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■ Electret manufacturing method 0 Japanese Patent Application No. 45-836850 Application No.
45 (1970) Sept. 24 @ Shoko Akishita Uji City Udo City 75 Uchiichi Maruyama Shindo Takeshi
Nobuyuki Uji City Uji City Shimoaki Ishizuka 21 Do Fujiwara Shin Uji City Uji Uzan 55 Doko
Watanabe Yasumitsu Kyoto Shishimizu Town Fushimi-ku 209 Shimomachi-cho Ehime Gyoto
Kyoto Prefecture Kuse-gun Joyo-cho Oji Kuse Small character Southgakiuchi 50 ■ 500 agent
unity corp. DESCRIPTION The present invention relates to a method for producing an electret
characterized in that a dielectric composed of an organic polymer substance to which a liquid
crystal substance is added is oriented and polarized in a direct current strong electric field in a
heated state. In the context of the present invention, the term electret means a dielectric which
has the opposite sign of the charge on both sides of the film or plate, is charged throughout the
material, and has a permanent polarization which is not merely the surface charge. Applications
of an electrometer, a voltmeter condenser microphone, a radiation calibration meter, a DC high
voltage power supply, a dust collector, an electrostatic storage device, etc., are considered using
the electrostatic property of the electret, that is, a permanent electrostatic field to the outside.
Conventionally, as a method for manufacturing electrets, a dielectric such as a polymer substance
is maintained at a temperature higher than the second-order transition point, and in some cases,
higher than the melting point, and internal ions or [111111] are released from dipolar freezing.
The DC electric field is applied between the metallic electrodes arranged on both sides of the
electrostatic body, causing the movement of ions, the movement of charges from the array
electrode of the dipole to the dielectric, and holding for a certain period of time. It is known how
to stop heating, return the dielectric to room temperature, remove the applied voltage when it
cools and solidifies, and electretize it, and the dielectric thus obtained has dipole orientation and
ion polarization. keeping. However, in the case of using a polymer substance as the starting
material for electret, sufficient dipole orientation is obtained because the molecular mobility is
small due to the polymer substance or higher or even in the molten state. Therefore, the surface
charge density of the resulting polymer electret is low, and the surface charge decays with time,
which is not practically sufficient. As a result of various studies to improve such conventional
defects, the present inventors have conventionally become an electret which can be put to
practical use because the surface charge density is small and the surface charge is significantly
attenuated with the passage of time. It has been found that even if there is no polymeric
dielectric material, it is possible to easily produce a minute stable electret with sufficient surface
charge density and oral change by mixing a liquid crystal forming material into the polymeric
That is, according to the present invention, before forming the polymer dielectric material into a
film, a plate or other molded product, the liquid crystal forming substance is added and mixed,
and the polymer dielectric obtained by blending the liquid crystal forming substance is a starting
material of electret It is characterized by being a substance. The liquid crystal forming material
itself has an ability to electretize. However, since the liquid crystal forming substance is usually a
low molecular substance, it has low resistance to deformation, and it is difficult to produce an
electret which can be put to practical use by itself. On the other hand, although ordinary polymer
substances have a certain level of strength, electrets of sufficient performance can not be
obtained [111111] EndPage: 1 because of the above-mentioned drawbacks. However, a liquid
crystal forming substance having a special molecular aggregation state in a certain temperature
range is added to the polymer dielectric, and the dielectric molded product which is oriented and
polarized in a direct current strong electric field is remarkably promoted in orientation
polarization and surface charge It is an electret with high density, low surface charge decay, and
sufficient strength for practical use. In the present invention, the term "liquid crystal" means all
those having fluidity as liquid in a certain temperature range and having the same optical
anisotropy as crystals, and the following compounds may be used. The liquid crystal is classified
into smectic phase, nematic phase and cholesteric phase according to its state, and the smectic
phase is aligned such that elongated molecules form a layer, and long axes of molecules in the
layer are all parallel and perpendicular to the layer plane doing. Substances which give a smectic
phase at a certain temperature range include ethyl-P-azoxybenzoate potassium oleate,
ammonium oleate and the like. Unlike the smectic phase, the nematic phase no longer has a
layered structure, but is aligned by striking only the long axis. Substances which give a nematic
phase at a certain temperature range include P-azoxyanisole, 4-4 'dimethoxystilbene, trans-Pmethoxycinnamic acid, Pn-glopyoxybenzoic acid and the like. The cholesteric phase resembles
the nematic phase in the arrangement of molecules in each layer, the molecular layer is very five,
the major axis of the molecule is parallel to the plane of the layer, and the direction of the
molecular axis of each layer is the direction of the molecular axis of the adjacent layer And
slightly offset, and it has a helical structure as a whole. Compounds of this type include a large
number of cholesterol-based derivatives, such as cholesterol acetate. The present invention adds
a direct current strong electric field to a polymer dielectric molded product mixed with a
compound capable of becoming a liquid crystal as described above within a temperature range
capable of forming a liquid crystal phase, preferably a polymer dielectric and It is a method of
orientating and polarizing liquid crystals, cooling and solidifying while maintaining a strong
electric field, and obtaining an excellent electret.
Hereinafter, the present invention will be more specifically described by way of examples, but the
present invention is not limited to the examples in any way. EXAMPLE 1 A mixture of
polyethylene terephthalate-adipate copolyester (50: 50) melt-kneaded with equal amounts (by
weight) of cholesteryl acetate is placed in a quartz glass container, and a copper lower electrode
grounded in a nitrogen atmosphere and a DC power supply. Hold between the copper upper
electrode plate connected. When the temperature in the constant temperature bath reaches 110
° C and the temperature in the constant temperature bath reaches 110 ° C, apply a DC voltage
of V (electric 20 KV / CIIL applied to the molten sample) between the electrodes for 1 hour and
then stop heating , Turn off the voltage when the temperature inside the thermostatic chamber
returns to 30 ° C. The sample thickness at this time is 2.071! 7711 quartz glass container
thickness is 2. Omrn, the air gap length between the dielectric sample and the upper electrode is
3. Qi! iであった。 The obtained plate is heterocharged 4.5 × 10-'coulomb / cr1. Surface
charge density of 100 x 100 h after production and oppositely charged to 4.0 x 10 'coulombs /
cd, with a stable surface charge density of at least 3.5 x 10 -9 klons / cd for at least 5000 hours.
Gave. Incidentally, a plate-like product obtained by the copolyester alone under the same
production conditions has a heterocharge of 1.5 × 10 −9 coulombs / cd immediately after
production, and a surface charge of 0.5 × 10 ′ coulombs / al after 1000 hours. Attenuated to
density. EXAMPLE 26 A plate obtained by melt molding a mixture of 10 parts by weight of nylon
and 1 part by weight of P-azoxyanisole is directly held between electrodes, with a thickness of □
am, 115 ° C., 5 The dielectric manufactured under the conditions of V (25 at V / (m), 3 hours)
has a surface charge density of homocharge 6 × 10 ′ coulomb / ca, and charge decay is almost
recognized within 5000 hours. It was not. On the other hand, the 6-nylon homopolymer gives a
surface charge density of 2.5 × 10 ′ coulomb / cd of homocharge under the same production
conditions, but attenuates to the order of 1010 after 1000 hours.
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