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June 8, 1974 3. Patent applicant [phase] Japan Patent Office published patent publication ■
Japanese Patent Laid-Open Publication No. 50-1-566990 Japanese Patent Publication No. 50
(1975) 12.18 Japanese Patent Application No. 4.9- 乙 4.1-7 [phase] filing date 111 id7. (197, g)
1. r Request for examination not yet filed (3 pages in total) Office serial number No. 1,
description of invention
Method of manufacturing electret
3. Detailed Description of the Invention The present invention relates to a method of
manufacturing a thin film electret. Small-sized electrets are used for acoustic devices such as
pickups, microphones and speakers, which are manufactured by cutting them out of film-like or
plate-like electrets. However, in this manufacturing process, it is easy to lose surface charge, and
it is difficult to form an ultra-small, ultra-thin electret. The present invention aims at solving the
above-mentioned drawbacks of the conventional manufacturing method, and the figure shows
the manufacturing apparatus. A vacuum chamber 1 made of glass is kept at high vacuum by a
vacuum pump connected to the exhaust port 11. Numeral 7 is a metal crucible, in which particles
8 of a polymer substance to be a material of electret are accommodated. The crucible 7 is
surrounded by and supported by a support 4 made of a heat-resistant electrically insulating
material such as alumina. A heater 5 is embedded in the supporting unit 4 and is connected to a
heating power supply 10 via a lead 9. An electrode 2 on which the substrate 6 is mounted is
disposed in the upper air of the crucible 7 so as to be opposed to the opening of the screw 7, and
the electrode 2 is connected to the external terminal 12. The external terminal 12 can be
selectively connected to one terminal 1 or the like of the AC high voltage power supply 15 and
one terminal 14 of the DC high voltage power supply 16. The other terminal of both power
supplies 15.16 is connected to the crucible 7. A wire mesh 6 is tensioned at the top opening of
the crucible 7, which is provided to prevent scattering of the particles 8 in the crucible 7 and to
make the tII film deposited on the substrate 3 uniform. Not necessarily necessary. Polyethylene,
polytetrafluoroethylene or the like is suitable as the polymer substance to be the material of
EndPage: 1 electret. Next, an example of a method for producing an electret using
polytetrafluoroethylene-hexafluoropropylene copolymer (abbreviated as FBP ') will be described.
First, particles 8 of FEP are put into the tail 7 and the vacuum chamber 1 is covered, and then the
air in the vacuum chamber 1 is exhausted from the exhaust port 11 to make the inside into a
high vacuum. This is because if there is residual gas, the electrical insulation of the formed thin
film is reduced. Next, current is supplied to the heater 5 to heat the crucible 7 to 450 to 48 ° C.
The particles 8 of F'EP are thereby evaporated and adhere to the substrate 3. At this time, the
degree of vacuum rises to 1 o-10 "Torr. The vapor deposition film formed on the substrate 3 in
this state is weak in mechanical strength and can not withstand long-term use such as vibration
detection, but the terminals 12 and 15 are connected at this vapor deposition, and the tail 7 and
electrode When an alternating current electric field of 700 v is applied between 2 and glow
discharge, the mechanical strength of the deposited film is increased.
After completion of vapor deposition, the terminal 12 is switched to the terminal 14 side, and a
direct current corona discharge is caused between the electrode 2 and the crucible 7, electric
charges are accumulated in the deposited film, and a thin film electret is obtained on the
substrate 3. . The surface charge density after one week of the elm ′ ′ ′ ′ ′ ′ ′ obtained
as described above was IX10 = O / ul. As described above, according to the present invention, the
polymer substance is vacuum deposited on the surface of the substrate under glow discharge,
and then corona charging is performed, so that the surface shape of the substrate is complex,
even when it is ultra small. The thin film electret having high mechanical strength can be
obtained without requiring post-processing, and the surface charge can be prevented from being
attenuated by the post-processing. Also, various polymeric substances can be deposited in
multiple layers, and it is possible to obtain a surface charge density that is even more dogfriendly.
4 is a vertical cross-sectional front view of a manufacturing apparatus used in the present
invention. 1 ... vacuum chamber, 2 ... electrode, 5 ... substrate, 7. ··· Crucible, 8 · · · particles of
polymer material, 15 · · · AC high voltage power supply, 16 · · · DC high piezoelectric 'source.
Patent applicant Nippon Victor Co., Ltd. Atsushio Inuka EndPage: 26, Other than the address
mentioned above Address, Chuo-ku, Tokyo 8-12-15, Chuo-ku, Tokyo Address (the same place)
EndPage: 3