Piezoelectric element and wearable device

Abstract

To provide a piezoelectric element with excellent durability, as the electrodes do not break due to expansion and contraction of a piezoelectric layer.SOLUTION: A piezoelectric element has a pair of electrodes and a piezoelectric layer located between the pair of electrodes, and the electrode is a liquid metal film or a porous substrate impregnated with liquid metal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a piezoelectric element and a wearable device. [Background technology]

[0002] There is a so-called haptics technology (touch sensation technology) that provides a user with skin sensation feedback by applying force, vibration, movement, etc. In the haptics technology, the tactile sensation is fed back via a wearable device having an actuator.

[0003] As an actuator, for example, one that includes a sheet-shaped dielectric elastomer layer and electrodes provided on both sides of the layer is known (Patent Documents 1 and 2). When a voltage is applied to such an actuator via the electrodes, the dielectric elastomer layer expands and contracts due to the inverse piezoelectric effect. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-226258 A [Patent Document 2] JP 2020-57340 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional piezoelectric elements such as actuators, stress is applied to the electrodes when a piezoelectric layer such as a dielectric elastomer layer expands and contracts, and if the expansion and contraction is repeated, or if the expansion and contraction is large, even a single expansion and contraction may cause the electrode layer to break. SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a piezoelectric element that is excellent in durability and in which breakage of electrodes due to expansion and contraction of the piezoelectric layer does not occur. [Means for solving the problem]

[0006] The present invention has the following aspects. <1> A pair of electrodes and a piezoelectric layer located between the pair of electrodes, A piezoelectric element, wherein the electrode is a film of liquid metal or a porous substrate impregnated with liquid metal. <2> Further, an insulating layer is provided on a surface of at least one of the pair of electrodes opposite to the piezoelectric layer side. <1> The piezoelectric element according to claim 1 . <3> The piezoelectric layer is a resin molded body containing a cured product of a curable resin. <1> or <2> The piezoelectric element according to claim 1 . <4> the piezoelectric layer is a resin molded body having a base material which is a cured product of a curable resin, and one or more dielectric particle groups which are located in the base material and extend in any direction; the dielectric particle group is composed of two or more dielectric particles oriented in the arbitrary direction, the dielectric particle group has a region a in which the dielectric particles are spaced apart from each other in the arbitrary direction, The pair of electrodes face each other in an orientation direction of the dielectric particles in the dielectric particle group. <1> ~ <3> 13. The piezoelectric element according to claim 12 . <5> <1> ~ <4> A wearable device having the piezoelectric element according to any one of claims 1 to 5. <6> On a flexible substrate, <1> ~ <4> A wearable device comprising: a piezoelectric element according to any one of claims 1 to 5; a driver IC; a gyro sensor; an acceleration sensor; and a storage battery that serves as a power source for these sensors. Effect of the Invention

[0007] According to the present invention, it is possible to provide a piezoelectric element having excellent durability in which breakage of the electrode layer due to expansion and contraction of the piezoelectric layer does not occur. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view of a piezoelectric element according to an embodiment. [Diagram 2] 2 is a cross-sectional view of the piezoelectric element shown in FIG. 1 taken along line II-II. [Diagram 3] FIG. 2 is a perspective view of a resin molded body according to one embodiment. [Figure 4] 4 is a side view of a dielectric particle group in the resin molding shown in FIG. 3. [Diagram 5] 4 is a cross-sectional view showing an example of an apparatus for producing the resin molded body shown in FIG. [Figure 6] FIG. 2 is a cross-sectional view of a piezoelectric element according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In this specification and claims, the use of "to" indicating a range of numerical values ​​means that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0010] (Piezoelectric element) The piezoelectric element of the present invention has a pair of electrodes and a piezoelectric layer located between the pair of electrodes. Examples of the piezoelectric element include an actuator, a vibrator, a speaker, and a sensor. Hereinafter, one embodiment of the piezoelectric element of the present invention will be described using an actuator 10 shown in FIGS. 1 and 2 as an example.

[0011] As shown in Figures 1 and 2, the actuator 10 of this embodiment has a pair of electrodes 11, a piezoelectric layer 12 located between the pair of electrodes 11 and in contact with the electrodes 11, and an insulating layer 13 located in contact with the electrode 11 on the surface of each of the pair of electrodes 11 opposite the piezoelectric layer 12 side. Incidentally, the insulating layer 13 is not necessarily essential, and the insulating layer 13 may not be provided. The insulating layer 13 may be provided on only one surface of the pair of electrodes 11.

[0012] In this embodiment, the electrode 11 partially covers the surface of the piezoelectric layer 12 in a plan view, that is, in an XZ plane view seen from the thickness direction (Y direction) of the piezoelectric layer 12. The electrode 11 is circular in a plan view. The positions of the pair of electrodes 11 are the same in a plan view. The piezoelectric layer 12 and the insulating layer 13 are each rectangular in a plan view. Between the piezoelectric layer 12 and the insulating layer 13, wiring 14 is provided together with the electrode 11. The wiring 14 extends from the electrode 11 to the outer edge of the piezoelectric layer 12 along an arbitrary direction perpendicular to the Y direction (the X direction in FIG. 1). The wiring 14 provided on one surface of the piezoelectric layer 12 and the wiring 14 provided on the other surface extend in opposite directions (-X direction, +X direction). These wirings 14 are connected to a power source (not shown) via other wiring 15, so that a voltage can be applied between the electrodes 11. The surface of the piezoelectric layer 12 that is not covered with the electrodes 11 or the wiring 14 is in contact with the insulating layer 13 .

[0013] <Electrode> The electrode 11 may be a membrane of liquid metal or a porous substrate impregnated with liquid metal. Conventionally, solid electrodes have been used for piezoelectric elements such as actuators, and there is a risk of breakage due to expansion and contraction of the piezoelectric layer 12. Since the electrode 11 is a film of liquid metal or a porous substrate impregnated with liquid metal, it follows the expansion and contraction of the piezoelectric layer 12 and does not break.

[0014] The liquid metal may be either a pure metal or an alloy, so long as it is in a liquid state at the temperature during use of the actuator 10. The temperature during use of the actuator 10 is, for example, 15 to 60°C. The melting point of the liquid metal is preferably less than 60° C., more preferably less than 30° C., and even more preferably less than 15° C. If the melting point is less than 65° C., it can be easily melted with low energy. The boiling point of the liquid metal is preferably above 3000° C., more preferably above 2500° C., and even more preferably above 2000° C. If the boiling point is above 3000° C., it is easy to melt with low energy. The boiling point is a value at 101.3 kPa.

[0015] Examples of the liquid metal include a eutectic alloy of gallium and indium, and a eutectic alloy of gallium, indium, and tin (registered trademark: Galinstan). As the liquid metal, a eutectic alloy of gallium and indium is preferable because of its excellent safety and high electrical conductivity.

[0016] Examples of the porous substrate include fibrous substrates such as woven fabric, nonwoven fabric, knitted fabric, etc. Examples of the fibers constituting the fibrous substrate include conductive copper fibers and nylon fibers. As the porous substrate, a fibrous substrate made of nylon fibers is preferable.

[0017] The size of the electrode 11 is not particularly limited and is determined appropriately taking into consideration the application and the like. The thickness of electrode 11 is preferably 0.01 to 100 μm, and more preferably 0.1 to 50 μm. If the thickness of electrode 11 is equal to or more than the lower limit, it is superior in terms of suppressing the temperature rise per unit volume, and if it is equal to or less than the upper limit, it is superior in terms of reducing the film thickness of the entire device. The thickness of the electrode 11 is measured by a laser thickness gauge with no voltage applied.

[0018] <Wiring> Since the wiring 14 is provided between the piezoelectric layer 12 and the insulating layer 13, similar to the electrode 11, it is preferably a liquid metal film or a porous substrate impregnated with liquid metal. The width of the wiring 14 is, for example, 0.1 to 10 mm. The other wiring 15 is not particularly limited, and known wiring can be used.

[0019] <Piezoelectric layer> The piezoelectric layer 12 is a layer made of a piezoelectric material. The piezoelectric material is not particularly limited and is appropriately determined taking into consideration the application, etc. Examples of the piezoelectric body include dielectric elastomers, such as urethane elastomers, silicone elastomers, acrylic elastomers, polyether elastomers, and crosslinked polyrotaxanes.

[0020] From the viewpoint of preventing plastic deformation of the resin, a resin molded body containing a cured resin is preferable as the piezoelectric layer 12. The resin molded body may consist of only the cured resin, or may further contain components other than the cured resin (for example, a derivative particle group described later).

[0021] The term "cured resin" is a concept that excludes fluids (liquids, slurries, and sols) and is in the form of a solid or gel. The cured resin is typically a cured product of a curable resin. The type of the curable resin can be appropriately determined in consideration of the application of the piezoelectric element. Examples of the curable resin include energy ray curable resins such as thermosetting resins and photocurable resins. Examples of the thermosetting resin include silicone resins, polyurethanes, thermosetting polyimides, phenolic resins, unsaturated polyesters, etc. Examples of the photocurable resin include acrylic resins, epoxy resins, etc.

[0022] As the resin molded body, the following resin molded body A is preferable because it can increase the amount of displacement when a voltage is applied and can transmit a larger stimulus. Resin molding A: A resin molding having a base material which is a cured product of a curable resin, and one or more dielectric particle groups located in the base material and extending in an arbitrary direction, the dielectric particle group consisting of two or more dielectric particles oriented in the arbitrary direction, and the dielectric particle group having a region a where the dielectric particles are spaced apart from each other in the arbitrary direction. When the piezoelectric layer 12 is a resin molded body A, the pair of electrodes 11 face each other in the orientation direction of the dielectric particles in the dielectric particle group. That is, the resin molded body A is disposed so that the orientation direction of the dielectric particles is the thickness direction (Y direction) of the piezoelectric layer 12. An embodiment of the resin molded body A will be described below.

[0023] 3 has a base material 110 and one or more dielectric particle groups 120 located within the base material 110. The resin molded body 12A is a composition having the base material 110 and the dielectric particle groups 120. In this embodiment, the resin molded body 12A is a rectangular flat plate in a plan view. The dielectric particle group 120 extends in the thickness direction (Y direction) of the resin molded body 12A.

[0024] The base material 110 is a hardened product of a hardening resin. The curable resin is as described above. Of the above curable resins, from the viewpoint of reducing the viscosity of the dispersion liquid used in the manufacturing method described below and making it easier to orient the dielectric particles, the resin constituting the base material 110 is preferably a thermosetting resin, and more preferably a silicone resin.

[0025] The flexural modulus of the base material 110 is preferably 0.1 to 100,000 MPa, more preferably 1.0 to 10,000 MPa, and even more preferably 10 to 2,000 MPa. When the flexural modulus is equal to or greater than the lower limit, the mechanical strength can be further increased. When the flexural modulus is equal to or less than the upper limit, the amount of displacement of the resin molded body 12A can be further increased.

[0026] The dielectric particle group 120 includes two or more dielectric particles oriented in the Y direction. The dielectric particle group 120 has, for example, a cylindrical or polygonal columnar shape extending in the Y direction. Any one of the dielectric particle groups 120 and another adjacent one of the dielectric particle groups 120 are spaced apart from each other in the X direction and the Z direction (i.e., the planar direction). That is, the dielectric particle groups 120 are spaced apart from each other in the directions (X direction, Z direction) perpendicular to the orientation direction (Y direction) of the dielectric particles. In the dielectric particle group 120 of FIG. 4, the dielectric particles 122 are oriented in the Y direction and form a group of columns extending in the Y direction. The orientation refers to a state in which the distribution of the dipole moment directions is biased in a certain direction from a random state. In this embodiment, the dipole moment directions of the dielectric particles 122 are biased in the Y direction.

[0027] The dielectric particles 122 have insulating properties. From the viewpoint of more easily orienting the dielectric particles 122 in the manufacturing method described below, it is preferable that the dielectric particles 122 have magnetic properties. Examples of the dielectric particles 122 include particles of an insulating magnetic material, particles of an insulating material such as ceramics, particles of an insulating material coated with an insulating magnetic material, etc. Examples of the insulating magnetic material include insulating ferrite (Ni-Zn-Cu ferrite), etc.

[0028] The average particle diameter of the dielectric particles 122 is, for example, preferably 10 to 100 μm, more preferably 10 to 80 μm, and even more preferably 10 to 50 μm. When the average particle diameter of the dielectric particles 122 is equal to or greater than the above lower limit, the orientation can be further improved. When the average particle diameter of the dielectric particles 122 is equal to or less than the above upper limit, the packing density of the dielectric particles 122 in the dielectric particle group 120 can be further increased. The packing density of the dielectric particles 122 in the dielectric particle group 120 is the content of the dielectric particles 122 in the dielectric particle group 120 on a volume basis. The average particle size of the dielectric particles 122 is a weight average particle size determined by a particle size distribution meter (laser diffraction / scattering method).

[0029] The aspect ratio of the dielectric particles 122 is preferably 1.0 to 200, more preferably 1.0 to 100, and even more preferably 1.0 to 10. When the aspect ratio of the dielectric particles 122 is equal to or greater than the above lower limit, the orientation can be further improved. When the aspect ratio of the dielectric particles 122 is equal to or less than the above upper limit, the packing density of the dielectric particles 122 in the dielectric particle group 120 can be further increased. The aspect ratio is a value determined by a microscope (static image analysis method).

[0030] 4, the dielectric particle group 120 has one or more regions a in which the dielectric particles 122 are spaced apart from each other in the Y direction (i.e., the orientation direction). In this embodiment, the dielectric particle group 120 has two regions a on a virtual line P extending in the Y direction. The number of regions a of the dielectric particle group 120 may be one or more, preferably two or more, and more preferably three or more. The upper limit of the number of regions a is, for example, five.

[0031] The length L of the dielectric particle group 120 in the Y direction is appropriately determined taking into consideration the length (thickness) of the base material 110 in the Y direction, the intended use, etc. The length L is, for example, preferably 1 to 100% of the length of the base material 110 in the Y direction, more preferably 10 to 75%, and even more preferably 20 to 50%. The length L is the maximum length in the Y direction. The length L is a value measured by X-ray CT. Both ends of the dielectric particle group 120 in the Y direction may or may not be exposed on the surface of the base material 110. When the resin molded body 12A is used as a piezoelectric layer, from the viewpoint of preventing electrical conduction with the electrode layer, it is preferable that both ends of the dielectric particle group 120 in the Y direction are not exposed from the base material 110 (both ends are covered by the base material 110). In other words, it is preferable that the length L is less than 100% of the length of the base material 110 in the Y direction. The length L can be adjusted by combining the distance between the magnetic pins of the magnetic field generating device used in the curing step described below, the content of the dielectric particles in the dispersion, the viscosity of the dispersion, and the like.

[0032] When a straight imaginary line P is drawn in the orientation direction of the dielectric particles in the dielectric particle group 120, the length of the region a on the imaginary line P (i.e., the distance between the dielectric particles 122) Da is preferably 1 to 250 μm, more preferably 1 to 100 μm, and even more preferably 1 to 20 μm. When the length Da is equal to or greater than the above lower limit, the amount of displacement can be increased. When the length Da is equal to or less than the above upper limit, the packing density of the dielectric particles 122 in the dielectric particle group 120 can be increased. The length Da is a value measured by X-ray CT. The length Da can be adjusted by combining the distance between the magnetic pins of the magnetic field generating device used in the curing step described below, the content of the dielectric particles in the dispersion, the viscosity of the dispersion, and the like.

[0033] The ratio (tDa / L ratio) of the total tDa of the lengths Da on the straight virtual line P to the length L of the dielectric particle group 120 is preferably 0.05 to 0.9, more preferably 0.05 to 0.6, and even more preferably 0.1 to 0.3. When the tDa / L ratio is equal to or greater than the lower limit, the amount of displacement can be increased. When the tDa / L ratio is equal to or less than the upper limit, the packing density of the dielectric particles 122 in the dielectric particle group 120 can be increased. The tDa / L ratio is obtained by dividing the tDa on the virtual line P by the length L. In the tDa / L ratio, virtual lines P are drawn at different positions in the X direction or Z direction for one dielectric particle group 120, tDa on each virtual line P is obtained, and the average value is used as tDa. The number of virtual lines P is, for example, four. For example, when measuring Da, two virtual lines P are drawn at different positions when viewed from the X direction, and two virtual lines P are drawn at different positions when viewed from the Z direction.

[0034] The ratio (by number) of the dielectric particles 120 having a tDa / L ratio in the above range (specific dielectric particles) is preferably 50% or more, more preferably 75% or more, and even more preferably 100%. That is, the specific dielectric particles 120 may be a part or the whole.

[0035] The ratio (β / α ratio) of the area β occupied by the dielectric particles 122 in the ZY plane view (i.e., viewed from the X direction) to the area α occupied by the dielectric particles 122 in the XZ plane view (i.e., viewed from the Y direction) is preferably more than 1.2 and not more than 500, more preferably more than 1.2 and not more than 250, and even more preferably more than 1.2 and not more than 100. When the β / α ratio is equal to or more than the lower limit, the degree of orientation of the dielectric particles 122 in the Y direction is higher. The ratio (γ / α ratio) of the area γ occupied by the dielectric particles 122 in the XY plane view (i.e., viewed from the Z direction) to the area α is preferably more than 1.2 and not more than 500, more preferably more than 1.2 and not more than 250, and even more preferably more than 1.2 and not more than 100. When the γ / α ratio is equal to or more than the lower limit, the degree of orientation of the dielectric particles 122 in the Y direction is higher. The areas α, β, and γ are values ​​measured by X-ray CT observation. The measurement range is, for example, 1.2 to 17.7 mm 2Let the areas α, β, and γ be 1 mm 2 Calculate as the area per unit.

[0036] The volume ratio of the dielectric particle group 120 to the resin molded body 12A is, for example, preferably 0.01 to 50 volume %, more preferably 0.05 to 20 volume %, and even more preferably 0.1 to 10 volume %. When the volume ratio of the dielectric particle group 120 to the resin molded body 12A is equal to or greater than the above lower limit, the piezoelectric performance can be further improved. When the volume ratio of the dielectric particle group 120 to the resin molded body 12A is equal to or less than the above upper limit, short circuits between the dielectric particle groups 120 can be more reliably prevented. The volume of the dielectric particle group 120 is obtained by using a volume rendering method for the X-ray CT image.

[0037] The content (filling density) of the dielectric particles 122 in the dielectric particle group 120 on a volume basis is, for example, preferably 1 to 75 volume %, more preferably 1 to 50 volume %, and even more preferably 1 to 25 volume %. When the content of the dielectric particles 122 in the dielectric particle group 120 is equal to or greater than the above lower limit, the piezoelectric performance can be further improved. When the content of the dielectric particles 122 in the dielectric particle group 120 is equal to or less than the above upper limit, the length Da is increased, the tDa / L ratio is increased, and the displacement amount is further increased. The volumes of the dielectric particle group 120 and the dielectric particles 122 are obtained by using a volume rendering method on the X-ray CT image.

[0038] The number of the dielectric particles 120 is 1 to 100 pieces / mm when viewed from the XZ plane. 2 is preferable, and 1 to 50 pieces / mm 2 More preferably, 1 to 25 pieces / mm 2 is more preferable. When the number of the dielectric particle groups 120 is equal to or greater than the lower limit, the piezoelectric performance can be further improved. The more the dielectric particles 122 are, the more likely it is that the dielectric particles 122 are filled up to the ends in the XZ plane view, and the dielectric particles are exposed to the outside of the piezoelectric layer, resulting in electrical conduction. Therefore, when the number of the dielectric particle groups 120 is equal to or less than the upper limit, electrical conduction can be more reliably prevented.

[0039] It is preferable that no dielectric particles 122 are present in the region b between any of the dielectric particle groups 120 and other dielectric particle groups 120 adjacent to the arbitrary dielectric particle group 120. When the dielectric particles 122 are present in the region b, the content of the dielectric particles 122 in the region b is preferably less than 1 volume %, more preferably less than 0.5 volume %, and even more preferably less than 0.1 volume %. That is, the content of the dielectric particles 122 in the region b is preferably 0 volume % or more and less than 1 volume %, more preferably 0 volume % or more and less than 0.5 volume %, more preferably 0 volume % or more and less than 0.1 volume %, and particularly preferably 0 mass %. When the content of the dielectric particles 122 in the region b is equal to or less than the above upper limit, the leakage current suppression effect can be further enhanced. The "leak current suppression effect" is an effect of suppressing a drop in applied voltage.

[0040] In the region b, the separation distance Db between any one of the dielectric particle groups 120 and another one of the dielectric particle groups 120 adjacent thereto can be appropriately determined in consideration of the use of the resin molded body 12A, etc. The separation distance Db is, for example, preferably 10 to 500 μm, more preferably 10 to 250 μm, and even more preferably 10 to 100 μm. When the separation distance Db is equal to or greater than the above lower limit, electrical conduction between the dielectric particle groups 120 can be more reliably prevented. When the separation distance Db is equal to or less than the above upper limit, the packing density of the dielectric particles 122 in the dielectric particle groups 120 can be more increased. The separation distance Db is the distance between the closest outer edges of the dielectric particle groups 120. The separation distance Db can be adjusted by a combination of the separation distance of the magnetic pins of the magnetic field generating device used in the curing step described later, the content of the dielectric particles in the dispersion liquid, the viscosity of the dispersion liquid, and the like. The distance Db is a value measured by X-ray CT.

[0041] In the above embodiment, the resin molded body A is a flat plate having a rectangular shape in plan view, but the shape of the resin molded body A can be appropriately determined in consideration of the application. The shape of the resin molded body A may be, for example, a flat plate having a polygonal shape other than a rectangular shape in plan view, a flat plate having a circular shape in plan view, a cylinder, a polygonal prism, or a polyhedron.

[0042] The above-mentioned resin molding A can be manufactured, for example, by a manufacturing method including a process of curing an uncured resin while orienting the dielectric particles in any direction in a dispersion liquid in which two or more dielectric particles are dispersed, and then curing the uncured resin (curing process). Hereinafter, one embodiment of the method for producing the resin molded body A will be described.

[0043] The method for producing the resin molded body A of this embodiment includes a filling step, a curing step, and a demolding step. An example of a manufacturing apparatus used in the manufacturing method of this embodiment will be described. The manufacturing apparatus 200 in FIG. 5 includes a pair of magnetic field generating units 210 facing each other in the Y direction, a pair of molds 220 facing each other in the Y direction, and a spacer 230. The pair of molds 220 are positioned between the pair of magnetic field generating units 210. The spacer 230 is positioned between the pair of molds 220, circumferentially arranged in a plan view, and forms a rectangular space 202 therein. The space 202 is a space surrounded by the pair of molds 220 and the spacer 230. In this embodiment, an insulating sheet 240 is positioned on the inner surface of the mold 220 (the surface facing the space 202). The magnetic field generating unit 210 has a magnetic pin 212 .

[0044] For example, a resin frame can be used as the spacer 230. The thickness of the spacer 230 is appropriately determined depending on the desired thickness of the resin molded body.

[0045] An example of the insulating sheet 240 is a polyimide sheet. The thickness of the insulating sheet 240 is not particularly limited.

[0046] In the filling step, the dispersion liquid 250 is poured into the space 202. At this time, it is preferable that the space 202 is filled with the dispersion liquid 250 to be liquid-tight.

[0047] The dispersion 250 has two or more dielectric particles dispersed in an uncured resin. The content of the dielectric particles in the dispersion liquid 250 is preferably 1 to 30 mass %, more preferably 1 to 20 mass %, and even more preferably 1 to 10 mass %, relative to the total mass of the dispersion liquid 250. When the content of the dielectric particles in the dispersion liquid 250 is equal to or more than the above lower limit, the number of regions a in the dielectric particle group and the length Da of the region a can be made more appropriate. When the content of the dielectric particles in the dispersion liquid 250 is equal to or more than the above lower limit, the dielectric particle groups 120 in the regions b can be spaced apart at a more appropriate distance (separation distance Db) in the curing step.

[0048] The content of the uncured resin in the dispersion 250 is preferably 10 to 100 mass %, more preferably 20 to 100 mass %, and even more preferably 50 to 100 mass %, relative to the total mass of the dispersion 250. When the content of the uncured resin in the dispersion 250 is equal to or more than the above lower limit, the viscosity of the dispersion 250 can be increased.

[0049] The dispersion liquid 250 may contain components (optional components) other than the uncured resin and the dielectric particles. Examples of the optional components include pigments, polymerization initiators, polymerization accelerators, etc. The type and content of the optional components in the dispersion liquid 250 can be appropriately determined depending on the type of uncured resin, the type of the optional components, etc.

[0050] The viscosity of the dispersion liquid 250 is, for example, preferably 1000 to 20000 mP·s, and more preferably 1000 to 10000 mP·s. When the viscosity is equal to or greater than the lower limit, the dispersion liquid 250 can be handled more easily. When the viscosity is equal to or less than the upper limit, the dispersion liquid 250 quickly spreads throughout the space 202 when filled therein, and the dielectric particle group 120 can be more easily formed in the orientation operation described below. The viscosity of the dispersion 250 is a value measured at 25° C. using a Brookfield viscometer. The viscosity of the dispersion 250 can be adjusted by combining the type of uncured resin, the temperature of the dispersion 250, and the like.

[0051] The dispersion liquid may be prepared in advance, or may be prepared (prepared) before the filling step.

[0052] After the filling step, a curing step is performed in which the dielectric particles in the dispersion are oriented (orientation operation) while the uncured resin is cured to form a base material (curing operation). After the filling step, a magnetic field is generated between the magnetic pins 212 of the opposing magnetic field generating units 210 (orientation operation). When the magnetic field is generated, the dielectric particles in the dispersion liquid in the space 202 are oriented in the Y direction, forming the dielectric particle group 120. The magnetic flux density in the orientation operation can be determined taking into consideration the type of dielectric particles, the desired thickness of the resin molded article, and the like. For example, it is preferably 0.01 to 10T, and more preferably 0.05 to 5T. The orientation time in the orientation operation (the time during which magnetic force is applied) can be determined taking into consideration the magnetic flux density, the type of dielectric particles, the desired thickness of the resin molded body, etc., and is, for example, preferably 1 to 30 minutes, more preferably 3 to 15 minutes.

[0053] While the orientation operation is being carried out, the uncured resin in the dispersion is cured to form a resin molded body (curing operation). The method for curing the uncured resin is determined according to the type of the uncured resin. For example, if the uncured resin is a thermosetting resin, the dispersion in the space 202 is heated to cure the uncured resin. The heating temperature can be appropriately determined according to the type of the uncured resin. If the uncured resin is a thermoplastic resin, the dispersion is cooled to cure the uncured resin (the above is the curing process).

[0054] In the demolding step, the resin molded body in which the uncured resin has been cured is removed from the manufacturing apparatus 200. In this manner, a resin molded body is obtained.

[0055] In the above embodiment, the orientation is performed by applying a magnetic field, but the present invention is not limited to this, and the dielectric particles may be oriented by other methods.

[0056] The size of the piezoelectric layer 12 is not particularly limited and is determined appropriately taking into consideration the application and the like. The size of the piezoelectric layer 12 is, for example, 10 to 100 mm in the X direction, 0.1 to 2.0 mm in the Y direction, and 10 to 100 mm in the Z direction. The size of the piezoelectric layer 12 is determined by measuring any 10 points by X-ray CT and averaging the measurements.

[0057] <Insulating layer> An example of the insulating layer 13 is a resin layer. The resin is not particularly limited as long as it has insulating properties, and examples include a cured product of a curable resin, a thermoplastic resin, and the like. Examples of the curable resin include the same as the curable resin in the resin molded body described above. Examples of the thermoplastic resin include polyvinyl chloride, and the like. "Having insulating properties" means having an insulation resistance of 1 to 100 TΩ·m.

[0058] The thickness of the insulating layer 13 is not particularly limited, and is appropriately determined taking into consideration the material of the insulating layer 13, the application of the actuator 10, and the like. When the insulating layer 13 is a resin layer and the actuator 10 is used in a wearable device, the insulating layer 13 has a thickness at its thinnest part of preferably 1 μm or more, more preferably 5 μm or more, and a thickness at its thickest part of preferably 200 μm or less, more preferably 100 μm or less. If the thickness at the thinnest part of the insulating layer 13 is equal to or more than the lower limit, insulation can be ensured, and if the thickness at the thickest part is equal to or less than the upper limit, deformation of the piezoelectric layer is not hindered.

[0059] The thickness of the entire actuator 10 is not particularly limited, and is determined appropriately taking into consideration the application of the actuator 10, etc. When the actuator 10 is used in a wearable device, the thickness of the actuator 10 is preferably, for example, 0.2 to 5 mm. If the thickness of the actuator 10 is equal to or greater than the lower limit, mechanical strength can be ensured, and if the thickness is equal to or less than the upper limit, the actuator 10 can be worn without a sense of discomfort.

[0060] <Manufacturing method> Examples of a method for manufacturing the actuator 10 include the following manufacturing method A and manufacturing method B. Manufacturing method A: A method of sequentially forming a liquid metal film (electrode 11 and wiring 14) and an insulating layer 13 on one surface of a piezoelectric layer 12, and then sequentially forming a liquid metal film (electrode 11 and wiring 14) and an insulating layer 13 on the other surface of the piezoelectric layer 12. Manufacturing method B: A method of successively forming a liquid metal film (electrodes 11 and wiring 14), a piezoelectric layer 12, a liquid metal film (electrodes 11 and wiring 14) and an insulating layer 13 on one surface of the insulating layer 13.

[0061] In both manufacturing methods A and B, each step can be performed on any substrate such as glass. For example, in manufacturing method A, the piezoelectric layer 12 is placed on the substrate, and a liquid metal film (electrodes 11 and wiring 14) and insulating layer 13 are successively formed thereon, and then the formed laminate (piezoelectric layer 12 / liquid metal film / insulating layer 13) is peeled off from the substrate and inverted, and placed again on the substrate, and the liquid metal film and insulating layer 13 are successively formed thereon.

[0062] When the piezoelectric layer 12 is the above-mentioned resin molded body A, the method for forming the resin molded body A is as described above. An example of a method for forming the piezoelectric layer 12 other than the resin molding A is a method in which a piezoelectric layer forming composition containing a material for forming the piezoelectric layer 12 (e.g., a dielectric elastomer or a curable resin) and, if necessary, a liquid medium is applied, and then dried and cured as necessary. The piezoelectric layer 12 may be an existing piezoelectric material.

[0063] An example of a method for forming a liquid metal film on the surface of piezoelectric layer 12 or insulating layer 13 in a pattern corresponding to electrodes 11 and wiring 14 is a method in which a mask pattern is placed on the surface of piezoelectric layer 12 or insulating layer 13 to cover areas on which a liquid metal film is not to be formed, and liquid metal is applied to areas of the surface that are not covered by the mask pattern. The mask pattern may be, for example, a prefabricated one that is placed on the surface of the piezoelectric layer 12 or the insulating layer 13, or may be formed by applying a mask material to the surface of the piezoelectric layer 12 or the insulating layer 13 and patterning it by a known patterning technique such as lithography. After applying the liquid metal, the mask pattern is peeled off before forming the insulating layer 13 or the piezoelectric layer 12. The liquid metal can be applied by a known method such as dispenser application.

[0064] An example of a method for forming the insulating layer 13 is to apply an insulating layer forming composition containing a material for forming the insulating layer 13 (e.g., a curable resin or a thermoplastic resin) and, if necessary, a liquid medium, and then dry and harden the composition if necessary. An existing resin film may be used as the insulating layer 13 .

[0065] In addition, in each of the above manufacturing methods A and B, an impregnated material in which a porous substrate is impregnated with liquid metal may be disposed on the surface of the piezoelectric layer 12 or the insulating layer 13, instead of a film of liquid metal. In this case, a porous substrate may be disposed on the surface of the piezoelectric layer 12 or the insulating layer 13, and the porous substrate may be impregnated with liquid metal to form an impregnated material, or a previously prepared impregnated material may be disposed on the surface of the piezoelectric layer 12 or the insulating layer 13.

[0066] <How to use> A method for using the actuator 10 will now be described. Electricity is supplied to the electrodes 11 via the wiring 15 and the wiring 14, and a voltage is applied between the electrodes 11. When a voltage is applied between the electrodes 11, the piezoelectric layer 12 expands and contracts in response to the applied voltage. Therefore, by using the actuator 10, it is possible to transmit a stimulus to the user.

[0067] The above describes an embodiment of the present invention. However, each configuration and combination thereof in the above embodiment is merely an example, and addition, omission, substitution, and other modifications of the configuration are possible without departing from the spirit of the present invention.

[0068] For example, the shapes of the electrodes, piezoelectric layer, insulating layer, and wiring are not limited to those shown in the drawings, and can be appropriately determined taking into consideration the application. The shape of the piezoelectric layer may be, for example, a flat plate having a polygonal shape other than a rectangle in plan view, a flat plate having a circular shape in plan view, a cylinder, a polygonal prism, or a polyhedron. The shape of the electrodes may be a polygonal shape in plan view. The electrodes may cover the entire surface of the piezoelectric layer, as shown in FIG.

[0069] The actuator 10A shown in Figure 6 has a pair of electrodes 11, a piezoelectric layer 12 located between the pair of electrodes 11 and in contact with the electrodes 11, and an insulating layer 13 located on the surface of each of the pair of electrodes 11 and in contact with the electrode 11. In actuator 10A, electrode 11 covers the entire surface of piezoelectric layer 12. Wiring 14 is not provided, and wiring 15 is connected directly to electrode 11.

[0070] The piezoelectric element of the present invention can be applied to, for example, a wearable device. Examples of wearable devices include smart wear, immersive game consoles (controllers, etc.), and VR devices (tactile reproduction gloves, etc.).

[0071] An example of a wearable device having the piezoelectric element of the present invention is one having, on a flexible substrate, the piezoelectric element of the present invention, a driver IC, a gyro sensor, an acceleration sensor, and a storage battery that serves as the power source for these sensors. Examples of the flexible substrate include fabrics such as woven fabrics, nonwoven fabrics, and textiles, and fibers such as artificial silk threads. The flexible substrate may be in the form of a glove, a sleeve, or the like. Such a wearable device can wirelessly recognize finger movements and provide tactile sensations. EXAMPLES

[0072] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0073] (Production Example 1) An actuator having the configuration shown in FIGS. 1 and 2 was fabricated in the following manner. 33.4 mg of dielectric particles were added to 2 g of thermosetting resin and stirred to prepare a dispersion liquid. This dispersion liquid was degassed at 9.3 Pa (preparation operation). The dispersion was filled into the space surrounded by the mold (52 mm × 76 mm) and the spacer (filling step), and the dispersion was heated (140°C, 5 minutes) while applying a magnetic force to harden it (orientation and hardening steps), to obtain a resin molded body (thickness 120 μm), which was used as the piezoelectric layer. A liquid metal, indium / gallium eutectic alloy, was applied in the form of a film (thickness 20 μm) on one surface of the obtained piezoelectric layer, followed by forming polymethylsiloxane (insulating layer, thickness 14 μm) using a spin coater. In the same manner as above, a liquid metal, indium / gallium eutectic alloy, was applied in the form of a film (20 μm) on the other surface of the piezoelectric layer, followed by the formation of polymethylsiloxane (insulating layer, 14 μm thick) using a spin coater to produce the actuator. When a voltage was applied between the electrodes of the obtained actuator, the piezoelectric layer repeatedly expanded and contracted.

[0074] (Production Example 2) 2 g of thermosetting resin was applied onto a glass plate (52 mm x 76 mm) using a spin coater and heated (110°C, 20 minutes) to form a piezoelectric layer (thickness 50 µm). A liquid metal, an indium / gallium eutectic alloy, was applied in the form of a film (thickness: 20 μm) on one surface of the obtained piezoelectric layer, and then polymethylsiloxane (insulating layer, thickness: 14 μm) was formed using a spin coater. In the same manner as above, a liquid metal, indium / gallium eutectic alloy, was applied in the form of a film (thickness 20 μm) on the other surface of the piezoelectric layer, followed by sequentially forming polymethylsiloxane (insulating layer, thickness 14 μm) using a spin coater to produce the actuator.

[0075] An actuator similar to the above was also produced by the following method. Polymethylsiloxane was applied onto a glass plate (52 mm x 76 mm) using a spin coater and heated (110°C, 20 minutes) to form an insulating layer (thickness 14 µm). An indium / gallium eutectic alloy, which is a liquid metal, was applied to the upper surface of the obtained insulating layer in the form of a film (thickness 20 μm). Next, 2 g of a thermosetting resin was applied to the upper surface with a spin coater and heated (110°C, 20 minutes) to form a piezoelectric layer (thickness 50 μm). Further, an indium / gallium eutectic alloy, which is a liquid metal, was applied to the upper surface in the form of a film (thickness 20 μm). Next, polymethylsiloxane (insulating layer, thickness 14 μm) was sequentially formed with a spin coater. [Explanation of symbols]

[0076] 10 Actuator (piezoelectric element) 11 electrodes 12 Piezoelectric layer 12A Resin molding 13 Insulating layer 14, 15 Wiring 110 Base material 120 Dielectric Particles 122 Dielectric particles 200 Manufacturing equipment 210 Magnetic field generating unit 212 Magnetic pin 220 Mold 230 Spacer 250 Dispersion a area

Claims

1. A pair of electrodes and a piezoelectric layer located between the pair of electrodes, A piezoelectric element, wherein the electrode is a film of liquid metal or a porous substrate impregnated with liquid metal.

2. The piezoelectric element according to claim 1 , further comprising an insulating layer on a surface of at least one of the pair of electrodes opposite to the piezoelectric layer.

3. The piezoelectric element according to claim 1 , wherein the piezoelectric layer is a resin molded body containing a cured product of a curable resin.

4. the piezoelectric layer is a resin molded body having a base material which is a cured product of a curable resin, and one or more dielectric particle groups which are located in the base material and extend in any direction; The dielectric particle group is composed of two or more dielectric particles oriented in the arbitrary direction, the dielectric particle group has a region a in which the dielectric particles are spaced apart from each other in the arbitrary direction, The piezoelectric element according to claim 1 , wherein the pair of electrodes faces each other in an orientation direction of the dielectric particles in the dielectric particle group.

5. A wearable device comprising the piezoelectric element according to any one of claims 1 to 4.

6. A wearable device comprising, on a flexible substrate, the piezoelectric element according to any one of claims 1 to 4, a driver IC, a gyro sensor, an acceleration sensor, and a storage battery as a power source for these sensors.

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