JP2016058617A - Method of manufacturing electret - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an electret capable of controlling the charge amount of an electret material, i.e., the absolute value of surface potential as an electret index, in the increasing direction.SOLUTION: A method of manufacturing an electret has a deposition step for forming a coating film on the substrate surface by using a coating liquid where a fluorine-containing resin is dispersed into a solvent, a drying step for drying the coating film following to the deposition step, a charge injection step for injecting charges into a resin film of fluorine-containing resin obtained after the drying step, and a heating step for heating the resin film of fluorine-containing resin after the charge injection step.SELECTED DRAWING: None

Description

  The present invention relates to an electret manufacturing method.

  An electret is a substance in which electric charges are injected into a dielectric, and is known as a substance that can generate an electrostatic field semipermanently. There are several methods for producing electrets, and examples include methods using corona discharge, electron beam, soft ionization using soft X-rays or vacuum ultraviolet rays, ion doping, and the like.

  Corona discharge can be charged in the atmosphere in a short time and can produce a stable electret. For this reason, it is employed in a wide range of applications such as the manufacture of microphones and filters. Recently, it is used as a charging method for the electrode portion of the vibration power generation element. For example, a method of manufacturing an electret using a corona discharge device provided with a corona needle and a grid is used (see Patent Document 1).

  The electret charging method by electron beam irradiation is one of the oldest charging methods. Advantages include easy control of the penetration depth of electrons into the electret, current density, and in-plane uniformity by adjusting the acceleration voltage. As a specific method of using an electron beam, for example, an olefin resin sheet is irradiated with an electron beam and air molecules in the vicinity of the olefin resin sheet are ionized to inject charges into the olefin resin. There is a method of charging a sheet (see Patent Document 2).

  Further, as a method for producing electret fine particles, “emulsified particles are obtained by emulsifying a fluorine-containing material containing vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer in a liquid in which the fluorine-containing material is not compatible. And a method of producing electret fine particles by applying electron beam irradiation, radiation irradiation or corona discharge to the emulsified particles ”(see Patent Document 3).

  There is also an electret manufacturing method using soft X-rays. A soft X-ray is an electromagnetic wave having an energy of several tens of keV or less, and has a lower energy than a hard X-ray, and therefore has a low ability to transmit an object. As an example of use, Hagiwara et al. Of NHK Science and Technology Research Laboratories irradiate a dielectric placed inside a Si microphone made by MEMS with a soft X-ray through a 2 μm thick Si diaphragm to produce an electret. Proposed method. (See Non-Patent Document 1) (K. Hagiwara, M. Goto, Y. Iguchi, Y. Yasuno, H. Kodama, K. Kidokoro, and T. Tajima, “Soft Xray charging method for a silicon electret condenser microphone,” Appl. Phys. Exp., 3, 091502, 3pp, 2010.)

An electret manufacturing method using vacuum ultraviolet rays will be described. The vacuum ultraviolet ray means an ultraviolet ray having a wavelength of 200 nm or less and showing a large attenuation in the air. It is known that, at a certain pressure, a large amount of ions / electrons are generated as compared with corona discharge or soft X-ray, and an electret is produced at a high speed. For example, a method for producing an electret by attaching a deuterium lamp (wavelength 120 to 160 nm) to a vacuum chamber capable of maintaining a constant nitrogen pressure has been proposed. (See Non-Patent Document 2) (Honzumi, M., Hagiwara, K., Iguchi, Y., and Suzuki, Y., “High-Speed Electret Charging Method Using Vacuum UV Irradiation,” Appl. Phys. Lett., Vol. 98, Issue 5, 052901 (2011))
In this way, development of various electretization techniques as well as corona discharge is underway.

On the other hand, attempts have been made to improve electret properties from the material aspect. For example, an electret comprising a resin composition containing a block copolymer exhibiting a microphase separation structure has been disclosed (see Patent Document 4).
Further, it is disclosed that an electret having a large surface charge density can be obtained by an electret characterized by containing a fluorinated aromatic resin containing a fluorinated aromatic polymer as a main component (see Patent Document 5). .

  As described above, the development of materials having high electret properties has been promoted by the development of electret methods and electret materials. However, electret materials have long-term stability of electret properties, retention of electret properties in high-temperature environments, etc., and are one barrier in the practical application of electret devices including vibration power generators. .

In addition, control of the surface potential, which is one of the indices of electret properties, is a very important technology for practical use of electret devices. Currently, it is known that electretization by corona discharge uses a grid electrode to control the amount of charge by controlling the applied voltage. In other electretization techniques, the control of the charge amount is studied by controlling the applied voltage, current, atmosphere, pressure, and the like.
In addition, from the viewpoint of long-term stability of electret properties, it is very important to control the electret material surface potential after electretization in the direction of increasing the absolute value, but there is still a technology that makes this possible. The current situation is not.

  In view of the above-described current problems, the present invention provides an electret manufacturing method capable of controlling the electrified electret material charge amount, that is, the direction of increasing the absolute value of the surface potential as an electret index. Objective.

The present invention for solving the above problems has the following aspects.
(1) a film forming step of forming a coating film on a substrate surface using a coating liquid in which a fluorine-containing resin is dispersed in a solvent;
A drying step of drying the coating film after the film formation step;
A charge injection step of injecting charges into the resin film of the fluororesin obtained after the drying step by electron beam irradiation;
A heating step of heating the resin film of the fluororesin after the charge injection step;
A method for producing an electret, comprising:

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the electret which can be controlled to the direction which increases the electrification amount of electret electret material, ie, the absolute value of surface potential, as an electret parameter | index can be provided.

It is a schematic block diagram of a corona charging device.

Next, the form for implementing this invention is demonstrated.
In the method for producing an electret according to the present invention, first, a fluororesin is dispersed in a solvent to prepare a coating solution, and a coating film is formed on the substrate surface using this coating solution (film forming step). . Then, the coating film is sufficiently dried to produce a fluororesin resin film (drying step). Subsequently, charges are injected into the resin film by electron beam irradiation (charge injection step). Finally, the electret of this invention can be obtained by heating a resin film (heating process).
Each material will be described in detail below.

"substrate"
The substrate is preferably made of a conductive material. This is because, when the resin film formed on the substrate is electretized, it is considered that the charge held on the resin film can be stabilized because the substrate is conductive. Specific examples of the conductive material include gold, silver, copper, nickel, chromium, aluminum, titanium, tungsten, molybdenum, tin, cobalt, palladium, platinum, and alloys containing at least one of these as a main component. Can be mentioned. Further, examples thereof include metal oxide conductive films such as ITO (Indium Tin Oxide) and IZO (Indium Zinc Oxide), and organic conductive films made of polyaniline, polypyrrole, PEDOT / PSS, carbon nanotubes, and the like. Further, the substrate may be made of any other material not described above, and is not particularly limited to the above, but it can be said that a conductive material is suitable.

<Coating film and resin film>
The coating film is formed on the substrate surface using a coating liquid in which a fluorine-containing resin is dispersed in a solvent, and includes a fluorine-containing resin and a solvent. Then, by drying the coated film, the solvent is evaporated, and a dried resin film of fluorine-containing resin is obtained.
When the fluorine-containing resin to be dispersed in the coating liquid is not a polymerizable resin, the resin film of the fluorine-containing resin dried by evaporation of the solvent from the coating film is obtained. On the other hand, when the fluorine-containing resin dispersed in the coating liquid is polymerizable and the coating liquid contains other compounds that react with the polymerizable fluorine-containing resin, it is added when the coating film is dried. The polymerizable fluorine-containing resin and other compounds react with heat. Thereby, the resin film which consists of a fluorine-containing resin which contains the fluorine-containing resin disperse | distributed to the coating liquid in frame | skeleton is obtained.

《Coating fluid》
In the present invention, the coating liquid used for forming the coating film is obtained by dispersing the fluororesin in a solvent. More specifically, the polymer (A) described later is dispersed in a solvent, or the polymer (A) and other components other than the polymer (A) are dispersed or dissolved in a solvent. It will be.
Any solvent may be used as long as it can disperse or dissolve each component contained in the coating solution, and a solvent that disperses at least the polymer (A) is used.
When the other component is contained, the solvent alone can be used to form a uniform solution as long as the solvent in which the polymer (A) is dispersed disperses or dissolves the other component. Moreover, you may use together the other solvent which disperse | distributes or melt | dissolves this other component.

  As said other component, it is preferable that the silane coupling agent which has an amino group, or the compound (C) mentioned later is contained. It is particularly preferred that the coating liquid contains a silane coupling agent having an amino group as another component. If the polymer (A) and a silane coupling agent having an amino group are contained in the coating liquid, these react with each other when the coating film is dried, and a film made of a resin having an aminosilane skeleton is formed. The Thereby, the thermal stability of the electric charge held by the electret formed is further improved, and the temporal stability and the like are also improved. This effect is particularly remarkable when the polymer (A) is a polymer having an aliphatic ring in the main chain and a carboxy group or a carbonyl group as a terminal group. This is presumably because the nanocluster structure derived from the silane coupling agent having an amino group functions as a site for storing charges in the electret. The nanocluster structure derived from the amino group-containing silane coupling agent is formed by causing nanophase separation between the polymer (A) and the amino group-containing silane coupling agent.

The coating liquid may be obtained by preparing a composition containing each component in advance and dispersing or dissolving it in a solvent, or by dispersing or dissolving each component in each solvent and mixing each solution. May be.
As a method for producing the composition in the case of preparing a composition containing each component in advance, the solid and the solid, or the solid and the liquid may be mixed by kneading, eutectic extrusion, etc. Each solution dispersed or dissolved in may be mixed. Among these, it is more preferable to mix each solution.
For example, when the polymer (A) and a silane coupling agent having an amino group are used in combination, the coating solution is prepared by dispersing the polymer (A) in an aprotic fluorinated solvent, A silane coupling agent solution in which a silane coupling agent having a group is dispersed or dissolved in a protic fluorine-containing solvent is prepared, and the polymer (A) solution having an amino group and the silane coupling agent solution are mixed. It is preferable to obtain by this. The aprotic fluorinated solvent and the protic fluorinated solvent will be described later.

[Fluorine-containing resin]
The fluorine-containing resin used in the present invention is a resin having a fluorine atom (F atom).
The fluorine-containing resin in the present invention is not particularly limited, and in addition to the known fluorine-containing resins, fluorine-containing oils, fluorine-containing adhesives, fluorine-containing elastomers, fluorine-containing paint varnishes, polymerizable fluorine-containing resins, etc. It is mentioned as a resin material.
As said fluorine-containing resin, tetrafluoroethylene resin etc. are mentioned. Specific examples include polymers of tetrafluoroethylene (TFE) and derivatives thereof (FR ¹ C = CR ¹ R ² , R ¹ = F or H, R ² = F, H, Cl, or any). .
Examples of the fluorine-containing oil include perfluoropolyether oil and low-polymer trifluoroethylene chloride. Specific examples include perfluoropolyether oil (trade name “DEMNUM” manufactured by Daikin Industries), ethylene trifluoride chloride low polymer (trade name “DAIFLOY” manufactured by Daikin Industries), and the like.
Examples of the fluorine-containing adhesive include an ultraviolet curable fluorinated epoxy adhesive. Specific examples include (trade name “Optodyne” manufactured by Daikin Industries).
Examples of the fluorine-containing elastomer include linear fluoropolyether compounds. Specific examples include (trade names “SIFEL3590-N”, “SIFEL2610”, and “SIFEL8470” manufactured by Shin-Etsu Chemical Co., Ltd.).
Examples of the fluorine-containing paint varnish include a tetrafluoroethylene / vinyl monomer copolymer (trade name “Zeffle” manufactured by Daikin Industries).

Examples of the polymerizable fluorine-containing resin include polymerizable amorphous fluororesins (trade name “CYTOP” manufactured by Asahi Glass).
CYTOP has A type (terminal functional group is —COOH), M type (terminal functional group is —CONH to Si (OR) n), and S type (terminal group is —CF ₃ ). The fluorinated resin is dispersed or dissolved in a solvent and can be used for forming a resin film.
CYTOP (EGG-811) is obtained by mixing CYTOP (A type) with a silane coupling agent having an amino group and dispersing or dissolving in a solvent. CYTOP (EGG-811) has a COOH group at the resin end, and -COOH reacts with a silane coupling agent by heating during film formation.
Teflon (registered trademark) AF1601S is an amorphous fluororesin solution and is a polymerizable fluororesin. Teflon (registered trademark) FEP is a fluororesin in which tetrafluoroethylene and hexafluoropropylene are copolymerized.

Moreover, it is preferable that the said fluorine-containing resin has the following polymers (A) which have an aliphatic ring in a principal chain.
-Polymer (A)-
The polymer (A) is a polymer having an aliphatic ring in the main chain. The aliphatic ring contributes to improvement of charge retention performance. “Aliphatic ring” refers to a ring having no aromaticity. The aliphatic ring may have a carbocyclic structure in which the ring skeleton is composed only of carbon atoms, or has a heterocyclic structure in which the ring skeleton includes atoms (heteroatoms) other than carbon atoms. May be. Examples of the hetero atom include an oxygen atom and a nitrogen atom. The aliphatic ring may be saturated or unsaturated. The number of atoms constituting the ring skeleton of the aliphatic ring is preferably 4 to 7, and more preferably 5 or 6. That is, the aliphatic ring is preferably a 4-membered ring to a 7-membered ring, and more preferably a 5-membered ring or a 6-membered ring.

Examples of the aliphatic ring include a saturated or unsaturated aliphatic hydrocarbon ring, an aliphatic heterocyclic ring in which a part of carbon atoms in the aliphatic hydrocarbon ring is substituted with a hetero atom such as an oxygen atom or a nitrogen atom, A fluorine-containing aliphatic ring in which a hydrogen atom in an aliphatic hydrocarbon ring or an aliphatic heterocyclic ring is substituted with a fluorine atom is preferred.
The aliphatic ring may have a substituent (excluding a fluorine atom). “It may have a substituent” means that part or all of the hydrogen atom or fluorine atom bonded to the carbon atom constituting the ring skeleton of the aliphatic ring may be substituted with a substituent. Means.

Among the above, the polymer (A) preferably has a fluorine-containing aliphatic ring or an aliphatic hydrocarbon ring in the main chain.
“Having an aliphatic ring in the main chain” means that at least one of carbon atoms constituting the ring skeleton of the aliphatic ring is a carbon atom constituting the main chain of the polymer (A). . At least one of the carbon atoms derived from the polymerizable double bond of the monomer used for the polymerization of the polymer (A) is a carbon atom constituting the main chain. For example, in the case where the polymer (A) is a fluoropolymer obtained by polymerizing a cyclic monomer as described later, two carbon atoms constituting the double bond are carbon atoms constituting the main chain. It becomes. 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.

The polymer (A) preferably has a reactive functional group. In particular, when the polymer (A) is used in combination with a silane coupling agent or compound (C) having an amino group, the polymer (A) is a functional group or a functional group possessed by the silane coupling agent having an amino group. The compound (C) preferably has a reactive functional group capable of reacting with the polar functional group. A “reactive functional group” can form a bond by reacting with other components blended together with the polymer (A) or between the molecules of the polymer (A) when heated or the like. It means a group having reactivity. By having a reactive functional group, the effect of the present invention is improved.
Considering the strength of interaction with the silane coupling agent or compound (C) having an amino group and ease of introduction into the polymer, the reactive functional group of the polymer (A) is It is preferably a functional group. That is, the functional group includes a carboxy group, a carbonyl group, an acid halide group, an alkoxycarbonyl group, a carbonyloxy group, a carbonate group, a sulfo group, a phosphono group, a hydroxy group, a thiol group, a silanol group, and an alkoxysilyl group. At least one selected from is preferred.

Among the above, the polymer (A) preferably has a carboxy group or a carbonyl group.
The weight average molecular weight of the polymer (A) is preferably 50,000 or more, more preferably 150,000 or more, further preferably 200,000 or more, and particularly preferably 250,000 or more. When the weight average molecular weight is 50,000 or more, film formation can be easily performed. Moreover, the heat resistance of a film | membrane improves that it is 200,000 or more, and the thermal stability as an electret improves.
On the other hand, if the weight average molecular weight is too large, it may be difficult to dissolve in a solvent, and there may be a problem that a film forming process is limited. Therefore, the weight average molecular weight of the polymer (A) is preferably 1 million or less, more preferably 850,000 or less, further preferably 650,000 or less, and particularly preferably 550,000 or less.

In consideration of charge retention performance as an electret, the polymer (A) preferably has a relative dielectric constant of 1.8 to 8.0, more preferably 1.8 to 5.0, and more preferably 1.8 to 3 0.0 is particularly preferred. The relative dielectric constant is a value measured at a frequency of 1 MHz in accordance with ASTM D150.
Further, the polymer (A) is preferably one having a high volume resistivity and a high dielectric breakdown voltage.
The volume resistivity of the polymer (A) is preferably 10 ¹⁰ Ωcm to ^{10 20} Ωcm, more preferably 10 ¹⁶ Ωcm to 10 ¹⁹ Ωcm. The volume resistivity is measured according to ASTM D257.
The dielectric breakdown voltage of the polymer (A) is preferably 10 kV / mm to 25 kV / mm, more preferably 15 kV / mm to 22 kV / mm. The breakdown voltage is measured according to ASTM D149.
As the polymer (A), a highly hydrophobic polymer is preferable in order to eliminate water that adversely affects insulation and maintain high insulation.
Specifically, the polymer (A) is preferably a fluoropolymer described later.

(Fluoropolymer)
The fluoropolymer is a fluoropolymer having an aliphatic ring in the main chain. Examples of the aliphatic ring include those described above.
Here, the “fluorinated polymer” is a polymer having a fluorine atom in its structure. In the fluoropolymer, the fluorine atom may be bonded to the carbon atom constituting the main chain or may be bonded to the side chain. From the viewpoint of obtaining a polymer suitable for electretization having a low water absorption and low dielectric constant, a high dielectric breakdown voltage, and a high volume resistivity, it preferably has at least fluorine atoms bonded to carbon atoms constituting the main chain. . That is, the fluoropolymer preferably has a fluorinated aliphatic ring in the main chain.

In particular, the fluorine-containing aliphatic ring is a fluorine-containing aliphatic ring having a heterocyclic structure having one or two etheric oxygen atoms in the skeleton. It is preferable from the viewpoint of easy acquisition of the coalescence.
The fluorine-containing aliphatic ring may have a substituent.

Preferred fluorine-containing 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.
“Cyclic polymer” means a polymer having a cyclic structure. “Unit” means a repeating unit constituting a polymer. Hereinafter, the compound represented by the formula (1) is also referred to as “compound (1)”. The same applies to units, compounds and the like represented by other formulas. For example, the unit represented by formula (3-1) is also referred to as “unit (3-1)”.

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 formulas of the compound (1) and the compound (2), 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. It is.
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. Specific examples include a trifluoromethoxy 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.
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 composed only of units formed by the cyclic fluorine-containing monomer, and is a copolymer having the units and other units. Also good.
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, monomers having a reactive functional group in the side chain, tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), and the like.
A polymer obtained by copolymerization of a cyclic fluorine-containing monomer and a diene fluorine-containing monomer is considered as a fluorine-containing cyclic polymer (I ′).

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 following compound (3) is preferable.
_{CF 2 = CF-Q-CF} = CF 2 ··· (3)
In the formula of the compound (3), Q may have an etheric oxygen atom, and a part of the fluorine atom may be substituted with a halogen atom other than the fluorine atom, preferably 1 to 5, preferably 1 to 3 perfluoroalkylene groups which may have a branch. Examples of halogen atoms other than fluorine include chlorine atom and bromine atom.
Q is preferably a perfluoroalkylene group having an etheric oxygen atom. In that case, the etheric oxygen atom in the perfluoroalkylene group may be present at one end of the group, may be present at both ends of the group, and is present between the carbon atoms of the group. You may do it. From the viewpoint of cyclopolymerizability, it is preferably present at one end of the group.

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 units formed by the cyclopolymerization of the compound (3) include the following units (3-1) to (3-
4) and the like.

As the fluoropolymer, one synthesized by polymerizing the above-described monomers may be used, or a commercially available product may be used.
CYTOP (registered trademark, manufactured by Asahi Glass Co., Ltd.) is a commercially available fluoropolymer having a fluorine-containing aliphatic ring containing an etheric oxygen atom in the main chain and having a carboxy group or a carbonyl group at the end of the main chain. Can be mentioned.

-Polymer (A ')-
The polymer (A ′) is obtained by reacting the polymer (A) with another compound. In this case, the coating solution may be a coating solution in which the polymer (A) and other compounds other than the polymer (A) are dispersed or dissolved. Thereby, the dry resin film which consists of a polymer (A ') with which the polymer (A) and other compound reacted was obtained after a drying process.
As the other compound, a silane coupling agent having an amino group or a compound (C) having a molecular weight of 50 to 2,000 having two or more polar functional groups (excluding the silane coupling agent) is preferable. In particular, a silane coupling agent having an amino group is preferable. Thereby, the thermal stability of the electric charge held by the electret formed is further improved, and the temporal stability and the like are also improved. This effect is particularly remarkable when the polymer (A) is a polymer having an aliphatic ring in the main chain and a carboxy group or a carbonyl group as a terminal group.
Examples of the reaction product include those produced by reacting each component when the coating liquid in which the polymer (A) and the other components are dispersed or dissolved in a solvent is heated. Examples of the heating include baking when forming a film by volatilizing a solvent, and heat treatment when forming a curved surface having a predetermined curvature radius that continuously curves from the upper surface to the side surface of the pattern film.

(Silane coupling agent having amino group)
It does not specifically limit as a silane coupling agent which has an amino group, A conventionally well-known or well-known thing can be utilized over a wide range.
Considering availability, etc., particularly preferred silane coupling agents having an amino group are γ-aminopropylmethyldiethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyl. Triethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, and N- (β-aminoethyl) -γ- 1 or more selected from aminopropyltriethoxysilane.
The content of the amino group-containing silane coupling agent is preferably 0.1% by mass to 20% by mass, and 0.3% by mass to 10% by mass with respect to the total amount of the polymer (A) and the silane coupling agent. % Is more preferable, and 0.5% by mass to 5% by mass is most preferable. Within this range, the polymer (A) can be uniformly mixed, and phase separation is unlikely to occur when each component is dispersed or dissolved in a solvent to form a coating solution.

(Compound (C))
The compound (C) is a compound having two or more polar functional groups and a molecular weight of 50 to 2,000 (excluding the silane coupling agent).
The “polar functional group” is a functional group having one or both of the following properties (1a) and (1b).
(1a): Two or more types of atoms having different electronegativity are included, and the functional group has polarity due to polarization.
(1b): Polarization is caused by the difference in electronegativity with carbon bonded to the functional group.
Specific examples of the polar functional group having only the above characteristic (1a) include a hydroxyphenyl group.
Specific examples of the polar functional group having only the characteristic (1b) include a primary amino group (—NH ₂ ), a secondary amino group (—NH—), a hydroxy group, and a thiol group.
Specific examples of polar functional groups having both the above characteristics (1a) and (1b) include sulfo group, phosphono group, carboxy group, carbonyl group, alkoxycarbonyl group, acid halide group, formyl group, isocyanate group, cyano group. Group, a carbonyloxy group (—C (O) —O—) carbonate group (—O—C (O) —O—) and the like.

The molecular weight of the compound (C) is preferably 50 to 2,000, and more preferably 100 to 2,000. When the molecular weight of the compound (C) is 50 or more, it is difficult to volatilize and it is easy to remain in the film after film formation. Further, when the molecular weight of the compound (C) is 2,000 or less, the compatibility is improved without phase separation from the polymer (A).
As the compound (C), pentane-1,5-diamine, hexane-1,6-diamine, cyclohexane-1,2-diamine, cyclohexane-1,3-diamine, cyclohexane-1,4-diamine, 1,2 -Diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, triaminomethylamine, tris (2-aminoethyl) amine, tris (3-aminopropyl) amine, cyclohexane-1,3,5-triamine , Cyclohexane-1,2,4-triamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 2,4,6-triaminotoluene, 1,3,5-tris (2 -Aminoethyl) benzene, 1,2,4-tris (2-aminoethyl) benzene, 2,4,6-tris (2-aminoethyl) tolu More preferred is at least one selected from the group consisting of ethylene, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and polyethyleneimine, tris (2-aminoethyl) amine, tris (3-aminopropyl) amine, cyclohexane-1, Most preferred is at least one selected from the group consisting of 3-diamine, hexane-1,6-diamine, diethylenetriamine and polyethyleneimine.

A compound (C) may be used individually by 1 type, and may use 2 or more types together. For example, a compound having two polar functional groups and a compound having three or more polar functional groups may be mixed and used.
The content of the compound (C) is preferably 0.01% by mass to 30% by mass of the content of the polymer (A), and more preferably 0.05% by mass to 10% by mass. When the content is 0.01% by mass or more, an effect obtained by blending the compound (C) is sufficiently obtained, and sufficient thermal stability of the charge, stability over time, etc. can be secured as an electret. When the content is 30% by mass or less, the miscibility with the polymer (A) is good, and the distribution in the coating liquid becomes uniform.

[solvent]
The coating liquid contains at least the polymer (A) or the polymer (A) and the other component in a solvent capable of dispersing or dissolving the polymer (A) or the polymer (A) and the other component. Dispersed or dissolved. What is necessary is just to select suitably as this solvent according to the polymer (A) to be used or a polymer (A) and said other component. The other component is a silane coupling agent having the amino group that reacts with the polymer (A), the compound (C), or the like.
For example, when using the said fluoropolymer as a polymer (A), a fluorine-containing organic solvent can be used as a solvent.
As the fluorine-containing organic solvent, an aprotic fluorine-containing solvent is preferable. The “aprotic fluorine-containing solvent” is a fluorine-containing solvent having no proton donating property.
Examples of the aprotic fluorine-containing solvent include polyfluoroaromatic compounds such as 1,4-bis (trifluoromethyl) benzene, polyfluorotrialkylamine compounds such as perfluorotributylamine, and polyfluoros such as perfluorodecalin. Cycloalkane compounds, polyfluorocyclic ether compounds such as perfluoro (2-butyltetrahydrofuran), perfluoropolyethers, polyfluoroalkane compounds, hydrofluoroethers (HFE), and the like can be used.
As the fluorine-containing organic solvent, it is preferable to use only an aprotic fluorine-containing solvent because of its high solubility and good solvent.
Further, the boiling point of the fluorine-containing organic solvent is preferably 65 ° C to 220 ° C. If the boiling point of the fluorine-containing organic solvent is 100 ° C. or higher, it is easy to form a uniform coating film during coating.

The solvent for dispersing or dissolving the silane coupling agent having an amino group or the compound (C) is preferably a protic fluorine-containing solvent. The “protic fluorine-containing solvent” is a fluorine-containing solvent having proton donating properties.
As the protic fluorine-containing solvent, for example, fluorine-containing alcohols such as 2- (perfluorooctyl) ethanol, fluorine-containing carboxylic acids, amides of fluorine-containing carboxylic acids, fluorine-containing sulfonic acids and the like can be used.
The solvent used for preparing the coating liquid preferably has a low water content. The water content is preferably 100 ppm or less, and more preferably 20 ppm or less.
The concentration of the polymer (A) in the coating liquid is preferably 0.1% by mass to 30% by mass, and more preferably 0.5% by mass to 20% by mass.
What is necessary is just to set the solid content density | concentration of a coating liquid suitably according to the film thickness to form.
Usually, it is 0.1 mass%-30 mass%, and 0.5 mass%-20 mass% are preferable.
The solid content is calculated by heating the coating liquid whose mass was measured at 200 ° C. for 1 hour under normal pressure to distill off the solvent and measuring the mass of the remaining solid content.

In particular, when the electret contains a material containing an aliphatic ring in the main chain and a reaction product of a polymer having a carboxy group or a carbonyl group as a terminal group and a silane coupling agent having an amino group, Thermal stability is further improved. The electret is also excellent in adhesion to the substrate.
Examples of the polymer having an aliphatic ring in the main chain and having a carboxy group or a carbonyl group as a terminal group include the aforementioned CYTOP (manufactured by Asahi Glass Co., Ltd.). The A type of CYTOP has a carboxy group (—COOH) as a terminal group, the M type has a carbonyl group (—CONH—Si (OR) n)), and the S type has a fluoromethyl group (— CF ₃ ).
In addition, the above-mentioned CYTOP (EGG-811) includes a polymer having an aliphatic ring in the main chain and having a carboxy group or a carbonyl group as a terminal group and a silane coupling agent having an amino group. Can be mentioned. CYTOP (EGG-811) is a mixture of CYTOP (A type) with a silane coupling agent having an amino group, and the terminal group is a carboxy group (—COOH). For this reason, COOH and a silane coupling agent react by the heating at the time of a drying process.

《Electron beam irradiation device》
The electron beam irradiation apparatus is not particularly limited as long as the apparatus has an ability to irradiate an electron beam. In the examples of the present application, an electron beam irradiation source (EB engine) manufactured by Hamamatsu Photonics Co., Ltd. was used. The EB engine can accelerate the thermoelectrons generated from the filament with a high voltage to increase energy, and take out the electron beam from the window foil into the atmosphere. A material having good transparency is used for the exit window, and a low-energy electron beam can be efficiently irradiated. The line irradiation type low energy electron beam irradiation source EB-ENGINE can vary the acceleration voltage from 40 kV to 70 kV, and can scan the electron beam uniformly to irradiate a 150 mm wide sample.

《Thermal energy》
The thermal energy source is not particularly limited, and any thermal energy source may be used as long as it can give thermal energy to the resin film. For example, any heat energy source such as a heater, laser irradiation, infrared irradiation, frictional heat, and the like can be considered.
In the case of heating, if the resin film is brought into direct contact with the surface of the resin film, the resin film may be deteriorated. Further, the supply of thermal energy from the substrate side is also preferable from the viewpoint of not contacting the resin film.
In this invention, it heated using the heating means in a corona charging device (made by Ricoh Co., Ltd.). A schematic diagram of the corona charging device is shown in FIG.

<Surface potential measurement>
The surface potential meter used for the surface potential measurement is not particularly limited as long as the surface potential can be detected. In the present invention, a surface potential meter, Model 344 manufactured by Trek Japan Co., Ltd. was used, and Model 6000B-7C was used as a probe.
The sample-sensor distance was 1 mm, and a sample area of 5 mmΦ was measured.
-On the increase rate of surface potential-
The increase rate of the surface potential is expressed by the following calculation formula using the initial surface potential V ₀ and the surface potential V ₁ after heating.
Increase rate = | {(V ₁ −V ₀ ) / V ₀ } | × 100
| {(V ₁ −V ₀ ) / V ₀ } | means an absolute value.

<Production example>
<Film formation process>
The method for forming a film on the substrate is not particularly limited as long as the film can be formed, and examples thereof include a spin coating method, a blade coating method, an applicator coating method, a dip coating method, and a spray coating method.

<< Drying process >>
The drying step after the film forming step is not particularly limited, and examples thereof include a circulation dryer heating method, a hot plate heating method, and a vacuum overheating method. As drying conditions, it is preferable to sufficiently dry for 1 hour or more at a temperature equal to or higher than the boiling point of the solvent to be used. The resin can be solidified by sufficiently drying it so that the solvent does not remain, and electrons can be trapped in the resin film by electron beam irradiation in the charge injection step described later. When the pressure is reduced and drying is performed at a low temperature, it is necessary to further dry the resin over a sufficient time.

-Thickness of the formed resin film-
The thickness of the resin film is preferably 10 μm to 100 μm. More preferably, it is 10 micrometers-60 micrometers. More preferably, it is 15 micrometers-30 micrometers.

《Charge injection process》
The sample placed under the electron beam irradiation source is irradiated with an electron beam. The acceleration voltage of the electron beam is preferably 1 kV to 10 kV. More preferably, it is 40 kV-70 kV.
Since the acceleration voltage of the electron beam is related to the penetration depth of the electron beam, it is preferable to select an acceleration voltage suitable for the material of the sample, particularly the specific gravity. When the specific gravity is doubled, the penetration depth of the electron beam is about ½. In addition, when the acceleration voltage is too hard, there is a possibility that charge traps do not occur due to destruction or deterioration of the sample and the electron beam passing through the sample.
As a charge injection method, electron beam irradiation is preferable. In other methods, it is difficult to trap the charge inside the sample, and furthermore, the charge trapped inside by the heat treatment cannot move to the vicinity of the surface.
The electron beam irradiation atmosphere is preferably an inert gas. Argon, nitrogen, etc. are mentioned. Moreover, the state with a high degree of vacuum may be sufficient. The oxygen partial pressure is preferably 100 ppm or less. If the oxygen partial pressure is too high, oxygen plasma is generated, and there is a possibility that the surface of the sample deteriorates or the composition is broken.
In order not to lower the electret property, it is preferable that the electret is not brought into contact with a solvent or moisture. For this reason, when irradiating an electron beam, it is preferable that the resin film is sufficiently dry and the solvent does not remain.

《Heating process》
The conditions of the heating process after the charge injection process will be described. The heating temperature is preferably 60 ° C. or higher and 180 ° C. or lower. When the heating temperature is 60 ° C. or higher, sufficient energy can be given to move the charge trapped inside the resin film. In addition, when the heating temperature is 180 ° C. or lower, the deterioration of the resin film and the disappearance of the charges trapped inside the resin film can be suppressed. A more preferable range of the heating temperature is 120 ° C. or higher and 170 ° C. or lower.
The heating time is not particularly limited, but is preferably 1 minute or more and 15 minutes or less. If the heating time is 1 minute or longer, a sufficient amount of heat can be given to move the charge. Moreover, it can suppress that a resin film deteriorates because it is 15 minutes or less.
The charges injected by the electron beam are accumulated inside the resin film. The penetration depth of the charge is affected by the acceleration voltage of the electron beam, the specific gravity of the resin film, and the like. The charge accumulated inside is easily moved by the thermal motion of the resin film by the external heat energy. At that time, electric charge is gradually generated on the surface of the resin film. As a result, the surface potential is detected by an external surface potential sensor, and the absolute value of the surface potential increases.

The control of the increase in the surface potential according to the present invention is difficult to realize in cases other than the fluorine-containing resin because the charge holding ability is low. A fluororesin is suitable because it has high insulating properties and is resistant to deterioration caused by electron beam irradiation.
In the conventional electret method, it is generally known that heating is performed at the time of charging, but heating after electret is not performed because it usually leads to a decrease in electret properties. However, in the case of electron beam irradiation, since charges are injected deeply in the depth direction of the resin film, it was found that charges can be transferred by heating after electretization. Therefore, it is possible to control the absolute value of the surface potential in the increasing direction by heating after the electron beam irradiation.

Moreover, although this invention concerns on the manufacturing method of the electret of following (1), following (2)-(7) is also included as embodiment.
(1) a film-forming film forming step of forming a coating film on the substrate surface using a coating liquid in which a fluorine-containing resin is dispersed in a solvent;
A drying step of drying the coating film after the film formation step;
A charge injection step of injecting charges into the resin film of the fluororesin obtained after the drying step by electron beam irradiation;
A heating step of heating the resin film of the fluororesin after the charge injection step;
A method for producing an electret, comprising:
(2) The method for producing an electret according to (1) above, wherein the fluororesin in the resin film after the drying step has an aminosilane skeleton.
(3) The fluororesin in the resin film after the drying step is a polymer (A) having an aliphatic ring in the main chain or a polymer obtained by reacting the polymer (A) with another compound ( The method for producing an electret according to the above (1) or (2), comprising A ′).
(4) The polymer (A ′) is a polymer having a reaction product of the polymer (A) and a silane coupling agent having an amino group. Method for manufacturing the electret.
(5) The method for producing an electret according to any one of (1) to (4) above, wherein the fluorine-containing resin in the coating liquid has a carboxy group or a carbonyl group as a terminal group.
(6) The heating step is a step of controlling an increase rate of an absolute value of a surface potential in a resin film of a fluororesin after the charge injection step by controlling a heating temperature (1) The manufacturing method of the electret in any one of (5) thru | or (5).
(7) In the heating step, the heating temperature is 60 ° C. or higher and 180 ° C. or lower, and the heating time is 1 minute or longer and 15 minutes or shorter. The manufacturing method of the electret of description.

Below, the specific example of the said embodiment is described as an Example. The present invention is not limited to the following examples.
[Example 1]
A polymerizable fluorine-containing resin (CYTOP EGG-811: manufactured by Asahi Glass Co., Ltd.) was formed on a 40 mm square copper plate (thickness 1 mm) by spin coating. CYTOP EGG-811 is obtained by dispersing or dissolving a polymerizable fluorine-containing resin having a terminal functional group of -COOH and a silane coupling agent having an amino group in a solvent. A coating solution was prepared using this, and a resin film was formed on the substrate (the copper plate). After film formation, it was heated at 280 ° C. for 1 hour and sufficiently dried. As a result, a resin film of a fluorine-containing resin in which a resin having a terminal functional group of —COOH and a silane coupling agent having an amino group reacted and the solvent was sufficiently evaporated to be dried was obtained. The film thickness of the fluorine-containing resin measured after heat drying was 28 μm. The obtained resin-coated sample was irradiated with an electron beam under the following conditions.
Acceleration voltage: 50 kV
Tube current: 2mA
Absorbed dose: 154.6kGy (calculated value)
Oxygen partial pressure: 100 ppm or less Filling gas: N ₂
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Initial surface potential: -82 [V]
The sample after electron beam irradiation was heated at 160 ° C. for 10 minutes on a hot plate provided in a corona charging device (manufactured by Ricoh Co., Ltd.). Thereafter, the sample was allowed to cool to room temperature, and the surface potential of the sample was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Surface potential after heating: -228 [V]
The surface potential of the electret could be increased by heating the sample subjected to electron beam irradiation and applying thermal energy.

[Comparative Example 1]
A fluorine-containing resin-coated sample produced by the same procedure as in Example 1 was corona charged under the following conditions. For the corona charging, a charging device that generates corona discharge (corona charging device shown in FIG. 1: manufactured by Ricoh Co., Ltd.) was used.
Charger applied voltage: 4.2 kV
Grid applied voltage: 100V
Sample heating temperature: 100 ° C
The surface potential of the sample after corona charging was measured. (Used by Trek Co., main unit: Model 344, probe: Model 6000B-7C)
Initial surface potential: -98 [V]
After corona charging, the plate was heated on a hot plate at 160 ° C. for 10 minutes, and then naturally cooled to room temperature, and then the surface potential was measured (manufactured by Trek, main unit: Model 344, probe: Model 6000B-7C was used).
Surface potential after heating: -92 [V]
Even when thermal energy was applied, the surface potential could not be increased.
In the case of electron beam irradiation, the electron beam penetrates deeply into the fluorine-containing resin film of the resin coat sample, so that it is considered that charges are accumulated inside. On the other hand, in the corona charging, charges are accumulated on the very surface of the resin-coated sample.
Therefore, in the case of electron beam irradiation, the charge accumulated inside the fluorine-containing resin film is activated by thermal energy, and the accumulated charge springs out on the surface of the resin-coated sample by making it easy to move. Conceivable.

[Example 2] to [Example 4]
The experiment was performed in the same manner as in Example 1 except that the thickness of the resin film of the sample and the heating temperature were changed.
The results are shown in Table 1.

[Comparative Example 2] to [Comparative Example 4]
The experiment was performed in the same manner as in Comparative Example 1 except that the thickness of the resin film of the sample and the heating temperature were changed.
The results are shown in Table 1.

[Example 5] to [Example 8]
The experiment was performed in the same manner as in Example 1 except that the sample resin, the sample film thickness, and the heating temperature were changed.
The results are shown in Table 1.

[Comparative Example 5] to [Comparative Example 8]
The experiment was performed in the same manner as in Comparative Example 1 except that the resin, film thickness, and heating temperature of the sample were changed.
The results are shown in Table 1.

[Example 9] to [Example 11]
The experiment was performed in the same manner as in Example 4 except that the heating temperature was changed to 100 ° C, 120 ° C, and 140 ° C.
The results are shown in Table 1.

[Comparative Example 9] to [Comparative Example 11]
The experiment was performed in the same manner as in Comparative Example 4 except that the heating temperature was changed to 100 ° C, 120 ° C, and 140 ° C.
The results are shown in Table 1.
From the results of Examples 4 and 9 to 11, it is understood that the increase rate of the absolute value of the surface potential can be controlled by controlling the heating temperature. On the other hand, it can be seen from the results of Comparative Examples 4 and 9 to 11 that the rate of increase in the absolute value of the surface potential cannot be controlled by controlling the heating temperature in corona charging.

[Example 12]
A dispersion film of Teflon (registered trademark) FEP (Mitsui / DuPont Fluorochemical Co., Ltd.) was applied to a Cu substrate to form a coating film. Subsequently, the film was dried at 150 ° C. for 60 minutes to obtain a fluororesin resin film having a thickness of about 400 μm.
The obtained resin-coated sample was irradiated with an electron beam under the following conditions.
Acceleration voltage: 50 kV
Tube current: 2mA
Absorbed dose: 154.6kGy (calculated value)
Oxygen partial pressure: 100 ppm or less Filling gas: N ₂
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Initial surface potential: -5 [V]
The sample after electron beam irradiation was heated on a hot plate at 160 ° C. for 10 minutes, and then allowed to cool naturally to room temperature, and then the surface potential was measured (using Trek Corp., main body: Model 344, probe: Model 6000B-7C). did).
Surface potential after heating: −13 [V]
The surface potential could be increased by applying thermal energy to the sample subjected to electron beam irradiation.

[Comparative Example 12]
A resin film was prepared in the same manner as in Example 12. The obtained resin-coated sample was corona charged under the following conditions.
Charger applied voltage: 4.2 kV
Grid applied voltage: 100V
Sample heating temperature: 100 ° C
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Initial surface potential: -95 [V]
After corona charging, the plate was heated on a hot plate at 160 ° C. for 10 minutes, and then naturally cooled to room temperature, and then the surface potential was measured (manufactured by Trek, main unit: Model 344, probe: Model 6000B-7C was used).
Surface potential after heating: -21 [V]
Even when thermal energy was applied, the surface potential could not be increased.

[Example 13]
In Teflon (registered trademark) AF1601S (Mitsui / DuPont Fluorochemical Co., Ltd.), 3- (2-aminoethylamino) propyltrimethoxysilane as an additive was dispersed so as to be 1.5% by mass, and was added onto the Cu substrate. The coated film was formed by coating. Teflon (registered trademark) AF1601S is obtained by dispersing Teflon (registered trademark) AF1600 (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) in a fluorine-based solvent. The coating film was dried at 150 ° C. for 60 minutes to obtain a resin-coated sample on which a 24 μm resin film was formed.
The obtained resin-coated sample was irradiated with an electron beam under the following conditions.
Acceleration voltage: 50 kV
Tube current: 2mA
Absorbed dose: 154.6kGy (calculated value)
Oxygen partial pressure: 100 ppm or less Filling gas: N ₂
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, using main body: Model 344, probe: Model 6000B-7C).
Initial surface potential: -64 [V]
After irradiation, the plate was heated on a hot plate at 160 ° C. for 10 minutes, and then allowed to cool naturally to room temperature, and then the surface potential was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C).
Surface potential after heating: -101 [V]
The surface potential could be increased by applying thermal energy to the sample subjected to electron beam irradiation.

[Comparative Example 13]
A resin-coated sample produced in the same manner as in Example 13 was corona charged under the following conditions.
Charger applied voltage: 4.2 kV
Grid applied voltage: 100V
Sample heating temperature: 100 ° C
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Initial surface potential: -96 [V]
After corona charging, the plate was heated on a hot plate at 160 ° C. for 10 minutes, and then naturally cooled to room temperature, and then the surface potential was measured (manufactured by Trek, main unit: Model 344, probe: Model 6000B-7C was used).
Surface potential after heating: -64 [V]
Even when thermal energy was applied, the surface potential could not be increased.

[Comparative Example 14]
A sample in which a PET resin layer was formed on a Cu substrate was prepared. For the PET resin layer, an insulating adhesive is coated on a Cu substrate, and a PET sheet (Lumirror (registered trademark) X30: manufactured by Toray Industries, Inc.) is pasted thereon, and a sufficient pressure is applied to adhere the PET sheet. Formed with. The film thickness of the PET resin layer was 30 μm.
The obtained resin-coated sample was irradiated with an electron beam under the following conditions.
Acceleration voltage: 50 kV
Tube current: 2mA
Absorbed dose: 154.6kGy (calculated value)
Oxygen partial pressure: 100 ppm or less
Filling gas: N ₂
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Initial surface potential: -2 [V]
After irradiation, the plate was heated on a hot plate at 160 ° C. for 10 minutes, and then naturally cooled to room temperature, and then the surface potential was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C was used).
Surface potential after heating: -1 [V]
Even when the sample subjected to electron beam irradiation was heated, the surface potential could not be increased.

[Comparative Example 15]
A resin-coated sample produced in the same manner as in Comparative Example 14 was corona charged under the following conditions.
Charger applied voltage: 4.2 kV
Grid applied voltage: 100V
Sample heating temperature: 100 ° C
The surface potential of the sample after electron beam irradiation was measured (manufactured by Trek, using main body: Model 344, probe: Model 6000B-7C).
Initial surface potential: -88 [V]
After corona charging, the plate was heated on a hot plate at 160 ° C. for 10 minutes, and then naturally cooled to room temperature, and then the surface potential was measured (manufactured by Trek, main body: Model 344, probe: Model 6000B-7C).
Surface potential after heating: -7 [V]
Even when thermal energy was applied, the surface potential could not be increased.
Table 1 below shows the results of these experiments.

1 Corona charger (grid mountable)
2 Metal plate 3 Heater 4 High voltage power supply

Japanese Patent No. 5381979 JP 2014-037451 A Japanese Patent No. 4774130 Japanese Patent No. 4753609 JP 2009-088444 A

K. Hagiwara, M. Goto, Y. Iguchi, Y. Yasuno, H. Kodama, K. Kidokoro, and T. Tajima, “Soft Xray charging method for a silicon electret condenser microphone,” Appl. Phys. Exp., 3 , 091502, 3pp, 2010. Honzumi, M., Hagiwara, K., Iguchi, Y., and Suzuki, Y., “High-Speed Electret Charging Method Using Vacuum UV Irradiation,” Appl. Phys. Lett., Vol. 98, Issue 5, 052901 ( 2011)

Claims (7)

A film forming step of forming a coating film on the substrate surface using a coating liquid in which a fluorine-containing resin is dispersed in a solvent;
A drying step of drying the coating film after the film formation step;
A charge injection step of injecting charges into the resin film of the fluororesin obtained after the drying step by electron beam irradiation;
A heating step of heating the resin film of the fluororesin after the charge injection step;
A method for producing an electret, comprising:   The method for producing an electret according to claim 1, wherein the fluorine-containing resin in the resin film after the drying step has an aminosilane skeleton.   The fluororesin in the resin film after the drying step is a polymer (A) having an aliphatic ring in the main chain or a polymer (A ′) obtained by reacting the polymer (A) with another compound. The manufacturing method of the electret of Claim 1 or 2 characterized by the above-mentioned.   The said polymer (A ') is a polymer which has a reaction product of the said polymer (A) and the silane coupling agent which has an amino group, The manufacture of the electret of Claim 3 characterized by the above-mentioned. Method.   The method for producing an electret according to any one of claims 1 to 4, wherein the fluorine-containing resin in the coating liquid has a carboxy group or a carbonyl group as a terminal group.   The heating step is a step of controlling an increase rate of an absolute value of a surface potential in a resin film of a fluorine-containing resin after the charge injection step by controlling a heating temperature. The manufacturing method of the electret in any one. The method for producing an electret according to any one of claims 1 to 6, wherein the heating step has a heating temperature of 60 ° C or higher and 180 ° C or lower and a heating time of 1 minute or longer and 15 minutes or shorter. .

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