JP7112661B2 - Biaxially oriented polypropylene film, metallized film and capacitor - Google Patents

Description

The present invention relates to biaxially oriented polypropylene films with improved dielectric breakdown strength (ES). It also relates to a metallized film having the biaxially oriented polypropylene film and a capacitor.

Conventionally, biaxially oriented polypropylene films have been used in electronic and electrical equipment, and because of their excellent electrical properties such as withstand voltage and low dielectric loss properties, as well as high moisture resistance, they are used in applications such as high voltage capacitors, various switching power supplies, It is widely used as a dielectric film for capacitors such as filter capacitors and smoothing capacitors for converters and inverters.

For example, Patent Document 1 discloses a method for producing a biaxially oriented polypropylene film for capacitors, and describes incorporating a polypropylene having a long-chain branched structure or a crosslinked structure into a polypropylene resin. In addition, the polypropylene having the above-mentioned long chain branched structure or crosslinked structure can be obtained by a method of obtaining a partially crosslinked structure by a method such as electron beam irradiation in the post-polymerization process of the resin, or by adding a cross-linking aid and a peroxide to the polypropylene. It is described that a long-chain branched structure or a crosslinked structure is introduced into the molecular chain by a method of kneading and kneading.

Patent Document 2 discloses a metallized biaxially oriented polypropylene film made of a polypropylene resin obtained by mixing a linear polypropylene with a branched polypropylene whose melt tension and melt flow index at a specific temperature satisfy a specific relational expression. The branched polypropylene obtained by an electron beam crosslinking method (Profax PF-814 manufactured by Basell) or obtained by crosslinking modification with a peroxide [Daploy HMS-PP manufactured by Borealis (WB130HMS, WB135HMS )] can be used.

Patent Document 3 discloses a biaxially stretched polypropylene film for capacitors containing a specific amount of branched chain polypropylene, obtained by an electron beam crosslinking method as the branched chain polypropylene (Profax PF-814 manufactured by Basell ) or those obtained by cross-linking modification with peroxide [Daploy HMS-PP (WB130HMS, WB135HMS) manufactured by Borealis] can be used.

Patent Document 4 discloses an invention relating to a polypropylene film for capacitors obtained by biaxially stretching a polypropylene resin. -814 and Daploy HMS-PP (WB130HMS, WB135HMS and WB140HMS) manufactured by Borealis, etc. can be used.

JP 2007-84813 A Japanese Patent Application Laid-Open No. 2007-290380 JP 2011-122142 A JP 2014-231584 A

In Patent Document 1, by adding or containing a polypropylene resin having a long chain branched structure or a crosslinked structure to a polypropylene resin with high stereoregularity, the effect of improving the stretchability of a polypropylene film can be obtained. is disclosed.

In Patent Document 2, by mixing a specific branched-chain polypropylene with a linear polypropylene, the spherulite size generated in the cooling process of a melt-extruded resin sheet can be controlled to be small, and insulation defects generated in the stretching process can be controlled. The effect of being able to keep the generation low is disclosed. Furthermore, while branched-chain polypropylene has an action similar to that of an α-crystal nucleating agent, it is possible to form a rough surface by crystal transformation as long as it is added in a small amount. It is also disclosed that a biaxially oriented polypropylene film can be obtained that can be formed in a small size and densely, has excellent uniformity of protrusions, and has a surface roughness with an excellent balance of roughness density. .

Patent Document 3 discloses that the polypropylene film contains a specific amount of branched chain polypropylene, so that the spherulite size generated in the cooling step of the melt-extruded resin sheet can be more easily controlled to be small, and the spherulite size generated in the stretching step can be reduced. It is disclosed that the generation of insulation defects can be suppressed and a polypropylene film having excellent voltage resistance can be obtained. Furthermore, branched-chain polypropylene has an effect like an α-crystal nucleating agent, and if the addition amount is within a certain range, it is possible to form a rough surface due to crystal transformation, thereby reducing the above-mentioned spherulite size. Combined with this, the size of the crater-like projection group can be small and dense, and the biaxially oriented polypropylene film having excellent uniformity of projections and excellent surface roughness without coarse projections can be obtained. disclosed.

In Patent Document 4, by including long-chain branched polypropylene in polypropylene resin, the crystallite size obtained from the α-crystal (040) reflecting surface of polypropylene is made finer, the birefringence is increased, and the surface roughness is improved. is disclosed to improve long-term voltage resistance.

However, polypropylene resins having a long-chain branched structure or a crosslinked structure obtained by electron beam crosslinking or peroxide modification described in Patent Documents 1 to 3 are due to crosslinking and modification in the post-polymerization process of the resin. It has been found that a film having excellent dielectric breakdown strength (ES) cannot be obtained due to a large amount of gel components that cause insulation defects.

Furthermore, the polypropylene resin having a long-chain branched structure or a crosslinked structure obtained by electron beam crosslinking or peroxide modification has poor compatibility with linear polypropylene because the branched chain length and branching spacing are not appropriate. , Since a uniform composition and surface shape of the film cannot be obtained from dry blending with linear polypropylene, it has also been found that there is a problem that it is difficult to improve the dielectric breakdown strength (ES) as in Patent Document 3. rice field.

Accordingly, an object of the present invention is to provide a biaxially oriented polypropylene film having excellent dielectric breakdown strength (ES).

As a result of intensive studies, the present inventors have found that a polypropylene A having a strain hardening parameter of less than 3 and a polypropylene B having a strain hardening parameter of 3 or more and 20 or less are contained as resin components. The inventors have found that the above problems can be solved by an axially stretched polypropylene film, and have completed the present invention.

The present invention includes the following aspects.
[1] Polypropylene A having a strain hardening parameter of less than 3;
A biaxially stretched polypropylene film characterized by containing polypropylene B having a strain hardening parameter of 3 or more and 20 or less as a resin component.
[2] The biaxially oriented polypropylene film of [1], wherein the polypropylene B is a long chain branched polypropylene.
[3] The biaxially stretched polypropylene film according to [1] or [2], wherein the polypropylene B has a gel fraction of 1000 mass ppm or less based on the mass of the polypropylene B.
Note that "the gel fraction of the polypropylene B is 1000 ppm by mass or less based on the mass of the polypropylene B" means that "the gel fraction of the polypropylene B is 1000 by mass when the polypropylene B is taken as a whole. mass ppm or less”.
[4] The biaxially oriented polypropylene film according to any one of [1] to [3], wherein the polypropylene B is obtained by polymerizing propylene using a metallocene catalyst.
[5] The biaxially oriented polypropylene film according to any one of [1] to [4], wherein the polypropylene B has a molecular weight distribution (Mw/Mn) of 1.5 or more and 4.5 or less.
[6] The biaxial stretching according to any one of [1] to [5], wherein the mass ratio of the polypropylene A and polypropylene B is polypropylene A: polypropylene B = 50:50 to 99.9:0.1 polypropylene film.
[7] The biaxially oriented polypropylene film according to any one of [1] to [6], wherein the polypropylene A has a molecular weight distribution (Mw/Mn) of 7.0 or more and 12.0 or less.
[8] The biaxially stretched polypropylene film according to any one of [1] to [7], which is used for capacitors.
[9] A metallized film having a metal film on at least one surface of the polypropylene film according to any one of [1] to [8].
[10] A capacitor comprising the metallized film of [9].

According to the present invention, by using polypropylene A having a strain hardening parameter of less than 3 and polypropylene B having a strain hardening parameter of 3 or more and 20 or less as the resin components of the biaxially stretched polypropylene film, the dielectric breakdown can be prevented. A biaxially oriented polypropylene film with excellent strength is obtained.

FIG. 1 shows a conceptual diagram of the curability parameter (λ).

≪1. Film according to the present embodiment>>
A biaxially oriented polypropylene film according to one embodiment of the present invention will be described below.
The film according to the present embodiment contains polypropylene A having a strain hardening parameter of less than 3 and polypropylene B having a strain hardening parameter of 3 or more and 20 or less as resin components. Biaxially oriented polypropylene characterized by being It's a film.

を求め、伸長粘度測定から非定常一軸伸長粘度関数η_Ｅ（ｔ）を求め、η_Ｅ（ｔ）において歪の大きさが２以上で伸長粘度が最大となる点における時間をｔ_ｍａｘとして、下記の（Ａ）式：

により歪み硬化性パラメータ（λ）を得る。なお、粘度成長関数

については、以下の（Ｂ）式：

（ただしω＝１／ｔとする。）で得られる。ここで、Ｇ’（ω）は角速度ωの関数としての貯蔵弾性率、Ｇ’（ω／２）はω／２の関数としての貯蔵弾性率、Ｇ”（ω）は各速度ωの関数としての損失弾性率、Ｇ”（ω／２）はω／２の関数としての損失弾性率、ｔは時間である。上記の歪み硬化性パラメータを得る方法は概要であり、当該歪み硬化性パラメータを得る方法の詳細については本願明細書の［実施例］の項目で記載する。 <Strain hardening parameter (λ)>
The strain hardening parameter (λ) is determined as follows. A press sheet is obtained from the resin pellets, and the shear viscoelasticity and elongational viscosity are measured using the press sheet. Viscosity growth function from shear viscoelasticity measurements

is obtained, and the unsteady uniaxial elongational viscosity function η _E (t) is obtained from the elongational viscosity measurement, and the time at the point where the strain is 2 or more and the elongational viscosity is the _maximum in η _E (t) is as follows. (A) formula of:

gives the strain hardening parameter (λ). Note that the viscosity growth function

For, the following formula (B):

(where ω=1/t). where G′(ω) is the storage modulus as a function of angular velocity ω, G′(ω/2) is the storage modulus as a function of ω/2, and G″(ω) is a function of each velocity ω , G″(ω/2) is the loss modulus as a function of ω/2, and t is time. The method of obtaining the above strain hardening parameter is an outline, and the details of the method of obtaining the strain hardening parameter are described in the [Example] section of the present specification.

The strain hardening parameter (λ) thus obtained is a parameter that captures the phenomenon called strain hardening, in which the elongational viscosity rapidly grows with time when a certain strain is exceeded.
When the strain hardening parameter is large, it indicates that the strain hardening property is large and the resistance to extensional deformation is large, that is, the degree of entanglement of molecular chains is large. When the strain hardening parameter is small, it indicates that the strain hardening property is small and the degree of entanglement of molecular chains is small.
The strain hardening phenomenon is observed in macromolecules with branches and occurs because the inhibition of molecular contraction causes the internal strain of the molecular chain, especially the molecular chain segment between branch points, to increase greatly with the external strain. In addition to the elongation of the main chain segment, the stress generated by the compression of the branch segment also contributes to strain hardening.
Therefore, the strain hardening parameter is calculated when only the branched structure of the polymer is different, and based on the Molecular Stress Function (MSF) theory [W. H. Wagner, M. Yamaguchi, M.; Takahashi, J.; Rheol. , vol. 47, p. 779 (2003)], it varies greatly depending on the length of the branched chain, and increases as the branched chain length increases.

The unsteady uniaxial elongational viscosity function η _E (t) can be measured at any strain rate using a uniaxial elongational viscosity measuring device. Moreover, the shear viscoelasticity can be measured using a dynamic viscoelasticity measuring device such as a rheometer.

<Principle>
The reason why the biaxially oriented polypropylene film has excellent dielectric breakdown strength when used for capacitors is as follows. However, even if the reason why the biaxially stretched polypropylene film is excellent in the above effect is different from the reason described below, it is clearly within the scope of the present invention.
Polypropylene having a strain hardening parameter (nonlinearity parameter) of less than 3 means that there is almost no strain hardening property of elongational viscosity, and a dynamically weak portion such as a thin portion of the sheet is easily deformed locally. Therefore, since such a stretched film has low thickness uniformity, dielectric breakdown is likely to occur in thin portions existing in the film, and the strength of dielectric breakdown is likely to be lowered. Conversely, in polypropylene with a strain hardening parameter of more than 20, adjacent polymer chains significantly inhibit molecular chain contraction motion between branched chains, resulting in (a) an increase in free volume and (b) crystal defects. and the generation of microvoids, making it difficult to increase the dielectric breakdown strength. In addition, a highly branched component such as a gel has low compatibility with polypropylene having a strain hardening parameter of less than 3, and is likely to cause insulation defects due to voids around the gel when stretched. Therefore, by combining polypropylene A with a strain hardening parameter of less than 3 and polypropylene B with a strain hardening parameter of 3 or more and 20 or less as a resin component, while suppressing the occurrence of thin portions due to the polypropylene A, branching Molecular chain contraction motion between chains is not inhibited. As a result, the dielectric breakdown strength can be improved when the film is used for a capacitor.

<Polypropylene A>
Polypropylene A has a strain hardening parameter of less than 3.

The strain hardening parameter of polypropylene A is preferably 2.5 or less, more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably 1.2 or less. If the strain hardening parameter of polypropylene A is the above, it is preferable because good moldability can be obtained and a film excellent in mechanical strength can be obtained. The lower limit of the strain hardening parameter is usually 1. Therefore, the strain hardening parameter of polypropylene A is 1 or more.
In addition, if a film is formed only with a resin having a strain hardening parameter of 3 or more, entanglement between molecular chains will become conspicuous at a high take-up speed, and melt rupture during forming will easily occur.

The gel fraction in polypropylene A is preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, more preferably 800 ppm by mass or less, relative to the mass of polypropylene A in the resin component (by mass when polypropylene A is taken as a whole) is 500 mass ppm or less, more preferably 200 mass ppm or less, and particularly preferably 100 mass ppm or less. Moreover, the lower the gel fraction of polypropylene A, the better. Therefore, the lower limit is not particularly limited, but is, for example, 0 ppm by mass, 1 ppm by mass, or the like.

The gel fraction is the mass ratio of the gel component in the resin. A gel component refers to a network structure formed by cross-linking a polymer. If the gel fraction in polypropylene A is 1000% by mass or less, insulation defects in the film are reduced, and a biaxially stretched polypropylene film having excellent dielectric breakdown strength can be obtained, which is preferable.

The gel fraction was measured as follows.
(1) About 1 g of a weighed sample was put into 200 mL of xylene and heated at 120±5° C. for 12 hours.
(2) The resulting liquid was filtered through a weighed 200-mesh wire mesh.
(3) The filtered mesh was dried at room temperature for 8 hours and at 80°C for 3 hours.
(4) The filtered mesh was weighed, and the ratio of the residue was taken as the gel fraction.

The weight average molecular weight (Mw) of polypropylene A is preferably 250,000 or more and 450,000 or less, more preferably 250,000 or more and 400,000 or less. When the weight average molecular weight of polypropylene A is 250,000 or more and 450,000 or less, the resin fluidity is moderate, the thickness of the cast raw sheet is easy to control, and it is easy to produce a thin stretched film. can be. Furthermore, it is preferable because the thickness of the sheet and film is less likely to be uneven, and the sheet can have appropriate stretchability.

The molecular weight distribution (weight average molecular weight/number average molecular weight (Mw/Mn)) of polypropylene A is preferably 7.0 or more and 12.0 or less, more preferably 7.5 or more and 12.0 or less, still more preferably 7.5 It is more than or equal to 11.0 or less, and particularly preferably 8.0 or more and 10.0 or less.
Further, the molecular weight distribution (Z average molecular weight/number average molecular weight (Mz/Mn)) of polypropylene A is more preferably 25.0 or more and 60.0 or less, still more preferably 25.0 or more and 50.0 or less, especially It is preferably 40.0 or more and 50.0 or less.

The weight average molecular weight (Mw), number average molecular weight (Mn), Z average molecular weight and molecular weight distribution (Mw/Mn and Mz/Mn) of polypropylene A can be measured using a gel permeation chromatograph (GPC) device. can. In the present invention, HLC-8121GPC-HT (trade name), a high-temperature GPC measuring instrument with a built-in differential refractometer (RI) manufactured by Tosoh Corporation, was used for measurement. As a GPC column, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation were used by connecting them. The column temperature was set to 140° C., and trichlorobenzene was passed as an eluent at a flow rate of 1.0 ml/10 minutes to obtain measured values of Mw and Mn. A standard polystyrene manufactured by Tosoh Corporation was used to prepare a calibration curve for the molecular weight M, and the measured values were converted to polystyrene values to obtain Mw, Mn and Mz. Further, the base 10 logarithm of the molecular weight M of standard polystyrene is referred to as the logarithmic molecular weight ("Log(M)").

In the molecular weight differential distribution curve of polypropylene A, the difference obtained by subtracting the differential distribution value when Log (M) = 6.0 from the differential distribution value when logarithmic molecular weight Log (M) = 4.5 is Log ( When the differential distribution value when M) = 6.0 is 100% (reference), it is preferably 8.0% or more and 18.0% or less, more preferably 10.0% or more and 17.0% or less, still more preferably is 11.0 or more and 16.0 or less, particularly preferably 12.0% or more and 16.0% or less.

Such a differential distribution value can be obtained as follows using GPC. A curve of intensity against time (also commonly referred to as an "elution curve") obtained by a GPC differential refractometer (RI) detector is used. Using a calibration curve obtained with standard polystyrene, the elution curve is converted to a curve showing intensity versus Log(M) by transforming the time axis to logarithmic molecular weight (Log(M)). Since the RI detection intensity is proportional to the component concentration, if the total area of the intensity curve is set to 100%, an integral distribution curve for the logarithmic molecular weight Log(M) can be obtained. A differential distribution curve is obtained by differentiating this integral distribution curve by Log(M). Therefore, "differential distribution" means the differential distribution of the concentration fraction with respect to the molecular weight. From this curve, the differential distribution value at a specific Log(M) can be read to obtain the above relationship.

The mesopentad fraction ([mmmm]) of polypropylene A is preferably 94.0% or more and less than 98.0%, more preferably 94.5% or more and 97.9% or less, still more preferably 94.5% or more and 97.9%. 5% or less, particularly preferably 95.0% or more and 97.0% or less. When the mesopentad fraction [mmmm] of polypropylene A is 94.0% or more and less than 98.0%, moderately high stereoregularity moderately improves the crystallinity of the resin, and the initial voltage resistance and long-term There is a tendency that the voltage resistance over a period of time is moderately improved. On the other hand, the rate of solidification (crystallization) is appropriate when the cast material sheet is formed, and it can have moderate stretchability.

The mesopentad fraction ([mmmm]) is an index of stereoregularity that can be obtained by high temperature nuclear magnetic resonance (NMR) measurements. Specifically, for example, it can be measured using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR), JNM-ECP500, manufactured by JEOL Ltd. The observation nucleus is ¹³ C (125 MHz), the measurement temperature is 135° C., and o-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixture ratio = 4/1) is used as the solvent. For the measurement method by high-temperature NMR, for example, refer to the method described in "Japan Analytical Chemistry/Polymer Analysis Research Council, New Edition, Handbook for Polymer Analysis, Kinokuniya Shoten, 1995, p. 610". It can be carried out.

The measurement mode is single-pulse proton broadband decoupling, the pulse width is 9.1 μsec (45° pulse), the pulse interval is 5.5 sec, the number of integration times is 4500, and the shift standard is CH ₃ (mmmm)=21.7 ppm. be able to.

The pentad fraction, which represents the degree of stereoregularity, is a combination of pentads (mmmm and mrrm etc.) is calculated as a percentage based on the integrated value of the intensity of each signal. Each signal derived from mmmm, mrrm, etc. can be attributed with reference to, for example, "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)".

In particular, polypropylene A has a weight average molecular weight (Mw) of 250,000 or more and 450,000 or less;
Molecular weight distribution (Mw/Mn) from 7.0 to 12.0; Z average molecular weight/number average molecular weight (Mz/Mn) from 20.0 to 70.0; Logarithmic molecular weight Log (M) in the molecular weight distribution curve The difference obtained by subtracting the differential distribution value when Log(M)=6.0 from the differential distribution value when Log(M)=4.5 is 8.0% or more and 18.0% or less; and mesopentad fraction ([mmmm]) is preferably 94.0% or more and less than 98.0%.

In this case, the logarithmic molecular weight Log ( M) = 4.5 as a representative distribution value of the component with a molecular weight of around 1 million on the high molecular weight side (hereinafter also referred to as "high molecular weight component"), Log (M) = around 6.0 , it is understood that the low-molecular-weight component is higher at a ratio of 8.0% or more and 18.0% or less.

That is, even if the molecular weight distribution Mw/Mn is 7.0 to 12.0, it merely represents the width of the molecular weight distribution width, and the high molecular weight component and low molecular weight component in it are quantitatively I don't know the relationship. Polypropylene A preferably has a wide molecular weight distribution and at the same time contains a large amount of components with a molecular weight of 10,000 to 100,000 at a rate of 8.0% or more and 18.0% or less compared to the component with a molecular weight of 1,000,000. .

For polypropylene A, the difference obtained by subtracting the differential distribution value when Log (M) = 6.0 from the differential distribution value when logarithmic molecular weight Log (M) = 4.5 is Log (M) = 6.0 Assuming that the differential distribution value at the time is 100% (reference), when it is 8.0% or more and 18.0% or less, the low molecular weight component is 8.0% or more and 18.0% or more when compared with the high molecular weight component. Since it is contained in a large amount at a rate of 0% or less, the crystallite size becomes smaller, and it becomes easier to obtain the desired orientation and roughened surface, which is preferable.

The melt tension of polypropylene A at 230° C. is preferably 1 g or less. When the melt tension of polypropylene A at 230° C. is within the above range, the flow characteristics in the molten state are excellent, and therefore unstable flow such as melt fracture is less likely to occur. Therefore, since the film thickness uniformity is good, there is an advantage that a thin portion that is likely to cause dielectric breakdown is less likely to be formed. For the melt tension, using Capilograph 1B manufactured by Toyo Seiki Co., Ltd., the resin was extruded into a string under the following conditions, and the tension detected by the pulley when wound around a roller was defined as the melt tension.
Capillary: diameter 2.0 mm, length 40 mm
Cylinder diameter: 9.55mm
Cylinder extrusion speed: 20 mm/min Winding speed: 4.0 m/min Temperature: 230°C
If the melt tension is extremely high, the resin may break at a take-up speed of 4.0 m/min. It was taken as the melting tension.

The melt flow rate (MFR) of polypropylene A at 230° C. is preferably 1 to 10 g/10 min, more preferably 1.5 to 8 g/10 min, and particularly preferably 2 to 6 g/10 min. When the MFR at 230° C. of polypropylene A is within the above range, it is excellent in flow characteristics in a molten state, so unstable flow such as melt fracture is less likely to occur, and breakage during stretching is suppressed. Therefore, since the film thickness uniformity is good, there is an advantage that the formation of a thin portion where dielectric breakdown is likely to occur is suppressed. The melt flow rate (MFR) was measured using a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS K 7210:1999.

Polypropylene A can be produced using a generally known polymerization method. There are no particular restrictions as long as the polypropylene A that can be used for the film of the present embodiment can be produced. Examples of such polymerization methods include a gas phase polymerization method, a bulk polymerization method and a slurry polymerization method.

The polymerization may be single-stage (single-stage) polymerization using one polymerization reactor, or may be multi-stage polymerization using at least two or more polymerization reactors. Furthermore, hydrogen or comonomers may be added to the reactor as molecular weight modifiers.

A generally known Ziegler-Natta catalyst or the like can be used as the catalyst, and is not particularly limited as long as the polypropylene resin according to the present embodiment can be obtained. The catalyst can also include cocatalyst components and donors. Molecular weight, molecular weight distribution, stereoregularity, etc. can be controlled by adjusting the catalyst and polymerization conditions.

As a method for obtaining polypropylene A having a strain hardening parameter of less than 3, for example, each polymerization method is adopted to obtain a polypropylene with a branched structure with a short branch chain in the polypropylene molecule, or a branched structure with many branched structures in the polypropylene molecule Obtaining a polypropylene having no chain (nearly linear) is exemplified. In other words, the strain hardening parameter tends to increase when the branched chain in the polypropylene molecule is long when only the branched structure of the polymer is different and when the MSF theory is followed. Polypropylene A having a strain hardening parameter of less than 3 can be obtained by appropriately adjusting (a) the length, (b) the number (amount), and (c) the distribution. When obtaining this polypropylene A, (i) the polymerization method and conditions such as temperature and pressure during polymerization, (ii) the shape of the reactor during polymerization, (iii) the presence or absence of additives, types and The polypropylene A can be selectively obtained by appropriately selecting or adjusting the amount used, (iv) the type and amount of the polymerization catalyst used, and the like. Polymerization methods include a slurry method using an inert solvent, a bulk method using the monomer itself (eg, propylene) as a solvent without substantially using an inert solvent, a solution polymerization method, and each monomer substantially without using a liquid solvent. is maintained in a gaseous state. The reactor for polymerization may be single-stage polymerization using one polymerization reactor, or may be multi-stage polymerization using two or more polymerization reactors. As for additives, hydrogen, various comonomers, etc. may be added to the reactor as molecular weight modifiers to carry out the polymerization. A Ziegler-Natta catalyst or the like can be used as the polymerization catalyst, and the polymerization catalyst may contain co-catalyst components and donors. The molecular weight, molecular weight distribution, stereoregularity, etc. of the polypropylene resin can be controlled by appropriately adjusting the polymerization catalyst and other polymerization conditions. By controlling the molecular weight, molecular weight distribution, stereoregularity, branching (amount, length, distribution) and the like of this polypropylene resin, the strain hardening parameter can be controlled.

When the composition of the molecular weight distribution is adjusted by the polymerization conditions, the composition of the molecular weight distribution and the molecular weight can be easily adjusted by using a polymerization catalyst. Examples of the method of obtaining by a multistage polymerization reaction include the following methods.

Polymerization is carried out at elevated temperatures in the presence of a catalyst in multiple reactors, a high molecular weight polymerization reactor and a low or medium molecular weight reactor. The high and low molecular weight components of the product resin are adjusted in any order in the reactor. First, in the first polymerization step, propylene and catalyst are supplied to the first polymerization reactor. Hydrogen as a molecular weight modifier is mixed with these components in the amount necessary to reach the desired molecular weight of the polymer. For example, in the case of slurry polymerization, the reaction temperature is about 70 to 100° C., and the residence time is about 20 to 100 minutes. Multiple reactors can be used, for example, in series, in which case the polymerization product of the first step is continuously sent to the next reactor along with additional propylene, catalyst, molecular weight modifier, followed by Then, second polymerization is carried out in which the molecular weight is adjusted to a lower or higher molecular weight than in the first polymerization step. By adjusting the yield (production volume) of the first and second reactors, it is possible to adjust the composition (structure) of the high molecular weight component and the low molecular weight component.

The catalyst may also contain co-catalyst components and donors. The molecular weight distribution can be controlled by appropriately adjusting the catalyst and polymerization conditions.

When adjusting the structure of the molecular weight distribution of the polypropylene raw material resin by peroxide decomposition, a method of peroxide treatment using a decomposing agent such as hydrogen peroxide or an organic peroxide is preferable.
When a peroxide is added to a collapsible polymer such as polypropylene, a hydrogen abstraction reaction occurs from the polymer, and some of the resulting polymer radicals recombine and cause a cross-linking reaction, but most of the radicals undergo secondary decomposition (β cleavage ) and split into two polymers with smaller molecular weights. Therefore, the high-molecular-weight components are decomposed at a high probability, thereby increasing the low-molecular-weight components and making it possible to adjust the structure of the molecular weight distribution.

Examples of methods for obtaining a resin containing an appropriate amount of low-molecular-weight components by peroxide decomposition include the following methods.

Polypropylene powder or pellets obtained by polymerization, and an organic peroxide such as 1,3-bis-(tertiary-butyl peroxide isopropyl)-benzene at 0.001% by mass to 0.5% by mass. %, while considering the composition (structure) of the target high molecular weight component and low molecular weight component, and melt kneading at a temperature of about 180 ° C. to 300 ° C. with a melt kneading machine. can also

When adjusting the content of the low-molecular-weight component by blending (resin mixing), it is preferable to dry-mix or melt-mix at least two or more resins having different molecular weights. In general, a two-type polypropylene mixed system in which the main resin is mixed with about 1 to 40% by mass of an additive resin having a higher or lower average molecular weight is preferable because it is easy to adjust the amount of the low molecular weight component. used.

Moreover, in the case of this mixing adjustment, the melt flow rate (MFR) may be used as a measure of the average molecular weight. In this case, the difference in MFR between the main resin and the additive resin should be about 1 to 30 g/10 minutes from the viewpoint of convenience during adjustment.

Methods for adjusting the "differential distribution value difference" include, for example, a method of adjusting the polymerization conditions, a method of adjusting the molecular weight distribution, a method of using a decomposing agent, a method of selectively decomposing high molecular weight components, a method of A method of mixing molecular weight resins can be mentioned. The differential distribution value difference can be adjusted to a desired value by using these methods alone or in combination of two or more.

As polypropylene A, commercially available products (for example, polypropylene manufactured by Prime Polymer Co., Ltd.) can also be used.

The content of polypropylene A in the film of the present embodiment is preferably 50% by mass or more and 99.9% by mass or less, more preferably 60% by mass or more and 99.5% by mass or less, still more preferably 70% by mass, based on the resin component. % by mass to 99% by mass, particularly preferably 80% by mass to 98.5% by mass, and more preferably 90% by mass to 98% by mass. In addition, the film of the present embodiment can contain one or more polypropylene A.

<Polypropylene B>
Polypropylene B has a strain hardening parameter of 3 or more and 20 or less. If the strain hardening parameter exceeds 20, excessive residual stress and anisotropy will occur in the film, causing problems such as impact resistance and stress crack resistance.

The strain hardening parameter of polypropylene B is preferably 3.5 or higher, more preferably 4 or higher, even more preferably 5 or higher, and particularly preferably 5.5 or higher. If the strain hardening parameter is 3 or more, the melt tension is less likely to decrease due to repeated kneading, and the strain hardening property of the resin during extensional deformation is maintained, which is preferable.
The strain hardening parameter of polypropylene B is preferably 18 or less, more preferably 16 or less, even more preferably 14 or less, and particularly preferably 12 or less. If the strain hardening parameter of polypropylene B is 20 or less, the melt tension is less likely to decrease due to repeated kneading, and the strain hardening property of the resin during extensional deformation is maintained, which is preferable.

As described in <Strain Hardening Parameter (λ)>, the strain hardening parameter tends to increase as the branched chains in the polypropylene molecule become longer. Therefore, polypropylene B can be obtained by adjusting the branched structure in the polypropylene molecule, the molecular chain length of the branched structure, and the like. Polypropylene B is preferably long chain branched polypropylene. When the polypropylene B is a long-chain branched polypropylene, it is preferable because the strain hardening parameter is moderate.

A method for producing polypropylene B includes, for example, a method of polymerizing propylene using a metallocene catalyst. Metallocene catalysts are generally metallocene compounds that form catalysts for polymerization to produce olefin macromers. In the case of polypropylene obtained by polymerizing propylene using a metallocene catalyst (metallocene catalyst type polypropylene), the branch chain length and branch chain spacing of polypropylene are moderate, and excellent compatibility with linear polypropylene and It is preferable because a uniform composition and surface shape can be obtained. In the production of polypropylene B, other conditions other than the type and amount of catalyst used, such as (i) polymerization method and conditions such as temperature and pressure during polymerization, (ii) reactor during polymerization Form, (iii) presence or absence, type and amount of use of additives, (iv) methods for adjusting molecular weight, molecular weight distribution, and stereoregularity, (v) methods for adjusting differences in differential distribution values, etc. The conditions may be the same as those described in Polypropylene A>.

In addition, when a metallocene catalyst is used in the polymerization of polypropylene B, long-chain branched polypropylene can be obtained without cross-linking and modification in the post-polymerization process, so the gel fraction caused by the post-process decreases and dielectric breakdown occurs. It is preferable because a biaxially oriented polypropylene film excellent in strength can be obtained.

Furthermore, the polypropylene obtained by polymerizing propylene using a metallocene catalyst can be obtained by a method such as electron beam irradiation in the post-polymerization process of the resin to obtain a partially crosslinked structure, or by adding a cross-linking aid and a peroxide. is added to polypropylene and kneaded to produce a polypropylene resin having a long-chain branched structure or a crosslinked structure. .

The gel fraction of polypropylene B is preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, still more preferably 500 ppm by mass relative to the mass of polypropylene B in the resin component (by mass when polypropylene B is taken as a whole). It is mass ppm or less, particularly preferably 100 mass ppm or less. When the gel fraction of polypropylene B is 1000 ppm by mass or less, insulation defects are reduced and a biaxially stretched polypropylene film having excellent dielectric breakdown strength is obtained, which is preferable. Also, the lower the gel fraction of polypropylene B, the better. Therefore, the lower limit is not particularly limited, but is, for example, 0 ppm by mass, 1 ppm by mass, 10 ppm by mass, 250 ppm by mass, and the like. The gel fraction of polypropylene B can be measured as described above.

The weight average molecular weight (Mw) of polypropylene B is preferably 150,000 or more and 600,000 or less, more preferably 200,000 or more and 500,000 or less, still more preferably 250,000 or more and 450,000 or less, particularly preferably 260,000 or more and 420,000 or less. be. When the weight average molecular weight of polypropylene B is 150,000 or more and 600,000 or less, the resin fluidity is moderate, the thickness of the cast raw sheet is easy to control, and it is easy to produce a thin stretched film. can be Furthermore, it is preferable because the thickness of the sheet and film is less likely to be uneven, and the sheet can have appropriate stretchability.

The molecular weight distribution (weight average molecular weight/number average molecular weight (Mw/Mn)) of polypropylene B is preferably 1.5 or more and 4.5 or less, more preferably 1.8 or more and 4.2 or less, and still more preferably 2.0. 4.0 or less, particularly preferably 2.1 or more and 3.9 or less, and more particularly preferably 2.2 or more and 3.8 or less.
Further, the molecular weight distribution (Z average molecular weight/number average molecular weight (Mz/Mn)) of polypropylene B is preferably 4.0 or more and 9.0 or less, more preferably 4.2 or more and 8.8 or less, further preferably 4 0.5 or more and 8.5 or less, particularly preferably 5.0 or more and 8.2 or less.

The weight average molecular weight (Mw), number average molecular weight (Mn), Z average molecular weight (Mz) and molecular weight distribution (Mw/Mn and Mz/Mn) of polypropylene B are measured using a gel permeation chromatograph (GPC) device. can do. More specifically, for example, it can be measured by high-temperature GPC-MALS measurement, that is, by a high-temperature GPC apparatus (HLC-8121GPC/HT; manufactured by Tosoh) equipped with a light scattering detector (DAWN EOS; manufactured by Wyatt Technology).
As a column, TSKgel guard column HHR (30) (7.8 mm ID × 7.5 cm) and three TSKgel GMH-HR-H (20) HT (7.8 mm ID × 30 cm), both manufactured by Tosoh Corporation, were connected. used. The column temperature was set to 140° C., and trichlorobenzene was run as an eluent at a flow rate of 1.0 ml/min to obtain measured values of Mw and Mn.

The molecular weight, molecular weight distribution, and the like of polypropylene B can be controlled by adjusting the catalyst and polymerization conditions, as described above.

The melt tension of polypropylene B at 230° C. is preferably 1 to 50 g, more preferably 2 to 40 g, even more preferably 4 to 30 g. When the melt tension at 230° C. of polypropylene B is within the above range, the flow characteristics in the molten state are excellent, and unstable flow such as melt fracture is less likely to occur. Therefore, since the film thickness uniformity is good, there is an advantage that a thin portion that is likely to cause dielectric breakdown is less likely to be formed.

The melt flow rate (MFR) of polypropylene B at 230° C. is preferably 0.1 to 12 g/10 min, more preferably 0.5 to 11 g/10 min, even more preferably 1 to 10 g/10 min. When the MFR at 230° C. of polypropylene B is within the above range, it is excellent in flow characteristics in a molten state, so unstable flow such as melt fracture is less likely to occur, and breakage during stretching is suppressed. Therefore, since the film thickness uniformity is good, there is an advantage that the formation of a thin portion where dielectric breakdown is likely to occur is suppressed.

The content of polypropylene B in the film of the present embodiment is preferably 0.1% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more and 40% by mass or less, still more preferably 1.0% by mass or more, based on the resin component. 5% by mass or more and 30% by mass or less, particularly preferably 3% by mass or more and 20% by mass or less, and more particularly preferably 3.5% by mass or more and 10% by mass or less. In addition, the film of the present embodiment can contain polypropylene B of one or more types.

Typical commercial products of polypropylene B include, for example, MFX3 and MFX6 manufactured by Japan Polypropylene Corporation, MFX8 manufactured by Japan Polypropylene Corporation, and the like.

<Resin component>
The mass ratio of polypropylene A and polypropylene B contained in the film of this embodiment is preferably polypropylene A: polypropylene B = 50: 50 to 99.9: 0.1, more preferably 60: 40 to 99: 1, and further It is preferably 70:40 to 90:10, particularly preferably 75:25 to 85:15.
The total mass% of polypropylene A and polypropylene B with respect to the total resin components constituting the film of the present embodiment is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and particularly preferably 100% by mass. % by mass (that is, the resin components constituting the film of the present embodiment are two kinds of polypropylene A and polypropylene B). Examples of resin components other than polypropylene A and polypropylene B (other resin components) include olefin resins that do not correspond to polypropylene A and polypropylene B, and the like.

<Additive>
The film of the present embodiment may further contain at least one additive in addition to the resin component. The "additive" is an additive generally used for polypropylene, and is not particularly limited as long as the biaxially oriented polypropylene film aimed at by the present invention can be obtained. Additives include, for example, β crystal nucleating agents, antioxidants, necessary stabilizers such as chlorine absorbers and UV absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and the like. When such an additive is used, the film of the present embodiment can contain the additive in an amount that does not adversely affect the biaxially oriented polypropylene film intended by the present invention.

The "β crystal nucleating agent" is generally used for polypropylene, and is not particularly limited as long as the biaxially oriented polypropylene film aimed at by the present invention can be obtained. The β-crystal nucleating agent can be dry-blended or melt-blended with a polypropylene raw material, pelletized, and used, or can be used by charging into an extruder together with polypropylene pellets. By using a β-crystal nucleating agent, the surface roughness of the film can be adjusted to a desired roughness. A typical commercial product of the β-crystal nucleating agent is Engestar NU-100 manufactured by Shin Nippon Chemical Co., Ltd., for example. When the film of the present embodiment contains a β-crystal nucleating agent, its content is preferably 1 to 1000 ppm by mass, more preferably 1 to 1000 ppm by mass relative to the mass of the resin component (in terms of mass when the resin component is taken as a whole). 50 to 600 mass ppm.

The "antioxidant" is generally called an antioxidant, is used for polypropylene, and is not particularly limited as long as the biaxially oriented polypropylene film aimed at by the present invention can be obtained. Antioxidants are commonly used for two purposes. One purpose is to suppress thermal deterioration and oxidative deterioration in the extruder, and the other purpose is to contribute to suppression of deterioration and improvement in capacitor performance during long-term use as a film for capacitors. An antioxidant that suppresses thermal and oxidative deterioration in an extruder is also called a "primary agent", and an antioxidant that contributes to improving capacitor performance is also called a "secondary agent".

Two types of antioxidants may be used for these two purposes, or one type of antioxidant may be used for these two purposes.

Examples of the primary agent include 2,6-di-tert-butyl-para-cresol (common name: BHT). The primary agent is usually added for the purpose of suppressing thermal deterioration and oxidative deterioration in the extruder during the preparation of the polypropylene resin composition, which will be described later in <Method for producing film of the present embodiment>. can. Most of the antioxidant added to the polypropylene resin composition for this purpose is consumed during the molding process in the extruder, and hardly remains in the film after film formation. Therefore, when the film of the present embodiment contains the primary agent, the content thereof is usually less than 100 ppm by mass relative to the mass of the resin component (in terms of mass when the resin component is taken as a whole).

Secondary agents include hindered phenol-based antioxidants having carbonyl groups.

"Hindered phenolic antioxidant having a carbonyl group" is usually a hindered phenolic antioxidant having a carbonyl group, especially as long as the biaxially stretched polypropylene film aimed at by the present invention can be obtained. not be restricted.

Examples of hindered phenolic antioxidants having a carbonyl group include 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), pentaerythrutil tetrakis[3-( 3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1010), 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate] (trade name: Irganox 1035), octadecyl-3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), N,N'- Hexamethylene bis(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamamide) (trade name: Irganox 1098), etc., have high molecular weight and are highly compatible with polypropylene. Pentaerythrutil tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which has low volatility and excellent heat resistance, is particularly preferred.

The film of the present embodiment may contain one or more hindered phenol-based antioxidants (secondary agent) having a carbonyl group for the purpose of suppressing deterioration that progresses over time during long-term use. When the film of the present embodiment contains one or more hindered phenol-based antioxidants having a carbonyl group, the content is relative to the mass of the resin component (in terms of mass when the resin component is taken as a whole), It is preferably 4000 mass ppm or more and 6000 mass ppm or less, more preferably 4500 mass ppm or more and 6000 mass ppm or less. It is preferable that the content of the hindered phenol-based antioxidant having a carbonyl group in the film is 4000 ppm by mass or more and 6000 ppm by mass or less from the viewpoint of appropriate effect expression.

A capacitor film containing the film of the present embodiment containing a hindered phenolic antioxidant having a carbonyl group that has good compatibility with polypropylene at the molecular level in an optimum specific range has long-term durability. It is preferable because it improves.

The "chlorine absorbent" is generally called a chlorine absorbent, is used for polypropylene, and is not particularly limited as long as the biaxially oriented polypropylene film aimed at by the present invention can be obtained. Examples of chlorine absorbents include metal soaps such as calcium stearate. When such a chlorine absorbent is used, the film of the present embodiment can contain the chlorine absorbent in an amount that does not adversely affect the biaxially oriented polypropylene film intended by the present invention.

<Thickness>
The thickness of the film of the present embodiment is preferably 0.8 μm or more and 50 μm or less, more preferably 1.0 μm or more and 30 μm or less, still more preferably 1.5 μm or more and 20 μm or less, and particularly preferably 1. It is 7 μm or more and 10 μm or less, more preferably 1.8 μm or more and 7 μm or less.
Also, the thickness of the film of the present embodiment is preferably more than 15 μm and less than 50 μm. The thickness of the film of this embodiment is more preferably greater than 16 μm and less than 30 μm, and even more preferably greater than 17 μm and less than 20 μm. The film of the present embodiment is preferably a film with an extremely thin thickness.

The thickness of the film of the present invention refers to a value measured according to JIS-C2330 using a micrometer (JIS-B7502).

<Dielectric breakdown strength (ES)>
The AC dielectric breakdown strength (ES) of the film of the present embodiment is preferably 240 [V _AC /μm] or more, more preferably 243 [V _AC /μm] or more, and still more preferably 245 [V _AC /μm]. That's it.
In addition, the DC dielectric breakdown strength (ES) of the film of the present embodiment is preferably 465 [V _DC /μm] or more, more preferably 470 [V _DC /μm] or more, further preferably 480 [V _DC /μm] or more. μm] or more.

The DC dielectric breakdown strength (ES) of a biaxially stretched film can be measured according to JIS C 2330:2010 and JIS C 2151:2006 17.2.2 (dielectric breakdown voltage/plate electrode method). The AC dielectric breakdown strength (ES) of the biaxially stretched film is determined according to the above JIS C 2330: 2010 and JIS C 2151: 2006 17.2.2 (breakdown voltage/plate electrode It can be measured according to the law). For the measurement, for example, a withstand voltage tester can be used.

<Melting point in the first run>
The first-run melting point of the film of the present embodiment is preferably 166° C. or higher, more preferably 168° C. or higher, and even more preferably 169° C. or higher. When the melting point in the first run is 166° C. or more, the thickness of the lamella is required to maintain the dielectric breakdown strength. Also, the melting point in the first run is preferably 188° C. or lower, more preferably 187° C. or lower, and even more preferably 185° C. or lower. The upper limit of the melting point in the first run is equal to or lower than the equilibrium melting point of polypropylene (the melting point when the lamella thickness is infinite), and is preferably 187° C. or lower from the viewpoint of moldability. The melting point in the first run is a value determined in the first run of differential scanning calorimetry, and specifically, it is a value measured by the method described in Examples.

<Melting enthalpy in the first run>
The first-run melting enthalpy of the film of the present embodiment is preferably 10 5 J/g or more, more preferably 10 6 J/g or more, and still more preferably 10 7 J/g or more. When the melting enthalpy in the first run is 105 J/g or more, the degree of crystallinity is required to maintain the dielectric breakdown strength. Also, the melting enthalpy in the first run is preferably 150 J/g or less, more preferably 130 J/g or less, still more preferably 120 J/g or less. When the melting enthalpy in the first run is 150 J/g or less, the film has appropriate thin film stretchability. The melting enthalpy in the first run is a value determined in the first run of differential scanning calorimetry, and specifically, it is a value measured by the method described in Examples.

<Crystallization temperature in the first run>
The first-run crystallization temperature of the film of the present embodiment is preferably 112.8° C. or higher, more preferably 112.9° C. or higher, and even more preferably 113° C. or higher. When the crystallization temperature in the first run is 112.8° C. or higher, the size of spherulites generated in the cooling process of the melt-extruded resin sheet can be controlled to be small, and the generation of insulation defects generated in the stretching process can be suppressed to a low level. can be done. Also, the crystallization temperature in the first run is preferably 125° C. or lower, more preferably 123° C. or lower, and even more preferably 122° C. or lower. When the crystallization temperature in the first run is 125° C. or lower, a rough surface can be formed by crystal transformation. The crystallization temperature in the first run is the value determined in the first run of differential scanning calorimetry, and specifically, the value measured by the method described in Examples.

<Crystallization enthalpy in the first run>
The first-run crystallization enthalpy of the film of the present embodiment is preferably −150 J/g or more, more preferably −130 J/g or more, still more preferably −120 J/g or more, and particularly preferably −110 J/g or more. be. When the crystallization enthalpy in the first run is -150 J/g or more, the film has appropriate thin film stretchability. The enthalpy of crystallization in the first run is preferably −98 J/g or less, more preferably −100 J/g or less, and still more preferably −102 J/g or less. When the crystallization enthalpy in the first run is −98 J/g or less, the degree of crystallinity is required to maintain the dielectric breakdown strength. The enthalpy of crystallization in the first run is a value determined in the first run of differential scanning calorimetry, and specifically, it is a value measured by the method described in Examples.

<Melting point in second run>
The second run melting point of the film of the present embodiment is preferably 160° C. or higher, more preferably 161° C. or higher, and still more preferably 162° C. or higher. When the melting point in the second run is 160° C. or higher, it is easy to obtain a film having a lamella thickness necessary for maintaining dielectric breakdown strength. Also, the melting point in the second run is preferably 188° C. or lower, more preferably 170° C. or lower, and even more preferably 165° C. or lower. It is preferable from the viewpoint of moldability that the melting point in the second run is 188° C. or lower. The second-run melting point is a value determined by second-run differential scanning calorimetry, and specifically, a value measured by the method described in Examples.

<Melting enthalpy in the second run>
The second-run melting enthalpy of the film of the present embodiment is preferably 95 J/g or more, more preferably 97 J/g or more, and still more preferably 98 J/g or more. When the melting enthalpy in the second run is 95 J/g or more, the degree of crystallinity necessary for maintaining dielectric breakdown strength can be easily obtained. Also, the melting enthalpy in the second run is preferably 110 J/g or less, more preferably 105 J/g or less, still more preferably 103 J/g or less. When the melting enthalpy in the second run is 110 J/g or less, the film has appropriate thin film stretchability. The melting enthalpy in the second run is the value obtained in the second run of differential scanning calorimetry, and specifically, the value measured by the method described in Examples.

≪2. Method for producing the film of the present embodiment>>
The biaxially stretched polypropylene film of the present embodiment is produced by a generally known method for producing a biaxially stretched polypropylene film, for example, polypropylene A and polypropylene B are mixed with other resins and / or additives as necessary. It can be produced by preparing a cast raw fabric sheet from the polypropylene resin composition obtained by the above, and then biaxially stretching the cast raw fabric sheet.

<Preparation of polypropylene resin composition>
The method for preparing the polypropylene resin composition is not particularly limited, but polymerized powder or pellets of polypropylene A and polypropylene B are dried using a mixer or the like together with other resins and / or additives as necessary. A method of blending, and a method of supplying polymer powders or pellets of polypropylene A and polypropylene B, optionally with other resins and/or additives, to a kneader and melt-kneading to obtain a melt-blended resin composition. etc., but any of them is fine.

The mixer and the kneader are not particularly limited, and the kneader may be of single-screw type, twin-screw type, or more multi-screw type. Furthermore, in the case of a screw type with two or more shafts, it may be a co-rotating kneading type or a counter-rotating kneading type.

In the case of blending by melt-kneading, the kneading temperature is not particularly limited as long as good kneading is obtained, but it is preferably in the range of 170 to 320°C, more preferably in the range of 200 to 300°C, and still more preferably. is between 230°C and 270°C. A too high kneading temperature invites deterioration of the resin, which is not preferable. In order to suppress deterioration during kneading and mixing of the resin, the kneader may be purged with an inert gas such as nitrogen. The melt-kneaded resin can be pelletized to an appropriate size using a generally known granulator to obtain pellets of the melt-blended resin composition.

During the preparation of the polypropylene resin composition, the primary agent as an antioxidant described in <Additives> can be added for the purpose of suppressing thermal deterioration and oxidative deterioration in the extruder.
When the polypropylene resin composition contains a primary agent, the content thereof is preferably 1000 ppm by mass to 5000 ppm by mass relative to the mass of the resin component (in mass when the resin component is taken as a whole). Most of the antioxidants for this purpose are consumed during the molding process in the extruder, and hardly remain in the film after film formation.

The hindered phenol-based antioxidant having a carbonyl group described in <Additives> above can be added to the polypropylene resin composition as a secondary agent.
When the polypropylene resin composition contains a hindered phenolic antioxidant having a carbonyl group, its content is preferably 100 mass ppm to the mass of the resin component (by mass when the resin component is taken as a whole). 10000 mass ppm, more preferably 5500 mass ppm to 7000 mass ppm. Not a little hindered phenolic antioxidants having carbonyl groups are also consumed in the extruder.
When the polypropylene resin composition does not contain a primary agent, a larger amount of hindered phenol-based antioxidant having a carbonyl group can be used. This is because the consumption of the hindered phenolic antioxidant having a carbonyl group increases in the extruder. When the polypropylene resin composition does not contain a primary agent and contains a hindered phenolic antioxidant having a carbonyl group, the content is relative to the mass of the resin component (when the resin component is taken as a whole, the mass ) 6000 mass ppm to 8000 mass ppm or less.

The total ash content resulting from polymerization catalyst residues and the like contained in the polypropylene resin composition is preferably as low as possible in order to improve electrical properties. The total ash content is preferably 50 ppm by mass or less, more preferably 40 ppm by mass or less, and even more preferably 30 ppm by mass or less based on the mass of the resin component (by mass when the resin component is taken as a whole).

<Preparation of cast raw fabric sheet>
The cast raw sheet is obtained by supplying pellets of a dry blend resin composition and / or melt blend resin composition prepared in advance to an extruder, heating and melting, passing through a filtration filter, preferably 170 ° C. to 320 ° C., more preferably from 200 ° C. to 300 ° C., and melted and extruded from a T-die, preferably from 40 ° C. to 140 ° C., more preferably from 80 ° C. to 140 ° C., still more preferably from 90 to 140 ° C., particularly preferably at 90 ° C. It can be obtained by cooling and solidifying with at least one or more metal drums maintained at a temperature (casting temperature) of up to 120° C., more preferably 90 to 105° C.

The thickness of the cast raw sheet is not particularly limited as long as the biaxially stretched polypropylene film targeted by the present invention can be obtained, but is preferably 0.05 mm to 2 mm, more preferably 0.1 mm. ~1 mm.

In addition, during the production process of the cast raw sheet (especially in the extruder), polypropylene is not a little subjected to thermal deterioration (oxidation deterioration) and shear deterioration. The degree of progress of such deterioration, that is, changes in molecular weight distribution and stereoregularity, is determined by nitrogen purge in the extruder (suppression of oxidation), screw shape in the extruder (shear force), internal shape of the T-die during casting ( shear force), the amount of antioxidant added (suppression of oxidation), the winding speed during casting (elongation force), and the like.

<Stretching treatment>
The film of the present embodiment can be produced by subjecting the raw cast sheet to a stretching treatment. A sequential biaxial stretching method is preferable as the stretching method. As the sequential biaxial stretching method, first, the cast material sheet is preferably kept at a temperature of 100 to 180° C., more preferably 140 to 160° C., passed between rolls having a speed difference, and stretched 3 to 7 times in the machine direction. and immediately cool to room temperature. By appropriately adjusting the temperature of this longitudinal stretching step, the β-crystals are melted and transformed into α-crystals, and the unevenness becomes apparent. Subsequently, the stretched film is led to a tenter and stretched 3 to 11 times in the width direction at a temperature of preferably 160° C. or higher, more preferably 160 to 180° C., then relaxed, heat-set, and wound up.

The wound film can be cut into a desired product width after being subjected to aging treatment in an atmosphere of about 20 to 45°C.

By such a stretching process, a film having excellent mechanical strength and rigidity is obtained, and the unevenness of the surface is made clearer, resulting in a finely roughened biaxially stretched film.

In addition, the biaxially stretched polypropylene film of the present embodiment may be subjected to corona discharge treatment online or offline after the stretching and heat setting steps are completed in the post-process such as the metal vapor deposition process for the purpose of improving the adhesive properties. can. Corona discharge treatment can be performed using a known method. It is preferable to use air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof as the atmospheric gas.

≪3. Metallized Film and Capacitor Containing the Film of the Present Embodiment>>
This embodiment, in another aspect, is a metallized film having a metal film on at least one side of a polypropylene film.

As a method for metallizing the surface of the film of this embodiment, for example, a vacuum deposition method and a sputtering method can be exemplified, but the method is not particularly limited. A vacuum vapor deposition method is preferable from the viewpoint of productivity, economy, and the like. Examples of the vacuum deposition method include a crucible method and a wire method in general, but the method is not particularly limited, and an optimum method can be selected as appropriate. The metal used can be, for example, single metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures thereof, and alloys thereof. Considering capacitor performance, etc., at least one selected from the group consisting of zinc and aluminum is preferable. A metal film obtained by vapor deposition is also referred to as a metal deposition film.

The film resistance value of the metal film is preferably 1 to 100Ω/□ from the viewpoint of the electrical characteristics of the capacitor. Even within this range, a high value is desirable from the viewpoint of self-healing (self-repairing) characteristics, and the membrane resistance is preferably 5 Ω/□ or more, more preferably 10 Ω/□ or more. From the viewpoint of safety as a capacitor element, the film resistance is preferably 50Ω/□ or less, more preferably 20Ω/□ or less. The film resistance value of a metal film can be measured in the metal film by, for example, a two-probe method known to those skilled in the art. The film resistance value of the metal film can be adjusted, for example, by adjusting the output of the evaporation source to adjust the evaporation amount. Although the thickness of the metal film is not particularly limited, it is preferably 1 nm to 100 nm.

When a metal film is formed on one side of the film, an insulating margin is formed without deposition of a certain width from one end of the film so that the film becomes a capacitor when the film is wound. Furthermore, in order to strengthen the bonding between the metallized polypropylene film and the metallikon electrode, it is preferable to form a heavy edge structure at the end opposite to the insulating margin, and the film resistance of the heavy edge is preferably 2 to 8 Ω/□. , and more preferably 3 to 6 Ω/□.

The margin pattern for metallization by vapor deposition is not particularly limited, but from the viewpoint of improving characteristics such as security of the capacitor, a pattern including a so-called special margin such as a fishnet pattern or a T margin pattern is used. When applied to one side of the film of the embodiment, security is enhanced, and it is effective in terms of prevention of breakage of capacitors and prevention of short circuits, and is thus preferable.

Generally known methods such as a tape method and an oil method can be used for forming the margin without any limitation.

When obtaining flat capacitors, the films of the present embodiments with attached electrodes or metallized are wound singly or in pairs or more, preferably in pairs. The number of windings can be appropriately selected according to the use of the capacitor. For example, in the case of flat type capacitors, it is about 500 to 2000 times. Winding can be performed using an automatic winder. The wound element can be heat-treated under pressure and/or under heat. The pressure under the pressurization is, for example, about 200 to 1000 kPa. Further, the temperature under the heating is, for example, about 60 to 130°C. For example, zinc metal is thermally sprayed onto the heat-treated device end faces. A flat capacitor can thus be obtained.

Since the metallized film of the present embodiment has excellent dielectric breakdown strength, it is suitable as a dielectric film for capacitors such as high-voltage capacitors, various switching power supplies, filter capacitors such as converters and inverters, and smoothing capacitors. can be used. It may also be used as a smoothing capacitor for inverter power supply circuits that control drive motors used in electric vehicles, hybrid vehicles, and the like.

Also, the film of this embodiment can be used as a capacitor by attaching electrodes. The method of attaching the electrodes is not particularly limited, and generally known methods can be used. Also, the electrodes are not particularly limited, and electrodes that are commonly used to manufacture capacitors can be used. Examples of electrodes include metal foil, paper metallized on at least one side, plastic film, and the like. As the metal used, the metals described above can be used.

This embodiment is, in another aspect, a capacitor comprising a metallized film having a metal film on at least one side of the polypropylene film of this embodiment.

The film of the present embodiment has a high dielectric breakdown strength and can therefore be very suitably used for capacitors.

The capacitance of the capacitor is preferably 5 μF or more, more preferably 10 μF or more, and still more preferably 20 μF or more.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the embodiments.

[Polypropylene resin]
The polypropylene resins used to produce the polypropylene films of Examples and Comparative Examples are shown in Table 1 below. Moreover, unless otherwise specified, descriptions of "parts" and "%" indicate "parts by mass" and "% by mass", respectively.

As polypropylene resin A, polypropylene having a number average molecular weight (Mn), a weight average molecular weight (Mw), a z average molecular weight (Mz), a molecular weight distribution (Mw/Mn), and a molecular weight distribution (Mz/Mn) shown in Table 1 below Resin A1 (isotactic polypropylene, manufactured by Prime Polymer Co., Ltd.; hereinafter referred to as resin A1) was used. These values are values measured in the form of raw material resin pellets according to the above measuring method.
As polypropylene resin B, the number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw/Mn), and molecular weight distribution (Mz/Mn) shown in Table 1 below. of each polypropylene was used. In particular,
Polypropylene B1 (WAYMAX MFX6 manufactured by Japan Polypropylene Co., Ltd., long-chain branched polypropylene obtained by polymerizing propylene using a metallocene catalyst; hereinafter referred to as resin B1),
Polypropylene B2 (WAYMAX MFX8 manufactured by Japan Polypropylene Corporation, a long-chain branched polypropylene obtained by polymerizing propylene using a metallocene catalyst; hereinafter referred to as resin B2),
Polypropylene B3 (WAYMAX MFX3 manufactured by Japan Polypropylene Co., Ltd., long-chain branched polypropylene obtained by polymerizing propylene using a metallocene catalyst; hereinafter referred to as resin B3)
was used.
As the polypropylene resin B',
B'4 (Daploy WB135HMS manufactured by Borealis AG, long chain branched polypropylene obtained by crosslinking modification with peroxide; hereinafter referred to as resin B'4),
was used.
Table 1 shows strain hardening parameters, weight average molecular weights (Mw), molecular weight distributions (Mw/Mn), and molecular weight distributions (Mz/Mn) of the polypropylene resins A1 and B1 to B'4.

を求めた。

ただしω＝１／ｔとする。
ここで、Ｇ’（ω）は角速度ω の関数としての貯蔵弾性率、Ｇ’（ω／２）はω／２の関数としての貯蔵弾性率、Ｇ”（ω）は角速度ω の関数としての損失弾性率、ｔは時間である。
（５）一方、伸長粘度測定により得られた非定常一軸伸長粘度曲線η_Ｅ（ｔ）において、歪の大きさが２以上で伸長粘度が最大となる点における時間をｔ_ｍａｘとし、下記式（Ａ）により伸長粘度の非線形性パラメータ、すなわち歪み硬化性パラメータ（λ）を求めた。なお、λについての概念図を図１に示した。

（６）なお、式（Ｂ）により得られる粘度成長関数と、非定常一軸伸長粘度曲線との間で、短時間側の線形領域の重なりが悪い場合には、非定常一軸伸長粘度曲線における線形部分の中点付近が重なるようにシフトさせてから歪み硬化性パラメータλを求めた。これは、伸長粘度測定において、歪の開放等で想定値よりも断面積が増加する場合、粘度が小さいために試料が垂れ下がり断面積が低下する場合があるため、その誤差を軽減するための措置である。 <Strain hardening parameter>
a) Dynamic viscoelasticity measuring device: ARES-G2 (manufactured by TA Instruments)
Jig: Cone plate (25 mmφ, 0.1 rad.)
Temperature: 230°C
Frequency: 100 to 0.01rad. /sec.
b) Elongational viscosity measuring device: ARES-G2 (manufactured by TA Instruments)
Jig: Elongation viscosity Fixture temperature: 230°C
Strain rate: 0.1/s. However, when the torque was low under these conditions and the elongational viscosity could not be measured, the strain rate was set at 1.0/s.
Pre-strain: 0.2mm
Measurement procedure:
(1) The resin pellets were thermally compressed at 230° C. for 5 minutes using a hot press to prepare a pressed sheet of about 0.6 mm. The obtained press sheet was subjected to shear viscoelasticity measurement (frequency dispersion) and extensional viscosity measurement using a rheometer ARES-G2 manufactured by TA Instruments.
(2) Shear viscoelasticity measurement (frequency dispersion) was performed by sandwiching the press sheet between cone plate jigs (25 mmφ, 0.1 rad) and measuring at 230° C. with a frequency of 100 to 0.01 rad/sec.
(3) Elongational viscosity was measured at 230° C. using an elongational viscosity measuring jig at a strain rate of 0.1/s after applying a preliminary strain of 0.2 mm. When the torque was low under these conditions and the elongational viscosity could not be measured, the strain rate was set at 1.0/s. The elongational viscosity measuring jig is a jig for measuring the elongational viscosity of a highly viscous substance such as a molten polymer, and is composed of a fixed part and a rotating drum so that it can be pulled at a constant Henky strain rate. there is
(4) The data obtained by shear viscoelasticity measurement (frequency dispersion) is expressed by the following formula (B) based on the method described in "Kunihiro Ozaki, Asa Murai, Nobuo Bessho, Kinhoseki, Journal of the Japanese Society of Rheology, Vol. 4, 166 (1976)". indicated viscosity growth function

asked for

However, ω=1/t.
where G'(ω) is the storage modulus as a function of angular velocity ω, G'(ω/2) is the storage modulus as a function of ω/2, and G''(ω) is the storage modulus as a function of angular velocity ω. Loss modulus, t is time.
(5) On the other hand, in the unsteady uniaxial elongational viscosity curve η _E (t) obtained by elongational viscosity measurement, the time at which the strain is 2 or more and the elongational viscosity is maximum is t _max , and the following formula ( A) was used to determine the nonlinearity parameter of elongational viscosity, that is, the strain hardening parameter (λ). A conceptual diagram of λ is shown in FIG.

(6) In addition, between the viscosity growth function obtained by formula (B) and the unsteady uniaxial elongational viscosity curve, if the overlap of the linear region on the short time side is poor, the linearity in the unsteady uniaxial elongational viscosity curve The strain hardening parameter λ was obtained after shifting so that the portions near the midpoints overlapped. In extensional viscosity measurement, if the cross-sectional area increases more than the expected value due to the release of the strain, etc., the sample may sag and the cross-sectional area may decrease due to the low viscosity, so this is a measure to reduce the error. is.

<Gel fraction>
The measurement conditions for the gel fraction of each resin were as follows.
Sample amount: about 1 g
Solvent: xylene (200 mL)
Heating temperature: 120°C
Heating time: 12 hours Filtration mesh: 200 mesh wire net Drying: Room temperature x 8 hours + 80°C x 3 hours
About 1 g of weighed sample was added to 200 mL of xylene and heated at 120° C. for 12 hours. The resulting liquid was filtered through a weighed 200-mesh wire mesh. The filtered mesh was dried at room temperature for 8 hours and at 80° C. for 3 hours. The filtered mesh was weighed, and the ratio of the residue was defined as the gel fraction.

<Measurement of Polypropylene Number Average Molecular Weight (Mn), Weight Average Molecular Weight (Mw), Z Average Molecular Weight (Mz), Molecular Weight Distribution (Mw/Mn), Molecular Weight Distribution (Mz/Mn) and Differential Distribution Value>
Using GPC (gel permeation chromatography), the number average molecular weight of polypropylene (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw/Mn), molecular weight distribution ( Mz/Mn), the differential distribution value of the distribution curve was measured.
A differential refractometer (RI) built-in high-temperature GPC apparatus HLC-8121GPC-HT manufactured by Tosoh Corporation was used. As columns, three TSKgelGMHHR-H(20)HT manufactured by Tosoh Corporation were connected, and one TSKgel guard column HHR(30) was used. At a column temperature of 140° C., 1.0 ml of 0.05 wt % 2,6-di-tert-butyl-para-cresol (common name: BHT) in 1,2,4-trichlorobenzene was used as an eluent. /min to obtain the number average molecular weight (Mn), weight average molecular weight (Mw) and z average molecular weight (Mz). A molecular weight distribution (Mz/Mn) was obtained using the values of Mz and Mn, and a molecular weight distribution (Mw/Mn) was obtained using the values of Mw and Mn. The measurement conditions are as follows.
GPC device: HLC-8121GPC/HT (manufactured by Tosoh)
Light scattering detector: DAWN EOS (Wyatt Technology),
Column: TSKgel guard column HHR (30) (7.8 mm ID × 7.5 cm) × 1 + TSKgel GMHHR-H (20) HT (7.8 mm ID × 30 cm) × 3 (manufactured by Tosoh)
Eluent: 0.05 wt% BHT in 1,2,4-trichlorobenzene
Flow rate: 1.0 mL/min
Sample concentration: 2 mg/mL
Injection volume: 300 μL
Column temperature: 140°C
System temperature: 40°C
Pretreatment: A sample was precisely weighed, an eluent was added, dissolved by shaking at 140° C. for 1 hour, and hot filtered through a 0.5 μm sintered metal filter.

<Differential distribution value difference>
The differential distribution value difference was obtained by the following method. First, the time curve (elution curve) of the intensity distribution detected using the RI detector is converted to the distribution curve for the molecular weight M (Log (M)) of the standard polystyrene using the calibration curve prepared using the standard polystyrene. Converted. Next, after obtaining the integral distribution curve for Log (M) when the total area of the distribution curve is 100%, this integral distribution curve is differentiated by Log (M), so that the differential distribution for Log (M) I was able to get the curve From this differential distribution curve, differential distribution values were read when Log(M)=4.5 and Log(M)=6.0. A series of operations up to obtaining a differential distribution curve were performed using analysis software incorporated in the GPC measuring apparatus used. Further, the measurement of the differential distribution value and the calculation of the difference in the differential distribution value were performed only for the resin A1.
As a result of the measurement and calculation, the differential distribution value when Log (M) = 6.0 was subtracted from the difference in the differential distribution value of Resin A1 (the differential distribution value when Log (M) = 4.5) , difference) was 11.7.

<Measurement of mesopentad fraction ([mmmm])>
Polypropylene 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 spectrometer (high-temperature FT-NMR).
Measuring machine: High temperature FT-NMR JNM-ECP500 manufactured by JEOL Ltd.
Observation nuclei: ¹³ C (125 MHz)
Measurement temperature: 135°C
Solvent: ortho-dichlorobenzene [ODCB: mixed solvent of ODCB and deuterated ODCB (4/1)]
Measurement mode: Single pulse proton broadband decoupling Pulse width: 9.1 μsec (45° pulse)
Pulse interval: 5.5 sec
Accumulation times: 4500 times Shift standard: CH ₃ (mmmm) = 21.7 ppm
It was calculated as a percentage (%) from the intensity integral value of each signal derived from a combination of pentads (mmmm, mrrm, etc.). Regarding the attribution of each signal derived from mmmm, mrrm, etc., reference was made to the description of spectra in, for example, "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)." The mesopentad fraction was measured only for the resin A1. The mesopentad fraction of Resin A1 was 97.8%.

<Measurement of melt flow rate>
It was measured using a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd. at a measurement temperature of 230° C. according to JIS K 7210:1999.

<Measurement of melt tension>
Using Capilograph 1B manufactured by Toyo Seiki Co., Ltd., the resin was extruded in the form of a string under the following conditions, and the tension detected by the pulley when wound around a roller was defined as the melt tension.
Capillary: diameter 2.0 mm, length 40 mm
Cylinder diameter: 9.55mm
Cylinder extrusion speed: 20 mm/min Winding speed: 4.0 m/min Temperature: 230°C
If the melt tension is extremely high, the resin may break at a take-up speed of 4.0 m/min. Melt tension.

Using the polypropylene resin described above, polypropylene films of Examples 1 , 3, 5 and 6, Reference Examples 1-2 and Comparative Examples 1-6 were produced and their physical properties were evaluated.

[Example 1]
A dry-blended resin composition in which resin A1 and resin B1 were continuously weighed and mixed at A1/B1=80/20 (mass ratio) was supplied to an extruder. After melting the dry-blended resin composition at a temperature of 230 ° C., it was extruded using a T-die, wound around a metal drum whose surface temperature (casting temperature) was kept at 45 ° C., and solidified to obtain a cast original with a thickness of 900 µm. A counter sheet was produced. This cast raw sheet is stretched 5 times in the machine direction and then 10 times in the transverse direction at 165 ° C. using a batch type biaxial stretching machine KARO IV manufactured by Bruckner Co., to obtain a biaxially stretched PP film having a thickness of 18 μm. got Table 2 summarizes the compounding ratio of the resin and the physical properties of the film obtained.

[ Reference example 1 ]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that resin B2 was used instead of resin B1. The thickness of the obtained biaxially oriented polypropylene film was 18 μm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Example 3]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the resin A1 and resin B1 were used at the mass ratio shown in Table 1. The thickness of the obtained biaxially oriented polypropylene film was 18 µm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[ Reference example 2 ]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 3, except that resin B2 was used instead of resin B1. The thickness of the obtained biaxially oriented polypropylene film was 18 μm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Example 5]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that resin B3 was used instead of resin B1. The thickness of the obtained biaxially oriented polypropylene film was 18 μm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Example 6]
A dry-blended resin composition in which resin A1 and resin B1 were continuously weighed and mixed at A1/B1=98/2 (mass ratio) was supplied to an extruder. After melting the dry-blended resin composition at a temperature of 250 ° C., it is extruded using a T-die, and solidified by winding it around a metal drum whose surface temperature (casting temperature) is kept at 95 ° C. to obtain a cast raw roll with a thickness of 100 μm. manufactured the sheet. This unstretched cast material sheet was kept at a temperature of 140° C., passed between rolls provided with a speed difference, stretched 4.5 times in the machine direction, and immediately cooled to room temperature. Subsequently, the stretched film was introduced into a tenter and stretched 10 times in the width direction at a transverse stretching temperature of 158° C., followed by relaxation and heat setting to wind up a biaxially stretched polypropylene film having a thickness of 2.5 μm.

[Comparative Example 1]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that only the resin A1 was used alone as the resin component. The thickness of the obtained biaxially oriented polypropylene film was 18 µm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Comparative Example 2]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that resin B'4 was used instead of resin B1. The thickness of the obtained biaxially oriented polypropylene film was 18 μm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Comparative Example 3]
When an attempt was made to obtain a biaxially oriented polypropylene film in the same manner as in Example 1, except that only resin B1 was used alone as the resin component, a smooth cast sheet could not be produced due to melt fracture during extrusion molding. . Therefore, when the obtained cast sheet was stretched, breakage occurred, and a stretched film could not be obtained.

[Comparative Example 4]
When an attempt was made to obtain a biaxially oriented polypropylene film in the same manner as in Example 1, except that only the resin B2 was used alone as the resin component, a smooth cast sheet could not be produced due to melt fracture during extrusion molding. . Therefore, when the obtained cast sheet was stretched, breakage occurred, and a stretched film could not be obtained.

[Comparative Example 5]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 6, except that only resin A1 was used instead of the dry blend of resin A1 and resin B1. The thickness of the obtained biaxially oriented polypropylene film was 2.5 μm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Comparative Example 6]
Example 6 except that a dry blend of resin A1 and resin B'4 (A1/B'4 = 98/2 (mass ratio)) was used instead of the dry blend of resin A1 and resin B1. A biaxially oriented polypropylene film was obtained in the same manner. The thickness of the obtained biaxially oriented polypropylene film was 2.5 μm. Table 2 summarizes the compounding ratio of the resin and the physical properties of the obtained film.

[Method for measuring characteristic values]
Methods for measuring characteristic values in Examples , Reference Examples, and Comparative Examples are as follows.

<Thickness of biaxially oriented polypropylene film>
It was measured according to JIS-C2330 using a micrometer (JIS-B7502).

<Dielectric breakdown strength>
The dielectric breakdown strength (ES) of the biaxially stretched film was measured according to JIS C 2330:2010 and JIS C 2151:2006 17.2.2 (dielectric breakdown voltage/plate electrode method). Measurement was performed at an ambient temperature of 100°C. The boost rate was 100 Vac/sec, the breaking current at breakdown was 10 mA, and the number of measurements was 18. Here, the value obtained by dividing the measured average voltage value by the thickness of the film was used for evaluation as dielectric breakdown strength. The film and the electrode jig were set in a high-temperature bath with air circulation, and the measurement was performed at an evaluation temperature of 100°C.
In addition, for Examples 1 , 3, 5 , Reference Examples 1 , 2, and Comparative Examples 1 and 2, the strength of AC dielectric breakdown (ES) was measured, and Example 6, Comparative Example 5, and Comparative Examples For Example 6, the DC breakdown strength (ES) was measured. In general, applying a voltage with an alternating current results in a higher load than applying a voltage with a direct current. Therefore, for Examples 1 , 3, and 5 , Reference Examples 1 and 2, and Comparative Examples 1 and 2 with a thickness of 18 μm, the load was not sufficient when measured with a direct current, and appropriate evaluation could not be performed. It was measured. On the other hand, in Example 6, Comparative Example 5, and Comparative Example 6, which have a thickness of 2.5 μm, a sufficient load can be applied with a direct current, so the measurement was performed with a direct current.

<Measurement of melting point, melting enthalpy, crystallization temperature, and crystallization enthalpy in first run>
5 mg samples were cut out from the biaxially stretched polypropylene films of Examples, Reference Examples, and Comparative Examples, sealed in aluminum pans, and input-compensated differential scanning calorimetry was performed using a differential scanning calorimeter (Diamond DSC manufactured by Perkin-Elmer). rice field. In the measurement, the temperature was raised from 30° C. to 280° C. at a rate of 20° C./min (first run) in a nitrogen atmosphere. From the results of the first run, the melting point, melting enthalpy, crystallization temperature, and crystallization enthalpy were obtained.

<Measurement of Melting Point and Melting Enthalpy in Second Run>
After the first run, the temperature was maintained at 280° C. for 5 minutes, then cooled to 30° C. at a cooling rate of 20° C./min, and maintained at 30° C. for 5 minutes. After that, the temperature was raised from 30° C. to 280° C. at a rate of 20° C./min in a nitrogen atmosphere (second run). The melting point and melting enthalpy were obtained from the results of the second run.

<Fabrication of capacitor element>
On the surface of the biaxially stretched polypropylene film of each example, a metal film was formed by applying a T-margin vapor deposition pattern with a vapor deposition resistance of 12Ω/□ by aluminum vapor deposition to obtain a metallized film. After slitting to a small width, the two metallized films were put together and wound for 1360 turns at a winding tension of 200 g using an automatic winding machine 3KAW-N2 manufactured by Kaito Seisakusho Co., Ltd.
The element-wound element was subjected to heat treatment at 120° C. for 4 hours while being pressed, and then the end faces of the element were thermally sprayed with zinc metal to obtain a flat capacitor. The capacitance of the finished capacitor was 100 μF (±5 μF).

As is clear from Examples 1 to 6, the film of the present invention has high dielectric breakdown strength and is extremely suitable as a capacitor film.

Claims (5)

Polypropylene A having a strain hardening parameter of less than 3;
Polypropylene B having a strain hardening parameter of 3 or more and 20 or less is contained as a resin component,
The polypropylene B is a long-chain branched polypropylene obtained by polymerizing propylene using a metallocene catalyst,
The mass ratio of the polypropylene A and the polypropylene B is polypropylene A: polypropylene B = 50: 50 to 99.9: 0.1,
The molecular weight distribution (Mw/Mn) of the polypropylene B is 1.5 or more and 4.5 or less (except when it is 3.5 or more) ,
The molecular weight distribution (Mw/Mn) of the polypropylene A is 7.0 or more and 12.0 or less,
The molecular weight distribution (Mw / Mn) is measured by using HLC-8121GPC-HT type, which is a high-temperature GPC device with a built-in differential refractometer (RI) manufactured by Tosoh Corporation, and TSKgel GMHHR-H manufactured by Tosoh Corporation as a column. (20) Three HT are connected, and one TSKgel guard column HHR (30) is used. -Di-tertiary-butyl-para-cresol is a value obtained by measuring by flowing at a flow rate of 1.0 ml / min, and the measurement conditions are as follows <Measurement conditions> Biaxial Oriented polypropylene film.
<Measurement conditions>
GPC device: HLC-8121GPC/HT (manufactured by Tosoh)
Light scattering detector: DAWN EOS (Wyatt Technology)
Column: TSKgel guard column HHR (30) (7.8 mm ID × 7.5 cm) × 1 + TSKgel GMHHR-H (20) HT (7.8 mm ID × 30 cm) × 3 (manufactured by Tosoh)
Eluent: 0.05 wt% 2,6-di-tert-butyl-para-cresol in 1,2,4-trichlorobenzene
Flow rate: 1.0 mL/min
Sample concentration: 2 mg/mL
Injection volume: 300 μL
Column temperature: 140°C
System temperature: 40°C
Pretreatment: A sample is precisely weighed, an eluent is added, dissolved by shaking at 140°C for 1 hour, and hot filtered through a 0.5 µm sintered metal filter. The biaxially stretched polypropylene film according to claim 1 , wherein the polypropylene B has a gel fraction of 1000 mass ppm or less based on the mass of the polypropylene B. The biaxially oriented polypropylene film according to claim 1 or 2 , which is used for capacitors. A metallized film having a metal film on at least one side of the polypropylene film according to any one of claims 1 to 3 . A capacitor comprising the metallized film of claim 4 .

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