WO2010030011A1

WO2010030011A1 - Electret film and electret comprising same

Info

Publication number: WO2010030011A1
Application number: PCT/JP2009/065961
Authority: WO
Inventors: 弘小池; 誠一郎飯田
Original assignee: 株式会社ユポ・コーポレーション
Priority date: 2008-09-12
Filing date: 2009-09-11
Publication date: 2010-03-18

Abstract

Disclosed is an electret film (ii) that can stably maintain a high charge state over a long period of time and is formed by injecting charges into a porous resin film (i) having high dielectric strength. Specifically, the electret film (ii) is characterized in that a porous resin film (i) which comprises a core layer (A) having a biaxially stretched porous resin film and a surface layer (B) having a stretched resin film provided on at least one side of the core layer (A), has a water vapor permeation coefficient of 0.1 to 2.5 g∙mm/m²∙24 hr, and has a surface resistivity (at least one surface thereof) of 1 × 10¹³ to 9 × 10¹⁷ Ω is subjected to direct current high-voltage discharge treatment to electretize the film (i). Also disclosed is an electret (iii) comprising the electret film (ii) and an electroconductive layer.

Description

Electretized film and electret including the same

The present invention relates to an electret film and an electret including the same, and more particularly, as an electret film in which charge density is stable by accumulating charges inside the film and a material for an electric / electronic input / output device including the electret film. The present invention relates to an electret including a conductive layer having various performances.

An electret is a material that forms an electric field to the outside (applies an electric force) while maintaining electric polarization semi-permanently even in the absence of an external electric field, and has been difficult to conduct electricity in the past. Or a material obtained by treating a part of the material semi-permanently by thermally or electrically treating the material or an inorganic material, that is, a material that is charged with static electricity or a material that retains an electric charge.
Conventionally, electrets made of a polymer material are used in various forms such as a film, a sheet, a fiber, and a non-woven fabric depending on the use mode. In particular, electret filters formed by molding electrets have been widely used for applications such as air filters that efficiently adsorb minute dust, allergens, and the like by an electric field.
Similarly, an electret of a porous resin film made of a polymer material is known to have an excellent adsorptive power. For example, a self-adhesive film obtained by electretizing a porous resin film has been proposed. (Patent Document 1)

An electret using a porous resin film is known to exhibit a piezoelectric effect, and can be used for vibration measurement, vibration control, sound generation, sound detection, and the like. For this reason, electrets using such porous resin films make use of their light weight to provide electrical equipment such as vibrators, acceleration sensors, ultrasonic sensors, pressure sensors, and vibration control devices for acoustic devices such as speakers, headphones, and microphones. -Applications for various applications have been proposed as materials for electronic input / output devices. (Patent Document 2)
An electret made of a porous resin film is said to be able to retain a large amount of charge in the pores inside the film, thereby obtaining an electret having excellent performance and stability. However, in order to accumulate more charges inside the film, it is ideal to process at a higher voltage during charge injection. However, in general porous resin films, the insulation resistance is low, and the surface direction Therefore, when the applied voltage is increased, local discharge concentration occurs and the porous resin film is partially broken.

Moreover, it is said that the performance as a piezoelectric element improves the electret using this, when a porous resin film is expanded in the thickness direction using high-pressure gas (nonpatent literature 1).
As a method of expanding the porous resin film in the thickness direction in this way, a film having pores is created by biaxial stretching in advance, and a high-pressure gas is infiltrated into this, followed by heat treatment under reduced pressure. A method for obtaining a porous resin film having a high expansion ratio has been proposed (Patent Document 3). These porous resin films having a high expansion ratio were considered to be able to obtain electrets with excellent performance and stability by retaining more charges in the pores inside the film.
However, in order to actually accumulate more charges inside the film, it is necessary to discharge the film at a higher voltage during charge injection.
At this time, as seen in Non-Patent Document 1 and Patent Document 3 above, a high-pressure gas is infiltrated into a film made of polypropylene and having pores formed in advance by biaxial stretching of all layers, and then heat-treated under reduced pressure. The porous resin film having a high expansion ratio thus obtained is inferior in the uniformity of the film surface and has large irregularities, so that when the applied voltage is increased, local discharge concentration occurs, and the porous resin film There was a problem that the film was partially destroyed beyond the insulation resistance of the film.

On the other hand, in order to use an electret using a porous resin film in an electric / electronic input / output device, it is necessary to provide a conductive layer for transmitting an electric signal on at least one surface thereof.
As a method for providing a conductive layer, coating of a conductive paint or vapor deposition of metal or the like is common, but the coating method has a drawback that the electret itself deteriorates in performance when the temperature is raised excessively in the drying process. In addition, the vapor deposition method has a drawback in that the vaporized metal directly contacts the electret, so that the temperature of the electret rises and the performance is reduced as in the coating method.

Japanese National Table No. 10-504248 Japanese Patent Publication No. 05-041104 Japanese Patent No. 3675827

In the present invention, a porous resin film (i) having high insulation resistance can be used for charge injection at a higher voltage than a conventional porous resin film, and a high charge state can be stably maintained over a long period of time. It aims at providing the electret film (ii) which can be performed.
In addition, the present invention comprises a porous resin film that has excellent film uniformity compared to conventional porous resin films and is capable of charge injection at a high voltage, resulting in stable high charge state over a long period of time. The object of the present invention is to provide an electret film having excellent performance as an electric / electronic input / output device material.
Furthermore, an object of the present invention is to provide an electret having a conductive layer in which the performance reduction of the electret is small when the conductive layer is installed.

As a result of intensive studies to solve these problems, the present inventors have found that a porous resin film (i) having a specific structure is suitable for the same use, and by electretizing it, It has been found that an electret film (ii) having the desired characteristics can be provided, and the present invention has been completed.
That is, the present invention has the following configuration.
(1) A core layer (A) including a biaxially stretched resin film having pores and a surface layer (B) including a stretched resin film on at least one surface of the core layer (A), and having a water vapor transmission coefficient The porous resin film (i) having a surface resistance of 0.1 × 2.5 g · mm / m ² · 24 hr and a surface resistance value of at least one surface of 1 × 10 ¹³ to 9 × 10 ¹⁷ Ω is DC An electret film (ii) characterized by being subjected to high-voltage discharge treatment to be electret.
(2) The electret film (ii) according to (1) above, wherein the stretched resin film in the surface layer (B) is a uniaxially stretched resin film.
(3) The above (2) is characterized in that the porous resin film (i) is impregnated with a non-reactive gas under a pressurized condition and then subjected to a heat treatment under a non-pressurized condition. The electret film (ii) described.

(4) The thickness of the core layer (A) is 10 to 500 μm, and the thickness of the surface layer (B) is 5 to 500 μm, according to any one of the above (1) to (3) Electretized film (ii).
(5) The electret film (ii) according to any one of (1) to (4) above, wherein the stretched resin film in the core layer (A) and the surface layer (B) contains a thermoplastic resin. ).
(6) The core layer (A) contains 50 to 97% by weight of the thermoplastic resin, and 3 to 50% by weight of at least one kind of inorganic fine powder and organic filler, and the surface layer (B) has a thermoplastic resin of 30 to 97%. The electret film (ii) according to (5) above, which contains 3% by weight and 3 to 70% by weight of at least one of inorganic fine powder and organic filler.
(7) The electret film (ii) according to (5) or (6) above, wherein the thermoplastic resin is a polyolefin resin.

(8) The above (1) to (7), wherein the surface layer (B) is laminated on the core layer (A), and then the laminate is stretched in at least one axial direction to form each layer as a stretched resin film. The electret film (ii) according to any one of the above.
(9) The electret film (ii) according to any one of (1) to (8) above, wherein the porosity of the porous resin film (i) is 1 to 70%.
(10) The electret according to any one of (3) to (8) above, wherein the porosity of the porous resin film (i) subjected to pressure treatment and heat treatment is 5 to 95% Film (ii).

(11) The electret film according to any one of (1) to (10) above, further comprising an anchor coat layer (C) on at least one surface of the porous resin film (i) ii).
(12) The electret film (ii) according to the above (11), wherein the anchor coat layer (C) has a basis weight of 0.001 to 5 g / m ² .
(13) The electret according to any one of (1) to (12) above, wherein the porous resin film (i) is subjected to direct current high-voltage discharge treatment in a discharge voltage range of 10 KV to 100 KV to form an electret. Film (ii).
(14) The electret film according to any one of the above (1) to (13), wherein charge injection is performed from the surface of the surface layer (B) of the porous resin film (ii) in the DC high-voltage discharge treatment (Ii).

(15) The electret film (ii) according to any one of (1) to (14), the adhesive layer (D), and the surface resistance value is 1 × 10 ⁻² to 9 × 10 ⁷ Ω. The electret (iii) provided with the conductive layer characterized by containing the dielectric film (F) provided with the conductive layer (E) in this order.
(16) The electret (iii) provided with the conductive layer as described in (15) above, wherein the dielectric film (F) is a stretched film or a non-stretched film containing a thermoplastic resin.
(17) The electret (iii) provided with the conductive layer as described in (15) or (16) above, wherein the dielectric film (F) has a thickness of 0.1 to 100 μm.
(18) The electret having the conductive layer as described in any one of (15) to (17) above, wherein the conductive layer (E) is formed by applying a conductive paint or depositing a metal (Iii).
(19) An electret (iii) comprising the conductive layer according to any one of (15) to (18) above, wherein the thickness of the conductive layer (E) is from 0.01 to 10 μm.
(20) When the dielectric film (F) provided with the conductive layer (E) is laminated on the electret film (ii), the conductive layer (E) is laminated so as to be an outermost layer. An electret (iii) comprising the conductive layer according to any one of (15) to (19) above.

By using the porous resin film (i) of the present invention, it is possible to inject more charge, and it is possible to obtain an electret film (ii) having a charge holding ability that is more stable for a longer period than before. Moreover, the electret (iii) provided with the conductive layer of the present invention has high energy conversion efficiency and high mass productivity without reducing the performance of the electret when the conductive layer (E) is provided in the electret material. It becomes possible to provide an output material.

It is sectional drawing of the one aspect | mode of the porous resin film (i) of this invention. It is a schematic diagram of an example of the batch type electretization apparatus which can be used by this invention. It is a schematic diagram of an example of the continuous electretization apparatus which can be used by this invention. It is a schematic diagram of an example of the batch type electretization apparatus which can be used by this invention. It is a schematic diagram of an example of the continuous electretization apparatus which can be used by this invention. The schematic diagram of an example of the process form at the time of pressurizing a porous resin film (i). The schematic diagram of an example of a pressurization processing apparatus. The schematic diagram of an example of a heat processing apparatus. Explanatory drawing of the falling ball apparatus used in the Example. It is a partial expanded sectional view of one mode of electret (iii) provided with the conductive layer of the present invention.

Below, the electret film of this invention is demonstrated in detail. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
The electretized film (ii) of the present invention includes a core layer (A) including a biaxially stretched resin film having pores, and a surface layer (B) including a stretched resin film on at least one side of the core layer (A). It consists of a porous resin film (i) having

[Core layer (A)]
The core layer (A) used in the present invention is mainly used for retaining electric charges therein. Therefore, the core layer (A) includes a biaxially stretched resin film having pores.
The core layer (A) preferably includes a thermoplastic resin that is a polymer material that has a certain thickness or more and is difficult to conduct electricity in order to ensure capacitance, and shows a state with porosity. By having the vacancies formed inside by stretching, it has a structure that can easily hold the electric charge.
The core layer (A) used in the present invention is preferably a layer that is expanded in the thickness direction by increasing the internal pressure of the pores by a pressure treatment and a heat treatment described later.
Such a core layer (A) is preferably made of a thermoplastic resin, which is a polymer material that has a certain thickness or more and is difficult to conduct electricity in order to ensure capacitance, and has a structure with porosity. As shown, it has a structure that is easy to hold charges by having pores formed by stretching and then expanded by pressure treatment and heat treatment. The thickness of the core layer (A) is preferably in the range of 10 to 500 μm, more preferably in the range of 20 to 300 μm, and particularly preferably in the range of 30 to 100 μm. The thickness of these core layers (A) is the same when they are expanded in the thickness direction. If the thickness is less than 10 μm, the core layer (A) has a small capacitance and is not suitable for use in electrets, and it becomes difficult to control molding with a uniform thickness, and dielectric breakdown occurs during electret processing described later. It is not preferable because local discharge is likely to occur and local discharge is likely to occur. On the other hand, if it exceeds 500 μm, it is difficult to reach the inside of the layer at the time of charge injection, which is not preferable because the desired performance of the present invention cannot be exhibited.

The core layer (A) is preferably made of a thermoplastic resin that is a polymer material that hardly conducts electricity, but the type of the thermoplastic resin to be used is not particularly limited. For example, high density polyethylene, medium density polyethylene, low density polyethylene, propylene resin, polyolefin resin such as polymethyl-1-pentene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, maleic acid modified polyethylene, Functional group-containing polyolefin resins such as maleic acid-modified polypropylene, polyamide resins such as nylon-6 and nylon-6,6, polyethylene terephthalate and copolymers thereof, polybutylene terephthalate, polybutylene succinate, polylactic acid, aliphatic Polyester resins such as polyester, polycarbonate, atactic polystyrene, syndiotactic polystyrene and the like can be used. Among these thermoplastic resins, it is preferable to use a polyolefin resin or a functional group-containing polyolefin resin having a low hygroscopic property and a high insulating property.

Examples of polyolefin resins include homopolymers of olefins such as ethylene, propylene, butene, butylene, butadiene, isoprene, chloroprene, methylpentene, and cyclic olefins, and copolymers composed of two or more of these olefins. . Specific examples of the polyolefin resin include high density polyethylene, medium density polyethylene, propylene resin, copolymers of ethylene and other olefins, and copolymers of propylene and other olefins.
Among these polyolefin-based resins, propylene-based resins are preferable in terms of processability, insulating properties, cost, and the like. Examples of the propylene-based resin include propylene homopolymers such as isotactic or syndiotactic and polypropylene having various degrees of stereoregularity, and mainly composed of propylene, ethylene, 1-butene, Examples thereof include copolymers obtained by copolymerizing α-olefins such as 1-hexene, 1-heptene and 4-methyl-1-pentene. The copolymer may be a binary system or a ternary system, and may be a random copolymer or a block copolymer.
When a propylene resin is used as the thermoplastic resin, 2 to 25% by weight of a resin having a melting point lower than that of polypropylene (propylene homopolymer) is used in order to improve the stretch moldability described later. It is preferable. Examples of such a resin having a low melting point include high density or low density polyethylene.

Specific examples of the functional group-containing polyolefin resin include a copolymer with a functional group-containing monomer copolymerizable with the olefins. Such functional group-containing monomers include styrenes such as styrene and α-methylstyrene, vinyl acetate, vinyl alcohol, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl caproate, vinyl laurate, vinyl stearate, vinyl benzoate. , Vinyl esters of carboxylic acid such as vinyl butylbenzoate and vinyl cyclohexanecarboxylate, acrylic acid, methacrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl ( (Meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dicyclope Acrylic acid esters such as Tanyl (meth) acrylate, (meth) acrylamide, N-metalol (meth) acrylamide, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclopentyl vinyl ether, cyclohexyl vinyl ether, benzyl vinyl ether, phenyl vinyl ether, etc. Vinyl ethers are particularly representative. One or two or more of these functional group-containing monomers may be appropriately selected and polymerized as necessary.

Further, these polyolefin resins and functional group-containing polyolefin resins can be used if necessary by graft modification. A known technique can be used for graft modification. Specific examples of the graft monomer include graft modification with an unsaturated carboxylic acid or a derivative thereof. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid and the like. As the unsaturated carboxylic acid derivative, acid anhydrides, esters, amides, imides, metal salts and the like can also be used. Specifically, maleic anhydride, itaconic anhydride, citraconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, maleic acid Monoethyl ester, maleic acid diethyl ester, fumaric acid monomethyl ester, fumaric acid dimethyl ester, itaconic acid monomethyl ester, itaconic acid diethyl ester, acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide , Maleic acid-N, N-diethylamide, maleic acid-N-monobutylamide, maleic acid-N, N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monoethyl Amides, fumaric acid-N, N-diethylamide, fumaric acid-N-monobutylamide, fumaric acid-N, N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, Examples include potassium acrylate and potassium methacrylate.

Graft modified products that can be used are those obtained by graft modification by adding 0.005 to 10% by weight, preferably 0.01 to 5% by weight, of graft monomers to polyolefin resins or functional group-containing polyolefin resins. is there.
As the thermoplastic resin used for the core layer (A), one type may be selected from the above thermoplastic resins and used alone, or two or more types may be selected and used in combination. .
It is desirable that the thermoplastic resin used for the core layer (A) is obtained by adding at least one of an inorganic fine powder and an organic filler. By adding the inorganic fine powder or the organic filler, it becomes easy to form pores in the core layer (A) by the stretching process described later.
More specifically, the core layer (A) preferably contains 50 to 97% by weight of the above thermoplastic resin and 3 to 50% by weight of at least one kind of inorganic fine powder and organic filler. Further, the core layer (A) more preferably contains 60 to 95% by weight of a thermoplastic resin and 5 to 40% by weight of at least one of inorganic fine powder and organic filler.
If the content of the inorganic fine powder and organic filler, which are the nucleating agent for the pores, is less than 3% by weight, the number of pores formed in the stretching process described below will be small and the charge storage capacity will be inferior, achieving the intended purpose. Hard to do. On the other hand, if it exceeds 50% by weight, the formed pores communicate with each other. Therefore, even if the charge is introduced, the structure is such that the charge easily escapes from the surface or end surface of the porous resin film (i) via the communication hole, and the charge tends to be unstable, which is not preferable. In addition, when the non-reactive gas permeates during the pressurizing process, the non-reactive gas permeated through the non-reactive gas during the pressurizing process easily escapes from the porous resin film (i) and does not easily expand even when heat-treated. There is a tendency.

When adding an inorganic fine powder, one having an average particle size of usually 0.01 to 15 μm, preferably 0.05 to 5 μm, more preferably 0.1 to 3 μm, particularly preferably 0.5 to 2.5 μm. use. Specific examples of the inorganic fine powder include calcium carbonate, calcined clay, silica, diatomaceous earth, white clay, talc, titanium oxide, barium sulfate, alumina, zeolite, mica, sericite, bentonite, sepiolite, vermiculite, dolomite, wallast. Knight, glass fiber, etc. can be used. In the present invention, the average particle size was referred to the manufacturer catalog value.
When an organic filler is added, it is preferable to select a different type of resin from the thermoplastic resin that is the main component. For example, when the thermoplastic resin is a polyolefin resin, examples of the organic filler include polyethylene terephthalate, polybutylene terephthalate, polycarbonate, nylon-6, nylon-6,6, cyclic olefin polymer, polystyrene, and polymethacrylate. A polymer having a melting point higher than the melting point of the polyolefin resin, such as 170 to 300 ° C., or a glass transition temperature, such as 170 to 280 ° C., and incompatible can be used.

In the thermoplastic resin used for the core layer (A), a heat stabilizer (antioxidant), a light stabilizer, a dispersant, a lubricant and the like can be optionally added as necessary. When a heat stabilizer is added, it is usually added within a range of 0.001 to 1% by weight based on the resin. As specific examples of the heat stabilizer, sterically hindered phenol-based, phosphorus-based, amine-based stabilizers can be used. When a light stabilizer is added, it is usually added within a range of 0.001 to 1% by weight based on the resin. Specific examples of the light stabilizer include sterically hindered amine-based, benzotriazole-based, and benzophenone-based light stabilizers. The dispersant and the lubricant are used for the purpose of dispersing the inorganic fine powder in the resin, for example. The amount used is usually in the range of 0.01 to 4% by weight based on the resin. Specific examples thereof include silane coupling agents, higher fatty acids such as oleic acid and stearic acid, metal soaps, polyacrylic acid, polymethacrylic acid or salts thereof.

In the present invention, the core layer (A) is stretched in the biaxial direction of the film width direction and the flow direction. By stretching, a large number of holes are formed inside the layer, and charges are accumulated inside the holes, so that the electret film (ii) has excellent charge retention performance.
The vacancies formed in the core layer (A) desirably have a large individual volume, a large number, and shapes independent from each other, from the viewpoint of maintaining electric charge. The size of the pores can be increased by extending in the biaxial direction rather than extending in only one direction. In particular, those stretched in the biaxial direction of the film in the width direction and the flow direction can form disk-like vacancies that are stretched in the plane direction. It is easy to accumulate polarized charges. Therefore, a biaxially stretched resin film is used for the core layer (A) of the present invention.
In the present invention, when the porous resin film (i) is infiltrated with a non-reactive gas under a pressurized condition and then subjected to a heat treatment under a non-pressurized condition, the porous film before the pressure treatment is performed. The core layer (A) in the conductive resin film (i) is stretched in the biaxial direction of the film width direction and the flow direction. A large number of pores are preliminarily formed inside the layer by stretching. It is desirable that the pores formed in the porous resin film (i) have a large individual volume, a large number, and shapes independent from each other from the viewpoint of maintaining electric charge. The size of the pores can be increased by extending in the biaxial direction rather than extending in only one direction. In particular, a film stretched in the biaxial direction of the film in the width direction and the flow direction can form a disk-shaped hole stretched in the surface direction, and therefore, the pressure hole and the heat treatment are further applied to increase the thickness of the hole. When it is expanded in the direction, it is possible to form vacancies with large volumes, and when charges are injected, positively and negatively polarized electric charges are easily accumulated, and charge retention performance when an electret film (ii) is obtained. Will be excellent. Therefore, a biaxially stretched resin film is used for the core layer (A) in the porous resin film (i) of the present invention.

[Surface layer (B)]
The surface layer (B) used in the present invention improves the insulation resistance during the electretization treatment of the porous resin film (i) and improves the retention of charges accumulated in the core layer (A). Is a layer made of a stretched film provided on at least one side of the core layer (A), preferably on both sides.
When the porous resin film (i) is infiltrated with a non-reactive gas under pressure and then subjected to heat treatment under non-pressure, the surface layer (B) is a conventional porous resin. It is a layer that has excellent film surface uniformity compared to a film, and enables charge injection at a high voltage during electretization of the porous resin film (i) of the present invention. Moreover, it plays the role which prevents that the non-reactive gas from a core layer (A) spread | diffuses outside from a pressurization process to a heat processing. Furthermore, it plays a role of improving the dielectric strength of the porous resin film (i) and improving the retention of charges accumulated in the core layer (A). The surface layer (B) in the present invention is a layer made of a stretched resin film provided on at least one side of the core layer (A), preferably on both sides.
The surface layer (B) preferably includes a thermoplastic resin, which is a polymer material having a thickness greater than or equal to a certain level in order to improve insulation resistance, and is difficult to conduct electricity, but introducing a charge into the core layer (A). In order to form pores as much as possible, it preferably has a uniaxially stretched resin film structure.
The thickness of the surface layer (B) is preferably in the range of 5 to 500 μm, more preferably in the range of 7 to 300 μm, further preferably in the range of 9 to 100 μm, and in the range of 10 to 50 μm. Particularly preferred is the range of 10 to 30 μm. If the thickness is less than 5 μm, the effect of improving the insulation resistance of the porous resin film (i) is insufficient, and charge injection at a high voltage cannot be performed, and an electret film (ii) having a high charge is obtained. It's hard to be done. On the other hand, if it exceeds 500 μm, it is difficult to reach the inside of the interior during electretization, and the desired performance of the present invention cannot be exhibited, which is not preferable.

As a thermoplastic resin which comprises a surface layer (B), the thing similar to the thermoplastic resin quoted by the term of the core layer (A) can be used. From the viewpoint of stretching properties, it is preferable to use the same kind of resin as the thermoplastic resin used for the surface layer (B) and the core layer (A).
The surface layer (B) may or may not contain an inorganic fine powder or an organic filler, but it is contained from the viewpoint of modifying electrical characteristics such as the dielectric constant of the surface layer (B). Is preferable. When it contains, the thing similar to the inorganic fine powder and organic filler quoted by the term of the core layer (A) can be used.
More specifically, the surface layer (B) preferably contains 30 to 97% by weight of the above-mentioned thermoplastic resin and 3 to 70% by weight of at least one kind of inorganic fine powder and organic filler.
Furthermore, the surface layer (B) preferably contains 40 to 95% by weight of a thermoplastic resin and 5 to 60% by weight of at least one of inorganic fine powder and organic filler, 50 to 90% by weight of thermoplastic resin, and It is particularly preferable to contain 10 to 50% by weight of at least one of inorganic fine powder and organic filler. When the content of the inorganic fine powder and the organic filler is less than 3% by weight, the effect of improving the electrical characteristics cannot be sufficiently obtained. On the other hand, if it exceeds 70% by weight, the structure is such that the charge easily escapes due to the dielectric effect of the inorganic fine powder itself and the formation of pores communicating with each other, and the charge tends to be unstable, which is not preferable.

When the surface layer (B) contains an inorganic fine powder or an organic filler, the same kind of inorganic fine powder or organic filler used in the core layer (A) or a different kind may be used.
In particular, the addition of an inorganic fine powder is generally suitable for modifying the electrical characteristics of the surface layer (B) because of its higher dielectric constant than that of a thermoplastic resin.
In particular, when a resin having a low dielectric constant such as a polyolefin-based resin is used as the thermoplastic resin, the core layer (A) due to the dielectric effect when a high voltage is applied during electret treatment by containing an inorganic fine powder or an organic filler. The charge can reach the core layer (A), and after the electretization, the low dielectric property of the polyolefin resin as the main component has an effect of retaining the charge of the core layer (A) without escaping.

As described above, the surface layer (B) is a layer made of a stretched resin film. This is because the uniformity of thickness (film thickness) can be improved by stretching, and electrical characteristics such as insulation resistance can be made uniform. If the thickness of the layer (B) is not uniform, local discharge concentration is likely to occur particularly in a thin portion during charge injection using a high voltage, and effective charge injection cannot be expected.
Further, the surface layer (B) is preferably a uniaxially stretched resin film with low pore formation efficiency. When the surface layer (B) is a biaxially stretched resin film, pores are formed with inorganic fine powder or organic filler as the core as in the core layer (A). The effect of holding is reduced.

The surface layer (B) is preferably stretched in at least a uniaxial direction after being laminated with the core layer (A). By stretching after laminating with the core layer (A), the uniformity of the film thickness as the porous resin film (i) is improved rather than laminating stretched films, resulting in electrical characteristics such as insulation resistance. Will improve.

In the present invention, when the porous resin film (i) is infiltrated with a non-reactive gas under pressure and then subjected to heat treatment under non-pressure, the porous resin before pressure treatment The surface layer (B) in the film (i) is a layer containing a uniaxially stretched resin film as described above. In this respect, the electretized film (ii) of the present invention is greatly improved in performance as compared with the conventional film. In the surface layer (B) of the present invention, the uniformity of thickness (film thickness) is improved by stretching to improve the electrical characteristics such as withstand voltage. If the thickness of the surface layer (B) is not uniform, local discharge concentration is likely to occur particularly in a thin portion during charge injection using a high voltage, and effective charge injection cannot be expected. When the surface layer (B) is a biaxially stretched film as in the conventional case, as with the core layer (A), pores are easily formed with inorganic fine powder or organic filler as the core, followed by pressure treatment As a result, large pores are easily formed by the heat treatment, and as a result, the uniformity of thickness (film thickness) is impaired, and the intended purpose cannot be achieved. Further, by forming these holes, the purpose of preventing the non-reactive gas from the core layer (A) from diffusing to the outside between the pressurizing treatment and the heat treatment, and the core layer ( A) It is difficult to achieve the purpose of improving the retention of charges accumulated inside. Therefore, when performing the said process, the surface layer (B) in the porous resin film (i) of this invention uses the resin film extended uniaxially with low formation efficiency of a void | hole.

The surface layer (B) may have a multilayer structure of two or more layers in addition to the single layer structure. In the case of a multilayer structure, the design of the porous resin film (i) having higher charge retention performance by changing the type and content of the thermoplastic resin, inorganic fine powder, and organic filler used in each layer Is possible.
The surface layer (B) is provided on at least one side of the core layer (A), and may be provided on both sides. When the surface layer (B) is provided on both surfaces of the core layer (A), the front and back may have the same composition and configuration, or may have different compositions and configurations (see FIG. 1).
[Porous resin film (i)]
The porous resin film (i) in the present invention comprises a laminated film of a core layer (A) / surface layer (B) (biaxially stretched resin film / stretched resin film (preferably uniaxially stretched resin film)) as a minimum constituent unit. To do.

[Lamination]
For the lamination of the core layer (A) and the surface layer (B), various known methods can be used. Specific examples include a co-extrusion method using a multilayer die using a feed block and a multi-manifold, an extrusion lamination method using a plurality of dies, and the like. Furthermore, a method of combining a coextrusion method using a multilayer die and an extrusion lamination method can be mentioned.
As described above, the core layer (A) is preferably a biaxially stretched film, and the surface layer (B) is preferably a uniaxially stretched film. And from a viewpoint of the uniformity of a film thickness, it is preferable to extend | stretch at least uniaxial direction after lamination | stacking with a core layer (A) and a surface layer (B). By stretching both layers after laminating, the uniformity of the film thickness as the porous resin film (i) is improved rather than laminating the stretched films, and as a result, the electrical characteristics such as withstand voltage are improved. .
Therefore, the lamination of the core layer (A) and the surface layer (B) is preferably performed by extrusion lamination of the surface layer (B) on the core layer (A) stretched in the uniaxial direction. After the surface layer (B) is extrusion-laminated on the core layer (A), the laminate is stretched in a direction substantially perpendicular to the stretching axis of the core layer (A), whereby the core layer (A) is biaxial. A porous resin film (i) having a uniform film thickness is obtained in which a stretched film is used and the surface layer (B) is a uniaxially stretched film.

[Stretching]
Stretching of the core layer (A), the surface layer (B), and the porous resin film (i) that is a laminate thereof can be performed by various known methods.
As the stretching method, the longitudinal stretching method utilizing the peripheral speed difference of the roll group, the transverse stretching method using a tenter oven, the rolling method, the simultaneous biaxial stretching method using a combination of a tenter oven and a linear motor, the tenter oven and the pantograph The simultaneous biaxial stretching method by a combination etc. can be mentioned. Moreover, the simultaneous biaxial stretching method by the tubular method which is a stretching method of an inflation film can be mentioned.
The temperature at the time of stretching can be performed within the range from the glass transition point temperature to the melting point of the crystal part of the main thermoplastic resin used in each layer. When the porous resin film (i), which is a laminate of the core layer (A) and the surface layer (B), is stretched, it is stretched together with the layer having a higher set basis weight (usually the core layer (A)). What is necessary is just to set temperature.

The stretching temperature is a temperature 1 to 70 ° C. lower than the melting point of the thermoplastic resin used as an index. Specifically, when the thermoplastic resin of each layer is a propylene homopolymer (melting point 155 to 167 ° C.), it is 100 to 166 ° C., and when it is a high density polyethylene (melting point 121 to 136 ° C.), it is 70 to 135 ° C. ° C. The stretching speed is preferably in the range of 20 to 350 m / min.
The draw ratio is not particularly limited, and is appropriately determined in consideration of the characteristics of the thermoplastic resin used for the porous resin film (i), the porosity to be described later, and the like.
For example, when a propylene homopolymer or a copolymer thereof is used as a thermoplastic resin, the draw ratio is about 1.2 to 12 times, preferably 2 to 10 times when drawn in a uniaxial direction. In the case of stretching in the biaxial direction, the area magnification (product of the vertical magnification and the horizontal magnification) is 1.5 to 60 times, preferably 4 to 50 times. When other thermoplastic resins are used, the stretching ratio is 1.2 to 10 times, preferably 2 to 5 times when stretched in a uniaxial direction, and 1.5 to 20 times the area magnification when stretched in a biaxial direction. Times, preferably 4 to 12 times.

[Anchor coat layer (C)]
The porous resin film (i) may be laminated on one or both sides in order to further expand the use after electretization by laminating multiple materials, and to improve the adhesion to an adhesive or a deposited metal film. It is preferable to have an anchor coat layer (C).
A polymer binder is preferably used for the anchor coat layer (C). Specific examples of such a polymer binder include polyethyleneimine, alkyl-modified polyethyleneimine having 1 to 12 carbon atoms, poly (ethyleneimine-urea). And polyethyleneimine polymers such as ethyleneimine adducts of polyamine polyamides and epichlorohydrin adducts of polyamine polyamides, acrylic amide-acrylic acid ester copolymers, acrylic acid amide-acrylic acid ester-methacrylic acid ester copolymers, Examples include polyacrylamide derivatives, acrylic ester polymers such as oxazoline group-containing acrylic ester polymers, polyvinyl alcohol and modified products thereof, polyvinyl pyrrolidone, polyethylene glycol, and the like. Polyurethanes, polyurethane, ethylene-vinyl acetate copolymer, polyvinylidene chloride, chlorinated polypropylene, maleic acid-modified polypropylene, acrylic acid-modified polypropylene, and other polypropylene polymers, acrylonitrile-butadiene copolymer, polyester and other organic solvent dilutions Resin or water dilution resin etc. are mentioned. Among these, a polyethyleneimine polymer, a polyvinyl alcohol polymer, and a polypropylene polymer are preferable because of their excellent anchoring effect on the porous resin film (i).

The film thickness of the anchor coat layer (C) is preferably 0.001 to 5 g / m ² , more preferably 0.005 to 3 g / m ² in terms of solid content basis weight, and 0.01 to 1 g. / M ² is more preferable. When the basis weight of the layer (C) is less than 0.001 g / m ² , the effect of providing the anchor coat layer (C) cannot be sufficiently obtained. On the other hand, if it exceeds 5 g / m ² , it is difficult to keep the film thickness of the anchor coat layer (C) as the coating layer uniform, and the electrical characteristics of the porous resin film (i) due to the fluctuation of the film thickness. Of the anchor coating layer (C) itself, the anchor effect is reduced due to insufficient cohesive strength of the anchor coat layer (C), or the surface resistance value of the anchor coat layer (C) is reduced to less than 1 × 10 ¹³ W, When the porous resin film (i) is converted into an electret, it is difficult to inject charges, and the core layer (A) is not reached and the desired performance of the present invention is not exhibited.

As a method of providing the anchor coat layer (C) on the porous resin film (i), it is preferable to use a method in which a coating material containing the polymer binder is applied onto the porous resin film (i). The coating can be formed by forming a coating film on the porous resin film (i) with a known coating apparatus and drying it. Specific examples of coating devices include, for example, die coaters, bar coaters, comma coaters, lip coaters, roll coaters, curtain coaters, gravure coaters, spray coaters, squeeze coaters, blade coaters, reverse coaters, air knife coaters, etc. Is mentioned.
The lamination of the anchor coat layer (C) to the porous resin film (i) is preferably performed before performing the electretization process described later.
Further, when the porous resin film (i) is infiltrated with a non-reactive gas under pressure and then subjected to heat treatment under non-pressure, the timing for installing the anchor coat layer (C) is: Step of porous resin film (i) before carrying out pressure treatment and heat treatment described later, step of porous resin film (i) before carrying out pressure treatment and heat treatment, pressure treatment and heating The stage of the porous resin film (i) which processed can be considered, and all can be implemented. Considering the rationality of equipment and processes, it is preferable to carry out at the stage of the porous resin film (i) before performing the pressure treatment and the heat treatment.

[Pressure treatment]
In the present invention, the preferred porous resin film (i) is prepared by placing the aforementioned resin film in a pressure vessel, introducing a non-reactive gas into the vessel, and applying pressure to the inside of the core layer (A). It is obtained by infiltrating a non-reactive gas into the pores and expanding the pores by a heat treatment described later.
Specific examples of the non-reactive gas used include inert gases such as nitrogen, carbon dioxide, helium, neon, argon, chlorofluorocarbon, and halon, or mixed gases and air thereof. Even when a gas other than a non-reactive gas is used, an expansion effect can be obtained. From the viewpoint of safety during pressure treatment and the safety of the obtained porous resin film (i), methane, ethane, propane, It is desirable to use the non-reactive gas described above without using a reactive gas such as butane.

The pressure during the pressure treatment is preferably in the range of 0.2 to 10 MPa, more preferably 0.3 to 8 MPa, and still more preferably 0.4 to 6 MPa. When the applied pressure is less than 0.2 MPa, the pressure is low, so that the gas cannot be sufficiently permeated into the porous resin film (i), and a sufficient expansion effect cannot be obtained. On the other hand, if it exceeds 10 MPa, the pores of the core layer (A) cannot withstand the internal pressure during the subsequent heat treatment, and burst, resulting in holes and tears in the porous resin film (i).
The time for performing the pressure treatment is preferably 1 hour or more, more preferably in the range of 1 to 50 hours. If the pressure treatment time is less than 1 hour, the non-reactive gas cannot be fully filled in the entire core layer (A). On the contrary, in the porous resin film (i) in which the non-reactive gas is sufficiently filled in the pores of the core layer (A) in a short time of less than 1 hour, the gas emission after the treatment is similarly the same. As soon as before or during the heat treatment described later, the infiltrated gas diffuses and a stable expansion ratio cannot be obtained.
When the porous resin film (i) is long and pressure treatment is performed in the form of winding, a buffer sheet as shown in FIG. 6 is provided so that the non-reactive gas can easily penetrate into the winding. It is desirable to prepare a material that has been wound together with and to process it. Specific examples of the buffer sheet include a foamed polystyrene sheet, a foamed polyethylene sheet, a foamed polypropylene sheet, a non-woven fabric, a woven fabric, and a paper having a continuous void. This winding is put into a pressurized container as shown in FIG. 7, and a pressure treatment is performed with a non-reactive gas.

[Heat treatment]
The porous resin film (i) can be obtained by fixing the shape of a resin film having pores expanded by pressure treatment by heat treatment.
After the pressure treatment, the porous resin film (i) is expanded by the differential pressure by returning it to a non-pressure condition. However, in this state, the permeated non-reactive gas gradually escapes, and the porous resin film (i) returns to its original thickness.
Therefore, heat treatment promotes inelastic deformation (plastic deformation) of the thermoplastic resin in the expanded shape, and even after the non-reactive gas escapes from the film and the pores fall to atmospheric pressure. The expansion effect can be maintained.

The temperature of the heat treatment is within a known temperature range suitable for stretching the thermoplastic resin, which is not lower than the glass transition temperature of the thermoplastic resin mainly used for the core layer (A) and not higher than the melting point of the crystal part. it can. More specifically, when the thermoplastic resin of the core layer (A) is a propylene homopolymer (melting point: 155 to 167 ° C.), the temperature is in the range of 80 to 160 ° C.
As the heating method, various conventionally known methods can be used. As a specific example, when the porous resin film (i) is a single wafer, heating in an oven, heating on a heat plate, radiant heating by radiating infrared rays from an infrared heater to the film surface, etc. Can be mentioned. Also, when the porous resin film (i) is long and is in the form of winding, hot air heating that blows hot air from the nozzle onto the film surface, and radiant heating that radiates infrared rays from the infrared heater to the film surface And contact heating for bringing the film into contact with a roll or plate with a temperature control function.

The heating time of the porous resin film (i) is determined by the treatment temperature and the heat transfer rate, but is preferably in the range of 1 to 100 seconds, more preferably 2 to 80 seconds, still more preferably 3 to 60 seconds. It is. If the heat treatment time is less than 1 second, the porous resin film (i) cannot be heated uniformly, and the film thickness after the heat treatment is not stable. On the other hand, if it exceeds 100 seconds, the gas escapes from the porous resin film (i) whose gas permeability is improved by heating, and the film thickness is reduced during the heat treatment.
Since the elastic modulus of the porous resin film (i) obtained by the heat treatment is low and the pores are easily crushed when a load is applied, the non-contact type hot air heating or radiation heating tends to obtain a higher expansion ratio. It is in. FIG. 8 shows an example of a non-contact type heat treatment apparatus.

[Porous resin stretched film (i)]
The porous resin film (i) obtained through the above laminating step and stretching step and then, if necessary, through pressure treatment and heat treatment, is suitable for forming an electret film (ii) by charge injection. Designed as a thing. The porous resin film (i) has a certain range of porosity in order to ensure the capacitance, and in order to prevent the accumulated charge from escaping to the outside, The surface resistance value is greater than or equal to the value.
In the present invention, the pores in the porous resin film (i) are places where electric charges are retained, so that the larger the ratio, the greater the capacitance can be ensured. Since the number of vacancies increases, it becomes difficult to stably maintain a high charge state over a long period of time.
The water vapor transmission coefficient of the porous resin film (i) determines the presence or absence of such communicating pores. If the water vapor transmission coefficient is large, electric charges are likely to be discharged due to the surface of the communicating holes and intervening water vapor. The surface specific resistance value of the porous resin film (i) also determines the ease of charge release from the porous resin film (i). If the surface resistivity is too small, discharge through the film surface is likely to occur.

[Thickness]
The thicknesses of the porous resin film (i) and electret film (ii) in the present invention were measured using a thickness meter in accordance with JIS-K-7130: 1999.
The thickness of each of the core layer (A) and the surface layer (B) is such that a film as a measurement target sample is cooled to a temperature of −60 ° C. or lower with liquid nitrogen, and a razor blade is placed on a sample placed on a glass plate (Sick Japan Co., Ltd., trade name: Proline Blade) is cut perpendicularly to the surface direction to create a sample for cross-section measurement, and the cross-section of the obtained sample is scanned with a scanning electron microscope (JEOL ( Measured by the above method using a product name, JSM-6490), and determining the thickness ratio by distinguishing the boundary line between the core layer (A) and the surface layer (B) from the pore shape and composition. Calculated from the thickness of the entire film layer.

[Porosity]
In the porous resin film (i), the porosity calculated by the following formula (1) is preferably 1 to 70%, more preferably 10 to 60%, and more preferably 20 to 50%. It is particularly preferred. It is preferable to have a large number of these pores independently as fine pores inside the film. Due to the presence of pores, the number of interfaces in the resin film is increased, and the performance of accumulating charges inside the resin film is improved compared with a resin film having no pores, thereby obtaining an electret film (ii) with high performance. Can do. However, excessive vacancies can cause charge to escape.

When the porous resin film (i) is infiltrated with a non-reactive gas under a pressurized condition and then subjected to a heat treatment under a non-pressurized condition, the resin film before the treatment has a fine void inside the film. It has a large number of holes, and the porosity calculated by the above formula (1) is preferably 1 to 50%, more preferably 10 to 45%. If the porosity is less than 1%, the effect of expansion due to permeation of the non-reactive gas cannot be sufficiently obtained. On the other hand, if the porosity exceeds 50%, communication between the pores occurs, and the non-reactive gas tends to escape and a sufficient expansion effect tends not to be obtained.
By carrying out the above-described pressure treatment and heat treatment on the resin film, the resulting porous resin film (i) has a higher porosity than the resin film.
The porous resin film (i) after performing the pressure treatment and the heat treatment preferably has a porosity of 5 to 95% calculated by the previous formula (1) and is 10 to 80%. More preferably, it is more preferably 12 to 70%, and particularly preferably 15 to 60%. When the porosity is less than 5%, the charge storage capacity is low, and the obtained electret (iii) is inferior in performance as a material for an electric / electronic input / output device. On the other hand, if it exceeds 95%, the outflow of charges through the communicating vacancies is likely to occur, and the performance of the obtained electret (ii) is likely to deteriorate with time. Moreover, the elastic modulus of the porous resin film (i) becomes extremely inferior, the resilience in the thickness direction is lowered, and the durability is inferior.

[Water vapor transmission coefficient]
The water vapor transmission coefficient (g · mm / m ² · 24 hr) of the porous resin film (i) is a permeation rate at a temperature of 40 ° C. and a relative humidity of 90% by a cup method in accordance with JIS-Z-0208: 1976. It is a value obtained by measuring humidity (g / m ² · 24 hr) and converting from the thickness (mm) of the film. The surface layer (B) of the porous resin film (i) of the present invention has an insulating effect so that electric charges accumulated in the core layer (A) do not escape to the outside, but when the effect is low The water vapor transmission coefficient becomes high, and the charge holding ability is inferior. Or when many of the said void | holes in the porous resin film (i) of this invention are connecting, a water-vapor-permeation coefficient becomes high similarly and a charge retention capability becomes inferior.

The water vapor transmission coefficient of the porous resin film (i) of the present invention is in the range of 0.1 to 2.5 g · mm / m ² · 24 hr, preferably 0.2 to 1.5 g · mm / m ² · It is within the range of 24 hr, and particularly preferably within the range of 0.3 to 1.0 g · mm / m ² · 24 hr. When the water vapor transmission coefficient of the porous resin film (i) exceeds 2.5 g · mm / m ² · 24 hr, the chargeability under high humidity is remarkably lowered, and the desired performance of the present invention is not exhibited. On the other hand, a thermoplastic resin that can be a main component of the porous resin film (i), for example, a polyolefin-based resin has a water vapor transmission coefficient of around 0.1 g / m ² · 24 hr, so that it is less than 0.1 g / m ² · 24 hr. It is difficult to produce a porous resin film (i). As described above, these water vapor transmission coefficients can be adjusted mainly by the amount of pores (porosity), its size, and shape.

[Surface resistance]
The surface resistance value (Ω) of the porous resin film (i) was measured under the conditions of a temperature of 23 ° C. and a relative humidity of 50% by a double ring method in accordance with JIS-K-6911: 1995.
The porous resin film (i) of the present invention has a surface resistance of at least one surface of 1 × 10 ¹³ to 9 × 10 ¹⁷ Ω, preferably 1 × 10 ¹⁴ to 9 × 10 ¹⁶ Ω, particularly preferably. Is in the range of 5 × 10 ¹⁴ to 9 × 10 ¹⁵ Ω.
When the surface resistance value is less than 1 × 10 ¹³ Ω, when the porous resin film (i) is subjected to electret treatment, the charge easily escapes through the surface, and sufficient charge injection is not performed. On the other hand, if the surface resistance exceeds 9 × 10 ¹⁷ Ω, it becomes difficult to remove dust and dirt adhering to the porous resin film (i), and local discharge tends to occur during electret processing. Therefore, the partial porous resin film (i) is easily broken and is not preferable. These surface resistances can be adjusted mainly by the selection of the thermoplastic resin to be used and the basis weight of the anchor coat layer (C) described above.

[Electretization]
In order to use the porous resin film (i) of the present invention as an electret film (ii), an electret treatment by direct current high voltage discharge is performed.
According to the conventional method, several processing methods can be considered for the electretization process. For example, a method of holding both surfaces of the porous resin film (i) with a conductor and applying a DC high voltage or a pulsed high voltage (electroelectretization method) or a method of electretization by irradiating γ rays or electron beams ( Radio electretization method) and the like are known.
Among them, the electretization method (electroelectretization method) using a direct current high voltage has a small apparatus and a small burden on workers and the environment, and is as high as the porous resin film (i) of the present invention. Suitable for electretization of molecular materials.

As a preferred example of an electretization apparatus that can be used in the present invention, a porous resin film (i) is fixed between a needle electrode 6 connected to a DC high voltage power source 5 and a ground electrode 7 as shown in FIG. Applying voltage, passing a porous resin film (i) while applying a predetermined voltage between a needle electrode 8 connected to a DC high voltage power source and a roll 9 connected to the ground as shown in FIG. 4, the porous resin film (i) is fixed between the wire electrode 10 connected to the DC high voltage power source and the ground electrode 7 as shown in FIG. 4, and the wire electrode 10 is moved while applying a predetermined voltage, FIG. As shown in FIG. 2, there is one that allows the porous resin film (i) to pass through while applying a predetermined voltage between the wire electrode 11 connected to the DC high voltage power source and the roll 9 connected to the ground.

The present invention is characterized in that a larger amount of electric charge is accumulated in the inside by electretization by direct current high voltage discharge. The voltage of the electretization treatment is such that the thickness of the porous resin film (i), the porosity, the material of the resin or filler, the treatment speed, the shape, material, size of the electrode to be used, and the electret film to be finally obtained ( Although it can be changed depending on the charge amount of ii), the preferable range is 10 to 100 KV, more preferably 12 to 70 KV, and still more preferably 15 to 50 KV. If the electretization voltage is less than 10 KV, the amount of charge injection is insufficient, and the initial performance of the present invention tends to be difficult to exhibit. On the other hand, if it exceeds 100 KV, local spark discharge tends to occur, and partial destruction of the porous resin film (i) tends to occur. On the other hand, if it exceeds 100 KV, a current flowing from the surface of the porous resin film (i) through the end face to the ground electrode tends to be generated, and the electretization efficiency tends to be deteriorated.

In the electretization treatment, an excessive charge may be injected into the porous resin film (i). In this case, a discharge phenomenon occurs from the treated electret film (ii), resulting in inconvenience in the subsequent process. There is a case. Therefore, the electret film (ii) can be subjected to a charge removal process for surplus charges after the electret process. By performing the charge removal process, it is possible to remove the charge applied excessively by the electret process and prevent the discharge phenomenon. As the charge removal process, a known charge remover such as a voltage application type charge remover (ionizer) or a self-discharge charge remover can be used. These general static eliminators can remove the charge on the surface, but do not remove the charge accumulated in the core layer (A), particularly in the vacancies. Therefore, there is no influence that the performance of the electret film (ii) is greatly reduced by the charge removal treatment.

The electretization treatment is desirably performed at a temperature not lower than the glass transition temperature of the main thermoplastic resin used for the porous resin film (i) and not higher than the melting point of the crystal part. If the glass transition point or higher, the molecular motion of the amorphous portion of the thermoplastic resin is active, and a molecular arrangement suitable for a given charge is formed, so that an efficient electret treatment is possible. On the other hand, if the melting point is exceeded, the porous resin film (i) cannot maintain its structure, and thus the desired performance of the present invention cannot be obtained.

[Dielectric film (F)]
The electret (iii) provided with the conductive layer of the present invention is obtained by laminating the dielectric film (F) on at least one surface of the electret film (ii) via the adhesive layer (D). As the dielectric film (F), a stretched film or an unstretched film made of a thermoplastic resin can be used.
The type of thermoplastic resin used for the dielectric film (F) is not particularly limited. For example, high density polyethylene, medium density polyethylene, low density polyethylene, propylene resin, polyolefin resin such as polymethyl-1-pentene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, maleic acid modified polyethylene, Functional group-containing polyolefin resins such as maleic acid-modified polypropylene, polyamide resins such as nylon-6 and nylon-6,6, polyethylene terephthalate and copolymers thereof, thermoplastic polyester resins such as polybutylene terephthalate and aliphatic polyester Polycarbonate, atactic polystyrene, syndiotactic polystyrene and the like can be used.
The film thickness of the dielectric film (F) is preferably from 0.1 to 100 μm, more preferably from 0.5 to 70 μm, still more preferably from 1 to 50 μm. If the film thickness is less than 0.1 μm, the thickness is too thin and wrinkles are likely to occur when stacking, and defects are likely to occur in the conductive layer (E). On the other hand, if it exceeds 100 μm, the signal does not reach the electret film (ii) through the dielectric film, or it is difficult for sound and vibration to be transmitted to the electret film (ii). When used, the performance is inferior.

[Conductive layer (E)]
The dielectric film (F) needs to have a conductive layer (E) on one side. Examples of the method for providing the conductive layer (E) on the dielectric film (F) include application of a conductive paint and vapor deposition of metal.
Specific examples of the conductive paint include metal particles such as gold, silver, platinum, copper, and silicon, tin-doped indium oxide (ITO), antimony-doped tin oxide (ATO), fluorine-doped tin oxide (FTO), and aluminum dope. Conductive metal oxide particles such as zinc oxide and carbon particles mixed with a solution and / or dispersion of a binder component such as acrylic resin, urethane resin, ether resin, ester resin, epoxy resin, or polyaniline , Solutions and / or dispersions of conductive resins such as polypyrrole and polythiophene. The conductive coating can be formed by forming a coating film on a support with a known coating apparatus and drying it. Specific examples of the coating apparatus include a die coater, a bar coater, a comma coater, a lip coater, a roll coater, a curtain coater, a gravure coater, a spray coater, a blade coater, a reverse coater, and an air knife coater.
As a specific example of the metal vapor deposition film, a thin film is formed by vaporizing a metal such as aluminum, zinc, gold, silver, platinum, nickel under reduced pressure and directly adhering to the surface of the dielectric film (F), Or the said metal is vaporized under reduced pressure, once adheres to the surface of a transfer film, a thin film is formed, and it is made to transfer on the surface of a dielectric film (F) etc. next.
The film thickness of the conductive layer (E) is preferably from 0.01 to 10 μm, more preferably from 0.03 to 7 μm, still more preferably from 0.05 to 5 μm. If the film thickness is less than 0.01 μm, the conductive layer tends to be uneven in signal transmission performance. On the other hand, if the thickness exceeds 10 μm, the conductive layer becomes heavy and it becomes difficult to transmit sound and vibration, resulting in poor performance when used in an electric / electronic input / output device.

[Adhesive layer (D)]
The electret (iii) provided with the conductive layer of the present invention is obtained by laminating the dielectric film (F) on at least one surface of the electret film (ii) via the adhesive layer (D).
When laminating the dielectric film (F) provided with the conductive layer (E) on the electret film (ii), the dielectric layer (E) may be laminated so that the conductive layer (E) becomes the outermost layer. And the adhesive layer (D) may be laminated. In general, it is preferable to laminate so that the conductive layer (E) provided on the laminated dielectric film (F) is the outermost layer (facing the side opposite to the electret film (ii)). If the conductive layer (E) is installed so as to face the electret film (ii), it becomes easier to pick up electrical signals, but it is difficult to install a signal transmission cable or connector on the conductive layer (E). turn into.
Lamination is performed by applying an adhesive such as a solvent-based adhesive, a water-dispersed adhesive, or a hot-melt adhesive on the electret film (ii) or the dielectric film (F). The adhesive layer can be provided by a technique, and the lamination can be performed through the adhesive layer, or a usual technique such as a melt lamination using a heat-fusible film or a melt-extruded film can be used. These adhesive layers are usually preferably provided on the dielectric film (F) first because the heat history on the electret film (ii) is reduced.

Examples of solvent-based adhesives and water-dispersed adhesives include resins made of acrylic resins, urethane resins, ether resins, ester resins, epoxy resins, rubber resins, silicone resins, ABS resins, etc. The components are dissolved, dispersed, emulsion-dispersed and diluted in a phase using a conventionally known solvent to obtain a liquid adhesive that is fluid and can be applied in the form of a solution type or an emulsion type. Representative.
These adhesives are applied by a die coater, bar coater, comma coater, lip coater, roll coater, gravure coater, spray coater, blade coater, reverse coater, air knife coater, or the like. Thereafter, smoothing is performed as necessary, and an adhesive layer is formed through a drying step.
These adhesives are generally applied so that the basis weight is 0.5 to 25 g / m ² and an adhesive layer is provided.
When using an adhesive, apply the adhesive on the surface of the dielectric film (F) that does not have the conductive layer (E), then stack the electret film (ii), and apply pressure with a pressure roll. That's fine.

Examples of the hot-melt adhesive include polyolefin resins such as polyethylene and ethylene / vinyl acetate copolymers, polyamide resins, polybutyral resins, urethane resins, and the like.
When using a hot-melt adhesive, apply it to the surface of the dielectric film (F) that does not have the conductive layer (E) by methods such as beat coating, curtain coating, and slot coating, or melt from the die. The film may be extruded and laminated, then the electret film (ii) may be stacked and pressure bonded with a pressure roll.
When the electret film (ii) and the dielectric film (F) are laminated before or after the electret treatment of the porous resin film (i), the dielectric film (F) is provided on both sides. At least one side must be after performing the electretization process. Even if the electretization process is performed after the dielectric film (F) is laminated on both sides, the charge may escape through the conductive layer (E), so that the charge reaches the inside of the porous resin film (i). The desired performance of the present invention cannot be achieved.
One mode of the electret (iii) provided with the conductive layer of the present invention is shown in FIG.

Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples, and Test Examples. The materials, amounts used, ratios, operations, and the like shown below can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. The% described below is% by weight unless otherwise specified.
Table 1 summarizes the materials used in the production examples, examples and comparative examples of the electret film (ii) of the present invention.

[Production Example 1]
After kneading the thermoplastic resin composition a with an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 135 ° C. and stretched 5 times in the machine direction using a number of roll groups having different peripheral speed differences to obtain a 5 times stretched film. Subsequently, after kneading the plastic resin composition c with an extruder set at 250 ° C., the plastic resin composition c is supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, and this is the surface and back surface of the 5-fold stretched film adjusted as described above Each was laminated to obtain a laminated film having a three-layer structure. Next, this laminated film was cooled to 60 ° C., heated again to about 145 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to the end, the ears are slit and the thickness is 60 μm and the porosity is 26 with a three-layer structure (c / a / c = 10/40/10 μm, stretched layer configuration (one axis / 2 axes / 1 axis)). % Porous resin film was obtained.

[Production Example 2]
After kneading the thermoplastic resin composition b in an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 150 ° C. and stretched 4 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4 times stretched film. Subsequently, after kneading the plastic resin composition d with an extruder set at 250 ° C., the plastic resin composition d was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. Each of these layers was laminated to obtain a laminated film having a three-layer structure. Next, this laminated film is cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 7.5 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to 60 ° C., the ears are slit and a three-layer structure (d / b / d = 20/60/20 μm, stretched layer configuration (1 axis / 2 axes / 1 axis)) with a thickness of 100 μm, pores A porous resin film having a rate of 38% was obtained.

[Production Example 3]
After kneading the thermoplastic resin composition f with an extruder set at 220 ° C., the thermoplastic resin composition f was supplied to an extrusion die set at 240 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 145 ° C., and stretched 4 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4 times stretched film. Next, after kneading the plastic resin composition g with an extruder set at 230 ° C., the plastic resin composition g was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. Each was laminated to obtain a laminated film having a three-layer structure. Next, the laminated film was cooled to 60 ° C., heated again to about 145 ° C. using a tenter oven, stretched 7 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to a point, the ears are slit and the thickness is 80 μm and the porosity is 24 with a three-layer structure (g / f / g = 15/50/15 μm, stretched layer configuration (one axis / 2 axes / 1 axis)). % Porous resin film was obtained.

[Production Example 4]
After kneading the thermoplastic resin composition b in an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 150 ° C. and stretched 4.5 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4.5 times stretched film. Next, after kneading the plastic resin composition d with an extruder set at 250 ° C., the plastic resin composition d was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. And a laminated film having a three-layer structure. Next, this laminated film was cooled to 60 ° C., heated again to about 145 ° C. using a tenter oven, stretched seven times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to the end, the ears are slit, the thickness is 120 μm, and the porosity is 45 in a three-layer structure (d / b / d = 10/100/10 μm, stretched layer configuration (one axis / 2 axes / 1 axis)). % Porous resin film was obtained.

[Production Example 5]
After kneading the thermoplastic resin composition b in an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 150 ° C. and stretched 4 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4 times stretched film. Next, the plastic resin composition d was kneaded with an extruder set at 250 ° C., then supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was laminated on one side of the 4 × stretched film adjusted as described above. Thus, a laminated film having a two-layer structure was obtained. Next, the laminated film was cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to the end, the ear part is slit, and a porous resin film having a two-layer structure (d / b = 20/60 μm, stretched layer structure (one axis / 2 axes)) with a thickness of 80 μm and a porosity of 41% is obtained. Obtained.

[Production Example 6]
The thermoplastic resin composition a and the thermoplastic resin composition e are kneaded in individual extruders set at 230 ° C., then supplied to a feed block type multilayer die set at 250 ° C., and e / a / The layers were laminated in the order of e and extruded into a sheet shape, which was cooled by a cooling device to obtain a three-layer unstretched sheet. This unstretched sheet was heated to 135 ° C. and stretched 5 times in the longitudinal direction to obtain a 5-fold stretched film. Next, this 5-fold stretched film is cooled to 60 ° C., heated again to about 155 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C., After cooling to 60 ° C., the ears are slit, and a three-layer structure (e / a / e = 1/40/1 μm, stretched layer configuration (two axes / 2 axes / 2 axes)) with a thickness of 42 μm, pores A porous resin film having a rate of 23% was obtained.

[Production Example 7]
After kneading the thermoplastic resin composition b in an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 150 ° C. and stretched 4.5 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4.5 times stretched film. Next, this 4.5 times stretched film was cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 7.5 times in the transverse direction, and then annealed in an oven adjusted to 160 ° C. After the treatment and cooling to 60 ° C., the ears were slit to obtain a porous resin film having a single layer structure with a thickness of 60 μm and a porosity of 44%.
The composition of the obtained porous resin film is shown in Table 2 below.

[Examples 1 to 6, Comparative Example 3]
Corona surface treatment was applied to both surfaces of the porous resin films obtained in Production Examples 1 to 5, the anchor agents listed in Table 1 were combined, and the coating amount (basis weight) after drying was as shown in Table 3 It was coated as such, and dried in an oven at 80 ° C. for 30 minutes, and an anchor coat layer (C) was provided to obtain a porous resin film (i). The electretization apparatus shown in FIG. 2 set to a distance between the needles of 10 mm and a distance between the main electrode and the ground electrode of 10 mm was used, and the following tests were conducted. Finally, a direct current high voltage discharge treatment was performed at the applied voltage shown in Table 3 to obtain an electret film (ii).

[Comparative Examples 1 and 2]
The porous resin film obtained in Production Examples 6 and 7 was used as it was to obtain a porous resin film (i). The electretization apparatus shown in FIG. 2 set to a distance between the needles of 10 mm and a distance between the main electrode and the ground electrode of 10 mm was used, and the following tests were conducted. Finally, a direct current high voltage discharge treatment was performed at the applied voltage shown in Table 3 to obtain an electret film (ii).
[Test example]
(Spark discharge voltage test)
The porous resin film (i) obtained in each example and each comparative example is placed on the 7 ground electrodes of the electretization apparatus shown in FIG. 2, and the applied voltage is gradually increased from 1 KV to cause local spark discharge. Was used to measure the voltage at which the porous resin film (i) was broken. The results are shown in Table 3.

(Charging potential test)
The porous resin film (i) obtained in each example and each comparative example is placed on the ground electrode 7 board, and electretization is performed at an applied voltage 1 KV lower than the voltage at which local spark discharge is generated in the above spark discharge test. Was given. The treated porous resin film (i) surface (treated surface) is once covered with aluminum foil (product name: Myfoil), the surplus charge remaining on the surface is removed, and the aluminum foil is further removed. After peeling off, move to a constant temperature room with a temperature of 25 ° C. and a relative humidity of 60% while being held on the 7 ground electrodes, and the surface potential of each electret film (ii) in the same environment is measured with a surface potential meter ( Measurement was performed immediately after the treatment and after 30 days using a product of Keyence Co., Ltd. (trade name: high-accuracy electrostatic sensor SK), and evaluated according to the following criteria. The evaluation results and the measured surface potential are shown in Table 3.
○: Good: the surface potential after 30 days is 200 V or more X: Bad: the surface potential after 30 days is less than 200 V As shown in Table 3, the electret film (ii) of the present invention has more It was confirmed that the charge was retained for a long period of time.

(Adhesive adhesion)
A polyurethane adhesive (manufactured by Toyo Ink, trade name: Tomoflex TM319) and a curing agent (manufactured by Toyo Ink, trade name: Tomoflex CAT-11B) are mixed at a ratio of 1: 1 and diluted with ethyl acetate. Thus, an adhesive paint having a solid content of 20% by weight was prepared. An adhesive paint was applied to one side of the electret films (ii) obtained in Examples 1 to 3 and Comparative Examples 1 to 3 so that the coating amount after drying was 2 g / m ² , After drying in an oven for 60 seconds, the adhesive was folded in two so that the adhesive was on the inside, and a sample for adhesive adhesion evaluation was prepared. The prepared sample was aged in an oven set at 40 ° C. for 3 days, then cut to a width of 10 mm and a length of 150 mm, and adhered using a tensile / compression tester (manufactured by Shimadzu Corp., Autograph; AGS-D) The peel adhesion strength between (ii) was measured by T-peeling at a tensile speed of 300 mm / min according to JIS-K-6854-3, and evaluated according to the following criteria. Table 3 shows the evaluation results and the measured peel adhesion strength.
○: Good: Peel strength of 150 g / cm or more X: Poor: Peel strength of less than 150 g / cm

(Example of electret film (ii) subjected to pressure and heat treatment)
The materials used in the production examples, examples, and comparative examples of the electret film (ii) of the present invention are shown in Table 1 and Table 4 below.

[Production Example 11]
After kneading the thermoplastic resin composition a with an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 135 ° C. and stretched 5.0 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 5-fold stretched film.
Next, after kneading the plastic resin composition c with an extruder set at 250 ° C., the mixture was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. Each was laminated to obtain a laminated film having a three-layer structure. Next, this laminated film is cooled to 60 ° C., heated again to about 145 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. Cooling to 0 ° C., slitting the ears, a three-layer structure (c / a / c = 10/40/10 μm, stretched layer configuration (one axis / 2 axes / 1 axis)), a thickness of 60 μm, a porosity of 26 % Resin film was obtained.

[Production Example 12]
After kneading the thermoplastic resin composition b in an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 150 ° C. and stretched 4.5 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4.5 times stretched film.
Next, after kneading the plastic resin composition d with an extruder set at 250 ° C., the plastic resin composition d was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. And a laminated film having a three-layer structure. Next, this laminated film is cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 7.5 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. Thereafter, it is cooled to 60 ° C., the ears are slit, and a three-layer structure (d / b / d = 20/60/20 μm, stretched layer structure (one axis / 2 axes / 1 axis)) is 100 μm in thickness and has pores A resin film having a rate of 38% was obtained.

[Production Example 13]
After kneading the thermoplastic resin composition b in an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 145 ° C., and stretched 4 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4 times stretched film.
Next, the plastic resin composition d was kneaded with an extruder set at 250 ° C., then supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. Each of these layers was laminated to obtain a laminated film having a three-layer structure. Next, this laminated film is cooled to 60 ° C., heated again to about 155 ° C. using a tenter oven, stretched 7 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to 0 ° C. and slitting the ear, the thickness is 100 μm and the porosity is 39 in a three-layer structure (d / b / d = 10/80/10 μm, stretched layer configuration (one axis / 2 axes / 1 axis)) % Resin film was obtained.

[Production Example 14]
After kneading the thermoplastic resin composition a with an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 145 ° C., and stretched 4 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4 times stretched film.
Next, after kneading the plastic resin composition a with an extruder set at 250 ° C., the mixture was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. Each of these layers was laminated to obtain a laminated film having a three-layer structure. Next, the laminated film is cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. Cooling to 0 ° C., slitting the ears, a three-layer structure (a / a / a = 15/40/15 μm, stretched layer structure (one axis / 2 axes / 1 axis)), thickness 70 μm, porosity 9 % Resin film was obtained.

[Production Example 15]
The thermoplastic resin composition a and the thermoplastic resin composition e are kneaded in individual extruders set at 230 ° C., then each is supplied to a feed block die set at 250 ° C., and e / The layers were laminated in the order of a / e and extruded into a sheet shape, which was cooled by a cooling device to obtain a non-stretched sheet having a three-layer structure. This unstretched sheet was heated to 135 ° C. and stretched 5 times in the machine direction using a number of roll groups having different peripheral speed differences to obtain a 5 times stretched film.
Next, this 5-fold stretched film is cooled to 60 ° C., heated again to about 145 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C., Thereafter, it is cooled to 60 ° C., then the ear is slit, and a three-layer structure (e / a / e = 1/40/1 μm, stretched layer structure (two axes / 2 axes / 2 axes)) is 42 μm in thickness and empty. A resin film having a porosity of 23% was obtained.

[Production Example 16]
After kneading the thermoplastic resin composition b with an extruder set at 230 ° C., it is supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which is cooled by a cooling device to obtain an unstretched sheet. It was. This unstretched sheet was heated to 150 ° C. and stretched 4.5 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4.5 times stretched film.
Next, this 4.5 times stretched film was cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 7.5 times in the transverse direction, and then annealed in an oven adjusted to 160 ° C. After the treatment, cooling to 60 ° C. was performed, and the ear portion was slit to obtain a resin film having a single layer structure (biaxial stretching) with a thickness of 60 μm and a porosity of 44%.
The composition of the obtained resin film is shown in Table 5 below.

[Examples 11 to 14, Comparative Examples 11 to 13]
Corona surface treatment was applied to both surfaces of the resin films obtained from Production Examples 11 to 16, and the anchor coating agents described in Table 1 and Table 4 were combined and the coating amount (basis weight) after drying was as shown in Table 6. Coating was performed as described, and drying was performed in an oven at 80 ° C. for 30 minutes to provide an anchor coat layer (C).
This resin film is cut into A4 size, placed in a pressure vessel, air is then introduced into the vessel and pressurized for 8 hours at a pressure of 1.0 MPa, taken out and immediately heat treated in an oven set at 95 ° C. for 30 seconds. It implemented and obtained the porous resin film (i).
Next, using the electretization apparatus shown in FIG. 2, the porous resin film (i) obtained above on the ground electrode board set to have a distance between the main electrodes of 10 mm and a distance between the main electrode and the ground electrode of 10 mm. The applied voltage was gradually increased from 1 KV, and the voltage at which the porous resin film (i) was destroyed by local spark discharge was measured. Thereafter, electret treatment was performed at a voltage 1 KV lower than the spark discharge voltage to obtain electret films (ii) of Examples 11 to 14 and Comparative Examples 11 to 13.

[Test example]
In order to evaluate the suitability of the electret films (ii) obtained in Examples 11 to 14 and Comparative Examples 11 to 13 as materials for electric / electronic input / output devices, it is shown in Table 4 on both front and back surfaces of the film (ii). The conductive paints I and II were coated so that the coating amount after drying would be the coating amount shown in Table 7, and allowed to stand at room temperature (23 ° C.) for 24 hours to dry, and then the conductive layer (E ). The film was cut to a size of 10 cm x 10 cm, and lead wires were attached to the front and back surfaces using conductive tape (manufactured by Sumitomo 3M Co., Ltd., product name: AL-25BT) to form an electret with a conductive layer (E). Film (ii) was prepared. In this test, in order to avoid heating the electret film (ii), the conductive layer (E) was provided by drying at room temperature for a long time. However, from the viewpoint of mass productivity, coating is disadvantageous, and the conductive layer ( The electret (iii) provided with the conductive layer is easily obtained when the conductive film (F) provided with E) is bonded.

(Conductive layer adhesion)
The conductive layer (E) provided on the electret film (ii) was rubbed 10 times with a nail, and the adhesion of the conductive layer (E) was evaluated according to the following criteria. Table 7 shows the evaluation results.
○: Good not peeled ×: Bad The conductive layer (E) peels from the film (ii) (generated voltage)
A conductive layer in which an iron ball having a diameter of 11 mm and a weight of 5.5 g is installed on an insulating film (unstretched polypropylene film 100 μm) from a height of 3.6 cm using the falling ball apparatus shown in FIG. (E) Dropped onto electret (iii), sampled voltage signal into high-speed recorder (manufactured by Keyence Co., Ltd., product name: GR-7000), and measured the maximum voltage generated by impact of falling ball 5 times The average value was calculated and evaluated according to the following criteria. Table 7 shows the evaluation results and the measured maximum voltage (average value).
○: Good Maximum voltage (average value) is 200 mV or more △: Slightly defective Maximum voltage (average value) is 50 mV or more and less than 200 mV ×: Failure Maximum voltage (average value) is less than 50 mV

As shown in Table 7, the electret films (ii) of Examples 11 to 14 have high voltage generation efficiency, good performance as piezoelectric elements, and excellent performance as materials for electric / electronic input / output devices. I had it.

(Example of electret provided with conductive layer)
The materials used in the production examples and examples of the electret (iii) provided with the conductive layer of the present invention are summarized in Table 1 and Table 8 below.

[Production Example 21]
The thermoplastic resin composition a was kneaded in an extruder set at 230 ° C., then supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. This unstretched sheet was heated to 135 ° C. and stretched 5 times in the machine direction.
The plastic resin composition c was kneaded with an extruder set at 250 ° C., then extruded into a sheet and laminated on the front and back surfaces of the 5-fold stretched film prepared above to obtain a laminated film having a three-layer structure.
Next, this three-layer laminated film is cooled to 60 ° C., heated again to about 145 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then heat-treated in a heat setting zone adjusted to 160 ° C. It was.
Then, after cooling to 60 ° C., the ears are slit, the corona surface treatment is applied to both sides, and the anchor agent A is applied to both sides so that the coating amount after drying is 0.01 g / m ^2. Dry in an oven at 0 ° C. to provide an anchor layer (D), and have a three-layer [10/40/10 μm: stretched layer structure (1 axis / 2 axis / 1 axis)] structure with a thickness of 60 μm and a porosity of 26 % Porous resin film (i) was obtained.

[Production Example 22]
The thermoplastic resin composition b was kneaded in an extruder set at 230 ° C., then supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. This unstretched sheet was heated to 150 ° C. and stretched 4 times in the longitudinal direction.
After the plastic resin composition d was kneaded with an extruder set at 250 ° C., it was extruded into a sheet and laminated on the front and back surfaces of the 4 × stretched film prepared above to obtain a laminated film having a three-layer structure.
Next, this three-layer laminated film is cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 7.5 times in the transverse direction, and then heat-treated in a heat setting zone adjusted to 160 ° C. Went.
Then, after cooling to 60 ° C., the ears are slit, the corona surface treatment is applied to both sides, and the anchor agent B is applied to both sides so that the coating amount after drying is 0.02 g / m ^2. Dry in an oven at 0 ° C. to provide an anchor layer (D), and have a three-layer [20/60/20 μm: stretched layer structure (1 axis / 2 axis / 1 axis)] structure with a thickness of 100 μm and a porosity of 38 % Porous resin film (i) was obtained.

[Production Example 23]
After kneading the thermoplastic resin composition a with an extruder set at 230 ° C., it was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape, which was cooled by a cooling device to obtain an unstretched sheet. . This unstretched sheet was heated to 145 ° C., and stretched 4 times in the longitudinal direction using a number of roll groups having different peripheral speed differences to obtain a 4 times stretched film.
Next, after kneading the plastic resin composition a with an extruder set at 250 ° C., the mixture was supplied to an extrusion die set at 250 ° C. and extruded into a sheet shape. Each of these layers was laminated to obtain a laminated film having a three-layer structure.
Next, the laminated film was cooled to 60 ° C., heated again to about 150 ° C. using a tenter oven, stretched 8 times in the transverse direction, and then subjected to an annealing treatment in an oven adjusted to 160 ° C. After cooling to the bottom, the ears are slit, the corona surface treatment is applied to both sides, and the anchor agent C is applied to both sides so that the coating amount after drying is 1.0 g / m ^2. / A / a = 16/40/16 μm, a stretched layer structure (1 axis / 2 axis / 1 axis)), a thickness of 72 μm, and a porosity of 9%, a porous resin film (i) was obtained.

[Production Examples 24 to 26]
The porous resin films (i) obtained in Production Examples 21 to 23 were cut into A4 size, placed in a pressure vessel, pressurized at 1.0 MPa for 8 hours, and taken out immediately in an oven set at 95 ° C. for 30 hours. Heat treatment was performed for 2 seconds.
The structure of the obtained porous resin film (i) is shown in Table 9 below.

[Examples 21 to 24 and 26]
The porous resin films (i) obtained in Production Examples 21 to 24 and 26 were formed on the ground electrode board of the electretization apparatus shown in FIG. ), The applied voltage is gradually increased from 1 KV, the voltage at which the porous resin film (i) is destroyed by local spark discharge is measured, electret treatment is performed at a voltage 1 KV lower than this spark discharge voltage, Film (ii) was obtained.
On the opposite side of the conductive layer of the dielectric film (I or II) described in Table 8, the adhesive paint described in Table 8 was applied with a bar coater so that the coating amount after drying was 4 g / m ^2. And after drying for 1 minute in the oven set to 40 degreeC, it bonded on both surfaces of the electret film (ii), respectively, and produced the electret (iii) provided with the conductive layer. Table 10 shows the types of dielectric films used.

[Example 25]
In the oven set at 40 ° C., the adhesive paint described in Table 8 was applied to the opposite surface of the conductive layer of the dielectric film I with a bar coater so that the coating amount after drying was 4 g / m ^2. After drying for 1 minute, it was bonded to one side of the porous resin film (i) obtained in Production Example 25.
A dielectric film I of a porous resin film (i) is bonded onto the ground electrode board of the electretization apparatus shown in FIG. 2 set to a distance between the main electrodes of 10 mm and a distance between the main electrodes and the ground electrode of 10 mm. With the surface not facing the main electrode, the applied voltage is gradually increased from 1 KV, and the voltage at which the porous resin film (i) is destroyed by local spark discharge is measured. At a voltage 1 KV lower than this spark discharge voltage The electret process was implemented and the electret film (ii) was obtained.
Furthermore, the adhesive paint described in Table 1 was applied to the opposite surface of the conductive layer of another dielectric film I so that the coating amount after drying was 4 g / m ² , and the oven was set at 40 ° C. After drying for 1 minute, this was bonded to the electret-treated surface of the electret film (ii) to produce an electret (iii) provided with a conductive layer.

[Comparative Example 21]
The porous resin film (i) obtained in Production Example 25 is placed on the ground electrode board of the electretization apparatus shown in FIG. 2 set to a distance between the main electrodes of 10 mm and a distance between the main electrodes and the ground electrode of 10 mm. The voltage is gradually increased from 1 KV, and the voltage at which the porous resin film (i) is broken by local spark discharge is measured. The electret film is subjected to electret treatment at a voltage 1 KV lower than the spark discharge voltage (ii). Got.
This electretized film (ii) is 5 cm square, and a conductive layer (E) is formed by 0.03 μm gold vapor deposition film on both sides using a gold vapor deposition device (trade name: Ion Sputter E101, manufactured by Hitachi, Ltd.). did.

[Test example]
(Generated voltage)
The electret (iii) provided with the conductive layer of Examples 21 to 26 and Comparative Example 21 was cut into a size of 5 cm × 5 cm, and a conductive tape (manufactured by Sumitomo 3M Co., Ltd., trade name: AL-25BT) was used. Lead wires are attached to the front and back surfaces, and using a falling ball apparatus shown in FIG. It was dropped on an electret (iii) equipped with a conductive layer placed on top of it, and the voltage signal from the sample was taken into a high-speed recorder (manufactured by Keyence Co., Ltd., product name: GR-7000) and generated by the impact of a falling ball The maximum voltage was measured 5 times, the average value was calculated, and evaluated according to the following criteria. The evaluation results and the measured maximum voltage are shown in Table 10.
○: Good Maximum voltage (average value) is 200 mV or more Δ: Slightly good Maximum voltage (average value) is 10 mV or more and less than 200 mV ×: Defect Maximum voltage (average value) is less than 10 mV

As shown in Table 10, it can be seen that the electrets (iii) including the conductive layers of Examples 21 to 26 can convert the impact energy of the falling ball into an electric signal.
Further, it can be seen that in Comparative Example 21 in which the electretized film (ii) is directly provided with the conductive layer, the accumulated charge escapes due to the heat of the metal vapor deposition treatment, and the performance cannot be exhibited. .
Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
The present application includes a Japanese patent application filed on September 12, 2008 (Japanese Patent Application No. 2008-234641), a Japanese patent application filed on September 12, 2008 (Japanese Patent Application No. 2008-234642), and September 12, 2008. Japanese patent application filed (Japanese Patent Application No. 2008-234643), Japanese patent application filed on August 31, 2009 (Japanese Patent Application No. 2009-200196), Japanese patent application filed on August 31, 2009 (Japanese Patent Application No. 2009- No. 200019) and Japanese Patent Application (Japanese Patent Application No. 2009-200198) filed on Aug. 31, 2009, the contents of which are incorporated herein by reference.

By using the porous resin film (i) of the present invention, it is possible to inject more charge, and as a result, it is possible to obtain an electret film (ii) exhibiting stable charge retention ability for a long period of time. Further, by using the porous resin film (i) of the present invention that has been subjected to pressure and heat treatment, more charge injection becomes possible, and as a result, an electret film (ii) that exhibits excellent voltage generation capability Can be obtained. Therefore, the electretized film (ii) of the present invention is a printing material such as a charge adsorption type label, a poster, an advertisement, an industrial material such as an air filter or a dust removal mat, a speaker, a headphone, an ultrasonic vibrator, an ultrasonic motor , Vibration control devices, microphones, ultrasonic sensors, pressure sensors, acceleration sensors, strain sensors, fatigue / crack sensors, and materials for electrical and electronic input / output devices such as power generators.
The electret (iii) provided with the conductive layer of the present invention is characterized in that a conductive layer is indirectly provided on the electret film (ii), and there is no deterioration in quality in the processing step and high mass productivity. . Therefore, materials for electrical / electronic input / output devices such as speakers, headphones, ultrasonic transducers, ultrasonic motors, vibration control devices, microphones, ultrasonic sensors, pressure sensors, acceleration sensors, strain sensors, fatigue / crack sensors, and power generation devices As such, industrial applicability is great.

1 Porous resin film (i)
2 Core layer (A)
3, 4 Surface layer (B)
5 DC high

voltage power supply

6, 8 Needle electrode 7 Ground electrode 9

Roll

10, 11 connected to ground Wire electrode 15 Winding 16 prepared for pressure treatment Porous resin film (i)
17 Buffer sheet 18 Pressure vessel 19 Pressure vessel lid 20 Pressure valve 21 Pressure reducing valve 22 Stand 23 Shaft 24 Compressor 25 Porous resin film (i) winding device 26 Buffer sheet winding device 27 Hot air device 28

Guide roll

29, 30 Cooling roll 31 Electret with conductive layer (E) (iii)
32 Insulating

films

33 and 34 Lead wire 35 Transparent acrylic pipe 36 Iron ball 37 Electromagnet 38 High-speed recorder 41 Electret (iii) provided with conductive layer
42 Electretized film (ii)
43, 44 Dielectric film (F)
45, 46 Adhesive layer (D)
47, 48 Conductive layer (E)
49 Core layer (A)
50, 51 Surface layer (B)

Claims

It contains a core layer (A) containing a biaxially stretched resin film having pores and a surface layer (B) containing a stretched resin film on at least one side of the core layer (A), and has a water vapor transmission coefficient of 0.1. DC porous high voltage discharge is applied to the porous resin film (i) having a surface resistance of 1 × 10 13 to 9 × 10 17 Ω of about 2.5 g · mm / m 2 · 24 hr and a surface resistance value of at least one surface of 1 × 10 13 to 9 × 10 17 Ω An electret film (ii) characterized by being processed into an electret.
The electret film (ii) according to claim 1, wherein the stretched resin film in the surface layer (B) is a uniaxially stretched resin film.
The electretization according to claim 2, wherein the porous resin film (i) is impregnated with a non-reactive gas under a pressurized condition and then subjected to a heat treatment under the non-pressurized condition. Film (ii).
The electret film (ii) according to any one of claims 1 to 3, wherein the core layer (A) has a thickness of 10 to 500 µm, and the surface layer (B) has a thickness of 5 to 500 µm. ).
The electret film (ii) according to any one of claims 1 to 4, wherein the stretched resin film in the core layer (A) and the surface layer (B) contains a thermoplastic resin.
The core layer (A) contains 50 to 97% by weight of a thermoplastic resin, and 3 to 50% by weight of at least one kind of inorganic fine powder and organic filler, and the surface layer (B) contains 30 to 97% by weight of a thermoplastic resin, The electret film (ii) according to claim 5, further comprising 3 to 70% by weight of at least one of inorganic fine powder and organic filler.
The electret film (ii) according to claim 5 or 6, wherein the thermoplastic resin is a polyolefin resin.
8. The surface layer (B) is laminated on the core layer (A), and then the laminate is stretched in at least uniaxial direction to form each layer as a stretched resin film. Electretized film (ii).
The electret film (ii) according to any one of claims 1 to 8, wherein the porosity of the porous resin film (i) is 1 to 70%.
The electret film (ii) according to any one of claims 3 to 8, wherein the porosity of the porous resin film (i) subjected to the pressure treatment and the heat treatment is 5 to 95%.
The electret film (ii) according to any one of claims 1 to 10, further comprising an anchor coat layer (C) on at least one surface of the porous resin film (i).
The electret film (ii) according to claim 11, wherein the basis weight of the anchor coat layer (C) is 0.001 to 5 g / m 2 .
The electret film (ii) according to any one of claims 1 to 12, wherein the porous resin film (i) is electretized by subjecting the porous resin film (i) to a direct current high voltage discharge treatment in a discharge voltage range of 10 KV to 100 KV.
The electret film (ii) according to any one of claims 1 to 13, wherein charge is injected from the surface of the surface layer (B) of the porous resin film (i) in a direct current high voltage discharge treatment.
The electret film (ii) according to any one of claims 1 to 14, an adhesive layer (D), and a conductive layer (E) having a surface resistance value of 1 × 10 −2 to 9 × 10 7 Ω The electret (iii) provided with the conductive layer characterized by containing the provided dielectric film (F) in this order.
The electret (iii) provided with the conductive layer according to claim 15, wherein the dielectric film (F) is a stretched film or a non-stretched film containing a thermoplastic resin.
The electret (iii) provided with the conductive layer according to claim 15 or 16, wherein the dielectric film (F) has a thickness of 0.1 to 100 µm.
The electret (iii) provided with the conductive layer according to any one of claims 15 to 17, wherein the conductive layer (E) is formed by application of a conductive paint or metal deposition.
The electret (iii) provided with the conductive layer according to any one of claims 15 to 18, wherein the conductive layer (E) has a thickness of 0.01 to 10 µm.
16. When the dielectric film (F) provided with the conductive layer (E) is laminated on the electret film (ii), the conductive layer (E) is laminated so as to be the outermost layer. An electret (iii) comprising the conductive layer according to any one of .about.19.