Polymer composite piezoelectrics, piezoelectric films, piezoelectric speakers, flexible displays

Abstract

The present invention provides a polymer composite piezoelectric body capable of obtaining a piezoelectric film that can output a higher sound pressure when used in a piezoelectric speaker, a piezoelectric film using the polymer composite piezoelectric body, and a piezoelectric speaker and a flexible display using the piezoelectric film. The polymer composite piezoelectric body of the present invention includes a polymer matrix and piezoelectric particles, and the polymer matrix includes a polymer having a group represented by formula (1). Formula (1) *-L<supgt;1< / supgt>-CR<supgt;1< / supgt;R<supgt;2< / supgt>-CN, in formula (1), L<supgt;1< / supgt> represents a divalent linking group other than a divalent aliphatic hydrocarbon group. R<supgt;1< / supgt> and R<supgt;2< / supgt> each independently represent a hydrogen atom, an alkyl group, or an aryl group.

Description

Technical Field

[0001] The present invention relates to a polymer composite piezoelectric body, a piezoelectric film using the polymer composite piezoelectric body, and a piezoelectric loudspeaker and a flexible display screen using the piezoelectric film. Background Art

[0002] As displays such as liquid crystal displays and organic EL (electroluminescence) displays become thinner and lighter, speakers used in these thin displays are also required to be lighter and thinner. In addition, as flexible displays using flexible substrates such as plastic are developed, speakers used in flexible displays are also required to be flexible.

[0003] The existing speakers are usually in the shape of a funnel-shaped so-called cone or a spherical dome. However, if such speakers are built into the above-mentioned thin display, it is not possible to fully achieve thinness, and the lightness or flexibility may be impaired. In addition, when the speakers are mounted externally, it is inconvenient to carry.

[0004] Therefore, as a thin speaker that can be integrated with a thin display or a flexible display without sacrificing lightness or flexibility, a technology using a piezoelectric film that is flexible and has a property of expanding and contracting in response to applied voltage has been proposed.

[0005] For example, as a piezoelectric film that is sheet-shaped and flexible and can stably reproduce high-quality sound, there is proposed a piezoelectric film (electroacoustic conversion film) disclosed in Patent Document 1. The piezoelectric film disclosed in Patent Document 1 includes: a polymer composite piezoelectric body (piezoelectric layer) in which piezoelectric particles are dispersed in a viscoelastic matrix composed of a polymer material having viscoelasticity at room temperature, thin film electrodes formed on both sides of the polymer composite piezoelectric body, and a protective layer formed on the surface of the thin film electrode.

[0006] Previous technical literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-014063 Summary of the invention

[0009] Technical issues to be solved by the invention

[0010] In recent years, further improvement of the sound pressure has been expected in such piezoelectric films.

[0011] The present inventors have studied the sound pressure characteristics of a piezoelectric speaker using the piezoelectric film described in Patent Document 1 and have found that the characteristics do not meet current requirements and that further improvements are required.

[0012] The purpose of the present invention is to solve the problems of the prior art and to provide a polymer composite piezoelectric body that can obtain a piezoelectric film that can output higher sound pressure when used in a piezoelectric speaker, a piezoelectric film using the polymer composite piezoelectric body, and a piezoelectric speaker and a flexible display using the piezoelectric film.

[0013] Means for solving technical problems

[0014] In order to solve this problem, the present invention has the following structure.

[0015] [1] A polymer composite piezoelectric body comprising: a polymer matrix including a polymer having a group represented by the formula (1) described below; and piezoelectric particles.

[0016] [2] The polymer composite piezoelectric body according to [1], wherein the polymer has a repeating unit represented by the formula (2) described below.

[0017] [3] The polymer composite piezoelectric body according to [2], wherein L 1 It represents -O-, -S-, -CO-, -NH-, or a group formed by combining two or more of them.

[0018] [4] A polymer composite piezoelectric according to any one of [1] to [3], wherein the polymer is a polymer having only repeating units represented by formula (2), or a polymer having repeating units represented by formula (2) and repeating units containing polar groups other than cyano groups.

[0019] [5] The polymer composite piezoelectric body according to any one of [1] to [4], wherein the content of the piezoelectric particles is 50% by volume or more relative to the total volume of the polymer composite piezoelectric body.

[0020] [6] The polymer composite piezoelectric according to any one of [1] to [5], wherein the piezoelectric particles include ceramic particles having a perovskite-type or wurtzite-type crystal structure.

[0021] [7] The polymer composite piezoelectric according to [6], wherein the piezoelectric particles include any one of lead zirconate titanate, lead lanthanum zirconate titanate, barium titanate, zinc oxide, and a solid solution of barium titanate and bismuth ferrite.

[0022] [8] A piezoelectric film comprising: the polymer composite piezoelectric body described in any one of [1] to [7]; and

[0023] Two thin film electrodes stacked on both sides of a polymer composite piezoelectric body.

[0024] [9] A piezoelectric speaker comprising the piezoelectric film described in [8].

[0025]

[10] A flexible display screen, comprising: a flexible display screen having flexibility and having the piezoelectric film described in [8] attached to the surface opposite to the image display surface.

[0026] Effects of the Invention

[0027] According to the present invention, there are provided a polymer composite piezoelectric body that can obtain a piezoelectric film capable of outputting a higher sound pressure when used in a piezoelectric speaker, a piezoelectric film using the polymer composite piezoelectric body, and a piezoelectric speaker and a flexible display using the piezoelectric film. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a cross-sectional view conceptually showing an example of the piezoelectric film of the present invention.

[0029] Figure 2 It is used to illustrate Figure 1 A conceptual diagram of the method for manufacturing a piezoelectric film is shown.

[0030] Figure 3 It is used to illustrate Figure 1 A conceptual diagram of the method for manufacturing a piezoelectric film is shown.

[0031] Figure 4 It is used to illustrate Figure 1 A conceptual diagram of the method for manufacturing a piezoelectric film is shown.

[0032] Figure 5 It is conceptually used Figure 1 FIG. 1 is a diagram showing an example of a piezoelectric speaker using a piezoelectric film.

[0033] Figure 6 This is a diagram conceptually showing an example in which the flexible display panel of the present invention is used in an organic electroluminescent display.

[0034] Figure 7 This is a diagram conceptually showing an example of using the flexible display screen of the present invention for electronic paper.

[0035] Figure 8 This is a diagram conceptually showing an example in which the flexible display panel of the present invention is used in a liquid crystal display.

[0036] Fig. 9 This is a diagram conceptually showing the structure of a general throat microphone. DETAILED DESCRIPTION

[0037] Hereinafter, the polymer composite piezoelectric body, piezoelectric film, piezoelectric speaker, flexible display screen, throat vibration microphone and sensor for musical instrument of the present invention will be described in detail according to the preferred embodiments shown in the accompanying drawings.

[0038] The description of the structural conditions described below is completed based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0039] In addition, in this specification, the numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0040] Furthermore, unless otherwise specified, the bonding direction of the divalent groups marked in this specification is not limited. For example, when Y in a compound represented by the general formula "XYZ" is -COO-, Y may be -CO-O- or -O-CO-. That is, the above compound may be "X-CO-OZ" or "XO-CO-Z".

[0041] For example, the polymer composite piezoelectric body of the present invention is formed into a sheet and thin film electrodes (electrode layers) are provided on both sides to be used as a piezoelectric film. For example, such a piezoelectric film can be used as a vibration plate of an electroacoustic transducer such as a piezoelectric speaker, a microphone, and an audio sensor.

[0042] If the piezoelectric film is stretched in the in-plane direction by applying a voltage to the piezoelectric film, the electroacoustic transducer absorbs the stretching, so the piezoelectric film moves upward (in the direction of sound diffusion). Conversely, if the piezoelectric film is contracted in the in-plane direction by applying a voltage to the piezoelectric film, the electroacoustic transducer absorbs the contraction, so the piezoelectric film moves downward.

[0043] The electroacoustic transducer converts vibration (sound) and electrical signals by vibrating based on the repeated expansion and contraction of the piezoelectric film. The electrical signal is input into the piezoelectric film and the sound is played according to the vibration corresponding to the electrical signal, or the vibration of the piezoelectric film caused by receiving sound waves is converted into an electrical signal or used to provide touch or transport objects through vibration.

[0044] Specifically, various audio devices such as pickups (instrument sensors) used in musical instruments such as guitars, speakers (e.g., full-range speakers, tweeters, mid-range speakers, and woofers), headphone speakers, noise cancellers, and microphones can be cited. In addition, the piezoelectric film of the present invention is a non-magnetic body, so it can be preferably used as a noise canceller for MRI (magnetic resonance imaging).

[0045] Furthermore, the electroacoustic transducer using the piezoelectric film of the present invention is thin, light and flexible, and therefore can be preferably used in wearable products such as hats, scarves and clothes, thin displays such as televisions and digital signage, buildings that function as sound machines, etc., car roofs, curtains, umbrellas, wallpapers, windows and beds, etc.

[0046] exist Figure 1 A cross-sectional view schematically showing an example of the piezoelectric film of the present invention is shown.

[0047] like Figure 1 As shown, the piezoelectric film 10 of the present invention comprises: a piezoelectric layer 12 which is a sheet-like object having piezoelectric properties, a lower thin film electrode 14 stacked on one side of the piezoelectric layer 12, a lower protective layer 18 stacked on the lower thin film electrode 14, an upper thin film electrode 16 stacked on the other side of the piezoelectric layer 12, and an upper protective layer 20 stacked on the upper thin film electrode 16.

[0048] In the piezoelectric film 10, the piezoelectric layer 12 as a polymer composite piezoelectric body is composed of a polymer composite piezoelectric body. The polymer composite piezoelectric body is conceptually shown in FIG. Figure 1 The piezoelectric particles 26 are dispersed in a polymer matrix 24 composed of a polymer material.

[0049] The piezoelectric layer 12 is the polymer composite piezoelectric body of the present invention.

[0050] Among them, the polymer composite piezoelectric body (piezoelectric layer 12) preferably has the following requirements: In the present invention, room temperature refers to 0 to 50°C.

[0051] (i) Flexibility

[0052] For example, when a newspaper or magazine is held in a lightly rolled-up document-like state for carrying, it will be continuously subjected to relatively slow and large bending deformation of less than a few Hz from the outside. At this time, if the polymer composite piezoelectric body is hard, a correspondingly large bending stress will be generated, which may cause cracks at the interface between the polymer matrix and the piezoelectric particles and eventually lead to destruction. Therefore, the polymer composite piezoelectric body is required to have moderate softness. In addition, if the strain energy can be diffused to the outside as heat, the stress can be relaxed. Therefore, it is expected that the loss tangent of the polymer composite piezoelectric body is moderately large.

[0053] (ii) Sound quality

[0054] The piezoelectric particles are vibrated at a frequency in the audio bandwidth of 20Hz to 20kHz. Through this vibration energy, the entire vibration plate (polymer composite piezoelectric body) vibrates as a whole, and the speaker plays sound. Therefore, in order to improve the transmission efficiency of vibration energy, the polymer composite piezoelectric body is required to have appropriate hardness. In addition, if the frequency characteristics of the speaker are smooth, the change in sound quality when the lowest resonance frequency f0 changes with the change in curvature also becomes smaller. Therefore, it is expected that the loss tangent of the polymer composite piezoelectric body is moderately large.

[0055] As is well known, the lowest resonance frequency f0 of a speaker diaphragm is given by the following equation: Where s is the stiffness of the vibration system and m is the mass.

[0056] [Formula 1]

[0057]

[0058] At this time, the greater the curvature of the piezoelectric film (i.e., the larger the curvature radius of the curved portion), the lower the mechanical stiffness s, so the lowest resonance frequency f0 becomes smaller. In other words, the sound quality (volume, frequency characteristics) of the speaker changes according to the curvature radius of the piezoelectric film.

[0059] In summary, it is desirable that the polymer composite piezoelectric body be rigid to vibrations of 20 Hz to 20 kHz and flexible to vibrations of a few Hz or less. Furthermore, it is desirable that the loss tangent of the polymer composite piezoelectric body be appropriately large for vibrations of all frequencies below 20 kHz.

[0060] Generally, polymer solids have a viscoelastic relaxation mechanism. As the temperature rises or the frequency decreases, large-scale molecular motion can be observed, resulting in a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum (absorption) in the loss modulus. Among them, the relaxation caused by the micro-Brownian motion of the molecular chains in the amorphous region is called the main dispersion, and a very large relaxation phenomenon can be found. The temperature at which this main dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most prominently manifested.

[0061] In the polymer composite piezoelectric (piezoelectric layer 12), by using a polymer material having a glass transition point at room temperature (in other words, a polymer material having viscoelasticity at room temperature) as a matrix, a polymer composite piezoelectric that is hard against vibrations of 20 Hz to 20 kHz and flexible against slow vibrations of several Hz or less can be realized. In particular, from the perspective of preferably showing this performance, it is preferred to use a polymer material having a glass transition temperature at a frequency of 1 Hz at room temperature as a matrix of the polymer composite piezoelectric.

[0062] The polymer material constituting the polymer matrix preferably has a maximum value of the loss tangent Tanδ of 0.5 or more at a frequency of 1 Hz based on a dynamic viscoelasticity test at room temperature.

[0063] Therefore, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the polymer matrix / piezoelectric particle interface in the maximum bending moment portion is relaxed, and higher flexibility can be expected.

[0064] Furthermore, the storage modulus (E') of the polymer material constituting the polymer matrix at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 100 MPa or more at 0°C and 10 MPa or less at 50°C.

[0065] This can reduce the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force, and can also demonstrate rigidity against acoustic vibrations of 20 Hz to 20 kHz.

[0066] Furthermore, the relative dielectric constant of the polymer material constituting the polymer matrix is ​​more preferably 10 or more at 25° C. Thus, when voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric particles in the polymer matrix, and thus a larger deformation amount can be expected.

[0067] However, on the other hand, in consideration of ensuring good moisture resistance, etc., a polymer material having a relative dielectric constant of 10 or less at 25°C is preferred.

[0068] In the polymer composite piezoelectric body (piezoelectric layer 12) of the present invention, as a polymer material constituting the polymer matrix 24 that preferably satisfies these conditions, a polymer having a base pattern represented by formula (1) (hereinafter also referred to as "specific polymer") is used. In formula (1), * represents a bonding position.

[0069] Formula (1)*-L 1 -CR 1 R 2 -CN

[0070] In formula (1), L 1 represents a divalent linking group other than a divalent aliphatic hydrocarbon group. 1 It represents a divalent linking group excluding a divalent aliphatic hydrocarbon group.

[0071] Moreover, as a divalent aliphatic hydrocarbon group, an alkylene group, an alkenylene group, and an alkynylene group are mentioned, for example.

[0072] Examples of divalent linking groups other than the above-mentioned divalent aliphatic hydrocarbon groups include -O-, -CO-, -S-, -SO2, -NRa- (Ra represents a hydrogen atom or an alkyl group), an arylene group, or a group formed by combining two or more of them (e.g., -COO-, -CONH-, etc.).

[0073] Among them, from the viewpoint of more excellent effect of the present invention, as L 1 , preferably -O-, -S-, -CO-, -NH- or a combination of two or more of them, more preferably -COO-. That is, the group represented by formula (1) is preferably -CO-O-CR 1 R 2 -CN or -O-CO-CR 1 R 2 -CN.

[0074] R 1 and R 2Each independently represents a hydrogen atom, an alkyl group or an aryl group.

[0075] By R 1 and R 2 The number of carbon atoms in the alkyl group represented is not particularly limited, but is preferably 1 to 5, more preferably 1 to 3, from the viewpoint of achieving more excellent effects of the present invention.

[0076] By R 1 and R 2 The aryl group represented by may be a monocyclic or polycyclic group, and an example thereof is phenyl.

[0077] The group represented by formula (1) may be directly bonded to the polymer main chain or may be bonded via a linking group. However, it is preferably directly bonded to the polymer main chain from the viewpoint of achieving more excellent effects of the present invention.

[0078] In the specific polymer, the polymer skeleton bonded to the group represented by the above formula (1) is not particularly limited, and examples thereof include a polyacrylate skeleton, a polymethacrylate skeleton, a polyacrylamide skeleton, a polymethacrylamide skeleton, a polyester skeleton, a polyurethane skeleton, a polyurea skeleton, a polyamide skeleton, a polycarbonate skeleton, a polyolefin skeleton, a polyether skeleton, a polyvinyl ether skeleton and a polystyrene skeleton.

[0079] Among them, the specific polymer preferably has a repeating unit represented by formula (2) from the viewpoint of achieving more excellent effects of the present invention.

[0080] [Chemical formula 2]

[0081]

[0082] L in formula (2) 1 , R 1 and R 2 The meaning of is the same as L in formula (1) 1 , R 1 and R 2 have the same meaning.

[0083] R 3 represents a hydrogen atom or an alkyl group.

[0084] By R 3 The number of carbon atoms in the alkyl group represented is not particularly limited, but is preferably 1 to 5, more preferably 1 to 3, from the viewpoint of achieving more excellent effects of the present invention.

[0085] Among them, the repeating unit represented by the formula (2) is preferably a repeating unit represented by the formula (2-1) or a repeating unit represented by the formula (2-2) because the effects of the present invention are more excellent.

[0086] The definitions of the groups in formula (2-1) and formula (2-2) are as described above.

[0087] [Chemical formula 3]

[0088]

[0089] The content of the repeating unit represented by formula (2) in the specific polymer is not particularly limited. From the perspective of the more excellent effect of the present invention, it is preferably 50 mol% or more, more preferably 80 mol% or more, and further preferably 90 mol% or more relative to all the repeating units in the specific polymer. As the upper limit, 100 mol% can be cited.

[0090] The repeating unit represented by formula (2) may be used alone or in combination of two or more. When the specific polymer has two or more repeating units represented by formula (2), the total amount thereof is preferably within the above range.

[0091] The specific polymer may have other repeating units in addition to the repeating unit represented by formula (2).

[0092] The other repeating unit may be a repeating unit having a cyano group (CN) or a repeating unit not having a cyano group.

[0093] From the viewpoint of achieving more excellent effects of the present invention, the other repeating unit is preferably a repeating unit having a polar group other than a cyano group. Examples of the polar group include a hydroxyl group, a carboxyl group, and an amino group.

[0094] As the repeating unit having a polar group other than a cyano group, a repeating unit represented by formula (3) is preferred.

[0095] [Chemical formula 4]

[0096]

[0097] In formula (3), R 4 represents a hydrogen atom or an alkyl group.

[0098] By R 4 The number of carbon atoms in the alkyl group represented is not particularly limited, but is preferably 1 to 5, more preferably 1 to 3, from the viewpoint of achieving more excellent effects of the present invention.

[0099] L 2 represents a single bond or a divalent linking group. 2 The divalent linking group represented by L can be exemplified by the above 1 A divalent linking group represented by L and a divalent aliphatic hydrocarbon group. 2The divalent linking group represented by is preferably -O-, -CO-, a divalent aliphatic hydrocarbon group, or a group formed by combining two or more of them (e.g., -CO-O-alkylene-, etc.).

[0100] X represents a hydroxyl group, a carboxyl group or an amino group.

[0101] Among them, from the viewpoint of more excellent effects of the present invention, the repeating unit represented by the formula (3) includes a repeating unit represented by the formula (3-1).

[0102] [Chemical formula 5]

[0103]

[0104] In formula (3-1), L 3 represents a single bond or -CO-O-alkylene-*1. In addition, *1 represents a bonding position to X.

[0105] X and R 4 The definition of is as above.

[0106] When the specific polymer has a repeating unit represented by formula (3), the content of the repeating unit represented by formula (3) is not particularly limited. From the perspective of achieving a better effect of the present invention, it is preferably 1 to 40 mol %, more preferably 5 to 25 mol %, relative to all repeating units in the specific polymer.

[0107] The repeating unit represented by formula (3) may be used alone or in combination of two or more. When the specific polymer has two or more repeating units represented by formula (3), the total amount thereof is preferably within the above range.

[0108] In addition, the specific polymer may have a repeating unit other than the repeating unit, for example, a repeating unit represented by formula (4) having a polar group other than a cyano group.

[0109] [Chemical formula 6]

[0110]

[0111] In formula (4), R 5 represents a hydrogen atom or an alkyl group.

[0112] By R 5 The number of carbon atoms in the alkyl group represented is not particularly limited, but is preferably 1 to 5, more preferably 1 to 3, from the viewpoint of achieving more excellent effects of the present invention.

[0113] R 6 It represents an alkyl group.

[0114] By R 6The number of carbon atoms in the alkyl group represented is not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5 from the viewpoint of achieving more excellent effects of the present invention.

[0115] From the perspective of achieving a more excellent effect of the present invention, the specific polymer is preferably a polymer having only a repeating unit represented by formula (2), or a polymer having a repeating unit represented by formula (2) and a repeating unit containing a polar group other than a cyano group (preferably a repeating unit represented by formula (3)).

[0116] Specific examples of the specific polymer are shown below.

[0117] [Chemical formula 7]

[0118]

[0119] The weight average molecular weight of the specific polymer is not particularly limited, but is preferably 5,000 to 300,000, more preferably 8,000 to 100,000, from the viewpoint of achieving more excellent effects of the present invention.

[0120] In this specification, the weight average molecular weight of a polymer is measured by the following apparatus and conditions.

[0121] Measuring device: Trade name "LC-20AD" (manufactured by SHIMADZU CORPORATION)

[0122] Column: Shodex KF-801×2, KF-802 and KF-803 (manufactured by SHOWA DENKO KK)

[0123] Measuring temperature: 40℃

[0124] Eluent: tetrahydrofuran, sample concentration 0.1-0.2 mass%

[0125] Flow rate: 1mL / min

[0126] Detector: UV-VIS detector (trade name "SPD-20A", manufactured by SHIMADZU CORPORATION)

[0127] Molecular weight: Standard polystyrene conversion

[0128] The specific polymer can be synthesized by a known method.

[0129] The polymer matrix 24 including a specific polymer may include a plurality of specific polymers as required.

[0130] Furthermore, the polymer matrix 24 constituting the polymer composite piezoelectric body of the present invention may contain other dielectric polymers in addition to the above-mentioned specific polymers as needed for the purpose of adjusting dielectric properties and mechanical properties.

[0131] Examples of other dielectric polymers that can be added include fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, polyvinylidene fluoride-trifluoroethylene copolymers, and polyvinylidene fluoride-tetrafluoroethylene copolymers; dicyandiamide-vinyl acetate copolymers; cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypolytriglucose, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethylpolytriglucose, cyanoethylpolyhydroxymethylene, cyanoethylglycidolpolytriglucose, cyanoethylsucrose, and cyanoethylsorbitol; and synthetic rubbers such as nitrile rubber and chloroprene rubber.

[0132] Among them, polymer materials having a cyanoethyl group can be preferably used.

[0133] Furthermore, in the polymer matrix 24 of the piezoelectric layer 12 , other dielectric polymers are not limited to one type, and multiple types may be used.

[0134] Furthermore, in addition to the dielectric polymer, the polymer matrix 24 may also include thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene and isobutylene, and thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica for the purpose of adjusting the glass transition point Tg of the polymer matrix 24.

[0135] Furthermore, in order to improve the adhesiveness, the polymer matrix 24 may contain a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin.

[0136] When dielectric polymers other than the specific polymer are used in the polymer matrix 24 of the piezoelectric layer 12 , the content of the dielectric polymers is not limited, but is preferably 30% by mass or less in terms of the ratio of the dielectric polymers in the polymer matrix 24 .

[0137] The piezoelectric layer 12 (polymer composite piezoelectric body) is formed by dispersing piezoelectric particles 26 in such a polymer matrix.

[0138] The piezoelectric particles 26 are preferably composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

[0139] Examples of materials constituting the piezoelectric particles 26 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO 3 ), zinc oxide (ZnO), and a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe 3 ).

[0140] The particle size of the piezoelectric particles 26 may be appropriately selected according to the size and application of the piezoelectric thin film 10. The particle size of the piezoelectric particles 26 is preferably 1 to 10 μm.

[0141] By setting the particle size of the piezoelectric particles 26 to the above range, a preferable result can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

[0142] In addition, Figure 1 In the embodiment, the piezoelectric particles 26 in the piezoelectric layer 12 are uniformly and regularly dispersed in the polymer matrix 24, but the present invention is not limited to this.

[0143] That is, the piezoelectric particles 26 in the piezoelectric layer 12 may be dispersed irregularly in the matrix 24 as long as they are (preferably) uniformly dispersed.

[0144] In the piezoelectric film 10, the amount ratio of the polymer matrix 24 to the piezoelectric particles 26 in the piezoelectric layer 12 can be appropriately set according to the size or thickness of the piezoelectric film 10 in the surface direction, the application of the piezoelectric film 10, the required characteristics of the piezoelectric film 10, etc.

[0145] The volume fraction of the piezoelectric particles 26 in the piezoelectric layer 12 is preferably 30 volume % or more, more preferably 50 volume % or more, and the upper limit is preferably 70 volume % or less.

[0146] By setting the amount ratio of the polymer matrix 24 to the piezoelectric particles 26 within the above range, a preferred result can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

[0147] Furthermore, in the piezoelectric film 10 , the thickness of the piezoelectric layer 12 is not limited and may be appropriately set according to the size of the piezoelectric film 10 , the application of the piezoelectric film 10 , the characteristics required for the piezoelectric film 10 , and the like.

[0148] The thickness of the piezoelectric layer 12 is preferably 8 to 300 μm, more preferably 8 to 40 μm, further preferably 10 to 35 μm, and most preferably 15 to 25 μm.

[0149] By setting the thickness of the piezoelectric layer 12 within the above range, it is possible to obtain a preferable result in terms of ensuring both rigidity and appropriate flexibility.

[0150] The piezoelectric layer 12 is preferably subjected to polarization treatment (Poling) in the thickness direction. The polarization treatment will be described in detail below.

[0151] like Figure 1 As shown, the piezoelectric film 10 of the present invention has the following structure: a lower thin film electrode 14 is provided on one side of the piezoelectric layer 12, and a lower protective layer 18 is preferably provided on the lower thin film electrode 14, and an upper thin film electrode 16 is provided on the other side of the piezoelectric layer 12, and an upper protective layer 20 is preferably provided on the upper thin film electrode 16. In the piezoelectric film 10, the upper thin film electrode 16 and the lower thin film electrode 14 form an electrode pair.

[0152] In other words, the piezoelectric film 10 of the present invention has a structure in which both surfaces of the piezoelectric layer 12 are sandwiched by an electrode pair, namely, an upper thin-film electrode 16 and a lower thin-film electrode 14 , and preferably further sandwiched by an upper protective layer 20 and a lower protective layer 18 .

[0153] In this way, the region sandwiched between the upper thin-film electrode 16 and the lower thin-film electrode 14 is driven according to the applied voltage.

[0154] In addition to these layers, the piezoelectric film 10 may also have, for example, an adhesive layer for pasting the thin film electrode and the piezoelectric layer 12 and an adhesive layer for pasting the thin film electrode and the protective layer. As long as the pasting layer can paste the pasting objects to each other, a known adhesive (adhesive and adhesive) can be used. In addition, the adhesive can also preferably use the same material as the polymer material (i.e., polymer matrix 24) from which the piezoelectric particles 26 are removed from the piezoelectric layer 12. In addition, the adhesive layer may be provided on both sides of the upper thin film electrode 16 side and the lower thin film electrode 14 side, or may be provided on only one side of the upper thin film electrode 16 side and the lower thin film electrode 14 side.

[0155] Furthermore, in addition to these layers, the piezoelectric film 10 may include an electrode lead portion for leading electrodes from the upper thin-film electrode 16 and the lower thin-film electrode 14 , and an insulating layer for covering an exposed region of the piezoelectric layer 12 to prevent short circuits and the like.

[0156] As an electrode lead-out portion, a thin film electrode and a protective layer can be provided at a portion protruding outwardly along the surface direction of the piezoelectric layer, or a portion of the protective layer can be removed to form a hole, and a conductive material such as silver paste can be inserted into the hole to make the conductive material and the thin film electrode electrically conductive to serve as an electrode lead-out portion.

[0157] In addition, in each thin film electrode, the electrode lead portion is not limited to one, and may have two or more electrode lead portions. In particular, in the case of a structure in which a portion of the protective layer is removed and a conductive material is inserted into the hole portion to form the electrode lead portion, it is preferred to have three or more electrode lead portions in order to more reliably ensure the conduction of electricity.

[0158] In the piezoelectric film 10, the upper protective layer 20 and the lower protective layer 18 play the role of covering the upper thin film electrode 16 and the lower thin film electrode 14 while giving the piezoelectric layer 12 appropriate rigidity and mechanical strength. That is, in the piezoelectric film 10 of the present invention, the piezoelectric layer 12 composed of the polymer matrix 24 and the piezoelectric particles 26 shows very excellent flexibility to slow bending deformation, but on the other hand, there is a case where the rigidity or mechanical strength is insufficient depending on the application. In order to compensate for this deficiency, the piezoelectric film 10 is provided with the upper protective layer 20 and the lower protective layer 18.

[0159] The lower protective layer 18 and the upper protective layer 20 are only arranged at different positions, but have the same structure. Therefore, in the following description, when there is no need to distinguish between the lower protective layer 18 and the upper protective layer 20, the two components are also collectively referred to as protective layers.

[0160] In a more preferred embodiment, the piezoelectric film 10 shown in the figure is stacked on two thin film electrodes and has a lower protective layer 18 and an upper protective layer 20. However, the present invention is not limited thereto, and a structure having only one of the lower protective layer 18 and the upper protective layer 20 may be used.

[0161] The protective layer is not limited, and various sheets can be used. As an example, various resin films can be preferably exemplified. Among them, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins can be preferably used because of their excellent mechanical properties and heat resistance.

[0162] The thickness of the protective layer is not limited. Furthermore, the thickness of the upper protective layer 20 and the lower protective layer 18 are substantially the same, but may be different.

[0163] If the rigidity of the protective layer is too high, not only will the expansion and contraction of the piezoelectric layer 12 be restricted, but also the flexibility will be impaired. Therefore, except when mechanical strength and good handling properties as a sheet-like object are required, it is more advantageous to make the protective layer thinner.

[0164] According to the research conducted by the present inventors, when the thickness of the upper protective layer 20 and the lower protective layer 18 are each less than or equal to twice the thickness of the piezoelectric layer 12 , a preferable result can be obtained in terms of both ensuring rigidity and achieving appropriate flexibility.

[0165] For example, when the thickness of the piezoelectric layer 12 is 50 μm and the lower protective layer 18 and the upper protective layer 20 are made of PET, the thickness of the lower protective layer 18 and the upper protective layer 20 are preferably 100 μm or less, more preferably 50 μm or less, and further preferably 25 μm or less.

[0166] In the piezoelectric film 10, an upper thin film electrode 16 is formed between the piezoelectric layer 12 and the upper protective layer 20, and a lower thin film electrode 14 is formed between the piezoelectric layer 12 and the lower protective layer 18. In the following description, the upper thin film electrode 16 is also referred to as the upper electrode 16, and the lower thin film electrode 14 is also referred to as the lower electrode 14.

[0167] The upper electrode 16 and the lower electrode 14 are provided in order to apply an electric field to the piezoelectric thin film 10 (piezoelectric layer 12 ).

[0168] The lower electrode 14 and the upper electrode 16 are substantially the same. Therefore, in the following description, when there is no need to distinguish between the lower electrode 14 and the upper electrode 16, both members are collectively referred to as thin film electrodes.

[0169] In the present invention, the material for forming the thin film electrode is not limited, and various conductors can be used. Specifically, conductive polymers such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium, molybdenum, alloys thereof, indium tin oxide, and PEDOT / PPS (polyethylene dioxythiophene-polystyrene sulfonate) can be exemplified.

[0170] Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified. Among them, copper is more preferred for reasons such as conductivity, cost, and flexibility.

[0171] Furthermore, there is no limitation on the method for forming thin film electrodes, and various known methods can be used, such as vapor deposition methods (vacuum film forming methods) such as vacuum evaporation and sputtering, film forming methods based on plating, methods of pasting foils formed from the above materials, and coating methods.

[0172] Among them, a thin film of copper or aluminum formed by vacuum deposition can be particularly preferably used as the thin film electrode because the flexibility of the piezoelectric thin film 10 can be ensured. Among them, a thin film of copper formed by vacuum deposition can be preferably used.

[0173] The thickness of the upper electrode 16 and the lower electrode 14 is not limited. Also, the thickness of the upper electrode 16 and the lower electrode 14 is substantially the same, but may be different.

[0174] However, as with the protective layer, if the rigidity of the thin film electrode is too high, not only will the expansion and contraction of the piezoelectric layer 12 be restricted, but also the flexibility will be impaired. Therefore, the thin film electrode is more advantageously thinner as long as the resistance does not become too high.

[0175] In the piezoelectric film 10 , it is preferable that the product of the thickness and the Young's modulus of the thin film electrode is smaller than the product of the thickness and the Young's modulus of the protective layer because flexibility is not significantly impaired.

[0176] For example, in the case of a combination in which the protective layer is PET (Young's modulus: about 6.2 GPa) and the thin film electrode is composed of copper (Young's modulus: about 130 GPa), if the thickness of the protective layer is set to 25 μm, the thickness of the thin film electrode is preferably less than 1.2 μm, more preferably less than 0.3 μm, and further preferably less than 0.1 μm.

[0177] As described above, the piezoelectric film 10 has a structure in which the piezoelectric layer 12 in which the piezoelectric particles 26 are dispersed in the polymer matrix 24 containing a specific polymer is sandwiched between the upper electrode 16 and the lower electrode 14 , and the upper protective layer 20 and the lower protective layer 18 are further sandwiched between them.

[0178] In such a piezoelectric film 10 , it is preferable that a local maximum value at which the loss tangent (Tan δ) at a frequency of 1 Hz based on dynamic viscoelasticity measurement becomes 0.1 or more exists at room temperature.

[0179] Thus, even if the piezoelectric film 10 is subjected to relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, thereby preventing cracks from being generated at the interface between the polymer matrix and the piezoelectric particles.

[0180] The storage modulus (E′) of the piezoelectric film 10 at a frequency of 1 Hz based on dynamic viscoelasticity measurement is 10 to 30 GPa at 0° C., and preferably 1 to 10 GPa at 50° C.

[0181] As a result, the piezoelectric film 10 can have a large frequency dispersion of the storage modulus (E') at room temperature, that is, it can be hard to vibrations of 20 Hz to 20 kHz and flexible to vibrations of a few Hz or less.

[0182] In addition, in the piezoelectric film 10, the product of the thickness and the storage modulus (E') at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 1.0×10 6 ~2.0×10 6 N / m, 1.0×10 at 50°C 5 ~1.0×10 6 N / m.

[0183] Thus, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic characteristics.

[0184] 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 by dynamic viscoelasticity measurement.

[0185] This makes the frequency characteristics of the speaker using the piezoelectric film 10 smooth, and also makes it possible to reduce the amount of change in sound quality when the lowest resonance frequency f0 changes with changes in the curvature of the speaker (piezoelectric film 10 ).

[0186] exist Figure 2 to Figure 4 An example of a method for manufacturing the piezoelectric thin film 10 is conceptually shown in FIG.

[0187] First, if Figure 2 As shown in FIG. 1 , a lower electrode stack 11 a is prepared, which is a sheet-like product in which the lower electrode 14 is formed on the lower protective layer 18 .

[0188] Furthermore, prepare Figure 4 The sheet-like structure in which the upper thin-film electrode 16 and the upper protective layer 20 are stacked is an upper electrode stack 11c.

[0189] The lower electrode stack 11a can be manufactured as follows: a copper thin film or the like is formed on the surface of the lower protective layer 18 by vacuum evaporation, sputtering, plating, etc. as the lower thin film electrode 14. Similarly, the upper electrode stack 11c can be manufactured as follows: a copper thin film or the like is formed on the surface of the upper protective layer 20 by vacuum evaporation, sputtering, plating, etc. as the upper thin film electrode 16.

[0190] Alternatively, a commercially available sheet-like product in which a copper thin film or the like is formed on a protective layer may be used as the lower electrode stack 11 a and / or the upper electrode stack 11 c .

[0191] The lower electrode stack 11 a and the upper electrode stack 11 c may be completely the same or different.

[0192] In addition, when the protective layer is very thin and has poor handling properties, a protective layer with a separator (temporary support) may be used as needed. In addition, as a separator, PET with a thickness of 25 to 100 μm or the like may be used. The separator may be removed after the thin film electrode and the protective layer are thermally pressed.

[0193] Then, if Figure 3 As shown, after applying a coating (coating composition) to become the piezoelectric layer 12 on the lower electrode 14 of the lower electrode stack 11a, it is cured to form the piezoelectric layer 12, thereby producing a stack 11b stacked with the lower electrode stack 11a and the piezoelectric layer 12.

[0194] First, a coating material is prepared by dissolving a specific polymer in an organic solvent, adding piezoelectric particles 26 such as PZT particles, and stirring and dispersing the mixture.

[0195] The organic solvent is not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used.

[0196] The lower electrode stack 11a is prepared, and after the coating is prepared, the coating is cast (applied) on the lower electrode stack 11a, and the organic solvent is evaporated and dried. Figure 3 As shown in FIG. 1 , a stacked body 11 b is produced in which a lower electrode 14 is provided on a lower protective layer 18 and a piezoelectric layer 12 is stacked on the lower electrode 14 .

[0197] The method for casting the coating material is not limited, and any known method (coating device) such as a bar coater, a slide coater, and a doctor blade can be used.

[0198] Alternatively, if the specific polymer is a substance that can be heated and melted, it can be prepared as follows: Figure 3 The laminated body 11b shown in the figure is prepared by heating and melting a specific polymer, adding / dispersing piezoelectric particles 26 into the melt, and extruding the melt. Figure 2 The lower electrode stack 11a shown is extruded in a sheet shape and cooled.

[0199] Furthermore, as described above, in the piezoelectric film 10 , a polymer piezoelectric material such as PVDF (polyvinylidene fluoride) other than the specific polymer may be added to the polymer matrix 24 .

[0200] When adding these polymer piezoelectric materials to the polymer matrix 24, the polymer piezoelectric materials added to the above-mentioned coating material may be dissolved or added to the specific polymer that has been heated and melted and heated and melted.

[0201] Next, the piezoelectric layer 12 of the stacked body 11 b including the lower electrode 14 on the lower protective layer 18 and the piezoelectric layer 12 formed on the lower electrode 14 is subjected to a polarization treatment (poling).

[0202] The method of polarizing the piezoelectric layer 12 is not limited, and a known method can be used.

[0203] As an example, electric field polarization can be exemplified by directly applying a DC electric field to the piezoelectric layer 12. When electric field polarization is performed, the upper electrode 16 can be formed before the polarization treatment, and the upper electrode 16 and the lower electrode 14 can be used to perform the electric field polarization treatment.

[0204] Furthermore, regarding the polarization treatment, when manufacturing the piezoelectric thin film 10 of the present invention, polarization is performed in the thickness direction rather than in the surface direction of the piezoelectric layer 12 (polymer composite piezoelectric body).

[0205] Before the polarization treatment, a rolling treatment may be performed using a heating roller or the like to smooth the surface of the piezoelectric layer 12. By performing the rolling treatment, the thermocompression bonding step described later can be smoothly performed.

[0206] Then, if Figure 4 As shown in FIG. 1 , an upper electrode laminate 11 c prepared in advance is laminated on the piezoelectric layer 12 side of a laminate 11 b subjected to polarization treatment so that the upper electrode 16 faces the piezoelectric layer 12 .

[0207] Furthermore, the laminate 11b and the upper electrode laminate 11c are bonded together by heat pressing with a heat pressing device or a pair of heated rollers in a manner of sandwiching the lower protective layer 18 and the upper protective layer 20, thereby producing a laminate 11b and an upper electrode laminate 11c. Figure 1 The piezoelectric film 10 of the present invention is shown.

[0208] Alternatively, the piezoelectric film 10 of the present invention may be produced by bonding (preferably, press-bonding) the stacked body 11 b and the upper electrode stacked body 11 c with an adhesive.

[0209] The piezoelectric film 10 of the present invention manufactured in this way is polarized in the thickness direction rather than in the plane direction, and even if no stretching treatment is performed after the polarization treatment, a large piezoelectric property can be obtained. The piezoelectric film 10 of the present invention does not have in-plane anisotropy in the piezoelectric property, and when a driving voltage is applied, it expands and contracts isotropically in all directions in the plane direction.

[0210] The piezoelectric film 10 of the present invention can be manufactured using sliced ​​lower electrode stacks 11a and upper electrode stacks 11c, but is preferably manufactured using a roll-to-roll process. In the following description, the roll-to-roll process is also referred to as "RtoR".

[0211] As is known to all, RtoR is a manufacturing method in which a raw material is drawn out from a roll formed by winding a long strip of raw material, transported along the long side direction, subjected to various treatments such as film formation or surface treatment, and the treated raw material is wound into a roll again.

[0212] When the piezoelectric film 10 is manufactured by the above-described manufacturing method through RtoR, a first roll formed by winding the long-shaped lower electrode stack 11 a and a second roll formed by winding the long-shaped upper electrode stack 11 c are used.

[0213] Volume 1 and Volume 2 can be identical.

[0214] The lower electrode stack 11a is drawn out from the first roll and transported along the long side direction, and a coating containing the above-mentioned specific polymer and piezoelectric particles 26 is coated on the lower electrode 14 of the lower electrode stack 11a, and dried by heating etc. to form a piezoelectric layer 12 on the lower electrode 14, thereby producing a stack 11b in which the lower electrode stack 11a and the piezoelectric layer 12 are stacked.

[0215] Next, the piezoelectric layer 12 is polarized. When the piezoelectric film 10 is manufactured by RtoR, the stack 10b is transported, and the piezoelectric layer 12 is polarized by rod-shaped electrodes extending in a direction perpendicular to the transport direction of the stack 10b. In addition, the rolling treatment may be performed before the polarization treatment as described above.

[0216] Next, the upper electrode stack 11c is pulled out from the second roll, the upper electrode stack 11c and the stack 11b are conveyed, and the upper thin film electrode 16 is directed toward the piezoelectric layer 12 by using a known method such as lamination roll lamination to stack the upper electrode stack 11c on the stack 10b.

[0217] Thereafter, the stacked body 10 b and the upper electrode stacked body 11 c are sandwiched and conveyed by a pair of heating rollers to be thermocompressed, thereby completing the piezoelectric film 10 of the present invention, and the piezoelectric film 10 is wound into a roll.

[0218] In the above example, the piezoelectric film 10 of the present invention is manufactured by transporting the sheet (laminated body) only once in the longitudinal direction by RtoR, but the present invention is not limited to this.

[0219] For example, after forming a stacked body and performing polarization treatment, the stacked body 11b is temporarily wound into a roll. Then, the stacked body 11b can be drawn out from the stacked body roll and conveyed in the longitudinal direction, and the upper electrode stack 11c can be stacked and thermocompressed as described above to produce the piezoelectric film 10, and the piezoelectric film 10 can be wound into a roll.

[0220] exist Figure 5 2 is a conceptual diagram showing an example of a flat-plate piezoelectric speaker using the piezoelectric film 10 of the present invention.

[0221] The piezoelectric speaker 40 is a flat-plate type piezoelectric speaker using the piezoelectric film 10 of the present invention as a vibration plate for converting an electrical signal into vibration energy. The piezoelectric speaker 40 can also be used as a microphone, a sensor, and the like.

[0222] The piezoelectric speaker 40 includes a piezoelectric film 10 , a housing 42 , and a pressing cover 48 .

[0223] The housing 42 is a cylindrical frame body with one side open, formed of plastic or the like. A tube 42a inserted through the housing 42 is provided on the side surface of the housing 42.

[0224] The pressing cover 48 is a frame body having a substantially L-shaped cross section, and is inserted into and fitted on the open surface side of the housing 42 .

[0225] The piezoelectric speaker 40 covers the housing 42 with the piezoelectric film 10 in a manner that the open surface is closed, and the pressing cover 48 is fitted into the housing 42 from above the piezoelectric film 10, thereby hermetically sealing the open surface of the housing 42 with the piezoelectric film 10. In addition, as needed, an O-ring or the like for maintaining airtightness may be provided between the upper surface of the side wall of the housing 42 and the piezoelectric film 10.

[0226] In this state, the air in the housing 42 is exhausted from the pipe 42a, thereby Figure 5 As shown, the piezoelectric film 10 is held in a concave state. Conversely, the piezoelectric film 10 may be held in a convex state by introducing air into the housing 42 through the tube 42a.

[0227] In the piezoelectric speaker 40 , when the piezoelectric film 10 is stretched in the in-plane direction by applying a driving voltage to the lower electrode 14 and the upper electrode 16 , the piezoelectric film 10 , which has become concave due to the reduced pressure, moves downward to absorb the stretch.

[0228] On the contrary, when the piezoelectric film 10 contracts in the in-plane direction by applying a driving voltage to the lower electrode 14 and the upper electrode 16 , the concave piezoelectric film 10 moves upward to absorb the contraction.

[0229] The piezoelectric speaker 40 generates sound by the vibration of the piezoelectric film 10 .

[0230] In addition, in the piezoelectric film 10 of the present invention, conversion from expansion and contraction motion to vibration can also be achieved by keeping the piezoelectric film 10 in a curved state.

[0231] Therefore, the piezoelectric film 10 of the present invention can function as a piezoelectric speaker having flexibility even when it is bent, rather than as a Figure 5 The piezoelectric speaker 40 shown as a plate having rigidity functions.

[0232] The piezoelectric speaker using the piezoelectric film 10 of the present invention can be stored in a bag by taking advantage of its good flexibility, for example, by rolling or folding it. Therefore, the piezoelectric film 10 of the present invention can realize a piezoelectric speaker that is easy to carry even if it has a certain size.

[0233] Furthermore, as described above, the piezoelectric film 10 of the present invention has excellent softness and flexibility, and there is no anisotropy of piezoelectric properties within the plane. Therefore, the piezoelectric film 10 of the present invention has little change in sound quality when it is bent in any direction, and the sound quality also changes little with respect to the change in curvature. Therefore, the piezoelectric speaker using the piezoelectric film 10 of the present invention has a high degree of freedom in the installation location, and, as described above, can be installed in various objects. For example, by installing the piezoelectric film 10 of the present invention in a bent state in clothing such as suits and portable items such as bags, a so-called wearable speaker can be realized.

[0234] The flexible display screen of the present invention is a flexible display screen using the piezoelectric film of the present invention as a speaker.

[0235] Specifically, the piezoelectric film 10 of the present invention is mounted as a speaker on the surface of a flexible sheet-shaped display device such as a flexible organic EL display device, a flexible liquid crystal display device, or a flexible electronic paper, on the side opposite to the image display surface. In the following description, the surface on the side opposite to the image display surface of the display device is also referred to as the "back side of the display device".

[0236] In addition, the flexible display screen can be a color display or a monochrome display.

[0237] As described above, the piezoelectric film 10 of the present invention has excellent softness and flexibility and has no anisotropy of piezoelectric characteristics within a plane. Therefore, the piezoelectric film 10 of the present invention has little change in sound quality even when bent in any direction, and also has little change in sound quality with change in curvature.

[0238] Therefore, the flexible display screen equipped with the speaker of the present invention, which is formed by installing the piezoelectric film 10 of the present invention on a flexible image display device, has excellent flexibility and is not affected by the bending direction or amount caused by the hand-held state, etc., that is, it can preferably respond to any deformation and output audio with stable sound quality.

[0239] use Figure 6 to Figure 8 , an example of a flexible display screen using the piezoelectric film of the present invention as a speaker is described.

[0240] Figure 6 This is a cross-sectional view conceptually showing an example of the flexible display panel of the present invention in which the piezoelectric film of the present invention is used in an organic EL (electroluminescence) display.

[0241] Figure 6 The organic EL display 60 shown is a speaker-mounted organic EL flexible display screen in which the piezoelectric film 10 of the present invention is attached to the back surface of a flexible sheet-shaped organic EL display device 62 .

[0242] In the flexible display of the present invention, there is no limitation on the method of mounting the piezoelectric film 10 of the present invention on the back of a flexible sheet-like image display device such as the organic EL display device 62. That is, any known method of mounting (bonding) sheets face to face can be used.

[0243] As an example, there can be cited a method of attaching with an adhesive, a method of attaching by hot melt, a method of using double-sided tape, a method of using adhesive tape, a method of using a clamp such as a roughly C-shaped clip to clamp the multiple stacked sheets at the ends or end edges, a method of using a clamp such as rivets to clamp the multiple stacked sheets within a surface (excluding the image display surface), a method of clamping the multiple stacked sheets from both sides using a protective film (at least the image display side is transparent), and a method of using these simultaneously.

[0244] When the display device and the piezoelectric film 10 are attached using an adhesive or the like, the entire surface may be attached, only the entire circumference of the end portion may be attached, or dots may be attached at appropriately set locations such as the four corners and the center, or all of these may be used simultaneously.

[0245] In the organic EL display 60, the piezoelectric film 10 is the piezoelectric film 10 of the present invention described above, which is composed of a piezoelectric layer 12 composed of a polymer composite piezoelectric body, a lower thin film electrode 14 arranged on one side of the piezoelectric layer 12 and an upper thin film electrode 16 arranged on the other side, a lower protective layer 18 arranged on the surface of the lower thin film electrode 14 and an upper protective layer 20 arranged on the surface of the upper thin film electrode 16.

[0246] On the other hand, the organic EL display device 62 is a well-known sheet-shaped organic EL display device (organic EL display panel) having flexibility.

[0247] That is, as an example, the organic EL display device 62 is constructed as follows: an anode 68 having a pixel electrode having a switching circuit such as a TFT (Thin Film Transistor) is formed on a substrate 64 such as a plastic film, a light-emitting layer 70 using an organic EL material is provided on the anode 68, a transparent cathode 72 made of ITO (indium tin oxide) or the like is provided on the light-emitting layer 70, and a transparent substrate 74 formed of a transparent plastic or the like is provided on the cathode 72.

[0248] Furthermore, a hole injection layer or a hole transport layer may be provided between the anode 68 and the light emitting layer 70, and an electron transport layer or an electron injection layer may be provided between the light emitting layer 70 and the cathode 72. Furthermore, a protective film such as a gas barrier film may be provided on the transparent substrate 74.

[0249] Although not shown in the figure, wiring for driving the piezoelectric film 10 , ie, the speaker, is connected to the lower electrode 14 and the upper electrode 16 of the piezoelectric film 10 . Furthermore, wiring for driving the organic EL display device 62 is connected to the anode 68 and the cathode 72 .

[0250] This also applies to the electronic paper 78 and the liquid crystal display 94 described later.

[0251] exist Figure 7 FIG. 4 conceptually shows an example of the flexible display screen of the present invention in which the piezoelectric film of the present invention is used for electronic paper.

[0252] Figure 7 The electronic paper 78 shown is a speaker-mounted electronic paper in which the piezoelectric film 10 of the present invention is attached to the back surface of a flexible sheet-shaped electronic paper device 80 .

[0253] In the electronic paper 78, the piezoelectric film 10 is the same as described above.

[0254] On the other hand, the electronic paper device 80 is a well-known flexible electronic paper. That is, as an example, the electronic paper device 80 is configured as follows: a lower electrode 84 having a pixel electrode having a switching circuit such as a TFT is formed on a substrate 82 such as a plastic film, a display layer 86 having microcapsules 86a containing positively or negatively charged white pigments and black pigments arranged on the lower electrode 84, a transparent upper electrode 90 made of ITO or the like is provided on the display layer 86, and a transparent substrate 92 formed of transparent plastic or the like is provided on the upper electrode 90.

[0255] in addition, Figure 7 The example shown is an example in which the flexible display screen of the present invention is used for an electronic paper of an electrophoretic method using microcapsules, but the present invention is not limited thereto.

[0256] That is, in the flexible display screen of the present invention, all known electronic papers can be used as long as they are flexible sheets. For example, it is possible to utilize an electrophoretic method that does not use microcapsules, a chemical change method that utilizes redox reactions, an electronic powder method, an electrowetting method, and a liquid crystal method.

[0257] exist Figure 8 An example in which the piezoelectric film of the present invention is used in a liquid crystal display (LCD) is conceptually shown.

[0258] Figure 8 The illustrated liquid crystal display 94 is a speaker-mounted liquid crystal flexible display screen in which the piezoelectric film 10 of the present invention is attached to the back surface of a flexible sheet-shaped liquid crystal display device 96 .

[0259] In the liquid crystal display 94, the piezoelectric film 10 is the same as described above.

[0260] On the other hand, the liquid crystal display device 96 is a well-known flexible sheet-shaped liquid crystal display device (liquid crystal display panel). That is, as an example, the liquid crystal display device 96 includes a flexible edge-light type light guide plate 98 and a light source 100 for inputting backlight from the end of the light guide plate 98. As an example, the liquid crystal display device 96 is configured as follows: a polarizer 102 is provided on the light guide plate 98, a transparent lower substrate 104 is provided on the polarizer 102, a transparent lower electrode 106 having a pixel electrode having a switching circuit such as a TFT is formed on the lower substrate 104, a liquid crystal layer 108 is provided on the lower electrode 106, a transparent upper electrode 110 made of ITO or the like is provided on the liquid crystal layer 108, a transparent upper substrate 112 is provided on the upper electrode 110, a polarizer 114 is provided on the upper substrate 112, and a protective film 116 is provided on the polarizer 114.

[0261] The flexible display screen of the present invention is not limited to organic EL displays, electronic paper, and liquid crystal displays, and can be used as an image display device using various display devices as long as it is a flexible sheet-shaped display device (display panel).

[0262] The throat-vibration microphone and the sensor for musical instrument of the present invention are throat-vibration microphones and the sensor for musical instrument using the piezoelectric film of the present invention.

[0263] The piezoelectric film 10 of the present invention comprises: a piezoelectric layer 12 in which piezoelectric particles 26 are dispersed in a polymer matrix 24, a lower thin film electrode 14 and an upper thin film electrode 16 arranged on the surface of the piezoelectric layer 12, and a lower protective layer 18 and an upper protective layer 20 arranged on the surfaces of the respective thin film electrodes. In the piezoelectric film 10, the piezoelectric layer 12 also has the performance of converting vibration energy into electrical signals.

[0264] Therefore, utilizing this point, the piezoelectric film 10 of the present invention can also be preferably used for a microphone or a sensor (pickup) for a musical instrument.

[0265] exist Fig. 9 An example of a general throat microphone is conceptually shown in FIG.

[0266] like Fig. 9 As shown, the existing general throat vibration microphone 120 has the following complex structure: a piezoelectric ceramic 126 such as PZT is stacked on a metal plate 128 such as a brass plate, an elastic buffer pad 130 is installed on the lower surface of the stack and a spring 132 is installed on the upper surface to support it in a housing 124, and signal lines 134 and 136 are led out from the housing.

[0267] In contrast, the throat-vibrator microphone of the present invention, which uses the piezoelectric film 10 of the present invention as a sensor for converting an audio signal into an electrical signal, can be constructed by, for example, only providing an attachment mechanism on the piezoelectric film 10 and providing a simple structure of a signal line that extracts the electrical signal output by the piezoelectric layer 12 (the lower electrode 14 and the upper electrode 16).

[0268] The throat-vibration microphone of the present invention having such a structure can function as a throat-vibration microphone simply by attaching the piezoelectric film 10 provided with a signal line for extracting an electrical signal near the vocal cords.

[0269] And, using Fig. 9 The conventional throat microphone having the piezoelectric ceramic 126 and the metal plate 128 shown has a very small loss tangent, and therefore is prone to strong resonance, causing the frequency characteristics to fluctuate sharply, and thus tends to have a metallic tone.

[0270] In contrast, as described above, the piezoelectric film 10 of the present invention has excellent flexibility and acoustic characteristics and little change in sound quality when deformed, so it can be attached to the throat of a person having a complex curve and can reproduce sounds faithfully from bass to treble.

[0271] That is, according to the present invention, it is possible to realize a throat vibration microphone that can output an audio signal extremely close to the human voice, has no wearing feeling, has a simple structure, is ultra-lightweight and saves space.

[0272] In the throat-vibration microphone of the present invention, there is no limitation on the method of attaching the piezoelectric film 10 to the vicinity of the vocal cords, and various known methods of attaching a sheet-like object can be used.

[0273] Furthermore, the piezoelectric film 10 may be housed in an extremely thin housing or bag and attached to the vicinity of the vocal cords instead of directly attaching the piezoelectric film 10 to the vicinity of the vocal cords.

[0274] Furthermore, the musical instrument sensor of the present invention, which uses the piezoelectric film 10 of the present invention as a sensor for converting an audio signal into an electrical signal, can be constructed by, for example, only providing an attachment mechanism on the piezoelectric film 10 and providing a simple structure of a signal line that extracts the electrical signal output by the piezoelectric layer 12 (the lower electrode 14 and the upper electrode 16).

[0275] The musical instrument sensor of the present invention having such a structure functions as a musical instrument sensor (ie, a pickup) simply by attaching the piezoelectric film 10 provided with a signal line for extracting an electrical signal to a part of a musical instrument.

[0276] Similar to the aforementioned throat-vibration microphone, the piezoelectric film 10 of the present invention is thin and flexible, so the flexibility and acoustic characteristics of the musical instrument sensor of the present invention are excellent and the sound quality changes little when deformed. Therefore, it can be attached to the frame surface of a musical instrument with a complex curve and can faithfully reproduce the sound of the musical instrument from bass to treble.

[0277] In addition, the musical instrument sensor of the present invention has almost no mechanical restrictions on the frame surface of the vibrating musical instrument, so the influence on the original sound of the musical instrument caused by installing the pickup can be minimized.

[0278] Similar to the throat vibration microphone, the instrument sensor of the present invention is not limited to the method of attaching to the instrument, and various known sheet-like object attaching methods can be used. In addition, the instrument sensor of the present invention can also be attached to the instrument by placing the piezoelectric film 10 in an extremely thin shell or bag.

[0279] As described above, the piezoelectric film 10 of the present invention expands and contracts in the plane direction by application of voltage and preferably vibrates in the thickness direction by the expansion and contraction in the plane direction. Therefore, when used in a piezoelectric speaker, for example, it exhibits good acoustic characteristics capable of outputting sound at a high sound pressure.

[0280] The piezoelectric film 10 of the present invention showing such good acoustic characteristics and high piezoelectric expansion and contraction performance can also function well as a piezoelectric vibration element that vibrates a vibrated body such as a vibration plate by laminating a plurality of sheets.

[0281] When stacking the piezoelectric film 10, as long as there is no possibility of short circuit, the piezoelectric film to be stacked may not have the upper protective layer 20 and / or the lower protective layer 18. Alternatively, the piezoelectric film without the upper protective layer 20 and / or the lower protective layer 18 may be stacked via an insulating layer.

[0282] For example, the stack of piezoelectric films 10 can be attached to a vibration plate to serve as a speaker that outputs sound by vibrating the vibration plate with the stack of piezoelectric films 10. In other words, the stack of piezoelectric films 10 functions as a so-called exciter that outputs sound by vibrating the vibration plate.

[0283] By applying a driving voltage to the stacked piezoelectric films 10, each piezoelectric film 10 expands and contracts in the surface direction, and by the expansion and contraction of each piezoelectric film 10, the stack of piezoelectric films 10 as a whole expands and contracts in the surface direction. By the expansion and contraction in the surface direction of the stack of piezoelectric films 10, the vibration plate to which the stack is attached is bent, and as a result, the vibration plate vibrates in the thickness direction. The vibration in the thickness direction generates sound. The vibration plate vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10, and generates sound corresponding to the driving voltage applied to the piezoelectric film 10.

[0284] Therefore, at this time, the piezoelectric film 10 itself does not output sound.

[0285] Although the rigidity of each piezoelectric film 10 is low and the expansion force is small, the rigidity becomes higher and the expansion force of the stacked body as a whole becomes larger by stacking the piezoelectric films 10. As a result, even if the vibration plate has a certain degree of rigidity, the stacked body of piezoelectric films 10 can sufficiently bend the vibration plate by applying a large force and make the vibration plate sufficiently vibrate in the thickness direction so that the vibration plate can generate sound.

[0286] In the stack of piezoelectric thin films 10 , the number of stacked piezoelectric thin films 10 is not limited, and the number of stacked piezoelectric thin films 10 may be appropriately set so as to obtain a sufficient vibration amount, for example, according to the rigidity of a vibration plate to be vibrated.

[0287] Furthermore, if the piezoelectric film 10 has sufficient expansion and contraction force, one piezoelectric film 10 of the present invention can be used as the same actuator (piezoelectric vibration element).

[0288] The vibration plate that vibrates by the stacked body of the piezoelectric thin films 10 of the present invention is also not limited, and various sheet-shaped objects (plate-shaped objects, thin films) can be used.

[0289] As an example, there can be mentioned resin films made of PET, etc., foamed plastics made of expanded polystyrene, cardboard materials such as corrugated cardboard materials, glass plates, and wood, etc. Furthermore, as long as it can be sufficiently bent, a device such as a display device can also be used as a vibration plate.

[0290] In the stack of piezoelectric thin films 10, adjacent piezoelectric thin films are preferably bonded together with an adhesive layer (adhesive) and the stack of piezoelectric thin films 10 and the vibration plate are also preferably bonded together with an adhesive layer.

[0291] The adhesive layer is not limited, and various adhesive layers that can be used to paste the materials of the pasting object can be used. Therefore, the adhesive layer can be composed of an adhesive or a binder. It is preferred to use a binder layer composed of a binder that can obtain a solid hard adhesive layer after pasting.

[0292] The above also applies to a laminated body formed by folding the long piezoelectric film 10 described later.

[0293] There is no limitation on the polarization direction of each of the stacked piezoelectric thin films 10 in the stacked body of the piezoelectric thin films 10. As described above, the polarization direction of the piezoelectric thin film 10 of the present invention refers to the polarization direction in the thickness direction.

[0294] Therefore, in the stacked body of the piezoelectric thin films 10 , the polarization directions of all the piezoelectric thin films 10 may be the same, or piezoelectric thin films having different polarization directions may exist.

[0295] Among them, in the stacked body of the piezoelectric thin films 10 , the piezoelectric thin films 10 are preferably stacked so that the polarization directions of the adjacent piezoelectric thin films 10 are opposite to each other.

[0296] In the piezoelectric film 10, the polarity of the voltage applied to the piezoelectric layer 12 depends on the polarization direction. Therefore, regardless of whether the polarization direction is from the upper electrode 16 to the lower electrode 14 or from the lower electrode 14 to the upper electrode 16, the polarity of the upper electrode 16 and the polarity of the lower electrode 14 are set to the same polarity in all the stacked piezoelectric films 10.

[0297] Therefore, by making the polarization directions of adjacent piezoelectric films 10 opposite to each other, even if the electrodes of adjacent piezoelectric films 10 are in contact with each other, there is no possibility of a short circuit because the contacting electrodes have the same polarity.

[0298] The stack of the piezoelectric thin films 10 can be formed into a structure in which a plurality of piezoelectric thin films 10 are stacked by folding the long-length piezoelectric thin film 10 once or more (preferably a plurality of times).

[0299] The structure in which the long-strip piezoelectric film 10 is folded and stacked has the following advantages.

[0300] That is, in a stacked body in which a plurality of sliced ​​piezoelectric films 10 are stacked, it is necessary to connect the upper electrode 16 and the lower electrode 14 to a driving power source for each piezoelectric film. In contrast, in a structure in which a long strip of piezoelectric film 10 is folded and stacked, the stacked body can be formed using only one long strip of piezoelectric film 10. Furthermore, in a structure in which a long strip of piezoelectric film 10 is folded and stacked, only one power source is required for applying a driving voltage, and further, electrodes can be drawn from the piezoelectric film 10 at one location.

[0301] Furthermore, in a structure in which the long-strip piezoelectric films 10 are folded and stacked, the polarization directions of the adjacent piezoelectric films 10 are necessarily opposite to each other.

[0302] The polymer composite piezoelectric body, piezoelectric film, piezoelectric speaker, flexible display, throat vibration microphone and sensor for musical instruments of the present invention are described in detail above, but the present invention is not limited to the above examples and various improvements or changes can be made without departing from the main purpose of the present invention.

[0303] Example

[0304] Below, enumerate specific embodiment of the present invention, the present invention is described in more detail. In addition, the present invention is not limited to this embodiment, and the materials, usage, ratio, processing content and processing sequence etc. shown in the following embodiments can be appropriately changed as long as they do not depart from the gist of the present invention.

[0305] <Synthesis Example 1: Synthesis of Monomer M-1>

[0306] Acrylic acid (72.1 g), chloroacetonitrile (75.5 g) and ethyl acetate (600 mL) were mixed. Triethylamine (121.4 g) was added dropwise to the obtained solution, and the mixture was reacted at 80° C. for 4 hours. After the obtained solution was cooled to room temperature, the precipitated salt was removed by filtration. After the obtained solution was washed with water and dilute hydrochloric acid, it was dried with magnesium sulfate. After that, the obtained solution was concentrated under reduced pressure to obtain a monomer M-1 (106.7 g) represented by the following formula.

[0307] [Chemical formula 8]

[0308]

[0309] <Synthesis Example 2: Synthesis of Monomer M-2>

[0310] Methacrylic acid (86.1 g), chloroacetonitrile (75.5 g) and ethyl acetate (600 mL) were mixed. Triethylamine (121.4 g) was added dropwise to the obtained solution, and the mixture was reacted at 80° C. for 4 hours. After the obtained solution was cooled to room temperature, the precipitated salt was filtered out. After the obtained solution was washed with water and dilute hydrochloric acid, it was dried with magnesium sulfate. After that, the obtained solution was concentrated under reduced pressure to obtain a monomer M-2 (120.1 g) represented by the following formula.

[0311] [Chemical formula 9]

[0312]

[0313] <Synthesis Example 3: Synthesis of the polymer of Example 1>

[0314] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of monomer M-1 (20.0 g) and azobisisobutyronitrile (AIBN) (98 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the obtained solution was heated to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 40,000.

[0315] <Synthesis Example 4: Synthesis of the polymer of Example 2>

[0316] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of monomer M-1 (18.4 g), methyl acrylate (1.6 g) and AIBN (250 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 16,000.

[0317] <Synthesis Example 5: Synthesis of the polymer of Example 3>

[0318] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of monomer M-1 (17.9 g), 2-hydroxyethyl acrylate (2.1 g) and AIBN (155 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 25,000.

[0319] <Synthesis Example 6: Synthesis of the polymer of Example 4>

[0320] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of monomer M-1 (18.7 g), acrylic acid (1.3 g) and AIBN (62 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 65,000.

[0321] <Synthesis Example 7: Synthesis of the polymer of Example 5>

[0322] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of monomer M-2 (20.0 g) and AIBN (433 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 8,000.

[0323] <Synthesis Example 8: Synthesis of the polymer of Example 6>

[0324] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of monomer M-1 (16.6 g), acrylonitrile (3.4 g) and AIBN (58 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 80,000.

[0325] <Synthesis Example 9: Synthesis of the polymer of Example 7>

[0326] Polyvinyl alcohol (2.0 g) and water (15.1 g) were added to a three-necked flask. Cyanoacetic acid (3.9 g), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (8.7 g) and acetone (10 g) were mixed with the solution and reacted at 25°C for 8 hours. If the solution was left to stand after the reaction, it would be divided into two phases, so the upper phase was separated and added dropwise to ion exchange water to obtain a precipitate. After filtering the precipitate, it was dried. The obtained solid substance was dissolved in acetone, precipitated in ion exchange water, filtered and dried to obtain a polymer. The weight average molecular weight of the obtained polymer was 40,000.

[0327] <Synthesis Example 10: Synthesis of polymer of Comparative Example 1>

[0328] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of 2-cyanoethyl methacrylate (20.0 g manufactured by FUJIFILM Wako Pure Chemical Corporation) and AIBN (78 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution having a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 40,000.

[0329] <Synthesis Example 11: Synthesis of polymer of Comparative Example 3>

[0330] Cyclohexanone (5.0 g) was added to a three-necked flask and heated to 80°C under a nitrogen atmosphere. A solution of methyl methacrylate (15.8 g), acrylonitrile (4.2 g) and AIBN (379 mg) dissolved in cyclohexanone (15.0 g) was added dropwise to the solution over 3 hours. After the addition was completed, the temperature was raised to 90°C and stirred for 3 hours to terminate the reaction. By adding cyclohexanone (26.2 g) to the obtained solution, a cyclohexanone solution with a polymer concentration of 30% by mass was obtained. The weight average molecular weight of the obtained polymer was 15,000.

[0331] <Examples 1 to 7, Comparative Examples 1 to 3: Preparation of piezoelectric thin films>

[0332] Through the aforementioned Figure 2 to Figure 4 The method shown in the figure produced Figure 1 The piezoelectric film 10 is shown.

[0333] First, PZT particles were added to a 30 mass % cyclohexanone solution of a predetermined polymer used in each example and comparative example at the following composition ratio, and the solution was dispersed using a propeller mixer (rotation speed 2000 rpm) to prepare a coating material for forming the piezoelectric layer 12 .

[0334] ·PZT particles…………300 parts by mass

[0335] · 30 mass % cyclohexanone solution of a predetermined polymer ... 100 parts by mass

[0336] As PZT particles, commercially available PZT raw material powder was sintered at 1000 to 1200° C., and then pulverized and classified to an average particle size of 5 μm.

[0337] On the other hand, two sheets (corresponding to the lower electrode laminate 11a and the upper electrode laminate 11c) were prepared by vacuum-evaporating a copper thin film with a thickness of 0.1 μm on a PET film with a thickness of 4 μm. That is, in this example, the lower thin film electrode 14 and the upper thin film electrode 16 are copper-evaporated films with a thickness of 0.1 μm, and the lower protective layer 18 and the upper protective layer 20 are PET films with a thickness of 4 μm.

[0338] The previously prepared coating material for forming the piezoelectric layer 12 was applied to the copper-deposited film (lower thin-film electrode 14) of the sheet (lower electrode laminate 11a) using a slide coater. The coating material was applied until the thickness of the dried coating film reached 40 μm.

[0339] Next, the coating on the copper vapor-deposited film (lower thin film electrode 14) was heated and dried on a hot plate at 120°C, thereby evaporating cyclohexanone. Thus, a laminate (laminate 11b) was prepared in which the copper lower thin film electrode 14 was formed on the PET lower protective layer 18 and the piezoelectric layer 12 with a thickness of 40 μm was formed thereon.

[0340] The piezoelectric layer 12 of the stacked body 11b is polarized.

[0341] The upper electrode laminate 11 c is laminated on the laminate 11 b subjected to the polarization treatment so that the upper thin film electrode 16 (copper thin film side) faces the piezoelectric layer 12 .

[0342] Next, the stack of the stack 11 b and the upper electrode stack 11 c was thermocompressed at 120° C. using a laminating device to bond the piezoelectric layer 12 to the lower thin-film electrode 14 and the upper thin-film electrode 16 , thereby producing the piezoelectric film 10 .

[0343] <Production of Piezoelectric Speakers>

[0344] Cut out from the prepared piezoelectric film A circular test piece was made. Figure 5 The piezoelectric speaker shown.

[0345] The outer shell is a cylindrical container with one side open, and the size of the opening is used. A plastic cylindrical container with a depth of 10 mm.

[0346] The piezoelectric film was arranged to cover the opening of the housing, and after the peripheral portion was fixed by pressing the cover, the air in the housing was exhausted from the tube, and the pressure in the housing was maintained at 0.09 MPa to bend the piezoelectric film into a concave shape, thereby producing a piezoelectric speaker.

[0347] <Piezoelectric characteristics: Sound pressure evaluation>

[0348] The sound pressure level of the fabricated piezoelectric speaker was measured.

[0349] Specifically, a microphone was placed at a distance of 0.5 m from the center of the piezoelectric film of the piezoelectric speaker, and a 1 kHz, 10 V0-P sine wave was input between the upper and lower electrodes of the piezoelectric film to measure the sound pressure level. The evaluation was performed according to the following criteria.

[0350] Based on the difference in sound pressure level from Comparative Example 2 (sound pressure level of each Example or Comparative Example - sound pressure level of Comparative Example 2), evaluation was performed as follows.

[0351] The case where the difference in sound pressure level from Comparative Example 2 is 2 dB or more is "A"

[0352] The case where the difference in sound pressure level from Comparative Example 2 is 1 dB or more and less than 2 dB is "B"

[0353] The case where the difference in sound pressure level from Comparative Example 2 is less than 1 dB is "C"

[0354] The results are summarized in Table 1.

[0355] In Table 1, the column "Polymer" shows the structure of the polymer used. The numerical value in the structural formula of each polymer shows the content (mol %) of each repeating unit relative to all repeating units in the polymer.

[0356] [Table 1]

[0357]

[0358] As shown in Table 1, by using a predetermined polymer composite piezoelectric body, the desired effect can be obtained.

[0359] Among them, according to the comparison of Examples 1 to 7, it was confirmed that when the specific polymer is a polymer having only repeating units represented by the above formula (2), or a polymer having repeating units including repeating units represented by the above formula (2) and repeating units including polar groups other than cyano groups (preferably repeating units represented by the above formula (3)), a better effect can be obtained.

[0360] According to the above results, the effect of the present invention is obvious.

[0361] Explanation of symbols

[0362] 10-piezoelectric film, 11a-lower electrode stack, 11b-stack, 11c-upper electrode stack, 12-piezoelectric layer, 14-lower (thin film) electrode, 16-upper (thin film) electrode, 18-lower protective layer, 20-upper protective layer, 24-polymer matrix, 26-piezoelectric particles, 40-piezoelectric speaker, 42-housing, 48-frame, 60-organic EL display, 62-organic EL display device, 64, 82-substrate, 68-anode, 70-light-emitting layer, 72-cathode, 74, 92-transparent substrate, 78-electronic paper, 80-electronic paper device, 84, 106-lower electrode, 86-display layer, 86a-microcapsule, 90, 110-upper electrode, 94-liquid crystal display, 96-liquid crystal display device, 98-light guide plate, 100-light source, 102, 114-polarizer, 104-lower substrate, 108-liquid crystal layer, 112-upper substrate, 116-protective film, 120-throat vibration microphone, 126-piezoelectric ceramic, 128-metal plate, 130-buffer pad, 132-spring, 134, 136-signal line.

Claims

1. A polymer composite piezoelectric body, comprising: A polymer matrix comprising a polymer; and The piezoelectric particles include ceramic particles having a perovskite crystal structure or a wurtzite crystal structure, The polymer has a repeating unit represented by formula (2), In formula (2), R 1 and R 2 Each independently represents a hydrogen atom or an alkyl group, R 3 represents a hydrogen atom or an alkyl group, L 1 It represents a group consisting of a combination of two or more of -O-, -S- and -CO-.

2. The polymer composite piezoelectric body according to claim 1, wherein: The polymer is a polymer having only the repeating unit represented by the formula (2), or a polymer having the repeating unit represented by the formula (2) and a repeating unit containing a polar group other than a cyano group.

3. The polymer composite piezoelectric body according to claim 1 or 2, wherein: The content of the piezoelectric particles is 50 volume % or more relative to the total volume of the polymer composite piezoelectric body.

4. The polymer composite piezoelectric body according to claim 1, wherein: The piezoelectric particles include any one of lead zirconate titanate, lead lanthanum zirconate titanate, barium titanate, zinc oxide, and a solid solution of barium titanate and bismuth ferrite.

5. A piezoelectric film having: The polymer composite piezoelectric body according to any one of claims 1 to 4; and Two thin film electrodes are stacked on both sides of the polymer composite piezoelectric body. 6 . A piezoelectric speaker comprising the piezoelectric film according to claim 5 . 7 . A flexible display screen, wherein the piezoelectric film according to claim 5 is mounted on a surface opposite to an image display surface of the flexible display screen.

Images