Biaxially-stretched polypropylene film, biaxially-stretched polypropylene film for capacitor, metallized film for capacitor, and capacitor

Abstract

Provided is a biaxially-stretched polypropylene film in which dielectric breakdown at a high temperature is suppressed.　The present invention pertains to a biaxially-stretched polypropylene film which contains a polypropylene resin, which exhibits a loss modulus of not less than 318 MPa at 120°C when a dynamic viscoelasticity measurement is performed while increasing the temperature from -60°C to 160°C at 5°C / min., and in which the crystallite size of α-crystals as measured by a wide angle X-ray diffraction method is not more than 12.7 nm. In this biaxially-stretched polypropylene film, dielectric breakdown at a high temperature is suppressed, and a high dielectric breakdown voltage is obtained.

Description

Biaxially oriented polypropylene film, Biaxially oriented polypropylene film for capacitors, Metallized film for capacitors, Capacitors

[0001] The present invention relates to a biaxially oriented polypropylene film, a biaxially oriented polypropylene film for a capacitor, a metallized film for a capacitor, and a capacitor.

[0002] Biaxially oriented polypropylene films containing polypropylene resins have excellent electrical properties, such as high voltage resistance and low dielectric loss, as well as high moisture resistance. Utilizing these properties, biaxially oriented polypropylene films are preferably used in electronic and electrical devices, for example, as dielectric films for capacitors, such as filter capacitors and smoothing capacitors, for high-voltage capacitors, various switching power supplies, converters, inverters, etc.

[0003] Biaxially oriented polypropylene films have also begun to be used as capacitors for inverter power supply devices that control the drive motors of electric vehicles and hybrid vehicles, for which demand has been increasing in recent years. In particular, capacitors used in automobiles are constantly exposed to high temperatures, so they are required to have reduced dielectric breakdown even at high temperatures and to function stably as capacitors. From this perspective, improving the performance of biaxially oriented polypropylene films is extremely important, and research into modifying polypropylene resins is currently being actively conducted.

[0004] For example, Patent Document 1 proposes a polypropylene film having a tan δ of 0.25 or less in the main orientation direction at 150° C. and a Young's modulus of 50 MPa or more in the direction perpendicular to the main orientation at 130° C. Such a polypropylene film is said to be excellent in heat resistance, mechanical strength, and quality.

[0005] International Publication No. 2022 / 210693

[0006] Incidentally, the polypropylene film described in Patent Document 1 is controlled so that the loss modulus E in the direction perpendicular to the main orientation at 0°C is small from the viewpoint of quality, and in particular, the loss tangent tanδ (loss modulus ÷ storage modulus) at high temperatures is small, thereby suppressing the movement of molecular chains and thereby improving the heat resistance of the film.

[0007] However, the inventors have conducted studies and found that if the loss modulus (particularly the loss modulus at high temperatures) is too small, the dielectric breakdown in a high-temperature environment is likely to decrease, and that a polypropylene resin having excellent heat resistance as disclosed in Patent Document 1 does not necessarily suppress dielectric breakdown at high temperatures.

[0008] The present invention has been made in view of the above, and has an object to provide a biaxially oriented polypropylene film in which dielectric breakdown at high temperatures is suppressed.

[0009] As a result of extensive research to achieve the above object, the inventors have discovered that the above object can be achieved by controlling the loss modulus at 120°C and the crystallite size of α crystals within a predetermined range, and have thus completed the present invention.

[0010] That is, the present invention encompasses, for example, the following subjects: Item 1. A biaxially oriented polypropylene film containing a polypropylene resin, wherein the loss modulus at 120°C when dynamic viscoelasticity is measured while increasing the temperature from -60°C to 160°C at a rate of 5°C / min is 318 MPa or more, and the crystallite size of α crystals measured by wide-angle X-ray diffraction is 12.7 nm or less. Item 2. The z-average molecular weight of the polypropylene resin is 8.0 × 10 ５ That's it, 15.0 x 10 ５ Item 3. A biaxially oriented polypropylene film for a capacitor, comprising the biaxially oriented polypropylene film of item 1 or 2. Item 4. A metallized film for a capacitor, having a metal film on one or both sides of the biaxially oriented polypropylene film for a capacitor of item 3. Item 5. A capacitor, comprising the metallized film for a capacitor of item 4.

[0011] The biaxially oriented polypropylene film of the present invention is inhibited from undergoing dielectric breakdown at high temperatures and has a high dielectric breakdown voltage.

[0012]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0013] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. In addition, in this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the lower and upper limits.

[0014] The biaxially stretched polypropylene film of the present invention contains a polypropylene resin and satisfies the following physical properties 1 and 2. Physical property 1: When dynamic viscoelasticity is measured while raising the temperature from -60°C to 160°C at a rate of 5°C / min, the loss modulus at 120°C is 318 MPa or more. Physical property 2: The crystallite size of α crystals measured by wide-angle X-ray diffraction is 12.7 nm or less.

[0015] The biaxially oriented polypropylene film of the present invention satisfies the physical properties 1 and 2, thereby suppressing dielectric breakdown at high temperatures and having a high dielectric breakdown voltage. Therefore, the biaxially oriented polypropylene film of the present invention can be suitably used for capacitor applications. In this specification, "at high temperatures" particularly means an environment of 120°C.

[0016] The biaxially oriented polypropylene film of the present invention can suppress dielectric breakdown at high temperatures by having a loss modulus of 318 MPa or more as defined in Property 1. If the loss modulus is less than 318 MPa, the biaxially oriented polypropylene film of the present invention cannot suppress dielectric breakdown at high temperatures and cannot have a high dielectric breakdown voltage.

[0017] The loss modulus is preferably 320 MPa or more, more preferably 325 MPa or more, even more preferably 330 MPa or more, and particularly preferably 335 MPa or more. The loss modulus is preferably 450 MPa or less, more preferably 430 MPa or less, even more preferably 415 MPa or less, even more preferably 400 MPa or less, and particularly preferably 390 MPa or less.

[0018] The biaxially stretched polypropylene film of the present invention can suppress dielectric breakdown at high temperatures by having an α crystallite size of 12.7 nm or less as defined in Property 2. If the crystallite size exceeds 12.7 nm, the biaxially stretched polypropylene film of the present invention cannot suppress dielectric breakdown at high temperatures and cannot have a high dielectric breakdown voltage.

[0019] The crystallite size is preferably 10.4 nm or more, more preferably 11.0 nm or more, even more preferably 11.5 nm or more, and particularly preferably 12 nm or more.

[0020] In the biaxially oriented polypropylene film of the present invention, the loss modulus defined in Property 1 and the crystallite size defined in Property 2 can be controlled by the type of polypropylene resin contained in the biaxially oriented polypropylene film. In particular, they can be easily controlled by selecting polypropylene A and polypropylene B described below, and can also be controlled by the ratio of polypropylene A and polypropylene B.

[0021] The biaxially oriented polypropylene film of the present invention can be obtained by biaxially stretching one or more polypropylene resins. In the present invention, the polypropylene resins can be selected so that the resulting biaxially oriented polypropylene film satisfies the physical properties 1 and 2.

[0022] In the present invention, examples of polypropylene resins that can be used to satisfy the physical properties 1 and 2 include linear polypropylene and branched polypropylene. Among these, the polypropylene resin preferably contains at least linear polypropylene, or preferably contains both linear polypropylene and branched polypropylene. That is, the polypropylene resin for constituting the biaxially oriented polypropylene film of the present invention may be linear polypropylene alone, or may contain a combination of linear polypropylene and branched polypropylene.

[0023] Hereinafter, the linear polypropylene will be referred to as "polypropylene A," and the branched polypropylene will be referred to as "polypropylene B."

[0024] (Polypropylene A) Examples of polypropylene A include propylene homopolymers such as isotactic polypropylene and syndiotactic polypropylene; copolymers of propylene and ethylene; and ultra-high molecular weight polypropylene. Preferred examples of polypropylene A include propylene homopolymers, and isotactic polypropylene is more preferred, with isotactic polypropylene obtained by homopolymerizing polypropylene in the presence of an olefin polymerization catalyst being even more preferred. Polypropylene A may be a single type or a combination of two or more types. When polypropylene A is a mixture of two or more types of polypropylene, the physical properties of polypropylene A described below (e.g., Mz, MFR, mesopentad fraction, etc.) mean physical properties obtained by measuring the mixture.

[0025] Polypropylene A has a z-average molecular weight (Mz) of 8 x 10 ５ That's it, 15 x 10 ５ In this case, the resulting biaxially stretched polypropylene film is likely to satisfy the physical properties 1 and 2. The z-average molecular weight of polypropylene A is preferably less than 10 × 10 ５ More preferably, it is 11×10 or more. ５More preferably, it is 11.5×10 or more. ５ It is particularly preferable that the value is 14.8×10 or more. ５ More preferably, it is 14.5×10 or less. ５ Even more preferably, it is 14.3×10 or less. ５ It is particularly preferred that:

[0026] The Mz / Mn value (Mn is number average molecular weight) of the polypropylene A is, for example, preferably 15 or more, more preferably 20 or more, even more preferably 22 or more, and particularly preferably 25 or more, and is more preferably 45 or less, even more preferably 40 or less, and particularly preferably 38 or less.

[0027] The weight-average molecular weight (Mw) of polypropylene A is not particularly limited, and is preferably, for example, 250,000 or more and 450,000 or less. The weight-average molecular weight (Mw) of polypropylene A is more preferably 270,000 or more, even more preferably 290,000 or more, and particularly preferably 300,000 or more, from the viewpoint of easily satisfying physical properties 1 and 2, and from the viewpoint of thickness uniformity, mechanical properties, thermo-mechanical properties, etc. of the biaxially oriented polypropylene film, and is more preferably 400,000 or less, even more preferably 380,000 or less, from the viewpoint of stretchability.

[0028] Herein, the weight average molecular weight (Mw), number average molecular weight (Mn), Z-average molecular weight, and molecular weight distribution of polypropylene refer to values ​​measured using a gel permeation chromatograph (GPC) device. More specifically, for example, measurements can be made using a high-temperature GPC measuring instrument with a built-in differential refractive index (RI) system, HLC-8121GPC-HT (trade name), manufactured by Tosoh Corporation. Three TSKgel GMHHR-H(20)HT columns manufactured by Tosoh Corporation are connected and used as GPC columns. The column temperature is set to 140°C, and trichlorobenzene is run as the eluent at a flow rate of 1.0 ml / 10 min, to obtain measured values ​​of Mw and Mn. Alternatively, a calibration curve for the molecular weight M can be created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​can be converted to polystyrene values ​​to obtain Mw, Mn, and Mz.

[0029] The melt flow rate (MFR) of polypropylene A at 230°C under a load of 2.16 kg is preferably, for example, 2.5 g / 10 min or more and 3.8 g / 10 min or less. In this case, the resulting biaxially oriented polypropylene film is likely to be prevented from undergoing dielectric breakdown at high temperatures, and can have a higher dielectric breakdown voltage.

[0030] The melt flow rate (MFR) of polypropylene A is more preferably 2.7 g / 10 min or more, even more preferably 2.9 g / 10 min or more, and particularly preferably 3 g / 10 min or more, and is more preferably 3.7 g / 10 min or less, even more preferably 3.6 g / 10 min or less, and particularly preferably 3.5 g / 10 min or less. The MFR of polypropylene can be measured in accordance with JIS K 7210-1999.

[0031] The mesopentad fraction ([mmmm]) of polypropylene A is preferably 94% or more and 99% or less, more preferably 95% or more and 98.5% or less. In this case, the polypropylene A has a moderately high stereoregularity, which moderately improves the crystallinity of the resin, and the initial voltage resistance and long-term voltage resistance are likely to be improved. In addition, the moderate solidification (crystallization) rate during molding of the cast raw sheet allows the desired stretchability to be obtained.

[0032] The mesopentad fraction ([mmmm]) is an index of stereoregularity that can be obtained by high-temperature nuclear magnetic resonance (NMR) measurement. Specifically, it can be measured using, for example, a high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR) JNM-ECP500 manufactured by JEOL Ltd. The observation nucleus is 13C (125 MHz), the measurement temperature is 135°C, and the solvent used to dissolve the polypropylene resin is ortho-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4 / 1). Measurement by high-temperature NMR can be performed, for example, with reference to the method described in "New Edition Polymer Analysis Handbook, edited by Japan Analytical Chemistry and Polymer Analysis Research Forum, Kinokuniya Shoten, 1995, p. 610."

[0033] The measurement mode by high-temperature NMR was single pulse proton broadband decoupling, pulse width was 9.1 μsec (45° pulse), pulse interval was 5.5 sec, number of accumulations was 4500, and shift reference was CH ３ (mmmm) = 21.7 ppm. The pentad fraction, which indicates the degree of stereoregularity, is calculated as a percentage based on the integral value of the intensity of each signal derived from a combination of five pentads (pentads) consisting of meso (m) pentads arranged in the same direction and racemo (r) pentads arranged in the opposite direction (mmmm, mrrm, etc.). The signals derived from mmmm, mrrm, etc. can be assigned by referring to, for example, "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" or the like.

[0034] The heptane-insoluble fraction (HI) of polypropylene A is preferably 97.0% or more and 98.5% or less. The higher the heptane-insoluble fraction, the higher the stereoregularity of the polypropylene. When the heptane-insoluble fraction is within the above range, the moderately high stereoregularity leads to a moderate improvement in the crystallinity of the polypropylene resin in the polypropylene film, which tends to improve the dielectric breakdown strength at high temperatures and also tends to improve the stretchability. The heptane-insoluble fraction can be measured by adding about 3 g of polypropylene to about 150 mL of heptane and performing Soxhlet extraction for 8 hours, based on the sample mass before and after extraction.

[0035] The melt tension of polypropylene A at 230°C is not particularly limited and is, for example, about 1 g. The melt tension can be measured using a Capillograph 1B manufactured by Toyo Seiki Seisakusho, Ltd., by extruding polypropylene into a string shape under the following conditions: capillary: diameter 2.0 mm, length 40 mm, cylinder diameter: 9.55 mm, cylinder extrusion speed: 20 mm / min, winding speed: 4.0 m / min, temperature: 230°C, and measuring the tension detected on the pulley when the polypropylene is wound around a roller.

[0036] Polypropylene A can be obtained by a known production method, or can be obtained from a commercially available product, etc. Examples of commercially available polypropylene A include "HPT-S" manufactured by Taihan Yuhh Co., Ltd.

[0037] Polypropylene A may contain additives as needed. The "additives" are additives generally used in polypropylene resins, and are not particularly limited as long as the biaxially oriented polypropylene film of the present invention can be obtained.

[0038] Examples of additives include necessary stabilizers such as antioxidants, chlorine absorbers, and ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and colorants. The types of these additives are not particularly limited, and include a wide range of additives contained in known biaxially oriented polypropylene films. Polypropylene A can contain such additives in amounts that do not adversely affect the biaxially oriented polypropylene film of the present invention.

[0039] (Polypropylene B) Polypropylene B is a polypropylene having a branched chain and is a polypropylene other than polypropylene A. Preferred examples of polypropylene B include long-chain branched polypropylenes.

[0040] Examples of long-chain branched polypropylene resins include long-chain branched polypropylene resins obtained by polymerizing propylene using a metallocene catalyst, and long-chain branched polypropylenes obtained by crosslinking modification with peroxides.

[0041] The Mw of polypropylene B is not particularly limited, and is preferably, for example, 250,000 or more and 650,000 or less. From the viewpoint of easily satisfying physical properties 1 and 2 and from the viewpoint of the thickness uniformity, mechanical properties, thermo-mechanical properties, etc. of the biaxially oriented polypropylene film, the Mw of polypropylene B is more preferably 300,000 or more, even more preferably 350,000 or more, and more preferably 600,000 or less, and even more preferably 550,000 or less.

[0042] The Mw / Mn value of polypropylene B is, for example, preferably 2.5 or more, more preferably 2.8 or more, even more preferably 3 or more, and particularly preferably 3.2 or more, from the viewpoint that the biaxially oriented polypropylene film is likely to satisfy physical property 1 and physical property 2, and is preferably 5 or less, more preferably 4.8 or less, even more preferably 4.6 or less, and particularly preferably 4.5 or less.

[0043] The Mz of polypropylene B is 6 x 10 ５ That's it, 25 x 10 ５ In this case, the resulting biaxially stretched polypropylene film is likely to satisfy properties 1 and 2. The z-average molecular weight of polypropylene B is preferably 7 × 10 or less. ５ More preferably, it is 7.5 × 10 or more. ５ More preferably, it is 8×10 or more. ５ It is particularly preferable that the value is 24×10 or more. ５ More preferably, it is 23×10 or less. ５More preferably, it is 19.5×10 or less. ５ It is particularly preferred that:

[0044] The melt tension of polypropylene B at 230°C is not particularly limited and is, for example, 3 g or more and 30 g or less. In this case, the resulting biaxially oriented polypropylene film is likely to satisfy physical properties 1 and 2. The melt tension of polypropylene B at 230°C is preferably 4 g or more, more preferably 5 g or more, and is preferably 28 g or less, more preferably 25 g or less.

[0045] Polypropylene B may be one type alone or a combination of two or more types. When polypropylene B is a mixture of two or more types of polypropylenes, the physical properties of polypropylene B, like those of polypropylene A, are those obtained by measuring the properties of the mixture.

[0046] Polypropylene B can be obtained by a known production method or can be obtained from a commercially available product, etc. Examples of commercially available polypropylene B include MFX8, EX8000, and EX4000 manufactured by Japan Polypropylene Corporation.

[0047] Polypropylene B may contain the above-mentioned additives in an amount that does not adversely affect the biaxially oriented polypropylene film of the present invention.

[0048] (Polypropylene Resin) The polypropylene resin constituting the biaxially stretched polypropylene film of the present invention may be one containing at least one type of polypropylene A without containing polypropylene B, or may be one containing at least one type of polypropylene A and at least one type of polypropylene B. For example, the polypropylene resin may consist of only at least one type of polypropylene A, or may consist of only at least one type of polypropylene A and at least one type of polypropylene B.

[0049] The polypropylene resin may contain other polypropylenes in addition to polypropylene A and polypropylene B, provided that the effects of the present invention are not impaired. "Other polypropylene resins" are resins generally considered to be polypropylene resins, and are not particularly limited as long as the biaxially oriented polypropylene film of the present invention, which is the object of the present invention, can be obtained. The polypropylene resin of the present invention may contain such other polypropylene resins in an amount that does not adversely affect the polypropylene film of the present invention.

[0050] When the polypropylene resin contains at least one type of polypropylene A and at least one type of polypropylene B, the ratio of the two can be adjusted within a range that satisfies physical properties 1 and 2. In order to make the biaxially oriented polypropylene film more likely to satisfy the above-mentioned physical properties 1 and 2, the content of polypropylene A in the polypropylene resin, based on the total mass of the polypropylene resin, can be 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more.

[0051] The polypropylene resin has a z-average molecular weight of 8.0 × 10 ５ That's it, 15.0 x 10 ５ In this case, the resulting biaxially stretched polypropylene film is likely to satisfy the physical properties 1 and 2. The z-average molecular weight of the polypropylene resin is preferably less than 10 × 10 ５ More preferably, it is 11×10 or more. ５ More preferably, it is 11.5×10 or more. ５ It is particularly preferable that the value is 14.8×10 or more. ５ More preferably, it is 14.5×10 or less. ５ Even more preferably, it is 14.3×10 or less. ５ It is particularly preferred that:

[0052] The Mz / Mn value of the polypropylene (Mn is the number average molecular weight) is, for example, preferably 15 or more, more preferably 20 or more, even more preferably 22 or more, and particularly preferably 25 or more, and is more preferably 45 or less, even more preferably 40 or less, and particularly preferably 38 or less.

[0053] The polypropylene resin may contain the additives in an amount that does not adversely affect the biaxially oriented polypropylene film of the present invention.

[0054] The method for preparing the polypropylene resin is not particularly limited. For example, when the polypropylene resin contains polypropylene A and polypropylene B, the polypropylene resin can be prepared by dry mixing or melt mixing these resins. The mixing method is not particularly limited, and examples thereof include a method in which polymer powders or pellets are dry blended using a mixer or the like, and a method in which polymer powders or pellets of polypropylene A and polypropylene B are supplied to a kneader and melt-kneaded. The mixer used for mixing is also not particularly limited, and examples thereof include a single-screw type, a twin-screw type, or a multi-screw type having more than one screw. In the case of a twin-screw or more screw type, either a co-rotating or counter-rotating kneading type can be used.

[0055] In the case of blending by melt kneading, there are no particular limitations on the kneading temperature as long as good kneading can be achieved, and it is generally in the range of 200°C to 300°C, preferably 230°C to 270°C.

[0056] (Biaxially oriented polypropylene film) The biaxially oriented polypropylene film of the present invention can be obtained by biaxially stretching the polypropylene resin. More specifically, the biaxially oriented polypropylene film of the present invention can be obtained by biaxially stretching a cast raw sheet of the polypropylene resin. The cast raw sheet is an unstretched sheet.

[0057] Cast raw sheets can be molded, for example, by known methods. For example, cast raw sheets can be molded using the aforementioned polypropylene resin pellets, powder, or pellets prepared by melt-kneading in advance. Specifically, polypropylene resin is fed into an extruder, the molten resin is passed through a filtration filter, and then heated and melted and melt-extruded from a T-die. Subsequently, the resin is cooled and solidified on at least one metal drum, thereby molding an unstretched cast raw sheet. The heat-melting temperature is, for example, 170°C to 320°C, preferably 200°C to 300°C. The cooling temperature on the metal drum is, for example, 10°C to 140°C, preferably 15°C to 120°C, and more preferably 20°C to 105°C.

[0058] The thickness of the cast raw sheet is not particularly limited as long as the biaxially oriented polypropylene film of the present invention can be obtained, and is usually 0.05 mm to 2 mm, preferably 0.1 mm to 1 mm.

[0059] The biaxially oriented polypropylene film of the present invention can be obtained by biaxially stretching the cast raw sheet. The stretching is performed by biaxially orienting the film in both the longitudinal and transverse directions. The stretching method can be simultaneous or sequential biaxial stretching, with sequential biaxial stretching being preferred.

[0060] An example of a sequential biaxial stretching method is to maintain a cast raw sheet at a temperature of approximately 100 to 180°C (longitudinal stretching temperature), pass it through rolls with a speed difference, stretch it 3 to 7 times (longitudinal stretching ratio) in the machine direction, and immediately cool it to room temperature. After cooling, the stretched film is introduced into a tenter and stretched 3 to 11 times (transverse stretching ratio) in the width direction at a stretching angle of 5 to 17° (transverse stretching angle) and a temperature of 150°C or higher (transverse stretching temperature), followed by relaxation, heat setting, and winding. The wound film can be subjected to an aging treatment in an atmosphere of approximately 20 to 45°C and then cut to the desired product width.

[0061] The transverse stretching angle refers to the angle formed by a straight line Lx connecting one edge Px in the width direction of the stretched film at the start of the transverse stretching process and one edge Py in the width direction (on the same side as Px) of the stretched film at the end of the transverse stretching process, and a straight line Ly starting from Px and parallel to the extrusion direction.

[0062] The biaxially oriented polypropylene film of the present invention can be subjected to corona discharge treatment online or offline after the stretching and heat setting processes in order to improve adhesive properties in subsequent processes such as metal deposition. Corona discharge treatment can be performed using a known method. The atmospheric gas used is preferably air, carbon dioxide, nitrogen, or a mixture thereof.

[0063] The biaxially oriented polypropylene film of the present invention satisfies the physical properties 1 and 2, and therefore exhibits a high breakdown voltage and is inhibited from undergoing breakdown at high temperatures, particularly at 120°C. Therefore, the biaxially oriented polypropylene film of the present invention is suitable for use in capacitors. The thickness of the biaxially oriented polypropylene film of the present invention is not particularly limited and is, for example, 0.1 to 100 μm, preferably 1 to 50 μm.

[0064] The biaxially oriented polypropylene film for capacitors of the present invention is not particularly limited as long as it contains the biaxially oriented polypropylene film of the present invention, and can have, for example, the same configuration as known biaxially oriented polypropylene films for capacitors.

[0065] (Metallized Film for Capacitors) In one aspect, the present invention relates to a metallized film for capacitors (sometimes simply referred to as "metallized film") having a metal film on one or both sides of the biaxially oriented polypropylene film for capacitors described above.

[0066] In the metallized film, the metal film can function as an electrode. Examples of the metal film include metal foil, paper with at least one side metallized, and plastic film with at least one side metallized. The metal can be, for example, a single metal such as zinc, lead, silver, chromium, aluminum, copper, or nickel, a mixture of multiple metals thereof, or an alloy thereof. However, considering the environment, economy, and capacitor performance, zinc and aluminum are preferred.

[0067] The metal film can be formed by, for example, vacuum deposition or sputtering, with vacuum deposition being preferred from the viewpoints of productivity and economy. Examples of vacuum deposition include the crucible method and the wire method.

[0068] From the viewpoint of the electrical characteristics of the capacitor, the film resistance of the metal film is preferably about 1 to 100 Ω / □, more preferably 5 Ω / □ or more, and even more preferably 10 Ω / □ or more. Furthermore, from the viewpoint of safety as a capacitor, the film resistance of the metal film is more preferably 50 Ω / □ or less, and even more preferably 30 Ω / □ or less. The film resistance of the metal film can be measured during metal vapor deposition, for example, by the four-terminal method known to those skilled in the art. The film resistance of the metal film can be adjusted, for example, by adjusting the output of the evaporation source to adjust the amount of evaporation. As a precaution, in this specification, the unit "Ω / □" means "Ω / square."

[0069] When forming a metal film on one side of the film, an insulating margin is formed without vapor deposition for a certain width from one end of the film so that the film will become a capacitor when rolled up. Furthermore, to strengthen the bond between the metallized film and the metallikon electrode, it is preferable to form a heavy edge structure on the end opposite the insulating margin. The film resistance of the heavy edge is usually about 1 to 8 Ω / □, and preferably about 1 to 5 Ω / □. The thickness of the metal film is not particularly limited, and is preferably, for example, 1 to 200 nm.

[0070] There are no particular limitations on the margin pattern, and from the viewpoint of improving the characteristics of the capacitor, such as safety, it may be a pattern including a so-called special margin, such as a fishnet pattern, a T-margin pattern, etc. As a method for forming the margin, any known method can be used without any limitations, such as a tape method in which masking is performed with tape during vapor deposition, or an oil method in which masking is performed by applying oil.

[0071] The metallized film can be processed into the capacitor of the present invention described below by winding the film along its longitudinal direction. That is, two metallized films are stacked and wound together so that the metal-deposited film and the polypropylene film are alternately laminated, and then a pair of metallikon electrodes is formed on both end surfaces by metal spraying to produce a film capacitor.

[0072] The metallized film for capacitors can be used to fabricate capacitors. As long as the capacitor contains the metallized film for capacitors, other configurations of the capacitor are not particularly limited, and the capacitor may have a configuration similar to that of a known capacitor, for example.

[0073] The capacitor includes the biaxially oriented polypropylene film of the present invention, and therefore can have a high breakdown voltage.

[0074] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0075] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0076] Polypropylene A1, polypropylene A2, polypropylene A3, and polypropylene A4 were prepared as linear polypropylenes (polypropylene A), and polypropylene B1, polypropylene B2, polypropylene B3, and polypropylene B4 were prepared as branched polypropylenes (polypropylene B).

[0077] [Polypropylene A] Polypropylene A1: Prime Polymer Co., Ltd. Polypropylene A2: Daehan Yuhwa Co., Ltd. "HPT-S" Polypropylene A3: Borealis Co., Ltd. "HC300BF" Polypropylene A4: Daehan Yuhwa Co., Ltd. "S802M"

[0078] [Polypropylene B] Polypropylene B1: Japan Polypropylene Corporation "MFX8" Polypropylene B2: Japan Polypropylene Corporation "MFX6" Polypropylene B3: Japan Polypropylene Corporation "EX8000" Polypropylene B4: Japan Polypropylene Corporation "EX4000"

[0079] Table 1 shows the measurements of Mn, Mw, Mz, Mw / Mn, Mz / Mn, MFR, heptane insolubles, melt tension and mesopentad fraction of the various polypropylenes A and B described above.

[0080]

[0081] Example 1 A polypropylene resin consisting of 100 parts by mass of polypropylene A1 was fed to an extruder, melted at a resin temperature of 240°C, extruded using a T-die, and solidified by wrapping around a metal drum whose surface temperature was maintained at 23°C to produce an unstretched cast raw sheet having a thickness of approximately 300 μm. The obtained unstretched cast raw sheet was stretched 4.6 times in the machine direction and then 9.4 times in the transverse direction at a temperature of 165°C using a Brückner batch-type biaxial stretching machine KARO IV to produce a biaxially stretched polypropylene film having a thickness of 7.0 μm.

[0082] Example 2 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 99 parts by mass of polypropylene A1 and 1 part by mass of polypropylene B1.

[0083] Example 3 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 99 parts by mass of polypropylene A1 and 1 part by mass of polypropylene B3.

[0084] Example 4 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 97 parts by mass of polypropylene A1 and 3 parts by mass of polypropylene B4.

[0085] Example 5 A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to 100 parts by mass of Polypropylene A2.

[0086] Example 6 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 60 parts by mass of polypropylene A2 and 40 parts by mass of polypropylene A4.

[0087] Comparative Example 1 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 97 parts by mass of polypropylene A1 and 3 parts by mass of polypropylene B1.

[0088] Comparative Example 2 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 97 parts by mass of polypropylene A1 and 3 parts by mass of polypropylene B2.

[0089] Comparative Example 3 A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to 100 parts by mass of Polypropylene A3.

[0090] Comparative Example 4 A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to 100 parts by mass of Polypropylene A4.

[0091] Comparative Example 5 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the polypropylene resin was changed to a mixture of 65 parts by mass of polypropylene A3 and 35 parts by mass of polypropylene A4.

[0092] (Evaluation Method) The z-average molecular weight, loss modulus at 120°C, crystallite size of α crystals, and breakdown voltage at 120°C of the biaxially stretched polypropylene films obtained in each Example and Comparative Example were evaluated by the following methods.

[0093] (z-average molecular weight (Mz)) The z-average molecular weight was measured using a gel permeation chromatograph (GPC) device. Specifically, it was measured using a high-temperature GPC measuring instrument HLC-8121GPC-HT (trade name) with a built-in differential refractive index (RI) system manufactured by Tosoh Corporation. Three TSKgel GMHHR-H (20) HT columns manufactured by Tosoh Corporation were connected and used as the GPC column. The column temperature was set to 140°C, and trichlorobenzene was used as the eluent at a flow rate of 1.0 ml / 10 min to perform the measurement. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured value was converted to a polystyrene value to obtain Mz.

[0094] (Loss Modulus at 120°C) The measurement conditions and procedure for the loss modulus (E'') at 120°C were as follows. A Seiko Instruments Inc. "Viscoelasticity Measuring Apparatus (Model: DMS6100)" was used as the dynamic viscoelasticity measuring instrument. For the measurement, a biaxially oriented polypropylene film was used, which was obtained by biaxially stretching a cast sheet obtained by extruding raw materials having each blending ratio shown in Table 1, and this film was cut into a strip measuring 40 mm in the longitudinal direction and 8 mm in the transverse direction. The measurement was carried out in accordance with JIS-K7244 (1999 edition) under the measurement conditions shown below, and the temperature dependence of the biaxially oriented polypropylene film was measured under the conditions shown below. Test mode: Tensile mode Distance between chucks: 20 mm Vibration frequency: 1 Hz Strain amplitude: 10 μm Minimum tension: 100 mN Tension gain: 1.2 Initial force amplitude: 100 mN Temperature range: -60 to 160°C Heating rate: 5°C / min Measurement atmosphere: In air Measurement thickness: 6.0 or 7.0 μm From the measurement results obtained, the loss modulus (E'') of the biaxially oriented polypropylene film at a temperature dispersion of 120°C (vibration frequency 1H) was determined.

[0095] (α-Crystallite Size) The crystallite size of the α-crystal of the biaxially stretched polypropylene film was measured using wide-angle X-ray diffraction (XRD). The measurement conditions were as follows: Measuring instrument: Rigaku's Distop X-ray diffractometer "MiniFlex300" X-ray generation output: 30 KV, 10 mA Irradiation X-ray: Monochromator monochromatized CuKα ray (wavelength 0.15418 nm) Detector: Scinturation counter Goniometer scanning: 2θ / θ interlocking scanning From the obtained data, the half-width of the diffraction reflection peak of the α-crystal (040) plane was calculated using an analytical computer and the integrated powder X-ray analysis software PDXL, which is included as standard with the instrument. Specifically, the crystallite size was determined from the half-width of the diffraction reflection peak of the α-crystal (040) plane of the biaxially stretched polypropylene film using Scherrer's formula shown below (1): D = K × λ / (β × Cosθ) (1). In the present invention, the shape factor constant K was set to 0.94. Here, D is the crystallite size (nm), K is a constant (shape factor), λ is the X-ray wavelength used (nm), β is the determined half-width, and θ is the diffraction Bragg angle.

[0096] (Breakdown voltage) The dielectric breakdown voltage (BDV) of a biaxially oriented polypropylene film was measured 16 times at room temperature (25°C) and 120°C under the following test conditions using an electrode configuration as specified in JIS C2151 (2006) 17.2.2 (flat electrode method). The applied voltage at the time when a leakage current of the upper limit reference value below was detected during voltage increase was taken as the BDV. The BDV was divided by the film thickness (µm), and the average of 12 points excluding the top 2 and bottom 2 points out of the 16 measurement results was calculated as the dielectric breakdown voltage (V ＤＣ / μm). Test piece: Approximately 150 mm × 150 mm Conditioning of test piece: 30 minutes under atmospheric conditions Power source: Direct current Atmosphere: In air, 120°C Testing machine: DC withstand voltage / insulation resistance tester TOS9213AS manufactured by Kikusui Electronics Co., Ltd. Voltage rise rate: 100 V / s Current detection response speed: MID Upper limit reference value: 5 mA

[0097] Table 2 shows the z-average molecular weight, loss modulus at 120°C, and α crystallite size of the biaxially oriented polypropylene film, as well as the evaluation results of the breakdown voltage at 120°C. Table 2 also shows the preparation conditions of the polypropylene resin constituting the biaxially oriented polypropylene film. Note that the "improvement rate in breakdown voltage at 120°C" in Table 2 refers to the rate of increase in breakdown voltage based on the breakdown voltage of Comparative Example 1. Also, "PP resin" in Table 2 means polypropylene resin, and refers to polypropylene resin A alone or a mixture of polypropylene resin A and polypropylene resin B.

[0098] From Table 2, it was found that a biaxially stretched polypropylene film that satisfies physical properties 1 and 2, i.e., a biaxially stretched polypropylene film that has a loss modulus of 318 MPa or more at 120°C when dynamic viscoelasticity is measured while heating from -60°C to 160°C at a rate of 5°C / min, and has an α crystallite size of 12.7 nm or less as measured by wide-angle X-ray diffraction, is suppressed from undergoing dielectric breakdown at high temperatures and has a high dielectric breakdown voltage.

[0099]

Claims

1. A biaxially oriented polypropylene film containing a polypropylene resin, which has a loss modulus of 318 MPa or more at 120°C when dynamic viscoelasticity is measured while heating from -60°C to 160°C at a rate of 5°C / min, and has an α crystallite size of 12.7 nm or less as measured by wide-angle X-ray diffraction.

2. The z-average molecular weight of the polypropylene resin is 8.0 × 10 ５ That's it, 15.0 x 10 ５ 2. The biaxially oriented polypropylene film of claim 1, wherein the tensile strength is less than 1 / 2.

3. A biaxially oriented polypropylene film for a capacitor, comprising the biaxially oriented polypropylene film according to claim 1 or 2.

4. A metallized film for capacitors, comprising the biaxially oriented polypropylene film for capacitors according to claim 3, having a metal film on one or both sides thereof.

5. A capacitor comprising the metallized film for a capacitor according to claim 4.

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