JP2011226852A - Manufacturing method of pressure sensitive sensor, pressure sensitive sensor, and elastic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a pressure sensitive sensor with high sensitivity, a pressure sensitive sensor and an elastic composition.SOLUTION: A manufacturing method of a pressure sensitive sensor has a process (S1) to obtain a mixture by mixing a material that exhibits rubber elasticity at 25°C, or a raw material thereof and conductive particles, and a process (S2) to orient the conductive particles by applying voltage to the mixture. The process (S1) to obtain mixture is a process to mix the raw material and the conductive particles, and the manufacturing method preferably further has a process (S3) to vulcanize the mixture after the process (S2) to orient the conductive particles.

Description

  The present invention relates to a method of manufacturing a pressure sensor, a pressure sensor, and an elastic composition, and more specifically, rubber elasticity, and a feeling that enables on-off switch function, pressure measurement, or pressure distribution measurement. The present invention relates to a pressure sensor manufacturing method, a pressure sensitive sensor, and an elastic composition.

  As sensors for detecting pressure, sensors made of perovskite ceramics using the piezoelectric effect and pressure-sensitive conductive rubber sensors are known. Of these, the pressure-sensitive conductive rubber sensor, including its application, was well studied until around the 1970s. Recently, however, there are few efforts to improve the performance of pressure-sensitive rubber materials used in pressure-sensitive rubber sensors, even though there are efforts to apply technology related to pressure-sensitive conductive rubber sensor devices.

  Technologies related to conventional pressure-sensitive sensors are disclosed in, for example, Patent Documents 1 to 6 and Non-Patent Document 1 below. Patent Document 1 discloses a pressure sensor that detects a pressure in a mold cavity during vulcanization when a raw tire molded on a synthetic core is vulcanized in a mold. Patent Document 2 discloses a touch device including a printed circuit board and a conductive elastic layer. Patent Document 3 discloses a pressure-sensitive conductive rubber composition obtained by blending conductive particles in a rubber base material, wherein the conductive particles are graphite particles having a diameter of about 40 to 160 μm. Is disclosed. Patent Document 4 discloses a technique in which a pressure-sensitive conductive elastic body is used in a measuring device that electrically measures the length of two points to be pressed. Patent Document 5 discloses a technique of using a pressure-sensitive conductive rubber for an application for measuring a tread of a vehicle. Patent Document 6 discloses a pressure-sensitive sensor that measures pressure based on a change in capacitance between a rubber and a contact due to an increase in contact area between the rubber and the contact under pressure. ing. Non-Patent Document 1 discloses a technique that uses pressure-sensitive conductive rubber as a road sensor, musical instrument sensor, zoom switch, or load sensor.

  The conventional pressure-sensitive conductive rubber sensor has a material design in which conductive particles are in contact with each other in the direction along the surface of the pressure-sensitive conductive rubber sensor without being subjected to compressive force. It has become. This pressure-sensitive conductive rubber sensor senses pressure by utilizing the property that the contact resistance of the conductive particles changes due to compressive strain when receiving a compressive force in the thickness direction.

JP 2003-181846 A JP-A-52-51827 JP-A-53-79937 JP 52-68437 A JP-A-53-19051 JP 2002-25377 A

“Introduction and application of pressure sensitive conductive rubber”, [online], [March 10, 2008 search], Internet (URL: http://pcr.lar.jp/psecrsyoukai.html)

However, the conventional pressure-sensitive conductive rubber sensor has a problem of poor sensitivity. That is, the conventional pressure-sensitive conductive rubber sensor has a low surface specific resistance (for example, 10 ³ Ω / sq or less) because the conductive particles are in contact with each other inside the rubber even when it is not subjected to compressive force. ), The amount of change in conductivity (contact resistance of conductive particles) when subjected to compressive force in the thickness direction was small. Specifically, the conventional pressure-sensitive conductive rubber sensor can only obtain an electrical resistance change of 0.5 digits or less when 10% compression strain is applied.

  The conventional pressure-sensitive conductive rubber sensor has low sensitivity, so it can be used as a pressure sensor that requires high sensitivity or for applications where pressure distribution is measured by spreading electrodes in a network (application for pressure mapping). It was difficult to use.

  Ideally, the pressure-sensitive conductive rubber sensor desirably has a sufficiently large surface specific resistance, a small resistance in the thickness direction, and a large change in conductivity with respect to deformation. Nevertheless, since the conventional pressure-sensitive conductive rubber sensor has a low surface resistivity, the thickness is increased (for example, about 10 cm) in order to ensure a resistance difference between the surface resistivity and the thickness (film thickness) direction. There was a need. For this reason, the conventional pressure-sensitive conductive rubber sensor cannot be used as a thin film pressure-sensitive rubber sensor or a device for measuring pressure distribution, and is used as a sensor that uses only a change in electrical conductivity in the vertical direction. It was.

  Accordingly, an object of the present invention is to provide a pressure-sensitive sensor manufacturing method, a pressure-sensitive sensor, and an elastic composition with good sensitivity.

  A method for producing a pressure-sensitive sensor according to one aspect of the present invention includes a step of obtaining a mixture by mixing a material exhibiting rubber elasticity at 25 ° C. or a raw material thereof and conductive particles, and applying a voltage to the mixture. And orienting the conductive particles.

  Preferably, in the manufacturing method, the step of obtaining the mixture is a step of mixing the raw material and the conductive particles, and further includes a step of vulcanizing the mixture after the step of orienting the conductive particles.

  Preferably, in the above production method, the addition amount of the conductive particles in the step of obtaining the mixture is in the range from the addition amount at which the percolation transition starts to the addition amount at which the percolation transition is completed.

  A pressure-sensitive sensor according to another aspect of the present invention is manufactured using any one of the manufacturing methods described above.

  The elastic composition according to still another aspect of the present invention includes a material exhibiting rubber elasticity at 25 ° C. and conductive particles. The volume resistivity in a state that can be elastically deformed at 25 ° C. and 10% compressive strain is applied is 1/10 or less of the volume resistivity in an unstrained state.

  Preferably, in the elastic composition, the addition amount of the conductive particles is in a range from the addition amount at which the percolation transition starts to the addition amount at which the percolation transition is completed.

  Preferably, the elastic composition includes a silicone rubber having a content of 50% by mass or more and less than 99% by mass as a material exhibiting rubber elasticity.

  In the elastic composition, the conductive particles are preferably made of carbon.

  A pressure-sensitive sensor according to still another aspect of the present invention includes any one of the elastic compositions described above and two electrodes that sandwich the elastic composition.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a pressure sensitive sensor with a favorable sensitivity, a pressure sensitive sensor, and an elastic composition can be provided.

It is a figure which shows the manufacturing method of the elastic composition in the 1st Embodiment of this invention. It is a figure which shows the measuring apparatus for measuring the volume specific resistance of the material of powder. It is a figure for demonstrating the measuring method of volume specific resistance using the measuring apparatus of FIG. It is a top view which shows typically the structure of the pressure sensor in the 2nd Embodiment of this invention. It is sectional drawing in alignment with the VV line | wire of FIG. 4 in the pressure sensor of the state in which the pressure is not applied. It is a figure which shows the electrode pattern of the lower electrode of FIG. It is a figure which shows the electrode pattern of the upper electrode of FIG. It is a figure which shows typically the structure of the pressure measurement apparatus main body vicinity to which the pressure sensor in the 2nd Embodiment of this invention is connected. It is sectional drawing which shows typically the structure of the pressure sensor of the state to which the pressure was applied. It is a figure for demonstrating how to measure the pressure value in the specific position in a pressure-sensitive sensor. It is a figure which shows typically the relationship between the addition rate of the electroconductive particle in an insulator, and the electrical resistance of an insulator. It is a figure which shows typically the mode of the arrangement | sequence of the electroconductive particle in an insulator. It is a figure which shows the simulation result of the relationship between the volume fraction (addition amount) of the electroconductive particle whose aspect ratio is 1, and the logarithm value of volume specific resistance. It is a figure which shows the relationship between the tensile strain and volume specific resistance at the time of performing a tensile test with respect to the material which added the electroconductive particle to the insulator. It is a photomicrograph of a thin film by two-way system of the SnO ₂ sol and an acrylic latex. It is a figure which shows the relationship between the distortion | strain and the logarithm value of volume specific resistance in the rubber sheet obtained in Example 1 of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  [First Embodiment]

  FIG. 1 is a diagram showing a method for producing an elastic composition (for example, pressure-sensitive conductive rubber) according to the first embodiment of the present invention.

  Referring to FIG. 1, first, a raw material of a material exhibiting rubber elasticity at 25 ° C. (room temperature) (hereinafter sometimes referred to as rubber-like material) and conductive particles (conductive fine particles) are mixed. To obtain a mixture (S1).

The rubber-like material may be any of an insulator, a semiconductor, and a conductor, but is preferably an insulator (insulating material). The rubber-like material is preferably a material having a resistivity of 10 ¹⁰ Ωcm or more and exhibiting rubber elasticity at room temperature. It is also possible to use a material having a resistivity of less than 10 ¹⁰ Ωcm as the rubber-like material. However, in order to obtain a pressure-sensitive sensor having a high surface resistivity, the rubber-like material preferably has a resistivity of 10 ¹¹ Ωcm or more. Silicone rubber is a particularly preferable material as a rubber-like material because it has a resistivity of 10 ¹² Ωcm or more and high durability.

  Accordingly, as the raw material of the rubber-like material, for example, liquid silicone rubber, rubber-based raw materials (raw rubber, etc.) are used. When silicone rubber is used as the rubbery material, the content of silicone rubber relative to the whole is preferably 50 mass percent or more and less than 99 mass percent.

As the conductive particles, for example, particles of conductive polymers such as metal particles, metal oxide particles, polyaniline, polypyrrole, or polyacetylene, carbon particles, and the like are used. The conductive particles used in the present invention are preferably particles having a resistivity of 10 ⁶ Ωm or less, and particularly preferably made of carbon from the viewpoint of low conductivity and economy. The addition amount of the conductive particles is preferably in the range from the addition amount at which the percolation transition starts to the addition amount at which the percolation transition is completed (near the percolation transition threshold).

  In the mixing step (S1), insulating particles such as mica may be further mixed.

  Next, the obtained mixture is molded, for example, by placing it in a mold, and a voltage is applied to the molded mixture (S2). A voltage may be applied to the mixture as it is in the mold. When the rubber-like material is molded into a plate shape, it is preferable that a voltage is applied along the thickness direction of the plate. By thus applying a voltage to the rubber-like material (rubber), the conductive particles blended in the rubber-like material are oriented along the thickness direction of the plate-like rubber-like material, and anisotropic conductivity is generated.

  The applied voltage may be either an AC voltage or a DC voltage. The applied voltage is preferably 400 V / mm or more, and more preferably 500 V / mm or more. Furthermore, when a high voltage of 2 kV / mm or more is applied, it becomes easy to orient the conductive particles even when the rubber-like material is a high-viscosity rubber. On the other hand, when the applied voltage is 10 kV / mm or less, deterioration of rubber elasticity of the rubber-like material due to application of voltage can be suppressed.

  The voltage application time is preferably 1 minute or longer in consideration of the rubber relaxation phenomenon. However, if sufficient orientation is confirmed, the voltage application time may be 1 minute or less. When the voltage application time is 1 minute or less, the process time is shortened and the productivity can be improved. The voltage application time is more preferably 3 minutes or more. On the other hand, the voltage application time is preferably less than 1 hour from the economical viewpoint.

  When a voltage (electric field) is applied while the rubber-like material is melted, the conductive particles gather on the electrode and are easily segregated on the surface. Therefore, it is preferable to apply a voltage so that the conductive particles can pass in the thickness direction so that the conductive particles do not segregate on the surface of the rubber-like material. When insulating particles such as mica are added, the controllable range (operation window) can be widened.

  Subsequently, the mixture is vulcanized by placing it in an oven (vulcanizing tube) (S3). Thereby, the raw material of a rubber-like material bridge | crosslinks and it becomes a rubber-like material. An elastic composition is obtained by the above process. In the case of obtaining a pressure sensitive sensor, a step of sandwiching the obtained elastic composition between two electrodes may be further performed.

  In the mixing step (S1), a rubber-like material may be mixed with conductive particles instead of the raw material of the rubber-like material. In this case, the vulcanization step may not be performed. Implementation of the vulcanization process is optional.

  The voltage application step (S2) may be performed at any timing. The voltage application step is preferably performed before the vulcanization step, but the vulcanization step may be performed while performing the voltage application step (the vulcanization may be performed while applying the voltage). However, when a voltage application step is performed when a thermoplastic elastomer is used as the rubber-like material, the temperature is preferably set to 50 ° C. or more, and may be set to less than 200 ° C. in order to prevent excessive current flow. preferable.

  According to the said manufacturing method, the elastic composition containing the material which shows rubber elasticity at 25 degreeC, and electroconductive particle is obtained. This elastic composition is elastically deformable at 25 ° C., and the volume resistivity in a state where 10% compressive strain is applied changes to a value of 1/10 or less of the volume resistivity in an unstrained state ( The volume resistivity decreases by 10 times or more).

  Here, the volume specific resistance value (resistance value) of the powder material such as the conductive particles in the above is measured by the following method, for example.

  FIG. 2 is a diagram showing a measuring apparatus for measuring the volume resistivity of the powder material. In addition, (b) has shown sectional drawing in alignment with the IIA-IIA line | wire of (a), and the dimension of each part is written in (b).

  Referring to FIG. 2, measuring apparatus 100 includes pressure portions 101 and 102 made of stainless steel, a case 104 made of Teflon (registered trademark), and a terminal 103. The housing 104 has a cylindrical shape, and cylindrical pressurizing portions 101 and 102 are arranged in a hollow portion inside the housing 104 so as to overlap each other. The terminal 103 is electrically connected to the lower pressure portion 102.

  FIG. 3 is a diagram for explaining a method of measuring volume resistivity using the measuring apparatus of FIG.

  Referring to FIG. 3, first, 1 g of powder material 200 is put on pressurization portion 102, and pressurization portion 101 is placed on material 200. Next, the measuring apparatus 100 is placed on a table vibrator in a non-pressurized state and is vibrated for 10 minutes. Subsequently, a voltage is applied between the pressure part 101 and the terminal 103 while applying a load of 300 kgw (pressure P) to the material 200 through the pressure part 101. Then, the current value flowing through the material 200 is measured, and the resistance R is calculated from the current value. Next, the volume resistivity ρ is calculated from the thickness T and the resistance R of the material 200 based on the calculation formula ρ = 3 × R / T. A value obtained by dividing the obtained volume resistivity ρ by 100 is the volume resistivity of the material 200.

  [Second Embodiment]

  In the present embodiment, a pressure-sensitive sensor using the elastic composition manufactured in the first embodiment will be described.

  FIG. 4 is a top view schematically showing the configuration of the pressure-sensitive sensor according to the second embodiment of the present invention. FIG. 5 is a cross-sectional view taken along the line VV of FIG. 4 in the pressure-sensitive sensor in a state where no pressure is applied. 4 and 5, the pressure sensor 1 mainly includes a lower electrode (first electrode) 10, an upper electrode (second electrode) 20, and an anisotropic conductive sheet 3. The anisotropic conductive sheet 3 corresponds to the elastic composition in the first embodiment. An upper electrode 20 is disposed on the lower electrode 10, and the anisotropic conductive sheet 3 is sandwiched between the lower electrode 10 and the upper electrode 20. The lower electrode 10 and the upper electrode 20 measure the resistance value of the anisotropic conductive sheet 3.

  FIG. 6 is a diagram showing an electrode pattern of the lower electrode of FIG. FIG. 6 shows a surface on the side in contact with the anisotropic conductive sheet. Referring to FIG. 6, lower electrode 10 includes a substrate 13, a plurality of electrode patterns 11 a to 11 d, and connection electrode patterns 12 a to 12 d. Electrode patterns 11 a to 11 d made of, for example, copper are formed on the lower end portion of the substrate 13. The substrate 13 is a polyimide substrate such as an FPC (Flexible Printed Circuits) substrate. Each of the electrode patterns 11a to 11d is formed on the substrate 13 and extends, for example, in the vertical direction in FIG. The rectangular area in which the electrode patterns 11 a to 11 d are formed is in direct contact with the anisotropic conductive sheet 3. Further, the substrate 13 has a connection portion 13a protruding upward in FIG. 6, and each of the connection electrode patterns 12a to 12d is formed at the tip of the connection portion 13a on the substrate 13. Each of the electrode patterns 11a to 11d and each of the connection electrode patterns 12a to 12d are electrically connected.

  FIG. 7 is a diagram showing an electrode pattern of the upper electrode in FIG. FIG. 7 transparently shows the surface on the side in contact with the anisotropic conductive sheet for convenience of explanation. Referring to FIG. 7, the upper electrode 20 includes a substrate 23, a plurality of electrode patterns 21 a to 21 d..., And connection electrode patterns 22 a to 22 d. Electrode patterns 21 a to 21 d made of, for example, copper are formed on the lower end portion of the substrate 23. The substrate 23 is, for example, a polyimide substrate. Each of the electrode patterns 21a to 21d is formed on the substrate 23 and extends, for example, in the horizontal direction in FIG. The rectangular area in which the electrode patterns 21 a to 21 d are formed is in direct contact with the anisotropic conductive sheet 3. Each of the electrode patterns 11 a to 11 d and each of the electrode patterns 21 a to 21 d intersect with each other when seen in a plan view, and this intersecting portion is a portion for detecting the resistance value of the anisotropic conductive sheet 3. Moreover, the board | substrate 23 has the connection part 23a which protruded in the upper direction in FIG. 7, and each of connection electrode pattern 22a-22d is formed in the front-end | tip of the connection part 23a on the board | substrate 23. FIG. Each of electrode patterns 21a-21d and each of connection electrode patterns 22a-22d are electrically connected.

  In FIGS. 6 and 7, only representative electrode patterns are denoted by reference numerals. The number and shape of the electrode patterns are arbitrary. As the width of the electrode pattern is reduced and the number thereof is increased, the number of locations where the resistance value is detected can be increased.

  Subsequently, a method for measuring pressure using the pressure-sensitive sensor in the present embodiment will be described.

  First, as shown in FIG. 8, the pressure-sensitive sensor is connected to a pressure measuring device main body (hereinafter sometimes referred to as the device main body).

  FIG. 8 is a diagram schematically showing a configuration in the vicinity of the main body of the pressure measuring device to which the pressure sensitive sensor according to the second embodiment of the present invention is connected.

  Referring to FIG. 8, apparatus main body 30 and computer 40 are electrically connected. The apparatus main body 30 includes mounting sockets 31 and 32 and lock portions 31a and 32a. The connection electrode patterns 12a to 12d of the lower electrode 10 and the connection electrode patterns 22a to 22d of the upper electrode 20 are configured to be aligned in the horizontal direction in FIG. Each of the connection electrode patterns 12a to 12d of the lower electrode 10 is inserted into the mounting socket 31 and fixed by the lock portion 31a. Similarly, each of the connection electrode patterns 22a to 22d of the upper electrode 20 is inserted into the attachment socket 32 and fixed by the lock portion 32a. Thereby, the pressure sensor and the apparatus main body 30 are electrically connected.

  Next, the pressure-sensitive sensor 1 is arranged at a location where the pressure is measured, and the pressure is sensed. FIG. 9 is a cross-sectional view schematically showing the configuration of the pressure-sensitive sensor in a state where pressure is applied.

  Referring to FIG. 9, when pressure is applied, pressure sensor 1 is deformed into a concave shape. Since the A portion is most pressurized, the deformation (compression) is the largest, and the C portion is not deformed because no pressure is applied, and the B portion has a lower pressure than the A portion. Because it is added, it is slightly deformed. Since the resistance value of the anisotropic conductive sheet 3 changes according to the deformation, the resistance value at the position B is higher than the resistance value at the position A, and the resistance value at the position C is higher than the resistance value at the position B. It is high. Therefore, the resistance value of the anisotropic conductive sheet 3 when pressure is applied to the pressure sensor 1 is measured by the lower electrode 10 and the upper electrode 20.

  Next, referring to FIG. 8, the measured resistance value is transmitted to the apparatus main body 30. The apparatus main body 30 specifies a measurement position by selecting an arbitrary pattern among the electrode patterns 11a to 11d and an arbitrary pattern among the electrode patterns 21a to 21d by the switch unit, and is measured at the specified position. The local resistance value of the anisotropic conductive sheet 3 is converted into a pressure value. And the resistance value in a desired area | region is converted into a pressure value by switching the position to specify sequentially.

  FIG. 10 is a diagram for explaining how to measure a pressure value at a specific position in the pressure sensor. 8 and 10, each of electrode patterns 11a to 11d and each of electrode patterns 21a to 21d intersect, for example, at a right angle. For example, when obtaining the pressure values of the intersecting portions 40a to 40d, the intersecting portion 40a is first identified by selecting the electrode pattern 11a and the electrode pattern 21a, and the resistance value measured at the intersecting portion 40a becomes the pressure value. Converted. Next, the intersection part 40b is specified by selecting the electrode pattern 11a and the electrode pattern 21b, and the resistance value measured at the intersection part 40b is converted into a pressure value. Next, the intersection part 40c is specified by selecting the electrode pattern 11b and the electrode pattern 21a, and the resistance value measured at the intersection part 40c is converted into a pressure value. Next, the intersection part 40d is specified by selecting the electrode pattern 11b and the electrode pattern 21b, and the resistance value measured at the intersection part 40d is converted into a pressure value.

  The pressure value obtained in the apparatus main body 30 may be output to the computer 40. The apparatus main body 30 may perform A / D conversion and serial data output. The computer 40 may create a two-dimensional diagram regarding the pressure distribution using software and display it on a display.

  The pressure-sensitive sensor may be used for the purpose of detecting a pressure contact force between members that are in pressure contact with each other in the apparatus main body and adjusting the pressure contact force to be appropriate. That is, when the first member and the second member are in pressure contact in the apparatus main body, the first pressure is set so that the pressure detected in the second mode or the other mode becomes an appropriate target value. The position of at least one of the member and the second member can be adjusted. In addition, the first member and the second member are controlled so that the pressure detected in the aspect of the second embodiment or other aspects, for example, approaches an appropriate target value by the control of the control unit provided in the apparatus main body. It is possible to control the pressure contact.

  For this purpose, the pressure-sensitive sensor is disposed between the first member and the second member, or at least a part of either the first member, the second member, or one of the members is configured by the pressure-sensitive sensor. A configuration in which the pressure-sensitive sensor is arranged on a pressing member for pressing one member of the first and second members against the other member may be employed.

  [Effect of the embodiment]

  According to the above-described embodiment, the conductive particles can be oriented in the thickness direction in the rubber-like material by applying a voltage in a state where the rubber-like material and the conductive particles are mixed. As a result, anisotropy occurs between the conductivity in the thickness direction (longitudinal direction) and the conductivity in the direction along the surface (lateral direction), and electricity easily passes in the thickness direction, but electricity passes in the direction along the surface. It becomes difficult. As a result, the surface specific resistance of the elastic composition can be increased, and the volume specific resistance with respect to the surface specific resistance can be lowered. In addition, since the volume resistivity with respect to the surface resistivity is low, the rate of change of the volume resistivity with respect to strain increases, and an elastic composition and a pressure-sensitive sensor with good sensitivity can be obtained. According to the above-described embodiment, the elastic composition (pressure-sensitive conductive rubber) can be used in a thin film state and exhibits a resistance change of one digit or more with respect to a slight strain.

  Here, when conductive particles are dispersed in a polymer that is an insulator, a phenomenon called percolation transition occurs. Assuming that the dispersion of the conductive particles is purely dependent only on the probability, the ease of the percolation transition is the probability of the dispersion of the conductive particles (the probability of where one conductive particle is in the insulator) Depending on the aspect ratio, which is the ratio of the short diameter to the long diameter of the conductive fine particles, or the amount of conductive particles added, the percolation transition occurs uniformly throughout the material.

  However, in an actual system, the ease of percolation transition varies depending on the interaction between the insulator and conductive particles, the interaction between other added materials and these substances, and the process conditions. . In addition, in the case of a combination of an insulator and conductive particles, in which the conductive particles are difficult to disperse into the insulator, that is, when the insulator is difficult to wet the surface of the conductive particles, the conductive particles in the insulator If the amount of the conductive particles aggregates and exceeds a certain value, it cannot be mixed with the insulator. This difficulty in wetting can generally be improved by further adding a third component such as a surfactant having an affinity for both the insulator and the conductive particles. There are limits. In addition to the third component such as a surfactant, the dispersibility of the conductive particles can also be controlled by adding another (different type) fine particles that are easily dispersed in the insulator as the third component. Can do.

  Recently, a method for controlling the dispersibility of fine particles in the presence of a magnetic field or an electric field has also been studied. In particular, a method for controlling the dispersion state of fine particles by applying an electric field has been well studied in the field of electrorheological fluid (ERF), which was popular around 1990. Dispersion of conductive particles can be controlled by processes using electric and magnetic fields, but in processes where external field forces do not work, relaxation of the polymer that is the matrix until the material hardens, flow, thermal convection, Or the influence of evaporation of the solvent (however, when the solvent is used) works. Furthermore, when the insulator is molded into a sheet shape, segregation of conductive particles on the surface or the central portion may occur.

  These phenomena observed when conductive particles are dispersed in an insulator (polymer material) not only affect the variations of pressure sensors (polymer semiconductor sensors), but also affect the performance of the pressure sensors. It has a big impact. On the other hand, the percolation transition occurs when the addition rate of the conductive particles is within a certain range. For this reason, if the addition rate of electroconductive particle is set more than the range like the conventional pressure sensitive sensor, the dispersion | variation in a pressure sensitive sensor will become small and performance will be stabilized.

  In a semiconductor material sheet manufactured by dispersing conductive particles in an insulator, if segregation does not occur (ie, it is a homogeneous material and only percolation transition occurs), the surface resistivity and the sheet The relationship of the following formula (1) is established between the thickness and the volume resistivity. On the other hand, when a pressure-sensitive sensor is manufactured without applying voltage as in the prior art, segregation is likely to occur, and when segregation occurs (in the case of a non-uniform material), the formula (1) The relationship will no longer hold. For example, when the conductive particles are segregated on the sheet surface, the following equation (2) is established. Further, when the conductive particles are segregated at the center of the sheet, the relationship of the following formula (3) is established. Further, when the electric field is applied and the conductive particles are controlled to be easily arranged in the thickness direction of the sheet as in the manufacturing method of the above-described embodiment, the relationship of the following formula (3) is established. When the conductive particles are segregated, all become anisotropic.

  In the pressure-sensitive sensor of the above-described embodiment, the pressure applied to the surface of the pressure-sensitive sensor is detected as a resistance change in the thickness direction by flowing a current in the thickness direction of the pressure-sensitive sensor. As shown, the surface direction (lateral direction) of the pressure-sensitive sensor is preferably close to the insulator, and the thickness direction (vertical direction) is preferably close to the semiconductor. According to the pressure-sensitive sensor of the above-described embodiment, such a state can be realized. By establishing the relationship such as the equation (4), the displacement sensitivity in the thickness direction can be improved without being affected by the direction along the surface.

  Surface specific resistance × sheet thickness = volume specific resistance Formula (1)

  Surface specific resistance x sheet thickness <volume specific resistance (2)

  Surface specific resistance x sheet thickness> Volume specific resistance Formula (3)

  Surface specific resistance × sheet thickness >> Volume specific resistance Formula (4)

  Insulating particles such as mica serve to control contact / non-contact of conductive particles depending on the presence or absence of pressure received by the elastic composition (turn on / off the connection of particles). That is, insulating particles such as mica are removed from the row of conductive particles when an electric field is applied, and work to increase the electric resistance in the direction along the surface of the elastic composition (lateral direction). For this reason, by further adding insulating particles such as mica to the rubber-like material and the conductive particles, the relationship of the formula (4) is more easily established. In the elastic composition in the above-described embodiment, since a path of conductive particles is formed in the thickness direction by applying a voltage at the time of manufacture, even if insulating particles are present, the conductivity becomes high. Can be maintained, and the SN (Signal-Noise ratio) ratio and sensitivity can be increased. Furthermore, when sensing is used with alternating current instead of direct current, the sensitivity can be further improved.

  The reason why the sensitivity is improved by the addition of mica in the above-described embodiment is presumed as follows. That is, when mica is simply mixed with the rubber-like material and the conductive particles (without applying a voltage during production), both the mica and the conductive particles (carbon) are uniformly dispersed. On the other hand, when a voltage is applied at the time of manufacture as in the above-described embodiment, the conductive particles form a conductive path, and the mica is around the conductive path of conductive particles (connection of conductive particles). Align and disperse and retain conductive path. Therefore, when there is no mica, when the material is distorted, each particle of conductive particles (carbon particles) is subjected to stress, and part of the conductive path is easily broken. Therefore, by adding mica to the rubber-like material and conductive particles, stress can be applied to the conductive particles (carbon), and the contact pressure of the conductive particles increases and the resistance decreases. -Increased resistance sensitivity.

  According to the above-described embodiment, by setting the addition amount of the conductive particles within a range from the addition amount of the conductive particles at which the percolation transition starts to the addition amount of the conductive particles at which the percolation transition is completed, Sensitivity can be further improved. This will be described below.

  FIG. 11 is a diagram schematically showing the relationship between the addition rate of conductive particles in the insulator and the electrical resistance of the insulator. FIG. 12 is a diagram schematically showing a state of arrangement of conductive particles in an insulator.

  Referring to FIGS. 11 and 12, when the amount of conductive particles added to the insulator (dispersion amount of conductive fine particles) is increased, the conductive particles are separated from each other when the amount added is small. Although it is (state (a) in FIG. 12), it becomes easy to connect the conductive particles by chance with a certain addition amount as a threshold (state (b) in FIG. 12), percolation transition occurs, and the electric resistance decreases rapidly. To do. After the percolation transition is completed, the electric resistance is low (state (c) in FIG. 12).

  The ease with which the percolation transition occurs (the probability that the conductive particles are accidentally connected) is determined by the state of the field where the conductive particles are placed (the interaction between the binder and the particles, the presence or absence of an electric field, etc.).

  FIG. 13 is a diagram showing a simulation result of the relationship between the volume fraction (addition amount) of conductive particles having an aspect ratio of 1 and the logarithmic value of volume resistivity. A curve indicated by L1 in FIG. 13 is a simulation result curve when random numbers that facilitate alignment in the vertical direction are generated (in the case of a probability that percolation transition is likely to occur (transition promotion)), and a curve indicated by L2 in FIG. FIG. 6 is a curve of a simulation result when random numbers that make it easier to arrange in the horizontal direction are generated (in the case of a probability that percolation transfer is difficult to occur (transfer relaxation)).

  Referring to FIG. 13, a curve L1 which is a simulation result when the probability of percolation transfer is likely to occur and a curve L2 which is a simulation result when the probability of percolation transfer is difficult to occur are the volume fractions at which the percolation transfer occurs. The ranges are different from each other. Therefore, in the range A from the volume fraction A1 at which the percolation transition starts when the percolation transition is likely to occur to the volume fraction A2 at which the percolation transition is completed when the percolation transition is unlikely to occur, the insulating material These conductive particles are presumed to be in the state of the percolation transition.

  The volume fraction (addition amount) of the conductive particles in which the percolation transition occurs is determined by the interaction between the binder (insulating particles) and the conductive particles unless an external force is applied. When an external force is applied, even process factors change, for example.

  FIG. 14 is a diagram illustrating a relationship between tensile strain and volume resistivity when a tensile test is performed on a material in which conductive particles are added to an insulator. A curve L3 in FIG. 14 is a result for a material in which the volume fraction of the conductive particles is set within the range A in FIG. 13, and a straight line L4 in FIG. 14 is a percolation transition of the volume fraction of the conductive particles. This is a result of a material set higher than the volume fraction of completion of (a material set to a volume fraction on the right side of the position A2 on the horizontal axis in FIG. 13).

  Referring to FIG. 14, when a tensile force is applied in the direction along the surface of the material, an elongation strain occurs in the direction along the surface of the material, and the compressive force in the thickness direction caused by the Poisson's ratio causes the thickness direction. Compression distortion occurs. In the curve L3, the volume resistivity is temporarily reduced by the compressive strain (compressive force) in the thickness direction. When the tensile force increases, the tensile force in the direction along the surface has a stronger influence on the volume resistivity than the compressive force in the thickness direction, and the volume resistivity increases with an increase in tensile strain.

  On the other hand, when paying attention to the straight line L4, the volume resistivity value monotonously increases as the tensile strain increases in the material in which the percolation transition is completed (completed). This is because, in a material in which the percolation transition has been completed (completed), the conductive particles exist in close contact with each other, and therefore, the conductive particles are conductive by a tensile force rather than the effect of the decrease in the volume resistivity due to the initial compressive strain. This is because the influence of the increase in the volume resistivity due to the separation of the conductive particles is greater.

  The result of FIG. 14 is a change in volume resistivity when a tensile force is applied to the material, but the characteristic of the change in volume resistivity when a compressive force is applied to the material is also the same as the result of FIG. Become. That is, in the material in which the volume fraction of the conductive particles is set within the range A in FIG. 13, the effect of lowering the volume specific resistance value due to compressive strain is increased.

  Accordingly, the addition amount of the conductive particles is set within the range from the addition amount of the conductive particles at which the percolation transition starts to the addition amount of the conductive particles at which the percolation transition is completed (near the percolation transition threshold) (conductive particles). Is set to a volume fraction in the range A in FIG. 13), the volume resistivity can be lowered, and the value of the surface resistivity with respect to the volume resistivity can be increased. As a result, it can be used as a pressure-sensitive sensor.

  On the other hand, in the conventional pressure-sensitive sensor, in order to use the change in contact resistance of the conductive particles due to pressure, the conductivity is increased up to the amount exceeding the added amount of conductive particles that completes the percolation transition (the amount exceeding the threshold for percolation transition). A large amount of conductive particles is added. With such an added amount, both the volume specific resistance and the surface specific resistance become low, and the sensitivity in the direction along the surface (lateral direction) cannot be increased. Therefore, it is difficult to finely measure the planar pressure distribution as in the present embodiment. In addition, even in a conventional pressure-sensitive sensor that uses a change in capacitance, the resistance cannot be increased because the resistance value is too low.

FIG. 15 is a micrograph of a thin film of a binary system of SnO ₂ sol and acrylic latex.

Referring to FIG. 15, in the case of SnO ₂ sol alone ((a) in FIG. 15), SnO ₂ has a length of less than ₂ nm, and no SnO ₂ array is observed. On the other hand, when SnO ₂ sol was added to the acrylic latex at a volume fraction included in the range A in FIG. 13 to produce a thin film having a thickness of 0.1 μm ((b) in FIG. 15), SnO 2 Each of ₂ is connected to each other in the horizontal direction in FIG. 15 and has a length of about 50 nm.

Therefore, it can be seen that when controlled by advanced techniques, a network of conductive particles (SnO ₂ ) extending in the vertical direction in FIG. 15 is well formed without applying an electric field.

  Next, examples of the present invention will be described.

  Example 1

  In a mortar, carbon (DENKA CARBON (registered trademark), manufactured by Denki Chemical Co., Ltd.) 0.236 g, liquid silicone rubber (KE-106, manufactured by Shin-Etsu Chemical Co., Ltd.) 1.5 g, and a curing agent (CAT-RG, 0.7 g of Shin-Etsu Chemical Co., Ltd.) was added and mixed for 5 minutes. Furthermore, 8.5 g of liquid silicone rubber and 0.3 g of a curing agent were added and mixed for 5 minutes. Next, the obtained mixture (composition) was kneaded with three rolls for 10 minutes and defoamed. Next, the mixture after defoaming was filled (transferred) into a mold capable of forming a sheet having a thickness of 300 μm, and the mold was allowed to stand for 1 hour. Subsequently, a voltage of 400 V was applied to the mold filled with the mixture for 3 minutes. Thereafter, the mold after voltage application was placed in an oven, and the mixture was vulcanized in the oven for 30 minutes.

The rubber sheet (elastic composition) obtained by the above steps had a thickness of 300 μm, a surface specific resistance of 6 × 10 ⁸ Ω / sq, and a volume resistivity of 1.5 × 10 ⁷ Ωcm. Furthermore, when the response of volume specific resistance to strain was measured for this rubber sheet, the result of FIG. 16 was obtained. Referring to FIG. 16, the logarithmic value of the volume resistivity, which was about 6.8 in the unstrained state, is reduced to about 4.9 in the state where 10% compression strain is applied. From this result, it can be seen that the volume resistivity value in a state where 10% compressive strain is applied is reduced to 1/10 or more (about 1/100) of the volume resistivity value in an unstrained state.

  (Example 2)

  In a mortar, 0.26 g of carbon, 0.1 g of mica fine powder, 1.5 g of liquid silicone rubber, and 0.7 g of a curing agent were added and mixed for 5 minutes. Furthermore, 8.5 g of liquid silicone rubber and 0.3 g of a curing agent were added and mixed for 5 minutes. Next, the obtained mixture (composition) was kneaded with three rolls for 10 minutes and defoamed. Next, the mixture after defoaming was filled into a mold, and the mold was allowed to stand for 1 hour. Subsequently, a voltage of 400 V was applied to the mold filled with the mixture for 3 minutes. Thereafter, the mold after voltage application was placed in an oven, and the mixture was vulcanized in the oven for 30 minutes.

The rubber sheet obtained by the above steps had a thickness of 300 μm, a surface specific resistance of 3.2 × 10 ⁹ Ω / sq, and a volume resistivity of 6.0 × 10 ⁷ Ωcm. With respect to the volume resistivity with respect to the strain, a linear response similar to that shown in FIG. 16 was obtained, and the volume resistivity with a 10% compressive strain applied was 1.6 × 10 ⁶ Ωcm.

  (Example 3)

A rubber sheet was produced in the same manner as in Example 2 except that the voltage applied to the mold filled with the mixture was 180V. The obtained rubber sheet had a thickness of 300 μm, a surface specific resistance of 3.2 × 10 ⁹ Ω / sq, and a volume resistivity of 6.0 × 10 ⁷ Ωcm. With respect to the volume resistivity with respect to the strain, a linear response similar to that shown in FIG. 16 was obtained, and the volume resistivity with a 10% compressive strain applied was 1.6 × 10 ⁶ Ωcm.

  Example 4

  A gel-dispersed aqueous solution was produced by slowly adding 500 g of a 17% by mass stannic chloride aqueous solution to 1800 g of saturated ammonium bicarbonate while stirring with a lab mixer. Subsequently, the produced gel was taken out by decantation, and this gel was washed with distilled water many times. Next, after confirming that silver nitrate is properly deposited in the distilled water used for washing the gel and precipitation is not possible, an aqueous solution whose pH is adjusted to about 9 by adding ammonia water to 1000 ml of distilled water is prepared. Produced. Subsequently, the gel was added to this aqueous solution, and the gel was dispersed in the aqueous solution by vigorously stirring the aqueous solution with a lab mixer. Subsequently, 2 g of antimony oxide gel synthesized by the same method as described above was added to the dispersion to prepare a gel slurry. Subsequently, a cylindrical electric furnace with a wall surface made of quartz was heated and held at 350 ° C., and the adjusted gel slurry was sprayed into the electric furnace to be powdered, and the obtained powder was dried and collected. Let the powder obtained by the above process be the powder P1.

  Subsequently, 6 g of powder P1, 1.5 g of liquid silicone rubber, and 0.7 g of a curing agent were added to the mortar and mixed for 5 minutes. Furthermore, 8.5 g of liquid silicone rubber and 0.3 g of a curing agent were added and mixed for 5 minutes. Next, the obtained mixture (composition) was kneaded with three rolls for 10 minutes and defoamed. Next, the mixture after defoaming was filled (transferred) into a mold, and the mold was allowed to stand for 1 hour. Subsequently, a voltage of 400 V was applied to the mold filled with the mixture for 3 minutes. Thereafter, the mold after voltage application was placed in an oven, and the mixture was vulcanized in the oven for 30 minutes.

The obtained rubber sheet had a thickness of 300 μm, a surface specific resistance of 2.1 × 10 ¹⁰ Ω / sq, and a volume resistivity of 3.6 × 10 ⁶ Ωcm. With respect to the volume resistivity with respect to the strain, a linear responsiveness similar to that of FIG. 16 was obtained, and the volume resistivity with a 10% compressive strain applied was 1.6 × 10 ³ Ωcm.

  (Example 5)

  100 g of SBR (styrene-butadiene rubber) (manufactured by JSR Corporation), 3 g of zinc oxide, 1.3 g of powdered sulfur for rubber, and TBBS (N-tert-butyl-2-benzothiazolylsulfur) as a vulcanization accelerator 1 g of phenamide), 1 g of stearic acid, and 6 g of carbon black (HAF) were mixed with two rolls for 15 minutes, and filled into a mold with an electrode for producing flat rubber. Vulcanization was carried out at 140 ° C. for 5 minutes while applying an alternating current of 300 V to the mold.

The resulting rubber sheet had a thickness of 300 μm, a surface specific resistance of 2.1 × 10 ⁸ Ω / sq, and a volume resistivity of 5.5 × 10 ⁶ Ωcm. With respect to the volume resistivity with respect to the strain, a linear response similar to that shown in FIG. 16 was obtained, and the volume resistivity with a 10% compressive strain applied was 5.6 × 10 ³ Ωcm.

  (Example 6)

  A pressure sensitive sensor was produced by sandwiching the rubber sheet (rubber sensor) obtained in Example 1 between the upper electrode and the lower electrode. Each of the upper electrode and the lower electrode had a substrate made of a polyimide film and a plurality of electrode patterns (linear electrodes having a width of 5 mm) arranged on the substrate at intervals of 1 cm. Each extending direction of the electrode pattern in the upper electrode and each extending direction of the electrode pattern in the lower electrode are orthogonal to each other, and a plurality of electrodes in each of the upper electrode and the lower electrode with the rubber sheet sandwiched therebetween The pattern was arranged in a grid pattern. When a load is applied to an arbitrary position in the pressure sensor, the resistance decreases to 1/10 between the electrodes corresponding to the position.

  (Comparative Example 1)

  In a mortar, carbon (DENKA CARBON (registered trademark), manufactured by Denki Chemical Co., Ltd.) 0.236 g, liquid silicone rubber (KE-106, manufactured by Shin-Etsu Chemical Co., Ltd.) 1.5 g, and a curing agent (CAT-RG, 0.7 g of Shin-Etsu Chemical Co., Ltd.) was added and mixed for 5 minutes. Furthermore, 8.5 g of liquid silicone rubber (KE-106, manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.3 g of a curing agent (CAT-RG, manufactured by Shin-Etsu Chemical Co., Ltd.) were added and mixed for 5 minutes. Next, the obtained mixture (composition) was kneaded with three rolls for 10 minutes and defoamed. Next, the mixture after defoaming was filled into a mold, and the mold was allowed to stand for 1 hour. Subsequently, without applying a voltage, the mold filled with the mixture was placed in an oven, and the mixture was vulcanized in the oven for 30 minutes.

The obtained rubber sheet had a thickness of 300 μm, a surface specific resistance of 8.5 × 10 ⁸ Ω / sq, and a volume resistivity of 7.6 × 10 ⁷ Ωcm. The volume resistivity in a state where 10% compressive strain was applied was 2.6 × 10 ⁷ Ωcm.

  In the present specification, the volume resistivity is measured by, for example, the four probe method. The surface specific resistance is measured, for example, by a double ring method. The surface specific resistance is measured using Hiresta MCP-HT450 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) in the case of a resistance of 1000Ω / sq or more, and 4 in the case of a resistance of 1000Ω / sq or less. It may be measured by the terminal method. Further, when the impedance is measured by alternating current, the impedance may be measured using a film electrode 16451B (manufactured by Agilent Technologies).

  The above-described embodiments and examples are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Pressure sensor 3 Anisotropic conductive sheet 10 Lower electrode 11a-11d, 21a-21d Electrode pattern 12a-12d, 22a-22d Connection electrode pattern 13,23 Board | substrate 13a, 23a Connection part 20 Upper electrode 30 Apparatus main body 31,32 Mounting socket 31a, 32a Locking part 40 Computer 40a-40d Crossing part 100 Measuring device 101, 102 Pressurizing part 103 Terminal 104 Case 200 Powder material

Claims (9)

A step of obtaining a mixture by mixing a material exhibiting rubber elasticity at 25 ° C. or a raw material thereof and conductive particles;
And a step of orienting the conductive particles by applying a voltage to the mixture. The step of obtaining the mixture is a step of mixing the raw material and the conductive particles,
The method for producing a pressure-sensitive sensor according to claim 1, further comprising a step of vulcanizing the mixture after the step of orienting the conductive particles.   The pressure-sensitive sensor production according to claim 1 or 2, wherein an addition amount of the conductive particles in the step of obtaining the mixture is in a range from an addition amount at which percolation transition starts to an addition amount at which percolation transition is completed. Method.   The pressure-sensitive sensor manufactured using the manufacturing method in any one of Claims 1-3. A material that exhibits rubber elasticity at 25 ° C. and conductive particles;
An elastic composition that is elastically deformable at 25 ° C. and has a volume resistivity in a state of 10% compressive strain that is 1/10 or less of a volume resistivity in an unstrained state.   The elastic composition according to claim 5, wherein the addition amount of the conductive particles is in a range from an addition amount at which percolation transition starts to an addition amount at which percolation transition is completed.   The elastic composition of Claim 5 or 6 containing the silicone rubber whose content with respect to the whole is 50 to 99 mass percent as said material which shows rubber elasticity.   The elastic composition according to claim 5, wherein the conductive particles are made of carbon. The elastic composition according to any one of claims 5 to 8,
A pressure-sensitive sensor comprising two electrodes sandwiching the elastic composition.