JPH11273990A - Polypropylene film for heat-resistant capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve electrical characteristics at a high temperature and machining property such as a forming property by using polypropylene with a specific isotactic pentad percentage and making specific an F5 value in a flow direction, the heat shrinkage rate in the width direction, and the surface roughness of at least one surface. SOLUTION: Polypropylene with an isotactic pendad percentage of approximately 96 % is used. Then, an F5 value at 20 deg.C in the flow direction of the polypropylene is set to approximately 50 Mpa. The heat shrinkage rate in the width direction at 120 deg.C is set to approximately 0.5 or less. Further, surface roughness Ra on at least one surface of a film is set to approximately 0.1 μm or longer. The surface roughness Ra of the film is preferably set to approximately 0.1-0.2 μm, thus reducing the deformation of an element at a heat treatment temperature of 120 deg.C when creating a capacitor and improving the electrical characteristics of the capacitor at that temperature or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene film for a capacitor which has excellent electric characteristics at a high temperature.

[0002]

2. Description of the Related Art Biaxially stretched polypropylene films are widely used as industrial and packaging films, and have excellent electrical properties (low dielectric loss and high withstand voltage). Widely used. Generally, biaxially oriented polypropylene film for capacitors is subjected to corona discharge treatment or plasma treatment after stretching,
Activate the film surface to provide a functional group. In the case of a film for vapor deposition, a metal such as Al or Zn is vapor-deposited on this film in a vacuum so as to be 1 to 15 Ω / □,
Thereafter, it is wound and used by an element winding machine. In recent years, due to the denseness of substrates and the accompanying miniaturization of capacitors, in addition to thin films, films that can withstand high-temperature use have been demanded. Is required.

However, a polypropylene film generally has low heat resistance, and is not suitable for use as a capacitor particularly at a temperature of 90 ° C. or higher, and a capacitor using polypropylene is limited to a maximum operating temperature of 90 ° C. or lower. That is the fact. In order to solve these problems, attempts have been made to increase the stereoregularity of polypropylene or to reduce the heat shrinkage, but this is not sufficient.

[0004] The inventors of the present invention have conducted intensive studies, and in order to use a capacitor at a high temperature, hot pressing at a temperature higher than the temperature at which the capacitor is used is used at a lower temperature. We obtained the knowledge that this would lead to stability of the capacitor element, and could improve the heat resistance problem to some extent.

However, in the case of thin films used at high temperatures, it has been found that this is not sufficient.
That is, in the case of a thin film, there are further problems such as poor slipperiness between the films, lack of rigidity, and a large heat shrinkage. As a result, when heat-treating the capacitor at a high temperature, particularly when forming a flat type device, the moldability is insufficient, and the deformation of the device and the warping phenomenon of the film of the metallikon portion occur, which significantly impairs the electrical characteristics at a high temperature. There's a problem. Therefore, the present inventors conducted further research,
Research on the physical properties of the film, independent of the conditions of the heat press, led to the present invention.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitor-use polypropylene film which has excellent electrical properties at a high temperature and excellent processability such as moldability, in order to solve the above-mentioned conventional disadvantages. I do.

[0007]

That is, the first invention of the present invention uses polypropylene having an isotactic pentad fraction of 96% or more, and has an F5 value of 50 in the flow direction.
MPa or more and heat shrinkage in the width direction of 0.5% at 120 ° C
Hereinafter, at least one surface has a surface roughness Ra of 0.1 μm
The present invention relates to a polypropylene film for a heat-resistant capacitor characterized by the above. The second invention of the present invention relates to the polypropylene film according to the first invention, wherein at least one surface has a surface roughness Ra of 0.1 to 0.2 μm.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to obtain a high degree of crystallinity, a polypropylene having an isotactic pentad fraction of 96% or more, preferably 97% or more is required for polypropylene for obtaining a film for a capacitor of the present invention. is there. When the isotactic pentad fraction is less than 96%, the crystallinity of the film is low, and the film has insufficient stiffness. Therefore, when the heat treatment is performed at a temperature exceeding 120 ° C., the end face of the capacitor element is warped, and the electric characteristics are deteriorated. The ash content of the polypropylene raw material is 50 ppm or less. When a polypropylene raw material having an ash content exceeding 50 ppm is used, the breakdown voltage is reduced due to an increase in insulation defects.

Using this raw material, a film for a capacitor is obtained. As the film of the present invention, a biaxially stretched film is used. As a characteristic of the polypropylene film for a heat-resistant capacitor of the present invention, it is necessary that the F5 value at 20 ° C. in the flow direction (hereinafter referred to as MD) is 50 MPa or more. If the F5 value is less than 50 MPa, the thin film does not have sufficient rigidity, so that a clean flat element cannot be obtained. As a result, a gap is formed between the film layers of the device, and T
an δ increases and the breakdown voltage decreases. Also, wrinkles are involved in the element, which significantly impairs the electrical characteristics.

As a characteristic of the polypropylene film for a heat-resistant capacitor of the present invention, the heat shrinkage at 120 ° C. needs to be 0 to 0.5% in the width direction (hereinafter referred to as TD). When the heat shrinkage of TD exceeds the upper limit,
When the element is hot-pressed, the metallikon portion on the element end face is warped and the metallicone strength is reduced, and when charging and discharging are repeated, there arises a problem that tan δ increases.

Further, the characteristics of the polypropylene film for a heat-resistant capacitor of the present invention include a surface roughness Ra of the film.
Is at least one side of 0.1 or more, preferably 0.1 to
It needs to be 0.20 μm. When the surface roughness is less than the lower limit, in the case of a flat type capacitor, the film does not slip during hot pressing, so that it does not become a clean elliptical shape, wrinkles at the center of the element, and impairs electrical characteristics. If the upper limit is exceeded, not only the capacity reduction rate, which is an important characteristic of the capacitor, increases, but also the withstand voltage decreases.

Although the thickness of the film of the present invention is not limited, it is effective for a thin film having a thickness of 3 to 15 μm, and is particularly effective for a thin film having a thickness of 3 to 7 μm.

The method for producing a film of the present invention varies depending on required quality characteristics and the like. For example, a polypropylene resin melted at a melting point or higher is extruded from a slit T-die and cooled at 30 to 95 ° C. After cooling and solidifying the sheet, the sheet is cooled to 100 ° C to 150 ° C in the longitudinal direction.
Stretched 4 to 6 times at a temperature of 120 ° C.
It is stretched 8 to 12 times at a temperature of 160 ° C.
It can be obtained by subjecting a film having a thickness of 3 μm to 15 μm heat-treated at a temperature of 170 ° C. to a corona discharge treatment on one side with an energy of 1000 J / m to 6000 J / m.

[0014]

Next, the present invention will be described in more detail based on examples.

Example 1 Crystalline polypropylene (isotactic pentad fraction: 96%, melt index:
(2.0 g / 10 min) The resin was supplied to an extruder, extruded from a T-die, wound around a drum having a surface temperature of 90 ° C., and a sheet having a thickness of 250 μm was obtained. This unstretched sheet is
The film was stretched 5.0 times in the longitudinal direction at a temperature of 100 ° C., immediately cooled to room temperature, and then stretched 10 times at a temperature of 160 ° C. with a tenter. After heat treatment, a corona discharge treatment was performed. Was obtained. The thickness was 5 μm. The heat shrinkage, surface roughness and F5 value of this film were measured. Its physical properties are as shown in Table 1.
One side of this film was evaporated with Zn to form a metallized polypropylene film.

After slitting this metallized polypropylene film, it was wound to form a capacitor element having a capacitance of 6 μF. Next, the capacitor element is crushed flat, sandwiched between iron metal plates, placed in a vacuum cooker while applying a pressure of 1.47 MPa, and heated from normal temperature to 130 ° C. in a vacuum of 7 Pa.
The hot press process was performed until To obtain electrical connection to the deposited electrode, a metallikon layer made of metal spray of Zn was formed to form a capacitor element, and after a lead wire was sprayed, a mold outer layer was formed using an epoxy resin to manufacture a capacitor. This capacitor was evaluated for change in capacitance, Tan δ, and device end face warpage. Table 1 shows the results.

The capacitor manufactured by this method was good without warping at both ends of the capacitor element. 120
The dimensional change of the capacitor element after the heat treatment at a temperature of ° C. is small. Further, the capacitance of the capacitor obtained by performing 150 cycles of the intermittent durability test in which the voltage / temperature was turned on for 1 cycle for 6 hours at an ambient temperature of 120 ° C. and for 2 hours off was good with little change in the capacitance. In addition, DC300
In a charging test in which a voltage of V was charged and a short-circuit discharge was caused by the stored charge through a resistance of 0.5Ω, good results were obtained with no change in dielectric loss.

Example 2 Using the same raw materials as in Example 1, the surface temperature of the drum was set to 8
9 ° C and the heat treatment temperature after transverse stretching with a tenter is 2
A film having the physical properties shown in Table 1 was obtained in the same manner as in Example 1 except that the temperature was lowered by ° C. Using this film, a capacitor was prepared in the same manner as in Example 1, and the same items were evaluated. Table 1 shows the results.

Example 3 A raw material resin having an isotactic pentad fraction of 97% was used, and the temperature of the drum when extruded from a T-die was set to 92.
A film having the physical properties shown in Table 1 was obtained in the same manner as in Example 1 except that the temperature was changed to ° C. Example 1 using this film
A capacitor was prepared in the same manner as described above, and the same items were evaluated. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 The physical properties shown in Table 1 were obtained in the same manner as in Example 1 except that a raw resin having an isotactic pentad fraction of 97% was used, and the heat treatment temperature after the transverse stretching with a tenter was lowered by 3 ° C. Was obtained. Using this film, a capacitor was prepared in the same manner as in Example 1, and the same items were evaluated. Table 1 shows the results.

Comparative Example 2 Using the raw material having an isotactic pentad fraction of 95%, the physical properties shown in Table 1 were obtained in the same manner as in Example 1 except that the heat treatment temperature after the transverse stretching with a tenter was lowered by 2 ° C. Was obtained. Using this film, a capacitor was prepared in the same manner as in Example 1, and the same items were evaluated. Table 1 shows the results.

Comparative Example 3 A film having the physical properties shown in Table 1 was obtained in the same manner as in Example 1 except that a raw material having an isotactic pentad fraction of 95% was used. Using this film, a capacitor was prepared in the same manner as in Example 1, and the same items were evaluated. Table 1 shows the results.

The measuring method is as follows. Isotactic pentad fraction: Stereoregularity was measured by 13-NMR. Heat shrinkage: Measured according to JIS C 2330 and expressed in%. Surface roughness: measured according to JIS B 0601, μm
It was expressed by. Cutoff value 0.8 mm. F5 value: In a tensile test according to JIS C 2330, the strength when the film was deformed by 5% was represented by MPa. Capacitance change: An intermittent durability test in which the capacitor was turned on for 6 hours at a temperature of 115 ° C. at an ambient temperature of 1 hour and turned off for 2 hours was performed 150 cycles, and the change in capacitance of the capacitor was measured. Judgment was made based on the following criteria. ◎ Very few. ○ Fewer. △ Somewhat large. × Large. Tan δ: A charge test was conducted in which a capacitor was charged with a voltage of 300 V DC and short-circuited with its own stored charge via a 0.5 Ω resistor to measure the dielectric loss. Judgment was made based on the following criteria. ◎ Very small. ○ Small. △
Somewhat large. × Large. Warpage of the element end face: When the shift width of the film in the element was 0.5 mm, the warpage of the film on the end face of the element was visually judged. Judgment was made based on the following criteria. ◎ Very small. ○ Small. △ Somewhat large. × Large.

[0024]

[Table 1]

[0025]

According to the present invention, it is possible to obtain a polypropylene film for a heat-resistant capacitor in which the deformation of the element is reduced at a heat treatment temperature of 120 ° C. at the time of manufacturing the capacitor and the electrical characteristics of the capacitor are improved at a temperature lower than 120 ° C. .

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Claims (2)

[Claims] An isotactic pentad fraction of 96%
Using the above polypropylene, the F5 value in the flow direction is 50 MPa or more and the heat shrinkage in the width direction is 0.1 mm at 120 ° C.
5% or less, at least one surface has a surface roughness Ra of 0.1
A polypropylene film for heat-resistant capacitors, having a thickness of at least μm. 2. The surface roughness Ra of at least one surface is:
The polypropylene film according to claim 1, which has a thickness of 0.1 to 0.2 µm.