Transparent touch panel and a method of manufacturing the same

An optically transparent touch panel includes an upper substrate provided with an upper conductive layer formed on a lower surface thereof, and a lower substrate provided with a lower conductive layer formed on an upper surface thereof in a manner to confront the upper conductive layer with a predetermined space. The upper and lower substrates are bonded together with a spacer having a modulus of elasticity between 104 and 106 Pa. The touch panel has a long usable life with the capability of downsizing the whole body, while maintaining a required effective operating area.

FIELD OF THE INVENTION

The present invention relates to an optically transparent touch panel used for operating a variety of electronic devices. The invention also relates to a method of manufacturing the touch panel.

BACKGROUND OF THE INVENTION

There has been rapid progress in performance and diversification of electronic devices in recent years. In pace with the progress, there has been an upward surge in number of devices equipped with optically transparent touch panels in front of display devices such as LCD's and the like. In any such device, a user visually catches and selects characters, marks, signs, and the like displayed in a display device through a touch panel, and switches individual functions by operating the optically transparent touch panel.

Referring toFIG. 2, a description is provided of a conventional optically transparent touch panel of such kind.FIG. 2is a sectional view of a conventional optically transparent touch panel. In the figure, optically transparent upper substrate11is provided with optically transparent upper conductive layer12formed on a lower surface thereof. A pair of upper electrodes17is provided at both ends of the upper conductive layer12. In addition, optically transparent lower substrate13is provided with optically transparent lower conductive layer14formed on a upper surface thereof in the like manner as the upper conductive layer12. A pair of lower electrodes18is provided on a upper surface of the lower conductive layer14at both ends thereof in the like manner as the upper electrodes17, but in a direction orthogonal to the upper electrodes17. Also formed are plurality of dot spacers15at regular intervals in order to maintain a predetermined space from the upper conductive layer12. Spacer16, which develops adhesion by heat curing, is composed of bisphenol A type epoxy resin having 3.2×107Pa in modulus of elasticity. The spacer16is formed into a frame-like shape on any of the lower surface of upper substrate11and the upper surface of lower substrate13along the periphery thereof. The spacer16thus bonds together the upper substrate11and the lower substrate13along their periphery in a manner that the upper conductive layer12and the lower conductive layer14confront with respect to each other with a predetermined space between them. The optically transparent touch panel is constructed as described above.

In the structure described above, the upper electrodes17and the lower electrodes18are connected to a detector circuit of an electronic device. When the user depresses any point in an effective operational area of the touch panel with a finger, pen and the like, the upper substrate11deforms around the depressed point. This causes the upper conductive layer12to come into contact with the lower conductive layer14. The depressed point is determined by detecting a ratio of resistances between the upper electrodes17as well as that of the lower electrodes18. In this instance, the effective operational area defines an upper surface area of the upper substrate11other than a portion bonded by the spacer16, and it is the area available for depressing operation and detection of the depressed point.

In the above-discussed optically transparent touch panel of the prior art, however, the upper conductive layer12receives a large bending stress around an edge of the spacer16when a depressing force is applied in the vicinity of the spacer16, and this stress becomes greater the closer the depressed point is to the spacer16. Since this stress tends to accelerate fatigue of the upper conductive layer12, an area near the spacer16cannot be used as the operational area of the optically transparent touch panel. As a result, the effective operational area is restricted by this portion of unusable area. It is therefore inevitable to increase overall dimensions by an amount as great as this unusable area to provide a given size of effective operational area, which makes the whole touch panel bulky.

SUMMARY OF THE INVENTION

An optically transparent touch panel of this invention comprises an upper substrate provided with an upper conductive layer formed on a lower surface thereof, and a lower substrate provided with a lower conductive layer formed on an upper surface thereof in a manner to confront the upper conductive layer with a predetermined space, wherein the upper substrate and the lower substrate are bonded together with a spacer having a modulus of elasticity between 104and 106Pa.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a cross sectional view of an optically transparent touch panel according to an exemplary embodiment of this invention. Optically transparent upper substrate1has upper conductive layer2formed on a lower surface thereof. Upper substrate1consists of a polyethylene terephthalate film, a polycarbonate film and the like, and the upper conductive layer2is formed by vacuum spattering indium-tin oxide, tin oxide and the like. A pair of electrodes7is formed by printing silver paste, carbon paste and the like, and they are located at both ends of the upper conductive layer2. Optically transparent lower substrate3made of a glass plate, acrylic resin, polycarbonate resin and the like has optically transparent lower conductive layer4formed on an upper surface thereof in the same manner as the upper conductive layer2. A pair of lower electrodes8is also provided on an upper surface of the lower conductive layer4at both ends thereof in the like manner as the upper electrodes7, but in a direction orthogonal to the upper electrodes7. There are also plurality of dot spacers5formed at regular intervals in order to maintain a predetermined space from the upper conductive layer2. The dot spacers5are formed of an insulation material such as epoxy and silicone. Spacer6, which develops adhesion by heat curing, is composed of thermosetting resin having 104to 106Pa in modulus of elasticity with a principal component of epoxy composite, urethane composite or silicone composite, and it is formed by means of coating or printing. The spacer6is formed into a frame-like shape on any of the lower surface of the upper substrate1and the upper surface of the lower substrate3along the periphery thereof. The spacer6thus bonds together the upper substrate1and the lower substrate3along their periphery in a manner that the upper conductive layer2and the lower conductive layer4confront with respect to each other with a predetermined space therebetween, to constitute the optically transparent touch panel.

An epoxy composite suitable for the spacer6here is epoxy resin denatured with a rubber component such as polybutadiene, polyisoprene and polyacrylonitrile butadiene, that is rubber-denatured epoxy resin as is known.

Beside those listed above, any of silicone-denatured epoxy resin, fatty acid-denatured epoxy resin, and epoxy resin denatured with a component containing a conjugate double bond in fatty acid may be used as the epoxy composite for the spacer6. In addition, urethane-denatured epoxy resin, polyether-denatured epoxy resin, and polysulfide-denatured epoxy resin may also be used.

Any of the above seven types of denatured epoxy resin can be used singly or in any combination of two or more.

In addition, any one or a combination of the above seven types of denatured epoxy resin can be used in further combination with an ordinary epoxy compound, as the epoxy composite for the spacer6. The ordinary epoxy compound here includes such epoxy materials as bisphenol A type epoxy resin, novolak type epoxy resin, alicyclic type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, (di-) glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, and any of the above materials diluted with epoxy diluent. Some examples of the epoxy diluent are styrene oxide, alcoholic glycidyl ether such as butyl-glycidyl ether, glycidyl ester of carboxylic acid, certain types of silane such as glycidic hydroxypropyl trimetoxy silane.

A urethane composite suitable for use as the spacer6includes di-, tri- and tetra-polyisocyanates of monocyclic- and heterocyclic-aromatics, aliphatics, and/or alicyclics, or a mixture of any of the above. Or, a composite of any of the above group materials may be used by adding polyester polyol (diol or polyol) and polyether polyol (diol or polyol).

Further, a silicone composite suitable for the spacer6includes any such materials that have structures of di-methyl silicone, methyl vinyl silicone, methyl phenyl vinyl silicone, and fluoro silicone groups.

In addition, any of the above materials can be used together with a hardening agent. There is no specific limitation on the hardening agent of the epoxy composite, and one or more different kinds of hardening agent may be used as appropriate to the epoxy composite to be used together. Some examples of the hardening agent suitable here are amine, polyamine, amine adduct, amine salt, polyamide, imidazole derivative, dicyandiamide, ureic compound, melamine derivative, Lewis acidic salt, ketimine, acid hydrazide, acid anhydride, polythiol, sulfide derivative, phenolic resin, amino resin, and the like.

Also, the spacer6can be formed of any resin that can be hardened by irradiation of ultraviolet rays or an electron beam. Such resins that can be hardened by ultraviolet rays include radical polymerized hardening resin and cationic polymerized hardening resin. An example of the radical polymerized hardening resin is acrylic (vinyl polymerization type) resin with a principal component of (meta-) acrylic oligomer or (meta-) acrylic monomer having a urethane structure, which is to be added with a photo-polymerization initiator. Any of benzoyl alkyl ether, benzophenone, acetophenone and thioxanthone group materials may be used as the photo-polymerization initiator. Alternatively usable is polythiol polyene (addition polymerization type) resin with a principal component of polyene (allylic unsaturated resin) or polythiol (mercapto group containing resin) in combination with a photo-polymerization initiator of benzophenones. An example of the cationic polymerized hardening resin is epoxy-ring-opening polymeric resin with a principal component of any resin having an epoxy structure in combination with a photo-polymerization initiator of aromatic diazonium salt, aromatic halonium salt and aromatic sulfonium salt, which generate Lewis acid when subjected to light. Resins that can be hardened by an electron beam are radical polymerized hardening resin and cationic polymerized hardening resin, which can be hardened also by ultraviolet rays as described above. The method of hardening with an electron beam does not require the addition of any photo-polymerization initiator, since it can irradiate higher energy than ultraviolet rays to promote polymerization of the principal component.

Additionally, filler, plasticizer, solvent leveling agent and thixotropic agent may be added to the above materials as needed to control the viscosity. Materials suitable as the filler are silica, metallic oxides such as alumina, metal carbonate compounds such as calcium carbonate, metal sulfate compounds such as barium sulfate, metal silicate compounds such as talc, and the like.

The optically transparent touch panel constructed as above has the upper electrodes7and the lower electrodes8connected to a detector circuit in an electronic device. Using a finger, pen and the like, when a user depresses any point in an effective operational area, where is functional for depressing operation and detection of the depressed point on a surface of the upper substrate1other than a portion over the spacer6, the upper substrate1deforms. This causes the depressed point of the upper conductive layer2to come into contact with the lower conductive layer4. The detector circuit detects the depressed point according to a ratio of resistances between the upper electrodes7as well as that of the lower electrodes8.

Details will be provided next in a concrete manner of a method of manufacturing the optically transparent touch panel that uses any such spacers6described above, and how it is evaluated.

First, bisphenol A type epoxy resin, amine hardener, silica filler and talc were mixed in a ratio of 100:7:15:40 by weight. Using this mixture, the spacer16was formed with a thickness of 50 μm and width of 3 mm in a manner as described in the background of the invention. Then, an optically transparent touch panel as the prior art example was produced, which is designated as sample No. 0.

Next, as a sample of epoxy composite according to this exemplary embodiment, first prepared was a composite comprising glycidyl ester type epoxy resin, amine hardener and silica filler. They were mixed in a ratio of 100:30:10 by weight. The mixture was heated at 150° C. for 30 minutes to form spacer6of 50 μm in thickness and 3 mm in width, and an optically transparent touch panel was produced, which is then designated as sample No. 1.

Further, a urethane composite was prepared as another sample, which comprises polyether polyol, methylethyl ketoxime block isocyanate, hardening accelerator (di-n-butyl tin dilaurate) and silica filler. They were mixed in a ratio of 100:30:1:10 by weight. The mixture was heated at 150° C. for 30 minutes to form spacer6, and another optically transparent touch panel was produced, which is designated as sample No. 2.

Furthermore, a silicone composite comprising methyl vinyl silicone resin was heated at 150° C. for one hour to form spacer6, and still another optically transparent touch panel was produced, which is designated as sample No. 3.

As a radical polymerized hardening resin, another mixture was prepared with urethane acrylate, which represents acrylic oligomer having a urethane structure, phenoxy ethylacrylate, photo polymerization initiator and silica filler. The mixing ratio was 100:95:6:10 by weight. The mixture was irradiated with ultraviolet rays of 800 mJ/cm2to form spacer6, and an optically transparent touch panel was produced, which is designated as sample No. 4.

Furthermore, as a cationic polymerized hardening resin, still another mixture was prepared with epoxidized polybutadiene, which represents a resin of an epoxy structure, polycaprolactone triol, photo polymerization initiator (triphenyl sulfonium hexafluorophosphate derivative) and silica filler. The mixing ratio was 100:100:3:10 by weight. The mixture was irradiated with ultraviolet rays of 1000 mJ/cm2to form spacer6, and an optically transparent touch panel was again produced, which is designated as sample No. 5.

In addition to the above, another mixture was prepared with urethane acrylate, which represents acrylic oligomer having a urethane structure, polyethylene diacrylate and filler. The mixing ratio was 100:80:10 by weight. This mixture was irradiated by electron beam of 20 kJ/kg to form spacer6, and an optically transparent touch panel was produced, which is designated as sample No. 6.

Furthermore, another composite was prepared which comprises polybutadiene rubber-denatured epoxy resin, polyamine hardener, and silica filler. The weight ratio of this mixture is 100:35:5. This mixture was heated at 150° C. for 30 minutes to form spacer6of 50 μm in thickness and 3 mm in width, and another optically transparent touch panel was produced, which is designated as sample No. 7.

Moreover, still another composite was prepared by mixing urethane-denatured epoxy resin, hardener of dicyandiamide and silica filler with a weight ratio of 100:30:25. This mixture was also heated at 150° C. for 30 minutes to form spacer6in the like manner, and another optically transparent touch panel was produced, which is designated as sample No. 8.

Table 1 shows modulus of elasticity in relation to loss tangent, which is defined as a ratio of viscous component to elastic component for each of the above samples, No. 0 to No. 8.

The optically transparent touch panels of the sample numbers 0 through 8 were evaluated. A pen having a pen point of 0.8 mm diameter made of polyacetal resin was slid reciprocally for a distance of 20 mm along a track 1.5 mm inside of and in parallel with the spacer6, while applying a downward pressure of 500 g. Following the above, resistance was measured on a depressed point, and a ratio of this resistance value to the initial resistance was determined as to whether it was within a predetermined value. A usable life is defined here as a number of strokes of the reciprocal sliding motion when the ratio of resistances exceeds the predetermined value.

As is obvious from Table 1, the sample numbers 1 through 8 of this exemplary embodiment exhibit 104to 106Pa in modulus of elasticity, which is a substantial improvement over the sample number 0 of the prior art which shows the modulus of elasticity of 3.2×107.

Also, it is known through comparison among the sample numbers 1 and 2, as well as between sample numbers 4, 5 and 6 that any of them having a smaller value of loss tangent shows an increased usable life even though their moduli of elasticity are generally equal.

In this exemplary embodiment, as described, the upper substrate1provided with upper conductive layer2formed on the lower surface thereof and the lower substrate3provided with lower conductive layer4formed on the upper surface thereof in a manner to confront the upper conductive layer2with a predetermined space are bonded together with the spacer6having a modulus of elasticity between 104and 106Pa. The optically transparent touch panel is then constructed. When the touch panel is depressed in the vicinity of the spacer6, the spacer6shrinks in response to the compressive force since it has the moderate elasticity between 104and 106Pa. Because this reduces bending stress of the upper conductive layer2in an area around an edge of the spacer6, it is not likely to cause fatigue so easily. In addition, the touch panel as a whole can be downsized while keeping the required effective operating area because the area near the spacer6can also be used as the effective operating area.

If spacer6has a modulus of elasticity of less than 104Pa, the spacer is considered too soft such that it does not restore itself easily into the original shape when the touch panel is depressed near the spacer, and in an extreme case, the spacer turns into a gel-form, which is difficult to use for practical purposes. On the other hand, the touch panel poses the same problem as before, if the modulus of elasticity exceeds 106Pa.

Furthermore, it is desirable to maintain 0.5 or less in loss tangent of the spacer6. If loss tangent of the spacer6is greater than 0.5, the spacer6becomes too soft and loses restorability. In other words, the smaller the value of loss tangent, the less viscosity and the easier the spacer6is to restore in shape. The spacer6can thus return into the original shape immediately after completion of a depressing operating near the spacer6, so as to shorten the duration of stress imposed on the upper conductive layer2around the edge of the spacer6. This can further reduce the fatigue, and hence increases the usable life against the sliding operation. On the other hand, a lower limit of the loss tangent is approximately 0.05. Any composite having a smaller value than that is required to use a resin that has rigid molecular structure. Such a resin is not adequately deformable, however, to satisfy the function of elastic spacer, since it generally has physical properties of high modulus of elasticity and hardness.

When the spacer is formed with radical polymerized hardening resin or cationic polymerized hardening resin that hardens by irradiation of an electron beam, the addition of photo polymerization initiator is not needed. The method of hardening with an electron beam can form the spacer easier, since it can irradiate higher energy than ultraviolet rays to promote polymerization of the principal component.

As described above, an advantage according to the present invention is to provide the optically transparent touch panel that has a long life with the capability of downsizing the whole body while keeping the required effective operating area.