Laminated piezoelectric body and manufacturing method for same

Abstract

Provided is a laminated piezoelectric body that can suppress discoloration of a fluorine-based resin piezoelectric film under conditions of high-temperature and high-humidity and maintain high transparency. The laminated piezoelectric body has a fluorine-based resin piezoelectric film and an antistatic layer disposed on at least one side of the fluorine-based resin piezoelectric film. The surface resistivity is 1.0x106 Ω / m2 to 1.0×1012 Ω / m2 inclusive, the hue b* after storage in an environment of 85°C and 85% RH for 500 hours is less than 3.0, and the piezoelectric constant d33 is 7.0 pC / N to 40.0 pC / N inclusive.

Description

Laminated piezoelectric body and method for manufacturing the same

[0001] The present invention relates to a laminated piezoelectric body and a method for manufacturing the same.

[0002] Various touch-type input devices that are attached to displays of electronic equipment and detect operation input by touching an operation surface have been proposed. As such a touch-type input device, a three-dimensional touch sensor that performs position detection (two-dimensional) and pressure detection (one-dimensional) has been proposed. Specifically, a touch sensor that detects position coordinates has been proposed in which a pressure-sensitive sensor is attached, so that in addition to detecting position coordinates, the magnitude of pressing can be detected at the same time (see Patent Documents 1 and 2). In such a touch panel, since it is necessary to visually recognize an image accurately, development of a piezoelectric film having high transparency and a high piezoelectric constant is expected.

[0003] As such a piezoelectric film, piezoelectric films containing a polymer compound such as polylactic acid or a fluorine-based resin as a main component have been studied. However, these piezoelectric films are easily charged by friction and vibration during conveyance in roll-to-roll processes such as wet coating, and static electricity is likely to be generated. Therefore, sparks caused by static electricity and dust adsorption to the piezoelectric film resulting from static electricity tend to cause poor appearance and performance degradation of piezoelectric devices.

[0004] In response to this, a laminated piezoelectric body in which an antistatic layer is laminated on a piezoelectric film has been proposed (see Patent Document 3). Patent Document 3 discloses that a coating liquid containing a conductive material and melamine resin as a binder resin is applied onto a fluorine-based resin piezoelectric film and then cured to form an antistatic layer.

[0005] Japanese Patent Application Laid-Open No. 2010-26938 International Publication No. WO 2019 / 102635 International Publication No. WO 2024 / 203685

[0006] However, according to studies conducted by the present inventors, it has been found that in a laminated piezoelectric body in which an antistatic layer containing a large amount of melamine resin is formed on a fluororesin piezoelectric film, the fluorine-based resin piezoelectric film discolors over time when exposed to a high-temperature and high-humidity environment for a long period of time, which reduces the transparency of the laminated piezoelectric body.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a laminated piezoelectric material and a method for manufacturing the same that can maintain high transparency and exhibit less discoloration of the fluororesin piezoelectric film under high temperature and high humidity conditions.

[0008] The present invention relates to the following laminated piezoelectric material and method for manufacturing the same: [1] A laminated piezoelectric material comprising a fluororesin piezoelectric film and an antistatic layer disposed on at least one surface of the fluororesin piezoelectric film, wherein the surface resistivity is 1.0 × 10 ６ Ω / sq. More than 1.0×10 １２ The hue b is less than or equal to Ω / sq. and is obtained after being held for 500 hours in an environment of 85°C and 85% RH. ＊ The piezoelectric constant d is less than 3.0. ３３ [2] A laminated piezoelectric material having a surface resistivity of 7.0 pC / N or more and 40.0 pC / N or less. ６ Ω / sq. More than 1.0×10 １２ The coefficient of gravity is less than or equal to Ω / sq., the atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer determined by X-ray photoelectron spectroscopy is 0.020 or less, and the piezoelectric constant d ３３ A laminated piezoelectric material having a density of 7.0 pC / N or more and 40.0 pC / N or less. [3] The laminated piezoelectric material according to [1] or [2], wherein the antistatic layer is in contact with at least one surface of the fluororesin piezoelectric film. [4] The difference in hue Δb before and after holding in an environment of 85°C and 85% RH for 500 hours. ＊[1] to [3] a laminated piezoelectric material according to any one of the following, wherein the ratio is less than 1.8. [5] A laminated piezoelectric material according to any one of the following, wherein the total light transmittance is 85% or more. [6] A laminated piezoelectric material according to any one of the following, wherein the antistatic layer is sandwiched between the hard coat layer and the fluororesin piezoelectric film. [7] A laminated piezoelectric material according to any one of the following, wherein the atomic ratio of fluorine atoms to carbon atoms in the fluororesin piezoelectric film, as determined by X-ray photoelectron spectroscopy, is 0.010 or more. [8] A laminated piezoelectric material according to any one of the following, wherein the fluororesin piezoelectric film mainly contains constituent units derived from vinylidene fluoride. [9] A laminated piezoelectric material according to any one of the following, wherein the thickness of the antistatic layer is 10 nm or more and 400 nm or less.

[10] The laminated piezoelectric material according to any one of [1] to [9], wherein the antistatic layer comprises a conductive material and a binder resin, and the binder resin comprises at least one of polyester and a (meth)acrylic resin.

[11] The laminated piezoelectric material according to any one of [1] to

[10] , wherein the antistatic layer substantially does not contain nitrogen atoms.

[12] A method for manufacturing a laminated piezoelectric material according to any one of [1] to

[11] , comprising the step of applying a composition comprising a conductive material and a binder resin onto the fluororesin piezoelectric film, and then drying to form an antistatic layer.

[13] The method for manufacturing a laminated piezoelectric material according to

[12] , wherein the binder resin comprises at least one of polyester and a (meth)acrylic resin.

[14] The method for manufacturing a laminated piezoelectric material according to

[12] or

[13] , further comprising the step of forming a hard coat layer on the antistatic layer.

[0009] According to the present invention, it is possible to provide a laminated piezoelectric material and a method for manufacturing the same that exhibits minimal discoloration of the fluororesin piezoelectric film under high temperature and high humidity conditions and maintains high transparency.

[0010] Figure 1 is a schematic cross-sectional view showing a laminated piezoelectric material according to one embodiment of the present invention.

[0011] 1. Laminated piezoelectric material: The laminated piezoelectric material includes a fluororesin piezoelectric film and an antistatic layer. The laminated piezoelectric material may further include other layers such as a hard coat layer to prevent damage to the antistatic layer.

[0012] The following describes in detail a laminated piezoelectric body according to one embodiment of the present invention. However, the laminated piezoelectric body is not limited to this embodiment.

[0013] Figure 1 is a schematic cross-sectional view showing a laminated piezoelectric body 10 according to one embodiment of the present invention. As shown in Figure 1, the laminated piezoelectric body 10 includes a fluororesin piezoelectric film 11, an antistatic layer 12, and a hard coat layer 13.

[0014] 1-1. Fluorine-based resin piezoelectric film 11 The fluorine-based resin piezoelectric film can be any film whose main component is a fluorine-based resin. A fluorine-based resin is a resin obtained by polymerizing an olefin monomer containing at least fluorine. Containing a fluorine-based resin as the main component means that the content of constituent units derived from olefin monomers containing fluorine, relative to the total mass of the fluorine-based resin film, is 50% by mass or more. The content of fluorine-based resin relative to the total mass of the fluorine-based resin piezoelectric film is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less.

[0015] Fluorine-based resins can be homopolymers or copolymers obtained by polymerizing tetrafluoroethylene (TFE) or vinylidene fluoride (VDF), etc. Examples of fluorine-based resins obtained by polymerizing TFE include copolymers of TFE with one or more substances selected from the group consisting of ethylene, perfluoroalkyl vinyl ether, VDF, 1-chloro-1-fluoroethylene, chlorotrifluoroethylene (CTFE), and hexafluoropropylene (HFP). Examples of fluorine-based resins obtained by polymerizing VDF include homopolymers of VDF, as well as copolymers of VDF with one or more substances selected from the group consisting of 1-chloro-1-fluoroethylene, 1-chloro-2-fluoroethylene, trifluoroethylene, TFE, CTFE, tetrafluoropropene, HFP, and perfluoroalkyl vinyl ether, etc.

[0016] Of these, from the viewpoint of further enhancing the piezoelectric properties of the fluororesin piezoelectric film, at least a fluororesin obtained by polymerizing VDF as an olefin monomer containing fluorine, i.e., a resin containing constituent units derived from VDF, is preferred. As the resin containing constituent units derived from VDF, a homopolymer of VDF, a copolymer of VDF and trifluoroethylene, a copolymer of VDF and HFP, a copolymer of VDF and TFE, a copolymer of VDF, trifluoroethylene, TFE and CTFE, and a copolymer of VDF, trifluoroethylene, TFE and 1-chloro-1-fluoroethylene are more preferred, and a homopolymer of VDF is even more preferred. One of these fluororesins may be used alone, or multiple types may be used in combination.

[0017] The fluororesin piezoelectric film preferably contains constituent units derived from VDF as its main component. Containing constituent units derived from VDF as its main component means that the content of constituent units derived from VDF relative to the total mass of the fluororesin piezoelectric film is 50% by mass or more. The content of the resin containing constituent units derived from VDF, preferably a homopolymer of VDF, relative to the total mass of the fluororesin piezoelectric film is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less.

[0018] The content rate of structural units derived from VDF contained in the fluororesin piezoelectric film and the content rate of the resin having VDF as a structural unit can be １９ measured by quantitative analysis using an internal standard with ¹⁹F-NMR.

[0019] The atomic ratio of fluorine atoms to carbon atoms of the fluororesin piezoelectric film determined by X-ray photoelectron spectroscopy (XPS) is, for example, preferably 0.010 or more, more preferably 0.020 or more. When the above atomic ratio is 0.010 or more, it can be determined that the fluororesin piezoelectric film contains a fluororesin or is mainly composed of a fluororesin. The above atomic ratio of fluorine atoms to carbon atoms can be calculated from the ratio of the quantitative value of fluorine to the quantitative value of carbon (quantitative value of fluorine / quantitative value of carbon) in a wide spectrum obtained by XPS measurement described later.

[0020] The piezoelectric constant d of the fluororesin piezoelectric film ３３ only needs to be in a range such that the piezoelectric constant d of the laminated piezoelectric body ３３ falls within the range described later. Specifically, the piezoelectric constant of the fluororesin piezoelectric film is preferably 7.0 pC / N or more and 40.0 pC / N or less, more preferably 10.0 pC / N or more and 40.0 pC / N or less, still more preferably 13.0 pC / N or more and 35.0 pC / N or less, and particularly preferably 15.0 pC / N or more and 30.0 pC / N or less. When the piezoelectric constant of the fluororesin piezoelectric film is 7.0 pC / N or more, the amount of electric charge generated by the piezoelectric effect is larger, so that pressure sensitivity can be further improved. When the piezoelectric constant of the fluororesin piezoelectric film is 40.0 pC / N or less, for example, appearance defects caused by a decrease in surface flatness of the fluororesin piezoelectric film resulting from polarization treatment can be made less likely to occur.

[0021] The piezoelectric constant of the fluororesin piezoelectric film is the piezoelectric constant d obtained by the direct quasi-static method (d ３３ meter method, Berlin coat method) ３３The test method can be measured in accordance with ISO 19622:2018. Specifically, a piezoelectric constant measuring device (e.g., PIEZOTEST PM300 piezometer system) is used to hold a test piece of fluororesin piezoelectric film with a holding force of 1.0 N at a measurement temperature of 25°C, and the charge generated when an alternating force of 0.15 N and a frequency of 110 Hz is applied is measured. The charge of the piezoelectric film is measured over a range including the center of the surface of the fluororesin piezoelectric film (in the case of a rectangular fluororesin piezoelectric film, the range including the intersection of the diagonals), and the piezoelectric constant d is calculated from that value. ３３ The absolute value of the piezoelectric constant d of the fluorine-based resin piezoelectric film ３３ This can be used as a representative value. If the length of one side of the piezoelectric film is 30 cm or more, a rectangle with sides of 30 cm shall be arbitrarily assumed, and the range including the intersection of the diagonals of the rectangular film shall be measured. If both sides of the piezoelectric film are 30 cm or more, a square with sides of 30 cm shall be arbitrarily set on the piezoelectric film, and the measurement range shall be set according to the method described above.

[0022] Piezoelectric constant d of fluororesin piezoelectric film ３３ This can be adjusted mainly by the type of resin contained in the fluororesin piezoelectric film and the manufacturing conditions (polarization treatment and stretching treatment conditions). For example, among fluororesins, the more constituent units derived from VDF the resin contains, the higher the piezoelectric constant d of the fluororesin piezoelectric film. ３３ It tends to become larger. Also, by strengthening the polarization treatment or stretching treatment, the piezoelectric constant d of the fluororesin piezoelectric film can be increased. ３３ It tends to grow large.

[0023] The thickness of the fluororesin piezoelectric film is not particularly limited, but for example, 25 μm to 120 μm is preferred. When the thickness of the fluororesin piezoelectric film is 25 μm or more, the amount of charge generated by the piezoelectric effect increases, making it easier to obtain higher piezoelectricity. The thickness of the fluororesin piezoelectric film is more preferably 30 μm or more, and even more preferably 35 μm or more. When the thickness of the fluororesin piezoelectric film is 120 μm or less, the transparency of the fluororesin piezoelectric film is less likely to be impaired, so 100 μm or less is more preferred, and 80 μm or less is even more preferred. From a similar viewpoint, the thickness of the fluororesin piezoelectric film is more preferably 35 μm to 80 μm.

[0024] The thickness of a fluororesin piezoelectric film can be measured, for example, by a method using a micrometer (JIS C 2151:2019), but it can also be measured by known methods such as a laser displacement meter, a capacitance displacement meter, or an infrared light meter. Here, the thickness can be measured using the above method over a range including the center of the surface of the fluororesin piezoelectric film (in the case of a rectangular fluororesin piezoelectric film, the range including the intersection of the diagonals), and the measured value can be taken as the thickness of the fluororesin piezoelectric film. If the length of one side of the piezoelectric film is 30 cm or more, a rectangle with sides of 30 cm can be arbitrarily assumed, and the range including the intersection of the diagonals of the rectangular film can be measured. If both sides of the piezoelectric film are 30 cm or more, a square with sides of 30 cm can be arbitrarily set on the piezoelectric film, and the measurement range can be set according to the above method.

[0025] 1-2. Antistatic layer 12 The antistatic layer is disposed on at least one surface of the fluororesin piezoelectric film. In Figure 1, the antistatic layer is disposed in contact with one surface of the fluororesin piezoelectric film. The antistatic layer can suppress static electricity generated in the laminated piezoelectric body. Note that the antistatic layer may consist of only one layer or two or more layers.

[0026] Conventionally, as described above, melamine resin has been used as the binder resin for the antistatic layer. That is, the antistatic layer is formed by applying a coating solution containing a conductive material and a binder resin to a piezoelectric film and then curing it. Fluorine-based piezoelectric films tend to lose transparency and piezoelectricity when heated. Therefore, melamine resin has been used as a binder resin that can be heat-cured at a relatively low temperature and in a short time. Furthermore, melamine resin was considered preferable from the viewpoint of ensuring solvent resistance when further forming layers such as a hard coat layer on the antistatic layer.

[0027] However, our investigations have revealed that when a laminated piezoelectric body having an antistatic layer containing a large amount of melamine resin on a fluororesin piezoelectric film is used or stored in a high-temperature, high-humidity environment, the fluororesin piezoelectric film discolors, and as a result, the transparency of the laminated piezoelectric body decreases.

[0028] The reason for this is unclear, but it is speculated that: When an antistatic layer containing a large amount of melamine resin is exposed to a high-temperature, high-humidity environment for a predetermined period of time or longer, the melamine resin is likely to decompose and generate amines. When these generated amines come into contact with a fluororesin piezoelectric film, the fluororesin piezoelectric film undergoes a dehydrofluoride reaction, causing it to discolor and become more yellowish. This phenomenon is particularly pronounced when the antistatic layer is in contact with the fluororesin piezoelectric film, but it is not limited to this case; it may also occur when the layers are arranged in between, as long as the generated amines permeate through those layers.

[0029] In response to this, the present inventors have found that by using a resin that generates a small amount of amines that cause the dehydrofluoride reaction, i.e., a resin with a low nitrogen atom content, preferably a resin that does not contain nitrogen atoms (e.g., polyester or (meth)acrylic resin), as the binder resin for the antistatic layer, discoloration due to the dehydrofluoride reaction of the fluororesin piezoelectric film can be suppressed. Furthermore, even when using a resin containing nitrogen atoms, such as melamine resin, as the binder resin for the antistatic layer, the discoloration due to the dehydrofluoride reaction of the fluororesin piezoelectric film can be reduced by reducing the content of the resin in the antistatic layer. As a result, even after use or storage in a high-temperature, high-humidity environment, the hue b of the laminated piezoelectric material can be maintained. ＊ The value can be kept low.

[0030] Furthermore, such an antistatic layer can be formed by applying a composition containing the above-mentioned resin onto a fluororesin piezoelectric film and then drying it at a relatively low temperature. Therefore, high-temperature heat treatment is unnecessary, and discoloration of the fluororesin piezoelectric film due to heating can be suppressed.

[0031] In other words, the antistatic layer preferably comprises a conductive material and a binder resin. At least a portion of the binder resin may be crosslinked. That is, the antistatic layer may be obtained by applying a composition comprising the conductive material and the binder resin and then drying it, or by crosslinking it as necessary.

[0032] The conductive material may be an ionic conductive material or an electron conductive material.

[0033] Examples of ion-conducting conductive materials include (a) cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups; (b) anionic antistatic agents having anionic groups such as sulfonic acid bases, sulfate ester bases, phosphate ester bases, and phosphonic acid bases; (c) amphoteric antistatic agents such as amino acid-based and aminosulfate ester-based agents; and (d) nonionic antistatic agents such as amino alcohol-based, glycerin-based, and polyethylene glycol-based agents.

[0034] Examples of electron-conducting conductive materials include conductive polymer compounds and other conductive materials. Examples of conductive polymer compounds include polyacetylene and its derivatives, polythiophene and its derivatives, polypyrrole and its derivatives, and polyaniline and its derivatives. Among these, polyacetylene and its derivatives, and polythiophene and its derivatives, which are conductive polymer compounds that do not contain nitrogen atoms, are preferred from the viewpoint of further suppressing the generation of amines under high temperature and high humidity conditions, and polythiophene and its derivatives are more preferred from the viewpoint of further improving transparency and conductivity. These conductive polymer compounds may have functional groups such as sulfone groups, hydroxyl groups, mercapto groups, and carboxyl groups. Examples of conductive materials other than conductive polymer compounds include carbon nanotubes and graphene.

[0035] Among these, from the viewpoint of making it easier to reduce the surface resistivity of the laminated piezoelectric material and less likely to cause bleed-out, it is preferable that the conductive material includes an electron-conducting conductive material, and more preferably a conductive polymer or carbon nanotube.

[0036] The binder resin may be a thermoplastic resin or a thermosetting resin. Preferably, the binder resin contains a resin that does not contain nitrogen atoms in its molecule. Examples of such binder resins include (meth)acrylic resins, polyesters, ethylene-vinyl acetate copolymers (EVA), polyvinyl alcohol, polystyrene, polyvinyl acetate, polyethylene glycol, silicone compounds, epoxy resins, etc. These resins may have functional groups such as hydroxyl groups, methylol groups, carboxyl groups, sulfonyl groups, and epoxy groups. This allows the resins to self-crosslink or to be thermally crosslinked via a crosslinking agent. Among these, (meth)acrylic resins and polyesters are preferred, and polyesters are more preferred, from the viewpoint of less coating repulsion on fluororesin piezoelectric films and ease of drying at relatively low temperatures. That is, it is preferable that the binder resin contains at least one of polyester and (meth)acrylic resins. (Meth)acrylic refers to either or both acrylic and methacrylic.

[0037] (Polyester) Polyester is a resin produced by dehydrating and condensing polyalcohols (e.g., ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanediol, etc.) and polycarboxylic acids (e.g., terephthalic acid, 2,6-naphthalenedicarboxylic acid, etc.), and mainly contains constituent units having ester bonds. "Mainly contains" means that the content of constituent units having ester bonds relative to the total constituent units of the resin is 50% by mass or more. The content of constituent units having ester bonds is preferably 60% by mass or more, and more preferably 70% by mass or more.

[0038] Typical examples of polyesters include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and unsaturated polyesters. By changing the combination of polyalcohol and polycarboxylic acid, polyesters with different properties can be produced. Furthermore, by combining them with different monomers, copolymer polyesters can be produced.

[0039] Examples of copolymerized polyesters include polyester urethane, polyester epoxy, and polyester acrylate, which exhibit excellent adhesion to conductive polymer materials and conductive fillers. These resins can be used as emulsions.

[0040] (Meth)acrylic resins) Meth)acrylic resins are resins that mainly contain constituent units derived from monomers having (meth)acryloyl groups. "Mainly contain" means that the content of constituent units derived from the above monomers relative to the total constituent units of the resin is 50% by mass or more. The content of constituent units derived from monomers having (meth)acryloyl groups is preferably 60% by mass or more, and more preferably 70% by mass or more. (Meth)acryloyl means either acryloyl or methacryloyl or both.

[0041] (Meth)acrylic resins are polymers of (meth)acrylic monomers or copolymers thereof with other monomers copolymerizable thereto.

[0042] Examples of (meth)acrylic monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and hydroxyethyl (meth)acrylate; (meth)acrylamides; and (meth)acrylic acid, with acrylic acid esters and acrylic acid being preferred.

[0043] Other examples of copolymerizable monomers include monofunctional monomers such as ethylenically unsaturated carboxylic acids (e.g., maleic acid, itaconic acid), styrenes (e.g., styrene, α-methylstyrene, vinyltoluene), saturated fatty acid vinyls (e.g., vinyl acetate, vinyl propionate), and vinyl compounds (e.g., 1,4-divinyloxybutane, divinylbenzene); and bifunctional or more monomers such as polyfunctional (meth)acrylates like diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, propylene glycol di(meth)acrylate, and N,N'-methylenebis(acrylamide).

[0044] The binder resin may be of one type or two or more types. For example, polyester and (meth)acrylic resin may be used in combination. In that case, the polyester content in the antistatic layer may be higher than the (meth)acrylic resin content.

[0045] Furthermore, our studies have shown that thermoplastic resins such as polyester and (meth)acrylic resins have sufficient solvent resistance. When the hard coat layer contains a cured product of a (meth)acrylic curable composition, the affinity between the antistatic layer and the hard coat layer can be further enhanced, and a crosslinking reaction can be induced between the (meth)acrylic compound and the (meth)acrylic resin contained in the antistatic layer by the photopolymerization initiator contained in the hard coat layer. This further enhances the interlayer adhesion between the antistatic layer and the hard coat layer. In other words, by including a (meth)acrylic resin in the antistatic layer, it is possible to ensure solvent resistance while also further enhancing adhesion to the hard coat layer.

[0046] Furthermore, the binder resin may contain a resin that includes nitrogen atoms in its molecule, as long as it does not impair the effects of the present invention. For example, when a conductive polymer compound that does not contain nitrogen atoms is used as a conductive material, the nitrogen atom content in the antistatic layer can be reduced by increasing the content of the conductive polymer compound and decreasing the content of the melamine resin, thereby reducing the amount of amine generated.

[0047] The content of the conductive material in the antistatic layer should be within a range that satisfies the surface resistivity of the laminated piezoelectric material as described later. For example, when the conductive material is a conductive polymer compound, the content is preferably 10% by mass or more and 60% by mass or less. Of these, when a resin that does not contain nitrogen atoms, such as polyester or (meth)acrylic resin, is used as the binder resin, the content of the conductive material in the antistatic layer may be less than the content of the binder resin. For example, the content of the conductive material in the antistatic layer may be 10% by mass or more and 40% by mass or less, and the content of the binder resin may be 60% by mass or more and 90% by mass or less. On the other hand, when a resin containing nitrogen atoms, such as melamine resin, is used as the binder resin, the content of the conductive material in the antistatic layer is preferably equal to or greater than the content of the binder resin. For example, it is preferable that the content of the conductive material in the antistatic layer is 50% by mass or more and 60% by mass or less, and the content of the binder resin is preferably 40% by mass or more and 50% by mass or less. When the conductive material is a carbon nanotube or other material other than a conductive polymer compound, the aforementioned content is preferably 10% by mass or more and 40% by mass or less.

[0048] The above composition may further contain a crosslinking agent as needed. The crosslinking agent should be one that reacts with the functional groups of the resin to cause crosslinking. The crosslinking agent is preferably one that does not contain nitrogen atoms, and for example, polyepoxy crosslinking agents are included.

[0049] Furthermore, the above composition may further contain a diluent as needed. The diluent can be any agent capable of dispersing the resin, and may be water or a water-soluble solvent. Examples of water-soluble solvents include alcohol-based solvents such as methanol, ethanol, and isopropyl alcohol.

[0050] Commercially available products can be used as conductive materials and binder resins. For example, conductive material dispersions include conductive coating agents using conductive polymer compounds (PEDOT:PSS), which are composites of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (e.g., Denatron P-400MP-A from Nagase ChemteX Corporation), and conductive coating agents using carbon nanotubes (e.g., Denatron C-169PF-A). Binder resin solutions can also be binder resin dispersions containing ethylene-vinyl acetate copolymer (EVA) (e.g., Polysol EVA P-3PN from Resonaq Corporation).

[0051] As described above, the antistatic layer preferably has a low nitrogen atom content, and more preferably contains virtually no nitrogen atoms. For example, the nitrogen (nitrogen atom) content relative to the total mass of the antistatic layer is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 10% by mass or less. Of these, the range in which the antistatic layer contains virtually no nitrogen atoms can be, for example, a nitrogen (nitrogen atom) content relative to the total mass of the antistatic layer of 10% by mass or less. The nitrogen atom content in the antistatic layer can be calculated from the product of the binder resin content in the antistatic layer and the nitrogen atom content in the binder resin used (calculated from the chemical structure).

[0052] The surface resistivity of the antistatic layer should be within a range such that the surface resistivity of the laminated piezoelectric material falls within the range described below. That is, the surface resistivity of the antistatic layer is preferably the same as or lower than the surface resistivity of the laminated piezoelectric material, specifically 1.0 × 10⁻⁶. ４ Ω / sq. More than 1.0×10 １０ Ω / sq. is preferably less than or equal to 1.0 × 10⁻¹⁰. ５ Ω / sq. More than 1.0×10 ９ Ω / sq. or less is more preferable.

[0053] The surface resistivity of the antistatic layer can be measured in accordance with JIS C 2139-3-2:2018 using, for example, a known resistivity meter (e.g., a high resistivity meter (Hyresistor UX, model number: MCP-HT800, URS probe, manufactured by Nitto Seiko Analytech Co., Ltd.)). The measurement is performed over a range including the center of the surface of the antistatic layer (or the range including the intersection of the diagonals in the case of a rectangular laminated piezoelectric material), and the measured surface resistivity is taken as a representative value.

[0054] The atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer, as determined by X-ray photoelectron spectroscopy, is 0.020 or less, preferably 0.000 to 0.020, and more preferably 0.000 to 0.015. When the above atomic ratio is 0.020 or less, the generation of amines can be reduced, thereby reducing discoloration of the fluorine-based piezoelectric film due to the dehydrofluorination reaction.

[0055] The atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer contained in a multilayer piezoelectric material can be measured by photoelectron spectroscopy (XPS). If there is another layer such as a hard coat layer on the antistatic layer, the other layer is removed by argon ion etching to expose the antistatic layer, and then measured by XPS. The measurement procedure is described below using the example of a case where there is a hard coat layer. (1) Cut the multilayer piezoelectric material into a 6 mm x 6 mm square and attach the sample to an 8 mm x 8 mm Si wafer with the side with the antistatic layer facing upwards. (2) After fixing the sample to the dedicated sample stage of the X-ray photoelectron spectrometer (general-purpose photoelectron spectrometer JPS-9010MC manufactured by JEOL Ltd.) with tape, evacuate the sample overnight in the preparation chamber of the instrument to dry it. (3) Perform depth profiling (depth measurement) according to the following procedure. The etching rate is SiO ２The etching speed was set to 40 nm / min, and each etching pass of the sample was set to 10 seconds. Etching was performed from the outermost surface, and a wide spectrum was obtained after each etching by XPS measurement as described below. The measurement endpoint was defined as the point where the atomic ratio of oxygen atoms to carbon atoms was 0.050 or less. The elements measured were carbon (C), nitrogen (N), oxygen (O), and fluorine (F). The orbitals and measurement energy ranges of each element measured are as follows: C is C1s 278-298 eV, N is N1s 391-413 eV, O is O1s 523-545 eV, and F is F1s 676-703 eV. The conditions for the XPS measurement are as follows. (XPS measurement conditions) ・X-ray source: Al-Kα ・Measurement range: 100.0 eV to 1350.0 eV ・X-ray beam diameter: φ200 μm ・X-ray intensity: 12 kV / 25 mA ・Photoelectron extraction angle: 90 degrees relative to the sample surface ・Sputter ions: Ar (600 V / 13 mA) (4) Background correction is performed on the wide spectra obtained from each XPS measurement using the Shirley method. The background setting ranges for each element are as follows: C is 250.0-300.0 eV for C1s, N is 380.0-415.0 eV for N1s, O is 510.0-545.0 eV for O1s, and F is 670.0-710.0 eV for F1s. After background correction, the peak areas of C1s, N1s, O1s and F1s are calculated. The abundance (quantitative values) of carbon, nitrogen, oxygen, and fluorine are calculated by dividing the above peak areas by their respective relative sensitivity coefficients. The relative sensitivity coefficients used are those specific to the instrument. The ratio of the quantitative value of nitrogen to the quantitative value of carbon (quantitative value of nitrogen / quantitative value of carbon) is defined as the atomic ratio of nitrogen atoms to carbon atoms; the ratio of the quantitative value of oxygen to the quantitative value of carbon (quantitative value of oxygen / quantitative value of carbon) is defined as the atomic ratio of oxygen atoms to carbon atoms; and the ratio of the quantitative value of fluorine to the quantitative value of carbon (quantitative value of fluorine / quantitative value of carbon) is defined as the atomic ratio of fluorine atoms to carbon atoms. The maximum value of the atomic ratio of nitrogen atoms to carbon atoms obtained from XPS measurements of three test pieces prepared from the same sample is then defined as the "atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer" as a representative value.Furthermore, the maximum value of the atomic ratio of fluorine atoms to carbon atoms at the measurement endpoint obtained in each XPS measurement is defined as the "atomic ratio of fluorine atoms to carbon atoms in the fluorine-based piezoelectric film."

[0056] Furthermore, if the antistatic layer is exposed on the surface of the multilayer piezoelectric material (i.e., there are no other layers such as a hard coat layer on the antistatic layer), XPS measurement should be performed in the same manner as above, except that etching is not performed, and the ratio of the obtained quantitative values ​​of nitrogen and carbon (quantitative value of nitrogen / quantitative value of carbon) should be defined as the "atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer".

[0057] The thickness of the antistatic layer is not particularly limited, but is preferably, for example, 10 nm to 400 nm. A thickness of 10 nm or more imparts high conductivity to the laminated piezoelectric material, thus further preventing the generation of static electricity. A thickness of 400 nm or less imparts high conductivity to the piezoelectric constant d in the laminated piezoelectric material. ３３ This can suppress the decrease in [the value]. From a similar viewpoint, the thickness of the antistatic layer is more preferably 30 nm to 400 nm, and even more preferably 45 nm to 300 nm.

[0058] The thickness of the antistatic layer can be measured using a spectroscopic interferometric thickness gauge (e.g., Optical NanoGauge C13027-11, manufactured by Hamamatsu Photonics). The measurement is performed over a range including the center of the multilayer piezoelectric surface (for example, a range including the intersection of the diagonals in the case of a rectangular multilayer piezoelectric surface), and the measured thickness can be used as a representative value. The thickness of each of the following layers can be measured in the same manner.

[0059] 1-3. Hard Coat Layer 13 The hard coat layer can suppress the increase of haze by making it difficult for scratches to occur on the surface of the antistatic layer during the manufacturing of the laminated piezoelectric material. In Figure 1, the hard coat layer is located on the opposite side of the fluororesin piezoelectric film, with the antistatic layer in between. Note that the hard coat layer may consist of only one layer or two or more layers.

[0060] The hard coat layer preferably contains a cured product of a curable composition containing a polymerizable compound.

[0061] (Polymerizable Compounds) Polymerizable compounds may be monomers, oligomers, or polymers. Polymerizable compounds may be thermosetting compounds or ionizing radiation compounds, but are preferably ionizing radiation compounds. Ionizing radiation may usually be ultraviolet (UV) or electron beams (EB).

[0062] Ionizing radiation compounds are compounds having ionizing radiation-curable functional groups. Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, and ring-opening polymerizable groups such as epoxy groups and oxetanyl groups. Among these, compounds having ethylenically unsaturated bonding groups are preferred, compounds having two or more ethylenically unsaturated bonding groups are more preferred, and polyfunctional (meth)acrylate compounds are even more preferred. (Meth)acrylate means either or both acrylate and methacrylate.

[0063] Among the polyfunctional (meth)acrylate compounds, examples of bifunctional (meth)acrylate monomers include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxydiaacrylate, bisphenol A tetrapropoxydiaacrylate, and 1,6-hexanediol diacrylate. Examples of trifunctional or more (meth)acrylate monomers include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and isocyanuric acid-modified tri(meth)acrylate. Furthermore, the above (meth)acrylate monomers may have a modified molecular skeleton, and those modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc., can also be used.

[0064] Furthermore, examples of polyfunctional (meth)acrylate oligomers include acrylate polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and polyether (meth)acrylate. Urethane (meth)acrylate can be obtained, for example, by the reaction of polyhydric alcohols and organic diisocyanates with hydroxy (meth)acrylate.

[0065] (Polymerization Initiator) When the ionizing radiation-curable compound is an ultraviolet-curable compound, the curable composition preferably contains a photopolymerization initiator. Examples of photopolymerization initiators include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler ketone, benzoin, benzyl methyl ketal, benzoyl benzoate, α-acyloxime ester, thioxanthone, etc.

[0066] (Other components) The curable composition may further contain other components as needed. For example, the curable composition may further contain particles to suppress blocking during the manufacture of the laminated piezoelectric material or to adjust the refractive index. The particles may be inorganic or organic particles.

[0067] Examples of inorganic particles include particles such as silica (silicon oxide), titanium oxide, zirconium oxide, aluminum oxide, zinc oxide, and tin oxide, as well as diamond powder, sapphire particles, boron carbide particles, silicon carbide particles, and antimony pentoxide particles. Examples of organic particles include resin particles such as acrylic resin, acrylic-styrene copolymer, and silicone resin. Among these, inorganic particles are preferred because they do not impair the transparency of the hard coat layer, and silica particles are more preferred. The surface of the inorganic particles may be treated with a surface modifier such as a silane coupling agent.

[0068] Furthermore, the curable composition may further contain a diluent. The diluent is preferably one with a polarity similar to that of the particles. Examples of diluents include organic solvents such as alcohol-based solvents, ketone-based solvents, ester-based solvents, carbonate-based solvents, and aromatic solvents.

[0069] The refractive index of the hard coat layer is not particularly limited, but may be higher than that of the fluororesin piezoelectric film. For example, the refractive index of the hard coat layer is preferably 1.40 or more and less than 1.60, more preferably 1.45 or more and less than 1.60, even more preferably 1.47 or more and 1.57 or less, and particularly preferably 1.49 or more and 1.55 or less.

[0070] In this specification, the refractive index refers to the refractive index at a wavelength of 589 nm. The refractive index of each layer can be determined by measuring the psi (Ψ) and delta (△) using a multi-incidence-angle high-speed spectroscopic ellipsometer (e.g., J.A. Wollam M-2000) and calculating the refractive index at a wavelength of 589 nm from these values. The above measurement is performed over a range including the center of the surface of each layer (or, in the case of a rectangular surface, the range including the intersection of the diagonals), and the measured value can be used as a representative value. If the length of one side of the rectangle is 30 cm or more, a rectangle with sides of 30 cm is arbitrarily assumed, and the range including the intersection of the diagonals of the rectangle is measured. If both sides of the rectangle are 30 cm or more, a square with sides of 30 cm is arbitrarily set within the rectangle, and the measurement range is set according to the above method.

[0071] The thickness of the hard coat layer is not particularly limited, but is preferably 50 nm or more, more preferably 300 nm to 3000 nm, even more preferably 500 nm to 2000 nm, and particularly preferably 500 nm to 1500 nm.

[0072] 1-4. Other multilayer piezoelectric materials may further include other layers as needed. Examples of other layers include optical adjustment layers.

[0073] 1-4-1. Optical Adjustment Layer The optical adjustment layer can further reduce the color tint of the laminated piezoelectric material by appropriately adjusting its refractive index and thickness. The optical adjustment layer may be placed on the antistatic layer, or on the opposite side of the antistatic layer, separated by a hard coat layer. Furthermore, the optical adjustment layer may consist of only one layer or two or more layers.

[0074] The refractive index of the optical adjustment layer is preferably higher than that of the hard coat layer. This further suppresses defects in the appearance of the laminated piezoelectric material caused by interference between light incident on and reflected by the hard coat layer and light reflected at the interface between the optical adjustment layer and the hard coat layer. From the above viewpoint, the refractive index of the optical adjustment layer is preferably 1.60 or more and less than 1.80, more preferably 1.63 or more and less than 1.78, and even more preferably 1.65 or more and 1.75 or less.

[0075] The material for the optical adjustment layer can be any material that satisfies such refractive index requirements. For example, the refractive index may be adjusted by adding metal oxide particles to the curable composition exemplified as the material for the hard coat layer. The metal oxide particles are preferably refractive index materials with a refractive index of 1.50 or higher. Examples of such metal oxide particles include aluminum oxide, titanium oxide, zirconium oxide, zinc oxide, and tin oxide, with titanium oxide and zirconium oxide being preferred.

[0076] The thickness of the optical adjustment layer is not particularly limited, but it should be 0.05 μm or more. For example, the thickness of the optical adjustment layer may be 0.05 μm or more and 0.50 μm or less, or 0.08 μm or more and 0.18 μm or less. By having the thickness of the optical adjustment layer within the above range, the color of the laminated piezoelectric material can be further reduced.

[0077] 1-5. Physical properties of the laminated piezoelectric material 10 (surface resistivity) The surface resistivity of the laminated piezoelectric material is 1.0 × 10⁻⁶ ６ Ω / sq. More than 1.0×10 １２ It is less than or equal to Ω / sq. and 1.0 × 10⁻⁶ ８ Ω / sq. More than 5.0×10 １１ Ω / sq. is preferably less than or equal to 1.0 × 10⁻¹⁰. ９ Ω / sq. More than 5.0×10 １０ A value of Ω / sq. or less is more preferable. The surface resistivity of the laminated piezoelectric material is 1.0 × 10⁻⁶. １２ If the coefficient is less than or equal to Ω / sq., sufficient antistatic properties can be imparted to the surface of the laminated piezoelectric material.

[0078] The surface resistivity of a laminated piezoelectric material can be measured in the same manner as described above, except that the representative value is the surface resistivity measured over a range including the center of the side of the laminated piezoelectric material where the antistatic layer is located relative to the fluororesin piezoelectric film (the surface of the hard coat layer 13 in Figure 1) (in the case of a rectangular laminated piezoelectric material, the range including the intersection of the diagonals). For example, if the antistatic layer is on the outermost surface, the measurement should be performed on the surface of the antistatic layer, and if the hard coat layer formed on the antistatic layer is on the outermost surface, the measurement should be performed on the surface of the hard coat layer.

[0079] The surface resistivity of a laminated piezoelectric material can be adjusted by the layer configuration, such as the composition and thickness of the antistatic layer. For example, the higher the conductive material / binder resin content of the antistatic layer and the greater the thickness of the antistatic layer, the lower the surface resistivity tends to be. Also, the closer the antistatic layer is to the surface of the laminated piezoelectric material, the lower the surface resistivity tends to be.

[0080] (b ＊ Value, △b ＊ ) Hue b of a multilayer piezoelectric material after being held for 500 hours in an environment of 85°C and 85% RH. ＊ The value is less than 3.0, preferably between -3.0 and 2.0, more preferably between -1.5 and 1.5, even more preferably between -1.0 and 1.0, and particularly preferably between 0.0 and 0.8. Hue b after holding the laminated piezoelectric material under the above environment. ＊ If the value is less than 3.0, discoloration of the fluororesin piezoelectric film when stored or used under high temperature and high humidity conditions is reduced, and the transparency of the laminated piezoelectric material can be well maintained.

[0081] Furthermore, the hue difference Δb before and after holding a laminated piezoelectric material in an environment of 85°C and 85% RH for 500 hours is also measured. ＊ The hue difference Δb is preferably less than 1.8, more preferably 0.0 to 1.4, even more preferably 0.0 to 1.0, particularly preferably 0.0 to 0.8, and very preferably 0.0 to 0.6. ＊ If the value is less than 1.8, the discoloration of the fluororesin piezoelectric film before and after holding under the above conditions will be less, and the transparency of the laminated piezoelectric material can be maintained more effectively.

[0082] b of laminated piezoelectric material ＊ and △b ＊ This can be measured by a method compliant with JIS Z 8722:2009. 1) From 25 cm away from the laminated piezoelectric material. ２ 1) Cut out six laminated piezoelectric materials into a square to create six test laminates. 2) For each of the three test laminates prepared in 1) before moist heat storage, measure the hue b of the area including the center of each test laminate (including the intersection of the diagonals) using a spectrocolorimeter SD7000 (manufactured by Nippon Denshoku Industries Ltd.) in accordance with JIS Z 8722:2009. ＊ Measure the value. Hue b of three test laminates. ＊ The average value of the hue b of the laminated piezoelectric material before saving. ＊ This value will be considered representative. 3) Next, three of the test laminates prepared in 1) that were not used in the measurement in 2) are each fixed to a SUS plate with tape at all four corners, and placed in a constant temperature and humidity chamber (LH44-14 manufactured by Nagano Science Co., Ltd.) set to a temperature of 85°C and a humidity of 85% RH, and kept under these conditions for 500 hours. After that, the test laminates are removed from the constant temperature and humidity chamber, and for each of the three stored test laminates, the hue b is measured in the area including the center of each test laminate (the area including the intersection of the diagonals). ＊ The value was measured in the same manner as described above, and the hue b of the three test laminates was measured. ＊ Hue b of the laminated piezoelectric material after saving the average value ＊ This value will be used as a representative value. 4) Hue b after saving ＊ Representative value of the value and hue b before saving ＊ The difference in typical values ​​of the laminated piezoelectric material before and after saving the hue difference Δb ＊ Set this as the value.

[0083] b of laminated piezoelectric material ＊ Values ​​and △b ＊ This can be adjusted by the type of resin and nitrogen content contained in the antistatic layer. For example, discoloration of fluororesin piezoelectric films can be reduced by using a resin that does not contain nitrogen atoms as the binder resin for the antistatic layer, or by selecting conductive materials and binder resins that reduce the nitrogen content of the antistatic layer.

[0084] (Piezoelectric constant) Piezoelectric constant d of a laminated piezoelectric material ３３The piezoelectric constant d of the laminated piezoelectric material is 7.0 pC / N or more and 40.0 pC / N or less, preferably 10.0 pC / N or more and 40.0 pC / N or less, more preferably 13.0 pC / N or more and 35.0 pC / N or less, and even more preferably 15.0 pC / N or more and 30.0 pC / N or less. ３３ When the piezoelectric constant d of a multilayer piezoelectric material is 7 pC / N or higher, higher pressure sensitivity is more likely to be obtained. ３３ If the coefficient of particle size (d) is 40 pC / N or less, the above-mentioned surface defects can be further reduced. The piezoelectric constant of a laminated piezoelectric material can be measured in the same way as the piezoelectric constant of a fluororesin piezoelectric film, except that the following point is different: d of the two surfaces of the laminated piezoelectric material ３３ This is measured, for example, using a piezometer system PM300. The d measured on each of the two surfaces of the laminated piezoelectric material is ３３ The absolute values ​​of the measured values ​​are compared, and the one with the larger absolute value is used as the piezoelectric constant d of the laminated piezoelectric material. ３３ The following applies: Measurements on each surface will be taken within the area including the center of the surface of the laminated piezoelectric material (or, in the case of a rectangular laminated piezoelectric material, within the area including the intersection of the diagonals).

[0085] Piezoelectric constant d of a multilayer piezoelectric material ３３ This can be adjusted, for example, by the piezoelectric constant of a fluororesin piezoelectric film. By increasing the piezoelectric constant of the fluororesin piezoelectric film, the piezoelectric constant of the laminated piezoelectric body can also be increased.

[0086] (Total light transmittance) From the viewpoint of application to touch panels, for example, the laminated piezoelectric material preferably has high transparency. Specifically, the total light transmittance of the laminated piezoelectric material is preferably 85% or more.

[0087] The total light transmittance of a laminated piezoelectric material can be measured using a haze meter (for example, NDH7000SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1:1997. Specifically, the total light transmittance in the area including the center of the surface of the laminated piezoelectric material (in the case of a rectangular laminated piezoelectric material, the area including the intersection of the diagonals) is measured using the above method, and this value can be used as a representative value. If the length of one side of the laminated piezoelectric material is 30 cm or more, a rectangle with sides of 30 cm is arbitrarily assumed, and the area including the intersection of the diagonals of the rectangular film is measured. If both sides of the laminated piezoelectric material are 30 cm or more, a square with sides of 30 cm is arbitrarily set on the laminated piezoelectric material, and the measurement range is set according to the above method.

[0088] The total light transmittance of a multilayer piezoelectric material can be adjusted by the layer configuration, the refractive index of each layer, and its thickness. For example, including a hard coat layer in the multilayer piezoelectric material can further reduce its haze.

[0089] (Nitrogen content) It is preferable that the laminated piezoelectric material contains substantially no nitrogen atoms in the entire layer arranged on the fluororesin piezoelectric film. Substantially no nitrogen atoms means that the nitrogen atom content relative to the total mass of the layer arranged on the fluororesin piezoelectric film is preferably 1.00% by mass or less, more preferably 0.50% by mass or less, more preferably 0.25% by mass or less, and even more preferably 0.10% by mass or less.

[0090] 2. Manufacturing Method of Laminated Piezoelectric Materials Laminated piezoelectric materials can be manufactured by any method. For example, the laminated piezoelectric material shown in Figure 1 can be manufactured by (1) preparing a fluororesin piezoelectric film, (2) forming an antistatic layer on the fluororesin piezoelectric film, and (3) forming a hard coat layer on the antistatic layer. If the laminated piezoelectric material does not include a hard coat layer, step (3) can be omitted.

[0091] (1) Steps to prepare the fluororesin piezoelectric film The fluororesin piezoelectric film may be one that has been manufactured in advance or it may be manufactured in advance. For example, the fluororesin piezoelectric film can be obtained through a process of manufacturing a fluororesin film (film-making process), a process of stretching the fluororesin film (stretching process), and a process of polarization (polarization process).

[0092] (Film Forming Process) Fluorine resin films can be manufactured by any method, such as melt extrusion, hot pressing, or solution casting. Among these, it is preferable that fluorine resin films be manufactured by melt extrusion, as this method makes it easier to obtain fluorine resin piezoelectric films of a certain thickness or greater.

[0093] (Stretching process) In the stretching process, the manufactured fluororesin film is stretched. The stretching process is preferably performed as needed to increase the proportion of β-type crystals in the fluororesin. β-type crystals have a large polarization structure. The stretching direction may be the TD direction or the MD direction, with the MD direction being more preferable.

[0094] The stretching method is not particularly limited and can be carried out using known stretching methods such as the tenter method or the roll-to-roll method.

[0095] The stretching ratio can be, for example, between 3.0 and 6.0 times. When the stretching ratio is 3.0 times or higher, dislocations to the β-type crystal become more sufficient, which not only makes it easier to exhibit higher piezoelectricity but also enhances transparency. When the stretching ratio is 6.0 times or lower, fracture due to stretching can be further suppressed.

[0096] (Polarization Process) In the polarization process, a DC voltage is applied to the fluororesin film to impart piezoelectricity to it. In the polarization process, a fluororesin piezoelectric film with high piezoelectricity can be obtained by applying a DC voltage to a fluororesin film in which the proportion of polar β-type crystals has been increased in the stretching process. The applied DC voltage can be adjusted according to the thickness of the stretched film. For example, the applied voltage can be between 1.0 kV and 50.0 kV.

[0097] (2) Step to form an antistatic layer A composition containing the conductive material and binder resin (antistatic composition) is applied to the obtained fluororesin piezoelectric film and then dried to form an antistatic layer. The composition may be prepared using, for example, an emulsion of a resin such as the polyester or (meth)acrylic resin described above.

[0098] The method of applying the above composition is not particularly limited and may be any of the following: spin coating, gravure coating, die coating, bar coating, dip coating, etc.

[0099] The drying method for the above composition may be any method that can remove the diluent, for example, by heating and drying the coated composition. The heating temperature is preferably above the temperature at which the diluent can be removed and below the heat distortion temperature of the fluororesin in the fluororesin piezoelectric film, for example, it can be 60°C to 130°C. The heat distortion temperature can be measured, for example, in accordance with JIS K 7191-2:2015.

[0100] (3) Step of forming a hard coat layer After applying the hard coat layer curable composition described above onto the obtained antistatic layer, it is dried and cured to form a hard coat layer.

[0101] The coating and drying method for the above-mentioned curable composition can be the same as the coating and drying method described above. The heating temperature should be within a range that allows the solvent to volatilize and be below the heat distortion temperature of the fluororesin constituting the piezoelectric film, for example, 40°C to 100°C.

[0102] The curing of the above-mentioned curable composition may be by heat or by ionizing radiation. Curing by ionizing radiation can be performed by irradiation with ultraviolet light or electron beams. Furthermore, curing by heat and curing by ionizing radiation may be used in combination.

[0103] 3. Applications Multilayer piezoelectric materials can be used in a variety of applications. In particular, because multilayer piezoelectric materials exhibit high transparency and high piezoelectricity, they can be preferably used as piezoelectric sensors in touch panels mounted on various electronic devices.

[0104] 4. Modifications In the above embodiment, an example of a laminated piezoelectric body having the layer configuration shown in Figure 1 was shown, but the layer configuration of the laminated piezoelectric body is not limited thereto. For example, the laminated piezoelectric body 10 does not have to include the hard coat layer 13. Also, the laminated piezoelectric body 10 may further include an optical adjustment layer in place of or in addition to the hard coat layer 13.

[0105] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0106] 1. Fabrication of Laminated Piezoelectric Material 1-1. Laminated Piezoelectric Material 1 A film made of vinylidene fluoride resin (manufactured by Kureha Corporation, KF Polymer) was stretched to a stretch ratio of 4.2 times in the film transport direction (MD direction). Next, the stretched film was subjected to polarization treatment by passing it between the electrodes while applying a DC voltage of 11.0 kV between the ground electrode and the needle electrode, thereby fabricating a piezoelectric film 1 (fluorine-based resin piezoelectric film) with a thickness of 42 μm.

[0107] Next, on one side of the piezoelectric film 1, a coating paint for forming an antistatic layer was applied using a multi-coater (Hirano Texseed Co., Ltd.), which was a mixture of an aqueous conductive polymer dispersion (Denatron P-406A, manufactured by Nagase ChemteX Corporation) containing 1.2% by mass of a conductive polymer (PEDOT:PSS) composed of a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid as solid content, and a binder resin dispersion (Denatron P-406B, manufactured by Nagase ChemteX Corporation) containing 20.8% by mass of polyester emulsion as solid content, in a mass ratio of 4:1. The coating paint was then applied and heat-treated at 100°C for 40 seconds to form an antistatic layer with a thickness of 130 nm.

[0108] Next, a hard coat agent (BS-CH271, manufactured by Arakawa Chemical Industries, Ltd., a (meth)acrylic UV-curable composition containing amorphous silica with an average particle size of 60 nm) was applied to the antistatic layer using a multi-coater, then heat-treated at 80°C for 30 seconds, followed by an integrated light intensity of 400 mJ / cm². ２ A laminated piezoelectric material 1 was fabricated by irradiating it with UV light and photocuring it to form a 750 nm thick hard coat layer (refractive index 1.50 at a wavelength of 589 nm).

[0109] 1-2. Laminated piezoelectric material 2 Laminated piezoelectric material 2 was fabricated in the same manner as laminated piezoelectric material 1, except that the thickness of the antistatic layer was changed to 60 nm.

[0110] 1-3. Laminated piezoelectric body 3 A laminated piezoelectric body 3 was obtained in the same manner as laminated piezoelectric body 2, except that the mixing ratio of the conductive polymer aqueous dispersion (Denatron P-406A) and the binder resin dispersion (Denatron P-406B) was changed to 6.6:3.4 (mass ratio).

[0111] 1-4. Laminated piezoelectric body 4 A laminated piezoelectric body 4 was obtained in the same manner as laminated piezoelectric body 2, except that a hard coat layer was not laminated.

[0112] 1-5. Laminated piezoelectric body 5 A laminated piezoelectric body 5 was fabricated by applying an antistatic coating paint (Denatron C-453, manufactured by Nagase ChemteX Corporation) consisting of a binder solution containing carbon nanotubes and (meth)acrylic resin emulsion as conductive materials, with a solid content concentration of 4.1% by mass, to one side of the piezoelectric film 1 using a multicoater (manufactured by Hirano Tecseed Corporation), and then heat-treating it at 90°C for 40 seconds to form an antistatic layer with a thickness of 50 nm.

[0113] 1-6. Multilayer piezoelectric 6 A hard coat agent (BS-CH271, manufactured by Arakawa Chemical Industries, Ltd.) is applied to the antistatic layer of the multilayer piezoelectric 5 using a multi-coater, then heat-treated at 80°C for 30 seconds, and further subjected to an integrated light intensity of 400 mJ / cm². ２ A laminated piezoelectric body 6 was fabricated by irradiating it with UV light and photocuring it to form a 750 nm thick hard coat layer (refractive index 1.50 at a wavelength of 589 nm).

[0114] 1-7. Laminated Piezoelectric 7 A coating paint for forming an antistatic layer was applied to one side of the piezoelectric film 1 using a multi-coater (Hirano Texseed Co., Ltd.), which was a mixture of the conductive polymer aqueous dispersion (Denatron P-406A) and a binder resin dispersion (Denatron C-453B manufactured by Nagase ChemteX Corporation) containing 20.0% by mass of (meth)acrylic resin emulsion as solid content, in a mass ratio of 4:1. The coating paint was then heat-treated at 100°C for 40 seconds to form an antistatic layer with a thickness of 60 nm.

[0115] After applying a hard coat agent (BS-CH271, manufactured by Arakawa Chemical Industries, Ltd.) to the aforementioned antistatic layer using a multi-coater, the area is heat-treated at 80°C for 30 seconds, and then subjected to an integrated light intensity of 400 mJ / cm². ２ A laminated piezoelectric body 7 was fabricated by irradiating it with UV light and photocuring it to form a 750 nm thick hard coat layer (refractive index 1.50 at a wavelength of 589 nm).

[0116] 1-8. Laminated piezoelectric body 8 A coating paint for forming an antistatic layer was applied to one side of the piezoelectric film 1 using a multicoater (Hirano Texseed Co., Ltd.), which was a mixture of the conductive polymer aqueous dispersion (Denatron P-406A) and a binder resin dispersion (Polysol EVA P-3PN, manufactured by Resonaq Corporation) containing 49.0% by mass of ethylene-vinyl acetate copolymer (EVA) as solid content, in a mass ratio of 19:2. The coating paint was then heat-treated at 100°C for 40 seconds to form an antistatic layer with a thickness of 60 nm.

[0117] After applying a hard coat agent (BS-CH271, manufactured by Arakawa Chemical Industries, Ltd.) to the aforementioned antistatic layer using a multi-coater, the area is heat-treated at 80°C for 30 seconds, and then subjected to an integrated light intensity of 400 mJ / cm². ２ A laminated piezoelectric body 8 was fabricated by irradiating it with UV light and photocuring it to form a 750 nm thick hard coat layer (refractive index 1.50 at a wavelength of 589 nm).

[0118] 1-9. Laminated Piezoelectric 9 A coating paint for forming an antistatic layer was applied to one side of the piezoelectric film 1 using a multi-coater (Hirano Texseed Co., Ltd.), which was prepared by mixing a conductive polymer aqueous dispersion (Nagase ChemteX Corporation: P-400MP-A) containing 3.4% by mass of PEDOT:PSS as a conductive polymer as a solid content concentration and a binder resin dispersion (Nagase ChemteX Corporation: P-400MP-B) containing 20.8% by mass of melamine resin emulsion as a solid content concentration in a mass ratio of 9:1. The coating paint was then heat-treated at 130°C for 40 seconds to form an antistatic layer with a thickness of 60 nm.

[0119] After applying a hard coat agent (BS-CH271, manufactured by Arakawa Chemical Industries, Ltd.) to the aforementioned antistatic layer using a multi-coater, the area is heat-treated at 80°C for 30 seconds, and then subjected to an integrated light intensity of 400 mJ / cm². ２A laminated piezoelectric material 9 was fabricated by irradiating it with UV light and photocuring it to form a 750 nm thick hard coat layer (refractive index 1.50 at a wavelength of 589 nm).

[0120] 1-10. Laminated piezoelectric body 10 A laminated piezoelectric body 10 was obtained in the same manner as laminated piezoelectric body 9, except that the mixing ratio of the conductive polymer aqueous dispersion (P-400MP-A) and the binder resin dispersion (P-400MP-B) was changed to 6:1 (mass ratio).

[0121] 1-11. Laminated piezoelectric body 11 A laminated piezoelectric body 11 was obtained in the same manner as laminated piezoelectric body 9, except that the mixing ratio of the conductive polymer aqueous dispersion (P-400MP-A) and the binder resin dispersion (P-400MP-B) was changed to 4:1 (mass ratio).

[0122] 1-12. Laminated piezoelectric body 12 A laminated piezoelectric body 12 was obtained in the same manner as laminated piezoelectric body 11, except that a hard coat layer was not laminated.

[0123] 1-13. Laminated Piezoelectric Body 13 A conductive polymer aqueous dispersion (C-169PF-A, manufactured by Nagase ChemteX Corporation) containing 0.93% by mass of single-walled carbon nanotubes as a solid content concentration as a conductive material, and a binder resin dispersion (C-169PF-B, manufactured by Nagase ChemteX Corporation) containing 7.9% by mass of melamine resin emulsion as a solid content concentration, were mixed in a mass ratio of 3:2 to form an antistatic layer-forming coating paint (C-169PF, manufactured by Nagase ChemteX Corporation). This coating paint was applied to one side of the piezoelectric film 1 using a multi-coater (manufactured by Hirano Tecseed Corporation), and heat-treated at 130°C for 1 minute to form an antistatic layer with a thickness of 50 nm, thereby fabricating a laminated piezoelectric body 13.

[0124] 1-14. Laminated piezoelectric material 14 A hard coat agent (BS-CH271, manufactured by Arakawa Chemical Industries, Ltd.) is applied to the antistatic layer of the laminated piezoelectric material 13 using a multi-coater, then heat-treated at 80°C for 30 seconds, and further subjected to an integrated light intensity of 400 mJ / cm². ２ A laminated piezoelectric material 14 was fabricated by irradiating it with UV light and photocuring it to form a 750 nm thick hard coat layer (refractive index 1.50 at a wavelength of 589 nm).

[0125] 1-15. Laminated piezoelectric body 15 Laminated piezoelectric body 15 was manufactured in the same manner as laminated piezoelectric body 2, except that the mixing ratio of the conductive polymer aqueous dispersion (Denatron P-406A) and the binder resin dispersion (Denatron P-406B) was changed to 3:2 (mass ratio).

[0126] 2. Evaluation Method for Multilayer Piezoelectric Materials 2-1. Thickness of Antistatic Layer and Hard Coat Layer The thickness of each layer was measured using a spectroscopic interferometric film thickness gauge (Optical NanoGauge C13027-11, Hamamatsu Photonics). Specifically, the thickness of each layer was measured at three arbitrary points within the range including the intersection of the diagonals of the surfaces of a rectangular multilayer piezoelectric material, and the arithmetic mean was calculated.

[0127] 2-2. Surface Resistivity Surface resistivity was measured in accordance with JIS C 2139-3-2:2018 using a high resistivity meter (Nitto Seiko Analytech Co., Ltd., Highrestor UX, model number: MCP-HT800, URS probe). The measurement area was defined as the range including the intersection of the diagonals of the rectangular laminated piezoelectric surface, and the measured value was taken as the representative value.

[0128] 2-3. Piezoelectric constant d ３３ Piezoelectric constant d in accordance with ISO 19622:2018 ３３ The piezoelectric constant was measured. Specifically, a piezoelectric constant measuring device (PIEZOTEST PM300 piezometer system) was used to hold a laminated piezoelectric material with a holding force of 1.0 N, and the charge generated when an alternating force of 0.15 N and a frequency of 110 Hz was applied was measured. The piezoelectric constant was calculated using the absolute value of the measured value.

[0129] The piezoelectric constant of the multilayer piezoelectric material was measured on two separate surfaces of the multilayer piezoelectric material. ３３ The absolute values ​​of the measured values ​​are compared, and the one with the larger absolute value is used as the piezoelectric constant d of the laminated piezoelectric material. ３３ The measurement locations on each surface were defined as the area including the intersection of the diagonals of the rectangular laminated piezoelectric surface, and the measured values ​​were taken as representative values.

[0130] 2-4. hue b ＊ and the difference in hue before and after preservation △b ＊ Value 1) 25 cm from the laminated piezoelectric material ２Six laminated piezoelectric materials were cut out from a square to form six test laminates. 2) For each of the three test laminates prepared in 1) before moist heat storage, the hue b of the area including the center of each test laminate (including the intersection of the diagonals) was measured using a spectrocolorimeter SD7000 (manufactured by Nippon Denshoku Industries Ltd.) in accordance with JIS Z 8722:2009. ＊ The values ​​were measured. Hue b of three test laminates. ＊ The average value of the hue b of the laminated piezoelectric material before saving. ＊ The value was taken as a representative value. 3) Next, three of the test laminates prepared in 1) that were not used in the measurement in 2) were each fixed to a SUS plate with tape at the four corners of the test laminate, and placed in a constant temperature and humidity chamber (LH44-14 manufactured by Nagano Science Co., Ltd.) set to a temperature of 85°C and a humidity of 85% RH, and were kept under the same conditions for 500 hours. After that, the test laminates were removed from the constant temperature and humidity chamber, and for each of the three stored test laminates, the hue b was measured in the area including the center of each test laminate (the area including the intersection of the diagonals). ＊ The value was measured in the same manner as described above, and the hue b of the three test laminates was measured. ＊ Hue b of the laminated piezoelectric material after saving the average value ＊ This value was used as a representative value. 4) Hue b after saving ＊ Representative value of the value and hue b before saving ＊ The difference in typical values ​​of the laminated piezoelectric material before and after saving the hue difference Δb ＊ It was set as the value.

[0131] 2-5. Sensory Evaluation of Hue The hue of the laminated piezoelectric material after storage was visually observed and evaluated according to the following criteria: A: Almost no yellow hue is perceptible to the eye. B: A slight yellow hue is perceptible, but at a level that does not pose a practical problem. C: The yellow hue is clearly noticeable and at a level that poses a practical problem. If the level is B or higher, it is considered to be within an acceptable range and does not pose a practical problem.

[0132] 2-6. Total Light Transmittance The total light transmittance of the laminated piezoelectric material was measured using a haze meter (NDH7000SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1:1997, within the range including the intersection of the diagonals of the rectangular laminated piezoelectric material's surfaces, and this value was taken as the representative value.

[0133] 2-7. Atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer (1) The laminated piezoelectric material was cut into a 6 mm x 6 mm square, and the measurement sample was attached to an 8 mm x 8 mm Si wafer with the side with the antistatic layer facing upwards. (2) The measurement sample was fixed with tape to the dedicated sample stage of the X-ray photoelectron spectrometer (general-purpose photoelectron spectrometer JPS-9010MC manufactured by JEOL Ltd.), and then the sample was dried by vacuuming it overnight in the preparation chamber of the instrument. (3) Depth profiling (depth measurement) was performed according to the following procedure. The etching rate was SiO ２Etching was performed from the outermost surface at a conversion rate of 40 nm / min, with each etching step of the sample taking 10 seconds. A wide spectrum was obtained after each etching step using XPS measurement, as described below. XPS measurements were performed after each etching step until the atomic ratio of oxygen atoms to carbon atoms was 0.050 or less. The measurement point at which the atomic ratio of oxygen atoms to carbon atoms was 0.050 or less was defined as the endpoint of the measurement. The elements measured were carbon (C), nitrogen (N), oxygen (O), and fluorine (F). The orbitals and measurement energy ranges for each element are as follows: C is C1s 278-298 eV, N is N1s 391-413 eV, O is O1s 523-545 eV, and F is F1s 676-703 eV. The conditions for the XPS measurement were as follows. (XPS measurement conditions) ・X-ray source: Al-Kα ・Measurement range: 100.0 eV to 1350.0 eV ・X-ray beam diameter: φ200 μm ・X-ray intensity: 12 kV / 25 mA ・Photoelectron extraction angle: 90 degrees relative to the sample surface ・Sputter ions: Ar (600 V / 13 mA) ・Relative sensitivity coefficient of C1s: 4.2586 ・Relative sensitivity coefficient of N1s: 7.5129 ・Relative sensitivity coefficient of O1s: 11.9144 ・Relative sensitivity coefficient of F1s: 17.3911 (4) Background correction was performed on the wide spectra obtained from each XPS measurement using the Shirley method. The background setting ranges for each element are as follows. C is C1s at 250.0–300.0 eV, N1s at 380.0–415.0 eV, O1s at 510.0–545.0 eV, and F1s at 670.0–710.0 eV. After background correction, the peak areas of C1s, N1s, O1s, and F1s were calculated. By dividing these peak areas by their respective relative sensitivity coefficients, the abundance (quantitative values) of carbon, nitrogen, oxygen, and fluorine were calculated. Instrument-specific values ​​were used for the relative sensitivity coefficients. The ratio of the quantitative value of nitrogen to the quantitative value of carbon (quantitative value of nitrogen / quantitative value of carbon) was defined as the atomic ratio of nitrogen atoms to carbon atoms; the ratio of the quantitative value of oxygen to the quantitative value of carbon (quantitative value of oxygen / quantitative value of carbon) was defined as the atomic ratio of oxygen atoms to carbon atoms; and the ratio of the quantitative value of fluorine to the quantitative value of carbon (quantitative value of fluorine / quantitative value of carbon) was defined as the atomic ratio of fluorine atoms to carbon atoms.Then, the maximum value of the nitrogen atom-to-carbon atom ratio obtained from the XPS measurement of each of the three test pieces prepared from the same sample was used as the representative value for the "nitrogen atom-to-carbon atom ratio of the antistatic layer." In addition, the maximum value of the fluorine atom-to-carbon atom ratio at the measurement endpoint obtained from each XPS measurement was used as the representative value for the "fluorine atom-to-carbon atom ratio of the fluororesin piezoelectric film." The measured fluorine atom-to-carbon atom ratio of the fluororesin piezoelectric film was 0.135.

[0134] Furthermore, if the antistatic layer is exposed on the surface of the multilayer piezoelectric material (i.e., there are no other layers such as a hard coat layer on the antistatic layer), XPS measurement was performed in the same manner as above, except that etching was not performed, and the ratio of the obtained quantitative values ​​of nitrogen and carbon (quantitative value of nitrogen / quantitative value of carbon) was defined as the "atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer".

[0135] 3. Results The fabrication conditions and evaluation results for each laminated piezoelectric material are shown in Tables 1 to 3. For reference, the evaluation results for the fluororesin piezoelectric film alone are also shown.

[0136]

[0137]

[0138]

[0139] As shown in Table 2, the atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer of laminated piezoelectric materials 11 and 12, which used a predetermined amount or more of melamine resin in the antistatic layer, exceeded 0.020. Furthermore, the hue b after storage was observed in laminated piezoelectric materials 11 to 14. ＊ The value was 3.0 or higher. Laminated piezoelectric material 15 did not provide sufficient antistatic properties because the surface resistivity of the antistatic layer was high. In contrast, as shown in Tables 1 to 2, laminated piezoelectric materials 1 to 8 using (meth)acrylic resin, polyester, or ethylene-vinyl acetate copolymer (EVA) for the antistatic layer, and laminated piezoelectric materials 9 and 10 using a small amount of melamine resin, had a low atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer of 0.020 or less, resulting in a low hue b after storage. ＊The value is also low, below 3.0, indicating minimal discoloration.

[0140] Furthermore, depth profiling analysis using XPS revealed a peak originating from N1s in the laminated piezoelectric material 11. In contrast, no peak originating from N1s was observed in the laminated piezoelectric material 2, indicating a nitrogen atom abundance of 0 atomic percent. These findings demonstrate that XPS measurement can be used to determine the amount and atomic ratio of nitrogen atoms contained in the antistatic layer.

[0141] This application claims priority under Japanese Patent Application No. 2025-057035, filed on 28 March 2025. All contents described in the specification and drawings of said application are incorporated herein by reference.

[0142] According to the laminated piezoelectric material of the present invention, discoloration of the fluororesin piezoelectric film under high temperature and high humidity conditions is minimized, and high transparency can be maintained. Therefore, this laminated piezoelectric material can be suitably used as a piezoelectric sensor for touch panels.

[0143] 10. Laminated piezoelectric material 11. Fluorine-based resin piezoelectric film 12. Antistatic layer 13. Hard coat layer

Claims

1. A fluororesin piezoelectric film and an antistatic layer disposed on at least one surface of the fluororesin piezoelectric film, wherein the surface resistivity is 1.0 × 10 ６ Ω / sq. More than 1.0×10 １２ The hue b is less than or equal to Ω / sq. and is determined after being held for 500 hours in an environment of 85°C and 85% RH. ＊ The piezoelectric constant d is less than 3.

0. ３３ A laminated piezoelectric material having a capacitance of 7.0 pC / N or more and 40.0 pC / N or less.

2. A fluororesin piezoelectric film and an antistatic layer disposed on at least one surface of the fluororesin piezoelectric film, wherein the surface resistivity is 1.0 × 10 ６ Ω / sq. More than 1.0×10 １２ The impedance is less than or equal to Ω / sq., the atomic ratio of nitrogen atoms to carbon atoms in the antistatic layer determined by X-ray photoelectron spectroscopy is 0.020 or less, and the piezoelectric constant d is less than or equal to Ω / sq. ３３ A laminated piezoelectric material having a capacitance of 7.0 pC / N or more and 40.0 pC / N or less.

3. The laminated piezoelectric body according to claim 1 or 2, wherein the antistatic layer is in contact with at least one surface of the fluororesin piezoelectric film.

4. The difference in hue (Δb) before and after holding in an environment of 85°C and 85% RH for 500 hours. ＊ A laminated piezoelectric material according to claim 1 or 2, wherein the ratio is less than 1.

8.

5. The laminated piezoelectric material according to claim 1 or 2, wherein the total light transmittance is 85% or more.

6. The laminated piezoelectric body according to claim 1 or 2, further comprising a hard coat layer disposed on the opposite side of the fluororesin piezoelectric film, sandwiching the antistatic layer.

7. The laminated piezoelectric material according to claim 1 or 2, wherein the atomic ratio of fluorine atoms to carbon atoms in the fluorine-based resin piezoelectric film, as determined by X-ray photoelectron spectroscopy, is 0.010 or more.

8. The laminated piezoelectric body according to claim 1 or 2, wherein the fluorine-based resin piezoelectric film mainly contains constituent units derived from vinylidene fluoride.

9. The laminated piezoelectric material according to claim 1 or 2, wherein the thickness of the antistatic layer is 10 nm or more and 400 nm or less.

10. The laminated piezoelectric body according to claim 1 or 2, wherein the antistatic layer comprises a conductive material and a binder resin, and the binder resin comprises at least one of polyester and (meth)acrylic resin.

11. The laminated piezoelectric material according to claim 1 or 2, wherein the antistatic layer substantially does not contain nitrogen atoms.

12. A method for manufacturing a laminated piezoelectric material according to claim 1 or 2, comprising the step of applying a composition containing a conductive material and a binder resin onto a fluororesin piezoelectric film, and then drying it to form an antistatic layer.

13. The method for manufacturing a laminated piezoelectric material according to claim 12, wherein the binder resin comprises at least one of polyester and (meth)acrylic resin.

14. The method for manufacturing a laminated piezoelectric material according to claim 12, further comprising the step of forming a hard coat layer on the antistatic layer.

Images