JP2007169595A - Polypropylene film for capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene film for a capacitor, having small heat shrinkage at a high-temperature region, and exhibiting excellent characteristics especially when used at high potential gradient (=applied voltage per unit thickness) in a biaxially oriented polypropylene film usable as a dielectric substance for the capacitor. <P>SOLUTION: The polypropylene film for the capacitor comprises a polypropylene resin (A) containing a polybutene-1 and having 160-170°C melting point, and has 0.03-0.1 μm ten point-average roughness (Rz) at least on one film surface, and 90-130% gloss. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

 The present invention relates to a biaxially stretched polypropylene film used as a dielectric of a capacitor, and more particularly to a polypropylene film suitable for a vapor deposition capacitor having a film thickness of 10 μm or less.

Polypropylene film has a high dielectric breakdown voltage and low dielectric loss among plastic films, and is therefore excellent as a dielectric for a capacitor, and is particularly preferably used as a high voltage capacitor and an AC capacitor. In recent years, there has been a growing demand for higher rated capacitor temperatures and larger capacitor capacities, and it has been proposed to use biaxially stretched polypropylene films made of highly stereoregular polypropylene resin as dielectrics (patents). Literatures 1-3).
Japanese Patent Laid-Open No. 10-156938 (Claims) JP-A-10-156939 (Claims) JP, 10-156940, A (Claims) However, when such a resin composition is adopted, biaxial stretching becomes difficult or stretched by increasing the crystallinity of the polypropylene resin. Even if it is possible, when trying to produce a thin film with a thickness of 5 μm or less, the film thickness is inferior in uniformity, or there are many voids and the dielectric breakdown voltage is lowered. There was a problem.

Therefore, as an attempt to improve stretchability, proposals using specific propylene-1-butene copolymers have been made (Patent Documents 4 and 5).
JP 59-149909 A (Claims) JP, 2002-128825, A (Claim 1, Claim 3) When such a resin composition is selected, although extensibility is surely improved, the melting point is lowered, so that the heat resistance preferable as a capacitor is not necessarily Couldn't get.

  The present invention provides a polypropylene film for a capacitor that is excellent in thickness uniformity, processability, long-term reliability, and heat resistance.

The present invention proposes the following configurations in order to solve the above-described problems.
(1) It comprises a polypropylene resin (A) containing polybutene-1 and having a melting point of 160 to 170 ° C., and the ten-point average roughness (Rz) of at least one film surface is 0.03 to 2.0 μm. A polypropylene film for capacitors, characterized in that the gloss is 90 to 130%.
(2) The polypropylene film for a capacitor according to (1), wherein the polybutene-1 contained in the polypropylene resin (A) is 0.01 to 3% by weight.
(3) The polypropylene film for capacitors according to (1) or (2), wherein the soluble part of cold xylene is 3% by weight or less.
(4) The polypropylene film for capacitors according to any one of (1) to (3), wherein the film thickness is 1.5 to 5.0 μm.
(5) The polypropylene film for capacitors according to any one of (1) to (4), wherein the F5 value in the longitudinal direction is 55 MPa or more.
(6) Both surfaces of the film are subjected to surface treatment, each surface wetting tension is in the range of 37 to 48 mN / m, and the difference in wetting tension between one surface and the other surface is 2 mN / m or more. The polypropylene film for capacitors according to any one of (1) to (5).
(7) The capacitor-use polypropylene film according to any one of (1) to (6), wherein the capacitor is a flat type vapor deposition capacitor having an aspect ratio of 1.5 or more.

The film of the present invention has the following effects.
(1) It has excellent withstand voltage characteristics and has excellent characteristics for a film capacitor designed with a high potential gradient (= applied voltage per unit thickness).
(2) Since the slipperiness of the film is good, it is suitable for winding type capacitors because it has excellent vapor deposition processability, slit processability, and element winding properties.
(3) Especially when used as a flat capacitor, it has good crushability at the time of device manufacture, so it is possible to manufacture highly uniform devices with little distortion, reducing variations in capacitor device characteristics, and improving yield. Leads to.

  In the following, the present invention will be described in detail along with preferred embodiments.

  The polypropylene resin (A) constituting the polypropylene film for a capacitor of the present invention (hereinafter referred to as the present film) will be described.

  That is, the polypropylene resin (A) (hereinafter referred to as resin (A)) mainly contains polypropylene resin and contains polybutene-1, and the polypropylene resin and polybutene-1 constituting the resin (A) are both isotactic structures. Resin.

  The polypropylene resin is preferably a resin having a high stereoregularity and a narrow molecular weight distribution in order to improve heat resistance. Specifically, the stereoregularity is preferably 0.96 or more, more preferably 0.98 or more in terms of mesopentad fraction (mmmm) measured by NMR. Note that the upper limit of the mesopentad fraction is 1 for an ideal isotactic structure, and it can be said that the current technology has a limit of about 0.99. However, the present technology is not limited to the existing technology. The molecular weight distribution preferably has a polydispersity (Mw / Mn) value of 6 or less, more preferably 5 or less, defined by the ratio of the number average molecular weight (Mn) to the weight average molecular weight (Mw). It is. In order to obtain such a polypropylene resin having a narrow molecular weight distribution, a high molecular weight resin is once manufactured, and melt-kneaded together with a peroxide or the like at the time of melt pelletization to reduce the molecular weight or polymerization. The use of a metallocene catalyst as the catalyst is exemplified.

  Polybutene-1 has a melting point of 100 to 130 ° C., preferably 110 to 125 ° C., and a melt flow index (according to ASTM D1238E method) of 1 to 30 g / 10 minutes because of excellent compatibility with polypropylene. Here, it is well known that the crystal system of polybutene-1 exhibits polymorphism, and it is known that the crystal structure I, II, I ′, II ′ can be taken. The melting peak temperature of I is defined as the melting point.

  In order to bring polybutene-1 to such a melting point, it is preferable to limit the amount of comonomer to 1 mol% or less and at the same time improve the stereoregularity by appropriately selecting the catalyst to be used. Specifically, polybutene 1 manufactured by Mitsui Chemicals, Tuffmer BL4000, BL3110, and BL3450 are exemplified.

  There have been many studies on blend systems of polypropylene and polybutene-1 (for example, A. Siegmann, J. Appl. Polym. Sci. Vol. 27, 1053-1065 (1982)). In the present invention, it is known that a specific compatible system is formed. However, the present inventors have improved the stretchability by slightly adding polybutene-1 to polypropylene, and have insulation defects such as voids generated during stretching. It has been found that it can be significantly reduced.

  It is preferable that melting | fusing point of resin (A) is 160-170 degreeC, More preferably, it is 163-170 degreeC, More preferably, it is 163-168 degreeC. If the melting point is too low, the pressure resistance decreases, and if it is too high, problems such as deterioration of stretchability during film production may occur.

  In order to set the melting point of the resin (A) within the above range, the melting point of the polypropylene resin kneaded with the polybutene 1 is preferably 160 to 170 ° C., preferably 163 to 170 ° C. In order to make the melting point of the polypropylene resin within the above-mentioned preferable range, it is preferable to select a polymerization catalyst as appropriate in order to obtain a polymer with high regularity and to keep the comonomer amount to 1 mol% or less.

  The polybutene-1 contained in the resin (A) is preferably 0.01 to 3% by weight, more preferably 0.05 to 3% by weight, still more preferably 0.1 to 2%. It is preferable that it is weight%. If the content of polybutene-1 is too small, the effect of improving stretchability is small and inferior to thick spots, and voids in the film may increase, resulting in poor withstand voltage. On the other hand, when there is too much content of polybutene-1, there exists a possibility that a rough unevenness | corrugation may be formed in the surface exceeding a compatible range, or the high temperature withstand voltage in 80 degreeC or more may fall.

  The intrinsic viscosity of the resin (A) is preferably 1.4 to 2.0 dl / g, more preferably 1.6 to 1.9 dl / g. If the intrinsic viscosity is lower than the range constituting the film of the present invention, the mechanical properties are inferior, causing problems in the capacitor manufacturing process, which may increase insulation defects. On the other hand, if the intrinsic viscosity is too high, not only the heat shrinkage but also the thickness unevenness may worsen, resulting in a decrease in withstand voltage.

  Further, the cold xylene soluble part contained in the resin (A) is preferably 3% by weight or less, more preferably 2% by weight or less, and particularly preferably 1.5% by weight or less. The dielectric breakdown voltage at a high temperature of 80 ° C. or higher is high, and good characteristics can be obtained.

  In order to make the cold xylene soluble part in the above range, a method using a highly stereoregular catalyst and a method of washing the polypropylene powder obtained by polymerization with a solvent such as alcohol or propylene as appropriate are effective. The methods can be combined as appropriate. If such washing is strengthened, the cold xylene soluble part can be reduced, but industrially the lower limit is about 0.3 wt% to 0.5 wt%.

  Further, the resin (A) may contain a crystal nucleating agent such as an α crystal nucleating agent and / or a β crystal nucleating agent. The inclusion of a crystal nucleating agent is preferable because the melt crystallization temperature rises and the crystallization speed increases, so that the safety during clearing in a high-temperature atmosphere is improved. Here, the crystal nucleating agent is preferably an organic crystal nucleating agent that does not deteriorate the electrical characteristics. Specifically, sorbitol derivatives (“Gelol MD” (New Nippon Rika), rosin compounds (“Pine Crystal” KM-1500 (Arakawa Chemical)), branched-chain polyolefin (“HMS-PP” (Basell), etc. Such a crystal nucleating agent may cause an adverse electrical effect such as lowering the dielectric breakdown voltage, and the addition amount is preferably as small as possible. The preferred addition amount in A) is preferably 10 to 10,000 ppm, more preferably 50 to 5,000 ppm, and the melt crystallization temperature is in the range of 115 to 125 ° C. due to the addition of the crystal nucleating agent. And preferred.

  The ash content resulting from the catalyst residue contained in the film of the present invention is preferably 50 ppm or less, and more preferably 30 ppm or less because the withstand voltage characteristics are improved. Such ash is evaluated by measuring the residue remaining after burning a polypropylene film or resin. For example, a film of weight W (g) is put in a platinum crucible, sufficiently burned with a gas burner, and further heated at 750 ° C. It is treated with an electric furnace for 1 hour for complete ashing, and the weight W ′ (g) of the obtained ash is measured and defined as (W ′ / W) × 1,000,000 (ppm).

  In order to make ash into such a range, it can achieve by raising the activity of a polymerization catalyst and wash | cleaning the obtained polypropylene resin. As a particularly preferred polymerization method, a method in which polymerization is allowed to proceed in a medium by a solvent method or a bulk method and washing in a subsequent step is preferable. The smaller the ash content, the better. However, within the current polymerization technique, around 10 ppm is the lower limit level that can be industrially achieved.

  In addition, it is preferable to add a thermal stabilizer and an antioxidant for imparting chemical stability of the polypropylene resin to the film of the present invention. Specifically, phenolic, hindered amine, phosphite, Lactones and tocopherols are exemplified. Specifically, dibutylhydroxytoluene, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (Ciba Specialty Chemicals Co., Ltd.) ): Registered trademark Irganox 1010), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxy) benzene (Ciba Specialty Chemicals): registered trademark Irganox 1330), Tris (2,4-di-t-butylphenyl) phosphite (Ciba Specialty Chemi) Luz (Ltd.): registered trademark Irgafos168), and the like. Among these, at least one selected from phenolic antioxidants or a combination thereof, a combination of phenolic and phosphite, and phenolic and lactone, phenolic and phosphite and lactone Is preferable from the viewpoint of improving the stability of polypropylene.

  The addition amount is preferably 1000 to 10,000 ppm in the polypropylene film constituting the film of the present invention as the total amount of the antioxidant.

  The polypropylene film for capacitors of the present invention preferably has a longitudinal F5 value of 55 MPa or more, more preferably 60 to 100 MPa. If the F5 value in the longitudinal direction is too low, not only the handling properties are inferior but also the electrical properties at high temperatures tend to be inferior. On the other hand, if the F5 value is too high, the film shrinks greatly in the temperature range of 80 ° C. or higher, so that the shape is likely to change when the capacitor is finished, resulting in a decrease in reliability.

  In order to obtain a film having the F5 value as described above, a method in which the above-described polypropylene resin is melt-extruded to form a cooling sheet and then heated again to be biaxially stretched is preferable. In particular, the biaxial stretching method of the tenter method is preferable because the thickness uniformity is excellent, and the sequential biaxial stretching method is particularly excellent in high temperature characteristics. In particular, when the sequential biaxial stretching method using the tenter method is used, in order to obtain the above F5 value, the melt-extruded, cooled and solidified sheet was heated to 130 to 150 ° C. with a heating roll or the like, and then a peripheral speed difference was provided 1 A method of stretching 4.5 to 8 times, preferably 4.8 to 7.5 times between a pair or a plurality of rolls is preferably used. In addition, the addition of a crystal nucleating agent is effective in improving the F5 value, and the F5 value can be improved by adding a crystal nucleating agent as described above.

  Next, as the surface roughness of the film of the present invention, the ten-point average roughness (Rz) of at least one film surface is preferably 0.03 to 2.0 μm, more preferably 0.06 to 2.0 μm, More preferably, it is 0.08-1.5 micrometers. Moreover, Preferably it is 0.06-0.3 micrometer, More preferably, it is 0.08-0.25 micrometer. These preferable ten-point average roughness values are preferably satisfied on both sides (both sides) of the film.

  When Rz is too small, the clearing property is inferior and the capacitor is easily broken. On the other hand, if Rz is too large, the dielectric breakdown voltage is inferior.

  Further, the gloss of the surface is preferably 90 to 130%, more preferably 100 to 130%, and particularly preferably 110 to 125%. If the gloss is too low, the element winding property is lowered, and the yield in the capacitor manufacturing process may be lowered. On the other hand, if the gloss is too high, the clearing property may be deteriorated.

  In the present invention, in order to obtain such surface roughness and gloss, it can be obtained by appropriately controlling the selection of polypropylene resin and polybutene-1 resin, the cooling temperature condition of the unstretched sheet, and the stretching condition. However, it is preferable to control the amount of polybutene-1 added and the cooling conditions for the unstretched sheet, and particularly preferably, the method for controlling the cooling conditions for the unstretched sheet is economical and has excellent controllability. Here, the unstretched sheet is a non-oriented sheet when biaxially stretched, and is obtained by molding a molten resin into a sheet or tube shape. The specific cooling conditions depend on the resin temperature at the time of melting, the sheet take-up speed, the cooling device, etc. and cannot be clearly defined. However, when the resin is extruded into a sheet and cooled and solidified on the cooling drum, the cooling drum It can be said that a preferable temperature is about 80 to 100 ° C.

  Since the film of the present invention has the above-described structure, it has excellent withstand voltage and excellent handling properties, and thus has suitable characteristics for a thin film film capacitor, and the film thickness is particularly in the range of 1.5 to 5 μm. It is preferable because its performance is effectively expressed, and a particularly preferable thickness range is 2 to 4 μm.

  The film of the present invention is preferably provided with a capacitor electrode layer by metal vapor deposition to constitute a capacitor. However, in order to provide adhesion of the metal vapor deposition layer at that time, at least one surface of the film is subjected to surface treatment, and the surface is wetted. The tension is preferably 38 to 48 mN / m. A more preferable range is 40 to 46 mN / m. If the wetting tension is too low, the adhesion of the deposited metal is inferior, and the metal may fall off during the processing step. On the other hand, if it is too high, the vapor deposition metal may adhere to the film surface, which may reduce the clearing property.

  Here, the surface treatment is a process for adding a polar group such as carbonyl group, carboxyl group, hydroxyl group and amino group to the film surface. Specifically, corona discharge treatment, plasma treatment, glow treatment, ozone treatment, flame treatment. Various coatings and the like are exemplified. Among these, the corona discharge treatment is a preferable method because it is economical.

  The surface treatment can be performed not only on one side but also on both sides. In this case, it can be used for a double-sided vapor deposition capacitor. Moreover, even if it is single-sided vapor deposition, it is preferable because the wetting tension on the non-metal vapor deposition surface side is high, so that the mold determination at the time of capacitor element molding is improved and the life characteristics are improved. The surface treatment strength at this time may be the same as that on the vapor deposition surface side, but is 2 mN / m or more lower than the vapor deposition surface side from the viewpoint of preventing film interlayer blocking in the steps after vapor deposition. Is preferred.

  Since the film of the present invention is excellent in element winding property and voltage resistance as described above, it can be preferably used as a capacitor having various structures for a film capacitor. Specifically, it is a wound type capacitor (round or flat type) from the shape, a multilayer capacitor, and from an electrode configuration, an evaporated metal capacitor (single side and / or double side), a metal foil-fired capacitor, and an oil-impregnated type as a dielectric configuration , Dry type and so on. However, the film of the present invention is particularly preferably used for a wound type capacitor, particularly a flat type wound type capacitor. The film of the present invention contains polybutene-1 slightly, and the mechanism is unknown, but it is excellent in mold determination in the pressing process when flattening after element firing, and the elastic recovery phenomenon to a round shape hardly occurs. As a result, long-term life characteristics are improved. In particular, it has characteristics suitable for flat capacitors having an aspect ratio of 1.5 or more. Here, the aspect ratio is defined by the ratio of the major axis to the minor axis in the elliptical cross-sectional shape of the wound capacitor element. The larger the ratio, the greater the flatness. When the aspect ratio is 1, the aspect ratio is a circle.

  The aspect ratio is usually at most 6 or less, preferably 5 or less, since both electrical characteristics and compactness can be achieved.

  Hereinafter, although the manufacturing method of this invention film is demonstrated, it is not limited to the following description.

  The polypropylene resin (A) is composed of a polypropylene resin and a polybutene 1 resin. Each resin is melt-kneaded using a twin-screw extruder or the like and then pelletized, or each resin is dry blended. Examples thereof include a method of leading to a film forming apparatus and a method of adding as butene-1 and / or polybutene-1 during polymerization of polypropylene resin. In this, polypropylene resin and polybutene-1 resin are kneaded in advance so as to have a predetermined concentration, or pelletized, or a pellet in which polybutene-1 is added to polypropylene resin at a high concentration (so-called master pellet) is prepared. In addition, the method of kneading and extruding with the polypropylene resin so as to have a predetermined concentration in the extruder of the film forming machine is economical and preferable, but in the method of introducing polybutene-1 in the prepolymerization stage of the polypropylene resin, Since the effect is further enhanced by the fine dispersion of polybutene-1 in polypropylene, it may be appropriately selected according to the purpose.

  Next, the film of the present invention is produced by a biaxial stretching method, but may be either a tenter method or a tubular (bubble) method. Among these, the tenter method is preferable because the thickness unevenness and flatness are improved. The tenter method further includes a simultaneous biaxial stretching method and a sequential biaxial stretching method, and either method may be used. In the present invention, the sequential biaxial stretching method is particularly preferable because the capacitor characteristics are good. Hereinafter, a method for obtaining the film of the present invention by sequential biaxial stretching will be described, but the present invention is not limited thereto.

  The resin prepared as described above is melt-kneaded by an extruder at 230 to 270 ° C., and melt-extruded into a sheet form from a T-type slit die via a polymer filter.

  The resin thus melt-kneaded is removed from the extruder by a polymer filter and then guided to the die, and is then brought into close contact with air pressure on a metal drum controlled at 70 to 100 ° C. to form a sheet. Is done.

  The sheet obtained here is preheated by a heated metal roll, the film temperature is raised to 130 to 155 ° C., and 4 to 9 times, preferably 4.5 to between a pair of rolls provided with a peripheral speed difference. The film is stretched in the longitudinal direction by 8 times, preferably 4.8 to 7.5 times, preferably 5 to 7 times, particularly preferably 5.5 to 7 times, to obtain a uniaxially stretched film. Next, both ends in the width direction of the uniaxially stretched film are held by clips, guided to a heating oven, preheated to 150 to 170 ° C., and then stretched by 7 to 12 times, preferably 8 to 11 times in the width direction. And annealing at 140 to 160 ° C. while allowing 0 to 20% relaxation in the width direction. After trimming both edge portions of the biaxially stretched film thus obtained, the corona discharge treatment is performed, and then wound into a roll.

  The wound film is subjected to an aging treatment in an atmosphere of 20 to 40 ° C. and then cut into a necessary product width.

Next, measurement methods and evaluation methods used in the examples of the present invention will be described.
(1) Gloss (Glossiness)
According to JIS K 7105 (1981), the average value of 5 data measured under the conditions of an incident angle of 60 ° and a light receiving angle of 60 ° using a digital variable angle gloss meter UGV-5D manufactured by Suga Test Instruments Co., Ltd. And
(2) Intrinsic viscosity ([η])
0.1 mg of a sample was dissolved in 100 ml of tetralin at 135 ° C., and this solution was measured using a viscometer in a constant temperature bath at 135 ° C., and the intrinsic viscosity [η] was determined from the specific viscosity S according to the following formula (unit: : Dl / g).

[Η] = (S / 0.1) × (1 + 0.22 × S)
(3) Content of polybutene-1
The content of polybutene was determined from the ratio of methyl carbon derived from polypropylene and methyl carbon derived from polybutene 1 by ¹³ C-NMR method.

  The measurement conditions are as follows.

A. Equipment JNM GX-270 manufactured by JEOL Datum
B. Measurement method Gated decoupling method C.I. 140 ° C
D. Measurement nuclear frequency 67.940MHz
E. Pulse width 17.0μsec (90 ° pulse)
F. Solvent o-dichlorobenzene, benzene-d6
(4) CXS value (cold xylene solubles)
After dissolving 0.5 g of a polypropylene film sample in 100 ml of boiling xylene and allowing to cool, 2
The polypropylene component dissolved in the filtrate after recrystallization in a constant temperature water bath at 0 ° C. for 1 hour is quantified by liquid chromatography (X (g)). Precision value of sample 0.5g (X0 (g)
) Using the following formula.

CXS value (% by weight) = X / X0 × 100
(5) Measurement of mesopentad fraction (mmmm) Measurement condition apparatus for dissolving a sample in a solvent and obtaining a mesopentad fraction (mmmm) under the following conditions using ¹³ C-NMR: DRX-500 manufactured by Bruker
Measurement nucleus: 13C nucleus (resonance frequency: 125.8 MHz)
Measurement concentration: 10 wt%
Solvent: benzene / heavy orthodichlorobenzene = 1: 3 mixed solution Measurement temperature: 130 ° C.
Spin rotation speed: 12Hz
NMR sample tube: 5 mm tube Pulse width: 45 ° (4.5 μs)
Pulse repetition time: 10 seconds Data point: 64K
Number of conversions: 10,000 times Measurement mode: complete decoupling
The Fourier transform was performed with the analysis condition LB (line broadening factor) being 1.0, and the mmmm peak was 21.86 ppm. Peak splitting is performed using WINFIT software (manufactured by Bruker). At that time, the peak splitting is performed from the peak on the high magnetic field side as shown below, and the soft automatic fitting is performed to optimize the peak splitting. Then, mmmm and ss (mmmm spinning sideband peak) The sum of the peak fractions is defined as the mesopentad fraction (mmmm).
The measurement is performed with n = 5, and the average value is obtained.

peak
(A) mrrm
(B) (c) rrrrm (divided as two peaks)
(D) rrrr
(E) mrmm + rmrr
(F) mmrr
(G) mmmr
(H) ss (mmmm spinning sideband peak)
(I) mmmm
(J) rmmr
(6) Melting point, melt crystallization temperature (° C)
The measurement was performed under the following conditions using a Seiko RDC220 differential scanning calorimeter.
<Sample preparation>
A sample of 5 mg is enclosed in an aluminum pan for measurement. In addition, when the metal vapor deposition etc. are given to the film, it removes suitably.
<Measurement>
The film is melted / recrystallized / remelted in the following steps (a) → (b) → (c). The melting point of the resin was defined as the highest melting peak temperature among melting peaks observed at 2nd Run. The average value of n = 3 was obtained.

(A) 1st Run 30 ° C. → 280 ° C. (temperature increase rate 20 ° C./min)
(B) Tmc held at 280 ° C. for 5 minutes and then cooled to 30 ° C. at 20 ° C./min. (C) 2nd Run 30 ° C. → 280 ° C. (temperature increase rate 20 ° C./min)
(7) Centerline average roughness (Ra) and ten-point average roughness (Rz)
Measured according to JIS B-0601 (1982) using a “non-contact three-dimensional fine shape measuring instrument (ET-30HK)” and “three-dimensional roughness analyzer (MODEL SPA-11)” manufactured by Kosaka Laboratory Ltd. . The number of measurements was 3, and the average value was used. The detailed conditions are as follows.

    Measurement surface treatment: Aluminum was vacuum-deposited on the measurement surface to obtain a non-contact method.

Measurement length: 1mm
Horizontal magnification: 200x Vertical magnification: 20000x Cutoff: 0.25mm
Width direction feed speed: 0.1 mm / sec Length direction feed pitch: 10 μm
Number of feeds in the length direction: 20 times Measurement direction: width direction of the film (8) 140 ° C. heat shrinkage rate In accordance with JIS-Z-1712 (1997), sample film in a hot air oven at 140 ° C. for 15 minutes or less The rate of dimensional change when held under these conditions is defined as the heat shrinkage rate. The MD (longitudinal direction) of film formation is preferably 6% or less, and the TD (width direction) is preferably 3% or less.

(A) Sample width 10mm x length 200mm
(B) Oven conditions: 140 ° C., load 3 g
(C) The measurement length is obtained by the following equation using a read value of the film length L1 (mm) before and after the processing with reference to L0 = 100 mm before the processing.

Thermal contraction rate (%) = (L0−L1) / L0 × 100
(9) Wetting tension Measured according to JIS K 6768 (1999) using a mixed liquid of formamide and ethylene glycol monoether (unit: mN / m).
(10) Film thickness According to 7.4.1.1 of JIS C-2330 (2001), the thickness of the micrometer method was defined as the film thickness. The unit is μm.
(11) Dielectric breakdown voltage (V / μm)
According to JIS C2330 (2001 edition) 7.4.11.2 B method (plate electrode method).

  The measurement temperature was 80 ° C.

The measurement was performed 20 times for each sample, and an average value Xmin of four values was obtained from 20 average values Xav and minimum values. Even if Xav is large and good, if Xmin is small, the variation is large, which may cause a problem. Therefore, Xmin is preferably 60% or more of Xav.
(12) Evaluation of vapor deposition capacitor characteristics Films obtained in each of Examples and Comparative Examples described later were provided with a margin portion in a direction perpendicular to the longitudinal direction with a film resistance of 5 Ω / sq using a vacuum vapor deposition machine manufactured by ULVAC. A vapor deposition pattern having a so-called T-shaped margin pattern was applied to obtain a vapor deposition reel having a width of 50 mm.

  Next, using this reel, the capacitor element was wound up with an element winding machine manufactured by Minato Seisakusho, metallized, and then heat-treated at 120 ° C. for 16 hours in a vacuum. Potting with resin finished the capacitor element. The capacitance of the capacitor element at this time was 10 μF.

  Using the thus obtained five capacitor elements, a so-called step-up test is repeated in which a voltage of 500 VDC is applied to the capacitor element at room temperature and the applied voltage is increased stepwise by 50 VDC after 10 minutes. It was. The change in capacitance at this time was measured and plotted on a graph, and the voltage at which the capacitance reached 80% of the initial value was divided by the film thickness to obtain the withstand voltage. Moreover, after raising the voltage until the electrostatic capacity decreased to 5% or less with respect to the initial value, the capacitor element was disassembled and the state of destruction was examined and evaluated as follows.

Status Rank No change in element shape and no penetration failure is observed: 4
There is no change in the element shape, and penetration-like breakdown within 10 layers of the film is observed: 3
A change in the element shape is observed, or penetration destruction exceeding 10 layers is observed: 2
Device breaks down: 1
Rank 4 can be used without any problem, but ranks 3 to 2 can be used depending on conditions, deposition thickness and pattern. Below rank 1, a practical problem occurs.

(13) F5 value in the longitudinal direction In the case of a film roll, the longitudinal direction is the winding direction.

    Measured according to JIS-K7161 (1994) and defined as stress per cross-sectional area when stretched by 5% (unit: MPa).

(14) Evaluation of stretchability Polypropylene resin is extruded into a sheet form from an extruder, cooled and solidified on a cooling drum, then stretched in the longitudinal direction with a roll-type stretching device, and further stretched in the width direction with a stenter device. The film was guided to a stretching apparatus and evaluated for stretchability when stretched under the following standard conditions.

<Standard stretching conditions>
Sheet cooling conditions: Cooling drum temperature 80 ° C
Sheet thickness: 400 μm in average thickness excluding the film forming edge
Stretching condition in the longitudinal direction: temperature 140 ° C, magnification 5 times, stretching condition in the width direction: temperature 155 ° C, mechanical magnification 7 times, where the mechanical magnification is the ratio of the distance between the entrance and exit of the film gripping device arranged on both sides of the stenter device Defined.

<Extendability evaluation>
Judgment was made as follows from the shape of the edge of the film coming out of the stenter device. Here, the edge portion is an end portion of the film gripped by the clip gripping device, and there is a thickness step between the biaxially stretched portion stretched in the width direction by the stenter device after uniaxial stretching and the uniaxial stretched portion not stretched in the width direction. Although it is formed, whether the stretchability is good or not is determined by the shape of the stepped portion (boundary portion).

Edge boundary shape, etc. Rank Formed almost straight in the longitudinal direction: 4
There is a whisker-like structure irregularly in the vicinity of the boundary although it is straight: 3
Edge shape is unstable, such as waviness or uniaxially stretched parts split into multiple parts: 2
Film tears occur frequently and cannot be formed: 1
Rank 4 is most preferable, but if it is rank 3, there is no problem in uniform stretching by optimizing the conditions. Although it is possible to form a film by optimizing the stretching conditions even at rank 2, it is possible to generate irregular tears or the like particularly when forming a thin film, and to reduce productivity. evaluated.

Hereinafter, description will be made based on the implementation and comparative examples.
1. Preparation of polypropylene resin As the polypropylene resin and polybutene-1 resin, resins having the characteristics shown in Table 1 were used.
2. Film-forming method In each of the Examples and Comparative Examples, a biaxially stretched film was obtained by the following film-forming method.

  Polypropylene resin pellets and polybutene-1 resin pellets were dry blended so that the amount of polybutene-1 added was 10% by weight, and then extruded into a gut shape in a water-cooled bath melt-kneaded at 240 ° C. by a twin screw extruder. After cooling and solidification, it was cut into pellets to obtain master pellets containing 10% by weight of polybutene-1.

  Next, the polypropylene resin pellets and the master pellets described above are mixed as appropriate so as to obtain a predetermined amount of polybutene-1, extruded from a T-type die from a single screw extruder, and then on a cooling drum at 90 ° C. Made into a sheet.

  Next, the sheet was guided to a roll stretching apparatus and stretched in the longitudinal direction, and then guided to a transverse stretching apparatus and stretched 7 times in the width direction at a mechanical magnification. The draw ratio and temperature were changed in each implementation and comparative example.

Examples 1-3
Using PP-1 as the polypropylene resin and PB-1 as the polybutene-1 resin, the content of PB-1 is 0.1 wt% (Example 1), 0.5 wt% (Example 2), 2 wt% ( Example 3). All the resins were excellent in the rank rating of 3 or more in the evaluation of stretchability under standard conditions.

  Next, for the purpose of evaluating as a capacitor film, the molten sheet extruded from the die was cooled and solidified at a cooling drum temperature of 85 ° C., and then stretched at 144 ° C. in the longitudinal direction at 4.9 times and at 158 ° C. in the lateral direction. As a result, the film was stretched 9 times in the lateral direction at an effective magnification. Subsequently, after heat-fixing at 162 degreeC in the heat setting zone in the same horizontal extending | stretching machine, the corona discharge process was given to one side and it wound up.

  The film characteristics and electrical characteristics obtained in this way are shown in Table 2. All films had high dielectric breakdown voltages and small variations. In addition, there was no problem with the breakdown mode of the capacitor.

Example 4
When the stretchability was evaluated by setting the content of the polybutene-1 resin PB-1 to 3.5 wt% in the polypropylene resin PP-1, it was excellent as rank 4. Next, a sample for capacitor evaluation was obtained in the same manner as in Example 1. The surface roughness of the film thus obtained was slightly large at 2.2 B on the B side, the gloss was low at less than 100%, and the voltage resistance was slightly inferior.

Comparative Example 1
Although only PP-1 was evaluated as a polypropylene resin, the stretchability was as low as rank 2. Next, the resin was cooled and solidified at a cooling drum temperature of 85 ° C., and a film was formed under the same film forming conditions as in Example 1 to obtain a sample. As shown in Table 2, the film thus obtained had a low dielectric breakdown voltage and a large variation. In addition, a short mode tendency appears as a breakdown mode in the capacitor characteristics.

Comparative Example 2
A biaxially stretched film was obtained in the same manner as in Example 2, except that the cooling drum temperature was 60 ° C. The Rz of the film thus obtained was smoothed to 0.05 μm and the breakdown voltage was high, but the breakdown mode of the capacitor became a complete short mode.

Example 5
PP-1 is used as the polypropylene resin and PB-2 is used as the polybutene 1 resin. After cooling and solidifying at a cooling drum temperature of 90 ° C., it is stretched 5 times at 135 ° C. in the longitudinal direction and then 9.5 at 157 ° C. in the width direction. The film was stretched twice to obtain a biaxially stretched film. Both film characteristics and capacitor characteristics were excellent.

Comparative Example 3
Using an ethylene propylene copolymer having a melting point of 158 ° C. as a polypropylene resin, adding 2% by weight of polybutene (PB-1), cooling and solidifying at a cooling drum temperature of 85 ° C., and then stretching to 5 times at 140 ° C. in the longitudinal direction And then stretched in the width direction at 154 ° C. to obtain a biaxially stretched film. The properties of the film thus obtained are shown in Table 2, but were inferior in pressure resistance.

Example 6
Using the resin composition of Example 2, it was melt-extruded in the same manner as in Example 2, cooled and solidified with a 95 ° C. cooling drum, and then stretched 4.2 times at 144 ° C. in the longitudinal direction. Subsequently, the film was stretched in the transverse direction at 158 ° C. As a result, the film was stretched 8.5 times in the lateral direction at an effective magnification. Subsequently, after heat-fixing at 162 degreeC in the heat setting zone in the same horizontal extending | stretching machine, both surfaces were corona-discharge-treated and wound up.

  The film properties and electrical properties thus obtained are shown in Table 2. The Young's modulus in the longitudinal direction was as low as 48 MPa, and although the reliability was good in the step-up test, the withstand voltage was slightly low.

Example 7
A film was obtained under the same film forming conditions except that the draw ratio in the longitudinal direction was set to 5.3 times in Example 6. As shown in Table 2, the Young's modulus in the longitudinal direction was as high as 60 MPa, and in the step-up test, both reliability and withstand voltage were high and good.

   The polypropylene film obtained by the present invention is excellent in slipperiness and thickness uniformity, and thus is particularly suitable for use as a vapor deposition capacitor, but can also be used for other foil wound capacitors. Moreover, besides a capacitor use, it can also be preferably used as a thermosetting member molding application (so-called mold release application), a protective film, a food packaging application, and an adhesive tape.

Claims (7)

It consists of a polypropylene resin (A) containing polybutene-1 and having a melting point of 160 to 170 ° C., the ten-point average roughness (Rz) of at least one film surface is 0.03 to 2.0 μm, and the gloss is A polypropylene film for capacitors, characterized in that it is 90 to 130%. 2. The polypropylene film for capacitors according to claim 1, wherein the polybutene-1 contained in the polypropylene resin (A) is 0.01 to 3% by weight. The polypropylene film for capacitors according to claim 1 or 2, wherein the cold xylene soluble part is 3% by weight or less. The polypropylene film for capacitors according to any one of claims 1 to 3, wherein the film thickness is 1.5 to 5.0 µm. The F5 value in the longitudinal direction is 55 MPa or more. The polypropylene film for capacitors according to any one of claims 1 to 4. A surface treatment is applied to both surfaces of the film, any surface wetting tension is in the range of 37 to 48 mN / m, and the difference in wetting tension between one surface and the other surface is 2 mN / m or more. The polypropylene film for capacitors according to any one of 1 to 5. The polypropylene film for a capacitor according to any one of claims 1 to 6, wherein the capacitor is a flat type vapor deposition capacitor having an aspect ratio of 1.5 or more.