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 polypropylene film integrated with a metal layer, and a film capacitor.

Background Art

[0002] The polypropylene film can be used as a dielectric of a capacitor. For example, it can be used as a dielectric of a capacitor in an inverter that constitutes a power control unit of a hybrid vehicle, an electric vehicle, or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A capacitor using a polypropylene film as a dielectric is desirably small, lightweight, and high-capacity, and has excellent heat resistance at a high temperature of about 120°C (100°C to 120°C) from the viewpoint of the above-described use environment (for example, an environment where the temperature rises in an engine room, self-heating of the capacitor, etc.). Specifically, it is required that the decrease in the capacitance of the capacitor is suppressed even when used for a long time at the above high temperature (excellent life performance), and the thermal shrinkage (deformation) of the capacitor is suppressed in repeated use between the above high temperature and low temperature assuming the inside of an engine room (excellent thermal shock resistance), etc.

[0005] Furthermore, the polypropylene film used to manufacture the above-mentioned capacitor is required to exhibit excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at the above-mentioned high temperature, even when the film thickness is as thin as less than 20 μm, and also to suppress thermal shrinkage in the mechanical direction (MD) at temperatures exceeding the above-mentioned high temperature, up to about 150°C (excellent heat shrinkage resistance).

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

[0007] The present invention has been made in view of the above-mentioned problems, and its purpose 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 a method for manufacturing the same.

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

[0009] The inventors diligently studied polypropylene films. As a result, they found that polypropylene films in which the weight-average molecular weight Mw and number-average molecular weight Mn (Mw / Mn), the Z-average molecular weight Mz, and the weight fraction w when the logarithmic molecular weight Log(M) = 4.0 in the integral molecular weight distribution curve are all within a specific range possess the aforementioned film performance, and that capacitors using such polypropylene films possess the aforementioned capacitor performance, leading to the completion of the polypropylene film and film capacitor of the present invention. They also found that the above-mentioned polypropylene film can be suitably manufactured by a manufacturing method that includes a step of melting the polypropylene resin composition at a specific shear rate.

[0010] In other words, the present invention relates to the following polypropylene film, metal layer integrated polypropylene film, film capacitor, and methods for manufacturing the same. 1. A polypropylene film, wherein the polypropylene resin constituting the 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 650,000 and 945,000. • 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 4.2%. A polypropylene film characterized by the following features. 2. Polypropylene film as described in item 1 above, for use in capacitors. 3. A polypropylene film as described in item 1 or 2 above, which is a biaxially oriented film. 4. Thermomechanical analysis showed a reading of 2.17 N / mm². 2 A polypropylene film according to any one of items 1 to 3 above, wherein when the temperature is raised from 25°C to 155°C at a rate of 10°C / min under a load, and a heating dimensional change curve is drawn with temperature on the horizontal axis and the dimensional change rate in the mechanical direction (MD) of the film on the vertical axis, the dimensional change rate is 0% or more during the heating process from 25°C to 155°C. 5. Dielectric breakdown strength at DC voltage at 120℃ (V DC120℃ ) and dielectric breakdown strength (V) at AC voltage at 120°C AC120℃ ) difference (V DC120℃ -V AC120℃ A polypropylene film as described in any of items 1 to 4 above, wherein the voltage is 280V / μm or more and 300V / μm or less. 6. A polypropylene film according to any of items 1 to 5 above, wherein the Mz exceeds 700,000. 7. The molecular weight distribution (Mw / Mn) is 5.0 or more and 6.6 or less. The above Mz is between 720,000 and 790,000. The aforementioned weight fraction w is 3.5% or more and 3.7% or less. A polypropylene film as described in any of items 1 to 6 above. 8. The polypropylene resin contains polypropylene resin A and polypropylene resin B, wherein 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 aforementioned polypropylene resin A is 275,000 or more and less than 350,000. The molecular weight distribution (Mw / Mn) of the aforementioned polypropylene resin A is 5.8 or more and 10.0 or less. • Melt flow rate (MFR) of the polypropylene resin A A ) is between 4.8g / 10 min and 5.5g / 10 min. A polypropylene film as described in any of items 1 to 7 above. 9. The polypropylene resin contains polypropylene resin A and polypropylene resin B, wherein 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 aforementioned polypropylene resin B is between 385,000 and 550,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.4 or more and 11.0 or less. • Melt flow rate (MFR) of the polypropylene resin BB ) is 0.1 g / 10 min or more and 2.2 g / 10 min or less, The polypropylene film according to any one of the above items 1 to 8. 10. The polypropylene film according to item 8 or 9 above, 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% by mass. 11. The polypropylene film according to any one of the above 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 the above items 1 to 11, and having a metal layer laminated on one or both sides of the polypropylene film. A metal layer-integrated polypropylene film. 13. Having the wound metal layer-integrated polypropylene film according to item 12 above, or having a configuration in which a plurality of the metal layer-integrated polypropylene films according to item 12 above are laminated. A film capacitor. 14. A method for producing a polypropylene film according to any one of the above items 1 to 11, comprising a step of melting a polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B at a temperature of 225 ° C or more and 270 ° C or less and a shear rate of 2000 s -1 or more and 15000 s -1 or less, The MFR of the polypropylene resin A A and the MFR of the polypropylene resin B B The differential MFR A -MFR B is 1.5 g / 10 min or more, The content of the polypropylene resin A in the polypropylene resin composition is more than the content of the polypropylene resin B in the polypropylene resin composition. A method for producing a polypropylene film, characterized by this. 15. The method for producing a polypropylene film according to item 14 above, wherein the polypropylene film is for a capacitor. 16. The method for manufacturing a polypropylene film according to item 14 or 15, wherein the polypropylene film is a biaxially oriented film. 17. A method for producing a polypropylene film according to any one of items 14 to 16 above, wherein the ratio of the mass of polypropylene resin A to the total mass of polypropylene resin B is 65 to 75% by mass. 18. A method for producing a polypropylene film according to any one of items 14 to 17 above, wherein the thickness of the polypropylene film is 1.0 μm or more and 2.4 μm or less. 19. A method for manufacturing a metal-layer integrated polypropylene film, comprising the manufacturing method described in any of items 14 to 18 above, and further comprising the step of forming a metal layer on at least one surface of the polypropylene film. 20. A method for manufacturing a film capacitor, comprising the manufacturing method described in item 19 above, and further comprising the step of winding the metal layer integrated polypropylene film. [Effects of the Invention]

[0011] The polypropylene film of the present invention exhibits excellent dielectric breakdown strength when a DC voltage is applied at high temperatures 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. This is because the polypropylene resin constituting the film 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 when the logarithmic molecular weight Log(M) = 4.0 in the integral molecular weight distribution curve, all within specific ranges. Furthermore, it exhibits excellent heat shrinkage resistance in that thermal shrinkage in the mechanical direction (MD) is suppressed at temperatures exceeding the above high temperature of approximately 150°C. Furthermore, the film capacitor of the present invention, which uses the polypropylene film as a capacitor derivative, exhibits excellent heat resistance at high temperatures of approximately 120°C (100°C to 120°C). Specifically, it has excellent lifespan in that the decrease in capacitance of the capacitor is suppressed even when used for a long time at the above high temperatures, and it also has excellent thermal shock resistance in that the 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 the present invention is suitable for film capacitor applications. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the results of thermomechanical analysis (TMA) of the polypropylene films prepared in Example 1, Comparative Example 5, and Comparative Example 14. The horizontal axis represents temperature, and the vertical axis represents the rate of change in the mechanical direction (MD) of the film, plotting the dimensional change curves due to heating. [Figure 2] This is a schematic diagram showing the external characteristics of a jumbo roll after aging, excluding approximately 100 mm from both ends. Figure (A) is a schematic diagram showing the case where there are no circumferential molds (vertical molds) with a depth of 0.5 mm or more, and (B) is a schematic diagram illustrating the case where there are two circumferential molds (vertical molds) with a depth of 0.5 mm or more. [Modes for carrying out the invention]

[0013] The following describes in detail the polypropylene film, metal-layer integrated polypropylene film, and film capacitor of the present invention, as well as the methods for manufacturing them.

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

[0015] In this specification, the terms “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consist of,” and “consist solely of.”

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

[0017] 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 is sometimes called the length direction or flow direction. Next, the transverse direction of the film is the same as the Transverse Direction (hereinafter referred to as the "TD direction"). The TD direction is sometimes called the width direction.

[0018] Polypropylene film The polypropylene film of the present invention is composed of a polypropylene resin which 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 650,000 and 945,000. • 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 4.2%. It is characterized by the following: Hereinafter, these will be 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-described characteristics, exhibits excellent dielectric breakdown strength (dielectric breakdown strength) when a DC voltage is applied at high temperatures 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, because the polypropylene resin constituting the film 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 when the logarithmic molecular weight Log(M) = 4.0 in the integral molecular weight distribution curve, all within specific ranges. Furthermore, it exhibits excellent heat shrinkage resistance in that thermal shrinkage in the mechanical direction (MD) is suppressed at temperatures exceeding the above-described high temperature, up to approximately 150°C. Furthermore, the film capacitor of the present invention, which uses 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 the 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 the present invention is suitable for film capacitor applications. In addition, although the polypropylene film of the present invention is not limited to whether or not it is stretched, it is preferable that it is a biaxially oriented film considering the above applications.

[0020] In this invention, both sides 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 during element winding in capacitor manufacturing. The second surface can also be rough.

[0021] 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.

[0022] The density of the aforementioned polypropylene film is not limited, but considering capacitor applications, for example, 919 g / cm³ is suitable. 3 More than 925g / cm 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.

[0023] The polypropylene film of the present invention 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.

[0024] 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 5.6 or higher, even more preferably 5.8 or higher, even 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 6.8 or lower, more preferably 6.7 or lower, and even more preferably 6.6 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).

[0025] The polypropylene film of the present invention has an Mz of 650,000 to 945,000 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).

[0026] Mz can be between 650,000 and 945,000, but the lower limit is preferably above 700,000, more preferably above 710,000, and even more preferably above 720,000. The upper limit is preferably below 920,000, more preferably below 850,000, and even more preferably below 790,000. By keeping Mz 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, in particular, suppresses thermal shrinkage in the mechanical direction (MD). If Mz exceeds 945,000, which is outside the range of the present invention, the thermal shrinkage of the polypropylene film at high temperatures tends to increase.

[0027] The polypropylene film of the present invention has a weight fraction w of 2.6% or more and 4.2% or less when the logarithmic molecular weight Log(M) = 4.0 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).

[0028] The weight fraction w may be between 2.6% and 4.2%, but the lower limit is 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 having the weight fraction w within this range, as a result of the combined effect with other requirements, a polypropylene film is obtained that has excellent dielectric breakdown strength at high temperatures and suppresses thermal shrinkage in the mechanical direction (MD). Furthermore, by having the weight fraction w within this range, the film capacitor of the present invention using the polypropylene film as a capacitor derivative has excellent thermal shock resistance in that thermal compression (deformation) of the capacitor is suppressed during repeated use between high and low temperatures.

[0029] In a preferred embodiment, the polypropylene film of the present invention 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 5.0 or more and 6.6 or less. The above Mz is between 720,000 and 850,000. The aforementioned weight fraction w is 3.3% or more and 3.7% or less. This can be achieved. By using a polypropylene resin with such physical properties, it becomes easier to obtain a polypropylene film that has excellent dielectric breakdown strength at high temperatures and suppresses thermal shrinkage in the mechanical direction (MD).

[0030] In a more preferred embodiment, the polypropylene film of the present invention comprises the polypropylene resin constituting the polypropylene film (or, if the polypropylene resin is composed of a mixture of multiple resins, after mixing), The molecular weight distribution (Mw / Mn) is 5.0 or more and 6.6 or less. The above Mz is between 720,000 and 790,000. The aforementioned weight fraction w is 3.5% or more and 3.7% or less. This can be achieved. By using a polypropylene resin with such physical properties, it becomes easier to obtain a polypropylene film that has excellent dielectric breakdown strength at high temperatures and suppresses thermal shrinkage in the mechanical direction (MD).

[0031] In this specification, the polypropylene resin constituting the polypropylene film has Mw, Mn, Mz, molecular weight distribution (Mw / Mn), and weight fraction w, and when the polypropylene resin is composed of multiple resins, the polypropylene resin A and polypropylene resin B have 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, and molecular weight differential distribution value difference (D M The method for measuring the weight fraction w is as described in the examples.

[0032] The polypropylene film of the present invention 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.

[0033] 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.

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

[0035] When the polypropylene film of the present invention 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." Furthermore, when the polypropylene film contains only one type of polypropylene resin, that polypropylene resin is also designated as a main component and referred to herein as the "main component polypropylene resin."

[0036] The polypropylene film of the present invention may contain two or more types of polypropylene resin (particularly two types), for example, polypropylene resin B (blended resin) together with polypropylene resin A (base resin, which is the main component) described below. The following will provide an illustrative explanation of the case in which two types of polypropylene resin, polypropylene resin A (base resin) and polypropylene resin B (blended 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, 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.

[0038] The weight-average molecular weight Mw of 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 340,000 or less. When Mw is 250,000 or more and less than 350,000, the thickness of the cast raw material sheet can be easily controlled in the manufacturing process of the polypropylene film, and thickness variations are less likely to occur.

[0039] 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 low thermal shrinkage and good thermal shock resistance.

[0040] The z-average molecular weight Mz of polypropylene resin A is preferably 700,000 to 1,550,000, more preferably 750,000 to 1,500,000. When Mz is between 700,000 and 1,550,000, it is easier to obtain a film with high dielectric strength at high temperatures.

[0041] 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, and more preferably 9.5 or lower. When the Mw / Mn is between 5.0 and 10.0, the stretchability improves, making it easier to obtain thin films.

[0042] 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.

[0043] 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, when the logarithmic molecular weight Log(M) = 6.0, the differential distribution value is preferably 17.0 or higher, more preferably 20.0 or higher. The upper limit is preferably 24.0 or lower, more preferably 22.0 or lower. Furthermore, the difference 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 (the difference in molecular weight differential distribution value (D) M)) is preferably 8.0 to 18.0, more preferably 8.0 to 11.0, even more preferably 8.2 to 10.0, and even more preferably 8.4 to 8.8.

[0044] Comparing the components with a logarithmic molecular weight of Log(M) = 4.5 as a representative distribution value for the low molecular weight components (10,000 to 100,000) of polypropylene resin A (250,000 to less than 350,000) and the components with a logarithmic molecular weight of Log(M) = 6.0 as a representative distribution value for the high molecular weight components (around 1,000,000) of polypropylene resin A, it can be seen that the low molecular weight components are more abundant by 8.0% to 18.0%.

[0045] 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 the present invention 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.

[0046] The weight fraction w of polypropylene resin A preferably has a lower limit of 3.8% or more, and more preferably 4.0% or more. The upper limit is preferably 4.4% or less, and more preferably 4.2% or less. When the weight fraction w of polypropylene resin A is within this range, and combined 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 4.2%, it becomes easier to obtain a polypropylene film that has excellent dielectric breakdown strength at high temperatures and suppresses thermal shrinkage in the mechanical direction (MD).

[0047] Melt flow rate (MFR) of polypropylene resin A at 230°C AThe amount 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. Also, MFR A The upper limit is preferably 10.0g / 10 min or less, more preferably 8.0g / 10 min or less, and even more preferably 6.0g / 10 min or less. A The melt flow rate can also be set to between 4.8 g / 10 min and 5.5 g / 10 min. 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.

[0048] In a preferred embodiment, the polypropylene film of the present invention is made of polypropylene resin A. The Mw of the aforementioned polypropylene resin A is 275,000 or more and less than 350,000. The molecular weight distribution (Mw / Mn) of the aforementioned polypropylene resin A is 5.8 or more and 10.0 or less. • Melt flow rate (MFR) of the polypropylene resin A A ) is between 4.8g / 10 min and 5.5g / 10 min. 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.

[0049] Furthermore, in a more preferred embodiment, the polypropylene film of the present invention is made of polypropylene resin A, The Mw of the aforementioned polypropylene resin A is between 280,000 and 300,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin A is 6.0 or more and 6.5 or less. • Melt flow rate (MFR) of the polypropylene resin A A ) is 5.0g / 10 min or more and 5.5g / 10 min or less. It can be a mode of action.

[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 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.

[0051] 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.

[0052] The content of polypropylene resin B is preferably less than 50% by weight, more 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 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, and even more preferably 25% by weight or more, relative to 100% by weight of the polypropylene resin. Examples of polypropylene resin B include isotactic polypropylene. In addition, in the present invention, 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 65% by weight or more and 75% by weight or less is particularly preferred.

[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 between 350,000 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 variations are less likely to occur.

[0054] 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 low thermal shrinkage and good thermal shock resistance.

[0055] 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 1.7 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.

[0056] 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, and even more preferably 7.5 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.

[0057] 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.

[0058] 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. In addition, the difference 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 (the difference in molecular weight differential distribution value (D) M )) is preferably -11.0 to 7.0, more preferably -6.0 to 0.0, and even more preferably -4.0 to -2.0.

[0059] 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 slightly different quantitative relationship between high molecular weight and low molecular weight components. This leads to a certain kind of fine mixing (phase separation) state, which is considered preferable as it facilitates the refinement of crystal size. Furthermore, even at the same stretching ratio, it tends to become more highly oriented, and the surface is also more likely to exhibit fine roughening, which is considered preferable. When the polypropylene resin contains polypropyn 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 in any way for these reasons.

[0060] The weight fraction w of polypropylene resin B has a lower limit of preferably 2.0% or more, and 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 2.6% to 4.2%, making it easier to obtain a polypropylene film with excellent dielectric breakdown strength at high temperatures and suppressed thermal shrinkage in the mechanical direction (MD).

[0061] Melt flow rate (MFR) at 230°C in polypropylene resin B B The MFR 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 0.1g / 10 min or more, more preferably 0.5g / 10 min or more, and even more preferably 1.5g / 10 min or more.

[0062] Furthermore, the MFR of polypropylene resin A as the main component base resin A and the MFR of polypropylene resin B, which is a blended resin B Difference MFR A -MFR B It is preferable to set it to 1.5g / 10min or more. In other words, MFR A is MFR B Larger than the above difference MFR A -MFR B The MFR is preferably 1.6g / 10 min or more, more preferably 2.0g / 10 min or more, and even more preferably 3.0g / 10 min or more. A -MFR BIf the value is less than 1.5 g / 10 min (this includes negative values), in the manufacturing process of polypropylene film, a sea-island phase separation structure may not be formed at the stage of casting the raw material sheet, 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, MFR A and MFR B Even if the difference is large, MFR B If the above difference is larger (MFR A -MFR B If the value is negative, the size of the islands in the sea-island phase separation structure will be very small.

[0063] In a preferred embodiment, the polypropylene film of the present invention is made of polypropylene resin B. The Mw of the aforementioned polypropylene resin B is between 385,000 and 550,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.4 or more and 11.0 or less. • Melt flow rate (MFR) of the polypropylene resin B B ) is between 0.1g / 10 min and 2.2g / 10 min. 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.

[0064] A more preferred embodiment of the present invention is a polypropylene film in which polypropylene resin B is used. The Mw of the aforementioned polypropylene resin B is between 390,000 and 550,000. The molecular weight distribution (Mw / Mn) of the polypropylene resin B is 8.5 or more and 11.0 or less. • Melt flow rate (MFR) of the polypropylene resin B B ) is between 1.0g / 10 min and 2.1g / 10 min. It can be a mode of action.

[0065] 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.

[0066] 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.

[0067] 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), are used. However, in the present invention, the polypropylene film can 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.

[0068] The polypropylene film of the present invention may further contain additives. Examples of additives include 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 oriented film, a uniaxially oriented film, or an unoriented film, but it is preferably a biaxially oriented film.

[0070] The polypropylene film of the present invention 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 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 manufactured by winding this metal-layer integrated polypropylene film or by laminating multiple metal-layer integrated polypropylene films.

[0071] Considering the above-mentioned applications for capacitors, it is desirable that the polypropylene film of the present invention has the following dielectric breakdown strength and heat shrinkage resistance characteristics.

[0072] The dielectric breakdown strength (V) of the polypropylene film of the present invention at 100°C under AC voltage. AC100℃ The voltage is preferably 240 V / μm or higher, more preferably 245 V / μm or higher, and even more preferably 250 V / μm or higher. The upper limit of dielectric breakdown strength at AC voltage at 100°C is preferably higher, for example, 270 V / μm or 265 V / μm.

[0073] The dielectric breakdown strength (V) of the polypropylene film of the present invention at 110°C under AC voltage. AC110℃ The voltage is preferably 240 V / μm or higher, more preferably 242 V / μm or higher, and even more preferably 244 V / μm or higher. The upper limit of dielectric breakdown strength at AC voltage at 110°C is preferably higher, for example 260 V / μm or 255 V / μm.

[0074] Dielectric breakdown strength (V) of the polypropylene film of the present invention at AC voltage at 120°C AC120℃ The voltage is preferably 230 V / μm or higher, more preferably 235 V / μm or higher, and even more preferably 238 V / μm or higher. The upper limit of dielectric breakdown strength at AC voltage at 120°C is preferably higher, for example 250 V / μm or 245 V / μm.

[0075] The dielectric breakdown strength (V) of the polypropylene film of the present invention at a DC voltage of 120°C. DC120℃ The dielectric breakdown strength at DC voltage at 120°C is preferably 520V / μm or higher, more preferably 527V / μm or higher, and even more preferably 532V / μm or higher. A higher upper limit is preferable for dielectric breakdown strength at DC voltage at 120°C, such as 550V / μm or 540V / μm.

[0076] The V of the polypropylene film of the present invention AC120℃ and the aforementioned V DC120℃ The sum of (V AC120℃ +V DC120℃ The V is preferably 750V / μm or higher, more preferably 760V / μm or higher, and even more preferably 770V / μm or higher. AC120℃ and the aforementioned V DC120℃ The upper limit of the total value is preferable as it is higher, for example, 1000V / μm, 900V / μm, 850V / μm, etc.

[0077] The V of the polypropylene film of the present invention DC120℃ and the aforementioned V AC120℃ The difference with (V DC120℃ -V AC120℃ The difference is preferably 300V / μm or less. This relatively small difference has the advantage of making dielectric breakdown less likely even with superimposed currents (currents where DC and AC overlap). The lower limit of the difference is preferably 280V / μm or more, and can be set, for example, between 280V / μm and 300V / μm.

[0078] The polypropylene film of the present invention exhibits excellent heat shrinkage resistance. Specifically, in thermomechanical analysis (TMA) of the polypropylene film, it exhibits a shrinkage resistance of 2.17 N / mm². 2When the temperature is increased from 25°C to 155°C at a rate of 10°C / min under a load, and a heating dimensional change curve is drawn with temperature on the horizontal axis and the dimensional change rate in the mechanical direction (MD) of the film on the vertical axis, it is desirable that the dimensional change rate is 0% or more during the heating process from 25°C to 155°C. Here, a dimensional change rate of 0% or more (i.e., not falling below 0%) means that no thermal shrinkage is observed. The method for thermomechanical analysis (TMA) is as described in the examples.

[0079] Figure 1 shows the results of the thermomechanical analysis of the polypropylene films prepared in Example 1, Comparative Example 5, and Comparative Example 14. The horizontal axis represents temperature, and the vertical axis represents the rate of change in the mechanical direction (MD) of the film, plotting the resulting dimensional change curves during heating. As can be seen from Figure 1, the polypropylene film prepared in Example 1 shows a rate of change in the mechanical direction of the film of 0% or more throughout the entire heating process from 25°C to 155°C. On the other hand, the polypropylene films prepared in Comparative Example 5 and Comparative Example 14 have a temperature range during the heating process from 25°C to 155°C where the rate of change in the mechanical direction of the film is less than 0%.

[0080] Manufacturing method of polypropylene film The method for manufacturing the polypropylene film of the present invention described above is not limited, but the polypropylene film of the present invention can be suitably manufactured by employing, for example, the following manufacturing method (hereinafter referred to as "the method for manufacturing the polypropylene film of the present invention").

[0081] The method for producing the polypropylene film of the present invention is the method for producing the polypropylene film of the present invention as described above, A polypropylene resin composition containing at least polypropylene resin A and polypropylene resin B is subjected to a temperature of 225°C to 270°C and a shear rate of 2000 s. -1 More than 15000s -1 The following steps include melting: The melt flow rate (MFR) of the aforementioned polypropylene resin A. A ) and the (MFR) of the polypropylene resin B B ) difference MFRA -MFR B However, it is 1.5g / 10 minutes 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:

[0082] 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.

[0083] The present invention'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 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 relative to the base resin. The terms "polypropylene resin A" and "polypropylene resin B" in the present invention's method for producing a polypropylene film correspond to the terms "polypropylene resin A" and "polypropylene resin B" in the aforementioned section on polypropylene film, and the following are the values ​​of each resin: 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, and molecular weight differential distribution value difference (D M The explanations of weight fraction w and MFR are as described above, but in the present invention's method for producing polypropylene resin, MFR is particularly important. A and MFR B Difference MFR A -MFR B Use products that contain 1.5g / 10 minutes or more.

[0084] There are no particular limitations on the method of mixing the resins applicable to the manufacturing method of the present invention, 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.

[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 with more than one screw. In the case of a twin-screw type, either a co-rotating or staggered rotation kneading type is acceptable.

[0086] 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.

[0087] 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).

[0088] 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.

[0089] In the present invention's method for producing polypropylene film, first, polypropylene resin pellets, dry-mixed polypropylene resin pellets, or mixed polypropylene resin pellets prepared by pre-melting and kneading are supplied to an extruder and heated and melted.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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 true: 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 4.2%, and in combination with other requirements, a film capacitor using polypropylene film as a capacitor derivative can be obtained in which thermal shock resistance is suppressed during repeated use between high and low temperatures.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] The polypropylene film of the present invention 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 the present invention 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 the present invention 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.

[0100] Metal layer integrated polypropylene film capacitors and methods for manufacturing the same 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, taking into consideration processing into capacitors.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] Any method known to form a margin, such as the tape method or the oil method, can be used without any limitations.

[0105] Furthermore, the metal-layer-integrated polypropylene film of the present invention can be laminated or wound into a film capacitor using conventionally known methods.

[0106] 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]

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

[0108] [Table 1]

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

[0110] 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.

[0111] 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.

[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 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.

[0113] <<Differential distribution value when logarithmic molecular weight Log(M) = 4.5, differential distribution value when logarithmic molecular weight Log(M) = 6.0, and difference in molecular weight differential distribution value (D M ) Measurement≫ Furthermore, 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 by 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. Also, the difference between the differential distribution value for Log(M) = 4.5 and the differential distribution value for Log(M) = 6.0 was calculated as the molecular weight differential distribution value difference (D M The series of operations to obtain the differential distribution curve were performed using the analysis software built into the GPC measurement device used.

[0114] <<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.

[0115] ≪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.

[0116] Examples 1-14 and Comparative Examples 1-18 [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.

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

[0118] 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.

[0119] ≪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.

[0120] <<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 ≪Measurement of dielectric breakdown strength of polypropylene film: DC (direct current)≫ The dielectric breakdown voltage (BDV) of polypropylene films in the examples and comparative examples 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 measurement results was defined as the dielectric breakdown strength ES (VDC / μm). Test specimen: Approximately 150mm x 150mm Conditioning of test specimens: 30 minutes under atmospheric conditions Power supply: DC Ambient temperature: 120°C in the air 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 ≪Measurement of dielectric breakdown strength of polypropylene film: AC≫ The dielectric breakdown voltage (BDV) of the films in 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 (Plane 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 8 values ​​obtained by excluding the top 2 and bottom 2 values ​​from the 12 measurements was defined as the dielectric breakdown strength ES (VAC / μm). Test specimen: approximately 150mm x 150mm Conditioning of test specimens: 30 minutes under atmospheric conditions Power supply: AC Ambient environment: In the air, at 100°C, 110°C, and 120°C. Testing equipment: Kikusui Electronics Co., Ltd. TOS5051A withstand voltage tester Voltage rise rate: 100V / s Upper limit: 5mA ≪Thermomechanical analysis (TMA)≫ Thermomechanical analysis was performed as follows. Equipment: Seiko Instruments EXSTAR6000 and TMA / SS6000; Film width: 4mm Chuck spacing: 15mm Load: 2.17 N / mm 2 Measurement temperature range: 25℃~155℃ Heating rate: 10°C / min When a heating dimensional change curve was drawn with temperature on the horizontal axis and the rate of change in the mechanical direction (MD) of the film on the vertical axis, a pass rating "A" was given if the rate of change in dimensions was 0% or more during the heating process from 25°C to 155°C, and a fail rating "C" was given if it was less than 0%.

[0121] <<Winding quality (wrinkles) of jumbo rolls after aging>> The appearance of the jumbo roll, excluding approximately 100 mm from both ends after aging, was evaluated from the perspective of winding quality (wrinkles). The type described below (vertical type) refers to a winding defect that occurs parallel to the circumferential direction, resembling a ribbed metal can, commonly known as MD wire or can shape. If there are no circumferential molds (vertical molds) with a depth of 0.5 mm or more, the result is "AA" (Excellent). If there is only one circumferential mold (vertical mold) with a depth of 0.5 mm or more, it is classified as "Good A". If there are two or three circumferential molds (vertical molds) with a depth of 0.5 mm or more, it is classified as "B". A defect "C" was defined as the presence of four or more circumferential molds (vertical molds) with a depth of 0.5 mm or more. In the case of "Excellent" "AA," even if circumferential molds (vertical molds) are present, their depth is less than 0.5 mm, and they are distributed almost evenly in the width direction. Here, "Excellent" "AA" and "Good" "A" are acceptable (within the tolerance range), while "Average" "B" and "Defective" "C" are unacceptable. [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.

[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 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.

[0123] 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.

[0124] 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).

[0125] 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.

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

[0127] <<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 ("A"), and a yield of less than 95% was evaluated as poor ("C").

[0128] ≪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.

[0129] (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), a rate between -4% and -6% was classified as "B", and a rate exceeding -6% was classified as "Poor" (C).

[0130] Thermal shock resistance (rate of change of tanδ) The obtained capacitors were placed in a thermal shock test apparatus (ESPEC TSA-101S-W), and a rapid temperature rise / fall cycle was repeated 500 times between a lower limit temperature of -40°C and an upper limit temperature of 105°C. Specifically, one set consisted of holding the capacitor at -40°C for 50 minutes and then holding it at 105°C for 50 minutes, and this was repeated 500 times. The temperature change was achieved by forcibly exchanging the air by blowing in air at the set temperature. The temperature change time was also included in the 50-minute holding time.

[0131] The tanδ was measured before and after the thermal shock test using a Hioki Corporation LCR HiTester 3522-50. The rate of increase in tanδ was calculated using the following formula.

[0132] (Increase in tanδ) = [(tanδ after thermal shock test) - (tanδ before thermal shock test)] / (tanδ before thermal shock test) × 100 (%) The test was conducted using three samples, and the average value was used for evaluation.

[0133] An increase rate of 100% or less was classified as "Good" ("A"), an increase rate between 100% and 105% was classified as "B", and an increase rate exceeding 105% was classified as "Poor" ("C").

[0134] ≪Consideration≫ The polypropylene films of the present invention produced in Examples 1 to 14 exhibit excellent dielectric breakdown strength when a DC voltage is applied at high temperatures 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. This is because the polypropylene resin constituting the film 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 when the logarithmic molecular weight Log(M) = 4.0 in the integral molecular weight distribution curve, all within a predetermined range. Furthermore, the films exhibit excellent heat shrinkage resistance in that thermal shrinkage in the mechanical direction (MD) is suppressed at temperatures exceeding the above high temperature of approximately 150°C. Furthermore, the film capacitors fabricated in the examples exhibit excellent heat resistance at high temperatures of approximately 120°C (100°C to 120°C). Specifically, they have excellent lifespan in that the decrease in capacitance of the capacitor is suppressed even when used for extended periods at the aforementioned high temperatures, and they also exhibit excellent thermal shock resistance in that the thermal compression (deformation) of the capacitor is suppressed during repeated use between high and low temperatures, as would be expected in an engine compartment. In addition, the polypropylene film of the present invention has yielded favorable evaluation results in terms of the appearance (winding quality (wrinkles)) of the jumbo roll after aging, vapor deposition processability during capacitor fabrication, and element winding processability.

Claims

1. A polypropylene film, wherein the polypropylene resin constituting the 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 6.7 or lower. - The average molecular weight Mz is between 650,000 and 945,000. - 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 4.2%. A polypropylene film characterized by the following features.

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

3. A polypropylene film according to claim 1 or 2, which is a biaxially oriented film.

4. Thermomechanical analysis showed a load of 2.17 N / mm². ２ The polypropylene film according to any one of claims 1 to 3, wherein when the temperature is raised from 25°C to 155°C at a rate of 10°C / min under a load, and a heating dimensional change curve is drawn with temperature on the horizontal axis and the dimensional change rate in the mechanical direction (MD) of the film on the vertical axis, the dimensional change rate is 0% or more during the heating process from 25°C to 155°C.

5. Dielectric breakdown strength at DC voltage at 120°C (V ＤＣ１２０℃ ) and dielectric breakdown strength (V) at AC voltage at 120°C ＡＣ１２０℃ ) difference (V ＤＣ１２０℃ -V ＡＣ１２０℃ A polypropylene film according to any one of claims 1 to 4, wherein the coefficient of gravity 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 above Mz is between 720,000 and 790,000, - The weight fraction w is 3.5% or more and 3.7% or less. A polypropylene film according to any one of claims 1 to 6.

8. The polypropylene resin contains polypropylene resin A and polypropylene resin B, and polypropylene resin A and polypropylene resin B have different Mw, Mw / Mn, and differential distribution values ​​when the logarithmic molecular weight Log(M) = 4.5 in the molecular weight distribution curve, 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 (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. A polypropylene film according to any one of claims 1 to 7.

9. The polypropylene resin contains polypropylene resin A and polypropylene resin B, and polypropylene resin A and polypropylene resin B have different Mw, Mw / Mn, and differential distribution values ​​when the logarithmic molecular weight Log(M) = 4.5 in the molecular weight distribution curve, 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 between 385,000 and 550,000. - 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. A 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 polypropylene resin A to the total mass of polypropylene resin B is 65 to 75% by 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. A polypropylene film according to any one of claims 1 to 11, The polypropylene film has a metal layer laminated on one or both sides, Polypropylene film with an integrated metal layer.

13. Having a wound metal layer integrated polypropylene film according to claim 12, or having a configuration in which a plurality of metal layer integrated polypropylene films according to claim 12 are laminated, Film capacitor.

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