JPWO2015053346A1 - Piezoelectric film - Google Patents

Abstract

An object of the present invention is to provide a piezoelectric film having high transparency (particularly haze value), high shape and visual uniformity, and high polarizability. In the present invention, the total light transmittance is 90% or more; the total haze value is 4.0% or less; A coefficient of variation of 10% or less; a piezoelectric film is provided.

Description

  The present invention relates to a piezoelectric film.

Conventionally, various organic dielectric films and inorganic dielectric films have been known as piezoelectric films or films.
Among these, the polarized vinylidene fluoride / tetrafluoroethylene copolymer film has the advantage of having transparency and flexibility unlike the inorganic dielectric film, so that it can be applied to various applications. Is possible.
For example, Patent Document 1 discloses a polarized vinylidene fluoride / tetrafluoroethylene copolymer film for a touch panel or a touch pressure detection as a piezoelectric film.

JP 2011-222679 A

However, in recent years, high transparency is demanded for members used in touch panels, and the polarized vinylidene fluoride / tetrafluoroethylene copolymer film described in Patent Document 1 is transparent (particularly haze value). There was room for improvement.
In addition, the polarized vinylidene fluoride / tetrafluoroethylene copolymer film described in Patent Document 1 is improved in shape and visual uniformity (less wrinkles and sagging) and uniformity of polarizability. There was room for.
Accordingly, an object of the present invention is to provide a piezoelectric film having high transparency (particularly haze value), high shape and visual uniformity, and high uniformity of polarizability.

As a result of intensive studies, the present inventors have
A total light transmittance of 90% or more;
The total haze value is 4.0% or less; and the coefficient of variation in thickness is 10% or less when the thickness is measured at 10 locations every 1 cm square over the entire plane direction;
It has been found that the above problems can be solved by the piezoelectric film, and as a result of further studies, the present invention has been completed.

  The present invention includes the following aspects.

Item 1.
A total light transmittance of 90% or more;
The total haze value is 4.0% or less; and the coefficient of variation in thickness is 10% or less when the thickness is measured at 10 locations every 1 cm square over the entire plane direction;
Piezoelectric film.
Item 2.
Item 2. The piezoelectric film according to Item 1, wherein the total haze value is 2.0% or less.
Item 3.
Item 3. The piezoelectric film according to Item 1 or 2, comprising an organic piezoelectric film.
Item 4.
Item 3. The piezoelectric film according to Item 1 or 2, comprising a polarized vinylidene fluoride polymer film.
Item 5.
Step A for preparing an unstretched and non-polarized vinylidene fluoride polymer film by a casting method;
Step B for polarizing the non-stretched and non-polarized vinylidene fluoride polymer film; and Step C for heat-treating the non-stretched vinylidene fluoride-based polymer film at any time with respect to Step B
Item 5. A method for producing a piezoelectric film according to Item 4, comprising:
Item 6.
Item 5. The roll of piezoelectric film according to any one of Items 1 to 4, wherein the ratio of the thickness of the thicker end to the thickness of the central portion in the axial direction of the roll is in the range of 70 to 130%. A role that is within.
Item 7.
Item 6. A piezoelectric panel, film capacitor, or electrowetting device comprising the piezoelectric film according to any one of Items 1 to 4 or the piezoelectric film produced by the production method according to Item 5.
Item 8.
The input device which has a piezoelectric film of any one of Claims 1-4, or a piezoelectric film manufactured by the manufacturing method of Claim 5.
Item 9.
Item 9. An electronic device having the input device according to Item 8.

  According to the present invention, a piezoelectric film having high transparency and less variation in thickness is provided.

In this specification, “detection” of “touch position” means determination of touch position, while “detection” of “touch pressure” means presence / absence of pressure, speed, magnitude, or a combination thereof. Means the decision.
As used herein, the term “touch” includes touching, touching, pushing, pushing, and touching.
In this specification, the term “polarization” means that a surface is charged. That is, the polarizing film can be an electret.

Piezoelectric film The piezoelectric film of the present invention comprises:
A total light transmittance of 90% or more;
The total haze value is 4.0% or less; and the coefficient of variation in thickness is 10% or less when the thickness is measured at 10 points per 1 cm square over the entire plane direction.
Hereinafter, the piezoelectric film of the present invention will be described in detail.

The piezoelectric film of the present invention is composed of an organic piezoelectric film. The “organic piezoelectric film” is a film (polymer film) formed from a polymer that is an organic substance. Examples of the “organic piezoelectric film” include a polarized vinylidene fluoride polymer film, an odd-chain nylon piezoelectric film, and polylactic acid. The “organic piezoelectric film” may contain components other than the polymer. The “organic piezoelectric film” includes a film made of the polymer and a film in which an inorganic substance is dispersed in the polymer.
The content of the polymer in the piezoelectric film of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass. The upper limit of the content is not particularly limited, and may be, for example, 100% by mass or 99% by mass.
The polymer is preferably a vinylidene fluoride polymer.
The piezoelectric film of the present invention is preferably composed of a polarized vinylidene fluoride polymer film.
In this specification, examples of the “vinylidene fluoride polymer film” include a vinylidene fluoride / tetrafluoroethylene copolymer film, a vinylidene fluoride / trifluoroethylene copolymer film, and a polyvinylidene fluoride film. Can be mentioned.
The vinylidene fluoride polymer film is preferably a vinylidene fluoride / tetrafluoroethylene copolymer film.
The “vinylidene fluoride polymer film” may contain an additive usually used for a resin film.

  The “vinylidene fluoride polymer film” is a film composed of a vinylidene fluoride polymer and contains a vinylidene fluoride polymer.

As an example of the “vinylidene fluoride polymer”,
(1) a copolymer of vinylidene fluoride and one or more monomers copolymerizable therewith; and (2) polyvinylidene fluoride.

Examples of “monomer copolymerizable with this” in “(1) copolymer of vinylidene fluoride and one or more monomers copolymerizable therewith” include trifluoroethylene, tetrafluoroethylene , Hexafluoropropylene, chlorotrifluoroethylene, and vinyl fluoride.
The “one or more monomers copolymerizable therewith” or one of them is preferably tetrafluoroethylene.
Preferable examples of the “vinylidene fluoride polymer” include a vinylidene fluoride / tetrafluoroethylene copolymer.
The “vinylidene fluoride / tetrafluoroethylene copolymer” may contain repeating units derived from monomers other than vinylidene fluoride and tetrafluoroethylene as long as the properties relating to the present invention are not significantly impaired.
The “(1) copolymer of vinylidene fluoride and one or more monomers copolymerizable therewith” contains 50 mol% or more (preferably 60 mol% or more) of repeating units derived from vinylidene fluoride. )contains.
The molar ratio of (a repeating unit derived from tetrafluoroethylene) / (a repeating unit derived from vinylidene fluoride) in the “vinylidene fluoride / tetrafluoroethylene copolymer” is preferably 5/95 to 36/64. Within the range, more preferably within the range of 15/85 to 25/75, still more preferably within the range of 18/82 to 22/78.

The “vinylidene fluoride / tetrafluoroethylene copolymer” may contain a repeating unit derived from a monomer other than vinylidene fluoride and tetrafluoroethylene as long as the properties of the present invention are not significantly impaired. Usually, the content of such repeating units is 10 mol% or less. Such a monomer is not limited as long as it is copolymerizable with a vinylidene fluoride monomer or a tetrafluoroethylene monomer.
(1) Fluoromonomer (eg, vinyl fluoride (VF), trifluoroethylene (TrFE), 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, 1,1,2-trifluorobutene-4-silane-1-butene, perfluoroalkyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluoroacrylate, 2, 2,2-trifluoroethyl acrylate, 2- (2) hydrocarbon monomers (eg, ethylene, propylene, maleic anhydride, vinyl ether, vinyl ester, allyl glycidyl ether, acrylic acid monomers, methacrylic acid monomers, vinyl acetate) It is done.

  Preferable examples of the “inorganic substance” include inorganic oxide particles. By containing the “inorganic oxide particles”, the high dielectric film of the present invention can have a high dielectric constant. In addition, this makes it possible to significantly improve the volume resistivity while maintaining a high dielectric constant.

  Preferable examples of the “inorganic substance” include inorganic oxide particles. By containing the “inorganic oxide particles”, the piezoelectric film of the present invention can have a high dielectric constant. Further, the volume resistivity can be greatly improved while maintaining a high dielectric constant. Moreover, electrical insulation can be improved.

  The “inorganic oxide particles” are preferably at least one selected from the group consisting of the following inorganic oxide particles (B1) to (B3).

[Inorganic oxide particles (B1)] Inorganic oxide particles of group 2, group 3, group 4, group 12 or group 13 metal element of the periodic table, or these inorganic oxide composite particles As the metal element, Examples include Be, Mg, Ca, Sr, Ba, Y, Ti, Zr, Zn, and Al. Among these, oxides of Al, Mg, Y, and Zn are preferable because they are general-purpose and inexpensive, and have a high volume resistivity.
Among them, specifically, particles of at least one metal oxide selected from the group consisting of Al ₂ O ₃ , MgO, ZrO ₂ , Y ₂ O ₃ , BeO, and MgO · Al ₂ O ₃ have a volume. This is preferable from the viewpoint of high resistivity.
Among these, Al ₂ O ₃ having a crystal structure of γ type has a large specific surface area and is dispersed in the “polymer” such as a vinylidene fluoride polymer, particularly a vinylidene fluoride / tetrafluoroethylene copolymer. From the viewpoint of good properties.

[Inorganic oxide particles (B2)] Formula: M ¹ _a1 M ² _b1 O _c1 (wherein M ¹ is a Group 2 metal element; M ² is a Group 4 metal element; a1 is 0.9 to 1.1) in it, b1 is at 0.9 to 1.1; c1 is a 2.8 to 3.2; the ^{M 1} and ^{M 2} can be one or two or more metal elements, respectively) Inorganic composite oxide particles represented As the “Group 4 metal element”, for example, Ti and Zr are preferable.
As the “Group 2 metal element”, for example, Mg, Ca, Sr, and Ba are preferable.
Among the “inorganic composite oxide particles”, specifically, at least one selected from the group consisting of BaTiO ₃ , SrTiO ₃ , CaTiO ₃ , MgTiO ₃ , BaZrO ₃ , SrZrO ₃ , CaZrO ₃ , and MgZrO _3. Inorganic oxide particles are preferred because of their high volume resistivity.

[Inorganic oxide particles (B3)] Group 2, group 3, group 4, group 12 or group 13 metal element oxides of silicon and inorganic oxide composite particles of silicon oxide "B3)" is a composite particle of the "inorganic oxide" of the "inorganic oxide particle (B1)" and silicon oxide.
Specific examples the "inorganic oxide particles (B3)", for _example, at least selected from _{3A1 2 O 3 · 2SiO 2,} 2MgO · SiO 2, ZrO 2 · SiO 2, and the group consisting of MgO · SiO ₂ 1 Examples include inorganic oxide particles.

The “inorganic oxide particles” are not necessarily highly dielectric and can be appropriately selected depending on the application of the piezoelectric film of the present invention. For example, when one kind of general-purpose and inexpensive metal oxide particles (B1) (particularly, Al ₂ O ₃ particles and MgO particles) is used, the volume resistivity can be improved. The relative dielectric constant (1 kHz, 25 ° C.) of these one kind of metal oxide particles (B1) is usually less than 100, preferably 10 or less.

  The “inorganic oxide particles” include inorganic oxide particles (for example, inorganic oxide particles (B2)) having ferroelectricity (relative permittivity (1 kHz, 25 ° C.) of 100 or more) for the purpose of improving the dielectric constant. (B3)) may be used. Examples of the inorganic material constituting the ferroelectric inorganic oxide particles (B2) and (B3) include composite metal oxides, composites thereof, solid solutions, and sol-gel bodies, but are not limited thereto. is not.

  The piezoelectric film of the present invention can contain 0.01 to 300 parts by mass, more preferably 0.1 to 100 parts by mass of the “inorganic oxide particles” with respect to 100 parts by mass of the “polymer”. If the content of the “inorganic oxide particles” is too large, it may be difficult to uniformly disperse the “inorganic oxide particles” in the “polymer”. ) May be reduced. Moreover, when the said content becomes 300 mass parts or more, there exists a possibility that a film may become weak and tensile strength may fall. In this respect, the upper limit of the content is preferably 200 parts by mass, more preferably 150 parts by mass. When the content is too small, it is difficult to obtain an effect of improving electrical insulation. In this respect, the lower limit of the content is preferably 0.1 parts by mass, more preferably 0.5 parts by mass, and still more preferably 1 part by mass. On the other hand, when a high total light transmittance and a low total haze value are required for the piezoelectric film of the present invention, the content is preferably smaller, and the piezoelectric film of the present invention has a particularly high total light. When light transmittance and a low total haze value are required, the piezoelectric film of the present invention can preferably not contain the “inorganic oxide particles”. As described above, when the piezoelectric film of the present invention is required to have a high total light transmittance and a low total haze value, specifically, the case where the piezoelectric film of the present invention is used for a piezoelectric panel such as a touch panel can be mentioned. .

  The average primary particle diameter of the “inorganic oxide particles” is preferably small, and so-called nanoparticles having an average primary particle diameter of 1 μm or less are particularly preferable. By uniformly dispersing such inorganic oxide nanoparticles, the electrical insulation of the film can be significantly improved with a small amount of blending. The average primary particle size is preferably 800 nm or less, more preferably 500 nm or less, and still more preferably 300 nm or less. The lower limit of the average primary particle size is not particularly limited, but the average primary particle size is preferably 10 nm or more, more preferably 20 nm or more, and still more preferably, from the viewpoint of manufacturing difficulty, difficulty of uniform dispersion, and cost. It is 50 nm or more. Here, when a high total light transmittance and a low total haze value are required for the piezoelectric film of the present invention, the average primary particle diameter is preferably smaller. The average primary particle size of the “inorganic oxide particles” is calculated using a laser diffraction / scattering particle size distribution measuring device LA-920 (trade name) (Horiba Seisakusho) or an equivalent product thereof.

The relative dielectric constant (25 ° C., 1 kHz) of the “inorganic oxide particles” is preferably 10 or more. From the viewpoint of increasing the dielectric constant of the piezoelectric film, the relative dielectric constant is preferably 100 or more, more preferably 300 or more. The upper limit of the relative dielectric constant is not particularly limited, but is usually about 3000. The relative dielectric constant (ε) (25 ° C., 1 kHz) of the “inorganic oxide particles” is determined by measuring the capacity (C) using an LCR meter, the capacity, the electrode area (S), the thickness of the sintered body ( From d), it is a value calculated by the formula C = εε ₀ × S / d (ε ₀ vacuum dielectric constant).

  The piezoelectric film of the present invention may contain other components such as an affinity improver as necessary.

The “affinity improver” is contained in the piezoelectric film of the present invention when the “inorganic oxide particles” are contained in the piezoelectric film of the present invention.
The “affinity improver” increases the affinity between the “inorganic oxide particles” and the “polymer”, uniformly disperses the “inorganic oxide particles” in the “polymer”, The “inorganic oxide particles” and the “polymer” can be firmly bonded in the film, the generation of voids can be suppressed, and the relative dielectric constant can be increased.

  As the “affinity improver”, a coupling agent, a surfactant, or an epoxy group-containing compound is effective.

  Examples of the “coupling agent” include organic titanium compounds, organic silane compounds, organic zirconium compounds, organic aluminum compounds, and organic phosphorus compounds.

  Examples of the “organic titanium compound” include coupling agents such as alkoxytitanium, titanium chelate, and titanium acylate. Among these, alkoxy titanium and titanium chelate are preferable examples from the viewpoint of good affinity with the “inorganic oxide particles”.

  Specific examples thereof include tetraisopropyl titanate, titanium isopropoxyoctylene glycolate, diisopropoxy bis (acetylacetonato) titanium, diisopropoxytitanium diisostearate, tetraisopropylbis (dioctylphosphite) titanate, and Examples thereof include isopropyl tri (n-aminoethyl-aminoethyl) titanate and tetra (2,2-diallyloxymethyl-1-butyl) bis (di-tridecyl) phosphite titanate.

  The “organosilane compound” may be a polymer type or a low molecular type, and examples thereof include monoalkoxysilanes, dialkoxysilanes, trialkoxysilanes, and tetraalkoxysilanes. Can be mentioned. In addition, vinyl silane, epoxy silane, amino silane, methacryloxy silane, mercapto silane, and the like can be suitably used.

  When alkoxysilane is used, the volume resistivity, which is the effect of surface treatment, can be further improved (improvement of electrical insulation) by hydrolysis.

  Examples of the “organic zirconium compound” include alkoxyzirconium and zirconium chelate.

  Examples of the organoaluminum compound include alkoxyaluminum and aluminum chelate.

  Examples of organic phosphorus compounds include phosphites, phosphates, and phosphate chelates.

  The “surfactant” as the affinity improver may be a polymer type or a low molecular type, and examples thereof include a nonionic surfactant, an anionic surfactant, and A cationic surfactant is mentioned. Among these, a high molecular weight surfactant is preferable from the viewpoint of good thermal stability.

  Examples of the “nonionic surfactant” include a polyether derivative, a polyvinylpyrrolidone derivative, and an alcohol derivative, and in particular, from the viewpoint of good affinity with the “inorganic oxide particles”. Ether derivatives are preferred.

  Examples of the “anionic surfactant” include polymers containing sulfonic acid, carboxylic acid, and salts thereof. Among them, preferred examples of the affinity with the “polymer” include acrylic acid derivative polymer (poly (acrylic acid) derivative) and methacrylic acid derivative polymer (poly (methacrylic acid) derivative). Is mentioned.

  Examples of the “cationic surfactant” include amine compounds, compounds having a nitrogen-containing complex ring such as imidazoline, and halogenated salts thereof.

  The “epoxy group-containing compound” as the “affinity improver” may be a low molecular weight compound or a high molecular weight compound, and examples thereof include an epoxy compound and a glycidyl compound. Among them, a low molecular weight compound having one epoxy group is preferable from the viewpoint of particularly good affinity with the “polymer”.

  As a preferable example of the “epoxy group-containing compound”, the compound having the formula:

  (In the formula, R represents a hydrogen atom, a methyl group, an oxygen atom or a nitrogen atom which may have an intervening C 2-10 hydrocarbon group or an optionally substituted aromatic ring group. L is 0. Or m represents 0 or 1, and n represents an integer of 0 to 10).

等の、ケトン基、又はエステル基を有する化合物が挙げられる。As a specific example,

Examples thereof include compounds having a ketone group or an ester group.

  The “affinity improver” can be used in an amount within the range in which the effects of the present invention are not lost. Specifically, from the viewpoint of uniform dispersion and the high relative dielectric constant of the obtained film, The amount thereof is preferably within a range of 0.01 to 30 parts by mass, more preferably within a range of 0.1 to 25 parts by mass, and further preferably 1 to 20 parts with respect to 100 parts by mass of “inorganic oxide particles”. Within the range of parts by mass.

  Furthermore, the piezoelectric film of the present invention may contain additives other than these as long as the effects of the present invention are not lost.

The piezoelectric film of the present invention has a total light transmittance of 90% or more.
The total light transmittance of the piezoelectric film of the present invention is preferably 92% or more, more preferably 95% or more. Although the upper limit of the total light transmittance is not limited, the total light transmittance of the piezoelectric film of the present invention is usually 99% or less.
In the present specification, “total light transmittance” is obtained by a light transmission test using Hazeguard II (product name) (Toyo Seiki Seisakusho) or an equivalent product based on ASTM D1003.

The total haze value of the piezoelectric film of the present invention is 4.0% or less.
The total haze value of the piezoelectric film of the present invention is preferably 3.0% or less, more preferably 2.0% or less, and still more preferably 1.0% or less. The lower the total haze value, the better. The lower limit is not limited, but the total haze value of the piezoelectric film of the present invention is usually 0.1 or more.
In this specification, “total haze” is obtained by haze (HAZE, turbidity) test using Hayes Guard II (product name, Toyo Seiki Seisakusho) or its equivalent in accordance with ASTM D1003. It is done.

The internal haze value of the piezoelectric film of the present invention is preferably 2.0% or less, more preferably 1.5% or less, still more preferably 1.2% or less, and still more preferably 1.0% or less. The lower the internal haze value, the better. The lower limit is not limited, but the internal haze value of the piezoelectric film of the present invention is usually 0.1% or more.
In the present specification, “inner haze” means that in the method for measuring the total haze value, water is put into a glass cell, a film is inserted therein, and the haze value is measured. Is obtained.

The external haze value of the piezoelectric film of the present invention is preferably 2.0 or less, more preferably 1.5% or less, and still more preferably 1.0% or less. The lower the external haze value is, the better. The lower limit is not limited, but the external haze value of the piezoelectric film of the present invention is usually 0.1% or more.
In the present specification, the “outer haze value” (outer haze) is calculated by subtracting the internal haze value from the total haze value of the film.

The thickness of the piezoelectric film of the present invention is, for example, in the range of 0.5 to 100 μm, in the range of 0.8 to 50 μm, in the range of 0.8 to 40 μm, in the range of 3 to 100 μm, or in the range of 3 to 50 μm. Within the range, within the range of 6-50 μm, within the range of 9-40 μm, within the range of 10-40 μm, or within the range of 10-30 μm. The preferred thickness can vary depending on the application of the piezoelectric film of the present invention. For example, when the piezoelectric film of the present invention is used for a piezoelectric panel such as a touch panel, the thickness of the piezoelectric film of the present invention is preferably in the range of 10 to 40 μm, more preferably in the range of 10 to 30 μm. When the piezoelectric film of the present invention is used in an electrowetting device, the thickness of the piezoelectric film of the present invention is preferably in the range of 0.5 to 5 μm, more preferably 0.8 to 2 μm, and the present When the piezoelectric film of the present invention is used for a Fim capacitor, the thickness of the piezoelectric film of the present invention is preferably in the range of 1.5 to 12 μm.
The piezoelectric film of the present invention is preferably an unstretched piezoelectric film.
In relation to this, the piezoelectric film of the present invention has high thickness uniformity. Specifically, preferably, the piezoelectric film of the present invention has a variation coefficient of thickness of ± 10% or less measured at 10 points per 1 cm square over the entire plane direction.

The electromechanical coupling coefficient of the piezoelectric film of the present invention is usually in the range of 0.1 to 0.01, preferably in the range of 0.09 to 0.02, more preferably in the range of 0.08 to 0.03. It is.
The rate of change of the electromechanical coupling coefficient of the piezoelectric film of the present invention is preferably 10% or less, more preferably 8% or less, and even more preferably 6% or less.
In this specification, the electromechanical coupling coefficient may be abbreviated as kt.

  In the present invention, the “electromechanical coupling coefficient” (kt value) of the piezoelectric film is determined by forming an Al vapor-deposited electrode on both sides of the piezoelectric film, cutting out a 13 mm disk at a predetermined portion of the piezoelectric film, and analyzing the impedance analyzer (Hewlett Packard). 4194A) or an equivalent thereof, and calculated by the method described in H. Ohigashi et al., “The application of ferroelectric polymer, Ultrasonic transducers in the megahertz range”.

In this specification, “rate of change of electromechanical coupling coefficient” is the rate of change of electromechanical coupling coefficient when heated at 85 ° C. for 10 hours unless otherwise specified.
The "rate of change of electromechanical coupling coefficient" is
(1) measuring the electromechanical coupling coefficient (kt before heating) of the piezoelectric film;
(2) heating the piezoelectric film in air at 85 ° C. for 10 hours;
(3) Allowing the piezoelectric film to stand at room temperature and cooling to room temperature, and (4) Measuring the electromechanical coupling coefficient (kt after heating) of the piezoelectric film after the heating and cooling. “Kt before heating” and “kt after heating” are determined by calculating into the following equation.
Change in electromechanical coupling coefficient (%) =
((Kt after heating−kt before heating) / kt before heating) × 100
Change rate of electromechanical coupling coefficient (%) = | Change amount of electromechanical coupling coefficient (%) |
In this specification, “room temperature” is a temperature within a range of 15 to 35 ° C.

The piezoelectric film of the present invention has high shape uniformity and visual uniformity (that is, less wrinkles and deflection (curvature in a state where no tension other than tension due to gravity is applied)).
Moreover, the piezoelectric film of the present invention has high uniformity of polarizability.

Manufacturing Method The piezoelectric film of the present invention is, for example,
Step A for preparing a non-stretched and non-polarized polymer film (eg, non-polarized vinylidene fluoride polymer film) by a casting method;
Step B for polarizing the non-stretched and non-polarized polymer film; and Step C for heat-treating the non-stretched polymer film at any time with respect to Step B
It can manufacture by the manufacturing method containing.

Process A (film preparation process)

The manufacturing method of “the non-stretched and non-polarized film” by the casting method is, for example,
(1) A liquid composition obtained by dissolving or dispersing a polymer (eg, vinylidene fluoride polymer) and desired components (eg, inorganic oxide particles and affinity improver) in a solvent. The step of dissolving the liquid to prepare a liquid composition;
(2) a step of casting (coating) the liquid composition on a substrate; and (3) a step of vaporizing the solvent to form a film:
It is a manufacturing method containing.

The dissolution temperature in the preparation of the liquid composition is not particularly limited, but a higher dissolution temperature is preferable because dissolution can be promoted. However, if the melting temperature is too high, the resulting film tends to be colored, so the melting temperature is preferably from room temperature to 80 ° C.
From the viewpoint of preventing such coloring, preferred examples of the solvent include ketone solvents (eg, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetone, diethyl ketone, dipropyl ketone), ester solvents ( Examples include ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl lactate), ether solvents (eg, tetrahydrofuran, methyltetrahydrofuran, dioxane), and amide solvents (eg, dimethylformamide (DMF), dimethylacetamide). It is done. These solvents may be used alone or in combination of two or more. As the solvent, an amide solvent which is a solvent widely used for dissolving polyvinylidene fluoride (PVDF) may be used, but the content of the amide solvent in the solvent is desirably 50% or less.

  Casting (application) of the liquid composition onto the substrate is performed by casting (applying) the liquid composition onto the substrate by knife coating method, cast coating method, roll coating method, gravure coating method, A conventional method such as a blade coating method, a rod coating method, an air doctor coating method, or a slot die method may be used. Of these, the gravure coating method or the slot die method is preferable because it is easy to operate, has little variation in film thickness, and is excellent in productivity. As the base material, for example, a polyethylene terephthalate (PET) film can be used.

The solvent can be vaporized by a conventional drying method such as heating.
Although the drying temperature in the vaporization of the solvent can be appropriately determined according to the type of the solvent, etc., it is usually in the range of 20 ° C. to 200 ° C., more preferably in the range of 40 ° C. to 170 ° C. The drying time is usually in the range of 1 to 600 seconds, preferably in the range of 10 to 120 seconds.
The drying temperature is preferably changed from a low temperature (eg, 40 to 100 ° C.) to a high temperature (eg, 120 to 200 ° C.) in terms of obtaining a film having a low haze value. This can be achieved, for example, by dividing the drying zone into several zones and transferring the film from the cold zone to the hot zone.
Specifically, for example, the drying zone is divided into 5 zones of 50 ° C., 80 ° C., 120 ° C., and 150 ° C., and the film (or the cast solution before film formation) is removed from the 50 ° C. zone to 150 ° C. It is sufficient to move continuously to the zone. In this case, the heating time in each zone is preferably in the range of 1 to 100 seconds, in the range of 1 to 100 seconds, in the range of 1 to 100 seconds, and in the range of 1 to 100 seconds, respectively. .

  What is necessary is just to set the thickness of the non-polarizing film prepared at the process A according to the piezoelectric film to be obtained.

Process B (polarization process)
In step B, the non-polarized film is polarized.

The non-polarized copolymer film (hereinafter sometimes simply referred to as “non-polarized film”) used in Step B is preferably not stretched. Also preferably, in the production method of the present invention, the non-polarized film is not stretched.
As a result, the thickness of the obtained piezoelectric film of the present invention is small.

  The polarization treatment in step B can be performed by a conventional method such as corona discharge treatment.

The polarization treatment in step B is preferably performed by corona discharge.
For the corona discharge, either a negative corona or a positive corona may be used, but it is desirable to use a negative corona from the viewpoint of easy polarization of the non-polarized resin film.

The corona discharge treatment is not particularly limited. For example, as described in Japanese Patent Application Laid-Open No. 2011-181748, the nonpolarized film is applied using a linear electrode; or the nonpolarized film is a needle. The application can be performed by using the electrode.
The conditions for the corona discharge treatment may be appropriately set based on common sense in the technical field to which the present invention belongs. If the corona discharge treatment conditions are too weak, the piezoelectricity of the resulting piezoelectric film may be insufficient. On the other hand, if the corona discharge treatment conditions are too strong, the resulting piezoelectric film may have point defects. is there.
For example, when continuous application is performed roll-to-roll using a linear electrode, it varies depending on the distance between the linear electrode and the non-polarized film, the film thickness, etc., for example, -15 to -25 kV DC electric field. The processing speed is, for example, 10 to 500 cm / min.
Alternatively, the polarization treatment may be performed by, for example, sandwiching and applying the flat electrode from both sides of the non-polarized film in addition to the corona discharge. Specifically, for example, when the application is performed by sandwiching the non-polarized film from both sides with a flat plate electrode, a DC electric field of 0 to 400 MV / m (preferably 50 to 400 MV / m), and 0.1 second to 60 minutes. The conditions for the application time can be adopted.

Process C (heat treatment process)
Step C is performed at any time with respect to Step B. That is, step C can be performed before step B, simultaneously with step B, or after step B. When the process C is performed after the process B, the heat treatment of the process C can be performed on the polarized film obtained in the process B or the portion where the polarization has been completed in the process B. That is, while performing the polarization process of the process B, the heat treatment of the process C may be performed on the portion where the polarization process has been completed.
The method of the heat treatment is not particularly limited. For example, the unstretched polymer film (hereinafter sometimes simply referred to as the film) is sandwiched between two metal plates, and the metal plate is heated; Heating the roll in a thermostat; or in the production of the film in a roll-to-roll manner, heating the metal roll and bringing the film into contact with the heated metal roll; or This can be done by passing it through a heated furnace in a roll-to-roll manner. Here, when the process C is performed after the process B, the polarizing film may be heat-treated alone, or may be laminated on another type of film or metal foil to form a laminated film and heat-treated. . In particular, when the heat treatment is performed at a high temperature, the latter method is preferable because the polarizing film is less likely to wrinkle.
The temperature of the heat treatment may vary depending on the kind of the polarized film to be heat-treated, and is preferably in the range of (melting point of the polarizing film to be heat-treated) -100 ° C. to (melting point of the polarized film to be heat-treated + 40) ° C. Is within.
Specifically, the temperature of the heat treatment is preferably 80 ° C. or higher, more preferably 85 ° C. or higher, and still more preferably 90 ° C. or higher.
The temperature of the heat treatment is preferably 170 ° C. or lower, more preferably 160 ° C. or lower, and still more preferably 140 ° C. or lower.
The time for the heat treatment is usually 10 seconds or longer, preferably 0.5 minutes or longer, more preferably 1 minute or longer, and further preferably 2 minutes or longer.
Moreover, although the upper limit of the said heat processing time is not limited, Usually, the time of the said heat processing is 60 minutes or less.
The conditions for the heat treatment are preferably 90 ° C. or more and 1 minute or more.

  After the heat treatment, the film is cooled to a predetermined temperature. The temperature is preferably in the range of 0 ° C. to 60 ° C. and can be room temperature. The cooling rate may be slow cooling or rapid cooling, and rapid cooling is preferable from the viewpoint of productivity. The rapid cooling can be performed by means such as air blowing.

Piezoelectric Film Roll The piezoelectric film of the present invention can preferably be stored and shipped as a roll.
The elastic modulus of the piezoelectric film of the present invention is preferably 500 MPa or more from the viewpoint of suppressing the generation of wrinkles when forming such a roll. The elastic modulus can be adjusted by selecting the material of the film.
The roll of the piezoelectric film of the present invention may consist only of the piezoelectric film of the present invention, or may be a form in which a protective film or the like is laminated and wound on the piezoelectric film of the present invention. You may provide the piezoelectric film of this invention wound.
The roll of the piezoelectric film of the present invention preferably has a width of 50 mm or more and a length of 20 m or more.
The roll of the piezoelectric film of the present invention can be prepared, for example, by winding the piezoelectric film of the present invention using a winding roller and a winding roller.
Here, from the viewpoint of suppressing the deflection of the film, it is preferable that the unwinding roller and the take-up roller be parallel to each other, as is usually done.
Further, from the viewpoint of suppressing the deflection of the film, among the piezoelectric films of the present invention, a film having an elastic modulus of 500 MPa or more may be used.
As a roller, in order to improve the slipperiness of the film of the present invention, a roller having a good slipperiness, specifically a roller coated with a fluororesin, a plated roller, or a roller coated with a release agent is used. Is preferred.
Here, when the film thickness is non-uniform, so-called roll earing (high edge; the end portion becomes thicker than the central portion in the axial direction of the roll; both end portions are thinner than the central portion. In some cases, both ends are recessed compared to the center; or when the thickness changes from one end to the other in an inclined manner, the end on the side where the film thickness is thinner is recessed) Unevenness of the roll thickness occurs, which may cause wrinkles. In addition, this may cause the film to bend (bend in a state in which no tension other than that due to gravity is applied) when the film is rolled out.
Generally, for the purpose of preventing the roll from standing, the end of the film that is the end of the roll is slitted (slit). However, if the film thickness varies widely from the end of the film, the end of the roll It is difficult to prevent the roll from standing and dents with only the roller.
In general, the larger the width of the film (for example, 100 mm or more) and the longer the length of the film (for example, 50 m or more), the more likely the ear standing, the dent and the deflection are generated.
However, since the thickness of the piezoelectric film of the present invention is high, the width of the film can be widened (for example, 100 mm in width by simply slitting the end of the film, which is the end of the roll). Even when the length of the film is long (e.g., 50 m or more), it is possible to obtain a roll in which the ear standing, the dent, and the deflection are suppressed.
The ear (film edge) removed by the slit can be collected and recycled as a raw material for the piezoelectric film of the present invention.
The roll of the piezoelectric film of the present invention has high thickness uniformity, and preferably the ratio of the thickness of the thicker end to the thickness of the central portion in the axial direction of the roll is in the range of 70 to 130%. Is within.
Thereby, the deflection | deviation of the film unwound from this is suppressed by the roll of the piezoelectric film of this invention.

It is preferable that the surface roughness Ra of the roller used for manufacturing the piezoelectric film and the roll of the present invention is 1 μm or less. In this specification, “surface roughness Ra” is “arithmetic average height” defined in JIS B0601: 2001.
Moreover, it is preferable that the roller used for manufacture of the piezoelectric film of the present invention and the roll thereof has at least a surface material of polytetrafluoroethylene (PTFE), chrome plating, or stainless steel (SUS).
By these things, the wrinkle of a film can be suppressed.

Apply
Piezoelectric panel The piezoelectric film of the present invention can be used for a piezoelectric panel (eg, a touch panel capable of detecting touch pressure).
The touch panel having the piezoelectric film of the present invention can detect both the touch position and the touch pressure, and even when exposed to an extremely high temperature, the touch pressure detection performance is hardly deteriorated and the transparency is high.
The piezoelectric film of the present invention can be used for touch panels of all types such as a resistive film type and a capacitance type.
When the piezoelectric film of the present invention is used for a touch panel, it does not necessarily need to be used for detection of both the touch position and the touch pressure, and the piezoelectric film of the present invention has either a touch position or a touch pressure. It may also be used for detection.
The piezoelectric panel having the piezoelectric film of the present invention is preferably,
A first electrode (preferably a transparent electrode);
The piezoelectric film of the present invention (preferably a transparent piezoelectric film);
A second electrode (preferably a transparent electrode);
In this order.
The first electrode is directly or indirectly disposed on one main surface of the piezoelectric film of the present invention, and the second electrode is directly or indirectly disposed on the other main surface of the piezoelectric film of the present invention. The
Examples of the electrodes include ITO (indium tin oxide) electrodes, tin oxide electrodes, metal nanowires, metal nanoparticles, and organic conductive resins.

  The touch panel having the piezoelectric film of the present invention can be used for an input device (that is, an input device having the piezoelectric film of the present invention). An input device having the touch panel can perform input based on a touch position, a touch pressure, or both. An input device having the touch panel can include a position detection unit and a pressure detection unit.

  The input device can be used for electronic devices (eg, mobile phones (eg, smart phones), personal digital assistants (PDAs), tablet PCs, ATMs, automatic ticket vending machines, and car navigation systems). An electronic device including the input device can be operated and operated based on a touch position, a touch pressure, or both.

Electrowetting Device The piezoelectric film of the present invention has electrowetting properties and can be used for an electrowetting device. Here, the “electrowetting” means that the wettability of the surface of the film is changed from hydrophobic (water repellent) to hydrophilic using an electric field. The “electrowetting device” means a device using the “electrowetting”.
The piezoelectric film of the present invention includes an optical element, a display device (display), a variable focus lens, a light modulation device, an optical pickup device, an optical recording / reproducing device, a developing device, a droplet manipulation device, and an analytical instrument (eg, sample analysis). Therefore, it can be suitably used for an electrowetting device in a chemical, biochemical, and biological analysis instrument) in which a minute conductive liquid needs to be moved.
The piezoelectric film of the present invention can have a high dielectric constant and a low dielectric loss tangent. Thereby, a conductive liquid can be driven with a low voltage.

Film Capacitor The piezoelectric film of the present invention can have a high dielectric constant and a low dielectric loss tangent. Thereby, a conductive liquid can be driven with a low voltage.
Moreover, since the piezoelectric film of the present invention can have a high relative dielectric constant and a low dielectric loss tangent, it can be suitably used as a film for a film capacitor. Further, it is advantageous as a film for a film capacitor in that the high dielectric property, which is a characteristic of vinylidene fluoride resin, is not impaired even when a voltage is applied for a long time.

Transparent Cover Film The piezoelectric film of the present invention can be used as a transparent cover film because it is made of a vinylidene resin excellent in weather resistance and has very high transparency. In this case, for example, weather resistance can be imparted to these films by laminating a polycarbonate or PET film on the piezoelectric film of the present invention.

  Since the piezoelectric film of the present invention has flexibility, it can be suitably used for various applications.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.
Hereinafter, the molar ratio of the repeating unit derived from tetrafluoroethylene / the repeating unit derived from vinylidene fluoride in the vinylidene fluoride / tetrafluoroethylene copolymer may be represented by “TFE / VDF”.

Example 1
(Preparation of non-polarized film)
A vinylidene fluoride / tetrafluoroethylene copolymer (TFE / VDF = 20/80) was dissolved in methyl ethyl ketone (MEK) to prepare a paint having a solid content of 25 wt%.
Thereafter, the paint was cast (casted) on a PET film using a die coater and dried to prepare a film having a thickness of 20 μm. At this time, for drying, the drying apparatus is divided into four zones, and the drying temperatures are set to 50 ° C., 80 ° C., 120 ° C., and 150 ° C. from the entrance side, and the passing time of each zone is 24 seconds, 24 hours. This was done by passing the film (or cast paint) through a second, 24 seconds, and 24 seconds setting the moving speed.
(Polarization treatment)
Then, the said film was peeled off from the said PET film, the said polymer film was pinched | interposed from the upper and lower sides using a metal electrode, and it applied and polarized for 150 minutes at room temperature, and the polarized film was obtained.
(Heat treatment)
Thereafter, the polarized film was heated in a hot air dryer at 90 ° C. for 10 minutes, and then allowed to stand at room temperature to cool to room temperature, whereby the piezoelectric film of Example 1 was obtained.

Comparative Example 1
A piezoelectric film (thickness 20 μm) of Comparative Example 1 was obtained in the same manner as in Example 1 except that the drying temperature was set to the same 120 ° C. in all four zones.

Comparative Example 2
A piezoelectric film having a thickness of 100 μm was prepared in the same manner as in Example 1. Thereafter, stretching was performed to obtain a film of Comparative Example 2 having a thickness of 20 μm.

  For the piezoelectric films of Example 1, Comparative Example 1 and Comparative Example 2, the following methods were used for total light transmittance, haze value (total haze value, external haze value, internal haze value), thickness variation coefficient, and kt value. The rate of change was determined. The results are shown in Table 1 below.

The total light transmittance haze guard II was used and measured based on ASTM D1003.
HAZE test: Measured based on ASTM D1003 using Hazeguard II manufactured by Toyo Seiki Seisakusho.

Haze value (total haze value, external haze value, internal haze value)
Using haze guard II (product name) (Toyo Seiki Seisakusho Co., Ltd.), all haze values were measured based on ASTM D1003.
The internal haze value was obtained by measuring the haze value in the same manner as the total haze value except that water was put in a glass cell and a film was inserted therein. The external haze value was calculated by subtracting the internal haze value from the total haze value of the film.

Coefficient of variation of thickness The thickness was measured at 10 locations every 1 cm square over the entire plane of the film, and the coefficient of variation of the thickness of the film was calculated.
The average value of the 10 points measured was taken as the average thickness, and the coefficient of variation in thickness was calculated using the following formula.
Coefficient of variation of thickness (%) = ± [(maximum value of thickness−average value of thickness) + (average value of thickness−minimum value of thickness)] ÷ average value of thickness ÷ 2 × 100
There was no change in the coefficient of variation of thickness before polarization, after polarization, and after heat treatment.

The kt value change rate electromechanical coupling coefficient (kt value) is obtained by forming an Al vapor-deposited electrode on both sides of a piezoelectric film, cutting out a disk having a diameter of 13 mm from a predetermined portion of the piezoelectric film, The measurement was carried out using the method described in H. Ohigashi et al., “The application of ferroelectric polymer, Ultrasonic transducers in the megahertz range”.
Change rate of electromechanical coupling coefficient (kt value change rate) is
(1) measuring the electromechanical coupling coefficient (kt before heating) of the piezoelectric film;
(2) heating the piezoelectric film in air at 85 ° C. for 10 hours;
(3) Allowing the piezoelectric film to stand at room temperature and cooling to room temperature, and (4) Measuring the electromechanical coupling coefficient (kt after heating) of the piezoelectric film after the heating and cooling. The determined “kt before heating” and “kt after heating” were determined by calculating into the following equations.
Change in electromechanical coupling coefficient (%) =
((Kt after heating−kt before heating) / kt before heating) × 100
Change rate of electromechanical coupling coefficient (%) = | Change amount of electromechanical coupling coefficient (%) |

  From the above results, (1) the film dried at a constant temperature has a high haze value, and (2) the stretched piezoelectric film has a large coefficient of variation in thickness, whereas the drying temperature is changed from low to high. The dried film was found to have a small coefficient of variation in thickness and a small haze value.

Test example 1 (polarization uniformity)
The unpolarized films in Example 1 and Comparative Example 2 were cut out in a size of 10 cm × 10 cm, respectively, in the same manner as in Example 1, except that the application conditions were severe, under the condition of 400 kV / cm, A DC voltage was applied. In the obtained polarized film, the number of holes having a diameter of 0.5 mm or more was examined. As a result, one hole was observed in the film of Example 1, and 18 holes were observed in the film of Comparative Example 2.
This revealed that the film of Example 1 having a small thickness variation coefficient has high polarization uniformity.

これにより、厚さの変動係数が小さい実施例１のフィルムのロールでは、耳立ち及びフィルムのたわみが抑制されていることが明らかになった。 After rolling (slit) the end surfaces of the piezoelectric films of the roll example 1 and the comparative example 2 so as to have a film width of 100 mm, the film having a length of 50 m was wound up to obtain a roll of film. The thickness of the central portion and the end portion of the roll in the axial direction were measured, and the ratio was calculated.
The film was unwound from the roll, and the presence or absence of film deflection (curvature in a state where no tension other than tension due to gravity was applied) was visually observed.

Thereby, in the roll of the film of Example 1 with a small variation coefficient of thickness, it became clear that the ear stand and the deflection of the film were suppressed.

Examples 3 and 4 and Comparative Example 3
(Preparation of non-polarized film)
A vinylidene fluoride / tetrafluoroethylene copolymer (TFE / VDF = 20/80) was dissolved in methyl ethyl ketone (MEK) to prepare a paint having a solid content of 20 wt%.
Thereafter, the coating material is cast (casting) on a PET film using a die coater and dried to prepare films having thicknesses of 1.5 μm (Example 3) and 3 μm (Example 4). did. At this time, for drying, the drying apparatus is divided into four zones, and the drying temperatures are set to 50 ° C., 80 ° C., 120 ° C., and 120 ° C. from the entrance side, and the passing time of each zone is 24 seconds, 24 hours. This was done by passing the film (or cast paint) through a second, 24 seconds, and 24 seconds setting the moving speed.
As Comparative Example 3, casting (casting) and drying were performed in the same manner as in Examples 3 and 4 to prepare a film having a thickness of 8 μm, and then the film was stretched to prepare a film having a thickness of 3 μm. .
For the polarizing films of Examples 2 and 3 and Comparative Example 3, in the same manner as described in Example 1, total light transmittance, haze value (total haze value, external haze value, internal haze value), and The coefficient of variation of thickness was determined. The results are shown in Table 3 below.
Each of the obtained films was stuck on a glass with ITO (Nippon Sheet Glass Co., Ltd.) 80Ω with a roll press. On top of this, spin-coating was applied using a die-free GF500 (Daikin Kogyo Co., Ltd.) as a water repellent layer to a thickness of 0.1 μm.

Test example 2 (electrowetting)
A 20 μL water droplet was placed on the water repellent layer on each film of Examples 2 and 3 and Comparative Example 3, and the contact angle was measured. Thereafter, a contact angle was measured by applying a voltage of 50 V by connecting a + (plus) electrode to a water droplet and a-(minus) electrode to ITO.

The results are shown in Table 3 below.

Electrowetting requires a high total light transmittance, a low haze value, and a large contact angle difference between water droplets before and after voltage application. As can be seen from this result, the difference in the contact angle between the water droplets before and after the voltage application is small when the variation coefficient of the film thickness is high. This is considered to be because water droplets originally spread easily due to the rough surface.
Further, as seen in the comparison between Examples 3 and 4, the thinner the film thickness, the more advantageous the contact angle difference.

  The piezoelectric film of the present invention can be used for a piezoelectric panel such as a touch panel that can detect a touch pressure.

Claims (9)

A total light transmittance of 90% or more;
The total haze value is 4.0% or less; and the coefficient of variation in thickness is 10% or less when the thickness is measured at 10 locations every 1 cm square over the entire plane direction;
Piezoelectric film. The piezoelectric film according to claim 1, wherein the total haze value is 2.0% or less. The piezoelectric film according to claim 1, comprising an organic piezoelectric film. The piezoelectric film according to claim 1 or 2, comprising a polarized vinylidene fluoride polymer film. Step A for preparing an unstretched and non-polarized vinylidene fluoride polymer film by a casting method;
Step B for polarizing the non-stretched and non-polarized vinylidene fluoride polymer film; and Step C for heat-treating the non-stretched vinylidene fluoride-based polymer film at any time with respect to Step B
The manufacturing method of the piezoelectric film of Claim 4 containing this. It is a roll of the piezoelectric film of any one of Claims 1-4, Comprising: Ratio of the thickness of the thicker edge part with respect to the thickness of the center part of the axial direction of a roll is 70 to 130%. A role that is within range. A piezoelectric panel, a film capacitor, or an electrowetting device comprising the piezoelectric film according to any one of claims 1 to 4 or the piezoelectric film produced by the production method according to claim 5. The input device which has a piezoelectric film of any one of Claims 1-4, or a piezoelectric film manufactured by the manufacturing method of Claim 5. An electronic apparatus comprising the input device according to claim 8.