Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
  • B32B15/085—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyolefins
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
  • C08L23/12—Polypropene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L53/00—Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G4/00—Fixed capacitors; Processes of their manufacture
  • H01G4/002—Details
  • H01G4/018—Dielectrics
  • H01G4/06—Solid dielectrics
  • H01G4/14—Organic dielectrics
  • H01G4/18—Organic dielectrics of synthetic material, e.g. derivatives of cellulose
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G4/00—Fixed capacitors; Processes of their manufacture
  • H01G4/32—Wound capacitors

Definitions

• the present invention relates to a biaxially oriented polypropylene film that is particularly suitable for use in film capacitor applications.
• the film In order to use a film as a dielectric for film capacitors in the above fields, it is important that the film has excellent heat resistance (dimensional stability, etc.) at the operating temperature and stable electrical performance (voltage resistance, etc.) in a temperature range 10°C to 20°C higher than the operating temperature. In addition, when considering future applications for power semiconductors using silicon carbide (SiC), it is said that the operating temperature of film capacitors will become even higher, and it is estimated that the requirements for heat resistance will also increase.
• SiC silicon carbide
• polypropylene film which is relatively excellent in heat resistance and voltage resistance among polyolefin films, is used as the dielectric of film capacitors, but as described in Non-Patent Document 1, the upper limit of the operating temperature of polypropylene film is said to be about 110°C.
• films for film capacitors are also required to have improved dielectric breakdown voltage in high-temperature environments exceeding 110°C. In other words, it has been extremely difficult for conventional polypropylene films to stably maintain voltage resistance in such temperature environments.
• a laminate has been proposed in which one layer is a cyclic olefin resin layer with a glass transition temperature exceeding 130°C and the other layer is a polypropylene resin layer, and these layers are laminated alternately (for example, Patent Document 1).
• Such a laminate has a layered structure in which two types of layers with different relative dielectric constants are alternately stacked, and therefore can maintain a large capacitance while having excellent heat resistance and voltage resistance.
• films have been proposed that have improved processability by co-extrusion and co-stretching when forming a laminate of cyclic olefin resin and polypropylene resin (e.g., Patent Documents 2 and 3). Furthermore, a film has been proposed that has improved thermal dimensional stability in high-temperature environments by blending cyclic olefin resin and polypropylene resin, forming a film, and biaxially stretching the film (e.g., Patent Document 4).
• Motonobu Kawai "Film Capacitor Advances: From Cars to Energy”
• Nikkei Electronics Nikkei BP, September 17, 2012, pp. 57-62
• the film of Patent Document 1 is not a laminate by coextrusion, but a laminate in which a cyclic olefin resin layer is formed on a polypropylene film by a coating method. Therefore, the cyclic olefin resin layer is easily peeled off, and the processability in a high-temperature environment and the performance and reliability when used as a film capacitor are not sufficient.
• the base layer of the laminated structure of the film of Patent Document 2 is also a single cyclic olefin resin. Therefore, it is difficult to increase the areal stretch ratio, and the voltage resistance in a high-temperature environment is insufficient, so the performance and reliability when used as a film capacitor are not sufficient.
• the base layer of the laminated structure of the film of Patent Document 3 is also a cyclic olefin resin, and an elastomer is contained to improve the stretchability to increase the areal stretch ratio, but the voltage resistance in a high-temperature environment is not satisfactory, and the performance and reliability when used as a film capacitor are not sufficient.
• the film of Patent Document 4 is a film simply made by blending a cyclic olefin resin and a polypropylene resin, so it is difficult to increase the areal stretch ratio when stretched. As a result, the voltage resistance in high-temperature environments was insufficient, and the performance and reliability of the film capacitors was not sufficient.
• the objective of the present invention is to provide a biaxially oriented polypropylene film that has excellent processability, can be used as a dielectric in a film capacitor in a high-temperature environment, and has a long life when used as a film capacitor.
• the present invention is a biaxially oriented polypropylene film that contains resin A having an alicyclic structure in the side chain.
• the present invention provides a biaxially oriented polypropylene film that has excellent processability, can be used as a dielectric for a film capacitor in a high-temperature environment, and has an excellent lifespan when used as a film capacitor.
• Patent Documents 1 to 4 are prone to breakage during processing, resulting in reduced yields, and why their life spans are shortened when used for long periods as dielectrics in film capacitors.
• the films in Patent Documents 1 to 4 contain cyclic olefin resins (hereafter referred to as COPs) that have cyclic olefins in the main chain in order to increase the withstand voltage at high temperatures.
• COPs are generally brittle and have low impact resistance, so it was thought that these films break from the COP parts during processing, or that insulation breakdown progresses from the peeling points caused by impacts, shortening their lifespan.
• the film in the above patent document has improved heat resistance by incorporating COP into polypropylene resin and then stretching it, but the dispersibility of COP in the polypropylene resin and the ability of the COP domain to follow deformation during stretching may be insufficient.
• the stretchability of the unstretched film decreases, and the molecular chains of the polypropylene resin relax when the temperature rises instantaneously, so that when the obtained film is used as a dielectric in a film capacitor, the equivalent series resistance increases and the life of the film capacitor is shortened.
• the biaxially oriented polypropylene film of the present invention is a biaxially oriented polypropylene film that contains resin A having an alicyclic structure in the side chain.
• the biaxially oriented polypropylene film of the present invention will be specifically described below. Note that hereinafter, the biaxially oriented polypropylene film may be simply referred to as a film. Furthermore, when the upper and lower limits of the preferred ranges are stated separately below, the combination of these can be arbitrary.
• the biaxially oriented polypropylene film of the present invention is not a microporous film and does not have many pores.
• the biaxially oriented polypropylene film of the present invention means a biaxially oriented polypropylene film other than a microporous film.
• a microporous film is defined as a film that has a pore structure penetrating both surfaces of the film and has an air permeability of 5,000 seconds/100 ml or less when measured at a temperature of 23°C and a relative humidity of 65% using a B-type Gurley tester according to JIS P 8117 (1998).
• Biaxially oriented polypropylene film refers to a biaxially oriented sheet-like molded product whose main component is polypropylene resin, and the main component refers to a component that is contained in an amount of more than 50% by mass but not exceeding 100% by mass when all components constituting the film are taken as 100% by mass. Note that when a film contains multiple components equivalent to polypropylene resin, even if each component is less than 50% by mass, as long as the total of these components exceeds 50% by mass, polypropylene resin is considered to be the main component.
• Polypropylene resin is a resin that contains more than 50 mol% but not more than 100 mol% propylene units when the total constituent units constituting the resin are taken as 100 mol%, and does not fall under the category of "Resin A having an alicyclic structure in the side chain" described below.
• the biaxially oriented polypropylene film of the present invention contains resin A having an alicyclic structure in a side chain (hereinafter, "resin A having an alicyclic structure in a side chain” may be referred to as “resin A”).
• resin A refers to a resin that contains 0.1 mol % or more and 100 mol % or less of structural units 1 to 4 represented by the following chemical formulas in total, when all structural units constituting the resin are taken as 100 mol %.
• the above structural units contained in the molecular chain of resin A may be any one of 1 to 4 types.
• a structural unit refers to the smallest structural unit having 2 or more carbon atoms contained in the molecular chain of the resin.
• the other structural units that make up resin A are arbitrary, but examples include structural units 5 and 6 represented by the following chemical formulas.
• polyvinylcyclohexane obtained by hydrogenating polystyrene it is preferable to use polyvinylcyclohexane obtained by hydrogenating polystyrene.
• Known types of polyvinylcyclohexane include crystalline isotactic polyvinylcyclohexane obtained by hydrogenating isotactic polystyrene, crystalline syndiotactic polyvinylcyclohexane obtained by hydrogenating syndiotactic polystyrene, and amorphous atactic polyvinylcyclohexane obtained by hydrogenating atactic polystyrene.
• amorphous atactic polyvinylcyclohexane from the viewpoints of ensuring stability and stretchability during molding, increasing the film voltage resistance by stretching so as not to form insulation defects, and increasing the lifespan.
• isotactic polyvinylcyclohexane and syndiotactic polyvinylcyclohexane have melting points higher than 300°C, and if a suitable content (described later) capable of enhancing the effects of the present invention is to be contained, co-extrusion and moldability with polypropylene may be significantly deteriorated, making them undesirable resins from the viewpoints of economy and obtaining the effects of the present invention.
• the biaxially oriented polypropylene film of the present invention is primarily composed of polypropylene resin, and there are no particular limitations on the layer structure as long as it contains resin A, but from the viewpoint of achieving both stretchability and heat resistance, it is preferable for the film to have at least one layer that contains both polypropylene resin and resin A.
• polypropylene resin has better stretchability than resin A, but its heat resistance is inferior. Therefore, by having a layer that contains both polypropylene resin and resin A, a biaxially oriented polypropylene film with excellent stretchability and heat resistance can be obtained.
• the polyolefin film of the present invention preferably has a storage modulus E' in the main orientation axis direction at 145°C of 1.0 x 108 Pa or more and 1.0 x 1013 Pa or less (hereinafter, the storage modulus E' in the main orientation axis direction at 145°C may be simply referred to as "storage modulus E'").
• the storage modulus E' can be measured by a dynamic viscoelasticity method, and the details of the measurement method will be described later.
• the biaxially oriented polypropylene film of the present invention can suppress the increase in equivalent series resistance when the temperature rises instantaneously. Therefore, when such a biaxially oriented polypropylene film is used as a dielectric of a film capacitor, the life of the film capacitor is improved.
• the storage modulus E' in the biaxially oriented polypropylene film of the present invention is more preferably 1.2 x 10 8 Pa or more, even more preferably 5.0 x 10 8 Pa or more, and particularly preferably 5.5 x 10 8 Pa or more.
• the storage modulus of the biaxially oriented polypropylene film of the present invention to 1.0 ⁇ 10 8 Pa or 1.0 ⁇ 10 13 Pa or the above-mentioned preferred range, for example, biaxial stretching of an unstretched polypropylene film containing resin A, or inclusion of a resin A having a glass transition temperature of 140° C. or higher in a suitable amount range described later, are effective.
• the storage modulus E' can be easily adjusted by making the total content of the added resin A satisfy the suitable amount described later.
• the stretching conditions are not particularly limited, but it is preferable to perform biaxial stretching in the range of the glass transition temperature of resin A +3° C. to the glass transition temperature of resin A +50° C. so that the areal stretching ratio is 35 times or more, preferably 40 times or more, more preferably 42 times or more, more preferably 50 times or more, and particularly preferably 55 times or more.
• the main orientation axis direction in the biaxially oriented polypropylene film of the present invention is described below.
• the main orientation axis direction refers to the direction in which the molecular chain orientation of the polypropylene resin is greatest within the film plane.
• stretching is usually performed in the longitudinal and width directions, and generally, the direction of the larger stretching ratio becomes the main orientation axis direction. If the stretching directions (longitudinal and width directions) are specified but the ratio is unknown, the maximum load until breakage is measured for each direction in a tensile test at 23°C described below, and the direction with the larger measured value can be determined as the main orientation axis direction.
• the main orientation axis direction can be easily determined, but in the case of a film whose stretch direction and stretch ratio are unknown, the main orientation axis direction can be determined by the following method. Specifically, a rectangle measuring 50 mm in length and 10 mm in width is cut out to form sample ⁇ 1>, and the direction of the long side of sample ⁇ 1> is defined as 0°. Next, a rectangular sample ⁇ 2> of the same size is taken so that the long side direction is rotated 15° to the right from the 0° direction, and rectangular samples ⁇ 3> to ⁇ 12> are taken by rotating the long side direction of the rectangular sample by 15° each in the same manner.
• each rectangular sample is set in a tensile tester with an initial chuck distance of 20 mm so that the long side direction is the tensile direction (measurement direction), and a tensile test is performed at a tensile speed of 300 mm/min in an atmosphere of 23°C.
• the maximum load until the sample breaks is read, and the value divided by the cross-sectional area (film thickness x width) of the sample before the test is calculated as the stress of the maximum point strength.
• the long side direction of the sample with the largest value is defined as the main orientation axis direction of the biaxially oriented polypropylene film, and the direction perpendicular to this in the film plane is defined as the direction perpendicular to the main orientation axis of the biaxially oriented polypropylene film.
• the resin A is amorphous.
• an amorphous resin By using an amorphous resin, it is possible to increase the stretchability and easily prevent insulation defects from occurring during stretching, which would reduce the lifespan of the film capacitor.
• the fact that the resin A is amorphous can be confirmed by a general measurement method such as powder X-ray diffraction.
• a general measurement method such as powder X-ray diffraction.
• the thickness of the biaxially oriented polypropylene film of the present invention can be adjusted as appropriate depending on the application, but from the viewpoint of improving heat resistance by biaxial orientation, it is preferably 0.5 ⁇ m or more and 60 ⁇ m or less. From the same viewpoint, the upper limit of the thickness of the biaxially oriented polypropylene film is more preferably 40 ⁇ m, and even more preferably 30 ⁇ m.
• the thickness is preferably 10 ⁇ m or less, more preferably 6.0 ⁇ m or less, even more preferably 3.5 ⁇ m or less, and particularly preferably 3.0 ⁇ m or less, from the viewpoint of miniaturizing the film capacitor.
• the thickness of the biaxially oriented polypropylene film is preferably 1.0 ⁇ m or more, more preferably 1.5 ⁇ m or more, from the viewpoint of suppressing film breakage during film formation.
• the thickness of the biaxially oriented polypropylene film 10 ⁇ m or less By making the thickness of the biaxially oriented polypropylene film 10 ⁇ m or less, the effect of improving heat resistance by resin A can be made greater, the voltage resistance in a high-temperature environment can be improved, and the size of the film capacitor element can be reduced.
• the thickness of the biaxially oriented polypropylene film can be measured with a known electronic micrometer, and the details will be described later.
• the thickness of the biaxially oriented polypropylene film can be adjusted by known methods. Specifically, the thickness of the biaxially oriented polypropylene film can be reduced by narrowing the lip gap of the die, reducing the amount of molten resin discharged from the extruder, increasing the rotation speed of the casting drum, increasing the stretch ratio, etc. These methods may be used in combination as appropriate.
• the biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage rate in the main orientation axis direction at 135°C of -10% or more and 5.0% or less.
• a heat shrinkage rate in the main orientation axis direction at 135°C is more preferably 2.5% or less, and even more preferably 1.2% or less.
• film capacitors are generally used in a form in which an exterior resin is filled around the components consisting of a film roll and electrodes that function as a dielectric.
• the heat shrinkage rate in the main orientation axis direction at 135°C can be calculated by heating a biaxially oriented polypropylene film for 10 minutes in an oven kept at 135°C and calculating the length in the main orientation axis direction before and after heating. The detailed measurement method is described later.
• the thermal shrinkage rate in the main orientation axis direction is set at 135°C to between -10% and 5.0% or less, or within the above preferred range, for example, a method is given in which the heat treatment temperature is set to a temperature equal to or higher than the glass transition temperature of resin A, and the relaxation treatment rate, which will be described later, is set to 10% or more.
• the thickness direction length of the domain in the cross section in the main orientation axis direction-thickness direction is 0.0010 ⁇ m or more and 1.0 ⁇ m or less.
• the main orientation axis direction-thickness direction cross section refers to a cross section of the biaxially oriented polypropylene film cut along a plane parallel to the main orientation axis direction and perpendicular to the film surface.
• the "thickness direction length of the domain in the cross section in the main orientation axis direction-thickness direction" may be referred to as the "thickness direction length of the domain".
• the thickness direction length of the domain is 0.50 ⁇ m or less, even more preferable that it is 0.20 ⁇ m or less, and particularly preferable that it is 0.10 ⁇ m or less. From the above viewpoint, the shorter the thickness direction length of the domain is, the better, but from the viewpoint of feasibility, it is preferable that it is 0.0010 ⁇ m or more, and more preferably 0.0050 ⁇ m or more.
• the thickness direction length of the domain can be measured by cutting the biaxially oriented polypropylene film using a microtome method to obtain an ultra-thin slice having a cross section in the main orientation axis direction-thickness direction, and then observing and analyzing the image of the ultra-thin slice using a transmission electron microscope (TEM). The detailed measurement method will be described later.
• TEM transmission electron microscope
• Methods for making the length of the domain in the thickness direction 0.0010 ⁇ m or more and 1.0 ⁇ m or less, or within the above-mentioned preferred range include using a resin A having a cyclic structure in the side chain with one of the preferred structures described above, compounding resin A having a cyclic structure in the side chain with polypropylene in advance (pre-mixing) by stretching at a high ratio, and lowering the extrusion temperature to increase the shear applied in the extruder.
• pre-mixing by stretching at a high ratio
• lowering the extrusion temperature to increase the shear applied in the extruder.
• the biaxially oriented polypropylene film of the present invention preferably has an internal haze of 0.0% or more and 5.0% or less. By keeping the internal haze within this range, the biaxially oriented polypropylene film is less susceptible to dielectric breakdown, and when used as a dielectric in a film capacitor, the life of the film capacitor can be increased. From the above perspective, it is more preferable that the internal haze of the biaxially oriented polypropylene film is 2.0% or less.
• the lower limit of the internal haze of the biaxially oriented polypropylene film is theoretically 0.0%, but considering the viewpoint of enhancing the life improvement effect when made into a film capacitor brought about by the improvement in heat resistance by resin A, it is preferable that it is 0.4%, and more preferably 0.6%.
• the internal haze of the biaxially oriented polypropylene film can be measured by a known haze meter, and the measurement method will be described in detail later.
• the glass transition temperature of the resin A used can be set to 165°C or lower, preferably 160°C or lower, to ensure sufficient fluidity during stretching, and to perform stretching at a temperature higher than the glass transition temperature of resin A.
• the glass transition temperature of resin A can be increased, for example, by increasing the ratio of the aforementioned structural units 1 to 4 in the structural units of resin A, and can be decreased by increasing the ratio of the aforementioned structural unit 6.
• the internal haze of the biaxially oriented polypropylene film can also be reduced by reducing the amount of resin A.
• the biaxially oriented polypropylene film of the present invention it is preferable that at least one resin A has a glass transition temperature of 120°C or higher and 160°C or lower.
• the biaxially oriented polypropylene film contains resin A having a glass transition temperature of 127°C or higher, even more preferable that the biaxially oriented polypropylene film contains resin A having a glass transition temperature of 137°C or higher, and particularly preferable that the biaxially oriented polypropylene film contains resin A having a glass transition temperature of 143°C or higher.
• the glass transition temperature of the resin can be measured in accordance with JIS K7121-1987 as follows. Using a differential scanning calorimeter, 3 mg of the resin is heated from 30° C. to 260° C. at a rate of 20° C./min in a nitrogen atmosphere, then held at 260° C. for 5 minutes, and cooled to 30° C. at a rate of 20° C./min. After being held at 20° C. for 5 minutes, the temperature is raised again from 30° C. to 260° C. at a rate of 20° C./min. The glass transition temperature (Tg) is calculated from the DSC curve obtained during the reheating process according to the following formula.
• the biaxially oriented polypropylene film of the present invention preferably contains 0.2% by mass or more and 45% by mass or less of resin A when the entire biaxially oriented polypropylene film is taken as 100% by mass.
• the content of resin A is calculated by adding up all the resins A.
• the content of resin A is preferably less than 10% by mass, more preferably less than 3.0% by mass. Since there is a trade-off with the heat resistance described above, in order to make a small film capacitor while improving the heat resistance, the content of resin A is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, particularly preferably 1.2% by mass or more, that is, 1.2% by mass or more and less than 3.0% by mass is the most preferable. Furthermore, after setting the content of resin A in these preferable ranges, the storage modulus E' of the film in the main orientation axis direction at 145 ° C.
• a method for controlling the storage modulus within the above-mentioned range while setting the content of resin A within the above-mentioned preferred range there can be mentioned a method of using a highly stereoregular polypropylene resin having a mesopentad fraction of 0.973 or more, and a method of stretching the film so that the areal stretch ratio is preferably 55 times or more, more preferably 60 times or more.
• antioxidants are included among these additives, the type and amount of antioxidant added are important from the viewpoint of long-term heat resistance.
• such antioxidants are sterically hindered phenol-based, and at least one of them is preferably a high molecular weight type with a molecular weight of 500 or more.
• BHT 2,6-di-t-butyl-p-cresol
• the total content of high molecular weight antioxidants with a molecular weight of 500 or more is preferably in the range of 0.1 to 1.0 parts by mass per 100 parts by mass of the total resin. If the amount of antioxidant is too small, the long-term heat resistance may be poor, and if the amount of antioxidant is too large, blocking at high temperatures due to bleed-out of these antioxidants may have an adverse effect on the film capacitor element. From the above perspective, the content of the antioxidant is more preferably 0.2 to 0.7 parts by mass, and even more preferably 0.3 to 0.5 parts by mass, per 100 parts by mass of the total resin.
• each layer contains 0.3 to 0.5 parts by mass of high molecular weight antioxidants with a molecular weight of 500 or more, from the viewpoint of suppressing defects such as fish eyes and improving quality and voltage resistance performance.
• the content of these resins is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, assuming that the entire resin components constituting the biaxially oriented polypropylene film are 100% by mass.
• the biaxially oriented polypropylene film of the present invention can be preferably used as a dielectric for film capacitors.
• the type of film capacitor is not limited here, and specifically, from the viewpoint of electrode configuration, it may be either a laminated film capacitor of metal foil and film, or a metal-vapor-deposited film capacitor. It is also preferably used in oil-immersed type film capacitors impregnated with insulating oil, and dry capacitors that do not use insulating oil at all. However, due to the characteristics of the biaxially oriented polypropylene film of the present invention, it is particularly preferably used as a metal-vapor-deposited film capacitor. From the viewpoint of shape, it may be either a wound type or a laminated type (the film capacitor of the present invention will be described later).
• Biaxially oriented polypropylene film usually has a low surface energy, making it difficult to stably apply metal vapor deposition to it, so it is preferable to perform a surface treatment before vapor deposition in order to improve adhesion to the metal film.
• surface treatments include corona discharge treatment, plasma treatment, glow discharge treatment, and flame treatment.
• the biaxially oriented polypropylene film of the present invention can be obtained by obtaining a polypropylene resin sheet using a resin composition containing polypropylene resin as the main component and resin A, and then biaxially stretching, heat treating and relaxing the sheet.
• the biaxial stretching method any of the inflation simultaneous biaxial stretching method, tenter simultaneous biaxial stretching method and tenter sequential biaxial stretching method may be used, but among them, it is preferable to adopt the tenter sequential biaxial stretching method and the tenter simultaneous biaxial stretching method in terms of controlling the mechanical properties and thermal dimensional stability while increasing the film formation stability, crystalline/amorphous structure, surface properties, and especially the stretch ratio of the present invention. Furthermore, it is more preferable to adopt the tenter sequential biaxial stretching method in terms of bringing the storage modulus at 145°C of the biaxially oriented polypropylene film of the present invention into the above-mentioned preferred range.
• the biaxially oriented polypropylene film of the present invention can be produced through a casting step in which a resin composition containing a polypropylene resin and resin A is melt-extruded onto a support to form a polypropylene resin sheet, and a stretching step in which the polypropylene resin sheet is stretched in the longitudinal and transverse directions, in that order.
• a casting step and a stretching step in this order means that the casting step and the stretching step are present in this order, regardless of whether there are other steps upstream of the casting step, between the casting step and the stretching step, or downstream of the stretching step.
• stretching in the longitudinal and width directions includes both a sequential biaxial stretching method in which stretching in the longitudinal direction is performed followed by stretching in the width direction, and a simultaneous biaxial stretching method in which stretching in the longitudinal and width directions is performed simultaneously.
• the sequential biaxial stretching method is preferred.
• the method for producing the biaxially oriented polypropylene film of the present invention will be described in more detail below.
• the biaxially oriented polypropylene film of the present invention is not limited to that obtained by the method below.
• the biaxially oriented polypropylene film of the present invention it is preferable to compound resin A, polypropylene resin, and an antioxidant in advance in order to improve the dispersion state of resin A and polypropylene resin and increase the dielectric breakdown voltage of the resulting biaxially oriented polypropylene film at high temperatures.
• twin-screw extruders in particular from the viewpoint of achieving a good dispersion state.
• the resin temperature during compounding is preferably within the following temperature range from the viewpoint of improving the dispersion state between the polymer having an alicyclic structure in the side chain and the polypropylene resin and further increasing the dielectric breakdown voltage at high temperatures of the obtained biaxially oriented polypropylene film.
• it is preferable that it is 300°C or less, and more preferably 280°C or less.
• the content of resin A in the resin composition obtained by compounding is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 5% by mass or more, and particularly preferably 9% by mass or more, when the total compounding components are taken as 100% by mass.
• the content of resin A in the resin composition obtained by compounding is preferably 45% by mass or less, and more preferably 40% by mass or less.
• the amount of antioxidant is preferably 0.1 parts by mass or more per 100 parts by mass of the resin component in the resin composition obtained by compounding, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more.
• the upper limit is 1.0 part by mass.
• the resulting biaxially oriented polypropylene film has a high melting point and is suitable for use at high temperatures, which is preferable.
• the resin composition obtained by compounding with polypropylene resin is fed to a single screw extruder after adjusting the amount of resin A to a desired level (preferably 0.2% by mass or more and 45% by mass or less, when the entire resin composition is taken as 100% by mass), and after passing through a filtration filter, is extruded into a sheet from a slit nozzle.
• the extrusion temperature is preferably 200°C or more and 290°C or less.
• the molten sheet extruded from the slit nozzle is then solidified on a temperature-controlled casting drum to obtain a polypropylene resin sheet.
• the biaxially oriented polypropylene film of the present invention preferably has at least one layer containing both polypropylene resin and resin A.
• the biaxially oriented polypropylene film of the present invention has a monolayer structure, it is preferable that the biaxially oriented polypropylene film consists only of a layer containing both polypropylene resin and resin A.
• the biaxially oriented polypropylene film of the present invention has a laminated structure, from the viewpoint of suppressing film rupture when the areal stretch ratio is increased, a two-type two-layer structure of layer A/layer B, a two-type three-layer structure of layer B/layer A/layer B, etc. are preferable.
• At least layer A contains both polypropylene resin and resin A.
• the content of resin A in layer B is less than that of layer A, preferably 3% by mass or less, more preferably 1% by mass or less, when the mass of the entire layer B is 100% by mass, and it is most preferable that layer B does not contain resin A.
• the composition of layer B on both sides may be the same or different.
• resin A may be contained in only one of the multiple layers, or in two or more layers.
• the biaxially oriented polypropylene film of the present invention has a laminated structure, which increases the stretchability, and even if the content of resin A is increased to the preferred range, it can be stretched at a high area ratio within the preferred range, making it easy to significantly increase the life of the film capacitor when used.
• the method for forming the biaxially oriented polypropylene film of the present invention into a laminated structure is not particularly limited, but for example, the following method can be adopted.
• a resin composition obtained by compounding polypropylene resin and resin A is mixed and fed to a single screw extruder, and as the raw material for layer B, only polypropylene resin is fed to another single screw extruder.
• the molten resin is laminated into a two-layer structure of layer A/layer B or a three-layer structure of layer B/layer A/layer B using a feed block method with melt co-extrusion, and this is extruded into a sheet from a slit-shaped die and solidified on a temperature-controlled casting drum to obtain an unstretched polypropylene film.
• the temperature of the casting drum is preferably 10°C or higher and 110°C or lower, and more preferably 10°C or higher and 95°C or lower.
• the molten sheet may be adhered to the casting drum by any of the following methods: electrostatic application, adhesion methods using the surface tension of water, air knife method, press roll method, underwater casting method, air chamber method, etc.
• the air knife method is preferred because it provides good flatness and allows control of surface roughness. It is also preferable to appropriately adjust the position of the air knife so that air flows downstream of the film production to prevent vibration of the film.
• the air temperature of the air knife is preferably 5°C or higher and 130°C or lower.
• the unstretched polypropylene film is biaxially stretched to obtain a biaxial orientation.
• a sequential biaxial stretching method in which the film is stretched sequentially in the longitudinal direction and the width direction, or a simultaneous biaxial stretching method in which the film is stretched simultaneously, may be used.
• the sequential biaxial stretching method will be described below.
• the unstretched polypropylene film is brought into contact with a roll set to a predetermined longitudinal stretching temperature, and stretched in the longitudinal direction at a predetermined ratio.
• the longitudinal stretching temperature is preferably 140°C or higher from the viewpoint of suppressing film breakage, and in particular, when the glass transition temperature of resin A is 140°C or higher, it is preferable to set the temperature to a temperature equal to or higher than the glass transition temperature of resin A from the viewpoint of increasing the compatibility of resin A with polypropylene resin and increasing the high-temperature withstand voltage of the biaxially oriented polypropylene film obtained by increasing the compatibility of resin A with polypropylene resin.
• the longitudinal stretching temperature is preferably 170°C or lower, more preferably 165°C or lower, and even more preferably 160°C or lower.
• the stretch ratio in the longitudinal direction is preferably 3.5 times or more, more preferably 4.0 times or more, and even more preferably 5.0 times or more.
• the stretch ratio in the longitudinal direction is preferably 15 times or less, more preferably 10 times or less.
• the film is introduced into the preheating chamber of the tenter, preheated to a temperature of ⁇ 3°C of the atmospheric temperature of the stretching chamber, and then introduced into the stretching chamber, where the uniaxially oriented polypropylene film is stretched in the width direction while both ends of the film in the width direction are held by clips.
• the atmospheric temperature of the stretching chamber (width direction stretching temperature) at this time is preferably 150°C or higher, more preferably 155°C or higher, and even more preferably 160°C or higher, from the viewpoint of uniformly stretching resin A, which has a high glass transition temperature, and improving the heat resistance of the biaxially oriented polypropylene film.
• the width direction stretching temperature is preferably 190°C or lower, more preferably 185°C or lower.
• the stretching ratio in the width direction is preferably 5.0 times or more, more preferably 6.5 times or more, and even more preferably 8.3 times or more.
• the stretching ratio in the width direction is preferably 20.0 times or less, more preferably 17.0 times or less, and even more preferably 15.0 times or less.
• the areal stretch ratio is preferably 20.0 times or more from the viewpoint of forming the film into a thin film and suppressing the orientation relaxation of the polypropylene resin when the temperature rises instantaneously.
• the areal stretch ratio is the longitudinal stretch ratio multiplied by the widthwise stretch ratio.
• the widthwise stretch ratio refers to the stretch ratio after stretching in the width direction and before the relaxation treatment is performed.
• the areal stretch ratio is more preferably 31 times or more, even more preferably 39 times or more, and particularly preferably 45 times or more.
• the heat treatment temperature is preferably 150°C to 167°C.
• the relaxation treatment rate is preferably 5% or more, more preferably 7% or more, even more preferably 9% or more, particularly preferably 10% or more, and most preferably 15% or more.
• the relaxation treatment is more preferably 25% or less, and even more preferably 18% or less.
• the biaxially oriented polypropylene film After undergoing heat treatment and relaxation treatment, the biaxially oriented polypropylene film is guided to the outside of the tenter, and the clips on both ends in the width direction are released in a room temperature atmosphere. After that, the edges of the film are slit in the winder process, and the biaxially oriented polypropylene film is wound into a roll. Before winding the biaxially oriented polypropylene film, it is preferable to perform a surface treatment such as a corona discharge treatment on at least one side in air, nitrogen, carbon dioxide gas, or a mixture of these gases in order to improve the adhesion of the evaporated metal.
• a surface treatment such as a corona discharge treatment on at least one side in air, nitrogen, carbon dioxide gas, or a mixture of these gases in order to improve the adhesion of the evaporated metal.
• the manufacturing conditions to be considered in order to obtain the biaxially oriented polypropylene film of the present invention are as follows. It is preferable to satisfy all of these manufacturing conditions, but they do not necessarily have to be all present and may be combined as appropriate.
• the preheating temperature before the width direction stretching is the width direction stretching temperature +5°C or more and +15°C or less
• simultaneous biaxial stretching may be adopted.
• - Contains resin A.
• the mesopentad fraction of the main component, polypropylene resin is 0.960 or more. Pre-mixing resin A with polypropylene resin.
• the content of resin A is 0.2% by mass or more and 45% by mass or less when the total components of the biaxially oriented polypropylene film are 100% by mass.
• the area stretch ratio of the biaxial stretching is 20.0 times or more.
• the stretch ratio in the width direction is 5.0 times or more.
• - Heat treatment and relaxation treatment are performed after biaxial stretching.
• the heat treatment temperature after biaxial stretching is 150°C or higher and 190°C or lower.
• the metal film laminated film of the present invention has a metal film on at least one side of the biaxially oriented polypropylene film of the present invention.
• This metal film laminated film can be obtained by providing a metal film on at least one side of the biaxially oriented polypropylene film of the present invention described above.
• the method of forming the metal film is not particularly limited, but a preferred method is to deposit aluminum or an alloy of aluminum and zinc on at least one side of the biaxially oriented polypropylene film to form a metal film such as a vapor deposition film that will become the internal electrode of the film capacitor.
• a metal film such as a vapor deposition film that will become the internal electrode of the film capacitor.
• other metal components such as nickel, copper, gold, silver, and chromium can also be deposited simultaneously with or successively to the aluminum.
• a protective layer can be provided on the vapor deposition film using oil or the like. If the surface roughness of the biaxially oriented polypropylene film differs between the front and back, it is preferable to provide a metal film on the smooth surface side to form a metal film laminated film from the viewpoint of increasing voltage resistance.
• the metal film laminated film of the present invention can be annealed or heat treated at a specific temperature as necessary after the metal film is formed.
• the annealing temperature is preferably in the range of T°C to (T+50)°C, where T [°C] is the temperature at which it is expected to be used, and more preferably in the range of (TgA-50)°C to (TgA+20)°C, where TgA [°C] is the glass transition temperature of resin A used in the metal film laminated film of the present invention.
• at least one side of the metal film laminated film can be coated with a resin such as polyphenylene oxide.
• the film capacitor of the present invention uses the metal film laminated film of the present invention. That is, the film capacitor of the present invention has the metal film laminated film of the present invention.
• the film capacitor of the present invention can be obtained by laminating or winding the above-mentioned metal film laminated film of the present invention by various methods. Examples of preferred manufacturing methods for wound film capacitors are as follows.
• Aluminum is vapor-deposited under reduced pressure on one side of a biaxially oriented polypropylene film.
• the film is vapor-deposited in stripes with margins running in the longitudinal direction.
• a blade is then used to slit the center of each vapor-deposited section and the center of each margin on the surface, producing a tape-like take-up reel with a margin on one side of the surface.
• Two tape-like take-up reels with a left margin and one with a right margin are stacked together and wound so that the vapor-deposited section extends beyond the margin in the width direction, to obtain a wound body.
• one side is vapor deposited in stripes with a margin running in the longitudinal direction, and the other side is vapor deposited in stripes so that the longitudinal margin is located in the center of the vapor deposition area on the back side.
• a blade is cut into the center of the margins on both sides to create a tape-like take-up reel with a margin on one side on each side (for example, if there is a margin on the right side of the front side, there will be a margin on the left side on the back side).
• the resulting reel and one unvapor-deposited laminated film are overlapped and wound in two so that the metallized film extends beyond the laminated film in the width direction to obtain a wound body.
• a method for obtaining the film capacitor of the present invention using the metal layer laminated film of the present invention includes, for example, removing the core material from the wound body produced as described above, pressing the wound body, spraying metallicon on both end faces to form external electrodes, and welding lead wires to the metallicon to form a wound film capacitor.
• Film capacitors have a wide range of applications, including power control units for electric automobiles such as electric vehicles, hybrid vehicles, and fuel cell vehicles, electric aircraft such as drones, railway vehicles, solar power generation and wind power generation, and general home appliances, and the film capacitor of the present invention can also be suitably used for these applications.
• the biaxially oriented polypropylene film of the present invention can be used for various applications such as packaging films, release films, process films, sanitary products, agricultural products, construction products, and medical products, and can be particularly preferably used for applications that include a heating process in film processing.
• the power control unit, electric automobile, and electric aircraft of the present invention will be described below.
• the power control unit of the present invention has the film capacitor of the present invention.
• the power control unit is a system that manages power in electric automobiles, electric aircraft, and the like that have mechanisms that are driven by electricity. By installing the film capacitor of the present invention in the power control unit, it is possible to reduce the size of the power control unit itself, improve its heat resistance, and make it more efficient, resulting in improved fuel efficiency for electric automobiles, electric aircraft, and the like that are equipped with the power control unit of the present invention.
• the electric vehicle of the present invention has the power control unit of the present invention.
• the electric vehicle refers to a vehicle that has a mechanism that is driven by electric power, such as an electric vehicle, a hybrid vehicle, or a fuel cell vehicle.
• the power control unit of the present invention can be made compact, and also has excellent heat resistance and efficiency, so that equipping an electric vehicle with the power control unit of the present invention leads to improved fuel efficiency, etc.
• the electric aircraft of the present invention has the power control unit of the present invention.
• the electric aircraft refers to an aircraft having a mechanism that is driven by electricity, such as a manned electric aircraft or a drone.
• the power control unit of the present invention can be made compact, and also has excellent heat resistance and efficiency, so that equipping an electric aircraft with the power control unit of the present invention leads to improved fuel efficiency, etc.
• ⁇ Tensile test> First, the biaxially oriented polypropylene film was cut into a rectangle of 50 mm length x 10 mm width to obtain sample ⁇ 1>, and the direction of the long side of sample ⁇ 1> was defined as 0°. Next, a rectangular sample ⁇ 2> of the same size was taken so that the long side direction was rotated 15° to the right from the 0° direction, and rectangular samples ⁇ 3> to ⁇ 12> were taken by rotating the long side direction of the rectangular sample by 15° each in the same manner.
• each rectangular sample was set in a tensile tester with an initial chuck distance of 20 mm so that the long side direction was the tensile direction (measurement direction), and a tensile test was performed at a tensile speed of 300 mm/min in an atmosphere of 23°C.
• the maximum load until the rectangular sample broke was read, and the value divided by the cross-sectional area (film thickness x width) of the sample before the test was calculated as the stress of the maximum point strength.
• the long side direction of the sample with the maximum value was determined as the main orientation axis direction of the biaxially oriented polypropylene film.
• Tg Melting point and glass transition temperature of resin
• Tg melting point and glass transition temperature
• the peak temperature of the endothermic peak was taken as the melting point of the resin, and the glass transition temperature (Tg) was calculated according to the following formula.
• the peak temperature of the endothermic peak with the highest peak temperature was taken as the peak temperature of the measurement.
• Glass transition temperature (extrapolated glass transition onset temperature+extrapolated glass transition finish temperature)/2.
• Apparatus and conditions> Apparatus: EXSTAR DMS6100 (Seiko Instruments Inc.) Test mode: tension mode Chuck distance: 20 mm Frequency: 10Hz Distortion amplitude: 10.0 ⁇ m Gain: 1.5 Initial force amplitude: 400 mN Temperature range: -100 to 180°C Temperature rise rate: 5° C./min. Measurement atmosphere: in air Measurement thickness: the film thickness in (1) above was used.
• Thickness length of domain in film main orientation axis direction-thickness direction cross section Using a microtome method, an ultrathin section having a main orientation axis direction-thickness direction cross section of a biaxially oriented polypropylene film was taken (the main orientation axis direction-thickness direction cross section refers to a direction parallel to the main orientation axis direction and perpendicular to the film surface). The taken section was stained with RuO4 , and the cross section was observed using a transmission electron microscope (TEM) under the following conditions to obtain an image. At this time, since resin A was stained blacker than polypropylene-based resins, the following measurements were performed on the black-stained areas as domains.
• TEM transmission electron microscope
• the thickness direction length of the domain was measured by first selecting five domains in the upward direction in order of proximity to the center of the layer containing both polypropylene resin and resin A in the acquired image without moving the field of view from the center of the field of view, and then selecting five domains in the downward direction. The thickness direction length of the selected domains was measured, and the average value was taken as the thickness direction length of the domain of resin A.
• the field of view was moved from one end to the other end to obtain multiple images, and the length of the domain in the main orientation axis direction was determined from the image that was joined together. If 10 domains could not be selected in one field of view, the field of view was moved to another field of view, and observation was continued until the measurement of 10 domains was completed.
• a deposition film A was provided with a deposition pattern having a so-called T-shaped margin (longitudinal pitch (period) of 17 mm, fuse width of 0.5 mm) in which a margin was provided in a direction perpendicular to the longitudinal direction by masking oil, and a deposition film B was provided with no deposition pattern having a T-shaped margin.
• the obtained deposition films A and B were slit, respectively, to obtain deposition reels A and B with a film width of 50 mm (end margin width of 2 mm).
• the deposition reels A and B were alternately overlapped, and the deposition film was wound up using an element winding machine (KAW-4NHB) manufactured by Kaito Seisakusho, Inc., so that the element capacitance after finishing as a film capacitor element was 10 ⁇ F, and metallicon processing was performed. Thereafter, the biaxially oriented polypropylene film was subjected to a heat treatment for 12 hours while reducing the pressure in an atmosphere at ⁇ 5° C., which is the glass transition temperature of the resin A used in the biaxially oriented polypropylene film, and a lead wire was attached to complete the film capacitor element.
• KAW-4NHB element winding machine manufactured by Kaito Seisakusho, Inc.
• D In all cases where T was 125° C., 130° C., and 140° C., the element capacitance after the test was less than 8.5 ⁇ F.
• the thickness of the biaxially oriented polypropylene film produced under the conditions described in the Examples and Comparative Examples was measured at 50 points at 5 cm intervals in the longitudinal direction using a contact-type electronic micrometer (K-312A type) manufactured by Anritsu Corporation under an atmosphere of 23 ° C. and 65% RH.
• the standard deviation of the thickness of the obtained 50 points was taken as ⁇ and the average as Z, and the performance of the film was evaluated according to the following criteria.
• the insulation breakdown voltage test was performed 30 times, and the obtained value was divided by the thickness of the film (measured in (1) above) to convert it to V/ ⁇ m, and the average value of the three values from the fourth point to the sixth point in ascending order from the smallest value out of the total 30 measured values (calculated values) was obtained as the low-voltage breakdown value. From the evaluated low-voltage breakdown value, the scarcity of regions with low withstand voltage was evaluated as follows.
• S means that there is almost no region of low withstand voltage, and it is suitable for use in a small-sized film capacitor with a high rated voltage at high temperatures;
• A, B, and C mean that film capacitors with a low rated voltage can be used in a small-sized form; and
• D means that the film capacitor is not suitable for use because it is too large.
• B The low voltage breakdown value was 200 V/ ⁇ m or more and 240 V/ ⁇ m or more.
• C The low voltage breakdown value was 150 V/ ⁇ m or more and 200 V/ ⁇ m or less.
• D The low voltage breakdown value was lower than 150 V/ ⁇ m.
• Measurement conditions and equipment Bruker DRX-500 ⁇ Measurement nucleus: 13C nucleus (resonance frequency: 125.8MHz) ⁇ Measurement concentration: 10% by weight
• NMR sample tube 5 mm tube Pulse width: 45° (4.5 ⁇ s) Pulse repetition time: 10 seconds
• Peak division was performed using WINFIT software (manufactured by Bruker). At that time, peak division was performed from the peak on the high magnetic field side as follows, and further automatic fitting of the software was performed to optimize the peak division, and the sum of the peak fractions of mmmm and ss (spinning side band peak of mmmm) was taken as the mesopentad fraction (mmmm).
• Raw material (A3) The components were mixed so that the polypropylene resin 1 was 59.5 parts by mass, the raw material (C3) was 40 parts by mass, and the antioxidant was 0.5 parts by mass, and the components were kneaded and extruded in a twin-screw extruder set at 260°C. The strands were then water-cooled and chipped.
• Raw material (A4) The components were mixed so that the polypropylene resin 1 was 59.5 parts by mass, the raw material (C4) was 40 parts by mass, and the antioxidant was 0.5 parts by mass, and the components were kneaded and extruded in a twin-screw extruder set at 260°C. The strands were then water-cooled and chipped.
• Example 1 A resin composition in which each component was mixed so that the raw material (A1) was 30.0 parts by mass, the polypropylene resin 1 was 69.7 parts by mass, and the antioxidant was 0.3 parts by mass was fed to a single-screw extruder.
• the resin composition was melted at a temperature of 250 ° C., and foreign matter was removed with a sintered filter with a cut of 80 ⁇ m whose temperature was adjusted to 250 ° C., and the molten resin composition was discharged from a T-die in the form of a sheet. Thereafter, the molten sheet was adhered to a casting drum whose surface temperature was kept at 90 ° C.
• Comparative Example 4 the film was cooled on a cast drum, and the contact surface side of the film with the casting drum was subjected to a corona discharge treatment in the atmosphere at a treatment intensity of 25 W min/m 2 , to obtain a polypropylene film.

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