JP3491697B2 - Polystyrene film for capacitors - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a syndiotactic polystyrene film for a capacitor, and more particularly, to a film having good electric characteristics and heat resistance, excellent dielectric breakdown voltage and excellent thickness. The present invention relates to a polystyrene film for capacitors having excellent uniformity. [0002] A biaxially stretched film obtained by biaxially stretching and heat setting a resin composition containing a syndiotactic polystyrene-based polymer as a main component has excellent heat resistance, electrical properties, etc. (Japanese Patent Laid-Open No. 2-1438)
51, JP-A-3-124750, JP-A-5-200858). [0003] However, in these conventional syndiotactic polystyrene-based films, the breakdown voltage is poor or the thickness of the film is increased due to unevenness in the breakdown voltage and the capacitance after the capacitor is used. Was found to occur. When the dielectric breakdown voltage becomes poor, it is necessary to make the film thicker, and as a result, there is a problem that the volume of the capacitor becomes large. In addition, it was found that there was a problem that the reliability of the capacitor could not be obtained when the variation in the capacitance and the breakdown voltage was large. SUMMARY OF THE INVENTION An object of the present invention is to provide a polystyrene film for a capacitor having good electric characteristics and heat resistance, excellent in dielectric breakdown voltage, and excellent in thickness uniformity. [0004] The polystyrene-based film of the present invention 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. An object of the present invention is to provide a polystyrene-based film for a capacitor having good properties, excellent dielectric breakdown voltage, and excellent thickness uniformity. The polystyrene-based polymer having a stereoregular syndiotactic structure used in the present invention has a tacticity in which a phenyl group or a substituted phenyl group as a side chain is determined by a nuclear magnetic resonance method. 85% or more for two) and 50 for pentads (five constituent units)
% Or more of the syndiotactic structure. Examples of the polystyrene-based polymer include polystyrene, poly (p-, m- or o-methylstyrene), and poly (2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene). ), Poly (alkylstyrene) such as poly (p-tert-butylstyrene), 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 ( Poly (halogen-substituted alkylstyrene) such as p-, m- or o-chloromethylstyrene, 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); and Include poly (vinylbenzyldimethoxyphosphide). In the present invention, among the polystyrene polymers, polystyrene is particularly preferred. Also,
The polystyrene polymer having a syndiotactic structure used in the present invention does not necessarily need to be a single compound, and a polystyrene polymer having an atactic structure or an isotactic structure as long as the syndiotacticity is within the above range. Or 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, a film having excellent elongation characteristics and heat resistance cannot be obtained. The upper limit of the weight-average molecular weight is not particularly limited. However, if the weight-average molecular weight is 1500,000 or more, breakage occurs due to an increase in stretching tension, and thus it is not preferable. The syndiotactic polystyrene polymer used in the present invention may be, if necessary, a compound in which known antioxidants, antistatic agents, fine particles for imparting lubricity and the like are blended in appropriate amounts. it can. The amount is based on 100% by weight of the syndiotactic polystyrene polymer.
10% by weight or less is desirable. If the content exceeds 10% by weight, breakage is likely to occur 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; and silicone resins; and organic polymers such as cross-linked polystyrene. The addition of particles and the like is exemplified.
These fine particles may be used alone or in combination of two or more.The average particle system of the fine particles to be used is 0.01 μm or more and 2.0 μm or less, particularly 0.1 μm or less.
It is preferably from 05 μm to 1.5 μm, and the degree of dispersion of the particle diameter (the ratio between the standard deviation and the average particle diameter) is preferably 25% or less. The added amount is preferably from 0.005% to 2.0% by weight, more preferably from 0.1% to 1.0% by weight, based on 100% by weight of the syndiotactic polystyrene-based polymer.
The following is preferred. The average refractive index is adjusted by adjusting 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. For example, in addition to a sequential biaxial stretching method in which longitudinal stretching and transverse stretching are sequentially performed, a horizontal / longitudinal / longitudinal stretching method is used. , Vertical / horizontal / vertical stretching method,
A stretching method such as a longitudinal / longitudinal / lateral stretching method can be employed, and is selected according to various properties such as required strength and dimensional stability. In addition, a heat setting treatment, a vertical relaxation treatment, a horizontal relaxation treatment and the like can be performed. Particularly, the film forming conditions as shown in the examples are preferable, and the present invention can be achieved. In addition, in order to improve the adhesive properties of the deposited layer, an adhesive layer can be provided by in-line coating or off-line coating, or corona treatment, flame plasma treatment, or the like 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. If the average refractive index is more 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 increases, so that the reliability as a capacitor is lowered. Further, the polystyrene-based film of the present invention
Heat shrinkage at 150 ° C. is 3% or less, preferably 2.5%
Or less, more preferably 2% or less. 3% heat shrinkage
If it is larger, shrinkage or disorder in flatness occurs in the capacitor manufacturing process, which leads to defective products. Here, if the film is exposed to a high temperature for a long time to lower the heat shrinkage, the abrasion resistance becomes poor, so that the 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 a horizontal and / or vertical relaxation treatment after the heat setting treatment. Here, the longitudinal relaxation treatment after longitudinal stretching is at or above the stretching temperature, the relaxation treatment is performed at a temperature lower than the cold crystallization temperature, and the heat setting treatment is performed at a temperature of 220 ° C. or more and less than the melting point within 30 seconds, preferably within 20 seconds, The relaxation treatment in the horizontal and vertical directions is preferably performed at a temperature not higher than the maximum temperature of the heat setting treatment so that the flatness is not disturbed. EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to only 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, width direction and thickness direction using an Abbe refractometer 4T manufactured by Atago Optical Co., Ltd.
The refractive indices in these three directions were averaged to obtain an average refractive index. (2) Dielectric breakdown voltage This was performed according to JIS C-2318. Using a 10 KV DC withstanding voltage tester, the voltage at the time when the film was broken and short-circuited was read at an increase rate of 100 V / sec in an atmosphere of 23 ° C. and 50% RH. (3) Uneven thickness The center of the film in the width direction was measured along the longitudinal direction using a continuous thickness measuring instrument manufactured by Micron Keisoku Co., Ltd., and calculated by the following equation. Thickness unevenness = (maximum thickness-minimum thickness) / average thickness x 100% First grade: Uneven thickness 10% or more Second grade: Thickness irregularity 8-10% Third grade: Thickness irregularity 6-8% Fourth grade: Thickness irregularity 4 to 6% Class 5: Uneven thickness of 4% or less (4) Thermal shrinkage at 150 ° C. The shrinkage of the film was measured for 30 minutes in an atmosphere of 150 ° C. under no tension. (5) Observation of fine particles having an average particle diameter with a scanning electron microscope (S-510, manufactured by Hitachi, Ltd.) Particles were painted black. This image was measured for the horizontal Feret diameter of each particle using a Luzex 500 image analyzer manufactured by Nireco Co., Ltd., and the average value was defined as the average particle diameter. Also,
The degree of variation in particle diameter was calculated by the following equation. Variation = (standard deviation of particle diameter / average particle diameter) x 100
Example 1 As a lubricant, silica having an average particle diameter of 0.5 μm, a degree of dispersion of 20%, and an area shape coefficient of 80% was added to 100% by weight of syndiotactic polystyrene (weight average molecular weight: 300,000) by 0.5%.
After mixing the polymer chip added by weight% and the polymer chip without added lubricant at a ratio of 1: 9 by weight, dried, melted at 290 ° C., extruded from a T-die having a lip gap of 800 μm, It was closely adhered to a cooling roll at 50 ° C. by an electrostatic loading method and solidified by cooling to obtain a 60 μm amorphous sheet. The amorphous sheet was first preheated to 95 ° C. with a metal roll, stretched three times in the machine direction using a ceramic roll having a surface temperature of 141 ° C., cooled, and further stretched 1.2 times in the machine direction using a metal roll at 120 ° C. . Next, the film was preheated to 120 ° C. by a tenter, stretched twice in the transverse direction at a stretching temperature of 120 ° C., further stretched 1.6 times at 150 ° C., and heat-set at 255 ° C. for 12 seconds. Then, it was subjected to a 3% transverse relaxation treatment at 225 ° C. The thickness of the obtained film was 5.3 μm, and the running property and the handling property were good. In addition, even when an aluminum thin film was laminated by vapor deposition, the flatness was good, and it was determined that this was preferable as a film for a capacitor. Table 1 shows the physical properties of the obtained film. Example 2 The procedure of Example 1 was repeated except that the film was stretched 2.4 times in a ceramic roll at 141 ° C., cooled once, and then stretched 1.5 times with 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 that the film was preferable as a film for capacitors. Table 1 shows the physical properties of the obtained film. Comparative Example 1 The procedure of Example 1 was repeated, except that the film was stretched 2.4 times in a longitudinally stretched 141 ° C. ceramic roll, not cooled, and further stretched 1.5 times with a 120 ° C. metal roll. The thickness of the obtained film was 5.3 μm, and even when an aluminum thin film was laminated by vapor deposition, slight unevenness was observed in the flatness, but it was judged that there was no problem as a film for a capacitor. Table 1 shows the physical properties of the obtained film. Comparative Example 2 As a lubricant, silica having an average particle diameter of 0.5 μm, a degree of dispersion of 20%, and an area shape factor of 80% was added in an amount of 0.5 to 100% by weight of syndiotactic polystyrene (weight average molecular weight: 300,000).
After mixing the polymer chip added by weight% and the polymer chip without added lubricant at a ratio of 1: 9 by weight, dried, melted at 290 ° C., extruded from a T-die having a lip gap of 800 μm, It was adhered to a cooling roll at 50 ° C. by an electrostatic printing method and cooled and solidified to obtain a 48 μm amorphous sheet. The amorphous sheet was first preheated to 95 ° C. by a metal roll, and stretched three times in the machine direction using a ceramic roll having a surface temperature of 141 ° C. Next, the film is preheated to 120 ° C. with a tenter, stretched twice in the transverse direction at a stretching temperature of 120 ° C., and further stretched for 15 minutes.
After stretching 1.5 times at 0 ° C., it was heat-set at 255 ° C. for 12 seconds. Then, it was subjected to a 3% transverse relaxation treatment at 225 ° C. The thickness of the obtained film was 5.3 μm. The flatness of the film was poor, and it was judged that it was not preferable as a film for a capacitor. 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 performed 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. The resulting film was degraded in flatness by laminating an aluminum thin film by vapor deposition, and was judged to be not preferable as a capacitor film. From the table, it can be seen that the films obtained in Examples 1 and 2 are excellent in dielectric breakdown voltage and have a small variation in film thickness, so that they are excellent as films for capacitors. As described above, according to the present invention, a polystyrene-based capacitor for a capacitor having an excellent dielectric breakdown voltage and an excellent thickness uniformity is obtained by adopting the constitution as described in the claims. A film is provided, and thus the industrial value of the present invention is great. [Table 1]

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B29C 55/12 C08J 5/18

Claims (1)

(57) [Claims] 1. The average refractive index of a styrene polymer having a syndiotactic structure is 1.582 or more and 1.590 or less, and the shrinkage at 150 ° C. is 3% or less. A polystyrene film for capacitors characterized by the following.