Transparent conductive piezoelectric film, touch panel, and method for manufacturing transparent conductive piezoelectric film

Abstract

The purpose of the present invention is to provide a conductive piezoelectric film having excellent transparency. A transparent conductive piezoelectric film (11) according to the present invention has a 450-nm wavelength transmittance of 75% or more, a 550-nm wavelength transmittance of 85% or more, and a piezoelectric constant d33 of 5 pC / N to 40 pC / N inclusive, and includes a transparent electrode layer (4).

Description

[Technical field]

[0001] The present invention relates to a transparent conductive piezoelectric film, a touch panel, and a method for producing a transparent conductive piezoelectric film. [Background technology]

[0002] Touch panels are widely used as devices that allow information to be input by touching a screen. A touch panel is a device in which a light-transmitting input device is arranged on a display device such as a liquid crystal panel. A typical type of touch panel is a capacitive touch panel that utilizes the change in electrical capacitance that occurs between the screen and a finger. In recent years, various capacitive touch panels have been devised that detect the amount of pressure applied when touched in addition to touch position information. In such touch panels, a conductive piezoelectric film is used in which a transparent conductive layer made of a metal oxide such as indium oxide containing tin oxide (tin-doped indium oxide, ITO) or zinc oxide is laminated on a piezoelectric film to detect the amount of pressure applied when touched.

[0003] Incidentally, in the manufacturing process of conventional conductive films in which the substrate is not a piezoelectric film, a technique for crystallizing a metal oxide layer by annealing is known (see, for example, Patent Document 1). The annealing treatment increases the transmittance of the short wavelength region of visible light, improves the transparency of the conductive film, suppresses yellow coloring, and reduces the surface resistance value, thereby increasing the conductivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-074792 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the piezoelectric film has a lower heat resistance than other conductive film substrates, the yellow coloring may become more pronounced by the annealing treatment. In order to obtain a conductive piezoelectric film with sufficient conductivity without the annealing treatment, it is necessary to increase the thickness of the metal oxide layer, but the increase in the thickness of the metal oxide layer with insufficient crystallization tends to reduce the transparency of the conductive piezoelectric film and cause the yellow coloring to become more pronounced. When a conductive piezoelectric film with insufficient transparency and yellow coloring is used as a component of an input device for a touch panel, there is a problem that it is difficult to accurately express the color of the display device placed under the input device.

[0006] An object of one aspect of the present invention is to provide a conductive piezoelectric film having excellent transparency. [Means for solving the problem]

[0007] In order to solve the above problems, a transparent conductive piezoelectric film according to one embodiment of the present invention has a transmittance of 75% or more at a wavelength of 450 nm and a transmittance of 85% or more at a wavelength of 550 nm, and a piezoelectric constant d 33 a surface resistance value of the transparent electrode layer being 50 Ω / sq or more and less than 300 Ω / sq, and

[0008] In addition, in order to solve the above-mentioned problems, one embodiment of a method for producing a transparent conductive piezoelectric film according to one aspect of the present invention is a method for producing a laminated film configured by stacking a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer in this order on at least one surface of a transparent piezoelectric film, and includes a first step of producing the transparent piezoelectric film to form a film having a refractive index of 1.30 or more and less than 1.45; a second step of forming the first transparent coating layer having a refractive index of 1.60 or more and less than 1.80 on at least one surface of the transparent piezoelectric film; a third step of forming the second transparent coating layer on a surface of the first transparent coating layer, the second transparent coating layer having a refractive index of 1.30 or more and less than 1.50 and a thickness of 10 nm or more and less than 70 nm; and a fourth step of forming the transparent electrode layer on a surface of the second transparent coating layer, the transparent conductive piezoelectric film being formed. Effect of the Invention

[0009] According to one aspect of the present invention, a conductive piezoelectric film having excellent transparency can be realized. [Brief description of the drawings]

[0010] [Figure 1] 1 shows a transparent conductive piezoelectric film 11 according to one embodiment of the present invention. [Diagram 2] 1 is a transparent conductive piezoelectric film 12 according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, one embodiment of the present invention will be described in detail.

[0012] [Transparent conductive piezoelectric film] A transparent conductive piezoelectric film according to one embodiment of the present invention is a film in which a transparent electrode layer is provided to a piezoelectric film. The transparent conductive piezoelectric film of this embodiment has a transmittance of 75% or more at a wavelength of 450 nm and a transmittance of 85% or more at a wavelength of 550 nm, and a piezoelectric constant d33 The piezoelectric constant is 5 pC / N or more and 40 pC / N or less. The transparent conductive piezoelectric film has excellent piezoelectric properties, transparency, and conductivity, and can be suitably used in devices such as touch panels.

[0013] (transmittance) In the transparent conductive piezoelectric film of this embodiment, the transmittance at a wavelength of 450 nm may be 75% or more, and the transmittance at a wavelength of 550 nm may be 85% or more. By making the transmittance at wavelengths of 450 nm and 550 nm of the transparent conductive piezoelectric film within the above ranges, a transparent conductive piezoelectric film with reduced color and no turbidity can be obtained. Therefore, the film can be suitably used in devices that require transparency. For example, when used in devices such as touch panels, the film is preferable because it is transparent and does not interfere with the display screen of the touch panel.

[0014] The transmittance at a wavelength of 450 nm is preferably 78% or more, and more preferably 80% or more. A transparent conductive piezoelectric film having a transmittance at a wavelength of 450 nm within this range can be determined to be a film with particularly reduced yellowness.

[0015] Furthermore, the transparent conductive piezoelectric film has a transmittance at a wavelength of 550 nm of 85% or more, preferably 87% or more, and more preferably 89% or more. A transparent conductive piezoelectric film having a transmittance at a wavelength of 550 nm within this range can be judged to be a transparent conductive piezoelectric film that transmits light sufficiently and has high transparency when used for optical purposes such as in devices.

[0016] The 450 nm wavelength transmittance and 550 nm wavelength transmittance of the transparent conductive piezoelectric film may be 97% or less, as long as the desired effect is sufficiently obtained in the above case. The 450 nm wavelength transmittance and 550 nm wavelength transmittance are preferably closer to 100%. Hereinafter, in this specification, "transparency" refers to optical properties evaluated by the 450 nm wavelength transmittance and 550 nm wavelength transmittance, and "transparent" or "highly transparent" refers to a state in which the 450 nm wavelength transmittance is 75% or more and the 550 nm wavelength transmittance is 85% or more.

[0017] (Piezoelectric constant) The piezoelectric constant d of the transparent conductive piezoelectric film of this embodiment 33 The piezoelectric constant d of the transparent conductive piezoelectric film is preferably 5 pC / N or more, more preferably 8 pC / N or more, and even more preferably 10 pC / N or more. 33 The piezoelectric constant may be 40 pC / N or less, preferably 30 pC / N or less, and more preferably 20 pC / N or less. Such a piezoelectric constant is achieved by the piezoelectric film included in the transparent conductive piezoelectric film.

[0018] Piezoelectric constant d 33 indicates the amount of voltage displacement in the stress direction relative to the applied stress. Piezoelectric constant d 33 The larger the piezoelectric constant d, the larger the voltage generated relative to the stress, which is preferable for use in any device. 33 In particular, it is preferable that the piezoelectric constant d is not lower than the lower limit in order to provide the transparent conductive piezoelectric film with sufficient piezoelectric properties. 33 In particular, it is preferable that the upper limit of the above range is not exceeded in terms of the surface properties of the film.

[0019] Such a piezoelectric constant d 33Transparent conductive piezoelectric films having a piezoelectric constant d are expected to be applied to a wide range of devices. For example, they are expected to be applied to sensors such as pressure sensors and vibration sensors, switches, energy harvesting elements, and actuators in the fields of acoustics, security, transportation, and medicine. 33 A transparent conductive piezoelectric film having the above range is particularly suitable for use in a touch panel.

[0020] (Transparent electrode layer) The transparent conductive piezoelectric film includes a transparent electrode layer. The transparent electrode layer has a structure that is transparent, conductive, and has a planar extent. The shape of the transparent electrode layer when viewed in a plan view may be appropriately set depending on the application of the transparent conductive piezoelectric film. Details of the transparent electrode layer will be described in <Specific examples of transparent conductive piezoelectric films>.

[0021] The surface resistance of the transparent conductive piezoelectric film may be determined according to the application. For example, from the viewpoint of realizing a transparent conductive piezoelectric film having both high transparency and conductivity, the surface resistance may be 50 Ω / sq or more, 70 Ω / sq or more, or even 90 Ω / sq or more. The surface resistance may be less than 480 Ω / sq. When the surface resistance is within this range, it becomes possible to use the film as a conductive film in any device. Furthermore, the surface resistance may be less than 300 Ω / sq. A transparent conductive piezoelectric film having a surface resistance within this range has a small surface resistance and can be suitably used in devices such as touch panels.

[0022] <Examples of transparent conductive piezoelectric films> The transparent conductive piezoelectric film may be a laminated film formed by stacking a plurality of arbitrary layers to obtain the above-mentioned transparent conductive piezoelectric film. The transparent conductive piezoelectric film is a laminated film having a structure in which a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer are stacked in this order on at least one surface of the transparent piezoelectric film.

[0023] In this embodiment, "superimposed in this order" means that in a laminate including the above layers, the layers are adjacently disposed in the order listed.

[0024] As an example of the transparent conductive piezoelectric film, a transparent conductive piezoelectric film 11 is shown in Fig. 1. The transparent conductive piezoelectric film 11 is a laminated film configured by laminating a first transparent coating layer 2, a second transparent coating layer 3, and a transparent electrode layer 4 in this order on one surface of a transparent piezoelectric film 1. Note that the transparent conductive piezoelectric film 11 is not limited to the configuration shown in Fig. 1, and may further include other layer structures.

[0025] The transparent conductive piezoelectric film 11 may be a transparent conductive piezoelectric film in which the transparent piezoelectric film 1 and the first transparent coating layer 2 are laminated with a third transparent coating layer 5 interposed therebetween. That is, a transparent conductive piezoelectric film may be provided with a third transparent coating layer 5 between the transparent piezoelectric film 1 and the first transparent coating layer 2. Such a transparent conductive piezoelectric film is shown in FIG. 2 as a transparent conductive piezoelectric film 12. The transparent conductive piezoelectric film 12 is a laminated film configured by laminating a third transparent coating layer 5, a first transparent coating layer 2, a second transparent coating layer 3, and a transparent electrode layer 4 in this order on one surface of the transparent piezoelectric film 1.

[0026] In the transparent conductive piezoelectric film 11, for example, the refractive index of the transparent piezoelectric film 1 is 1.30 or more and less than 1.45, the refractive index of the first transparent coating layer 2 is 1.60 or more and less than 1.80, the refractive index of the second transparent coating layer 3 is 1.30 or more and 1.50 or less, and the refractive index of the transparent electrode layer 4 is 1.80 or more and 2.20 or less. When the refractive indexes of the layers are within the ranges, the transparent conductive piezoelectric film 11 can be made to have high transparency. In particular, when the refractive indexes of the first transparent coating layer 2 and the second transparent coating layer 3 are within the ranges, the transmittance at a wavelength of 550 nm is improved.

[0027] When the transparent conductive piezoelectric film 11 is the transparent conductive piezoelectric film 12, the refractive index of the third transparent coating layer 5 may be 1.45 or more and less than 1.60. By providing the third transparent coating layer 5, the transparency of the transparent conductive piezoelectric film 12 can be improved.

[0028] In this embodiment, the "refractive index" refers to the refractive index at a wavelength of 589 nm.

[0029] The refractive index of the first transparent coating layer 2 and the second transparent coating layer 3 was measured in accordance with JIS K7142. Specifically, each coating layer prepared experimentally was measured three times at 25.0±1.0° C. using an Abbe refractometer by irradiating each layer with measuring light having a wavelength of 589 nm, and the average of the measured values ​​was taken as the refractive index.

[0030] The refractive index of the transparent electrode layer 4 was measured by a multi-angle high-speed spectroscopic ellipsometer (JA Woollam: M-2000) to measure psi (Ψ) and delta (Δ), and the refractive index at a wavelength of 589 nm was calculated therefrom.

[0031] The refractive index of the transparent piezoelectric film 1 was measured in accordance with ASTM D542.

[0032] In the transparent conductive piezoelectric film 11, for example, the thickness of the second transparent coating layer 3 is 10 nm or more and 70 nm or less. Even if the refractive index of each layer is within a predetermined range, if the thickness of the second transparent coating layer 3 is outside the range, the transmittance at a wavelength of 450 nm may be low, resulting in a yellowish transparent conductive piezoelectric film. By setting the refractive index of each layer within a predetermined range and the thickness of the second transparent coating layer 3 within the range, the transparent conductive piezoelectric film 11 can achieve both a high level of transmittance at a wavelength of 450 nm and a high level of transmittance at a wavelength of 550 nm.

[0033] Furthermore, in the transparent conductive piezoelectric film 11, the transparent electrode layer 4 has a thickness of, for example, 13 nm or more and less than 40 nm. When the transparent electrode layer 4 has a thickness in this range, the transparent conductive piezoelectric film 11 can be provided with suitable surface resistance and transparency.

[0034] Below, a detailed description is given of each layer in the transparent conductive piezoelectric film 11 and the transparent conductive piezoelectric film 12. In the transparent conductive piezoelectric film 11, by setting the refractive index of each layer within the "more preferred" range described below, a transparent conductive piezoelectric film with higher transparency can be obtained.

[0035] (Transparent piezoelectric film 1) The transparent piezoelectric film 1 included in the transparent conductive piezoelectric film 11 refers to a film that has piezoelectricity and is transparent. Here, the "transparent" of the transparent piezoelectric film 1 refers to a film that has excellent transmittance at wavelengths of 450 nm and 550 nm. Specifically, the transmittance of the transparent piezoelectric film 1 at a wavelength of 450 nm may be 88% or more, and preferably 90% or more. In addition, the transmittance of the transparent piezoelectric film 1 at a wavelength of 550 nm may be 89% or more, and preferably 91% or more.

[0036] The refractive index of the transparent piezoelectric film 1 is, for example, 1.30 or more and less than 1.45. The refractive index of the transparent piezoelectric film 1 may be within this range, but is preferably 1.34 or more, and more preferably 1.36 or more. The refractive index is preferably 1.44 or less, and more preferably 1.43 or less.

[0037] In this embodiment, the transparent piezoelectric film 1 is a resin film. The resin in this embodiment is a film having a piezoelectric constant d 33 Any resin may be used, and it may be a single resin or a combination of two or more resins, as long as it has the piezoelectric properties represented by the following formula: Resins that satisfy the above conditions include fluororesins, polyamide 11, cellulose, polyurethane, and polyurea.

[0038] Among the above resins, fluororesin is preferred. The transparent piezoelectric film is made of fluororesin, which provides excellent transparency and piezoelectric constant d 33 It is possible to obtain a transparent conductive piezoelectric film having excellent piezoelectric properties represented by the formula: ##EQU1## In this embodiment, "made of fluororesin" means that the composition constituting the transparent piezoelectric film is mainly composed of fluororesin. Furthermore, "mainly composed of fluororesin" means that the fluororesin is the most abundant component among the resin components in the composition. The content of fluororesin in the composition is preferably 51% by mass or more, more preferably 80% by mass or more, and particularly preferably 100% by mass. In other words, it is particularly preferable that the transparent piezoelectric film 1 is a film made of fluororesin.

[0039] Among fluororesins, vinylidene fluoride resins are preferred. Examples of vinylidene fluoride resins include homopolymers of vinylidene fluoride and copolymers thereof. The content of constituent units derived from monomers other than vinylidene fluoride in the vinylidene fluoride copolymer may be appropriately determined within a range that allows the transparent piezoelectric film to exhibit characteristics according to its intended use.

[0040] Examples of monomers other than vinylidene fluoride in the vinylidene fluoride copolymer include hydrocarbon monomers and fluorine compounds. Examples of the hydrocarbon monomers include vinyl fluoride (VF), trifluoroethylene (TrFE), tetrafluoroethylene (TeFE), hexafluoropropene (HFP), 1-chloro-1-fluoro-ethylene (1,1-CFE), 1-chloro-2-fluoro-ethylene (1,2-CFE), 1-chloro-2,2-difluoroethylene (CDFE), chlorotrifluoroethylene (CTFE), trifluorovinyl monomer, 1,1,2-trifluorobutene-4-bromo-1-butene, and 1,1,2-trifluorobutene-4-silane. Fluoromonomers such as 1-butene, perfluoroalkyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluoroacrylate, 2,2,2-trifluoroethyl acrylate, and 2-(perfluorohexyl)ethyl acrylate; and hydrocarbon monomers such as ethylene, propene, maleic anhydride, vinyl ether, vinyl ester, allyl glycidyl ether, acrylic acid monomers, methacrylic acid monomers, and vinyl acetate. Among these, trifluoroethylene, tetrafluoroethylene, and hexafluoropropene are preferred as monomers other than vinylidene fluoride in the copolymer.

[0041] For example, the vinylidene fluoride copolymer may be a binary copolymer such as vinylidene fluoride copolymer (VDF / TrFE) obtained by copolymerizing vinylidene fluoride and trifluoroethylene, vinylidene fluoride copolymer (VDF / HFP) obtained by copolymerizing vinylidene fluoride and hexafluoropropene, and vinylidene fluoride-based copolymer (VDF / TeFE) obtained by copolymerizing vinylidene fluoride and tetrafluoroethylene. The binary copolymer is preferably one in which the mixing ratio of vinylidene fluoride to comonomer is 50:50 to 90:10. For example, vinylidene fluoride copolymer (VDF / TeFP) obtained by copolymerizing vinylidene fluoride and tetrafluoroethylene at a mixing ratio of 80:20 can be mentioned. Alternatively, it may be a ternary copolymer such as vinylidene fluoride copolymer (VDF / TFE / HFP) obtained by copolymerizing vinylidene fluoride, trifluoroethylene, and hexafluoropropene in a mixing ratio of 40:40:20.

[0042] In this embodiment, a homopolymer of vinylidene fluoride and a copolymer of vinylidene fluoride and tetrafluoroethylene are preferably used.

[0043] The transparent piezoelectric film of the present embodiment may contain various additives within the range in which the effects of the present embodiment can be obtained. The additives may be one or more types, and examples thereof include a plasticizer, a lubricant, a crosslinking agent, an ultraviolet absorber, a pH adjuster, a stabilizer, an antioxidant, a surfactant, and a pigment.

[0044] The thickness of the transparent piezoelectric film 1 in this embodiment can be appropriately determined within a range in which the effects of this embodiment can be obtained, depending on the application of the transparent conductive piezoelectric film 11. If the thickness of the transparent piezoelectric film 1 is too thin, the mechanical strength may be insufficient, and if the thickness is too thick, the effect may plateau or the transparency may be insufficient, making it difficult to use for optical applications. From this perspective, the thickness of the transparent piezoelectric film 1 may be 20 μm or more, preferably 30 μm or more, and more preferably 35 μm or more. In addition, the thickness of the transparent piezoelectric film 1 may be less than 200 μm, preferably 120 μm or less, and more preferably 80 μm or less.

[0045] (Transparent electrode layer 4) The transparent electrode layer 4 in this embodiment is a layered electrode superimposed on the second transparent coating layer 3 .

[0046] The transparent electrode layer 4 in this embodiment has a structure that has a planar spread and is conductive and sufficiently transparent, and can also be called a transparent conductive layer. Even if the material constituting the transparent electrode layer 4 itself does not have transparency, the layer only needs to exhibit sufficient transparency in a structure that allows the transparent electrode layer 4 to perform its function. For example, the transparent electrode layer 4 may be composed of a conductive member or composition that has high transparency, or may be composed of a conductive material that does not have transparency but has an extremely thin or extremely fine structure that can exhibit sufficient transparency.

[0047] The transparent electrode layer 4 may be formed on a transparent substrate and, together with the substrate, adhered to the second transparent coating layer 3. The transparent electrode layer 4 may be disposed on at least one side of the transparent piezoelectric film 1. In the case where the first transparent coating layer 2 and the second transparent coating layer 3 are formed on both sides of the transparent piezoelectric film, the transparent electrode layer 4 may be disposed on at least one of the second transparent coating layers 3.

[0048] The material constituting the transparent electrode layer 4 is not limited, and a metal oxide of at least one metal selected from the group consisting of In, Sn, Zn, Ga, Sb, Ti, Si, Zr, Mg, Al, Au, Ag, Cu, Pd, and W is preferably used. As the metal oxide, ITO, zinc oxide, antimony-tin composite oxide (ATO), etc. are preferably used, and ITO is particularly preferably used. The metal oxide may be doped with a metal atom shown in the above group, if necessary.

[0049] In the transparent conductive piezoelectric film 11 of this embodiment, in order to prevent discoloration of the transparent piezoelectric film 1, it is necessary to avoid heating at high temperatures during processing. For this reason, when the material of the transparent electrode layer 4 is a metal oxide, the metal oxide may become amorphous. For example, it is possible to confirm that the transparent electrode layer 4 is made of an amorphous material by an image observed with a transmission electron microscope. In this specification, a material in which no crystals other than microcrystals are observed is called amorphous, and a material in which crystals have grown to the extent that crystal grains are observed is called crystalline.

[0050] The amorphous nature of the transparent electrode layer 4 can be determined by using an X-ray diffraction method, and the amorphous nature can be adjusted by the presence or absence and the degree of carrying out a step for promoting crystallization in the production of the transparent electrode layer 4, such as annealing after the formation of the transparent electrode layer 4.

[0051] In one embodiment, the transparent electrode layer 4 is made of an indium-tin composite oxide. In yet another embodiment, the transparent electrode layer 4 is made of an indium-tin composite oxide, and no peak of the indium-tin composite oxide is detected in X-ray diffraction. This configuration makes it possible to obtain a transparent electrode layer 4 that is amorphous and has a refractive index within a suitable range.

[0052] The refractive index of the transparent electrode layer 4 is, for example, 1.80 or more and 2.20 or less. There are no limitations on the refractive index of the transparent electrode layer 4 as long as it is within this range, and it is preferably 1.83 or more, and more preferably 1.85 or more. In addition, the refractive index of the transparent electrode layer 4 is preferably 2.00 or less, and more preferably 1.94 or less.

[0053] In particular, a transparent conductive piezoelectric film including a transparent electrode layer 4 having a refractive index of 1.94 or less is a film produced without high-temperature heating. Therefore, the transparency and color of the transparent piezoelectric film 1 are not impaired by high-temperature treatment, making it possible to produce a suitable transparent conductive piezoelectric film. Among these, a transparent conductive piezoelectric film including a transparent electrode layer 4 having a refractive index of 1.94 or less and further being amorphous is preferred.

[0054] On the other hand, when the material of the transparent electrode layer 4 is amorphous, the material itself is yellowish. The transparent conductive piezoelectric film 11 on which such a transparent electrode layer 4 is deposited tends to be a colored film even if other layers are transparent. However, as in the transparent conductive piezoelectric film 11 according to one embodiment of the present invention, a transparent conductive piezoelectric film 11 having suitable optical properties can be achieved by adjusting the refractive index of each layer.

[0055] The thickness of the transparent electrode layer 4 may be 13 nm or more, preferably 15 nm or more, and more preferably 20 nm or more. If the thickness of the transparent electrode layer 4 is too thin, the electrical resistance of the transparent conductive piezoelectric film 11 may become high, and discontinuous portions may be formed in the transparent electrode layer 4. When the thickness of the transparent electrode layer 4 is not below the lower limit described above, the transparent conductive piezoelectric film 11 can be a continuous coating having good electrical conductivity with a surface resistance value of less than 480 Ω / sq.

[0056] In particular, the thickness of the transparent electrode layer 4 is preferably 20 nm or more. By making the thickness of the transparent electrode layer 4 20 nm or more, a more suitable transparent conductive piezoelectric film having a surface resistance value of less than 300 Ω / sq can be obtained.

[0057] On the other hand, the thickness of the transparent electrode layer 4 may be less than 40 nm, but is preferably less than 38 nm, and more preferably less than 35 nm. If the thickness of the transparent electrode layer 4 is too thick, it may cause a decrease in transparency. By not exceeding the above-mentioned upper limit of the transparent electrode layer 4, the transparency of the transparent conductive piezoelectric film can be increased. The thickness of the transparent electrode layer 4 is determined by the following method, which is determined by observing a cross section of the transparent conductive piezoelectric film 11.

[0058] The transparent conductive piezoelectric film is embedded in epoxy resin, and the epoxy resin block is cut so that the cross section of the transparent conductive piezoelectric film is exposed. The exposed cross section of the transparent conductive piezoelectric film is observed using a scanning electron microscope (SU3800, Hitachi High-Tech Corporation) at an accelerating voltage of 3.0 kV and a magnification of 50,000 times, and the thickness of each coating layer and transparent electrode layer in the transparent conductive piezoelectric film is measured.

[0059] In measuring the thickness of each coating layer and transparent electrode layer, the thickness of each coating layer and transparent electrode layer is measured at any two points, and the average of the measurements obtained for each layer is taken as the thickness of each layer. In addition, under the above observation conditions, the interface of each layer is observed as a substantially smooth line. In this case, the thickness of each layer is measured by measuring the distance between the lines.

[0060] As described above, the thickness of the transparent electrode layer 4 is important from the viewpoint of maintaining the conductivity and improving the transparency of the transparent conductive piezoelectric film 11. Furthermore, by using a preferred combination of the refractive indexes and respective thicknesses of the first transparent coating layer, the second transparent coating layer, and the transparent electrode layer of the transparent conductive piezoelectric film 11, as well as the optional third transparent coating layer, the interfacial reflections of the layers are suitably adjusted to cancel each other out, thereby further improving the transparency.

[0061] (First transparent coating layer 2) In this embodiment, the first transparent coating layer 2 is a layer located between the transparent piezoelectric film 1 and the second transparent coating layer 3 .

[0062] The refractive index of the first transparent coating layer 2 is 1.60 or more and less than 1.80. There is no limitation on the refractive index of the first transparent coating layer 2 as long as it is within this range, but it is preferably 1.63 or more, and more preferably 1.65 or more. In addition, the refractive index of the first transparent coating layer 2 is preferably 1.75 or less, and more preferably 1.72 or less.

[0063] The material of the first transparent coating layer 2 may be appropriately selected from any usable material as long as it satisfies such a refractive index. The material may be an inorganic material or an organic material, or may be an inorganic-organic mixed material or a composite material thereof. In addition, it may be one type of material or a mixed material or composite material of two or more types of materials, but from the viewpoint of improving the transparency of the transparent conductive piezoelectric film, it is preferable that it is one type of material or a composite material further containing metal oxide particles described later. In addition, the material of the coating layer may be the material of the hard coat layer. Examples of the material include melamine resin, urethane resin, (meth)acrylic acid ester resin, silane compound, and metal oxide. Note that "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid, and means one or both of them. In particular, (meth)acrylic acid ester resin is preferable from the viewpoints of sufficient transparency, a wide variety of materials, and low raw material prices.

[0064] The material of the first transparent coating layer 2 may contain other materials necessary to form a transparent coating layer. In the case of a material for a transparent coating layer made of a (meth)acrylic ester resin, a composition generally consisting of a mixture of an initiator, an oligomer, a monomer and other components may be used. In this case, the physical properties of the transparent coating layer are mainly determined by the oligomer and the monomer. Examples of the oligomer include monofunctional or polyfunctional (meth)acrylate. Examples of the monomer include urethane (meth)acrylate, epoxy (meth)acrylate, and polyester (meth)acrylate.

[0065] Metal oxide particles may be added to the above-mentioned materials to adjust the refractive index of the first transparent coating layer 2. The metal oxide particles have a refractive index of 1.50 or more. Examples of the metal oxide particles include aluminum oxide, titanium oxide, zirconium oxide, zinc oxide, and tin oxide, and among these, titanium oxide and zirconium oxide are preferred.

[0066] The first transparent coating layer 2 may further include a material for exhibiting an arbitrary function. For example, the first transparent coating layer 2 may include an antistatic agent. Examples of the antistatic agent include a surfactant, antimony pentoxide, indium-tin oxide (ITO), and a conductive polymer.

[0067] The suitable thickness of the first transparent coating layer 2 varies depending on the presence or absence of the third transparent coating layer 5 in the transparent conductive piezoelectric film. In the transparent conductive piezoelectric film 11 not including the third transparent coating layer 5, the thickness of the first transparent coating layer 2 may be 400 nm or more, preferably 450 nm or more, and more preferably 500 nm or more. The thickness of the first transparent coating layer 2 may be less than 1300 nm, preferably 1000 nm or less, and more preferably 800 nm or less.

[0068] In the case of a transparent conductive piezoelectric film not including the third transparent coating layer 5, the first transparent coating layer is required not only to have a predetermined refractive index in order to increase the transparency of the transparent conductive piezoelectric film, but also to prevent scratches and irregularities on the surface of the transparent piezoelectric film 1. When the thickness of the first transparent coating layer 2 is not below the lower limit, scratches and irregularities on the surface of the transparent piezoelectric film 1 can be prevented, and the transparency of the transparent piezoelectric film 1 is increased. On the other hand, it is preferable that the thickness of the first transparent coating layer 2 is not above the upper limit, from the viewpoints of thinning the transparent piezoelectric film and increasing the transparency of the film.

[0069] In the transparent conductive piezoelectric film 12 including the third transparent coating layer 5, the thickness of the first transparent coating layer 2 may be 60 nm or more, preferably 70 nm or more, and more preferably 83 nm or more. The thickness of the first transparent coating layer 2 may be less than 300 nm, preferably 250 nm or less, and more preferably 230 nm or less. When the thickness of the first transparent coating layer is within this range, transparency can be imparted to the transparent conductive piezoelectric film 11.

[0070] (Second transparent coating layer 3) The second transparent coating layer 3 in this embodiment is a layer located between the first transparent coating layer 2 and the transparent electrode layer 4 .

[0071] The refractive index of the second transparent coating layer 3 is, for example, 1.30 or more and 1.50 or less. The refractive index of the second transparent coating layer 3 may be within this range, but is preferably 1.35 or more, and more preferably 1.37 or more. The refractive index of the second transparent coating layer 3 is preferably 1.48 or less, and more preferably 1.47 or less.

[0072] The material of the second transparent coating layer 3 may be appropriately selected from any available material as long as it satisfies such a refractive index. For example, a material may be appropriately selected from the materials exemplified as the materials of the first transparent coating layer 2 so as to have an appropriate refractive index. In addition, in order to adjust the refractive index, one or more metal fluorides selected from the group consisting of NaF, Na3AlF6, LiF, MgF2, CaF2, and BaF2 or silicon dioxide may be contained. Among these, silicon dioxide is preferable.

[0073] Furthermore, the materials of the second transparent coating layer 3 may include other materials necessary to constitute a transparent coating layer, similar to the materials described for the materials of the first transparent coating layer 2 .

[0074] The thickness of the second transparent coating layer 3 may be 10 nm or more and 70 nm or less. The thickness of the second transparent coating layer 3 is preferably 15 nm or more, and more preferably 20 nm or more. The thickness of the second transparent coating layer 3 is preferably 68 nm or less, and more preferably 65 nm or less. When the thickness of the second transparent coating layer 3 is within the above range, the transparency and color of the transparent conductive piezoelectric film 11 can be improved.

[0075] (Third transparent coating layer 5) The third transparent coating layer 5 is a layer that is optionally provided on the transparent conductive piezoelectric film. When the third transparent coating layer 5 is present, the third transparent coating layer 5 is a layer that is in direct contact with the transparent piezoelectric film 1. For example, as in the transparent conductive piezoelectric film 12, the third transparent coating layer 5 is a layer that is located between the transparent piezoelectric film 1 and the first transparent coating layer 2. In addition, when the first transparent coating layer 2 is present only on one side of the transparent piezoelectric film 1, the third transparent coating layer 5 may be provided on the other side of the transparent piezoelectric film 1. The transparent conductive piezoelectric film 11 may have the third transparent coating layer 5 on both sides of the transparent piezoelectric film 1.

[0076] The third transparent coating layer 5 may have a refractive index of 1.45 or more, preferably 1.48 or more, and more preferably 1.50 or more. The third transparent coating layer 5 may have a refractive index of less than 1.60, preferably less than 1.58, and more preferably less than 1.55. By providing such a third transparent coating layer 5 on at least one surface of the transparent piezoelectric film 1, the transparency of the transparent conductive piezoelectric film 12 can be improved.

[0077] The material of the third transparent coating layer 5 may be appropriately selected from all available materials as long as it satisfies such a refractive index. For example, a material may be appropriately selected from the materials exemplified as the materials of the first transparent coating layer 2 so as to have an appropriate refractive index. The third transparent coating layer 5 may also be a transparent surface protection layer for preventing scratches, also called a hard coat layer. It is preferable that the material realizes a suitable refractive index and further has excellent scratch resistance.

[0078] In order to prevent blocking between films and to improve adhesion, inorganic particles and polymer beads may be added to the material of the third transparent coating layer 5. Examples of the inorganic particles that can be used include synthetic silica, talc, diatomaceous earth, calcium carbonate, feldspar, and quartz, and synthetic silica is particularly preferred in terms of improving the quality of the plastic film. Examples of synthetic silica include SiO2.

[0079] The thickness of the third transparent coating layer 5 may be 500 nm or more, preferably 700 nm or more, and more preferably 900 nm or more. When the thickness of the third transparent coating layer 5 is not below the lower limit, a protective effect for the transparent piezoelectric film 1 can be expected. From the viewpoint of thinning the film, the thickness of the third transparent coating layer 5 may be 1400 nm or less, preferably 1200 nm or less, and more preferably 1100 nm or less. When the thickness of the third transparent coating layer is not above the upper limit, the piezoelectric constant d 33 It is possible to suppress deterioration of the piezoelectric properties represented by the following equation: ##EQU1## It is also possible to suppress deterioration in quality, such as cracking and curling of the transparent conductive piezoelectric film caused by heating in the process of incorporating the transparent conductive piezoelectric film into a device. By setting the thickness of the third transparent coating layer 5 within the above range, it is possible to obtain a transparent conductive piezoelectric film 12 with improved transparency.

[0080] 〔device〕 A device according to an embodiment of the present invention includes the transparent conductive piezoelectric film according to the embodiment described above. The device may be any type as long as it includes the transparent conductive piezoelectric film according to this embodiment. For example, the position and number of the transparent conductive piezoelectric films can be appropriately determined depending on the application or intended function of the device.

[0081] The transparent conductive piezoelectric film according to one embodiment has suitable conductivity and a high piezoelectric constant as described above. In addition, each layer of the transparent conductive piezoelectric film can be made into an ink and can be formed by coating or printing. Furthermore, the transparent conductive piezoelectric film according to one embodiment has chemical stability and film flexibility. Due to these characteristics, the transparent conductive piezoelectric film according to one embodiment is being considered for application to devices such as flexible pressure sensors and vibration sensors, energy harvesting elements, and actuators. Note that the transparent conductive piezoelectric film according to one embodiment of the present invention is particularly suitable for application to touch panels and the like due to its conductivity and piezoelectricity.

[0082] In addition, when the transparent conductive piezoelectric film according to one embodiment is applied to a device, in the manufacture thereof, the transparent adhesive sheet may be formed not only on any transparent coating layer but also on another layer that is adhered to the transparent coating layer via the transparent adhesive sheet. In this case, the transparent adhesive sheet layer may or may not be on the transparent coating layer side.

[0083] In a device incorporating the transparent conductive piezoelectric film according to an embodiment, the transparent conductive piezoelectric film also functions as an electrode, so that it is possible to eliminate the electrode layer made of, for example, PET / ITO, which is included in conventional devices, and therefore the layer structure of the device can be simplified compared to conventional devices.

[0084] [Method for manufacturing transparent piezoelectric film] Hereinafter, a method for manufacturing a transparent conductive piezoelectric film will be described with reference to a method for manufacturing a transparent conductive piezoelectric film 11. The method for manufacturing the transparent conductive piezoelectric film 11 is a method for manufacturing a laminated film in which a first transparent coating layer 2, a second transparent coating layer 3, and a transparent electrode layer 4 are laminated in this order on at least one surface of a transparent piezoelectric film 1. The manufacturing method includes a first step of manufacturing a transparent piezoelectric film 1 to form a film having a refractive index of 1.30 or more and less than 1.45, a second step of forming a first transparent coating layer 2 having a refractive index of 1.60 or more and less than 1.80 on at least one surface of the transparent piezoelectric film 1, a third step of forming a second transparent coating layer 3 having a refractive index of 1.30 or more and less than 1.50 and a thickness of 10 nm or more and 70 nm or less on the surface of the first transparent coating layer 2, and a fourth step of forming a transparent electrode layer 4 having a refractive index of 1.80 or more and less than 2.20 and a thickness of 20 nm or more and less than 40 nm on the surface of the second transparent coating layer 3.

[0085] The first step may be a step of producing the transparent piezoelectric film 1, and steps may be changed or added as appropriate depending on the type of transparent piezoelectric film 1 to be produced. For example, the transparent piezoelectric film 1 can be produced by successively carrying out a step of producing a resin film by a conventionally known method such as a casting method, a heat pressing method, or a melt extrusion method, a step of stretching the resin film, and a step of polarizing a non-polarized resin film.

[0086] The second to fourth steps can be suitably carried out by utilizing known coating methods such as wet coating and dry coating. In general, the wet coating method is suitable for forming a layer having a large thickness since a material is applied to form a layer, and the dry coating method is suitable for forming a layer having a small thickness since a material is finely deposited to form a layer. By applying known techniques according to such advantages, each of the second to fourth steps can be suitably carried out.

[0087] The second step is a step of forming a first transparent coating layer. The second step can be performed by a known method, for example, a wet coating method or a dry coating method.

[0088] The wet coating method is particularly preferred in terms of productivity and manufacturing costs. In the second step using the wet coating method, the material for the first transparent coating layer may be applied to at least one surface of the transparent piezoelectric film 1 produced in the first step. The application method may be a conventionally known method and is not particularly limited. In terms of productivity and manufacturing costs, the wet coating method is particularly preferred. The wet coating method may be a known method, and representative methods include, for example, roll coating, spin coating, dip coating, and gravure coating. Among these, methods that can form layers continuously, such as roll coating and gravure coating, are preferred in terms of productivity.

[0089] The material for the first transparent coating layer 2 may be applied using, for example, a bar coater or a gravure coater. After application of the material, the material may be dried at 50°C to 180°C for 0.5 to 60 minutes. Furthermore, the dried coating film of the first transparent coating layer 2 may be solidified by UV irradiation. The solidification by UV irradiation may be performed, for example, using a UV irradiation device with 50 to 1200 mJ / cm. 2 The conditions such as the device, the concentration of the material, and the temperature used in the second step may be appropriately changed depending on the material, the film thickness, etc. of the first transparent coating layer 2.

[0090] In the second step using the dry coating method, a material for the first transparent coating layer may be applied to at least one surface of the transparent piezoelectric film 1 produced in the first step by a known dry coating method. Representative examples of the dry coating method include sputtering, vacuum deposition, and ion plating. These methods may be appropriately selected depending on the required film thickness.

[0091] For example, when a sputtering method is adopted as the second step, the metal constituting the first transparent coating layer is used as the target material. The target material can be appropriately selected from known target materials according to the desired refractive index of the first transparent coating layer. In addition, the sputtering gas can be, for example, an inert gas such as Ar. In addition, a reactive gas such as oxygen gas can be used in combination as necessary.

[0092] The third step is a step of forming a second transparent coating layer. In the third step, a coating made of the material of the second transparent coating layer 3 may be applied to the first transparent coating layer 2 prepared in the second step by a known method. For example, the material of the second transparent coating layer 3 may be applied by a wet coating method, similar to the first transparent coating layer 2. Also, depending on the material of the second transparent coating layer 3, it is possible to form a coating by a dry coating method such as a sputtering method. The conditions of the device, material concentration, temperature, etc. of the third step may be the same as those of the second step. The film thickness of the second transparent coating layer 3 can be adjusted by adjusting the material concentration or sputtering time.

[0093] The fourth step is a step of forming a transparent electrode layer. In the fourth step, the transparent electrode layer 4 may be formed on the second transparent coating layer 3 prepared in the third step by a known method. The transparent electrode layer 4 may be formed by attaching the material of the transparent electrode layer 4 by a method such as a sputtering method, a vacuum deposition method, or an ion plating method. Alternatively, in the formation of the transparent electrode layer 4, the material of the transparent electrode layer may be applied by a wet coating method in the same manner as the first transparent coating layer 2 and the second transparent coating layer 3.

[0094] The fourth step will be described in more detail below, taking as an example a configuration in which the transparent electrode layer is formed by employing a sputtering method in the fourth step. When the sputtering method is employed, the target material may be the above-mentioned inorganic material constituting the transparent electrode layer 4, and preferably ITO. The tin oxide concentration of ITO is, for example, 0.5 mass% or more, preferably 2 mass% or more, and, for example, 15 mass% or less, preferably 13 mass% or less, and more preferably 7 mass% or less.

[0095] The sputtering gas may be, for example, an inert gas such as Ar. If necessary, a reactive gas such as oxygen gas may be used in combination. When a reactive gas is used in combination, the flow rate of the reactive gas is not particularly limited, but is, for example, 0.1% to 5% of the total flow rate of the sputtering gas and the reactive gas.

[0096] The air pressure during sputtering is, for example, 1 Pa or less, and preferably 0.7 Pa or less, from the viewpoints of suppressing a decrease in the sputtering rate, discharging stability, and the like.

[0097] The power source used in the sputtering method may be, for example, any of a DC power source, an AC power source, an MF power source, and an RF power source, or a combination of these.

[0098] The manufacturing method of this embodiment may further include other steps as long as it includes the first to fourth steps. For example, a third transparent coating layer 5 may be formed on the transparent piezoelectric film 1 between the first and second steps. The third transparent coating layer 5 may be formed by applying the material of the third transparent coating layer 5 onto the transparent piezoelectric film 1 produced in the first step by a known method.

[0099] Furthermore, a step of adding other layer configurations to the transparent conductive piezoelectric film 11 may be added. Also, a step of corona treating the transparent piezoelectric film 1 to enhance adhesion with the first transparent coating layer 2 may be added.

[0100] According to the manufacturing method of this embodiment, a transparent conductive piezoelectric film 11 having high transparency and a suitable color can be manufactured.

[0101] In the manufacturing method of this embodiment, it is not necessary to perform an annealing treatment of the transparent electrode layer 4 after the fourth step. By not performing the annealing treatment, the color of the transparent piezoelectric film 1 is not impaired, and therefore it is possible to produce a transparent conductive piezoelectric film 11 that is suitable for use in devices such as displays.

[0102] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present invention.

[0103] (summary) The present invention can also be expressed as follows.

[0104] The transparent piezoelectric film according to the first embodiment has a transmittance of 75% or more at a wavelength of 450 nm and a transmittance of 85% or more at a wavelength of 550 nm, and a piezoelectric constant d 33 The piezoelectric film has a surface resistance of 50 Ω / sq or more and less than 300 Ω / sq. Such a transparent conductive piezoelectric film has excellent piezoelectric properties, transparency, and conductivity, and can be suitably used in a wide range of devices.

[0105] A transparent conductive piezoelectric film according to the present embodiment 2 is configured by stacking a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer in this order on at least one surface of the piezoelectric film in the present embodiment 1, wherein the refractive index of the transparent piezoelectric film is 1.30 or more and less than 1.45, the refractive index of the first transparent coating layer is 1.60 or more and less than 1.80, the refractive index of the second transparent coating layer is 1.30 or more and less than 1.50, and the refractive index of the transparent electrode layer is 1.80 or more and 2.20 or less. This configuration can impart preferable transparency to the transparent conductive piezoelectric film.

[0106] The transparent conductive piezoelectric film according to the present embodiment 3 is the same as that of the present embodiment 2, and further includes a third transparent coating layer having a refractive index of 1.45 or more and less than 1.60 between the transparent piezoelectric film and the first transparent coating layer, the first transparent coating layer having a thickness of 60 nm or more and 300 nm or less, the second transparent coating layer having a thickness of 10 nm or more and 70 nm or less, and the transparent electrode layer having a thickness of 20 nm or more and less than 40 nm. This configuration can impart preferable transparency and electrical properties (surface resistance value) to the transparent conductive piezoelectric film.

[0107] The transparent conductive piezoelectric film according to the present embodiment 4 is configured by stacking the third transparent coating layer, the first transparent coating layer, the second transparent coating layer, and the transparent electrode layer in this order on one surface of the transparent piezoelectric film, and by providing another third transparent coating layer on the other surface of the transparent piezoelectric film in the present embodiment 3. This configuration can improve the transparency of the transparent conductive piezoelectric film.

[0108] The transparent conductive piezoelectric film according to the present embodiment 5 is the same as that of the present embodiment 2, in which the first transparent coating layer has a thickness of 400 nm or more and 1000 nm or less, the second transparent coating layer has a thickness of 10 nm or more and 70 nm or less, and the transparent electrode layer has a thickness of 20 nm or more and less than 40 nm. This configuration can impart preferable transparency and electrical properties (surface resistance value) to the transparent conductive piezoelectric film.

[0109] The transparent conductive piezoelectric film according to the present embodiment 6 is configured by stacking the first transparent coating layer, the second transparent coating layer, and the transparent electrode layer in this order on one surface of the transparent piezoelectric film in accordance with the present embodiment 5, and by providing another third transparent coating layer on the other surface of the transparent piezoelectric film, the third transparent coating layer having a refractive index of 1.45 or more and less than 1.60. This configuration can improve the transparency of the transparent conductive piezoelectric film.

[0110] The transparent conductive piezoelectric film according to Aspect 7 is the transparent piezoelectric film containing a fluorine-based resin as a main component in any one of Aspects 1 to 6. This configuration makes it possible to provide a transparent piezoelectric film with a favorable refractive index.

[0111] The transparent conductive piezoelectric film according to aspect 8 is such that the refractive index of the transparent electrode layer is 1.94 or less in any of aspects 1 to 7. Such a transparent conductive piezoelectric film is a film produced without high temperature heating, and is therefore preferable in that it does not impair the color of the transparent piezoelectric film.

[0112] A touch panel according to the ninth aspect is a touch panel comprising the transparent conductive piezoelectric film according to any one of the first to eighth aspects.

[0113] The manufacturing method according to the tenth aspect is a method for manufacturing a laminated film in which a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer are stacked in this order on at least one surface of a transparent piezoelectric film, and includes a first step of manufacturing the transparent piezoelectric film to form a film having a refractive index of 1.30 or more and less than 1.45; a second step of forming the first transparent coating layer on at least one surface of the transparent piezoelectric film; a third step of forming the second transparent coating layer on a surface of the first transparent coating layer, the second transparent coating layer having a refractive index of 1.30 or more and less than 1.50 and a thickness of 10 nm or more and less than 70 nm; and a fourth step of forming the transparent electrode layer on a surface of the second transparent coating layer, the second transparent coating layer having a refractive index of 1.80 or more and less than 2.20 and a thickness of 20 nm or more and less than 40 nm. EXAMPLES

[0114] An embodiment of the present invention will now be described.

[0115] [Production of Transparent Conductive Piezoelectric Film] <Example 1> (First step: Preparation of transparent piezoelectric film) A resin film (thickness, 120 μm) made of polyvinylidene fluoride (manufactured by Kureha Corporation) with an inherent viscosity of 1.3 dl / g was stretched to a stretch ratio of 4.2 times. After stretching, the film was passed through a polarizing roll to perform a polarization treatment, and a piezoelectric film was obtained. At that time, the polarization treatment was performed by applying a DC voltage that was increased from 0 kV to 12.0 kV. The film after the polarization treatment was further heat-treated at 130°C for 1 minute to obtain a transparent piezoelectric film with a refractive index of 1.42 and a thickness of 40 μm.

[0116] (Second step: formation of first transparent coating layer) An amorphous silica-containing UV-curable resin composition made of acrylic resin was applied to the upper surface (side A) of the transparent piezoelectric film, and after drying at 80°C, 400 mJ / cm 2 A third transparent coating layer (thickness 1000 nm, refractive index 1.52) was formed on the lower surface (side B) of the transparent piezoelectric film by irradiating ultraviolet light with an integrated light amount of 400 mJ / cm2. Next, a third transparent coating layer (thickness 1000 nm, refractive index 1.52) was formed on the lower surface (side B) of the transparent piezoelectric film by the same method. Next, a zirconium oxide particle-containing ultraviolet curing resin composition was applied to the upper surface of the third transparent coating layer (side A), and dried at 80°C. 2 A first transparent coating layer (thickness: 99 nm, refractive index: 1.65) was formed by irradiating the film with ultraviolet light at an integrated light amount of 1.0001 to 1.0001.

[0117] (Third step: formation of second transparent coating layer) Next, a hollow silica-containing ultraviolet-curable resin composition made of an acrylic resin is applied onto the first transparent coating layer, and after drying at 80°C, 400 mJ / cm 2 A second transparent coating layer (thickness: 44 nm, refractive index: 1.37) was formed by irradiating the film with ultraviolet light at an integrated light amount of 1.0001 to 1.0001.

[0118] (Fourth step: Formation of transparent electrode layer) Next, on the second transparent coating layer, a sintered material containing 97% by mass of indium oxide and 3% by mass of tin oxide was used as a target to form an ITO film having a refractive index of 1.88 and a thickness of 30 nm, which was a transparent electrode layer. Thus, a transparent conductive piezoelectric film was obtained, and the obtained transparent conductive piezoelectric film was designated as Example 1.

[0119] <Example 2> Except for changing the thickness of the second transparent coating layer to 61 nm, a transparent conductive piezoelectric film was obtained in the same manner as in Example 1. The obtained transparent conductive piezoelectric film was designated as Example 2.

[0120] <Example 3> A transparent conductive piezoelectric film was obtained in the same manner as in Example 1, except that the first transparent coating layer had a refractive index of 1.70 and a thickness of 105 nm, and the second transparent coating layer had a refractive index of 1.40 and a thickness of 20 nm. The obtained transparent conductive piezoelectric film was designated Example 3.

[0121] <Example 4> A third transparent coating layer was not formed on the A-side and B-side of the transparent piezoelectric film, and a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer were formed in this order on the A-side of the transparent piezoelectric film. A transparent conductive piezoelectric film was obtained in the same manner as in Example 3, except that the thickness of the first transparent coating layer was 533 nm and the thickness of the second transparent coating layer was 69 nm. The obtained transparent conductive piezoelectric film was designated as Example 4.

[0122] <Example 5> A transparent conductive piezoelectric film was obtained in the same manner as in Example 3, except that the first transparent coating layer had a thickness of 219 nm, a refractive index of 1.74, and a thickness of the second coating layer of 34 nm. The obtained transparent conductive piezoelectric film was designated as Example 5.

[0123] <Example 6> Except for changing the thickness of the transparent electrode layer to 22 nm, a transparent conductive piezoelectric film was obtained in the same manner as in Example 1. The obtained transparent conductive piezoelectric film was designated as Example 6.

[0124] <Example 7> A transparent conductive piezoelectric film was obtained in the same manner as in Example 1, except that the thickness of the transparent electrode layer was set to 34 nm.

[0125] <Example 8> (Formation of the first transparent coating layer) In the same manner as in Example 1, a third transparent coating layer was formed on both sides of the transparent piezoelectric film, and a first transparent coating layer (thickness 83 nm, refractive index 1.65) was further formed on side A.

[0126] (Formation of second transparent coating layer) Next, a SiO2 film was formed on the first transparent coating layer by sputtering using Si as a target material. -4 After evacuating the chamber to a vacuum of less than Pa, a mixture of Ar gas and oxygen gas was introduced into the chamber and a 25 nm thick SiO2 film was deposited to form a second transparent coating layer (thickness 25 nm, refractive index 1.46).

[0127] (Formation of transparent electrode layer) A transparent electrode layer was formed on the second transparent coating layer in the same manner as in Example 1. In this manner, a transparent conductive piezoelectric film was obtained.

[0128] <Example 9> A transparent conductive piezoelectric film was obtained in the same manner as in Example 8, except that the thickness of the first transparent coating layer was set to 99 nm. The obtained transparent conductive piezoelectric film was designated as Example 9.

[0129] <Example 10> A transparent conductive piezoelectric film was obtained in the same manner as in Example 8, except that the thickness of the first transparent coating layer was set to 139 nm. The obtained transparent conductive piezoelectric film was designated as Example 10.

[0130] <Example 11> A transparent conductive piezoelectric film was obtained in the same manner as in Example 8, except that the first transparent coating layer had a thickness of 105 nm and a refractive index of 1.70.

[0131] <Comparative Example 1> Except for not forming the third transparent coating layer, the first transparent coating layer, and the second transparent coating layer, a conductive piezoelectric film was obtained in the same manner as in Example 1. The conductive piezoelectric film obtained was designated as Comparative Example 1.

[0132] <Comparative Example 2> Except for changing the thickness of the second transparent coating layer to 80 nm, a conductive piezoelectric film was obtained in the same manner as in Example 1. The conductive piezoelectric film obtained was designated as Comparative Example 2.

[0133] <Comparative Example 3> A conductive piezoelectric film was obtained in the same manner as in Example 2, except that the thickness of the second transparent coating layer was set to 151 nm.

[0134] <Comparative Example 4> Except for changing the thickness of the transparent electrode layer to 45 nm, a conductive piezoelectric film was obtained in the same manner as in Example 1. The conductive piezoelectric film obtained was designated as Comparative Example 4.

[0135] <Comparative Example 5> A conductive piezoelectric film was obtained in the same manner as in Example 1, except that the first transparent coating layer had a thickness of 100 nm and a refractive index of 1.52, and the second transparent coating layer had a thickness of 80 nm and a refractive index of 1.40. The obtained conductive piezoelectric film was designated Comparative Example 5.

[0136] <Comparative Example 6> A conductive piezoelectric film was obtained in the same manner as in Example 1, except that the first transparent coating layer had a thickness of 105 nm, the second transparent coating layer had a thickness of 29 nm, and the refractive index was 1.51. The conductive piezoelectric film obtained was designated Comparative Example 6.

[0137] <Comparative Example 7> A conductive piezoelectric film was obtained in the same manner as in Example 1, except that the thickness of the transparent electrode layer was set to 15 nm.

[0138] <Comparative Example 8> A conductive piezoelectric film was obtained in the same manner as in Example 8, except that the first transparent coating layer had a thickness of 40 μm and a refractive index of 1.55, the second transparent coating layer had a thickness of 40 μm, and indium oxide containing 36 mass % of tin oxide was used as a sputtering target. The obtained conductive piezoelectric film was designated Comparative Example 8.

[0139] [Measurement of thickness of each layer] The thicknesses of the transparent coating layer and the transparent electrode layer constituting the transparent conductive piezoelectric film and the conductive piezoelectric film (hereinafter, simply referred to as "conductive piezoelectric film") of Examples 1 to 11 and Comparative Examples 1 to 8 were determined by the following method of observation using an electron microscope. In this method, first, the transparent conductive piezoelectric film is embedded in an epoxy resin, and the epoxy resin block is cut so that the cross section of the transparent conductive piezoelectric film is exposed. The exposed cross section of the transparent conductive piezoelectric film is observed using a scanning electron microscope ("SU3800", manufactured by Hitachi High-Technologies Corporation) under conditions of an acceleration voltage of 3.0 kV and a magnification of 50,000 times. Then, the thicknesses of the transparent conductive piezoelectric film and each film or layer in the transparent conductive piezoelectric film are measured.

[0140] The refractive index of each layer of the conductive piezoelectric films of Examples 1 to 11 and Comparative Examples 1 to 8 is shown in Table 1.

[0141] [Table 1]

[0142] The thickness of each layer of the conductive piezoelectric films of Examples 1 to 11 and Comparative Examples 1 to 8 is shown in Table 2.

[0143] [Table 2]

[0144] 〔evaluation〕 The conductive piezoelectric films of Examples 1 to 11 and Comparative Examples 1 to 8 were evaluated for their physical properties and optical properties.

[0145] <Physical property evaluation> (Surface resistance value) The surface resistance (Ω / sq) of each of the conductive piezoelectric films of Examples 1 to 11 and Comparative Examples 1 to 8 was measured using a resistivity meter (LorestaGP MCP-T610, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) in accordance with JIS K 7194. The measurement was performed three times, and the average of the three measurements was determined as a representative value. If the surface resistance is 50 Ω / sq or more and less than 480 Ω / sq, it can be determined that there is no practical problem in device applications such as touch panels.

[0146] (Piezoelectric constant d 33 value) The piezoelectric constant d of each of the conductive piezoelectric films of Examples 1 to 11 and Comparative Examples 1 to 8 33 The sample was clipped with 0.2 N and the generated charge was read when a force of 0.15 N, 110 Hz was applied using a piezoelectric constant measuring device ("Piezometer System PM300", manufactured by PIEZOTEST). 33 The measured value of is a positive or negative value depending on the front and back of the film being measured, but in this specification, the absolute value is described. 33 A value of 5 pC / N or more and 40 pC / N or less can be determined to be satisfactory for practical use in devices such as touch panels.

[0147] <Optical property evaluation> (transmittance) The transmittance at a wavelength of 450 nm and the transmittance at a wavelength of 550 nm of each of the conductive piezoelectric films of Examples 1 to 11 and Comparative Examples 1 to 8 were measured using a spectrophotometer (SD7000 manufactured by Nippon Denshoku Industries Co., Ltd.). If the transmittance at a wavelength of 450 nm is 75% or more, it can be judged that there is no practical problem in the use of devices such as touch panels, and if it is 78% or more, it is more preferable, and if it is 80% or more, it is even more preferable. If the transmittance at a wavelength of 550 nm is 85% or more, it can be judged that there is no practical problem in the use of devices such as touch panels, and if it is 87% or more, it is more preferable, and if it is 89% or more, it is even more preferable.

[0148] The results of the above evaluations are shown in Table 3.

[0149] [Table 3]

[0150] As shown in Table 3, all of the conductive piezoelectric films of Examples 1 to 11 have physical properties that are practically acceptable for use in devices such as touch panels, and further have high transparency that satisfies both the transmittance at wavelengths of 450 nm and 550 nm. In contrast, none of the conductive piezoelectric films of Comparative Examples 1 to 8 satisfied both the transmittance at wavelengths of 450 nm and 550 nm. [Industrial Applicability]

[0151] The present invention can be used in devices where piezoelectric properties are required. [Explanation of symbols]

[0152] 1 Transparent piezoelectric film 2. First transparent coating layer 3 Second transparent coating layer 4 Transparent electrode layer 5 Third transparent coating layer 11, 12 Transparent conductive piezoelectric film

Claims

1. A piezoelectric element comprising a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer laminated in this order on at least one surface of a transparent piezoelectric film; The refractive index of the transparent piezoelectric film is 1.30 or more and less than 1.45, The refractive index of the first transparent coating layer is 1.60 or more and less than 1.80; The second transparent coating layer has a thickness of 10 nm or more and 70 nm or less, and a refractive index of 1.30 or more and less than 1.50; The transparent electrode layer has a thickness of 20 nm or more and less than 40 nm and a refractive index of 1.80 or more and 2.20 or less, a third transparent coating layer having a refractive index of 1.45 or more and less than 1.60 on the other surface of the transparent piezoelectric film; The transmittance at a wavelength of 450 nm is 75% or more, and the transmittance at a wavelength of 550 nm is 85% or more, Piezoelectric constant d ３３ is 5 pC / N or more and 40 pC / N or less, A transparent conductive piezoelectric film, wherein the surface resistance of the transparent electrode layer is 50 Ω / sq or more and less than 300 Ω / sq.

2. A third transparent coating layer having a refractive index of 1.45 or more and less than 1.60 is provided between the transparent piezoelectric film and the first transparent coating layer; The thickness of the first transparent coating layer is 60 nm or more and 300 nm or less; The transparent conductive piezoelectric film according to claim 1 .

3. The thickness of the first transparent coating layer is 400 nm or more and 1000 nm or less; The transparent conductive piezoelectric film according to claim 1 .

4. The transparent conductive piezoelectric film according to any one of claims 1 to 3, wherein the transparent piezoelectric film contains a fluorine-based resin as a main component.

5. 4. The transparent conductive piezoelectric film according to claim 1, wherein the transparent electrode layer has a refractive index of 1.94 or less.

6. A touch panel comprising the transparent conductive piezoelectric film according to any one of claims 1 to 3.

7. A method for producing a laminated film comprising: a first transparent coating layer, a second transparent coating layer, and a transparent electrode layer laminated in this order on at least one surface of a transparent piezoelectric film; A first step of producing the transparent piezoelectric film forms a film having a refractive index of 1.30 or more and less than 1.45; a second step of forming the first transparent coating layer having a refractive index of 1.60 or more and less than 1.80 on at least one surface of the transparent piezoelectric film; a third step of forming the second transparent coating layer on the surface of the first transparent coating layer, the second transparent coating layer having a refractive index of 1.30 or more and less than 1.50 and a thickness of 10 nm or more and 70 nm or less; and a fourth step of forming the transparent electrode layer on the surface of the second transparent coating layer, the transparent electrode layer having a refractive index of 1.80 or more and 2.20 or less and a thickness of 20 nm or more and less than 40 nm.

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