Piezoelectric material, piezoelectric film, and composition for piezoelectric material

Abstract

The present invention relates to a piezoelectric material containing polyvinylidene fluoride and a (meth)acrylic polymer including a structural unit that is derived from a (meth)acrylic monomer which is represented by formula (I). (I) (In the formula, R1 represents a hydrogen atom or an alkyl group having 1-3 carbon atoms, where at least one hydrogen atom of R1 may be substituted with a halogen atom; and R2 represents a straight-chain or branched alkyl group having 1-10 carbon atoms, an alicyclic hydrocarbon group having 3-12 carbon atoms and including an alicyclic structure that has 3-6 carbon atoms, a phenyl group, or a phenyl alkylene group including an alkylene group that has 1-4 carbon atoms, where at least one carbon atom of the alkyl group, the alicyclic hydrocarbon group, the phenyl group, and the phenyl alkylene group may be substituted with -O-, -N-, or -S-.)

Description

Technical Field

[0001] The present invention relates to a piezoelectric material, a piezoelectric film, and a composition for a piezoelectric material.

Background Art

[0002] Polyvinylidene fluoride (PVDF) is used as a piezoelectric material having excellent piezoelectric properties. This piezoelectric material is used in various piezoelectric elements such as piezoelectric sensors, transducers, and pyroelectric infrared sensors.

[0003] For example, Patent Documents 1 and 2 describe a piezoelectric body containing polyvinylidene fluoride.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a material containing polyvinylidene fluoride is used as a piezoelectric body, poling treatment is usually performed. For example, Patent Document 1 describes that a material containing polyvinylidene fluoride is poled by stretching to impart piezoelectric properties to the material, and Patent Document 2 describes that a relatively high voltage is applied to a material containing polyvinylidene fluoride for poling treatment to impart piezoelectric properties.

[0006] However, depending on the use of the piezoelectric material, it may be required to be an un-stretched material from the viewpoint of other material properties than the piezoelectric properties. Further, when applying a high voltage to impart piezoelectric properties, since the applied high voltage can affect other material physical properties than the piezoelectricity, depending on the use where the piezoelectric material is used, it may not satisfy other material properties than the piezoelectric properties.

[0007] Therefore, an object of the present invention is to provide a piezoelectric material capable of imparting piezoelectric properties even when a high voltage is not applied, stretching treatment, etc. are not performed, a piezoelectric film containing the piezoelectric material, and a composition for a piezoelectric material for obtaining the piezoelectric material.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by a piezoelectric material containing polyvinylidene fluoride and a (meth)acrylic polymer containing a structural unit derived from a specific (meth)acrylic monomer, and have completed the present invention. That is, the present invention includes the following aspects.

[0009] 〔1〕Polyvinylidene fluoride, and Formula (I):

Chemical formula

Chemical formula

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a piezoelectric material capable of imparting piezoelectric properties even when high voltage is not applied or stretching treatment is not performed, a piezoelectric film containing the piezoelectric material, and a composition for a piezoelectric material for obtaining the piezoelectric material.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. 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. In this specification, the numerical range indicated by "~" includes its upper and lower limits.

[0012] The piezoelectric material of the present invention contains polyvinylidene fluoride and a specific (meth)acrylic polymer containing a halogen atom. The inventors have found that a material containing polyvinylidene fluoride and a specific (meth)acrylic polymer exhibits piezoelectric properties even without performing stretching, polarization treatment by applying a high voltage, and / or adding other compounds. Furthermore, it has been found that when stretching, applying a high voltage, etc. are performed on the material, the piezoelectric properties can be further improved. Note that the piezoelectric material of the present invention may be one to which conventional techniques for developing and improving piezoelectric properties such as stretching treatment, polarization treatment at a relatively high voltage, and addition of a compound are applied as long as the material characteristics required in the application of the piezoelectric material are satisfied.

[0013] Although the detailed reason why the piezoelectric material of the present invention exhibits piezoelectric properties without performing stretching, polarization treatment by applying a high voltage, addition of a compound, etc. is not clear, it is presumed that the halogen atom contained in the specific (meth)acrylic polymer interacts with the dipoles in the structural unit of polyvinylidene fluoride.

[0014] <(meth)acrylic polymer> The (meth)acrylic polymer contained in the piezoelectric material of the present invention has the formula (I):

Chemical formula

[0015] The structural unit derived from the (meth)acrylic monomer represented by the formula (I) is the following formula (II):

Chemical formula

[0016] In the above formula (I), at least one hydrogen atom of 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.

[0017] From the viewpoint of easily improving the piezoelectric properties, the amount of the halogen atom contained in the structural unit derived from the (meth)acrylic monomer represented by the formula (I) is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more per structural unit. As an example of the method for specifying the amount of the above halogen atom, there are a method of analyzing a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer, and a method of analyzing a (meth)acrylic monomer which is a raw material monomer. When analyzing a (meth)acrylic polymer, it may be analyzed by pyrolysis gas chromatography. When analyzing a (meth)acrylic monomer, it may be analyzed by a nuclear magnetic resonance apparatus (NMR), but is not limited to these methods.

[0018] From the viewpoint of easily improving the piezoelectric properties, the ratio (molar ratio) of the halogen atom to all the atoms constituting the (meth)acrylic polymer is preferably 5 mol% or more, more preferably 10 mol% or more. Also, the upper limit of the above ratio is not particularly limited and may be 70 mol% or less, or may be 60 mol% or less. The amount of the above halogen atom 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 analyzing a (meth)acrylic polymer by NMR, it can be determined based on (total area of halogen atoms / area of internal standard substance) × 100.

[0019] The halogen atom contained in the (meth)acrylic monomer represented by formula (I) is preferably a monohalogen group (preferably a monofluoro group), and / or an alkyl group having 1 to 10 halogen atoms (preferably fluorine atoms) and 1 to 10 carbon atoms. More preferably, it is 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). Even more preferably, it is an alkyl group having 3 to 6 carbon atoms and 1 to 10 halogen atoms (preferably fluorine atoms). It is preferable that it is contained in the (meth)acrylic monomer from the viewpoint of easily increasing the dipole. Specific examples of such groups include a monofluoro group (especially a monofluoro group as R1), a trifluoromethyl group, a difluoromethyl group, a monofluoromethyl group, a trifluoroethyl group, a difluoroethyl group, a monofluoroethyl group, an octafluoropropyl group, a heptafluoropropyl group, a hexafluoropropyl group, a pentafluoropropyl group, a tetrafluoropropyl group, a trifluoropropyl group, a difluoropropyl group, a monofluoropropyl group, an octafluorobutyl group, a heptafluorobutyl group, a hexafluorobutyl group, a pentafluorobutyl group, a tetrafluorobutyl group, a trifluorobutyl group, a difluorobutyl group, a monofluorobutyl group, an octafluoropentyl group, a heptafluoropentyl group, a hexafluoropentyl group, a pentafluoropentyl group, a tetrafluoropentyl group, a trifluoropentyl group, a difluoropentyl group, a monofluoropentyl group, a trichloromethyl group, a dichloromethyl group, and a monochloromethyl group. The halogen atom contained in the (meth)acrylic monomer represented by the formula (I) is more preferably a group selected from the group consisting of a trifluoropropyl group, a difluoropropyl group, a monofluoropropyl group, a trichloropropyl group, a dichloropropyl group, and a monochloropropyl group, and it is preferable that it is contained in the (meth)acrylic monomer from the viewpoint of easily increasing the dipole. In other words, the (meth)acrylic polymer of the present invention preferably contains a structural unit derived from the (meth)acrylic monomer represented by the formula (I) and containing a group selected from the group consisting of a monofluoro group, a trifluoropropyl group, a difluoropropyl group, a monofluoropropyl group, a trichloropropyl group, a dichloropropyl group, and a monochloropropyl group.

[0020] In the above formula (I), R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and at least one hydrogen atom of R1 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 a group in which at least one hydrogen atom of these groups is substituted with a halogen atom may also be used. 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 still more preferably a fluorine atom.

[0021] Specific examples of R1 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.

[0022] In the above formula (I), R2 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 containing an alicyclic structure having 3 to 6 carbon atoms, (3) a phenyl group, or (4) a phenylalkylene group containing 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-, and 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 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. Further, at least one hydrogen atom of R2 may be substituted with a halogen atom.

[0023] Here, the statement that at least one hydrogen atom of R2 may be substituted with a halogen atom means that, for example, when R2 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, or 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 substituting alkyl group having 1 to 6 carbon atoms and / or alkoxy group having 1 to 6 carbon atoms may be substituted with a halogen atom. The same applies when R2 is the above (2) to (4). Note that examples of the halogen atom include the atoms described above for R1, and the preferred description regarding the halogen atom of R1 also applies to R2.

[0024] In the alkyl group having 1 to 6 carbon atoms and the alkyl group in the alkoxy group having 1 to 6 carbon atoms, the number of carbon atoms of the alkyl group is preferably 1 to 4, more preferably 1 to 2. The alkyl chain moiety in the alkyl group having 1 to 6 carbon atoms and the alkoxy group may be either linear or branched.

[0025] When R2 in the above formula (I) represents 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 the present specification, the alkyl group may be either linear or branched. Examples of the alkyl group include, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, 1,1-dimethylpropyl group, isoamyl group, n-hexyl group, isohexyl group, n-octyl group and the like. 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. R2 in the above formula (I) is preferably a linear or branched alkyl group having 1 to 10 carbon atoms having 1 to 10 halogen atoms, more preferably a linear or branched alkyl group having 2 to 10 carbon atoms having 2 to 10 halogen atoms, still more preferably a linear or branched alkyl group having 3 to 8 carbon atoms having 3 to 8 halogen atoms, and even more preferably a linear or branched alkyl group having 3 to 6 carbon atoms having 3 to 8 halogen atoms, from the viewpoint of easily enhancing the piezoelectric properties.

[0026] Examples of the alkyl group having 1 to 10 carbon atoms substituted with a hydroxyl group include, for example, hydroxymethyl group, hydroxyethyl group, hydroxy n-propyl group, hydroxyisopropyl group, hydroxy n-butyl group, hydroxyisobutyl group, hydroxy tert-butyl group and the like.

[0027] 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 the 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. If the carbon number of the alkyl group forming the main chain is 1 to 10, the carbon number of the entire alkyl group may exceed 10. Examples of such an alkyl group include, for example, a 2-ethylhexyl group. In the case of a group in which the carbon number of the entire alkyl group does not exceed 10, the group is also a group included in the definition of a branched alkyl group having 1 to 10 carbon atoms.

[0028] An 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 a group include, for example, a methoxyethyl group, an ethoxyethyl group, and a methoxybutyl group.

[0029] Examples of the alkyl group having 1 to 10 carbon atoms substituted with a hydroxyl group and an alkoxy group having 1 to 6 carbon atoms include a hydroxyalkoxy group having 1 to 6 carbon atoms and a group having an alkyl group having 1 to 6 carbon atoms, specifically, a hydroxymethoxyethyl group, a hydroxyethoxyethyl group, a hydroxypropyloxypropyl group, and the like.

[0030] Among the above alkyl groups, from the viewpoint of availability, an alkyl group 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 is preferable, an alkyl group 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 is preferable, and an alkyl group 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 is even more preferable.

[0031] Among the above alkyl groups, from the viewpoint of the productivity of the (meth)acrylic monomer represented by the above formula (I), R2 in the formula (I) preferably represents (1) a linear or branched alkyl group having 1 to 10 carbon atoms, and at least one carbon atom of the alkyl group is a group substituted with -O-. Examples of such R2 include the formula (III):

Chemical formula

[0032] The linear or branched alkyl group having 1 to 10 carbon atoms, which may be optionally 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 have at least one hydrogen atom substituted with a halogen atom.

[0033] 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, examples of the alicyclic structure having 3 to 6 carbon atoms include 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.

[0034] Examples of the alicyclic hydrocarbon group 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 substituted with an oxygen atom (-O-), include an epoxy group in which one carbon atom of the alicyclic hydrocarbon group having 3 carbon atoms is substituted with an oxygen atom, an oxetanyl ring in which one carbon atom of the alicyclic hydrocarbon group having 4 carbon atoms is substituted with an oxygen atom, a dioxolane ring in which two carbon atoms of the alicyclic hydrocarbon group having 5 carbon atoms are substituted with oxygen atoms, a dioxane ring in which two carbon atoms of the alicyclic hydrocarbon group having 6 carbon atoms are substituted with oxygen atoms, and the like. Note that the hydrogen atoms on these rings may be substituted with an alkyl group having 1 or 2 carbon atoms. Specific examples of such groups include 3-ethyl-3-oxetanylmethyl acrylate, 2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate, cyclic trimethylolpropane formal acrylate, and the like.

[0035] The alicyclic hydrocarbon group having 3 to 12 carbon atoms and containing 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 as described above, may have at least one hydrogen atom substituted with a halogen atom.

[0036] In the above formula (I), R2 may represent a (3)phenyl group. Further, at least one hydrogen atom on the phenyl ring in 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 the hydrogen atom at the para position, is substituted with an alkyl group having 1 to 4 (preferably 1 or 2) carbon atoms 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.

[0037] The phenyl group described above, 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, etc., may have at least one hydrogen atom substituted with a group substituted with a halogen atom. When R2 is such a group, it is easy to improve other properties of the piezoelectric material such as elongation and flexibility of the piezoelectric material.

[0038] When R2 in the above formula (I) represents 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.

[0039] Examples of the phenylalkylene group in which at least one carbon atom of the alkylene group is substituted with -O- include the formula (IV):

Chemical formula

[0040] The phenylalkylene group described above, in which at least one hydrogen atom on 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 / or 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, may be a group in which at least one hydrogen atom thereof is substituted with a halogen atom. When R2 is such a group, it is easy to improve other properties of the piezoelectric material such as elongation and flexibility.

[0041] Preferable examples of the (meth)acrylic polymer contained in the piezoelectric material of the present invention include a (meth)acrylic polymer containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I), wherein R1 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, R2 represents a linear or branched alkyl group having 1 to 10 (preferably 1 to 4, more preferably 1 to 2) carbon atoms, and here, at least one carbon atom of the alkyl group in R2 may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alkyl group in R2 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.

[0042] Another preferred example of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is that R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R2 represents a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 4, more preferably 1 to 2), wherein at least one carbon atom of the alkyl group in R2 may be substituted with -O-, -N- or -S-, at least one hydrogen atom of the alkyl group in R2 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 atoms of R2 are substituted with a halogen, and a (meth)acrylic polymer containing a structural unit derived from the (meth)acrylic monomer represented by the above formula (I). More specific examples of the (meth)acrylic polymer include those in which R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R2 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 R2 may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alkyl group in R2 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, 2,2-dichloroethyl (meth)acrylate.

[0043] Another preferred example of the (meth)acrylic polymer contained in the piezoelectric material of the present invention is that R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R2 represents an alicyclic hydrocarbon group having 3 to 12 carbon atoms containing an alicyclic structure having 3 to 6 carbon atoms, and here, at least one carbon atom of the alicyclic hydrocarbon group in R2 may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alicyclic hydrocarbon group in R2 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 atoms of R2 are substituted with a halogen. Examples thereof include (meth)acrylic polymers containing structural units derived from the (meth)acrylic monomers represented by the above formula (I). When the piezoelectric material contains the (meth)acrylic polymer, it is easy to improve other properties of the piezoelectric material such as elongation and flexibility. More specific examples of the (meth)acrylic polymer include those in which R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R2 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 R2 may be substituted with -O-, -N- or -S-, and at least one hydrogen atom of the alicyclic hydrocarbon group in R2 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.

[0044] Specific examples of the (meth)acrylic polymer 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.

[0045] The (meth)acrylic polymer contained in the piezoelectric material of the present invention may have only structural units derived from one type of (meth)acrylic monomer represented by the above formula (I), or may have structural units derived from two or more types of (meth)acrylic monomers represented by the above formula (I). Further, the (meth)acrylic polymer contained in the piezoelectric material of the present invention may contain structural units derived from at least one other monomer within a range that does not impair the properties of the piezoelectric material of the present invention. 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), or may be a copolymer of two or more types of (meth)acrylic monomers represented by the above formula (I), or may be a copolymer of at least one (meth)acrylic monomer represented by the above formula (I) and at least one other monomer.

[0046] Examples of other monomers that can copolymerize with the (meth)acrylic monomer represented by the above formula (I) include carboxyl group-containing monomers, carboxylic acid alkyl ester monomers other than (meth)acrylic monomers that give structural units represented by formula (I), amide group-containing monomers, aryl group-containing monomers, styrene-based monomers, nitrogen atom-containing monomers, fatty acid vinyl ester monomers, betaine monomers, and the like.

[0047] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, crotonic acid and the like.

[0048] Examples of the carboxylic acid alkyl ester monomer other than the (meth)acrylic monomer that gives the structural unit represented by formula (I) include alkyl acrylates having 11 to 20 carbon atoms in the alkyl group such as dodecyl (meth)acrylate and stearyl (meth)acrylate, and itaconic acid alkyl esters having 1 to 4 carbon atoms in the alkyl group such as methyl itaconate and ethyl itaconate.

[0049] Examples of the amide group-containing monomer include alkyl (meth)acrylamides having 1 to 8 carbon atoms in the alkyl group 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.

[0050] Examples of the aryl group-containing monomer include aryl (meth)acrylates having 6 to 12 carbon atoms in the aryl group such as benzyl (meth)acrylate.

[0051] Examples of the styrene monomer include styrene, α-methylstyrene and the like.

[0052] Examples of the nitrogen atom-containing monomer include N-vinylpyrrolidone, N-vinylcaprolactam and the like.

[0053] Examples of the fatty acid vinyl ester monomer include vinyl acetate, vinyl propionate and the like.

[0054] 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 - 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 - α - sulfobetaine, 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,Sulfobetaine monomers such as 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-methacryloyloxybutyl-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, N-methacryloyloxybutyl-N,N-dimethylammonium butyl-α-sulfobetaine, and N-(meth)acryloyloxyalkyl-N,N-dimethylammonium alkyl-α-sulfobetaine are exemplified.,

[0055] When producing a (meth)acrylic polymer, the content of the (meth)acrylic monomer represented by formula (I) in the monomer components is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 90% by mass or more, particularly still more preferably 93% by mass or more, and most preferably 95% by mass or more, from the viewpoint of easily improving the piezoelectric properties, with respect to the total amount of the monomer components when producing the (meth)acrylic polymer. Also, the upper limit of the above content is not particularly limited and may be 100% by mass or less, and 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 copolymerizable with the (meth)acrylic monomer represented by formula (I), the content of the other monomers is preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less, particularly preferably 10% by mass or less, particularly still more preferably 7% by mass or less, and most preferably 5% by mass or less, from the viewpoint of easily improving the piezoelectric properties of the piezoelectric material, with respect to the total amount of the monomer components when producing the (meth)acrylic polymer. Also, when the above other monomers are contained, the lower limit of the content is not particularly limited and may be 1% by mass or more, 2% by mass or more, or 3% by mass or more with respect to the mass of all the monomer components.

[0056] When producing the (meth)acrylic polymer, the monomer component may contain an appropriate amount of a crosslinkable monomer as long as it does not inhibit 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) included 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), and / or (2) not included in the main chain of a polymer containing a structural unit derived from the acrylic monomer represented by the above formula (I), but bonds to the 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). In either form of (1) and (2), since the (meth)acrylic polymer contains a structural unit derived from the crosslinkable monomer, 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 with a higher molecular weight.

[0057] Examples of the crosslinkable monomer include polyfunctional monomers such as (meth)acrylamide compounds having two or more, preferably two, (meth)acryloyl groups, such as alkylene bis(meth)acrylamides having 1 to 4 carbon atoms in the alkylene group, such as methylene bisacrylamide and methylene bismethacrylamide; (meth)acrylate compounds having two or more, preferably two or three, (meth)acryloyl groups, such as 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, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate; amine compounds having two or more, preferably two or three, carbon-carbon double bonds, such as diallylamine and triallylamine; and aromatic compounds having two or more, preferably two or three, carbon-carbon double bonds, such as divinylbenzene and diallylbenzene. However, the present invention is not limited to such examples. These crosslinkable monomers may be used alone or in combination of two or more thereof.

[0058] 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, still more preferably 100,000 or more, and particularly preferably 150,000 or more. When the weight average molecular weight of the (meth)acrylic polymer is equal to or higher than the above lower limit value, it is easy to enhance the strength and durability of the piezoelectric material. Further, from the viewpoint of the ease of producing 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, still 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 such as measurement conditions are as described in the examples.

[0059] ((Production method of (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.

[0060] Examples of the method for polymerizing the monomer component include bulk polymerization method, solution polymerization method, emulsion polymerization method, suspension polymerization method, etc., but the present invention is not limited only to such examples. Among these polymerization methods, from the viewpoint of the productivity of the (meth)acrylic polymer, the bulk polymerization method and the solution polymerization method are preferable.

[0061] When polymerizing the monomer component by solution polymerization, a solvent is used. As the solvent, a non-aqueous organic solvent is preferred. Examples of non-aqueous organic solvents include hydrocarbon-based organic solvents such as hexane, heptane, octane, isooctane, decane, and liquid paraffin; ether-based organic solvents such as dimethyl ether, diethyl ether, and tetrahydrofuran; ketone-based organic solvents such as acetone and methyl ethyl ketone; ester-based organic solvents such as methyl acetate, ethyl acetate, butyl acetate, and γ-butyrolactone; chloride-based organic solvents such as methylene chloride, chloroform, and carbon tetrachloride; dimethylformamide, diethylformamide, dimethyl sulfoxide, dioxane, and the like. However, the present invention is not limited only to such examples. These organic solvents may be used alone or in combination of two or more. The amount of the solvent varies depending on the type of the solvent and thus cannot be generally limited, but usually, it is preferably about 100 to 1000 parts by mass per 100 parts by mass of the monomer component.

[0062] When polymerizing the monomer component, a polymerization initiator can be used. Examples of the polymerization initiator include a photopolymerization initiator and a thermal polymerization initiator. Among these polymerization initiators, a photopolymerization initiator is preferred from the viewpoint of leaving no thermal history on 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, disulfide derivatives, and the like. If desired, two or more of them may be used in combination.

[0063] Examples of the photoinitiator 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'-di-tert-butyldiphenyliodonium 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-diphenylethane-1-one, phenylglyoxylic acid methyl ester, 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)], bis(η5-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyltitanium] and other free radical photoinitiators, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(p-methoxyphenylvinyl)-1,3,5-triazine, diphenyliodonium tetrafluoroborate, 4,4'-di-tert-butyldiphenyliodonium tetrafluoroborate, 4-diethylaminophenylbenzenediazonium hexafluorophosphate, diphenyl-4-phenylthiophenylsulfonium hexafluorophosphate and other cationic ring-opening photoinitiators. However, the present invention is not limited to such examples only.These photoinitiators may be used alone or in combination of two or more thereof.

[0064] Examples of the thermal polymerization initiator 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. However, the present invention is not limited to such examples. These polymerization initiators may be used alone or in combination of two or more thereof.

[0065] The amount of the polymerization initiator varies depending on the type of the polymerization initiator and the like and thus cannot be determined unconditionally. Usually, it is preferably about 0.01 to 20 parts by mass per 100 parts by mass of the monomer component.

[0066] When polymerizing the monomer component, a chain transfer agent can be used to adjust the molecular weight of the resulting (meth)acrylic polymer. Examples of the chain transfer agent include compounds having a thiol group such as lauryl mercaptan, dodecyl mercaptan, and thioglycerol; and inorganic salts such as sodium hypophosphite and sodium bisulfite. However, the present invention is not limited to such examples. These chain transfer agents may be used alone or in combination of two or more thereof. The amount of the chain transfer agent varies depending on the type of the chain transfer agent and the like and thus cannot be determined unconditionally. Usually, it is preferably about 0.01 to 10 parts by mass per 100 parts by mass of the monomer component.

[0067] The atmosphere during the polymerization of the monomer component is not particularly limited and may be in the air or in an inert gas atmosphere such as nitrogen gas or argon gas.

[0068] The temperature for polymerizing the monomer components is not particularly limited, and it is usually preferably about 5 to 100 °C. The time required to polymerize the monomer components is arbitrary because it varies depending on the polymerization conditions and cannot be determined unconditionally, but it is usually about 1 to 20 hours.

[0069] The polymerization reaction can be arbitrarily terminated when the amount of the remaining monomer components reaches 20% by mass or less. The amount of the remaining monomer components can be measured, for example, using gel permeation chromatography.

[0070] By polymerizing the monomer components as described above, the (meth)acrylic polymer contained in the piezoelectric material of the present invention can be obtained.

[0071] (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 component monomer. The main component monomer is a monomer that occupies more than 50 mol% in the monomer mixture. Specifically, from the viewpoint of facilitating the imparting of piezoelectric properties to the piezoelectric material, the amount of the structural unit derived from vinylidene fluoride in polyvinylidene fluoride is preferably more than 50 mol%, more preferably 60 mol% or more, still more preferably 70 mol% or more, even more preferably 80 mol% or more, particularly preferably 90 mol% or more, particularly more preferably 91 mol% or more, particularly still more preferably 93 mol% or more, even more preferably 95 mol% or more, even more preferably 97 mol% or more, extremely preferably 99 mol% or more, and most preferably 100 mol% with respect to the total amount of structural units. Polyvinylidene fluoride is preferably selected from the group consisting of a homopolymer of vinylidene fluoride and a copolymer having a structural unit derived from vinylidene fluoride of 91 mol% or more and a structural unit derived from other monomers of 9 mol% or less based on the total amount of all structural units of polyvinylidene fluoride. The upper limit of the amount of the structural unit derived from vinylidene fluoride is 100 mol% or less. In other words, the fact that the amount of the structural unit derived from vinylidene fluoride is 100 mol% with respect to 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 optionally contain inevitable impurities as well.

[0072] As described above, the polyvinylidene fluoride contained in the piezoelectric material of the present invention may be a homopolymer of vinylidene fluoride, or may be a copolymer having structural units derived from vinylidene fluoride in an amount exceeding 50 mol% based on the total amount of structural units and structural units derived from other monomers in an amount less than 50 mol%. More preferably, it is selected from the group consisting of a homopolymer of vinylidene fluoride and a copolymer having structural units derived from vinylidene fluoride in an amount of 91 mol% or more and structural units derived from other monomers in an amount of 9 mol% or less based on the total amount of structural units of polyvinylidene fluoride, and even more preferably is a homopolymer of vinylidene fluoride. When the polyvinylidene fluoride is the above copolymer, examples of other monomers include tetrafluoroethylene, hexafluoropropylene, hexafluoropropylene oxide, perfluoropropyl vinyl ether, chlorotrifluoroethylene, and the like. These other monomers can be used alone or in combination of two or more. The polyvinylidene fluoride may be a homopolymer of vinylidene fluoride and / or a copolymer of vinylidene fluoride and at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, hexafluoropropylene oxide, perfluoropropyl vinyl ether, and chlorotrifluoroethylene.

[0073] 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, still 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.

[0074] For the polyvinylidene fluoride contained in the piezoelectric material of the present invention, commercially available products may be used. Examples of commercially available polyvinylidene fluoride include, for example, "Poly(vinylidene fluoride)" manufactured by Aldrich, "KF Polymer W#1100" manufactured by Kuraray, and the like.

[0075] (Composition for Piezoelectric Material and Piezoelectric Material) From the viewpoint of easily improving the piezoelectric properties, 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, still 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, 85% by mass or more, based on the entire piezoelectric material. Also, from the viewpoint of easily exhibiting other functions (such as improvement in elongation and / or flexibility in the piezoelectric material) obtained by containing the specific (meth)acrylic polymer, 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, still more preferably 95% by mass or less, particularly preferably 90% by mass or less, and may be 85% by mass or less, 80% by mass or less.

[0076] From the viewpoints of easily improving the piezoelectric properties and easily exhibiting other functions obtained by containing 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, still more preferably 5% by mass or more, particularly preferably 10% by mass or more, and may be 15% by mass or more, 20% by mass or more, based on the entire piezoelectric material. Also, from the viewpoint of easily enhancing the piezoelectric properties, 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, still 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, 15% by mass or less.

[0077] The piezoelectric materials of the present invention also include embodiments containing materials other than polyvinylidene fluoride and specific (meth)acrylic polymers (hereinafter referred to as other materials). Examples of other materials include copolymers and elastomers other than polyvinylidene fluoride and specific (meth)acrylic polymers, additives such as antioxidants and ultraviolet absorbers, thermal conductive fillers, and conductive fillers, but are not limited thereto. The piezoelectric materials of the present invention may contain these other materials alone or in combination of two or more kinds.

[0078] 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, still 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, 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. 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, still more preferably 95% by mass or less, particularly preferably 90% by mass or less, and may be 85% by mass or less, 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 not less than the above lower limit, it is easy to enhance the piezoelectric properties of the piezoelectric material. Also, when the amount of polyvinylidene fluoride is not more than the above upper limit, it is easy to exhibit other functions obtained by including the above-mentioned specific (meth)acrylic polymer.

[0079] 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 also be calculated from the charging ratio of the raw materials. Therefore, after determining the structure of polyvinylidene fluoride contained in the piezoelectric material and the structure of the specific (meth)acrylic polymer, they are separated from the piezoelectric material by a known method, or a specific (meth)acrylic polymer having the same structure is prepared and analyzed by the above-described analysis method or the like, whereby the structure and amount of polyvinylidene fluoride and the (meth)acrylic polymer constituting the piezoelectric material may be analyzed. Similarly, 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.

[0080] The method for producing the piezoelectric material of the present invention is not particularly limited. For example, after applying and drying a solution containing polyvinylidene fluoride, the specific (meth)acrylic polymer, and a solvent, a step of crystallizing polyvinylidene fluoride by heat treatment, and a step of generating piezoelectric characteristics by applying a voltage and polarizing at least a part of polyvinylidene fluoride may be used for production. Note that drying and heat treatment may be performed simultaneously. As another example, 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 generating piezoelectric characteristics by applying a voltage and polarizing at least a part of polyvinylidene fluoride are included in the method for producing a piezoelectric material. In the above production method, a stretching treatment may be performed from the viewpoint of further enhancing the piezoelectric characteristics. Note that the piezoelectric material of the present invention is likely to generate piezoelectric characteristics without performing a stretching treatment and / or applying a high voltage, and thus can be suitably used as a piezoelectric material used at high temperatures and a piezoelectric material for which mechanical characteristics are required.

[0081] A composition containing polyvinylidene fluoride and the specific (meth)acrylic polymer for manufacturing a piezoelectric material, (optionally, a solution further containing a solvent) is hereinafter also referred to as "composition for piezoelectric material". The composition for piezoelectric material also includes a composition containing polyvinylidene fluoride and a monomer constituting the specific (meth)acrylic polymer. The present invention also provides these compositions for piezoelectric material. In addition, in this specification, the descriptions regarding the (meth)acrylic polymer and polyvinylidene fluoride contained in the piezoelectric material of the present invention are similarly applicable to the specific (meth)acrylic polymer and polyvinylidene fluoride contained in the composition for piezoelectric material of the present invention.

[0082] The solvent that may be contained in the composition for piezoelectric material is not particularly limited as long as it can dissolve polyvinylidene fluoride and the specific (meth)acrylic polymer. For example, N,N-dimethylformamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, diethyl carbonate, etc.

[0083] The composition for piezoelectric material of the present invention is not particularly limited. For example, it may be produced by a step of mixing polyvinylidene fluoride, the specific (meth)acrylic polymer and, if necessary, a solvent while heating as necessary, and a step of dissolving polyvinylidene fluoride and the (meth)acrylic polymer in the solvent. Further, the composition for piezoelectric material may be produced by a step 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 composition for piezoelectric material is also the composition for piezoelectric material of the present invention. The composition for piezoelectric material containing a monomer constituting polyvinylidene fluoride and the specific (meth)acrylic polymer can be produced in the same manner.

[0084] Next, a step of applying the composition for a piezoelectric material of the present invention onto a substrate, a step of polymerizing monomers constituting the specific (meth)acrylic polymer as necessary, a step of crystallizing at least a part of polyvinylidene fluoride by heat treatment, and a step of performing poling treatment by applying an alternating voltage and / or a direct current voltage to generate piezoelectric properties, whereby the piezoelectric material of the present invention can be manufactured. For example, when the piezoelectric material of the present invention is a piezoelectric film, the composition for a piezoelectric material of the present invention may be applied onto the surface of a substrate to manufacture a piezoelectric film, and the piezoelectric film may be peeled off from the substrate to form a film or a sheet. Further, for example, when the piezoelectric material of the present invention is a piezoelectric wire, the composition for a piezoelectric material 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.

[0085] The method of drying the applied composition for a piezoelectric material of the present invention is not particularly limited, and it may be dried by heating at a temperature at which the solvent evaporates under atmospheric pressure conditions or reduced pressure conditions, etc. For example, it is preferable to perform drying at a temperature of 15 to 80°C.

[0086] The temperature of the heat treatment in manufacturing the piezoelectric material of the present invention is preferably equal to or higher than the Curie point and equal to or lower than the melting point of polyvinylidene fluoride. The heating time is preferably 30 minutes or longer, more preferably 2 hours or longer. By performing such heat treatment, polyvinylidene fluoride can be crystallized.

[0087] The piezoelectric material of the present invention may be a piezoelectric film, a piezoelectric wire, or a piezoelectric block. As described above, since the piezoelectric material of the present invention has certain piezoelectric properties without performing a stretching treatment, it is particularly suitable for use in forming a piezoelectric material on the surface of a substrate by applying the composition for a piezoelectric material of the present invention to the above-described substrate or the like. That is, one aspect of the piezoelectric material of the present invention is an aspect in which no stretching treatment is performed, and one aspect of the method for manufacturing the piezoelectric material of the present invention is an aspect in which no stretching treatment is performed on a cured product or the like of the composition for a piezoelectric material in the manufacturing process.

[0088] The piezoelectric material of the present invention containing polyvinylidene fluoride and the specific (meth)acrylic polymer can exhibit piezoelectric properties even in a higher temperature range as compared with a piezoelectric material not containing the specific (meth)acrylic polymer. A piezoelectric material mainly composed of polyvinylidene fluoride needs to be subjected to a stretching treatment or to be applied with a high voltage in order to obtain piezoelectric properties when not containing the specific (meth)acrylic polymer. In particular, in order to obtain a piezoelectric material having high piezoelectric properties, the force applied in the stretching treatment has to be increased. In that case, however, in order to prevent the orientation due to the stretching treatment from being lost, the upper limit of the temperature at which the piezoelectric material can be used tends to be lowered. Also, 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 without performing a stretching treatment. 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 a high-temperature range such as, for example, 60°C to 150°C, 60°C to 120°C, 60°C to 110°C, etc. Further, since poling treatment can be performed without necessarily applying a relatively high voltage, the possibility of other properties of the piezoelectric material being degraded is also low. Note that, for a piezoelectric material used at a high temperature as described above, relatively high piezoelectric properties may not be required in some cases.

[0089] The piezoelectric properties of the piezoelectric material of the present invention can be represented, for example, by the piezoelectric constant d 33 . The piezoelectric material of the present invention only needs to be such that the piezoelectric constant d 33 can be significantly observed in the measurement method of the piezoelectric constant d 33 described in the examples to be described later. This is because if the piezoelectric constant d 33 can be significantly observed in the measurement method of the piezoelectric constant d 33 described in the examples to be described later, it can be evaluated that the piezoelectric material has sufficient piezoelectric properties depending on the use 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.

[0090] The piezoelectric material of the present invention is particularly suitable as a member of sensors such as touch sensors, acceleration sensors, vibration sensors, ultrasonic sensors, a member of a strain gauge, a member of a transducer, and the like.

Example

[0091] Next, the present invention will be described in more detail with reference to examples. However, these examples are for explaining the present invention and do not limit the present invention in any way. Also, unless otherwise specified, “%” and “parts” in the examples mean “mass %” and “parts by mass”, respectively.

[0092] (Weight average molecular weight) The weight average molecular weight was measured by gel permeation chromatography (GPC). Specifically, a 0.5 mass % solution obtained by dissolving a (meth)acrylic polymer in tetrahydrofuran was used as a measurement sample. The measurement conditions are as follows. Equipment: Manufactured by Tosoh Corporation, product number: HLC-8320GPC Column: Manufactured by Tosoh Corporation, product numbers: TSKgel G5000H and TSKgel G3000H Eluent: Tetrahydrofuran Flow rate: 1.0 mL / min Temperature: 40 °C Detector: RI Molecular weight standard: Standard polystyrene

[0093] Production Example 1: Preparation of (meth)acrylic polymer B1 (Poly-3FPMA) (1) Preparation of 3,3,3-trifluoropropyl methacrylate (3FPMA) In a 1 L five-necked glass 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. While stirring on an ice bath, 44.1 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (hereinafter referred to as EDC) was added, and stirring was continued for 10 hours. The resulting reaction mixture was washed with water, concentrated, and then purified by distillation under reduced pressure to obtain 21.9 g of 3,3,3-trifluoropropyl methacrylate (3FPMA) as a colorless transparent liquid (GC purity; 99%, yield; 55%). [Chemical formula] 1H-NMR (CDCl3, ppm) of 3FPMA: 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)

[0094] (2) Preparation of (meth)acrylic polymer B1 (Poly-3FPMA) The 3FPMA synthesized as described above was polymerized by the following procedure to produce a (meth)acrylic polymer B1 (Poly-3FPMA). In a 30 mL glass container, 0.22 g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (trade name "Irgacure TPO" manufactured by BASF, hereinafter referred to as "TPO") as a polymerization initiator was dissolved in 22.1 g of 3FPMA produced in (1) above to obtain a mixture containing 3FPMA and the polymerization initiator. After injecting the mixture of TPO and 3FPMA into a transparent glass mold (length: 100 mm, width: 100 mm, depth: 4 mm), the mixture was irradiated with ultraviolet light (irradiation dose: 1.0 mW / m 2 ) to polymerize 3FPMA and obtain a (meth)acrylic polymer B1 (Poly-3FPMA). When the weight average molecular weight (Mw) of the obtained Poly-3FPMA was measured by GPC, it was 294,000. [Chemistry]

[0095] Production Example 2: Preparation of (Meth)acrylic Polymer B2 (Poly-3FPMA) 3.0 g of 3FPMA produced in the above (1) and 7.0 g of butyl acetate were added to a 50 mL glass flask equipped with a nitrogen inlet tube, a thermometer, and a stirrer, and stirred to obtain a mixed solution. After introducing nitrogen from the nitrogen inlet tube into this mixed solution for 30 minutes, the temperature inside 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 adding AIBN, the temperature inside the flask was maintained at 80 °C for 5.5 hours with stirring, and then cooled to 35 °C or lower. The solution inside the flask was taken out to obtain (meth)acrylic polymer B2 (Poly-3FPMA). When the weight average molecular weight (Mw) of the obtained Poly-3FPMA was measured by GPC, it was 16,000. [Chemistry]

[0096] Production Example 3: Preparation of (Meth)acrylic Polymer B3 (Poly-3FEMA) (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 Co., Ltd., trade name: Biscoat 3FEMA) was used instead of 3FPMA. When the weight average molecular weight (Mw) of the obtained Poly-3FEMA was measured by GPC, it was 15,000. [Chemistry]

[0097] Production Example 4: Preparation of (Meth)acrylic Polymer B4 (Poly-8FM) Instead of 3FPMA, a (meth)acrylic polymer B4 (Poly-8FM) was obtained in the same manner as in Production Example 2, except that 1H,1H,5H-octafluoropentyl methacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name: Biscoat 8FM) was used. When the weight average molecular weight (Mw) of the obtained Poly-8FM was measured by GPC, it was 20,000.

Chemical formula

[0098] Production Example 5: Preparation of (meth)acrylic polymer B5 (Poly-(3FPMA / EA)) A (meth)acrylic polymer B5 (Poly-(3FPMA / EA)) was obtained in the same manner as in Production Example 1, except that the composition of the mixture containing the polymerization initiator was changed to 3.40 g of ethyl acrylate (EA), 24.75 g of 3FPMA, and 0.28 g of TPO. When the weight average molecular weight (Mw) of the obtained Poly-(3FPMA / EA) was measured by GPC, it was 320,000.

Chemical formula

[0099] Production Example 6: Preparation of (meth)acrylic polymer B6 (Poly-FMA) 1.51 g of methyl 2-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, nitrogen was introduced into the contents from the nitrogen inlet tube for 30 seconds of bubbling, and then 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 a (meth)acrylic polymer B6 (Poly-FMA). When the weight average molecular weight (Mw) of the obtained Poly-FMA was measured by GPC, it was 210,000.

Chemical formula

[0100] Production Example 7: Preparation of (Meth)acrylic Polymer B7 (Poly-MMA) A (meth)acrylic polymer B7 (Poly-MMA) was obtained in the same manner as in Production Example 2, except that methyl methacrylate (MMA) was used instead of 3FPMA. When the weight-average molecular weight (Mw) of the obtained Poly-MMA was measured by GPC, it was 16,000. [Chemical formula]

[0101] Production Example 8: Preparation of (Meth)acrylic Polymer B8 (Poly-EA) A (meth)acrylic polymer B8 (Poly-EA) was obtained in the same manner as in Production Example 2, except that EA was used instead of 3FPMA. When the weight-average molecular weight (Mw) of the obtained Poly-EA was measured by GPC, it was 20,000. [Chemical formula]

[0102] Example 1: Production of Composition 1 for Piezoelectric Material and Piezoelectric Material 1 0.75 g of PVDF-A1 (PVDF manufactured by Aldrich, weight-average molecular weight 500,000 - 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 Composition 1 for piezoelectric material containing vinylidene fluoride A1 and (meth)acrylic polymer B1 in the mass ratio shown in Table 1.

[0103] The piezoelectric material composition 1 manufactured as described above was applied onto a glass substrate using an applicator, left standing for 30 seconds, then dried in a warm air dryer at 70°C for 20 minutes, and thereafter, the temperature of the warm air dryer was set to 160°C and dried for 1 hour, and then slowly cooled to room temperature to form a film. When the thickness of the film was measured using a stylus profiler system (manufactured by Bruker, product name: Dektak150), it was 30 μm. Thereafter, the film was peeled off from the glass substrate.

[0104] Next, the above-mentioned film was placed in a resistance heating type vacuum evaporator (manufactured by Cryovac, product name: RVC-2-ICP,), and gold was thermally evaporated onto both sides of the film at a pressure of 2×10 -4 Pa or less to form electrodes. A triangular wave alternating current with an electric field amplitude of 150 MV / m and a frequency of 0.1 Hz was applied to the film with electrodes formed on both sides thus obtained using a high voltage device (manufactured by Matsueda Precision Co., Ltd., product name: HEOPS-1B30) to fabricate the piezoelectric material 1.

[0105] The piezoelectric constant d of the film of the piezoelectric material 1 according to Example 1 33 was measured using a piezoelectric constant measuring device (manufactured by Lead Techno, product name: LPF-02). Specifically, the measurement was performed according to the following procedure. (1) The piezoelectric material 1 was clamped with a measuring element. (2) The load applied by the measuring element to the piezoelectric material 1 was set to 1 N and left standing. (3) The load applied from the measuring element to the piezoelectric material 1 was increased by 3 N and set so that the load applied from the measuring element to the piezoelectric material 1 film became 4 N. (4) The amount of charge generated at the moment when a force of 4 N was applied was measured. (5) The load applied from the measuring element to the piezoelectric material 1 was decreased by 3 N to 1 N. (6) The above (3) to (5) were performed 4 times, and the average value of the measured values of the charge amount measured in the 2nd to 4th times was taken as the charge amount of the piezoelectric material 1, and this average charge amount was divided by the measurement load (4 N) to calculate the piezoelectric constant d 33 of the piezoelectric material 1. The obtained results are shown in a table.

[0106] 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. Table 1 shows the results of the same measurements performed on the obtained piezoelectric material. Note that PVDF-A2 is PVDF (weight average molecular weight 250,000 to 280,000) manufactured by Kureha Corporation. Also, the ratios in Table 1 represent the ratios of PVDF and the (meth)acrylic polymer in the entire piezoelectric material by weight %, and d 33 In the N.D. for represents less than the measurement limit value.

[0107] Furthermore, in some of the examples, the piezoelectric constant of the stretched piezoelectric material was measured. Specifically, first, a PET film was placed on a hot plate set at 150°C, and the piezoelectric material was placed on this PET film and heated for 10 minutes. Then, the piezoelectric material was stretched by hand, and the piezoelectric constant d 33 of the piezoelectric material cooled to room temperature was measured by the same method as above. The piezoelectric constant of the stretched piezoelectric material is the value shown in parentheses in Table 1.

[0108]

Table 1

[0109] Example 12 Piezoelectric material 12 was adjusted from a composition for a piezoelectric material with A1:B1 = 75:25 in the same manner as in Example 1, except for the following changes. (1) Instead of DMF, it was dissolved in 5.7 g of N-methylpyrrolidone (NMP) as the solvent, and the solid content was set to 15%. (2) In forming the film, instead of a glass substrate, a stainless steel substrate was used, and it was dried under reduced pressure at 110°C for 2 hours using a vacuum dryer. Then, the temperature of the hot air dryer was set to 190°C, and the film (film thickness: about 40 μm) was annealed by standing for 4 hours. (3) Electrodes were not formed on both sides of the film. As a high-voltage device, after applying a DC voltage of -19 kV for 30 minutes instead of triangular-wave alternating current using an electret processing device (manufactured by Wedge Co., Ltd.), the film was peeled off from a stainless-steel substrate and used as the piezoelectric material 12. <Measurement of piezoelectric constant d 33 > For the piezoelectric material 12, the piezoelectric constant d was measured in the same manner as in Example 1 and the like. 33 As a result of the measurement, the d of the piezoelectric material 12 33 was 7.3 pC / N.

[0110] It was confirmed that the piezoelectric materials of the present invention containing polyvinylidene fluoride and specific (meth)acrylic polymers shown in Examples 1 to 12 have piezoelectric properties without undergoing stretching treatment. 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 a specific (meth)acrylic polymer did not exhibit piezoelectric properties.

Claims

1. Polyvinylidene fluoride, and Formula (I): 【Chemical 1】 [Wherein, R １ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, where at least one hydrogen atom of R １ may be substituted with a halogen atom, R ２ 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, Here, 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 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; R ２ At least one hydrogen atom of which may be substituted with a halogen atom, However, R １ and / or R ２ in which at least one hydrogen atom thereof is substituted with a halogen atom) A (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer represented by A piezoelectric material, wherein the amount of polyvinylidene fluoride is 60 to 99% by mass based on the total weight of polyvinylidene fluoride and the (meth)acrylic polymer contained in the piezoelectric material.

2. The piezoelectric material according to Claim 1, wherein the amount of polyvinylidene fluoride is 99 to 60% by mass based on the entire piezoelectric material, and the amount of the (meth)acrylic polymer is 1 to 40% by mass based on the entire piezoelectric material.

3. A piezoelectric film containing the piezoelectric material according to Claim 1 or 2.

4. Polyvinylidene fluoride, and Formula (I): 【Chemical Formula 2】 [Wherein, R １ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, where at least one hydrogen atom of R １ may be substituted with a halogen atom. R ２ represents a linear or branched alkyl group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms containing an alicyclic structure having 3 to 6 carbon atoms, a phenyl group, or a phenylalkylene group containing an alkylene group having 1 to 4 carbon atoms, Here, 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 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; R ２ At least one hydrogen atom of which may be substituted with a halogen atom, However, R １ and / or R ２ in which at least one hydrogen atom is substituted with a halogen atom) A (meth)acrylic monomer represented by and / or a (meth)acrylic polymer containing a structural unit derived from the (meth)acrylic monomer A composition for a piezoelectric material containing the same, wherein the amount of the polyvinylidene fluoride is 60 to 99% by mass based on the total weight of the polyvinylidene fluoride, the (meth)acrylic monomer, and the (meth)acrylic polymer containing structural units derived from the (meth)acrylic monomer in the composition for a piezoelectric material.

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