Polypropylene film

Abstract

This polypropylene film is characterized in that the tanδ of the main orientation direction at 150ºC is 0.25 or less and the Young's modulus of a direction orthogonal to the main orientation direction is 50 MPa or more at 130ºC.　The present invention provides a polypropylene film with excellent heat resistance, mechanical strength, and quality.

Description

[Technical Field]

[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 film. [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 in capacitor applications.

[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 after lamination for heat curing. Also, in capacitor applications, it is used in the high-temperature environment inside motors. Thus, the required level of heat resistance for films used in industrial materials and capacitor applications has been increasing in recent years.

[0004] However, conventional polypropylene films have a lower melting point compared to polyethylene terephthalate (PET) films, and their heat resistance is insufficient in processes above 100°C, limiting their applications. For example, since polypropylene films generally have a melting point of around 160°C, they exhibit high shrinkage and insufficient mechanical strength in temperatures close to their melting point, such as 150°C, making them unsuitable for use as process films in high-temperature environments.

[0005] One indicator of heat resistance is thermal shrinkage stress. Thermal shrinkage stress is the stress that acts in the shrinkage direction when a film is heated to a predetermined temperature while being held at a certain length. If the thermal shrinkage stress is high, problems such as warping or delamination may occur when the film is bonded to an adherend at a predetermined temperature. Generally, methods to reduce thermal shrinkage stress include relaxing the orientation of amorphous components by applying heat treatment at high temperatures, or reducing high molecular weight components by using low molecular weight polypropylene resin. However, relaxing amorphous components by high-temperature heat treatment can reduce thermal shrinkage stress, but it can also reduce mechanical strength at high temperatures. In addition, low molecular weight polypropylene resins have low melt tension when softened by heating, and using low molecular weight polypropylene resins can reduce film-forming properties. For these reasons, it has been difficult to achieve both low thermal shrinkage stress and low mechanical strength and film-forming properties at high temperatures.

[0006] As examples of polypropylene films with improved heat resistance, Patent Document 1 describes an example in which thermal shrinkage stress was reduced by adjusting the preheating roll temperature during longitudinal stretching using a highly crystalline polypropylene resin. Patent Documents 2 and 3 also describe examples in which the thermal shrinkage rate was reduced by increasing the crystallinity using a polypropylene resin mainly composed of low molecular weight components. Furthermore, Patent Document 4 describes an example in which the voltage resistance at high temperatures was improved and shrinkage stress was reduced by using a polypropylene resin with a low amount of polypropylene components dissolved in xylene. [Prior art documents] [Patent Documents]

[0007] [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 project] [Problems that the invention aims to solve]

[0008] However, while the methods described in Patent Documents 1 and 4 improve heat resistance, there is a problem in that further improvement in heat resistance is necessary when considering use in the above-mentioned applications. In addition, the method described in Patent Document 2 has a low Young's modulus at high temperatures, which can lead to deterioration of the film's flatness or even breakage when transported at high temperatures and high tension near the film's melting point. Furthermore, the polypropylene film described in Patent Document 3 has a high thermal shrinkage rate in the main orientation direction, which causes the film to shrink and wrinkle easily when transported at high temperatures.Therefore, the object of the present invention is to solve the above-mentioned problems. That is, to provide a polypropylene film with excellent heat resistance, mechanical strength, and quality. [Means for solving the problem]

[0009] To solve the above-mentioned problems, the polypropylene film of the present invention has the following configuration. Specifically, the polypropylene film of the present invention is characterized in that the tanδ in the main orientation direction at 150°C is 0.25 or less, and the Young's modulus in the direction orthogonal to the main orientation at 130°C is 50 MPa or more. [Effects of the Invention]

[0010] Because the polypropylene film of the present invention has excellent heat resistance, mechanical strength, and quality, it can be widely and suitably used as an industrial material film, surface protection film, process film, release film, and capacitor film, etc. [Brief explanation of the drawing]

[0011] [Figure 1] This is an example of a graph showing the temperature dependence of tanδ in a polypropylene film. [Figure 2]This is an example of a graph showing the crystallization temperature Tc0 of a polypropylene film.

Embodiments for Carrying out the Invention

[0012] The polypropylene film of the present invention is a polypropylene film characterized in that tanδ in the main orientation direction at 150 °C is not more than 0.25, and the Young's modulus in the direction perpendicular to the main orientation at 130 °C is 50 MPa or more.

[0013] The polypropylene film refers to a film containing polypropylene resin in an amount exceeding 50% by mass and not exceeding 100% by mass when the total components constituting the film are 100% by mass. The content of the polypropylene resin in the polypropylene film is preferably 70% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, still more preferably 95% by mass or more and 100% by mass or less, particularly preferably 96% by mass or more and 100% by mass or less, and most preferably 97% by mass or more and 100% by mass or less when the total components constituting the film are 100% by mass. In the case where a plurality of components corresponding to the polypropylene resin are contained, if the total of these components exceeds 50% by mass and does not exceed 100% by mass, it shall be regarded as a polypropylene film. The polypropylene resin refers to a resin in which the propylene unit occupies more than 50 mol% and not more than 100 mol% of all the constituent units constituting the resin.

[0014] From the perspective of improving heat resistance, it is important that the tanδ in the main orientation direction at 150°C of the polypropylene film of the present invention is 0.25 or less. From the above perspective, the tanδ in the main orientation direction at 150°C is preferably 0.23 or less, more preferably 0.21 or less, and even more preferably 0.19 or less. Tanδ is also called the loss tangent and correlates with the degree of molecular chain mobility in the film. Generally, as shown in FIG. 1, in the region above 100°C, it increases as the temperature rises. The tanδ in the main orientation direction at 150°C is an index that correlates with the degree of molecular chain mobility in the film near 150°C. The inventors have found that reducing this value, in other words, suppressing the movement of molecular chains at high temperatures, can suppress the heat shrinkage stress of the polypropylene film under high temperatures and enhance the heat resistance. Note that the smaller the tanδ in the main orientation direction at 150°C, the better, and the lower limit is not particularly limited, but is substantially about 0.01.

[0015] Here, the main orientation direction in the present invention refers to the direction in the film plane. When the Young's modulus is measured at each angle of 0° to 175° in 5° increments with respect to an arbitrary direction taken as 0°, the direction showing the highest value is the main orientation direction. The direction orthogonal to the main orientation direction refers to the direction orthogonal to the main orientation direction in the film plane. The Young's modulus can be measured using a tensile testing machine, and the details of the measurement method are shown in the examples. When the width of the sample is less than 50 mm and the Young's modulus cannot be obtained with a tensile testing machine, the crystal orientation of the α crystal (110) plane of the polypropylene film by wide-angle X-ray is measured as follows, and the main orientation direction is determined based on the following criteria. That is, X-rays (CuKα rays) are incident perpendicular to the film surface, and the crystal peak at 2θ = about 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 taken as the main orientation direction, and the direction orthogonal to it is taken as the direction orthogonal to the main orientation direction. Also, in the present invention, the direction parallel to the film-forming direction of the polypropylene film is called 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 called the width direction or the TD direction.

[0016] If the tanδ in the main orientation direction at 150°C is greater than 0.25, the heat resistance of the polypropylene film is insufficient. Therefore, if such a polypropylene film is used as a process film or release film, the quality may be compromised due to warping or partial delamination of the adherend when it is bonded to the adherend and passed through a high-temperature process, caused by the difference in thermal shrinkage stress between the film and the adherend. The tanδ in the main orientation direction at 150°C can be measured using dynamic viscoelasticity, and details of the measurement method are shown in the examples.

[0017] To achieve a tanδ of 0.25 or less in the main orientation direction at 150°C, 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, it is effective to use a highly crystalline resin with a narrow molecular weight distribution Mz / Mw, a significantly reduced high molecular weight component, and a low cold xylene soluble portion (CXS), and to relax the shrinkage in the width direction at high temperatures after transverse stretching, thereby shrinking the film in the main orientation direction (for example, a relaxation rate of 12% or more).

[0018] From the viewpoint of increasing mechanical strength, the polypropylene film of the present invention has a Young's modulus of 50 MPa or more in the direction orthogonal to the main orientation at 130°C, preferably 70 MPa or more, more preferably 90 MPa or more, and even more preferably 110 MPa or more. If the Young's modulus in the direction orthogonal to the main orientation at 130°C is less than 50 MPa, the mechanical strength will be insufficient. Therefore, when the polypropylene film is used as a process film or release film, if high tension is applied in the direction orthogonal to the main orientation at the time when it is bonded to the adherend and passes through a high-temperature process, the polypropylene film may deform, wrinkle, or break. The higher the Young's modulus in the direction orthogonal to the main orientation at 130°C, the better, and although there is no particular upper limit, it is substantially around 10,000 MPa. Furthermore, the Young's modulus in the direction orthogonal to the main orientation at 130°C can be measured using a tensile testing machine equipped with an oven capable of high-temperature heating, and details of the measurement method are shown in the examples.

[0019] When high-temperature heat treatment is applied to reduce tanδ and relax the shrinkage of amorphous components, the Young's modulus may decrease. Furthermore, while it was common practice to increase Young's modulus by stretching at high stretch ratios, resins with reduced high molecular weight components exhibit lower melt tension when softened by heating, leading to decreased film-forming stability and potentially preventing stretching at high ratios. For these reasons, achieving both low tanδ and high Young's modulus in polypropylene films, particularly at high temperatures, has traditionally been difficult. However, by using methods that define the composition of the polypropylene film within the range described later, and the film-forming conditions within the range described later, it is possible to achieve both low tanδ and high Young's modulus. In particular, using a highly crystalline resin with a low cold xylene-soluble portion (CXS) and setting the casting drum temperature to a low temperature (10°C to 40°C) to uniformly refine the spherulites in the unstretched sheet, and then lengthening the stretching section during longitudinal stretching, while thoroughly heating both sides with a radiation heater during the stretching section, is effective in reducing stretching stress and uniformly stretching the film longitudinally.

[0020] From the viewpoint of quality, the polypropylene film of the present invention preferably has a tanδ in the direction orthogonal to the main orientation at 150°C of 0.25 or less, more preferably 0.23 or less, even more preferably 0.21 or less, and particularly preferably 0.19 or less. The tanδ in the direction orthogonal to the main orientation at 150°C is an index that correlates with the degree of mobility of molecular chains in the film around 150°C, and reducing this value improves the heat resistance of the film. If the tanδ in the direction orthogonal to the main orientation at 150°C is greater than 0.25, the polypropylene film may shrink in the direction orthogonal to the main orientation when wound as a roll and stored at high temperatures, causing wrinkles in the roll and impairing its quality. The lower limit of the tanδ in the direction orthogonal to the main orientation at 150°C is preferably as small as possible and is not particularly limited, but is substantially around 0.01. The tanδ in the direction orthogonal to the main orientation at 150°C can be measured by the same method as the tanδ in the main orientation at 150°C.

[0021] To achieve a tanδ of 0.25 or less in the direction orthogonal to the main orientation at 150°C, or within the preferred range described above, the composition of the polypropylene film and the film-forming conditions can be adjusted to the range described later. In particular, it is effective to use a highly crystalline resin with a narrow molecular weight distribution Mz / Mw, a significantly reduced high molecular weight component, and a low cold xylene soluble portion (CXS); to uniformly refine the spherulites in the unstretched sheet by setting the casting drum temperature to a low temperature (10°C to 40°C); to lengthen the stretching section during longitudinal stretching; to stretch the film uniformly in the longitudinal stretching section while sufficiently heating both sides with a radiation heater to reduce the stretching stress; and to shrink the film in the direction orthogonal to the main orientation by loosening the conveying tension in the conveying flow direction on a high-temperature roll after transverse stretching.

[0022] From the viewpoint of quality, the polypropylene film of the present invention has a loss modulus of elasticity E'' in the direction orthogonal to the main orientation at 0°C of 3.5 × 10 8 It is preferable that the pressure is Pa or less. More preferably, 3.0 × 10 8 Pa or less, more preferably 2.5 × 10 8 Pa or less, particularly preferably 2.0 × 10 8 It is less than or equal to Pa. The smaller the value of the loss modulus E'' in the direction orthogonal to the principal orientation at 0°C, the better, and although there is no particular lower limit, it is practically 0.1 × 10⁻⁶. 8 It is approximately Pa. The loss modulus E'' in the direction orthogonal to the principal orientation at 0°C can be measured using dynamic viscoelasticity, and details of the measurement method are shown in the examples.

[0023] The loss modulus E'' correlates with the degree of relaxation of molecular chains in polypropylene film, and the loss modulus E'' in the direction orthogonal to the principal orientation at 0°C is 3.5 × 10⁻⁶. 8 When the Pa value is greater than Pa, the degree of amorphous relaxation around 0°C increases. As a result, when polypropylene film is wound into a roll and stored at or near room temperature, the polypropylene film may shrink in the direction perpendicular to the principal orientation, causing wrinkles in the roll and compromising its quality.

[0024] The loss modulus E'' in the direction orthogonal to the principal orientation at 0°C is 3.5 × 10⁻⁶. 8 To achieve a Pa or lower pressure, 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, it is effective to use a resin with a high crystallization temperature to reduce the size of spherulites formed during casting, and to uniformly refine the spherulites in the unstretched sheet by setting the temperature of the casting drum to a low temperature (10°C to 40°C), and then to lengthen the stretching section during longitudinal stretching, and to stretch the film longitudinally while sufficiently heating both sides with a radiation heater during the stretching section.

[0025] The polypropylene film of the present invention preferably has a product of the Young's modulus in the direction orthogonal to the main orientation at 130°C and the film thickness of 500 N / m or more, more preferably 700 N / m or more, even more preferably 900 N / m or more, and particularly preferably 1100 N / m or more. The product of the Young's modulus in the direction orthogonal to the main orientation at 130°C and the film thickness corresponds to the tension per unit width of the film generated when the film is pulled in the direction orthogonal to the main orientation at 130°C. If this value is less than 500 N / m, problems may occur when the film is exposed to high temperatures during the processing steps. For example, when a polypropylene film is used as a release film, if high tension is applied in the direction orthogonal to the main orientation at the time when it is laminated with a particularly easily deformable substrate and passed through a high-temperature process, deterioration of the film's flatness, deformation of the substrate, and breakage of the film may occur. From the above viewpoint, there is no particular upper limit to the product of the Young's modulus in the direction orthogonal to the main orientation at 130°C and the film thickness, but it is substantially around 1,000,000 N / m. The thickness of the polypropylene film can be measured using a known micro-thickness gauge.

[0026] As a method of setting the product of the Young's modulus in the direction orthogonal to the main orientation at 130°C and the film thickness to 500 N / m or more 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 later and the film-forming conditions are within the range described later. In particular, by using a highly crystalline resin with a low cold xylene-soluble part (CXS) or by lowering the temperature of the casting drum to uniformly refine the spherulites in the unstretched sheet, and then lengthening the stretching section during longitudinal stretching and stretching while sufficiently heating both sides with a radiation heater in the stretching section, it is effective to longitudinally stretch the film uniformly while reducing the stretching stress. Also, the product of the Young's modulus in the direction orthogonal to the main orientation at 130°C and the film thickness can be adjusted by adjusting the thickness.

[0027] The thickness of the polypropylene film of the present invention is appropriately adjusted according to the application and is not particularly limited, but it is preferably 0.5 μm or more and 100 μm or less from the viewpoint of handling properties. The upper limit of the thickness is more preferably 60 μm, further preferably 30 μm, and particularly preferably 16 μm. The lower limit is more preferably 0.9 μm, further preferably 4.0 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 reduce other physical properties.

[0028] The polypropylene film of the present invention has a crystallization temperature Tc 10 (°C) measured at a temperature drop rate of 10°C / min and a crystallization temperature Tc 40 (°C) measured at a temperature drop rate of 40°C / min. When the crystallization temperature at a temperature drop rate of 0°C / min obtained by the extrapolation point method using these is defined as Tc0 (°C) and the melting point of the film is defined as Tm (°C), it is preferable that Tc0 + Tm ≥ 280. The value of Tc0 + Tm is more preferably 285 or more, and further preferably 290 or more. Tc0 is an index of the ease of crystallization, and the higher Tc0 is, the easier it is to crystallize. Also, Tm is the melting point of the film, and the higher Tm is, the higher the heat resistance of the film. The upper limit of the value of Tc0 + Tm is not particularly limited, but is substantially about 350.

[0029] By setting the Tc0+Tm value to 280 or higher, the film has a high melting point and exhibits high heat resistance even in temperature ranges close to the melting point, such as 150°C. Furthermore, in this configuration, crystallization proceeds quickly, and coarse spherulites are less likely to form during casting. As a result, the structure of the polypropylene film becomes more uniform, reducing breakage during stretching and the decrease in film strength.

[0030] Tc 10 and Tc 40 This can be measured using a differential scanning calorimeter (DSC) by the following procedure. Specifically, 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 held for 5 minutes. Then, it is cooled from 250°C to 25°C at a rate of 10°C / min. The peak temperature of the exothermic curve obtained during this cooling is called Tc 10 The polypropylene film is heated from 25°C to 250°C at a rate of 20°C / min and held for 5 minutes. Then, it is cooled from 250°C to 25°C at a rate of 40°C / min. The peak temperature of the exothermic curve obtained during this cooling is defined as Tc 40 Next, as shown in Figure 2, plot the cooling rate on the horizontal axis and the crystallization temperature obtained for each cooling rate on the vertical axis, and Tc 40 From Tc 10 A straight line is drawn towards the target, and the crystallization temperature Tc0 is defined as the temperature obtained when the cooling rate is extrapolated to 0°C / min. If multiple peak temperatures are observed, the temperature of the highest peak in the range of 80°C to 130°C is used as the crystallization temperature of the polypropylene film. The DSC is not particularly limited as long as it is capable of measurement and any known DSC can be used; for example, the EXSTAR DSC6220 manufactured by Seiko Instruments can be used.

[0031] To achieve a Tc0+Tm value of 280 or higher or within the preferred range described above, methods for increasing Tc0 and Tm can be used individually or in combination. To increase Tc0, a method can be used in which the composition of the polypropylene film is within the range described later. In particular, it is preferable to include a component that has nucleating agent activity, and among these, it is preferable to include branched polypropylene. Furthermore, to increase Tm, 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, it is preferable to use a highly crystalline resin with a low cold xylene soluble portion (CXS).

[0032] From the viewpoint of reducing quality degradation after exposure to high-temperature environments, the polypropylene film of the present invention preferably has a static friction coefficient μs of 0.80 or less after heat treatment at 130°C for 10 minutes. More preferably it is 0.70 or less, even more preferably 0.60 or less, and particularly preferably 0.50 or less. When polypropylene film is used as a protective film, it may go through various high-temperature processes. For example, when polypropylene film is used as a release film for thermosetting resins, it may be heat-cured at a temperature of 100°C or higher after being laminated to the thermosetting resin. Polypropylene film generally has lower heat resistance compared to polyester films commonly used as process films, and when subjected to temperatures of 100°C or higher, the surface softens or deforms, and the static friction coefficient increases excessively. As a result, slipperiness is impaired, and winding misalignment may occur when winding the film after the heating process.

[0033] A μs of 0.80 or less after heating at a higher temperature of 130°C reduces the likelihood of wrinkles forming on the conveyor roll when passing through high-temperature processes above 100°C, and also reduces winding misalignment when winding together with the workpiece. There is no particular lower limit to the static friction coefficient μs after heating at 130°C for 10 minutes, but it is practically around 0.10.

[0034] To achieve a μs of 0.80 or less or within the preferred range described above after heat treatment at 130°C for 10 minutes, for example, a method can be used in which the 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 form fine protrusions on the surface by creating a laminated structure of polypropylene film and then forming the surface layer with an alloy structure containing an olefin resin such as poly-4-methylpentene-1 resin. The μs after heating can be measured in accordance with JIS K 7125 (1999).

[0035] The polypropylene film of the present invention preferably has a tensile elongation of 35% or more in the principal orientation direction. More preferably, it is 40% or more, even more preferably 45% or more, and particularly preferably 50% or more. 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. Tensile elongation may have a trade-off relationship with mechanical strength, and from the viewpoint of balancing with mechanical strength, the upper limit of the tensile elongation in the principal orientation direction is preferably 300% or less, more preferably 200% or less, and even more preferably 80% or less. The tensile elongation in the principal orientation direction can be evaluated using a tensile testing machine, and details of the measurement method are shown in the examples.

[0036] Increasing the stretching 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 high 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 crossover.

[0037] 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. If the maximum height St on both sides of the film exceeds 2.0 μm, when high tension is applied when the polypropylene film is laminated to an adherend and passed through a high-temperature process, the adherend may partially peel off at the areas with high St, resulting in a loss of quality. 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.

[0038] 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, it is effective to uniformly refine the spherulites in the unstretched sheet by lowering the temperature of the casting drum, lengthen the stretching section during longitudinal stretching, and stretch the film while sufficiently heating both sides with a radiation heater during the longitudinal stretching section, thereby reducing the stretching stress and uniformly stretching the film longitudinally.

[0039] The following describes a polypropylene resin (sometimes referred to as polypropylene resin A) that is most suitable as the most abundant component in the polypropylene film of the present invention.

[0040] From the viewpoint of productivity and film properties, polypropylene resin A is preferably a linear polypropylene resin.

[0041] The upper limit of the molecular weight distribution Mz / Mw of polypropylene resin A is preferably 4.2, more preferably 3.7, and even more preferably 3.2. The lower limit of Mz / Mw is practically around 1.2. If Mz / Mw is greater than 4.2, when heat is applied to the film, there are many high molecular weight components that are relaxed, which may impair heat resistance. In order to achieve the above values ​​for the molecular weight distribution Mz / Mw of polypropylene resin A, methods such as 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 are preferably employed.

[0042] The melt flow rate (MFR) of polypropylene resin A is preferably in the range of 2.0 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 particularly 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 cold xylene-soluble portion (CXS) of 3.5% by mass or less. Satisfying this condition improves the dimensional stability and heat resistance of the resulting polypropylene film.

[0044] Here, the cold xylene-soluble portion (CXS) refers to the polypropylene components dissolved in xylene when the sample is completely dissolved in xylene and then precipitated at room temperature. These components are thought to be those that are difficult to crystallize due to reasons such as low stereoregularity and low molecular weight. If a large amount of such components is present in polypropylene resin A, the thermal dimensional stability of the polypropylene film may be poor. Therefore, from the above viewpoint, the CXS is more preferably 2.0% by mass or less, and even more preferably 1.5% by mass or less. A lower CXS is preferable, but the lower limit is about 0.1% by mass. To set the CXS within the above preferred range, methods such as adjusting the polymerization catalyst and process polymerization conditions, increasing the catalytic activity when obtaining the resin, and washing the obtained resin with a solvent or the propylene monomer itself can be used.

[0045] 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 0.2% or more and 9.5% or less. The upper limit is more preferably 8.0% or less, even more preferably 6.5% or less, and most preferably 5.0% or less. 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 lower thermal shrinkage stress. In addition, shrinkage at room temperature over time after the polypropylene film is wound into a roll is suppressed, and the flatness of the film roll is maintained.

[0046] Polypropylene resin A may contain copolymer components made from 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%.

[0047] The ethylene content as a copolymer component of polypropylene resin A is preferably 5 mol% or less, when the total constituent units of polypropylene resin A are considered to be 100 mol%. More preferably, it is 3 mol% or less, and even more preferably 1 mol% or less. A higher ethylene content tends to reduce crystallinity and improve the transparency of the resulting polypropylene film. However, by limiting the ethylene content to 5 mol% or less, the decrease in strength and the deterioration of thermal shrinkage stress due to reduced heat resistance in the resulting polypropylene film are mitigated. Furthermore, resin degradation during the extrusion process is reduced, and the occurrence of fish eyes in the polypropylene film resulting from this can also be reduced.

[0048] Polypropylene resin A is a linear polypropylene, and it is preferable that it satisfies the above-mentioned 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 from Prime Polymer Co., Ltd., and FLX80E4, WF836DG3, FS2011DG3, D101, and W101 from Sumitomo Chemical Co., Ltd.

[0049] 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 due to its nucleating effect, thereby improving the heat resistance and mechanical strength of the film.

[0050] From the viewpoint of extrusion stability, the molecular weight-to-free (MFR) of branched polypropylene resin is preferably 0.5 g / 10 min to 9 g / 10 min (230°C, 21.18 N load). More preferably, the lower limit of the MFR of branched polypropylene resin is 2 g / 10 min. More preferably, the upper limit of the MFR of branched polypropylene resin is 8 g / 10 min. In order to achieve the above values ​​for the MFR of branched polypropylene resin, methods to control the average molecular weight and molecular weight distribution are employed. More specifically, methods to control the molecular weight and molecular weight distribution of the polypropylene resin are preferably employed, such as adjusting the hydrogen gas concentration during polymerization, selecting catalysts and / or co-catalysts appropriately, and selecting their composition. Lowering the molecular weight increases the MFR, and the more low molecular weight components there are in the molecular weight distribution, the higher the MFR.

[0051] 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. In order to achieve the above values ​​for melt tension, methods such as controlling the average molecular weight, molecular weight distribution, and degree of branching in the polypropylene resin are employed. In particular, when long-chain branching is present, the melt tension can be dramatically increased, and it can be adjusted to a preferred value by adjusting the molecular chains of the long-chain branching and the degree of branching.

[0052] While several types of branched polypropylene resins are commercially available, including those with Ziegler-Natta catalysts and metallocene catalysts, it is more preferable to enhance the stretchability by adding a small amount of Ziegler-Natta catalyst-based branched polypropylene resin, which has a broad molecular weight distribution, when used in combination with polypropylene resin A.

[0053] 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.

[0054] 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.

[0055] 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 color inhibitors, as long as they do not impair the objectives of the present invention. Among these, the selection of the type and amount of antioxidant is important from the viewpoint of antioxidant bleed-out. Specifically, such antioxidants are preferably sterically hindered phenolic types, and at least one of them is preferably a high molecular weight type with a molecular weight of 500 or more. Various specific examples can be given, but 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) 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 per 100 parts by mass of the total 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. On the other hand, if the amount of antioxidants is too high, the transparency of the polypropylene film may decrease due to the bleeding out of these antioxidants. From the above viewpoint, a more preferable content of antioxidants is 0.05 to 0.9 parts by mass per 100 parts by mass of the total polypropylene resin, and even more preferably 0.1 to 0.8 parts by mass.

[0057] Furthermore, the polypropylene film of the present invention may contain nucleating agents to the extent that it does not contradict the purpose. Specific examples of nucleating agents include α-nucleating agents (such as dibenzylidene sorbitols, 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 reduction 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 polypropylene 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 can 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 polypropylene 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 100% by mass of the total resin components are preferably as follows: From the viewpoint of heat resistance and mechanical strength of the film, polypropylene resin A is preferably 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.

[0060] Furthermore, in the polypropylene film of the present invention, 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 being more preferable and 5% by mass being even more preferable. 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.

[0061] 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 and flatness of the polypropylene film are maintained. Methods to achieve 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.

[0062] 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) is 6.5, as measured by gel permeation chromatography. The upper limit is more preferably 8.0% or less, and even more preferably 6.0% or less. A differential distribution value of 1.0% or more when the logarithmic molecular weight Log(M) is 6.5 ensures sufficient high molecular weight components that form tie molecules during stretching, thereby improving uniformity during stretching. On the other hand, a differential distribution value of 10% or less when the logarithmic molecular weight Log(M) is 6.5 prevents an excess of molecular chains that relax when heat is applied to the polypropylene film, suppressing an increase in thermal shrinkage stress. Furthermore, shrinkage at room temperature over time after the polypropylene film is wound into a roll is suppressed, and the flatness of the polypropylene film constituting the film roll can be maintained.

[0063] The polypropylene film of the present invention is not particularly limited in its layer structure and can be single-layer or laminated. However, from the viewpoint of satisfying different properties such as heat resistance, rigidity, and slipperiness, it is preferable to have a surface layer (I) and a base layer (II). When the polypropylene film has a single-layer structure, it is preferable that the main component of the polypropylene film itself is polypropylene resin. When the polypropylene film has a laminated structure, it is more preferable to have at least two layers in which polypropylene resin is the main component. A "layer in which polypropylene resin is the main component" refers to a layer in which, when the total components constituting the layer are taken as 100% by mass, polypropylene resin is contained in an amount greater than 50% by mass and less than or equal to 100% by mass. The determination of whether or not a layer falls under the category of "layer in which polypropylene resin is the main component" shall be made for each layer individually, not for multiple layers as a whole.

[0064] 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.

[0065] 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.

[0066] The polypropylene film of the present invention is preferably produced by biaxial stretching using the resin described above. The biaxial stretching method may be any of the following: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential biaxial stretching using a roll stretcher and tenter. However, among these, sequential biaxial stretching using a roll stretcher and tenter is preferred in terms of controlling film formation stability, thickness uniformity, and the high rigidity and dimensional stability of the resulting polypropylene film.

[0067] The following describes one aspect of the method for producing the polypropylene film of the present invention, using a polypropylene film with a two-layer, three-component structure as an example; however, the polypropylene film of the present invention is not necessarily limited to this.

[0068] First, polypropylene resin A (95 parts by mass) and branched-chain polypropylene resin (5 parts by mass) are dry-blended and supplied to a single-screw extruder for the base layer (II) (hereinafter sometimes referred to as layer B), and polypropylene resin A (98 parts by mass) and poly-4-methylpentene-1 resin (2 parts by mass) are supplied to a single-screw extruder for the surface layer (I) (hereinafter sometimes referred to as layer A). Then, melt extrusion is performed at 200 to 280°C, more preferably 220 to 280°C, and even more preferably 240 to 270°C for each layer. 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 an unstretched sheet having an A / B / A layer structure.

[0069] 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. By setting it within the above range, uniform fine protrusions made of poly-4-methylpentene-1 resin can be formed on the film surface, providing slipperiness. Note that the layer configuration may be a two-layer laminate configuration of A layer / B layer, provided that the effects of the present invention are not impaired. When the layer configuration of A layer / B layer is used, 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.

[0070] Furthermore, the casting drum has a surface temperature of 10 to 40°C, preferably 15 to 30°C, more preferably 15 to 25°C, and particularly preferably 20 to 25°C. By setting the temperature of the casting drum within the above preferred range, the spherulites in the undrawn sheet can be uniformly refined, improving uniformity during drawing. 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 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, preferably 15 to 30°C, more preferably 15 to 25°C, and particularly preferably 20 to 25°C. The blown air velocity is preferably 130 to 150 m / s. Furthermore, it is preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation to prevent vibration of the sheet. In the case of a two-layer laminated structure of two types, A layer and B layer, it is preferable to have the B layer side facing the casting drum.

[0071] 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. In this case, the stretching section during longitudinal stretching 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 between 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.

[0072] 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.

[0073] Next, the uniaxially oriented film is guided to a tenter by gripping both ends in the width direction with clips, preheated, and then transversely stretched to 8.5 to 14.0 times, preferably 9.0 to 13.0 times, and more preferably 9.5 to 12.0 times in the width direction. The preheating temperature is 165 to 180°C, preferably 168 to 180°C, and more preferably 170 to 180°C. The stretching temperature is 148 to 165°C, 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, more preferably 10°C or more, and even more preferably 16°C or more compared to the stretching temperature, uniform stretching can be achieved across the entire width of the film, thickness variations are reduced, and a film roll with good flatness and less wrinkle formation can be obtained. Because uniaxially oriented film has a large neck-down, the film width is narrow, and even when stretched transversely with a normal tenter rail pattern, the transverse stretching ratio can be increased. Such methods are preferable from the viewpoint of improving the heat resistance of polypropylene films.

[0074] In the subsequent heat treatment and relaxation process, the film is held taut at both ends in the width direction with clips, and while being relaxed by a relaxation rate of 12-25%, preferably 14-20%, more preferably 16-20%, in the width direction, it is heat-set at a temperature of 165°C to less than 180°C, preferably 168°C to less than 180°C, more preferably 170°C to less than 180°C. After that, while the film is still held taut at both ends in the width direction with clips, it is guided to the outside of the tenter through a cooling process of 80-100°C, and the clips at both ends in the width direction are released. Next, the film edge is slit in the winder process, and the polypropylene film is wound into a roll. By setting the heat treatment temperature to 5°C or more, preferably 8°C or more, more preferably 10°C or more higher than the transverse stretching temperature, residual stress in the film can be relieved and thermal shrinkage stress can be reduced.

[0075] Furthermore, it is preferable from the viewpoint of heat resistance of the obtained polypropylene film to heat the polypropylene film with a hot roll as it passes through the bridge after being discharged from the tenter. The temperature of the hot roll is preferably 80 to 120°C. By setting the temperature of the hot roll to 80°C or higher, smooth sliding between the hot roll and the polypropylene film is ensured, and the occurrence of wrinkles and deterioration of flatness in the polypropylene film are reduced. The heating time with the hot roll 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 it is about 2.0 seconds.

[0076] 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 suitable for use as a surface protection film, process film, release film, and packaging film due to its excellent heat resistance, mechanical strength, and quality.

[0077] Here, surface protection film refers to a film that is applied to an object such as a molded body or film to prevent scratches and contamination that occur during processing or transportation. Process film refers to a film that is applied 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. Release film refers to a film with high release properties that is applied 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. Packaging film refers to a film used to package food and various other products. [Examples]

[0078] The present invention will be described in detail below with reference to examples. The characteristics were measured and evaluated by the following methods.

[0079] (1) Film thickness The thickness was measured using a micro-thickness gauge (manufactured by Anritsu Corporation). The film was sampled in 10cm square sections, and the thickness was measured at five arbitrarily selected points. The average value of the obtained measurements was defined as the film thickness (μm).

[0080] (2) tanδ (loss tangent), E'' (loss modulus) A rectangular test specimen (5 mm wide x 20 mm long), cut from a polypropylene film with the measurement direction as the longer side, was mounted on the apparatus chuck under a 23°C atmosphere. It was then cooled to -100°C, and tanδ and E'' were measured from -100°C to 180°C after the start of heating. A viscoelastic-temperature curve was plotted using the dynamic viscoelastic method, and tanδ and E'' were calculated at each temperature. The test was performed with n=3, and the average values ​​obtained were defined as tanδ and E'' in the measurement direction. The measurement apparatus and conditions are as follows. • 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.

[0081] (3) Young's modulus at 130°C A rectangular sample measuring 150 mm in length (measurement direction) and 10 mm in width was cut from a polypropylene film. The sample was placed in a tensile testing machine (Orientec "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 50 mm, and the chuck-and-sample was placed in an oven heated to 130°C for 1 minute. After that, a tensile test was 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). Each sample was measured 5 times, and the average value was taken as the Young's modulus of that sample at 130°C.

[0082] (4) Tensile elongation and Young's modulus at room temperature A rectangular sample measuring 150 mm in length (measurement direction) and 10 mm in width 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 and Young's modulus were calculated according to the method specified in JIS K7161 (2014). Measurements were taken five times for each sample, and the average values ​​were taken as the tensile elongation and Young's modulus of that sample. The width direction was set to 0°, and the Young's modulus was similarly measured in each direction forming an angle from 0° to 175° in 5° increments relative to the width direction, and the direction showing the highest value was designated as the principal orientation direction.

[0083] (5) Crystallization temperature Tc0 determined by extrapolation method 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 2, 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.

[0084] (6) 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. Each sample was measured three times, and the average value was used for evaluation.

[0085] (7) Static friction coefficient μs in the direction orthogonal to the principal orientation after heat treatment at 130°C for 10 minutes Two pieces of polypropylene film were cut to a width of 6.5 cm (in the direction of the film's main orientation) and a length of 12 cm (in the direction perpendicular to the film's main orientation) to form test specimens. These were sandwiched between sheets of paper and heated in an oven maintained at 130°C for 10 minutes under zero load. After removal, they were allowed to cool at room temperature. Subsequently, the static friction coefficient (μs) of the test specimens in the direction perpendicular to the main orientation was measured at 25°C and 65% RH in accordance with JIS K 7125 (1999) using a slip tester manufactured by Toyo Seiki Co., Ltd. The measurement was performed with the two specimens aligned in the direction perpendicular to the main orientation and with different sides of the film in contact with each other. The same measurement was performed five times for each sample, and the average value of the obtained values ​​was calculated to determine the static friction coefficient (μs) of that sample.

[0086] (8) 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 polynomial quartic 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, with n=3 (number of measurements = 3) for each side. The average value for each side was calculated and adopted as the St for each side. The table shows the larger of the St values ​​for both sides of the film. • 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.

[0087] (9) 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] (10) Evaluation of flatness when film is heated A 500mm wide polypropylene film was subjected to corona treatment on the side with the lowest St value. An acrylic emulsion adhesive (EX243, manufactured by E-Tech Co., Ltd.) was then applied to the treated surface. The film was then placed in a 130°C drying oven and transported for 60 seconds under a transport tension of 200N to remove the solvent from the coating, resulting in a film with an adhesive layer thickness of 1μm. This adhesive film was then wound into a 200m roll to form an adhesive film roll. Next, 1m of the 500mm wide adhesive film was unwound and subjected to free tension (the film hanging vertically due to its own weight), and uniform tensions of 1kg / m and 3kg / 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 obtained values ​​were used to evaluate the flatness 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] (11) Evaluation of warpage when bonding substrates The adhesive film obtained in (10) above and 40 μm thick "Zeonor Film" (registered trademark) manufactured by Nippon Zeon Co., Ltd. were cut to 20 cm in width and 30 cm in length. The adhesive layer of the adhesive film and the "Zeonor Film" (registered trademark) were placed on top of each other so that they were in contact, and the two pieces were bonded together so that the length direction was aligned to obtain a bonded sample. The bonded sample was heated in an oven at 150°C for 60 seconds, then allowed to cool to room temperature, and the curvature of the bonded sample in the width direction was measured. The curvature was measured by placing the bonded sample on a horizontal surface with the "Zeonor Film" (registered trademark) on the bottom and measuring the height relative to the horizontal surface at the midpoint of the long side. The same measurement was performed on the long sides of both sides, and the average value was taken as the curvature of the sample. The evaluation was performed according to the following criteria. S: Curvature is less than 1 mm. A: The curvature is between 1mm and 5mm. B: Curvature of 5mm or more but less than 10mm. C: Warping of 10mm or more, or delamination of the polypropylene film and "Zeonor Film" (registered trademark).

[0090] (12) 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 by gel permeation chromatography. The molecular weight was corrected using a calibration curve prepared with the standard samples listed below, and the differential distribution value, weight-average molecular weight Mw, and Z-average molecular weight Mz were determined when the logarithmic molecular weight Log(M) of the sample was 6.5. The measurement equipment and conditions are as follows. • 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.

[0091] (13) 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.

[0092] (Polypropylene resin, etc.) For the production of the polypropylene films in the examples and comparative examples, polypropylene resins having the differential distribution values ​​for molecular weight distribution Mz / Mw, CXS, MFR, and Log(M) = 6.5, as 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 used. In addition, the following branched-chain polypropylene resins and non-polypropylene resins were used, and in some examples and some comparative examples, the raw materials for producing the polypropylene films were prepared in advance as follows.

[0093] <Polypropylene resin A> 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.

[0094] <Other polypropylene resins> Polypropylene resin 4 (PP4): Manufactured by Prime Polymer Co., Ltd. Polypropylene resin 5 (PP5): Manufactured by Prime Polymer Co., Ltd.

[0095] <Branched chain polypropylene resin> 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 g / 10 min) 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 g / 10 min).

[0096] [Table 1]

[0097] <Resins other than polypropylene> 4-methyl-1-pentene polymer 1: MX004, manufactured by Mitsui Chemicals, Inc.

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

[0099] (Example 1) Polypropylene resin 2 and polypropylene raw material 1 were dry-blended in a ratio of 80:20 (by mass) and supplied to a single-screw extruder for the surface layer (I). Polypropylene resin 1 and branched-chain polypropylene resin 1 were dry-blended in a ratio of 95:5 (by mass) 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, and discharged onto a casting drum with a surface temperature controlled to 25°C, where it was pressed tightly against the casting drum with an air knife. Subsequently, compressed air at 20°C was blown onto the uncooled drum surface of the sheet on the casting drum at an air velocity of 140 m / s to cool and solidify the sheet to obtain an unstretched sheet. Next, the unstretched sheet was preheated to 140°C using ceramic rolls, and a uniaxially oriented film was obtained by stretching it 5.7 times in the longitudinal direction while heating the sheet from both sides with a radiation heater between rolls at 120°C with a difference in peripheral speed. At this time, 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 (stretching section) 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 155°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 it was heated for 1.0 second on a 115°C hot roll before being wound onto a core to obtain a 25 μm thick polypropylene film. The physical properties and evaluation results of the obtained film are shown in Table 2.

[0100] (Examples 2-5, Comparative Examples 1-5) Polypropylene films were obtained in the same manner as in Example 1, except that the composition of each layer and the film-forming conditions 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 raw materials, in the surface layer (I) of Comparative Examples 2 and 5, polypropylene resin 2 and polypropylene raw material 1 were dry-blended in a ratio of 80:20 (mass ratio), similar to the surface layer (I) of Example 1. In the surface layer (I) of Example 4 and Comparative Example 4, polypropylene resin 3 and polypropylene raw material 2 were dry-blended in a ratio of 70:30 (mass ratio). In the surface layer (I) and base layer (II) of the other examples, each resin component was dry-blended in the ratios shown in Table 2.

[0101] [Table 2]

[0102] Note that since Example 3 and Comparative Example 1 have a single-layer structure, they are treated as having no surface layer, and their composition is described in the section on base layer (II). [Industrial applicability]

[0103] 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, building materials, medical products, and capacitor films. In particular, it is preferable to use it as a surface protection film, process film, release film, or capacitor film due to its excellent heat resistance, mechanical strength, and quality.

Claims

1. A polypropylene film comprising a polypropylene resin having a cold xylene-soluble portion (CXS) of 1.1% by mass or more and 2.7% by mass or less, a tanδ in the main orientation direction at 150°C of 0.25 or less, a Young's modulus in the direction orthogonal to the main orientation at 130°C of 50 MPa or more, and a molecular weight distribution Mz / Mw of 1.5 or more and less than 4.

5.

2. The polypropylene film according to claim 1, wherein the tanδ in the direction orthogonal to the main orientation at 150°C is 0.25 or less.

3. The loss modulus E'' in the direction orthogonal to the principal orientation at 0°C is 3.5 × 10⁻⁶. ８ A polypropylene film according to claim 1 or 2, wherein the hardness is Pa or less.

4. A polypropylene film according to any one of claims 1 to 3, characterized in that the product of the Young's modulus in the direction orthogonal to the main orientation at 130°C and the thickness of the film is 500 N / m or more.

5. 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 The crystallization temperature at a cooling rate of 0°C / min, determined by extrapolation using (°C), is Tc ０ When Tm (°C) is the melting point of the film, then Tc ０ A polypropylene film according to any one of claims 1 to 4, satisfying +Tm ≥ 280.

6. A polypropylene film according to any one of claims 1 to 5, wherein the static friction coefficient μs after heat treatment at 130°C for 10 minutes is 0.80 or less.

7. A polypropylene film according to any one of claims 1 to 6, characterized in that the tensile elongation in the principal orientation direction is 35% or more.

8. A polypropylene film according to any one of claims 1 to 7, wherein the maximum height St on both sides of the film is less than 2.0 μm.

9. A polypropylene film according to any one of claims 1 to 8, 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.

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

11. A process film having a polypropylene film according to any one of claims 1 to 10.

12. A release film having a polypropylene film according to any one of claims 1 to 10.

13. A protective film having a polypropylene film according to any one of claims 1 to 10.

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