CAPACITIVE TOUCH PANEL SENSOR WITH IMPROVED TRANSPARENCY
This invention relates to a touch panel sensor that is arranged on a front surface of a liquid crystal display device, or the like, and operates as an input device.
Background
A touch panel as a display integration type input device arranged on a front surface of a display has gained a wide application because it is easy and convenient to operate. Various types of touch panels are available, including optical, ultrasonic, resistive, capactive, etc. Among them, resistive touch panels have been most widely used because of the simple construction. Resistive touch panels employ a construction in which two transparent conductor films oppose each other through a spacer. When pushed by a finger or a stylus, the opposing conductor films come into mutual contact and input is made (see JP Kokai 10-48625).
Capacitive touch panels detect the change of an electrostatic capacitance of a sensor supplied with a voltage when a finger of a person approaches the sensor, and performs the input operation. It is believed that detection positional accuracy can be much improved by arranging electrodes in a specific pattern (see JP Kokai 2002-326301). It is also believed that in comparison with the resistive sensors, capacitive sensors can provide a touch panel having longer service life and higher reliability due to the lack of a movable topsheet.
Summary of the Invention Many touch panels known in the art use an ITO film as the transparent conductor film. Because this ITO film has a refractive index as high as about 2.0, a reflection factor of a sensor portion of the touch panel becomes high and recognition performance is deteriorated. In touch panel sensors using an ITO substrate having ITO electrodes arranged in a pattern, the reflection factor greatly varies between the ITO electrode portions and portions not having the electrode. Therefore, the ITO electrode portion and the portion not having the electrode can be clearly distinguished, and display recognition performance is remarkably inferior.
In JP Kokai 10-48625, reflected light from the ITO film is offset by use of a circular polarization plate and a 1/4 wavelength plate. Because such polarization plates are used, however, a -transmission factor drops and the panel is colored when viewed from an oblique direction. In JP Kokai 2002-326301, the reflection factor is lowered by disposing a non-reflecting layer as a base of the ITO layer. However, the ITO electrode portion is left exposed during a production process and it becomes difficult to prevent defects during production steps and to manage the cost of production and the production process.
It is therefore an object of the invention to provide an electrostatic capacitance type touch panel that has high recognition performance and high reliability and can be produced at a low cost.
To solve the problems described above, the invention provides a touch panel sensor formed by serially stacking an insulating transparent substrate on which a transparent conductor film is arranged in a predetermined pattern; an insulating non- reflecting layer arranged on at least the transparent conductor film; a transparent adhesive layer; and a transparent surface substrate; wherein the touch panel sensor satisfies the relation r3 < ri < r2 where ri is a refractive index of the insulating non-reflecting layer, r2 is a refractive index of the transparent conductor film and r3 is a refractive index of the transparent adhesive layer. In the invention, the non-reflecting layer having the refractive index ri smaller than the refractive index r2 of the transparent conductor film but greater than the refractive index r3 of the adhesive layer is interposed between the transparent electrode film arranged on the substrate and the adhesive layer for bonding the surface substrate in order to lower the reflection factor in the transparent electrode film and to improve recognition performance.
Brief Description of the Drawings
Fig. 1 is a schematic sectional view showing a construction of a touch panel sensor according to the invention. Fig. 2 shows a construction of a PET film having ITO electrodes used in the
Examples.
Detailed Description
A touch sensor according to the invention will be hereinafter explained with reference to the drawings. Fig. 1 is a sectional view showing an example of the touch panel sensor according to the invention. In the touch panel sensor 1 of the invention, transparent conductor films 3 are arranged in a predetermined pattern on a main surface of an insulating transparent substrate 2. A transparent surface substrate 6 is bonded to this transparent conductor film 3 through a transparent adhesive layer 5. An insulating non- reflecting layer 4 is arranged between the adhesive layer 5 and at least the insulating transparent electrode film 3. The insulating transparent' substrate 2 is not particularly limited and various kinds of plastic materials and glass having transparency can be used. Specific examples of the plastic materials include polyethylene terephthalate, polycarbonate, polyether sulfone, polypropylene, polyamide, polyacryl, cellulose propionate, and so forth. The insulating transparent substrate 2 preferably has a refractive index of about 1.4 to about 1.7. Particularly preferred are polyethylene terephthalate having a refractive index of 1.66 and polycarbonate having a refractive index of 1.55 to 1.59.
The thickness of the insulating transparent substrate 2 is preferably about 12 μm to about 10 cm in consideration of the fact that it is fitted to the display. When the thickness is smaller than 12 μm, handling becomes difficult and when it exceeds 10 cm, fitting property drops.
The transparent conductor film 3 is formed in a predetermined pattern on a main surface of the insulating transparent substrate 2. A thin film of metal oxides that are ordinarily used such as indium tin oxide (ITO), tin antimony oxide, indium oxide, tin oxide, zinc oxide, zinc aluminum oxide, indium zinc oxide, etc., or gold, silver, copper, aluminum, etc, are used for the transparent conductor film 3. The transparent conductor film 3 can be formed by methods ordinarily used in the past such as vacuum deposition, sputtering, ion plating, ion beam process, coating, and so forth, and can be shaped into a predetermined pattern by etching.
The thickness of the transparent conductor film 3 is not particularly limited. To obtain a surface resistance having high conductivity of 103Ω/square or below, however, the thickness is preferably at least 10 run. On the other hand, when the thickness is too great, transparency drops. Therefore, a particularly preferred thickness is about 10 to
about 300 nm.
The insulating non-reflecting layer 4 is formed on this transparent conductor film 3. A refractive index n of this insulating non-reflecting layer 4 is set in such a manner as to satisfy the relation r3 < n < r2 when a refractive index of the transparent conductor film is r2 and a refractive index of a transparent adhesive layer 5 that is disposed on the insulating reflection-preventing layer 4 and will be later described is r3.
The refractive index of the transparent conductor film 3 is generally about 1.9 to about 2.0 and the refractive index of the transparent adhesive layer 5 is generally 1.5 or below. Therefore, the refractive index of the insulating non-reflecting layer 4 is preferably 1.5 to 1.9.
Materials of the insulating non-reflecting layer 4 include inorganic materials such as AI2O3 (refractive index: 1.62), Sb2Oa (refractive index: 1.7), CeF3 (refractive index: 1.63), MgO (refractive index: 1.75), polymer type organic materials such as polystyrene, polyester, polyether sulfone, thiourea type polymer or organic-inorganic hybrid materials. Though this insulating non-reflecting layer 4 can be formed by vacuum deposition, sputtering, ion plating and coating, polyester, polystyrene, polyether sulfone, etc., can form easily and within a short time a thin film having uniform surface property by a solvent coating method, and are therefore preferred, in particular. >
The thickness of the insulating non-reflecting layer 4 is generally 10 to 1 ,000 nm. When the thickness is less than 10 nm, the surface property is inferior and when it exceeds 1,000 nm, the production cost increases. The thickness is more preferably 70 to 110 nm.
The insulating non-reflecting layer 4 may well be arranged on at least the transparent conductor film 3 but may be arranged on the insulating transparent substrate 2, too. In other words, the transparent conductor film 3 is formed on the entire surface of the insulating transparent substrate 2 during the production process and after the insulating non-reflecting layer 4 is further formed, etching is applied, so that the insulating non- reflecting layer 4 is arranged on only the transparent conductor film 3. When the transparent conductor film 3 is formed and then the insulating non-reflecting layer 4 is formed after etching, the insulating non-reflecting layer 4 is arranged not only on the transparent conductor film 3 but also on the transparent substrate 2.
The insulating non-reflecting layer 4 may be either a single layer or a multiple- layer of two or more layers so long as the requirement for the refractive indices described
above is satisfied. In the case of the single layer, it is difficult to lower the reflection factor of the sensor portion of the touch panel sensor throughout the entire visible wavelength range. When the multiple-layer is used, the reflection factor of the sensor portion of the touch panel can be lowered throughout the entire visible wavelength range. However, the greater the number of layers, the higher becomes the production cost. From the aspect of the production cost, therefore, the insulating non-reflecting layer 4 is preferably the single layer. In the case of the single layer, the insulating non-reflecting layer 4 is formed by use of a material whose refractive index falls between the refractive index of the transparent conductor film 3 and that of the transparent adhesive layer 5. In the case of the multiple-layer, it is preferred to alternately stack a material having a low refractive index and a material having a high refractive index into at least two layers from the aspect of optical design.
After the insulating non-reflecting layer 4 is formed in this way, the transparent surface substrate 6 is bonded through the transparent adhesive layer 5. To bond the transparent surface substrate 6, it is possible to dispose the transparent adhesive layer 5 on the transparent surface substrate 6 and then to bond the transparent adhesive layer 5 onto the insulating non-reflecting layer 4. Alternatively, it is possible to dispose the transparent adhesive layer 5 on the insulating non-reflecting layer 4 and to bond the transparent surface substrate 6 on the transparent adhesive layer 5. A known insulating adhesive can be used for the transparent adhesive layer 5.
Examples are an acrylic adhesive, a rubber adhesive, a silicone adhesive and an epoxy tackifier or adhesive.
The same material as the material of the insulating transparent substrate 2 can be used for the transparent surface substrate 6. In other words, it is possible to use plastic materials such as polyethylene terephthalate, polycarbonate, polyether sulfone, polypropylene, polyamide, polyacryl, cellulose propionate, or glass. The thickness is preferably about 12 μm to about 10 cm. When the thickness is less than 12 μm, handling is difficult. When the thickness exceeds 10 cm, transparency drops. Antireflecting treatment, anti-glare treatment, fingerprint preventing-treatment, and so forth, may be applied to this transparent surface substrate 6.
A hard coat layer for improving the surface property and a non-reflecting layer for further lowering the reflection factor of the transparent conductor film 3, that are not
shown, may be interposed between the insulating transparent substrate 2 and the transparent conductor film 3. A melamine resin, a urethane resin, an alkyd resin, an acrylic resin, etc., can be used for the hard coat layer. Silicon dioxide can be used for the non-reflecting layer. An electromagnetic wave preventing film for eliminating noise signals from the back may be bonded to the surface of the insulating transparent substrate
2 opposite to the surface on which the transparent conductor film 3 is arranged.
Since the insulating non-reflecting layer 4 for providing a predetermined refractive index is interposed between the transparent conductor film 3 and the transparent adhesive layer 5 in the invention, the reflection factor from the transparent conductor film 3 can be lowered, and the difference of the reflection factors between the portion of the transparent conductor film 3 and the portion not having the transparent conductor film 3 in the electrostatic capacitance type touch sensor can be reduced. As a result, it is possible to prevent lowering of recognition performance due to reflected light and to provide a touch panel having improved appearance and high reliability. When the insulating non- reflecting layer 4 is a multiple-layer, the reflection factor can be lowered in a broad visible wavelength range and a touch panel having higher recognition performance can be acquired.
The touch sensor according to the invention can be produced by the following two methods, for example. According to the first method, an ITO film as the transparent conductor film, for example, is coated by sputtering to the insulating transparent substrate. Next, this ITO film is etched to form a pattern of ITO. After ITO electrodes are formed, the insulating non-reflecting layer is coated and wires to a controller portion are connected to the ITO electrodes. Finally, the transparent surface substrate is bonded through the transparent adhesive layer. According to the second method, the insulating non-reflecting layer is coated before etching of the ITO film described above. A pattern is formed in the
ITO film and the insulating non-reflecting layer, and etching is carried out to form the insulating non-reflecting layer on only the ITO electrodes. Next, the ITO electrodes are wired to the controller. Finally, the transparent surface substrate is bonded through the transparent adhesive layer. When a material capable of solvent coating is used for the insulating non-reflecting layer, the non-reflecting effect can be accomplished extremely easily and economically. Though the number of production steps increases when this non-reflecting layer is
disposed, the non-reflecting layer protects the transparent conductor film during the production process and plays the role of preventing disconnection. Therefore, it becomes possible to prevent the increase of the resistivity resulting from disconnection and degradation of the transparent conductor film, to lower the defect ratio of the sensors and eventually to economically produce the products.
Examples
Example 1 : A 1% solution of polystyrene (refractive index: 1.59), a product of Wako Junyaku
K. K., was prepared by use of a mixed solvent of methyl ethyl ketone: toluene = 50:50 (wt%). This solution was applied to a PET film having ITO electrodes, a product of 3M Touch System Co., by using a bar coater. The ITO electrodes had a stripe shape as shown in Fig. 2. The width of each ITO electrode 8 disposed on the PET film 7 was 4.5 mm and the width of the portions not having the ITO electrode was 0.7 mm. The thickness of the resulting polystyrene layer was 110 nm. A non-reflecting PET film ("ReaLook 7702UV", trade name) having an adhesive, a product of Nippon Yushi K. K., was bonded to the polystyrene layer and a touch panel sensor not having wiring to a controller portion was produced.
Example 2:
A touch sensor was produced in the same way as in Example 1 except that a solvent-soluble polyester resin ("Bilon 28SS", refractive index = 1.56), a product of Toyo Boseki K. K., was used in place of polystyrene.
Comparative Example 1 :
A touch sensor was produced in the same way as in Example 1 except that polystyrene was not coated.
Comparative Example 2:
A touch sensor was produced in the same way as in Example 1 except that a PET film not having the ITO electrodes was used in place of the PET film having the ITO
electrodes.
Examination by eye:
The samples produced in Examples 1 and 2 and Comparative Example 1 were examined by eye. The result was shown in Table 1.
[Table 1]
It was found from the examination by eye that the ITO electrodes could not be distinguished in Examples having the non-reflecting layer of polystyrene or polyester but in Comparative Example 1 not having the non-reflecting layer, the ITO electrodes could be distinguished by eye when the touch panel sensor was observed from the upper surface.
Measurement of reflection factor:
The reflection factors of the samples produced in Example 1, Comparative example 1 and Comparative Example 2 were measured. The reflection factors at 500 nm were measured by using a spectral reflectance meter of 5° and -5° ("MPC-3100, a product of Shimazu Seisakusho K. K.) The result was shown in Table 2.
[Table 2]
The sample of Example 1 could lower the reflection factor much more than the sample of Comparative Example 1. The touch panel sensor according to the invention could thus reduce reflected light. As a result, the difference of the reflection factors
between the portion having the ITO electrode and the portion not having the ITO electrode could be reduced, and a touch panel sensor having excellent recognition property could be acquired.