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Patent office commissioner Saito Hideo 1, name of the representative of the invention
Represented the name of the representative post posting Bridge ■ ■ JP-A 51-854990 published
Japan. (1976) 7.27 Internal Serial Number Specification 1, Title of the Invention 1, Title of the
Invention A method of manufacturing a high performance piezoelectric film
-21 inventor
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for
producing a piezoelectric film of polyvinylidene fluoride polymer, and more specifically to
stretching an unstretched film having particularly low molecular orientation birefringence to a
specific magnification or more at a low temperature. To. The present invention provides a
method of obtaining a high-performance piezoelectric film. It is known that a molded product
with high piezoelectricity can be obtained by performing a polarization operation of applying a
DC electric field under heating conditions to a copolymer molded product mainly composed of
polyvinylidene fluoride or vinylidene fluoride. ing. Furthermore, in this case, when polarization is
carried out at a relatively low temperature of 150 ° C. or less at a relatively low temperature of
5 ° to 150 ° C., it is non-orientated or α-type having an α-type crystal structure. It is also
known that high piezoelectricity can be obtained as compared to the one obtained by polarizing a
film. However, even if it is attempted to obtain a polyvinylidene fluoride high piezoelectricity film
industrially based on these findings, there is a large variation in the piezoelectricity of the film
obtained through polarization, and always high piezoelectricity The film which it has is not
obtained. The most industrially easy method for producing a polyvinylidene fluoride film having
a 15β type crystal structure is a method in which a melt extruded polyvinylidene fluoride
polymer is uniaxially stretched at a temperature of 150 c or less. If 20EndPage: 1 increases the
draw ratio in the temperature drawing operation, it tends to induce a drop in the withstand
voltage of film cutting and uneven rounding of the thickness, and a film with a constant draw
ratio and uniform thickness is always obtained W & vsa When stretching is performed at a
magnification close to the natural stretching ratio at which cutting or variation in thickness does
not occur or stb, the piezoelectric constant 41 obtained by polarizing this stretched film is a,
oX10- "C, g. s, e, s, u are often the following cases, and their values are not constant. 41 is 4.0 ×
10-M C, g, B, 8.8. The value of -u is an extremely large value as compared with the piezoelectric
constant of a piezoelectric material obtained by polarizing other polymer films such as polyvinyl
difluoride lyso polyvinyl chloride, polycarbonate, nylon 11, etc. It is still unsatisfactory when
used as a vibrating membrane of a container. In some cases, piezoelectric compounds of 5.0 ×
10 ′ ′ ′ ′ ′ ′ c, g, s, e, s, u, or more may be obtained as the piezoelectric constant of poly
(vinyl fluoride) / poly (vinyl fluoride) / Since OX10-'c, g, s, e, s, u, and the like are often obtained,
if a method by which such a film with high piezoelectricity can be surely obtained is found, then
piezoelectricity can be obtained. The application of films is expected to show great progress.
As a result of intensive studies, the inventor i found that the degree of molecular orientation of
the unstretched film, that is, the value of 5 birefringence Δn in the stretching direction of the
unstretched film and the stretching ratio greatly contribute to the piezoelectricity of the unipolar
film. The unstretched film is manufactured to have as little flow orientation as possible 10 such
that Δ of the stretching direction of the unstretched film is & OX 1g-s or less, preferably & 0x10
"to 0.5x 10" ", 150 ° C or less S found by stretching at a stretching temperature of 5 times or
more and polarizing this stretched film, and a film having extremely high piezoelectricity can not
be obtained. As a method of measuring Δn, there are, for example, a method of measuring with
an Abbé 15 dioptric needle, a method of measuring with a polarization microscope, etc., although
any method may be used, but all the measured values in the present specification are Libe. A
Beretsk convector is attached to a polarizing plate I11 '□ mirror manufactured by Tsuzushi Co.
and measured with strange white light. The relationship between Δn of the unstretched film
obtained by the present inventors et al. And the piezoelectric constant gs + of the film obtained
by the stretching ratio and the polarization is, for example, as shown in FIG. That is, it is a
piezoelectric film which is formed by stretching a polyfluorovinyl-iJ-den unstretched film having
various values of Δn with a thickness of 40 μ to 150 μ and uniaxially stretching it at, for
example, 85 times and 100 ° C. Constant was determined, but as a novel fact, it was found that
the α and I constants were significantly different depending on the values of the 6 episodes of
the unstretched film under the same polarization conditions and same stretching conditions. And
nine. The Δ 延伸 of the unstretched film is such that the flow orientation of the molecules at the
T-die exit 迄, and the molecular orientation by withdrawal from the die exit to the cooling point
are determined by the crystallization rate by cooling. Therefore, the higher the temperature of
the extruded molten resin, the smaller the draw-down rate from the T-die slit to the molded film,
the smaller the distance from the T-die outlet to the cooling point 迄 ′, and the larger the
ambient temperature, the smaller Δ is , It is general in the nature of polymer viscoelasticity. (1)
Furthermore, the crystallization temperature of polyvinylidene fluoride is near 155 ° C., the
cooling temperature has a high seed crystallization rate close to the crystallization temperature,
the molecular orientation strain is frozen, and Δn becomes large. Therefore, a film with any Δ
spirit can be molded by devising or losing the above-mentioned various factors that regulate the
5Δ calculation at the time of extrusion molding, and the temperature of the unstretched film
with a small Δ 箕 is 150 ° C. or less If a film stretched by & 5 times or more is polarized, a large
film of 41 constant size is always obtained.
-21 inventor
The present invention will be described in detail below with reference to the drawings.
Polyvinylidene fluoride obtained by suspension polymerization and having a melting point of 1
° C. 76 ° C. is subjected to seed 15-axial stretching in a range of 1.2 × 1 mA with a thickness
of 40 μ by T-die melt extrusion, followed by 110 ° C. 3 × relaxation heat treatment To obtain a
stretched film. At this time, the drawing speed is 繋 8, and the draw ratio is appropriately
determined by the unstretched film 20EndPage: Each film's natural draw ratio is determined by
the Δn of 2 film. Various stretched films of 8μ to 10μ were obtained. If one example is
described with respect to this magnification, the natural stretching magnification at 85 ° C. of
the unstretched film having Δ security & 4 × 10-m is about S, which is about 5 times, and the
cleavage magnification is about 5.0 times. On both sides of the obtained 9 stretched film,
aluminum was deposited on both sides by a vacuum deposition method to give a film resistance
of 50 to LO ° 4 (film thickness 'about sooA') to obtain a deposited film. Insulate the periphery of
this vapor deposition film and stretch it on a wooden frame, using aluminum vapor deposition
films on both sides in a warm [120 ° C dry-heat furnace as both electrodes, direct current
voltage of 7 goxv / I11 · according to each film thickness Was applied for 5 minutes, and then
air-cooled to 11 normal temperatures in a voltage applied state to obtain a piezoelectric film. The
relationship between the d 定 数 constant, which is the piezoelectric coefficient when stress is
applied in the stretching direction, and the Δ 爲 of the unstretched film corresponding to each
piezoelectric film is represented by using the stretching ratio 'as a parameter There is a first
design 1. The award constant shows the value measured about one week after the polarization,
since the award piezoelectricity is somewhat unstable immediately after the polarization and
becomes stable after dropping about 10% in several days. The hatched portion located on the
right side in FIG. 1 is a non-stretchable 5 region by cutting when stretching at a temperature of
85 ° C. For example, the Δ field has a value of & 5 × 10− ′ ′ and 2 unstretched) Means that
the one having a Δ 爲 of 4.2 × 10− ′ ′ cuts at a draw ratio of 4.5 times or more by 3.5 times
or more. Further, the left and side hatched portions in FIG. 1 have a magnification of 10 or less of
the natural stretching magnification determined by Δn of the unstretched film, and indicate
uniform non-stretchable regions in order to leave stretching residues in the stretched film. An
unstretched film with a haze of 1.8 × 10 -3 is a satisfactory film film leaving a stretching residue
in a stretched film at a stretching ratio of 4.0 or less and a stretching ratio of 3.5 or less in the
case of 44 × 10-s It means that it can not be obtained. The non-stretchable 15 region is
generally used in polymer stretching and is not particularly novelty of the present invention.
One of the features of the present invention is that the unstretched film having a Δn value
LOX10- ′ ′ or more obtained by ordinary molding is twisted by stretching, and the daI
constant having commercial performance can not be obtained. As apparent from FIG. 1, the
higher the −axis stretch ratio, the larger the value of 481 constant is obtained, but at the same
time the value of the Δ answer of the unstretched film is small, in particular, the value is 2.0 ×
10− to 50 × 10. A uniaxially stretched film of unstretched film, which is -8, indicates that
each magnification gives the largest d □ constant. The reason for showing the maximum value is
not clear yet, but is provided as a clear and novel fact from the results of many experiments by
the present inventors. Here, the non-stretchable region in FIG. 1 has a property of slightly
changing depending on the material of the base in the laminate stretching method by the
stretching conditions such as temperature and stretching speed and the device of stretching
operation such as laminate stretching. For example, using a resin film with a natural draw ratio
higher than polyvinylidene fluoride at a low temperature of 130 ° C. or less and easy plastic
deformation as a substrate and simultaneously with an unstretched film of polyvinylidene
fluoride and laminating and stretching. A high magnification is also obtained, so a high constant
can be obtained. The present invention discloses that the value of the molecular orientation
mechanism jIl-ratio Δ 舊 of the stretched film and the stretching ratio are dominant factors in
the value of the dll constant, regardless of whether or not any stretching method L is applied. It is
On page 5, the effects of the present invention were confirmed in stretched films having different
thicknesses, but similar results were shown. That is, polyvinylidene fluoride having a melting
point of 176 ° C. obtained by suspension polymerization is extruded with a T-die, and the
thickness has various Δ10 calculated values of 0.7 × 10−′a to 6.5 × 1 g−s. An unstretched
film of 150μ was obtained. This unstretched film is stretched at a stretching temperature of 100
° C. in one direction at a magnification of 3.5 to 5, selected in a range of 5, stretched, continued,
120 ° C. 5% relaxation heat treatment thickness An uniaxially stretched 15 film of 27 μ to 35
μ was obtained. A metallized film in which aluminum was formed into a film resistance of 2.5 Ω
/ (: d to S, 5 Ω / cIi) was formed on both sides of the obtained film by vacuum evaporation.
Metallized films of each group are insulated on a wooden frame by insulating around 20EndPage:
3 to a size of 2005 m × 200 ■, with both sides of the deposited film as both electrodes, DC
voltage of 750 KV 15 in a dry heat atmosphere at 120 ° C. Was applied for 5 minutes, and after
quenching to room temperature, the voltage was released to obtain a piezoelectric film.
The relationship between the dll constant of each sample and the Δ9 of the unstretched film is
shown in FIG. 2 with the draw ratio as a parameter. In this case, too, the tendency of FIG. The
same relationship as-the figure is obtained. That is, in the case of an unstretched film having a
Δ5.0 value of 5.0 × 10 13 or more, most of the −axially stretched films have 41 constants of
−OX 10 − ′ c. g, s, e, s, u, only the following piezoelectric films can be obtained; conversely,
Δ〜 is 2.0 × 1 G ′ ′, 55 × magnification, and dal constant of 2.7 μm thickness is & 2 ′ ×
10 --Q, g, 8. e, 8. u, further. Isle, the 780xv /-, when polarized at nine? , 5 × 10′′Q, g, 8. Q, 8.
In the case of u, and polymeric piezoelectric films, values which can not be conceived at all are
obtained. 1 and 2 are different in applied voltage at the time of polarization, but in the case of
FIG. 1, the film wire thickness in the case of FIG. It was something that could not be raised. The
applied voltage also has a great influence on the piezoelectric coefficient, so that the applied
voltage does not cause dielectric breakdown of the film-preferably as high as possible, preferably
500 Ki 5 or more, more preferably 600 KV / cfR or more and the withstand voltage of the film or
less. As the polyvinylidene fluoride polymer referred to in the present invention, a copolymer
containing vinylidene fluoride as a living organism also exhibits high polarity and high
piezoelectricity is confirmed, and it is substantially 10 It is to be understood that the copolymer
has a vinylidene fluoride content of 80 moles X or more having the following characteristics. The
copolymer of heptamic acid is selected from tetrafluoroethylene, hexafluoropropylene,
trichloropentaethylenediethylene, vinyl fluoride, per 70 ropinyl alkyl ether, vinyl acetate,
ethylene goup, or 91 or more species thereof. It may be more than. When a piezoelectric film is
applied as a vibrating film of a sound conversion unit without any mention, the magnitude of the
ds1 constant and Herdhoe /, and the sound pressure sensitivity of an acoustic device such as a
speaker are almost proportional to each other, 41 constant The larger the sound quality, the
better the quality of the audio equipment. For example, in the sensitivity measuring device of the
test used by the present inventors et al., In order to obtain the sound pressure sensitivity of 110
cLB at an input voltage of 10 v, the polyvinylidene fluoride piezoelectric film no dal constant is 6.
Ox10-'c, g, s, e, s, u, necessary, this feeling [110 dB is the quality of the sound equipment. Is an
important factor in determining Therefore, the present invention provides a method for easily
producing a constant, though it is high, by controlling the value of Δ 贋 of an unstretched film of
polyvinylidene fluoride polymer, and the industrial advantage is high.
r4. Brief Description of the Drawings Fig. 1 shows the relationship between Δ-le of the
unstretched film of polyvinylidene fluoride and the d 酊 constant of the stretched polarized film,
Fig. 1 shows a stretching temperature of 85 ° C and Fig. 2 shows E105 °. It is the case of C-05
or more Agent Attorney Shibuya Osamu 'i. 1 1520 EndPage: 4 <rr: 7 rl ', 9 / y) It γ (n
sv °
v trap gg' yotx) trap c, attached list of documents (1) 1 description (2) 1 drawing 8) Request 1
copy 2 (4) Power of attorney 1 6 Inventors other than the above Sinikishiki! Chisagi UchiFukushima Iwaki-shi, Kashiwa-cho □ Shonai 62 Uchida EndPage: 5
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