spring constant) in the contact mode. The average surface
roughness (Ra) and the maximum height (Ry) were determined by
scanning a 1 .mu.m.sup.2 area.
Surface Resistance of ITO Film
[0090] The surface electric resistance (.OMEGA./square) of the ITO
film was measured using a two-terminal method.
Light Transmittance
[0091] The visible light transmittance was measured at a light
wavelength of 550 nm using a spectroscopic analyzer UV-240
manufactured by Shimadzu Corporation.
Pen Input Durability
[0092] A polyacetal pen (0.8 mm in pen nib R) was allowed to slide
300,000 times under a load of 500 g on the panel plate surface
formed of the transparent conductive film. After the sliding, the
linearity (%) of the transparent conductive film was measured as
described below, and the pen input durability was evaluated.
Method for Measuring Linearity
[0093] A voltage of 5 V was applied to the transparent conductive
film, in which an output voltage was measured between a
voltage-applied terminal A (measurement start point) and a terminal
B (measurement end point).
[0094] The linearity was calculated from the formulae:
E.sub.XX (theoretical value)={X(E.sub.B-E.sub.A)/(B-A)}+E.sub.A
Linearity (%)=[(E.sub.xx-E.sub.x)/(E.sub.B-E.sub.A)].times.100,
wherein
E.sub.A is the output voltage at the measurement start point A,
E.sub.B is the output voltage at the measurement end point B, Ex is
the output voltage at each measurement point X, and E.sub.XX is the
theoretical value.
[0095] The outline of the measurement of the linearity is shown in
FIG. 4. In a touch panel-equipped image display, the position of
the pen displayed on the screen is determined from a resistance
value of a portion where an upper panel and a lower panel are
brought into contact with each other by pressing with the pen. The
resistance value is determined assuming that the output voltage is
distributed on the surface of the upper and lower panels according
to the theoretical line (ideal line). Accordingly, if the measured
voltage value deviates from the theoretical line as shown in FIG.
4, the actual position of the pen will not well synchronize with
the pen position on the screen that is determined from the
resistance value. Such a deviation from the theoretical line
corresponds to the linearity. The larger the linearity value, the
larger the deviation of the actual pen position from the pen
position on the screen.
Reliability in High-Temperature, High-Humidity Environment
[0096] The transparent conductive film obtained in each Example was
named sample A. Sample A was left in an environment at 60.degree.
C. and 95% R.H. for 500 hours. After the treatment, the sample was
named sample B. These samples were each measured for surface
electric resistance (a/square) in the same manner as those
described above, and the ratio (Rs/RA) of the resistance (Rs) of
the sample B to the resistance (RA) of the sample A was calculated
for evaluation of the reliability.
TABLE-US-00001 TABLE 1 Sputtering Conditions Evaluations Film
Discharge Transparent Conductor Layer Surface Light Pen Input
Reliability Temperature Power Thickness Surface Characteristics
Resistance Transmittance Durability (Resistance (.degree. C.)
(W/cm.sup.2) d (nm) Ra(nm) Ra/d Ry(nm) Ry/d (.OMEGA./square) (%)
(Linearity) (%) Change Ratio) Example 1 100 6.35 22 0.80 0.036
12.60 0.57 300 90 1.0 1 Example 2 100 5.33 22 0.50 0.022 11.50 0.52
300 90 1.0 1 Example 3 100 4.44 22 0.45 0.020 10.80 0.49 300 90 1.0
1 Example 4 100 4.13 22 0.40 0.018 9.00 0.41 300 90 1.5 1
Comparative 40 4.44 22 0.35 0.016 7.00 0.32 300 90 2.0 1 Example 1
Comparative 100 3.81 22 0.30 0.014 6.81 0.31 300 90 2.5 1 Example 2
Comparative 100 3.17 22 0.30 0.014 6.56 0.30 300 90 3.0 1 Example 3
Comparative 100 6.35 12 0.40 0.033 6.50 0.54 800 91 50.0 2 Example
4
* * * * *