JP2021167419A - Biaxially oriented polypropylene film, metalized film and capacitor - Google Patents

Abstract

To provide a biaxially oriented polypropylene film excellent in dielectric breakdown strength (ES).SOLUTION: A biaxially oriented polypropylene film includes, as a resin component, a polypropylene A whose strain hardening parameter is less than 3, and a polypropylene B whose strain hardening parameter is 3-20.SELECTED DRAWING: None

Description

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

Conventionally, biaxially stretched polypropylene films have been used in electronic and electrical equipment, and because of their excellent electrical characteristics such as withstand voltage and low dielectric loss characteristics, as well as high moisture resistance, for example, high voltage capacitors, various switching power supplies, etc. It is widely used as a dielectric film for filters such as converters and inverters and capacitors for smoothing capacitors.

For example, Patent Document 1 discloses a method for producing a biaxially stretched polypropylene film for a capacitor, and describes that polypropylene having a long-chain branched structure or a crosslinked structure is contained in a polypropylene resin. Further, polypropylene having the above-mentioned long-chain branched structure or crosslinked structure can have a partially crosslinked structure by a method such as irradiation with an electron beam in a subsequent step of resin polymerization, or a crosslinking aid and a peroxide are added to polypropylene. It is described that a long-chain branched structure or a crosslinked structure is introduced into the molecular chain by the method of kneading.

Patent Document 2 describes a metallized biaxially oriented polypropylene film made of a polypropylene resin in which linear polypropylene is mixed with branched polypropylene in which the melt tension at a specific temperature and the melt flow index satisfy a specific relational expression. Disclosed, as branched polypropylene obtained by electron beam cross-linking method (Profax PF-814 manufactured by Basell) and obtained by cross-linking modification with peroxide [Daploy HMS-PP manufactured by Borearis (WB130HMS, WB135HMS). )] Can be used.

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

Patent Document 4 discloses an invention relating to a polypropylene film for a capacitor obtained by biaxially stretching a polypropylene resin, that the polypropylene resin can contain long-chain branched polypropylene, and that the long-chain branched polypropylene is a Profax PF manufactured by Basell. It is described that -814, Borealis's Daploy HMS-PP (WB130HMS, WB135HMS and WB140HMS) and the like can be used.

Japanese Unexamined Patent Publication No. 2007-84813 JP-A-2007-290380 Japanese Unexamined Patent Publication No. 2011-122142 Japanese Unexamined Patent Publication No. 2014-231584

Patent Document 1 provides an effect that the stretchability of a polypropylene film is improved by adding or containing a polypropylene resin having a long-chain branched structure or a crosslinked structure to a polypropylene resin having high stereoregularity. Is disclosed.

In Patent Document 2, by mixing a specific branched chain polypropylene with linear polypropylene, the spherulite size generated in the cooling step of the melt-extruded resin sheet can be controlled to be small, and the insulation defects generated in the stretching step can be controlled. The effect of keeping the production low is disclosed. Furthermore, while the branched chain polypropylene has an α-crystal nucleating agent-like action, it is possible to form a rough surface by crystal transformation within the range of addition in a small amount, and in combination with the above-mentioned effect of reducing the spherulite size, the crater. It is also disclosed that a biaxially oriented polypropylene film having a small size, which can be formed densely, has excellent uniformity of protrusions, and has a surface roughness having an excellent balance of roughness densities can be obtained. ..

In Patent Document 3, when the polypropylene film contains branched chain polypropylene in a specific amount, the spherulite size produced in the cooling step of the melt-extruded resin sheet can be more easily controlled to be smaller, and the spherulite size is produced in the stretching step. The effect that the generation of insulation defects can be suppressed to a small value and a polypropylene film having excellent withstand voltage can be obtained is disclosed. Further, the branched polypropylene has an effect of reducing the above-mentioned spherulite size by being able to form a rough surface by crystal transformation if the amount added is in a certain range while having an action like an α crystal nucleating agent. Combined with this, the size of the crater-shaped protrusions can be reduced and densely formed, and the biaxially stretched polypropylene film having excellent protrusion uniformity and excellent surface roughness without coarse protrusions can be obtained. It is disclosed.

According to 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, birefringence is increased, and the surface roughness is further increased. The effect of improving the withstand voltage for a long period of time is disclosed by making the value smaller.

However, the polypropylene resin 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 is caused by crosslinking and modification in a subsequent step of resin polymerization. It was found that there is a problem that a film having excellent insulation fracture strength (ES) cannot be obtained because there are many gel components that cause insulation defects.

Further, the polypropylene resin having a long chain branched structure or a crosslinked structure obtained by the above electron beam cross-linking or peroxide modification has poor compatibility with linear polypropylene because the branched chain length and the branched chain spacing are not appropriate. It has also been found that since a uniform composition and a surface shape of a film cannot be obtained from a dry blend with linear polypropylene, there arises a problem that it is difficult to improve the strength of insulation failure (ES) as in Patent Document 3. rice field.

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

As a result of diligent studies, the present inventors have characterized that polypropylene A having a strain curability parameter of less than 3 and polypropylene B having a strain curability parameter of 3 or more and 20 or less are contained as resin components. It has been found that the above-mentioned problems can be solved by the axially stretched polypropylene film, and the present invention has been completed.

The present invention includes the following aspects.
[1] Polypropylene A having a strain curability parameter of less than 3 and
A biaxially stretched polypropylene film comprising polypropylene B having a strain curability parameter of 3 or more and 20 or less as a resin component.
[2] The biaxially stretched polypropylene film according to [1], wherein the polypropylene B is a long-chain branched polypropylene.
[3] The biaxially stretched polypropylene film according to [1] or [2], wherein the gel fraction of the polypropylene B is 1000 mass ppm or less based on the mass of the polypropylene B.
In addition, "the gel fraction of the polypropylene B is 1000 mass ppm 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." It means "mass is less than ppm".
[4] The biaxially stretched 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 stretched 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 polypropylene A to polypropylene B is polypropylene A: polypropylene B = 50: 50 to 99.9: 0.1. Polypropylene film.
[7] The biaxially stretched 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 a capacitor.
[9] A metallized film having a metal film on at least one side of the polypropylene film according to any one of [1] to [8].
[10] A capacitor containing the metallized film according to [9].

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

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

≪1. Film according to this embodiment ≫
Hereinafter, the biaxially stretched polypropylene film according to the embodiment of the present invention will be described.
The film according to the present embodiment contains polypropylene A having a strain curability parameter of less than 3 and polypropylene B having a strain curability parameter of 3 or more and 20 or less as resin components. It is 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 curability parameter (λ)>
The strain curability parameter (λ) is calculated as follows. A press sheet is obtained from the resin pellets, and the shear viscoelasticity and extensional viscosity are measured using the press sheet. Viscosity growth function from shear viscoelasticity measurement

Look, determine the unsteady uniaxial elongational viscosity function eta _{E (t)} from the measurement of extensional viscosity, eta _E time at the point where the magnitude of the distortion elongational viscosity becomes maximum at 2 or more in _(t) as t _max, the following Equation (A):

To obtain the strain curability parameter (λ). Viscosity growth function

Regarding the following equation (B):

(However, ω = 1 / t.) Here, G'(ω) is the storage elastic modulus as a function of the angular velocity ω, G'(ω / 2) is the storage elastic modulus as a function of ω / 2, and G "(ω) is a function of each velocity ω. Loss elastic modulus, G "(ω / 2) is the loss elastic modulus as a function of ω / 2, and t is time. The method for obtaining the strain curability parameter is an outline, and the details of the method for obtaining the strain curability parameter will be described in the item of [Example] of the present specification.

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

The unsteady uniaxial extensional viscosity function η _E (t) can be measured at an arbitrary strain rate using a uniaxial extensional viscosity measuring device. Further, the shear viscoelasticity can be measured by using a dynamic viscoelasticity measuring device such as a rheometer.

<Principle>
The biaxially stretched polypropylene film is excellent in dielectric breakdown strength when used for a capacitor for the following reasons. However, it is specified here that the reason why the biaxially stretched polypropylene film is excellent in the above effect is within the scope of the present invention even if it is different from the following reasons.
Polypropylene having a strain curability parameter (non-linearity parameter) of less than 3 means that there is almost no strain curability of extensional viscosity, and mechanically weak parts such as thin-walled parts of the sheet are easily deformed locally. Therefore, since such a stretched film has low thickness uniformity, dielectric breakdown is likely to occur in the thin portion existing in the film, and the strength of dielectric breakdown is likely to be lowered. On the contrary, in polypropylene having a strain curability parameter of more than 20, the adjacent polymer chains significantly inhibit the molecular chain contraction motion between the branched chains, resulting in (a) increase in free volume and (b) crystal defects. And microvoids are generated, and it becomes difficult to increase the strength of dielectric breakdown. In addition, highly branched components such as gel have low compatibility with polypropylene having a strain curability parameter of less than 3, and insulation defects due to voids are likely to occur around the gel due to the stretching operation. Therefore, by combining polypropylene A having a strain curability parameter of less than 3 and polypropylene B having a strain curability parameter of 3 or more and 20 or less to form a resin component, branching is performed while suppressing the generation of thin-walled portions due to the polypropylene A. The interchain molecular chain contraction movement is not inhibited. As a result, when the film is used for a capacitor, the strength of dielectric breakdown can be improved.

<Polypropylene A>
The strain curability parameter of polypropylene A is less than 3.

The strain curability parameter of polypropylene A is preferably 2.5 or less, more preferably 2.0 or less, still more preferably 1.5 or less, and particularly preferably 1.2 or less. When the strain curability parameter of polypropylene A is the above, it is preferable because good moldability can be obtained and a film having excellent mechanical strength can be obtained. The lower limit of the strain curability parameter is usually 1. Therefore, the strain curability parameter of polypropylene A is 1 or more.
Further, when film molding is performed only with a resin having a strain curability parameter of 3 or more, entanglement between molecular chains appears remarkably at a high take-up speed, and melt breakage during molding is likely to occur.

The gel fraction in polypropylene A is preferably 1000 mass ppm or less, more preferably 800 mass ppm or less, and even more preferably, 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. Further, the smaller the gel fraction of polypropylene A, the more preferable. Therefore, the lower limit is not particularly limited, but is, for example, 0 mass ppm, 1 mass ppm, or the like.

The gel fraction is the mass ratio of the gel component in the resin. The gel component refers to a polymer in which a network structure is formed by cross-linking. When 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 the weighed sample was put into 200 mL of xylene and heated at 120 ± 5 ° C. for 12 hours.
(2) The obtained 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, and 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 appropriate, the thickness of the cast raw sheet is easily controlled, and a thin stretched film can be easily produced. Can be. Further, it is preferable because the thickness of the sheet and the 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, and further preferably 7.5. It is 11.0 or more, and particularly preferably 8.0 or more and 10.0 or less.
The molecular weight distribution of polypropylene A (Z average molecular weight / number average molecular weight (Mz / Mn)) is more preferably 25.0 or more and 60.0 or less, still more preferably 25.0 or more and 50.0 or less, and in particular. 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) apparatus. can. In the present invention, the measurement was performed using HLC-8121GPC-HT (trade name), which is a high temperature GPC measuring machine with a built-in differential refractometer (RI) manufactured by Tosoh Corporation. As the GPC column, three TSKgel GMHHR-H (20) HTs manufactured by Tosoh Corporation were used in combination. The column temperature was set to 140 ° C., and trichlorobenzene was flowed as an eluent at a flow rate of 1.0 ml / 10 minutes to obtain measured values of Mw and Mn. A calibration curve relating to the molecular weight M was prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured values were converted into polystyrene values to obtain Mw, Mn and Mz. Further, the logarithm of the base 10 of the molecular weight M of standard polystyrene is referred to as a logarithmic molecular weight (“Log (M)”).

In polypropylene A, the difference obtained by subtracting the differential distribution value when Log (M) = 6.0 from the differential distribution value when the logarithmic molecular weight Log (M) = 4.5 is the difference in the molecular weight differential distribution curve. Assuming that 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 preferable. Is 11.0 or more and 16.0 or less, and particularly preferably 12.0% or more and 16.0% or less.

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

The mesopentad fraction ([mm mm]) 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. It is 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%, the crystallinity of the resin is moderately improved due to the moderately high stereoregularity, and the initial withstand voltage resistance and long-term The withstand voltage resistance tends to be moderately improved. On the other hand, the rate of solidification (crystallization) at the time of molding the cast raw fabric sheet is appropriate, and it may have appropriate stretchability.

The mesopentad fraction ([mm mm]) is an index of stereoregularity that can be obtained by high temperature nuclear magnetic resonance (NMR) measurements. Specifically, for example, measurement can be performed using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) manufactured by JEOL Ltd., JNM-ECP500. The observation nucleus is ¹³ C (125 MHz), the measurement temperature is 135 ° C., and o-dichlorobenzene (ODCB: ODCB and deuterated ODCB mixed solvent (mixing ratio = 4/1) is used as the solvent. For the measurement method by high temperature NMR, refer to, for example, the method described in "Japan Analytical Chemistry / Polymer Analysis Research Council, New Edition Polymer Analysis Handbook, Kii Kuniya Bookstore, 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 integrations is 4500, and the shift reference is CH ₃ (mm mm) = 21.7 ppm. be able to.

The pentad fraction, which represents the degree of stereoregularity, is a combination (mmmm and mrrm) of the quintuplets (pentads) of the "meso (m)" lined up in the same direction and the "racemo (r)" lined up in different directions. Etc.), which is calculated as a percentage based on the integral value of the intensity of each signal. Each signal derived from mmmm, mrrm, etc. can be assigned with reference to, for example, "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" and the like.

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) is 7.0 or more and 12.0 or less; Z average molecular weight / number average molecular weight (Mz / Mn) is 20.0 or more and 70.0 or less; The difference obtained by subtracting the differential distribution value when Log (M) = 6.0 from the differential distribution value when = 4.5 is 8.0% or more and 18.0% or less; and the mesopentad fraction ([mmmm]). Is preferably 94.0% or more and less than 98.0%.

In this case, the logarithmic molecular weight Log (hereinafter, also referred to as “low molecular weight component”) is represented by a logarithmic molecular weight Log (hereinafter, also referred to as “low molecular weight component”) having a molecular weight of 10,000 to 100,000 on the low molecular weight side based on the Mw value (250,000 to 450,000). The component of M) = 4.5 is used as a typical distribution value of the component having a molecular weight of about 1 million on the high molecular weight side (hereinafter, also referred to as “high molecular weight component”), and the component of Log (M) = about 6.0. It is understood that the proportion of low molecular weight components is 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 indicates the width of the molecular weight distribution, and the quantitative components of the high molecular weight component and the low molecular weight component in it. 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 having a molecular weight of 10,000 to 100,000 in a proportion of 8.0% or more and 18.0% or less as compared with a component having a molecular weight of 1 million. ..

For polypropylene A, the difference obtained by subtracting the differential distribution value when Log (M) = 6.0 from the differential distribution value when the logarithmic molecular weight Log (M) = 4.5 is Log (M) = 6.0. Assuming that the differential distribution value at the time of 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 ratio of 0% or less, the crystallite size becomes smaller, and it becomes easier to obtain a desired orientation and a 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, unstable flow such as melt fracture is unlikely to occur because the flow characteristics in the molten state are excellent. Therefore, since the film thickness uniformity is good, there is an advantage that it is difficult to form a thin-walled portion where dielectric breakdown is likely to occur. As the melt tension, a capillograph 1B manufactured by Toyo Seiki Co., Ltd. was used, and the tension detected by the pulley when the resin was extruded into a string shape and wound on a roller under the following conditions was defined as the melt tension.
Capillaries: diameter 2.0 mm, length 40 mm
Cylinder diameter: 9.55 mm
Cylinder extrusion speed: 20 mm / min Winding speed: 4.0 m / min Temperature: 230 ° C
When the melting tension is extremely high, the resin may break at a take-up speed of 4.0 m / min. In such a case, the take-up speed is lowered to increase the tension at the maximum take-up speed. The melt tension was used.

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 of polypropylene A at 230 ° C. is within the above range, unstable flow such as melt fracture is unlikely to occur because the flow characteristics in the molten state are excellent, and fracture during stretching is also suppressed. Therefore, since the film thickness uniformity is good, there is an advantage that the formation of a thin-walled 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. As long as polypropylene A that can be used for the film of the present embodiment can be produced, there is no particular limitation. Examples of such a polymerization method include a vapor phase polymerization method, a massive polymerization method and a slurry polymerization method.

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

As the catalyst, a generally known Ziegler-Natta catalyst or the like can be used, and the polypropylene resin according to the present embodiment is not particularly limited as long as it can be obtained. In addition, the catalyst can include a co-catalyst component and a donor. By adjusting the catalyst and polymerization conditions, the molecular weight, molecular weight distribution, stereoregularity, and the like can be controlled.

As a method for obtaining polypropylene A having a strain curability parameter of less than 3, for example, each polymerization method is adopted to obtain polypropylene having a branched structure with a short branched chain in the polypropylene molecule, or a large number of branched structures in the polypropylene molecule. It is possible to obtain polypropylene which does not have (nearly linear). In other words, the strain curability parameter tends to be larger when the branched chain in the polypropylene molecule is long when only the branched structure of the polymer is different and according to the MSF theory, so that the branched chain in the polypropylene molecule tends to be large. By appropriately adjusting (a) length, (b) number (quantity), (c) distribution, etc., polypropylene A having a strain curability parameter of less than 3 can be obtained. When obtaining this polypropylene A, (i) polymerization method and conditions such as temperature and pressure during polymerization, (ii) morphology of reactor during polymerization, (iii) presence / absence and type of additives, 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, and the like. The polymerization method includes a slurry method using an inert solvent, a bulk method using the monomer itself (eg, propylene) as a solvent without substantially using the inert solvent, a solution polymerization method, and each monomer substantially without using a liquid solvent. Examples include the gas phase method for keeping the gas in a gaseous state. The reactor at the time of polymerization may be one-stage polymerization using one polymerization reactor, or may be multi-stage polymerization using two or more polymerization reactors. As for the additive, hydrogen, various comonomer and the like may be added to the reactor as a molecular weight adjusting agent to carry out the polymerization. As the polymerization catalyst, a Ziegler-Natta catalyst or the like can be used, and the polymerization catalyst may contain a co-catalyst component or a donor. 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. The strain curability parameter can be controlled by controlling the molecular weight, molecular weight distribution, stereoregularity, branching (amount, length, distribution), etc. of the polypropylene resin.

When adjusting the composition of the molecular weight distribution according to the polymerization conditions, the composition of the molecular weight distribution and the molecular weight can be easily adjusted by using the polymerization catalyst. Examples of the method obtained by the multi-stage polymerization reaction include the following methods.

In the presence of a catalyst, polymerization is carried out at a high temperature by a plurality of reactors of a high molecular weight polymerization reactor and a low molecular weight or medium molecular weight reactor. The high molecular weight component and the low molecular weight component of the produced resin are adjusted in any order in the reactor. First, in the first polymerization step, propylene and a catalyst are supplied to the first polymerization reactor. Along with these components, hydrogen as a molecular weight modifier is mixed in the amount required to reach the required 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 minutes to 100 minutes. Multiple reactors can be used, for example, in series, in which case the polymerization product of the first step is continuously delivered to the next reactor with additional propylene, catalyst and molecular weight modifier. Then, the second polymerization in which the molecular weight is adjusted to a low molecular weight or a high molecular weight is performed from the first polymerization step. By adjusting the yield (production amount) of the first and second reactors, it is possible to adjust the composition (composition) of the high molecular weight component and the low molecular weight component.

The catalyst may include a co-catalyst component or a donor. The molecular weight distribution can be controlled by appropriately adjusting the catalyst and the polymerization conditions.

When adjusting the composition of the molecular weight distribution of the polypropylene raw material resin by peroxidation decomposition, a method by peroxidation treatment with a decomposition agent such as hydrogen peroxide or an organic oxide is preferable.
When a peroxide is added to a disintegrating polymer such as polypropylene, a hydrogen abstraction reaction occurs from the polymer, and the generated polymer radicals are partially recombined to cause a cross-linking reaction, but most of the radicals are secondary decomposition (β-cleavage). ), And it is known that it is divided into two polymers with smaller molecular weights. Therefore, the decomposition proceeds from the high molecular weight component with a high probability, so that the low molecular weight component increases and the composition of the molecular weight distribution can be adjusted.

As a method for obtaining a resin containing an appropriate amount of a low molecular weight component by peroxidative decomposition, for example, the following method can be exemplified.

0.001% by mass to 0.5% by mass of polymerized powder or pellets of polypropylene obtained by polymerization and, for example, 1,3-bis- (terrary-butyl peroxide isopropyl) -benzene as an organic peroxide. %, Adjusted and added while considering the composition (composition) of the target high molecular weight component and low molecular weight component, and melt-kneaded at a temperature of about 180 ° C to 300 ° C with a melt-kneader machine. You can also.

When adjusting the content of low molecular weight components by blending (resin mixing), it is preferable to dry-mix or melt-mix at least two or more different molecular weight resins. In general, two types of polypropylene mixed systems in which an additive resin having a higher or lower average molecular weight than the main resin is mixed in an amount of about 1 to 40% by mass are preferable because the amount of low molecular weight components can be easily adjusted. It will be used.

Further, in the case of this mixing adjustment, the melt flow rate (MFR) may be used as a guideline for the average molecular weight. In this case, it is preferable that the difference in MFR between the main resin and the added resin is about 1 to 30 g / 10 minutes from the viewpoint of convenience at the time of adjustment.

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

As the polypropylene A, a commercially available product (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, based on the resin component. It is mass% or more and 99 mass% or less, particularly preferably 80 mass% or more and 98.5 mass% or less, and more particularly preferably 90 mass% or more and 98 mass% or less. Further, the film of the present embodiment may contain one kind or two or more kinds of polypropylene A.

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

The strain curability parameter of polypropylene B is preferably 3.5 or more, more preferably 4 or more, still more preferably 5 or more, and particularly preferably 5.5 or more. When the strain curability parameter is 3 or more, the melt tension is less likely to decrease due to repeated kneading, and the strain curability of the resin at the time of elongation and deformation is maintained, which is preferable.
The strain curability parameter of polypropylene B is preferably 18 or less, more preferably 16 or less, still more preferably 14 or less, and particularly preferably 12 or less. When the strain curability parameter of polypropylene B is 20 or less, the melt tension is less likely to decrease due to repeated kneading, and the strain curability of the resin during elongation and deformation is maintained, which is preferable.

As described in <Strain curability parameter (λ)>, the strain curability parameter tends to increase when the branched chain in the polypropylene molecule is long. Therefore, polypropylene B can be obtained by adjusting the branched structure in the polypropylene molecule, the molecular chain length in the branched structure, and the like. Polypropylene B is preferably long-chain branched polypropylene. When polypropylene B is a long-chain branched polypropylene, it is preferable because the strain curability parameter becomes appropriate.

Examples of the method for producing polypropylene B include a method of polymerizing propylene using a metallocene catalyst. The metallocene catalyst is generally a metallocene compound that forms a polymerization catalyst that produces olefin macromers. In the case of polypropylene obtained by polymerizing propylene using a metallocene catalyst (metallocene-catalyzed polypropylene), the branched chain length and the branched chain spacing of polypropylene are appropriate, 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, and (ii) reactor during polymerization. The morphology, (iii) presence / absence of additives, type and amount used, (iv) molecular weight, molecular weight distribution, and stereoregularity adjustment methods, (v) differential distribution value adjustment methods, etc. It may be the same as each condition described in polypropylene A>.

Further, when a metallocene catalyst is used for the polymerization of polypropylene B, a long-chain branched polypropylene can be obtained without cross-linking and modification in the post-polymerization step, so that the gel fraction due to the post-step is reduced and insulation fracture occurs. It is preferable because an excellent biaxially stretched polypropylene film can be obtained due to the strength of the above.

Further, polypropylene obtained by polymerizing propylene using a metallocene catalyst can be obtained by forming a partially crosslinked structure by a method such as irradiation with an electron beam in a subsequent step of resin polymerization, a crosslinking aid and a peroxide. Is preferable because the amount of residual radicals (ionic carriers) is smaller than that of a polypropylene resin having a long-chain branched structure or a crosslinked structure produced by a method of adding and kneading the resin to polypropylene, and the resin is less likely to be colored over time. ..

The gel fraction of polypropylene B is preferably 1000 mass ppm or less, more preferably 800 mass ppm or less, still more preferably 500 mass ppm or less (in terms of mass when polypropylene B is taken as a whole) with respect to the mass of polypropylene B in the resin component. It is mass ppm or less, particularly preferably 100 mass ppm or less. When the gel fraction of polypropylene B is 1000 mass ppm or less, insulation defects are reduced and a biaxially stretched polypropylene film having excellent dielectric breakdown strength can be obtained, which is preferable. Further, the smaller the gel fraction of polypropylene B, the better. Therefore, the lower limit is not particularly limited, but is, for example, 0 mass ppm, 1 mass ppm, 10 mass ppm, 250 mass ppm, or 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, further preferably 250,000 or more and 450,000 or less, and 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 appropriate, the thickness of the cast raw fabric sheet can be easily controlled, and a thin stretched film can be easily produced. Can be. Further, it is preferable because the thickness of the sheet and the 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 further preferably 2.0. More than 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.
The molecular weight distribution of polypropylene B (Z average molecular weight / number average molecular weight (Mz / Mn)) is preferably 4.0 or more and 9.0 or less, more preferably 4.2 or more and 8.8 or less, and further preferably 4. It is 5.5 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) apparatus. can do. More specifically, for example, it can be measured by a high temperature GPC-MALS measurement, that is, a high temperature GPC device (HLC-8121 GPC / HT; manufactured by Tosoh) equipped with a light scattering detector (DAWN EOS; manufactured by Wyatt Technology).
As columns, TSKgel guardcolumn HHR (30) (7.8 mm ID x 7.5 cm) and three TSKgel GMH-HR-H (20) HT (7.8 mm ID x 30 cm) manufactured by Tosoh Corporation are connected. Used. The column temperature was set to 140 ° C., and trichlorobenzene was flowed 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, etc. of polypropylene B can be controlled by adjusting the catalyst and the polymerization conditions as described above.

The melting tension of polypropylene B at 230 ° C. is preferably 1 to 50 g, more preferably 2 to 40 g, still more preferably 4 to 30 g. When the melt tension of polypropylene B at 230 ° C. is within the above range, unstable flow such as melt fracture is unlikely to occur because the flow characteristics in the molten state are excellent. Therefore, since the film thickness uniformity is good, there is an advantage that it is difficult to form a thin-walled portion where dielectric breakdown is likely to occur.

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, and even more preferably 1 to 10 g / 10 min. When the MFR of polypropylene B at 230 ° C. is within the above range, unstable flow such as melt fracture is unlikely to occur because the flow characteristics in the molten state are excellent, and fracture during stretching is also suppressed. Therefore, since the film thickness uniformity is good, there is an advantage that the formation of a thin-walled 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, more preferably 0.5% by mass or more and 40% by mass or less, and further preferably 1. It is 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. Further, the film of the present embodiment may contain one kind or two or more kinds of polypropylene B.

Representative 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 to polypropylene B contained in the film of the present 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, and particularly preferably 75:25 to 85:15.
The total mass% of polypropylene A and polypropylene B with respect to the entire resin component 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% (that is, there are two types of resin components constituting the film of the present embodiment, polypropylene A and polypropylene B). Examples of the resin component (other resin component) other than polypropylene A and polypropylene B include olefin-based resins that do not fall under either polypropylene A or polypropylene B.

<Additives>
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 stretched polypropylene film intended by the present invention can be obtained. Additives include, for example, β-crystal nucleating agents, antioxidants, necessary stabilizers such as chlorine absorbers and ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents and the like. When such an additive is used, the film of the present embodiment may contain the additive in an amount that does not adversely affect the biaxially stretched 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 stretched polypropylene film of the present invention can be obtained. The β-crystal nucleating agent can be dry-blended or melt-blended with a polypropylene raw material and pelletized for use, or can be put into an extruder together with polypropylene pellets for use. The surface roughness of the film can be adjusted to a desired roughness by using a β-crystal nucleating agent. Examples of typical commercially available β-crystal nucleating agents include NJester NU-100 manufactured by Shin Nihon Rika Co., Ltd. When the film of the present embodiment contains a β-crystal nucleating agent, the content thereof is preferably 1 to 1000 mass ppm, more preferably 1 to 1000 mass ppm, based on the mass of the resin component (by mass when the resin component is taken as a whole). It is 50 to 600 mass ppm.

The "antioxidant" is generally called an antioxidant, and is not particularly limited as long as it can be used for polypropylene and the biaxially stretched polypropylene film intended 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 suppressing deterioration and improving capacitor performance in long-term use as a film for capacitors. An antioxidant that suppresses thermal deterioration and oxidative deterioration in an extruder is also referred to as a "primary agent", and an antioxidant that contributes to improving capacitor performance is also referred to as a "secondary agent".

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

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

Examples of the secondary agent include a hindered phenolic antioxidant having a carbonyl group.

The "Hindered phenolic antioxidant having a carbonyl group" is usually a hindered phenolic antioxidant having a carbonyl group, and is particularly effective as long as the biaxially stretched polypropylene film of the present invention can be obtained. There are no restrictions.

Examples of the hindered phenolic antioxidant having a carbonyl group include triethylene glycol-bis [3- (3-terriary-butyl-5-methyl-4-hydroxyphenyl) propionate] (trade name: Irganox 245). ), 1,6-Hexanediol-bis [3- (3,5-ditershally-butyl-4-hydroxyphenyl) propionate] (trade name: Irganox 259), pentaerythrultyl tetrakis [3-( 3,5-Di-tersary butyl-4-hydroxyphenyl) propionate] (trade name: Irganox 1010), 2,2-thio-diethylenebis [3- (3,5-di-tersary-butyl-4-) Hydroxyphenyl) propionate] (trade name: Irganox 1035), octadecyl-3- (3,5-ditershally-butyl-4-hydroxyphenyl) propionate (trade name: Irganox 1076), N, N'- Hexamethylenebis (3,5-ditershally-butyl-4-hydroxy-hydrocinnamamide) (trade name: Irganox 1098) and the like can be mentioned, but they have a high molecular weight and are highly compatible with polypropylene. Pentaerythrutyl tetrakis [3- (3,5-di-terrific butyl-4-hydroxyphenyl) propionate], which has low volatility and excellent heat resistance, is particularly preferable.

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

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

The "chlorine absorber" is generally called a chlorine absorber, and is not particularly limited as long as it is used for polypropylene and the biaxially stretched polypropylene film intended by the present invention can be obtained. Examples of the chlorine absorber include metal soaps such as calcium stearate. When such a chlorine absorber is used, the film of the present embodiment can contain the chlorine absorber in an amount that does not adversely affect the biaxially stretched 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, and more preferably 1.8 μm or more and 7 μm or less.
Further, the thickness of the film of the present embodiment is preferably larger than 15 μm and less than 50 μm. The thickness of the film of the present 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 having 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).

<Strength of dielectric breakdown (ES)>
AC breakdown strength of the film of the present embodiment (ES) is preferably 240 _{[V AC} / μm] or more, more preferably 243 _{[V AC} / μm] or more, more preferably 245 _{[V AC} / μm] That is all.
Further, the intensity of the direct current breakdown of the film of the present embodiment (ES) is preferably 465 _{[V DC} / μm] or more, more preferably 470 _{[V DC} / μm] or more, more preferably 480 _{[V DC} / μm] or more.

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

<Melting point in first run>
The melting point of the film of the present embodiment in the first run is preferably 166 ° C. or higher, more preferably 168 ° C. or higher, still more preferably 169 ° C. or higher. When the melting point in the first run is 166 ° C. or higher, the thickness of the lamella required to maintain the strength of dielectric breakdown is obtained. The melting point of the first run is preferably 188 ° C. or lower, more preferably 187 ° C. or lower, and further preferably 185 ° C. or lower. The upper limit of the melting point in the first run is not less than the equilibrium melting point of polypropylene (the melting point when the thickness of the lamella is infinite), and is preferably 187 ° C. or less from the viewpoint of moldability. The melting point in the first run is a value obtained in the first run of differential scanning calorimetry, and specifically, is a value measured by the method described in Examples.

<Melting enthalpy in the first run>
The melting enthalpy of the film of the present embodiment in the first run is preferably 105 J / g or more, more preferably 106 J / g or more, still more preferably 107 J / g or more. When the melting enthalpy in the first run is 105 J / g or more, the crystallinity required to maintain the strength of dielectric breakdown is obtained. The melting enthalpy in the first run is preferably 150 J / g or less, more preferably 130 J / g or less, and further preferably 120 J / g or less. When the melting enthalpy in the first run is 150 J / g or less, it has appropriate thin film stretchability. The melting enthalpy in the first run is a value obtained in the first run of differential scanning calorimetry, and specifically, is a value measured by the method described in Examples.

<Crystallization temperature in fast run>
The crystallization temperature of the film of the present embodiment in the first run is preferably 112.8 ° C. or higher, more preferably 112.9 ° C. or higher, still more preferably 113 ° C. or higher. When the crystallization temperature in the first run is 112.8 ° C. or higher, the size of spherulite formed in the cooling step of the melt-extruded resin sheet can be controlled to be small, and the formation of insulation defects generated in the stretching step can be suppressed to a low level. Can be done. 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, rough surface formation by crystal transformation becomes possible. The crystallization temperature in the first run is a value obtained in the first run of differential scanning calorimetry, and specifically, is a value measured by the method described in Examples.

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

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

<Melting enthalpy in the second run>
The melting enthalpy of the film of the present embodiment in the second run is preferably 95 J / g or more, more preferably 97 J / g or more, still more preferably 98 J / g or more. When the melting enthalpy in the second run is 95 J / g or more, it is easy to obtain the crystallinity required to maintain the strength of dielectric breakdown. The melting enthalpy in the second run is preferably 110 J / g or less, more preferably 105 J / g or less, and further preferably 103 J / g or less. When the melting enthalpy in the second run is 110 J / g or less, the thin film has appropriate stretchability. The melting enthalpy in the second run is a value obtained in the second run of the differential scanning calorimetry, and specifically, it is a 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 obtained by mixing a generally known method for producing a biaxially stretched polypropylene film, for example, polypropylene A and polypropylene B, with other resins and / or additives, if necessary. It can be produced by producing a cast raw fabric sheet from the polypropylene resin composition obtained by the above process, 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 the polymer 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, or a method of supplying polypropylene A and polypropylene polymer powders or pellets together with other resins and / or additives, if necessary, to a kneader and melt-kneading to obtain a melt-blended resin composition. However, it doesn't matter which one.

The mixer and the kneader are not particularly limited, and the kneader may be either a single-screw screw type, a double-screw screw type, or a higher multi-screw screw type. Further, in the case of a screw type having two or more axes, either a kneading type that rotates in the same direction or that rotates in a different direction may be used.

In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as good kneading can be obtained, but is preferably in the range of 170 to 320 ° C, more preferably in the range of 200 ° C to 300 ° C, and more preferably. Is 230 ° C to 270 ° C. A too high kneading temperature is not preferable because it causes deterioration of the resin. 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.

When preparing the polypropylene resin composition, a primary agent as an antioxidant described in the above <Additive> 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 mass ppm to 5000 mass ppm (in terms of mass when the resin component is taken as a whole) with respect to the mass of the resin component. Most of the antioxidant for this purpose is consumed in the molding process in the extruder, and hardly remains in the film after film forming.

The hindered phenolic antioxidant having a carbonyl group described in the above <Additive> 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, the content thereof is preferably from 100% by mass to the mass of the resin component (by mass when the resin component is taken as a whole). It is 10000 mass ppm, more preferably 5500 mass ppm to 7000 mass ppm. Not a little in the extruder, a hindered phenolic antioxidant having a carbonyl group is also consumed.
When the polypropylene resin composition does not contain a primary agent, more hindered phenolic antioxidants 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, its content is based on the mass of the resin component (by mass when the resin component is taken as a whole). ) 6000 mass ppm to 8000 mass ppm or less.

The total ash content due to the polymerization catalyst residue and the like contained in the polypropylene resin composition is preferably as small as possible in order to improve the electrical characteristics. The total ash content is preferably 50 mass ppm or less, more preferably 40 mass ppm or less, still more preferably 30 mass ppm or less, relative to the mass of the resin component (by mass when the resin component is taken as a whole).

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

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

In the process of producing the cast raw sheet (particularly in the extruder), polypropylene undergoes not a little thermal deterioration (oxidative deterioration) and shear deterioration. The degree of progress of such deterioration, that is, changes in molecular weight distribution and stereoregularity, is determined by the nitrogen purge in the extruder (suppression of oxidation), the screw shape in the extruder (shearing force), and the internal shape of the T-die during casting (the internal shape of the T-die during casting). It can be suppressed by the shearing force), the amount of the antioxidant added (suppression of oxidation), the winding speed at the time of casting (extension force), and the like.

<Stretching treatment>
The film of the present embodiment can be produced by subjecting the cast raw fabric sheet to a stretching treatment. As the stretching method, a sequential biaxial stretching method is preferable. As a sequential biaxial stretching method, first, the cast raw sheet is kept at a temperature of preferably 100 to 180 ° C., more preferably 140 to 160 ° C., passed between rolls provided with a speed difference, and 3 to 7 times in the flow direction. And immediately cool to room temperature. By appropriately adjusting the temperature of this longitudinal stretching step, β crystals are melted and transferred to α crystals, and unevenness becomes apparent. Subsequently, the stretched film is guided to a tenter and laterally 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-fixed, and wound.

The wound film can be aged in an atmosphere of about 20 to 45 ° C. and then cut to a desired product width.

By such a stretching step, a film having excellent mechanical strength and rigidity is obtained, and surface irregularities are further clarified to obtain a finely roughened biaxially stretched film.

Further, the biaxially stretched polypropylene film of the present embodiment may be subjected to a corona discharge treatment online or offline after the stretching and heat fixing steps are completed in order to improve the adhesive properties in a post-process such as a metal vapor deposition processing step. can. The corona discharge treatment can be performed by 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 including the film of this embodiment ≫
In another aspect, the present embodiment is a metallized film having a metal film on at least one side of the polypropylene film.

Examples of the method for metallizing the surface of the film of the present embodiment include a vacuum vapor deposition method and a sputtering method, but are not particularly limited. The vacuum deposition method is preferable from the viewpoint of productivity and economy. As the vacuum vapor deposition method, a crucible method, a wire method, or the like can be generally exemplified, but the method is not particularly limited, and the optimum method can be appropriately selected. The metals used may be elemental metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures thereof, and alloys thereof, although environmentally friendly and economical. Considering the performance of the capacitor, at least one selected from the group consisting of zinc and aluminum is preferable. The metal film obtained by vapor deposition is also referred to as a metal vapor deposition film.

The film resistance value of the metal film is preferably 1 to 100 Ω / □ from the viewpoint of the electrical characteristics of the capacitor. It is desirable that the film resistance is high even within this range from the viewpoint of self-healing (self-healing) characteristics, and the film resistance is preferably 5 Ω / □ or more, more preferably 10 Ω / □ or more. Further, from the viewpoint of safety as a capacitor element, the film resistance is preferably 50 Ω / □ or less, more preferably 20 Ω / □ or less. The film resistance value of the metal film can be measured in the metal film by, for example, a two-terminal 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 amount of evaporation. The thickness of the metal film is not particularly limited, but is preferably 1 nm to 100 nm.

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

The margin pattern when metallizing by vapor deposition is not particularly limited, but from the viewpoint of improving the characteristics such as the safety 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, it is preferable because it enhances safety and is effective from the viewpoints of breaking the capacitor and preventing short circuit.

As a method for forming the margin, a generally known method such as a tape method or an oil method can be used without any limitation.

When obtaining a flat capacitor, the film of the present embodiment to which an electrode is attached or metallized is wound alone or in combination of two or more, preferably two in phase. The number of turns can be appropriately selected according to the application of the capacitor and the like. For example, in the case of a flat capacitor, about 500 to 2000 times can be mentioned. The winding can be performed using an automatic winding machine. The element wound element can be heat-treated under pressure and / or heating. The pressure under the pressure is, for example, about 200 to 1000 kPa. The temperature under the heating is, for example, about 60 to 130 ° C. For example, zinc metal is sprayed on the end face of the heat-treated device. As a result, a flat capacitor can be obtained.

Since the metallized film of the present embodiment has excellent dielectric breakdown strength, it is suitable as a dielectric film for high-voltage capacitors, various switching power supplies, filter capacitors such as converters and inverters, and capacitors such as smoothing capacitors. Can be used. Further, it may be used as a capacitor for smoothing an inverter power supply circuit that controls a drive motor used in an electric vehicle, a hybrid vehicle, or the like.

Further, it can also be used as a capacitor by attaching an electrode to the film of the present embodiment. The method of attaching the electrode is not particularly limited, and a generally known method can be used. The electrode is not particularly limited, and an electrode usually used for manufacturing a capacitor can be used. Examples of the electrode include a metal foil, paper having at least one side metallized, a plastic film, and the like. As the metal used, the above-mentioned metal can be used.

In another aspect, the present embodiment is a capacitor containing a metallized film having a metal film on at least one side of the polypropylene film of the present embodiment.

Since the film of the present embodiment has high dielectric breakdown strength, it can be extremely suitably used for a capacitor.

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

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the embodiments of the examples.

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

As the 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-mentioned measuring method.
The polypropylene resin B has the following 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. Each polypropylene was used. In particular,
Polypropylene B1 (WAYMAX MFX6 manufactured by Japan Polypropylene Corporation, 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, 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 Corporation, long-chain branched polypropylene obtained by polymerizing propylene using a metallocene catalyst; hereinafter referred to as resin B3)
Was used.
As polypropylene resin B',
B'4 (Daploy WB135HMS manufactured by Borealis AG, long-chain branched polypropylene obtained by cross-linking modification with peroxide; hereinafter referred to as resin B'4),
Was used.
Table 1 shows the strain curability parameters, weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of 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 curability parameter>
a) Dynamic viscoelasticity measuring device: ARES-G2 (manufactured by TA Instruments)
Jig: Cone plate (25 mmφ, 0.1 rad.)
Temperature: 230 ° C
Frequency: 100-0.01 rad. / Sec.
b) Extensional viscosity measuring device: ARES-G2 (manufactured by TA Instruments)
Jig: Extensional viscosity fixture temperature: 230 ° C
Strain rate: 0.1 / s. However, when the torque was low under this condition and the extensional viscosity could not be measured, the strain rate was set to 1.0 / s.
Preliminary strain: 0.2 mm
Measurement procedure:
(1) The resin pellets were heat-compressed at 230 ° C. for 5 minutes using a hot press to prepare a press 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 carried out by sandwiching a press sheet in a cone plate jig (25 mmφ, 0.1 rad) and measuring at 230 ° C. at a frequency of 100 to 0.01 rad / sec.
(3) The extensional viscosity was measured at 230 ° C. using an extensional 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 extensional viscosity could not be measured, the strain rate was set to 1.0 / s. The above-mentioned extensional viscosity measuring jig is a jig for measuring the extensional viscosity of a highly viscous substance such as a molten polymer, and is composed of a fixed portion 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) was applied to the following equation (B) based on the method described in "Kunihiro Ozaki, Asahi Murai, Nobuo Bessho, Journal of the Society of Rheology, Vol. 4, 166 (1976)". Viscoelastic growth function shown

Asked.

However, ω = 1 / t.
Here, G'(ω) is the storage elastic modulus as a function of the angular velocity ω, G'(ω / 2) is the storage elastic modulus as a function of ω / 2, and G "(ω) is a function of the angular velocity ω. Elastic modulus lost, t is time.
(5) On the other hand, in the unsteady uniaxial extensional viscosity curve η _E (t) obtained by measuring the extensional viscosity, the time at the point where the magnitude of strain is 2 or more and the extensional viscosity is maximized is t _max , and the following equation ( The non-linear parameter of extensional viscosity, that is, the strain curability parameter (λ) was obtained from A). A conceptual diagram of λ is shown in FIG.

(6) If the linear region on the short-time side does not overlap well between the viscosity growth function obtained by the equation (B) and the unsteady uniaxial extensional viscosity curve, the linearity in the unsteady uniaxial extensional viscosity curve The strain curability parameter λ was obtained after shifting so that the vicinity of the midpoint of the portion overlapped. This is a measure to reduce the error in the extensional viscosity measurement because when the cross-sectional area increases more than the assumed value due to strain release etc., the sample may hang down due to the small viscosity and the cross-sectional area may decrease. Is.

<Gel fraction>
The measurement conditions for the gel fraction of each resin were as follows.
Sample amount: Approximately 1 g
Solvent: xylene (200 mL)
Heating temperature: 120 ° C
Heating time: 12 hours Filtration mesh: 200 mesh Wire mesh drying: Room temperature x 8 hours + 80 ° C x 3 hr
About 1 g of the weighed sample was placed in 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 percentage of residue was taken as the gel fraction.

<Measurement of 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 of polypropylene>
Using GPC (Gel Permeation Chromatography), polypropylene number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mw / Mn) under the following conditions. Mz / Mn), the differential distribution value of the distribution curve was measured.
An HLC-8121GPC-HT type high temperature GPC device with a built-in differential refractometer (RI) manufactured by Tosoh Corporation was used. As a column, three TSKgel GMHR-H (20) HTs manufactured by Tosoh Corporation were connected, and one TSKgel guardcolumn HHR (30) was used. At a column temperature of 140 ° C., 1.0 ml of 1,2,4-trichlorobenzene plus 0.05 wt% 2,6-ditertiary-butyl-para-cresol (generic name: BHT) as an eluent. The measurement was carried out at a flow rate of / min to obtain a number average molecular weight (Mn), a weight average molecular weight (Mw) and a z average molecular weight (Mz). The molecular weight distribution (Mz / Mn) was obtained using the values of Mz and Mn, and the molecular weight distribution (Mw / Mn) was obtained using the values of Mw and Mn. The measurement conditions are as follows.
GPC device: HLC-8121 GPC / HT (manufactured by Tosoh)
Light scattering detector: DAWN EOS (Wyatt Technology),
Column: TSKgel guardcolumn HHR (30) (7.8 mm ID x 7.5 cm) x 1 + TSKgel GMHR-H (20) HT (7.8 mm ID x 30 cm) x 3 (manufactured by Tosoh)
Eluent: 0.05 wt% BHT on 1,2,4-trichlorobenzene
Flow velocity: 1.0 mL / min
Sample concentration: 2 mg / mL
Injection volume: 300 μL
Column temperature: 140 ° C
System temperature: 40 ° C
Pretreatment: The sample was precisely weighed, an eluent was added, the sample was dissolved by shaking at 140 ° C. for 1 hour, and heat filtration was performed with a 0.5 μm sintered metal filter.

<Difference in differential distribution value>
The difference in the differential distribution values was obtained by the following method. First, the time curve (elution curve) of the intensity distribution detected by the RI detector is used as 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 an integral distribution curve for Log (M) when the total area of the distribution curve is 100%, the differential distribution for Log (M) is obtained by differentiating this integral distribution curve with Log (M). I was able to get a curve. From this differential distribution curve, the differential distribution values when Log (M) = 4.5 and Log (M) = 6.0 were read. A series of operations until the differential distribution curve was obtained was performed using the analysis software built in the GPC measuring device 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 measurement and calculation, the difference between the above differential distribution values of the resin A1 (the differential distribution value when Log (M) = 4.5 was subtracted from the differential distribution value when Log (M) = 6.0. , Difference) was 11.7.

<Measurement of mesopentad fraction ([mmmm])>
Polypropylene was dissolved in a solvent, and a mesopentad fraction ([mm mm]) was determined under the following conditions using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR).
Measuring machine: High temperature FT-NMR JNM-ECP500 manufactured by JEOL Ltd.
Observation nucleus: 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
Number of integrations: 4500 times Shift reference: CH ₃ (mmmm) = 21.7ppm
It was calculated as a percentage (%) from the intensity integral value of each signal derived from the combination of quintuplets (pentads) (mmmm, mrrm, etc.). Regarding the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of the spectrum such as "T. Hayashiet al., Polymer, Vol. 29, p. 138 (1988)" was referred to. The mesopentad fraction was measured only for the resin A1. The mesopentad fraction of the resin A1 was 97.8%.

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

<Measurement of melt tension>
Using Capillograph 1B manufactured by Toyo Seiki Co., Ltd., the tension detected in the pulley when the resin was extruded into a string shape and wound on a roller under the following conditions was defined as the melt tension.
Capillaries: diameter 2.0 mm, length 40 mm
Cylinder diameter: 9.55 mm
Cylinder extrusion speed: 20 mm / min Winding speed: 4.0 m / min Temperature: 230 ° C
When the melting tension is extremely high, the resin may break at a take-up speed of 4.0 m / min. In such a case, the take-up speed is lowered to increase the tension at the maximum take-up speed. The melt tension is used.

Using the polypropylene resin described above, polypropylene films of Examples 1 to 6 and Comparative Examples 1 to 6 were produced, and their physical characteristics were evaluated.

[Example 1]
A dry blend resin composition in which the resin A1 and the resin B1 were continuously weighed and mixed at A1 / B1 = 80/20 (mass ratio) was supplied to the extruder. After melting the dry blend resin composition at a temperature of 230 ° C., it is extruded using a T-die, wound around a metal drum whose surface temperature (casting temperature) is maintained at 45 ° C. and solidified, and cast raw material having a thickness of 900 μm. Manufactured anti-sheet. This cast raw sheet was stretched 5 times in the flow direction and then 10 times in the lateral direction at 165 ° C. using a batch type biaxial stretching machine KARO IV manufactured by Brueckner, and a biaxially stretched PP film having a thickness of 18 μm was stretched. Got Table 2 summarizes the resin compounding ratio and the physical characteristic values of the obtained film.

[Example 2]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that the resin B2 was used instead of the resin B1. The thickness of the obtained biaxially stretched polypropylene film was 18 μm. Table 2 summarizes the resin compounding ratio and the physical characteristic values 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 the resin B1 were used in the mass ratios shown in Table 1. The thickness of the obtained biaxially stretched polypropylene film was 18 μm. Table 2 summarizes the resin compounding ratio and the physical characteristic values of the obtained film.

[Example 4]
A biaxially stretched polypropylene film was obtained in the same manner as in Example 3 except that the resin B2 was used instead of the resin B1. The thickness of the obtained biaxially stretched polypropylene film was 18 μm. Table 2 summarizes the resin compounding ratio and the physical characteristic values of the obtained film.

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

[Example 6]
A dry blend resin composition in which the resin A1 and the resin B1 were continuously weighed and mixed at A1 / B1 = 98/2 (mass ratio) was supplied to the extruder. After melting the dry blend resin composition at a temperature of 250 ° C., it is extruded using a T-die, wound around a metal drum whose surface temperature (cast temperature) is maintained at 95 ° C., and solidified to solidify the cast raw fabric having a thickness of 100 μm. Manufactured the sheet. The unstretched cast raw sheet was kept at a temperature of 140 ° C., passed between rolls provided with a speed difference, stretched 4.5 times in the flow direction, and immediately cooled to room temperature. Subsequently, the stretched film was guided to a tenter, stretched 10 times in the width direction at a transverse stretching temperature of 158 ° C., relaxed and heat-fixed, and a biaxially stretched polypropylene film having a thickness of 2.5 μm was wound up.

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

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

[Comparative Example 4]
An attempt was made to obtain a biaxially stretched polypropylene film in the same manner as in Example 1 except that resin B2 was used alone as the resin component, but a smooth cast sheet could not be produced due to melt fracture during extrusion molding. .. Therefore, when the obtained cast sheet was stretched, it was broken 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 stretched polypropylene film was 2.5 μm. Table 2 summarizes the resin compounding ratio and the physical characteristic values of the obtained film.

[Comparative Example 6]
Example 6 and 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. Similarly, a biaxially stretched polypropylene film was obtained. The thickness of the obtained biaxially stretched polypropylene film was 2.5 μm. Table 2 summarizes the resin compounding ratio and the physical characteristic values of the obtained film.

[Measurement method of characteristic value, etc.]
The method of measuring the characteristic value in the examples and the comparative examples is as follows.

<Thickness of biaxially stretched polypropylene film>
Measurements were made in accordance with JIS-C2330 using a micrometer (JIS-B7502).

<Dielectric breakdown strength>
The withstand voltage of the biaxially stretched film was measured by measuring the dielectric breakdown strength (ES) according to JIS C 2330: 2010 and JIS C 2151: 2006 17.2.2 (dielectric breakdown voltage / flat plate electrode method). The measurement was performed at an atmospheric temperature of 100 ° C. The boosting speed was 100 Vac / sec, the breaking current at the time of destruction was 10 mA, and the number of measurements was 18. Here, the measured average voltage value divided by the film thickness was used for evaluation as the dielectric breakdown strength. A film and an electrode jig were set in a blower circulation type high temperature bath, and measurement was performed at an evaluation temperature of 100 ° C.
The strength (ES) of AC dielectric breakdown was measured for Examples 1 to 5 and Comparative Examples 1 and 2, and DC dielectric breakdown was measured for Example 6, Comparative Example 5, and Comparative Example 6. Strength (ES) was measured. In general, applying a voltage with alternating current has a higher load than applying a voltage with direct current. Therefore, Examples 1 to 5 and Comparative Examples 1 to 2 having a thickness of 18 μm were measured by alternating current because the load was not sufficient when measured by direct current and appropriate evaluation could not be performed. On the other hand, Example 6, Comparative Example 5, and Comparative Example 6 having a thickness of 2.5 μm were measured by direct current because a sufficient load can be applied by direct current.

<Measurement of melting point, melting enthalpy, crystallization temperature, and crystallization enthalpy in fast run>
A 5 mg sample was cut out from the biaxially stretched polypropylene films of Examples and Comparative Examples, sealed in an aluminum pan, and the input compensation differential scanning calorimetry was performed with a differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer). In the measurement, the temperature was raised (first run) at 20 ° C./min from 30 ° C. to 280 ° C. in a nitrogen atmosphere. From the results of the first run, the melting point, melting enthalpy, crystallization temperature, and crystallization enthalpy were determined.

<Measurement of melting point and melting enthalpy in the second run>
After the first run, it was held at 280 ° C. for 5 minutes, then cooled to 30 ° C. under the condition of a temperature lowering rate of 20 ° C./min, and held at 30 ° C. for 5 minutes. Then, the temperature was raised (second run) from 30 ° C. to 280 ° C. at 20 ° C./min under a nitrogen atmosphere. From the results of the second run, the melting point and the melting enthalpy were determined.

<Manufacturing of capacitor elements>
A metal film was obtained by applying a T-margin thin-film deposition pattern on the surface of the biaxially stretched polypropylene film of each example by aluminum vapor deposition with a vapor deposition resistance of 12 Ω / □ to form a metal film. After slitting to a small width, two metallized films were combined and wound for 1360 turns at a winding tension of 200 g using an automatic winding machine 3KAW-N2 manufactured by Minato Seisakusho Co., Ltd.
The element wound element was heat-treated at 120 ° C. for 4 hours while being pressed, and then zinc metal was sprayed on the element end face 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 a high dielectric breakdown strength and is extremely suitable as a film for a capacitor.

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

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

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

[Measurement method of characteristic value, etc.]
The methods for measuring characteristic values in Examples, Reference Examples, and Comparative Examples are as follows.

<Dielectric breakdown strength>
The withstand voltage of the biaxially stretched film was measured by measuring the dielectric breakdown strength (ES) according to JIS C 2330: 2010 and JIS C 2151: 2006 17.2.2 (dielectric breakdown voltage / flat plate electrode method). The measurement was performed at an atmospheric temperature of 100 ° C. The boosting speed was 100 Vac / sec, the breaking current at the time of destruction was 10 mA, and the number of measurements was 18. Here, the measured average voltage value divided by the film thickness was used for evaluation as the dielectric breakdown strength. A film and an electrode jig were set in a blower circulation type high temperature bath, and measurement was performed at an evaluation temperature of 100 ° C.
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 Comparison were performed. For Example 6, the strength of DC dielectric breakdown (ES) was measured. In general, applying a voltage with alternating current has a higher load than applying a voltage with direct current. Therefore, for Examples 1, 3, 5 , and Comparative Examples 1 and 2 having a thickness of 18 μm, the load is not sufficient when measured with direct current, and appropriate evaluation cannot be performed. Therefore, alternating current is used. It was measured. On the other hand, Example 6, Comparative Example 5, and Comparative Example 6 having a thickness of 2.5 μm were measured by direct current because a sufficient load can be applied by direct current.

<Measurement of melting point, melting enthalpy, crystallization temperature, and crystallization enthalpy in fast run>
A 5 mg sample was cut out from the biaxially stretched polypropylene films of Examples, Reference Examples, and Comparative Examples, sealed in an aluminum pan, and input compensation differential scanning calorimetry was performed with a differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer). rice field. In the measurement, the temperature was raised (first run) at 20 ° C./min from 30 ° C. to 280 ° C. in a nitrogen atmosphere. From the results of the first run, the melting point, melting enthalpy, crystallization temperature, and crystallization enthalpy were determined.

Claims (10)

Polypropylene A with a strain curability parameter of less than 3 and
A biaxially stretched polypropylene film comprising polypropylene B having a strain curability parameter of 3 or more and 20 or less as a resin component. The biaxially stretched polypropylene film according to claim 1, wherein the polypropylene B is a long-chain branched polypropylene. The biaxially stretched polypropylene film according to claim 1 or 2, wherein the gel fraction of the polypropylene B is 1000 mass ppm or less based on the mass of the polypropylene B. The biaxially stretched polypropylene film according to any one of claims 1 to 3, wherein the polypropylene B is obtained by polymerizing propylene using a metallocene catalyst. The biaxially stretched polypropylene film according to any one of claims 1 to 4, wherein the polypropylene B has a molecular weight distribution (Mw / Mn) of 1.5 or more and 4.5 or less. The biaxially stretched polypropylene film according to any one of claims 1 to 5, wherein the mass ratio of polypropylene A to polypropylene B is polypropylene A: polypropylene B = 50: 50 to 99.9: 0.1. The biaxially stretched polypropylene film according to any one of claims 1 to 6, wherein the polypropylene A has a molecular weight distribution (Mw / Mn) of 7.0 or more and 12.0 or less. The biaxially stretched polypropylene film according to any one of claims 1 to 7, which is for a capacitor. A metallized film having a metal film on at least one side of the polypropylene film according to any one of claims 1 to 8. The capacitor including the metallized film according to claim 9.

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