JPH06290990A - Metallized polypropylene film for capacitor - Google Patents

Abstract

PURPOSE:To realize a metallized polypropylene film which can provide a capacitor excelling in breakdown voltage and dielectric loss tangent by applying a metallic layer to the surface of a specified polypropylene film and making the thickness of the metallic layer thicker on the edge of the lead takeout side than on the normal part in a heavy edge construction. CONSTITUTION:A polypropylene film 1, the surface atomic ratio of which is that the number of nitrogen atoms/the number of carbon atoms is in the range of over 0.11 and under 0.22 and the number of oxygen atoms/the number of carbon atoms is in the range of over 0.1 and under 0.20, is used. A metallic layer 2 comprising zinc or aluminum alone or two kinds of zinc and aluminum is applied to the surface of this polypropylene film 1. And a heavy edge construction 4 is to be employed where the thickness of this metallic layer 2 so that the edge of the lead takeout side is thicker than a normal part 3. Further, the film resistance of the normal part 3 of this metallic layer 2 is set in a range over 6OMEGA/square and under 50OMEGA/square and the film resistance of the heavy edge part 4 in a range over 1.0OMEGA and under 5.0OMEGA/square.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a metallized polypropylene film for capacitors.

[0002]

2. Description of the Related Art Polypropylene film is widely used as an industrial material because of its excellent properties. Recently, the use of providing a metal layer on a polypropylene film is rapidly increasing due to changes in market demand. Among them, for capacitors, the transition to a metallized polypropylene film in which a film and a metal layer are integrated is remarkable because it can be downsized and can provide self-healing property as compared with a conventional metal foil wound.

An important electrical characteristic of the application is a withstand voltage characteristic. This withstand voltage depends on the thickness of the metal layer, and the thinner the thickness, the higher the withstand voltage characteristic. At this time, in the metallized dielectric for capacitors, the thickness of the metal layer is determined by the film resistance (unit: Ω
/ □) (generally, the higher the film resistance, the thinner the metal layer).

For this reason, various attempts have been made to increase the film resistance, but when the film resistance is increased, the adhesion of the metal layer to the film is reduced, and it becomes difficult to form a uniform and strong metal layer.

Therefore, various studies have been carried out to make up for the drawbacks. For example, JP-A-58-60521 and JP-A-3-83312 propose modification of the film surface by selecting a corona discharge method. Has been done.

[0006]

[Patent Document 1] Japanese Unexamined Patent Application Publication No. Sho 5
In Japanese Patent Laid-Open No. 8-60521, since oxygen atoms are not retained on the surface of the film, sufficient metal adhesion cannot be obtained, and uneven thickness occurs in the metal layer, which is a problem in practical use.

Further, in JP-A-3-83312, when the film resistance is increased to improve the withstand voltage of the capacitor, not only a uniform metal layer thickness cannot be obtained, but also important characteristics of the capacitor. The dielectric loss tangent, which is one of the above problems, became high (worse), which sometimes hindered practical use.

In view of the above problems, the present invention provides a metallized polypropylene film capable of obtaining a capacitor having excellent withstand voltage and dielectric loss tangent.

[0009]

The metallized polypropylene film for capacitors of the present invention has a surface atomic composition ratio of the number of nitrogen atoms / the number of carbon atoms (hereinafter referred to as N / C) of 0.11 or more and 0.22 or less. And the number of oxygen atoms / the number of carbon atoms (hereinafter referred to as O / C) is in the range of 0.01 or more and 0.20 or less, the metal layer is applied to the surface of the polypropylene film, and It is characterized by having a heavy edge structure in which the end portion on the lead take-out side is thicker than the normal portion.

The N / C at the surface of the polypropylene film (normally within 10 nm depth from the surface) is 0.
It is preferably 11 or more and 0.22 or less, and more preferably 0.12 or more and 0.18 or less. If N / C is less than this lower limit, a uniform and strong metal layer cannot be obtained when a film resistance of 10 Ω / □ or more is formed. Conversely, N /
When C exceeds the upper limit of the above range, the static electricity of the film and the metallized film becomes high and the slipperiness deteriorates. As a result, problems such as breakage due to blocking and wrinkles during work such as winding of capacitor elements occur, which impedes practical use.

The O / C is preferably in the range of 0.01 or more and 0.20 or less, more preferably 0.05.
It is above 0.15. If the upper and lower limits are exceeded, N /
It causes the same trouble as in the case of C.

If the surface on which the metal layer is provided is one side, the atomic composition ratio of that surface may be as described above. If the surface on which the metal layer is provided is both surfaces, the atomic composition ratio on both sides is the above. It should be like. Incidentally, when the surface layer on which the metal layer is provided has only oxygen atoms, or vice versa, the adhesion between the film and the metal layer was poor. As a result, defects such as uneven thickness of the metal layer occur.

Further, in the metallized polypropylene film for capacitors of the present invention, the thickness of the metal layer is thicker at the lead-out side end than at the normal part in order to obtain good withstand voltage and dielectric loss tangent of the capacitor. , It must be a heavy edge structure.

That is, it is necessary to increase the film resistance in order to obtain good withstand voltage characteristics, while it is necessary to decrease the film resistance (in particular, the side from which the leads are taken out) in order to obtain good dielectric loss tangent characteristics. . It is generally well known that the higher the membrane resistance, the higher the withstand voltage. This is because the self-healing function peculiar to the metallized dielectric is enhanced as the metal layer is thinner.

On the other hand, it is known that the dielectric loss tangent is lower (better) as the film resistance is lower, but most of them are metal sprayed on the end face of the capacitor element to take out the lead and the metal layer on the film. It is governed by the contact resistance with and the lower the contact resistance, the lower the dielectric loss tangent. This is the reason why it is necessary to thicken the metal layer on the metal spraying side.

Regarding the film resistance of the metal layer, in order to obtain good withstand voltage and dielectric loss tangent of the capacitor, the film resistance of the normal part is 6 Ω / □ or more and 50 Ω / □ or less, and the film resistance of the heavy edge part is 1. It must be in the range of 0Ω / □ to 5.0Ω / □. If the film resistance of the normal part exceeds 50 Ω / □, the dielectric loss tangent becomes high and the performance as a capacitor deteriorates. Further, if the film resistance of the normal portion is less than 6Ω / □, the self-recovery property is deteriorated and the withstand voltage of the capacitor is lowered. Preferably, the membrane resistance of the normal part is 8 Ω / □ or more and 40 Ω /
□ or less, more preferably 10 Ω / □ or more and 35 Ω / □ or less. Also, the film resistance at the heavy edge is 1.0Ω /
If it is less than □, the amount of heat generated at the time of forming and processing the metal layer becomes excessive, causing thermal deformation of the film, which impedes practical use. On the other hand, when it exceeds 5.0 Ω / □, the dielectric loss tangent is deteriorated. Preferably, 1.5Ω / □ or more and 4.5Ω /
□ Below.

The metal constituting the metal layer is zinc or aluminum alone, or a combination of zinc and aluminum. This is because good capacitor characteristics can be obtained and the metal layer can be formed relatively easily. Also, in the case of using zinc alone, it is general to provide a small amount of a different kind of metal serving as a core at the same time for the purpose of improving the metal adhesion. Examples of the nuclear metal include copper, tin, silver and aluminum, but are not particularly limited.

As a method for forming the metal layer, an induction heating type vacuum deposition method, a sputtering method, an ion beam method and the like are exemplified, but the method is not particularly limited.

Polymers of polypropylene film used in the present invention include homopolymers, propylene and other α-
It may be a copolymer with an olefin (eg, ethylene, butene) or a mixture of polypropylene and another α-olefin polymer (eg, polyethylene, polybutene).

The film of the present invention may be an unstretched film, a uniaxially stretched film or a biaxially stretched film, but it is preferable to use a biaxially stretched film which is excellent in processability and dimensional stability at high temperature. . Of course, the stretching method may be either a tenter method or an inflation method.

Surface roughness (Ra) of the film used here
Is preferably 0.02 μm or more and 0.15 μm or less, and more preferably 0.03 μm or more and 0.12 μm or less. Below this lower limit, the slipping of the film becomes poor, so the workability of film processing and element winding is poor, and wrinkles and winding misalignment occur. On the other hand, when Ra exceeds this upper limit, the amount of corona discharge inside the capacitor increases, and the capacitance of the capacitor decreases greatly due to the scattering and disappearance of the metal layer. The surface roughness (Ra) of the polypropylene film tends to increase as the crystallization rate of the raw material increases, the cooling rate when cooling and solidifying the molten polymer decreases, the stretching temperature increases, and the stretching ratio decreases. Yes, these can be appropriately selected and combined to obtain a desired surface.

Alternatively, polypropylene may be added with inorganic or organic particles, or various polymers such as polymethylpentene may be mixed. In general, Ra of these additives increases as the amount of addition increases.

The specifications of the margin of the metallized film of the present invention (the portion without the metal layer provided in the metallized surface for the purpose of electrical insulation) are not particularly limited, and other than the usual type, for example, the TD margin. , An island-shaped metal layer called T-shaped margin may be formed. Of course, the type of capacitor using the film of the present invention is not particularly limited. For example, it may be a wound type, a laminated type, a dry type, or an oil immersion type.

Next, an example of the method for producing the metallized film of the present invention will be described. However, the present invention is not limited to the following manufacturing method.

A polypropylene resin having an isotacticity of 95.0% or more is melted at a temperature of 200 to 290 ° C. and extruded into a sheet form from a slit T-die.
It is cooled and solidified with a chill roll at 5 to 98 ° C. Next 110
Stretching 4 to 7 times in the longitudinal direction at a temperature of 150 ° C., then
Stretched 6 to 12 times in the width direction at a temperature of 145 to 165 ° C.,
Further, heat treatment is performed at a temperature of 150 to 165 ° C. This film is placed in a mixed gas atmosphere of nitrogen and carbon dioxide gas,
Corona discharge treatment is performed on the surface of the film on which the metal layer is provided with an electric energy amount of 00 to 7500 J / m ² . N / C and O / C are greatly influenced by the mixed gas concentration and the electric energy amount of the corona discharge treatment.
In order to obtain / C, the nitrogen / carbon dioxide ratio of the mixed gas is 70
/ 30 to 98/2 is preferable.

This film is set in a vacuum vapor deposition device,
On the corona discharge treated surface of the film, the normal part of zinc is 6
~ 50Ω / □, heavy edge 1.0-5.0Ω / □
It is vapor-deposited so as to have the film resistance of. At this time, a margin is provided along the edge opposite to the heavy edge portion. This vapor-deposited film is slit into, and two sheets of this film are stacked and wound to form a capacitor element. This element is subjected to end face metal spraying, attached with lead wires, and then packaged to form a capacitor.

[0027]

[Characteristic Measuring Method and Evaluation Method] Next, the measuring method and evaluation method used in the present invention will be described.

(1) Atomic composition ratio of film surface layer ESCA spectrometer ES2 manufactured by Kokusai Electric Co., Ltd.
The film surface was measured under the following conditions using a 00 type.

Excitation X-ray: Al K-ray α (1486.6 eV) X-ray output: 10 KV, 20 mA Temperature: 20 ° C. Kinetic energy correction: The kinetic energy value of neutral carbon (> CH ₂ ) was adjusted to 1202.0 eV. It was From the obtained spectrum, the area ratio of the C _1S peak and the O _1S peak was calculated as
The value of O / C was used, and the area ratio of the peak of C _{1S and} the peak of N _{1S was used} as the value of N / C.

(2) Membrane resistance Using a thin film resistance measuring instrument manufactured by Toyo Metalizing Co., Ltd.,
A sample having a width of 50 mm and a length of 250 mm was taken from the central portion in the width direction of the film for the normal part, and a sample having a width of 5 mm and a length of 250 mm was taken from the film edge on the heavy edge side for the heavy edge part and measured.

(3) Dielectric loss tangent LCR meter (Type AG-431) manufactured by Ando Electric Co., Ltd.
Using 1), the dielectric loss tangent was measured under the conditions of a voltage of 1 V and a frequency of 1 KHz in an atmosphere of 25 ° C.

(4) Withstand voltage An AC voltage was applied to the capacitor at a boosting rate of 100 V / sec, and the voltage at which the capacitor was broken was measured.

(5) Element winding property An element winding was carried out in the same manner as in the usual capacitor manufacturing process, and the behavior during the process and the state of the finished element were investigated. The main element winding conditions at this time are as follows.

Element winding machine: KMW-2HC manufactured by Minato Manufacturing Co., Ltd. Element winding speed: 2000 rpm Tensile force: 700 g The determination was as follows.

◯: Good ×: At least one of wrinkles and shifts

(6) Uniformity of Metal Thickness One metallized film was placed on a color viewer made by Uchida, and an area of 2 m ² was visually observed by transmitted light.

The judgment criteria are as follows.

◯: Good ×: Metallic film has uneven density

(7) Surface roughness According to JIS-B-0601. The cutoff is 0.
It was set to 25 mm.

[0040]

EXAMPLES Next, the present invention will be explained based on examples.

Example 1 A polypropylene resin having an isotactic index (II) of 97.0% was melted at an extruder temperature of 255 ° C., extruded through a slit T-die, and cooled and solidified by a chill roll at 50 ° C. After that, the sheet is lengthwise 13
Stretched 4.7 times at a temperature of 0 ° C., then 155 in the width direction
The film was stretched 9 times at a temperature of ° C and further heat-treated at a temperature of 160 ° C to obtain a polypropylene film having a thickness of 6 µm. The nitrogen / carbon dioxide volume ratio on one side of this film is 90 /
In a mixed gas atmosphere of 10, corona discharge treatment was performed with an electric energy amount of 5000 J / m ² . This film was set in a vacuum vapor deposition machine, and copper was used as a nucleating metal on the surface that had been subjected to corona discharge treatment, and the film resistance of the normal part was 15Ω / □ and the film resistance of the heavy edge part was 2.5Ω / □. Zinc was vapor-deposited so that After slitting this film, the element is wound to make a capacitor element, and the end face of the element is subjected to metal spraying,
The lead was taken out from this sprayed metal. Next, potting was performed with an epoxy resin to obtain a capacitor. At this time,
The capacitance of the capacitor was 10 μF.

The metallized polypropylene film and the capacitor were evaluated.

Example 2 The same procedure as in Example 1 was carried out except that the vapor deposition metal was a mixture of zinc and aluminum. The zinc weight ratio of the metal layer at this time was 95%.

Example 3 The electric energy amount of corona discharge treatment was 3000 J / m ^2.
Example 1 was repeated except that

Example 4 Example 4 was carried out in the same manner as in Example 1 except that the film resistance of the normal part was 10 Ω / □.

Example 5 Example 5 was carried out in the same manner as in Example 1 except that aluminum was used as the vapor deposition metal.

Comparative Example 1 The amount of electric energy in corona discharge treatment was 800 J /
It was carried out in the same manner as in Example 1 except that m ^{2 was used} and the treatment was performed in an air atmosphere.

Comparative Example 2 The amount of electric energy of corona discharge treatment was 8000 J / m ^2.
Example 1 was repeated except that

Comparative Example 3 The procedure of Example 1 was repeated except that the film resistance of the normal part was 55 Ω / □ and the film resistance of the heavy edge part was 6.5 Ω / □.

Comparative Example 4 The procedure of Example 1 was repeated except that the film resistance of the normal part was 5Ω / □ and the film resistance of the heavy edge part was 0.8Ω / □.

Comparative Example 5 Both the film resistance of the normal part and the film resistance of the heavy edge part were 10
The same procedure as in Example 1 was carried out except that Ω / □ was used.

Examples 1 to 5, Comparative Examples 1 to 5
The results are shown in Table 1.

[0053]

[Table 1]

[0054]

According to the present invention, it is possible to obtain a metallized polypropylene film for a capacitor which can achieve a capacitor having good withstand voltage characteristics, dielectric loss tangent characteristics, and capacity change rate. The metallized polypropylene film of the present invention is excellent in the uniformity of the metal layer and the workability such as element winding.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a cross section of a metallized polypropylene film for capacitors of the present invention.

[Explanation of symbols]

 1: Polypropylene film 2: Metal layer 3: Normal part 4: Heavy edge part 5: Margin

Claims (1)

[Claims] 1. The surface atomic composition ratio is such that the number of nitrogen atoms / the number of carbon atoms is in the range of 0.11 to 0.22 and the number of oxygen atoms / the number of carbon atoms is 0.01 to 0.2.
The surface of the polypropylene film in the range of 0 or less is coated with a metal layer consisting of zinc or aluminum alone or two kinds of zinc and aluminum, and the thickness of the metal layer is larger than that of the normal portion at the end on the lead take-out side. A thicker edge structure, and the film resistance of the normal part of the metal layer is 6Ω / □ or more and 50Ω / □ or less, and the film resistance of the heavy edge part is 1.0Ω / □ or more and 5.0Ω / □ or less. Metallized polypropylene film for capacitors, which is in the range.