JPH04165063A - Production of metallized polypropylene film for capacitor - Google Patents

Abstract

PURPOSE:To easily produce a metallized PP film for the capacitor excellent in dielectric strength and adhesion to a metal vapor-deposited layer by treating an extremely thin biaxially oriented PP film with specified low-temp. plasma and then forming the metal vapor-deposited layer. CONSTITUTION:An inorg. gas contg. 5-50% oxygen is passed over the surface of a biaxially oriented PP film having 4-10mum thickness at 0.005-5Torr vacuum to treat the surface with low-temp. plasma. The treatment is performed by impressing a high-frequency power at several hundred kHz to several MHz, and the power at about 1-25kW per area of the film to be treated is preferably impressed. The wetting index of the treated surface is controlled to 38-50 in this way. Al, Zn, Cu, a Zn-Al alloy, etc., are then vapor-deposited thereon. Consequently, the variance in thickness of the effective layer of the film dielectric layer is reduced, the adhesion of the metal vapor-deposited layer is enhanced, and a metallized PP film for the capacitor with the dielectric strength made constant is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a metallized polypropylene film for capacitors, and in particular to a method for manufacturing a metallized polypropylene film for capacitors, in particular, a method for manufacturing a metallized polypropylene film for use in a capacitor, and in particular, a method for manufacturing a metallized polypropylene film for use in a capacitor. This invention relates to a method for producing a metallized polypropylene film for capacitors that has excellent adhesion, high voltage resistance, and little variation in quality.

(Prior technology) - Plastic film capacitors were not used in fixed capacitors until now because it was difficult to obtain thin, heat-resistant films, but recently, ultra-thin plastic films have begun to be manufactured. Therefore, development of applications in this direction has been progressing.

In particular, biaxially oriented polypropylene film (hereinafter referred to as "biaxially oriented").

OPP film) has low dielectric loss, relatively high temperature resistance, and can be made as thin as 4 μm, so it is used as a dielectric layer for capacitors, such as small fixed capacitors and oil-impregnated capacitors. It's starting to look like this.

In this case, the electrode layer is made of vapor-deposited aluminum, zinc, or a mixture thereof, but the adhesion between the film dielectric layer and the vapor-deposited metal layer is poor, and when it is immersed in insulating oil, There were drawbacks such as the vapor deposited layer peeling off from the film surface and the vapor deposited metal layer scattering and falling off due to partial discharge of the capacitor when high voltage was applied.

Therefore, in order to solve this problem, the applicant first performed corona treatment or plasma treatment on the surface of the PP film to form fine irregularities on the film surface, and developed a method to increase the adhesion by increasing the surface area. (Japanese Patent Application No. 2-203041), but the ultra-thin O with a thickness of 4 to 10μ
When PP film is subjected to strong surface treatment to increase adhesion, the thickness of the effective layer of the film dielectric layer varies, which causes good adhesion but large variations in the dielectric strength of the capacitor, making it difficult to use. There was a problem that it could not withstand.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to reduce the variation in the thickness of the effective layer of the film dielectric layer in an ultra-thin OPP film with a thickness of 4 to 10 μm, The adhesion between the film surface and the metal vapor deposited layer is high, and the dielectric strength of the resulting capacitor can be kept constant. An object of the present invention is to provide a method for manufacturing a metallized polypropylene film for a capacitor.

(Means for Solving the Problems) A method for manufacturing a metallized polypropylene film for a capacitor according to the present invention provides a biaxially oriented polypropylene film having a thickness of 4 to 10μl, which is coated with at least 5 to 500 μl under a reduced pressure of 0.005 to 5 Torr. The method is characterized in that low temperature plasma treatment is performed while passing an inorganic gas containing 50% oxygen to a wettability index of 38 to 50 on the treated surface, and then a metal vapor deposited layer is formed thereon.

To explain this, as a result of intensive research to solve the above-mentioned problem, the inventors of the present invention preliminarily coated the surface of an ultrathin biaxially stretched polypropylene film with a thickness of 4 to 10 μ
After performing low temperature plasma treatment under a reduced pressure of 5 to 5 Torr while passing inorganic gas containing at least 5 to 50% oxygen to bring the wettability index of the treated surface to 38 to 50, the treated surface is further coated with: When depositing A1, Zn, Cu, Sn, Zn-Al alloy, etc., the dielectric strength is the same as the original thickness of the film because there is little variation in the effective layer thickness of the film dielectric layer, and the film The inventors have discovered that it is possible to obtain a metalized polypropylene film for capacitors with excellent quality and stability in which the surface and the metal vapor-deposited layer are in close contact with each other, and the present invention has been achieved.

In the plasma treatment according to the method of the present invention, the OPP film is installed in a plasma treatment apparatus capable of reducing pressure, and the pressure is 0.00.
This is carried out by applying high frequency power, for example, at a frequency of several hundred KHz to several MHz, between the electrodes while passing an inorganic gas containing at least 5 to 50% oxygen under conditions of 5 to 5 Torr.

Components other than oxygen of the above inorganic gas include He, Ne, and A.
There are r, H,, N, Co, Co, etc., and these are used alone or in a mixture of two or more types.

The gas pressure is 0.005 to 5 torr, preferably 0.00 to 1 torr, and if the gas pressure is less than 0.005 torr or more than 5 torr, it may be difficult to generate plasma or damage the film due to abnormal discharge, etc. This results in a decrease in film strength, generation of pinholes, thermal deformation, and accompanying deterioration in the electrical properties of the film.

In addition, the irradiation time of the low temperature plasma is preferably within 30 seconds, especially within 15 seconds; outside this range, the same phenomenon as above occurs, so it is not preferable (as a 1° low temperature plasma generator, the internal electrode There are various types such as type, external electrode type, coil type, capacitive coupling, and inductive coupling, but among these, the internal electrode type is preferable because it is excellent in short-time processing or processing of long objects.

In addition, regarding the power applied between the electrodes, if it is too large, the film will be deformed and deteriorated due to heat generation, which is undesirable.
As mentioned above, it is preferable to control the voltage to less than 25 kV/m2.

At 25 kV/m" or more, the wetting index of the obtained film surface becomes 50 or more, resulting in an excessively rough surface, and at 1 kV/m"
If it is less than 38, the wetting index will be 38 or less, and the deposited metal will easily peel off.

This treatment makes it possible to maximize the effective layer thickness of the dielectric layer of the film.

That is, when a dielectric with a dielectric constant E exists between the electrodes,
The capacitance C of the capacitor is expressed as c=ts/L[F], where S is the electrode area [m2] and L is the inter-electrode spacing [m].

Further, if the thickness of the film is t and the amount of change in thickness due to plasma treatment is Δt, then L=t −Δtc=tS/t−Δt (F) Dielectric strength kV/
By minimizing Δt, the size of the m layer can be increased without changing the capacitor tray.

By performing low-temperature plasma treatment under the above conditions, the above-mentioned surface has a wettability index of 38 to 50. Preferably 40-45
OPP film is obtained, and when metal evaporation is performed using this OPP film, not only the adhesion with the metal evaporation layer is significantly improved, but also the metallized polypropylene for capacitors has high dielectric strength and electrical properties with little variation. A film is obtained.

In addition, the material of the metal layer includes A1. Zn, Cu,
Examples include Sn, Zn-Al alloy, etc., and A1 or Zn-Al alloy is particularly preferred for use in capacitor films.

Hereinafter, specific embodiments of the present invention will be explained with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Example) After installing an OPP film with a thickness of 4 μm into a low-temperature plasma processing apparatus, the pressure inside the apparatus was reduced to 0.002). In this state, ventilate dry air and reduce the pressure to 0.05.
After adjusting and holding the film at a constant temperature, a high-frequency power of 13.56 MHz was applied at 3 kv/m and plasma treatment was performed at room temperature for about 4 seconds. A sample was taken from this film and the wettability index was measured. )Met.

Next, this film was vacuum evaporated using an electron beam method, and a Zn-Al alloy (Zn
A metal layer with a content of 5%) was formed to produce a metallized OPP film.

When the adhesion of this metal vapor deposited layer was measured by the tape peel test described below, no peeling was observed. In addition, the dielectric strength of the metallized OPP film was measured and the result was 32 ± 0.
．． It was 5 kV/am (n = 10).

-Tape peeling test: After cutting the metal-deposited surface vertically and horizontally at 1 cm intervals with a sharp knife, the tape is suddenly peeled off and the adhesion is evaluated.

(Comparative example) After installing an OPP film with a thickness of 4 μm into the low temperature plasma processing equipment as in the example, the pressure inside the equipment was reduced to 0.002 μm.
The pressure was reduced to torr. In this state, argon gas is vented,
After adjusting and holding the pressure at 0.05 Torr, 110kHz,
Plasma treatment was performed for approximately 3 seconds by applying a power of 20 to 111/m" per anode. When the surface of this OPP film was observed using an electron microscope, it was found that the diameter was 0.01 to 0.05.
Since the presence of unevenness with a density of 1,000 to 2,000 pieces/m was confirmed, a sample was taken from this film and the wettability index was measured and found to be 54 (n=10).

This film was vacuum-deposited by an electron beam method to form a metal layer of Zn-A 1 alloy (Zn content 5%) with a thickness of 0.05 μm on the surface, thereby producing a metalized OPP film.

When the adhesion of this metal vapor deposited layer was measured by the same tape peel test as in the example, no peeling was observed. In addition, the results of measuring the dielectric strength of metallized OPP film are as follows:
It was 30±5 kV/mm (n=10).

Comparing these results with the Examples, it was found that the present invention is superior.

(Effects of the Invention) According to the present invention, it is possible to easily obtain a metallized film for capacitors that has excellent dielectric strength and adhesion to a metal vapor deposited layer by taking advantage of the unique characteristics of an ultra-thin biaxially stretched polypropylene film. can.

Claims (1)

[Claims] 1. A biaxially oriented polypropylene film with a thickness of 4 to 10 μm is coated with at least 5 to 5
Low-temperature plasma treatment is performed while passing inorganic gas containing 0% oxygen, and the wettability index of the treated surface is 38 to 50.
1. A method for producing a metallized polypropylene film for a capacitor, the method comprising: forming a metallized polypropylene film thereon;