Laminated piezoelectric film and method for manufacturing the same

Abstract

To provide a laminated piezoelectric film in which the adhesive film is difficult to peel off. [Solution] Piezoelectric constant d 33 A laminated piezoelectric film comprising: a fluorine-based piezoelectric film having a fluorine ratio of 10.0 pC / N or more and 40.0 pC / N or less, and a tensile strength in the slow phase axis direction determined from the in-plane birefringence of the film as defined in JIS C 5876-1:2009 of 50 N to 1600 N; an adhesive film; and an adhesive layer for bonding the fluorine-based piezoelectric film and the adhesive film, having a glass transition temperature of -100°C or more and 0°C or less as measured in accordance with JIS K 6240:2001.

Description

[Technical Field]

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

[0002] Polylactic acid films and fluoropolymer films are known to exhibit piezoelectric properties through stretching and polarization treatments. In particular, flexible piezoelectric films prepared from polymer films are widely used in piezoelectric sensors for small portable devices. Piezoelectric films are used with thin-film electrodes to detect the charge generated by pressure, and protective films to prevent surface scratches. Furthermore, fluoropolymer films are sometimes used as laminated piezoelectric films with electrodes and protective films laminated on top.

[0003] Piezoelectric films are typically stored and transported in rolls. During transport, vibrations can cause electric charge to accumulate on the film's surface. This accumulated charge can attract foreign matter or cause scratches on the film's surface. Therefore, a removable protective film is often laminated to the surface of piezoelectric films during storage and transport. Piezoelectric films are also sometimes used with other layers, such as electrode layers, laminated onto them.

[0004] To laminate other layers onto a piezoelectric film, an adhesive layer is sometimes used. For example, Patent Document 1 describes a method of bonding a release film coated with an adhesive to the surface of a polylactic acid-based piezoelectric film. Patent Document 1 also describes peeling the release film from the laminate produced in this way to expose the adhesive, and then attaching another film to the exposed adhesive. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2016 / 140110 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Fluorine-based piezoelectric films are chemically stable and have poor adhesion due to their low surface energy. Therefore, the adhesives used for bonding fluorine-based piezoelectric films are limited. Furthermore, because fluorine-based piezoelectric films have high piezoelectric properties, their surface is charged. This charge makes it difficult to uniformly apply adhesive to the surface of a fluorine-based piezoelectric film. Additionally, applying adhesive to the surface of a fluorine-based piezoelectric film can sometimes reduce its piezoelectric properties due to heat treatment required to remove the solvent contained in the adhesive.

[0007] The method described in Patent Document 1 allows for the formation of an adhesive layer on the surface of a piezoelectric film without applying an adhesive to the surface of the piezoelectric film. However, when a release film is bonded to a piezoelectric film using commonly used adhesives such as urethane, acrylic, and ester-based adhesives according to the method described in Patent Document 1, the adhesive strength between the piezoelectric film and the electrode film is low when the release film is subsequently peeled off and the electrode film is bonded, resulting in a problem where the electrode film is prone to peeling.

[0008] Furthermore, the applications of piezoelectric films have expanded in recent years, and their use in more severe conditions than before is being considered. For such applications, there is a need for the development of fluorine-based piezoelectric films with high tensile strength that will not break even under large stresses.

[0009] It is expected that the piezoelectric film will deform under high stress. The piezoelectric film is used as a laminated piezoelectric film by laminating it with an electrode film or the like. Under high stress, the piezoelectric film will deform significantly, and the adhesive layer formed with the general-purpose adhesive described above may not be able to adequately follow the large deformation of the piezoelectric film. This may lead to the rupture of the adhesive layer or electrode film, or the delamination of the electrode film from the piezoelectric film. If the electrode film delaminates, the electrode layer may not be able to adequately sense the charge generated by the fluorine-based piezoelectric film, which may reduce the pressure detection sensitivity of the laminated piezoelectric film or make pressure detection difficult.

[0010] The present invention has been made in view of the above problems, and aims to provide a laminated piezoelectric film in which the adhesive film is difficult to peel off, and a method for manufacturing the same. [Means for solving the problem]

[0011] An embodiment of the present invention for solving the above problems relates to the following laminated piezoelectric films [1] to [5]. [1] Piezoelectric constant d 33 A laminated piezoelectric film comprising: a fluorine-based piezoelectric film having a fluorine ratio of 10.0 pC / N or more and 40.0 pC / N or less, and a tensile strength in the slow phase axis direction determined from the in-plane birefringence of the film as defined in JIS C 5876-1:2009 of 50 N or more and 1600 N or less; an adhesive film; and an adhesive layer for bonding the fluorine-based piezoelectric film and the adhesive film, having a glass transition temperature of -100°C or more and 0°C or less as measured in accordance with JIS K 6240:2001. [2] The fluorine-based piezoelectric film is a laminated piezoelectric film according to [1], wherein vinylidene fluoride resin is the main component. [3] The laminated piezoelectric film according to [1] or [2], wherein the thickness of the fluorine-based piezoelectric film is 10 μm or more and 350 μm or less. [4] The adhesive film has a surface resistivity of 1.0 × 10 4 A laminated piezoelectric film according to any one of [1] to [3], having a conductive layer with a density of Ω / sq. or less. [5] The laminated piezoelectric film according to any one of [1] to [4], wherein the peel strength between the fluorine-based piezoelectric film and the conductive layer measured in accordance with JIS K 6854-2:1999 is 2 N / 15 mm or more and 40 N / 15 mm or less.

[0012] Another embodiment of the present invention for solving the above problems relates to a method for manufacturing a laminated piezoelectric film described in the following [6] to [7]. [6] A step of applying an adhesive to the release surface of a release film and drying it to form an adhesive layer having a glass transition temperature of -100°C or more and 0°C or less measured in accordance with JIS K 6240:2001, and the piezoelectric constant d 33 is 10.0 pC / N or more and 40.0 pC / N or less, and a fluorine-based piezoelectric film having a tensile strength in the slow axis direction obtained from the film in-plane birefringence defined in JIS C 5876-1:2009 of 50 N or more and 1600 N or less is bonded to the release film by the adhesive layer, and a method for manufacturing a laminated piezoelectric film according to any one of [1] to [4]. [7] A step of peeling the release film from the laminated piezoelectric film and transferring the adhesive layer to the fluorine-based piezoelectric film, and a surface resistivity of 1.0 × 10 4 Ω / sq. or less, and a method for manufacturing a laminated piezoelectric film according to [6], which comprises a step of bonding an electrode film having a conductive layer to the fluorine-based piezoelectric film by the adhesive layer. [Advantages of the Invention]

[0013] According to the present invention, there are provided a laminated piezoelectric film having high interlayer adhesion of a fluorine-based piezoelectric film and a method for manufacturing the same. [Brief Description of the Drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing a state of manufacturing a laminated piezoelectric film (first laminated film) in one embodiment of the present invention. [Figure 2] FIG. 2 is a partially enlarged view of the region X shown in FIG. 1, and is a schematic diagram showing a state in which an adhesive is applied to a conveyed release film. [Figure 3] Figure 3 is a partially enlarged view of the region Y shown in Figure 1, and is a schematic diagram showing a state in which an adhesive layer is formed on the transferable release film. [Figure 4] Figure 4 is a partially enlarged view of the region Z shown in Figure 1, and is a schematic diagram showing a state in which a piezoelectric film is bonded to the release film by an adhesive layer. [Figure 5] Figure 5 is a schematic diagram showing a state of manufacturing a laminated piezoelectric film (second laminated film) in another embodiment of the present invention. [Figure 6] Figure 6 is a partially enlarged view of the region V shown in Figure 5, and is a schematic diagram showing a state of peeling a release film from the laminated piezoelectric film and transferring an adhesive layer to a fluorine-based piezoelectric film. [Figure 7] Figure 7 is a partially enlarged view of the region W shown in Figure 5, and is a schematic diagram showing a state in which an electrode film is bonded to the fluorine-based piezoelectric film to which the adhesive layer has been transferred.

Embodiments for Carrying Out the Invention

[0015] [Laminated Piezoelectric Film] One embodiment of the present invention relates to a laminated piezoelectric film having a fluorine-based piezoelectric film, an adherend film, and an adhesive layer that bonds the fluorine-based piezoelectric film and the adherend film.

[0016] (Fluorine-based Piezoelectric Film) The fluorine-based piezoelectric film may contain a fluororesin as a main component. A fluororesin is a resin obtained by polymerizing a monomer composed of an olefin containing fluorine, and a fluorine-based piezoelectric film containing a fluororesin as a main component means that the ratio of the fluororesin to the total mass of the piezoelectric film is 50% by mass or more. The ratio of the content of the fluororesin to the total mass of the 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.

[0017] The Fluororesins can be homopolymers or copolymers obtained by polymerizing tetrafluoroethylene or vinylidene fluoride. Examples of fluororesins obtained by polymerizing tetrafluoroethylene include copolymers of tetrafluoroethylene with ethylene, perfluoroalkyl vinyl ether, vinylidene fluoride, 1-chloro-1-fluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene. Examples of fluororesins obtained by polymerizing vinylidene fluoride include homopolymers of vinylidene fluoride, as well as copolymers of vinylidene fluoride with 1-chloro-1-fluoroethylene, 1-chloro-2-fluoroethylene, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, tetrafluoropropene, hexafluoropropylene, and perfluoroalkyl vinyl ether.

[0018] Of these, from the viewpoint of facilitating polarization of the fluororesin film, which is the material for the piezoelectric film, fluororesins obtained by polymerizing vinylidene fluoride are preferred, more preferably a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and trifluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride, trifluoroethylene and tetrafluoroethylene, a copolymer of vinylidene fluoride, trifluoroethylene, tetrafluoroethylene and chlorotrifluoroethylene, and a copolymer of vinylidene fluoride, trifluoroethylene, tetrafluoroethylene and 1-chloro-1-fluoroethylene, with a homopolymer of vinylidene fluoride being even more preferred. These fluororesins may be used individually or in combination of multiple types.

[0019] The fluororesin is preferably a fluororesin mainly composed of vinylidene fluoride (vinylidene fluoride resin), and more preferably a homopolymer of vinylidene fluoride. "Mainly composed of vinylidene fluoride" means that the content of vinylidene fluoride relative to the total mass of the fluororesin is 50% by mass or more. The vinylidene fluoride content is the ratio of the mass of constituent units derived from vinylidene fluoride to the total mass of the fluororesin. The content of these resins relative to the total mass of the fluororesin 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.

[0020] In particular, since high piezoelectric properties can be expected from fluororesins, a higher content of the polypolymer of vinylidene fluoride is preferable. The content of the polypolymer relative to the total mass of the fluororesin is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass.

[0021] For fluoropolymer resins, the measurement temperature was 260°C and the shear rate during measurement was 50 s. -1The melt viscosity measured is preferably 600 Pa·s to 4000 Pa·s, more preferably 1000 Pa·s to 3500 Pa·s, and even more preferably 1000 Pa·s to 2400 Pa·s. Resins with lower melt viscosity can be formed by extrusion at relatively low temperatures. Fluorine resins with lower melt viscosity have shorter molecular chains and less entanglement, allowing for higher stretch ratios. Furthermore, the shorter molecular chains allow for easier free movement due to heat, and selective arrangement of molecular chains during cooling facilitates crystallization. Since the melt viscosity of fluororesins does not change even after going through the film formation, stretching, and polarization processes, the melt viscosity of the raw material fluororesin and fluororesin film can be determined by measuring the melt viscosity of the piezoelectric film. Also, when filtering the molten fluororesin during film manufacturing, the lower the melt viscosity, the less likely the filter is to clog, making filtration easier. Therefore, it becomes unnecessary to raise the melting temperature to enable filtration, and it is less likely that spot-like irregularities will occur on the film surface due to the resin denature and generation of foreign matter caused by heat. The higher the melt viscosity, the larger the molecular weight of the resin, making selective arrangement of molecular chains difficult and crystallization less likely, thus stabilizing the various physical properties of the film.

[0022] The melt viscosity is measured in accordance with ASTM D 3835:2016 (ISO 11443:2021, JIS K 7199:1999). Specifically, a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.) is used, with a capillary die of φ1 mm inner diameter x 10 mm tube length, measured at a temperature of 260°C and a shear rate of 50 s. -1 This is the viscosity measured using [the specified method].

[0023] Fluorine resin piezoelectric film has a piezoelectric constant d 33 The piezoelectric constant d is 10.0 pC / N or greater, preferably 10.0 pC / N to 40.0 pC / N, and more preferably 15.0 pC / N to 40.0 pC / N. 33 The larger the value, the higher the pressure detection sensitivity of the laminated piezoelectric film can be.

[0024] The piezoelectric constant of the fluororesin piezoelectric film is measured in accordance with ISO 19622:2018, which is a test method for the piezoelectric constant d 33 by the direct quasi-static method (meter method, Berlincourt method). Specifically, a piezoelectric constant measuring device (PiezoTest, piezometer system PM300) is used to hold the fluororesin piezoelectric film, which is the test piece, with a holding force of 1.0 N, and the charge generated when an alternating force with an amplitude of 0.15 N and a frequency of 110 Hz is applied is measured. The charge is measured on the polarization surface of the fluororesin piezoelectric film, and the piezoelectric constant is calculated using the absolute value of the measured value. Then, measurements are taken at a total of five locations, including the center in the width direction of the fluororesin piezoelectric film and two locations each set at intervals of 50 mm in the directions from the center in the width direction to both widths, and the average value of the piezoelectric constants obtained from these is taken as the piezoelectric constant d 33 of the fluororesin piezoelectric film.

[0025] The fluororesin piezoelectric film has a tensile strength in the slow axis direction obtained from the in-plane birefringence defined in JIS C 5876-1:2009 of 50 N or more and 1600 N or less, preferably 90 N or more and 1100 N or less, more preferably 250 N or more and 1100 N or less, and even more preferably 250 N or more and 950 N or less. The greater the tensile strength, the less likely the fluororesin piezoelectric film is to break even when the laminated piezoelectric film is greatly deformed under a large pressure.

[0026] The tensile strength of the fluororesin piezoelectric film is measured in accordance with JIS K 7127:1999. Specifically, a strip-shaped film with a length of 50 mm parallel to the slow axis detected by the in-plane birefringence of the film defined in JIS C 5876-1:2009 and a width of 10 mm perpendicular to the slow axis is cut out from the film. Next, using a tensile testing machine (Orientec Co., Ltd. Tensilon RTC-1210A), the tensile strength of each test piece is measured at a tensile speed of 50 mm / min in an environment with a measurement temperature of 23°C, with the strip-shaped film as the test piece, and this is taken as the tensile strength of the fluororesin piezoelectric film.

[0027] ​​The thickness of the fluororesin piezoelectric film is not particularly limited, but is preferably 10 μm to 350 μm, more preferably 30 μm to 300 μm, even more preferably 40 μm to 300 μm, and particularly preferably 40 μm to 150 μm. The thicker the film, the higher its tensile strength can be.

[0028] The thickness of fluororesin piezoelectric films is generally measured using a micrometer (JISC 2151:2019), but it can also be measured using other known methods such as laser displacement meters, capacitance displacement meters, or infrared radiation.

[0029] The fluororesin piezoelectric film preferably has a retardation of 100 nm to 3000 nm, more preferably 500 nm to 3000 nm, and even more preferably 750 nm to 3000 nm. The greater the retardation, the higher the molecular orientation of the fluororesin, the higher the proportion of β-crystals, and the easier it is to improve piezoelectricity.

[0030] Retardation is defined as the value measured using the parallel nicol rotation method with a light source having a wavelength of 589.1 nm.

[0031] (Adhesive film) The film to be adhered is a film that is adhered to a fluorine-based piezoelectric film by an adhesive layer. The material of the film to be adhered may be a polymer compound or a metal foil.

[0032] The type of polymer compound is not limited, and polyester films such as polyethylene terephthalate (PET) film and polyethylene naphthalate (PEN) film, syndiotactic polystyrene (SPS) film, polypropylene film, nylon film, and polyimide film can be used.

[0033] The film to be adhered to may be a single-layer film or a multi-layer film.

[0034] The adhesive film as a multilayer film can be a release film made by coating a polymer film such as PET film with a silicone coating or a non-silicone material, a conductive film (electrode film) in which a conductive layer such as indium tin composite oxide (ITO) is formed by sputtering onto a PET film, a film hard-coated on a PET film, or a coated film in which the surface of the above polymer compound is coated with various coating materials.

[0035] The material of the release film used as the adhesive film is not limited, and release films such as polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, other polyester films, syndiotactic polystyrene (SPS) film, and PET film coated with silicone or non-silicone materials can be used.

[0036] The electrode film used as the adhesive film may be a film in which a conductive layer is formed on the surface of a base film, or it may be a film having only a single conductive layer made of a conductive material such as copper foil. Furthermore, to protect the conductive layer, a protective film may be laminated on top of it, or the conductive layer may be coated with resin.

[0037] The type of base film is not particularly limited, and polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, syndiotactic polystyrene (SPS) film, polyimide film, etc., can be used.

[0038] The thickness of the base film is not particularly limited, but is preferably 12 μm to 150 μm, more preferably 25 μm to 100 μm, and even more preferably 25 μm to 75 μm.

[0039] The surface resistivity of the conductive layer is 1.0 × 10⁻⁶. 4 It is less than or equal to Ω / sq. and 1.0 × 10⁻⁶ -4 Ω / sq. or more 5.0×10 2Preferably less than Ω / sq., and 1.0 × 10⁻⁶ -4 Ω / sq. or more 3.0×10 2 Ω / sq. or less is more preferable, and 1.0 × 10 -4 Ω / sq. or more 1.0×10 2 A value of Ω / sq. or less is even more preferable. The lower the surface resistivity, the higher the conductivity of the conductive layer can be.

[0040] The surface resistivity of the conductive layer can be measured using a resistivity meter (e.g., LorestaGP MCP-T610, manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS K 7194:1994. Three measurements should be taken, and the average of the three measurements should be used as the representative value. If measurement is not possible using this method, the volume resistivity should be measured in accordance with JIS C 2139-3-1:2018, and the surface resistivity should be obtained by dividing the measured volume resistivity by the thickness of the conductive layer.

[0041] The conductive layer may be a transparent conductive layer or an opaque conductive layer.

[0042] The transparent conductive layer may be formed from a metal oxide or from a conductive polymer.

[0043] Examples of metal oxides include metal oxides containing one or more of the following: In, Sn, Zn, Ga, Sb, Ti, Si, Zr, Mg, Al, Au, Ag, Cu, Pd, and W. For example, the metal oxide can be indium tin composite oxide (ITO), antimony tin composite oxide (ATO), fluorine-doped tin oxide (FTO), Al-doped zinc oxide (AZO), Ga-doped zinc oxide (GZO), etc., with indium tin composite oxide (ITO) and antimony tin composite oxide (ATO) being preferred. The conductive layer 624 preferably contains indium oxide as its main component, and more preferably contains indium tin composite oxide (ITO) as its main component. Containing as a main component means that the indium oxide content in the conductive layer 624 is 60% by mass or more, preferably 90% by mass or more.

[0044] Examples of conductive polymers include polythiophene, polypyrrole, polyaniline, polyacetylene, poly(p-phenylene), poly(p-phenylene vinylene), and polyfluorene. These may be used individually or in combination of two or more. Of these, polythiophene is preferred, and a mixture of poly-3,4-ethylenedioxythiophene and polystyrene sulfonic acid (PEDOT / PSS) is more preferred.

[0045] The conductive layer may also be a metal nanowire or metal mesh formed from a conductive material such as copper or silver.

[0046] These conductive layers can be formed on a substrate film by known film-forming methods such as sputtering or coating and drying a solution containing the conductive layer material. Alternatively, the conductive layer may be bonded to the substrate film using an adhesive.

[0047] The conductive layer can serve as an electrode for applying a voltage to the fluorine-based piezoelectric film to deform it, or for extracting the charge generated in the fluorine-based piezoelectric film by deformation. Therefore, it is preferable that the conductive layer be formed in the shape of an electrode or processed into the shape of an electrode.

[0048] The thickness of the conductive layer is not particularly limited, but a greater thickness can lower the resistivity, and a smaller thickness is less likely to impair the transparency of the laminated piezoelectric film. For example, when formed from a metal oxide, the thickness of the conductive layer is preferably 20 nm to 40 nm, more preferably 22 nm to 37 nm, and more preferably 24 nm to 35 nm. When formed from a conductive polymer, the thickness of the conductive layer is preferably 50 nm to 1500 nm, more preferably 150 nm to 1000 nm, and even more preferably 250 nm to 600 nm. Furthermore, when formed from copper foil, the thickness of the conductive layer is preferably 15 μm to 100 μm, and more preferably 30 μm to 80 μm.

[0049] The thickness of the film to be adhered is not particularly limited, but is preferably 12 μm to 250 μm, more preferably 16 μm to 75 μm, and even more preferably 25 μm to 50 μm.

[0050] (Adhesive layer) The adhesive layer is a layer formed by an adhesive that adheres the fluororesin piezoelectric film to the film to be adhered. The adhesive layer is a layer formed by an adhesive that adheres the fluororesin piezoelectric film to the film to be adhered, allowing for peeling as needed.

[0051] The adhesive layer has a glass transition temperature of -100°C or higher and 0°C or lower, measured in accordance with JIS K 6240:2001, preferably -100°C or higher and -10°C or lower, more preferably -90°C or higher and -20°C or lower, and even more preferably -85°C or higher and -30°C or lower. In a piezoelectric laminated film in which a fluorine-based piezoelectric film and a film to be adhered are bonded via an adhesive layer with a low glass transition temperature, even if plastic deformation occurs, the adhesive layer undergoes plastic deformation, relieving stress, suppressing delamination of the adhesive film, and providing good conformability to deformation of the laminated piezoelectric film.

[0052] General-purpose adhesives such as urethane, acrylic, and ester-based adhesives (adhesives with high glass transition temperatures) require aging after application to the film surface to enhance their tackiness. This aging process increases the adhesion between the films during the initial bonding of the fluorine-based piezoelectric film and the film to be bonded (such as a release film). However, as the adhesive layer formed by these general-purpose adhesives undergoes a crosslinking reaction during aging, the crosslinking density increases, causing the adhesive layer to harden. Consequently, when attempting to peel off the film to be bonded and bond another film (such as an electrode film), the tackiness decreases. Therefore, when using these adhesives, while tackiness is present during the initial bonding with the release film, the adhesion between the films does not increase when the release film is peeled off after aging and the electrode film is bonded via the adhesive layer transferred to the piezoelectric film.

[0053] On the other hand, some types of adhesives that form the adhesive layer have a low glass transition temperature. Adhesives formed with adhesives that have a low glass transition temperature can maintain high tackiness even after repeated bonding and peeling of the bonded film, thus maintaining high tackiness between the fluorine-based piezoelectric film and the bonded film. Furthermore, the glass transition temperature of adhesives with a low glass transition temperature does not change even when films are bonded together or when bonded films are peeled apart.

[0054] As the adhesive material for the adhesive layer, industrial adhesives such as styrene-butadiene rubber (SBR) adhesives and acrylonitrile-butadiene rubber (NBR) adhesives can be used.

[0055] The thickness of the adhesive layer is not particularly limited, but is preferably 2 μm to 75 μm, more preferably 5 μm to 50 μm, and even more preferably 10 μm to 35 μm.

[0056] (Peel strength) The peel strength between the fluorine-based piezoelectric film and the adherend film of the laminated piezoelectric film, measured in accordance with JIS K 6854-2:1999, is preferably 2.0 N / 15 mm or more and 40.0 N / 15 mm or less, more preferably 3.0 N / 15 mm or more and 30.0 N / 15 mm or less, and even more preferably 5.0 N / 15 mm or more and 30.0 N / 15 mm or less.

[0057] The peel strength between the fluorine-based piezoelectric film and the adherend film may be varied depending on the type of adherend film.

[0058] For example, when a release film is attached to a fluorine-based piezoelectric film with the intention of peeling it off later, the peel strength is preferably 20.0 mN / 50 mm or more and 1000.0 mN / 50 mm or less, more preferably 30.0 mN / 50 mm or more and 750.0 N / 50 mm or less, and even more preferably 50.0 mN / 50 mm or more and 500.0 mN / 50 mm or less.

[0059] Furthermore, when the electrode film is attached to the fluorine-based piezoelectric film, the peel strength is preferably 2.0 N / 15 mm or more and 40.0 N / 15 mm or less, more preferably 3.0 N / 15 mm or more and 30.0 N / 15 mm or less, and even more preferably 5.0 N / 15 mm or more and 30.0 N / 15 mm or less.

[0060] [Manufacturing method for laminated piezoelectric film] (Method for manufacturing a laminated piezoelectric film having a release layer) Another embodiment of the present invention relates to a method for manufacturing a laminated piezoelectric film.

[0061] Figure 1 is a schematic diagram showing the manufacturing process of a laminated piezoelectric film (hereinafter also simply referred to as the "first laminated film") having a release film as the film to be adhered. The first laminated film is manufactured by applying an adhesive to the release film, drying the adhered adhesive to form an adhesive layer, and then adhering a fluorine-based piezoelectric film to the release film using the formed adhesive layer. As shown in Figure 1, in this embodiment, the first laminated film is manufactured using a roll-to-roll method. The arrows in Figure 1 indicate the direction of film transport (the same applies to Figures 2 to 7).

[0062] Because piezoelectric films often have a charged surface due to their piezoelectric properties, applying an adhesive directly to a fluorine-based piezoelectric film can result in uneven application. In contrast, a method that involves forming an adhesive layer on a release film and transferring it to the fluorine-based piezoelectric film avoids exposure to heat treatment or organic solvents during the process of forming the adhesive layer on the surface of the fluorine-based piezoelectric film. Therefore, performance degradation of the fluorine-based piezoelectric film during the process from adhesive application to drying can be suppressed. Furthermore, by storing the film without removing the release film, the release film not only acts as a protective film but can also be stored as a fluorine-based piezoelectric film with an adhesive layer.

[0063] Figure 2 is a magnified view of region X shown in Figure 1, illustrating the process of applying adhesive to the transported release film. Figure 3 is a magnified view of region Y shown in Figure 1, illustrating the process of forming an adhesive layer on the transported release film. Figure 4 is a magnified view of region Z shown in Figure 1, illustrating the process of adhesion between the release film and the fluorine-based piezoelectric film by the adhesive layer.

[0064] Specifically, the release film 100 is fed from the first supply roll 110 and transported by the guide roll 150a. Then, the adhesive 122 is applied to the surface of the transported release film 100 from the die head 120. The release film 100 coated with adhesive 122 is transported by the guide roll 150b and the adhesive 122 is dried inside the dryer 130 while being transported by guide rolls 150c to 150g. This removes the solvent in the adhesive 122 and forms an adhesive layer 124 on the surface of the release film 100 (step for forming the adhesive layer). The release film with the adhesive layer 124 formed is transported by guide rolls 150h and 150i and is bonded to the fluorine-based piezoelectric film 200 supplied from the second supply roll 210 at the first nip section 140. As a result, the fluorine-based piezoelectric film 200 is adhered to the release film 100 by the adhesive layer 124, and a laminated piezoelectric film 300 is formed (step of laminating the fluorine-based piezoelectric film).

[0065] Note that some guide rolls have been omitted in Figure 1 for the sake of clarity. The number of guide rolls is not limited to what is shown in Figure 1, and more guide rolls may be placed between each component.

[0066] (Process for forming an adhesive layer) First, the release film 100 is unfurled from the first supply roll 110.

[0067] The thickness of the release film 100 is not particularly limited, but is preferably 12 μm to 250 μm, more preferably 16 μm to 75 μm, and even more preferably 25 μm to 50 μm. The thinner the release film 100, the easier it is for the shape of the water droplets on the guide roll to be transferred to the adhesive layer 124. Therefore, this embodiment suppresses the generation of water droplets on the guide roll due to condensation and improves the uniformity and smoothness of the adhesive layer 124, resulting in a significant improvement in the adhesive strength of the fluorine-based piezoelectric film 200 and the transparency of the laminated piezoelectric film 300.

[0068] The released release film 100 is transported by the guide roll 150a directly below the die head 120 (coating device).

[0069] The die head 120 is positioned opposite the backup roll 121. The die head 120 then dispenses adhesive 122 and applies the adhesive 122 to the release surface of the release film 100, which is supported and moved by the backup roll 121. At this time, the gap between the die head 120 and the release film 100, the amount dispensed from the die, etc., are adjusted to change the thickness of the adhesive 122 that is applied and the thickness of the adhesive layer 124 that will be formed in the next step by removing the solvent.

[0070] The adhesive 122 to be applied is an adhesive that serves as the material for the adhesive layer described above, and has a glass transition temperature of -100°C or higher and 0°C or lower, preferably -100°C or higher and -10°C or lower, more preferably -100°C or higher and -20°C or lower, and even more preferably -85°C or higher and -30°C or lower. By using such an adhesive with a low glass transition temperature, a release film can be laminated to a fluorine-based piezoelectric film without several days of aging, and the first laminated film can be manufactured using a roll-to-roll method.

[0071] The adhesive 122 contains a solvent. The type of solvent is not particularly limited and can be any solvent that dissolves the solid components of the adhesive. Furthermore, the amount of solvent in the adhesive is not particularly limited and can be set according to the target viscosity or other factors depending on the application method of the adhesive.

[0072] The amount of solvent applied is also changed according to the thickness of the adhesive 122 applied from the die head 120. In this embodiment, the amount of solvent with a boiling point of 100°C or less contained in the adhesive 122, which is adjusted by the die head 120, applied per minute per centimeter in the direction perpendicular to the film flow direction (TD direction) is preferably 1.0 g / (cm·min) or more and 10.0 g / (cm·min) or less, more preferably 1.0 g / (cm·min) or more and 5.0 g / (cm·min) or less, and even more preferably 2.0 g / (cm·min) or more and 3.0 g / (cm·min) or less. In application by die coater, the range of solution viscosity in which good application is possible is limited. In order to increase the film application speed while maintaining the application thickness, it is necessary to increase the film transport speed and increase the amount of adhesive applied by the die head 120. However, increasing the amount of adhesive applied increases the amount of solvent with a boiling point of 100°C or less applied. Solvents with a boiling point below 100°C tend to volatilize easily as the release film 100 is transported from the die head 120 to the inlet of the dryer 130, and the latent heat of vaporization absorbed during volatilization easily cools the guide roll 150b placed between them. Therefore, by reducing the amount of solvent applied, the generation of water droplets on the guide roll 150b due to condensation caused by the cooling of the guide roll 150b by the latent heat of vaporization can be suppressed. On the other hand, if the amount of adhesive applied is reduced, the amount of volatilization of solvents with a boiling point below 100°C will decrease, thus suppressing cooling by the latent heat of vaporization, but this is undesirable because it reduces the amount of adhesive applied to the film.

[0073] Furthermore, the thickness of the adhesive layer 124 formed by removing the solvent in the next step is 2 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less, more preferably 20 μm or more and 50 μm or less, and particularly preferably 20 μm or more and 40 μm or less. Increasing the thickness of the adhesive layer can increase the adhesive strength. On the other hand, making the thickness of the adhesive layer moderately thin can suppress a decrease in the detection sensitivity of piezoelectricity due to the adhesive layer and condensation due to an increase in the amount of solvent used.

[0074] The release film 100 (see Figure 2), to which the adhesive 122 has been applied, is transported to the dryer 130 by the guide roll 150b.

[0075] The dryer 130 is a roll-support type heater that heats the release film 100, which is conveyed inside by multiple guide rolls 150c to 150g, with hot air. The dryer 130 heats the release film 100 to remove the solvent from the adhesive 122 and form the adhesive layer 124.

[0076] The internal temperature of the dryer 130 is 40°C to 80°C, preferably 40°C to 55°C, and more preferably 50°C to 55°C. This allows for sufficient removal of the solvent from the adhesive 122.

[0077] The release film 100 (see Figure 3), which has an adhesive layer 124 formed by the removal of the solvent, is conveyed to the first nip section 140 by guide rolls 150h and 150i.

[0078] According to the inventors' findings, when an adhesive is applied to the release film 100 using a roll-to-roll method as in this embodiment and then dried, the uniformity and smoothness of the adhesive layer are easily lost during the drying process, making it difficult to form an adhesive layer 124 with a smooth surface. This is thought to be because condensation forms on the surface of the guide roll used to transport the film, causing water droplets to adhere to it.

[0079] In other words, the adhesive used when manufacturing laminated piezoelectric films requires high adhesion to the fluororesin, which is the material for fluororesin piezoelectric films. In particular, because fluororesins have non-adhesive properties and chemical resistance, adhesion to other resin films is difficult, and the types of adhesives that can be used are limited. Therefore, when manufacturing laminated piezoelectric films containing fluororesin films, an even larger amount of adhesive is required. Furthermore, the types of solvents used to dissolve the adhesive are also limited, and the amount of solvent required increases with the amount of adhesive used.

[0080] Therefore, in this embodiment, the solvent evaporates from the adhesive 122 applied to the release film 100 during transport, absorbing a large amount of latent heat of vaporization. As a result, the release film 100 coated with the adhesive 122 is rapidly cooled during transport. As the cooled release film 100 continuously passes through the guide rolls, the guide rolls are continuously cooled by the release film 100, eventually causing condensation and the formation of water droplets on their surface. When water droplets adhere to the surface of the guide rolls, the shape of the water droplets is transferred to the adhesive layer, thereby reducing the uniformity and smoothness of the adhesive layer. Furthermore, in the dryer, the large amount of volatile solvent condenses on the guide rolls cooled by the latent heat of vaporization of the solvent, which can further reduce the uniformity and smoothness of the adhesive layer.

[0081] This phenomenon of condensation or solvent condensation on the guide roll surface occurs when a large amount of adhesive is used, such as in the adhesion of fluoropolymer resin films. The large amount of solvent contained in the adhesive volatilizes, absorbing a large amount of latent heat of vaporization.

[0082] In contrast, the smoothness of the adhesive layer 124 can be improved by keeping the guide roll warm, heating it, or using a material with low thermal conductivity for the guide roll's surface, thereby suppressing condensation on the guide roll surface and the aggregation of the solvent.

[0083] (Process of transferring adhesive to a fluorine-based piezoelectric film) Subsequently, the release film 100 with an adhesive layer 124 formed on it and the fluorine-based piezoelectric film 200 unwound from the second supply roll 210 are transported to the first nip section 140. The adhesive layer 124 of the release film 100 and the fluorine-based piezoelectric film 200 are brought into contact and pressurized by two opposing pressure rolls 142 and 144. This forms a laminated piezoelectric film 300 (first laminated film) in which the release film 100 and the fluorine-based piezoelectric film 200 are bonded together by the adhesive layer 124 (see Figure 4).

[0084] The pressure applied during lamination is not particularly limited; it should be set so that the peel strength of the release film from the fluorine-based piezoelectric film is within the range described above.

[0085] The laminated piezoelectric film 300, formed by adhering the release film 100 and the fluorine-based piezoelectric film 200 together, is wound onto the first winding roll 310 and stored therein.

[0086] The laminated piezoelectric film 300, in which the release film manufactured in this manner is bonded with an adhesive layer, has high uniformity and can also have high interlayer adhesion. Furthermore, because the adhesive is applied to the release film, a uniform adhesive layer can be formed, and the decrease in the piezoelectric properties of the fluorine-based piezoelectric film due to the drying of the adhesive is less likely to occur.

[0087] Since the laminated piezoelectric film 300 is protected on the surface by the release film 100, foreign matter is less likely to adhere to or scratch the surface of the fluorine-based piezoelectric film 200. Therefore, the laminated piezoelectric film 300 can be used for storing and transporting the fluorine-based piezoelectric film 200.

[0088] (Method for manufacturing a laminated piezoelectric film having a conductive layer) From the first laminated film described above, a laminated piezoelectric film having a conductive layer (hereinafter also simply referred to as the "second laminated film") can be manufactured.

[0089] Figure 5 is a schematic diagram showing the manufacturing process of the second laminated film in this embodiment. The second laminated film is manufactured by peeling off the release film 100 from the first laminated film (laminated piezoelectric film 300) manufactured in the first embodiment, transferring the adhesive layer 124 to the fluorine-based piezoelectric film 200, and then adhering the electrode film to the fluorine-based piezoelectric film 200 using the transferred adhesive layer. As shown in Figure 5, in this embodiment, the second laminated film is manufactured using a roll-to-roll method.

[0090] Figure 6 is a partially enlarged view of region V shown in Figure 5, and is a schematic diagram showing the process of peeling the release film 100 from the laminated piezoelectric film 300 and transferring the adhesive layer 124 to the fluorine-based piezoelectric film 200. Figure 7 is a partially enlarged view of region W shown in Figure 5, and is a schematic diagram showing the process of the fluorine-based piezoelectric film 200, to which the adhesive layer 124 has been transferred, and the electrode film 600 being adhered together. The electrode film 600 may be a multilayer film in which a conductive layer is formed on a base film, or it may be a single-layer film without a base film such as a metal foil. In this embodiment, the electrode film 600 has a protective film 605 on the side opposite to the side that is adhered to the fluorine-based piezoelectric film 200.

[0091] Specifically, the laminated piezoelectric film 300 is fed out from the third supply roll 510 and transported (process of preparing the laminated piezoelectric film). Then, the release film 100 is peeled off from the laminated piezoelectric film 300 by the release roll 520 and the adhesive layer 124 is transferred to the fluorine-based piezoelectric film 200 (process of transferring the adhesive layer). Next, at the second nip section 530, an electrode film having a conductive layer is adhered to the fluorine-based piezoelectric film 200 to which the adhesive layer 124 has been transferred (process of adhering the electrode film).

[0092] (Process for preparing laminated piezoelectric film) First, a laminated piezoelectric film 300 is prepared. The laminated piezoelectric film 300 is a laminated film manufactured in the first embodiment, having a fluorine-based piezoelectric film 200, an adhesive layer 124, and a release film 100. In this embodiment, the laminated piezoelectric film 300, which is a roll, is placed on a third supply roll 510 and unwound from the third supply roll 510 for transport.

[0093] (Steps to transfer the adhesive layer) Next, the release roll 520 is brought into contact with the surface of the laminated piezoelectric film 300 on the side with the release film 100, and the release film 100 is peeled off (Figure 6). The peeled release film 100 is transported and wound onto the second winding roll 410 for recovery.

[0094] At this point, the release roll 520 peels off only the release film 100. The adhesive layer 124 is then transferred to the fluorine-based piezoelectric film 200. The fluorine-based piezoelectric film 200, with the adhesive layer 124 transferred to it, is then transported to the second nip section 530.

[0095] (Process of applying adhesive to the electrode film) At the second nip section 530, the fluorine-based piezoelectric film 200 with the adhesive layer 124 transferred to it and the electrode film 600 unwound from the fourth supply roll 610 are transported. The adhesive layer 124 transferred to the fluorine-based piezoelectric film 200 and the electrode film 600 are brought into contact and pressurized by two opposing pressure rolls 532 and 534. As a result, a laminated piezoelectric film 700 (second laminated film) is formed in which the fluorine-based piezoelectric film 200 and the electrode film 600 are adhered together by the adhesive layer 124 (see Figure 7).

[0096] The laminated piezoelectric film 700, formed by adhering the electrode film 600 and the fluorine-based piezoelectric film 200 together, is wound onto the third winding roll 710 and stored therein.

[0097] [Other embodiments] It should be noted that the embodiments described above are exemplary embodiments of the present invention, and it goes without saying that the present invention may include embodiments other than those described above within the scope of its core technical concept.

[0098] For example, in the above explanation, it was stated that the first laminated film is manufactured first, and then the second laminated film is manufactured from the first laminated film using a separate device. However, the manufacturing of the first laminated film and the second laminated film may be carried out continuously using the same device.

[0099] Furthermore, the method of applying and drying the adhesive is not limited to the exemplified method, and any known method may be used. Similarly, the method of drying the adhesive using a dryer is not limited to the exemplified method, and any known method may be used.

[0100] Laminated piezoelectric films can be used in a variety of applications, including piezoelectric films for touch sensors and touch panels, actuators, protective films, and phase difference films. [Examples]

[0101] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0102] 1. Fabrication of fluorine-based piezoelectric film 1-1. Fluorine-based piezoelectric film 1 Polyvinylidene fluoride resin (manufactured by Kureha Corporation, a resin containing 100% by mass of polyvinylidene fluoride homopolymer) was melted in a single-screw extruder and then extruded into a film from a T-die. The extruded film was brought into contact with a cooling roll to obtain an unstretched film with a thickness of 160 μm. In the subsequent stretching process, the unstretched film was stretched to a stretch ratio of 4.1 times in the transport direction (MD direction), and then polarization treatment was performed by applying a DC voltage of 17.5 kV to obtain a fluorine-based piezoelectric film 1 with a thickness of 42 μm.

[0103] 1-2. Fluorine-based piezoelectric film 2 A fluorine-based piezoelectric film 2 was obtained in the same manner as the fabrication of fluorine-based piezoelectric film 1, except that an unstretched film with a thickness of 120 μm was stretched at a stretching ratio of 4.0 to adjust the thickness of the polyvinylidene fluoride film to 28 μm, and then polarization treatment was performed by applying a DC voltage of 16.1 kV.

[0104] 1-3. Fluorine-based piezoelectric film 3 A fluorine-based piezoelectric film 3 was obtained in the same manner as the preparation of fluorine-based piezoelectric film 1, except that an unstretched film with a thickness of 320 μm was stretched at a stretching ratio of 3.8 times to adjust the thickness of the polyvinylidene fluoride film to 80 μm, and then polarization treatment was performed by applying a DC voltage of 19.3 kV.

[0105] 1-4. Fluorine-based piezoelectric film 4 A fluorine-based piezoelectric film 4 was obtained in the same manner as the preparation of fluorine-based piezoelectric film 1, except that an unstretched film with a thickness of 480 μm was stretched at a stretching ratio of 4.2 times to prepare a polyvinylidene fluoride film with a thickness of 110 μm, and then polarization treatment was performed by applying a DC voltage of 20.0 kV.

[0106] 1-5. Fluorine-based piezoelectric film 5 A fluorine-based piezoelectric film 5 was obtained in the same manner as the preparation of fluorine-based piezoelectric film 1, except that an unstretched film with a thickness of 1190 μm was stretched at a stretching ratio of 4.0 to adjust the thickness of the polyvinylidene fluoride film to 300 μm, and then polarization treatment was performed by applying a DC voltage of 29.8 kV.

[0107] 2. Preparation and manufacturing of electrode films 2-1. Indium Oxide A transparent electrode precursor film (Tetrite TCF KH100NMH3-100-U8, manufactured by Oike Kogyo Co., Ltd., produced by sputtering indium tin oxide (ITO) onto a polyethylene terephthalate (PET) film) was crystallized at 150°C for 90 minutes to produce electrode film 1 having a transparent electrode.

[0108] 2-2. Silver nanowires An electrode film 2 having a transparent electrode was fabricated by applying a coating solution containing silver nanowires to a polyethylene terephthalate (PET) film and drying it.

[0109] 2-3. Conductive polymer An electrode film 3 having a transparent electrode was prepared by coating a polyethylene terephthalate (PET) film with a conductive polymer coating solution containing polyethylene dioxythiophene and drying it.

[0110] 2-4.Copper foil Copper foil was used as the electrode film 4.

[0111] 3. Fabrication of laminated piezoelectric film 3-1. Example 1 A laminated piezoelectric film (first laminated film) was fabricated by the roll-to-roll method using an apparatus having the schematic configuration shown in Figure 1.

[0112] A 38 μm thick silicone-coated film (Separator-SP-PET 03-25-BUT, manufactured by Mitsui Chemicals Tohcello Co., Ltd.) wound on a roll was unwound and moved while being held by a guide roll. An SBR-based adhesive (Scotch-Grip 4693, manufactured by 3M Japan Ltd. ("Scotch-Grip" is a registered trademark of the company)) containing 10% by mass of acetone and 64% by mass of cyclohexane as solvents was applied to the silicone-coated surface of the film using a die coater with the die head lip gap set to 200 μm, so that a 135 μm wet film was formed.

[0113] A film coated with adhesive was guided into a dryer using guide rolls, and the solvent was evaporated inside the dryer to produce a release film with an adhesive layer 35 μm thick.

[0114] Each step, from adhesive application to lamination, was carried out continuously while the film was moved at a transport speed of 3 m / min using multiple guide rolls.

[0115] The adhesive layer of the release film was bonded to the fluorine-based piezoelectric film prepared above to create a laminated piezoelectric film 1-1 (first laminated film).

[0116] Next, a laminated piezoelectric film (second laminated film) was fabricated by the roll-to-roll method using an apparatus having the schematic configuration shown in Figure 5. The release film of the laminated piezoelectric film 1-1 was peeled off by a roll, and the ITO surface of electrode film 1 was bonded to the adhesive layer laminated on the fluorine-based piezoelectric film to produce a laminated piezoelectric film 1-2 (second laminated film) having a fluorine-based piezoelectric film, a conductive layer, and an adhesive layer that bonds them together.

[0117] 3-2. Example 2 Laminated piezoelectric film 2-2 (second laminated film) was fabricated in the same manner as laminated piezoelectric film 1, except that electrode film 2 (silver nanowire) was used as the electrode film.

[0118] 3-3. Example 3 Laminated piezoelectric film 3-2 (second laminated film) was fabricated in the same manner as the fabrication of laminated piezoelectric film 1, except that electrode film 3 (conductive polymer) was used as the electrode film.

[0119] 3-4. Example 4 Laminated piezoelectric film 4-2 (second laminated film) was fabricated in the same manner as the fabrication of laminated piezoelectric film 1, except that electrode film 4 (copper foil) was used as the electrode film.

[0120] 3-5. Example 5 Laminated piezoelectric film 5-1 (first laminated film) and laminated piezoelectric film 5-2 (second laminated film) were manufactured in the same manner as the laminated piezoelectric film 4, except that fluorine-based piezoelectric film 2 was used as the fluorine-based piezoelectric film.

[0121] 3-6. Example 6 Laminated piezoelectric film 6-1 (first laminated film) and laminated piezoelectric film 6-2 (second laminated film) were manufactured in the same manner as the laminated piezoelectric film 4, except that fluorine-based piezoelectric film 3 was used as the fluorine-based piezoelectric film.

[0122] 3-7. Example 7 Laminated piezoelectric films 7-1 (first laminated film) and 7-2 (second laminated film) were fabricated in the same manner as the laminated piezoelectric film 4, except that fluorine-based piezoelectric film 3 was used as the fluorine-based piezoelectric film.

[0123] 3-8. Example 8 Laminated piezoelectric film 8-1 (first laminated film) and laminated piezoelectric film 8-2 (second laminated film) were manufactured in the same manner as the laminated piezoelectric film 4, except that fluorine-based piezoelectric film 5 was used as the fluorine-based piezoelectric film.

[0124] 3-9. Comparative Example 1 Laminated piezoelectric film 9-1 (first laminated film) was manufactured in the same manner as laminated piezoelectric film 1, except that the adhesive was changed to a urethane-based adhesive made by curing LIS-7059 manufactured by Toyo Morton Co., Ltd. with the hardener LCR-1585. After aging laminated piezoelectric film 9-1 at 60°C for 7 days, the release film was peeled off and it was laminated with copper foil to manufacture laminated piezoelectric film 9-2 (second laminated film).

[0125] 3-10. Comparative Example 2 Laminated piezoelectric film 10-1 (first laminated film) was manufactured in the same manner as laminated piezoelectric film 1, except that the adhesive was changed to an acrylic adhesive made by curing LIS-7011 manufactured by Toyo Morton Co., Ltd. with the hardener LCR-1585. After aging laminated piezoelectric film 10-1 at 60°C for 7 days, the release film was peeled off and it was laminated with copper foil to manufacture laminated piezoelectric film 10-2 (second laminated film).

[0126] 3-11. Comparative Example 3 Laminated piezoelectric film 11-1 (first laminated film) was fabricated in the same manner as laminated piezoelectric film 1, except that the adhesive was changed to an ester-based adhesive made by curing TM-K76 manufactured by Toyo Morton Co., Ltd. with the hardener LCR-1585. After aging laminated piezoelectric film 11-1 at 60°C for 7 days, the release film was peeled off and it was laminated with copper foil to fabricate laminated piezoelectric film 11-2 (second laminated film).

[0127] 4. Evaluation The following measurements were performed on the fluorine-based piezoelectric films 1-5, adhesive, and laminated piezoelectric films 1-2 to 11-2 prepared using the method described above.

[0128] 4-1. Measurement of fluorine-based piezoelectric films 4-1-1. Piezoelectric constant d 33 Piezoelectric constant d of fluororesin piezoelectric film 33 This is the direct quasi-static method (d 33Piezoelectric constant d (by the Meter method and the Berlincoat method) 33 The measurement was performed in accordance with ISO 19622:2018, the standard test method. Specifically, a piezoelectric constant measuring device (PIEZOTEST PM300 piezometer system) was used to hold the fluororesin piezoelectric film test piece with a holding force of 1.0 N, and the charge generated when an alternating force of 0.15 N amplitude and 110 Hz frequency was applied was measured. The charge was measured on the polarization surface of the fluororesin piezoelectric film, and the piezoelectric constant was calculated using the absolute value of the measured value. Measurements were then taken at a total of five locations: the center in the width direction of the fluororesin piezoelectric film, and two locations set at 50 mm intervals in both directions from the center in the width direction. The average value of the piezoelectric constants obtained from these measurements was determined as the piezoelectric constant d of the fluororesin piezoelectric film. 33 That's what I decided.

[0129] 4-1-2. Tensile strength The tensile strength of the fluororesin piezoelectric film was measured in accordance with JIS K 7127:1999. Specifically, strips of film measuring 50 mm in length parallel to the slow axis and 10 mm in width perpendicular to the slow axis, as detected by the in-plane birefringence of the film as defined in JIS C 5876-1:2009, were cut from the film. Next, the tensile strength of each strip of film was measured using a tensile testing machine (Tensilon RTC-1210A, manufactured by Orientec Co., Ltd.) at a tensile speed of 50 mm / min in an environment of measurement temperature 23°C, and this was defined as the tensile strength of the fluororesin piezoelectric film.

[0130] 4-2. Measurement of adhesive (glass transition temperature) The glass transition temperature of the adhesive was measured in accordance with JIS K 6240:2001.

[0131] 4-3. Measurement of laminated piezoelectric film (second laminated film) (peel strength) The peel strength between the fluorine-based piezoelectric film and the electrode film was measured in accordance with JIS K 6854-2:1999.

[0132] Tables 1 to 3 show the types of fluorine-based piezoelectric films, adhesives, electrode films, and laminated piezoelectric films, as well as the measurement results for the fluorine-based piezoelectric films, adhesives, and laminated piezoelectric films.

[0133] [Table 1]

[0134] [Table 2]

[0135] [Table 3] [Industrial applicability]

[0136] The fluorine-based piezoelectric film according to the present invention is less likely to peel off the adhered film. [Explanation of symbols]

[0137] 100 release film 110 First feed roll 120 Die Head 121 Backup Role 122 Adhesive 124 Adhesive layer 130 Dryer 140 First nip section 142, 144 Pressure Roll 150a~150i Guide Roll 200 Fluorine-based piezoelectric film 210 Second supply roll 300-layer piezoelectric film (first layer film) 310 First winding roll 410 Second winding roll 510 Third feed roll 520 release roll 530 Second nip section 532, 534 Pressure Roll 600 electrode film 605 Protective Film 610 Fourth feed roll 700-layer piezoelectric film (second layer film) 710 Third winding roll

Claims

1. Piezoelectric constant d ３３ A fluorine-based piezoelectric film having a density of 10.0 pC / N or more and 40.0 pC / N or less, and a tensile strength in the slow phase axis direction determined from the in-plane birefringence of the film as defined in JIS C 5876-1:2009 of 50 N or more and 1600 N or less, Adhesive film and An adhesive layer for bonding the fluorine-based piezoelectric film and the adhesive film, wherein the adhesive layer has a glass transition temperature of -100°C or higher and 0°C or lower, as measured in accordance with JIS K 6240:2001. A laminated piezoelectric film having the following characteristics.

2. The aforementioned fluorine-based piezoelectric film mainly consists of vinylidene fluoride resin. The laminated piezoelectric film according to claim 1.

3. The thickness of the fluorine-based piezoelectric film is 10 μm or more and 350 μm or less. The laminated piezoelectric film according to claim 1.

4. The aforementioned adhesive film has a surface resistivity of 1.0 × 10 ４ Having a conductive layer with a density of Ω / sq. or less, The laminated piezoelectric film according to claim 1.

5. The peel strength between the fluorine-based piezoelectric film and the conductive layer, measured in accordance with JIS K 6854-2:1999, is 2 N / 15 mm or more and 40 N / 15 mm or less. The laminated piezoelectric film according to claim 4.

6. A step of applying an adhesive to the release surface of a release film and drying it to form an adhesive layer having a glass transition temperature of -100°C or higher and 0°C or lower, as measured in accordance with JIS K 6240:2001, Piezoelectric constant d ３３ The process includes a step of laminating a fluorine-based piezoelectric film, which has a density of 10.0 pC / N or more and 40.0 pC / N or less, and a tensile strength in the slow axis direction determined from the in-plane birefringence of the film as defined in JIS C 5876-1:2009, to the release film with the adhesive layer, A method for manufacturing a laminated piezoelectric film according to claim 1.

7. The steps include peeling the release film from the laminated piezoelectric film and transferring the adhesive layer to the fluorine-based piezoelectric film, Surface resistivity is 1.0 × 10 ４ The process includes a step of laminating an electrode film having a conductive layer with a conductivity of Ω / sq. or less to the fluorine-based piezoelectric film using the adhesive layer. A method for manufacturing a laminated piezoelectric film according to claim 6.

Images