JP2015111640A - Method for producing piezoelectric film - Google Patents

Abstract

Kind Code: A1 A method for producing a piezoelectric film is provided in which plastic deformation, scratches, and adhesion to a heating roll of a polarized film are suppressed, and as a result, the polarized film can be stably heated. SOLUTION: A step 1 of arranging a protective film 2 on at least one main surface of a polarized film 3 so as to be adjacent directly or via another layer; a step 2 of heating the polarized film 3 through the protective film 2 by contacting with 1; [Selection drawing] Fig. 2

Description

  The present invention relates to a method for manufacturing 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, when the method of heating by directly applying a heating roll to the polarizing film is performed according to the study by the present inventors, a strong force (generated by the vertical drag from the heating roll, the tension and the heating roll surface) is applied to the polarizing film. Heat is applied after applying a shearing force generated by frictional force, etc., so that the polarized film may be plastically deformed, adhered to the heating roll, or scratched, resulting in stable It was found that there was a problem that heating could not be performed.
Accordingly, an object of the present invention is to provide a method for manufacturing a piezoelectric film, in which plastic deformation and scratches of the polarizing film, adhesion to a heating roll, and the like are suppressed, and as a result, the polarizing film can be stably heated. And

As a result of intensive studies, the present inventors have
Step 1 of disposing a protective film adjacent to at least one main surface of the polarizing film, and
Step 2 of heating the polarization film through the protective film by contacting the protective film with one or more heating rolls,
As a result of further studies, the present inventors have completed the present invention.

  The present invention includes the following aspects.

Item 1.
Step 1 of disposing a protective film on at least one main surface of the polarizing film so as to be adjacent directly or via another layer, and
Step 2 of heating the polarization film through the protective film by contacting the protective film with one or more heating rolls,
A method for producing a piezoelectric film, comprising:
Item 2.
Item 2. The manufacturing method according to Item 1, wherein at least one of the holding angles described later formed by the protective film and the heating roll is 180 ° or more.
<Hugging angle>
A central angle formed by an arc formed from the point where the protective film starts to contact the peripheral surface of the heating roll to the point where the protective film is about to leave the peripheral surface.
Item 3.
Item 3. The manufacturing method according to Item 1 or 2, wherein the piezoelectric film is for a piezoelectric touch panel.

  In the method for producing a piezoelectric film of the present invention, plastic deformation, scratches, surface defects and adhesion to a heating roll of the polarizing film are suppressed, and as a result, the polarizing film can be stably heated.

It is a heating process in the manufacturing method of the present invention using one heating roll. It is a heating step in the production method of the present invention using two heating rolls and two guide rolls (a holding angle of 210 ° between the protective film and the heating roll and a heating roll diameter of 300 mm). It is a heating process in the production method of the present invention using two heating rolls and four guide rolls (a holding angle of a protective film and a heating roll of 270 °, a heating roll diameter of 300 mm). It is a heating process in the production method of the present invention using three heating rolls and two guide rolls (a holding angle of 230 ° between a protective film and a large heating roll, a large heating roll diameter of 300 mm).

Meaning of Terms In this specification, “detection” of “touch position” means determination of touch position, while “detection” of “touch pressure” means presence / absence of pressure, speed, magnitude (strength), Or the change of these, or the determination of these combination is meant.
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.

Manufacturing method of piezoelectric film The manufacturing method of the piezoelectric film of the present invention includes:
Step 1 of disposing a protective film on at least one main surface of the polarizing film so as to be adjacent directly or via another layer, and
Step 2 of heating the polarization film through the protective film by contacting the protective film with one or more heating rolls,
It is characterized by including.

Step 1 (Step of placing a polarizing film and a protective film)
In the method for producing a piezoelectric film of the present invention, in step 1, before the polarizing film is heated, the protective film is disposed on at least one main surface of the polarizing film so as to be adjacent to each other directly or via another layer. . Thereby, in the process 2 mentioned later, the said polarizing film can be heated via the said protective film.
In this specification, “arranging so as to be adjacent” means that after performing step 2 described later,
(1) A laminate having a protective film and a piezoelectric film, and
(2) The protective film is a laminate that is disposed on at least one main surface of the piezoelectric film directly or adjacently via another layer,
It means that the polarizing film and the protective film are arranged so that can be obtained. In the said process 1, when arrange | positioning so that a protective film and a polarized film may adhere | attach, when any arrange | positioning so that a protective film and a polarized film may adjoin without adhering, any aspect is also included.

The protective film is used to protect the polarizing film (and the piezoelectric film). Examples of the resin constituting the protective film include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PP (polypropylene), and PE (polyethylene). In addition, the protective film in this invention includes the extended | stretched protective film.
The thickness of the protective film is usually in the range of 10 to 200 μm, preferably in the range of 30 to 50 μm.
Another layer may be provided on the main surface of the protective film. Moreover, when arrange | positioning a protective film and a polarizing film, the said other layer may be arrange | positioned between the said protective film and a polarizing film. In this case, in step 1, a protective film is disposed on at least one main surface of the polarizing film so as to be adjacent to each other via the other layer. Examples of the other layer include an adhesive layer. The other layer includes one layer or two or more layers.
Examples of the adhesive layer include EVA (ethylene-vinyl acetate copolymer), acrylic resin, silicone resin, polyolefin resin, and the like.
The thickness of the other layer is not particularly limited.

  The polarized film can be produced, for example, by the step A of polarizing a non-polarized polymer film (eg, non-polarized vinylidene fluoride polymer film). Hereinafter, the process A will be described in detail.

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

  The “non-polarized polymer film” used in step A can be produced by a known method such as a casting method, a hot press method, or a melt extrusion method. The “non-polarized polymer film” used in step A is preferably a film produced by a casting method.

The production method of “non-polarized polymer film” by the casting method is, for example,
(1) A step of preparing a liquid composition by dissolving or dispersing a polymer (eg, vinylidene fluoride polymer) and desired components (eg, an inorganic substance and an affinity improver) in a solvent;
(2) A process comprising casting (applying) the liquid composition on a substrate; and (3) vaporizing the solvent to form a film.
In the present specification, examples of the “vinylidene fluoride polymer” include vinylidene fluoride / tetrafluoroethylene copolymer, vinylidene fluoride / trifluoroethylene copolymer, and polyvinylidene fluoride.
The vinylidene fluoride polymer is preferably a vinylidene fluoride / tetrafluoroethylene copolymer.

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.

The liquid composition may contain an inorganic material as necessary.
Preferable examples of the “inorganic substance” include inorganic oxide particles. By containing the “inorganic oxide particles”, it is possible to adjust electrical properties, mechanical properties, and the like.

  The liquid composition may contain other components such as an affinity improver as necessary.

  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, tetraisopropyl bis (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).

  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, the amount is 100 mass of “inorganic oxide particles”. The amount is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, and still more preferably 1 to 20 parts by mass with respect to parts.

  Furthermore, the said liquid composition may contain additives other than these in the range which does not lose the effect of this invention.

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.

  The liquid composition is cast (applied) onto a substrate by a knife coating method, a cast coating method, a roll coating method, a gravure coating method, a blade coating method, a rod coating method, an air doctor coating method, or a slot die method. The conventional method such as the above 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 and the like, it is usually in the range of 20 ° C to 200 ° C, preferably in the range of 40 ° C to 170 ° C.
The drying temperature may be a constant temperature or may be changed. By changing the drying temperature from a low temperature (eg, 40 to 100 ° C.) to a high temperature (eg, 120 to 200 ° C.), the haze value of the resulting film can be lowered. This can be achieved, for example, by dividing the drying zone into several zones and the film (or cast solution before film formation) enters the cold zone and moves to the hot zone.
Specifically, for example, the drying zone may be divided into four zones of 50 ° C., 80 ° C., 120 ° C., and 150 ° C., and the film may be continuously moved from the zone of 50 ° C. to the zone of 150 ° C.
The drying time in the vaporization of the solvent is usually in the range of 1 to 600 seconds, preferably in the range of 10 to 300 seconds.

The “non-polarized vinylidene fluoride polymer film” (hereinafter sometimes simply referred to as “non-polarized film”) used in Step A is preferably not stretched. Also preferably, in the production method of the present invention, the non-polarized film is not stretched. That is, the piezoelectric film obtained by the production method of the present invention (hereinafter also referred to as the piezoelectric film of the present invention) is preferably an unstretched piezoelectric film.
The piezoelectric film of the present invention thus obtained has a high thickness uniformity. Specifically, preferably, in the piezoelectric film of the present invention, the variation coefficient of the thickness measured at 10 points per 1 cm square over the whole film is ± 20% or less of the average film thickness.

  The non-polarized film used in step A may be heat-treated after film formation.

  The thickness of the non-polarized film used in step A may be determined according to the piezoelectric film to be obtained.

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

The polarization treatment in step A 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 JP 2011-181748 A, a non-polarized film is applied using a linear electrode; or the non-polarized film is a needle. The application can be performed by using the electrode. In addition, a corona discharge process is normally performed in the state in which the protective film is not affixed.

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.

Another layer may be provided on the main surface of the polarizing film. Moreover, when arrange | positioning a polarizing film and a protective film, the said other layer may be arrange | positioned between the said polarizing film and a protective film. In this case, in step 1, a protective film is disposed on at least one main surface of the polarizing film so as to be adjacent to each other via the other layer. Examples of the other layer include an electrode layer. The other layer includes one layer or two or more layers.
Examples of the electrode layer include ITO (indium tin oxide) and tin oxide.
The thickness of the other layer is not particularly limited.

Step 2 (heating step)
In step 2, the polarizing film is heated (heat treatment step).
The heating method of the polarized film in the process 2 heats the polarized film through the protective film when the protective film is in contact with one or more heating rolls. That is, in step 2, the polarizing film is not heated so as to be in direct contact with the heating roll, but the protective film is heated so as to be in direct contact with the heating roll, and is polarized by the heat of the protective film. The heated film is heated. By this step, plastic deformation and scratches of the polarized film, adhesion to the heating roll, and the like are suppressed, and as a result, the polarized film can be stably heated.
Step 2 is performed after Step 1 or simultaneously with Step 1. That is, in step 2, after the protective film is disposed adjacent to at least one main surface of the polarizing film, or the protective film is disposed adjacent to at least one main surface of the polarized film. However, the polarized film obtained by the polarization treatment in step A is heated.

  In step 2, as described above, one or more heating rolls are used. The diameter of the heating roll is usually 0.03 to 2 m, preferably 0.05 to 0.5 m.

In step 2, the central angle formed by the arc formed from the point where the protective film starts to contact the peripheral surface of the heating roll to the point where the protective film is about to leave the peripheral surface (hereinafter also referred to as a holding angle), It is preferable that it is 180 degrees or more. In this case, the polarizing film can be gently heated to the target temperature via the protective film. The holding angle can be increased by installing a guide roll described later.
When two or more heating rolls are used, it is a preferable embodiment that the holding angle of 180 ° or more is formed with at least one heating roll. In a more preferred embodiment, a holding angle of more than 0 ° is formed.

The temperature of the heating 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 heating temperature is preferably 80 ° C. or higher, more preferably 85 ° C. or higher, and still more preferably 90 ° C. or higher.
The heating temperature is preferably 170 ° C. or lower, more preferably 160 ° C. or lower, and still more preferably 140 ° C. or lower.
The heating time is usually 10 seconds or longer, preferably 0.5 minutes or longer, more preferably 1 minute or longer, and even more preferably 2 minutes or longer.
Moreover, although the upper limit of the said heating time is not limited, Usually, the said heating time is 60 minutes or less.
The heating condition is preferably 90 ° C. or higher and 1 minute or longer.
In the present specification, the melting point of a film is a maximum value in a heat of fusion curve obtained when the temperature is raised at a rate of 10 ° C./min using a differential scanning calorimetry (DSC) apparatus.

Each aspect in the process 2 is shown below. As shown in FIG. 1, the aspect which heats a polarizing film through a protective film with one heating roll includes this invention. Moreover, as shown in FIG. 2, the aspect which heats a polarizing film via a protective film with two heating rolls also includes this invention. In addition, as shown in FIG. 2, the holding angle of the said heating roll can be increased by installing a guide roll between a heating roll and a heating roll. The guide roll may be in direct contact with the protective film or may be in direct contact with the polarization film. In addition, other layers (an adhesion layer, an electrode layer, etc.) may be provided between the polarizing film and the protective film.
As shown in FIG. 3, with respect to the mode of FIG. 2, there is also a mode in which the holding angle of each heating roll is further increased by installing a guide roll before the first heating roll and after the last heating roll. The present invention. Moreover, as shown in FIG. 4, a protective film is disposed on both main surfaces of the polarized film (arrangement of protective film A / polarized film / protective film B), and from both sides of the protective film A and protective film B. A mode of heating the polarizing film is also included. In addition, in the aspect of FIG. 4, other layers (an adhesion layer, an electrode layer, etc.) are provided between the protective film A and the polarizing film and / or between the protective film B and the polarizing film. Also good.

Piezoelectric Film The piezoelectric film obtained by the production method of the present invention is a film having a uniform shape in which plastic deformation, scratches, adhesion to a heating roll, and the like are suppressed.
The piezoelectric film of the present invention is preferably 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.
The “vinylidene fluoride polymer film” is a film composed of a vinylidene fluoride polymer and contains a vinylidene fluoride polymer.

The piezoelectric film of the present invention preferably has a total light transmittance of 85% or more.
The total light transmittance of the piezoelectric film of the present invention is more preferably 90% or more, still more preferably 92% or more, and still 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 thereof based on ASTM D1003.

The total haze value of the piezoelectric film of the present invention is preferably 4.0% or less, more preferably 3.0% or less, still more preferably 2.0% or less, still more preferably 1.5% or less, and most 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 0.2% or more.
In this specification, “total haze” is based on ASTM D1003 and is determined by haze (HAZE, turbidity) test using Hazeguard II (product name) (Toyo Seiki Seisakusho) or its equivalent. can get.

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% 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 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 change rate of the electromechanical coupling coefficient of the piezoelectric film of the present invention is preferably 10% or less, more preferably 8% or less, and still 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) 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 position of the piezoelectric film, and analyzing the impedance analyzer (Hewlett-Packard Company). 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 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 film capacitor, the thickness of the piezoelectric film of the present invention is preferably in the range of 1.5 to 12 μm.

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 be composed only of the piezoelectric film of the present invention, or in a form in which the above-mentioned protective film is laminated on the piezoelectric film of the present invention (a laminate having a piezoelectric film and a protective film). Alternatively, a core such as a paper tube and the piezoelectric film of the present invention wound around the core may be provided.
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 (preferably a touch panel capable of detecting a touch pressure)) and the like.
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.
A piezoelectric panel having the piezoelectric film of the present invention has the piezoelectric film and electrode of the present invention, 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, and the second electrode is directly or indirectly disposed on the other main surface of the piezoelectric film.
Examples of the electrode include an ITO (indium tin oxide) electrode and a tin oxide electrode.

  When a piezoelectric panel (e.g., a touch panel (preferably a touch panel capable of detecting a touch pressure)) having the piezoelectric film of the present invention is pressed with a finger or the like, an electrical signal corresponding to a temporal change in strain of the piezoelectric film of the present invention is obtained. Therefore, if the piezoelectric panel is used, the presence / absence of pressure, speed, size (strength), or a change thereof, or a combination thereof can be determined. Here, the magnitude of the pressure (that is, the static pressure) can be determined using the integrated value of the electric signal.

In the piezoelectric panel having the piezoelectric film of the present invention, one or two or more (preferably two) piezoelectric films of the present invention can be used.
When two or more (preferably two) piezoelectric films of the present invention are used, the two or more piezoelectric films of the present invention may be bonded together by an adhesive sheet. The pressure-sensitive adhesive sheet is not particularly limited as long as the piezoelectric films of the present invention can be bonded to each other, and can be composed of one or more layers. That is, when the said adhesive sheet consists of one layer, the said adhesive sheet consists of an adhesive layer, and when the said adhesive sheet consists of two or more layers, the both outer layers are adhesive layers. When the said adhesive sheet consists of 3 or more layers, the said adhesive sheet may have a base material layer as an inner layer.
The pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet can be a layer containing an acrylic pressure-sensitive adhesive as a pressure-sensitive adhesive.
The base material layer in the pressure-sensitive adhesive sheet may be a transparent film, and may preferably be a film of polyimide, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyparaphenylene sulfide, or polyamideimide, for example.

For example, a piezoelectric panel (e.g., a touch panel (preferably a touch panel capable of detecting a touch pressure)) having the piezoelectric film of the present invention is preferably
A first electrode;
A piezoelectric film of the first invention;
An adhesive sheet;
A piezoelectric film of the second invention;
A second electrode;
In this order.
The first electrode is disposed on the outer surface of the piezoelectric film of the first present invention, and the second electrode is disposed on the outer surface of the piezoelectric film of the second present invention.
Although the piezoelectric film of the present invention may have pyroelectricity, in the piezoelectric panel (eg, touch panel (preferably, touch panel capable of detecting touch pressure)), the piezoelectric film of the first invention and the second book The piezoelectric film of the invention is arranged so that the surfaces where charges of the same polarity (for example, positive charge and positive charge) are generated by the temperature rise are on the outside, and the potential difference between the two surfaces is set to the first electrode. When the electrical signal is obtained with the second electrode, the electrical signal due to pyroelectricity is reduced, and the electrical signal due to piezoelectricity can be selectively obtained.

  The touch panel having the piezoelectric film of the present invention can be used for an input device and a touch sensor device. The input device having the touch panel (that is, the input device having the piezoelectric film of the present invention) is input based on the touch position, the touch pressure, or both (for example, input based on the magnitude (strength) of pressure such as writing pressure) Is possible. The input device having the touch panel and the touch sensor device can include a position detection unit and a pressure detection unit.

The input device is an electronic device (eg, mobile phone (eg, smart phone), personal digital assistant (PDA), tablet PC, ATM, automatic ticket vending machine, digitizer, touch pad, car navigation system, FA (factory automation) device. It can be used for a touch panel display (touch panel monitor). An electronic device having the input device has an operation and an operation based on the touch position, the touch pressure, or both (for example, an operation such as changing the thickness of a line displayed on the screen according to the writing pressure in paint software). Is possible.
The touch sensor device can be used for electronic devices (eg, collision sensors, robot cleaners).
The electronic device may include the touch input device of the present invention or the touch sensor device of the present invention, or may include the touch input device of the present invention or the touch sensor device of the present invention.
Since the piezoelectric film of the present invention has flexibility, it can be suitably used for various applications.

The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples.
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
(1) A paint having a solid content of 25 wt% was prepared by dissolving vinylidene fluoride / tetrafluoroethylene copolymer (TFE / VDF = 20/80) in methyl ethyl ketone (MEK). Thereafter, the paint was filtered through a filter, and the filtrate was applied to a PET film with a die coater. By further drying, a vinylidene fluoride / tetrafluoroethylene copolymer film (copolymer film thickness: 30 μm) was produced on the PET film. At this time, the drying was performed at a peripheral speed of 8 m / min in a drying furnace in which the drying temperatures of the four zones (2 m per zone) were set to 50 ° C./80° C./120° C./150° C., respectively.
(2) Next, the copolymer film is peeled from the PET film, the copolymer film is sandwiched from above and below using a metal electrode, and a DC voltage is applied at room temperature for 5 minutes under the condition of 300 kV / cm, The copolymer film was polarized. As a result, a polarizing film (polarized film thickness: 30 μm, polarized film width: 500 mm) was obtained.
(3) A self-adhesive stretched polypropylene (OPP) protective film having a thickness (film thickness) of 30 μm and a width of 500 mm was prepared.
(4) The protective film is placed on the polarizing film, and one side of the protective film is disposed so as to contact a heating roll (dielectric heating type heating roll having a diameter of 300 mm and a width of 700 mm), and 0.2 m / min. The polarizing film was heated at 95 ° C. by two heating rolls while continuously feeding the protective film and the polarizing film at a peripheral speed of 5 ° C.
(5) As a result, it was confirmed that a piezoelectric film was obtained in which the piezoelectricity did not change even under an environment of 85 ° C. × 24 hours and the dents and scratches were not visually recognized on the surface.
Comparative Example 1
The polarizing film was heat-treated under the same conditions as in Example 1 except that the arrangement of the polarizing film and the protective film was reversed. Specifically, the polarizing film was placed in direct contact with the heating roll, and the polarizing film was heat-treated. As a result, many scratches due to contact with the heating roll were confirmed on the surface of the polarized film, and it was confirmed that continuous heating treatment of the polarized film having a high optical function was difficult under these conditions.

1. Heating roll
2. Protective film
3. Polarized film
4. Holding angle (°)
5. Guide roll (dancer roll)

Claims (3)

Step 1 of disposing a protective film on at least one main surface of the polarizing film so as to be adjacent directly or via another layer, and
Step 2 of heating the polarization film through the protective film by contacting the protective film with one or more heating rolls,
A method for producing a piezoelectric film, comprising: The manufacturing method of Claim 1 whose at least 1 of the below-mentioned holding angle which the said protective film and the said heating roll form is 180 degrees or more.
<Hugging angle>
A central angle formed by an arc formed from the point where the protective film starts to contact the peripheral surface of the heating roll to the point where the protective film is about to leave the peripheral surface.   The manufacturing method according to claim 1, wherein the piezoelectric film is for a piezoelectric touch panel.

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