Manufacturing method of polypropylene film

Abstract

The present invention aims to provide a method for manufacturing a polypropylene resin sheet and a polypropylene film, which have excellent film processability in a vapor deposition process where evaporated metals such as aluminum and silica are thinned onto the surface of the film, and which have excellent voltage resistance characteristics as a film capacitor. [Solution] A method for manufacturing a polypropylene film, comprising a casting step of extruding a molten polypropylene resin composition in a sheet shape from a nozzle and cooling and solidifying it in a casting device to obtain a resin sheet, wherein the thickness of the resin sheet is measured at 10 mm intervals in the transport direction for 5 minutes from the center in the width direction to 30 mm inside both ends, and the thickness uniformity R / AVE is calculated from the average value, and when X is the number for which the difference in R / AVE between adjacent measurement points is 3.0% or greater, the value of the following formula 1 is in the range of 0 to 5.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing a polypropylene film that has high voltage resistance in a high-temperature and high-voltage environment when used as a dielectric for a film capacitor.

BACKGROUND ART

[0002] Polypropylene films are excellent in transparency, mechanical properties, electrical properties and the like, and are therefore used in a variety of applications such as packaging applications, tape applications, and electrical applications including cable wrapping and film capacitors.

[0003] Among these, in film capacitor applications, the film is particularly preferably used as a dielectric for film capacitors due to its excellent high voltage resistance characteristics and low loss characteristics. Recently, various types of electrical equipment are being converted to inverters, and accordingly, demands for smaller size and larger capacity of film capacitors are increasing. In particular, in applications such as automobiles (including hybrid cars and electric vehicles), solar power generation, and wind power generation, the operating environment is becoming hotter (indicating 85°C or higher and 125°C or lower), and the demand for heat resistance for film capacitors is rising.

[0004] Improving the heat resistance of a film capacitor means improving the voltage resistance at high temperatures, and in order to achieve this and downsizing at the same time, it is necessary to achieve both thinning of the polypropylene film used for the film capacitor and voltage resistance. Apart from the raw material properties of polypropylene resins, there have hitherto been known methods for adjusting the temperature of the film in the film production process, and adjusting the longitudinal and transverse stretching ratios, stretching magnification, and stretching speed, as production methods for producing such polypropylene films.

[0005] Furthermore, in film manufacturing, it is known that poor adhesion between the resin sheet discharged from the T-die and the cooling roll can lead to uneven cooling, resulting in uneven thickness of the molded resin sheet and film. As a method to improve this, a method is known in which, in an air blowing device such as an air knife or air chamber that is installed to cool the molten resin sheet discharged from the T-die at the winding portion of the cooling roll and to ensure it adheres to the roll, an air passage is separately formed on the T-die side at the edge of the air blowing port of the air blowing device, thereby reducing the flapping of the resin sheet (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Public Gazette No. 61-121923 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the method described in Patent Document 1, the pressure decreases in the space surrounded by the air blown out from the air outlet of the air knife, the air flowing upstream in the conveying direction, and the air flowing in the air passage, generating a vortex. This vortex causes vibration of the resin sheet 3. Therefore, it was difficult to manufacture a polypropylene film with minimal thickness unevenness in the conveying direction and minimal air entrapment using the method described in Patent Document 1.

[0008] Therefore, the present invention aims to solve the above problems and provide a method for manufacturing a polypropylene film that can produce a polypropylene film with less thickness unevenness in the conveying direction and less air entrapment by improving the airflow near the air knife. [Means for solving the problem]

[0009] To solve the aforementioned problems, the manufacturing apparatus and manufacturing method for polypropylene film of the present invention have the following configuration. (1) A method for manufacturing a polypropylene film, comprising a casting step of extruding a molten polypropylene resin composition in a sheet shape from a nozzle and cooling and solidifying it in a casting device to obtain a resin sheet, wherein the thickness of the resin sheet is measured at 10 mm intervals in the transport direction for 5 minutes in a section from the center in the width direction to 30 mm inside both ends, and the thickness uniformity R / AVE is calculated from the average value, and when X is the number for which the difference in R / AVE between adjacent measurement points is 3.0% or greater, the value of the following formula 1 is in the range of 0 to 5.

[0010]

number

[0011] (2) The method for manufacturing a polypropylene film as described in (1), wherein the sheet width of the resin sheet is 500 to 1200 mm. (3) A method for manufacturing a polypropylene film according to (1) or (2), wherein the sheet conveying speed of the resin sheet is 10 to 100 m / min. (4) A method for producing a polypropylene film according to (1) or (2), wherein the sheet thickness of the resin sheet is 100 to 500 μm. (5) A method for producing a polypropylene film according to (1) or (2), wherein the film thickness of the polypropylene film is 1 to 4 μm. [Effects of the Invention]

[0012] The present invention enables the stable production of polypropylene films by achieving high adhesion without vibration of the resin sheet. Furthermore, the film obtained under the above conditions provides a method for manufacturing polypropylene films that can achieve both processability in the vapor deposition process and voltage resistance characteristics. [Brief explanation of the drawing]

[0013] [Figure 1] This is an enlarged view of the area near the air knife of the resin sheet manufacturing apparatus according to Embodiment 1, and is a cross-sectional view perpendicular to the width direction. [Figure 2]This is a partially enlarged view near the air outlet and exhaust port of FIG. 1. [Figure 3] This is an enlarged view near the air outlet and exhaust port of the air knife of the resin sheet manufacturing apparatus according to Embodiment 2, and is a cross-sectional view perpendicular to the width direction. [Figure 4] This is an enlarged view near the air outlet and exhaust port of the air knife of the resin sheet manufacturing apparatus according to Embodiment 3, and is a cross-sectional view perpendicular to the width direction. [Modes for Carrying Out the Invention]

[0014] Hereinafter, the present invention will be described in detail. The present invention relates to a method for producing a polypropylene film, which comprises a casting step of discharging a molten polypropylene resin composition in a sheet form from a die, and cooling and solidifying the discharged composition with a casting apparatus to obtain a resin sheet, wherein the thickness unevenness R / AVE is calculated from the average value obtained by measuring the thickness of the resin sheet in the conveying direction for 5 minutes at 10 mm intervals in the section from the central portion in the width direction to 30 mm inward from both end portions, and when the number X is defined as the number of adjacent measurement points where the difference in R / AVE is 3.0% or more, the value of the following formula 1 is in the range of 0 to 5.

[0015] [Mathematical Formula]

[0016] Hereinafter, the meanings of each term in the present invention will be described.

[0017] "Polypropylene resin composition" refers to a resin composition containing polypropylene as the main component, and "polypropylene film" refers to a sheet-shaped molded article containing polypropylene as the main component. "Polypropylene" refers to a resin containing propylene units in an amount of more than 50 mol% and 100 mol% or less, based on 100 mol% of all structural units constituting the resin. The main component refers to a component that accounts for more than 50 mass% and 100 mass% or less of all constituent components of the composition or film. At this time, when a plurality of components corresponding to polypropylene are contained, even if each individual component is less than 50 mass%, if the sum of these components exceeds 50 mass%, polypropylene is regarded as the main component. Hereinafter, the main component can be interpreted in the same manner.

[0018] The polypropylene resin composition may be composed solely of polypropylene, or may contain other components. Examples of other components include polyolefin resins such as polyethylene, polystyrene, and polymethylpentene, polyamide resins such as nylon 6 and nylon 66, aramid resins, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polybutylene succinate, and polyethylene-2,6-naphthalate, polycarbonate resins, polyarylate resins, polyacetal resins, polyphenylene sulfide resins, tetrafluoroethylene resins, trifluoroethylene resins, chlorotrifluoroethylene resins, tetrafluoroethylene-hexafluoropropylene copolymers, fluororesins such as vinylidene fluoride resins, acrylic resins, methacrylic resins, polyacetal resins, polyglycolic acid resins, polylactic acid resins, and the like. In addition, various additives, for example, antioxidants, antistatic agents, crystal nucleating agents, inorganic particles, organic particles, viscosity reducers, heat stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, dopants for adjusting the refractive index, and the like may be added to the polypropylene resin composition.

[0019] A "die" is a device that extrudes a polypropylene resin composition molten in an extruder into a sheet shape from the die and forms it. A "casting device" is a device that cools and solidifies the sheet material extruded from the die into a resin sheet by pressing it against a metal roll with adjustable temperature, and then transports it downstream. An "air knife" is a device that blows air onto the sheet material to press it against the metal roll of the casting device. The air supply source is not particularly limited, but examples include blowers and compressors. The "conveying direction" is the direction in which the resin sheet is conveyed by the casting device, and is also called the longitudinal direction. The "width direction" is the direction perpendicular to the conveying direction within the surface of the resin sheet.

[0020] A "discharge port" is one of the components of the air knife and is an opening that blows air to make the resin sheet adhere tightly to the casting device. The shape of the opening is not particularly limited, but examples include slits and porous structures. An "exhaust port" is one of the components of the air knife and is located upstream of the discharge port in the conveying direction and is an opening that discharges air. The shape of the opening is not particularly limited, but examples include slits and porous structures. The power source for exhaust is not particularly limited, but examples include blowers and vacuum pumps. The shortest distance between the exhaust port and the discharge port is preferably 5 to 100 mm. An "air intake port" is one of the components of the air knife and is located upstream of the discharge port in the conveying direction and downstream of the exhaust port in the conveying direction and is an opening that supplies air. The shape of the opening is not particularly limited, but examples include slits and porous structures. The power source for air intake is not particularly limited, but examples include blowers and pressure pumps, and natural air intake from the atmosphere is also acceptable. In the case of natural air intake, a mechanism for adjusting the air intake flow rate may be provided. "Air outlet direction" refers to the direction in which air is blown out from the outlet or air intake.

[0021] The present invention relates to a method for producing a polypropylene film, which includes a casting step in which a molten polypropylene resin composition is extruded in a sheet shape from a die and cooled and solidified in a casting device to obtain a resin sheet. Methods such as electrostatic application, air knife method, nip roll method, and underwater casting method can be used to adhere the molten sheet to the casting device, but the air knife method is preferred from the viewpoint of suppressing thickness unevenness, high-speed film formation, and control of the film surface shape. In this configuration, the sheet width of the obtained resin sheet can be adjusted by the slit width of the die. The sheet width is preferably 500 to 1200 mm, more preferably 600 to 1100 mm, and even more preferably 700 to 1000 mm, from the viewpoint of preventing film tearing during biaxial stretching in a subsequent process and increasing production capacity.

[0022] Furthermore, regarding the gap in the "air intake port," which is one of the components of the air knife, from the viewpoint of ensuring that the sheet-like material discharged from the nozzle flows stably into the casting device, it is preferable that the slit be 0.5 to 1.5 mm, more preferably 0.7 to 1.2 mm, and even more preferably 0.9 to 1.1 mm. However, from the same viewpoint, the air velocity of the air blown out from the air intake port is preferably 5 to 25 m / s, more preferably 7 to 20 m / s, and even more preferably 9 to 15 m / s.

[0023] Furthermore, the sheet conveying speed is preferably 10 to 100 m / min, more preferably 20 to 90 m / min, and even more preferably 30 to 80 m / min, from the viewpoint of sheet adhesion with the casting device and production capacity. Furthermore, the sheet thickness is preferably 100 to 500 μm, more preferably 125 to 475 μm, and even more preferably 150 to 450 μm, from the viewpoint of film thickness after biaxial stretching and cooling and solidification on the casting drum. The sheet thickness of the resin sheet can be adjusted by the lip gap of the die, the rotation speed of the casting device, and the amount of molten polypropylene resin composition discharged from the extruder.

[0024] In the method for producing a polypropylene film of the present invention, the polypropylene film may be an unoriented film (i.e., a resin sheet), a uniaxially oriented film, or a biaxially oriented film, but from the viewpoint of use in film capacitors and the like, a biaxially oriented film is preferred. A biaxially oriented film means a film in which molecules are oriented in two directions, and this is obtained by stretching in two orthogonal directions (usually the transport direction and the width direction). The method for biaxially stretching a resin sheet will be described in detail below.

[0025] The resin sheet is preferably further cooled with a cooling roll, and the temperature of the cooling roll is preferably between 10°C and 60°C. Setting the cooling roll temperature to 10°C or higher makes it easier to raise the film to the desired temperature in the subsequent high-temperature heat treatment process. On the other hand, setting the cooling temperature to 60°C or lower reduces crystal formation in the resin sheet, making it easy to reduce variations in the surface shape of the biaxially oriented polypropylene film obtained after biaxial stretching in the transport direction.

[0026] Next, it is preferable to stretch the resin sheet in the transport direction during the longitudinal stretching process. More specifically, the resin sheet is passed through a preheated roll controlled to a temperature of 110°C to 150°C, preferably 120°C to 150°C, and stretched in the transport direction (longitudinal stretching) at a predetermined stretching speed and stretching ratio based on the peripheral speed difference between the rolls. The longitudinal stretching ratio is preferably 4.0 to 7.0 times, and more preferably 5.0 to 7.0 times. By setting the longitudinal stretching ratio to 4.0 times or more, the surface shape of the resulting biaxially oriented polypropylene film becomes uniform and the dielectric strength characteristics are also improved. On the other hand, if the longitudinal stretching ratio is 7.0 times or less, film breakage in the longitudinal stretching process and the subsequent transverse stretching process is reduced. Subsequently, it is also preferable to cool the uniaxially oriented polypropylene film obtained by longitudinal stretching, and the temperature at this time is preferably 20°C to 30°C.

[0027] Next, it is preferable to grasp both ends in the width direction of the uniaxially oriented polypropylene film obtained by longitudinal stretching with clips and stretch it in the width direction (transverse stretching) at a stretching ratio of 5.0 to 15.0 times using a tenter-type stretcher controlled at a temperature of 140°C to 170°C. Furthermore, it is also preferable to heat-set the film at a temperature of 150 to 170°C while allowing it to relax by 5 to 15% in the width direction.

[0028] Next, at least one side of the biaxially oriented film can be subjected to corona discharge treatment in air, nitrogen, carbon dioxide, or a mixture thereof. This condition affects the dielectric strength and vapor deposition processability of the resulting biaxially oriented polypropylene film. More specifically, the distance between the processing roll and the electrode is preferably 1.5 mm to 2.5 mm, and more preferably 1.8 mm to 2.2 mm. The running speed of the biaxially oriented film is preferably 200 m / min to 300 m / min, and more preferably 230 m / min to 270 m / min. The discharge power value of the electrode is preferably 3.5 kW to 11.9 kW, more preferably 5.8 kW to 11.0 kW, and even more preferably 5.8 kW to 7.8 kW. By performing corona discharge treatment under these conditions, it becomes easy to set the dielectric strength and wettability of the processed surface of the resulting biaxially oriented polypropylene film within a suitable range.

[0029] Such biaxially oriented polypropylene films possess both excellent voltage resistance and vapor deposition processability, making them suitable for use in film capacitors. From the viewpoint of film formation properties, mechanical strength, voltage resistance, and capacitance per unit volume when used as a dielectric in film capacitors, the thickness of the biaxially oriented polypropylene film is 1.0 μm to 4.0 μm, more preferably 2.0 μm to 3.0 μm. A thickness of 1.0 μm or more provides physical advantages in film formation properties, mechanical strength, and voltage resistance, while a thickness of 4.0 μm or less ensures sufficient capacitance per unit volume when used as a dielectric in film capacitors, leading to miniaturization of film capacitors. The thickness of the polypropylene film can be measured by the micrometer method in accordance with JIS C 2330 (2014) and can be adjusted by the discharge rate from the extruder, the take-up speed of the cast drum, the slit width of the die, the stretching ratio, etc.

[0030] Next, the edges of the biaxially oriented polypropylene film, held by clips, are cut and removed, and the biaxially oriented polypropylene film with the ends removed is wound onto a winding machine as a master roll. Finally, the biaxially oriented polypropylene film unwound from the master roll is slit to a specific width using a slitter, and the resulting film roll is wound onto a core to obtain a biaxially oriented polypropylene film roll.

[0031] The polypropylene film obtained by the present invention's method for manufacturing polypropylene films is preferably used as a dielectric for film capacitors, but is not limited to the type of film capacitor. Specifically, from the viewpoint of electrode configuration, it may be either a foil-wound film capacitor or a metal-deposited film capacitor, and it is also preferably used in oil-immersion type film capacitors containing insulating oil or dry-type film capacitors that do not use insulating oil at all. Furthermore, from the viewpoint of shape, it may be either a wound type or a laminated type. Due to the properties of the polypropylene film of the present invention, it is particularly preferably used as a metal-deposited film capacitor.

[0032] When the polypropylene film of the present invention is a biaxially oriented polypropylene film, it is preferable that its main component is a highly stereoregular polypropylene resin, more specifically, a highly stereoregular polypropylene resin having a mesopentad fraction of 0.960 to 0.995, a CXS of 0.5% to 4.0% by mass, an MFR of 0.5 g / 10 min to 5.0 g / 10 min, and a melt tension (MS) of 15 cN or less.

[0033] From the above viewpoint, the mesopentad fraction of the highly stereoregular polypropylene resin is more preferably 0.965 to 0.990, and even more preferably 0.970 to 0.985. From a similar viewpoint, the CXS of the highly stereoregular polypropylene resin is more preferably 0.5% to 3.0% by mass, and even more preferably 0.5% to 20% by mass. From a similar viewpoint, the MFR of the highly stereoregular polypropylene resin is more preferably 10 g / 10 min to 4.5 g / 10 min, and even more preferably 15 g / 10 min to 4.0 g / 10 min. From a similar viewpoint, the MS of the highly stereoregular polypropylene resin is more preferably 12 cN or less, and even more preferably 10 cN or less.

[0034] Furthermore, if the polypropylene film of the present invention is a biaxially oriented polypropylene film, it is preferable to include a melt-tension polypropylene resin, more specifically, a melt-tension polypropylene resin having an MFR of 10 g / 10 min or more and 5.0 g / 10 min or less, and an MS greater than 15.0 cN and 35.0 cN or less. By adopting this configuration, it is possible to reduce the deterioration of stretchability during film formation of biaxially oriented polypropylene films and to manufacture films with improved heat resistance and high voltage resistance at high temperatures.

[0035] Furthermore, when the biaxially oriented polypropylene film contains both a highly stereoregular polypropylene resin and a melt-tension polypropylene resin, the mass ratio of the two (highly stereoregular polypropylene resin: melt-tension polypropylene resin) is preferably 90.0-80.0:10.0-20.0, more preferably 85.0-80.0:15.0-20.0, and even more preferably 83.0-80.0:17.0-20.0. This configuration reduces the deterioration of stretchability during film formation of the biaxially oriented polypropylene film and improves the heat resistance and high-temperature dielectric strength of the resulting biaxially oriented polypropylene film.

[0036] The present invention relates to a method for manufacturing a polypropylene film, comprising a casting step of extruding a molten polypropylene resin composition in a sheet shape from a die and cooling and solidifying it in a casting device to obtain a resin sheet, wherein the thickness of the resin sheet is measured at 10 mm intervals in the transport direction for 5 minutes from the center in the width direction to 30 mm inside both ends, and the thickness uniformity R / AVE is calculated from the average value, and when X is the number for which the difference in R / AVE between adjacent measurement points is 3.0% or greater, the value of the following formula 1 is in the range of 0 to 5.

[0037]

number

[0038] One method that satisfies Equation 1 is to obtain a resin sheet according to Embodiments 1 to 3 described below.

[0039] [Embodiment 1] A method for manufacturing a resin sheet according to Embodiment 1 will now be described. Figure 1 is an enlarged view of the area around the air knife in Embodiment 1, and Figure 2 is a partially enlarged view of the area around the air outlet and exhaust port in Figure 1; both are cross-sectional views perpendicular to the width direction. As shown in Figure 1, in this embodiment, the air knife 4 is equipped with an air outlet 6, an air intake port 7, and an exhaust port 8 on the surface facing the casting device 2, in order from the downstream side in the conveying direction.

[0040] The manufacturing method for the resin sheet in this embodiment is as follows: Resin sheet material is discharged from a nozzle as a resin sheet 3 toward the casting device 2. Air 10 is blown from the outlet 6 toward the resin sheet 3 to make the resin sheet 3 adhere closely to the casting device 2, and the resin sheet 3 is cooled and solidified while being transported by the casting device 2. As shown in Figure 2, the air 10a blown from the outlet 6 and flowing upstream in the transport direction is exhausted from the exhaust port 8 so as not to vibrate the resin sheet 3. At this time, the pressure decreases in the space surrounded by air 10, air 10a and the air 12 exhausted from the exhaust port 8. If left as is, vortices may be generated in this low-pressure space, causing vibration of the resin sheet 3. Therefore, the generation of vortices is suppressed by supplying air 11 from the air inlet 7 between the outlet 6 and the exhaust port 8 in this low-pressure space. Here, in order to stably supply a constant amount of air 11 from the air inlet 7, it is more preferable to forcibly exhaust from the exhaust port 8 using a blower or the like. Alternatively, air taken in from outside the air knife through the air intake port 7 may be allowed to flow into the space between the air knife 4 and the casting device 2, and the air 10a that has been blown out from the outlet port 6 and flowed upstream in the conveying direction, along with the air that has flowed in through the air intake port 7, may be drawn in through the exhaust port 8.

[0041] Thus, this embodiment allows for the suppression of vibrations in the resin sheet, enabling the stable manufacture of resin sheets.

[0042] [Embodiment 2] A method for manufacturing a resin sheet according to Embodiment 2 will now be described. Figure 3 is an enlarged view of the area around the air outlet and exhaust port of the air knife of Embodiment 2, and is a cross-sectional view perpendicular to the width direction. As shown in Figure 3, the difference between this embodiment and Embodiment 1 is that the air blowing direction of the air intake port 7 (the direction in which the air 11 is blown out) is inclined downstream in the conveying direction rather than perpendicular to the surface of the casting device 2. The other configurations are the same as in Embodiment 1, and the effect of the air 11 supplied from the air intake port 7 in suppressing vortices is also the same as in Embodiment 1.

[0043] Since the air 11 tends to flow towards the exhaust port 8 side, that is, the upstream side in the conveying direction, this configuration allows a sufficient amount of air 11 to be supplied to the downstream side in the conveying direction, that is, the outlet 6 side, and further suppresses vortices. It is more preferable that the air outlet direction of the air supply port 7 is inclined 20 to 70 degrees downstream in the conveying direction rather than perpendicular to the surface of the casting device 2.

[0044] [Embodiment 3] A method for manufacturing a resin sheet according to Embodiment 3 will now be described. Figure 4 is an enlarged view of the area around the air outlet and exhaust port of the air knife of Embodiment 3, and is a cross-sectional view perpendicular to the width direction. As shown in Figure 4, the difference between this embodiment and Embodiment 1 is that the shortest distance 30 between the upstream edge of the opening of the air intake port 7 in the conveying direction and the casting device 2 is shorter than the shortest distance 31 between the downstream edge of the opening of the air intake port 7 in the conveying direction and the casting device 2. The other configurations are the same as in Embodiment 1, and the effect of the air 11 blown out from the air intake port 7 in suppressing vortices is also the same as in Embodiment 1.

[0045] Since the air 11 tends to flow towards the exhaust port 8 side, that is, the upstream side in the conveying direction, this configuration allows a sufficient amount of air 11 to be supplied to the downstream side in the conveying direction, that is, the outlet 6 side, and further suppresses vortices. It is more preferable that the shortest distance 30 is 0.2 to 0.8 times the shortest distance 31. [Examples]

[0046] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The properties were measured and evaluated by the following methods, and the following methods and raw materials were used.

[0047] [Measurement and evaluation methods] (1) Mesopentad fraction (mmmm) Dissolve the polypropylene resin sample in a solvent. 13 The mesopentade fraction (mmmm) was measured and calculated using 1C-NMR (Reference: New Edition Polymer Analysis Handbook, edited by the Japan Society for Analytical Chemistry and the Polymer Analysis Research Group, 1995, pp. 609-611). The measurement equipment and conditions are as follows.

[0048] A. Measuring device and conditions Equipment: Bruker DRX-500 Nucleus for measurement: 13 C nucleus (resonance frequency: 125.8MHz) Measured concentration: 10% by mass Solvent: Benzene / deuterated orthodichlorobenzene = mass ratio 13 mixed solution Measurement temperature: 130℃ Spin speed: 12Hz NMR sample tube: 5mm tube Pulse width: 45° (4.5μs) Pulse repetition time: 10 seconds Data points: 64K Number of conversions: 10,000 Measurement mode: complete decoupling.

[0049] B.Analysis conditions A Fourier transform was performed with a line broadening factor (LB) of 10, resulting in a mmmm peak of 2186 ppm. Peak splitting was then performed using WINFIT software (Bruker). The peak splitting was performed starting from the high-field side, and automatic fitting was then performed using the accompanying software. After optimizing the peak splitting, the sum of the mmmm peak fractions was calculated. This measurement was repeated five times, and the average value was taken as the mesopentad fraction (mmmm) of the sample. (Peak splitting) (a)mrrm (b)(c)rrrm (split into two peaks) (d)rrrr (e)mrmr (f)mrmm+rmrr (g)mmrr (h)rmmr (i)mmmr (j)mmmm.

[0050] (2) Melt Flow Index (MFR) (Unit: g / 10min) Measurements were taken at 230°C and with a weight of 2.16 kg, in accordance with JIS K 7210-1 (2014).

[0051] (3) Melt tension (MS) (unit: cN) The following procedure was used to measure the tension using a melt tension tester (capillary diameter 2.1 mm, cylinder diameter 9.55 mm) manufactured by Toyo Seiki Seisakusho Co., Ltd. First, polypropylene resin was heated to 230°C and melted. Next, the molten polypropylene resin was extruded into strands at an extrusion speed of 15 mm / min, and the tension was measured when these strands were pulled back at a speed of 6.5 m / min. The obtained value was defined as MS(cN).

[0052] (4) Cold xylene soluble portion (CXS Unit: mass%) 0.5 g of polypropylene resin was dissolved in 100 ml of boiling xylene at 135°C, allowed to cool, and then recrystallized in a constant temperature water bath at 20°C for 1 hour. After that, solid matter such as crystals was removed by filtration, and the polypropylene components dissolved in the filtrate were quantified by liquid chromatography. Let X0 (g) be the mass of polypropylene resin before dissolution in boiling xylene, and X (g) be the mass of polypropylene components dissolved in the filtrate. CXS was calculated from the following formula (1). Formula (1): CXS(mass%)=(X / X0)×100 (5) Thickness of polypropylene resin sheet (unit: μm) If the molten resin sheet vibrates between the time it is extruded from the nozzle and when it comes into contact with the casting device, thickness variations occur in the conveying direction. The thickness and thickness variations of the resin sheet were measured for 5 minutes each in the conveying direction at 10 mm intervals in a section from the center in the width direction to 30 mm inside both ends, using Yokogawa Electric Corporation's WEBFREX NV online thickness gauge, which is capable of measuring thicknesses from 10 to 2000 μm using an infrared detection method. The R value of the thickness at each measurement point obtained from the above measurement was divided by the average thickness to calculate the R / AVE. Furthermore, the number X at which the difference in R / AVE between adjacent measurement points is 3.0% or greater was calculated using the obtained value, and the value of Equation 1 below was also calculated.

[0053]

number

[0054] (6) Thickness of biaxially oriented polypropylene film (unit: μm) The thickness of the biaxially oriented polypropylene film was measured using the micrometer method in accordance with JIS C 2330 (2014).

[0055] (7) Surface temperature and uniformity of the cast drum, longitudinal stretching preheating roll, and longitudinal stretching cooling roll The surface temperatures of the cast drum, longitudinal stretch preheating roll, and longitudinal stretch cooling roll were measured using a thermograph (FLUKE Ti29 industrial / commercial thermograph, measurable temperature range -20°C to 600°C), and the average, maximum, and minimum values ​​were recorded. The obtained average value was defined as the surface temperature of the cast drum and longitudinal stretch roll, and the difference between the obtained maximum and minimum values ​​was defined as the surface temperature unevenness of the cast drum and longitudinal stretch roll.

[0056] (8) Wetting tension (unit: mN / m) In accordance with JIS K 6768 (1999), the wetting tension of the corona-treated surface of a biaxially oriented polypropylene film was measured using a test mixture of ethylene glycol monoethyl ether, formamide, and methanol.

[0057] (9) Dielectric breakdown voltage (BDV film withstand voltage performance) From an intermediate product roll with a width of 7,700 mm, 250 mm was cut from both ends in the width direction to obtain a biaxially oriented polypropylene film sample measuring 200 mm (conveying direction) x 7,200 mm (width direction). This sample was then divided into 36 equal parts to obtain 200 mm x 200 mm test pieces. The center portion of each test piece was then used as the measurement site, and a BDV test was performed at 23°C and in a 65% RH atmosphere in accordance with JIS C2330 (2014). In the manufacturing of the biaxially oriented polypropylene film in each example, a method was adopted to obtain multiple final product rolls from one intermediate product roll, and since it was assumed that there would be no difference in the properties of each final product roll, test pieces were taken from the intermediate product roll.

[0058] (10) Evaluation of device processability in film capacitor manufacturing (processability during vapor deposition) Aluminum was vacuum-deposited onto the corona-treated side of a polypropylene film using a vacuum deposition machine manufactured by ULVAC, Inc., to achieve a surface resistance of 15 Ω / sq. The aluminum was deposited in a stripe pattern with a margin running along the longitudinal direction (79.0 mm wide deposited area, 10 mm wide margin, repeated). Next, slits were made by cutting into the center of each deposited area and each margin, creating a tape-like winding reel with a total width of 40 mm and a 0.5 mm margin at either the left or right end. Two of these reels, one with the left margin and one with the right margin, were overlapped and wound together so that the deposited portion extended 0.5 mm beyond the margin in the width direction, resulting in a winding body with a capacitance of 120 μF. KAW-4NHB manufactured by Kaito Seisakusho Co., Ltd. was used for winding. Finally, the winding body was heat-treated for 10 hours in a reduced-pressure atmosphere at 140°C. The winding body was visually inspected, and any with wrinkles or distortions in appearance or shape were considered defective. 300 similar wound bodies were produced and the same evaluation was repeated, and the processability of the wound bodies was evaluated according to the following criteria. ◎: No defective products. 〇: Less than 1 defective item. △: Two or more defective items but less than three. ×: 4 or more defective items.

[0059] (11) Life evaluation of film capacitors (evaluation of film capacitor characteristics) A winding with a capacitance of 120 μF was obtained by the method described in (10). Then, the non-defective windings were heat-treated for 10 hours in a reduced-pressure atmosphere at 140°C. After that, Metallicon was sprayed onto both ends in the width direction to form external electrodes, and lead wires were welded to the Metallicon to obtain a film capacitor. Next, the life evaluation of 15 film capacitors was performed using the following procedure. First, the capacitance (C0) was measured at room temperature. Then, a voltage of 325 VDC / μm (650 V applied when the thickness is 20 μm) was applied to the film capacitor at a high temperature of 120°C for 1000 hours. After that, the capacitance (C) was measured at room temperature, and the rate of change of capacitance (ΔC) before and after voltage application was calculated from the following formula (3). The capacitance was measured using an LCR high tester 3522-50 manufactured by HIOKI E.E. CORPORATION. Equation (3): ΔC=((C0-C) / C0)×100 The average of the rate of change (ΔC) of capacitance before and after voltage application for 15 film capacitors was used as the rate of change of capacitance before and after voltage application for that sample, and it was evaluated according to the following criteria. A smaller rate of change (ΔC) of capacitance before and after voltage application indicates that the decrease in capacitance at high temperatures is suppressed, and the lifespan evaluation of the film capacitor is considered good. ◎: ΔC is less than 2% ○: ΔC is between 2% and less than 3% △: ΔC is between 3% and less than 5% ×: ΔC is 5% or more.

[0060] (12) Yield during processing (processing defect rate) A film roll with a width of 620 to 1050 mm and a length of 60,000 m was slit and wound up. The resulting film roll was used as an evaluation sample, and the yield (processing defect rate) during film roll processing was calculated using the following formula. Yield rate during processing (processing defect rate) (%) = Number of defective items / Total number of items processed × 100 The following evaluation criteria were used. ◎ and ○ indicate that the product can be used without any problems, while △ indicates that it can be used depending on the processing conditions. ◎: 95% or more ○: 90% or more but less than 95% △: 85% or more but less than 90% ×: Less than 85%.

[0061] [Raw materials] (1) Resin Highly stereoregular polypropylene resin (A): Borclean (trademark) HC300BF, manufactured by Borealis, is a highly stereoregular polypropylene resin with a mesopentad fraction of 0.980%, a CXS of 12% by mass, an MFR of 3.3 g / 10 min, and an MS of 10 cN. High melt-tension polypropylene resin (I): Borealis' "Daploy" (trademark) (WB135HMS) is a high melt-tension polypropylene resin with an MFR of 2.5 g / 10 min and an MS of 320 cN.

[0062] (2) Antioxidants Antioxidant 1: BASF Japan's "Irganox" (registered trademark) 1010 Antioxidant 2: 2,6-di-t-butyl-p-cresol (BHT).

[0063] [Example 1] This section describes the results of actually manufacturing a resin sheet using a resin sheet manufacturing apparatus and evaluating the thickness variations caused by vibration in the resin sheet. The specific sheet manufacturing conditions and evaluation method in this embodiment are as follows.

[0064] (1) Resin sheet material Linear polypropylene, MFR 5.0 g / 10 min. Here, MFR was measured in accordance with JIS K 7210-1 (2014) at a temperature of 230°C and a load of 2.16 kg.

[0065] (2) Extrusion A resin sheet material was extruded using an extruder at a flow rate of 250 kg / h, and after passing through a gear pump and filter, it was supplied to a die. The temperature of the apparatus up to the die was 250°C.

[0066] (3) Nozzle The resin sheet material was extruded as a resin sheet from an outlet with a width of 1000 mm and a gap of 1.5 mm, and formed into a sheet shape.

[0067] (4) Casting device The resin sheet was pressed tightly onto a roll that was temperature-controlled to 90°C, and then cooled and solidified.

[0068] (5) Air knife The air knife is equipped with an air outlet, an air inlet, and an air exhaust port on the side facing the casting device, in order from the downstream side in the conveying direction. Air is blown from the air outlet towards the point where the resin sheet makes contact with the casting device, air is also blown from the air inlet, and air is discharged from the air exhaust port. The air outlet has a slit shape with a width of 1200 mm and a gap of 0.5 mm, and the air blowing direction is tilted 40 degrees downstream in the conveying direction from the direction perpendicular to the surface of the casting device, and the blower was adjusted so that the air velocity blown out from the slit was 100 m / s. The air inlet has a slit shape with a width of 1200 mm and a gap of 0.5 mm, and the air blowing direction is perpendicular to the surface of the casting device, and the blower was adjusted so that the air velocity blown out from the slit was 20 m / s. The exhaust port has a slit shape with a width of 1200 mm and a gap of 0.5 mm, and the blower was adjusted so that the air velocity exhausted from the slit was 40 m / s. The air knife was installed so that the shortest distance between the upstream edge of the air intake opening in the conveying direction and the casting device was 5 mm, and the shortest distance between the downstream edge of the air intake opening in the conveying direction and the casting device was also 5 mm.

[0069] [Example 2] Except for changing the upstream side of the air intake to open to the atmosphere, the sheet was collected in the same manner as in Example 1.

[0070] [Example 3] The sheet was collected in the same manner as in Example 1, except that the direction of air blowing from the air intake was changed to be tilted 40 degrees downstream in the conveying direction rather than perpendicular to the surface of the casting device.

[0071] [Example 4] Except for changing the shortest distance between the upstream edge of the air intake opening in the transport direction and the casting device to 3 mm, the sheet was sampled in the same manner as in Example 1.

[0072] [Example 5] The sheet was collected in the same manner as in Example 1, except that the air intake was made into a slit with a gap of 1.0 mm and the blower was adjusted so that the air velocity blown out from the slit was 10 m / s.

[0073] [Comparative Example 1] The sheet was collected in the same manner as in Example 1, except that the air knife did not have an air intake.

[0074] [Comparative Example 2] The sheet was collected in the same manner as in Example 1, except that the air intake was made into a slit with a gap of 0.2 mm and the blower was adjusted so that the air velocity blown out from the slit was 50 m / s.

[0075] [Evaluation Results] In Example 1, the value of Equation 1 was 4.5. The effect of each example and comparative example was evaluated by the extent to which air entrapment and thickness unevenness increased or decreased compared to Example 1. In Example 2, which used an air knife with the upstream side of the air intake vented to the atmosphere, the value of Equation 1 was 4.4, which was the same result as in Example 1. In Example 3, which used an air knife with the air blowing direction from the air intake tilted 40 degrees downstream in the conveying direction rather than perpendicular to the surface of the casting device, the value of Equation 1 was 2.3, and the thickness unevenness was reduced compared to Example 1. In Example 4, which used an air knife in which the shortest distance between the upstream edge of the air intake opening in the conveying direction and the casting device was shorter than the shortest distance between the downstream edge of the air intake opening in the conveying direction and the casting device, the value of Equation 1 was 1.8, and the thickness unevenness was reduced compared to Example 1. In Example 5, with a slit gap of 1.0 mm in the air intake and an air velocity of 10 m / s blown out from the slit, the value of Equation 1 was 1.5, and the thickness unevenness was reduced compared to Example 1. Furthermore, all of Examples 1 to 5 satisfied the above formula 1.

[0076] Comparative Example 1, which used an air knife without an air intake, had a value of 5.8 in Equation 1, indicating significantly worse thickness uniformity than Example 1. Comparative Example 2, which had an air intake slit gap of 0.2 mm and an air velocity of 50 m / s blown out from the slit, had a value of 5.5 in Equation 1, indicating worse thickness uniformity than Example 1. Note that Comparative Examples 1 and 2 did not satisfy the above Equation 1. [Industrial applicability]

[0077] The present invention is not limited to manufacturing apparatus and methods for resin sheets, but can also be applied to air knives for drying and foreign matter removal, although its scope of application is not limited to these. [Explanation of Symbols]

[0078] 2 Casting device 3. Resin sheet 4 Air Knife 6 Air outlet 7 Air supply port 8 exhaust vents 10, 10a, 10b, 11, 11a, 11b, 12 Airflow 30 The shortest distance between the upstream edge of the air intake opening in the transport direction and the casting device. 31 The shortest distance between the downstream edge of the air intake opening in the transport direction and the casting device.

Claims

1. A method for manufacturing a polypropylene film, comprising a casting step of extruding a molten polypropylene resin composition in a sheet shape from a nozzle and cooling and solidifying it in a casting device to obtain a resin sheet, wherein the thickness of the resin sheet is measured at 10 mm intervals in the transport direction for 5 minutes in a section from the center in the width direction to 30 mm inside both ends, and the thickness unevenness R / AVE is calculated from the average value, and when X is the number for which the difference in R / AVE between adjacent measurement points is 3.0% or greater, the value of the following formula 1 is in the range of 0 to 5. [Math 1]

2. A method for manufacturing a polypropylene film according to claim 1, wherein the sheet width of the resin sheet is 500 to 1200 mm.

3. A method for producing a polypropylene film according to claim 1 or 2, wherein the sheet conveying speed of the resin sheet is 10 to 100 m / min.

4. A method for producing a polypropylene film according to claim 1 or 2, wherein the sheet thickness of the resin sheet is 100 to 500 μm.

5. A method for producing a polypropylene film according to claim 1 or 2, wherein the film thickness of the polypropylene film is 1 to 4 μm.

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