JP6769064B2 - Biaxially oriented polypropylene film for capacitors, metal film laminated film and film capacitors - Google Patents

Description

The present invention relates to a biaxially oriented polypropylene film, and more particularly to a biaxially oriented polypropylene film for a capacitor, which is excellent in withstand voltage, suitable vapor deposition processability, and element processability as a dielectric for a capacitor.

Biaxially oriented polypropylene film is excellent in transparency, mechanical properties, electrical properties, etc., and is therefore used in various applications such as packaging, tape, cable wrapping, and electrical applications such as capacitors.

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

Recently, various electric facilities are being converted to inverters, and along with this, the demand for miniaturization and large capacity of capacitors is increasing. Therefore, the film is becoming thinner and has higher performance, and there is an increasing demand for productivity improvement such as cost reduction by reducing the member cost by downsizing in addition to the performance aspect. In response to such market demands, it has become important to significantly reduce costs while improving vapor deposition processing and element workability in addition to increasing the withstand voltage and thinning of biaxially oriented polypropylene films. The situation.

The surface of such a biaxially oriented polypropylene film needs to be appropriately roughened from the viewpoint of withstand voltage, vapor deposition processability, and element processability, especially in film slipperiness, winding property, and vapor deposition capacitor. Is particularly important because it imparts vapor deposition workability and safety as a capacitor.

Especially for thin-film deposition capacitors, the workability of thin-film deposition greatly affects the production yield, and poor vapor deposition quality significantly impairs pressure resistance, safety, etc. in terms of performance, so proper surface roughening is important. Become. Here, the safety property means that in a metal-deposited capacitor having a metal-deposited film formed on the dielectric film as an electrode, the vapor-deposited metal is scattered by the discharge energy at the time of abnormal discharge to restore the insulating property and prevent a short circuit. As a result, it is a function that maintains the function of the capacitor or prevents destruction, and is an extremely useful function from the viewpoint of safety.

As such a roughening method, mechanical methods such as embossing method and sandblasting method, chemical methods such as chemical etching with a solvent, a method of stretching a sheet mixed with a different polymer such as polyethylene, and β crystals are generated. A method of stretching the sheet (see, for example, Patent Documents 1 and 2) and the like have been proposed.

However, the mechanical and chemical methods have low roughness densities, and the method of stretching a sheet on which β crystals are formed tends to cause coarse protrusions, which is not always sufficient in terms of roughness density, coarse protrusions, and number of protrusions. Sometimes I couldn't say that. In addition, the film roughened by these methods is processed as a raw material as a film roll, such as film breakage and fluttering during unwinding due to blocking, etc., especially during vapor deposition under vacuum, wrinkles during transportation, and meandering. In some cases, sexual defects may occur and productivity may be significantly deteriorated. Further, when the capacitor is formed, the oil impregnation between the film layers becomes insufficient and an unimpregnated portion is likely to be partially formed, which may shorten the capacitor life.

In addition, the biaxially oriented polypropylene film produced by either method does not have sufficient safety under severe conditions of a potential gradient of 180 V / μm or more as a capacitor usage condition, and causes a problem in terms of reliability. There is. Here, the potential gradient is the voltage applied to the dielectric film divided by the film thickness, and is the applied voltage per unit film thickness.

Regarding the roughness density and the uniformity of protrusions, a high melt tension polypropylene film (see, for example, Patent Document 3) or a laminate of such a high melt tension polypropylene film and a normal polypropylene film (see, for example, Patent Document 4). However, when the high melt tension polypropylene resin itself is used as a capacitor, it is not possible to obtain sufficient heat resistance and pressure resistance due to the structure of the resin, and the insulation breakdown voltage is significantly reduced, especially at high temperatures. There's a problem. Further, it is very difficult to obtain a uniform laminated thickness structure by the technique of laminating a high melt tension polypropylene resin, and the actual situation is that the dielectric film is not practically satisfactory due to impaired uniformity. Further, Japanese Patent No. 3508515 (Patent Document 5) discloses a biaxially stretched polypropylene film in which the degree of surface roughness is controlled and a method for producing the same, but the degree of roughness on both sides of the film should be sufficiently controlled. Is inadequate and difficult.

JP-A-51-63500 Japanese Unexamined Patent Publication No. 2001-324607 Japanese Unexamined Patent Publication No. 2001-72778 Japanese Unexamined Patent Publication No. 2001-129944 Japanese Patent No. 3508515

The present inventors have come up with the present invention as a result of diligent studies to solve the above problems. The present invention does not provide a biaxially oriented polypropylene film for capacitors, which exhibits excellent withstand voltage and reliability, and ensures stable vapor deposition workability and element workability, especially in general equipment and new energy capacitor applications. Is to be.

The above-mentioned problems are that the peel strength is 2 g / 5 cm or less, and the thickness t1 (μm) by the micrometer method is 2. 8 [mu] m or more 7.0μm Ri der hereinafter has a projection on both sides, the one surface A side, when the other side was a B-side, which satisfies all the following formulas, biaxially oriented polypropylene capacitor Achievable with film.
PBmin ≥ 200 (nm)
PBmax ≤ 1,800 (nm)
0.4 ≤ PB700-1000 / PB ≤ 0.8
However,
PBmin: Minimum protrusion height (nm) on the B surface
PBmax: Maximum protrusion height (nm) on the B surface
PB700-1000: Number of protrusions with a height of 700 nm or more and less than 1000 nm existing on the B surface per 0.1 mm ^2.
PB: Total number of protrusions on the B surface per 0.1 mm ²

Since the present invention can provide a biaxially oriented polypropylene film for capacitors that has both excellent vapor deposition workability and high withstand voltage, it can be applied to various applications such as capacitors and other electrical applications, and in particular, capacitors. It is suitable for applications, preferably for new energy applications such as photovoltaic power generation, wind power generation, and general equipment.

It is the schematic which shows the preparation state of a set sample for measuring the peel strength of a polypropylene film. It is a schematic diagram which shows the method of setting the set sample set in a constant temperature bath for measuring the peel strength of a polypropylene film. It is the schematic which shows the method of measuring the peel strength of a polypropylene film.

The biaxially oriented polypropylene film of the present invention has a peel strength of 3 g / 5 cm or less and a thickness t1 (μm) by a micrometer method of 2.5 μm or more and 7.0 μm or less.

If the peel strength exceeds 2 g / 5 cm, film breakage and fluttering due to blocking will be large when the product is unwound from the take-up side, especially during vapor deposition processing using double-sided corona-treated raw fabric, and the tension during transportation will be large. Fluctuations cause problems such as wrinkles and meandering, which tends to reduce the quality and quality of the vapor-deposited raw material and reduce productivity. Also, regarding the thickness t1, 2. If it is less than 8 μm, deterioration of quality such as heat loss during vapor deposition, wrinkles, and film breakage, and deterioration of workability are likely to occur. When the thickness t1 exceeds 7.0 μm, it is disadvantageous for miniaturization due to the relationship between the capacitance and the capacitor size.

From the above viewpoint, the peel strength is preferably 1 g / 5 cm or less.

Through diligent studies, the present inventors have a high correlation between the withstand voltage and vapor deposition workability of the film and the peel strength value, and the peel strength value is controlled to be low in order to improve the withstand voltage and vapor deposition workability. We have found that it is important to do so.

Further, the biaxially oriented polypropylene film of the present invention is biaxially oriented for a capacitor having protrusions on both sides of the film from the viewpoint of improving workability and further reducing the cost as a capacitor and increasing the withstand voltage even in the production of a capacitor. When the polypropylene film has one surface as the A surface and the other surface as the B surface, it is preferable that all of the following formulas are satisfied.

PBmin ≥ 200 (nm)
PBmax ≤ 1,800 (nm)
0.4 ≤ PB700-1000 / PB ≤ 0.8
However,
PBmin: Minimum protrusion height (nm) on the B surface
PBmax: Maximum protrusion height (nm) on the B surface
PB700-1000: Number of protrusions with a height of 700 nm or more and less than 1000 nm existing on the B surface per 0.1 mm ² PB: Total number of protrusions existing on the B surface per 0.1 mm ² Here, the A surface is in contact with the cooling drum. It is preferable that the surface is a surface, and further, both sides A and B are preferably surface-treated by corona discharge or the like. When the minimum protrusion height PBmin on the B surface is less than 200 (nm), the protrusions are small, the amount of air during film lamination is small, the film adhesion becomes strong, the peelability during unwinding decreases, and blocking and fluttering occur. Transport and workability tend to deteriorate. Further, when the maximum protrusion height PBmax of the B surface exceeds 1,800 (nm), the protrusions are large, and in particular, the withstand voltage and safety when AC is applied tend to be lowered, and the capacitor performance tends to be lowered.

Further, when PB700-1000 / PB is 0.4 or more and 0.8 or less, the amount of air becomes appropriate at the time of film lamination and the peelability is good, and the transportability and workability at the time of unwinding are improved, and as a capacitor. Withstand voltage is good. In order to control the protrusion height and the number of protrusions on the B surface within the above-mentioned preferable ranges, it can be achieved by setting the longitudinal stretching step at the time of film formation as a specific condition, as will be described later.

Next, according to a preferred embodiment of the biaxially oriented polypropylene film for a capacitor of the present invention, it is preferable that all of the following equations are satisfied.

PAmin ≥ 200 (nm)
PAmax ≤ 1,500 (nm)
0.3 ≤ PA350-550 / PA ≤ 0.9
However,
PAmin: Minimum protrusion height (nm) on surface A
PAmax: Maximum protrusion height (nm) on surface A
PA350-550: Number of protrusions with a height of 350 nm or more and less than 550 nm existing on the A surface per 0.1 mm ² PA: Total number of protrusions existing on the A surface per 0.1 mm ² Minimum protrusion height PAmin on the A surface When is less than 200 (nm), the protrusions are small, the amount of air during film lamination is small, the film adhesion is strong, the peelability at the time of unwinding is lowered, and the transport and workability are likely to be deteriorated due to blocking and fluttering. Further, when the maximum protrusion height PAmax on the A surface exceeds 1,500 (nm), the protrusions are large, and in particular, the withstand voltage and safety when AC is applied are lowered, and the capacitor performance is lowered.

Further, when PA350-550 / PA is 0.3 or more and 0.9 or less, the amount of air becomes appropriate at the time of film lamination, the peelability is good, the transportability at the time of unwinding, and the workability are improved, and as a capacitor. Withstand voltage is good. In order to control the protrusion height and the number of protrusions on the A surface within the above-mentioned preferable ranges, it can be achieved by setting the longitudinal stretching step at the time of film formation as a specific condition, as will be described later.

According to a preferred embodiment of the biaxially oriented polypropylene film for a capacitor of the present invention, it is preferable that PA and PB satisfy the following formula.

PA ≧ 300
PB ≧ 700
When PA and PB do not satisfy the above formula, problems such as film breakage and fluttering are likely to occur during unwinding during vapor deposition, and transportability and vapor deposition processability tend to decrease, resulting in a decrease in productivity. In order to control the number of protrusions on the A surface and the B surface within the above-mentioned preferable range, it can be achieved by setting the longitudinal stretching step at the time of film formation as a specific condition, as will be described later.

The dielectric breakdown voltage of the biaxially oriented polypropylene film of the present invention at 25 ° C. is preferably 600 V / μm or more. If the dielectric breakdown voltage at 25 ° C. is less than 600 V / μm, when the obtained film is a capacitor element, the withstand voltage resistance may be low and it may not be practical, and the film thickness (t1) by the micrometer method is thin. Indeed, this tendency is strong. The breakdown voltage at 25 ° C. is more preferably 650 V / μm or more, still more preferably 700 V / μm or more. The higher the breakdown voltage, the more likely it is that a highly reliable element with excellent withstand voltage can be manufactured when used as a capacitor element. There is no particular upper limit, but for example, film forming property, handleability and withstand voltage property. Is preferably 1,200 V / μm or less in order to balance at a high level. In order to control the dielectric breakdown voltage in a preferable range, the mesopentad fraction of polypropylene to be used should be set in a preferable range described later, and in order to make the protrusion height on the film surface uniform, the preheating microstretching ratio of longitudinal stretching described later will be described. Can be achieved by setting the above-mentioned preferable range, setting the thickness within the above-mentioned preferable range, suppressing insulation defects, and the like.

Next, polypropylene preferably used for the biaxially oriented polypropylene film of the present invention will be described. In the present invention, polypropylene usually used for packaging materials and capacitors can be used, but preferably the cold xylene-soluble portion (hereinafter referred to as CXS) is 4% by mass or less and the mesopentad fraction is 0.95 or more. It is preferably polypropylene. If these conditions are not met, film forming stability may be inferior, or voids may be formed in the film when producing a biaxially oriented film, resulting in a large decrease in dimensional stability and withstand voltage. There is.

Here, the cold xylene-soluble portion (CXS) refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene at 135 ° C. and then precipitated at 20 ° C., which is a three-dimensional rule. It is considered that it corresponds to a component that is difficult to crystallize because of its low property and low molecular weight. If a large amount of such a component is contained in the resin, problems such as inferior thermal dimensional stability of the film and a decrease in the dielectric breakdown voltage at a high temperature may occur. Therefore, the CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. In order to obtain polypropylene having such CXS, a method of increasing the catalytic activity when obtaining the resin, a method of washing the obtained resin with a solvent or the propylene monomer itself, and the like can be used.

From the same viewpoint, the mesopentad fraction of polypropylene is preferably 0.95 or more, and more preferably 0.97 or more. The mesopentad fraction is an index showing the stereoregularity of the polypropylene crystal phase measured by nuclear magnetic resonance spectroscopy (NMR method), and the higher the value, the higher the crystallinity, the higher the melting point, and the higher the temperature. This is preferable because the insulation breakdown voltage becomes high. The upper limit of the mesopentad fraction is not specified. In order to obtain a resin having such high stereoregularity, a method of washing the resin powder obtained with a solvent such as n-heptane, a method of appropriately selecting a catalyst and / or a cocatalyst, a method of appropriately selecting a composition, and the like are used. It is preferably adopted.

The polypropylene has a melt flow index (MFR) of 1 to 10 g / 10 minutes (230 ° C., 21.18 N load), and particularly preferably 2 to 5 g / 10 minutes (230 ° C., 21.18 N load). Those in the range are 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 adopted.

Such polypropylene is mainly composed of a homopolymer of propylene, but may contain a copolymerization component due to other unsaturated hydrocarbons as long as the object of the present invention is not impaired, or a polymer in which propylene is not alone. May be blended. Examples of the monomer components constituting such copolymerization components and blends include ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene. -1,1-Hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2 -Norbornene and the like. From the viewpoint of dielectric breakdown resistance and dimensional stability, the copolymerization amount or blend amount is preferably less than 1 mol% in terms of copolymerization amount and less than 10% by mass in terms of blend amount.

Further, in such polypropylene, various additives such as crystal nucleating agent, antioxidant, heat stabilizer, slip agent, antistatic agent, blocking inhibitor, filler and viscosity adjusting agent are used as long as the object of the present invention is not impaired. It can also contain agents, anti-coloring agents and the like.

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

Further, the biaxially oriented polypropylene film of the present invention may contain branched chain polypropylene (H) from the viewpoint of improving withstand voltage, and when added, the content thereof is 0.05 to 0.05 to the entire film. It is preferably 10% by mass, more preferably 0.5 to 8% by mass, and even more preferably 1 to 5% by mass. By containing the branched-chain polypropylene (H), the size of spherulite formed in the cooling step of the melt-extruded resin sheet can be easily controlled to be small, the formation of insulation defects generated in the stretching step can be suppressed to a small size, and the withstand voltage resistance. An excellent polypropylene film can be obtained.

Further, the film of the present invention is preferably composed of a mixture of the above-mentioned polypropylene and the said branched-chain polypropylene (H). In this case, the branched-chain polypropylene (H) has a relationship in which the melt tension (MS) and the melt flow index (MFR) when measured at 230 ° C. are log (MS)> −0.56 log (MFR) +0.74. It is particularly preferable that the branched polypropylene (H) satisfies the formula.

A branched polypropylene (H) having a relational expression in which the melt tension (MS) and the melt flow index (MFR) measured at 230 ° C. satisfy the relational expression of log (MS)> −0.56 log (MFR) +0.74 is obtained. A method of blending polypropylene containing a large amount of high molecular weight components, a method of blending an oligomer or a polymer having a branched structure, and a long-chain branched structure in a polypropylene molecule as described in JP-A-62-121704. , Or a method as described in Japanese Patent No. 2869606, or the like is preferably used.

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

The branched-chain polypropylene (H) preferably satisfies the above formula, but is not particularly limited, and the melt flow index (MFR) is in the range of 1 to 20 g / 10 minutes from the viewpoint of film forming property. The one in the range of 1 to 10 g / 10 minutes is more preferable. Further, the melt tension is preferably in the range of 1 to 30 cN, and more preferably in the range of 2 to 20 cN. Further, the branched chain polypropylene (H) referred to here is a polypropylene having 5 or less internal trisubstituted olefins in 10,000 carbon atoms. The presence of this internal trisubstituted olefin can be confirmed by the proton ratio of the ¹ H-NMR spectrum.

In the present invention, a crystal nucleating agent can be added within a range not contrary to the object of the present invention. As described above, the branched chain polypropylene (H) already has an α-crystal or β-crystal crystal nucleating agent effect by itself, but another α-crystal nucleating agent (dibenzylidene sorbitols, sodium benzoate, etc.) ), Β-crystal nucleating agent (amide compound such as potassium 1,2-hydroxystearate, magnesium benzoate, N, N'-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone compound, etc.) it can. However, since excessive addition of the above-mentioned other type of nucleating agent may cause a decrease in stretchability and a decrease in withstand voltage due to void formation or the like, the content is usually 0.5% by mass or less, preferably 0.5% by mass or less, based on the total amount of polypropylene. It is preferably 0.1% by mass or less, more preferably 0.05% by mass or less.

The biaxially oriented polypropylene film of the present invention has a structure excellent in high withstand voltage and vapor deposition processability, so that it is excellent in withstand voltage and handling, and is therefore suitable for a thin film capacitor, particularly a micrometer. The film thickness (t1) according to the method is 2. The performance is effectively exhibited in the range of 8 μm or more and 7.0 μm or less. More preferable thickness is 2. It is 8 μm or more and 6.0 μm or less, and more preferably 2.8 μm or more and 5.0 μm or less.

The biaxially oriented polypropylene film of the present invention is preferably used as a dielectric film for a capacitor, and particularly in terms of the type of capacitor, a metal vapor-deposited film capacitor is preferable from the viewpoint of electrode configuration. It is also preferably used for oil-immersed capacitors impregnated with insulating oil and dry capacitors that do not use insulating oil at all. Further, from the viewpoint of shape, it may be a winding type or a laminated type. However, due to the characteristics of the film of the present invention, it is particularly preferably used as a wound metal vapor deposition film capacitor.

The biaxially oriented polypropylene film of the present invention can be obtained by biaxially stretching using a raw material capable of imparting the above-mentioned characteristics. As a biaxial stretching method, any of the inflation simultaneous biaxial stretching method, the stent simultaneous biaxial stretching method, and the stent sequential biaxial stretching method can be obtained. Among them, film forming stability, thickness uniformity, and film surface It is preferable to adopt the stenter sequential biaxial stretching method in terms of controlling the protrusion height, the number of protrusions, and the peeling strength.

Next, the method for producing the biaxially oriented polypropylene film of the present invention will be described in more detail. First, a polypropylene resin is melt-extruded onto a support to form a polypropylene resin sheet, and the polypropylene resin sheet is sequentially biaxially stretched in the order of longitudinal stretching and lateral stretching, and then heat-treated and relaxed to produce a biaxially oriented polypropylene film. .. At that time, from the preheated portion of the longitudinal stretching to just before the stretching portion, a fine stretching of 1.05 to 1.20 times is performed, and a further stretching of 4.0 to 7.0 times is performed at the stretching portion. Next, the edge of the film is gripped with a clip and laterally stretched, and in the next step, heat treatment and relaxation treatment are performed while tension gripping in the width direction with the clip.

Hereinafter, the description will be more specific, but the present invention is not necessarily limited to this. First, high melt tension polypropylene (branched chain polypropylene (H)) is blended with the above-mentioned polypropylene, melt-extruded, passed through a filtration filter, extruded from a slit-shaped mouthpiece at a temperature of 230 to 260 ° C., and 60 to 110 ° C. The unstretched sheet is obtained by solidifying on a cooling drum controlled to the temperature of. As the adhesion method to the cooling drum, any of the electrostatic application method, the adhesion method using the surface tension of water, the air knife method, the press roll method, the underwater casting method, etc. may be used, but the flatness is high. The air knife method, which is good and can control the height of protrusions and the number of protrusions on the film surface, is preferable. The air temperature of the air knife is 0 to 100 ° C., preferably 20 to 70 ° C., and the blowout air speed is preferably 130 to 150 m / sec from the viewpoint of controlling the height of protrusions and the number of protrusions on the film surface, and the uniformity in the width direction is maintained. In order to improve the air knife, it is preferable that the air knife has a double tube structure. Further, it is preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation so as not to cause vibration of the film.

Next, this unstretched film is biaxially stretched and biaxially oriented. First, the unstretched film is heated by passing it through a preheating roll maintained at 120 to 150 ° C. in the preheating section, and finely stretched at a stretching speed of 20 to 100% / min at a magnification of 1.05 to 1.20 times. Subsequently, the sheet was passed through a stretching roll maintained at a temperature of 130 ° C. to 150 ° C. at the stretching portion, and stretched 4.0 to 7.0 times in the longitudinal direction at a stretching speed of 10,000 to 150,000% / min. After that, cool to room temperature. In this case, as the stretching ratio in the longitudinal direction, it is preferable to employ stretching that stretches 4.5 to 6.5 times and then cools to room temperature. Further, in the stretched portion, it is also preferable to use a radiation heater that instantly raises the film temperature immediately before stretching on both the A and B sides. Furthermore, by keeping the gap distance from the film in the range of 1 mm to 10 mm with a radiation heater, adding heat in the range of 11 kW to 15 kW, and stretching at high temperature, the controllability of the heat history is further improved and the protrusions on the film surface. It is suitable for controlling the height and the number of protrusions. It is preferable to take the stretching method and the stretching ratio in order to control the protrusion height and the number of protrusions on the A and B surfaces of the biaxially oriented polypropylene film of the present invention within a preferable range as described above.

The fine stretching in the preheating step of the longitudinal stretching enhances the adhesion between the film and the roll, makes the temperature inside the film uniform, and the stretched portion is stretched at a higher magnification to align the crystals, so that the surface is easily roughened uniformly. When the surface is uniformly roughened, it becomes easy to control the protrusion height and the number of protrusions on the A and B surfaces of the biaxially oriented polypropylene film of the present invention within a preferable range as described above. If the fine stretching in the preheating part is lower than 1.05 times, the adhesion force in the preheating roll weakens, the internal temperature of the film becomes non-uniform, leading to uneven characteristics and stretching, and the rigidity in the longitudinal direction of the biaxially oriented polypropylene film becomes uneven. The film may be lowered, resulting in a decrease in in-plane rigidity, resulting in a film having inferior withstand voltage resistance. On the other hand, if it exceeds 1.20 times, the film may be broken or wrinkled in the preheated micro-stretched section, which may cause a problem in film production. From this point of view, the microstretching of the preheated portion of the longitudinal stretching is preferably 1.05 to 1.20 times, more preferably 1.06 to 1.15 times, still more preferably 1.08 to 1.08 to 1.20 times. The range is 1.12 times. The draw ratio of the stretched portion is preferably 4.0 to 7.0 times, more preferably 4.5 to 6.0 times.

After that, the stretched film is subsequently guided to a stenter for lateral stretching. Next, the end of the film is gripped with a clip and the lateral stretch is stretched 7 to 13 times in the width direction at a temperature of 140 to 165 ° C., and then the film is relaxed by 2 to 20% in the width direction while being tension-grasped in the width direction. After heat-fixing at a temperature of 140 to 165 ° C., the film is guided to the outside of the stenter through a cooling process at 100 to 150 ° C., the clip at the end of the film is released, and the edge of the film is slit in the winder process. Take up the film product roll.

Here, in order to improve the adhesiveness of the vapor-deposited metal on the surface to be vapor-deposited before winding the film, it is preferable to perform the corona discharge treatment in air, nitrogen, carbon dioxide gas, or a mixed gas thereof. Since polypropylene film usually has low surface energy and it is difficult to stably perform metal vapor deposition in a vapor-deposited capacitor application, it is preferable to perform surface treatment in advance for the purpose of improving metal adhesion. .. This surface treatment is preferably performed on at least one surface, but more preferably on both sides.

Specific examples of the surface treatment include corona discharge treatment, plasma treatment, glow treatment, and flame treatment. Normally, the surface wetting tension of a polypropylene film is about 30 mN / m, but it is possible to set the wetting tension of at least one surface to 37 to 50 mN / m, preferably 39 to 48 mN / m by these surface treatments. It is preferable because it has excellent adhesiveness to and has good safety. In particular, by applying the corona treatment, it is possible to apply the desired wet tension. If it is less than 37 mN / m, the film tends to have poor adhesiveness to the metal film, and the vapor deposition processability such as wrinkles, meandering, and tearing is lowered, which may lower the safety property of the vapor deposition capacitor. If it exceeds 50 mN / m, the peel strength cannot be controlled, wrinkles and meandering occur, and the vapor deposition processability deteriorates, which may reduce the safety property of the vapor deposition capacitor.

In order to keep the peel strength within the target range, it is important to control the wetting tension, the height of protrusions on the film surface, and the number of protrusions as described above. By controlling the application of the wetting tension within the following range with the E value, for example, suitable wettability can be imparted, which is beneficial in achieving the desired peel strength. The E value is defined as the corona discharge power strength for 1 minute that the film receives per unit area, and is expressed by W · min / m ² . Actually, it is calculated by the following formula.

E value = W / (L × v)
However,
W: Corona discharge power (W)
L: Electrode width (m)
v: Film formation speed (m / min)
Since E value and 5.0~9.0W · min / ^{m 2} at side A, can maintain proper wettability by at side B and 8.5~12.5W · min / ^{m 2,} It is preferable in controlling the peel strength of the biaxially oriented polypropylene film of the present invention. Further, when the E value satisfies the following formula in consideration of the protrusion height and the number of protrusions on the film surface and the wettability, it is preferable in further controlling the peel strength, and stable process and productivity are enabled.

Eb value / Ea value> 1.5
Eb: B-side processing E value (W · min / m ² )
Ea: A-side processing E value (W · min / m ² )
In the present invention, it is also preferable to provide a metal film on the surface of the above-mentioned biaxially oriented polypropylene film to form a metal film laminated film. The method is not particularly limited, but for example, a method of depositing aluminum or the like on one side or both sides of a polypropylene film to provide a metal film such as an aluminum vapor deposition film as an internal electrode of a film capacitor is preferably used. At this time, other metal components such as nickel, copper, gold, silver, chromium and zinc can be vapor-deposited simultaneously or sequentially with aluminum. Further, a protective layer may be provided on the vapor-deposited film with oil or the like.

In the present invention, if necessary, after forming the metal film, the metal film laminated film can be annealed at a specific temperature or heat-treated. Further, at least one side of the metal film laminated film may be coated with polyphenylene oxide or the like for insulation or other purposes.

The film resistance value of the metal film laminated film thus obtained is preferably 1 to 20 Ω / □. If the film resistance value is less than 1 Ω / □, the metal layer is thick, so that so-called heat loss occurs during vapor deposition, and defects such as whitening and perforation may occur in the film. If the film resistance value exceeds 20Ω / □, the capacitance change may become large when the capacitor element is used. The film resistance value can be controlled by the composition of the metal layer and the thickness of the metal layer. The film resistance value is more preferably 1.2 to 15 Ω / □.

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

Aluminum is deposited on one or both sides of a polypropylene film under reduced pressure. At that time, the film is deposited on one side or both sides in a striped shape having a margin portion running in the longitudinal direction of the film. Next, in the case of one side, a blade is inserted in the center of each vapor deposition portion and the center of each margin portion on the surface to make a slit, and a tape-shaped take-up reel having a margin on one side is created. Two tape-shaped take-up reels with a left or right margin, one each for the left margin and one for the right margin, are overlapped and wound so that the vapor-deposited portion protrudes from the margin portion in the width direction. To get.

When vapor deposition is performed on both sides, vapor deposition is performed in a striped shape having a margin portion running in the longitudinal direction of one surface, and the other surface is striped so that the margin portion in the longitudinal direction is located in the center of the back surface side vapor deposition portion. Deposit in the form. Next, a blade is inserted in the center of each of the front and back margins to slit, and a tape-shaped take-up reel having a margin on one side (for example, if there is a margin on the right side of the front surface, a margin on the left side on the back surface) is produced. Two reels and one undeposited laminated film are laminated and wound so as to protrude from the laminated film in the width direction to obtain a wound body. In that case, the undeposited laminated film is preferably a single-sided corona-treated or double-sided corona-treated laminated film in the case of a polypropylene film. Since it is a corona-treated combination, stable winding is possible without any deviation or wrinkles when overlapping and winding.

A wound film capacitor can be obtained by removing the core material from the wound body produced as described above, pressing the core material, spraying metallicon on both end surfaces to form an external electrode, and welding a lead wire to the metallicon.

The applications of film capacitors are wide-ranging, such as for railway vehicles, automobiles (hybrid cars, electric vehicles), solar power generation / wind power generation, and general household appliances, and the film capacitors of the present invention are also suitable for these applications. Can be used.

The method for measuring the characteristic value and the method for evaluating the effect in the present invention are as follows.

(1) Film thickness (t1) by micrometer method (unit: μm)
A total of 10 locations at any location were measured with a contact-type film thickness meter, Mitutoyo Co., Ltd. Lightmatic VL-50A (10.5 mmφ super hard spherical stylus, measuring load 0.06 N), and the average value was measured. The thickness of the biaxially oriented polypropylene film was used.

(2) Peeling strength (unit: g / 5 cm)
Two films were cut into rectangles having a length of 50 mm and a width of 100 mm, and the films were overlapped so that the A side and the B side were in contact with each other. The two stacked films 1, 1'were sandwiched between two sheets of paper 2, 2', and the outside thereof was sandwiched between two bakelite plates 3, 3'. A weight 4 having a load of 1 kg and a bottom area of 12 cm ² is placed on the edge of the sample (see FIG. 1), and the whole is set in a constant temperature bath 5 set to 120 ± 2 ° C. in advance (see FIG. 2). After leaving for 10 minutes, a bakelite plate A sample sandwiched between 3 and 3'(a stack of films 1 and 1') was taken out. The entire longitudinal direction of the end side of the film 1'without the weight is attached to the measuring table 8 with a double-sided tape 7 having a width of 10 mm, and the end side without the weight of the film 1 is attached via a pulling jig 9. A spring scale 10 was attached. The pulling jig 9 used was a 5 cm square plastic sheet having holes for attaching the spring scale 10, and the film 1 and the pulling jig 9 were attached using double-sided tape 7'. The contact area between the film 1 and the pulling jig 9 was set to 5 cm ² . The spring scale 10 was a hanging scale manufactured by Oba Keiki Seisakusho Co., Ltd., and used a spring scale 10 having a maximum load of 50 g and a measurement accuracy of 1 g. The spring scale 10 was pulled vertically at a speed of 1 cm / sec, and the maximum value indicated by the spring scale 10 was visually read until the films were completely separated from each other, and that value was taken as the peel strength (see FIG. 3). The peel strength measurement was performed in an environment of room temperature of 23 ° C. and humidity of 65% RH.

The measurement was performed 10 times, and the average value was adopted.

(3) Evaluation of protrusion height and number of protrusions According to JIS B-0601 (1982), "Non-contact 3D fine shape measuring instrument (ET-30HK)" and "3D roughness analyzer (3D roughness analyzer)" manufactured by Kosaka Research Institute Co., Ltd. It was measured using MODEL SPA-11) ”. The measurement was repeated 10 times in the longitudinal direction, and the height of protrusions and the number of protrusions were determined as the average values. The detailed conditions and data processing for one measurement are as follows.

<Minimum protrusion height (PAmin, PBmin), maximum protrusion height (PAmax, PBmax) (unit: nm)>
The detected values detected by the measuring instrument are output as a histogram at intervals of 50 nm. For example, when a protrusion of 100 nm or more and less than 150 nm is present as a detected value, the protrusion height is counted as 100 nm. The minimum protrusion height is the slice height that is counted first every slice with a height of 0 nm to 50 nm, and the maximum protrusion height is the slice height immediately before the slice that continues counting and the detected value becomes 0. Shown.

<PA350-550 (Unit: Pieces / 0.1mm ² )>
The value on the A-plane side of the histogram is the sum of all the detected protrusions having a height of 350 nm or more and less than 550 nm, which is converted into the number per 0.1 mm ² .

<PB700-1000 (Unit: Pieces / 0.1mm ² )>
The value on the B-plane side of the histogram is the sum of all the detected protrusions having a height of 700 nm or more and less than 1000 nm, converted into the number per 0.1 mm ² .

<Total number of protrusions (unit: piece / 0.1 mm ² )>
The total number of protrusions indicates the value obtained by converting the number of protrusions detected at the sampling intervals in the width direction and the length direction shown in the item of measurement conditions into the number per 0.1 mm ² .
-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 speed: 0.1 mm / sec Measurement range (width direction x length direction): 1.0 mm x 0.249 mm
Reference plane for height dimensions: LOWER (lower side)
Width sampling interval: 2 μm
Sampling interval in the length direction: 10 μm
Number of samples in the length direction: 25 Cutoff: 0.25 mm / sec Magnification in the width direction: 200 times Magnification in the length direction: 20,000 times Waviness, roughness Cut: None ・ Measurement method Dedicated sample holder for measurement To use. The sample holder is two removable metal plates with a circular hole in the center, and the sample is sandwiched between them and the film is stretched to the four sides of the sample holder to fix it, and the film in the central circular part is fixed. It was measured.

(4) Film dielectric breakdown voltage at 25 ° C (unit: V / μm)
JIS C2330 (2010) 6.2. Measurement was performed 40 times according to method b (flat plate electrode method), the average value was obtained, divided by the film thickness (μm) of the measured sample, and expressed in V / μm. Dielectric breakdown measurement was performed in an environment of room temperature of 25 ° C. and humidity of 65% RH. As the film thickness, the value measured in (1) above was used.

(5) Surface Wetting Tension The surface treated with a mixed solution of formamide and ethylene glycol monoethyl ether, methanol and water was measured based on the measuring method specified in JIS K6768 (1999).

(6) Double-sided thin-film deposition processability After vacuum-depositing aluminum on both sides of the polypropylene film obtained in each of the examples and comparative examples described later with a vacuum vapor deposition machine manufactured by ULVAC Co., Ltd. so that the film resistance becomes 8Ω / □. Zinc was vacuum deposited.

At that time, vapor deposition was performed on both sides in a striped shape having a margin portion running in the longitudinal direction (repetition of a width of the vapor deposition portion of 49.0 mm and a width of the margin portion of 1.0 mm).

In the above vapor deposition process, visually observe from the beginning to the end of unwinding of the original and fabric products in the section from the passage of the margin nozzle on one side to the margin nozzle on the other side, and wrinkles and meandering are used as the following criteria. Judged by. (Hereinafter referred to as vapor deposition processability). In addition, the presence or absence of film breakage due to blocking during unwinding was also determined as follows.

<Evaporation workability>
The situation in which film meandering was continuously generated over 100 m during film transport due to wrinkles and meandering was determined below.

A: Maximum film meandering width less than 0.3 mm B: Maximum film meandering width 0.3 mm or more and 0.6 mm or less C: Maximum film meandering width more than 0.6 mm <Film breakage>
The number of film breaks when the above vapor deposition processability evaluation was performed 10 times was evaluated according to the following criteria.

A: No film break B: Film break 1 time C: Film break 2 times or more (7) Evaluation of vapor deposition capacitor characteristics (withstand voltage at 85 ° C, safety)
A margin portion is provided in the direction perpendicular to the longitudinal direction with a film resistance of 8Ω / □ by an alloy formulation in which aluminum and zinc are vapor-deposited on the films obtained in each of the examples and comparative examples described later with a vacuum vapor deposition machine manufactured by ULVAC Co., Ltd. A thin-film deposition pattern having a so-called T-shaped margin pattern provided was applied to obtain a thin-film deposition reel having a width of 50 mm.

Next, using this reel, a capacitor element is wound by an element winding machine (KAW-4NHB) manufactured by Minato Seisakusho Co., Ltd., a metallikon is applied, and then a heat treatment is performed at a temperature of 125 ° C. for 10 hours under reduced pressure to lead. A wire was attached and the capacitor element was finished. The capacitance of the capacitor element at this time was 10 μF.

Using the 10 capacitor elements thus obtained, an AC voltage of 100 V / μm is applied to the capacitor elements at a high temperature of 85 ° C., and after 10 minutes have passed at the voltage, gradually stepwise at 10 V / μm / 1 minute. A so-called step-up test was performed in which the AC applied voltage was repeatedly increased. At this time, the change in capacitance is measured and plotted on a graph, and the voltage at which the capacitance is 70% of the initial value is divided by the film thickness (described above) to evaluate the withstand voltage, and 180 V / μm or more is used. Make it possible level. Further, after increasing the voltage until the capacitance decreased to 10% or less of the initial value, the capacitor element was disassembled and the state of destruction was examined, and the safety property was evaluated as follows.

AA: No penetrating fracture is observed.

A: Penetration fracture within 10 layers of film is observed.

B: Penetration fracture over 10 layers of film is observed.

C: The element shape is destroyed.
AA can be used without any problem, but A can be used depending on the conditions. B and C cause practical problems.

Hereinafter, the effects of the present invention will be further described with reference to examples. In addition, Examples 3, 6 , 7, 11, 13, 16 , 17 , and 20 are reference examples.

(Example 1)
A branched polypropylene resin (high melt tension polypropylene Profax PF-814) is blended with 1.5% by mass of a polypropylene resin having a mesopentad fraction of 0.98 and a melt flow index (MFR) of 3 g / 10 min. It was supplied to an extruder having a temperature of 260 ° C., melt-extruded into a sheet from a T-shaped slit die at a resin temperature of 255 ° C., and the molten sheet was cooled and solidified on a cooling drum having a diameter of 1.2 m held at 80 ° C. At that time, the sheet and the cooling drum were brought into close contact with each other by the air knife method. The air temperature was 70 ° C. and the air speed was 150 m / sec.

Next, the sheet was preheated at 130 ° C. and slightly stretched at a stretching speed of 100% / min and a stretching ratio of 1.12 times. Subsequently, the sheet was kept at a temperature of 144 ° C., passed between rolls provided with a peripheral speed difference, and stretched 4.6 times in the longitudinal direction. At that time, the stretched portion was stretched by supplementing the amount of heat with the radiation heater output of 12 kW on both sides A and B and the gap with the film being 4 mm. The film was subsequently led to a stenter, stretched 10 times in the width direction at a temperature of 164 ° C., then heat treated at 155 ° C. with 6% relaxation in the width direction, then cooled at 130 ° C. to a film thickness of 4 A 0.0 μm biaxially oriented polypropylene film was obtained. Further, a corona discharge treatment was performed in the atmosphere with a treatment intensity of 7 W · min / m ² on the surface on the A side and 11 W · min / m ² on the surface on the B side. The characteristics of the biaxially oriented polypropylene film thus obtained are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 2)
A film was formed in the same manner as in Example 1 except that the fine draw ratio of the sheet was 1.05 times to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 3)
A film was formed in the same manner as in Example 1 except that the cooling drum temperature was set to 60 ° C. to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 4)
A film was formed in the same manner as in Example 1 except that the cooling drum temperature was 110 ° C. and the preheating roll temperature was 120 ° C. to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 5)
A film was formed in the same manner as in Example 1 except that the air temperature of the air knife was set to 100 ° C. to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 6)
A film was formed in the same manner as in Example 1 except that the air temperature of the air knife was set to 20 ° C. to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 7)
A film was formed in the same manner as in Example 1 except that the air speed of the air knife was set to 130 m / sec to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 8)
A film was formed in the same manner as in Example 1 except that the temperature of the preheating roll was 150 ° C. and the magnification was 1.08 times to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 9)
A film was formed in the same manner as in Example 1 except that the magnification of the preheating roll was 1.15 times to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 10)
A film was formed in the same manner as in Example 1 except that the magnification of the preheating roll was 1.06, to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 11)
A film was formed in the same manner as in Example 1 except that the speed of the preheating roll was 20% / min and the magnification was 1.20 times to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 12)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the radiation heater output was 15 kW on both sides A and B and the gap between the film and the film was 1 mm. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 13)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the radiation heater output was 11 kW on both sides A and B and the gap between the film and the film was 10 mm. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 14)
5.5W · min / ^{m 2} on the surface of the A side, except for performing the corona discharge treatment in the air on the surface of the B side in the processing intensity of 9.0W · min / ^{m 2} from Example 1 A film was formed in the same manner to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 15)
8.0W · min / ^{m 2} on the surface of the A side, except for performing the corona discharge treatment in the air on the surface of the B-side in the process the strength of 12.5W · min / ^{m 2} from Example 1 A film was formed in the same manner to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 16)
5.0W · min / ^{m 2} on the surface of the A side, except for performing the corona discharge treatment in the air on the surface of the B side in the processing intensity of 8.5W · min / ^{m 2} from Example 1 A film was formed in the same manner to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 17)
The surface on the A-side side was not treated, and the surface on the B-side side was subjected to a corona discharge treatment in the air at a treatment strength of 12.5 W · min / m ^{2 in} the same manner as in Example 1. , A biaxially oriented polypropylene film was obtained. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 18)
A film was formed in the same manner as in Example 1 except that the film thickness was 5.5 μm to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 19)
A film was formed in the same manner as in Example 1 except that the film thickness was 7.0 μm to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Example 20)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the film thickness was 2.5 μm. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

(Comparative Example 1)
The film was formed in the same manner as in Example 1 except that the corona discharge power Ea on the A side was 10 W · min / m ² and the corona discharge power Eb on the B side was 13 W · min / m ² . A biaxially oriented polypropylene film was obtained. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 2)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the output of the radiation heater was 0 kW on both sides A and B. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 3)
A film was formed in the same manner as in Example 1 except that the air temperature of the air knife was set to 110 ° C. to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 4)
A film was formed in the same manner as in Example 1 except that the air speed of the air knife was set to 120 m / sec to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 5)
A film was formed in the same manner as in Example 1 except that the air speed of the air knife was set to 160 m / sec, to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 6)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the preheating roll was slightly stretched at a stretching speed of 110% / min and a stretching ratio of 1.21 times. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 7)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the preheating roll was slightly stretched at a stretching speed of 15% / min and a stretching ratio of 1.04 times. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 8)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the radiation heater output was 16 kW on both sides A and B and the gap between the film and the film was 11 mm. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 9)
A film was formed in the same manner as in Example 1 except that the film thickness was 7.1 μm to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 10)
A biaxially oriented polypropylene film was obtained by forming a film in the same manner as in Example 1 except that the film thickness was 2.4 μm. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1. Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film.

(Comparative Example 11)
5.6W · min / ^{m 2} on the surface of the A side, except for performing the corona discharge treatment in the air on the surface of the B side in the processing intensity of 8.0W · min / ^{m 2} from Example 1 A film was formed in the same manner to obtain a biaxially oriented polypropylene film. The characteristics of the obtained biaxially oriented polypropylene film are as shown in Table 1.

Table 1 also shows the dielectric breakdown voltage and element processability of the obtained film. It was excellent in withstand voltage and element workability.

1 Film 1'Film 2 Paper 2'Paper 3 Bakelite board 3'Bakelite board 4 Weight 5 Constant temperature bath 6 Set sample set 7 Double-sided tape 7'Double-sided tape 8 Measuring stand 9 Pulling jig 10 Spring scale

Claims (6)

The peel strength is 2 g / 5 cm or less, and the thickness t1 (μm) by the micrometer method is 2. A biaxially oriented polypropylene film for capacitors that is 8 μm or more and 7.0 μm or less, has protrusions on both sides, and satisfies all of the following equations when one surface is the A side and the other side is the B side. ..
PBmin ≥ 200 (nm)
PBmax ≤ 1,800 (nm)
0.4 ≤ PB700-1000 / PB ≤ 0.8
However,
PBmin: Minimum protrusion height (nm) on the B surface
PBmax: Maximum protrusion height (nm) on the B surface
PB700-1000: Number of protrusions with a height of 700 nm or more and less than 1000 nm existing on the B surface per 0.1 mm ² PB: Total number of protrusions existing on the B surface per 0.1 mm ² The biaxially oriented polypropylene film for a capacitor according to claim 1, which has protrusions on both sides, and when one surface is the A surface and the other surface is the B surface, all of the following equations are satisfied.
PAmin ≥ 200 (nm)
PAmax ≤ 1,500 (nm)
0.3 ≤ PA350-550 / PA ≤ 0.9
However,
PAmin: Minimum protrusion height (nm) on surface A
PAmax: Maximum protrusion height (nm) on surface A
PA350-550: Number of protrusions with a height of 350 nm or more and less than 550 nm existing on the A surface per 0.1 mm ² PA: Total number of protrusions existing on the A surface per 0.1 mm ² The biaxially oriented polypropylene film for a capacitor according to claim 1 or 2, wherein PA and PB satisfy the following formula.
PA ≧ 300
PB ≧ 700 A metal film laminated film in which metal films are provided on both sides of the biaxially oriented polypropylene film for a capacitor according to any one of claims 1 to 3. The metal film laminated film according to claim 4, wherein the surface electrical resistance of the metal film is in the range of 1 to 20 Ω / □. A film capacitor using the metal film laminated film according to claim 4 or 5.