JP7711047B2 - Piezoelectric material, piezoelectric film, and composition for piezoelectric material - Google Patents

Description

The present invention relates to piezoelectric materials, piezoelectric films, and compositions for piezoelectric materials.

Polyvinylidene fluoride (PVDF) is used as a piezoelectric material with excellent piezoelectric properties. This piezoelectric material is used in various piezoelectric elements, such as piezoelectric sensors, transducers, and infrared pyroelectric sensors.

For example, Patent Documents 1 and 2 describe piezoelectric materials containing polyvinylidene fluoride.

JP 2008-304558 A JP 2011-192665 A

When a material containing polyvinylidene fluoride is used as a piezoelectric body, it is usually subjected to a polarization process. For example, Patent Document 1 describes a method of polarizing a material containing polyvinylidene fluoride by stretching it to impart piezoelectric properties to the material, and Patent Document 2 describes a method of polarizing a material containing polyvinylidene fluoride by applying a relatively high voltage to the material to impart piezoelectric properties to the material.

However, depending on the application of the piezoelectric material, it may be required that the material be unstretched from the viewpoint of material properties other than the piezoelectric properties. Furthermore, when piezoelectric properties are imparted by applying a high voltage, the applied high voltage may affect material properties other than the piezoelectric properties, and therefore, depending on the application of the piezoelectric material, material properties other than the piezoelectric properties may not be satisfied.

Therefore, the object of the present invention is to provide a piezoelectric material that can be imparted with piezoelectric properties even without application of high voltage, stretching treatment, etc., a piezoelectric film containing the piezoelectric material, and a piezoelectric material composition for obtaining the piezoelectric material.

As a result of intensive research into solving the above problems, the inventors discovered that the above problems could be solved by a piezoelectric material containing polyvinylidene fluoride and a (meth)acrylic polymer containing structural units derived from a specific (meth)acrylic monomer, and thus completed the present invention. That is, the present invention includes the following aspects.

[1] Polyvinylidene fluoride, and
Formula (I):
[During the ceremony,
R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, in which at least one hydrogen atom of R ₁ may be substituted with a halogen atom;
_R2 represents a linear or branched alkyl group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, a phenyl group, or a phenylalkylene group including an alkylene group having 1 to 4 carbon atoms;
wherein at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenylalkylene group may be substituted with -O-, -N-, or -S-;
at least one hydrogen atom of the alkyl group, the alicyclic hydrocarbon group and the alkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms;
at least one hydrogen atom on the phenyl ring of the phenyl group and the phenylalkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group;
At least one hydrogen atom of _R2 may be substituted with a halogen atom;
However, at least one hydrogen atom of R ₁ and/or R ₂ is substituted with a halogen atom.
A piezoelectric material containing a (meth)acrylic polymer including a structural unit derived from a (meth)acrylic monomer represented by the following formula:
[2] The piezoelectric material according to [1], wherein the amount of polyvinylidene fluoride is 99 to 40 mass% based on the entire piezoelectric material, and the amount of (meth)acrylic polymer is 1 to 60 mass% based on the entire piezoelectric material.
[3] A piezoelectric film comprising the piezoelectric material described in [1] or [2] above.
[4] Polyvinylidene fluoride, and
Formula (I):
[During the ceremony,
R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, in which at least one hydrogen atom of R ₁ may be substituted with a halogen atom;
_R2 represents a linear or branched alkyl group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, a phenyl group, or a phenylalkylene group including an alkylene group having 1 to 4 carbon atoms;
wherein at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenylalkylene group may be substituted with -O-, -N-, or -S-;
at least one hydrogen atom of the alkyl group, the alicyclic hydrocarbon group and the alkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms;
at least one hydrogen atom on the phenyl ring of the phenyl group and the phenylalkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group;
At least one hydrogen atom of _R2 may be substituted with a halogen atom;
However, at least one hydrogen atom of R ₁ and/or R ₂ is substituted with a halogen atom.
and/or a (meth)acrylic polymer containing a structural unit derived from the (meth)acrylic monomer.

According to the present invention, it is possible to provide a piezoelectric material that can be imparted with piezoelectric properties even without application of high voltage, stretching treatment, etc., a piezoelectric film containing the piezoelectric material, and a piezoelectric material composition for obtaining the piezoelectric material.

The following describes in detail the embodiments of the present invention. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention. Note that in this specification, the range of numerical values indicated by "~" includes the upper and lower limits.

The piezoelectric material of the present invention contains polyvinylidene fluoride and a specific (meth)acrylic polymer containing halogen atoms. The inventors have found that a material containing polyvinylidene fluoride and a specific (meth)acrylic polymer exhibits piezoelectric properties even when it is not subjected to polarization treatment by stretching or application of high voltage, and/or addition of other compounds. Furthermore, they have found that the piezoelectric properties can be further improved when the material is stretched or applied with high voltage. The piezoelectric material of the present invention may be one to which conventional techniques for exhibiting and improving piezoelectric properties, such as stretching, polarization treatment at a relatively high voltage, and addition of compounds, are applied, as long as the material properties required for the application of the piezoelectric material are satisfied.

The detailed reason why the piezoelectric material of the present invention exhibits piezoelectric properties without polarization treatment by stretching or applying a high voltage, the addition of compounds, etc. is not clear, but it is speculated that this is due to interaction between halogen atoms contained in certain (meth)acrylic polymers and dipoles in the structural units of polyvinylidene fluoride.

<(Meth)acrylic polymer>
The (meth)acrylic polymer contained in the piezoelectric material of the present invention has the formula (I):
[During the ceremony,
R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, in which at least one hydrogen atom of R ₁ may be substituted with a halogen atom;
_R2 represents a linear or branched alkyl group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, a phenyl group, or a phenylalkylene group including an alkylene group having 1 to 4 carbon atoms;
wherein at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenylalkylene group may be substituted with -O-, -N-, or -S-;
at least one hydrogen atom of the alkyl group, the alicyclic hydrocarbon group and the alkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms;
at least one hydrogen atom on the phenyl ring of the phenyl group and the phenylalkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group;
At least one hydrogen atom of _R2 may be substituted with a halogen atom;
However, at least one hydrogen atom of R ₁ and/or R ₂ is substituted with a halogen atom.
In other words, the (meth)acrylic polymer contained in the piezoelectric material of the present invention is a polymer of monomers containing at least the (meth)acrylic monomer represented by the above formula (I). In this specification, (meth)acrylic represents acrylic and/or methacrylic.

The structural unit derived from the (meth)acrylic monomer represented by formula (I) is represented by the following formula (II):
(R ₁ and R ₂ in formula (II) are as defined for R ₁ and R ₂ in formula (I)).
The (meth)acrylic polymer contained in the piezoelectric material of the present invention contains at least a structural unit represented by the above formula (II). In this specification, the description of R ₁ and R ₂ in formula (I) also applies to R ₁ and R ₂ in formula (II).

In the above formula (I), at least one hydrogen atom in _R1 and/or _R2 is substituted with a halogen atom. Therefore, the (meth)acrylic polymer contained in the piezoelectric material of the present invention contains a halogen atom. From the viewpoint of easily improving the piezoelectric properties, the halogen atom is preferably at least one atom selected from the group consisting of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, more preferably a fluorine atom and/or a chlorine atom, and even more preferably a fluorine atom.

The amount of halogen atoms contained in the structural unit derived from the (meth)acrylic monomer represented by formula (I) is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more in one structural unit, from the viewpoint of easily improving the piezoelectric properties. Examples of a method for identifying the amount of halogen atoms include a method for analyzing a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer, and a method for analyzing a (meth)acrylic monomer that is a raw material monomer. When analyzing a (meth)acrylic polymer, analysis can be performed by pyrolysis gas chromatography. When analyzing a (meth)acrylic monomer, analysis can be performed by a nuclear magnetic resonance (NMR) spectrometer, but is not limited to these methods.

The ratio (molar ratio) of halogen atoms to all atoms constituting the (meth)acrylic polymer is preferably 5 mol% or more, more preferably 10 mol% or more, from the viewpoint of facilitating improvement of piezoelectric properties. The upper limit of the ratio is not particularly limited, and may be 70 mol% or less, or 60 mol% or less. The amount of halogen atoms can be determined by analyzing the (meth)acrylic polymer by NMR, high resolution mass spectrometry (HRMS), etc., but is not limited to these methods. For example, when the (meth)acrylic polymer is analyzed by NMR, it can be determined based on (total area of halogen atoms / area of internal standard substance) x 100.

From the viewpoint of easily increasing the dipole, it is preferable that the halogen atom contained in the (meth)acrylic monomer represented by formula (I) is contained in the (meth)acrylic monomer preferably as a monohalogen group (preferably a monofluoro group) and/or an alkyl group having 1 to 10 carbon atoms and 1 to 10 halogen atoms (preferably fluorine atoms), more preferably as a monohalogen group (preferably a monofluoro group) and/or an alkyl group having 2 to 8 carbon atoms and 1 to 10 halogen atoms (preferably fluorine atoms), and even more preferably as an alkyl group having 3 to 6 carbon atoms and 1 to 10 halogen atoms (preferably fluorine atoms). Specific examples of such groups include monofluoro groups (particularly monofluoro groups as _R1 ), trifluoromethyl groups, difluoromethyl groups, monofluoromethyl groups, trifluoroethyl groups, difluoroethyl groups, monofluoroethyl groups, octafluoropropyl groups, heptafluoropropyl groups, hexafluoropropyl groups, pentafluoropropyl groups, tetrafluoropropyl groups, trifluoropropyl groups, difluoropropyl groups, monofluoropropyl groups, octafluorobutyl groups, heptafluorobutyl groups, hexafluorobutyl groups, pentafluorobutyl groups, tetrafluorobutyl groups, trifluorobutyl groups, difluorobutyl groups, monofluorobutyl groups, octafluoropentyl groups, heptafluoropentyl groups, hexafluoropentyl groups, pentafluoropentyl groups, tetrafluoropentyl groups, trifluoropentyl groups, difluoropentyl groups, monofluoropentyl groups, trichloromethyl groups, dichloromethyl groups, and monochloromethyl groups.
The halogen atom contained in the (meth)acrylic monomer represented by formula (I) is preferably contained in the (meth)acrylic monomer as a group selected from the group consisting of trifluoropropyl group, difluoropropyl group, monofluoropropyl group, trichloropropyl group, dichloropropyl group and monochloropropyl group, from the viewpoint of easily increasing dipole.In other words, the (meth)acrylic polymer of the present invention preferably comprises the structural unit derived from the (meth)acrylic monomer represented by formula (I), which comprises the group selected from the group consisting of monofluoro group, trifluoropropyl group, difluoropropyl group, monofluoropropyl group, trichloropropyl group, dichloropropyl group and monochloropropyl group.

R ₁ in the above formula (I) represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and at least one hydrogen atom of R ₁ may be substituted with a halogen atom. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, and a propyl group, and at least one hydrogen atom of these groups may be substituted with a halogen atom. The halogen atom is preferably at least one atom selected from the group consisting of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, more preferably a fluorine atom and/or a chlorine atom, and even more preferably a fluorine atom.

Specific examples of R ₁ include, but are not limited to, a hydrogen atom, a fluoro group, a trifluoromethyl group, a difluoromethyl group, a monofluoromethyl group, a trifluoroethyl group, a difluoroethyl group, a monofluoroethyl group, and a monochloromethyl group.

R ₂ in the above formula (I) represents (1) a linear or branched alkyl group having 1 to 10 carbon atoms, (2) an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, (3) a phenyl group, or (4) a phenylalkylene group including an alkylene group having 1 to 4 carbon atoms, wherein at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenylalkylene group may be substituted with -O-, -N-, or -S-, at least one hydrogen atom of the alkyl group, the alicyclic hydrocarbon group, and the alkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, and at least one hydrogen atom on the phenyl ring in the phenyl group and the phenylalkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group. In addition, at least one hydrogen atom of _R2 may be substituted with a halogen atom.

Here, "at least one hydrogen atom of R ₂ may be substituted with a halogen atom" means, for example, that when R ₂ represents the above (1) linear or branched alkyl group having 1 to 10 carbon atoms, at least one hydrogen atom contained in the linear or branched alkyl group may be substituted with a halogen atom, and when at least one hydrogen atom of the alkyl group is substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, at least one hydrogen atom in the substituted alkyl group having 1 to 6 carbon atoms and/or an alkoxy group having 1 to 6 carbon atoms may be substituted with a halogen atom. The same applies when R ₂ is the above (2) to (4). Examples of the halogen atom include the atoms described above for R ₁ , and the preferred descriptions regarding the halogen atom of R ₁ also apply to R ₂ .

The number of carbon atoms in the alkyl group having 1 to 6 carbon atoms and the alkyl group in the alkoxy group having 1 to 6 carbon atoms is preferably 1 to 4, more preferably 1 to 2. The alkyl chain portion in the alkyl group and alkoxy group having 1 to 6 carbon atoms may be either linear or branched.

When R ₂ in the above formula (I) represents (1) a linear or branched alkyl group having 1 to 10 carbon atoms, the number of carbon atoms of the alkyl group is preferably 1 to 6, more preferably 1 to 4, from the viewpoint of the productivity of the (meth)acrylic monomer represented by the above formula (I). In this specification, the alkyl group may be either linear or branched. Examples of the alkyl group include, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1,1-dimethylpropyl group, an isoamyl group, an n-hexyl group, an isohexyl group, and an n-octyl group. At least one carbon atom of the alkyl group having 1 to 10 carbon atoms may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alkyl group having 1 to 10 carbon atoms may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms. In view of easiness in enhancing the piezoelectric properties, R ₂ in the above formula (I) preferably represents a linear or branched alkyl group having 1 to 10 carbon atoms and having 1 to 10 halogen atoms, more preferably a linear or branched alkyl group having 2 to 10 carbon atoms and having 2 to 10 halogen atoms, further preferably a linear or branched alkyl group having 3 to 8 carbon atoms and having 3 to 8 halogen atoms, and even more preferably a linear or branched alkyl group having 3 to 6 carbon atoms and having 3 to 8 halogen atoms.

Examples of alkyl groups having 1 to 10 carbon atoms substituted with a hydroxyl group include, for example, a hydroxymethyl group, a hydroxyethyl group, a hydroxy n-propyl group, a hydroxyisopropyl group, a hydroxy n-butyl group, a hydroxyisobutyl group, and a hydroxy tert-butyl group.

An alkyl group having 1 to 10 carbon atoms substituted with an alkyl group having 1 to 6 carbon atoms is a group in which an alkyl group having 1 to 10 carbon atoms forms the main chain, and at least one hydrogen atom of the alkyl group is substituted with an alkyl group having 1 to 6 carbon atoms. As long as the alkyl group portion that forms the main chain has 1 to 10 carbon atoms, the total number of carbon atoms in the alkyl group may exceed 10. An example of such an alkyl group is 2-ethylhexyl. In addition, when the total number of carbon atoms in the alkyl group does not exceed 10, the group is also included in the definition of a branched alkyl group having 1 to 10 carbon atoms.

The alkyl group having 1 to 10 carbon atoms substituted with an alkoxy group having 1 to 6 carbon atoms is preferably an alkyl group having 1 to 6 carbon atoms substituted with an alkoxy group having 1 to 6 carbon atoms. Examples of such groups include a methoxyethyl group, an ethoxyethyl group, and a methoxybutyl group.

Examples of alkyl groups having 1 to 10 carbon atoms substituted with a hydroxyl group and an alkoxy group having 1 to 6 carbon atoms include groups having a hydroxyalkoxy group having 1 to 6 carbon atoms and an alkyl group having 1 to 6 carbon atoms, specifically, a hydroxymethoxyethyl group, a hydroxyethoxyethyl group, a hydroxypropyloxypropyl group, etc.

Among the above alkyl groups, from the viewpoint of availability, preferred are alkyl groups having 1 to 6 carbon atoms which may be substituted with a hydroxyl group and/or an alkoxy group having 1 to 2 carbon atoms, preferred are alkyl groups having 1 to 4 carbon atoms which may be substituted with a hydroxyl group and/or an alkoxy group having 1 to 2 carbon atoms, and even more preferred are alkyl groups having 1 to 2 carbon atoms which may be substituted with a hydroxyl group and/or an alkoxy group having 1 to 2 carbon atoms.

Among the above alkyl groups, from the viewpoint of the productivity of the (meth)acrylic monomer represented by the above formula (I), it is preferable that R ₂ in formula (I) is (1) a linear or branched alkyl group having 1 to 10 carbon atoms, at least one carbon atom of the alkyl group being substituted with -O-. Examples of such R ₂ include those represented by formula (III):
[During the ceremony,
m and n each independently represent the number 2 or 3;
X represents a hydrogen atom or a methyl group;
At least one hydrogen atom in formula (III) may be substituted with a hydroxyl group, an alkyl group having 1 or 2 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms.
At least one hydrogen atom of the group may be substituted with a halogen atom. Preferred examples of such groups include a trifluoromethoxyethyl group and a trifluoromethoxypropyl group.

The linear or branched alkyl group having 1 to 10 carbon atoms, which may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms as described above, may be a group in which at least one hydrogen atom is substituted with a halogen atom.

When _R2 in the above formula (I) represents (2) an alicyclic hydrocarbon group having 3 to 12 carbon atoms containing an alicyclic structure having 3 to 6 carbon atoms, an example of the alicyclic structure having 3 to 6 carbon atoms is cyclohexane. At least one carbon atom of the alicyclic hydrocarbon group having 3 to 12 carbon atoms may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alicyclic hydrocarbon group having 3 to 12 carbon atoms may be substituted with a hydroxyl group, an alkyl group having 1 or 2 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms.

Examples of alicyclic hydrocarbon groups having 3 to 12 carbon atoms and containing an alicyclic structure having 3 to 6 carbon atoms, in which at least one carbon atom is replaced with an oxygen atom (-O-), include an epoxy group in which one carbon atom of an alicyclic hydrocarbon group having 3 carbon atoms is replaced with an oxygen atom, an oxetanyl ring in which one carbon atom of an alicyclic hydrocarbon group having 4 carbon atoms is replaced with an oxygen atom, a dioxolane ring in which two carbon atoms of an alicyclic hydrocarbon group having 5 carbon atoms are replaced with oxygen atoms, and a dioxane ring in which two carbon atoms of an alicyclic hydrocarbon group having 6 carbon atoms are replaced with oxygen atoms. The hydrogen atoms on these rings may be replaced with an alkyl group having 1 or 2 carbon atoms. Specific examples of such groups include 3-ethyl-3-oxetanyl methyl acrylate, 2-methyl-2-ethyl-1,3-dioxolan-4-yl) methyl acrylate, and cyclic trimethylolpropane formal acrylate.

The above-mentioned alicyclic hydrocarbon group having 3 to 12 carbon atoms and including an alicyclic structure having 3 to 6 carbon atoms, which may be substituted with a hydroxyl group, an alkyl group having 1 or 2 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, may be a group in which at least one hydrogen atom is substituted with a halogen atom.

R ₂ in the above formula (I) may represent (3) a phenyl group. In addition, at least one hydrogen atom on the phenyl ring of the phenyl group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms. A group in which at least one hydrogen atom on the phenyl ring, particularly a hydrogen atom at the para position, is substituted with an alkyl group having 1 to 4 carbon atoms (preferably 1 or 2), and the hydrogen atom of the alkyl group having 1 to 4 carbon atoms is substituted with a halogen atom, is preferable from the viewpoint of easily improving other properties of the piezoelectric material, such as elongation and flexibility.

The above-mentioned phenyl group, in which at least one hydrogen atom on the phenyl ring may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, may be a group in which at least one hydrogen atom is substituted with a halogen atom. When _R2 is such a group, other properties of the piezoelectric material, such as the elongation and flexibility of the piezoelectric material, are likely to be improved.

When R ₂ in the above formula (I) represents (4) a phenylalkylene group containing an alkylene group having 1 to 4 carbon atoms, at least one carbon atom of the alkylene group may be substituted with -O-, -N- or -S-, and at least one hydrogen atom on the phenyl ring may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group.

Examples of the phenylalkylene group in which at least one carbon atom of the alkylene group is substituted with -O- include a phenylalkylene group represented by the formula (IV):
[p and q are each independently 2 or 3]
and groups in which at least one hydrogen atom in the alkylene portion and phenyl ring portion of the group is substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group. At least one hydrogen atom in the above groups may be substituted with a halogen atom. When _R2 is the above group, other properties of the piezoelectric material, such as elongation and flexibility, are easily improved.

The phenyl alkylene group described above may have at least one hydrogen atom substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, and/or at least one hydrogen atom substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group, and may have at least one hydrogen atom substituted with a halogen atom. When _R2 is such a group, other properties of the piezoelectric material, such as elongation and flexibility, are easily improved.

A preferred example of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer represented by the above formula (I), in which _{R 1} represents a halogen atom or an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a halogen atom, and R ₂ represents a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 4, more preferably 1 to 2), in which at least one carbon atom of the alkyl group in R ₂ may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alkyl group in R 2 may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms.

Another preferred example of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer represented by the above formula (I), in which _{R 1} represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ represents a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 4, more preferably 1 to 2), and at least one carbon atom of the alkyl group in R ₂ may be substituted with -O-, -N-, or -S-, at least one hydrogen atom of the alkyl group in R ₂ may be substituted with a hydroxyl group, an alkyl group having 1 or 2 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, and at least one hydrogen atom of R 2 (preferably two or more, more preferably three or more) is substituted with a halogen. More specific examples of the (meth)acrylic polymer include compounds in which R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ represents a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 4, more preferably 1 to 3), at least one carbon atom of the alkyl group in R ₂ may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alkyl group in R ₂ is substituted with an alkyl group having 1 or 2 carbon atoms in which at least one hydrogen atom is substituted with a halogen atom. Examples of such compounds include 3,3,3-trifluoropropyl (meth)acrylate, 3,3,3-trichloropropyl (meth)acrylate, 4,4,4-trifluorobutyl (meth)acrylate, 4,4,4-trichlorobutyl (meth)acrylate, 2,2-difluoroethyl (meth)acrylate, and 2,2-dichloroethyl (meth)acrylate.

Another preferred example of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer represented by the above formula (I), in which _{R 1} represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ represents an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, where at least one carbon atom of the alicyclic hydrocarbon group in R ₂ may be substituted with -O-, -N- or -S-, at least one hydrogen atom of the alicyclic hydrocarbon group in R ₂ may be substituted with a hydroxyl group, an alkyl group having 1 or 2 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms, and at least one (preferably two or more, more preferably three or more) hydrogen atom of R 2 is substituted with a halogen. When the piezoelectric material contains the (meth)acrylic polymer, other properties of the piezoelectric material such as elongation and flexibility are easily improved. More specific examples of the (meth)acrylic polymer include compounds in which R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ represents an alicyclic hydrocarbon group having 3 to 12 carbon atoms containing an alicyclic structure having 3 to 6 carbon atoms, at least one carbon atom of the alicyclic hydrocarbon group in R ₂ may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alicyclic hydrocarbon group in R ₂ is substituted with an alkyl group having 1 or 2 carbon atoms in which at least one hydrogen atom is substituted with a halogen atom. Examples of such compounds include 4-(trifluoromethyl)cyclohexyl (meth)acrylate and 4-(trichloromethyl)cyclohexyl (meth)acrylate.

Specific examples of (meth)acrylic polymers contained in the piezoelectric material of the present invention include, but are not limited to, 3,3,3-trifluoropropyl (meth)acrylate, 3,3,3-trichloropropyl (meth)acrylate, 4,4,4-trifluorobutyl (meth)acrylate, 4,4,4-trichlorobutyl (meth)acrylate, 2,2-difluoroethyl (meth)acrylate, 2,2-dichloroethyl (meth)acrylate, 4-(trifluoromethyl)cyclohexyl (meth)acrylate, and 4-(trichloromethyl)cyclohexyl (meth)acrylate.

The (meth)acrylic polymer contained in the piezoelectric material of the present invention may have only one structural unit derived from the (meth)acrylic monomer represented by the above formula (I), or may have structural units derived from two or more (meth)acrylic monomers represented by the above formula (I). In addition, the (meth)acrylic polymer contained in the piezoelectric material of the present invention may contain structural units derived from at least one other monomer, as long as the properties of the piezoelectric material of the present invention are not impaired. In other words, the (meth)acrylic polymer contained in the piezoelectric material of the present invention may be a homopolymer of the (meth)acrylic monomer represented by the above formula (I), a copolymer of two or more (meth)acrylic monomers represented by the above formula (I), or a copolymer of at least one (meth)acrylic monomer represented by the above formula (I) and at least one other monomer.

Examples of other monomers that can be copolymerized with the (meth)acrylic monomer represented by formula (I) above include carboxyl group-containing monomers, carboxylic acid alkyl ester monomers other than the (meth)acrylic monomers that give the structural unit represented by formula (I), amide group-containing monomers, aryl group-containing monomers, styrene-based monomers, nitrogen atom-containing monomers, fatty acid vinyl ester monomers, and betaine monomers.

Examples of carboxyl group-containing monomers include (meth)acrylic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, and crotonic acid.

Examples of carboxylic acid alkyl ester monomers other than (meth)acrylic monomers that provide the structural unit represented by formula (I) include alkyl acrylates having an alkyl group with 11 to 20 carbon atoms, such as dodecyl (meth)acrylate and stearyl (meth)acrylate, and alkyl itaconates having an alkyl group with 1 to 4 carbon atoms, such as methyl itaconate and ethyl itaconate.

Examples of amide group-containing monomers include alkyl(meth)acrylamides in which the alkyl group has 1 to 8 carbon atoms, such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-tert-butyl(meth)acrylamide, N-octyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide.

Examples of aryl group-containing monomers include aryl (meth)acrylates in which the aryl group has 6 to 12 carbon atoms, such as benzyl (meth)acrylate.

Examples of styrene-based monomers include styrene and α-methylstyrene.

Examples of nitrogen atom-containing monomers include N-vinylpyrrolidone and N-vinylcaprolactam.

Examples of fatty acid vinyl ester monomers include vinyl acetate and vinyl propionate.

Examples of betaine monomers include N-acryloyloxymethyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-methacryloyloxymethyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-methacryloyloxymethyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-methacryloyloxymethyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-methacryloyloxymethyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium butyl ...ethyl-α-sulfobetaine, N-acryloyloxymethyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-acryloyloxymethyl-N,N- N-acryloyloxyethyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-methacryloyloxyethyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-acryloyloxyethyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-methacryloyloxyethyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-acryloyloxyethyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-methacryloyloxyethyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-acryloyloxyethyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-methacryloyloxyethyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-acryloyloxypropyl-N,N-dimethylammonium methyl N-methacryloyloxypropyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-acryloyloxypropyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-methacryloyloxypropyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-acryloyloxypropyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-methacryloyloxypropyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-acryloyloxypropyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-methacryloyloxypropyl-N,N-dimethylammonium butyl-α-sulfobetaine, N-acryloyloxybutyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-methacryloyloxypropyl-N,N-dimethylammonium butyl-α-sulfobetaine Examples of sulfobetaine monomers include N-(meth)acryloyloxyalkyl-N,N-dimethylammonium alkyl-α-sulfobetaine, such as N-acryloyloxybutyl-N,N-dimethylammonium methyl-α-sulfobetaine, N-acryloyloxybutyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-methacryloyloxybutyl-N,N-dimethylammonium ethyl-α-sulfobetaine, N-acryloyloxybutyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-methacryloyloxybutyl-N,N-dimethylammonium propyl-α-sulfobetaine, N-acryloyloxybutyl-N,N-dimethylammonium butyl-α-sulfobetaine, and N-methacryloyloxybutyl-N,N-dimethylammonium butyl-α-sulfobetaine.

The content of the (meth)acrylic monomer represented by formula (I) in the monomer components when producing the (meth)acrylic polymer is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, particularly preferably 93% by mass or more, and most preferably 95% by mass or more, based on the total amount of the monomer components when producing the (meth)acrylic polymer, from the viewpoint of easily improving the piezoelectric properties. The upper limit of the content is not particularly limited, and may be 100% by mass or less, or may be 99% by mass or less, 98% by mass or less, or 97% by mass or less. When the monomer components when producing the (meth)acrylic polymer contain other monomers that can be copolymerized with the (meth)acrylic monomer represented by formula (I), the content of the other monomer is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, particularly preferably 10% by mass or less, particularly more preferably 7% by mass or less, and most preferably 5% by mass or less, based on the total amount of the monomer components when producing the (meth)acrylic polymer, from the viewpoint of easily improving the piezoelectric properties of the piezoelectric material. When the other monomer is contained, the lower limit of the content is not particularly limited and may be 1 mass % or more, 2 mass % or more, or 3 mass % or more based on the mass of the total monomer components.

The monomer components used in producing the (meth)acrylic polymer may contain an appropriate amount of a crosslinkable monomer within a range that does not impair the object of the present invention. As described above, the (meth)acrylic polymer contained in the piezoelectric material of the present invention is a polymer containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I). The crosslinkable monomer is (1) contained as a structural unit in the main chain of a polymer containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I) to bond (crosslink) polymers containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I) together, and/or (2) not contained in the main chain of a polymer containing a structural unit derived from the acrylic monomer represented by the above formula (I) but bonded to a side chain of a polymer containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I) to bond (crosslink) polymers containing a structural unit derived from the acrylic monomer represented by the above formula (I) together. In either embodiment (1) or (2), the (meth)acrylic polymer contains a structural unit derived from a crosslinkable monomer, whereby a plurality of polymers containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I) are bonded to form a single polymer having a higher molecular weight.

Examples of crosslinkable monomers include (meth)acrylamide compounds having two or more, preferably two, (meth)acryloyl groups, such as alkylene bis(meth)acrylamides having an alkylene group with 1 to 4 carbon atoms, such as methylene bisacrylamide and methylene bismethacrylamide; ethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 2-n-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, ) acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and other (meth)acrylate compounds having two or more, preferably two or three, (meth)acryloyl groups; amine compounds having two or more, preferably two or three, carbon-carbon double bonds, such as diallylamine and triallylamine; and polyfunctional monomers such as divinylbenzene and diallylbenzene, and other aromatic compounds having two or more, preferably two or three, carbon-carbon double bonds, but the present invention is not limited to these examples. These crosslinkable monomers may be used alone or in combination of two or more.

The weight average molecular weight of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is preferably 10,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, and particularly preferably 150,000 or more. If the weight average molecular weight of the (meth)acrylic polymer is equal to or more than the above lower limit, the strength and durability of the piezoelectric material are easily increased. In addition, from the viewpoint of ease of production of the (meth)acrylic polymer, the weight average molecular weight of the (meth)acrylic polymer is preferably 2,000,000 or less, more preferably 1,500,000 or less, even more preferably 1,000,000 or less, and particularly preferably 750,000 or less. The weight average molecular weight of the (meth)acrylic polymer can be measured using gel permeation chromatography. Details of the measurement conditions, etc. are as described in the examples.

(Method of producing (meth)acrylic polymer)
The (meth)acrylic polymer contained in the piezoelectric material of the present invention can be obtained, for example, by polymerizing a monomer component.

Methods for polymerizing the monomer components include, for example, bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization, but the present invention is not limited to these examples. Among these polymerization methods, bulk polymerization and solution polymerization are preferred from the viewpoint of manufacturability of (meth)acrylic polymers.

When the monomer components are polymerized by the solution polymerization method, a solvent is used. A non-aqueous organic solvent is preferable as the solvent. Examples of non-aqueous organic solvents include hydrocarbon organic solvents such as hexane, heptane, octane, isooctane, decane, and liquid paraffin; ether organic solvents such as dimethyl ether, diethyl ether, and tetrahydrofuran; ketone organic solvents such as acetone and methyl ethyl ketone; ester organic solvents such as methyl acetate, ethyl acetate, butyl acetate, and γ-butyrolactone; chloride organic solvents such as methylene chloride, chloroform, and carbon tetrachloride; dimethylformamide, diethylformamide, dimethylsulfoxide, and dioxane, but the present invention is not limited to these examples. These organic solvents may be used alone or in combination of two or more kinds. The amount of the solvent varies depending on the type of the solvent and cannot be generally limited, but it is usually preferable that the amount is about 100 to 1000 parts by mass per 100 parts by mass of the monomer components.

A polymerization initiator can be used when polymerizing the monomer components. Examples of the polymerization initiator include photopolymerization initiators and thermal polymerization initiators. Among these polymerization initiators, photopolymerization initiators are preferred from the viewpoint of not leaving a thermal history in the (meth)acrylic elastomer. Examples of the polymerization initiator include 2,2'-azobisisobutyronitrile, methyl azoisobutyrate, azobisdimethylvaleronitrile, benzoyl peroxide, potassium persulfate, ammonium persulfate, benzophenone derivatives, phosphine oxide derivatives, benzoketone derivatives, phenylthioether derivatives, azide derivatives, diazo derivatives, and disulfide derivatives, and two or more of these may be used in combination as desired.

Examples of photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-biimidazole, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(p-methoxyphenylvinyl)-1,3,5-triazine, diphenyliodonium tetrafluoroborate, diphenyliodonium hexafluorophosphate, 4,4'-ditert-butyldiphenylphosphine oxide ... phenyliodonium tetrafluoroborate, 4-diethylaminophenylbenzenediazonium hexafluorophosphate, benzoin, 2-hydroxy-2-methyl-1-phenylpropan-2-one, benzophenone, thioxanthone, 2,4,6-trimethylbenzoyldiphenylacylphosphine oxide, triphenylbutylborate tetraethylammonium, diphenyl-4-phenylthiophenylsulfonium hexafluorophosphate, 2,2-dimethoxy-1,2-diphenylethan-1-one, phenylglucuronide Photoradical polymerization initiators such as 2,4,6-trimethylbenzoyl-3-(1H-pyrrol-1-yl)phenyltitanium, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 1,2-octanedione, 1-[4-(phenylthio)-2-(o-benzoyloxime)], and bis(η5-2,4-cyclopentadiene-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyltitanium], 2,4,6-tris(trichloromethyl)-1, Examples of photo-cationic ring-opening polymerization initiators include 3,5-triazine, 2,4-bis(trichloromethyl)-6-(p-methoxyphenylvinyl)-1,3,5-triazine, diphenyliodonium tetrafluoroborate, 4,4'-ditert-butyldiphenyliodonium tetrafluoroborate, 4-diethylaminophenylbenzenediazonium hexafluorophosphate, diphenyl-4-phenylthiophenylsulfonium hexafluorophosphate, etc., but the present invention is not limited to these examples. These photo-polymerization initiators may be used alone or in combination of two or more.

Examples of thermal polymerization initiators include azo-based polymerization initiators such as dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobisisobutyronitrile (AIBN), dimethyl 2,2'-azobisisobutyrate, and azobisdimethylvaleronitrile, and peroxide-based polymerization initiators such as benzoyl peroxide, potassium persulfate, and ammonium persulfate, but the present invention is not limited to these examples. These polymerization initiators may be used alone or in combination of two or more.

The amount of polymerization initiator cannot be determined in general because it varies depending on the type of polymerization initiator, but it is usually preferable to use about 0.01 to 20 parts by mass per 100 parts by mass of monomer components.

When polymerizing the monomer components, a chain transfer agent can be used to adjust the molecular weight of the resulting (meth)acrylic polymer. Examples of chain transfer agents include compounds having a thiol group, such as lauryl mercaptan, dodecyl mercaptan, and thioglycerol; and inorganic salts, such as sodium hypophosphite and sodium hydrogen sulfite, but the present invention is not limited to these examples. These chain transfer agents may be used alone or in combination of two or more. The amount of the chain transfer agent varies depending on the type of the chain transfer agent, and cannot be determined in general, but it is usually preferable that the amount is about 0.01 to 10 parts by mass per 100 parts by mass of the monomer components.

The atmosphere in which the monomer components are polymerized is not particularly limited, and may be air or an inert gas atmosphere such as nitrogen gas or argon gas.

There are no particular limitations on the temperature at which the monomer components are polymerized, and a temperature of about 5 to 100°C is usually preferred. The time required to polymerize the monomer components varies depending on the polymerization conditions and cannot be determined in general, so is arbitrary, but is usually about 1 to 20 hours.

The polymerization reaction can be terminated at any time when the amount of remaining monomer components is 20% by mass or less. The amount of remaining monomer components can be measured, for example, by gel permeation chromatography.

By polymerizing the monomer components in the manner described above, the (meth)acrylic polymer contained in the piezoelectric material of the present invention can be obtained.

(Polyvinylidene fluoride)
The polyvinylidene fluoride contained in the piezoelectric material of the present invention is a polymer obtained by polymerizing vinylidene fluoride as a main monomer. The main monomer is a monomer that occupies more than 50 mol% of the monomer mixture. Specifically, the amount of structural units derived from vinylidene fluoride in polyvinylidene fluoride is preferably more than 50 mol%, more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, particularly preferably 90 mol% or more, particularly preferably 91 mol% or more, particularly more preferably 93 mol% or more, even more preferably 95 mol% or more, especially more preferably 97 mol% or more, extremely preferably 99 mol% or more, and most preferably 100 mol% with respect to the amount of all structural units, from the viewpoint of easily imparting piezoelectric properties to the piezoelectric material. The polyvinylidene fluoride is preferably selected from the group consisting of homopolymers of vinylidene fluoride and copolymers having structural units derived from vinylidene fluoride of 91 mol% or more and structural units derived from other monomers of 9 mol% or less based on the amount of all structural units of polyvinylidene fluoride. The upper limit of the amount of structural units derived from vinylidene fluoride is 100 mol% or less. In other words, the amount of structural units derived from vinylidene fluoride being 100 mol% of the total structural units means that the polyvinylidene fluoride contained in the piezoelectric material of the present invention is a homopolymer of vinylidene fluoride. Polyvinylidene fluoride may also contain unavoidable impurities in some cases.

As described above, the polyvinylidene fluoride contained in the piezoelectric material of the present invention may be a homopolymer of vinylidene fluoride, or a copolymer having structural units derived from vinylidene fluoride that are more than 50 mol% based on the amount of all structural units and structural units derived from other monomers that are less than 50 mol%, and more preferably is selected from the group consisting of a homopolymer of vinylidene fluoride and a copolymer having structural units derived from vinylidene fluoride that are 91 mol% or more based on the amount of all structural units of polyvinylidene fluoride and structural units derived from other monomers that are 9 mol% or less, and is even more preferably a homopolymer of vinylidene fluoride. When polyvinylidene fluoride is the above copolymer, examples of the other monomers include tetrafluoroethylene, hexafluoropropylene, hexafluoropropylene oxide, perfluoropropyl vinyl ether, and chlorotrifluoroethylene. The other monomers can be used alone or in combination of two or more. Polyvinylidene fluoride may be a homopolymer of vinylidene fluoride and/or a copolymer of vinylidene fluoride and other monomers (e.g., at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, hexafluoropropylene oxide, perfluoropropyl vinyl ether, and chlorotrifluoroethylene).

The weight average molecular weight of the polyvinylidene fluoride contained in the piezoelectric material of the present invention is not particularly limited, but from the viewpoint of easily improving the piezoelectric properties, it is preferably 100,000 or more, more preferably 300,000 or more, even more preferably 500,000 or more, even more preferably 550,000 or more, and particularly preferably 600,000 or more. The upper limit of the weight average molecular weight is not particularly limited, and is, for example, about 2,000,000 or less. The weight average molecular weight can be measured by a known method.

The polyvinylidene fluoride contained in the piezoelectric material of the present invention may be commercially available. Examples of commercially available polyvinylidene fluoride include "Poly(vinylidene fluoride)" manufactured by Aldrich Corporation and "KF Polymer W#1100" manufactured by Kureha Corporation.

(Piezoelectric material composition and piezoelectric material)
The amount of polyvinylidene fluoride contained in the piezoelectric material of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 65% by mass or more, even more preferably 70% by mass or more, particularly preferably 75% by mass or more, and may be 80% by mass or more, or 85% by mass or more, based on the entire piezoelectric material, from the viewpoint of easily improving the piezoelectric properties. Also, the amount of polyvinylidene fluoride contained in the piezoelectric material of the present invention is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 95% by mass or less, particularly preferably 90% by mass or less, or may be 85% by mass or less, or may be 80% by mass or less, from the viewpoint of easily exerting other functions (e.g., improving the elongation and/or flexibility of the piezoelectric material) obtained by including the specific (meth)acrylic polymer.

The amount of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more, and may be 15% by mass or more, or 20% by mass or more, based on the entire piezoelectric material, from the viewpoint of easily improving the piezoelectric properties and easily exerting other functions obtained by including the above-mentioned specific (meth)acrylic polymer. Also, the amount of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, particularly preferably 25% by mass or less, and may be 20% by mass or less, or 15% by mass or less, based on the entire piezoelectric material, from the viewpoint of easily improving the piezoelectric properties.

The piezoelectric material of the present invention also includes embodiments containing materials other than polyvinylidene fluoride and the specific (meth)acrylic polymer (hereinafter referred to as other materials). Examples of other materials include, but are not limited to, copolymers and elastomers other than polyvinylidene fluoride and the specific (meth)acrylic polymer, additives such as antioxidants and ultraviolet absorbers, thermally conductive fillers, and conductive fillers. The piezoelectric material of the present invention may contain these other materials alone or in combination of two or more.

The amount of polyvinylidene fluoride contained in the piezoelectric material of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 65% by mass or more, even more preferably 70% by mass or more, particularly preferably 75% by mass or more, and may be 80% by mass or more, or 85% by mass or more, based on the total weight of polyvinylidene fluoride and (meth)acrylic polymer contained in the piezoelectric material of the present invention. In addition, the amount of polyvinylidene fluoride contained in the piezoelectric material of the present invention is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 95% by mass or less, particularly preferably 90% by mass or less, and may be 85% by mass or less, or 80% by mass or less, based on the total weight of polyvinylidene fluoride and (meth)acrylic polymer contained in the piezoelectric material of the present invention. When the amount of polyvinylidene fluoride is equal to or greater than the above lower limit, the piezoelectric properties of the piezoelectric material are easily improved. When the amount of polyvinylidene fluoride is equal to or less than the above upper limit, it is easy to exhibit other functions obtained by including the above-mentioned specific (meth)acrylic polymer.

The structure and amount of polyvinylidene fluoride in the piezoelectric material, and the structure and amount of the specific (meth)acrylic polymer can be analyzed using, for example, an infrared spectrometer (IR), a nuclear magnetic resonance spectrometer (NMR), etc., but are not limited thereto. These amounts may be calculated from the raw material charge ratio. Therefore, after determining the structure of polyvinylidene fluoride and the structure of the specific (meth)acrylic polymer contained in the piezoelectric material, they may be separated from the piezoelectric material by a known method, or a specific (meth)acrylic polymer with the same structure may be prepared and analyzed by the above-mentioned analysis method, etc., to analyze the structure and amount of polyvinylidene fluoride and the (meth)acrylic polymer that constitute the piezoelectric material. In the same manner, the amount of halogen atoms contained in the (meth)acrylic polymer and the amount of halogen atoms contained in the structural unit derived from the (meth)acrylic monomer can also be specified.

The method for producing the piezoelectric material of the present invention is not particularly limited, but may be, for example, a step of applying and drying a solution containing polyvinylidene fluoride, the specific (meth)acrylic polymer, and a solvent, followed by a step of crystallizing polyvinylidene fluoride by heat treatment, and a step of applying a voltage to polarize at least a portion of polyvinylidene fluoride to generate piezoelectric properties. The drying and heat treatment may be performed simultaneously. Another example is a method for producing a piezoelectric material including a step of mixing polyvinylidene fluoride, a monomer constituting the specific (meth)acrylic polymer, and, if necessary, a solvent, a step of polymerizing the monomer to obtain the specific (meth)acrylic polymer, a step of crystallizing polyvinylidene fluoride by heat treatment, and a step of applying a voltage to polarize at least a portion of polyvinylidene fluoride to generate piezoelectric properties. In the above-mentioned production method, a stretching process may be performed in order to further enhance the piezoelectric properties. Furthermore, since the piezoelectric material of the present invention is likely to generate piezoelectric properties without being subjected to a stretching treatment and/or application of a high voltage, it can be suitably used as a piezoelectric material to be used at high temperatures or as a piezoelectric material that requires mechanical properties.

A composition containing polyvinylidene fluoride and the specific (meth)acrylic polymer for producing a piezoelectric material (and optionally a solution further containing a solvent) is also referred to as a "piezoelectric material composition" below. The piezoelectric material composition also includes a composition containing polyvinylidene fluoride and a monomer constituting the specific (meth)acrylic polymer. The present invention also provides these piezoelectric material compositions. In this specification, the descriptions regarding the (meth)acrylic polymer and polyvinylidene fluoride contained in the piezoelectric material of the present invention also apply to the specific (meth)acrylic polymer and polyvinylidene fluoride contained in the piezoelectric material composition of the present invention.

The solvent that may be optionally included in the piezoelectric material composition is not particularly limited as long as it is a solvent that can dissolve polyvinylidene fluoride and the specific (meth)acrylic polymer, but examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, diethyl carbonate, etc.

The piezoelectric material composition of the present invention is not particularly limited, and may be produced, for example, by a process of mixing polyvinylidene fluoride, the specific (meth)acrylic polymer, and a solvent as necessary while heating as necessary, and a process of dissolving polyvinylidene fluoride and the (meth)acrylic polymer in the solvent. The piezoelectric material composition may also be produced by a process of mixing polyvinylidene fluoride, a monomer constituting the specific (meth)acrylic polymer, and a solvent while heating as necessary. In this case, the composition containing the specific (meth)acrylic polymer obtained after polymerizing the monomer constituting the specific (meth)acrylic polymer contained in the piezoelectric material composition is also the piezoelectric material composition of the present invention. A piezoelectric material composition containing a monomer constituting polyvinylidene fluoride and the specific (meth)acrylic polymer can also be produced in the same manner.

Next, the piezoelectric material of the present invention can be produced by applying the piezoelectric material composition of the present invention to a substrate, polymerizing the monomers constituting the specific (meth)acrylic polymer as necessary, crystallizing at least a portion of polyvinylidene fluoride by heat treatment, and applying an AC voltage and/or a DC voltage to generate piezoelectric characteristics. For example, when the piezoelectric material of the present invention is a piezoelectric film, the piezoelectric film may be produced by applying the piezoelectric material composition of the present invention to the surface of the substrate, or the piezoelectric film may be peeled off from the substrate to produce a film or sheet. Furthermore, when the piezoelectric material of the present invention is a piezoelectric wire, the piezoelectric material composition of the present invention may be applied to a conductive wire such as a copper wire, for example, a single wire made of a conductive material, by a known method.

The method for drying the applied piezoelectric material composition of the present invention is not particularly limited, and the composition may be dried by heating at a temperature at which the solvent evaporates under atmospheric pressure or reduced pressure conditions. For example, it is preferable to dry the composition at a temperature of 15 to 80°C.

The temperature of the heat treatment when producing the piezoelectric material of the present invention is preferably above the Curie point and below the melting point of polyvinylidene fluoride. The heating time is preferably 30 minutes or more, more preferably 2 hours or more. By carrying out such heat treatment, polyvinylidene fluoride can be crystallized.

The piezoelectric material of the present invention may be a piezoelectric film, a piezoelectric wire, or a piezoelectric block (lump). As described above, the piezoelectric material of the present invention has certain piezoelectric properties even without stretching, and is therefore particularly suitable for applications in which a piezoelectric material is formed on the surface of a substrate by applying the piezoelectric material composition of the present invention to the substrate or the like described above. That is, one aspect of the piezoelectric material of the present invention is one in which no stretching treatment has been performed, and one aspect of the method for producing a piezoelectric material of the present invention is one in which no stretching treatment is performed on the cured product of the piezoelectric material composition or the like in the production process.

The piezoelectric material of the present invention, which contains polyvinylidene fluoride and the specific (meth)acrylic polymer, can exhibit piezoelectric properties even in a higher temperature range compared to a piezoelectric material that does not contain the specific (meth)acrylic polymer. When a piezoelectric material mainly composed of polyvinylidene fluoride does not contain the specific (meth)acrylic polymer, it is necessary to perform a stretching process or apply a high voltage to obtain piezoelectric properties. In particular, in order to obtain a piezoelectric material with high piezoelectric properties, the force applied in the stretching process must be large, but in that case, the upper limit of the temperature at which the piezoelectric material can be used tends to be lowered in order to prevent the orientation caused by the stretching process from being lost. In addition, physical properties other than the piezoelectric properties of the piezoelectric material may be impaired. On the other hand, the piezoelectric material of the present invention has certain piezoelectric properties even without stretching. Therefore, the piezoelectric material of the present invention is suitable as a piezoelectric material used in a high-temperature environment. The piezoelectric material of the present invention can exhibit piezoelectric properties even in high temperature ranges such as 60°C to 150°C, 60°C to 120°C, and 60°C to 110°C. Furthermore, since the polarization process can be performed without necessarily applying a relatively high voltage, there is little risk of other properties of the piezoelectric material being deteriorated. Note that, for piezoelectric materials used at high temperatures such as those described above, relatively high piezoelectric properties may not be required.

The piezoelectric properties of the piezoelectric material of the present invention can be expressed, for example, by the piezoelectric constant d _33. The piezoelectric material of the present invention may be one in which the piezoelectric constant d ₃₃ can be significantly observed by the method for measuring the piezoelectric constant d ₃₃ described in the Examples described later. If the piezoelectric constant d ₃₃ can be significantly observed by the method for measuring the piezoelectric constant d ₃₃ described in the Examples described later, it can be evaluated that the piezoelectric material has sufficient piezoelectric properties depending on the application of the piezoelectric material. As an example, the piezoelectric constant d ₃₃ of the piezoelectric material of the present invention is preferably 0.5 pC/N or more, more preferably 0.8 pC/N or more.

The piezoelectric material of the present invention is particularly suitable as a component of sensors such as touch sensors, acceleration sensors, vibration sensors, ultrasonic sensors, etc., as a component of strain gauges, as a component of transducers, etc.

Next, the present invention will be described in more detail with reference to examples. However, these examples are for the purpose of explaining the present invention and do not limit the present invention in any way. In addition, unless otherwise specified, "%" and "parts" in the examples mean "% by mass" and "parts by mass", respectively.

(Weight average molecular weight)
The weight average molecular weight was measured by gel permeation chromatography (GPC). Specifically, a 0.5% by mass solution obtained by dissolving a (meth)acrylic polymer in tetrahydrofuran was used as a measurement sample. The measurement conditions were as follows:
Equipment: Tosoh Corporation, product number: HLC-8320GPC
Column: Tosoh Corporation, product numbers: TSKgel G5000H and TSKgel G3000H
Eluent: tetrahydrofuran Flow rate: 1.0 mL/min Temperature: 40° C.
Detector: RI
Molecular weight standards: Standard polystyrene

Production Example 1: Preparation of (meth)acrylic polymer B1 (Poly-3FPMA) (1) Preparation of 3,3,3-trifluoropropyl methacrylate (3FPMA) In a 1L glass five-neck flask equipped with a reflux condenser, a water separator, an air inlet tube, a thermometer and a stirrer, 25.0 g of 3,3,3-trifluoropropanol, 18.9 g of methacrylic acid, and 5.36 g of N,N-dimethyl-4-aminopyridine were dissolved in 200 g of dichloromethane, and 44.1 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (hereinafter, EDC) was added while stirring on an ice bath, and stirring was continued for 10 hours. The resulting reaction mixture was washed with water, concentrated, and then purified by vacuum distillation to obtain 21.9 g of 3,3,3-trifluoropropyl methacrylate (3FPMA) as a colorless transparent liquid (GC purity: 99%, yield: 55%).
H-NMR of 3FPMA (CDCl ₃ , ppm): 1.95 (3H, t), 2.44-2.59 (2H, m), 4.38 (2H, t), 5.58-5.62 (1H, m), 6.13-6.14 (1H, m)

(2) Preparation of (meth)acrylic polymer B1 (Poly-3FPMA) The 3FPMA synthesized as described above was polymerized according to the following procedure to produce a (meth)acrylic polymer B1 (Poly-3FPMA).
In a 30 mL glass vessel, 0.22 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (trade name "Irgacure TPO" manufactured by BASF, hereinafter referred to as "TPO") as a polymerization initiator was dissolved in 22.1 g of the 3FPMA produced in (1) above to obtain a mixture containing 3FPMA and the polymerization initiator. The mixture of TPO and 3FPMA was poured into a transparent glass mold (length: 100 mm, width: 100 mm, depth: 4 mm), and then the mixture was irradiated with ultraviolet light (irradiation dose: 1.0 mW/m ² ) to polymerize the 3FPMA, thereby obtaining a (meth)acrylic polymer B1 (Poly-3FPMA). The weight average molecular weight (Mw) of the obtained Poly-3FPMA was measured by GPC and found to be 294,000.

Production Example 2: Preparation of (meth)acrylic polymer B2 (Poly-3FPMA) 3.0 g of 3FPMA produced in (1) above and 7.0 g of butyl acetate were added and stirred in a 50 mL capacity glass flask equipped with a nitrogen inlet tube, a thermometer and a stirrer to obtain a mixed solution. After nitrogen was introduced into this mixed solution from the nitrogen inlet tube for 30 minutes, the temperature in the flask was raised from room temperature to 80°C, and 0.015 g of 2,2'-azobis(isobutyronitrile) (manufactured by Otsuka Chemical Co., Ltd., hereinafter referred to as "AIBN") was added as a polymerization initiator. After the addition of AIBN, the mixture was stirred while maintaining the temperature in the flask at 80°C for 5.5 hours, and then cooled to 35°C or less. The solution in the flask was taken out to obtain (meth)acrylic polymer B2 (Poly-3FPMA). The weight average molecular weight (Mw) of the resulting Poly-3FPMA was measured by GPC and found to be 16,000.

Production Example 3: Preparation of (meth)acrylic polymer B3 (Poly-3FEMA) A (meth)acrylic polymer B3 (Poly-3FEMA) was obtained in the same manner as in Production Example 2, except that 2,2,2-trifluoroethyl methacrylate (manufactured by Osaka Organic Chemical Industry Ltd., product name: Viscoat 3FEMA) was used instead of 3FPMA. The weight average molecular weight (Mw) of the obtained Poly-3FEMA was measured by GPC and was found to be 15,000.

Production Example 4: Preparation of (meth)acrylic polymer B4 (Poly-8FM) Except for using 1H,1H,5H-octafluoropentyl methacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., product name: Viscoat 8FM) instead of 3FPMA, (meth)acrylic polymer B4 (Poly-8FM) was obtained in the same manner as in Production Example 2. The weight average molecular weight (Mw) of the obtained Poly-8FM was measured by GPC and was found to be 20,000.

Production Example 5: Preparation of (meth)acrylic polymer B5 (Poly-(3FPMA/EA)) Except for changing the composition of the mixture containing the polymerization initiator to 3.40 g of ethyl acrylate (EA), 24.75 g of 3FPMA, and 0.28 g of TPO, (meth)acrylic polymer B5 (Poly-(3FPMA/EA)) was obtained in the same manner as in Production Example 1. The weight average molecular weight (Mw) of the obtained Poly-(3FPMA/EA) was measured by GPC and was found to be 320,000.

Production Example 6: Preparation of (meth)acrylic polymer B6 (Poly-FMA) 1.51 g of 2-methyl fluoroacrylate (FMA) and 6.08 g of γ-butyrolactone were added to a 50 mL glass flask equipped with a nitrogen inlet tube, a thermometer, and a stirrer, and the mixture was stirred. Then, 0.02 g of TPO was added as a polymerization initiator, and nitrogen was introduced into the contents from the nitrogen inlet tube, bubbling was performed for 30 seconds, and the glass flask was sealed. Then, the contents were irradiated with ultraviolet light for 2 hours (irradiation dose: 1.0 mW/cm ² ) while stirring, to obtain (meth)acrylic polymer B6 (Poly-FMA). The weight average molecular weight (Mw) of the obtained Poly-FMA was measured by GPC and found to be 210,000.

Production Example 7: Preparation of (meth)acrylic polymer B7 (Poly-MMA) Except for using methyl methacrylate (MMA) instead of 3FPMA, (meth)acrylic polymer B7 (Poly-MMA) was obtained in the same manner as in Production Example 2. The weight average molecular weight (Mw) of the obtained Poly-MMA was measured by GPC and was found to be 16,000.

Production Example 8: Preparation of (meth)acrylic polymer B8 (Poly-EA) Except for using EA instead of 3FPMA, (meth)acrylic polymer B8 (Poly-EA) was obtained in the same manner as in Production Example 2. The weight average molecular weight (Mw) of the obtained Poly-EA was measured by GPC and was found to be 20,000.

Example 1: Production of piezoelectric material composition 1 and piezoelectric material 1 0.75 g of PVDF-A1 (PVDF manufactured by Aldrich, weight average molecular weight 500,000 to 550,000), 0.25 g of the (meth)acrylic polymer B1 (Poly-3FPMA) obtained in Production Example 1, and 9.00 g of DMF as a solvent were mixed in a stoppered flask to produce piezoelectric material composition 1 containing vinylidene fluoride A1 and (meth)acrylic polymer B1 in the mass ratio shown in Table 1.

The piezoelectric material composition 1 produced as described above was applied to a glass substrate using an applicator and left to stand for 30 seconds, then dried in a hot air dryer at 70°C for 20 minutes, then heated to 160°C and dried for 1 hour, and then slowly cooled to room temperature to form a film. The thickness of the film was measured using a stylus profiling system (manufactured by Bruker, product name: Dektak150) and found to be 30 μm. The film was then peeled off from the glass substrate.

Next, the above film was placed in a resistance heating vacuum deposition machine (Cryovac, product name: RVC-2-ICP), and gold was heated and deposited on both sides of the film at an atmospheric pressure of 2×10 ⁻⁴ Pa or less to form electrodes. A triangular wave AC voltage with an electric field amplitude of 150 MV/m and a frequency of 0.1 Hz was applied to the film thus obtained with electrodes formed on both sides using a high voltage device (Matsusada Precision, product name: HEOPS-1B30), to produce piezoelectric material 1.

The piezoelectric constant d ₃₃ of the film of the piezoelectric material 1 according to Example 1 was measured using a piezoelectric constant measuring device (manufactured by Lead Techno Corporation, product name: LPF-02).
Specifically, the measurements were carried out according to the following procedure.
(1) The piezoelectric material 1 was clamped between the measuring probes.
(2) The load applied by the probe to the piezoelectric material 1 was set to 1 N and the material was left stationary.
(3) The load applied from the probe to the piezoelectric material 1 was increased by 3N, and the load applied from the probe to the piezoelectric material 1 film was set to 4N.
(4) The amount of charge generated the moment a force of 4 N was applied was measured.
(5) The load applied from the probe to the piezoelectric material 1 was reduced by 3 N to 1 N.
(6) The above steps (3) to (5) were repeated four times, and the average of the charge amounts measured the second to fourth times was taken as the charge amount of piezoelectric material 1. This average charge amount was divided by the measurement load (4 N) to calculate the piezoelectric constant _d33 of piezoelectric material 1. The results are shown in the table.

Examples 2 to 11 and Comparative Examples 1 to 3
A piezoelectric material was prepared in the same manner as in Example 1, except that the composition of the piezoelectric material was changed to the composition shown in Table 1. The results of similar measurements on the obtained piezoelectric material are shown in Table 1. PVDF-A2 is PVDF (weight average molecular weight 250,000 to 280,000) manufactured by Kureha Corporation. The percentages in Table 1 represent the percentages of PVDF and (meth)acrylic polymers in the entire piezoelectric material in weight percent, and N.D. at d ₃₃ represents less than the measurement limit.

Furthermore, in some examples, the piezoelectric constant of the stretched piezoelectric material was measured. Specifically, a PET film was first placed on a hot plate set at 150° C., and a piezoelectric material was placed on the PET film and heated for 10 minutes. The piezoelectric material was then stretched by hand, and the piezoelectric constant d ₃₃ of the piezoelectric material cooled to room temperature was measured in the same manner as above. The piezoelectric constant of the stretched piezoelectric material is the value shown in parentheses in Table 1.

Example 12
A piezoelectric material 12 was prepared from a piezoelectric material composition having a composition ratio of A1:B1=75:25 in the same manner as in Example 1, except for the following changes.
(1) The solvent was changed from DMF to 5.7 g of N-methylpyrrolidone (NMP) to adjust the solid content to 15%.
(2) In forming the film, a stainless steel substrate was used instead of a glass substrate, and the film was dried under reduced pressure at 110°C for 2 hours in a vacuum dryer. Thereafter, the temperature of the hot air dryer was increased to 190°C, and the film was allowed to stand for 4 hours to obtain an annealed film (film thickness: approximately 40 μm).
(3) No electrodes were formed on either side of the film, and a DC voltage of −19 kV was applied for 30 minutes instead of a triangular AC voltage using an electret processing device (manufactured by Wedge Corporation) as a high-voltage device. The film was then peeled off from the stainless steel substrate to obtain piezoelectric material 12.
<Measurement of piezoelectric constant _d33 >
The piezoelectric constant d ₃₃ of the piezoelectric material 12 was measured in the same manner as in Example 1. As a result of the measurement, the d ₃₃ of the piezoelectric material 12 was 7.3 pC/N.

It was confirmed that the piezoelectric materials of the present invention containing polyvinylidene fluoride and a specific (meth)acrylic polymer shown in Examples 1 to 12 have piezoelectric properties even without stretching. In contrast, the materials of Comparative Example 1 containing only polyvinylidene fluoride, and Comparative Examples 2 and 3 containing polyvinylidene fluoride and a (meth)acrylic polymer that is not the specific (meth)acrylic polymer, did not exhibit piezoelectric properties.

Claims (4)

Polyvinylidene fluoride, and
Formula (I):
[During the ceremony,
R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, in which at least one hydrogen atom of R ₁ may be substituted with a halogen atom;
_R2 represents a linear or branched alkyl group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, a phenyl group, or a phenylalkylene group including an alkylene group having 1 to 4 carbon atoms;
wherein at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenylalkylene group may be substituted with -O-, -N-, or -S-;
at least one hydrogen atom of the alkyl group, the alicyclic hydrocarbon group and the alkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms;
at least one hydrogen atom on the phenyl ring of the phenyl group and the phenylalkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group;
At least one hydrogen atom of _R2 may be substituted with a halogen atom;
However, at least one hydrogen atom of R ₁ and/or R ₂ is substituted with a halogen atom.
A piezoelectric material containing a (meth)acrylic polymer including a structural unit derived from a (meth)acrylic monomer represented by the following formula: 2. The piezoelectric material according to claim 1, wherein the amount of polyvinylidene fluoride is 99 to 60 mass % based on the entire piezoelectric material, and the amount of (meth)acrylic polymer is 1 to 40 mass % based on the entire piezoelectric material. A piezoelectric film comprising the piezoelectric material according to claim 1 or 2. Polyvinylidene fluoride, and
Formula (I):
[During the ceremony,
R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, in which at least one hydrogen atom of R ₁ may be substituted with a halogen atom;
_R2 represents a linear or branched alkyl group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms including an alicyclic structure having 3 to 6 carbon atoms, a phenyl group, or a phenylalkylene group including an alkylene group having 1 to 4 carbon atoms;
wherein at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenylalkylene group may be substituted with -O-, -N-, or -S-;
at least one hydrogen atom of the alkyl group, the alicyclic hydrocarbon group and the alkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, and/or an alkoxy group having 1 to 6 carbon atoms;
at least one hydrogen atom on the phenyl ring of the phenyl group and the phenylalkylene group may be substituted with a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and/or a cyano group;
At least one hydrogen atom of _R2 may be substituted with a halogen atom;
However, at least one hydrogen atom of R ₁ and/or R ₂ is substituted with a halogen atom.
and/or a (meth)acrylic polymer containing a structural unit derived from the (meth)acrylic monomer , wherein the amount of polyvinylidene fluoride is 60 to 99 mass % based on the total weight of the polyvinylidene fluoride, the (meth)acrylic monomer, and the (meth)acrylic polymer containing a structural unit derived from the (meth)acrylic monomer in the piezoelectric material composition .