JPS59101998A - Electret device and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an electret device by a simple work and in a short time by providing an electret film on a metallic plate or a fixed plate having a desired vibration characteristic. CONSTITUTION:A thin film 32 of a high polymer material, for instance, FEP resin is formed on the surface of an oscillatory thin plate 31 having a desired vibration characteristic. An oscillatory electret plate 3 is formed by performing a polarization electrostatic charge processing to this FEP32. Subsequently, the electret plate 3 is fitted and fixed to a back plate 6' being a fixed plate which becomes an opposed electrode through a space ring 4. In this way, an electret device can be manufactured by a simple work and in a short time. Also, even in case when an electret film is formed on the back plate, the same effect can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret device that uses an electret element to extract an electrical signal in response to applied pressure, and a method for manufacturing the same.

An electret device usually has an electric machine on one side of a vibrating electret element, which is formed by applying a predetermined tension to a polymer membrane and causing a polarized Vi electric current, and also has an electric device installed on one side of the vibrating electret element to form a back air chamber of a predetermined size. It is constructed by providing a fixing plate opposite to the electric left element. When pressure is applied to such an electret device, the electret element vibrates,
A voltage corresponding to this vibration displacement amount IC is applied to the above electrode and other electrodes.
For example, this occurs between ground and ground. Taking advantage of this property, electret devices are used in condenser microphones, keyboard switches, pushbutton switches, and the like.

An example of an electret device used in an electret condenser microphone will be described below.

To give an example of a conventional electret element as a component of an electret device, a fluororesin film is used as the polymer film, and one surface of this film is coated with a metal material, such as A4 Ni.

An electrode film is formed using Ni0r, Or, etc. by a vacuum evaporation method, a sputtering method, an electron beam method, etc., and the film is fixed to an annular holding metal plate by applying tension so as to obtain the frequency characteristics required for the microphone. Thereafter, the film is polarized and charged, and subjected to predetermined treatments such as aging to complete the film. An electret device is produced in which the electret element and the fixed plate are opposed to each other via a space ring, and the space surrounded by the electret element, the space ring, and the fixed plate has a back air chamber.

When this electret device is incorporated into a microphone, the electret element vibrates due to sound pressure, and a 1u pressure corresponding to the vibration is generated between the aforementioned electrode and the microphone case, that is, ground.

However, the above-mentioned electret element has 111
In order to bond the fluororesin film on which the polar film is formed and the annular holding metal plate while applying a predetermined tension to the film, there is a problem in that a high temperature state must be maintained for a long time.

In order to overcome the above problems, an electrode film made of an ultraviolet-transparent material is formed in place of the electrode film formed of the above-mentioned metal material, and an ultraviolet-curable adhesive is used in place of the thermosetting adhesive used above. using ll in a shorter time than the above
There is a device designed to make 5li (for example, see Japanese Patent Application No. 57-158756 filed by the applicant of the present invention).
.

The latter electret element will be described with reference to FIGS. 1 and 2. A light-transmitting electrode film 12A is formed on the polymer film 12α, for example, a fluorine-based synthetic resin film, by a vapor deposition method or the like. Tension is applied to the polymer membrane thus formed so as to obtain the resonance characteristics necessary for the microphone. While applying tension, an adhesive 12C such as ultraviolet curable ink is applied to the electrode film 12h and fixed to the presser ring 12d. Ultraviolet rays are irradiated from the polymer membrane 12α side to dry the adhesive 12C, and the polymer membrane 12α provided with the IT electrode f12b is fixed to the holding ring 12d while maintaining a predetermined tension. The polymer film 12α and the electrode film 12b are cut along the outer periphery of the holding ring 12d. The polymer film 12α thus formed is polarized and charged to form an electret element that can extract a voltage according to the amount of displacement.

Aging is performed as the final process, and the electret device is completed.

Furthermore, the completed electret element is incorporated into a microphone as an electret device as described above.

Although the manufacturing time of the electret element manufactured in this way is reduced to about one tenth of that of the former, it is desired to further shorten the manufacturing time1 and reduce the price.

Another problem with conventional devices is that sensitivity cannot be easily improved.

One way to improve sensitivity is to increase the surface potential of the polymer membrane, for example. However, due to constraints on the stability of the surface potential, it is not possible to increase the surface potential very much, and this method cannot be expected to improve sensitivity much. Another method is to reduce the resonance space,
Since the vibration space for external sound pressure input needs to be of a predetermined size, it cannot be reduced below a certain value.
In this respect as well, there is a problem that the sensitivity cannot be improved that much.

The main object of the present invention is to use a metal plate with predetermined vibration characteristics, thereby eliminating the need to apply tension as in the past, and to provide a simple structure on one side of the vibrating metal plate or on one side of the fixed plate. The object of the present invention is to obtain an electret device that can be manufactured easily and in a short time based on the idea of forming an electret film through a process.

Another object of the present invention is to obtain an electret device that achieves improved sensitivity while enjoying the above-mentioned effects.

The electret device of the present invention will be described below with reference to FIGS. 6 and 4.

A vibrating thin plate 31 having vibration characteristics necessary for use as a microphone is prepared in advance. As such a vibrating thin plate, a metal plate similar to that conventionally used as a diaphragm of a microphone using carbon or the like can be used. For example, it is made of duralumin, stainless steel, aluminum, brass, etc. with a thickness of about 20 to 100 μm.

On the surface of the vibrating thin plate 61 described above, a fine polymeric material, such as a fluororesin material such as FIP (4), fluorinated ethylene/67, propylene copolymer) resin, is uniformly applied by printing, coating, or spraying. F
An IP film 32 is formed.

The thickness of this coating film is about 20 to 100 μm. M32 is fixed to the thin plate 51 while drying the film 32 formed on the thin plate 31 by dry baking or the like. This drying time is about 60 minutes. This fixation is caused by the thin plate 61
This is done so that the film 52 will not peel off from the thin plate 31 or change its characteristics even if the film 52 is vibrated for a long period of time.

The vibrating thin plate 31 to which the PEP film 62 is fixed in this way is cut into a predetermined shape in order to be incorporated into an electret microphone.

The FIP membrane 32 is subjected to polarization charging treatment. As a polarization charging treatment, the present applicant has previously filed a patent application filed in 1983-1032.
Although it can be carried out by a method such as No. 52, since the polarization charging treatment is not the subject of the present invention, a detailed description thereof will be omitted.

Finally, an aging treatment is performed to obtain a completed electret device (FIG. 4).

FIG. 5 is a cross-sectional view of the electret device manufactured as described above integrated with the back plate 6' and incorporated into an electret condenser microphone as an electret device. In Fig. 5, 1 is the opening 1
2 is a presser ring, 3 is a vibrating electret plate according to the present invention composed of a diaphragm 31 and an IFIP membrane 32, 4 is a space ring, 6 is a
' is a back plate provided with an opening 6a', 7 is an inner case, 8 is a terminal board provided with 7Bp and an electric circuit such as a resistor, 9.10 is a terminal, and 11 is a back air chamber (or resonance space). , 12 are connection lines.

In the electret device according to the present invention, the vibrating electret plate 3 vibrates in response to sound pressure from the opening 1α, and generates a voltage corresponding to the vibration. The diaphragm 31, which serves as the electrode of the vibrating electret plate 6, is connected to the electrical circuit via the holding ring 2 and the front cover 1, and the back plate 6', which serves as the corresponding electrode, is connected to the electrical circuit via the connecting wire 12. Since the electret device is connected, the voltage change is signal-processed in the electric circuit and then output to the terminals 9 and 10. Illustrated in the figure. As is clear from FIG. 6, an electret device with sufficient performance was obtained.

The electret device of the present invention having the above-mentioned vibrating electret plate uses the above-mentioned metal material such as duralumin as the diaphragm, so once the material, plate thickness, dimensions, etc. are determined, the resonant frequency is determined by these, and it has uniform characteristics. This has the effect that the following can be obtained.

In addition, compared to the conventional method, the method for manufacturing the vibrating electron plate described above includes a process of attaching electrodes to a p:icp film,
The process of applying tension to the jP film is not necessary, which has the advantage of shortening manufacturing time, improving quality, and lowering costs.

Furthermore, since no ultraviolet light is used, the equipment and work become easier.

Another embodiment of the invention will be described with reference to FIGS. 7 and 8. This embodiment uses a so-called electret type back plate in which an electret film is not formed on the metal diaphragm but on the back plate.

The electret type cup plate 6 shown in FIG. 7 is manufactured as follows. A fine flaw similar to that shown in FIG. 4 is placed on the metal back plate 1.

A PEP film 62 is formed by uniformly depositing a base resin thread material, such as FEiP resin, into a thin film by printing or the like. The FEP film 62 is fixed to the back plate 61 by dry baking or the like. The back plate 61 and the nP film 62 are formed into a predetermined shape in order to be incorporated into a microphone. The FIP film 62 on the back plate 61 is polarized and charged. A completed electret back plate 6 is obtained by aging. Other manufacturing conditions are the same as those of the electret type diaphragm 3 shown in FIG.

FIG. 8 shows a cross-sectional view of a microphone in which the electret device having the electret type back plate 6 of FIG. 7 is incorporated into an electret condenser microphone. In FIG. 8, the same parts are given the same reference numerals as in FIG. 7.

In the microphone shown in FIG. 8, a metal diaphragm 5 made of the same material as the vibrating thin plate 31 described above vibrates due to the positive sound entering through the opening 19, and the vibration of the diaphragm 5 is transmitted via the resonance space 11 to an electret-shaped ballast. , communicated to Kublat B,
It is configured so that voltage changes in response to sound pressure caused by the polarized and charged Fmp membrane 62 are outputted to terminals 9 and 10 via an electric circuit.

The characteristics of the microphone in FIG. 8 were the same as those in FIG. 6. Therefore, it shows sufficient performance.

Yet another embodiment of the invention will be described below with reference to FIG.

FIG. 9 shows the vibratory electric train shown in FIG. 4.

7 is a sectional view of an electret condenser microphone in which the top plate 3 and the electret type plate 6 shown in FIG. 7 are combined together to form an electret device. [The dynamic electret plate 3, the electret type plate 6, and the electret plate 6 are provided facing each other with a predetermined interval spaced apart through the space ring 4, as shown in FIG. 5 or 8, and are surrounded by these elements. The space in which this occurs functions as a resonance space 11. Other elements in FIG. 9 are the same as in FIG. 5 or FIG. 8.

The vibrating electret plate 6 is charged with a surface electric potential 1, and the electret type back plate 6 is charged with a surface potential V2 having a polarity opposite to that of the vibrating electret plate. If the same sound pressure as in Fig. 5 or 8 is applied, the voltage extracted in Fig. 5 or 8 is proportional to 1 11 or IV21, but in the case shown in Fig. 9 A voltage proportional to 1Vil+IV21 is extracted. For example, when charged so that 1V11=1V21, a sensitivity twice as high as that of FIG. 5 or FIG. 8 was obtained. Therefore, Figure 5 or 8
Compared to the one shown in the figure or the conventional one, we were able to achieve twice the sensitivity. Since the vibrating electret plate 6 and the electret type back plate 6 can be easily formed as described above, an electret device combining them can be easily manufactured. This electret device has significantly improved sensitivity.

Since the electret device according to the present invention can be formed into any shape and size, it can be used not only for microphones but also for other purposes, such as speakers, acoustic transducers such as pickups, physical measurement instruments such as tension meters, keyboards, and non-contact devices. It can be used in information processing devices such as switches.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the manufacturing process of a conventional electret element, Fig. 2 is a cross-sectional view of an electret element manufactured by the manufacturing process of Fig. 1, and Fig. 6 is an electret type vibration as an embodiment of the present invention. Diagram showing the manufacturing process of the board, No. 4
The figure is a cross-sectional view of an electret-type diaphragm manufactured by the manufacturing process shown in Figure 3, and Figure 5 is a cross-sectional view of a microphone manufactured using the electret diaphragm shown in Figure 4 and assembled into an electret device and incorporated into a microphone. 6 is a characteristic diagram of the microphone shown in FIG. 5, FIG. 7 is a cross-sectional view of an electret back plate as another embodiment of the present invention, and FIG. 8 is a diagram showing the electret back plate shown in FIG. FIG. 9 is a cross-sectional view of a microphone incorporating an electret device as yet another embodiment of the present invention. (Explanation of symbols) 1... 7 four-piece cover, 2... Presser ring, Ro... Vibrating electret plate, 61... Vibrating thin plate, 32... FHP membrane, 4... Space ring , 5... Vibration plate, 6... Electret type back plate, 61...
Back plate, 62... FEP membrane, 7... Inner case, 8... Terminal board, 9.10... Terminal, 11... Resonance space. $5 times [dB] 40023571K 235710 to [Hz] 70th Fig. 9

Claims (1)

[Claims] 1. A metal plate having predetermined vibration characteristics and a fixing plate provided oppositely to the metal plate at a predetermined distance, one surface of the metal plate or the fixing plate 1. An electret device comprising an electret film formed by coating and fixing a polymer material in a thin film on one surface of the electret film, and polarizing and charging the film. 2. The electret device according to claim 1, further comprising an electret film formed by coating and fixing a polymeric material in the form of a thin film on the surface of the metal plate, and polarizing and charging the surface of the metal plate. 6. The electret device according to claim 1, further comprising an electret film formed by coating and fixing a polymeric material in the form of a thin film on the surface of the fixing plate and polarizing and charging the surface. 4. A method for manufacturing an electret device comprising a metal plate having predetermined vibration characteristics and a fixing plate provided opposite to the metal plate at a predetermined distance, wherein one surface of the metal plate or the fixing plate Print, spray,
A method for manufacturing an electret device, which comprises coating a polymer material in a thin film form by painting or the like, fixing it by dry baking, and forming an electret film by polarizing and charging.