JP5975681B2 - Speaker diaphragm film - Google Patents

Description

  The present invention relates to a speaker diaphragm, and more particularly to a speaker diaphragm film suitable for use in electrostatic speakers and ultrasonic speakers.

  In recent years, along with miniaturization and high functionality of ultra-thin type displays using liquid crystal devices and organic EL devices and mobile communication terminals such as mobile phones, miniaturization, thinning, and power saving have been achieved for the speakers installed. There is a growing demand for improved sound quality. In particular, since the electrostatic speaker system has flexibility, it can be expected as a useful speaker system for an organic EL display. However, as a problem of the electrostatic speaker, it is necessary to apply a high potential to the vibrating membrane to charge it, so that a safety problem remains. In addition, when used in a dry environment for a long time, dust adheres to the vibration film surface. If dust adheres to the surface of the diaphragm, the sound quality and volume will be affected. Furthermore, when the electrostatic speaker is left in a humid environment for a long time, there is a problem that the charged vibrating membrane is discharged and the charge is lowered, making it difficult to produce sound.

As a method for solving such a problem, a method of suppressing the influence of humidity using a film obtained by treating a polymer film surface with a conductive polymer as a vibration membrane (Patent Document 1), or a member having a dust collecting function Proposed methods to install and suppress the adhesion of dust (Patent Document 2) and a method to make it difficult to generate discharge by not forming a conductive film on the surface of the vibrating membrane on the edge (Patent Document 3) Has been.
Japanese Unexamined Patent Publication No. 7-046697 JP 2008-148195 A JP 2010-016603 A

  However, in the method of suppressing the influence of humidity by using a film obtained by treating the surface of the polymer film with a conductive polymer as a vibrating membrane, it is possible to take measures against humidity. It is necessary to apply a high potential in order to cause dust adhesion or charging, and this is not a fundamental measure. In addition, in a method of suppressing the adhesion of dust and dust by installing a member having a dust collecting function, or a method of making it difficult for discharge to occur by not forming a conductive film on the edge of the vibrating membrane, Although the structure becomes complicated and the speaker system becomes thicker or the discharge can be partially mitigated, it is impossible to prevent the discharge from the surface of the diaphragm, and the system must be applied with a high potential. This is not a fundamental improvement because it is necessary.

  Therefore, the present invention has been made to solve the above-described problems, and is extremely lightweight and has a self-charging property due to friction, so that it is not necessary to apply a high voltage for charging and dust Provides a new speaker diaphragm that can build an electrostatic speaker system by maintaining a stable charged state because dust and dust are difficult to adhere to and can be easily removed by vibration. There is to do.

That is, according to the first aspect of the present invention, a film formed of a fluorine-based polymer has an amorphous non-crystalline part in at least a part of the surface layer part, and the mass per unit area of the film is 15 mg / dm. ^A film for a speaker diaphragm, wherein the film is ² or more and 350 mg / dm ² or less.

  A film suitable for a speaker diaphragm film that is light and excellent in strength and excellent in chargeability by being made into a film for a speaker diaphragm in which at least a part of the surface of a fluorine-based polymer film is made amorphous. Can be formed. Here, the diaphragm film of the present invention only needs to have at least part of its surface made amorphous, so the entire film may be made amorphous or from an amorphous fluoropolymer. A film that includes

According to a second aspect of the present invention, a film formed of a fluorine-based polymer has an amorphous non-crystalline part in at least a part of a surface layer part, and the mass per unit area of the film is 15 mg / dm ^2. The film for a speaker diaphragm, having a thickness of 350 mg / dm ² or less and an arithmetic average roughness Ra of the film having the amorphous portion of 5 nm to 500 nm.

  A third invention is the yield point strength of the film measured in accordance with the tensile property test specified in JIS K 7127 in the first or second invention, and the yield in the resin flow direction of the film. The point strength and the yield point strength in the direction orthogonal to the resin flow direction are both 7N or more, and the yield point in the direction perpendicular to the resin flow direction and the resin flow direction of the film, respectively. The average value of the elongation of the speaker diaphragm is 5% or more.

  A fourth invention is characterized in that, in any one of the first to third inventions, the amorphous part is formed on the entire surface of the surface layer part of the film as a speaker diaphragm. This is a film for a speaker diaphragm.

  According to a fifth invention, in any one of the first to third inventions, the plurality of amorphous parts are averagely distributed within an operating range of at least a speaker diaphragm of a surface layer part of the film. This is a film for a speaker diaphragm.

  According to a sixth aspect of the present invention, at least part of the surface layer of the film is made amorphous by irradiating the surface of the film formed of a fluorine-based polymer with ionizing radiation at a temperature equal to or higher than the melting point of the film. It is a manufacturing method of the film for speaker diaphragms characterized by tempering.

  According to a seventh aspect of the present invention, at least a part of the surface layer of the film is made amorphous by irradiating the surface of the film formed of a fluorine-based polymer with ionizing radiation at a temperature equal to or higher than the melting point of the film. It is a method for producing a film for a speaker diaphragm, characterized by stretching a film that has been refined and at least partially amorphous.

  The film for a speaker diaphragm in the present invention is a fluorine-based polymer film in which at least a part of the surface layer portion is made amorphous. Therefore, since it has excellent self-charging properties, it can be easily triboelectrically charged by vibration of the vibrating membrane, and has a feature that a charged state is easily maintained due to its low dielectric constant. Therefore, it is not necessary to apply a high voltage for charging, the risk of electric shock due to high voltage is eliminated, and the vibration membrane can be kept charged for a long time, so it has excellent acoustic characteristics even when it is not used for a long time. Can be maintained.

  Furthermore, when it is the structure which has a fine unevenness | corrugation on the film surface, adhesion of dust and dirt to the film surface is suppressed. In addition, even if dust or dirt adheres to the surface, the contact area between the dust and dirt and the film surface is extremely small due to the formation of fine irregularities. Detach. Therefore, even if it is used for a long time, a change in sound quality, a decrease in sound volume, and the like can be suppressed. Therefore, it is possible to provide a film for a speaker diaphragm capable of constructing a new highly safe electrostatic speaker system that does not require a transformer for applying a high voltage.

  Furthermore, in the film for a speaker diaphragm in the present invention, a film for a speaker diaphragm having desired mechanical characteristics can be provided by controlling the processing conditions when the surface layer of the fluoropolymer film is made amorphous. . For example, a surface layer of a crystalline PTFE (polytetrafluoroethylene) film using a known technique such as irradiation with ionizing radiation such as an electron beam or γ-ray in an environment where the temperature is higher than the crystalline melting point and the oxygen concentration is low. When the is modified to be amorphous, the cross-linking of the polymer proceeds, whereby the elongation in the stress-strain characteristics of the film can be reduced and the strength can be improved. As described above, according to the present invention, it is extremely useful for practical design of an excellent speaker diaphragm film that is easily charged by friction due to non-crystallization of the surface layer and difficult to discharge after charging. Can provide material.

FIG. 3 is a cross-sectional view of the speaker diaphragm film of the first embodiment. It is sectional drawing of the film for speaker diaphragms of 2nd Embodiment. It is sectional drawing of the film for speaker diaphragms of 3rd Embodiment.

(First embodiment)
Hereinafter, the film for the speaker diaphragm of the embodiment of the present invention will be described in detail.

  FIG. 1 is an enlarged view of a part of a cross section of a speaker diaphragm film 100 (hereinafter also referred to as “diaphragm film 100”) according to an embodiment of the present invention. The speaker diaphragm film 100 of the present embodiment is a thin film in which the surface layer portion of the fluorine-based polymer film 1 constituting the main body of the speaker diaphragm is made amorphous. Although FIG. 1 shows a state in which the entire surface layer of the fluorinated polymer film 1 is made amorphous, it is sufficient that at least a part of the surface layer of the fluorinated polymer film 1 is made amorphous. The qualitized surface layer portion 2 may be arranged like a sea-island sea or island. However, when it is used as the speaker diaphragm film 100, the non-crystallized portion exists on the entire surface of the film for the range (operation range) that is expected to vibrate and operate as the diaphragm. In the case of a sea-island shape, it is preferable that the non-crystallized portion exists with little variation (evenly within the operating range).

  The speaker diaphragm film 100 of this embodiment is formed using a film or sheet made of a fluorine-based polymer. Specific examples of the fluoropolymer include PTFE (polytetrafluoroethylene), PVF (polyvinyl fluoride), FEP (fluorinated ethylene propylene copolymer), ETFE (ethylene tetrafluoroethylene), and PVDF (poly vinylidene difluoride). And thermoplastic resins such as tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA). When the thickness of the film made of these fluoropolymers is 1.0 μm or less, handling becomes difficult. In addition, since the mass becomes higher at 20 μm or more, high energy is required to vibrate the diaphragm, and much power consumption is required. Therefore, the thickness of the speaker diaphragm film 100 is preferably 1.0 μm or more and 20 μm or less.

  The film 100 in which the surface layer portion using these fluoropolymers is made amorphous is low in dielectric constant, low in water absorption, and excellent in moisture resistance. It has characteristics that are difficult to discharge depending on the environment, and can exhibit excellent characteristics as the speaker diaphragm film 100. The thickness of the non-crystallized surface layer portion 2 is not particularly limited, but the thickness that can exhibit the characteristics that the dielectric constant is low, the moisture absorption is low, the moisture absorption is low, and the surface is easily charged is 0. 01 μm or more is preferable. The thickness of the non-crystalline surface layer portion 2 in consideration of the change in mechanical properties of the film due to the non-crystalline surface portion of the film 100 and the energy and productivity required for non-crystalline state You can decide.

  Here, the diaphragm film 100 according to the present embodiment is sufficient if at least part of the surface is made amorphous and the surface layer portion 2 made amorphous is formed. The whole is non-crystalline, or is a non-crystalline fluoropolymer such as Cytop (registered trademark) (trade name: manufactured by Asahi Glass Co., Ltd.) or Teflon AF ("Teflon" is a registered trademark). ) (Trade name: manufactured by DuPont Co., Ltd.) and tetrafluoroethylene-perfluorodioxole copolymer (TFE / PDD) (Mitsui / DuPont Fluorochemical Co., Ltd.), etc. It may be formed.

The diaphragm film 100 in the present embodiment needs to have a mass per unit area of 15 mg / dm ² or more and 350 mg / dm ² or less. When the mass is 350 mg / dm ² or more, high energy is required to vibrate the vibrating membrane. On the other hand, if it is 15 mg / dm ² or less, the strength as a vibrating membrane is insufficient, and the handleability becomes difficult.

  In addition, the speaker diaphragm film 100 of the present embodiment is orthogonal to the MD (Machine Directrion: resin flow direction) and TD (Transverse Directrion: MD direction) of the film, which are measured by a tensile characteristic test of JIS K 7127. The strength (N) at the yield point in the (direction) direction is preferably 7N or more in both the MD direction and the TD direction. In addition, from the use as a film for a speaker diaphragm, a material suitable for practical design can be supplied as long as it is about 7 to 8 N in both the MD direction and the TD direction.

  Moreover, it is preferable that the average value of the two directions of MD direction or TD direction is 5% or more about the elongation (%) in the yield point measured by the same test. In particular, if the elongation in either the MD direction or the TD direction is 10% or more and 50% or less, a slight potential change can be converted into a large displacement, and an energy efficient film for a speaker diaphragm can be configured.

  As a method of forming the surface layer portion 2 which is made amorphous by making the surface layer portion of the fluorine-based polymer film 1 non-crystalline, for example, a crystalline film or sheet made of a fluorine-containing polymer is used. Known techniques such as a method of modifying crystalline films and sheets to amorphous by irradiating with ionizing radiation such as electron beams and γ rays in an environment where the oxygen concentration is extremely low at a temperature above the crystalline melting point Can be used. In particular, by controlling the irradiation energy such as electron beam and γ, that is, the irradiation amount of ionizing radiation such as electron beam and γ such as acceleration voltage and irradiation time, only the surface layer portion of the fluoropolymer film 1 is made amorphous. Thereby, the film 100 for speaker diaphragms of this embodiment can be formed.

  In addition, by overlaying a mask made of a material that does not transmit ionizing radiation such as electron beams and γ on the fluorine-based polymer film, and emitting ionizing radiation such as electron beams and γ from the top, electron beams, γ, etc. The surface layer portion 2 that is made amorphous can be formed only in the portion through which the ionizing radiation passes. When the material is made non-crystalline by this method, the non-crystallized portion 2 is formed in the surface layer portion of the fluorine-based polymer film 1 in a state of being arranged like a sea-island island or the sea.

  According to the present embodiment described above, it is possible to provide the speaker diaphragm film 100 that can suppress the discharge and stably maintain the charged state. Therefore, the speaker diaphragm film 100 of the present embodiment can also provide an excellent effect that the sound output is stable over time. In addition, the speaker diaphragm film 100 of the present embodiment is very thin and lightweight, but is excellent in strength, and is therefore optimal for a diaphragm film for an electrostatic speaker.

(Second Embodiment)
Next, the speaker diaphragm film 200 of the second embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 2 is an enlarged view of a part of the cross section of the speaker diaphragm film 200 according to the embodiment of the present invention. The speaker diaphragm film 200 of the present embodiment has a surface layer portion of the fluorine-based polymer film 1 made amorphous and has minute irregularities 3 on the surface of the fluorine-based polymer film 1. The speaker diaphragm film 200 having the unevenness 3 has a surface arithmetic average roughness Ra of 5 nm to 500 nm, preferably 5 nm to 100 nm, more preferably 5 nm to 50 nm.

  The minute unevenness 3 on the surface of the speaker diaphragm film 200 of the present embodiment is obtained by embossing the surface of the fluorine-based polymer film 1, a nanoimprinting method, a physical method such as oxygen plasma, or a chemical method. It is formed by processing by a chemical method such as etching. The non-crystallized surface layer portion 2 may be formed by forming the irregularities on the surface of the crystalline fluorine-based polymer film or sheet, and then forming the surface layer portion non-crystalline, or before forming the irregularities, the film Alternatively, the surface layer portion of the sheet may be made amorphous, and then unevenness may be formed.

  For example, when a crystalline and porous film such as PTFE is used, a speaker diaphragm having fine irregularities can be used without special processing by utilizing pores that are originally present. It is also possible to form the film 200.

  Furthermore, Cytop (registered trademark) (trade name: manufactured by Asahi Glass Co., Ltd.), Teflon AF ("Teflon" is a registered trademark) (trade name: manufactured by DuPont), which is an amorphous fluoropolymer, Fluorocarbon resins such as tetrafluoroethylene-perfluorodioxole copolymer (TFE / PDD) (manufactured by Mitsui / DuPont Fluorochemical Co., Ltd.) have a molecular structure that is cyclic or contains a cyclic structure. It can be dissolved in a solvent. A thin film is formed from a solution in which these fluorine-based resins are dissolved using a known method such as spin coating or dip coating, and when the solvent is evaporated, fine unevenness is formed by controlling the evaporation rate of the solvent. You can also.

The unevenness 3 reduces the contact area between dust and dirt adhering to the surface of the charged speaker diaphragm film 200 and the surface of the diaphragm film 200. Therefore, the dust and dirt adhering to the surface are easily detached by the vibration of the speaker diaphragm film 200. Therefore, the diaphragm film 200 having the unevenness 3 can suppress the accumulation of dust and dirt on the surface of the speaker diaphragm film 200.

  FIG. 2 also shows that the non-crystalline surface layer portion 2 is formed on the entire surface of the fluoropolymer film 1, but at least a part of the surface of the fluoropolymer film 1 is non-crystalline. It is the same as that in FIG. 1 that it may be crystallized.

(Third embodiment)
Next, the speaker diaphragm film 300 according to the third embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 3 is an enlarged view of a part of a cross section of the speaker diaphragm film 300 according to the embodiment of the present invention. The speaker diaphragm film 300 of the present embodiment has irregularities formed on the surface layer portion of the fluoropolymer film 1 as in the second embodiment, but the irregularities are formed by the non-crystalline surface layer portion 2 itself. This is different from the second embodiment. That is, the speaker diaphragm film 300 of the present embodiment has a partially non-crystalline surface layer 2 on the surface side of the non-amorphous fluoropolymer film 1 or is non-crystalline. The surface of the surface layer portion 2 is partially formed with a recess, whereby the speaker diaphragm film 300 has an uneven surface. In the case where the surface layer portion 2 that is partially amorphous is present on the surface side of the non-amorphous fluoropolymer film 1, the surface portion is a crystalline portion (bottom portion of the recess) and amorphous And the surface of the speaker diaphragm film 300 has a minute uneven shape.

  The fine irregularities of the speaker diaphragm film 300 of the present embodiment may have an arithmetic average roughness Ra of 5 nm to 500 nm, preferably 5 nm to 100 nm, more preferably 5 nm to 50 nm.

  As a method for forming fine irregularities, first, for example, an electron beam is applied to a crystalline film or sheet made of a fluorine-containing polymer at a temperature equal to or higher than its crystalline melting point and in an environment having a low oxygen concentration. The surface layer of a crystalline film or sheet is modified to be amorphous using a known technique such as irradiation with ionizing radiation such as γ-rays. Then, stretch or emboss the film or sheet whose surface is modified to amorphous, mechanical polishing by sandblasting, nanoimprinting method, physical method such as oxygen plasma, chemical etching, etc. By this chemical method, irregularities can be formed on the surface.

  Here, a method for forming fine irregularities by stretching will be described. The non-crystallized surface layer portion 2 formed on the surface side of the fluorine-based polymer film 1 is improved in strength but inferior in ductility as compared with the non-crystallized portion (crystallized portion). Therefore, when the fluoropolymer film 1 having the surface layer portion 2 made amorphous at the surface side is stretched by pulling from both sides, the non-crystallized portion is stretched as it is, but becomes amorphous. The surface layer portion 2 is not stretched. If it does so, the surface layer part 2 which does not extend | stretch will be pulled by the part which is not crystallized to extend | stretch, and will tear in a tension | pulling direction. Thereby, it becomes a form in which the surface layer portion 2 amorphous in an island shape exists on the stretched non-crystallized film, and as a result, irregularities are formed on the surface of the fluoropolymer film 1. In the case of forming irregularities by the stretching method, it is easy to control the arithmetic average roughness Ra of the film surface and the mass per unit area of the film by changing the stretching direction and the stretching ratio. This is suitable for the production of the speaker diaphragm film 300.

  Further, the surface of the non-crystallized surface layer part 2 is removed by removing a part of the non-crystallized surface layer part 2 in the thickness direction by a physical method such as embossing or sandblasting or a chemical method such as etching. Unevenness may be formed on the part.

  In addition, you may form an unevenness | corrugation in the surface of the fluorine-type polymer film 1 combining the process by extending | stretching and another physical method or a chemical method.

  Furthermore, the speaker diaphragm film 300 of the present embodiment has minute irregularities on the surface, as in the second embodiment. Due to the unevenness, the contact area between dust and dirt adhering to the surface of the speaker diaphragm film 300 and the film is reduced. Therefore, the dust adhering to the surface is easily detached by vibration of the speaker diaphragm film 300, and accumulation of dust and dust is suppressed. Furthermore, even if dust or dirt adheres to the surface, it is easily detached, so that it is possible to form an excellent speaker diaphragm film 300 with little change in sound quality and decrease in volume even when used for a long time. .

  In the embodiment according to the present invention described above, the thickness of the non-crystallized surface layer portion 2 is determined from the fluorine-containing polymer as a method for amorphizing the surface layer portion of the fluoropolymer film or sheet. When using techniques such as irradiating ionizing radiation such as electron beams and gamma rays in an environment where the crystalline film or sheet is at a temperature above its crystalline melting point and in a low oxygen concentration, electron beams, gamma rays, etc. May be adjusted by appropriately selecting the irradiation energy determined by the irradiation energy, that is, the acceleration voltage, the irradiation time, and the like. The thickness of the non-crystallized surface layer 2 is determined in consideration of changes in mechanical properties of the film or sheet due to non-crystallizing the surface layer, energy required for non-crystallization, and productivity. You can decide.

  In addition, since the diaphragm film of the present invention only needs to have at least a part of the surface thereof made amorphous, for example, a sea-island-like sea or island dotted with non-crystalline surface layer portions 2 They may be arranged, the entire film may be made amorphous, or the entire film may be originally an amorphous fluoropolymer. Here, when the non-crystallized surface layer portion 2 is arranged like a sea-island sea or island, at least an operation range scheduled to be operated as a film for a speaker diaphragm is a sea-island shape having a substantially uniform distribution. It is desirable from the viewpoint of sound quality when used as the speaker diaphragm film 300. That is, on the surface of the diaphragm film, when the non-crystallized surface layer portion 2 is an island and the non-amorphous portion is the sea, there is little variation in the size and shape of the island within the above operating range. It is preferable that the islands are formed on the entire surface of the film so that the islands are less scattered and distributed (average distribution). If the distribution of the non-crystallized surface layer portion 2 is uneven or the size thereof is uneven, the sound quality varies depending on the formed diaphragm film, which is not preferable. As an example of forming an amorphous part with little variation, for example, an amorphous part such as a checkered pattern or a polka dot pattern can be formed.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

<Production of film for speaker diaphragm>
Example 1
PFA film (Daikin Kogyo Co., Ltd., NEOFLON PFA thickness: 12.5μm) is irradiated with 5Mrad of electron beam at an acceleration voltage of 150kV in an atmosphere with a temperature of 300 ℃ and oxygen concentration of 300ppm or less to make the entire PFA film non-crystallized. Example 1 (all the films were non-crystallized) was designated as Example 1.

(Example 2)
A PFA film (manufactured by Daikin Industries, Ltd., NEOFLON PFA thickness 25 μm) is irradiated with 5 Mrad of electron beam at an acceleration voltage of 80 kV in an atmosphere of 300 ° C and oxygen concentration of 300 ppm or less, and then stretched using a calendar processing machine. A film having a thickness of 13.5 μm was designated as Example 2.

(Example 3)
A PFA film (Daikin Kogyo Co., Ltd., NEOFLON PFA thickness 12.5μm) was irradiated with 5Mrad of electron beam at an acceleration voltage of 150kV in an atmosphere with a temperature of 300 ° C and an oxygen concentration of 300ppm or less. Example 3 in which fine irregularities were formed was referred to as Example 3.

Example 4
A SUS325 mesh plate is placed on a PFA film (Daikin Kogyo Co., Ltd., NEOFLON PFA thickness: 12.5 μm), and an electron beam is irradiated at an acceleration voltage of 150 kV for 5 Mrad in an atmosphere of 300 ° C and oxygen concentration of 300 ppm or less. A PFA film having an amorphous part and a non-amorphous part in a sea-island shape was produced as Example 4.

(Comparative Example 1)
A PFA film (Daikin Kogyo Co., Ltd., NEOFLON PFA thickness: 12.5 μm) without any treatment was used as Comparative Example 1 to evaluate the characteristics.

(Comparative Example 2)
Comparative Example 2 was obtained by irradiating an electron beam with an acceleration voltage of 150 kV for 5 Mrad without heating a PFA film (Daikin Kogyo Co., Ltd., Neoflon PFA thickness: 12.5 μm).

(Comparative Example 3)
A comparative example 3 was prepared by the same method as in Example 2 except that no stretching treatment was performed.

  The following tests were performed on the above examples and comparative examples to evaluate the characteristics.

(Charge amount)
For the amount of charge, cut each sample to a size of 10 x 10 cm and use an electrostatic charge meter (Faraday cage type KQ-1400) to which a coulomb meter (NK-1001) manufactured by Kasuga Electric Co., Ltd. was connected. Measured. Furthermore, after the measurement, the test sample was left for 1 week in an environment of 50 ° C. and humidity 90% RH (Relative Humidity), and then the charge amount was measured again by the same method.

(Surface roughness)
As an evaluation of the surface roughness of the speaker diaphragm films of Examples and Comparative Examples, the arithmetic average roughness Ra was measured with a stylus type surface roughness meter (DEKTAK3030ST manufactured by ULVAC, Inc.).

(Dustproof)
Dust resistance was evaluated using a cotton linter (diameter 1.5 μm, length 1 mm or less, manufactured by Japan Air Cleaners Association), which is relatively similar to dust in homes and buildings. After the test sample (10 x 10 cm) is rubbed and charged with a feather hammer, the cotton linter is sprinkled evenly, and then lightly impacted, the weight is measured, and the weight difference between the test sample before and after the cotton linter is adhered is measured and evaluated. did. At that time, the charge amount was measured before and after the cotton linter was adhered.

(Sound output status)
An electrostatic speaker was constructed in which each sample was a diaphragm, the electrode was a SUS325 mesh plate, and the buffer member was a PET nonwoven fabric. The electrostatic speaker has a structure of a known electrostatic speaker. Specifically, the electrostatic speaker is configured such that a diaphragm is sandwiched between a pair of electrode plates via a buffer material. The sound output state of the created electrostatic speaker was evaluated with a sound level meter (NL-20 manufactured by Lion Co., Ltd.). At that time, in the case of 80 dB or more, the sound output was evaluated as (◯), the case of 40 dB or more and less than 80 dB was evaluated as (Δ), and the case of less than 40 dB was evaluated as (×).

(Stress-strain characteristics)
According to the test method for tensile properties of JIS K 7127, the film to be measured is parallel to the MD (Machine Directrion: resin flow direction) and TD (Transverse Directrion: direction perpendicular to the MD direction) width 50 mm. A strip-shaped sample with each direction being the longitudinal direction was cut out to obtain a test piece so that the holding interval was 200 mm. Each sample is set in a tensile tester RTG-1210 (manufactured by A & D), and from the stress-strain curve, which is a curve of elongation and tensile load when a tensile load is applied at a speed of 100 mm / min. The load and elongation are shown in Table 1 as strength [N] and elongation [%].

  The results of the evaluation test are shown in Tables 1 to 3.

  As described above, from the results of Table 2, with respect to Comparative Example 1 which is a crystalline film, the irradiation energy of the electron beam, that is, the irradiation amount of the electron beam such as the acceleration voltage and the irradiation time is appropriately selected, and the entire film is obtained. Non-crystallized Example 1 and Example 3, Example 2 in which a part of the surface layer portion of the film is made non-crystalline, and a sea-island structure in which the crystalline part is the sea part and the non-crystalline part is the island part In Example 4, the discharge was suppressed and the charged state could be stably maintained. These examples show that the sound output is stable over time and is suitable for a speaker diaphragm film.

  In Comparative Example 2, since the crystalline fluororesin film that has not been made amorphous is irradiated with an electron beam without appropriate heating in the vicinity of the melting point of the film, the main chain cleavage of the molecule proceeds, A significant decrease in mechanical strength and elongation is observed. In Comparative Example 3, the mass per unit area is large, the thickness is high, and the flexibility is low.

  Furthermore, from Table 3 which is the result of the dustproof test, it is difficult for dust and dirt to adhere to the film by forming minute irregularities of 500 nm or less on the film surface. Even when dust or dirt adheres to the film, the contact area between the surface of the film and the dust or dirt is small.

  Compared with Examples 1 and 2 in which the film surface or the whole is made amorphous, for the mechanical properties when the electron beam irradiation energy, that is, the electron beam irradiation amount such as the acceleration voltage and irradiation time is appropriately selected. From the comparison with Example 1, strength improvement is recognized in Examples 1 and 2.

  Therefore, it was confirmed that the film obtained in the present invention is a useful speaker diaphragm film that has excellent charging characteristics and maintains performance over a long period of time.

100, 200, 300 Speaker diaphragm film 1 Fluoropolymer film 2 Non-crystalline surface layer portion

Claims (6)

A film formed of a fluorine-based polymer has an amorphous non-crystalline part in at least a part of the surface layer part, and the mass per unit area of the film is 15 mg / dm ² or more and 350 mg / dm ² or less. And the arithmetic average roughness Ra of the surface of the film having the amorphous portion is 5 nm or more . Speaker diaphragm film according to claim 1, wherein the arithmetic average roughness Ra of the surface of the film there is a previous SL amorphous portion is 5nm or more 500nm or less.   The yield point strength of the film measured in accordance with the tensile property test specified in JIS K 7127, and the yield point strength in the resin flow direction and the yield point strength in the direction perpendicular to the resin flow direction. However, both are 7N or more, and the average value of the respective elongation at the yield point in the resin flow direction and the direction perpendicular to the resin flow direction of the film is 5% or more. The film for a speaker diaphragm according to claim 1 or 2.   The film for a speaker diaphragm according to any one of claims 1 to 3, wherein the amorphous part is formed at least on the entire surface of the surface layer portion of the film as a speaker diaphragm. .   The speaker vibration according to any one of claims 1 to 3, wherein a plurality of the amorphous portions are averagely distributed within an operating range of at least a surface portion of the film as a speaker diaphragm. Board film. By irradiating the surface of the film formed of a fluorine-based polymer with ionizing radiation at a temperature equal to or higher than the melting point of the film, at least a part of the surface layer portion of the film is made amorphous.
A method for producing a film for a speaker diaphragm, comprising stretching a film that is at least partially amorphous.

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