JP2011122143A - Biaxially oriented polypropylene film for capacitor and metallized film and film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polypropylene film for a capacitor which exhibits excellent withstand voltage property and reliability in the application for a high voltage capacitor and secures stable element processibility. <P>SOLUTION: The biaxially oriented polypropylene film for the capacitor has projecting parts on both surfaces, wherein the thickness (t1) (μm) is 1-5 μm, the minimum height of the projecting part Pmin (nm) in every surfaces is ≥100, the maximum height of the projecting part Pmax (nm) is ≤1,200 and when one of the surface is expressed by A surface and another surface is expressed by B surface, all the following formulas are satisfied. that are 0.5≤Pa250-450/Pa≤0.8, 0.5≤Pb250-450/Pb≤0.8, 0.7≤Pa250-450/Pb250-450≤1.2 and 0.7≤Pa/Pb≤1.2, where Pa250-450 is the number of the projecting parts having ≥250 nm and ≤450 nm height per 0.1 mm<SP>2</SP>present on A surface and Pb250-450 is the number of the projecting parts having ≥250 nm and ≤450 nm height per 0.1 mm<SP>2</SP>present on B surface, Pa is the number of the projecting parts per 0.1 mm<SP>2</SP>present on A surface and Pb is the number of the projecting parts per 0.1 mm<SP>2</SP>present on B surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polypropylene film suitable for packaging, industrial use, and the like, and more specifically, a biaxially stretched polypropylene for a capacitor excellent in high voltage resistance and suitable element workability as a dielectric for a capacitor. Related to film.

  Biaxially stretched polypropylene films are excellent in transparency, mechanical properties, electrical properties, and the like, and are therefore used in various applications such as packaging applications, tape applications, cable wrapping, and electrical applications including capacitors.

  Among these, the capacitor application is particularly preferably used for high voltage capacitors because of its excellent withstand voltage characteristics and low loss characteristics, not limited to DC applications and AC applications.

  Recently, various types of electrical equipment are being converted to inverters, and accordingly, the demand for smaller capacitors and larger capacities has increased. In response to such demands in the market, especially for automotive applications (including hybrid car applications), it has become essential to make thinner films while improving the voltage resistance and device processability of biaxially oriented polypropylene films. .

  Such a biaxially stretched polypropylene film needs to be appropriately roughened from the viewpoint of voltage endurance and device processability, and this is particularly effective in improving the slipping property and oil impregnation property of the film or in the deposition capacitor. It is particularly important for imparting sex. Here, the term “security” refers to a metal-deposited capacitor that uses a metal-deposited film formed on the dielectric film as an electrode. In the event of abnormal discharge, the deposited metal scatters due to discharge energy, thereby recovering insulation and preventing short circuits. Thus, the function of the capacitor is maintained or prevented from being destroyed, and it is an extremely useful function from the viewpoint of safety.

  Such roughening methods include mechanical methods such as embossing and sandblasting, chemical methods such as chemical etching with solvents, methods of stretching sheets mixed with different types of polymers such as polyethylene, and generating β crystals. A method of stretching a sheet (see, for example, Patent Documents 1 and 2) has been proposed.

  However, the mechanical method and the chemical method have a low roughness density, and the method of stretching the sheet on which the β crystal is formed tends to generate coarse protrusions, which is not necessarily sufficient in terms of the roughness density, the coarse protrusions, and the number of protrusions. There was a case that I could not say. Further, the film roughened by these methods may be insufficiently impregnated with oil between the film layers at the time of capacitor formation, and partly unimpregnated portions are likely to be formed, and the capacitor life may be reduced. In the method of stretching a sheet blended with a different polymer such as polyethylene, there is little remaining of bubbles at the time of capacitor formation, but when the film is recycled, the different polymer may adversely affect and there is a problem that the recyclability is poor. .

  Also, the biaxially stretched polypropylene film produced by any of the methods may cause problems in terms of reliability due to insufficient safety under the severe conditions where the potential gradient is 350 V / μm or more as the usage conditions of the capacitor. There is. Here, the potential gradient is obtained by dividing the voltage applied to the dielectric film by the film thickness, and is the applied voltage per unit film thickness.

  Moreover, about roughness density and the uniformity of protrusions, a high melt tension polypropylene film (see, for example, Patent Document 4) or a film in which such a high melt tension polypropylene film and a normal polypropylene film are laminated (see, for example, Patent Document 3). However, when the high melt tension polypropylene resin itself is used as a capacitor, sufficient heat resistance and pressure resistance cannot be obtained due to the resin structure, and the dielectric breakdown voltage at a particularly high temperature is significantly reduced. There is a problem to do. In addition, in the technology of laminating high melt tension polypropylene resin, it is very difficult to obtain a uniform laminated thickness structure especially for a thin film having a film thickness of 5 μm or less. It is not the case. In addition, Patent Document 5 discloses a biaxially stretched polypropylene film whose surface roughness is controlled and a method for producing the same, but it is insufficient and difficult to make both surfaces of the film have the same level of roughness. is there.

  Further, for Patent Documents 5 and 6 that define the roughness on at least one side of the film surface, as a method of forming a fine rough surface, the β crystal fraction of the cast raw sheet is within a certain range. It is said that the winding property and the pressure resistance can be balanced. However, the production method cannot sufficiently control the roughness of both surfaces of the film, and the fine roughness of the obtained film sufficiently satisfies the pressure resistance and device processability particularly required for automotive applications. It was not a thing.

JP-A 51-63500 JP 2001-324607 A JP 2001-129944 A JP 2001-72778 A Patent Publication No. 3508515 JP 2007-308604 A JP 2008-133446 A

  The present inventors have conceived the present invention as a result of intensive studies in order to solve the above problems. The present invention is intended to provide a biaxially stretched polypropylene film for a capacitor that exhibits excellent voltage resistance and reliability even in high voltage capacitor applications and ensures stable device processability.

  Such a biaxially stretched polypropylene film for a capacitor provides a biaxially stretched polypropylene film that is excellent in uniformity of projections suitable for capacitors and the like, has a high roughness density, and has surfaces with few coarse projections on both sides.

  The present invention for solving the above-described problems has the following features.

  (1) A biaxially oriented polypropylene film for a capacitor having protrusions on both sides, the thickness t1 (μm) is 1 to 5 μm, and the minimum protrusion height Pmin (nm) is 100 or more for any surface; Biaxially stretched polypropylene film for capacitors satisfying all of the following formulas when the maximum protrusion height Pmax (nm) is 1,200 or less, and one surface is an A surface and the other surface is a B surface. .

0.5 ≦ Pa250-450 / Pa ≦ 0.8
0.5 ≦ Pb250-450 / Pb ≦ 0.8
0.7 ≦ Pa250-450 / Pb250-450 ≦ 1.2
0.7 ≦ Pa / Pb ≦ 1.2
However,
Pa250-450: number per 0.1mm ² of the heights below 250nm or 450nm present in side A projection Pb250-450: ² per 0.1mm of the surface B of less than height 250nm or 450nm present in side projection Pa: Number of protrusions present on the A surface per 0.1 mm ² Pb: Number of protrusions present on the B surface per 0.1 mm ² (2) Pa and Pb satisfy the following formula (1 The biaxially stretched polypropylene film for capacitors as described in 1).

| Pa-Pb | ≦ 200
(3) The biaxially stretched polypropylene film for capacitors according to (1) or (2), wherein the 10-point average roughness (SRz) of any surface is 500 nm or more and 1,000 nm or less.

  (4) The biaxially stretched polypropylene film for capacitors according to any one of (1) to (3), wherein the centerline surface roughness (SRa) of any surface is 20 nm or more and 40 nm or less.

  (5) The ratio SRz / SRa of the centerline surface roughness (SRa) and the 10-point average roughness (SRz) is 22 or more and 32 or less for any of the above (1) to (4) The biaxially stretched polypropylene film for a capacitor according to any one of the above.

  (6) The biaxially stretched polypropylene film for capacitors according to any one of (1) to (5) above, containing 0.05 to 3% by mass of the branched polypropylene (H).

  (7) A metallized film in which a metal film is provided on at least one surface of the biaxially stretched polypropylene film for capacitors according to any one of (1) to (6).

  (8) The metallized film according to (7), wherein the surface electrical resistance of the metal film is in the range of 1 to 20Ω / □.

  (9) A film capacitor using the metallized film according to (7) or (8).

  According to the present invention, by having excellent surface characteristics, it is excellent in workability even for a thin film, and has a high withstand voltage even under a wide range of atmospheric temperature conditions from low temperature (−40 ° C.) to high temperature (85 ° C.). Since the biaxially stretched polypropylene film for capacitors that exhibits the properties can be provided, it is particularly suitable for capacitor applications, preferably for automobiles.

  Hereinafter, the biaxially stretched polypropylene film for a capacitor, metallized film, and film capacitor of the present invention will be described in more detail.

  The polypropylene film for a capacitor of the present invention has protrusions on both surfaces, and the thickness t1 (μm) is 1 to 5 μm. In addition, this thickness is the thickness by a micrometer method so that it may mention later.

  Further, for any surface, the minimum protrusion height Pmin (nm) is 100 or more, the maximum protrusion height Pmax (nm) is 1,200 or less, and one surface is the A surface and the other surface is the other surface. When the surface is B, all the following formulas are satisfied.

0.5 ≦ Pa250-450 / Pa ≦ 0.8
0.5 ≦ Pb250-450 / Pb ≦ 0.8
0.7 ≦ Pa250-450 / Pb250-450 ≦ 1.2
0.7 ≦ Pa / Pb ≦ 1.2
However,
Pa250-450: number per 0.1mm ² of the heights below 250nm or 450nm present in side A projection Pb250-450: ² per 0.1mm of the surface B of less than height 250nm or 450nm present in side projection Pa: Number of projections present on the A plane per 0.1 mm ² Pb: Number of projections present on the B plane per 0.1 mm ² First, the thickness t1 will be described.

  The biaxially stretched polypropylene film for capacitors of the present invention preferably has a film thickness of 1 to 5 μm by a micrometer method from the viewpoint of capacitor element size and film formation stability. The film thickness by the micrometer method is more preferably 1.2 to 4 μm, and particularly preferably 1.5 to 3 μm. If the film is too thin, the mechanical strength and dielectric breakdown strength may be inferior. On the other hand, if the film is too thick, it is difficult to form a film having a uniform thickness, and when used as a dielectric for a capacitor, the capacity per volume becomes small.

  The film of the present invention has a minimum protrusion height Pmin of 100 nm or more on any surface. If this minimum protrusion height Pmin is less than 100 nm, the film cannot be wound well due to poor air escape, and in the vapor deposition process, the slit process and the capacitor element winding process, the film tends to be scratched during transportation, which tends to be a defect. It is in. In particular, in the capacitor element winding process, wrinkles are likely to occur, the interlayer gap is narrow, local interlayer adhesion occurs, and the breakdown voltage tends to decrease due to electric field concentration.

  Moreover, the film of the present invention has a maximum protrusion height Pmax of 1,200 nm or less on any surface. When the maximum projection height Pmax exceeds 1,200 nm, the dielectric breakdown is likely to be reduced due to the coarse projection, and the minimum thickness of the film is reduced and the breakdown voltage is likely to be reduced.

  Moreover, the film of this invention is satisfying the following formula | equation, when one surface is A surface and the other surface is B surface.

0.5 ≦ Pa250-450 / Pa ≦ 0.8
0.5 ≦ Pb250-450 / Pb ≦ 0.8
However,
Pa250-450: number per 0.1mm ² of the heights below 250nm or 450nm present in side A projection Pb250-450: ² per 0.1mm of the surface B of less than height 250nm or 450nm present in side projection Pa: Number of protrusions present on the A surface per 0.1 mm ² Pb: Number of protrusions present on the B surface per 0.1 mm ^{2 In} the above formula, the value of Pa250-450 / Pa, Pb250-450 / If the Pb value is less than 0.5 or exceeds 0.8, the film cannot be wound well due to poor air escape, and it is easy to be damaged during transportation in the vapor deposition process, slit process and capacitor element winding process. Tend to cause defects. In particular, in the capacitor element winding process, wrinkles are likely to occur, the interlayer gap is narrow and local interlayer adhesion occurs, and the breakdown voltage tends to decrease due to electric field concentration.

  The film of the present invention also satisfies the following formula.

0.7 ≦ Pa250-450 / Pb250-450 ≦ 1.2
0.7 ≦ Pa / Pb ≦ 1.2
In the above formula, when the value of Pa250-450 / Pb250-450 and the value of Pa / Pb are less than 0.7 or more than 1.2, the difference in the number of protrusions on both sides becomes large, and the difference in surface properties on both sides As a result, the variation between the film layers in the case of a capacitor is increased, and particularly when the impregnated type capacitor is formed, the oil impregnation between the film layers becomes insufficient, and a non-impregnated part is likely to be partially formed, and the capacitor life is likely to be reduced. Especially for high voltage capacitors, not limited to DC applications and AC applications, the values of Pa250-450 / Pb250-450 and Pa / Pb are both 0.8 or more and 1.1 regardless of impregnation type or non-impregnation type. It is preferable that the film has the following properties, which further improves the capacitor life and provides a capacitor film having excellent electrical characteristics.

  Moreover, in this invention, it is preferable that Pa and Pb satisfy | fill the following formula.

| Pa-Pb | ≦ 200
If the value of | Pa−Pb | is 200 or less, the surface disparity between the two surfaces is further reduced, the uniformity of the gap between the films at the time of capacitor formation is increased, the capacitor life is improved, and a capacitor film having excellent electrical characteristics is obtained. be able to.

  Here, the technical background of the present invention will be described. In order to improve the voltage resistance and device processability of the polypropylene film, it is important to control the surface roughness, protrusion height, and protrusion count on both sides of the polypropylene film. In addition, in order to improve the voltage resistance and capacitor element processability, the uniformity of the gap between the films and the ease of slipping between the films or the transport roll are important. It is required to reduce adhesion and residual stress. For this reason, in this invention, the parameter | index which cannot be expressed with the conventional 2-dimensional or 3-dimensional centerline surface roughness is employ | adopted. That is, it is possible to obtain suitable element workability and high withstand voltage by capturing a protrusion having a height in the range of 250 nm or more and less than 450 nm as a control target.

  Moreover, it is preferable that the 10-point average roughness (SRz) of both surfaces of the biaxially stretched polypropylene film for capacitors of the present invention is 500 nm or more. If the SRz is less than 500 nm, the film cannot be wound up due to poor air escape or the like, the roll shape may be disturbed, and the slit process and capacitor element formation may not be performed properly. On the other hand, when SRz exceeds 1,000 nm, the dielectric breakdown voltage may be lowered, and SRz is preferably 500 to 1,000 nm. SRz is more preferably 600 to 950 nm, and particularly preferably 700 to 900 nm. This makes it possible to obtain a film having improved workability and improved workability in the slit process and the capacitor element process.

  The biaxially stretched polypropylene film for capacitors of the present invention has a center line average roughness (SRa) of 40 nm or less. If the center line average roughness (SRa) is greater than 40 nm, air may easily enter between layers when the films are laminated, leading to deterioration of the capacitor element. Further, when a metal layer is formed on the film, a hole or the like is generated in the metal layer, and the dielectric breakdown strength and device life at high temperatures are reduced, or charges are concentrated when a voltage is applied, which easily causes insulation defects. On the other hand, if SRa is less than 20 nm, the slippage of the film is lowered, the handling property is inferior, or when the capacitor element is impregnated with the insulating oil, the insulating oil does not uniformly penetrate between the film layers, and the capacity changes during continuous use. May grow. Therefore, the center line average surface roughness (SRa) on both surfaces of the film is preferably 20 to 40 nm, more preferably 25 to 35 nm, whereby the winding property in the capacitor element process and the capacitance when the capacitor is obtained. It is possible to obtain a film with improved changes and excellent workability and capacitor characteristics.

  The biaxially stretched polypropylene film for capacitors of the present invention preferably has a 10-point average roughness (SRz) within a certain range with respect to the centerline average surface roughness (SRa). That is, in any aspect, the ratio of SRz to SRa (SRz / SRa) is preferably in the range of 22 to 32, more preferably in the range of 24 to 30, and particularly preferably 25 to 25. It is within the range of 29.

  If the value of this ratio (SRz / SRa) is too large, the ratio of coarse protrusions increases, so that air may enter between layers when the films are laminated, leading to deterioration of the capacitor element. In addition, when a metal layer is formed on a film, a hole or the like is generated in the metal layer, and the dielectric breakdown strength and device life at high temperatures are reduced, or charges are concentrated when a voltage is applied, which easily causes insulation defects. On the other hand, if this ratio (SRz / SRa) is too small, handling properties and stability during film conveyance may be inferior.

  As described above, the film of the present invention defined for the surface protrusions has a characteristic surface formation that is excellent in surface uniformity and excellent in balance of roughness density. And, if a capacitor is produced using such a biaxially stretched polypropylene film, even if dielectric breakdown occurs, an appropriate clearance is maintained between the film layers, so the capacitor life can be maintained without breaking, It has an excellent function of stably exhibiting safety.

  In addition, values of the above-mentioned protrusion height, the number of protrusions, SRz, SRa, etc. are based on JIS B-0601 (1982), “Non-contact three-dimensional fine shape measuring instrument (ET-30HK)” manufactured by Kosaka Laboratory Ltd. and It can be measured using a “three-dimensional roughness analyzer (MODEL SPA-11)”. Details of measurement conditions and the like will be described later.

  The biaxially stretched polypropylene film for capacitors of the present invention preferably contains 0.05 to 3 mass% of branched polypropylene (H). Furthermore, the film of the present invention is preferably composed of a mixture of linear polypropylene and the branched polypropylene (H). In this case, the branched polypropylene (H) has a relationship that the melt tension (MS) and the melt flow index (MFR) measured at 230 ° C. are log (MS)> − 0.56 log (MFR) +0.74. A branched polypropylene (H) satisfying the formula is particularly preferable.

  A branched polypropylene (H) satisfying the relational expression of melt tension (MS) and melt flow index (MFR) measured at 230 ° C. log (MS)> − 0.56 log (MFR) +0.74 is obtained. Include a method of blending polypropylene containing a large amount of high molecular weight components, a method of blending oligomers or polymers having a branched structure, and a long-chain branched structure in a polypropylene molecule as described in JP-A-62-1121704. Preferably, a method of introducing a thiol or a method described in Japanese Patent No. 2869606 is preferably used.

  Generally, independent granular protrusions can be formed by a method of stretching a sheet containing a different polymer such as polyethylene, but the melt tension (MS) and melt flow index (MFR) measured at 230 ° C. are log (MS). The biaxially stretched polypropylene film containing the branched polypropylene (H) satisfying the relational expression> −0.56 log (MFR) +0.74 is obtained by a method of stretching a sheet in which a different polymer such as polyethylene is blended. It is possible to easily obtain a surface that is finer than the surface of the axially oriented polypropylene film, has few coarse projections, and has excellent uniformity of projections.

  By containing 0.05 to 3 mass% of branched polypropylene (H), the size of the spherulite generated in the cooling process of the melt-extruded resin sheet can be easily controlled to be small, and the generation of insulating defects generated in the stretching process Can be made small, and a polypropylene film excellent in voltage resistance can be obtained.

Furthermore, the branched polypropylene (H) can form a rough surface by crystal transformation as long as the addition amount is within a certain range while having an α-crystal nucleating agent action. Combined with the effect of reducing the spherulite size, the crater size described later can be made small and dense, excellent in uniformity of protrusions, and excellent characteristic surface roughness without coarse protrusions. A biaxially oriented polypropylene film can be provided. More preferably, the branched polypropylene (H) is preferably contained in an amount of 0.05 to 2% by mass, and particularly preferably 0.05 to 1% by mass, thereby further improving the winding property and voltage resistance. Thus, a film excellent in device processability and capacitor characteristics can be obtained. The branched polypropylene (H) mentioned here is a polypropylene having 5 or less internal 3-substituted olefins per 10,000 carbon atoms. The presence of this internal trisubstituted olefin can be confirmed by the proton ratio in the ¹ H NMR spectrum.

  As a method for forming the film surface of the present invention, a technique utilizing crystal transformation is suitable. This method does not require the addition of impurities that lower the electrical characteristics and can degrade electrical characteristics such as dielectric breakdown voltage compared to the method of adding resin or inorganic and / or organic particles that are incompatible with polypropylene. It is preferably employed because of its low nature. Hereinafter, the surface form obtained by crystal transformation will be described.

The surface formation method by crystal transformation is a method for forming a surface using two crystal systems of polypropylene described in the literature (M. Fujiyama, Journal of Applied Polymer Science 36, P.985-1948 (1988)). Yes, α-crystal (monoclinic, crystal density 0.936 g / cm ² ) spherulites and β-crystal (hexagonal, crystal density 0.922 g / cm ² ) spherulites are generated in unstretched sheets. In the stretching process, the thermally unstable β-crystal is transformed into α-crystal to form irregularities on the film surface.The basic unit of surface irregularities obtained by this method is spherulite The shape is a crater shape formed in an arc shape, that is, a form in which convex portions are arranged in a circular or elliptical shape is observed, which is obtained by the crystal transformation. Typical surface shape is a lot of crater shapes formed in an elliptical shape A portion (convex portion) that is formed by being present and projecting from the film surface has a crater shape by being connected in an arc shape, and according to the present technology, unevenness is present in the absence of β-crystal spherulites. The arcuate protrusion (crater) is characterized by a change in the aspect ratio corresponding to the ratio of the aspect ratio when biaxially extending, and the aspect ratio is 1, In isotropic stretching, it becomes almost circular and becomes flat as the aspect ratio increases, and the shape obtained by the sequential biaxial stretching method usually has a major axis in the lateral direction of the film (the width direction of the film roll). Depending on how the spherulites are formed, a plurality of craters having different shapes may be overlapped, and the arc may be arcuate or semi-arc shaped without being circularly closed.

  As one of the methods for generating the characteristic surface shape of the present invention, a material having a nucleating agent effect is added to increase the nucleation capability, the number of nuclei is increased, and a large number of small fine protrusions are present, which is relatively flat. For example, it is possible to form a surface having few protrusions and uniform protrusions. Examples of the raw material having the nucleating agent effect include the above-described branched polypropylene (H). Since the above crater shape can be controlled by controlling the amount of the branched polypropylene (H) added and the film forming conditions, the characteristic surface shape of the present invention can be generated as a result. Become.

  Moreover, it is preferable that the biaxially stretched polypropylene film for capacitors of the present invention is composed of a mixture of the above-described branched polypropylene (H) and linear polypropylene. Thereby, the melt crystallization temperature of ordinary polypropylene is about 110 ° C., but can be increased to 115 ° C. or higher. That is, in the process of self-healing of the capacitor, the safety is easily recovered due to the high melt crystallization temperature. In other words, the vapor deposition metal around the discharge part is scattered by the discharge energy generated when the dielectric film causes dielectric breakdown for some reason, and the film itself partially melts due to partial high temperature at that time. High crystallization temperature makes it easy to recrystallize immediately and to recover the insulating property. When the ambient temperature of the capacitor becomes high, it is difficult to recrystallize normally and it is difficult to recover the insulation, but in the present invention, by increasing the melt crystallization temperature, it becomes easier to recrystallize at a high temperature during dielectric breakdown. , Security can be improved.

  In the present invention, it is preferable to use a linear polypropylene which is a commonly used polypropylene mixed with a branched polypropylene (H) effective as a raw material having a nucleating agent effect. That is, branched polypropylene (H) is used as an α-crystal or β-crystal nucleating agent, and as such branched polypropylene (H), the melt tension (MS) and melting when measured at 230 ° C. It is preferable to use a branched polypropylene having a flow index (MFR) satisfying a relational expression of log (MS)> − 0.56 log (MFR) +0.74.

  Here, the melt tension measured at 230 ° C. is measured according to the melt flow index (MFR) measurement shown in JIS-K7210 (1999). Specifically, using a melt tension tester manufactured by Toyo Seiki, polypropylene is heated to 230 ° C., molten polypropylene is discharged at an extrusion speed of 15 mm / min to form a strand, and this strand is taken up at a speed of 6.4 m / min. The tension at the time was measured and used as the melt tension (unit cN). The melt flow index (MFR) measured at 230 ° C. is a value (unit: g / 10 minutes) measured at a load of 21.18 N according to JIS-K7210 (1999).

The branched polypropylene (H) is not particularly limited as long as the above formula is satisfied, but the melt flow index (MFR) is in the range of 1 to 20 g / 10 min from the viewpoint of film forming properties. A thing in the range of 1-10 g / 10min is more preferable. Moreover, about melt tension, what exists in the range of 1-30 cN is preferable, and what exists in the range of 2-20 cN is more preferable. If the melt tension is small, the uniformity of the projections is inferior, and the ratio of the 10-point average roughness SRz to the centerline average surface roughness SRa (SRz / SRa) increases, making it easy to form coarse projections. The larger the melt tension, the higher the uniformity of the protrusions, and the ratio (SRz / SRa) tends to decrease, so that it is easy to form a dense surface (the number of protrusions per unit area is large).
For this reason, the use of branched polypropylene (H) is particularly suitable for satisfying the following formula characteristically expressing dense surface formation.

0.5 ≦ Pa250-450 / Pa ≦ 0.8
0.5 ≦ Pb250-450 / Pb ≦ 0.8
In order to obtain the branched polypropylene (H), as described above, a method of blending an oligomer or polymer having a branched structure, a long-chain branched structure in a polypropylene molecule as described in JP-A-62-1121704. The method described in Japanese Patent No. 2869606 or the like is preferably used. Specific examples include “Profax PF-814” manufactured by Basell, and “Daploy HMS-PP” manufactured by Borealis (WB130HMS, WB135HMS, etc.). Among them, a resin obtained by an electron beam cross-linking method is included in the resin. It is preferably used because it has few gel components. The characteristic when such HMS resin is added to polypropylene (PP) is that the melt crystallization temperature of PP is usually in the vicinity of 110 ° C., but rises to a range of 115 to 130 ° C.

  In the present invention, the content of such branched polypropylene (H) in the film is preferably 0.05 to 3% by mass, and more preferably 0.05 to 2% by mass, particularly preferably. Is 0.05-1 mass%. By setting it as this content, at least two melting peaks observed when measured by 2nd-Run appear in the polypropylene resin constituting the film. That is, in addition to the first melting peak (temperature 160 to 172 ° C.), it has a shoulder peak (148 to 157 ° C.), and it is possible to form a dense surface with uniform protrusions and few coarse protrusions. . In addition, by making such a content, excellent uniformity of protrusions, excellent characteristic surface shape without coarse protrusions, and excellent workability even under a wide range of atmospheric temperature from -40 ° C to over 80 ° C. And a biaxially stretched polypropylene film for a capacitor exhibiting high withstand voltage can be produced.

  In the above-described biaxially stretched polypropylene film of the present invention, the A surface is preferably a corona-treated surface on which metal deposition is performed, and the B surface is preferably a non-treated surface that is not subjected to corona treatment.

  Next, the linear polypropylene used for the biaxially stretched polypropylene film of the present invention will be described. Linear polypropylene is usually used for packaging materials and capacitors, but preferably has a cold xylene soluble part (hereinafter CXS) of 4% or less and a mesopentad fraction of 0.95 or more. Polypropylene is preferred. If these conditions are not satisfied, the film-forming stability may be inferior, or voids may be formed in the film when producing a biaxially stretched film, resulting in a large decrease in dimensional stability and dielectric breakdown resistance. There is a case.

  Here, the cold xylene-soluble part (CXS) refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene and then deposited at room temperature, and has low stereoregularity. It is considered that it corresponds to a component that is difficult to crystallize due to low molecular weight. If many such components are contained in the resin, problems such as inferior thermal dimensional stability of the film and reduction in dielectric breakdown voltage at high temperatures may occur. Therefore, CXS is preferably 4% or less, more preferably 3% or less, and particularly preferably 2% or less. In order to obtain such a linear polypropylene having CXS, methods such as a method for enhancing the catalytic activity in obtaining a resin and a method for washing the obtained resin with a solvent or propylene monomer itself can be used.

  From the same viewpoint, the mesopentad fraction of the linear polypropylene is preferably 0.95 or more, more preferably 0.97 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene measured by a nuclear magnetic resonance method (NMR method). The higher the numerical value, the higher the crystallinity, the higher the melting point, and the higher the temperature. This is preferable because the dielectric breakdown voltage is increased. There is no particular limitation on the upper limit of the mesopendart fraction. In order to obtain a resin with high stereoregularity in this way, there are a method of washing resin powder obtained with a solvent such as n-heptane, a method of selecting a catalyst and / or promoter, and a composition as appropriate. Preferably employed.

  As such a linear polypropylene, the melt flow index (MFR) is more preferably 1 to 10 g / 10 min (230 ° C., 21.18 N load), particularly preferably 2 to 5 g / 10 min (230 ° C., 21.18 N). The range of (load) is preferable from the viewpoint of film forming property. In order to set the melt flow index (MFR) to the above value, a method of controlling the average molecular weight or the molecular weight distribution is employed.

  Such linear polypropylene is mainly composed of a propylene homopolymer, but may contain other unsaturated hydrocarbon copolymerization components or the like as long as the object of the present invention is not impaired. No polymer may be blended. For example, ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene as monomer components constituting such a copolymer component or blend. 1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- Examples include norbornene. From the viewpoint of dielectric breakdown resistance and dimensional stability, the copolymerization amount or blend amount is preferably less than 1 mol% in copolymerization amount and less than 10 mass% in blend amount.

  The linear polypropylene has various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slip agent, an antistatic agent, an antiblocking agent, and a filler as long as the object of the present invention is not impaired. , A viscosity modifier, a coloring inhibitor, and the like can also be contained.

  Among these, selection of the kind and addition amount of the antioxidant is important from the viewpoint of long-term heat resistance. That is, the antioxidant is a phenolic compound having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various compounds such as 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6- Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, Irganox (registered trademark) 1330: molecular weight 775.2 manufactured by Ciba Geigy) or tetrakis [methylene-3 (3,5-di-t- Butyl-4-hydroxyphenyl) propionate] methane (for example, Irganox 1010 manufactured by Ciba-Geigy Corporation: molecular weight 1177.7) is preferably used in combination. The total content of these antioxidants is preferably in the range of 0.03 to 1.0 mass% with respect to the total amount of polypropylene. If the amount of the antioxidant is too small, the long-term heat resistance may be poor. If the amount of the antioxidant is too large, the capacitor element may be adversely affected by blocking at a high temperature due to bleeding out of these antioxidants. The more preferable content is 0.1 to 0.9% by mass, and particularly preferably 0.2 to 0.8% by mass.

  In the present invention, a crystal nucleating agent can be added as long as it does not contradict the purpose of the present invention. As described above, the branched polypropylene (H) has an α-crystal or β-crystal nucleating agent effect itself, but other α-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.) ), Β crystal nucleating agents (amide compounds such as potassium 1,2-hydroxystearate, magnesium benzoate, N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, quinanacridon compounds, etc.) and the like. . However, in the present invention, by adding these crystal nucleating agents, it is difficult to obtain the desired surface roughness, there is a possibility of adversely affecting electrical properties such as a decrease in volume resistivity at high temperatures, The amount added is preferably less than 0.1% by mass, more preferably substantially not added.

  Moreover, it is preferable that the glossiness of the biaxially stretched polypropylene film surface for capacitors of the present invention is in the range of 100 to 130%, more preferably 110 to 120%. That is, lowering the gloss level means increasing the light scattering density on the film surface, that is, increasing the unevenness of the film surface, increasing the number of protrusions per unit area and increasing the roughness density. . However, if the glossiness is reduced to less than 100%, the liquid impregnation property is improved, but the number of protrusions increases due to the formation of dense protrusions, so that the amount of air accumulation between the protrusions increases, and the film layers are slippery and the elements are wound. It becomes difficult to wind the film into a roll shape. On the other hand, when the glossiness exceeds 130%, it is difficult to form a flat capacitor element that is difficult to slip between the film layers, and the safety is deteriorated because sufficient clearance between the film layers cannot be maintained. Arise. The glossiness of 110 to 120% is more preferable because the element winding property, pressure resistance, and security are improved.

  Further, the ash content of the biaxially stretched polypropylene film for capacitors of the present invention is preferably 50 ppm or less (weight basis, the same shall apply hereinafter), more preferably 30 ppm or less, and particularly preferably 20 ppm or less. If the ash content is too large, the dielectric breakdown resistance of the film is lowered, and the dielectric breakdown strength may be lowered when a capacitor is used. In order to make the ash content within this range, it is important to use a raw material with little catalyst residue, but a method of reducing contamination from the extrusion system as much as possible, for example, taking a bleed time of 1 hour or more, A method of sufficiently washing the path with a polymer before actually starting film formation can be employed.

  The biaxially stretched polypropylene film for capacitors of the present invention is preferably used as a dielectric film for capacitors, but is not limited to the type of capacitor. Specifically, from the viewpoint of electrode configuration, either a foil wound capacitor or a metal vapor deposition film capacitor may be used, and it is also preferably used for an oil immersion type capacitor impregnated with insulating oil or a dry type capacitor not using insulating oil at all. It is done. Further, from the viewpoint of shape, it may be a winding type or a laminated type. However, it is particularly preferably used as a metal vapor deposition film capacitor because of the characteristics of the film of the present invention.

  In addition, since a polypropylene film usually has a low surface energy and it is difficult to stably deposit metal, it is preferable to perform a surface treatment in advance for the purpose of improving metal adhesion. Specific examples of the surface treatment include corona discharge treatment, plasma treatment, glow treatment, and flame treatment. Usually, the surface wetting tension of a polypropylene film is about 30 mN / m, but it is possible to adjust the wetting tension to 37 to 50 mN / m, preferably about 39 to 48 mN / m by these surface treatments. It is preferable because it is excellent in safety and has good security.

  The biaxially stretched polypropylene film for capacitors of the present invention is obtained by biaxially stretching using the raw materials that can give the above-described properties. The biaxial stretching method can be obtained by any of the inflation simultaneous biaxial stretching method, the stenter simultaneous biaxial stretching method, and the stenter sequential biaxial stretching method. Among them, the film forming stability, the thickness uniformity, In terms of controlling the surface shape, it is preferable to employ a stenter sequential biaxial stretching method.

  Next, although the manufacturing method of the biaxially-stretched polypropylene film for capacitors of this invention is demonstrated below, it is not necessarily limited to this.

  First, high melt tension polypropylene (branched polypropylene (H)) is blended with linear polypropylene, melt extruded, passed through a filtration filter, extruded from a slit base at a temperature of 220 to 280 ° C., and then on a cooling drum. To obtain an unstretched sheet. Here, in order to obtain the film of the present invention, it is preferable to appropriately control the temperature of the cooling drum for the purpose of appropriately generating β crystals. Here, in order to efficiently generate β crystals, it is preferable to maintain the resin temperature at which the β crystal generation efficiency is maximized for a predetermined time, and the temperature is usually 115 to 135 ° C. The holding time is preferably 1 second or longer. In order to realize these conditions, the process can be determined as appropriate according to the resin temperature, the extrusion amount, the take-up speed, etc., but from the viewpoint of productivity, the diameter of the cooling drum greatly affects the holding time. In addition, the diameter of the drum is preferably at least 1 m. Further, the cooling drum temperature to be selected is preferably 70 to 120 ° C., more preferably 80 to 110 ° C., particularly preferably, although it includes a certain degree of freedom because other factors influence as described above. Is in the range of 85-100 ° C. If the casting drum temperature is too high, the crystallization of the film may proceed excessively, making stretching in subsequent steps difficult, and voids may be formed in the film, resulting in a decrease in dielectric breakdown resistance. As an adhesion method to the casting drum, any method of an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. may be used. The air knife method is preferable because it is good and the surface roughness can be controlled.

  In the air knife method under normal conditions that has been conventionally performed, it has been very difficult to make the surface roughness of the film the same surface roughness. This is because the heat history received by the film on the non-drum surface not in contact with the casting drum is different from the heat history received by the film in contact with the casting drum surface, and the crystal formation of the original fabric cannot be controlled respectively. It was difficult to make the both surfaces have the same degree of roughness (number of protrusions per unit area (Pa, Pb)). Therefore, as one of the methods for obtaining the film of the present invention, a method of raising the air temperature of the air knife imparting adhesion to the casting drum using a heater and blowing hot air is adopted. Is preferred. As a result, the film temperature on the non-drum surface side can be controlled, and the heat history received by the film on the non-drum surface side can be brought close to the heat history received by the film in contact with the casting drum surface side. Each generation can be controlled. For this reason, the same degree of roughening can be achieved on both sides.

  The air temperature of the air knife is preferably 60 to 120 ° C, more preferably 70 to 110 ° C, and particularly preferably 80 to 100 ° C. If the air temperature of the air knife is too high, the crystallization of the film will proceed too much, making stretching in later steps difficult, and voids may be formed in the film, resulting in reduced dielectric breakdown resistance. On the other hand, if the air temperature of the air knife is too low, crystal formation is insufficient and it is difficult to obtain the desired surface roughness (Pa, Pb).

  Further, the blown air speed of the air knife is preferably 130 to 150 m / s, and preferably has a double tube structure in order to improve the width direction uniformity. When the air speed is less than 130 m / s, sufficient adhesion to the cast drum cannot be imparted and the film-forming property deteriorates. When the air speed exceeds 150 m / s, the adhesion to the uniform cast drum cannot be achieved. Defects such as film properties, quality unevenness and thickness unevenness are likely to occur. In order to prevent vibration of the film, it is preferable to adjust the position of the air knife so that air flows downstream of the film formation.

  Until now, the reason why the air temperature of the air knife has not been controlled, that is, the reason for using air at normal temperature, is the effect on the capacitor characteristics due to the difference in projection height and projection density on the front and back surfaces of the film. This is probably because it was not clear. In addition, the effect of controlling the temperature of the air knife and using high-temperature air was thought to be that the casting stability was impaired and the film formation became unstable. In the present invention, as an example of solving the above problem, it is disclosed to simultaneously control the air flow rate as described above. Thereby, when using high temperature air, the problem that an air volume falls because air viscosity becomes high and pressure loss becomes large can also be solved.

  Next, this unstretched film is biaxially stretched and biaxially oriented. First, the unstretched film is preheated by passing it through a roll maintained at 120 to 150 ° C., then the sheet is kept at a temperature of 130 ° C. to 150 ° C. and passed between rolls having a difference in peripheral speed, and 2-6 in the longitudinal direction. After stretching by a factor of 2, it is cooled to room temperature. Subsequently, the stretched film is guided to a stenter, stretched 5 to 15 times in the width direction at a temperature of 150 to 170 ° C, and then heated at a temperature of 140 to 170 ° C while giving 2 to 20% relaxation in the width direction. After fixing, a film is obtained by performing corona discharge treatment in air, nitrogen, carbon dioxide gas or a mixed gas thereof in order to improve the adhesion of the deposited metal to the surface to be deposited.

  In the present invention, the method for forming a metallized film by providing a metal film on the surface of the above-described biaxially stretched polypropylene film for capacitors is not particularly limited. For example, aluminum is vapor-deposited on at least one surface of the polypropylene film to form the interior of the film capacitor. A method of providing a metal film such as an aluminum vapor deposition film to be an electrode is preferably used. At this time, other metal components such as nickel, copper, gold, silver, chromium, and zinc can be deposited simultaneously or sequentially with aluminum. In addition, a protective layer can be provided on the deposited film with oil or the like.

  The thickness of the metal film is preferably in the range of 20 to 100 nm from the viewpoint of electrical characteristics and self-heeling properties of the film capacitor. For the same reason, the surface electrical resistance value of the metal film is preferably in the range of 1 to 20Ω / □. The surface electrical resistance value can be controlled by the type of metal used and the film thickness. A method for measuring the surface electrical resistance will be described later.

  In the present invention, if necessary, after the metal film is formed, the metallized film can be subjected to an aging treatment at a specific temperature or a heat treatment. Also, a coating such as polyphenylene oxide can be applied to at least one side of the metallized film for insulation or other purposes.

  The metallized film thus obtained can be laminated or wound by various methods to obtain a film capacitor. An example of a preferred method for producing a wound film capacitor is as follows.

  Aluminum is vacuum deposited on one side of the polypropylene film. In that case, it vapor-deposits in the stripe form which has the margin part which runs in a film longitudinal direction. Next, a tape-shaped take-up reel having a margin on one side is prepared by inserting a blade into the center of each vapor deposition section on the surface and the center of each margin section. Two tape-shaped take-up reels with margins on the left or right are wound on each other so that the vapor deposition part protrudes from the margin part in the width direction. Get. The core material is removed from the wound body and pressed, and the metallicon is sprayed on both end faces to form external electrodes, and a lead wire is welded to the metallicon to obtain a wound film capacitor. The film capacitors are used for various purposes such as for vehicles, home appliances (TVs, refrigerators, etc.), general noise prevention, automobiles (hybrid cars, power windows, wipers, etc.) and power supplies. Capacitors can also be suitably used for these applications.

  The characteristic value measurement method and the effect evaluation method in the present invention are as follows.

(1) Film thickness (μm)
The micrometer method thickness was measured according to 7.4.1.1 of JIS C-2330 (2001).

(2) Gloss (Glossiness)
According to JIS K-7105 (1981), the average value of five data measured under the conditions of an incident angle of 60 ° and a light receiving angle of 60 ° using a digital variable angle gloss meter UGV-5D manufactured by Suga Test Instruments Co., Ltd. It was.

(3) Melt flow index (MFR)
According to JIS-K7210 (1999), measurement was performed at a measurement temperature of 230 ° C. and a load of 21.18N.

(4) Melt tension (MS)
It measured according to the apparatus for MFR measurement shown by JIS-K7210 (1999). Using a Toyo Seiki melt tension tester, the polypropylene is heated to 230 ° C., the molten polypropylene is discharged at an extrusion speed of 15 mm / min to form a strand, and the tension when the strand is taken up at a speed of 6.5 m / min is measured. The melt tension was used.

(5) Melting point, melt crystallization temperature (° C)
The measurement was performed under the following conditions using a Seiko RDC220 differential scanning calorimeter.

<Sample preparation>
A sample of 5 mg is enclosed in an aluminum pan for measurement. In addition, when metal vapor deposition etc. are given to the film, it removes suitably.

<Measurement>
The film is melted / recrystallized / remelted in the following steps (a) → (b) → (c). The melting point of the resin was defined as the highest melting peak temperature among melting peaks observed at 2nd Run. Three measurements were taken, and the average value was taken as the melting point.

(A) 1st Run 30 ° C. → 280 ° C. (temperature increase rate 20 ° C./min)
(B) Tmc held at 280 ° C. for 5 minutes and then cooled to 30 ° C. at 20 ° C./min. (C) 2nd Run 30 ° C. → 280 ° C. (temperature increase rate 20 ° C./min)
(6) Mesopentad fraction (mmmm)
The sample was dissolved in a solvent, and the mesopentad fraction (mmmm) was determined using ¹³ C-NMR under the following conditions (Reference: New edition of Polymer Analysis Handbook) Editorial 1995 P609-611).

A. Measurement conditions Apparatus: Bruker, DRX-500
Measurement nucleus: ¹³ C nucleus (resonance frequency: 125.8 MHz)
Measurement concentration: 10 wt%
Solvent: benzene / heavy orthodichlorobenzene = mass ratio 1: 3 mixed solution Measurement temperature: 130 ° C.
Spin rotation speed: 12Hz
NMR sample tube: 5 mm tube Pulse width: 45 ° (4.5 μs)
Pulse repetition time: 10 seconds Data point: 64K
Number of conversions: 10,000 times Measurement mode: complete decoupling
B. Analysis condition LB (line broadening factor) was set to 1.0, and Fourier transform was performed to set the mmmm peak to 21.86 ppm. Peak splitting is performed using WINFIT software (manufactured by Bruker). At that time, the peak splitting is performed from the peak on the high magnetic field side as follows, and the attached software is automatically fitted to optimize the peak splitting, and then mmmm and ss (mmmm spinning sideband peaks ) Was defined as the mesopentad fraction (mmmm).
The measurement was performed 5 times, and the average value was defined as the mesopentad fraction.

Peak (a) mrrm
(B) (c) rrrrm (divided as two peaks)
(D) rrrr
(E) mrmm + rmrr
(F) mmrr
(G) mmmr
(H) ss (mmmm spinning sideband peak)
(I) mmmm
(J) rmmr
(7) Number of internal 3-substituted olefins A sample is dissolved in a solvent, and the number of internal 3-substituted olefins is determined under the following conditions using ¹ H NMR.

A. Measurement conditions Apparatus: ECX400P type nuclear magnetic resonance apparatus manufactured by JEOL Measurement nucleus: ¹ H nucleus (resonance frequency: 500 MHz)
Measurement concentration: 2 wt%
Solvent: Heavy orthodichlorobenzene Measurement temperature: 120 ° C
Pulse width: 45 °
Pulse repetition time: 7 seconds Conversion count: 512 times Measurement mode: non decoupling
B. Analysis conditions Based on the chemical shift of orthodichlorobenzene of 7.10 ppm, the signal in the 5.0 to 5.2 ppm region is assigned to the proton of the internal trisubstituted olefin, and the integral ratio of the broad signal of 0.5 to 2.0 ppm. To determine the proton ratio of the internal trisubstituted olefin.

(8) Cold xylene soluble part (CXS)
Dissolve 0.5 g of polypropylene film sample in 100 ml of boiling xylene, allow to cool, recrystallize in a constant temperature water bath at 20 ° C. for 1 hour, and then determine the polypropylene components dissolved in the filtrate by liquid chromatography. (X (g)). Using the precision value (X0 (g)) of 0.5 g of the sample, the following formula is used.

CXS (mass%) = (X / X0) × 100
(9) Centerline average roughness (SRa), Ten-point average roughness (SRz)
Measured according to JIS B-0601 (1982) using a “non-contact three-dimensional fine shape measuring instrument (ET-30HK)” and “three-dimensional roughness analyzer (MODEL SPA-11)” manufactured by Kosaka Laboratory Ltd. . The measurement is repeated 10 times in the longitudinal direction, and the average value is obtained as center line average roughness (SRa), ten-point average roughness (SRz), total number of protrusions, number of protrusions, and further the ratio (SRz / SRa) is determined. It was. Detailed conditions and data processing for one measurement were as follows.

(A) Minimum protrusion height (Pamin, Pbmin), maximum protrusion height (Pamax, Pbmax) (unit: nm)
Detection values detected by the measuring device are output as histograms at intervals of 50 nm. For example, when a protrusion having a detection value of 100 nm or more and less than 150 nm is present, the slice value (Z) is counted in a column labeled 150 nm. Here, the minimum protrusion height is a slice width lower limit value of the slice value (Z) from which the count value is first output. That is, if the slice value (Z) from which the count value is output first is a column of 150 nm, the minimum protrusion height Pmin is 100 nm. Similarly, the maximum protrusion height is the slice width lower limit value of the slice value (Z) for which the count value was last output. That is, if the slice value (Z) from which the count value was last output is a column of 1000 nm, the maximum protrusion height Pmax is 950 nm.

(In the case of plane A, Pamin and Pamax are indicated, and in the case of plane B, Pbmin and Pbmax are indicated respectively.)
(B) Total number of protrusions Pa, Pb (unit: pieces / 0.1 mm ² )
The total number of protrusions indicates the sum of all the values obtained by converting the number of protrusions detected at the sampling interval in the width direction and the length direction shown in the measurement condition item to the number per 0.1 mm ² .

  Specifically, it is the sum of the count values detected in the histogram obtained by the measuring device.

(C) Number of protrusions Pa250-450 (pieces / 0.1 mm ² ) on the A side 250 nm or more and less than 450 nm
Regarding the value on the A-plane side of the histogram, the total of the number of detected protrusions corresponding to a height of 250 nm or more and less than 450 nm is shown. Specifically, the slice value (Z) is the sum of the count values in the column corresponding to 300 to 450 nm.

(D) Number of protrusions Pb250-450 (pieces / 0.1 mm ² ) on the B surface side from 250 nm to less than 450 nm
Same as (c) above. Specifically, for the value on the B-plane side of the histogram, the slice value (Z) is the sum of the count values in the column corresponding to 300 to 450 nm.

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

Measurement direction: Film width direction Width direction feed rate: 0.1 mm / second Measurement range (width direction × length direction): 1.0 mm × 0.249 mm
Reference plane of height dimension: LOWER (lower side)
Width direction sampling interval: 2 μm
Sampling interval in the length direction: 10 μm
Number of samplings in the length direction: 25 Cutoff: 0.25 mm / second Magnification in the width direction: 200 times Magnification in the length direction: 20,000 times Waviness, roughness Cut: None Measuring method Dedicated sample holder for film measurement Is used. The sample holder is a detachable metal plate with a circular hole in the center. The sample is sandwiched between the sample holders, and the film is fixed to the four sides of the sample holder. The film was measured for roughness.

Measurement results: data processing Table 1 shows examples of measurement results obtained by the above method. When the data is shown in Table 1, each parameter of the present invention is read as follows.

Side A SRa 30.1nm
SRz 810nm
Pamin 250nm
Pamax 950nm
Pa250-450 181 / 0.1mm ² (rounded off to the nearest decimal place)
Pa 371 pieces / 0.1mm ² (rounded off after the decimal point)
B side SRa 30.3nm
SRz 868nm
Pbmin 250nm
Pbmax 950nm
170 Pb250-450 / 0.1mm ² (rounded to the nearest decimal place)
Pb 303 pieces / 0.1mm ² (rounded off after the decimal point)
| Pa-Pb | 68 pieces / 0.1mm ² (rounded off after decimal point)
(10) Metal film resistance The metallized film is cut into a rectangular shape with a full width (50 mm) in the length direction of 10 mm in the length direction, and the resistance of the metal film between 30 mm in the width direction is measured by the 4-terminal method. The membrane resistance per 10 mm × 10 mm was calculated by multiplying the obtained measurement value by the measurement width (10 mm) and dividing the interelectrode distance (30 mm). (Unit: Ω / □)
(11) Film breakdown voltage (V / μm)
According to JIS C2330 (2001) 7.4.11.2 B method (plate electrode method), an average value is obtained, and divided by the micrometer method film thickness (μm) (described above) of the measured sample, V / μm The notation.

(12) Device processability during capacitor manufacturing (device winding yield)
Aluminum was vacuum-deposited on one side of the polypropylene film obtained in each of Examples and Comparative Examples described later with a ULVAC vacuum evaporator so that the film resistance was 8 Ω / sq. At that time, vapor deposition was performed in a stripe shape having a margin portion running in the longitudinal direction (repetition of a vapor deposition portion width of 39.0 mm and a margin portion width of 1.0 mm). Next, a blade was put in the center of each vapor deposition part and the center of each margin part and slitted, and a take-up reel was formed into a tape having a width of 20 mm and a margin of 0.5 mm on the left or right. Two reels, each having a left margin and a right margin, were overlapped and wound so that the vapor deposition portion protruded 0.5 mm from the margin portion in the width direction, and wound with a capacitance of about 10 μF. Got. KAW-4NHB manufactured by Minato Seisakusho was used for element winding.

  When manufacturing the above capacitors, visually observe from the beginning of winding to the end of winding, reject wrinkles and misalignment, and indicate the percentage of the number of rejected products as a percentage of the total number of manufactured It was used as an index of property (hereinafter referred to as element winding yield). The higher the element winding yield, the better. 95% or more was evaluated as “good”, less than 95% as 80% or more as “Δ”, and less than 80% as “bad”. “◯” or “Δ” is a practical level.

(13) Evaluation of vapor deposition capacitor characteristics Films obtained in each of Examples and Comparative Examples described later were provided with a margin portion in a direction perpendicular to the longitudinal direction at a film resistance of 8 Ω / sq with aluminum using a vacuum vapor deposition machine manufactured by ULVAC. A vapor deposition pattern having a so-called T-shaped margin pattern was applied to obtain a vapor deposition reel having a width of 50 mm.

  Next, using this reel, the capacitor element was wound up with an element winding machine (KAW-4NHB) manufactured by Minato Seisakusho, and after metallization, heat treatment was performed at a temperature of 105 ° C. for 10 hours under reduced pressure, and lead wires were The mounting capacitor element was finished. The capacitance of the capacitor element at this time was 5 μF.

  Using the 10 capacitor elements thus obtained, a voltage of 500 VDC is applied to the capacitor element at room temperature, and the applied voltage is gradually increased in steps of 50 VDC / 1 minute after 10 minutes at that voltage. A so-called step-up test was performed. The capacitance change at this time was measured and plotted on a graph. The voltage at which the capacitance became 70% of the initial value was divided by the micrometer film thickness (described above) to evaluate the withstand voltage, and 350 V / μm. The above is the usable level. Moreover, after raising the voltage until the electrostatic capacity decreased to 10% or less with respect to the initial value, the capacitor element was disassembled, the state of destruction was examined, and the safety was evaluated as follows.

    (Double-circle): There is no change of element shape and penetration destruction is not observed.

    ◯: There is no change in the element shape, and penetrating destruction within 10 layers of the film is observed.

    (Triangle | delta): A change is recognized by an element shape or the penetration-like destruction exceeding 10 layers is observed.

    X: Element shape is destroyed.

  ◎ can be used without problems, but ◯ can be used depending on conditions. Δ and × cause practical problems.

  Hereinafter, an example is given and the effect of the present invention is further explained.

Example 1
As a linear polypropylene, a polypropylene resin manufactured by Prime Polymer Co., Ltd., which has a mesopendart fraction of 0.985 and a melt mass flow rate (MFR) of 2.6 g / 10 min, has a mesopendart fraction of 0.985, Extruder with a temperature of 250 ° C. blended with a polypropylene resin having a mass flow rate (MFR) of 4.0 / 10 min and 0.5% by mass of a branched-chain polypropylene resin (high melt tension polypropylene Profax PF-814) manufactured by Basell. And melt extruded into a sheet form from a T-shaped slit die at a resin temperature of 250 ° C., and the molten sheet is cooled on a 1 m diameter cooling casting drum held at 90 ° C. with an air knife temperature of 90 ° C. and an air speed of 140 m / s. And solidified by cooling. The retention time at 110 to 135 ° C. was 2.8 seconds as a result of measurement with a radiation thermometer. Next, the sheet was gradually preheated to 140 ° C., then kept at a temperature of 145 ° C., passed between rolls provided with a difference in peripheral speed, and stretched 4.8 times in the longitudinal direction. At that time, the drawing portion was stretched by using a radiation heater output of 3.5 kW to supplement the amount of heat. Subsequently, the film was guided to a tenter, stretched 10 times in the width direction at a temperature of 158 ° C., then heat-treated at 155 ° C. while giving 6% relaxation in the width direction, and then cooled to a film thickness of 3.0 μm. An axially stretched polypropylene film was obtained. Further, a corona discharge treatment was performed on the surface on the A surface side in the atmosphere with a treatment strength of 25 W · min / m ² . The properties of the biaxially stretched polypropylene film thus obtained were as shown in Tables 2 and 3. Table 4 also shows the withstand voltage (dielectric breakdown voltage) and element workability (element winding yield) of the obtained film. Both withstand voltage and device processability were excellent.

(Example 2)
Except for an air knife temperature of 80 ° C., a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Example 3)
Except for the air knife temperature of 70 ° C., a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

Example 4
Except for an air knife temperature of 65 ° C., a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Example 5)
Except for an air knife temperature of 100 ° C. and a flow rate of 130 m / min, a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Example 6)
Except for an air knife temperature of 100 ° C., a flow rate of 130 m / min, and a cooling drum temperature of 85 ° C., a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Examples 7 and 8)
Except for the thickness of the biaxially stretched polypropylene film and the air knife temperature of 65 ° C., a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

Example 9
Except for the thickness of the biaxially stretched polypropylene film, the air knife temperature of 65 ° C., and the cooling drum temperature of 80 ° C., a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Example 10)
Except for the thickness of the biaxially stretched polypropylene film, the air knife temperature of 65 ° C, and the cooling drum temperature of 85 ° C, a film was formed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 1)
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that an air knife was used at room temperature (about 45 ° C.) without temperature control and no branched polypropylene resin was added. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 2)
Use an air knife at room temperature (about 45 ° C) without temperature control, do not add branched polypropylene resin, and form a biaxially oriented polypropylene film in the same manner as in Example 1 except that the cooling drum temperature is 80 ° C. Obtained. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 3)
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that the temperature was not controlled and an air knife was used at room temperature (about 45 ° C.) and the cooling drum temperature was 70 ° C. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 4)
Biaxial stretching was performed in the same manner as in Example 1 except that the temperature was not controlled and an air knife was used at room temperature (about 45 ° C), the flow rate was 130 m / min, the cooling drum temperature was 80 ° C, and the thickness was changed. A polypropylene film was obtained. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 5)
Using an air knife at room temperature (about 45 ° C) without temperature control, preheating and stretching temperature were each increased by 5 ° C (longitudinal stretching preheating 145 ° C, stretching 150 ° C), and film formation was performed in the same manner. A biaxially stretched polypropylene film was obtained. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 6)
Using an air knife at room temperature (about 45 ° C) without temperature control, the preheating and stretching temperature were each increased by 2 ° C (longitudinal stretching preheating 142 ° C, stretching 147 ° C), and film formation was performed in the same manner. A biaxially stretched polypropylene film was obtained. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 7)
Example using an air knife at room temperature (about 45 ° C) without temperature control, except that the cooling drum temperature was 85 ° C, and the preheating and stretching temperatures were each reduced by 5 ° C (longitudinal stretching preheating 135 ° C, stretching 140 ° C). Film formation was performed in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 8)
Except that the air knife was used at room temperature (about 45 ° C) without temperature control, the cooling drum temperature was 97 ° C, the preheating and stretching temperature were increased by 3 ° C (longitudinal stretching preheating 143 ° C, stretching 148 ° C) and the thickness was changed Formed a film in the same manner as in Example 1 to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 9)
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that an air knife was used at room temperature (about 45 ° C.) without temperature control. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 10)
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that the temperature was not controlled and an air knife was used at room temperature (about 45 ° C.) and the thickness was changed. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 11)
The film was formed in the same manner as in Example 1 except that the temperature was not controlled and an air knife was used at room temperature (about 45 ° C.), and the thickness was changed by 70 ° C. cooling drum, 2 ° C. stretching temperature (147 ° C.) An axially stretched polypropylene film was obtained. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 12)
A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that the temperature was not controlled and an air knife was used at room temperature (about 45 ° C.) and the thickness was changed to 80 ° C. on the cooling drum. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

(Comparative Example 13)
Except for temperature control, using an air knife at room temperature (about 45 ° C.), stretching 4.5 times in the longitudinal direction, and using a radiation heater output of 10 kW in the stretching section to make up the heat amount and stretching as in Example 1. Film formation was performed to obtain a biaxially stretched polypropylene film. The characteristics of the obtained biaxially stretched polypropylene film are shown in Tables 2, 3, and 4.

Claims (9)

A biaxially stretched polypropylene film for a capacitor having protrusions on both sides, a thickness t1 (μm) of 1 to 5 μm, a minimum protrusion height Pmin (nm) of 100 or more on any surface, and a maximum protrusion height A biaxially stretched polypropylene film for a capacitor having a thickness Pmax (nm) of 1,200 or less and satisfying all of the following formulas when one surface is an A surface and the other surface is a B surface.
0.5 ≦ Pa250-450 / Pa ≦ 0.8
0.5 ≦ Pb250-450 / Pb ≦ 0.8
0.7 ≦ Pa250-450 / Pb250-450 ≦ 1.2
0.7 ≦ Pa / Pb ≦ 1.2
However,
Pa250-450: number per 0.1mm ² of the heights below 250nm or 450nm present in side A projection Pb250-450: ² per 0.1mm of the surface B of less than height 250nm or 450nm present in side projection Pa: Number of protrusions present on the A surface per 0.1 mm ² Pb: Number of protrusions present on the B surface per 0.1 mm ² The biaxially stretched polypropylene film for capacitors according to claim 1, wherein Pa and Pb satisfy the following formula.
| Pa-Pb | ≦ 200 The biaxially oriented polypropylene film for capacitors according to claim 1 or 2, wherein the 10-point average roughness (SRz) of any surface is 500 nm or more and 1,000 nm or less. The biaxially stretched polypropylene film for capacitors according to any one of claims 1 to 3, wherein the centerline surface roughness (SRa) of any surface is 20 nm or more and 40 nm or less. The capacitor according to any one of claims 1 to 4, wherein the ratio SRz / SRa of the center line surface roughness (SRa) and the 10-point average roughness (SRz) is 22 or more and 32 or less for any surface. Biaxially stretched polypropylene film. The biaxially stretched polypropylene film for capacitors according to any one of claims 1 to 5, comprising 0.05 to 3% by mass of branched polypropylene (H). A metallized film in which a metal film is provided on at least one side of the biaxially stretched polypropylene film for capacitors according to claim 1. The metallized film according to claim 7, wherein the surface electric resistance of the metal film is in the range of 1 to 20 Ω / □. A film capacitor comprising the metallized film according to claim 7 or 8.