Polypropylene film

Abstract

This invention relates to a polypropylene film, characterized in that the maximum value Dmax and minimum value Dmin of tanδ in the main alignment direction satisfy the relationship of Equation 1 within the temperature range of -10℃ to 50℃, and the tensile elongation in the orthogonal direction of the main alignment at 90℃ is 70% or more. Equation 1: 0.00≦(Dmax-Dmin) / Dmax≦0.30 This invention provides a polypropylene film that can maintain its quality even after undergoing high-temperature processing steps.

Description

[Technical Field]

[0001] This invention relates to a polypropylene film with excellent heat resistance, mechanical strength, and quality, which is suitable for use in industrial materials applications. [Previous Technology]

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

[0003] One of the required properties of polypropylene film is heat resistance. For example, when polypropylene film is used as a cover film for thermosetting resins, it is exposed to high temperatures during the thermosetting process after lamination. Similarly, when used as a capacitor film, it is exposed to high temperatures inside motors. In recent years, the demand for higher levels of heat resistance in polypropylene film has been increasing for such applications.

[0004] One of the indicators of heat resistance of polypropylene film is heat shrinkage rate. Generally, to reduce heat shrinkage rate, methods such as increasing the crystallinity of polypropylene resin, reducing the high molecular weight component, or setting a high stretch ratio can be used. However, while increasing the crystallinity of polypropylene resin or performing high stretch ratio will improve the mechanical strength of polypropylene film, it will also reduce tensile elongation and make it brittle. Furthermore, low molecular weight polypropylene resin has low melt tension when softened by heating, resulting in a decrease in tensile elongation when made into film. Based on the above, it is conventionally difficult to obtain polypropylene film that balances high tensile elongation and low heat shrinkage rate.

[0005] Regarding polypropylene films with improved heat resistance, for example, Patent Document 1 describes an example where a highly crystalline polypropylene resin is used and the temperature of the preheating roller during longitudinal stretching is adjusted to reduce heat shrinkage stress. Furthermore, Patent Documents 2 and 3 describe examples where a polypropylene resin with a predominantly low molecular weight is used to increase crystallinity, thereby achieving low heat shrinkage. Moreover, Patent Document 4 describes an example where a polypropylene resin with a low polypropylene content dissolved in xylene is used to improve voltage resistance at high temperatures and reduce shrinkage stress. [Prior Art Documents] [Patent Documents]

[0006] Patent Literature 1: International Publication No. 2020 / 196602 Patent Literature 2: Japan Special Bulletin No. 2014-55283 Patent Literature 3: International Publication No. 2020 / 137791 Patent Literature 4: Japan Special Publication No [Invention Contents]

[0007] [Inventing the topic to solve]

[0008] However, the polypropylene thin film described in the aforementioned patent literature 1 and 4 has the problem of insufficient heat resistance. Also, the low tensile elongation of the main fitting in the orthogonal direction of the polypropylene film recorded in the patent literature 2 makes it problematic at the point where the film is easily broken when transported at high temperatures and high tension. Also, the high heat shrinkage in the main alignment direction of the polypropylene film recorded in the patent literature 3 will shrink when the film is carried at high temperatures, which is a problem at the point where it is prone to wrinkles. Therefore, when these polypropylene films are used for applications requiring processing in high-temperature environments, it is difficult to maintain quality after processing steps at high temperatures. [Means used to solve problems]

[0009] In order to solve the above problems, the polypropylene film of the present invention is a polypropylene film characterized by the relationship between the maximum value Dmax and the minimum value Dmin of tanδ in the main alignment direction in the range above -10°C and below 50°C satisfying equation 1 , and the tensile elongation in the main alignment orthogonal direction at 90°C is more than 70%, formula 1:0.00≦0. [Effect of the invention]

[0010] According to the present invention it is possible to provide a polypropylene film that maintains quality even after processing steps at high temperature [Implementation]

[0012] [The form used to implement the invention]

[0013] The polypropylene film of the present invention is a polypropylene film characterized by the relationship between the maximum value Dmax and the minimum value Dmin of tanδ in the main alignment direction in the range above -10°C and below 50°C satisfying Equation In the following, the polypropylene thin films of the present invention are described specifically. Formula 1: 0.00≦(Dmax-Dmin) / Dmax≦0.30.

[0014] The term "polypropylene film" refers to a sheet-like molded body containing more than 50% and less than 100% by mass of polypropylene resin when all components constituting the film are defined as 100% by mass. The amount of polypropylene resin in the polypropylene film is preferably 90% by mass or more and less than 100% by mass, more preferably 95% by mass or more and less than 100% by mass, further preferably 96% by mass or more and less than 100% by mass, particularly preferably 97% by mass or more and less than 100% by mass, and most preferably 98% by mass or more and less than 100% by mass. The polypropylene film of the present invention may contain only one type of polypropylene resin, but preferably contains two or more types of polypropylene resin. Furthermore, when the film contains two or more types of polypropylene resin, if the combined percentage of these components is more than 50% by mass and less than 100% by mass, it is considered that polypropylene resin is the main component.

[0015] Furthermore, the term "polypropylene resin" refers to a resin in which propylene units account for more than 50 mol% and less than 100 mol% of all the constituent units constituting the resin. Also, in this invention, the direction in which the polypropylene film is formed (or the winding direction in the case of a film roll) is referred to as the film-forming direction, the long side direction, or the MD direction, and the direction orthogonal to the film-forming direction within the film surface is referred to as the width direction or the TD direction.

[0016] From the viewpoint of improving heat resistance, which affects the quality after high-temperature processing, it is important that the polypropylene film of the present invention has a maximum value Dmax and a minimum value Dmin of tanδ in the main alignment direction within the range of -10℃ to 50℃, satisfying the relationship of Equation 1. Equation 1: 0.00≦(Dmax-Dmin) / Dmax≦0.30.

[0017] tanδ, also known as loss tangent, is related to the degree of molecular chain mobility in polypropylene film. As shown in Figure 1, tanδ generally reaches its maximum near 0°C. If it decreases due to higher temperatures, it will rise again and increase to a level exceeding the maximum value near 0°C. (Dmax-Dmin) / Dmax represents the amount by which tanδ decreases from its maximum near 0°C. The inventors have discovered that reducing this value, suppressing molecular chain mobility over a wide temperature range, will improve the heat resistance of polypropylene film and suppress thermal shrinkage.

[0018] When the value of (Dmax-Dmin) / Dmax is greater than 0.30, the thermal shrinkage of the polypropylene film increases. Therefore, for example, when such a polypropylene film is used as a release film, wrinkles may occur at the point when it is bonded to the substrate and subjected to a high-temperature step, resulting in quality loss. From the above perspective, (Dmax-Dmin) / Dmax is preferably 0.28 or less, more preferably 0.27 or less, further preferably 0.25 or less, and especially preferably 0.22 or less. The lower limit of the value of (Dmax-Dmin) / Dmax is essentially 0.00.

[0019] (Dmax-Dmin) / Dmax can be determined using a dynamic viscoelasticity evaluation device through the following procedure. First, a polypropylene film test piece with a width of 5 mm and a length of 20 mm is cut with the main alignment direction as the long side. The test piece is mounted on the device fixture at 23°C under nitrogen gas, and then cooled to -60°C. The tanδ is measured from the point when the temperature reaches -50°C after the start of heating until it reaches 150°C. Next, a viscoelasticity-temperature curve is plotted using the dynamic viscoelasticity method. Dmax and Dmin are determined using the tanδ at each temperature, and (Dmax-Dmin) / Dmax is obtained from these values. Furthermore, tanδ can be measured using a known device such as the Rheogel-E4000 (manufactured by UBM), under the conditions shown in the example.

[0020] In order to make the value of (Dmax-Dmin) / Dmax less than 0.30, methods can be used, for example, to set the raw material composition of the polypropylene film within the range described later, and to set the film forming conditions within the range described later. In particular, it is more effective to use a highly crystalline raw material with a narrow molecular weight distribution Mz / Mw, a significant reduction in high molecular weight components, and a low cold xylene soluble portion (CXS); or to set the surface temperature of the casting drum within the range of 10 to 40°C; and to draw the film down on a high-temperature (above 80°C) roller after transverse stretching, causing the film to shrink in the direction orthogonal to the main alignment direction.

[0021] From the viewpoint of improving mechanical strength, which affects the stability of processing steps at high temperatures, the polypropylene film of the present invention is important in that its tensile elongation in the principal alignment orthogonal direction at 90°C is 70% or more. The principal alignment orthogonal direction here refers to a direction orthogonal to the principal alignment direction within the plane. The principal alignment direction refers to the direction in which the Young's modulus is highest when any direction within the film plane is defined as 0°, and the angles from 0° to 175° are formed in 5° increments. Furthermore, the Young's modulus can be measured using a tensile testing machine, and details of the measurement method are shown in the examples. When the sample width is less than 50 mm and the Young's modulus cannot be obtained using a tensile testing machine, the crystal alignment of the α-crystal (110) plane of the polypropylene film is measured using wide-angle X-rays, and the principal alignment direction is determined based on the following criteria. That is, for the surface of the thin film, X-rays (CuKα line) are incident in the vertical direction and the crystallization peak at 2θ=14° (α crystal (110) plane) is scanned in the circumferential direction. The direction with the highest diffraction intensity of the obtained diffraction intensity distribution is defined as the principal alignment direction, and the direction orthogonal to it is defined as the principal alignment orthogonal direction.

[0022] When the tensile elongation in the main orthogonal direction at 90°C is less than 70%, for example, when using a polypropylene film as a release film, there is a possibility that the film will break due to high tension applied in the main orthogonal direction during the step of bonding with the substrate at high temperature. From the above viewpoint, the tensile elongation in the main orthogonal direction at 90°C is preferably 90% or more, more preferably 110% or more, and even more preferably 130% or more. On the other hand, the upper limit of the tensile elongation in the main orthogonal direction at 90°C is not particularly limited, but in practice, about 400% is the upper limit.

[0023] Furthermore, the tensile elongation at 90°C in the orthogonal direction of the principal alignment can be determined using a tensile testing machine equipped with a high-temperature heating oven. First, a polypropylene film is cut into rectangles of 150mm (orthogonal direction of principal alignment) × 10mm (principal alignment direction) to obtain a sample. Next, the sample is assembled into the tensile testing machine with the initial clamping distance set to 50mm, and then placed in an oven preheated to 90°C for 1 minute. Afterward, a tensile test is performed at a tensile speed of 300mm / min, and the elongation at fracture is recorded as the tensile elongation. Furthermore, any tensile testing machine capable of this measurement can be used, such as the ORIENTEC "Tensilon" (registered trademark) UCT-100.

[0024] Generally, if the proportion of high molecular weight components in a polypropylene film is reduced, it becomes difficult for the tension to propagate throughout the film when high tension is applied, and the elongation at break tends to decrease. Furthermore, if the proportion of highly crystalline polypropylene resin with low cold xylene-soluble fraction (CXS) is increased, the amorphous components that alleviate stress when tension is applied will be insufficient, resulting in a lower elongation at break. Therefore, it is conventionally difficult to maintain elongation at break while simultaneously improving heat resistance. However, it has been found that by using methods such as defining the raw material composition of the polypropylene film within the range described below, and defining the film-forming conditions within the range described below, it is possible to achieve an elongation at break of 70% or more in the main alignment orthogonal direction at 90°C. In particular, more effective methods include: increasing the stretching range during longitudinal stretching (e.g., 200 mm or more), and stretching the film while fully heating both sides of the film using a radiation heater or the like, thereby reducing tensile stress and uniformly stretching longitudinally; or increasing the relaxation rate (e.g., 12% or more) during the relaxation process after transverse stretching and heating the film using a hot roller when passing through the transverse zone.

[0025] From the viewpoint of heat resistance, the polypropylene film of the present invention is preferably characterized by the following: when the maximum value of tanδ in the main alignment direction is defined as LP at a temperature above -30°C and below 30°C, the temperature at which tanδ in the main alignment direction becomes equal to LP in the range of 30°C and above and below 150°C is 80°C or below. More preferably, it is 70°C or below; further preferably, it is 60°C or below; and most preferably, it is 55°C or below. The temperature at which tanδ in the main alignment direction becomes equal to LP, as shown in FIG2, corresponds to the temperature at which the maximum value of tanδ near 0°C begins to exceed. The inventors have found that keeping this temperature low improves the heat resistance of the polypropylene film. By keeping the temperature at which tanδ in the main alignment direction becomes equal to LP at 80°C or below, shrinkage in the orthogonal direction of the main alignment direction can be reduced when the polypropylene film is wound into a roll and stored at high temperature, thus suppressing the formation of wrinkles in the polypropylene film roll. As a result, the quality of the polypropylene film roll can be maintained to a high degree.

[0026] In order to achieve a temperature at which the tanδ of the main alignment direction equals LP at 80°C or a more preferred range, a method can be used to define the raw material composition of the polypropylene film within the range described later. Preferably, a highly crystalline raw material with a narrow molecular weight distribution (Mz / Mw), significantly reduced high molecular weight components, and low CXS is used. The lower limit of the temperature at which the tanδ of the main alignment direction equals LP is substantially 30°C.

[0027] From the viewpoint of heat resistance, the polypropylene film of the present invention preferably has a sum of α(110) crystallite sizes in the main alignment direction and its orthogonal direction of 20.0 nm or less. More preferably, it is 18.0 nm or less, further preferably 17.0 nm or less, and most preferably 16.0 nm or less. By ensuring that the sum of α(110) crystallite sizes in the main alignment direction and its orthogonal direction is 20.0 nm or less, shrinkage in the orthogonal direction of the polypropylene film can be reduced when the film is rolled up and stored at high temperatures, thus suppressing wrinkles in the polypropylene film roll. As a result, the quality of the polypropylene film roll can be maintained to a high degree. From the above viewpoint, the lower limit of the sum of α(110) crystallite sizes in the main alignment direction and its orthogonal direction is not particularly limited, but is substantially around 10 nm.

[0028] Furthermore, by making the sum of the crystal sizes of α(110) in the main alignment direction and its orthogonal direction less than 20.0 nm, the size of the amorphous regions between crystals in the polypropylene film can be suppressed. Therefore, when using the polypropylene film for various applications, suppressing the size of the amorphous regions in this way brings a variety of advantages. For example, when the polypropylene film is used as a release film, after being bonded to the substrate and subjected to high temperature, the release property when peeling the polypropylene film from the substrate can be highly maintained, which can reduce the reduction in productivity. Moreover, the crystal size of α(110) can be measured by X-ray diffraction, and the details of the measurement method are shown in the embodiments.

[0029] In order to make the sum of the α(110) crystallite sizes in the main alignment direction and its orthogonal direction 20.0 nm or less, or in a more preferred range, methods can be used, for example, to define the raw material composition of the polypropylene film within the range described later, and to define the film-forming conditions within the range described later. In particular, it is more effective to: use raw materials with high crystallization temperatures to reduce the number of spherulites formed during casting; reduce the extrusion temperature and the temperature of the casting drum to increase cooling during casting; and increase the stretching range during longitudinal stretching, and stretch the film while fully heating both sides of the film with a radiation heater within the stretching range.

[0030] From the viewpoint of balancing improved heat resistance and reduced formation of coarse spherulites, the polypropylene film of the present invention preferably satisfies the following condition when the crystallization temperature at a cooling rate of 0°C / min is defined as Tc0 (°C) and the melting point of the polypropylene film is defined as Tm (°C): Tc0 + Tm ≥ 280. 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. The value of Tc0 + Tm is more preferably 285 or higher, and even more preferably 290 or higher. Tc0 is an indicator of crystallization ease; a high Tc0 indicates easy crystallization. Furthermore, Tm is the melting point of the polypropylene film; a high Tm indicates high heat resistance of the polypropylene film. When the value of Tc0 + Tm is above 280, the crystallization rate is moderately maintained, and it becomes less likely to form coarse spherulites during casting. As a result, the decrease in elongation at break in the direction orthogonal to the main alignment direction and the increase in crystallite size can be suppressed. From the above point of view, there is no particular upper limit to the value of Tc0 + Tm, but in practice, around 350 is the upper limit.

[0031] In order to make the value of Tc0 + Tm 280 or higher, or the preferred range described above, methods for increasing Tc0 and Tm can be used alone or in combination. To increase Tc0, a method can be used to define the composition of the polypropylene film within the range described later. In particular, it is preferable to add a component with nucleating agent properties, among which branched chain polypropylene resin is preferred. Furthermore, to increase Tm, methods can be used, for example, to define the composition of the polypropylene film within the range described later, and also to define the film-forming conditions within the range described later. Regarding the composition, it is particularly preferable to use a highly crystalline raw material with a low cold xylene soluble fraction (CXS). Furthermore, regarding the film-forming conditions, it is also effective to increase the stretching range during longitudinal stretching, and to stretch the film while simultaneously heating both sides thoroughly using a radiant heater within the stretching range, thereby reducing tensile stress and uniformly stretching the film longitudinally.

[0032] Tc10, Tc40, and Tc0 can be measured using a differential scanning calorimeter (DSC). The specific measurement method is as follows: First, using DSC, 3 mg of polypropylene film is heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere and held for 5 minutes. Then, the film is 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 is defined as Tc10. Next, the polypropylene film is heated from 25°C to 250°C at a rate of 20°C / min and held for 5 minutes. Subsequently, the film is 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 is defined as Tc40. Plot Tc10 and Tc40 obtained in this manner with the horizontal axis representing the cooling rate and the vertical axis representing the crystallization temperature obtained at each cooling rate, as shown in Figure 3. Draw a straight line from Tc40 through Tc10, and define the crystallization temperature at a cooling rate of 0℃ / min as Tc0. There are no particular restrictions on the DSC system as long as it can perform the above measurements; any known device can be used. Specific examples include the EXSTAR DSC6220 manufactured by Seiko Instruments Inc. (the same applies to the Tm measuring device described later).

[0033] Tm can be measured using a differential scanning calorimeter (DSC). The specific measurement method is as follows. Using DSC, 3 mg of polypropylene film is heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere, and the peak temperature of the endothermic curve obtained during this heating is defined as Tm.

[0034] From the viewpoint of improving the flatness during heating and thus enhancing the suitability of processing after the heating step, the static friction coefficient μs of the polypropylene film of the present invention after heating at 90°C for 10 minutes is preferably 0.80 or less. Here, the static friction coefficient μs of 0.80 or less means that the static friction coefficient μs when the different surfaces of the film are overlapped is 0.80 or less (the preferred range described below is also the same). 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 using polypropylene film as a release film for thermosetting resin films, the thermosetting resin sometimes hardens in the temperature range of about 80°C to 100°C after being laminated to the sheet thermosetting resin. Compared with polyester film, which is often used as a process film such as a release film, polypropylene film generally has lower heat resistance, and the film surface softens and its slipability decreases when heat of about 90°C is applied. By reducing the μs after heating to below 0.8, when using polypropylene film as a release film, for example, the film can slide on the transport roller at the point of passing through the high-temperature step, and the stress is evenly distributed, which can reduce the formation of wrinkles or the winding deviation that occurs when it is wound together with the substrate.

[0035] In order to achieve a static friction coefficient μs of 0.80 or less, or a more preferred range, after heating at 90°C for 10 minutes, methods can be used, for example, by defining the composition of the polypropylene film within the range described later, and by defining the film-forming conditions within the range described later. In particular, a more effective method is to alloy an olefin resin such as poly(4-methylpentene-1) resin onto the surface of the polypropylene film and form fine protrusions on its surface; or to form protrusions after biaxial stretching by heating the casting drum at high temperature to form spherulites during casting. The lower limit of μs after heating is not particularly limited, but in practice, about 0.1 is the lower limit. Furthermore, μs after heating can be measured according to JIS K 7125 (1999).

[0036] The polypropylene film of the present invention preferably has a tensile elongation in the main alignment direction of 35% or more. With a tensile elongation in the main alignment direction of 35% or more, film breakage can be reduced when the film is pulled from a roll of pre-wound polypropylene film for use. From the above viewpoint, the tensile elongation in the main alignment direction is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. On the other hand, the upper limit of the tensile elongation in the main alignment direction is not particularly limited, but is substantially around 1000%. Furthermore, the tensile elongation in the main alignment direction is evaluated using a tensile testing machine, which will be described in detail later.

[0037] Generally, when increasing the stretch ratio to improve mechanical strength or performing high-stress stretching at low temperatures, the elongation at break tends to decrease. Furthermore, if the ratio of highly crystalline polypropylene resin with a low cold xylene-soluble fraction (CXS) is increased, the amorphous components that alleviate stress during tension application will be insufficient, resulting in a lower elongation at break. Therefore, it is conventionally difficult to maintain elongation at break while using highly crystalline raw materials. However, it has been found that by using methods such as defining the raw material composition of the polypropylene film within the range described later, and defining the film-forming conditions within the range described later, it is possible to achieve an elongation at break of 35% or more in the main alignment direction. In particular, a more effective method is to increase the stretching range during longitudinal stretching (e.g., 200 mm or more), and to perform stretching while fully heating both sides of the film using a radiant heater or similar device within the stretching range, thereby reducing tensile stress and uniformly stretching longitudinally; or to increase the relaxation rate (e.g., 12% or more) during the relaxation treatment after transverse stretching and to use a hot roller for heating when passing through the transverse zone.

[0038] The polypropylene film of the present invention preferably has a maximum height St on both sides of the film that is less than 2.0 μm. More preferably, it is less than 1.5 μm, further preferably less than 1.0 μm, and most preferably less than 0.5 μm. By ensuring that the maximum height St on both sides of the film is less than 2.0 μm, when the polypropylene film is laminated to the substrate and wound into a film roll, the quality degradation caused by protrusions on the surface of the polypropylene film contacting the substrate and causing depressions to be transferred to the substrate can be reduced. The lower limit of the maximum height St on both sides of the film is not particularly limited, but is substantially around 0.01 μm.

[0039] In order to make the maximum height St on both sides of the film less than 2.0 μm or the preferred range described above, methods can be used, for example, to define the composition of the polypropylene film as described later, and to define the film-forming conditions as described later. In particular, a more effective method is to set the surface temperature of the casting drum in the range of 10 to 40°C to uniformly refine the spherulites in the unstretched sheet, increase the stretching range during longitudinal stretching, and stretch the film while fully heating both sides using a radiation heater in the longitudinal stretching range, thereby reducing the tensile stress and uniformly stretching the film longitudinally.

[0040] The thickness of the polypropylene film of the present invention is adjustable according to the application and is not particularly limited, but from an operational point of view, it is preferably 0.5 μm to 100 μm. 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, more preferably 1.5 μm, further preferably 4.0 μm, particularly preferably 8.0 μm, and most preferably 11 μm. The thickness of the polypropylene film can be adjusted by means of the extruder screw speed, the width of the unstretched sheet, the film forming speed, the stretch ratio, etc., without reducing other physical properties. Furthermore, the thickness of the polypropylene film can be measured using a known micro-thickness gauge.

[0041] The polypropylene film of the present invention preferably has a molecular weight distribution Mz / Mw of less than 4.5, more preferably less than 4.0, and even more preferably less than 3.5. 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 moderated when heat is applied, thus maintaining the heat resistance of the polypropylene film. As for the method of making the molecular weight distribution Mz / Mw of the polypropylene film reach the above-mentioned value, the following methods are preferred: adjusting the hydrogen concentration during the polymerization of polypropylene resin; or appropriately selecting the catalyst and / or auxiliary catalyst, adjusting the composition and polymerization amount of each polymerization tank in continuous polymerization, etc.

[0042] Hereinafter, a suitable polypropylene resin (polypropylene resin A) will be described as the component most abundant 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.

[0043] The molecular weight distribution Mz / Mw of polypropylene resin A is preferably below 4.2, more preferably below 3.7, and even more preferably below 3.2. The lower limit of Mz / Mw of polypropylene resin A is approximately 1.2. When the Mz / Mw of polypropylene resin A is below 4.2, there are fewer high molecular weight components that are moderated during heating, thus maintaining the heat resistance of the polypropylene film. Regarding the method of achieving the above-mentioned molecular weight distribution Mz / Mw of polypropylene resin A, the following methods are preferred: adjusting the hydrogen concentration during polymerization; or appropriately selecting the catalyst and / or auxiliary catalyst, adjusting the composition of each polymerization tank in continuous polymerization, and adjusting the polymerization amount, etc.

[0044] From the viewpoint of film-forming properties and film strength, 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). The lower limit of MFR is more preferably 2.5 g / 10 min, further preferably 3.0 g / 10 min. The upper limit is more preferably 10 g / 10 min, further preferably 8.0 g / 10 min, and most preferably 6.5 g / 10 min. To achieve the above-mentioned MFR values ​​for polypropylene resin A, methods such as controlling the average molecular weight and molecular weight distribution can be used. More specifically, methods such as adjusting the hydrogen concentration during polymerization or appropriately selecting the catalyst and / or auxiliary catalyst, selecting the composition, and controlling the molecular weight or molecular weight distribution of the polypropylene resin can be used. By reducing the high molecular weight components, the MFR will increase.

[0045] Preferably, the CXS content of polypropylene resin A is 3.5% by mass or less. By satisfying this requirement, the reduction in dimensional stability and heat resistance of the obtained polypropylene film can be suppressed. Here, CXS refers to the polypropylene component dissolved in xylene when the sample is completely dissolved in xylene and precipitated at room temperature. This is considered to be a component that is difficult to crystallize due to its low stereoregularity or low molecular weight. If polypropylene resin A contains a large amount of such components, the thermal dimensional stability of the obtained polypropylene film may be poor. Therefore, from the above point of view, CXS is preferably 2.0% by mass or less. The lower the CXS, the better, but in practice, about 0.1% by mass is the lower limit. As for methods to achieve the above-mentioned preferred range of CXS, methods such as adjusting the polymerization catalyst and process polymerization conditions, improving the catalyst activity when obtaining polypropylene resin A, and washing the obtained resin with solvent or propylene monomer itself can be used.

[0046] In the molecular weight distribution curve determined by gel permeation chromatography, the differential distribution value of polypropylene resin A with a logarithmic molecular weight Log(M) = 6.5 is preferably 0.2% to 9.5%. The upper limit is more preferably 8.0%, further preferably 6.5%, and most preferably 5.0%. With a differential distribution value of 0.2% or more when the logarithmic molecular weight Log(M) is 6.5, there will be sufficient high molecular weight components of tie molecules during stretching, and the uniformity during stretching will be increased. On the other hand, with a differential distribution value of 9.5% or less when the logarithmic molecular weight Log(M) is 6.5, there are fewer molecular chains undergoing moderate heating when the polypropylene film is heated, and the thermal shrinkage rate is lower. Furthermore, after the polypropylene film is rolled into a roll, the shrinkage at room temperature over time is also suppressed, and the planarity of the film roll can be maintained.

[0047] Polypropylene resin A may also contain copolymer components based on other unsaturated hydrocarbons, etc., without prejudice to the purpose of the present invention. Examples of monomer components constituting 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, norcamphene, 5-methyl-2-norcamphene, etc. From the perspective of dimensional stability when the polypropylene film is formed, when the total constituent units constituting polypropylene resin A are defined as 100 mol%, the copolymer content is preferably less than 10 mol%, more preferably less than 5 mol%, further preferably less than 3 mol%, and most preferably less than 1 mol%.

[0048] When the total constituent units of polypropylene resin A are defined as 100 mol%, the content of ethylene units, which are copolymer components of polypropylene resin A, is preferably 5 mol% or less. More preferably, it is 3 mol% or less, and even more preferably, it is 1 mol% or less. The more ethylene units there are, the lower the crystallinity becomes, which makes it easier to improve the transparency when making the film, but the strength and heat resistance will decrease. By setting the ethylene units in polypropylene resin A to 5 mol% or less, the decrease in strength and the deterioration of the heat shrinkage rate that accompanies the decrease in heat resistance when making polypropylene films can be mitigated. Furthermore, by setting the ethylene units in polypropylene resin A to 5 mol% or less, the deterioration of the resin during the extrusion process can also be mitigated, and the formation of fish eyes when making polypropylene films can also be suppressed.

[0049] The polypropylene resin is a linear polypropylene of type A, preferably satisfying the aforementioned preferred conditions. Examples of such polypropylene resins include: F-704NP, F-704NT, ​​F-300SP, F113G, E-100GPL, E-105GM, E-200GP, E-203GP, Y-400GP, and E111G manufactured by Prime Polymer Co., Ltd.; and FLX80E4, WF836DG3, FS2011DG3, D101, and W101 manufactured by Sumitomo Chemical Co., Ltd.

[0050] In addition to linear polypropylene resin A, the polypropylene film of the present invention may also contain branched polypropylene resin. Branched polypropylene resin has the effect of nucleating α-crystals or β-crystals. Therefore, by including branched polypropylene resin, the formation of coarse spherulites can be suppressed during casting through its nucleating effect, and the heat resistance and tensile elongation of the polypropylene film can be improved, thereby reducing the crystallite size.

[0051] From the viewpoint of extrusion stability, the preferred MFR of branched polypropylene resin is 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 further preferably 6 g / 10 min. The upper limit of the MFR of branched polypropylene resin is more preferably 8 g / 10 min. Methods for achieving the above-mentioned MFR values ​​for branched polypropylene resin include controlling the average molecular weight and molecular weight distribution. More specifically, methods such as adjusting the hydrogen concentration during polymerization or appropriately selecting the catalyst and / or auxiliary catalyst, selecting the composition, and controlling the molecular weight and molecular weight distribution of the polypropylene resin are preferred. MFR is an indicator of resin flowability, representing the amount of resin extruded from the barrel at a given temperature and load; the lower the resin viscosity, the higher the MFR. Generally speaking, molecular weight is related to viscosity. The lower the absolute value of the molecular weight, the lower the viscosity of the resin, and the higher the MFR value.

[0052] From the viewpoint of tensile uniformity, the melt tension of branched polypropylene resin is preferably 3 gf or higher and 40 gf or lower. The lower limit of melt tension is preferably 4 gf, and further preferably 6 gf. The upper limit is preferably 30 gf, and further preferably 25 gf. Methods for achieving the above-mentioned melt tension include controlling the average molecular weight and molecular weight distribution, and the degree of branching in the polypropylene resin. In particular, when long-chain branches are present, the melt tension can be significantly increased, and optimal values ​​can be achieved by producing a polypropylene resin with long-chain branches or adjusting the degree of branching.

[0053] Branched chain polypropylene resins are commercially available in various forms, such as Ziegler-Natta catalyst-based and metallocene catalyst-based resins. However, from the viewpoint of using it in combination with polypropylene resin A, it is better to add a small amount of Ziegler-Natta catalyst-based branched chain polypropylene resin with a wide molecular weight distribution to supplement the tensile properties.

[0054] Without prejudice to the purpose of the present invention, the polypropylene film of the present invention may contain various resins different from polypropylene. Among these, a polyolefin resin is preferred because it has high affinity with polypropylene resin and can improve dispersibility with polypropylene resin. Regarding the polyolefin resin, by containing, for example, 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 slip properties. Among these, poly(4-methylpentene-1) resin (PMP) is preferred because of its particularly high affinity with polypropylene resin.

[0055] From the viewpoint of imparting slip properties, in the case of a laminated film, a resin different from polypropylene is preferably added to the surface layer, and the amount is preferably 0.1 to 20 parts by weight, more preferably 0.1 to 15 parts by weight, further preferably 0.1 to 10 parts by weight, and especially preferably 0.1 to 5.0 parts by weight relative to the total amount of polypropylene resin in the surface layer. In the case of a single-layer film, the amount is preferably 0.1 to 10 parts by weight, more preferably 0.1 to 5.0 parts by weight, further preferably 0.1 to 3.0 parts by weight, and especially preferably 0.1 to 1.0 parts by weight relative to the total amount of polypropylene resin. If too much of a resin different from polypropylene is added, the transparency of the film may deteriorate, or the heat resistance or rigidity may decrease. Furthermore, if too little is added, the effect of imparting slip properties may be poor.

[0056] Without prejudice to the purpose of the present invention, the polypropylene film of the present invention may also contain various additives, such as: crystallizing nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, anti-coloring agents, etc.

[0057] Among these, from the viewpoint of antioxidant exudation, it is important to select the type and amount of antioxidant added. That is, for such antioxidants, it is preferable to be a phenolic antioxidant with steric hindrance, and at least one of them is a high molecular weight type with a molecular weight of 500 or more. For specific examples, various examples can be given, such as 2,6-di-tert-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox" (registered trademark) 1330: molecular weight 775.2) or tetra[methylene-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 1010: molecular weight 1177.7), etc., used alone or in combination.

[0058] The total content of these antioxidants relative to the total amount of polypropylene resin is preferably in the range of 0.01 to 1.0 parts by weight. If the antioxidant is too little, polymer degradation and film discoloration may occur during the extrusion process, or the long-term heat resistance may be poor. If the antioxidant is too much, the transparency may decrease due to the leaching of these antioxidants. From the above point of view, the more preferred content of antioxidants is 0.05 to 0.90 parts by weight, and the most preferred content is 0.10 to 0.80 parts by weight.

[0059] Without departing from the purpose, the polypropylene film of the present invention may contain a nucleating agent. Specific examples of nucleating agents include: α-crystal nucleating agents (dibenzylsorbitol derivatives, sodium benzoate, phosphate metal salts, etc.), β-crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, N,N'-dicyclohecyl-2,6-naphthalene dicarboxamide and other amide compounds, quinacridone compounds, etc.). However, excessive addition of the above-mentioned other types of nucleating agents may cause a decrease in tensile strength or a decrease in transparency and strength due to void formation. Therefore, the amount added is generally 0.5 parts by weight or less relative to 100 parts by weight of total acrylic resin, preferably 0.1 parts by weight or less, more preferably 0.05 parts by weight or less, and preferably substantially not included.

[0060] The polypropylene film of the present invention preferably does not contain inorganic particles. Polypropylene resin, which is preferably used as the main component of the polypropylene film of the present invention, has low affinity for inorganic particles. Therefore, during the manufacturing process, inorganic particles may detach from the film and contaminate the production line and the finished product. Furthermore, if large protrusions are formed due to the high hardness of inorganic particles, there may be instances of embossing onto the resin layer of optical components. When used as a protective film or a substrate film for manufacturing high-quality products such as display components, this can sometimes lead to quality degradation. From the above perspective, the polyolefin film of the present invention preferably also does not contain lubricants such as organic particles.

[0061] In the polypropylene film of the present invention, the proportions of polypropylene resin A and branched polypropylene resin relative to the total amount of resin components are preferably below. From the viewpoint of heat resistance and mechanical strength of the film, polypropylene resin A is preferably more than 50% by mass and less than 99.9% by mass. The lower limit of the proportion of polypropylene resin A is more preferably 60% by mass, and more preferably 70% by mass. The upper limit is more preferably 99% by mass, and more preferably 98% by mass. In the case where the film contains two or more components equivalent to polypropylene resin A, these components are combined and considered as the content of polypropylene resin A in the film. Regarding the proportion of branched polypropylene resin, in the whole film, it is preferably 0.1% by mass and more than 30% by mass, and the upper limit is more preferably 10% by mass, and more preferably 5% by mass. In the case where the film contains two or more components equivalent to branched polypropylene resin, these components are combined and considered as the content of branched polypropylene resin in the film.

[0062] In the molecular weight distribution curve determined by gel permeation chromatography, the differential distribution value of the polypropylene film of the present invention at a logarithmic molecular weight Log(M) = 6.5 is preferably 1.0% to 10%. The upper limit is more preferably 8.0%, and further preferably 6.0%. With a differential distribution value of 1.0% or more at a logarithmic molecular weight Log(M) of 6.5, sufficient high molecular weight components of linking molecules are present during stretching, increasing the uniformity during stretching. On the other hand, with a differential distribution value of 10% or less at a logarithmic molecular weight Log(M) of 6.5, fewer molecular chains are moderated when heat is applied to the polypropylene film, resulting in a lower thermal shrinkage rate. Furthermore, when the polypropylene film is rolled into a roll, shrinkage at room temperature over time is suppressed, maintaining the planarity of the film roll.

[0063] The polypropylene film of the present invention is not particularly limited in its layer composition and can be either a single layer or a laminated structure. From the viewpoint of satisfying different characteristics such as heat resistance, rigidity, and slip resistance, it is preferable to have at least two layers with polypropylene resin as the main component. For example, if the layers with polypropylene resin as the main component are a surface layer (I) and a base layer (II), and the polypropylene film is a laminated structure of these layers, it is preferable that the polypropylene film itself has polypropylene resin as the main component, and the base layer (II) described later has polypropylene resin as its main component. In the case of a laminated polypropylene film, it is more preferable to have at least two layers with polypropylene resin as the main component. The term "layer with polypropylene resin as the main component" refers to a layer containing more than 50% and less than 100% polypropylene resin when all components constituting the layer are set to 100% by mass. Furthermore, the determination of whether it meets the criteria of "layer with polypropylene resin as the main component" is not based on a combination of multiple layers but on each individual layer. In the case of a two-layer structure, the layer with the thicker layer is considered the base layer (II).

[0064] The polypropylene film of the present invention may contain only one type of polypropylene resin, but preferably contains two or more types of polypropylene resin. When the layer contains two or more components equivalent to polypropylene resin, and the combined calculation of these components is more than 50% by mass and less than 100% by mass, then the layer is considered as a "layer with polypropylene resin as the main component".

[0065] When all components of the constituent layers are defined as 100% by mass, the content of polypropylene resin in the "layer with polypropylene resin as the main component" is preferably 90% by mass or more and 100% by mass, further preferably 95% by mass or more and 100% by mass, even more preferably 96% by mass or more and 100% by mass, particularly preferably 97% by mass or more and 100% by mass, and most preferably 98% by mass or more and 100% by mass. Furthermore, when the polypropylene film of the present invention is composed of a single layer, the main component of the polypropylene film itself is polypropylene resin. When the polypropylene film is composed of multiple layers, it is preferable that the main component of the base layer (II) described later is polypropylene resin.

[0066] Preferably, the polypropylene film of the present invention is biaxially stretched by sheeting the aforementioned polypropylene. Regarding the biaxial stretching method, it can be obtained by blow molding and simultaneous biaxial stretching, stenter simultaneous biaxial stretching, or successive biaxial stretching using a roller stretcher and a stenter. However, in terms of controlling film stability, thickness uniformity, high film rigidity, and dimensional stability, the successive biaxial stretching method using a roller stretcher and a stenter is preferred.

[0067] Next, taking two types of three-layer polypropylene films as examples, one aspect of the polypropylene film manufacturing method of the present invention will be described, but the polypropylene film of the present invention is not limited to this.

[0068] First, a uniaxial extruder is used to dry-blend polypropylene resin A and branched chain polypropylene resin at a mass ratio of, for example, 95:5, and then supplied to a base layer (II) (hereinafter, sometimes referred to as layer B). A uniaxial extruder is also used to supply polypropylene resin A and poly4-methylpentene-1 resin at a mass ratio of, for example, 98:2, to a surface layer (I) (hereinafter, sometimes referred to as layer A). Subsequently, melt extrusion is performed at 200–280°C (more preferably 220–280°C, and even more preferably 240–270°C). Then, 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, sprayed onto a casting drum, and cooled and cured, thereby obtaining a laminated unstretched sheet having layers of A / B / A layers. In this case, when the layer thickness ratio is expressed as 1 / X / 1 representing the layer thickness ratio of layer A / layer B / layer A, X is preferably 8 or more and 60 or less, more preferably 15 or more and 55 or less, and even more preferably 20 or more and 50 or less. Furthermore, when the layer configuration has layers A and B, when the layer thickness ratio of layer A / layer B is expressed as 1 / X, X is preferably 4 or more and 60 or less, more preferably 7 or more and 55 or less, and even more preferably 10 or more and 50 or less. By achieving the above ranges, uniform fine protrusions caused by poly(4-methylpentene-1) resin can be formed on the film surface, which can impart slipperiness. Furthermore, without impairing the effectiveness of the present invention, the layer configuration can also be made into two two-layer lamination configurations of layer A / layer B.

[0069] Furthermore, the surface temperature of the casting drum is 10–40°C, preferably 15–33°C, further preferably 15–30°C, particularly preferably 15–25°C, and most preferably 20–25°C. Regarding the sealing method of the casting drum, any of the following methods can be used: electrostatic application, sealing method utilizing the surface tension of water, air knife method, press roll method, underwater casting method, etc., but the air knife method, which provides good planarity and allows for control of surface roughness, is preferred. From the viewpoint of cooling the non-cooled drum surface 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 10–40°C, more preferably 15–30°C, further preferably 15–25°C, and particularly preferably 20–25°C. The blowing air velocity is preferably 130–150 m / s. Furthermore, to prevent sheet vibration, it is preferable to adjust the position of the air knife so that the airflow is directed to the downstream side of the film forming process. Moreover, in the case of a two-layer lamination structure (A layer / B layer), it is preferable to designate the A layer side as the casting drum side.

[0070] The obtained unstretched sheet is introduced into a longitudinal stretching step. In this step, the unstretched sheet is preheated by contacting metal rollers maintained at 110°C to 150°C (preferably 120°C to 150°C, more preferably 130°C to 150°C), and stretched in the longitudinal direction by 4.6 to 7.0 times (more preferably 5.2 to 6.8 times, more preferably 5.5 to 6.5 times) between rollers with a set circumferential speed difference, and then cooled to room temperature. At this point, the interval (stretching range) between the two rollers with the circumferential speed difference is preferably 200 mm or more, more preferably 250 mm or more, and more preferably 300 mm or more. Furthermore, the upper limit of the stretching range is preferably 1000 mm. The longitudinal stretching system utilizes the difference in circumferential speed between two metal rollers for stretching. However, before and after stretching, the film is pressed against the metal rollers using clamping rollers, thereby making it less prone to slipping on the metal rollers. The aforementioned stretching interval refers to the distance from the clamping position of the metal rollers before stretching to the clamping position of the metal rollers after stretching.

[0071] The temperature (longitudinal stretching temperature) of the rollers with the circumferential speed difference is preferably set to 80°C to 130°C during stretching. More preferably, the longitudinal stretching temperature is 80°C to 125°C, and even more preferably, 80°C to 120°C. Furthermore, it is preferable to place radiant heaters on the upper and lower sides of the two rollers with the circumferential speed difference, and to heat the sheet from both sides while stretching. The output of the radiant heaters is preferably 1.0 kW or more on both sides, more preferably 2.0 kW or more, and even more preferably 2.6 kW or more. Furthermore, the distance between the heat source of the radiant heater and the sheet surface is preferably 10 mm to 200 mm. By setting the rollers for the preheating step of longitudinal stretching and the rollers with the circumferential speed difference at a low temperature, the relaxation of the polypropylene resin molecular chains is suppressed as much as possible, and stretching is performed simultaneously using radiant heaters, thereby enabling more uniform stretching even in this formulation with a low molecular weight component. Furthermore, by increasing the stretching range, the neck-down during stretching increases, resulting in uniform high alignment of the film. Therefore, this is effective in improving the Young's modulus of the main alignment orthogonal directions of the obtained polypropylene film.

[0072] Next, the uniaxially stretched film obtained in the longitudinal stretching step is guided to a tenter frame by holding the two ends in the width direction with a clamp and preheated. Then, it is stretched laterally in the width direction by 8.5 to 14 times, more preferably 9.0 to 13 times, and even more preferably 9.5 to 12 times. The preheating temperature is preferably 165 to 180°C, more preferably 168 to 180°C, and even more preferably 170 to 180°C. The stretching temperature is preferably 148 to 165°C, more preferably 148 to 160°C, and even more preferably 148 to 155°C. By increasing the preheating temperature by 5°C or more (preferably 8°C or more, more preferably 10°C or more) compared to the stretching temperature, it becomes possible to uniformly stretch the film across its width with high alignment, thereby achieving an increase in elongation and a reduction in crystallite size. Because of the large necking, uniaxially stretched films have a narrow width. Even when using a standard tenter frame rail pattern for transverse stretching, the transverse stretching ratio can be increased. Therefore, this stretching method is better from the perspective of improving heat resistance.

[0073] In the subsequent heat treatment and relaxation steps, while holding the polypropylene film taut in the width direction using clamps, the film is relaxed at a relaxation rate of 12-20% (more preferably 14-20%, even more preferably 16-20%) in the width direction. It is then heat-fixed at a temperature of 165°C or higher but lower than 180°C (more preferably 168°C or higher but lower than 180°C, even more preferably 170°C or higher but lower than 180°C), and then cooled at 80-100°C while still holding the film taut in the width direction, before being guided to the outside of the tenter frame. The clamps at the ends of the polypropylene film obtained in this manner are released, and the film edges are cut during the winding step to wind the polypropylene film into a finished product roll. The heat treatment temperature is set to be at least 5°C higher (more preferably 8°C higher, even more preferably 10°C higher) than the transverse stretching temperature, thereby mitigating residual stress within the polypropylene film and reducing heat shrinkage and increasing tensile elongation.

[0074] Furthermore, when the polypropylene film exiting the tenter frame passes through the cross-section, from the viewpoint of improving heat resistance and tensile elongation, it is preferable to use a heated roller for heating. The heating temperature is preferably 80–120°C, more preferably 90–110°C. At temperatures above 120°C, the slip resistance of the heated roller and the polypropylene film is impaired, wrinkles are generated, and the flatness deteriorates. 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 a productivity point of view, about 2.0 seconds is the upper limit.

[0075] The polypropylene film of the present invention, obtained as described above, can be used in a wide variety of industrial applications, such as packaging films, surface protective films, process films, hygiene products, agricultural products, building products, medical products, and capacitor films. However, due to its particularly excellent heat resistance, mechanical strength, and quality, it is best used as a packaging film, surface protective film, process film, and release film. Here, a surface protective film refers to a film that is attached to a molded body or film and has the function of preventing scratches and contamination during processing and transportation. A process film refers to a film that is attached to a molded body or film and prevents scratches and contamination during manufacturing and processing, and is discarded when used as a final product. A release film refers to a film with high release properties, that is attached to a molded body or film and prevents scratches and contamination during processing and transportation, and has the function of being easily peeled off and discarded when used as a final product. Packaging film refers to the film used to wrap items, primarily food products, to improve their quality, storage efficiency, and ease of use. [Example]

[0076] Hereinafter, the present invention will be described in detail through examples. Furthermore, the characteristics were measured and evaluated by the following methods.

[0077] (1) The film thickness was measured using a micro thickness gauge (manufactured by Anritsu). Five points were randomly measured on a 10cm square sample of polypropylene film, and the average value was defined as the film thickness (μm).

[0078] (2) tanδ (loss tangent) A rectangular test piece (5 mm wide × 20 mm long) cut from a polypropylene film with the main alignment direction as the long side was mounted on the fixture of the device at 23°C under nitrogen atmosphere. It was then cooled to -100°C, and the tanδ from -100°C to 180°C was measured using the following apparatus and conditions. The viscoelastic-temperature curve was plotted using the dynamic viscoelastic method, and Dmax, Dmin, and Lp were determined using the tanδ at each temperature, as shown in Figures 1 and 2. The experiment was conducted with n=3, and the average values ​​were defined as Dmax, Dmin, and Lp of the polypropylene film. <Apparatus and Measurement Conditions> Apparatus: Rheogel-E4000 (UBM manufactured) Geometry: Tensile clamp spacing: 10 mm Frequency: 10 Hz Strain: 0.1~0.2% Temperature range: -100~180℃ Heating rate: 5℃ / min Measurement gas environment: Nitrogen.

[0079] (3) Young's Modulus: A rectangular sample with a length of 150 mm (measurement direction) × 10 mm was cut from a polypropylene film, with the arbitrary direction defined as the measurement direction. The sample was assembled in a tensile testing machine (ORIENTEC "Tensilon" (registered trademark) UCT-100) with an initial clamping distance of 50 mm in a way that allows stretching in the measurement direction. The tensile speed was set to 300 mm / min and a tensile test was performed on the film. The Young's modulus was calculated according to the method specified in JIS K7161 (2014). The same measurement was performed 5 times and the average value obtained was defined as the Young's modulus of the sample in the measurement direction. Next, the measurement direction was set to 0°, and the Young's modulus was measured in the same way for each direction that formed an angle from 0° to 175° in 5° increments. The direction showing the highest value was defined as the principal alignment direction.

[0080] (4) Tensile elongation in the main alignment direction at room temperature: Rectangular samples with a length of 150 mm (main alignment direction) × 10 mm were cut from polypropylene film. The samples were assembled into a tensile testing machine (ORIENTEC "Tensilon" (registered trademark) UCT-100) with an initial clamping distance of 50 mm, and a tensile test was performed on the film at a tensile speed of 300 mm / min at room temperature. The tensile elongation was calculated according to the method specified in JIS K7161 (2014). Each sample was tested 5 times and the average value was taken as the tensile elongation in the main alignment direction of the sample.

[0081] (5) Tensile elongation in the main alignment orthogonal direction at 90°C: A rectangular sample with a length of 150 mm (main alignment orthogonal direction) × width of 10 mm was cut from a polypropylene film. The sample, along with its fixture, was placed in an oven heated to 90°C and heated for 1 minute. Then, the sample was assembled into a tensile testing machine (ORIENTEC "Tensilon" (registered trademark) UCT-100) with an initial fixture spacing of 50 mm to stretch it in the width direction. The tensile speed was set to 300 mm / min, and the tensile elongation was calculated according to the method specified in JIS K7161 (2014). The same measurement was performed 5 times, and the average value obtained was defined as the tensile elongation in the main alignment orthogonal direction of the sample at 90°C.

[0082] (6) Crystallite size of the main alignment and its orthogonal direction α(110) The polypropylene film was cut into strips with a length of 4 cm (main alignment direction) and a width of 1 mm (main alignment orthogonal direction), and the strips were overlapped to make the thickness 1 mm to prepare a sample. The sample was placed between the X-ray source and the detector so that X-rays could penetrate from the surface of the sample, and the X-ray diffraction was measured by scanning the angle (2θ / θ) of the X-ray source and the detector symmetrically with respect to the film surface. In the obtained diffraction profile, the crystallite size in the main alignment direction was obtained from the half-value width βe of the crystallization peak in 2θ = about 14° (α crystal (110) plane) using the following formulas (1) and (2). Also, the crystallite size in the main alignment orthogonal direction was obtained in the same way for the polypropylene film strip with a length of 4 cm (main alignment orthogonal direction) and a width of 1 mm (main alignment direction). Furthermore, the measuring apparatus and conditions are as follows.

[0083] [Mathematical Expression 1]

[0084] [Mathematical Expression 2]

[0085] Here, λ: X-ray wavelength (=0.15418nm), βe: half-width of diffraction peak, βo: correction value for half-width (=0.6), K: Scherrer constant (=1.0). (Measuring Apparatus) • X-ray diffraction apparatus: Brucker AXS D8 ADVANCE (sealed tube type) • X-ray source: CuKα line • Output: 40kV-40mA • Slit system: DS=0.3° • Detector: LynxEye (high-speed detector) • Scan: 2θ-θ continuous scan • Measurement range: 2θ=5~80° • Step size: 0.02° • Scanning speed: 1 second / step.

[0086] (7) The crystallization temperature Tc0 was determined by the extrapolation method. A differential scanning calorimeter (EXSTAR DSC6220, Seiko Instruments Co., Ltd.) was used. 3 mg of polypropylene film was heated from 25°C to 250°C at 20°C / min and held for 5 minutes in a nitrogen atmosphere. Then, the temperature was lowered from 250°C to 25°C at 10°C / min, and the peak temperature of the exothermic curve obtained during this cooling was defined as Tc10. Subsequently, the polypropylene film was heated from 25°C to 250°C at 20°C / min and held for 5 minutes. Then, the temperature was lowered from 250°C to 25°C at 40°C / min, and the peak temperature of the exothermic curve obtained during this cooling was defined as Tc40. Secondly, as shown in Figure 3, the cooling rate was plotted on the horizontal axis, and the crystallization temperature at each cooling rate was plotted on the vertical axis. A straight line was drawn from Tc40 towards Tc10, and the crystallization temperature at the point of interpolation at a cooling rate of 0℃ / min was defined as Tc0. Furthermore, when multiple peak temperatures were observed in the measurements of Tc10 and Tc40, the temperature of the highest peak in the range of 80℃ to 130℃ was used as the crystallization temperature of the polypropylene film. The measurements were performed three times for each sample, and the average value was used for evaluation.

[0087] (8) Melting point Tm: A differential scanning calorimeter (EXSTAR DSC6220, Seiko Instruments Co., Ltd.) was used. In a nitrogen atmosphere, 3 mg of polypropylene film was heated from 25 °C to 250 °C at a rate of 20 °C / min. The peak temperature of the endothermic curve obtained at this temperature was defined as Tm ( °C). The determination was performed three times for each sample, and the average value obtained was defined as the Tm ( °C) of the polypropylene film.

[0088] (9) Static friction coefficient μs in the main alignment orthogonal direction after heat treatment at 90°C for 10 minutes: A polypropylene film was cut into pieces with a width of 6.5 cm (main alignment direction) and a length of 12 cm (orthogonal direction). The test piece was sandwiched in paper and heated in an oven at 130°C under zero load for 10 minutes. After being removed and cooled at room temperature, the test was performed using a Toyo Seiki (Group) slip tester at 25°C and 65%RH according to JIS K 7125 (1999). Furthermore, the test was performed by overlapping the orthogonal directions of the main alignment and the different surfaces of the film, i.e., overlapping so that the surface of one film was in contact with the back of another film. Five identical tests were performed on one sample, and the average value of the obtained values ​​was calculated and determined as the static friction coefficient (μs) of the polypropylene film.

[0089] (10) Melt tension was measured using an apparatus according to JIS K 7199 (1999) under the following conditions. • Apparatus: Capillary chromatography 1BPMD-i (Toyo Seiki Co., Ltd.) equipped with a melt tension tester • Temperature: 230°C (using an incubator) • Mold: L=8 (mm), D=2.095 (mm) • Extrusion speed: 20 mm / min • Extraction speed: 15.7 m / min • Sample mass: 15-20 g.

[0090] (11) The planarity of the film during heating is achieved by using a gravure coating machine to dilute an acrylic adhesive (manufactured by Soken Chemical Co., Ltd., "SK Dyne" (registered trademark) 1310) with ethyl acetate, toluene, and methyl ethyl ketone (MEK), and to mix 2.0 parts by weight of a hardener (manufactured by Nippon Polyurethanes Co., Ltd., "Coronate" (registered trademark) D-90) with 100 parts by weight of the solid component of the adhesive. The film is then coated on one side of a 500 mm wide polypropylene film, guided to a drying oven at 90 °C and transported for 30 seconds, and the solvent in the coating is removed to obtain an adhesive film with an adhesive layer of 1 μm thickness. Subsequently, the adhesive film was rolled into a 200m roll to form an adhesive film roll. Then, a 1m long, 500mm wide strip of adhesive film was rolled out without tension (the film hanging vertically due to its own weight), with uniform width, and tensions of 1kg / m and 3kg / m were applied. The strip was then visually inspected for wrinkles, dents, or other flatness defects. The evaluation was based on the following criteria: S: No flatness defects under no tension. A: Flatness defects were visible under no tension, but disappeared under a tension of 1kg / m width. B: Flatness defects were visible under a tension of 1kg / m width, but disappeared under a tension of 3kg / m width. C: Flatness defects were visible even under a tension of 3kg / m width.

[0091] (12) Film fracture under high tension: A 500mm wide polypropylene film was guided to a drying oven at 90°C and lifted to the specified tension at a speed of 100N / second. After reaching the specified tension, the tension was applied for another 30 seconds and the film was transported. The presence or absence of polypropylene film fracture was visually confirmed. S: No fracture even under tension of 400N or more. A: Fracture under tension of 300N or more but less than 400N. B: Fracture under tension of 200N or more but less than 300N. C: Fracture under tension of less than 200N.

[0092] (13) Differential distribution value and molecular weight distribution Mz / Mw when log molecular weight Log(M) = 6.5: Using 1,2,4-trichlorobenzene as solvent, the mixture was stirred at 165°C for 30 minutes to dissolve the polypropylene film. Subsequently, the mixture was filtered using a 0.5 μm filter, and the molecular weight distribution of the filtrate was measured. The differential distribution value when the log molecular weight Log(M) was 6.5 was read.

[0093] Furthermore, the weight-average molecular weight Mw and the Z-average molecular weight Mz of the sample were determined using a molecular weight calibration curve prepared with the following standard samples. • Apparatus: Agilent Technologies PL-GPC220 high-temperature GPC apparatus • Detector: Agilent Technologies differential refractive index detector (RI detector) • Column: Agilent Technologies PL1110-6200 (20μm MIXED-A) × 2 • Flow rate: 1.0 mL / min • Column temperature: 145 °C • Injection volume: 0.500 mL • Sample concentration: 0.1 wt% • Standard samples: Tosoh monodisperse polystyrene and Tokyo Chemical Industry Co., Ltd. dibenzyl.

[0094] (14) Cold xylene-soluble fraction (CXS) The raw material was polypropylene resin. 0.5 g was dissolved in 100 ml of xylene at 135°C, cooled, 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 defined as X (g), and the precision value of 0.5 g of the sample was defined as X0 (g), calculated using the following formula: Formula: CXS (mass%) = (X / X0) × 100.

[0095] (15) The maximum height (St) measurement was performed using Ryoka Systems Inc.'s "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC, and the surface shape was obtained by performing surface correction on the captured image using the accompanying analysis software with a fourth-order polynomial approximation. Furthermore, the maximum height (St) represents the difference between the maximum height (Peak) and the minimum height (Valley) within the measurement area. The measurement conditions are as follows. The measurement was performed on both sides of the film, with n=3 (number of measurements = 3 times), and the average value of each side was obtained, which was used as the St of each side. Furthermore, the table records the larger of the St values ​​of the two sides of the film. • Apparatus: “VertScan” (registered trademark) 2.0 R5300GL-Lite-AC (manufactured by Ryoka Systems Inc.) • Measurement conditions: SONY HR-57 1 / 2 inch CCD camera • 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 × 0.939mm.

[0096] (Polypropylene resin, etc.) Polypropylene resin having molecular weight distributions Mz / Mw and CXS as shown in Table 1 below was used to manufacture the polypropylene films of the Examples and Comparative Examples. Furthermore, these values ​​were evaluated in the form of resin pellets. Three types of resin were prepared as polypropylene resin A, and two types of resin were prepared as other polypropylene resins. In addition, regarding the branched chain polypropylene resin, the following branched chain polypropylene resin was used.

[0097] Polypropylene Resin 1 (PP1): Made by Prime Polymer Co., Ltd. Polypropylene Resin 2 (PP2): Made by Prime Polymer Co., Ltd. Polypropylene Resin 3 (PP3): Made by Sumitomo Chemical Co., Ltd. Polypropylene Resin 4 (PP4): Made by Prime Polymer Co., Ltd. Polypropylene Resin 5 (PP5): Made by Prime Polymer Co., Ltd. Branched Chain Polypropylene Resin 1 (Branched PP1): Ziegler-Natta Catalyst-based Branched Chain Polypropylene Resin (PF-814, made by Basell Corporation, melt tension: 15gf, MFR: 3.0) Branched Chain Polypropylene Resin 2 (Branched PP2): Metallocene Catalyst-based Branched Chain Polypropylene Resin (“WAYMAX” (registered trademark) MFX6, made by Japan Polypropylene Corporation, melt tension: 13gf, MFR: 3.0).

[0098] [Table 1] type Mz / Mw CXS MFR Log(M) = 6.5 Differential distribution value PP raw material A PP1 2.8 1.9% 3.0 4.9 PP2 3.3 2.7% 2.0 6.3 PP3 4.3 1.1% 7.0 8.2 PP4 4.7 0.8% 7.0 13.1 PP5 5.8 4.5% 4.0 15.0

[0099] Polypropylene raw material D: Polypropylene resin 2 and 4-methyl-1-pentene polymer 1 (described later) are fed from the metering hopper to the twin-shaft extruder in a mass ratio of 90:10, melt-mixed at 260°C, and the molten resin composition is ejected from the die in bundles and cooled and solidified in a water bath at 25°C, and then cut into sheets.

[0100] Polypropylene raw material E: Polypropylene resin 3 and 4-methyl-1-pentene polymer 2 (described later) are fed from the metering hopper to the twin-screw extruder in a mass ratio of 90:10, melt-mixed at 260°C, and the molten resin composition is ejected from the die in bundles and cooled and solidified in a water bath at 25°C, and then cut into sheets.

[0101] 4-Methyl-1-pentene polymer 1: Mitsui Chemicals (stock) MX004.

[0102] (Example 1) Polypropylene resin 2 and polypropylene raw material D were dry-blended at a mass ratio of 80:20 as raw materials for the surface layer (I) and then fed to a single-shaft extruder for the surface layer (I). Polypropylene resin 1 and branched chain polypropylene resin 1 were dry-blended at a mass ratio of 95:5 as raw materials for the base layer (II) and then fed to a single-shaft extruder for the base layer (II). After melt extrusion of each resin mixture at 260°C and removal of foreign matter using a sintering filter with a 20μm retention, the mixture was laminated using a feed block type A / B / A composite T-die to achieve a thickness ratio of 1 / 30 / 1 for the surface layer (I) / base layer (II) / surface layer (I). The mixture was then sprayed onto a casting drum with the surface temperature controlled at 25°C and air at a temperature of 20°C was blown through an air knife at a speed of 140m / s to ensure close contact with the casting drum. Subsequently, compressed air at 20°C, blown at a speed of 140 m / s, was sprayed onto the uncooled drum surface of the sheet on the casting drum for cooling, resulting in an unstretched sheet. Next, the unstretched sheet was preheated to 135°C using ceramic rollers, and stretched 5.7 times along its long side while being heated from both sides by a radiant heater between rollers with a circumferential speed difference of 108°C. The heat source of the radiant heater was fixed at a position 90 mm from the sheet surface. The distance between the rollers creating the circumferential speed difference was 320 mm, and the output of the radiant heater was set to 2.8 kW. Next, the obtained uniaxially stretched film was fed into a tenter frame by gripping both ends in the width direction using clamps, 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 a 20% relaxation in the width direction. Subsequently, after a cooling step of 100°C, the film is guided to the outside of the tenter frame. The clamps at both ends in the width direction of the film are released, and after being heated with hot rollers at 110°C for 1.8 seconds in the crossing zone, it is wound onto a core to obtain a polypropylene film with a thickness of 24 μm. The physical properties and evaluation results of the obtained film are shown in Table 2.

[0103] (Examples 2-5, Comparative Examples 1-4) Except that the raw material composition and film-forming conditions of each layer were set as shown in Table 2, polypropylene films were obtained in the same manner as in Example 1. The thickness was adjusted by adjusting the ejection volume during extrusion or by adjusting the speed of the casting drum. The physical properties and evaluation results of the obtained films are shown in Table 2. Furthermore, regarding the mixing of the surface materials, in the surface layer (I) of Comparative Example 2, polypropylene resin 2 and polypropylene raw material D were dry-blended at a ratio of 80:20 (mass ratio), just as in the surface layer (I) of Example 1. In the surface layer (I) of Example 4, polypropylene resin 3 and polypropylene raw material E were dry-blended at a ratio of 70:30 (mass ratio). In the surface layer (I) and base layer (II) of other examples, polypropylene raw materials D or E were not used, and the resin components were dry-blended at the ratios shown in Table 2. Also, in Example 4, the surface layer (I) side was brought into contact with the casting roller.

[0104] [Table 2] project Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Surface layer (Ⅰ) PP resin A PP1 (parts by weight) - - - - - - - 95 - PP2 (parts by weight) 98 - - - - - 98 - - PP3 (parts by weight) - - - 97 - - - - - PP resin PP4 (parts by weight) - - - - - - - - - PP5 (parts by weight) - 95 - - 100 - - - - Branched PP resin Branch PP1 (parts by weight) - 5 - - - - - - - Branch PP2 (parts by weight) - - - - - - - 5 - 1 part by weight of 4-methyl-1-pentene polymer 2 - - 3 - - 2 - - Grassroots (II) PP resin A PP1 (parts by weight) 95 - 97 - - - - - - PP2 (parts by weight) - - - 50 95 - - - - PP3 (parts by weight) - 100 - 50 - - - 30 100 PP resin PP4 (parts by weight) - - - - - - 100 70 - PP5 (parts by weight) - - - - 5 100 - - - Branched PP resin Branch PP1 (parts by weight) 5 - - - - - - - - Branch PP2 (parts by weight) - - 3 - - - - - - Film forming conditions Melt extrusion temperature (°C) 260 260 260 260 260 260 260 250 260 Stacking ratio (Top layer (I) / Base layer (II) / Top layer (I)) / (Top layer (I) / Base layer (II)) 1 / 30 / 1 1 / 10 / 1 single membrane 1 / 20 1 / 18 / 1 single membrane 1 / 6 / 1 1 / 80 / 1 single membrane Casting drum temperature (°C) 25 18 38 32 38 30 77 95 45 Air temperature (°C) 20 28 38 32 42 45 50 50 30 Stretching along the long side Preheating temperature (°C) 135 120 118 135 112 135 142 100 153 Tensile temperature (°C) 108 120 128 115 125 135 142 120 128 Multiplier (times) 5.7 6.2 4.8 5.2 5.7 4.5 5.1 6.3 4.8 Tension range (mm) 320 220 260 320 400 220 150 100 100 Radiant heater output (kW) 2.8 1.5 2.5 3.2 0.8 2.3 1.5 Unused Unused Width direction stretching Preheating temperature (°C) 176 166 178 175 168 170 169 160 179 Tensile temperature (°C) 153 160 170 157 160 180 161 170 173 Stretch ratio (times) 9.8 10.2 8.7 9.3 11.8 8.2 8.8 10.8 9.4 Heat treatment Heat treatment temperature (°C) 178 169 166 175 167 168 158 170 148 Relaxation rate (%) in the width direction 20 15 13 18 13 6 11 20 11 Cooling temperature (°C) 100 90 80 100 100 50 70 80 100 Heating in the crossing area Temperature (°C) 110 85 Unprocessed 117 92 70 Unprocessed 130 Unprocessed Time (seconds) 1.8 0.4 0.7 0.5 0.2 3.0 Thickness (μm) twenty four 12 18 20 25 20 2.3 50 25 Mz / Mw 3.3 4.4 2.9 3.9 3.6 5.8 4.8 5.4 3.5 Differential distribution value (%) of Log(M) = 6.5 5.3 8.3 2.6 7.1 6.7 15.2 12.4 13.1 6.1 (Dmax-Dmin) / Dmax 0.15 0.27 0.29 0.23 0.28 0.40 0.33 0.28 0.32 Elongation (%) in the main alignment orthogonal direction at 90℃ 135 75 115 100 85 95 80 65 70 The temperature at which tanδ becomes equal to Lp (°C) 48 67 77 57 73 92 85 78 88 α(110) crystallite size (nm) 14.2 19.3 21.1 17.9 19.8 20.4 22.5 25.6 twenty one Tc0+Tm(℃) 292 288 297 278 275 271 275 282 291 μs(-) after heating at 90℃ 0.48 0.65 0.82 0.53 0.93 0.85 0.61 0.90 0.90 Elongation (%) in the principal alignment direction 43 37 68 55 41 51 45 32 32 Maximum height St (μm) 0.6 0.4 1.5 1.0 2.2 1.2 1.7 7.1 2.3 Planarity during heating S A B S B C C B C Fracture under high tension S B S A B A B C A

[0105] Since Examples 3, 1, and 4 are single-layer structures, they are treated as having no surface layer (I). [Possibility of Industrial Application]

[0106] As described above, the polypropylene film of the present invention can be used in a wide variety of industrial applications such as packaging film, surface protection film, process film, hygiene products, agricultural products, building products, medical products, or capacitor film. Due to its excellent heat resistance, mechanical strength, and quality, it can be better used as a surface protection film, process film, and release film. [Simplified Explanation of the Diagram]

[0011] Figure 1 is an example of a graph showing the temperature dependence of tanδ of a polypropylene film in the main alignment direction, representing Dmax and Dmin. Figure 2 is an example of a graph showing the temperature dependence of tanδ of a polypropylene film in the main alignment direction, representing Lp and the temperature at which tanδ becomes equal to Lp. Figure 3 is an example of a graph showing the crystallization temperature Tc0 of a polypropylene film.

Claims

1. A polypropylene film, characterized in that the maximum value Dmax and minimum value Dmin of tanδ in the principal alignment direction satisfy the relationship of Equation 1 in the range of -10℃ to 50℃; the tensile elongation in the principal alignment orthogonal direction at 90℃ is 70% or more; the static friction coefficient μs after heat treatment at 90℃ for 10 minutes is 0.80 or less; and when the crystallization temperature with a cooling rate of 0℃ / min is defined as Tc0 (℃) and the melting point of the polypropylene film is defined as Tm (℃), Tc0 + Tm ≥ 290; wherein, The crystallization temperature at a cooling rate of 0℃ / min is obtained by extrapolation using the crystallization temperature Tc10 (℃) measured at a cooling rate of 10℃ / min and the crystallization temperature Tc40 (℃) measured at a cooling rate of 40℃ / min. Equation 1: 0.00≦(Dmax-Dmin) / Dmax≦0.

30.

2. The polypropylene film of claim 1, wherein when the maximum value of tanδ in the main alignment direction above -30°C and below 30°C is defined as LP, the temperature range in which tanδ in the main alignment direction becomes equal to the aforementioned LP is below 80°C in the range above 30°C and below 150°C.

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

4. The polypropylene film of claim 1 or 2, wherein the tensile elongation in the main alignment direction is 35% or more.

5. The polypropylene film of claim 1 or 2, wherein the maximum height St on both sides of the film is less than 2.0 μm.

6. The polypropylene film of claim 1 or 2, wherein the molecular weight distribution Mz / Mw is less than 4.

5.

7. The polypropylene film of claim 1 or 2, wherein the differential distribution value at a logarithmic molecular weight Log(M) = 6.5 in the molecular weight distribution curve determined by gel permeation chromatography is greater than 1.0% and less than 10%.

8. The polypropylene film of claim 1 or 2, having at least two layers with polypropylene resin as the main component.

9. A process film having a polypropylene film as claimed in any one of claims 1 to 8.

10. A release film having a polypropylene film as claimed in any one of claims 1 to 8.

11. A surface protective film having a polypropylene film as claimed in any one of claims 1 to 8.

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