Multilayer piezoelectric material, touch panel, and method for manufacturing a multilayer piezoelectric material

Abstract

A laminated piezoelectric body having a piezoelectric film that contains a fluorine-based resin as a main component and has a piezoelectric constant d33 of 7 to 40 pC / N, a charge dispersion layer that is disposed on at least one surface of the piezoelectric film and has a surface resistivity of 1.0×104 to 1.0×1012 Ω / sq, 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 is 80% or greater.

Description

[Technical Field]

[0001] The present invention relates to a laminated piezoelectric material, a touch panel, and a method for manufacturing a laminated piezoelectric material. [Background technology]

[0002] Generally, touch panels detect the two-dimensional position of the touch panel surface by touching it with a finger or pen. To avoid misinterpretation of input on a touch panel, it is desirable that selection and execution be separated. Specifically, it is desirable that the two-dimensional position of the touch surface be selected, and that the selection be executed by applying pressure to the touch surface. Therefore, the application of pressure-sensitive sensors to touch panels to detect pressure on the touch surface is being considered.

[0003] As the pressure sensor described above, the application of a piezoelectric film that generates a voltage in response to pressure has been proposed. Piezoelectric films made of polymer materials such as fluororesins and polylactic acid are known (see, for example, Patent Documents 1 and 2).

[0004] To apply these piezoelectric films to touch panels, it is preferable to directly place indium tin oxide (ITO) as a transparent electrode on the piezoelectric film. To form a transparent electrode using ITO, an ITO film is formed on a substrate, and the crystallinity of the ITO is increased by heat treatment, thereby reducing the resistance of the transparent electrode and increasing its transparency. The above-mentioned substrate is heat-treated (annealed) at several hundred degrees Celsius if it is a glass substrate, and at 140-150°C if it is a polyethylene terephthalate (PET) film. When an ITO film is formed on a piezoelectric film containing a fluororesin, there was a problem that the color tended to change when treated at the high temperatures described above, making it difficult to maintain high transparency.

[0005] In contrast, Patent Documents 3 and 4 disclose a transparent piezoelectric sheet in which a piezoelectric film and a transparent electrode film are laminated via a transparent adhesive layer. In Patent Document 4, even when a transparent electrode is disposed on the piezoelectric film via a transparent adhesive layer, it is possible not only to detect a touch pressure but also to use an existing transparent electrode film, so that high transparency can be maintained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, according to the studies by the present inventors, when a laminated piezoelectric body in which a transparent electrode film is laminated on a piezoelectric film containing a fluorine-based resin via a transparent adhesive layer is used as a pressure-sensitive sensor as shown in Patent Document 4, a problem has been found that the signal strength is small.

[0008] When the signal strength is small, the electrical signal generated by the pressure sensitivity is likely to be buried in noise, and the S / N ratio is likely to be low. Therefore, there has been a problem that the pressing cannot be detected with high sensitivity.

[0009] 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 a laminated piezoelectric body that can detect pressing with high sensitivity while maintaining transparency.

Means for Solving the Problems

[0010] [1] A laminated piezoelectric body that contains a fluororesin as a main component and has a piezoelectric constant d 33 of 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 and 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, and the laminated piezoelectric body having a total light transmittance of 80% or more. [2] The laminated piezoelectric body according to [1], wherein the thickness of the charge dispersion layer is 10 nm or more and 1000 nm or less. [3] The laminated piezoelectric body according to [1] or [2], wherein the fluororesin is a polymer containing a structural unit derived from vinylidene fluoride as a main component. [4] The laminated piezoelectric body according to [3], wherein the fluororesin is a vinylidene fluoride homopolymer. [5] The laminated piezoelectric body according to any one of [1] to [4], wherein the thickness of the transparent adhesive layer is 10 μm or more and 100 μm or less. [6] The laminated 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. [7] A touch panel including the laminated piezoelectric body according to any one of [1] to [6]. [8] A method for manufacturing a laminated piezoelectric body according to any one of [1] to [6], the method including: a step of preparing the piezoelectric film; a step of applying a composition for a charge dispersion layer on at least one surface of the piezoelectric film to form the charge dispersion layer; and a step of bonding the charge dispersion layer and the transparent electrode of the laminate through the transparent adhesive layer. [9] In the step of preparing the piezoelectric film, the method for manufacturing a laminated piezoelectric body according to [8], wherein after stretching a film containing a fluororesin as a main component, a polarization treatment is performed.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a laminated piezoelectric material, a touch panel, and a method for manufacturing a laminated piezoelectric material that can detect pressure with high sensitivity while maintaining transparency. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing the configuration of the laminated piezoelectric body according to this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing a modified laminated piezoelectric material. [Modes for carrying out the invention]

[0013] As described above, the reason why the signal intensity of the laminated piezoelectric body, which consists of a piezoelectric film mainly composed of fluororesin and a transparent electrode film laminated with a transparent adhesive layer in between, is low is presumed to be as follows.

[0014] The polarization behavior that occurs when pressure is applied differs depending on the type of resin. For example, polylactic acid has a piezoelectric constant d 14 Polarization occurs. That is, when pressure is applied to a piezoelectric film containing polylactic acid in a direction perpendicular to the film surface, the shear stress generated by the resulting bending of the film causes polarization in a direction perpendicular to the shear surface. Therefore, the polarized charge on the film surface is not limited to the area where the film is pressed, but tends to occur over a relatively wide area of ​​the film surface.

[0015] On the other hand, fluororesins mainly have a piezoelectric constant d 33 It has piezoelectric properties. Piezoelectric constant d 33This indicates that applying stress in three axial directions (z-axis direction) causes polarization in those three directions. In other words, when pressure is applied to a piezoelectric film containing a fluororesin in a direction perpendicular to the film surface (three axial directions), charge polarization occurs in that perpendicular direction (three axial directions). Therefore, charge polarization tends to occur locally in the pressed area of ​​the film surface, and the charge density in the pressed area becomes very high. In that area, there is a risk that the increase in charge density in response to stress will reach a saturation state. Therefore, when the charge density is saturated, sufficient charge is not induced to the electrode on the opposite side of the piezoelectric film via the transparent adhesive layer, and the signal strength tends to decrease.

[0016] Therefore, in this invention, a charge dispersion layer is placed on at least one surface of a piezoelectric film mainly composed of a fluororesin. As a result, even if a region with a locally high charge density occurs in the piezoelectric film, the charge can be dispersed and made uniform by the charge dispersion layer. This makes it possible to avoid charge density saturation. Furthermore, even if the piezoelectric film and the transparent electrode film are laminated with a transparent adhesive layer in between, sufficient charge is induced on the transparent electrode side, so the signal intensity can be increased and the detection sensitivity can be improved. The laminated piezoelectric body and its manufacturing method according to one embodiment of the present invention will be described below.

[0017] 1. Multilayer piezoelectric material Figure 1 is a schematic cross-sectional view showing the configuration of the laminated piezoelectric body 100 according to this embodiment.

[0018] As shown in Figure 1, the laminated piezoelectric body 100 according to 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.

[0019] Hereinafter, in this specification, the first charge dispersion layer 120 and the second charge dispersion layer 130 will be collectively referred to as the "charge dispersion layer"; the first transparent electrode film 140 and the second transparent electrode film 150 will be collectively referred to as the "transparent electrode film"; and the first transparent adhesive layer 160 and the second transparent adhesive layer 170 will be collectively referred to as the "transparent adhesive layer".

[0020] 1-1. Piezoelectric film 110 The piezoelectric film 110 contains a fluororesin as a main component, and the piezoelectric constant d 33 is adjusted to be 7 pC / N or more and 40 pC / N or less. When the d of the piezoelectric film 110 33 is 7 pC / N or more, the amount of charge generated by pressing is sufficient, so it functions with high sensitivity as a pressure sensor. When the piezoelectric constant d of the piezoelectric film 33 is 40 pC / N or less, the unevenness on the film surface caused by polarization treatment can be further reduced, so that appearance defects can be reduced. From the same viewpoint, the piezoelectric constant d of the piezoelectric film 33 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.

[0021] The piezoelectric constant d 33 is one of the indexes indicating the polarization behavior when a certain pressure is applied. The larger the piezoelectric constant d 33 is, the greater the degree of polarization generated when a certain pressure is received, and the greater the charge density.

[0022] The piezoelectric constant d of the piezoelectric film 110 33 [[ID=二十七]] can be calculated by measuring the charge generated when stress is applied in the thickness direction of the piezoelectric film at a constant speed, and the piezoelectric constant d of the piezoelectric ceramic by the direct quasi-static method (d 33 meter method, Berlincourt method) 33 can be measured in accordance with the test method ISO 19622:2018 of 33 Specifically, using a piezoelectric constant measuring device (for example, manufactured by PIEZOTEST, piezometer system PM300), clip a sample of the piezoelectric film with 1 N, and read the generated charge when a force of 0.15 N and 110 Hz is applied.

[0023] [[ID=三十七]] The piezoelectric constant d of the piezoelectric film 110 33This 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 fluororesins, the more constituent units derived from vinylidene fluoride a resin contains, the higher the piezoelectric constant d of the piezoelectric film. 33 It tends to become larger. Also, by strengthening the polarization treatment or stretching treatment, the piezoelectric constant d of the piezoelectric film can be increased. 33 It tends to grow large.

[0024] As described above, the piezoelectric film 110 contains a fluororesin as its main component. Containing a fluororesin as its main component means that the content of resins with fluororesin as a constituent unit (including the fluororesin itself) within the total mass of the resin constituting the piezoelectric film is 50% by mass or more. The fluororesin content is preferably 60% by mass or more, and more preferably 80% or more. The upper limit of the above content is not particularly limited and may be 100% by mass or 90% by mass or less.

[0025] From the viewpoint of easily obtaining a high piezoelectric effect among fluororesins, it is preferable that the fluororesin is a polymer that mainly contains constituent units derived from vinylidene fluoride.

[0026] In a polymer containing vinylidene fluoride as the main component, the content of vinylidene fluoride-derived structural units is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the total amount of structural units in the polymer. The higher the content, the easier it is to obtain a higher piezoelectric effect. The upper limit of the content is not particularly limited and may be 100% by mass or 90% by mass or less.

[0027] The polymer described above may further contain constituent units derived from monomers copolymerizable with vinylidene fluoride, to the extent that it does not impair the effects of the present invention. Examples of monomers copolymerizable with vinylidene fluoride include fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene chloride, and vinyl fluoride. Two or more of these monomers may be included.

[0028] In particular, the piezoelectric constant d of piezoelectric film 33 From the viewpoint of easily increasing the size and improving the sensitivity of the pressure sensor to which the piezoelectric film is applied, it is preferable that the piezoelectric film is a polyvinylidene fluoride homopolymer.

[0029] The thickness of the piezoelectric film 110 is preferably, for example, 25 μm or more and 120 μm or less. When the thickness of the piezoelectric film is 25 μm or more, the amount of charge generated by the piezoelectric effect increases, making it easier to increase the signal strength. The thickness of the piezoelectric film is more preferably 30 μm or more, and even more preferably 35 μm or more. When the thickness of the piezoelectric film is 120 μm or less, the transparency of the piezoelectric film is less likely to be impaired, and is more preferably 100 μm or less, and even more preferably 80 μm or less. From a similar viewpoint, the thickness of the piezoelectric film is more preferably 35 μm or more and 80 μm or less.

[0030] 1-2. First charge distribution layer 120, second charge distribution layer 130 (First charge distribution layer 120) The first charge dispersion layer 120 is arranged on one surface of the piezoelectric film. The first charge dispersion layer 120 increases the mobility of polarization charges locally generated by pressing on one surface of the piezoelectric film 110 within the charge dispersion layer, thereby reducing saturation and counting errors that occur when detecting polarization charges, and improving the sensitivity of the piezoelectric sensor.

[0031] The first charge dispersion layer 120 is conductive. One indicator of conductivity is surface resistivity. The surface resistivity of the first charge dispersion layer 120 is 1.0 × 10⁻⁶. 4Ω / sq. or more 1.0×10 12 The resistance is less than or equal to Ω / sq. The surface resistivity is 1.0 × 10⁻⁶. 12 If the surface resistivity is Ω / sq. or less, the first charge dispersion layer 120 has sufficient conductivity, so that the charge generated at the pressed portion of the piezoelectric film 110 by pressing moves easily within the charge dispersion layer, and when detecting polarization charge, it can be detected as a signal without saturation or counting errors. As a result, the signal strength can be increased even in laminated piezoelectric materials with a transparent adhesive layer. On the other hand, if the surface resistivity is 1.0 × 10⁻⁶ 4 If the resistivity is Ω / sq. or higher, the transparency of the first charge dispersion layer 120 is less likely to be impaired. From a similar viewpoint, the surface resistivity of the first charge dispersion layer 120 is 1.0 × 10⁻⁶. 4 Ω / sq or more 1.0×10 9 A ratio of Ω / sq or less is more preferable, and 1.0 × 10 6 Ω / sq or more 1.0×10 9 A value of Ω / sq or less is particularly preferred. Surface resistivity can be measured, for example, using a known resistivity meter in accordance with JIS K 6911.

[0032] The surface resistivity can be adjusted by the thickness of the first charge dispersion layer 120, and by the type and content of conductive polymers and conductive materials contained in the first charge dispersion layer 120. For example, increasing the thickness of the first charge dispersion layer 120 will decrease the surface resistivity. Also, increasing the content of conductive polymers and conductive materials in the first charge dispersion layer 120 will decrease the surface resistivity.

[0033] The first charge dispersion layer 120 is configured such that its surface resistivity falls within the above range. The first charge dispersion layer 120 contains a conductive polymer or a conductive material other than a conductive polymer. In this embodiment, the first charge dispersion layer 120 may also contain a cured product of a curable composition comprising a conductive polymer or a conductive material other than a conductive polymer, a polymerizable compound, and an optional curing agent.

[0034] 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, and the like. Among these, polythiophene or its derivatives are preferred from the viewpoint of high transparency and high conductivity.

[0035] Examples of conductive materials include carbon nanotubes and graphene.

[0036] The polymerizable compound may be either a thermopolymerizable compound or a photopolymerizable compound. Examples include acrylic compounds, epoxy compounds, oxetane compounds, polyurethane compounds, polyimide resins, melamine resins, silicone compounds, and vinyl acetate.

[0037] The thickness of the first charge dispersion layer 120 is limited to a range that can disperse the charge generated on the piezoelectric film 110, and is preferably, for example, 10 nm to 1000 nm. If the thickness of the first charge dispersion layer 120 is 10 nm or more, the polarization charge generated on the surface of the piezoelectric film 110 is made more easily movable within the charge dispersion layer, and saturation and counting errors that occur when detecting polarization charges can be further reduced, making it easier to further increase the signal strength. If the thickness of the first charge dispersion layer 120 is 1000 nm or less, discoloration caused by conductive polymers, etc., and appearance defects caused by surface irregularities of the piezoelectric film 110 are less likely to occur, and transparency is less likely to be impaired. From a similar viewpoint, the thickness of the first charge dispersion layer 120 is more preferably 20 nm to 800 nm, even more preferably 30 nm to 600 nm, and particularly preferably 40 nm to 400 nm.

[0038] (Second charge distribution layer 130) The second charge dispersion layer 130 is located on the other surface of the piezoelectric film 110. Piezoelectric constant d 33In the piezoelectric film, charges are polarized on both sides of the piezoelectric film in response to pressure. Therefore, it is preferable to install the charge dispersion layer on both sides of the piezoelectric film. The second charge dispersion layer 130, on the other side of the piezoelectric film on which the first charge dispersion layer is installed, similarly increases the mobility of locally generated polarization charges within the charge dispersion layer due to pressure, thereby reducing saturation and counting errors that occur when detecting polarization charges and improving the sensitivity of the piezoelectric sensor.

[0039] In this embodiment, the second charge dispersion layer 130 has the same or similar configuration as the first charge dispersion layer 120 described above, and a detailed explanation is omitted. That is, the configuration, materials, and properties of the second charge dispersion layer 130 are the same as those of the first charge dispersion layer 120 described above.

[0040] The composition of the first charge dispersion layer 120 and the composition of the second charge dispersion layer 130 may be the same or different. Furthermore, the thickness of the first charge dispersion layer 120 and the thickness of the second charge dispersion layer 130 may be the same or different.

[0041] 1-3. First transparent electrode film 140, second transparent electrode film 150 (First transparent electrode film 140) The first transparent electrode film 140 is positioned on the side of the piezoelectric film 110 that faces the first charge dispersion layer 120. The first transparent electrode film 140 includes a substrate layer 141 and a first transparent electrode 142; the first transparent electrode 142 detects the charge generated in the piezoelectric film 110 as an electrical signal via the first charge dispersion layer 120.

[0042] 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 heat-resistant material capable of withstanding the heat required to crystallize ITO or the like. Examples of such transparent resins include polyesters such as polyethylene terephthalate (PET). Among these, PET is preferred.

[0043] The thickness of the substrate layer 141 is not particularly limited as long as it can support the first transparent electrode 142, but is preferably 2 μm to 300 μm, more preferably 10 μm to 200 μm, even more preferably 20 μm to 150 μm, and particularly preferably 30 μm to 130 μm.

[0044] The first transparent electrode 142 is positioned on the surface of the substrate layer 141 facing the first charge dispersion layer 120. The first transparent electrode 142 is preferably an inorganic electrode such as ITO (indium tin oxide) or tin oxide, with ITO being more preferable.

[0045] (Second transparent electrode film 150) The second transparent electrode film 150 is positioned 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 in the piezoelectric film 110 as an electrical signal via the second charge dispersion layer 130.

[0046] In this embodiment, the second transparent electrode film 150 has the same configuration as the first transparent electrode film 140 described above. 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 described above.

[0047] Furthermore, 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 or different.

[0048] 1-4. First transparent adhesive layer 160, second transparent adhesive layer 170 (1st transparent adhesive layer 160) The first transparent adhesive layer 160 is positioned between the first charge dispersion layer 120 and the first transparent electrode 142, and adheres the piezoelectric film 110 on which the first charge dispersion layer 120 is positioned to the first transparent electrode 142.

[0049] The first transparent adhesive layer 160 is preferably transparent and has elasticity sufficient to transmit the 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-based adhesives. Among these, acrylic adhesives are preferred from the viewpoint of tackiness and elasticity.

[0050] The thickness of the first transparent adhesive layer 160 is not particularly limited, but is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 80 μm or less, and even more preferably 20 μm or more and 60 μm or less. When the thickness of the first transparent adhesive layer is 10 μm or more, it is easier to adhere the first charge dispersion layer 120 and the first transparent electrode 142 more effectively. When the thickness of the first transparent adhesive layer 160 is 100 μm or less, preferably 60 μm or less, the amount of charge extracted from the first charge dispersion layer 120 increases, making it easier to increase the signal intensity.

[0051] (Second transparent adhesive layer 170) The second transparent adhesive layer 170 is positioned between the second charge dispersion layer 130 and the second transparent electrode 152, and adheres the piezoelectric film 110 on which the second charge dispersion layer 130 is positioned 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 and the adhesive contained in the first transparent adhesive layer 160 may be the same or different.

[0052] 1-5. Other layers The laminated piezoelectric body 100 may further have other layers as long as they do not impair 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.

[0053] The thickness of each layer constituting the laminated piezoelectric body 100 can be determined by measuring at least three points at 5 mm intervals within a range including the center of the surface of the laminated piezoelectric body 100 using a spectroscopic interferometric film thickness gauge (for example, "Optical NanoGauge C13027-11" manufactured by Hamamatsu Photonics), and calculating the arithmetic mean value. The refractive index of each layer can be measured by the method described in JIS K7142, and the refractive index can be set by identifying the main material constituting each layer. For example, the refractive index of the piezoelectric film containing 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.

[0054] 1-6. Physical Properties The laminated piezoelectric material 100 has high transparency. The total light transmittance of the laminated piezoelectric material 100 is preferably 80% or more. The total light transmittance of the laminated piezoelectric material 100 can be measured using a haze meter (for example, NDH7000SP II manufactured by Nippon Denshoku Industries Ltd.) in accordance with the method described in JIS K 7361-1.

[0055] 1-7.Effect In the laminated piezoelectric body 100 according to the above embodiment, as described above, when pressure is applied in a direction perpendicular to the surface of the piezoelectric film 110 (in the three axial directions), polarization occurs in the three axial directions, and the piezoelectric effect is exhibited. As a result, polarized charges are induced on the surface of the piezoelectric film 110, and a distribution of charge density occurs on the surface of the piezoelectric film 110 due to the pressure distribution of the applied pressure.

[0056] In this embodiment, the piezoelectric film 110 has a first charge dispersion layer 120 and a second charge dispersion layer 130 on its surface. This eliminates and uniformizes the locally generated charge density distribution on the surface of the piezoelectric film 110. As a result, it can detect pressure with high sensitivity, and therefore has high detection sensitivity to pressing operations when used as a pressure sensor for a touch panel.

[0057] 2. Manufacturing method of multilayer piezoelectric material The laminated piezoelectric material according to this embodiment can be manufactured by (1) preparing a laminate including a piezoelectric film and a charge dispersion layer, and (2) bonding the charge dispersion layer of the prepared laminate and the transparent electrode of a transparent electrode film via a transparent adhesive layer. The piezoelectric film, charge dispersion layer, transparent adhesive layer, and transparent electrode film are the piezoelectric film, charge dispersion layer, transparent adhesive layer, and transparent electrode film described above, respectively.

[0058] (1) Regarding the process of preparing the laminate The above laminate can be obtained by (1-1) a step of obtaining a piezoelectric film containing a fluororesin, and (1-2) a step of forming a charge dispersion layer on at least one surface of the obtained piezoelectric film.

[0059] (1-1) Process for manufacturing piezoelectric film A piezoelectric film can be obtained by a process of polarization treatment of a film containing a fluororesin. The film containing the fluororesin may be a stretched film or an unstretched film. In this embodiment, from the viewpoint of exhibiting a high piezoelectric effect, it is preferable to stretch the film containing the fluororesin before polarization treatment.

[0060] Films containing fluororesins can be manufactured by any method, such as melt extrusion or solution casting. Among these methods, films containing fluororesins are preferably manufactured by melt extrusion. In melt extrusion, the fluororesin and any additives are heated and melted in the cylinder of an extruder, and then extruded from a die to obtain the film.

[0061] The resulting film has a structure in which α-type crystals (with a helical main chain) and β-type crystals (with a planar zigzag main chain) are mixed. The β-type crystals have a large polarization structure. By stretching the film, the α-type crystals can be converted into β-type crystals, and the stretching process may be performed as needed to convert the fluororesin into β-type crystals.

[0062] The stretching method is not particularly limited and can be carried out using known stretching methods such as the tenter method or the drum method.

[0063] The stretching ratio is, for example, between 3.0 and 6.0 times. A stretching ratio of 3.0 times or higher makes it easier to adjust the film thickness and strength to an appropriate range, and also facilitates polarization. At a stretching ratio of 3.0 times or higher, the dislocation reaction of the β-type crystal proceeds sufficiently, leading to higher piezoelectricity and improved transparency. A stretching ratio of 6.0 times or lower further suppresses breakage due to stretching.

[0064] The resulting stretched film is subjected to polarization treatment. Polarization treatment can be performed, for example, by applying a DC voltage between a ground electrode and a needle electrode. The voltage can be adjusted according to the thickness of the stretched film, but for example, it can be between 1kV and 50kV.

[0065] In this embodiment, as described above, a piezoelectric film can be obtained by polarizing a stretched film.

[0066] (1-2) Steps to form a charge dispersion layer After applying a curable composition containing, for example, the conductive polymer or conductive material described above to the surface of the obtained piezoelectric film, it is dried and cured to form a charge dispersion layer.

[0067] The above composition may further contain water or a solvent in addition to the components described above. Examples of solvents include alcoholic solvents such as methanol, ethanol, and isopropyl alcohol.

[0068] The coating method is not particularly limited and may be any of the following: spin coating, gravure coating, die coating, bar coating, dip coating, etc.

[0069] The above composition can be dried by heating the coated composition. The heating temperature is preferably above a temperature that can remove the solvent and below the heat distortion temperature of the fluororesin constituting the piezoelectric film, for example, it can be between 100°C and 150°C. The heat distortion temperature can be measured, for example, in accordance with JIS K 7191-2:2015. Furthermore, the above composition may be cured by photocuring or by thermal curing. In the case of thermal curing, drying and thermal curing may be performed simultaneously.

[0070] (2) Regarding the bonding process The charge-dispersion layer of the laminate and the transparent electrode film are bonded together via a transparent adhesive layer.

[0071] The bonding method is not particularly limited, but it can be performed by bonding a transparent adhesive layer onto the charge dispersion layer of the laminate, and then bonding the transparent adhesive layer to the transparent electrode film. The bonding is performed so that the transparent electrode of the transparent electrode film faces the transparent adhesive layer.

[0072] The laminated piezoelectric material according to this embodiment can be used for various applications. In particular, because the laminated piezoelectric material according to this embodiment has high transparency and can detect pressure with high sensitivity, it can be preferably used as a pressure sensor for touch panels mounted on various electronic devices.

[0073] 3. Variant In the above embodiment, the charge dispersion layer is arranged on both sides of the piezoelectric film, but it may also be arranged on only one side.

[0074] Figure 2 is a schematic cross-sectional view showing a modified laminated piezoelectric body 100. As shown in Figure 2, the modified laminated piezoelectric body 100 can be configured in the above embodiment except that the second charge dispersion layer 130 is omitted. Furthermore, if the laminated piezoelectric body 100 has other layers, there may be other layers between the piezoelectric film 110 and the second transparent electrode 152. [Examples]

[0075] The present invention will be further described below with reference to examples and comparative examples. The technical scope of the present invention is not limited thereto.

[0076] 1. Evaluation of physical properties (1) Thickness of the charge dispersion layer The thickness of the charge dispersion layer formed on a piezoelectric film was measured using a spectroscopic interferometric film thickness gauge (Hamamatsu Photonics "Optical NanoGauge C13027-11"). Specifically, the thickness of the charge dispersion layer on the piezoelectric film was measured at 30 points at 5 mm intervals, including the center of the surface, and the arithmetic mean was calculated. The refractive index of each layer was set according to the material of each layer; it was set to 1.42 for the piezoelectric film containing PVDF and 1.50 for the charge dispersion layer.

[0077] (2)Surface resistivity A piezoelectric film with a charge dispersion layer was cut to a size of 100 mm x 100 mm to obtain a sample film. The surface resistivity of the charge dispersion layer of the sample film was measured using a surface resistance meter F-109 (manufactured by HOZAN Corporation) in accordance with JIS 6911. The measurement conditions were an output of 100 W, and the value was read after 10 seconds.

[0078] (3) Piezoelectric constant (Piezoelectric constant d) 33 ) Direct quasi-static method (d 33 Piezoelectric constant d of piezoelectric ceramics by the Meter method, Berlin coat method 33 The test method conforms to ISO 19622:2018, and the piezoelectric constant d 33 The piezoelectric constant d of the piezoelectric film was measured. Specifically, the piezoelectric constant d of the piezoelectric film was measured. 33 The piezoelectric constant d of the piezoelectric film was measured using a piezoelectric constant measuring device ("Piezometer System PM300", manufactured by PIEZOTEST). The sample was clipped with 1N, and the generated charge was read when a force of 0.15N and 110Hz was applied. 33 The measured value is obtained at a measurement temperature of 25°C, and the value will be positive or negative depending on whether the front or back of the film being measured is the front or back side; however, in this specification, the absolute value is given.

[0079] (Piezoelectric constant d) 14 ) Aluminum was deposited on both sides of the piezoelectric film. The film was then cut into sections of 120 mm in a direction 45° to the stretching direction (MD direction) of the piezoelectric film, and 10 mm in a direction perpendicular to the 45° direction, to obtain a rectangular film measuring 120 mm x 10 mm. This was used as the sample for measurement. Next, the sample was set in a tensile testing machine with a chuck distance of 70 mm, ensuring it did not sag. Then, a periodic force was applied to the sample at a speed of 5 mm / min, alternating between 4 N and 9 N. To measure the amount of charge generated in the sample in response to the applied force, a capacitor with capacitance Qm (F) was connected in parallel to the sample, and the terminal voltage Vm of this capacitor Cm (95 nF) was measured via a buffer amplifier. The generated charge Q(C) was calculated as the product of the capacitor capacitance Cm and the terminal voltage Vm. Piezoelectric constant d 14 This was calculated using the following formula. d 14 =(2×t) / L×Cm·ΔVm / ΔF t: Sample thickness (m) L: Distance between chucks (m) Cm: Capacitance (F) of parallel connected capacitors ΔVm / ΔF: Ratio of the change in voltage across the capacitor terminals to the change in force.

[0080] 2. Fabrication and evaluation of multilayer piezoelectric materials [Example 1] (1) Fabrication of piezoelectric film A polyvinylidene fluoride film (manufactured by Kureha Corporation, a film containing 100% by mass of polyvinylidene fluoride homopolymer) was stretched to a stretch ratio of 4.2 times in the MD direction. Polarization treatment was then performed by applying a DC voltage between the ground electrode and the needle electrode, increasing from 0kV to 11.0kV, to obtain a piezoelectric film. This resulted in a piezoelectric film with a thickness of 42μm.

[0081] (2) Formation of a charge dispersion layer A solution was applied to the A-side of the obtained piezoelectric film using a gravure coater (multi-coater manufactured by Hirano Tecseed Co., Ltd.), by mixing liquid A of paint P-400MP-A (manufactured by Nagase ChemteX Corporation), which contains PEDOT:PSS as a conductive polymer, and liquid B of paint P-400MP-B (manufactured by Nagase ChemteX Corporation), in a mixing ratio of 4:1. The solution was then heat-treated at 130°C for 1 minute to form a charge dispersion layer with a thickness of 50 nm.

[0082] (3) Formation of a transparent adhesive layer Next, an Optical Clear Adhesive (OCA) sheet (Nitto Denko Corporation, CS9862UA, 50 μm thick) was laminated onto the charge dispersion layer formed on side A of the piezoelectric film and onto side B of the piezoelectric film, respectively.

[0083] (4) Fabrication of transparent electrode film Next, a transparent electrode precursor film (Tetrite TCF KH100NMH3-100-U8, manufactured by Oike Kogyo Co., Ltd., which was obtained by sputtering indium tin oxide (ITO) onto a polyethylene terephthalate (PET) film) was crystallized at 150°C for 90 minutes to produce a transparent electrode film.

[0084] (5) Fabrication of laminated piezoelectric material Then, the ITO side of the transparent electrode film was laminated to the OCA sheet attached to the charge dispersion layer on side A of the piezoelectric film, and to the OCA sheet attached to side B of the piezoelectric film. A 1.1 mm thick glass was further laminated to the transparent electrode film on side A of the piezoelectric film to create a laminated piezoelectric body.

[0085] [Example 2] A laminated piezoelectric material was obtained in the same manner as in Example 1, except that the thickness of the charge dispersion layer was set to 130 nm.

[0086] [Example 3] A 50 nm thick charge dispersion layer was formed on side A of the piezoelectric film using the same method as in Example 1. Then, paint MT-3 (Arakawa Chemical Industries, Ltd.), containing PEDOT:PSS, was applied to side B of the piezoelectric film. After drying at 80°C, 400 mJ / cm² was irradiated using a UV irradiation device (GS Yuasa Corporation: CSOT-40). 2 A charge dispersion layer with a thickness of 700 nm was formed by irradiating with ultraviolet light using the accumulated light intensity.

[0087] Then, OCA sheets were laminated to the charge dispersion layers on sides A and B of the piezoelectric film, and transparent electrode films were further laminated to each OCA sheet. A 1.1 mm thick glass was then laminated to the transparent electrode film on side A of the piezoelectric film to obtain a laminated piezoelectric body.

[0088] [Example 4] A laminated piezoelectric material was obtained in the same manner as in Example 1, except that the thickness of the OCA sheet was set to 25 μm.

[0089] [Example 5] A laminated piezoelectric material was obtained in the same manner as in Example 1, except that coating liquid A was changed to paint C-169PF-A (Nagase ChemteX Corporation) containing single-wall carbon nanotubes, coating liquid B was changed to paint C-169PF-B (Nagase ChemteX Corporation), and the mixing ratio of liquid A to liquid B was changed to 3:2.

[0090] [Comparative Example 1] A laminated piezoelectric material was obtained in the same manner as in Example 1, except that a charge dispersion layer was not formed.

[0091] [Comparative Example 2] (1) Fabrication of piezoelectric film To 100 parts by mass of polylactic acid (product name: Ingeo™ biopolymer) manufactured by NatureWorks LLC, 1.0 part by mass of a stabilizer [a mixture of 10 parts by mass of Stabaxol P400 manufactured by Rhein Chemie, 70 parts by mass of Stabaxol I manufactured by Rhein Chemie, and 20 parts by mass of Carbodilite LA-1 manufactured by Nisshinbo Chemical] was added and dry-blended to prepare the raw material. This raw material was placed in the hopper of an extrusion molding machine, extruded from a T-die while being heated to 210°C, and brought into contact with a cast 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 its original size in the MD direction at 70°C using a roll-to-roll method to obtain a uniaxially oriented film. The thickness of the film was 49.2 μm. Next, the uniaxially oriented film was annealed by contacting it on a roll at 145°C for 15 seconds using a roll-to-roll method, and then rapidly cooled to produce a polylactic acid-based piezoelectric film.

[0092] (2) Formation of an antistatic hard coat layer An antistatic hard coat coating (Shin-Etsu Polymer, Sepulzida® HC-A) was applied to one side of the obtained piezoelectric film using an applicator, dried at 60°C for 5 minutes, and then exposed to a metal halide lamp with an integrated light intensity of 1000 mJ / cm². 2 By irradiating the piezoelectric film with ultraviolet light, an antistatic hard coat layer was formed on one side of the piezoelectric film.

[0093] (3) Fabrication of multilayer piezoelectric materials After laminating an OCA sheet to both the film surface and the antistatic hard coat layer surface of the obtained piezoelectric film in the same manner as in Example 1, a transparent electrode film was laminated to them. 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.

[0094] [evaluation] The total light transmittance and pressure signal of the laminated piezoelectric materials of Examples 1-5 and Comparative Examples 1 and 2 were evaluated by the following method.

[0095] (Total light transmittance) The total light transmittance of the laminated piezoelectric materials of the examples and comparative examples was measured using a haze meter ("NDH7000SP II", manufactured by Nippon Denshoku Industries Ltd.) in accordance with the method described in JIS K 7361-1.

[0096] (Detection of pressure signal) A laminated piezoelectric material measuring 171.7 mm in length and 233.5 mm in width was installed in a touch panel linearity evaluation system (manufactured by Nippon Nobel Co., Ltd.) with the stretching direction of the piezoelectric film as one axis and the thickness direction as three axes. The center of the glass surface of the laminated piezoelectric material was pressed from all three axes with a force of 8 N using a robot's pressing terminal (tip diameter 3 mm), and the signal intensity obtained at that time was measured.

[0097] To detect the pressure signal, positive and negative lead wires were drawn from the terminals of the ITO electrodes of the multilayer piezoelectric material and connected to an amplifier. The voltage signal amplified by the amplifier was then converted into a digital signal via an AD converter and filtering circuit, and the strength of the piezoelectric signal was calculated by integrating the resulting digital signals.

[0098] Table 1 shows the configuration and evaluation results of the laminated piezoelectric materials for Examples 1-5 and Comparative Examples 1 and 2.

[0099] [Table 1]

[0100] As shown in Table 1, the laminated piezoelectric material of Comparative Example 1, which did not have a charge dispersion layer on the piezoelectric film containing fluororesin, showed low signal intensity. Furthermore, the laminated piezoelectric material of Comparative Example 2, which used a piezoelectric film containing polylactic acid, also showed low signal intensity despite having a charge dispersion layer.

[0101] In contrast, Examples 1 to 5, in which a charge dispersion layer is provided on at least one surface of a piezoelectric film containing a fluororesin, all exhibit high signal intensity while maintaining high transparency.

[0102] In particular, it can be seen that the signal intensity can be further increased by providing charge dispersion layers on both sides of a piezoelectric film containing a fluororesin (comparison of Examples 1 and 3).

[0103] Furthermore, it can be seen that the signal strength can be further increased by reducing the thickness of the transparent adhesive layer (comparison between Examples 1 and 4).

[0104] Furthermore, the surface resistance of the charge dispersion layer is 7.1 × 10⁻⁶. 6 It can be seen that the signal strength can be further increased by using Ω (comparison between Examples 1 and 5).

[0105] This application claims priority under Japanese Patent Application No. 2023-48026, filed on 24 March 2023. All information contained in the specification and drawings of said application is incorporated herein by reference. [Industrial applicability]

[0106] According to the present invention, it is possible to provide a laminated piezoelectric material and a touch panel that can detect pressure with high sensitivity while maintaining transparency. Therefore, the laminated piezoelectric material is suitable as a pressure sensor for a touch panel. [Explanation of Symbols]

[0107] 100 Multilayer Piezoelectric 110 Piezoelectric film 120 First charge distribution layer 130 Second charge distribution layer 140 First transparent electrode film 150 Second transparent electrode film 160 1st transparent adhesive layer 170 2nd transparent adhesive layer

Claims

1. A laminated piezoelectric material, It contains a fluororesin as its main component, and has a piezoelectric constant d ３３ A piezoelectric film having a density of 7 pC / N or more and 40 pC / N or less, Distributed on at least one surface of the piezoelectric film, with a surface resistivity of 1.0 × 10 ４ Ω / sq. More than 1.0×10 １２ A charge dispersion layer with a value of Ω / sq. Transparent electrode and A transparent adhesive layer disposed between the transparent electrode and the charge dispersion layer. It has, The total light transmittance of the laminated piezoelectric material is 80% or more. Multilayer piezoelectric material.

2. The thickness of the charge dispersion layer is 10 nm or more and 1000 nm or less. The laminated piezoelectric material according to claim 1.

3. The aforementioned fluororesin is a polymer that mainly contains constituent units derived from vinylidene fluoride. The laminated piezoelectric material according to claim 1.

4. The aforementioned fluorine-based resin is a polyvinylidene fluoride homopolymer. The laminated piezoelectric body according to claim 3.

5. The thickness of the transparent adhesive layer is 10 μm or more and 100 μm or less. The laminated piezoelectric material according to claim 1.

6. The thickness of the piezoelectric film is 25 μm or more and 120 μm or less. The laminated piezoelectric material according to claim 1.

7. A laminated piezoelectric body according to any one of claims 1 to 6, Touch panel.

8. A method for manufacturing a laminated piezoelectric body according to claim 1, The steps include preparing the piezoelectric film, A step of forming the charge dispersion layer by applying a charge dispersion layer composition to at least one surface of the piezoelectric film, The process includes bonding the charge dispersion layer and the transparent electrode via a transparent adhesive layer. A method for manufacturing a multilayer piezoelectric material.

9. In the step of preparing the piezoelectric film, A film containing a fluororesin as the main component is stretched and then subjected to polarization treatment. A method for manufacturing a laminated piezoelectric material according to claim 8.

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