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

Abstract

To provide a polypropylene film having excellent dielectric breakdown strength and heat shrinkage resistance at high temperature, and to provide a film capacitor using the polypropylene film and having excellent life performance and excellent thermal shock resistance at high temperature.SOLUTION: The polypropylene film is composed of a polypropylene resin, in the polypropylene resin: a molecular weight distribution (Mw / Mn) of a weight average molecular weight Mw and a number average molecular weight Mn is 5.0 or more and 6.7 or less; a Z-average molecular weight Mz is 650000 or more and 945000 or less; and a weight fraction w at a logarithmic molecular weight Log (M)=4.0 in an integral molecular weight distribution curve is 2.6% or more and 4.2% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene film, a metal layer-integrated polypropylene film, and a film capacitor. [Background technology]

[0002] The polypropylene film can be used as a dielectric for a capacitor, for example, in an inverter that constitutes a power control unit for a hybrid vehicle, an electric vehicle, or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 056404 Summary of the Invention [Problem to be solved by the invention]

[0004] Capacitors that use polypropylene film as a capacitor dielectric are required to be small, lightweight, and have high capacity, while also having excellent heat resistance at high temperatures of around 120°C (100°C to 120°C), in consideration of the above-mentioned operating environments (for example, the environment in an engine compartment where temperatures rise, and the capacitor's own heat generation). Specifically, they are required to suppress the decrease in capacitance of the capacitor even when used for long periods at the above-mentioned high temperatures (excellent life performance), and to suppress thermal compaction (deformation) of the capacitor when used repeatedly between the above-mentioned high and low temperatures, as is assumed in an engine compartment (excellent thermal shock resistance).

[0005] Furthermore, polypropylene films for producing the above-mentioned capacitors are required to have excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at the above-mentioned high temperatures, even when the film is thin, such as less than 20 μm, and excellent dielectric breakdown strength when an AC voltage is applied, and further to have suppressed thermal shrinkage in the machine direction (MD) at temperatures up to about 150°C, which exceeds the above-mentioned high temperatures (excellent heat shrinkage resistance).

[0006] However, the polypropylene film and capacitor using the same described in Patent Document 1 do not comprehensively satisfy the capacitor performances of excellent life performance and excellent thermal shock resistance, and the film performances of excellent dielectric breakdown strength and excellent heat shrinkage resistance, and there is room for further improvement.

[0007] The present invention has been made in view of the above-mentioned problems, and its object is to provide a polypropylene film having excellent dielectric breakdown strength and heat shrinkage resistance at high temperatures, a film capacitor using the polypropylene film having excellent life performance and excellent thermal shock resistance at high temperatures, and methods for manufacturing the same.

[0008] Another object of the present invention is to provide a metal layer-integrated polypropylene film having the above polypropylene film, a film capacitor having the metal layer-integrated polypropylene film, and methods for producing the same. [Means for solving the problem]

[0009] The present inventors conducted extensive research into polypropylene films. As a result, they discovered that polypropylene films containing polypropylene resins having molecular weight distributions (Mw / Mn) of weight-average molecular weight Mw and number-average molecular weight Mn, Z-average molecular weight Mz, and weight fraction w at logarithmic molecular weight Log(M) = 4.0 in the integrated molecular weight distribution curve, each falling within a specific range, exhibit the aforementioned film performance, and that capacitors using such polypropylene films exhibit the aforementioned capacitor performance. They also discovered that the polypropylene film and film capacitor of the present invention can be suitably produced by a production method including a step of melting a polypropylene resin composition at a specific shear rate.

[0010] That is, the present invention relates to the following polypropylene film, metal layer-integrated polypropylene film, film capacitor, and methods for producing the same. 1. A polypropylene film, wherein the polypropylene resin constituting the polypropylene film is The molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn is 5.0 or more and 6.9 or less, The Z-average molecular weight Mz is 650,000 or more and 945,000 or less, 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 4.2% or less. A polypropylene film characterized by: 2. The polypropylene film according to item 1, which is for use in a capacitor. 3. The polypropylene film according to item 1 or 2, which is a biaxially stretched film. 4. Thermomechanical analysis: 2.17N / mm 2 4. The polypropylene film according to any one of items 1 to 3, wherein when the film is heated from 25°C to 155°C at a rate of 10°C / min under a load of 0.5°C, and a heating dimensional change curve is plotted with the horizontal axis representing temperature and the vertical axis representing dimensional change in the machine direction (MD) of the film, the dimensional change during the heating process from 25°C to 155°C is 0% or more. 5. Dielectric breakdown strength at 120℃ under DC voltage (V DC120℃ ) and the dielectric breakdown strength (V AC120℃ ) and the difference (V DC120℃ -V AC120℃ 5. The polypropylene film according to any one of items 1 to 4, wherein the surface tension (Tc) is 280 V / μm or more and 300 V / μm or less. 6. The polypropylene film according to any one of items 1 to 5, wherein the Mz exceeds 700,000. 7. The molecular weight distribution (Mw / Mn) is 5.0 or more and 6.6 or less, The Mz is 720,000 or more and 790,000 or less, The weight fraction w is 3.5% or more and 3.7% or less; 7. The polypropylene film according to any one of items 1 to 6. 8. The polypropylene resin contains polypropylene resin A and polypropylene resin B, and the content of polypropylene resin A in the polypropylene resin is greater than the content of polypropylene resin B in the polypropylene resin; The Mw of the polypropylene resin A is 275,000 or more and less than 350,000, The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 5.8 or more and 10.0 or less, The melt flow rate (MFR A ) is 4.8g / 10min or more and 5.5g / 10min or less, 8. The polypropylene film according to any one of items 1 to 7. 9. The polypropylene resin contains polypropylene resin A and polypropylene resin B, and the content of polypropylene resin A in the polypropylene resin is greater than the content of polypropylene resin B in the polypropylene resin; The Mw of the polypropylene resin B is 385,000 or more and 550,000 or less, The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.4 or more and 11.0 or less, The melt flow rate (MFRB ) is 0.1g / 10min or more and 2.2g / 10min or less, 9. The polypropylene film according to any one of items 1 to 8. 10. The polypropylene film according to item 8 or 9, wherein the proportion of the mass of the polypropylene resin A to the total mass of the polypropylene resin A and the polypropylene resin B is 65 to 75 mass %. 11. The polypropylene film according to any one of items 1 to 10, wherein the thickness of the polypropylene film is 1.0 μm or more and 6.0 μm or less. 12. The polypropylene film according to any one of items 1 to 11 above, A metal layer laminated on one or both sides of the polypropylene film, Polypropylene film with integrated metal layer. 13. A film having a wound metal layer-integrated polypropylene film according to item 12, or a film having a structure in which a plurality of metal layer-integrated polypropylene films according to item 12 are laminated. Film capacitor. 14. The method for producing a polypropylene film according to any one of items 1 to 11, comprising: subjecting a polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B to a temperature of 225°C or higher and 270°C or lower and a shear rate of 2000 s -1 More than 15000s -1 Melting the MFR of the polypropylene resin A A and the MFR of the polypropylene resin B B Differential MFR A -MFR B is 1.5g / 10min or more, The content of the polypropylene resin A in the polypropylene resin composition is greater than the content of the polypropylene resin B in the polypropylene resin composition. A method for producing a polypropylene film. 15. The method for producing a polypropylene film according to item 14, wherein the polypropylene film is for use in a capacitor. 16. The method for producing a polypropylene film according to item 14 or 15, wherein the polypropylene film is a biaxially stretched film. 17. The method for producing a polypropylene film according to any one of items 14 to 16, wherein the ratio of the mass of the polypropylene resin A to the total mass of the polypropylene resin A and the polypropylene resin B is 65 to 75 mass %. 18. The method for producing a polypropylene film according to any one of items 14 to 17, wherein the polypropylene film has a thickness of 1.0 μm or more and 2.4 μm or less. 19. A method for producing a metal layer-integrated polypropylene film, comprising the method according to any one of items 14 to 18, and further comprising the step of forming a metal layer on at least one surface of the polypropylene film. 20. A method for producing a film capacitor, comprising the method according to item 19, and further comprising a step of winding the metal layer-integrated polypropylene film. [Effects of the Invention]

[0011] The polypropylene film of the present invention has a polypropylene resin constituting the film, and the molecular weight distribution (Mw / Mn) of the weight-average molecular weight Mw and the number-average molecular weight Mn, the Z-average molecular weight Mz, and the weight fraction w at the logarithmic molecular weight Log(M)=4.0 in the integrated molecular weight distribution curve are all within specific ranges. Therefore, even when the film is thin, such as 6.0 μm or less, it has excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at a high temperature of about 120°C (100°C to 120°C) and excellent dielectric breakdown strength when an AC voltage is applied. Furthermore, it has excellent heat shrinkage resistance in that heat shrinkage in the machine direction (MD) is suppressed at temperatures up to about 150°C, which exceeds the above-mentioned high temperature. Furthermore, the film capacitor of the present invention, which uses the polypropylene film as a capacitor dielectric, has excellent heat resistance at high temperatures of about 120°C (100°C to 120°C), and specifically, has excellent life performance in that the decrease in capacitance of the capacitor is suppressed even when used for a long period of time at the high temperatures, and also has excellent thermal shock resistance in that the thermal compaction (deformation) of the capacitor is suppressed when used repeatedly between the high and low temperatures assumed to be in an engine compartment. Therefore, the polypropylene film of the present invention is suitable for use in film capacitors. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows the results of thermomechanical analysis (TMA) of the polypropylene films produced in Example 1, Comparative Example 5, and Comparative Example 14, and shows the results of drawing dimensional change curves over time, with the horizontal axis representing temperature and the vertical axis representing the dimensional change rate in the machine direction (MD) of the film. [Figure 2] 1A and 1B are schematic diagrams showing the external appearance of a jumbo roll after aging, excluding approximately 100 mm from both ends, in which (A) is a schematic diagram showing a case where there are no circumferential dies (vertical dies) with a depth of 0.5 mm or more, and (B) is a schematic diagram showing an example where there are two circumferential dies (vertical dies) with a depth of 0.5 mm or more. DETAILED DESCRIPTION OF THE INVENTION

[0013] The polypropylene film, metal layer-integrated polypropylene film, and film capacitor of the present invention, as well as methods for producing them, will be described in detail below.

[0014] In this specification, polypropylene may be abbreviated as PP, and polypropylene resin may be abbreviated as PP resin.

[0015] In this specification, the expressions "contain" and "comprise" include the concepts of "contain", "include", "consist essentially of" and "consist only of".

[0016] In this specification, the expression "capacitor" includes the concepts of "capacitor," "capacitor element," and "film capacitor."

[0017] In this specification, the directions of polypropylene films are as follows. First, the machine direction of the film is the same as the machine direction (hereinafter referred to as "MD direction"). The MD direction is sometimes called the length direction or flow direction. Next, the lateral direction of the film is the same as the transverse direction (hereinafter referred to as "TD direction"). The TD direction is sometimes called the width direction.

[0018] Polypropylene film The polypropylene film of the present invention is characterized in that the polypropylene resin constituting the polypropylene film is The molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn is 5.0 or more and 6.9 or less, The Z-average molecular weight Mz is 650,000 or more and 945,000 or less, 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 4.2% or less. These are hereinafter abbreviated as "Mw", "Mn", "molecular weight distribution (Mw / Mn)", "Mz", "weight fraction w", etc.

[0019] The polypropylene film of the present invention having the above-mentioned characteristics has a molecular weight distribution (Mw / Mn) of weight-average molecular weight Mw and number-average molecular weight Mn, a Z-average molecular weight Mz, and a weight fraction w at logarithmic molecular weight Log(M)=4.0 in an integrated molecular weight distribution curve, each of which falls within a specific range. Therefore, even when the film is thin, such as 6.0 μm or less, it has excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at a high temperature of about 120°C (100°C to 120°C) and excellent dielectric breakdown strength when an AC voltage is applied. Furthermore, it has excellent heat shrinkage resistance in that heat shrinkage in the machine direction (MD) is suppressed at temperatures up to about 150°C, which exceeds the above-mentioned high temperature. Furthermore, the film capacitor of the present invention using the polypropylene film as a capacitor dielectric exhibits excellent heat resistance at high temperatures of approximately 120°C (100°C to 120°C). Specifically, the capacitor exhibits excellent life performance in that the capacitance of the capacitor is suppressed from decreasing even when used for a long period of time at the high temperatures. The film capacitor also exhibits excellent thermal shock resistance in that the capacitor is prevented from thermally compressing (deforming) during repeated use between the high and low temperatures assumed to be used in an engine compartment. Therefore, the polypropylene film of the present invention is suitable for use in film capacitors. The polypropylene film of the present invention may or may not be stretched, but is preferably a biaxially stretched film, taking the above-mentioned applications into consideration.

[0020] In the present invention, both surfaces of the polypropylene film can be defined as a first surface and a second surface. The first surface can be rough. If the first surface is rough, wrinkles are less likely to occur when winding the element in the capacitor fabrication. The second surface can also be rough.

[0021] The thickness of the polypropylene film is preferably 0.8 μm or more and 6.0 μm or less from the viewpoint of ensuring miniaturization and high capacitance of the capacitor when used in a capacitor. Specifically, it is preferably 5.5 μm or less, more preferably 3.5 μm or less, even more preferably 3.0 μm or less, and particularly preferably 2.4 μm or less. Furthermore, from the viewpoint of manufacturing, 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.

[0022] The density of the polypropylene film is not critical, but considering its use in a capacitor, it is preferably 919 g / cm 3 . 3 More than 925g / cm 3 It is preferable to set it as follows: The density of the polypropylene film in this specification is measured by the method described in the Examples.

[0023] In the polypropylene film of the present invention, the polypropylene resin constituting the polypropylene film (after mixing when the polypropylene resin is a mixture of multiple resins) has a molecular weight distribution (Mw / Mn) of 5.0 or more and 6.9 or less.

[0024] The molecular weight distribution (Mw / Mn) may be 5.0 or more and 6.9 or less, with the lower limit being preferably 5.2 or more, more preferably 5.6 or more, even more preferably 5.8 or more, even more preferably 6.0 or more, even more preferably 6.2 or more, and even more preferably 6.3 or more. The upper limit is preferably 6.8 or less, more preferably 6.7 or less, and even more preferably 6.6 or less. By having the molecular weight distribution (Mw / Mn) within this range, in combination with other requirements, a polypropylene film can be obtained that has excellent dielectric breakdown strength at high temperatures and suppressed heat shrinkage in the machine direction (MD).

[0025] In the polypropylene film of the present invention, the polypropylene resin constituting the polypropylene film (after mixing when the polypropylene resin is composed of a mixture of multiple resins) has an Mz of 650,000 or more and 945,000 or less.

[0026] Mz may be from 650,000 to 945,000, with the lower limit preferably exceeding 700,000, more preferably 710,000 or more, and even more preferably 720,000 or more. The upper limit is preferably 920,000 or less, more preferably 850,000 or less, and even more preferably 790,000 or less. By ensuring that Mz is within this range, in combination with other requirements, a polypropylene film can be obtained that exhibits excellent dielectric breakdown strength at high temperatures and that exhibits reduced thermal shrinkage, particularly in the machine direction (MD). If Mz exceeds 945,000, which is outside the range of the present invention, the heat shrinkability of the polypropylene film at high temperatures is likely to increase.

[0027] In the polypropylene film of the present invention, the weight fraction w at logarithmic molecular weight Log(M)=4.0 in the integrated molecular weight distribution curve of the polypropylene resin constituting the polypropylene film (in the case where the polypropylene resin is a blend of multiple resins, after blending) is 2.6% or more and 4.2% or less.

[0028] The weight fraction w may be 2.6% or more and 4.2% or less, with the lower limit being preferably 2.8% or more, more preferably 3.0% or more, even more preferably 3.2% or more, and even more preferably 3.4% or more. The upper limit is preferably 4.1% or less, more preferably 4.0% or less, even more preferably 3.7% or less, and even more preferably 3.6% or less. By ensuring that the weight fraction w is within this range, in combination with other factors, a polypropylene film can be obtained that exhibits excellent dielectric breakdown strength at high temperatures and reduced thermal shrinkage in the machine direction (MD). Furthermore, by ensuring that the weight fraction w is within this range, the film capacitor of the present invention using the polypropylene film as a capacitor dielectric exhibits excellent thermal shock resistance in that thermal compaction (deformation) of the capacitor is suppressed during repeated use at high and low temperatures.

[0029] In a preferred embodiment of the polypropylene film of the present invention, the polypropylene resin constituting the polypropylene film (in the case where the polypropylene resin is a mixture of a plurality of resins, after mixing) is: The molecular weight distribution (Mw / Mn) is 5.0 or more and 6.6 or less, The Mz is 720,000 or more and 850,000 or less, The weight fraction w is 3.3% or more and 3.7% or less; By using a polypropylene resin having such physical properties, it becomes easier to obtain a polypropylene film that has excellent dielectric breakdown strength at high temperatures and that is suppressed in thermal shrinkage in the machine direction (MD).

[0030] In a more preferred embodiment of the polypropylene film of the present invention, the polypropylene resin constituting the polypropylene film (after mixing, in the case where the polypropylene resin is composed of a mixture of multiple resins) is: The molecular weight distribution (Mw / Mn) is 5.0 or more and 6.6 or less, The Mz is 720,000 or more and 790,000 or less, The weight fraction w is 3.5% or more and 3.7% or less; By using a polypropylene resin having such physical properties, it becomes easier to obtain a polypropylene film that has excellent dielectric breakdown strength at high temperatures and that is suppressed in thermal shrinkage in the machine direction (MD).

[0031] The Mw, Mn, Mz, molecular weight distribution (Mw / Mn), and weight fraction w of the polypropylene resin constituting the polypropylene film in this specification, and the 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 value difference (D M ) and weight fraction w are measured by the methods described in the Examples.

[0032] The polypropylene film of the present invention contains a polypropylene resin. The content of the polypropylene resin is preferably 90% by weight or more, more preferably 95% by weight or more, based on the entire polypropylene film (when the entire polypropylene film is taken as 100% by weight). The upper limit of the content of the polypropylene resin is, for example, 100% by weight, 98% by weight, etc., based on the entire polypropylene film.

[0033] The lower the total ash content of the polypropylene resin, the better 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. The lower the total ash content, the fewer impurities such as polymerization catalyst residues there are.

[0034] The polypropylene resin may contain one type of polypropylene resin alone, or may contain two or more types of polypropylene resins.

[0035] When the polypropylene film of the present invention contains two or more polypropylene resins, the polypropylene resin with the largest content is herein positioned as the main component and is referred to herein as the "main component polypropylene resin" or "base resin." When the polypropylene film contains only one type of polypropylene resin, this polypropylene resin is also herein positioned as the main component and is referred to herein as the "main component polypropylene resin."

[0036] When the polypropylene film of the present invention contains two or more (particularly two) types of polypropylene resins, it can contain, for example, the following polypropylene resin A (base resin as the main component) and the following polypropylene resin B (blend resin). Hereinafter, an example will be described in which two types of polypropylene resins, polypropylene resin A (base resin) and polypropylene resin B (blend resin), are used.

[0037] 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, based on 100% by weight of polypropylene resin. The upper limit of the content of polypropylene resin A 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, based on 100% by weight of polypropylene resin. An example of polypropylene resin A is isotactic polypropylene.

[0038] The weight average molecular weight Mw of the polypropylene resin A is preferably 250,000 or more and less than 350,000, more preferably 280,000 or more and less than 350,000, and even more preferably 280,000 or more and less than 340,000. When Mw is 250,000 or more and less than 350,000, it is easy to control the thickness of the cast raw sheet in the polypropylene film production process, and thickness unevenness is unlikely to occur.

[0039] The number average molecular weight Mn of the polypropylene resin A is preferably 30,000 or more and 54,000 or less, more preferably 33,000 or more and 52,000 or less, and even more preferably 33,000 or more and 47,000 or less. When Mn is 30,000 or more and 54,000 or less, a capacitor element having small thermal shrinkage and good thermal shock resistance is easily obtained.

[0040] The z-average molecular weight Mz of the polypropylene resin A is preferably 700,000 or more and 1,550,000 or less, more preferably 750,000 or more and 1,500,000 or less. When Mz is 700,000 or more and 1,550,000 or less, a film having high dielectric breakdown strength at high temperatures is likely to be obtained.

[0041] The molecular weight distribution (Mw / Mn) of the polypropylene resin A is preferably 5.0 or more, more preferably 5.5 or more, and even more preferably 6.0 or more. The Mw / Mn of the polypropylene resin A is preferably 10.0 or less, and more preferably 9.5 or less. When the Mw / Mn is 5.0 or more and 10.0 or less, the stretchability is improved, and a thin film can be easily obtained.

[0042] The molecular weight distribution (Mz / Mn) of the polypropylene resin A is preferably from 10 to 70, more preferably from 15 to 60, and even more preferably from 15 to 50. When Mz / Mn is from 10 to 70, stretchability is improved, making it easier to obtain a thin film.

[0043] In the molecular weight distribution curve of polypropylene resin A, the differential distribution value when the logarithmic molecular weight Log(M) is 4.5 is preferably 28.0 or more. The upper limit is preferably 32.0 or less. Furthermore, the differential distribution value when the logarithmic molecular weight Log(M) is 6.0 is preferably 17.0 or more, more preferably 20.0 or more. The upper limit is preferably 24.0 or less, more preferably 22.0 or less. Furthermore, the difference (molecular weight differential distribution value difference (D)) obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) is 4.5 from the differential distribution value when the logarithmic molecular weight Log(M) is 6.0 is M)) is preferably 8.0 or more and 18.0 or less, more preferably 8.0 or more and 11.0 or less, even more preferably 8.2 or more and 10.0 or less, and even more preferably 8.4 or more and 8.8 or less.

[0044] From the Mw value of polypropylene resin A (250,000 or more and less than 350,000), when comparing components with a logarithmic molecular weight Log(M) of 4.5, which is a representative distribution value of 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"), with components with a logarithmic molecular weight Log(M) of around 6.0, which is a representative distribution value of 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"), it can be seen that the low molecular weight components predominate by 8.0% or more and 18.0% or less.

[0045] In other words, even if the molecular weight distribution Mw / Mn is 5.0 to 10.0, this merely indicates the width of the molecular weight distribution, and does not reveal the quantitative relationship between the high molecular weight and low molecular weight components. Therefore, it is preferable that the polypropylene resin A according to the present invention has a wide molecular weight distribution and also contains a large proportion of components with a molecular weight of 10,000 to 100,000, in a ratio of 8.0% to 18.0% compared to the component 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 of the polypropylene film.

[0046] The lower limit of the weight fraction w of polypropylene resin A is preferably 3.8% or more, more preferably 4.0% or more. The upper limit is preferably 4.4% or less, more preferably 4.2% or less. When the weight fraction w of polypropylene resin A is within this range and is combined with the weight fraction w of polypropylene resin B described below so that the weight fraction w after mixing of polypropylene resin A and polypropylene resin B is 2.6% or more and 4.2% or less, a polypropylene film that has excellent dielectric breakdown strength at high temperatures and suppressed thermal shrinkage in the machine direction (MD) can be easily obtained.

[0047] Melt flow rate (MFR) of polypropylene resin A at 230°C A) is preferably 4.8 g / 10 min or more, more preferably 5.0 g / 10 min or more, and even more preferably 5.5 g / 10 min or more. A The upper limit of the MFR is preferably 10.0 g / 10 min or less, more preferably 8.0 g / 10 min or less, and even more preferably 6.0 g / 10 min or less. A The melt flow rate (MFR) can be set to 4.8 g / 10 min or more and 5.5 g / 10 min or less. The melt flow rate (MFR) in this specification is measured by the method described in the Examples. The unit of the melt flow rate, g / 10 min, is also called dg / min.

[0048] In a preferred embodiment of the polypropylene film of the present invention, the polypropylene resin A is The Mw of the polypropylene resin A is 275,000 or more and less than 350,000, The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 5.8 or more and 10.0 or less, The melt flow rate (MFR A ) is 4.8g / 10min or more and 5.5g / 10min or less, By using polypropylene resin A having such physical properties, molding of a cast sheet (stretched precursor) using an extruder can be easily carried out.

[0049] In a more preferred embodiment of the polypropylene film of the present invention, the polypropylene resin A is The Mw of the polypropylene resin A is 280,000 or more and 300,000 or less, The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 6.0 or more and 6.5 or less, The melt flow rate (MFR A ) is 5.0g / 10min or more and 5.5g / 10min or less, This can be an embodiment.

[0050] 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 a 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 leads to a moderate improvement in the crystallinity of the polypropylene resin in the polypropylene film, thereby improving the dielectric breakdown strength at high temperatures. Furthermore, in the polypropylene film production process, the solidification (crystallization) rate during cast molding of the raw sheet becomes moderate, resulting in moderate stretchability. The heptane insoluble content (HI) in this specification is measured according to the method described in the Examples.

[0051] The total ash content of polypropylene resin A is preferably as low as possible in terms of 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.

[0052] The content of polypropylene resin B is 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, relative to 100% by weight of polypropylene resin. The lower limit of the content of polypropylene resin B is, for example, preferably 10% by weight or more, more preferably 15% by weight or more, and even more preferably 25% by weight or more, relative to 100% by weight of polypropylene resin. Examples of polypropylene resin B include isotactic polypropylene. In the present invention, a particularly preferred embodiment is one in which the ratio of the mass of polypropylene resin A to the total mass of polypropylene resin A and polypropylene resin B is 65% by weight or more and 75% by weight or less.

[0053] The Mw of polypropylene resin B is preferably 350,000 or more, more preferably 390,000 or more. The Mw of polypropylene resin B is preferably 550,000 or less, more preferably 450,000 or less, and even more preferably 400,000 or less. When the Mw is 350,000 or more and 550,000 or less, it is easy to control the thickness of the cast raw sheet in the polypropylene film production process, and thickness unevenness is unlikely to occur.

[0054] The Mn of the polypropylene resin B is preferably 40,000 or more and 54,000 or less, more preferably 42,000 or more and 50,000 or less, and even more preferably 44,000 or more and 48,000 or less. When the Mn is 40,000 or more and 54,000 or less, a capacitor element having small thermal shrinkage and good thermal shock resistance is easily obtained.

[0055] The Mz of the polypropylene resin B is preferably more than 1.55 million and not more than 2 million, more preferably from 1.58 million to 1.7 million. When the Mz is more than 1.55 million and not more than 2 million, a film having high dielectric breakdown strength at high temperatures is easily obtained.

[0056] The molecular weight distribution (Mw / Mn) of polypropylene resin B is preferably 5.0 or more, more preferably 5.5 or more, even more preferably 7.0 or more, and even more preferably 7.5 or more. The upper limit of Mw / Mn in polypropylene resin B is, for example, 11.0 or less, preferably 10.0 or less, and more preferably 8.5 or less. When Mw / Mn is 5.0 or more and 11.0 or less, stretchability is improved and a thin film can be easily obtained.

[0057] The molecular weight distribution (Mz / Mn) of the polypropylene resin B is preferably 30 or more and 40 or less, more preferably 33 or more and 36 or less. When Mz / Mn is 30 or more and 40 or less, stretchability is improved and a thin film can be easily obtained.

[0058] In the molecular weight distribution curve of polypropylene resin B, the differential distribution value when the logarithmic molecular weight Log(M) is 4.5 is preferably 24.0 or more, more preferably 27.0 or more. The upper limit is preferably 35.0 or less, more preferably 32.0 or less. Furthermore, the differential distribution value when the logarithmic molecular weight Log(M) is 6.0 is preferably 28.0 or more, more preferably 30.0 or more. The upper limit is preferably 35.0 or less, more preferably 33.0 or less. Furthermore, the molecular weight differential distribution value difference (D M )) is preferably −11.0 or more and 7.0 or less, more preferably −6.0 or more and 0.0 or less, and even more preferably −4.0 or more and −2.0 or less.

[0059] When the polypropylene resin contains the above-mentioned polypropylene resins A and B, the differences in Mw, Mw / Mn, and differential distribution values ​​of polypropylene resins A and B are different, i.e., the molecular weight distribution structure is different. Therefore, the polypropylene film obtained by mixing and molding them exhibits a finely mixed (phase-separated) state, which is considered preferable because the quantitative relationship between the high molecular weight component and the low molecular weight component is slightly different, and the crystal size is easily refined. Furthermore, even at the same stretch ratio, there is a tendency for high orientation to occur, and the surface is easily roughened, which is considered preferable. When the polypropylene resin contains polypropylene resins A and B, the present invention is considered to exhibit excellent effects for the reasons described above, but the present invention is not limited by these reasons.

[0060] The lower limit of the weight fraction w of polypropylene resin B is preferably 2.0% or more, more preferably 3.0% or more. The upper limit is preferably 5.0% or less, more preferably 4.2% or less. When the weight fraction w of polypropylene resin B is within this range and is combined with the weight fraction w of polypropylene resin A described above, the weight fraction w after mixing of polypropylene resin A and polypropylene resin B is 2.6% or more and 4.2% or less, making it easier to obtain a polypropylene film that has excellent dielectric breakdown strength at high temperatures and reduced thermal shrinkage in the machine direction (MD).

[0061] Melt flow rate (MFR) of polypropylene resin B at 230°C 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 2.1 g / 10 min or less. B The lower limit 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.

[0062] The MFR of polypropylene resin A, which is the base resin of the main component, is A and MFR of polypropylene resin B, which is a blend resin B Differential MFR A -MFR B It is preferable to set the MFR to 1.5g / 10min or more. A is MFR B The difference MFR is greater than the above. A -MFR B The differential MFR is preferably 1.6 g / 10 min or more, more preferably 2.0 g / 10 min or more, and even more preferably 3.0 g / 10 min or more. A -MFR BIf the MFR is less than 1.5 g / 10 min (this includes negative values), a sea-island phase separation structure is not formed at the time of forming the raw sheet by casting in the polypropylene film manufacturing process, or even if it is formed, the size of the islands is very small, so that it may be difficult to obtain a polypropylene film with excellent dielectric breakdown strength at high temperatures. A and MFR B Even if the difference is large, B is larger (the difference MFR A -MFR B becomes negative), the size of the islands in the sea-island phase separation structure becomes very small.

[0063] In a preferred embodiment of the polypropylene film of the present invention, the polypropylene resin B is The Mw of the polypropylene resin B is 385,000 or more and 550,000 or less, The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.4 or more and 11.0 or less, The melt flow rate (MFR B ) is 0.1g / 10min or more and 2.2g / 10min or less, By using polypropylene resin B having such physical properties, molding of a cast sheet (stretched precursor) using an extruder can be easily carried out.

[0064] In a more preferred embodiment of the polypropylene film of the present invention, the polypropylene resin B is The Mw of the polypropylene resin B is 390,000 or more and 550,000 or less, The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.5 or more and 11.0 or less, The melt flow rate (MFR B ) is 1.0g / 10min or more and 2.1g / 10min or less, This can be an embodiment.

[0065] The heptane insoluble content of the polypropylene resin B is preferably 97.5% or more, more preferably 98.0% or more, even more preferably more than 98.5%, particularly preferably 98.6% or more. The heptane insoluble content is preferably 99.5% or less, more preferably 99.0% or less.

[0066] The lower the total ash content of polypropylene resin B, the better 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.

[0067] Although the above description exemplifies the use of two polypropylene resins, polypropylene resin A (base resin) and polypropylene resin B (blend resin), the polypropylene film of the present invention can also contain a resin other than polypropylene resin. In this case, the total amount of polypropylene resin A and polypropylene resin B, when the total resin is taken as 100% by weight, can be, for example, 90% by weight or more, 95% by weight or more, or even 100% by weight.

[0068] The polypropylene film of the present invention may further contain additives, such as antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and colorants.

[0069] The polypropylene film of the present invention may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film, but is preferably a biaxially stretched film.

[0070] The polypropylene film of the present invention is preferably used for a capacitor, and specifically, can be suitably used as a dielectric for a capacitor. As will be described later, the polypropylene film of the present invention can be a metal layer-integrated polypropylene film having a metal layer laminated on one or both sides, and a film capacitor can be produced by winding this metal layer-integrated polypropylene film or by laminating multiple metal layer-integrated polypropylene films.

[0071] In consideration of the above-mentioned use in capacitors, the polypropylene film of the present invention preferably has the following properties of dielectric breakdown strength and heat shrinkage resistance.

[0072] The dielectric breakdown strength (V AC100℃ ) is preferably 240 V / μm or more, more preferably 245 V / μm or more, and even more preferably 250 V / μm or more. The upper limit of the dielectric breakdown strength at an AC voltage at 100°C is preferably as high as possible, and is, for example, 270 V / μm or 265 V / μm.

[0073] The dielectric breakdown strength (V AC110℃ ) is preferably 240 V / μm or more, more preferably 242 V / μm or more, and even more preferably 244 V / μm or more. The upper limit of the dielectric breakdown strength at an AC voltage at 110°C is preferably as high as possible, and is, for example, 260 V / μm or 255 V / μm.

[0074] The dielectric breakdown strength (V AC120℃ ) is preferably 230 V / μm or more, more preferably 235 V / μm or more, and even more preferably 238 V / μm or more. The upper limit of the dielectric breakdown strength at an AC voltage at 120°C is preferably as high as possible, and is, for example, 250 V / μm or 245 V / μm.

[0075] The dielectric breakdown strength (V DC120℃ ) is preferably 520 V / μm or more, more preferably 527 V / μm or more, and even more preferably 532 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, and is, for example, 550 V / μm or 540 V / μm.

[0076] The V of the polypropylene film of the present invention AC120℃ and the aforementioned V DC120℃ The total value of (V AC120℃ +V DC120℃ ) is preferably 750 V / μm or more, more preferably 760 V / μm or more, and even more preferably 770 V / μm or more. AC120℃ and the aforementioned V DC120℃ The higher the upper limit of the total value, the better, and examples thereof include 1000 V / μm, 900 V / μm, and 850 V / μm.

[0077] The V of the polypropylene film of the present invention DC120℃ and the aforementioned V AC120℃ Difference with (V DC120℃ -V AC120℃ The difference is preferably 300 V / μm or less. Such a relatively small difference has the advantage that breakdown is unlikely to occur even with a superimposed current (a current in which a direct current and an alternating current are superimposed). The lower limit of the difference is preferably 280 V / μm or more, and can be set, for example, between 280 V / μm and 300 V / μm.

[0078] The polypropylene film of the present invention has excellent heat shrinkage resistance. Specifically, the polypropylene film has a shrinkage resistance of 2.17 N / mm 2When the temperature is raised from 25°C to 155°C at a rate of 10°C / min under a load of 0°C, and a heating dimensional change curve is plotted with the horizontal axis representing temperature and the vertical axis representing the dimensional change rate in the machine direction (MD) of the film, it is desirable that the dimensional change rate be 0% or more during the temperature rise process from 25°C to 155°C. Here, a dimensional change rate of 0% or more (i.e., not below 0%) means that no thermal shrinkage is observed. The thermomechanical analysis (TMA) method is as described in the Examples.

[0079] Figure 1 shows the results of the thermomechanical analysis of the polypropylene films produced in Example 1, Comparative Example 5, and Comparative Example 14. The graph shows the heating dimensional change curves, with the horizontal axis representing temperature and the vertical axis representing the dimensional change rate in the machine direction (MD) of the film. As can be seen from Figure 1, the polypropylene film produced in Example 1 had a dimensional change rate in the machine direction of the film of 0% or more throughout the entire temperature rise process from 25°C to 155°C. On the other hand, the polypropylene films produced in Comparative Examples 5 and 14 had a temperature range during the temperature rise process from 25°C to 155°C where the dimensional change rate in the machine direction of the film was less than 0%.

[0080] Polypropylene film manufacturing method The above-mentioned method for producing the polypropylene film of the present invention is not limited, but the polypropylene film of the present invention can be suitably produced, for example, by adopting the following production method (hereinafter referred to as the "production method for the polypropylene film of the present invention").

[0081] The method for producing a polypropylene film of the present invention is a method for producing the polypropylene film of the present invention described above, A polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B is heated at a temperature of 225°C or higher and 270°C or lower at a shear rate of 2000 s -1 More than 15000s -1 Melting the The melt flow rate (MFR A ) and the polypropylene resin B (MFR B ) differential MFRA -MFR B is 1.5g / 10min or more, The content of the polypropylene resin A in the polypropylene resin composition is greater than the content of the polypropylene resin B in the polypropylene resin composition. It is characterized by:

[0082] This production method can provide a polypropylene film with good dielectric breakdown strength at high temperatures, which is believed to be due to the sea-island phase separation structure (particularly, the appropriate island size) of the cast raw sheet, which is achieved by using two specific different polypropylene resins.

[0083] In the method for producing a polypropylene film of the present invention, a polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B is used. Here, the content of polypropylene resin A in the polypropylene resin composition being 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 base resin that is the main component, and polypropylene resin B is a blend resin with the base resin. The terms "polypropylene resin A" and "polypropylene resin B" in the method for producing a polypropylene film of the present invention correspond to the terms "polypropylene resin A" and "polypropylene resin B" in the above-mentioned section on polypropylene film, and the 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 value difference (D M ), weight fraction w, and MFR are as described above. In the method for producing a polypropylene resin of the present invention, the MFR A and MFR B Differential MFR A -MFR B Use one with a molecular weight of 1.5g / 10min or more.

[0084] The method of mixing resins to be applied to the production method of the present invention is not particularly limited, but examples thereof include a method of dry-blending polymer powders or pellets of the base resin and the blend resin using a mixer or the like, and a method of supplying polymer powders or pellets of the base resin and the blend resin to a kneader and melt-kneading them to obtain a kneaded product.

[0085] 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 having two or more screws. In the case of a twin or more screw type, the kneader may be either a co-rotating or counter-rotating type.

[0086] In the case of melt-kneading, the kneading temperature is not particularly limited as long as a good kneaded product is obtained. Generally, the temperature 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. To suppress resin degradation during kneading and mixing, the kneader may be purged with an inert gas such as nitrogen. The melt-kneaded resin may be pelletized to an appropriate size using a commonly known granulator. This allows the production of mixed polypropylene raw material resin pellets.

[0087] The total ash content of the polypropylene raw material resin, which is caused by polymerization catalyst residues and the like, is preferably 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 100 parts by weight of the polypropylene resin.

[0088] The polypropylene resin may contain an additive. The "additive" is an additive generally used in polypropylene resins, and is not particularly limited as long as a polypropylene film can be obtained. Examples of the additive include an antioxidant, a chlorine absorber, an ultraviolet absorber, a lubricant, a plasticizer, a flame retardant, and an antistatic agent. The polypropylene resin may contain the additive in an amount that does not adversely affect the polypropylene film.

[0089] In the method for producing a polypropylene film of the present invention, first, polypropylene resin pellets, dry-mixed polypropylene resin pellets, or mixed polypropylene resin pellets previously prepared by melt-kneading are fed into an extruder and heated to melt.

[0090] The polypropylene resin composition is melted at 225° C. or higher and 270° C. or lower. Specifically, the extruder temperature setting during heating and melting the polypropylene resin composition is 225° C. or higher and 270° C. or lower. As a result, on the assumption that the specific polypropylene resin composition is used, a sea-island phase separation structure is formed at the time of cast molding into a raw sheet, as described below, and ultimately a polypropylene film having excellent dielectric breakdown strength at high temperatures is obtained.

[0091] The polypropylene resin composition was heated to a temperature of 225°C or higher and 270°C or lower at a shear rate of 2000 s -1 More than 15000s -1 Assuming that the specific polypropylene resin composition is used, a sea-island phase separation structure is formed at the time of cast molding of the raw sheet, as described below, and ultimately a polypropylene film with excellent dielectric breakdown strength at high temperatures is obtained. -1 If the extrusion rate is lower than this, the extrusion rate will not be constant, and the shape and dimensions of the raw sheet will become irregular or will fluctuate regularly, making the raw sheet more likely to break during transport or stretching.

[0092] In addition, the shear rate is 15000 s -1If the shear rate exceeds this, a phenomenon called breakup occurs in the extruder, causing unmelted material to be extruded, making it impossible to obtain a uniform raw sheet, making it more likely to break during stretching, or excessive heat is generated when passing through the tip clearance, causing significant deterioration of the polypropylene resin composition, and even if a uniform raw sheet is obtained, the dielectric breakdown strength of the film obtained by stretching will be reduced. The shear rate can be adjusted by the cylinder diameter, screw rotation speed, and screw groove depth of the extruder.

[0093] The shear rate is 2000 s -1 More than 15000s -1 Anything less than this is fine, but preferably 2000s -1 More than 10000s -1 Below 2000s, preferably -1 More than 2300s -1 By keeping the shear rate within this range, it becomes easier to obtain a polypropylene film having a weight fraction w of 2.6% or more and 4.2% or less, and in combination with other requirements, a film capacitor using the polypropylene film as a capacitor dielectric can obtain excellent thermal shock resistance in that thermal compaction (deformation) of the capacitor is suppressed during repeated use at high and low temperatures.

[0094] Next, the molten resin composition is extruded into a sheet using a T-die and cooled and solidified on at least one metal drum to form an unstretched cast raw sheet. The surface temperature of the metal drum (the temperature of the metal drum that first comes into contact with the extruded material after extrusion) is preferably 50°C or higher and 105°C or lower, more preferably 60°C or higher and 100°C or lower. The surface temperature of the metal drum can be determined depending on the physical properties of the polypropylene resin used. If the surface temperature of the metal drum is significantly lower than 50°C, it is difficult to obtain a good polypropylene film without uneven stretching or breakage during stretching.

[0095] The thickness of the cast raw sheet is not particularly limited as long as the polypropylene film can be obtained, but is usually preferably 0.05 mm or more and 2 mm or less, and more preferably 0.1 mm or more and 1 mm or less.

[0096] The polypropylene film can be produced by stretching the cast polypropylene raw sheet. Biaxial stretching, which involves biaxial orientation in both the longitudinal and transverse directions, is preferred, and sequential biaxial stretching is preferred. In the sequential biaxial stretching method, for example, the cast raw sheet is first maintained at a temperature of 110°C to 170°C (preferably 135°C to 170°C) and stretched in the machine direction by passing it between rolls with a speed difference. The stretching ratio in the machine direction is preferably 3.5 to 5.5 times, more preferably 4.2 to 5.4 times. Subsequently, the sheet is introduced into 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. The sheet is then relaxed and heat-set to a ratio of 2 to 10 times. This produces a biaxially stretched polypropylene film.

[0097] The thickness of the polypropylene film is preferably 0.8 μm or more and 6.0 μm or less, as described above, from the viewpoint of ensuring miniaturization and high capacitance of the capacitor when used in a capacitor. Specifically, the thickness is preferably 5.5 μm or less, more preferably 3.5 μm or less, even more preferably 3.0 μm or less, and particularly preferably 2.4 μm or less. Furthermore, from the viewpoint of manufacturing, 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.

[0098] The polypropylene film may be subjected to corona discharge treatment online or offline after the stretching and heat setting steps in a post-process such as a metal deposition process, in order to enhance adhesive properties. Corona discharge treatment can be performed using a known method. It is preferable to perform the treatment using air, carbon dioxide gas, nitrogen gas, or a mixture thereof as the atmospheric gas.

[0099] The polypropylene film of the present invention thus obtained, even when the film is as thin as 6.0 μm or less, 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 excellent dielectric breakdown strength when an AC voltage is applied. It also exhibits excellent heat shrinkage resistance, in that thermal shrinkage in the machine direction (MD) is suppressed at temperatures exceeding the above-mentioned high temperature, up to approximately 150°C. Furthermore, the film capacitor of the present invention using the polypropylene film as a capacitor dielectric exhibits excellent heat resistance at high temperatures of approximately 120°C (100°C to 120°C). Specifically, it exhibits excellent life performance, in that the decrease in capacitance of the capacitor is suppressed even when used for long periods at such high temperatures. It also exhibits excellent thermal shock resistance, in that the thermal compaction (deformation) of the capacitor is suppressed during repeated use between the above-mentioned high and low temperatures, as is typical in engine compartments. Therefore, the polypropylene film of the present invention is suitable for use in film capacitors, and can preferably be used as a capacitor dielectric for the inverters in hybrid and electric vehicles.

[0100] Metal layer integrated polypropylene film capacitor and its manufacturing method In consideration of processing into a capacitor, the polypropylene film of the present invention 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.

[0101] The metal layer functions as an electrode. Examples of metals that can be used for the metal layer include simple metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures of multiple metals, and alloys of multiple metals. However, zinc and aluminum are preferred in consideration of the environment, economy, and capacitor performance.

[0102] Examples of methods for laminating a metal layer on one or both sides of a polypropylene film include vacuum deposition and sputtering. Vacuum deposition is preferred from the viewpoints of productivity and economy. Examples of vacuum deposition methods include the crucible method and the wire method, but the method is not particularly limited and an optimal method can be selected as appropriate.

[0103] The margin pattern used when laminating the metal layer by vapor deposition is not particularly limited, but in order to improve the safety and other properties of the capacitor, it is preferable to apply a pattern including a so-called special margin, such as a fishnet pattern or T-margin pattern, to one side of the polypropylene film. This is effective in terms of increasing safety and preventing capacitor damage and short circuits.

[0104] As a method for forming the margin, any generally known method such as a tape method or an oil method can be used without any limitation.

[0105] The metal layer-integrated polypropylene film of the present invention can be laminated or wound by a conventionally known method to form a film capacitor.

[0106] That is, the film capacitor may have a structure in which multiple metal layer-integrated polypropylene films are laminated, or may have a wound metal layer-integrated polypropylene film. Such a film capacitor can be suitably used as a capacitor for inverter power supply devices that control the drive motors of electric vehicles, hybrid vehicles, etc. In addition, it can be suitably used in railway vehicles, wind power generation, solar power generation, general home appliances, etc. [Example]

[0107] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. ≪Resin≫ Details of the resins (PP resins A1 to A6 and PP resins B1 to B8) used in the examples and comparative examples are summarized in Table 1 below, and the methods for measuring each physical property are also described.

[0108] [Table 1]

[0109] PP resin A1 to A6: Prime Polymer Co., Ltd. PP resin B1: S802M Type A, manufactured by Daehan Yuhhwa Co., Ltd. PP resin B2: Borealis Co., Ltd., HC300BF PP resin B3: S800 manufactured by Daehan Yuhhwa Co., Ltd. PP resin B4: Samsung Total Co., Ltd., HU300 PP resin B5: Daehan Yuhhwa Co., Ltd., HPT-1 Type A PP resin B6: Daehan Yuhhwa Co., Ltd., HPT-1 Type B PP resin B7: S802M Type B, manufactured by Daehan Oil & Gas Co., Ltd. PP resin B8: S802M Type C, manufactured by Daehan Oil & Gas Co., Ltd.

[0110] <Measurement of 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, the average molecular weight and molecular weight distribution of each polypropylene resin were measured using SEC (size exclusion chromatography) under the following conditions. Apparatus: HLC-8321GPC / HT (detector: differential refractometer (RI)) (manufactured by Tosoh Corporation) Column: TSKgel guard column HHR(30)HT (7.5 mm I.D. x 7.5 cm) x 1 + TSKgel GMHHR-H(20)HT (7.8 mm I.D. x 30 cm) x 3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (Fujifilm Wako Pure Chemical Industries, Ltd., for GPC) + BHT (0.05%) Flow rate: 1.0mL / min Detection condition: polarity-(-) Injection volume: 0.3mL Column temperature: 140℃ System temperature: 40°C Sample concentration: 1 mg / mL Sample pretreatment: The sample was weighed, dissolved in a solvent (1,2,4-trichlorobenzene with 0.1% BHT) and shaken at 140°C for 1 hour, then filtered through a 0.5µm sintered filter. Calibration curve: A calibration curve of a quintic approximation curve was prepared using standard polystyrene from Tosoh Corporation. However, the molecular weight was converted to the molecular weight of polypropylene using the Q-factor.

[0111] From the obtained calibration curve and SEC chromatogram, the molecular weight (logarithmic value) was plotted on the horizontal axis and the integral value of the concentration fraction on the vertical axis using the analysis software for the measurement device to obtain an integrated molecular weight distribution curve. The differential value (slope of the integral molecular weight distribution curve) of the integrated molecular weight distribution curve at each molecular weight was calculated, and the molecular weight (logarithmic value) was plotted on the horizontal axis and the differential value on the vertical axis to obtain a differential molecular weight distribution curve.

[0112] 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 calculated using the Mw and Mn values. Furthermore, the value when the logarithmic molecular weight Log(M) = 4.0 on the integrated molecular weight distribution curve was taken as the weight fraction w. This weight fraction w indicates the weight fraction of molecules with a logarithmic molecular weight Log(M) = 4.0, i.e., a molecular weight of 10,000 or less.

[0113] <<Differential distribution value when logarithmic molecular weight Log(M) = 4.5, differential distribution value when logarithmic molecular weight Log(M) = 6.0, and molecular weight differential distribution value difference (D M ) Measurement≫ For each polypropylene resin, the differential distribution values ​​at logarithmic molecular weight Log(M) = 4.5 and at logarithmic molecular weight Log(M) = 6.0 were obtained by the following method. First, the time curve (elution curve) of the intensity distribution detected using the RI detector was converted into a distribution curve versus the molecular weight M (Log(M)) of the standard polystyrene using a calibration curve prepared using the above-mentioned standard polystyrene. Next, an integral distribution curve versus Log(M) was obtained when the total area of ​​the distribution curve was taken as 100%, and then this integral distribution curve was differentiated by Log(M) to obtain a differential distribution curve versus Log(M). From this differential distribution curve, the differential distribution values ​​at Log(M) = 4.5 and Log(M) = 6.0 were read. The difference between the differential distribution value at Log(M) = 4.5 and the differential distribution value at Log(M) = 6.0 was defined as the molecular weight differential distribution value difference (D M The series of operations leading up to obtaining the differential distribution curve was carried out using the analysis software built into the GPC measurement device used.

[0114] <<Heptane insolubles (HI) measurement>> Each polypropylene resin was press-molded to a size of 10 mm x 35 mm x 0.3 mm to prepare a measurement sample weighing approximately 3 g. Next, approximately 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble content was calculated from the sample mass before and after extraction.

[0115] <Melt flow rate (MFR) measurement> The melt flow rate (MFR) of the raw resin pellets used in the examples and comparative examples was measured in accordance with JIS K 7210 condition M using a melt indexer manufactured by Toyo Seiki Co., Ltd. Specifically, a 4 g sample was first 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. The weight of the sample extruded from the bottom hole over 30 seconds was then measured, and the MFR (unit: g / 10 min or g / 10 min) was calculated. The above measurement was repeated three times, and the average value was used as the measured MFR.

[0116] Examples 1 to 14 and Comparative Examples 1 to 18 [Production of biaxially oriented polypropylene film and evaluation of its properties] Polypropylene resins A and B were weighed according to Table 2 and mixed in the weight ratio shown in Table 2 to obtain a dry blend resin composition. The dry blend resin composition was then fed into an extruder and melted at the melting temperature and shear rate shown in Table 2. The molten resin was extruded using a T-die and solidified by winding it around a metal drum maintained at a surface temperature of 95°C to produce a cast raw sheet. The unstretched cast raw sheet was maintained at 140°C and stretched 4.5 times in the machine direction by passing it between rolls with different speeds, and immediately cooled to room temperature. The stretched film obtained by stretching in the machine direction was then introduced into a tenter and stretched 10 times in the width direction at a transverse stretching temperature of 158°C. It was then relaxed and heat-set at a relaxation rate of 12% to obtain a biaxially oriented polypropylene film approximately 5 m wide and 2.3 μm thick. Approximately 80,000 m of the film was wound around a 400 mm diameter iron core under the atmosphere shown in Table 2 to form a jumbo roll. The biaxially stretched polypropylene film thus wound was subjected to aging treatment by being treated in an atmosphere at 35° C. for 24 hours.

[0117] [Table 2-1] [Table 2-2]

[0118] 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) during aging of the jumbo roll are described below. The results of each measurement and evaluation are also shown in Table 2.

[0119] <Measurement of polypropylene film thickness> The thickness was measured using a Citizen Seimitsu MEI-11 paper thickness meter (measurement pressure 100 kPa, drop rate 3 mm / sec, measurement probe φ = 16 mm, measurement force 20.1 N) in an environment of 23 ± 2°C temperature and 50 ± 5% RH. The samples were cut from the roll with 10 or more sheets stacked together, and were handled carefully to prevent wrinkles or air from entering the film during cutting. Five measurements were taken for each 10-sheet stack sample, and the average of the five measurements was divided by 10 to calculate the thickness.

[0120] <Measurement of Polypropylene Film Density> The density of the polypropylene film was measured according to JIS K7112 (1999) D method. Measuring device: Shibayama Scientific Instruments Manufacturing Co., Ltd. Density gradient tube specific gravity measuring device Type A Gradient: Aqueous ethanol solution Measurement temperature: 23±0.5℃ Number of measurements: n=3 <Measurement of dielectric breakdown strength of polypropylene film: direct current (DC)> The dielectric breakdown voltage (BDV) of the polypropylene films according to the Examples and Comparative Examples was measured 16 times under the following test conditions using the electrode configuration specified in JIS C2151 (2006) 17.2.2 (Plate Electrode Method). The BDV was determined as the applied voltage at which a leakage current of the upper limit reference value shown below was detected during voltage increase. The BDV was then divided by the film thickness (μm), and the average of 12 points, excluding the top two and bottom two points, was determined as the dielectric breakdown strength ES (VDC / μm). Test piece: approx. 150mm x 150mm Conditioning of specimen: 30 minutes at ambient conditions Power supply: DC Atmosphere: Air, 120℃ Testing machine: Kikusui Electronics Co., Ltd. DC withstand voltage / insulation resistance tester TOS9213AS Voltage rise rate: 100V / s Current detection response speed: MID Upper limit: 5mA <Measurement of dielectric breakdown strength of polypropylene film: Alternating current (AC)> The dielectric breakdown voltage (BDV) of the films according to the examples and comparative examples was measured 12 times under the following test conditions using the electrode configuration described in JIS C2151 (2006) 17.2.2 (flat electrode method). The applied voltage at the point when a leakage current of the upper limit reference value below was detected during voltage increase was taken as the BDV. The BDV was divided by the film thickness (μm), and the average value of the 8 points excluding the top 2 and bottom 2 points out of the 12 measurement results was taken as the dielectric breakdown strength ES (VAC / μm). Test piece: Approximately 150 mm x 150 mm Conditioning of specimen: 30 minutes at ambient conditions Power supply: AC Atmosphere: Air, 100℃, 110℃, 120℃ Testing machine: Kikusui Electronics Co., Ltd. withstand voltage testing machine TOS5051A Voltage rise rate: 100V / s Upper limit: 5mA ≪Thermomechanical analysis (TMA)≫ Thermomechanical analysis was carried out as follows. Equipment: Seiko Instruments EXSTAR6000 and TMA / SS6000 Film width: 4mm Chuck distance: 15mm Load: 2.17N / mm 2 Measurement temperature range: 25℃~155℃ Heating rate: 10°C / min When a heating dimensional change curve was drawn with the horizontal axis representing temperature and the vertical axis representing the dimensional change rate in the machine direction (MD) of the film, a dimensional change rate of 0% or more during the temperature rise process from 25°C to 155°C was rated as pass (A), and a dimensional change rate of less than 0% was rated as fail (C).

[0121] <Jumbo roll winding quality (wrinkles) after aging> After aging, the appearance of the jumbo roll, excluding approximately 100 mm from both ends, was evaluated from the perspective of winding quality (wrinkles). Note that the following type (vertical type) refers to a defect in the winding shape that occurs parallel to the circumferential direction, such as a ribbed metal can, commonly known as MD line or can shape. If there are no circumferential molds (vertical molds) with a depth of 0.5 mm or more, the grade is "AA". If there is only one circumferential mold (vertical mold) with a depth of 0.5 mm or more, it is rated as "A". If there are two or three circumferential types (vertical types) with a depth of 0.5 mm or more, it is classified as "B". If there were four or more circumferential molds (vertical molds) with a depth of 0.5 mm or more, it was rated as poor "C." In the case of excellent "AA," even if there were circumferential molds (vertical molds), they were less than 0.5 mm deep and were distributed almost evenly across the width. Here, excellent "AA" and good "A" are acceptable (within the acceptable range), while fair "B" and poor "C" are unacceptable. [Production of film capacitors and evaluation of their characteristics] Using the biaxially stretched polypropylene films obtained in each of the Examples and Comparative Examples, film capacitors were produced according to the following procedure.

[0122] 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 applying aluminum vapor deposition so that the surface resistivity of the metal film was 20 Ω / □. Next, the metal layer-integrated polypropylene film was slit to the desired width, and two sheets of metal layer-integrated polypropylene film were combined and wound using a Kaito Seisakusho automatic winding machine, model 3KAW-N2, at a winding speed of 4 m / s, a winding tension of 180 g, and a contact roller pressure of 260 g, with the number of turns set to achieve a device capacitance of 50 μF.

[0123] The wound element was flattened by pressing, and then zinc metal was sprayed onto the end faces of the element while the pressing load was still applied to form electrode extraction parts, and the element was then heat-treated at 120°C for 15 hours to harden it.

[0124] After thermal curing, leads were soldered to the end faces of the elements and sealed with epoxy resin to obtain flat film capacitors.The capacitance of the obtained film capacitors was all 50μF (±3μF).

[0125] The methods for evaluating the vapor deposition processability, element winding processability, and life characteristics and thermal shock resistance of the film capacitors obtained in each example and comparative example are shown below. The results of each evaluation are also shown in Table 2.

[0126] ≪Vapour-deposition processability≫ The film after deposition was rated as "A" if the rate of wrinkles due to thermal deformation was less than 5%, and "C" if it was 5% or more.

[0127] <Element winding processability evaluation> Two small rolls obtained by vapor deposition and slitting were overlapped and wound around the left and right margin reels, with the vapor-deposited portion extending beyond the margin in the width direction (element winding process). The winding was performed using an automatic winding machine, Model 3KAW-N2, manufactured by Kaito Seisakusho Co., Ltd., with a winding tension of 200 g and 1,360 turns. The winding was visually inspected from start to finish, and any wrinkles or misalignment were deemed unacceptable. The percentage of unacceptable rolls relative to the total number of rolls produced was used as an index of processability (hereinafter referred to as element winding yield). The higher the element winding yield, the better. A roll of 95% or higher was rated as good (A), and a roll of less than 95% was rated as poor (C).

[0128] <Life characteristics (rate of change in capacitance)> The initial capacitance of the obtained capacitors before testing was measured using a Hioki E.E. Corporation LCR HiTester 3522-50. Next, a DC voltage of 800 V (348 V / μm) was continuously applied to the capacitors for 500 hours in a high-temperature chamber at 115°C. The capacitance of the capacitors after 500 hours was measured in the same way, and the rate of change in capacitance 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.

[0129] (Capacitance change rate) = [(Capacitance after voltage load) - (Initial capacitance)] / (Initial capacitance) x 100 (%) A capacity change rate of -4% or less after 500 hours was rated as good (A), a rate of more than -4% but not exceeding -6% was rated as "B", and a rate of more than -6% was rated as poor (C).

[0130] <Thermal shock resistance (rate of change of tan δ)> The obtained capacitor was placed in a thermal shock tester (Espec TSA-101S-W) and subjected to 500 cycles of rapid temperature increase and decrease between a lower limit temperature of -40°C and an upper limit temperature of 105°C. Specifically, a set of 50 minutes at -40°C and 50 minutes at 105°C was repeated 500 times. The temperature was switched by forcibly replacing the air by blowing in air at the set temperature. The time for switching the temperature was also included in the 50-minute holding time.

[0131] Tan δ before and after the thermal shock test was measured using an LCR HiTester 3522-50 manufactured by Hioki E.E. Corp. The rate of increase in tan δ was calculated using the following formula.

[0132] (Increase in tan δ) = [(tan δ after thermal shock test) - (tan δ before thermal shock test)] / (tan δ before thermal shock test) × 100 (%) The test was carried out on three samples, and the average value was used for evaluation.

[0133] An increase rate of 100% or less was rated as good (A), an increase rate of more than 100% but less than 105% was rated as "B", and an increase rate of more than 105% was rated as poor (C).

[0134] ≪Consideration≫ The polypropylene films of the present invention produced in Examples 1 to 14 have a molecular weight distribution (Mw / Mn) of weight-average molecular weight Mw and number-average molecular weight Mn, a Z-average molecular weight Mz, and a weight fraction w at logarithmic molecular weight Log(M)=4.0 in an integrated molecular weight distribution curve, all within predetermined ranges. Therefore, even when the film is thin, such as 6.0 μm or less, the film has excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at a high temperature of about 120°C (100°C to 120°C) and excellent dielectric breakdown strength when an AC voltage is applied. Furthermore, the film has excellent heat shrinkage resistance in that heat shrinkage in the machine direction (MD) is suppressed at temperatures up to about 150°C, which exceeds the above-mentioned high temperature. The film capacitors produced in the examples have excellent heat resistance at high temperatures of around 120°C (100°C to 120°C), and specifically, have excellent life performance in that the decrease in capacitance of the capacitor is suppressed even when used for long periods at such high temperatures.They also have excellent thermal shock resistance in that the thermal compaction (deformation) of the capacitor is suppressed when used repeatedly at such high and low temperatures as is assumed in an engine compartment.Furthermore, the polypropylene film of the present invention has also obtained good evaluation results in terms of the appearance (winding quality (wrinkles)) after aging of the jumbo roll, and the vapor deposition processability and element winding processability during capacitor production.

Claims

1. A polypropylene film, wherein the polypropylene resin constituting the polypropylene film is The molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn is 5.0 or more and 6.7 or less, The Z-average molecular weight Mz is 650,000 or more and 945,000 or less, In the integrated molecular weight distribution curve, the weight fraction w is 2.6% or more and 4.2% or less when the logarithmic molecular weight Log(M) = 4.

0. A polypropylene film characterized by:

2. The polypropylene film according to claim 1, which is used for a capacitor.

3. 3. The polypropylene film according to claim 1, which is a biaxially stretched film.

4. Thermomechanical analysis: 2.17 N / mm ２ 4. The polypropylene film according to claim 1, wherein, when the film is heated from 25°C to 155°C at a rate of 10°C / min under a load of 0.5 g / min, and a heating dimensional change curve is plotted with the horizontal axis representing temperature and the vertical axis representing dimensional change in the machine direction (MD) of the film, the dimensional change during the heating process from 25°C to 155°C is 0% or more.

5. Dielectric breakdown strength at 120°C under DC voltage (V ＤＣ１２０℃ ) and the dielectric breakdown strength (V ＡＣ１２０℃ ) and the difference (V ＤＣ１２０℃ -V ＡＣ１２０℃ 5. The polypropylene film according to claim 1, wherein the surface tension (Tc) of the polypropylene film is 280 V / μm or more and 300 V / μm or less.

6. The polypropylene film according to any one of claims 1 to 5, wherein the Mz exceeds 700,000.

7. The molecular weight distribution (Mw / Mn) is 5.0 or more and 6.6 or less, The Mz is 720,000 or more and 790,000 or less, The weight fraction w is 3.5% or more and 3.7% or less, The polypropylene film according to any one of claims 1 to 6.

8. the polypropylene resin contains polypropylene resin A and polypropylene resin B, the polypropylene resin A and the polypropylene resin B have different Mw, Mw / Mn, and differential distribution value at a logarithmic molecular weight Log(M)=4.5 in a molecular weight distribution curve, and the content of the polypropylene resin A in the polypropylene resin is greater than the content of the polypropylene resin B in the polypropylene resin; The Mw of the polypropylene resin A is 275,000 or more and less than 350,000, The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 5.8 or more and 10.0 or less, The melt flow rate (MFRA) of the polypropylene resin A is 4.8 g / 10 min or more and 5.5 g / 10 min or less at a test temperature of 230°C and a load of 2.16 kg. The polypropylene film according to any one of claims 1 to 7.

9. the polypropylene resin contains polypropylene resin A and polypropylene resin B, the polypropylene resin A and the polypropylene resin B have different Mw, Mw / Mn, and differential distribution value at a logarithmic molecular weight Log(M)=4.5 in a molecular weight distribution curve, and the content of the polypropylene resin A in the polypropylene resin is greater than the content of the polypropylene resin B in the polypropylene resin; The Mw of the polypropylene resin B is 385,000 or more and 550,000 or less, The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.4 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 2.2 g / 10 min or less at a test temperature of 230°C and a load of 2.16 kg. The polypropylene film according to any one of claims 1 to 8.

10. The polypropylene film according to claim 8 or 9, wherein the ratio of the mass of the polypropylene resin A to the total mass of the polypropylene resin A and the polypropylene resin B is 65 to 75 mass%.

11. The polypropylene film according to any one of claims 1 to 10, wherein the thickness of the polypropylene film is 1.0 µm or more and 6.0 µm or less.

12. The polypropylene film according to any one of claims 1 to 11, A metal layer laminated on one or both sides of the polypropylene film, Polypropylene film with integrated metal layer.

13. The metal layer-integrated polypropylene film according to claim 12 is wound, or a plurality of the metal layer-integrated polypropylene films according to claim 12 are laminated. Film capacitor.

Images