JPS5991032A - Manufacture of high-molecular piezoelectric film - Google Patents

Abstract

PURPOSE:To obtain a uniform film whose piezoelectric modulus is very high, by stretching one part of the one side of a crystalline high-molecular film having a glass transition point of 0 deg.C or below, when the film should be stretched at a temperature in a specified range at the start of the stretching. CONSTITUTION:A polyvinylidene fluoride film 8 is attached to support devices 5, and the inside of a thermostatic chamber 1 is kept at a temperature in the range of (Tg+10)-25 deg.C. Then an end part of the film 8 is heated by a sheathed heater 6 to 80-170 deg.C, and a threaded lever 4 is rotated to effect the stretching. Electrodes are arranged on opposite surfaces of the stretching film, then with a direct current field being applied, the temperature is elevated to a temperature lower than the melting temperature by 10-120 deg.C, and the elevated temperature is kept for a certain period. Thereafter when it is cooled to the room temperature and the direct current field is eliminated, a piezoelectric material can be obtained that has a uniform thickness and a high piezoelectric modulus when it is polarized, and is thin and large in area and easy to be molded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polymeric piezoelectric film. More specifically, the present invention relates to a method for producing an 11-6 molecule piezoelectric film having a large piezoelectric constant using a crystalline polymer having a glass transition point of OC or lower.

Piezoelectricity f', l: is known as a property of a crystalline body that does not have a center of symmetry.9 Utilizing its energy conversion function, piezoelectric materials can be used for audio transducer-1 medical transducer, super Sound wave transducer-1 Widely applied to physical measurement transducers, sensing elements, etc.

Currently, piezoelectric materials in general use include inorganic type materials such as quartz crystal, Rochelle salt, and 1) Z'l''.

(- or I/) Although these materials have a high piezoelectric constant, they are hard and brittle, so they are difficult to mold, and it is very difficult to manufacture thin piezoelectric materials with a large area.

On the other hand, stretched films of certain polymeric substances, such as natural polymers such as collagen and cellulose, and polymeric substances typified by polyr-methyl-L-glutamate, exhibit piezoelectricity.

In addition, it has been revealed that when synthetic polymer films such as polyvinylidene fluoride, polyvinyl fluoride, polyacrylonitrile, and polycarbonate are stretched and a DC electric field is applied to them and then cooled in that state, they exhibit piezoelectricity. . In particular, it is known that among the above synthetic polymers, IIL stretched film of polyvinylidene fluoride exhibits the largest piezoelectric constant.

However, the piezoelectric constant d%+ of the stretched film of polyvinylidene fluoride is 5.0X10-' CgS, elslu
However, in practice, there were restrictions.

When stretching polyvinylidene fluoride, it is empirically known that it is better to stretch at the lowest temperature possible, for example, at room temperature or below, to obtain a film with a high electrical conductivity. ing. However, it increased by 111 due to low humidity [1. It is difficult to obtain a uniform film. In other words, at low temperatures, the elastic modulus of the polymer 'e' increases and it has to be stretched at high tension, resulting in film breakage and non-uniform film thickness. , results in an unfavorable surface condition.

The present inventors have discovered that the glass transition point (hereinafter referred to as Tg) is OC
Vg-NOC is a film made of the following crystalline polymer.
) It was discovered that a uniform film with an extremely high piezoelectric constant could be obtained by heating a part of one end of the film at a temperature within a specific range at the start of stretching when stretching in a temperature range of ~5°C. , completed the invention.

The present invention provides a method for producing a polymer piezoelectric material exhibiting a large piezoelectric constant.
) to 5C, a part of one end of the film is heated at a temperature of 10C below the melting point of the film at the start of stretching.
-100t? No. 3 (14) of the polymer piezoelectric film, which is characterized by heating and stretching at a low temperature.

The crystalline polymer with Tg below OC used in the present invention is
Preferred is polyvinylidene fluoride resin. Polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (hereinafter abbreviated as VDF) and copolymers containing VDF as a main component and one or more other monomers that can be copolymerized with this. . Further, the above polymer may be polymerized by any method such as emulsion polymerization, suspension polymerization, solution polymerization, etc.

t as a monomer copolymerizable with vinylidene fluoride,
Vinyl fluoride, tetrafluoroethylene, trifluoroethylene,
Ethylene trifluoride chloride, fluoropyrene hexafluoride, perfluorovinyl ether.

Examples include, but are not limited to, Hegiza Fluo "1 Isobutene Boar".

For example, the above 111 polyvinylidene fluoride resin is heated to an appropriate thickness (for example, 3(
) ~ 200ha 1) (3) This melting method is to form a film with a '1゛ die for 1A type + trtt, or an inflation die for η + + -Alternatively, forming a film using a heating press-
This is the way to do it. The "dissolution method" is a method in which the resin is dissolved in a good solvent (for example, a polar solvent such as dimethylformamide or dimethyl sulfoxide) to form a film by casting.

The film was then stretched (at a temperature range of Tg +-1 (l U) to Z5 U) [7. A film containing oriented type (B-type) crystals was prepared by conventional methods. and,
The film may break at defective areas, or a film with uneven thickness can only be created. (Stretching at a humidity lower than Tg + 10 r is impossible, and the film breaks and rolls from 1 to 1.

) In the present invention, at the start of stretching, a part of one end of the film is heated to determine the stretching start point. Thereby, a piezoelectric film that is uniform and has an extremely high piezoelectric constant can be produced. The part of one end of the film in the present invention is the hatched part M in FIG. 2, and the width a is usually 5010% between the film supports.
Within If the thickness exceeds 10 inches, the uniformity of the film thickness may be impaired, which may pose a problem.

The above heating temperature is 10 tl" or higher than the melting point of the film.
Temperatures 100C lower are preferred, with the melting point of the film -10
If it is less than 0r, the effect will be small and the wiper film with a melting point exceeding -10U will melt and break, which is not preferable. There are no particular restrictions on the heating time.

Furthermore, the amount of oriented ■-type (B-type) crystals changes depending on the stretching ratio, which affects the piezoelectric constant, so the larger the stretching ratio is, the better. In particular, the stretching ratio is preferably "C, 3".The stretching speed is usually I-+m/+n,
in −5(it) w/++t in , fjf
& or lQmm/min ~10ft 7m
i n deai).

FIG. 1 shows an example of the apparatus used in the manufacturing method described in this article.

In the figure, 1 is a constant temperature bath, and 2 is a stretching device. This device 2 consists of a screw 4 supported by a bearing 3, a film support 5 screwed onto the screw 4, a sheath heater 6, and a slider 7 for adjusting the current supplied thereto. and an AC power source.

First, the polyvinylidene fluoride film 8 is attached to the film support 5 of the stretching device 1-2, and the inside of the constant temperature bath 1 (Tg
-1-toc) to 25'C.

Next, the end portion of the film 8 is heated to 80'G-170°C by the sheath heater 6 to determine the stretching start point, and when the screw 4''r4 is rotated, the film support 71.5 moves in the direction away from the U. Film 8 is stretched in the direction of the arrow.

Note that the method of heating the film is limited to the method using a sheath heater, and may also be a method of heating by blowing warm air (hot air).

Metal films are supported on the front and back surfaces of the stretched film produced by the above method to form cities and poles. Electrodes are formed on both sides of the film by vacuum evaporation.

Chemical plating, metal coating, conductive paste, metal foil.

This can be done by various methods such as bonding metal plates.

A DC electric field is applied to the electrodes of the stretched film at room temperature, and the film is heated to 10 to 12 degrees below the melting temperature.
The temperature was raised to 0C and maintained at that temperature for a certain period of time.

Next, after applying a DC electric field and cooling to room temperature,
The DC electric field was removed and polarization was performed to create a piezoelectric film. There is no particular limit to the above temperature increase rate. The maximum temperature during polarization may be maintained for 5 minutes or more, and is usually an additional hour to 1 hour.

Further, the applied voltage is lower than the dielectric breakdown voltage of the resin film, and is usually 100 to 1500 kv/cm.

The polymer piezoelectric film produced by the manufacturing method of the present invention is
9mm, has a high usage rate, and is thin”, iT++
We provide a piezoelectric material with a large f+'t that is easy to mold (
J (can.

Using a 40 mm extruder, polyvinylidene fluoride (manufactured by Tsurupei Co., Ltd. NRE 1.010
) (tA!It point 170℃ glass transition point -40C) was formed into a film with a thickness of about 100 μm at 250C, the stretching temperature was set to room temperature 25C, and a sheath heater heated to 9 Or at the beginning of stretching was attached to a part of the end of the film. The stretching start point was determined by pressing for about 3 seconds. Next, the sheath heater was removed, and using an apparatus as shown in FIG.
It was uniaxially stretched to a stretching ratio of 4.5 times. The stretching speed is 5~m/
m, in.〇Gold was vacuum deposited on the front and back sides of the stretched film to form electrodes, and at room temperature of 25C, 1
Raising the temperature while applying a DC electric field of 000 kv/cm,
Hold at 80C for 30 minutes 1~ then cool to room 8] Again. Thereafter, the DC electric field was removed and electret formation was performed to obtain a polymer piezoelectric film.

Example 2 A polymer field-shaped film was obtained in the same manner as in Example 1 except that the sheath heater temperature was set to 120C at the start of stretching.

Example 3 A polymer piezoelectric film was heated to 111C in the same manner as in Example 1, except that the sheath heater temperature was set to 160C at the start of stretching.
is.

Comparative Example 1 A polymer piezoelectric film was obtained in the same manner as in Example 1 except that the sheath heater temperature was set to 600.

Comparative Example 2 The sheath heater temperature of Example 1 was 180C, and other QJ5
Although uniaxial stretching was carried out in the same manner as in Example 1, the film melted (7) and broke.

Comparative Example 3 A film prepared in the same manner as in Actual Mli Example 1 was uniaxially stretched at a stretching ratio of 4.5 times in chamber g1. Furthermore, it was made into an electret under the same conditions as in Example 1 to obtain a polymer piezoelectric film.

Example Stretching temperature of Example 1: OC1 Sheath heater temperature: 120
A polymer piezoelectric film was obtained in the same manner as in Example 1 except that the t:X stretching ratio was 3.5 times.

Comparative Example 4 Everything was the same as in Comparative Example 3, except that the stretching temperature and OC1 stretching ratio were changed to 3.5 times.

In this case, compared to Example 4, the yield of the stretched film was much worse, falling to about 30 when Example 4 was taken as 100. This is because more things break.

Example 5 A polymer film was obtained in the same manner as in Example 1 except that the stretching temperature in Example 1 was -30r, the sheath heater temperature was 120c, and the stretching ratio was 3 times.

Comparative Example 5 A polymer piezoelectric film was obtained in the same manner as in Comparative Example 3 except that the stretching temperature in Comparative Example 3 was changed to -30c1 and the stretching ratio was changed to 3 times.

In this case, the yield of the stretched film becomes even worse, dropping to about 10 when the yield in Example 5 is set to 1 (10).

Furthermore, even if it were possible to stretch it, it would not be possible to obtain a film with a uniform thickness, but it could be made into an electret to obtain a film fc.

Comparative Example 6 Stretching was carried out using the stretching temperature of Comparative Example 3 as -45C1 and the stretching ratio as 318, but the film was completely broken.

Comparison) Example 7 A polymer piezoelectric film was obtained in the same manner as in Example 3, except that the stretching temperature in Comparative Example 3 was changed to 40υ.

ear! soil, 111' according to Examples 1 to 5 and Comparative Examples 1 to 7
,) cotton 1.16 molecules Kawa Shigeju film's m lightning 1 rate d31
Table 1 shows the results of measuring the thickness and thickness variations of

[Brief explanation of the drawing]

FIG. 1 shows an example of an apparatus 1 to 1 used in the method for producing a polymeric pressure film of the present invention, and FIG. 2 is an enlarged schematic diagram of a part of a stretching apparatus 2. As shown in FIG. 1... Constant temperature 4W'i, 2... Stretching device, 6... Sheath heater, 8... Film.

Claims (1)

[Claims] When stretching a film made of a crystalline polymer with a glass transition point of OC or lower at a temperature range of 1 (ltl?) to 5C, one end of the film is stretched at the melting point of the film at the start of stretching. From Hl tr -100
U. A method for producing a polymer piezoelectric film, which comprises heating and stretching at a low temperature.