Driver unit and headphones

Abstract

Provided are a driver unit for headphones that includes a piezoelectric film having a molded curved part, and headphones. The driver unit can suppress deformation of the curved part of the piezoelectric film when the headphones are worn, and can suppress deterioration of sound quality. The driver unit comprises: a piezoelectric film which includes a piezoelectric layer composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both surfaces of the piezoelectric layer; and a perforated plate having at least one through-hole. The piezoelectric film has a curved part which is molded to protrude on one main surface side and to be recessed on the other main surface side. The perforated plate is stacked on the recessed surface side of the curved part of the piezoelectric film. The through-hole provides communication between a first air chamber, which is defined by the recessed surface of the piezoelectric film and the perforated plate, and the outside.

Description

Driver units and headphones

[0001] The present invention relates to a driver unit and a headphone using the same.

[0002] It has been proposed to use a piezoelectric film in which a piezoelectric layer is sandwiched between an electrode layer and a protective layer as a thin speaker.

[0003] For example, Patent Document 1 describes an electroacoustic converter film (piezoelectric film) that has a polymer composite piezoelectric body formed by dispersing piezoelectric particles in a viscoelastic matrix made of a polymer material that has viscoelasticity at room temperature, and a pair of electrodes laminated on both sides of the polymer composite piezoelectric body, and has one or more convex portions that are molded in a convex shape so as to protrude from one of the main surfaces.

[0004] International Publication No. 2016 / 017632

[0005] The present inventors have considered using a piezoelectric film in a headphone driver unit. When used as a headphone driver unit, it is necessary for the unit to be small, lightweight, and generate high-quality sound over a wide frequency range. Therefore, the present inventors have considered that when using a piezoelectric film in a headphone driver unit, it would be appropriate to use the piezoelectric film itself as a diaphragm, and to use a piezoelectric film having one or more convex portions (curved portions) formed in a convex shape so as to protrude from one main surface, as a configuration that enables a wide frequency range with a diaphragm (piezoelectric film) that is large enough to be mounted on headphones.

[0006] In headphones, it is known that sound pressure in the low frequency range can be improved by making the internal air chamber (inside the housing) approximately sealed by tightly fitting the ear pads to the ear, so-called sealed or semi-sealed type headphones.

[0007] However, according to the inventor's research, in a configuration in which headphones are incorporated with a driver unit having a piezoelectric film with a curved portion formed in a convex shape so as to protrude from one of the main surfaces, when the ear pads are brought into close contact with the ears to make the housing approximately sealed, high-frequency resonances and the like occur within the housing, causing variations in the frequency characteristics in the high-frequency range (also known as undulations, peaks and dips in the frequency characteristics), and making it impossible to obtain flat frequency characteristics.

[0008] The object of the present invention is to solve the problems of the conventional technology, and to provide a driver unit and headphones that can improve frequency characteristics when the driver unit is applied to headphones and includes a piezoelectric film with a molded curved portion.

[0009] In order to solve the above-mentioned problems, the present invention has the following configuration. [1] A driver unit comprising: a piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer; and a plate-shaped perforated plate having at least one through-hole, wherein the piezoelectric film has a curved portion that protrudes from one main surface side and is recessed toward the other main surface side, and the perforated plate is laminated on the concave side of the curved portion of the piezoelectric film, and the through-hole connects a first air chamber defined by the concave surface of the piezoelectric film and the perforated plate to the outside. [2] The driver unit according to [1], wherein the ratio of the total area of ​​the through-holes to the area of ​​the curved portion of the piezoelectric film in a planar view is 3% to 70%. [3] The driver unit according to [1] or [2], wherein the perforated plate has a sound-absorbing layer made of a porous material that is arranged on the surface opposite the piezoelectric film so as to cover the through-hole. [4] A driver unit according to any one of [1] to [3], wherein the boundary line of the curved portion of the piezoelectric film has a circular shape. [5] A driver unit according to any one of [1] to [4], which has a series resistor connected between the electrode layer of the piezoelectric film and a signal source that drives the piezoelectric film. [6] A headphone comprising: the driver unit according to any one of [1] to [5], a housing having an opening and accommodating the driver unit, and an ear pad arranged on the opening side of the housing. [7] The headphone according to [6], wherein the second air chamber defined by the driver unit and the housing is in communication with the outside. [8] The headphone according to [6] or [7], wherein the housing is arranged on the concave side of the piezoelectric film of the driver unit. [9] The headphones described in [6], which have a protector ring placed between the driver unit and the ear pad in contact with the ear pad, the protector ring has an opening that penetrates in a direction perpendicular to the surface that contacts the ear pad, the protector ring contacts an area of ​​30% or more of the total area of ​​the ear pad when viewed in the direction perpendicular to the surface that contacts the ear pad, and the shortest distance between the protector ring and the piezoelectric film of the driver unit is 0.3 mm or more.

[0010] According to the present invention, it is possible to provide a driver unit and headphones that can improve frequency characteristics when the driver unit is applied to headphones and includes a piezoelectric film having a molded curved portion.

[0011] 20 is a cross-sectional view conceptually showing an example of headphones of the present invention having a driver unit of the present invention. FIG. 21 is an exploded perspective view of the driver unit shown in FIG. 1. FIG. 22 is a perspective view of a piezoelectric film included in the driver unit shown in FIG. 1. FIG. 23 is a cross-sectional view of the piezoelectric film of FIG. 3. FIG. 24 is a plan view of the piezoelectric film of FIG. 3. FIG. 25 is a plan view conceptually showing another example of a piezoelectric film. FIG. 26 is a diagram for explaining the operation of the driver unit of the present invention. FIG. 27 is a diagram conceptually showing another example of headphones of the present invention having a driver unit of the present invention. FIG. 28 is a cross-sectional view conceptually showing an example of the configuration of a piezoelectric film. FIG. 29 is a conceptual view for explaining an example of a method for manufacturing a piezoelectric film. FIG. 29 is a conceptual view for explaining an example of a method for manufacturing a piezoelectric film. FIG. 29 is a block diagram conceptually showing an example of a circuit for driving a driver unit. FIG. 20 is a graph showing the relationship between frequency and sound pressure. FIG. 21 is a graph showing the relationship between frequency and sound pressure. FIG. 22 is a graph showing the relationship between frequency and sound pressure. FIG. 23 is a conceptual view for explaining the operation of headphones having a driver unit of a comparative example. FIG. 24 is a diagram conceptually showing another example of a piezoelectric film included in a driver unit of the present invention. FIG. 25 is a partially enlarged cross-sectional view of FIG. 20. FIG. 1 is a cross-sectional view conceptually showing another example of headphones of the present invention having a driver unit of the present invention. FIG. 2 is a view conceptually showing an example of headphones of the present invention pressed against an artificial ear. FIG. 3 is a view conceptually showing another example of headphones of the present invention pressed against an artificial ear. FIG. 4 is a view for explaining the area ratio of contact between the protector ring and the ear pad. FIG. 5 is a cross-sectional view conceptually showing another example of headphones of the present invention having a driver unit of the present invention. FIG. 6 is a graph showing the relationship between frequency and sound pressure. FIG. 7 is a graph showing the relationship between frequency and sound pressure. FIG. 8 is a graph showing the relationship between frequency and sound pressure.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A driver unit and a headphone according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0013] The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0014] [Driver unit and headphones] The driver unit of the present invention is a driver unit comprising: a piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer; and a perforated plate having at least one through-hole, wherein the piezoelectric film has a curved portion that is formed to protrude on one main surface side and recess on the other main surface side, the perforated plate is laminated on the concave side of the curved portion of the piezoelectric film, and the through-hole connects a first air chamber defined by the concave surface of the piezoelectric film and the perforated plate to the outside.

[0015] The headphones of the present invention are headphones having the above-mentioned driver unit, a housing that houses the driver unit in an opening, and ear pads that are placed on the side of the driver unit opposite the housing.

[0016] <Driver Unit> FIG. 1 is a cross-sectional view conceptually showing an example of a headphone of the present invention having an example of a driver unit of the present invention.

[0017] The headphones 200 shown in FIG. 1 include a driver unit 100 , a housing 202 , ear pads 204 , and an ear pad locking member 206 .

[0018] Fig. 2 shows an exploded perspective view of the driver unit 100. As shown in Figs. 1 and 2, the driver unit 100 has a holding member 106, a piezoelectric film 10, a perforated plate 102, a holding member 108, a porous material 104, and a fastening member 110.

[0019] The piezoelectric film 10 is a piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer, and has a curved portion 10a that is molded to protrude from one main surface and recess into the other main surface. Details of each layer that makes up the piezoelectric film 10 will be described later.

[0020] Fig. 3 shows a perspective view of the piezoelectric film 10. Fig. 4 shows a cross-sectional view of the piezoelectric film 10. Fig. 5 shows a plan view of the piezoelectric film 10. The plan view is a view seen from a direction perpendicular to the main surface of the flat portion of the piezoelectric film 10 (a region where the curved portion 10a is not formed), that is, a view seen from the direction of arrow b in Fig. 4. In the present invention, the main surface refers to the largest surface of the sheet-like material.

[0021] 3 to 5, the piezoelectric film 10 has a generally circular outer shape in a plan view, and has a curved portion 10a formed in its approximate center, with a diameter Ds and a height H, protruding (in a convex shape) from one of its main surfaces. Furthermore, the curved portion 10a is recessed and formed in a concave shape when viewed from the main surface opposite the main surface from which the curved portion 10a protrudes. In other words, the piezoelectric film 10 can also be said to have a recess molded therein.

[0022] 3 to 5, the shape of the curved portion 10a in plan view is substantially circular. That is, the shape formed by the boundary line of the curved portion 10a is circular. Also, in the example shown in FIGS. 3 to 5, the shape of the curved portion 10a is a shape consisting of a part of a sphere (substantially a spherical crown shape).

[0023] The shape of the curved portion 10a is not particularly limited, but is preferably a part of a sphere or a part of a spheroid. The shape of the curved portion in plan view is also not particularly limited, and may be a substantially elliptical shape as shown in FIG.

[0024] Furthermore, the shape of the curved portion when viewed in a cross section perpendicular to the main surface of the piezoelectric film is preferably entirely curved as shown in Fig. 4, but is not limited thereto and may have a flat portion in part. For example, the curved portion may have a flat top.

[0025] Furthermore, if the curved portion 10a when viewed in a cross section perpendicular to the principal surface of the piezoelectric film 10 is an arc and the straight line connecting the two end points of the arc is a chord, the angle θ between the principal surface of the holding member 106 and the chord does not need to be a right angle (90°). For example, if the chord length is 60 mm and the distance from the midpoint of the arc to the midpoint of the chord, i.e., the arrow height, is 5 mm, the angle between the tangent line at each end point of the arc and the chord is known as the tangent chord theorem, which states that the angle between the tangent line and the chord is equal to the inclined angle of the arc. In this case, the inclined angle is 18.9°. In other words, as long as the angle θ between the principal surface of the holding member 106 and the chord is 18.9° or greater, interference between the curved portion 10a of the piezoelectric film 10 and the holding member 106 can be avoided.

[0026] When a voltage is applied to the electrode layers (electrode pair) sandwiching the piezoelectric layer of the piezoelectric film 10, the piezoelectric layer is driven to expand and contract in response to the applied voltage. At this time, the expansion and contraction in the planar direction is converted into vibration in the direction perpendicular to the plane at the curved portion 10a, and the electrical signal is converted into vibration (sound).

[0027] There are no particular limitations on the diameter Ds and height H of the curved portion 10a of the piezoelectric film 10, and these may be set appropriately depending on the size of the housing of the headphones 200 into which the driver unit 100 is incorporated, the size of the ear pads, etc. From the viewpoint of improving sound pressure in the audible range, the diameter Ds of the curved portion 10a is preferably 30 mm to 80 mm, more preferably 40 mm to 70 mm, and even more preferably 50 mm to 60 mm. Furthermore, the height H of the curved portion 10a is preferably 1 mm to 10 mm, more preferably 2 mm to 7 mm, and even more preferably 3 mm to 5 mm. While abnormal deformation of the curved portion 10a, as described below, is less likely to occur as the diameter Ds is smaller, the driver unit 100 of the present invention can effectively suppress abnormal deformation of the curved portion 10a. Therefore, from the viewpoint of improving sound pressure in the audible range, it is preferable that the diameter Ds be within the above range.

[0028] Furthermore, in order to efficiently convert the expansion and contraction in the plane direction of the piezoelectric film when a voltage is applied into vibration in the direction perpendicular to the plane, thereby improving sound pressure, it is preferable that the ratio H / Ds of the diameter Ds to the height H of the curved portion 10a satisfies 0<H / Ds≦0.15. The upper limit of the ratio H / Ds is preferably 0.1 or less, more preferably 0.075 or less, and even more preferably 0.05 or less. The lower limit is preferably 0.003 or more, and more preferably 0.005 or more.

[0029] A perforated plate 102 is laminated on the concave side of the curved portion 10a of the piezoelectric film 10. In the illustrated example, the perforated plate 102 is in direct contact with the concave side of the piezoelectric film 10.

[0030] The perforated plate 102 is disposed on the concave side of the curved portion 10a of the piezoelectric film 10, and defines a first air chamber 101 enclosed between the concave surface and the plate.

[0031] One or more through holes 102a that connect the first air chamber 101 to the outside are formed in the approximate center of the perforated plate 102. In the illustrated example, 13 through holes 102a are arranged in a staggered pattern. The opening cross section of each through hole 102a is approximately circular.

[0032] There are no particular limitations on the number or size of the through holes 102a formed in the perforated plate 102. In the illustrated example, all of the through holes 102a have the same diameter, but this is not a limitation and the through holes 102a may have different diameters. It is also preferable that the ratio of the total area of ​​the through holes 102a to the area of ​​the vibration region of the piezoelectric film 10, i.e., the area of ​​the curved portion 10a in a plan view, is 3% to 70%. This point will be described in detail later.

[0033] The arrangement of the through holes 102a is not particularly limited as long as it allows communication between the first air chamber 101 and the outside. Furthermore, when there are multiple through holes 102a, there is no particular limit to the arrangement pattern of the multiple through holes 102a.

[0034] In a plan view, the perforated plate 102 has insertion holes 102b near its end for inserting fastening members 110, which will be described later. The number and arrangement of the insertion holes 102b in the perforated plate 102 may be set to match the number and arrangement of the screw holes 106a in the holding member 106. In the illustrated example, a total of eight insertion holes 102b are provided at regular intervals in the circumferential direction. However, the number and arrangement of the insertion holes 102b are not limited to this. Alternatively, the perforated plate 102 may not have insertion holes 102b, and its outer diameter may be sized so as not to overlap the positions of the screw holes 106a in the holding member 106, so that it is simply clamped between the holding members 106 and 108.

[0035] There are no particular restrictions on the thickness of the perforated plate 102. From the viewpoint of reducing the size and weight of the driver unit 100, the thickness is preferably 0.1 mm to 5 mm, more preferably 0.2 mm to 3 mm, and even more preferably 0.3 mm to 1 mm.

[0036] As the perforated plate 102, various plate-like materials (sheet-like materials, films) can be used.

[0037] Examples of perforated plate 102 include resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins, foamed plastics made of foamed polystyrene, foamed styrene, and foamed polyethylene, plywood, cork board, leather such as cowhide, carbon sheets, various paperboards such as Japanese paper, various corrugated cardboards made by gluing other paperboards to one or both sides of corrugated paperboard, various metals such as stainless steel, aluminum, copper, and nickel, and thin-film metals made of various alloys. Furthermore, perforated plate 102 may be a composite material made by laminating films made of these materials, and may be subjected to various surface treatments such as anodizing.

[0038] The holding members 106 and 108 are members for holding the piezoelectric film 10 and the perforated plate 102 in a stacked state. The holding members 106 and 108 are annular (ring-shaped) plate members. The holding member 106 is arranged on the piezoelectric film 10 side, and the holding member 108 is arranged on the perforated plate 102 side, sandwiching the piezoelectric film 10 and the perforated plate 102 and holding the piezoelectric film 10 and the perforated plate 102 in a stacked state.

[0039] The diameter of the opening of the holding member 106 is larger than the diameter of the curved portion 10 a of the piezoelectric film 10 in a plan view, and is large enough to allow the curved portion 10 a (convex portion) to pass through. The holding member 106 abuts against at least a portion of the edge portion of the piezoelectric film 10.

[0040] In a plan view, the holding member 106 has threaded holes 106a near its end for threaded engagement with fastening members 110, which will be described later. The number and arrangement of the threaded holes 106a in the holding member 106 may be set as appropriate. In the illustrated example, a total of eight threaded holes 106a are provided at regular intervals in the circumferential direction. However, the number and arrangement of the threaded holes 106a are not limited to this.

[0041] The opening of the holding member 108 is sized so as not to block the through-holes 102a of the perforated plate 102. Furthermore, the holding member 108 has insertion holes 108a near its end in a plan view for inserting fastening members 110, which will be described later. The number and arrangement of the insertion holes 108a in the holding member 108 may be set to match the number and arrangement of the screw holes 106a in the holding member 106. In the illustrated example, a total of eight insertion holes 108a are provided at regular intervals in the circumferential direction. However, the number and arrangement of the insertion holes 108a are not limited to this.

[0042] As shown in Figure 1, a screw, which is a fastening member 110, is inserted from the holding member 108 side through the insertion hole 108a of the holding member 108 and the insertion hole 102b of the perforated plate, and is screwed into the screw hole 106a of the holding member 106, so that the holding member 106 and the holding member 108 clamp and hold the piezoelectric film 10 and the perforated plate 102.

[0043] In the illustrated example, the holding members 106 and 108 have a substantially circular outer shape in a plan view and a substantially circular opening, but this is not limited thereto and various shapes are possible as long as they can properly clamp the piezoelectric film 10 and the perforated plate 102. Furthermore, the holding members 106 and 108 do not have to have the same shape. For example, the holding members 106 and 108 may have openings with different diameters or different thicknesses.

[0044] The thickness of the holding members 106 and 108 is preferably 0.3 mm to 5 mm, more preferably 0.5 mm to 3 mm, and even more preferably 1 mm to 2 mm.

[0045] The holding members 106 and 108 may be made of the same material as the material of the perforated plate 102 described above.

[0046] In the illustrated example, the holding members 106 and 108 are configured to be fixed by fastening members (screws) 110 while sandwiching the piezoelectric film 10 and the perforated plate 102, but this is not limited to this. Various known methods can be used to fix the holding members 106 and 108, such as a method using bolts and nuts, a method using a fixing jig, etc. Also, the perforated plate 102 may not have a holding member 108, and the perforated plate 102 may also function as a holding member. In other words, the perforated plate 102 and the holding member 108 may be formed integrally.

[0047] The porous material 104 is disposed on the surface of the perforated plate 102 opposite to the piezoelectric film 10 so as to cover the through holes 102a. In the illustrated example, the perforated plate 102 has a plurality of through holes 102a, and therefore the porous material 104 is disposed so as to cover the plurality of through holes 102a. The porous material 104 corresponds to the sound absorbing layer in the present invention.

[0048] The porous material 104 has many small holes or voids formed therein and is a member through which gas can pass. The porous material 104 acts as a resistance to the air flow between the first air chamber 101 and the second air chamber which are connected by the through-holes 102a of the perforated plate 102, and functions as a pressure regulating valve. This point will be described in detail later.

[0049] There are no particular limitations on the porous material 104, and any known porous material can be used as appropriate. For example, various known porous materials can be used, such as foams and foam materials (urethane foam (e.g., Calmflex F manufactured by Inoac Corporation, urethane foam manufactured by Hikari Corporation, etc.), soft urethane foam, sintered ceramic particle material, phenol foam, melamine foam, polyamide foam, etc.). Furthermore, nonwoven fabric or woven fabric can also be used as the porous material. As the nonwoven fabric, various known nonwoven fabrics can be used, such as nonwoven sound-absorbing materials (microfiber nonwoven fabrics (e.g., Thinsulate by 3M Co., Ltd.), polyester nonwoven fabrics (e.g., White Qon by Tokyo Bouon Co., Ltd., QonPET by Bridgestone KBG Corporation, Micromat by Softprene Kogyo Co., Ltd., and these products are also available in a two-layer structure consisting of a thin, high-density surface nonwoven fabric and a low-density back nonwoven fabric), plastic nonwoven fabrics such as acrylic fiber nonwoven fabric, natural fiber nonwoven fabrics such as wool and felt, metal nonwoven fabrics, and glass nonwoven fabrics), as well as materials containing minute air bubbles (glass wool, rock wool, nanofiber sound-absorbing materials (silica nanofiber, acrylic nanofiber (e.g., XAI by Mitsubishi Chemical Corporation))).

[0050] Alternatively, a plurality of porous materials (nonwoven fabrics, woven fabrics) having different flow resistances may be laminated, or at least two or more types of porous materials, nonwoven fabrics, and woven fabrics may be laminated.

[0051] There are no particular restrictions on the thickness of the porous material (nonwoven fabric, woven fabric), and the thickness may be such that the desired speed of inflow and outflow of gas (air) from the first air chamber 101 can be achieved depending on the type of porous material (nonwoven fabric, woven fabric). The thickness of the porous material (nonwoven fabric, woven fabric) is preferably 1 mm to 50 mm, more preferably 3 mm to 30 mm, and even more preferably 5 mm to 20 mm.

[0052] In addition, in the illustrated example, the porous material 104 is configured to be placed on the side of the perforated plate 102 opposite the piezoelectric film 10, but this is not limited to this, and the porous material (non-woven fabric, woven fabric) may also be placed within the through holes 102a of the perforated plate 102.

[0053] The driver unit 100 having the above-described configuration is incorporated into headphones 200.

[0054] <Headphones> Headphones 200 have a headband (not shown) and a pair of housings arranged at both ends of the headband, and are connected to audio equipment (not shown) (such as a music player or smartphone) via a wired or wireless connection.

[0055] FIG. 1 is a cross-sectional view conceptually showing a portion of a headphone, and comprises a housing 202 forming the outer shell of the headphone, a driver unit 100 housed within the housing 202, an ear pad 204 arranged on the side of the driver unit 100 opposite the housing 202 side, and an ear pad locking member 206 for locking the ear pad 204 to the housing 202.

[0056] The housing 202 has an opening on the surface that faces the ear of the user when the headphone 200 is worn by the user, and the driver unit 100 is arranged in the housing 202 so as to cover at least a part of this opening.

[0057] The shape of the housing 202 may be the same as that of a conventional headphone housing, such as a substantially cylindrical shape with a bottom, a substantially spherical crown shape, or a shape that is roughly a part of an ellipsoid.

[0058] 1, the driver unit 100 is arranged with the piezoelectric film 10 side facing the opening of the housing 202 and the porous material 104 side facing the inside (bottom) of the housing 202. In other words, the housing 202 is arranged on the concave side of the piezoelectric film 10.

[0059] As shown in Fig. 1, in the headphones, a second air chamber 201 is formed, which is defined by the perforated plate 102 of the driver unit 100 and the housing 202. The second air chamber 201 communicates with the first air chamber 101 via the through-hole 102a and the porous material 104. In the example shown in Fig. 1, the housing 202 has a through-hole 202a in the bottom surface, and the second air chamber 201 communicates with the outside.

[0060] 1, the housing 202 has a through-hole 202a in the bottom surface thereof, thereby allowing the second air chamber 201 to communicate with the outside, but this is not limited to this. For example, the housing 202 may have a through-hole in the side surface thereof. Alternatively, the housing 202 may have a gap between the housing 202 and the driver unit 100, thereby allowing the second air chamber 201 to communicate with the outside. The housing 202 may not have the through-hole 202a. In other words, the headphones may be completely sealed.

[0061] 1, the porous material 104 is filled in a portion of the second air chamber 201, but this is not limiting, and the porous material 104 may be filled in the entire area of ​​the second air chamber 201. Furthermore, the porous material 104 may be divided into a plurality of pieces and placed in the second air chamber 201.

[0062] The ear pads 204 are cushioned, substantially annular (donut-shaped) members that cover the user's ears when the user wears the headphones 200. The ear pads 204 are arranged on the opening side of the housing 202, i.e., on the driver unit 100 side. In the illustrated example, the ear pads 204 are engaged with ear pad engaging members 206, and are fixed by connecting the ear pad engaging members 206 to the housing 202 or the driver unit 100.

[0063] There are no particular limitations on the ear pads 204, and any conventionally known ear pads 204 can be used as appropriate.

[0064] Although not shown, the headphones 200 may further include components that are included in conventionally known headphones 200, such as a circuit for driving the driver unit 100 and a cover for protecting the driver unit 100.

[0065] Next, the operation of the headphones 200 having the driver unit 100 of the present invention having such a configuration will be described.

[0066] As mentioned above, the present inventors considered using a piezoelectric film for a headphone driver unit, the piezoelectric film having a piezoelectric layer including a polymer composite piezoelectric material formed by dispersing piezoelectric particles in a matrix of a polymer material, and electrode layers provided on both sides of the piezoelectric layer. When used as a headphone driver unit, the piezoelectric film must be small and lightweight so that it can be mounted in the headphones, and must generate high-quality sound over a wide frequency range. Therefore, the present inventors considered it appropriate to use a piezoelectric film that uses the piezoelectric film itself as a diaphragm and has a convex portion (curved portion) formed in a convex shape protruding from one main surface, as a configuration that can achieve a wide frequency range with a piezoelectric film that is large enough to be mounted in headphones.

[0067] Here, in headphones, it is known that sound pressure in the low frequency range can be improved by making the internal air chamber (inside the housing) approximately sealed by tightly fitting the ear pads to the ear, so-called sealed or semi-sealed type.

[0068] However, according to the inventor's research, in a configuration in which headphones are incorporated with a driver unit having a piezoelectric film with a curved portion formed in a convex shape so as to protrude from one of the main surfaces, when the ear pads are brought into close contact with the ears to make the housing approximately sealed, resonance due to standing waves occurs within the housing, causing variations in the frequency characteristics (also known as undulations, peaks and dips in the frequency characteristics) particularly in the high-frequency range, and it has been found that this creates a problem in that a flat frequency characteristic cannot be obtained.

[0069] In contrast, headphones 200 having driver unit 100 of the present invention have driver unit 100 in the form of a perforated plate 102 having through holes 102a on the concave side of curved portion 10a of piezoelectric film 10, and more preferably, an acoustic layer made of porous material on the back side thereof, thereby suppressing resonance within housing 202 and suppressing variations in frequency characteristics in the high frequency range (waves in the frequency characteristics, peaks and dips), thereby achieving flat frequency characteristics.

[0070] Furthermore, it has been found that in a configuration in which a driver unit including a piezoelectric film having a curved portion formed in a convex shape so as to protrude from one main surface is incorporated into headphones, the curved portion of the piezoelectric film may deform from its molded shape (hereinafter referred to as abnormal deformation), resulting in a problem of degraded sound quality. Specifically, as shown in FIG. 19 , in conventional headphones 1000, when the ear pad 204 is pressed against the user's ear U when wearing the headphones (arrow X in FIG. 19 ), the ear pad 204 deforms, ensuring adequate airtightness in the air chamber surrounded by the ear U, the ear pad 204, and the driver unit (piezoelectric film 10). At this time, the volume of this air chamber decreases, causing the air pressure in the ear-side air chamber to increase. At this time, a pressure difference occurs between the air chamber on the ear side (convex side) of the piezoelectric film 10 and the air chamber on the housing side (concave side). With a soft piezoelectric film, even a relatively small pressure difference can cause abnormal deformation of the molded curved portion. It was found that if this curved section were to undergo abnormal deformation, the frequency characteristics would change and sound quality would deteriorate, as shown by comparing the solid and dashed lines in the graph of Figure 16. It can be seen that sound pressure in the low frequency range in particular decreases.

[0071] Furthermore, when removing the headphones, a difference in air pressure fluctuations may occur between the ear pad side of the piezoelectric film 10 and the opposite side (housing 202 side), causing the curved portion to deform abnormally.

[0072] In contrast, in headphones 200 having driver unit 100 of the present invention, as shown in Fig. 7, when headphones 200 are worn, ear pad 204 is pressed against the user's ear U (arrow X in Fig. 7), causing ear pad 204 to deform, ensuring a moderate level of airtightness in the air chamber surrounded by ear U, ear pad 204, and driver unit 100 (piezoelectric film 10), and the volume of this air chamber decreases, causing the air pressure within the air chamber to rise. At this time, first air chamber 101 on the concave side of piezoelectric film 10 is separated from the second air chamber by perforated plate 102, and preferably the back side of perforated plate 102 is covered with porous material 104, preventing air within first air chamber 101 from instantly escaping into the second air chamber (arrow Y in Fig. 7), and as a result, deformation of the piezoelectric film due to pressure rise in the air chamber on the ear side can be suppressed. During this time, air in the ear-side air chamber surrounded by the ear U, ear pad 204, and driver unit 100 (piezoelectric film 10) also escapes through the ear pad 204 (arrow Z in FIG. 7 ) or through the gap between the ear pad 204 and the ear U, gradually decreasing the air pressure in this air chamber. This maintains a pressure balance between the convex side of the piezoelectric film 10 facing the ear pad 204 and the concave side facing the opposite side (housing 202), preventing abnormal deformation of the curved portion 10a. This also prevents changes in frequency characteristics and deterioration in sound quality, as shown by the solid and dashed lines in the graph in FIG. 15 . As shown in FIG. 15 , flat frequency characteristics are achieved from the low to high frequency ranges. For ease of explanation, the retaining members 106, 108, and fastening member 110 are omitted from FIG. 7 .

[0073] Furthermore, when removing the headphones 200, a difference in air pressure fluctuation between the surface of the piezoelectric film 10 facing the ear pad 204 and the surface on the opposite side (the housing 202 side) can be prevented, thereby preventing deformation of the curved portion 10a.

[0074] In this way, the headphones 200 having the driver unit 100 of the present invention have a perforated plate 102 with through holes 102a and a porous material 104 arranged on the concave side of the piezoelectric film 10 on which the curved portion 10a is formed, thereby slowing down the pressure fluctuations in the first air chamber 101 on the concave side when the headphones 200 are put on or taken off, thereby preventing abnormal deformation of the curved portion 10a.

[0075] Furthermore, in a preferred embodiment, the driver unit 100 of the present invention has a sound-absorbing layer made of porous material 104 on the rear side (opposite the piezoelectric film 10) of the perforated plate 102. In headphones 200 having such a driver unit 100, the configuration having the perforated plate 102 on the concave side (rear side) of the piezoelectric film 10 and the sound-absorbing layer made of porous material 104 on the rear side is a so-called composite sound-absorbing structure, and by selecting the aperture ratio of the perforated plate 102 and the thickness and material of the rear-side sound-absorbing layer, a wide range of sound-absorbing characteristics can be realized, allowing for arbitrary selection of porous-type sound absorption, plate vibration-type sound absorption, and resonator-type sound absorption characteristics. Therefore, the generation of standing waves within the housing can be suppressed, and undulations and peaks and dips in the frequency characteristics can be improved, resulting in a flat frequency characteristic.

[0076] 1, the driver unit 100 is arranged with the piezoelectric film 10 side facing the opening of the housing 202 and the porous material 104 side facing the inside (bottom) of the housing 202, and the housing 202 is arranged on the concave side of the piezoelectric film 10, but this is not limited to this. As with headphones 200b shown in FIG. 8, the driver unit 100 may be arranged with the piezoelectric film 10 side facing the inside of the housing 202 and the porous material 104 side facing the opening of the housing 202. In other words, the housing 202 may be arranged on the convex side of the piezoelectric film 10.

[0077] In the case of the configuration of the headphones 200b shown in FIG. 8, resonance due to standing waves within the housing 202 can also be suppressed, and variations in frequency characteristics in the high frequency range can be suppressed, thereby achieving flat frequency characteristics.

[0078] 1, the driver unit 100 is configured to have porous material 104 arranged to cover the through-holes 102a of the perforated plate 102, but this is not limited to this, and the driver unit 100 may be configured without porous material 104, as in the driver unit 100b shown in Fig. 9. The driver unit 100b shown in Fig. 9 has the same configuration as the driver unit 100 shown in Fig. 1, except that it does not have porous material 104.

[0079] As mentioned above, the combination of the perforated plate 102 and the porous material 104 is a so-called composite sound-absorbing structure, and by selecting the aperture ratio of the perforated plate 102, the thickness and material of the sound-absorbing layer on the back side, etc., a wide range of sound-absorbing characteristics can be realized, allowing for the selection of porous sound-absorbing, plate vibration sound-absorbing, and resonator sound-absorbing characteristics as desired. Therefore, the generation of standing waves within the housing can be suppressed, and undulations and peaks and dips in the frequency characteristics can be improved to obtain flat frequency characteristics. On the other hand, the perforated plate 102 alone can achieve sound-absorbing characteristics having the characteristics of both plate vibration and resonator types, so it is somewhat effective in suppressing the generation of standing waves within the housing.

[0080] From the viewpoint of improving undulations and peaks and dips in the frequency characteristics in the high frequency range and obtaining flat frequency characteristics, it is preferable that the ratio of the total area of ​​the through holes 102a to the area of ​​the vibration region of the piezoelectric film 10, i.e., the area of ​​the curved portion 10a in a planar view, is 3% to 70%, more preferably 25% to 65%, and even more preferably 40% to 60%.

[0081] Furthermore, from the viewpoint of improving undulations in the frequency characteristics in the high frequency range, peaks and dips, etc., and obtaining flat frequency characteristics, the diameter (circle equivalent diameter) of each through hole 102a of the perforated plate 102 is preferably 0.01 mm to 10 mm, more preferably 0.1 mm to 6 mm, and even more preferably 0.5 mm to 4 mm.

[0082] Even in the driver unit 100b that does not have the porous material 104, by appropriately setting the total area and diameter of the through holes 102a of the perforated plate 102, it is possible to improve the undulations and peaks / dip in the frequency characteristics and obtain a flat frequency characteristic.

[0083] <Piezoelectric Film> Next, the layer structure of the piezoelectric film 10 will be described. The piezoelectric film 10 has a piezoelectric layer made of a polymer composite piezoelectric containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer. When a voltage is applied to the electrode layers (electrode pair) sandwiching the piezoelectric layer, the piezoelectric layer expands and contracts in response to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the plane direction. This allows the piezoelectric film 10 to exhibit piezoelectric performance.

[0084] Fig. 10 shows an enlarged view of a portion of the piezoelectric film 10. The piezoelectric film 10 shown in Fig. 10 includes a piezoelectric layer 20, which is a sheet-like material having piezoelectricity, a first electrode layer 24 laminated on one side of the piezoelectric layer 20, a first protective layer 28 laminated on the side of the first electrode layer 24 opposite the piezoelectric layer 20, a second electrode layer 26 laminated on the other side of the piezoelectric layer 20, and a second protective layer 30 laminated on the side of the second electrode layer 26 opposite the piezoelectric layer 20. That is, the piezoelectric film 10 has a configuration in which the piezoelectric layer 20 is sandwiched between electrode layers, and a protective layer is laminated on the side of the electrode layer that is not in contact with the piezoelectric layer.

[0085] In the present invention, the piezoelectric layer 20 is a polymer composite piezoelectric material that contains piezoelectric particles 36 in a matrix 34 containing a polymer material, as conceptually shown in FIG.

[0086] It is preferable to use a polymer material that has viscoelasticity at room temperature as the material for the matrix 34 (which also serves as a matrix and binder) of the polymer composite piezoelectric material that constitutes the piezoelectric layer 20. In this specification, "room temperature" refers to a temperature range of about 0 to 50°C.

[0087] Here, it is preferable that the polymer composite piezoelectric material (piezoelectric material layer 20) satisfies the following requirements.

[0088] (i) Flexibility: For example, when a portable piezoelectric material is held loosely bent like a newspaper or magazine, it is constantly subjected to relatively slow, large external bending deformation at frequencies of a few Hz or less. If the polymer composite piezoelectric material is too hard, a correspondingly large bending stress will be generated, which may cause cracks at the interface between the polymer matrix and the piezoelectric particles, eventually leading to destruction. Therefore, polymer composite piezoelectric materials must be moderately flexible. Furthermore, if the strain energy can be diffused to the outside as heat, stress can be alleviated. Therefore, the loss tangent of the polymer composite piezoelectric material must be moderately large.

[0089] (ii) Sound Quality Speakers vibrate piezoelectric particles at frequencies in the audio band between 20 Hz and 20 kHz, and the resulting vibration energy causes the entire polymer composite piezoelectric material (piezoelectric film) to vibrate as a unit, reproducing sound. Therefore, polymer composite piezoelectric materials must have an appropriate hardness to increase the efficiency of vibration energy transmission. Furthermore, if the frequency characteristics of a speaker are smooth, the amount of change in sound quality when the lowest resonance frequency changes with changes in curvature will also be small. Therefore, the loss tangent of a polymer composite piezoelectric material must be appropriately large.

[0090] In summary, the polymer composite piezoelectric material is required to be hard against vibrations of 20 Hz to 20 kHz, and soft against vibrations of a few Hz or less. The loss tangent of the polymer composite piezoelectric material is also required to be appropriately large for vibrations of all frequencies below 20 kHz.

[0091] Generally, polymer solids have a viscoelastic relaxation mechanism, and large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum (absorption) in the loss modulus with increasing temperature or decreasing frequency. Among these, relaxation caused by micro-Brownian motion of molecular chains in the amorphous region is called primary dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most pronounced. In a polymer composite piezoelectric (piezoelectric layer 20), by using a polymer material with a glass transition point at room temperature—in other words, a polymer material with viscoelasticity at room temperature—as the matrix, a polymer composite piezoelectric that behaves hard in response to vibrations of 20 Hz to 20 kHz and soft in response to slow vibrations of a few Hz or less is realized. In particular, in order to favorably exhibit this behavior, it is preferable to use a polymer material with a glass transition point at room temperature, i.e., 0 to 50°C, as the matrix of the polymer composite piezoelectric.

[0092] Various known polymeric materials having viscoelasticity at room temperature can be used. Preferably, a polymeric material is used that has a maximum value of loss tangent Tanδ of 0.5 or more at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature, i.e., 0 to 50°C. This alleviates stress concentration at the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment when the polymer composite piezoelectric element is slowly bent by an external force, and high flexibility can be expected.

[0093] Furthermore, the polymer material having viscoelasticity at room temperature preferably has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 100 MPa or more at 0° C. and 10 MPa or less at 50° C. This reduces the bending moment that occurs when the polymer composite piezoelectric body is slowly bent by an external force, and allows the body to behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

[0094] Furthermore, it is more preferable for a polymer material that has viscoelasticity at room temperature to have a relative dielectric constant of 10 or more at 25°C. This allows a higher electric field to be applied to the piezoelectric particles in the matrix when a voltage is applied to the polymer composite piezoelectric, and a large amount of deformation can be expected. However, on the other hand, in consideration of ensuring good moisture resistance, it is also preferable for the polymer material to have a relative dielectric constant of 10 or less at 25°C.

[0095] Examples of polymeric materials that satisfy these conditions and have viscoelasticity at room temperature include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride-co-acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Commercially available products such as Hybrar 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymeric materials. Of these, it is preferable to use a material having a cyanoethyl group as the polymeric material, and cyanoethylated PVA is particularly preferable.

[0096] As a polymeric material having viscoelasticity at room temperature, it is preferable to use a polymeric material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. That is, in the present invention, it is preferable to use a polymeric material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA, as the matrix 34 of the piezoelectric layer 20. In the following description, the above-mentioned polymeric materials, typified by cyanoethylated PVA, will also be collectively referred to as "polymeric materials having viscoelasticity at room temperature."

[0097] These polymeric materials having viscoelasticity at room temperature may be used alone or in combination (mixture) of two or more kinds.

[0098] The matrix 34 using such a polymeric material having viscoelasticity at room temperature may contain a plurality of polymeric materials in combination as needed. That is, in addition to a viscoelastic material such as cyanoethylated PVA, other dielectric polymeric materials may be added to the matrix 34 as needed for the purpose of adjusting the dielectric properties and mechanical properties.

[0099] Examples of the dielectric polymer material that can be added include fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, Examples of suitable dielectric polymers include polymers having a cyano or cyanoethyl group, such as cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl sucrose, and cyanoethyl sorbitol, as well as synthetic rubbers such as nitrile rubber and chloroprene rubber. Among these, polymeric materials having a cyanoethyl group are preferred. Furthermore, the matrix 34 of the piezoelectric layer 20 is not limited to one type of dielectric polymeric material, and multiple types may be added.

[0100] In addition to the dielectric polymer material, in order to adjust the glass transition temperature Tg, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and thermosetting resins such as phenol resin, urea resin, melamine resin, alkyd resin, and mica may be added to the matrix 34. Furthermore, in order to improve adhesion, tackifiers such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added.

[0101] When a material other than a polymeric material having viscoelasticity such as cyanoethylated PVA is added to the matrix 34 of the piezoelectric layer 20, the amount of the material added is not particularly limited, but is preferably 30 mass % or less in terms of the ratio to the matrix 34. This allows the properties of the polymeric material to be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, thereby achieving favorable results in terms of increasing the dielectric constant, improving heat resistance, and improving adhesion between the piezoelectric particles 36 and the electrode layer.

[0102] The piezoelectric layer 20 is a layer made of a polymer composite piezoelectric material containing piezoelectric particles 36 in such a matrix 34. The piezoelectric particles 36 are dispersed in the matrix 34. Preferably, the piezoelectric particles 36 are dispersed uniformly (approximately uniformly) in the matrix 34.

[0103] The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure. Examples of ceramic particles that make up the piezoelectric particles 36 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe) (BFBT).

[0104] There are no limitations on the particle size of the piezoelectric particles 36, and it may be selected appropriately depending on the size and intended use of the piezoelectric film 10. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle size of the piezoelectric particles 36 within this range, favorable results can be obtained in that the piezoelectric film 10 can achieve both high piezoelectric properties and flexibility.

[0105] The piezoelectric particles 36 in the piezoelectric layer 20 may be dispersed uniformly and regularly in the matrix 34, or may be dispersed irregularly in the matrix 34 as long as they are dispersed uniformly.

[0106] In the piezoelectric film 10, there are no limitations on the quantitative ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20, and this may be set appropriately depending on the size and thickness in the plane direction of the piezoelectric film 10, the intended use, the required properties, and the like. The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore even more preferably 50 to 80%. By setting the quantitative ratio of the matrix 34 to the piezoelectric particles 36 within the above range, favorable results can be obtained, such as the ability to achieve both high piezoelectric properties and flexibility.

[0107] In the piezoelectric film 10, there are no particular limitations on the thickness of the piezoelectric layer 20, and it may be set appropriately depending on the characteristics required of the piezoelectric film 10. A thicker piezoelectric layer 20 is advantageous in terms of rigidity, such as the stiffness of the sheet-like material, but the voltage (potential difference) required to expand or contract the piezoelectric film 10 by the same amount increases. The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility.

[0108] Furthermore, the piezoelectric layer 20 is preferably polarized (poled) in the thickness direction. When a voltage is applied to the electrode layers (electrode pair) sandwiching the piezoelectric layer 20, the piezoelectric particles 36 in the piezoelectric layer 20 expand and contract in the polarization direction in response to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the plane direction. This allows the piezoelectric film 10 to exhibit piezoelectric performance.

[0109] 10, the piezoelectric film 10 has a first electrode layer 24 on one surface of the piezoelectric layer 20, with a first protective layer 28 thereon, and a second electrode layer 26 on the other surface of the piezoelectric layer 20, with a second protective layer 30 thereon. Here, the first electrode layer 24 and the second electrode layer 26 form an electrode pair.

[0110] That is, the piezoelectric film 10 has a configuration in which both sides of the piezoelectric layer 20 are sandwiched between an electrode pair, i.e., a first electrode layer 24 and a second electrode layer 26, and this laminate is sandwiched between a first protective layer 28 and a second protective layer 30. In this way, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts in response to an applied voltage. Note that the terms "first" and "second" in the electrode layer and protective layer are used for convenience in explaining the piezoelectric film 10. Therefore, the terms "first" and "second" in the present invention have no technical meaning and are unrelated to the actual state of use.

[0111] In addition to these layers, the piezoelectric film 10 of the present invention may have, for example, an adhesive layer for adhering the electrode layer to the piezoelectric layer 20, and an adhesive layer for adhering the electrode layer to the protective layer. The adhesive may be an adhesive or a pressure-sensitive adhesive. The adhesive may also suitably be the same material as the polymer material of the piezoelectric layer 20 excluding the piezoelectric particles 36, i.e., the matrix 34. The adhesive layer may be provided on both the first electrode layer 24 side and the second electrode layer 26 side, or on only one of the first electrode layer 24 side and the second electrode layer 26 side.

[0112] In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the first electrode layer 24 and the second electrode layer 26 and also serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20, which is composed of a matrix 34 and piezoelectric particles 36, exhibits excellent flexibility with respect to slow bending deformation, but may lack rigidity or mechanical strength depending on the application. To compensate for this, the first protective layer 28 and the second protective layer 30 are provided in the piezoelectric film 10. The first protective layer 28 and the second protective layer 30 have the same configuration but differ in their location. Therefore, in the following description, when there is no need to distinguish between the first protective layer 28 and the second protective layer 30, both components will be collectively referred to as the protective layer.

[0113] The protective layer is not limited and may be made of various sheet-like materials, and various resin films are preferred examples thereof. Among these, resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, etc. are preferred because of their excellent mechanical properties and heat resistance.

[0114] There is no limitation on the thickness of the protective layer. The first protective layer 28 and the second protective layer 30 are basically the same in thickness, but may be different in thickness. If the protective layer is too rigid, not only will it restrict the expansion and contraction of the piezoelectric layer 20, but it will also impair flexibility. Therefore, except in cases where mechanical strength or good handleability as a sheet-like material is required, a thinner protective layer is more advantageous.

[0115] In the piezoelectric film 10, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility, as long as the thickness of the protective layer is no more than twice the thickness of the piezoelectric layer 20. For example, when the thickness of the piezoelectric layer 20 is 50 μm and the protective layer is made of PET, the thickness of the protective layer is preferably no more than 100 μm, more preferably no more than 50 μm, and even more preferably no more than 25 μm.

[0116] In the piezoelectric film 10, a first electrode layer 24 is formed between the piezoelectric layer 20 and the first protective layer 28, and a second electrode layer 26 is formed between the piezoelectric layer 20 and the second protective layer 30. The first electrode layer 24 and the second electrode layer 26 are provided to apply a voltage to the piezoelectric layer 20 (piezoelectric film 10).

[0117] The first electrode layer 24 and the second electrode layer 26 are basically the same except for their positions. Therefore, in the following description, when there is no need to distinguish between the first electrode layer 24 and the second electrode layer 26, both components will be collectively referred to as electrode layers.

[0118] In the present invention, there are no limitations on the material for forming the electrode layer, and various conductors can be used. Specific examples include metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, alloys thereof, laminates and composites of these metals and alloys, and indium tin oxide. Alternatively, conductive polymers such as PEDOT / PPS (polyethylenedioxythiophene-polystyrene sulfonate) are also exemplified. Among these, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferred examples for the electrode layer. Among these, copper is more preferred from the viewpoints of conductivity, cost, flexibility, and the like.

[0119] There are also no limitations on the method for forming the electrode layer, and various known methods can be used, such as vapor phase deposition methods (vacuum film formation methods) such as vacuum deposition and sputtering, film formation by plating, and methods of attaching foil formed from the above-mentioned materials.

[0120] Among these, thin films of copper, aluminum, etc. formed by vacuum deposition are particularly suitable for use as electrode layers because they can ensure the flexibility of the piezoelectric film 10. Among these, thin films of copper formed by vacuum deposition are particularly suitable.

[0121] There is no limit to the thickness of the electrode layer. The first electrode layer 24 and the second electrode layer 26 are basically the same in thickness, but may be different in thickness. Here, as with the protective layer described above, if the electrode layer is too rigid, it not only restricts the expansion and contraction of the piezoelectric layer 20, but also impairs flexibility. Therefore, the thinner the electrode layer, the more advantageous it is, as long as the electrical resistance does not become too high.

[0122] In the piezoelectric film 10, it is preferable that the product of the thickness and Young's modulus of the electrode layer be less than the product of the thickness and Young's modulus of the protective layer, since this does not significantly impair flexibility. For example, in the case of a combination in which the protective layer is made of PET (Young's modulus: approximately 6.2 GPa) and the electrode layer is made of copper (Young's modulus: approximately 130 GPa), if the protective layer is 25 μm thick, the thickness of the electrode layer is preferably 1.2 μm or less, more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

[0123] As described above, the piezoelectric film 10 has a structure in which a piezoelectric layer 20, which is formed by dispersing piezoelectric particles 36 in a matrix 34 containing a polymer material, is sandwiched between a first electrode layer 24 and a second electrode layer 26, and this laminate is further sandwiched between a first protective layer 28 and a second protective layer 30. In such a piezoelectric film 10, a maximum value of loss tangent (Tan δ) at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement preferably exists at room temperature, and more preferably a maximum value of 0.1 or greater exists at room temperature. This allows the strain energy to be effectively diffused to the outside as heat, even when the piezoelectric film 10 is subjected to a relatively slow, large bending deformation from the outside at a frequency of a few Hz or less, thereby preventing cracks from occurring at the interface between the polymer matrix and the piezoelectric particles.

[0124] The piezoelectric film 10 preferably has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 10 to 30 GPa at 0°C and 1 to 10 GPa at 50°C. This condition also applies to the piezoelectric layer 20. This allows the piezoelectric film 10 to have a large frequency dispersion in the storage modulus (E') at room temperature. In other words, it behaves hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of a few Hz or less.

[0125] The piezoelectric film 10 has a thickness multiplied by a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 1.0×10 5 ~2.0 x 10 6 N / m, 1.0 x 10 at 50°C 5 ~1.0 x 10 6 N / m. This condition also applies to the piezoelectric layer 20. This allows the piezoelectric film 10 to have appropriate rigidity and mechanical strength without impairing its flexibility and acoustic properties.

[0126] Furthermore, the piezoelectric film 10 preferably has a loss tangent (Tan δ) of 0.05 or more at 25°C and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. This condition also applies to the piezoelectric layer 20. This makes the frequency characteristics of a speaker using the piezoelectric film 10 smooth, and the lowest resonance frequency f ０ It is also possible to reduce the amount of change in sound quality when the

[0127] In the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric film 10, the piezoelectric layer 20, etc. may be measured by a known method. For example, a dynamic viscoelasticity measuring device DMS6100 manufactured by SII NanoTechnology, Inc. may be used. Examples of measurement conditions include a measurement frequency of 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz, and 20 Hz), a measurement temperature of −50° C. to 150° C., a temperature rise rate of 2° C. / min. (in a nitrogen atmosphere), a sample size of 40 mm×10 mm (including the clamping area), and a chuck distance of 20 mm.

[0128] In the driver unit 100, an external power supply (signal source) is connected to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 to apply a drive voltage that expands and contracts the piezoelectric film 10, i.e., to supply drive power (drive signal). There are no restrictions on the external power supply (signal source), and it may be a DC power supply or an AC power supply. The drive voltage may also be set appropriately depending on the thickness and material of the piezoelectric layer 20 of the piezoelectric film 10, so that the piezoelectric film 10 can be properly driven.

[0129] There are no limitations on the method for drawing electrodes from the first electrode layer 24 and the second electrode layer 26, and various known methods can be used. Examples include a method of connecting a conductor such as copper foil to the first electrode layer 24 and the second electrode layer 26 to draw the electrodes to the outside, and a method of forming through holes in the first protective layer 28 and the second protective layer 30 using a laser or the like and filling the through holes with a conductive material to draw the electrodes to the outside. Suitable examples of electrode drawing methods include the methods described in Japanese Patent Application Laid-Open No. 2014-209724 and Japanese Patent Application Laid-Open No. 2016-015354.

[0130] As described above, the piezoelectric film 10 includes a piezoelectric layer 20 made of a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material, and electrode layers (first electrode layer 24 and second electrode layer 26) provided on both sides of the piezoelectric layer 20. The piezoelectric film 10 also includes protective layers (first protective layer 28 and second protective layer 30) provided on each electrode layer. When a voltage is applied to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 having such a piezoelectric layer 20, the piezoelectric particles 36 expand and contract in the polarization direction in response to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is approximately 0.01 to 0.1%.

[0131] As described above, the thickness of the piezoelectric layer 20 is preferably approximately 10 to 300 μm. Therefore, expansion and contraction in the thickness direction is extremely small, at a maximum of approximately 0.3 μm. In contrast, the piezoelectric film 10, i.e., the piezoelectric layer 20, has a size in the planar direction that is much larger than its thickness. Therefore, for example, if the diameter of the curved portion 10 a of the piezoelectric film 10 is 10 cm, the application of a voltage will cause the piezoelectric film 10 (curved portion 10 a) to expand and contract in the planar direction by a maximum of approximately 0.1 mm.

[0132] This vibration in the thickness direction causes the piezoelectric film 10 to generate sound. That is, the driver unit 100 vibrates in accordance with the magnitude of the voltage (drive voltage) applied to the piezoelectric film 10, and generates sound in accordance with the drive voltage applied to the piezoelectric film 10.

[0133] <Method for Manufacturing Piezoelectric Film> Hereinafter, an example of a method for manufacturing the piezoelectric film 10 will be described with reference to FIGS.

[0134] First, a sheet-like material 11a is prepared, in which a first electrode layer 24 is formed on the surface of a first protective layer 28, as shown in Fig. 11. Further, a sheet-like material 11c is prepared, in which a second electrode layer 26 is formed on the surface of a second protective layer 30, as conceptually shown in Fig. 13.

[0135] The sheet-like material 11a may be produced by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, or the like. Similarly, the sheet-like material 11c may be produced by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, or the like. Alternatively, a commercially available product having a copper thin film or the like formed on a protective layer may be used as the sheet-like material 11a and / or the sheet-like material 11c. The sheet-like material 11a and the sheet-like material 11c may be of the same type or different types.

[0136] If the protective layer is very thin and difficult to handle, a protective layer with a separator (temporary support) may be used as needed. The separator may be made of PET or the like having a thickness of 25 to 100 μm. The separator may be removed after the electrode layer and the protective layer are thermocompression bonded.

[0137] 12, a coating material (coating composition) that will become the piezoelectric layer 20 is applied onto the first electrode layer 24 of the sheet-like material 11a, and then cured to form the piezoelectric layer 20. In this way, a piezoelectric laminate 11b is produced in which the sheet-like material 11a and the piezoelectric layer 20 are laminated together.

[0138] Various methods can be used to form the piezoelectric layer 20, depending on the material used to form the piezoelectric layer 20. As an example, a polymer material such as the cyanoethylated PVA described above is first dissolved in an organic solvent, and then piezoelectric particles 36 such as PZT particles are added and stirred to prepare a coating material. There are no limitations on the organic solvent, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used. After preparing the sheet material 11a and preparing the coating material, the coating material is cast (applied) onto the sheet material 11a, and the organic solvent is evaporated and dried. This produces a piezoelectric laminate 11b, as shown in FIG. 12, which has a first electrode layer 24 on a first protective layer 28 and a piezoelectric layer 20 laminated on the first electrode layer 24.

[0139] There are no limitations on the method for casting the paint, and all known methods (applicators) such as a bar coater, a slide coater, a doctor knife, etc. Alternatively, if the polymer material is heat-meltable, the polymer material may be heated and melted, and piezoelectric particles 36 may be added to produce a melt, which may then be extruded into a sheet shape onto the sheet-like material 11a shown in Fig. 11 by extrusion molding or the like, and cooled to produce the piezoelectric laminate 11b shown in Fig. 12.

[0140] As described above, in the piezoelectric layer 20, in addition to the polymer material having viscoelasticity at room temperature, a polymer piezoelectric material such as PVDF may be added to the matrix 34. When adding such a polymer piezoelectric material to the matrix 34, the polymer piezoelectric material to be added may be dissolved in the coating material. Alternatively, the polymer piezoelectric material to be added may be added to a polymer material that has been heated and melted and has viscoelasticity at room temperature, and then the resulting mixture may be heated and melted.

[0141] After the piezoelectric layer 20 is formed, it may be subjected to calendering as necessary. Calendering may be performed once or multiple times. As is well known, calendering is a process in which a surface to be treated is heated and pressed with a heating press or a heating roller, etc., to perform flattening or the like.

[0142] Next, the piezoelectric layer 20 of the piezoelectric laminate 11b is subjected to polarization (poling). The piezoelectric layer 20 may be polarized before the calendaring process, but is preferably polarized after the calendaring process. There are no limitations on the method for polarizing the piezoelectric layer 20, and known methods can be used. Examples include electric field poling, in which a DC electric field is directly applied to the target to be polarized, and corona poling. When electric field poling is performed, the second electrode layer 26 may be formed before the polarization process, and the electric field poling may be performed using the first electrode layer 24 and the second electrode layer 26. Furthermore, in the piezoelectric film 10 of the present invention, polarization is performed in the thickness direction of the piezoelectric layer 20, rather than in the plane direction.

[0143] Next, as shown in Fig. 13, the previously prepared sheet material 11c is laminated on the piezoelectric layer 20 side of the polarization-treated piezoelectric laminate 11b, with the second electrode layer 26 facing the piezoelectric layer 20. Furthermore, this laminate is thermocompression-bonded using a heating press and a heating roller, etc., with the first protective layer 28 and the second protective layer 30 sandwiched between them, thereby bonding the piezoelectric laminate 11b and the sheet material 11c together, thereby producing the piezoelectric film 10 as shown in Fig. 10. Alternatively, the piezoelectric laminate 11b and the sheet material 11c may be bonded together using an adhesive, and preferably further compressed to produce the piezoelectric film 10. The adhesive used in this process may be the same material as the matrix of the piezoelectric layer 20.

[0144] Next, in a molding process, the manufactured piezoelectric film 10 is heat-compression molded to form a curved portion 10a that protrudes from one main surface of the piezoelectric film 10 and is recessed from the other main surface. The method of heat-compression molding is not particularly limited, and various known resin film processing methods can be used. As an example, the piezoelectric film 10 can be heat-compression molded using a molding device having a mold with a shape corresponding to the shape of the curved portion 10a to be molded, thereby molding the curved portion 10a into a desired shape.

[0145] The piezoelectric film 10 may be manufactured using cut sheets 11a and 11c, or may be manufactured using a roll-to-roll process.

[0146] The piezoelectric film thus produced may be cut into desired shapes for various applications. The piezoelectric film 10 thus produced is polarized in the thickness direction, not in the plane direction, and exhibits significant piezoelectric properties without the need for stretching after polarization. Therefore, the piezoelectric film 10 has no in-plane anisotropy in its piezoelectric properties, and when a driving voltage is applied, it expands and contracts isotropically in all directions in the plane direction.

[0147] The piezoelectric film 10 included in the driver unit 100 may be configured as a single piezoelectric film 10, as described above, in which a piezoelectric layer 20 is sandwiched between a first electrode layer 24 and a second electrode layer 26, and this is sandwiched between a first protective layer 28 and a second protective layer 30 (as shown in FIG. 10 ). Alternatively, a laminate of multiple piezoelectric films 10 may be used. A laminate of multiple piezoelectric films 10 is preferable because it allows the shape of the curved portion 10a to be stably maintained even when the piezoelectric film 10 is enlarged. A laminate of multiple piezoelectric films 10 may be formed via an adhesive layer. An adhesive layer is preferred for its adhesive strength. Specific examples of materials for forming the adhesive layer include thermoplastic polyester-based hot-melt materials. The thickness of the adhesive layer is preferably 5 to 50 μm, more preferably 10 to 30 μm.

[0148] When stacking multiple piezoelectric films 10, first, multiple piezoelectric films 10 cut to a predetermined size are prepared, and the piezoelectric films 10 are laminated together by adhering them with a hot melt adhesive or the like. At this time, it is preferable to prevent the electrode lead-out portions of each piezoelectric film 10 from contacting each other. For example, if the piezoelectric film 10 is configured to have an out-island portion that protrudes in the surface direction for electrode lead-out, it is preferable to laminate the piezoelectric films 10 so that the out-island portions do not overlap.

[0149] Next, a laminate of a plurality of piezoelectric films 10 is heat-compressed and molded to form a curved portion.

[0150] Then, electrodes are drawn out from the electrode layer of each piezoelectric film. For example, if each piezoelectric film has an island portion, through-holes can be drilled in the protective layer of the island portion by laser processing or the like, and the through-holes can be filled with a conductive material to draw the electrodes out.

[0151] The two electrode layers of each piezoelectric film are connected to an external power source (signal source), and wiring is connected so that an AC signal of the appropriate polarity is applied in accordance with the polarization direction of each piezoelectric layer so that each piezoelectric film operates in phase.

[0152] <Preferred embodiment of driver unit> In a driver unit including the piezoelectric film 10, when the frequency characteristics are such that the sound pressure in the treble range is higher than that in the bass range, by inserting a series resistor into the input signal, the voltage applied to the piezoelectric film 10 in the treble range can be lowered, the sound pressure in the treble range can be gradually reduced, and the frequency characteristics can be flattened. This makes it easier to hear the bass range that was previously masked by the sound pressure in the treble range being higher than that in the bass range.

[0153] Specifically, as shown in the block diagram of Fig. 14, a resistor 222 is connected between a signal source 220 and the piezoelectric film 10. The signal source 220 is connected to headphones and may be any of various known players. The resistor 222 is disposed, for example, inside the headphones (inside the housing) and connected to the middle of the wiring that is connected to the electrode layer of the piezoelectric film 10.

[0154] In a piezoelectric film, a configuration in which a piezoelectric layer, which is a dielectric, is sandwiched between a pair of electrodes can be represented by an equivalent circuit in which capacitance, equivalent series inductance, and equivalent series resistance are connected in series, similar to a capacitor, etc. Here, since equivalent series inductance does not contribute in the audible range (20 Hz to 20 kHz) in which piezoelectric films are used, the piezoelectric film 10 can be represented by an equivalent circuit in which capacitance C and equivalent series resistance ESR are connected in series.

[0155] In such an equivalent circuit, the capacitive reactance Xc = 1 / (2π × f × C) due to the electrostatic capacitance C is inversely proportional to the frequency f of the power supply, so as the frequency increases, the capacitive reactance Xc decreases. This capacitive reactance Xc is the ratio of the voltage to the current when driving the piezoelectric layer.

[0156] For simplicity, let's consider the impedance Z of the piezoelectric film as consisting only of capacitive reactance Xc. Let's assume that the impedance Z is 8000Ω when the frequency f is 100 Hz. A 200Ω resistor is connected in series to the piezoelectric film, and an effective voltage of 10 Vrms is applied. As shown in Table 1 below, the voltage Vrms1 across the piezoelectric film is approximately 9.8 V, and the voltage Vrms2 across the resistor is approximately 0.2 V. Next, when the frequency f is 1000 Hz, the impedance Z of the piezoelectric film is 800Ω, so the voltage Vrms1 across the piezoelectric film is 8.0 V, and the voltage Vrms2 across the resistor is 2.0 V. Next, when the frequency f is 10000 Hz, the impedance Z of the piezoelectric film is 80Ω, so the voltage Vrms1 across the piezoelectric film is approximately 2.9 V, and the voltage Vrms2 across the resistor is approximately 7.1 V. Furthermore, when the frequency f is 20,000 Hz, the impedance Z of the piezoelectric film is 40 Ω, so the voltage Vrms1 applied to the piezoelectric film is approximately 1.7 V, and the voltage Vrms2 across the resistor is approximately 8.3 V. Table 1 also shows the results of calculating the amount of change in sound pressure from the voltage ratio.

[0157]

[0158] In this way, when a resistor is connected in series to a piezoelectric film, the higher the frequency of the applied voltage (signal), the smaller the voltage applied to the piezoelectric film. Here, because the piezoelectric film is voltage-driven, the higher the frequency, the smaller the voltage applied to the piezoelectric film, and the lower the sound pressure can be made in the higher frequency range compared to when there is no resistor. Therefore, in a driver unit equipped with a piezoelectric film, if the sound pressure in the high frequency range is higher than in the low frequency range, connecting a resistor in series to the piezoelectric film can lower the voltage applied to the piezoelectric film in the high frequency range, gradually reducing the sound pressure in the high frequency range and flattening the frequency characteristics.

[0159] The value of the resistor connected to the piezoelectric film may be set appropriately depending on the area, frequency characteristics, drive voltage, impedance, etc. of the piezoelectric film. When the driver unit (curved portion of the piezoelectric film) has a diameter of 6 cm, the series resistance value is preferably 100 to 1000 Ω, more preferably 200 to 700 Ω, and even more preferably 300 to 500 Ω.

[0160] The configuration in which a resistor is connected in series between the piezoelectric film and the signal source can achieve flatter frequency characteristics when combined with a driver unit having the above-mentioned piezoelectric film with a curved portion and a perforated plate laminated on the concave side of the curved portion, and a first air chamber defined by the concave surface of the piezoelectric film and the perforated plate communicates with the outside via through holes formed in the perforated plate. However, the configuration in which a resistor is connected in series between the piezoelectric film and the signal source is not limited to combinations with driver units of the above-mentioned configuration, and can achieve the effect of flattening the frequency characteristics when combined with a driver unit (electro-acoustic transducer) including a piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer.

[0161] In the above example, the piezoelectric film 10 of the driver unit has a first electrode layer 24 and a first protective layer 28 on one side of the piezoelectric layer 20, and a second electrode layer 26 and a second protective layer 30 on the other side, but this is not limited to this.

[0162] FIG. 20 conceptually shows another example of the piezoelectric film included in the driver unit of the present invention.

[0163] The piezoelectric film 40 shown in Figure 20 has a configuration in which a reinforcing sheet 42 is laminated to the above-mentioned piezoelectric film 10, and the laminate (piezoelectric film 40) in which the piezoelectric film 10 and the reinforcing sheet 42 are laminated has a curved portion 40a that is molded so as to protrude on one main surface side and recess on the other main surface side.

[0164] Fig. 21 shows a partially enlarged cross-sectional view of a piezoelectric film 40. The piezoelectric film 40 shown in Fig. 21 includes a piezoelectric layer 20, which is a sheet-like material having piezoelectric properties, a first electrode layer 24 laminated on one side of the piezoelectric layer 20, a first protective layer 28 laminated on the side of the first electrode layer 24 opposite the piezoelectric layer 20, a second electrode layer 26 laminated on the other side of the piezoelectric layer 20, a second protective layer 30 laminated on the side of the second electrode layer 26 opposite the piezoelectric layer 20, a reinforcing sheet 40 laminated on the side of the second protective layer 30 opposite the piezoelectric layer 20, and an adhesive layer 44 that adheres the second protective layer 30 to the reinforcing sheet 40. Note that the piezoelectric layer 20, the first electrode layer 24, the first protective layer 28, the second electrode layer 26, and the second protective layer 30 have the same configurations as those in the example shown in Fig. 10, and therefore description thereof will be omitted. The adhesive layer 44 may also be weakly adhesive so as to be easily peelable.

[0165] The reinforcing sheet 42 is a sheet-like member, and various resin films are suitable examples thereof. Examples of resin films used for the reinforcing sheet 42 include resin films similar to those used for the protective layer described above. Nonwoven fabrics, woven fabrics, etc. can also be used for the reinforcing sheet 42. Examples of nonwoven fabrics and woven fabrics used for the reinforcing sheet 42 include the nonwoven fabrics and woven fabrics used for the porous material described above. Paper or Japanese paper can also be used as the nonwoven fabric, and cheesecloth can also be used as the woven fabric.

[0166] By having the piezoelectric film 40 have the reinforcing sheet 42 and integrally forming the curved portion 40a, abnormal deformation of the curved portion 40a can be more suitably suppressed when putting on or taking off headphones incorporating a driver unit having this piezoelectric film 40. Furthermore, even when the headphones are not being put on, but an impact is applied due to being dropped or the user accidentally touching the curved portion 40a of the piezoelectric film 40, the presence of the reinforcing sheet 42 in the piezoelectric film 40 makes the curved portion 40a less likely to deform abnormally. This also improves handling during manufacturing.

[0167] Furthermore, once the curved portion is abnormally deformed, even if it returns to its original shape, traces of the deformation remain, which may result in poor appearance or affect acoustic performance. However, by providing the piezoelectric film 40 with the reinforcing sheet 42, traces of the deformation are less likely to remain.

[0168] The effect of such a reinforcing sheet 42 can also be obtained in a driver unit that does not have a perforated plate.

[0169] The thickness of the reinforcing sheet 42 depends on the thickness of the protective layer, the material of the reinforcing sheet 42, etc., but from the viewpoint of suppressing abnormal deformation of the curved portion 40a, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. On the other hand, if the reinforcing sheet 42 is too thick, the vibration of the piezoelectric film 40 may be suppressed, resulting in a decrease in sound pressure. Therefore, the thickness of the reinforcing sheet 42 is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less.

[0170] Here, if the protective layer is sufficiently thick without affecting sound pressure, the abnormal deformation of the curved portion 40a when putting on or taking off the headphones can be more effectively suppressed. Furthermore, abnormal deformation of the curved portion 40a when an impact is applied or when the curved portion 40a is accidentally touched can also be suppressed. Meanwhile, as mentioned above, it is necessary to extend the electrodes from the electrode layer of the piezoelectric film to the outside. From a manufacturing perspective, it is desirable to extend the electrodes after forming the curved portion. Furthermore, from a manufacturing perspective, it is desirable to extend the electrodes by forming through-holes in the protective layer using a laser or the like, filling the through-holes with a conductive material, and then extending the electrodes to the outside. When forming through-holes in the protective layer using a laser or the like, it is necessary to thin the protective layer from the perspectives of manufacturing throughput and the quality stability of the through-holes. In this case, the thickness of the protective layer is preferably 1 μm to 10 μm, and more preferably 3 μm to 6 μm.

[0171] In this way, when it is necessary to make the protective layer thin, the piezoelectric film 40 having the reinforcing sheet 42 can more suitably suppress deformation of the curved portion 40a.

[0172] When the piezoelectric film 40 has the reinforcing sheet 42, to form a through hole in the protective layer using a laser or the like, for example, after forming a curved portion 40a in the piezoelectric film 40 having the reinforcing sheet 42, the reinforcing sheet 42 is partially peeled back (peeled off) at the peripheral portion (see reference numeral 10c in FIG. 5) outside the curved portion 40a, and the protective layer is subjected to laser processing to form a through hole, and after filling the through hole with a conductive material, a lead wire made of a metal foil such as Cu is adhered to the conductive material, thereby drawing an electrode to the outside. Note that good adhesion is achieved between the conductive material and the lead wire as the conductive material dries.

[0173] In this way, in order to make the reinforcing sheet 42 peelable, it is preferable to use a weak adhesive layer to adhere the reinforcing sheet 42 to the protective layer.

[0174] 20, the reinforcing sheet 42 is arranged on the convex side of the piezoelectric film 40, but this is not limitative and the reinforcing sheet 42 may be arranged on the concave side. Alternatively, the reinforcing sheet 42 may be arranged on both sides of the piezoelectric film 40.

[0175] Here, it is preferable that the headphones of the present invention have a protector ring disposed between the driver unit and the ear pad in contact with the ear pad, the protector ring has an opening that penetrates in a direction perpendicular to the surface that contacts the ear pad, the protector ring contacts an area of ​​30% or more of the total area of ​​the ear pad when viewed in the direction perpendicular to the surface that contacts the ear pad, and the shortest distance between the protector ring and the piezoelectric film of the driver unit is 0.3 mm or more. This configuration will be explained using Fig. 22.

[0176] Fig. 22 is a cross-sectional view conceptually illustrating another example of headphones of the present invention. Headphones 230 shown in Fig. 22 include a housing 202 forming an outer shell, a driver unit 100 housed in the housing 202, ear pads 204 arranged on the side of the driver unit 100 opposite the housing 202, and a protector ring 232 arranged between the ear pads 204 and the driver unit 100. In the example shown in Fig. 22, the housing 202, the driver unit 100, and the ear pads 204 have the same configuration as the example shown in Fig. 1, so their description will be omitted. Also, although ear pad locking members are not shown in Fig. 22, the headphones 230 shown in Fig. 22 may also include ear pad locking members.

[0177] The protector ring 232 is a circular (ring-shaped) plate member with an opening. The protector ring 232 is disposed in contact with the ear pad 204 to prevent the ear pad 204 from deforming toward the driver unit 100 and coming into contact with the piezoelectric film 10 (curved portion 10a) when the user puts on the headphones 230. This point will be explained using Figures 23 and 24.

[0178] Fig. 23 is a diagram showing a state in which headphones 200 without a protector ring 232 are pressed against an artificial ear (measurement device) M with a load applied from above. Fig. 24 is a diagram showing a state in which headphones 230 with a protector ring 232 are pressed against an artificial ear (measurement device) M with a load applied from above.

[0179] 23 , if the headphones 200 do not have the protector ring 232, depending on the shape, size, and material of the ear pad 204, the positional relationship between the ear pad 204 and the driver unit 100 (piezoelectric film 10), and the pressure applied to the headphones 200, the ear pad 204 may deform toward the driver unit 100 and come into contact with the curved portion 10 a of the piezoelectric film 10, causing deformation of the curved portion 10 a. Deformation of the curved portion 10 a will result in a deterioration in sound quality.

[0180] 24 , by providing the headphones 230 with a protector ring 232, even if a pressing force is applied to the headphones 200, the ear pads 204 can be prevented from deforming toward the driver unit 100, and can be prevented from coming into contact with the piezoelectric film 10 (curved portion 10 a). Preventing the ear pads 204 from coming into contact with the piezoelectric film 10 (curved portion 10 a) can prevent abnormal deformation of the curved portion 10 a of the piezoelectric film 10, and can prevent deterioration in sound quality that would otherwise accompany deformation of the curved portion 10 a. Furthermore, by preventing the ear pads 204 from deforming toward the driver unit 100, the ear pads 204 are effectively compressed over a wider area, which increases the airtightness of the space formed by the user's ears and the ear pads 204, and can further improve the sound pressure in the mid-to-low frequency range.

[0181] The effect of such a protector ring 232 can also be obtained in headphones having a driver unit that does not have a perforated plate.

[0182] In the example shown in FIG. 22 , one surface of the protector ring 232 contacts the ear pad 204, and the other surface contacts the driver unit 100 (holding member 106). Note that the present invention is not limited to this. A spacer or the like may be provided between the other surface of the protector ring 232 and the driver unit 100 (holding member 106), or the holding member 106 may also serve as the spacer. By providing a spacer or having the holding member 106 also serve as the spacer, the distance between the protector ring 232 and the piezoelectric film 10, i.e., the distance between the ear pad 204 and the piezoelectric film 10, can be appropriately adjusted. Furthermore, the protector ring 232 and the holding member 106 may be integrated into one component. Although omitted from FIG. 22 , the locking member 206 may also have the function of the protector ring 232, and may further be integrated into the holding member 106.

[0183] Furthermore, it is preferable that the protector ring 232 contacts an area of ​​30% or more of the total area of ​​the ear pad when viewed from a direction perpendicular to the surface that contacts the ear pad 204. This point will be explained using FIG.

[0184] FIG. 25 is a view of the ear pad 204 and the protector ring 232 as viewed from a direction perpendicular to the plane where the protector ring 232 contacts the ear pad 204 (viewed from side to side in FIG. 22).

[0185] 25 , the area indicated by the hatching slanting upward to the right is the ear pad 204, and the area where the hatching slanting upward to the left and the hatching slanting upward to the right overlap is the area where the ear pad 204 contacts the protector ring 232. In other words, the ratio of the area where the hatching slanting upward to the left and the hatching slanting upward to the right overlap (the area where the protector ring 232 contacts the ear pad 204) to the area of ​​the area indicated by the hatching slanting upward to the right (the total area of ​​the ear pad 204) is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more.

[0186] This prevents the ear pads 204 from deforming toward the driver unit 100 when the user puts on the headphones 230, and prevents the ear pads 204 from coming into contact with the piezoelectric film 10, thereby preventing abnormal deformation of the curved portion 10a of the piezoelectric film 10.

[0187] Furthermore, the shortest distance t (see the enlarged view in FIG. 22) between the protector ring 232 and the piezoelectric film 10 of the driver unit 100 is preferably 0.3 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. Note that the shortest distance t between the protector ring 232 and the piezoelectric film 10 is the distance when the piezoelectric film 10 is not driven.

[0188] This prevents the piezoelectric film 10 from coming into contact with the protector ring 232 even when the piezoelectric film 10 is driven and vibrates. Furthermore, when a user puts on the headphones 230, the ear pads 204 deform toward the driver unit 100, preventing the ear pads 204 from coming into contact with the piezoelectric film 10 and preventing abnormal deformation of the curved portions 10 a of the piezoelectric film 10.

[0189] The inner diameter (diameter of the opening) of the protector ring 232 may be larger, smaller, or approximately the same as the inner diameter of the ear pad 204. The inner diameter of the protector ring 232 is preferably about −10 mm to +10 mm with respect to the inner diameter of the ear pad 204.

[0190] Furthermore, there are no particular limitations on the thickness of the protector ring 232, but from the viewpoints of preventing deformation of the protector ring 232 when the ear pad 204 is pressed, miniaturization of the headphones 232, etc., a thickness of 0.5 mm to 10 mm is preferable, 1 mm to 7 mm is more preferable, and 2 mm to 5 mm is even more preferable.

[0191] Furthermore, a grill may be provided at the opening of the protector ring, or a protector ring with an integrated grill may be used. Fig. 26 is a cross-sectional view conceptually showing another example of headphones of the present invention. The headphones shown in Fig. 26 have the same configuration as the headphones shown in Fig. 22 except that they have a protector ring 233 instead of the protector ring 232.

[0192] The protector ring 233 has a grill-like portion with multiple holes formed in the center thereof, i.e., directly below the central hole of the ear pad 204. This prevents abnormal deformation of the piezoelectric film 10 due to physical contact with a finger or the like, while allowing sound to reach the ear.

[0193] It is desirable that the contact surface of the protector ring 233 with the ear pad 204 be flat, but in order to ensure that the shortest distance t between the protector ring 233 and the piezoelectric film 10 is 0.3 mm or more, the central portion (grill portion) may be curved as necessary, as shown in Figure 26.

[0194] The driver unit and headphones of the present invention have been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may of course be made within the scope of the gist of the present invention.

[0195] The present invention will be described in more detail below with reference to specific examples of the present invention. However, the present invention is not limited to these examples, and the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

[0196] Example 1 <Preparation of Piezoelectric Film> A piezoelectric film was prepared using the method shown in Figures 11 to 13. First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) using the following composition ratio. PZT particles were then added to this solution as piezoelectric particles using the following composition ratio, and the mixture was stirred using a propeller mixer (2000 rpm) to prepare a coating material for forming a piezoelectric layer: 300 parts by weight of PZT particles, 30 parts by weight of cyanoethylated PVA, and 70 parts by weight of DMF. The PZT particles used were prepared by sintering commercially available PZT raw material powder at 1000 to 1200°C, followed by crushing and classifying the powder to an average particle size of 2 μm.

[0197] Meanwhile, sheets 11a and 11b were prepared by vacuum-depositing a 0.1 μm-thick copper thin film on a 4 μm-thick PET film. In this example, the first and second electrode layers were 0.3 μm-thick copper-deposited thin films, and the first and second protective layers were 4 μm-thick PET films. To facilitate easy handling during the process, the PET films were equipped with 50 μm-thick separators (PET temporary support). After thermocompression bonding of sheet 11c, the separators were removed from each protective layer.

[0198] The paint for forming the piezoelectric layer prepared previously was applied to the first electrode layer (copper vapor-deposited thin film) of the sheet-like material 11a using a slide coater. The paint was applied so that the thickness of the coating film after drying would be 50 μm. The sheet-like material with the paint applied was then heated and dried on a hot plate at 120°C to evaporate the DMF. This produced a piezoelectric laminate 11b having a copper first electrode layer on a PET first protective layer, and a 50 μm-thick piezoelectric layer (polymer composite piezoelectric layer) on top of that.

[0199] The produced piezoelectric layer was subjected to polarization treatment in the thickness direction.

[0200] A sheet-like material 11c, which was a PET film with a copper thin film deposited thereon, was laminated on the polarization-treated piezoelectric laminate, with the second electrode layer (the copper thin film side) facing the piezoelectric layer. Next, the laminate of the piezoelectric laminate and the sheet-like material was thermocompression-bonded at a temperature of 120°C using a laminator, thereby adhering and bonding the piezoelectric layer and the second electrode layer to produce a piezoelectric film as shown in FIG.

[0201] Next, the produced piezoelectric film was molded into a shape having the curved portion 10a as shown in Figure 1 by a heat compression molding method using a hot press machine (AH-2003 manufactured by AS ONE Corporation) in a mold having a shape corresponding to the shape of the curved portion 10a to be molded. The shape of the curved portion 10a was a part of a sphere. When viewed from a direction perpendicular to the main surface of the piezoelectric film, the shape of the curved portion 10a was circular, with a diameter of 60 mm and a height of 5 mm.

[0202] Thereafter, the piezoelectric film 10 was cut out to a size of 64 mm in diameter with the curved portion 10a at the center. In this manner, the piezoelectric film 10 having the curved portion was produced.

[0203] <Fabrication of the driver unit> A 100 μm thick copper plate was prepared as a perforated plate. The copper plate was cut to a diameter of 86 mm, and 13 through-holes with a diameter of 4 mm were formed in a staggered pattern in the approximate center (see Figure 2). The total area of ​​the through-holes was 6% of the area of ​​the vibration region (curved portion) of the piezoelectric film. In addition, eight insertion holes were provided at equal intervals around the circumference near the end.

[0204] Two holding members were prepared by cutting a 3 mm thick acrylic plate into two rings with an outer diameter of 86 mm and an inner diameter of 60 mm. Eight insertion holes were provided at equal intervals around the circumference near the end of one holding member. Eight screw holes were provided at equal intervals around the circumference near the end of the other holding member.

[0205] A holding member having a screw hole, a piezoelectric film, a perforated plate, and a holding member having an insertion hole were stacked in this order, and screws serving as fastening members were inserted into the insertion holes from the holding member on the perforated plate side and screwed into the screw holes of the holding member on the piezoelectric film side, thereby sandwiching the piezoelectric film and the perforated plate between the two holding members. The perforated plate was stacked on the concave side of the curved portion of the piezoelectric film.

[0206] A 15 mm thick urethane foam (UBTK manufactured by Bridgestone Corporation) was cut into a 60 mm diameter piece for the porous material. This porous material was placed on the surface of the perforated plate facing the holding member to create a driver unit. The porous material was attached to the perforated plate with adhesive, taking care not to block the through-holes with the adhesive.

[0207] Comparative Example 1 A driver unit was produced in the same manner as in Example 1, except that the perforated plate and porous material were not used.

[0208] [Evaluation] The driver units of the examples and comparative examples thus produced were housed in a housing, and ear pads were placed on the opening side of the housing to produce a test unit simulating headphones.

[0209] The driver unit was placed in the opening of the housing with the concave surface of the curved portion facing the housing, and the earpad was placed on the opposite side of the driver unit from the housing to form a test unit. In this case, there was a gap between the driver unit and the housing, and the second air chamber defined by the driver unit and the housing was configured to communicate with the outside.

[0210] The ear pad side of the fabricated test unit was placed without load on a headphone measurement artificial ear (TYPE2015E manufactured by ACO Corporation), and a sine sweep signal with a frequency of 20 Hz to 20 kHz and an applied voltage of 10 Vpp was input to the piezoelectric film to measure the sound pressure. Next, with the test unit pressed against the headphone measurement artificial ear with a pressing force of 200 g, a sine sweep signal with a frequency of 20 Hz to 20 kHz and an applied voltage of 10 Vpp was input to the piezoelectric film to measure the sound pressure.

[0211] Graphs of the frequency characteristics of Example 1 and Comparative Example 1 are shown in Figures 15 and 16, respectively. As shown in Figure 16, in Comparative Example 1, peaks and dips occur in the sound pressure in the high-frequency range, resulting in undulations in the frequency characteristics. Furthermore, as shown by the dashed line in Figure 16, when a load is applied and the piezoelectric film is pressed against the coupler, the sound pressure in the low-frequency range is lower than the sound pressure in the mid- and high-frequency ranges. After the test, the piezoelectric film was observed and found to have deformed in its curved portion. This is thought to be due to a pressure difference occurring between the coupler side and the opposite side of the piezoelectric film when the test unit was pressed against the coupler, which deformed the shape of the curved portion and caused a change in the frequency characteristics.

[0212] In contrast, Example 1 shown in Figure 15 shows that flat frequency characteristics are achieved, with no change in sound pressure across a wide frequency range from low to high frequencies. It can also be seen that there is little change in frequency characteristics with or without a load. After the test, the piezoelectric film was observed and no deformation of the curved portion was observed.

[0213] Example 2 A driver unit was fabricated in the same manner as in Example 1, except that a series resistor (360 Ω) was connected to the wiring connected to the electrode layer of the piezoelectric film.

[0214] The ear pad side of the fabricated test unit was placed without load on an artificial ear for headphone measurement (TYPE2015E manufactured by ACO Corporation), and a sine sweep signal with a frequency of 20 Hz to 20 kHz and an applied voltage of 10 Vpp was input to the piezoelectric film to measure the sound pressure.

[0215] FIG. 17 shows the measurement results of the frequency characteristics of Examples 1 and 2 under no load.

[0216] As shown in Figure 17, when there is no resistance between the piezoelectric film and the signal source (Example 1), the sound pressure in the frequency band of 1.0 kHz or more is slightly higher than the sound pressure in the frequency band of less than 1.0 kHz. However, Example 2, in which a resistance is connected in series between the piezoelectric film and the signal source, can reduce the sound pressure in the frequency band of 1.0 kHz or more, making the frequency characteristics flatter.

[0217] [Examples 2B to 2D] For Examples 2B to 2D, test units were fabricated in the same manner as in Example 2, except that the resistance values ​​of the series resistors in Example 2 were set to 100 Ω, 200 Ω, and 400 Ω, respectively, and their frequency characteristics were measured. The results are shown in Figure 18.

[0218] 18, when there is no resistance between the piezoelectric film and the signal source, the sound pressure in the frequency band of 1.0 kHz or higher is slightly higher than the sound pressure in the frequency band below 1.0 kHz, but by connecting a resistor in series between the piezoelectric film and the signal source, the sound pressure in the frequency band of 1.0 kHz or higher can be reduced, making the frequency characteristics flatter. It can also be seen that the amount of reduction in sound pressure only in the frequency band of 1.0 kHz or higher can be adjusted by changing the value of the connected resistor, without affecting the sound pressure in the frequency band below 1.0 kHz.

[0219] Example 3 In Example 1, when producing the piezoelectric film, after laminating the sheet-like material 11c (see FIG. 13), one side of a 50 μm-thick PET separator was left intact to form the curved portion 40a. This separator was used as the reinforcing sheet 42. The curved portion 40a was formed so that the side facing the reinforcing sheet 42 was convex. The shape of the curved portion 40a was a part of a sphere. When viewed from a direction perpendicular to the main surface of the piezoelectric film, the shape of the curved portion 40a was circular, with a diameter of 60 mm and a height of 5 mm.

[0220] Thereafter, the piezoelectric film 40 was cut out to a size of 70 mm in diameter with the curved portion 40a at the center. In this manner, the piezoelectric film 40 having the curved portion 40a and the PET film with a thickness of 50 μm as the reinforcing sheet 42 was produced.

[0221] Using the produced piezoelectric film 40, a driver unit was produced in the same manner as in Example 1.

[0222] Example 4 A piezoelectric film 40 was produced in the same manner as in Example 3, except that a 25 μm thick PET separator was used as the reinforcing sheet 42, and a driver unit was fabricated.

[0223] Example 5 A piezoelectric film 40 was produced in the same manner as in Example 3, except that a nonwoven fabric (Japanese paper) having a thickness of 15 μm was used as the reinforcing sheet 42 and the piezoelectric film 40 was produced as follows, and a driver unit was produced.

[0224] In the production of the piezoelectric film, after laminating the sheet-like material 11c, the two separators were removed, and a 15 μm-thick nonwoven fabric (Japanese paper) was attached to one of the protective layers, followed by molding the curved portion 40a to produce the piezoelectric film. A 12 μm-thick hot melt sheet was used to attach the nonwoven fabric (Japanese paper).

[0225] Example 6 A piezoelectric film 40 was produced in the same manner as in Example 5, except that a nonwoven fabric (Japanese paper) with a thickness of 40 μm was used as the reinforcing sheet 42, and a driver unit was fabricated.

[0226] Example 7 A piezoelectric film 40 was produced in the same manner as in Example 5, except that a woven fabric (cheese cloth) having a thickness of 50 μm was used as the reinforcing sheet 42, and a driver unit was fabricated.

[0227] [Reference Examples 1 to 5] As Reference Examples 1 to 5, driver units were fabricated in the same manner as in Examples 3 to 7, except that the perforated plate and porous material were not included.

[0228] [Evaluation] With ear pads attached to the convex side of the curved portion of the driver units produced in Examples 1, 3 to 7, Comparative Example 1, and Reference Examples 1 to 5, the driver units were placed with the ear pads facing downwards on a transparent acrylic plate, and a load was applied from above. The state of the curved portion of the piezoelectric film was observed from below the acrylic plate at loads of 100 g, 200 g, 300 g, 400 g, 500 g, and 600 g. Cases without deformation were rated A, and cases with deformation were rated C. The results are shown in Table 2.

[0229]

[0230] Table 2 shows that Examples 3 to 7, which have a reinforcing sheet, can more effectively suppress abnormal deformation of the curved portion compared to Example 1, which does not have a reinforcing sheet. A comparison between Comparative Example 1 and Reference Examples 1 to 5 also shows that the presence of a reinforcing sheet can more effectively suppress abnormal deformation of the curved portion. The pressure exerted when wearing typical headphones is approximately 200 g-force to 400 g-force.

[0231] [Example 8] The driver unit of Example 1 was housed in a housing, the following protector ring was placed on the opening side of the housing, and ear pads were placed so as to be in contact with the protector ring, thereby producing a test unit simulating headphones.

[0232] The protector ring was prepared by cutting an acrylic plate having a thickness of 3 mm into a ring shape having an outer diameter of 74 mm and an inner diameter of 40 mm.

[0233] In the test unit, the shortest distance t between the protector ring and the piezoelectric film was 1 mm. When viewed perpendicularly to the surface in contact with the ear pad, the protector ring contacted the ear pad over 85% of its total area. The ear pad had an inner diameter of approximately 32 mm, an outer diameter of approximately 72 mm, and a thickness of approximately 15 mm.

[0234] [Evaluation] First, the ear pad side of the test unit prepared in Example 1 was placed on an artificial ear for measuring headphones (TYPE2015E manufactured by ACO Corporation) and pressed against it with loads of 200 g and 500 g, respectively. In this state, a sine sweep signal with a frequency of 20 Hz to 20 kHz and an applied voltage of 10 Vpp was input to the piezoelectric film to measure the sound pressure.

[0235] A graph of the frequency characteristics is shown in FIG.

[0236] As shown in Figure 27, the sound pressure is lower, especially in the low frequency range, when the load is 500g compared to when the load is 200g. This is thought to be because when the test unit is pressed against the artificial ear, the ear pad deforms and comes into contact with the piezoelectric film.

[0237] Next, the ear pad side of the test unit prepared in Example 8 was placed on a headphone measurement artificial ear (TYPE2015E manufactured by ACO Corporation) and pressed with a load of 500 g. In this state, a sine sweep signal with a frequency of 20 Hz to 20 kHz and an applied voltage of 10 Vpp was input to the piezoelectric film to measure the sound pressure. A graph of the frequency characteristics is shown in Figure 28. The results for Example 1 with a load of 200 g are also shown.

[0238] As shown in Figure 28, the test unit of Example 8 with a protector ring did not experience a drop in sound pressure even when pressed against an artificial ear with a load of 500g. Furthermore, compared to the results for Example 1 with a load of 200g, Example 8 exhibited improved sound pressure in the mid-low frequency range. This is thought to be because the protector ring prevents the ear pad from deforming toward the driver unit and effectively compresses the ear pad over a wider area, thereby increasing the airtightness of the space between the artificial ear and the ear pad, thereby further improving sound pressure in the mid-low frequency range.

[0239] Example 8B A driver unit was fabricated in the same manner as in Example 8, except that a series resistor (360 Ω) was connected to the wiring connected to the electrode layer of the piezoelectric film.

[0240] The ear pad side of the fabricated test unit was placed on a headphone measurement artificial ear (TYPE2015E manufactured by ACO CORPORATION) with a load of 400 g, and a sine sweep signal with a frequency of 20 Hz to 20 kHz and an applied voltage of 10 Vpp was input to the piezoelectric film to measure the sound pressure.

[0241] FIG. 29 shows the measurement results of the frequency characteristics of Example 8 and Example 8B.

[0242] 29, it can be seen that Example 8B, in which a resistor is connected in series between the piezoelectric film and the signal source, can reduce the sound pressure in the frequency band above 1.0 kHz, making the frequency characteristics flatter. From the above, the effects of the present invention are clear.

[0243] REFERENCE SIGNS LIST 10 Piezoelectric film 10a Curved portion 10c Edge portion 11a, 11c Sheet-like material 11b Piezoelectric laminate 20 Piezoelectric layer 24 First electrode layer 26 Second electrode layer 28 First protective layer 30 Second protective layer 34 Matrix 36 Piezoelectric particles 40 Piezoelectric film 40a Curved portion 42 Reinforcement sheet 44 Adhesive layer 100, 100b Driver unit 101 First air chamber 102 Perforated plate 102a Through hole 102b Insertion hole 104 Porous material 106 Holding member 106a Screw hole 108 Holding member 108a Insertion hole 110 Fastening member 200, 200b Headphones 201 Second air chamber 202 Housing 202a Through hole 204 Ear pad 206 Ear pad locking member 220 Signal source 222 Resistor 230 Headphone 232 Protector ring U User's ear M Measuring device (artificial ear)

Claims

1. A driver unit comprising: a piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer; and a plate-shaped perforated plate having at least one through hole, wherein the piezoelectric film has a curved portion that protrudes on one main surface side and is molded to be recessed on the other main surface side, the perforated plate is laminated on the concave side of the curved portion of the piezoelectric film, and the through hole connects a first air chamber defined by the concave surface of the piezoelectric film and the perforated plate to the outside.

2. The driver unit according to claim 1, wherein the ratio of the total area of ​​the through holes to the area of ​​the curved portion of the piezoelectric film in a plan view is 3% to 70%.

3. A driver unit as described in claim 1, further comprising a sound absorbing layer made of a porous material arranged to cover said through holes on the surface of said perforated plate opposite said piezoelectric film.

4. The driver unit according to claim 1, wherein the boundary line of the curved portion of the piezoelectric film has a circular shape.

5. A driver unit as claimed in claim 1, further comprising a series resistor connected between said electrode layer of said piezoelectric film and a signal source which drives said piezoelectric film.

6. A headphone comprising: a driver unit according to any one of claims 1 to 5; a housing having an opening and accommodating said driver unit; and an ear pad arranged on the opening side of said housing.

7. The headphones according to claim 6, wherein a second air chamber defined by the driver unit and the housing communicates with the outside.

8. The headphone according to claim 6, wherein the housing is disposed on the concave side of the piezoelectric film of the driver unit.

9. The headphones of claim 6, further comprising a protector ring disposed between the driver unit and the ear pad in contact with the ear pad, the protector ring having an opening penetrating in a direction perpendicular to the surface in contact with the ear pad, the protector ring being in contact with an area of ​​30% or more of the total area of ​​the ear pad when viewed in the direction perpendicular to the surface in contact with the ear pad, and the shortest distance between the protector ring and the piezoelectric film of the driver unit being 0.3 mm or more.

Images