Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/85—Piezoelectric or electrostrictive active materials
  • H10N30/857—Macromolecular compositions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
  • B32B7/02—Physical, chemical or physicochemical properties
  • B32B7/025—Electric or magnetic properties
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/02—Forming enclosures or casings
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/88—Mounts; Supports; Enclosures; Casings
  • H10N30/883—Additional insulation means preventing electrical, physical or chemical damage, e.g. protective coatings
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/04—Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
  • H10N30/045—Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning by polarising
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/09—Forming piezoelectric or electrostrictive materials
  • H10N30/098—Forming organic materials

Definitions

• the present invention relates to a laminated piezoelectric body and a method for manufacturing the same.
• Touch panels are attached to the displays of electronic devices and are used to operate the devices. There are various types of touch panels, but capacitive touch panels are often used because they have a simple structure, are inexpensive to make, and can be made relatively large. Capacitive touch panels are prone to malfunctions due to the complex signal processing required.
• a touch panel detects a two-dimensional position (position coordinates) on the surface of the touch panel by touching the surface with a finger, pen, or the like.
• position coordinates position coordinates
• piezoelectric films As a pressure sensor for use in touch panels, the use of piezoelectric films that generate voltage in response to pressure has been proposed.
• Known piezoelectric films include those that contain polymeric materials such as polylactic acid and fluorine-based resins.
• piezoelectric films Although these piezoelectric films have excellent transparency, they are easily charged by friction or vibration, and are prone to generating static electricity. When static electricity is generated, foreign matter can easily adhere to the piezoelectric film, which can lead to a deterioration in quality. Furthermore, if the surface of the piezoelectric film is scratched during handling, visibility is likely to decrease when used in a touch panel. For this reason, there is a demand for piezoelectric films that are antistatic and scratch-resistant.
• Patent Document 2 discloses a laminated piezoelectric body that includes a piezoelectric film containing polylactic acid and a surface layer that contains a conductive material (A) and a polymer (B) disposed thereon.
• the surface layer is a hard coat layer that has antistatic properties, and therefore the laminated piezoelectric body is said to have good antistatic properties and scratch resistance.
• JP 2010-26938 A International Publication No. 2016/098597
• the laminated piezoelectric body of Patent Document 2 has a problem that the surface of the hard coat layer has poor slipperiness, and when wound into a roll, for example, the laminated piezoelectric bodies are likely to adhere to each other and stick to each other (blocking).
• the piezoelectric film containing polylactic acid used in Patent Document 2 has a low piezoelectric constant d14 of 6.4 pC/N, so there is also a problem that it is difficult to obtain a sufficient piezoelectric effect.
• the present inventors have found a new problem in which, when an antistatic layer is formed on a piezoelectric film containing a fluororesin having a high piezoelectric constant d33 and sufficient piezoelectric effect, coating spots occur in the resulting laminated piezoelectric body, resulting in reduced visibility.
• the present invention was made in consideration of the above circumstances, and aims to provide a laminated piezoelectric body that has high piezoelectricity, anti-blocking properties, and antistatic properties without reducing visibility, and a method for manufacturing the same.
• a laminated piezoelectric body comprising a piezoelectric film containing a fluorine-based resin as a main component, an antistatic layer having a thickness of 10 nm to 250 nm and disposed on at least one surface of the piezoelectric film, and a hard coat layer disposed on the antistatic layer and having a maximum surface height Rz of 40 nm to 150 nm, wherein the surface resistivity of the laminated piezoelectric body measured on the hard coat layer is 1.0 ⁇ 10 ⁇ /sq.
• the present invention provides a laminated piezoelectric body that has high piezoelectricity, anti-blocking properties, and antistatic properties without reducing visibility, and a method for manufacturing the same.
• laminated piezoelectric elements having a piezoelectric film mainly composed of fluororesin produce coating spots that were not an issue with laminated piezoelectric elements having a piezoelectric film made of polylactic acid.
• the coating spots are caused by uneven coating of the antistatic layer. It is believed that the coating unevenness is caused by picking up fine irregularities on the surface of the piezoelectric film. It is believed that the unevenness on the surface of the piezoelectric film is formed in the process of stretching and poling a film containing a fluororesin as a main component in order to develop a high piezoelectric effect (piezoelectric constant d 33 ).
• the thickness of the antistatic layer disposed on the piezoelectric film containing a fluororesin is set to a predetermined value or less. If the antistatic layer is applied thickly, the antistatic layer will be applied thickly to the concave parts of the piezoelectric film, resulting in large coating unevenness of the antistatic layer on the laminated piezoelectric body. In contrast, by applying the antistatic layer thinly, unevenness in the thickness of the antistatic layer is reduced, and the variation itself caused by the unevenness of the surface of the piezoelectric film is also reduced, making it less likely that coating unevenness will occur. This reduces coating unevenness on the laminated piezoelectric body and suppresses a decrease in visibility.
• the laminated piezoelectric body according to this embodiment includes a piezoelectric film, an antistatic layer, and a hard coat layer.
• Piezoelectric film is a film containing a fluorine-based resin as a main component, and the piezoelectric constant d 33 is adjusted to 7 pC/N or more and 40 pC/N or less.
• the piezoelectric constant d 33 of the piezoelectric film is 7 pC/N or more, the amount of charge generated by the piezoelectric effect is sufficient, so that high pressure sensitivity is easily obtained.
• the piezoelectric constant d 33 of the piezoelectric film is 40 pC/N or less, for example, the unevenness of the film surface caused by the polarization treatment can be further reduced, so that the appearance defect can be reduced.
• the piezoelectric constant d 33 of the piezoelectric film is more preferably 10 pC/N or more and 35 pC/N or less, even more preferably 10 pC/N or more and 27 pC/N or less, and particularly preferably 10 pC/N or more and 24 pC/N or less.
• the piezoelectric constant d33 is one of the indicators of the polarization behavior when a certain pressure is applied.
• the larger the piezoelectric constant d33 the greater the degree of polarization that occurs when a certain pressure is applied, and the greater the charge density. Therefore, the greater the degree of charging of the piezoelectric film.
• the piezoelectric constant d 33 of the piezoelectric film can be measured in accordance with the test method for the piezoelectric constant d 33 of piezoelectric ceramics ISO 19622: 2018 using a direct quasi-static method (d 33 meter method, Berlincourt method). Specifically, a piezoelectric constant measuring device (e.g., Piezometer System PM300, manufactured by PIEZOTEST) is used to clip a sample of the piezoelectric film with 1.0 N and read the generated charge when a force of 0.15 N and 110 Hz is applied.
• a piezoelectric constant measuring device e.g., Piezometer System PM300, manufactured by PIEZOTEST
• the piezoelectric constant d 33 of the piezoelectric film can be adjusted mainly by the type of resin contained in the piezoelectric film and the manufacturing conditions (conditions of polarization and stretching). For example, among fluororesins, the more structural units derived from vinylidene fluoride a resin contains, the larger the piezoelectric constant d 33 of the piezoelectric film tends to be. In addition, the stronger the polarization and stretching processes, the larger the piezoelectric constant d 33 of the piezoelectric film tends to be.
• the piezoelectric film contains a fluororesin as a main component.
• “Containing a fluororesin as a main component” means that the content of resins having fluororesin as a constituent unit (including fluororesin itself) in the total mass of resins constituting the piezoelectric film is 50 mass% or more.
• the fluororesin content is preferably 60 mass% or more, and more preferably 80 mass% or more. There is no particular limit to the upper limit of the above content, and it may be 100 mass% or 90 mass% or less.
• the fluororesin is a polymer containing a structural unit derived from vinylidene fluoride as a main component.
• the content of the constituent units derived from vinylidene fluoride contained as a main component in the above polymer 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, based on the total amount of the constituent units of the above polymer.
• the above polymer may further contain a structural unit derived from a monomer copolymerizable with vinylidene fluoride, to the extent that the effect of the present invention is not impaired.
• monomers copolymerizable with vinylidene fluoride include fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, trifluorochloroethylene, and vinyl fluoride. Two or more of these monomers may be contained.
• vinylidene fluoride homopolymer is preferred from the viewpoint of easily increasing the piezoelectric constant d33 of the piezoelectric film and increasing the sensitivity of a pressure-sensitive sensor to which the piezoelectric film is applied.
• the thickness of the piezoelectric film is preferably, for example, 25 ⁇ m or more and 120 ⁇ m or less. When the thickness of the piezoelectric film is 25 ⁇ m or more, a larger amount of charge is generated due to the piezoelectric effect, and higher piezoelectricity is easily obtained.
• the thickness of the piezoelectric film is more preferably 30 ⁇ m or more, and even more preferably 35 ⁇ m or more. When the thickness of the piezoelectric film is 120 ⁇ m or less, the transparency of the piezoelectric film is less likely to be impaired, and 100 ⁇ m or less is more preferable, and 80 ⁇ m or less is even more preferable. From the same viewpoint, the thickness of the piezoelectric film is more preferably 35 ⁇ m or more and 80 ⁇ m or less.
• the antistatic layer has the function of preventing the laminated piezoelectric body from being charged.
• the antistatic layer is disposed on at least one surface of the piezoelectric film.
• the surface resistivity of the antistatic layer is adjusted so that the surface resistivity measured on the hard coat layer is in the range described below. Therefore, the surface resistivity of the antistatic layer is preferably lower than the surface resistivity measured on the hard coat layer, specifically, it is preferably 1.0 ⁇ 10 4 ⁇ /sq. or more and 1.0 ⁇ 10 9 ⁇ /sq. or less, and more preferably 1.0 ⁇ 10 5 ⁇ /sq. or more and 1.0 ⁇ 10 8 /sq. or less.
• the surface resistivity of the antistatic layer is 1.0 ⁇ 10 9 ⁇ /sq. or less, it is easy to lower the surface resistivity measured on the hard coat layer, and it is easy to provide sufficient antistatic properties.
• the surface resistivity can be measured, for example, using a known resistivity meter in accordance with JIS K 6911.
• the surface resistivity can be adjusted by the thickness of the antistatic layer and the type and content of the conductive material contained in the antistatic layer. For example, the thicker the antistatic layer, the smaller the surface resistivity. Also, the higher the content of the conductive material, the smaller the surface resistivity.
• the antistatic layer includes a conductive material.
• the antistatic layer can include a cured product of a curable composition that includes a conductive material, a polymerizable compound, and an optional curing agent.
• the conductive material may be any material that provides the antistatic layer with a surface resistivity within the above range, and may be either an ion-conductive conductive material or an electron-conductive conductive material.
• ion-conductive conductive materials include (a) cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups; (b) anionic antistatic agents having anionic groups such as sulfonate groups, sulfate ester groups, phosphate ester groups, and phosphonate groups; (c) amphoteric antistatic agents such as amino acid-based and amino sulfate-based agents; and (d) nonionic antistatic agents such as amino alcohol-based, glycerin-based, and polyethylene glycol-based agents.
• cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups
• anionic antistatic agents having anionic groups such as sulfonate groups, sulfate ester groups, phosphate ester groups, and phosphonate groups
• Examples of electronically conductive conductive materials include conductive polymers and other conductive materials.
• Examples of conductive polymers include polyacetylene or its derivatives, polythiophene or its derivatives, polypyrrole or its derivatives, polyaniline or its derivatives, etc. Among these, polythiophene or its derivatives are preferred from the viewpoint of high transparency and high conductivity.
• Examples of conductive materials other than conductive polymers include carbon nanotubes, graphene, etc.
• an electronically conductive conductive material from the viewpoint of making it easier to reduce the surface resistivity of the laminated piezoelectric body and making it less likely that bleed-out will occur.
• the electronically conductive conductive materials carbon nanotubes are more preferable from the viewpoint of making the surface resistivity of the antistatic layer lower, and thus making the surface resistivity measured on the hard coat layer lower.
• the polymerizable compound may be a thermally polymerizable compound or a photopolymerizable compound, and examples thereof include acrylic compounds, epoxy compounds, oxetane compounds, polyurethane compounds, polyimide resins, melamine resins, silicone compounds, vinyl acetate, etc.
• acrylic compounds epoxy compounds, oxetane compounds, polyurethane compounds, polyimide resins, melamine resins, silicone compounds, vinyl acetate, etc.
• the same polymerizable compounds as those for forming the hard coat layer described below may be used.
• the thickness of the antistatic layer may be within a range that can provide antistatic properties, for example, 10 nm to 250 nm.
• the thickness of the antistatic layer is 10 nm or more, the surface resistivity of the antistatic layer can be lowered, and therefore the surface resistivity measured on the hard coat layer can also be lowered, making it easier to obtain high antistatic properties.
• the thickness of the antistatic layer is 250 nm or less, coating unevenness caused by the unevenness of the surface of the piezoelectric film is less likely to occur, and coating spots are even less likely to occur.
• the thickness of the antistatic layer is more preferably 15 nm to 220 nm, even more preferably 20 nm to 190 nm, and particularly preferably 20 nm to 160 nm.
• the hard coat layer has the function of increasing the scratch resistance of the surface of the laminated piezoelectric body, as well as increasing the slipperiness and suppressing blocking.
• the hard coat layer may be a single layer or multiple layers. At least one hard coat layer is preferably disposed on the antistatic layer. Also, at least one hard coat layer is preferably disposed on the outermost surface of the laminated piezoelectric body.
• the hard coat layer has a suitable surface roughness.
• the maximum height Rz of the surface of the hard coat layer is adjusted to 40 nm or more and 150 nm or less.
• the surface Rz of the hard coat layer is 40 nm or more, it has sufficient slip properties, so that blocking between the laminated piezoelectric bodies can be suppressed.
• the surface Rz of the hard coat layer is 150 nm or less, it is possible to suppress a decrease in transparency due to an increase in haze.
• the surface Rz of the hard coat layer is more preferably 40 nm or more and 100 nm or less, even more preferably 40 nm or more and 80 nm or less, and particularly preferably 40 nm or more and 60 nm or less.
• the Rz of the surface of the hard coat layer can be measured using a surface roughness measuring device (such as the "SURFCOM1500” manufactured by Tokyo Seimitsu Co., Ltd.) according to a method conforming to JIS B 0601-2013. Rz is measured in the width direction (TD direction) of the laminated piezoelectric body at any 10 points on the hard coat layer, and the average value is calculated.
• a surface roughness measuring device such as the "SURFCOM1500” manufactured by Tokyo Seimitsu Co., Ltd.
• the Rz of the surface of the hard coat layer can be adjusted by the average particle size of the particles contained in the hard coat layer. For example, if the average particle size of the particles contained in the hard coat layer is increased, the Rz tends to increase.
• the hard coat layer can be a resin layer containing particles.
• the resin layer containing particles is preferably obtained by curing a curable composition containing a polymerizable compound and particles.
• the polymerizable compound may be any one of a monomer, an oligomer, and a polymer.
• the polymerizable compound may be a thermosetting compound or an ionizing radiation compound, and is preferably an ionizing radiation compound.
• the ionizing radiation may usually be ultraviolet light (UV) or an electron beam (EB).
• the ionizing radiation-curable compound is a compound having an ionizing radiation-curable functional group.
• the ionizing radiation-curable functional group include ethylenically unsaturated bond groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, and ring-opening polymerizable groups such as epoxy groups and oxetanyl groups.
• ethylenically unsaturated bond groups such as (meth)acryloyl groups, vinyl groups, and allyl groups
• ring-opening polymerizable groups such as epoxy groups and oxetanyl groups.
• compounds having an ethylenically unsaturated bond group are preferred, compounds having two or more ethylenically unsaturated bond groups are more preferred, and polyfunctional (meth)acrylate compounds are even more preferred.
• examples of bifunctional (meth)acrylate monomers include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxy diacrylate, bisphenol A tetrapropoxy diacrylate, 1,6-hexanediol diacrylate, etc.
• trifunctional or higher (meth)acrylate monomers examples include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, isocyanuric acid-modified tri(meth)acrylate, etc.
• the above (meth)acrylate monomers may have a part of the molecular skeleton modified, and those modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc. may also be used.
• polyfunctional (meth)acrylate oligomers include acrylate polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and polyether (meth)acrylate.
• Urethane (meth)acrylate can be obtained, for example, by reacting a polyhydric alcohol and an organic diisocyanate with a hydroxy (meth)acrylate.
• the curable composition preferably contains a photopolymerization initiator, such as one or more selected from acetophenone, benzophenone, ⁇ -hydroxyalkylphenone, Michler's ketone, benzoin, benzyl methyl ketal, benzoyl benzoate, ⁇ -acyloxime ester, thioxanthones, etc.
• a photopolymerization initiator such as one or more selected from acetophenone, benzophenone, ⁇ -hydroxyalkylphenone, Michler's ketone, benzoin, benzyl methyl ketal, benzoyl benzoate, ⁇ -acyloxime ester, thioxanthones, etc.
• the particles may be inorganic particles or organic particles.
• inorganic particles examples include silica particles, titanium dioxide particles, zirconia particles, aluminum oxide particles, diamond powder, sapphire particles, boron carbide particles, silicon carbide particles, antimony pentoxide particles, etc.
• organic particles include resin particles such as acrylic resin, acrylic-styrene copolymer, silicone resin, etc. Among these, inorganic particles are preferred, and silica particles are more preferred, since they are less likely to impair the transparency of the hard coat layer.
• the surfaces of the inorganic particles may be treated with a surface modifier such as a silane coupling agent.
• the average primary particle size of the particles is preferably 10 nm or more and 200 nm or less, and more preferably 30 nm or more and 100 nm or less. By setting the average primary particle size of the particles within the above range, the Rz of the surface of the hard coat layer can be adjusted to the above range.
• the average primary particle size of the particles in the hard coat layer can be measured by observing 10 points on the surface of the hard coat layer using a scanning electron microscope (SEM) at an acceleration voltage of 2.0 kV and a magnification of 50,000 times, and taking the average of the observed values.
• the diameter of each of any 10 particles can be determined by measuring the area of each particle, calculating the diameter equivalent to a circle with said area, and taking the arithmetic mean of the diameters of each particle as the average primary particle size.
• the particle content in the hard coat layer is preferably 3% by mass or more and 80% by mass or less, and more preferably 6% by mass or more and 70% by mass or less, relative to the curable composition.
• the particle content is 3% by mass or more, the Rz of the surface of the hard coat layer tends to be larger, and the anti-blocking properties tend to be improved.
• the particle content is 80% by mass or less, the decrease in transparency due to an increase in haze can be further suppressed.
• the thickness of the hard coat layer is preferably 300 nm or more and 3000 nm or less.
• the thickness of the hard coat layer is 300 nm or more, it is easier to improve the scratch resistance of the laminated piezoelectric body.
• the thickness of the hard coat layer is 3000 nm or less, it is easier to obtain higher antistatic properties because the surface resistivity of the laminated piezoelectric body can be made lower.
• the surface thickness of the hard coat layer is more preferably 500 nm or more and 1500 nm or less, and even more preferably 700 nm or more and 1200 nm or less.
• the ratio (T2/T1) of the thickness of the hard coat layer (T2) to the thickness of the antistatic layer (T1) can be, for example, 3 to 26, although this depends on the surface resistivity of the antistatic layer.
• the smaller the ratio the thinner the hard coat layer and the thicker the antistatic layer, so that the surface resistivity measured on the hard coat layer can be lowered.
• each layer constituting the piezoelectric laminate can be measured using a spectroscopic interference film thickness meter (for example, the Optical NanoGauge C13027-11 manufactured by Hamamatsu Photonics).
• the refractive index of each layer can be measured using the method described in JIS K7142; for example, the refractive index of the substrate is set to 1.42, and the refractive index of the coating to 1.50.
• the thickness of each layer in an area including the center of the surface of the piezoelectric laminate is measured at three or more points spaced 5 mm apart, and the arithmetic mean value is calculated as the thickness of each layer.
• the antistatic layer and the hard coat layer included in the laminated piezoelectric body may each be one layer or two or more layers.
• the laminated piezoelectric body may further include layers other than those described above. However, from the viewpoint of easily obtaining high antistatic properties, it is preferable that the antistatic layer and the hard coat layer are in contact with each other.
• the laminated piezoelectric element can have the following layer structure. Piezoelectric film/Antistatic layer/Hard coat layer Hard coat layer/Piezoelectric film/Antistatic layer/Hard coat layer
• the surface resistivity is reduced. Specifically, the surface resistivity measured on the hard coat layer of the laminated piezoelectric body is 1.0 When the surface resistivity of the laminated piezoelectric body is 1.0 ⁇ 10 12 ⁇ /sq. or less, sufficient antistatic properties are obtained. When the surface resistivity of the laminated piezoelectric body is 1.0 ⁇ 10 6 ⁇ /sq. or more, unintended electrostatic discharge is more easily suppressed.
• the surface resistivity is more preferably 1.0 ⁇ 10 8 ⁇ /sq. or more and 5.0 ⁇ 10 11 ⁇ /sq. or less.
• the surface resistivity of the laminated piezoelectric body is the surface resistivity of the antistatic layer. It can be measured in the same manner as above.
• the surface resistivity of the laminated piezoelectric body can be adjusted mainly by the surface resistivity of the antistatic layer and the thickness of the hard coat layer. By lowering the surface resistivity of the antistatic layer and reducing the thickness of the hard coat layer, the surface resistivity of the laminated piezoelectric body tends to be lower.
• the laminated piezoelectric body preferably has high transparency. Specifically, the total light transmittance of the laminated piezoelectric body is preferably 85% or more, and more preferably 90% or more.
• the total light transmittance of the laminated piezoelectric body can be measured using a haze meter (e.g., NDH7000SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) based on the method described in JIS K 7361-1.
• a haze meter e.g., NDH7000SP II, manufactured by Nippon Denshoku Industries Co., Ltd.
• the total light transmittance of the laminated piezoelectric body can be adjusted by the thickness of the antistatic layer and the average particle size of the particles contained in the hard coat layer. For example, reducing the thickness of the antistatic layer makes it less likely that coating spots will occur, and the total light transmittance is likely to be higher. Also, reducing the average particle size of the particles in the hard coat layer is likely to increase the total light transmittance.
• the piezoelectric constant d 33 of the laminated piezoelectric body is adjusted to 7 pC/N or more and 40 pC/N or less.
• the piezoelectric constant d 33 of the laminated piezoelectric body is 7 pC/N or more, the amount of charge generated by the piezoelectric effect is sufficient, so that high pressure sensitivity is easily obtained.
• the piezoelectric constant d 33 of the laminated piezoelectric body is 40 pC/N or less, for example, the unevenness of the film surface caused by the polarization treatment can be further reduced, so that the appearance defect can be reduced.
• the piezoelectric constant d 33 of the laminated piezoelectric body is more preferably 10 pC/N or more and 40 pC/N or less, more preferably 10 pC/N or more and 27 pC/N or less, and particularly preferably 13 pC/N or more and 24 pC/N or less.
• the piezoelectric constant d 33 of the laminated piezoelectric body can be adjusted mainly by the piezoelectric constant d 33 of the piezoelectric film. If the piezoelectric constant d 33 of the piezoelectric film is high, the piezoelectric constant d 33 of the laminated piezoelectric body tends to be high as well.
• the laminated piezoelectric element according to the above embodiment has high piezoelectricity because it contains a piezoelectric film with a piezoelectric constant d33 equal to or greater than a predetermined value.
• the laminated piezoelectric body has a laminated structure of an antistatic layer and a hard coat layer having a predetermined Rz or more, and the surface resistivity of the hard coat layer of the laminated piezoelectric body is adjusted to a predetermined value or less, thereby achieving both antistatic properties and antiblocking properties.
• the thickness of the antistatic layer is adjusted to a predetermined value or less, which reduces coating unevenness of the antistatic layer caused by the unevenness of the surface of the piezoelectric film containing a fluorine-based resin, thereby suppressing coating spots caused by the unevenness, thereby suppressing deterioration of visibility.
• the laminated piezoelectric body according to this embodiment can be manufactured through the steps of (1) preparing a piezoelectric film containing a fluorine-based resin, (2) applying an antistatic material to at least one surface of the prepared piezoelectric film and drying the material to form an antistatic layer, and (3) applying a curable resin composition onto the antistatic layer and curing the composition to form a hard coat layer.
• the piezoelectric film, the antistatic layer, and the hard coat layer are the piezoelectric film, the antistatic layer, and the hard coat layer, respectively, described above.
• the piezoelectric film containing a fluororesin may be a commercially available product or may be manufactured.
• the piezoelectric film can be obtained through a process of subjecting a film containing a fluororesin to a polarization treatment.
• the film containing a fluororesin may be a stretched film or an unstretched film.
• Films containing fluororesin can be manufactured by any method, such as melt extrusion (extrusion molding) or solution casting. Of these, from the viewpoint of easily obtaining a piezoelectric film of a specified thickness or more, it is preferable to manufacture films containing fluororesin by melt extrusion.
• melt extrusion method the fluororesin and any additives are heated and melted in the cylinder of an extruder, and then extruded from a die to obtain a film.
• the obtained film has a structure that is a mixture of ⁇ -type crystals (main chain has a helical structure) and ⁇ -type crystals (main chain has a planar zigzag structure).
• ⁇ -type crystals have a large polarization structure.
• the stretching direction may be either the TD direction or the MD direction, and is more preferably the MD direction.
• the stretching method is not particularly limited, and can be performed by known stretching methods such as the tenter method and drum method.
• the stretching ratio is, for example, 3.0 times or more and 6.0 times or less.
• the stretching ratio is 3.0 times or more, it is easier to adjust the thickness and polarity of the film to a more appropriate range.
• the stretching ratio is 3.0 times or more, the rearrangement reaction of the ⁇ -type crystals proceeds sufficiently, making it easier to develop higher piezoelectricity and also making it possible to further increase transparency.
• the stretching ratio is 6.0 times or less, breakage due to stretching can be further suppressed.
• the obtained stretched film is polarized.
• the polarization process can be performed, for example, by applying a DC voltage between a ground electrode and a needle-shaped electrode.
• the voltage can be adjusted according to the thickness of the stretched film, and can be, for example, 1 kV or more and 50 kV or less.
• a piezoelectric film can be obtained by polarizing the stretched film.
• Step of Forming Antistatic Layer For example, a curable composition containing the above-mentioned conductive material is applied onto the obtained piezoelectric film, and then dried and cured to form an antistatic layer.
• the antistatic material may further contain water or a solvent.
• the solvent include alcohol-based solvents such as methanol, ethanol, and isopropyl alcohol.
• 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.
• the drying method involves heating the applied antistatic material.
• the heating temperature is preferably a temperature at which the solvent can be removed or higher and at or below the thermal deformation temperature of the fluororesin that constitutes the piezoelectric film, and can be, for example, 100°C or higher and 150°C or lower.
• the thermal deformation temperature can be measured, for example, in accordance with JIS K 7191-2:2015.
• Step of Forming a Hard Coat Layer A coating liquid containing the above-mentioned curable composition is applied onto the obtained antistatic layer, and then dried and cured to form a hard coat layer.
• the coating liquid may further contain a dilution solvent as necessary.
• the dilution solvent is preferably one that has a polarity similar to that of the particles.
• Examples of dilution solvents include organic solvents such as alcohol-based solvents, ketone-based solvents, ester-based solvents, carbonate-based solvents, and aromatic solvents.
• the coating liquid can be applied in the same manner as the coating method described above.
• the coating liquid can also be dried in the same manner as the drying method described above.
• the heating temperature may be within a range in which the solvent can be volatilized and removed, and is equal to or lower than the thermal deformation temperature of the fluorine-based resin that constitutes the piezoelectric film, and may be, for example, 60°C or higher and 100°C or lower.
• Curing may be by heat or by ionizing radiation. Curing by ionizing radiation can be achieved by exposure to ultraviolet light or electron beams. Curing by heat and curing by ionizing radiation may also be used in combination.
• the laminated piezoelectric element according to the present embodiment can be used for various applications.
• the laminated piezoelectric element according to the present embodiment has high transparency and visibility while exhibiting high piezoelectricity, it can be preferably used as a pressure-sensitive sensor for touch panels mounted on various electronic devices.
• Piezoelectric constant (piezoelectric constant d33 )
• the piezoelectric constant d 33 was measured in accordance with ISO 19622:2018, a test method for the piezoelectric constant d 33 of piezoelectric ceramics using a direct quasi-static method (d 33 meter method, Berlin Court method). Specifically, the piezoelectric constant d 33 of the laminated piezoelectric body was measured using a piezoelectric constant measuring device ("Piezometer System PM300", manufactured by PIEZOTEST Co., Ltd.) by clipping the sample with 1 N and reading the generated charge when a force of 0.15 N and 110 Hz was applied. The actual measured value of the piezoelectric constant d 33 was measured at a temperature of 25°C, and was a positive or negative value depending on the front and back of the film being measured, but the absolute value was described in this specification.
• a capacitor with a capacitance of 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 amount of generated charge Q (C) was calculated as the product of the capacitor capacitance Cm and the terminal voltage Vm.
• Example 1 Preparation and evaluation of laminated piezoelectric body
• a polyvinylidene fluoride film (Kureha Corporation, a film containing 100% by mass of vinylidene fluoride homopolymer) was stretched to a stretch ratio of 4.2 times in the MD direction, and then a DC voltage was applied between the ground electrode and the needle electrode while increasing from 0 kV to 11.0 kV, thereby performing a polarization process, and a piezoelectric film with a thickness of 42 ⁇ m was obtained.
• the piezoelectric constant d33 of the piezoelectric film was measured by the above method and found to be 15 pC/N.
• a hard coat agent (BS-CH271 manufactured by Arakawa Chemical Industries, Ltd., the average particle size of amorphous silica is 60 nm) was applied onto the antistatic layer using a multi-coater, and then heat-treated at 80°C for 2 minutes, and then photocured by irradiating UV with an integrated light quantity of 200 mJ/ cm2 to form a hard coat layer with a thickness of 700 nm.
• a laminated piezoelectric body having a laminated structure of piezoelectric film/antistatic layer/hard coat layer was obtained.
• Example 2 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the thickness of the hard coat layer was changed to 2000 nm.
• Example 3 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the thickness of the antistatic layer was changed to 140 nm.
• Example 4 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the heat treatment conditions for forming the antistatic layer were changed to 120° C. for 60 minutes.
• Example 5 A solution (C-169PF) obtained by mixing paint C-169PF-A (manufactured by Nagase ChemteX Corporation) containing single-walled carbon nanotubes and paint C-169PF-B (manufactured by Nagase ChemteX Corporation) containing a crosslinking agent in a ratio of 3:2 was applied to surface A of the piezoelectric film using a multi-coater (manufactured by Hirano Techseed Co., Ltd.), and the film was heat-treated at 130°C for 1 minute to form an antistatic layer.
• a laminated piezoelectric body was obtained in the same manner as in Example 1, except that the antistatic layer was formed.
• Example 6 A hard coat layer having a thickness of 700 nm was further formed on the B side of the piezoelectric film of the laminated piezoelectric body produced in Example 1 by the same method as in Example 1 to obtain a laminated piezoelectric body, thereby obtaining a laminated piezoelectric body having a laminated structure of hard coat layer/piezoelectric film/antistatic layer/hard coat layer.
• Example 7 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the hard coating agent was changed to TYAB-M101 (average particle size of amorphous silica: 80 nm) manufactured by Toyochem Co., Ltd.
• Example 1 Neither an antistatic layer nor a hard coat layer was formed, and the piezoelectric film of Example 1 was used as it was.
• Example 2 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the hard coating agent containing amorphous silica was changed to a hard coating agent not containing amorphous silica (BS-575, manufactured by Arakawa Chemical Industries, Ltd.).
• Example 3 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the thickness of the antistatic layer was changed to 5 nm.
• Example 4 A laminated piezoelectric body was obtained in the same manner as in Example 1, except that the thickness of the antistatic layer was changed to 260 nm.
• Example 5 An antistatic layer was formed in the same manner as in Example 1, except that the heat treatment conditions during formation of the antistatic layer were changed to 160° C. and 60 minutes. However, the appearance of the laminated piezoelectric body was poor, and a hard coat layer was not formed.
• Example 6 An attempt was made to form an antistatic layer in the same manner as in Example 1, except that the heat treatment conditions during formation of the antistatic layer were changed to 80° C. and 0.67 minutes. However, the antistatic layer was not cured sufficiently, and a hard coat layer was not formed.
• Example 7 An antistatic hard coat agent (MT-3/manufactured by Arakawa Chemical Industries, Ltd.) was applied to the piezoelectric film of Example 1 using a multi-coater, and heat-treated at 80°C for 2 minutes, and then irradiated with UV light at an integrated light amount of 400 mJ/ cm2 using a UV irradiation device CSOT-40 (manufactured by GS Yuasa Corporation) to obtain a laminated piezoelectric body. As a result, a laminated piezoelectric body having a laminated structure of a piezoelectric film/antistatic hard coat layer was obtained.
• a UV irradiation device CSOT-40 manufactured by GS Yuasa Corporation
• the raw material was then placed in an extrusion molding machine hopper, extruded from a T-die while being heated to 210°C, and contacted with a cast roll at 50°C to produce a pre-crystallized film having a thickness of 150 ⁇ m.
• the pre-crystallized film was uniaxially stretched in the MD direction at 70°C by a roll-to-roll method up to 3.5 times to obtain a uniaxially stretched film.
• the thickness of the obtained uniaxially stretched film was 49.2 ⁇ m.
• the obtained uniaxially stretched film was annealed by contacting it with a roll at 145° C.
• the piezoelectric constant d 14 of the piezoelectric film was measured by the above-mentioned method and was found to be 6 pC/N.
• Total Light Transmittance The total light transmittance of the laminated piezoelectric body was measured using a haze meter ("NDH7000SP II", manufactured by Nippon Denshoku Industries Co., Ltd.) based on the method described in JIS K 7361-1.
• the manufacturing conditions and layer structures of the laminated piezoelectric bodies of Examples 1 to 7 and Comparative Examples 1 to 8 are shown in Table 1.
• the evaluation results of the laminated piezoelectric bodies of Examples 1 to 7 and Comparative Examples 2 to 4 and 7 are shown in Table 2.
• the laminated piezoelectric elements of Examples 1 to 7 all exhibited no color unevenness, exhibited high piezoelectric constants, and were found to have high blocking resistance and antistatic properties.
• the total light transmittance can be increased by making the antistatic layer thinner (comparison between Examples 1 and 3).
• the laminated piezoelectric material of the present invention has high piezoelectricity, anti-blocking property, and antistatic property without reducing visibility, and is therefore suitable for use as a pressure-sensitive sensor in a touch panel.

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