Electrostatic capacitance sensor

Abstract

This electrostatic capacitance sensor (1A) comprises: a sensor part (20) that includes a sensor electrode (22) that forms electrostatic capacitance with an object to be detected (100); and a molded part (11) that is interposed between the object to be detected (100) and the sensor electrode (22). The molded part (11) includes an insulator (12) that is composed of an insulating material having electrical insulation, and fillers (13) that are dispersed in the insulator (12) and include conductor fillers or dielectric fillers.

Description

Capacitive Sensor

[0001] The present invention relates to a capacitance sensor. For designated countries where incorporation by reference of literature is permitted, the content of Japanese Patent Application No. 2024-110485 filed in Japan on July 9, 2024 is incorporated by reference into this specification and made a part of the description of this specification.

[0002] A capacitance-type sensor module is known that includes a housing having an operation surface, a capacitance-type sensor sheet laminated on the side of the housing opposite the operation surface and having a plurality of electrodes formed thereon, and a circuit board disposed on the side opposite the operation surface of the capacitance-type sensor sheet at a distance and connected to the plurality of electrodes (see, for example, Patent Document 1). In this capacitance-type sensor module, when an input object approaches the electrodes via the operation surface of the housing, the capacitance-type sensor sheet detects a change in capacitance between the input object and the electrodes.

[0003] Japanese Patent Application Laid-Open No. 2023-112268

[0004] In the capacitance type sensor module of the above-mentioned conventional technology, if the thickness of the housing increases, the distance between the input body and the electrode also increases, resulting in a problem of reduced sensitivity.

[0005] An object of the present invention is to provide a capacitance sensor that can improve sensitivity.

[0006] [1] Aspect 1 of the present invention is a capacitance sensor comprising a sensor section including a sensor electrode that forms a capacitance between itself and a detected object, and an insulating section interposed between the detected object and the sensor electrode, wherein the insulating section includes an insulator made of an insulating material having electrical insulating properties, and a conductive filler or a dielectric filler dispersed in the insulator.

[0007] [2] Aspect 2 of the present invention may be a capacitance sensor according to aspect 1, wherein the insulating portion includes the conductive filler, and the electrical resistivity of the conductive filler is lower than the electrical resistivity of the insulating material.

[0008] [3] A third aspect of the present invention may be a capacitance sensor according to the second aspect, wherein the conductive filler is made of carbon or a metal material.

[0009] [4] A fourth aspect of the present invention may be a capacitance sensor according to the first aspect, wherein the insulating portion includes the dielectric filler, and the dielectric constant of the dielectric filler is higher than the dielectric constant of the insulating material.

[0010] [5] A fifth aspect of the present invention may be the capacitance sensor of the fourth aspect, wherein the dielectric filler has a relative dielectric constant of 100 or more.

[0011] [6] A sixth aspect of the present invention may be the capacitance sensor of the fourth or fifth aspect, wherein the dielectric filler is made of a metal oxide.

[0012] [7] A seventh aspect of the present invention may be the capacitance sensor according to any one of the first to sixth aspects, wherein the insulating portion is directly laminated on the sensor portion.

[0013] [8] Aspect 8 of the present invention is a capacitance sensor according to any one of aspects 1 to 6, wherein the capacitance sensor further includes an adhesive layer interposed between the insulating portion and the sensor portion.

[0014] [9] A ninth aspect of the present invention is a capacitance sensor according to the seventh or eighth aspect, wherein the insulating portion includes a molded portion in which at least a portion of the insulating portion is three-dimensionally molded, and the sensor portion may be laminated on the molded portion.

[0015]

[10] Aspect 10 of the present invention is a capacitance sensor according to aspect 9, wherein the insulating portion is a housing including the molded portion, and the sensor portion may be a capacitance sensor laminated on the inner surface of the housing.

[0016]

[11] Aspect 11 of the present invention may be a capacitance sensor in any one of aspects 1 to 10, wherein the insulating portion is located on the opposite side of the sensor portion and includes a contact surface that comes into contact with the object to be detected.

[0017] In the present invention, the insulating portion interposed between the object to be detected and the sensor electrode contains conductive fillers or dielectric fillers dispersed in the insulator, which improves the effective dielectric constant of the insulating portion and thereby suppresses the decrease in sensitivity that accompanies an increase in the distance between the object to be detected and the sensor electrode.

[0018] Fig. 1 is a cross-sectional view of a capacitance sensor according to an embodiment of the present invention. Fig. 2 is an enlarged cross-sectional view showing part II in Fig. 1. Fig. 3 is a plan view of a sensor section according to an embodiment of the present invention. Fig. 4(a) is an enlarged cross-sectional view illustrating a capacitance sensor according to a comparative example, and Fig. 4(b) is an enlarged cross-sectional view illustrating the effect of a conductive filler in a molded section of a capacitance sensor according to an embodiment of the present invention. Fig. 5 is an enlarged cross-sectional view showing a modified example of a capacitance sensor according to an embodiment of the present invention.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] FIG. 1 is a cross-sectional view of a capacitance sensor 1A in this embodiment, FIG. 2 is an enlarged cross-sectional view showing a portion II in FIG. 1, and FIG. 3 is a plan view of a sensor unit 20 in this embodiment.

[0021] The capacitance sensor 1A of this embodiment is a sensor that detects contact or approach of the detectable object 100 by detecting a change in capacitance value caused by the detectable object 100. The detectable object 100 is not particularly limited as long as it can form capacitance with a sensor electrode 22 (see FIGS. 2 and 3 ), which will be described later, and examples thereof include the human body and a touch pen. Furthermore, the potential of the detectable object 100 is not particularly limited, but can be considered to be ground.

[0022] The capacitance sensor 1A in this embodiment can be applied to, but is not limited to, touch screens of smartphones and tablet devices, track pads of PC operation units, switch parts of home appliances, control panels for automobiles, or grip detection sensors for steering wheels.

[0023] 1, the capacitance sensor 1A of this embodiment includes a housing 10 and a sensor unit 20. The housing 10 corresponds to an example of an "insulating unit" in the aspects of the present invention.

[0024] The housing 10 in this embodiment is a highly rigid member and houses the sensor unit 20 therein. The housing 10 includes a molded portion 11 that is molded into a three-dimensional shape. In this embodiment, the molded portion 11 is molded into a three-dimensional shape having a substantially U-shaped cross section, but is not limited thereto and may be molded into any three-dimensional shape that suits the intended use of the capacitance sensor 1A. The housing 10 may also be a flexible member, and the material constituting such a member is not particularly limited, but examples include resins such as polyurethane.

[0025] The molded portion 11 includes a contact surface 11a that comes into contact with the detection object 100. When the detection object 100 approaches or comes into contact with the contact surface 11a, the capacitance sensor 1A detects the contact or approach of the detection object 100 based on a change in capacitance between the detection object 100 and a sensor electrode 22 (see FIGS. 2 and 3) described later.

[0026] The molded portion 11 does not have to be in direct contact with the detection object 100. For example, a cover layer made of glass, resin, fiber, leather, or the like may be laminated on the molded portion 11. Even if the detection object 100 comes into contact with the cover layer, the capacitance sensor 1A can detect the approach of the detection object 100.

[0027] As shown in Figure 2, the molded portion 11 includes an insulator 12 and a plurality of fillers 13. The insulator 12 is made of an insulating material having insulating properties and electrically insulates the detection object 100 from the sensor portion 20. Examples of such an insulating material include, but are not limited to, a resist material obtained by hardening a resist ink containing polycarbonate, polypropylene, polyurethane, urethane acrylate resin, etc., or a two-component mixed resin. The relative dielectric constant of the insulating material constituting the insulator 12 is, but is not limited to, approximately 3 to 10.

[0028] A plurality of fillers 13 are dispersed in the insulator 12. Note that, although Fig. 2 illustrates an ellipsoidal filler as the filler 13 in this embodiment, the shape of the filler 13 is not limited thereto. The shape of the filler 13 may be spherical, polyhedral, scale-like, needle-like, or the like.

[0029] The filler 13 is a conductive filler or a dielectric filler. The material constituting the conductive filler is not particularly limited, but examples thereof include carbon and metal. The metal is not particularly limited, but examples thereof include copper, silver, nickel, etc.

[0030] On the other hand, the material constituting the dielectric filler is a dielectric having a higher dielectric constant than the insulating material constituting the insulator 12. Examples of this dielectric include, but are not limited to, inorganic dielectrics. Furthermore, it is preferable to use a ferroelectric as the dielectric, and it is particularly preferable that the dielectric constant of this ferroelectric is 100 or more. Examples of such ferroelectrics include, but are not limited to, metal oxides such as titanium oxide, barium titanate, and zinc zirconate.

[0031] Furthermore, the particle diameter D of the filler 13 is preferably 5 nm to 100 μm (5 nm≦D≦100 μm). If the particle diameter D is 100 μm or less, the dispersibility of the filler 13 in the insulating material during molding is improved. Furthermore, the particle diameter of the filler 13 is not too large, and the viscosity of the mixed paste of the liquid insulating material and the filler 13 does not become too high during molding. Furthermore, cracks caused by the filler 13 are unlikely to occur when the insulating material is hardened. In other words, if the particle diameter D is 100 μm or less, the occurrence of molding defects can be suppressed and moldability can be improved. Note that the particle diameter of the filler 13 in this embodiment is the median diameter D ５０ This median diameter D ５０ Although not particularly limited, it can be calculated by a laser diffraction scattering method or the like.

[0032] In addition, the volume ratio P of the filler 13 in the molding portion 11 ｖ is preferably 5 vol% to 40 vol% (5 vol%≦P ｖ≦40 vol%). This volume ratio P ｖ If the volume ratio P is 5 vol % or more, the effective dielectric constant of the molded portion 11 can be further improved. ｖ If the volume ratio P is 40 vol % or less, the occurrence of molding defects can be suppressed and moldability can be improved, as described above. ｖ If the content of the insulating material is 40 vol % or less, the deterioration of the insulating properties of the molded portion 11 can be suppressed.

[0033] 1 and 2, the sensor unit 20 in this embodiment is laminated on the inner surface 11b of the housing 10. The sensor unit 20 is disposed on the inner surface 11b at a position corresponding to the contact surface 11a, and faces the object to be detected 100 via the molded portion 11 when the object to be detected 100 comes into contact with the contact surface 11a. As shown in Fig. 3, the sensor unit 20 includes a substrate 21, a plurality of sensor electrodes 22, and a plurality of lead-out wires 23. The number of sensor electrodes 22 may be one, and similarly, the number of lead-out wires 23 may also be one.

[0034] The substrate 21 is not particularly limited, but is a film-like resin material. Examples of the resin material constituting the substrate 21 include polyimide, liquid crystal polymer, polyethylene terephthalate, polyethylene naphthalate, polyetherimide, polyether ether ketone, and aramid.

[0035] A plurality of sensor electrodes 22 are provided on the main surface of the substrate 21 so as to be interposed between the substrate 21 and the molded portion 11. Each of the sensor electrodes 22 is a self-capacitance type capacitance sensor, and forms a capacitance between itself and the object 100 to be detected.

[0036] The lead wires 23 are electrically connected to the sensor electrodes 22. The lead wires 23 are electrically connected to a circuit device (not shown) that can apply a voltage to the sensor electrodes 22, and a voltage is applied to the sensor electrodes 22 from the circuit device (not shown) via the lead wires 23. The circuit device (not shown) may be housed inside the housing 10 together with the sensor unit 20, or may be arranged outside the housing 10.

[0037] The sensor electrodes 22 and the lead wires 23 can be formed by printing a conductive paste on the substrate 21 and solidifying (curing) it. Examples of methods for printing the conductive paste include screen printing, gravure offset printing, flexographic printing, and inkjet printing. The conductive paste is formed by mixing conductive particles and a binder resin with water or a solvent and various additives.

[0038] Specific examples of conductive particles include silver, copper, nickel, tin, bismuth, zinc, indium, palladium, alloys thereof, metal salts thereof, carbon, and conductive polymers such as PEDOT / PSS. Specific examples of binder resins include acrylic resins, polyester resins, epoxy resins, vinyl resins, urethane resins, phenolic resins, polyimide resins, silicone resins, and fluororesins. Examples of solvents contained in the conductive paste include α-terpineol, butyl carbitol acetate, butyl carbitol, 1-decanol, butyl cellosolve, diethylene glycol monoethyl ether acetate, and tetradecane. The binder resin may be omitted from the conductive paste. Alternatively, a conductive ink may be used instead of the conductive paste.

[0039] Alternatively, the sensor electrode 22 and the lead-out wiring 23 may be formed on the substrate 21 by a subtractive method, an additive method (either a full-additive method or a semi-additive method), or the like. In this case, examples of materials constituting the sensor electrode 22 and the lead-out wiring 23 include metal materials such as copper and aluminum.

[0040] The sensor electrodes 22 may be mutual capacitance type electrostatic capacitance sensors. ｘ ) and a receiving electrode (R ｘIn this mutual capacitance type capacitance sensor, capacitance is formed between the object to be detected 100 and the transmitting electrode, which causes a change in capacitance between the transmitting electrode and the receiving electrode. The mutual capacitance type capacitance sensor detects contact or approach of the object to be detected 100 by detecting this change in capacitance.

[0041] In a mutual capacitance type capacitance sensor, the transmitting electrodes may be formed on a different layer from the receiving electrodes, and the two may intersect in a grid pattern in a transmitted plan view. For example, although not particularly limited, the transmitting electrodes may be provided on the front surface of the substrate 21 so as to extend in the X direction, and the receiving electrodes may be provided on the back surface of the substrate 21 so as to extend in the Y direction.

[0042] The capacitance sensor 1A described above can be manufactured by injection molding, such as, but not limited to, insert molding. Specifically, insert molding involves first placing the sensor unit 20 as an insert part in a mold. Next, pellets made of the insulating material described above are loaded into a molding machine, and the pellets are heated and melted while being transported toward the mold by the molding machine's screw. At the same time, filler 13 is loaded into the molding machine, and the filler 13 is diffused into the molten insulating material to create a mixed paste of the insulating material and the filler 13. This mixed paste is injected into a mold and then hardened, thereby manufacturing the capacitance sensor 1A including the housing 10 and the sensor unit 20. The capacitance sensor 1A according to this embodiment may also be manufactured using other molding methods.

[0043] The capacitance sensor 1A of this embodiment as described above has the following effects. First, the effects when the filler 13 is a conductive filler will be described. Fig. 4(a) is an enlarged cross-sectional view illustrating a capacitance sensor 1C of a comparative example, and Fig. 4(b) is an enlarged cross-sectional view illustrating the effect of the conductive filler in the molded portion 11 of the capacitance sensor 1A of this embodiment.

[0044] 4A, the capacitance sensor 1C of the comparative example includes a sensor portion 20C including a sensor electrode 22C and an insulating molded portion 11C laminated on the sensor electrode 22C. The molded portion 11C of the comparative example does not have a conductive filler dispersed in an insulator 12C.

[0045] When the detection object 100 is brought into contact with such a molded portion 11C, an electric field E Ｃ This electric field E Ｃ The length of the path is the thickness T of the molded portion 11C. ０ The capacitance formed between the object to be detected 100 and the sensor electrode 22C is substantially equal to the electric field E Ｃ Since the thickness T of the molded portion 11C is inversely proportional to the length of the path, ０ If the capacitance between the object to be detected 100 and the sensor electrode 22C becomes large, the capacitance formed between the object to be detected 100 and the sensor electrode 22C becomes small. As a result, the amount of change in capacitance due to the object to be detected 100 approaching or coming into contact with the object to be detected 100 also becomes small, and the sensitivity of the capacitance sensor 1C decreases.

[0046] As shown in Fig. 4(a), the conductive fillers 13a dispersed in the insulator 12 can be regarded as a virtual parallel plate capacitor 30 formed in the insulator 12. For convenience, Fig. 4(a) illustrates an example in which the parallel plate capacitor 30 has two parallel plates (a first virtual parallel plate 31 and a second virtual parallel plate 32).

[0047] 4(b), in the capacitance sensor 1A according to this embodiment, when the object to be detected 100 is brought close to the molded portion 11, an electric field E is generated between the object to be detected 100 and the sensor electrode 22. At this time, since the first imaginary parallel plates 31, 32 are conductors, free electrons inside the first imaginary parallel plates 31, 32 move due to the action of the electric field E, and dielectric polarization (electrostatic induction) is generated.

[0048] 4A, in the first imaginary parallel plate 31, negative charges (free electrons) move in the +Z direction as if attracted by the positive charges of the object to be detected 100, and the positive charges move in the -Z direction opposite to the negative charges. Similarly, in the second imaginary parallel plate 32, negative charges (free electrons) move in the +Z direction, and positive charges move in the -Z direction opposite to the negative charges.

[0049] As a result, it can be considered that three capacitors connected in series are formed between the object to be detected 100 and the first imaginary parallel plate 31, between the first and second imaginary parallel plates 31, 32, and between the second imaginary parallel plate 32 and the sensor electrode 22. Inside the first and second imaginary parallel plates 31, 32, the electric field generated by electrostatic induction cancels out the electric field E, so the electric potentials inside the first imaginary parallel plates 31, 32 become equipotential. Therefore, the thicknesses of the first and second imaginary parallel plates 31, 32 can be excluded from the length of the path of the electric field E.

[0050] Therefore, the length of the path of the electric field E can be considered to be the thickness of the insulator 12 interposed between the object to be detected 100 and the sensor electrode 22. As a result, the length of the path of the electric field E is the distance d between the object to be detected 100 and the first imaginary parallel plate 31. １ and the distance d between the first imaginary parallel plate 31 and the second imaginary parallel plate 32 ２ and the distance d between the second imaginary parallel plate 32 and the sensor electrode 22 ３ The total distance (d １ +d ２ +d ３ This total distance (d １ +d ２ +d ３ ) is the thickness T of the molded portion 11 ０ Since it is smaller than (d １ +d ２ +d ３ <T ０ ), the capacitance formed between the object to be detected 100 and the sensor electrode 22 can be increased. In this way, the effective dielectric constant of the molded portion 11 can be improved, so that the distance between the object to be detected 100 and the sensor electrode 22 (in this example, the thickness T of the molded portion 11) can be reduced. ０) can be suppressed. Furthermore, when the thicknesses of the molded portions 11 and 11C are the same, the present embodiment can improve the sensitivity compared to the comparative example.

[0051] Furthermore, if the filler 13 is a dielectric filler, the electric field E between the object to be detected 100 and the sensor electrode 22 polarizes the dielectric filler, weakening the electric field E, and the voltage between the object to be detected 100 and the sensor electrode 22 becomes smaller than a predetermined voltage. To increase this voltage to the predetermined voltage (i.e., to generate an electric field that equals the predetermined voltage), a circuit device (not shown) sends more charge to the sensor electrode 22, thereby increasing the capacitance formed between the object to be detected 100 and the sensor electrode 22. In this way, the effective dielectric constant of the molded portion 11 can be improved, thereby suppressing a decrease in sensitivity that accompanies an increase in the distance between the object to be detected 100 and the sensor electrode 22. Furthermore, when the molded portions 11 and 11C have the same thickness, the present embodiment can improve sensitivity compared to the comparative example.

[0052] It should be noted that the above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, the elements disclosed in the above embodiments are intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0053] For example, in the capacitance sensor 1A in the above embodiment, the sensor unit 20 is directly laminated on the housing 10 by insert molding, but this is not limiting. The sensor unit 20 may be laminated on the housing 10 via an adhesive layer 40. Fig. 5 is an enlarged cross-sectional view showing a modified example of the capacitance sensor 1A in this embodiment.

[0054] The capacitance sensor 1B in this modified example further includes an adhesive layer 40 interposed between the molded portion 11 and the sensor portion 20. Such capacitance sensor 1B can be manufactured by manufacturing the housing 10 and the sensor portion 20 separately and then adhering them together via the adhesive layer 40.

[0055] Even in such a modified example, as in the above embodiment, the filler 13 can suppress the decrease in sensitivity that occurs with an increase in the distance between the detection object 100 and the sensor electrode 22.

[0056] Furthermore, in the above embodiment, the housing 10 is exemplified as an "insulating portion" in the aspect of the present invention. Such a housing 10 can be suitably used in, but is not limited to, electronic devices such as the touch screen, track pad, switch, or control panel described above. Meanwhile, the "insulating portion" in the aspect of the present invention may be an insulating member other than the housing 10. For example, the insulating member may be a flexible insulating sheet member. Because such a sheet member is easily bendable, it can be deformed to fit the outer shape of the component to which the capacitance sensors 1A and 1B are to be attached. Although not particularly limited, such a sheet member can be suitably used in a grip sensor or the like by arranging it so as to fit the curved surface of the steering wheel rim.

[0057] Furthermore, although not particularly limited, the sensor unit 20 may have a shield layer formed on the front or back surface of the substrate 21 to shield noise from the sensor electrode 22. Furthermore, the substrate 21 may be omitted from the sensor unit 20.

[0058] DESCRIPTION OF SYMBOLS 1A, 1B... Capacitive sensor 10... Housing (insulating part) 11... Molded part 11a... Contact surface 11b... Inner surface 12... Insulator 13... Filler 20... Sensor part 21... Substrate 22... Sensor electrode 23... Lead wiring 30... Parallel plate capacitor 31... First imaginary parallel plate 32... Second imaginary parallel plate 40... Adhesive layer 100... Object to be detected

Claims

1. A capacitance sensor comprising: a sensor section including a sensor electrode that forms capacitance between itself and an object to be detected; and an insulating section interposed between the object to be detected and the sensor electrode, wherein the insulating section includes an insulator made of an insulating material having electrical insulating properties, and a conductive filler or a dielectric filler dispersed in the insulator.

2. A capacitance sensor according to claim 1, wherein the insulating portion includes the conductive filler, and the electrical resistivity of the conductive filler is lower than the electrical resistivity of the insulating material.

3. A capacitance sensor according to claim 2, wherein the conductive filler is made of carbon or a metal material.

4. A capacitance sensor according to claim 1, wherein the insulating portion includes the dielectric filler, and the dielectric constant of the dielectric filler is higher than the dielectric constant of the insulating material.

5. A capacitance sensor according to claim 4, wherein the dielectric filler has a relative dielectric constant of 100 or more.

6. A capacitance sensor according to claim 4 or 5, wherein the dielectric filler is made of a metal oxide.

7. A capacitance sensor according to any one of claims 1 to 6, wherein the insulating section is laminated directly on the sensor section.

8. A capacitance sensor according to any one of claims 1 to 6, further comprising an adhesive layer interposed between the insulating portion and the sensor portion.

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