JP2009253050A - Electret and electrostatic induction type conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electret excellent in thermal stability of an electric charge and to provide an electrostatic induction type conversion device with the electret. <P>SOLUTION: The electret includes a layer comprising organic/inorganic composite materials containing organic high molecules and inorganic fine particles having a relative permittivity of 2.0 to 4.0&times;10<SP>3</SP>. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electret and an electrostatic induction conversion element including the electret.

Conventionally, electrostatic induction type conversion elements such as power generation devices and microphones using an electret in which an electric charge is injected into an insulating material have been proposed.
As such an electret material, a chain-like fluorine-containing resin such as polytetrafluoroethylene has been mainly used. Recently, it has been proposed to use a polymer having a fluorinated aliphatic ring structure in the main chain as the material of the electret (for example, Patent Document 1).
JP 2006-180450 A

However, the conventional electret has a problem that the injected charge has insufficient thermal stability and has low charge retention characteristics at high temperatures. Such a problem causes deterioration of the characteristics of the electrostatic induction conversion element using the electret, and hence improvement is required.
This invention is made | formed in view of the said conventional subject, and makes it a subject to provide the electret excellent in the thermal stability of an electric charge, and an electrostatic induction type conversion element provided with this electret.

The first aspect of the present invention that solves the above-described problems has a layer made of an organic-inorganic composite material containing an organic polymer and inorganic fine particles having a relative dielectric constant of 2.0 to 4.0 × 10 ^3. Is an electret characterized by
2nd aspect of this invention is an electrostatic induction type conversion element provided with the electret of said 1st aspect.

  ADVANTAGE OF THE INVENTION According to this invention, the electrostatic induction type conversion element provided with the electret excellent in the thermal stability of an electric charge and this electret can be provided.

Hereinafter, the best mode for carrying out the present invention will be described.
In the following specification, the “repeating unit” constituting the polymer may be abbreviated as “unit”.
The unit represented by the formula (a1) is also referred to as “unit (a1)”. The same applies to units, compounds and the like represented by other formulas. For example, the monomer represented by formula (1) is also referred to as “monomer (1)”.

<Organic inorganic composite material>
The electret of the present invention has a layer made of an organic-inorganic composite material containing an organic polymer and inorganic fine particles. The organic-inorganic composite material can contain a dispersion aid as required.

[Organic polymer]
The organic polymer is preferably selected from the following viewpoints.
(I) Having high insulating properties Organic polymers having a high volume resistivity and a high dielectric breakdown voltage are preferably used. The volume resistivity of the polymer compound (a) is preferably 10 ¹⁰ to 10 ²⁰ Ωcm, and more preferably 10 ¹⁶ to 10 ¹⁹ Ωcm. The volume resistivity is measured according to ASTM D257.
Moreover, 10-25 kV / mm is preferable and, as for the dielectric breakdown voltage of a high molecular compound (a), 15-22 kV / mm is more preferable. The breakdown voltage is measured according to ASTM D149.
In order to maintain a high insulating property, it is preferable to be hydrophobic in order to eliminate water that adversely affects the insulating property.

Examples of highly hydrophobic organic polymers include fluorine-containing resins, polymers having an aliphatic ring structure in the main chain, polyethylene, polypropylene, polystyrene, polyurethane, polydimethylsiloxane, polyethylene terephthalate, polycarbonate, and the like.
Among them, those containing a fluorine atom, those having an aliphatic ring structure in the main chain, and those having both are preferably used.
Here, “aliphatic ring structure” refers to a ring structure having no aromaticity. Examples of the aliphatic ring structure include a saturated or unsaturated hydrocarbon ring structure which may have a substituent, and some of the carbon atoms in the hydrocarbon ring structure are heteroatoms such as an oxygen atom and a nitrogen atom. Examples thereof include a substituted heterocyclic structure, a fluorine-containing aliphatic ring structure in which a hydrogen atom in the hydrocarbon ring structure or the heterocyclic structure is substituted with a fluorine atom, and the like.
Further, “having an aliphatic ring structure in the main chain” means that at least one of carbon atoms constituting the aliphatic ring structure is a carbon atom constituting the main chain of the polymer.

(Ii) Obtaining a stable organic-inorganic composite material The organic polymer is preferably excellent in dispersibility of inorganic fine particles so that a stable organic-inorganic composite material can be obtained.
In order to improve the dispersibility of the inorganic fine particles, the organic polymer preferably has a polar functional group at the end of the main chain and / or side chain. By using an organic polymer having a polar functional group at the end of the main chain and / or side chain, specifically, the following effects can be obtained.
(A) When the polar functional group is directly bonded or adsorbed to the surface of the inorganic fine particles, the organic polymer as a matrix functions simultaneously as a dispersant, and the nano-sized inorganic fine particles are uniformly distributed in the organic polymer. A dispersed organic-inorganic composite material is formed.
(B) Since the organic polymer functions as a dispersant, the amount of the dispersion aid used can be reduced.

In addition, if a highly hydrophobic organic polymer is used, the difference in affinity between the organic polymer solution and the dispersion of inorganic fine particles using a dispersion medium that can be phase-separated with the solvent of the solution, such as water, should be used. Thus, an organic-inorganic composite material can be easily manufactured.
That is, a highly hydrophobic organic polymer is preferable from the viewpoint of obtaining high insulating properties and a stable organic-inorganic composite material.
Among these, when a fluorine-containing resin is used, a fluorine-containing organic solvent can be used as a solvent for the fluorine-containing resin. In that case, an organic-inorganic composite material can be produced using an organic solvent other than the fluorine-containing organic solvent as a dispersion medium for the inorganic fine particles. In particular, it is preferable to avoid the use of water as a dispersion medium for the inorganic fine particles because the insulating property of the organic-inorganic composite material can be easily maintained.

From the above viewpoint, the main chain of the organic polymer preferably has an aliphatic ring structure or preferably contains fluorine, and more preferably has a fluorine-containing aliphatic ring structure. Specifically, the following (α) to (γ) are preferable, and (α) is particularly preferable.
(Α) A polymer having a fluorinated aliphatic ring structure in the main chain (hereinafter referred to as “fluorinated cyclic polymer”).
(Β) A polymer having an aliphatic hydrocarbon ring structure in the main chain (hereinafter referred to as “cycloolefin polymer”).
(Γ) Fluorinated resin having no aliphatic ring structure in the main chain (hereinafter referred to as “acyclic fluorinated resin”)
In any case of (α) to (γ), those having a polar functional group at the end of the main chain and / or side chain are preferred.
Therefore, an organic polymer which is a fluorine-containing cyclic polymer and has a polar functional group at the end of the main chain and / or side chain is particularly preferred.
Hereinafter, each of “fluorinated cyclic polymer”, “cycloolefin polymer”, “acyclic fluoropolymer”, and “polar functional group” at the end of the main chain and / or side chain will be described in detail.

(Fluorine-containing cyclic polymer)
The “fluorinated cyclic polymer” is a fluoropolymer having a fluorinated aliphatic ring structure in the main chain as described above, and at least one of the carbon atoms constituting the fluorinated aliphatic ring structure is the fluorinated polymer. What is a carbon atom which comprises the principal chain of a fluoropolymer.
Of the carbon atoms constituting the fluorinated alicyclic structure, the carbon atoms constituting the main chain are derived from the polymerizable double bond of the monomer constituting the fluorinated polymer.
For example, when the fluorine-containing polymer is a fluorine-containing polymer obtained by polymerizing a cyclic monomer as described later, two carbon atoms constituting the double bond and a carbon atom constituting the main chain Become.
Further, in the case of a fluorinated polymer obtained by cyclopolymerizing a monomer having two polymerizable double bonds, among the four carbon atoms constituting the two polymerizable double bonds At least two are carbon atoms constituting the main chain.
As the fluorine-containing aliphatic ring structure, the ring skeleton may be composed only of carbon atoms, or may be a heterocyclic structure containing hetero atoms such as oxygen atoms and nitrogen atoms in addition to carbon atoms. . The fluorine-containing aliphatic ring is preferably a fluorine-containing aliphatic ring having 1 to 2 oxygen atoms in the ring skeleton.
The number of atoms constituting the ring skeleton of the fluorine-containing aliphatic ring structure is preferably 4 to 7. That is, the fluorine-containing aliphatic ring structure is preferably a 4- to 7-membered ring.

Preferred fluorine-containing cyclic polymers include the following fluorine-containing cyclic polymers (I ′) and fluorine-containing cyclic polymers (II ′).
Fluorine-containing cyclic polymer (I ′): a polymer having units based on a cyclic fluorine-containing monomer.
Fluorine-containing cyclic polymer (II ′): a polymer having units formed by cyclopolymerization of a diene fluorine-containing monomer.

The fluorinated cyclic polymer (I ′) has units based on “cyclic fluorinated monomer”. “Cyclic fluorine-containing monomer” means a monomer having a polymerizable double bond between carbon atoms constituting a fluorine-containing aliphatic ring, or a carbon atom constituting a fluorine-containing aliphatic ring and a fluorine-containing fat. It is a monomer having a polymerizable double bond with a carbon atom outside the group ring.
As the cyclic fluorine-containing monomer, the following compound (1) or compound (2) is preferable.

In the formula, X ¹¹ , X ¹² , X ¹³ , X ¹⁴ , Y ¹¹ and Y ¹² are each independently a fluorine atom, a perfluoroalkyl group or a perfluoroalkoxy group.
The perfluoroalkyl group in X ¹¹ , X ¹² , X ¹³ , X ¹⁴ , Y ¹¹ and Y ¹² preferably has 1 to 7 carbon atoms, and more preferably 1 to 4 carbon atoms. The perfluoroalkyl group is preferably linear or branched, and more preferably linear. Specific examples include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, and the like, and a trifluoromethyl group is particularly preferable.
Examples of the perfluoroalkoxy group in X ¹¹ , X ¹² , X ¹³ , X ¹⁴ , Y ¹¹ and Y ¹² include those in which an oxygen atom (—O—) is bonded to the perfluoroalkyl group.
X ¹¹ is preferably a fluorine atom.
X ¹² is preferably a fluorine atom, a trifluoromethyl group, or a perfluoroalkoxy group having 1 to 4 carbon atoms, more preferably a fluorine atom or a trifluoromethoxy group.
X ¹³ and X ¹⁴ are each independently preferably a fluorine atom or a C 1-4 perfluoroalkyl group, more preferably a fluorine atom or a trifluoromethyl group.
Y ¹¹ and Y ¹² are each independently preferably a fluorine atom, a perfluoroalkyl group having 1 to 4 carbon atoms, or a perfluoroalkoxy group having 1 to 4 carbon atoms, and more preferably a fluorine atom or a trifluoromethyl group.

In the compound (1), X ¹³ and X ¹⁴ may be bonded to each other to form a fluorine-containing aliphatic ring together with the carbon atom to which X ¹³ and X ¹⁴ are bonded.
As this fluorine-containing aliphatic ring, a 4-6 membered ring is preferable.
The fluorine-containing aliphatic ring is preferably a saturated aliphatic ring.
The fluorine-containing aliphatic ring may have an etheric oxygen atom (—O—) in the ring skeleton. In this case, the number of etheric oxygen atoms in the fluorine-containing aliphatic ring is preferably 1 or 2.
In the compound (2), Y ¹¹ and Y ¹² may be bonded to each other to form a fluorine-containing aliphatic ring together with the carbon atom to which Y ¹¹ and Y ¹² are bonded.
As this fluorine-containing aliphatic ring, a 4-6 membered ring is preferable.
The fluorine-containing aliphatic ring is preferably a saturated aliphatic ring.
The fluorine-containing aliphatic ring may have an etheric oxygen atom (—O—) in the ring skeleton. In this case, the number of etheric oxygen atoms in the fluorine-containing aliphatic ring is preferably 1 or 2.
Preferable specific examples of compound (1) include compounds (1-1) to (1-5).
Preferable specific examples of compound (2) include compounds (2-1) to (2-2).

The fluorine-containing cyclic polymer (I ′) may be a homopolymer of the above-mentioned cyclic fluorine-containing monomer, and a copolymer of the cyclic fluorine-containing monomer and other monomers It may be.
However, the proportion of the units based on the cyclic fluorinated monomer in the fluorinated cyclic polymer (I ′) is 20 mol with respect to the total of all repeating units constituting the fluorinated cyclic polymer (I ′). % Or more is preferable, 40 mol% or more is more preferable, and 100 mol% may be sufficient.
The other monomer is not particularly limited as long as it is copolymerizable with the cyclic fluorine-containing monomer. Specific examples include diene fluorine-containing monomers described later, tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), and the like.

The fluorinated cyclic polymer (II ′) has units formed by cyclopolymerization of the “diene fluorinated monomer”. The “diene fluorine-containing monomer” is a monomer having two polymerizable double bonds and fluorine atoms. Although it does not specifically limit as this polymerizable double bond, A vinyl group, an allyl group, an acryloyl group, and a methacryloyl group are preferable.
As the diene fluorine-containing monomer, the compound (3) is preferable.
_{CF 2 = CF-Q-CF} = CF 2 ··· (3).
In formula, Q is a C1-C3 perfluoroalkylene group which may have an etheric oxygen atom and in which a part of the fluorine atom may be substituted with a halogen atom other than the fluorine atom. Examples of halogen atoms other than fluorine include chlorine atom and bromine atom.
When Q is a perfluoroalkylene group having an etheric oxygen atom, the etheric oxygen atom in the perfluoroalkylene group may be present at one end of the group, and is present at both ends of the group. Or may be present between the carbon atoms of the group. From the viewpoint of cyclopolymerizability, it is preferably present at one end of the group.
Examples of the unit formed by the cyclopolymerization of the compound (3) include repeating units of the following formulas (3-1) to (3-4).

Specific examples of the compound (3) include the following compounds.
CF ₂ = CFOCF ₂ CF = CF ₂ ,
CF ₂ = CFOCF (CF ₃ ) CF═CF ₂ ,
CF ₂ = CFOCF ₂ CF ₂ CF = CF ₂ ,
CF ₂ = CFOCF ₂ CF (CF ₃ ) CF═CF ₂ ,
CF ₂ = CFOCF (CF ₃ ) CF ₂ CF = CF ₂ ,
CF ₂ = CFOCFClCF ₂ CF = CF ₂ ,
_{CF 2 = CFOCCl 2 CF 2 CF} = CF 2,
CF ₂ = CFOCF ₂ OCF = CF ₂ ,
_{CF 2 = CFOC (CF 3)} 2 OCF = CF 2,
CF ₂ = CFOCF ₂ CF (OCF ₃ ) CF═CF ₂ ,
CF ₂ = CFCF ₂ CF = CF ₂ ,
CF ₂ = CFCF ₂ CF ₂ CF = CF ₂ ,
_{CF 2 = CFCF 2 OCF 2 CF} = CF 2.

The fluorinated cyclic polymer (II ′) may be composed only of units formed by cyclopolymerization of the diene-based fluorinated monomer, and a copolymer having the units and other units. It may be a polymer.
However, the proportion of the units formed by cyclopolymerization of the diene-based fluorinated monomer in the fluorinated cyclic polymer (II ′) is the total number of repeating units constituting the fluorinated cyclic polymer (II ′). Is preferably 50 mol% or more, more preferably 80 mol% or more, and most preferably 100 mol%.
The other monomer is not particularly limited as long as it is copolymerizable with the diene fluorine-containing monomer. Specific examples include cyclic fluorine-containing monomers such as the above-mentioned compound (1) and compound (2), tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether) and the like.

(Cycloolefin polymer)
The “cycloolefin polymer” is a polymer having an aliphatic hydrocarbon ring structure in the main chain as described above, and at least two of the carbon atoms constituting the aliphatic hydrocarbon ring structure are the main chain of the polymer. Means something built into
The cycloolefin polymer has a unit having an aliphatic hydrocarbon ring structure (hereinafter sometimes referred to as a unit (a1)), and the unit (a1) constitutes the aliphatic hydrocarbon ring structure. At least two of the carbon atoms to be incorporated into the main chain of the polymer.
Preferred examples of the cycloolefin polymer include those containing the unit (a1-1).

[Wherein, R is a divalent hydrocarbon group which may have a substituent, m is an integer of 0 to 10, r is 0 or 1, and s is 0 or 1. ]

In formula (a1-1), the hydrocarbon group of R “may have a substituent” means that part or all of the hydrogen atoms of the hydrocarbon group may be substituted with a substituent. Means that.
Examples of the substituent include an aryl group such as an alkyl group, a cycloalkyl group, an alkoxy group, and a phenyl group, and a polycyclic aliphatic hydrocarbon group such as an adamantyl group.
The alkyl group as a substituent may be linear or branched, and preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms. As the alkyl group, a methyl group, an ethyl group, a propyl group, and an isopropyl group are preferable, and a methyl group and an ethyl group are particularly preferable.
The cycloalkyl group as a substituent preferably has 3 to 10 carbon atoms, and more preferably 5 to 8 carbon atoms. As the cycloalkyl group, a cyclopentyl group or a cyclohexyl group is particularly preferable.
Examples of the alkoxy group as a substituent include those in which an oxygen atom (—O—) is bonded to the alkyl group.

The hydrocarbon group for R may be a chain or a ring. The hydrocarbon group may be saturated or unsaturated, and preferably saturated.
The chain hydrocarbon group is preferably a linear alkylene group which may have a substituent, and the number of carbon atoms is preferably 1 to 4, more preferably 2 to 3, and most preferably 2. Specific examples include a dimethylene group.
The cyclic hydrocarbon group is preferably a group obtained by removing two hydrogen atoms from a monocyclic or polycyclic cycloalkane which may have a substituent. Examples of monocyclic cycloalkanes include cyclopentane and cyclohexane. Examples of the polycyclic cycloalkane include norbornane and adamantane. Among these, cyclopentane or norbornane is preferable.

In formula (a1-1), m is an integer of 0-10.
When m is an integer of 1 or more, as in the unit (a1-11) described later, the polymer main chain is not an ortho-position of the aliphatic hydrocarbon ring structure, but is bonded with one or more methylene chains. As a result, the aliphatic hydrocarbon ring structure is incorporated into the polymer main chain. In this case, m is preferably 1 to 3, and most preferably 1.
When m is 0, the aliphatic hydrocarbon ring structure is incorporated into the polymer main chain by bonding the polymer main chain to the ortho position of the aliphatic hydrocarbon ring structure as in the unit (a1-21) described later. It is.
r and s may each be 0 or 1.
In particular, when m is 0, r and s are preferably 0. When m is 1, r and s are preferably 1.

  Preferred examples of the unit (a1-1) include the following units (a1-11) and units (a1-21).

[Wherein, R ¹ and R ² are each independently a hydrogen atom, an alkyl group or a cycloalkyl group, and R ¹ and R ² may be bonded to each other to form a ring. ]

[Wherein, R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group or a cycloalkyl group, and R ³ and R ⁴ may be bonded to each other to form a ring. ]

In formula (a1-11), examples of the alkyl group and cycloalkyl group in R ¹ and R ² include the same groups as those described above as the alkyl group and cycloalkyl group as the substituent.
R ¹ and R ² may be bonded to each other to form a ring together with the carbon atom to which R ¹ and R ² are bonded. In this case, the ring formed is preferably a monocyclic or polycyclic cycloalkane. Examples of monocyclic cycloalkanes include cyclopentane and cyclohexane. Examples of the polycyclic cycloalkane include norbornane and adamantane. Among these, cyclopentane or norbornane is preferable.
The ring may have a substituent. Examples of the substituent include the same as those described as the substituent that the hydrocarbon group of R may have.
Specific examples of the unit (a1-11) when R ¹ and R ² form a ring include the following unit (a1-11-1) and unit (a1-12-1).

[Wherein, R ¹¹ represents a hydrogen atom or an alkyl group. ]

Examples of the alkyl group for R ¹¹ include the same alkyl groups as the substituents that the hydrocarbon group for R may have, and a methyl group is particularly preferable.
In the present invention, the unit (a1-11) is preferably ^one in which R ¹ and R ² form a ring, or ^one in which at least one of R ¹ and R ² is a cycloalkyl group.

In formula (a1-21), R ³ and R ⁴ are the same as R ¹ and R ² , respectively.
Specific examples of the unit (a1-21) when R ³ and R ⁴ form a ring include the following unit (a1-21-1) and unit (a1-21-2).

[Wherein R ¹³ represents a hydrogen atom or an alkyl group. ]

Examples of the alkyl group for R ¹³ include the same alkyl groups listed as the substituents that the hydrocarbon group for R may have, and a methyl group is particularly preferable.

A cycloolefin polymer may contain any 1 type in the above units as a unit (a1), and may contain 2 or more types.
In the cycloolefin polymer, the proportion of the unit (a1) is preferably at least 30 mol%, more preferably at least 40 mol%, even if it is 100 mol%, based on the total of all repeating units constituting the cycloolefin polymer. Good.

The cycloolefin polymer may contain units other than the unit (a1) (hereinafter sometimes referred to as unit (a2)).
As the unit (a2), any unit conventionally used in cycloolefin polymers can be used and is not particularly limited.
The unit (a2) is preferably a unit based on an olefin which may have a substituent. Examples of the unit include the following unit (a2-1).

[Wherein R ⁵ represents a hydrogen atom, an alkyl group or an aryl group. ]

In the formula, examples of the alkyl group for R ⁵ include the same alkyl groups as those described above as the substituent that the hydrocarbon group for R may have.
Examples of the aryl group include benzyl group, phenyl group, p-tolyl group, m-tolyl group, p-fluorophenyl group, m-fluorophenyl group, o-fluorophenyl group, p-trifluorophenyl group, m-trifluoro group. A phenyl group, o-trifluorophenyl group, 1-naphthyl group, 2-naphthyl group, etc. are mentioned.

As the cycloolefin polymer used in the present invention, the following cycloolefin polymer (I) and cycloolefin polymer (II) are particularly preferable.
Cycloolefin polymer (I): a cycloolefin polymer containing the unit (a1-11).
Cycloolefin polymer (II): a cycloolefin polymer containing the unit (a1-21) and the unit (a2).

Cycloolefin polymer (I) may contain 1 type as a unit (a1-11), and may contain 2 or more types.
Moreover, the cycloolefin polymer (I) may contain units other than the unit (a1-11) as long as the effects of the present invention are not impaired.
In the cycloolefin polymer (I), the proportion of the units (a1-11) is preferably 80 mol% or more, more preferably 90 mol% or more with respect to the total of all repeating units constituting the cycloolefin polymer (I). 100 mol% is particularly preferred. That is, as the cycloolefin polymer (I), a polymer composed only of the unit (a1-11) is particularly preferable.

Cycloolefin polymer (II) may contain 1 type as a unit (a1-21) and a unit (a2), respectively, and may contain 2 or more types.
Moreover, cycloolefin polymer (II) may contain units other than unit (a1-21) and unit (a2) in the range which does not impair the effect of this invention.
In the cycloolefin polymer (II), the proportion of the unit (a1-21) is preferably from 20 to 70 mol%, preferably from 30 to 50 mol%, based on the total of all repeating units constituting the cycloolefin polymer (II). More preferred. Moreover, 30-80 mol% is preferable with respect to the sum total of all the repeating units which comprise the said cycloolefin polymer (II), and, as for the ratio of a unit (a2), 50-70 mol% is more preferable.
The ratio (molar ratio) of the content of the unit (a1-21) and the unit (a2) in the cycloolefin polymer (II) is unit (a1-21): unit (a2) = 20: 80 to 70: The range of 30 is preferable, and the range of 30:70 to 50:50 is more preferable.
Preferable specific examples of the cycloolefin polymer (II) include copolymers containing two types of units represented by the following formulas (II-1) and (II-2), respectively.

[Wherein, R ¹³ and R ⁵ are the same as defined above. ]

As the cycloolefin polymer, a commercially available one may be used or synthesized.
The following (1) to (7) are known as methods for synthesizing cycloolefin polymers.
(1) A method of addition copolymerization of norbornenes and olefin (for example, a method shown in the following reaction formula (1 ′)).
(2) A method of hydrogenating a ring-opening metathesis polymer of norbornene (for example, a method shown in the following reaction formula (2 ′)).
(3) A method of transannular polymerization of alkylidene norbornene (for example, a method shown in the following reaction formula (3 ′)).
(4) A method of addition polymerization of norbornene (for example, a method shown in the following reaction formula (4 ′)).
(5) A method of hydrogenating 1,2- and 1,4-addition polymers of cyclopentadiene (for example, a method shown in the following reaction formula (5 ′)).
(6) A method of hydrogenating 1,2- and 1,4-addition polymers of cyclohexadiene (for example, a method shown in the following reaction formula (6 ′)).
(7) A method of cyclopolymerizing a conjugated diene (for example, a method shown in the following reaction formula (7 ′)).

In each reaction formula, R ^{1 to} R ⁵ are the same as described above.
R ^{6 to} R ⁷ are each independently an alkyl group, and examples of the alkyl group include the same alkyl groups listed as the substituents that the hydrocarbon group of R may have.

Among these, cycloolefin polymers obtained by the method (1) (addition copolymers of norbornenes and olefins) and cycloolefin polymers obtained by the method (2) (ring-opening metathesis polymers of norbornenes) Hydrogenated polymer) is preferable from the viewpoint of excellent film forming property and easy synthesis.
Examples of the norbornene addition copolymer include those sold under the trade names of Apel (registered trademark) (manufactured by Mitsui Chemicals) and TOPAS (registered trademark) (manufactured by Ticona).
There are various hydrogenated polymers of ring-opening metathesis polymers of norbornenes, but they have transparency, low hygroscopicity, and heat resistance. Therefore, ZEONEX (registered trademark) (manufactured by Nippon Zeon Co., Ltd.) ), Zeonoa (registered trademark) (manufactured by Nippon Zeon Co., Ltd.), Arton (registered trademark) (manufactured by JSR Co., Ltd.), and polymers sold under the trade names are preferred.

(Non-cyclic fluorine-containing resin)
The “acyclic fluorine-containing resin” refers to a fluorine-containing resin having no aliphatic hydrocarbon ring structure in the main chain as described above.
Examples of non-cyclic fluorine-containing resins include polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer (PFA), and fluoroolefin-alkyl vinyl ether copolymer. A fluoroolefin-vinyl ether copolymer is preferred from the viewpoint that the resin itself is highly amorphous and has excellent dispersibility when an organic-inorganic composite material is used.

  The fluoroolefin-vinyl ether copolymer includes a repeating unit based on a fluoroolefin selected from tetrafluoroethylene and chlorotrifluoroethylene, a repeating unit based on a vinyl ether, and, if necessary, excluding the fluoroolefin and vinyl ether. And a copolymer having a repeating unit based on a monomer (preferably vinyl esters, allyl ethers, allyl esters, isopropenyl ethers or isopropenyl esters).

As vinyl ethers, vinyl ethers having 10 or less carbon atoms such as alkyl vinyl ether, fluoroalkyl vinyl ether, hydroxyalkyl vinyl ether, cycloalkyl vinyl ether, and hydroxycycloalkyl vinyl ether are preferable.
As the vinyl esters, vinyl esters having 10 or less carbon atoms such as vinyl acetate and vinyl pivalate are preferable.
As allyl ethers, alkyl allyl ethers having 10 or less carbon atoms and hydroxyalkyl allyl ethers are preferable.
The isopropenyl ether is preferably an alkyl isopropenyl ether or hydroxyalkyl isopropenyl ether having 10 or less carbon atoms.
As the allyl esters, allyl acetate and the like are preferable.
As isopropenyl esters, acetic acid isopropenyl ester and the like are preferable.

(Polar functional group)
The organic polymer preferably has a polar functional group at the end of the main chain and / or side chain. The polar functional group is any of the following functional groups.
(A) A functional group containing two or more types of atoms having different electronegativity and having polarity due to polarization in the functional group.
(B) A functional group that causes polarization due to a difference in electronegativity with carbon bonded to the functional group.

Specific examples of polar functional groups include carboxy group, sulfo group, phosphono group, amide group, acid halide group, formyl group, amino group, hydroxy group, thiol group, phenol group, silanol group, alkoxy group, alkoxysilyl group. One or more selected from the group consisting of cyano group and the like are preferable.
From the viewpoint of the strength of polarity and ease of introduction to the end of the organic polymer, a carboxy group, a sulfo group, a phosphono group, an acid halide group, a hydroxy group, a thiol group, a silanol group, and an alkoxysilyl group are more preferable. When the inorganic fine particles are metal oxide fine particles, a carboxy group and an alkoxysilyl group are particularly preferable from the viewpoint of high affinity.
Moreover, as a polar functional group, the functional group of the same polarity as the functional group of the below-mentioned dispersion assistant is preferable, and the same functional group as the functional group of the below-mentioned dispersion assistant is more preferable.

The polar functional group is preferably present at the end of the main chain of the organic polymer.
The number of polar functional groups is preferably at least one per molecule of the organic polymer and not more than half of the degree of polymerization of the organic polymer. If the number of polar functional groups is less than half of the degree of polymerization, the organic polymer does not function as a surfactant, so in the production of an organic-inorganic composite material, the step of separating from the dispersion medium of the inorganic fine particle dispersion Does not inhibit phase separation. Moreover, it is easy to maintain the insulating property of the organic polymer.

The above “fluorinated cyclic polymer”, “cycloolefin polymer”, and “acyclic fluororesin” preferably have polar functional groups at the ends of the main chain and / or side chain.
Cytop (registered trademark, manufactured by Asahi Glass Co., Ltd.) may be mentioned as a commercial product of a fluorine-containing cyclic polymer having a polar functional group at the end of the main chain and / or side chain. Examples of commercially available non-cyclic fluorine-containing resins having a polar functional group at the end of the main chain and / or side chain include Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), Lumiflon (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. . Lumiflon is a fluoroolefin-vinyl ether copolymer having a carboxy group at the end of the side chain.
In addition to the above, as a compound having a polar functional group at the end of the main chain and / or side chain, polyether (polyethylene glycol, etc.), polyamide, polyester, polystyrene, polypropylene, acrylic resin, polyurethane, aramid resin, etc. Is mentioned.

The number average molecular weight of the organic polymer is preferably 3,000 to 1,000,000, more preferably 10,000 to 300,000.
The relative dielectric constant of the organic polymer is preferably 1.8 to 8.0, more preferably 1.8 to 5.0, and particularly preferably 1.8 to 3.0.
Usually, when an organic polymer is used alone, the lower the relative dielectric constant, the better the electrical insulation, but if it is too low, the amount of charge that can be stored cannot be sufficiently obtained. In the case of the present invention, by dispersing inorganic fine particles having excellent charge retention characteristics in an insulating organic polymer, the amount of charge that can be stored even when using an organic polymer with high insulating properties (low relative dielectric constant) is obtained. It can be made large enough. Therefore, it is considered that the electret can hold charges more stably and improve the thermal stability of charge holding.

[Inorganic fine particles]
The inorganic fine particles used in the present invention have a relative dielectric constant of 2.0 to 4.0 × 10 ³ , preferably 2.5 to 2.0 × 10 ³ , and 2.5 to 1.5 × 10 ^{3. 3} is more preferable. If the relative dielectric constant is 2.0 or more, the electret is excellent in charge retention characteristics and thermal stability. On the other hand, when the relative dielectric constant is 4.0 × 10 ³ or less, it is possible to prevent a decrease in insulation due to an excessive increase in the dielectric constant of the whole organic-inorganic composite material.
The relative dielectric constant of the inorganic fine particles is preferably 5 or more, more preferably 10 or more, higher than that of the organic polymer. If the difference is 5 or more, the electret is more excellent in charge retention characteristics and thermal stability.

The inorganic fine particles are preferably metal oxide fine particles.
Metal oxides include silicon oxide, titanium oxide, zirconium oxide, aluminum oxide, cerium oxide, tin oxide, manganese dioxide, nickel oxide, cobalt oxide, zinc oxide, iron oxide, barium titanate, strontium titanate, potassium niobate From the viewpoint of charge retention stability and thermal stability as an electret when combined with an organic polymer, silicon oxide, titanium oxide, zirconium oxide, aluminum oxide, cerium oxide, tin oxide, manganese dioxide Nickel oxide, iron oxide or barium titanate is preferred.

  As the inorganic fine particles, inorganic fine particles whose surface is positively charged in an acidic aqueous dispersion are preferable from the viewpoint that an anionic functional group (carboxy group or the like) is easily bonded or adsorbed. Examples of the inorganic fine particles include fine particles of metal oxides (titanium oxide, zirconium oxide, aluminum oxide, cerium oxide, tin oxide, etc.) having an isoelectric point of 4 or more.

The metal oxide fine particles may be fine particles whose surfaces are coated with other metal oxides. The fine particles include silicon oxide fine particles coated with aluminum oxide or the like; low acid resistant metal oxides (cobalt oxide, zinc oxide, etc.) coated with a high acid resistant metal oxide (aluminum oxide, silicon oxide, etc.) .)) And the like. By coating the silicon oxide fine particles with aluminum oxide or the like, the phase is easily transferred to the solvent phase in which the organic polymer exists.
A part of the surface of the inorganic fine particles may be modified with a hydrocarbon group. The modification with the hydrocarbon group is performed, for example, by treating the surface of the inorganic fine particles with a silane coupling agent having a hydrocarbon group. By modifying with a hydrocarbon group, the inorganic fine particles can be phase-shifted to the solvent phase in which the organic polymer is present with less dispersion aid. As a result, since the inorganic fine particles can be dispersed in the organic polymer without impairing the properties of the inorganic fine particles, an organic-inorganic composite material having excellent charge retention stability and thermal stability as an electret can be easily obtained.

The average primary particle diameter of the inorganic fine particles is preferably 2 to 400 nm. If the average primary particle size of the inorganic fine particles is 2 nm or more, the surface area per volume is relatively small, and the dispersibility of the inorganic fine particles in the organic polymer is good even if the amount of the dispersing aid is reduced. It becomes. If the average primary particle diameter of the inorganic fine particles is 400 nm or less, the particle size is sufficiently smaller than the film thickness of the molded body, and there are no irregularities during film formation. can get. Therefore, the average primary particle diameter of the inorganic fine particles is preferably 5 to 100 nm from the viewpoint of reducing the amount of the dispersion aid used and increasing the visible light transmittance.
The average primary particle diameter of the inorganic fine particles is measured by a dynamic scattering method in a dispersion state.

Some inorganic fine particles are not primary particles but some are dispersed in a secondary aggregated state in the dispersion. In the case of the inorganic fine particles, the average secondary particle diameter of the inorganic fine particles is preferably 30 to 120 nm.
The shape of the inorganic fine particles is preferably a shape close to a sphere from the viewpoint of suppressing the specific surface area in order to suppress the use amount of the dispersion aid. In the case of plate-like inorganic fine particles, fine particles having a major axis of 15 nm or more are preferred.

[Dispersion aid]
The dispersion aid plays the following role.
(I) Assist the organic polymer in binding or adsorbing to the inorganic fine particles.
(Ii) The inorganic fine particles in the dispersion are expelled from the dispersion, that is, the inorganic fine particles are rapidly phase-shifted to the phase in which the organic polymer exists.
(Iii) Suppress the aggregation of inorganic fine particles, that is, relieve mechanical stress.
Therefore, once the organic-inorganic composite material is formed, the dispersion aid is no longer necessary and may be removed by a method such as extraction or fractional distillation.

Examples of the dispersion aid include an organic compound having a polar functional group and having an affinity for an organic polymer.
As a polar functional group, the same functional group as the above-mentioned organic polymer is mentioned, and a carboxy group is particularly preferable.
The polar functional group is preferably a functional group having the same polarity as the functional group of the organic polymer described above, from the viewpoint of promoting the binding or adsorption of the organic polymer to the inorganic fine particles. A functional group identical to the group is more preferred.
The polarity of the polar functional group is preferably as strong as possible. Specifically, when the acidity of the carboxy group is used as an index, pKa is preferably 4.8 or less, more preferably 4.6 or less, and particularly preferably 4 or less. .

Examples of the organic compound include aliphatic compounds, fluorine-containing aliphatic compounds, aromatic compounds, fluorine-containing aromatic compounds having a polar functional group.
The aliphatic compound is preferably an alkyl group having 3 or more carbon atoms, more preferably an alkyl group having 5 or more carbon atoms, from the viewpoint of affinity with an organic polymer. The alkyl group may be linear or branched.

In the dispersion aid, the polarity of the functional group and the affinity with the organic polymer are generally contradictory. For example, propionic acid has a higher affinity for organic polymers than acetic acid, but has a low polarity (pKa is high).
As a dispersion aid in which both the polarity of the functional group and the affinity with the organic polymer are compatible, one or more of the hydrogen atoms bonded to the α-position carbon atom of the alkyl group bonded to the carboxy group is halogen. Examples include substituted organic acids. Examples of the organic acid include perfluorovaleric acid, perfluorohexanoic acid, tridecafluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, 2,2-trifluoromethylpropionic acid and the like, and tridecafluoroheptane Acid is preferred.
In addition to the above, as a dispersion aid in which both the polarity of the functional group and the affinity with the organic polymer are compatible, one or more of the α-position carbon atoms of the alkyl group bonded to the carboxy group is hydrogen. An organic acid substituted with a functional group larger than an atom may be mentioned. As the organic acid, 2-ethylhexanoic acid (octylic acid) and an amino acid whose amino group is protected with a protecting group are preferred. Examples of the amino acid include F-moc amino acid and N-acetylamino acid. Moreover, you may synthesize | combine and use this amino acid. More preferably, the hydrophobicity (affinity with an organic polymer) of the amino acid is increased by binding a hydrophobic compound to the functional group of the amino acid side chain.

[Other ingredients]
In addition to the organic polymer, inorganic fine particles, and dispersion aid, the organic-inorganic composite material may include a surface treatment agent for inorganic fine particles, moisture as water adsorbed on the inorganic fine particles, a dispersion medium for inorganic fine particles, and the like. However, from the viewpoint of improving electret characteristics, the smaller the water content, the better.

<Method for producing organic-inorganic composite material>
The organic-inorganic composite material is preferably produced by a production method having the following steps (a) to (c). Moreover, it can manufacture by adding one or more of the following (d)-(f) process as needed.
(A) A solution in which an organic polymer is dissolved in a solvent (hereinafter referred to as an organic polymer solution), and a dispersion in which inorganic fine particles are dispersed in a dispersion medium that can be phase-separated with the solvent (hereinafter referred to as dispersion of inorganic fine particles). And a liquid).) To obtain an emulsion.
(B) A step of separating the emulsion into a solvent phase and a dispersion medium phase.
(C) The process of collect | recovering the phase of a solvent as a dispersion liquid of an organic inorganic composite material.
(D) The process of removing an acid radical or a base root from the dispersion liquid of an organic inorganic composite material as needed.
(E) The process of removing a water | moisture content from the dispersion liquid of an organic inorganic composite material as needed.
(F) The process of removing a solvent from the dispersion liquid of an organic inorganic composite material as needed, and obtaining a solid organic inorganic composite material.

[Step (a)]
Examples of the solvent include organic solvents.
As the organic solvent, when the dispersion medium is water, an organic solvent which does not dissolve or hardly dissolves in water, for example, perfluorotributylamine, perfluorohexane, 1, 1, 1, 2, 3, 4, 4, 5,5,5-decafluoro-3-methoxy-2- (trifluoromethyl) pentane, toluene, benzene, styrene, xylene, hexane, methyl ethyl ketone, ethyl acetate and the like. When the dispersion medium is an organic solvent, a fluorine-containing organic solvent is exemplified.

  As the fluorine-containing organic solvent, an aprotic fluorine-containing solvent is preferable. Examples of the aprotic fluorine-containing solvent include the following fluorine-containing compounds.

  Polyfluoroaromatic compounds such as perfluorobenzene, pentafluorobenzene, 1,3-bis (trifluoromethyl) benzene, 1,4-bis (trifluoromethyl) benzene, perfluorotributylamine, perfluorotripropylamine, etc. Polyfluorotrialkylamine compounds, perfluorodecalin, perfluorocyclohexane, polyfluorocycloalkane compounds such as perfluoro (1,3,5-trimethylcyclohexane), and polyfluoro cyclic ethers such as perfluoro (2-butyltetrahydrofuran) Compound, perfluoropolyether,

  Perfluorohexane, perfluorooctane, perfluorodecane, perfluorododecane, perfluoro (2,7-dimethyloctane), 1,1,2-trichloro-1,2,2-trifluoroethane, 1,1,1 -Trichloro-2,2,2-trifluoroethane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1,1,1,3-tetrachloro-2,2,3 3-tetrafluoropropane, 1,1,3,4-tetrachloro-1,2,2,3,4,4-hexafluorobutane, perfluoro (1,2-dimethylhexane), perfluoro (1,3 -Dimethylhexane), 2H, 3H-perfluoropentane, 1H-perfluorohexane, 1H-perfluorooctane, 1H-perfluorodecane, 1H, 1H, 1H, H, 2H-perfluorohexane, 1H, 1H, 1H, 2H, 2H-perfluorooctane, 1H, 1H, 1H, 2H, 2H-perfluorodecane, 3H, 4H-perfluoro-2-methylpentane, 2H, Polyfluoroalkane compounds such as 3H-perfluoro-2-methylpentane, 1H-1,1-dichloroperfluoropropane, and 1H-1,3-dichloroperfluoropropane.

These aprotic fluorine-containing solvents can be used alone or in combination. In addition to these, a wide range of compounds can be used. For example, a fluorine-containing solvent such as hydrofluoroether (HFE) is suitable. Such a fluorine-containing solvent is a general formula R ^a —O—R ^b (R ^a is ^a linear or branched polyfluoroalkyl group having 5 to 12 carbon atoms which may have an ether bond, and R ^b is a linear or branched alkyl group having 1 to 5 carbon atoms or a polyfluoroalkyl group.

When the number of carbon atoms of R ^a is 4 or less difficult to dissolve the fluorinated cyclic structure-containing polymer, for the number of carbon atoms of R ^a is in the case of 13 or more is industrially hard to obtain, the number of carbon atoms of R ^a is 5 It is selected from the range of ˜12. 6-10 are preferable and, as for carbon number of ^Ra , 6-7 and 9-10 are more preferable.

  A polyfluoroalkyl group is a group in which two or more of the hydrogen atoms of the alkyl group are substituted with fluorine atoms, a perfluoroalkyl group in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms, and The group includes a group in which two or more hydrogen atoms are substituted with fluorine atoms and one or more hydrogen atoms in the alkyl group are substituted with halogen atoms other than fluorine atoms. As halogen atoms other than fluorine atoms, chlorine atoms are preferred.

  The polyfluoroalkyl group is preferably a group in which 60% or more of hydrogen atoms in the corresponding alkyl group are substituted with fluorine atoms, and more preferably 80% or more. More preferred polyfluoroalkyl groups are perfluoroalkyl groups.

When R ^a has an ether bond, if the number of ether bonds is too large, the solubility is inhibited. Therefore, 1 to 3 ether bonds in R ^a are preferable, and 1 to 2 are more preferable.
When the carbon number of ^Rb is 6 or more, the solubility of the fluorine-containing ring structure-containing polymer is significantly inhibited. Preferred examples of R ^b are a methyl group, an ethyl group, a trifluoroethyl group, a tetrafluoroethyl group, a tetrafluoropropyl group, and the like.

If the molecular weight of the fluorinated solvent is too large, not only will the viscosity of the fluorinated polymer composition be increased, but also the solubility of the fluorinated ring structure-containing polymer will be reduced, so 1000 or less is preferred.
Moreover, in order to improve the solubility of a fluorine-containing ring structure containing polymer, the fluorine content of the fluorine-containing solvent is preferably 60 to 80% by weight. The following can be illustrated as a preferable fluorine-containing solvent.

F (CF ₂ ) ₄ OCH ₃ , HCF ₂ CF ₂ OCH ₂ CF ₃ , HCF ₂ CF ₂ CH ₂ OCH ₂ CF ₃ , F (CF ₂ ) ₅ OCH ₃ , F (CF ₂ ) ₆ OCH ₃ , F (CF ₂ ) ₇ OCH ₃ , F (CF ₂ ) ₈ OCH ₃ , F (CF ₂ ) ₉ OCH ₃ , F (CF ₂ ) ₁₀ OCH ₃ , H (CF ₂ ) ₆ OCH ₃ , (CF ₃ ) ₂ CF (OCH ₃ ) CFCF ₂ CF ₃ , F (CF ₂ ) ₃ OCF (CF ₃ ) CF ₂ OCH ₃ , F (CF ₂ ) ₃ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) CF ₂ OCH ₃ , F (CF _{2 ) 8 OCH 2 CH 2 CH 3} , (CF 3) 2 CFCF 2 CF 2 OCH 3, F (CF 2) 2 O (CF 2) 4 OCH 2 CH 3.

Of these fluorine-containing solvents, (CF ₃ ) ₂ CF (OCH ₃ ) CFCF ₂ CF ₃ is particularly suitable.
The boiling point of the solvent is preferably 68 to 216 ° C. If the boiling point of the fluorine-containing organic solvent is 100 ° C. or higher, water can be easily removed in the step (d).

  Specific examples of the organic polymer solution include a perfluorotributylamine solution of a fluorinated cyclic polymer having a carboxy group at the end of the main chain, and a perfluorotrimethyl-vinyl ether copolymer perfluoropolymer having a carboxy group at the end of the side chain. Examples include a fluorohexane solution.

  The concentration of the organic polymer is preferably 1 to 23% by mass and more preferably 2 to 15% by mass in the solution (100% by mass). When the concentration of the organic polymer is 1% by mass or more, the dispersibility of the inorganic fine particles in the organic polymer is good. If the concentration of the organic polymer is 23% by mass or less, the viscosity of the resulting dispersion of the organic-inorganic composite material is suppressed, and the organic-inorganic composite material is difficult to gel (solidify). The dispersion can be used for spin coating without problems.

  The amount of the organic polymer is preferably such that the volume fraction of the organic polymer is 10 to 99.8% by volume in the solid content (100% by volume) of the obtained organic-inorganic composite material. % Is more preferred. When the volume fraction of the organic polymer is 99.8% by volume or less, the mechanical properties of the organic-inorganic composite material are sufficiently improved. If the volume fraction of the organic polymer is 10% by volume or more, the coating film of the organic-inorganic composite material is unlikely to become brittle.

The dispersion medium capable of phase separation with the solvent is preferably water from the viewpoint of ease of phase separation. It is preferable to use an organic solvent from the viewpoint of easily improving the insulating property of the organic-inorganic composite material. If the solvent is a fluorine-containing organic solvent, a solvent that can be phase-separated from the fluorine-containing organic solvent can be selected from among organic solvents other than the fluorine-containing organic solvent.
Examples of the organic solvent that can be phase-separated with the fluorine-containing organic solvent include toluene, hexane, tetrahydrofuran, isopropanol, ethanol, methanol, methyl ethyl ketone, methyl isobutyl ketone, acetone, xylene, n-butanol, N, N-dimethylacetamide, ethylene glycol, Examples thereof include polypropylene glycol.

  When the organic polymer has an anionic functional group (carboxy group or the like) as a polar functional group and the dispersion medium is water, the pH of the dispersion is preferably 7 or less (acidic). When the pH of the dispersion exceeds 7, an organic polymer having an anionic functional group may be gelled by ammonium ions, metal ions, and the like derived from compounds added to make the dispersion alkaline. In addition, binding or adsorption of organic polymer to inorganic fine particles is difficult to occur. The pH of the dispersion is more preferably 1 to 7, and further preferably lower than the isoelectric point of the inorganic fine particles (metal oxide).

  Specific examples of inorganic fine particle dispersions include metal oxide (silicon oxide, titanium oxide, zirconium oxide, aluminum oxide, cerium oxide, tin oxide, iron oxide, etc.) acidic aqueous dispersions of fine particles, metal oxide fine particles An organic solvent (toluene, isopropanol, tetrahydrofuran, etc.) dispersion liquid, etc. are mentioned.

  The concentration of the inorganic fine particles is preferably 0.2 to 50% by mass and more preferably 1 to 30% by mass in the dispersion (100% by mass). When the concentration of the inorganic fine particles is 0.2% by mass or more, an organic-inorganic composite material can be obtained directly. When the concentration of the inorganic fine particles is less than 0.2% by mass, phase separation in the step (b) becomes difficult. When the concentration of the inorganic fine particles is 50% by mass or less, the aggregation of the inorganic fine particles and the gelation (solidification) of the organic-inorganic composite material do not occur when the organic polymer solution and the inorganic fine particle dispersion are mixed. When the concentration of the inorganic fine particles exceeds 50% by mass, the organic polymer or the dispersion aid does not quickly cover all the inorganic fine particles during the mixing operation in the step (a), and the partially coated inorganic fine particles Since it becomes amphiphilic, the phase separation in the step (b) becomes difficult.

The amount of the inorganic fine particles is determined based on the volume fraction of the inorganic fine particles in the solid content (100% by volume) of the organic / inorganic composite material from the viewpoint of the electrical properties (insulation characteristics) of the obtained organic / inorganic composite material and the thermal stability of the obtained electret. The rate is preferably 0.02 to 38% by volume, more preferably 0.02 to 35% by volume. When the volume fraction of the inorganic fine particles is 38% by volume or less, the viscosity of the dispersion liquid of the organic-inorganic composite material is suppressed, and the coating film of the organic-inorganic composite material is not easily brittle.
More preferably, it is 0.02-15 volume%. In order to facilitate handling of the obtained organic-inorganic composite material and to reduce the amount of the dispersion aid used, the volume fraction of the inorganic fine particles is more preferably less than 10%, and even more preferably less than 8%. If the volume fraction of the inorganic fine particles is 0.02% by volume or more, the electret obtained from the organic-inorganic composite material is excellent in thermal stability.

The dispersion aid is preferably added to the organic polymer solution.
The amount of the dispersion aid is determined by the relationship between the number of functional groups of the organic polymer and the surface area of the inorganic fine particles. The smaller the molecular weight of the organic polymer, the more polar functional groups per molecule, and the smaller the diameter of the inorganic fine particles. The larger the surface area per volume, the lower the amount of dispersing aid used. In addition, when a part of the surface of the inorganic fine particle is already modified with a hydrocarbon group, the amount of the dispersion aid can be further reduced.

  As a method of mixing an organic polymer solution and a dispersion of inorganic fine particles to obtain an emulsion, there is a method in which the organic polymer solution and the dispersion of inorganic fine particles are placed in a container and stirred with a known stirrer or the like. Can be mentioned. As the stirring method, a method of stirring using a planetary mill or a method of gently stirring with a stirring bar or a stirring blade is preferable. When vigorously stirred or stirred so as to involve an air phase, a part of the obtained organic-inorganic composite material becomes an emulsion containing a dispersion medium.

  When mixing the organic polymer solution and the inorganic fine particle dispersion, the amount of the organic polymer solution (volume) is 100 parts by volume, and the inorganic fine particle dispersion is 5 to 300 parts by volume. It is preferably 10 to 200 parts by volume. When the amount of the dispersion of inorganic fine particles relative to the organic polymer solution is less than 5 parts by volume, the operability and the recovery amount when removing the phase-separated dispersion medium in (ii) of step (b) are deteriorated. When the amount of the dispersion of inorganic fine particles with respect to the organic polymer solution exceeds 300 parts by volume, a part of the organic polymer begins to act on emulsification of the solvent and the dispersion medium, and even if the solid content concentration is high. The significance of the present invention that the dispersion is possible is diminished. When using a dispersion of inorganic fine particles having a relatively low concentration and increasing the inorganic fine particle content in the obtained organic / inorganic composite material, the dispersion of the organic / inorganic composite material obtained in step (c) or (d) is used. The liquid may be used in place of the organic polymer solution, and the steps (a) and after may be repeated. In order to reduce that part of the resulting organic-inorganic composite material becomes an emulsion containing a dispersion medium, the organic polymer solution and the inorganic fine particle dispersion are mixed at room temperature to the solvent and the dispersion during mixing. You may heat between below the boiling point of a medium, and 0.1-5 mass% alcohol may be added to the organic polymer solution previously with respect to the organic-inorganic composite material obtained.

[Step (b)]
Examples of the method for separating the emulsion into the solvent phase and the dispersion medium phase include the following methods.
(I) A method in which the emulsion is phase-separated into a solvent phase and a dispersion medium phase by centrifugation.
(Ii) A method in which the emulsion is allowed to stand and phase-separated into a solvent phase and a dispersion medium phase based on a difference in specific gravity between the solvent and the dispersion medium.

[(C) Step]
In the steps (a) and (b), the inorganic fine particles in the dispersion are phase-shifted to the organic polymer solution via the interface, and the polar functional group of the organic polymer is inorganic in the solvent phase. By directly binding or adsorbing to the surface of the fine particles, an organic-inorganic composite material in which nano-sized inorganic fine particles are uniformly dispersed in the organic polymer of the matrix is formed.
Therefore, in the step (c), the solvent phase is recovered as a dispersion of the organic-inorganic composite material. Recovery of the solvent phase is performed by a known liquid separation operation.

[Step (d)]
When the dispersion medium of the inorganic fine particles is water, acid radicals or base roots are mixed in the dispersion liquid of the organic-inorganic composite material. If a dispersion of an organic-inorganic composite material mixed with a large amount of these is used as a molded or coated film as it is, it will corrode due to heat during drying or afterwards, so that the mechanical properties are liable to deteriorate and the color tends to be colored. Therefore, acid roots or base roots are removed from the dispersion of the organic-inorganic composite material as necessary.
As a method for removing the acid or base root, a washing method with water is preferable. Acidic or basic relaxation by neutralization should not be used because it produces salts in organic-inorganic composites.
When the dispersion medium of the inorganic fine particles is an organic solvent, the influence of the acid root or base root can be ignored. Therefore, when the organic-inorganic composite material is used for applications that require electrical insulation or the like, or for applications that are formed to a thickness exceeding 1 μm, where the volatilization of moisture is difficult, an organic solvent is preferable as the dispersion medium for the inorganic fine particles. .
If the organic-inorganic composite material is formed, the dispersion aid is no longer necessary, and may be removed by extraction at the same time in the step (d).

[(E) Process]
When the dispersion medium of the inorganic fine particles is water, water is mixed in the dispersion liquid of the organic-inorganic composite material. If the dispersion liquid of organic-inorganic composite material mixed with water is used as it is as a coating liquid, pores are formed by evaporation of water when the coating film is dried, so mechanical properties are likely to deteriorate, and charge injection is performed during electretization. May interfere. Moreover, if the coating film is insufficiently dried, there is a risk of causing a decrease in insulation. Therefore, moisture is removed from the dispersion of the organic-inorganic composite material as necessary.

The following method is mentioned as a water removal method.
(I) A method of evaporating water by heating a dispersion of an organic-inorganic composite material at 100 ° C. or higher and below the boiling point of the organic polymer solvent.
(Ii) A method of adding a dehydrating agent to the dispersion of the organic-inorganic composite material.

When the dispersion medium of the inorganic fine particles is an organic solvent, mixing of water can be sufficiently suppressed if the environment in the steps (a) and (b) is taken into consideration. When the organic-inorganic composite material is used for applications requiring electrical insulation, an organic solvent is preferable as the dispersion medium for the inorganic fine particles.
If the organic-inorganic composite material is formed, the dispersion aid is no longer necessary, and may be removed by a method such as extraction or fractionation in the step (e).

[Step (f)]
The organic-inorganic composite material dispersion may be a solid organic-inorganic composite material by removing the solvent from the organic-inorganic composite material dispersion as necessary.

In the method for producing an organic-inorganic composite material described above, a solution in which an organic polymer is dissolved in a solvent is mixed with a dispersion in which inorganic fine particles are dispersed in a dispersion medium capable of phase separation with the solvent. After being obtained, the emulsion is phase-separated into a solvent phase and a dispersion medium phase, and the solvent phase is recovered as a dispersion of an organic-inorganic composite material. Despite the use of a sufficient amount of solvent (dispersion medium) necessary to enhance the dispersibility, the amount of solvent contained in the resulting dispersion of the organic-inorganic composite material is changed to the dispersion of the conventional organic-inorganic composite material. Compared with the liquid, it can be reduced to about a half, that is, the solid content concentration can be about doubled compared with the dispersion of the conventional organic-inorganic composite material. Therefore, the obtained dispersion liquid of the organic-inorganic composite material can be used as it is as a coating liquid without being concentrated, and a coating film having a sufficient thickness can be formed.
Moreover, in the organic-inorganic composite material of the present invention, since the organic polymer itself functions as a dispersant, the amount of the dispersion aid used can be reduced.

<Electret>
The electret of the present invention is obtained by injecting electric charge into a layer made of the organic-inorganic composite material (hereinafter referred to as “composite material layer”).
The electret of this invention may have layers other than a composite material layer as needed. Examples of other layers that can be laminated with the composite material layer include a protective layer, a layer made of only the organic polymer, and a layer made of an inorganic material similar to the component of the inorganic fine particles.

The electret of the present invention can be obtained by forming the composite material layer and injecting electric charges.
The film forming method of the composite material layer is not particularly limited, and a conventionally known film forming method may be used depending on the material to be used. For example, the film may be formed by a wet coating method, or the film may be formed by press molding a film. Moreover, you may form into a film by dry processes, such as vapor deposition, CVD, and sputtering. Especially, it is preferable to form into a film by the wet coating method from a viewpoint of a film forming process.

In the case of forming a film by a wet coating method, it can be carried out by coating the surface of the substrate with a coating liquid containing an organic-inorganic composite material and drying it by baking or the like.
In order to obtain a composite material layer, the dispersion obtained without performing the step (f) may be used as it is as a coating solution. Further, the solid organic-inorganic composite material obtained by performing the step (f) may be dissolved again in a solvent and used as a coating liquid.
As the solvent in the case of dissolving again in the solvent, the solvent used in the step (a) can be used. You may add the said dispersion aid as needed.
What is necessary is just to set suitably the solid content concentration of the organic polymer in a coating liquid according to the film thickness to form. Usually, it is 0.1-30 mass%, and 0.5-20 mass% is preferable.

  As a coating method, a conventionally known method can be used as a method for forming a film from a solution, and is not particularly limited. Specific examples of such a method include a roll coater method, a cast method, a dipping method, a spin coat method, a water cast method, a Langmuir-Blodget method, a die coat method, an ink jet method, and a spray coat method. Printing techniques such as letterpress printing, gravure printing, lithographic printing, screen printing, and flexographic printing can also be used.

  As the substrate for coating the coating liquid, any material can be used as long as it can be connected to the ground when injecting electric charge into the coating film obtained by coating. Examples of preferable materials include conductive metals such as gold, platinum, copper, aluminum, chromium, and nickel. Also, the material may be an insulating material other than a conductive metal, for example, a semiconductor material such as silicon, an inorganic material such as glass, an organic polymer material such as polyethylene terephthalate, polyimide, polycarbonate, and acrylic resin. As long as the surface is coated with a metal film by a method such as sputtering, vapor deposition, or wet coating, it can be used.

The substrate may be a flat plate with a smooth surface, or may have irregularities formed thereon. Moreover, it may be patterned into various shapes. In particular, when the above-described insulating substrate is used, the unevenness or pattern may be formed on the insulating substrate itself, or the unevenness or pattern may be formed on the metal film coated on the surface. A conventionally known method can be used as a method for forming irregularities or patterns on the substrate, and is not particularly limited. As a method for forming the unevenness or pattern, either a vacuum process or a wet process may be used. Specific examples of such a method include a vacuum process, a sputtering method through a mask, a vapor deposition method through a mask, and a wet process such as a roll coater method, a casting method, a dipping method, a spin coating method, a water casting method, a Langmuir Examples include a blow jet method, a die coating method, an ink jet method, and a spray coating method. Printing techniques such as letterpress printing, gravure printing, lithographic printing, screen printing, and flexographic printing can also be used. Further, as a method for forming fine irregularities or patterns, a nanoimprint method, a photolithography method, or the like can be used.
Note that the substrate may be peeled off after the charge injection.

After the coating, it is preferable to dry the dispersion medium of the dispersion and the solvent in which the solid organic-inorganic composite material is redissolved by baking or the like.
Drying conditions are preferably higher than the boiling point of the solvent as the dispersion medium or the redissolved solvent.

  What is necessary is just to set suitably the shape and magnitude | size of a composite material layer according to the shape and magnitude | size of a desired electret. The electret is generally used as a film having a thickness of 1 to 200 μm. It is particularly preferable to use it as a film having a thickness of 10 to 20 μm because it is advantageous in terms of electret characteristics and processing.

As a method for injecting charges into the composite material layer, any method can be used as long as it is a method for charging an insulator. For example, the corona discharge method described in GMSessler, Electrets Third Edition, pp20, Chapter 2.2 “Charging and Polarizing Methods” (Laplacian Press, 1998), electron beam collision method, ion beam collision method, radiation irradiation method, light irradiation method, A contact charging method, a liquid contact charging method, or the like is applicable. In particular, the electret of the present invention preferably uses a corona discharge method or an electron beam collision method.
Moreover, as a temperature condition at the time of injecting the charge, it is preferable to perform at a temperature higher than the glass transition temperature of the organic polymer from the viewpoint of the stability of the charge retained after the injection, and in particular, a glass transition temperature of about +10 to 20 ° C. It is preferable to carry out under temperature conditions. Furthermore, it is preferable to apply a high voltage as the applied voltage when injecting the charge, as long as it is lower than the dielectric breakdown voltage of the composite material layer. In the composite material layer in the present invention, a high voltage of ± 6 to ± 30 kV can be applied, and voltage application of ± 8 to ± 15 kV is particularly preferable. In particular, when the organic polymer used for the composite material is a fluorine-containing resin, the composite material layer can hold a negative charge more stably than a positive charge, so a voltage of −8 to −15 kV is applied. More preferably.

The electret of the present invention is suitable as an electrostatic induction conversion element that converts electrical energy and kinetic energy.
Examples of the electrostatic induction conversion element include a vibration generator, an actuator, and a sensor. The structures of these electrostatic induction conversion elements may be the same as those conventionally known except that the electret of the present invention is used as the electret.

  The electret of the present invention has higher thermal stability of injected charges and is superior in charge retention characteristics at high temperatures as compared to conventional electrets. Therefore, the electrostatic induction conversion element using the electret has characteristics such that characteristics are hardly deteriorated and characteristics are less dependent on the environment.

Specific examples of the above embodiment will be described below as examples. The present invention is not limited to the following examples.
The relative dielectric constants of materials used in the following examples are all values measured at a frequency of 1 MHz in accordance with ASTM D150. The volume resistivity is a value measured by ASTM D257. The dielectric breakdown voltage is a value measured by ASTM D149.
In each of the following examples, the film thickness was measured using a light interference type film thickness measuring device C10178 manufactured by Hamamatsu Photonics.

<Example 1>
[Production of Dispersion A]
As an organic polymer, a fluorine-containing cyclic polymer having a repeating unit of the following formula (A) as a main component and having a carboxy group at the end of the main chain (Cytop, manufactured by Asahi Glass Co., Ltd., relative permittivity 2.1, differential scanning) Glass transition temperature measured by thermal analysis (DSC): 108 ° C., volume resistivity value> 10 ¹⁷ Ωcm, dielectric breakdown voltage 19 kV / mm) was measured using a fluorine-containing organic solvent (Cytop CT-solv180, manufactured by Asahi Glass Co., Ltd.) 1.2 g (in terms of polymer mass) of a solution (Cytop solution CTL-823A manufactured by Asahi Glass Co., Ltd., hereinafter referred to as CT-A) dissolved at a concentration of 23% by mass was collected, and solv180 was described. To obtain 13.7 g of a solution having a concentration of the fluorinated cyclic polymer of 8.8% by mass. 10 mg of tridecafluoroheptanoic acid (hereinafter referred to as C6RfA) was added to this solution as a dispersion aid, and the mixture was further stirred to obtain a solution of a fluorinated cyclic polymer.

Toluene dispersion of zirconium oxide fine particles (relative dielectric constant 12.5) (manufactured by Sumitomo Osaka Cement Co., Ltd., average primary particle size: 7 nm, specific gravity: 0.96, concentration: 9.9% by mass, hereinafter referred to as Zr toluene sol). ) Was placed in a container containing the above-mentioned fluorocyclic polymer solution and stirred for 5 minutes to obtain an emulsion.
The emulsion was centrifuged at 400 G for 5 minutes and phase separated into a solv 180 phase and a toluene phase. The upper phase was a toluene phase, and the lower phase was a solv 180 phase.

 Next, after the toluene phase was removed by decantation, the solv 180 phase was filtered using a filter (pore size: 0.4 μm), placed in a 120 ° C. ventilated oven for 2 hours to remove the remaining toluene, and organic An inorganic composite dispersion A was obtained. The toluene phase was dried, leaving 7.8 mg of solids.

  Assuming that the fluorine-containing cyclic polymer and C6RfA charged first are all phase-shifted to the sol180 phase, and the zirconium oxide fine particles are phase-shifted to the sol180 phase except for the weight remaining in the toluene phase. The mass fraction of the zirconium oxide fine particles in the solid content (100 mass%) of the material was calculated to be 3.2 mass%. Further, the volume fraction of the zirconium oxide fine particles in the solid content (100% by volume) of the organic-inorganic composite material, the specific gravity of the fluorine-containing cyclic polymer is 2.03, the specific gravity of C6RfA is 1.792, and the specific gravity of the titanium oxide fine particles. Was calculated as 3.9 and found to be 1.2% by volume.

[Manufacture of electret A]
The dispersion liquid A was spin-coated on a 3 cm square copper substrate having a thickness of 350 μm, and then baked at 200 ° C. and dried to obtain a composite material layer A having a thickness of 15 μm.
An electret A was obtained by injecting electric charge into the obtained composite material layer A by corona discharge. Charge injection was performed according to the following procedure using a corona charging apparatus whose schematic configuration is shown in FIG. 1 at 120 ° C. under a charging voltage of −8 kV and a charging time of 3 minutes.
That is, a high voltage of −8 kV is applied between the corona needle 14 and the copper substrate 10 by the DC high voltage power supply device 12 (HAR-20R5; manufactured by Matsusada Precision) using the copper substrate 10 as an electrode while being heated by the heater 19. By applying, charges were injected into the composite material layer 11 (composite material layer A in this example) formed on the copper substrate 10. In this corona charging device, the negative ions discharged from the corona needle 14 are made uniform by the grid 16 and then poured onto the composite material layer 11 to inject charges. A voltage of −600 V is applied to the grid 16 from the grid power supply 18. Reference numeral 17 denotes an ammeter.

<Example 2>
[Production of Dispersion B]
1.2 g (in terms of polymer mass) of CT-A was collected and diluted with solv 180 to obtain 13.7 g of a solution having a polymer concentration of 8.8% by mass. To this solution, 12 mg of C6RfA was added and further stirred to obtain a solution of a fluorinated cyclic polymer.
An aqueous dispersion of titanium oxide fine particles (relative dielectric constant 100) (manufactured by Ishihara Sangyo Co., Ltd., STS-01, average primary particle size: 5 nm, specific gravity: 1.3, concentration: 30% by mass, hereinafter referred to as STS-01). 0.06 ml was put into a container containing the above-mentioned solution of the fluorinated cyclic polymer and stirred for 5 minutes to obtain an emulsion.
The emulsion was centrifuged at 400 G for 5 minutes to separate into a solv 180 phase and a water phase. The upper phase was a water phase, and the lower phase was a fluorine-containing organic solvent phase.

  Next, the water phase was removed by decantation, and then the solv 180 phase was filtered using a filter (pore size: 0.4 μm), placed in a 120 ° C. ventilated oven for 2 hours to remove the remaining water, and organic An inorganic composite dispersion B was obtained. When the water phase was dried, no solids were observed.

  The mass fraction of titanium oxide fine particles in the solid content (100% by mass) of the organic-inorganic composite material on the assumption that all of the fluorine-containing cyclic polymer, titanium oxide fine particles, and C6RfA charged first were transferred to the sorb180 phase. Was calculated to be 1.9% by mass. Further, the volume fraction of the titanium oxide fine particles in the solid content (100% by volume) of the organic-inorganic composite material, the specific gravity of the fluorine-containing cyclic polymer is 2.03, the specific gravity of C6RfA is 1.792, and the specific gravity of the titanium oxide fine particles. Was 1.0% by volume when calculated as 3.9.

[Manufacture of electret B]
The same procedure as in Example 1 was performed except that the dispersion A was replaced with the dispersion B. A composite material layer B was obtained.
An electret B was obtained by injecting electric charge into the obtained composite material layer B by corona discharge. Charge injection was performed in the same manner as in Example 1 except that the composite material layer A was replaced with the composite material layer B.

<Example 3>
[Production of Dispersion C]
1.2 g (in terms of polymer mass) of CT-A was collected and diluted with solv 180 to obtain 13.7 g of a solution having a polymer concentration of 8.8% by mass. To this solution, 45 mg of tridecafluoroheptanoic acid (hereinafter referred to as C6RfA) as a dispersion phase aid was added and further stirred to obtain a solution of a fluorinated cyclic polymer.
Toluene dispersion of zirconium oxide fine particles (relative dielectric constant 12.5) (manufactured by Sumitomo Osaka Cement Co., Ltd., average primary particle size: 7 nm, specific gravity: 0.96, concentration: 9.9% by mass, hereinafter referred to as Zr toluene sol). 2 ml) was put into a container containing the above-mentioned fluorine-containing cyclic polymer solution and stirred for 5 minutes to obtain an emulsion.
The emulsion was centrifuged at 400 G for 5 minutes and phase separated into a solv 180 phase and a toluene phase. The upper phase was a toluene phase, and the lower phase was a solv 180 phase.

  Next, after the toluene phase was removed by decantation, the solv 180 phase was filtered and placed in a 120 ° C. ventilated oven for 2 hours to remove the remaining toluene, thereby obtaining a dispersion A of an organic-inorganic composite material. The toluene phase was dried, leaving 30.6 mg of solids.

  First, the fluorine-containing cyclic polymer charged and the C6RfA were all phase-shifted to the sorb180 phase, and the zirconium oxide fine particles were phase-shifted to the sorb180 phase except for the weight remaining in the toluene phase. The mass fraction of zirconium oxide fine particles in the solid content (100% by mass) of the material was calculated to be 11.3% by mass. Further, the volume fraction of zirconium oxide fine particles in the solid content (100% by volume) of the organic-inorganic composite material, the specific gravity of the fluorine-containing cyclic polymer is 2.03, the specific gravity of C6RfA is 1.792, and the specific gravity of the titanium oxide fine particles. When calculated as 3.9, it was 4.5% by volume.

[Manufacture of electret C]
The same procedure as in Example 1 was performed except that the dispersion A was replaced with the dispersion C. A composite material layer C was obtained.
An electret C was obtained by injecting electric charge into the obtained composite material layer C by corona discharge. The charge injection was performed in the same manner as in Example 1 except that the composite material layer A was replaced with the composite material layer C.

<Comparative Example 1>
Asahi Glass Cytop solution containing the repeating unit of the above formula (A) (CTL-809A, a solution of Asahi Glass Cytop used in Dispersion A in solv 180 at a concentration of 9%) A fluorine-containing resin layer D was obtained in the same manner as in Example 1 except for the above.
An electret D was obtained by injecting electric charge into the obtained fluororesin layer D by corona discharge. Charge injection was performed in the same manner as in Example 1 except that the composite material layer A was replaced with the fluorine-containing resin layer D.

[Test Example 1: Charge test]
The electrets A, B, C, and D obtained above were subjected to a charge test according to the following procedure.
The electrets A, B, C, and D immediately after the charge is injected by corona charging under conditions of a charging voltage of -8 kV and a charging time of 3 minutes are returned to room temperature (25 ° C.), respectively, and their surface potential (initial surface potential) Was measured. Each electret was stored for 400 hours under the conditions of 20 ° C. and 60% RH, and then returned to room temperature to measure the surface potential (surface potential after 400 hours).
For the surface potential (V), a surface potential meter (model 279; manufactured by Monroe Electronics) was used, and the surface potential of nine measurement points of each electret (set in a grid pattern every 3 mm from the center of the membrane, see FIG. 2). It measured and calculated | required as those average values. The results are shown in Table 1.

[Test Example 2: Thermal stability test]
With respect to the electrets A, B, and D, a thermal stability test was performed by the following procedure using an apparatus whose schematic configuration is shown in FIG.
First, as shown in FIG. 3, the counter electrode 20 was disposed so as to face the electret 21 (electret A, B, C, or D) on the copper substrate 10.
Next, the temperature of the portion indicated by the broken line in FIG. 3 is heated at a constant rate (1 ° C./min) by heating with a heater, and the amount of charge released from each electret A, B, D is determined. The current value i flowing from the counter electrode 20 was measured with an ammeter 22 (a microammeter (manufactured by Keithley, Model 6517A)) to determine the discharge start temperature and the discharge peak temperature. The results are shown in Table 1.
Here, the discharge peak temperature indicates the temperature at which the current value detected at the time of discharge is maximized, and the discharge start temperature is the current value (at the start of discharge) obtained by the ammeter 22 using the following formula. The temperature at which the current value is detected.
Current value at start of discharge = {(current value at discharge peak temperature) − (current value before discharge)} × 0.1 + (current value before discharge)

The thermal stability test is a method called Thermal Stimulated Discharge method (hereinafter referred to as TSD method). In this method, the electret 21 and the counter electrode 20 form a capacitor. Therefore, when the electret 21 is heated, the charge trapped in the film becomes unstable, and when the charge near the surface disappears due to diffusion or the like, the charge stored in the counter electrode 20 also decreases. Therefore, the thermal stability of each electret A, B, D can be evaluated by measuring the magnitude of the current value flowing from the counter electrode 20.
As for the thermal stability evaluation of electret C, it was stored in a constant temperature oven (inert oven DN410I manufactured by Yamato Scientific Co., Ltd.) kept at 125 ° C. together with electret D, and the change with time of surface potential decay was measured. . The potential remaining rate shown in Table 1 is defined by the following equation.
(Potential residual ratio) = {(surface potential after 70 hours) / (surface potential before throwing into the oven)} * 100

As shown in Table 1, each of the electrets A and B had a higher discharge start temperature and a discharge peak temperature than the electret D, and the thermal stability of the injected charge was improved. In addition, regarding the electret C, the potential remaining rate after storage at 125 ° C. for 70 hours is significantly improved compared to the electret D, and the thermal stability of the injected charge is improved. I can say that.
Also, regarding the surface potential, electrets A, B, and C had a higher surface potential at the initial stage and after 400 hours than electret D, respectively, and were confirmed to have excellent charge retention characteristics.

It is a schematic block diagram of the corona charging device used for the charge injection. It is a figure which shows the setting position of the measurement point of surface potential. It is a schematic block diagram of the apparatus used by the thermal stability test.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Copper board | substrate, 11 ... Composite material layer, 12 ... DC high voltage power supply device, 14 ... Corona needle, 16 ... Grid, 17 ... Ammeter, 18 ... Power supply for grids, 19 ... Heater, 20 ... Counter electrode, 21 ... Electret 22 ... Ammeter.

Claims (10)

An electret comprising a layer made of an organic-inorganic composite material including an organic polymer and inorganic fine particles having a relative dielectric constant of 2.0 to 4.0 × 10 ³ .   The electret according to claim 1, wherein the inorganic fine particles are metal oxide fine particles.   3. The metal oxide is one or more selected from the group consisting of silicon oxide, titanium oxide, zirconium oxide, aluminum oxide, cerium oxide, tin oxide, manganese dioxide, nickel oxide, iron oxide, and barium titanate. The electret as described in.   The electret according to any one of claims 1 to 3, wherein a part of the surface of the inorganic fine particle is modified with a hydrocarbon group.   The electret according to any one of claims 1 to 4, wherein the organic polymer has a polar functional group at an end of a main chain and / or a side chain.   The polar functional groups are carboxy group, sulfo group, phosphono group, amide group, acid halide group, formyl group, amino group, hydroxy group, thiol group, phenol group, silanol group, alkoxy group, alkoxysilyl group and cyano group The electret of Claim 5 which is 1 or more types chosen from the group which consists of.   The electret according to any one of claims 1 to 6, wherein the organic polymer has an aliphatic ring structure.   The electret according to any one of claims 1 to 7, wherein the organic polymer is a fluorine-containing resin. The electret according to any one of claims 1 to 8, wherein the organic-inorganic composite material is produced by a production method having the following steps (a) to (c).
(A) A step of mixing the solution in which the organic polymer is dissolved in a solvent and a dispersion in which the inorganic fine particles are dispersed in a dispersion medium capable of phase separation with the solvent to obtain an emulsion.
(B) A step of separating the emulsion into the solvent phase and the dispersion medium phase.
(C) A step of recovering the solvent phase as a dispersion of the organic-inorganic composite material.   An electrostatic induction conversion element comprising the electret according to claim 1.

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