Polypropylene film

Abstract

This polypropylene film is characterized in that the maximum value Dmax and the minimum value Dmin of tanδ in the main alignment direction within a range of -10°C to 50°C satisfy the relationship of formula 1, and that the tensile elongation in a main alignment orthogonal direction at 90°C is 70% or more. Formula 1: 0.00≤(Dmax-Dmin) / Dmax≤0.30 Provided is a polypropylene film capable of maintaining quality even after being subjected to a processing step at a high temperature.

Description

Polypropylene film

[0001] The present invention relates to a polypropylene film that is excellent in heat resistance, mechanical strength and quality and can be suitably used as an industrial material.

[0002] Polypropylene films have excellent surface releasability and mechanical properties, making them suitable for use as release films and process films for a variety of components, including plastic products, building materials, and optical components. Furthermore, their excellent electrical properties make them suitable for use as capacitor films.

[0003] One of the properties required for polypropylene films is heat resistance. For example, when polypropylene films are used as cover films for thermosetting resins, they may be exposed to high temperatures during heat curing after being bonded to the film. Furthermore, when used as a film for capacitors, they are exposed to high temperatures inside motors. For these applications, the level of heat resistance required for polypropylene films has been increasing in recent years.

[0004] The heat shrinkage rate is one indicator of the heat resistance of polypropylene films. Generally, attempts to reduce the heat shrinkage rate have been made by increasing the crystallinity of the polypropylene resin, reducing the high-molecular-weight component, or increasing the stretching ratio. However, while methods for increasing the crystallinity of the polypropylene resin and stretching at a high ratio improve the mechanical strength of the polypropylene film, they can also reduce the tensile elongation and make the film brittle. Furthermore, low-molecular-weight polypropylene resins have low melt tension when softened by heat, which can reduce the tensile elongation of the film. For these reasons, it has traditionally been difficult to obtain polypropylene films that combine high tensile elongation and low heat shrinkage.

[0005] As an example of a polypropylene film with improved heat resistance, Patent Document 1 describes an example in which a highly crystalline polypropylene resin is used and the preheat roll temperature during longitudinal stretching is adjusted to reduce heat shrinkage stress. Patent Documents 2 and 3 describe examples in which a polypropylene resin primarily containing a low molecular weight is used and crystallinity is increased to reduce heat shrinkage. Patent Document 4 describes an example in which a polypropylene resin with a low polypropylene component dissolved in xylene is used to improve voltage resistance at high temperatures and reduce shrinkage stress.

[0006] International Publication No. 2020 / 196602 Japanese Patent Application Laid-Open No. 2014-55283 International Publication No. 2020 / 137791 Japanese Patent Application Laid-Open No. 2020-132882

[0007] However, the polypropylene films described in Patent Documents 1 and 4 mentioned above have a problem of insufficient heat resistance. Furthermore, the polypropylene film described in Patent Document 2 has a problem in that it has low tensile elongation in the direction perpendicular to the main orientation, and is prone to film rupture when transported at high temperature and high tension. Furthermore, the polypropylene film described in Patent Document 3 has a problem in that it has a high thermal shrinkage rate in the main orientation direction, and is prone to shrinkage and wrinkling when transported at high temperature. Therefore, when these polypropylene films are used in applications requiring processing in a high-temperature environment, it is difficult to maintain their quality after undergoing a processing step at high temperature. Therefore, an object of the present invention is to solve the above-mentioned problems and provide a polypropylene film that can maintain its quality even after undergoing a processing step at high temperature.

[0008] In order to solve the above-mentioned problems, the polypropylene film of the present invention is characterized in that the maximum value Dmax and minimum value Dmin of tan δ in the main orientation direction in the temperature range of -10°C to 50°C satisfy the relationship of Formula 1, and the tensile elongation in the direction perpendicular to the main orientation at 90°C is 70% or more. Formula 1: 0.00≦(Dmax−Dmin) / Dmax≦0.30.

[0009] According to the present invention, it is possible to provide a polypropylene film that can maintain its quality even after undergoing a processing step at high temperatures.

[0010] 1 is an example of a graph showing the temperature dependence of tan δ in the main orientation direction of a polypropylene film, showing Dmax and Dmin. 2 is an example of a graph showing the temperature dependence of tan δ in the main orientation direction of a polypropylene film, showing Lp and the temperature at which tan δ becomes equal to Lp. 3 is a graph showing the crystallization temperature T of a polypropylene film. ｃ０ 1 is an example of a graph showing

[0011] The polypropylene film of the present invention is characterized in that the maximum value Dmax and minimum value Dmin of tan δ in the main orientation direction in the temperature range of -10°C to 50°C satisfy the relationship of Formula 1, and the tensile elongation in the direction perpendicular to the main orientation direction at 90°C is 70% or more. The polypropylene film of the present invention is specifically described below. Formula 1: 0.00≦(Dmax−Dmin) / Dmax≦0.30.

[0012] A polypropylene film refers to a sheet-like molded product containing more than 50% by mass and less than or equal to 100% by mass of polypropylene resin, where the total mass of all components constituting the film is 100% by mass. The amount of polypropylene resin in the polypropylene film is preferably 90% by mass or more and less than or equal to 100% by mass, more preferably 95% by mass or more and less than or equal to 100% by mass, even more preferably 96% by mass or more and less than or equal to 100% by mass, particularly preferably 97% by mass or more and less than or equal to 100% by mass, and most preferably 98% by mass or more and less than or equal to 100% by mass. The polypropylene film of the present invention may contain only one type of polypropylene resin, but preferably contains two or more types of polypropylene resin. When two or more types of polypropylene resin are contained in the film, if the total mass of these components is more than 50% by mass but less than or equal to 100% by mass, the polypropylene resin is considered to be the main component.

[0013] The term "polypropylene resin" refers to a resin in which propylene units account for more than 50 mol % and not more than 100 mol % of all structural units constituting the resin. In the present invention, the direction in which a polypropylene film is formed (the winding direction in the case of a film roll) is referred to as the film-forming direction, longitudinal direction, or MD direction, and the direction perpendicular to the film-forming direction in the plane of the film is referred to as the width direction or TD direction.

[0014] From the viewpoint of improving heat resistance, which affects the quality after processing at high temperatures, it is important that the maximum value Dmax and minimum value Dmin of tan δ in the main orientation direction in the temperature range of −10° C. or higher and 50° C. or lower satisfy the relationship of Formula 1: 0.00≦(Dmax−Dmin) / Dmax≦0.30.

[0015] Tan δ, also known as loss tangent, correlates with the degree of molecular chain mobility in polypropylene film. Generally, as shown in Figure 1, tan δ reaches a maximum near 0°C, decreases once at elevated temperatures, then begins to increase again, reaching a level exceeding the maximum value near 0°C. (Dmax - Dmin) / Dmax is an index showing the amount by which tan δ decreases from its maximum near 0°C. The present inventors have discovered that reducing this value and suppressing molecular chain mobility over a wide temperature range increases the heat resistance of polypropylene film and suppresses thermal shrinkage.

[0016] If the value of (Dmax - Dmin) / Dmax is greater than 0.30, the thermal shrinkage of the polypropylene film will be large. Therefore, for example, when such a polypropylene film is used as a release film, wrinkles may occur when the film is laminated to an adherend and passed through a high-temperature process, resulting in a loss of quality. From the above viewpoints, (Dmax - Dmin) / Dmax is preferably 0.28 or less, more preferably 0.27 or less, even more preferably 0.25 or less, and particularly preferably 0.22 or less. The lower limit of the value of (Dmax - Dmin) / Dmax is substantially 0.00.

[0017] (Dmax - Dmin) / Dmax can be measured using a dynamic viscoelasticity evaluation device according to the following procedure. First, a polypropylene film test piece, 5 mm wide x 20 mm long, cut with the long side in the main orientation direction is attached to the device's chuck in a nitrogen atmosphere at 23°C, cooled to -60°C, and tan δ is measured from the point at which the temperature reaches -50°C until it reaches 150°C after the start of heating. Next, a viscoelasticity-temperature curve is drawn using the dynamic viscoelasticity method, and Dmax and Dmin are determined using tan δ at each temperature, from which (Dmax - Dmin) / Dmax is calculated. Tan δ can be measured using a known device, such as a Rheogel-E4000 (manufactured by UBM), under the conditions shown in the examples.

[0018] To achieve a (Dmax-Dmin) / Dmax value of 0.30 or less, for example, a method can be used in which the raw material composition of the polypropylene film is within the range described below and the film-forming conditions are within the range described below. In particular, it is effective to use a highly crystalline raw material with a narrow molecular weight distribution Mz / Mw, a significant reduction in high molecular weight components, and a low cold xylene solubles (CXS), to set the surface temperature of the casting drum in the range of 10 to 40°C, and to draw down the film in the conveying direction on a high-temperature (80°C or higher) roll after transverse stretching, and to shrink the film in the direction perpendicular to the main orientation.

[0019] From the viewpoint of enhancing mechanical strength, which affects the stability of processing at high temperatures, it is important that the polypropylene film of the present invention has a tensile elongation of 70% or more in the direction orthogonal to the main orientation at 90°C. Here, the "orthogonal to the main orientation" refers to the direction perpendicular to the main orientation in-plane. The "main orientation" refers to the direction showing the highest Young's modulus when an arbitrary direction is set as 0° and the Young's modulus is measured in each direction forming an angle of 0° to 175° in 5° increments relative to the arbitrary direction in the film plane. The Young's modulus can be measured using a tensile tester; details of the measurement method are shown in the Examples. If the sample width is less than 50 mm and the Young's modulus cannot be determined using a tensile tester, the crystal orientation of the α-crystal (110) plane of the polypropylene film is measured using wide-angle X-rays as follows, and the direction is determined as the main orientation based on the following criteria. That is, X-rays (CuKα rays) are incident perpendicularly to the film surface, and the crystal peak at 2θ = approximately 14° (α crystal (110) plane) is scanned in the circumferential direction. The direction with the highest diffraction intensity in the obtained diffraction intensity distribution is defined as the main orientation direction, and the direction perpendicular to this is defined as the direction perpendicular to the main orientation direction.

[0020] If the tensile elongation in the direction orthogonal to the main orientation at 90°C is less than 70%, for example, when a polypropylene film is used as a release film, the film may break due to the high tension in the direction orthogonal to the main orientation when it is laminated to an adherend and passed through a high-temperature process. From the above viewpoint, the tensile elongation in the direction orthogonal to the main orientation at 90°C is preferably 90% or more, more preferably 110% or more, and even more preferably 130% or more. On the other hand, the upper limit of the tensile elongation in the direction orthogonal to the main orientation at 90°C is not particularly limited, but is substantially about 400%.

[0021] The tensile elongation in the direction perpendicular to the main orientation at 90°C can be measured by the following procedure using a tensile tester equipped with an oven capable of high-temperature heating. First, a polypropylene film is cut into a rectangular sample measuring 150 mm (direction perpendicular to the main orientation) x 10 mm (direction perpendicular to the main orientation). Next, the sample is set in the tensile tester with an initial chuck distance of 50 mm, and placed in an oven heated to 90°C together with the chuck for 1 minute. Thereafter, a tensile test is performed at a pulling rate of 300 mm / min, and the elongation at the time of sample breakage is read and used as the tensile elongation. Any tensile tester capable of performing measurements may be used; for example, Orientec's "Tensilon" (registered trademark) UCT-100 or the like may be used.

[0022] Generally, reducing the proportion of high-molecular-weight components in a polypropylene film makes it difficult to propagate tension throughout the entire film when high tension is applied, which tends to reduce tensile elongation. Furthermore, increasing the proportion of a highly crystalline polypropylene resin with a low cold xylene solubles (CXS) content results in a shortage of amorphous components that relieve stress when tension is applied, further reducing tensile elongation. Therefore, it has been difficult to improve heat resistance while maintaining tensile elongation. However, it has been found that, for example, by using a method in which the raw material composition of the polypropylene film is within the range described below and the film-forming conditions are within the range described below, it is possible to achieve a tensile elongation of 70% or more in the direction perpendicular to the main orientation at 90°C. In particular, it is effective to extend the stretching section during longitudinal stretching (e.g., 200 mm or more) and stretch both sides of the film while sufficiently heating them with a radiation heater or the like in the stretching section, thereby achieving uniform longitudinal stretching while reducing the stretching stress, or to increase the relaxation rate (e.g., 12% or more) during the relaxation treatment after transverse stretching and heat the film with a hot roll when passing through the transfer section.

[0023] From the viewpoint of heat resistance, the polypropylene film of the present invention has a maximum value of tan δ in the main orientation direction at temperatures of −30° C. or higher and lower than 30° C., which is L Ｐ When the temperature is in the range of 30° C. or more and less than 150° C., tan δ in the main orientation direction is L Ｐis preferably 80° C. or less, more preferably 70° C. or less, even more preferably 60° C. or less, and particularly preferably 55° C. or less. Ｐ The temperature at which tan δ in the main orientation direction becomes equal to L corresponds to the temperature at which tan δ begins to exceed the maximum value around 0°C, as shown in Figure 2, and the inventors have found that keeping this temperature low improves the heat resistance of polypropylene films. Ｐ When the temperature at which the temperature becomes equal to the principal orientation is 80° C. or less, shrinkage in the direction perpendicular to the principal orientation is reduced during storage at high temperatures after the polypropylene film is wound into a roll, and thus the occurrence of wrinkles in the polypropylene film roll is suppressed. As a result, the quality of the polypropylene film roll can be maintained at a high level.

[0024] tan δ in the main orientation direction is L Ｐ In order to make the temperature at which the temperature becomes equal to 80°C or less or in the above-mentioned preferred range, a method can be used in which the raw material composition of the polypropylene film is set within the range described below. In particular, it is preferable to use a highly crystalline raw material with a narrow molecular weight distribution Mz / Mw, a significantly reduced high molecular weight component, and a low CXS. Ｐ The lower limit of the temperature at which the temperature becomes equal to the temperature of the liquid crystal layer is substantially 30°C.

[0025] From the viewpoint of heat resistance, the polypropylene film of the present invention preferably has a sum of the α(110) crystallite sizes in the main orientation direction and the direction perpendicular thereto of 20.0 nm or less. More preferably, it is 18.0 nm or less, even more preferably 17.0 nm or less, and particularly preferably 16.0 nm or less. When the sum of the α(110) crystallite sizes in the main orientation direction and the direction perpendicular thereto is 20.0 nm or less, shrinkage in the direction perpendicular to the main orientation is reduced during storage at high temperatures after the polypropylene film is wound into a roll, thereby suppressing the occurrence of wrinkles in the polypropylene film roll. As a result, the quality of the polypropylene film roll can be maintained at a high level. From the above viewpoint, the lower limit of the sum of the α(110) crystallite sizes in the main orientation direction and the direction perpendicular thereto is not particularly limited, but is substantially about 10 nm.

[0026] In addition, by making the sum of the crystallite sizes of α (110) in the main orientation direction and the perpendicular direction less than 20.0 nm, the size of the amorphous regions between the crystals in the polypropylene film is reduced. Therefore, reducing the size of the amorphous regions in this way brings various advantages when the polypropylene film is used in various applications. For example, when the polypropylene film is used as a release film, after being bonded to an adherend and passing through a high-temperature process, high releasability is maintained when the polypropylene film is peeled from the adherend, and a decrease in productivity is reduced. The crystallite size of α (110) can be measured by X-ray diffraction, and details of the measurement method are shown in the examples.

[0027] To make the sum of the crystallite sizes of the α(110) in the main orientation direction and the perpendicular direction to the main orientation direction 20.0 nm or less or within the above-mentioned preferred range, for example, a method can be used in which the raw material composition of the polypropylene film is set within the range described below and the film-forming conditions are set within the range described below. In particular, it is effective to use a raw material with a high crystallization temperature to reduce the size of spherulites formed during casting, to lower the extrusion temperature or the temperature of the casting drum to increase cooling during casting, or to lengthen the stretching section during longitudinal stretching and stretch both sides of the film while sufficiently heating them with a radiation heater in the stretching section.

[0028] From the viewpoint of achieving both improved heat resistance and reduced formation of coarse spherulites, the polypropylene film of the present invention has a crystallization temperature Tc measured at a temperature decreasing rate of 10°C / min. １０ (°C) and the crystallization temperature Tc measured at a temperature drop rate of 40°C / min ４０ The crystallization temperature at a temperature drop rate of 0°C / min was calculated by the extrapolation point method using the ０ (°C), and the melting point of the polypropylene film is Tm (°C), ０ It is preferable that Tm≧280 be satisfied. ０ The value of +Tm is more preferably 285 or more, and even more preferably 290 or more. ０ is an index of ease of crystallization, and Tc ０A high Tc means that the film is easily crystallized. Tm is the melting point of the polypropylene film, and a high Tm means that the polypropylene film has high heat resistance. ０ When the value of +Tm is 280 or more, the crystallization rate is kept at a moderate level, and coarse spherulites are less likely to form during casting. As a result, the decrease in the breaking elongation in the direction perpendicular to the main orientation direction and the increase in the crystallite size are suppressed. From the above viewpoint, Tc ０ There is no particular upper limit to the +Tm value, but the upper limit is substantially about 350.

[0029] Tc ０ To make the value of +Tm 280 or more or in the above preferred range, Tc ０ These methods for increasing Tc and Tm can be used alone or in combination. ０ In order to increase Tm, a method can be used in which the composition of the polypropylene film is set within the range described below. In particular, it is preferable to add a component having a nucleating agent effect, and among these, it is preferable to add a branched polypropylene resin. In addition, in order to increase Tm, for example, a method can be used in which the composition of the polypropylene film is set within the range described below and the film-forming conditions are set within the range described below. With regard to the composition, it is particularly preferable to use a highly crystalline raw material with a low cold xylene solubles (CXS). In addition, with regard to the film-forming conditions, it is also effective to lengthen the stretching section during longitudinal stretching and stretch while sufficiently heating both sides with a radiation heater in the stretching section, thereby achieving uniform longitudinal stretching while reducing the stretching stress.

[0030] Tc １０ , Tc ４０ , Tc ０ can be measured by a differential scanning calorimeter (DSC), and the specific measurement method is as follows: First, using a DSC, 3 mg of polypropylene film is heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere and held for 5 minutes. Then, the temperature is lowered from 250°C to 25°C at a rate of 10°C / min, and the peak temperature of the exothermic curve obtained during this temperature decrease is taken as T ｃ１０Furthermore, the temperature of the polypropylene film is increased from 25°C to 250°C at a rate of 20°C / min and maintained at this temperature for 5 minutes. Thereafter, the temperature is decreased from 250°C to 25°C at a rate of 40°C / min, and the peak temperature of the heat generation curve obtained during this temperature decrease is defined as T ｃ４０ The Tc measured in this way １０ , Tc ４０ The horizontal axis represents the cooling rate, and the vertical axis represents the crystallization temperature determined at each cooling rate. ｃ４０ From T ｃ１０ Draw a straight line passing through the line, and the crystallization temperature when the temperature drop rate is 0 °C / min is T ｃ０ The DSC is not particularly limited as long as it is capable of performing the above measurement, and any known DSC can be used, and a specific example is EXSTAR DSC6220 manufactured by Seiko Instruments (the same applies to the Tm measurement device described below).

[0031] Tm can be measured by a differential scanning calorimeter (DSC), and the specific measurement method is as follows: Using DSC, 3 mg of polypropylene film is heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere, and the peak temperature of the endothermic curve obtained during this temperature increase is taken as Tm.

[0032] From the viewpoint of improving the flatness during heating and improving the processability after the heating process, the polypropylene film of the present invention preferably has a static friction coefficient μs of 0.80 or less after heating at 90°C for 10 minutes. Here, a static friction coefficient μs of 0.80 or less means that the static friction coefficient μs is 0.80 or less when measured with the front and back surfaces of the film overlapping each other (the same applies to the preferred range described below). The static friction coefficient μs after heating at 90°C for 10 minutes is more preferably 0.70 or less, and even more preferably 0.60 or less. For example, when a polypropylene film is used as a release film for a thermosetting resin film, it may be laminated to a sheet-shaped thermosetting resin and then the thermosetting resin may be cured at a temperature range of about 80°C to 100°C. Generally, polypropylene films have lower heat resistance than polyester films, which are often used as process films such as release films, and the film surface may soften and become less slippery when exposed to heat of about 90°C. By setting the μs after heating to 0.8 or less, when the polypropylene film is used as, for example, a release film, the film may slip on the conveying roll when passing through a high-temperature process, causing wrinkling due to uniformly distributed stress, and the film may also be prevented from slipping when wound up together with the adherend.

[0033] To achieve a static friction coefficient μs of 0.80 or less or within the above-mentioned preferred range after heating at 90°C for 10 minutes, for example, a method can be used in which the composition of the polypropylene film is within the range described below and the film-forming conditions are within the range described below. Particularly effective methods include alloying an olefin resin such as poly(4-methylpentene-1) resin on the surface layer of the polypropylene film and forming fine protrusions on the surface, and heating the casting drum to form spherulites during casting, thereby forming protrusions after biaxial stretching. There is no particular restriction on the lower limit of μs after heating, but the lower limit is essentially around 0.1. The μs after heating can be measured in accordance with JIS K 7125 (1999).

[0034] The polypropylene film of the present invention preferably has a tensile elongation in the main orientation direction of 35% or more. A tensile elongation in the main orientation direction of 35% or more can reduce breakage of the film when the polypropylene film is unwound from a roll and used. From the above viewpoints, the tensile elongation in the main orientation direction is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. On the other hand, the upper limit of the tensile elongation in the main orientation direction is not particularly limited, but is substantially about 1000%. The tensile elongation in the main orientation direction is evaluated using a tensile tester, as will be described in detail below.

[0035] Increasing the stretch ratio or performing high-stress stretching at low temperatures to improve mechanical strength generally tends to reduce tensile elongation. Furthermore, increasing the proportion of highly crystalline polypropylene resin with a low cold xylene solubles (CXS) content leads to a shortage of amorphous components that relieve stress when tension is applied, further reducing tensile elongation. Therefore, it has traditionally been difficult to maintain tensile elongation while using highly crystalline raw materials. However, it has been found that, for example, by using a method in which the raw material composition of the polypropylene film is within the range described below and the film-forming conditions are within the range described below, it is possible to achieve a tensile elongation of 35% or more in the main orientation direction. In particular, it is effective to lengthen the stretching section during longitudinal stretching (e.g., 200 mm or more) and stretch both sides of the film while sufficiently heating them with a radiation heater or the like in the stretching section, thereby achieving uniform longitudinal stretching while reducing the stretching stress, or to increase the relaxation rate (e.g., 12% or more) in the relaxation treatment after transverse stretching and heat the film with a hot roll when passing through the transfer section.

[0036] The polypropylene film of the present invention preferably has a maximum height St of less than 2.0 μm on both sides of the film. More preferably, it is less than 1.5 μm, even more preferably less than 1.0 μm, and particularly preferably less than 0.5 μm. By having a maximum height St of less than 2.0 μm on both sides of the film, when the polypropylene film is laminated to an adherend and wound up as a film roll, it is possible to reduce deterioration in quality, such as when protrusions on the surface of the polypropylene film come into contact with the adherend and depressions are transferred to the adherend. The lower limit of the maximum height St of both sides of the film is not particularly limited, but is substantially about 0.01 μm.

[0037] To make the maximum height St on both sides of the film less than 2.0 μm or within the above-mentioned preferred range, for example, a method can be used in which the composition of the polypropylene film is within the range described below and the film-forming conditions are within the range described below. In particular, it is effective to make the spherulites in the unstretched sheet uniformly fine by setting the surface temperature of the casting drum in the range of 10 to 40° C., lengthen the stretching section during longitudinal stretching, and stretch while sufficiently heating both sides with a radiation heater in the longitudinal stretching section, thereby uniformly longitudinally stretching the film while reducing the stretching stress.

[0038] The thickness of the polypropylene film of the present invention is not particularly limited and is adjusted appropriately depending on the application, but is preferably 0.5 μm or more and 100 μm or less from the viewpoint of handleability. The upper limit of the thickness is more preferably 60 μm, even more preferably 30 μm, and particularly preferably 16 μm. The lower limit is more preferably 0.9 μm, more preferably 1.5 μm, even more preferably 4.0 μm, particularly preferably 8.0 μm, and most preferably 11 μm. The thickness of the polypropylene film can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film-forming speed, the stretching ratio, etc., within a range that does not deteriorate other physical properties. The thickness of the polypropylene film can be measured using a known micro thickness meter.

[0039] The polypropylene film of the present invention preferably has a molecular weight distribution Mz / Mw of less than 4.5, more preferably 4.0 or less, and even more preferably 3.5 or less. The lower limit of Mz / Mw of the polypropylene film is substantially about 1.5. When the Mz / Mw of the polypropylene film is less than 4.5, the amount of high molecular weight components that relax when heated is small, and the heat resistance of the polypropylene film is maintained. Methods for adjusting the molecular weight distribution Mz / Mw of the polypropylene film to the above value include preferably adjusting the hydrogen gas concentration during polymerization of the polypropylene resin, selecting a catalyst and / or co-catalyst, and appropriately adjusting the composition and polymerization amount of each polymerization vessel in continuous polymerization.

[0040] The polypropylene resin (polypropylene resin A) that is most preferably contained in the polypropylene film of the present invention will be described below. From the viewpoints of productivity and film properties, the polypropylene resin A is preferably a linear polypropylene resin.

[0041] The molecular weight distribution Mz / Mw of polypropylene resin A is preferably less than 4.2, more preferably 3.7 or less, and even more preferably 3.2 or less. The lower limit of Mz / Mw of polypropylene resin A is substantially about 1.2. When Mz / Mw of polypropylene resin A is less than 4.2, there are fewer high molecular weight components that relax when heated, and the heat resistance of the polypropylene film is maintained. Methods for adjusting the molecular weight distribution Mz / Mw of polypropylene resin A to the above value include adjusting the hydrogen gas concentration during polymerization, selecting a catalyst and / or co-catalyst, and appropriately adjusting the composition and polymerization amount of each polymerization vessel in continuous polymerization.

[0042] The melt flow rate (MFR) of polypropylene resin A is preferably in the range of 2 g / 10 min to 20 g / 10 min (230°C, 21.18 N load) from the viewpoint of film formability and film strength. The lower limit of MFR is more preferably 2.5 g / 10 min, and even more preferably 3.0 g / 10 min. The upper limit is more preferably 10 g / 10 min, even more preferably 8.0 g / 10 min, and most preferably 6.5 g / 10 min. In order to adjust the MFR of polypropylene resin A to the above value, a method of controlling the average molecular weight and molecular weight distribution is adopted. More specifically, a method of adjusting the hydrogen gas concentration during polymerization, or a method of appropriately selecting a catalyst and / or co-catalyst and composition to control the molecular weight and molecular weight distribution of the polypropylene resin is preferably adopted. The MFR is increased by reducing high molecular weight components.

[0043] The polypropylene resin A preferably has a CXS of 3.5% by mass or less. By satisfying these requirements, the dimensional stability and heat resistance of the resulting polypropylene film are prevented from decreasing. Here, CXS refers to the polypropylene components dissolved in xylene when a sample is completely dissolved in xylene and then precipitated at room temperature. This is considered to be a component that is difficult to crystallize due to low stereoregularity or low molecular weight. If a large amount of such components is contained in the polypropylene resin A, the resulting polypropylene film may have poor thermal dimensional stability. Therefore, from the above perspective, the CXS is more preferably 2.0% by mass or less. The lower the CXS, the better, but the lower limit is substantially about 0.1% by mass. Methods for adjusting the CXS within the above preferred range include adjusting the polymerization catalyst and process polymerization conditions, increasing the catalytic activity when obtaining the polypropylene resin A, and washing the resulting resin with a solvent or propylene monomer itself.

[0044] In a molecular weight distribution curve measured by gel permeation chromatography, the differential distribution value when the logarithmic molecular weight Log(M) of polypropylene resin A is 6.5 is preferably 0.2% or more and 9.5% or less. The upper limit is more preferably 8.0%, even more preferably 6.5%, and most preferably 5.0%. When the differential distribution value when the logarithmic molecular weight Log(M) is 6.5 is 0.2% or more, a sufficient amount of high molecular weight components that become tie molecules during stretching is present, thereby improving uniformity during stretching. On the other hand, when the differential distribution value when the logarithmic molecular weight Log(M) is 6.5 is 9.5% or less, fewer molecular chains relax when the polypropylene film is heated, resulting in a low heat shrinkage rate. Furthermore, after the polypropylene film is wound into a roll, room temperature shrinkage over time is suppressed, maintaining the flatness of the film roll.

[0045] Polypropylene resin A may contain copolymerization components such as copolymerization components with other unsaturated hydrocarbons, as long as the objectives of the present invention are not impaired. Examples of monomer components constituting such copolymerization components include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and 5-methyl-2-norbornene. From the viewpoint of dimensional stability when made into a polypropylene film, the copolymerization amount is preferably less than 10 mol%, more preferably 5 mol% or less, even more preferably 3 mol% or less, and most preferably 1 mol% or less, when all structural units constituting polypropylene resin A are taken as 100 mol%.

[0046] The content of ethylene units as copolymerization components in polypropylene resin A is preferably 5 mol% or less, when all structural units constituting polypropylene resin A are taken as 100 mol%. It is more preferably 3 mol% or less, and even more preferably 1 mol% or less. The more ethylene units there are, the lower the crystallinity and the easier it is to improve the transparency of a film formed therefrom, but the strength and heat resistance are also reduced. By controlling the ethylene units in polypropylene resin A to 5 mol% or less, the decrease in strength when formed into a polypropylene film and the deterioration of the heat shrinkage rate associated with the decrease in heat resistance are alleviated. Furthermore, by controlling the ethylene units in polypropylene resin A to 5 mol% or less, resin degradation during the extrusion process is also reduced, and the occurrence of fisheyes when formed into a polypropylene film is also suppressed.

[0047] The polypropylene resin A is preferably a linear polypropylene that satisfies the above-mentioned preferred conditions. Examples of such polypropylene resins include F-704NP, F-704NT, ​​F-300SP, F113G, E-100GPL, E-105GM, E-200GP, E-203GP, Y-400GP, and E111G polypropylene resins manufactured by Prime Polymer Co., Ltd., and FLX80E4, WF836DG3, FS2011DG3, D101, and W101 polypropylene resins manufactured by Sumitomo Chemical Co., Ltd.

[0048] The polypropylene film of the present invention can contain a branched polypropylene resin in addition to the linear polypropylene resin A. The branched polypropylene resin has a crystal nucleating effect for α crystals or β crystals. Therefore, by including the branched polypropylene resin, the nucleating effect suppresses the formation of coarse spherulites during casting, thereby improving the heat resistance and tensile elongation of the polypropylene film and further reducing the crystallite size.

[0049] From the viewpoint of extrusion stability, the MFR of the branched polypropylene resin is preferably 0.5 g / 10 min or more and 9 g / 10 min or less (230°C, 21.18 N load). The lower limit of the MFR of the branched polypropylene resin is more preferably 2 g / 10 min, and even more preferably 6 g / 10 min. The upper limit of the MFR of the branched polypropylene resin is more preferably 8 g / 10 min. Methods for adjusting the MFR of the branched polypropylene resin to the above values ​​include methods of controlling the average molecular weight and molecular weight distribution. More specifically, methods such as adjusting the hydrogen gas concentration during polymerization and appropriately selecting a catalyst and / or co-catalyst and composition to control the molecular weight and molecular weight distribution of the polypropylene resin are preferably used. MFR is an index of resin fluidity and indicates the amount of resin extruded from a cylinder under a constant temperature and load. The lower the viscosity of the resin, the higher the MFR. Generally, molecular weight is correlated with viscosity; the lower the absolute value of the molecular weight, the lower the viscosity of the resin and the higher the MFR.

[0050] From the viewpoint of stretching uniformity, the melt tension of the branched polypropylene resin is preferably 3 gf or more and 40 gf or less. The lower limit of the melt tension is more preferably 4 gf, and even more preferably 6 gf. The upper limit is more preferably 30 gf, and even more preferably 25 gf. Methods for adjusting the melt tension to the above values ​​include methods of controlling the average molecular weight, molecular weight distribution, and degree of branching in the polypropylene resin. In particular, when long chain branches are present, the melt tension can be dramatically increased, and can be adjusted to a preferred value by using a polypropylene resin having molecular chains with long chain branches or adjusting the degree of branching.

[0051] Several branched-chain polypropylene resins are commercially available, such as those based on Ziegler-Natta catalysts and metallocene catalysts. From the viewpoint of using the resin in combination with polypropylene resin A, it is more preferable to add a small amount of a branched-chain polypropylene resin based on Ziegler-Natta catalysts having a wide molecular weight distribution to supplement stretchability.

[0052] The polypropylene film of the present invention can contain various resins other than polypropylene, provided that the object of the present invention is not impaired. Among these, polyolefin resins are preferred because they have high affinity with polypropylene resins and can enhance dispersibility in polypropylene resins. Examples of polyolefin resins that can be used include poly(4-methylpentene-1) resins (PMP), cyclic olefin polymers (COP), cyclic olefin copolymers (COC), and α-olefin elastomers, which can form fine protrusions on the film surface and enhance slipperiness. Among these, poly(4-methylpentene-1) resins (PMP) are preferably used because of their particularly high affinity with polypropylene resins.

[0053] In the case of a laminated film, the resin other than polypropylene is preferably added to the surface layer from the viewpoint of imparting lubricity, and is preferably added in an amount of 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, even more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5.0 parts by mass, relative to the total amount of polypropylene resin in the surface layer. In the case of a monolayer film, the amount is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5.0 parts by mass, even more preferably 0.1 to 3.0 parts by mass, and particularly preferably 0.1 to 1.0 parts by mass, relative to the total amount of polypropylene resin. If the amount of the resin other than polypropylene added is too large, the transparency of the film may be deteriorated, or the heat resistance and rigidity may be reduced. On the other hand, if the amount added is too small, the effect of imparting lubricity may be inferior.

[0054] The polypropylene film of the present invention may contain various additives, such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slipping agent, an antistatic agent, an antiblocking agent, a filler, a viscosity modifier, and a color inhibitor, within the scope of the present invention.

[0055] Among these, the selection of the type and amount of antioxidant is important from the viewpoint of antioxidant bleed-out. That is, such antioxidants are preferably sterically hindered phenol-based antioxidants, with at least one of them being a high molecular weight type having a molecular weight of 500 or more. Specific examples include various antioxidants, but it is preferable to use 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) together with 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox" (registered trademark) 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 1010: molecular weight 1177.7), either alone or in combination.

[0056] The total content of these antioxidants is preferably in the range of 0.01 to 1.0 parts by mass relative to the total amount of polypropylene resin. If the amount of antioxidant is too small, the polymer may deteriorate during the extrusion process, resulting in coloration of the film, or the film may have poor long-term heat resistance. If the amount of antioxidant is too large, the transparency may decrease due to bleed-out of the antioxidant. From the above viewpoints, the amount of antioxidant is more preferably 0.05 to 0.90 parts by mass, and particularly preferably 0.10 to 0.80 parts by mass.

[0057] The polypropylene film of the present invention may contain a crystal nucleating agent to the extent that it does not interfere with the object. Specific examples of crystal nucleating agents include α-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, metal phosphate esters, etc.), and β-crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone compounds, etc.). However, since excessive addition of the above-mentioned other nucleating agents may cause a decrease in stretchability or a decrease in transparency and strength due to void formation, the amount added is usually 0.5 parts by mass or less, preferably 0.1 parts by mass or less, and more preferably 0.05 parts by mass or less, per 100 parts by mass of the total amount of propylene resin. It is preferable that substantially no nucleating agents are added.

[0058] The polypropylene film of the present invention preferably does not contain inorganic particles. The polypropylene resin that can be preferably used as the main component of the polypropylene film of the present invention has low affinity with inorganic particles, so the inorganic particles may fall off the film during the production process, contaminating the production line or the product. Furthermore, if large protrusions are formed by inorganic particles with high hardness, irregularities may be transferred to the resin layer of an optical component, which may cause a decrease in quality when used as a protective film or a manufacturing base film for products requiring high quality, such as display components. From the above perspective, the polyolefin film of the present invention preferably does not contain a lubricant such as organic particles.

[0059] In the polypropylene film of the present invention, the proportions of polypropylene resin A and branched polypropylene resin relative to the total amount of resin components are preferably as follows: It is preferable that polypropylene resin A is more than 50% by mass and not more than 99.9% by mass from the viewpoint of the heat resistance and mechanical strength of the film. The lower limit of the proportion of polypropylene resin A is more preferably 60% by mass, and even more preferably 70% by mass. The upper limit is more preferably 99% by mass, and even more preferably 98% by mass. When two or more components corresponding to polypropylene resin A are contained in the film, the sum of these components is considered to be the content of polypropylene resin A in the film. The proportion of branched polypropylene resin is preferably 0.1% by mass or more and not more than 30% by mass of the entire film, and the upper limit is more preferably 10% by mass, and even more preferably 5% by mass. When two or more components corresponding to branched polypropylene resins are contained in the film, the sum of these components is considered to be the content of branched polypropylene resin in the film.

[0060] In the molecular weight distribution curve of the polypropylene film of the present invention measured by gel permeation chromatography, the differential distribution value at a logarithmic molecular weight Log(M) of 6.5 is preferably 1.0% or more and 10% or less. The upper limit is more preferably 8.0%, and even more preferably 6.0%. When the differential distribution value at a logarithmic molecular weight Log(M) of 6.5 is 1.0% or more, a sufficient amount of high-molecular-weight components that become tie molecules during stretching is present, thereby improving uniformity during stretching. On the other hand, when the differential distribution value at a logarithmic molecular weight Log(M) is 10% or less, fewer molecular chains relax when the polypropylene film is heated, resulting in a low heat shrinkage rate. Furthermore, after the polypropylene film is wound into a roll, room-temperature shrinkage over time is suppressed, and the flatness of the film roll is maintained.

[0061] The polypropylene film of the present invention is not particularly limited in terms of its layer structure and can be either a single layer or a laminated structure. However, from the viewpoint of satisfying different properties such as heat resistance, rigidity, and slipperiness, it is preferable to have at least two layers whose main component is polypropylene resin. For example, if the polypropylene resin-based layers are the surface layer (I) and the base layer (II), and the polypropylene film has a laminated structure having these layers, it is preferable that the polypropylene film itself is mainly composed of polypropylene resin, and that the main component of the base layer (II) described below is also polypropylene resin. If the polypropylene film has a laminated structure, it is more preferable to have at least two layers whose main component is polypropylene resin. A "layer whose main component is polypropylene resin" refers to a layer containing more than 50% by mass but not more than 100% by mass of polypropylene resin, assuming that the total components constituting the layer are 100% by mass. Note that the determination of whether or not a film falls under the category of a "layer whose main component is polypropylene resin" is made layer by layer, not for multiple layers collectively. In the case of a two-layer structure, the layer with the thicker lamination thickness is considered to be the base layer (II).

[0062] The polypropylene film of the present invention may contain only one type of polypropylene resin, but preferably contains two or more types of polypropylene resin. When a layer contains two or more components corresponding to polypropylene resin, the layer is considered to be a "layer mainly composed of polypropylene resin" if the total amount of these components is more than 50 mass % and not more than 100 mass %.

[0063] The content of polypropylene resin in the "layer containing polypropylene resin as the main component" is more preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, even more preferably 96% by mass or more and 100% by mass or less, particularly preferably 97% by mass or more and 100% by mass or less, and most preferably 98% by mass or more and 100% by mass or less, when all components constituting the layer are taken as 100% by mass. When the polypropylene film of the present invention has a single-layer structure, the main component of the polypropylene film itself is polypropylene resin. When the polypropylene film has a laminated structure, it is preferable that the main component of the base layer (II) described below is polypropylene resin.

[0064] The polypropylene film of the present invention is preferably obtained by forming the above-mentioned polypropylene into a sheet and biaxially stretching the sheet. The biaxial stretching method may be any of simultaneous biaxial stretching by inflation, simultaneous biaxial stretching by tenter, and sequential biaxial stretching by a roll-type stretching machine and a tenter. Among these, the sequential biaxial stretching by a roll-type stretching machine and a tenter is preferably employed in terms of film formation stability, thickness uniformity, and control of high rigidity and dimensional stability of the film.

[0065] Next, one embodiment of the method for producing a polypropylene film of the present invention will be described using a polypropylene film having a two-kind three-layer structure as an example, but the polypropylene film of the present invention is not necessarily limited to this.

[0066] First, polypropylene resin A and a branched polypropylene resin are dry-blended, for example, in a mass ratio of 95:5, and fed to a single-screw extruder for the base layer (II) (hereinafter sometimes referred to as layer B). Polypropylene resin A and a poly(4-methylpentene-1) resin are then dry-blended, for example, in a mass ratio of 98:2, and fed to a single-screw extruder for the surface layer (I) (hereinafter sometimes referred to as layer A). Subsequently, each is melt-extruded at 200 to 280°C, more preferably 220 to 280°C, and even more preferably 240 to 270°C. After removing foreign matter and modified polymers using a filter installed midway through the polymer tube, the mixture is laminated in a multi-manifold A-layer / B-layer / A-layer composite T-die, extruded onto a casting drum, and cooled and solidified to obtain a laminated unstretched sheet having a layer structure of A-layer / B-layer / A-layer. In this case, when the lamination thickness ratio of Layer A / Layer B / Layer A is expressed as 1 / X / 1, X is preferably 8 to 60, more preferably 15 to 55, and even more preferably 20 to 50. Furthermore, in the case of a layer structure of Layer A / Layer B, when the lamination thickness ratio of Layer A / Layer B is expressed as 1 / X, X is preferably 4 to 60, more preferably 7 to 55, and even more preferably 10 to 50. By setting the thickness within the above range, uniform fine protrusions due to the poly-4-methylpentene-1 resin are formed on the film surface, thereby imparting lubricity. Furthermore, the layer structure may be a two-layer structure of Layer A / Layer B, provided that the effects of the present invention are not impaired.

[0067] The surface temperature of the casting drum is 10 to 40°C, preferably 15 to 33°C, more preferably 15 to 30°C, particularly preferably 15 to 25°C, and most preferably 20 to 25°C. The method of adhesion to the casting drum may be any of electrostatic application, adhesion methods utilizing the surface tension of water, air knife methods, press roll methods, underwater casting methods, etc., but the air knife method is preferred because it provides good flatness and allows control of surface roughness. From the perspective of cooling the non-cooled drum surface side of the sheet on the casting drum, it is preferable to lower the air temperature of the air knife. The air temperature of the air knife is preferably 10 to 40°C, more preferably 15 to 30°C, even more preferably 15 to 25°C, and particularly preferably 20 to 25°C. The blown air speed is preferably 130 to 150 m / s. It is also preferable to appropriately adjust the position of the air knife so that air flows downstream of the film production process to prevent vibration of the sheet. In the case of a two-type two-layer laminate structure of layer A / layer B, it is preferable that the layer A side is located on the casting drum side.

[0068] The resulting unstretched sheet is introduced into the longitudinal stretching process. In the longitudinal stretching process, the unstretched sheet is preheated by contacting it with a metal roll maintained at 110°C to 150°C, preferably 120°C to 150°C, and more preferably 130°C to 150°C. The sheet is then stretched between rolls with different peripheral speeds to 4.6 to 7.0 times its original length, more preferably 5.2 to 6.8 times its original length, and even more preferably 5.5 to 6.5 times its original length, and then cooled to room temperature. The distance between the two rolls with different peripheral speeds (stretching zone) is preferably 200 mm or more, more preferably 250 mm or more, and even more preferably 300 mm or more. The upper limit of the stretching zone is preferably 1000 mm. Longitudinal stretching utilizes the difference in peripheral speed between the two metal rolls. The film is pressed against the metal rolls before and after stretching using nip rolls to prevent the film from slipping on the metal rolls. The stretching section refers to the distance from the nip position of the metal rolls before stretching to the nip position of the metal rolls after stretching.

[0069] The temperature of the rolls with differential peripheral speeds (longitudinal stretching temperature) is preferably 80°C or higher and 130°C or lower during stretching. The longitudinal stretching temperature is more preferably 80°C or higher and 125°C or lower, and even more preferably 80°C or higher and 120°C or lower. It is also preferable to place radiation heaters on the upper and lower sides of the two rolls with differential peripheral speeds, and stretch the sheet while heating it from both sides. The output of the radiation heaters is preferably 1.0 kW or higher for both the upper and lower sides, more preferably 2.0 kW or higher, and even more preferably 2.6 kW or higher. The distance between the heat source of the radiation heater and the sheet surface is preferably 10 mm or higher and 200 mm or lower. The rolls in the preheating step for longitudinal stretching and the rolls with differential peripheral speeds are set to low temperatures to minimize relaxation of the molecular chains of the polypropylene resin, and the film is heated all at once with the radiation heater and stretched simultaneously, thereby enabling more uniform stretching even with this formulation, which contains a small amount of high-molecular-weight components. Furthermore, by lengthening the stretching section, neckdown during stretching increases, resulting in a uniformly highly oriented film. Therefore, it is effective in improving the Young's modulus of the resulting polypropylene film in the direction perpendicular to the main orientation.

[0070] Next, the uniaxially stretched film obtained in the longitudinal stretching step is guided into a tenter with both widthwise ends held with clips and preheated, and then transversely stretched 8.5 to 14 times, more preferably 9.0 to 13 times, and even more preferably 9.5 to 12 times. The preheating temperature is preferably 165 to 180°C, more preferably 168 to 180°C, and even more preferably 170 to 180°C. The stretching temperature is preferably 148 to 165°C, more preferably 148 to 160°C, and even more preferably 148 to 155°C. By increasing the preheating temperature by 5°C or more, preferably 8°C or more, and more preferably 10°C or more, higher than the stretching temperature, uniform high-orientation stretching is possible across the entire width of the film, leading to improved tensile elongation and reduced crystallite size. Since uniaxially stretched films have a large neckdown, the film width is narrow, and even when stretched transversely using a normal tenter rail pattern, the transverse stretching ratio can be increased. Therefore, such stretching is preferable from the viewpoint of improving heat resistance.

[0071] In the subsequent heat treatment and relaxation treatment steps, the film is heat-set at a temperature of 165°C or higher but lower than 180°C, more preferably 168°C or higher but lower than 180°C, and even more preferably 170°C or higher but lower than 180°C, while being tension-held in the width direction with clips, while being relaxed at a relaxation rate of 12 to 20%, more preferably 14 to 20%, and even more preferably 16 to 20% in the width direction. Then, while being tension-held in the width direction with clips, the film is cooled at 80 to 100°C and then guided to the outside of the tenter. The clips on the ends of the resulting polypropylene film are released, and the film edges are slit in a winding process, resulting in a polypropylene film being wound into a product roll. By setting the heat treatment temperature at a temperature 5°C or higher, more preferably 8°C or higher, and even more preferably 10°C or higher than the transverse stretching temperature, residual stress within the polypropylene film can be alleviated, resulting in a reduced thermal shrinkage and improved tensile elongation.

[0072] Furthermore, when the polypropylene film emerges from the tenter and passes through the transfer, it is preferable to heat it with a hot roll from the viewpoint of improving heat resistance and tensile elongation. The heating temperature is preferably 80 to 120°C, more preferably 90 to 110°C. At temperatures above 120°C, the smoothness between the hot roll and the polypropylene film is impaired, and wrinkles may occur, resulting in poor flatness. The heating time is preferably 0.2 seconds or more, more preferably 0.4 seconds or more, and even more preferably 0.5 seconds or more. There is no particular upper limit to the heating time, but from the viewpoint of productivity, the upper limit is about 2.0 seconds.

[0073] The polypropylene film of the present invention obtained as described above can be used for various industrial applications, such as packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, medical products, and capacitor films. However, due to its particularly excellent heat resistance, mechanical strength, and quality, it is preferably used as a packaging film, surface protection film, process film, and release film. Here, the term "surface protection film" refers to a film that is attached to an object such as a molded body or film to protect it from scratches and contamination that occur during processing or transportation. The term "process film" refers to a film that is attached to an object such as a molded body or film to protect it from scratches and contamination that occur during manufacturing or processing, and is discarded when used as a final product. The term "release film" refers to a film that has high releasability and that is attached to an object such as a molded body or film to protect it from scratches and contamination that occur during processing or transportation, and can be easily peeled off and discarded when used as a final product. The term "packaging film" refers to a film used to wrap items, including food, to improve their quality, storage efficiency, and convenience during use.

[0074] The present invention will be described in detail below with reference to examples. The properties were measured and evaluated by the following methods.

[0075] (1) Film Thickness: Measured using a micro thickness meter (manufactured by Anritsu Corporation). A polypropylene film was sampled in a 10 cm square area, and measurements were taken at five random points, and the average value was taken as the film thickness (μm).

[0076] (2) tanδ (loss tangent) A rectangular test piece (5 mm wide x 20 mm long) cut from a polypropylene film with the long side in the main orientation direction was attached to the chuck of an apparatus under a nitrogen atmosphere at 23°C, cooled to -100°C once, and measured for tanδ from -100°C to 180°C after the start of heating using the apparatus and conditions below. A viscoelasticity-temperature curve was drawn using the dynamic viscoelasticity method, and Dmax, Dmin, L were calculated using tanδ at each temperature as shown in Figures 1 and 2. ｐ The test was carried out with n=3, and the average values ​​were used to determine the Dmax, Dmin, and L of the polypropylene film. ｐ<Apparatus and measurement conditions> Apparatus: Rheogel-E4000 (manufactured by UBM) Geometry: Tension Distance between chucks: 10 mm Frequency: 10 Hz Strain: 0.1 to 0.2% Temperature range: -100 to 180°C Heating rate: 5°C / min Measurement atmosphere: Nitrogen.

[0077] (3) Young's modulus A rectangular sample measuring 150 mm in length (measurement direction) x 10 mm was cut out from a polypropylene film, with an arbitrary direction as the measurement direction. The sample was set in a tensile tester (Orientec "Tensilon" (registered trademark) UCT-100) so that it was pulled in the measurement direction with an initial chuck distance of 50 mm, and then a tensile test of the film was performed at a tensile speed of 300 mm / min, and the Young's modulus was calculated according to the method specified in JIS K7161 (2014). The same measurement was performed five times, and the average value obtained was used as the Young's modulus in the measurement direction of the sample. Next, the measurement direction was set to 0°, and the Young's modulus was similarly measured in each direction forming an angle of 0° to 175° in 5° increments relative to the measurement direction, and the direction showing the highest value was designated as the main orientation direction.

[0078] (4) Tensile elongation in the main orientation direction at room temperature A rectangular sample measuring 150 mm in length (main orientation direction) x 10 mm was cut out from a polypropylene film. The sample was set in a tensile tester (Orientec "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 50 mm, and a tensile test of the film was performed at room temperature at a tensile speed of 300 mm / min, and the tensile elongation was calculated according to the method specified in JIS K7161 (2014). Measurements were performed five times for each sample, and the average value was used as the tensile elongation in the main orientation direction of the sample.

[0079] (5) Tensile elongation in the direction perpendicular to the main orientation at 90 ° C. A rectangular sample measuring 150 mm in length (direction perpendicular to the main orientation) x 10 mm in width was cut out from a polypropylene film. The sample was placed in an oven heated to 90 ° C. with the chuck attached and heated for 1 minute. The sample was then placed in a tensile tester (Orientec "Tensilon" (registered trademark) UCT-100) so that it was pulled in the width direction with an initial chuck distance of 50 mm. A tensile test was then performed on the film at a pulling speed of 300 mm / min, and the tensile elongation was calculated according to the method specified in JIS K7161 (2014). The same measurement was performed five times, and the average of the obtained values ​​was used as the tensile elongation of the sample in the direction perpendicular to the main orientation at 90 ° C.

[0080] (6) Crystallite size of the main orientation and its perpendicular direction α (110) Polypropylene film was cut into strips 4 cm long (main orientation direction) and 1 mm wide (direction perpendicular to the main orientation), and the strips were stacked to a thickness of 1 mm to prepare a sample. The sample was placed between the X-ray source and the detector so that X-rays penetrated through the sample surface, and X-ray diffraction was measured by scanning the angle (2θ / θ) between the X-ray source and the detector symmetrically with respect to the film surface. In the obtained diffraction profile, the crystallite size in the main orientation direction was calculated from the half-width βe of the crystal peak at 2θ = approximately 14° (α crystal (110) plane) using the following formulas (1) and (2). In addition, the crystallite size in the direction perpendicular to the main orientation was also calculated for polypropylene film cut into strips 4 cm long (direction perpendicular to the main orientation) and 1 mm wide (direction perpendicular to the main orientation). The measurement equipment and conditions were as follows.

[0081]

[0082]

[0083] where λ is the X-ray wavelength (= 0.15418 nm), βe is the half-width of the diffraction peak, βo is the correction value of the half-width (= 0.6), and K is the Scherrer constant (= 1.0). (Measurement Apparatus) X-ray Diffraction Apparatus: D8 ADVANCE (sealed tube type) manufactured by Brucker AXS X-ray Source: CuKα ray Output: 40 kV-40 mA Slit System: DS = 0.3° Detector: LynxEye (high-speed detector) Scan: 2θ-θ continuous scan Measurement Range: 2θ = 5 to 80° Step Width: 0.02° Scan Speed: 1 second / step.

[0084] (7) Crystallization temperature T obtained by extrapolation point method ｃ０ Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), 3 mg of polypropylene film was heated in a nitrogen atmosphere from 25°C to 250°C at a rate of 20°C / min and held for 5 minutes. The film was then cooled from 250°C to 25°C at a rate of 10°C / min, and the peak temperature of the heat-release curve obtained during this cooling process was taken as Tc. １０ Thereafter, the polypropylene film was heated from 25°C to 250°C at a rate of 20°C / min and held at that temperature for 5 minutes. Then, the film was cooled from 250°C to 25°C at a rate of 40°C / min, and the peak temperature of the heat generation curve obtained during this cooling process was defined as Tc ４０ Next, as shown in FIG. 3, the horizontal axis represents the cooling rate and the vertical axis represents the crystallization temperature determined at each cooling rate. ４０ From Tc １０ The crystallization temperature when a straight line is drawn toward the temperature drop rate of 0 ° C. / min is calculated as Tc ０ In addition, Tc １０ and Tc ４０ When multiple peak temperatures were observed in the measurement, the highest peak temperature in the range of 80° C. to 130° C. was used as the crystallization temperature of the polypropylene film. The measurement was carried out three times for each sample, and the average value was used for evaluation.

[0085] (8) Melting Point (Tm) Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments, Inc.), 3 mg of polypropylene film was heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere, and the peak temperature of the endothermic curve obtained during this temperature increase was taken as Tm (°C). The measurement was carried out three times for each sample, and the average of the obtained values ​​was taken as the Tm (°C) of the polypropylene film.

[0086] (9) Static friction coefficient μs in the direction perpendicular to the main orientation after 10 minutes of heat treatment at 90°C Polypropylene film was cut into a width of 6.5 cm (in the direction of the main orientation of the film) and a length of 12 cm (in the direction perpendicular to the main orientation of the film). The test piece was sandwiched between paper and heated for 10 minutes in an oven maintained at 130°C under zero load. After heating, it was removed and cooled at room temperature. Then, using a slip tester manufactured by Toyo Seiki Co., Ltd., the static friction coefficient was measured at 25°C and 65% RH in accordance with JIS K 7125 (1999). The measurement was performed in the direction perpendicular to the main orientation, with the front and back surfaces of the film overlapping each other, i.e., with the front surface of one film in contact with the back surface of the other film. The same measurement was performed five times for each sample, and the average of the obtained values ​​was calculated and used as the static friction coefficient (μs) of the polypropylene film.

[0087] (10) Melt tension Measurement was carried out using an apparatus conforming to JIS K 7199 (1999) under the following conditions: Apparatus: Capillograph 1BPMD-i with melt tension tester (manufactured by Toyo Seiki Co., Ltd.) Temperature: 230°C (using a heat-retaining chamber) Die: L = 8 (mm), D = 2.095 (mm) Extrusion speed: 20 mm / min Take-up speed: 15.7 m / min Sample mass: 15 to 20 g.

[0088] (11) Flatness of film when heated An acrylic adhesive (manufactured by Soken Chemical & Engineering Co., Ltd., "SK Dyne" (registered trademark) 1310) was diluted with ethyl acetate, toluene, and methyl ethyl ketone (MEK) and 2.0 parts by mass of a curing agent (manufactured by Nippon Polyurethane Industry Co., Ltd., "Coronate" (registered trademark) D-90) was mixed with 100 parts by mass of the solid content of the adhesive to form an adhesive layer coating. The film was then coated using a gravure coater, and the film was introduced into a drying oven at 90°C and transported for 30 seconds to remove the solvent in the coating, thereby obtaining an adhesive film with an adhesive layer thickness of 1 μm. The adhesive film was then wound into a roll with a length of 200 m to form an adhesive film roll. Next, 1 m of the 500 mm wide adhesive film was unwound, and free tension (a state in which the film was hanging vertically under its own weight) was applied uniformly across the entire width of the film, with tensions of 1 kg / m and 3 kg / m applied evenly, and the presence or absence of poor flatness such as wrinkles or dents was visually confirmed. The evaluation was performed according to the following criteria. S: No poor flatness was observed with free tension. A: Poor flatness was observed with free tension, but the poor flatness disappeared with a tension of 1 kg / m width. B: Poor flatness was observed with a tension of 1 kg / m width, but the poor flatness disappeared with a tension of 3 kg / m width. C: Poor flatness was observed even with a tension of 3 kg / m width.

[0089] (12) Breakability when high tension is applied to the film A 500 mm wide polypropylene film was introduced into a drying oven at 90°C, and the tension was increased to a predetermined level at a rate of 100 N / sec. After the predetermined tension was reached, the film was conveyed under tension for 30 seconds, and the polypropylene film was visually inspected for breakage. S: No breakage occurred even at a tension of 400 N or more. A: Breakage occurred at a tension of 300 N or more but less than 400 N. B: Breakage occurred at a tension of 200 N or more but less than 300 N. C: Breakage occurred at a tension of less than 200 N.

[0090] (13) Differential distribution value and molecular weight distribution Mz / Mw when logarithmic molecular weight Log(M) = 6.5 A polypropylene film was dissolved in 1,2,4-trichlorobenzene as a solvent by stirring at 165°C for 30 minutes. The film was then filtered using a 0.5 µm filter, and the molecular weight distribution of the filtrate was measured, and the differential distribution value when the logarithmic molecular weight Log(M) was 6.5 was read.

[0091] The weight-average molecular weight Mw and Z-average molecular weight Mz of the sample were determined using a molecular weight calibration curve prepared using the following standard samples: Apparatus: Agilent high-temperature GPC apparatus PL-GPC220 Detector: Agilent differential refractive index detector (RI detector) Column: Agilent PL1110-6200 (20 μm MIXED-A) × 2 Flow rate: 1.0 mL / min Column temperature: 145°C Injection volume: 0.500 mL Sample concentration: 0.1 wt% Standard samples: Tosoh monodisperse polystyrene, Tokyo Chemical Industry dibenzyl.

[0092] (14) Cold Xylene Soluble Fraction (CXS) For the raw material polypropylene resin, 0.5 g was dissolved in 100 ml of xylene at 135°C and allowed to cool. After allowing to cool, the polypropylene-based component dissolved in the filtrate was quantified by liquid chromatography. The amount of the polypropylene-based component dissolved in the filtrate was determined by X (g) and the precise weight of a 0.5 g sample was determined by X0 (g), and the CXS was calculated using the following formula: Formula: CXS (mass%) = (X / X0) x 100.

[0093] (15) Maximum Height (St) Measurements were performed using Ryoka Systems' "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC, and the attached analysis software was used to perform surface correction of the photographed image using a polynomial fourth-order approximation to determine the surface shape. The maximum height (St) refers to the difference between the maximum height (Peak) and the minimum height (Valley) within the measurement area. The measurement conditions are as follows: Measurements were performed on both sides of the film with n = 3 (number of measurements = 3), and the average value of each side was calculated and adopted as the St for each side. The larger of the St values ​​for both sides of the film is listed in the table. Apparatus: "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC (manufactured by Ryoka Systems Co., Ltd.) Measurement conditions: CCD camera SONY HR-57 1 / 2 inch Objective lens: 5x Intermediate lens: 0.5x Wavelength filter: 530 nm white Measurement mode: Wave Measurement software: VS-Measure Version 5.5.1 Analysis software: VS-Viewer Version 5.5.1 Measurement area: 1.252 mm x 0.939 mm.

[0094] (Polypropylene Resin, etc.) Polypropylene resins having the molecular weight distributions Mz / Mw and CXS shown in Table 1 below were used to produce the polypropylene films of the Examples and Comparative Examples. These values ​​were evaluated in the form of resin pellets. Three types of polypropylene resin A and two types of other polypropylene resins were prepared. The following branched polypropylene resins were also used.

[0095] Polypropylene resin 1 (PP1): manufactured by Prime Polymer Co., Ltd. Polypropylene resin 2 (PP2): manufactured by Prime Polymer Co., Ltd. Polypropylene resin 3 (PP3): manufactured by Sumitomo Chemical Co., Ltd. Polypropylene resin 4 (PP4): manufactured by Prime Polymer Co., Ltd. Polypropylene resin 5 (PP5): manufactured by Prime Polymer Co., Ltd. Branched polypropylene resin 1 (branched PP1): Ziegler-Natta catalyst-based branched polypropylene resin (PF-814 manufactured by Basell, melt tension: 15 gf, MFR: 3.0) Branched polypropylene resin 2 (branched PP2): metallocene catalyst-based branched polypropylene resin ("WAYMAX" (registered trademark) MFX6, manufactured by Japan Polypropylene Corporation, melt tension: 13 gf, MFR: 3.0).

[0096]

[0097] Polypropylene raw material D: Polypropylene resin 2 and 4-methyl-1-pentene polymer 1 (described later) were supplied from a metering hopper to a twin-screw extruder in a mass ratio of 90:10, and melt-kneaded at 260°C. The molten resin composition was extruded from a die in the form of strands, cooled and solidified in a water bath at 25°C, and cut into chips.

[0098] Polypropylene raw material E: Polypropylene resin 3 and 4-methyl-1-pentene polymer 2 (described later) were supplied from a metering hopper to a twin-screw extruder in a mass ratio of 90:10, and melt-kneaded at 260°C. The molten resin composition was extruded from a die in the form of strands, cooled and solidified in a water bath at 25°C, and cut into chips.

[0099] 4-Methyl-1-pentene polymer 1: MX004 manufactured by Mitsui Chemicals, Inc.

[0100] (Example 1) As a raw material for the surface layer (I), polypropylene resin 2 and polypropylene raw material D were dry-blended at 80:20 (mass ratio) and supplied to a single-screw extruder for the surface layer (I). As a raw material for the base layer (II), polypropylene resin 1 and branched polypropylene resin 1 were dry-blended at 95:5 (mass ratio) and supplied to a single-screw extruder for the base layer (II). Each resin mixture was melt-extruded at 260 ° C., and after removing foreign matter with a 20 μm cut sintered filter, the surface layer (I) / base layer (II) / surface layer (I) was laminated in a feed block type A / B / A composite T die so that the thickness ratio was 1 / 30 / 1, and then discharged onto a casting drum with a surface temperature controlled at 25 ° C., and air at a temperature of 20 ° C. was blown at a speed of 140 m / s with an air knife to adhere to the casting drum. Thereafter, compressed air at 20°C was blown onto the uncooled drum surface of the sheet on the casting drum at an air speed of 140 m / s to cool it, obtaining an unstretched sheet. Subsequently, the unstretched sheet was preheated to 135°C with a ceramic roll, and stretched 5.7 times in the longitudinal direction while heating the sheet from both sides with a radiation heater between rolls at 108°C with a peripheral speed difference. The heat source of the radiation heater was fixed at a position 90 mm away from the sheet surface. The distance between the rolls with a peripheral speed difference was 320 mm, and the output of the radiation heater was set to 2.8 kW. Next, the obtained uniaxially stretched film was introduced into a tenter-type stretching machine with both ends in the width direction held by clips, preheated at 176°C for 3 seconds, stretched 9.8 times in the width direction at 153°C, and heat-treated at 178°C while providing 20% ​​relaxation in the width direction. The film was then cooled to 100°C and led to the outside of the tenter, the clips at both ends in the width direction of the film were released, and the film was heated at a transfer point with a hot roll at 110°C for 1.8 seconds, and then wound around a core to obtain a polypropylene film with a thickness of 24 µm. The physical properties and evaluation results of the obtained film are shown in Table 2.

[0101] (Examples 2 to 5, Comparative Examples 1 to 4) Polypropylene films were obtained in the same manner as in Example 1, except that the raw material composition and film-forming conditions for each layer were as shown in Table 2. The thickness was adjusted by adjusting the extrusion rate and the casting drum speed. The physical properties and evaluation results of the obtained film are shown in Table 2. Regarding the mixing of the raw materials for the surface layer, for the surface layer (I) of Comparative Example 2, polypropylene resin 2 and polypropylene raw material D were dry-blended at an 80:20 (mass ratio) ratio, as in the surface layer (I) of Example 1. For the surface layer (I) of Example 4, polypropylene resin 3 and polypropylene raw material E were dry-blended at a 70:30 (mass ratio). For the surface layer (I) and base layer (II) of the other Examples, polypropylene raw materials D and E were not used, and the resin components were dry-blended in the ratios shown in Table 2. For Example 4, the surface layer (I) side was brought into contact with the casting roll.

[0102]

[0103] Example 3 and Comparative Examples 1 and 4 have a single layer structure and were treated as if they did not have the surface layer (I).

[0104] As described above, the polypropylene film of the present invention can be used for various industrial applications such as packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, medical products, and capacitor films. However, since the polypropylene film of the present invention is particularly excellent in heat resistance, mechanical strength, and quality, it can be preferably used as a surface protection film, process film, or release film.

Claims

1. A polypropylene film characterized in that the maximum value Dmax and the minimum value Dmin of tan δ in the main orientation direction in the range of -10°C or more and 50°C or less satisfy the relationship of Formula 1, the tensile elongation in the direction perpendicular to the main orientation at 90°C is 70% or more, and the static friction coefficient μs after heat treatment at 90°C for 10 minutes is 0.80 or less. Formula 1: 0.00≦(Dmax-Dmin) / Dmax≦0.30

2. The maximum value of tan δ in the main alignment direction at −30° C. or higher and lower than 30° C. is L Ｐ When the temperature is in the range of 30° C. or more and less than 150° C., tan δ in the main alignment direction is Ｐ The polypropylene film according to claim 1, wherein the temperature at which the film becomes equal to is 80° C. or less.

3. 3. The polypropylene film according to claim 1 or 2, wherein the sum of the crystallite sizes of the α(110) in the main orientation direction and the perpendicular direction thereto is 20.0 nm or less.

4. Crystallization temperature Tc measured at a temperature drop rate of 10°C / min １０ (°C) and the crystallization temperature Tc measured at a temperature drop rate of 40°C / min ４０ The crystallization temperature at a temperature drop rate of 0°C / min was calculated by the extrapolation point method using the ０ (°C) and the melting point of the polypropylene film is Tm (°C), ０ The polypropylene film according to any one of claims 1 to 3, wherein +Tm≧280 is satisfied.

5. The polypropylene film according to any one of claims 1 to 4, characterized in that the tensile elongation in the main orientation direction is 35% or more.

6. The polypropylene film according to any one of claims 1 to 5, wherein the maximum height St of both sides of the film is less than 2.0 µm.

7. The polypropylene film according to any one of claims 1 to 6, having a molecular weight distribution Mz / Mw of less than 4.

5.

8. The polypropylene film according to any one of claims 1 to 7, wherein in a molecular weight distribution curve measured by gel permeation chromatography, a differential distribution value at a logarithmic molecular weight Log(M)=6.5 is 1.0% or more and 10% or less.

9. The polypropylene film according to any one of claims 1 to 8, having at least two layers mainly composed of polypropylene resin.

10. A process film comprising the polypropylene film according to any one of claims 1 to 9.

11. A release film comprising the polypropylene film according to any one of claims 1 to 9.

12. A surface protection film comprising the polypropylene film according to any one of claims 1 to 9.