Input device

The present invention relates to an input device for use on a display device, such as a liquid crystal display device (LCD), CRT, etc.

In a conventional input device, for example as shown in Figure 16, respective, opposed, surfaces of a high molecular resin film substrate 1 and a glass substrate 2 have transparent electrodes 3 and 4 of ITO film, SnO₂ film etc. formed thereon in a stripe like or other desired pattern. The arrangement is such that the substrates 1 and 2 are spaced apart by a pre-determined amount by means of a spacer 5 and a seal member 6. The electrodes 3 and 4 on the respective surfaces of the substrates 1 and 2 are connected, for example to a control circuit substrate and the like (not shown) via flexible connecting members 7, which may each comprise a flexible heat seal provided on the surface with connecting wiring 7a, a flexible printed circuit, etc.

In this case, since the glass substrate 2 and the electrode 4 on that substrate are both formed from inorganic materials, the bonding properties thereof are good. However, since the film substrate 1 and the electrode 3 on the substrate 1 are formed from an organic material and an inorganic material, respec­tively, there is a possibility that their bonding is deficient.

Consequently, when the flexible connecting member 7 is directly connected to the electrode 3 on the film substrate 1 by the use of a conductive adhesive agent etc. peeling of the above described electrode 3 from the film substrate 1 can occur if the flexible connecting member 7 is carelessly pulled, for example.

Therefore, as shown in Figure 16, a relay electrode 8 for leading out to the exterior has hitherto been formed on the glass substrate 2, and a vertically conducting portion of the lower transparent electrode 4 on the glass substrate 2, which constitutes a terminal part of the relay electrode 8, is conductively connected to a vertically conducting portion of the upper transparent electrode 3 on the film substrate 1 via a conductive adhesive agent layer 9, while the flexible connecting member 7 is conductively connected to an external connecting terminal, constituting the other terminal part of the relay electrode 8, via a conductive adhesive agent layer 10. A continuous seal member 6 is formed around the conductive adhesive agent layer 9 as shown in Figure 14.

The conventional input device as described above exhibits various problems in relation to the film substrate 1 and the glass substrate 2 in that the film substrate 1 may shrink relative to the glass substrate 2 during heat pressing or the like in the production process for the input device due to a difference in their co-efficients of thermal expansion, or alter­natively the film substrate 1 may expand relative to the glass substrate 2 when the device is left under high humidity due to a difference in expansion rates. Thus, excessive stress may be created between the relay electrode 8 and the electrode 3 on the film substrate 1 causing cracks to occur in the electrode 3 on the film substrate l, the electrode 3 to be peeled off from the film substrate 1, or the conductive adhesive agent layer 9 to be peeled off from the electrode 3.

Further, when the continuous seal member 6 is formed about the conductive adhesive agent layer 9, it traverses at least one of the transparent electrodes of the upper and lower substrates. Figures 13 and 14 show an example thereof in which the transparent electrode 3 passing through the seal member 6 generates a strong bending stress in the region of the seal member, causing cracks 14. Such bending and cracking results in an increase in resistance, and has been the cause of inferior operation of the input device.

In order to prevent the occurrence of cracks 14, it has been proposed to omit portions of the seal member 6 traversing the transparent electrode 3. Figure 15 shows an example of such an arrangement. In this case, however, the length of the seal member 6 extending around the conductive adhesive agent layer 9 is insufficient, and so a deficiency in sealing ability occurs. Again, this tends to produce peeling of the conductive adhesive agent layer 9 from the transparent electrode 3 due to deformation of the film substrate 1 after a period of use, whereby inferior operation can be expected.

Further, since the electrode 3 is formed either directly on the film substrate or on an undercoat layer of thin film, if the input device is employed for digitiser like use for inputting a line picture on an input surface, the shock of a pen and fingers at the time of inputting is applied directly to the electrode, and it is possible for cracks to be created in the electrode, or for the electrode on one of the substrates to be transposed onto the other of the substrates, whereby the characteristics of the input device are significantly harmed.

The present invention seeks to minimise or reduce at least some of the above problems in a simple manner.

In accordance with the present invention, there is provided an input device having a pair of opposed transparent substrates, and transparent electrodes provided respectively on the inner surfaces of the substrates, the electrode on one of the substrates being conductively connected to the electrode on the other of the substrates by way of a conductive adhesive agent layer, characterised by a conductive synthetic resin thin film layer softer than said conductive adhesive agent layer interposed between the respective electrode on one of the substrates and the conductive adhesive agent layer.

The conductive synthetic resin thin film layer has a stress absorbing action between the respective electrode and the conductive adhesive agent layer, and consequently substantially prevents the occurrence of cracks and peeling of the electrode from the film substrate. Additionally, the bond with the conductive adhesive agent layer may be improved.

In a preferred embodiment, the respective electrode is formed with a slit, and the conductive synthetic resin thin film layer enters the slit and extends into contact with the associated substrate.

Preferably, sealing means between the substrates and about the conductive adhesive agent layer are dis­continuous. For example, the sealing means may comprise in combination a continuous seal circumscribing a substantial proportion of the conductive adhesive agent layer and a discontinuous seal adjacent a remaining portion of the conductive adhesive agent layer.

Such sealing means conveniently provide adequate sealing while reducing the occurrence of electrode cracks found in the conventional structure.

A further preferred feature is an elastic layer in at least one of the substrates to provide a shock absorbing action. This is particularly advantageous in preventing cracks in one of the electrodes and trans­posing one of the electrodes during an input operation due to shock.

The present invention will be described further, by way of example, with reference to the accompanying drawings, in which:-

• Figure 1 is a vertical section through a first embodiment of an input device according to the present invention;
• Figure 2 is a fragmentary detail of a portion of Figure 1;
• Figure 3 is a plan view taken along the line III -­III of Figure 2;
• Figure 4 is a view corresponding to Figure 2 and showing another embodiment of the present invention;
• Figure 5 is a plan view taken along the line V - V of Figure 4;
• Figure 6 is a view corresponding to Figure 2 and showing a further embodiment of the present invention;
• Figure 7 is a plan view taken along the line VII - VII of Figure 6;
• Figures 8 to 10 are views corresponding to Figure 2 and showing variations on the substrate structure of Figure 2;
• Figure 11 is a view corresponding to Figure 2 and showing a variation on the sealing structure of Figure 2;
• Figure 12 is a plan view taken along the line VIII - VIII of Figure 11; and Figures 13 to 16 are views of conventional input devices.

An input device according to the present invention is shown in Figures 1 and 3, in which respective, opposed, surfaces of a high molecular resin film substrate 1 and a glass substrate 2 have transparent electrodes 3 and 4 of ITO film, SnO₂ film etc. formed thereon in a stripe like or other desired pattern. The arrangement is such that the substrates 1 and 2 are spaced apart by a pre-determined amount by means of a spacer 5 and a seal member 6.

The electrodes 3 and 4 on the respective surfaces of the substrates 1 and 2 are connected, for example to a control circuit substrate and the like (not shown) via flexible connecting members 7, which may each comprise a heat seal provided on the surface with connecting wiring 7a, a flexible printed circuit, etc.

A relay electrode 8 for leading out to the exterior is formed on the glass substrate 2, and the lower transparent electrode 4 on the glass substrate 2, which constitutes a terminal part of the relay electrode 8, is conductively connected to the upper transparent electrode 3 on the film substrate 1 by way of a conductive adhesive agent layer 9. The flexible connecting member 7 is conductively connected to an external connecting terminal, constituting the other terminal part of the relay electrode 8, by way of a conductive adhesive agent layer 10. A continuous seal member 6 is formed around the conductive adhesive agent layer 9.

In this example, a conductive synthetic resin thin film layer 11 is interposed between opposed surfaces of the electrode 3 on the film substrate 1 and the conductive adhesive agent layer 9 over substantially the entire boundary area between the two.

The conductive adhesive agent layer 9 comprises, for example, a silver filler containing epoxy adhesive agent mixed with a metallic material such as copper powder or the like of a pre-determined diameter.

The conductive synthetic resin thin film layer 11 is softer than the above described conductive adhesive agent layer 9 and has elastic properties and conductive properties. Any suitable material, for example a urethane adhesive agent containing paste like silver filler etc., may be used for the layer 11 and may be painted on the surface of the electrode 3 on the film substrate 1 to form a thin film having a thickness of, for example, about 20 µm to 30 µm. After forming the conductive synthetic resin thin film layer 11, the electrode 3 on the film substrate 1 and the relay electrode 8 on the glass substrate 2 are then conductively connected via the thin film layer 11.

Figures 4 and 5 show another embodiment of the present invention, in which like parts are indicated by the same reference numerals as in Figures 1 to 3. In this instance, a portion of the electrode 3 attached to the film substrate 1 in the region of the conductive synthetic thin film layer 11 is cut out to form at least one electrode opening 3a, and a part 11a of the conductive synthetic resin thin film layer 11 enters the opening 3a so as to contact directly and adhere closely to the film substrate 1. In Figure 4, an example is shown in which the electrode opening 3a is formed to have a slit like shape in the lengthwise direction of the electrode 3.

When a part of the conductive synthetic resin thin film layer 11 is made to adhere directly and closely to the film substrate 1 by forming an opening 3a in a portion of the electrode 3 on the film substrate, peeling of the electrode 3 from the substrate 1 and the like can effectively be prevented since the conductive synthetic resin thin layer 11 in general has better bonding properties in relation to the film substrate 1 than the electrode 3 of ITO or the like.

The electrode opening 3a may be formed, for example, after providing the electrode layer over the whole surface of the film substrate 1 and simultaneously with patterning by etching or the like.

In particular, when the formation of the opening 3a is carried out by etching, the film substrate surface in the opening 3a is activated in comparison with the untreated film substrate surface, and the strength of the bond between the conductive synthetic resin thin film layer 11 and the film substrate 1 can be further increased.

According to need, it is also possible to make a part of the conductive adhesive agent layer 9 adhere directly and closely to the glass substrate 2 by forming an opening of arbitrary shape, such as a slit like opening similar to that described above, in the relay electrode 8. By creating a bond between the conductive adhesive agent layer 9 and the glass substrate 2 as described above in the case of the conductive synthetic resin thin film layer 11 and the film substrate 1, an improvement in reliability together with an improvement in the close bonding properties of the input device can be obtained.

Also, according to need, a conductive synthetic resin thin film layer similar to the one described above may be interposed in the boundary area between the relay electrode 8 on the glass substrate 2 and the conductive adhesive agent layer 9.

Figures 6 and 7 show a further embodiment of the present invention. Again, like parts are represented by the same reference numerals. In this example, the terminal part 3b of the electrode 3 on the film substrate 1 is formed a little shorter than usual and a conductive synthetic resin thin film layer 11 is provided directly on the surface of the film substrate 1 as an extension of the electrode 3 with a part 11b of the conductive synthetic resin thin film layer 11 being made to cover the terminal part 3b of the electrode 3. Otherwise, the construction is the same as that in the previous examples.

When the electrode 3 is formed a little shorter than usual as described above and the conductive synthetic resin thin film layer 11 is directly formed on the surface of the film substrate 1 in the longitudinal direction of the electrode 3 to cover the terminal part 3b thereof, the thin film layer 11 and the film substrate 1 adhere well, and peeling of the electrode 3 from the substrate 1 can more effectively be prevented.

When the electrode 3 on the film substrate 1 is removed by etching before the formation of the above described thin film layer 11, the bond between the layer 11 and the film substrate 1 is strong. In addition, when the electrode 3 on the film substrate 1 and the conductive adhesive agent layer 9 are formed in such a manner that they do not overlap in a plane as shown in Figure 7, excessive stress on the electrode 3 due to thermal shrinkage and the like of the substrate can be substantially reduced, and the formation of cracks and the occurrence of peeling can further be decreased.

A first variation on the embodiment illustrated in Figure 2 is shown in Figure 8, wherein the film substrate 1 is replaced by a substrate having an elastic layer 12 formed from an elastic resin disposed between two layers of a supporting film 13. No change was observed in the resistance value of the input device having an elastic layer in the substrate, even after repeating an input operation two million times, although, in comparison with an input device having a single layer film substrate such as that as shown in Figure 2, the device had input resistive properties of 250 g load by the silicone rubber of 6 mmø. Hitherto, cracks tended to appear in the electrode after an input operation had been repeated about one million times, and the electrode on the film substrate tended to be transposed onto the electrode on the glass substrate, whereby an increase in resistance value was seen, but this problem may be solved by employing the elastic layer 12.

The elastic layer 12 may be softer than the film material used in the supporting film 13, and may be any suitable material, which is elastic and has high optical transmissivity. For example, a resin selected from the urethane resins, the silicone resins, the epoxy resins etc. may be coated on the first supporting film 13 and the second supporting film 13 may be laminated thereon.

Alternatively, the elastic layer 12 may be made into a film first and may then have the supporting film 13 laminated on both surfaces thereof.

Figures 9 and 10 show alternative possibilities, in which one of the supporting films 13 is omitted. Even in the cases where the position of the elastic layer 12 is changed, as shown in Figures 9 and 10, the input resistive properties were observed to be stable for more than two million input operations.

In Figures 11 and 12, another shape for the seal employed in the present invention is shown. In this instance, sealing is provided by the seal member 6 bounding the circumference of the conductive adhesive agent layer 9 and fixing the spacing between the substrates 1 and 2, and by a discontinuous seal 15. A silicone adhesive agent may be used as the seal 15 and seal member 6. As shown, each part of the seal 15 is positioned centrally of a respective one of the upper substrate electrodes 3, and each part has a length equal to two thirds of the width of the upper substrate electrode 3.

By forming a discontinuous seal on the upper substrate electrode 3 around the circumference of the conductive adhesive agent layer 9, the generating of cracks in the upper substrate electrode 3 due to stress is avoided, and the overall seal strength is preserved. As a result, the reliability of the device is signifi­cantly improved.

As explained above, in the present invention, by providing a soft conductive synthetic resin thin film layer 11 between the electrode 3 on the film substrate 1 and the conductive adhesive agent layer 9, when a shift occurs between the electrode 3 on the film substrate 1 and the relay electrode 8 due to a difference in the rate of thermal expansion or the like between the film substrate 1 and the glass substrate 2, the shift is absorbed by the elasticity of the soft conductive synthetic resin thin film layer 11 whereby the formation of cracks in the electrode 3 and the peeling of the electrode 3 from the film substrate 1 can be prevented before they happen. Consequently, an input device having good resistive properties can be provided.

Also, by forming a slit in at least one of the upper and lower electrodes on the film substrate 1 and the glass substrate 2, respectively, the strength of the bond between the conductive adhesive agent layer 9 or the conductive synthetic resin thin film layer 11 and the relevant substrate can be improved. This also has the effect of providing the input device with good resistive properties.

In addition, by forming the seal around the conductive connections between the upper and lower electrodes as a combination of a continuous seal and a discontinuous seal, the occurrence of cracks in one of the electrodes can be prevented, and the seal strength of the input device is assured and a good resistivity can be obtained.

Further, by providing an elastic layer having a shock absorbing action under the transparent electrode of one of the substrates, shocks transmitted from fingers and pens are not applied directly to the electrode, and cracks in and transposing of the electrode are prevented, which again enhances the resistive properties of the input device.