JPS6239600B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret, that is, a polarized This invention relates to an electrode plate having a polymer film.

By placing an electrode plate with an electret attached on one side of the electrode plate and a diaphragm facing each other and applying an electric signal between them, the diaphragm is vibrated in accordance with the electric signal, and the electric signal is converted into an acoustic signal. Electrostatic speakers that convert
In addition, the electrode plate electret and the diaphragm are placed opposite each other, and the diaphragm is vibrated by the acoustic signal, and the change in capacitance between the electrode plate electret and the diaphragm at that time is used to convert the acoustic signal into an electrical signal. Electrostatic microphones have also been put into practical use.

In order to produce the electrode plate electrets used in these electrostatic electroacoustic transducers, conventionally, for example, a polarized polymer film, so-called electret film, was adhered to the electrode plate with an adhesive. This method has the disadvantage that the adhesive has an adverse effect on the electret film, deteriorating the properties of the electret and increasing loss. Furthermore, it is difficult to uniformly adhere the electret film to the electrode plate, and mechanical distortion is likely to occur, reducing charging and shortening the service life. Furthermore, the work of adhering the electret film to the electrode plate is complicated, making it difficult to mass-produce, and the quality varies.

On the other hand, a method is also known in which a polymer film is heated and welded to an electrode plate near its melting point, and then the polymer film on the electrode plate is converted into an electret.
In this method, when the polymer film is welded to the electrode plate, the thickness of the polymer film becomes uneven due to heating, and as a result, it becomes physically unstable and has a short life. In addition, it was necessary to perform the treatment at high temperatures in order to heat the polymer film to near its melting point, resulting in poor workability.

An object of the present invention is to provide an electrode electret that is easy to manufacture, suitable for mass production, and that is physically stable and has a long life.

According to this invention, the intervening polymer film is interposed between the polarized polymer film and the electrode plate. This intervening polymer film has a melting point lower than that of the polarizing polymer film,
Moreover, the thickness is smaller than that of the polarizing polymer film. Hole 3 in Figures 1 and 2
A suitable number of holes 80 corresponding to holes 4 and 56 are passed through. To make this electrode plate electret, a polarizing polymer film is thermally welded to a conductive film, that is, an electrode plate, via an intervening polymer film. The heat-welded polarizing polymer film is polarized. The intervening polymer film has a melting point lower than that of the polarizing polymer film, and the temperature of the thermal welding is performed near the melting point of the intervening polymer film. Therefore, thermal welding is performed at a relatively low temperature, resulting in good workability. Further, the thickness of the polarizing polymer film does not change due to the heat welding, and the thickness remains uniform. Therefore, it is physically stable, electrically superior, and has a long life. The thickness of the intervening polymer film is preferably thinner than the thickness of the polarizing polymer film. Furthermore, thermal welding involves heating and pressurizing at the same time. After polarizing the polymer film for polarization in advance, the polymer film for polarization may be thermally welded to the electrode plate via an intervening polymer film. In this case as well, the thermal welding temperature is lower than the melting temperature of the polarizing polymer film, so there is no fear that the thickness of the polarizing polymer film will change, and deterioration in polarization can be ignored.
In addition, when a polymer film polarized in this way is thermally welded to an electrode plate via an intervening polymer film, the temperature time and the temperature time of aging for polarization are approximately equal, so the aging for polarization is By performing this at the time of thermal welding, the overall processing time can be shortened.

Before describing embodiments of the electrode plate electret according to the present invention, an example of an electro-acoustic transducer using the electrode plate electret will be explained. FIG. 1 shows an example of an electro-acoustic transducer used in a headphone.
3 are integrally formed, and electrode plates 14 and 15 are arranged so as to be in contact with the inner surfaces of these flanges 12 and 13, respectively, and to close the openings at both ends of the case 11. A diaphragm 16 is arranged between and opposite the electrode plates 14 and 15 with ring-shaped insulating spacers 17 and 18 interposed therebetween, respectively. The diaphragm 16 is constructed by depositing conductive layers 21 and 22 on both sides of a polymer film 19 such as a polyester resin having a thickness of 3 to 6 μm, for example, by vapor deposition of a metal such as aluminum. Metal rings 23 and 24 are interposed between the conductive layers 21 and 22 and the spacers 17 and 18, respectively. The electrode plates 14 and 15 each consist of a conductor, that is, an electrode plate 25 and 26, and an electret film 27 and 28 attached to these electrode plates 25 and 26, respectively. Tsuba 1
2 and 13.

Note that the electrode plate electret 14 of this invention,
Intervening polymer films 31 and 32 are interposed between the electret films 27 and 28 and the electrode plates 25 and 26, respectively. Sound emitting holes 33 and 34 are formed through the electrode plate electrets 14 and 15. The electrical signal from the signal source 35 is applied to the primary side of the transformer 36, and the
Both ends on the next side are electrically connected to electrode plates 25 and 26, respectively, and the middle point is electrically connected to metal rings 21 and 22. As a result, the diaphragm 16 is driven in a push-pull manner to vibrate in response to the electrical signal from the signal source 35, and an acoustic signal is obtained. Note that one of the conductive layers 21 and 22 of the diaphragm 16 may be omitted.

FIG. 2 shows an example of an electrostatic microphone, in which a microphone unit section 42 and an impedance conversion section 43 are arranged in the axial direction within a cylindrical case 41. The cylindrical capsule 4 is inscribed in the case 41 in the microphone unit part 42.
4 is housed in a case 41, a sound guide hole 46 is formed in the front end plate 45 of the capsule 44, and the sound guide hole 46 is covered with a dustproof cloth 47. A diaphragm 48 is disposed on the inner surface of the front end plate 45 in close proximity to each other. The diaphragm 48 is composed of a polymer film 49 and a conductive layer 51 adhered to it by metal vapor deposition.The conductive layer 51 is attached to a metal ring 52 from the conductive layer 51 side, and the metal ring 52 is in contact with the inner surface of the end plate 45. Ru. An electrode plate electret 54 is opposed to the diaphragm 48 with a ring-shaped spacer 53 in between.
The electrode plate electret 54 is held by an electrode holding section 55. The electrode holding part 55 is made of a bottomed cylindrical body made of synthetic resin, and the electrode plate electret 54 is held on the open surface thereof, and the inside thereof is used as a back chamber. A ventilation hole 56 is formed through the electrode plate electret 54 .

The electrode plate electret 54 consists of an electrode plate 57 and an electret film 58 attached thereto, and furthermore, in the present invention, an intervening polymer film 59 is interposed between the electrode plate 57 and the electret film 58. There is. In the impedance conversion unit 43, a cylinder 61 is arranged behind the capsule 44 and in almost contact with the inner peripheral surface of the case 41, and a wiring board 62 is placed in contact with the back surface of the cylinder 61. Both ends of the case 41 are bent to the front side of the front end plate 45 of the capsule 44 and the back side of the wiring board 62, respectively, so that the microphone unit 42 and the impedance conversion section 43 are mechanically connected. An impedance conversion circuit 63 is formed in the cylindrical body 61 of the wiring board 62, and the impedance conversion circuit 63 is connected to the electrode plate 57 of the electrode plate electret through the bottom plate of the electrode holding portion 55. The diaphragm 48 vibrates due to the acoustic signal coming from the front through the sound guide hole 46, and the capacitance between the diaphragm 48 and the electrode plate electret 54 changes.
The electrical signal is output as a low impedance signal by the impedance conversion circuit 63.

This invention relates to electrode plate electrets 14, 15, 54, etc. used in electro-acoustic transducers as shown in FIGS. 1 and 2, and as shown in FIG. A polarizing polymer film 73 is attached on top with an intervening polymer film 72 interposed therebetween.

Examples of the polarizing polymer film 73 include tetrafluoroethylene-hexafluoropropylene copolymer film (FEP), polycarbonate film (PC), polyethylene film (PE), polyvinylidene fluoride film (PVF ₂ ), and polypropylene film (PP). ) etc. are used. The thermal bonding temperature range of these polymer films is 282~371℃ and 204~
221°C, 121-204°C, 204-218°C, and 140-204°C. For example, when used for headphones, the polarizing polymer film 73 has a diameter of 50 to 60 mm;
It is formed to a thickness of about 75 to 125 μm, and if necessary, in order to improve adhesion, one side is treated with a naphthalene solution of metallic sodium to make it relatively rough, or one side is coated with aluminum, nickel, etc. A commonly used method such as metal vapor deposition can be used.

Similarly, the intervening polymer film 72 has a diameter of 50 mm.
~60mm and a thickness of approximately 10~30μ, and is inserted between the electrode plate 71 and the polarizing polymer film 73. At this time, the laminated body 7 of the electrode plate 71, the intervening polymer film 72, and the polarizing polymer film 73 is placed so that the surface of the polarizing polymer film 73 that has been subjected to the above-mentioned treatment is in contact with the intervening polymer film 72.
form 4.

Next, this laminate 74 is attached to the intervening polymer film 7.
The polarizing polymer film 73 is bonded to the electrode plate 71 via the intervening polymer film 72 by heating at an ambient temperature within the thermal bonding temperature range of No. 2.

As shown in FIG. 4, an apparatus for performing this heat welding includes, for example, a peelable body 77 made of, for example, polytetrafluoroethylene film (PTFE film) placed on a base 76 in a constant temperature bath 75. An electrode plate 71, an intervening polymer film 72, and a polarizing polymer film 73 are stacked in this order to form a laminate 74. This peeling body 77 has heat resistance of 300° C. or more, and can peel the laminate 74 and the items above and below it without thermal adhesion.

In this example, a plurality of laminates 74 are bonded together at the same time, and a desired plurality of laminates 74 are stacked up one after another via peeling bodies 77. Further, a weight 78 of about 2 kg, for example, is placed on the peeling body 77 of the uppermost layer.

In this state, the inside of the constant temperature bath 75 is set to a predetermined temperature within the thermal bonding temperature range of the intervening polymer film 72 used. For example, when a polycarbonate film is used as the intervening polymer film 72, the temperature is 210 to 250°C, when a polyethylene film is used, it is about 150°C, when a polyvinylidene fluoride film is used, it is about 220°C, and when a polypropylene film is used, the temperature is about 220°C. When used, the temperature should be approximately 200℃.
The constant temperature bath 75 is maintained at this set temperature for approximately one hour, and then allowed to cool naturally.

Another method for performing this welding is, for example, as shown in FIG. An electrode plate 71 made of aluminum or the like with a thickness of about 0.6 to 1 mm is fed in the direction of arrow 79, and a supply bobbin 8 is placed on the electrode plate 72.
The intervening polymer film 72 wound around 1 is sent out via the guide roller 82. Furthermore, a polarizing polymer film 7 wound around a supply bobbin 83 is placed thereon.
3 is sent out via the guide roller 84. The polarizing polymer film 73 has a thickness of 75 to 125 μm, and the surface in contact with the intervening polymer film 72 is treated with a naphthalene solution of metallic sodium to give a relatively rough surface, or is made of aluminum or nickel. It is possible to use a material that has been subjected to metal vapor deposition treatment. The thickness of the intervening polymer film 72 is 20~
A material of about 30μ is used. This electrode plate 71,
The laminate 74 of the intervening polymer film 72 and the polarizing polymer film 73 is sandwiched between heat rollers 85 and fed into a heating furnace 86 at a predetermined speed. Inside the heating furnace 86 is the intervening polymer film 7 as described above.
The temperature is set at a predetermined temperature within the thermal bonding temperature range of No. 2. Although not shown, a heat roller that applies a predetermined pressure is also disposed within the heating furnace 86, and the laminate 74 passes through the heating furnace 86 while being heated and pressurized for a predetermined period of time. In this way, the polarizing polymer film 7
3 is an electrode plate 7 via an intervening polymer film 72.
1.

The laminate 74 consisting of the polarizing polymer film 73, the intervening polymer film 72, and the electrode plate 71 that have been bonded to each other through the thermal welding process in this way is then subjected to a polarization treatment to the polarizing polymer film 73. It is then transferred to the polarization step where it performs. Before that, holes 80 (FIG. 6) corresponding to the holes 34, 56 in FIGS. 1 and 2 are formed, for example, by pressing. When the laminate is formed continuously as shown in FIG. 5, the holes 80 can be formed at the same time so as to be punched into the shape of the electrode plate electret used in the intended electro-acoustic transducer.

FIG. 6 shows an example of this polarization process, in which a laminate 74 that has undergone a thermal welding process is placed on a substrate (not shown). The positive electrode of a power source 87 is connected to the electrode plate 71, which is the lowest layer of the laminate 74, and the laminate 74
A needle electrode 88 is arranged perpendicularly to the laminate 74 about 50 mm above the center of the polarizing polymer film 73, which is the top layer of the polarizing polymer film 73, and this needle electrode 88 is connected to the negative electrode of a power source 87. . In this state, the electrode plate 71
A DC voltage of about 25 KV is applied between the electrodes 88 and the electrodes 88 for about 20 to 30 minutes.
The voltage is applied for a minute to cause corona discharge to occur on the surface of the polarizing polymer film 73. After this polarization treatment, the laminate 74 is aged at approximately 150° C. for approximately one hour to complete all steps.

Example Melting point is 260~ as polymer film 73 for polarization
A 125 μm thick ethylene tetrafluoride-propylene hexafluoride copolymer film at 280° C. was used, and one side of the film was made slightly rough with a naphthalene solution. The melting point of the intervening polymer film 72 is 220 to 230°C.
A polycarbonate film with a thickness of 20 μ is used, and an aluminum electrode plate 71 with a thickness of 1 mm is used.
A polarizing polymer film 73 was fused at 240°C.
This fused polarizing polymer film 73 is
By the needle electrode corona discharge method described in Fig.
After polarization at 25KV, aging was performed at 150°C for 1 hour. The result is that the initial value of the surface potential is
It was 850V. This sample was subjected to a temperature acceleration test at 90°C, and the time required for the sample to decay to -1 dB, ie, the initial value of 0.891, was 1920 hours.

On the other hand, using the same polarizing polymer film, it was fused to the same electrode plate at 280°C without using an intervening polymer film, and the polarizing polymer film was polarized under the same conditions as before. Then, it was further aged. The surface potential of this sample is approximately -850V, which is the same as when using an intervening polymer film.
However, in the temperature acceleration test, the time required for -1 dB attenuation was 150 hours, which was significantly shorter than when using an intervening polymer film.

As described above, according to the electrode plate electret according to the present invention, since the intervening polymer film is used and fused at its thermal bonding temperature, the fusion temperature is relatively low and processing is easier. Moreover, since the melting temperature of the polarizing polymer film is higher than this fusion temperature, the polarizing polymer film welded to the electrode plate can have a uniform thickness, and is physically stable and has a long life. It will be done. Furthermore, workability is better than when bonding with adhesive, and each part is reliably fused. Furthermore, it is suitable for mass production.

In the above, the polarizing polymer film was fused to the electrode plate and then electrified. However, it is also possible to polarize the polarizing polymer film in advance and fuse the polarized film to the electrode plate via the intervening polymer film. You may wear it. In this case, since the fusion is performed at a temperature lower than the melting temperature of the polarizing polymer film, there is almost no deterioration of the polarization previously given to the polarizing polymer film. In addition, since the temperature and time conditions during fusion are almost the same as the aging conditions for electrification, aging for this polarization can be done at the same time as heating during fusion, which shortens the overall manufacturing time. be able to.

Furthermore, in the above description, the polarization polymer film can be polarized not only by corona discharge, but also by thermal polarization, electron beam polarization, or the like. However, the corona discharge polarization method allows polarization in an indoor atmosphere at room temperature, and the equipment is simple.
According to the corona discharge polarization method, a laminate 74 having holes 80 as shown in FIG. You can also do In this case, a conductive belt conveyor may be used, it may be electrically grounded, and the electrode plate 71 may be brought into contact with this belt conveyor.

The surface of the electrode plate to which the intervening polymer film is thermally welded may be made rough by, for example, No. 80 to No. 600 sandplast, that is, sand spraying. In this case, the unevenness of the rough surface will have a riveting effect on the intervening polymer film, making it difficult for the intervening polymer film to peel off. In addition, when polarizing a polymer film for polarization after attaching it to an electrode plate, the effective area during polarization becomes large due to the unevenness of the rough surface of the electrode plate, scattering of potential lines occurs, and the polarization amount per unit area increases. As the number of potential lines in the polymer film increases, there is less variation in the number of potential lines per unit area, and a large number of potential lines can be obtained.In other words, the applied voltage per unit area becomes equivalently large, and polarization also increases. The polarization is sufficiently strong and uniform polarization is obtained, and the polarization is also stable.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an electroacoustic transducer for an electrostatic headphone, FIG. 2 is a sectional view showing an example of an electrostatic microphone, and FIG. 3 is an example of an electrode plate electret according to the present invention. 4 is a sectional view showing an example of a fusing device for simultaneously thermally welding a plurality of laminates, and FIG. The diagram shown in FIG. 6 is a diagram for explaining the polarization method. 71: Electrode plate, 72: Intervening polymer film,
73: Polymer film for polarization.

Claims (1)

[Claims] 1. Comprising an electrode plate, a polarized polymer film, and an intervening polymer film that has a melting point lower than that of the polarization polymer film and is fused to the polarization polymer film and the electrode plate. Electrode plate electret.