Fluorine resin film, fluorine resin piezoelectric film, method for producing same, and laminated piezoelectric body

Abstract

A fluorine-based resin film having a melt viscosity η of 600 Pa・s or more and 4000 Pa・s or less and a lamellar crystal long period of 11.5 nm or less, measured at a temperature of 260℃ and a shear rate of 50 s ‑1 The melt viscosity η measured below is 600 Pa・s or more and 4000 Pa・s or less, and the lamellar crystal long period measured by small-angle X-ray scattering is 11.5 nm or less.

Description

Technical Field

[0001] This invention relates to a fluoropolymer resin film, a method for manufacturing the same, and a laminated piezoelectric material. Background Technology

[0002] Fluorine resin films are used in various applications such as interior and exterior building components, surface materials for molded products, surface or back protection materials for solar cell modules, and fuel cell components due to their high weather resistance, heat resistance, stain resistance, chemical resistance, solvent resistance, mechanical properties, and reprocessability. Among these applications, the high weather resistance, stain resistance, and chemical resistance make them particularly desirable for protective films and optical components, leading to a high demand for fluorine resin films with high transparency.

[0003] Furthermore, it is known that fluorinated resin films can be transformed into piezoelectric films through polarization treatment. These piezoelectric films are used in touch panels and the like, thus requiring high transparency. The transparency of the piezoelectric film is largely determined by the transparency of the fluorinated resin film before polarization treatment; therefore, it is desirable to develop fluorinated resin films with high transparency. It should be noted that, in this specification, fluorinated resin piezoelectric film or piezoelectric film refers to a piezoelectric constant d determined by the method described later. 33 It is a fluorinated resin membrane with a ratio of 1.0 pC / N or higher.

[0004] As a method for manufacturing fluorinated resin films, there are known methods that use a solution containing dissolved fluorinated resin and manufacture the film by solution casting (Patent Document 1, etc.) and methods that heat-melt the fluorinated resin and extrude it (Patent Document 2).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2015 / 064324

[0008] Patent Document 2: Japanese Patent Application Publication No. 05-102548 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In solution casting, a large amount of polar organic solvent is used in the dissolution of fluorinated resins, necessitating solvent recovery. This not only increases manufacturing costs but also requires consideration of the impact of organic solvents on the working and natural environments. Furthermore, since polar organic solvents are used in the dissolution of fluorinated resins, any residual solvent in the fluorinated resin film may hinder polarization during the piezoelectric film manufacturing process. Therefore, it is preferable to extrude the hot-melted fluorinated resin into a film without using organic solvents.

[0011] On the other hand, in the method of hot melting and extruding fluorinated resins, if the temperature is raised to a high temperature, adverse conditions such as resin modification and the generation of decomposition products (foreign matter) may occur.

[0012] To suppress resin decomposition and other modifications, and to facilitate extrusion molding based on a hot melt method, a fluoropolymer resin with low melt viscosity is preferred. However, fluoropolymer resin films formed by extruding hot melted resin have the problem of low transparency.

[0013] Especially for piezoelectric films used in touch panels, high transparency and high piezoelectric constant are desired. In order to manufacture highly transparent fluoropolymer piezoelectric films, the fluoropolymer film used as the material is expected to have high transparency.

[0014] The present invention was made in view of the above-mentioned problems, and its object is to provide a fluoropolymer film with high transparency and high piezoelectricity through stretching and polarization treatment, a fluoropolymer piezoelectric film with high transparency and piezoelectricity, a method for manufacturing the same, and a laminated piezoelectric body.

[0015] Solution for solving the problem

[0016] One embodiment of the present invention for solving the above problems relates to a fluorinated resin film as described below [1] to [5].

[0017] [1] A fluoropolymer resin membrane, wherein the fluoropolymer resin membrane is tested at a temperature of 260°C and a shear rate of 50 s during the test. -1 The measured melt viscosity η is above 600 Pa·s and below 4000 Pa·s, and the lamellar length period determined by small-angle X-ray scattering is below 11.5 nm.

[0018] [2] According to the fluorinated resin membrane of [1], wherein the fluorinated resin membrane is a piezoelectric membrane with a thickness of 80 μm or more and 1000 μm or less.

[0019] [3] The fluorinated resin membrane according to [1] or [2], wherein the fluorinated resin membrane contains structural units derived from vinylidene fluoride as the main component.

[0020] [4] The fluoropolymer membrane according to any one of [1] to [3], wherein the arithmetic mean of the maximum and minimum widths of the membrane when viewed from above, i.e., the number of foreign objects with a size of 100 μm or more, is 7 per 0.25 m. 2 the following.

[0021] [5] The fluorinated resin film according to any one of [1] to [4], wherein the surface with the smaller surface height roughness Rz as determined according to JIS B 0601:2001 is 0.50 μm or less.

[0022] One embodiment of the present invention for solving the above problems relates to a method for manufacturing a fluorinated resin film as described below [6] to [7].

[0023] [6] A method for manufacturing a fluoropolymer resin membrane, the method being a method for manufacturing a fluoropolymer resin membrane according to any one of [1] to [5], the method comprising the following steps: measuring at a temperature of 260°C and a shear rate of 50s during the measurement. -1 A fluorinated resin with a melt viscosity η of 600 Pa·s or higher and 4000 Pa·s or lower is heated and melted; the heated and melted fluorinated resin is extruded and formed into a film; and the film is cooled by contacting it with a cooling roller with a surface temperature of 125°C or lower.

[0024] [7] According to the method for manufacturing a fluorinated resin membrane as described in [6], in the heating and melting step, the fluorinated resin is melted at a temperature that is 75°C or higher and 105°C or lower than the melting point of the fluorinated resin, and the method for manufacturing a fluorinated resin membrane further includes the step of filtering the fluorinated resin melted at the temperature with a filter having a filtration accuracy of 10 μm or higher and 40 μm or lower.

[0025] One embodiment of the present invention for solving the above problems relates to a fluorinated resin piezoelectric film as described below [1] to [5].

[0026] [1] A fluoropolymer piezoelectric film, wherein the fluoropolymer piezoelectric film is tested at a temperature of 260°C and a shear rate of 50 s during the test. -1 The measured melt viscosity η is above 600 Pa·s and below 4000 Pa·s; the lamellar length period determined by small-angle X-ray scattering is below 11.5 nm; the retardation is above 100 nm and below 2000 nm; and the piezoelectric constant d... 33 It is above 5.0 pC / N and below 40.0 pC / N.

[0027] [2] The fluorinated resin piezoelectric film according to [1] has an internal haze of less than 1.2%.

[0028] [3] The fluorinated resin piezoelectric film according to [1] or [2], wherein the surface with the smaller surface height roughness Rz as determined according to JIS B 0601:2001 is 0.50 μm or less.

[0029] [4] The fluoropolymer piezoelectric film according to any one of [1] to [3], wherein the arithmetic mean of the maximum and minimum widths of the film when viewed from above, i.e., the number of foreign objects with a size of 100 μm or more, is 7 per 0.25 m. 2the following.

[0030] [5] The fluorinated resin piezoelectric film according to any one of [1] to [4], wherein the fluorinated resin piezoelectric film contains structural units derived from vinylidene fluoride as the main component.

[0031] One embodiment of the present invention for solving the above problems relates to a method for manufacturing a piezoelectric film as described below [6] to [8].

[0032] [6] A method for manufacturing a fluoropolymer piezoelectric film, wherein the method for manufacturing a fluoropolymer piezoelectric film is according to any one of [1] to [5], and the method for manufacturing a fluoropolymer piezoelectric film comprises the following steps: measuring at a temperature of 260°C and a shearing speed of 50s during the measurement. -1 Fluorine resin with a measured melt viscosity η of 600 Pa·s or higher and 4000 Pa·s or lower is heated and melted; the molten fluorine resin is extruded and formed into a film; the film is cooled by contacting a cooling roller with a surface temperature of 125°C or lower; the cooled film is stretched; and the cooled film is polarized.

[0033] [7] In the method for manufacturing a fluorinated resin piezoelectric film according to [6], in the melting process, the fluorinated resin is melted at a temperature that is at least 75°C higher and at least 105°C higher than the melting point of the fluorinated resin.

[0034] [8] The method for manufacturing a fluorinated resin piezoelectric film according to [6] or [7] includes the following step: filtering the fluorinated resin melted in the melting step with a filter having a filtration accuracy of 10 μm or more and 40 μm or less.

[0035] One embodiment of the present invention for solving the above problems relates to the laminated piezoelectric material described below [1] to [6].

[0036] [1] A laminated piezoelectric material comprising a fluorinated resin piezoelectric film according to any one of [1] to [5], wherein the total light transmittance of the laminated piezoelectric material is 80% or more.

[0037] [2] According to [1], the laminated piezoelectric material further includes an electrode layer disposed on at least one surface of the fluorinated resin piezoelectric film, the electrode layer having a surface resistivity of 1.0 × 10⁻⁶. -1 Ω / sq. or higher and 1.0 × 10 4 Below Ω / sq.

[0038] [3] According to the stacked piezoelectric material of [2], wherein the electrode layer comprises at least one selected from the group consisting of a metal film, a metal oxide film, a metal nanowire, a metal mesh, a conductive polymer compound, a carbon nanotube, and graphene.

[0039] [4] The laminated piezoelectric material according to any one of [1] to [3], wherein the laminated piezoelectric material further comprises a hard coating layer disposed on at least one surface of the fluoropolymer piezoelectric film.

[0040] [5] A laminated piezoelectric material according to any one of [1] to [4], wherein the laminated piezoelectric material further comprises an antistatic layer disposed on at least one surface of the fluoropolymer piezoelectric film, the antistatic layer having a surface resistivity of 1.0 × 10⁻⁶. 4 Ω / sq. or higher and 1.0 × 10 9 Below Ω / sq.

[0041] [6] A laminated piezoelectric material according to any one of [1] to [5], wherein an antistatic layer and a hard coating layer are sequentially disposed on at least one surface of the fluorinated resin piezoelectric film, and the surface resistivity measured on the hard coating layer is 1.0 × 10⁻⁶. 6 Ω / sq. or higher and 1.0 × 10 12 Below Ω / sq.

[0042] Invention Effects

[0043] According to the present invention, a fluorinated resin film with high transparency and a fluorinated resin piezoelectric film, a method for manufacturing the same, and a laminated piezoelectric body are provided. Attached Figure Description

[0044] Figure 1 This represents the relationship between the long period of the lamellar crystal and the piezoelectric constant d. 33 A diagram showing the relationships between them.

[0045] Figure 2 This is a schematic diagram illustrating a laminated piezoelectric material according to one embodiment of the present invention. Detailed Implementation

[0046] One embodiment of the present invention relates to a fluoropolymer film and a fluoropolymer piezoelectric film that can be manufactured from therein.

[0047] [Materials for fluorinated resin films and fluorinated resin piezoelectric films]

[0048] Fluoropolymer resin films and fluoropolymer resin piezoelectric films are either films with fluoropolymer resin as the main component or not. Fluoropolymer resin refers to a resin obtained by polymerizing monomers composed of fluorinated olefins. "Comprising fluoropolymer resin as the main component" means that the structural units derived from monomers composed of fluorinated olefins account for 50% or more of the total mass of the fluoropolymer resin film. The ratio of fluoropolymer resin content to the total mass of the fluoropolymer resin film is preferably 50% or more and 100% or less, more preferably 70% or more and 100% or less, and even more preferably 90% or more and 100% or less.

[0049] Fluoropolymers can be homopolymers or copolymers obtained by polymerizing tetrafluoroethylene (TFE), vinylidene fluoride (VDF), etc. Examples of fluoropolymers obtained by polymerizing TFE include copolymers of ethylene, perfluoroalkyl vinyl ethers, VDF, 1-chloro-1-fluoroethylene, trifluorochloroethylene (CTFE), and hexafluoropropylene (HFP) with TFE. Examples of fluoropolymers obtained by polymerizing VDF include homopolymers of VDF, and copolymers of 1-chloro-1-fluoroethylene, 1-chloro-2-fluoroethylene, trifluoroethylene, TFE, CTFE, tetrafluoropropylene, HFP, and perfluoroalkyl vinyl ethers with VDF.

[0050] Among these, from the viewpoint of easily polarizing fluorinated resin films, fluorinated resins obtained by polymerizing monomers containing VDF are preferred; homopolymers of VDF, copolymers of VDF and HFP, copolymers of VDF and trifluoroethylene, copolymers of VDF and TFE, copolymers of VDF, trifluoroethylene, TFE, and CTFE, and copolymers of vinylidene fluoride VDF, trifluoroethylene, TFE, and 1-chloro-1-fluoroethylene are more preferred; homopolymers of VDF are even more preferred. Only one of these fluorinated resins may be used, or multiple resins may be used in combination.

[0051] Fluoropolymer resin films and fluorine resin piezoelectric films preferably contain VDF-derived structural units as main components, and most preferably homopolymers of VDF. Containing VDF-derived structural units as main components means that the VDF-derived structural units account for 50% or more of the total mass of the fluorine resin film and the fluorine resin piezoelectric film. The VDF-derived structural units account for 50% or more and 100% or less of the total mass of the fluorine resin film and the fluorine resin piezoelectric film, more preferably 70% or more and 100% or less, and even more preferably 90% or more and 100% or less.

[0052] Among them, fluorinated resin films and fluorinated resin piezoelectric films are preferred because they are expected to have high piezoelectricity. Therefore, the higher the content of the homopolymer of vinylidene fluoride, the better. The content of the homopolymer relative to the total mass of the fluorinated resin 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.

[0053] The content of VDF-based structural units in fluorinated resin films and fluorinated resin piezoelectric films can be determined by using... 19 F-NMR was used for determination using quantitative analysis with an internal standard.

[0054] Fluorine resin films and fluorine resin piezoelectric films were measured at a temperature of 260℃ and a shear rate of 50 s. -1 The measured melt viscosity is 600 Pa·s or higher and 4000 Pa·s or lower, preferably 600 Pa·s or higher and 3500 Pa·s or lower, and more preferably 600 Pa·s or higher and 2400 Pa·s or lower. Resins with lower melt viscosity are more likely to form films through extrusion at lower melt temperatures. However, resins with low melt viscosity facilitate molecular chain movement, leading to selective molecular chain alignment during film formation and easier crystal growth. Because the refractive indices of light differ between crystalline and amorphous regions, crystal growth in the resin increases light scattering at the interface between the crystalline and amorphous regions, resulting in decreased film transparency. In contrast, even with fluorinated resins with low melt viscosity, rapid cooling of the film after formation can suppress crystal growth, reduce light scattering, and yield a highly transparent film. The lamellar period length determined by X-ray diffraction is a good indicator of the film's crystallite size; the smaller the crystallite size, the shorter the lamellar period length. Furthermore, the lower the melt viscosity, the easier it is to filter using a filter, and the lower the melt temperature can be maintained. Therefore, it is less likely to produce spot-like unevenness on the film surface caused by resin modification.

[0055] Melt viscosity was determined according to ASTM D 3835:2016 (ISO 11443:2021, JIS K 7199:1999). Specifically, a capillary rheometer (manufactured by Toyo Seiki Co., Ltd., CAPILOGRAPH 1D) was used, employing a capillary mold with an inner diameter of φ1mm and a tube length of 10mm, at a measurement temperature of 260°C and a shear rate of 50s. -1 The viscosity was measured below.

[0056] [Characteristics of fluorinated resin films and fluorinated resin piezoelectric films]

[0057] The properties of the fluorinated resin film and the fluorinated resin piezoelectric film of this embodiment will be described below. It should be noted that the physical property values ​​described below are values ​​measured by the methods described below.

[0058] (Methods for determining physical properties)

[0059] The lamellar length period of fluorinated resin films and fluorinated resin piezoelectric films can be determined by measuring the X-ray diffraction pattern of the fluorinated resin film using a small-angle X-ray scattering (SAXS) measuring device, and calculated using a black reflective method. Specifically, a fluorinated resin film is set up in a SAXS measuring device as an X-ray source, and CuKα rays (wavelength λ = 0.15418 nm) monochromated with a Ni filter are irradiated. A two-dimensional detector is used to measure the two-dimensional diffraction pattern. Then, the X-ray scattering intensity (B(2θ)) of air is subtracted from the X-ray scattering intensity (B(2θ)) of the X-ray scattering (diffraction) intensity (I(2θ)) for a diffraction angle 2θ in the range of 0.200° to 2.000° is obtained.

[0060] With regard to the background of I(2θ), the X-ray intensity is obtained by linear approximation based on the diffraction angle 2θ, which shows the lowest X-ray intensity in the range of 2θ = 0.200° to 0.450°, and the X-ray intensity at 2θ = 2.000°. Then, by subtracting the background from I(2θ), the diffraction angle 2θ at which the X-ray intensity becomes maximum (peak) is obtained from the resulting X-ray intensity curve, and the lamellar length period L is obtained by the black reflection method shown in Equation 1.

[0061] [Formula 1]

[0062]

[0063] Regarding the thickness of non-piezoelectric fluoropolymer films, it is typically measured using a micrometer (JIS C2151:2019), but it can also be measured using known methods such as laser displacement meters, electrostatic capacitance displacement meters, or infrared methods. Then, with the intersection of the two diagonals of the fluoropolymer film designated as center point A, and the long side direction designated as the width direction, the thickness is measured at three points: center point A (the measurement point) and two other measurement points located 30 mm away from center point A on a line segment parallel to the long side passing through center point A. The average value of these measurements is taken as the thickness of the fluoropolymer film. It should be noted that when the fluoropolymer film is circular or polygonal, the film is cut into a rectangle to maximize the area, and the thickness is measured using the above method.

[0064] On the other hand, the thickness of the piezoelectric fluoropolymer film (fluoropolymer piezoelectric film) is measured in the same way as the thickness of the non-piezoelectric film, except for the setting of the measurement points. Specifically, the fast axis direction determined by measuring the birefringence of the piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film is designated as point A. The thickness is measured at a total of three measurement points: point A (the measurement point) and two other measurement points set at 30mm intervals from point A in the width direction along the line segment passing through point A. The average value of these measurements is taken as the thickness of the fluoropolymer piezoelectric film.

[0065] Regarding the amount of foreign matter, the thinner the film, the higher the proportion present near the surface, thus making it easier to detect foreign matter by looking down at the film. Therefore, to quantify the amount of foreign matter in the film, the film thickness for foreign matter measurement is set to 40 μm or less. Twenty-five rectangular films (observation sheets) are cut consecutively adjacent to each other from a fluoropolymer film (including fluoropolymer piezoelectric films) with a thickness of 40 μm or less, and the sum of the number of foreign matter measured from each of the aforementioned observation sheets is calculated. For fluoropolymer films with a thickness exceeding 40 μm, after stretching the film to a thickness of 35 μm to 40 μm or less, the number of foreign matter is measured using the method described below. Specifically, films with a thickness of 0.010 μm are cut consecutively adjacent to each other from the measured film. 2 Twenty-five observation slides (100mm x 100mm) were prepared. The sum of the number of foreign objects measured on each observation slide was then calculated. At this point, the foreign objects were observed and marked using transmitted light, and the marked areas were observed under a microscope to determine the size of the foreign objects. The size of the foreign object was defined as the arithmetic mean of its maximum and minimum widths.

[0066] The surface roughness Rz of a non-piezoelectric fluoropolymer film was measured according to JIS B 0601:2001. Specifically, a surface roughness meter (KEYENCE Corporation, VK-X260 shape analysis laser microscope) conforming to JIS B 0601:2001 was used. The intersection of the diagonals of a rectangular fluoropolymer film was designated as center point A. With the long side direction defined as the width direction, the surface roughness Rz was measured at three points: center point A (the measurement point) and two other measurement points located 30 mm away from center point A on a line segment parallel to the long side passing through center point A. The average value of these measurements was taken as the surface roughness of the fluoropolymer film. It should be noted that when the fluoropolymer film is circular or polygonal, the film is cut into a rectangle to maximize the surface area, and the surface roughness is measured using this method. It should be noted that the surface roughness Rz of the fluoropolymer film tends to be smaller on the contact surface with the cooling roller compared to the non-contact surface. This is because pressing the fluoropolymer film against the cooling roller reduces surface unevenness. This tendency is maintained even in stretched and polarized fluoropolymer piezoelectric films. Here, the measurement result for the surface with smaller surface roughness Rz (the contact surface with the cooling roller) is defined as the aforementioned surface height roughness Rz.

[0067] On the other hand, apart from setting the measurement points, the surface height roughness Rz of the fluoropolymer piezoelectric film is measured using the same method as that used for measuring Rz of films without piezoelectricity. Specifically, the fast axis direction determined by measuring the birefringence of the piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film is designated as point A. The surface height roughness Rz is measured at a total of three measurement points: point A (the measurement point) and two other measurement points set at 30mm intervals from point A in the width direction along the line segment passing through point A. The average value of these measurements is taken as the surface height roughness Rz of the fluoropolymer piezoelectric film.

[0068] The haze of the non-piezoelectric fluoropolymer membrane was measured according to JIS K 7136:2000. Specifically, a haze meter (Nippon Denshoku Kogyo Co., Ltd., NDH7700SP II) was used. The intersection of the diagonals of the rectangular fluoropolymer membrane was designated as center point A. With the long side direction defined as the width direction, haze was measured at three points: center point A (the measurement point) and two additional measurement points located 30 mm away from center point A on a line segment parallel to the long side passing through center point A. The average value of these measurements was taken as the haze of the fluoropolymer membrane. It should be noted that when the fluoropolymer membrane is circular or polygonal, it is cut into a rectangle to maximize the area, and the haze is measured using the above method. The haze of the fluoropolymer membrane was divided by its thickness to obtain the haze per unit thickness of the fluoropolymer membrane.

[0069] In addition to setting the measurement points, the haze of the fluoropolymer piezoelectric film is measured in the same way as described above. Specifically, the fast axis direction determined by measuring the birefringence of the fluoropolymer piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film is designated as point A. The haze is measured at a total of three measurement points: point A (the measurement point) and two other measurement points set at 30mm intervals from point A in the width direction along the line segment passing through point A. The average value of these measurements is taken as the haze of the fluoropolymer piezoelectric film.

[0070] At this time, a transparent coating is formed on the surface of the membrane being measured. The haze measured under the assumption that external haze caused by scratches on the membrane surface has been removed is taken as the internal haze of the membrane. Specifically, the fast axis direction determined by measuring the birefringence of the fluorine resin piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the membrane is designated as point A. A 30mm × 30mm measurement sample is cut out with point A as the center of the diagonal of the measurement sample. Two measurement samples are cut out along both ends of the width direction adjacent to the measurement sample, for a total of three measurement samples. For the three cut measurement samples, a hard coating agent (manufactured by Arakawa Chemical Industry Co., Ltd., BS CH271) is applied to one surface of each measurement sample using a bar coater and dried at 80°C for 30 minutes. Then, an ultraviolet (UV) irradiation device (manufactured by GS NIPPON DENCHI, CSOT040) is used to irradiate the sample with a target cumulative light intensity of 400mJ / cm². 2A 2 μm thick coating was formed by irradiating the film with UV light. Assuming that these coatings removed external haze caused by scratches on the film surface, the measured haze value was taken as the internal haze. The average value of three similarly measured samples was taken as the representative value of the fluorinated resin piezoelectric film.

[0071] The retardation setting of the fluoropolymer piezoelectric film was determined using a light source with a wavelength of 587.8 nm via the parallel Nicol rotation method. The fast and slow axes were then determined based on in-plane birefringence. The slow axis direction coincides with the average direction of the molecular chains oriented through stretching and extrusion. Therefore, if stretching is performed along the MD direction (mechanical direction) of the film, the MD direction aligns with the slow axis direction.

[0072] The piezoelectric constant of fluorinated resin piezoelectric films can be based on the direct quasi-static method (d 33 The piezoelectric constant d of the measuring instrument method and the quasi-static method (Berlincourt method) 33 The test method is determined according to ISO 19622:2018. Specifically, a piezoelectric constant measuring device (PIEZOTEST, Piezometer System PM300) is used. The fluoropolymer piezoelectric film used as the test piece is held with a holding force of 1.0 N, and an alternating force of 0.15 N at a frequency of 110 Hz is applied. The charge generated at this time is measured. The charge is measured on the polarization surface of the fluoropolymer piezoelectric film, and the piezoelectric constant is calculated using the absolute value of the measured value. At this time, the fast axis direction determined by the measurement of the birefringence of the fluoropolymer piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film is designated as point A. The piezoelectric constant d is measured at a total of three points: point A (the measuring point) and two other measuring points located 30 mm away from point A in the width direction on the line segment passing through point A. 33 The piezoelectric constants determined by these measurements are set as the average value of the piezoelectric constants d of the fluoropolymer resin piezoelectric film. 33 .

[0073] (Characteristics of fluorinated resin membranes)

[0074] The lamellar period of the fluorinated resin film, determined by small-angle X-ray scattering, is 11.5 nm or less, preferably 8.0 nm or more and 11.0 nm or less, and more preferably 8.5 nm or more and 10.8 nm or less. The shorter the lamellar period, the smaller the size of the resin crystals contained in the fluorinated resin film. By reducing the crystal size, the transparency of the fluorinated resin film and the transparency of the piezoelectric film made from it can be improved. Furthermore, according to the present inventors, the shorter the lamellar period, the easier it is to further increase the piezoelectric constant d during polarization treatment of the fluorinated resin film. 33This suggests that the shorter the lamellar period, the smaller the crystal size in the film. This is believed to be because the appropriate crystal size can increase the orientation polarization during the polarization process, thereby increasing d... 33 .

[0075] The thickness of the fluoropolymer resin film is preferably 80 μm or more and 1000 μm or less, more preferably 100 μm or more and 500 μm or less, even more preferably 100 μm or more and 300 μm or less, even more preferably 120 μm or more and 200 μm or less, and particularly preferably 120 μm or more and 180 μm or less. A thicker film is more advantageous in terms of mechanical properties such as wear resistance, durability, and insulation. Furthermore, it is less prone to surface unevenness caused by wrinkles resulting from stretching processes. On the other hand, a thinner film is more advantageous in terms of optical properties such as transparency and cost.

[0076] Regarding foreign matter, the thinner the membrane, the higher the proportion of foreign matter near the surface, thus making it easier to detect foreign matter when viewed from above. Therefore, to quantify the amount of foreign matter in the membrane, the membrane thickness used for foreign matter measurement is set to 40 μm or less. When using a fluoropolymer membrane with a top-view thickness of 40 μm or less, the number of foreign matter larger than 100 μm is preferably 7 per 0.25 μm. 2 Below, 0 units / 0.25m is preferred. 2 More than 5 per 0.25m 2 The following is a further preferred option: 0 units / 0.25m 2 More than 3 per 0.25m 2 The following is particularly preferred: 0 units / 0.25m 2 More than 1 per 0.25m 2 the following.

[0077] When viewing a fluoropolymer resin film with a thickness of 40 μm or less from above, the number of foreign objects larger than 200 μm is preferably 0 per 0.25 μm. 2 More than 3 per 0.25m 2 Below, 0 units / 0.25m is preferred. 2 More than 2 per 0.25m 2 The following is a further preferred option: 0 units / 0.25m 2 More than 1 per 0.25m 2 The following is particularly preferred: 0 units / 0.25m 2 .

[0078] When viewing a fluoropolymer resin film with a thickness of 40 μm or less from above, the number of foreign objects smaller than 100 μm is preferably 0 per 0.25 μm. 2 More than 50 per 0.25m 2 Below, 0 units / 0.25m is preferred.2 More than 25 per 0.25m 2 The following is a further preferred option: 0 units / 0.25m 2 More than 16 per 0.25m 2 the following.

[0079] The fewer these foreign objects there are, the better the transparency of the fluorinated resin film will be, and the more uniform the stretching and polarization will be during the stretching and polarization treatment of the fluorinated resin film.

[0080] The surface roughness Rz of the fluoropolymer film is preferably 0.50 μm or less, more preferably 0.01 μm or more and 0.50 μm or less, even more preferably 0.01 μm or more and 0.45 μm or less, and particularly preferably 0.01 μm or more and 0.40 μm or less. The smoother the surface of the fluoropolymer film, the less likely it is to develop haze, resulting in excellent transparency. Furthermore, a smaller surface roughness Rz indicates fewer wrinkles or unevenness in the film.

[0081] The haze per unit thickness of the fluorinated resin film is preferably 0.00% / μm or more and less than 0.35% / μm, more preferably 0.00% / μm or more and less than 0.30% / μm, and even more preferably 0.00% / μm or more and less than 0.25% / μm.

[0082] (Characteristics of fluoropolymer piezoelectric films)

[0083] The lamellar period of the fluorinated resin piezoelectric film obtained by small-angle X-ray scattering is 11.5 nm or less, preferably 8.0 nm or more and 11.0 nm or less, and more preferably 8.5 nm or more and 11.0 nm or less. It can be said that the shorter the lamellar period, the smaller the crystal size of the resin contained in the fluorinated resin piezoelectric film. Furthermore, by reducing the crystal size, the transparency of the fluorinated resin piezoelectric film can be improved. In addition, according to the inventors' understanding, if the lamellar period is 11.5 nm or less, it is easier to further increase the piezoelectric constant d during polarization treatment of the fluorinated resin film. 33 .

[0084] The retardation of the fluorinated resin piezoelectric film is 100 nm or more and 2000 nm or less, preferably 500 nm or more and 1800 nm or less, and more preferably 700 nm or more and 1600 nm or less. The greater the retardation, the higher the molecular orientation of the fluorinated resin film, the more fully the proportion of β crystals is increased, and it is easier to obtain a fluorinated resin piezoelectric film with a high piezoelectric constant through a polarization process.

[0085] The piezoelectric constant d of fluoropolymer resin piezoelectric film 33The value is 5.0 pC / N or higher and 40.0 pC / N or lower, preferably 8.0 pC / N or higher and 40.0 pC / N or lower, and more preferably 10.0 pC / N or higher and 30.0 pC / N or lower.

[0086] For fluoropolymer piezoelectric films, the haze of the film is preferably 0.0% or more and 10.0% or less, more preferably 0.0% or more and 5.0% or less, and even more preferably 0.0% or more and 3.0% or less. The lower the haze, the higher the transparency of the fluoropolymer piezoelectric film.

[0087] The internal haze of the fluoropolymer piezoelectric film is preferably less than 1.2%, more preferably 0.3% or more and 1.1% or less, and even more preferably 0.1% or more and 1.0% or less. The lower the internal haze, the higher the transparency of the fluoropolymer piezoelectric film.

[0088] The surface roughness Rz of the fluoropolymer piezoelectric film is preferably 0.50 μm or less, more preferably 0.05 μm or more and 0.50 μm or less, even more preferably 0.05 μm or more and 0.40 μm or less, and particularly preferably 0.05 μm or more and 0.30 μm or less. The smoother the surface of the fluoropolymer piezoelectric film, the less likely it is to develop haze on the surface, resulting in excellent transparency. Furthermore, a smaller surface roughness Rz indicates fewer wrinkles or unevenness in the film.

[0089] When viewing a fluoropolymer piezoelectric film with a thickness of 40 μm or less from above, the number of foreign objects larger than 100 μm is preferably 0 per 0.25 μm. 2 More than 7 per 0.25m 2 Below, 0 units / 0.25m is preferred. 2 More than 5 per 0.25m 2 The following is a further preferred option: 0 units / 0.25m 2 More than 3 per 0.25m 2 The following is particularly preferred: 0 units / 0.25m 2 More than 1 per 0.25m 2 the following.

[0090] When viewing a fluorinated resin piezoelectric film with a thickness of 40.0 μm or less from above, the number of foreign objects larger than 200 μm is preferably 0 per 0.25 μm. 2 More than 3 per 0.25m 2 Below, 0 units / 0.25m is preferred. 2 More than 2 per 0.25m 2 The following is a further preferred option: 0 units / 0.25m 2 More than 1 per 0.25m 2 the following.

[0091] When viewing a fluorinated resin piezoelectric film with a thickness of 40 μm or less from above, the number of foreign objects smaller than 100 μm is preferably 0 per 0.25 μm. 2 More than 50 per 0.25m 2 Below, 0 units / 0.25m is preferred. 2 More than 25 per 0.25m 2 The following is a further preferred option: 0 units / 0.25m 2 More than 16 per 0.25m 2 the following.

[0092] The fewer these foreign objects there are, the better the transparency of the fluorinated resin piezoelectric film will be, and the more uniform the stretching and polarization will be.

[0093] The thickness of the fluorinated resin piezoelectric film is not particularly limited, but is preferably 10.0 μm or more and 200.0 μm or less, more preferably 15.0 μm or more and 80.0 μm or less, further preferably 20.0 μm or more and 80.0 μm or less, particularly preferably 30.0 μm or more and 80.0 μm or less, very preferably 35.0 μm or more and 70.0 μm or less, and most preferably 35.0 μm or more and 50.0 μm or less. A thicker film is more advantageous for electrical properties such as insulation and piezoelectric characteristics. A thinner film is more advantageous for optical properties such as transparency and for lower cost.

[0094] [other]

[0095] It should be noted that as long as the fluorinated resin film meets the above-mentioned physical properties, it can contain resins other than fluorinated resins or other additives.

[0096] Examples of resins other than fluorinated resins mentioned above include: polyesters such as polycarbonate, polyethylene terephthalate, and polyethylene naphthalate, silicone resins, polyethers, polyvinyl acetate, and polyolefins such as polyethylene and polypropylene, which can be added to improve flexibility; acrylic resins, epoxy resins, polyethylene oxide, polypropylene oxide, polyphenylene ether, polyphenylene sulfide, polyamides, polyimides, polyamide-imides, polystyrene, and polybenzimidazole, which can be added to improve strength; and odd-numbered polyamides, cyanopulglan polysaccharides, and copper phthalocyanine polymers, which can be added to further improve dielectric properties.

[0097] [Manufacturing methods of fluorinated resin films and fluorinated resin piezoelectric films]

[0098] The manufacturing methods of the above-mentioned fluorinated resin films and fluorinated resin piezoelectric films are not particularly limited, but preferably include the process of forming a film by extruding the hot-melted resin.

[0099] For example, a fluorinated resin membrane can be manufactured by performing a process of heating and melting the aforementioned fluorinated resin (melting process) and a process of forming the filtered fluorinated resin into a membrane (film forming process). At this time, a further process of filtering the fluorinated resin melted in the melting process (filtration process) can be performed.

[0100] Furthermore, piezoelectricity can be imparted to fluorinated resin films by performing stretching processes (stretching processes) and polarization processes (polarization processes).

[0101] (Melting process)

[0102] In the melting process, the fluoropolymer resin is heated and melted. This process can be carried out, for example, by melt-blending the fluoropolymer resin using an extruder.

[0103] If the fluorinated resin molten in the melting process contains solvent components, the residual solvent components that have not evaporated may hinder the polarization of subsequent processes. Therefore, the content of the aforementioned solvent components in the fluorinated resin is preferably low, preferably 1% by mass or less relative to the total mass of the fluorinated resin, more preferably 0.1% by mass or less. In particular, the content of polar solvents relative to the total mass of the fluorinated resin is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 1 ppm or less.

[0104] The melting temperature of the fluoropolymer resin is preferably a temperature 75°C or higher and 105°C or lower than the melting point of the fluoropolymer resin, more preferably a temperature 75°C or higher and 100°C or lower than the melting point of the fluoropolymer resin, even more preferably a temperature 80°C or higher and 100°C or lower than the melting point of the fluoropolymer resin, and particularly preferably a temperature 85°C or higher and 95°C or lower than the melting point of the fluoropolymer resin. By setting the melting temperature to 75°C or higher than the melting point of the fluoropolymer resin, the viscosity of the fluoropolymer resin can be reduced to a level suitable for filtration in the next process. By setting the melting temperature to 105°C or lower than the melting point of the fluoropolymer resin, decomposition, condensation, and other processes of the fluoropolymer resin caused by heating can be suppressed, as well as the generation of decomposition products. By suppressing the generation of these decomposition products, the amount of foreign matter in the fluoropolymer resin film can be reduced, and the transparency and smoothness of the fluoropolymer resin film can be improved. Furthermore, by suppressing the generation of the aforementioned decomposition products, the clogging of the filter caused by these products can be suppressed during the filtration of fluorinated resins, thereby improving the filtration efficiency of the fluorinated resins.

[0105] According to the inventors' understanding, for fluorinated resins, in order to achieve a filterable viscosity from a resin with high melt viscosity, a high temperature is required. However, heating to high temperatures can easily lead to decomposition, condensation, and other phenomena, causing filter clogging. Therefore, it is difficult to melt and filter fluorinated resins. In contrast, the inventors have discovered that by setting the melting temperature of a fluorinated resin with an appropriate melt viscosity within the aforementioned range, fluorinated resins can be filtered efficiently. By setting the melting temperature of the fluorinated resin within the aforementioned range and filtering the fluorinated resin, which has been reduced in viscosity through melting, fluorinated resins can be filtered without the use of polar solvents. Furthermore, by not using solvents, it is less likely to cause solvent hindrance to polarization during polarization treatment caused by polar solvents remaining in the fluorinated resin film. Moreover, since polar solvents are essentially not used in the film-forming process, the burden on the working environment and the natural environment can be reduced, as can the manufacturing costs for recovering polar solvents.

[0106] (Filtration process)

[0107] In the filtration process, the fluorinated resin, which has been molten and reduced in viscosity during the melting process, is filtered. There are no particular limitations on the filtration method; any method that allows the molten fluorinated resin to pass through the filter is acceptable. Known filter types such as pleated or disc filters can be used.

[0108] The filter used in the filtration process preferably has a filtration accuracy of 10 μm or more and 40 μm or less, more preferably 10 μm or more and 35 μm or less, and even more preferably 15 μm or more and 30 μm or less. Using a filter with a filtration accuracy of 10 μm or more facilitates the filtration of the molten fluorinated resin; furthermore, the filtration pressure does not become excessively high, and the filtration time can be shortened. Furthermore, by using a filter with a filtration accuracy of 10 μm or more, the filtration pressure does not become excessively high, and the filtration time can be shortened. By using a filter with a filtration accuracy of 40 μm or less, foreign matter in the fluorinated resin can be sufficiently removed, resulting in a fluorinated resin membrane with fewer foreign matter.

[0109] It should be noted that filtration of fluorinated resins is achieved through a multi-layered filter composed of multiple layers with different shapes and mesh sizes. Furthermore, the filtration precision of a filter for fluorinated resins indicates its filtration efficiency, meaning the filter can retain particles of a specified size with a defined filtration efficiency. For example, in this specification, a filtration precision of 10 μm means that the filter can retain particles larger than 10 μm with a filtration efficiency of 95% or higher.

[0110] In this process, the fluorinated resin can be passed through multiple filters, or the fluorinated resin can be filtered multiple times. For example, a filter with low filtration precision (high filtration precision value) located at the beginning can be used to remove large foreign objects, and then a filter with high filtration precision (low filtration precision value) located at the end can be used to remove finer foreign objects. In this case, the filtration precision is set to the value of the filter with the highest filtration precision.

[0111] The filter can be installed between the extruder and the die head in the film-forming process. Alternatively, the filter can be installed in an extruder or melt mixing unit that is different from the extruder in the film-forming process, and the fluorinated resin filtered by the filter can be fed into the extruder in the film-forming process for film formation.

[0112] (Film forming process)

[0113] In the film-forming process, the fluorinated resin filtered in the filtration process is formed into a film.

[0114] The film-forming method is not particularly limited, and known methods such as extruding molten and filtered fluorinated resin from a T-die and cooling it by contacting it with a cooling roller can be used. In this embodiment, the surface temperature of the cooling roller is set to 125°C or below. By rapidly cooling the extruded fluorinated resin film with a cooling roller of low surface temperature, a large number of tiny crystals can be formed, shortening the lamellar growth period of the obtained fluorinated resin film. It should be noted that, according to the inventors' understanding, the crystallization rate of the fluorinated resin with low melt viscosity used in this embodiment differs from that of the fluorinated resin with higher melt viscosity, and the lamellar growth period of the obtained fluorinated resin film can easily vary significantly due to the temperature of the cooling roller. Therefore, in this embodiment, the temperature adjustment of the cooling roller is considered important. The surface temperature of the cooling roller is preferably 5°C or higher and 110°C or lower, more preferably 20°C or higher and 80°C or lower, and even more preferably 30°C or higher and 60°C or lower.

[0115] Thus, the fluorinated resin film of this embodiment can be obtained. The manufactured fluorinated resin film can be directly wound and stored, or it can be conveyed to subsequent processes such as stretching or polarization.

[0116] (Stretching process)

[0117] In the stretching process, the fluoropolymer resin film after film formation is subjected to uniaxial stretching. In the stretching process, the fluoropolymer resin film formed in the film formation process can be stretched directly, or the temporarily wound fluoropolymer resin film can be stretched by heating or other means as needed.

[0118] The stretching direction is not limited as long as it is uniaxial stretching. In the stretching process of mass production, it is preferable to continuously stretch the fluoropolymer film uniaxially. Specifically, the fluoropolymer film can be conveyed using multiple rollers while uniaxial stretching is performed along the conveying direction (MD direction). The stretching ratio (the ratio in the MD direction) is 2.5 times or more and 6.0 times or less, more preferably 3.5 times or more and 5.0 times or less. By setting the stretching ratio to 2.5 times or more, the proportion of β crystals (described later) is sufficiently increased, and a fluoropolymer film with a high piezoelectric constant can be easily obtained through the polarization process. By setting the stretching ratio to 6.0 times or less, the fluoropolymer film is less likely to break during the stretching process. In the film after uniaxial stretching in the MD direction, the MD direction is the slow axis, and the direction orthogonal to the stretching direction (TD direction) is the fast axis direction.

[0119] (Polarization process)

[0120] In the polarization process, a direct current voltage is applied to the fluoropolymer film to impart piezoelectricity. Fluoropolymers or copolymers containing VDF undergo a stretching process, transforming from α-crystalline to β-crystalline structures, thus increasing the proportion of β-crystalline particles. By applying a direct current voltage to the fluoropolymer film with the increased proportion of polar β-crystalline particles, a fluoropolymer film with a high piezoelectric constant can be obtained.

[0121] The applied DC voltage is preferably 7.0kV or higher and 50.0kV or lower, more preferably 7.5kV or higher and 30.0kV or lower.

[0122] The stretching and polarization processes can be performed simultaneously, or the polarization process can be performed after the stretching process.

[0123] The fluorine-based piezoelectric resin film after the polarization process can be wound into rolls for storage and transportation.

[0124] [use]

[0125] The aforementioned fluorinated resin films can be used in the manufacture of fluorinated resin piezoelectric films, and also in various applications such as interior and exterior trim materials for automobiles, furniture, and building materials, protective films, and phase retardation films. Furthermore, the aforementioned fluorinated resin piezoelectric films can be used in touch sensors and touch panels, piezoelectric films for actuators, interior and exterior trim materials for automobiles, furniture, and building materials, protective films, and phase retardation films, among other applications.

[0126] One embodiment of the present invention relates to a laminated piezoelectric material.

[0127] [Layered piezoelectric materials]

[0128] The aforementioned fluoropolymer film can be used as a piezoelectric film. By stacking the fluoropolymer piezoelectric film (hereinafter also simply referred to as "piezoelectric film") with other functional layers or films, a laminated piezoelectric body can be formed. The laminated piezoelectric body may include an antistatic layer as needed to prevent static electricity generated during operation. From the viewpoint of preventing damage to the antistatic layer or adjusting the hue, a hard coating layer or an optical adjustment layer may be included. Furthermore, the laminated piezoelectric body may include an electrode layer for detecting electrical signals generated by the piezoelectricity of the piezoelectric film, as needed. In addition, to further prevent the fluoropolymer piezoelectric film from discoloring over time and reducing its transparency when moisture penetrates from the outside under high temperature and humidity conditions, a moisture-proof layer may be included. When the electrode layer is a film with excellent moisture-proof properties, such as a metal film or a metal oxide film, this film may also be used as a moisture-proof layer. On the other hand, when the electrode layer includes metal nanowires, metal meshes, etc., the metal may be oxidized, resulting in reduced conductivity. Therefore, the laminated piezoelectric body may further include an outer coating layer on the non-adhesive surface of the electrode layer (the side opposite to the piezoelectric film).

[0129] That is, the laminated piezoelectric material includes at least the aforementioned piezoelectric film. The laminated piezoelectric material may further include one or more of the following on at least one surface of the piezoelectric film: an antistatic layer, a hard coating layer, an optical adjustment layer, a moisture-proof layer, an electrode layer, and an outer coating layer. These layers can be combined arbitrarily. For example, the laminated piezoelectric material may include an electrode layer on at least one surface of the piezoelectric film, and further include an antistatic layer and an outer coating layer.

[0130] The following is a detailed description of a laminated piezoelectric material and its manufacturing method according to one embodiment of the present invention. However, the laminated piezoelectric material is not limited to this embodiment.

[0131] Figure 2 This is a schematic cross-sectional view showing the stacked piezoelectric material of this embodiment.

[0132] like Figure 2 As shown, the stacked piezoelectric body 10 may sequentially include a piezoelectric film 11, an antistatic layer 12, a hard coating layer 13, an optical adjustment layer 14, and an electrode layer 15. Each layer will be described below.

[0133] (Piezoelectric film)

[0134] The fluoropolymer piezoelectric film can be used as the piezoelectric film. The piezoelectric constant d of the piezoelectric film... 33 The thickness of the piezoelectric film can be related to the piezoelectric constant d of the fluorine resin piezoelectric film mentioned above. 33 Same thickness.

[0135] (Antistatic layer)

[0136] An antistatic layer may be disposed on at least one side of the piezoelectric film. In this embodiment, the antistatic layer is preferably in contact with the piezoelectric film. The antistatic layer makes the stacked piezoelectric material less prone to static electricity generation.

[0137] The antistatic layer may comprise a cured product of a curable composition containing a conductive material. The curable composition containing the conductive material may comprise the conductive material, a curable resin, and a crosslinking agent as needed, or it may comprise both the conductive material and the crosslinking agent.

[0138] Conductive materials can be either ion-conducting or electron-conducting.

[0139] Examples of ion-conducting conductive materials include: (a) quaternary ammonium salts, pyridinium salts, and cationic antistatic agents with cationic groups such as primary to tertiary amino groups; (b) anionic antistatic agents with anionic groups such as sulfonate groups, sulfate groups, phosphate groups, and phosphonate groups; (c) amphoteric antistatic agents such as amino acid-based and aminosulfate-based agents; and (d) nonionic antistatic agents such as amino alcohol-based, glycerol-based, and polyethylene glycol-based agents.

[0140] Examples of electronically conductive materials include conductive polymers and other conductive materials. Examples of conductive polymers include polyacetylene or its derivatives, polythiophene or its derivatives, polypyrrole or its derivatives, and polyaniline or its derivatives. Among these, polythiophene or its derivatives are preferred from the viewpoint of high transparency and high conductivity. These conductive polymers may possess functional groups such as sulfonic acid groups, amino groups, amide groups, hydroxyl groups, mercapto groups, and carboxyl groups. Examples of conductive materials other than conductive polymers include carbon nanotubes and graphene.

[0141] Among these, from the viewpoint of easily reducing the surface resistivity of the stacked piezoelectric material and being less prone to leakage, conductive materials containing electronic conductivity are preferred, and carbon nanotubes are even more preferred.

[0142] Examples of curable resins include acrylic resins, epoxy resins, polyurethane resins, polyimide resins, melamine resins, polyester resins, polyvinyl alcohol resins, polystyrene resins, polyvinyl acetate resins, organosilicon compounds, and polyethylene glycol, which have functional groups such as hydroxyl, hydroxymethyl, carboxyl, sulfonyl, epoxy, and amino groups.

[0143] A crosslinking agent is any agent that reacts with the functional groups of a curable resin or conductive polymer to crosslink them. Examples of crosslinking agents include melamine-based crosslinking agents, polycarbodiimide-based crosslinking agents, polyoxazolidine-based crosslinking agents, polyepoxy-based crosslinking agents, and polyisocyanate-based crosslinking agents.

[0144] As described above, the curing resin and crosslinking agent used to obtain the antistatic layer are sometimes amine-based curing resins and crosslinking agents, such as melamine resin (also referred to as "amine materials"). From the viewpoint of low-temperature curing properties, melamine resin is sometimes preferred. On the other hand, such amine materials can produce amines (bases) under high temperature and humidity conditions, causing defluorination of fluorinated resins, which can sometimes lead to discoloration of the piezoelectric film. Even in such cases, by providing the aforementioned electrode layer or moisture-proof layer, amines are less likely to be generated, further suppressing discoloration of the piezoelectric film in the laminated piezoelectric body.

[0145] The surface resistivity of the antistatic layer is preferably, for example, 1.0 × 10⁻⁶. 4 Ω / sq. or higher and 1.0 × 10 9 Ω / sq. or less, preferably 1.0 × 10 Ω / sq. 5 Ω / sq. or higher and 1.0 × 10 8 / sq. below. If the surface resistivity of the antistatic layer is 1.0 × 10 9 Below Ω / sq., the surface resistivity of the laminated piezoelectric can be further reduced, thus fully imparting antistatic properties. To prevent deterioration of the laminated piezoelectric, treatment is sometimes performed while a hard coating is formed on the antistatic layer. When the surface resistivity measured from the hard coating is 1.0 × 10⁻⁶... 6 Ω / sq. or higher and 1.0 × 10 12 Sufficient antistatic properties are easily obtained when the surface resistivity is below Ω / sq. A surface resistivity of 1.0 × 10⁻⁶ is more preferably measured on the hard coating. 8 Ω / sq. or higher and 5.0 × 10 11 Below Ω / sq.

[0146] The surface resistivity of the antistatic layer can be measured, for example, using a known resistivity meter (e.g., a high resistivity meter (Nittoseiko Analytech, Hiresta UX, model: MCP-HT800, URS probe) according to JIS K 6911).

[0147] The thickness of the antistatic layer is not particularly limited, but is preferably 0.010 μm or more and 0.40 μm or less. If the thickness of the antistatic layer is 0.010 μm or more, the generation of static electricity in the laminated piezoelectric material can be further suppressed. If the thickness of the antistatic layer is 0.40 μm or less, discoloration of the piezoelectric film in the laminated piezoelectric material is less likely to occur. From the same point of view, the thickness of the antistatic layer is more preferably 0.030 μm or more and 0.40 μm or less, and even more preferably 0.045 μm or more and 0.30 μm or less.

[0148] The thickness of the antistatic layer can be measured using a spectroscopic interferometer (e.g., Hamamatsu Photonics "Optical NanoGauge C13027-11"). The thickness of each layer is measured at three locations, including the central area of ​​the surface of the stacked piezoelectric material, and can be expressed as its arithmetic mean. The thicknesses of the subsequent layers can also be measured using the same method.

[0149] (Hard coating)

[0150] A hard coating layer can be disposed between the piezoelectric film and the electrode layer. In this embodiment, the hard coating layer is disposed adjacent to the piezoelectric film (see reference). Figure 2 The hard coating fills in the surface imperfections of the piezoelectric film, making it smooth, and is less likely to cause damage to the surface of the piezoelectric film during the manufacturing process of the laminated piezoelectric material. This further reduces the haze of the laminated piezoelectric material.

[0151] The thickness of the hard coating is not particularly limited, but is 0.05 μm or more, preferably 0.3 μm or more and 3.0 μm or less, more preferably 0.5 μm or more and 2.0 μm or less, and even more preferably 0.5 μm or more and 1.5 μm or less.

[0152] As described above, the refractive index of the hard coating is preferably higher than that of the piezoelectric film and lower than that of the electrode layer. Specifically, the refractive index of the hard coating is preferably 1.40 or higher and less than 1.60, more preferably 1.47 or higher and less than 1.57, and even more preferably 1.49 or higher and less than 1.55. When the refractive index of the hard coating is within the above range, the transmittance can be further improved, and interference fringes can be further suppressed.

[0153] The refractive index difference between the hard coating and the piezoelectric film is preferably 0.01 or higher and 0.20 or lower. When the refractive index difference is 0.01 or higher, the transmittance can be further improved, and when it is 0.20 or lower, interference fringes can be further suppressed.

[0154] The hard coating can be made of any material that meets the above refractive index, and is usually a resin layer. The resin layer can be formed by applying a coating liquid containing resin and then drying it, or by applying a curable composition containing a polymeric compound and then drying and curing it.

[0155] The polymerizable compound can be any of a monomer, oligomer, or polymer. It can be a thermosetting compound or an ionizing radioactive compound, but is preferably an ionizing radioactive compound. Ionizing radiation is typically ultraviolet (UV) or an electron beam (EB).

[0156] Ionizing radiation-curable compounds are compounds possessing ionizing radiation-curable functional groups. Examples of ionizing radiation-curable functional groups include olefinic unsaturated groups such as (meth)acryloyl, vinyl, and allyl, as well as ring-opening polymerizable groups such as epoxy and oxetyl groups. Among these, compounds possessing olefinic unsaturated groups are preferred, compounds possessing two or more olefinic unsaturated groups are more preferred, and polyfunctional (meth)acrylate compounds are even more preferred. (Meth)acrylate refers to one or both of acrylates and methacrylates.

[0157] Examples of difunctional (meth)acrylate monomers in multifunctional (meth)acrylate compounds include ethylene glycol dimethacrylate, bisphenol A tetraethoxydiacrylate, bisphenol A tetrapropoxydiacrylate, and 1,6-hexanediol diacrylate. Examples of trifunctional or higher (meth)acrylate monomers include trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, dipentaerythritol tetramethacrylate, and isocyanuric acid modified trimethacrylate. Furthermore, the aforementioned (meth)acrylate monomers can be monomers whose molecular backbone is partially modified, or monomers modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl groups, cyclic alkyl groups, aromatic compounds, bisphenols, etc.

[0158] Furthermore, examples of multifunctional (meth)acrylate oligomers include acrylate polymers such as polyurethane (meth)acrylates, epoxy (meth)acrylates, polyester (meth)acrylates, and polyether (meth)acrylates. Polyurethane (meth)acrylates are obtained, for example, by reacting polyols and organic diisocyanates with hydroxy (meth)acrylates.

[0159] 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-hydroxyalkyl phenyl ketone, mistral ketone, benzoin, benzyl methyl ketal, benzoyl benzoate, α-acyl oxime ester, thioxanones, etc.

[0160] The curable composition may further contain other components besides those mentioned above, as needed. For example, from the viewpoint of suppressing adhesion of the hard coating during the manufacturing process or adjusting the refractive index, the curable composition may further contain particles. The particles may be inorganic or organic particles.

[0161] Examples of inorganic particles include particles of silicon dioxide (silicon dioxide), titanium dioxide, 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. From the viewpoint of minimizing damage to the transparency of the hard coating, inorganic particles are preferred, and silicon dioxide particles are more preferred. The surface of the inorganic particles can be treated with surface modifiers such as silane coupling agents.

[0162] It should be noted that, as described later, the laminated piezoelectric material may further include an optical adjustment layer between the antistatic layer and the electrode layer. The combined thickness of the hard coating layer and the optical adjustment layer is preferably 0.30 μm or more and 4.0 μm or less. If the combined thickness is 4.0 μm or less, it can further suppress the intrusion of moisture from the outside through these layers, making it easier to maintain the color-suppressing effect of the piezoelectric film achieved by providing a moisture-proof layer. Furthermore, if the combined thickness is 0.30 μm or less, it can suppress the hue of the laminated piezoelectric material and improve transparency. From the same viewpoint, the combined thickness is more preferably 0.50 μm or more and 3.0 μm or less, and even more preferably 0.60 μm or more and 2.0 μm or less.

[0163] (Optical adjustment layer)

[0164] An optical adjustment layer can be disposed between the hard coating layer and the transparent conductive layer. By appropriately adjusting the refractive index and thickness, the optical adjustment layer can suppress the color tone of the stacked piezoelectric material.

[0165] Specifically, as described above, the refractive index of the optical adjustment layer is preferably higher than that of the hard coating layer and lower than that of the transparent conductive layer. The stacked piezoelectric material containing such an optical adjustment layer can suppress hue through interference between light incident on and reflected from the hard coating layer and light reflected at the interface between the optical adjustment layer and the hard coating layer.

[0166] From the above perspective, the refractive index of the optical adjustment layer is preferably 1.60 or higher and less than 1.80, more preferably 1.63 or higher and less than 1.78, and even more preferably 1.65 or higher and less than 1.75.

[0167] The refractive index difference between the optical adjustment layer and the hard coating layer is preferably 0.05 or higher. If the refractive index difference is 0.05 or higher, the transmittance can be further improved.

[0168] The thickness of the optical adjustment layer is not particularly limited, as long as it is 0.05 μm or more. For example, the thickness of the optical adjustment layer can be 0.05 μm or more and 0.5 μm or less, or 0.09 μm or more and 0.18 μm or less. By keeping the thickness of the optical adjustment layer within the above range, the color tone of the stacked piezoelectric material can be suppressed.

[0169] The material for the optical adjustment layer can be any material that satisfies such a refractive index. For example, it could be a material in which metal oxide particles are added to a curable composition, exemplified as a hard coating material, to adjust the refractive index.

[0170] The metal oxide particles are preferably 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.

[0171] (Transparent electrode)

[0172] Transparent electrodes (electrode layers) can be formed by sputtering conductive materials onto a piezoelectric film having layers formed, or by mixing conductive materials with resin and coating them.

[0173] The electrode layer only needs to be disposed on at least one side of the piezoelectric film. The shape of the electrode layer is not limited; it can be nanowires, a mesh, or a thin film. The thin film can be a single layer or a multilayer stack.

[0174] The conductive material constituting the electrode layer is not limited, but preferably at least one metal and metal oxide selected from the group consisting of In, Sn, Zn, Ga, Sb, Ti, Si, Zr, Mg, Al, Au, Ag, Cu, Pd, and W. The metal oxide may further contain metal atoms from the group listed above, as needed. Indium tin oxide (ITO), antimony tin oxide (ATO), etc., are preferred among the metal oxides, with ITO being particularly preferred. Another representative example of a conductive material for the electrode layer includes at least one selected from the group consisting of metal nanowires, metal meshes, conductive polymers, carbon nanotubes, and graphene. Among these, metal nanowires and metal meshes include silver nanowires, silver meshes, copper nanowires, and copper meshes. Conductive polymers include polyacetylene and its derivatives, polythiophene and its derivatives, polypyrrole and its derivatives, polyaniline and its derivatives, etc.

[0175] In this embodiment, metal oxides are preferred as conductive materials, and ITO is more preferred.

[0176] It should be noted that silver nanowires have attracted attention as conductive materials suitable for large-area, high-functionality, lightweight, low-resistance, high-transparency, and high-flexibility applications in accompanying devices. In particular, silver nanowires can be used to form flexible electrode layers through wet processing, promising effective utilization in various applications. However, since silver nanowires are composed of metallic silver, their conductivity tends to decrease under high humidity and high temperature conditions, whether under sunlight or artificial light. Therefore, it is preferable to use an external coating agent such as a UV-curable resin to coat, dry, and cure the external coating agent on the silver nanowire film to form a protective layer (external coating). This allows the formation of an electrode layer on the substrate that imparts abrasion resistance and durability, achieving long-term stability of surface resistance under sunlight.

[0177] The lower the surface resistivity of the electrode layer, the easier it is to detect minute signals from the piezoelectric film. On the other hand, to reduce the surface resistivity of the electrode layer, it is necessary to thicken the electrode layer or increase the amount of conductive material forming the electrode layer, which tends to reduce transparency. Therefore, the surface resistivity of the electrode layer is 1.0 × 10⁻⁶. -1 Ω / sq. or higher and 1.0 × 10 4 The preferred value is 1.0 × 10⁻⁶. -1 Ω / sq. or higher and 1.0 × 10 3 Hereinafter, 1.0 × 10 is further preferred. -1 Ω / sq. or higher and 1.0 × 10 2 The following are particularly preferred: 1.0 Ω / sq. or higher and 1.0 × 10⁻⁶. 2 the following.

[0178] The surface resistivity (Ω / sq.) of the electrode layer was measured using a resistivity meter (LorestaGP MCP-T610, manufactured by MITSUBISHI CHEMICAL ANALYTECH) according to JIS K 7194-1994, via the DC four-probe method. When an outer coating is formed on the electrode layer, the surface resistivity measured on the outer coating is taken as the surface resistivity of the electrode layer. Since volume resistivity is the product of surface resistivity and thickness, the surface resistivity was measured according to the method for measuring volume resistivity. The surface resistivity was measured within the range including the intersection of the diagonals of the stacked piezoelectric elements.

[0179] The thickness of the electrode layer is not limited, but from the viewpoint of good conductivity, a thicker electrode layer is preferred. On the other hand, if the electrode layer is too thick, transparency may decrease; if the electrode layer is too thin, resistance may increase. Furthermore, discontinuous conductive portions may form in the film structure. The thickness is preferably 10 nm or more and 55 nm or less, more preferably 15 nm or more and 55 nm or less, further preferably 20 nm or more and 55 nm or less, even more preferably 20 nm or more and 45 nm or less, and particularly preferably 20 nm or more. The thickness of the electrode layer can be determined by a known method, namely, by observing a cross-section of such a laminate. Regarding the thickness of the electrode layer, a cross-section containing the intersection of the diagonals of the laminated piezoelectric body is observed using a scanning electron microscope (“SU3800”, manufactured by Hitachi HighTech Co., Ltd.) at an accelerating voltage of 3.0 kV and a magnification of 50,000x, and the thickness of the electrode layer is measured as the thickness of the electrode layer of the laminated piezoelectric body.

[0180] It should be noted that in the above embodiments, an electrode layer is formed on the optical adjustment layer, but this is not a limitation. For example, as described above, if the electrode layer contains metal nanowires or metal mesh as conductive materials, the optical adjustment layer may be omitted. Furthermore, in this case, from the viewpoint of suppressing the oxidation of the metal nanowires or metal mesh, an outer coating layer may be further disposed on the electrode layer. When an outer coating layer is disposed on the electrode layer, the surface resistivity of the electrode layer refers to the surface resistivity measured on the outer coating layer.

[0181] Furthermore, in the above embodiments, an electrode layer is formed on the optical adjustment layer, but it is also possible to form a transparent electrode film on the surface of a substrate such as glass or polymer material by bonding it to the optical adjustment layer.

[0182] (Transparent electrode film)

[0183] Transparent electrodes can be used in combination with existing substrate films. Existing electrode layers can be electrode layers formed by laminating the above electrode layers onto a substrate containing any one or more polymeric materials such as polyethylene terephthalate (PET), cyclic olefin polymers (COP), and polycarbonate (PC), or onto a substrate containing inorganic materials such as glass.

[0184] The substrate is a transparent resin layer used to support the electrode layer. The transparent resin contained in the substrate is preferably a material with heat resistance that can withstand the heat used to crystallize ITO, etc. Examples of such transparent resins include polyesters such as polyethylene terephthalate (PET). PET is preferred.

[0185] The thickness of the substrate is not particularly limited as long as it can support the electrode layer. It is preferably 2 μm or more and 300 μm or less, more preferably 10 μm or more and 200 μm or less, even more preferably 20 μm or more and 150 μm or less, and particularly preferably 30 μm or more and 130 μm or less.

[0186] The electrode layer is disposed on the piezoelectric film side of the substrate. Figure 2 The middle layer is the side facing the optical adjustment layer. As an electrode layer, inorganic electrodes such as ITO (indium tin oxide) and tin oxide are preferred, and ITO is more preferred.

[0187] (moisture-proof layer)

[0188] Furthermore, in the above embodiments, the laminated piezoelectric material has a piezoelectric film. However, to further prevent the piezoelectric film from discoloring over time and reducing its transparency when moisture penetrates from the outside under high temperature and humidity conditions, a moisture-proof layer may be included. The material of the moisture-proof layer is not particularly limited as long as it is transparent and can inhibit the penetration of moisture. It is preferably composed of inorganic oxides, and more preferably a thin film of inorganic oxides (such as vapor-deposited film).

[0189] Inorganic oxides refer to oxides of metals, oxides of nonmetals, or oxides of metalloids. Examples of inorganic oxides include: aluminum oxide, zinc oxide, antimony oxide, indium oxide, indium tin oxide, calcium oxide, cadmium oxide, silver oxide, gold oxide, chromium oxide, silicon oxide, cobalt oxide, zirconium oxide, tin oxide, titanium oxide, iron oxide, copper oxide, nickel oxide, platinum oxide, palladium oxide, bismuth oxide, magnesium oxide, manganese oxide, molybdenum oxide, vanadium oxide, and barium oxide, with indium tin oxide and silicon oxide being particularly preferred.

[0190] There is no particular limitation on the thickness of the moisture-proof layer. From the viewpoint of balancing moisture resistance and transparency, it is preferably 0.005 μm or more and 0.100 μm or less, more preferably 0.010 μm or more and 0.060 μm or less, and even more preferably 0.015 μm or more and 0.050 μm or less.

[0191] [Properties of laminated piezoelectrics]

[0192] (Piezoelectric constant d33)

[0193] The piezoelectric constant d of the laminated piezoelectric material 33 For example, a piezoelectric constant d of 7.0 pC / N or higher and 40.0 pC / N or lower is preferred. 33 A piezoelectric constant above 7.0 pC / N makes it easier to obtain higher piezoresistive properties. If the piezoelectric constant d of the laminated piezoelectric material... 33 If the piezoelectric constant is below 40.0 pC / N, the appearance defects mentioned above can be further reduced. Considering the same point, the piezoelectric constant d of the laminated piezoelectric material... 33More preferably, the piezoelectric constant is 10.0 pC / N or more and 40.0 pC / N or less; even more preferably, it is 13.0 pC / N or more and 35.0 pC / N or less; and particularly preferably, it is 15.0 pC / N or more and 30.0 pC / N or less. Except for setting the measurement location at the intersection of the diagonals of the laminated piezoelectric body, the piezoelectric constant d of the laminated piezoelectric body... 33 It can be measured using the same method as described above.

[0194] The piezoelectric constant d of the laminated piezoelectric material 33 For example, the piezoelectric constant d of the piezoelectric film, which is one of the components of a laminated piezoelectric material, can be used. 33 To make adjustments. When the piezoelectric constant d of the piezoelectric film... 33 At high speeds, the piezoelectric constant d of the laminated piezoelectric material is... 33 It is also easy to increase.

[0195] (Total transmittance)

[0196] For example, from the viewpoint of application in touch panels, the laminated piezoelectric material preferably has high transparency. Specifically, the total light transmittance of the laminated piezoelectric material is preferably 80% or more, more preferably 85% or more.

[0197] The total transmittance of a multilayer piezoelectric material can be measured using a haze meter (e.g., NDH7000SPII, manufactured by Nippon Denshoku Kogyo Co., Ltd.) based on the method described in JIS K 7361-1. The total transmittance is measured at the intersection of the diagonals containing the multilayer piezoelectric material.

[0198] The total transmittance of a multilayer piezoelectric material can be adjusted by the layer composition, the refractive index of each layer, and the thickness. For example, if the multilayer piezoelectric material includes a hard coating, the haze of the multilayer piezoelectric material can be further reduced, thus making it easier to increase the total transmittance.

[0199] (hue b) * Value, Δb * )

[0200] The hue b* value of the laminated piezoelectric material is preferably -5.0 or higher and 5.0 or lower. Setting the hue b* value to -5.0 or higher and 5.0 or lower achieves good transparency and visual clarity. (b* value of the laminated piezoelectric material before storage) * The value is preferably -5.0 or higher and 5.0 or lower. Furthermore, the color difference Δb before and after storing the laminated piezoelectric material at 85°C and 85%RH for 500 hours is measured. * Preferably, it is 4.0 or less, more preferably 3.5 or less. If the Δb of the laminated piezoelectric material before and after preservation... * When the value is below 4.0, the hue of the laminated piezoelectric material changes less under high temperature and high humidity, thus maintaining good transparency and visual clarity.

[0201] b of the multilayer piezoelectric * The value can be measured using a spectrophotometer (e.g., SD7000, manufactured by Nippon Denshoku Kogyo Co., Ltd.) according to the method of JIS Z 8722. The b value of the laminated piezoelectric material... * The value is measured at the intersection of the diagonals containing the stacked piezoelectric elements.

[0202] Regarding the preserved laminated piezoelectric material b * In terms of value, the laminated piezoelectric material is cut out to a length of 25cm. 2 A square shape was formed, and the four corners of the laminated piezoelectric were fixed to a SUS plate with tape. The plate was then placed in a constant temperature and humidity bath set at 85°C and 85%RH. After maintaining these conditions for 500 hours, the b-value of the laminated piezoelectric removed from the bath was measured using the same method as described above. * The value is sufficient.

[0203] b of the multilayer piezoelectric * Value, Δb * The thickness of the antistatic layer and the composition and thickness of the moisture-proof layer can be adjusted. For example, reducing the thickness of the antistatic layer can reduce b. * Value, Δb * Furthermore, increasing the thickness of the moisture-proof layer can reduce discoloration of the piezoelectric film caused by moisture intrusion, and can reduce b * Value, Δb * .

[0204] [Manufacturing method of laminated piezoelectrics]

[0205] Layered piezoelectrics can be manufactured using any method. For example, Figure 2 The stacked piezoelectric material can be manufactured by the following steps: (1) preparing a fluorine resin piezoelectric film; (2) forming an antistatic layer on the piezoelectric film; (3) forming a hard coating layer on the antistatic layer; (4) forming an optical adjustment layer on the hard coating layer; and (5) forming an electrode layer on the optical adjustment layer.

[0206] It should be noted that if the laminated piezoelectric does not contain a hard coating, step (3) can be omitted, and steps (4) and (5) can also be omitted as needed.

[0207] Furthermore, if the electrode layer contains metal nanowires or metal mesh as conductive materials, step (4) can be omitted. In addition, from the viewpoint of further suppressing the oxidation of metal nanowires or metal mesh, steps (6) of forming an outer coating on the electrode layer and (7) of forming a moisture-proof layer can be further performed.

[0208] In addition, instead of step (5), step (6) of forming a transparent adhesive (OCA) layer on the hard coating or optical adjustment layer can be performed after step (2) or step (3); and step (8) of attaching an electrode film on the OCA layer.

[0209] (The process of preparing the piezoelectric film)

[0210] The piezoelectric film containing fluorinated resin can use the above-mentioned fluorinated resin piezoelectric film.

[0211] (The process of forming the antistatic layer)

[0212] After coating the obtained piezoelectric film with the curable composition containing the above-mentioned antistatic layer, it is dried and cured to form an antistatic layer. From the viewpoint of improving low-temperature curing performance, the curable composition for the antistatic layer is preferably a curable composition containing a conductive material and an amine material, and more preferably a curable composition containing a conductive material and a melamine resin.

[0213] The curable composition described above may further contain water and a solvent. Examples of solvents include alcohol-based solvents such as methanol, ethanol, and isopropanol.

[0214] There are no particular limitations on the coating method of the above-mentioned curable composition, and it can be any of the following: spin coating, gravure coating, mold coating, rod coating, dip coating, etc.

[0215] The drying of the above-mentioned curable composition can be performed by heating the coated curable composition. The heating temperature is preferably above a temperature that removes the solvent and below the heat distortion temperature of the fluoropolymer forming the piezoelectric film; for example, it can be set to 100°C or higher and 150°C or lower. The heat distortion temperature can be determined, for example, according to JIS K 7191-2:2015.

[0216] (The process of forming a hard coating)

[0217] In this embodiment, after coating the piezoelectric film or antistatic layer with the curing composition for the hard coating, the mixture is dried and cured to form a hard coating.

[0218] The above-described curable composition may further contain a diluent. Preferably, the diluent has a polarity close to that of the particles. Examples of diluents include organic solvents such as alcohols, ketones, esters, carbonates, and aromatics.

[0219] The coating of the aforementioned curable composition can be performed using known wet processes. Examples of representative wet processes include dip coating, spray coating, spin coating, gravure coating, die coating, roll coating, cast coating, and curtain coating. From a productivity perspective, methods that allow for continuous layer formation, such as roll coating and gravure coating, are preferred.

[0220] The coating and drying methods for the above-described curable composition can be the same as those described above. It should be noted that the heating temperature only needs to be within the range that allows the solvent to evaporate and is below the heat distortion temperature of the fluoropolymer constituting the piezoelectric film; for example, it can be set to 60°C or higher and 100°C or lower.

[0221] The curing of the above-described curable composition can be based on heat or on ionizing radiation. Ionizing radiation-based curing can be achieved by irradiation with ultraviolet light or an electron beam. Alternatively, both heat-based and ionizing radiation-based curing methods can be used concurrently.

[0222] (The process of forming the optical adjustment layer)

[0223] Similar to the process of forming a hard coating, after applying the above-mentioned curable composition onto the piezoelectric film, antistatic layer, or hard coating, it is dried and cured to form an optical adjustment layer. However, when the electrode layer uses metal nanowires or metal mesh as the conductive material, the optical adjustment layer can be omitted due to the high transparency of the conductive layer.

[0224] (The process of forming the electrode layer)

[0225] An electrode layer can be formed by sputtering a transparent conductive material onto an optical adjustment layer or by coating a solution containing a transparent conductive material and a resin.

[0226] When the electrode layer uses metal nanowires or metal mesh as conductive materials, the conductive materials may oxidize and deteriorate, leading to an increase in resistance. Therefore, an outer coating can be formed on the electrode layer.

[0227] [Other Implementation Methods]

[0228] It should be noted that the above-described embodiments are exemplary embodiments of the present invention, and the present invention can of course include embodiments other than those described above within the scope of its core technical concept.

[0229] Example

[0230] The present invention will be described in detail based on the embodiments, but the present invention is not limited to these embodiments.

[0231] It should be noted that the melt viscosity of the fluoropolymer resin used as the material was determined according to ASTM D 3835:2016 (ISO 11443:2021, JIS K 7199:1999). Specifically, a capillary rheometer (manufactured by Toyo Seiki Co., Ltd., CAPILOGRAPH 1D) was used, employing a capillary mold with an inner diameter of φ1mm and a tube length of 10mm, at a measurement temperature of 260℃ and a shear rate of 50s. -1 The viscosity was measured below.

[0232] In addition, the melting point of the fluorinated resin was set as the maximum peak temperature of the endothermic curve in the DSC curve obtained by sealing 5 mg of the test sample in an aluminum dish and setting it in a differential scanning calorimeter (manufactured by Shimadzu Corporation, DSC-60A), under a nitrogen atmosphere, with a heating rate of 10 °C / min, from room temperature to 230 °C.

[0233] The melting temperature during membrane manufacturing is set to the highest temperature in the conduit from the extruder to the filtration unit.

[0234] [Experiment 1] Fabrication and evaluation of fluoropolymer resin membranes

[0235] In Experiment 1, unstretched and unpolarized fluorinated resin membranes were fabricated, and various properties and haze after stretching and polarization were evaluated.

[0236] 1. Fluorine resin membrane

[0237] 1-1. Membrane fabrication

[0238] Membranes 1 to 7 and membrane 10, all of which are fluorine-based resin membranes, are prepared in the following order.

[0239] 1-1-1. Membrane 1-1

[0240] Polyvinylidene fluoride (PVDF) homopolymer with a melt viscosity of 800 Pa·s and a melting point of 173°C was melted using a single-screw extruder with a diameter of φ50 mm, filtered through a pleated polymer filter with a filtration accuracy of 20 μm, and extruded into a film through a T-die. At this point, the melt temperature and filtration temperature were both 260°C. The extruded film was then brought into contact with a cooling roller with a surface temperature of 50°C while maintaining a temperature above 150°C, resulting in an unstretched fluoropolymer film with a thickness of 183 μm, i.e., film 1-1.

[0241] 1-1-2. Membrane 1-2

[0242] Without installing a filter on the single-screw extruder, membrane 1-2 was obtained in the same manner as membrane 1-1.

[0243] 1-1-3. Membrane 1-3

[0244] Without installing a filter on the single-screw extruder, the surface temperature of the cooling roller was set to 70°C. Otherwise, membrane 1-3 was obtained in the same manner as membrane 1-1.

[0245] 1-1-4. Membrane 1-4

[0246] Using PVDF with a melt viscosity of 2500 Pa・s and a melting point of 173 °C, the surface temperature of the cooling roller was set to 110 °C. Otherwise, membrane 1-4 was obtained in the same manner as membrane 1-1.

[0247] 1-1-5. Membrane 1-5

[0248] Using a homopolymer of vinylidene fluoride (PVDF) prepared by mixing PVDF with a melt viscosity of 2500 Pa·s and a melting point of 173 °C and PVDF with a melt viscosity of 4500 Pa·s and a melting point of 173 °C at a mass ratio of 1:1, with the surface temperature of the cooling roller set to 110 °C, membrane 1-5 was obtained in the same manner as membrane 1-1.

[0249] 1-1-6. Membrane 1-6

[0250] The surface temperature of the cooling roller was set to 130°C. Otherwise, membrane 1-6 was obtained in the same manner as membrane 1-1.

[0251] 1-1-7. Membrane 1-7

[0252] Using PVDF with a melt viscosity of 2500 Pa·s and a melting point of 173°C, the melt temperature was set to 280°C. No filter was installed on the single-screw extruder, and the surface temperature of the cooling roller was set to 140°C. Otherwise, membrane 1-7 was obtained in the same manner as membrane 1-1.

[0253] 1-1-8. Membrane 1-8 (Cannot be manufactured)

[0254] Using PVDF with a melt viscosity of 4500 Pa·s and a melting point of 173°C, I wanted to make membrane 8 in the same way as membrane 1-1, but the resin clogged the filter and I could not get a membrane.

[0255] 1-1-9. Membrane 1-9 (Cannot be manufactured)

[0256] Using PVDF with a melt viscosity of 2500 Pa·s and a melting point of 173°C, and a pleated polymer filter with a filtration accuracy of 5 μm, membrane 9 was to be fabricated in the same manner as membrane 1-1, but the filter was clogged by resin and the membrane could not be obtained.

[0257] 1-1-10. Membrane 1-10

[0258] 100g of PVDF with a melt viscosity of 2500 Pa·s and a melting point of 173℃ was weighed and added to 900ml of n-methylpyrrolidone (NMP). The mixture was stirred while the temperature was raised to 60℃ and stirred for 6 hours to prepare a resin solution. The resin solution was filtered through a filter with a filtration precision of 40μm. The resin solution was then fed into an automatic coating machine to prepare a coating film with a thickness of 600μm. After drying at 120℃ for 1 hour, film 1-10 was obtained. Film 1-10 has a high surface roughness Rz, making it difficult to accurately detect the amount of foreign matter.

[0259] 1-2. Evaluation of Fluorine Resin Membranes

[0260] For the unstretched films obtained, namely films 1-1 to 1-7 and 1-10, the lamellar length period, thickness, number of foreign matter, surface roughness Rz and haze were determined by the following method.

[0261] 1-2-1. Lamellar Long Period

[0262] The X-ray diffraction patterns of each film were measured using a small-angle X-ray scattering apparatus, and the lamellar length period was calculated using a black reflective method.

[0263] Specifically, each membrane was placed in a small-angle X-ray scattering measurement apparatus (manufactured by Rigaku Co., Ltd., NANO-Viewer) equipped with a two-dimensional detector, and used as an X-ray source to irradiate CuKα rays (wavelength λ = 0.15418 nm) monochromated by a Ni filter, and the two-dimensional diffraction pattern of the membrane was measured. Then, based on the X-ray diffraction (scattering) intensity, the X-ray diffraction intensity (A(2θ)) for the diffraction angle 2θ in the range of 0.200° to 2.000° was calculated. Since A(2θ) includes the X-ray scattering intensity of air (B(2θ)), B(2θ) was measured without the membrane in the case of no membrane, and B(2θ) was subtracted from A(2θ) to obtain the X-ray diffraction intensity of the membrane (I(2θ)).

[0264] With regard to the background of I(2θ), the X-ray intensity is obtained by linear approximation based on the diffraction angle 2θ, which shows the lowest X-ray intensity in the range of 2θ = 0.200° to 0.450°, and the X-ray intensity at 2θ = 2.000°. Then, by subtracting the background from I(2θ), the diffraction angle 2θ, where the X-ray intensity is maximized, is obtained. The lamellar period is then determined using the black reflection formula of Equation 1.

[0265] [Formula 2]

[0266]

[0267] (Methods for measuring small-angle X-ray scattering (diffraction))

[0268] • Measuring device: NANO-Viewer.

[0269] • X-ray source: CuKα (monochromatic: Ni filter).

[0270] • Applied current: 20mA, Applied voltage: 40kV.

[0271] • First slit: φ0.7mm, Second slit: φ0.6mm, Third slit: φ0.8mm.

[0272] • Camera length: 830mm.

[0273] • Detector: Imaging plate.

[0274] • Measurement time: 2 hours.

[0275] • Correction of diffraction angle: Si (111) plane.

[0276] • Sample shape and size: Using the stretching direction (MD) as the length direction of the sample, cut the membrane into pieces 30 mm long and 10 mm wide to serve as the sample. The sample is set up so that the length of the measuring fixture is the same as the sample length (the stretching direction of the membrane). In this case, one or more samples are overlapped and adjusted to achieve a total thickness of 200 ± 20 μm.

[0277] • The sampling width is set to 0.001° when converting a two-dimensional diffraction image obtained using an X-ray two-dimensional detector to an X-ray scattering (diffraction) intensity curve for a diffraction angle of 2θ.

[0278] 1-2-2. Thickness

[0279] A digital linear gauge (manufactured by Ono Gymnastics Co., Ltd., DG525H) and a gauge holder (manufactured by Ono Gymnastics Co., Ltd., SH-022) are used. Specifically, the intersection of the diagonals of a rectangular fluoropolymer film is designated as the center point A, and the long side direction is designated as the width direction. The thickness is measured at three points: the center point A (the measurement point) and two other measurement points located 30 mm away from the center point A on a line segment parallel to the long side passing through the center point A. The average value of these measurements is taken as the thickness of the fluoropolymer film.

[0280] 1-2-3. Number of foreign objects

[0281] The fluoropolymer membrane was uniaxially stretched with a thickness ranging from 35.0 μm to 40.0 μm, and 25 sheets with a thickness of 0.010 μm were cut from the fluoropolymer membrane by cutting from consecutive adjacent positions of each membrane. 2A rectangular membrane (observation sheet) with a size of 100mm × 100mm. Calculate the sum of the number of foreign objects observed and measured on each observation sheet, for every 0.250m... 2 The number of foreign objects is determined. At this point, the foreign objects are observed and marked using transmitted light, and the marked areas are observed under a microscope to determine the size of the foreign objects. The size of the foreign object is defined as the arithmetic mean of its maximum and minimum width. Thus, the number of foreign objects larger than 200 μm, those between 100 μm and 200 μm, and those smaller than 100 μm is determined.

[0282] 1-2-4. Surface height roughness Rz

[0283] A surface roughness meter (KEYENCE Corporation, VK-X260 shape analysis laser microscope) conforming to JIS B 0601:2001 was used. Specifically, the intersection of the diagonals of the piezoelectric film was designated as the center point A, and the long side direction was designated as the width direction. The surface height roughness Rz was measured at three points: point A (the measurement point) and two other measurement points spaced 30 mm apart on the line segment passing through point A in the width direction. The average value of these measurements was taken as the surface height roughness Rz of the fluoropolymer film.

[0284] 1-2-5. Haze

[0285] A haze meter (NDH7700SP II, manufactured by Nippon Denshoku Kogyo Co., Ltd.) was used. The haze was measured according to ISO 14782:2021. Specifically, the intersection of the diagonals of a rectangular fluoropolymer film was designated as center point A. With the long side direction defined as the width direction, the haze was measured at three points: center point A (the measurement point) and two additional measurement points located 30 mm away from center point A on a line segment parallel to the long side passing through center point A. The average value of these measurements was taken as the haze of the fluoropolymer film. The haze was then divided by the film thickness measured in (1-2-2) to obtain the haze per unit thickness of the fluoropolymer film.

[0286] 1-3. Evaluation Results of Fluorine Resin Membranes

[0287] 1-3-1. Physical properties of fluorinated resin films

[0288] The fabrication conditions and evaluation results for each membrane are shown in Tables 1 and 2. It should be noted that membrane 10 has high haze and is opaque, making it impossible to determine the amount of foreign matter.

[0289]

[0290]

[0291] 1-3-2. Relationship between lamellar long period and piezoelectric constant

[0292] Membranes 1-1 and 1-6 are fed into a uniaxial stretching device equipped with multiple metal rollers and pinch rollers. The rotational speed ratio of each roller is adjusted to stretch the membrane to 4.6 times in the flow direction. Then, a voltage of 7.0 kV to 10.0 kV is applied from the surface of the membrane in the thickness direction to polarize the membrane.

[0293] The piezoelectric constant d of the polarized film was determined according to ISO 19622:2018. 33 Specifically, a piezoelectric constant measuring device (PIEZOTEST Piezometer System PM300) was used. A fluoropolymer film, serving as the test piece, was held with a holding force of 1.0 N, and an alternating force of 0.15 N at a frequency of 110 Hz was applied. The charge generated during this process was measured. The charge was measured on the polarized surface of the film, and the piezoelectric constant was calculated using the absolute value of the measured values. The fast axis direction, determined by the birefringence measurement, was defined as the width direction. Any point A was designated as the midpoint of the line segment connecting the two ends of the width direction of the film. The piezoelectric constant d was measured at three points: point A (the measurement point) and two other measurement points located 30 mm away from point A in each direction along the width direction. 33 The average value of the piezoelectric constants obtained from them is set as the piezoelectric constant d of the film. 33 .

[0294] The applied voltage and piezoelectric constant d of film 1-1 (crystal length period of 9.6 nm) and film 1-6 (crystal length period of 12.4 nm) were compared. 33 The relationship is shown in Figure 1 .

[0295] like Figure 1 As shown, compared with films 1-6 with large lamellar period, the piezoelectric constant d of film 1-1 with small lamellar period is... 33 high.

[0296] [Experiment 2] Fabrication and Evaluation of Fluorine Resin Piezoelectric Films

[0297] In Experiment 2, fluorinated resin films were stretched and polarized to prepare fluorinated resin piezoelectric films, which were then evaluated.

[0298] 2. Fluorine resin piezoelectric film

[0299] 2-1. Method for preparing fluoropolymer piezoelectric films

[0300] 2-1-1. Piezoelectric film 2-1

[0301] The membrane 1-1 obtained in Experiment 1 was fed into a uniaxial stretching device equipped with multiple metal rollers and pinch rollers. The rotational speed ratio of each roller was adjusted to stretch it to 4.6 times in the flow direction. Then, a voltage of 8.0 kV was applied from the surface of the membrane in the thickness direction to obtain the piezoelectric membrane 2-1.

[0302] 2-1-2. Piezoelectric film 2-2

[0303] The voltage applied for polarization was set to 8.8 kV. Otherwise, the piezoelectric film 2-1 was stretched in the same way as the piezoelectric film 2-1, and the piezoelectric film 2-2 was obtained from the film 1-2.

[0304] 2-1-3. Piezoelectric film 2-3

[0305] The surface temperature of the cooling roller was set to 110℃. Otherwise, the same membrane 1-11 as the membrane 1-1 in Experiment 1 was made. The membrane 1-11 was stretched and polarized in the same way as the piezoelectric membrane 2-2 to obtain the piezoelectric membrane 2-3.

[0306] 2-1-4. Piezoelectric film 2-4

[0307] Using PVDF with a melt viscosity of 2500 Pa·s and a melting point of 173°C, the surface temperature of the cooling roller was set to 80°C. Otherwise, membrane 1-12 was obtained in the same manner as the membrane in Experiment 1. Membrane 1-12 was used as the material. Otherwise, piezoelectric membrane 2-4 was obtained in the same manner as the piezoelectric membrane 2-1.

[0308] 2-1-5. Piezoelectric film 2-5

[0309] Using PVDF with a melt viscosity of 2500 Pa·s and a melting point of 173 °C, the surface temperature of the cooling roller was set to 110 °C. Otherwise, membrane 1-13 was obtained in the same manner as the membrane in Experiment 1. Using membrane 1-13 as the material, the voltage applied after stretching was set to 8.8 kV. Otherwise, piezoelectric membrane 2-5 was obtained in the same manner as the piezoelectric membrane 2-1.

[0310] 2-1-6. Piezoelectric film 2-6

[0311] The membrane 1-5 obtained in Experiment 1 was stretched and polarized in the same way as the piezoelectric membrane 2-2 to obtain the piezoelectric membrane 2-6.

[0312] 2-1-7. Piezoelectric film 2-7

[0313] The membrane 1-6 obtained in Experiment 1 was stretched and polarized in the same way as the piezoelectric membrane 2-1 to obtain the piezoelectric membrane 2-7.

[0314] 2-1-8. Piezoelectric film 2-8

[0315] Using PVDF with a melt viscosity of 4500 Pa·s and a melting point of 173 °C, a single-screw extruder without a filter was used. The melt temperature was set to 280 °C and the surface temperature of the cooling roller was set to 140 °C. Otherwise, membranes 1-14 were prepared in the same manner as the membrane prepared in Experiment 1. Using membranes 1-15, the voltage applied after stretching was set to 9.5 kV. Otherwise, piezoelectric membranes 2-8 were obtained in the same manner as the piezoelectric membrane 1.

[0316] 2-1-9. Piezoelectric film 2-9

[0317] A voltage of 8.0 kV was applied from the surface of the membrane 1-10 obtained in Experiment 1 along the thickness direction to obtain piezoelectric membranes 2-9. Piezoelectric membranes 2-9 do not have piezoelectric properties, but are still referred to as piezoelectric membranes here.

[0318] 2-2. Evaluation of Fluorine Resin Piezoelectric Films

[0319] For the obtained piezoelectric films 2-1 to 2-9, the lamellar period, retardation, and piezoelectric constant d were determined by the following method. 33 Haze, internal haze, surface roughness Rz, number and thickness of foreign objects.

[0320] 2-2-1. Lamellar Long Period

[0321] The measurements were performed in the same manner as in Experiment 1.

[0322] 2-2-2. Delay

[0323] The retardation of a 20mm × 20mm membrane was measured using a KOBRA-HB measuring machine manufactured by Prince and a parallel Nicol rotation method with a measurement wavelength of 587.8nm as the light source. The fast and slow axes were determined based on in-plane birefringence. The slow axis direction coincides with the average direction of the molecular chains oriented through stretching and extrusion. In this case, the membrane was stretched in the flow direction (mechanical direction), therefore the MD direction coincides with the slow axis direction.

[0324] 2-2-3. Piezoelectric constant d 33

[0325] The piezoelectric constant of the fluorinated resin piezoelectric film was measured using the same method as in Experiment 1 (1-3-2). Specifically, the fast axis direction determined by measuring the birefringence of the fluorinated resin piezoelectric film was defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film was designated as point A. The piezoelectric constant d was measured at three points: point A (the measurement point) and two other measurement points located 30 mm away from point A in each direction along the width direction of the line segment passing through point A. 33The piezoelectric constants determined by these measurements are set as the average value of the piezoelectric constants d of the fluoropolymer resin piezoelectric film. 33 .

[0326] 2-2-4. Membrane Haze

[0327] Except for the setting of the measurement points, the haze of the fluoropolymer piezoelectric film was measured in the same way as the measurement method (1-2-5) in Experiment 1. Specifically, the fast axis direction obtained by measuring the birefringence of the fluoropolymer piezoelectric film was determined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film was designated as point A. The piezoelectric constant haze was measured at a total of three measurement points: point A (the measurement point) and two other measurement points located 30 mm away from point A in each direction along the line segment in the width direction passing through point A. The average value of the piezoelectric constants obtained from these measurements was taken as the haze of the fluoropolymer piezoelectric film.

[0328] 2-2-5. Internal Haze

[0329] The fast axis direction, determined by measuring the birefringence of the fluorinated resin piezoelectric film, is defined as the width direction. Point A is any point on the midpoint line connecting the two ends of the width direction of the film. A 30mm × 30mm sample is cut with point A as the center of the diagonal of the sample. Two more samples are cut adjacent to the sample along both ends of the width direction, resulting in a total of three samples. For each of the three cut samples, a hard coating agent (Arakawa Chemical Industry Co., Ltd., BSCH271) is applied to one surface using a rod coater and dried at 80°C for 30 minutes. Then, an ultraviolet (UV) irradiation device (GS NIPPON DENCHI, CSOT040) is used, with a target cumulative light intensity of 400 mJ / cm². 2 A 2 μm thick coating was formed by irradiating the film with UV light. Assuming that these coatings removed external haze caused by scratches on the film surface, the measured haze value was taken as the internal haze. The average value of three similarly measured samples was taken as the representative value of the fluorinated resin piezoelectric film.

[0330] 2-2-6. Surface height roughness Rz

[0331] Except for the setting of the measurement points, the surface height roughness Rz of the fluoropolymer piezoelectric film is measured using the same method as that used for measuring Rz of films without piezoelectricity. Specifically, the fast axis direction determined by measuring the birefringence of the piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film is designated as point A. The surface height roughness Rz is measured at a total of three measurement points: point A (the measurement point) and two other measurement points set at 30mm intervals from point A in the width direction along the line segment passing through point A. The average value of these measurements is taken as the surface height roughness Rz of the fluoropolymer piezoelectric film.

[0332] 2-2-7. Number of foreign objects

[0333] Since the thickness of the fluorinated resin piezoelectric film is less than 40 μm, uniaxial stretching was not performed to adjust the film thickness. Otherwise, the measurements were performed in the same manner as in Experiment 1 (1-2-3).

[0334] 2-2-8. Thickness

[0335] Except for the setting of the measurement points, the thickness of the fluoropolymer piezoelectric film is measured in the same way as the measurement method (1-2-2) for Rz of a non-piezoelectric film. Specifically, the fast axis direction determined by measuring the birefringence of the piezoelectric film is defined as the width direction. Any point on the midpoint line of the line segment connecting the two ends of the width direction of the film is designated as point A. The thickness is measured at a total of three measurement points: point A (the measurement point) and two measurement points set at 30mm intervals from point A to both ends on the line segment passing through point A in the width direction. The average value of these measurements is taken as the thickness of the fluoropolymer piezoelectric film.

[0336] 2-3. Evaluation Results of Fluorine-Based Piezoelectric Films

[0337] The fabrication conditions and evaluation results for each membrane are shown in Tables 3 and 4.

[0338]

[0339]

[0340] [Experiment 3] Fabrication and Evaluation of Laminated Piezoelectrics

[0341] In Experiment 3, laminated piezoelectric bodies were fabricated using fluorine-based resin piezoelectric films and evaluated.

[0342] 3. Laminated piezoelectric materials

[0343] 3-1. Fabrication Method of the Constituent Elements of a Laminated Piezoelectric Material

[0344] 3-1-1. Antistatic layer

[0345] (1) Antistatic layer 1

[0346] Using a gravure coating machine (Hirano Tecseed Co., Ltd.), a solution prepared by mixing coating P-400MP-A (manufactured by Nagase Chemtex Co., Ltd.) containing PEDOT:PSS as a conductive polymer and coating P-400MP-B (manufactured by Nagase Chemtex Co., Ltd.) containing a crosslinking agent and a conductivity enhancer at a ratio of 4:1 was applied using the multi-functional coating machine (Hirano Tecseed Co., Ltd.). The mixture was then heat-treated at 130°C for 0.67 minutes to form an antistatic layer with a thickness of 80 nm. The surface resistivity of the antistatic layer was 1.2 × 10⁻⁶. 8 Ω / sq.

[0347] (2) Antistatic layer 2

[0348] A solution (C-169PF) was prepared by mixing a coating containing monolayer carbon nanotubes, C-169PF-A (manufactured by Nagase Chemtex Co., Ltd.), and a coating containing a crosslinking agent, C-169PF-B (manufactured by Nagase Chemtex Co., Ltd.), in a 3:2 ratio, using a multi-functional coating machine (manufactured by Hirano Tecseed). The mixture was then heat-treated at 130°C for 1 minute to form an antistatic layer 2 with a thickness of 100 nm. The surface resistivity of the antistatic layer was 7.1 × 10⁻⁶. 6 Ω / sq.

[0349] 3-1-2. Formation of Hard Coating

[0350] After applying a hard coating agent (BS-CH271 manufactured by Arakawa Chemical Industry Co., Ltd., amorphous silica with an average particle size of 60 nm) using a multi-functional coating machine, the mixture was heat-treated at 80°C for 2 minutes, followed by irradiation with a cumulative light intensity of 200 mJ / cm². 2 The UV light cures it, forming a hard coating with a thickness of 700 nm and a refractive index of 1.50.

[0351] 3-1-3. Optical Adjustment Layer

[0352] A UV-curable composition containing zirconium oxide particles (OPSTARRA004 manufactured by Arakawa Chemical Industry Co., Ltd.) was coated and dried at 40°C for 30 seconds, followed by a curing time of 250 mJ / cm². 2 The accumulated light intensity irradiates ultraviolet light to form an optical adjustment layer (thickness 102nm, refractive index 1.65).

[0353] 3-1-4. Transparent Electrode

[0354] (1) Transparent electrode layer 1

[0355] In a magnetron sputtering apparatus, an indium-tin metal target (with a tin content of 3% by mass relative to the sum of the indium and tin content) is mounted as the target material, and a piezoelectric film with a defined layer is mounted as the substrate. Then, while winding the piezoelectric film with the defined layer, dehydration and degassing are performed, and the vacuum is reduced to 7 × 10⁻⁶. -5 Pa. Next, the substrate temperature was set to room temperature (25°C), and a mixed gas consisting of 99.2 mol% argon and 0.8 mol% oxygen was introduced into the chamber. While venting the gas in the chamber to make the pressure in the chamber 0.4 Pa, a transparent electrode layer with a thickness of 30 nm, which is essentially composed of indium tin composite oxide, was formed by reactive sputtering, thus obtaining a stacked piezoelectric.

[0356] (2) Transparent electrode layer 2

[0357] A transparent electrode layer with a thickness of 80 nm was formed by coating a silver nanowire-containing coating T-AG230 (manufactured by Starlight PMC Co., Ltd.) with an appropriate dilution of alcohol using a coating machine and drying it with hot air at 40°C for 30 seconds. Then, a solution of T-YP462 (manufactured by Starlight PMC Co., Ltd.) mixed with T-YP562 (manufactured by Starlight PMC Co., Ltd.) as an additive was coated onto the transparent electrode layer using a coating machine and dried with hot air at 40°C for 60 seconds, followed by a final drying at 330 mJ / cm². 2 The accumulated light intensity from the ultraviolet radiation forms a protective layer with a thickness of 80 nm. Here, the transparent electrode layer and the protective layer are collectively referred to as transparent electrode layer 2.

[0358] (3) Transparent electrode film

[0359] A transparent electrode film was fabricated by sputtering indium tin oxide (ITO) onto a polyethylene terephthalate (PET) film using a pre-film (manufactured by Oike Kogyo Co., Ltd., Tetolight TCF KH100NMH3-100-U8) and then crystallizing it at 150°C for 90 minutes. The surface resistivity of the transparent electrode film 1 was 100 Ω / sq. Next, an optically clear adhesive (OCA) sheet (Nitto Denko Co., Ltd., CS9862UA, 50 μm thick) was bonded onto a polymer piezoelectric film with the aforementioned layers formed thereon. A release film was peeled off from the OCA sheet, and the conductive layer of the transparent electrode film was then bonded to the OCA sheet with the conductive layer facing it.

[0360] 3-2. Layer Composition of Laminated Piezoelectrics

[0361] 3-2-1. Laminated piezoelectric material 1

[0362] The antistatic layer 1 is formed on surface A of the piezoelectric film 2-1, and then a hard coating is formed on the antistatic layer 1 to produce the laminated piezoelectric body 1.

[0363] 3-2-2. Laminated piezoelectric material 2

[0364] A transparent electrode layer 1 is formed on the hard coating of the stacked piezoelectric 1 to fabricate the stacked piezoelectric 2.

[0365] 3-2-3. Laminated piezoelectric materials 3

[0366] A transparent electrode film is bonded onto the hard coating of the laminated piezoelectric 1 to create the laminated piezoelectric 3.

[0367] 3-2-4. Laminated piezoelectric material 4

[0368] Transparent electrode layer 2 is used instead of transparent electrode layer 1. Otherwise, a stacked piezoelectric body 4 is fabricated in the same manner as the stacked piezoelectric body 2.

[0369] 3-2-5. Laminated piezoelectric materials 5

[0370] The antistatic layer 1 is changed to the antistatic layer 2. Otherwise, the laminated piezoelectric body 5 is made in the same way as the laminated piezoelectric body 4.

[0371] 3-2-6. Laminated piezoelectric material 6

[0372] An optical adjustment layer is formed between the hard coating layer and the transparent electrode layer 1. In addition, a stacked piezoelectric body 6 is fabricated in the same manner as the stacked piezoelectric body 2.

[0373] 3-2-7. Laminated piezoelectric materials 7

[0374] An antistatic layer 1 is formed on surface A of the piezoelectric film 1, and a transparent electrode film 1 is attached to the antistatic layer 1 to create a stacked piezoelectric body 7.

[0375] 3-2-8. Laminated piezoelectric material 8

[0376] An antistatic layer 1 is formed on surface A of the piezoelectric film 1, and then a transparent electrode layer 1 is formed on the antistatic layer 1 to create a stacked piezoelectric body 8.

[0377] 3-2-9. Laminated piezoelectric elements 9

[0378] Transparent electrode layer 1 is changed to transparent electrode layer 2. Otherwise, a stacked piezoelectric body 9 is fabricated in the same manner as the stacked piezoelectric body 8.

[0379] 3-2-10. Laminated piezoelectric material 10

[0380] An antistatic layer 1 is formed on surface A of the piezoelectric film 1, followed by the formation of an optical adjustment layer on the antistatic layer 1, and then a transparent electrode layer 1 is formed on the optical adjustment layer to produce a stacked piezoelectric body 10.

[0381] 3-2-11. Laminated piezoelectric material 11

[0382] A hard coating is formed on surface A of the piezoelectric film 1 to replace the antistatic layer 1. Otherwise, a laminated piezoelectric body 11 is fabricated in the same manner as the laminated piezoelectric body 8.

[0383] 3-2-12. Laminated piezoelectric material 12

[0384] The transparent electrode layer 1 is replaced with the transparent electrode layer 2. Otherwise, the stacked piezoelectric body 12 is fabricated in the same manner as the stacked piezoelectric body 11.

[0385] 3-2-13. Laminated piezoelectric material 13

[0386] The hard coating layer is formed on surface A of the piezoelectric film 1, and then the optical adjustment layer 1 is formed on the hard coating layer. A transparent electrode layer 1 is formed on the optical adjustment layer 1 to produce a stacked piezoelectric body 13.

[0387] 3-2-14. Laminated piezoelectric material 14

[0388] The hard coating is replaced with an optical adjustment layer, and otherwise, the stacked piezoelectric 14 is fabricated in the same manner as the stacked piezoelectric 11.

[0389] 3-2-15. Laminated piezoelectric material 15

[0390] An antistatic layer 1 is formed on surface A of the piezoelectric film 1, and a hard coating layer is formed on surface B of the piezoelectric film 1. The adhesive separator protecting the PET protective film (Sun A Kaken Co., Ltd., SAT TM30125T) is peeled off, and the PET protective film is then bonded to the hard coating layer on surface B. Next, a hard coating layer and an optical adjustment layer are formed on the antistatic layer 1 on surface A, and then a transparent electrode layer 1 is formed on the optical adjustment layer to fabricate a laminated piezoelectric body 15.

[0391] 3-2-16. Laminated piezoelectric material 16

[0392] An antistatic layer 1 is formed on surface A of the piezoelectric film 1, and a hard coating layer is formed on surface B of the piezoelectric film 1. The adhesive separator protecting the PET protective film (Sun A Kaken Co., Ltd., SAT TM30125T) is peeled off, and the PET protective film is then bonded to the hard coating layer on surface B. Next, a hard coating layer and a transparent electrode layer 2 are formed on the antistatic layer 1 on surface A to fabricate a laminated piezoelectric body 16.

[0393] 3-3. Evaluation of laminated piezoelectrics

[0394] For the obtained laminated piezoelectric bodies 1 to 16, the piezoelectric constant d was determined by the following method. 33 Total transmittance, surface resistivity, haze, and b * .

[0395] 3-3-1. Piezoelectric constant

[0396] The value measured within the range including the intersection of the diagonals of the laminated piezoelectric material is taken as the piezoelectric constant d of the laminated piezoelectric material. 33 The representative value was otherwise determined in the same manner as in Experiment 2 (2-2-3).

[0397] 3-3-2. Total transmittance

[0398] Regarding the total transmittance of the laminated piezoelectric, a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., NDH7000SP II) was used to measure the range of the intersection of the diagonals of the laminated piezoelectric according to JIS K 7361-1, and its value was set as the representative value.

[0399] 3-3-3. Surface resistivity

[0400] (1) Surface resistivity of the antistatic layer

[0401] The surface resistivity of the antistatic layer of the laminated piezoelectric material is measured, for example, using a known resistivity meter (e.g., a high resistivity meter (Nittoseiko Analytech, Hiresta UX, model: MCP-HT800, URS probe) according to JIS C2139-3-2:2018). The measurement location is the representative value of the surface resistivity of the antistatic layer measured within the area encompassing the intersection of the diagonals of the rectangular laminated piezoelectric material.

[0402] (2) Surface Resistivity of Transparent Electrode Regarding the surface resistivity of the transparent electrode of the laminated piezoelectric, a resistivity meter (“LorestaGP MCP-T610”, manufactured by Nittoseiko Analytech) was used to measure the surface resistivity using the DC four-probe method according to JIS K 7194. Since volume resistivity is the product of surface resistivity and thickness, the surface resistivity was measured according to the method for measuring volume resistivity. The measurement location was the representative value of the surface resistivity of the transparent electrode measured within the area containing the intersection of the diagonals of the rectangular laminated piezoelectric. In the case where a protective layer is formed on the electrode, the surface resistivity was measured from the protective layer.

[0403] 3-3-4. Haze

[0404] Regarding the haze value of the laminated piezoelectric, a haze meter ("NDH7000SP II", manufactured by Nippon Denshoku Kogyo Co., Ltd.) was used, and the haze measurement results of the range including the intersection of the diagonals of the laminated piezoelectric were taken as representative values ​​according to JIS K7136.

[0405] 3-3-5. Hue difference Δb * value

[0406] Using a spectrophotometer (manufactured by Nippon Denshoku Kogyo Co., Ltd., SD7000) and in accordance with JIS Z 8722 method, the measurement results of the range including the intersection of the diagonals of the laminated piezoelectric material before humid heat storage were taken as hue b. * The representative value of the value.

[0407] 3-3-6. Thickness

[0408] The thickness of the antistatic layer was measured using a spectroscopic interferometer (e.g., "Optical NanoGauge C13027-11" manufactured by Hamamatsu Photonics). The thickness of each layer was measured within the range of the intersection of the diagonals of the stacked piezoelectric materials. The thickness of all layers except the transparent electrode and the piezoelectric film was also measured using the same method.

[0409] Regarding the thickness of the transparent electrode, a cross-section of the laminated piezoelectric material was observed using a scanning electron microscope (“SU3800”, manufactured by Hitachi HighTech Co., Ltd.) at an accelerating voltage of 3.0 kV and a magnification of 50,000x. The thickness of the transparent electrode, including the area encompassing the intersection of the diagonals of the laminated piezoelectric material, was measured. The obtained measurements were taken as representative values ​​for the thickness of the transparent electrode.

[0410] 3-4. Results

[0411] The fabrication conditions and evaluation results of each layered piezoelectric element are shown in Tables 5 and 6.

[0412]

[0413] (The "0" and "0" in the laminated piezoelectric bodies 15 and 16 refer to the hard coating formed on both sides of the piezoelectric film.)

[0414]

[0415] This application claims priority to Japanese Patent Application No. 2024-006090 and No. 2024-006097, both filed on January 18, 2024. The matters set forth in the original description, claims, and drawings of those applications are incorporated herein by reference.

[0416] Industrial availability

[0417] The fluorinated resin film and fluorinated resin piezoelectric film of the present invention have high transparency.

[0418] Explanation of reference numerals in the attached figures

[0419] 10: Multilayer piezoelectric materials;

[0420] 11: Piezoelectric film;

[0421] 12: Antistatic layer;

[0422] 13: Hard coating;

[0423] 14: Optical adjustment layer;

[0424] 15: Electrode layer.

Claims

1. A fluoropolymer resin membrane, wherein the fluoropolymer resin membrane is subjected to a measurement temperature of 260°C and a shear rate of 50 s during the measurement. -1 The measured melt viscosity η is above 600 Pa·s and below 4000 Pa·s. The lamellar period determined by small-angle X-ray scattering is less than 11.5 nm.

2. The fluorinated resin membrane according to claim 1, wherein, The fluorinated resin film is a piezoelectric film with a thickness of 80 μm or more and 1000 μm or less.

3. The fluorinated resin membrane according to claim 1, wherein, The fluorinated resin membrane contains structural units derived from vinylidene fluoride as its main component.

4. The fluorinated resin membrane according to claim 1, wherein, The arithmetic mean of the maximum and minimum widths of the membrane when viewed from above, i.e., the number of foreign objects larger than 100 μm, is 7 per 0.25 m. 2 the following.

5. The fluorinated resin membrane according to claim 1, wherein, The surface with the smaller surface roughness Rz, as determined according to JIS B 0601:2001, has an Rz of less than 0.50 μm.

6. A method for manufacturing a fluoropolymer resin membrane, the method for manufacturing a fluoropolymer resin membrane according to any one of claims 1 to 5, the method comprising the following steps: measuring at a temperature of 260°C and a shear rate of 50 s during the measurement. -1 Fluoropolymer resins with a measured melt viscosity η of 600 Pa·s or higher and 4000 Pa·s or lower were heated and melted. The heated and melted fluoropolymer resin is extruded and formed into a film; and The film after film formation is cooled by contacting a cooling roller with a surface temperature below 125°C.

7. The method for manufacturing a fluorinated resin film according to claim 6, wherein, In the heating and melting process, the fluorinated resin is melted at a temperature that is at least 75°C higher than the melting point of the fluorinated resin but less than 105°C higher. The method for manufacturing the fluorinated resin membrane further includes the following step: filtering the fluorinated resin molten at the stated temperature using a filter with a filtration accuracy of 10 μm or more and 40 μm or less.

8. A fluoropolymer piezoelectric film, wherein the fluoropolymer piezoelectric film is tested at a temperature of 260°C and a shear rate of 50 s during the test. -1 The measured melt viscosity η is above 600 Pa·s and below 4000 Pa·s. The lamellar length determined by small-angle X-ray scattering is less than 11.5 nm, the retardation is greater than 100 nm and less than 2000 nm, and the piezoelectric constant d... 33 It is above 5.0 pC / N and below 40.0 pC / N.

9. The fluorine-based resin piezoelectric film according to claim 8, wherein, The internal haze is less than 1.2%.

10. The fluorine-based resin piezoelectric film according to claim 8, wherein, The surface with the smaller surface roughness Rz, as determined according to JIS B 0601:2001, has an Rz of less than 0.50 μm.

11. The fluorine-based resin piezoelectric film according to claim 8, wherein, The arithmetic mean of the maximum and minimum widths of the membrane when viewed from above, i.e., the number of foreign objects larger than 100 μm, is 7 per 0.25 m. 2 the following.

12. The fluorine-based resin piezoelectric film according to claim 8, wherein, The fluorinated resin piezoelectric film contains a homopolymer of vinylidene fluoride.

13. A method for manufacturing a fluoropolymer piezoelectric film, wherein the method for manufacturing the fluoropolymer piezoelectric film is the method for manufacturing a fluoropolymer piezoelectric film according to any one of claims 8 to 12, and the method for manufacturing the fluoropolymer piezoelectric film comprises the following steps: measuring at a temperature of 260°C and a shearing speed of 50 s during the measurement. -1 Fluoropolymer resins with a measured melt viscosity η of 600 Pa·s or higher and 4000 Pa·s or lower were heated and melted. The molten fluorinated resin is extruded and formed into a film; The film after film formation is cooled by contacting a cooling roller with a surface temperature below 125°C. The cooled film is stretched; The cooled film is then polarized.

14. The method for manufacturing a fluorinated resin piezoelectric film according to claim 13, wherein, In the melting process, the fluorinated resin is melted at a temperature that is at least 75°C higher and at least 105°C higher than the melting point of the fluorinated resin.

15. The method for manufacturing a fluorinated resin piezoelectric film according to claim 14, wherein, The method for manufacturing the fluorine resin piezoelectric film includes the following steps: filtering the fluorine resin melted in the melting step using a filter with a filtration accuracy of 10 μm or more and 40 μm or less.

16. A laminated piezoelectric material comprising the fluoropolymer piezoelectric film according to claim 8, wherein the total light transmittance of the laminated piezoelectric material is 80% or more.

17. The laminated piezoelectric material according to claim 16, wherein, The stacked piezoelectric material further includes an electrode layer disposed on at least one surface of the fluoropolymer piezoelectric film, the electrode layer having a surface resistivity of 1.0 × 10⁻⁶. -1 Ω / sq. or higher and 1.0 × 10 4 Below Ω / sq.

18. The laminated piezoelectric material according to claim 17, wherein, The electrode layer comprises at least one selected from the group consisting of metal films, metal oxide films, metal nanowires, metal meshes, conductive polymer compounds, carbon nanotubes, and graphene.

19. The laminated piezoelectric material according to claim 16 or 17, wherein, The stacked piezoelectric material further includes a hard coating layer disposed on at least one surface of the fluoropolymer piezoelectric film.

20. The laminated piezoelectric material according to claim 16 or 17, wherein, The laminated piezoelectric material further includes an antistatic layer disposed on at least one surface of the fluoropolymer piezoelectric film, the antistatic layer having a surface resistivity of 1.0 × 10⁻⁶. 4 Ω / sq. or higher and 1.0 × 10 9 Below Ω / sq.

21. The laminated piezoelectric material according to claim 16 or 17, wherein, An antistatic layer and a hard coating layer are sequentially disposed on at least one surface of the fluorine resin piezoelectric film, and the surface resistivity of the hard coating layer is measured to be 1.0 × 10⁻⁶. 6 Ω / sq. or higher and 1.0 × 10 12 Below Ω / sq.

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