JPS59104911A - Dielectric film - Google Patents

Abstract

PURPOSE:To obtain a homogeneous dielectric film that is high in dielectric constant and dielectric strength and can be spread widely, by forming an uncrosslinked polyvinylidene fluoride type resin having a specified inherent viscosity value by a solution process into a film having a specified degree of surface orientation and a specified thickness. CONSTITUTION:To a copolymer (A) of 95mol% or more vinylidene fluoride (i) and 5mol% or less copolymerizable monomer is added a mixed resin (B) 95wt% or more vinylidene fluoride homopolymer or vinylidene fluoride copolymer and another polymer (e.g. a polymethacrylic acid methyl ester, etc.), then a solvent (C) (e.g. dimethylformamide, etc.) is added to produce a solution containing 0.3- 20wt% of the resins, and then a film is formed whose inherent viscosity is 2.2dl/g or more that is measured as a DMF solution having a concentration of 0.4g/dl at 30 deg.C. Then the intended film is produced whose degree of surface orientation is 0.25 or more and thickness is 10mum or less. USE:It can be used as a condenser film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a homogeneous cell film made of a polyvinylidene fluoride resin that has a high dielectric constant and dielectric strength and can be formed into a wide area as required.

Polyvinylidene fluoride resin films obtained by forming a film by the T-die method or blow molding method and then stretching it are known to have a high dielectric constant and insulating force, but the thickness is 1' It is not easy to obtain a homogeneous film of 0 μm or less, especially 5 μm or less over a wide area. In short, the reason for this is that it is difficult to control the molding conditions to the extent that the above-mentioned thin film can be molded homogeneously. Specifically, this is due to non-uniformity in temperature due to convection in the atmosphere immediately after exiting the die, non-uniformity in extrusion amount due to pulsation of scraping or gear pumps, and limitations in resin temperature control.

On the other hand, a polyvinylidene fluoride resin film formed by a solution method is homogeneous as long as it is unstretched, but its dielectric constant is smaller than that obtained by other film forming methods. Furthermore, the dielectric strength is low due to the formation of voids due to evaporation of the solvent. For these reasons, there have been no reports of practical use of a polyvinylidene fluoride resin film produced by a solution method as an attractant material on an industrial scale.

In view of the current situation, it is an object of the present invention to provide a homogeneous dielectric film made of polyvinylidene fluoride resin, which has high dielectric constant and dielectric strength, and can be made to have a wide area as required. .

As a result of research for the above-mentioned purpose, the present inventors found that 10μ of uncrosslinked polyvinylidene fluoride resin of polymer a
A film formed by a solution method to a thickness of less than m (hereinafter referred to as
It has been found that a film (sometimes referred to as a "cast film") can be obtained homogeneously even over a wide area, and that the molecular chain axes are oriented parallel to the film plane, that is, the degree of plane orientation is high. Moreover, a cast film with such a high degree of plane orientation has a high dielectric constant close to that of a stretched film, and its dielectric strength is significantly higher than that of a conventional cast film of polyvinylidene fluoride resin with a conventional degree of polymerization. I found that it has been improved.

The dielectric film of the present invention is based on the above-mentioned findings. More specifically, the dielectric film of the present invention has an inherent viscocity of 2.2 (11/g) measured as a dimethylformamide solution at a concentration of 0.4 gz41 and a temperature of 30°C. It consists of a film formed by a solution method of the above uncrosslinked polyvinylidene fluoride resin, and has a degree of plane orientation of 0.25 or more and a thickness of 10
The time element is µm or less.

The present invention will be explained in more detail below.

The "polyvinylidene fluoride resin" as used in the present invention refers to vinylidene fluoride homopolymer (hereinafter referred to as JFVDFJ), as well as a type of monomer that can be copolymerized with vinylidene fluoride at a mole ratio of 95 or more and vinylidene fluoride. or a copolymer with two or more types and 5 molt or less, and the above PVDF or vinylidene fluoride copolymer with 95% IW% or more as the main component, and other polymers to the extent that the dielectric properties of PVDF' are not particularly affected. It shall contain a mixed resin combined with. Examples of monomers copolymerizable with vinylidene fluoride include vinyl fluoride, ethylene trifluoride, ethylene trifluoride chloride, ethylene tetrafluoride, propylene hexafluoride, and ethylene. Examples of polymers to be mixed with the vinylidene fluoride homopolymer or copolymer include single or copolymers of the above monomers, polymethyl methacrylate, polymethyl acrylate, polycarbonate, polyester, and the like.

Polyvinylidene fluoride resin (hereinafter referred to as “P”) used in the present invention
VDF type 11 fat) has a concentration of 0.46/d.
A material having an inherent viscosity (hereinafter simply referred to as "inherent viscosity" without measuring conditions) measured as a dimethylformamide solution at a temperature of 30° C. and a temperature of 2.2 d1/g or more is used. This is P
This is because if the degree of polymerization of the VDF-based resin is low, it becomes difficult for the molecular armor to be planarly oriented, making it impossible to obtain a film with a high dielectric constant. 2
．． 4tll/g.

In particular, those having an inherent viscosity of 3.0 dl/g or more are preferably used.

On the other hand, although a high degree of polymerization is fine in terms of film properties, it reduces the solubility in solvents, so it is necessary to keep the resin concentration of the solution quite low (which is impractical) when forming a film by the solution method. There is a drawback that.For this reason,
Preferably 10 dl/g or less, even more preferably 9
dl/g or less, particularly preferably 86-1/g or less:
/Healent viscosities are used.

Further, in the present invention, crosslinked PVDF-based resins are inappropriate. The reason for this is that crosslinked PvDF-based resins are difficult to plane-orient during film formation by a solution method, and do not provide a film with a high dielectric constant. In terms of manufacturing method, PvDF-based resins polymerized at high temperatures generate branching and thermal cross-linking structure, which is undesirable for the same reasons as mentioned above. Therefore, as a PVDF resin, -500 to 80
Those obtained by polymerization at a temperature of 0.degree. C. are preferably used.

The dielectric film of the present invention is obtained by forming the film using the above-mentioned PVDF-based resin all-resin method.

The solvent used for forming the solution is not particularly different from those used in conventional methods, and may be any solvent that is made entirely of PVDF resin at room temperature or under heating. for example,
Polar organic solvents such as dimethylacetamide, dimethylformamide, methyl ethyl ketone, and dimethyl sulfoxide are preferably used.

The resin concentration in the solution varies depending on the degree of polymerization of the PVDF-based 1t+resin, but the thinner the solution concentration, the more likely a film with a higher degree of plane orientation can be obtained. However, if the solution concentration is low, the amount of evaporation of the solvent required to obtain a film of the same thickness increases, so in practice, the weight ratio is 0.3 to 20.
．． Approximately 5 to 10 percent of the focus is appropriate.

The dielectric film of the present invention is produced by applying a uniform PVDF resin solution of a predetermined concentration as described above to a solution film forming method that is known per se. It is obtained by forming a wet film by casting or coating on a substrate such as a polymer film that is difficult to dissolve in a solvent, evaporating the solvent, and peeling it off from the substrate if necessary. In order to obtain a film of uniform thickness, for example, a glass rod or a Mayer bar can be used. Furthermore, when producing a wide film, a roll or the like can be used for the base material to which the solution is applied and for winding up the product film. In the film-forming process, it is preferable to heat the film to an extent that compensates for a decrease in the surface temperature of the wet film due to heat of vaporization due to evaporation of the solvent. Furthermore, if the film is heated too much, plane orientation of the film becomes difficult to occur, so it is naturally preferable to slow down the volatilization rate of the solvent. Specifically, it is preferable to evaporate the solvent at a constant temperature between about 30° C. and the boiling point of the solvent under pressure to volatilize the solvent.

As mentioned above, in order to obtain the dielectric film of the present invention,
It is preferable to use a solution with a relatively low concentration, and in order to obtain a homogeneous film with a high degree of plane orientation using such a low concentration solution, there is a certain limit to the thickness. In other words, when trying to obtain a thick film from a dilute solution, evaporation of the solvent causes uneven distribution of the resin concentration in the film thickness direction (lower concentration on the substrate side), and the film after drying also has uneven distribution in the thickness direction. There is a problem in that not only the thickness is uniform but also the thickness is uneven in the horizontal direction of the film. Therefore, the individual thickness of the dielectric film of the present invention is suppressed to 10 μm or less, particularly 5 μm or less. The lower limit of the film thickness is not particularly limited,
It is also easy to form a homogeneous film of 1 μm or less by adjusting the solution concentration.

The dielectric film of the present invention obtained as described above is
It has a high degree of plane orientation. Such plane orientation is caused by Pol
ymer Journal Volume 3, Page 600 (197
This can be confirmed using Hase's method as shown in 2010).

More specifically, the dielectric film of the present invention has a degree of plane orientation π determined by the following formula of 0.25 or more, preferably 0.3 by selecting the degree of polymerization of the PVDF' resin, solution concentration, etc. described above. Above, it is particularly preferably defined as 0.35 or more.

Here, Δθ is the diffraction plane that cuts perpendicularly to the molecular chain axis of the crystal with a higher content of α-type crystals or β-type crystals of PVDF, that is, in a wide-angle x-ray diffraction photograph obtained with a flat plate camera. The half width of the intensity distribution curve obtained by measuring the intensity distribution along concentric circles with a microdensitometer for the diffraction arc of the (002) plane for α-type crystals and the (001) plane for β-type crystals. It is. For X-ray diffraction, the film to be irradiated is thin, so multiple layers of the same film are stacked to a total thickness of 1 mm, hardened with an adhesive (for example, isocyanate-based non-toxic adhesive), and then cut into a wide rod shape. Perpendicularly to the edge plane (i.e. formed by a collection of film end faces), for example,
All you have to do is make the line incident.

As described above, according to the present invention, by forming a film using a PVDF resin all-resin liquid-liquid method, which has a higher degree of polymerization than is generally used, it has a high dielectric constant and dielectric strength, and can be formed over a wide area if necessary. A thin and homogeneous dielectric film can be obtained. Such a dielectric film is especially suitable as a capacitor film.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Example 1 580 g of water in which 0.2 g of methylcellulose as a suspending agent was dissolved was placed in a 11 autoclave equipped with a stirrer, and 2 g of isopropyl peroxydicarbonate as an initiator and other polymerization aids were added. After that, 200g of vinylidene fluoride monomer was introduced under pressure, and polymerization was started at 20°C with stirring. Initial gauge pressure is 37.4 kg/cm2
After 70 hours, the gauge pressure was 12.7 kg/am”
The residual pressure was purged to terminate the polymerization.

The obtained polymer was thoroughly washed and then dried. The solution viscosity of this polymer at 30°C was measured at a concentration of 4 g/l using dimethylformamide as a solvent and was 6.8.
ηinh (inherent viscosity) of cll/g was shown. A 1.5% solution of this polymer was prepared using dimethylformamide as a solvent, and after coating it on a glass plate and adjusting the atmosphere to go'c, the pressure was gradually reduced to obtain the highest IQ.
mmHg, and the temperature was gradually increased to 100°C. This period lasted about 2 hours. Furthermore, it remained in that state for 1 day and night (1
After maintaining the temperature for 6 hours), it was dried to easily form a film with a thickness of 4 μm.

This film (cast film)! The physical properties are shown in the table below. Here, the relative permittivity is measured using multi-frequency LO
19℃ by R meter (Yokogawa, Hewlett-Packard Co., Ltd. H “YHP 4274A J”)
I KHz value.

Also, to measure dielectric strength, cast film is zcm x 2c.
Cut to a size of m, with a diameter of Bmm on the top surface and a diameter of g on the bottom surface.
After depositing A1 on a circular shape of mm in diameter, bringing the lower surface into contact with a stainless steel flat plate and the upper surface into close contact with a stainless steel cylinder with a diameter of B mm, the voltage required for dielectric breakdown when an electric field is applied at 19°C is calculated as the voltage required for dielectric breakdown per unit thickness. This is the value converted into a hit.

Example 2 and Comparative Example 1 The solution f used during film formation was changed, and the film thickness was 2
The same operation as in Example 1 was performed except that μ was set to 40μ. The results are shown in the table.

As is clear from comparing Example 2 with Example 1, it was not recognized that the dielectric constant was large when the change in plane orientation was too severe. Regarding the film thickness of 40μ (Comparative Example 1), 40μ is an approximate value, and the film thickness is extremely uneven and the surface is wavy.
Physical property measurements were difficult.

Example 3 and Comparative Example 2 Polymerization and measurement were carried out in the same manner as in Example 1 except that the amount of polymerization initiator was changed, and the respective inherent viscosities were 2.4 (11/g, 1°) as shown in the table. A polymer of Odl/g was obtained. Using the obtained polymer, a film was formed in the same manner as in Example 1 and its physical properties were measured. The results are shown in the table. It is also recognized that the dielectric constant is increased due to the higher dielectric strength.It is also recognized that the dielectric strength is improved in the case of the present invention.

Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] 1. Solution method for uncrosslinked polyvinylidene fluoride resin having an inherent viscocity of 2.2 dl/g or more measured as a dimethylformamide solution at a concentration of 1 O, 4 g/ax and a temperature of 30°C. 1. A dielectric film comprising a film-formed product according to the invention, and having a degree of plane orientation of 0.25 or more and a thickness of 10 μm or less. 2. The dielectric monolithic film according to claim 1, which has a degree of plane orientation of 0.3 or more. 3. The dielectric film according to claim 1 or 2, wherein the polyvinylidene fluoride resin constituting the film has an inherent viscosity of 2.4 to 10 dl/g. 4. Inherent viscosity power of polyvinylidene fluoride resin constituting the film 3.0 to 8.0 di 7
The dielectric film according to claim 1 or 2, which is: g. 5. The dielectric film according to any one of claims 1 to 4, which has a thickness of 5 μm or less.