U.S. patent application number 11/455991 was filed with the patent office on 2010-09-02 for touchscreen with carbon nanotube conductive layers.
This patent application is currently assigned to Eastman Kodak Company. Invention is credited to Charles C. Anderson, Glen C. Irvin, JR., Debasis Majumdar, Lawrence A. Rowley, Todd M. Spath.
Application Number | 20100220074 11/455991 |
Document ID | / |
Family ID | 38704789 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100220074 |
Kind Code |
A1 |
Irvin, JR.; Glen C. ; et
al. |
September 2, 2010 |
TOUCHSCREEN WITH CARBON NANOTUBE CONDUCTIVE LAYERS
Abstract
The present invention is directed to a touchscreen comprising
touch side electrode and device side electrode wherein each
electrode comprises an insulating substrate and an exposed
electrically conductive layer, wherein said exposed electrically
conductive layers are adjacent and separated by dielectric spacers,
and wherein only one of the exposed electrically conductive layers
comprises carbon nanotubes.
Inventors: |
Irvin, JR.; Glen C.;
(Rochester, NY) ; Spath; Todd M.; (Hilton, NY)
; Anderson; Charles C.; (Penfield, NY) ; Rowley;
Lawrence A.; (Rochester, NY) ; Majumdar; Debasis;
(Rochester, NY) |
Correspondence
Address: |
Paul A. Leipold;Patent Legal Staff
Eastman Kodak Company, 343 State Street
Rochester
NY
14650-2201
US
|
Assignee: |
Eastman Kodak Company
|
Family ID: |
38704789 |
Appl. No.: |
11/455991 |
Filed: |
June 20, 2006 |
Current U.S.
Class: |
345/174 ;
345/104 |
Current CPC
Class: |
G06F 3/045 20130101 |
Class at
Publication: |
345/174 ;
345/104 |
International
Class: |
G09G 3/36 20060101
G09G003/36; G06F 3/045 20060101 G06F003/045 |
Claims
1. A touchscreen comprising touch side and device side electrodes
wherein each electrode comprises in order an insulating substrate,
an exposed electrically conductive layer, wherein said exposed
electrically conductive layers are adjacent and separated by
dielectric spacers, and wherein said exposed electrically
conductive layers comprise single wall carbon nanotubes and wherein
said carbon nanotubes comprise covalently attached hydrophilic
species.
2. The touchscreen of claim 1 wherein the hydrophilic species is
present in an amount of between 0.5 and 5 atomic %.
3. The touchscreen of claim 1 wherein said hydrophilic species
comprises carboxylic acid or carboxylic acid salt or mixtures
thereof.
4. The touchscreen of claim 1 wherein said hydrophilic species
comprises a sulfur containing group selected from: SO.sub.xZ.sub.y
Wherein x ranges from 1-3 and Z may be a Hydrogen atom or a metal
cation of such metals as Na, Mg, K, Ca, Zn, Mn, Ag, Au, Pd, Pt, Fe,
Co and y may range from 0 or 1.
5. The touchscreen of claim 1 wherein said carbon nanotubes have an
outer diameter of between 0.5 and 5 nanometers.
6. The touchscreen of claim 1 wherein said carbon nanotubes
comprise bundles of a diameter of between 1 and 50 nanometers.
7. The touchscreen of claim 1 wherein said carbon nanotubes
comprise bundles of a diameter of between 1 and 20 nanometers.
8. The touchscreen of claim 1 wherein said carbon nanotubes have a
length of between 20 nanometers and 50 microns.
9. The touchscreen of claim 1 wherein said carbon nanotubes
comprise bundles of a length of between 20 nanometers and 50
microns.
10. The touchscreen of claim 1 wherein said carbon nanotubes are
metallic carbon nanotubes.
11. The touchscreen of claim 1 wherein said hydrophilic species
comprises sulfonic acids or sulfonic acid salts or mixtures
thereof.
12. The touchscreen of claim 1 wherein said carbon nanotubes are
open end carbon nanotubes.
13. The touchscreen of claim 1 wherein said covalently attached
hydrophilic species is present on the outside wall of said carbon
nanotube.
14. The touchscreen of claim 1 wherein the electronically
conductive layer comprising carbon nanotubes further comprises a
binder.
15. The touchscreen of claim 1 wherein said electronically
conductive layer adjacent said substrate has a sheet resistance of
between 10 and 10.sup.6 Ohm per square.
16. The touchscreen of claim 1 wherein said electronically
conductive layer comprising carbon nanotubes have a sheet
resistance of between 10.sup.2 to 10.sup.4 Ohm per square.
17. The touchscreen of claim 1 wherein said electronically
conductive layer comprises a binder.
18. The touchscreen of claim 17 wherein said binder comprises water
soluble or water dispersible polymers.
19. The touchscreen of claim 1 wherein said touchscreen is capable
of greater than 500,000 single point actuations.
20. A touchscreen comprising touch side and device side electrodes
wherein each electrode comprises in order an insulating substrate,
an exposed electrically conductive layer, wherein said exposed
electrically conductive layers are adjacent and separated by
dielectric spacers, and wherein said exposed electrically
conductive layers comprise single wall carbon nanotubes and wherein
said carbon nanotubes comprise covalently attached hydrophilic
species; and wherein said touchscreen has a visible light
transparency of greater than 70 percent.
21. The touchscreen of claim 1 wherein said substrates have a
visible light transparency of greater than 70 percent and comprise
polyethyleneterephthalate, polyethylenenaphthalate, polycarbonate
or glass.
22. The touchscreen of claim 1 wherein said touch side substrate
further comprises an anti-glare coat.
23. The touchscreen of claim 1 wherein said touch side substrate
further comprises an anti-reflection coat.
24. The touchscreen of claim 1 wherein said touch side substrate
further comprises a hardcoat having a pencil hardness greater than
2H.
25. The touchscreen of claim 1 wherein said touch side substrate
further comprises a ultra violet light absorbing layer.
26. A touchscreen comprising touch side and device side electrodes
wherein each electrode comprises in order an insulating substrate,
an exposed electrically conductive layer, wherein said exposed
electrically conductive layers are adjacent and separated by
dielectric spacers, and wherein said exposed electrically
conductive layers comprise single wall carbon nanotubes and wherein
said carbon nanotubes comprise covalently attached hydrophilic
species; wherein said touchscreen has a visible light transparency
of greater than 70 percent: and wherein the average force required
to actuate a point on the touchscreen does not change by more than
100 percent over 500,000 single point actuations.
27. A device comprising a display device having attached thereto a
touchscreen comprising touch side and device side electrodes
wherein each electrode comprises an exposed electrically conductive
layer, wherein said exposed electrically conductive layers are
adjacent and separated by dielectric spacers, and wherein at least
the first electrically conductive layers or the exposed
electrically conductive layers comprise carbon nanotubes and
wherein said carbon nanotubes comprise covalently attached
hydrophilic species; and wherein said touchscreen has a visible
light transparency of greater than 70 percent.
28. The device of claim 27 wherein said display device comprises a
LCD based display.
29. The device of claim 28 wherein said LCD comprises a polarizer
plate and the touchscreen is adhesively attached to said polarizer
plate.
30. A touchscreen comprising touch side and device side electrodes
wherein each electrode comprises in order an insulating substrate,
an exposed electrically conductive layer, wherein said exposed
electrically conductive layers are adjacent and separated by
dielectric spacers, and wherein said exposed electrically
conductive layers comprise single wall carbon nanotubes and wherein
said carbon nanotubes comprise covalently attached hydrophilic
species: and wherein the average force required to actuate a point
on the touchscreen does not change by more than 50 percent over
500,000 single point actuations.
31. The touchscreen of claim 27 wherein the average force required
to actuate a point on the touchscreen does not change by more than
100 percent over 500,000 single point actuations.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to touchscreens for
electronic devices. In particular the invention provides a
touchscreen comprising touch side and device side electrodes
wherein each electrode comprises in order an insulating substrate,
an exposed electrically conductive layer, wherein said exposed
electrically conductive layers are adjacent and separated by
dielectric spacers, and wherein said exposed electrically
conductive layers comprise single wall carbon nanotubes and wherein
said carbon nanotubes comprise covalently attached hydrophilic
species.
BACKGROUND OF THE INVENTION
[0002] Devices such as flat-panel displays typically contain a
substrate provided with an indium tin oxide (ITO) layer as a
transparent electrode. The coating of ITO is carried out by vacuum
sputtering methods, which involve high substrate temperature
conditions up to 250.degree. C., and therefore, glass substrates
are generally used. The high cost of the fabrication methods and
the low flexibility of such electrodes, due to the brittleness of
the inorganic ITO layer as well as the glass substrate, limit the
range of potential applications. As a result, there is a growing
interest in making all-organic devices, comprising plastic resins
as a flexible substrate and carbon nanotube or organic
electroconductive polymer layers as an electrode. Such plastic
electronics allow low cost devices with new properties. Flexible
plastic substrates can be provided with an electroconductive
polymer layer by continuous hopper or roller coating methods
(compared to batch process such as sputtering) and the resulting
organic electrodes enable the "roll to roll" fabrication of
electronic devices which are more flexible, lower cost, and lower
weight. Touchscreens (also referred to as touch panels or touch
switches) are widely used in conventional CRTs and in flat-panel
display devices in computers and in particular with portable
computers. FIG. 1 shows a typical prior art resistive-type
touchscreen 10 comprising a first electrode 15 that is on the side
of the touchscreen that is nearer to the device that is referred
herein below as the device side electrode and a second electrode 16
that is on the side of the touchscreen that is nearer to the user
that is referred herein below as the touch side electrode. Device
side electrode 15 comprises a transparent substrate 12, having a
first conductive layer 14. Touch side electrode 16 comprises a
transparent support 17, that is typically a flexible transparent
support, and a second conductive layer 18 that is physically
separated from the first conductive layer 14 by dielectric
(insulating) spacer elements 20. A voltage is developed across the
conductive layers. The conductive layers 14 and 18 have a
resistance selected to optimize power usage and position sensing
accuracy. Deformation of the touch side electrode 16 by an external
object such as a finger or stylus causes the second conductive
layer 18 to make electrical contact with first conductive layer 14,
thereby transferring a voltage between the conductive layers. The
magnitude of this voltage is measured through connectors (not
shown) connected to metal bus bar conductive patterns (not shown)
formed on the edges of conductive layers 18 and 14 to locate the
position of the deforming object.
[0003] ITO is commonly employed as the transparent conductive layer
on the device side and touch side electrodes. However, ITO tends to
crack under stress and with the result that the conductivity of the
electrodes, especially for the touch side electrode, is diminished
and the performance of the touchscreen degraded. More flexible
conductive polymer-containing layers have also been considered for
this application, but these conductive polymers are softer and less
physically durable than ITO and therefore such conductive layers
tend to degrade after repeated contacts.
[0004] Single wall carbon nanotubes (SWCNTs) are essentially
graphene sheets rolled into hollow cylinders thereby resulting in
tubules composed of sp.sup.2 hybridized carbon arranged in hexagons
and pentagons, which have outer diameters between 0.4 nm and 10 nm.
These SWCNTs are typically capped on each end with a hemispherical
fullerene (buckyball) appropriately sized for the diameter of the
SWCNT. However, these end caps may be removed via appropriate
processing techniques leaving uncapped tubules. SWCNTs can exist as
single tubules or in aggregated form typically referred to as ropes
or bundles. These ropes or bundles may contain several or a few
hundred SWCNTs aggregated through Van der Waals interactions
forming triangular lattices where the tube-tube separation is
approximately 3-4 .ANG.. Ropes of SWCNTs may be composed of
associated bundles of SWCNTs.
[0005] The inherent properties of SWCNTs make them attractive for
use in many applications. SWCNTs can possess high (e.g. metallic
conductivities) electronic conductivities, high thermal
conductivities, high modulus and tensile strength, high aspect
ratio and other unique properties. Further, SWCNTs may be metallic,
semi-metallic, or semiconducting dependant on the geometrical
arrangement of the carbon atoms and the physical dimensions of the
SWCNT. To specify the size and conformation of single-wall carbon
nanotubes, a system has been developed, described below, and is
currently utilized. SWCNTs are described by an index (n, m), where
n and m are integers that describe how to cut a single strip of
hexagonal graphite such that its edges join seamlessly when the
strip is wrapped into the form of a cylinder. When n=m e.g. (n, n),
the resultant tube is said to be of the "arm-chair" or (n, n) type,
since when the tube is cut perpendicularly to the tube axis, only
the sides of the hexagons are exposed and their pattern around the
periphery of the tube edge resembles the arm and seat of an arm
chair repeated n times. When m=0, the resultant tube is said to be
of the "zig zag" or (n,0) type, since when the tube is cut
perpendicular to the tube axis, the edge is a zig zag pattern.
Where n.noteq.m and m=0, the resulting tube has chirality. The
electronic properties are dependent on the conformation; for
example, armchair tubes are metallic and have extremely high
electrical conductivity. Other tube types are semimetals or
semi-conductors, depending on their conformation. SWCNTs have
extremely high thermal conductivity and tensile strength
irrespective of the chirality. The work functions of the metallic
(approximately 4.7 eV) and semiconducting (approximately 5.1 eV)
types of SWCNTs are different.
[0006] Similar to other forms of carbon allotropes (e.g. graphite,
diamond) these SWCNTs are intractable and essentially insoluble in
most solvents (organic and aqueous alike). Thus, SWCNTs have been
extremely difficult to process for various uses. Several methods to
make SWCNTs soluble in various solvents have been employed. One
approach is to covalently functionalize the ends of the SWCNTs with
either hydrophilic or hydrophobic moieties. A second approach is to
add high levels of surfactant and/or dispersants (small molecule or
polymeric) to help solubilize the SWCNTs.
[0007] Lavin et al. in U.S. Pat. No. 6,426,134 disclose a method to
form polymer composites using SWCNTs. This method provides a means
to melt extrude a SWCNT/polymer composite wherein at least one end
of the SWCNT is chemically bonded to the polymer, where the polymer
is selected from a linear or branched polyamide, polyester,
polyimide, or polyurethane. This method is limited to melt
extrusion which can limit opportunities for patterning or device
making. The chemically bonded polymers identified typically have
high molecular weights and could interfere with some material
properties of the SWCNTs (e.g. electronic or thermal transport) via
wrapping around the SWCNTs and preventing tube-tube contacts.
[0008] Connell et al in US Patent Application Publication
2003/0158323 A1 describes a method to produce polymer/SWCNT
composites that are electronically conductive and transparent. The
polymers (polyimides, copolyimides, polyamide acid,
polyaryleneether, polymethylmethacrylate) and the SWCNTs or MWCNTs
are mixed in organic solvents (DMF, N,N-dimethlacetamide,
N-methyl-2-pyrrolidinone, toluene,) to cast films that have
conductivities in the range of 10.sup.-5-10.sup.-12 S/cm with
varying transmissions in the visible spectrum. Additionally,
monomers of the resultant polymers may be mixed with SWCNTs in
appropriate solvents and polymerized in the presence of these
SWCNTs to result in composites with varying weight ratios. The
conductivities achieved in these polymer composites are several
orders of magnitude too low for use in most electronic devices as
electronic conductors or EMI shields. Additionally, the organic
solvents used are toxic, costly and pose problems in processing.
Moreover, the polymers used or polymerized are not conductive and
can impede tube-tube contact further increasing the resistivity of
the composite.
[0009] Kuper et al in Publication WO 03/060941A2 disclose
compositions to make suspended carbon nanotubes. The compositions
are composed of liquids and SWCNTs or MWCNTs with suitable
surfactants (cetyl trimethylammonium bromide/chloride/iodide). The
ratio by weight of surfactant to SWCNTs given in the examples range
from 1.4-5.2. This method is problematic, as it needs extremely
large levels of surfactant to solubilize the SWCNTs. The surfactant
is insulating and impedes conductivity of a film deposited from
this composition. The surfactant may be washed from the film but
this step adds complexity and may decrease efficiency in
processing.
[0010] Papadaopoulos et al. in U.S. Pat. No. 5,576,162 describe an
imaging element, which comprises carbon nanofibers to be used
primarily as an anti-static material within the imaging element.
These materials do not provide a highly transparent and highly
conductive (low sheet resistance, R.sub.S) layer.
[0011] Smalley et al in U.S. Pat. No. 6,645,455 disclose methods to
chemically derivatize SWCNTs to facilitate solvation in various
solvents. Primarily the various derivative groups (alkyl chains,
acyl, thiols, aminos, aryls etc.) are added to the ends of the
SWCNTs. The side-walls of the SWCNTs are functionalized primarily
with fluorine groups resulting in fluorinated SWCNTs. The
solubility limit of such "fluorotubes" in 2-propanol is
approximately 0.1 mg/mL and in water or water/acetone mixtures the
solubility is essentially zero. The fluorinated SWCNTs were
subjected to further chemical reactions to yield methylated SWCNTs
and these tubes have a low solubility in Chloroform but not other
solvents. In addition, the method discloses functionalization of
the tubule ends with various functionalization groups (acyl, aryl,
aralkyl, halogen, alkyl, amino, halogen, thiol. Further, the
sidewall functionalization is done with fluorine only, which gives
limited solubility in alcohols. Additionally, the fluorinated
SWCNTs are insulators due to the fluorination. Moreover, the
chemical transformations needed to add these functional groups to
the end points of the SWCNTs require additional processing steps
and chemicals which can be hazardous and costly.
[0012] Smalley et al. in U.S. Pat. No. 6,683,783 disclose methods
to purify SWCNT materials resulting in SWCNTs with lengths from
5-500 nm. Within this patent, formulations are disclosed that use
0.5 wt % of a surfactant, Triton X-100 to disperse 0.1 mg/mL of
SWCNT in water. The method discloses functionalization of the
tubule ends with various functionalization groups (acyl, aryl,
aralkyl, halogen, alkyl, amino, halogen, thiol) but the end
functionalization alone may not be enough to produce viable
dispersions via solubilization. The chemical transformations needed
to add these functional groups to the end points of the SWCNTs
require additional processing steps and chemicals which can be
hazardous and costly.
[0013] Rinzler et al. in PCT Publication WO2004/009884 A1 disclose
a method of forming SWCNT films on a porous membrane such that it
achieves 200 ohms/square and at least 30% transmission at a
wavelength of 3 um. This method needs a porous membrane (e.g.
polycarbonate or mixed cellulose ester) with a high volume of
porosity with a plurality of sub-micron pores as a substrate.
Further, the membrane is set within a vacuum filtration system.
Moreover, the weight percent of the dispersion used to make the
SWCNT film was 0.005 mg/mL in an aqueous solution.
[0014] Blanchet-Fincher et al in Publication WO 02/080195A1 and in
US 20040065970 A1 illustrate high conductivity compositions
composed of polyaniline (PANI) and SWCNTs or MWCNTs and methods to
deposit such compositions from a donor element onto a receiver
substrate. The nitrogen base salt derivative of emeraldine
polyaniline is mixed with SWCNTs in organic solvents (toluene,
xylene, turpinol, aromatics) and cast into films with conductivity
values of 62 S/cm (1 wt % SWCNT in PANI) and 44 S/cm (2wt % SWCNT
in PANI). These films alternatively may be produced as part of a
multi-layer donor structure suitable as use for a material transfer
system. The PANI/SWCNT composite are transferred from the donor
sheet to a suitable receiver substrate in imagewise form. PANI is a
highly colored conductive polymer and may result in a conductive
composite with unsatisfactory displays.
[0015] Hsu in WO 2004/029176 A1 disclose compositions for
electronically conducting organic polymer/nanoparticle composites.
Polyaniline (Ormecon) or PEDT (Baytron P) are mixed with Molybdenum
nanowires or carbon nanotubes (8 nm diameter, 20 um length, 60
S/cm). The compositions disclosed in this invention have marginal
conductivity.
[0016] Arthur et al in PCT Publication WO 03/099709 A2 disclose
methods for patterning carbon nanotubes coatings. Dilute
dispersions (10 to 100 ppm) of SWCNTs in isopropyl alcohol (IPA)
and water (which may include viscosity modifying agents) are spray
coated onto substrates. After application of the SWCNT coating, a
binder is printed in imagewise fashion and cured. Alternatively, a
photo-definable binder may be used to create the image using
standard photolithographic processes. Materials not held to the
substrate with binder are removed by washing. Dilute dispersions
(10 to 100 ppm) of SWCNTs in isopropyl alcohol (IPA) and water with
viscosity modifying agents are gravure coated onto substrates.
Dilute dispersions (10 to 100 ppm) of SWCNTs in isopropyl alcohol
(IPA) and water are spray coated onto substrates. The coated films
are then exposed through a mask to a high intensity light source in
order to significantly alter the electronic properties of the
SWCNTs. A binder coating follows this step. The dispersion
concentrations used in these methods make it very difficult to
produce images via direct deposition (inkjet etc.) techniques.
Further, such high solvent loads due to the low solids dispersions
create long process times and difficulties handling the excess
solvent. In addition, these patterning methods are subtractive
processes, which unnecessarily waste the SWCNT material via
additional removal steps thereby incurring cost and process
time.
[0017] Luo et al in International Publication Number
WO2005/086982A2 and US Patent Publication Number US2005/0209392A1
disclose use of carbon nanotubes in general for LC displays,
touchscreens, and EMI shielding windows.
[0018] Transparent electronically-conductive layers (TCL) of metal
oxides such as indium tin oxide (ITO), antimony doped tin oxide,
and cadmium stannate (cadmium tin oxide) have been used in the
manufacture of electrooptical display devices such as liquid
crystal display devices (LCDs), electroluminescent display devices,
photocells, touchscreens, solid-state image sensors and
electrochromic windows or as components of these devices such as
electromagnetic interference (EMI) shielding.
[0019] As indicated herein above, the art discloses a wide variety
of electronically conductive TCL compositions that can be
incorporated in electronic devices. However, the stringent
requirements of high transparency, low sheet resistance,
flexibility, and robustness under repeated contacts demanded by
modern display devices and, especially, touchscreens is extremely
difficult to attain with the TCL compositions described in the
prior art. Thus, there is still a critical need for transparent
conductors that can be coated roll-to-roll on a wide variety of
substrates under typical manufacturing conditions using
environmentally desirable components. In addition to providing
superior touchscreen electrode performance, the TCL layers also
must be highly transparent, must resist the effects of humidity
change, be physically robust, and be manufacturable at a reasonable
cost.
Problem to be Solved by the Invention
[0020] There is a need to provide improved touchscreen electrodes,
preferably obtained by wet coating, roll-to-roll manufacturing
methods, that more effectively meet the demanding requirements of
touchscreens than those of the prior art.
SUMMARY OF THE INVENTION
[0021] The present invention provides a touchscreen comprising
touch side and device side electrodes wherein each electrode
comprises in order an insulating substrate, an exposed electrically
conductive layer, wherein said exposed electrically conductive
layers are adjacent and separated by dielectric spacers, and
wherein said exposed electrically conductive layers comprise single
wall carbon nanotubes and wherein said carbon nanotubes comprise
covalently attached hydrophilic species.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1. A schematic diagram showing a section of a resistive
touchscreen of the prior art.
[0023] FIG. 2. A schematic diagram showing a section of a resistive
touchscreen employing symmetric electrodes of the present
invention.
[0024] FIG. 3. An exploded view showing the construction of a
touchscreen of the present invention.
[0025] FIGS. 4A and 4B. Schematic diagrams of pristine single wall
carbon nanotubes having tubules with closed ends and with open
ends.
[0026] FIGS. 5A and 5B. Schematic diagrams of functionalized single
wall carbon nanotubes having tubules with closed ends and with open
ends
[0027] FIG. 6. An exploded view showing the touchscreen fabricated
in this invention for testing of single and multilayer electrodes
of the instant invention.
[0028] FIG. 7. Shows, based on the results of Comparative Example 1
below, the on-state resistance profile as a function of single
point actuations for a single layer Bekaert ITO touch switch.
[0029] FIG. 8. Shows, based on the results of Comparative Example 1
below, the force to actuate the touchswitch as a function of single
point actuations for single layer of Bekaert ITO.
[0030] FIG. 9. Shows, based on the results of Comparative Example 2
below, the force to actuate the touchswitch as a function of single
point actuations for single layer conductor Keytec ITO Touch
Switch.
[0031] FIG. 10. Shows, based on the results of Comparative Example
2 below, the on-state resistance profile as a function of single
point actuations for single layer conductor Keytec ITO Touch
Switch.
[0032] FIG. 11. Shows, based on the results of Instant Invention
Example 1 below, the force to actuate the touchswitch as a function
of single point actuations for a symmetric electrode touch switch
with hydrophilic functionalized Single Wall Carbon Nanotubes at
32.3 mg/m.sup.2 coating weight as per the instant invention.
[0033] FIG. 12. Shows, based on the results of Instant Invention
Example 1 below, the on-state resistance profile as a function of
single point actuations for an asymmetric electrode touch switch
with hydrophilic functionalized Single Wall Carbon Nanotubes at
64.6 mg/m.sup.2 coating weight as per the instant invention.
[0034] FIG. 13. Shows, based on the results of Instant Invention
Example 2 below, the force to actuate the touchswitch as a function
of single point actuations for a symmetric electrode touch switch
with hydrophilic functionalized Single Wall Carbon Nanotubes at
32.3 mg/m.sup.2 coating weight as per the instant invention.
[0035] FIG. 14. Shows, based on the results of Instant Invention
Example 2 below, the on-state resistance profile as a function of
single point actuations for an asymmetric electrode touch switch
with hydrophilic functionalized Single Wall Carbon Nanotubes at
64.6 mg/m.sup.2 coating weight as per the instant invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The present invention provides numerous advantages over the
existing prior art. The present invention provides solution
coatable resistive touchscreen electrodes, which are highly
resistant to compressive stresses (touches by finger or stylus).
The present invention allows for roll-to-roll coating of
touchscreen electrodes thereby reducing complexity and cost of the
manufacturing method.
[0037] The present invention provides a touchscreen comprising
touch side and device side electrodes wherein each electrode
comprises in order an insulating substrate, an exposed electrically
conductive layer, wherein said exposed electrically conductive
layers are adjacent and separated by dielectric spacers, and
wherein said exposed electrically conductive layers comprise single
wall carbon nanotubes and wherein said carbon nanotubes comprise
covalently attached hydrophilic species.
[0038] Touchscreens of the present invention comprise electrodes
that are symmetric in composition. That is, the same conductive
material is employed in the exposed electrically conductive layer
on the touch side electrode compared to the exposed electrically
conductive layer on the device side electrode. In the present
invention, the touch side electrode or the device side electrode
has an exposed electrically conductive layer that comprises carbon
nanotubes. Additionally, electrodes that are on opposite sides of
the spacer elements may also be called opposing electrodes. Such
opposing electrodes of the present invention comprise electrodes
that are symmetric in composition. Such electrodes, although
comprising the same materials may have different thicknesses and/or
sheet resistance.
[0039] Touchscreens of the present invention, wherein the exposed
conductive layers comprise carbon nanotubes, provide improved
durability of the touchscreen compared with conventional
touchscreens employing (symmetrical composition) touch side and
device side electrodes comprising ITO. These and other advantages
will be apparent from the detailed description below.
[0040] FIG. 2 shows one embodiment of a resistive-type touchscreen
of the invention 39 including a device side electrode 25 and a
touch side electrode 26. Device side electrode 25 comprises in
order, an insulating substrate 29 and an exposed electrically
conductive layer 24 in contact with said substrate. Touch side
electrode 26 comprises in order, an insulating substrate 27 and an
exposed electrically conductive layer 28 in contact with said
substrate. Wherein said exposed electrically conductive layers 24
and 28 are adjacent and separated by dielectric spacers 32.
Preferably, the exposed electrically conductive layers have a sheet
resistance of between 100 and 10.sup.6 Ohm per square. In the
embodiment depicted in FIG. 2, the exposed electrically conductive
layers 24 and 28 comprise carbon nanotubes. Preferably, the carbon
nanotubes are single wall carbon nanotubes (SWCNT).
[0041] Resistive touchscreens of the invention preferably are
mechanically robust to point actuations by objects (plastic or
metal stylus, fingers etc.). A touchscreen is activated or actuated
when the touch side and device side electrodes contact. Over time,
repetitive contact and the force applied during such contact damage
prior art touchscreens. Such damage requires that increasingly
larger forces are necessary to actuate the touchscreen. In a
preferred embodiment of the instant invention, the force required
to actuate a point on the touchscreen does not change by more than
500 percent over 500,000 single point actuations. More preferably,
the force required to actuate the touchscreen does not change by
more than 100 percent and most preferably more than 50 percent. A
single point actuation is the application of an object at a single
point on the touchscreen to activate such touchscreen.
[0042] The carbon nanotubes suitable for use in the conductive
layers of the invention may be formed by any known methods in the
art (laser ablation, CVD, arc discharge). The carbon nanotubes are
preferred to have minimal or no impurities of carbonaceous
impurities that are not carbon nanotubes (graphite, amorphous,
diamond, non-tubular fullerenes) or metal impurities. It is found
that the transparency increases significantly with reduced levels
of metallic and carbonaceous impurities. Conductive layer film
quality, as evidenced by layer uniformity, surface roughness, and a
reduction in particulates, also improves with a decrease in the
amount of metal and carbonaceous impurities. Multiwall carbon
nanotubes (MWCNT) may also be used in the present invention in
place of or mixed with SWCNTs.
[0043] To achieve high electronic conductivity, metallic SWCNTs are
the most preferred type of carbon nanotube but semimetallic and
semiconducting SWCNTs may also be used. A pristine SWCNT means that
the surface of the SWCNT is free of covalently functionalized
materials either through synthetic prep, acid cleanup of
impurities, annealing or directed functionalization. For the
purpose of the present invention, however, the SWCNTS are
preferably functionalized. The preferred functional group is a
hydrophilic species selected from carboxylic acid, carboxylate
anion (carboxylic acid salt), hydroxyl, sulfur containing groups,
carbonyl, phosphates, nitrates or combinations of these hydrophilic
species. In some applications other types of functionalization such
as polymer, small molecule or combinations thereof may be required.
For example, such functionalization may improve the compatibility
of the SWCNT in a particular polymer matrix.
[0044] Turning now to FIG. 4, pristine SWCNTs with either open or
closed ends are illustrated. SWCNTs that are pristine are
essentially intractable in most solvents, especially aqueous media,
without the use of high levels of dispersants. Therefore, it is not
possible to use only pristine SWCNTs and water to produce an
aqueous coating composition. FIG. 5 exemplifies the basic structure
of covalently functionalized SWCNTs. The X in FIG. 5 may be
selected from one of the hydrophilic species listed above. It is
worth noting that the X may be positioned at any point on the
SWCNT, external or internal surface, open or closed end, or
sidewall. It is preferred that the X be uniformly distributed
across the external surface, potentially for the most
effectiveness.
[0045] The most preferred covalent surface functionalization is
carboxylic acid or a carboxylic acid salt or mixtures thereof
(hereafter referred to as only carboxylic acid). For carboxylic
acid based functionalization, the preferred level of functionalized
carbons on the SWCNT is 0.5-100 atomic percent, where 1 atomic
percent functionalized carbons would be 1 out of every 100 carbons
in the SWCNT have a functional group covalently attached. The
functionalized carbons may exist anywhere on the nanotubes (open or
closed ends, external and internal sidewalls). As already
mentioned, preferably the functionalization is on the external
surface of the SWCNTs. More preferably the functionalized percent
range is 0.5-50 atomic percent, and most preferably 0.5-5 atomic
percent. Functionalization of the SWCNTs with these groups within
these atomic percent ranges allows the preparation of stable
dispersions at the solids loadings necessary to form highly
conductive, transparent films by conventional coating means. This
method allows for very effective dispersion in substantially
aqueous dispersions and does not require a dispersion aid.
Additionally, the most efficient level of functionalization will
provide the desired dispersion without significantly altering the
electronic properties of the carbon nanotubes. The ease of
dispersion is critical to the present invention due to providing a
facile method for coating substrates and manufacturing by solution
based means, preferably web coating. Without covalent hydrophilic
functionalization, the present invention is not enabled, thereby
select single wall carbon nanotubes must be used to produce
resistive touchscreens of the invention. Preferably 0.5-5 atomic
percent of covalent hydrophilic functionalization is present on the
single wall carbon nanotubes. Transparency is defined as a
conductive layer that has greater than 60% bulk transmission. This
transparency may be achieved by producing thin coatings with
thicknesses less than 1 micrometer.
[0046] The functionalization may be carried out by a number of
routes. Typically, the raw material (unfunctionalized) SWCNTs are
added to a bath of strongly oxidizing agents (hydrochloric acid,
hydrofluoric acid, hydrobromic acid, hydroiodic acid, sulfuric
acid, oleum, nitric acid, citric acid, oxalic acid, chlorosulfonic
acid, phosphoric acid, trifluoromethane sulfonic acid, glacial
acetic acid, monobasic organic acids, dibasic organic acids,
potassium permanganate, persulfate, cerate, bromate, hydrogen
peroxide, dichromate) which may be mixtures. Sulfuric acid, nitric
acid, permanganate, and chlorosulfonic acids are preferred due to
the efficacy of the oxidation and functionalization. Temperatures
from 20.degree. C.-120.degree. C. are typically used in reflux of
this mixture of SWCNTs and strong oxidizing agents with appropriate
agitation over 1 hr--several days process time. At the end of this
process, the raw SWCNTs are now functionalized SWCNTs. The residual
oxidizing agents are removed via separation technologies
(filtration wash, centrifugation, cross-flow filtration) such that
a powder of the functionalized SWCNTs (primarily carboxylic acid
functionalities) remains after appropriate heating to dry.
[0047] The pH of the dispersion and the coating composition is
important. As the pH becomes more basic (above the pKa of the
carboxylic acid groups), the carboxylic acid will be ionized
thereby making the carboxylate anion, a bulky, repulsive group,
which can aid in the stability. Preferred pH ranges from 3-10 pH.
More preferred pH ranges from 3-6.
[0048] The length of the SWCNTs may be from 20 nm-1 m, more
typically from 20 nm to 50 .mu.m. The SWCNTs may exist as
individual SWCNTs or as bundles of SWCNTs. The diameter of a SWCNT
in the conductive layer may be 0.05 nm-5 nm. The SWCNTs in bundled
form may have diameters ranging from 1 nm-1 .mu.m. Preferably such
bundles will have diameters less than 50 nm and preferably less
than 20 nm and lengths of between 20 nm and 50 .mu.m. It is
important that higher surface area is achieved to facilitate
transfer of electrons and higher available surface area is achieved
by having smaller bundle sizes thereby exposing surfaces of SWCNTs
which may be at the internal position of the bundles and not
accessible. The ends of the SWCNTs may be closed by a hemispherical
buckyball of appropriate size. Alternatively, both of the ends of
the SWCNTs may be open. Some cases may find one end open and the
other end closed.
[0049] The functionalized SWCNTs (produced as described above or
purchased from a vendor) are used to form aqueous dispersions with
SWCNT solids loadings in the 0.05-10 wt % (500-100000) ppm range.
More preferably the SWCNT solids loadings are 0.1-5wt %. Most
preferably the solid loadings are 0.1-1 wt % SWCNT. This solids
loading range allows for facile coating to occur and also minimizes
the viscosity such that roll coating and/or inkjet printing can be
performed in standard practice. The functionalized SWCNTs are often
in powder/flake form and require energy to disperse. A typical
dispersion process may use a high shear mixing apparatus
(homogenizer, microfluidizer, cowles blade high shear mixer,
automated media mill, ball mill) for several minutes to an hour. We
have also found that standard ultrasonication and bath sonication
may be sufficient to disperse the functionalized SWCNTs. Typically,
a 1000 ppm SWCNT dispersion in deionized water is formed by bath
sonication for 2-24 hrs (dependant on the level of hydrophilic
functionalization). After the dispersion process, pH can be
adjusted to desired range. A centrifugation or filtration process
is used to remove large particulates. The resultant dispersion will
be stable for several months on standing (dependant on the level of
hydrophilic functionalization). This dispersion has solids loadings
high enough to produce conductive coatings in single pass modes for
many coating techniques.
[0050] The conductive layer of the invention should contain about
0.1 to about 1000 mg/m.sup.2 dry coating weight of the
functionalized SWCNT. Preferably, the conductive layer should
contain about 0.5 to about 500 mg/m.sup.2 dry coating weight of the
functionalized SWCNT. This range of SWCNT in the dry coating is
easily accessible by standard coating methods, will give the best
transmission properties, and minimizes cost to achieve the desired
sheet resistance. The actual dry coating weight of the SWCNTs
applied is determined by the properties for the particular
conductive functionalized SWCNT employed and by the requirements
for the particular application, the requirements may include, for
example, the conductivity, transparency, optical density, cost, etc
for the layer.
[0051] In a preferred embodiment, the layer containing the
conductive SWCNTs is prepared by applying a mixture containing:
[0052] a) a SWCNT according to Formula I;
##STR00001##
wherein each of R.sup.1 and R.sup.2 independently represents
carboxylic acid, carboxylate anion (carboxylic acid salt),
hydroxyl, sulfur containing groups, carbonyl, phosphates, nitrates,
and the tube is a single wall carbon nanotube composed of carbon
atoms substantially in hexagonal configuration, and, optionally
[0053] b) a dispersant and, optionally
[0054] c) a polymeric binder.
The R.sup.1 and R.sup.2 substituents may be uniformly or
non-uniformly distributed across the SWCNT. The dispersant loading
in the dispersion is preferred to be minimal to none. The maximum
dispersant loading is preferred to be 50 wt % of the weight of the
SWCNT. The more preferred dispersant loading is less than 5 wt % of
the weight of the SWCNT. The most preferred dispersant loading is 0
wt %. With decreasing levels of dispersant, the electronic
conductivity increases. There are many dispersants which may be
chosen. Preferred dispersants are octylphenol ethoxylate (TX-100),
sodium dodecyl sulfate, sodium dodecylbenzenesulfonate,
poly(styrene sulfonate), sodium salt, poly(vinylpyrrolidone), block
copolymers of ethylene oxide and propylene oxide (Pluronics or
Poloxamers), Polyoxyethylene alkyl ethers (Brij 78, Brij 700), and
cetyl or dodecyltrimethylammonium bromide. These dispersants are
able to effectively disperse carbon nanotubes at low dispersant
loadings which is preferred so that the impact on electronic
conductivity is minimal. Appropriate mixtures of these dispersants
may be utilized.
[0055] Additionally, a preferred embodiment for functionalization
of this invention can preferably be where the functional group is a
sulfur containing group selected from:
R--SO.sub.xZ.sub.y
Where R is a carbon within the lattice of a SWCNT, x may range from
1-3 and Z may be a Hydrogen atom or a metal cation such metals as
Na, Mg, K, Ca, Zn, Mn, Ag, Au, Pd, Pt, Fe, Co and y may range from
0-1 or combinations these hydrophilic species. The sulfur
containing groups listed above may be sulfonic acid, sulfonic acid
and/or sulfonic acid and/or the corresponding anions or mixtures
thereof. The most preferred sulfur containing group covalent
surface functionalization is sulfonic acid or a sulfonic acid salt
or mixtures thereof (hereafter referred to as only sulfonic acid).
Covalently attached sulfonic acid gives best dispersions of carbon
nanotubes amongst the sulfur containing groups.
[0056] For environmental reasons, substantially aqueous dispersions
of carbon nanotubes (meaning at least 60 wt % water in the
dispersion) are preferred for application of the carbon nanotube
layer.
[0057] The transparency of the conductive layer of the invention
can vary according to need. For use as an electrode in a
touchscreen, the conductive layer is desired to be highly
transparent. Accordingly, the visual light transmission value T for
the conductive layer of the invention is >65%, preferably
.gtoreq.70%, more preferably .gtoreq.80%, and most preferably
.gtoreq.90%. The conductive layer need not form an integral whole,
need not have a uniform thickness and need not be contiguous with
the base substrate. Preferably, the touchscreen of the invention
has a transparency of at least 70% in the visible light range so
that it may improve the viewing through the resistive touchscreen
to a display located adjacent to the device side electrode. The
electrode formed by the conductive layer is preferred to be
continuous to aid in the selection process by stylus (finger, metal
or plastic) input of the resistive touchscreen.
[0058] While the nanotubes can be applied without the addition of a
film-forming polymeric binder, a film-forming binder can be
employed to improve the physical properties of the layers. In such
an embodiment, the layers may comprise from about 1 to 95% of the
film-forming polymeric binder. However, the presence of the film
forming binder may increase the overall sheet resistance of the
layers. The optimum weight percent of the film-forming polymer
binder varies depending on the electrical properties of the carbon
nanotubes and the electronically conductive polymer, the chemical
composition of the polymeric binder, and the requirements for the
particular touchscreen application.
[0059] Polymeric film-forming binders useful in the conductive
layers of this invention can include, but are not limited to,
water-soluble or water-dispersible hydrophilic polymers such as
gelatin, gelatin derivatives, maleic acid or maleic anhydride
copolymers, polystyrene sulfonates, cellulose derivatives (such as
carboxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate
butyrate, diacetyl cellulose, and triacetyl cellulose),
polyethylene oxide, polyvinyl alcohol, and poly-N-vinylpyrrolidone.
Other suitable binders include aqueous emulsions of addition-type
homopolymers and copolymers prepared from ethylenically unsaturated
monomers such as acrylates including acrylic acid, methacrylates
including methacrylic acid, acrylamides and methacrylamides,
itaconic acid and its half-esters and diesters, styrenes including
substituted styrenes, acrylonitrile and methacrylonitrile, vinyl
acetates, vinyl ethers, vinyl and vinylidene halides, and olefins
and aqueous dispersions of polyurethanes and polyesterionomers.
[0060] Other ingredients that may be included in the conductive
layers include but are not limited to surfactants, defoamers or
coating aids, charge control agents, thickeners or viscosity
modifiers, antiblocking agents, coalescing aids, crosslinking
agents or hardeners, soluble and/or solid particle dyes, matte
beads, inorganic or polymeric particles, adhesion promoting agents,
bite solvents or chemical etchants, lubricants, plasticizers,
antioxidants, colorants or tints, and other addenda that are
well-known in the art. Preferred bite solvents can include any of
the volatile aromatic compounds disclosed in U.S. Pat. No.
5,709,984, as aromatic compounds, comprising an aromatic ring
substituted with at least one hydroxy group or a hydroxy
substituted substituents group. These compounds include phenol,
4-chloro-3-methyl phenol, 4-chlorophenol, 2-cyanophenol,
2,6-dichlorophenol, 2-ethylphenol, resorcinol, benzyl alcohol,
3-phenyl-1-propanol, 4-methoxyphenol, 1,2-catechol,
2,4-dihydroxytoluene, 4-chloro-2-methyl phenol, 2,4-dinitrophenol,
4-chlororesorcinol, 1-naphthol, 1,3-naphthalenediol and the like.
These bite solvents are particularly suitable for polyester based
polymer sheets of the invention. Of this group, the most preferred
compounds are resorcinol and 4-chloro-3-methyl phenol. Preferred
surfactants suitable for these coatings include nonionic and
anionic surfactants. Preferred cross-linking agents suitable for
these coatings include silane compounds such as those disclosed in
U.S. Pat. No. 5,370,981.
[0061] The conductive layers of the invention can be formed on any
rigid or flexible substrate. The substrates can be transparent,
translucent or opaque, and may be colored or colorless. Preferably,
the substrate is colorless and transparent. Rigid substrates can
include glass, metal, ceramic and/or semiconductors. Suitable rigid
substrate thickness ranges from 50 um-7000 um, depending on the
actual material employed for the rigid substrate. Flexible
substrates, especially those comprising a plastic substrate, are
preferred for their versatility and ease of manufacturing, coating
and finishing.
[0062] The flexible plastic substrate can be any flexible polymeric
film. "Plastic" means a high polymer, usually made from polymeric
synthetic resins, which may be combined with other ingredients,
such as curatives, fillers, reinforcing agents, colorants, and
plasticizers. Plastic includes thermoplastic materials and
thermosetting materials.
[0063] The flexible plastic film must have sufficient thickness and
mechanical integrity so as to be self-supporting, yet should not be
so thick as to be totally rigid. Suitable flexible plastic
substrate thickness ranges from 5 um-500 um. To reduce the weight
of the touchscreen while providing mechanical rigidity and thermal
resistance, the thickness is preferably 50-250 um. Another
significant characteristic of the flexible plastic substrate
material is its glass transition temperature (Tg). Tg is defined as
the glass transition temperature at which plastic material will
change from the glassy state to the rubbery state. It may comprise
a range before the material may actually flow. Suitable materials
for the flexible plastic substrate include thermoplastics of a
relatively low glass transition temperature, for example up to
150.degree. C., as well as materials of a higher glass transition
temperature, for example, above 150.degree. C. The choice of
material for the flexible plastic substrate would depend on factors
such as manufacturing process conditions, such as deposition
temperature, and annealing temperature, as well as
post-manufacturing conditions such as in a process line of a
displays manufacturer. Certain of the plastic substrates discussed
below can withstand higher processing temperatures of up to at
least about 200.degree. C., some up to 300.degree.-350.degree. C.,
without damage.
[0064] Typically, the flexible plastic substrate is a polyester
including polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polyester ionomer, polyethersulfone (PES),
polycarbonate (PC), polysulfone, a phenolic resin, an epoxy resin,
polyester, polyimide, polyetherester, polyetheramide, cellulose
nitrate, cellulose acetate, poly(vinyl acetate), polystyrene,
polyolefins including polyolefin ionomers, polyamide, aliphatic
polyurethanes, polyacrylonitrile, polytetrafluoroethylenes,
polyvinylidene fluorides, poly(methyl (x-methacrylates), an
aliphatic or cyclic polyolefin, polyarylate (PAR), polyetherimide
(PEI), polyethersulphone (PES), polyimide (PI), Teflon
poly(perfluoro-alboxy) fluoropolymer (PFA), poly(ether ether
ketone) (PEEK), poly(ether ketone) (PEK), poly(ethylene
tetrafluoroethylene)fluoropolymer (PETFE), and poly(methyl
methacrylate) and various acrylate/methacrylate copolymers (PMMA)
natural and synthetic paper, resin-coated or laminated paper,
voided polymers including polymeric foam, microvoided polymers and
microporous materials, or fabric, or any combinations thereof.
[0065] Aliphatic polyolefins may include high density polyethylene
(HDPE), low density polyethylene (LDPE), and polypropylene,
including oriented polypropylene (OPP). Cyclic polyolefins may
include poly(bis(cyclopentadiene)). A preferred flexible plastic
substrate is a cyclic polyolefin or a polyester. Various cyclic
polyolefins are suitable for the flexible plastic substrate.
Examples include Arton.RTM. made by Japan Synthetic Rubber Co.,
Tokyo, Japan; Zeanor T made by Zeon Chemicals L. P., Tokyo Japan;
and Topas.RTM. made by Celanese A. G., Kronberg Germany. Arton is a
poly(bis(cyclopentadiene)) condensate that is a film of a polymer.
Alternatively, the flexible plastic substrate can be a polyester. A
preferred polyester is an aromatic polyester such as Arylite.
Although the substrate can be transparent, translucent or opaque,
for most display applications transparent members comprising
transparent substrate(s) are preferred. Although various examples
of plastic substrates are set forth above, it should be appreciated
that the flexible substrate can also be formed from other materials
such as flexible glass and ceramic.
[0066] The most preferred flexible plastic substrate is polyester
because of its superior mechanical and thermal properties as well
as its availability in large quantity at a moderate price. The
particular polyester chosen for use can be a homo-polyester or a
copolyester, or mixtures thereof as desired. The polyester can be
crystalline or amorphous or mixtures thereof as desired. Polyesters
are normally prepared by the condensation of an organic
dicarboxylic acid and an organic diol and, therefore, illustrative
examples of useful polyesters will be described herein below in
terms of these diol and dicarboxylic acid precursors.
[0067] Polyesters which are suitable for use in this invention are
those which are derived from the condensation of aromatic,
cycloaliphatic, and aliphatic diols with aliphatic, aromatic and
cycloaliphatic dicarboxylic acids and may be cycloaliphatic,
aliphatic or aromatic polyesters. Exemplary of useful
cycloaliphatic, aliphatic and aromatic polyesters which can be
utilized in the practice of their invention are poly(ethylene
terephthalate), poly(cyclohexlenedimethylene), terephthalate)
poly(ethylene dodecate), poly(butylene terephthalate),
poly(ethylene naphthalate), poly(ethylene(2,7-naphthalate)),
poly(methaphenylene isophthalate), poly(glycolic acid),
poly(ethylene succinate), poly(ethylene adipate), poly(ethylene
sebacate), poly(decamethylene azelate), poly(ethylene sebacate),
poly(decamethylene adipate), poly(decamethylene sebacate),
poly(dimethylpropiolactone), poly(para-hydroxybenzoate)(Ekonol),
poly(ethylene oxybenzoate) (A-tell), poly(ethylene isophthalate),
poly(tetramethylene terephthalate, poly(hexamethylene
terephthalate), poly(decamethylene terephthalate),
poly(1,4-cyclohexane dimethylene terephthalate) (trans),
poly(ethylene 1,5-naphthalate), poly(ethylene 2,6-naphthalate),
poly(1,4-cyclohexylene dimethylene terephthalate), (Kodel) (cis),
and poly(1,4-cyclohexylene dimethylene terephthalate (Kodel)
(trans). Polyester compounds prepared from the condensation of a
diol and an aromatic dicarboxylic acid is preferred for use in this
invention. Illustrative of such useful aromatic carboxylic acids
are terephthalic acid, isophthalic acid and an .alpha.-phthalic
acid, 1,3-napthalenedicarboxylic acid, 1,4 napthalenedicarboxylic
acid, 2,6-napthalenedicarboxylic acid, 2,7-napthalenedicarboxylic
acid, 4,4'-diphenyldicarboxylic acid,
4,4'-diphenysulfphone-dicarboxylic acid,
1,1,3-trimethyl-5-carboxy-3-(p-carboxyphenyl)-idane, diphenyl ether
4,4'-dicarboxylic acid, bis-p(carboxy-phenyl) methane, and the
like. Of the aforementioned aromatic dicarboxylic acids, those
based on a benzene ring (such as terephthalic acid, isophthalic
acid, orthophthalic acid) are preferred for use in the practice of
this invention. Amongst these preferred acid precursors,
terephthalic acid is particularly preferred acid precursor.
[0068] Preferred polyesters for use in the practice of this
invention include poly(ethylene terephthalate), poly(butylene
terephthalate), poly(1,4-cyclohexylene dimethylene terephthalate)
and poly(ethylene naphthalate) and copolymers and/or mixtures
thereof. Among these polyesters of choice, poly(ethylene
terephthalate) is most preferred because of its low cost, high
transparency, and low coefficient of thermal expansion.
[0069] The aforesaid substrate can comprise a single layer or
multiple layers according to need. The multiplicity of layers may
include any number of auxiliary layers such as hard coat layers,
antistatic layers, tie layers or adhesion promoting layers,
abrasion resistant layers, curl control layers, conveyance layers,
barrier layers, splice providing layers, UV absorption layers,
optical effect providing layers, such as antireflective and
antiglare layers, waterproofing layers, adhesive layers, and the
like.
[0070] In a preferred embodiment the touch side electrode further
comprises an anti-glare layer, polarizing layer, anti-reflection
layer, ultra violet light absorbing layer, or abrasion resistant
hard coat layer on the side of the substrate opposite to the
electrically conductive layers. Preferably, the anti-glare or hard
coat layer has a pencil hardness (using the Standard Test Method
for Hardness by Pencil Test ASTM D3363) of at least 1H, more
preferably a pencil hardness of 2H to 8H.
[0071] Particularly effective hard coat layers for use in the
present invention comprise radiation or thermally cured
compositions, and preferably the composition is radiation cured.
Ultraviolet (UV) radiation and electron beam radiation are the most
commonly employed radiation curing methods. UV curable compositions
are particularly useful for creating the abrasion resistant layer
of this invention and may be cured using two major types of curing
chemistries, free radical chemistry and cationic chemistry.
Acrylate monomers (reactive diluents) and oligomers (reactive
resins and lacquers) are the primary components of the free radical
based formulations, giving the cured coating most of its physical
characteristics. Photo-initiators are required to absorb the UV
light energy, decompose to form free radicals, and attack the
acrylate group C.dbd.C double bond to initiate polymerization.
Cationic chemistry utilizes cycloaliphatic epoxy resins and vinyl
ether monomers as the primary components. Photo-initiators absorb
the UV light to form a Lewis acid, which attacks the epoxy ring
initiating polymerization. By UV curing is meant ultraviolet curing
and involves the use of UV radiation of wavelengths between 280 and
420nm preferably between 320 and 410 nm.
[0072] Examples of UV radiation curable resins and lacquers usable
for the abrasion layer useful in this invention are those derived
from photo polymerizable monomers and oligomers such as acrylate
and methacrylate oligomers (the term "(meth)acrylate" used herein
refers to acrylate and methacrylate), of polyfunctional compounds,
such as polyhydric alcohols and their derivatives having
(meth)acrylate functional groups such as ethoxylated
trimethylolpropane tri(meth)acrylate, tripropylene glycol
di(meth)acrylate, trimethylolpropane tri(meth)acrylate, diethylene
glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate,
pentaerythritol tri(meth)acrylate, dipentaerythritol
hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, or neopentyl
glycol di(meth)acrylate and mixtures thereof, and acrylate and
methacrylate oligomers derived from low-molecular weight polyester
resin, polyether resin, epoxy resin, polyurethane resin, alkyd
resin, spiroacetal resin, epoxy acrylates, polybutadiene resin, and
polythiol-polyene resin, and the like and mixtures thereof, and
ionizing radiation-curable resins containing a relatively large
amount of a reactive diluent. Reactive diluents usable herein
include monofunctional monomers, such as ethyl (meth)acrylate,
ethylhexyl (meth)acrylate, styrene, vinyltoluene, and
N-vinylpyrrolidone, and polyfunctional monomers, for example,
trimethylolpropane tri(meth)acrylate, hexanediol (meth)acrylate,
tripropylene glycol di(meth)acrylate, diethylene glycol
di(meth)acrylate, pentaerythritol tri(meth)acrylate,
dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, or neopentyl glycol di(meth)acrylate.
[0073] Among others, in the present invention, conveniently used
radiation curable lacquers include urethane (meth)acrylate
oligomers. These are derived from reacting diisocyanates with a
oligo(poly)ester or oligo(poly)ether polyol to yield an isocyanate
terminated urethane. Subsequently, hydroxy terminated acrylates are
reacted with the terminal isocyanate groups. This acrylation
provides the unsaturation to the ends of the oligomer. The
aliphatic or aromatic nature of the urethane acrylate is determined
by the choice of diisocyanates. An aromatic diisocyanate, such as
toluene diisocyanate, will yield an aromatic urethane acrylate
oligomer. An aliphatic urethane acrylate will result from the
selection of an aliphatic diisocyanate, such as isophorone
diisocyanate or hexyl methyl diisocyanate. Beyond the choice of
isocyanate, polyol backbone plays a pivotal role in determining the
performance of the final the oligomer. Polyols are generally
classified as esters, ethers, or a combination of these two. The
oligomer backbone is terminated by two or more acrylate or
methacrylate units, which serve as reactive sites for free radical
initiated polymerization. Choices among isocyanates, polyols, and
acrylate or methacrylate termination units allow considerable
latitude in the development of urethane acrylate oligomers.
Urethane acrylates like most oligomers, are typically high in
molecular weight and viscosity. These oligomers are multifunctional
and contain multiple reactive sites. Because of the increased
number of reactive sites, the cure rate is improved and the final
product is cross-linked. The oligomer functionality can vary from 2
to 6.
[0074] Among others, conveniently used radiation curable resins
include polyfunctional acrylic compounds derived from polyhydric
alcohols and their derivatives such as mixtures of acrylate
derivatives of pentaerythritol such as pentaerythritol
tetraacrylate and pentaerythritol triacrylate functionalized
aliphatic urethanes derived from isophorone diisocyanate. Some
examples of urethane acrylate oligomers used in the practice of
this invention that are commercially available include oligomers
from Sartomer Company (Exton, Pa.). An example of a resin that is
conveniently used in the practice of this invention is CN 968.RTM.
from Sartomer Company.
[0075] A photo polymerization initiator, such as an acetophenone
compound, a benzophenone compound, Michler's benzoyl benzoate,
.alpha.-amyloxime ester, or a thioxanthone compound and a
photosensitizer such as n-butyl amine, triethylamine, or
tri-n-butyl phosphine, or a mixture thereof is incorporated in the
ultraviolet radiation curing composition. In the present invention,
conveniently used initiators are 1-hydroxycyclohexyl phenyl ketone
and 2-methyl-1-[4-(methyl thio)
phenyl]-2-morpholinopropanone-1.
[0076] The UV polymerizable monomers and oligomers are coated and
dried, and subsequently exposed to UV radiation to form an
optically clear cross-linked abrasion resistant layer. The
preferred UV cure dosage is between 50 and 1000 mJ/cm.sup.2. This
dosage range gives the most efficient curing kinetics.
[0077] The thickness of the hard coat layer is generally about 0.5
to 50 micrometers preferably 1 to 20 micrometers, more preferably 2
to 10 micrometers. This thickness range is preferred due to cost
and performance.
[0078] An antiglare layer provides a roughened or textured surface
that is used to reduce specular reflection. All of the unwanted
reflected light is still present, but it is scattered rather than
specularly reflected. For the purpose of the present invention, the
antiglare layer preferably comprises a radiation cured composition
that has a textured or roughened surface obtained by the addition
of organic or inorganic (matting) particles or by embossing the
surface. The radiation cured compositions described hereinabove for
the hard coat layer are also effectively employed in the antiglare
layer. Surface roughness is preferably obtained by the addition of
matting particles to the radiation cured composition. Suitable
particles include inorganic compounds having an oxide, nitride,
sulfide or halide of a metal, metal oxides being particularly
preferred. As the metal atom, Na, K, Mg, Ca, Ba, Al, Zn, Fe, Cu,
Ti, Sn, In, W, Y, Sb, Mn, Ga, V, Nb, Ta, Ag, Si, B, Bi, Mo, Ce, Cd,
Be, Pb and Ni are suitable, and Mg, Ca, B and Si are more
preferable. An inorganic compound containing two types of metal may
also be used. A particularly preferable inorganic compound is
silicon dioxide, namely silica.
[0079] The polymer substrate can be formed by any method known in
the art such as those involving extrusion, coextrusion, quenching,
orientation, heat setting, lamination, coating and solvent casting.
It is preferred that the polymer substrate is an oriented sheet
formed by any suitable method known in the art, such as by a flat
sheet process or a bubble or tubular process. The flat sheet
process involves extruding or coextruding the materials of the
sheet through a slit die and rapidly quenching the extruded or
coextruded web upon a chilled casting drum so that the polymeric
component(s) of the sheet are quenched below their solidification
temperature.
[0080] The quenched sheet is then biaxially oriented by stretching
in mutually perpendicular directions at a temperature above the
glass transition temperature of the polymer(s). The sheet may be
stretched in one direction and then in a second direction or may be
simultaneously stretched in both directions. The preferred stretch
ratio in any direction is at least 3:1. After the sheet has been
stretched, it is heat set by heating to a temperature sufficient to
crystallize the polymers while restraining to some degree the sheet
against retraction in both directions of stretching.
[0081] The polymer sheet may be subjected to any number of coatings
and treatments, after extrusion, coextrusion, orientation, etc. or
between casting and full orientation, to improve its properties,
such as printability, barrier properties, heat-sealability,
spliceability, adhesion to other substrates and/or imaging layers.
Examples of such coatings can be acrylic coatings for printability,
polyvinylidene halide for heat seal properties, etc. Examples of
such treatments can be flame, plasma and corona discharge
treatment, ultraviolet radiation treatment, ozone treatment and
electron beam treatment to improve coatability and adhesion.
Further examples of treatments can be calendaring, embossing and
patterning to obtain specific effects on the surface of the web.
The polymer sheet can be further incorporated in any other suitable
substrate by lamination, adhesion, cold or heat sealing, extrusion
coating, or any other method known in the art.
[0082] Dielectric spacers, that may be dot-shaped for example, are
provided on the surface of the conductive layer at regular
distances, such as every few millimeters. The spacers are made of
polymeric resin, and each spacer is about 10 um in height and 10 um
to 50 um in diameter. Suitable polymeric resin that may be employed
to prepare the spacers include light or thermal hardened epoxy,
acrylated-urethanes, acrylic, and other compositions well known by
the skilled artisan. The spacers alternatively may be filled with
nanoparticles such as silica, alumina, zinc oxide and others in
order to modify the physical properties of the spacers.
[0083] Alternatively, it is known to form the spacers for example
by spraying through a mask or pneumatically sputtering small
diameter transparent glass or polymer particles, as described in
U.S. Pat. No. 5,062,198 issued to Sun, Nov. 5, 1991. The
transparent glass or polymer particles are typically 45 microns in
diameter or less and mixed with a transparent polymer adhesive in a
volatile solvent before application. The spacers may also be
prepared by lithographic techniques that are well known in the
art.
[0084] Preferably, the electronically conductive layer comprising
carbon nanotubes has a sheet resistance of between 10.sup.1 to
10.sup.6 Ohm per square. More preferably, the exposed electrically
conductive layer has a sheet resistance of between 100 and 10.sup.6
Ohm per square. Most preferably, the electrically conductive layer
has a sheet resistance of between 100 and 10,000 Ohm per
square.
[0085] Resistive touchscreens of the invention preferably are
mechanically robust to point actuations by objects (plastic or
metal stylus, fingers etc.). A touchscreen is activated or actuated
when the touch side and device side electrodes contact. Over time,
repetitive contact and the force applied during such contact damage
prior art touchscreens. Such damage requires that increasingly
larger forces are necessary to actuate the touchscreen. In a
preferred embodiment of the instant invention, the force required
to actuate a point on the touchscreen does not change by more than
500 percent over 500,000 single point actuations. More preferably,
the force required to actuate the touchscreen does not change by
more than 100 percent and most preferably more than 50 percent. As
the force needed to actuate increases, it reduces the accuracy of
the input selection and also the increased force may further
degrades the properties of the conductive layers. A single point
actuation is the application of an object at a single point on the
touchscreen to activate such touchscreen.
[0086] The conventional construction of a resistive touch screen
involves the sequential placement of materials upon the substrates.
The substrates are formed as described herein above, then uniform
conductive layers are applied to the substrates. The bus bars are
applied to the touch side electrode and the spacers and bus bars
are applied to the device side electrode and, finally, the touch
side electrode is attached to the device side electrode.
[0087] FIG. 3 is an exploded view showing the construction of a
touchscreen 100 of the present invention. As shown in FIG. 3, the
touchscreen 100 is mainly composed of a touch side electrode 110
and a device side electrode 120. The touch side electrode 110 and
the device side electrode 120 are set facing each other, with
dielectric spacers 30 being placed in between them so that an air
gap is formed between the substrates.
[0088] As shown in FIG. 3, the touch side electrode 110 is provided
with a pair of bus bars 141 and 142 which are adhered to the
exposed electrically conductive layer along its ends to be opposed
to each other in the A direction. The touch side electrode 110 is
also provided with a pair of connector electrodes 143 and 144 at
its edge, to which connectors (not shown) are connected. The bus
bars 141 and 142 are connected to the pair of connector electrodes
143 and 144 via wiring patterns 145 and 146. The bus bars,
connector electrodes, and wiring patterns comprise high
conductivity materials. Suitable high conductivity materials
include carbon black, silver, gold, platinum, palladium, copper or
combinations of these materials. These materials may be applied by
vacuum deposition, inkjet printing, thermal transfer, silk screen
printing or other methods. These materials may be thermally or
light hardened.
[0089] As shown in FIG. 3, the device side electrode 120 is
provided with a pair of bus bars 251 and 252 which are adhered to
the exposed electrically conductive layer along its ends to be
opposed to each other in the B direction that is perpendicular to
the A direction. The device side electrode 120 is also provided
with a pair of connector electrodes 253 and 254 at its edge, to
which connectors (not shown) are connected. The pair of bus bars
251 and 252 are connected to the pair of connector electrodes 253
and 254 via wiring patterns 255 and 256. Dot-shaped spacers 30, for
example, are provided on the surface of the exposed conductive
layer deposed on device side electrode 120, such as every few
millimeters. The spacers 30 are made of light-hardening acrylic
resin for example, and each spacer is about 10 .mu.m in height and
10 .mu.m to 50 .mu.m in diameter. Respective outer regions of the
touch side electrode 110 and the device side electrode 120 are
bonded together by an adhesive 40.
[0090] Touchscreens prepared as described above may be employed in
a variety of display devices. In a preferred embodiment, the
display device comprises a liquid crystal display (LCD).
Conveniently, the touchscreen of the invention may be adhesively
attached to a polarizer plate within the liquid crystal display
device.
[0091] The conductive layers of the invention can be applied by any
method known in the art. Particularly preferred methods include
coating from a suitable liquid medium coating composition by any
well known coating method such as air knife coating, gravure
coating, hopper coating, roller coating, spray coating,
electrochemical coating, inkjet printing, flexographic printing,
and the like. The first electrically conductive layer and the
exposed electrically conductive layer may be applied sequentially
or simultaneously.
[0092] Alternatively, the conductive layers can be transferred to a
receiver member comprising the substrate from a donor member by the
application of heat and/or pressure. An adhesive layer may be
preferably present between the donor member and the receiver member
substrate to facilitate transfer. The two conductive layers may be
applied onto each substrate simultaneously from a single donor
element or sequentially from two separate donor members as
described in copending commonly assigned U.S. patent application
Ser. No. 10/969,889 filed Oct. 21, 2004, Ser. No. 11/062,416 filed
Feb. 22, 2005, and Ser. No. 11/022,155 filed Dec. 22, 2004.
[0093] Besides the conductive layers of the invention, the
aforementioned thermal transfer element may comprise a number of
auxiliary layers. These auxiliary layers may include radiation
absorption layers, which can be a light to heat conversion layer,
interlayer, release layer, adhesion promoting layer, operational
layer (which is used in the operation of a device), non-operational
layer (which is not used in the operation of a device but can
facilitate, for example, transfer of a transfer layer, protection
from damage and/or contact with outside elements).
[0094] Thermal transfer of the conductive layers of the invention
can be accomplished by the application of directed heat on a
selected portion of the thermal transfer element. Heat can be
generated using a heating element (e.g., a resistive heating
element), converting radiation (e.g., a beam of light) to heat,
and/or applying an electrical current to a layer of thermal
transfer element to generate heat.
[0095] Typically, a very smooth surface, with low roughness (Ra) is
desired for maximizing optical and barrier properties of the coated
substrate. Preferred Ra values for the conductive layer of the
invention is less than 1000 nm, more preferably less than 100 nm,
and most preferably less than 20 nm. The reduced surface roughness
is desired to optimize optical properties. However, it is to be
understood that if for some application a rougher surface is
required higher Ra values can be attained within the scope of this
invention, by any means known in the art.
Examples
[0096] The following non-limiting examples further describe the
practice of the instant invention.
[0097] The atomic % of carboxylic acids on the SWCNT has been
determined by titration methods as described below. The level of
carboxylic acids we determined for the SWCNTs used in the instant
invention was 2.74 atomic %.
[0098] The methods used to determine the amount of hydrophilic
carboxylic acid covalently attached are described below.
[0099] The Titrimetric Determination of Strong Acid Levels in
Single-Walled Carbon Nanotubes
[0100] A nonaqueous titration procedure is given for the
determination of strong acid in Single-Walled Carbon Nanotubes
(SWCNT). Samples are dispersed in a solvent system of 50/2 (v/v)
distilled tetrahydrofuran (THF)/methanol. The dispersion is
titrated with 0.1 N hexadecyltrimethylammonium hydroxide (HDTMAH).
Typically two end points are recorded. The first is due to stronger
acids associated with the SWCNT. These may be residual mineral acid
from the surface derivatization reactions or acid functions
attached to the SWCNT surface. A second end point is also observed
but is typically too noisy to be utilized quantitatively. The
strong acid in the SWCNT sample is subtracted from the total acids
found by sodium hydroxide back titration to give the net level of
carboxylic acid in the SWCNT.
[0101] Equipment [0102] 1) Metrohm Model 716 Titrino with Brinkmann
Titrino Workcell software, or equivalent, and equipped with a 1-ml
amberized glass buret. [0103] 2) Indicator electrode--combination
glass pH/Ag/AgCl reference. Metrohm Model 6.0202.100, or
equivalent. The filling solution for the electrode is 0.1N
tetramethyl-ammonium chloride in methanol.
[0104] Reagents [0105] 1) 0.1 N Hexadecyltrimethylammonium
hydroxide (HDTMAH) in .about.9:1(v) toluene: methanol (Note 1).
[0106] 2) Distilled tetrahydrofuran (THF) (Note 2) [0107] 3)
Methanol, reagent grade such as J. T. Baker 9093-33.
[0108] Procedure [0109] 1) Weigh to the nearest 0.1 mg
approximately 30 to 150 mg of the SWCNT sample into a 100 ml beaker
(Note 3). [0110] 2) Add 50 ml distilled THF and 2 ml methanol.
[0111] 3) Cover with Parafilm and stir for 15 minutes. [0112] 4)
Titrate the sample with 0.1N HDTMAH utilizing the Titrino equipped
with a 1 ml buret. [0113] 5) Titrate a blank of 50/2 THF/MeOH under
the same conditions.
[0114] Calculations
[0115] The Titroprocessor will mark the potentiometric end point(s)
automatically. Only the first end point (positive HNP) is used in
the following calculation. Subsequent end points are ignored.
EP = End Point ##EQU00001## Strong Acid ( meq / g ) = [ ( ml EP #1
) - ( ml Blank ) ] .times. N HDTMAH ( grams of sample )
##EQU00001.2## Net Carboxylic Acid ( meq / g ) = [ Total Acids (
from NaOH Back - Titration ) ( meq / g ) ] - [ Strong Acid ( meq /
g ) ] ##EQU00001.3##
Examples of Single layer Conductors Used to Construct Touch
Switches
TABLE-US-00001 [0116] TABLE I Sheet Coating Coating Conductor
Substrate # of Resistance Composition ID Type Type Layers
(ohms/square) Used A Bekaert ITO 102 um PET 1 300 NA B Keytec ITO
203 um PET 1 400 NA C Layer with 32.3 mg/m.sup.2 102 um PET 1 1700
H SWCNT D Layer with 64.6 mg/m2 102 um PET 1 670 V SWCNT
[0117] Coatings A & B were supplied by the vendors Bekaert and
Keytec, respectively. The Bekaert ITO is coated onto a 102 um PET
substrate. The Keytec sample had a coating on the opposite surface
of the ITO on PET. The PET used in the Keytec sample is a 203 um
substrate.
[0118] Coatings C, and D were produced as follows. The following
ingredients were used to form the coating composition for forming
the multilayer examples and single layer comparative examples:
Ingredients for Coating Composition
[0119] (a) Ethanol; [0120] (b) SWCNTs: P3 swcnt product supplied by
Carbon Solutions (2.74 atomic % covalent hydrophilic
functionalization)
[0121] The following coating compositions were prepared for coating
suitable substrates to form the electrically conductive layer
examples:
Coating Composition H
[0122] P3 SWCNT--0.10 wt % in water [0123] Ethanol--25 wt % in
water [0124] Balance high purity water
Coating Composition V
[0124] [0125] P3 SWCNT--0.20 wt % in water [0126] Ethanol--25 wt %
in water [0127] Balance high purity water
[0128] The substrate used was polyethylene terephthalate (PET). The
PET substrate was photographic grade with a thickness of 102 .mu.m
and surface roughness Ra of 0.5 nm. On the coating side (frontside)
of the PET a thin vinylidene chloride copolymer primer layer was
applied at a thickness of 80 nm. The coating composition H or V was
applied to the frontside surface of the substrate by a hopper at
different wet coverages to give dry coverages of SWCNT of between
10 mg/m.sup.2 and 100 mg/m.sup.2, and each coating was dried at
82.degree. C. for five minutes. In this manner, examples of
electrically conductive layers were created as per the instant
invention, wherein conductive layers having different dry coverage
of SWCNTs were coated on the surface of the substrate in one layer.
The sheet resistance, R.sub.S, (ohms/square) of the coatings was
measured by a 4-point electrical probe.
[0129] In order to evaluate the robustness of the conductive layers
used as symmetric electrodes of the instant invention, small
touchscreens (termed touch switch hereafter) were created and
tested as described below.
[0130] Turning to FIG. 6 single layer conductor material
combinations were evaluated for mechanical robustness by
constructing a single pole-single throw touchscreen as follows:
[0131] A 1.27 cm.times.3.8 cm "bottom" (device side) conductive
coating 302 on flexible substrate was cut from a larger coated
sheet. The bottom conductive coating 302 was attached, conductive
side up, along one long edge of a 25 mm.times.75 mm glass
microscope slide 301. The bottom conductive coating 302 was
retained by (2) 3.8 cm lengths of copper foil 304 tape (3M 1181 EMI
Shielding Tape) applied across the 1.27 cm ends of the film strip
and extending beyond the 2.5 cm dimension of the slide. The excess
tape was folded back on itself to form an attachment tab for
electrical connection.
[0132] Sixteen spacer dots 303 of non-critical dimension were
applied in a 4.times.4 matrix over the central 1.27 cm.times.1.27
cm square area of the bottom conductor. Spacer dot 303 dimensions
can be called out as 0.1-1.0 mm diameter, preferably 0.1-0.3 mm
diameter for uniformity of actuation force. Dots were comprised of
epoxy (Devcon No. 14250) applied by hand using a pointed
applicator. A 1.27 cm square of non-conducting double sided tape
305 (Polyken) was applied to the glass slide adjacent to the spacer
dot matrix.
[0133] A 1.27 cm.times.3.8 cm strip of "top" (touch side)
conductive coating 306 on flexible substrate was attached,
conductive side down, over the double sided tape to form a "T"
arrangement with one end of the strip covering the spacer dot array
and the other end extending beyond the 2.54 cm dimension of the
glass slide. A 2.54 cm length of conductive copper foil 304 tape
was wrapped around the overhanging top conductor to form an
electrical attachment.
[0134] A line of silver conducting paint (Ernest Fullam No. 14810)
was applied across the copper tape/conductor layer interfaces to
augment the conductive adhesive of the foil tape.
Single Point Actuation Testing Method
[0135] Completed touchscreens were placed in the stationary nest of
a test apparatus consisting of a brushless linear motor and force
mode motion control. A polyurethane 0.79 cm spherical radius
hemisphere switch actuating "finger" (McMaster-Carr #95495K1) is
mounted to a load cell, which is in turn mounted to the moving
linear motor stage. The finger was pressed against the switch with
a force profile consisting of zero force for 125 mS, a linear ramp
to peak force over 125 mS, a hold at peak force for 125 mS, and a
linear load reduction over 125 mS. The loading pattern was repeated
continuously at 2 actuations/second for the duration of the test.
Peak force was set for 200-300 grams force. The touchscreen was
electrically loaded by supplying a regulated 5V differential
between the top and bottom conductors. At the mid point of the peak
force period, the connections to the test device were
electronically switched to force current in the reverse direction
during the second half of the actuation cycle. Current flow through
the touchscreen was monitored as a function of time and actuation
force.
[0136] The touchscreen was considered to make and break at a
resistance of or below 12 kOhms. The data recorded were on-state
resistance and the force required to achieve an on state e.g. to
make a switch in state. A touchscreen was considered to fail when
routinely exceeding 12 kOhms on-state resistance.
Comparative Example 1
Single Layer ITO Conductor Touchscreen
[0137] A touchscreen was constructed using Coating A from Table I
(Bekaert ITO--Lot #5189376). The single point actuation testing was
performed and gave the results indicated in FIGS. 7 and 8 below.
The single layer of Bekaert ITO began to show significant changes
in force to actuate as early as completing 10,000 single point
actuations (SPA). The on-state resistance showed significant
deviation as early as 85,000 SPA. At 88,000 SPA, the single layer
of Bekaert ITO routinely exceeded an on-state resistance of 12,000
ohms and failed. Addtionally, by 88,000 SPA the actuation force was
highly scattered and not stable. It is clear from the figures that
as the number of actuations increase, the reliability of the
touchscreen decreases as evidenced by the significant scatter in
the data which corresponds to higher forces required to actuate and
increasing on-state resistance which are not desirable.
Additionally, the highly scattered data illustrates potential
problems with resolution of point selection.
Comparative Example 2
Single Layer Keytec ITO Conductor Touchscreen
[0138] A touchscreen was constructed using Coating B from Table I
(400 ohm/square Keytec ITO). The SPA testing was performed and gave
the results indicated in FIGS. 9 and 10 below. The single layer of
Keytec ITO had a linear increase in the force to actuate and began
to show significant changes in force to actuate as early as
completing 25,000 SPA. The on-state resistance showed significant
deviation as early as 35,000 SPA. At 38,000 SPA, the single layer
of Keytec ITO permanently exceeded an on-state resistance of 12,000
ohms, reaching a value of 13,000+ ohms and continued to increase to
values as high as 10,000,000 ohms. Addtionally, by 30,000 SPA the
actuation force experienced an exponential increase and failed
shortly thereafter with significant scatter in the force to
actuate. It is clear from the figures that as the number of
actuations increase, the reliability of the single layer Keytec ITO
based touchscreen decreases as evidenced by the significant scatter
in the data which corresponds to higher forces required to actuate
and increasing on-state resistance which are not desirable.
Additionally, the highly scattered data illustrates potential
problems with resolution of point selection.
Instant Invention Example 1
Symmetric Electrode Touch Switch with Single Wall Carbon
Nanotubes
[0139] A touchscreen was constructed using Coating C from Table I
as electrodes (SWCNT at 32.3 mg/m.sup.2). The single point
actuation testing was performed and gave the results indicated in
FIGS. 11 and 12 below. This symmetric electrode touchscreen
demonstrated little change in the force to actuate after completing
1.1 Million SPA without failure, as compared to the comparative
examples that all exhibit significant increases in the force to
actuate as the number of SPA cycles increased prior to failure. The
on-state resistance of instant invention example 1 shows
essentially no deviation after 1.1 Million SPA. This symmetric
electrode touchscreen demonstrates the significant robustness and
operability conferred by using the instant invention.
Instant Invention 2
Symmetric Electrode Touch Switch with Single Wall Carbon
Nanotubes
[0140] A touchscreen was constructed using Coating D from Table I
(SWCNT at 64.6 mg/m.sup.2) as the electrodes. The single point
actuation testing was performed and gave the results indicated in
FIGS. 13 and 14 below. This symmetric electrode touchscreen
demonstrated essentially no change in the force to actuate after
completing 1.1 Million SPA without failure, as compared to the
comparative examples that all exhibit significant increases in the
force to actuate as the number of SPA cycles increased prior to
failure. The on-state resistance of the instant invention example
shows essentially no deviation after 1.1 Million SPA. This
symmetric electrode comprising covalently attached hydrophilic
functionalization SWCNTs touchscreen demonstrates the significant
robustness and operability conferred by using the instant
invention.
[0141] As shown in the instant invention examples, it is surprising
and clearly obvious that the instant invention gives significant
improvements in robustness and device performance as demonstrated
above. The fact that the instant invention can sustain
significantly more actuations than the comparative example
touchscreens without failing (or failing later) and/or noticeable
change in operation is important due to the improved reliability of
the instant invention touchscreen including resolution, and
linearity. For instance, as the force to actuate increases for a
touchscreen (use a cellphone with a touchscreen component as
example) over time it will be increasingly difficult to select
certain points on the touchscreen whereas the instant invention
clearly would not suffer such problems. It is apparent that the
exemplary embodiment can provide drastically enhanced conductor
and/or electrode robustness.
[0142] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
PARTS LIST
[0143] 10 prior art resistive-type touchscreen [0144] 12 device
side transparent substrate [0145] 14 first conductive layer, device
side [0146] 15 device side first electrode [0147] 16 touch side
electrode [0148] 17 touch side transparent support [0149] 18 second
conductive layer, touch side [0150] 20 dielectric spacer element
[0151] 39 resistive-type touchscreen of the invention [0152] 24
device side exposed electrically conductive layer of the invention
[0153] 25 device side electrode of the invention [0154] 26 touch
side electrode of the invention [0155] 27 touch side electrode
insulating substrate of the invention [0156] 28 touch side exposed
electrically conductive layer [0157] 29 device side electrode
insulating substrate of the invention [0158] 32 dielectric spacer
element [0159] 100 resistive touchscreen of the invention [0160]
110 touch side electrode [0161] 120 device side electrode [0162] 30
dielectric spacers [0163] 141 touch side bus bar [0164] 142 touch
side bus bar [0165] 143 touch side connector electrode [0166] 144
touch side connector electrode [0167] 145 touch side wiring pattern
[0168] 146 touch side wiring pattern [0169] 251 device side bus
bars [0170] 252 device side bus bar [0171] 253 device side
connector electrode [0172] 254 device side connector electrode
[0173] 255 device side wiring pattern [0174] 256 device side wiring
pattern [0175] 40 bonding adhesive [0176] 301 microscope slide
[0177] 302 bottom device side electrode [0178] 303 dielectric
spacer dots [0179] 304 copper foil tape [0180] 305 double sided
adhesive tape [0181] 306 top touch side electrode
* * * * *