JP6052032B2 - Biaxially stretched polypropylene film - Google Patents

Description

  The present invention relates to a biaxially stretched polypropylene film suitably used as a dielectric film of a capacitor.

Biaxially stretched polypropylene films have electrical properties such as excellent withstand voltage performance and low dielectric loss characteristics, and are further widely used as dielectric films for capacitors, for example, because they have high moisture resistance. Specifically, it is preferably used for high voltage capacitors, capacitors used for filtering and smoothing of various switching power supplies, converters, inverters and the like.
In particular, a capacitor using a biaxially stretched polypropylene film has begun to be widely used as a smoothing capacitor in an inverter power supply circuit for controlling a drive motor of an electric vehicle, a hybrid vehicle, or the like, which has been increasingly demanded in recent years.

A capacitor for an inverter power supply device used in such an automobile or the like has a small size, a light weight, and a high capacity, and can withstand a high voltage over a long period of time in a wide temperature range of about −40 ° C. to 100 ° C. and has a capacitance. To maintain stable operation.
Therefore, a film used as a dielectric film for a capacitor is made to be 1-6 μm thick and extremely thin (high stretching performance) in order to meet the demand for miniaturization and high capacity of the capacitor, and more. A high high temperature breakdown strength is required that does not cause breakdown even when a higher DC voltage is applied at a high temperature.

In order to improve the dielectric breakdown strength, for example, as shown in Patent Document 1 and the like, it is effective to make the polypropylene resin highly stereoregular and highly crystalline. In order to show high dielectric breakdown strength at high temperatures, for example, as exemplified in Patent Document 2, the ratio (Mw / Mn) of the number average molecular weight (Mn) and the weight average molecular weight (Mw) of the polypropylene resin is low. It is effective to use a resin having a narrow molecular weight distribution.
However, these high crystallinity and narrowing of the molecular weight distribution improve the stretchability and film thickness uniformity necessary to stably produce ultra-thin films and obtain electrical characteristics with little variation. In general, it is extremely difficult to produce ultra-thin films that are incompatible with each other and have high dielectric breakdown strength at high temperatures and little variation in thickness and the like.

  On the other hand, as a method for improving the stretchability while maintaining high dielectric breakdown strength, as exemplified in Patent Document 3, the molecular weight distribution is widened to include a large amount of ultrahigh molecular weight components and low molecular weight components. Discloses a method of imparting stretchability. However, if there are many components with low molecular weight and low crystallinity that are contained when the molecular weight distribution is widened in this way, it may cause insulation defects such as movement in the film at high temperatures. In some cases, the dielectric breakdown strength may be lowered, and the performance may be insufficient in response to the recent demand for higher capacitor use temperature.

JP-A-8-294962 JP 2012-209541 A JP 2007-137888 A

As described above, the market demands (1) Improvement of dielectric breakdown strength at high temperature, and (2) Improvement of stretchability and uniformity of thickness for ultra-thin film (higher capacitance of capacitor element) It is in a very difficult situation to obtain a propylene film for a capacitor that can simultaneously satisfy the above.
An object of the present invention is to provide a biaxially stretched polypropylene film that can produce a capacitor for electronic and electrical equipment that has these two characteristics and can be used in a small size, large capacity, and high temperature.

The present invention has the following configuration.
[1] Isotactic having a molecular weight distribution (Mw / Mn), which is a ratio of a weight average molecular weight (Mw) and a number average molecular weight (Mn) obtained by a gel permeation chromatograph (GPC) method, of 5 or more and 10 or less A biaxially oriented polypropylene film comprising a mixed resin in which a tic polypropylene resin (A) and a polypropylene resin (B) having a molecular weight distribution (Mw / Mn) of 3 or less are mixed.
[2] The mesopentad fraction [mmmm], which is the degree of stereoregularity obtained by high temperature nuclear magnetic resonance (NMR) measurement, of the polypropylene resin (B) is 30% or more and 60% or less. Biaxially oriented polypropylene film.
[3] The mixing ratio of the isotactic polypropylene resin (A) is 80% by mass or more and 99.5% by mass or less, and the mixing ratio of the polypropylene resin (B) is 0.5% by mass or more and 20% by mass or less. The biaxially stretched polypolypropylene film according to any one of [1] or [2], comprising a mixed resin.
[4] The biaxially stretched polypropylene film according to any one of [1] to [3], wherein the polypropylene resin (B) is a polypropylene resin obtained by polymerization using a single site catalyst.
[5] The weight average molecular weight (Mw) of the polypropylene resin (B) measured by gel permeation chromatography is 30,000 or more and 150,000 or less, [2] according to any one of [1] to [4] Axial oriented polypropylene film.
[6] The biaxially stretched polypropylene film according to any one of [1] to [5], wherein the polypropylene resin (B) is a homopolymer of propylene.
[7] The weight average molecular weight (Mw) of the isotactic polypropylene resin (A) measured by gel permeation chromatography is 250,000 to 450,000, [1] to [6] The biaxially stretched polypropylene film described.
[8] The isotactic polypropylene resin (A) has a mesopentad fraction [mmmm], which is a degree of stereoregularity determined by high temperature nuclear magnetic resonance (NMR) measurement, of 95% or more and 98.5% or less. The biaxially stretched polypropylene film according to any one of [1] to [7].
[9] In the differential distribution curve of the molecular weight by the gel permeation chromatography method of the biaxially stretched polypropylene film, the log ₁₀ (M) = 6 from the differential distribution value when the logarithmic molecular weight Log ₁₀ (M) = 4.5. The biaxially stretched polypropylene film according to any one of [1] to [8], wherein a difference (Δdw) obtained by subtracting the differential distribution value is 14% or more and 22% or less.
[10] The biaxially stretched polypropylene film according to any one of [1] to [9], wherein the haze degree of the biaxially stretched polypropylene film measured according to JIS-C2330 is 1% or more and 5% or less.

  According to the present invention, a small, large-capacity and high-temperature dielectric breakdown strength at a high temperature combined with stretchability and uniformity of thickness for extremely thin film (capacitance of a capacitor element). A biaxially stretched polyolefin film capable of producing a usable capacitor for electronic and electrical equipment can be provided.

Hereinafter, the present invention will be described in detail.
(Isotactic polypropylene resin (A))
Isotactic polypropylene resin is a resin having crystallinity and is suitable for use in a dielectric film of a capacitor from the viewpoint of electrical characteristics. The isotactic polypropylene resin (A) is a homopolymer of propylene. As a polymerization method for producing the isotactic polypropylene resin (A), a known polymerization method can be employed. Examples of the polymerization method include a gas phase polymerization method, a bulk polymerization method, and a slurry polymerization method. There is no restriction | limiting in particular as a polymerization catalyst, The solid-state titanium catalyst containing titanium, magnesium, a halogen, etc. can be used.

The isotactic polypropylene resin (A) has a molecular weight distribution (Mw / Mn) of 5 which is a ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) method. 10 or less. The molecular weight distribution (Mw / Mn) is more preferably 6 or more and 10 or less, and further preferably 8 or more and 9.5 or less. An isotactic polypropylene resin having a molecular weight distribution (Mw / Mn) value in the above range tends to improve the stretchability and easily improve the dielectric breakdown strength of the biaxially stretched polypropylene film.
When the molecular weight distribution (Mw / Mn) exceeds 10, it is not preferable because the dielectric breakdown strength is easily lowered at a high temperature. The reason for this is not necessarily clear, but when the molecular weight distribution is made very wide in this way, there are probably many low molecular weight and low crystallinity components such as a molecular weight of 3000 or less, which are It is presumed that it sometimes causes insulation defects by moving within the film.
On the other hand, when the molecular weight distribution (Mw / Mn) is less than 5, there is a tendency that the stretchability is inferior and breakage or the like occurs and the film cannot be stably produced, or the film has poor thickness uniformity during stretching. Yes.

The GPC apparatus used for the GPC method is not particularly limited, and is a commercially available high-temperature GPC apparatus capable of analyzing the molecular weight of polyolefins, for example, a built-in differential refractometer (RI) manufactured by Tosoh Corporation. A high temperature GPC measuring machine, HLC-8121GPC-HT, etc. can be used.
Specifically, a GPC column manufactured by Tosoh Co., Ltd. and three TSKgel GMHHR-H (20) HT connected together is used, the column temperature is set to 140 ° C., and trichlorobenzene is used as the eluent. Used and measured at a flow rate of 1.0 ml / min. Standard polystyrene manufactured by Tosoh Corporation is used for the production of the calibration curve, and the measurement results are converted into polypropylene values.

  The isotactic polypropylene resin (A) preferably has a weight average molecular weight (Mw) of 250,000 to 500,000, more preferably 350,000 to 450,000, obtained by the GPC method. When the weight average molecular weight is 500,000 or less, the resin fluidity is excellent and the stretchability when producing a very thin biaxially stretched polyolefin film is excellent. When the weight average molecular weight is 250,000 or more, the biaxially oriented polypropylene film is excellent in terms of thickness uniformity, mechanical properties, thermo-mechanical properties, and the like.

  As a method for controlling the molecular weight distribution (Mw / Mn) and the weight average molecular weight (Mw) to the above-mentioned values, the polymerization temperature, the polymerization time, the type and amount of the polymerization catalyst during polymerization may be appropriately adjusted.

In order to control the molecular weight distribution (Mw / Mn), the molecular weight distribution of the isotactic polypropylene resin (A) may be adjusted by peroxidation treatment.
When a decomposition agent such as hydrogen peroxide or organic (peroxide) is added to a collapsible polymer such as polypropylene, a hydrogen abstraction reaction occurs from the polymer, and the resulting polymer radicals partially recombine and cause a crosslinking reaction. It is known that most radicals undergo secondary decomposition (β-cleavage) and are separated into two polymers having smaller molecular weights. Therefore, decomposition proceeds with a high probability from the high molecular weight component, thereby increasing the low molecular weight component and controlling the molecular weight distribution.
As a method for the peroxidation treatment, for example, an organic (per) oxide (for example, 1,3-bis- (tertiary-butyl peroxide isopropyl)- Benzene, etc.) is added within a range of about 0.001 to 0.5% by mass in consideration of the target molecular weight distribution, and melt kneaded at a temperature of about 180 to 300 ° C. in a melt kneader. Etc. can be illustrated.

Further, at least two or more types of isotactic polypropylene resins may be used by dry blending or melt-kneading so as to satisfy the ranges of molecular weight distribution (Mw / Mn) and weight average molecular weight (Mw).
There is no particular limitation on the mixer used for dry blending and the kneading machine used for melt kneading, and a kneading machine of a single screw type, a twin screw type, or a multi-screw type can be used as appropriate. Further, in the case of a screw type having two or more axes, either a kneading type rotating in the same direction or rotating in a different direction may be used.

The isotactic polypropylene resin (A) preferably has a mesopentad fraction [mmmm], which is the degree of stereoregularity determined by high-temperature nuclear magnetic resonance (NMR) measurement, of 95% or more and 98.5% or less. % To 98% is more preferable.
When the mesopentad fraction [mmmm] is 95% or more, the crystallinity of the resin is improved by the high stereoregular component, and the dielectric breakdown strength at a high temperature is easily obtained. On the other hand, by setting the mesopentad fraction [mmmm] to 98.5% or less, the speed of solidification (crystallization) of the cast sheet in the cast sheet manufacturing process described later is set to an appropriate speed, and the metal drum for forming the cast sheet The peelability from the (cooling molding roll) is improved, and the stretchability is easily improved.

There is no particular limitation on the high-temperature NMR apparatus used for measuring the mesopentad fraction [mmmm], and a commercially available high-temperature nuclear magnetic resonance (NMR) apparatus capable of measuring the stereoregularity of polyolefins, for example, A high temperature Fourier transform nuclear magnetic resonance apparatus (high temperature FT-NMR) manufactured by JEOL Ltd., JNM-ECP500, etc. can be used.
The observation nucleus is 13C (125 MHz), the measurement temperature is 135 ° C., and the solvent is ortho-dichlorobenzene (ODCB: ODCB and deuterated ODCB mixed solvent (mixing ratio = 4/1 (V / V))). Used. The method by high temperature NMR can be performed by a known method, for example, the method described in “Edited by Japan Analytical Chemistry / Polymer Analysis Research Committee, New Edition Polymer Analysis Handbook, Kinokuniya, 1995, p. 610”.
Measurement mode is single pulse proton broadband decoupling, pulse width is 9.1 μsec (45 ° pulse), pulse interval is 5.5 sec, integration is 4500 times, shift reference is CH ₃ (mmmm) = 21.7 ppm. The

  The pentad fraction representing the degree of stereoregularity is a combination of a quintet (pentad) of a consensus “meso (m)” arranged in the same direction and a consensus “rasemo (r)” arranged in the same direction (mmmm or mrrm). Etc.) is calculated as a percentage from the integrated intensity value of each signal derived from. Regarding the attribution of each signal derived from mmmm, mrrm, etc., reference is made to the description of the spectrum such as “T. Hayashi et al., Polymer, 29, 138 (1988)”.

  The melting point of the isotactic polypropylene resin (A) measured by the DSC (Differential Scanning Calorimetry) method is preferably 158 ° C. or higher, more preferably 161 ° C. or higher. A temperature of 158 ° C. or higher is preferred because the dielectric breakdown strength at high temperatures tends to be good. The upper limit is preferably 170 ° C. or lower, and more preferably 168 ° C. or lower. By making it 170 degrees C or less, it becomes easy to improve the drawability and the uniformity of thickness of a film.

The DSC apparatus used for the measurement of the melting point is not particularly limited, and is a commercially available DSC apparatus capable of measuring the melting point of polyolefins, for example, Perkin Elmer, Inc. A company-made Diamond DSC can be used.
The measurement conditions for the melting point are as follows. First, about 5 mg of polypropylene resin is weighed, sealed in an aluminum sample holder, and set in a DSC apparatus. The temperature is raised from 30 ° C. to 280 ° C. at a rate of 20 ° C./min under a nitrogen flow and held for 5 minutes. Thereafter, the temperature is lowered to 30 ° C. at a rate of 20 ° C./min and held for 5 minutes. Next, the temperature is raised again at 20 ° C./minute, the melting peak of the crystal is measured, and the top temperature of the endothermic peak is measured. When showing a plurality of endothermic peaks, the temperature at the top of the maximum endothermic peak is measured. The above measurement was repeated three times, and the average value of the three points was taken as the melting point.

  According to JIS-K7210 (1999) of isotactic polypropylene resin (A), the melt flow index (MFR) measured at a measurement temperature of 230 ° C. and a load of 21.18 N is 2 g / 10 min or more, 7 g / 10 min. Or less, more preferably 3 g / 10 min or more and 5 g / 10 min or less. By setting it within this range, it becomes easy to improve the stretchability and thickness uniformity of the film.

(Polypropylene resin B)
Polypropylene resin B is a propylene homopolymer or a crystalline resin composition mainly composed of propylene having a molecular weight distribution (Mw / Mn) of 3 or less obtained by the GPC method. Use of a propylene homopolymer is preferred because it tends to increase the dielectric breakdown strength. Polypropylene resin B may be used individually by 1 type, and may use 2 or more types together.
The smaller the value of the molecular weight distribution (Mw / Mn), the narrower the molecular weight distribution is. The lower limit is theoretically 1 but this means a single molecular weight resin and is obtained industrially. This is difficult at present, and is practically 1.5 or more.
The molecular weight distribution (Mw / Mn) can be 2.8 or less, 2.6 or less, 2.5 or less, 2.3 or less, 2.0 or less, 1.8 or less. It is preferable. By setting the molecular weight distribution (Mw / Mn) to 3 or less, it is possible to hardly generate a low molecular weight and low crystallinity component that is considered to be a cause of insulation defects when the film is used at a high temperature. Conceivable.
However, when such a polypropylene resin having a small Mw / Mn is used alone, the stretchability of the film tends to be lowered, and the uniformity of the thickness tends to be lowered. However, the present inventors have found that by using this in a mixture with the above-mentioned isotactic polypropylene resin A, the film can be used in a state where the stretchability and thickness uniformity of the film are good. It was.

  The polypropylene resin (B) preferably has a weight average molecular weight (Mw) obtained by the GPC method of 30,000 to 150,000, more preferably 60,000 to 130,000. By setting the weight average molecular weight to 30,000 or more, it is considered that a component having low molecular weight and low crystallinity, which is considered to cause an insulation defect when the film is used at a high temperature, can be hardly generated. Moreover, it becomes easy to improve the drawability and the uniformity of thickness of a film by setting it as 150,000 or less.

  As a method for obtaining a polypropylene resin having a narrow molecular weight distribution, there is a method in which an organic (per) oxide is added to a polymer powder or pellets of a polypropylene resin obtained by polymerizing in advance and melt kneaded. In order to obtain a polypropylene resin (B) having a very narrow molecular weight distribution (Mw / Mn) of 3 or less, a method obtained by polymerization using a single site catalyst is preferably used.

The single-site catalyst refers to a catalyst constituted by substantially homogeneous polymerization active sites. Specifically, a metallocene-based transition metal compound (so-called Kaminsky catalyst) or a non-metallocene-based transition metal compound ( And a polymerization catalyst composed of a Brookhardt catalyst, a phenoxyimine complex, etc.) and a co-catalyst (methylaluminoxane, boron compound, etc.).
As a preferable single site catalyst, a metallocene catalyst having a metallocene transition metal compound as a main component can be exemplified. As the metallocene catalyst, a non-bridged metallocene catalyst such as biscyclopentadienylzirconium dichloride or a substituted product thereof can also be used. Moreover, the catalyst described in Unexamined-Japanese-Patent No. WO2003 / 087172 gazette pages 11-22 can be used conveniently.

The polypropylene resin (B) has a mesopentad fraction [mmmm], which is the degree of stereoregularity determined by high temperature nuclear magnetic resonance (NMR) measurement, of 20% or more, 25% or more, 27% or more, 30% or more, 32%. 35% or more, 37% or more, 40% or more, 42% or more, 70% or less, 65% or less, 62% or less, 60% or less, 57% or less, 55% or less, 52% or less, 50% or less, It can be 47% or less. The mesopentad fraction [mmmm] is preferably 30% to 60%, more preferably 35% to 55%, and still more preferably 40% to 50%.
By setting the mesopentad fraction [mmmm] to 30% or more, it is possible to hardly generate a low molecular weight and low crystallinity component that is likely to cause insulation defects when the film is used at a high temperature. Conceivable. Moreover, it becomes easy to improve the drawability and the uniformity of thickness of a film by setting it as 60% or less.

  As the polypropylene resin (B), those sold as "L-MODU (registered trademark) series" by Idemitsu Kosan Co., Ltd. can be suitably used. Specific product names include “L-MODU S400”, “L-MODU S600”, “L-MODU S900”, “L-MODU S901”, and the like.

As for the mixing ratio of the isotactic polypropylene resin (A) and the polypropylene resin (B), the mixing ratio of the isotactic polypropylene resin (A) is 80% or more and 99.5% or less, and the mixing ratio of the polypropylene resin (B) is 0. It is preferable to mix at 5% or more and 20% or less. More preferably, the mixing ratio of the isotactic polypropylene resin (A) is 85% or more and 99% or less, the mixing ratio of the polypropylene resin (B) is 1% or more and 15% or less, and the more preferable mixing ratio is isotactic. The mixing ratio of the polypropylene resin (A) is 94% or more and 98% or less, and the mixing ratio of the polypropylene resin (B) is 2% or more and 6% or less.
By setting the mixing ratio, it is easy to achieve both improvement in dielectric breakdown strength at high temperature and improvement in film stretchability and thickness uniformity.

A differential distribution value in a differential distribution curve of molecular weight by GPC method of a film made of a mixture of this isotactic polypropylene resin (A) and polypropylene resin (B) is obtained by GPC method as follows. That is, a time curve (generally referred to as an elution curve) of an intensity distribution detected by a differential refraction (RI) detector of GPC is obtained by using a calibration curve obtained from a substance having a known molecular weight, and a logarithmic molecular weight (Log ₁₀ ( Mw)) to a distribution curve. Here, since the RI detection intensity is proportional to the component concentration, an integral distribution curve with respect to the logarithmic molecular weight Log ₁₀ (Mw) when the total area of the distribution curve is 100% is obtained. The differential distribution curve is obtained by differentiating the integral distribution curve with Log ₁₀ (Mw). Thus, the differential distribution here means a differential distribution with respect to the molecular weight of the concentration fraction. From this curve, the differential distribution value at a specific Log ₁₀ (Mw) can be read.

The logarithmic molecular weight is the logarithm of the weight average molecular weight (Mw) (Log ₁₀ (Mw)), and the differential distribution value at Log ₁₀ (Mw) = 4.5 as the representative value of the low molecular weight component is the representative of the high molecular weight component. As the value, the differential distribution value when Log ₁₀ (Mw) = 6 is adopted, and “the difference obtained by subtracting the differential distribution value when the logarithmic molecular weight is 6 from the differential distribution value when the logarithmic molecular weight is 4.5 (Δdw ) Means that the amount of the component (low molecular weight component) having a weight average molecular weight (Mw) of 10 ^4.5 is larger than the amount of the component (high molecular weight component) having a weight average molecular weight (Mw) of 10 ⁶ The value of the difference (Δdw) being “positive” means that the amount of the low molecular weight component is larger than the amount of the high molecular weight component.
The difference (Δdw) obtained by subtracting the differential distribution value when Log ₁₀ (M) = 6 from the differential distribution value when Log ₁₀ (M) = 4.5 in the differential distribution curve of molecular weight by the GPC method is 14 % Is preferably 21% or less and more preferably 16% or more and 19% or less.
The molecular weight distribution is adjusted by mixing the isotactic polypropylene resin (A) and the polypropylene resin (B), and the weight distribution from the differential distribution value of the component having a weight average molecular weight (Mw) of 10 ^4.5 (low molecular weight component) When the difference (Δdw) obtained by subtracting the differential distribution value of the component having a mean molecular weight (Mw) of 10 ⁶ (high molecular weight component) is within the above range, the dielectric breakdown strength at high temperature of the film, the stretchability and thickness of the film It is easy to achieve both uniformity.

(Other ingredients)
You may mix | blend antioxidant with the biaxially stretched polypropylene film of this invention. Antioxidant has a role as a primary agent that is blended for the purpose of suppressing heat and oxidative deterioration in an extruder during the production of biaxially oriented polypropylene film, and deterioration over time when used as a capacitor for a long time. And at least a role as a secondary agent to be blended for the purpose of suppressing the above.
Depending on these two roles, different types of antioxidants may be used, or one type of antioxidant may have two roles.

  When different types of antioxidants are used, for example, 2,6-di-tert-butyl-para-cresol (generic name: BHT) is used as the primary agent for the purpose of suppressing deterioration in the extruder. It is preferable to add about 1000 to 4000 ppm in the resin composition. Most of the antioxidant blended for this purpose is consumed in the molding process in the extruder, and hardly remains in the biaxially oriented polypropylene film. Therefore, the remaining amount is generally less than 100 ppm, which is preferable in that the antioxidant has almost no influence on the film characteristics.

As the secondary agent, it is preferable to use one or more hindered phenol antioxidants having a carbonyl group. Thereby, the effect which suppresses deterioration with time at the time of long-term use as a capacitor | condenser can be provided with respect to a biaxially stretched polypropylene film.
As the hindered phenol-based antioxidant having a carbonyl group, triethylene glycol-bis [3- (3-tertiary-butyl-5-methyl-4-hydroxyphenyl) propionate) (trade name: Irganox 245), 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (trade name: Irganox 259), pentaerythryl tetrakis [3- (3 5-Di-tertiary-butyl-4-hydroxyphenyl) propionate] (trade name: Irganox 1010), 2,2-thio-diethylenebis [3- (3,5-di-tertiary-butyl-4- Hydroxyphenyl) propionate] (trade name: Irganox 1035), octadecyl-3- 3,5-di-tertiary-butyl-4-hydroxyphenyl) propionate (trade name: Irganox 1076), N, N′-hexamethylenebis (3,5-di-tertiary-butyl-4-hydroxy-) Hydrocinnamamide) (trade name: Irganox 1098) and the like, but is high molecular weight, highly compatible with polypropylene, low volatility and excellent heat resistance, pentaerythryl tetrakis [3- ( 3,5-di-tertiary-butyl-4-hydroxyphenyl) propionate] is most preferred.

The content of the hindered phenol-based antioxidant having a carbonyl group is preferably 4000 to 6000 ppm, more preferably 4500 to 6000 ppm, as the abundance (residual amount) in the biaxially stretched polypropylene film based on mass. When it is less than 4000 ppm, the effect of suppressing deterioration over time when used as a capacitor for a long time tends to be insufficient. On the other hand, if it exceeds 6000 ppm, the antioxidant itself may become a charge carrier (a certain kind of impurity), and as a result, a current is generated under a high voltage, and the destruction phenomenon of the capacitor element called thermal runaway or rupture, etc. On the contrary, long-term tolerance may be lost.
At least a part of the hindered phenol-based antioxidant having a carbonyl group is consumed in the extruder during production of the biaxially oriented polypropylene film. Therefore, in order to make the existing amount in the biaxially stretched polypropylene film of the hindered phenol-based antioxidant having a carbonyl group within the above range, the added amount before extrusion is about 1000 to 2000 ppm than the target existing amount. It is preferable to make it larger.

In the biaxially stretched polypropylene film of the present invention, various additives (stabilizers such as chlorine absorbers and ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, etc.) are optionally added. It can add within the range which does not impair the effect of this invention.
The total ash content contained in the biaxially stretched polypropylene film is preferably as small as possible in order to improve the dielectric breakdown strength, preferably 50 ppm or less, and more preferably 40 ppm or less.

[Production method of biaxially oriented polypropylene film]
The biaxially stretched polypropylene film of the present invention is a polypropylene resin composition obtained by mixing an isotactic polypropylene resin (A), a polypropylene resin (B), and antioxidants and various additives that are added as necessary. Can be produced by a method comprising a preparation step for preparing a cast sheet, a cast sheet production step for producing a cast sheet from the polypropylene resin composition obtained by the preparation step, and a stretching step for biaxially stretching the obtained cast sheet.

  The layer structure of the biaxially stretched polypropylene film of the present invention may be a single layer structure or a structure of two or more layers, but in the case of a structure of two or more layers, each layer satisfies the requirements necessary for the present invention. There is a need to be. As long as the requirements necessary for the present invention are satisfied, the type of resin, the mixing ratio, and the like may be different for each layer, or may be the same.

(Preparation process)
The preparation process can be performed by dry blending or melt kneading, but dry blending is preferred because the process is simple and manufacturing costs are superior.
As a mixing apparatus in the case of dry blending, any of a batch type such as a tumbler and a wing mixer and a continuous type measuring mixer can be preferably used.
In the case of melt kneading, the resin temperature is preferably 200 to 250 ° C. If it exceeds 250 ° C., the isotactic propylene resin may be thermally deteriorated and the dielectric breakdown strength of the film may be reduced. If the resin temperature at the time of melt-kneading is lower than 200 ° C., kneading is insufficient, the film components become non-uniform, and the stretchability and thickness uniformity may decrease.
There is no restriction | limiting in particular in a kneading machine, The thing of a 1 axis screw type, a 2 axis screw type, and a multi-axis screw type can be used suitably. In the case of a screw type with two or more shafts, it can be used by adjusting the kneading conditions so that the resin deterioration does not become large regardless of whether the kneading type is rotating in the same direction or rotating in the same direction. When a rotating twin screw type is used, it is preferable that the resin hardly deteriorates by heat.

(Cast sheet manufacturing process)
The cast sheet manufacturing process for forming a cast sheet (raw sheet) before stretching is supplied to the extruder by the polypropylene resin composition such as powder or pellets prepared in the above preparation process, heated and melted, After passing through a filter, it is melt extruded from a T die.
The resin temperature during extrusion molding is preferably 210 to 250 ° C. If it exceeds 250 ° C., the isotactic propylene resin may be thermally deteriorated and the dielectric breakdown voltage of the film capacitor may be lowered. If the resin temperature at the time of melt-kneading is lower than 210 ° C., kneading is insufficient, the film components become non-uniform, and the stretchability and thickness uniformity may decrease.

  By appropriately adjusting the opening and temperature of the lip portion of the T die used for melt extrusion, the thickness of the cast sheet and the thickness after stretching can be finely adjusted. It is preferable to continuously measure the thickness after stretching and adjust the opening and temperature of the lip portion of the T die so that the thickness becomes more uniform.

Next, the resin layer melt-extruded from the T die is cooled and solidified by one or more cooling molding rolls maintained at 10 to 140 ° C., whereby an unstretched cast sheet is obtained. 70-110 degreeC is preferable, as for the temperature of a cooling molding roll, 80-105 degreeC is more preferable, and 90-100 degreeC is further more preferable.
When two or more cooling molding rolls are used, it is preferable that the second-stage (second) cooling molding roll is brought into contact with the surface opposite to the surface in contact with the first-stage cooling molding roll. The temperature of the second-stage cooling molding roll is preferably 30 to 90 ° C.

The temperature of the cooling molding roll affects the size and amount of β crystals generated in the cast sheet. It is well known that the β-crystal of the cast sheet is crystallized into α-crystal by being heated at the time of stretching to form irregularities mainly in a crater shape on the surface of the stretched film.
In general, when the temperature of the cooling molding roll is low, the unevenness is small and / or small, and it is easy to suppress that the thickness of the film becomes locally thin and causes insulation defects. If it is high, this unevenness will be large and / or large, and at the time of processing such as winding and rewinding the film, or at the time of element winding when manufacturing a capacitor, an appropriate gap is generated between the films, There is a tendency that wrinkles and lateral misalignment are less likely to occur and the processability is improved.
On the other hand, the temperature of the cooling molding roll also affects the uniformity of the thickness of the cast sheet and the uniformity of the thickness of the film after stretching, and the uniformity of the thickness may decrease if the temperature is too high or too low. is there.
For this reason, it is preferable to control the temperature of the cooling molding roll within the above-described temperature range so that the dielectric breakdown strength and the uniformity of the thickness are good.

In order to control the amount and size of the unevenness described above, it is preferable to measure the degree of haze of the stretched film according to JIS-K7136. In the transparent film, the degree of haze changes due to light scattering on the surface, so that the roughened state of the film surface can be indirectly evaluated. And since the apparatus which can implement continuously the measurement which can be converted into the haze degree according to JIS-K7136 is marketed, it comes out to use as a suitable parameter | index.
The haze degree of the biaxially stretched polypropylene film is preferably 1% or more and 4% or less. More preferably, it is 1.5% or more and 3.5% or less.
The haze degree tends to slightly decrease as the addition amount of the polypropylene resin (B) increases. However, the haze degree can be adjusted by adjusting the temperature of the cooling molding roll to be slightly higher as long as the amount is within the above-described range of the mixing amount. Can be adjusted within the range.

  In the cast sheet manufacturing process, the thickness of the cast sheet to be manufactured is not particularly limited, but is usually 0.05 to 2 mm. This thickness is preferably adjusted appropriately in order to continuously measure the thickness after stretching and to obtain the target thickness.

(Stretching process)
In the stretching process, a biaxial stretching process is performed on the cast sheet obtained in the cast sheet manufacturing process. As the biaxial stretching method, both simultaneous biaxial stretching and sequential biaxial stretching can be employed.
As an example of the sequential biaxial stretching method, first, the cast sheet is preferably maintained at a temperature of 130 to 155 ° C., more preferably 135 to 150 ° C., and passed between rolls provided with a speed difference (longitudinal direction, The film is longitudinally stretched 4 to 8 times in the MD direction (longitudinal stretching step). Subsequently, the longitudinally stretched stretched film is guided to a tenter, preferably at a temperature of 155 ° C. or more, more preferably 160 to 175 ° C., in the direction perpendicular to the flow direction (lateral direction, width direction, TD direction) of 8 to After transverse stretching by 12 times (lateral stretching step), the transverse stretching ratio is relaxed and heat-set by about 10% (relaxation step).
As an example of the simultaneous biaxial stretching method, the cast sheet is guided to a tenter, and is preferably stretched 4 to 12 times in the flow direction at a temperature of 155 ° C. or more, more preferably 160 to 175 ° C. Is stretched 4 to 12 times in the direction orthogonal to the stretching (stretching step), and the ratio of longitudinal stretching and transverse stretching is relaxed and heat-fixed by about 10% (relaxation step).
By appropriately adjusting the temperature in each stretching step to the above range, it is possible to stretch with good stretchability and uniform thickness. Further, since the haze degree tends to increase when the temperature in each stretching step is high, it is preferable to appropriately adjust the temperature in each stretching step while measuring the haze degree.
The relaxed and heat-set film is subjected to a corona discharge treatment, which will be described later, if necessary, and is wound up by a winder. The wound film is subjected to an aging treatment in an atmosphere of about 20 to 45 ° C. and then cut to a desired product width.

When the total draw ratio of the biaxially stretched polypropylene film is increased, the dielectric breakdown strength of the film capacitor tends to be improved. This is presumed to be due to the fact that the molecular chains of the film stretched at a high stretch ratio are strongly oriented in the stretching direction, making it difficult for current to flow even when a voltage is applied.
The total draw ratio, which is the product of the stretch ratio in the longitudinal direction after relaxation and the stretch ratio in the transverse direction after relaxation, is preferably 40 times or more, more preferably 45 times or more, and the dielectric breakdown of the film. Great effect to improve strength. On the other hand, if the total draw ratio becomes too high, there is a possibility that productivity will be reduced due to stretch breakage. Therefore, the total draw ratio is preferably 70 times or less.

  The thickness of the biaxially stretched polypropylene film is preferably 1 to 6 μm, more preferably 1.5 to 4 μm, and more preferably 1.5 to 3.5 μm from the viewpoint of miniaturization of the film capacitor and stable productivity. More preferably, 1.8-3 micrometers is especially preferable.

(Corona discharge treatment process)
After the stretching process, on-line or off-line corona discharge treatment is performed on the roughened surface of the biaxially stretched polypropylene film for the purpose of enhancing the adhesive properties in the subsequent process such as providing a metal vapor deposition film. Is preferred. Although a well-known method can be employ | adopted for a corona discharge process, it is preferable to use air, a carbon dioxide gas, nitrogen gas, and these mixed gas as atmospheric gas.
In addition, you may corona discharge-process on both surfaces of a biaxially-stretched polypropylene film, and may provide a metal vapor deposition film on both surfaces.

(Example of film capacitor production)
Examples of a method for providing a metal vapor deposition film on a biaxially stretched polypropylene film include a vacuum vapor deposition method and a sputtering method, and the vacuum vapor deposition method is preferable from the viewpoint of productivity and economy. What is necessary is just to select suitably from well-known methods, such as a crucible method type and a wire system, as a vacuum evaporation method.
As metal constituting the metal vapor deposition film, zinc, lead, silver, chromium, aluminum, copper, nickel, etc. can be used alone, multiple kinds of mixtures, alloys, etc. Is preferably zinc or aluminum.

The margin pattern of the metal vapor deposition film is not particularly limited, but a pattern including a so-called special margin such as a fish net pattern or a T margin pattern is preferable from the viewpoint of the security of the film capacitor. When a biaxially stretched polypolypropylene film obtained by providing a metal vapor deposition film with a pattern including a special margin is used, the film capacitor is excellent in security and can prevent the film capacitor from being broken or short-circuited.
As a method for forming the margin, a known method such as a tape method in which masking is performed with a tape at the time of vapor deposition or an oil method in which masking is performed by application of oil can be employed.

  The biaxially stretched polypropylene film of the present invention provided with a metal vapor-deposited film is processed into a film capacitor through a winding process of winding along the longitudinal direction of the film. As a configuration of the film capacitor, for example, a method of welding a metal to both ends of a wound product (element body) obtained by winding and providing an external electrode, and further welding a lead wire to the external electrode, etc. Manufactured.

  The biaxially stretched polyolefin film of the present invention is excellent in dielectric breakdown strength at high temperature, and since the thickness uniformity is good, there is little variation in device performance such as capacitance, and because the stretchability is good, the thickness is thin as described above. It is easy to be within the range, and high capacitance is easy to develop. Therefore, it can be suitably used for a small-sized capacitor having a capacitance of 5 μF or more, preferably 10 μF or more, more preferably 20 μF or more.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, the scope of the present invention is not limited to these. Moreover, unless otherwise indicated, the part in an example shows "mass part" and% shows "mass%".

In the following examples, the following commercially available resins (a) to (d) were used as isotactic polypropylene resins. Each of the resins (a) to (d) contains 5500 ppm of pentaerythrityl tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant. In addition, the isotactic polypropylene resin (d) is one that has been subjected to peroxide treatment using 1,3-bis- (tertiary-butyl peroxide isopropyl) -benzene.
・ Isotactic polypropylene resin (a)
Mw: 400,000, Mw / Mn: 8.9, [mmmm] value: 97.8%, melting point 162 ° C., MFR 4.1 g / 10 min.
・ Isotactic polypropylene resin (b)
Mw: 350,000, Mw / Mn: 7.9, [mmmm] value: 95.8%, melting point 163 ° C., MFR 3.1 g / 10 min.
・ Isotactic polypropylene resin (c)
Mw: 300,000, Mw / Mn: 4.3, [mmmm] value: 93.7%, melting point 160 ° C., MFR 2.9 g / 10 min.
・ Isotactic polypropylene resin (d)
Mw: 330,000, Mw / Mn: 10.8, [mmmm] value: 97.2%, melting point 162 ° C., MFR 6.4 g / 10 min.

[Example 1]
L-MODU (registered trademark) S901 manufactured by Idemitsu Kosan Co., Ltd. (Mw: 120,000, Mw / Mn: 2, [mmmm]) using 96% by mass of isotactic polypropylene resin (a) and polypropylene resin (B). (Value: 44.6%) 4% by mass was mixed by a continuous metering mixer and supplied to a single-screw kneading type extruder.
It is heated and melted so that the resin temperature becomes 230 ° C. with an extruder, and after passing through a filter, it is melt-extruded from a T-die and pressed against the first cooling molding roll having a surface temperature of 96 ° C. using an air knife. It was. Next, the opposite surface was pressed against a second-stage cooling molding roll having a surface temperature of 70 ° C. to cool and solidify to obtain a cast sheet. The thickness of the cast sheet was appropriately adjusted so that the thickness of the biaxially stretched polypropylene film measured as needed was 2.5 μm. The cast sheet had a thickness of about 0.15 mm.
Subsequently, the cast sheet was heated to 146 ° C., passed through a roll having a speed difference, and stretched 5 times in the longitudinal direction. Next, the stretched film was guided to a tenter, heated to 165 ° C., stretched 10 times in the transverse direction, relaxed to 9 times, and heat-set at 170 ° C.
Next, the surface of the biaxially stretched film pressed against the first-stage cooling molding roll was subjected to corona discharge treatment in an air atmosphere and wound up with a winder. The wound roll was subjected to an aging treatment in an atmosphere of 35 ° C. for 24 hours to obtain a biaxially stretched polypropylene film having a thickness of 2.5 μm.
Table 1 shows the results of various measurements and evaluations on the obtained biaxially stretched polypropylene film.

[Example 2]
The same procedure as in Example 1 was performed except that isotactic polypropylene resin (a) was 88% by mass and polypropylene resin (B) was changed to 12% by mass of L-MODU (registered trademark) S901 manufactured by Idemitsu Kosan Co., Ltd. Thus, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

Example 3
The same procedure as in Example 1 was conducted except that isotactic polypropylene resin (a) was 82% by mass, polypropylene resin (B), and L-MODU (registered trademark) S901 made by Idemitsu Kosan Co., Ltd. was 18% by mass. Thus, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

Example 4
L-MODU (registered trademark) S600 (Mw: 70,000, Mw / Mn: 2, [mmmm], manufactured by Idemitsu Kosan Co., Ltd., with 99% by mass of isotactic polypropylene resin (a) and polypropylene resin (B). A biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the value was changed to 1% by mass.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

Example 5
The same procedure as in Example 1 was performed except that isotactic polypropylene resin (b) was 88% by mass and polypropylene resin (B) was 12% by mass of L-MODU (registered trademark) S901 manufactured by Idemitsu Kosan Co., Ltd. Thus, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

[Comparative Example 1]
A biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the isotactic polypropylene resin (a) was 100% by mass and the polypropylene resin (B) was not used.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

[Comparative Example 2]
A biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the isotactic polypropylene resin (b) was 100% by mass and the polypropylene resin (B) was not used.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

[Comparative Example 3]
Example 1 except that the isotactic polypropylene resin (c) was 96% by mass and the polypropylene resin (B) was 4% by mass of L-MODU (registered trademark) S901 manufactured by Idemitsu Kosan Co., Ltd. Thus, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

[Comparative Example 4]
A biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the isotactic polypropylene resin (d) was 100% by mass and the polypropylene resin (B) was not used.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

[Comparative Example 5]
Example 1 except that the isotactic polypropylene resin (d) was 96% by mass and the polypropylene resin (B) was 4% by mass of L-MODU (registered trademark) S901 manufactured by Idemitsu Kosan Co., Ltd. Thus, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained.
Table 1 shows the results of measurements and evaluations similar to those in Example 1.

[Various measurement methods and evaluation methods]
Various measurement methods and evaluation methods in the above Examples and Comparative Examples are shown below.
(1) Measurement of weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and difference (Δdw) Measurement was performed using GPC under the following conditions.
Measuring instrument: manufactured by Tosoh Corporation, differential refractometer (RI) built-in high-temperature GPC, HLC-8121GPC-HT type Column: manufactured by Tosoh Corporation, three TSKgel GMHHR-H (20) HT columns Column temperature: 140 ° C
Eluent: Trichlorobenzene Flow rate: 1.0 ml / min
For the production of the calibration curve, standard polystyrene manufactured by Tosoh Corporation was used, and the measurement results were converted to polypropylene values.
The difference (Δdw) was obtained by the following method.
First, the time curve (elution curve) of the intensity distribution detected by the RI detector was used as a distribution curve for the molecular weight (Log ₁₀ (Mw)) using a calibration curve. Then, after obtaining the integral distribution curve for Log (Mw) in the case where the total area of distribution curve 100%, the integral distribution curve in _Log 10 (Mw), by _{differentiating, Log} 10 (Mw) A differential distribution curve for was obtained.
From this differential distribution curve, the differential distribution values when Log ₁₀ (Mw) = 4.5 and Log ₁₀ (Mw) = 6 were read, and the difference (Δdw) was obtained.
A series of operations until obtaining the differential distribution curve can be normally performed using analysis software built in the GPC measurement apparatus.

(2) Measurement of the mesopentad fraction [mmmm] of the polypropylene resin The polypropylene resin was dissolved in a solvent, and the mesopentad fraction [mmmm] was obtained under the following conditions using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR). Asked.
Measuring instrument: JEOL Ltd., high temperature FT-NMR JNM-ECP500
Observation nucleus: 13C (125MHz)
Measurement temperature: 135 ° C
Solvent: Ortho-dichlorobenzene [ODCB: Mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4/1 (V / V))]
Measurement mode: Single pulse proton broadband decoupling Pulse width: 9.1 μsec (45 ° pulse)
Pulse interval: 5.5 sec
Integration count: 4500 shift standard: CH ₃ (mmmm) = 21.7 ppm
It calculated by the percentage (%) from the intensity | strength integral value of each signal derived from the combination (mmmm, mrrm, etc.) of a pentad (pentad). Regarding the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of spectra such as “T. Hayashi et al., Polymer, 29, 138 (1988)” was referred to.

(3) Measurement of melting point of polypropylene resin Perkin Elmer, Inc. The measurement was performed under the following conditions using a Diamond DSC manufactured by the company.
First, about 5 mg of polypropylene resin is weighed, sealed in an aluminum sample holder, and set in a DSC apparatus. The temperature is raised from 30 ° C. to 280 ° C. at a rate of 20 ° C./min under a nitrogen flow and held for 5 minutes. Thereafter, the temperature is lowered to 30 ° C. at a rate of 20 ° C./min and held for 5 minutes. Next, the temperature is raised again at 20 ° C./minute, the melting peak of the crystal is measured, and the top temperature of the endothermic peak is measured. When showing a plurality of endothermic peaks, the temperature at the top of the maximum endothermic peak is measured. The above measurement was repeated three times, and the average value of the three points was taken as the melting point.

(4) Melt flow index (MFR) measurement of polypropylene resin According to JIS-K7210 (1999), measurement was performed at a measurement temperature of 230 ° C. and a load of 21.18 N using a Toyo Seiki Seisakusho melt indexer. .

(5) Measurement of haze degree of film It measured based on JIS-K7136 using Nippon Denshoku Industries Co., Ltd. haze meter NDH-5000.

(6) Film thickness measurement It measured based on JIS-C2330 using Citizen Seimitsu Co., Ltd. paper thickness measuring device MEI-11.

(7) Evaluation of uniformity of film thickness (6) Ten points are measured at equal intervals in the width direction of the film by the same method. At this time, 10 points are measured at regular intervals for an area having a length of 80% or more of the film width. The variation (maximum value−minimum value) is calculated from the maximum and minimum values of each measured value. The calculated value was judged according to the following criteria.
A: The variation is less than 4% of the film thickness, which is very good.
○: Good variation is 4% or more and less than 6% of the film thickness.
Δ: Variation is 6% or more and less than 8% of the film thickness, which is somewhat problematic in use.
X: The variation is 8% or more of the film thickness, and there is a problem in use.

(8) Evaluation of stretchability of film It was determined according to the following criteria depending on the situation during biaxial stretching.
○: No breakage or uneven stretching is observed in the film, which is good.
Δ: The film is not torn, but stretching unevenness is recognized, and there is a slight problem in production.
X: The film is torn and has a manufacturing problem.

(9) Evaluation of dielectric breakdown strength at high temperature of the film The voltage resistance of the biaxially stretched polypropylene film is in accordance with JIS-C2330 7.4.11.2 (dielectric breakdown voltage / plate electrode method: method B). The breakdown voltage value was evaluated by measuring with a direct current (DC). A film and an electrode jig were set in an air circulation type thermostatic chamber, and measurement was performed at an evaluation temperature of 100 ° C. The boosting speed was 100 V / sec, and the breaking current at the time of breakdown was 10 mA. A value obtained by dividing the measured average voltage value by the thickness of the film was used for evaluation as dielectric breakdown strength at high temperature.
The dielectric breakdown strength at a high temperature is suitably 420 V _DC / μm or more for practical use. More preferably, it is 450 V _DC / μm or more.

(Discussion)
The biaxially stretched polypropylene film of Example 1 using isotactic polypropylene resin (a) and containing 4% by mass of polypropylene resin (B), and Example 2 containing 12% by mass is uniform in stretchability and thickness. And the dielectric breakdown strength at high temperature were both excellent.
The biaxially stretched polypropylene film of Example 3 containing 18% by mass of the polypropylene resin (B) and Example 4 containing 1% by mass of the polypropylene resin (B) has excellent stretchability and thickness uniformity, and high temperature. Although both dielectric breakdown strengths were inferior to Example 1, they were excellent.
On the other hand, the biaxially stretched polypropylene film of Comparative Example 1 and Comparative Example 2 containing 4% by mass of polymethylpentene containing no polypropylene resin (B) has stretchability and uniformity of thickness, and insulation at high temperature. Both fracture strengths were inferior.

  The biaxially stretched polypropylene film of Example 5 using the isotactic polypropylene resin (b) having a molecular weight distribution (Mw / Mn) of 7.9 is uniform in stretchability and thickness, and dielectric breakdown strength at high temperature. The biaxially stretched polypropylene film of Comparative Example 3 using the isotactic polypropylene resin (c) having a molecular weight distribution (Mw / Mn) of 4.3 was excellent in stretchability and thickness uniformity. The dielectric breakdown strength at high temperatures was both inferior.

The biaxially stretched polypropylene film of Comparative Example 4 using the isotactic polypropylene resin (d) whose molecular weight distribution is adjusted by peroxide treatment without using the polypropylene resin (B) is not stretchable or uniform in thickness. Although it was excellent, the dielectric breakdown strength at high temperature was inferior.
The biaxially stretched polypropylene film of Comparative Example 5 containing 4% by mass of the polypropylene resin (B) in the isotactic polypropylene resin (d) having a molecular weight distribution (Mw / Mn) of 10.8 is also uniform in stretchability and thickness. Although the properties were excellent, the dielectric breakdown strength at high temperatures was poor.

  The biaxially stretched polypropylene film of the present invention can be preferably used for small and large-capacity capacitors such as automobiles and power applications that require high voltage and heat resistance.

Claims (10)

A biaxially oriented polypropylene film,
The film has a molecular weight distribution (Mw / Mn), which is a ratio of a weight average molecular weight (Mw) and a number average molecular weight (Mn) obtained by a gel permeation chromatograph (GPC) method, of 5 to 10 the isotactic polypropylene resin (a), the Ri Do a molecular weight distribution (Mw / Mn) of the polypropylene resin (B) and is mixed mixed resin is 3 or less,
The polypropylene resin (B) has a mesopentad fraction [mmmm], which is the degree of stereoregularity determined by high temperature nuclear magnetic resonance (NMR) measurement, of 30% or more and 60% or less.
The polypropylene resin (B) is a homopolymer of propylene.
A biaxially stretched polypropylene film characterized by that . A mixed resin in which the mixing ratio of the isotactic polypropylene resin (A) is 80% by mass or more and 99.5% by mass or less, and the mixing ratio of the polypropylene resin (B) is 0.5% by mass or more and 20% by mass or less. The biaxially stretched polypolypropylene film according to claim 1, comprising: The biaxially stretched polypropylene film according to claim 1 or 2 , wherein the polypropylene resin (B) is a polypropylene resin obtained by polymerization using a single site catalyst. The biaxially stretched polypropylene film according to any one of claims 1 to 3 , wherein the polypropylene resin (B) has a weight average molecular weight (Mw) measured by a gel permeation chromatography method of 30,000 to 150,000. . The weight average molecular weight (Mw) measured by the gel permeation chromatograph method of the said isotactic polypropylene resin (A) is 250,000 or more and 450,000 or less, The 2 of any one of Claims 1-4 Axial oriented polypropylene film. The mesopentad fraction [mmmm], which is the degree of stereoregularity determined by high temperature nuclear magnetic resonance (NMR) measurement, of the isotactic polypropylene resin (A) is 95% or more and 98.5% or less. The biaxially stretched polypropylene film according to any one of to 5 . In the differential distribution curve of the molecular weight of the biaxially stretched polypropylene film by the gel permeation chromatography method, the differential distribution value at the time of Log ₁₀ (M) = 6 from the differential distribution value at the time of log molecular weight Log ₁₀ (M) = 4.5 The biaxially stretched polypropylene film according to any one of claims 1 to 6 , wherein a difference (Δdw) obtained by subtracting the distribution value is 14% or more and 22% or less. The biaxially stretched polypropylene film according to any one of claims 1 to 7, wherein a haze degree measured according to JIS-C2330 of the biaxially stretched polypropylene film is 1% or more and 5% or less.   The metal vapor deposition film containing film in which the metal vapor deposition film is formed in the biaxially-stretched polypropylene film of any one of Claims 1-8.   The film capacitor containing the metal vapor deposition film containing film of Claim 9.