U.S. patent application number 09/776289 was filed with the patent office on 2001-11-29 for touch screen with polarizer and method of making same.
Invention is credited to Geaghan, Bernard O..
Application Number | 20010046604 09/776289 |
Document ID | / |
Family ID | 22658343 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046604 |
Kind Code |
A1 |
Geaghan, Bernard O. |
November 29, 2001 |
Touch screen with polarizer and method of making same
Abstract
A topsheet for a touch screen includes a support layer having a
touch surface and a second surface opposite the touch surface; a
polarizer layer having a first surface and a second surface with
the first surface of the polarizer in contact with the second
surface of said support layer; and a first conductive layer in
contact with the second surface of said polarizer.
Inventors: |
Geaghan, Bernard O.; (Salem,
NH) |
Correspondence
Address: |
Iandiorio & Teska
260 Bear Hill Road
Waltham
MA
02451-1018
US
|
Family ID: |
22658343 |
Appl. No.: |
09/776289 |
Filed: |
February 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60179873 |
Feb 2, 2000 |
|
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|
Current U.S.
Class: |
428/412 ;
428/480 |
Current CPC
Class: |
G02F 1/13338 20130101;
G06F 3/045 20130101; G06F 3/0412 20130101; G02F 1/133528 20130101;
Y10T 428/31507 20150401; G06F 3/041 20130101; Y10T 428/31786
20150401 |
Class at
Publication: |
428/412 ;
428/480 |
International
Class: |
B32B 027/36; B32B
027/06 |
Claims
What is claimed is:
1. A topsheet for a touch screen comprising a support layer having
a touch surface and a second surface opposite the touch surface; a
polarizer layer having a first surface and a second surface with
the first surface in contact with the second surface of said
support layer; and a first conductive layer in contact with the
second surface of said polarizer.
2. The topsheet structure of claim 1 wherein the support layer is a
polyester sheet.
3. The topsheet structure of claim 1 wherein the support layer is a
polycarbonate sheet.
4. The topsheet structure of claim 1 wherein the polarizer layer
includes a K type polarizer.
5. The topsheet structure of claim 1 including a first hardcoat
layer in contact with the second surface of said polarizer layer
and said first conductive layer is in contact with said first
hardcoat layer.
6. The topsheet structure of claim 5 wherein said first hardcoat
layer has a roughened finish.
7. The topsheet structure of claim 5 including an adhesion
promoting agent in contact with the second surface of said
polarizer layer.
8. The topsheet structure of claim 1 including a second hardcoat
layer in contact with the touch surface of said support layer.
9. The topsheet structure of claim 1 wherein said first conductive
layer includes a plurality of discrete sections of a conductive
material.
10. The topsheet structure of claim 1 wherein the touch screen is a
resistive film type touch screen and said first conductive layer
engages a second conductive layer of the touch screen.
11. A method of manufacturing a topsheet for a touch screen
comprising providing a support layer having a touch surface and a
second surface opposite the touch surface; laminating a polarizer
layer to the touch surface of said support layer, said polarizer
layer having a top surface and a bottom surface; and coating the
bottom surface of said polarizer layer with at least a conductive
layer.
12. The method of manufacturing a topsheet of claim 11 further
comprising applying a first hardcoat layer to the bottom surface of
said polarizer layer prior to said coating step.
13. The method of manufacturing a topsheet of claim 12 further
comprising applying an adhesion promoting agent to the bottom
surface of said polarizer prior to the step of applying said first
hardcoat layer.
14. The method of manufacturing a topsheet of claim 12 wherein said
hardcoat layer includes a rough surface.
15. The method of manufacturing a topsheet of claim 11 further
comprising coating the touch surface of said support layer with a
second hardcoat layer.
16. The method of manufacturing a topsheet of claim 12 wherein said
coating step is a vacuum sputtering process.
17. The method of manufacturing a topsheet of claim 16 further
comprising plasma etching said first hardcoat layer prior to said
vacuum sputtering process.
18. The method of manufacturing a topsheet of claim 11 further
comprising applying at least one thin film metal oxide layer to the
bottom surface of said polarizer layer prior to said coating
step.
19. The method of manufacturing a topsheet of claim 12 further
comprising applying at least one thin film metal oxide layer to
said first hardcoat layer prior to the coating step.
20. The method of manufacturing a topsheet of claim 11 wherein said
coating step is a vacuum sputtering process.
21. The method of manufacturing a topsheet of claim 20 further
comprising plasma etching said polarizer layer prior to said
coating step.
Description
RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional
application Ser. No. 60/179,873 filed Feb. 2, 2000 entitled
"POLARIZER TOUCH SCREEN FOR A LIQUID CRYSTAL DISPLAY DEVICE."
FIELD OF INVENTION
[0002] This invention relates to a touch screen with a polarizer in
the top sheet and to such a touch screen integrated with an LCD,
with one polarizer of the LCD in the topsheet of the touch
screen.
BACKGROUND OF INVENTION
[0003] Touch screens are widely used in many applications,
including computer interfaces, LCDs, and many of today's small
portable devices such as personal data assistants and cellular
telephones. Touch screen/LCD combinations are especially useful in
such portable devices. Touch screens include, but are not limited
to, resistive film type and capacitive touch screens.
[0004] The optical efficiency of typical resistive film type touch
screens is 75 to 85%. LCDs are even less efficient, due to the
polarizer layers which are inherent to polarizers, with typical
optical efficiencies of only 50% being common.
[0005] Polarizer layers have been added to touch screens to improve
the optical efficiency of touch screen/LCD combinations, however,
the polarizer layer was placed above the polycarbonate support
layer, i.e., closer to the touch surface of the touch screen. This
implementation exposes the polarizer layer to substantial physical
contact. Because the polarizer layer is less durable than the
polyethylene terephthalate (PET) layer which is near the touch
surface of typical touch screens, such a placement of the polarizer
layer results in a less durable touch screen.
[0006] Additionally, the placement of the polarizer above the
support layer requires that the support layer be optically
isotropic for the touch screen/LCD combination to function
properly. This results in a thicker and more costly touch screen
because the polycarbonate support layer cannot be made from a drawn
polycarbonate material, which is cheaper and may be drawn to much
smaller thicknesses than polycarbonate materials which are cast or
formed by other methods. Also, drawn polycarbonate material is not
sufficiently optically isotropic for such applications.
[0007] One such structure is disclosed in the article "Vanguard of
Liquid Crystal and PDP Development" by Y. Mitani, et al. (Japan,
1997) and is shown in FIG. 1. This structure includes a polarizer
56, comprising polyvinylalcohol (PVA) polarizing layer 50
sandwiched between two cellulose triacetate (CTA) layers 52, 54.
This is coated on the top surface with a hardcoat 58, which reduces
scratches on the top surface. The polarizer is bonded to
polycarbonate support layer 60 coated with indium tin oxide (ITO)
layer 62. The polycarbonate provides physical support required of a
topsheet, and is optically isotropic.
SUMMARY OF THE INVENTION
[0008] It is therefore an object of this invention to provide an
improved touch screen with a polarizer which is more durable.
[0009] It is a further object of this invention to provide such an
improved touch screen which is lower in cost.
[0010] It is a further object of this invention to provide such an
improved touch screen which is lighter in weight.
[0011] It is a further object of this invention to provide such an
improved touch screen which is thinner.
[0012] It is a further object of this invention to provide a method
of manufacturing such a polarizing topsheet for a touch screen.
[0013] This invention follows from the realization that touch
screens can benefit greatly from having a polarizer layer below the
support layer of the topsheet to provide the optical benefits of a
polarizer layer while being more durable, less costly, thinner and
lighter than polarizer layers above the support layer.
[0014] The present invention features a topsheet for a touch screen
including a support layer having a touch surface and a second
surface opposite the touch surface, a polarizer layer having a
first surface and a second surface with the first surface of the
polarizer in contact with the second surface of the support layer,
and a first conductive layer in contact with the second surface of
the polarizer.
[0015] In a preferred embodiment, the support layer may be a
polyester sheet or it may be a polycarbonate sheet. The polarizer
layer may include a K type polarizer. A first hardcoat layer may be
in contact with the second surface of the polarizer layer and the
first conductive layer may be in contact with the first hardcoat
layer. The first hardcoat layer may have a roughened finish.
[0016] An adhesion promoting agent may be in contact with the
second surface of the polarizer layer. A second hardcoat layer may
be in contact with the touch surface of the support layer. The
first conductive layer may include a plurality of discrete sections
of conductive material.
[0017] The touch screen may be a resistive film type touch screen,
and the first conductive layer may engage a second conductive layer
of the touch screen.
[0018] This invention also features a method for manufacturing a
topsheet including providing a support layer having a touch surface
and a second surface opposite the touch surface, laminating a
polarizer layer to the second surface of the support layer, the
polarizer layer having first and second surfaces, and coating the
second surface of the polarizer layer with at least a conductive
coating.
[0019] In a preferred embodiment, the method may also include
applying a first hardcoat layer to the second surface of the
polarizer layer prior to the coating step. An adhesion promoting
agent may be applied to the second surface of the polarizer layer
before applying the first hardcoat layer. The hardcoat layer may
include a rough surface. A second hardcoat layer may be applied to
the touch surface of the support layer.
[0020] The coating step may be a vacuum sputtering process. The
polarizer layer may be vacuum etched prior to the coating step. The
first hardcoat layer may be plasma etched before the vacuum
sputtering process. A thin film metal oxide layer may be applied to
the second surface of the polarizer layer before the coating step.
A thin film metal oxide layer may be applied to the first hardcoat
layer before the coating step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Other objects, features and advantages will occur to those
skilled in the art from the following description of a preferred
embodiment and the accompanying drawings, in which:
[0022] FIG. 1 is a cross-sectional view of a prior art topsheet
with polarizer;
[0023] FIG. 2 is a cross-sectional view of a topsheet with a
polarizer according to the present invention;
[0024] FIG. 3 is a cross-sectional view of a touch screen with a
topsheet with a polarizer, combined with an LCD, according to the
present invention;
[0025] FIG. 4 is a cross-sectional view of a topsheet with a
polarizer and a thin metal oxide film, according to the present
invention; and
[0026] FIG. 5 is a flow diagram of a method of manufacturing a
topsheet with a polarizer layer according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present invention features a polarizer topsheet as shown
in FIG. 2 which overcomes the technology problems found in prior
art. The polarizer topsheet in FIG. 2 has a PET or polycarbonate
support layer 70 laminated above the polarizer 72. The thickness of
the PET or polycarbonate support layer is between 0.001 and 0.010
inches. This construction with the support layer above the
polarizer protects the polarizer material from damage caused by the
crushing pressure on the topsheet resulting from finger or stylus
contact. It also reduces the potential for damage due to flexing of
the topsheet as it is pressed by a finger or stylus, by reducing
the radius of flex of the polarizer material.
[0028] A hardcoat 74 may be coated on the top surface of the
topsheet. This protects the topsheet from scratches. Hardcoat is
typically a cured acrylic resin, coated onto the surface of a
substrate by applying a liquid acrylic material, then evaporating
away the solvents in the liquid, then curing the acrylic with UV
light. The acrylic may also contain silica particles. These
transparent particles give a roughened finish to the cured
hardcoat, giving it anti-glare optical properties. Hardcoat
materials and coating services such as the Terrapin product from
Tekra Advanced Technologies Group in Berlin, Wisconsin have proven
suitable for the purposes described herein.
[0029] A hardcoat 76 may also be coated on the bottom surface of
the topsheet, between the polarizer 72 and the conductive coating
78. This hardcoat protects the polarizer and reduces the
dehydration and other effects of vacuum and heat on the polarizer
during the conductive coating process. In addition, an anti-glare
hardcoat under the conductive coating has the effect of diffusing
light that is reflected from the adjacent conductive coating layer,
reducing glare and also reducing Newton rings which otherwise form
due to the proximity of two reflective conductive coating layers
separated by an air gap and spacer dots. The hardcoat between the
polarizer and the conductive coating also protects the polarizer
from physical damage when pressure is put onto the topsheet by
finger touch or stylus. Such pressure causes flexing of the
topsheet and also can cause damage where the touch screen spacer
dots are pressed against the topsheet causing local, severe
deformation of the topsheet. The relatively high durometer of the
acrylic and silica hardcoat relative to the polarizer material
reduces local stresses on the polarizer material under touch or
stylus pressure.
[0030] The conductive coating described herein is typically ITO
(indium tin oxide) with a conductivity between 100 ohms per square
and 2000 ohms per square. For higher resistance in the range of
1000 to 4000 ohms per square, tin antimony oxide is sometimes used.
These coatings are typically applied onto sheets of organic
materials such as PET, using a vacuum sputtering process. The
vacuum sputtering process may include plasma etching of the support
layer, followed by sputtering of one or more coats of metal oxides.
For touch screen use, the last layer to be deposited is a
conductive layer, so the surface is conductive. Thin film layers of
silicon dioxide and/or titanium oxides may be used in combination
with the conductive layer in suitable thicknesses to form an
anti-reflective stack. Typical thickness of each layer for this
purpose is 1/4 wave of visible light. The lower layers of metal
oxides may also be selected to serve the purpose of enhancing
adhesion of the conductive metal oxide layer. Deposition of such
layers of thin film metal oxides is done by Neovac of Santa Rosa,
Calif. and others.
[0031] A resistive film type touch screen 10 with a topsheet 8
including a polarizer layer 6 combined with an LCD 12 is shown in
FIG. 3. Touch screen 10 includes substrate 4, typically glass,
coated with a transparent conductor 1, typically Indium Tin Oxide
(ITO). The ITO is typically applied in a vacuum sputtering process
which may also include additional layers of sputtered materials
such as silicon dioxide (SiO.sub.2) adjacent to the ITO 1. Topsheet
8 is separated from substrate 4 by spacer dots 2. Topsheet 8
includes a layer of plastic 3, typically PET, polarizer layer 6,
and ITO layer 5.
[0032] The LCD 12 comprises a layer of liquid crystal material 14
sandwiched between 2 substrates 16, 18, typically made of glass.
Layers of ITO 20, 22 are deposited on each substrate adjacent to
the liquid crystal material. Electrical signals are selectively
applied to specified areas of the liquid crystal material via
signal lines patterned in the ITO. Polarizer 26 is laminated onto
glass substrate 18. With polarizer layer 6 in topsheet 8, there is
no need for a polarizer layer on glass substrate 16, as would be
typical of an LCD without topsheet 8 according to the present
invention.
[0033] All materials between the two polarizers of an LCD must be
optically isotropic. An LCD functions by orienting light into
certain polarities, and any material which diffuses, refracts, or
changes polarity of light will reduce the performance of the LCD.
Glass and some polycarbonates are optically isotropic. PET is not.
Thus, the construction of a polarizer topsheet must use all
isotropic materials below the polarizer layer. Materials meeting
this requirement include some polycarbonates and cellulose
triacetate (CTA). By placing polarizer layer 6 below support layer
3, it is possible to use non-optically isotropic PET for layer
3.
[0034] There are several types of polarizing materials, including
reflective polarizers, dichroic polarizers, and hybrid combinations
of reflective and dichroic polarizers, as described in U.S. Pat.
No. 6,096,375. Dichroic polarizer types include H type and K type.
Both H and K types were invented by Land and Rogers, and are
described in U.S. Pat. Nos. 2,173,304; 2,255,940; and 2,306,108. H
polarizers are used in many commercial applications, including
virtually all current LCD displays. H polarizers are made by linear
orientation (stretching) of a polyvinylalcohol (PVA) film, the
surface of which is then imbibed with an iodine solution which
forms the required chromophores. A boron complex is then used to
stabilize the coating. Sheets of cellulose triacetate (CTA) are
then laminated on both sides of the film to protect the relatively
vulnerable polarizing layer. K polarizers also start with a PVA
sheet, but the PVA molecular structure of linked H--C--H and
H--C--OH molecules are selectively dehydrated to form a
polyvinylene of linked HC molecules. Sufficiently long, oriented
chains of the HC structure absorb light in the visible
spectrum.
[0035] The molecular structure of K polarizers are more stable than
H polarizers, so K polarizers are more robust for general use
issues including temperature range. In spite of these advantages, K
polarizers have not gained wide commercial use due to problems
including cost, polarizing efficiency, and lack of absorbance in
the red region of crossed K polarizers. These disadvantages are
balanced however, by the K polarizer's particular advantages in
areas that are uniquely important for touch screen applications,
including resistance to degradation by flexing, and resistance to
degradation by crushing pressure of a stylus tip, and compatibility
with chemicals such as acrylics used in hardcoats and with the
chemicals used in PSA's (pressure sensitive adhesives).
[0036] Polarizer touch screens are used to great advantage on LCD
displays. The upper polarizer required by an LCD may be laminated
with the topsheet of the touch screen 8, rather than being mounted
on the top glass substrate 16 of the LCD. The touch screen may then
be placed over the LCD display, or alternatively the touch screen
substrate 4 may be eliminated, and transparent conductor 1 may be
coated directly onto the LCD substrate 16, so the LCD substrate 16
serves as the substrate of the touch screen. This fully integrated
touch screen/LCD configuration is possible only if the top LCD
polarizer is moved to the topsheet 8.
[0037] There are several advantages of such a polarizer touch
screen and LCD combination. The optical efficiency may be improved,
e.g., ambient light reflections can be significantly reduced. The
structure allows omission of the touch screen substrate, with the
topsheet mounted directly on the LCD. This reduces thickness and
weight. Cost may be minimized because of reduced components, and
because integration may be done as part of the LCD manufacturing
process.
[0038] A preferred embodiment of the topsheet structure 80 is shown
in FIG. 4. PET is used for the support layer 82. PET is lower in
cost than polycarbonate. PET is proven structurally and optically
appropriate for the topsheet application, and it is available in
thinner sheets than polycarbonate. Optically isotropic
polycarbonate cannot be made by drawing the material into sheets.
This limits the minimum thickness of polycarbonate sheets to the
range of 0.010 inches, which is greater than the optimal topsheet
thickness of 0.005 to 0.008 inches. Polycarbonate is also more
expensive than PET.
[0039] Though any polarizer 84 may be laminated to the PET layer,
the preferred polarizer material is a K type polarizer. 3M Optical
Systems Division in Norwood, Mass., formerly a division of
Polaroid, sells a commercially available K polarizer known as
"KE".
[0040] Optically isotropic hardcoat material is used for hardcoat
86. Cured acrylic hardcoat materials such as the brand name
Terrapin from Tekra Advanced Technologies Group in Berlin, Wis.
have sufficiently low birefringence to qualify for this
purpose.
[0041] An adhesion promoter 83 may be used to improve the bond
between the polyvinylene based K polarizer and the acrylic hardcoat
86. It was found that silane primer vinyltrimethoxysilane,
[Si(OCH.sub.3).sub.3] applied to the polarizer surface immediately
prior to hardcoating, provided sufficient adhesion to withstand the
demanding requirements of a touch screen. The primer that was found
best is made by Witco of Greenwich, Conn., USA under the brand name
Silquest A-171. K polarizers are sufficiently chemically stable to
tolerate application of the silane adhesion promoter without
degrading optical performance of the polarizer.
[0042] Second hardcoat 88 may be applied to the touch surface of
support layer 82. Topsheet structure 80 comprising support layer
82, polarizer 84, adhesion promoter 83 and first hardcoat 86 is
vacuum sputter coated with conductive coating 90. The design of
topsheet structure 80 allows it to withstand the temperatures and
high vacuum environment of the sputter coating process, as well as
vacuum plasma etching process. Thin film metal oxide layer 92 may
be applied to conductive coating 90. Thin film metal oxide layer 92
may be a multi-layer structure and may be useful as an
anti-reflective stack.
[0043] A method 100 for manufacturing a topsheet with a polarizer
layer is shown in FIG. 5. Method 100 includes the steps of
providing a support layer having a touch surface and a second
surface opposite the touch surface, step 102, laminating a
polarizer, having a first surface and a second surface, to the
second surface of the support layer, step 106, and coating the
second surface of the polarizer with a conductive layer, step 116.
Applying a first hardcoat layer to the polarizer, step 110, may be
done prior to coating step 116. Applying an adhesion promoting
agent to the polarizer, step 108, may be done prior to applying
step 110. After applying step 110, plasma etching of the hardcoat
layer, step 112, may be performed. Applying a thin film metal oxide
layer, step 114 may be performed before coating step 116. Step 114
may be performed more than once to that a multi-layer
anti-reflective stack is formed. Applying a second hardcoat layer
to the touch surface of the support layer, step 104, may also be
performed.
[0044] The improved topsheet of this invention may be used to
advantage in several different configurations. These include a
resistive polarizer touch screen overlaid on an LCD; a resistive
polarizer touch screen, laminated to an LCD; and a fully integrated
LCD and resistive polarizer touch screen. These improved
configurations can reduce optical reflectance of the touch screen
by 15% to 30% while reducing thickness of the touch screen by as
much as 85%.
[0045] While polarizer touch screens can be used to greatest cost
advantage on LCD's, they are also useful with any type of display
including CRT's, OLED's, and plasma displays in applications where
minimizing reflections is important. For example, when a display
and touch screen are used outdoors, the display must be readable in
a wide range of ambient light conditions, including direct sunlight
and darkness. Examples of such applications include outdoor ATM
machines, ticketing machines, and gasoline pumps. Where sunlight
readability is required, a polarizer touch screen's reduced
reflections become a major benefit worth the added cost of a
polarizer.
[0046] Although specific features of the invention are shown in
some drawings and not in others, this is for convenience only as
each feature may be combined with any or all of the other features
in accordance with the invention. The words "including",
"comprising", "having", and "with" as used herein are to be
interpreted broadly and comprehensively and are not limited to any
physical interconnection. Moreover, any embodiments disclosed in
the subject application are not to be taken as the only possible
embodiments.
[0047] Other embodiments will occur to those skilled in the art and
are within the following claims:
* * * * *