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■ Manufacturing method of piezoelectric polymer moldings ■ Japanese Patent Application No.
45-102666 [Phase] Application No. 45 (1970) I January 24 @ inventor Murayama DC Iwaki City
Iwaki City 16 Kanamachi Maehara Same Takao Iwaki City Koshicho Ochiai 28 1 @ Applicants
Atsushi Chemical Industry Co., Ltd. Tokyo Chuo Ward Nihonbashi-Horidomecho l 8 [Yes]
Attorney Attorney Shigeru Shibuya
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows that the piezoelectric constant is 110-8c0.
The relationship between the temperature and voltage of electretization which becomes s, e, s, u
or more is shown. FIG. 2 shows a block diagram of an apparatus for measuring polarization
generated when compressive stress is applied to the piezoelectric film of the present invention.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for
producing a piezoelectric molded article having a polyvinylidene fluoride resin as a base material.
Heretofore, inorganic substances such as quartz crystal, Rochelle salt, titanium salt, barium
titanate, and ceramics are known as substances having piezoelectricity. Also, relatively recently,
among biomaterials and synthetic polymers, those having piezoelectricity have been known and
studied. In living tissues, bone, skin, blood vessel, trachea, muscle, hair, ivory, silk thread,
bamboo, wood and the like are known, and it is considered that most of the proteins are
piezoelectric. Among synthetic polymers, piezoelectricity is also observed in uniaxially stretched
films of amino acid polymers such as polybenzyl glutamate and polymethyl glutamate. Apart
from these, when a direct current high voltage is applied at a relatively high temperature to the
synthetic polymer film and it is cooled as it is, both sides of the film become polarized and the socalled electret 75. It was known from [111111] Recent progress in research on polymer electrets
has investigated the piezoelectricity of various electrets, and in particular the lifetime of polar
polymer films such as polyvinyl chloride, polyvinyl fluoride, polyvinylidene fluoride (hereinafter
referred to as PVDF). Long piezoelectricity has been found. In the case of a piezoelectric polymer
film, in general, in the case of being referred to as piezoelectricity, it is subjected to tensile
piezoelectricity, and when tensile stress is applied to the film, the piezoelectric constant α
derived from polarization polarized in the direction perpendicular to the surface is measured. Do.
Conventionally, a piezoelectric film of PVDF is realized by electretization of a −axially stretched
film, for example, uniaxial stretching of PVDF several times at 120 to 150 ° C., and an electric
field of about 300 KV / crrL at 80 to 90 ° C. The electretization is performed below, and a PVDF
piezoelectric film having a maximum piezoelectric constant d31 of about -7c, g, s, e, s, and u at a
tensile direction of -8 is obtained. In this case, however, the piezoelectricity is highly anisotropic,
and the piezoelectric constant of tension in the direction perpendicular to the stretching direction
is about 1/10 or less of that in the stretching direction. In the case of using a film having large
anisotropy in such a piezoelectric constant, for example, as a diaphragm of a speaker, electrodes
are provided on both sides of the film to make an acoustic voltage act. In some cases, it is not
desirable to have a sex, and in some cases, it is desirable to have a piezoelectricity that is not
directional. The present inventors have invented a method for producing a non-anisotropic PVDF
molding having strong piezoelectricity based on many years of research on PVDF electrets.
In the present invention, when a direct voltage V of 200 KV / mm or more and 150'OKV / mm or
less is applied to an unoriented PVDF film or molded product, an experimental formula -0, 5 V +
250 (° C) (where V is an electret of KV unit) With regard to obtaining a high performance nonanisotropic piezoelectric PVDF film by performing electretization at a temperature higher than or
equal to the value of the direct current voltage, the conventional pressure can be obtained at the
non-anisotropic [111111] EndPage point. It is completely different from the Samurai film. In
PVDF, there are mainly two crystal forms of α-type and β-type, and so-called winter type is
exhibited. The PVCF film is obtained by cooling from the molten state. In this case, a molded
article of α-type crystal type is obtained. In the case of molding by pressing or the like, almost
non-oriented molded products can be obtained, but in a strict sense, completely non-oriented
molded products can not be present, and orientation occurs when the polymer flows or
originates therefrom. The degree of this orientation can be a standard for measurement of
birefringence. ° Birefringence (Δn) was measured using white light. In the case of a T-die sheet
produced by applying a considerable draft above the melting point, it exhibits birefringence of
about 1 oxl'03, so that it can be treated as an unstretched PVCF molded article having more
birefringence than this. And unoriented PVCF moldings are those having a birefringence of less
than or equal to 1 ′ ′ ′ OX] O−s. In this case, the anisotropy of the piezoelectricity is small.
The non-oriented PVDF / l / m obtained in this way electretizes the molding. A film or a molded
product is sandwiched between the electrodes as in ordinary electretization, a direct current
voltage is applied, kept at a constant temperature above room temperature for a certain period of
time, and then lowered to room temperature under voltage application. The electrodes may be in
close contact by vapor deposition or the like, or may have a gap therebetween. The higher the
applied voltage (V) or less than the withstand voltage, the better, but practically it is preferably
15 o 'KvA or more and lsoo KV / m. In order to increase the applied voltage, it is necessary to use
carefully shaped noodles (with the exception of foreign substances, moldings processed so as to
be free from voids and cracks more carefully). The electretization time is one if it is sufficient for
the temperature to rise, and generally 10 minutes to 2 hours is selected, but a longer one is
preferable for sufficient orientation of the dipole. When the voltage is high, the electretization
temperature may be low (but the piezoelectric constant is an empirical formula at polarization
temperature of zero degree (° C.) or more, as described in the example, in order to obtain a
value of 101 [111 111] or more). It is necessary to electretize at a base temperature T (° C.) = −
0.5 V + 250 (° C.) (where V is the unit of electret direct current voltage in KV units 3 or more).
The piezoelectric PVDF film or molded product obtained in this manner has almost no anisotropy
(, birefringence Δn is 8 to 9 ×), and even those of 0-3 have an anisotropy of 20% or less. It was
not. Also, as seen from the examples, the piezoelectric constant is about the same as that of a
uniaxially stretched film. This is surprising, contrary to the fact that piezoelectricity is a property
of crystals and high orientation is expected due to its orientation. The piezoelectric film or the
molded product thus obtained has the advantage that it is extremely easy to design cars because
it has no anisotropy when used in an acoustic transducer. In addition, it is possible to easily
manufacture not only films but also thick sheets, pipes, block-shaped and other shapes, as they
do not require orientation, and general applications for applying piezoelectricity, for
electromechanical conversion, pressure detection A wide range of industrial applications such as
pressure sensitive elements can be considered. The present invention will be described in more
detail by way of the following examples, but is not limited thereto. EXAMPLE 1 The powder of
PVDF obtained by suspension ben- gony polymerization was formed into a film of 100μ using a
hot press at 250 ° C. The birefringence (.DELTA.n) of this film was 0.45.times.10@-3, and the
directional polarity was small. This thing was electretized. The electretization is performed on a
stainless steel electrode, and is maintained at a constant temperature ('T) for 1 hour while
applying a DC high voltage (V), and then allowed to cool to room temperature. Electretization was
performed by changing the voltage (V) and the temperature (T). The piezoelectric constant was
then measured. In this case there was little directionality. [111111] EndPage: 2 The result is
shown in FIG. The vertical axis represents the electretization temperature, and the horizontal axis
represents the numerical value V of the electretization DC voltage in KV units], Ocog, s, e, 's, u or
more points with black circles and the following points with white circles did. As a lower limit at
which black circles are plotted in the case where the polarization temperature T is equal to or
higher than zero degrees (.degree. C.), the following equation was obtained. If the temperature at
the time of direct current voltage (V) is T ('c) = -0, 5 V + 250 (' c) or more obtained by the above
empirical formula, the piezoelectric constant is 10 'c0 g, s, e, s, u or more I understand that it will
be. The piezoelectric material of the product made in this way was extremely stable, for example,
the sample of ■ showed almost no attenuation when kept at room temperature for half a year.
Example 2 PVDF powder obtained by suspension polymerization was extruded with a T-die, and
was drafted and formed into a film of lOOμ.
The birefringence was 6.0 × 103. The product was electretized by maintaining it at 150 ° C.
and 2300 for 30 minutes with v / crIl, and it was cooled to room temperature after rl111111.
The piezoelectric constant of itself was measured in the draft direction and in the direction
perpendicular thereto. Bi-directional anisotropy is extremely small. Example 3 A 50 micron film
was obtained as in Example 2. The birefringence was 7.8 × 1.0-8. Similarly, this was electretized
at 150 ° C. and 300 with ■ / CrIL, and the piezoelectric constant was measured. [111111]
EndPage: 3 Example 4 A 50 μ film having a birefringence of 9 × 10 'and a 50 μ uniaxially
stretched film as an example at 150 ° C. prepared in the same manner as in Example 2.
[111111] Further, the piezoelectric constant □ of the tension in the draft direction of a nonstretched film used for producing a control example film at 90 ° C. and electretized at 300 with
■ / − is 5.2 × 10′e, g, s, e, s, and u, and the piezoelectricity of the non-oriented film is not so
different from the piezoelectricity of the 3-fold-oriented α-type film. Example 5 A '100μ PVCF
film obtained as in Example 2 was treated with iso ° C.-C: 300. After applying a KV / crrL
voltage for 30 minutes and cooling to room temperature, it was electretized. The measurement
will be described below with reference to FIG. Electrodes 2 of lcr / L × 1 crf L were attached to
both sides of the piezoelectric film 10. The instantaneous voltage generated when 1 kg of weight
3 is covered or removed on this electrode is a 50 μ film obtained by stretching a 150 μ nonstretched film at 160 ° C. and tripled the film of the FET rl 111 111 example. The birefringence
index is 17 ×] 0 ′ ′, and X-ray diffraction shows α-type crystal form. When used in the circuit
4 using [111111] and measured with the oscillograph 5, a value of 40 mV was obtained. This
indicates that this film acts as a pressure sensitive element. Since the polarization generated by
the applied pressure is different, it is possible to apply a pressure sensitive element to obtain a
signal according to stress.
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