JP2001048998A - Biaxially oriented polypropylene film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biaxially oriented polypropylene film having excellent heat resistance, breakdown resistance characteristics and proper heat shrinkability useful as a film for a film for a capacitor. SOLUTION: This biaxially oriented polypropylene film has two or more endothermic peaks caused by melting when measured by a differential scanning calorimeter in which one of the peaks is higher than 160 deg.C and the other is in the range of 130-155 deg.C. The film has >=85 J/g total melt calorie and 0.02-0.2 μm average surface roughness Ra of central line on at least one side of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polypropylene film which is excellent in heat resistance and dielectric breakdown resistance, has a suitable surface roughness and heat shrinkability, and is suitable as a dielectric for capacitors.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene films are excellent in optical properties, mechanical properties, electrical properties and the like, and are therefore used in various applications such as packaging applications, tape applications, and electrical applications such as capacitors.

When such a biaxially oriented polypropylene film is used as a dielectric for a capacitor, characteristics such as dielectric breakdown resistance and heat resistance are required. In addition, if the capacitor element is impregnated with insulating oil, and the capacitor capacity is to be reduced during continuous use and the increase in leakage current is suppressed, the shape of the film surface is designed so that the insulating oil penetrates uniformly between the film layers. In addition, during the production of the capacitor element, heat treatment is performed to cause tightness of the winding, and it is also necessary to maintain the shape and expel air between the film layers.In this case, an appropriate heat shrinkage is required. Required.

It is effective to increase the crystallinity of the film in order to improve the dielectric breakdown resistance. For this purpose, polypropylene having high crystallinity is used, and the temperature of the casting drum is set high during film formation to cool the film. A method is often used in which the rate of solidification is reduced so that spherulites of polypropylene are sufficiently grown. However, in this case, although the crystallinity of the film is increased, the stretchability is reduced in the subsequent stretching process, voids are formed in the film, and the dielectric breakdown resistance is sometimes reduced. Further, when the temperature of the casting drum is set low in order to avoid the generation of voids, there is a problem that it is difficult to design the surface shape of the film.

In order to solve such a problem, Japanese Patent Laid-Open Publication No.
9126, JP-A-10-119127, JP-A-10-156938, JP-A-10-1569
No. 39 and JP-A-10-156940 disclose a biaxially oriented polypropylene film in which isotacticity and stereoregularity are simultaneously controlled. Such biaxially oriented polypropylene film certainly has excellent heat resistance and dielectric breakdown resistance at high temperatures, but because of its high heat resistance, the film deformation due to rapid heating in a short time, that is, the heat shrinkage ratio, is relatively low. In many cases, the characteristics are not always sufficient when it is desired to utilize the heat shrinkage during processing of the capacitor element.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a biaxially oriented polypropylene film having a suitable surface roughness and heat shrinkage suitable for a capacitor despite having high heat resistance and high dielectric breakdown resistance. To provide.

[0007]

Means for Solving the Problems The present inventors have found that heat resistance,
Despite having high dielectric breakdown resistance, as a result of diligent examination to provide a biaxially oriented polypropylene film having appropriate heat shrinkage and film surface characteristics suitable for capacitors, as measured by a differential scanning calorimeter It has been found that a biaxially oriented polypropylene film having a specific heat of fusion and a specific endothermic peak can achieve such an object, and have completed the present invention.

That is, the biaxially oriented polypropylene film according to the present invention has two or more endothermic peaks associated with melting as measured by a differential scanning calorimeter, and one of the peaks is higher than 160 ° C. One of the peaks of
0-155 ° C, and the total heat of fusion is 85 J /
g or more, and the center line average surface roughness Ra of at least one surface of the film is in the range of 0.02 to 0.2 μm.

Further, the biaxially oriented polypropylene film according to the present invention has at least one of a polypropylene resin layer (A layer) having a single endothermic peak at 160 ° C. or higher due to melting when measured by a differential scanning calorimeter. On one side, there are two or more endothermic peaks associated with melting as measured by a differential scanning calorimeter, and one of the peaks is higher than 160 ° C, and one of the remaining peaks is in the range of 130 to 155 ° C. The total heat of fusion is 85 J / g or more;
The center line average surface roughness Ra of the film surface is 0.02 to
A layer (layer B) in the range of 0.2 μm is laminated.

In the biaxially oriented polypropylene film, the heat shrinkage at 100 ° C. is 0.2 to 2 in the longitudinal direction.
%, And preferably in the range of -1 to 1% in the width direction.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene used for the biaxially oriented polypropylene film of the present invention mainly comprises a homopolymer of propylene, but other copolymerizable components with unsaturated hydrocarbons within a range not to impair the object of the present invention. And the like, or a polymer in which propylene is not alone may be blended. As a monomer component constituting such a copolymer component or a blend, for example, ethylene,
Propylene (in the case of copolymerized blends), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene
1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene,
Allylbenzene, cyclopentene, norbornene, 5-
Methyl-2-norbornene and the like. The copolymerization amount or the blending amount is preferably less than 1 mol% and the blending amount less than 10% by weight from the viewpoint of dielectric breakdown resistance and heat resistance.

The isotactic index (II) of the biaxially oriented polypropylene film of the present invention is not particularly limited, but is preferably 98 to 99.5% from the viewpoint of film forming properties.
Here, the isotactic index is defined as the ratio of the weight of the insoluble content to the weight of the film before extraction when the film is extracted with boiling n-heptane. If the isotactic index is too high, the
When a biaxially oriented film is produced as disclosed in Japanese Patent No. 6709, stretchability is poor and film formation becomes extremely difficult. On the other hand, if the isotactic index is too small, the heat resistance and the dielectric breakdown resistance are greatly reduced. A more preferred isotactic index is 98.5 to 99.5%.
And more preferably 98.7 to 99.3%. In order to obtain a polypropylene film having such an isotactic index, a low-molecular-weight component easily soluble in boiling n-heptane of a polypropylene resin as a raw material, and a low stereoregularity, the ratio of a so-called atactic portion is appropriately low. A method such as selecting an object can be adopted.

The stereoregularity of the biaxially oriented polypropylene film of the present invention is not particularly limited, but the isotactic pentad fraction preferably exceeds 97%. Here, the isotactic pentad fraction refers to the conformation of two adjacent repeating units in the pentad fraction based on the absorption peak of the methyl group determined from ¹³ C-NMR of polypropylene, as a meso (m). ) And racemo (denoted by r)
When expressed by, it means the ratio of the absorption peak derived from the mmmm conformation. A film with a large isotactic pentad fraction (hereinafter sometimes abbreviated as mmmm) is made of polypropylene composed of molecules having extremely long isotactic segments,
It can be a film with high crystallinity, high heat resistance, and high dielectric breakdown resistance. mmmm is more preferably 98% or more, more preferably 98.5% or more, in view of high heat resistance and high dielectric breakdown resistance. To impart such stereoregularity, it is effective to control the stereoregularity of the polypropylene resin as a raw material to a high degree. A method for producing such a raw material is achieved by using a catalyst system (solid catalyst, externally added electron-donating compound) and their purity when polymerizing polypropylene. The higher the mmmm of the polypropylene resin as the raw material, the higher the mmmm of the polypropylene film is observed.However, extreme thermal deterioration in the extrusion system of the raw material also reduces the mmmm. Structural measures such as avoiding stagnation and extrusion conditions are appropriately selected.

[0014] The intrinsic viscosity of the biaxially oriented polypropylene film of the present invention is not particularly limited.
Those having a range of 10 dl / g are preferred. Also, 230
The melt flow rate at 2.degree. C. and a load of 2.16 kg is preferably 2 to 5 g / 10 minutes from the viewpoint of film forming properties. In order to set the intrinsic viscosity and the melt flow rate to the above values,
A method of controlling the average molecular weight or the molecular weight distribution is adopted.

The ash content of the biaxially oriented polypropylene film of the present invention is preferably at most 30 ppm, more preferably at most 25 ppm, even more preferably at most 20 ppm.
ppm or less. If the ash content is too large, the dielectric breakdown resistance of the film may decrease, and the dielectric strength of a capacitor using the film may decrease. In order to keep the ash content within this range, it is important to use a raw material with little residual catalyst, but a method such as minimizing contamination from the extrusion system during film formation, for example, bleeding time of 1 hour or more is required. Such a method can be adopted.

The polypropylene used in the biaxially oriented polypropylene film of the present invention contains known additives such as a nucleating agent, an antioxidant, a heat stabilizer, a slipping agent, and an antistatic as long as the object of the present invention is not impaired. Agents, anti-blocking agents, fillers, viscosity modifiers, anti-coloring agents and the like.

Among these, selection of the type and amount of the antioxidant is important for long-term heat resistance. The antioxidant added to the biaxially oriented polypropylene film of the present invention is a phenolic agent having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various ones. For example, along with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4), 1,3,5-
Trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, “Irganox” 1330 manufactured by Ciba Geigy: molecular weight 775.2) or tetrakis [methylene-3 (3,3) 5-Di-t-butyl-4-hydroxyphenyl) propionate] methane (for example, "Irganox" 1010 manufactured by Ciba-Geigy, Inc .: molecular weight 1)
177.7) and the like are preferably used in combination. The total content of these antioxidants is 0.0% based on the total amount of polypropylene.
A range of 3 to 1% by weight is preferred. If the amount of the antioxidant is too small, long-term heat resistance may be poor. If the amount of the antioxidant is too large, blocking at a high temperature due to bleed out of the antioxidant may adversely affect the capacitor element. A more preferred content is 0.1 to 0.9.
% By weight, and more preferably 0.2 to 0.8% by weight.
It is.

The addition of a crystal nucleating agent has an effect on the surface roughness and transparency of the film, but the dielectric breakdown strength tends to deteriorate. Therefore, the addition amount is preferably less than 0.1% by weight. Preferably, it is not substantially added.

The polypropylene film of the present invention is obtained by using a raw material capable of giving the above-mentioned properties and performing biaxial orientation. The biaxial orientation method can be obtained by any of inflation simultaneous biaxial stretching method, stenter simultaneous biaxial stretching method, and stenter sequential biaxial stretching method, and among them, film forming stability, thickness uniformity, film From the viewpoint of controlling the heat of fusion and the endothermic peak accompanying the melting, those formed by a stenter sequential biaxial stretching method are preferably used.

The biaxially oriented polypropylene film of the present invention has two or more endothermic peaks associated with melting as measured by a differential scanning calorimeter, and one of the peaks is at 160 ° C.
It must be higher (hereinafter abbreviated as high temperature peak) and one of the remaining peaks is at 130-155 ° C (hereinafter abbreviated as low temperature peak). Since the high-temperature side peak contributes to heat resistance and the low-temperature side peak contributes to appropriate heat shrinkage, it is difficult to achieve both heat resistance and appropriate heat shrinkage if only one endothermic peak is included. The biaxially oriented polypropylene film of the present invention has a temperature higher than 160 ° C. and
It may have a peak outside the range of 55 ° C., but preferably does not have a peak. Further, it is more preferable not to have a peak other than a temperature higher than 160 ° C and a range of 140 to 155 ° C. Both the high-temperature side peak and the low-temperature side peak may be composed of a plurality of peaks or a single peak, but it is more preferable that the peak is composed of a single peak. The ratio of the heat of fusion between the high-temperature peak and the low-temperature peak is not particularly limited. However, from the viewpoint of heat resistance, the heat of fusion of the high-temperature peak is preferably larger than the heat of fusion of the low-temperature peak.

The biaxially oriented polypropylene film of the present invention needs to have a total heat of fusion of 85 J / g or more as measured by a differential scanning calorimeter. The heat of fusion here means that about 5 mg of a sample was measured using a differential scanning calorimeter.
It was obtained by measuring at a heating rate of 0 ° C./min. A more preferable heat of fusion is 90 J / g or more, and still more preferably 95 J / g or more. When the heat of fusion is in this range, the dielectric breakdown resistance and the heat resistance are improved.

The biaxially oriented polypropylene film (Layer B) is a polypropylene resin layer (Layer A) having a single endothermic peak at 160 ° C. or more as a result of melting when measured by a differential scanning calorimeter. It is preferable to form a laminate on at least one side, because the dielectric breakdown resistance is further improved and the dielectric breakdown strength of a capacitor using the same is improved.

By forming a laminate, it is possible to suppress a decrease in dielectric breakdown resistance due to minute internal voids generated in the biaxially oriented polypropylene film (layer B).
At this time, the thickness configurations of the A layer and the B layer are 20: 1 to 1:
It is preferably in the range of 20.

The method for obtaining a biaxially oriented polypropylene film having such properties is not particularly limited. For example, using a raw material capable of giving the above-described properties, (1) melt-extrusion from a slit die by a stenter sequential biaxial stretching method. ,
Examples include a method of performing processing when an unstretched film is obtained using a casting drum, and (2) a method of performing processing in a step after preparing a uniaxially stretched film from the unstretched film. Specifically, (1) a polypropylene raw material is supplied to an extruder, melt-extruded from a slit die at a temperature of 220 to 320 ° C, wound around a casting drum maintained at a temperature of 50 to 85 ° C, and cooled and solidified. When making a stretched film, cool air below 50 ° C, preferably 5-4
A method in which cold air at 0 ° C. is blown onto one side of the film at a speed of 10 to 200 m / s to cool the film. (2) A polypropylene raw material is supplied to an extruder, and is melt-extruded from a slit die at a temperature of 220 to 320 ° C. and cast. The unstretched film obtained by winding around a drum and solidifying by cooling was passed through a roll maintained at 120 to 150 ° C. to be preheated, and then the sheet was kept at a temperature of 130 ° C. to 150 ° C. to provide a peripheral speed difference. After passing between rolls and stretching in the longitudinal direction by 2 to 6 times, cooling to room temperature is not immediately performed, but is maintained at 120 to 150 ° C. for 0.5 to 5 seconds. Here, a specific method of maintaining the temperature at 120 to 150 ° C. for 0.5 to 5 seconds when cooling to room temperature in the method (2) is not particularly limited, but a roll maintained at 120 to 150 ° C. Examples include a method using a heater.

The biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage in the longitudinal direction when heated at 100 ° C. for 15 minutes in the range of 0.2 to 2%. If the heat shrinkage is too large, dimensional changes occur when the metal layer as an electrode is formed, wrinkles are formed in the film roll, and mechanical deformation due to heat during the production of the capacitor element is too large, so that the film roll and the external electrode and Stress may occur at the contact portion of the capacitor, and the capacity of the capacitor may be greatly reduced or the element may be destroyed. If the heat shrinkage in the longitudinal direction is too small, the tightness due to heat treatment at the time of producing the capacitor element becomes insufficient, which may adversely affect the shape retention and the capacity change rate. More preferably, the heat shrinkage in the longitudinal direction is 0.4 to 1.8%, and more preferably 0.4 to 1.8%.
A range of 5 to 1.5% is preferred.

The biaxially oriented polypropylene film of the present invention has a heat shrinkage in the width direction when heated at 100 ° C. for 15 minutes.
It is preferably in the range of 1 to 1%. If the heat shrinkage in the width direction is too large, dimensional changes may occur during the formation of the metal layer as an electrode, and the film roll may be wrinkled. If the heat shrinkage in the width direction is too small, the shape of the capacitor may be deformed or peeling may occur between film layers, which may result in a decrease in capacity or a decrease in dielectric strength. More preferably, the heat shrinkage in the width direction is -0.5 to 1%, more preferably 0 to 0.8%.

The biaxially oriented polypropylene film of the present invention has a center line average surface roughness R of at least one surface of the film.
Although a may be in the range of 0.02 to 0.2 μm, it is more preferable that a is in the range of 0.02 to 0.2 μm on both surfaces. If the center line average roughness is too large, air will enter between the layers when the films are laminated, leading to deterioration of the capacitor element, and when a metal layer is formed on the film, holes will be formed in the metal layer and the like at the time of high temperature. The dielectric breakdown strength and the element life are reduced, and electric charges are concentrated when a voltage is applied, which causes insulation defects. On the other hand, if it is too small, the film will slip poorly, and the handling properties will be poor, or if the capacitor element is impregnated with insulating oil, the insulating oil will not uniformly penetrate between the film layers, resulting in a large capacity change during continuous use. A more preferable range of the center line average surface roughness of at least one surface of the film is 0.03 to 0.15 μm, and more preferably 0.04 to 0.1 μm.

The thickness of the biaxially oriented polypropylene film of the present invention is preferably 2 to 30 μm, more preferably 2.5 to 20 μm, and still more preferably 2.5 to 10 μm.
It is. If the thickness of the film is too small, the dielectric strength and mechanical strength may be poor. If the thickness of the film is too large, it is difficult to form a film of uniform thickness, and when used as a dielectric for capacitors,
It is not preferable because the capacity per volume becomes small.

When a metal layer is formed on the biaxially oriented polypropylene film of the present invention, it is preferable to perform a corona discharge treatment or a plasma treatment on the surface on which the metal layer is formed in order to increase the adhesive strength. The corona discharge treatment is preferably carried out in air, carbon dioxide gas, nitrogen gas or a mixed gas thereof as an atmosphere gas during the treatment. In the plasma treatment, various gases are placed in a plasma state and the film surface is chemically modified, for example, a method described in JP-A-59-98.
No. 140, for example.

The method for forming a metal layer on the biaxially oriented polypropylene film of the present invention includes, but is not particularly limited to, a vacuum deposition method, a sputtering method, and an ion beam method. The metal to be used is not particularly limited, and aluminum, zinc, copper, tin, silver, nickel and the like are preferably used.

In the present invention, the film resistance of the metallized film is preferably in the range of 1 to 40 Ω / □. More preferably, it is 1.2 to 30 Ω / □. If the film resistance is too small, the thickness of the deposited film is so large that heat loss occurs during the deposition, and an avatar-shaped surface defect or a hole in a thin film of about 4 μm may occur. If the film resistance is too large, when the deposited film clears during the application of electricity, the film is likely to disappear and the change in capacitance may be large.

The specifications of the margin provided when the metal layer is formed on the biaxially oriented polypropylene film of the present invention (the portion without the metal layer provided on the surface on which the metal layer is formed for the purpose of electrical insulation, etc.) are other than the normal type. There are no particular restrictions on the configuration, depending on the purpose, such as various types provided with a fuse mechanism.

The type of the capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric is a dry type,
An oil immersion type or the like may be used, but is not particularly limited.

Next, a method for producing the biaxially oriented polypropylene film of the present invention and a method for producing a capacitor comprising the biaxially oriented polypropylene film of the present invention will be described below, but the present invention is not necessarily limited thereto.

The polypropylene raw material is supplied to an extruder, heated and melted, and passed through a filtration filter.
Melt extrusion from a slit die at a temperature of 50 ° C.
It is wound around a casting drum maintained at a temperature of ° C. and cooled and solidified to form an unstretched film. At this time, if the temperature of the casting drum is too high, the crystallization of the film may proceed too much, making it difficult to stretch the film in a subsequent step, or voids may be formed in the film, and the dielectric breakdown resistance may decrease. If the casting drum temperature is too low, the surface roughness may be too small. Examples of the method of adhesion to the casting drum include an electrostatic application method, an adhesion method using surface tension of water, an air knife method, a press roll method,
Any method such as an underwater casting method may be used, but as a method for obtaining the polypropylene film of the present invention, an air knife method having good flatness and capable of controlling the surface roughness is effective. In particular, the air knife method has an advantage that the cooling rate of the film can be controlled by adjusting the temperature and wind speed of the blown air in addition to the role of adhering the film to the casting drum, so that the differential scanning calorimeter of the present invention is used. It is suitable for obtaining a biaxially oriented polypropylene film having a specific heat of fusion and a specific endothermic peak as measured by the above. In particular, it is preferable that the temperature of the air used in the air knife method is lower than 50 ° C. and the wind speed is set to 10 to 200 m / s.

Next, the unstretched film is biaxially stretched and biaxially oriented. First, unstretched film is 120-150
Preheated by passing through a roll maintained at a temperature of 130 ° C. to 150 ° C., and subsequently passed between rolls provided with a peripheral speed difference at a temperature of 130 ° C. to 150 ° C., and stretched 2 to 6 times in the longitudinal direction. Cooling. When cooling to room temperature here, do not immediately cool,
It is preferable to maintain the temperature at 120 to 150 ° C. for 0.5 to 5 seconds because the biaxially oriented polypropylene film of the present invention is easily obtained. Subsequently, the stretched film was guided to a stenter, stretched 5 to 15 times in the width direction at a temperature of 155 to 165 ° C., and then relaxed by 2 to 20% in the width direction.
It is heat-set at a temperature of 40 to 160 ° C. and wound up. afterwards,
In order to improve the adhesion of the deposited metal to the surface on which the deposition is performed, a corona discharge treatment is performed in air, nitrogen, carbon dioxide, or a mixed gas thereof, and the film is wound by a winder.

The obtained film is set in a vacuum evaporation apparatus, and oil is applied to the film using a gravure coater to form an insulating groove according to the purpose. Then, a metal according to the purpose is applied to a predetermined film. Deposit on the resistor. This vapor deposition film is slit to form a pair of vapor deposition reels on two reels for producing a capacitor element. Thereafter, it is wound into an element shape, pressed into a flat shape by hot pressing, metal sprayed at the end (metallicon step), leads are taken out, and if necessary, an insulating oil is impregnated, and a capacitor is formed through an exterior.

The biaxially oriented polypropylene film of the present invention can be used in various packaging applications other than the above-mentioned capacitor applications, for example, by laminating it with a heat seal layer, and as an adhesive tape or a polished film (print laminate). Can also be suitably used.

The method of measuring and evaluating the characteristic values in the present invention are as follows. (1) Isotactic index (II) A sample is extracted with n-heptane at a temperature of 60 ° C or less for 2 hours to remove additives to polypropylene. Then 13
Vacuum dry at 0 ° C. for 2 hours. From this, a sample of weight W (mg) is taken, placed in a Soxhlet extractor and extracted with boiling n-heptane for 12 hours. Next, the sample was taken out, sufficiently washed with acetone, vacuum-dried at 130 ° C. for 6 hours, and then cooled to room temperature, and the weight W ′ (mg) was measured and determined by the following equation. II = (W ′ / W) × 100 (%)

(2) Isotactic Pentad Fraction A sample was dissolved in o-dichlorobenzene, and JN
Using an M-GX270 device, a resonance frequency of 67.93 MH
The ¹³ C-NMR was measured at z. For the assignment of the obtained spectra and the calculation of the pentad fraction, see T.W. Hay
, et al. [Polymer, 29, 13]
8 to 143 (1988)], the peak derived from the methyl group was found to have an mmmm peak of 21.855 pp.
Each peak was assigned as m, the peak area was determined, and the ratio to the total peak area derived from the methyl group was expressed as a percentage. Detailed measurement conditions are as follows. Measurement solvent: o-dichlorobenzene (90 wt%) / benzene-D ₆ (10 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 Point: 32K Total number of times: 8168 Measurement mode: Noise decoupling

(3) Center line average surface roughness Ra Measured using a stylus type surface roughness meter according to JIS-B0601. In addition, using a high-precision thin film step measuring device (model: ET-10) manufactured by Kosaka Laboratory Co., Ltd., a stylus diameter cone type 0.5 μmR, load 5 mg, cut-off is 0.08 mm.
And

(4) Calorie of melting, melting peak Differential scanning calorimeter DSC (RD) manufactured by Seiko Denshi Kogyo KK
C220) and the temperature was raised from room temperature to 280 ° C. at a rate of 10 ° C./min using about 5 mg of a sample. With respect to the endothermic peak observed at this time, the heat of crystal fusion was calculated from the sum of the peak areas.

(5) Heat Shrinkage Ratio The film was 260 mm long in the machine and width directions, respectively.
Sampling is performed 10 mm in width, a mark is placed at 30 mm from both ends, and the original size (L ₀ : 200 mm) is obtained. A weight of 3 g is applied to the lower end of this sample,
And heat-treat for 15 minutes. Thereafter, the sample was taken out, the marked length (L ₁ ) was measured, and the heat shrinkage was calculated by the following equation. Heat shrinkage = [(L ₀ −L ₁ ) / L ₀ ] × 100 (%)

(6) Film dielectric breakdown strength (BDV) Measured according to JIS-C-2110. 1 thickness on cathode
00μm, 10cm square aluminum foil electrode, brass 2 for cathode
Using a 5 mmφ electrode, sandwiching the film between them, and using a DC high-voltage stabilized power supply manufactured by Kasuga Electric Co., Ltd., 200 V
A voltage is applied while increasing the voltage at a speed of
The case where the flow was A or more was regarded as the breakdown. The value obtained by dividing the voltage at that time by the film thickness at the measurement point was defined as the dielectric breakdown strength, and the average value was measured at 30 points.

(7) Capacitor element life test AC voltage of 60 V / μm per film thickness (frequency 6
0 Hz) was applied to the capacitor element, and the time until the element was broken in an atmosphere at 105 ° C. was measured.

(8) Film Thickness Configuration The film cross-sectional configuration was observed using a transmission electron microscope (TEM) to measure the thickness configuration.

[0047]

EXAMPLES The effects of the present invention will be further described below with reference to examples. Example 1 II: 99.0%, mmmm: 99.4%, Ash: 19
0.3 wt% of 2,6-di-t-butyl-p-cresol (BHT) and telorakis [methylene-3 (3,5-di-t-butyl-4-hydroxyphenyl) propionate] in ppm of polypropylene raw material Methane (“Irganox” 1010 manufactured by Ciba-Geigy Co., Ltd.) was added to the extruder and added at 0.4% by weight, melted at a temperature of 240 ° C., extruded into a sheet from a T-type die, and heated at a temperature of 70 ° C. Using air knife method for casting drum, air temperature 30 ℃
And cooled and solidified. Then, the sheet is
After preheating at 0 ° C., the roll was continuously kept at a temperature of 135 ° C. and passed between rolls provided with a peripheral speed difference, and stretched 5 times in the longitudinal direction.
It was kept at 130 ° C. for 1 second. Subsequently, the film was guided to a tenter and stretched 10 times in the width direction at a temperature of 160 ° C.
Next, a heat treatment was performed at 150 ° C. while giving 8% relaxation in the width direction to obtain a biaxially oriented polypropylene film having a thickness of 5.5 μm. Further, a corona discharge treatment was performed in the atmosphere at a treatment intensity of 30 W · min / m ² . II, mmmm and ash content of the obtained film did not change from those of the raw material. This film was set in a vacuum evaporation machine, copper was used as a nucleation metal, and zinc was applied to the corona treated surface with a film resistance of 4.0.
It deposited so that it might be Ω / □. This film was slit to obtain a metallized film having a total width of 38 mm and a margin width of 1 mm. The element was wound using a pair of two reels of the obtained film, metal sprayed on an end face of the element, and a lead wire was taken out therefrom to produce a capacitor element having a capacity of 5 μF. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Example 2 II: 98.5%, mmmm: 99.0%, Ash: 20
A biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Example 1 except that a polypropylene raw material of ppm was used. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Example 3 A biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Example 1 except that the same polypropylene raw material as in Example 1 was used, and the temperature of the casting drum was set at 50 ° C. and the air temperature was set at 30 ° C. . Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Example 4 The same procedure as in Example 1 was carried out except that the same polypropylene raw material as in Example 1 was used, the casting drum temperature was 50 ° C., the air temperature was 30 ° C., the film was stretched 6 times in the longitudinal direction, and 11 times in the width direction. A biaxially oriented polypropylene film and a capacitor element were obtained by the method. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Example 5 As the layer A resin, II was 98.5% and mmmm was 98.5%.
0%, ash content of 15ppm using polypropylene raw material,
Using the polypropylene raw material of Example 1 as the B-layer resin, each was supplied to a separate extruder, melted at a temperature of 240 ° C., and extruded in a sheet form from a two-layer, two-layer T-type die. A biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Example 1. At this time, the thickness ratio between the layer A and the layer B was 5: 1. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Comparative Example 1 The same polypropylene raw material as in Example 1 was wound around a casting drum at 30 ° C. and solidified by cooling. Next, the sheet was preheated at 135 ° C., continuously passed at a temperature of 140 ° C. between rolls provided with a peripheral speed difference, and stretched 5 times in the longitudinal direction. Subsequently, the film was guided to a tenter, stretched 10 times in the width direction at a temperature of 160 ° C., and then subjected to a heat treatment at 150 ° C. while giving 8% relaxation in the width direction to obtain a biaxially oriented polypropylene film having a thickness of 5.5 μm. Was. Further, a capacitor element was manufactured in the same manner as in Example 1. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Comparative Example 2 A biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Comparative Example 1 except that the same polypropylene raw material as in Example 1 was used and the temperature of the casting drum was set at 85 ° C. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

Comparative Example 3 II: 96.0%, mmmm: 92.5%, Ash: 21
A biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Example 1 except that a polypropylene raw material of ppm was used. Table 1 summarizes the evaluation results of the obtained biaxially oriented polypropylene film and the capacitor element.

[0055]

[Table 1]

[0056]

According to the biaxially oriented polypropylene film of the present invention, by regulating the endothermic peak characteristic, the heat of fusion, and Ra within a specific range, the biaxially oriented polypropylene film is excellent in heat resistance and dielectric breakdown resistance, and has a suitable surface roughness. Heat shrinkability can be imparted, and a film particularly suitable as a film for a capacitor can be obtained.

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Claims (3)

[Claims] 1. There are two or more endothermic peaks associated with melting when measured by a differential scanning calorimeter, and one of the endothermic peaks
One above 160 ° C. and one of the remaining peaks
155 ° C., the total heat of fusion is 85 J / g or more, and the center line average surface roughness Ra of at least one surface of the film is in the range of 0.02 to 0.2 μm. Biaxially oriented polypropylene film. 2. A differential scanning calorimeter was used to measure at least one surface of a polypropylene resin layer (A layer) having a single endothermic peak at 160 ° C. or higher due to melting when measured by a differential scanning calorimeter. In this case, there are two or more endothermic peaks associated with the melting, one of the peaks is higher than 160 ° C., one of the remaining peaks is in the range of 130 to 155 ° C., and the total heat of fusion is 85 J / g or more. Yes, and
The center line average surface roughness Ra of the film surface is 0.02 to
A biaxially oriented polypropylene film, wherein a layer (layer B) in a range of 0.2 μm is laminated. 3. The heat shrinkage at 100.degree.
The biaxially oriented polypropylene film according to claim 1 or 2, wherein the thickness is in the range of 2-2% and -1 to 1% in the width direction.