JPH07156263A - Polystyrene-based film for capacitor - Google Patents

Abstract

PURPOSE:To obtain a syndiotactic polystyrene-based film for a capacitor, or more concretely, one which is favorable in electrical characteristics and heat resistance and excellent in dielectric breakdown voltage and thickness uniformity. CONSTITUTION:This film is made of a styrene-based polymer having the mean refractive index ranging from 1.582 or more to 1.590 or less and the contraction percentage at 150 deg.C of 3% or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a syndiotactic polystyrene film for a capacitor, and more specifically, a polystyrene film for a capacitor which has good electrical characteristics and heat resistance, excellent dielectric breakdown voltage and excellent thickness uniformity. It is about.

[0002]

2. Description of the Related Art A biaxially stretched film obtained by biaxially stretching and heat-fixing a resin composition containing a syndiotactic polystyrene-based polymer as a main component is excellent in heat resistance and electric properties and is developed as a dielectric for a film capacitor. (Japanese Patent Laid-Open No. 2-1438
51, JP-A-3-124750, JP-A-5-200858).

[0003]

However, in these conventional syndiotactic polystyrene films, the dielectric breakdown voltage is defective, or the variation in the dielectric breakdown voltage due to an increase in the unevenness of the film or the variation in the capacitance after being formed into a capacitor. It turned out to occur. When the dielectric breakdown voltage becomes defective, it is necessary to make the film thick, resulting in a problem that the volume of the capacitor becomes large. Further, it was found that there is a problem that the reliability of the capacitor cannot be obtained when the variations in the capacitance and the breakdown voltage are large. An object of the present invention is to provide a polystyrene-based film for a capacitor, which has good electric characteristics and heat resistance, excellent dielectric breakdown voltage, and excellent thickness uniformity.

[0004]

Means for Solving the Problems The polystyrene film of the present invention is made of a styrene polymer having a syndiotactic structure and has an average refractive index of 1.582 or more and 1.590 or less, and has good electrical properties and heat resistance. The present invention provides a polystyrene-based film for capacitors, which has excellent dielectric breakdown voltage and thickness uniformity.

The polystyrene-based polymer having stereoregular syndiotactic structure used in the present invention has a tacticity in which the side chain phenyl group or substituted phenyl group is quantified by a nuclear magnetic resonance method, which is a diad (constituent unit). 85% or more for 2) and 50 for pentad (5 units)
It is desirable that the structure has a syndiotactic structure of not less than%.

Examples of the polystyrene polymer include polystyrene, poly (p-, m- or o-methylstyrene), poly (2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene. ), Poly (alkylstyrene) such as poly (p-tertiarybutylstyrene), poly (p-, m- or o-chlorostyrene),
Poly (halogenated styrene) such as poly (p-, m- or o-bromostyrene), poly (p-, m- or o-fluorostyrene), poly (o-methyl-p-fluorostyrene), poly ( p-, m- or o-chloromethylstyrene) and other poly (halogen-substituted alkylstyrenes), poly (p-, m- or o-methoxystyrene), poly (p-, m- or o-ethoxystyrene), etc. Poly (alkoxystyrene), poly (p-, m-
Or poly (carboxyalkylstyrene) such as o-carboxymethylstyrene), poly (alkyletherstyrene) such as poly (p-vinylbenzylpropylether), poly (alkylsilylstyrene) such as poly (p-trimethylsilylstyrene), Examples include poly (vinylbenzyldimethoxyphosphide) and the like.

In the present invention, polystyrene is particularly preferable among the polystyrene polymers. Also,
The polystyrene polymer having a syndiotactic structure used in the present invention is not necessarily a single compound, and if the syndiotacticity is within the above range, a polystyrene polymer having an atactic structure or an isotactic structure is used. It may be a mixture of, a copolymer and a mixture thereof. The polystyrene-based polymer used in the present invention has a weight average molecular weight of 10,000 or more, more preferably 50,000 or more. If the weight average molecular weight is less than 10,000, it is not possible to obtain a film having excellent strength and elongation characteristics and heat resistance. The upper limit of the weight average molecular weight is not particularly limited, but if it is 1500,000 or more, breakage occurs due to an increase in stretching tension, which is not preferable.

The syndiotactic polystyrene-based polymer used in the present invention may contain, if necessary, known compounds such as antioxidants, antistatic agents, and fine particles for imparting slipperiness. it can. The compounding amount is based on 100% by weight of the syndiotactic polystyrene polymer.
10% by weight or less is desirable. If it exceeds 10% by weight, breakage easily occurs during stretching, resulting in poor production stability.

The fine particles include, for example, metal oxides such as silica, titanium dioxide, talc, kaolinite and zeolite, salts of metals such as calcium carbonate, calcium phosphate and barium sulfate, or organic polymers such as silicone resins and crosslinked polystyrene. The addition of particles and the like is exemplified.
These fine particles may be used alone or in combination of two or more, but the average particle size of the fine particles used is 0.01 μm or more and 2.0 μm or less, and particularly, 0.
The thickness is preferably 05 μm or more and 1.5 μm or less, and the degree of variation in particle size (ratio between standard deviation and average particle size) is preferably 25% or less. The addition amount is preferably 0.005% by weight or more and 2.0% by weight or less, particularly 0.1% by weight or more and 1.0% by weight, based on 100% by weight of the syndiotactic polystyrene polymer.
The following are preferred.

The above-mentioned average refractive index is adjusted by the film forming conditions. The production conditions are not particularly limited as long as the average refractive index of the obtained film is within a predetermined range, and for example, a sequential biaxial stretching method in which longitudinal stretching and transverse stretching are performed in order, as well as a transverse / longitudinal / longitudinal stretching method. , Longitudinal / transverse / longitudinal stretching method,
A stretching method such as a longitudinal / longitudinal / horizontal stretching method can be adopted, and the stretching method is selected according to various characteristics such as required strength and dimensional stability. Further, heat setting treatment, vertical relaxation treatment, lateral relaxation treatment, etc. can be performed. In particular, the film forming conditions as shown in the examples are preferable, and the present invention can be achieved. Further, in order to improve the adhesive property and the like of the vapor deposition layer, an adhesive layer can be provided by in-line coating or off-line coating, corona treatment or flame plasma treatment can be performed.

The average refractive index of the polystyrene film of the present invention is 1.582 or more, more preferably 1.584 or more.
If the average refractive index is less than 1.582, the dielectric breakdown voltage becomes poor. The upper limit of the average refractive index is 1.590 or less, more preferably 1.589 or less. When the average refractive index is larger than 1.590, the thickness unevenness becomes large, the fluctuation of the absolute value of the breakdown voltage of the film becomes large, and the capacitance change becomes large, so that the reliability as a capacitor becomes low.

Further, the polystyrene film of the present invention
Heat shrinkage at 150 ℃ is less than 3%, preferably 2.5%
Hereafter, it is more preferably 2% or less. Heat shrinkage rate is 3%
If it is larger, shrinkage and irregularity of flatness occur in the manufacturing process of the capacitor, leading to defective products. Here, since the abrasion resistance becomes poor when the film is exposed to a high temperature for a long time in order to reduce the heat shrinkage rate, a relaxation treatment is performed after the longitudinal stretching treatment, and the heat setting temperature and time are kept within a certain range, Further, if necessary, it is preferable to perform lateral and / or longitudinal relaxation treatment after the heat setting treatment. Here, the longitudinal relaxation treatment after the longitudinal stretching is a stretching temperature or higher, a relaxation treatment at a cold crystallization temperature or lower, and a heat setting treatment is performed at 220 ° C. or higher and at a temperature lower than the melting point within 30 seconds, preferably within 20 seconds, The relaxation treatment in the horizontal and vertical directions is preferably such that the flatness is not disturbed at a temperature not higher than the maximum temperature of the heat setting treatment.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition,
The evaluation method of the film is shown below.

(1) Average Refractive Index The refractive index of the film was measured in the longitudinal direction, the width direction and the thickness direction using an Abbe refractometer 4T manufactured by Atago Optical Co., Ltd.
The refractive indexes in these three directions were averaged to obtain the average refractive index.

(2) Dielectric breakdown voltage It was performed according to JIS C-2318. Using a 10KV DC withstanding voltage tester, the voltage when the film was broken and short-circuited was read at a boosting rate of 100V / sec in an atmosphere of 23 ° C and 50% RH.

(3) Thickness unevenness A continuous thickness measuring instrument manufactured by Micron Instruments Co., Ltd. was used to measure the central portion in the width direction of the film along the longitudinal direction, and the thickness was calculated by the following formula. Thickness unevenness = (maximum thickness-minimum thickness) / average thickness x 100% Grade 1: Thickness unevenness of 10% or more Grade 2: Thickness unevenness 8 to 10% Grade 3: Thickness unevenness 6 to 8% Grade 4: Thickness unevenness 4-6% Grade 5: Thickness unevenness 4% or less

(4) Thermal Shrinkage Ratio at 150 ° C. The shrinkage ratio of the film in an atmosphere of 150 ° C. for 30 minutes without tension was determined.

(5) Average particle size Fine particles are observed with a S-510 scanning electron microscope manufactured by Hitachi, Ltd., and photographed ones are magnified and copied to trace the outer shape of the fine particles and optionally 200 particles. Particles are painted black. This image was measured for the Feret diameter in the horizontal direction of each particle using a Luzex 500 type image analyzer manufactured by Nireco Corporation, and the average value was taken as the average particle diameter. Also,
The degree of variation in particle size was calculated by the following formula. Variability = (standard deviation of particle size / average particle size) x 100
(%)

Example 1 As a lubricant, silica having an average particle size of 0.5 μm, a degree of variation of 20%, and an area shape factor of 80% was added to 0.5% of syndiotactic polystyrene (weight average molecular weight 300000) 100% by weight.
After mixing the polymer chip added with the weight% and the polymer chip not added with the lubricant in a weight ratio of 1: 9, dried, melted at 290 ° C., and extruded from a T-die having a lip gap of 800 μm, It was brought into close contact with a 50 ° C. chill roll by an electrostatic loading method and solidified by cooling to obtain an amorphous sheet of 60 μm. The amorphous sheet was first preheated to 95 ° C. by a metal roll, longitudinally stretched 3 times using a ceramic roll having a surface temperature of 141 ° C., then cooled, and further stretched 1.2 times longitudinally using a metal roll at 120 ° C. . Then, the film was preheated to 120 ° C. with a tenter, stretched in the transverse direction at a stretching temperature of 120 ° C. by 2 times, further stretched at 150 ° C. by 1.6 times, and then heat set at 255 ° C. for 12 seconds. After that, 3% lateral relaxation treatment was performed at 225 ° C. The thickness of the obtained film was 5.3 μm, and the running property and handling property were good. Further, even when the aluminum thin films were laminated by vapor deposition, the flatness was good, and it was judged to be preferable as a film for capacitors. Table 1 shows the physical properties of the obtained film.

Example 2 The same procedure as in Example 1 was carried out except that longitudinal stretching was performed 2.4 times on a ceramic roll at 141 ° C., then cooled once, and further stretched 1.5 times on a metal roll at 120 ° C. The thickness of the obtained film was 5.3 μm, and the flatness was good even when an aluminum thin film was laminated by vapor deposition, and it was judged to be preferable as a film for capacitors. Table 1 shows the physical properties of the obtained film.

Comparative Example 1 The same procedure as in Example 1 was carried out except that longitudinal stretching was performed at a ceramic roll of 141 ° C. for 2.4 times, followed by no cooling, and further at 120 ° C. for a metal roll of 1.5 times. The thickness of the obtained film was 5.3 μm, and even when a thin aluminum film was laminated by vapor deposition, a slight weeping was observed in the planarity, but it was judged that there is no problem as a film for capacitors. Table 1 shows the physical properties of the obtained film.

Comparative Example 2 As a lubricant, silica having an average particle size of 0.5 μm, a degree of variation of 20%, and an area shape factor of 80% was added to 0.5% by weight of syndiotactic polystyrene (weight average molecular weight 300,000).
After mixing the polymer chip added with the weight% and the polymer chip not added with the lubricant in a weight ratio of 1: 9, dried, melted at 290 ° C., and extruded from a T-die having a lip gap of 800 μm, It was brought into close contact with a cooling roll at 50 ° C by an electrostatic printing method and solidified by cooling to obtain an amorphous sheet of 48 µm. The amorphous sheet was first preheated to 95 ° C. with a metal roll and stretched 3 times in the machine direction using a ceramic roll with a surface temperature of 141 ° C. The film is then preheated to 120 ° C with a tenter and stretched in the transverse direction at a stretching temperature of 120 ° C by a factor of 2 for a further 15
After stretching 1.5 times at 0 ° C, it was heat-set at 255 ° C for 12 seconds. After that, 3% lateral relaxation treatment was performed at 225 ° C. The thickness of the obtained film was 5.3 μm. It was judged that the film had poor flatness and was not preferable as a film for capacitors. Table 1 shows the physical properties of the obtained film.

Comparative Example 3 The procedure of Example 1 was repeated except that the heat setting treatment was carried out at 215 ° C. for 20 seconds. The thickness of the obtained film was 5.3 μm. Table 1 shows the physical properties of the obtained film. It was determined that the obtained film was not preferable as a film for capacitors because it had an uneven surface due to laminating an aluminum thin film by vapor deposition.

From the table, it can be seen that the films obtained in Examples 1 and 2 are excellent as dielectric films because they have excellent dielectric breakdown voltage and small fluctuations in the film thickness.

[0025]

As described above, the present invention provides a polystyrene-based film for capacitors, which has an excellent dielectric breakdown voltage and an excellent thickness uniformity by adopting the constitution as described in the claims. Therefore, the industrial value of the present invention is great.

[0026]

[Table 1]

Claims (1)

[Claims] 1. A polystyrene-based film for a capacitor, which comprises a styrene-based polymer having a syndiotactic structure and has an average refractive index of 1.582 or more and 1.590 or less and a shrinkage ratio at 150 ° C. of 3% or less. .