Method for producing pressure-sensitive conductive elastomer and pressure sensor

Abstract

To provide a method of manufacturing a pressure-sensitive conductive elastomer capable of increasing a resistance value between an electrode and the pressure-sensitive conductive elastomer in a no-load state without providing a spacer around the electrode when forming a pressure sensor, and to provide the pressure sensor using the pressure-sensitive conductive elastomer manufactured by the method.SOLUTION: A method for producing a pressure-sensitive conductive elastomer of the present invention includes a mixing step of mixing a non-conductive elastomer, conductive particles, non-conductive particles having an irregular shape and a particle diameter larger than that of the conductive particles, and a solvent to form a mixture, a rolling and curing step of rolling the mixture and curing the mixture to form a sheet, and a slicing step of slicing the sheet vertically along a width direction from a central portion in a thickness direction to expose surfaces of the non-conductive particles present on a sliced surface side in a protruding state. Further, the pressure sensor of the present invention is disposed such that the surface on the side where the exposed non-conductive resin particles protrude faces the thin film conductive member.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a pressure-sensitive conductive elastomer that exhibits a high electrical resistance when not pressurized and exhibits a lower electrical resistance as the pressure increases when pressurized, and that can form a pressure sensor with a wide dynamic range and long life, and to a pressure sensor that uses a pressure-sensitive conductive elastomer produced by this method. [Background technology]

[0002] Conventionally, pressure sensors for measuring pressure have been developed using strain gauges or piezoelectric ceramics such as lead zirconate titanate. These sensors generally use highly rigid materials, which limits the degree of freedom in design. For this reason, many pressure sensors using pressure-sensitive conductive elastomers have been developed. Known pressure sensors use a pressure-sensing mechanism that detects changes in resistance due to changes in the contact area between the electrode and the pressure-sensitive conductive elastomer surface.

[0003] For example, Patent Document 1 (Japanese Patent No. 4528878) discloses a pressure sensor 50, as shown in Figures 9A and 9B of the present application, in which an electrode layer 52 is formed on the surface of a first substrate 51, and a concave-convex layer 57 is formed on the surface of a second substrate 54, which is arranged above the first substrate 51 via a spacer 53, facing the electrode layer 52, using an insulating resin 56 containing non-conductive particles 55, and a resistor layer 58 of a certain thickness containing at least carbon powder is formed on the surface of the concave-convex layer 57, and the total thickness of the thickness t1 of the concave-convex layer 57 between the non-conductive particles 55 and the thickness t2 of the resistor layer 58 is smaller than the particle diameter of the non-conductive particles 55 contained in the concave-convex layer 57, and the resistor layer 58 is formed on and between the non-conductive particles 55.

[0004] According to this pressure sensor 50, a change in the load applied to at least one of the first substrate 51 and the second substrate 54 changes the contact area of ​​the resistor layer 58 with the electrode layer 52, and the load applied to the substrates is sensed by detecting a change in resistance value corresponding to this change in contact area.

[0005] Furthermore, Patent Document 2 (JP 2015-114178 A) discloses a pressure sensor 60 having a contact member 61 made of an elastic resistor having a predetermined conductive resistance, and a pair of electrodes 63 insulated from each other and provided on a circuit board 62 with which the contact member 61 comes into contact, as shown in Figure 10 of the present application, in which when the contact member 61 is pressed, the contact member 61 and the pair of electrodes 63 come into contact, and the contact area between them changes, thereby changing the resistance value between the pair of electrodes 63.

[0006] Paragraph

[0022] of Patent Document 2 describes a contact member 61 in which a conductive medium is mixed with an elastic body. Note that known examples of pressure-sensitive conductive elastomers in which a conductive medium is mixed with an elastic body are those described in Patent Document 3 (Japanese Patent No. 4630964) and Patent Document 4 (Japanese Patent No. 6757539). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4528878 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-114178 [Patent Document 3] Patent No. 4630964 [Patent Document 4] Patent No. 6757539 Summary of the Invention [Problem to be solved by the invention]

[0008] The pressure sensor 50 disclosed in Patent Document 1 requires a process for providing a concave-convex layer 57 in addition to the resistor layer 58, while the pressure sensor 60 disclosed in Patent Document 2 requires the contact member 61, which is a pressing elastic body, to be formed into a convex shape, and therefore both require special processes, such as a mold, to create such a concave-convex shape. Additionally, in both pressure sensors, if the electrode comes into contact with the substrate in an unloaded state, a current will flow, so the electrode and the resistor layer must be separated when no load is applied. Therefore, the pressure sensor 50 disclosed in Patent Document 1 is provided with a spacer 53. Furthermore, although the pressure sensor 60 disclosed in Patent Document 2 does not mention a spacer, the fact that the contact member 61 and the circuit board 62 are separated in an unloaded state suggests that a spacer is used between the contact member 61 and the circuit board 62.

[0009] The present invention aims to provide a method for manufacturing a pressure-sensitive conductive elastomer that can maintain a high resistance value between an electrode and a pressure-sensitive conductive elastomer in an unloaded state when a pressure sensor is formed, even without providing spacers around the electrode as in Patent Documents 1 and 2, and that does not require the separate formation of an uneven layer or convex shape on the surface of the pressure-sensitive conductive elastomer as disclosed in Patent Documents 1 and 2, and a pressure sensor that uses a pressure-sensitive conductive elastomer manufactured by this manufacturing method. [Means for solving the problem]

[0010] The method for producing a pressure-sensitive conductive elastomer of the present invention is characterized by comprising a mixing step of mixing a non-conductive elastomer, conductive particles, and non-conductive particles that are irregular in shape and have a particle size larger than the conductive particles to form a mixture, a rolling and curing step of rolling and curing the mixture to form a sheet, and a slicing step of slicing the sheet vertically from the center in the thickness direction along the width direction.

[0011] In the method for producing a pressure-sensitive conductive elastomer of the present invention, a mixture of a non-conductive elastomer, conductive particles, and non-conductive particles of irregular shape and larger in particle size than the conductive particles is used, and a sheet obtained through a rolling and curing process is then sliced ​​perpendicularly from the middle of the thickness direction along the width direction, thereby dividing the sheet into at least two parts in the thickness direction. By undergoing this slicing process, the surfaces of the non-conductive particles present on the sliced ​​surface side of the at least two parts of the sheet can be left exposed and protruding.

[0012] Therefore, when a pressure sensor is formed using the pressure-sensitive conductive elastomer produced according to the present invention, the sliced ​​surface is arranged so as to contact the surface of at least one of the pair of electrodes of the pressure sensor, and when no pressure is applied, the surfaces of the non-conductive particles present on the sliced ​​surface side of the pressure-sensitive conductive elastomer come into contact with the electrode surface in a protruding, exposed state, thereby substantially insulating the pair of electrodes and enabling the interelectrode resistance to be extremely large without using a spacer as in the conventional example.

[0013] In other words, the non-conductive particles with exposed surfaces present on the surface side play the role of spacers in the conventional method. In addition, since the non-conductive particles with exposed surfaces present on the surface side are a material mixed in the mixing process, the above-mentioned effect can be achieved by the material that constitutes the non-conductive elastomer.

[0014] When pressure is applied, the protruding non-conductive particles gradually sink into the pressure-sensitive conductive elastomer, gradually increasing the contact area between the pressure-sensitive conductive elastomer and the electrodes, thereby reducing the resistance between the pair of electrodes and enabling pressure detection, as with the uneven layer or convex shape of Patent Documents 1 and 2. Furthermore, because it is a pressure-sensitive conductive elastomer, when pressure is applied, the thickness of the pressure-sensitive conductive elastomer decreases in response to the magnitude of the applied pressure, increasing the conductive path caused by the short-circuited conductive particles, thereby reducing the resistance between the pair of electrodes and enabling pressure detection.

[0015] In the method for producing a pressure-sensitive conductive elastomer of the present invention, the non-conductive particles added to the pressure-sensitive conductive elastomer are not only larger in particle size than the conductive particles but also irregular in shape. If the non-conductive resin particles have an irregular shape, when pressure is applied to the pressure-sensitive conductive elastomer and the non-conductive resin particles come into contact with each other, the non-conductive particles are more likely to maintain contact without slipping. Therefore, when a pressure sensor is formed using the pressure-sensitive conductive elastomer produced by the present invention, the upper limit of pressure detection is higher and the dynamic range is wider than when spherical or regular-shaped non-conductive resin particles are used.

[0016] The non-conductive particles to be added to the pressure-sensitive conductive elastomer may be made of elastomers such as silicone or urethane elastomers, or resins such as acrylic, styrene, or polyamide elastomers. In particular, silicone elastomer particles or hollow silicone elastomer particles are preferably used.

[0017] If the cutting edge of the blade used in the slicing process is too sharp, these non-conductive particles may be cut. In this state, even if the surface of the non-conductive particles, which are insulating materials, is exposed on the sliced ​​surface side, they may not protrude from the sliced ​​surface side. Therefore, it is preferable to use a blade with an intentionally blunted cutting edge in the slicing process so that the non-conductive particles are less likely to be cut.

[0018] Furthermore, in a pressure sensor using a pressure-sensitive conductive elastomer that has not undergone a slicing process, some unevenness is formed due to the presence of conductive particles and non-conductive particles contained on the surface of the pressure-sensitive conductive elastomer, but this unevenness will have parts where the conductive particles are located closer to the surface than the non-conductive particles, so a conductive path is formed between the pair of electrodes even when no load is applied, resulting in a smaller dynamic range.

[0019] The resin component that can be used as the non-conductive elastomer in the method for producing a pressure-sensitive conductive elastomer of the present invention can be appropriately selected from well-known resin components used in pressure sensors, such as urethane resin, epoxy resin, methacrylate resin, phenolic resin, and silicone rubber. These resin components can be used alone or in combination of two or more. Of these, silicone rubber is particularly preferred from the viewpoint of compatibility with other components.

[0020] Conductive particles that can be used in the method for producing a pressure-sensitive conductive elastomer of the present invention include carbon black, graphite, copper, aluminum, nickel, iron, and metal oxides such as conductive tin oxide and conductive titanium oxide. These may be used alone or in combination of two or more. Among these conductive particles, nanometer-sized carbon particles are preferred from the viewpoints of miscibility and dispersibility with non-conductive elastomers. Examples of nanometer-sized carbon particles include carbon black, spherical carbon particles, acicular carbon particles, plate-like carbon particles, and hollow shell-structured carbon particles.

[0021] The use of nanometer-sized carbon particles as conductive particles increases the mechanical strength of the pressure-sensitive conductive elastomer, improving the reproducibility of changes in electrical resistance and durability against repeated compressive deformation. This is because the nanometer-sized carbon particles form a unique particle network structure within the silicone rubber. On the other hand, the use of micrometer-sized carbon particles, such as amorphous graphite or flaky graphite, requires a larger amount of compounding to exhibit conductivity than nanometer-sized carbon particles. Furthermore, it is difficult to disperse them uniformly throughout the pressure-sensitive conductive elastomer, which adversely affects the elongation and tensile strength of the pressure-sensitive conductive elastomer.

[0022] In the method for producing a pressure-sensitive conductive elastomer of the present invention, it is preferable that the conductive particles have an average particle size of 5 to 500 nm and are added to the mixture in an amount of 5 to 40 vol% (volume %), and the non-conductive resin particles have an average particle size of 10 to 100 μm and are added to the mixture in an amount of 5 to 40 vol%.

[0023] If the average particle size of the conductive particles is less than 10 nm, it becomes difficult to uniformly disperse the conductive particles, and the change in the electrical resistance value of the pressure-sensitive conductive elastomer becomes small. If the particle size of the conductive particles exceeds 500 nm, the reproducibility of the change in electrical resistance value in response to repeated compressive deformation of the pressure-sensitive conductive elastomer and its durability against repeated compressive deformation become poor. If the conductive particle content is less than 5 vol%, the electrical resistance value of the pressure-sensitive conductive elastomer becomes too high. Furthermore, if the conductive particle content exceeds 40 vol%, the elongation and elasticity of the pressure-sensitive conductive elastomer decrease, and it becomes difficult to maintain the insulating properties of the pressure-sensitive conductive elastomer when no pressure is applied.

[0024] The average particle size of the non-conductive particles is preferably larger than that of the conductive particles, on the order of micrometers. However, if the average particle size of the non-conductive particles is less than 10 μm, it is not possible to form sufficiently large irregularities, which may result in electrical conduction between a pair of electrodes even when no pressure is applied, which is undesirable. Furthermore, if the average particle size of the non-conductive particles exceeds 100 μm, the height of the protruding non-conductive particles becomes too large, which may result in a state in which the pressure-sensitive conductive elastomer and the electrode layer do not come into contact even when pressure is applied, or in which contact does not occur until a certain level of pressure is applied, which may result in the formation of a dead zone, which is undesirable.

[0025] If the non-conductive particle content is less than 5 vol%, electrical continuity may occur between the pair of electrodes even when no pressure is applied, which is undesirable. Furthermore, if the non-conductive particle content exceeds 40 vol%, the surface of the pressure-sensitive conductive elastomer may not come into contact with the electrode layer even when pressure is applied, or may not come into contact until a certain level of pressure is applied, which is undesirable, and thus a dead zone may appear.

[0026] Furthermore, the method for producing a pressure-sensitive conductive elastomer of the present invention may further include conductive fibers. These conductive fibers, in conjunction with the conductive particles, can impart conductivity to the pressure-sensitive conductive elastomer and increase its strength, leading to a longer lifespan of the pressure sensor. Examples of conductive fibers that can be used include inorganic conductive fibers (Dentol WK-200B, WK-500, or WK-500B (product names, Otsuka Chemical Co., Ltd.) in which a tin oxide-based conductive layer is formed on the surface of commercially available potassium titanate fibers or titanium dioxide fibers. Although this is not a critical limit, the conductive fibers may have a fiber length of approximately 5 to 30 μm.

[0027] Furthermore, if the inorganic conductive fibers have a fiber length of about 5 to 30 μm, their thickness (diameter) is so thin that it approaches the nanometer size. Furthermore, because the conductive fibers are pressed down during the rolling and curing process, they no longer protrude beyond the non-conductive particles from the sliced ​​surface. Even if the conductive fibers were present nearly perpendicular to the sliced ​​surface, they would be sliced ​​during the slicing process and would no longer protrude beyond the non-conductive particles. Therefore, their effect on the conductivity between the pressure-sensitive conductive elastomer and the electrodes during pressure sensor formation can be virtually ignored.

[0028] The method for producing a pressure-sensitive conductive elastomer of the present invention may further contain nanometer-sized ceramic particles having an average particle size of 5 to 500 nm in the range of 1 to 50 vol%, as in the invention disclosed in Patent Document 3. These nanometer-sized ceramic particles may be surface-treated with a silane coupling agent or silyl agent having a functional group that reacts with and bonds to inorganic substances and a functional group that reacts with, bonds to, or interacts with organic substances. The inclusion of such nanometer-sized ceramic particles allows for more uniform dispersion of the conductive particles in the non-conductive elastomer, increases the mechanical strength of the composite, inhibits crack formation in the resulting pressure-sensitive conductive elastomer, and, even if cracks do form, suppresses their propagation and expansion on a molecular or nanometer scale, thereby dramatically improving the mechanical strength and durability of the pressure-sensitive conductive elastomer.

[0029] The pressure sensor of the present invention is characterized in that it comprises a plurality of thin-film conductive members arranged on the surface of a flexible sheet in a mutually insulated state, and a pressure-sensitive conductive elastomer manufactured by any one of the above methods arranged on the surface of the plurality of thin-film conductive members so as to straddle the plurality of thin-film conductive members, and the surface sliced ​​in the slicing process is arranged so as to face the plurality of thin-film conductive members.

[0030] Furthermore, a pressure sensor according to yet another embodiment of the present invention is a pressure sensor comprising a first thin-film conductive member arranged on the surface of a first flexible sheet, a second thin-film conductive member arranged on the surface of a second flexible sheet, and a pressure-sensitive conductive elastomer manufactured by any of the manufacturing methods described above, which is arranged so as to be sandwiched between the first thin-film conductive member of the first sheet and the second thin-film conductive member of the second sheet, and is characterized in that the surface sliced ​​in the slicing process is arranged so as to face the first or second thin-film conductive member.

[0031] According to the pressure sensor of this aspect, the surface sliced ​​in the slicing process becomes the surface on which the non-conductive resin particles protrude, and therefore a planar pressure sensor that can achieve the above-mentioned effects is obtained. [Effects of the Invention]

[0032] As described above, if a pressure sensor is formed using a pressure-sensitive conductive elastomer manufactured by the method for manufacturing a pressure-sensitive conductive elastomer of the present invention, the resistance value between the electrode and the pressure-sensitive conductive elastomer can be kept high in an unloaded state without providing a spacer around it, and since there is no need to separately form an uneven layer or a convex shape, the manufacturing process for the pressure sensor can be simplified and costs can be reduced. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1A is a flow chart for sequentially explaining the steps for producing a pressure-sensitive conductive elastomer of the present invention, and FIG. 1B is an enlarged schematic cross-sectional view of a pressure-sensitive conductive elastomer sheet. [Figure 2] FIG. 2A is an enlarged schematic cross-sectional view of a pressure-sensitive conductive elastomer sheet during a slicing process, and FIG. 2B is a cross-sectional view of the pressure-sensitive conductive elastomer sheet after slicing. [Figure 3] FIG. 2 is a cross-sectional view of a first pressure sensor. [Figure 4] FIG. 4 is a diagram showing the response characteristics of the first to third pressure sensors. [Figure 5] (a) to (c) are 3D perspective images of the top surface, bottom surface, and slice surface of a sliced ​​sheet in a preliminary experiment example, and (A) to (C) are similar 3D surface images. [Figure 6] FIG. 10 is a diagram showing the response characteristics of the pressure sensors of Experimental Examples 1 and 2. [Figure 7] FIG. 10 is a diagram showing response characteristics of pressure sensors according to Experimental Examples 1 and 3. [Figure 8] 1 is a cross-sectional view of a pressure sensor in which electrodes are abutted on both sides of a pressure-sensitive conductive elastomer sheet used in Experimental Example 1. FIG. [Figure 9] FIG. 8A is a longitudinal sectional view of a conventional pressure sensor, and FIG. 8B is a partially enlarged view thereof. [Figure 10] FIG. 10 is a vertical cross-sectional view of another conventional pressure sensor. DETAILED DESCRIPTION OF THE INVENTION

[0034] Specific embodiments of the present invention will be described below, focusing on the manufacturing method, with reference to the drawings. However, the various examples shown below are merely examples for embodying the technical concept of the present invention, and are not intended to limit the present invention to those shown in these examples. The present invention is equally applicable to other embodiments included within the scope of the claims.

[0035] First, the manufacturing process of the pressure-sensitive conductive elastomer according to the present invention will be described in detail with reference to Figures 1 and 2. Figure 1A is a flow chart sequentially illustrating the manufacturing process of the pressure-sensitive conductive polymer according to the present invention, and Figure 1B is an enlarged schematic cross-sectional view of the pressure-sensitive conductive elastomer sheet manufactured through the process of Figure 1A. Figure 2A is an enlarged schematic cross-sectional view of the pressure-sensitive conductive elastomer sheet manufactured through the process of Figure 1A during the slicing process, and Figure 2B is a cross-sectional view of the pressure-sensitive conductive elastomer sheet after slicing.

[0036] 1A, the manufacturing process 10 of the pressure-sensitive conductive elastomer of the present invention includes a first dispersing / mixing step 11 in which conductive particles and non-conductive particles are mixed, and a second dispersing / mixing step 12 in which a non-conductive elastomer is added to the mixture obtained in the first dispersing / mixing step 11 and further mixed. Then, the slurry material obtained in the second dispersing / mixing step 12 is passed through a calender molding machine and rolled with rollers to be cured in a rolling / curing step 13 to form a pressure-sensitive conductive elastomer sheet 20.

[0037] The conductive elastomer sheet 20 produced in this manner has a configuration in which conductive particles 22 and non-conductive particles 23 having a larger particle size than the conductive particles 22 are dispersed substantially uniformly in the non-conductive elastomer 21, as shown in Figure 1B.

[0038] Next, as shown in FIG. 2A, a splitting machine (not shown) is used to slice the conductive elastomer sheet 20 vertically from the center in the thickness direction along the width direction, thereby exposing the surfaces of the non-conductive particles 23 present on the sliced ​​surface side in a protruding state (slicing step 14). In FIG. 2A, reference numeral 24 denotes the cutting edge of the splitting machine. The sliced ​​pressure-sensitive conductive elastomer sheet is then divided into an upper sliced ​​sheet 25 and a lower sliced ​​sheet 26, as shown in FIG. 2B. Hereinafter, the top surface of the upper sliced ​​sheet 25 will be referred to as the top surface 27, the bottom surface of the lower sliced ​​sheet 26 will be referred to as the bottom surface 28, and the surfaces of the upper sliced ​​sheet 25 and the lower sliced ​​sheet 26 will be referred to as the sliced ​​surfaces 29.

[0039] 2B, on this sliced ​​surface 29, some of the non-conductive particles 23 are exposed and protruding from the non-conductive elastomer 21 containing the conductive particles 22. In other words, since the non-conductive particles 23 are insulating, these protruding portions are also insulating.

[0040] [Preliminary experiment example] Next, a preliminary experimental example of the present invention will be described with reference to Figs. 3 to 5. Fig. 3 is a cross-sectional view of a first pressure sensor in the preliminary experimental example. Fig. 4 is a diagram showing the response characteristics of the first to third pressure sensors in the preliminary experimental example. Fig. 5(a) to (c) are 3D oblique images of the top surface, bottom surface, and slice surface of a sliced ​​sheet in the preliminary experimental example, and Figs. 5(A) to (C) are similar 3D surface images.

[0041] The materials used in the preliminary experimental examples are as follows. A one-component, room-temperature-curing liquid silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KE-445B) was used as the non-conductive elastomer. The conductive particles used were spherical carbon particles (manufactured by Mitsubishi Chemical Corporation, product name: Ketjenblack EC600JD, particle size: 20-40 nm, average particle size: 34 nm) and conductive ceramic fibers made of potassium titanate and tin oxide (manufactured by Otsuka Chemical Co., Ltd., product name: Dentol WK200B, needle-shaped crystals with an average fiber length of 10-20 μm). The non-conductive particles used were nanometer-sized gamma-alumina particles (manufactured by Taimei Chemical Industry Co., Ltd., product name: Taimicron TM-300, primary particle size 7 nm), spherical silicone resin powder (manufactured by Dow-Toray Industries, Inc., product name: EP-5500, average particle size 3 μm), and amorphous silicone resin powder (manufactured by Nikko Rica Corporation, product name: MSP-150). This amorphous silicone resin powder has an average particle size of 20 μm and a particle size distribution of 1 to 106 μm, which is larger than the particle size of conductive particles such as ketjen black and conductive ceramic fibers.

[0042] To prepare the pressure-sensitive conductive elastomer, first, Ketjen black and conductive ceramic fibers as conductive particles, gamma-alumina particles as non-conductive particles, spherical silicone resin powder, and amorphous silicone resin powder were thoroughly mixed and stirred (first mixing step). Next, a one-component liquid silicone rubber was added as a non-conductive elastomer before curing, and then thoroughly dispersed (second dispersing and mixing step) to obtain a slurry mixture. The blending ratios of each component in the preliminary experimental example after the second dispersing and mixing step were as shown in Table 1 below.

[0043] [Table 1]

[0044] Next, this slurry mixture was subjected to a dispersion process for 3 minutes using a planetary centrifugal stirring and degassing machine and then dispersed again. This slurry mixture was then rolled using a calendar molding machine and cured to produce a conductive elastomer sheet 20 with a thickness of 0.3 mm. As shown in FIG. 1B, the cross section of this conductive elastomer sheet 20 shows that Ketjen Black, conductive ceramic fibers, γ-alumina particles, and spherical silicone resin powder serving as conductive particles 22 are uniformly dispersed in non-conductive elastomer 21 (note that the conductive ceramic fibers, γ-alumina particles, and spherical silicone resin powder are not shown in FIGS. 1A, 2A, 2B, and 3). Furthermore, amorphous silicone resin powder serving as non-conductive particles 23, which has an average particle size larger than that of the conductive particles 22, is also substantially uniformly dispersed.

[0045] The conductive elastomer sheet 20 produced here is substantially electrically conductive due to contact between the conductive particles, which are made of Ketjen black, a conductive fine particle in the non-conductive elastomer 21, and conductive ceramic fibers.As the non-conductive elastomer 21 is pressed and its thickness becomes thinner, the contact area between the conductive particles increases and the electrical resistance decreases, making it possible to detect pressure from this change in resistance value.

[0046] Next, using a splitting machine, the conductive elastomer sheet 20 was sliced ​​vertically from the center in the thickness direction along the width direction, as shown in Figures 2A and 2B, to create a pair of pressure-sensitive conductive elastomer sheets 20A. On the sliced ​​surface 29 of each of the pair of pressure-sensitive conductive elastomer sheets 20A, as shown in Figure 2B, part of the amorphous silicone resin powder as non-conductive particles 23 protrudes from the non-conductive elastomer 21 containing conductive particles 22. In other words, since the amorphous silicone resin powder is insulating, these protruding portions are also insulating.

[0047] [First to third pressure sensors] Of the pair of sheets that had undergone this slicing process, the upper sliced ​​sheet and the lower sliced ​​sheet were each cut into a 5 mm x 5 mm square sheet (area: 25 mm2), and three types of pressure sensors were formed as follows, and the pressure-sensitive characteristics of each were measured. The configurations of these three types of pressure sensors will be explained with reference to Figure 3, which is a cross-sectional view of the first pressure sensor.

[0048] First, polymer films 31 and 32 made of PET were prepared, and a pair of parallel thin-film electrodes 33 were formed on the surface of one of the polymer films 31, spaced 1 mm apart. Note that only one of the electrodes is shown in FIG. 3. Then, to form a first pressure sensor 30, the upper sliced ​​sheet 25 in FIG. 2B was placed so that the sliced ​​surface 29 was in contact with the surface of the thin-film electrode 33, and the other polymer film 32 was placed on the surface of the top surface 27 for protection, thereby forming the first pressure sensor 30. In the first pressure sensor 30, the non-conductive particles 23 protruding from the sliced ​​surface 29 are in contact with the thin-film electrode 33.

[0049] Although not shown, the second pressure sensor is the first pressure sensor 30, but is arranged such that the top surface 27 of the sliced ​​upper sheet 25 is in contact with the surface of the thin-film electrode 33, and the sliced ​​surface 29 is in contact with the protective polymer film 32. That is, in the second pressure sensor, the top surface 27 of the sliced ​​upper sheet 25 is in direct contact with the thin-film electrode 33.

[0050] Furthermore, the third pressure sensor, also not shown, uses a sliced ​​lower sheet 27 instead of the sliced ​​upper sheet 25 in the first pressure sensor 30, and is arranged so that its bottom surface 28 contacts the surface of the thin-film electrode 33 and its sliced ​​surface 29 contacts another protective polymer film 32. That is, in the third pressure sensor, the bottom surface 28 of the sliced ​​lower sheet 26 is in direct contact with the thin-film electrode 33.

[0051] [Measurement of pressure-sensitive characteristics of the first to third pressure sensors] For each of the first to third pressure sensors manufactured as described above, the pressure-sensitive characteristics were measured by measuring the electrical resistance between the pair of thin-film electrodes while changing the magnitude of the load applied to the pressure sensor. The results are summarized in Figure 4.

[0052] 4, the response curves of the second and third pressure sensors are substantially similar, but the first pressure sensor shows a change in resistance value in response to a change in pressure even in a lower load range than the second and third pressure sensors, demonstrating pressure sensitivity, and also showing a change in resistance in a higher load range. In other words, the first pressure sensor has better sensitivity than the second and third pressure sensors, and also has a larger dynamic range.

[0053] This is because, in the first pressure sensor 30, the amorphous silicone resin powder as the non-conductive particles 23 protruding from the sliced ​​surface 29 to the side facing the thin film electrode 32 is insulating. (1) When no pressure is applied from the polymer film 32 side, the non-conductive particles 23 function as a spacer, and the portion of the non-conductive elastomer 21 containing the conductive particles 22 is not substantially in contact with the thin film electrode 33, resulting in no electrical conduction between the pair of thin film electrodes. (2) When pressure is applied from the polymer film 32 side, the amorphous silicone resin powder as the non-conductive particles 23 gradually sinks into the non-conductive elastomer 21, and then the non-conductive elastomer 21 portion comes into contact with the thin film electrode 33, so that electrical conduction occurs between the pair of electrodes, making it possible to detect pressure. This shows that:

[0054] In contrast, the second and third pressure sensors: (3) Even when no pressure is applied from the polymer film side, the non-conductive elastomer part containing conductive nano-sized carbon black particles is in contact with the thin film electrode, which means that the resistance value tends to drop sharply on the low load side, demonstrating a strong ON-OFF characteristic.

[0055] As described above, from the description in Figure 4, it was confirmed that the protrusion of amorphous silicone resin powder as non-conductive particles 23 from the sliced ​​surface 29 on the side facing the thin film electrode 33 leads to improvements in the sensitivity and dynamic range of the pressure sensor.

[0056] The surface conditions of the top and bottom surfaces of the sliced ​​sheet and the surface of the slices in the above preliminary experiment will now be described with reference to Figure 5. In Figure 5, (a) to (c) are 3D oblique images (2500x magnification) of the top, bottom, and surface of the sliced ​​sheet, respectively, and (A) to (C) are 3D surface images (2500x magnification) of the same. The curves on the right side and bottom side in Figures 5(A) to (C) represent the height changes of the crosshairs shown in Figures 5(A) to (C), respectively. Furthermore, the elongated portions in Figures 5(a) to (c) and (A) to (C) represent conductive ceramic fiber portions.

[0057] The technical meaning of each parameter shown in FIGS. 5(A) to 5(C) is as follows: Sa: arithmetic mean height Sz: Maximum height Sq: Root mean square height Sp: Maximum mountain height Sv: Maximum valley height

[0058] 5(a)-(c) and (A)-(C), it can be seen that although slight unevenness can be seen on the top and bottom surfaces, the unevenness on the sliced ​​surface is much greater than that on the top and bottom surfaces. Therefore, the difference in response characteristics of the first to third pressure sensors in the above preliminary experiment example is due to whether the side of the pressure-sensitive conductive elastomer that comes into contact with the electrode is the top surface (second pressure sensor), the bottom surface (second pressure sensor), or the sliced ​​surface (first pressure sensor), confirming that the points (1)-(3) above are correct.

[0059] In other words, it can be seen that slicing causes the non-conductive particles 23 to protrude and become exposed on the slice surface 29. This shows that the slicing process of slicing the conductive elastomer sheet 20 vertically from the center in the thickness direction along the width direction is extremely important. On the other hand, on the top surface 27 and bottom surface 28, the surfaces of the non-conductive particles 23 located on the surface are covered with the non-conductive elastomer 21 containing the conductive particles 22.

[0060] As for the conductive ceramic fiber portion, because it was pressed down during the rolling and hardening process, most of the conductive ceramic fiber exists along the slicing direction and does not protrude beyond the non-conductive particles from the sliced ​​surface. Also, even if the conductive ceramic fiber existed nearly perpendicular to the sliced ​​surface, it would be sliced ​​during the slicing process and would not protrude beyond the non-conductive particles.

[0061] [Experimental Examples 1 and 2] In Experimental Examples 1 and 2, we investigated the effects of the presence or absence of amorphous, non-conductive particles larger than the conductive particles on the pressure-sensitive characteristics. In Experimental Example 1, a 0.5 mm thick pressure-sensitive conductive elastomer was manufactured using a pressure-sensitive conductive elastomer with the same composition as that used in the preliminary experiment. A pressure sensor with the same configuration as the first pressure sensor was fabricated. In Experimental Example 2, the amorphous silicone resin powder with an average particle size of 20 μm was removed from the pressure-sensitive conductive elastomer with the same composition as that used in the preliminary experiment. Instead, the amount of nanometer-sized spherical silicone rubber was increased. A pressure-sensitive conductive elastomer with a thickness of 0.5 mm was fabricated using this pressure-sensitive conductive elastomer. The composition of the pressure-sensitive conductive elastomer used in Experimental Example 2 is listed in Table 1, along with the composition of the pressure-sensitive conductive elastomer used in Experimental Example 1 (the same as that used in the preliminary experiment). The response characteristics of each pressure sensor are shown in Figure 6.

[0062] [Table 2]

[0063] The results shown in Figure 6 reveal the following: Although some unevenness is observed on the sliced ​​surface of the pressure-sensitive conductive elastomer used in the pressure sensor of Experimental Example 2 (not shown), this unevenness is due to the conductive particles (Ketjen Black and conductive ceramic fibers) and the non-conductive particles (micrometer-sized spherical silicone resin powder and nanometer-sized γ-alumina). In contrast, the unevenness formed on the sliced ​​surface of the pressure-sensitive conductive elastomer used in the pressure sensor of Experimental Example 1 is due to amorphous non-conductive particles with an average particle size of 20 μm, which is larger than the conductive particles in Experimental Example 2. Therefore, the protrusion height is higher than that of the unevenness in Experimental Example 2. This is thought to be why the response characteristics of the pressure sensor of Experimental Example 2 were higher in sensitivity and had a wider dynamic range.

[0064] Furthermore, although not shown, the spherical silicone resin powder used as the non-conductive particles does not get caught on each other, as occurs with the irregularly shaped non-conductive particles shown in Figure 2B, for example. Therefore, the spherical non-conductive particles are uniformly arranged, and do not have the pronounced protrusions that occur with the irregularly shaped non-conductive particles. Therefore, it is clear that the irregular shape of the non-conductive particles is extremely important in the present invention.

[0065] [Experimental Example 3] From the results of Experimental Examples 1 and 2, it was confirmed that adding amorphous non-conductive particles with a larger particle size than the conductive particles to a pressure-sensitive conductive elastomer is effective in improving sensitivity and dynamic range, but in Experimental Example 3, an experiment was conducted to confirm the effective particle size range of amorphous non-conductive particles with a larger particle size than the conductive particles.

[0066] In Experimental Example 3, the amorphous silicone resin powder with an average particle size of 20 μm used in the pressure-sensitive conductive elastomer sheet of Experimental Example 1 was replaced with amorphous silicone resin powder with an average particle size of 6 μm (manufactured by Nikko Rica Corporation, product name: MSP-A37), and the other components were prepared in the same manner as in Experimental Example 1 to produce a pressure-sensitive conductive elastomer sheet. The composition of the pressure-sensitive conductive elastomer sheet of Experimental Example 3 is shown in Table 3, along with that of Experimental Example 1. The pressure-sensitive characteristics of the pressure sensor of Experimental Example 3 were measured, and the results are shown in Figure 7, along with the pressure-sensitive characteristics of the pressure sensor of Experimental Example 1.

[0067] [Table 3]

[0068] The results shown in Figure 7 reveal the following: The response characteristics of the pressure sensor of Experimental Example 3 are similar to those of Experimental Example 2 (see Figure 5), which does not contain non-conductive fine particles with an average particle size in the micrometer range, and essentially exhibit ON-OFF characteristics. The difference in the configuration of the pressure sensor of Experimental Example 1 and that of Experimental Example 3 is that the average particle size of the substantially amorphous non-conductive fine particles is different: 20 μm (Experimental Example 1) and 6 μm (Experimental Example 3). It should be noted that the upper limit of the average particle size of the non-conductive fine particles contained in the pressure-sensitive conductive elastomer sheet depends on the thickness of the pressure-sensitive conductive elastomer sheet, but it is estimated that a pressure sensor with the specified response characteristics can be obtained if it is 100 μm or less.

[0069] [Pressure sensors with different configurations] Note that pressure sensors using the pressure-sensitive conductive elastomer manufactured by the manufacturing method of the present invention are applicable not only to the example shown in Fig. 3 in which a pair of electrodes is formed on the surface of a flexible sheet and a pressure-sensitive conductive elastomer sheet is disposed on that surface, but also to a type in which a pair of electrodes is disposed on each side of the pressure-sensitive conductive elastomer. A pressure sensor with such a different configuration will be described using Fig. 8. Note that Fig. 8 is a longitudinal cross-sectional view of a pressure sensor with a different configuration from that shown in Fig. 3, and in Fig. 8, the same components as those shown in Fig. 3 are assigned the same reference numerals and detailed description thereof will be omitted.

[0070] The pressure sensor 30 shown in Figure 8 has a thin-film electrode 33 formed on the surface of a polymer film 31 made of PET, and a thin-film electrode 34 formed on the surface of another polymer film 32 made of PET, so that both sides of the upper sliced ​​sheet 25 in Figure 2B are sandwiched between the two thin-film electrodes 33 and 34. Here, an example is shown in which the sliced ​​surface 29 is arranged to contact the surface of the lower thin-film electrode 33, but the sliced ​​surface 29 may also be arranged to contact the upper thin-film electrode 34. Even with a pressure sensor 30 having such a different configuration, pressure-sensitive characteristics substantially similar to those of the pressure sensor of Experimental Example 1 can be obtained. [Explanation of symbols]

[0071] 10...Production process of the pressure-sensitive conductive polymer of the present invention 11...First dispersion and mixing process 12...Second dispersion and mixing process 13...Rolling and hardening process 14...Slicing process 20...Conductive elastomer sheet 20A...Pressure-sensitive conductive elastomer sheet 21...Non-conductive elastomer 22...Conductive particles 23...Non-conductive particles 24...Splitting machine cutting edge 25...Upper seat 26...Lower seat 27...Top 28...Bottom 29...Slice surface 30...Pressure sensor 31, 32...polymer film 33, 34...thin film electrode

Claims

1. A method for producing a pressure-sensitive conductive elastomer, comprising: a mixing step of mixing a non-conductive elastomer, conductive particles, non-conductive particles having an irregular shape and a particle size larger than that of the conductive particles, and a solvent to form a mixture; a rolling and curing step of rolling and curing the mixture to form a sheet; a slicing step of slicing the sheet vertically from the center in the thickness direction along the width direction; A method for producing a pressure-sensitive conductive elastomer, comprising:

2. the conductive particles have an average particle size of 5 to 500 nm and a blending ratio in the mixture of 5 to 40 vol %, 2. The method for producing a pressure-sensitive conductive elastomer according to claim 1, wherein the non-conductive resin particles have an average particle size of 10 to 100 μm and a blending ratio in the mixture of 5 to 40 vol %.

3. 3. The pressure-sensitive conductive elastomer according to claim 1, further comprising conductive fibers.

4. 10. A pressure sensor comprising: a plurality of thin-film conductive members arranged on a surface of a flexible sheet in a state insulated from one another; and the pressure-sensitive conductive elastomer according to claim 1 arranged on the surface of the plurality of thin-film conductive members so as to straddle between the plurality of thin-film conductive members, The pressure sensor is characterized in that the pressure-sensitive conductive elastomer is arranged so that the surfaces sliced ​​in the slicing step face the plurality of thin-film conductive members.

5. a thin-film conductive member disposed on a surface of a flexible first sheet; a thin-film conductive member disposed on a surface of a flexible second sheet; the pressure-sensitive conductive elastomer according to claim 1 , which is disposed so as to be sandwiched between the thin-film conductive member of the first sheet and the thin-film conductive member of the second sheet; A pressure sensor comprising: A pressure sensor characterized in that the pressure-sensitive conductive elastomer is arranged so that the surface sliced ​​in the slicing process faces the thin-film conductive member of the first or second sheet.

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