GB2172780A

GB2172780A - Transparent electrode element

Info

Publication number: GB2172780A
Application number: GB08606509A
Authority: GB
Inventors: Kazutoki Tahara; Yasutoshi Mizuishi; Toshihiko Egawa; Katsuyoshi Nakano; Tsutomu Suzuki; Kenichi Fukui; Yukio Fujitaya
Original assignee: Shin Etsu Polymer Co Ltd; Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Polymer Co Ltd; Shin Etsu Chemical Co Ltd
Priority date: 1985-03-18
Filing date: 1986-03-17
Publication date: 1986-09-24
Also published as: GB8606509D0; JPS61214301A

Abstract

A light-weight light-transmitting electrode or resistor element having high light transmission and electric conductivity useful as fixed display electrodes, antistatic plane heater elements, electrodes for terminal data-input instruments and the like is prepared by integrally bonding fine metal wires to at least one surface of a transparent substrate such as a film, sheet or plate of a plastic resin in a parallel alignment at a suitable pitch keeping spaces between wires with at least a part of each wire exposed above the substrate surface. The wires may be bonded to the substrate using a transparent adhesive or partially embedded in the substrate by hot pressing.

Description

SPECIFICATION Transparent electrode element BACKGROUND OF THE INVENTION The present invention relates to a transparent or other light-transmitting electrode element. In its preferred forms it concerns a light-weight transparent electrode element giving high light transmission and good electric conductivity and useful as a fixed electrode of display units, an antistatic plane heater element, an electrode for data-input terminal instruments and the like, which is prepared by integrally bonding fine metal wires in alignment on to the surface of a transparent substrate.

Conventionally known transparent electrode elements having high transparency and good electric conductivity include so-called Nesa glass prepared by vapor deposition of a thin layer of indium oxide doped with tin on the surface of a transparent substrate such as a glass plate and the like and transparent films made of a polyester resin and the like bearing a thin layer of a semiconductor or a metal on the surface prepared by means of spraying, smearing, reactive sputtering, reactive vapor deposition, ion plating and the like.

The transmission of visible light through these conventional transparent electrodes is usually in the range from 70 to 85 % and the surface resistivity thereof is in the range from 10 to 107 ohm/square. With these characteristic parameters, they are used in electrophotographic recording, fixed display units, optical memories, computer terminals, antistatic photoelectric transducer elements, plane heater units and the like.

Each of the above-mentioned transparent electrode elements of the prior art, however, has several disadvantages. For example, Nesa glass cannot be subjected to secondary processing or working such as bending, punching and the like due to the nature of the glass having no flexibility as a transparent substrate.

The transparent electrodes of Nesa glass must be prepared sheet by sheet with low productivity and their dimensions can rarely exceed 200 mm by 200 mm square. In addition, their weight cannot be so small as desired due to the high specific gravity of the glass of about 2.3. When a film of a plastic such as polyester resins is used as the substrate, there are also several problems such as the limitation in the selection of the transparent substrate material to those having high heat-resistance in consideration of the possible temperature rise to 250 "C or higher during the film-forming process and marked dependency of the bonding strength of the thin film on the hardness of the substrate material.Such a plastic filmsupported transparent electrode is poorly wear resistant due to the extremely small thickness of the electrode layer of about 50 nm or so to exhibit rapid increase in the resistivity when it is repeatedly used in input switching as a movable contact point when the number of the repeated switching operation has reached several hundred thousands of times. Furthermore, these electrodes are expensive because of the large investment in the installation for the film-forming facilities.

SUMMARY OF THE INVENTION The novel transparent or light transmitting electrode element of the invention comprises a transparent flat substrate and a plural number of fine metal wires integrally bonded to at least one surface of the transparent substrate in a parallel alignment with each other keeping a space between two adjacent wires, each of the wires being exposed on at least a part of the lateral surface thereof. The fine metal wires are bonded to the transparent substrate either by using a transparent adhesive or by embedding the wires partly in the surface layer of the transparent substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors have completed the present invention as a result of their extensive investigations on the kind of the substrate material and the fine metal wires, processing technique and the like based on the discovery that improved light-transmitting electrode elements can be obtained by integrally bonding fine metal wires to a transparent film, sheet or plate as a substrate in a parallel alignment keeping a suitable width of the space between two adjacent wires, that the thus obtained integral body is highly light-transmitting owing to the space left transparent between the wires as the electric conductors, that the products can be easily processed in a secondary fabrication work when the substrate is made of a material having high flexibility such as films and sheets of a plastic resin while a rigid substrate may serve simultaneously as a base support in the side of the fixed electrode and that industrial manufacture of the products of any desired dimensions can be conducted at low costs with ease because the integral bonding of the fine wires to the substrate can be easily carried out by using an adhesive or by compression molding under heating.

The transparent substrate as the base of the light-transmitting electrode element of the invention may be selected from general-purpose transparent sheet-like materials such as films and sheets of ABS resins, nylon resins, polypropylenes, polyvinyl chloride resins and the like. Although the electrode element can be prepared even of those materials having low heat-resistance, they can be replaced with any of synthetic resins having moderate heatresistance such as polycarbonate resins, polyester resins and, furthermore, by any of thermosetting resins such as epoxy resins, unsaturated polyesters and the like or even by elastomeric silicone rubbers each in the form of a sufficiently transparent film, sheet or plate having a thickness, preferably, in the range from 0.05 to 0.40 mm in order to secure flexibility.It is preferable that the thickness of the transparent substrate is at least three times of the diameter of the fine metal wires in order to have the wires embedded in the film, sheet or plate leaving at least a part of their surfaces exposed on the substrate surface as mentioned below.

The fine metal wires integrally bonded to the transparent substrate should be made of a metal selected from those having low electric resistivity used as a material of the contact points in data-input terminal equipments in view of the requirement of good electric conductivity. Exemplary thereof are copper wires having a volume resistivity of 1.72X10 6 ohm'cm, aluminum wires having a volume resistivity of 2.75X10 6 ohmcm, wires of phosphor bronze having a volume resistivity of 2 to 6X106 ohmcm, gold wires having a volume resistivity of 1 or 10 6 ohm cm, nickel wires having a volume resistivity of 7.24X 10 6 ohmcm, tungsten wires having a volume resistivity of 5.5X10 6 ohm-cm as well as wires of alloys of these metals and those plated with these metals.Wires of a metal having larger resistivity than the above named metals may also be used including stainless steel wires having a volume resistivity of 72X10 6 ohmcm and various kinds of high-resistivity wires used as a heater element or in EMI shield such as Nichrome wires having a volume resistivity of 1 lOX 10 6 ohm-cm and the like. The fine metal wire can be a solid wire or a stranded wire. The wire should preferably have a diameter in the range from 0.01 to 0.20 mm since wires having an excessively large diameter would decrease the light transmission although even metal wires having a diameter of 0.20 to 0.50 mm would not decrease the light transmission so much by adequately selecting the pitch of the parallel alignment, especially, when the electrode element is used as a heater element or EMI shield.

The light-transmitting electrode element of the invention can be obtained by integrally bonding the above described find metal wires to a transparent flat substrate in a parallel alignment keeping a pitch of 0.2 to 5 mm.

The parallel alignment of the wires is not limited to a single direction but the wires may be aligned in two or more of intersecting directions in a network-iike arrangement. Further, the pitch of the wire alignment may not be uniform over whole surface of the substrate but may be varied from portion to portion. It is optional that both of the surfaces of the substrate are provided with the metal wires integrally bonded thereto running either in the same direction or in different directions on each surface from the other.The procedure for the integral bonding of the wires is not particularly limitative and may be carried out in any of the methods including adhesive bonding in which the wires are put in alignment on the substrate surface coated in advance with a general-purpose transparent adhesive such as those of the acrylic resin type, polyurethane type, isocyanate type, epoxy resin type and the like or a hot-melt type adhesive. When the wires are desired to be partially embedded in the substrate, the wires are put on the substrate and pressed under an adequate pressure with heating so that the wires are forcibly sunk into the substrate softened by heating. When the substrate is made of a rubber, e.g. silicone rubber, the wires are put on the surface of an unvulcanized rubber sheet and sunk into the rubber sheet by cold pressing followed by hot-air vulcanization of the rubber under normal pressure.

The characteristic parameters of the light transmitting electrode element of the present invention can be easily controlled and those having high light transmission and a surface resistivity as low as 10 2 ohm/square can be obtained by appropriately selecting the materials of the substrates and the fine metal wires, diameter of the wires, density of the wires arranged in alignment and other parameters. For example, 95 % transmission of visible light is obtained by integrally bonding metal wires having a diameter of 0.020 mm at a pitch of 1 mm to the surface of a polycarbonate resin film having a thickness of 0.20 mm.Such a light-transmitting electrode element having a 90 % light transmission may have a surface resistivity of 2 to 5 ohm/square when stainless steel wires of 0.020 mm diameter having a high volume resistivity of 72X10 6 ohmcm are arranged in alignment at a pitch of 1 mm. The surface resistivity can be still lower when copper wires of the same diameter having a volume resistivity of 1.70X10 6 ohm cm are used in place of the stainless steel wires and values of 0.05 to 0.1 ohm/square and 0.025 to 0.5 ohm/square are obtained by arranging the copper wires at a pitch of 1 mm and 0.5 mm, respectively. Accordingly, the light-transmitting electrode element of the invention is useful as an electrode for fixed display units, antistatic plane heater elements, terminal data-input instruments and the like.

Examples are given in the following to illustrate the inventive light-transmitting electrode element in more detail..

Example 1 Stainless steel wires having a diameter of 0.022 mm (NAS 84S, manufactured by Nippon Seisen Co., Ltd.) were put in parallel with each other at a pitch of 1 mm on a polycarbonate resin film (lupilon Film FE-2000 (a product by Mitsubishi Gas Chemical Co., Inc.) having a thickness of 0.20 mm as the tran sparent substrate and pressed under a pressure of 120 kg/cm2 at 170 "C so that the wires were forcibly sunk into the resin film to give a light-transmitting electrode with the stainless steel wires embedded in the film. A radially peripheral portion of each wire having a thickness of 0.002 to 0.005 mm was protruded over the film surface. The transmission of visible light through this element was 90 % and the surface resistivity thereof was 3 to 5 ohm/square.The thus prepared light-transmitting electrode had good flexibility and was suitable as an electrode for a movable switching point. It was also highly abrasion-resistant as was indicated by the absence of any increase in the resistivity even after five million times of repeated switching tests.

Example 2 Two arrays of copper wires having a diameter of 0.050 mm were arranged in two directions perpendicularly intersecting each array with the other at a pitch of 0.5 mm in each direction on the same surface of the same resin film as used in Example 1 and then pressed under the same conditions as in the preceding example so as to be integrated wih the film. The wires in the upper array were also bent downwardly in the portions between the underlying wires in the iower array to be sunk into the substrate film. The transmission of visible light through the thus obtained light-transmitting electrode was 85 % and the surface resistivity thereof was as low as 0.05 ohm/square.

Example 3 Stainless steel wires having a diameter of 0.022 mm as used in Example 1 were arranged in parallel on a polyester resin film having a thickness of 0.25 mm (PET Lumirror 250T, a product by Toray, Inc.) as a transparent substrate coated in advance with an ethyl alcohol solution of a polyvinyl butyral resin (Slec B-BM-1, a product by Sekisui Chemical Industries Co., Ltd.) in a coating thickness of 0.025 mm as dried and were adhesively bonded to the substrate surface by gently pressing under a pressure of 120 "C to give a light-transmitting electrode. The radially peripheral portion of each stainless steel wire having a thickness of 0.012 to 0.013 mm was protruded over the surface of the adhesive layer.

The transmission of visible light through the electrode was 85 % and the surface resistivity thereof was 3 to 5 ohm/square.

Example 4 Tin-plated copper wires having a diameter of 0.100 mm were put and arranged in parallel at a pitch of 1 mm on an acrylic resin plate (Sumibex, a product by Sumitomo Chemical Industries Co., Ltd.) having a thickness of 2 mm as a transparent substrate and, further thereon, nylon filaments having a diameter of 0.050 mm were laid in a parallel alignment in a direction perpendicular to the underlying tinplated copper wires followed by pressing at 120 "C under a pressure of 100 kg/cm2 to give a light-transmitting electrode composed of an acrylic resin plate and copper wires and nylon filaments embedded therein. The nylon filaments were fusion-bonded to the underlying tin-plated copper wires. The transmission of visible light through the electrode was 83 % and the surface resistivity thereof was 3 to 5 ohm/square.The electrode was a rigid plate-like body and can be used as a fixed light-transmitting electrode plate also serving as a base support.

Example 5 Wires of phosphor bronze having a diameter of 0.035 mm were put and arranged in paralle at a pitch of 2 mm on the surface of a polyester resin film (PET Lumirror 250T, supra) having a thickness of 0.125 mm provided with a topping layer of a silicone rubber composition curable by the addition reaction (KE 164U, a product by Shin-Etsu Chemical Co., Ltd.) having a thickness of 0.01 mm as an elastomeric material after priming with a primer composition (Chemlok-607, a product by LORD Hughson Chemical Co., Ltd.) followed by cold-pressing under a pressure of 20 kg/cm2 at room temperature so that the phosphor bronze wires were sunk into the silicone rubber layer.Subsequent hot-air vulcanization of the silicone rubber for 30 minutes at 200 "C gave a light-transmitting electrode with the phosphor bronze wires embedded in the silicone rubber layer leaving a radially peripheral portion of each wire having a thickness of 0.002 to 0.005 mm protruded over the surface of the silicone rubber layer. The transmission of visible light through the electrode was 92 % and the surface resistivity thereof was 5 to 10 ohm/square.

A light-transmitting heater element having a resistance of about 100 ohm at room temperature was prepared by providing two lead wires bonded to the ends of the thus prepared light-transmitting electrode body by use of an electroconductive paste. The output of this heater element was 5 to 7 watts when an voltage of 25 volts was impressed between the lead wires to give a current of 200 to 300 mA therethrough. This light-transmitting heater element made of a silicone rubber and a polyester resin film was heat resistant and capable of withstanding a temperature of heating at 60 to 70 OC.

Example 6 A light-transmitting electrode electrically conductive on both surfaces was prepared in the same manner as in Example 1 except that the stainless steel wires were integrally bonded to both surfaces of a polycarbonate resin film as the substrate. The transmission of visible light through this light-transmitting electrode was 88 % and it was suitable as a light-transmitting EMI film by virtue of the electric conductivity on both surfaces.

Example 7 Stranded wires each composed of three intertwisted tin-plated copper wires having a diameter of 0.010 mm were put and arranged in parallel on a surface of the same polycarbonate resin film as used in Example 1 at a pitch of 0.3 mm followed by pressing under the same conditions as in Example 1 to give a light-transmitting electrode. The stranded wires of intertwisted tin-plated copper wires were embedded in the resin film each leaving a radially peripheral portion having a thickness of 0.005 to 0.007 mm over the film surface.

The transmission of visible light through the electrode was 85 % and the surface resistivity thereof was 1 ohm/square. A shielding effect of 20 to 30 dB was obtained when the thus prepared light-transmitting electrode was used as a light-transmitting EMI film and further a shielding effect of 30 to 60 dB was obtained by using two of the electrodes laid one on the other with the running direction of the array- of the wires on one electrode intersecting perpendicularly to the running direction of the wires on the other.

Claims

1. A light-transmitting electrode element which comprises a transparent substrate in a sheet-like form and a plural number of metal wires integrally bonded to at least one surface of the transparent substrate in a parallel alignment with each other keeping a space between adjacent wires, at least a part of each wire being exposed over the surface of the transparent substrate.

2. The light-transmitting electrode element as claimed in claim 1 wherein the metal wires are integrally bonded to the surface of the transparent substrate using a transparent adhesive.

3. The light-transmitting electrode element as claimed in claim 1 wherein the metal wires are integrally bonded to the surface of the transparent substrate by being embedded in the transparent substrate.

4. The light-transmitting electrode element as claimed in claim 1, 2 or 3 wherein the metal wires have a diameter in the range from 0.010 mm to 0.500 mm.

5. The light-transmitting electrode element as claimed in claim 1, 2, 3 or 4 wherein the metal wires are integrally bonded to the surface of the transparent substrate at a pitch in the range from 0.2 mm to 5 mm.

6. The light-transmitting electrode element as claimed in claim 1, substantially as described in any of the Examples.