JPS5816520A - Method of producing ekectret - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an electret, and particularly to a method for manufacturing an electret in which metal layers are integrated on both sides.

As is well known, an electret is an electrical polarization that persists permanently in a dielectric material that does not have spontaneous polarization.

It is defined as a substance that is characterized by being endowed with.

Electrets defined in this manner are broadly classified into electrets that can utilize piezoelectricity and non-electroactivity, and electrets that utilize surface potential generated by electric polarization.

Among these, the former type of electret, which utilizes piezoelectricity and pyroelectricity, usually has electrodes on both sides of a dielectric element, heats it to a predetermined temperature, applies a DC voltage to polarize it, and then reduces the applied voltage to zero. It can be obtained by

Although this electret does not generate an electrostatic field to the outside and cannot utilize surface potential, it has piezoelectricity and pyroelectricity.

On the other hand, electrets that can utilize the latter surface potential are electrostatic pickups, electrostatic microphones, electrostatic headphones, electrostatic speakers, and other mechanical-electrical transducers, and electrostatic-acoustic transducers. It is widely used as a power source, and is also used in electrometers, radiation dosimeters, DC polymer power supplies,
It can also be used in electrostatic storage devices, etc., and has high utility value.

Generally, the so-called thermal electretization method and electro-electretization method are used as methods for producing such electrets, but when these methods are used, electrets are produced as shown in curve A in Figure 2. The surface potential (hereinafter referred to as electret voltage) distribution tends to be uneven, and the electret voltage cannot always be controlled sufficiently. - It had an adverse effect on various characteristics of the acoustic transducer.

The present invention d In view of the above points, we provide a method for producing an electret (hereinafter simply referred to as electret) that utilizes surface potential, in which the voltage distribution of the electret is uniform and the electret voltage can be easily controlled. The purpose is to do.

The present invention deals with an electret in which gold TlI4# is integrated on both sides of the electret material, and the electret processing is performed by applying a full DC voltage across the gold 1, and then stopping this voltage application from the state where the DC voltage is applied. This purpose is achieved by means different from the method for producing electrets.

That is, the present invention has metal on both sides of the electret material;
In an electret element integrated with @, a dielectric material is closely pressed onto one side of the metal layer and then peeled off to form an electret. In other words, the method of the present invention is as shown in FIG. As shown, metal 1 (21° (2
This is based on the knowledge that the metal layer (2) becomes electrically charged when pressure is applied to the surface of the wire mesh layer on one side, that is, when the metal layer (2) is pressed and peeled off. The lifespan of the manufactured electret is no different from that of conventional electrets, and is extremely reliable.Furthermore, the pressure of the n-electric material to be applied and peeled off is applied to the dielectric material to be pressed and peeled off, and the metal layer +21. If the pressure is set at a level higher than that at which the two parts are completely adhered, it will be possible to achieve a reproducible starting pressure regardless of the applied pressure and unaffected by normal atmospheric temperature and humidity fluctuations. It was found that this can be obtained.

In addition, by manufacturing the electret by the method of the present invention, it is possible to obtain an electret with little variation in the electret voltage of each electret element, and since the electret material is integrated with a metal layer, the distribution of the electret voltage is uniform. If an electret can be obtained, it will be impossible.

As described above, the electric charge generation mechanism of the electret produced by the method of the present invention is frictional charging (melting/peel charging) between the gold 1 and the dielectric material. Any substance can be used as long as it has a different charge order from the metal. If a dielectric substance is used on the positive side of the metal, an electret with negative polarity can be obtained, and By using a dielectric material on the negative electrode side, a positive polarity electret can be obtained.

t, 75h12, In order to reliably obtain an electret with a practically usable electret voltage, the dielectric material to be pressurized should be selected appropriately, and the width of the charge-electrification order should be set to the metal. Large dielectric materials, such as polyamide, polymethyl methacrylate as the positive electrode side and polytetrafluoroethylene as the negative electrode side.

It is practically desirable to use polyethylene, polypropylene, etc.

The electret materials used in the method of the present invention may be those commonly used, such as polyethylene, polypropylene, and polyvinylidene fluoride.

Polymethyl methacrylate, polyethylene terephthalate, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, etc. can be used.

In addition, as a means of integrating metal layers on both sides of the electret material according to the method of the present invention, it can be carried out by using an ordinary adhesive or by vacuum evaporating the metal, but it can also be carried out by thermal fusion bonding with the metal. Among possible electret materials, thermal fusion is easier.

Hereinafter, the present invention will be explained in detail using specific examples.

First, as shown in the cross-sectional view of Figure 181, a 75 μm thick FBP Teflon film (trade name of Duho Co., Ltd., a fluoro-ethylene-propylene copolymer) as an electret material was coated with 0.3 μm thick Al 1lit- on both sides. A metal layer is provided by heat-sealing and integrated, a disk-shaped left-hand element 2 with a diameter of 60Ell is prepared, and the metal layer (2) is attached to a punch jig (not shown) while the metal layer (2) is fixed. As shown in Table 1, the dielectric materials polyamide and polymethyl methacrylate are located on the positive side in the electrification order with respect to metals, and polytetrafluoroethylene whose electrification order is on the negative side with respect to all metals.

After pressing closely with polyethylene and polypropylene at a pressure of 61 - (the electret voltage reached saturation at 5 -5), they were peeled off to form an electret. /? ! Table 1 shows the average value of the electret voltage of 10 electret elements for the r-rusting material. The range of variation in electret voltage was ±30V.

Table 1 Relationship between dielectric material and electret voltage in the present invention When the distribution of the electret voltage thus obtained was investigated, it was found to be uniformly distributed as shown by straight line B in FIG. Note that curve A in FIG. 2 shows the distribution of electret voltage when a conventional F'BP Teflon film without a metal layer of corona group [K] is made into an electret.

Next K・1st era's ``''!-4 1vri)L/2)
Of these, the polyamide + obtained negative polarity electret and the nine positive polarity electret obtained from polytetrafluoroethylene were heated at 160°C, 140°, 120°C, and 90°C with four sheets each. The time it takes for the electret voltage to attenuate by 13 dB is measured, and the result is 3.
Straight line A (negative polarity electret) and straight line B (positive polarity electret) in the figure were obtained, and it was confirmed that the electret had an excellent voltage life no different from conventional electrets.

Similarly, to check humidity resistance, 50℃, relative humidity 95%
When we left 10 of each in a humid atmosphere and measured the change in electret voltage over time, we found that curve 1 mA (negative polarity electret) and curve B in Figure 4 (shown in terms of retention rate).
(positive polarity electret) was obtained, and it was confirmed that the stability against humidity was superior to that of the conventional Elm 2 Toledo.The straight line C in Figure 3 shows the voltage life of the conventional negative polarity electret. , @4 Figure IIC shows the moisture resistance of the conventional negative polarity electret.

As described above, by using the method of the present invention, it is possible to obtain an electret with a uniform electret voltage distribution, excellent stability, and in which the electret voltage can be easily controlled a-f. Furthermore, by appropriately selecting the dielectric material to be pressurized and peeled off, it is possible to obtain an electret of arbitrary polarity.

Furthermore, when the electret obtained by the method of the present invention is applied to a mechanical-electrical converter (e.g., an electro-acoustic converter), especially when applied to a pickup cartridge, microphone, headphone, or speaker for audio equipment. In addition, it is possible to reduce distortion by making the electret pressure distribution uniform, to make the characteristics uniform by reducing the variation in the electret component, and to improve the yield.

[Brief explanation of the drawing]

FIG. 11 is a sectional view of the electret element obtained by the method of the present invention, and FIG. 2, 1m3, and 4 are characteristic diagrams of the electret obtained by the method of the present invention. (1)...Electret material 121+21...Metal layer (7317) Agent Patent attorney Rule Yu Chikamaro (
(and 1 other person) Figure 1 Figure 2 Figure 1 6-shi 1 Haze Wai Yu Y1 Keyword (-L-1) Figure 3

Claims (1)

[Claims] A method for manufacturing an electret, characterized in that an electret element is produced in which metal layers are integrated on both sides of an electret material, and a dielectric is closely applied and pressurized to one side of the metal layer, and then this is peeled off to form an electret. .