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

[Technical Field]

[0001] This invention relates to a polypropylene film that is excellent in heat resistance, mechanical strength, and quality, and can be suitably used for industrial material applications. [Background technology]

[0002] Polypropylene film is suitable for use as a release film or process film for various materials such as plastic products, building materials, and optical components due to its excellent surface release properties and mechanical properties. Furthermore, its excellent electrical properties make it suitable for use as a film for capacitors.

[0003] One of the required properties for polypropylene film is heat resistance. For example, when polypropylene film is used as a cover film for thermosetting resins, it may be exposed to high temperatures during the heat-curing process after lamination. Also, when used as a film for capacitors, it is exposed to high temperatures inside the motor. In such applications, the required level of heat resistance for polypropylene film has been increasing in recent years.

[0004] One indicator of the heat resistance of polypropylene film is its thermal shrinkage rate. Generally, methods to reduce thermal shrinkage rate include increasing the crystallinity of the polypropylene resin, reducing high molecular weight components, and setting a high stretch ratio. However, while increasing the crystallinity of the polypropylene resin and high-stretching methods improve the mechanical strength of the polypropylene film, they can also decrease tensile elongation and make it brittle. Furthermore, low molecular weight polypropylene resins have low melt tension when softened by heating, which can reduce the tensile elongation of the resulting film. For these reasons, it has been conventionally difficult to obtain a polypropylene film that achieves both high tensile elongation and low thermal shrinkage rate.

[0005] As examples of polypropylene films with improved heat resistance, Patent Document 1 describes an example in which a highly crystalline polypropylene resin is used and the preheating roll temperature during longitudinal stretching is adjusted to reduce thermal shrinkage stress. Patent Documents 2 and 3 describe an example in which a polypropylene resin mainly composed of low molecular weight is used and its crystallinity is increased to reduce heat yield. Furthermore, Patent Document 4 describes an example in which a polypropylene resin with a low amount of polypropylene component dissolved in xylene is used to improve voltage resistance at high temperatures and reduce shrinkage stress. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2020 / 196602 [Patent Document 2] Japanese Patent Publication No. 2014-55283 [Patent Document 3] International Publication No. 2020 / 137791 [Patent Document 4] Japanese Patent Publication No. 2020-132882 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the polypropylene films described in Patent Documents 1 and 4 had the problem of insufficient heat resistance. Furthermore, the polypropylene film described in Patent Document 2 had the problem of low tensile elongation in the direction orthogonal to the main orientation, making it prone to tearing when transported at high temperatures and high tension. In addition, the polypropylene film described in Patent Document 3 had the problem of high thermal shrinkage in the direction of the main orientation, causing the film to shrink and wrinkle when transported at high temperatures. Therefore, when these polypropylene films were used in applications requiring processing in high-temperature environments, it was difficult to maintain their quality after processing at high temperatures. Thus, the object of the present invention is to solve the above problems and provide a polypropylene film that can maintain its quality even after processing at high temperatures.

Means for Solving the Problems

[0008] In order to solve the above problems, the polypropylene film of the present invention is characterized in that the maximum value Dmax and the minimum value Dmin of tanδ in the main orientation direction in the range of -10°C or higher and 50°C or lower 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 higher. It is a polypropylene film. Formula 1: 0.00 ≦ (Dmax - Dmin) / Dmax ≦ 0.30.

Effects of the Invention

[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 a high temperature.

Brief Description of the Drawings

[0010] [Figure 1] It is an example of a graph showing the temperature dependence of tanδ in the main orientation direction of a polypropylene film, representing Dmax and Dmin. [Figure 2] It is an example of a graph showing the temperature dependence of tanδ in the main orientation direction of a polypropylene film, representing Lp and the temperature at which tanδ becomes equal to Lp. [Figure 3] It is an example of a graph showing the crystallization temperature Tc0 of a polypropylene film.

Embodiments for Carrying out the Invention

[0011] The polypropylene film of the present invention is characterized in that the maximum value Dmax and the minimum value Dmin of tanδ in the main orientation direction in the range of -10°C or higher and 50°C or lower 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 higher. It is a polypropylene film. Hereinafter, the polypropylene film of the present invention will be specifically described. Formula 1: 0.00 ≦ (Dmax - Dmin) / Dmax ≦ 0.30.

[0012] A polypropylene film refers to a sheet-shaped molded body that contains polypropylene resin in an amount exceeding 50% by mass and up to 100% by mass when the total components constituting the film are 100% by mass. The amount of polypropylene resin in the polypropylene film is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, still 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. The polypropylene film of the present invention may contain only one type of polypropylene resin, but preferably contains two or more types of polypropylene resins. When two or more types of polypropylene resins are contained in the film, as long as the total of these components is more than 50% by mass and up to 100% by mass, it is regarded as having polypropylene resin as the main component.

[0013] Also, the polypropylene resin refers to a resin in which the propylene unit in all the constituent units constituting the resin is more than 50 mol% and up to 100 mol%. In the present invention, the direction in which the polypropylene film is formed (the winding direction when it is a film roll) is referred to as the film-forming direction, the longitudinal direction or the MD direction, and the direction orthogonal to the film-forming direction in the film plane is referred to as the width direction or the TD direction.

[0014] From the viewpoint of enhancing the heat resistance that affects the quality after passing through a processing step at high temperature, it is important that the maximum value Dmax and the minimum value Dmin of tanδ in the main orientation direction in the range of -10°C or more and 50°C or less satisfy the relationship of Formula 1 for the polypropylene film of the present invention. Formula 1: 0.00 ≦ (Dmax - Dmin) / Dmax ≦ 0.30.

[0015] tanδ, also known as the loss tangent, correlates with the degree of molecular chain mobility in polypropylene film. Generally, as shown in Figure 1, tanδ reaches a maximum around 0°C, decreases temporarily as the temperature rises, then increases again to a level exceeding the maximum value around 0°C. (Dmax-Dmin) / Dmax is an index that shows the amount by which tanδ decreases from its maximum value around 0°C. The inventors have found that reducing this value and suppressing molecular chain mobility over a wide temperature range improves 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 greater. Therefore, for example, when such a polypropylene film is used as a release film, wrinkles may form when it is bonded to the adherend and passed through a high-temperature process, which may impair its quality. From the above viewpoint, (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 by the following procedure. First, a polypropylene film test piece measuring 5 mm wide x 20 mm long, cut with the main orientation direction as the longer side, is attached to the device chuck under a nitrogen atmosphere at 23°C, cooled to -60°C, and the tanδ is measured from the point when the temperature reaches -50°C until it reaches 150°C. Next, a viscoelasticity-temperature curve is drawn using the dynamic viscoelasticity method, and Dmax and Dmin are determined using the tanδ at each temperature, and (Dmax-Dmin) / Dmax is calculated from these values. Note that tanδ can be measured using a known device, such as Rheogel-E4000 (manufactured by UBM), and the conditions at that time are as shown in the examples.

[0018] To achieve a (Dmax-Dmin) / Dmax value of 0.30 or less, for example, the raw material composition of the polypropylene film can be set within the range described later, and the film-forming conditions can also be set within the range described later. In particular, it is effective to use highly crystalline raw materials with a narrow molecular weight distribution Mz / Mw, a significantly reduced high molecular weight component, and a low cold xylene soluble portion (CXS), to set the surface temperature of the casting drum to a range of 10 to 40°C, and to draw down the film in the direction of the conveying flow on a high-temperature (80°C or higher) roll after transverse stretching, thereby shrinking the film in the direction perpendicular to the main orientation.

[0019] In the present invention, it is important that the polypropylene film has a tensile elongation of 70% or more in the direction orthogonal to the principal orientation at 90°C, from the viewpoint of increasing mechanical strength, which affects the stability of the processing process at high temperatures. Here, the direction orthogonal to the principal orientation refers to the direction perpendicular to the principal orientation in the plane. The principal orientation direction is the direction that shows the highest value when the Young's modulus is measured in each direction that forms an angle from 0° to 175° in 5° increments with respect to any direction in the film plane, with any direction set as 0°. The Young's modulus can be measured using a tensile testing machine, and the details of the measurement method are shown in the examples. If the width of the sample is less than 50 mm and the Young's modulus cannot be determined with a tensile testing machine, the crystal orientation of the α(110) plane of the polypropylene film is measured by wide-angle X-ray as follows, and the principal orientation direction is determined based on the following criteria. Specifically, X-rays (CuKα rays) are incident perpendicular to the film surface, and the crystal peak at 2θ = approximately 14° (α-crystal (110) plane) is scanned circumferentially. The direction with the highest diffraction intensity in the obtained diffraction intensity distribution is defined as the principal orientation direction, and the direction perpendicular to it is defined as the principal orientation orthogonal direction.

[0020] If the tensile elongation in the direction orthogonal to the principal orientation at 90°C is less than 70%, for example, when a polypropylene film is used as a release film, high tension in the direction orthogonal to the principal orientation may be applied when it is bonded to the adherend and passed through a high-temperature process, causing the film to break. From this viewpoint, the tensile elongation in the direction orthogonal to the principal 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, there is no particular upper limit to the tensile elongation in the direction orthogonal to the principal orientation at 90°C, but it is practically upper at around 400%.

[0021] The tensile elongation in the direction perpendicular to the principal orientation at 90°C can be measured using a tensile testing machine equipped with a high-temperature oven by the following procedure. First, a sample is obtained by cutting a polypropylene film into a rectangle measuring 150 mm (perpendicular to the principal orientation) x 10 mm (perpendicular to the principal orientation). Next, the sample is set in the tensile testing machine with an initial chuck distance of 50 mm, and the chucks are placed into an oven heated to 90°C for 1 minute. After that, a tensile test is performed at a tensile speed of 300 mm / min, and the elongation at the time of sample fracture is read and taken as the tensile elongation. Any tensile testing machine capable of measurement is acceptable; for example, the Orientec "Tensilon" (registered trademark) UCT-100 can be used.

[0022] Generally, reducing the proportion of high molecular weight components in a polypropylene film makes it difficult to transmit tension throughout the film when high tension is applied, leading to a decrease in tensile elongation. Furthermore, increasing the proportion of highly crystalline polypropylene resin with a low cold xylene soluble portion (CXS) results in a lack of amorphous components to relieve stress when tension is applied, further reducing tensile elongation. Therefore, maintaining tensile elongation while improving heat resistance has traditionally been difficult. However, we have found that by using a method that sets the raw material composition of the polypropylene film within the range described below, and the film-forming conditions within the range described below, it is possible to achieve a tensile elongation of 70% or more in the direction orthogonal to the main orientation at 90°C. In particular, it is effective to lengthen the stretching section during longitudinal stretching (e.g., 200 mm or more), and to heat both sides of the film sufficiently with a radiation heater during the stretching section to reduce stretching stress and achieve uniform longitudinal stretching. Additionally, during the relaxation treatment after transverse stretching, increasing the relaxation rate (e.g., 12% or more) and heating with a hot roll as the film passes over the crossbars is effective.

[0023] The polypropylene film of the present invention has a maximum value of L for the tanδ in the main orientation direction at temperatures of -30°C or higher and less than 30°C, from the viewpoint of heat resistance. P In this case, the tanδ in the main orientation direction is L in the range of 30°C to less than 150°C. P The temperature at which this becomes equal is preferably 80°C or lower. More preferably 70°C or lower, even more preferably 60°C or lower, and particularly preferably 55°C or lower. The tanδ in the main orientation direction is L P The temperature at which this becomes equal corresponds to the temperature at which the maximum value of tanδ around 0°C begins to be exceeded, as shown in Figure 2. The inventors have found that keeping this temperature low improves the heat resistance of polypropylene film. P Because the temperature at which this occurs is 80°C or lower, shrinkage in the direction perpendicular to the principal orientation is reduced when the polypropylene film is wound into a roll and stored at high temperatures, thus 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.

[0024] The tanδ in the principal orientation direction is L P To make the temperature equal to 80°C or lower, or within the preferred range described above, the raw material composition of the polypropylene film can be set to the range described later. 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 low CXS. The tanδ in the main orientation direction is L P The lower limit of the temperature at which it becomes equal to is effectively 30°C.

[0025] From the viewpoint of heat resistance, the polypropylene film of the present invention preferably has a sum of crystallite sizes of α(110) in the main orientation direction and in the direction orthogonal 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. By having a sum of crystallite sizes of α(110) in the main orientation direction and in the direction orthogonal thereto of 20.0 nm or less, shrinkage in the direction orthogonal to the main orientation is reduced when the polypropylene film is wound into a roll and stored at high temperatures, thus 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, there is no particular lower limit to the sum of crystallite sizes of α(110) in the main orientation direction and in the direction orthogonal thereto, but it is substantially about 10 nm.

[0026] Furthermore, by reducing the sum of the crystallite sizes of α(110) in the main orientation direction and its orthogonal direction to less than 20.0 nm, the size of the amorphous region between crystals in the polypropylene film can be suppressed. Therefore, suppressing the size of the amorphous region in this way brings various advantages when using polypropylene film in various applications. For example, when polypropylene film is used as a release film, after lamination with an adherend and passing through a high-temperature process, high release properties are maintained when peeling the polypropylene film from the adherend, reducing the decrease in productivity. 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 α(110) in the main orientation direction and the direction orthogonal thereto 20.0 nm or less, or within the preferred range described above, for example, a method can be used in which the raw material composition of the polypropylene film is within the range described later, and the film formation conditions are within the range described later. 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 and the temperature of the casting drum to increase cooling during casting, and to lengthen the stretching section during longitudinal stretching, while sufficiently heating both sides of the film with a radiation heater during the stretching section.

[0028] The polypropylene film of the present invention achieves both improved heat resistance and reduced formation of coarse spherulites, and its crystallization temperature Tc measured at a cooling rate of 10°C / min 10 Crystallization temperature Tc measured at a cooling rate of 40°C / min (°C) 40 When the crystallization temperature at a cooling rate of 0°C / min, determined by extrapolation using (°C), is defined as Tc0 (°C), and the melting point of the polypropylene film is defined as Tm (°C), it is preferable that Tc0 + Tm ≥ 280. More preferably, the value of Tc0 + Tm is 285 or higher, and even more preferably 290 or higher. Tc0 is an indicator of the ease of crystallization, and a high Tc0 means that crystallization is easy. Tm is the melting point of the polypropylene film, and a high Tm means that the polypropylene film has high heat resistance. When the value of Tc0 + Tm is 280 or higher, the crystallization rate is kept at an appropriate level, and coarse spherulites are less likely to form during casting. As a result, the decrease in elongation at break in the direction perpendicular to the principal orientation direction and the increase in crystallite size are suppressed. From the above viewpoint, there is no particular upper limit to the value of Tc0 + Tm, but practically, the upper limit is around 350.

[0029] To make the value of Tc0 + Tm 280 or more or within the above-preferred range, methods for increasing Tc0 or Tm can be used alone or in combination. To increase Tc0, a method of setting the composition of the polypropylene film within the range described below can be used. In particular, it is preferable to add a component having a nucleating agent action, and among them, it is preferable to add a branched polypropylene resin. To increase Tm, for example, a method of setting the composition of the polypropylene film within the range described below and setting the film-forming conditions within the range described below can be used. Regarding the composition, it is particularly preferable to use a highly crystalline raw material with a low cold xylene soluble part (CXS). Regarding the film-forming conditions, it is also effective to extend the stretching section during longitudinal stretching and stretch uniformly while sufficiently heating both sides with a radiation heater in the stretching section to reduce the stretching stress.

[0030] Tc 10 , Tc 40 , Tc0 can be measured by a differential scanning calorimeter (DSC), and the specific measurement method is as follows. First, using DSC, 3 mg of the polypropylene film is heated from 25°C to 250°C at 20°C / min in a nitrogen atmosphere and held for 5 minutes. Then, it is cooled from 250°C to 25°C at 10°C / min, and the peak temperature of the exothermic curve obtained during this cooling is taken as T c10 . Further, the polypropylene film is heated from 25°C to 250°C at 20°C / min and held for 5 minutes. Then, it is cooled from 250°C to 25°C at 40°C / min, and the peak temperature of the exothermic curve obtained during this cooling is taken as T c40 . The Tc 10 , Tc 40 thus measured are plotted with the horizontal axis being the cooling rate and the vertical axis being the crystallization temperature obtained at each cooling rate. As shown in Figure 3, a straight line passing through T c40 to T c10 is drawn, and the crystallization temperature when the cooling rate is 0°C / min is T c0The DSC can be any known DSC capable of the above measurements, and no particular restrictions apply. Specific examples include the Seiko Instruments EXSTAR DSC6220 (the same applies to the Tm measurement device described later).

[0031] Tm can be measured using a differential scanning calorimeter (DSC), and the specific measurement method is as follows: Using a DSC, a 3 mg 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 heating is defined as Tm.

[0032] 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, from the viewpoint of improving flatness during heating and improving processability after the heating process. Here, a static friction coefficient μs of 0.80 or less means that the static friction coefficient μs measured when different surfaces of the front and back of the film are stacked together is 0.80 or less (the same applies to the preferred range described later). 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, the thermosetting resin may be cured at a temperature range of about 80°C to 100°C after being laminated to a sheet-like thermosetting resin. Generally, polypropylene films have lower heat resistance compared to polyester films, which are commonly used as process films such as release films, and the film surface may soften and its slipperiness may decrease when subjected to temperatures of about 90°C. By keeping the microsecond (μs) after heating below 0.8, when polypropylene film is used as a release film, for example, it is possible to reduce the slippage of the film on the conveyor roll during high-temperature processes, which can cause uneven stress distribution and wrinkles, as well as winding misalignment that occurs when winding the film together with the adherend.

[0033] To achieve a static friction coefficient μs of 0.80 or less or within the preferred range described above after heating at 90°C for 10 minutes, methods can be used in which the composition of the polypropylene film is within the range described later, and the film-forming conditions are within the range described later. In particular, methods such as alloying an olefin resin such as poly-4-methylpentene-1 resin onto the surface layer of the polypropylene film and forming fine protrusions on its surface, or forming spherulites during casting by raising the temperature of the casting drum to form protrusions after biaxial stretching, are effective. There is no particular lower limit to μs after heating, but it is practically 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 of 35% or more in the principal orientation direction. A tensile elongation of 35% or more in the principal orientation direction reduces film breakage when the polypropylene film is unwound from the roll and used. From this viewpoint, a tensile elongation of 40% or more in the principal orientation direction is preferable, more preferably 50% or more, and even more preferably 60% or more. On the other hand, there is no particular upper limit to the tensile elongation in the principal orientation direction, but it is substantially around 1000%. The tensile elongation in the principal orientation direction is evaluated using a tensile testing machine, and details will be described later.

[0035] Increasing the stretch ratio or performing high-stress stretching at low temperatures to enhance mechanical strength generally tends to decrease tensile elongation. Furthermore, increasing the proportion of highly crystalline polypropylene resin with a low cold xylene soluble portion (CXS) leads to a lack of amorphous components that relieve stress when tension is applied, further reducing tensile elongation. Therefore, maintaining tensile elongation while using highly crystalline raw materials has traditionally been difficult. However, we have found that by using a method that sets the raw material composition of the polypropylene film within the range described below, and the film-forming conditions 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 to stretch the film while sufficiently heating both sides of the film with a radiation heater or the like during the stretching section, thereby reducing the stretching stress and achieving uniform longitudinal stretching. It is also effective to increase the relaxation rate (e.g., 12% or more) during the relaxation treatment after transverse stretching, and to heat the film with a hot roll as it passes through the crossbars.

[0036] The polypropylene film of the present invention preferably has a maximum height St on both sides of the film of less than 2.0 μm. 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 on both sides of the film of less than 2.0 μm, when the polypropylene film is laminated to a substrate and wound up as a film roll, it is possible to reduce the deterioration of quality, such as when protrusions on the surface of the polypropylene film come into contact with the substrate and indentations are transferred to the substrate. The lower limit of the maximum height St on 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 preferred range described above, for example, a method can be used in which the composition of the polypropylene film is within the range described later, and the film-forming conditions are within the range described later. In particular, by setting the surface temperature of the casting drum in the range of 10 to 40°C, the spherulites in the unstretched sheet are uniformly refined, the stretching section during longitudinal stretching is lengthened, and the film is stretched uniformly while reducing the stretching stress by stretching both sides while sufficiently heating them with a radiation heater during the longitudinal stretching section.

[0038] The thickness of the polypropylene film of the present invention is not particularly limited and can be adjusted as appropriate depending on the application, but is preferably 0.5 μm to 100 μm from the viewpoint of handling. 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, even 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 formation speed, the stretching ratio, etc., within a range that does not degrade other physical properties. The thickness of the polypropylene film can be measured with a known micro-thickness gauge.

[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 the Mz / Mw of the polypropylene film is substantially around 1.5. When the Mz / Mw of the polypropylene film is less than 4.5, there are fewer high molecular weight components that are relaxed when heated, and the heat resistance of the polypropylene film is maintained. Methods for achieving the above-mentioned molecular weight distribution Mz / Mw of the polypropylene film include adjusting the hydrogen gas concentration when polymerizing the polypropylene resin, selecting catalysts and / or co-catalysts, and appropriately adjusting the composition and polymerization amount of each polymerization tank in continuous polymerization.

[0040] The following describes a polypropylene resin (polypropylene resin A) that is most suitable as the most abundant component in the polypropylene film of the present invention. From the viewpoint of productivity and film properties, 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 for polypropylene resin A is practically around 1.2. When the Mz / Mw of polypropylene resin A is less than 4.2, there are fewer high molecular weight components that are relaxed when heated, and the heat resistance of the polypropylene film is maintained. Methods to achieve the above values ​​for the molecular weight distribution Mz / Mw of polypropylene resin A include adjusting the hydrogen gas concentration during polymerization, selecting catalysts and / or co-catalysts, and appropriately adjusting the composition and polymerization amount of each polymerization tank 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-forming properties and film strength. The lower limit of the 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 achieve the above values ​​for the MFR of polypropylene resin A, methods such as controlling the average molecular weight and molecular weight distribution are employed. More specifically, methods such as adjusting the hydrogen gas concentration during polymerization, selecting catalysts and / or co-catalysts, and selecting their compositions as appropriate are preferably employed to control the molecular weight and molecular weight distribution of the polypropylene resin. Reducing high molecular weight components increases the MFR.

[0043] The polypropylene resin A preferably has a CXS of 3.5% by mass or less. Satisfying this condition suppresses a decrease in the dimensional stability and heat resistance of the resulting polypropylene film. Here, CXS refers to the polypropylene components dissolved in xylene when the sample is completely dissolved in xylene and then precipitated at room temperature. These are considered to be components that are difficult to crystallize due to reasons such as low stereoregularity or low molecular weight. If a large amount of such components is contained in polypropylene resin A, the thermal dimensional stability of the resulting polypropylene film may be poor. Therefore, from the above viewpoint, the CXS is more preferably 2.0% by mass or less. A lower CXS is preferable, but the lower limit is substantially around 0.1% by mass. Methods to bring the CXS within the above preferred range include adjusting the polymerization catalyst and process polymerization conditions, increasing the catalytic activity when obtaining polypropylene resin A, and washing the obtained resin with a solvent or the propylene monomer itself.

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

[0045] Polypropylene resin A may contain copolymer components made of other unsaturated hydrocarbons, etc., to the extent that it does not impair the objectives of the present invention. Examples of monomer components that constitute such copolymer 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 it is made into a polypropylene film, the copolymer 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 the total constituent units of polypropylene resin A are set to 100 mol%.

[0046] The content of ethylene units as copolymer components in polypropylene resin A is preferably 5 mol% or less, when the total constituent units of polypropylene resin A are set to 100 mol%. More preferably, it is 3 mol% or less, and even more preferably 1 mol% or less. The higher the amount of ethylene units, the lower the crystallinity and the easier it is to improve the transparency when it is made into a film, but the strength and heat resistance decrease. By keeping the ethylene unit content in polypropylene resin A at 5 mol% or less, the decrease in strength and the deterioration of the heat shrinkage rate due to the decrease in heat resistance when it is made into a polypropylene film are reduced. In addition, by keeping the ethylene unit content in polypropylene resin A at 5 mol% or less, the degradation of the resin during the extrusion process is also reduced, and the occurrence of fish eyes when it is made into a polypropylene film is suppressed.

[0047] Polypropylene resin A is a linear polypropylene, and it is preferable that it 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, E111G from Prime Polymer Co., Ltd., and FLX80E4, WF836DG3, FS2011DG3, D101, W101 from Sumitomo Chemical Co., Ltd.

[0048] The polypropylene film of the present invention may contain a branched polypropylene resin in addition to a linear polypropylene resin A. The branched polypropylene resin has a nucleating effect on α-crystals or β-crystals. Therefore, by including the branched polypropylene resin, the formation of coarse spherulites during casting is suppressed by its nucleating effect, 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 branched polypropylene resin is preferably 0.5 g / 10 min to 9 g / 10 min (230°C, 21.18 N load). The lower limit of the MFR of 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 branched polypropylene resin is more preferably 8 g / 10 min. Methods to achieve the above values ​​for the MFR of branched polypropylene resin include controlling the average molecular weight and molecular weight distribution. More specifically, methods such as adjusting the hydrogen gas concentration during polymerization, selecting catalysts and / or co-catalysts, and selecting their compositions as appropriate are preferred to control the molecular weight and molecular weight distribution of the polypropylene resin. MFR is an indicator of the fluidity of the resin, showing the amount of resin extruded from the cylinder under constant temperature and load. The lower the viscosity of the resin, the higher the MFR. Generally, molecular weight correlates 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 stretch uniformity, the melt tension of branched polypropylene resin is preferably 3 gf to 40 gf. 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 achieving the above melt tension values ​​include controlling the average molecular weight, molecular weight distribution, and the degree of branching in the polypropylene resin. In particular, the melt tension can be dramatically increased when long-chain branching is present, and a preferred value can be achieved by using a polypropylene resin with long-chain branched molecular chains or by adjusting the degree of branching.

[0051] Several types of branched polypropylene resins are commercially available, including those with Ziegler-Natta catalysts and metallocene catalysts. However, from the perspective of using them in combination with polypropylene resin A, it is more preferable to add a small amount of Ziegler-Natta catalyst-based branched polypropylene resin, which has a broad molecular weight distribution, to supplement its stretchability.

[0052] The polypropylene film of the present invention can contain various resins other than polypropylene, as long as the objectives of the present invention are not impaired. Among these, polyolefin resins are preferred because they have high affinity with polypropylene resin and can improve dispersibility in polypropylene resin. As polyolefin resins, for example, by including poly-4-methylpentene-1 resin (PMP), cyclic olefin polymer (COP), cyclic olefin copolymer (COC), α-olefin elastomer, etc., fine protrusions can be formed on the film surface, thereby improving slipperiness. Among these, poly-4-methylpentene-1 resin (PMP) is particularly preferred due to its high affinity with polypropylene resin.

[0053] In the case of laminated films, a resin other than polypropylene is preferably added to the surface layer from the viewpoint of imparting slipperiness, preferably in the 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 single-layer films, the amount of resin other than polypropylene 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 resin other than polypropylene added is too large, the transparency of the film may deteriorate, or the heat resistance and rigidity may decrease. Also, if the amount added is too small, the effect of imparting slipperiness may be inferior.

[0054] The polypropylene film of the present invention may also contain various additives, such as nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and anticoloring agents, to the extent that it does not impair the objectives 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. Specifically, such antioxidants should be sterically hindered phenolic types, and at least one of them should preferably be a high molecular weight type with a molecular weight of 500 or more. Various specific examples can be given, but for example, it is preferable to use 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox"® 1010: molecular weight 1177.7) alone or in combination with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4).

[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 antioxidants is too low, the polymer may deteriorate during the extrusion process, causing the film to become discolored or resulting in poor long-term heat resistance. If the amount of antioxidants is too high, the transparency may decrease due to the bleeding out of these antioxidants. From the above viewpoint, a more preferable content of antioxidants is 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 nucleating agent to the extent that it does not contradict the purpose. Specific examples of nucleating agents include α-nucleating agents (such as dibenzylidene sorbitol, sodium benzoate, and phosphate ester metal salts) and β-nucleating agents (such as potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, and quinacridone compounds). However, excessive addition of the above-mentioned nucleating agents may cause a decrease in stretchability and a decrease in transparency and strength due to void formation, etc. Therefore, 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, and it is preferable that it is substantially not present.

[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 for inorganic particles, so inorganic particles may detach from the film during the manufacturing process and contaminate the production line and products. In addition, if coarse protrusions are formed by highly hard inorganic particles, these may be transferred to the resin layer of optical components, which may cause a decrease in quality when used as a protective film or manufacturing base film for products requiring high quality, such as display components. From the above viewpoint, it is preferable that the polyolefin film of the present invention does not contain lubricants such as organic particles.

[0059] In the polypropylene film of the present invention, the proportions of polypropylene resin A and branched-chain polypropylene resin relative to the total amount of resin components are preferably as follows: From the viewpoint of heat resistance and mechanical strength of the film, it is preferable that the amount of polypropylene resin A is more than 50% by mass and 99.9% by mass or less. 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. If the film contains two or more components equivalent to polypropylene resin A, these components are added together and considered as the content of polypropylene resin A in the film. The proportion of branched-chain polypropylene resin is preferably 0.1% by mass or more and 30% by mass or less of the total film, with an upper limit of 10% by mass, and even more preferably 5% by mass. If the film contains two or more components equivalent to branched-chain polypropylene resin, these components are added together and considered as the content of branched-chain polypropylene resin in the film.

[0060] The polypropylene film of the present invention preferably has a differential distribution value of 1.0% or more and 10% or less when the logarithmic molecular weight Log(M) = 6.5 in the molecular weight distribution curve measured by gel permeation chromatography. The upper limit is more preferably 8.0%, and even more preferably 6.0%. When the differential distribution value when the logarithmic molecular weight Log(M) is 6.5 is 1.0% or more, there is a sufficient amount of high molecular weight components that become tie molecules when stretched, which improves uniformity during stretching. On the other hand, when the differential distribution value when the logarithmic molecular weight Log(M) is 6.5 is 10% or less, there are fewer molecular chains that relax when heat is applied to the polypropylene film, resulting in a lower thermal shrinkage rate. Furthermore, after the polypropylene film is wound into a roll, shrinkage at room temperature 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 its layer structure and can take the form of 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 mainly composed of polypropylene resin. For example, if the layers mainly composed of polypropylene resin are the surface layer (I) and the base layer (II), then in the case of a laminated structure having these layers, it is preferable that the polypropylene film itself is mainly composed of polypropylene resin, and furthermore, that the main component of the base layer (II), described later, is polypropylene resin. In the case of a laminated structure of polypropylene film, it is more preferable to have at least two layers mainly composed of polypropylene resin. A "layer mainly composed of polypropylene resin" refers to a layer that contains more than 50% by mass and 100% by mass of polypropylene resin when the total components constituting the layer are considered as 100% by mass. Note that the determination of whether or not a layer is a "layer mainly composed of polypropylene resin" shall be made for each layer individually, not for multiple layers as a whole. In the case of a two-layer structure, the layer with the thicker laminate thickness of the two layers 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 it is preferable to contain two or more types of polypropylene resins. If a layer contains two or more components equivalent to polypropylene resins, the layer shall be considered a "layer mainly composed of polypropylene resin" if the sum of these components is more than 50% by mass but not more than 100% by mass.

[0063] The polypropylene resin content in the "layer mainly composed of polypropylene resin" is more preferably 90% to 100% by mass, even more preferably 95% to 100% by mass, even more preferably 96% to 100% by mass, particularly preferably 97% to 100% by mass, and most preferably 98% to 100% by mass, when the total components constituting the layer are considered 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 later, is polypropylene resin.

[0064] The polypropylene film of the present invention is preferably obtained by forming the above-mentioned polypropylene into a sheet and then biaxially stretching it. The biaxial stretching can be performed by any of the following methods: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential biaxial stretching using a roll stretcher and tenter. Among these, sequential biaxial stretching using a roll stretcher and tenter is preferred in terms of controlling film formation stability, thickness uniformity, high rigidity, and dimensional stability of the film.

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

[0066] First, polypropylene resin A and branched polypropylene resin are dry-blended, for example, in a mass ratio of 95:5 and supplied to a single-screw extruder for the base layer (II) (hereinafter sometimes referred to as layer B). Then, polypropylene resin A and poly-4-methylpentene-1 resin are supplied to a single-screw extruder for the surface layer (I) (hereinafter sometimes referred to as layer A) in a mass ratio of 98:2. After that, melt extrusion is performed at 200-280°C, more preferably 220-280°C, and even more preferably 240-270°C. After removing foreign matter and modified polymers using a filter installed in the middle of the polymer tube, the layers are laminated using a multi-manifold type A / B / A layer composite T-die, discharged onto a casting drum, and cooled and solidified to obtain a laminated unstretched sheet having an A / B / A layer structure. In this case, when the layer 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, when there is a layer configuration of layer A / layer B, when the layer 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 layers within the above range, uniform fine protrusions made of poly-4-methylpentene-1 resin can be formed on the film surface, providing slipperiness. Furthermore, the layer configuration may be a two-layer laminate configuration of layer A / layer B, as long as it does not impair the effects of the present invention.

[0067] Furthermore, the casting drum has a surface temperature of 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. Any of the following methods can be used for adhesion to the casting drum: electrostatic application, adhesion using the surface tension of water, air knife method, press roll method, underwater casting method, etc. However, the air knife method is preferred because it provides good flatness and allows for control of surface roughness. From the viewpoint of cooling the uncooled 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 velocity is preferably 130 to 150 m / s. It is also preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation process to prevent vibration of the sheet. In the case of a two-layer laminated configuration with two types of layers, A and B, it is preferable to have the A layer on the casting drum side.

[0068] The obtained unstretched sheet is introduced into the longitudinal stretching process. In the longitudinal stretching process, the unstretched sheet is preheated by contacting it with metal rolls 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 longitudinally by 4.6 to 7.0 times, more preferably 5.2 to 6.8 times, and even more preferably 5.5 to 6.5 times between rolls with a difference in peripheral speed, and then cooled to room temperature. At this time, the distance between the two rolls with a difference in peripheral speed (stretching section) 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 section is preferably 1000 mm. Longitudinal stretching is performed using the difference in peripheral speed of two metal rolls. The film is pressed against the metal rolls using nip rolls while being transported before and after stretching, so that the film does not slip on the metal rolls. The stretched section mentioned above refers to the distance between the nip position of the metal roll before stretching and the nip position of the metal roll after stretching.

[0069] It is preferable to stretch the rolls with a difference in peripheral speed at a temperature of 80°C to 130°C. More preferably, the stretching temperature is 80°C to 125°C, and even more preferably 80°C to 120°C. It is also preferable to place radiation heaters on the upper and lower sides of the two rolls with a difference in peripheral speed and stretch the sheet while heating it from both sides. The output of the radiation heaters is preferably 1.0 kW or more for both the upper and lower sides, more preferably 2.0 kW or more, and even more preferably 2.6 kW or more. The distance between the heat source of the radiation heater and the sheet surface is preferably 10 mm to 200 mm. By setting the rolls in the preheating process for stretching and the rolls with a difference in peripheral speed to a low temperature, the relaxation of the molecular chains of the polypropylene resin is minimized, and by heating them rapidly with the radiation heaters and stretching them simultaneously, it is possible to stretch more uniformly even in this formulation which has few high molecular weight components. In addition, by lengthening the stretching section, the neck-down during stretching increases, and the film becomes uniformly highly oriented. Therefore, it is effective in improving the Young's modulus of the resulting polypropylene film in the direction orthogonal to the main orientation.

[0070] Next, the uniaxially oriented film obtained in the longitudinal stretching process is guided to a tenter by clipping both ends in the width direction and preheated, and then transversely stretched to 8.5 to 14 times, more preferably 9.0 to 13 times, and even more preferably 9.5 to 12 times in the width direction. 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 raising the preheating temperature by 5°C or more, preferably 8°C or more, and more preferably 10°C or more than the stretching temperature, uniform high-orientation stretching can be achieved across the entire width of the film, leading to improved tensile elongation and a reduction in crystallite size. Because uniaxially oriented films exhibit significant neck-down, they have a narrower film width, and even when stretched laterally using a standard tenter rail pattern, the lateral stretching ratio can be increased. Therefore, this type of stretching is preferable from the viewpoint of improving heat resistance.

[0071] In the subsequent heat treatment and relaxation processes, the film is held taut in the width direction with clips while being relaxed by a relaxation rate of 12-20%, more preferably 14-20%, and even more preferably 16-20% in the width direction, and then heat-set at a temperature of 165°C to less than 180°C, more preferably 168°C to less than 180°C, and even more preferably 170°C to less than 180°C. The film is then guided to the outside of the tenter after a cooling process at 80-100°C while still held taut in the width direction with clips. The clips at the ends of the resulting polypropylene film are released, the film edges are slit in the winder process, and the polypropylene film is wound into a product roll. By setting the heat treatment temperature to 5°C or more, more preferably 8°C or more, and even more preferably 10°C or more higher than the transverse stretching temperature, residual stress in the polypropylene film can be relieved, reducing the thermal shrinkage rate and improving the tensile elongation.

[0072] Furthermore, it is preferable to heat the polypropylene film as it passes through the bridges after emerging from the tenter using a hot roll, from the viewpoint of improving heat resistance and tensile elongation. The heating temperature is preferably 80 to 120°C, and more preferably 90 to 110°C. At temperatures above 120°C, the smoothness between the hot roll and the polypropylene film may be impaired, causing wrinkles and deterioration of 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 in a variety of industrial applications, such as packaging films, surface protection films, process films, sanitary products, agricultural products, building materials, medical products, and capacitor films. However, it is particularly preferable to use it as a packaging film, surface protection film, process film, or release film due to its excellent heat resistance, mechanical strength, and quality. Here, a surface protection film is a film that is attached to an object such as a molded body or film to prevent scratches and contamination that occur during processing or transportation. A process film is a film that is attached to an object such as a molded body or film to prevent scratches and contamination that occur during manufacturing or processing, and is discarded when the final product is used. A release film is a film that has high release properties and is attached to an object such as a molded body or film to prevent scratches and contamination that occur during processing or transportation, and can be easily peeled off and discarded when the final product is used. A packaging film is a film used to wrap items, such as food products, in order to improve the quality, storage efficiency, and convenience of use of those items. [Examples]

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

[0075] (1) Film thickness Measurements were taken using a micro-thickness gauge (manufactured by Anritsu Corporation). A 10cm square sample of polypropylene film was taken, and five measurements were taken at arbitrary points. The average value was taken as the film thickness (μm).

[0076] (2)tanδ(loss tangent) A rectangular test specimen (5 mm wide x 20 mm long) cut from polypropylene film with the main orientation direction as the longer side was mounted on the apparatus chuck under a nitrogen atmosphere at 23°C. It was then cooled to -100°C, and the tanδ was measured from -100°C to 180°C using the following apparatus and conditions. A viscoelastic-temperature curve was drawn using the dynamic viscoelastic method, and Dmax, Dmin, and L were calculated using the tanδ at each temperature, as shown in Figures 1 and 2.p The following was determined. The test was conducted with n=3, and the average values ​​were used for Dmax, Dmin, and L of the polypropylene film. p That's what I decided. <Equipment and Measurement Conditions> Device: Rheogel-E4000 (manufactured by UBM) Geometry: Tension Chuck spacing: 10mm Frequency: 10Hz Distortion: 0.1-0.2% Temperature range: -100 to 180°C Heating rate: 5°C / min Measurement environment: Under nitrogen.

[0077] (3) Young's modulus A rectangular sample measuring 150 mm (measurement direction) x 10 mm was cut from a polypropylene film, with the measurement direction set to an arbitrary direction. The sample was set on a tensile testing machine (Orientec "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 50 mm, and pulled in the measurement direction. A tensile test was then performed on the film 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 taken as the Young's modulus of the sample in the measurement direction. Next, with the measurement direction set to 0°, the Young's modulus was similarly measured in each direction forming an angle from 0° to 175° in 5° increments relative to the measurement direction, and the direction showing the highest value was taken as the principal orientation direction.

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

[0079] (5) Tensile elongation in the direction perpendicular to the principal orientation at 90°C A rectangular sample measuring 150 mm in length (orthogonal to the principal orientation) and 10 mm in width was cut from a polypropylene film. The sample, still in its chuck, was placed in an oven heated to 90°C for 1 minute. After heating, the sample was placed in a tensile testing machine (Orientec "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 50 mm, and pulled in the width direction. A tensile test was then performed on the film at a tensile 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 value obtained was taken as the tensile elongation of the sample in the direction orthogonal to the principal orientation at 90°C.

[0080] (6) Principal orientation and crystallite size of α(110) in the direction orthogonal thereto A polypropylene film was cut into strips 4 cm long (in the principal orientation direction) and 1 mm wide (in the direction perpendicular to the principal orientation direction), and stacked to a thickness of 1 mm to prepare the sample. The sample was placed between the X-ray source and the detector so that X-rays could pass 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. From the obtained diffraction profile, the crystallite size in the principal orientation direction was determined from the full width at half maximum βe of the crystal peak at 2θ = approximately 14° (α-crystal (110) plane) using the following equations (1) and (2). Similarly, the crystallite size in the direction perpendicular to the principal orientation was also determined for polypropylene films cut into strips 4 cm long (in the direction perpendicular to the principal orientation direction) and 1 mm wide (in the principal orientation direction). The measurement apparatus and conditions were as follows.

[0081]

number

[0082]

number

[0083] Here, λ is the X-ray wavelength (=0.15418 nm), βe is the full width at half maximum of the diffraction peak, βo is the correction value for the full width at half maximum (=0.6), and K is the Scherrer constant (=1.0). (Measuring device) • X-ray diffractometer: Brucker AXS D8 ADVANCE (sealed tube type) ·X-ray source: CuKα ray Output: 40kV-40mA • Slit system: DS = 0.3° • Detector: LynxEye (high-speed detector) • Scan: 2θ-θ continuous scan • Measurement range: 2θ = 5~80° Step width: 0.02° • Scanning speed: 1 second / step.

[0084] (7) Crystallization temperature T determined by extrapolation method c0 Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), a 3 mg polypropylene film was heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere and held for 5 minutes. Then, it was cooled from 250°C to 25°C at a rate of 10°C / min, and the peak temperature of the exothermic curve obtained during this cooling was recorded as Tc 10 The polypropylene film was then heated from 25°C to 250°C at a rate of 20°C / min and held for 5 minutes. Next, it was cooled from 250°C to 25°C at a rate of 40°C / min, and the peak temperature of the exothermic curve obtained during this cooling was defined as Tc 40 Next, as shown in Figure 3, the cooling rate was plotted on the horizontal axis and the crystallization temperature obtained for each cooling rate was plotted on the vertical axis, and Tc 40 From Tc 10 A straight line was drawn towards the target, and the crystallization temperature obtained by extrapolating to a cooling rate of 0°C / min was defined as Tc0. 10 Tc 40 In cases where multiple peak temperatures were observed during measurement, the highest peak temperature in the range of 80°C to 130°C was used as the crystallization temperature of the polypropylene film. Measurements were performed three times for each sample, and the average value was used for evaluation.

[0085] (8) Melting point Tm Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), a 3 mg polypropylene film was heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere. The peak temperature of the endothermic curve obtained during this heating process was defined as Tm(°C). Each sample was measured three times, and the average value of the obtained measurements was taken as the Tm(°C) of the polypropylene film.

[0086] (9) Static friction coefficient μs in the direction orthogonal to the main orientation after heat treatment at 90°C for 10 minutes Polypropylene film was cut to a width of 6.5 cm (in the direction of the main film orientation) and a length of 12 cm (in the direction perpendicular to the main film orientation). The test piece was sandwiched between paper and heated for 10 minutes in an oven maintained at 130°C with no load. After removal and cooling to room temperature, it was measured using a slip tester manufactured by Toyo Seiki Co., Ltd., in accordance with JIS K 7125 (1999), at 25°C and 65% RH. The measurement was performed with the main orientations perpendicular to each other and with different front and back surfaces of the films overlapping, that is, with the front surface of one film in contact with the back surface of the other film. The same measurement was performed 5 times for each sample, and the average value obtained was calculated and taken as the static friction coefficient (μs) of the polypropylene film.

[0087] (10) Melt tension Measurements were performed using equipment conforming to JIS K 7199 (1999) under the following conditions. • Equipment: Capillograph with melt tension tester 1BPMD-i (manufactured by Toyo Seiki Co., Ltd.) • Temperature: 230℃ (using a temperature-retaining chamber) Die: L=8(mm), D=2.095(mm) • Extrusion speed: 20 mm / min • Pickup speed: 15.7m / min Sample mass: 15-20g.

[0088] (11) Flatness of the film when heated An acrylic adhesive (manufactured by Soken Chemical Co., Ltd., "SK Dyne" (registered trademark) 1310) was diluted with ethyl acetate, toluene, and methyl ethyl ketone (MEK) on one side of a 500 mm wide polypropylene film. 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 solid content of the adhesive. This coating for the adhesive layer was applied using a gravure coater, and then transported to a 90°C drying oven for 30 seconds to remove the solvent from the coating, obtaining an adhesive film with an adhesive layer thickness of 1 μm. This adhesive film was then wound into a 200 m roll to form an adhesive film roll. Next, 1 m of the 500 mm wide adhesive film was unwound and subjected to free tension (the film hanging vertically due to its own weight), and uniform tensions of 1 kg / m and 3 kg / m were applied evenly across the entire width of the film. The presence or absence of defects in flatness such as wrinkles and dents was visually checked. The evaluation was conducted according to the following criteria. S: There were no areas with poor flatness under free tension. A: Areas with poor flatness were observed under free tension, but these areas with poor flatness disappeared under tension of 1 kg / m width. B: At a tension of 1 kg / m width, areas of flatness were observed, but at a tension of 3 kg / m width, these areas of flatness disappeared. Even with a tension of 3 kg / m width, areas of poor flatness were observed.

[0089] (12) Film fracture when high tension is applied A 500mm wide polypropylene film was introduced into a 90°C drying oven, and the tension was increased at a speed of 100 N / s to a predetermined level. After reaching the predetermined tension, the film was transported under tension for 30 seconds, and the presence or absence of breakage in the polypropylene film was visually confirmed. S: It did not break even under tensions of 400N or more. A: It fractured under a tension of 300N or more but less than 400N. B: It fractured under a tension of 200N or more but less than 300N. C: Fractured under a tension of less than 200N.

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

[0091] Furthermore, the weight-average molecular weight Mw and Z-average molecular weight Mz of the sample were determined using a molecular weight calibration curve created with the standard samples listed below. • Equipment: Agilent PL-GPC220 high-temperature GPC system • Detector: Agilent differential refractive index detector (RI detector) • Columns: Agilent PL1110-6200 (20μm MIXED-A) x 2 ·Flow rate: 1.0mL / min Column temperature: 145℃ ·Injection volume: 0.500mL • Sample concentration: 0.1 wt% • Standard samples: Monodisperse polystyrene manufactured by Tosoh Corporation, dibenzyl manufactured by Tokyo Chemical Industry Co., Ltd.

[0092] (14) Cold xylene soluble part (CXS) For the raw material, 0.5g of polypropylene resin was dissolved in 100ml of xylene at 135°C, allowed to cool, and then recrystallized in a constant temperature water bath at 20°C for 1 hour. The polypropylene components dissolved in the filtrate were then quantified by liquid chromatography. The amount of polypropylene components dissolved in the filtrate was X(g), and the refined weight of the 0.5g sample was X0(g). The following formula was used to calculate the polypropylene components. Formula: CXS(mass%)=(X / X0)×100.

[0093] (15) Maximum height (St) Measurements were performed using Ryoka Systems Co., Ltd.'s "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC. The surface shape was determined by correcting the captured image using a fourth-order polynomial approximation with the included analysis software. The maximum height (St) is 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, n=3 (number of measurements = 3), and the average value for each surface was used as the St for each surface. The larger of the St values ​​from both sides of the film is listed in the table. • Device: “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: 530nm white • Measurement mode: Wave • Measurement software: VS-Measure Version 5.5.1 • Analysis software: VS-Viewer Version 5.5.1 ·Measurement area: 1.252mm x 0.939mm.

[0094] (Polypropylene resin, etc.) For the production of the polypropylene films in the examples and comparative examples, polypropylene resins having the molecular weight distribution Mz / Mw and CXS shown in Table 1 below were used. 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-chain 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-chain polypropylene resin 1 (branched PP1): Ziegler-Natta catalyst-based branched-chain polypropylene resin (PF-814, manufactured by Basell, melt tension: 15 gf, MFR: 3.0) Branched-chain polypropylene resin 2 (branched PP2): Metallocene catalyst-based branched-chain polypropylene resin ("WAYMAX" (registered trademark) MFX6, manufactured by Nippon Polypropylene Co., Ltd., melt tension: 13 gf, MFR: 3.0).

[0096] [Table 1]

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

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

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

[0100] (Example 1) For the surface layer (I), polypropylene resin 2 and polypropylene raw material D were dry-blended in a mass ratio of 80:20 and supplied to a single-screw extruder for the surface layer (I). For the base layer (II), polypropylene resin 1 and branched-chain polypropylene resin 1 were dry-blended in a mass ratio of 95:5 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) were laminated in a thickness ratio of 1 / 30 / 1 using a feed-block type A / B / A composite T-die. The laminated material was then extruded into a casting drum with a surface temperature controlled to 25°C, and air at a temperature of 20°C was blown onto it at a speed of 140 m / s using an air knife to ensure close contact with the casting drum. Subsequently, the uncooled drum surface of the sheet on the casting drum was cooled by blowing 20°C compressed air at an air velocity of 140 m / s to obtain an unstretched sheet. Next, the unstretched sheet was preheated to 135°C with ceramic rolls, 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 difference in peripheral speed. The heat source of the radiation heater was fixed at a distance of 90 mm from the sheet surface. The distance between the rolls with the difference in peripheral speed was 320 mm, and the output of the radiation heater was set to 2.8 kW. Next, the obtained uniaxially oriented film was introduced into a tenter-type stretcher with both ends in the width direction gripped with clips, preheated at 176°C for 3 seconds, stretched 9.8 times in the width direction at 153°C, and then heat-treated at 178°C while allowing 20% ​​relaxation in the width direction. Subsequently, after a cooling process at 100°C, the film was guided to the outside of the tenter, the clips at both ends in the film width direction were released, and the film was heated for 1.8 seconds on a 110°C hot roll before being wound onto a core to obtain a 24 μm thick polypropylene film. The physical properties and evaluation results of the obtained film are shown in Table 2.

[0101] (Examples 2-5, Comparative Examples 1-4) 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. In this case, the thickness was adjusted by adjusting the discharge amount during extrusion and the speed of the casting drum. The physical properties and evaluation results of the obtained films are shown in Table 2. Regarding the mixing of the raw materials for the surface layer, in the surface layer (I) of Comparative Example 2, polypropylene resin 2 and polypropylene raw material D were dry-blended in a ratio of 80:20 (mass ratio), similar to the surface layer (I) of Example 1, while in the surface layer (I) of Example 4, polypropylene resin 3 and polypropylene raw material E were dry-blended in a ratio of 70:30 (mass ratio). In the surface layer (I) and base layer (II) of the other examples, polypropylene raw materials D and E were not used, and each resin component was dry-blended in the ratios shown in Table 2. In addition, in Example 4, the surface layer (I) side was brought into contact with the cast roll.

[0102] [Table 2]

[0103] Examples 3 and Comparative Examples 1 and 4 were treated as having a single-layer structure, and therefore the surface layer (I) was considered absent. [Industrial applicability]

[0104] As described above, the polypropylene film of the present invention can be used in a variety of industrial applications, including packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, medical products, and capacitor films. In particular, it is preferable to use it as a surface protection film, process film, or release film because of its excellent heat resistance, mechanical strength, and quality.

Claims

1. A polypropylene film characterized in that the maximum value Dmax and minimum value Dmin of tanδ in the main orientation direction in the range of -10°C to 50°C satisfy the relationship in Equation 1, the tensile elongation in the direction orthogonal to the main orientation at 90°C is 90% 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 polypropylene film according to claim 1, wherein when LP is the maximum value of tanδ in the main orientation direction at -30°C or higher and less than 30°C, the temperature at which tanδ in the main orientation direction becomes equal to LP in the range of 30°C or higher and less than 150°C is 80°C or lower.

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

4. A polypropylene film according to any one of claims 1 to 3, wherein the crystallization temperature at a cooling rate of 0°C / min is determined by extrapolation using the crystallization temperature Tc10 (°C) measured at a cooling rate of 10°C / min and the crystallization temperature Tc40 (°C) measured at a cooling rate of 40°C / min, and the crystallization temperature at a cooling rate of 0°C / min is determined by extrapolation, and the melting point of the polypropylene film is Tm (°C), such that Tc0 + Tm ≥ 280.

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

7. A polypropylene film according to any one of claims 1 to 6, wherein the molecular weight distribution Mz / Mw is less than 4.

5.

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

9. A 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 having a polypropylene film according to any one of claims 1 to 9.

11. A release film having a polypropylene film according to any one of claims 1 to 9.

12. A surface protective film having a polypropylene film according to any one of claims 1 to 9.

Images