JP2023132019A - Biaxially oriented polypropylene film - Google Patents

Abstract

To provide a biaxially oriented polypropylene film having high processability and voltage resistance as well as low energy loss.SOLUTION: In a biaxially oriented polypropylene film, if tanδ(0) is a dielectric loss tangent before a voltage impression test and tanδ(174) is a dielectric loss tangent after the voltage impression test of applying electric voltage 174 V/μm, a rate of change ΔD(174) of the dielectric loss tangent before and after the voltage impression test expressed by equation (1) is 1.0 to 3.0: ΔD(174)=tanδ(174)/tanδ(0) ...(1).SELECTED DRAWING: None

Description

The present invention relates to a biaxially oriented polypropylene film that has high voltage resistance under high temperature and high voltage environments when used as a dielectric of a capacitor.

Biaxially oriented polypropylene film has excellent transparency, mechanical properties, and electrical properties, so it is used in a variety of applications including packaging, tape, cable wrapping, and electrical applications such as capacitors.

Among these, in capacitor applications, it is particularly preferably used as a dielectric material for capacitors due to its excellent high withstand voltage characteristics and low loss characteristics. Recently, inverters are being used in various electrical equipment, and as a result, the demand for smaller capacitors and larger capacitors has become stronger. Furthermore, especially in automotive applications (including hybrid cars and electric vehicles), solar power generation, and wind power generation applications, the operating environment is becoming increasingly high temperature (meaning 85°C or higher and 125°C or lower), making capacitors more heat resistant. Demand is also increasing. Therefore, dielectric films are required to be thinner, more heat resistant, and have higher withstand voltage per thickness, and are also required to reduce the dielectric loss tangent tan δ in order to reduce the loss of electrical energy.

Techniques for controlling the dielectric loss tangent tan δ of a film include a method in which a polymerization catalyst is fragmented into nano-sized catalyst fragments and dispersed in polypropylene (for example, Patent Document 1), and a method in which an inorganic dielectric material is added to a base film depending on the thickness of the base film. A method of vapor deposition with a thickness of 0.5% to 10% has been proposed (for example, Patent Document 2). Furthermore, as a technique for controlling the dielectric loss tangent tan δ of a capacitor element, a technique has been proposed in which the thermal shrinkage rate of a biaxially oriented polypropylene film is reduced in order to suppress peeling of the metallicon in a capacitor element (for example, Patent Documents 3 to 5 ).

Special table 2014-531480 publication JP2020-004743A Japanese Patent Application Publication No. 10-156940 Japanese Patent Application Publication No. 2020-124905 Japanese Patent Application Publication No. 2020-124906

However, when the methods described in Patent Documents 1 and 2 are used to control the dielectric loss tangent tan δ of the film, the withstand voltage of the film tends to decrease due to the inclusion of catalyst residues and inorganic dielectrics. Furthermore, when the methods described in Patent Documents 3 to 5 are used to control the dielectric loss tangent tan δ of a capacitor element, it is not possible to suppress heat generation due to energy loss in the film, and it is difficult to control the dielectric loss tangent tan δ of a capacitor element. In this case, it could not be said that the dielectric loss tangent tan δ was sufficiently reduced. Therefore, an object of the present invention is to provide a biaxially oriented polypropylene film that has high processability, high voltage resistance, and low energy loss.

The above-mentioned problems can be achieved by the following. That is, the biaxially oriented polypropylene film of the present invention has the following properties when the dielectric loss tangent before the voltage application test is tan δ (0) and the dielectric loss tangent after the voltage application test applying a voltage of 174 V/μm is tan δ (174). The biaxially oriented polypropylene film is characterized in that the rate of change in dielectric loss tangent ΔD (174) before and after the voltage application test expressed by formula (1) is 1.0 or more and 3.0 or less.
ΔD (174) = tan δ (174)/tan δ (0) ... (1)

According to the present invention, it is possible to provide a biaxially oriented polypropylene film that has a stable higher-order structure and can suppress heat generation to a low level even in a high temperature and high voltage environment when used as a dielectric of a capacitor. Furthermore, the above properties of the biaxially oriented polypropylene film can improve the life of the capacitor.

Hereinafter, the biaxially oriented polypropylene film of the present invention will be explained in more detail. In addition, in the numerical range expressed using "~" below, the upper limit value and the lower limit value shall be included in the range, and the units of the upper limit value and the lower limit value shall be the same.

The biaxially oriented polypropylene film of the present invention is a biaxially oriented polypropylene film obtained by stretching a cast sheet in two orthogonal directions, usually the longitudinal direction and the width direction. In other words, the term "biaxial orientation" as used herein means stretching in two orthogonal directions, usually the longitudinal direction and the width direction. The longitudinal direction refers to the direction in which the film travels during the manufacturing process (in the case of a film roll, the winding direction), and the width direction refers to the direction perpendicular to the longitudinal direction within the plane of the film. In addition, a polypropylene film refers to a sheet-shaped molded product containing polypropylene resin as a main component, and polypropylene resin refers to a resin whose main constituent unit is a propylene unit. The main structural unit refers to a structural unit that is included in more than 50 mol% and less than 100 mol% when all the structural units constituting the resin are 100 mol%.Hereinafter, "main structural unit" can be interpreted in the same way. .

The polypropylene resin in the biaxially oriented polypropylene film of the present invention may include not only propylene homopolymers but also polypropylene copolymers and branched polypropylenes, which will be described later. In addition, in the present invention, the "main component" means a component whose proportion in 100% by mass of all components of the film is more than 50% by mass and 100% by mass or less, more preferably 80% by mass or more and 100% by mass. The content is more preferably 90% by mass or more and 100% by mass or less, particularly preferably 95% by mass or more and 100% by mass or less. Further, as components other than the polypropylene resin in the film, in addition to the resins described below, additives such as antioxidants and lubricants can be mentioned. In addition, when multiple types of polypropylene resins are included in the film, if the total content of all polypropylene resins exceeds 50% by mass, it can be interpreted as containing polypropylene resin as the main component.

As the polypropylene copolymer, a polypropylene copolymer copolymerized with another unsaturated hydrocarbon can be suitably used. Examples of copolymerization components of the polypropylene copolymer include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5- Ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5 -Methyl-2-norbornene and the like.

Furthermore, the biaxially oriented polypropylene film of the present invention may contain a polymer (resin) other than polypropylene resin. As other polymers, unsaturated hydrocarbons other than propylene, such as homopolymers and copolymers whose main constituent units are constituent units derived from the monomers listed as the above-mentioned copolymerization components, can be used. In addition, when the other polymer is a copolymer, propylene can also be used as a copolymerization component.

When the biaxially oriented polypropylene film of the present invention contains a polypropylene copolymer or other polymer, the content is not particularly limited as long as the main component of the film is a polypropylene resin. However, from the viewpoint of withstand voltage characteristics and dimensional stability of the biaxially oriented polypropylene film, the content of these components should be determined based on the propylene It is preferable that the amount of structural units other than the unit is 20 mol% or less in total. In addition, whether or not the content satisfies the above requirements is determined based on the total composition of the entire resin in the biaxially oriented polypropylene film, regardless of the number of components of the polypropylene copolymer and other polymers. The above requirements are satisfied if the total amount of structural units other than propylene units in the unit is 20 mol% or less. From the above viewpoint, the content of the polypropylene copolymer and other polymers is more preferably 1 mol% or less.

Further, the biaxially oriented polypropylene film of the present invention preferably contains linear polypropylene resin A as a main component and contains branched polypropylene resin H. Linear polypropylene resin A and branched polypropylene resin H will be described later.

The biaxially oriented polypropylene film of the present invention has a dielectric loss tangent of tan δ(0) before a voltage application test and a dielectric loss tangent after a voltage application test of 174 V/μm from the viewpoint of improving the life when used in a capacitor. When tan δ (174), it is important that the change rate ΔD (174) of the dielectric loss tangent before and after the voltage application test expressed by the following formula (1) is 1.0 or more and 3.0 or less.
ΔD(174)=tanδ(174)/tanδ(0) (1).

Here, the "voltage application test in which a voltage of 174 V/μm is applied" means a test in which a DC voltage is applied to the film using a flat sample electrode at 174 V/μm for 1 hour, and the dielectric loss tangent before and after the voltage application test is The rate of change ΔD (174) means the rate of change in the dielectric loss tangent due to the application of a voltage of 174 V/μm. Note that the "voltage application test in which a voltage of 130 V/μm is applied" and the "change rate ΔD (130) of dielectric loss tangent before and after the voltage application test" can be similarly defined except that the applied voltages are different.

Hereinafter, the voltage application test in which a voltage of 174V/μm is applied will be simply referred to as "174V/μm voltage application test", and the rate of change in dielectric loss tangent ΔD(174) before and after the voltage application test will be simply referred to as "ΔD(174)". be. Similarly, the voltage application test in which a voltage of 130 V/μm is applied and the rate of change in dielectric loss tangent ΔD (130) before and after the voltage application test are also referred to as "130 V/μm voltage application test" and "ΔD (130)". I can do it. Note that details of the 174 V/μm voltage application test and the 130 V/μm voltage application test will be described later.

Tan δ is an index indicating the degree of dielectric loss, and dielectric loss refers to the loss of part of the electrical energy applied to the dielectric as thermal energy. Generally, the larger the value of tan δ, the larger the ratio of energy lost as thermal energy to the applied electrical energy. When a capacitor is used for a long period of time, the tan δ of the dielectric material may increase due to various causes and a large amount of heat may be generated, which causes a reduction in the life of the capacitor.

By setting ΔD(174) to 3.0 or less, heat generation during use can be suppressed when used as a capacitor, and the life of the capacitor is improved, especially at high temperatures and high withstand voltages. Note that, since the dielectric loss tangent usually increases due to a voltage application test of 174 V/μm, ΔD(174) is substantially 1.0 or more from the viewpoint of feasibility. From the above viewpoint, ΔD(174) is preferably 1.0 or more and 2.7 or less, and more preferably 1.0 or more and 2.6 or less.

A method for adjusting ΔD(174) to 1.0 or more and 3.0 or less or the above preferable range is, for example, by adding a branched polypropylene resin H to a linear polypropylene resin A, molding it into a cast sheet, and then forming this into a cast sheet. A method of longitudinally stretching (stretching in the longitudinal direction) and rapidly cooling is preferably used. When using the above method, ΔD(174) is more likely to decrease by appropriately controlling the amount of branched polypropylene resin H and lowering the quenching temperature. More specifically, it is preferable to adjust the amount of the branched polypropylene resin H to a preferable range described below, and by adopting such an embodiment, the densification of the polypropylene crystal and the homogenization of the higher-order structure progress. , the higher-order structure of the film is stabilized. As a result, it becomes easy to set ΔD(174) to 1.0 or more and 3.0 or less, or the above-mentioned preferable range. Although there are no particular restrictions on the quenching method, for example, a method of rapidly cooling a uniaxially oriented film by passing it through a temperature-controlled conveyance roll while nipping it with a temperature-controlled nip roll is mentioned, and the temperature conditions at this time are as follows: The temperature of the roll is preferably 5°C or more and 15°C or less, more preferably 5°C or more and 13°C or less. The temperature of the nip roll is preferably 5°C or more and 15°C or less, more preferably 7°C or more and 13°C or less.

The biaxially oriented polypropylene film of the present invention has a dielectric loss tangent before and after a voltage application test expressed by the following formula (2), where tan δ (130) is the dielectric loss tangent after a voltage application test in which a voltage of 130 V/μm is applied. It is preferable that the rate of change ΔD(130) is 1.0 or more and 2.7 or less.
ΔD(130)=tanδ(130)/tanδ(0) (2).

By setting ΔD(130) to 2.7 or less, it is possible to suppress heat generation during use when used as a capacitor, and the life of the capacitor is improved, especially at high temperatures and high withstand voltages. Note that since the dielectric loss tangent usually increases due to a voltage application test of 130 V/μm, ΔD(130) is substantially 1.0 or more from the viewpoint of feasibility. From the above viewpoint, ΔD(130) is preferably 1.0 or more and 2.6 or less, more preferably 1.0 or more and 2.5 or less, and even more preferably 1.0 or more and 2.4 or less. .

A method for adjusting ΔD (130) to 1.0 to 2.7 or the above preferable range is, for example, by incorporating a branched polypropylene resin H into a high molecular weight polypropylene resin A, molding it into a cast sheet, and then molding this into a cast sheet. A method of longitudinal stretching and rapid cooling is preferably used. When using the above method, ΔD(130) is more likely to decrease by appropriately controlling the amount of branched polypropylene resin H and lowering the quenching temperature. More specifically, it is preferable to adjust the amount of the branched polypropylene resin H to a preferable range described below, and by adopting such an embodiment, ΔD (130) can be adjusted to 1.0 or more and 2.7 or less or the above. Achieving the desired range It is easy to achieve the above-mentioned preferable range, and the mechanism is as described above. As for the rapid cooling mentioned here, the method and conditions described for the method of setting ΔD (174) to 1.0 or more and 3.0 or less or the above-mentioned preferable range can be suitably employed.

The biaxially oriented polypropylene film of the present invention has a ratio of ΔD(174) to ΔD(130) (ΔD(174)/ΔD(130)) of 1.00 or more from the viewpoint of improving the life when used in a capacitor. It is preferably 1.20 or less. From the above viewpoint, the ratio of ΔD(174) to ΔD(130) (ΔD(174)/ΔD(130)) is more preferably 1.00 or more and 1.18 or less.

By setting ΔD(174)/ΔD(130) to 1.20 or less, heat generation during use can be suppressed when used as a capacitor, and the life of the capacitor is improved, especially at high temperatures and high withstand voltages. Note that as the applied voltage in the voltage application test increases, the rate of change in the dielectric loss tangent may increase but not decrease, so ΔD(174)/ΔD(130) is substantially 1.00 or more.

As a method for adjusting ΔD(174)/ΔD(130) to 1.20 or less or the above-mentioned preferable range, a method similar to the method for adjusting ΔD(174) and ΔD(130) described above can be used.

The biaxially oriented polypropylene film of the present invention preferably has a thickness (t) of 1.0 μm or more and 3.0 μm or less, from the viewpoint of achieving both mechanical strength and improving life when used in a capacitor. From the above viewpoint, the thickness (t) is more preferably 1.5 μm or more and 2.8 μm or less, and even more preferably 1.8 μm or more and 2.6 μm or less. By setting the thickness (t) to 1.0 μm or more, mechanical strength and voltage resistance can be appropriately controlled, and film breakage during film formation and processing can be prevented. On the other hand, by setting the thickness (t) to 3.0 μm or less, the capacitance per volume can be increased when used as a dielectric of a capacitor, and as a result, it can be suitably used as a dielectric of a capacitor.

The biaxially oriented polypropylene film of the present invention is preferably subjected to surface treatment such as corona discharge treatment, plasma treatment, glow treatment, flame treatment, etc. after biaxial stretching in order to improve adhesion to metal during metal vapor deposition. Polypropylene films usually have a low surface energy, and the surface wetting tension, which is an index thereof, is about 30 mN/m, so there is a problem in adhesion to metals. These surface treatments increase the surface energy of the polypropylene film, and by setting the surface wetting tension to 42 mN/m or more and 48 mN/m or less, the adhesion to metals is improved during metal vapor deposition. do. Note that these surface treatments may be used alone or in combination.

Next, the polypropylene resin used in the biaxially oriented polypropylene film of the present invention will be explained. The biaxially oriented polypropylene film of the present invention preferably contains a linear polypropylene resin A as a main component and a branched polypropylene resin H.

The linear polypropylene resin A used in the biaxially oriented polypropylene film of the present invention means an isotactic polypropylene resin. This isotactic polypropylene resin is known as a polypropylene resin commonly used for polypropylene films for capacitors. The linear polypropylene A used in the present invention has a mesopentad fraction (hereinafter referred to as mmmm) of 96.0% or more and 99.5% or less, and a melt flow index (hereinafter referred to as MFR) of 0.5 g/10 minutes or more.3. It is preferable that the melt tension is 0 g/10 minutes or less and the melt tension (hereinafter referred to as MS) is 0.1 g or more and 1.2 g or less. Examples of resins that can be suitably used as the linear polypropylene resin A include "Borclean" (trademark) manufactured by Borealis (such as HB300BF).

The mesopentad fraction (mmmm) of the linear polypropylene resin A is preferably 96.0% or more, more preferably 97.0% or more from the viewpoint of voltage resistance in a high temperature environment. mmmm is an index indicating stereoregularity of the crystal phase of polypropylene resin measured by nuclear magnetic resonance method (NMR method). The higher the numerical value of the polypropylene resin, the higher the crystallinity and melting point, and when formed into a film, the withstand voltage particularly at high temperatures is improved. In order to obtain such polypropylene resin with high stereoregularity, there are methods such as washing the obtained resin powder with a solvent such as n-heptane, selecting the catalyst and/or co-catalyst, and selecting the composition as appropriate. is preferably adopted.

The melt flow rate (MFR) of linear polypropylene resin A is 0.5 g/10 minutes or more and 3.0 g/10 minutes or less when measured in accordance with JIS K 7210-1 (2014). Preferably, it is 1.0 g/10 minutes or more and 2.9 g/10 minutes, more preferably 1.5 g/10 minutes or more and 2.8 g/10 minutes or less. When the MFR of the linear polypropylene resin A is within the above-mentioned preferred range, it has excellent film forming properties, so a biaxially oriented polypropylene film can be stably obtained, and when it is made into a biaxially oriented polypropylene film, it also has excellent withstand voltage characteristics. In order to keep the MFR of the polypropylene resin within the above range, it is preferable to appropriately select the type and composition of the catalyst and the polymerization temperature, or to carry out polymerization in the presence of hydrogen.

The melt tension (MS) of the linear polypropylene resin A is preferably 1.0 g or less. When the MS of the linear polypropylene resin A is 1.0 g or less, the flow characteristics are improved when the resin is melted, and the occurrence of film thickness unevenness and film formation tears can be suppressed. In order to bring the MS of the polypropylene resin within the above range, it is preferable to appropriately select the type and composition of the catalyst and the polymerization temperature, or to carry out polymerization in the presence of hydrogen.

In the biaxially oriented polypropylene film of the present invention, the content of the linear polypropylene resin A may be more than 90% by mass and 99% by mass or less, when the entire polypropylene resin constituting the film is 100% by mass. It is preferably 92% by mass or more and 98% by mass or less, and even more preferably 93% by mass or more and 97% by mass or less. When the content of the linear polypropylene resin A is within the above-mentioned preferred range, the stereoregularity of the biaxially oriented polypropylene film becomes high and the withstand voltage property is excellent.

Next, the branched polypropylene resin H will be explained. The branched polypropylene resin H used in the biaxially oriented polypropylene film of the present invention is a branched polypropylene resin having an MFR of 6.0 g/10 minutes or more and 13.0 g/10 minutes or less, and an MS of 1 .5g or more and 8.0g or less. To obtain such a branched polypropylene resin, there are two methods: using high-energy ionizing radiation on polypropylene resin (for example, Japanese Patent Application Laid-open No. 121704/1983), and reacting polypropylene resin with a specific organic peroxide (for example, , Japanese Patent No. 2869606), a method of reacting a thermally decomposable radical forming agent and an ethylenically-based polyfunctional unsaturated monomer with a polypropylene resin (for example, JP-A-10-330436), a method of using a specific catalyst during polymerization of a polypropylene resin. (For example, JP-A No. 2009-057542) is preferably used. Examples of resins that can be suitably used as the branched polypropylene resin H include "WAYMAX" (registered trademark) manufactured by Nippon Polypropylene Co., Ltd. (EX4000, MFX3, etc.).

The branched polypropylene resin H has a branched structure in its molecular chain. Note that the branched polypropylene resin is a polypropylene resin that has internal trisubstituted olefins at 5 or less positions per 10,000 carbon atoms, and the presence of this internal trisubstituted olefin indicates that protons in the ¹ H-NMR spectrum It can be confirmed by the ratio. The branched polypropylene resin has the function of an α-crystal nucleating agent, and if the amount added is within a certain range, it is possible to form a rough surface due to the crystal morphology. That is, the spherulite size of the polypropylene produced in the cooling process of the melt-extruded resin sheet can be controlled to be small, and a biaxially oriented polypropylene film with excellent voltage resistance properties can be obtained.

The MFR of the branched polypropylene resin H is preferably 6.0 g/10 minutes or more and 13.0 g/10 minutes or less, more preferably 6.5 g/10 minutes or more and 12.5 g/10 minutes or less. , more preferably 7.0 g/10 min % or more and 12.0 g/10 min % or less. When the MFR of the branched polypropylene resin H is within the above range, crystallization of the polypropylene proceeds efficiently and the higher-order structure of the film is stabilized, so that desired dielectric properties (ΔD (174), ΔD (130)) can be achieved. Easy to achieve. In order to keep the MFR of the polypropylene resin within the above range, it is preferable to appropriately select the type and composition of the catalyst and the polymerization temperature, or to carry out polymerization in the presence of hydrogen.

When the MFR of branched polypropylene resin H is MFR (H) and the MFR of linear polypropylene resin A is MFR (A), the difference in MFR between branched polypropylene resin H and linear polypropylene resin A (MFR (H)-MFR(A)) is preferably 5.0 g/10 minutes or more and 10.0 g/10 minutes or less, more preferably 5.5 g/10 minutes or more and 9.5 g/10 minutes or less, More preferably, it is 6.0 g/10 minutes or more and 9.5 g/10 minutes or less. When MFR(H)-MFR(A) is within the above range, crystallization of polypropylene proceeds efficiently and the higher-order structure of the film is stabilized, so desired dielectric properties (ΔD(174), ΔD(130)) are achieved. is easy to achieve. In order to make MFR(H)-MFR(A) within the above range, a combination of linear polypropylene resin A and branched polypropylene resin H is required so that MFR(H)-MFR(A) falls within the above range. Just choose.

The MS of the branched polypropylene resin H is preferably 1.5 g or more and 8.0 g or less, more preferably 2.0 g or more and 7.0 g or less, and even more preferably 3.0 g or more and 6.0 g or less. preferable. When the MS of the branched polypropylene resin H is within the above range, the polypropylene crystal becomes denser and the higher-order structure becomes more homogeneous, and the higher-order structure of the film is stabilized. ΔD(130)) is easily realized.

In the biaxially oriented polypropylene film of the present invention, the content of the branched polypropylene resin H is 1.0% by mass or more and 10% by mass or less when the entire polypropylene resin constituting the film is 100% by mass. The content is preferably 2.0% by mass or more and 8.0% by mass or less, and even more preferably 3.0% by mass or more and 7.0% by mass or less. When the content of the branched polypropylene resin H is within the above preferred range, the polypropylene crystal becomes denser and the higher-order structure becomes more homogeneous, and the higher-order structure of the film is stabilized. ), ΔD(130)).

The biaxially oriented polypropylene film of the present invention may contain various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, an antiblocking agent, and a filler as long as the object of the present invention is not impaired. It is also preferable to contain agents, viscosity modifiers, color inhibitors, etc.

Among the above-mentioned additives, the type of antioxidant and selection of the amount added are important from the viewpoint of long-term heat resistance. That is, the antioxidant is preferably a phenolic one having steric hindrance, and at least one of them is a high molecular weight type having a molecular weight of 500 or more. Specifically, for example, 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4), 1,3,5-trimethyl-2,4,6-tris (3,5-di -t-butyl-4-hydroxybenzyl)benzene (for example, "Irganox" (registered trademark) 1330 manufactured by BASF: molecular weight 775.2), tetrakis[methylene-3(3,5-di-t-butyl-4- Hydroxyphenyl)propionate]methane (for example, "Irganox" (registered trademark) 1010 manufactured by BASF, molecular weight 1177.7) is preferably used alone or in combination. The total content of these antioxidants is preferably 0.03 parts by mass or more and 1.0 parts by mass or less, more preferably 0.1 parts by mass or more and 0.9 parts by mass or less based on the total amount of the polypropylene resin. . When the antioxidant content in the polypropylene resin composition is 0.03 parts by mass or more, the antioxidant effect is easily obtained and long-term heat resistance is easily maintained. On the other hand, when the antioxidant content in the polypropylene resin composition is 1.0 parts by mass or less, high-temperature withstand voltage characteristics can be easily maintained.

The biaxially oriented polypropylene film of the present invention is produced by molding a polypropylene resin composition containing the above-mentioned linear polypropylene resin A as a main component and branched polypropylene resin H into a sheet shape, and then biaxially stretching the polypropylene resin composition. It is preferable to obtain As the method for biaxial stretching, any of the inflation simultaneous biaxial stretching method, tenter simultaneous biaxial stretching method, and tenter sequential biaxial stretching method may be adopted, but from the viewpoint of film forming stability and thickness uniformity, tenter It is preferable to employ a sequential biaxial stretching method. In particular, it is preferable to stretch in the width direction after stretching in the longitudinal direction.

Next, a method for producing a biaxially oriented polypropylene film of the present invention will be described below, but the method is not necessarily limited thereto.

First, the above-mentioned linear polypropylene resin A and branched polypropylene resin H are dry-blended in the above-mentioned preferable ratio, supplied to a single-screw melt extruder, and melt-extruded at a temperature of 200° C. or higher and 260° C. or lower. Next, a filter installed in the middle of the polymer tube removes foreign substances and modified polymers. Then, the molten sheet is discharged from the T-die onto a cast drum, and is cooled and solidified to form a cast sheet.

The temperature of the cast drum is preferably 70°C or more and 110°C or less, more preferably 75°C or more and 105°C or less, and even more preferably 80°C or more and 100°C or less, from the viewpoint of appropriately generating β crystals and spherulites. Even more preferred. By setting the cast drum temperature to 70°C or higher, the amount of β crystals formed in the cast sheet is prevented from decreasing too much, and in order to maintain the slipperiness of the film obtained after biaxial stretching, the film during film formation and processing is It is possible to prevent the occurrence of conveyance wrinkles in the conveyance process and deterioration of the winding appearance of the film roll. On the other hand, by setting the cast drum temperature to 110°C or less, it is possible to prevent excessive formation of β crystals in the cast sheet, and prevent the occurrence of meandering in the film conveyance process during film forming and processing. This makes it easier to prevent the appearance of the roll from deteriorating.

The molten sheet discharged from the T-die lands on the cast drum and is in close contact with the drum for preferably 1.0 seconds or more and 3.0 seconds or less. When the time of close contact is 1.0 seconds or more, the molten sheet is easily solidified, and it is easy to prevent it from breaking in the subsequent stretching process. On the other hand, if the contact time is 3.0 seconds or less, excessive formation of β-crystals in the cast sheet can be prevented, and the occurrence of meandering in the film conveyance process during film formation and processing can be prevented. This makes it easier to prevent the film roll from deteriorating in appearance.

In addition, methods such as electrostatic application method, air knife method, nip roll method, and underwater casting method can be used to bring the molten sheet into close contact with the cast drum. The air knife method is preferred from the viewpoint of controlling the surface properties.

Next, in a longitudinal stretching step, the cast sheet is stretched in the longitudinal direction (longitudinal stretching) to obtain a uniaxially oriented film. Specifically, it is preferable to pass the cast sheet through longitudinal stretching rolls whose temperature is controlled, and to stretch the cast sheet in the longitudinal direction at a predetermined stretching ratio due to the difference in circumferential speed between the rolls. The temperature of the longitudinal stretching rolls is preferably 135°C or higher and 155°C or lower. By setting the temperature of the longitudinal stretching rolls to 135° C. or higher, insufficient heat during longitudinal stretching can be prevented, and film breakage in the longitudinal stretching process can be easily reduced. On the other hand, by setting the temperature of the longitudinal stretching rolls to 155° C. or lower, the orientation of the uniaxially oriented film increases, and the withstand voltage of the biaxially oriented polypropylene film obtained after biaxial stretching tends to improve.

The longitudinal stretching ratio is preferably 4.0 times or more and 7.0 times or less, and more preferably 5.0 times or more and 7.0 times or less. By setting the longitudinal stretching ratio to 4.0 times or more, it is easy to reduce variations in the surface shape of the biaxially oriented polypropylene film obtained after biaxial stretching in the longitudinal direction and the width direction. The withstand voltage of the axially oriented polypropylene film is easily improved. On the other hand, by setting the longitudinal stretching ratio to 7.0 times or less, it is easy to reduce film breakage in the longitudinal stretching process and film tearing in the next transverse stretching process.

In order to obtain the biaxially oriented polypropylene film of the present invention, it is preferable to rapidly cool the uniaxially oriented film immediately after the longitudinal stretching step. Specifically, it is preferable that the uniaxially oriented film immediately after the longitudinal stretching step is subjected to a rapid cooling treatment by passing it through a temperature-controlled transport roll while nipping it with temperature-controlled nip rolls.

The conveyance roll temperature during the cooling treatment is preferably 5°C or more and 15°C or less, more preferably 5°C or more and 13°C or less. By setting the conveyance roll temperature to 5° C. or higher, it is possible to prevent the orientation of the uniaxially oriented film from becoming too high and to suppress film breakage during horizontal stretching, making it easy to maintain mass productivity. On the other hand, by setting the conveyor roll temperature to 15°C or less, the orientation of the film can be prevented from becoming low, and a stable higher-order structure that does not easily change due to voltage application can be easily formed. The characteristics (ΔD(174), ΔD(130)) are easily realized.

The nip roll temperature during the cooling treatment is preferably 5°C or more and 15°C or less, more preferably 7°C or more and 13°C or less. By setting the nip roll temperature to 5° C. or higher, the curling of the cast sheet on the nip rolls caused by the temperature difference between the front and back sides is reduced, which makes it easier to reduce tearing during the stretching process and ensure mass productivity. On the other hand, by setting the nip roll temperature to 15°C or less, the orientation of the film is prevented from becoming low, and a stable higher-order structure that does not easily change due to voltage application is easily formed, and the dielectric properties of the biaxially oriented film of the present invention are (ΔD(174), ΔD(130)) is easily realized.

The pressure of the nip roll during the cooling treatment is preferably 0.30 MPa or more and 0.60 MPa or less, more preferably 0.35 MPa or more and 0.55 MPa or less. By setting the nip roll pressure to 0.30 MPa or more, wrinkles and meandering of the film due to film shrinkage during cooling treatment are suppressed, which makes it easier to reduce tearing during the longitudinal stretching process and ensure mass production. . On the other hand, by setting the nip roll pressure to 0.60 MPa or less, deformation of the film due to pressure can be suppressed, making it easier to reduce breakage in the stretching process and ensure mass productivity.

The cooling treatment time is preferably 0.1 seconds or more and 1.0 seconds or less, more preferably 0.2 seconds or more and 0.9 seconds or less, and even more preferably 0.3 seconds or more and 0.8 seconds or less. preferable. By setting the cooling treatment time to 0.1 seconds or more, the orientation of the film is prevented from becoming low, and a stable higher-order structure that does not easily change due to voltage application is easily formed, which improves the dielectric properties of the biaxially oriented film of the present invention. The characteristics (ΔD(174), ΔD(130)) are easily realized. On the other hand, by setting the cooling treatment time to 1.0 seconds or less, wrinkles and meandering of the film due to film shrinkage during the cooling treatment are suppressed, reducing tearing during the longitudinal stretching process and ensuring mass productivity. becomes easier.

Next, both ends of the uniaxially oriented film in the width direction are held with clips, and stretched in the width direction at a stretching ratio of 8.0 times to 15 times (lateral Stretching) and then heat setting at a temperature of 150° C. or higher and 170° C. or lower and a relaxation rate of 5% or higher and 15% or lower to obtain a biaxially oriented polypropylene film.

Next, the biaxially oriented polypropylene film was subjected to corona discharge treatment in air, nitrogen, carbon dioxide, or a mixture thereof, and then both widthwise ends held with clips were cut and removed. It is wound up as an intermediate product using a winding machine. Finally, the biaxially oriented polypropylene film unwound from the intermediate product is slit to a specific width using a slitter, and wound around a core as a film roll to obtain a roll of the biaxially oriented polypropylene film of the present invention.

The biaxially oriented polypropylene film of the present invention is preferably used as a dielectric for capacitors, but is not limited to the type of capacitor. Specifically, from the viewpoint of electrode configuration, either a foil-wound capacitor or a metal vapor-deposited film capacitor may be used, and it is also preferable to use an oil-immersed type capacitor containing insulating oil or a dry type capacitor that does not use any insulating oil. used. Moreover, from the viewpoint of shape, it does not matter if it is a winding type or a laminated type. 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.

Next, a metal film laminate film using the biaxially oriented polypropylene film of the present invention will be explained. As a method for forming the metal film, a method is preferably used in which a metal such as aluminum is vapor-deposited on at least one side of a biaxially oriented polypropylene film to provide a metal film that will serve as an internal electrode of the film capacitor. At this time, other metal components such as nickel, copper, gold, silver, chromium, and zinc can also be deposited simultaneously or sequentially with the aluminum. Further, a protective layer may be provided on the metal film using oil or the like. The thickness of the metal film is preferably 20 nm or more and 100 nm or less from the viewpoint of the electrical characteristics and safety of the capacitor. Further, for the same reason, it is preferable that the surface resistance value of the metal film is 1 Ω/sq or more and 20 Ω/sq or less. The surface resistance value can be controlled by the metal type and film thickness used.

Next, a film capacitor using the biaxially oriented polypropylene film of the present invention will be explained. A film capacitor has a structure in which metal film laminated films are laminated or wound. An example of a method for manufacturing a wound film capacitor will be described below. First, aluminum is vacuum deposited on one side of a biaxially oriented polypropylene film. At this time, aluminum is vapor-deposited in the form of stripes with margins running in the longitudinal direction of the film. Next, a blade is inserted into the center of each vapor-deposited part and the center of each margin part on the surface to make a slit, thereby producing a tape-shaped take-up reel whose surface has a margin on one side. Two tape-shaped take-up reels with margins on the left or right are wound, one on the left margin and one on the right margin, overlapping each other so that the vapor-deposited part protrudes from the margin in the width direction to create a wound body. get. After the wound body is heat-treated, metallicon is thermally sprayed on both end faces in the width direction to form external electrodes, and lead wires are welded to the metallicon to obtain a wound film capacitor. Film capacitors are used in a wide variety of applications, including vehicles, home appliances (TVs, refrigerators, etc.), general miscellaneous protection, automobiles (hybrid cars, power windows, wipers, etc.), and power supplies. The film capacitor used can also be suitably used for these purposes.

Hereinafter, the present invention will be explained in detail with reference to Examples. In addition, the characteristics were measured and evaluated by the following method.

[Evaluation method of each characteristic]
(1) Mesopentad fraction (mmmm)
A polypropylene resin sample was dissolved in a solvent, and the mesopentad fraction (mmmm) was determined using ¹³ C-NMR under the following conditions (Reference: New Edition Polymer Analysis Handbook, Japan Society for Analytical Chemistry, Polymer Analysis Edited by Research Council, 1995, pp. 609-611).
A. Measurement conditions device: Bruker DRX-500
Measurement nucleus: ^13C nucleus (resonance frequency: 125.8MHz)
Measured concentration: 10wt%
Solvent: benzene/heavy orthodichlorobenzene = mass ratio 1:3 mixed solution Measurement temperature: 130°C
Spin speed: 12Hz
NMR sample tube: 5mm tube Pulse width: 45° (4.5μs)
Pulse repetition time: 10 seconds Data points: 64K
Number of conversions: 10,000 times Measurement mode: complete decoupling
B. Analysis Conditions Fourier transform was performed with LB (line broadening factor) set to 1.0, and the mmmm peak was set at 21.86 ppm. Peak division is performed using WINFIT software (manufactured by Bruker). At that time, we performed peak division as shown below starting from the peak on the high magnetic field side, and then performed automatic fitting using the attached software. After optimizing the peak division, the sum of mmmm peak fractions was determined. The above measurement was performed five times, and the average value was taken as the mesopentad fraction (mmmm) of this sample.
Peak (a) mrrm
(b) (c) rrrm (split as two peaks)
(d)rrrr
(e) mrmr
(f) mrmm+rmrr
(g)mmrr
(h)rmmr
(i)mmmr
(j)mmmm.

(2) Melt flow index (MFR) (unit: g/10min)
It was measured in accordance with JIS K 7210-1 (2014) at a temperature of 230°C and a load of 2.16 kg.

(3) Melt tension (MS) (unit: g)
Using Capillograph 1B manufactured by Toyo Seiki Seisakusho Co., Ltd. (capillary diameter 2.0 mm, capillary length 40 mm, cylinder diameter 9.55 mm), polypropylene resin was heated to 230°C, and molten polypropylene was extruded into a strand at an extrusion speed of 20 mm/min. After that, the tension was measured when the strand was pulled at a speed of 4.0 m/min.

(4) Rate of change in dielectric loss tangent (ΔD) before and after voltage application test
On the film roll corresponding to the center position in the width direction of the master roll, measurements A to F, which will be described later, were carried out in order at 10 points randomly sampled in the longitudinal direction from the center position of the film roll. ΔD was calculated for each measurement position, and the average value of the 10 locations was taken as the ΔD of that sample.

A. Measurement of dielectric loss tangent (tan δ (0)) before voltage application test Dielectric relaxation measurements were performed on the sample taken from the film roll using a Precision LCR meter E4980A manufactured by Agilent Technologies Co., Ltd. at a temperature of 25 ° C. under the following conditions. From the real part (resistance) ε' and imaginary part (reactance) ε' of the obtained complex impedance, the dielectric loss tangent (tan δ = imaginary part ε"/real part ε') at 2000 Hz is calculated and the dielectric value before the voltage application test is calculated. It was defined as tangent (tan δ(0)).
Applied voltage: 2V
Frequency: 20Hz ~ 2MHz
Measurement mode: Cp-D
Time: Long
Average: 16.

B. Voltage application test with a voltage of 130 V/μm In the sample whose dielectric loss tangent (tan δ (0)) was measured before the voltage application test, a flat sample electrode SEM-8310 manufactured by HIOKI Co., Ltd. connected to a DC high voltage power supply ELS19-10K05B1 manufactured by Element Co., Ltd. A voltage was applied for 1 hour at a temperature of 25° C. and a DC voltage of 130 V/μm. Note that when the thickness of the sample to be measured was 2.3 μm, the power supply voltage was set to 300V.

C. Measurement of dielectric loss tangent (tan δ (130)) after a voltage application test at a voltage of 130 V/μm The sample after a voltage application test at a voltage of 130 V/μm was heated to a temperature of 25°C using a Precision LCR meter E4980A manufactured by Agilent Technologies. Dielectric relaxation measurements were performed under the above conditions, and from the real part (resistance) ε' and imaginary part (reactance) ε' of the complex impedance obtained, the dielectric loss tangent at 2000 Hz (tan δ = imaginary part ε"/real part ε') was calculated and set as the dielectric loss tangent (tan δ(130)) after the voltage application test at a voltage of 130 V/μm.

D. Voltage application test with a voltage of 174 V/μm In the sample in which the dielectric loss tangent (tan δ (174)) was measured after the voltage application test with a voltage of 174 V/μm, a flat plate sample manufactured by HIOKI was connected to a DC high voltage power supply ELS19-10K05B1 manufactured by Element Co., Ltd. A voltage was applied for 1 hour at a temperature of 25° C. and a DC voltage of 174 V/μm. Note that when the thickness of the sample to be measured was 2.3 μm, the power supply voltage was set to 400V.

E. Measurement of dielectric loss tangent (tan δ (174)) after a voltage application test with a voltage of 174 V/μm The sample after the voltage application test with a voltage of 174 V/μm was heated to 25°C using a Precision LCR meter E4980A manufactured by Agilent Technologies. Dielectric relaxation measurements were performed under the above conditions, and from the real part (resistance) ε' and imaginary part (reactance) ε' of the complex impedance obtained, the dielectric loss tangent at 2000 Hz (tan δ = imaginary part ε"/real part ε') was calculated and set as the dielectric loss tangent (tan δ(174)) after the voltage application test at a voltage of 174 V/μm.

F. Calculation of dielectric loss tangent change rate (ΔD) before and after voltage application test Using tan δ (0), tan δ (130), and tan δ (174) obtained in A, C, and E above, the following formulas (1) and (2) are used. ) was used to calculate ΔD.
ΔD (174) = tan δ (174)/tan δ (0) ... (1)
ΔD(130)=tanδ(130)/tanδ(0) (2).

(5) Thickness (t) (unit: μm)
The thickness was measured by a micrometer method according to JIS C 2330 (2014).

(6) Wetting tension (unit: mN/m)
According to JIS K 6768 (1999), the wetting tension of the corona-treated surface of a biaxially oriented polypropylene film was measured using a mixed solution for ethylene glycol monoethyl ether, formamide, and methanol test.

(7) Element processability in capacitor manufacturing Aluminum was vacuum deposited on the corona-treated side of the biaxially oriented polypropylene film using a vacuum deposition machine manufactured by ULVAC Co., Ltd. to a thickness of 15 Ω/sq. At that time, aluminum was vapor-deposited in a stripe shape having a margin part running in the longitudinal direction (width of the vapor-deposited part was 79.0 mm, and width of the margin part was 1.0 mm repeatedly). Next, a blade was inserted into the center of each vapor deposition part and the center of each margin part to make a slit, thereby producing a tape-shaped take-up reel having a total width of 40 mm and having a margin part of 0.5 mm at either the left or right end. One reel from the left margin and one from the right margin of the obtained reel were wound by overlapping each other so that the vapor-deposited part protruded 0.5 mm from the margin part in the width direction to form a wound body with a capacitance of 120 μF. I got it. Note that KAW-4NHB manufactured by Kaito Seisakusho Co., Ltd. was used for winding the element. Finally, heat treatment was performed in a reduced pressure atmosphere at 130° C. for 10 hours to obtain a capacitor element.

(8) Capacitor Life Test Aluminum was vacuum deposited on the corona-treated side of the biaxially oriented polypropylene film using a vacuum deposition machine manufactured by ULVAC Co., Ltd. to a thickness of 15 Ω/sq. At that time, aluminum was vapor-deposited in a stripe shape having a margin part running in the longitudinal direction (width of the vapor-deposited part was 79.0 mm, and width of the margin part was 1.0 mm repeatedly). Next, a blade was inserted into the center of each vapor deposition part and the center of each margin part to make a slit, thereby producing a tape-shaped take-up reel having a total width of 40 mm and having a margin part of 0.5 mm at either the left or right end. One reel from the left margin and one from the right margin of the obtained reel were wound by overlapping each other so that the vapor-deposited part protruded 0.5 mm from the margin part in the width direction to form a wound body with a capacitance of 120 μF. I got it. Note that KAW-4NHB manufactured by Kaito Seisakusho Co., Ltd. was used for winding the element. Finally, it was heat treated in a reduced pressure atmosphere at 130° C. for 10 hours, metallicon was thermally sprayed on both end faces in the width direction to form external electrodes, and lead wires were welded to the metallicon to obtain a capacitor element. Next, the capacitor characteristics of 10 capacitor elements were evaluated. First, capacitance (C0) was measured at room temperature. Next, a voltage of 200 VDC/μm (when the thickness (t) was 2.3 μm, the applied voltage was 460 V) was applied to the capacitor element for 800 hours at a high temperature of 125°C. Thereafter, the capacitance (C) was measured at room temperature, and the rate of change in capacitance (ΔC) before and after voltage application was calculated from the following formula.
ΔC=((C0-C)/C0)×100
The average value of the capacitance change rate (ΔC) before and after voltage application of 10 capacitor elements was taken as the change rate of the sample, and evaluated according to the following criteria. In addition, the evaluation is excellent in the order of ◎○△×.
◎: ΔC is less than 2% ○: ΔC is 2% or more and less than 3% △: ΔC is 3% or more and less than 5% ×: ΔC is 5% or more.

[Resin, etc. used for manufacturing biaxially oriented polypropylene film]
The resins used for producing the biaxially oriented polypropylene films of each Example and each Comparative Example are as follows.
Linear polypropylene resin A1:
Polypropylene resin with mmmm of 98%, MFR of 2.5 g/10 min, and MS of 1.0 g (“Borclean” (trademark) HB300BF manufactured by Borealis)
Branched polypropylene resin H1:
Polypropylene resin with MFR of 9.0 g/10 min and MS of 5.0 g (“WAYMAX” (registered trademark) MFX3 manufactured by Nippon Polypro Co., Ltd.)
Branched polypropylene resin H2:
Polypropylene resin with MFR of 6.2 g/10 min and melt tension MS of 4.0 g (“WAYMAX” (registered trademark) EX4000 manufactured by Nippon Polypro Co., Ltd.)
Branched polypropylene resin H3:
A polypropylene resin (“Daploy” (trademark) WB135HMS manufactured by Borealis) having an MFR of 2.5 g/10 min and a melt tension MS of 32 g.

(Example 1)
Linear polypropylene resin A1 and branched polypropylene resin H1 were dry blended at a ratio of 95:5 (mass ratio) and supplied to a single-screw melt extruder. In addition, as an antioxidant at this time, "Irganox" (registered trademark) 1010 manufactured by BASF Japan, 0.4 parts by mass, 2,6-di-t-butyl-p-cresol, based on 100 parts by mass of the entire polypropylene resin. (BHT) was contained in an amount of 0.1 part by mass. The polypropylene resin mixture was melted at a temperature of 250° C. in a single-screw melt extruder, and foreign matter was removed using a sintered filter with a cut of 25 μm. Next, the molten polypropylene resin mixture was extruded into a sheet using a T-shaped slit die, and was solidified by being brought into close contact with a cast drum kept at a temperature of 90° C. using an air knife. The time period during which the cast drum and the molten sheet were in close contact with each other was 1.5 seconds. Here, the surface on the side that touches the cast drum was defined as the drum surface (D surface), and the surface on the side that does not touch the ground is defined as the non-drum surface (non-D surface). Next, the cast sheet was stretched in the longitudinal direction at a stretching ratio of 6.0 times using longitudinal stretching rolls at a temperature of 145°C. The uniaxially oriented film thus obtained was placed on a conveyor roll at a temperature of 10°C and rapidly cooled for 0.5 seconds while being nipped at a pressure of 0.45 MPa with nip rolls at a temperature of 10°C. Thereafter, both ends of the longitudinally stretched sheet obtained in the width direction are held with clips and introduced into a tenter, and stretched at a stretching ratio of 11 times in the width direction at 160°C, and further relaxed by 12% in the width direction at a temperature of 158°C. went. Thereafter, the drum surface (D surface) side of the film was slowly cooled to room temperature, and corona discharge treatment was applied to the drum surface (D surface) side at a treatment intensity of 25 W min/ ^m2 , and the edges of the film held with clips were cut and removed. The film from which the portion was removed was wound up using a winding machine. Next, the film was slit to have a film width of 0.82 m using a slitter, and wound around a core by 30,000 m in the longitudinal direction as a film roll to obtain a biaxially oriented polypropylene film with a thickness of 2.3 μm. The evaluation results are shown in Table 1.

(Examples 2-4, Comparative Examples 1-4)
A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1 except that the polypropylene resin composition and the cooling temperature of the uniaxially oriented film were as shown in Table 1. The evaluation results are shown in Table 1.

Regarding the polypropylene resin composition, the values are shown with the entire polypropylene resin being 100% by mass.

Since the biaxially oriented polypropylene film of the present invention has high voltage resistance, it can be suitably used as a dielectric material of a film capacitor.

Claims (3)

When the dielectric loss tangent before the voltage application test is tan δ (0) and the dielectric loss tangent after the voltage application test applying a voltage of 174 V/μm is tan δ (174), before and after the voltage application test shown by the following formula (1) A biaxially oriented polypropylene film, characterized in that the rate of change in dielectric loss tangent ΔD (174) is 1.0 or more and 3.0 or less.
ΔD (174) = tan δ (174)/tan δ (0) ... (1) When the dielectric loss tangent after a voltage application test in which a voltage of 130 V/μm is applied is tan δ (130), the rate of change in the dielectric loss tangent before and after the voltage application test ΔD (130) shown by the following formula (2) is 1. The biaxially oriented polypropylene film according to claim 1, wherein the biaxially oriented polypropylene film has a molecular weight of 0 or more and 2.7 or less.
ΔD (130) = tan δ (130)/tan δ (0) ... (2) 3. The second method according to claim 1 or 2, wherein the ratio of the ΔD(174) to the ΔD(130) (ΔD(174)/ΔD(130)) is 1.00 or more and 1.20 or less. Axially oriented polypropylene film.