JP2016024109A - Pressure-sensitive sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-sensitive sensor used for operation section of various kinds of electronic apparatuses capable of obtaining gentle changes in resistance value with respect to a pressing force.SOLUTION: A low resistance layer 12 is formed on the lower face of a base material 1; and a high resistance layer 13 is formed on the lower face of the low resistance layer 12. The high resistance layer 13 includes: conductive particles; a binder; and generally spherical elastic particles 14 which deforms with a predetermined load. The pressure-sensitive sensor is arranged so that maximum height of surface roughness on the lower face of the high resistance layer 13 is 4 -25 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pressure-sensitive sensor using a pressure-sensitive resistor whose resistance value changes according to a change in pressure or load, and relates to a pressure-sensitive sensor used in an operation unit of various electronic devices.

  In recent years, as various types of electronic devices such as mobile phones and car navigation systems have become highly functional and diversified, pressure-sensitive sensors used for these operations are required to be capable of various operations.

  Such a conventional pressure sensor will be described with reference to FIGS. 4 and 5. FIG.

  Note that, in these drawings, the cross-sectional views are shown by enlarging the dimension in the thickness direction for easy understanding of the configuration.

  FIG. 4 is a cross-sectional view of a conventional pressure-sensitive sensor. In FIG. 4, reference numeral 1 denotes a film-like substrate. A resistor layer 3 is formed on the lower surface of the resin layer by a synthetic resin in which carbon powder is dispersed. In the resistor layer 3, a plurality of particles 4 having different particle diameters such as synthetic resin are dispersed, and the lower surface of the resistor layer 3 is formed in an uneven shape to constitute a conductive sheet 5.

  Reference numeral 8 denotes a substrate disposed on the lower surface of the conductive sheet 5. A plurality of fixed contacts 6A and 6B such as silver and carbon are formed on the upper surface, and the fixed contacts 6A and 6B are formed between the conductive sheet 5 and the substrate 8. Spacers 7 are formed of insulating resin so as to surround 6B, and the pressure-sensitive sensor is configured such that the lower surface of the conductive sheet 5 and the fixed contacts 6A and 6B face each other with a predetermined gap.

  The pressure sensor configured as described above is attached to the operation unit of the electronic device, and a plurality of fixed contacts 6A and 6B are connected to the electronic circuit of the device (not shown) via lead wires (not shown). Connected).

  In the above configuration, when the upper surface of the conductive sheet 5 is pressed, the conductive sheet 5 bends downward and the lower surface of the resistor layer 3 comes into contact with the fixed contacts 6A and 6B, and is fixed via the resistor layer 3 therebetween. The contacts 6A and 6B are electrically connected.

  As the pressing force increases, the contact area of the lower surface of the resistor layer 3 formed in a concavo-convex shape with a plurality of particles 4 having different particle diameters to the fixed contacts 6A and 6B increases. The resistance value decreases with a large pressing force, and a resistance characteristic that gradually changes according to the pressing force can be obtained as shown by a curve A shown in the resistance characteristic diagram of FIG.

  The electronic circuit detects the electrical connection and the resistance value that changes according to the pressing force. For example, various functions of the device such as the movement speed of the cursor and pointer displayed on the display drawing change. The operation is performed.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2002-158103 A

  In the conventional pressure-sensitive sensor, since the surface roughness of the resistor layer 3 is as small as 0.1 to 3 μm, the change in the contact area between the resistor layer 3 and the fixed contacts 6A and 6B is sufficient with respect to the change in the pressing force. It wasn't. For this reason, when the load increases in the initial stage of pressing, the resistance value greatly decreases, and the resistance value does not change much even if the load is increased thereafter.

  That is, since the surface roughness is small, the resistor layer 3 and the fixed contacts 6A and 6B come into contact with each other even on a low pressing force. Therefore, as shown by curve A in FIG. 5, the slope of the curve in the low load region at the initial stage of contact becomes steep, the measurable load range cannot be widened, and the curve in the high load region is too small. The dynamic range was not sufficient.

  The present invention solves such a conventional problem, and an object of the present invention is to provide a pressure-sensitive sensor that can moderate a change in resistance value with respect to a change in pressing force.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention comprises a conductive sheet having a resistor layer on the bottom surface of a flexible substrate, and a fixed contact disposed at a position facing the resistor layer. , A pressure-sensitive sensor in which the conductive sheet is bent by the pressing operation, and the resistor layer and the fixed contact are in contact with each other, and the resistor layer is dispersed with elastic particles deformed by a predetermined load, and the surface of the surface facing the fixed contact This is a pressure-sensitive sensor having a maximum roughness of 4 μm to 25 μm, and since the maximum height of the surface roughness of the high resistance layer containing elastic particles is as large as 4 μm to 25 μm, In contrast, it is possible to provide a pressure-sensitive sensor that can moderately change the resistance value.

  According to a second aspect of the present invention, the elastic particles have an average particle diameter of 5 to 30 μm and are deformed by 5 to 15 μm with a load of 1 mN. Is appropriately deformed, so that a wide dynamic range of the resistance value can be secured.

  As described above, according to the present invention, it is possible to provide an advantageous effect that it is possible to provide a pressure-sensitive sensor that can moderate a change in resistance value with respect to a pressing force.

Sectional drawing of the pressure-sensitive sensor by one embodiment of this invention Sectional view during pressing operation Resistance characteristics Cross section of conventional pressure sensor Resistance characteristics

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. Note that, in these drawings, the cross-sectional views are shown by enlarging the dimension in the thickness direction for easy understanding of the configuration.

  In addition, the same code | symbol is attached | subjected to the part of the structure same as the structure demonstrated in the term of the prior art, and detailed description is simplified.

(Embodiment)
FIG. 1 is a cross-sectional view of a pressure-sensitive sensor according to an embodiment of the present invention, in which 11 is a film of polyethylene terephthalate, polycarbonate, polyurethane, polyimide, etc., and has a thickness of 25 to 200 μm. A low resistance layer 12 having a sheet resistance of 50Ω to 30 kΩ / □ is formed on the lower surface of the base material by a synthetic resin such as phenol, epoxy, phenoxy, or fluororubber in which carbon powder is dispersed.

  In addition to the above, the low resistance layer 12 may have a sheet resistance value of several Ω to several tens of Ω / □ in which silver, carbon, or the like is dispersed in polyester, epoxy, or the like.

  Reference numeral 13 denotes a high resistance layer formed on the lower surface of the low resistance layer 12, which is also formed of a synthetic resin in which carbon powder is dispersed. The high resistance layer 13 has an approximately spherical shape with an average particle diameter of 2 to 100 μm, preferably an average particle diameter of 5 to 30 μm, and an elasticity with a Shore A hardness of 30 to 90 HS such as urethane, acrylic, nylon, silicone, and olefin. The particles 14 are dispersed in an amount of about 10 to 80% by weight, preferably about 20 to 60% by weight, and the lower surface of the high resistance layer 13 is formed in an uneven shape to constitute the conductive sheet 15. The high resistance layer 13 has a sheet resistance value of 50 kΩ to 5 MΩ / □ and a thickness of 5 to 50 μm.

  In addition, after forming the low resistance body layer 12 in the base material 11 by screen printing in such a conductive sheet 15, the elastic particle 14 is disperse | distributed by screen printing using the plate of SUS300-100 mesh on this. The formed high resistance layer 13 can be formed.

  The elastic particles 14 are tough and elastic particles, and substantially spherical particles are used. When a load is applied to the elastic particles 14, a substantially spherical particle is compressed and crushed in the direction in which the load is applied, resulting in an ellipsoidal shape. At this time, if the elastic particle 14 deforms about 5 to 15 μm in the applied direction with respect to a load of 1 mN, the elastic particle 14 is appropriately deformed with respect to the pressing force. It is preferable because a wide range can be secured.

  In the case where elastic particles whose deformation with respect to a load of 1 mN is smaller than 5 μm are used, the change of the resistance value does not become smooth as the load increases, and the variation becomes large. In addition, when elastic particles with a deformation greater than 15 μm are used for a load of 1 mN, the resistance value greatly decreases when the load increases in the initial stage of pressing, and the resistance value changes much even when the load is further increased. It will be something that will not.

  Reference numeral 8 denotes a film-like substrate such as polyethylene terephthalate or polycarbonate, or a plate-like substrate such as paper phenol or glass-filled epoxy, which is disposed on the lower surface of the conductive sheet 15, and silver, carbon, copper foil, etc. The plurality of fixed contacts 6A and 6B are formed with a gap of about 0.05 to 0.2 mm.

  Further, a spacer 7 is formed of an insulating resin such as polyester or epoxy between the conductive sheet 15 and the substrate 8 so as to surround the fixed contacts 6A and 6B, and the lower surface of the high resistance layer 13 and the fixed contacts 6A and 6B are The pressure sensor is configured to face each other with a gap of about 10 to 100 μm.

  The pressure sensor configured as described above is mounted on the operation unit of the electronic device, and a plurality of fixed contacts 6A and 6B are connected to the electronic circuit (not shown) of the device via lead wires (not shown). Connected to.

  In the above configuration, when the upper surface of the conductive sheet 15 is pressed, the conductive sheet 15 bends downward as shown in the cross-sectional view of FIG. However, it contacts the fixed contacts 6A and 6B, and the fixed contacts 6A and 6B are electrically connected via the high-resistance layer 13 and the low-resistance layer 12.

  Here, the contact location on the lower surface of the high resistance layer 13 that is in contact with the fixed contacts 6 </ b> A and 6 </ b> B is a location where a bulge is formed in a large convex shape on the unevenness on the lower surface of the high resistance layer 13 as a result. That is, the portion of the lower surface of the high resistance layer 13 that forms a large bulge by the elastic particles 14 first comes into contact with the fixed contacts 6A and 6B.

  Further, when a pressing force is further applied, the elastic particles 14 are deformed, and the lower surface of the high resistance layer 13 other than the contact portion described above also contacts the fixed contacts 6A and 6B. That is, since the area of the contact location increases, the contact resistance decreases, and the resistance value between the fixed contacts 6A and 6B decreases.

  That is, as the pressing force increases, the contact area of the lower surface of the high resistance layer 13 formed in an uneven shape with the fixed contacts 6A and 6B increases. Then, the resistance value becomes low, and a resistance characteristic that gradually changes according to the pressing force can be obtained as shown by a curve C in the resistance characteristic diagram of FIG.

  The electronic circuit detects the electrical connection and the resistance value that changes according to the pressing force. For example, various functions of the device such as the movement speed of the cursor and pointer displayed on the display drawing change. The operation is performed.

  In the present invention, the lower surface of the high resistance layer 13 has a maximum surface roughness height Rz defined by JIS B0601: 2001 of 4 μm to 25 μm. The measurement conditions at this time were an evaluation length of 1.25 mm and a reference length of 0.25 mm.

  When the maximum height of the surface roughness is 4 μm or more and less than 8 μm, it is preferable because the resistance value can be gradually changed with respect to the pressing force (load) as shown by the curve B shown in FIG. Further, it is more preferable that the maximum height of the surface roughness is 8 μm or more and 25 μm or less. In this case, as shown by the curve C shown in FIG. Can be.

  When the maximum height of the surface roughness is less than 4 μm, the high resistance layer 13 and the fixed contacts 6A and 6B are almost in contact with each other even with a low pressing force, and the contact resistance is lowered. Therefore, as shown by the curve A shown in FIG. 3, the slope of the curve in the low load region at the beginning of contact becomes steep, the measurable load range cannot be widened, and the curve in the high load region is too small. The dynamic range will not be sufficient. Further, when the maximum height of the surface roughness exceeds 25 μm, the manner of contact between the high resistance layer 13 and the fixed contacts 6A and 6B causes variations among individuals, resulting in a low yield. When the maximum height of the surface roughness exceeds 35 μm, the yield reduction due to the variation among individuals becomes more remarkable.

  In the present invention, the value of the maximum height Rz of the surface roughness on the lower surface of the high resistance layer 13 is 4 μm or more and 25 μm or less. The value of the ten-point average roughness RzJIS is approximately correlated, and if the value is about 4 to 16 μm, the change in the resistance value with respect to the pressing force can be moderated similarly. A clear correlation was not obtained for the arithmetic average roughness Ra.

  In the above description, the sheet resistance value of the low resistance layer 12 is 50Ω to 30 kΩ / □, and the sheet resistance value of the high resistance layer 13 is 50 kΩ to 5 MΩ / □. The low resistance layer 12 has a tendency that the lower the resistance value, the better the sensitivity. Therefore, the low resistance layer 12 is more preferably set to about 50Ω to 10 kΩ / □. The higher resistance layer 13 has a higher resistance value, so that the dynamic range can be increased. Therefore, the sheet resistance value of 100 kΩ to 1 MΩ / □ is more preferable.

  In addition, the spacer 7 can be formed between the conductive sheet 15 and the substrate 8, and a plurality of fixed contacts 6 </ b> A and 6 </ b> B can be configured on the lower surface of the high resistance layer 13 of the conductive sheet 15. .

  The pressure-sensitive sensor according to the present invention can realize a sensor whose change in resistance value with respect to the pressing force is gradual, and is useful for operation units of various electronic devices.

6A, 6B Fixed contact 7 Spacer 8 Substrate 11 Base 12 Low resistance layer 13 High resistance layer 14 Elastic particle 15 Conductive sheet

Claims (2)

A conductive sheet having a resistor layer on the bottom surface of a flexible substrate;
It is composed of a fixed contact disposed at a position facing the resistor layer,
A pressure sensor in which the conductive sheet is bent by a pressing operation, and the resistor layer and the fixed contact are in contact with each other;
In the resistor layer, elastic particles that are deformed by a predetermined load are dispersed,
A pressure-sensitive sensor in which the maximum height of the surface roughness of the surface facing the fixed contact is 4 μm to 25 μm. The pressure-sensitive sensor according to claim 1, wherein the elastic particles have an average particle diameter of 5 to 30 μm and are deformed by 5 to 15 μm with a load of 1 mN.

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