Capacitor and method for manufacturing the same

Abstract

To provide a capacitor excellent in a withstand voltage at high temperature and long-term durability at high temperature, and a method for manufacturing the same.SOLUTION: With a capacitor, a pair of two metallized films each having a metal layer on one surface of a polypropylene film are overlapped and wound so that the metal layer and the polypropylene film are alternately laminated. The metallized film has elongation of 1.6% or less with respect to stress of 44 MPa or less, and an area void ratio of 5.5% or less of a cross section in parallel to both end surfaces of the capacitor located at a center of both end surfaces.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a capacitor and a method for manufacturing the same.

Background Art

[0002] Conventionally, in electronic and electrical devices, capacitors such as film capacitors have been used. Examples of such capacitors include high-voltage capacitors, filter capacitors such as converters and inverters, and smoothing capacitors.

[0003] Depending on the application, the above capacitors may be used at high temperatures. In addition, with the recent improvement in performance of electronic and electrical devices, a load is applied to the capacitor, and the capacitor may become hot, and there is a demand for a capacitor that can be used at high temperatures.

[0004] As a capacitor used at high temperatures, a capacitor formed by laminating and winding a metallized film having a metal layer on one side of a resin film such as a polypropylene film has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Although the above capacitor is also an excellent capacitor, there is room for improvement in terms of withstand voltage at high temperatures and long-term durability at high temperatures. In Patent Document 1, the stress when winding two metallized films as a pair and the porosity in the cross section of the capacitor are not examined. Further, in Patent Document 1, the porosity, the withstand voltage at high temperatures, and the long-term durability at high temperatures are not examined.

[0007] Therefore, there is a demand for the development of a capacitor excellent in withstand voltage at high temperatures and long-term durability at high temperatures, and a method for manufacturing the same.

[0008] An object of the present invention is to provide a capacitor excellent in withstand voltage at high temperatures and long-term durability at high temperatures, and a method for manufacturing the same.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that a capacitor is formed by laminating and winding a pair of two metallized films each having a metal layer on one side of a polypropylene film so that the metal layer and the polypropylene film are alternately laminated. According to a capacitor having a configuration in which the elongation of the metallized film with respect to a stress of 44 MPa or less is 1.6% or less, and the area porosity of a cross section parallel to both end faces in the middle of both end faces of the capacitor is 5.5% or less, the above object can be achieved. The present invention has been completed.

[0010] That is, the present invention relates to the following capacitor and a method for manufacturing the same. 1. A capacitor formed by laminating and winding a pair of two metallized films each having a metal layer on one side of a polypropylene film so that the metal layer and the polypropylene film are alternately laminated, wherein the elongation of the metallized film with respect to a stress of 44 MPa or less is 1.6% or less, and the area porosity of a cross section parallel to both end faces in the middle of both end faces of the capacitor is 5.5% or less. A capacitor characterized by the above. 2. The capacitor according to item 1, wherein the area porosity of a cross section parallel to both end faces in the middle of both end faces of the capacitor is 4.5% or less. 3. The capacitor according to item 1 or 2, wherein the area porosity is 0.1 to 4.5%. 4. The capacitor according to any one of items 1 to 3, wherein the thickness of the polypropylene film is 1 to 6 μm. 5. A method for manufacturing a capacitor, comprising: Using a pair of two metallized films each having a metal layer on one side of a polypropylene film, stacking them so that the metal layer and the polypropylene film are alternately laminated, and winding them under a stress of 44 MPa or less in Step 1; The metallized film has an elongation with respect to the stress during winding of 1.6% or less; The area porosity of a cross-section parallel to both end faces, in the middle of both end faces of the capacitor, is 5.5% or less; A manufacturing method characterized by the above. 6. The manufacturing method according to Item 5, wherein the area porosity of a cross-section parallel to both end faces, in the middle of both end faces of the capacitor, is 4.5% or less. 7. The manufacturing method according to Item 5 or 6, further comprising Step 2 of forming a pair of metallicon electrodes on both end faces of the capacitor after Step 1. 8. The manufacturing method according to any one of Items 5 to 7, wherein the thickness of the polypropylene film is 1 to 6 μm.

Effects of the Invention

[0011] The capacitor of the present invention is excellent in withstand voltage at high temperatures and long-term durability at high temperatures. Further, the manufacturing method of the present invention can easily manufacture the capacitor of the present invention.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0013] In this specification, with respect to the expressions "containing" and "including", the concepts of "containing", "including", "substantially consisting of", and "consisting only of" are included.

[0014] In this specification, with respect to the expression "capacitor", the concepts of "capacitor", "capacitor element", and "film capacitor" are included.

[0015] 1. Capacitor The capacitor of the present invention is a capacitor formed by winding two metallized films each having a metal layer on one side of a polypropylene film as a pair, such that the metal layer and the polypropylene film are alternately laminated and wound. The metallized film has an elongation of 1.6% or less with respect to a stress of 44 MPa or less, and the area porosity of a cross-section parallel to both end faces in the middle of both end faces of the capacitor is 5.5% or less. The capacitor of the present invention having the above characteristics has an elongation of 1.6% or less with respect to a stress of 44 MPa or less of the metallized film constituting the capacitor, so that the area porosity of a cross-section parallel to both end faces in the middle of both end faces of the capacitor can be 5.5% or less. The capacitor of the present invention has excellent withstand voltage characteristics at high temperatures and long-term durability at high temperatures due to the porosity being 5.5% or less.

[0016] The configuration of the capacitor of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a cross-section parallel to both end faces of the capacitor of the present invention. In FIG. 1, the capacitor 1 of the present invention includes both end faces 11 and 12. Also, in FIG. 1, the capacitor 1 of the present invention has a cross-section parallel to both end faces in the middle of both end faces 11 and 12, and the cross-section is cross-section 13.

[0017] The capacitor of the present invention has an area porosity of 5.5% or less in a cross-sectional area parallel to both end faces, in the middle of both end faces of the capacitor. When the area porosity exceeds 5.5%, the withstand voltage property at high temperatures and the long-term durability at high temperatures decrease. The area porosity is preferably 4.5% or less, more preferably 4.0% or less, still more preferably 3.8% or less, and particularly preferably 3.5% or less. Also, the lower limit of the area porosity is not particularly limited and may be 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more, 3.0% or more, etc.

[0018] In addition, in this specification, the measurement of the above area porosity is carried out by the measurement method described in the examples. However, in the measurement of the above area porosity, the winding length L of the first metallized film in the case of two stacked metallized films c1 , and the measurement method of the winding length L of the second metallized film in the case of two stacked metallized films c2 is not particularly limited, and for example, it can be measured by a method such as measurement with a distance meter or a method of obtaining from the product of the circumferential length of the transport roll of the element winding machine and the number of rotations measured by a tachometer. Both the distance meter and the tachometer are preferably non-contact types that do not physically affect the metallized film.

[0019] Also, in the measurement of the above area porosity, the weight M of the polypropylene film f , the width W of the polypropylene film f , and the length L of the polypropylene film f are not particularly limited, and for example, it is possible to measure by a method known at the time of manufacturing the film roll after cutting. Further, the measurement method of the density P of the polypropylene film f is not particularly limited, and for example, it is possible to use a densitometer.

[0020] The method for measuring the measured value Sc of the area of the cross-section 13 of the capacitor element is not particularly limited, and for example, it can be measured by a two-dimensional shape measuring instrument, a three-dimensional shape measuring instrument, X-ray CT, etc. X-ray CT can measure non-destructively even if the capacitor element is sealed with an epoxy resin. The cross-sectional shape of the capacitor element may be measured directly by the above measuring instrument, or after taking a mold, the area may be measured with the taken mold. The method of taking a mold is not particularly limited, and molding with plaster, silicone rubber, etc., or using a molding gauge can be used. Among these, the method using a molding gauge is preferable because it is less affected by contamination of the capacitor element.

[0021] Hereinafter, each member constituting the capacitor of the present invention will be described in detail.

[0022] (Polypropylene film) The polypropylene film of the present invention may be a biaxially oriented film, a uniaxially oriented film, or a non-oriented film. Among them, a biaxially oriented film is preferable.

[0023] The layer structure of the polypropylene film of the present invention is not particularly limited. The film of the present invention may be a single layer composed of one layer, or may be a plurality of layers having the same or different compositions. The polypropylene film of the present invention is preferably a film composed of one or more film-shaped molding layers, and more preferably a single-layer film (a film composed of one film-shaped molding layer). The polypropylene film of the present invention contains polypropylene resin as a main component. In this specification, containing polypropylene resin as a main component means containing 50% by mass or more of polypropylene resin with respect to the entire polypropylene film (when the entire polypropylene film is 100% by mass). The content of the polypropylene resin with respect to the entire polypropylene film is preferably 75% by mass or more, and more preferably 90% by mass or more. The upper limit of the content of the polypropylene resin is, for example, 100% by mass, 98% by mass, etc. with respect to the entire polypropylene film.

[0024] The polypropylene resin is not particularly limited, and those that can be used to form a polypropylene film can be widely used. Examples of the polypropylene resin include propylene homopolymers such as isotactic polypropylene and syndiotactic polypropylene; long-chain branched polypropylene; ultra-high molecular weight polypropylene, etc. Preferably, a propylene homopolymer (propylene homopolymer) is mentioned. Among them, from the viewpoint of heat resistance, isotactic polypropylene is more preferably mentioned, and more preferably, isotactic polypropylene obtained by homopolymerizing propylene in the presence of a catalyst for olefin polymerization is mentioned. The polypropylene resin may be a single type or a blend of two or more types.

[0025] The total ash content of the polypropylene resin is preferably as low as possible for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on the polypropylene resin. The lower limit of the total ash content is, for example, 2 ppm, 5 ppm, etc. The lower the total ash content, the less impurities such as polymerization catalyst residues.

[0026] In the polypropylene film constituting the capacitor of the present invention, the polypropylene resin can include, for example, only the following first polypropylene resin (first PP resin), or can also include the following second polypropylene resin (second PP resin) and / or long-chain branched polypropylene resin (long-chain branched PP resin) together with the first polypropylene resin.

[0027] The polypropylene resin can include a first polypropylene resin. When the polypropylene resin includes the first polypropylene resin, the content of the first polypropylene resin is preferably 50% by weight or more, more preferably 55% by weight or more, still more preferably 60% by weight or more, based on 100% by weight of the polypropylene resin. Regarding the upper limit of the content of the first polypropylene resin, examples include 100% by weight or less, 99% by weight or less, 98% by weight or less, 95% by weight or less, etc., based on 100% by weight of the polypropylene resin. Preferably, it is 90% by weight or less, more preferably 85% by weight or less, still more preferably 80% by weight or less, based on 100% by weight of the polypropylene resin. Thus, the polypropylene film of this embodiment can contain the first polypropylene resin as a main component. Examples of the first polypropylene resin include isotactic polypropylene. The first polypropylene resin may be used alone or in combination of two or more.

[0028] The weight average molecular weight Mw of the first polypropylene resin is preferably 250,000 or more and less than 400,000, more preferably 260,000 or more and 370,000 or less, still more preferably 270,000 or more and 350,000 or less. When Mw is 250,000 or more and less than 400,000, the resin fluidity becomes appropriate, the control of the thickness of the cast base sheet is easy, and it is easy to produce a thin stretched film with good thickness uniformity. Also, when Mw is 250,000 or more and less than 350,000, the resin fluidity becomes more appropriate, the control of the thickness of the cast base sheet is easy, and it is even easier to produce a thin stretched film with good thickness uniformity.

[0029] The number average molecular weight Mn of the first polypropylene resin is preferably 30,000 or more and 52,000 or less, more preferably 32,000 or more and 50,000 or less, still more preferably 34,000 or more and 48,000 or less.

[0030] The z average molecular weight Mz of the first polypropylene resin is preferably 600,000 or more and 1,650,000 or less, more preferably 700,000 or more and 1,600,000 or less, still more preferably 750,000 or more and 1,400,000 or less.

[0031] The molecular weight distribution (Mw / Mn) of the first polypropylene resin is preferably 5.0 or more, more preferably 5.5 or more. The Mw / Mn of the first polypropylene resin is preferably 11.0 or less, more preferably 10.0 or less, still more preferably 9.0 or less, and particularly preferably 8.0 or less. When the Mw / Mn of the first polypropylene resin is 5.0 or more and 11.0 or less, appropriate resin fluidity can be obtained during biaxial stretching, and it is easy to obtain an extremely thin biaxially stretched propylene film without thickness unevenness, which is preferable. Note that the molecular weight distribution Mw / Mn is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn.

[0032] The molecular weight distribution (Mz / Mn) of the first polypropylene resin is preferably 10 or more and 60 or less, more preferably 12 or more and 50 or less, still more preferably 15 or more and 45 or less, and particularly preferably 16 or more and 30 or less. Note that the molecular weight distribution Mz / Mn is the ratio of the z average molecular weight Mz to the number average molecular weight Mn.

[0033] In this specification, the weight average molecular weight (Mw), number average molecular weight (Mn), z average molecular weight (Mz), and molecular weight distribution (Mw / Mn and Mz / Mn) of the first polypropylene resin are values measured using a gel permeation chromatograph (GPC) apparatus. More specifically, they are values measured using the HLC-8121GPC-HT (trade name), a high-temperature GPC measuring machine with a built-in differential refractometer (RI), manufactured by Tosoh Corporation. As the GPC column, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation are connected and used. The column temperature is set to 140 °C, and trichlorobenzene is flowed as the eluent at a flow rate of 1.0 ml / 10 minutes to obtain measured values of Mw and Mn. A calibration curve regarding the molecular weight M is created using standard polystyrene manufactured by Tosoh Corporation, and the measured values are converted to polystyrene values to obtain Mw, Mn, and Mz.

[0034] The melt flow rate (MFR) of the first polypropylene resin at 230°C is preferably 8.0 g / 10 min or less, more preferably 7.0 g / 10 min or less, and even more preferably 6.0 g / 10 min or less. Also, the melt flow rate at 230°C is preferably more than 3.0 g / 10 min, and more preferably more than 3.5 g / 10 min. The melt flow rate at 230°C is measured in accordance with JIS K7210-1999 under a load of 2.16 kg at 230°C. The unit of the melt flow rate, g / 10 min, is also referred to as dg / min.

[0035] The heptane-insoluble content of the first polypropylene resin is preferably 97.0% or more. The heptane-insoluble content is preferably 99.0% or less. A higher heptane-insoluble content indicates a higher stereoregularity of the resin. When the heptane-insoluble content (HI) is 97.0% or more and 99.0% or less, due to the moderately high stereoregularity, the crystallinity of the polypropylene resin in the polypropylene film is moderately improved, and the withstand voltage property at high temperatures is improved. Furthermore, the rate of solidification (crystallization) during the formation of the cast base sheet becomes moderate, and it has moderate stretchability. The measurement method of the heptane-insoluble content (HI) is according to the method described in the examples.

[0036] For electrical properties, the total ash content of the first polypropylene resin is preferably as low as possible. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less based on the first polypropylene resin. The lower limit of the total ash content is, for example, 2 ppm, 5 ppm, etc.

[0037] The polypropylene resin can further contain a second polypropylene resin. The polypropylene film constituting the capacitor of the present invention preferably contains a second polypropylene resin in addition to the first polypropylene resin, and it is more preferably that the resin constituting the polypropylene film is the first polypropylene resin and the second polypropylene resin.

[0038] When the polypropylene resin contains a second polypropylene resin, the content of the second polypropylene resin is preferably 50% by weight or less, more preferably 49% by weight or less, still more preferably 45% by weight or less, and particularly preferably 40% by weight or less based on 100% by weight of the polypropylene resin. When the polypropylene resin contains a second polypropylene resin, examples of the lower limit of the content of the second polypropylene resin include 1% by weight or more, 2% by weight or more, 5% by weight or more, etc. based on 100% by weight of the polypropylene resin, and it is preferably 10% by weight or more, more preferably 15% by weight or more, and still more preferably 20% by weight or more based on 100% by weight of the polypropylene resin. Examples of the second polypropylene resin include isotactic polypropylene.

[0039] The Mw of the second polypropylene resin is preferably 300,000 or more, more preferably 350,000 or more, still more preferably more than 350,000, and particularly preferably 370,000 or more. The Mw of the second polypropylene resin is preferably 450,000 or less, more preferably 400,000 or less.

[0040] The Mn of the second polypropylene resin is preferably 40,000 or more and 54,000 or less, more preferably 42,000 or more and 50,000 or less, and still more preferably 44,000 or more and 48,000 or less.

[0041] The Mz of the second polypropylene resin is preferably more than 1.4 million and 3 million or less, more preferably more than 1.55 million and 2 million or less, and still more preferably 1.58 million or more and 1.7 million or less.

[0042] In the second polypropylene resin, the ratio of Mw to Mn (Mw / Mn) is preferably 5.5 or more, more preferably 7.0 or more, still more preferably 7.5 or more, and particularly preferably more than 8.0. The upper limit of Mw / Mn in the second polypropylene resin is, for example, 11.0, 10.0, 9.0, 8.5, etc.

[0043] In the second polypropylene resin, the ratio of Mz to Mn (Mz / Mn) is preferably 30 or more and 40 or less, more preferably more than 30 and 37 or less, and still more preferably 33 or more and 35 or less.

[0044] In this specification, the weight average molecular weight (Mw), number average molecular weight (Mn), z average molecular weight (Mz), and molecular weight distribution (Mw / Mn and Mz / Mn) of the second polypropylene resin are values measured using a gel permeation chromatograph (GPC) apparatus. More specifically, they are values measured using the HLC-8121GPC-HT (trade name), a high-temperature GPC measuring machine with a differential refractometer (RI) built in, manufactured by Tosoh Corporation. As the GPC column, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation are connected and used. The column temperature is set at 140°C, and trichlorobenzene is flowed as an eluent at a flow rate of 1.0 ml / 10 minutes to obtain measured values of Mw and Mn. A calibration curve regarding the molecular weight M is created using standard polystyrene manufactured by Tosoh Corporation, and the measured values are converted into polystyrene values to obtain Mw, Mn, and Mz.

[0045] The melt flow rate at 230°C of the second polypropylene resin is preferably less than 4.0 g / 10 minutes, more preferably 3.9 g / 10 minutes or less, still more preferably 3.8 g / 10 minutes or less, particularly preferably 3.5 g / 10 minutes or less, and most preferably 3.0 g / 10 minutes or less. Also, the melt flow rate at 230°C is preferably 1.0 g / 10 minutes or more, more preferably 1.5 g / 10 minutes or more, and still more preferably 2.0 g / 10 minutes or more.

[0046] The heptane-insoluble content of the second polypropylene resin is preferably 97.5% or more, more preferably 98.0% or more, still more preferably more than 98.5%, and particularly preferably 98.6% or more. Also, the heptane-insoluble content is preferably 99.5% or less, and more preferably 99.0% or less.

[0047] For the electrical properties, the total ash content of the second polypropylene resin is preferably as low as possible. Based on the second polypropylene resin, the total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less. The lower limit of the total ash content is, for example, 2 ppm, 5 ppm, etc.

[0048] The first polypropylene resin and the second polypropylene resin can be produced using generally known polymerization methods. There is no particular limitation as long as the first polypropylene resin and the second polypropylene resin that can be used for the polypropylene film constituting the capacitor of the present invention can be produced. Examples of such polymerization methods include gas-phase polymerization, bulk polymerization, and slurry polymerization.

[0049] The polymerization may be single-stage polymerization using one polymerization reactor or multi-stage polymerization using at least two or more polymerization reactors. Further, hydrogen or a comonomer may be added as a molecular weight regulator in the reactor.

[0050] As the catalyst for polymerization, generally known Ziegler-Natta catalysts can be used, and there is no particular limitation as long as the first polypropylene resin and the second polypropylene resin can be obtained. The catalyst may contain a cocatalyst component or a donor. By adjusting the catalyst and polymerization conditions, the molecular weight, molecular weight distribution, etc. can be controlled.

[0051] The molecular weight, molecular weight distribution, etc. of the first polypropylene resin and the second polypropylene resin can be adjusted by appropriately selecting, for example, (i) each condition such as the polymerization method and the temperature and pressure during polymerization, (ii) the form of the reactor during polymerization, (iii) the presence or absence, type, and amount of use of additives, (iv) the type and amount of use of the catalyst, etc.

[0052] Specifically, the adjustment of the molecular weight, molecular weight distribution, etc. of the first polypropylene resin and the second polypropylene resin can be carried out, for example, by a multi-stage polymerization reaction. Examples of the multi-stage polymerization reaction include the following methods.

[0053] First, in the first polymerization step, propylene and a catalyst are supplied to the first polymerization reactor. Together with these components, hydrogen as a molecular weight regulator is mixed in an amount necessary to reach the required molecular weight of the polymer. The reaction temperature is, for example, about 70 to 100 °C in the case of slurry polymerization, and the residence time is about 20 minutes to 100 minutes. A plurality of reactors can be used, for example, in series. In this case, the polymerization product of the first step is continuously sent to the next reactor together with additional propylene, catalyst, and molecular weight regulator, and then a second polymerization is carried out to adjust the molecular weight to a lower or higher molecular weight than that of the first polymerization step. By adjusting the yields (production amounts) of the first and second reactors, it is possible to adjust the composition (constitution) of the high molecular weight component and the low molecular weight component.

[0054] In addition, the adjustment of the molecular weight, molecular weight distribution, etc. of the first polypropylene resin and the second polypropylene resin can also be carried out by peroxide decomposition. For example, a method by peroxide treatment with a decomposing agent such as hydrogen peroxide or an organic peroxide can be exemplified.

[0055] When a peroxide is added to a degradable polymer such as polypropylene, a hydrogen abstraction reaction from the polymer occurs. The generated polymer radicals partially recombine and a cross-linking reaction also occurs, but most radicals undergo secondary decomposition (β-cleavage) and are divided into two polymers with a smaller molecular weight. That is, the decomposition proceeds with a higher probability for higher molecular weight components. As a result, the low molecular weight component increases, and the constitution of the molecular weight distribution can be adjusted.

[0056] When adjusting the content of the low molecular weight component by blending (resin mixing), it is advisable to dry mix or melt mix at least two or more resins with different molecular weights. Generally, a two-component polypropylene blend system in which 1 to 40% by mass of an additive resin having a higher or lower average molecular weight than the main resin is mixed is preferably used because it is easy to adjust the amount of the low molecular weight component.

[0057] Also, in the case of this mixing adjustment, the melt flow rate (MFR) may be used as a measure of the average molecular weight. In this case, from the viewpoint of convenience during adjustment, the difference in MFR between the main resin and the additive resin is preferably about 1 to 30 g / 10 min.

[0058] As the first polypropylene resin and the second polypropylene resin, commercially available products can also be used.

[0059] The polypropylene resin contained in the polypropylene film of the present invention can further contain a long-chain branched polypropylene resin. Among the above long-chain branched polypropylene resins, a long-chain branched polypropylene resin obtained by polymerizing propylene using a metallocene catalyst (hereinafter, also simply referred to as "long-chain branched polypropylene resin") is preferable. Specifically, when the above long-chain branched polypropylene resin is contained in the polypropylene resin, a large amount of β-crystals are formed in the cast sheet. And since the β-crystals are transferred to α-crystals by stretching the cast sheet containing β-crystals, unevenness is formed on the polypropylene film obtained by stretching due to the density difference between β-crystals and α-crystals, and it is preferable in that the surface can be suitably roughened.

[0060] Note that, instead of using a long-chain branched polypropylene resin polymerized using a metallocene catalyst, when using a long-chain branched polypropylene resin obtained by crosslinking modification with a peroxide, due to the α-crystal nucleation effect of the long-chain branched polypropylene resin obtained by crosslinking modification with a peroxide, the formation of α-crystals is promoted in the cast sheet, and the formation of β-crystals is greatly suppressed. Since the crystal transition does not occur even when the cast sheet containing α-crystals is stretched, it is difficult to form unevenness. Therefore, in order to roughen the polypropylene film, a long-chain branched polypropylene resin polymerized using a metallocene catalyst is preferable.

[0061] A metallocene catalyst is generally a metallocene compound that forms a polymerization catalyst for producing an olefin macromer. The long-chain branched polypropylene resin obtained by polymerizing propylene using a metallocene catalyst is preferable because the branch chain length and branch chain interval of polypropylene are appropriate, and excellent compatibility with linear polypropylene can be obtained. Also, it is preferable because a uniform composition and a uniform surface shape can be obtained. In the production of the long-chain branched polypropylene resin, other conditions other than the type and amount of the catalyst used, for example, (i) each condition such as the polymerization method and the temperature and pressure during polymerization, (ii) the form of the reactor during polymerization, (iii) the presence or absence, type and amount of additives used, etc., can be made the same as each condition described in the section on the production method of the first polypropylene resin and the second polypropylene resin can be the same as each condition described in the section on the production method of the first polypropylene resin and the second polypropylene resin

[0062] The content of the above long-chain branched polypropylene resin, with the total polypropylene resin in the polypropylene film being 100% by mass, is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more. Also, when the total polypropylene resin in the polypropylene film is 100% by mass, the content of the above long-chain branched polypropylene resin is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less, particularly preferably 7% by mass or less, and even more particularly preferably 5% by mass or less. The long-chain branched polypropylene resin may be used alone or in a mixture of two or more kinds.

[0063] The Mw of the long-chain branched polypropylene resin is preferably 150,000 or more and 600,000 or less, more preferably 200,0 or more and 500,000 or less, still more preferably 250,000 or more and 450,000 or less, and particularly preferably 350,000 or more and 420,000 or less.

[0064] The Mn of the long-chain branched polypropylene resin is preferably 100,000 or more and 300,000 or less, more preferably 100,000 or more and 250,000 or less, still more preferably 100,000 or more and 200,000 or less.

[0065] The Mz of the long-chain branched polypropylene resin is preferably 600,000 or more and 1,350,000 or less, more preferably 630,000 or more and 1,320,000 or less, still more preferably 670,000 or more and 1,280,000 or less, and particularly preferably 750,000 or more and 1,230,000 or less.

[0066] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the long-chain branched polypropylene resin is preferably 1.5 or more and 4.5 or less, more preferably 1.8 or more and 4.2 or less, still more preferably 2.0 or more and 4.0 or less, particularly preferably 2.1 or more and 3.9 or less, and especially preferably 2.2 or more and 3.0 or less.

[0067] The [(z-average molecular weight Mz) / (number-average molecular weight Mn)] of the long-chain branched polypropylene resin is preferably 4.0 or more and 9.0 or less, more preferably 4.2 or more and 8.8 or less, still more preferably 4.5 or more and 8.5 or less, and particularly preferably 5.0 or more and 8.2 or less.

[0068] The weight-average molecular weight (Mw), number-average molecular weight (Mn), z-average molecular weight (Mz), and molecular weight distribution (Mw / Mn and Mz / Mn) of the long-chain branched polypropylene resin are values measured using a gel permeation chromatograph (GPC) apparatus. More specifically, they are measured by high-temperature GPC-MALS measurement, that is, using a high-temperature GPC apparatus (HLC-8121GPC / HT; manufactured by Tosoh Corporation) equipped with a light scattering detector (DAWN EOS; manufactured by Wyatt Technology). As columns, three TSKgel GMH-HR-H(20)HT (7.8 mm ID × 30 cm) and one TSKgel guardcolumnHHR(30) (7.8 mm ID × 7.5 cm), all manufactured by Tosoh Corporation, are connected and used. The column temperature is set to 140°C, and as the eluent, 0.05 wt% of 2,6-di-tert-butyl-paracresol (common name: BHT) is flowed through 1,2,4-trichlorobenzene at a flow rate of 1.0 ml / min to obtain the measured values of Mw and Mn. A calibration curve regarding its molecular weight M is created using standard polystyrene manufactured by Tosoh Corporation, and the measured values are converted to the molecular weight of polypropylene using the Q-factor to obtain the number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz).

[0069] The melt flow rate (MFR) of the long-chain branched polypropylene resin at 230°C is preferably 0.1 to 12 g / 10 min, more preferably 0.5 to 5 g / 10 min, still more preferably 0.7 to 3.5 g / 10 min, and particularly preferably 1.0 to 2.2 g / 10 min.

[0070] The heptane-insoluble content (HI) of the long-chain branched polypropylene resin is preferably 98.0% or more, more preferably 98.2% or more, and even more preferably 98.5% or more. Also, the heptane-insoluble content (HI) of the long-chain branched polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less.

[0071] For electrical properties, the total ash content of the long-chain branched polypropylene resin is preferably as low as possible. Based on the long-chain branched polypropylene resin, the total ash content is preferably 450 ppm or less, more preferably 400 ppm or less.

[0072] Representative commercially available products of the long-chain branched polypropylene resin include, for example, MFX3, MFX6 manufactured by Japan Polypropylene Corporation, MFX8 manufactured by Japan Polypropylene Corporation, and the like.

[0073] When the total amount of the first polypropylene resin, the second polypropylene resin, and / or the long-chain branched PP is 100% by weight of the total polypropylene resin, for example, it can be 90% by weight or more, can also be 95% by weight or more, or can be 100% by weight.

[0074] The polypropylene film of the present invention may contain other resins (hereinafter also referred to as "other resins") in addition to the polypropylene resin. "Other resins" generally refer to resins other than the polypropylene resin that is the main component resin, and are not particularly limited as long as the intended polypropylene film can be obtained. Examples of other resins include other polyolefins other than polypropylene such as polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), poly(1-methylpentene), ethylene-propylene copolymers, propylene-butene copolymers, α-olefin copolymers such as ethylene-butene copolymers, vinyl monomer-diene monomer random copolymers such as styrene-butadiene random copolymers, vinyl monomer-diene monomer-vinyl monomer random copolymers such as styrene-butadiene-styrene block copolymers, and the like. The polypropylene film of the present invention can be contained in an amount that does not adversely affect the intended polypropylene film. The polypropylene film of the present invention may preferably contain 10 parts by mass or less, more preferably 5 parts by mass or less of other resins with respect to 100 parts by mass of the polypropylene resin. Further, the polypropylene film of the present invention may preferably contain 0.1 parts by mass or more, more preferably 1 part by mass or more of other resins with respect to 100 parts by mass of the polypropylene resin.

[0075] In addition to the resin component, the polypropylene film of the present invention may further contain at least one kind of additive. "Additive" generally refers to an additive used in polypropylene and is not particularly limited as long as the intended polypropylene film can be obtained. Additives include, for example, nucleating agents (α-crystal nucleating agents, β-crystal nucleating agents), antioxidants, necessary stabilizers such as chlorine absorbers and ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, inorganic fillers, organic fillers, and the like. Examples of the inorganic filler include barium titanate, strontium titanate, aluminum oxide, and the like. When using the above additives, they can be contained in an amount that does not adversely affect the intended polypropylene film.

[0076] The "nucleating agent" is generally used for polypropylene and is not particularly limited as long as the target polypropylene film can be obtained.

[0077] Examples of nucleating agents include α-nucleating agents that preferentially nucleate α-crystals and β-nucleating agents that preferentially nucleate β-crystals.

[0078] Among the α-nucleating agents, organic nucleating agents include dispersed nucleating agents and dissolved nucleating agents. Examples of dispersed nucleating agents include phosphate ester metal salt-based nucleating agents, carboxylic acid metal salt-based nucleating agents, rosin metal salt-based nucleating agents, etc. Examples of dissolved nucleating agents include sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, amide-based nucleating agents, etc.

[0079] Examples of β-nucleating agents include amide-based nucleating agents, di- or polycarboxylic acid metal salt-based nucleating agents, quinacridone-based nucleating agents, aromatic sulfonic acid-based nucleating agents, phthalocyanine-based nucleating agents, tetraoxaspiro compound-based nucleating agents, etc.

[0080] The nucleating agent can also be dry-blended or melt-blended with the polypropylene raw material, pelletized, and used, or it can be fed into an extruder together with polypropylene pellets and used. By using the nucleating agent, the surface roughness of the film can be adjusted to a desired roughness. Examples of representative commercially available products of the nucleating agent include, for example, as a β-nucleating agent, Njester NU-100 manufactured by Shin Nippon Rika Co., Ltd. When the polypropylene film of the present invention contains a β-nucleating agent, its content is preferably 1 to 1000 ppm by mass, more preferably 50 to 600 ppm by mass, based on the mass of the resin component (in terms of mass when the resin component is taken as a whole).

[0081] The "anti-oxidant" is generally called an antioxidant and is used in polypropylene. As long as the target polypropylene film can be obtained, there are no particular restrictions. Antioxidants are generally used for two purposes. One purpose is to suppress thermal degradation and oxidative degradation in the extruder, and the other purpose is to contribute to suppressing degradation during long-term use as a film for capacitors and improving capacitor performance. The antioxidant that suppresses thermal degradation and oxidative degradation in the extruder is also referred to as the "primary agent", and the antioxidant that contributes to improving capacitor performance is also referred to as the "secondary agent".

[0082] For these two purposes, two types of antioxidants may be used, or one type of antioxidant may be used for the two purposes.

[0083] Examples of the primary agent include 2,6-di-tert-butyl-p-cresol (common name: BHT). The primary agent can usually be added for the purpose of suppressing thermal degradation and oxidative degradation in the extruder when preparing the polypropylene resin composition described in the method for producing a polypropylene film described below. Most of the antioxidant added to the polypropylene resin composition for this purpose is consumed in the molding process in the extruder, and hardly remains in the film after film forming. Therefore, when the polypropylene film of the present invention contains a primary agent, its content is usually less than 100 mass ppm with respect to the mass of the resin component (by mass when the resin component is regarded as a whole).

[0084] Examples of the secondary agent include hindered phenol-based antioxidants having a carbonyl group.

[0085] The "hindered phenol-based antioxidant having a carbonyl group" is usually a hindered phenol-based antioxidant having a carbonyl group, and there are no particular restrictions as long as the target polypropylene film can be obtained.

[0086] Examples of hindered phenolic antioxidants having a carbonyl group include triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] (trade name: Irganox 245), 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 259), pentaerythrityl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1010), 2,2'-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1035), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide) (trade name: Irganox 1098), etc. Among them, pentaerythrityl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which has a high molecular weight, is rich in compatibility with polypropylene, has low volatility and excellent heat resistance, is particularly preferred.

[0087] The polypropylene film of the present invention may contain one or more hindered phenolic antioxidants (secondary agents) having a carbonyl group for the purpose of suppressing deterioration that progresses with time during long-term use. When the polypropylene film of the present invention contains one or more hindered phenolic antioxidants having a carbonyl group, the content thereof is preferably 2000 ppm by mass or more and 6000 ppm by mass or less, more preferably 3000 ppm by mass or more and 6000 ppm by mass or less, based on the mass of the resin component (by mass when the resin component is taken as a whole). From the viewpoint of appropriate effect manifestation, it is preferable that the content of the hindered phenolic antioxidant having a carbonyl group in the film is 2000 ppm by mass or more and 6000 ppm by mass or less.

[0088] A polypropylene film containing a hindered phenolic antioxidant having a carbonyl group that is highly compatible with polypropylene at the molecular level in an optimal specific range of amounts is preferable because its long-term durability is improved.

[0089] (Additive) The polypropylene film constituting the capacitor of the present invention may further contain an additive. Examples of the additive include a chlorine absorber, an ultraviolet absorber, a lubricant, a plasticizer, a flame retardant, an antistatic agent, a colorant, and the like.

[0090] The "chlorine absorber" is generally called a chlorine absorber and is used for polypropylene, and is not particularly limited as long as the target polypropylene film can be obtained. Examples of the chlorine absorber include metal soaps such as calcium stearate. When using such a chlorine absorber, it can be contained in an amount that does not adversely affect the target polypropylene film.

[0091] The thickness of the polypropylene film is preferably 1 to 20 μm, more preferably 1 to 10 μm, and still more preferably 1 to 6 μm. When the lower limit of the thickness is within the above range, the withstand voltage property is ensured, and the breakage of the polypropylene film is more suppressed. When the upper limit of the thickness is within the above range, if the capacitance is the same, the shape of the capacitor can be made smaller.

[0092] (Metallized film) The capacitor of the present invention includes a metallized film having a metal layer on one side of the above polypropylene film.

[0093] The metal layer functions as an electrode. As the metal used for the metal layer, for example, a single metal such as zinc, lead, silver, chromium, aluminum, copper, nickel, a mixture of a plurality of these, an alloy of these, etc. can be used. Among these, zinc and aluminum are preferable in terms of excellent environmental load, economy, and capacitor performance.

[0094] The method for laminating a metal layer on one side of a polypropylene film is not particularly limited, and examples thereof include a vacuum deposition method, a sputtering method, and the like. From the viewpoint of excellent productivity and economy, the vacuum deposition method is preferable. Examples of the vacuum deposition method include a crucible method, a wire method, and the like, and an optimum one can be appropriately selected.

[0095] The margin pattern when laminating the metal layer by vapor deposition is not particularly limited. From the viewpoint of further improving the safety of the capacitor and further suppressing the breakdown and short circuit of the capacitor, it is preferable to apply a pattern including a so-called special margin, such as a fishnet pattern or a T margin pattern, on one surface of the polypropylene film.

[0096] The method for forming the margin is not particularly limited, and it may be formed by a known method such as a tape method or an oil method.

[0097] In the capacitor of the present invention, the elongation of the metallized film with respect to a stress of 44 MPa or less is 1.6% or less. When the above elongation exceeds 1.6%, the withstand voltage property at high temperature and the long-term durability at high temperature decrease. The above elongation is preferably 1.5% or less, more preferably 1.3% or less, and even more preferably 1.0 or less. Further, the lower limit of the above elongation is not particularly limited, and it may be 0.1% or more, 0.3% or more, 0.5% or more, 1.5% or more, etc.

[0098] In this specification, the method for measuring the elongation with respect to the stress of 44 MPa or less is based on the method described in the examples.

[0099] The capacitor of the present invention is a capacitor formed by winding two metallized films each having a metal layer on one side of the above polypropylene film as a pair so that the metal layer and the polypropylene film are alternately laminated. The configuration of the capacitor will be described with reference to the drawings.

[0100] FIG. 2 is a schematic diagram showing a metallized film having a metal layer on one side of a polypropylene film. In FIG. 2, the metallized film 20 has a metal layer 21 on one side of the polypropylene film 22. The metal layer 21 has a metal vapor deposition layer 21a and an electrode extraction portion (heavy edge portion) 21b formed on the metal vapor deposition layer 21a. Further, an insulating portion 23 is formed on the surface of the polypropylene film 22, which is not covered by the metal layer 21 and the surface of the polypropylene film 22 is exposed. The width of the insulating portion 23 is not particularly limited as long as the capacitance when the area of the metal vapor deposition electrode becomes too small and it is used as a capacitor is not significantly impaired. For example, it may be 2 mm or more.

[0101] The film resistance of the metal vapor deposition layer 21a is not particularly limited, preferably 5 to 30 Ω / sq, and more preferably 10 to 25 Ω / sq.

[0102] The film resistance of the electrode extraction portion (heavy edge portion) 21b is preferably 1 to 7 Ω / sq, and more preferably 2 to 6 Ω / sq.

[0103] FIG. 3 is a schematic diagram showing a state in which two metallized films each having a metal layer on one side of a polypropylene film are overlapped so that the metal layer and the polypropylene film are alternately laminated. In FIG. 3, two metallized films 20 each having a metal layer 21 on one side of a polypropylene film 22 are overlapped so that the metal layer 21 and the polypropylene film 22 are alternately laminated. Further, in FIG. 3, the two metallized films 20 are arranged and laminated such that the electrode extraction portions (heavy edge portions) 21b are on the opposite sides. In the capacitor of the present invention, the two metallized films are used as a pair and wound in a state where the metal layer and the polypropylene film are alternately laminated so that the electrode extraction portions of each other protrude. The metallized film can be laminated and wound by a conventionally known method to form a capacitor.

[0104] The capacitor of the present invention may preferably have an extraction electrode on the end face of the capacitor element. The extraction electrode can be formed by irradiating the end face of the capacitor element with metallicon.

[0105] The capacitor of the present invention may have a lead formed on the above extraction electrode. The member for forming the lead is not particularly limited as long as it has conductivity, and known metal wires and metal plates used as leads of capacitors such as copper wires and copper plates can be used.

[0106] After attaching the extraction electrode and the lead as described above, the capacitor of the present invention may preferably be put into a resin case, filled with an epoxy resin in the gap, and cured to be resin-sealed. That is, the capacitor of the present invention may be coated with an epoxy resin.

[0107] The capacitor of the present invention can be suitably used for capacitor for inverter power equipment for controlling drive motors of electric vehicles, hybrid vehicles, etc. It can also be suitably used in applications such as for railway vehicles, for wind power generation, for solar power generation, and for general household appliances.

[0108] 2. Method for manufacturing a polypropylene film The polypropylene film constituting the capacitor of the present invention is preferably biaxially stretched as described above. When the polypropylene film is a biaxially stretched polypropylene film, the biaxially stretched polypropylene film can be produced by a generally known method for producing a biaxially stretched polypropylene film. For example, a cast sheet is produced from a polypropylene resin composition obtained by mixing a second polypropylene resin, and / or a long-chain branched polypropylene resin, or only the first polypropylene resin, together with the first polypropylene resin, if necessary, with other resins, additives, etc., and then the cast sheet is biaxially stretched.

[0109] In one aspect of the above polypropylene film, as described below, it is preferable to set the heating and melting temperature in the production of the cast sheet to a relatively high temperature, set the cooling drum temperature in the production of the cast sheet to a relatively high temperature, set the longitudinal stretching temperature to a relatively high temperature, and appropriately adjust other stretching conditions, etc. Further, in one aspect, it is preferable to set the heating and melting temperature in the production of the cast sheet to a relatively high temperature, and set the cooling drum temperature or the longitudinal stretching temperature in the production of the cast sheet to a relatively high temperature, etc.

[0110] 2-1. Preparation of a polypropylene resin composition The method for preparing the polypropylene resin composition is not particularly limited. However, (i) using the first polypropylene resin alone, or (ii) using the first polypropylene resin together with the second polypropylene resin and / or long-chain branched polypropylene resin, and dry-blending the polymerization powder or pellets of (i) or (ii) with other resins, additives, etc. as necessary using a mixer or the like, or feeding the polymerization powder or pellets of (i) or (ii) with other resins, additives, etc. as necessary into a kneader and melt-kneading to obtain a melt-blended resin composition, etc. can be mentioned.

[0111] The mixer and kneader are not particularly limited. The kneader may be of any type of single-screw type, twin-screw type, or multi-screw type with more than two screws. In the case of a twin-screw or more screw type, either a co-rotating or counter-rotating kneading type may be used.

[0112] In the case of blending by melt-kneading, the kneading temperature is not particularly limited as long as good kneading can be obtained, but it is preferably in the range of 170 to 320 °C, more preferably in the range of 200 °C to 300 °C, and even more preferably within the range of 230 °C to 270 °C. In order to suppress deterioration during the kneading and mixing of the resin, the kneader may be purged with an inert gas such as nitrogen. The melt-kneaded resin can generally be pelletized to an appropriate size using a known granulator to obtain pellets of the melt-blended resin composition.

[0113] When preparing the polypropylene resin composition, for the purpose of suppressing thermal degradation and oxidative degradation in the extruder, a primary agent as an antioxidant described in the above additive section can be added.

[0114] When the polypropylene resin composition contains a primary agent, its content is preferably 1000 mass ppm to 5000 mass ppm with respect to the mass of the resin component (by mass when the resin component is regarded as a whole). Most of this antioxidant for the purpose is consumed in the molding process in the extruder, and hardly remains in the film after film forming.

[0115] A hindered phenol-based antioxidant having a carbonyl group described in the above additive section can be added to the polypropylene resin composition as a secondary agent.

[0116] When the polypropylene resin composition contains a hindered phenol-based antioxidant having a carbonyl group, its content is preferably 100 mass ppm to 10000 mass ppm, more preferably 3000 mass ppm to 7000 mass ppm with respect to the mass of the resin component (by mass when the resin component is regarded as a whole). In the extruder, the hindered phenol-based antioxidant having a carbonyl group is also consumed to a certain extent.

[0117] When the polypropylene resin composition does not contain a primary agent, more hindered phenol-based antioxidant having a carbonyl group can be used. This is because the consumption amount of the hindered phenol-based antioxidant having a carbonyl group increases in the extruder. When the polypropylene resin composition does not contain a primary agent and contains a hindered phenol-based antioxidant having a carbonyl group, its content is 4000 mass ppm to 8000 mass ppm or less with respect to the mass of the resin component (by mass when the resin component is regarded as a whole).

[0118] 2-2. Production of a cast sheet The cast sheet can be obtained by supplying pellets of a previously prepared dry blend resin composition and / or a melt blend resin composition to an extruder, heating and melting them, passing them through a filtration filter, and then heating and melting them at a relatively high temperature, preferably 255°C to 320°C, more preferably 260°C to 300°C, even more preferably 265 to 280°C, and melt-extruding them from a T-die, and cooling and solidifying them on at least one or more metal drums maintained at a relatively high temperature, preferably 96°C to 120°C, more preferably 96°C to 110°C, even more preferably 96 to 100°C (casting temperature). At this time, it is preferable to press the melt-extruded resin composition onto the metal drum with an air knife. Note that the surface in contact with the metal drum is the first surface, and the opposite surface (the surface on the air knife side) is the second surface.

[0119] The thickness of the above cast sheet is not particularly limited, preferably 50 μm or more and 2000 μm or less, and more preferably 100 μm or more and 1000 μm or less.

[0120] During the production process of the cast sheet (especially in the extruder), polypropylene is subject to thermal degradation (oxidative degradation) and shear degradation to a certain extent. The degree of progress of such degradation, that is, the change in molecular weight distribution and stereoregularity, can be suppressed by nitrogen purging in the extruder (suppression of oxidation), the screw shape in the extruder (shearing force), the internal shape of the T-die during casting (shearing force), the addition amount of antioxidant (suppression of oxidation), the winding speed during casting (elongation force), etc.

[0121] 2-3. Stretching treatment The biaxially oriented polypropylene film can be manufactured by subjecting the cast sheet to a stretching process. As the stretching method, a sequential biaxial stretching method is preferred. As the sequential biaxial stretching method, first, the cast sheet is maintained at a relatively high temperature, preferably 142 to 180°C, more preferably 143 to 160°C, even more preferably 144 to 150°C, passed between rolls with a speed difference, and stretched preferably 3 to 7 times, more preferably 4 to 6 times in the flow direction, and immediately cooled to room temperature. Subsequently, the stretched film is guided to a tenter and transversely stretched preferably 3 to 11 times (preferably 8 to 11 times) in the width direction at a temperature of preferably 150 to 160°C, more preferably 150 to 159°C, even more preferably 150 to 158°C, and even more preferably 150 to 157°C, followed by relaxation and heat setting, and then wound into a roll.

[0122] The longitudinal stretching speed is preferably 100 to 100,000% / sec, more preferably 1,000 to 80,000% / sec, even more preferably 60,000 to 70,000% / sec, and even more preferably 65,000 to 70,000% / sec. The transverse stretching speed is preferably 10 to 800% / sec, more preferably 100 to 600% / sec, even more preferably 300 to 400% / sec, and even more preferably 300 to 350% / sec.

[0123] The film wound into a roll is subjected to an aging treatment in an atmosphere of about 20 to 45°C, and then slit (cut) to a desired product width with a slitter or the like while being unwound (fed out), and each is wound again.

[0124] Through such a stretching process, a film excellent in mechanical strength and rigidity is obtained.

[0125] It is preferable to perform corona discharge treatment on the polypropylene film online or offline after the stretching and heat setting processes are completed. By performing corona discharge treatment, the adhesion characteristics in subsequent processes such as metal vapor deposition processing can be enhanced. The corona discharge treatment can be performed using a known method. It is preferable to perform the treatment using air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof as the ambient gas.

[0126] 3. Method for manufacturing a metallized film In the production of the capacitor of the present invention, a metallized film having a metal layer on one side of the above polypropylene film is used. The metallized film having such a configuration can be usefully used as a metallized film for capacitors.

[0127] The metal layer functions as an electrode. As the metal used for the metal layer, for example, a single metal such as zinc, lead, silver, chromium, aluminum, copper, nickel, a mixture of plural kinds thereof, an alloy thereof, etc. can be used. Among these, zinc and aluminum are preferable in terms of excellent environmental load, economy, and capacitor performance.

[0128] The method of laminating the metal layer on at least one side (one side or both sides) of the polypropylene film is not particularly limited, and examples thereof include a vacuum evaporation method and a sputtering method. From the viewpoint of excellent productivity and economy, the vacuum evaporation method is preferable. Examples of the vacuum evaporation method include a crucible method and a wire method, and an appropriate optimal one can be selected.

[0129] The margin pattern when laminating the metal layer by vapor deposition is not particularly limited, and from the viewpoint of further improving the safety of the capacitor and further suppressing the destruction and short circuit of the capacitor, a pattern including a so-called special margin such as a fishnet pattern and a T-margin pattern is preferably applied on one surface of the polypropylene film.

[0130] The method of forming the margin is not particularly limited, and it may be formed by a known method such as a tape method or an oil method.

[0131] The thickness of the metallized film is not particularly limited, preferably 1 to 20 μm, more preferably 1 to 10 μm, and even more preferably 1 to 6 μm.

[0132] Hereinafter, a preferred method for manufacturing the metallized film will be described with reference to FIG. 4.

[0133] FIG. 4 is a schematic diagram showing a method for manufacturing a metallized film. The metallized film is preferably manufactured by the manufacturing apparatus described below. As shown in FIG. 4, the manufacturing apparatus for the metallized film includes a dielectric film supply unit 101, an insulating margin forming unit 102, a special vapor deposition pattern margin forming unit 103, a metal vapor deposition unit 104, a DC magnetron discharge electrode 105, and a metallized film winding unit 106.

[0134] The dielectric film supply unit 101 supports a biaxially stretched polypropylene film roll 2R around which a biaxially stretched polypropylene film 2 is wound, and supplies the biaxially stretched polypropylene film 2. The biaxially stretched polypropylene film 2 supplied from the biaxially stretched polypropylene film roll 2R is conveyed to the insulating margin forming unit 102.

[0135] The insulating margin forming unit 102 applies oil in a pattern corresponding to the pattern of the insulating margin to the metal vapor deposition surface 2a of the biaxially stretched polypropylene film 2 to form an oil mask. The oil mask is for preventing metal particles from adhering in the vapor deposition process to the portion that becomes the insulating margin in the metallized film 1. The insulating margin forming unit 102 vaporizes the oil stored in the oil tank and directly applies the oil to the metal vapor deposition surface 2a of the polypropylene film 2 through a nozzle (slit) provided in the tank to form an oil mask.

[0136] The special vapor deposition pattern margin forming section 103 applies oil in a pattern generally corresponding to the electrode pattern of the metal vapor deposition layer 3a onto the metal vapor deposition surface 2a of the biaxially stretched polypropylene film 2 to form an oil mask. The oil mask is for preventing metal particles from adhering during the vapor deposition process to the portions that will become the longitudinal and lateral margins in the metallized film 1. The special vapor deposition pattern margin forming section 103 includes an oil tank 103a, an anilox roll 103b, a transfer roll 103c, a plate roll 103d, and a backup roll 103e. The oil tank 103a vaporizes the stored oil and ejects it from a nozzle. The anilox roll 103b and the transfer roll 103c rotate with the oil ejected from the nozzle of the oil tank 103a adhering to their outer peripheral surfaces. The backup roll 103e faces the plate roll 103d with the polypropylene film 2 interposed therebetween and abuts against the cooling roll contact surface 2b of the biaxially stretched polypropylene film 2.

[0137] The biaxially stretched polypropylene film 2 that has passed through the insulation margin forming section 102 and the special vapor deposition pattern margin forming section 103 is conveyed to the vapor deposition section 104.

[0138] The vapor deposition section 104 includes metal vapor generation sections 104a and 104b, and a cooling roll 104c facing the metal vapor generation sections 104a and 104b with a biaxially stretched polypropylene film 2 interposed therebetween. The metal vapor generation section 104a generates metal vapor by supplying it onto a boat heated by passing an electric current through a wire of a metal which is a material of the metal vapor deposition layer 3a, and deposits the metal vapor on the metal vapor deposition surface 2a of the biaxially stretched polypropylene film 2. The metal vapor generation section 104b generates metal vapor by heating and evaporating a metal which is a material of the electrode extraction section 3b, and deposits it on the metal vapor deposition layer 3a previously formed on the metal vapor deposition surface 2a of the biaxially stretched polypropylene film 2 by the metal vapor generation section 104a in an overlapping manner. As a result, the metal vapor deposition layer in the electrode extraction section 3b portion becomes thicker than the metal vapor deposition layers in other portions, and a heavy edge structure is formed. Note that the metal vapor generated in the metal vapor generation sections 104a and 104b adheres to portions other than the oil mask formed on the metal vapor deposition surface 2a of the biaxially stretched polypropylene film 2 to form a metal vapor deposition electrode.

[0139] A voltage is applied to the cooling roll 104C, and due to the voltage application, the cooling roll contact surface 2b of the biaxially stretched polypropylene film 2 adheres closely to the cooling roll 104C to cool the biaxially stretched polypropylene film 2. The degree of adhesion of the cooling roll contact surface 2b to the cooling roll 104C is proportional to the applied voltage (V) of the cooling roll 104C, and is inversely proportional to the width (m) of the cooling roll and the vapor deposition rate (m / min). Therefore, the higher the voltage speed ratio per unit width of the cooling roll (unit: V·min / m 2 ), the closer the cooling roll contact surface 2b of the biaxially stretched polypropylene film 2 adheres to the cooling roll 104C, the higher the cooling efficiency, and it becomes possible to prevent damage caused by the heat of the vapor deposited metal. The voltage speed ratio per unit width of the cooling roll is preferably 0.20 V·min / m 2 or more and 0.45 V·min / m 2 or less. When the voltage speed ratio per unit width of the cooling roll is 0.20 V·min / m 2If it is smaller, the cooling roll contact surface 2b of the biaxially stretched polypropylene film 2 does not sufficiently adhere to the cooling roll 104C, resulting in poor cooling efficiency. The biaxially stretched polypropylene film or the metallized film is thermally damaged. As a result, the breakdown voltage resistance of the metallized film 1 decreases, and when it is made into a capacitor, the life is reduced due to dielectric breakdown or heat generation. Also, the voltage speed ratio per unit width of the cooling roll is 0.45 V·min / m 2 If it is larger, the cooling roll contact surface 2b of the biaxially stretched polypropylene film 2 sufficiently adheres to the cooling roll 104C, so the cooling efficiency improves, and the thermal damage to the biaxially stretched polypropylene film 2 or the metallized film 1 is reduced. However, discharge is likely to occur between the biaxially stretched polypropylene film 2 and the roll 104C, or between the metallized film 1 and the roll 104C. When discharge occurs, the biaxially stretched polypropylene film 2 or the metallized film 1 is electrically damaged and damaged. Also, even when discharge does not occur, the metallized film 1 is likely to be charged. When the metallized film 1 is wound into a roll at the metallized film winding section 106, electrical damage due to electrostatic discharge of the metallized film 1 occurs, causing damage to the metallized film 1. When the biaxially stretched polypropylene film 2 or the metallized film 1 is electrically damaged and damaged, the breakdown voltage resistance decreases, and when it is made into a capacitor, a reduction in life due to dielectric breakdown or heat generation is likely to occur. Also, when the metallized film 1 is charged, the slipperiness deteriorates, so wrinkles are likely to occur during winding at the metallized film winding section 106 or during the element winding process of capacitor manufacturing. Also, in the press treatment process after element winding in capacitor manufacturing, buckling is likely to occur due to the deterioration of slipperiness caused by charging. Wrinkles and buckling damage the metallized film 1 and are factors leading to a reduction in the life of the capacitor due to dielectric breakdown or heat generation, so they are not preferable. The voltage speed ratio per unit width of the cooling roll is 0.24 V·min / m 2 or more and 0.41 V·min / m 2 or less is more preferable.

[0140] The temperature of the cooling roll 104C is preferably -18°C or lower, more preferably -19°C or lower, from the viewpoint of preventing thermal damage to the biaxially stretched polypropylene film 2 or the metallized film 1.

[0141] The metallized film 1 formed by forming a metal vapor deposition electrode at the vapor deposition part 104 on the biaxially stretched polypropylene film 2 passes through the static electricity removing part 105. The static electricity removing part 105 is provided with DC magnetron discharge electrodes 105a, 105b, 105c, and 105d. In a state where argon gas is supplied, by supplying power to the DC magnetron discharge electrode parts 105a, 105b, 105c, and 105d, ions of argon gas are generated. When the metallized film 1 passes through the static electricity removing part 105 in a state where ions of argon gas are generated, the static electricity of the metallized film 1 is neutralized by the ions of argon gas, preventing the metallized film roll 1R from being charged. The degree of static electricity neutralization of the metallized film 1 by the ions of argon gas can be represented by the discharge amount. The discharge amount is proportional to the total power (W) of the DC magnetron discharge electrode parts 105a, 105b, 105c, and 105d, and inversely proportional to the width (m) of the DC magnetron discharge electrode part and the vapor deposition rate (m / min). Here, the widths of the DC magnetron discharge electrode parts 105a, 105b, 105c, and 105d are the same, and the width (m) of the DC magnetron discharge electrode part is the width per piece, not the total width of the DC magnetron discharge electrode parts 105a, 105b, 105c, and 105d. The discharge amount is 1.5 W·min / m 2 or more and 3.7 W·min / m 2 or less is preferable. When the discharge amount is greater than 3.7 W·min / m 2 the discharge of the DC magnetron discharge electrode parts 105a, 105b, 105c, and 105d becomes too strong, causing electrical damage to the metallized film 1 and resulting in damage. Also, even when no discharge occurs, the metallized film 1 is charged by the ions of argon gas. Further, when the discharge amount is 1.5 W·min / m 2If it is smaller, the static electricity of the metallized film 1 will not be sufficiently neutralized and it will become charged. When the metallized film 1 is electrically damaged, its withstand voltage property deteriorates, and when it is made into a capacitor, insulation breakdown and a reduction in lifespan due to heat generation are likely to occur. Also, when the metallized film 1 is charged, when it is wound into a roll at the metallized film winding section 106, electrical damage due to the discharge of static electricity of the metallized film 1 occurs, causing damage to the metallized film 1. When the metallized film 1 is damaged, its withstand voltage property deteriorates, and when it is made into a capacitor, insulation breakdown and a reduction in lifespan due to heat generation are likely to occur. Further, when the metallized film 1 is charged, its slipperiness deteriorates, so wrinkles are likely to occur during winding at the metallized film winding section 106 or during the element winding process of capacitor manufacturing. Also, in the pressing process after element winding in capacitor manufacturing, buckling is likely to occur due to the deterioration of slipperiness caused by charging. Wrinkles and buckling damage the metallized film 1 and are factors leading to insulation breakdown of the capacitor and a reduction in lifespan due to heat generation, so they are not preferable. The discharge amount is 1.9 W·min / m 2 or more and 3.3 W·min / m 2 or less is more preferable.

[0142] The metallized film 1 that has passed through the static eliminator 105 is conveyed to the metallized film winding section 106 and wound up to form a metallized film roll 1R.

[0143] Using the above manufacturing apparatus, a metallized electrode 3 can be formed on the metal vapor deposition surface 2a of the polypropylene film 2 to obtain the metallized film 1.

[0144] The capacitor of the present invention is a capacitor formed by stacking and winding two of the above metallized films in pairs such that the metal layer and the polypropylene film are alternately laminated. The said metallized film can be used in the manufacturing method of the capacitor of the present invention described later.

[0145] 4. Method for manufacturing a capacitor The manufacturing method of the capacitor of the present invention has a step 1 of winding at a stress of 44 MPa or less by overlapping two metallized films each having a metal layer on one side of a polypropylene film in pairs so that the metal layer and the polypropylene film are alternately laminated. The metallized film has an elongation with respect to the stress during winding of 1.6% or less, and the area porosity of a cross-section parallel to both end faces in the middle of both end faces of the capacitor is 5.5% or less. According to the manufacturing method of the present invention, the capacitor of the present invention excellent in withstand voltage property at high temperature and long-term durability at high temperature can be easily manufactured. Hereinafter, the manufacturing method of the present invention will be described.

[0146] (Step 1) Step 1 is a step of winding at a stress of 44 MPa or less by overlapping two metallized films each having a metal layer on one side of a polypropylene film in pairs so that the metal layer and the polypropylene film are alternately laminated.

[0147] As the metallized film having a metal layer on one side of the polypropylene film, the above-mentioned metallized film can be used.

[0148] In step 1, the above-mentioned two metallized films are overlapped in pairs so that the metal layer and the polypropylene film are alternately laminated and wound. The overlapping method is the same as the overlapping method described with reference to FIGS. 2 and 3 above.

[0149] In step 1, the overlapped metallized film shown in FIG. 3 is wound at a stress of 44 MPa or less. If the stress during winding exceeds 44 MPa, the withstand voltage property at high temperature and the long-term durability at high temperature are not sufficient. The stress during winding is preferably 40 MPa or less, more preferably 35 MPa or less. Also, the stress during winding is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 18 MPa or more. When the lower limit of the stress during winding is within the above range, the withstand voltage property at high temperature and the long-term durability at high temperature are further improved.

[0150] The method of winding the metallized film (element winding) is not particularly limited, and it may be wound by a conventionally known method such as winding with stress applied by a winding machine for capacitor use to form a capacitor.

[0151] In Step 1, the elongation of the metallized film with respect to the stress during winding is 1.6% or less. If the elongation exceeds 1.6%, the breakdown voltage resistance at high temperatures and the long-term durability at high temperatures will decrease. The elongation is preferably 1.5% or less, more preferably 1.3% or less, and even more preferably 1.0 or less. Also, the lower limit of the elongation is not particularly limited and may be 0.1% or more, 0.3% or more, 0.5% or more, 1.5% or more, etc.

[0152] In this specification, the method for measuring the elongation with respect to the stress during winding at a stress of 44 MPa or less is according to the method described in the examples.

[0153] Examples of the method for adjusting the stress during winding to 44 MPa or less include a method of adjusting with a winding machine during winding.

[0154] The capacitor manufactured by the manufacturing method of the present invention has an area porosity of 5.5% or less in a cross-sectional area parallel to the both end faces, in the middle of the both end faces of the capacitor. If the area porosity exceeds 5.5%, the breakdown voltage resistance at high temperatures and the long-term durability at high temperatures will decrease. The area porosity is preferably 4.5% or less, more preferably 4.0% or less, still more preferably 3.8% or less, and particularly preferably 3.5% or less. Also, the lower limit of the area porosity is not particularly limited and may be 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more, 3.0% or more, etc.

[0155] In this specification, the measurement of the area porosity is according to the measurement method described in the examples.

[0156] The thickness of the polypropylene film used in Step 1 is preferably 1 to 20 μm, more preferably 1 to 10 μm, and even more preferably 1 to 6 μm. When the lower limit of the thickness is within the above range, the withstand voltage property is ensured, and the breakage of the polypropylene film is more suppressed. When the upper limit of the thickness is within the above range, if the capacitance is the same, the shape of the capacitor can be made smaller.

[0157] In the manufacturing method of the present invention, after Step 1, the wound metallized film may be subjected to a flattening process. By the flattening process, unnecessary space is reduced, the element volume can be minimized, and the capacitance of the capacitor can be adjusted to an appropriate capacitance. The method of the flattening process is not particularly limited, and for example, a method of pressing the wound metallized film by a known method such as a press machine can be mentioned.

[0158] (Step 2) In the manufacturing method of the present invention, after Step 1, it may further have Step 2 of forming a pair of metallicon electrodes on both end faces of the capacitor. By performing metallicon irradiation on both end faces of the capacitor, a pair of extraction electrodes (metallicon electrodes) can be formed.

[0159] In the manufacturing method of the present invention, after Step 2, it preferably has a step of attaching leads to the extraction electrodes (metallicon electrodes) preferably formed by the above-mentioned metallicon spraying. The member for forming the leads is not particularly limited as long as it has conductivity, and a known metal wire used as a lead of a capacitor such as a copper wire can be used.

[0160] In the manufacturing method of the present invention, after attaching leads to the extraction electrodes as described above, preferably, it has a step of putting them in a resin case, filling the gap with an epoxy resin, and curing the epoxy resin. Through this step, a capacitor coated with an epoxy resin can be obtained.

Examples

[0161] The present invention will be described more specifically by way of examples. These examples are for the purpose of explaining the present invention and do not limit the present invention in any way. Unless otherwise specified, "parts" and "%" indicate "parts by mass" and "mass %", respectively.

[0162] (Polypropylene resin) The polypropylene resins used in the examples and comparative examples are shown in Table 1.

[0163] Resin A (the first polypropylene resin (the first PP resin)) shown in Table 1 is a product manufactured by Prime Polymer Co., Ltd. Resin B (the second polypropylene resin (the second PP resin)) is S802M manufactured by Korea Petrochemical. Resin C (the first polypropylene resin (the first PP resin)) is a product manufactured by Prime Polymer Co., Ltd. Resin D is MFX6 manufactured by Japan Polypropylene Corporation. Resins A, B, and C are all linear homopolypropylene resins (linear homo-PP resins). Resin D is a long-chain branched polypropylene resin (long-chain branched PP resin).

[0164] Table 1 shows the number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), melt flow rate (MFR), and heptane insolubles (HI) of the linear homopolypropylene resins. These values are the values in the form of raw resin pellets. The measurement methods are as follows.

[0165] Table 1 also shows the number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), melt flow rate (MFR), and heptane insolubles (HI) of the long-chain branched polypropylene resin. These values are the values in the form of raw resin pellets. The measurement methods are as follows.

[0166] (Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of linear polypropylene resin) Using GPC (gel permeation chromatography), the number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of each resin were measured under the following conditions.

[0167] Specifically, an HLC-8121GPC-HT type high-temperature GPC device with a built-in differential refractometer (RI) manufactured by Tosoh Corporation was used. As columns, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation were connected in series and used. At a column temperature of 140 °C, trichlorobenzene was used as the eluent and flowed at a flow rate of 1.0 ml / min for measurement. A calibration curve regarding its molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values were converted to the molecular weight of polypropylene using the Q-factor to obtain the number average molecular weight (Mn), weight average molecular weight (Mw), and z average molecular weight (Mz). The molecular weight distribution (Mw / Mn) was obtained using the values of Mw and Mn. Also, the molecular weight distribution (Mz / Mn) was obtained using the values of Mz and Mn.

[0168] (Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of long-chain branched polypropylene resin) Using GPC (gel permeation chromatography), the number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of each resin were measured under the following conditions.

[0169] Specifically, an HLC-8121GPC-HT type, a high-temperature GPC device with a built-in differential refractometer (RI) manufactured by Tosoh Corporation, was used. As columns, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation were connected in series, and one TSKgel guard column HHR(30) was also used. At a column temperature of 140 °C, as the eluent, 0.05 wt% of 2,6-di-tert-butyl-p-cresol (common name: BHT) was added to 1,2,4-trichlorobenzene and flowed at a flow rate of 1.0 ml / min for measurement. A calibration curve regarding its molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values were converted to the molecular weight of polypropylene using the Q-factor to obtain the number average molecular weight (Mn), weight average molecular weight (Mw), and z average molecular weight (Mz). Using the values of Mw and Mn, the molecular weight distribution (Mw / Mn) was obtained. Also, using the values of Mz and Mn, the molecular weight distribution (Mz / Mn) was obtained. The measurement conditions are as follows. GPC device: HLC-8121GPC / HT (manufactured by Tosoh) Light scattering detector: DAWNEOS (manufactured by Wyatt Technology) Column: One TSKgel guard column HHR(30) (7.8 mm ID × 7.5 cm) + three TSKgel GMHHR-H(20)HT (7.8 mm ID × 30 cm) (manufactured by Tosoh) Eluent: 0.05 wt% BHT in 1,2,4-trichlorobenzene Flow rate: 1.0 mL / min Sample concentration: 2 mg / mL Injection volume: 300 μL Column temperature: 140 °C System temperature: 40 °C Pretreatment: The sample was precisely weighed, the eluent was added, and it was shaken and dissolved at 140 °C for 1 hour, followed by heat filtration using a 0.5-μm sintered metal filter.

[0170] (Measurement of melt flow rate (MFR)) For each resin, the melt flow rate (MFR) in the form of raw resin pellets was measured in accordance with Condition M of JIS K7210 using a melt indexer manufactured by Toyo Seiki Seisaku-sho, Ltd. Specifically, first, a 4-g sample weighed out was inserted into a cylinder set at a test temperature of 230°C and preheated for 3.5 minutes under a load of 2.16 kg. Then, the weight of the sample extruded through the bottom hole in 30 seconds was measured to obtain the MFR (g / 10 min). The above measurement was repeated three times, and the average value was taken as the measured value of MFR. The results are shown in Table 1.

[0171] (Measurement of Heptane Insoluble Matter (HI)) For each resin, a measurement sample of about 3 g was prepared by press molding into a size of 10 mm × 35 mm × 0.3 mm. Next, about 150 mL of heptane was added, and Soxhlet extraction was performed for 8 hours. The heptane insoluble matter was calculated from the sample masses before and after extraction. The results are shown in Table 1.

[0172] (Measurement of Ash Content) For each resin in the form of raw resin pellets, the ash content was measured by the following measurement method. That is, about 200 g of the sample was weighed, transferred to a platinum dish, and heated at 800°C for 40 minutes to be ashed. The ratio (ppm) of the ash content was measured from the obtained ash residue. The results are shown in Table 1.

[0173] (Physical Property Values of Polypropylene Resin)

[0174]

Table 1

[0175] Manufacture of a biaxially stretched polypropylene film <Examples 1 to 6, and Comparative Example 1> (Two Components: Linear Homogeneous PP Resin + Linear Homogeneous PP Resin) The above-described Resin A and Resin B were dry-blended. The mixing ratio was (Resin A):(Resin B) = 75:25 by mass ratio.

[0176] Next, using the dry-blended resin, after melting at a resin temperature of 270 °C, it was extruded using a T-die and wound around a metal drum maintained at a surface temperature of 98 °C to solidify it. Thereby, a cast sheet with a thickness of 115 μm was produced. At this time, the cast sheet was produced while pressing the melt-extruded resin composition against the metal drum with an air knife. The obtained unstretched cast sheet was kept at a temperature of 146 °C, passed between rolls with a speed difference, stretched 5 times in the flow direction at a stretching speed of 67300% / second, and immediately cooled to room temperature. Subsequently, the stretched film was led to a tenter, stretched 10 times in the width direction at a stretching speed of 335% / second at a temperature of 155 °C, and then subjected to relaxation and heat setting. Next, corona discharge treatment was performed in the atmosphere at a treatment speed of 25 W·min / m 2 on the film surface (the side in contact with the metal drum), and then wound up and subjected to aging treatment in an atmosphere of about 30 °C. Thereby, a biaxially stretched polypropylene film with a thickness of 2.3 μm was obtained.

[0177] <Example 7 and Comparative Examples 2 and 3> (1 component: linear homopolymer PP resin) Instead of using the resin obtained by dry-blending Resin A and Resin B, a biaxially stretched polypropylene film was obtained in the same manner as in Examples 1 to 6 and Comparative Example 1, except that only the above-described Resin C was used.

[0178] <Examples 8 and 9 and Comparative Example 4> (2 components: linear homopolymer PP resin + long-chain branched PP resin) Instead of dry-blending Resin A and Resin B, the above-described Resin A and Resin D were dry-blended. The mixing ratio was (Resin A):(Resin D) = 99:1 by mass ratio. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Examples 1 to 6 and Comparative Example 1.

[0179] <Examples 10 and Comparative Examples 5 and 6> (4 components: linear homopolymer PP resin + linear homopolymer PP resin + linear homopolymer PP resin + long-chain branched PP resin) Instead of dry blending Resin A and Resin B, Resin A, Resin B, Resin C, and Resin D described above were dry blended. The mixing ratio was (Resin A):(Resin B):(Resin C):(Resin D) = 49:25:25:1 by mass ratio. Otherwise, in the same manner as in Examples 1 to 6 and Comparative Example 1, a biaxially stretched polypropylene film was obtained.

[0180] Manufacture of a film roll after cutting The film was unwound from the roll of the obtained biaxially stretched polypropylene film and cut with a slitter in the width direction. When winding the cut polypropylene film, a fiber-reinforced plastic core with an outer diameter of 176 mm was used, and a winding device equipped with a nip roll was used to wind the polypropylene film while applying surface pressure. The cutting conditions were a speed of 300 m / min, an unwinding tension of 40 N / m, a winding tension of 50 N / m, and a winding surface pressure of 400 N / m. The nip roll used was made of rubber with an outer diameter of 152 mm and a surface hardness of 40°, and the width (W f ) was 620 mm, the length (L f ) was 75,000 m, and the weight (M f ) was 33.60 kg, and a biaxially stretched polypropylene roll (cut film roll) was finished. The film during winding was visually observed to confirm that no wrinkles occurred. Also, the end face of the obtained cut film roll was observed to confirm that no deviation of 2 mm or more occurred. Also, for the cut film roll, the density (P f ) of the polypropylene film was measured with a densitometer (manufactured by Shimadzu Corporation, product name: Dry Automatic Densitometer AccuPyc II 1340), and the result was 0.91 g / cm 3 .

[0181] Manufacture of a metallized film On one side of the biaxially stretched polypropylene film of the obtained cut film roll, a vapor deposition device (manufactured by ULVAC, product name: Winding Type Vacuum Deposition Device EWE-060) was used, with a cooling roll temperature of -22°C, a voltage-speed ratio per unit width of the cooling roll of 0.32 V·min / m 2 , and a discharge amount of 2.5 W·min / m 2Under the conditions of [[ID=]], a special vapor deposition pattern margin and an insulating margin for imparting film capacitor security to the film roll after cutting were formed, and aluminizing was performed so that the surface resistivity of the metal film became 20 Ω / sq, thereby manufacturing a metallized film.

[0182] Characteristic evaluation of the metallized film (Stress and elongation with respect to stress when winding the metallized film) The stress and elongation with respect to stress when winding the metallized film were measured in accordance with JIS K-7127 (1999). The samples used for the measurement were cut out from the roll. The size of the sample was 200 mm in the MD direction (Machine Direction) of the roll and 15 mm in the orthogonal direction (width). After cutting out the sample, a tensile test was conducted using a tensile-compression tester (manufactured by Minebea Co., Ltd.) under the test conditions of a measurement temperature of 23°C, a chuck distance of 100 mm, and a tensile speed of 200 mm / min. Next, the stress (unit: MPa) and elongation with respect to stress (unit: %) when winding the film were determined by automatic analysis using the data processing software built into the same tester.

[0183] Manufacture of a capacitor <Examples 1 to 6 and Comparative Example 1> (Two components: linear homo-PP resin + linear homo-PP resin) The metallized film was slit into small rolls with a width of 30 mm. One small roll with an insulating margin (length in the width direction: 2 mm) on the left side when viewed from the unwind side and one small roll with an insulating margin (length in the width direction: 2 mm) on the right side when viewed from the unwind side were used. The two were combined so that the electrode extraction part of each protruded beyond the insulating margin of the small roll of the other metal layer-integrated polypropylene film, wound, and the element was prepared and pressed for flattening treatment. Note that winding (element winding) was performed using an automatic winding machine 3KAW-N2 type manufactured by Kaito Seisakusho Co., Ltd. The combined metallized film was adjusted to the stress during winding shown in Table 1 and wound 2566 turns under the conditions of a winding shaft diameter of 20 mm, a contact pressure of 280 gf, and a winding speed of 4 m / s.

[0184] Here, the winding length L of the first of the two stacked metallized filmsc1 is the product of the circumferential length and the number of rotations of the transport roll (diameter 20 mm) of the first metallized film of the automatic winder 3KAW-N2 type, and also the winding length L of the second metallized film stacked in two layers c2 was obtained from the product of the circumferential length and the number of rotations of the transport roll (diameter 20 mm) of the second metallized film of the automatic winder 3KAW-N2 type. The number of rotations was measured non-contact using a digital hand tachometer HT-5500 manufactured by Ono Sokki. Next, metal spraying was performed on the element end face of the flattened element under the conditions of a feed rate of 20 mm / s, a spraying voltage of 21 V, and a spraying pressure of 0.4 MPa, and a film electrode extraction part was formed to a thickness of 0.6 mm to 0.7 mm

[0185] The element with the film electrode extraction part formed was heat-treated in a vacuum atmosphere at 120 °C for 15 hours using a vacuum thermostat to be thermally cured. Thus, a flat film capacitor was manufactured

[0186] <Examples 7 to 10, and Comparative Examples 2 to 6> Instead of winding 2566 turns under the conditions of a winding shaft diameter of 20 mm, a contact pressure of 280 gf, and a winding speed of 4 m / s by adjusting the stress during winding shown in Tables 4 to 6, the stress during winding shown in Table 1 was adjusted, and winding was performed 2861 turns under the conditions of a winding shaft diameter of 24 mm, a contact pressure of 280 gf, and a winding speed of 4 m / s. Otherwise, flat film capacitors were manufactured in the same manner as in Examples 1 to 6 and Comparative Example 1

[0187] For each example and comparative example, various characteristics were evaluated under the following measurement conditions

[0188] Characteristic evaluation (Cross-sectional area porosity) The cross-sectional area porosity C of cross-section 13 of the capacitor (element) shown in Fig. 1 p was determined from the following formula (1) P c =(S c -S0) / Sc×100(%)(1) In formula (1), S cis the measured value of the area of the cross-section 13 of the capacitor element, and S0 is the theoretical area when it is assumed that there is no gap in the capacitor element. The theoretical area S0 is obtained by the following formula (2). S0 = L c × T f (2) In formula (2), L c is the total winding length of the element, and the total winding length of the element is obtained by the following formula (3). L c = L c1 + L c2 (3) In formula (3), L c1 is the winding length of the first metallized film in the double-layered metallized film, and L c2 is the winding length of the second metallized film in the double-layered metallized film. T f is the weight thickness of the polypropylene film used for the capacitor element. Strictly speaking, it is better to use the weight thickness of the metallized film. However, since the thickness of the vapor-deposited metal layer is on the order of nm and is almost equal to the thickness of the polypropylene film, it can be replaced with the weight thickness of the polypropylene film. T f is obtained by the following formula (4). T f = M f / (W f × L f × P f (4) In formula (4), M f is the weight of the polypropylene film, W f is the width of the polypropylene film, L f is the length of the polypropylene film, and P f is the density of the polypropylene film.

[0189] Note that the above measured value S cIt was measured by the following measurement method. That is, two needle true arcs MKO-4F manufactured by Kyushu Organ Needle Co., Ltd. were used, and the shape of cross-section 13, which is the middle of both end faces of the capacitor element and a plane parallel to both end faces, was molded by sandwiching it from both directions with two needle true arcs MKO-4F. Next, two needle true arcs MKO-4F that had been molded were placed on the measurement surface of the image dimension measuring instrument IM-8030 manufactured by Keyence Corporation. After arranging them so as to reproduce the molded shape, the area of cross-section 13 of the capacitor element was measured. At the time of measurement, it was carried out under the conditions shown in the parameter setting table 2 of the image dimension measuring instrument IM-8030 in accordance with the external shape of the capacitor element in advance. Also, in the above measurement method, as the area parameters of element setting, the width was 45.0000 and the height was 70.0000, but these should be appropriately set according to the shape of the capacitor element.

[0190]

Table 2

[0191] (Capacitance and Insulation Resistance Measurement Method) The capacitance (C) and insulation resistance (IR) were measured by the following method.

[0192] Capacitance (C) The 4-terminal probe 9140 was attached to the LCR high tester 3522-50 manufactured by Hioki E.E. Corporation. The two terminals (lead wires) of the capacitor were pinched with the 4-terminal probe 9140, and an AC voltage of 0.1V and 1kHz was applied by the built-in power supply of the LCR high tester 3522-50. When the display value became stable, the capacitance value was read. For the measurement conditions other than those described here, it conformed to "4.2.2 Capacitance" of JISC5101-16:2009.

[0193] Insulation resistance (IR) A shielding box SME-8350 was connected to the Megger DSM8104 manufactured by Hioki Electric Co., Ltd. A capacitor was placed inside the shielding box, and a DC voltage of 500 V was applied. The insulation resistance value at the time when 1 minute had elapsed was read. Regarding the measurement conditions other than those described here, they conformed to "4.2.4 Insulation Resistance" in JIS C5101-16:2009.

[0194] (Life test: Screening test) Regarding the above flat film capacitor, lead wires were soldered to the element end faces and sealed with epoxy resin. The epoxy resin was cured by heating at 90 °C for 2.5 hours and then further heating at 120 °C for 2.5 hours. The capacitance of the capacitor after epoxy resin sealing was 100 μF (±3 μF) for Examples 1 to 6 and Comparative Example 1, and 130 μF (±3 μF) for Examples 7 to 10 and Comparative Examples 2 to 6. The capacitor after epoxy resin sealing was placed in an environment of 105 °C, and a voltage of 325 V / μm was applied for 1000 hours.

[0195] <Capacitance change rate> The change rate of capacitance before and after the test was calculated according to the following formula. Capacitance change rate (%) = {[(Capacitance after the test) - (Capacitance before the test)] / (Capacitance before the test)} × 100 Based on the calculated capacitance change rate, evaluation was performed according to the following evaluation criteria. Note that D evaluation was excluded because there was a high possibility of short circuit failure during the severe test. A: -15% or more (Judgment: Continue the severe test) D: Less than -15% (Judgment: Stop the test)

[0196] <CR product> The product of the measured capacitance (C) and the insulation resistance (IR) was calculated and taken as the CR product. Based on the calculated CR product, evaluation was performed according to the following evaluation criteria. Note that D evaluation was excluded because there was a high possibility of short circuit failure during the severe test. A: 10000 F·Ω or more (Judgment: Continue the test) D: Less than 10000 F·Ω (Judgment: Stop the test)

[0197] Based on the evaluation of the CR product and the evaluation of the capacitance change rate, the long-term durability (life test) at high temperature was judged according to the following criteria. If the judgment is to continue the test, it is judged that there is no problem in actual use. Test continuation: The evaluations of both the CR product and the capacitance change rate are to continue the test. Test termination: The evaluation of at least one of the CR product and the capacitance change rate is to terminate the test.

[0198] (Severe test) The capacitors that received an A evaluation in the life test were placed in an environment of 105 °C, and a voltage of 370 V / μm was applied for 48 hours.

[0199] <CR product> The product of the measured capacitance (C) and the insulation resistance (IR) was calculated as the CR product. Based on the calculated CR product, evaluations were made according to the following evaluation criteria. If the evaluation is D or above, it is evaluated that there is no problem in actual use, and an E evaluation means that there is no withstand voltage property at high temperature and no long-term durability at high temperature. A: 5400 F·Ω or more B: 5000 F·Ω or more and less than 5400 F·Ω C: 4600 F·Ω or more and less than 5000 F·Ω D: 4200 F·Ω or more and less than 4600 F·Ω E: Less than 4200 F·Ω

[0200] <Capacitance change rate> The change rate of the capacitance before and after the test was calculated according to the following formula. Capacitance change rate (%) = {[(Capacitance after the test) - (Capacitance before the test)] / (Capacitance before the test)} × 100 Based on the calculated capacitance change rate, evaluations were made according to the following evaluation criteria. If the evaluation is D or above, it is evaluated that there is no problem in actual use, and an E evaluation means that there is no withstand voltage property at high temperature and no long-term durability at high temperature. A: -21% or more B: -23% or more and less than -21% C: -26% or more and less than -23% D: -30% or more and less than -26% Less than -30%

[0201] The results of the above characteristic evaluations of the examples and comparative examples are shown in Tables 3 to 6.

[0202] [Table 3]

[0203] [Table 4]

[0204] [Table 5]

[0205] [Table 6] [Explanation of Symbols]

[0206] 10: Capacitor element 11, 12: End faces 13: Cross section 20: Metallized film 21: Metal layer 21a: Metal vapor deposition layer 21b: Heavy edge part (electrode extraction part) 22: Polypropylene film 23: Insulating part 1: Metallized film 1R: Metallized film roll 2: Biaxially oriented polypropylene film 2a: Vapor deposition surface 2b: Cooling roll contact surface 2R: Biaxially oriented polypropylene film roll 101: Dielectric film supply part 102: Insulating margin formation part 103: Special vapor deposition pattern margin formation part 103d: Plate roll 104: Vapor deposition part 104a: Metal vapor generation section 104b: Metal vapor generation section (for generating electrode extraction section) 104c: Cooling roll 105: Electrostatic removal section 105a: DC magnetron discharge electrode 105b: DC magnetron discharge electrode 105c: DC magnetron discharge electrode 105d: DC magnetron discharge electrode 106: Metallized film winding section

Claims

1. A capacitor comprising a pair of metallized films, each having a metal layer on one side of a polypropylene film, stacked and wound together so that the metal layer and the polypropylene film are alternately laminated, The metallized film has an elongation of 1.6% or less at a stress of 44 MPa or less, The area porosity of a cross section parallel to both end faces at the middle of both end faces of the capacitor is 5.5% or less. A capacitor characterized by:

2. 2. The capacitor according to claim 1, wherein the area porosity of a cross section parallel to both end faces of the capacitor at the midpoint between the end faces is 4.5% or less.

3. 3. The capacitor according to claim 1, wherein the area porosity is 0.1 to 4.5%.

4. 3. The capacitor according to claim 1, wherein the polypropylene film has a thickness of 1 to 6 μm.

5. A method for manufacturing a capacitor, comprising: a step 1 of stacking a pair of metallized films, each having a metal layer on one side of a polypropylene film, so that the metal layer and the polypropylene film are alternately laminated, and winding the stacked films under a stress of 44 MPa or less; the metallized film has an elongation of 1.6% or less in response to stress when wound; The area porosity of a cross section parallel to both end faces at the middle of both end faces of the capacitor is 5.5% or less. A manufacturing method characterized by:

6. The manufacturing method according to claim 5, wherein the area porosity of a cross section parallel to both end faces, midway between both end faces of the capacitor, is 4.5% or less.

7. 7. The manufacturing method according to claim 5, further comprising, after step 1, step 2 of forming a pair of metallikon electrodes on both end surfaces of the capacitor.

8. The method according to claim 5 or 6, wherein the polypropylene film has a thickness of 1 to 6 μm.

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