JPH11273991A - Polypropylene film for capacitor and capacitor consisting of the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase high-temperature machining property and to improve electrical characteristics such as the breakdown voltage characteristics of a capacitor at a high temperature by making specific a heat shrinkage rate in the longitudinal direction, a heat shrinkage rate in the width direction, a strength on 100% extension in the longitudinal direction, and a mesopentad percentage. SOLUTION: In a polypropylene film, a heat shrinkage rate in the longitudinal direction is set to approximately 3.0% or less, and that is the width direction is set to approximately 0% or more and approximately 1.0% or less. Also, strength on 100% extension ion the longitudinal direction of the film is set to approximately 8.0 kg/mm<2> or more. Further, the mesopentad percentage of the polypropylene film is set to approximately 98.0% or more. Also, at least one surface of the polypropylene film is metallized. At this time, surface treatment such as corona discharge treatment is made to the surface where the film is metallized, thus improving a deposition machining property and a high-temperature machining property in the manufacturing process of a capacitor, simplifying the manufacturing process, and improving the electrical characteristics of withstand voltage and the like.

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, a metallized film for a capacitor which is excellent in high-temperature workability in a vapor deposition process and a capacitor manufacturing process, and has excellent heat and withstand voltage, and a film formed of at least a dielectric material. Related to the capacitor used in part of the above.

[0002]

2. Description of the Related Art A polypropylene film is widely used as a dielectric material or an insulator material in electrical applications because of its excellent electrical characteristics. Above all, the range of use as a dielectric material for capacitor applications is wide, and the demand for the material is growing remarkably.

[0003] The polypropylene film used for such a capacitor is increasingly required to be thinner in order to reduce the size and weight of the capacitor, and to be more stable when processed or used at high temperatures.

[0004] For this reason, in order to improve the vapor deposition processability, which is one of high temperature processes, for example, Japanese Patent Application Laid-Open No.
In Japanese Patent Publication No. 2 (1994), a method for defining the thermal behavior of a polypropylene film under a certain load is proposed. Further, Japanese Patent Application Laid-Open No. 2-170406 proposes a method for defining a friction coefficient at a high temperature.

[0005]

However, in these prior arts, for example, in Japanese Patent Application Laid-Open No. 1-144422, sufficient dimensional stability is not always required in a capacitor manufacturing process in which a higher temperature is imposed on a film than in a vapor deposition process. Was not obtained. In addition, Japanese Unexamined Patent Publication
In JP-A-170406, the dimensional stability in the manufacturing process of the capacitor is insufficient due to the further thinning, and the satisfactory electrical characteristics of the capacitor were not necessarily sufficiently satisfied.

Accordingly, the present invention provides a polypropylene film for a capacitor and a capacitor which are excellent not only in a vapor deposition process but also in high-temperature workability in a capacitor manufacturing process and are excellent in electrical characteristics such as withstand voltage characteristics of a capacitor at a high temperature. That is the task.

[0007]

In order to achieve the above object, a polypropylene film for a capacitor according to the present invention comprises:
The heat shrinkage in the length direction is 3.0% or less, the heat shrinkage in the width direction is 0% or more and 1.0% or less, and 10% in the length direction.
The strength at 0% elongation is 8.0 kg / mm ² or more, and the mesopentad fraction is 98.0% or more.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the heat shrinkage in the length direction must be 3.0% or less. If it exceeds 3.0%, wrinkles due to the heat received from the metal deposited during the vapor deposition processing are apt to occur, and the capacitor lacks dimensional stability in a high-temperature process such as heat treatment during the production of the capacitor, and stable capacitor characteristics cannot be obtained. It is preferably at most 2.7%, more preferably at most 2.5%.

Further, the heat shrinkage in the width direction of the polypropylene film of the present invention needs to be 0% or more and 1.0% or less. In a high-temperature process such as heat treatment during the production of a capacitor, if the content is less than 0%, the film elongates, so that the deposited metal cracks and the deposited film resistance increases, thereby deteriorating the dielectric loss tangent characteristics of the capacitor. If it exceeds, the end face of the capacitor element is curled, and the contact resistance with the metallikon metal increases, which further deteriorates the dielectric loss tangent of the capacitor, so that stable capacitor characteristics cannot be obtained. Preferably it is 0% or more and 0.7% or less, more preferably 0.1% or more and 0.5% or less.

The strength at the time of 100% elongation in the length direction of the polypropylene film of the present invention must be 8.0 kg / mm ² or more. If it is less than 8.0 kg / mm ² , the tensile strength is insufficient at the time of the vapor deposition processing, so that wrinkles are generated and productivity and economy are deteriorated. Preferably 10.0 kg /
mm ² or more, more preferably 12.0 kg / mm
² or more.

Further, the mesopentad fraction of the polypropylene film of the present invention must be 98.0% or more. The mesopentad fraction is the ratio of the isotactic tertiary structure to the whole, and is measured by ¹³ C-NMR. If the meso pentad fraction is less than 98.0%, not only the workability at high temperatures but also the high-temperature electrical characteristics of the capacitor may decrease. It is preferably at least 98.5%, more preferably at least 99.0%.

The additives and other polymers contained in the polypropylene film of the present invention may be appropriately selected and added according to the purpose, and are not particularly limited. Speaking of the examples of the phenolic antioxidant most frequently used as an additive, the amount of the phenolic antioxidant is preferably 0.02 wt% or more and 0.60 wt% or less. If it is less than 0.02 wt%, the antioxidant effect may be insufficient, and 0.60 wt%
If it exceeds, the insulation resistance may decrease.

Examples of phenolic antioxidants include tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane and 1,3,5 trimethyl-2,4,6- Tris (3,
5-di-tert-butyl-4-hydroxybenzyl) benzene, n-octadecyl-3- (4'-hydroxy-3 ', 5'-di-tert-butyl-phenyl) propionate, 2,2-thio [diphenyl -Bis-3 (3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, tris (2,4-di-
Tertiary-butylphenyl) phosphite, etc., which may be used alone or in combination of two or more. Among them, tetrakis [methylene-3 (3,5-diene) exhibiting good electric characteristics. -Tert-butyl-4
-Hydroxyphenyl) propionate] methane or 1,3,5 trimethyl-2,4,6-tris (3,5
-Di-tert-butyl-4-hydroxybenzyl) benzene is more preferred.

Furthermore, the polypropylene film of the present invention may be obtained by a tenter method or an inflation method, and may be a single layer or a composite. The tenter method and the biaxial stretching are preferred from the viewpoint of the above.

The ash content of the polypropylene film of the present invention is preferably 30 ppm or less from the viewpoint of withstand voltage characteristics.

Further, if the center line surface roughness Ra of the polypropylene film of the present invention is too small, it becomes difficult to slip, which may hinder its handling and workability, and if it is too large, the minimum thickness of the film becomes thin. Since the withstand voltage characteristics may be degraded, 0.02 μm or more and 0.20 μm
m or less.

The specification of the capacitor made of the polypropylene film of the present invention is not particularly limited.
For example, a dry type or an oil impregnated type may be used, and a flat type or a round type may be used. However, a flat type having a hot pressing step in manufacturing a capacitor is more suitable.

The field of the capacitor made of the polypropylene film of the present invention is not limited either. For example, the field may be an AC field, a DC field, or a high frequency field.

The electrode used in the capacitor made of the polypropylene film of the present invention is not particularly limited, and even if it is a metal foil such as an aluminum foil, the electrode is directly formed on the film by a metal deposition method or a sputtering method. A metallization method for forming may be used.

Examples of the metal used in the metallization method include aluminum, zinc, copper, tin, nickel, silver and the like singly or in combination, and are not particularly limited. From the viewpoints such as above, aluminum, zinc and copper are preferably used alone or in combination.

The margin specification in the case of metallization is not particularly limited, and may be a normal specification or a special specification such as division according to the purpose of providing a security function.

When an electrode is directly formed on a film by a metallization method or the like, a surface treatment such as a corona discharge treatment may be performed on the surface of the film on which an electrode layer is to be provided. In the case where one side is metallized, the curl of the metallized film is reduced by performing corona discharge treatment on the inner surface of the curl of the film and metallizing the surface.

Next, an example of a preferred method for producing a film and a capacitor according to the present invention will be described, but is not particularly limited.

A polypropylene resin having a mesopentad fraction of 98.0% or more and an intrinsic viscosity [η] of 1.6 to 2.3 is supplied to an extruder having a temperature of 220 to 270 ° C. to be melted and slit. It is extruded into a sheet form from the T die thus formed, and cooled and solidified by a cooling roll at a temperature of 20 to 95 ° C.
At this time, the thermal contraction rate decreases as the intrinsic viscosity [η] decreases, and the surface roughness increases as the cooling solidification temperature increases.

Next, the film is stretched 3 to 6 times in the longitudinal direction at a temperature of 100 to 150 ° C. Next, the film is stretched 6 to 12 times in the width direction at a temperature of 140 to 165 ° C. At this time, the lower the stretching temperature, the higher the heat shrinkage, and the higher the stretching ratio, the greater the strength at 100% elongation in the length direction. Thereafter, heat treatment is performed at a temperature of 140 to 165 ° C. The lower the heat treatment temperature, the higher the heat shrinkage.

The thus obtained polypropylene film is wound by a winder.

Next, the measurement method and the evaluation method used in the present invention will be described.

(1) Mesopentad fraction (mmmm) A sample was dissolved in o-dichlorobenzene / benzene-D6, and JNM-GX27 manufactured by JEOL Ltd. (JEOL) was dissolved.
0 device, at a resonance frequency of 67.93 MHz and ¹³ C-
NMR was measured. Regarding the assignment of the obtained spectrum and the calculation of the pentad fraction, see T.W. The method performed by Hayashi et al. [Polymer, 29, 138 (198)
8)], m
Each peak was assigned with the mmmmmm peak being 21.885 ppm, the peak area was determined, and the ratio to the total peak area derived from the methyl group was expressed as a percentage.

Measurement solvent: o-dichlorobenzene (90 w
t%) / benzene-D6 (10 wt%) Measurement concentration: 15 to 20 wt% Measurement temperature: 120 to 130 ° C. Resonance frequency: 67.93 MHz Pulse width: 10 μsec (45 ° pulse) Pulse repetition time: 7.091 sec Data points: 32K Integration frequency: 8168 Measurement mode: Noise decoupling

(2) Intrinsic viscosity [η] Measured in tetralin according to ASTM D 1601, expressed in dl / g.

(3) Strength at 100% elongation in the length direction According to JIS-C-2330, 6.3.3 tensile strength,
The strength at 100% elongation was determined.

(4) Heat shrinkage ratio According to 6.3.4 of JIS-C-2330.

(5) Evaporation workability Zinc was evaporated using a ULVAC vacuum evaporation machine, and the occurrence of wrinkles was examined. The film is 630mm in width and 300 in length
Cut and wound to a thickness of 00 m, and the specification of the vapor deposition product was 30 mm in width, 1.0 mm in margin width, and the film resistance was 3.5 Ω /.
□, 20 reels in the width direction and 5 divisions in the length direction, and a total of 100 reels were sampled and expressed by the wrinkle defect rate.

Wrinkle defect rate (%) = (number of wrinkled reels /
100 reels) x 100

(6) High temperature processability of capacitor element Of the vapor-deposited product obtained in the above (5), using a pair of wrinkles-free reels, winding the element by a conventional method, and heating the element at a temperature of 120 ° C. A capacitor element was prepared by hot pressing at a pressure of 20 kg / cm ² . Metallicon was applied to the end faces of the five capacitor elements, and the dielectric loss tangent of 1 V and 1 KHz was measured.
The average was determined. The capacitance of the capacitor element after pressing was 30 μF.

(7) Withstand Voltage of Capacitor An AC voltage of 50 is applied to the five capacitor elements obtained in (6) above.
The voltage was applied at a rate of 0 V / sec, and the average value of the breakdown values was determined. However, the measurement temperature was 80 ° C.

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

[0038]

Example 1 A polypropylene resin having a mesopentad fraction of 99.0% and an intrinsic viscosity [η] of 1.9 was added to tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxyphenyl). ) Propionate] methane 0.4 wt%
The mixture is supplied to an extruder at a temperature of 240 ° C., melted, extruded into a sheet from a slit T die,
It was cooled and solidified by a cooling roll at a temperature of 80 ° C.

Next, the film was stretched 5.0 times in the length direction at a temperature of 140 ° C., and then stretched 9.0 times in the width direction at a temperature of 160 ° C. After that, heat treatment is performed at a temperature of 150 ° C.
After performing corona discharge treatment on one side, it was wound up with a winder. The thickness of the thus obtained polyprofin film was 4 μm, the heat shrinkage in the length direction was 2.2%, and the heat shrinkage in the width direction was 0.2%. The strength at the time of 100% elongation in the length direction of the film was 12.5 kg / mm ² .

This film is slittered to a width of 630 m.
m, cut into a length of 30,000 m, and wound on a 6-inch core. The film was zinc-deposited by a ULVAC vacuum deposition machine, and the occurrence of wrinkles was examined. Evaporation product specifications are width 30mm, margin width 1.0mm, film resistance 3.5Ω /
□ and divided into 20 reels in the width direction and 5 in the length direction, and finished into a vapor deposition product having a total of 100 reels. The wrinkle defect rate is 0
%Met.

A pair of evaporated product reels is wound by an element winding machine, and the element is wound at a temperature of 120 ° C. and 20 kg / cm ^2.
To produce a capacitor element. Metallicon is applied to the end faces of the five capacitor elements, and 1V,
The dielectric loss tangent at 1 KHz was measured. The average value is 0.0
15%. The capacitance of the capacitor element after pressing was 30 μF.

Next, at a temperature of 80 ° C., an AC voltage was applied to the five capacitor elements at a step-up rate of 500 V / sec, and the breakdown value was examined. The average value was 1400V. Table 1 shows the results.

Example 2 The same as Example 1 except that a polypropylene resin having a mesopentad fraction of 98.0% was used. Although the withstand voltage of the capacitor was slightly low at 1100 V, there was no practical problem. Table 1 shows the results.

Example 3 The same as Example 1 except that the stretching temperature in the length direction was 135 ° C. and the stretching temperature in the width direction was 155 ° C. The heat shrinkage in the length direction is 2.8%, and the heat shrinkage in the width direction is 0.7%. In the film after vapor deposition, both ends thereof lose heat, so that the film slightly rises and becomes wrinkles, and the wrinkle defect rate is 5%. Although the dielectric loss tangent of the capacitor was as high as 0.028%, there was no practical problem. Table 1 shows the results
Shown in

Example 4 Example 1 was repeated except that the stretching ratio in the length direction was 4.7 times.
Same as 10.0k strength at 100% elongation in the length direction
g / mm ² , which was rather low, so that small wrinkles were generated in the film after vapor deposition, and the wrinkle defect rate was as large as 8%, but there was no practical problem. Table 1 shows the results.

Comparative Example 1 The same as Example 1 except that a polypropylene resin having a mesopentad fraction of 97.5% was used. Since the heat shrinkage ratio was high, the swelling at both ends of the film after the vapor deposition was large, and the wrinkle defect rate was 12%. The dielectric loss tangent was 0.053%, which was a practically problematic value.
The breakdown voltage was only 700 V in the withstand voltage of the capacitor, which was unsuitable for practical use. Table 1 shows the results.

Comparative Example 2 The same as Example 1 except that a polypropylene resin having an intrinsic viscosity [η] of 2.3 was used and the stretching temperature in the width direction was 155 ° C. The heat shrinkage in the length direction was 3.5%, and the heat shrinkage in the width direction was 1.2%. In the film after vapor deposition, the swelling at both ends was extremely large, and the wrinkle defect rate was 18%. . The dielectric loss tangent of the capacitor is 0.186%
It was too high to be practical. Table 1 shows the results.

Comparative Example 3 The same as Example 1 except that the stretching ratio in the length direction was 4 times. Strength at the time of 100% elongation in the length direction is 7.1 kg / m
m ^2, and the wrinkle defect rate was 27%, which was not practical. Table 1 shows the results.

[0049]

[Table 1]

[0050]

The polypropylene film for a capacitor of the present invention is excellent in vapor deposition workability and high-temperature workability in a capacitor manufacturing process, so that the manufacturing process of the capacitor can be simplified and electric characteristics such as withstand voltage characteristics can be improved. Are better.

Also, by using a capacitor, it is possible to use, for example, a resin which cures at a higher temperature as the exterior resin of the capacitor. Was obtained.

Claims (3)

[Claims] The heat shrinkage in the length direction is 3.0% or less, the heat shrinkage in the width direction is 0% or more and 1.0% or less, and the strength at 100% elongation in the length direction is 1. A polypropylene film for capacitors, having a weight of 8.0 kg / mm ² or more and a mesopentad fraction of 98.0% or more. 2. A metallized polypropylene film for a capacitor, wherein at least one side of the polypropylene film according to claim 1 is metallized. 3. A capacitor using the polypropylene film according to claim 1 at least as a part of a dielectric.