Laminated piezoelectric body, touch panel, and method for manufacturing laminated piezoelectric body

Abstract

A laminated piezoelectric body having: a piezoelectric film containing a fluorine-based resin as a main component and having a piezoelectric constant (d33) of 7-40 pC / N (inclusive); a charge dispersion layer that is disposed on at least one surface of the piezoelectric film and that has a surface resistivity of 1.0 * 104 Omega / sq. Or more and 1.0 * 1012 Omega / sq. Or less; a transparent electrode; and a transparent adhesive layer disposed between the transparent electrode and the charge dispersion layer, the total light transmittance of the laminated piezoelectric body being 80% or more.

Description

Technical Field

[0001] The present invention relates to a stacked piezoelectric body, a touch panel, and a method for manufacturing the stacked piezoelectric body. Background Art

[0002] Generally speaking, a touch panel detects the two-dimensional position of the touch panel surface by touching it with a finger, pen, or other device. To prevent misidentification of input, it is ideal to separate selection and execution. Specifically, it is ideal to execute the selection by selecting a two-dimensional position on the touch surface and applying pressure to the touch surface. Therefore, research is underway to apply pressure-sensitive sensors to touch panels that detect pressure on the touch surface.

[0003] As the pressure-sensitive sensor, a piezoelectric film that generates a voltage in response to pressure has been proposed. As the piezoelectric film, a piezoelectric film made of a polymer material such as a fluorine-based resin or polylactic acid is known (see, for example, Patent Documents 1 and 2).

[0004] In order to apply these piezoelectric films to touch panels, it is preferred to directly configure indium tin oxide (ITO) as a transparent electrode on the piezoelectric film. When using ITO to form a transparent electrode, an ITO film can be formed on a substrate, and the crystallinity of the ITO can be increased by heat treatment, thereby reducing the resistance value of the transparent electrode and improving transparency. When the above-mentioned substrate is a glass substrate, it is heat-treated (annealed) at several hundred degrees Celsius. When the above-mentioned substrate is a polyethylene terephthalate (PET) film, it is heat-treated (annealed) at 140°C to 150°C. In the case of forming an ITO film on a piezoelectric film containing a fluorine-based resin, if it is treated at a high temperature as described above, there is a problem that the color is easily changed and high transparency cannot be maintained.

[0005] In contrast, Patent Documents 3 and 4 disclose transparent piezoelectric sheets in which a piezoelectric film and a transparent electrode film are laminated via a transparent adhesive layer. Patent Document 4 demonstrates that even with a transparent electrode disposed on the piezoelectric film via a transparent adhesive layer, not only can touch pressure be detected, but also the existing transparent electrode film can be used, thus maintaining high transparency.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2016 / 098597

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2011-006596

[0010] Patent Document 3: International Publication No. 2020 / 152464

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 2011-222679 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] However, according to the research conducted by the present inventors, when a laminated piezoelectric body comprising a piezoelectric film made of a fluorine-based resin and a transparent electrode film laminated via a transparent adhesive layer as disclosed in Patent Document 4 is used as a pressure sensitive sensor, a problem of low signal strength has been discovered.

[0014] If the signal strength is low, the electrical signal generated by pressure sensing is easily drowned out by noise, and the signal-to-noise ratio is likely to decrease. Therefore, there is a problem that the pressure cannot be detected with high sensitivity.

[0015] The present invention has been made in view of the above circumstances, and an object thereof is to provide a laminated piezoelectric body, a touch panel, and a method for manufacturing the laminated piezoelectric body that can detect a press with high sensitivity while maintaining transparency.

[0016] Solutions for solving problems

[0017] [1] A laminated piezoelectric body comprising: a piezoelectric film containing a fluorine-based resin as a main component, and a piezoelectric constant d 33 7 pC / N or more and 40 pC / N or less; a charge dispersion layer, disposed on at least one surface of the piezoelectric film, having a surface resistivity of 1.0×10 4 Ω / sq. or more and 1.0×10 12 Ω / sq. or less; a transparent electrode; and a transparent adhesive layer disposed between the transparent electrode and the charge dispersion layer, wherein the total light transmittance of the stacked piezoelectric body is 80% or more.

[0018] [2] The laminated piezoelectric body according to [1], wherein the charge dispersion layer has a thickness of 10 nm to 1000 nm.

[0019] [3] The laminated piezoelectric body according to [1] or [2], wherein the fluorine-based resin is a polymer containing a structural unit derived from vinylidene fluoride as a main component.

[0020] [4] The laminated piezoelectric body according to [3], wherein the fluorine-based resin is a vinylidene fluoride homopolymer.

[0021] [5] The laminated piezoelectric body according to any one of [1] to [4], wherein the transparent adhesive layer has a thickness of 10 μm to 100 μm.

[0022] [6] The stacked piezoelectric body according to any one of [1] to [5], wherein the thickness of the piezoelectric film is 25 μm or more and 120 μm or less.

[0023] [7] A touch panel comprising the stacked piezoelectric body according to any one of [1] to [6].

[0024] [8] A method for manufacturing a stacked piezoelectric body according to any one of [1] to [6], comprising the following steps: a step of preparing the piezoelectric film; a step of coating a charge dispersion layer composition on at least one surface of the piezoelectric film to form the charge dispersion layer; and a step of bonding the charge dispersion layer of the stacked body to a transparent electrode via the transparent adhesive layer.

[0025] [9] The method for manufacturing a stacked piezoelectric body according to [8], wherein, in the step of preparing the piezoelectric film, a film containing a fluorine-based resin as a main component is stretched and then subjected to polarization treatment.

[0026] Effects of the Invention

[0027] According to the present invention, a laminated piezoelectric body, a touch panel, and a method for manufacturing a laminated piezoelectric body capable of detecting a press with high sensitivity while maintaining transparency can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic cross-sectional view showing the structure of the stacked piezoelectric body according to this embodiment.

[0029] Figure 2 Schematic cross-sectional view of a stacked piezoelectric body showing a modified example. DETAILED DESCRIPTION

[0030] As described above, the reason why the signal intensity of the stacked piezoelectric body in which the piezoelectric film containing a fluorine-based resin as a main component and the transparent electrode film are stacked via a transparent adhesive layer is low is speculated as follows.

[0031] The polarization behavior generated when pressure is applied varies depending on the type of resin. For example, polylactic acid produces a piezoelectric constant d 14 Polarization. Specifically, when a piezoelectric film made of polylactic acid is subjected to pressure perpendicular to the film surface, the shear stress generated by the deflection of the film causes polarization in the direction perpendicular to the shear plane. Therefore, the charges that generate polarization on the film surface are not limited to the pressure range of the film but are easily generated over a relatively wide range of the film surface.

[0032] On the other hand, fluorine-based resins mainly have a piezoelectric constant d 33 Piezoelectricity. Piezoelectric constant d 33It means that when stress is applied in the three-axis direction (z-axis direction), polarization will occur in the three-axis direction. That is, when the piezoelectric film containing fluorine-based resin is subjected to pressure in the direction perpendicular to the film surface (three-axis direction), polarization of charge will occur in the perpendicular direction (three-axis direction). Therefore, polarization of charge is likely to occur locally in the range of pressure on the film surface, and the charge density of the pressure-bearing part becomes very high. In this part, the increase in charge density relative to stress may become saturated. Therefore, if the charge density becomes saturated, the electrode on the opposite side of the piezoelectric film separated by the transparent adhesive layer cannot fully sense the charge, and the signal strength is likely to become smaller.

[0033] Therefore, in the present invention, a charge dispersion layer is configured on at least one surface of a piezoelectric film containing a fluorine-based resin as a main component. Thus, even if a high charge density is locally generated in the piezoelectric film, the charge dispersion layer can be used to disperse and evenly distribute the charge. This prevents saturation of the charge density. Furthermore, even if the piezoelectric film and the transparent electrode film are stacked with a transparent adhesive layer, sufficient charge can be induced on the transparent electrode side, thereby increasing signal strength and improving detection sensitivity. A stacked piezoelectric body and a method for manufacturing the same according to one embodiment of the present invention are described below.

[0034] 1. Laminated piezoelectric

[0035] Figure 1 It is a schematic cross-sectional view showing the structure of the stacked piezoelectric body 100 according to this embodiment.

[0036] like Figure 1 As shown, the stacked piezoelectric body 100 of this embodiment includes a piezoelectric film 110 , a first charge dispersion layer 120 , a second charge dispersion layer 130 , a first transparent electrode film 140 , a second transparent electrode film 150 , a first transparent adhesive layer 160 , and a second transparent adhesive layer 170 .

[0037] Hereinafter, in this specification, the first charge dispersion layer 120 and the second charge dispersion layer 130 are collectively referred to as “charge dispersion layers”; the first transparent electrode film 140 and the second transparent electrode film 150 are collectively referred to as “transparent electrode films”; and the first transparent adhesive layer 160 and the second transparent adhesive layer 170 are collectively referred to as “transparent adhesive layers”.

[0038] 1-1. Piezoelectric Film 110

[0039] The piezoelectric film 110 contains a fluorine-based resin as a main component, and has a piezoelectric constant d 33 Adjust to 7 pC / N or more and 40 pC / N or less. 33 If the piezoelectric constant d of the piezoelectric film is 7 pC / N or more, the amount of charge generated by pressing is sufficient, so the pressure sensor can function with high sensitivity.33 If the piezoelectric constant d of the piezoelectric film is less than 40 pC / N, the unevenness of the film surface caused by the polarization treatment can be further reduced, thereby reducing the appearance defects. 33 It is more preferably 10 pC / N or more and 30 pC / N or less, and even more preferably 12 pC / N or more and 30 pC / N or less.

[0040] Piezoelectric constant d 33 It is one of the indicators that indicates the polarization behavior when a certain pressure is applied. 33 The larger it is, the greater the degree of polarization produced when subjected to a certain pressure, and the greater the charge density.

[0041] The piezoelectric constant d of the piezoelectric film 110 33 It can be calculated by measuring the charge generated when stress is applied along the thickness direction of the piezoelectric film at a constant speed, and can be calculated by using the direct quasi-static method (d 33 The piezoelectric constant d of the piezoelectric ceramics (measurement method, Berlincourt method) 33 The test method ISO 19622:2018 is used to determine the piezoelectric constant d 33 Specifically, a piezoelectric constant measuring device (eg, Piezometer System PM300 manufactured by PIEZOTEST) is used to clamp a sample of the piezoelectric film at 1 N, and the generated charge when a force of 0.15 N and 110 Hz is applied is read.

[0042] The piezoelectric constant d of the piezoelectric film 110 33 The piezoelectric constant d of the piezoelectric film 110 can be adjusted mainly by the type of resin contained in the piezoelectric film 110 and the manufacturing conditions (polarization treatment and stretching treatment conditions). For example, among fluorine-based resins, the more the resin contains structural units derived from vinylidene fluoride, the higher the piezoelectric constant d of the piezoelectric film. 33 In addition, by enhancing the polarization treatment and stretching treatment, the piezoelectric constant d of the piezoelectric film is increased. 33 Easy to grow bigger.

[0043] As described above, the piezoelectric film 110 contains a fluorine-based resin as a main component. "Containing a fluorine-based resin as a main component" means that, in the total mass of the resin constituting the piezoelectric film, the content of resin containing the fluorine-based resin as a structural unit (including the fluorine-based resin itself) is 50% by mass or greater. The content of the fluorine-based resin is preferably 60% by mass or greater, more preferably 80% or greater. The upper limit of the above content is not particularly limited and may be 100% by mass or less, or 90% by mass or less.

[0044] From the viewpoint of easily obtaining a high piezoelectric effect also in a fluorine-based resin, the fluorine-based resin is preferably a polymer containing a structural unit derived from vinylidene fluoride as a main component.

[0045] The content of the structural unit derived from vinylidene fluoride in the polymer comprising the structural unit derived from vinylidene fluoride as the main component is relative to the total amount of the structural unit of the above-mentioned polymer, preferably 50 mass % or more, more preferably 70 mass % or more, further preferably 80 mass % or more, particularly preferably 90 mass % or more. The more above-mentioned content, the easier it is to obtain a higher piezoelectric effect. The upper limit value of above-mentioned content is not particularly limited, and can be 100 mass % or less, or can be 90 mass % or less.

[0046] The polymer may further comprise structural units derived from monomers copolymerizable with vinylidene fluoride, without prejudice to the effects of the present invention. Examples of monomers copolymerizable with vinylidene fluoride include fluorinated monomers such as trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and vinyl fluoride. It should be noted that these monomers may comprise two or more.

[0047] Among them, it is easy to increase the piezoelectric constant d of the piezoelectric film 33 From the viewpoint of improving the sensitivity of a pressure-sensitive sensor using the piezoelectric film, the piezoelectric film is preferably made of a vinylidene fluoride homopolymer.

[0048] The thickness of the piezoelectric film 110 is preferably, for example, not less than 25 μm and not more than 120 μm. When the thickness of the piezoelectric film is not less than 25 μm, the amount of charge generated by the piezoelectric effect is greater, and it is easier to increase the signal strength. The thickness of the piezoelectric film is more preferably not less than 30 μm, and further preferably not less than 35 μm. When the thickness of the piezoelectric film is not more than 120 μm, the transparency of the piezoelectric film is less likely to be impaired, and it is more preferably not more than 100 μm, and further preferably not more than 80 μm. From the same point of view, the thickness of the piezoelectric film is more preferably not less than 35 μm and not more than 80 μm.

[0049] 1-2. First Charge Dispersion Layer 120 and Second Charge Dispersion Layer 130

[0050] (First Charge Dispersion Layer 120)

[0051] The first charge dispersion layer 120 is disposed on one surface of the piezoelectric film. Furthermore, by increasing the mobility within the charge dispersion layer of polarized charges generated locally on one surface of the piezoelectric film 110 due to pressure, the first charge dispersion layer 120 can reduce saturation and missed counts that occur during polarized charge detection, thereby improving the sensitivity of the piezoelectric sensor.

[0052] The first charge dispersion layer 120 has electrical conductivity. One of the indicators of electrical conductivity is surface resistivity. The surface resistivity of the first charge dispersion layer 120 is 1.0×10 4 Ω / sq. or more and 1.0×10 12Ω / sq. or less. When the surface resistivity is 1.0×10 12 When the surface resistivity is less than 1.0×10 Ω / sq., the first charge dispersion layer 120 has sufficient conductivity. Therefore, the charge generated by pressing the pressing portion of the piezoelectric film 110 easily migrates within the charge dispersion layer, and when detecting polarized charge, it can be detected as a signal without saturation or missing counts. This can improve the signal strength even in a laminated piezoelectric body with a transparent adhesive layer. On the other hand, when the surface resistivity is 1.0×10 4 Ω / sq. or more, the transparency of the first charge dispersion layer 120 is less likely to be impaired. From the same viewpoint, the surface resistivity of the first charge dispersion layer 120 is more preferably 1.0×10 4 Ω / sq or more and 1.0×10 9 Ω / sq or less, particularly preferably 1.0×10 6 Ω / sq or more and 1.0×10 9 The surface resistivity can be measured, for example, using a known resistivity meter in accordance with JIS K 6911.

[0053] The surface resistivity can be adjusted by adjusting the thickness of the first charge dispersion layer 120 and the type and content of the conductive polymer and conductive material contained in the first charge dispersion layer 120. For example, increasing the thickness of the first charge dispersion layer 120 reduces the surface resistivity. Furthermore, increasing the content of the conductive polymer and conductive material in the first charge dispersion layer 120 further reduces the surface resistivity.

[0054] The first charge dispersion layer 120 may be configured so as to have a surface resistivity within the above-mentioned range. The first charge dispersion layer 120 may include a conductive polymer or a conductive material other than a conductive polymer. In this embodiment, the first charge dispersion layer 120 may also include a cured product of a curable composition containing a conductive polymer or a conductive material other than a conductive polymer, a polymerizable compound, and an optional curing agent.

[0055] Examples of conductive polymers include polyacetylene or its derivatives, polythiophene or its derivatives, polypyrrole or its derivatives, polyaniline or its derivatives, polyphenylene or its derivatives, polyphenylene vinylene or its derivatives, polynaphthalene or its derivatives, polyacene or its derivatives, etc. Among them, polythiophene or its derivatives are preferred from the viewpoint of high transparency and high conductivity.

[0056] Examples of the conductive material include carbon nanotubes and graphene.

[0057] The polymerizable compound can be a thermally polymerizable compound or a photopolymerizable compound, and examples thereof include an acrylic compound, an epoxy compound, an oxetane compound, a urethane compound, a polyimide resin, a melamine resin, a silicone compound, and a vinyl acetate.

[0058] The thickness of the first charge dispersing layer 120 is preferably, for example, 10 nm or more and 1000 nm or less, as long as the thickness is a range in which the electric charges generated in the piezoelectric film 110 are dispersed. If the thickness of the first charge dispersing layer 120 is 10 nm or more, the polarization charges generated on the surface of the piezoelectric film 110 are more likely to migrate within the charge dispersing layer, and the saturation and the missing counts generated at the time of detection of the polarization charges can be further reduced, so that the signal intensity is more likely to be further improved. If the thickness of the first charge dispersing layer 120 is 1000 nm or less, the color caused by the electrically conductive polymer and the appearance defect caused by the unevenness of the surface of the piezoelectric film 110 are less likely to occur, and the transparency is less likely to be impaired. From the same viewpoint, the thickness of the first charge dispersing layer 120 is more preferably 20 nm or more and 800 nm or less, further preferably 30 nm or more and 600 nm or less, and particularly preferably 40 nm or more and 400 nm or less.

[0059] (Second charge dispersing layer 130)

[0060] The second charge dispersing layer 130 is provided on the other surface of the piezoelectric film 110. With respect to the piezoelectric film having a piezoelectric constant d 33 , electric charges are polarized on both surfaces of the piezoelectric film in response to the pressure. Therefore, the charge dispersing layer is preferably provided on both surfaces of the piezoelectric film. On the other surface of the piezoelectric film on which the first charge dispersing layer is provided, the second charge dispersing layer 130 also functions to improve the mobility of the polarization charges locally generated in response to the pressure within the charge dispersing layer, thereby reducing the saturation and the missing counts generated at the time of detection of the polarization charges and improving the sensitivity of the piezoelectric sensor, as described above.

[0061] In the present embodiment, the second charge dispersing layer 130 has the same or similar configuration as the first charge dispersing layer 120 described above, and the detailed description is omitted. That is, the configuration, the material, and the physical properties of the second charge dispersing layer 130 are the same as those of the first charge dispersing layer 120 described above.

[0062] Note that the composition of the first charge dispersing layer 120 can be the same as or different from the composition of the second charge dispersing layer 130. In addition, the thickness of the first charge dispersing layer 120 can be the same as or different from the thickness of the second charge dispersing layer 130.

[0063] 1-3. First transparent electrode film 140 and second transparent electrode film 150

[0064] (First Transparent Electrode Film 140)

[0065] The first transparent electrode film 140 is disposed on the first charge dispersion layer 120 side relative to the piezoelectric film 110. The first transparent electrode film 140 includes a base layer 141 and a first transparent electrode 142. The first transparent electrode 142 detects the charges generated in the piezoelectric film 110 as electrical signals via the first charge dispersion layer 120.

[0066] The base layer 141 is a transparent resin layer for supporting the first transparent electrode 142. The transparent resin contained in the base layer 141 is preferably a material having heat resistance to withstand the heat used to crystallize ITO, etc. Examples of such transparent resins include polyesters such as polyethylene terephthalate (PET). Among them, PET is preferred.

[0067] The thickness of the base material layer 141 is not particularly limited as long as it can support the first transparent electrode 142, and is preferably 2 μm to 300 μm, more preferably 10 μm to 200 μm, further preferably 20 μm to 150 μm, and particularly preferably 30 μm to 130 μm.

[0068] The first transparent electrode 142 is disposed on the first charge dispersion layer 120 side surface of the base layer 141. As the first transparent electrode 142, for example, an inorganic electrode such as ITO (indium tin oxide) or tin oxide is preferable, and ITO is more preferable.

[0069] (Second Transparent Electrode Film 150)

[0070] The second transparent electrode film 150 is disposed on the second charge dispersion layer 130 side relative to the piezoelectric film 110. The second transparent electrode film 150 includes a substrate layer 151 and a second transparent electrode 152. The second transparent electrode 152 extracts the charge generated by the piezoelectric film 110 in the form of an electrical signal via the second charge dispersion layer 130.

[0071] In this embodiment, the second transparent electrode film 150 has the same configuration as the first transparent electrode film 140 . That is, the configuration, material, and physical properties of the second transparent electrode film 150 may be the same as those of the first transparent electrode film 140 .

[0072] It should be noted that the composition of the first transparent electrode 142 constituting the first transparent electrode film 140 and the composition of the second transparent electrode 152 constituting the second transparent electrode film 150 may be the same as or different from each other.

[0073] 1-4. First Transparent Adhesive Layer 160 and Second Transparent Adhesive Layer 170

[0074] (First Transparent Adhesive Layer 160)

[0075] The first transparent adhesive layer 160 is disposed between the first charge dispersion layer 120 and the first transparent electrode 142 , so as to bond the piezoelectric film 110 on which the first charge dispersion layer 120 is disposed to the first transparent electrode 142 .

[0076] The first transparent adhesive layer 160 is preferably transparent and has sufficient elasticity to transmit a pressing force to the piezoelectric film 110. Examples of adhesives included in the first transparent adhesive layer 160 include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, polyurethane adhesives, polyamide adhesives, epoxy adhesives, vinyl alkyl ether adhesives, and fluorine adhesives. Among these, acrylic adhesives are preferred from the perspectives of adhesiveness and elasticity.

[0077] The thickness of the first transparent adhesive layer 160 is not particularly limited, but is preferably 10 μm to 100 μm, more preferably 15 μm to 80 μm, and even more preferably 20 μm to 60 μm. A thickness of 10 μm or greater facilitates better adhesion between the first charge dispersion layer 120 and the first transparent electrode 142. A thickness of 100 μm or less, preferably 60 μm or less, increases the amount of charge extracted from the first charge dispersion layer 120, further enhancing signal strength.

[0078] (Second transparent adhesive layer 170)

[0079] The second transparent adhesive layer 170 is disposed between the second charge dispersion layer 130 and the second transparent electrode 152 to bond the piezoelectric film 110 on which the second charge dispersion layer 130 is disposed to the second transparent electrode 152. The adhesive contained in the second transparent adhesive layer 170 is the same as the adhesive contained in the first transparent adhesive layer 160 described above. The adhesive contained in the second transparent adhesive layer 170 may be the same as or different from the adhesive contained in the first transparent adhesive layer 160.

[0080] 1-5. Other layers

[0081] The laminated piezoelectric body 100 may further include other layers other than those described above, without impairing the effects of the present invention. For example, a hard coat layer may be further disposed between the first charge dispersion layer 120 and the first transparent adhesive layer 160 or between the second charge dispersion layer 130 and the second transparent adhesive layer 170.

[0082] Note that the thickness of each layer constituting the laminated piezoelectric body 100 can be measured using a spectroscopic interferometric film thickness meter (for example, "Optical Nano Gauge C13027-11" manufactured by Hitachi High-Tech Science Corporation) at three or more points at intervals of 5 mm in a range including the center of the face of the laminated piezoelectric body 100, and the arithmetic mean value thereof can be calculated to obtain. Note that the refractive index of each layer can be measured by the method described in JIS K 7142, and the refractive index can be set by determining the main material constituting each layer. For example, the refractive index of the piezoelectric film including PVDF can be set to 1.42, and the refractive index of the first charge dispersion layer 120 and the second charge dispersion layer 130 can be set to 1.50.

[0083] 1-6. Physical properties

[0084] The laminated piezoelectric body 100 has high transparency. The total light transmittance of the laminated piezoelectric body 100 is preferably, for example, 80% or more. The total light transmittance of the laminated piezoelectric body 100 can be measured using a haze meter (for example, NDH7000 SPII manufactured by Nippon Denshoku Industries Co., Ltd.) based on the method described in JIS K 7361-1.

[0085] 1-7. Action

[0086] As described above, the laminated piezoelectric body 100 of the above-described embodiment generates polarization in the 3-axis direction when a stress is applied in a direction perpendicular to the surface of the piezoelectric film 110 (3-axis direction), and exhibits a piezoelectric effect. Thus, charges are induced in the surface of the piezoelectric film 110, and the charge density of the surface of the piezoelectric film 110 is distributed according to the pressure distribution of the pressing.

[0087] In the present embodiment, the first charge dispersion layer 120 and the second charge dispersion layer 130 are provided on the surface of the piezoelectric film 110. Thus, it is possible to eliminate the distribution of the charge density locally generated on the surface of the piezoelectric film 110 and make it uniform. Thus, it is possible to detect the pressing with high sensitivity, and therefore, in the case where the laminated piezoelectric body is used as a pressure-sensitive sensor for a touch panel, the detection sensitivity to the pressing operation is high.

[0088] 2. Method for manufacturing laminated piezoelectric body

[0089] The laminated piezoelectric body of the present embodiment can be manufactured by the following steps: (1) a step of preparing a laminate including a piezoelectric film and a charge dispersion layer; and (2) a step of joining the charge dispersion layer of the prepared laminate and a transparent electrode of a transparent electrode film with a transparent adhesive layer. Note that the piezoelectric film, the charge dispersion layer, the transparent adhesive layer, and the transparent electrode film are the piezoelectric film, the charge dispersion layer, the transparent adhesive layer, and the transparent electrode film described above, respectively.

[0090] (1) Step of preparing laminate

[0091] The laminate can be obtained through the following steps: (1-1) obtaining a piezoelectric film containing a fluorine-based resin; and (1-2) forming a charge dispersion layer on at least one surface of the obtained piezoelectric film.

[0092] (1-1) Process for manufacturing a piezoelectric film

[0093] The piezoelectric film can be obtained by subjecting a film containing a fluorine-based resin to a polarization treatment. The film containing the fluorine-based resin may be a stretched film or an unstretched film. In this embodiment, from the perspective of exhibiting a high piezoelectric effect, it is preferred that the film containing the fluorine-based resin be stretched and then polarized.

[0094] The film comprising the fluorine-based resin can be manufactured by any method such as melt extrusion, solution casting, etc. Among them, the film comprising the fluorine-based resin is preferably manufactured by melt extrusion. In the melt extrusion method, the fluorine-based resin and any additives can be heated and melted in the barrel of an extruder and then extruded from a die head to obtain a film.

[0095] The resulting film has a structure that is a mixture of α-type crystals (with a helical main chain structure) and β-type crystals (with a planar zigzag main chain structure). β-type crystals have a highly polarizable structure. Stretching the film can convert α-type crystals to β-type crystals. The stretching process can be performed as needed to convert the fluororesin into β-type crystals.

[0096] The stretching method is not particularly limited, and a known stretching method such as a tenter method and a roll method can be used.

[0097] The stretching ratio is, for example, 3.0 times or more and 6.0 times or less. If the stretching ratio is 3.0 times or more, it is not only easy to adjust the thickness and strength of the film to a suitable range, but also more likely to produce polarization. If the stretching ratio is 3.0 times or more, the rearrangement reaction of the β-type crystal will fully proceed, not only easily showing higher piezoelectricity, but also can further improve transparency. If the stretching ratio is 6.0 times or less, then the fracture caused by stretching can be further suppressed.

[0098] The obtained stretched film is subjected to a polarization treatment. The polarization treatment can be performed, for example, by applying a DC voltage between a ground electrode and a needle-shaped electrode. The voltage can be adjusted according to the thickness of the stretched film and can be, for example, from 1 kV to 50 kV.

[0099] In this embodiment, a piezoelectric film can be obtained by polarizing the stretched film as described above. (1-2) Step of forming a charge dispersion layer

[0100] A curable composition containing, for example, the above-mentioned conductive polymer or conductive material is applied to the surface of the obtained piezoelectric film, and then dried and cured to form a charge dispersion layer.

[0101] In addition to the above components, the composition may further contain water and a solvent. Examples of the solvent include alcohol solvents such as methanol, ethanol, and isopropanol.

[0102] The coating method is not particularly limited, and may be any of spin coating, gravure coating, die coating, bar coating, and dip coating.

[0103] The composition can be dried by heating the applied composition. The heating temperature is preferably above a temperature at which the solvent can be removed and below the heat deformation temperature of the fluorine-based resin constituting the piezoelectric film, and can be, for example, 100°C to 150°C. The heat deformation temperature can be measured, for example, in accordance with JIS K 7191-2:2015. Furthermore, the composition can be cured by light curing or heat curing. In the case of heat curing, drying and heat curing can be performed simultaneously.

[0104] (2) About the bonding process

[0105] The charge dispersion layer and the transparent electrode film of the laminate are bonded together via a transparent adhesive layer.

[0106] The lamination method is not particularly limited and can be performed by laminating a transparent adhesive layer on the charge dispersion layer of the laminate and then laminating the transparent adhesive layer to the transparent electrode film with the transparent electrode of the transparent electrode film facing the transparent adhesive layer.

[0107] The laminated piezoelectric body of this embodiment can be used in various applications. In particular, the laminated piezoelectric body of this embodiment has high transparency and can detect pressure with high sensitivity, and can therefore be preferably used as a pressure-sensitive sensor for touch panels mounted on various electronic devices.

[0108] 3. Modifications

[0109] It should be noted that, in the above embodiment, the charge dispersion layers are disposed on both surfaces of the piezoelectric film, but they may be disposed on only one surface.

[0110] Figure 2 : is a schematic cross-sectional view showing a modified example of a stacked piezoelectric body 100. Figure 2 As shown, the stacked piezoelectric body 100 of the modified example can be configured as in the above embodiment except that the second charge dispersion layer 130 is omitted. Furthermore, if the stacked piezoelectric body 100 includes other layers, the other layers may be included between the piezoelectric film 110 and the second transparent electrode 152.

[0111] Example

[0112] The present invention will be further described below with reference to Examples and Comparative Examples, but the technical scope of the present invention is not limited thereto.

[0113] 1. Evaluation of physical properties

[0114] (1) Thickness of the charge dispersion layer

[0115] The thickness of the charge dispersion layer formed on the piezoelectric film was measured using a spectroscopic interferometry film thickness meter (Optical NanoGauge C13027-11, manufactured by Hamamatsu Photonics). Specifically, the thickness was measured at 30 locations at 5 mm intervals, including the center of the surface of the charge dispersion layer on the piezoelectric film, and the arithmetic mean was calculated. The refractive index of each layer was set according to the material of each layer; the piezoelectric film made of PVDF was set to 1.42, and the charge dispersion layer was set to 1.50.

[0116] (2) Surface resistivity

[0117] The piezoelectric film with the charge dispersion layer formed thereon was cut into a 100 mm x 100 mm sample film. The surface resistivity of the charge dispersion layer of the sample film was measured using a surface resistivity meter F-109 (manufactured by Hozan Co., Ltd.) in accordance with JIS 6911. The measurement conditions were an output of 100 W, and the value was read after 10 seconds.

[0118] (3) Piezoelectric constant (piezoelectric constant d 33 )

[0119] Based on the direct quasi-static method (d 33 The piezoelectric constant d of the piezoelectric ceramics (measurement method, Berlincourt method) 33 Test method ISO 19622:2018, determination of the piezoelectric constant d 33 Specifically, for the piezoelectric constant d of the piezoelectric film 33 Using a piezoelectric constant measuring device ("PiezoMeter System PM300", manufactured by PIEZOTEST), the sample was clamped at 1N and the generated charge was read when a force of 0.15N and 110Hz was applied. 33 The measured values ​​are positive or negative depending on the front or back of the film at a measurement temperature of 25° C., but absolute values ​​are described in this specification.

[0120] (piezoelectric constant d 14 )

[0121] Al was vapor-deposited on both surfaces of the piezoelectric film. The film was then cut into 120 mm sections at a 45° angle relative to the piezoelectric film's stretching direction (MD), and into 10 mm sections perpendicular to the 45° angle, resulting in a 120 mm x 10 mm rectangular film. This was used as a sample for measurement.

[0122] Next, the sample is placed in a tensile testing machine with a distance of 70 mm between the chucks in a non-relaxed manner. Then, a force is periodically applied to the sample at a speed of 5 mm / min, with the applied force reciprocating between 4 N and 9 N. At this time, in order to measure the amount of charge generated in the sample according to the applied force, a capacitor with an electrostatic capacitance Qm (F) is connected in parallel with the sample, and the terminal voltage Vm of the capacitor Cm (95 nF) is measured via a buffer amplifier. The amount of charge Q (C) generated is calculated by the product of the capacitor capacitance Cm and the terminal voltage Vm. Piezoelectric constant d 14 Calculated by the following formula.

[0123] d 14 =(2×t) / L×Cm·ΔVm / ΔF

[0124] t: sample thickness (m).

[0125] L: distance between chucks (m).

[0126] Cm: Capacitance of the parallel connected capacitor (F).

[0127] ΔVm / ΔF: The ratio of the change in voltage across the capacitor terminals to the change in force.

[0128] 2. Fabrication and Evaluation of Laminated Piezoelectrics

[0129] [Example 1]

[0130] (1) Fabrication of piezoelectric film

[0131] A polyvinylidene fluoride film (manufactured by Kureha Co., Ltd., containing 100% by mass of a vinylidene fluoride homopolymer) was stretched in the MD direction at a stretch ratio of 4.2 times. A polarization treatment was then performed by applying a DC voltage between a ground electrode and a needle-shaped electrode while increasing the DC voltage from 0 kV to 11.0 kV. This produced a piezoelectric film with a thickness of 42 μm.

[0132] (2) Formation of charge dispersion layer

[0133] On the A surface of the obtained piezoelectric film, a solution prepared by mixing liquid A of coating P-400MP-A (manufactured by Nagase ChemteX Co., Ltd.) containing PEDOT:PSS as a conductive polymer and liquid B of coating P-400MP-B (manufactured by Nagase ChemteX Co., Ltd.) in a ratio of 4:1 was applied using a gravure coater (Multi-Coater manufactured by Hirano Tecseed Co., Ltd.), and heat treated at 130°C for 1 minute to form a charge dispersion layer with a thickness of 50 nm.

[0134] (3) Formation of transparent adhesive layer

[0135] Next, optical clear adhesive (OCA) sheets (Nitto Denko Corporation, CS9862UA, 50 μm thick) were attached to the charge dispersion layer formed on the A surface of the piezoelectric film and to the B surface of the piezoelectric film, respectively.

[0136] (4) Fabrication of transparent electrode film

[0137] Next, a transparent electrode precursor film (Tetolight TCF KH100NMH3-100-U8, manufactured by Oike Industry Co., Ltd.) prepared by sputtering indium tin oxide (ITO) on a polyethylene terephthalate (PET) film was crystallized at 150° C. for 90 minutes to prepare a transparent electrode film.

[0138] (5) Fabrication of laminated piezoelectric bodies

[0139] The ITO surface of the transparent electrode film was then laminated to the OCA sheet of the charge dispersion layer attached to the A side of the piezoelectric film and the OCA sheet attached to the B side. A 1.1 mm thick glass was further laminated to the transparent electrode film on the A side of the piezoelectric film to create a laminated piezoelectric body.

[0140] [Example 2]

[0141] A laminated piezoelectric body was obtained in the same manner as in Example 1 except that the thickness of the charge dispersion layer was set to 130 nm.

[0142] [Example 3]

[0143] A charge dispersion layer with a thickness of 50 nm was formed on the A surface of the piezoelectric film by the same method as in Example 1. Then, a coating material MT-3 (Arakawa Chemical Industries, Ltd.) containing PEDOT:PSS was applied to the B surface of the piezoelectric film, dried at 80°C, and then irradiated with a UV irradiation device (CSOT-40, manufactured by GS Yuasa Co., Ltd.) at a concentration of 400 mJ / cm 2The accumulated light amount was irradiated with ultraviolet rays to form a charge dispersion layer with a thickness of 700 nm.

[0144] Then, OCA sheets were laminated to the charge dispersion layers on the A and B surfaces of the piezoelectric body, and transparent electrode films were laminated to each OCA sheet. 1.1 mm thick glass was further laminated to the transparent electrode film on the A surface side of the piezoelectric film to obtain a laminated piezoelectric body.

[0145] [Example 4]

[0146] A laminated piezoelectric body was obtained in the same manner as in Example 1 except that the thickness of the OCA sheet was set to 25 μm.

[0147] [Example 5]

[0148] The coating liquid A was changed to coating C-169PF-A (Nagase ChemteX Co., Ltd.) containing single-walled carbon nanotubes, the coating liquid B was changed to coating C-169PF-B (Nagase ChemteX Co., Ltd.), and the mixing ratio of liquid A to liquid B was changed to 3:2. Except for this, a stacked piezoelectric body was obtained in the same manner as in Example 1.

[0149] [Comparative Example 1]

[0150] A laminated piezoelectric body was obtained in the same manner as in Example 1 except that the charge dispersion layer was not formed.

[0151] [Comparative Example 2]

[0152] (1) Fabrication of piezoelectric film

[0153] A raw material was prepared by adding 1.0 part by mass of a stabilizer (a mixture of 10 parts by mass of Stabaxol P400, 70 parts by mass of Stabaxol I, and 20 parts by mass of Carbodilite LA-1) from Nisshinbo Chemical Co., Ltd.) to 100 parts by mass of polylactic acid (product name: Ingeo™ biopolymer) manufactured by NatureWorks LLC and dry-blending the mixture. This raw material was placed in the hopper of an extruder and extruded through a T-die while being heated to 210°C. The extruder then contacted a casting roll at 50°C to form a pre-crystallized film with a thickness of 150 μm. The pre-crystallized film was uniaxially stretched to 3.5 times in the machine direction at 70°C in a roll-to-roll manner to obtain a uniaxially stretched film. The film thickness was 49.2 μm. Next, the uniaxially stretched film was brought into contact with a roll at 145° C. for 15 seconds in a roll-to-roll manner to perform an annealing treatment, and then rapidly cooled to produce a polylactic acid-based piezoelectric film.

[0154] (2) Formation of antistatic hard coating

[0155] An antistatic hard coating (SEPLEGYDA (registered trademark) HC-A manufactured by Shin-Etsu Polymer) was applied to one side of the obtained piezoelectric film using an applicator, dried at 60°C for 5 minutes, and then irradiated with a metal halide lamp at a cumulative light intensity of 1000 mJ / cm 2 Ultraviolet rays are applied to form an antistatic hard coating on one side of the piezoelectric film.

[0156] (3) Fabrication of laminated piezoelectric bodies

[0157] An OCA sheet was laminated to the film surface and antistatic hard coat surface of the obtained piezoelectric film in the same manner as in Example 1, followed by a transparent electrode film. A 1.1 mm thick glass was further laminated to the transparent electrode film on the A-side of the piezoelectric film to obtain a laminated piezoelectric body.

[0158] [evaluate]

[0159] The total light transmittance and the pressing signal of the laminated piezoelectric bodies of Examples 1 to 5 and Comparative Examples 1 and 2 were evaluated by the following methods.

[0160] (Total light transmittance)

[0161] The total light transmittance of each of the laminated piezoelectric bodies of Examples and Comparative Examples was measured using a haze meter ("NDH7000SPII", manufactured by Nippon Denshoku Industries, Ltd.) in accordance with the method described in JIS K 7361-1.

[0162] (Detection of pressure signal)

[0163] A stacked piezoelectric body with a length of 171.7 mm in the longitudinal direction and 233.5 mm in the lateral direction was set in a touch panel linear evaluation system (manufactured by Japan Novel Co., Ltd.) in such a way that the stretching direction of the piezoelectric film was 1-axis and the thickness direction was 3-axis. The center of the glass surface of the stacked piezoelectric body was pressed with a force of 8 N using the robot's pressing terminal (diameter of the front end was 3 mm) from the 3-axis direction, and the signal intensity obtained at this time was measured.

[0164] To detect the pressure signal, positive and negative leads are drawn from the terminals of the ITO electrodes of the laminated piezoelectric body and connected to an amplifier. The voltage signal amplified by the amplifier is then converted to a digital signal via an A / D converter and a filter circuit. The resulting digital signal is then accumulated to calculate the piezoelectric signal strength.

[0165] Table 1 shows the configurations and evaluation results of the laminated piezoelectric bodies of Examples 1 to 5 and Comparative Examples 1 and 2.

[0166] [Table 1]

[0167]

[0168] As shown in Table 1, the stacked piezoelectric device of Comparative Example 1, in which no charge dispersion layer is provided on the piezoelectric film comprising a fluorine-based resin, exhibits low signal strength. Furthermore, the stacked piezoelectric device of Comparative Example 2, in which a piezoelectric film comprising polylactic acid is used, exhibits low signal strength regardless of whether or not a charge dispersion layer is provided.

[0169] In contrast, it was found that Examples 1 to 5 in which a charge dispersion layer was provided on at least one surface of a piezoelectric film made of a fluorine-based resin all maintained high transparency and had high signal strength.

[0170] In particular, it was found that providing charge dispersion layers on both surfaces of the piezoelectric film made of a fluorine-based resin further improved the signal intensity (comparison between Examples 1 and 3).

[0171] Furthermore, it was found that the signal intensity can be further improved by reducing the thickness of the transparent adhesive layer (comparison between Examples 1 and 4).

[0172] Furthermore, it is known that by setting the surface resistance of the charge dispersion layer to 7.1×10 6 Ω, which can further improve the signal strength (comparison between Examples 1 and 5).

[0173] This application claims the benefit of priority based on Japanese Patent Application No. 2023-48026, filed on March 24, 2023. The entire contents of the specification and drawings of that application are incorporated herein by reference.

[0174] Industrial applicability

[0175] According to the present invention, a laminated piezoelectric body and a touch panel can be provided that can detect a press with high sensitivity while maintaining transparency. Therefore, the laminated piezoelectric body is suitable as a pressure-sensitive sensor for a touch panel.

[0176] Description of Reference Numerals

[0177] 100: stacked piezoelectric body;

[0178] 110: piezoelectric film;

[0179] 120: first charge dispersion layer;

[0180] 130: second charge dispersion layer;

[0181] 140: first transparent electrode film;

[0182] 150: second transparent electrode film;

[0183] 160: first transparent adhesive layer;

[0184] 170: Second transparent adhesive layer.

Claims

1. A laminated piezoelectric body comprising: The piezoelectric film contains fluorine resin as a main component, and the piezoelectric constant d 33 7pC / N or more and 40pC / N or less; The charge dispersion layer is disposed on at least one surface of the piezoelectric film and has a surface resistivity of 1.0×10 4 Ω / sq. or more and 1.0×10 12 Ω / sq. or less; Transparent electrodes; as well as A transparent adhesive layer is disposed between the transparent electrode and the charge dispersion layer. The total light transmittance of the stacked piezoelectric body is greater than 80%.

2. The laminated piezoelectric body according to claim 1, wherein The charge dispersion layer has a thickness of 10 nm to 1000 nm.

3. The laminated piezoelectric body according to claim 1, wherein The fluorine-based resin is a polymer containing a structural unit derived from vinylidene fluoride as a main component.

4. The laminated piezoelectric body according to claim 3, wherein The fluorine-based resin is a vinylidene fluoride homopolymer.

5. The laminated piezoelectric body according to claim 1, wherein The transparent adhesive layer has a thickness of 10 μm or more and 100 μm or less. The laminated piezoelectric body according to claim 1 , wherein: The piezoelectric film has a thickness of 25 μm or more and 120 μm or less. 7 . A touch panel comprising the laminated piezoelectric body according to claim 1 .

8. A method for manufacturing a stacked piezoelectric body, which is the method for manufacturing a stacked piezoelectric body according to claim 1, comprising the following steps: A step of preparing the piezoelectric film; A step of coating a charge dispersion layer composition on at least one surface of the piezoelectric film to form the charge dispersion layer; and a step of laminating the charge dispersion layer and the transparent electrode via a transparent adhesive layer.

9. The method for manufacturing a laminated piezoelectric body according to claim 8, wherein: In the step of preparing the piezoelectric film, a film containing a fluorine-based resin as a main component is stretched and then subjected to a polarization treatment.

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