Polypropylene film, metal-layer integrated polypropylene film, and film capacitor

Abstract

Provided is a polypropylene film having a high dielectric breakdown strength at high temperatures.　Provided is a polypropylene film in which a polypropylene resin constituting the polypropylene film has a molecular-weight distribution (Mw / Mn) of the weight-average molecular weight Mw to the number-average molecular weight Mn of 5.0-6.9, has a Z-average molecular weight Mz of 950,000-1,500,000, and has a weight proportion w of 2.6-4.2% in an integral molecular-weight distribution curve when the logarithmic molecular weight Log(M) is 4.0.

Description

[Technical Field]

[0001] This disclosure relates to polypropylene films, metal-layer integrated polypropylene films, and film capacitors. [Background technology]

[0002] Polypropylene film can be used as a capacitor derivative. For example, it can be used as a capacitor derivative in an inverter that constitutes a power control unit in a hybrid vehicle, electric vehicle, etc. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 056404 [Overview of the project] [Problems that the invention aims to solve]

[0004] Capacitors using polypropylene film as a capacitor derivative should, from the perspective of the above-mentioned operating environment (for example, an environment where the temperature rises in the engine compartment, or the self-heating of the capacitor), be small, lightweight, and have high capacitance, while also possessing excellent heat resistance at high temperatures of around 120°C (100°C to 120°C). In other words, capacitors are required to have the safety to withstand long-term use under high temperature and high voltage conditions, and life performance to suppress the decrease in capacitance.

[0005] For the polypropylene film used to manufacture such capacitors, even if the film thickness is thin (for example, less than 20 μm), the dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at the aforementioned high temperature is required.

[0006] Under these circumstances, the primary objective of this disclosure is to provide a polypropylene film having high dielectric breakdown strength at high temperatures. Furthermore, this disclosure also aims to provide a metal-layer integrated polypropylene film and a film capacitor using the said polypropylene film. [Means for solving the problem]

[0007] The inventors of this disclosure diligently studied to solve the aforementioned problems. As a result, they found that a polypropylene film exhibits high dielectric breakdown strength at high temperatures if the molecular weight distribution (Mw / Mn) of the polypropylene resin constituting the polypropylene film is between 5.0 and 6.9, the average molecular weight Mz is between 950,000 and 1,500,000, and the weight fraction w when the logarithmic molecular weight Log(M) = 4.0 in the integral molecular weight distribution curve is between 2.6% and 4.0%. This disclosure was completed by further studies based on these findings.

[0008] In other words, this disclosure includes the following: Item 1. Polypropylene film, The polypropylene resin comprising the aforementioned polypropylene film is The molecular weight distribution (Mw / Mn) between the weight-average molecular weight Mw and the number-average molecular weight Mn is between 5.0 and 6.9. • The average molecular weight Mz is between 950,000 and 1,500,000. • In the integral molecular weight distribution curve, the weight fraction w when the logarithmic molecular weight Log(M) = 4.0 is between 2.6% and 4.0%. Polypropylene film. Item 2. Polypropylene film as described in Item 1, for use in capacitors. Item 3. A polypropylene film according to item 1 or 2, which is a biaxially oriented film. Item 4. The density measured in accordance with the provisions of Method D of JIS K7112:1999 is 919 kg / m³. 3 More than 925kg / m 3The polypropylene film described in any one of items 1 to 3 below. Item 5. A polypropylene film according to any one of items 1 to 4, wherein the dielectric breakdown strength (DCES) at a DC voltage at 120°C is 530 V / μm or higher. Item 6. The polypropylene resin contains polypropylene resin A and polypropylene resin B which is different from polypropylene resin A. The Mw of the aforementioned polypropylene resin A is 250,000 or more and less than 350,000. The molecular weight distribution (Mw / Mn) of the aforementioned polypropylene resin A is 5.5 or more and 10.0 or less. The melt flow rate (MFRA) of the polypropylene resin A is 3.0 g / 10 min or more and 10.0 g / 10 min or less. The polypropylene film according to any one of claims 1 to 5, wherein the content of polypropylene resin A in the polypropylene resin is greater than the content of polypropylene resin B in the polypropylene resin. Item 7. The polypropylene resin contains polypropylene resin A and polypropylene resin B which is different from polypropylene resin A. The Mw of the aforementioned polypropylene resin B is between 300,000 and 550,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 5.0 or more and 11.0 or less. The melt flow rate (MFRB) of the polypropylene resin B is 0.1 g / 10 min or more and 3.0 g / 10 min or less. The polypropylene film according to any one of claims 1 to 6, wherein the content of polypropylene resin A in the polypropylene resin is greater than the content of polypropylene resin B in the polypropylene resin. Item 8. The polypropylene film according to item 6 or 7, wherein the ratio of the mass of polypropylene resin A to the total mass of polypropylene resin B is 55% by mass or more and 75% by mass or less. Item 9. The polypropylene film according to any one of Items 1 to 8, wherein the thickness of the polypropylene film is 1.0 μm or more and 2.4 μm or less. Item 10. A polypropylene film, wherein the polypropylene resin constituting the polypropylene film has a Z-average molecular weight Mz of 950,000 or more and 1,500,000 or less, and an insulation breakdown strength (DCES) at a DC voltage at 120 °C is 530 V / μm or more. Item 11. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of Items 1 to 10 and a metal layer laminated on one or both sides of the polypropylene film. A metal layer-integrated polypropylene film. Item 12. A film capacitor having the wound metal layer-integrated polypropylene film according to Item 11 or having a structure in which a plurality of the metal layer-integrated polypropylene films according to Item 11 are laminated. Item 13. The film capacitor according to Item, 12, wherein an insulation resistance value at an ambient temperature of 115 °C is 20 MΩ·μF or more.

Advantages of the Invention

[0009] According to the present disclosure, a polypropylene film having a high insulation breakdown strength at high temperatures can be provided. Further, according to the present disclosure, a metal layer-integrated polypropylene film and a film capacitor using the polypropylene film can also be provided.

Modes for Carrying Out the Invention

[0010] Hereinafter, the polypropylene film, the metal layer-integrated polypropylene film, the film capacitor, and their manufacturing methods according to the present disclosure will be described in detail.

[0011] In this specification, the "~" in numerical ranges means "greater than or equal to" and "less than or equal to." That is, the notation α~β means α or greater and β or less, or β or greater and α or less, and the range includes α and β. Furthermore, if multiple lower limits and multiple upper limits are listed separately, any lower limit and upper limit may be selected and connected with "~".

[0012] In this specification, polypropylene may be abbreviated as PP, and polypropylene resin may be abbreviated as PP resin.

[0013] In this specification, the terms “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consist of,” and “consist solely of.”

[0014] In this specification, the term "capacitor" includes the concepts of "capacitor," "capacitor element," and "film capacitor."

[0015] In this specification, the orientation of the polypropylene film is as follows: First, the machine direction of the film is the same as the Machine Direction (hereinafter referred to as the "MD direction"). The MD direction may also be called the length direction or flow direction. Second, the transverse direction of the film is the same as the Transverse Direction (hereinafter referred to as the "TD direction"). The TD direction may also be called the width direction.

[0016] <Polypropylene film> The polypropylene film of this disclosure is characterized in that the polypropylene resin constituting the polypropylene film has a molecular weight distribution (Mw / Mn) of 5.0 to 6.9 between the weight-average molecular weight Mw and the number-average molecular weight Mn, a Z-average molecular weight Mz between 950,000 and 1,500,000, and a weight fraction w of 2.6% to 4.0% when the logarithmic molecular weight Log(M) = 4.0 in the integral molecular weight distribution curve. Hereinafter, weight-average molecular weight may be abbreviated as Mw, number-average molecular weight as Mn, molecular weight distribution as Mw / Mn, Z-average molecular weight as Mz, and weight fraction as w.

[0017] The polypropylene film of this disclosure has a high dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at a high temperature of approximately 120°C (100°C to 120°C), even when the film thickness is thin (for example, less than 20 μm, even less than 10 μm, and even less than 6 μm). Furthermore, the film capacitor of this disclosure, which uses the polypropylene film of this disclosure as a capacitor derivative, has excellent heat resistance at high temperatures of approximately 120°C (100°C to 120°C), and specifically, it has excellent life performance in that the decrease in capacitance of the capacitor is suppressed even when used for a long time at the above high temperature. Therefore, the polypropylene film of this disclosure is suitable for film capacitor applications. Furthermore, while the polypropylene film of this disclosure may or may not be stretched, it is preferable that it be a biaxially oriented film considering the above-mentioned applications.

[0018] Both sides of the polypropylene film in this disclosure can be defined as a first surface and a second surface. The first surface can be rough. A rough first surface makes it less likely for wrinkles to occur during element winding in capacitor fabrication. The second surface can also be rough.

[0019] The thickness of the polypropylene film is preferably 0.8 μm to 6.0 μm from the viewpoint of ensuring miniaturization and high capacitance of the capacitor when used in a capacitor. Specifically, 5.5 μm or less is preferred, 3.5 μm or less is more preferred, 3.0 μm or less is even more preferred, and 2.4 μm or less is particularly preferred. Furthermore, from a manufacturing viewpoint, the thickness of the polypropylene film is preferably 1.0 μm or more, more preferably 1.8 μm or more, and even more preferably 2.2 μm or more. The method for measuring the thickness of the polypropylene film in this specification is the method described in the examples.

[0020] The density of the aforementioned polypropylene film is not limited, but considering capacitor applications, for example, 919 kg / m² is suitable. 3 More than 925kg / m 3 The following settings are preferable. The method for measuring the density of the polypropylene film in this specification is as described in the examples.

[0021] The polypropylene film of this disclosure has a molecular weight distribution (Mw / Mn) of the polypropylene resin constituting the polypropylene film (or, if the polypropylene resin is composed of a mixture of multiple resins, after mixing) of 5.0 or more and 6.9 or less.

[0022] The molecular weight distribution (Mw / Mn) should be between 5.0 and 6.9, but the lower limit is preferably 5.2 or higher, more preferably 6.0 or higher, even more preferably 6.2 or higher, and even more preferably 6.3 or higher. The upper limit is preferably 6.5 or lower. By having the molecular weight distribution (Mw / Mn) within this range, as a result of the combined effect with other requirements, a polypropylene film can be obtained that has excellent dielectric breakdown strength at high temperatures and suppresses thermal shrinkage in the mechanical direction (MD).

[0023] The polypropylene film of this disclosure has an Mz of 950,000 or more and 1,500,000 or less of the polypropylene resin constituting the polypropylene film (or, if the polypropylene resin is composed of a mixture of multiple resins, the Mz after mixing).

[0024] Mz can be between 950,000 and 1,500,000, but the lower limit is preferably 1,000,000 or more, more preferably 1,050,000 or more, and even more preferably 1,100,000 or more. The upper limit is preferably 1,400,000 or less, more preferably 1,300,000 or less, and even more preferably 1,200,000 or less. By keeping Mz within this range, the combination of the molecular weight distribution Mw / Mn described above and the weight fraction w described later results in excellent dielectric breakdown strength at high temperatures.

[0025] The polypropylene film of this disclosure has a weight fraction w of 2.6% or more and 4.0% or less in the integral molecular weight distribution curve of the polypropylene resin constituting the polypropylene film (or after mixing if the polypropylene resin is composed of a mixture of multiple resins) when the logarithmic molecular weight Log(M) = 4.0.

[0026] The weight fraction w should be between 2.6% and 4.0%, but the lower limit is preferably 2.8% or higher, more preferably 3.0% or higher, even more preferably 3.2% or higher, and even more preferably 3.4% or higher. The upper limit is preferably 3.9% or lower. By keeping the weight fraction w within this range, the combination of the aforementioned molecular weight distribution Mw / Mn and the average molecular weight Z Mz results in excellent dielectric breakdown strength at high temperatures.

[0027] In a preferred embodiment, the polypropylene film of this disclosure comprises a polypropylene resin (or, if the polypropylene resin is composed of a mixture of multiple resins, after mixing), The molecular weight distribution (Mw / Mn) is 6.3 or more and 6.9 or less. The above Mz is between 1.04 million and 1.11 million, The aforementioned weight fraction w is 3.5% or more and 4.0% or less. This can be the configuration. By using a polypropylene resin with such physical properties, particularly high dielectric breakdown strength at high temperatures can be achieved.

[0028] The measurement methods for Mw, Mn, Mz, molecular weight distribution (Mw / Mn), and weight fraction w of the polypropylene resin constituting the polypropylene film in this specification, as well as the measurement methods for Mw, Mn, Mz, molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), differential distribution value when log(M) = 4.5, differential distribution value when log(M) = 6.0, molecular weight differential distribution value difference (DM), and weight fraction w of polypropylene resin A and polypropylene resin B when the polypropylene resin is composed of multiple resins, are as described in the examples.

[0029] The polypropylene film of this disclosure contains a polypropylene resin. The polypropylene resin content is preferably 90% by weight or more, more preferably 95% by weight or more, relative to the entire polypropylene film (when the entire polypropylene film is considered to be 100% by weight). The upper limit of the polypropylene resin content is, for example, 100% by weight, 98% by weight, etc., relative to the entire polypropylene film.

[0030] For polypropylene resins, a lower total ash content is preferable for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on the polypropylene resin. The lower limit of the total ash content is, for example, 2 ppm or 5 ppm. A lower total ash content means fewer impurities such as polymerization catalyst residue.

[0031] The polypropylene resin may consist of one type of polypropylene resin alone, or it may consist of two or more types of polypropylene resins.

[0032] If the polypropylene film contained in this disclosure contains two or more types of polypropylene resin, the polypropylene resin with the highest content is designated as the main component and referred to herein as the "main component polypropylene resin" or "base resin." If the polypropylene film contained in this disclosure contained only one type of polypropylene resin, that polypropylene resin was also designated as a main component and referred to herein as the "main component polypropylene resin." Furthermore, if the polypropylene film contained in this disclosure contained two or more types of polypropylene resin, a polypropylene resin different from the polypropylene resin with the highest content is referred to as the "blended resin."

[0033] The polypropylene film of this disclosure may, for example, include polypropylene resin B as a blended resin along with polypropylene resin A (the main component, which is the base resin) if the film contains two or more types of polypropylene resins (especially two types). Alternatively, one of the polypropylene resins A may be designated as the "base resin" and the other as the "blended resin." The following will provide an illustrative explanation of the case in which two types of polypropylene resins, polypropylene resin A as the base resin and polypropylene resin B as the blended resin, are used.

[0034] The content of polypropylene resin A is more than 50% by weight, preferably 55% by weight or more, more preferably 60% by weight or more, and even more preferably 65% ​​by weight or more, relative to 100% by weight of the polypropylene resin. Regarding the upper limit of the polypropylene resin A content, it is less than 100% by weight, preferably 95% by weight or less, more preferably 90% by weight or less, even more preferably 80% by weight or less, and even more preferably 75% by weight or less, relative to 100% by weight of the polypropylene resin. Examples of polypropylene resin A include isotactic polypropylene.

[0035] The weight-average molecular weight Mw of polypropylene resin A is preferably 250,000 to 360,000, more preferably 280,000 to 350,000, and even more preferably 300,000 to 350,000. For the upper limit, it is even more preferably less than 350,000. When Mw is between 250,000 and 360,000, the thickness of the cast raw material sheet is easily controlled during the polypropylene film manufacturing process, and thickness variations are less likely to occur.

[0036] The number-average molecular weight (Mn) of polypropylene resin A is preferably between 30,000 and 54,000, more preferably between 33,000 and 52,000, and even more preferably between 33,000 and 47,000. When Mn is between 30,000 and 54,000, it is easier to obtain a capacitor element with excellent heat resistance.

[0037] The z-average molecular weight Mz of polypropylene resin A is preferably between 1 million and 2 million, more preferably between 1.25 and 1.8 million. When Mz is between 1 million and 2 million, it is easier to obtain a film with high dielectric strength at high temperatures.

[0038] The molecular weight distribution (Mw / Mn) of polypropylene resin A is preferably 5.0 or higher, more preferably 5.5 or higher, and even more preferably 6.0 or higher. The Mw / Mn of polypropylene resin A is preferably 10.0 or lower, more preferably 9.5 or lower, and particularly preferably 8.5 or lower. When the Mw / Mn is between 5.0 and 10.0, the stretchability improves, making it easier to obtain thin films.

[0039] The molecular weight distribution (Mz / Mn) of polypropylene resin A is preferably between 10 and 70, more preferably between 15 and 60, and even more preferably between 15 and 50. When Mz / Mn is between 10 and 70, the stretchability is improved, and thin films can be easily obtained.

[0040] In the molecular weight distribution curve of polypropylene resin A, the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 is preferably 28.0 or higher. The upper limit is preferably 32.0 or lower. Also, the differential distribution value when the logarithmic molecular weight Log(M) = 6.0 is preferably 17.0 or higher, more preferably 20.0 or higher. The upper limit is preferably 30.0 or lower, more preferably 28.0 or lower. Furthermore, the difference (molecular weight differential distribution difference (DM)) obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 6.0 from the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 is preferably 4.0 or higher and 18.0 or lower, more preferably 4.5 or higher and 11.0 or lower.

[0041] Comparing the components with a logarithmic molecular weight of Log(M) = 4.5 as a representative distribution value for components with a molecular weight of 10,000 to 100,000 on the low molecular weight side (hereinafter also referred to as "low molecular weight components"), and components with a molecular weight of around 1,000,000 on the high molecular weight side (hereinafter also referred to as "high molecular weight components"), with components with a logarithmic molecular weight of around 6.0 as a representative distribution value, it can be seen that the low molecular weight components are more abundant by a proportion of 8.0% to 18.0%.

[0042] In other words, even if the molecular weight distribution Mw / Mn is 5.0 to 10.0, this only indicates a broad range of molecular weight distribution, and does not reveal the quantitative relationship between high molecular weight and low molecular weight components within it. Therefore, it is preferable that the polypropylene resin A according to this disclosure has a broad molecular weight distribution and contains a large amount of components with molecular weights of 10,000 to 100,000, at a ratio of 8.0% to 18.0% compared to components with a molecular weight of 1,000,000. This is preferable because it reduces the crystallite size and makes it easier to obtain a roughened surface for the polypropylene film.

[0043] The weight fraction w of polypropylene resin A has a lower limit of preferably 3.8% or more, and more preferably 4.0% or more. The upper limit is preferably 6.0% or less, and more preferably 5.0% or less. By having the weight fraction w of polypropylene resin A within this range, and combining it with the weight fraction w of polypropylene resin B (described later), the weight fraction w after mixing polypropylene resin A and polypropylene resin B becomes 2.6% to 4.0%, thereby achieving high dielectric breakdown strength at high temperatures.

[0044] The melt flow rate (MFRA) of polypropylene resin A at 230°C is preferably 3.0 g / 10 min or more, more preferably 3.5 g / 10 min or more. The upper limit of the MFRA is preferably 10.0 g / 10 min or less, more preferably 8.0 g / 10 min or less, even more preferably 6.0 g / 10 min or less, and particularly preferably 5.0 g / 10 min or less. The method for measuring the melt flow rate (MFR) in this specification is as described in the examples. The unit g / 10 min of the melt flow rate is also referred to as dg / min.

[0045] A preferred embodiment of the polypropylene film disclosed herein is a polypropylene resin A, The Mw of the aforementioned polypropylene resin A is 250,000 or more and less than 350,000. The molecular weight distribution (Mw / Mn) of the aforementioned polypropylene resin A is 5.5 or more and 10.0 or less. The melt flow rate (MFRA) of the polypropylene resin A is 3.0 g / 10 min or more and 10.0 g / 10 min or less. This can be the embodiment. By using polypropylene resin A with such physical properties, it becomes easier to mold cast sheets (stretched precursors) using an extruder.

[0046] Furthermore, in a more preferred embodiment, the polypropylene film of this disclosure is provided with respect to polypropylene resin A. The Mw of the aforementioned polypropylene resin A is 300,000 or more and less than 350,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 6.0 or more and 9.5 or less. The melt flow rate (MFRA) of the polypropylene resin A is 3.5 g / 10 min or more and 5.0 g / 10 min or less. It can be a modal form.

[0047] The heptane-insoluble content of polypropylene resin A is preferably 97.0% or more. The heptane-insoluble content is preferably 98.5% or less. A higher heptane-insoluble content indicates higher stereoregularity of the resin. When the heptane-insoluble content (HI) is 97.0% or more and 98.5% or less, the moderately high stereoregularity moderately improves the crystallinity of the polypropylene resin in the polypropylene film, improving the dielectric breakdown strength at high temperatures. Furthermore, in the manufacturing process of the polypropylene film, the solidification (crystallization) rate during the casting of the raw material sheet becomes moderate, resulting in moderate stretchability. The method for measuring the heptane-insoluble content (HI) in this specification is as described in the examples.

[0048] The total ash content of polypropylene resin A is preferable to be as low as possible for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on polypropylene resin A. The lower limit of the total ash content is, for example, 2 ppm or 5 ppm.

[0049] Polypropylene resin B is a different polypropylene resin from polypropylene resin A. The content of polypropylene resin B in the polypropylene film of this disclosure is preferably less than 50% by weight, preferably 49% by weight or less, more preferably 40% by weight or less, and particularly preferably 35% by weight or less, based on 100% by weight of the polypropylene resin. Furthermore, as a lower limit, the content of polypropylene resin B is preferably 10% by weight or more, more preferably 15% by weight or more, even more preferably 25% by weight or more, and particularly preferably 30% by weight or more, based on 100% by weight of the polypropylene resin. Examples of polypropylene resin B include isotactic polypropylene. In this disclosure, an embodiment in which the ratio of the mass of polypropylene resin A to the total mass of polypropylene resin A and polypropylene resin B is 55% by weight or more and 75% by weight or less is particularly preferred.

[0050] The Mw of polypropylene resin B is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 360,000 or more. The Mw of polypropylene resin B is preferably 550,000 or less, more preferably 450,000 or less, and even more preferably 420,000 or less. When the Mw is between 300,000 and 550,000, it is easy to control the thickness of the cast raw material sheet in the manufacturing process of the polypropylene film, and thickness unevenness is less likely to occur.

[0051] The manganese content (Mn) of polypropylene resin B is preferably between 40,000 and 54,000, more preferably between 42,000 and 50,000, and even more preferably between 44,000 and 48,000. When Mn is between 40,000 and 54,000, it is easier to obtain a capacitor element with excellent heat resistance.

[0052] The Mz of polypropylene resin B is preferably more than 1.55 million and 2 million or less, more preferably between 1.58 million and 1.9 million. When Mz is more than 1.55 million and 2 million or less, it is easier to obtain a film with high dielectric strength at high temperatures.

[0053] The molecular weight distribution (Mw / Mn) of polypropylene resin B is preferably 5.0 or higher, more preferably 5.5 or higher, even more preferably 7.0 or higher, even more preferably 7.5 or higher, and particularly preferably 8.0 or higher. The upper limit of Mw / Mn in polypropylene resin B is, for example, 11.0 or lower, preferably 10.0 or lower, and more preferably 8.5 or lower. When Mw / Mn is between 5.0 and 11.0, the stretchability is improved, and thin films are easily obtained.

[0054] The molecular weight distribution (Mz / Mn) of polypropylene resin B is preferably 30 to 40, more preferably 33 to 36. When Mz / Mn is between 30 and 40, the stretchability is improved, and thin films are easily obtained.

[0055] In the molecular weight distribution curve of polypropylene resin B, the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 is preferably 24.0 or higher, more preferably 27.0 or higher. The upper limit is preferably 35.0 or lower, more preferably 32.0 or lower. Furthermore, the differential distribution value when the logarithmic molecular weight Log(M) = 6.0 is preferably 28.0 or higher, more preferably 30.0 or higher. The upper limit is preferably 35.0 or lower, more preferably 33.0 or lower. Moreover, the difference (molecular weight differential distribution difference (DM)) obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 6.0 from the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 is preferably -11.0 or higher and 7.0 or lower, more preferably -6.0 or higher and 0.0 or lower, and even more preferably -4.0 or higher and -2.0 or lower.

[0056] When the polypropylene resin contains the aforementioned polypropylene resins A and B, the differences in Mw, Mw / Mn, and differential distribution values ​​between polypropylene resins A and B, that is, the differences in the molecular weight distribution, result in a polypropylene film obtained by mixing and molding having a subtly different quantitative relationship between high molecular weight and low molecular weight components. This leads to a certain state of fine mixing (phase separation), which is considered preferable as it facilitates the refinement of crystal size. Furthermore, even at the same stretching ratio, it tends to become highly oriented, and the surface is also more easily roughened, which is considered preferable. When the polypropylene resin contains polypropyn resins A and B, the present disclosure is considered to have excellent effects for the reasons stated above, but the present disclosure is not limited in any way for these reasons.

[0057] The weight fraction w of polypropylene resin B has a lower limit of preferably 2.0% or more, more preferably 2.5% or more, and even more preferably 3.0% or more. The upper limit is preferably 5.0% or less, and more preferably 4.2% or less. When the weight fraction w of polypropylene resin B is within this range, and combined with the weight fraction w of polypropylene resin A as described above, the weight fraction w after mixing polypropylene resin A and polypropylene resin B becomes 2.0% to 5.0%, it becomes easier to obtain a polypropylene film with excellent dielectric breakdown strength at high temperatures.

[0058] The melt flow rate (MFRB) at 230°C for polypropylene resin B is preferably 4.5 g / 10 min or less, more preferably 4.0 g / 10 min or less, even more preferably 3.0 g / 10 min or less, and even more preferably less than 2.8 g / 10 min. The lower limit of the MFRB is preferably 0.1 g / 10 min or more, more preferably 0.5 g / 10 min or more, and even more preferably 1.5 g / 10 min or more.

[0059] Furthermore, it is preferable to set the difference MFRA-MFRB between the MFRA of polypropylene resin A, which is the main component base resin, and the MFRB of polypropylene resin B, which is the blended resin, to 1.2 g / 10 min or more. In other words, MFRA is greater than MFRB. The above difference MFRA-MFRB is preferably 1.3 g / 10 min or more, more preferably 1.5 g / 10 min or more, and even more preferably 1.7 g / 10 min or more. If the above difference MFRA-MFRB is less than 1.2 g / 10 min (this less than 1.2 g / 10 min includes negative values), in the manufacturing process of the polypropylene film, a sea-island phase separation structure may not be formed at the time of casting the raw material sheet molding, or even if it is formed, the size of the islands may be very small, making it difficult to obtain a polypropylene film with excellent dielectric breakdown strength at high temperatures. In particular, even if the difference between MFRA and MFRB is large, if MFRB is larger (when the above difference MFRA-MFRB is negative), the size of the islands in the sea-island phase separation structure will be very small.

[0060] A preferred embodiment of the polypropylene film disclosed herein is a polypropylene resin B, The Mw of the aforementioned polypropylene resin B is between 300,000 and 550,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 5.0 or more and 11.0 or less. The melt flow rate (MFRB) of the polypropylene resin B is 0.1 g / 10 min or more and 3.0 g / 10 min or less. This can be the embodiment. By using polypropylene resin B with such physical properties, it becomes easier to mold cast sheets (stretched precursors) using an extruder.

[0061] A more preferred embodiment of the polypropylene film disclosed herein is a polypropylene resin B, The Mw of the aforementioned polypropylene resin B is between 350,000 and 400,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 7.8 or more and 8.8 or less. The melt flow rate (MFRB) of the polypropylene resin B is 1.8 g / 10 min or more and 2.8 g / 10 min or less. It can be a modal form.

[0062] The heptane-insoluble content of polypropylene resin B is preferably 97.5% or more, more preferably 98.0% or more, even more preferably more than 98.5%, and particularly preferably 98.6% or more. Furthermore, the heptane-insoluble content is preferably 99.5% or less, and more preferably 99.0% or less.

[0063] For polypropylene resin B, a lower total ash content is preferable for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on polypropylene resin B. The lower limit of the total ash content is, for example, 2 ppm or 5 ppm.

[0064] The above has provided an illustrative explanation of the case in which two types of polypropylene resin, Polypropylene Resin A (base resin) and Polypropylene Resin B (blended resin), but in this disclosure, the polypropylene film may also be composed of resins other than polypropylene resin. In that case, the total amount of Polypropylene Resin A and Polypropylene Resin B can be, for example, 90% or more by weight, 95% or more by weight, or 100% by weight, when the total amount of resin is considered to be 100% by weight. Furthermore, as mentioned above, one of the Polypropylene Resin A types may be designated as the "base resin" and the other as the "blended resin".

[0065] The polypropylene film of this disclosure may further contain additives. Examples of additives include antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and colorants.

[0066] The polypropylene film of this disclosure may be a biaxially oriented film, a uniaxially oriented film, or an unoriented film, but it is preferably a biaxially oriented film.

[0067] The polypropylene film of this disclosure is preferably for use in capacitors, and more specifically, it can be suitably applied as a dielectric material for capacitors. As described later, the polypropylene film of this disclosure can be a metal-layer integrated polypropylene film having a metal layer laminated on one or both sides, and a film capacitor can be manufactured by winding this metal-layer integrated polypropylene film or by including a configuration in which multiple metal-layer integrated polypropylene films are laminated.

[0068] Considering the above-mentioned applications for capacitors, it is desirable that the polypropylene film disclosed herein has the following dielectric breakdown strength and heat shrinkage resistance properties.

[0069] The dielectric breakdown strength (DCES100°C) of the polypropylene film of the present disclosure at a DC voltage of 100°C is preferably 550 V / μm or more, more preferably 560 V / μm or more, still more preferably 570 V / μm or more. The upper limit of the dielectric breakdown strength at a DC voltage of 120°C is preferably as high as possible, for example, 600 V / μm, 590 V / μm, etc.

[0070] The dielectric breakdown strength (DCES120°C) of the polypropylene film of the present disclosure at a DC voltage of 120°C is preferably 530 V / μm or more, more preferably 535 V / μm or more, still more preferably 540 V / μm or more, particularly preferably 545 V / μm or more. The upper limit of the dielectric breakdown strength at a DC voltage of 120°C is preferably as high as possible, for example, 560 V / μm, 555 V / μm, etc.

[0071] The volume resistivity (5-minute value) of the polypropylene film of the present disclosure is preferably 2×10 15 Ω·m or more and 4×10 15 Ω·m or less. Also, the volume resistivity (10-minute value) of the polypropylene film of the present disclosure is preferably 2×10 15 Ω·m or more and 4×10 15 Ω·m or less. The method for measuring the volume resistivity (5-minute value and 10-minute value) of the polypropylene film in this specification is according to the method described in the examples.

[0072] <Manufacturing method of polypropylene film> The manufacturing method of the polypropylene film of the present disclosure is not limited, but for example, by adopting the following manufacturing method (hereinafter referred to as "the manufacturing method of the polypropylene film of the present disclosure"), the polypropylene film of the present disclosure can be preferably manufactured.

[0073] The manufacturing method of the polypropylene film of the present disclosure is the method for manufacturing the aforementioned polypropylene film of the present disclosure, and a polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B is at a temperature of 225°C or more and 270°C or less and a shear rate of 2000 s -1More than 15000s -1 The following steps include melting: The difference between the melt flow rate (MFRA) of polypropylene resin A and the melt flow rate (MFRB) of polypropylene resin B, MFRA-MFRB, is 1.2 g / 10 min or more. The content of polypropylene resin A in the polypropylene resin composition is greater than the content of polypropylene resin B in the polypropylene resin composition. It is characterized by the following:

[0074] This manufacturing method makes it possible to provide a polypropylene film with good dielectric breakdown strength at high temperatures. This is thought to be due to the sea-island phase separation structure of the cast raw material sheet (particularly the appropriate island size) resulting from the use of two specific, different types of polypropylene resin.

[0075] The present disclosure's method for producing a polypropylene film uses a polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B. Here, the fact that the content of polypropylene resin A in the polypropylene resin composition is greater than the content of polypropylene resin B in the polypropylene resin composition means that, in the relationship between polypropylene resin A and polypropylene resin B, polypropylene resin A is the main component base resin, and polypropylene resin B is a blend resin to the base resin. The terms "polypropylene resin A" and "polypropylene resin B" in the method for manufacturing the polypropylene film of this disclosure correspond to the terms "polypropylene resin A" and "polypropylene resin B" in the section on polypropylene film mentioned above. The explanations of Mw, Mn, Mz, molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), differential distribution value when logarithmic molecular weight Log(M)=4.5, differential distribution value when logarithmic molecular weight Log(M)=6.0, molecular weight differential distribution difference (DM), weight fraction w, and MFR for each resin are as described above. In particular, the method for manufacturing the polypropylene resin of this disclosure uses resins in which the difference between MFRA and MFRB, MFRA-MFRB, is 1.2 g / 10 min or more.

[0076] There are no particular limitations on the method of mixing the resins applicable to the manufacturing method of the present disclosure, but examples include a method of dry blending the polymerized powder or pellets of the base resin and the blended resin using a mixer or the like, or a method of supplying the polymerized powder or pellets of the base resin and the blended resin to a kneader and melt-kneading them to obtain a kneaded product.

[0077] The mixer and the kneader are not particularly limited. The kneader may be a single-screw type, a twin-screw type, or a multi-screw type with more than one screw. In the case of a twin-screw type, either a co-rotating or staggered rotation kneading type is acceptable.

[0078] In the case of mixing by melt kneading, the mixing temperature is not particularly limited as long as a good mixture is obtained. Generally, it is in the range of 200°C to 300°C, and from the viewpoint of suppressing resin degradation, 230°C to 270°C is preferred. In addition, to suppress degradation during resin mixing, an inert gas such as nitrogen may be purged into the kneader. The melt-kneaded resin may be pelletized to an appropriate size using a generally known granulator. This makes it possible to obtain mixed polypropylene raw material resin pellets.

[0079] The total ash content, which originates from polymerization catalyst residues and other materials contained in the polypropylene raw material resin, should preferably be as low as possible to improve electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and particularly preferably 30 ppm or less, based on the polypropylene resin (100 parts by weight).

[0080] The polypropylene resin may contain additives. "Additives" are generally additives used in polypropylene resins and are not particularly limited as long as a polypropylene film can be obtained. Examples of such additives include antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, and antistatic agents. The polypropylene resin may contain these additives in amounts that do not adversely affect the polypropylene film.

[0081] In the method for manufacturing a polypropylene film according to the present disclosure, first, polypropylene resin pellets, dry-mixed polypropylene resin pellets, or mixed polypropylene resin pellets prepared in advance by melt-kneading are supplied to an extruder and heated and melted.

[0082] The polypropylene resin composition is melted at a temperature of 225°C to 270°C. Specifically, the extruder temperature set during heating and melting of the polypropylene resin composition is set to 225°C to 270°C. As a result, assuming the use of the above-mentioned specific polypropylene resin composition, a sea-island phase separation structure is formed at the stage of casting the raw material sheet, as described later, and ultimately a polypropylene film with excellent dielectric breakdown strength at high temperatures is obtained.

[0083] The polypropylene resin composition was subjected to a shearing rate of 2000 s at a temperature of 225°C to 270°C. -1 More than 15000s -1 The following melting process is performed. This, assuming the use of the specific polypropylene resin composition described above, forms a sea-island phase separation structure at the time of casting the raw material sheet, ultimately resulting in a polypropylene film with excellent dielectric breakdown strength at high temperatures. (Shear rate: 2000 s) -1 If the amount falls below a certain level, the extrusion rate becomes inconsistent, causing the shape and dimensions of the raw sheet to become irregular or to fluctuate regularly, making it more prone to breakage during transport and stretching of the raw sheet.

[0084] Also, the shear rate is 15,000 s. -1If the shear rate exceeds a certain value, unmelted material is extruded due to a phenomenon called breakup within the extruder, making it impossible to obtain a uniform raw sheet and increasing the likelihood of breakage during stretching. Alternatively, excessive heat generation when passing through the chip clearance can lead to significant degradation of the polypropylene resin composition, resulting in a decrease in the dielectric breakdown strength of the film obtained by stretching, even if a uniform raw sheet is obtained. The shear rate can be adjusted by the cylinder diameter and screw rotation speed of the extruder, as well as the screw groove depth.

[0085] The above shear rate is 2000s. -1 More than 15000s -1 The following is acceptable, but preferably 2000s -1 More than 10000s -1 The following is more2000s -1 More than 2300s -1 The following is the result: By keeping the shear rate within the applicable range, it becomes easier to obtain a polypropylene film with a weight fraction w of 2.6% to 4.0%, and in combination with other requirements, a film capacitor using polypropylene film as a capacitor derivative can be obtained that has excellent heat resistance.

[0086] Next, the molten resin composition is extruded into a sheet using a T-die, and then cooled and solidified in at least one metal drum to form an unstretched cast raw material sheet. The surface temperature of the metal drum (the temperature of the metal drum that first comes into contact with the material after extrusion) is preferably 50°C to 105°C, and more preferably 60°C to 100°C. The surface temperature of the metal drum can be determined according to the physical properties of the polypropylene resin used. If the surface temperature of the metal drum is significantly below 50°C, it becomes difficult to obtain good sheet moldability of the raw material sheet, making it difficult to obtain a good polypropylene film without uneven stretching or breakage during stretching.

[0087] The thickness of the cast raw material sheet is not particularly limited as long as the polypropylene film can be obtained, but is generally preferably 0.05 mm or more and 2 mm or less, and more preferably 0.1 mm or more and 1 mm or less.

[0088] The polypropylene film can be manufactured by stretching the polypropylene cast raw material sheet. Biaxial stretching, which orients the sheet biaxially in the longitudinal and transverse directions, is preferred, and sequential biaxial stretching is preferred as the stretching method. As an example of sequential biaxial stretching, first, the cast raw material sheet is kept at a temperature of 110°C to 170°C (preferably 135°C to 170°C) and stretched in the flow direction by passing it between rolls with a speed difference. The stretching ratio in the flow direction is preferably 3.5 to 5.5 times, and more preferably 4.2 to 5.4 times. Subsequently, the sheet is guided to a tenter and stretched in the transverse direction. The temperature during transverse stretching is preferably 150°C to 165°C, and the stretching ratio in the transverse direction is preferably 9 to 11 times. After that, relaxation and heat setting are performed to 2 to 10 times. By doing so, a biaxially oriented polypropylene film is obtained.

[0089] From the viewpoint of ensuring miniaturization and increased capacitance of the capacitor when used in a capacitor, the thickness of the polypropylene film is preferably 0.8 μm or more and 6.0 μm or less, as mentioned above. Specifically, 5.5 μm or less is preferred, 3.5 μm or less is more preferred, 3.0 μm or less is even more preferred, and 2.4 μm or less is particularly preferred. Furthermore, from a manufacturing viewpoint, the thickness of the polypropylene film is preferably 1.0 μm or more, more preferably 1.8 μm or more, and even more preferably 2.2 μm or more.

[0090] The polypropylene film may be subjected to corona discharge treatment online or offline after the stretching and heat setting processes are completed, in a subsequent process such as a metal vapor deposition process, for the purpose of improving its adhesive properties. Corona discharge treatment can be carried out using known methods. It is preferable to use air, carbon dioxide, nitrogen gas, or a mixture thereof as the atmospheric gas.

[0091] The polypropylene film obtained in this manner exhibits excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at a high temperature of approximately 120°C (100°C to 120°C) and when an AC voltage is applied, even when the film thickness is as thin as 6.0 μm or less. Furthermore, it has excellent heat shrinkage resistance in that thermal shrinkage in the mechanical direction (MD) is suppressed at temperatures exceeding the above high temperature, up to approximately 150°C. In addition, the film capacitor of this disclosure using the polypropylene film as a capacitor derivative has excellent heat resistance at high temperatures of approximately 120°C (100°C to 120°C). Specifically, it has excellent life performance in that the decrease in capacitance of the capacitor is suppressed even when used for a long time at the above high temperature, and it also has excellent thermal shock resistance in that thermal compression (deformation) of the capacitor is suppressed during repeated use between the above high and low temperatures, such as in an engine compartment. Therefore, the polypropylene film of this disclosure is suitable for film capacitor applications and, preferably, can be used as a capacitor derivative constituting an inverter in a hybrid vehicle or electric vehicle.

[0092] Metal layer integrated polypropylene film capacitors and methods for manufacturing the same The polypropylene film of this disclosure may be a metal-layer integrated polypropylene film having a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film, taking into consideration processing into capacitors.

[0093] The metal layer functions as an electrode. Suitable metals for the metal layer include, for example, individual metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, as well as mixtures of these metals and their alloys. However, considering environmental factors, economic efficiency, and capacitor performance, zinc and aluminum are preferred.

[0094] Methods for laminating a metal layer onto one or both sides of a polypropylene film include, for example, vacuum deposition and sputtering. From the viewpoint of productivity and economic efficiency, vacuum deposition is preferred. Examples of vacuum deposition methods include the crucible method and the wire method, but there are no particular limitations, and the most suitable method can be selected as appropriate.

[0095] While there are no particular limitations on the margin pattern when laminating metal layers by vapor deposition, it is preferable to apply a pattern including so-called special margins, such as a fishnet pattern or T-margin pattern, to one side of the polypropylene film in order to improve characteristics such as the safety of the capacitor. This enhances safety and is effective in preventing capacitor failure and short circuits.

[0096] Any method known to form a margin, such as the tape method or the oil method, can be used without any limitations.

[0097] Furthermore, the metal-layer-integrated polypropylene film of this disclosure can be laminated or wound into a film capacitor using conventionally known methods.

[0098] The film capacitor of this disclosure preferably has an insulation resistance of 20 MΩ·μF or more at an ambient temperature of 115°C. An example of such insulation resistance is 200 MΩ·μF or less. Here, the insulation resistance value is defined by the product of the capacitor's nominal capacitance and insulation resistance (C·IR product).

[0099] In other words, the film capacitor may have a structure in which multiple metal-layer-integrated polypropylene films are laminated, or it may have a wound metal-layer-integrated polypropylene film. Such a film capacitor can be suitably used as a capacitor for inverter power supply equipment that controls drive motors in electric vehicles and hybrid vehicles. In addition, it can be suitably used in railway vehicles, wind power generation, solar power generation, and general home appliances. [Examples]

[0100] The present disclosure will be specifically described below with reference to examples and comparative examples. However, the present disclosure is not limited to the examples. ≪Resin≫ Details of the resins used in the examples and comparative examples (PP resins A1-A7 and PP resins B1-B8) are summarized in Table 1 below, along with a description of the measurement methods for each physical property.

[0101] [Table 1]

[0102] PP resin A1: Manufactured by Borealis Co., Ltd. PP resin A2~A7: Manufactured by Prime Polymer Co., Ltd. PP resin B1: Manufactured by Daehan Oil & Chemical Co., Ltd. PP resin B2: Manufactured by Daehan Yuka Co., Ltd., product name "S800" PP resin B3: Manufactured by Samsung Total Co., Ltd., product name "HU300" PP resin B4: Manufactured by Daehan Oil & Chemical Co., Ltd. PP resin B5: Manufactured by Daehan Oil & Chemical Co., Ltd. PP resin B6: Manufactured by Daehan Oil & Chemical Co., Ltd. PP resin B7: Manufactured by Daehan Oil & Chemical Co., Ltd. PP resin B8: Manufactured by Daehan Oil & Chemical Co., Ltd.

[0103] Measurement of the number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), and weight fraction w of polypropylene resin. First, using SEC (size exclusion chromatography), the average molecular weight and molecular weight distribution of each polypropylene resin were measured under the following conditions. Equipment: HLC-8321GPC / HT (Detector: Differential Refractometer (RI)) (Manufactured by Tosoh Corporation) Columns: TSKgel guardcolumnHHR(30)HT (7.5mm I.D. × 7.5cm) × 1 + TSKgel GMHHR-H(20)HT (7.8mm I.D. × 30cm) × 3 (Manufactured by Tosoh Corporation) Eluent: 1,2,4-Trichlorobenzene (for GPC, manufactured by Fujifilm Wako Pure Chemical Industries) + BHT (0.05%) Flow rate: 1.0mL / min Detection condition: polarization-(-) Injection volume: 0.3mL Column temperature: 140℃ Temperature: 40°C Sample concentration: 1 mg / mL Sample preparation: The sample was weighed, and dissolved in solvent (1,2,4-trichlorobenzene with 0.1% BHT added) by shaking at 140°C for 1 hour. The mixture was then filtered by heating through a 0.5 μm sintered filter. Calibration Curve: A calibration curve of the fifth order approximation was created using standard polystyrene manufactured by Tosoh Corporation. However, the molecular weight was converted to the molecular weight of polypropylene using the Q-factor.

[0104] From the obtained calibration curve and SEC chromatogram, the integral values ​​of the concentration fraction were plotted on the x-axis with molecular weight (logarithmic value) and on the y-axis using analysis software for the measurement device to obtain the integral molecular weight distribution curve. The differential values ​​(slope of the integral molecular weight distribution curve) of the integral molecular weight distribution curve were determined for each molecular weight, and the differential values ​​were plotted on the x-axis with molecular weight (logarithmic value) and on the y-axis to obtain the differential molecular weight distribution curve.

[0105] From these curves, the number-average molecular weight Mn, weight-average molecular weight Mw, and Z-average molecular weight Mz were obtained. The molecular weight distribution (Mw / Mn) was then obtained using these values ​​of Mw and Mn. Furthermore, the weight fraction w was defined as the value at which the logarithmic molecular weight Log(M) = 4.0 in the integrated molecular weight distribution curve. This weight fraction w represents the weight fraction of molecules with a logarithmic molecular weight Log(M) = 4.0, i.e., a molecular weight of 10,000 or less.

[0106] <Measurement of differential distribution values ​​when logarithmic molecular weight Log(M) = 4.5, when logarithmic molecular weight Log(M) = 6.0, and the difference in molecular weight differential distribution values ​​(DM)> For each polypropylene resin, the differential distribution values ​​when the logarithmic molecular weight Log(M) = 4.5 and when the logarithmic molecular weight Log(M) = 6.0 were obtained using the following method. First, the time curve (elution curve) of the intensity distribution detected using an RI detector was converted into a distribution curve for the molecular weight M(Log(M)) of standard polystyrene using a calibration curve prepared using the standard polystyrene described above. Next, after obtaining the integral distribution curve for Log(M) with the total area of ​​the distribution curve set to 100%, the differential distribution curve for Log(M) was obtained by differentiating this integral distribution curve with respect to Log(M). From this differential distribution curve, the differential distribution values ​​for Log(M) = 4.5 and Log(M) = 6.0 were read. The difference between the differential distribution value for Log(M) = 4.5 and the differential distribution value for Log(M) = 6.0 was defined as the molecular weight differential distribution difference (DM). The series of operations up to obtaining the differential distribution curve was performed using the analysis software built into the GPC measurement device used.

[0107] <<Measurement of heptane insoluble matter (HI)>> For each polypropylene resin, a sample of approximately 3 g was prepared by press molding to 10 mm × 35 mm × 0.3 mm. Next, approximately 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble portion was calculated from the sample mass before and after extraction.

[0108] ≪Measuring Melt Flow Rate (MFR)≫ The melt flow rate (MFR) of the raw material resin pellets used in the examples and comparative examples was measured according to condition M of JIS K 7210 using the Melt Index from Toyo Seiki Co., Ltd. Specifically, first, a 4g sample was inserted into a cylinder heated to a test temperature of 230°C and preheated for 3.5 minutes under a load of 2.16 kg. Then, the weight of the sample extruded from the bottom hole over 30 seconds was measured to determine the MFR (unit: g / 10 min or g / 10 min). The above measurement was repeated three times, and the average value was taken as the measured value of MFR.

[0109] <Examples 1-6 and Comparative Examples 1-15> [Manufacturing of biaxially oriented polypropylene film and evaluation of its properties] According to Table 2, polypropylene resins A and B were weighed and mixed in the weight ratios shown in Table 2 to obtain a dry blend resin composition. Next, the dry blend resin composition was supplied to an extruder and melted at the melting temperature and shear rate shown in Table 2. This molten resin was extruded using a T-die and solidified on a metal drum maintained at a surface temperature of 95°C to produce a cast raw material sheet. The unstretched cast raw material sheet was kept at a temperature of 140°C and stretched 4.5 times in the flow direction by passing it between rolls with a speed difference, and then immediately cooled to room temperature. Subsequently, the stretched film obtained by stretching in the flow direction was led to a tenter and stretched 10 times in the width direction at a transverse stretching temperature of 158°C, then relaxed at a relaxation rate of 12% and heat-set to produce a biaxially oriented polypropylene film with a width of approximately 5 m and a thickness of 2.3 μm. Approximately 80,000 m of this film was wound onto a 400 mm diameter iron core under the atmosphere shown in Table 2 to form a jumbo roll. The wound-up biaxially oriented polypropylene film was subjected to an aging treatment by being treated in a 35°C atmosphere for 24 hours.

[0110] [Table 2]

[0111] Furthermore, in the film properties listed in Table 2, the Mz value for Comparative Example 5, which uses resin 3 as the base resin, is 1.18 million, and the Mz value for Comparative Example 6, which uses resin 2, is 1.8 million. In contrast, the Mz values ​​for resin 3 and resin 2 listed in Table 1 are 1.2 million and 1.9 million respectively, indicating that the Mz values ​​in the film properties are somewhat smaller in each case. This is thought to mean that the high molecular weight components were decomposed due to melting or other processes during the manufacturing of the film using polypropylene resin.

[0112] The following describes the methods for measuring the thickness, density, and dielectric breakdown strength of the biaxially oriented polypropylene films obtained in each example and comparative example, the method for performing thermomechanical analysis (TMA), and the method for evaluating the winding quality (wrinkles) of jumbo rolls during aging. The results of each measurement and evaluation are also shown in Table 2.

[0113] ≪Measurement of polypropylene film thickness≫ Under conditions of 23±2℃ and 50±5%RH humidity, a Citizen Seimitsu Co., Ltd. MEI-11 paper thickness gauge (measuring pressure 100kPa, descent speed 3mm / sec, measuring terminal φ=16mm, measuring force 20.1N) was used. Samples were cut from the roll while stacked in groups of 10 or more, and care was taken to prevent wrinkles or air bubbles from entering the film during cutting. Five measurements were taken on each of the 10-sheet stacked samples, and the thickness was calculated by dividing the average of the five measurements by 10.

[0114] <<Measurement of polypropylene film density>> The density of the polypropylene film was measured according to JIS K7112(1999)D method. Measuring device: Density gradient tube type specific gravity measuring device, Type A, manufactured by Shibayama Scientific Instruments Co., Ltd. Gradient solution: Ethanol aqueous solution Measurement temperature: 23±0.5℃ Number of measurements: n=3

[0115] ≪Measurement of dielectric breakdown strength of polypropylene film: DC≫ The dielectric breakdown voltage (BDV) of a polypropylene film at 100°C or 120°C was measured 16 times under the following test conditions, using the electrode configuration described in JIS C2151 (2006) 17.2.2 (Platform electrode method). The applied voltage at which the leakage current exceeding the upper limit specified below was detected during voltage boosting was defined as the BDV. The BDV was divided by the film thickness (μm), and the average of the 12 values ​​obtained by excluding the top 2 and bottom 2 values ​​from the 16 measurements was defined as the dielectric breakdown strength DCES (V / μm). Test specimen: Approximately 150mm x 150mm Conditioning of test specimens: 30 minutes under atmospheric conditions Power supply: DC Ambient environment: In air, at 100°C or 120°C Testing equipment: Kikusui Electronics Co., Ltd. DC withstand voltage / insulation resistance tester TOS9213AS Voltage rise rate: 100V / s Current detection response speed: MID Upper limit: 5mA

[0116] Volume resistivity <Measurement of volume resistivity ρV> The specific measurement procedure for volume resistivity is described below. Unless otherwise specified, measurements were taken as follows, based on JIS C 2139-3-1:2018. First, a jig for measuring volume resistivity (hereinafter simply referred to as the jig) was placed in a constant temperature chamber at 100°C. The configuration of the jig is as follows. A DC power supply and a DC ammeter were also connected to the jig.

[0117] <Jig for measuring volume resistivity> Main electrode (50mm diameter) Counter electrode (85mm diameter) Annular guard electrode surrounding the main electrode (outer diameter 80mm, inner diameter 70mm) Each electrode is made of gold-plated copper, and conductive rubber is attached to the surface that comes into contact with the sample. The conductive rubber used is EC-60BL(W300) manufactured by Shin-Etsu Silicone Co., Ltd., and the glossy side of the conductive rubber is attached so that it comes into contact with the gold-plated copper. Next, the resin films of the examples and comparative examples (hereinafter also referred to as "samples") were placed in a jig inside a constant temperature bath. Specifically, the main electrode and guard electrode were placed in close contact with one side of the sample, and the counter electrode was placed in close contact with the other side, and the sample and each electrode were pressed together with a load of 5 kgf. After that, it was left to stand for 30 minutes. Next, a voltage was applied to the sample to achieve a potential gradient of 200 V / μm. The current values ​​were read at 5 and 10 minutes after the voltage was applied, and the volume resistivity was calculated using the following formula. A Keithley 6517B (electrometer / insulation resistance meter) was used for voltage application and current measurement. Volume resistivity = [(Effective electrode area) × (Applied voltage)] / [(Sample thickness) × (Current value)] Here, the effective electrode area was calculated using the following formula. (Effective electrode area) = Pi × [[[(Diameter of main electrode) + (Inner diameter of guard electrode)] / 2] / 2] 2 This process was repeated three times, and the arithmetic mean, rounded to one significant figure, was defined as the volume resistivity (Ω·cm).

[0118] [Fabrication of film capacitors and evaluation of their characteristics] Using the biaxially oriented polypropylene films obtained in each example and comparative example, film capacitors were fabricated according to the following procedure.

[0119] A metal-layer integrated polypropylene film was obtained by forming a special vapor deposition pattern margin and an insulating margin on a biaxially oriented polypropylene film to provide film capacitor safety, and then vapor-depositing aluminum so that the surface resistivity of the metal film was 20 Ω / □. Next, the metal-layer integrated polypropylene film was slit to an arbitrary width, and then two of the metal-layer integrated polypropylene films were combined. Using a Kaito Manufacturing Co., Ltd. automatic winding machine 3KAW-N2, the metal-layer integrated polypropylene film was wound with a winding speed of 4 m / sec, a winding tension of 180 g, and a contact roller contact pressure of 260 g, setting the number of turns so that the element capacitance would be 50 μF.

[0120] The element-wound components were flattened by pressing, and then, while the pressing load was still applied, zinc metal was sprayed onto the end faces of the components to form electrode extraction sections. Finally, they were heat-treated at 120°C for 15 hours to cure them.

[0121] After heat curing, leads were soldered to the end faces of the element, and the capacitors were sealed with epoxy resin to obtain flattened film capacitors. The capacitance of all the obtained film capacitors was 50 μF (±3 μF).

[0122] The following describes the methods for evaluating the vapor deposition processability, element winding processability, and lifespan characteristics and thermal shock resistance of the film capacitors obtained in each example and comparative example. The results of each evaluation are also shown in Table 2.

[0123] ≪Vapour-deposition processability≫ A "○" indicates that the rate of wrinkles due to thermal deformation in the film after vapor deposition was less than 5%, while a "×" indicates that it was 5% or more.

[0124] <<Evaluation of element winding processability>> From the small windings obtained by vapor deposition and slitting, two windings were stacked and wound using a left-margin winding reel and a right-margin winding reel, with the vapor-deposited portion extending beyond the margin in the width direction (element winding process). Winding was performed using a 3KAW-N2 automatic winding machine manufactured by Kaito Seisakusho Co., Ltd., with a winding tension of 200g, for 1360 turns. During this process, the entire winding process was visually inspected from start to finish, and any windings with wrinkles or misalignment were deemed unacceptable. The percentage of unacceptable windings relative to the total number manufactured was used as an indicator of processability (hereinafter referred to as element winding yield). A higher element winding yield is preferable. A yield of 95% or higher was evaluated as good ("○"), and a yield of less than 95% was evaluated as poor ("×").

[0125] ≪Lifespan Characteristics (Rate of Change in Capacitance)≫ The initial capacitance of the obtained capacitors before testing was measured using a HIOKI LCR HiTester 3522-50. Next, the capacitors were subjected to a DC voltage of 800V (348V / μm) for 500 hours in a high-temperature chamber at 115°C. The capacitance of the capacitors after 500 hours was measured again, and the capacitance change rate before and after voltage loading was calculated using the following formula. The test was performed on two samples, and the average value was used for evaluation.

[0126] (Percentage change in capacitance) = [(Capacitance after voltage load) - (Initial capacitance)] / (Initial capacitance) × 100 (%) After 500 hours, a capacity change rate of -4% or less was classified as good ("○"), a change rate between -4% and -6% was classified as "△", and a change rate exceeding -6% was classified as poor ("×").

[0127] ≪Insulation resistance at high temperatures (high-temperature IR)≫ For each capacitor obtained as described above, the insulation resistance at 115°C was measured using the following method: A Hioki Electric Corporation DSM8104 super insulation resistance meter was connected to a SME-8350 shielding box. A metallized film capacitor element was placed inside the shielding box, and a DC voltage of 750V was applied. The insulation resistance value [in MΩ] after 1 minute was read. The value was rounded to two decimal places. For measurement conditions other than those described herein, the specifications of JIS C 5101-16:2009 "4.2.4 Insulation Resistance" were followed. The product of this measurement and the nominal capacitance of the capacitor element (50 μF) (C·IR product) is shown in Table 3.

[0128] [Table 3]

Claims

1. Polypropylene film, The polypropylene resin comprising the aforementioned polypropylene film is - The molecular weight distribution (Mw / Mn) between the weight-average molecular weight Mw and the number-average molecular weight Mn is 5.0 or higher and 6.9 or lower. - The average molecular weight Mz is between 950,000 and 1,500,000. - In the integral molecular weight distribution curve, the weight fraction w when the logarithmic molecular weight Log(M) = 4.0 is 2.6% or more and 4.0% or less. It is a biaxially oriented film. Polypropylene film.

2. A polypropylene film according to claim 1, for use in capacitors.

3. The density measured in accordance with the provisions of Method D of JIS K7112:1999 is 919 kg / m³ or more and 925 kg / m³. 3 The polypropylene film according to claim 1 or 2, which is as follows:

4. A polypropylene film according to any one of claims 1 to 3, wherein the dielectric breakdown strength (DCES) at a DC voltage at 120°C is 530 V / μm or more.

5. The aforementioned polypropylene resin contains polypropylene resin A and polypropylene resin B which is different from polypropylene resin A. The Mw of the aforementioned polypropylene resin A is 250,000 or more and less than 350,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 5.5 or more and 10.0 or less. - The melt flow rate (MFRA) of the polypropylene resin A is 3.0 g / 10 min or more and 10.0 g / 10 min or less. The polypropylene film according to any one of claims 1 to 4, wherein the content of polypropylene resin A in the polypropylene resin is greater than the content of polypropylene resin B in the polypropylene resin.

6. The aforementioned polypropylene resin contains polypropylene resin A and polypropylene resin B which is different from polypropylene resin A. The Mw of the aforementioned polypropylene resin B is between 300,000 and 550,000. - The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 5.0 or more and 11.0 or less. - The melt flow rate (MFRB) of the polypropylene resin B is 0.1 g / 10 min or more and 3.0 g / 10 min or less. The polypropylene film according to any one of claims 1 to 5, wherein the content of polypropylene resin A in the polypropylene resin is greater than the content of polypropylene resin B in the polypropylene resin.

7. The polypropylene film according to claim 5 or 6, wherein the ratio of the mass of polypropylene resin A to the total mass of polypropylene resin B is 55% by mass or more and 75% by mass or less.

8. The polypropylene film according to any one of claims 1 to 7, wherein the thickness of the polypropylene film is 1.0 μm or more and 2.4 μm or less.

9. A film capacitor having a wound metal layer integrated polypropylene film, or having a configuration in which multiple metal layer integrated polypropylene films are laminated together, The aforementioned metal-layer integrated polypropylene film comprises a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film. The aforementioned polypropylene film is a biaxially oriented film, The polypropylene resin constituting the aforementioned polypropylene film has a Z-average molecular weight Mz of 950,000 to 1,500,000. The aforementioned polypropylene film has a dielectric breakdown strength (DCES) of 530 V / μm or higher at a DC voltage at 120°C. The aforementioned film capacitor is a film capacitor having an insulation resistance of 20 MΩ·μF or more at an ambient temperature of 115°C.

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