WO2013011949A1

WO2013011949A1 - Heat-resistant electret material and condenser microphone

Info

Publication number: WO2013011949A1
Application number: PCT/JP2012/067953
Authority: WO
Inventors: 伴幸白川; 博幸長尾
Original assignee: 三菱樹脂株式会社
Priority date: 2011-07-15
Filing date: 2012-07-13
Publication date: 2013-01-24
Also published as: JP2013042484A

Abstract

Provided is a heat-resistant electret material with which charge retention is large, charge attenuation is small, and bonding between a metallic substrate and an electret layer formed from a fluorine resin, particularly polytetrafluoroethylene (PTFE), is superior. A heat-resistant electret material (10) comprises, upon a metallic substrate (1), an electret (3) which is formed from a fluorine resin, with a grounding resin layer (2) therebetween including a fluorine resin, silicon and/or a silicon compound, and conductive carbon. By introducing highly metallophilic silicon and/or a compound thereof into the grounding resin layer in a range which does not impair the electret material charge retention characteristics thereof, it is possible to improve adhesion between the metallic substrate, the grounding resin layer, and the electret layer.

Description

Heat-resistant electret material and condenser microphone

The present invention relates to a heat-resistant electret material capable of exhibiting high interlayer adhesion and charge retention characteristics even when high-heat-resistant polytetrafluoroethylene (PTFE) is used as the fluororesin of the electret layer, and the heat-resistant electret The present invention relates to a condenser-type microphone using a material.

An electret condenser microphone is known as one type of microphone. Electret type condenser microphones are relatively easy to miniaturize, but when they are used in mobile phones that have been further thinned in recent years, in addition to miniaturization, they are thinned. It is desirable to do. Further, as a characteristic of the condenser microphone using the electret material, the sensitivity is improved when the thickness of the electret layer (insulating resin layer) is reduced.

Electrets are ferroelectric materials, which have the property that they accumulate charge semi-permanently (charge electrets) or have semi-permanent electrical polarity due to oriented dipoles (dipole electrets). In the case of a macrophone, the electret is incorporated for the purpose of converting acoustic energy into a corresponding electrical signal by a potential difference displacement that occurs when either the electret fixed electrode or the counter electrode is vibrated by sound waves.

As the electret material used for the electret fixed electrode, a fluororesin having a larger charge amount than other resins is used. Among fluororesins, tetrafluoroethylene-hexafluoropropylene copolymer (FEP) is known to have little charge decay, and FEP fused to a metal plate is a condenser for microphones that is an electronic component. As currently used widely. The electrets based on fluorine-containing polymers are generally charged by, for example, negative corona discharge in air.

In recent years, the electronics industry has been working to reduce the use of hazardous substances from the viewpoint of environmental issues, one of which is “lead-free”. For this reason, even solder that has been conventionally used for joining electronic components is required to be lead-free, that is, joined with solder that does not contain lead. However, solder containing no lead has a higher melting point than conventional solder, and the soldering temperature needs to be 20 to 30 ° C. higher than conventional solder. Therefore, FEP is used for the insulating resin layer of the electret fixed electrode. If this is the case, there has been a problem that the FEP melts due to the soldering temperature, making it impossible to obtain good charging characteristics.

Therefore, as a resin material for the electret fixed electrode, a material having heat resistance with respect to the soldering temperature of lead-free solder and excellent charging characteristics is required. As such a material, polytetrafluoroethylene (PTFE) has been proposed. PTFE is preferable as a resin material for electret fixed electrodes because it has a large amount of charge and little charge decay, and since it has a higher melting point than FEP, it is also heat resistant to the soldering temperature of lead-free solder Have However, the PTFE film has a problem that it is difficult to adhere to a metal substrate. In order to improve the adhesiveness, there is a technique in which an adhesive layer made of a thermoplastic resin other than PTFE is provided between the metal substrate and the PTFE film.

However, when the adhesive layer is provided, the sensitivity as a fixed electrode may be impaired, and there is a problem that charging characteristics are deteriorated (charging attenuation is increased) by using a thermoplastic resin other than PTFE. Further, in order to improve the adhesion to a metal substrate with a PTFE film alone without providing an adhesive layer, it must be heat-sealed at a temperature greatly exceeding the melting point of PTFE (about 327 ° C.). When fused at a high temperature, there is a problem in that the charge decay increases.

Japanese Patent Application Laid-Open No. 2002-125297 describes an electret laminate in which a single thermoplastic resin film is adhered to the surface of a metal plate, but only an example using an FEP film as the thermoplastic resin film is disclosed. However, it is not clear how the PTFE film is adhered to the surface of the metal plate.

Japanese Patent No. 3692090 describes a multi-layer electret material in which an FEP film and a PTFE film are sequentially melt bonded on a metal plate. In this electret material, charge retention is achieved by laminating a fluororesin layer. There are disadvantages that are impaired. In addition, when FEP is used for the adhesive layer, the adhesive layer cannot be obtained unless the adhesive layer is thick, and the adhesive layer becomes thick. Has the disadvantage of not being suitable.

Japanese Patent Application Laid-Open No. 2010-279024 discloses a method of adding electric conductivity by adding carbon to a base resin layer provided between a metal substrate and an electret layer to enhance charge retention. ing. However, this method has a problem that the interlaminar adhesion between the metal substrate and the base resin layer is reduced due to the low metal affinity of carbon itself, and the interlaminar adhesion between the base resin layer and the electret layer is insufficient. is there.

JP 2002-125297 A Japanese Patent No. 3692090 JP 2010-279024 A

The present invention solves such problems of the prior art, and has a large charge holding power and low charge attenuation, and further from a metal substrate and a fluororesin, particularly polytetrafluoroethylene (PTFE). It is an object of the present invention to provide a heat-resistant electret material having excellent adhesiveness with an electret layer.

As a result of intensive studies to solve the above-mentioned problems, the present inventor made a base resin within a range that does not impair the charge retention characteristics of silicon (Si), a silicon compound, or a mixture thereof having high metal affinity as an electret material. It was found that the interlayer adhesion of the metal substrate / underlying resin layer / electret layer can be improved by introducing it into the layer.

The present invention has been achieved on the basis of such knowledge, and the gist thereof is as follows.

[1] An electret layer made of a fluororesin is formed on a metal base material through a base resin layer containing a fluororesin, silicon, a silicon compound, or a mixture thereof, and conductive carbon. Characteristic heat-resistant electret material.

[2] In [1], the thickness of the metal substrate is 10 to 500 μm, the thickness of the base resin layer is 1 to 50 μm, and the thickness of the electret layer is 8 to 50 μm. Heat-resistant electret material to be used.

[3] In [1] or [2], the proportion of silicon element in the total 100 mol% of fluorine element, silicon element and carbon element contained in the base resin layer is 1 to 50 mol%, A heat-resistant electret material having a ratio of 5 to 10 mol%.

[4] In [3], the ratio of silicon element and carbon element contained in the base resin layer is smaller than the ratio of carbon element on the metal substrate side, and on the electret layer side. A heat-resistant electret material characterized in that the proportion of silicon element is larger than the proportion of carbon element.

[5] The heat-resistant electret material according to any one of [1] to [4], wherein the fluororesin of the base resin layer contains polytetrafluoroethylene (referred to as “PTFE”) as a main component.

[6] The heat-resistant electret material according to any one of [1] to [5], wherein the fluororesin of the electret layer contains PTFE as a main component.

[7] In any one of [1] to [6], the metal base plate is made of stainless steel, aluminum, brass, iron, or an oxide thereof, and an alloy containing one or more of them. Or nickel, gold, silver, copper, tin, zinc, and platinum on the surface of a thin metal plate made of stainless steel, aluminum, brass, iron, or an oxide thereof, and an alloy containing one or more of these. A heat-resistant electret material comprising a thin metal plate coated with at least one conductive metal selected from the group consisting of:

[8] In any one of [1] to [7], the volume resistance value of the surface of the base resin layer on the electret layer side is 10 ¹⁰ Ω · m to 10 ¹³ Ω · m, and the volume of the electret layer A heat-resistant electret material having a resistance value of 10 ¹⁵ Ω · m or more.

[9] The heat-resistant electret material according to any one of [1] to [8], wherein the volume resistance value in the thickness direction of the base resin layer is larger on the electret layer side than on the metal substrate side .

[10] The heat-resistant electret material according to [9], wherein a volume resistance value at a thickness 1/2 of the base resin layer is greater than 10 ⁹ Ω · m and not more than 10 ¹² Ω · m.

[11] A condenser microphone using the heat-resistant electret material according to any one of [1] to [10].

According to the present invention, by introducing silicon (Si) having a high metal affinity, a silicon compound, or a mixture thereof (hereinafter sometimes referred to as “Si component”) into the base resin layer, Interlayer adhesion of the metal substrate / underlying resin layer / electret layer can be enhanced. That is, as is clear from the periodic table of elements, silicon is a substance that is closer to metal than carbon and has a higher metal affinity, and also has a higher affinity for fluorine (fluoride ions). Therefore, by including such a Si component in the base resin layer, the interlayer adhesion between the base resin layer and the metal base material can be improved. As a result, the interlayer of the metal base material / base resin layer / electret layer can be improved. It becomes possible to realize a heat-resistant electret material having excellent adhesion.

According to the present invention, the electret layer fluorine resin is preferable as a resin material for the electret fixed electrode because it has a large charge amount and little charge attenuation, and further has a higher melting point than FEP. By using PTFE having heat resistance even at the soldering temperature of the solder, it is possible to provide a heat resistant electret material having excellent interlayer adhesion and charge retention characteristics.

It is sectional drawing which shows embodiment of the heat-resistant electret material of this invention. It is a graph which shows the evaluation result of the electric charge retention characteristic of Examples 1, 2, Comparative Examples 1, 2, and Reference Examples 1, 2. It is a graph which shows the relationship between the thickness of a base resin layer, and a defect rate. It is a graph which shows the relationship between the thickness of an electret layer, and a charge retention. 3 is a graph showing displacement in mol% of silicon element and carbon element in the thickness direction of the base resin layer of the sample of Example 1. FIG. It is a graph which shows the displacement of the mol% of the silicon element and carbon element in the thickness direction of the base resin layer of the sample of Example 2. It is a graph which shows the displacement of the volume resistance value in the thickness direction of a base resin layer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of an embodiment of the heat-resistant electret material of the present invention, wherein 1 is a metal substrate, 2 is a base resin layer, and 3 is an electret layer.

The metal substrate used in the present invention is a thin metal plate made of stainless steel, aluminum, titanium, brass, copper, iron, or an oxide thereof, and an alloy containing one or more of these, or stainless steel, aluminum, It is selected from nickel, gold, silver, copper, tin, zinc, and platinum on the surface of a thin metal plate made of titanium, brass, copper, iron, oxides thereof, or an alloy containing one or more of these. It is preferably a thin metal plate coated (plated or vapor-deposited) with at least one conductive metal.

The thickness of the metal substrate is not particularly limited in terms of charge retention, but is usually 10 to 500 μm, and is 50 to 200 μm from the viewpoint of workability and the recent demand for smaller and lighter electronic devices. Preferably

The volume resistance value in the temperature range of 10 ° C. to 350 ° C. of the metal substrate used in the present invention is more than 60 × 10 ⁻⁸ Ω · m and less than 100 × 10 ⁻⁸ Ω · m. preferable.
The volume resistivity of the metal substrate is equal to or less than 60 × 10 ^-8 Ω · m is not preferable because can not retain the charge long stably holding the electret layer, 100 × 10 ^-8 Ω · In the case of m or more, the absolute amount of charges that can be held in the electret layer is reduced, which is not preferable.

The fluororesin used in the base resin layer and electret layer of the present invention may be either heat-meltable or non-heat-meltable, and is an unsaturated fluorinated hydrocarbon, unsaturated fluorinated chlorinated hydrocarbon, ether Examples thereof include polymers or copolymers such as group-containing unsaturated fluorinated hydrocarbons, or copolymers of these unsaturated fluorinated hydrocarbons with ethylene. For example, a polymer or copolymer of a monomer selected from tetrafluoroethylene, hexafluoropropylene, perfluoro (alkyl vinyl ether), vinylidene fluoride and vinyl fluoride, or a copolymer of these monomers and ethylene. it can. Of course, these can also be used independently and can also be used as 2 or more types of mixtures.

More specifically, a tetrafluoroethylene polymer (PTFE), a copolymer of tetrafluoroethylene and less than 2% by mass of a copolymerizable fluorine-containing monomer (modified PTFE), tetrafluoroethylene / perfluoro ( Alkyl vinyl ether) copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (CTFE), polyvinylidene fluoride ( PVDF), tetrafluoroethylene / hexafluoropropylene / perfluoro (alkyl vinyl ether) copolymer, polyvinylidene fluoride, and chlorotrifluoroethylene / ethylene copolymer are preferable. More preferably Ruoroechiren polymer (polytetrafluoroethylene) and / or tetrafluoroethylene and copolymers of copolymerizable fluorinated monomers of less than 2 wt% (modified PTFE).

When the electret layer is PTFE and / or modified PTFE, a treatment for increasing the crystallinity may be added after the electret layer is formed. The method for increasing the crystallinity of the PTFE resin layer is not particularly limited, and examples thereof include rolling, annealing, electron beam irradiation, and the like. A method of slow cooling after heat treatment using an oven or a heating furnace is the simplest and most common. However, since this method requires long-time treatment, recently, as another method, Japanese Patent Application Laid-Open No. 2007-039672 There is a method by EB (electron beam) irradiation described in the publication. The crystallinity of the PTFE layer (electret layer) is preferably in the range of 20 to 80%. If the degree of crystallinity is less than 20%, the charge retention becomes worse, whereas if it exceeds 80%, the elasticity of the material decreases and becomes hard and brittle, so various post-processing (bending, cutting, punching, punching, etc.) Sexuality gets worse.

Examples of the conductive carbon used in the base resin layer of the present invention include carbon black (Ketjen Black EC, furnace black, channel black, acetylene black, etc.), black pearl, carbon nanofiber, carbon nanotube, carbon nanohorn, and carbon nanoballoon. , Graphene, fullerene, and the like can be used. These may be used alone or in combination of two or more.

In addition, as a material for introducing the Si component into the base resin layer (hereinafter sometimes referred to as “Si component material”), a siloxane bond (—O—Si—O—) is formed in the coating film by heat curing. A silane coupling agent such as triethylsilanol, an alkoxysilane, a silicone, a metal alkoxide, an organic siloxane, an aqueous silicate solution, or the like used in Examples described later can be used.

More specifically, as the silane coupling agent, triethylsilanol, hydrolyzable organosilane, vinyl silane, methacryl silane, epoxy silane, amino silane, isocyanate silane and the like can be used.

As alkoxysilane, what is represented by following formula (1) can be used.
R ¹ _n (Si) (OR ² ) _4-n (1)
(Wherein R ¹ represents H or a linear, branched or cyclic alkyl group or aryl group having 1 to 8 carbon atoms, and R ² represents a linear or branched alkyl group having 1 to 6 carbon atoms. And n is an integer from 0 to 2).

Here, in the alkoxysilane represented by the formula (1), when n is 0, that is, Si (OR ² ) _{4 is referred} to as tetrafunctional alkoxysilane, and when n is 1, that is, R ¹ (Si). (OR ² ) ₃ is a trifunctional alkoxysilane, and n is 2, that is, R ¹ ₂ (Si) (OR ² ) ₂ is a bifunctional alkoxysilane, and n is 3, that is, R ¹ ₃ ( Si) (OR ² ) is a monofunctional alkoxysilane.

Specific examples of the tetrafunctional alkoxysilane that can be used in the present invention include tetramethoxysilane, tetraethoxysilane, tetra (n-propoxy) silane, tetra (i-propoxy) silane, and tetra (n-butoxy). Examples thereof include silane and tetra (t-butoxy) silane.

Specific examples of trifunctional alkoxysilanes include trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, Examples include isobutyltriethoxysilane, cyclohexyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, and allyltriethoxysilane.
Specific examples of the bifunctional alkoxysilane include dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane.

Of these, tetramethoxysilane, tetraethoxysilane, trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane and the like are particularly preferable.

As the silicone, polyether-modified silicone, epoxy-modified silicone, amino-modified silicone, and the like can be used in addition to straight silicon having only a methyl group or phenyl group as a substituent.

As the metal alkoxide, tetraethyl titanate, tetraethyl zirconate, aluminum isopropionate, or the like can be used.

As the organic siloxane, polydimethylsiloxane, polymethylvinylsiloxane, or the like can be used.

As the silicate of the silicate aqueous solution, atrium silicate, potassium silicate, hafnium silicate, or the like can be used.

The above Si component materials may be used alone or in any combination of two or more at any ratio.

The base resin layer of the heat-resistant electret material of the present invention is a base resin layer forming coating solution containing fluororesin, Si component material and conductive carbon, bar coating, spray coating, dip coating, spin coating, roller coating, impregnation coating. , Electrostatic coating, curtain flow coating (screen coating), gravure coating, die coating, slide coating, wire bar coating, knife coating, spin flow coating, etc. And can be obtained by drying and / or baking at a temperature of about room temperature to about 400 ° C. for 5 to 60 minutes. It can also be obtained by screen printing, gravure printing, or a method of laminating (thermocompression bonding) a previously prepared base resin layer film. In the case of the coating (coating) method, the heat-resistant electret material can be made thinner and thinner than the film laminating method.

The coating solution for forming the base resin layer can contain a binder resin, and the mass ratio of the binder resin to the fluororesin is preferably 5 to 50:95 to 50.
As the binder resin, for example, a resin having heat resistance equivalent to that of a fluororesin, that is, a thermal decomposition starting temperature of 300 ° C. or more and having adhesion to a metal substrate is preferable. Particularly suitable as such a binder resin are polyimide resin (PI), polyamideimide resin (PAI), polyphenylene sulfide resin (PPS), polyethersulfone resin (PES), polyetheretherketone (PEEK), polyether. Imide (PEI), polybenzimidazole (PBI), epoxy resin, or a mixture thereof. More preferably, it is PAI.

The binder resin may be dissolved in the liquid medium or may be uniformly dispersed in the liquid medium as fine particles. Liquid media that can be used include water, polar organic solvents, non-polar organic solvents, and mixtures thereof. When water is used as the liquid medium, it is preferable to add a surfactant to the liquid medium in order to reduce the surface tension of the liquid medium and improve the dispersibility of the binder resin and fluororesin powder.

If the binder resin is PI, PAI, PES, or the like and is relatively easily dissolved in an organic solvent such as N-methylpyrrolidone or a mixture of N-methylpyrrolidone and diacetone alcohol or xylene, the binder resin It is preferable to use by dissolving in a liquid medium. When the binder resin is PPS or the like and it is difficult to dissolve in an organic solvent, water containing a surfactant is used as the liquid medium, and the binder resin is used in the liquid medium. It is preferable to uniformly disperse and use.

The thickness of the base resin layer thus obtained is not particularly limited, but is preferably 1 to 50 μm. Thickness of the base resin layer that has conductivity and contributes to interlayer adhesion is desirable from the viewpoint of charge retention and interlayer adhesion. However, even if it is too large, the interlayer adhesion is caused by cohesive peeling in the layer. Sex is reduced. In general, a charge retention rate of 80% or more is sufficient when a heat-resistant electret material is used as a condenser microphone. Therefore, the film thickness of the base resin layer is particularly preferably in the range of 3 to 30 μm. A range of 5 to 20 μm is more preferable.

Further, the volume resistance value of the surface of the base resin layer on the electret layer side in the temperature range of 10 ° C. to 350 ° C. is preferably 10 ¹⁰ to 10 ¹³ Ω · m. If the volume resistance value of the surface of the base resin layer on the electret layer side is too small, it is not preferable because the charge retained in the electret layer cannot be stably maintained for a long time, and if it is too large, it is retained in the electret layer. This is not preferable because the absolute amount of charge that can be generated is reduced.

In addition, the base resin layer has a feature that the volume resistance value sequentially increases from the metal substrate side to the electret layer side in the thickness direction, and the volume resistance value at the thickness 1/2 of the base resin layer is 10 ^It is larger than ⁹ Ω · m and not more than 10 ¹² Ω · m, and the volume resistance value on the surface of the base resin layer on the electret layer side is not less than 10 ¹⁰ Ω · m, more preferably not less than 10 ¹¹ Ω · m and not more than 10 ¹³ Ω · m. It becomes.
The reason why the volume resistance value of the base resin layer is larger on the electret layer side than on the metal substrate side is not clear, but the proportion of conductive carbon (carbon element) contained in the base resin layer is a metal group as will be described later. This is thought to be due to the fact that the proportion of insulating silicon element decreases with increasing from the material side to the electret layer side.

The base resin layer of the heat-resistant electret material of the present invention has an elemental analysis for obtaining a good balance between the improvement in interlayer adhesion due to the inclusion of the Si component and the improvement in conductivity due to the inclusion of conductive carbon. The ratio of silicon element to the total of 100 mol% of fluorine element, silicon element and carbon element contained in the base resin layer determined by 1 is 1 to 5 mol%, and the ratio of carbon element is 5 to 10 mol%. Is preferred. If the ratio of silicon element is less than this range, the effect of improving interlayer adhesion by introducing the Si component into the base resin layer cannot be sufficiently obtained, and if it is too high, the conductivity of the base resin layer is lowered. As a result, the charge retention characteristics deteriorate. Further, the ratio of the carbon element corresponds to the total of the carbon element derived from the fluororesin and the carbon element derived from the conductive carbon and the carbon element derived from other carbon-containing components such as the binder resin in the base resin layer. However, if this ratio is too less than the above range, the conductivity of the base resin layer is insufficient, not only the charge retention characteristics are lowered, but also the flexibility is impaired, due to shear stress at the time of bending and punching, Problems such as film breakage (chips) and cracks occur. If the amount is too large, the heat resistance at high temperatures during soldering is reduced.

Further, the base resin layer of the heat-resistant electret material of the present invention is such that the ratio of silicon element and carbon element contained is smaller than the ratio of carbon element on the metal substrate side, and the electret layer On the side, the proportion of silicon element is higher than the proportion of carbon element. The reason for this is not clear, but the component gradient occurs in the process of volatilization of the solvent due to the specific gravity difference between the carbon element and the silicon element, so that more carbon elements gather than the silicon element on the metal substrate side, And since there is a tendency that more silicon element collects than carbon element on the electret layer side, adhesion between the base resin layer and the electret layer can be improved, and conductivity can be imparted to the base resin layer. It is thought that it will become.

In particular, in order to achieve both the above-mentioned interlayer adhesion and charge retention characteristics, the content of the Si component material in the above-described coating resin for forming the base resin layer is based on the fluororesin in the coating solution for forming the base resin layer. 1.0 to 115.0 mass%, particularly 1.1 to 111.0 mass% is preferable. The conductive carbon content is preferably 10.0 to 20.0% by mass, particularly 11.0 to 15.0% by mass, based on the fluororesin in the base resin layer forming coating solution.

The electret layer of the heat-resistant electret material of the present invention is a fluororesin-containing electret layer-forming coating solution prepared in the same manner as the base resin layer-forming coating solution except that it does not contain conductive carbon and Si component materials. And can be formed on the base resin layer in the same manner as the base resin layer.

In order to simplify the lamination process of the base resin layer and the electret layer, the above base resin layer-forming coating solution is applied onto a metal substrate and the temperature is about 100 to 200 ° C. for about 1 to 10 minutes. Then, the electret layer forming coating solution is applied onto the dried coating film, dried at about 100 to 200 ° C. for about 1 to 10 minutes, and finally heated and fired at about 350 to 450 ° C. for about 1 to 10 minutes. The base resin layer and the electret layer are preferably laminated on the metal substrate.

The thickness of the electret layer thus obtained is not particularly limited, but is preferably 8 to 50 μm, particularly preferably 15 to 45 μm. Further, the volume resistance value of the electret layer in the temperature range of 10 ° C. to 350 ° C. is preferably 10 ¹⁵ Ω · m or more. When the volume resistance value of the electret layer is less than 10 ¹⁵ Ω · m, the absolute amount of charges held in the electret layer is reduced, and the long-term holding stability of the held charges is also deteriorated. Absent.

The heat-resistant electret material of the present invention preferably has a metal substrate thickness of 50 to 500 μm, more preferably 80 to 300 μm, a base resin layer thickness of 1 to 50 μm, more preferably 2 to 20 μm, and an electret layer thickness. A laminated member having a thickness of 8 to 50 μm, more preferably 15 to 45 μm, and a resin layer having a small volume resistance value formed sequentially on a metal substrate. That is, a laminated member in which a base resin layer having a volume resistance value B is formed on a metal substrate having a volume resistance value A, and an electret layer having a volume resistance value C is further formed thereon as an outermost layer. The volume resistance value in the temperature range from 350 ° C. to 350 ° C. satisfies A <B <C, and the volume resistance value in the temperature range from 10 ° C. to 350 ° C. is 60 × 10 ⁻⁸ Ω · m <A <. A laminated member satisfying 100 × 10 ⁻⁸ Ω · m, 10 ¹⁰ Ω · m <B <10 ¹³ Ω · m, and C ≧ 10 ¹⁵ Ω · m is preferable.

The heat-resistant electret material of the present invention is a conductive metal substrate and electret layer containing a fluororesin, an Si component and conductive carbon between a metal thin plate base material and a fluororesin layer which is an electret layer. By providing a base resin layer with excellent adhesion to both of the above, it becomes possible to stably hold the charge charged by corona discharge for a long period of time, as well as excellent interlayer adhesion and durability, It is possible to reduce the thickness of the electret material.

Such a heat-resistant electret material according to the present invention can be manufactured by only a wet process, not a dry process that requires a high level of dustproof equipment, so that the electret material can be provided at a low cost. Moreover, since the heat-resistant electret material of the present invention is a thin-film electret material with high charge retention, the members (earphones, headphones, microphones, etc.) that use this material can be made more compact.

Hereinafter, the present invention will be described in more detail with reference to examples, reference examples, and comparative examples, but the present invention is not limited to these examples.

[Examples 1 and 2, Reference Examples 1 and 2, Comparative Examples 1 and 2]
<Preparation of coating solution for base resin layer formation>
As solids, PTFE (trade name “Polyflon M-112” manufactured by Daikin Industries, Ltd.) is 9.0% by mass, carbon black (trade name “Toka Black # 5500” manufactured by Tokai Carbon Co., Ltd.) is 1.0% by mass, As a solvent, distilled water was 80.0% by mass, furfurylamine was 4.0% by mass, N-methyl-2-pyrrolidone was 2.0% by mass, nonionic surfactant was 2.0% by mass, and triethylamine was 1.5% by mass. A liquid A consisting of 0.5% by mass of 2-mass% 2- (diethylamino) ethanol was prepared.
Separately, for the purpose of introducing silicon (Si) or silicon compound into the base resin layer, a solution prepared by adjusting triethylsilanol (silane coupling agent) manufactured by Tokyo Chemical Industry Co., Ltd. with distilled water to 10% by mass is liquid B. Used as.
A liquid and B liquid were mixed by the compounding quantity shown in Table 1, and it was set as the coating liquid for base resin layer formation.
In Table 1, the ratio of carbon black to the PTFE in the prepared coating solution for forming the base resin layer and the ratio of pure triethylsilanol are shown together.

<Electret layer forming coating solution>
50.0% by mass of PTFE resin (trade name “Polyflon M-112”, manufactured by Daikin Industries, Ltd.) as a solid content, 35.0% by mass of water as a solvent, 5.0% by mass of triethanolamine, aromatic Heavy oil 3.0 mass%, diethylene glycol mono-n-butyl ether 3.0 mass%, nonionic surfactant 3.0 mass%, 1,2,4-trimethylbenzene 0.7 mass%, 1,3,3 A coating solution for forming an electret layer consisting of 0.3% by mass of 5-trimethylbenzene was prepared.

<Manufacture of heat-resistant electret materials>
Using a stainless steel plate having a thickness of 100 μm (volume resistance value 72.7 × 10 ⁻⁸ Ω · m at 25 ° C., volume resistance value 90.0 × 10 ⁻⁸ Ω · m at 260 ° C.) After applying the base resin layer forming coating solution to the stainless steel 304 steel plate with a bar coater, drying at 100 ° C. for 20 minutes, and then applying the electret layer forming coating solution onto the formed base resin layer coating film. A laminated member in which a base resin layer and an electret layer are laminated on a metal substrate as shown in FIG. 1 by applying with a coater, drying at 100 ° C. for 20 minutes, and further heating and baking at 420 ° C. for 5 minutes. Obtained.
Next, the laminated member is subjected to a charging process by performing a corona discharge of -1,000 V using a high voltage power source amplification / control device (MODEL610-C manufactured by Trek Japan Co., Ltd.) in the atmosphere of normal temperature and normal pressure. In each case, samples of electret materials were produced.
The thickness of the base resin layer of each sample is 5 μm, and the thickness of the electret layer is 25 μm.

<Evaluation of charge retention characteristics>
Each sample was placed on a hot plate set at 260 ° C. and heated. Heating time is 5 times for 30 seconds (the sample is placed on the hot plate for 30 seconds and then picked up and cooled to room temperature, then the charge amount is measured, and then the sample is placed on the hot plate again for 30 seconds and loaded. The process of placing and measuring is repeated 5 times.) After that, standing at normal temperature, normal humidity, and normal pressure for 24 hours, measuring the charge amount, standing for 48 hours, and measuring the charge amount. The charge amount was measured with a surface potential meter (MODEL 344 manufactured by Trek Japan Co., Ltd.).
The residual charge amount relative to the initial charge amount was calculated as the charge retention rate, and the results are shown in FIG.

<Evaluation of interlayer adhesion>
Each sample is passed through a metal roll having a diameter of 300 mm with a load of linear pressure 10 kgf / cm, and the initial thickness (metal substrate = 100 μm, base resin layer = 5 μm, electret layer = 25 μm; total thickness = 130 μm) After rolling to 80% thickness (total thickness = 104 μm), a cross-cut cello tape peel test was performed by the method described in JIS-K5400. Table 2 shows the results (the number of squares remaining on the metal base material without peeling off the base resin layer when the cellophane was adhered and peeled out of the 100 squares).

<Analysis of element ratio in base resin layer>
The ratio of elements constituting the base resin layer of each sample was analyzed by fluorescent X-ray measurement (by Shimadzu “EDX-720”). The results are shown in Table 3.

<Volume resistance value / Surface resistance value>
About the base resin layer of each sample, volume resistance value and surface resistance value were measured by Hiresta UP (made by Mitsubishi Chemical Corporation). The results are shown in Table 4. The volume resistance value of the electret layer was 10 ¹⁵ Ω · m or more.

In addition, by using an XPS apparatus “PHI-5600” (manufactured by ULVAC-PHI Co., Ltd.) and etching using argon plasma, the base resin layers obtained in Example 1, Example 2 and Comparative Example 1 were thickened. Cutting was performed at intervals of 0.5 μm, and the displacement of the volume resistance value was measured. The results are shown in FIG.

<Coating hardness>
Each sample was evaluated for coating film hardness. The results are shown in Table 5. The hardness was measured on the surface of the electret layer based on JIS-K5400 using “553-M1” manufactured by Yasuda Seiki Co., Ltd. The value of the coating film hardness indicates that the coating film hardness is higher in the order of B → HB → F → B → H → 2H →.

<Summary of the above results>
(1) From the results shown in FIG. 2, when the Si component is included in the base resin layer, although a slight decrease in charge retention performance is observed, the Si component content is up to about 50 mol% in terms of element ratio. It can be seen from the results of Example 2 that there is no significant decrease in charge retention performance. In addition, it can be seen from Reference Example 2 that when the Si component is added in excess of 60 mol%, the charge retention performance is significantly reduced.
(2) From Table 2, it can be seen that when the Si resin component is included in the base resin layer, the interlayer adhesion is increased. However, from the results of Example 2 and Reference Example 2, it can be seen that no significant difference is observed when the Si content exceeds 50 mol%.
(3) From Reference Example 1 in Table 2, it can be seen that when the content of the Si component in the base resin layer is less than 1 mol%, a remarkable improvement effect in interlayer adhesion is not observed.
(4) From the results in Table 5, it can be confirmed that the hardness of the coating film is improved when the base resin layer contains the Si component. However, when there is too much content of Si component, it is unpreferable from a viewpoint of the electric charge retention performance of said (1).

<Effect of thickness of base resin layer>
Using the same base resin layer-forming coating solution and electret layer-forming coating solution as used in Example 1, changing the number of the bar coater and changing the coating amount of the base resin layer-forming coating solution, Samples with different thickness only were produced. The thickness of the base resin layer of the prepared sample was 0.1, 0.5, 1, 3, 5, 10, 25, 50, 60 μm, and the electret layer thickness was all 25 μm.
For each sample, the ratio of the number of peeled end portions due to friction and impact with the punching blade when 100 pieces were punched to a diameter of 5 mm by a punching press (peeling failure rate) was obtained. The results are shown in Table 6 and a graph illustrating the results is shown in FIG.
As is clear from FIG. 3, when the thickness of the base resin layer is less than 1 μm, the peeling failure rate is high, and when the thickness is 60 μm or more, cohesive peeling occurs in the layer and the peeling failure rate tends to increase. It is in.
Accordingly, it can be seen that a thickness range of 1 to 50 μm is appropriate for the base resin layer.

<Effect of thickness of electret layer>
Using the same base resin layer forming coating solution and electret layer forming coating solution as used in Example 1, changing the bar coater count and changing the coating amount of the electret layer forming coating solution, only the thickness of the electret layer Different samples were produced. The thicknesses of the base resin layers of the prepared samples were all 5 μm, and the thicknesses of the electret layers were 1, 2, 5, 6, 10, 20, 30, 40, 60 μm. For each electret layer thickness sample, similar to the above <Evaluation of charge retention characteristics>, repeated heating and cooling 5 times (the sample was placed on a hot plate for 30 seconds and then cooled to room temperature), Further, the charge retention performance after standing for 48 hours was measured. The result is shown in FIG.
As is apparent from FIG. 4, when the thickness of the electret layer is less than 5 μm, the charge retention performance is remarkably deteriorated. Energy is needed, material and energy are wasted. It is generally said that the thinner the electret layer is, the better the S / N ratio is. However, in the electret material of the present invention, the thickness range of the electret layer for which reduction in thickness and cost is required is 8 to It can be seen that 50 μm is suitable.

<Distribution of silicon and carbon elements contained in the base resin layer>
Among the elements (C, Si, F) constituting the base resin layer of each sample of Example 1 and Example 2 using an X-ray photoelectron spectrometer (“ESCA-3400” manufactured by Shimadzu Corporation), silicon element and carbon The ratio of elements (mol%) was measured by the following procedure.
The underlying resin layer was shaved from the electret layer side in the depth direction of the metal substrate layer by Ar ⁺ plasma etching in units of 0.5 μm, and surface layer elements were analyzed. The element ratio at each depth detected here was converted to mol% by the following formula. The etching conditions were ² kV and 20 mA with Ar ⁺ , and the etching rate was 5.0 nm / min. As the analysis conditions of the element ratio, Mg—Kα was used as the light source, and the measurement was performed under the conditions of an output of 8 kW × 30 mA and a degree of vacuum of 5 × 10 ⁻⁶ Pa.
The results are shown in FIG. 5 (Example 1) and FIG. 6 (Example 2).

5 and 6, it can be seen that in the thickness (depth) direction of the base resin layer, there is a distribution in the content of carbon element and silicon element from the metal substrate layer side to the electret layer side. That is, in the base resin layer, the silicon element content derived from the added silane coupling agent continuously increases from the metal substrate side toward the electret layer side, whereas the carbon element derived from conductive carbon. It can be seen that there is a slope in which the content of is continuously reduced.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on July 15, 2011 (Japanese Patent Application No. 2011-156677), which is incorporated by reference in its entirety.

Claims

An electret layer made of a fluororesin is formed on a metal substrate via a base resin layer containing a fluororesin, silicon, a silicon compound, or a mixture thereof, and conductive carbon. Heat-resistant electret material.
2. The heat-resistant electret according to claim 1, wherein the metal substrate has a thickness of 10 to 500 μm, the base resin layer has a thickness of 1 to 50 μm, and the electret layer has a thickness of 8 to 50 μm. Wood.
3. The ratio of silicon element to 100 mol% in total of fluorine element, silicon element and carbon element contained in the base resin layer is 1 to 50 mol%, and the ratio of carbon element is 5 to 10 in claim 1 or 2. A heat-resistant electret material characterized by being mol%.
In Claim 3, the ratio of the silicon element contained in the said base resin layer and the ratio of a silicon element is smaller than the ratio of a carbon element in the said metal base material side, and the silicon element is contained in the said electret layer side. A heat-resistant electret material characterized in that the proportion is higher than the proportion of carbon element.
5. The heat-resistant electret material according to claim 1, wherein the fluororesin of the base resin layer contains polytetrafluoroethylene (referred to as “PTFE”) as a main component.
6. The heat-resistant electret material according to claim 1, wherein the fluororesin of the electret layer contains PTFE as a main component.
The metal thin plate according to any one of claims 1 to 6, wherein the metal substrate is made of stainless steel, aluminum, brass, iron, or an oxide thereof, and an alloy containing one or more of these, or stainless steel. It is selected from nickel, gold, silver, copper, tin, zinc, and platinum on the surface of a thin metal plate made of steel, aluminum, brass, iron, or an oxide thereof, and an alloy containing one or more of these. A heat-resistant electret material comprising a thin metal plate coated with at least one conductive metal.
8. The volume resistance value of the surface of the base resin layer on the electret layer side is 10 10 Ω · m or more and 10 13 Ω · m or less, and the volume resistance value of the electret layer is any one of claims 1 to 7. A heat-resistant electret material characterized by being 10 15 Ω · m or more.
9. The heat-resistant electret material according to claim 1, wherein a volume resistance value in a thickness direction of the base resin layer is larger on the electret layer side than on the metal substrate side.
10. The heat-resistant electret material according to claim 9, wherein a volume resistance value at a thickness ½ of the base resin layer is greater than 10 9 Ω · m and less than or equal to 10 12 Ω · m.
A condenser microphone using the heat-resistant electret material according to any one of claims 1 to 10.