TOUCH PANEL

A touch panel includes a light transmissive substrate, an upper electrode, a light transmissive upper adhesive layer, a light transmissive conductive layer, a lower electrode, a lower light transmissive adhesive layer, and a protrusion. The upper electrode is formed on a lower surface of the substrate. The upper adhesive layer is formed on the lower surface of the substrate and a lower surface of the upper electrode. The conductive layer is formed on a lower surface of the upper adhesive layer. The lower electrode is formed on the lower surface of the upper adhesive layer and connected to the conductive layer. The lower adhesive layer is formed on the lower surface of the upper adhesive layer, a lower surface of the conductive layer, and a lower surface of the lower electrode. The protrusion is formed in the upper adhesive layer so as to connect the upper electrode and lower electrode.

DESCRIPTION OF EMBODIMENT

In each ofFIGS. 1 to 3C, a dimension of a touch panel is partially enlarged for easy understanding of a configuration thereof.

Exemplary Embodiment

FIG. 1is a partial cross-sectional view of a touch panel according to an embodiment of the present invention, andFIG. 2is an exploded perspective view of the touch panel according to the embodiment. InFIGS. 1 and 2, reference numeral11is a film-like or plate-like light transmissive substrate. As an example of film-like substrate11, a resin sheet made of one of polyethylene terephthalate, polycarbonate, cycloolefin polymer, polyethersulfone, or a combination of two or more thereof can be taken. As an example of film-like substrate11, a substrate made of one of glass and acrylic, or a combination thereof can be taken. Reference numeral12is an upper electrode made of one of silver, carbon, and a copper alloy, or a combination of two or more thereof. A plurality of upper electrodes12each having a thickness in a range from 2 μm to 30 μm are formed at a right end of an outer periphery of a lower surface of substrate11by printing or plating.

Reference numeral13is an ultraviolet curable upper adhesive layer made of a resin. The material of the resin is one of acrylate and methacrylate, or a combination thereof, for example. Upper adhesive layer13has a light transmissive property. Upper adhesive layer13is provided on substantially the entire lower surface of substrate11so as to expose a right end of each of upper electrodes12and cover a left end thereof. Although upper adhesive layer13exposes the right end of each upper electrode12, the portion to be exposed may be any end portion of each upper electrode12or an intermediate portion thereof, because it is only necessary that a part of each upper electrode12is exposed so as to be connected to an external connection of each upper electrode12. Upper adhesive layer13may be made of a material having an electron radiation curing property or a thermosetting property, in place of the ultraviolet-curing property.

Reference numerals14and15are each a light transmissive conductive layer. Conductive layer14includes a plurality of square-shaped parts connected in a substantially strip shape so as to extend in a front-rear direction, and a plurality of conductive layers14are buried in the lower surface of upper adhesive layer13. Conductive layer15includes a plurality of substantially rectangular-shaped conductive parts. The substantially rectangular-shaped conductive parts are formed for each substantially square-shaped gap in conductive layers14and connected in a left-right direction by connection parts15A each having a conductive property. Connection parts15A are formed on conductive layer14through an insulating layer so as not to electrically contact conductive layer14. Conductive layer15extends in the left-right direction perpendicular to the extending direction of conductive layer14in an electrically isolated manner from conductive layer14. A plurality of conductive layers15are also buried in the lower surface of upper adhesive layer13.

Conductive layers14and conductive parts and connection parts15A constituting of conductive layer15are each a part in which a plurality of metal thin wires are distributed in a resin. For example, the resin is made of one of light-transmissive acrylate and light-transmissive methacrylate, or a combination thereof and has the ultraviolet-curing property. The resin has an electron radiation curing property or a thermosetting property, in place of the ultraviolet-curing property. The metal thin wire has a diameter in a range from 10 nm to 300 nm and a length in a range from 1 μm to 100 μm. The material of the metal thin wire is one of silver, silver alloy, copper, copper alloy, a copper-nickel alloy, or a combination of two or more thereof, for example.

Conductive layers14and15are formed within a formation range of upper adhesive layer13. That is, conductive layers14and conductive layers15are all disposed on upper adhesive layer13and therefore do not directly contact the lower surface of substrate11.

Reference numeral16is a lower electrode having a thickness in a range from 50 nm to 200 nm and made of copper or a copper alloy. Lower electrode16is formed by sputtering and etching a metal. One end of lower electrode16is connected to conductive layer14or conductive layer15, and the other end thereof is drawn to a right end of an outer periphery of upper adhesive layer13and buried in the lower surface of upper adhesive layer13. Lower electrode16is provided in plural so as to correspond to conductive layers14and15. A leading part between one end and the other end of lower electrode16is preferably formed by a thin wire having a line width of 200 μm or less.

A plurality of protrusions12A formed on a lower surface of upper electrode12contact an upper surface of lower electrode16. That is, upper electrode12and lower electrode16are electrically connected to each other through protrusions12A. InFIG. 1, although two protrusions12A are formed to connect one upper electrode12and one lower electrode16, the number of protrusions12A may be one or three or more. It is preferable that a cross-sectional area of protrusion12A parallel to substrate11is reduced toward lower electrode16. This allows protrusion12A to penetrate upper adhesive layer13to reliably contact lower electrode16. A contact area between protrusion12A and the lower surface of upper electrode12is preferably larger than a contact area between protrusion12A and lower electrode16.

In order to obtain the abovementioned shape of protrusion12A, a silver paste in which conductive beads are previously mixed is screen-printed. For example, a spiked Ni powder having a diameter in a range from 3 μm to 60 μm, precious metal plated beads, and the like are mixed in a silver paste in which a silver powder is dispersed in a dilute solution of resin such as acrylic resin or epoxy resin, and resultant material is screen-printed to form protrusion12A. Even if insulating beads (e.g., glass beads) are used in place of the conductive beads, conductive protrusion12A can be formed because the insulating beads are covered by the silver paste.

Another formation method of protrusion12A includes forming upper electrode12using the silver paste through printing, sprinkling conductive beads (e.g., precious metal plated beads) over upper electrode12in a state where upper electrode is in an undried state, removing unnecessary beads other than those on a pattern of upper electrode12by air blow, followed by drying and fixing.

Reference numeral17is a lower adhesive layer having the light transmissive property and ultraviolet-curing property, as is the case of upper adhesive layer13. Moreover, like upper adhesive layer13, lower adhesive layer17may be made of a material having an electron radiation curing property or a thermosetting property, in place of the ultraviolet-curing property. It is preferable that upper adhesive layer13and lower adhesive layer17are cured by the same treatment.

Lower adhesive layer17covers the lower surface of upper adhesive layer13, lower electrode16, conductive layer14, and conductive layer15, thereby forming the touch panel.

The following describes a manufacturing method of the touch panel according to the present embodiment with reference toFIG. 1andFIGS. 3A to 3C.FIGS. 3A to 3Care partial cross-sectional views for explaining the manufacturing method of the touch panel according to the present embodiment.

As illustrated inFIG. 3A, in fabricating the touch panel according to the present embodiment, lower adhesive layer17is formed on an upper surface of film-like base material20. Lower adhesive layer17is formed in a uniform thickness in a formation range of the touch panel. Subsequently, there are formed the plurality of conductive layers14and conductive parts of the plurality of conductive layers15, and the plurality of connection parts15A (not illustrated) on an upper surface of lower adhesive layer17(connection parts15A are formed through the insulating layer). At the same time, a plurality of lower electrodes16are formed on an upper surface of lower adhesive layer17by a sputtering method. InFIG. 3A, the plurality of conductive layers15are formed in a depth direction of the view.

Then, as illustrated inFIG. 3B, substrate11on the lower surface of which upper electrode12and upper adhesive layer13are formed is placed on an upper surface of the touch panel ofFIG. 3A, and substrate11and touch panel are bonded through upper adhesive layer13. As illustrated inFIG. 3B, before bonding the touch panel ofFIG. 3Aand substrate11, protrusion12A is formed on the lower surface of upper electrode12, and protrusion12A is completely covered by upper adhesive layer13. At this time, upper adhesive layer13has not been fully cured. When the touch panel ofFIG. 3Aand substrate11are bonded to each other, protrusion12A penetrates upper adhesive layer13to be connected to lower electrode16. Thereafter, base material20is peeled off from lower adhesive layer17and, as illustrated inFIG. 3C, conductive layer14, conductive layer15, lower electrode16, and lower adhesive layer17are transferred onto the lower surface of upper adhesive layer13.

After that, an ultraviolet ray is irradiated onto the touch panel ofFIG. 3Cin which the plurality of protrusions12A formed on the lower surface of upper electrode12are brought into contact with the upper surface of lower electrode16to fully cure upper adhesive layer13. As a result, there is completed the touch panel in which, as shown inFIG. 1, upper adhesive layer13is stacked on the lower surface of substrate11, and conductive layer14, conductive layer15, lower adhesive layer17, and the like are stacked on the lower surface of upper adhesive layer13.

In this configuration, the ultraviolet ray is transmitted through substrate11, upper adhesive layer13, conductive layer14, conductive layer15, and lower adhesive layer17each having a light transmissive property, but not transmitted through upper electrode12and lower electrode16. This may result in insufficient curing of upper adhesive layer13at a portion between upper electrode12and lower electrode16. To prevent this, upper electrode12or lower electrode16in an ultraviolet irradiation side may be formed into a substantially lattice shape or a shape having a plurality of through holes. This allows reliable curing of upper adhesive layer13at the portion between upper electrode12and lower electrode16.

For example, when the ultraviolet ray is irradiated from lower adhesive layer17side, lower electrode16may be formed into a configuration including a portion having a line with a width of 200 μm or less or into a lattice shape. This preferably makes it easier for the ultraviolet ray from lower adhesive layer17side to be transmitted to upper adhesive layer13.

In a case where upper adhesive layer13has the electron radiation curing property, an electron ray is irradiated in place of the ultraviolet ray to fully cure upper adhesive layer13, and in a case where upper adhesive layer13has the thermosetting property, heating is applied to fully cure upper adhesive layer13.

The touch panel thus configured is disposed on a front surface of a display device such as a liquid crystal display device and mounted to an electronic device. The plurality of upper electrodes12drawn to the right end of the outer periphery of the lower surface of substrate11are electrically connected to an electronic circuit (not illustrated) of the electronic device through a flexible wiring board (not illustrated) or a connector (not illustrated).

In the above configuration, a user operates the electronic device by touching an upper surface of substrate11with his or her finger in response to display of the display device provided behind the touch panel in a state where voltage is applied from the electronic circuit to upper electrodes12sequentially. Electrostatic capacitance between conductive layers14and15is changed at a touched portion, and the touched portion is detected by the electronic circuit, whereby switching of various functions of the electronic device can be achieved.

For example, in a state where a plurality of menus are displayed on the display device provided behind the touch panel, the user touches the upper surface of substrate11with his or her finger at a portion corresponding to a desired menu. Then, a part of electrical charge of conductive layer15is conducted to the finger, resulting in a change in the capacitance between conductive layers14and15at the touched portion on the touch panel. Then, the electronic circuit detects the capacitance change, thus allowing a desired menu to be selected.

In the present invention, upper adhesive layer13, the plurality of conductive layers14and15each made of the light transmissive resin in which metal thin wires are dispersed, and lower adhesive layer17are formed on the lower surface of light transmissive substrate11in a stacked manner. This configuration allows reduction of a thickness of the touch panel excluding the substrate11to a range from 10 μm to 60 μm, thereby achieving thickness reduction of the entire touch panel. In other words, a thickness from the upper surface of upper adhesive layer13to the lower surface of lower adhesive layer17is in a range from 10 μm to 60 μm.

Moreover, the plurality of thin foil-like lower electrodes16are covered by upper adhesive layer13and lower adhesive layer17, the plurality of upper electrodes12each having comparatively larger thickness are connected respectively to lower electrodes16, and upper electrodes12formed on the lower surface of substrate11are connected to the electronic circuit. This prevents corrosion of lower electrode16due to humidity, allowing reliable operation.

Moreover, protrusion12A is formed on the lower surface of upper electrode12so as to contact lower electrode16, allowing upper electrode12and lower electrode16to be connected through protrusion12A. This allows reliable connection between upper electrode12and lower electrode16.

Hollow carbon thin wires each having a diameter in a range from 0.5 nm to 50 nm and a length in a range from 0.5 μm to 10 μm or carbon particles each having a particle diameter in a range from 2 nm to 100 nm may be distributed, in addition to the metal thin wires, in the light transmissive resin of each of conductive layers14and15. This enables absorption of reflection light from the metal thin wires to allow reduction of diffuse reflection.

As is clear from the above description, the present application is featured in that lower electrodes16formed corresponding respectively to conductive layers14and15are connected to upper electrodes12through protrusions12A. Moreover, the above-described arrangement state of conductive layers14and15advantageously reduce the entire thickness of the touch panel.

In the description of the above embodiment, terms related to directions such as “upper surface”, “lower surface”, “upper”, “lower”, “front-rear”, and “left-right” each indicate a relative direction only depending on a relative positional relationship among components of the touch panel such as the substrate, conductive layer, and insulating layer and do not indicate an absolute direction such as a vertical direction.

A touch panel according to the present embodiment includes a light transmissive substrate, an upper electrode, an upper adhesive layer, a conductive layer, a lower electrode, a lower adhesive layer, and a protrusion. The upper electrode is formed on a lower surface of the substrate. The upper adhesive layer is formed on the lower surface of the substrate and a lower surface of the upper electrode and has a light transmissive property. The conductive layer is formed on a lower surface of the upper adhesive layer and has a light transmissive property. The lower electrode is formed on the lower surface of the upper adhesive layer and connected to the conductive layer. The lower adhesive layer is formed on the lower surface of the upper adhesive layer, a lower surface of the conductive layer, and a lower surface of the lower electrode and has a light transmissive property. The protrusion is formed in the upper adhesive layer so as to connect the upper electrode and lower electrode. The upper adhesive layer, conductive layer, lower adhesive layer are formed on the lower surface of the substrate in a stacked manner, so that a thickness of the entire touch panel can be reduced. The protrusion formed on the lower surface of the upper electrode contacts the lower electrode, thereby achieving stable connection between the upper and lower electrodes. Thus, a touch panel allowing reliable operation can be obtained.

The touch panel according to the present invention has advantages in that the entire thickness thereof can be reduced and reliable operation can be ensured and is thus very useful as an operation unit of various electronic devices.